Alinaghi, Pouriya; Janssens, Martin; Choudhury, Goutam; Goren, Tom; Siebesma, A. Pier; Glassmeier, FranziskaAlinaghi, P., M. Janssens, G. Choudhury, T. Goren, A. P. Siebesma, F. Glassmeier, 2024: Shallow cumulus cloud fields are optically thicker when they are more clustered. Quarterly Journal of the Royal Meteorological Society, n/a(n/a). doi: 10.1002/qj.4783. Shallow trade cumuli over subtropical oceans are a persistent source of uncertainty in climate projections. Mesoscale organization of trade cumulus clouds has been shown to influence their cloud radiative effect (CRE) through cloud cover. We investigate whether organization can explain CRE variability independently of cloud-cover variability. By analyzing satellite observations and high-resolution simulations, we show that more clustered cloud fields feature geometrically thicker clouds with larger domain-averaged liquid water paths, smaller cloud droplets, and consequently larger cloud optical depths. The relationships between these variables are shaped by the mixture of deep cloud cores and shallower interstitial clouds or anvils that characterize cloud organization. Eliminating cloud-cover effects, more clustered clouds reflect up to 20 W/m 2\ ^2 \ more instantaneous shortwave radiation back to space. cloud microphysics; cloud organization; cloud radiative effect; partial correlation
Atlas, R. L.; Bretherton, C. S.; Sokol, A. B.; Blossey, P. N.; Khairoutdinov, M. F.Atlas, R. L., C. S. Bretherton, A. B. Sokol, P. N. Blossey, M. F. Khairoutdinov, 2024: Tropical Cirrus Are Highly Sensitive to Ice Microphysics Within a Nudged Global Storm-Resolving Model. Geophysical Research Letters, 51(1), e2023GL105868. doi: 10.1029/2023GL105868. Cirrus dominate the longwave radiative budget of the tropics. For the first time, the variability in cirrus properties and longwave cloud radiative effects (CREs) that arises from using different microphysical schemes within nudged global storm-resolving simulations from a single model, is quantified. Nudging allows us to compute radiative biases precisely using coincident satellite measurements and to fix the large-scale dynamics across our set of simulations to isolate the influence of microphysics. We run 5-day simulations with four commonly-used microphysics schemes of varying complexity (SAM1MOM, Thompson, M2005 and P3) and find that the tropical average longwave CRE varies over 20 W m−2 between schemes. P3 best reproduces observed longwave CRE. M2005 and P3 simulate cirrus with realistic frozen water path but unrealistically high ice crystal number concentrations which commonly hit limiters and lack the variability and dependence on frozen water content seen in aircraft observations. Thompson and SAM1MOM have too little cirrus. anvil; global cloud-resolving model; tropical cirrus; global storm-resolving model; ice microphysics; longwave cloud radiative effect
Baba, Yuya; Ujiie, Masashi; Ota, Yukinari; Yonehara, HitoshiBaba, Y., M. Ujiie, Y. Ota, H. Yonehara, 2024: Implementation and evaluation of a spectral cumulus parametrization for simulating tropical cyclones in JMA-GSM. Quarterly Journal of the Royal Meteorological Society, n/a(n/a). doi: 10.1002/qj.4689. A spectral cumulus parametrization (spectral scheme) developed using a cloud-resolving model simulation was implemented in Global Spectral Model of the Japan Meteorological Agency (JMA-GSM, GSM hereafter). The performance of the spectral scheme in terms of mean state, variability, and tropical cyclone (TC) properties was evaluated using atmosphere-only model experiments by comparing results of the original convection scheme (based on Arakawa–Schubert scheme, AS scheme) and the spectral scheme. Parameter tunings were first conducted for the spectral scheme, through which the climatological errors of the cloud cover in the Southern Ocean and temperature were greatly improved. The spectral scheme showed comparable climatological errors to the AS scheme in the increased resolutions. The spectral scheme greatly improved tropical variability, that is, response to El Niño/Southern Oscillation and Madden–Julian Oscillation. Analyses on TC statistical data revealed that the spectral scheme improved TC properties in terms of genesis frequency, intensity, and the response of TC to tropical variability. Specifically, significant improvements were seen in the Northern Hemisphere. Further analyses on the TC structure revealed that higher TC intensity was sustained for longer times by the spectral scheme than by the AS scheme. The reason for this is that the spectral scheme better simulates convective heating by considering coexistence of different cloud types with parametrized vertically varying entrainment rates, especially from low to mid-altitudes. The convective heating leads to a sharper vertical-radial circulation in the TC structure, causing stronger incoming moisture flux toward the TC centre, and resulting in a stronger TC intensity. Consequently, the spectral scheme can simulate a comparable mean state, better variability, and better TC properties compared with the original scheme by simulating a more detailed convective structure. Therefore, it has a potential to increase the TC forecast skill for operational GSM. convection scheme; tropical variability; atmospheric general circulation model; tropical cyclone
Bao, Fangling; Letu, Husi; Shang, Huazhe; Ri, Xu; Chen, Deliang; Yao, Tandong; Wei, Lesi; Tang, Chenqian; Yin, Shuai; Ji, Dabin; Lei, Yonghui; Shi, Chong; Peng, Yiran; Shi, JianchengBao, F., H. Letu, H. Shang, X. Ri, D. Chen, T. Yao, L. Wei, C. Tang, S. Yin, D. Ji, Y. Lei, C. Shi, Y. Peng, J. Shi, 2024: Advancing Cloud Classification Over the Tibetan Plateau: A New Algorithm Reveals Seasonal and Diurnal Variations. Geophysical Research Letters, 51(13), e2024GL109590. doi: 10.1029/2024GL109590. The cloud classification algorithm widely used in the International Satellite Cloud Climatology Project (ISCCP) tends to underestimate low clouds over the Tibetan Plateau (TP), often mistaking water clouds for high-level clouds. To address this issue, we propose a new algorithm based on cloud-top temperature and optical thickness, which we apply to TP using Advanced Himawari Imager (AHI) geostationary satellite data. Compared with Clouds and the Earth's Radiant Energy System cloud-type products and ISCCP results obtained from AHI data, this new algorithm markedly improved low-cloud detection accuracy and better aligned with cloud phase results. Validation with lidar cloud-type products further confirmed the superiority of this new algorithm. Diurnal cloud variations over the TP show morning dominance shifting to afternoon high clouds and evening mid-level clouds. Winter is dominated by high clouds, summer by mid-level clouds, spring by daytime low clouds and nighttime high clouds, and autumn by low and mid-level clouds. cloud classification; cloud-type algorithm; low clouds; Tibetan Plateau
Baran, Anthony J.; Manners, James; Field, Paul; Hill, AdrianBaran, A. J., J. Manners, P. Field, A. Hill, 2024: A novel new coupled two-moment parametrization for cirrus radiative properties and its impact in a cloud-aerosol resolving model (CASIM). AIP Conference Proceedings, 2988(1), 080003. doi: 10.1063/5.0183481. The latest assessment of the Intergovernmental Panel on Climate Change (IPCC) report that there is significant uncertainty in the radiative effect of aerosol-ice interactions on the Earth’s atmosphere radiation balance. This is partly owing to the lack of knowledge of the interaction between aerosol and ice, and how this interaction evolves the ice particle shapes, and particle size distribution (PSD). This is further exacerbated by the fact that current cloud-aerosol interaction models cannot adequately address this radiative uncertainty owing to an inherent lack of consistency between the two-moment microphysics and the evolving radiation fields. Here, we address this lack of consistency by directly coupling the global CASIM prognostic moments (i.e. mass and number) to the ice optical properties through the same assumed PSD (i.e. the generalized gamma function). We examine the impact of this consistent coupling on the outgoing top-of-atmosphere (TOA) short- and long-wave irradiance fields in the Met Office’s regional model, which was centered around Darwin, Australia, and compare them to the CERES short- and long-wave local midday irradiance measurements. We show that the consistent moment–ice optical coupling better describes the probability density function (PDF) of the CERES short-wave irradiance measurements than the current operational model ice optical parametrization. However, the PDF of the CERES long-wave measurements is better described by the current operational model parametrization than the consistent moment–ice optical coupling. This inconsistency between the short-wave and long-wave results is further discussed together with its potential resolution.
Barnett, Michelle L.; Kemp, Alan E. S.; Hickman, Anna E.; Purdie, Duncan A.Barnett, M. L., A. E. S. Kemp, A. E. Hickman, D. A. Purdie, 2024: Environmental controls on the interannual variability in chlorophyll and phytoplankton community structure within the seasonal sub surface chlorophyll maximum in the western English channel. Continental Shelf Research, 277, 105253. doi: 10.1016/j.csr.2024.105253. The subsurface chlorophyll maximum (SCM) is increasingly recognised as an important but understudied locus of primary production particularly in shelf seas. Here we report the results of a 4 year, repeat station, summer sampling programme (2013–2016) of a seasonally recurrent SCM in the Western English Channel. Interannual variability in phytoplankton community structure and chlorophyll distribution and intensity was strongly related to water column stability at the depth interval of the SCM and also to water temperature. The phytoplankton community was statistically distinct in each year. High stability, as evidenced by large Richardson numbers and a well-developed strong thermocline appeared to favour the growth of larger dinoflagellates (autotrophs or mixotrophs) and diatoms. Such conditions led to development of the most intense SCMs and these were sometimes dominated by a single or a few key species most prominently in 2015 with near monospecific concentrations of the dinoflagellate Tripos fusus with average peak SCM chlorophyll concentrations of 7.3 ± 4.4 μg l−1. By contrast, in years with low water column stability and intermittent turbulence at the thermocline (2014, 2016) there was greater chlorophyll dispersal and less intense SCM. In these low stability conditions, red fluorescent nano-phytoplankton, such as naked dinoflagellates, chlorophytes and prymnesiophytes, made a greater contribution to the community, possibly as a result of the advantages that motility and enhanced light utilisation efficiency confer within an SCM exposed to turbulence. It is also likely that turbulence disrupted the stability required by the larger dinoflagellates and diatoms. Several of the key SCM taxa were absent from surface waters including the dinoflagellates Tripos fusus, Tripos lineatus, and most of the Rhizosolenia/Proboscia diatoms, consistent with adaptations more suited to survival at depth in stratified waters. These traits include luxury nutrient uptake and storage and survival in low light (both groups) and mixotrophy (dinoflagellates). On the other hand, in 2013, diatoms including Pseudo-nitzschia spp. were abundant in both surface, SCM and bottom waters. The relatively cooler waters (11.6–12.1 °C on average in 2013 and 2016) were characterised by smaller diatoms (Chaetoceros spp. and Pseudo-nitzschia spp.) whereas the warmer waters (13.1 °C on average in 2014) contained larger diatoms (large Rhizosolenia spp., Lauderia annulata and Leptocylindrus danicus). There did not appear to be continuity of key species between years, other than for the dinoflagellate Tripos lineatus, which was significant in both 2013 and 2014 and present in 2015. In any given year, there was no correspondence between the key spring bloom phytoplankton species as monitored in the nearby Western Channel Observatory L4 station and the key SCM taxa. Phytoplankton community structure; Subsurface chlorophyll maximum; Thermocline stratification; Turbulence; Western English Channel
Barrientos-Velasco, Carola; Cox, Christopher J.; Deneke, Hartwig; Dodson, J. Brant; Hünerbein, Anja; Shupe, Matthew D.; Taylor, Patrick C.; Macke, AndreasBarrientos-Velasco, C., C. J. Cox, H. Deneke, J. B. Dodson, A. Hünerbein, M. D. Shupe, P. C. Taylor, A. Macke, 2024: Estimation of the radiation budget during MOSAiC based on ground-based and satellite remote sensing observations. EGUsphere, 1-53. doi: 10.5194/egusphere-2024-2193. Abstract. An accurate representation of the radiation budget is essential for investigating the radiative effect that clouds have on the climate system, especially in the Arctic, an environment highly sensitive to complex and rapid environmental changes. In this study, we analyse a unique dataset of observations from the central Arctic made during the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) expedition in conjunction with state-of-the-art satellite products from CERES (Clouds and the Earth's Radiant Energy System) to investigate the radiative effect of clouds and radiative closure at the surface and the top of the atmosphere (TOA). We perform a series of radiative transfer simulations using derived cloud macro- and microphysical properties as inputs to the simulations for the entire MOSAiC period, comparing our results to collocated satellite products and ice-floe observations. The radiative closure biases were generally within the instrumental uncertainty, indicating that the simulations are sufficiently accurate to realistically reproduce the radiation budget during MOSAiC. Comparisons of the simulated radiation budget relative to CERES show similar values in the terrestrial flux but relatively large differences in the solar flux, which is attributed to a lower surface albedo and a possible underestimation of atmospheric opacity by CERES. While the simulation results were consistent with the observations, more detailed analyses reveal an overestimation of simulated cloud opacity for cases involving geometrically thick ice clouds. In the annual mean, we found that the presence of clouds leads to a loss of 5.2 W m-2, of the atmospheric-surface system to space, while the surface gains 25 W m-2, and the atmosphere is cooled by clouds by 30.2 W m-2, during the MOSAiC expedition.
Barrientos-Velasco, Carola; Deneke, Hartwig; Griesche, Hannes J.; Hünerbein, Anja; Macke, Andreas; Seifert, Patric; Shupe, Matthew; Witthuhn, JonasBarrientos-Velasco, C., H. Deneke, H. J. Griesche, A. Hünerbein, A. Macke, P. Seifert, M. Shupe, J. Witthuhn, 2024: Investigation of the annual cycle of the cloud radiative effect based on CERES and Polarstern observations during MOSAiC. AIP Conference Proceedings, 2988(1), 060005. doi: 10.1063/5.0183726. The unique in-situ and remote-sensing observations obtained during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition from the ice-breaker Polarstern (from September 2019 to October 2020) were used to evaluate the Clouds and the Earth’s Radiant Energy System (CERES) satellite products over the central Arctic. Within the scope of this analysis, the consistency among CERES products, radiative transfer simulations based on shipborne remote-sensing observations (named T-CARS) and observed downward solar (SOL) and terrestrial (TER) radiative fluxes are assessed. It was found that during polar night (27 October 2019 to 13 March 2020), CERES products had systematic deviations around 0.2-21.6 Wm−2 compared to the observed broadband downward TER flux at the surface. During polar day (14 March 2020 to 30 September 2020), the flux differences of CERES relatively decreased to 2.2-15.8 Wm−2. T-CARS simulations show a good agreement for all conditions during polar night with mean biases around 0.6-6.4 Wm−2. Still, significant flux differences were found for the downward TER and SOL radiative fluxes for polar day. Preliminary calculations of the cloud radiative effect based on shipborne and satellite-based simulations indicate a warming effect of clouds at the surface of around 41 Wm−2 and 15 Wm−2 for polar night and polar day, respectively.
Bayoumi, S.; Moharram, N. A.; Shehata, A. I.; Imam, M. M.; El-Maghlany, W. M.Bayoumi, S., N. A. Moharram, A. I. Shehata, M. M. Imam, W. M. El-Maghlany, 2024: A multi-criteria performance assessment of concentrated solar power plants for site and technology selection in Egypt. International Journal of Environmental Science and Technology, 21(3), 2989-3004. doi: 10.1007/s13762-023-05114-1. The objective of this research is to investigate the implementation of two concentrated solar power (CSP) technologies in the 28 devoted locations in Egypt, in order to select the optimum site-specific CSP technology. This may be achieved by a validated thermo-economic simulation of power plants using the Sam advisory model and an investigation of the two proposed CSP technologies’ configurations to fulfill the power plant’s thermal demand. Simulations take into consideration the environmental, technical, financial, and economic aspects of the projects. Among many simulated parameters, three are considered to compare the two proposed technologies' configurations in the 28 locations utilizing geographic information system aid. Those parameters are the annual power production, the levelized cost of energy, and water consumption. A comparative analysis indicated that the solar tower requires 25% more land than the parabolic trough. The additional collecting area raised the net capital cost of the solar tower system by 15% over the parabolic trough model. As a result, the solar tower arrangement reduces the levelized cost of energy while increasing the yearly power generated and water required by the power plant. Simulation results favored the proposed solar tower configuration over the parabolic trough and recommended the implementation of such concentrated solar power projects in the central and eastern locations of Egypt. Sustainability; Concentrated solar power; Geographic information system; Multi-criteria decision analysis; Parabolic trough; Solar tower
Bhatti, Yusuf A.; Revell, Laura E.; McDonald, Adrian J.; Archibald, Alex T.; Schuddeboom, Alex J.; Williams, Jonny; Hardacre, Catherine; Mulcahy, Jane; Lin, DongqiBhatti, Y. A., L. E. Revell, A. J. McDonald, A. T. Archibald, A. J. Schuddeboom, J. Williams, C. Hardacre, J. Mulcahy, D. Lin, 2024: Aerosol and Dimethyl Sulfide Sensitivity to Sulfate Chemistry Schemes. Journal of Geophysical Research: Atmospheres, 129(12), e2023JD040635. doi: 10.1029/2023JD040635. Dimethyl sulfide (DMS) is the largest source of natural sulfur in the atmosphere and undergoes oxidation reactions resulting in gas-to-particle conversion to form sulfate aerosol. Climate models typically use independent chemical schemes to simulate these processes, however, the sensitivity of sulfate aerosol to the schemes used by CMIP6 models has not been evaluated. Current climate models offer oversimplified DMS oxidation pathways, adding to the ambiguity surrounding the global sulfur burden. Here, we implemented seven DMS and sulfate chemistry schemes, six of which are from CMIP6 models, in an atmosphere-only Earth system model. A large spread in aerosol optical depth (AOD) is simulated (0.077), almost twice the magnitude of the pre-industrial to present-day increase in AOD. Differences are largely driven by the inclusion of the nighttime DMS oxidation reaction with NO3, and in the number of aqueous phase sulfate reactions. Our analysis identifies the importance of DMS-sulfate chemistry for simulating aerosols. We suggest that optimizing DMS/sulfur chemistry schemes is crucial for the accurate simulation of sulfate aerosols. AOD; chemistry; clouds; DMS; modeling; sulfate
Bock, Lisa; Lauer, AxelBock, L., A. Lauer, 2024: Cloud properties and their projected changes in CMIP models with low to high climate sensitivity. Atmospheric Chemistry and Physics, 24(3), 1587-1605. doi: 10.5194/acp-24-1587-2024. Since the release of the first Coupled Model Intercomparison Project version 6 (CMIP6) simulations, one of the most discussed topics is the higher effective climate sensitivity (ECS) of some of the models, resulting in an increased range of ECS values in CMIP6 compared to previous CMIP phases. An important contribution to ECS is the cloud climate feedback. Although climate models have continuously been developed and improved over the last few decades, a realistic representation of clouds remains challenging. Clouds contribute to the large uncertainties in modeled ECS, as projected changes in cloud properties and cloud feedbacks also depend on the simulated present-day fields. In this study, we investigate the representation of both cloud physical and radiative properties from a total of 51 CMIP5 and CMIP6 models. ECS is used as a simple metric to group the models, as the sensitivity of the physical cloud properties to warming is closely related to cloud feedbacks, which in turn are known to have a large contribution to ECS. Projected changes in the cloud properties in future scenario simulations are analyzed by the ECS group. In order to help with interpreting the projected changes, model results from historical simulations are also analyzed. The results show that differences in the net cloud radiative effect as a reaction to warming among the three model groups are driven by changes in a range of cloud regimes rather than individual regions. In polar regions, high-ECS models show a weaker increase in the net cooling effect of clouds, due to warming, than the low-ECS models. At the same time, high-ECS models show a decrease in the net cooling effect of clouds over the tropical ocean and the subtropical stratocumulus regions, whereas low-ECS models show either little change or even an increase in the cooling effect. Over the Southern Ocean, the low-ECS models show a higher sensitivity of the net cloud radiative effect to warming than the high-ECS models.
Brendecke, Jordann; Dong, Xiquan; Xi, Baike; Zhong, Xiang; Li, Jiangnan; Barker, Howard W.; Pilewskie, PeterBrendecke, J., X. Dong, B. Xi, X. Zhong, J. Li, H. W. Barker, P. Pilewskie, 2024: Evaluation of clear-sky surface downwelling shortwave fluxes computed by three atmospheric radiative transfer models. Journal of Quantitative Spectroscopy and Radiative Transfer, 328, 109164. doi: 10.1016/j.jqsrt.2024.109164. In this study the clear-sky total, direct, and diffuse shortwave (SW) fluxes at the surface, have been calculated by three radiation transfer models (RTMs) – MODTRAN6.0 (M6.0), Canadian Centre for Climate Modelling and Analysis (CCCma), and Langley-modified Fu-Liou (NASA CERES). These calculations have been evaluated by surface measurements collected from seven sites that represent different climatological regimes with various surface scene types including ocean, grassland/continental, desert, and snow/sea ice. For pristine atmospheric conditions, SW fluxes predicted by CCCma and M6.0 shows little variation, which lays a baseline for further analysis. Note that computing time required by CCCma is ∼1000 times smaller than M6.0. Based on all samples collected from seven sites, mean differences of total, direct, and diffuse fluxes between surface measurements and CCCma / M6.0 / Fu-Liou are [5.3 / 2.4 / 0.9], [-2.2 / -5.1 / -13.7], and [7.5 / 7.5 / 14.6] W m-2, respectively. Histograms of differences between the three RTM calculations and surface measurements show that CCCma computed direct and diffuse fluxes have the smallest biases with standard deviations similar to those for M6.0, while Fu-Liou values have the largest biases and standard deviations. While Fu-Liou outperforms for total flux, especially for desert conditions, it is hampered by large biases for direct and diffuse across all scene types. The three RTMs are consistent with showing the least error for total flux and the largest in diffuse based on bias, correlation, and root mean square error. MODTRAN, CERES, Correlated -distribution, Shortwave Flux; Radiative transfer
Cao, Yunfeng; Yin, Mengxi; Tian, Jiaxin; Liang, ShunlinCao, Y., M. Yin, J. Tian, S. Liang, 2024: Increased summertime wildfire as a major driver of the clear-sky dimming in the Siberian Arctic from 2000 to 2020. Atmospheric Research, 306, 107458. doi: 10.1016/j.atmosres.2024.107458. A warming Arctic is expected to exacerbate wildfires in Siberia, potentially creating a critical feedback to the Arctic climate change. However, our understanding of these fire-climate interactions remains limited. This study investigated changes in East Siberian wildfires and their influence on fire emissions, aerosol optical depth (AOD), and the surface clear-sky insolation across the Siberian Arctic from 2000 to 2020 using satellite observations. Our analysis reveals a substantial increase in wildfires, with fire counts doubling (a 114% increase) and fire radiative power surging by 8.4 × 106 MW compared to the early 21st century. Over 93% of this increase occurred during the boreal summer months. These intensified wildfires led to a significant rise in aerosol emission (organic carbon, PM2.5, and black carbon) exceeding 75% in East Siberia. Consequently, fire-season AOD in the Siberian Arctic increased by 33% (6.0 × 10−2), with 85% (5.1 × 10−2) attributable to wildfire changes. The wildfire-associated increase in AOD resulted in enhanced clear-sky dimming of 4.1 ± 3.2 W m−2 across the Siberian Arctic from 2000 to 2020. These findings suggest a critical feedback mechanism: a warming Arctic drives increased wildfires in Siberia, which in turn significantly impact the Arctic surface radiative budget through enhanced clear-sky dimming. Future simulations and projections for the Arctic should prioritize incorporating the feedback effects of intensifying wildfires. Aerosol optical depth; Arctic amplification; Clear-sky dimming; Siberia wildfire
Carrigg, Joseph; Yu, Lisan; Menezes, Viviane V.; Chen, YanxuCarrigg, J., L. Yu, V. V. Menezes, Y. Chen, 2024: Autumnal Equinox Shift in Arctic Surface Energy Budget: Beaufort-Chukchi Seas Case Study. Journal of Geophysical Research: Oceans, 129(5), e2023JC020788. doi: 10.1029/2023JC020788. This study examines the annual cycle of the Surface Energy Budget (SEB) in the Beaufort-Chukchi seas, focusing on the autumn transition. Shipboard measurements from NASA's Salinity and Stratification at the Sea Ice Edge (SASSIE) experiment (8 September–2 October 2022) and satellite flux analysis for the entire 2022 were utilized to provide a comprehensive perspective of the SEB's seasonal dynamics. An important finding is the alignment of SEB’s autumnal transition with the September 22 equinox, marking the onset of prolonged Arctic darkness. This transition involved a shift from the summertime radiative heating to cooling conditions, characterized by outgoing longwave radiation surpassing incoming solar radiation and a notable increase in synoptic turbulent latent and sensible heat flux variability. The increased turbulent heat fluxes after the equinox were associated with increased occurrences of short-duration cold air outbreaks. These outbreaks seem to originate from cold mesoscale surface winds transitioning from cooling landmasses or ice caps to the warmer seas, driven by differential cooling rates between land/ice and ocean as solar irradiance declined. Turbulent heat losses, outpacing longwave emission by more than fivefold, accelerated ocean surface cooling in the subsequent 2 months, leading to the complete freeze-up of the Beaufort-Chukchi seas by late November. These findings underscore the substantial influence of astronomical seasons on the SEB, emphasizing their crucial role in Arctic climate dynamics. Arctic Ocean; autumnal equinox; Beaufort-Chukchi seas; cold air outbreaks; energy autumn transition; surface energy budget
Castant, Jérôme; Vantrepotte, Vincent; Frouin, Robert; Beaugrand, GrégoryCastant, J., V. Vantrepotte, R. Frouin, G. Beaugrand, 2024: Comprehensive gridded dataset of photosynthetically active radiation in the upper ocean from 1958 to 2022. Remote Sensing of Environment, 311, 114305. doi: 10.1016/j.rse.2024.114305. Photosynthetically Active Radiation (PAR) plays a crucial role in shaping marine ecosystems, influencing primary production, species interaction, and phytoplankton seasonal dynamics. However, comprehensive long-term (gap-free) datasets for both surface PAR and the diffuse Attenuation Coefficient of Photosynthetically Active Radiation (KdPAR) are currently lacking. In this study, we introduce two new extensive global 4D PAR gap-free datasets (Longitude x Latitude x Day x Depth) at a resolution of 0.25o latitude x 0.25o longitude from surface to 250 m covering the periods 1998–2022 and 1958–2022. The first dataset (1998–2022) is primarily derived from Globcolour (surface PAR and Chlorophyll-a), supplemented with missing surface PAR data estimated using the Environmental String Model (ESM) with key climatic ERA5 variables. Missing Chlorophyll-a data are interpolated by applying the DINEOF method (Data Interpolating Empirical Orthogonal Functions) and transformed into KdPAR. Visual and numerical evaluations closely approximate observations, demonstrating the accuracy of our approach. Subsequently, we extend our dataset back to 1958 using exclusively the ESM based on key climatic ERA5 variables. The ESM outperforms the Generalized Regression on Neural Network (GRNN) in computational efficiency while yielding similar results. Validation against in-situ measurements confirms the reliability of PAR and KdPAR surface products. Although the 1958–2022 dataset exhibits limited daily variability in PAR compared to the 1998–2022 dataset, it effectively captures critical spatial-temporal patterns, as demonstrated by correlative and comparative studies with El Niño indices. Furthermore, the similarity observed between euphotic depth (Zeu) derived from our ESM-based 4D PAR dataset (1958–2022), and the Mercator-Ocean hindcast model, along with in-situ data, underscores the robustness of our approach in capturing light availability at depth. Beer-Lambert law; Diffuse Attenuation Coefficient of Photosynthetically Active Radiation (KPAR); Environmental String Model (ESM); ERA5; Photosynthetically Active Radiation (PAR); Remote sensing
Cesana, Grégory V.; Pierpaoli, Olivia; Ottaviani, Matteo; Vu, Linh; Jin, Zhonghai; Silber, IsraelCesana, G. V., O. Pierpaoli, M. Ottaviani, L. Vu, Z. Jin, I. Silber, 2024: The correlation between Arctic sea ice, cloud phase and radiation using A-Train satellites. Atmospheric Chemistry and Physics, 24(13), 7899-7909. doi: 10.5194/acp-24-7899-2024. Climate warming has a stronger impact on Arctic climate and sea ice cover (SIC) decline than previously thought. Better understanding and characterization of the relationship between sea ice and clouds and the implications for surface radiation is key to improving our confidence in Arctic climate projections. Here we analyze the relationship between sea ice, cloud phase and surface radiation over the Arctic, defined as north of 60° N, using active- and passive-sensor satellite observations from three different datasets. We find that all datasets agree on the climatology of and seasonal variability in total and liquid-bearing (liquid and mixed-phase) cloud covers. Similarly, our results show a robust relationship between decreased SIC and increased liquid-bearing clouds in the lowest levels (below 3 km) for all seasons (strongest in winter) but summer, while increased SIC and ice clouds are positively correlated in two of the three datasets. A refined map correlation analysis indicates that the relationship between SIC and liquid-bearing clouds can change sign over the Bering, Barents and Laptev seas, likely because of intrusions of warm air from low latitudes during winter and spring. Finally, the increase in liquid clouds resulting from decreasing SIC is associated with enhanced radiative cooling at the surface. Our findings indicate that the newly formed liquid clouds reflect more shortwave (SW) radiation back to space compared to the surface, generating a cooling effect of the surface, while their downward longwave (LW) radiation is similar to the upward LW surface emission, which has a negligible radiative impact on the surface. This overall cooling effect should contribute to dampening future Arctic surface warming as SIC continues to decline.
Chao, Li-Wei; Zelinka, Mark D.; Dessler, Andrew E.Chao, L., M. D. Zelinka, A. E. Dessler, 2024: Evaluating Cloud Feedback Components in Observations and Their Representation in Climate Models. Journal of Geophysical Research: Atmospheres, 129(2), e2023JD039427. doi: 10.1029/2023JD039427. This study quantifies the contribution of individual cloud feedbacks to the total short-term cloud feedback in satellite observations over the period 2002–2014 and evaluates how they are represented in climate models. The observed positive total cloud feedback is primarily due to positive high-cloud altitude, extratropical high- and low-cloud optical depth, and land cloud amount feedbacks partially offset by negative tropical marine low-cloud feedback. Seventeen models from the Atmosphere Model Intercomparison Project of the sixth Coupled Model Intercomparison Project are analyzed. The models generally reproduce the observed moderate positive short-term cloud feedback. However, compared to satellite estimates, the models are systematically high-biased in tropical marine low-cloud and land cloud amount feedbacks and systematically low-biased in high-cloud altitude and extratropical high- and low-cloud optical depth feedbacks. Errors in modeled short-term cloud feedback components identified in this analysis highlight the need for improvements in model simulations of the response of high clouds and tropical marine low clouds. Our results suggest that skill in simulating interannual cloud feedback components may not indicate skill in simulating long-term cloud feedback components. CERES; cloud feedback; climate modeling; pattern effect
Chapman-Dutton, H. R.; Webster, M. A.Chapman-Dutton, H. R., M. A. Webster, 2024: The Effects of Summer Snowfall on Arctic Sea Ice Radiative Forcing. Journal of Geophysical Research: Atmospheres, 129(14), e2023JD040667. doi: 10.1029/2023JD040667. Snow is the most reflective natural surface on Earth. Since fresh snow on bare sea ice increases the surface albedo, the impact of summer snow accumulation can have a negative radiative forcing effect, which would inhibit sea ice surface melt and potentially slow sea-ice loss. However, it is not well known how often, where, and when summer snowfall events occur on Arctic sea ice. In this study, we used in situ and model snow depth data paired with surface albedo and atmospheric conditions from satellite retrievals to characterize summer snow accumulation on Arctic sea ice from 2003 to 2017. We found that, across the Arctic, ∼2 snow accumulation events occurred on initially snow-free conditions each year. The average snow depth and albedo increases were ∼2 cm and 0.08, respectively. 16.5% of the snow accumulation events were optically thick (>3 cm deep) and lasted 2.9 days longer than the average snow accumulation event (3.4 days). Based on a simple, multiple scattering radiative transfer model, we estimated a −0.086 ± 0.020 W m−2 change in the annual average top-of-the-atmosphere radiative forcing for summer snowfall events in 2003–2017. The following work provides new information on the frequency, distribution, and duration of observed snow accumulation events over Arctic sea ice in summer. Such results may be particularly useful in understanding the impacts of ephemeral summer weather on surface albedo and their propagating effects on the radiative forcing over Arctic sea ice, as well as assessing climate model simulations of summer atmosphere-ice processes. albedo; Arctic; radiation; sea ice; snow
Chatterjee, Dwaipayan; Schnitt, Sabrina; Bigalke, Paula; Acquistapace, Claudia; Crewell, SusanneChatterjee, D., S. Schnitt, P. Bigalke, C. Acquistapace, S. Crewell, 2024: Capturing the Diversity of Mesoscale Trade Wind Cumuli Using Complementary Approaches From Self-Supervised Deep Learning. Geophysical Research Letters, 51(12), e2024GL108889. doi: 10.1029/2024GL108889. At mesoscale, trade wind clouds organize with various spatial arrangements, shaping their effect on Earth's energy budget. Representing their fine-scale dynamics even at 1 km scale climate simulations remains challenging. However, geostationary satellites (GS) offer high-resolution cloud observation for gaining insights into trade wind cumuli from long-term records. To capture the observed organizational variability, this work proposes an integrated framework using a continuous followed by discrete self-supervised deep learning approach, which exploits cloud optical depth from GS measurements. We aim to simplify the entire mesoscale cloud spectrum by reducing the image complexity in the feature space and meaningfully partitioning it into seven classes whose connection to environmental conditions is illustrated with reanalysis data. Our framework facilitates comparing human-labeled mesoscale classes with machine-identified ones, addressing uncertainties in both methods. It advances previous methods by exploring transitions between regimes, a challenge for physical simulations, and illustrates a case study of sugar-to-flower transitions. artificial intelligence; cloud system transition; cloud variability; mesoscale cloud organization; self-supervision; tropical clouds
Chen, Yan; Wang, Guiling; Seth, AnjiChen, Y., G. Wang, A. Seth, 2024: Climatic Drivers for the Variation of Gross Primary Productivity Across Terrestrial Ecosystems in the United States. Journal of Geophysical Research: Biogeosciences, 129(8), e2024JG008168. doi: 10.1029/2024JG008168. Temperature and water stress are important factors limiting the gross primary productivity (GPP) in terrestrial ecosystems, yet the extent of their influence across ecosystems remains uncertain. This study examines how surface air temperature, soil water availability (SWA) and vapor pressure deficit (VPD) influence ecosystem light use efficiency (LUE), a critical metric for assessing GPP, across different ecosystems and climatic zones at 80 flux tower sites based on in situ measurements and data assimilation products. Results indicate that LUE increases with temperature in spring, with higher correlation coefficients in colder regions (0.79–0.82) than in warmer regions (0.68–0.78). LUE reaches a plateau earlier in the season in warmer regions. LUE variations in summer are mainly driven by SWA, exhibiting a positive correlation indicative of a water-limited regime. The relationship between the daily LUE and daytime temperature shows a clear seasonal hysteresis at many sites, with a higher LUE in spring than in fall under the same temperature, likely resulting from younger leaves being more efficient in photosynthesis. Drought stress influences LUE through SWA in all ranges of water availability; VPD variation under moderate conditions does not have a clear influence on LUE, but extremely high VPD (exceeding the threshold of 1.6 kPa, often observed during extreme drought-heat events) causes a dramatic reduction of LUE. Our findings provide insight into how ecosystem productivities respond to climate variability and how they may change under the influence of more frequent and severe heat and drought events projected for the future. hysteresis; light use efficiency; soil water availability; temperature; vegetation responses
Chen, Yanxu; Yu, LisanChen, Y., L. Yu, 2024: Mesoscale Meridional Heat Transport Inferred From Sea Surface Observations. Geophysical Research Letters, 51(5), e2023GL106376. doi: 10.1029/2023GL106376. The ocean regulates the Earth's climate by transporting heat from the equator to the poles. Here, we use satellite-based sea surface observations of air-sea heat fluxes and eddy detection to investigate the mesoscale heat transport. “Mesoscale” refers to both the Eulerian perspective as the spatio-temporal scales of ∼100 km and ∼1 month, as well as the Lagrangian aspect as isolated vortices identified from the dynamic topography. Paradoxically, there are a considerable number of mesoscale eddies inconsistent between their surface thermal and dynamic signals, that is, cold-core anticyclones and warm-core cyclones are globally prevalent. On account of such inconsistency, we show that the mesoscale meridional heat transport carried by geostrophic components is 10 times larger than (and opposite in direction to) that of the wind-driven Ekman components. An offset between SSH-SST coherent and incoherent eddies in the Ekman heat transport is apparent, whereas the geostrophic heat transport is contained within coherent eddies.
Chen, Ying; Haywood, Jim; Wang, Yu; Malavelle, Florent; Jordan, George; Peace, Amy; Partridge, Daniel G.; Cho, Nayeong; Oreopoulos, Lazaros; Grosvenor, Daniel; Field, Paul; Allan, Richard P.; Lohmann, UlrikeChen, Y., J. Haywood, Y. Wang, F. Malavelle, G. Jordan, A. Peace, D. G. Partridge, N. Cho, L. Oreopoulos, D. Grosvenor, P. Field, R. P. Allan, U. Lohmann, 2024: Substantial cooling effect from aerosol-induced increase in tropical marine cloud cover. Nature Geoscience, 17(5), 404-410. doi: 10.1038/s41561-024-01427-z. With global warming currently standing at approximately +1.2 °C since pre-industrial times, climate change is a pressing global issue. Marine cloud brightening is one proposed method to tackle warming through injecting aerosols into marine clouds to enhance their reflectivity and thereby planetary albedo. However, because it is unclear how aerosols influence clouds, especially cloud cover, both climate projections and the effectiveness of marine cloud brightening remain uncertain. Here we use satellite observations of volcanic eruptions in Hawaii to quantify the aerosol fingerprint on tropical marine clouds. We observe a large enhancement in reflected sunlight, mainly due to an aerosol-induced increase in cloud cover. This observed strong negative aerosol forcing suggests that the current level of global warming is driven by a weaker net radiative forcing than previously thought, arising from the competing effects of greenhouse gases and aerosols. This implies a greater sensitivity of Earth’s climate to radiative forcing and therefore a larger warming response to both rising greenhouse gas concentrations and reductions in atmospheric aerosols due to air quality measures. However, our findings also indicate that mitigation of global warming via marine cloud brightening is plausible and is most effective in humid and stable conditions in the tropics where solar radiation is strong. Climate change; Atmospheric science
Cheng, Lijing; Abraham, John; Trenberth, Kevin E.; Boyer, Tim; Mann, Michael E.; Zhu, Jiang; Wang, Fan; Yu, Fujiang; Locarnini, Ricardo; Fasullo, John; Zheng, Fei; Li, Yuanlong; Zhang, Bin; Wan, Liying; Chen, Xingrong; Wang, Dakui; Feng, Licheng; Song, Xiangzhou; Liu, Yulong; Reseghetti, Franco; Simoncelli, Simona; Gouretski, Viktor; Chen, Gengxin; Mishonov, Alexey; Reagan, Jim; Von Schuckmann, Karina; Pan, Yuying; Tan, Zhetao; Zhu, Yujing; Wei, Wangxu; Li, Guancheng; Ren, Qiuping; Cao, Lijuan; Lu, YayangCheng, L., J. Abraham, K. E. Trenberth, T. Boyer, M. E. Mann, J. Zhu, F. Wang, F. Yu, R. Locarnini, J. Fasullo, F. Zheng, Y. Li, B. Zhang, L. Wan, X. Chen, D. Wang, L. Feng, X. Song, Y. Liu, F. Reseghetti, S. Simoncelli, V. Gouretski, G. Chen, A. Mishonov, J. Reagan, K. Von Schuckmann, Y. Pan, Z. Tan, Y. Zhu, W. Wei, G. Li, Q. Ren, L. Cao, Y. Lu, 2024: New Record Ocean Temperatures and Related Climate Indicators in 2023. Advances in Atmospheric Sciences. doi: 10.1007/s00376-024-3378-5. The global physical and biogeochemical environment has been substantially altered in response to increased atmospheric greenhouse gases from human activities. In 2023, the sea surface temperature (SST) and upper 2000 m ocean heat content (OHC) reached record highs. The 0–2000 m OHC in 2023 exceeded that of 2022 by 15 ± 10 ZJ (1 Zetta Joules = 1021 Joules) (updated IAP/CAS data); 9 ± 5 ZJ (NCEI/NOAA data). The Tropical Atlantic Ocean, the Mediterranean Sea, and southern oceans recorded their highest OHC observed since the 1950s. Associated with the onset of a strong El Niño, the global SST reached its record high in 2023 with an annual mean of ∼0.23°C higher than 2022 and an astounding > 0.3°C above 2022 values for the second half of 2023. The density stratification and spatial temperature inhomogeneity indexes reached their highest values in 2023. climate; global warming; ocean heat content; salinity; stratification
Choudhury, Goutam; Goren, TomChoudhury, G., T. Goren, 2024: Thin Clouds Control the Cloud Radiative Effect Along the Sc-Cu Transition. Journal of Geophysical Research: Atmospheres, 129(10), e2023JD040406. doi: 10.1029/2023JD040406. In situ and spaceborne studies reveal the prevalence of thin clouds in the major Stratocumulus-to-Cumulus Transition (SCT) regions. Using instantaneous satellite and reanalysis data, this study investigates the properties of thin clouds in the Southeast Pacific Ocean and their impact on the cloud radiative effect (CRE). Our findings demonstrate that thin clouds are intrinsic to the SCT. The overcast stratocumulus-dominated regime exhibits a minimal presence of thin clouds, which become notably prominent after the clouds breakup into the cumulus-dominated regime. The regime dependence of the occurrence of thin clouds is also observed in terms of the marine cold-air outbreak parameter and the sea surface temperature. Thin clouds at a given cloud cover significantly modulate the shortwave (SW) and longwave (LW) components of CRE. SW CRE decreases by 46 %–65 % with increasing thin cloud cover. They account for a larger variance in cloud albedo than the combined influence of the liquid water path and effective radius. Furthermore, LW CRE decreases by about 12 %–52 % with thin cloud cover. An increase in the fraction of thin clouds also leads to a larger fraction of negative SW CRE offset by positive LW CRE at a given cloud cover. This LW compensation ranges from approximately 8 % at overcast cloud cover to as much as 19 % at about 50 % cloud cover. These findings elucidate the crucial role of thin clouds, and thus cloud morphology, in modulating CRE and underscore the necessity of their accurate representation in climate models. CERES; cloud morphology; cloud radiative effect; MODIS; stratocumulus-to-cumulus transition; thin clouds
Christensen, Matthew W.; Wu, Peng; Varble, Adam C.; Xiao, Heng; Fast, Jerome D.Christensen, M. W., P. Wu, A. C. Varble, H. Xiao, J. D. Fast, 2024: Aerosol-induced closure of marine cloud cells: enhanced effects in the presence of precipitation. Atmospheric Chemistry and Physics, 24(11), 6455-6476. doi: 10.5194/acp-24-6455-2024. The Weather Research Forecasting (WRF) version 4.3 model is configured within a Lagrangian framework to quantify the impact of aerosols on evolving cloud fields. Kilometer-scale simulations utilizing meteorological boundary conditions are based on 10 case study days offering diverse meteorology during the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA). Measurements from aircraft, the ground-based Atmosphere Radiation Measurement (ARM) site at Graciosa Island in the Azores, and A-Train and geostationary satellites are utilized for validation, demonstrating good agreement with the WRF-simulated cloud and aerosol properties. Higher aerosol concentration leads to suppressed drizzle and increased cloud water content in all case study days. These changes lead to larger radiative cooling rates at cloud top, enhanced vertical velocity variance, and increased vertical and horizontal wind speed near the base of the lower-tropospheric inversion. As a result, marine cloud cell area expands, narrowing the gap between shallow clouds and increasing cloud optical thickness, liquid water content, and the top-of-atmosphere outgoing shortwave flux. While similar aerosol effects are observed in lightly to non-raining clouds, they tend to be smaller by comparison. These simulations show a relationship between cloud cell area expansion and the radiative adjustments caused by liquid water path and cloud fraction changes. The adjustments are positive and scale as 74 % and 51 %, respectively, relative to the Twomey effect. While higher-resolution large-eddy simulations may provide improved representation of cloud-top mixing processes, these results emphasize the importance of addressing mesoscale cloud-state transitions in the quantification of aerosol radiative forcing that cannot be attained from traditional climate models.
Christophersen, H.; Nachamkin, J.; Davis, W.Christophersen, H., J. Nachamkin, W. Davis, 2024: Regional Cloud Forecast Verification Using Standard, Spatial, and Object-Oriented Methods. Wea. Forecasting, 39(3), 563-579. doi: 10.1175/WAF-D-23-0197.1. Abstract This study assesses the accuracy of the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) forecasts for clouds within stable and unstable environments (thereafter refers as “stable” and “unstable” clouds). This evaluation is conducted by comparing these forecasts against satellite retrievals through a combination of traditional, spatial, and object-based methods. To facilitate this assessment, the Model Evaluation Tools (MET) community tool is employed. The findings underscore the significance of fine-tuning the MET parameters to achieve a more accurate representation of the features under scrutiny. The study’s results reveal that when employing traditional pointwise statistics (e.g., frequency bias and equitable threat score), there is consistency in the results whether calculated from Method for Object-Based Diagnostic Evaluation (MODE)-based objects or derived from the complete fields. Furthermore, the object-based statistics offer valuable insights, indicating that COAMPS generally predicts cloud object locations accurately, though the spread of these predicted locations tends to increase with time. It tends to overpredict the object area for unstable clouds while underpredicting it for stable clouds over time. These results are in alignment with the traditional pointwise bias scores for the entire grid. Overall, the spatial metrics provided by the object-based verification methods emerge as crucial and practical tools for the validation of cloud forecasts. Significance Statement As the general Navy meteorological and oceanographic (METOC) community engages in collaboration with the broader scientific community, our goal is to harness community tools like MET for the systematic evaluation of weather forecasts, with a specific focus on variables crucial to the Navy. Clouds, given their significant impact on visibility, hold particular importance in our investigations. Cloud forecasts pose unique challenges, primarily attributable to the intricate physics governing cloud development and the complexity of representing these processes within numerical models. Cloud observations are also constrained by limitations, arising from both top-down satellite measurements and bottom-up ground-based measurements. This study illustrates that, with a comprehensive understanding of community tools, cloud forecasts can be consistently verified. This verification encompasses traditional evaluation methods, measuring general qualities such as bias and root-mean-squared error, as well as newer techniques like spatial and object-based methods designed to account for displacement errors.
Dai, AiguoDai, A., 2024: The diurnal cycle from observations and ERA5 in precipitation, clouds, boundary layer height, buoyancy, and surface fluxes. Climate Dynamics. doi: 10.1007/s00382-024-07182-6. Diurnal variations in precipitation, clouds and other related fields are of interest for many applications. Here I analyze surface and satellite observations and ERA5 data to quantify these variations and evaluate ERA5’s performance. Results show that ERA5 captures the observed seasonal climatology of precipitation and cloud amount remarkably well. Surface observations show that warm-season precipitation exhibits a robust diurnal cycle with an amplitude of ~ 20 to 50% of the daily mean and a peak around 14–18 local solar time (LST) over most land areas and 04–08 LST over most oceans. ERA5 approximately reproduces these features with a slightly earlier peak (by ~ 2 h) over both land and ocean and a stronger amplitude over land, mainly due to biases in its convective precipitation. The IMERG satellite product captures mainly the diurnal cycle of convective precipitation with a peak around 16–20 LST during the warm season. ERA5 oceanic precipitation shows robust diurnal variations that are comparable to observations despite its dampened marine surface diurnal cycle due to its use of daily-mean SST. This suggests a free-tropospheric control of oceanic precipitation diurnal cycle. Surface and satellite observations show more clouds (mainly from low clouds) during daytime (nighttime) over land (ocean). ERA5 total cloud diurnal anomalies are more comparable to surface observations than to ISCCP satellite product. Cloud base height shows a minimum in early afternoon and a maximum around midnight with a diurnal amplitude of ~ 150 m over warm-season land in surface observations; ERA5 approximately captures this diurnal cycle with a slightly stronger amplitude and earlier phase. Land planetary boundary layer height (PBLH) in ERA5 is around 250 m at night but increases after sunrise to a peak around 14–15 LST of about 1500–1900 m in the warm season and ~ 650 to 1100 m in the cold season, with largest diurnal amplitudes over summer drylands. ERA5 marine PBLH is higher in the cold season (~ 1000 m) than in the warm season (~ 530 m) in the extra-tropics, suggesting a dominant role by low-level wind-induced mixing. ERA5 CAPE shows out-of-phase diurnal variations over land and ocean, with near-noontime peak (minimum) and an early morning minimum (peak) over land (ocean). ERA5 CIN’s diurnal cycle is approximately out of phase with CAPE. ERA5 captures well the diurnal cycles and their land–ocean and seasonal differences in surface net shortwave and longwave (LWnet) radiation seen in CERES satellite product, with a near-noontime peak in land LWnet. A near-noontime peak is also seen in ERA surface sensible and latent heat fluxes over land, while oceanic PBLH, LWnet and heat fluxes show little diurnal variation in ERA5, which may be partly due to its use of daily-mean SST. Boundary layer; Clouds; Diurnal cycle; ERA5; Precipitation; Surface fluxes
Donahue, A. S.; Caldwell, P. M.; Bertagna, L.; Beydoun, H.; Bogenschutz, P. A.; Bradley, A. M.; Clevenger, T. C.; Foucar, J.; Golaz, C.; Guba, O.; Hannah, W.; Hillman, B. R.; Johnson, J. N.; Keen, N.; Lin, W.; Singh, B.; Sreepathi, S.; Taylor, M. A.; Tian, J.; Terai, C. R.; Ullrich, P. A.; Yuan, X.; Zhang, Y.Donahue, A. S., P. M. Caldwell, L. Bertagna, H. Beydoun, P. A. Bogenschutz, A. M. Bradley, T. C. Clevenger, J. Foucar, C. Golaz, O. Guba, W. Hannah, B. R. Hillman, J. N. Johnson, N. Keen, W. Lin, B. Singh, S. Sreepathi, M. A. Taylor, J. Tian, C. R. Terai, P. A. Ullrich, X. Yuan, Y. Zhang, 2024: To Exascale and Beyond—The Simple Cloud-Resolving E3SM Atmosphere Model (SCREAM), a Performance Portable Global Atmosphere Model for Cloud-Resolving Scales. Journal of Advances in Modeling Earth Systems, 16(7), e2024MS004314. doi: 10.1029/2024MS004314. The new generation of heterogeneous CPU/GPU computer systems offer much greater computational performance but are not yet widely used for climate modeling. One reason for this is that traditional climate models were written before GPUs were available and would require an extensive overhaul to run on these new machines. In addition, even conventional “high–resolution” simulations don't currently provide enough parallel work to keep GPUs busy, so the benefits of such overhaul would be limited for the types of simulations climate scientists are accustomed to. The vision of the Simple Cloud-Resolving Energy Exascale Earth System (E3SM) Atmosphere Model (SCREAM) project is to create a global atmospheric model with the architecture to efficiently use GPUs and horizontal resolution sufficient to fully take advantage of GPU parallelism. After 5 years of model development, SCREAM is finally ready for use. In this paper, we describe the design of this new code, its performance on both CPU and heterogeneous machines, and its ability to simulate real-world climate via a set of four 40 day simulations covering all 4 seasons of the year. cloud-resolving scales; diurnal cycle; E3SM; exascale; global atmosphere model; global climate model; global storm-resolving model; GPUs; heterogeneous computing; high-resolution global model; Kokkos
Donohoe, A.; Fajber, R.; Cox, T.; Armour, K. C.; Battisti, D. S.; Roe, G. H.Donohoe, A., R. Fajber, T. Cox, K. C. Armour, D. S. Battisti, G. H. Roe, 2024: Model Biases in the Atmosphere-Ocean Partitioning of Poleward Heat Transport Are Persistent Across Three CMIP Generations. Geophysical Research Letters, 51(8), e2023GL106639. doi: 10.1029/2023GL106639. The observed partitioning of poleward heat transport between atmospheric and oceanic heat transports (AHT and OHT) is compared to that in coupled climate models. Model ensemble mean poleward OHT is biased low in both hemispheres, with the largest biases in the Southern Hemisphere extratropics. Poleward AHT is biased high in the Northern Hemisphere, especially in the vicinity of the peak AHT near 40°N. The significant model biases are persistent across three model generations (CMIP3, CMIP5, CMIP6) and are insensitive to the satellite radiation and atmospheric reanalyzes products used to derive observational estimates of AHT and OHT. Model biases in heat transport partitioning are consistent with biases in the spatial structure of energy input to the ocean and atmosphere. Specifically, larger than observed model evaporation in the tropics adds excess energy to the atmosphere that drives enhanced poleward AHT at the expense of weaker OHT. climate models; climate dynamics; atmospheric circulation; ocean circulation
Dramé, Mamadou Simina; N'Diaye, Pape Mbagnick; Niang, Serigne Abdoul Aziz; Diallo, Ismaila; Sarr, Astou; Gueye, Ahmed; Niang, Demba NdaoDramé, M. S., P. M. N'Diaye, S. A. A. Niang, I. Diallo, A. Sarr, A. Gueye, D. N. Niang, 2024: On the characterization of Cloud occurrence and its impact on solar radiation in Mbour, Senegal. Journal of Atmospheric and Solar-Terrestrial Physics, 261, 106284. doi: 10.1016/j.jastp.2024.106284. The objective of this study is to evaluate the clouds seasonal occurrence characteristics, and to estimate their impact on solar radiation in Mbour, Senegal, West Africa. Here, we use datasets from various sources including: i) observations from the Clouds and Earth's Radiant Energy System satellite sensors, ii) in situ shortwave radiation measurement obtained from the Mbour station, and iii) the outgoing longwave radiation (OLR) obtained from the National Centers for Environmental Prediction reanalysis data. Results show a marked seasonality, associated with high spatial variation in terms of cloud occurrence over Senegal. The maximum cloud occurrences are observed during the wet summer season (June–October), whilst the minimum cloud occurrences are recorded during the long-dry season from November to May. During the monsoon season the cloud activity becomes more intense with a total cloud cover of about 80%, a cloud optical depth of around 7, and a high convective activity illustrated by a low OLR (below 240 W/m2). Likewise, across Senegal a strong north-south gradient of the cloud characteristics is observed. Based on quantitative comparison between cloud occurrence and radiation measurement, results show an important seasonal impact on available solar potential in Mbour. Conversely to the cloud occurrence, the maximum of both direct normal and global solar potentials is recorded during the dry season, coinciding with the period with clean sky. An investigation of the cloud influence on solar radiation on selected study cases indicates a decrease of 60% (80%) for the total (direct normal) radiation during the peak of the summer monsoon season. Clouds; Seasonal variation; Senegal; Solar potential; West Africa
Du, Yihan; Wang, Tianxing; Zhou, Yu; Letu, Husi; Li, Dahui; Xian, YuyangDu, Y., T. Wang, Y. Zhou, H. Letu, D. Li, Y. Xian, 2024: Toward User-Friendly All-Sky Surface Longwave Downward Radiation from Space: General Scheme and Product. doi: 10.1175/BAMS-D-23-0126.1. Longwave downward radiation (LWDR) is an important driving parameter in climate and hydrological models. Compared to traditional ground-based measurements, remote sensing has unique advantages in estimating global LWDR. However, for current remote sensing missions, as the typical available satellite-derived LWDR product with global coverage and hourly temporal resolution, the Clouds and the Earth’s Radiant Energy System-Synoptic (CERES-SYN) top of atmosphere and surface fluxes and clouds has a low spatial resolution (1° × 1°). There is still much room for improvement of the existing remote sensing LWDR products in terms of accuracy, spatiotemporal resolutions, and the ability to explain and quantify the changes of longwave radiation at various scales. To overcome these limitations, this paper developed a new global LWDR product with improved accuracy (RMSE < 30 W m−2 over the globe), high temporal resolution (hourly), and spatial resolution (5 km) based on Moderate Resolution Imaging Spectroradiometer (MODIS) measurements. It serves as a LWDR product within the Long-term Earth System spatiotemporally Seamless Radiation budget dataset (referred to as LessRad). As the first long-term high-resolution, spatiotemporally continuous LWDR product (2002–22, 1 h, 5 km), the LessRad reveals its advantages in studying the spatiotemporal variability of LWDR on finer scales. It also provides a valuable data source for various applications, such as analyzing land–atmosphere interactions and quantifying climate feedback, and thus is potentially helpful for understanding Earth’s energy budget and dynamics. Climate change; Longwave radiation; Radiation budgets
Dunn, R. J. H.; Blannin, J.; Gobron, N.; Miller, J. B.; Willett, K. M.; Ades, Melanie; Adler, Robert; Alexe, Mihai; Allan, Richard P.; Anderson, John; Anneville, Orlane; Aono, Yasuyuki; Arguez, Anthony; Pascual, Dolores Armenteras; Arosio, Carlo; Asher, Elizabeth; Augustine, John A.; Azorin-Molina, Cesar; Baez-Villanueva, Oscar M.; Barichivich, J.; Beck, Hylke E.; Bellouin, Nicolas; Benedetti, Angela; Blenkinsop, Stephen; Bock, Olivier; Bodin, Xavier; Bonte, Olivier; Bosilovich, Michael G.; Boucher, Olivier; Buehler, Stefan A.; Byrne, Michael P.; Campos, Diego; Cappucci, Fabrizio; Carrea, Laura; Chang, Kai-Lan; Christiansen, Hanne H.; Christy, John R.; Chung, Eui-Seok; Ciasto, Laura M.; Clingan, Scott; Coldewey-Egbers, Melanie; Cooper, Owen R.; Cornes, Richard C.; Covey, Curt; Crétaux, Jean-Francois; Crimmins, Theresa; Crotwell, Molly; Culpepper, Joshua; Cusicanqui, Diego; Davis, Sean; Jeu, Richard A. M. de; Degenstein, Doug; Delaloye, Reynald; DiGangi, Elizabeth; Dokulil, Martin T.; Donat, Markus G.; Dorigo, Wouter A.; Duchemin, Diane; Dugan, Hilary; Durre, Imke; Dutton, Geoff; Duveiller, Gregory; Estilow, Thomas W.; Estrella, Nicole; Fereday, David; Fioletov, Vitali E.; Flemming, Johannes; Foster, Michael J.; Frederikse, Thomas; Frith, Stacey M.; Froidevaux, Lucien; Füllekrug, Martin; Garforth, Judith; Garg, Jay; Godin-Beekmann, Sophie; Goodman, Steven; Goto, Atsushi; Grimm, Alice; Gruber, Alexander; Gu, Guojun; Guglielmin, Mauro; Hahn, Sebastian; Haimberger, Leopold; HalDunn, R. J. H., J. Blannin, N. Gobron, J. B. Miller, K. M. Willett, M. Ades, R. Adler, M. Alexe, R. P. Allan, J. Anderson, O. Anneville, Y. Aono, A. Arguez, D. A. Pascual, C. Arosio, E. Asher, J. A. Augustine, C. Azorin-Molina, O. M. Baez-Villanueva, J. Barichivich, H. E. Beck, N. Bellouin, A. Benedetti, S. Blenkinsop, O. Bock, X. Bodin, O. Bonte, M. G. Bosilovich, O. Boucher, S. A. Buehler, M. P. Byrne, D. Campos, F. Cappucci, L. Carrea, K. Chang, H. H. Christiansen, J. R. Christy, E. Chung, L. M. Ciasto, S. Clingan, M. Coldewey-Egbers, O. R. Cooper, R. C. Cornes, C. Covey, J. Crétaux, T. Crimmins, M. Crotwell, J. Culpepper, D. Cusicanqui, S. Davis, R. A. M. d. Jeu, D. Degenstein, R. Delaloye, E. DiGangi, M. T. Dokulil, M. G. Donat, W. A. Dorigo, D. Duchemin, H. Dugan, I. Durre, G. Dutton, G. Duveiller, T. W. Estilow, N. Estrella, D. Fereday, V. E. Fioletov, J. Flemming, M. J. Foster, T. Frederikse, S. M. Frith, L. Froidevaux, M. Füllekrug, J. Garforth, J. Garg, S. Godin-Beekmann, S. Goodman, A. Goto, A. Grimm, A. Gruber, G. Gu, M. Guglielmin, S. Hahn, L. Haimberger, . Hal, 2024: Global Climate. doi: 10.1175/BAMS-D-24-0116.1. "Global Climate" published on 22 Aug 2024 by American Meteorological Society.
Eastman, Ryan; McCoy, Isabel L.; Schulz, Hauke; Wood, RobertEastman, R., I. L. McCoy, H. Schulz, R. Wood, 2024: A survey of radiative and physical properties of North Atlantic mesoscale cloud morphologies from multiple identification methodologies. Atmospheric Chemistry and Physics, 24(11), 6613-6634. doi: 10.5194/acp-24-6613-2024. Three supervised neural network cloud classification routines are applied to daytime MODIS Aqua imagery and compared for the year 2018 over the North Atlantic Ocean. Routines surveyed here include the Morphology Identification Data Aggregated over the Satellite-era (MIDAS), which specializes in subtropical stratocumulus (Sc) clouds; sugar, gravel, flowers, and fish (SGFF), which is focused on shallow cloud systems in the tropical trade winds; and the community record of marine low-cloud mesoscale morphology supported by the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) dataset, which is focused on shallow clouds globally. Comparisons of co-occurrence and vertical and geographic distribution show that morphologies are classified in geographically distinct regions; shallow suppressed and deeper aggregated and disorganized cumulus are seen in the tropical trade winds. Shallow Sc types are frequent in subtropical subsidence regions. More vertically developed solid stratus and open- and closed-cell Sc are frequent in the mid-latitude storm track. Differing classifier routines favor noticeably different distributions of equivalent types. Average scene albedo is more strongly correlated with cloud albedo than cloud amount for each morphology. Cloud albedo is strongly correlated with the fraction of optically thin cloud cover. The albedo of each morphology is dependent on latitude and location in the mean anticyclonic wind flow over the North Atlantic. Strong rain rates are associated with middling values of albedo for many cumuliform types, hinting at a complex relationship between the presence of heavily precipitating cores and cloud albedo. The presence of ice at cloud top is associated with higher albedos. For a constant albedo, each morphology displays a distinct set of physical characteristics.
Francis, Diana; Fonseca, RicardoFrancis, D., R. Fonseca, 2024: Recent and projected changes in climate patterns in the Middle East and North Africa (MENA) region. Scientific Reports, 14(1), 10279. doi: 10.1038/s41598-024-60976-w. Observational and reanalysis datasets reveal a northward shift of the convective regions over northern Africa in summer and an eastward shift in winter in the last four decades, with the changes in the location and intensity of the thermal lows and subtropical highs also modulating the dust loading and cloud cover over the Middle East and North Africa region. A multi-model ensemble from ten models of the Coupled Model Intercomparison Project—sixth phase gives skillful simulations when compared to in-situ measurements and generally captures the trends in the ERA-5 data over the historical period. For the most extreme climate change scenario and towards the end of the twenty-first century, the subtropical highs are projected to migrate poleward by 1.5°, consistent with the projected expansion of the Hadley Cells, with a weakening of the tropical easterly jet in the summer by up to a third and a strengthening of the subtropical jet in winter typically by 10% except over the eastern Mediterranean where the storm track is projected to shift polewards. The length of the seasons is projected to remain about the same, suggesting the warming is likely to be felt uniformly throughout the year. Climate change; Climate sciences; Atmospheric science
Francis, Diana; Fonseca, Ricardo; Nelli, Narendra; Yarragunta, YesobuFrancis, D., R. Fonseca, N. Nelli, Y. Yarragunta, 2024: Unusually low dust activity in North Africa in June 2023: Causes, impacts and future projections. Atmospheric Research, 309, 107594. doi: 10.1016/j.atmosres.2024.107594. Dust activity during the pre-monsoon season in Africa has an impact on the monsoon circulation and the Atlantic hurricane season. During early June 2023 the atmosphere was relatively clear over West Africa and the eastern tropical Atlantic, in contrast with the dustier June 2020. The negative phase of the North Atlantic Oscillation suppressed dust lifting, with an equatorward shifted African Easterly Jet limiting its downstream advection. On the other hand, dust accumulated in the atmosphere over northeastern Africa, with the negative dust aerosol optical depth (DAOD) anomalies over western Africa and the positive anomalies over eastern Africa more than two standard deviations away from the climatological mean. The lack of dust led to an up to 55 W m−2 increase in the surface downward shortwave radiation flux and a 35 W m−2 decrease in the longwave flux, and is in line with the record-breaking sea surface temperatures over the eastern tropical Atlantic and the active start to the Atlantic hurricane season. In order to explore future projections of DAOD, a multi-model ensemble (MME) is constructed from 29 models that integrate the sixth phase of the Coupled Model Intercomparison Project (CMIP6). It captures the positive trend in the June DAOD over the eastern tropical Atlantic during 1980–2014, although the amplitude is roughly a factor of six smaller than the 0.0017 year−1 in the reanalysis dataset. The CMIP6 MME projects a further increase in DAOD in the region at a rate of up to 0.0003 year−1 in the most extreme climate change scenario for 2066–2100, which is comparable to that seen during the historical period, even though the mean values are projected to decrease by 0.03–0.06. While lower dust loadings may lead to improved air quality, they will likely further fuel pre-season and early season storms in the North Atlantic, which have become more frequent in recent decades. African Easterly Jet; Circumglobal Wavetrain; CMIP6; Dust aerosol optical depth; North Atlantic Oscillation; Radiation fluxes
Fu, Zhen; Zhang, Yi; Li, Xiaohan; Rong, XinyaoFu, Z., Y. Zhang, X. Li, X. Rong, 2024: Intercomparison of two model climates simulated by a unified weather-climate model system (GRIST), part I: mean state. Climate Dynamics. doi: 10.1007/s00382-024-07205-2. This study made an intercomparison of two model climates, simulated by a unified weather-climate model system (GRIST), under the Atmospheric Model Intercomparison Project (AMIP) experimental protocol. These two model AMIP simulations with PhysW and PhysC (AMIPW and AMIPC hereafter) are configured with different physics suites, but both generated by a unified dynamical core framework. PhysW and PhysC are originally designed for weather forecasting and climate simulation, respectively. Both AMIPW and AMIPC reach statistical equilibrium in the climate integration. They overall produce comparable model climates, while distinctive bias features also exist. Compared with the AMIP experiments of 54 climate models from CMIP6, both AMIPW and AMIPC demonstrate competitive performances in the mean state simulations. They capture the observed spatial distribution of large-scale circulation and precipitation, as well as replicate the seasonal migration and primary frequency-intensity structures of precipitation. However, due to different parameterization schemes such as convection and microphysics being utilized, the most notable differences between the models lie in processes related to moist physics. For instance, AMIPW tends to overestimate (underestimate) global shortwave (longwave) cloud radiative forcing, while AMIPC provides a more balanced estimation, with a significantly stronger longwave cloud radiative forcing over the tropics. In addition, AMIPC well reproduces cloud fraction and liquid content but underestimates cloud ice water content, whereas AMIPW significantly overestimates all these variables. Overall, the similarity between two model climates is higher than their discrepancy. The results demonstrate that the extent to which the selection of two distinct physics suites can influence the simulated model climate, within a unified model system. AMIP simulations; Mean state; Model comparison; Unified weather-climate model system
Gettelman, A.; Christensen, M. W.; Diamond, M. S.; Gryspeerdt, E.; Manshausen, P.; Stier, P.; Watson-Parris, D.; Yang, M.; Yoshioka, M.; Yuan, T.Gettelman, A., M. W. Christensen, M. S. Diamond, E. Gryspeerdt, P. Manshausen, P. Stier, D. Watson-Parris, M. Yang, M. Yoshioka, T. Yuan, 2024: Has Reducing Ship Emissions Brought Forward Global Warming?. Geophysical Research Letters, 51(15), e2024GL109077. doi: 10.1029/2024GL109077. Ships brighten low marine clouds from emissions of sulfur and aerosols, resulting in visible “ship tracks”. In 2020, new shipping regulations mandated an ∼80% reduction in the allowed fuel sulfur content. Recent observations indicate that visible ship tracks have decreased. Model simulations indicate that since 2020 shipping regulations have induced a net radiative forcing of +0.12 Wm−2. Analysis of recent temperature anomalies indicates Northern Hemisphere surface temperature anomalies in 2022–2023 are correlated with observed cloud radiative forcing and the cloud radiative forcing is spatially correlated with the simulated radiative forcing from the 2020 shipping emission changes. Shipping emissions changes could be accelerating global warming. To better constrain these estimates, better access to ship position data and understanding of ship aerosol emissions are needed. Understanding the risks and benefits of emissions reductions and the difficultly in robust attribution highlights the large uncertainty in attributing proposed deliberate climate intervention. aerosols; climate; global warming; sulfur
Gomez, James L.; Allen, Robert J.; Li, King-FaiGomez, J. L., R. J. Allen, K. Li, 2024: California wildfire smoke contributes to a positive atmospheric temperature anomaly over the western United States. Atmospheric Chemistry and Physics, 24(11), 6937-6963. doi: 10.5194/acp-24-6937-2024. Wildfires in the southwestern United States, particularly in northern California (nCA), have grown in size and severity in the past decade. As they have grown larger, they have been associated with large emissions of absorbing aerosols and heat into the troposphere. Utilizing satellite observations from MODIS, CERES, and AIRS as well as reanalysis from MERRA-2, the meteorology associated with fires during the wildfire season (June–October) was discerned over the nCA-NV (northern California and Nevada) region during the period 2003–2022. Wildfires in the region have a higher probability of occurring on days of positive temperature (T) anomalies and negative relative humidity (RH) anomalies, making it difficult to discern the radiative effects of aerosols that are concurrent with fires. To attempt to better isolate the effects of large fire emissions on meteorological variables, such as clouds and precipitation, variable anomalies on high fire emission days (90th percentile) were compared with low fire emission days (10th percentile) and were further stratified based on whether surface relative humidity (RHs) was anomalously high (75th percentile) or low (25th percentile) compared with typical fire season conditions. Comparing the simultaneously high fire emission and high RHs data with the simultaneously low fire emission and high RHs data, positive tropospheric T anomalies were found to be concurrent with positive AOD anomalies. Further investigation found that due to shortwave absorption, the aerosols heat the atmosphere at a rate of 0.041 ± 0.016 to 0.093 ± 0.019 K d−1, depending on whether RH conditions are anomalously positive or negative. The positive T anomalies were associated with significant negative 850–300 hPa RH anomalies during both 75th percentile RHs conditions. Furthermore, high fire emission days under high RHs conditions are associated with negative CF anomalies that are concurrent with the negative RH anomalies. This negative CF anomaly is associated with a significantly negative regional precipitation anomaly and a positive net top-of-atmosphere radiative flux anomaly (a warming effect) in certain areas. The T, RH, and CF anomalies under the simultaneously high fire emission and high RHs conditions compared with the simultaneously low fire emission and high RHs conditions have a significant spatial correlation with AOD anomalies. Additionally, the vertical profile of these variables under the same stratification is consistent with positive black carbon mass mixing ratio anomalies from MERRA-2. However, causality is difficult to discern, and further study is warranted to determine to what extent the aerosols are contributing to these anomalies.
Gomez, James L.; Allen, Robert J.; Li, King-FaiGomez, J. L., R. J. Allen, K. Li, 2024: Satellite Observations Reveal Northern California Wildfire Aerosols Reduce Cloud Cover in California and Nevada Through Semi-Direct Effects. EGUsphere, 1-32. doi: 10.5194/egusphere-2023-2827. Abstract. Wildfires in the southwestern United States, particularly in northern California (nCA), have grown in size and severity in the past decade. As they have grown larger, they have been associated with large emissions of absorbing aerosols in to the troposphere. Utilizing satellite observations from MODIS, CERES, AIRS, and CALIPSO, the meteorological effects of aerosols associated with fires during the wildfire season (June–October) were discerned over the nCA-NV (northern California and Nevada) region in the 2003–2022 time frame. As higher temperatures and low relative humidity RH dominate during high surface pressure ps atmospheric conditions, the effects of the aerosols on high (90th percentile) fire days compared to low fire (10th percentile) days were stratified based on whether ps was anomalously high or anomalously low (10th percentile). An increase in tropospheric temperatures was found to be concurrent with more absorbing aerosol aloft, which is associated with significant reductions in tropospheric RH during both 90th and 10th percentile ps conditions. Furthermore, high fire days under low ps conditions are associated with reduced cloud fraction CF, which is consistent with the traditionally-defined aerosol- cloud semi-direct effect. The reduced CF, in turn, is associated with reduced T OA SW radiative flux, a warmer surface, and less precipitation. These changes could create a positive feedback that could intensify fire weather, and therefore extend fire lifetime and impacts.
Green, J. K.; Zhang, Y.; Luo, X.; Keenan, T. F.Green, J. K., Y. Zhang, X. Luo, T. F. Keenan, 2024: Systematic Underestimation of Canopy Conductance Sensitivity to Drought by Earth System Models. AGU Advances, 5(1), e2023AV001026. doi: 10.1029/2023AV001026. The response of vegetation canopy conductance (gc) to changes in moisture availability (γgcm {\gamma _gc^m\) is a major source of uncertainty in climate projections. While vegetation typically reduces stomatal conductance during drought, accurately modeling how and to what degree stomata respond to changes in moisture availability at global scales is particularly challenging, because no global scale gc observations exist. Here, we leverage a collection of satellite, reanalysis and station-based near-surface air and surface temperature estimates, which are physically and statistically linked to γgcm {\gamma _gc^m\ due to the local cooling effect of gc through transpiration, to develop a novel emergent constraint of γgcm {\gamma _gc^m\ in an ensemble of Earth System Models (ESMs). We find that ESMs systematically underestimate γgcm {\gamma _gc^m\ by ∼33%, particularly in grasslands, croplands, and savannas in semi-arid and bordering regions of the Central United States, Central Europe, Southeastern South America, Southern Africa, Eastern Australia, and parts of East Asia. We show that this underestimation occurs because ESMs inadequately reduce gc when soil moisture decreases. As gc controls carbon, water and energy fluxes, the misrepresentation of modeled γgcm {\gamma _gc^m\ contributes to biases in ESM projections of gross primary production, transpiration, and temperature during droughts. Our results suggest that the severity and duration of droughts may be misrepresented in ESMs due to the impact of sustained gc on both soil moisture dynamics and the biosphere-atmosphere feedbacks that affect local temperatures and regional weather patterns. land surface temperature; emergent constraint; biosphere-atmosphere feedbacks; canopy conductance; Earth System Models; vegetation water stress
Griesche, Hannes Jascha; Barrientos-Velasco, Carola; Deneke, Hartwig; Hünerbein, Anja; Seifert, Patric; Macke, AndreasGriesche, H. J., C. Barrientos-Velasco, H. Deneke, A. Hünerbein, P. Seifert, A. Macke, 2024: Low-level Arctic clouds: a blind zone in our knowledge of the radiation budget. Atmospheric Chemistry and Physics, 24(1), 597-612. doi: 10.5194/acp-24-597-2024. Quantifying the role of clouds in the earth's radiation budget is essential for improving our understanding of the drivers and feedback mechanisms of climate change. This holds in particular for the Arctic, the region currently undergoing the most rapid changes. This region, however, also poses significant challenges to remote-sensing retrievals of clouds and radiative fluxes, introducing large uncertainties in current climate data records. In particular, low-level stratiform clouds are common in the Arctic but are, due to their low altitude, challenging to observe and characterize with remote-sensing techniques. The availability of reliable ground-based observations as reference is thus of high importance. In the present study, radiative transfer simulations using state-of-the-art ground-based remote sensing of clouds are contrasted with surface radiative flux measurements to assess their ability to constrain the cloud radiative effect. Cloud radar, lidar, and microwave radiometer observations from the PS106 cruise in the Arctic marginal sea ice zone in summer 2017 were used to derive cloud micro- and macrophysical properties by means of the instrument synergy approach of Cloudnet. Closure of surface radiative fluxes can only be achieved by a realistic representation of the low-level liquid-containing clouds in the radiative transfer simulations. The original, most likely erroneous, representation of these low-level clouds in the radiative transfer simulations led to errors in the cloud radiative effect of 54 W m−2. In total, the proposed method could be applied to 11 % of the observations. For the data, where the proposed method was utilized, the average relative error decreased from 109 % to 37 % for the simulated solar and from 18 % to 2.5 % for the simulated terrestrial downward radiative fluxes at the surface. The present study highlights the importance of jointly improving retrievals for low-level liquid-containing clouds which are frequently encountered in the high Arctic, together with observational capabilities both in terms of cloud remote sensing and radiative flux observations. Concrete suggestions for achieving these goals are provided.
Guendelman, Ilai; Merlis, Timothy M.; Cheng, Kai-Yuan; Harris, Lucas M.; Bretherton, Christopher S.; Bolot, Maximilien; Zhou, Linjiong; Kaltenbaugh, Alex; Clark, Spencer K.; Fueglistaler, StephanGuendelman, I., T. M. Merlis, K. Cheng, L. M. Harris, C. S. Bretherton, M. Bolot, L. Zhou, A. Kaltenbaugh, S. K. Clark, S. Fueglistaler, 2024: The Precipitation Response to Warming and CO2 Increase: A Comparison of a Global Storm Resolving Model and CMIP6 Models. Geophysical Research Letters, 51(7), e2023GL107008. doi: 10.1029/2023GL107008. Global storm-resolving models (GSRMs) that can explicitly resolve some of deep convection are now being integrated for climate timescales. GSRMs are able to simulate more realistic precipitation distributions relative to traditional Coupled Model Intercomparison Project 6 (CMIP6) models. In this study, we present results from two-year-long integrations of a GSRM developed at Geophysical Fluid Dynamics Laboratory, eXperimental System for High-resolution prediction on Earth-to-Local Domains (X-SHiELD), for the response of precipitation to sea surface temperature warming and an isolated increase in CO2 and compare it to CMIP6 models. At leading order, X-SHiELD's response is within the range of the CMIP6 models. However, a close examination of the precipitation distribution response reveals that X-SHiELD has a different response at lower percentiles and the response of the extreme events are at the lower end of the range of CMIP6 models. A regional decomposition reveals that the difference is most pronounced for midlatitude land, where X-SHiELD shows a lower increase at intermediate percentiles and drying at lower percentiles. climate change; precipitation; cloud resolving models
Gunnarson, Jacob L.; Stuecker, Malte F.; Zhao, SenGunnarson, J. L., M. F. Stuecker, S. Zhao, 2024: Drivers of future extratropical sea surface temperature variability changes in the North Pacific. npj Climate and Atmospheric Science, 7(1), 1-11. doi: 10.1038/s41612-024-00702-5. Under anthropogenic warming, future changes to climate variability beyond specific modes such as the El Niño-Southern Oscillation (ENSO) have not been well-characterized. In the Community Earth System Model version 2 Large Ensemble (CESM2-LE) climate model, the future change to sea surface temperature (SST) variability (and correspondingly marine heatwave intensity) on monthly timescales and longer is spatially heterogeneous. We examined these projected changes (between 1960–2000 and 2060–2100) in the North Pacific using a local linear stochastic-deterministic model, which allowed us to quantify the effect of changes to three drivers on SST variability: ocean “memory” (the SST damping timescale), ENSO teleconnections, and stochastic noise forcing. The ocean memory declines in most areas, but lengthens in the central North Pacific. This change is primarily due to changes in air-sea feedbacks and ocean damping, with the shallowing mixed layer depth playing a secondary role. An eastward shift of the ENSO teleconnection pattern is primarily responsible for the pattern of SST variance change. Atmospheric dynamics; Physical oceanography
Guo, Hao; Tian, Yunfei; Li, Junli; Meng, Xiangchen; Lv, Xiaoyu; Wang, Wei; Bao, Anming; Zhu, Li; Nzabarinda, Vincent; De Maeyer, PhilippeGuo, H., Y. Tian, J. Li, X. Meng, X. Lv, W. Wang, A. Bao, L. Zhu, V. Nzabarinda, P. De Maeyer, 2024: Unveiling the spatiotemporal impacts of the 2021 Central Asian drought on vegetation: A comprehensive quantitative analysis. Ecological Indicators, 165, 112238. doi: 10.1016/j.ecolind.2024.112238. In the growing season of 2021, a severe drought occurred in Central Asia impacting various local ecosystems and socio-economic conditions. However, there is limited research on the spatiotemporal characteristics of this drought and its effects on local vegetation. To address this gap, this study utilizes the standardized precipitation evapotranspiration index (SPEI) to quantitatively evaluate the spatiotemporal drought characteristics, and standardized anomalies to assess drought impacts on vegetation greenness and productivity. The drought-induced reduction in vegetation greenness and production was also decomposed into environmental drivers based on a random forest model. Our findings can be summarized as follows: During the 2021 growing season, Central Asia experienced one of the most severe drought events in the past 40 years, with approximately 42.57 % of the region facing record-breaking drought conditions. Abnormally low precipitation (PRE), prolonged high temperatures (TMP) and evapotranspiration also occurred during the drought event. The drought had a significant detrimental effect on vegetation, leading to an approximately 10 % reduction in vegetation greenness and around 13 % in productivity. Soil moisture (SM) was found to be the most critical factor influencing vegetation greenness loss during drought conditions. Leaf Area Index (LAI) and SM emerged as the primary drivers for the reduction of Gross Primary Productivity (GPP) and Solar-Induced Fluorescence (SIF). The antecedent environmental conditions had a significant impact on the decline in vegetation greenness and productivity during the 2021 drought event, accounting for approximately 30 %–35 % and 52–69 % of the respective losses. The findings of this study highlight the importance of taking into account antecedent climate factors when studying the impacts of drought on vegetation. Central Asia; Drought impacts; Extreme drought; Greenness and production; Vegetation response
Guo, Mengfei; Cheng, Jie; Zeng, QiGuo, M., J. Cheng, Q. Zeng, 2024: A data-driven model for estimating clear-sky surface longwave downward radiation over polar regions. IEEE Transactions on Geoscience and Remote Sensing, 1-1. doi: 10.1109/TGRS.2024.3418205. Polar regions play a crucial role in global climate change. Surface longwave downward radiation (SLDR) is a primary energy source for the polar surface, plays an essential role for studies of polar hydrology, temperature and climate. Therefore, accurately estimating the SLDR over polar regions is highly important. However, the accuracies of existing polar SLDR datasets and SLDR inversion methods are insufficient to meet the requirements of relevant research. In this study, we developed a data-driven model for high spatial resolution clear-sky SLDRs estimated from Moderate Resolution Imaging Spectroradiometer (MODIS) imagery in polar regions. The model comprises two layers: the first layer incorporates three machine learning models, namely, XGBoost, CNN and Transformer, while the second layer consists of a stacking meta-model. The ground measurements collected from 51 sites were used to train and validate the developed model. The bias, RMSE and R2 of the model training are zero, 14.15 W/m2 and 0.95, respectively, whereas the values for the validation are 0.49, 15.35 W/m2 and 0.9, respectively. We also compared the accuracies of the ERA5 and CERES-SYN SLDR data with the SLDR estimated by the developed model. The results indicate that the developed model is superior to the ERA5 and CERES-SYN SLDR models when evaluated at the validation sites. Additionally, we analyzed the performance of the developed model under different elevations and seasons, demonstrating its robustness in different situations. Climate change; Data models; Spatial resolution; Hydrology; MODIS; Machine learning; CNN; Surface Radiation Budget; Convolutional neural networks; Machine Learning; Polar Region; Radiation monitoring; Stacking; Surface longwave downward radiation (SLDR); Transformer; Transformers; XGBoost
Hakuba, Maria Z.; Fourest, Sébastien; Boyer, Tim; Meyssignac, Benoit; Carton, James A.; Forget, Gaël; Cheng, Lijing; Giglio, Donata; Johnson, Gregory C.; Kato, Seiji; Killick, Rachel E.; Kolodziejczyk, Nicolas; Kuusela, Mikael; Landerer, Felix; Llovel, William; Locarnini, Ricardo; Loeb, Norman; Lyman, John M.; Mishonov, Alexey; Pilewskie, Peter; Reagan, James; Storto, Andrea; Sukianto, Thea; von Schuckmann, KarinaHakuba, M. Z., S. Fourest, T. Boyer, B. Meyssignac, J. A. Carton, G. Forget, L. Cheng, D. Giglio, G. C. Johnson, S. Kato, R. E. Killick, N. Kolodziejczyk, M. Kuusela, F. Landerer, W. Llovel, R. Locarnini, N. Loeb, J. M. Lyman, A. Mishonov, P. Pilewskie, J. Reagan, A. Storto, T. Sukianto, K. von Schuckmann, 2024: Trends and Variability in Earth’s Energy Imbalance and Ocean Heat Uptake Since 2005. Surveys in Geophysics. doi: 10.1007/s10712-024-09849-5. Earth’s energy imbalance (EEI) is a fundamental metric of global Earth system change, quantifying the cumulative impact of natural and anthropogenic radiative forcings and feedback. To date, the most precise measurements of EEI change are obtained through radiometric observations at the top of the atmosphere (TOA), while the quantification of EEI absolute magnitude is facilitated through heat inventory analysis, where ~ 90% of heat uptake manifests as an increase in ocean heat content (OHC). Various international groups provide OHC datasets derived from in situ and satellite observations, as well as from reanalyses ingesting many available observations. The WCRP formed the GEWEX-EEI Assessment Working Group to better understand discrepancies, uncertainties and reconcile current knowledge of EEI magnitude, variability and trends. Here, 21 OHC datasets and ocean heat uptake (OHU) rates are intercompared, providing OHU estimates ranging between 0.40 ± 0.12 and 0.96 ± 0.08 W m−2 (2005–2019), a spread that is slightly reduced when unequal ocean sampling is accounted for, and that is largely attributable to differing source data, mapping methods and quality control procedures. The rate of increase in OHU varies substantially between − 0.03 ± 0.13 (reanalysis product) and 1.1 ± 0.6 W m−2 dec−1 (satellite product). Products that either more regularly observe (satellites) or fill in situ data-sparse regions based on additional physical knowledge (some reanalysis and hybrid products) tend to track radiometric EEI variability better than purely in situ-based OHC products. This paper also examines zonal trends in TOA radiative fluxes and the impact of data gaps on trend estimates. The GEWEX-EEI community aims to refine their assessment studies, to forge a path toward best practices, e.g., in uncertainty quantification, and to formulate recommendations for future activities. Argo; Earth’s energy imbalance; GEWEX; Ocean heat content; Radiation budget; Reanalysis
Hakuba, Maria Z.; Reynerson, Charles M.; Quadrelli, Marco B.; Wiese, David N.; Mccullough, ChristopherHakuba, M. Z., C. M. Reynerson, M. B. Quadrelli, D. N. Wiese, C. Mccullough, 2024: Modeling Radiation Pressure Accelerations: Earth Radiance Anisotropy, Spacecraft Shape and Global Sampling. 2024 IEEE Aerospace Conference, 1-7. doi: 10.1109/AERO58975.2024.10521289. In this study, we investigate the feasibility of a direct measurement of Earth’s Energy Imbalance (EEI) from space via radiation pressure accelerations. EEI represents one of the most challenging Earth observations for climate change research and quantifies the fundamental rate of global heating in response to radiative forcings and feedbacks. Using state-of-the-art mission design and orbit determination software, we simulate Sun’s and Earth’s radiative pressure impact on spacecrafts of different shapes. We derive the Earth radiation (shortwave and longwave) intercepted by the spacecraft from observed radiative fluxes (Clouds and Earth’s Radiant Energy System, CERES) and correct for radiance anisotropy using anisotropy factors derived from historical Earth Radiation Budget (ERB) missions. Anisotropy is a function of solar and satellite viewing geometry, as well as of scene type (surface and atmospheric properties) of each Earth element in view of the satellite at any point in time. In addition, we test the sensitivity of confounding forces, such as aerodynamic drag and Yarkovsky effects to spacecraft shape, and present preliminary results of a sampling study to quantify the bias of daily global mean net radiative flux associated with a sun-synchronous orbit crossing Earth’s equator at 12 pm local time. Our investigations and software development will inform instrument and mission requirements relevant to the accurate measurement of EEI. Earth; Extraterrestrial measurements; Satellites; Space vehicles; Anisotropic magnetoresistance; Sensitivity; Shape
Haslehner, Kerstin; Gasparini, Blaž; Voigt, AikoHaslehner, K., B. Gasparini, A. Voigt, 2024: Radiative Heating of High-Level Clouds and Its Impacts on Climate. Journal of Geophysical Research: Atmospheres, 129(12), e2024JD040850. doi: 10.1029/2024JD040850. The interactions of clouds with radiation influence climate. Many of these impacts appear to be related to the radiative heating and cooling from high-level clouds, but few studies have explicitly tested this. Here, we use simulations with the ICON-ESM model to understand how high-level clouds, through their radiative heating and cooling, influence the large-scale atmospheric circulation and precipitation in the present-day climate. We introduce a new method to diagnose the radiative heating of high-level clouds: instead of defining high-level clouds as all clouds at temperatures colder than −35°C, we define them as all clouds with a cloud top at temperatures colder than −35°C. The inclusion of the lower cloud parts at temperatures warmer than −35°C circumvents the creation of artificial cloud boundaries and strong artificial radiative heating at the temperature threshold. To isolate the impact of high-level clouds, we analyze simulations with active cloud-radiative heating, with the radiative heating from high-level clouds set to zero, and with the radiative heating from all clouds set to zero. We show that the radiative interactions of high-level clouds warm the troposphere and strengthen the eddy-driven jet streams, but have no impact on the Hadley circulation strength and the latitude of the Intertropical Convergence Zone. Consistent with their positive radiative heating and energetic arguments, high-level clouds reduce precipitation throughout the tropics and lower midlatitudes. Overall, our results confirm that the radiative interactions of high-level clouds have important impacts on climate and highlight the need for better representing their radiative interactions in models. climate modeling; cloud-radiative heating; high-level clouds
Hingmire, Dipti; Hirasawa, Haruki; Singh, Hansi; Rasch, Philip J.; Kim, Sookyung; Hazarika, Subhashis; Mitra, Peetak; Ramea, KalaiHingmire, D., H. Hirasawa, H. Singh, P. J. Rasch, S. Kim, S. Hazarika, P. Mitra, K. Ramea, 2024: South Asian Summer Monsoon Precipitation Is Sensitive to Southern Hemisphere Subtropical Radiation Changes. Geophysical Research Letters, 51(11), e2024GL108499. doi: 10.1029/2024GL108499. We study the sensitivity of South Asian Summer Monsoon (SASM) precipitation to Southern Hemisphere (SH) subtropical Absorbed Solar Radiation (ASR) changes using Community Earth System Model 2 simulations. Reducing positive ASR biases over the SH subtropics impacts SASM, and is sensitive to the ocean basin where changes are imposed. Radiation changes over the SH subtropical Indian Ocean (IO) shifts rainfall over the equatorial IO northward causing 1–2 mm/day drying south of equator, changes over the SH subtropical Pacific increases precipitation over northern continental regions by 1–2 mm/day, and changes over the SH subtropical Atlantic have little effect on SASM precipitation. Radiation changes over the subtropical Pacific impacts the SASM through zonal circulation changes, while changes over the IO modify meridional circulation to bring about changes in precipitation over northern IO. Our findings suggest that reducing SH subtropical radiation biases in climate models may also reduce SASM precipitation biases. ITCZ; monsoon; precipitation bias
Hodnebrog, Øivind; Myhre, Gunnar; Jouan, Caroline; Andrews, Timothy; Forster, Piers M.; Jia, Hailing; Loeb, Norman G.; Olivié, Dirk J. L.; Paynter, David; Quaas, Johannes; Raghuraman, Shiv Priyam; Schulz, MichaelHodnebrog, Ø., G. Myhre, C. Jouan, T. Andrews, P. M. Forster, H. Jia, N. G. Loeb, D. J. L. Olivié, D. Paynter, J. Quaas, S. P. Raghuraman, M. Schulz, 2024: Recent reductions in aerosol emissions have increased Earth’s energy imbalance. Communications Earth & Environment, 5(1), 1-9. doi: 10.1038/s43247-024-01324-8. The Earth’s energy imbalance is the net radiative flux at the top-of-atmosphere. Climate model simulations suggest that the observed positive imbalance trend in the previous two decades is inconsistent with internal variability alone and caused by anthropogenic forcing and the resulting climate system response. Here, we investigate anthropogenic contributions to the imbalance trend using climate models forced with observed sea-surface temperatures. We find that the effective radiative forcing due to anthropogenic aerosol emission reductions has led to a 0.2 ± 0.1 W m−2 decade−1 strengthening of the 2001–2019 imbalance trend. The multi-model ensemble reproduces the observed imbalance trend of 0.47 ± 0.17 W m−2 decade−1 but with 10-40% underestimation. With most future scenarios showing further rapid reductions of aerosol emissions due to air quality legislation, such emission reductions may continue to strengthen Earth’s energy imbalance, on top of the greenhouse gas contribution. Consequently, we may expect an accelerated surface temperature warming in this decade. Atmospheric science; Climate and Earth system modelling; Attribution
Hofer, Stefan; Hahn, Lily C.; Shaw, Jonah K.; McGraw, Zachary S.; Bruno, Olimpia; Hellmuth, Franziska; Pietschnig, Marianne; Mostue, Idunn Aa; David, Robert O.; Carlsen, Tim; Storelvmo, TrudeHofer, S., L. C. Hahn, J. K. Shaw, Z. S. McGraw, O. Bruno, F. Hellmuth, M. Pietschnig, I. A. Mostue, R. O. David, T. Carlsen, T. Storelvmo, 2024: Realistic representation of mixed-phase clouds increases projected climate warming. Communications Earth & Environment, 5(1), 1-12. doi: 10.1038/s43247-024-01524-2. Clouds are the main source of uncertainties when projecting climate change. Mixed-phase clouds that contain ice and supercooled-liquid particles are especially hard to constrain, and climate models neither agree on their phase nor their spatial extent. This is problematic, as models that underestimate contemporary supercooled-liquid in mixed-phase clouds will underestimate future warming. Furthermore, it has recently been shown that supercooled-liquid water in mixed-phase clouds is not homogeneously-mixed, neither vertically nor horizontally. However, while there have been attempts at observationally constraining mixed-phase clouds to constrain uncertainties in future warming, all studies only use the phase of the interior of mixed-phase clouds. Here we show, using novel satellite observations that distinguish between cloud-top and interior phase in mixed-phase clouds, that mixed-phase clouds are more liquid at the cloud top globally. We use these observations to constrain the cloud top phase in addition to the interior in a global climate model, leading to +1 °C more 21st century warming in NorESM2 SSP5-8.5 climate projections. We anticipate that the difference between cloud top and interior phase in mixed-phase clouds is an important new target metric for future climate model development, because similar mixed-phase clouds related biases in future warming are likely present in many climate models. Projection and prediction; Atmospheric science; Climate and Earth system modelling
Hsiao, Wei-Ting; Maloney, Eric D.Hsiao, W., E. D. Maloney, 2024: The Longwave Cloud-Radiative Feedback in Tropical Waves Derived by Different Precipitation Data Sets. Geophysical Research Letters, 51(11), e2024GL109143. doi: 10.1029/2024GL109143. Anomalous tropical longwave cloud-radiative heating of the atmosphere is generated when convective precipitation occurs, which plays an important role in the dynamics of tropical disturbances. Defining the observed cloud-radiative feedback as the reduction of top-of-atmosphere longwave radiative cooling per unit precipitation, the feedback magnitudes are sensitive to the observed precipitation data set used when comparing two versions of Global Precipitation Climatology Project, version 1.3 (GPCPv1.3) and the newer version 3.2 (GPCPv3.2). GPCPv3.2 contains larger magnitudes and variance of daily precipitation, which yields a weaker cloud-radiative feedback in tropical disturbances at all frequencies and zonal wavenumbers. Weaker cloud-radiative feedbacks occur in GPCPv3.2 at shorter zonal lengths on intraseasonal timescales, which implies a preferential growth at planetary scales for the Madden-Julian oscillation. Phase relationships between precipitation, radiative heating, and other thermodynamic variables in eastward-propagating gravity waves also change with the updated GPCPv3.2. cloud-radiative effect; convection; Madden-Julian oscillation; tropical waves
Hsiao, Wei-Ting; Maloney, Eric D.; Leitmann-Niimi, Nicolas M.; Kummerow, Christian D.Hsiao, W., E. D. Maloney, N. M. Leitmann-Niimi, C. D. Kummerow, 2024: Observed Relationships between Sea Surface Temperature, Vertical Wind Shear, Tropical Organized Deep Convection, and Radiative Effects. J. Climate, 37(4), 1277-1293. doi: 10.1175/JCLI-D-23-0262.1. Abstract Organized deep convective activity has been routinely monitored by satellite precipitation radar from the Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Mission (GPM). Organized deep convective activity is found to increase not only with sea surface temperature (SST) above 27°C, but also with low-level wind shear. Precipitation shows a similar increasing relationship with both SST and low-level wind shear, except for the highest low-level wind shear. These observations suggest that the threshold for organized deep convection and precipitation in the tropics should consider not only SST, but also vertical wind shear. The longwave cloud radiative feedback, measured as the tropospheric longwave cloud radiative heating per amount of precipitation, is found to generally increase with stronger organized deep convective activity as SST and low-level wind shear increase. Organized deep convective activity, the longwave cloud radiative feedback, and cirrus ice cloud cover per amount of precipitation also appear to be controlled more strongly by SST than by the deviation of SST from its tropical mean. This study hints at the importance of non-thermodynamic factors such as vertical wind shear for impacting tropical convective structure, cloud properties, and associated radiative energy budget of the tropics. Significance Statement This study uses tropical satellite observations to demonstrate that vertical wind shear affects the relationship between sea surface temperature and tropical organized deep convection and precipitation. Shear also affects associated cloud properties and how clouds affect the flow of radiation in the atmosphere. Although how vertical wind shear affects convective organization has long been studied in the mesoscale community, the study attempts to apply mesoscale theory to explain the large-scale mean organization of tropical deep convection, cloud properties, and radiative feedbacks. The study also provides a quantitative observational baseline of how vertical wind shear modifies cloud radiative effects and convective organization, which can be compared to numerical simulations.
Huang, Chuan Jiang; Wang, Gang; Chen, Siyu; Guo, Jingsong; Qiao, FangliHuang, C. J., G. Wang, S. Chen, J. Guo, F. Qiao, 2024: An effective parameterization of broadband ocean surface albedo applicable to all skies. Ocean Modelling, 190, 102394. doi: 10.1016/j.ocemod.2024.102394. The ocean surface albedo (OSA) is an important parameter in ocean and climate models for air-sea heat flux calculations. Current OSA schemes are either too simple, making them only suitable for clear sky conditions, or too complex, because they depend on parameters that are not often measured in conventional ocean observations. Using radiation observations at a fixed offshore platform, we propose a simple but effective parameterization scheme of OSA, in which the broadband OSA is an analytical function of both the solar zenith angle and atmospheric transparency. It depends only on the downward shortwave radiation measured at the ocean surface and applies to all sky conditions. During our 15-month radiation observations, the correlation coefficient between the calculated OSA and the observations reached 0.90 for all skies, and the root mean square deviation was 0.0130. Three other OSA observation datasets are also introduced to verify this scheme. Albedo; Heat flux; Numerical models; Parameterization; Solar radiation
Huang, Guan; Chen, Yonghang; Liu, Qiong; Wang, Pengtao; He, Qianshan; He, Qing; Li, Shuai; Shao, Weiling; Fan, TingHuang, G., Y. Chen, Q. Liu, P. Wang, Q. He, Q. He, S. Li, W. Shao, T. Fan, 2024: Accurate Shortwave Radiation Simulation with a Two-Layer Aerosol Model in Xinjiang Region. Journal of Meteorological Research, 38(1), 69-87. doi: 10.1007/s13351-024-3133-y. To harness the rich solar energy resources in Xinjiang Region of Northwest China, this study tries to address the issue of lack of downward surface shortwave radiation (DSSR) observations and the need to improve the accuracy of satellite retrieval and numerical simulation of DSSR under varied sky and meteorological conditions. (1) A two-layer aerosol model specific to Xinjiang was developed to capture the vertical distributions of aerosols based on multiple data sources including lidar, GPS sounding, ground meteorological observations, and profiles from the ECMWF reanalysis version 5 (ERA5) data. The results show that the ERA5/PBLH (planetary boundary layer height) and ERA5/ALH (aerosol layer height) could be used to establish the two-layer aerosol model and characterize the vertical distribution of aerosols in Xinjiang Region. (2) Using the Santa Barbara Discrete Atmospheric Radiative Transfer (SBDART) model, a localized inverse model of clear-sky DSSR was established. After parameter adjustment and using the optimal combination of input parameters for DSSR simulation together with the two-layer aerosol model, the model-simulated DSSR (DSSRSBD) under clear-sky conditions improved significantly compared to the initial results, with all fitting indices greatly improved. (3) In addition, the study demonstrated that the impact of the two-layer aerosol model on DSSR was more pronounced under dust conditions than clear-sky conditions. (4) Using the localized clear-sky DSSR inversion model and its required parameters, simulations were also conducted to capture the spatiotemporal distribution of DSSR under clear-sky conditions in Xinjiang from 2017 to 2019. The annual average DSSRSBD under clear-sky conditions in Xinjiang during 2017–2019 was 606.78 W m−2, while DSSR from CERES (DSSRCER) under the same conditions was generally higher (703.95 W m−2). (5) It is found that satellite remote sensing products experienced data loss in high-altitude snow areas, where numerical simulation technology could serve as a valuable complement. Clouds and the Earth’s Radiant Energy System (CERES); aerosol vertical distribution; downward surface shortwave radiation (DSSR); Santa Barbara Discrete Atmospheric Radiative Transfer (SBDART); Xinjiang
Huang, Han; Huang, Yi; Wei, Qiang; Hu, YongyunHuang, H., Y. Huang, Q. Wei, Y. Hu, 2024: Band-by-band spectral radiative kernels based on the ERA5 reanalysis. Scientific Data, 11(1), 237. doi: 10.1038/s41597-024-03080-y. Radiative kernel is a widely adopted method for diagnosing radiation variability and climate feedback. However, most of the existing radiative kernels are broadband flux kernels and lack the spectral information. Motivated by the growing interest in the spectral changes of the Earth radiation budget, we generate a new set of band-by-band radiative kernels based on the fifth generation European Center for Medium-Range Weather Forecasts (ERA5) reanalysis, which can be used for analyzing the spectrally decomposed changes in the top of atmosphere, surface and atmospheric radiation. The radiative sensitivity quantified by the ERA5 band-by-band kernel is compared to another spectral kernel and validated in a spectral radiation closure test. The use and benefits of the new ERA5 kernels are then demonstrated in an analysis of spectral feedbacks of an ensemble of global climate models (GCMs). Climate change; Atmospheric science
Jadhav, Ashwin Vijay; Rahul, P. R. C.; Kumar, Vinay; Dumka, Umesh Chandra; Bhawar, Rohini L.Jadhav, A. V., P. R. C. Rahul, V. Kumar, U. C. Dumka, R. L. Bhawar, 2024: Spatiotemporal Assessment of Surface Solar Dimming in India: Impacts of Multi-Level Clouds and Atmospheric Aerosols. Climate, 12(4), 48. doi: 10.3390/cli12040048. Surface solar radiation (SSR) is a fundamental energy source for an equitable and sustainable future. Meteorology-induced variability increases uncertainty in SSR, thereby limiting its reliability due to its intermittent nature. This variability depends on several meteorological factors, including clouds, atmospheric gases, and aerosol concentrations. This research investigates the detailed impact of different levels of clouds and aerosols on SSR across India. Utilizing satellite data with reanalysis retrievals, the research covers a span of three decades (30 years), from 1993 to 2022. Aerosols contributed to an average attenuation of ~13.33% on SSR, while high, mid, and low cloud conditions showed much stronger impacts, with an attenuation of ~30.80%, ~40.10%, and ~44.30%, respectively. This study reveals an alarming pattern of increasing cloud impact (Cimpact) on SSR in the recent decade, with a significant increasing rate of ~0.22% year−1 for high cloud (HCimpact) and ~0.13% year−1 for mid cloud (MCimpact) impact, while low cloud impact (LCimpact) showed minimal change. The trend of aerosol impact (Aimpact) also showed an average increase of ~0.14% year−1 across all regions. The findings underscore the imperative of considering climatic variables while studying the growing solar dimming. Our findings also will assist policymakers and planners in better evaluating the solar energy resources across India. India; surface solar radiation; aerosol impact; cloud impact; National Solar Mission; solar dimming; solar energy potential
Jia, H.; Hasekamp, O.; Quaas, J.Jia, H., O. Hasekamp, J. Quaas, 2024: Revisiting Aerosol–Cloud Interactions From Weekly Cycles. Geophysical Research Letters, 51(13), e2024GL108266. doi: 10.1029/2024GL108266. Weekly cycles (WCs) in cloud properties have been reported and linked to aerosol effects. Yet the extent to which human activities contribute to their occurrence remains unclear. Here, we revisit aerosol–cloud interactions from the WCs over central Europe using long-term satellite and reanalysis data. Significant WCs in aerosol and cloud droplet number concentration (Nd) are detected with minima/maxima on Monday/Friday, indicating a clear signal of the Twomey effect. Notably, Nd–to–aerosol sensitivity from WCs is found to decrease at larger aerosol concentrations, confirming the nonlinear behavior of the aerosol–Nd relation (in log–log space) reported previously, but from a distinct perspective. Nevertheless, no discernible WCs in liquid water path are found. The pronounced WCs in cloud cover are demonstrated to be driven by natural variability. Our results indicate that the WCs offer a useful pathway for investigating the Twomey effect, but are not as effective for detecting cloud adjustments. aerosol; aerosol-cloud interactions; cloud; weekly cycles
Jia, Jiajia; Zeng, Zhaoliang; Zhang, Wenqian; Zheng, Xiangdong; Wang, Yaqiang; Ding, MinghuJia, J., Z. Zeng, W. Zhang, X. Zheng, Y. Wang, M. Ding, 2024: The Performance of Downward Shortwave Radiation Products from Satellite and Reanalysis over the Transect of Zhongshan Station to Dome A, East Antarctica. Advances in Atmospheric Sciences, 41(8), 1574-1588. doi: 10.1007/s00376-023-3136-0. The downward shortwave radiation (DSR) is an important part of the Earth’s energy balance, driving Earth’s system’s energy, water, and carbon cycles. Due to the harsh Antarctic environment, the accuracy of DSR derived from satellite and reanalysis has not been systematically evaluated over the transect of Zhongshan station to Dome A, East Antarctica. Therefore, this study aims to evaluate DSR reanalysis products (ERA5-Land, ERA5, MERRA-2) and satellite products (CERES and ICDR) in this area. The results indicate that DSR exhibits obvious monthly and seasonal variations, with higher values in summer than in winter. The ERA5-Land (ICDR) DSR product demonstrated the highest (lowest) accuracy, as evidenced by a correlation coefficient of 0.988 (0.918), a root-mean-square error of 23.919 (69.383) W m−2, a mean bias of −1.667 (−28.223) W m−2 and a mean absolute error of 13.37 (58.99) W m−2. The RMSE values for the ERA5-Land reanalysis product at seven stations, namely Zhongshan, Panda 100, Panda 300, Panda 400, Taishan, Panda 1100, and Kunlun, were 30.938, 29.447, 34.507, 29.110, 20.339, 17.267, and 14.700 W m−2, respectively; with corresponding bias values of 9.887, −12.159, −19.181, −15.519, −8.118, 6.297, and 3.482 W m−2. Regarding seasonality, ERA5-Land, ERA5, and MERRA-2 reanalysis products demonstrate higher accuracies during spring and summer, while ICDR products are least accurate in autumn. Cloud cover, water vapor, total ozone, and severe weather are the main factors affecting DSR. The error of DSR products is greatest in coastal areas (particularly at the Zhongshan station) and decreases towards the inland areas of Antarctica. downward shortwave radiation; East Antarctic; Environmental Chemistry; reanalysis product; satellite product; validation; 东南极; 再分析产品; 卫星产品; 地表向下短波辐射; 验证研究
Jin, Yubin; Zeng, Zhenzhong; Chen, Yuntian; Xu, Rongrong; Ziegler, Alan D.; Chen, Wenchuang; Ye, Bin; Zhang, DongxiaoJin, Y., Z. Zeng, Y. Chen, R. Xu, A. D. Ziegler, W. Chen, B. Ye, D. Zhang, 2024: Geographically constrained resource potential of integrating floating photovoltaics in global existing offshore wind farms. Advances in Applied Energy, 100163. doi: 10.1016/j.adapen.2024.100163. Marine renewable energy is gaining prominence as a crucial component of the energy supply in coastal cities due to proximity and minimal land requirements. The synergistic potential of integrating floating photovoltaics with offshore wind turbines presents an encouraging avenue for boosting power production, amplifying spatial energy generation density, and mitigating seasonal output fluctuations. While the global promise of offshore wind-photovoltaic hybrid systems is evident, a definitive understanding of their potential remains elusive. Here, we evaluate the resource potential of the hybrid systems under geographical constraints, offering insights into sustainable and efficient offshore energy solutions. We compile a database with 11,198 offshore wind turbine locations from Sentinel-1 imagery and technical parameters from commercial project details. Our analysis reveals an underutilization of spatial resources within existing offshore wind farms, yielding a modest 26 kWh per square meter. Furthermore, employing realistic climate-driven system simulations, we find an impressive potential photovoltaic generation of 1,372 ± 18 TWh annually, over seven times higher than the current offshore wind capacity. Notably, floating photovoltaics demonstrated remarkable efficiency, matching wind turbine output with a mere 17% of the wind farm area and achieving an average 76% increase in power generation at equivalent investment costs. Additionally, the hybrid wind and photovoltaic systems exhibit monthly-scale complementarity, reflected by a Pearson correlation coefficient of -0.78, providing a consistent and reliable power supply. These findings support the notion that hybrid offshore renewable energy could revolutionize the renewable energy industry, optimize energy structures, and contribute to a sustainable future for coastal cities. energy complementarity; hybrid energy system; offshore photovoltaic power; offshore wind power
Johnson, G. C.; Lumpkin, R.; Alexander, Michael A.; Amaya, Dillon J.; Beckley, Brian; Boyer, Tim; Bringas, Francis; Carter, Brendan R.; Cetinić, Ivona; Chambers, Don P.; Chan, Duo; Cheng, Lijing; Dong, Shenfu; Elipot, Shane; Feely, Richard A.; Franz, Bryan A.; Fu, Yao; Gao, Meng; Garg, Jay; Giglio, Donata; Gilson, John; Goes, Marlos; Graham, Garrett; Hamlington, Benjamin D.; Hobbs, Will; Hu, Zeng-Zhen; Huang, Boyin; Ishii, Masayoshi; Jacox, Michael G.; Jersild, Annika; Jevrejeva, Svetlana; Johns, William E.; Killick, Rachel E.; Kuusela, Mikael; Landschützer, Peter; Leuliette, Eric; Liu, Chao; Locarnini, Ricardo; Lozier, Susan M.; Lyman, John M.; Merrifield, Mark A.; Mishonov, Alexey; Mitchum, Gary T.; Moat, Ben I.; Nerem, R. Steven; Oe, Mitsuho; Perez, Renellys C.; Pita, Ivenis; Purkey, Sarah G.; Reagan, James; Sato, Kanako; Schmid, Claudia; Smeed, David A.; Smith, Ryan H.; Stackhouse, Paul W.; Sukianto, Thea; Sweet, William; Thompson, Philip R.; Triñanes, Joaquin A.; Volkov, Denis L.; Wanninkhof, Rik; Weller, Robert A.; Westberry, Toby K.; Widlansky, Matthew J.; Willis, Josh K.; Yin, Xungang; Yu, Lisan; Zhang, Huai-minJohnson, G. C., R. Lumpkin, M. A. Alexander, D. J. Amaya, B. Beckley, T. Boyer, F. Bringas, B. R. Carter, I. Cetinić, D. P. Chambers, D. Chan, L. Cheng, S. Dong, S. Elipot, R. A. Feely, B. A. Franz, Y. Fu, M. Gao, J. Garg, D. Giglio, J. Gilson, M. Goes, G. Graham, B. D. Hamlington, W. Hobbs, Z. Hu, B. Huang, M. Ishii, M. G. Jacox, A. Jersild, S. Jevrejeva, W. E. Johns, R. E. Killick, M. Kuusela, P. Landschützer, E. Leuliette, C. Liu, R. Locarnini, S. M. Lozier, J. M. Lyman, M. A. Merrifield, A. Mishonov, G. T. Mitchum, B. I. Moat, R. S. Nerem, M. Oe, R. C. Perez, I. Pita, S. G. Purkey, J. Reagan, K. Sato, C. Schmid, D. A. Smeed, R. H. Smith, P. W. Stackhouse, T. Sukianto, W. Sweet, P. R. Thompson, J. A. Triñanes, D. L. Volkov, R. Wanninkhof, R. A. Weller, T. K. Westberry, M. J. Widlansky, J. K. Willis, X. Yin, L. Yu, H. Zhang, 2024: Global Oceans. doi: 10.1175/BAMS-D-24-0100.1. "Global Oceans" published on 22 Aug 2024 by American Meteorological Society.
Jones, William K.; Stengel, Martin; Stier, PhilipJones, W. K., M. Stengel, P. Stier, 2024: A Lagrangian perspective on the lifecycle and cloud radiative effect of deep convective clouds over Africa. Atmospheric Chemistry and Physics, 24(9), 5165-5180. doi: 10.5194/acp-24-5165-2024. The anvil clouds of tropical deep convection have large radiative effects in both the shortwave (SW) and longwave (LW) spectra with the average magnitudes of both over 100 W m−2. Despite this, due to the opposite sign of these fluxes, the net average of the anvil cloud radiative effect (CRE) over the tropics is observed to be neutral. Research into the response of the anvil CRE to climate change has primarily focused on the feedbacks of anvil cloud height and anvil cloud area, in particular regarding the LW feedback. However, tropical deep convection over land has a strong diurnal cycle which may couple with the shortwave component of the anvil cloud radiative effect. As this diurnal cycle is poorly represented in climate models it is vital to gain a better understanding of how its changes impact the anvil CRE. To study the connection between the deep convective cloud (DCC) lifecycle and CRE, we investigate the behaviour of both isolated and organised DCCs in a 4-month case study over sub-Saharan Africa (May–August 2016). Using a novel cloud tracking algorithm, we detect and track growing convective cores and their associated anvil clouds using geostationary satellite observations from the Meteosat Spinning Enhanced Visible and Infrared Imager (SEVIRI). Retrieved cloud properties and derived broadband radiative fluxes are provided by the Community Cloud retrieval for CLimate (CC4CL) algorithm. By collecting the cloud properties of the tracked DCCs, we produce a dataset of anvil cloud properties along their lifetimes. While the majority of DCCs tracked in this dataset are isolated, with only a single core, the overall coverage of anvil clouds is dominated by those of clustered, multi-core anvils due to their larger areas and lifetimes. We find that the anvil cloud CRE of our tracked DCCs has a bimodal distribution. The interaction between the lifecycles of DCCs and the diurnal cycle of insolation results in a wide range of the SW anvil CRE, while the LW component remains in a comparatively narrow range of values. The CRE of individual anvil clouds varies widely, with isolated DCCs tending to have large negative or positive CREs, while larger, organised systems tend to have a CRE closer to 0. Despite this, we find that the net anvil cloud CRE across all tracked DCCs is close to neutral (−0.94 ± 0.91 W m−2). Changes in the lifecycle of DCCs, such as shifts in the time of triggering, or the length of the dissipating phase, could have large impacts on the SW anvil CRE and lead to complex responses that are not considered by theories of LW anvil CRE feedbacks.
Jordan, G.; Henry, M.Jordan, G., M. Henry, 2024: IMO2020 Regulations Accelerate Global Warming by up to 3 Years in UKESM1. Earth's Future, 12(8), e2024EF005011. doi: 10.1029/2024EF005011. The International Maritime Organization (IMO) introduced new regulations on the sulfur content of shipping emissions in 2020 (IMO2020). Estimates of the climatic impact of this global reduction in anthropogenic sulfate aerosols vary widely. Here, we contribute to narrowing this uncertainty with two sets of climate model simulations using UKESM1. Using fixed sea-surface temperature atmosphere-only simulations, we estimate an IMO2020 global effective radiative forcing of 0.139 ± 0.019 Wm−2 and show that most of this forcing is due to aerosol-induced changes to cloud properties. Using coupled ocean-atmosphere simulations, we note significant changes in cloud top droplet number concentration and size across regions with high shipping traffic density, and—in the North Atlantic and North Pacific—these microphysical changes translate to a decrease in cloud albedo. We show that IMO2020 increases global annual surface temperature on average by 0.046 ± 0.010°C across 2020–2029; approximately 2–3 years of global warming. Furthermore, our model simulations show that IMO2020 helps to explain the exceptional warming in 2023, but other factors are needed to fully account for it. The year 2023 also had an exceptionally large decrease in reflected shortwave radiation at the top-of-atmosphere. Our results show that IMO2020 made that more likely, yet the observations are within the variability of simulations without the reduction in shipping emissions. To better understand the climatic impacts of IMO2020, a model intercomparison project would be valuable whilst the community waits for a more complete observational record. aerosol-cloud interactions; marine cloud brightening; shipping regulations
Joseph, Lionel P.; Deo, Ravinesh C.; Casillas-Pérez, David; Prasad, Ramendra; Raj, Nawin; Salcedo-Sanz, SanchoJoseph, L. P., R. C. Deo, D. Casillas-Pérez, R. Prasad, N. Raj, S. Salcedo-Sanz, 2024: Short-term wind speed forecasting using an optimized three-phase convolutional neural network fused with bidirectional long short-term memory network model. Applied Energy, 359, 122624. doi: 10.1016/j.apenergy.2024.122624. Wind energy is an environment friendly, low-carbon, and cost-effective renewable energy source. It is, however, difficult to integrate wind energy into a mixed energy grid due to its high volatility and intermittency. For wind energy conversion systems to be reliable and efficient, accurate wind speed (WS) forecasting is fundamental. This study cascades a convolutional neural network (CNN) with a bidirectional long short-term memory (BiLSTM) in order to obtain a model for hourly WS forecasting by utilizing several meteorological variables as model inputs to study their effects on predicted WS. For input selection, the mutation grey wolf optimizer (TMGWO) is used. For efficient optimization of CBiLSTM hyperparameters, a hybrid Bayesian Optimization and HyperBand (BOHB) algorithm is used. The combined usage of TMGWO, BOHB, and CBiLSTM leads to a three-phase hybrid model (i.e., 3P-CBiLSTM). The performance of 3P-CBiLSTM is benchmarked against the standalone and hybrid BiLSTMs, LSTMs, gradient boosting (GBRs), random forest (RFRs), and decision tree regressors (DTRs). The statistical analysis of forecasted WS reveals that the 3P-CBiLSTM is highly effective over the other benchmark forecasting methods. This objective model also registers the highest percentage of forecasted errors (≈ 53.4 – 81.8%) within the smallest error range ≤ |0.25| ms−1 amongst all tested study sites. Despite the remarkable results achieved, the CBiLSTM model cannot be generally understood, so the eXplainable Artificial Intelligence (xAI) technique was used for explaining local and global model outputs, based on Local Interpretable Model-Agnostic Explanations (LIME) and SHapley Additive exPlanations (SHAP). Both of the xAI methods determined that the antecedent WS is the most significant predictor of the short-term WS forecasting. Therefore, we aver that the proposed model can be employed to help wind farm operators in making quality decisions in maximizing wind power integration into the grid with reduced intermittency. Feature selection; Bidirectional LSTM; Convolutional neural networks; eXplainable Artificial Intelligence; Wind speed forecasting
Jouan, Caroline; Myhre, GunnarJouan, C., G. Myhre, 2024: Satellite-based analysis of top of atmosphere shortwave radiative forcing trend induced by biomass burning aerosols over South-Eastern Atlantic. npj Climate and Atmospheric Science, 7(1), 1-8. doi: 10.1038/s41612-024-00631-3. This study investigates long-term changes in the shortwave direct aerosol radiative effect (DARE) at the top of the atmosphere (TOA) induced by biomass burning aerosol (BBA) transported from southern Africa to the south-eastern Atlantic (SEA) stratocumulus region during extended fire seasons. The evolution since 2002 of aerosol, cloud properties, and TOA shortwave outgoing radiation from advanced passive satellite sensors are presented, as well as the observational trend in clear-sky DAREclr and the retrieval trend in all-sky DAREall. Supplemented by chemical transport model simulations, we estimate that DAREclr has become more negative (−0.09 ± 0.06 W m−2 yr−1) due to increased aerosol presence in SEA. Meanwhile, DAREall has become more positive ( + 0.04 ± 0.15 W m−2 yr−1) due to aerosols in cloudy sky regions. This study reveals satellite capabilities in capturing complex BBA-cloud-solar radiation interactions for accurate radiative forcing estimates and projections. Atmospheric dynamics; Atmospheric chemistry
Kang, Hyoji; Choi, Yong-Sang; Jiang, Jonathan H.Kang, H., Y. Choi, J. H. Jiang, 2024: Factors determining tropical upper-level cloud radiative effect in the radiative-convective equilibrium framework. Scientific Reports, 14(1), 13419. doi: 10.1038/s41598-024-62587-x. Investigation of the major factors determining tropical upper-level cloud radiative effect (TUCRE) is crucial for understanding cloud feedback mechanisms. We examined the TUCRE inferred from the outputs of historical runs and AMIP runs from CMIP6 models employing a radiative-convective equilibrium (RCE). In this study, we incorporated the RCE model configurations of atmospheric dynamics and thermodynamics from the climate models, while simplifying the intricate systems. Using the RCE model, we adjusted the global mean surface temperature to achieve energy balance, considering variations in tropical cloud fraction, regional reflectivity, and emission temperature corresponding to each climate model. Subsequently, TUCRE was calculated as a unit of K/%, representing the change in global mean surface temperature (K) in response to an increment in the tropical upper-level clouds (%). Our RCE model simulation indicates that the major factors determining the TUCRE are the emission temperatures of tropical moist-cloudy and moist-clear regions, as well as the fraction of tropical upper-level clouds. The higher determination coefficients between TUCRE and both the emission temperature of tropical moist regions and the upper-level cloud fraction are attributable to their contribution to the trapping effect on the outgoing longwave radiations, which predominantly determines TUCRE. Consequently, the results of this study underscore the importance of accurately representing the upper-level cloud fraction and emission temperature in tropical moist regions to enhance the representation of TUCRE in climate models. Atmospheric dynamics; Climate and Earth system modelling
Karumuri, Rama Krishna; Dasari, Hari Prasad; Gandham, Harikishan; Kunchala, Ravi Kumar; Attada, Raju; Ashok, Karumuri; Hoteit, IbrahimKarumuri, R. K., H. P. Dasari, H. Gandham, R. K. Kunchala, R. Attada, K. Ashok, I. Hoteit, 2024: Investigation of Dust-Induced Direct Radiative Forcing Over the Arabian Peninsula Based on High-Resolution WRF-Chem Simulations. Journal of Geophysical Research: Atmospheres, 129(13), e2024JD040963. doi: 10.1029/2024JD040963. This study investigates the impact of dust on radiation over the Arabian Peninsula (AP) during the reported high, low, and normal dust seasons (March–August) of 2012, 2014, and 2015, respectively. Simulations were performed using the Weather Research and Forecasting model coupled to a Chemistry module (WRF-Chem). The simulated seasonal horizontal and vertical dust concentrations, and their interannual distinctions, match well with those from two ground-based AERONET observations, and measurements from MODIS and CALIOP satellites. The maximum dust concentrations over the dust-source regions in the southern AP reach vertically upto 700 hPa during the high dust season, but only upto 900–950 hPa during the low/normal dust seasons. Stronger incoming low-level winds along the southern Red Sea and those from Iraq bring in higher-than-normal dust during the high dust summers. We conducted a sensitivity experiment by switching-off the dust module to assess the radiative perturbations due to dust. The results suggest that active dust-module improved the fidelity of simulated radiation fluxes distributions at the surface and top of the atmosphere vis-à-vis Clouds and the Earth's Radiant Energy System (CERES) measurements. Dust results in a 26 Wm−2 short-wave (SW) radiative forcing in the tropospheric-column over the AP. The SW radiative forcing increases by another 6–8 Wm−2 during the high dust season due to the increased number of extreme dust days, which also amplifies atmospheric heating. During extreme dust days, the heating rate exhibits a dipolar structure, with cooling over the Iraq region and warming of 40%–60% over the southern-AP. Arabian Peninsula; dust optical depth; heating rate; radiative forcing; WRF-chem
Kim, Doyeon; Kang, Sarah M.; Kim, Hanjun; Taylor, Patrick C.Kim, D., S. M. Kang, H. Kim, P. C. Taylor, 2024: Quantifying Changes in the Arctic Shortwave Cloud Radiative Effects. Journal of Geophysical Research: Atmospheres, 129(15), e2023JD040707. doi: 10.1029/2023JD040707. The shortwave cloud radiative effect (SWCRE) is important for the Arctic surface radiation budget and is a major source of inter-model spread in simulating Arctic climate. To better understand the individual contributions of various radiative processes to changes in SWCRE, we extend the existing Approximate Partial Radiative Perturbation (APRP) method by adding the absorptivity for the upward beam, considering differences in reflectivity between upward and downward beams, and analyzing the cloud masking effect resulting from changes in surface albedo. Using data from CMIP model experiments, the study decomposes the SWCRE over the Arctic surface and analyzes inter-model differences in quadrupled CO2 simulations. The study accounts for the influence of surface albedo, cloud amount, and cloud microphysics in the response of SWCRE to Arctic warming. In the sunlit season, CMIP models exhibit a strong, negative SWCRE with a large inter-model spread. Arctic clouds dampen the surface albedo feedback by reflecting incoming solar radiation and further decrease the shortwave radiation reflected by surface, a fraction of which is scattered back to the surface by clouds. Specifically, this accounts for the majority of the inter-model spread in SWCRE. In addition, increased (decreased) cloud amount and cloud liquid water reduce (increase) incoming shortwave fluxes at the surface, but they are found to be not critical to the Arctic surface radiation budget and its inter-model variation. Overall, the extended APRP method offers a useful tool for analyzing the complex interactions between clouds and radiative processes, accurately decomposes the individual SWCRE responses at the Arctic surface.
Kuhlbrodt, Till; Swaminathan, Ranjini; Ceppi, Paulo; Wilder, ThomasKuhlbrodt, T., R. Swaminathan, P. Ceppi, T. Wilder, 2024: A Glimpse into the Future: The 2023 Ocean Temperature and Sea Ice Extremes in the Context of Longer-Term Climate Change. Bull. Amer. Meteor. Soc., 105(3), E474-E485. doi: 10.1175/BAMS-D-23-0209.1. Abstract In the year 2023, we have seen extraordinary extrema in high sea surface temperature (SST) in the North Atlantic and in low sea ice extent in the Southern Ocean, outside the 4σ envelope of the 1982–2011 daily time series. Earth’s net global energy imbalance (12 months up to September 2023) amounts to +1.9 W m−2 as part of a remarkably large upward trend, ensuring further heating of the ocean. However, the regional radiation budget over the North Atlantic does not show signs of a suggested significant step increase from less negative aerosol forcing since 2020. While the temperature in the top 100 m of the global ocean has been rising in all basins since about 1980, specifically the Atlantic basin has continued to further heat up since 2016, potentially contributing to the extreme SST. Similarly, salinity in the top 100 m of the ocean has increased in recent years specifically in the Atlantic basin, and in addition in about 2015 a substantial negative trend for sea ice extent in the Southern Ocean began. Analyzing climate and Earth system model simulations of the future, we find that the extreme SST in the North Atlantic and the extreme in Southern Ocean sea ice extent in 2023 lie at the fringe of the expected mean climate change for a global surface-air temperature warming level (GWL) of 1.5°C, and closer to the average at a 3.0°C GWL. Understanding the regional and global drivers of these extremes is indispensable for assessing frequency and impacts of similar events in the coming years.
Li, Dahui; Wang, Tianxing; Zheng, Xiaopo; Zhang, Peng; Zheng, Lilin; Leng, Wanchun; Du, Yihan; Chen, Lin; Zhang, WanchunLi, D., T. Wang, X. Zheng, P. Zhang, L. Zheng, W. Leng, Y. Du, L. Chen, W. Zhang, 2024: Multi-Dimensional matrix MAPping (MDMAP): A new algorithm framework to derive top-of-atmosphere outgoing longwave radiation from space. Remote Sensing of Environment, 304, 114031. doi: 10.1016/j.rse.2024.114031. Outgoing Longwave Radiation (OLR) is an important component of the Earth's radiation budget and a key parameter for coupled models of the atmosphere, ocean, land, and other systems. It is of significant importance in studies related to Earth sciences such as weather forecasting, climate research, and disaster monitoring. Since narrowband sensors are more widely available and have higher spatial resolutions than broadband sensors, high-resolution OLR data are currently frequently estimated using narrowband sensors. This study proposes a novel physical method, namely the Multi-Dimensional matrix MAPping algorithm (MDMAP) framework, inspired by the scene classification ideas of Cloud and Earth's Radiant Energy System (CERES) and the differential absorption theory. The new framework aims to accurately retrieve OLR from the multi-channel infrared sensor, such as Moderate Resolution Imaging Spectroradiometer (MODIS). Corresponding to traditional algorithms, such as the polynomial regression algorithm (POLY) and lookup table algorithm (LUT), the new framework provides two distinct implementations of the MDMAP algorithm framework (MDMAP:POLY and MDMAP:LUT). The performances of both the traditional and the newly proposed algorithms are evaluated based on the radiative transfer simulation dataset and CERES SSF OLR products. The results show that the MDMAP algorithms behave more accurately than the traditional ones under most conditions, especially under clear-sky conditions. Specifically, a comprehensive analysis indicates that the new algorithms demonstrate smaller RMSEs than the traditional ones under various conditions, particularly in desert regions with the RMSE reduction exceeding 3 W/m2 (>30%). Moreover, the two new algorithms reveal enhanced robustness to noise uncertainties, and demonstrate remarkable generality and computational efficiency, implying their potential and better applicability in deriving believable OLR from most infrared sensors. Cloud and Earth's radiant energy system (CERES); Moderate resolution imaging Spectroradiometer (MODIS); Multi-Dimensional matrix MAPping (MDMAP); Outgoing longwave radiation (OLR); Polynomial regression; Radiation transfer simulation
Li, Na; Zhao, Ping; Zhou, ChangyanLi, N., P. Zhao, C. Zhou, 2024: The spatiotemporal variation of land surface heat fluxes in Tibetan Plateau during 2001–2022. Atmospheric Research, 297, 107081. doi: 10.1016/j.atmosres.2023.107081. The surface energy budget is important for understanding of energy and water cycle processes in the Tibetan Plateau (TP). In this study, the daily sensible (SH) and latent (LE) heat fluxes at the horizontal resolution of 1° are first estimated using the maximum entropy production (MEP) model (hereinafter SHMEP and LEMEP) in the entire TP during 2001–2022. The MEP model is built on physical and statistical principles to simulate surface heat fluxes. The surface net radiation, soil moisture (SM), and land surface temperature (LST) are the main driving variables for MEP model. To select the relatively accurate MEP input data, the merged surface net radiation (Rn–merged) under all-sky conditions are generated from CERES, ISCCP-FH, and ERA5 using the Bayesian Model Averaging scheme. Besides, the TP SM and LST from various data sources are evaluated using the in-situ observations at site scale. Based on the daily Rn–merged, ERA5 SM, CERES LST, and the MEP model, the daily SH and LE are estimated in the entire TP. The results show the daily SHMEP and LEMEP perform well at the validation sites, with the regional mean correlation coefficient (R) above 0.7, root-mean-square error (RMSE) of Latent heat flux; Maximum entropy production model; Multi-Source datasets; Sensible heat flux; Tibetan Plateau
Li, Ruixue; Jian, Bida; Li, Jiming; Wen, Deyu; Zhang, LijieLi, R., B. Jian, J. Li, D. Wen, L. Zhang, 2024: Understanding the variation of Reflected Solar Radiation: A Latitude- and month-based Perspective. EGUsphere, 1-45. doi: 10.5194/egusphere-2023-2882. Abstract. The hemispheric symmetry of planetary albedo (PA) is crucial for the Earth's energy budget. However, our understanding of hemispheric albedo is still limited, particularly regarding its variations at finer spatial and temporal scales. Using 21 years of radiation data from CERES-EBAF, this study quantifies the contribution rates of different latitudes to the hemispheric reflected solar radiation and examines their seasonal variations. Statistical results show that the northern latitudinal zones of 0° to 40° contribute more reflected radiation than the corresponding southern latitudes, but the southern latitudinal zones of 50° to 90° compensate for this. From the equator to 40°, the latitudinal contribution to the hemisphere is high in autumn and winter and low in spring and summer; however, after 50°, the situation is reversed. And even during extreme cases, anomalies of the cloud component contribution play a dominant role in anomalies of the total reflected radiation contribution of the latitudinal zone in most latitudinal zones. Additionally, this study evaluates the performance of four radiation data (including: satellite and reanalysis data) in reproducing hemisphere albedo and its hemispheric symmetry compared to CERES-EBAF data. Under different symmetry criteria, the applicability of different datasets to hemispheric symmetry of PA studies varies. Note that the Cloud_cci AVHRR performs better in capturing hemispheric symmetry. However, none of these datasets can decompose the different components of reflected radiation well. These results contribute to advancing our understanding of hemispheric symmetry variations and compensation mechanisms, reducing the uncertainty of model simulations, and improving algorithms for different radiation datasets.
Li, Tianci; Xin, Xiaozhou; Zhang, Hailong; Yu, Shanshan; Li, Li; Ye, Zhiqiang; Liu, Qinhuo; Cai, HeLi, T., X. Xin, H. Zhang, S. Yu, L. Li, Z. Ye, Q. Liu, H. Cai, 2024: Evaluation of Six Data Products of Surface Downward Shortwave Radiation in Tibetan Plateau Region. Remote Sensing, 16(5), 791. doi: 10.3390/rs16050791. The quantitative characterization of the thermal conditions in the Tibetan Plateau has long been a focal point of global research. Downward shortwave radiation, as a crucial component, plays an important role in numerous land surface processes while also serving as a significant indicator of the plateau’s thermal state. In order to gain a more comprehensive understanding of the Earth’s radiation budget in the Tibetan Plateau region, this study undertook an evaluation of six radiation products (ISCCP-FH, CERES-SYN, GLASS DSR, Himawari-8, MCD18A1, and ERA5). Two sets of ground measurements (downward shortwave radiation values from 10 CMA sites and 6 sites provided by the National Tibetan Plateau Data Center) in 2015 and 2016 were used as validation data to verify the accuracy of the remote sensing products. The results show that in the Tibetan Plateau region, CERESC products show the highest accuracy among the six data products with a bias (relative bias) of −7.57 W/m2 (3.46%), RMSE (relative RMSE) of 32.77 W/m2 (14.99%), and coefficient of determination of 0.80. Among all products, only the ERA5 products overestimated the value of downward shortwave radiation in the Tibetan Plateau region with a bias (relative bias) of 15.62 W/m2 (7.14%). By employing a spatial resolution upscaling approach, we assessed the influence of varying spatial resolutions on the validation accuracy, with the results indicating minimal impact. Through an analysis of the impact of cloud factors and aerosol factors on the validation accuracy, it is deduced that ERA5, Himawari-8, and MCD18A1 products are significantly influenced by cloud factors, whereas the CERES-SYN product is notably affected by aerosol factors. Tibetan Plateau; ERA5; CERES-SYN; downward shortwave radiation; aerosol optical depth; cloud optical thickness
Li, Xiaohan; Chu, Wenchao; Zhang, Yi; Wang, YimingLi, X., W. Chu, Y. Zhang, Y. Wang, 2024: Extending a dry-environment convection parameterization to couple with moist turbulence and a baseline evaluation in the GRIST model. Quarterly Journal of the Royal Meteorological Society, n/a(n/a). doi: 10.1002/qj.4763. This study presents an extension of a dry-environment convection scheme (Tiedtke–Bechtold) to couple with a boundary-layer moist turbulence scheme. The deep and shallow convective updraught is modified to develop in a moist environment and the large-scale budget of cloud condensate takes account of the influence of compensation subsidence. An ambiguous layer is introduced in the sub-cloud layer transport of shallow convection to mimic the non-local transport that is ignored in the moist local turbulence scheme. Long-term global simulation suggests that the modified convection and moist turbulence improve low cloud and short-wave cloud radiative forcing. This includes a more realistic climatological structure of stratocumulus-to-cumulus transition and ameliorated biases in liquid water path. For short to mid-term hindcasts in June 2021, the modified convection coupled with moist turbulence mitigates some regional over-forecasts of precipitation. They improve the forecast ability for light and moderate precipitation. The modified model still retains the capability to capture the diurnal features of continental rainfall. Convective parametrization; global cloud and precipitation modeling; physics–physics interaction
Li, Xuehua; Chen, Yunhao; Li, Kangning; Liu, Xiuyu; Gao, Shengjun; Ji, Weizhen; Cui, YingLi, X., Y. Chen, K. Li, X. Liu, S. Gao, W. Ji, Y. Cui, 2024: Generating station-like downward shortwave radiation data by using sky condition-guided model based on ERA5-Land data. Energy, 306, 132417. doi: 10.1016/j.energy.2024.132417. Accurate downward shortwave radiation (DSR) data is essential for the utilization of solar energy resources. However, existing various DSR data have certain limitations in applications. Among these, ERA5-Land DSR data is considered a relatively high-quality dataset. Nevertheless, it is reported notable deviations under different sky conditions, resulted from deficiencies in cloud and aerosol simulations. Therefore, this study aims to generate high-quality DSR data based on ERA5-Land data. We propose a sky condition-guided model using deviation characteristics of ERA5-Land DSR across different sky conditions as guidance, incorporating reliable cloud and aerosol parameters to provide atmosphere information. Consequently, station-like DSR data with accuracy close to station data is generated. Our model achieves high accuracy under different sky conditions, with RMSE below 32.19 W/m2. At the individual-station scale, 86.04 % of validation sites exhibit R values exceeding 0.9. At the seasonal scale, R values consistently surpass 0.87. Moreover, our data exhibits better accuracy compared to mainstream DSR datasets. Furthermore, it depicts the spatiotemporal variation of DSR and further reveals the photovoltaic potential in China, with relatively high values in the Tibetan Plateau and northwest China. The station-like DSR data is promising to advance the utilization of solar energy and accelerate the energy transition. Downward shortwave radiation; ERA5-Land reanalysis; Machine learning; Photovoltaic potential; Sky conditions; Solar energy
Li, Yize; Ge, Jinming; Du, Jiajing; Peng, Nan; Su, Jing; Hu, Xiaoyu; Zhang, Chi; Mu, Qingyu; Li, QinghaoLi, Y., J. Ge, J. Du, N. Peng, J. Su, X. Hu, C. Zhang, Q. Mu, Q. Li, 2024: Projection of Low Cloud Variation Through Robust Meteorological Linkage and Its Comparison With CMIP6 Models at the SACOL Site. Journal of Geophysical Research: Atmospheres, 129(16), e2023JD040668. doi: 10.1029/2023JD040668. Low clouds significantly influence Earth's energy budget by reflecting solar radiation. Consequently, inadequate representation of these clouds in models introduces the largest uncertainty in predicting future climate change. This study investigates low cloud cover (LCC) variation using 6 years (2014–2019) of high-precision ground-based Ka-band Zenith Radar (KAZR) observations at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). We analyze the relationship between observed low cloud properties and four large-scale meteorological factors: 700 hPa relative humidity, estimated inversion strength, low-level wind shear, and 700 hPa vertical velocity. These factors are identified as key parameters influencing low cloud evolution over this semi-arid region. We utilize principal component analysis to integrate these parameters into a single meteorological predictor (PC1) and establish a robust linkage between meteorological conditions and low cloud properties. By comparing LCC fluctuations derived from the meteorological factors with those directly simulated by models over the same period, we assess the projected LCC trends under various carbon emission scenarios. Contrary to the declining LCC projected by CMIP6 models outcomes, the LCC form PC1 shows a rising tendency by 2100 under global warming. This discrepancy implies that CMIP6 models may exaggerate the extent of future warming at the SACOL site. Our approach can be applied to a broader global distribution of low clouds to examine the differences between low cloud variations constrained by meteorological fields and those from direct model simulations. This will enhance our understanding of low cloud feedback on future climate change. KAZR; large scale meteorology; low cloud; principal component analysis; SACOL
Liang, Hui; Jiang, Bo; Liang, Shunlin; Wen, Jianguang; He, Tao; Zhang, Xiaotong; Peng, Jianghai; Li, Shaopeng; Han, Jiakun; Yin, XiuwanLiang, H., B. Jiang, S. Liang, J. Wen, T. He, X. Zhang, J. Peng, S. Li, J. Han, X. Yin, 2024: A novel Terrain Correction Sinusoidal Model for improving estimation of daily clear-sky downward shortwave radiation. IEEE Transactions on Geoscience and Remote Sensing, 1-1. doi: 10.1109/TGRS.2024.3452791. Downward shortwave radiation (DSR) is greatly affected by rugged terrains, which account for about 24% of the world’s surface. Yet, existing DSR products do not take into account topographical effects. Some topographic correction algorithms have been developed for estimating the clear-sky instantaneous DSR over rugged terrains (DSRins-rugged), but no specific algorithms are available to get the daily average DSR over rugged terrains (DSRdaily-rugged). The objective of this study is to develop an efficient and robust model to retrieve the clear-sky DSRdaily-rugged based on DSR satellite products. After examining ground measurements collected from several mountainous sites over the Chengde Experimental Area in China, we found that the clear-sky DSRins-rugged over a day follows a pseudo-sine curve, depending on aspect, slope, and other terrain factors, which form the foundation of our Terrain Correction Sinusoidal Model (TCSM). TCSM also includes a new simple shadow correction method. Validation against ground measurements showed that shadow-corrected clear sky TCSM DSRdaily-rugged estimated from in situ measurements, is highly accurate with an RMSE of 9.69 Wm-2, Bias of 0.93 Wm-2 and R2 of 0.99. After applying TCSM to correct the topographic effects of both the CERES SYN1degEd4A and MCD18A1 C6 DSR products, the accuracies significantly improved, with the validated RMSE reduced from 63.60 and 64.51 to 14.03 and 12.60 Wm-2, the Bias from -38.58 and -36.93 to 5.53 and -7.17 Wm-2, and R2 from 0.46 and 0.44 to 0.97 and 0.98, respectively. Additionally, the TCSM can be easily applied to other DSR products that do not consider the topographic effects. Accuracy; Area measurement; CERES; clear-sky; daily downward shortwave radiation; estimation; Estimation; Land surface; MCD18; remote sensing; Remote sensing; rugged terrain; Solar radiation; Surface topography; Terrain Correction Sinusoidal Model
Liang, Lusheng; Su, Wenying; Sejas, Sergio; Eitzen, Zachary; Loeb, Norman G.Liang, L., W. Su, S. Sejas, Z. Eitzen, N. G. Loeb, 2024: Next-generation radiance unfiltering process for the Clouds and the Earth's Radiant Energy System instrument. Atmospheric Measurement Techniques, 17(7), 2147-2163. doi: 10.5194/amt-17-2147-2024. The filtered radiances measured by the Clouds and the Earth's Radiant Energy System (CERES) instruments are converted to shortwave (SW), longwave (LW), and window unfiltered radiances based on regressions developed from theoretical radiative transfer simulations to relate filtered and unfiltered radiances. This paper describes an update to the existing Edition 4 CERES unfiltering algorithm (Loeb et al., 2001), incorporating the most recent developments in radiative transfer modeling, ancillary input datasets, and increased computational and storage capabilities during the past 20 years. Simulations are performed with the updated Moderate Resolution Atmospheric Transmission (MODTRAN) 5.4 version. Over land and snow, the surface bidirectional reflectance distribution function (BRDF) is characterized by a kernel-based representation in the simulations, instead of the Lambertian surface used in the Edition 4 unfiltering process. Radiance unfiltering is explicitly separated into four seasonally dependent land surface groups based on the spectral radiation similarities of different surface types (defined by the International Geosphere-Biosphere Programme); over snow, it is separated into fresh snow, permanent snow, and sea ice. This differs from the Edition 4 unfiltering process where only one set of regressions was used for land and snow, respectively. The instantaneous unfiltering errors are estimated with independent test cases generated from radiative transfer simulations in which the “true” unfiltered radiances from radiative transfer simulations are compared with the unfiltered radiances calculated from the regressions. Overall, the relative errors are mostly within ±0.5 % for SW, within ±0.2 % for daytime LW, and within ±0.1 % for nighttime LW for both CERES Terra Flight Model 1 (FM1) and Aqua FM3 instruments. The unfiltered radiances are converted to fluxes and compared to CERES Edition 4 fluxes. The global mean instantaneous fluxes for Aqua FM3 are reduced by 0.34 to 0.45 W m−2 for SW and increased by 0.25 to 0.46 W m−2 for daytime LW; for Terra FM1, they are reduced by 0.24 to 0.34 W m−2 for SW and increased by 0.08 to 0.28 W m−2 for daytime LW. Nighttime LW flux differences are negligible for both instruments.
Lin, Haoxian; Ding, Ke; Huang, Xin; Lou, Sijia; Xue, Lian; Wang, Zilin; Ma, Yue; Ding, AijunLin, H., K. Ding, X. Huang, S. Lou, L. Xue, Z. Wang, Y. Ma, A. Ding, 2024: Impacts of Northward Typhoons on Autumn Haze Pollution Over North China Plain. Journal of Geophysical Research: Atmospheres, 129(6), e2023JD040465. doi: 10.1029/2023JD040465. Although air quality in China has improved substantially over recent years, haze pollution events still occur frequently, especially over the North China Plain (NCP). Previous studies showed that typhoons are conducive to regional pollution events in eastern China; however, the underlying mechanism and quantitative understanding of the typhoons' impact on haze pollution remain unclear there. Here, based on ground-based and satellite observations, reanalysis data, and model simulations, we show that northward typhoons approaching China are essential for autumn haze pollution over NCP. Elevated relative humidity levels and enhanced pollution accumulation, caused by northward typhoons and the corresponding high-pressure systems, are responsible for the pollution enhancements over NCP. Compared with episodes without typhoon influence, cities near Taihang and Yan Mountain suffer from heavier haze pollution when typhoons approach, with PM2.5 concentrations increasing from 87.1 to 106.4 μg m−3. More water vapor from the Yellow and Bohai Seas and pollutants from eastern China are transported to these cities by typhoon-induced southeasterly wind anomalies, facilitating the chemical formation of aerosols there. In addition, by the block of mountains, these southeasterly wind anomalies also lead to stronger local accumulation over cities and an elevation of pollutants along the mountains. What is more, with the implementation of emission reduction, the relative changes of PM2.5 concentrations between typhoon-induced episodes and no-typhoon episodes increase. This work highlights the importance of understanding the impact of synoptical weather on PM2.5 transport, accumulation, and formation processes in haze pollution mitigation in eastern China.
Lin, Meiyun; Horowitz, Larry W.; Zhao, Ming; Harris, Lucas; Ginoux, Paul; Dunne, John; Malyshev, Sergey; Shevliakova, Elena; Ahsan, Hamza; Garner, Steve; Paulot, Fabien; Pouyaei, Arman; Smith, Steven J.; Xie, Yuanyu; Zadeh, Niki; Zhou, LinjiongLin, M., L. W. Horowitz, M. Zhao, L. Harris, P. Ginoux, J. Dunne, S. Malyshev, E. Shevliakova, H. Ahsan, S. Garner, F. Paulot, A. Pouyaei, S. J. Smith, Y. Xie, N. Zadeh, L. Zhou, 2024: The GFDL Variable-Resolution Global Chemistry-Climate Model for Research at the Nexus of US Climate and Air Quality Extremes. Journal of Advances in Modeling Earth Systems, 16(4), e2023MS003984. doi: 10.1029/2023MS003984. We present a variable-resolution global chemistry-climate model (AM4VR) developed at NOAA's Geophysical Fluid Dynamics Laboratory (GFDL) for research at the nexus of US climate and air quality extremes. AM4VR has a horizontal resolution of 13 km over the US, allowing it to resolve urban-to-rural chemical regimes, mesoscale convective systems, and land-surface heterogeneity. With the resolution gradually reducing to 100 km over the Indian Ocean, we achieve multi-decadal simulations driven by observed sea surface temperatures at 50% of the computational cost for a 25-km uniform-resolution grid. In contrast with GFDL's AM4.1 contributing to the sixth Coupled Model Intercomparison Project at 100 km resolution, AM4VR features much improved US climate mean patterns and variability. In particular, AM4VR shows improved representation of: precipitation seasonal-to-diurnal cycles and extremes, notably reducing the central US dry-and-warm bias; western US snowpack and summer drought, with implications for wildfires; and the North American monsoon, affecting dust storms. AM4VR exhibits excellent representation of winter precipitation, summer drought, and air pollution meteorology in California with complex terrain, enabling skillful prediction of both extreme summer ozone pollution and winter haze events in the Central Valley. AM4VR also provides vast improvements in the process-level representations of biogenic volatile organic compound emissions, interactive dust emissions from land, and removal of air pollutants by terrestrial ecosystems. We highlight the value of increased model resolution in representing climate–air quality interactions through land-biosphere feedbacks. AM4VR offers a novel opportunity to study global dimensions to US air quality, especially the role of Earth system feedbacks in a changing climate. drought; precipitation; extremes; air quality-climate interactions; Earth system feedbacks; high-resolution
Liu, Huancai; Shang, Lina; Li, Man; Zheng, Xiaoyu; Shi, PeihongLiu, H., L. Shang, M. Li, X. Zheng, P. Shi, 2024: WRF numerical simulation of summer precipitation and its application over the mountainous southern Tibetan Plateau based on different cumulus parameterization schemes. Atmospheric Research, 309, 107608. doi: 10.1016/j.atmosres.2024.107608. The extreme scarcity of meteorological observation data caused by harsh natural environments greatly limits our understanding of precipitation and related atmospheric processes over the mountainous regions of the southern Tibetan Plateau and its surrounding areas (hereafter mountainous southern TP). Precipitation simulation has been challenging in this region due to the complex topography and large elevation differences. Considering the high sensitivity of precipitation to the choice of cumulus parameterization scheme (CPS) over the TP, this study systematically evaluated the precipitation simulation performance of 11 CPSs in July 2018 using the WRF model. The characteristics of atmospheric circulation and gradient variation of precipitation were also revealed based on the optimal CPS over this region. The results indicated that the scale-aware schemes (KIAPS SAS [KSAS] and multi-scale Kain–Fritsch [MSKF]) demonstrated excellent potential for precipitation simulations. Due to the reasonable expression of atmospheric stability and the resulting accurate simulation of the timing and amount of regional heavy precipitation events, the KSAS scheme was superior to the MSKF scheme. The output of the KSAS-configured experiment revealed two main water vapor transport channels for the mountainous southern TP in summer, namely the southern monsoonal channel and the western westerly channel. Based on the precipitation profiles along the typical paths of these two channels (longitudinal path of 95.5°E and latitudinal path of 29.5°N), two precipitation belts and one precipitation belt existed on the southern and western slopes of the TP, respectively. Cumulus parameterization scheme; Evaluation; Gradient variation of precipitation; Mountainous southern Tibetan Plateau; WRF
Liu, Shuchang; Zeman, Christian; Schär, ChristophLiu, S., C. Zeman, C. Schär, 2024: Dynamical Downscaling of Climate Simulations in the Tropics. Geophysical Research Letters, 51(5), e2023GL105733. doi: 10.1029/2023GL105733. The long-existing double-Intertropical Convergence Zone (ITCZ) problem in global climate models (GCMs) hampers accurate climate simulations in the tropics. Using a regional climate model (RCM) over the tropical and sub-tropical Atlantic with a horizontal resolution of 12 km and explicit convection, we develop a bias-corrected downscaling methodology to produce limited-area simulations with a realistic ITCZ, despite the double ITCZ in the driving GCM. The methodology effectively removes GCM biases in the RCM boundary conditions, such as to produce more realistic large-scale driving conditions. We show that the double-ITCZ problem persists with conventional dynamical downscaling, but with bias-corrected downscaling the RCM simulations yield credible ITCZ with a realistic seasonal cycle. Detailed analysis attributes the main cause of the double-ITCZ problem of the selected GCM to the sea surface temperature bias. Compared to the GCM's AMIP simulations, RCMs with higher resolution allow explicit deep convection and enable a better simulation of tropical convection and clouds. regional climate model; bias-corrected downscaling; double-ITCZ; dynamical downscaling; pseudo-global warming approach
Lock, A. P.; Whitall, M.; Stirling, A. J.; Williams, K. D.; Lavender, S. L.; Morcrette, C.; Matsubayashi, K.; Field, P. R.; Martin, G.; Willett, M.; Heming, J.Lock, A. P., M. Whitall, A. J. Stirling, K. D. Williams, S. L. Lavender, C. Morcrette, K. Matsubayashi, P. R. Field, G. Martin, M. Willett, J. Heming, 2024: The performance of the CoMorph-A convection package in global simulations with the Met Office Unified Model. Quarterly Journal of the Royal Meteorological Society, n/a(n/a). doi: 10.1002/qj.4781. The impact on global simulations of a new package of physical parametrizations in the Met Office Unified Model is documented. The main component of the package is an entirely new convection scheme, CoMorph. This has a mass-flux structure that allows initiation of buoyant ascent from any level and the ability for plumes of differing originating levels to coexist in a grid box. It has a different form of closure, where the mass flux of initiation is dependent on local instability, and an implicit numerical solution for detrainment that yields smooth timestep behaviour. The scheme is coupled more consistently to the cloud, microphysics, and boundary-layer parametrizations and, as a result, significant changes to these have also been made. The package, called CoMorph-A, has been tested in a variety of single-column and idealized regimes. Here we test it in global configurations and evaluate it against observations using a range of standard metrics. Overall it is found to perform well against the control. Biases in the climatologies of the radiative fluxes are significantly reduced across the Tropics and subtropics, tropical and extratropical cyclone statistics are improved, and the Madden–Julian oscillation and other propagating tropical waves are strengthened. It also improves overall scores in numerical weather prediction trials, without revisions to the data assimilation. There is still work to do to improve the diurnal cycle of precipitation over land, where the peak remains too close to the middle of the day. convection; evaluation; global; parametrization; unified model
Loeb, Norman G.; Doelling, David R.; Kato, Seiji; Su, Wenying; Mlynczak, Pamela E.; Wilkins, Joshua C.Loeb, N. G., D. R. Doelling, S. Kato, W. Su, P. E. Mlynczak, J. C. Wilkins, 2024: Continuity in Top-of-Atmosphere Earth Radiation Budget Observations. doi: 10.1175/JCLI-D-24-0180.1. The Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) product combines CERES and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on the Terra and Aqua satellites to create a record of Earth’s Radiation Budget (ERB) and the associated cloud properties. As the Terra and Aqua orbits are no longer maintained at a fixed mean local time, EBAF recently transitioned to the CERES and Visible Infrared Imaging Radiometer Suite (VIIRS) instruments on NOAA-20 to avoid introducing a time-dependent bias in the record. To ensure smooth transitions between the Terra, combined Terra and Aqua (Terra+Aqua), and NOAA-20 portions of the record, regional climatological adjustments derived from the overlap period between missions are applied to anchor the entire record to Terra+Aqua. We estimate the random error in global monthly anomalies following the transitions to be
Loeb, Norman G.; Ham, Seung-Hee; Allan, Richard P.; Thorsen, Tyler J.; Meyssignac, Benoit; Kato, Seiji; Johnson, Gregory C.; Lyman, John M.Loeb, N. G., S. Ham, R. P. Allan, T. J. Thorsen, B. Meyssignac, S. Kato, G. C. Johnson, J. M. Lyman, 2024: Observational Assessment of Changes in Earth’s Energy Imbalance Since 2000. Surveys in Geophysics. doi: 10.1007/s10712-024-09838-8. Satellite observations from the Clouds and the Earth’s Radiant Energy System show that Earth’s energy imbalance has doubled from 0.5 ± 0.2 Wm−2 during the first 10 years of this century to 1.0 ± 0.2 Wm−2 during the past decade. The increase is the result of a 0.9 ± 0.3 Wm−2 increase absorbed solar radiation (ASR) that is partially offset by a 0.4 ± 0.25 Wm−2 increase in outgoing longwave radiation (OLR). Despite marked differences in ASR and OLR trends during the hiatus (2000–2010), transition-to-El Niño (2010–2016) and post-El Niño (2016–2022) periods, trends in net top-of-atmosphere flux (NET) remain within 0.1 Wm−2 per decade of one another, implying a steady acceleration of climate warming. Northern and southern hemisphere trends in NET are consistent to 0.06 ± 0.31 Wm−2 per decade due to a compensation between weak ASR and OLR hemispheric trend differences of opposite sign. We find that large decreases in stratocumulus and middle clouds over the sub-tropics and decreases in low and middle clouds at mid-latitudes are the primary reasons for increasing ASR trends in the northern hemisphere (NH). These changes are especially large over the eastern and northern Pacific Ocean, and coincide with large increases in sea-surface temperature (SST). The decrease in cloud fraction and higher SSTs over the NH sub-tropics lead to a significant increase in OLR from cloud-free regions, which partially compensate for the NH ASR increase. Decreases in middle cloud reflection and a weaker reduction in low-cloud reflection account for the increase in ASR in the southern hemisphere, while OLR changes are weak. Changes in cloud cover in response to SST increases imply a feedback to climate change yet a contribution from radiative forcing or internal variability cannot be ruled out. Climate change; Clouds; Earth radiation budget; Earth’s energy imbalance; Satellite
Lopes, Francisco M.; Dutra, Emanuel; Trigo, Isabel F.; Wild, MartinLopes, F. M., E. Dutra, I. F. Trigo, M. Wild, 2024: Evaluation of Downward Surface Longwave Flux Estimates Using Meteosat Cloud Observations. Journal of Geophysical Research: Atmospheres, 129(6), e2023JD040306. doi: 10.1029/2023JD040306. The downward surface longwave flux (DSLF) plays a relevant role in the Earth’s surface radiative budget, which is crucial to monitor, understand and model the impact of changes at local and global scales on surface temperature and surface conditions. This study focuses on the evaluation and intercomparison of four DSLF products: (a) a recently developed all-weather DSLF product based on the multivariate adaptive regression splines (MARS) algorithm driven by satellite cloud information from the Meteosat Second Generation (MSG) and ERA5 reanalysis screen variables; (b) the Satellite Application Facility on Land Surface Analysis (LSA SAF); (c) CERES Synoptic top-of-atmosphere and surface fluxes and clouds (CERES-SYN1deg) and (d) ERA5 reanalysis. The study covers the period 2005–2021 and the MSG region focusing on monthly means. The evaluation performed against 48 ground stations from the Baseline Surface Radiation Network (BSRN) and FLUXNET2015 networks showed that the MARS product outperforms the remaining products, particularly the LSA SAF, while ERA5 and CERES show similar performance metrics. The fours products are intercompared in terms of their mean spatial variability and temporal mean annual cycles and inter-annual variability in four selected regions, showing a high level of agreement, particularly between MARS, ERA5 and CERES. Our results highlight the clear added value of MARS with respect to LSA SAF, while providing higher spatial resolution (0.05°), constrained by satellite cloud information, when compared with ERA5 (0.25°) or CERES (1°). machine learning; all-weather; downward surface longwave fluxes; ECMWF-ERA5; Meteosat Second Generation; multivariate adaptive regression splines
Lu, Lu; Li, Ying; Liang, Lingjun; Ma, QianLu, L., Y. Li, L. Liang, Q. Ma, 2024: Diurnal Variation in Surface Incident Solar Radiation Retrieved by CERES and Himawari-8. Remote Sensing, 16(14), 2670. doi: 10.3390/rs16142670. The diurnal variation of surface incident solar radiation (Rs) has a significant impact on the Earth’s climate. Satellite-retrieved Rs datasets display good spatial and temporal continuity compared with ground-based observations and, more importantly, have higher accuracy than reanalysis datasets. Facilitated by these advantages, many scholars have evaluated satellite-retrieved Rs, especially based on monthly and annual data. However, there is a lack of evaluation on an hourly scale, which has a profound impact on sea–air interactions, climate change, agriculture, and prognostic models. This study evaluates Himawari-8 and Clouds and the Earth’s Radiant Energy System Synoptic (CERES)-retrieved hourly Rs data covering 60°S–60°N and 80°E–160°W based on ground-based observations from the Baseline Surface Radiation Network (BSRN). Hourly Rs were first standardized to remove the diurnal and seasonal cycles. Furthermore, the sensitivities of satellite-retrieved Rs products to clouds, aerosols, and land cover types were explored. It was found that Himawari-8-retrieved Rs was better than CERES-retrieved Rs at 8:00–16:00 and worse at 7:00 and 17:00. Both satellites performed better at continental sites than at island/coastal sites. The diurnal variations of statistical parameters of Himawari-8 satellite-retrieved Rs were stronger than those of CERES. Relatively larger MABs in the case of stratus and stratocumulus were exhibited for both hourly products. Smaller MAB values were found for CERES covered by deep convection and cumulus clouds and for Himawari-8 covered by deep convection and nimbostratus clouds. Larger MAB values at evergreen broadleaf forest sites and smaller MAB values at open shrubland sites were found for both products. In addition, Rs retrieved by Himawari-8 was more sensitive to AOD at 10:00–16:00, while that retrieved by CERES was more sensitive to COD at 9:00–15:00. The CERES product showed larger sensitivity to COD (at 9:00–15:00) and AOD (at 7:00–10:00) than Himawari-8. This work helps data producers know how to improve their future products and helps data users be aware of the uncertainties that exist in hourly satellite-retrieved Rs data. Himawari-8; CERES; diurnal variation; BSRN; solar radiation
Ma, Qianhui; Zhang, Chunyan; Wang, Donghai; Pang, ZihaoMa, Q., C. Zhang, D. Wang, Z. Pang, 2024: Summer Atmospheric Water Cycle under the Transition Influence of the Westerly and Summer Monsoon over the Yarlung Zangbo River Basin in the Southern Tibetan Plateau. Advances in Atmospheric Sciences. doi: 10.1007/s00376-023-3094-6. This study compares the summer atmospheric water cycle, including moisture sources and consumption, in the upstream, midstream, and downstream regions of the Yarlung Zangbo River Basin in the southern Tibetan Plateau. The evolutions of moisture properties under the influence of the westerly and summer southerly monsoon are examined using 5-yr multi-source measurements and ERA5 reanalysis data. Note that moisture consumption in this study is associated with clouds, precipitation, and diabatic heating. Compared to the midstream and downstream regions, the upstream region has less moisture, clouds, and precipitation, where the moisture is brought by the westerly. In early August, the vertical wet advection over this region becomes enhanced and generates more high clouds and precipitation. The midstream region has moisture carried by the westerly in June and by the southerly monsoon from July to August. The higher vertical wet advection maximum here forms more high clouds, with a precipitation peak in early July. The downstream region is mainly affected by the southerly-driven wet advection. The rich moisture and strong vertical wet advection here produce the most clouds and precipitation among the three regions, with a precipitation peak in late June. The height of the maximum moisture condensation is different between the midstream region (325 hPa) and the other two regions (375 hPa), due to the higher upward motion maximum in the midstream region. The diabatic heating structures show that stratiform clouds dominate the upstream region, stratiform clouds and deep convection co-exist in the midstream region, and deep convection systems characterize the downstream region. constrained variational analysis; atmospheric water cycle; moisture source and consumption; Yarlung Zangbo River Basin
Mardani, Masoud; Hoseinzadeh, Siamak; Garcia, Davide AstiasoMardani, M., S. Hoseinzadeh, D. A. Garcia, 2024: Developing particle-based models to predict solar energy attenuation using long-term daily remote and local measurements. Journal of Cleaner Production, 434, 139690. doi: 10.1016/j.jclepro.2023.139690. Iran has an annual average of 2.8–5.4 kW h/m2d of radiation and has a high capacity for extracting electricity from its solar resources. Tehran, the capital of Iran, is one of the most polluted cities in the world in terms of atmospheric aerosols. Due to the rising air pollution in Tehran, the existing research is outdated. An analysis of the loss of electricity generation due to particulates can significantly affect the feasibility of a photovoltaic power plant in Tehran. Several factors affect the electricity generation of photovoltaic systems. The most critical is solar radiation. The amount of solar radiation transmitted and, ultimately, the amount of electricity generated depends on several atmospheric factors. One of the most important factors is the concentration of suspended particles of different sizes. In the present work, linear models based on observed suspended particle concentrations, including PM10 and PM2.5, have been proposed for Tehran from 2014 to 2020 to anticipate the aerosol attenuation index due to aerosols. Based on the correlation coefficient values (R), in the first and last months of the year, November, December, and January, the models performed better to predict the aerosol attenuation index based on PM2.5. The R values were, in order, 0.1553, 0.2926, and 0.1341. As remote measurements, the NASA CERES syn 1-deg product parameters and, as ground observations, Surface Solar Radiation (SSR) and PM10 and PM2.5 concentrations were used to estimate the impacts of aerosols on radiation. With the help of the CERES syn 1-deg product, it is declared that, on average, 8.30% of the total radiation received was wasted due to the presence of aerosols. Considering observed SSR, CERES syn 1-deg product performance was validated, with RMSE and MBD values of 14.09% and 10.89%, respectively. Solar energy; Aerosols; Energy and environment analysis; Feasibility study; Pollution; Solar mapping
Masunaga, Hirohiko; Takahashi, HaniiMasunaga, H., H. Takahashi, 2024: The Energetics of the Lagrangian Evolution of Tropical Convective Systems. J. Atmos. Sci., 81(4), 783-799. doi: 10.1175/JAS-D-23-0141.1. Abstract The convective life cycle is often conceptualized to progress from congestus to deep convection and develop further to stratiform anvil clouds, accompanied by a systematic change in the vertical structure of vertical motion. This archetype scenario has been developed largely from the Eulerian viewpoint, and it has yet to be explored whether the same life cycle emerges itself in a moving system tracked in the Lagrangian manner. To address this question, Lagrangian tracking is applied to tropical convective systems in combination with a thermodynamic budget analysis forced by satellite-retrieved precipitation and radiation. A new method is devised to characterize the vertical motion profiles in terms of the column import or export of moisture and moist static energy (MSE). The bottom-heavy, midheavy, and top-heavy regimes are identified for every 1° × 1° grid pixel accompanying tracked precipitation systems, making use of the diagnosed column export/import of moisture and MSE. The major findings are as follows. The Lagrangian evolution of convective systems is dominated by a state of dynamic equilibrium among different convective regimes rather than a monotonic progress from one regime to the next. The transition from the bottom-heavy to midheavy regimes is fed with intensifying precipitation presumably owing to a negative gross moist stability (GMS) of the bottom-heavy regime, whereas the transition from the midheavy to top-heavy regimes dissipates the system. The bottom-heavy to midheavy transition takes a relaxation time of about 5 h in the equilibrating processes, whereas the relaxation time is estimated as roughly 20 h concerning the midheavy to top-heavy transition.
Mayer, Michael; Kato, Seiji; Bosilovich, Michael; Bechtold, Peter; Mayer, Johannes; Schröder, Marc; Behrangi, Ali; Wild, Martin; Kobayashi, Shinya; Li, Zhujun; L’Ecuyer, TristanMayer, M., S. Kato, M. Bosilovich, P. Bechtold, J. Mayer, M. Schröder, A. Behrangi, M. Wild, S. Kobayashi, Z. Li, T. L’Ecuyer, 2024: Assessment of Atmospheric and Surface Energy Budgets Using Observation-Based Data Products. Surveys in Geophysics. doi: 10.1007/s10712-024-09827-x. Accurate diagnosis of regional atmospheric and surface energy budgets is critical for understanding the spatial distribution of heat uptake associated with the Earth’s energy imbalance (EEI). This contribution discusses frameworks and methods for consistent evaluation of key quantities of those budgets using observationally constrained data sets. It thereby touches upon assumptions made in data products which have implications for these evaluations. We evaluate 2001–2020 average regional total (TE) and dry static energy (DSE) budgets using satellite-based and reanalysis data. For the first time, a consistent framework is applied to the ensemble of the 5th generation European Reanalysis (ERA5), version 2 of modern-era retrospective analysis for research and applications (MERRA-2), and the Japanese 55-year Reanalysis (JRA55). Uncertainties of the computed budgets are assessed through inter-product spread and evaluation of physical constraints. Furthermore, we use the TE budget to infer fields of net surface energy flux. Results indicate biases Earth’s energy imbalance; Energy budget; Reanalysis; Remote sensing; Surface energy flux
McKim, Brett; Bony, Sandrine; Dufresne, Jean-LouisMcKim, B., S. Bony, J. Dufresne, 2024: Weak anvil cloud area feedback suggested by physical and observational constraints. Nature Geoscience, 17(5), 392-397. doi: 10.1038/s41561-024-01414-4. Changes in anvil clouds with warming remain a leading source of uncertainty in estimating Earth’s climate sensitivity. Here we develop a feedback analysis that decomposes changes in anvil clouds and creates testable hypotheses for refining their proposed uncertainty ranges with observations and theory. To carry out this storyline approach, we derive a simple but quantitative expression for the anvil area feedback, which is shown to depend on the present-day measurable cloud radiative effects and the fractional change in anvil area with warming. Satellite observations suggest an anvil cloud radiative effect of about ±1 W m−2, which requires the fractional change in anvil area to be about 50% K−1 in magnitude to produce a feedback equal to the current best estimate of its lower bound. We use quantitative theory and observations to show that the change in anvil area is closer to about −4% K−1. This constrains the area feedback and leads to our revised estimate of 0.02 ± 0.07 W m−2 K−1, which is many times weaker and more constrained than the overall anvil cloud feedback. In comparison, we show the anvil cloud albedo feedback to be much less constrained, both theoretically and observationally, which poses an obstacle for bounding Earth’s climate sensitivity. Climate change; Atmospheric dynamics; Climate and Earth system modelling
Michibata, TakuroMichibata, T., 2024: Radiative effects of precipitation on the global energy budget and Arctic amplification. npj Climate and Atmospheric Science, 7(1), 1-11. doi: 10.1038/s41612-024-00684-4. Radiative forcing is an essential metric for accurate climate prediction. Clouds are a well-known source of uncertainty, but the radiative effects of precipitation (REP) are poorly understood and excluded from most general circulation models (GCMs). This is because conventional GCMs treat precipitation diagnostically, and thus, are transparent to shortwave and longwave radiation. In this study, we investigated the REP at global and regional scales by employing three sub-models incorporating (1) diagnostic precipitation, (2) prognostic precipitation without REP, and (3) prognostic precipitation with REP. We found that REP alters not only the local thermodynamic profile but also the remote precipitation rate and distribution through changes in atmospheric circulation. The polar surface temperature increases by more than 1 K in the winter when considering REP. The 34 CMIP6 models show systematic differences in Arctic amplification depending on REP, emphasising that GCMs should include REP to improve confidence in simulating atmosphere-ocean-cryosphere interactions. Cryospheric science; Atmospheric science
Mishra, Anoop Kumar; Tomar, Chander Singh; Kumar, Gajendra; Mitra, Ashim K.; Bhan, Subhash ChanderMishra, A. K., C. S. Tomar, G. Kumar, A. K. Mitra, S. C. Bhan, 2024: Performance Evaluation of INSAT-3D Derived Outgoing Long Wave Radiation Over India Using Remotely Sensed Observations. Journal of the Indian Society of Remote Sensing. doi: 10.1007/s12524-023-01800-2. This research work focuses on the comparison of Outgoing Long Wave Radiation (OLR) derived from the current operational Indian National SATellite-3D (INSAT-3D) with that from Clouds and the Earth’s Radiant Energy System (CERES), Advanced Very High Resolution Radiometer (AVHRR) and High Resolution Infra-Red Sounder (HIRS) at various temporal scales ranging from daily to monthly. INSAT-3D OLR was averaged over a 2.5° × 2.5° grid to enable comparison between the INSAT-3D, AVHRR, HIRS and CERES OLR. Results show that INSAT-3D derived OLR shows good comparison with HIRS and CERES. AVHRR underestimates, especially over the arid and semiarid regions, which may be attributed to the fact that OLR at the top of atmosphere is also sensitive to the vertical distribution of moisture and thus exclusion of Water Vapor (WV) channel from AVHRR OLR might have resulted in lower values of OLR. Also, the temporal sampling is important as INSAT-3D uses 48 half-hourly observations for computing the daily average, whereas, CERES, HIRS and AVHRR have only 2–3 diurnal samples for daily averages. Quantitative comparison of INSAT-3D OLR at daily scale shows a CC of 0.98, 0.91 and 0.88 with HIRS, CERES and AVHRR, respectively. Positive biases of 1.12 W/m2 and 5.93 W/m2 in INSAT-3D OLR have been reported with respect to HIRS and AVHRR, respectively. INSAT-3D shows a negative bias of − 5.09 W/m2 with CERES observations which is consistent with a previous study. On a monthly scale, INSAT-3D shows excellent agreement with CERES with a bias of 0.45 W/m2. The OLR monthly bias from INSAT-3D increases slightly to 7.98 W/m2 with respect to AVHRR at a monthly scale. Results reported in this study highlights the applicability of INSAT-3D for various meteorological and climatological studies. Clouds; Satellite; Convection; Radiation feedback; Sounder
Mishra, Manoj Kumar; Singh, Randhir; Vadnathani, Rakesh; Thapliyal, P. K.Mishra, M. K., R. Singh, R. Vadnathani, P. K. Thapliyal, 2024: Impact of vegetation greening on TOA clear-sky shortwave radiation in Northwest India. Climate Dynamics. doi: 10.1007/s00382-024-07321-z. Since 2000, Clouds and the Earth's Radiant Energy System (CERES) instruments on Aqua and Terra satellites have recorded top-of-atmosphere (TOA) clear-sky outgoing radiation fluxes. Over northwest India, analysis of these two decades of data revealed significant negative trends in reflected shortwave radiation, indicating positive shortwave radiative forcing. Aerosols; Climate change; Climate mitigation strategies; Land surface temperature; Northwest India; Top-of-atmosphere (TOA) shortwave flux; Vegetation dynamics
Motlaghzadeh, S.; Vasiuta, M.; Bister, M.; Navarro Trastoy, A.; Tuppi, L.; Mayer-Gürr, T.; Järvinen, H.Motlaghzadeh, S., M. Vasiuta, M. Bister, A. Navarro Trastoy, L. Tuppi, T. Mayer-Gürr, H. Järvinen, 2024: Weather-Induced Satellite Orbit Perturbations. Journal of Geophysical Research: Atmospheres, 129(8), e2023JD040009. doi: 10.1029/2023JD040009. Satellites in Earth's orbit are exposed to Earth radiation, consisting of reflected solar and emitted thermal radiation, thereby exerting a non-conservative force that causes acceleration and affects the orbits. Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission aiming to retrieve the Earth's gravity potential is critically dependent on accounting for this force and all other non-gravitational forces. There are both diurnal and seasonal variations in the Earth's radiation pressure, of which the seasonal variability can be represented by climatology. Nevertheless, the daily variations in the Earth's radiation pressure, due to the transient changes in the weather; for example, clouds and their properties, are not accounted for in the orbit perturbations studies. We show here that the top-of-atmosphere radiation fluxes computed with a numerical weather prediction (NWP) model explain most of the measured short-term variations in the radial acceleration of the GRACE-FO satellite. Our physics-based modeling corrects a hitherto unexplained lack of power spectral density in the measured accelerations. For example, we can accurately model the accelerations associated with a tropical storm in the Indian Ocean in December 2020, which would not be possible when using climatological data. Our results demonstrate that using a global numerical weather prediction model significantly improves the simulation of non-gravitational effects in the satellites' orbits. In the 7-day data set, OpenIFS-simulated acceleration exhibited higher accuracy than climatological-data-simulated acceleration (2.5 compared to 2.6 nms−2) and an improved precision (2.6 compared to 3.0 nms−2). This advancement contributes to a more precise orbit determination across various applications in Earth sciences. orbit; GRACE-FO; accelerometer
Moustaka, Anna; Korras-Carraca, Marios-Bruno; Papachristopoulou, Kyriakoula; Stamatis, Michael; Fountoulakis, Ilias; Kazadzis, Stelios; Proestakis, Emmanouil; Amiridis, Vassilis; Tourpali, Kleareti; Georgiou, Thanasis; Solomos, Stavros; Spyrou, Christos; Zerefos, Christos; Gkikas, AntonisMoustaka, A., M. Korras-Carraca, K. Papachristopoulou, M. Stamatis, I. Fountoulakis, S. Kazadzis, E. Proestakis, V. Amiridis, K. Tourpali, T. Georgiou, S. Solomos, C. Spyrou, C. Zerefos, A. Gkikas, 2024: Assessing Lidar Ratio Impact on CALIPSO Retrievals Utilized for the Estimation of Aerosol SW Radiative Effects across North Africa, the Middle East, and Europe. Remote Sensing, 16(10), 1689. doi: 10.3390/rs16101689. North Africa, the Middle East, and Europe (NAMEE domain) host a variety of suspended particles characterized by different optical and microphysical properties. In the current study, we investigate the importance of the lidar ratio (LR) on Cloud-Aerosol Lidar with Orthogonal Polarization–Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIOP-CALIPSO) aerosol retrievals towards assessing aerosols’ impact on the Earth-atmosphere radiation budget. A holistic approach has been adopted involving collocated Aerosol Robotic Network (AERONET) observations, Radiative Transfer Model (RTM) simulations, as well as reference radiation measurements acquired using spaceborne (Clouds and the Earth’s Radiant Energy System-CERES) and ground-based (Baseline Surface Radiation Network-BSRN) instruments. We are assessing the clear-sky shortwave (SW) direct radiative effects (DREs) on 550 atmospheric scenes, identified within the 2007–2020 period, in which the primary tropospheric aerosol species (dust, marine, polluted continental/smoke, elevated smoke, and clean continental) are probed using CALIPSO. RTM runs have been performed relying on CALIOP retrievals in which the default and the DeLiAn (Depolarization ratio, Lidar ratio, and Ångström exponent)-based aerosol-speciated LRs are considered. The simulated fields from both configurations are compared against those produced when AERONET AODs are applied. Overall, the DeLiAn LRs leads to better results mainly when mineral particles are either solely recorded or coexist with other aerosol species (e.g., sea-salt). In quantitative terms, the errors in DREs are reduced by ~26–27% at the surface (from 5.3 to 3.9 W/m2) and within the atmosphere (from −3.3 to −2.4 W/m2). The improvements become more significant (reaching up to ~35%) for moderate-to-high aerosol loads (AOD ≥ 0.2). CERES; AERONET; BSRN; clear-sky; CALIOP–CALIPSO; DREs; lidar ratio; NAMEE; RTM; SW
Nikolov, Ned; Zeller, Karl F.Nikolov, N., K. F. Zeller, 2024: Roles of Earth’s Albedo Variations and Top-of-the-Atmosphere Energy Imbalance in Recent Warming: New Insights from Satellite and Surface Observations. Geomatics, 4(3), 311-341. doi: 10.3390/geomatics4030017. Past studies have reported a decreasing planetary albedo and an increasing absorption of solar radiation by Earth since the early 1980s, and especially since 2000. This should have contributed to the observed surface warming. However, the magnitude of such solar contribution is presently unknown, and the question of whether or not an enhanced uptake of shortwave energy by the planet represents positive feedback to an initial warming induced by rising greenhouse-gas concentrations has not conclusively been answered. The IPCC 6th Assessment Report also did not properly assess this issue. Here, we quantify the effect of the observed albedo decrease on Earth’s Global Surface Air Temperature (GSAT) since 2000 using measurements by the Clouds and the Earth’s Radiant Energy System (CERES) project and a novel climate-sensitivity model derived from independent NASA planetary data by employing objective rules of calculus. Our analysis revealed that the observed decrease of planetary albedo along with reported variations of the Total Solar Irradiance (TSI) explain 100% of the global warming trend and 83% of the GSAT interannual variability as documented by six satellite- and ground-based monitoring systems over the past 24 years. Changes in Earth’s cloud albedo emerged as the dominant driver of GSAT, while TSI only played a marginal role. The new climate sensitivity model also helped us analyze the physical nature of the Earth’s Energy Imbalance (EEI) calculated as a difference between absorbed shortwave and outgoing longwave radiation at the top of the atmosphere. Observations and model calculations revealed that EEI results from a quasi-adiabatic attenuation of surface energy fluxes traveling through a field of decreasing air pressure with altitude. In other words, the adiabatic dissipation of thermal kinetic energy in ascending air parcels gives rise to an apparent EEI, which does not represent “heat trapping” by increasing atmospheric greenhouse gases as currently assumed. We provide numerical evidence that the observed EEI has been misinterpreted as a source of energy gain by the Earth system on multidecadal time scales. albedo; CERES; climate; energy imbalance; ENSO; gas law; IPCC; radiation; temperature; thermodynamics
Norris, Jesse; Thackeray, Chad W.; Hall, Alex; Madakumbura, Gavin D.Norris, J., C. W. Thackeray, A. Hall, G. D. Madakumbura, 2024: Historical sensible-heat-flux variations key to predicting future hydrologic sensitivity. npj Climate and Atmospheric Science, 7(1), 1-10. doi: 10.1038/s41612-024-00676-4. Under anthropogenic climate change (CC), the global hydrological cycle intensifies at a rate known as hydrologic sensitivity (HS). Global climate models (GCMs) exhibit substantial uncertainty in HS. Past work suggests that another form of HS, derived from internal climate variability (IV), is useful for constraining this uncertainty. However, these two forms of HS are weakly related. Here we show that decomposing HS under both CC and IV, based on the global energy budget, provides insight into the likely range of future HS. We find that sensible heat exchange between the atmosphere and ocean is not accounted for in the atmospheric energy budget under IV, masking the connection between HS under IV and CC. Removing this term, a closer relationship emerges. We use observations in conjunction with this relationship to suggest an upward shift in the likely range of future HS (66% confidence interval: 2.00–2.36 W m−2 K−1). Atmospheric dynamics; Projection and prediction
Ohishi, Shun; Miyoshi, Takemasa; Kachi, MisakoOhishi, S., T. Miyoshi, M. Kachi, 2024: Impact of atmospheric forcing on SST biases in the LETKF-based ocean research analysis (LORA). Ocean Modelling, 102357. doi: 10.1016/j.ocemod.2024.102357. In the previous study, the authors have produced an eddy-resolving ocean ensemble analysis product called the local ensemble transform Kalman filter (LETKF)-based ocean research analysis (LORA) over the western North Pacific and Maritime Continent regions using an ocean data assimilation system driven by the Japanese operational atmospheric reanalysis dataset known as the JRA-55. However, the LORA includes warm biases in sea surface temperature (SST) in coastal regions during the boreal winter. In this study, we perform sensitivity experiments with atmospheric forcing using an ocean forcing dataset known as the JRA55-do, which adjusts the JRA-55 to high-quality reference datasets to reduce biases and uncertainties. The results show that the nearshore warm SST biases are significantly improved by the JRA55-do. During the boreal autumn, the improvement comes from mainly two factors: (i) enhancement of surface cooling by latent heat releases caused by removing contamination of weak winds at the land grid cells, and (ii) weakening surface heating by downward shortwave radiation through the adjustment in the JRA55-do. During the boreal winter, enhanced cooling by the analysis increments suppresses the growth of the warm SST biases when the JRA55-do is used. However, if the JRA-55 dataset is used, the adaptive observation error inflation (AOEI) scheme acts negatively to keep the nearshore SST biases in winter. Based on the innovation statistics, the AOEI inflates the observation errors when the differences between the squared observation-minus-forecast innovations and the squared forecast ensemble spreads are larger than the prescribed observation error variance, and improves the accuracy in the open ocean, especially around the frontal regions. However, when substantial warm SST biases are formed in the previous season, AOEI's observation error inflation makes the analysis increments smaller and cannot suppress the warm biases. We also validate the analysis accuracy using various data such as sea surface height and horizontal velocities and find that the JRA55-do has significant advantages. Therefore, continuous maintenance and development of ocean forcing datasets are essential for ocean modeling and data assimilation. atmospheric reanalysis; SST bias; Ensemble Kalman filter; LORA; mixed-layer temperature budget; ocean forcing dataset
Okamoto, Hajime; Sato, Kaori; Nishizawa, Tomoaki; Jin, Yoshitaka; Nakajima, Takashi; Wang, Minrui; Satoh, Masaki; Suzuki, Kentaroh; Roh, Woosub; Yamauchi, Akira; Horie, Hiroaki; Ohno, Yuichi; Hagihara, Yuichiro; Ishimoto, Hiroshi; Kudo, Rei; Kubota, Takuji; Tanaka, ToshiyukiOkamoto, H., K. Sato, T. Nishizawa, Y. Jin, T. Nakajima, M. Wang, M. Satoh, K. Suzuki, W. Roh, A. Yamauchi, H. Horie, Y. Ohno, Y. Hagihara, H. Ishimoto, R. Kudo, T. Kubota, T. Tanaka, 2024: JAXA Level2 algorithms for EarthCARE mission from single to four sensors: new perspective of cloud, aerosol, radiation and dynamics. Atmospheric Measurement Techniques Discussions, 1-21. doi: 10.5194/amt-2024-101. Abstract. This article gives the overview of the Japan Aerospace Exploration Agency (JAXA) level 2 (L2) Standard and Research algorithms and products by Japanese science teams for EarthCARE Clouds, Aerosols and Radiation Explorer (EarthCARE), which is a JAXA and the European Space Agency (ESA) joint satellite mission. First three single sensor algorithms for 94GHz cloud profiling radar (CPR)-only, 355nm-atmospheric lidar with high spectral resolution function (ATLID)-only, and multi-spectral imager (MSI)-only retrievals, and their products were briefly reviewed. CPR-echo algorithms provide radar reflectivity factor, Doppler velocity, normalized radar cross section and path integral attenuation. CPR-only, CPR-ATLID synergy and CPR-ALTID-MSI synergy algorithms for standard cloud products provide cloud detection, cloud particle type and cloud microphysics, and the research products further provide Doppler velocity, terminal velocity and vertical air motion inside clouds. ATLID standalone algorithms produce aerosol, cloud and clear sky classification products as well as total aerosol extinction and extinction and number concentration of each aerosol types. ATLID-MSI synergy algorithms are developed to retrieve effective radius for each aerosol species in addition to the ATLID-only products. MSI algorithms retrieve cloud effective radius, ice and water content and cloud top pressure. Four sensor algorithms are prepared to produce shortwave and longwave radiative fluxes at the top of atmosphere, those at the surface and also heating rate profiles by using the outputs from CPR, ATLID and their synergy algorithms. The shortwave and longwave fluxes from the four sensor algorithms will then be compared with broad band radiation (BBR) to examine the consistency of the JAXA L2 retrievals. The algorithms are developed and evaluated by using observational data from satellites and ground-based instruments, and simulation data from the Japanese global cloud-resolving model, the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) with Joint simulator. As for space-borne data, existing space-borne satellites data such as CloudSat, CALIPSO, MODIS and CERES datasets are intensively used. For ground-based observations, High-sensitivity Ground-based Super Polarimetric Ice-crystal Detection and Explication Radar (HG-SPIDER) with a minimum sensitivity of -40 dBZ at 15 km and over -60 dBZ at 1 km, Electronic Scanning SPIDER (ES-SPIDER), 355 nm high spectral resolution lidar, multiple-field-of-view multiple scattering lidar and Doppler lidars are installed at EarthCARE super-site in Koganei, Tokyo and offers unique opportunities to evaluate and analyse EarthCARE data.
Olonscheck, Dirk; Rugenstein, MariaOlonscheck, D., M. Rugenstein, 2024: Coupled Climate Models Systematically Underestimate Radiation Response to Surface Warming. Geophysical Research Letters, 51(6), e2023GL106909. doi: 10.1029/2023GL106909. A realistic representation of top-of-the-atmosphere (TOA) radiation response to surface warming is key for trusting climate model projections. We show that coupled models with freely evolving ocean-atmosphere interactions systematically underestimate the observed global TOA radiation trend during 2001–2022 in 552 simulations. Locally, even if a simulation spontaneously reproduces observed surface temperature trends, TOA radiation trends are more likely under- than overestimated. This response bias stems from the models' inability to reproduce the observed large-scale surface warming pattern and from errors in the atmospheric physics affecting short- and longwave radiation. Models with a better representation of the TOA radiation response to local surface warming have a relatively low equilibrium climate sensitivity. Our bias metric is a novel process-based approach which links a model's current response to climate change to its behavior in the future. climate sensitivity; model evaluation; radiation; ocean-atmosphere interaction; pattern effect; large ensembles
Park, J. Minnie; McComiskey, Allison C.; Painemal, David; Smith Jr., William L.Park, J. M., A. C. McComiskey, D. Painemal, W. L. Smith Jr., 2024: Long-Term Trends in Aerosols, Low Clouds, and Large-Scale Meteorology Over the Western North Atlantic From 2003 to 2020. Journal of Geophysical Research: Atmospheres, 129(11), e2023JD039592. doi: 10.1029/2023JD039592. A continuous decrease in aerosols over the Western North Atlantic Ocean (WNAO) on a decadal timescale provides a long-term benchmark to evaluate how various natural and anthropogenic processes affect the manifestation of aerosol-cloud interactions in this region. Furthermore, the WNAO serves as a natural laboratory with diverse aerosol sources, marine boundary layer clouds more variable than those in marine stratocumulus deck regions, and unique flow regimes established by the Gulf Stream and the semi-permanent Bermuda High. We investigate how satellite-retrieved macrophysical and microphysical properties of low clouds and the surface shortwave irradiance changed from 2003 to 2020, in tandem with this aerosol decrease. The decadal changes in large-scale meteorology related to the North Atlantic Oscillation (NAO) are also examined. We find a reduction in low-cloud optical thickness, accompanied by fewer and larger cloud droplets, yet observe no significant changes in low-cloud fraction and liquid water path. Despite the reduction in low-cloud optical thickness together with aerosol decrease, a corresponding increase in the trends of surface shortwave irradiance, also known as surface brightening, is lacking. This absence of brightening is potentially related to concomitant changes found in large-scale meteorology associated with NAO—Bermuda High strengthening, sea surface warming, and atmospheric moistening— as well as an increase in high-level cloud fraction that can counteract the surface brightening. Ultimately, our findings suggest that spatial patterns of decadal meteorological variability introduce complexities in the surface cloud radiative effect over the WNAO, thereby complicating the isolation and examination of aerosol-cloud interactions. aerosol-cloud interactions; cloud radiative effect; dimming and brightening; marine boundary layer clouds; North Atlantic Oscillation
Park, Sungsu; Song, Chanwoo; Kim, Siyun; Kim, JuwonPark, S., C. Song, S. Kim, J. Kim, 2024: Parameterization of the Elevated Convection With a Unified Convection Scheme (UNICON) and Its Impacts on the Diurnal Cycle of Precipitation. Journal of Advances in Modeling Earth Systems, 16(3), e2023MS003651. doi: 10.1029/2023MS003651. To improve the simulation of nocturnal precipitation, we develop a parameterization for the elevated convection that is launched from the level of maximum grid-mean moist static energy, when grid-mean vertical flow is upward at the launching interface. The parameterized elevated convection is forced by both cold pool-driven and partially resolved external mesoscale organized flows. Properties of the external mesoscale flow are estimated from grid-mean vertical velocity and three dimensional advection tendencies of temperature and moisture. The new parameterization is implemented into a unified convection scheme (UNICON) and tested for both the single-column case at the Southern Great Plain (SGP) site in US and in global simulations. At the SGP site, the parameterized elevated convection strengthens nocturnal convection, increases nocturnal precipitation, and better simulates the observed diurnal cycle of precipitation. It appears that the elevated and surface-based convections interact with each other by stabilizing the atmospheric column, which affects subsequent convection. Global simulation shows that the elevated convection mostly occurs over the continents during the night, and also over the oceanic mid-latitude warm air advection and storm track regions during summer. Without degrading global mean climate, the elevated convection improves the simulation of nocturnal precipitation in the mid-US but simulates somewhat strong nocturnal precipitation in northeastern Asia. It seems that a key to simulate observed nocturnal precipitation is to appropriately parameterize the impacts of external organized flow on the elevated convection. convection parameterization; diurnal cycle of precipitation; elevated convection
Peng, Liran; Blossey, Peter N.; Hannah, Walter M.; Bretherton, Christopher S.; Terai, Christopher R.; Jenney, Andrea M.; Pritchard, MichaelPeng, L., P. N. Blossey, W. M. Hannah, C. S. Bretherton, C. R. Terai, A. M. Jenney, M. Pritchard, 2024: Improving Stratocumulus Cloud Amounts in a 200-m Resolution Multi-Scale Modeling Framework Through Tuning of Its Interior Physics. Journal of Advances in Modeling Earth Systems, 16(3), e2023MS003632. doi: 10.1029/2023MS003632. High-Resolution Multi-scale Modeling Frameworks (HR)—global climate models that embed separate, convection-resolving models with high enough resolution to resolve boundary layer eddies—have exciting potential for investigating low cloud feedback dynamics due to reduced parameterization and ability for multidecadal throughput on modern computing hardware. However low clouds in past HR have suffered a stubborn problem of over-entrainment due to an uncontrolled source of mixing across the marine subtropical inversion manifesting as stratocumulus dim biases in present-day climate, limiting their scientific utility. We report new results showing that this over-entrainment can be partly offset by using hyperviscosity and cloud droplet sedimentation. Hyperviscosity damps small-scale momentum fluctuations associated with the formulation of the momentum solver of the embedded large eddy simulation. By considering the sedimentation process adjacent to default one-moment microphysics in HR, condensed phase particles can be removed from the entrainment zone, which further reduces entrainment efficiency. The result is an HR that can produce more low clouds with a higher liquid water path and a reduced stratocumulus dim bias. Associated improvements in the explicitly simulated sub-cloud eddy spectrum are observed. We report these sensitivities in multi-week tests and then explore their operational potential alongside microphysical retuning in decadal simulations at operational 1.5° exterior resolution. The result is a new HR having desired improvements in the baseline present-day low cloud climatology, and a reduced global mean bias and root mean squared error of absorbed shortwave radiation. We suggest it should be promising for examining low cloud feedbacks with minimal approximation. superparameterization; climate modeling; cloud physics; atmospheric science; multi-scale modeling
Povea-Pérez, Yoania; Guilyardi, Éric; Fedorov, Alexey V.; Ferster, BradyPovea-Pérez, Y., É. Guilyardi, A. V. Fedorov, B. Ferster, 2024: The central role of the Atlantic meridional overturning circulation in the Bjerknes compensation. Climate Dynamics, 62(1), 575-587. doi: 10.1007/s00382-023-06926-0. Poleward heat (energy) transport plays a major role in shaping the Earth’s climate. Its oceanic and atmospheric components carry heat from low to high latitudes thus reducing the equator-to-pole temperature contrast. In quasi-equilibrium climate states, changes in the top-of-the-atmosphere (TOA) energy fluxes and ocean heat content remain small. In such conditions, anomalies in oceanic and atmospheric heat transport must have the same magnitude but opposite signs. This phenomenon is known as the Bjerknes compensation (BJC). The BJC hypothesis is of high importance in climate, since it imposes a strong constraint on climate variability at sufficiently long timescales (on sub-decadal and shorter timescales TOA flux variations may become comparable to other heat budget terms, interfering with BJC). However, to which extent BJC operates in the climate system and the key mechanisms of the compensation remain poorly understood. Here we analyze BJC in the IPSL-CM6A-LR climate model, focusing on its timescale dependence, its links to the Atlantic Meridional Overturning Circulation (AMOC), and the connection to Intertropical Convergence Zone (ITCZ) shifts. We show that BJC occurs in the model at both multi-decadal and centennial timescales, but is stronger on centennial timescales than decadal. In both cases BJC is initiated by variations in ocean heat transport induced by AMOC variability that are partially or fully compensated by atmospheric heat transport. For decadal timescales, we find two regions of a strong BJC at latitudes associated with the storm track region and the marginal ice zone in the Northern Hemisphere. Finally, on centennial timescales we observe a Bjerknes-like interbasin compensation between the Atlantic and Indo-Pacific heat transports, which is also related to strong centennial AMOC fluctuations and involves Southern Ocean zonal heat transport. Climate variability; Atlantic meridional overturning circulation; Bjerknes compensation; Poleward heat transport
Prajwal, K.; Kottayil, Ajil; Xavier, Prince; Legras, BernardPrajwal, K., A. Kottayil, P. Xavier, B. Legras, 2024: A new insight into monsoon intraseasonal variability as revealed from distinct wind-precipitation regimes over the southwest coast of India. Climate Dynamics. doi: 10.1007/s00382-024-07366-0. This study evaluates the observed non-linearity in the wind-precipitation relationship over India’s southwest coast and maps this non-linearity to monsoon intraseasonal oscillations. The wind-precipitation data is subjected to clustering, and five distinct regimes are identified. The large-scale dynamical and thermodynamical condition that leads to wind-precipitation clustering is explored. It uses novel observations from the Stratosphere–Troposphere wind profiler radar placed over Cochin (10.04° N; 76.33° E) for the period 2019–2021 to derive characteristics of monsoon low-level jets. Out of five wind-precipitation clusters, low wind low precipitation (LWLP) and low wind high precipitation clusters (LWHP) bear signatures of monsoon break conditions over central India. The occurrence of Madden Julian events or monsoon lows in LWHP generates heavy rainfall over the southwest coast. The high wind low precipitation (HWLP) cluster occurs during the weak phase of northward propagating monsoon intraseasonal oscillation (MISO) over the southwest coast, while the high wind high precipitation (HWHP) cluster lies within the strong phase of MISO. The fifth cluster, the high wind extreme precipitation cluster (HWEP), although technically lying within the strong phase of MISO, however has more apparent signatures of northwestward propagating monsoon depressions. The Lagrangian trajectories launched from 500 hPa level for each cluster reveal some intriguing aspects. The dry air intrusion from adjacent regions near the west coast makes the mid-troposphere dry over the southwest coast in LWLP and HWLP clusters. In HWHP and HWEP, strong moisture sources confined over the west coast create mid-troposphere moistening owing to the moisture supply from below 500 hPa. This study highlights that wind-precipitation clustering effectively defines sub-seasonal variability during the monsoon. Clustering; Convection; Intraseasonal oscillation; West coast
Prince, Hamish D.; L’Ecuyer, Tristan S.Prince, H. D., T. S. L’Ecuyer, 2024: Observed Energetic Adjustment of the Arctic and Antarctic in a Warming World. J. Climate, 37(8), 2611-2627. doi: 10.1175/JCLI-D-23-0294.1. Abstract Satellite observations reveal that decreasing surface albedo in both polar regions is increasing the absorption of solar radiation, but the disposition of this absorbed energy is fundamentally different. Fluxes of absorbed solar radiation, emitted thermal radiation, and net energy imbalances are assessed for both polar regions for the last 21 years in the Clouds and Earth’s Radiant Energy System record. Arctic absorbed solar radiation is increasing at 0.98 ± 0.69 W m−2 decade−1, consistent with the anticipated response to sea ice loss. However, Arctic thermal emission is responding at a similar rate of 0.94 ± 0.55 W m−2 decade−1. This is surprising since the radiative impact of ice loss would be expected to favor increasing solar absorption. We find however, that clouds substantially mask trends in Arctic solar absorption relative to clear sky while having only a modest impact on thermal emission trends. As a result, the Arctic net radiation imbalance has not changed over the period. Furthermore, variability of absorbed solar radiation explains two-thirds of the variability in annual thermal emission suggesting that Arctic thermal fluxes rapidly adjust to offset changes in solar absorption and re-establish equilibrium. Conversely, Antarctic thermal emission is not responding to the increasing (although not yet statistically significant) solar absorption of 0.59 ± 0.64 W m−2 decade−1 with less than a third of the annual thermal variability explained by accumulated solar absorption. The Arctic is undergoing rapid adjustment to increasing solar absorption resulting in no change to the net energy deficit, while increasing Antarctic solar absorption represents additional energy input into the Earth system. Significance Statement The polar regions of Earth are undergoing ice loss through ongoing global warming, reducing the ice cover and decreasing solar reflectivity, which would be expected to warm these regions. We use satellite observations to measure the trends in solar absorption and emitted thermal radiation over the Arctic and Antarctic for the last two decades. Arctic thermal emission is increasing at a compensating rate to solar absorption with a close relationship between these processes. Conversely, Antarctic thermal emission is not responding to solar absorption demonstrating that Antarctic surface temperatures are not significantly influenced by the region’s reflectivity. The Arctic is undergoing rapid adjustment to increasing solar absorption through warming, while increasing Antarctic solar absorption represents additional energy input into the Earth system.
Priya, J. S.; Krishnakumar, V.; Baiju, Sona; Sreelekshmi, R. G.; Shoufeer, AfnaPriya, J. S., V. Krishnakumar, S. Baiju, R. G. Sreelekshmi, A. Shoufeer, 2024: Study on the Seasonal and Spatial Variations of Cirrus Parameters, Radiative Characteristics and Precipitation over the Indian Subcontinent. Journal of the Indian Society of Remote Sensing. doi: 10.1007/s12524-024-01926-x. This study investigates the spatiotemporal oscillations of cirrus characteristics over the Indian subcontinent from 2013 to 2021 using Moderate Resolution Imaging Spectroradiometer observations. Analyzing Cirrus Fraction (CiF), Cirrus Reflectance (CiR), and radiative characteristics using the Clouds and the Earth’s Radiant Energy System data, the distinct spatial and seasonal fluctuations with respect to the regional precipitation characteristics is unveiled. Radiative characteristics demonstrate significant seasonal influences on Net Short-Wave Flux, Net Long Wave Flux, and Net Total Flux (NETF). Through linear regression analysis, a strong positive correlation is found between CiF, CiR and precipitation, indicating a robust linear relationship. Seasonal variations in cloud parameters and radiative characteristics are examined, revealing heightened Cloud Optical Thickness and Cloud Effective Radius during the South West monsoon season compared to other seasons. CiR and NETF are notably elevated during the Monsoon. These findings underscore the significant impact of the rain on cloud properties and energy flux dynamics over the Indian subcontinent. Cirrus cloud; Cirrus Fraction; Cirrus Reflectance; Indian subcontinent; MODIS; Precipitation
Raghuraman, Shiv Priyam; Medeiros, Brian; Gettelman, AndrewRaghuraman, S. P., B. Medeiros, A. Gettelman, 2024: Observational Quantification of Tropical High Cloud Changes and Feedbacks. Journal of Geophysical Research: Atmospheres, 129(7), e2023JD039364. doi: 10.1029/2023JD039364. The response of tropical high clouds to surface warming and their radiative feedbacks are uncertain. For example, it is uncertain whether their coverage will contract or expand in response to surface warming and whether such changes entail a stabilizing radiative feedback (iris feedback) or a neutral feedback. Global satellite observations with passive and active remote sensing capabilities over the last two decades can now be used to address such effects that were previously observationally limited. Using these observations, we show that the vertically averaged coverage exhibits no significant contraction or expansion. However, we find a reduction in coverage at the altitude where high clouds peak and are particularly radiatively-relevant. This results in a negative longwave (LW) feedback and a positive shortwave (SW) feedback which cancel to yield a near-zero high-cloud amount feedback, providing observational evidence against an iris feedback. Next, we find that tropical high clouds have risen but have also warmed, leading to a positive, but small, high-cloud altitude feedback dominated by the LW feedback. Finally, we find that high clouds have been thinning, leading to a near-zero high-cloud optical depth feedback from a cancellation between negative LW and positive SW feedbacks. Overall, high clouds lead the total tropical cloud feedback to be small due to the negative LW-positive SW feedback cancellations. clouds; climate sensitivity; feedbacks; high clouds; anvils; satellites
Ren, Zikun; Zhou, TianjunRen, Z., T. Zhou, 2024: Understanding the alleviation of “Double-ITCZ” bias in CMIP6 models from the perspective of atmospheric energy balance. Climate Dynamics. doi: 10.1007/s00382-024-07238-7. The simulation of tropical precipitation has been a challenge to climate models. The multi-model ensemble mean of CMIP6 models only show limited improvement relative to the CMIP3 and CMIP5 models. However, a simple ensemble mean may mask the improvement of individual models. Here we evaluated 20 CMIP6 models and their corresponding earlier version in CMIP5. The results show that the CMIP6 models is significantly improved in the tropical precipitation compared to their counterparts in CMIP5, and the alleviation of bias mainly happened in the top ten model pairs with largest RMSE reduction (TOP10). For the mean of TOP10, the antisymmetric (symmetric) bias mode in CMIP5 is significantly reduced by 55% (78%). Further energetics evaluation shows that, the CMIP5-to-CMIP6 decrease of antisymmetric bias in the bulk of TOP10 models is accompanied by more realistic southward cross-equatorial atmospheric energy transport ($${AET}_{EQ}$$), which is mainly contributed by the better representation of the extra-tropical surface turbulent flux ($$STF$$). On the other hand, the decrease in the symmetric bias of TOP10 models is associated with the enlargement of the negative bias in the seasonal contrast of $${AET}_{EQ}$$, which is caused by the alleviation of the biases in the seasonal contrast of extra-tropical $$STF$$. Our analysis revealed the improvement in the simulation of tropical precipitation in CMIP6, and we pointed out that the improvement is associated with the model-generational changes in the simulated atmospheric energy balances. Atmospheric energy balance; CMIP5,6; Double-ITCZ problem; Model improvement
Restrepo-Coupe, Natalia; Campos, Kleber Silva; Alves, Luciana F.; Longo, Marcos; Wiedemann, Kenia T.; de Oliveira, Raimundo Cosme; Aragao, Luiz E. O. C.; Christoffersen, Bradley O.; Camargo, Plinio B.; Figueira, Adelaine M. e S.; Ferreira, Maurício Lamano; Oliveira, Rafael S.; Penha, Deliane; Prohaska, Neill; da Araujo, Alessandro C.; Daube, Bruce C.; Wofsy, Steven C.; Saleska, Scott R.Restrepo-Coupe, N., K. S. Campos, L. F. Alves, M. Longo, K. T. Wiedemann, R. C. de Oliveira, L. E. O. C. Aragao, B. O. Christoffersen, P. B. Camargo, A. M. e. S. Figueira, M. L. Ferreira, R. S. Oliveira, D. Penha, N. Prohaska, A. C. da Araujo, B. C. Daube, S. C. Wofsy, S. R. Saleska, 2024: Contrasting carbon cycle responses to dry (2015 El Niño) and wet (2008 La Niña) extreme events at an Amazon tropical forest. Agricultural and Forest Meteorology, 353, 110037. doi: 10.1016/j.agrformet.2024.110037. Land surface models diverge in their predictions of the Amazon forest's response to climate change-induced droughts, with some showing a catastrophic collapse of forests, while others simulating resilience. Therefore, observations of tropical ecosystem responses to real-world droughts and other extreme events are needed. We report long-term seasonal dynamics of photosynthesis, respiration, net carbon exchange, phenology, and tree demography and characterize the effect of dry and wet events on ecosystem form and function at the Tapajós National Forest, Brazil, using over two decades of eddy covariance observations that include the 2015–2016 El Niño drought and La Niña 2008–2009 wet periods. We found strong forest responses to both ENSO events: La Niña saw forest net carbon loss from reduced photosynthesis (due to lower incoming radiation from increased cloudiness) even as ecosystem respiration (Reco) was maintained at mean seasonal levels. El Niño induced the opposite short-term effect, net carbon gains, despite significant reductions in photosynthesis (from a drought-induced halving of canopy conductance to CO2 and significant losses of leaf area), because drought suppression of Reco losses was even greater. However, long-term responses to the two climate perturbations were very different: transient during La Niña –the forest returned to its “normal” state as soon as the climate did, and long-lasting during El Niño –leaf area loss and associated declines in photosynthetic capacity (Pc) and canopy conductance were exacerbated and extended by feedbacks from higher temperatures and atmospheric evaporative demand and persisted for ∼3+ years after normal rainfall resumed. These findings indicate that these forests are more vulnerable to drought than to excess rain, because drought drives significant changes in forest structure (e.g., leaf-abscission and mortality) and ecosystem function (e.g. reduced stomatal conductance). As future Amazonian climate change increases frequencies of hydrological extremes, these mechanisms will determine the long-term fate of tropical forests. Amazonia; Carbon; Ecosystem-climate interactions; Eddy covariance; ENSO; Tropical forests; Water and energy flux seasonality
Sanatan, Binisia; Vinoj, V.; Landu, KiranmayiSanatan, B., V. Vinoj, K. Landu, 2024: The atmospheric aerosol spatial distribution and tropical intra-seasonal oscillations over the South Asian region. Atmospheric Pollution Research, 15(9), 102199. doi: 10.1016/j.apr.2024.102199. Intra-seasonal oscillations (ISO) are well known to modulate the weather phenomena which in turn are known to influence the atmospheric aerosol loading. This study investigates how aerosol loading is modulated in ISO spatio-temporal scales over the Indian region using long-term satellite aerosol optical depth data from Moderate Resolution Imaging Spectroradiometer (MODIS) sensor, onboard Terra Satellite. It is shown that Madden-Julian Oscillation (MJO) and Equatorial Rossby waves (ER) have the highest effect (15–20% of the mean) followed by Mixed-Rossby-gravity and Tropical depressions (MT), and Kelvin wave (KE) (5–15%). Further, a dipolar pattern in aerosol loading was observed, with poles over the Arabian Sea and the Bay of Bengal. These variabilities were found to be mainly driven by anomalous winds associated with the ISOs. Similar to aerosol, dipolar signatures in the atmospheric aerosol radiative forcing (ARF) were also observed with clearer patterns. However, the forcing poles are not centered exactly where aerosol poles were observed, indicating the effect of differential properties of aerosols on the aerosol radiative forcing. Quantitatively, at the surface level, modulation in ARF is up to 3 Wm-2 (15%) for MJO and ER, and up to 2 Wm-2 (5%) for KE and MT; in the atmosphere and at the top of the atmosphere, modulation is up to 2 Wm-2 (15%) for MJO and ER, and up to 1 Wm-2 (5%) for KE and MT. Aerosol distribution; Convectively coupled equatorial waves; India; Intra-seasonal oscillations; Pollution
Schneider, Tapio; Leung, L. Ruby; Wills, Robert C. J.Schneider, T., L. R. Leung, R. C. J. Wills, 2024: Opinion: Optimizing climate models with process knowledge, resolution, and artificial intelligence. Atmospheric Chemistry and Physics, 24(12), 7041-7062. doi: 10.5194/acp-24-7041-2024. Accelerated progress in climate modeling is urgently needed for proactive and effective climate change adaptation. The central challenge lies in accurately representing processes that are small in scale yet climatically important, such as turbulence and cloud formation. These processes will not be explicitly resolvable for the foreseeable future, necessitating the use of parameterizations. We propose a balanced approach that leverages the strengths of traditional process-based parameterizations and contemporary artificial intelligence (AI)-based methods to model subgrid-scale processes. This strategy employs AI to derive data-driven closure functions from both observational and simulated data, integrated within parameterizations that encode system knowledge and conservation laws. In addition, increasing the resolution to resolve a larger fraction of small-scale processes can aid progress toward improved and interpretable climate predictions outside the observed climate distribution. However, currently feasible horizontal resolutions are limited to O(10 km) because higher resolutions would impede the creation of the ensembles that are needed for model calibration and uncertainty quantification, for sampling atmospheric and oceanic internal variability, and for broadly exploring and quantifying climate risks. By synergizing decades of scientific development with advanced AI techniques, our approach aims to significantly boost the accuracy, interpretability, and trustworthiness of climate predictions.
Seiler, Christian; Kou-Giesbrecht, Sian; Arora, Vivek K.; Melton, Joe R.Seiler, C., S. Kou-Giesbrecht, V. K. Arora, J. R. Melton, 2024: The Impact of Climate Forcing Biases and the Nitrogen Cycle on Land Carbon Balance Projections. Journal of Advances in Modeling Earth Systems, 16(1), e2023MS003749. doi: 10.1029/2023MS003749. Earth System Models (ESMs) project that the terrestrial carbon sink will continue to grow as atmospheric CO2 increases, but this projection is uncertain due to biases in the simulated climate and how ESMs represent ecosystem processes. In particular, the strength of the CO2-fertilization effect, which is modulated by nutrient cycles, varies substantially across models. This study evaluates land carbon balance uncertainties for the Canadian Earth System Model (CanESM) by conducting simulations where the latest version of CanESM's land surface component is driven offline with raw and bias-adjusted CanESM5 climate forcing data. To quantify the impact of nutrient limitation, we complete simulations where the nitrogen cycle is enabled or disabled. Results show that bias adjustment improves model performance across most ecosystem variables, primarily due to reduced biases in precipitation. Turning the nitrogen cycle on increases the global land carbon sink during the historical period (1995–2014) due to enhanced nitrogen deposition, placing it within the Global Carbon Budget uncertainty range. During the future period (2080–2099), the simulated land carbon sink increases in response to bias adjustment and decreases in response to the dynamic carbon-nitrogen interaction, leading to a net decrease when both factors are acting together. The dominating impact of the nitrogen cycle demonstrates the importance of representing nutrient limitation in ESMs. Such efforts may produce more robust carbon balance projections in support of global climate change mitigation policies such as the 2015 Paris Agreement. climate change; climate forcing bias; land carbon balance; nitrogen cycle
Shan, Yunpeng; Fan, Jiwen; Zhang, Kai; Shpund, Jacob; Terai, Christopher; Zhang, Guang J.; Song, Xiaoliang; Chen, Chih-Chieh-Jack; Lin, Wuyin; Liu, Xiaohong; Shrivastava, Manish; Wang, Hailong; Xie, ShaochengShan, Y., J. Fan, K. Zhang, J. Shpund, C. Terai, G. J. Zhang, X. Song, C. Chen, W. Lin, X. Liu, M. Shrivastava, H. Wang, S. Xie, 2024: Improving Aerosol Radiative Forcing and Climate in E3SM: Impacts of New Cloud Microphysics and Improved Wet Removal Treatments. Journal of Advances in Modeling Earth Systems, 16(8), e2023MS004059. doi: 10.1029/2023MS004059. Numerous Earth system models exhibit excessive aerosol effective forcing at the top of the atmosphere (TOA), including the Department of Energy's Energy Exascale Earth System Model (E3SM). Here, in the context of the E3SM version 3 effort, the predicted particle property (P3) stratiform cloud microphysics scheme and an enhanced deep convection parameterization suite (ZM_plus) are implemented into E3SM. The ZM_plus includes a convective cloud microphysics scheme, a multi-scale coherent structure parameterization for mesoscale convective systems, and a revised cloud base mass flux formulation considering impacts of the large-scale environment. The P3 scheme improved cloud and radiation particularly over the Northern Hemisphere and the frequency of heavy precipitation over the tropics, and the ZM_plus improved clouds in the tropics. P3 decreases aerosol effective forcing by 0.15 W m−2, while the ZM_plus increases it by 0.27 W m−2, resulting from excessive direct (0.31 W m−2) and indirect forcing (−1.79 W m−2). The excessive aerosol forcings are due to aerosol overestimation associated with insufficient aerosol wet removal. By improving the physical treatments in the aerosol wet removal, we effectively mitigate anthropogenic aerosol overestimation and thus attenuate direct (0.09 W m−2) and indirect aerosol forcing (−1.52 W m−2). Adjustment to primary organic matter hygroscopicity reduces direct and indirect forcing to more reasonable values: −0.13 W m−2 and −1.31 W m−2, respectively. On climatology, improved aerosol treatments mitigate overestimation of aerosol optical depth. aerosol radiative forcing; aerosol-cloud interaction; cloud microphysics; convection; Earth system model; wet removal
She, Xiaojun; Li, Yao; Jiao, Wenzhe; Sun, Yuanheng; Ni, Xiangnan; Zuo, Zhenpeng; Knyazikhin, Yuri; Myneni, Ranga B.She, X., Y. Li, W. Jiao, Y. Sun, X. Ni, Z. Zuo, Y. Knyazikhin, R. B. Myneni, 2024: Varied responses of Amazon forests to the 2005, 2010, and 2015/2016 droughts inferred from multi-source satellite data. Agricultural and Forest Meteorology, 353, 110051. doi: 10.1016/j.agrformet.2024.110051. The Amazon forests play an integral role in the global carbon cycle and have a substantial impact on Earth's climate. However, it is increasingly susceptible to the effects of prolonged droughts, exacerbated by climate change and human activities. This vulnerability underscores the importance of understanding the forests’ reaction to such environmental stressors. Despite their significance, comprehensive cross-comparisons of the climate and vegetation responses during the 2005, 2010, and 2015/2016 drought episodes are not well-established. Here we utilize a range of gridded vegetation and climate datasets—including leaf area index (LAI), solar-induced chlorophyll fluorescence (SIF), enhanced vegetation index (EVI), vegetation optical depth (VOD), self-calibrating Palmer drought severity index (scPDSI), precipitation (P), land surface temperature (LST), and photosynthetically active radiation (PAR)—to thoroughly assess the climate and vegetation response to these three drought events. Our findings reveal that the extent of drought inhibition in the Amazon forests was 74.7 % in 2015, increasing to 81.3 % in 2016, a significant escalation from 49.6 % in 2005 and 57.7 % in 2010. The effects of these three droughts on vegetation varied in both physiological and structural aspects. The Amazon forests’ photosynthetic activity, greenness, and leaf area experienced comparable suppression in 2010 and 2015/2016 droughts. However, canopy water content exhibited more extensive and severe impacts during the 2015/2016 drought. Our findings indicate that varying sensitivities to water deficit and solar radiation lead to diverse spatial patterns and intensities of vegetation response, highlighting the complex dynamics of the Amazon forests under drought stress. Amazon forests; Drought; Leaf area; Solar radiation; Solar-induced chlorophyll fluorescence; Vegetation optical depth
Shen, Lixing; Zhao, Chuanfeng; Xu, Changsan; Yan, Yunwei; Chen, Annan; Yang, Yikun; Hang, Rui; Zhu, Yizhi; Zhang, Zhijiang; Song, XiangzhouShen, L., C. Zhao, C. Xu, Y. Yan, A. Chen, Y. Yang, R. Hang, Y. Zhu, Z. Zhang, X. Song, 2024: Effects of Sea Land Breeze on Air-Sea Turbulent Heat Fluxes in Different Seasons Using Platform Observation in East China Sea. Journal of Geophysical Research: Atmospheres, 129(5), e2023JD040001. doi: 10.1029/2023JD040001. Using 2-year platform observations, this study investigates seasonal characteristics of sea land breeze (SLB) and how it influences air-sea turbulent heat fluxes (THFs) in the coastal areas of East China Sea (ECS) in different seasons. Unlike other SLB studies, this study uses hourly observation on a sea platform to explore SLB's effect on both air-sea latent heat and sensible heat transferring. The results show that sea wind (SW) does not have an obvious seasonal variation pattern while land wind (LW) is stronger in autumn and winter. The SLB day number shows a clear seasonal variation pattern, which accounts for 38.04% and 18.23% of summertime and wintertime days, reaching its peak and bottom respectively. The latent heat flux (LHF) and sensible heat flux (SHF) are high in autumn and winter while low in summer. The SLB-contributed LHF and SHF reach peaks in autumn and winter, which are 61.07 and 7.39 W/m2 respectively. The contribution importance of SLB on air-sea sensible/latent heat transferring is highest in summer while lowest in winter. On SLB days, the SHF decreases significantly by at least about 50% while LHF decreases moderately in all seasons, among which spring witnesses an inversion of sensible heat transferring direction. The warming effect of SLB is mainly responsible for the slump of SHF on SLB days. Multiple factors including relative humidity (RH), background wind field and in situ radiation cause the LHF decrease together, whose changing range varies with season. sensible heat flux; East China Sea; latent heat flux; platform observation; sea land breeze; umbrella effect
Shen, Pengke; Zhao, ShuqingShen, P., S. Zhao, 2024: Intensifying urban imprint on land surface warming: Insights from local to global scale. iScience, 27(3), 109110. doi: 10.1016/j.isci.2024.109110. Increasing urbanization exacerbates surface energy balance perturbations and the health risks of climate warming; however, it has not been determined whether urban-induced warming and attributions vary from local, regional, to global scale. Here, the local surface urban heat island (SUHI) is evidenced to manifest with an annual daily mean intensity of 0.99°C–1.10°C during 2003–2018 using satellite observations over 536 cities worldwide. Spatiotemporal patterns and mechanisms of SUHI tightly link with climate-vegetation conditions, with regional warming effect reaching up to 0.015°C–0.138°C (annual average) due to surface energy alterations. Globally, the SUHI footprint of 1,860 cities approximates to 1% of the terrestrial lands, about 1.8–2.9 times far beyond the urban impervious areas, suggesting the enlargements of the imprint of urban warming from local to global scales. With continuous development of urbanization, the implications for SUHI-added warming and scaling effects are considerably important on accelerating global warming. Remote sensing; Climatology; Earth sciences; Global change; Environmental science
Siemes, Christian; van den IJssel, Jose; Visser, PieterSiemes, C., J. van den IJssel, P. Visser, 2024: Uncertainty of thermosphere mass density observations derived from accelerometer and GNSS tracking data. Advances in Space Research. doi: 10.1016/j.asr.2024.02.057. Thermosphere mass density and crosswind can be derived from accelerometer and GNSS tracking data. However, present datasets are often provided without comprehensive uncertainty specifications. We present a newly developed method that propagates measurement noise and errors in the satellite specification, thermosphere models, and radiation flux data to density observations to quantify their uncertainty. We focus specifically on density observations derived only from GNSS tracking data, which are limited in resolution along the orbit due to unavoidable smoothing. While the method can be applied to simulated and real data, making it useful for existing datasets and mission design, we demonstrated it using data from the GRACE B satellite. First, we compare the aerodynamic acceleration derived separately from the accelerometer and GNSS tracking data, highlighting the role of two significant noise sources: noise due to the differentiation of the positions and noise from the evaluation of the gravity vector at a noisy position. Averaging substantially reduces the noise in the aerodynamic acceleration as long as the differentiation noise dominates, which is the case at frequencies higher than the orbital frequency. Below, gravity vector evaluation noise becomes the dominating noise source, and consequently, averaging over longer periods leads to only marginal uncertainty reduction. Further, we investigate the uncertainty in the radiation pressure acceleration and demonstrate that averaging over one orbit substantially reduces the uncertainty in the along-track radiation pressure acceleration. We show that the uncertainty of density observations derived from the accelerometer data is about 4% of the density for data from 2003 when the GRACE B satellite was at 490 km altitude during high solar activity. In 2008, solar activity was very low, and the altitude was still 476 km, resulting in an uncertainty of 5%–20% because GNSS tracking noise and radiation pressure modeling errors play a much larger role as the aerodynamic acceleration becomes smaller. In the case of density observations derived only from GNSS tracking data, the uncertainty is about 5% in 2003 and 20%–50% in 2008 when averaging over one-third orbit. In 2008, GNSS tracking noise explains nearly all uncertainty in the density observation. Averaging over one orbit reduces the uncertainty to 4% and 5% in 2003 and 2008, respectively. Accelerometer; Uncertainty; GNSS tracking; Neutral density
Singh, Vivek; Srivastava, Atul Kumar; Gupta, Anu; Konduru, Rakesh Teja; Singh, Amarendra; Singh, Sumit; Kumar, Arun; Bisht, Deewan Singh; Singh, Abhay KumarSingh, V., A. K. Srivastava, A. Gupta, R. T. Konduru, A. Singh, S. Singh, A. Kumar, D. S. Bisht, A. K. Singh, 2024: Intensification mechanisms and moisture dynamics of super cyclonic storm ‘Amphan’ over the Bay of Bengal: Implications for aerosol re-distribution. Science of The Total Environment, 951, 175501. doi: 10.1016/j.scitotenv.2024.175501. The present research investigates the dynamics and underlying causes contributing to the exceptional intensity of Super Cyclonic Storm (SuCS) Amphan (16th to 21st May 2020) over the Bay of Bengal (BoB), as well as its impact on aerosol redistribution along the four cities of eastern coast and north-eastern India. Notably, the SuCS was formed during the first phase of the COVID-19 lockdown in India, giving it a unique aspect of study and analysis. Our analysis based on 30 years of climatology data from Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) reanalysis reveals ‘positive’ monthly anomalous winds (0.8 to 1.6 m/s) prevailed over the central BoB for May 2020. The present study further found the evolution of ‘barrier layer thickness’(BLT) leading up to landfall, noting a thickening trend from 8 to 3 days before landfall, contributing to maintaining warmer sea surface temperatures near the coast. Additionally, utilizing European Centre for Medium-Range Weather Forecasts (ECMWF), reanalysis version-5 (ERA-5) data, a mean positive sea surface temperature (SST) anomaly of 0.8 to 1 °C was observed ‘before’ cyclone period (10–15 May 2020) near the cyclogenesis point. A detailed examination of Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) vertical cross-section plots during the cyclone's intensification stage reveals the presence of high-altitude clouds composed primarily of ice crystals. Further, analysis also indicates that the cyclone transported Sea-salt PM2.5 aerosols from the ocean, dispersing them in the landfall region.The aerosol optical Depth (AOD) data obtained from the National Aeronautics and Space Administration's (NASA) ‘Clouds and the Earth's Radiant Energy System (CERES)’ mission and MERRA-2 were also analysed, revealing that the cyclone redistributed aerosols over the Bengal basin region (mainly over ‘Kolkata') and three other nearby cities along the track of the cyclone (i.e., Bhubaneswar (Odisha) Agartala (Tripura) and Shillong (Meghalaya) respectively). Aerosol optical depth; Amphan; Barrier layer thickness; COVID-19 lockdown; Sea salt PM; Super cyclonic storm
Song, Chanwoo; Park, SungsuSong, C., S. Park, 2024: A New Comprehensive Cloud Macrophysics Scheme With a Prognostic Dual-Triangular PDF. Journal of Advances in Modeling Earth Systems, 16(4), e2023MS003963. doi: 10.1029/2023MS003963. To improve cloud simulation in a general circulation model, we develop a new cloud macrophysics scheme that treats detrained cumulus generated by convective detrainment process separately from pure stratus; prognoses two symmetric triangular probability density functions of total specific humidity for each detrained cumulus and pure stratus; and diagnoses both cloud fraction and cloud condensate in all liquid, ice, and mixed-phases in a consistent and unified way without any adjustment to remove empty or very dense cloud. Supersaturation is allowed within ice cloud. The new scheme (“NEW”) is compared with the previous model (“OLD”) using single-column simulations for subtropical marine stratocumulus (DYCOMS2) and continental deep convection (ARM97) cases. In DYCOMS2, both NEW and OLD produce vertical profiles of grid-mean cloud condensate similar to large-eddy simulation. In ARM97, compared with OLD, NEW simulates less sporadic vertical profiles of in-cloud condensates, due to consistent diagnosis of cloud fraction and cloud condensate; more continuously-varying detrained cumulus with time, due to prognostic treatment of detrained cumulus; and ice cloud fraction and ice condensate similar to those of OLD, in spite of completely different treatment of ice cloud processes. The global performance of NEW is similar to OLD with improved relative humidity. Compared to OLD, NEW simulates more and improved cloud condensate, but less and degraded cloud fraction, particularly, in the lower troposphere. Detrained cumulus is moister and colder and has a larger moisture variance than pure stratus. Overall, NEW simulates stronger condensation-deposition rates than OLD, due in part to the separate treatment of detrained cumulus and pure stratus. general circulation model; cloud parameterization; cloud macrophysics scheme
Song, Ci; McCoy, Daniel T.; Eidhammer, Trude; Gettelman, Andrew; McCoy, Isabel L.; Watson-Parris, Duncan; Wall, Casey J.; Elsaesser, Gregory; Wood, RobertSong, C., D. T. McCoy, T. Eidhammer, A. Gettelman, I. L. McCoy, D. Watson-Parris, C. J. Wall, G. Elsaesser, R. Wood, 2024: Buffering of Aerosol-Cloud Adjustments by Coupling Between Radiative Susceptibility and Precipitation Efficiency. Geophysical Research Letters, 51(11), e2024GL108663. doi: 10.1029/2024GL108663. Aerosol-cloud interactions (ACI) in warm clouds are the primary source of uncertainty in effective radiative forcing (ERF) during the historical period and, by extension, inferred climate sensitivity. The ERF due to ACI (ERFaci) is composed of the radiative forcing due to changes in cloud microphysics and cloud adjustments to microphysics. Here, we examine the processes that drive ERFaci using a perturbed parameter ensemble (PPE) hosted in CAM6. Observational constraints on the PPE result in substantial constraints in the response of cloud microphysics and macrophysics to anthropogenic aerosol, but only minimal constraint on ERFaci. Examination of cloud and radiation processes in the PPE reveal buffering of ERFaci by the interaction of precipitation efficiency and radiative susceptibility. aerosol-cloud interactions; global climate models
Song, Qianghua; Wang, Chunzai; Yao, Yulong; Fan, HanjieSong, Q., C. Wang, Y. Yao, H. Fan, 2024: Unraveling the Indian monsoon’s role in fueling the unprecedented 2022 Marine Heatwave in the Western North Pacific. npj Climate and Atmospheric Science, 7(1), 1-8. doi: 10.1038/s41612-024-00645-x. An unprecedented marine heatwave (MHW) event occurred in the middle-high latitudes of the western North Pacific during the summer of 2022. We demonstrate that excessive precipitation thousands of kilometers away fuels this extreme MHW event in July 2022. In the upper atmosphere, a persistent atmospheric blocking system, forming over the MHW region, reduces cloud cover and increases shortwave radiation at the ocean surface, leading to high sea surface temperatures. Atmospheric perturbations induced by latent heat release from the extreme precipitation in the Indian summer monsoon region enhance this atmospheric blocking through the propagation of quasi-stationary Rossby waves. Our hypothesis is verified by using a numerical model that is forced with the observed atmospheric anomalous diabatic heating. This study sheds light on how a subtropical extreme event can fuel another extreme event at middle-high latitudes through an atmospheric teleconnection. Atmospheric dynamics; Physical oceanography
Song, Qianqian; Ginoux, Paul; Gonçalves Ageitos, María; Miller, Ron L.; Obiso, Vincenzo; Pérez García-Pando, CarlosSong, Q., P. Ginoux, M. Gonçalves Ageitos, R. L. Miller, V. Obiso, C. Pérez García-Pando, 2024: Modeling impacts of dust mineralogy on fast climate response. Atmospheric Chemistry and Physics, 24(12), 7421-7446. doi: 10.5194/acp-24-7421-2024. Mineralogical composition drives dust impacts on Earth's climate systems. However, most climate models still use homogeneous dust, without accounting for the temporal and spatial variation in mineralogy. To quantify the radiative impact of resolving dust mineralogy on Earth's climate, we implement and simulate the distribution of dust minerals (i.e., illite, kaolinite, smectite, hematite, calcite, feldspar, quartz, and gypsum) from Claquin et al. (1999) (C1999) and activate their interaction with radiation in the GFDL AM4.0 model. Resolving mineralogy reduces dust absorption compared to the homogeneous dust used in the standard GFDL AM4.0 model that assumes a globally uniform hematite volume content of 2.7 % (HD27). The reduction in dust absorption results in improved agreement with observation-based single-scattering albedo (SSA), radiative fluxes from CERES (the Clouds and the Earth's Radiant Energy System), and land surface temperature from the CRU (Climatic Research Unit) compared to the baseline HD27 model version. It also results in distinct radiative impacts on Earth's climate over North Africa. Over the 19-year (from 2001 to 2019) modeled period during JJA (June–July–August), the reduction in dust absorption in AM4.0 leads to a reduction of over 50 % in net downward radiation across the Sahara and approximately 20 % over the Sahel at the top of the atmosphere (TOA) compared to the baseline HD27 model version. The reduced dust absorption weakens the atmospheric warming effect of dust aerosols and leads to an alteration in land surface temperature, resulting in a decrease of 0.66 K over the Sahara and an increase of 0.7 K over the Sahel. The less warming in the atmosphere suppresses ascent and weakens the monsoon inflow from the Gulf of Guinea. This brings less moisture to the Sahel, which combined with decreased ascent induces a reduction of precipitation. To isolate the effect of reduced absorption compared to resolving spatial and temporal mineralogy, we carry out a simulation where the hematite volume content of homogeneous dust is reduced from 2.7 % to 0.9 % (HD09). The dust absorption (e.g., single-scattering albedo) of HD09 is comparable to that of the mineralogically speciated model on a global mean scale, albeit with a lower spatial variation that arises solely from particle size. Comparison of the two models indicates that the spatial inhomogeneity in dust absorption resulting from resolving mineralogy does not have significant impacts on Earth's radiation and climate, provided there is a similar level of dust absorption on a global mean scale before and after resolving dust mineralogy. However, uncertainties related to emission and distribution of minerals may blur the advantages of resolving minerals to study their impact on radiation, cloud properties, ocean biogeochemistry, air quality, and photochemistry. On the other hand, lumping together clay minerals (i.e., illite, kaolinite, and smectite), but excluding externally mixed hematite and gypsum, appears to provide both computational efficiency and relative accuracy. Nevertheless, for specific research, it may be necessary to fully resolve mineralogy to achieve accuracy.
Sorenson, Blake T.; Reid, Jeffrey S.; Zhang, Jianglong; Holz, Robert E.; Smith Sr., William L.; Gumber, AmandaSorenson, B. T., J. S. Reid, J. Zhang, R. E. Holz, W. L. Smith Sr., A. Gumber, 2024: Thermal infrared observations of a western United States biomass burning aerosol plume. Atmospheric Chemistry and Physics, 24(2), 1231-1248. doi: 10.5194/acp-24-1231-2024. Biomass burning smoke particles, due to their submicron particle size in relation to the average thermal infrared (TIR) wavelength, theoretically have negligible signals at the TIR channels. However, nearly instantaneous longwave (LW) signatures of thick smoke plumes can be frequently observed at the TIR channels from remotely sensed data, including at 10.6 µm (IR window), as well as in water-vapor-sensitive wavelengths at 7.3, 6.8, and 6.3 µm (e.g., lower, middle, and upper troposphere). We systematically evaluated multiple hypotheses as to causal factors of these IR signatures of biomass burning smoke using a combination of data from the Aqua MODerate resolution Imaging Spectroradiometer (MODIS), Aqua Cloud and the Earth Radiant Energy System (CERES), Geostationary Operational Environmental Satellite 16/17 (GOES-16/17) Advanced Baseline Imager, and Suomi-NPP Visible Infrared Imaging Radiometer Suite (VIIRS) and Cross-track Infrared Sounder (CrIS). The largely clear transmission of light through wildfire smoke in the near infrared indicates that coarse or giant ash particles are unlikely to be the dominant cause. Rather, clear signals in water vapor and TIR channels suggest that both co-transported water vapor injected to the middle to upper troposphere and surface cooling by the reduction of surface radiation by the plume are more significant, with the surface cooling effect of smoke aloft being the most dominant. Giving consideration of the smoke impacts on TIR and longwave, CERES indicates that large wildfire aerosol plumes are more radiatively neutral. Further, this smoke-induced TIR signal may be used to map very optically thick smoke plumes, where traditional aerosol retrieval methods have difficulties.
Sotiropoulou, Georgia; Lewinschal, Anna; Georgakaki, Paraskevi; Phillips, Vaughan T. J.; Patade, Sachin; Ekman, Annica M. L.; Nenes, AthanasiosSotiropoulou, G., A. Lewinschal, P. Georgakaki, V. T. J. Phillips, S. Patade, A. M. L. Ekman, A. Nenes, 2024: Sensitivity of Arctic Clouds to Ice Microphysical Processes in the NorESM2 Climate Model. doi: 10.1175/JCLI-D-22-0458.1. Ice formation remains one of the most poorly represented microphysical processes in climate models. While primary ice production (PIP) parameterizations are known to have a large influence on the modeled cloud properties, the representation of secondary ice production (SIP) is incomplete and its corresponding impact is therefore largely unquantified. Furthermore, ice aggregation is another important process for the total cloud ice budget, which also remains largely unconstrained. In this study, we examine the impact of PIP, SIP, and ice aggregation on Arctic clouds, using the Norwegian Earth System Model, version 2 (NorESM2). Simulations with both prognostic and diagnostic PIP show that heterogeneous freezing alone cannot reproduce the observed cloud ice content. The implementation of missing SIP mechanisms (collisional breakup, drop shattering, and sublimation breakup) in NorESM2 improves the modeled ice properties, while improvements in liquid content occur only in simulations with prognostic PIP. However, results are sensitive to the description of collisional breakup. This mechanism, which dominates SIP in the examined conditions, is very sensitive to the treatment of the sublimation correction factor, a poorly constrained parameter that is included in the utilized parameterization. Finally, variations in ice aggregation treatment can also significantly impact cloud properties, mainly through their impact on collisional breakup efficiency. Overall, enhancement in ice production through the addition of SIP mechanisms and the reduction in ice aggregation (in line with radar observations of shallow Arctic clouds) result in enhanced cloud cover and decreased TOA radiation biases, compared to satellite measurements, especially during the cold months. Significance Statement Arctic clouds remain a large source of uncertainty in projections of the future climate due to the poor representation of the microphysical processes that govern their life cycle. Ice formation is among the least understood processes. While it is widely recognized that better constraints on primary ice production (PIP) are needed to improve existing parameterizations, we show that secondary ice production (SIP) and ice aggregation can have also a significant impact on ice number concentrations. Constraining ice formation through the addition of missing SIP mechanisms and reducing ice aggregation can improve the representation of the cloud macrophysical properties and enhance total cloud cover in the Arctic region, which in turn contributes to decreased TOA radiation biases in the cold months. Arctic; Climate models; Cloud microphysics; Cloud parameterizations; Clouds; Secondary ice production
Stephens, Graeme L.; Shiro, Kathleen A.; Hakuba, Maria Z.; Takahashi, Hanii; Pilewskie, Juliet A.; Andrews, Timothy; Stubenrauch, Claudia J.; Wu, LongtaoStephens, G. L., K. A. Shiro, M. Z. Hakuba, H. Takahashi, J. A. Pilewskie, T. Andrews, C. J. Stubenrauch, L. Wu, 2024: Tropical Deep Convection, Cloud Feedbacks and Climate Sensitivity. Surveys in Geophysics. doi: 10.1007/s10712-024-09831-1. This paper is concerned with how the diabatically-forced overturning circulations of the atmosphere, established by the deep convection within the tropical trough zone (TTZ), first introduced by Riehl and (Malkus) Simpson, in Contr Atmos Phys 52:287–305 (1979), fundamentally shape the distributions of tropical and subtropical cloudiness and the changes to cloudiness as Earth warms. The study first draws on an analysis of a range of observations to understand the connections between the energetics of the TTZ, convection and clouds. These observations reveal a tight coupling of the two main components of the diabatic heating, the cloud component of radiative heating, shaped mostly by high clouds formed by deep convection, and the latent heating associated with the precipitation. Interannual variability of the TTZ reveals a marked variation that connects the depth of the tropical troposphere, the depth of convection, the thickness of high clouds and the TOA radiative imbalance. The study examines connections between this convective zone and cloud changes further afield in the context of CMIP6 model experiments of climate warming. The warming realized in the CMIP6 SSP5-8.5 scenario multi-model experiments, for example, produces an enhanced Hadley circulation with increased heating in the zone of tropical deep convection and increased radiative cooling and subsidence in the subtropical regions. This impacts low cloud changes and in turn the model warming response through low cloud feedbacks. The pattern of warming produced by models, also influenced by convection in the tropical region, has a profound influence on the projected global warming. Climate change; Cloud feedbacks; Tropical convection
Storto, Andrea; Yang, ChunxueStorto, A., C. Yang, 2024: Acceleration of the ocean warming from 1961 to 2022 unveiled by large-ensemble reanalyses. Nature Communications, 15(1), 545. doi: 10.1038/s41467-024-44749-7. Long-term changes in ocean heat content (OHC) represent a fundamental global warming indicator and are mostly caused by anthropogenic climate-altering gas emissions. OHC increases heavily threaten the marine environment, therefore, reconstructing OHC before the well-instrumented period (i.e., before the Argo floats deployment in the mid-2000s) is crucial to understanding the multi-decadal climate change in the ocean. Here, we shed light on ocean warming and its uncertainty for the 1961-2022 period through a large ensemble reanalysis system that spans the major sources of uncertainties. Results indicate a 62-year warming of 0.43 ± 0.08 W m−2, and a statistically significant acceleration rate equal to 0.15 ± 0.04 W m−2 dec−1, locally peaking at high latitudes. The 11.6% of the global ocean area reaches the maximum yearly OHC in 2022, almost doubling any previous year. At the regional scale, major OHC uncertainty is found in the Tropics; at the global scale, the uncertainty represents about 40% and 15% of the OHC variability, respectively before and after the mid-2000s. The uncertainty of regional trends is mostly affected by observation calibration (especially at high latitudes), and sea surface temperature data uncertainty (especially at low latitudes). Climate and Earth system modelling; Physical oceanography
Stubenrauch, Claudia J.; Kinne, Stefan; Mandorli, Giulio; Rossow, William B.; Winker, David M.; Ackerman, Steven A.; Chepfer, Helene; Di Girolamo, Larry; Garnier, Anne; Heidinger, Andrew; Karlsson, Karl-Göran; Meyer, Kerry; Minnis, Patrick; Platnick, Steven; Stengel, Martin; Sun-Mack, Szedung; Veglio, Paolo; Walther, Andi; Cai, Xia; Young, Alisa H.; Zhao, GuangyuStubenrauch, C. J., S. Kinne, G. Mandorli, W. B. Rossow, D. M. Winker, S. A. Ackerman, H. Chepfer, L. Di Girolamo, A. Garnier, A. Heidinger, K. Karlsson, K. Meyer, P. Minnis, S. Platnick, M. Stengel, S. Sun-Mack, P. Veglio, A. Walther, X. Cai, A. H. Young, G. Zhao, 2024: Lessons Learned from the Updated GEWEX Cloud Assessment Database. Surveys in Geophysics. doi: 10.1007/s10712-024-09824-0. Since the first Global Energy and Water Exchanges cloud assessment a decade ago, existing cloud property retrievals have been revised and new retrievals have been developed. The new global long-term cloud datasets show, in general, similar results to those of the previous assessment. A notable exception is the reduced cloud amount provided by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) Science Team, resulting from an improved aerosol–cloud distinction. Height, opacity and thermodynamic phase determine the radiative effect of clouds. Their distributions as well as relative occurrences of cloud types distinguished by height and optical depth are discussed. The similar results of the two assessments indicate that further improvement, in particular on vertical cloud layering, can only be achieved by combining complementary information. We suggest such combination methods to estimate the amount of all clouds within the atmospheric column, including those hidden by clouds aloft. The results compare well with those from CloudSat-CALIPSO radar–lidar geometrical profiles as well as with results from the International Satellite Cloud Climatology Project (ISCCP) corrected by the cloud vertical layer model, which is used for the computation of the ISCCP-derived radiative fluxes. Furthermore, we highlight studies on cloud monitoring using the information from the histograms of the database and give guidelines for: (1) the use of satellite-retrieved cloud properties in climate studies and climate model evaluation and (2) improved retrieval strategies. Cloud cover; Satellite remote sensing; Atmosphere; Cloud height; Cloud radiative properties; Cloud types; Microphysical properties
Sun-Mack, Sunny; Minnis, Patrick; Chen, Yan; Hong, Gang; Smith Jr., William L.Sun-Mack, S., P. Minnis, Y. Chen, G. Hong, W. L. Smith Jr., 2024: Identification of ice-over-water multilayer clouds using multispectral satellite data in an artificial neural network. Atmospheric Measurement Techniques, 17(10), 3323-3346. doi: 10.5194/amt-17-3323-2024. An artificial neural network (ANN) algorithm, employing several Aqua MODerate-resolution Imaging Spectroradiometer (MODIS) channels, the retrieved cloud phase and total cloud visible optical depth, and temperature and humidity vertical profiles is trained to detect multilayer (ML) ice-over-water cloud systems identified by matched 2008 CloudSat and CALIPSO (CC) data. The trained multilayer cloud-detection ANN (MCANN) was applied to 2009 MODIS data resulting in combined ML and single layer detection accuracies of 87 % (89 %) and 86 % (89 %) for snow-free (snow-covered) regions during the day and night, respectively. Overall, it detects 55 % and ∼ 30 % of the CC ML clouds over snow-free and snow-covered surfaces, respectively, and has a relatively low false alarm rate. The net gain in accuracy, which is the difference between the true and false ML fractions, is 7.5 % and ∼ 2.0 % over snow-free and snow/ice-covered surfaces. Overall, the MCANN is more accurate than most currently available methods. When corrected for the viewing-zenith-angle dependence of each parameter, the ML fraction detected is relatively invariant across the swath. Compared to the CC ML variability, the MCANN is robust seasonally and interannually and produces similar distribution patterns over the globe, except in the polar regions. Additional research is needed to conclusively evaluate the viewing zenith angle (VZA) dependence and further improve the MCANN accuracy. This approach should greatly improve the monitoring of cloud vertical structure using operational passive sensors.
Sunil, Sneha; Padmakumari, B.Sunil, S., B. Padmakumari, 2024: Optical and Radiative Characteristics of the Lower Part of Cirrus Clouds Over a Rain Shadow Region in South Peninsular India. Pure and Applied Geophysics, 181(5), 1697-1724. doi: 10.1007/s00024-024-03466-4. Cirrus (Ci) clouds have an important influence on Earth's radiation budget, and they remain one of the most significant uncertainties in predicting Earth's climate. In this study, we use ground-based radiometers along with a sky imager to monitor clouds and retrieve cloud properties (cloud fraction (CF), cloud optical depth (COD) and effective radii (Re)) over a rain shadow region in south peninsular India during September and October months, 2011. Lower part of Ci clouds are identified using the thresholds pertaining to COD and cloud base height (CBH). The optical and radiative properties of Ci clouds showed large variability on temporal and diurnal scales. The CF, COD and Re varied from 7 to 100%, 0.76 to 9.99, and 2.76 to 37.92 μm, respectively. The CBH and Cloud Base Temperature (CBT) are found to vary from 7.24 to 8.99 km and − 31.99 to − 13.75 °C. The Shortwave Cloud Radiative forcing (SWCRF) exerted by the lower part of Ci clouds over the region is observed to vary from − 435 to 148.87 W m−2 on a temporal scale with an average value of − 23.06 W m−2. The relationship between SWCRF and COD revealed radiative cooling effect with increase in COD with a dependency rate of − 18.53 W m−2/τ. SWCRF is found to be more sensitive to COD as compared to other cloud characteristics (CF, CBH and CBT). The case studies depict that the observed lower part of Ci clouds are advected from the ocean indicating the influence of large scale systems. Lower part of Ci optical and radiative properties showed wide variability depending up on the source of formation and evolution. This study also suggests that the high temporal variability of optical and radiative properties of Ci clouds needs to be well considered in climate models to reduce the uncertainty of cirrus radiative effects. Cirrus clouds; Cloud optical depth; Cloud properties; Cloud radiative forcing; SW radiation
Takasuka, Daisuke; Kodama, Chihiro; Suematsu, Tamaki; Ohno, Tomoki; Yamada, Yohei; Seiki, Tatsuya; Yashiro, Hisashi; Nakano, Masuo; Miura, Hiroaki; Noda, Akira T.; Nasuno, Tomoe; Miyakawa, Tomoki; Masunaga, RyusukeTakasuka, D., C. Kodama, T. Suematsu, T. Ohno, Y. Yamada, T. Seiki, H. Yashiro, M. Nakano, H. Miura, A. T. Noda, T. Nasuno, T. Miyakawa, R. Masunaga, 2024: How Can We Improve the Seamless Representation of Climatological Statistics and Weather Toward Reliable Global K-Scale Climate Simulations?. Journal of Advances in Modeling Earth Systems, 16(2), e2023MS003701. doi: 10.1029/2023MS003701. Toward the achievement of reliable global kilometer-scale (k-scale) climate simulations, we improve the Nonhydrostatic ICosahedral Atmospheric Model (NICAM) by focusing on moist physical processes. A goal of the model improvement is to establish a configuration that can simulate realistic fields seamlessly from the daily-scale variability to the climatological statistics. Referring to the two representative configurations of the present NICAM, each of which has been used for climate-scale and sub-seasonal-scale experiments, we try to find the appropriate partitioning of fast/local and slow/global-scale circulations. In a series of sensitivity experiments at 14-km horizontal resolution, we test (a) the tuning of terminal velocities of rain, snow, and cloud ice, (b) the implementation of turbulent diffusion by the Leonard term, and (c) enhanced vertical resolution. These tests yield reasonable convection triggering and convection-induced tropospheric moistening, and result in better performance than in previous NICAM climate simulations. In the mean state, double Intertropical Convergence Zone bias disappears, and the zonal contrast of equatorial precipitation, top-of-atmosphere radiation balance, vertical temperature profile, and position/strength of subtropical jet are reproduced dramatically better. Variability such as equatorial waves and the Madden–Julian oscillation (MJO) is spontaneously realized with appropriate spectral power balance, and the Asian summer monsoon, boreal-summer MJO, and tropical cyclone (TC) activities are more realistically simulated especially around the western Pacific. Meanwhile, biases still exist in the representation of low-cloud fraction, TC intensity, and precipitation diurnal cycle, suggesting that both higher spatial resolutions and further model development are warranted. climate simulation; global convection-resolving model; physics-dynamics coupling
Tan, Chuyan; McCoy, Daniel T.; Elsaesser, Gregory S.Tan, C., D. T. McCoy, G. S. Elsaesser, 2024: Constraints on Southern Ocean Shortwave Cloud Feedback From the Hydrological Cycle. Journal of Geophysical Research: Atmospheres, 129(6), e2023JD040489. doi: 10.1029/2023JD040489. Shifts in Southern Ocean (SO, 40–85°S) shortwave cloud feedback (SWFB) toward more positive values are the dominant contributor to higher effective climate sensitivity (ECS) in Coupled Model Intercomparison Project Phase 6 (CMIP6) models. To provide an observational constraint on the SO SWFB, we use a simplified physical model to connect SO SWFB with the response of column-integrated liquid water mass (LWP) to warming and the susceptibility of albedo to LWP in 50 CMIP5 and CMIP6 GCMs. In turn, we predict the responses of SO LWP using a cloud-controlling factor (CCF) model. The combination of the CCF model and radiative susceptibility explains about 50% of the variance in the GCM-simulated SWFB in the SO. Observations of SW radiation fluxes, LWP, and CCFs from reanalysis are used to constrain the SO SWFB. Observations suggest a SO LWP increase in response to warming and albedo susceptibility to LWP that is on the lower end relative to GCMs. The overall constraint on the contribution of SO to global mean SWFB is −0.168 to +0.051 W m−2 K−1, relative to −0.277 to +0.270 Wm−2 K−1. In summary, observations suggest SO SWFB is less likely to be as extremely positive as predicted by some CMIP6 GCMs, but more likely to range from moderately negative to weakly positive. climate; clouds; Southern Ocean; precipitation; feedback; moisture convergence
Tan, Ivy; Zelinka, Mark D.; Coopman, Quentin; Kahn, Brian H.; Oreopoulos, Lazaros; Tselioudis, George; McCoy, Daniel T.; Li, NinghuiTan, I., M. D. Zelinka, Q. Coopman, B. H. Kahn, L. Oreopoulos, G. Tselioudis, D. T. McCoy, N. Li, 2024: Contributions From Cloud Morphological Changes to the Interannual Shortwave Cloud Feedback Based on MODIS and ISCCP Satellite Observations. Journal of Geophysical Research: Atmospheres, 129(8), e2023JD040540. doi: 10.1029/2023JD040540. Abstract The surface temperature-mediated change in cloud properties, referred to as the cloud feedback, continues to dominate the uncertainty in climate projections. A larger number of contemporary global climate models (GCMs) project a higher degree of warming than the previous generation of GCMs. This greater projected warming has been attributed to a less negative cloud feedback in the Southern Ocean. Here, we apply a novel ?double decomposition method? that employs the ?cloud radiative kernel? and ?cloud regime? concepts, to two data sets of satellite observations to decompose the interannual cloud feedback into contributions arising from changes within and shifts between cloud morphologies. Our results show that contributions from the latter to the cloud feedback are large for certain regimes. We then focus on interpreting how both changes within and between cloud morphologies impact the shortwave cloud optical depth feedback over the Southern Ocean in light of additional observations. Results from the former cloud morphological changes reveal the importance of the wind response to warming increases low- and mid-level cloud optical thickness in the same region. Results from the latter cloud morphological changes reveal that a general shift from thick storm-track clouds to thinner oceanic low-level clouds contributes to a positive feedback over the Southern Ocean that is offset by shifts from thinner broken clouds to thicker mid- and low-level clouds. Our novel analysis can be applied to evaluate GCMs and potentially diagnose shortcomings pertaining to their physical parameterizations of particular cloud morphologies. climate; cloud feedback; MODIS; Southern Ocean; ISCCP; morphology
Tang, Wenjun; He, Junmei; Shao, Changkun; Song, Jun; Yuan, Zongtao; Yan, BowenTang, W., J. He, C. Shao, J. Song, Z. Yuan, B. Yan, 2024: Constructing a long-term global dataset of direct and diffuse radiation (10 km, 3 h, 1983–2018) separating from the satellite-based estimates of global radiation. Remote Sensing of Environment, 311, 114292. doi: 10.1016/j.rse.2024.114292. In addition to global radiation (Rg), direct radiation (Rdir) and diffuse radiation (Rdif) are important fundamental data urgently needed in scientific and industrial fields. However, compared with Rg, Rdir and Rdif have received little attention in the past, either in observations or in satellite retrievals, mainly due to the high cost of their observations and the difficulty of retrieving them effectively from satellites. In this study, a long-term global gridded dataset of Rdir and Rdif was constructed by separating from a high-precision satellite-based product of Rg using the Light Gradient Boosting Machine (LightGBM) model, trained with in-situ observations measured at the Baseline Surface Radiation Network (BSRN). The inputs to construct the dataset are the four variables of Rg, the cloud transmittance for Rg, the ratio of Rdif to Rg under clear sky condition (call the clear diffuse ratio), and the cosine of the solar zenith angle. The developed dataset was validated against in-situ observations and compared with other satellite-based products. Evaluations against the BSRN observations indicated that our proposed method has good generality and outperforms the machine learning-based direct estimation method of Hao et al. (2020). Independent validations were further performed against the observations measured at 17 China Meteorological Administration (CMA) radiation stations and the estimation based on sunshine duration observations at >2400 CMA routine meteorological stations, respectively. It was found that the accuracies of our estimates for both Rdir and Rdif were improved when upscaled to ≥ 30 km. Comparisons with three other satellite-based products indicate that our developed dataset of both Rdir and Rdif was generally more accurate than the global products of the Earth's Radiant Energy System (CERES) and Hao et al. (2020) based on the Deep Space Climate Observatory/Earth Polychromatic Imaging Camera (EPIC) (DSCOVER/EPIC) satellite, and the regional gridded product (JIEA) of Jiang et al. (2020a). The dataset developed in this study will contribute to ecological research and solar engineering applications. Dataset; Diffuse radiation; Direct radiation; Global radiation; Separation method
Thandlam, Venugopal; Kaagita, Venkatramana; Sakirevupalli, Venkatramana ReddyThandlam, V., V. Kaagita, V. R. Sakirevupalli, 2024: Long-term meteorological characteristics and extreme climate indices over Tirupati: a rapidly developing tropical city. Discover Cities, 1(1), 14. doi: 10.1007/s44327-024-00013-7. Tirupati’s climate has undergone significant changes in both temperature and precipitation patterns. While there has been a consistent increase in rainfall during the southwest monsoon, there is a concerning long-term trend of a decrease in total annual precipitation over the last 30 years. The city has experienced a rise in wet days during both the southwest and northeast monsoons, yet a recent decrease over the past three decades. Heavy precipitation events, particularly during the southwest monsoon, have shown a positive trend, whereas there have been no significant changes in heavy rainfall days during the northeast monsoon. Temperature trends reveal that there has been a warming scenario, with a significant positive trend in annual maximum temperatures and a consistent annual rise in mean minimum temperatures. A substantial decrease in cold and very cold days, especially during the last 30 years, suggests a broader warming trend impacting seasonal temperature variations in Tirupati. These findings highlight the complex interplay of monsoons, temperature variations, and changing precipitation patterns in Tirupati's climate over the years. Climate; Cold days; Dry days; Hot days; Monsoons; Precipitation; Temperature; Tirupati; Wet days
Thimsen, ElijahThimsen, E., 2024: Planetary Energy Flow and Entropy Production Rate by Earth from 2002 to 2023. Entropy, 26(5), 350. doi: 10.3390/e26050350. In this work, satellite data from the Clouds and Earth’s Radiant Energy System (CERES) and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments are analyzed to determine how the global absorbed sunlight and global entropy production rates have changed from 2002 to 2023. The data is used to test hypotheses derived from the Maximum Power Principle (MPP) and Maximum Entropy Production Principle (MEP) about the evolution of Earth’s surface and atmosphere. The results indicate that both the rate of absorbed sunlight and global entropy production have increased over the last 20 years, which is consistent with the predictions of both hypotheses. Given the acceptance of the MPP or MEP, some peripheral extensions and nuances are discussed. albedo; ecosystems; entropy generation; evolution; externalities; geoengineering; life; nonequilibrium thermodynamics; social sciences
Tselioudis, George; Rossow, William B.; Bender, Frida; Oreopoulos, Lazaros; Remillard, JasmineTselioudis, G., W. B. Rossow, F. Bender, L. Oreopoulos, J. Remillard, 2024: Oceanic cloud trends during the satellite era and their radiative signatures. Climate Dynamics. doi: 10.1007/s00382-024-07396-8. The present study analyzes zonal mean cloud and radiation trends over the global oceans for the past 35 years from a suite of satellite datasets covering two periods. In the longer period (1984–2018) cloud properties come from the ISCCP-H, CLARA-A3, and PATMOS-x datasets and radiative properties from the ISCCP-FH dataset, while for the shorter period (2000–2018) cloud data from MODIS and CloudSat/CALIPSO and radiative fluxes from CERES-EBAF are added. Zonal mean total cloud cover (TCC) trend plots show an expansion of the subtropical dry zone, a poleward displacement of the midlatitude storm zone and a narrowing of the tropical intertropical convergence zone (ITCZ) region over the 1984–2018 period. This expansion of the ‘low cloud cover curtain’ and the contraction of the ITCZ rearrange the boundaries and extents of all major climate zones, producing a more poleward and narrower midlatitude storm zone and a wider subtropical zone. Zonal mean oceanic cloud cover trends are examined for three latitude zones, two poleward of 50 ° and one bounded within 50oS and 50oN, and show upward or near-zero cloud cover trends in the high latitude zones and consistent downward trends in the low latitude zone. The latter dominate in the global average resulting in TCC decreases that range from 0.72% per decade to 0.17% per decade depending on dataset and period. These contrasting cloud cover changes between the high and low latitude zones produce contrasting low latitude cloud radiative warming and high latitude cloud radiative cooling effects, present in both the ISCCP-FH and CERES-EBAF datasets. The global ocean mean trend of the short wave cloud radiative effect (SWCRE) depends on the balance between these contrasting trends, which in the CERES dataset materializes as a SW cloud radiative warming trend of 0.12 W/m2/decade coming from the dominance of the low-latitude positive SWCRE trends while in the ISCCP-FH dataset it manifests as a 0.3 W/m2/decade SW cloud radiative cooling trend coming from the dominance of the high latitude negative SWCRE trends. The CERES cloud radiative warming trend doubles in magnitude to 0.24 W/m2/decade when the period is extended from 2016 to 2022, implying a strong cloud radiative heating in the past 6 years coming from the low latitude zone. Climate change; Cloud feedbacks; Clouds; Radiation
Uribe, Alejandro; Bender, Frida; Mauritsen, ThorstenUribe, A., F. Bender, T. Mauritsen, 2024: Constraining net long term climate feedback from satellite observed internal variability possible by mid 2030s. EGUsphere, 1-21. doi: 10.5194/egusphere-2024-1559. Abstract. Observing climate feedbacks to long term global warming, crucial climate regulators, is not feasible within the observational record. However, linking them to top-of-the-atmosphere flux variations in response to surface temperature fluctuations (internal variability feedbacks) is a viable approach. Here, we explore the use of this method of relating internal variability to forced climate feedbacks in models and applying the resulting relationship to observations to constrain forced climate feedbacks. Our findings reveal strong longwave and shortwave feedback relationships in models during the 14-year overlap with the CERES observational record. Yet, due to the weaker relationship between internal variability and forced climate longwave feedbacks, the net feedback relationship remains weak, even over longer periods extending beyond the CERES record. However, after about half a century, this relationship strengthens primarily due to a reinforcement of the relationship between internal variability and forced climate shortwave feedbacks. We therefore explore merging the satellite records with reanalysis to establish an extended data record. The resulting constraint suggests a stronger negative forced climate net feedback than the model´s distribution and an equilibrium climate sensitivity of about 2.5 K (2.14 K to 3.07 K, 5–95 % confidence intervals). Nevertheless, for example biogeochemical climate feedbacks, inactive on short time scales, and also not represented in most models, may lead to climate sensitivity being underestimated by this method. Also, continuous satellite observations until at least the mid-2030s are necessary for using purely observed estimate of the net internal variability feedback in constraining net forced climate feedback and, consequently, climate sensitivity.
Urraca, Ruben; Lanconelli, Christian; Gobron, NadineUrraca, R., C. Lanconelli, N. Gobron, 2024: Impact of the Spatio-Temporal Mismatch Between Satellite and In Situ Measurements on Validations of Surface Solar Radiation. Journal of Geophysical Research: Atmospheres, 129(10), e2024JD041007. doi: 10.1029/2024JD041007. Satellite and in situ sensors do not observe exactly the same measurand. This introduces a mismatch between both types of measurements in the spatial or temporal. The mismatch differences can be the dominant component in their comparison, so they have to be removed for an adequate validation of satellite products. With this aim, we propose a methodology to characterize the mismatch between satellite and in situ measurements of surface solar radiation, evaluating the impact of the mismatch on validations. The Surface Solar Radiation Data Set—Heliosat (SARAH-2) and the Baseline Surface Radiation Network are used to characterize the spatial and temporal mismatch, respectively. The mismatch differences in both domains are driven by cloud variability. At least 5 years are needed to characterize the mismatch, which is not constant throughout the year due to seasonal and diurnal cloud cover patterns. Increasing the mismatch can artificially improve the validation metrics under some circumstances, but the mismatch must be always minimized for a correct product assessment. Finally, we test two types of up-scaling methods based on SARAH-2 in the validation of degree-scale products. The fully data-driven correction removes all the mismatch effects (systematic and random) but fully propagates SARAH-2 uncertainty to the corrections. The model-based correction only removes the systematic mismatch difference, but it can correct measurements not covered by the high-resolution data set and depends less SARAH-2 uncertainty. remote sensing; satellite product; solar irradiance; spatial representativeness; validation
Vargas Zeppetello, Lucas R.; Trevino, Aleyda M.; Huybers, PeterVargas Zeppetello, L. R., A. M. Trevino, P. Huybers, 2024: Disentangling contributions to past and future trends in US surface soil moisture. Nature Water, 1-12. doi: 10.1038/s44221-024-00193-x. Climate model simulations and various aridity indices generally indicate that summertime surface soil moisture will decrease in the continental USA as a consequence of anthropogenic climate change. However, soil moisture observations from ground probes and satellites from 2011 to 2020 indicate positive summertime trends across 57% of the continental USA. To evaluate the mechanisms driving these trends, we have developed a two-layer land surface model that predicts surface temperature and soil moisture on the basis of observed variations in precipitation, solar radiation, vapour pressure and snowmelt. Of these four model forcings, we found that internal precipitation variability explains the largest fraction of the observed soil moisture trends from 2011 to 2020. Surface air warming and the response of plants to increasing atmospheric CO2 also influence the soil moisture trends, but these effects are small at decadal timescales and partly compensate for one another. Looking forwards, our results indicate that internal precipitation variability will dictate decadal soil moisture trends and that centennial soil moisture trends will primarily depend on changes in precipitation that are currently highly uncertain. Hydrology; Climate sciences
Wang, Gaofeng; Wang, Tianxing; Yuan, Hongyin; Leng, Wanchun; Letu, Husi; Xian, YuyangWang, G., T. Wang, H. Yuan, W. Leng, H. Letu, Y. Xian, 2024: Surface Shortwave Net Radiation Estimation From Space: Emphasizing the Effects of Aerosol, Solar Zenith Angles, and DEM. IEEE Transactions on Geoscience and Remote Sensing, 62, 1-21. doi: 10.1109/TGRS.2024.3350027. Shortwave net radiation (SWNR) plays an important role in the surface radiation balance and serves as the primary driving force for the exchange of surface and atmospheric materials. Although numerous algorithms exist for estimating SWNR, most of them tend to ignore the influence of aerosols and digital elevation model (DEM) on SWNR. Specifically, the impact of different aerosol types on SWNR can vary significantly, and the SWNR also exhibits considerable variations at different altitudes. It is true that many algorithms demonstrate higher accuracy in low-altitude regions with less polluted rural aerosol (nonabsorbent aerosol) areas. However, their accuracy tends to decrease when applied to high-altitude areas and heavily polluted urban aerosol (absorbent aerosol) regions. In this study, an improved all-sky parameterized algorithm is proposed to estimate SWNR by fully considering solar zenith angle (SZA), DEM, and different aerosol types, and rural and urban aerosol types are distinguished by a random forest (RF) method. The new algorithm is verified versus surface radiation budget network (SURFRAD) and baseline surface radiation network (BSRN) observations and compared with the traditional algorithms (Tang-2006 and Li-1993) and Clouds and the Earth’s Radiant Energy System (CERES) products. The results reveal that the new algorithm exhibits excellent accuracy at both instantaneous and hourly scales. For rural and urban aerosol types under all-sky conditions, the bias and root mean square error (RMSE) of the new algorithm are both less than 3.5 and 106.5 W/m on the instantaneous scale and less than 12 and 77 W/ \textm^2 on hourly scale, respectively. However, the existing algorithms show a significant overestimation (bias > 50 W/ \textm^2 ) for the urban aerosol type under various atmospheres conditions. For the CERES single scanner footprint (SSF) (instantaneous) and CERES SYNergy (CERES SYN, 1-hourly) products, the overestimation phenomenon is also detected under urban aerosol type, with bias greater than 40 and 15 W/ \textm^2 , respectively. Compared with the existing algorithms, the new algorithm demonstrates superior applicability under larger SZA conditions. When the SZA exceeds 70°, the rate of estimated effective value can be increased by up to 14%. In addition, the new algorithm can effectively solve the problem of underestimation in high-altitude areas, which frequently occurs in most existing algorithms (bias < -16 W/ \textm^2 ). The improved accuracy and applicability of the new algorithm, along with its strategy of distinguishing aerosol types, can provide valuable insights for the SWNR estimation from space. Satellites; Atmospheric modeling; Clouds; Spatial resolution; Remote sensing; aerosol optical depth (AOD); Aerosol; Aerosols; top-of-atmosphere (TOA) albedo; digital elevation mode; Geospatial analysis; perceptible water content (PWC); random forest (RF); shortwave net radiation (SWNR); solar zenith angle (SZA)
Wang, Hai; Zheng, Xiao-Tong; Cai, Wenju; Han, Zi-Wen; Xie, Shang-Ping; Kang, Sarah M.; Geng, Yu-Fan; Liu, Fukai; Wang, Chuan-Yang; Wu, Yue; Xiang, Baoqiang; Zhou, LeiWang, H., X. Zheng, W. Cai, Z. Han, S. Xie, S. M. Kang, Y. Geng, F. Liu, C. Wang, Y. Wu, B. Xiang, L. Zhou, 2024: Atmosphere teleconnections from abatement of China aerosol emissions exacerbate Northeast Pacific warm blob events. Proceedings of the National Academy of Sciences, 121(21), e2313797121. doi: 10.1073/pnas.2313797121. During 2010 to 2020, Northeast Pacific (NEP) sea surface temperature (SST) experienced the warmest decade ever recorded, manifested in several extreme marine heatwaves, referred to as “warm blob” events, which severely affect marine ecosystems and extreme weather along the west coast of North America. While year-to-year internal climate variability has been suggested as a cause of individual events, the causes of the continuous dramatic NEP SST warming remain elusive. Here, we show that other than the greenhouse gas (GHG) forcing, rapid aerosol abatement in China over the period likely plays an important role. Anomalous tropospheric warming induced by declining aerosols in China generated atmospheric teleconnections from East Asia to the NEP, featuring an intensified and southward-shifted Aleutian Low. The associated atmospheric circulation anomaly weakens the climatological westerlies in the NEP and warms the SST there by suppressing the evaporative cooling. The aerosol-induced mean warming of the NEP SST, along with internal climate variability and the GHG-induced warming, made the warm blob events more frequent and intense during 2010 to 2020. As anthropogenic aerosol emissions continue to decrease, there is likely to be an increase in NEP warm blob events, disproportionately large beyond the direct radiative effects.
Wang, Jilong; Yu, Guirui; Han, Lang; Yao, Yuan; Sun, Mingyu; Yan, ZhifengWang, J., G. Yu, L. Han, Y. Yao, M. Sun, Z. Yan, 2024: Ecosystem carbon exchange across China's coastal wetlands: Spatial patterns, mechanisms, and magnitudes. Agricultural and Forest Meteorology, 345, 109859. doi: 10.1016/j.agrformet.2023.109859. Coastal wetlands are of great importance for global carbon cycle and climate mitigation because of their strong carbon uptake capacity. However, the national-scale ecosystem carbon exchange dynamics in coastal wetlands, including magnitudes, spatial patterns, and controlling mechanisms, remains poorly understood. In this study, we utilized eddy covariance measurements from China's coastal wetlands to quantify carbon fluxes, assess their spatial patterns, and explore the controlling mechanisms. Integrating climate, vegetation, and soil factors, we constructed a cascaded relationship network to reveal the potential controlling mechanisms of spatial variations in carbon fluxes. The results revealed that gross primary production (GPP) and ecosystem respiration (ER) were 1405 ± 656 (mean ± sd) gC m−2 yr−1and 893 ± 465, respectively. Net ecosystem production (NEP) in coastal wetlands (567 ± 348 gC m−2 yr−1) exceeded China's terrestrial and marine ecosystems by 2–8 times, highlighting their significant carbon sink capacity. The carbon sink capacity in mangroves was significantly higher than salt marsh, exhibiting a twofold difference in NEP. Spatially, carbon fluxes displayed negative correlations with latitude, indicating the influence of climate features. Although tropical climate zone exhibited significantly higher carbon fluxes than temperate zone, no differences were observed between subtropics zone with others due to the distribution of mixed plants and largest area. The structural equation model (SEM) showed that the climate factors, including temperature, precipitation, and net radiation indirectly promoted GPP and ER through regulating the physiological process of mangrove and salt marsh, as well as soil carbon production and consumption. The cascaded relationship of climate-vegetation-soil showed in SEM explained 71–85 % of the spatial variations in GPP and ER, and ultimately accounted for 85 % of NEP. The carbon consumption efficiency (ER/GPP) in coastal vegetations was of 0.6, lower than that of global and China's terrestrial ecosystems, suggesting their strong efficiency in carbon fixation in coastal wetlands. Lastly, the scenario simulation results implied the importance of coastal vegetation restoration on enhancing blue carbon benefits. Blue carbon; Coastal wetlands; Ecosystem carbon fluxes; Spatial patterns
Wang, Jingyu; Lin, Yun; Wang, Xianfeng; Gu, Yu; Yim, Steve Hung-LamWang, J., Y. Lin, X. Wang, Y. Gu, S. H. Yim, 2024: Significant changes in cloud radiative effects over Southwestern United States during the COVID-19 flight reduction period. Science of The Total Environment, 910, 168656. doi: 10.1016/j.scitotenv.2023.168656. Aircraft-induced clouds (AICs) are one of the most visible anthropogenic atmospheric phenomena, which mimic the natural cirrus clouds and perturb global radiation budget by reducing incoming shortwave (SW) radiation and trapping outgoing longwave (LW) radiation. The COVID-19 pandemic has caused a 70 % global decline in flight numbers from mid-March to October 2020, which provided a unique opportunity to examine the climatic impact of AICs. Among various regions, Western Europe and the Contiguous United States experienced the most substantial reduction in air traffic during the COVID-19 pandemic. Interestingly, only the Southwestern United States demonstrated a significant decrease in cirrus clouds, leading to notable changes in shortwave (SW) and longwave (LW) cloud radiative effects. Such changes were likely due to the reduction in AICs. However, further investigations indicated that this region also experienced abnormal high pressure and low relative humidity in the middle and upper atmosphere, resulting in unusual subsidence and dryness that prohibit the formation and maintenance of cirrus cloud. While it remains challenging to quantify the exact climatic impact of reduced AICs, the remarkable anomalies documented in this study provide valuable observational benchmark for future modelling studies of the climatic impact AICs. COVID-19; Cloud radiative effect; Aircraft-induced clouds; Contrail; Flight reduction; Southwestern US
Wang, Meihua; Su, Jing; Han, Xinyi; Deng, Xingzhu; Peng, Nan; Liu, LeiWang, M., J. Su, X. Han, X. Deng, N. Peng, L. Liu, 2024: Changes in Daytime Cirrus Properties From the ISCCP-H Data Set and Their Impacts on the Radiation Energy Budget. Earth and Space Science, 11(9), e2023EA003352. doi: 10.1029/2023EA003352. The change in clouds during the day is critical to the Earth's energy balance and climatic evolution. However, there have been relatively few studies on cloud variations at daily timescales, owing to limitations of ground- and satellite-observations, especially for cirrus clouds. In this study, we examined the daytime cirrus variation (DCV) at the global scales and its associated effects on radiation budgets based on the International Satellite Cloud Climatology Project H data set. The changes in continental cirrus cover are more significant than that over the ocean, reaching a maximum of 17.3% in the afternoon. Over the tropical deep convection regions, cirrus cloud cover and optical depth exhibit large amplitudes during the daytime, closely linked to average properties of cirrus clouds. Using a process-based radiative transfer model, we calculated the variations in daytime cirrus cloud radiative forcing (CRF). After noon, cirrus clouds over both land and ocean generate the strongest shortwave (SW) cooling and longwave (LW) warming effects at the top of the atmosphere (TOA). At the global scale, daytime cirrus clouds cause an average net CRF of 3.6 W/m2 at the TOA. If the DCV is neglected in the model, the SW cooling and LW warming effects are overestimated by 2.5 and 1.8 W/m2 at the TOA, leading to a net radiation bias of 0.7 W/m2. The findings provide key information for targeting specific aspects of the cirrus parameterization scheme in climate models. daytime cirrus variation; ISCCP-H observations; physical properties; radiative effect
Wang, Mengjia; Ciais, Philippe; Fensholt, Rasmus; Brandt, Martin; Tao, Shengli; Li, Wei; Fan, Lei; Frappart, Frédéric; Sun, Rui; Li, Xiaojun; Liu, Xiangzhuo; Wang, Huan; Cui, Tianxiang; Xing, Zanpin; Zhao, Zhe; Wigneron, Jean-PierreWang, M., P. Ciais, R. Fensholt, M. Brandt, S. Tao, W. Li, L. Fan, F. Frappart, R. Sun, X. Li, X. Liu, H. Wang, T. Cui, Z. Xing, Z. Zhao, J. Wigneron, 2024: Satellite observed aboveground carbon dynamics in Africa during 2003–2021. Remote Sensing of Environment, 301, 113927. doi: 10.1016/j.rse.2023.113927. Vegetation dynamics in the African continent play an important role in the global terrestrial carbon cycle. Above-ground biomass carbon (AGC) stocks in Africa are sensitive to drought, fires and anthropogenic disturbances, and can be increased from forest restoration and tree plantation. However, there are large uncertainties in estimating changes that have occurred in AGC stocks in Africa over the past decades. Here, we used a microwave remote sensing-based vegetation index named Vegetation Optical Depth produced from X-band observations by INRAE Bordeaux (IB X-VOD) to describe the AGC dynamics in Africa covering recent decades. From 2003 to 2021, African AGC showed a net increase at a rate of +0.06 [+0.04, +0.07] PgC·yr−1 (the range represents the minimum and maximum AGC changes estimated by four calibrations), resulting from a large carbon gain of +0.55 [+0.46, +0.60] PgC·yr−1 during the first decade of the twenty-first century (period 1: 2003–2010) and a much weaker increase of +0.05 [+0.04, +0.07] PgC·yr−1 over the recent decade (period 2: 2013–2021). AGC gains were mainly found in non-forest woody areas, which contributed the most to the AGC changes during 2003–2021. Rainforests showed a minor AGC loss of −0.02 [−0.03, −0.02] PgC·yr−1, which emphasizes the need for forest conservation in Africa. Relationships between the AGC changes and potential forcing climate or anthropogenic variables suggested that human-induced deforestation and water stress (especially the vapor pressure deficit (VPD)) are the most important variables explaining the spatial and temporal AGC variations, respectively. For areas of rainforests, we identified a strong relationship between AGC and VPD (negative), soil moisture (positive) and radiation (positive). For areas of sparse vegetation (mainly located in drylands), AGC changes are largely dominated by changes in the soil water conditions. This study presents a new dataset for monitoring AGC dynamics at a continental scale over recent decades being independent of optical observations, quantifying the impacts of anthropogenic pressure and water stress on aboveground biomass carbon changes. Aboveground carbon dynamics; African continent; Vegetation optical depth
Wang, Xiaocong; Miao, Hao; Feng, Juan; Liu, YiminWang, X., H. Miao, J. Feng, Y. Liu, 2024: Comparison of Short-Term Cloud Feedbacks at Top of the Atmosphere and the Surface in Observations and AMIP6 Models. Journal of Geophysical Research: Atmospheres, 129(2), e2023JD039936. doi: 10.1029/2023JD039936. We compared short-term cloud feedback, defined at the top of the atmosphere (TOA), the atmospheric column (ATM), and the surface (SFC), between observations and models participating in Atmospheric Model Intercomparison Project Phase 6 (AMIP6) for the period 2000–2014. The globally averaged net cloud feedbacks observed at TOA, ATM, and SFC are −0.06 ± 0.63, −0.17 ± 0.70, and 0.11 ± 0.81 W m−2 K−1, respectively. While most models produced TOA cloud feedbacks that agreed with the observations within uncertainty ranges, the intermodel spread at SFC and within ATM was relatively larger. This demonstrates that models are diverse in how their TOA feedback is distributed between ATM and SFC. Because short-term cloud feedback is mainly driven by El Niño–Southern Oscillation (ENSO), the global-mean cloud feedback was further decomposed into components from the ENSO and non-ENSO regions. Results show that cloud feedback in these two regions tends to be inversely related. Compared to observations, almost all models overestimated the longwave cloud feedback in the ENSO region due to the overestimation of cloud amount changes for high-topped clouds. For these models, it is the offset between deviations in ENSO and non-ENSO regions that leads to the overall agreement of global mean with observations. Sensitivity tests show that the main conclusions still hold when alternative kernels are used in estimating cloud feedback. cloud feedback; climate sensitivity; hydrological sensitivity; cloud radiative kernel; El Niño-Southern Oscillation (ENSO)
Weaver, Clark; Wu, Dong L.; Bhartia, P. K.; Labow, Gordon; Haffner, David P.; Borgia, Lauren; McBride, Laura; Salawitch, RossWeaver, C., D. L. Wu, P. K. Bhartia, G. Labow, D. P. Haffner, L. Borgia, L. McBride, R. Salawitch, 2024: Comparison of Proxy-Shortwave Cloud Albedo from SBUV Observations with CMIP6 Models. doi: 10.1175/JCLI-D-23-0170.1. We construct a long-term record of top of atmosphere (TOA) shortwave (SW) albedo of clouds and aerosols from 340-nm radiances observed by NASA and NOAA satellite instruments from 1980 to 2013. We compare our SW cloud+aerosol albedo with simulated cloud albedo from both AMIP and historical CMIP6 simulations from 47 climate models. While most historical runs did not simulate our observed spatial pattern of the trends in albedo over the Pacific Ocean, four models qualitatively simulate our observed patterns. Those historical models and the AMIP models collectively estimate an equilibrium climate sensitivity (ECS) of ∼3.5°C, with an uncertainty from 2.7° to 5.1°C. Our ECS estimates are sensitive to the instrument calibration, which drives the wide range in ECS uncertainty. We use instrument calibrations that assume a neutral change in reflectivity over the Antarctic ice sheet. Our observations show increasing cloudiness over the eastern equatorial Pacific and off the coast of Peru as well as neutral cloud trends off the coast of Namibia and California. To produce our SW cloud+aerosol albedo, we first retrieve a black-sky cloud albedo (BCA) and empirically correct the sampling bias from diurnal variations. Then, we estimate the broadband proxy albedo using multiple nonlinear regression along with several years of CERES cloud albedo to obtain the regression coefficients. We validate our product against CERES data from the years not used in the regression. Zonal mean trends of our SW cloud+aerosol albedo show reasonable agreement with CERES as well as the Pathfinder Atmospheres–Extended (PATMOS-x) observational dataset. Significance Statement Equilibrium climate sensitivity is a measure of the rise in global temperature over hundreds of years after a doubling of atmospheric CO2 concentration. Current state-of-the-art climate models forecast a wide range of equilibrium climate sensitivities (1.5°–6°C), due mainly to how clouds, aerosols, and sea surface temperatures are simulated within these models. Using data from NASA and NOAA satellite instruments from 1980 to 2013, we first construct a dataset that describes how much sunlight has been reflected by clouds over the 34 years and then we compare this data record to output from 47 climate models. Based on these comparisons, we conclude the best estimate of equilibrium climate sensitivity is about 3.5°C, with an uncertainty range of 2.7°–5.1°C. Climate sensitivity; Cloud radiative effects; Cloud retrieval; Satellite observations
Wen, Qi; Liu, Kang; Li, Yan; Li, Xu; Song, WenjunWen, Q., K. Liu, Y. Li, X. Li, W. Song, 2024: Climatic characteristics and meteorology-sensitivity of surface solar radiation in reanalysis products compared to observations and satellite data over China. Atmospheric Environment, 334, 120713. doi: 10.1016/j.atmosenv.2024.120713. Due to the significant role of the surface solar radiation (SSR) in climate, hydrological, and biogeochemical cycles, this study evaluates the climatology, annual cycle, and interannual variability and meteorological sensitivity (total cloud cover (TCC), aerosol optical depth (AOD), and precipitable water (PW)) of six reanalysis SSR datasets (GLDAS, ERA5, NCEP1, NCEP2, JRA55, and MERRA2) using a satellite dataset (CERES SYN), and 130 radiation stations in China during 2001–2020. The results show that the climatology (R = 0.88–0.93) and annual cycle (R = 0.92–0.98) of the SSR datasets exhibit better spatial characteristics in these products compared to interannual variability (EOF1: R = 0.03–0.88; EOF2: R = 0.27–0.83). The GLDAS has relatively small estimation SSR error in the climatology but is limited to reproduce interannual variability (EOF1: R = 0.08). As the concentration of meteorological elements increases, the sensitivity of most SSRs errors to TCC increases, while the trend of sensitivity to AOD and PW decreases due to the mitigating effect of the corresponding tendency of TCC error reduction. The importance of PW for estimating SSRs increased significantly in high altitude, ranging from 29.5 to 53%. Overall, ERA5 is the most consistent in quality of the three time-scales and high-meteorological variability.
Wu, Wan; Liu, Xu; Yang, Qiguang; Currey, Jon Chris; Bartle, Aron D.; Thurston, Adam; Smith, Natividad M.; Shea, Yolanda L.; Bhatt, RajendraWu, W., X. Liu, Q. Yang, J. C. Currey, A. D. Bartle, A. Thurston, N. M. Smith, Y. L. Shea, R. Bhatt, 2024: The Angular Correction Algorithm for the Intercalibration of Satellite Instruments Using CLARREO Pathfinder as a Reference. IEEE Transactions on Geoscience and Remote Sensing, 62, 1-11. doi: 10.1109/TGRS.2024.3359972. The Climate Absolute Radiance and Refractivity (CLARREO) Pathfinder (CPF) mission will take Système Internationale (SI)-traceable spectral reflectance measurements of Earth at an unprecedented accuracy of 0.3% ( k = 1). CPF will also take measurements to support intercalibration of other satellite-based sensors. To achieve the desired intercalibration methodology uncertainty of 0.3% ( k = 1), the CPF intercalibration measurements need to closely match those from target sensors in time, space, angles, and wavelength. This article introduces an innovative angular correction method to significantly reduce errors due to angular mismatches between CPF and target sensor measurements. The method leverages the spectral correlations among the reflected solar (RS) radiances from the same surface target at two adjacent angles. Our studies have shown that the spectral radiance or reflectance difference measured at angles slightly deviating from the CPF observation angles can be accurately predicted based on the hyperspectral CPF measurements. The method will serve as part of the operational algorithms to support the core mission goal of conducting intercalibration analysis with measurements from the shortwave channel of the Clouds and the Earth’s Radiance Energy System (CERES) and the reflective solar bands of the Visible Infrared Imaging Radiometer Suite (VIIRS); however, it can also be extended for other reference-target intercalibration applications. Calibration; Sensors; Databases; Training; intercalibration; Wavelength measurement; Uncertainty; Angular correction; Climate Absolute Radiance and Refractivity (CLARREO) Pathfinder (CPF); climate benchmarking; Geometry; Système Internationale (SI)-traceable
Wu, Yuqing; Gao, Jing; Zhao, AibinWu, Y., J. Gao, A. Zhao, 2024: Cloud properties and dynamics over the Tibetan Plateau – A review. Earth-Science Reviews, 248, 104633. doi: 10.1016/j.earscirev.2023.104633. Cloud properties over the Tibetan Plateau (TP) and their underlying dynamics play a crucial role in the energy balance and regional water cycle of the climate system. In this review, we assess the progress in observational methods and model simulations of cloud macro- and micro-physical properties over the TP since the 1960s. We summarize the spatiotemporal patterns of cloud distribution and the main drivers, discussing the difficulties posed by cloud dynamics and their feedback into climate change on the TP. In short, we found that while the TP is warming and wetting, total cloud cover has decreased over the TP from 1960 to 2021 and from the southeast to the northwest, which typically exhibits the largest proportion of high cloud cover (HCC) and mid-high cloud cover. Meteorological elements (such as air temperature, precipitation), topography, and atmospheric circulation are the main factors influencing cloud formation. During the warm season (May–October), the intensification and northward shift of the South–Asian High and the South Asian monsoon lead to an uneven distribution of precipitation over the TP, while the Indian monsoon promotes the formation of low cloud cover. During the cold season (November–April), the northward expansion of the Hadley circulation inhibits the formation of HCC and middle cloud cover. The amount of cloud cover also affects climatic warming on the TP by radiative forcing. We end the review with a discussion of future research challenges, and propose to focus on improving the accuracy of model parameterizations to facilitate a deeper understanding of the effects of climate change on the TP and the associated water cycle processes. Tibetan plateau; Cloud properties; Cloud dynamics; Model development; Observational methods
Xing, Yuxuan; Chen, Yang; Yan, Shirui; Cao, Xiaoyi; Zhou, Yong; Zhang, Xueying; Shi, Tenglong; Niu, Xiaoying; Wu, Dongyou; Cui, Jiecan; Zhou, Yue; Wang, Xin; Pu, WeiXing, Y., Y. Chen, S. Yan, X. Cao, Y. Zhou, X. Zhang, T. Shi, X. Niu, D. Wu, J. Cui, Y. Zhou, X. Wang, W. Pu, 2024: Dust storms from the Taklamakan Desert significantly darken snow surface on surrounding mountains. Atmospheric Chemistry and Physics, 24(9), 5199-5219. doi: 10.5194/acp-24-5199-2024. The Taklamakan Desert (TD) is a major source of mineral dust emissions into the atmosphere. These dust particles have the ability to darken the surface of snow on the surrounding high mountains after deposition, significantly impacting the regional radiation balance. However, previous field measurements have been unable to capture the effects of severe dust storms accurately, and their representation on regional scales has been inadequate. In this study, we propose a modified remote-sensing approach that combines data from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite and simulations from the Snow, Ice, and Aerosol Radiative (SNICAR) model. This approach allows us to detect and analyze the substantial snow darkening resulting from dust storm deposition. We focus on three typical dust events originating from the Taklamakan Desert and observe significant snow darkening over an area of ∼ 2160, ∼ 610, and ∼ 640 km2 in the Tien Shan, Kunlun, and Qilian mountains, respectively. Our findings reveal that the impact of dust storms extends beyond the local high mountains, reaching mountains located approximately 1000 km away from the source. Furthermore, we observe that dust storms not only darken the snowpack during the spring but also in the summer and autumn seasons, leading to increased absorption of solar radiation. Specifically, the snow albedo reduction (radiative forcing) triggered by severe dust deposition is up to 0.028–0.079 (11–31.5 W m−2), 0.088–0.136 (31–49 W m−2), and 0.092–0.153 (22–38 W m−2) across the Tien Shan, Kunlun, and Qilian mountains, respectively. This further contributes to the aging of the snow, as evidenced by the growth of snow grain size. Comparatively, the impact of persistent but relatively slow dust deposition over several months during non-event periods is significantly lower than that of individual dust events. This highlights the necessity of giving more attention to the influence of extreme events on the regional radiation balance. This study provides a deeper understanding of how a single dust event can affect the extensive snowpack and demonstrates the potential of employing satellite remote sensing to monitor large-scale snow darkening.
Xu, Ri; Zhao, Jun; Bao, Shanhu; Shang, Huazhe; Bao, Fangling; Tana, Gegen; Wei, LesiXu, R., J. Zhao, S. Bao, H. Shang, F. Bao, G. Tana, L. Wei, 2024: Estimation of Top-of-Atmosphere Longwave Cloud Radiative Forcing Using FengYun-4A Geostationary Satellite Data. Remote Sensing, 16(8), 1415. doi: 10.3390/rs16081415. The distribution and variation of top-of-atmosphere longwave cloud radiative forcing (LCRFTOA) has drawn a significant amount of attention due to its importance in understanding the energy budget. Advancements in sensor and data processing technology, as well as a new generation of geostationary satellites, such as the FengYun-4A (FY-4A), allow for high spatiotemporal resolutions that are crucial for real-time radiation monitoring. Nevertheless, there is a distinct lack of official top-of-atmosphere outgoing longwave radiation products under clear-sky conditions (OLRclear). Consequently, this study addresses the challenge of constructing LCRFTOA data with high spatiotemporal resolution over the full disk region of FY-4A. After simulating the influence of atmospheric parameters on OLRclear based on the SBDART radiation transfer model (RTM), we developed a model for estimating OLRclear using infrared channels from the advanced geosynchronous radiation imager (AGRI) onboard the FY-4A satellite. The OLRclear results showed an RMSE of 5.05 W/m2 and MBE of 1.59 W/m2 compared to ERA5. The corresponding RMSE and MBE value compared to CERES was 6.52 W/m2 and 2.39 W/m2. Additionally, the calculated LCRFTOA results were validated against instantaneous, daily average, and monthly average ERA5 and CERES LCRFTOA products, supporting the validity of the algorithm proposed in this paper. Finally, the changes in LCRFTOA due to varied cloud heights (high, medium, and low cloud) were analyzed. This study provides the basis for comprehensive studies on the characteristics of top-of atmosphere radiation. The results suggest that high-height clouds exert a greater degree of radiative forcing more frequently, while low-height clouds are more frequently found in the lower forcing range. outgoing longwave radiation; cloud radiative forcing; satellite remote sensing; top-of-atmosphere; clear-sky; FengYun-4A
Xu, Xiaoqi; Heng, Zhiwei; Li, Yueqing; Wang, Shunjiu; Li, Jian; Wang, Yuan; Chen, Jinghua; Zhang, Peiwen; Lu, ChunsongXu, X., Z. Heng, Y. Li, S. Wang, J. Li, Y. Wang, J. Chen, P. Zhang, C. Lu, 2024: Improvement of cloud microphysical parameterization and its advantages in simulating precipitation along the Sichuan-Xizang Railway. Science China Earth Sciences, 67(3), 856-873. doi: 10.1007/s11430-023-1247-2. The Sichuan-Xizang Railway is an important part of the railway network in China, and geological disasters, such as mountain floods and landslides, frequently occur in this region. Precipitation is an important cause of these disasters; therefore, accurate simulation of the precipitation in this region is highly important. In this study, the descriptions for uncertain processes in the cloud microphysics scheme are improved; these processes include cloud droplet activation, cloud-rain autoconversion, rain accretion by cloud droplets, and the entrainment-mixing process. In the default scheme, the cloud water content of different sizes corresponds to the same cloud droplet concentration, which is inconsistent with the actual content; this results in excessive cloud droplet size, unreasonable related conversion rates of microphysical process (such as cloud-rain autoconversion), and an overestimation of precipitation. Our new scheme overcomes the problem of excessive cloud droplet size. The processes of cloudrain autoconversion and rain accretion by cloud droplets are similar to the stochastic collection equation, and the mixing mechanism of cloud droplets is more consistent with that occurred during the actual physical process in the cloud. Based on the new and old schemes, multiple precipitation processes in the flood season of 2021 along the Sichuan-Xizang Railway are simulated, and the results are evaluated using ground observations and satellite data. Compared to the default scheme, the new scheme is more suitable for the simulation of cloud physics, reducing the simulation deviation of the liquid water path and droplet radius from 2 times to less than 1 time and significantly alleviating the overestimation of precipitation intensity and range of precipitation center. The average root-mean-square error is reduced by 22%. Our results can provide a scientific reference for improving precipitation forecasting and disaster prevention in this region. Precipitation; Cloud microphysics; Model improvement; The Sichuan-Xizang Railway
Xue, Wenhao; Zhang, Jing; Deng, Xiaoqing; Tian, YuluXue, W., J. Zhang, X. Deng, Y. Tian, 2024: Responses of vegetation photosynthetic processes to aerosol-induced direct radiative effect in China. Atmospheric Environment, 329, 120557. doi: 10.1016/j.atmosenv.2024.120557. Aerosols play an essential role in the energy cycle of land-atmosphere systems through interactions with radiation and clouds. Aerosol-induced direct radiative effect (ADRE) has a large effect on the photosynthetic processes of vegetation in terrestrial ecosystems. We used the Fu-Liou radiation transfer model integrated with the Community Land Model (CLM) to quantify ADRE and the responses of vegetation photosynthetic processes to ADRE in China from 2001 to 2014. The aerosols exhibited a positive effect on the diffuse fraction and it increased at first and decreased later. Positive impacts of ADRE on the leaf area index (LAI) of both sun (LAISUN) and shaded leaves (LAISHA) were captured in most areas of China, with increases of 0.01 and 0.09, respectively. The changes in LAI caused by ADRE were consistent with aerosol loading in northern and eastern China. In addition, due to the large decrease in total radiation caused by aerosols, ADRE reduced the photosynthetic rate of sun leaves. However, when the aerosol optical depth (AOD) ranged from 0.50 to 0.57, ADRE had positive effects on the photosynthetic rate of shaded leaves, and the AOD interval for positive impacts on the photosynthetic rate was different in each subregion of China. Mechanistic analysis found that ADRE could reduce the ribulose 1,5-bisphosphate (RuBP) carboxylase-limited rate of carboxylation and enhance the light-limited rate. When the AOD was around 0.47, the positive impacts of ADRE on the light-limited rate peaked throughout China (∼0.149 μmol m−2 s−1). China; Aerosol-induced direct radiative effect; Community land model; Fu-liou model; Leaf area index; Photosynthesis
Yamauchi, Akira; Suzuki, Kentaroh; Oikawa, Eiji; Sekiguchi, Miho; Nagao, Takashi; Ishida, HarumaYamauchi, A., K. Suzuki, E. Oikawa, M. Sekiguchi, T. Nagao, H. Ishida, 2024: Description and validation of the Japanese algorithm for radiative flux and heating rate products with all four EarthCARE instruments: Pre-launch test with A-Train. Atmospheric Measurement Techniques Discussions, 1-24. doi: 10.5194/amt-2024-78. Abstract. This study developed the Level 2 (L2) atmospheric radiation flux and heating rate product by a Japanese team for Earth Clouds, Aerosols, and Radiation Explorer (EarthCARE). This product offers vertical profiles of downward and upward longwave (LW) and shortwave (SW) radiative fluxes and their atmospheric heating rates. This paper describes the algorithm developed for generating products, including the atmospheric radiative transfer model and input datasets, and its validation against measurement data of radiative fluxes. In the testing phase before the EarthCARE launch, we utilized A-Train data that provided input and output variables analogous to EarthCARE, so that the developed algorithm could be directly applied to EarthCARE after its launch. The results include comparisons of radiative fluxes between radiative transfer simulations and satellite/ground-based observations that quantify errors in computed radiative fluxes at the top of the atmosphere against Clouds and Earth's Radiant Energy System (CERES) observations and their dependence on cloud type with varying thermodynamic phases. For SW fluxes, the bias was 24.4 Wm-2, and the root mean square error (RMSE) was 36.3 Wm-2 relative to the CERES observations at spatial and temporal scales of 5° and 1 month, respectively. On the other hand, LW exhibits a bias of -10.7 Wm-2 and an RMSE of 14.2 Wm-2. When considering different cloud phases, the SW water cloud exhibited a bias of -11.7 Wm-2 and an RMSE of 46.2 Wm-2, while the LW showed a bias of 0.8 Wm-2 and an RMSE of 6.0 Wm-2. When ice clouds were included, the SW bias ranged from 58.7 to 81.5 Wm-2 and the RMSE from 72.8 to 91.6 Wm-2 depending on the ice-containing cloud types, while the corresponding LW bias ranged from -8.8 to -28.4 Wm-2 and the RMSE from 25.9 to 31.8 Wm-2, indicating that the primary source of error was ice-containing clouds. The comparisons were further extended to various spatiotemporal scales to investigate the scale dependency of the flux errors. The SW component of this product exhibited an RMSE of approximately 30 Wm-2 at spatial and temporal scales of 40° and 40 days, respectively, whereas the LW component did not show a significant decrease in RMSE with increasing spatiotemporal scale. Radiative transfer simulations were also compared with ground-based observations of the surface downward SW and LW radiative fluxes at selected locations. The results show that the bias and RMSE for SW are -17.6 Wm-2 and 172.0 Wm-2, respectively, which are larger than those for LW that are -5.6 Wm-2 and 19.0 Wm-2, respectively.
Yamazaki, K.; Miura, H.Yamazaki, K., H. Miura, 2024: Reproducibility of Equatorial Kelvin Waves in a Superparameterized MIROC: 1. Implementation and Verification of Blockwise-Coupled SP-MIROC. Journal of Advances in Modeling Earth Systems, 16(5), e2023MS003836. doi: 10.1029/2023MS003836. The potential scope of superparameterization (SP) was extended to higher resolutions of the global climate model (GCM) component by devising a technique called blockwise coupling. In this method, a horizontal average of multiple GCM columns, instead of one, is coupled to a cloud-resolving model (CRM) domain. This enables SP-GCMs to reduce the computational cost drastically, enabling higher-resolution GCMs to be superparameterized. A blockwise-coupled SP-GCM called SP-MIROC was implemented by coupling the climate model MIROC6 to the CRM SCALE-RM. The 4 × 4-bundled SP-MIROC successfully reproduced horizontal patterns and frequency distributions of precipitation and realistic amplitudes of equatorial Kelvin waves (EKWs), which were underestimated in the standard MIROC6. As discussed in Yamazaki and Miura (2024b, https://doi.org/10.1029/2023MS003837) of this study, the amplitude boost of EKWs was enabled by a top-heavy heating in SP-MIROC. Comparison of power spectra between the 4 × 4-bundled SP-MIROC and nonbundled SP-MIROC indicated that the effective resolution of dynamic variables was not degraded by the blockwise technique. Rather, spectra in the 4 × 4-bundled SP-MIROC were more realistic than those in the nonbundled SP-MIROC. Although the 4 × 4-bundling limits convective coupling in the smallest GCM scale, it could offer the best match of resolutions between the GCM-handled dynamics and SP-derived physics because the effective resolution of the dynamics is lower than the nominal grid spacing. superparameterization; global model
Yang, Kai; Chen, Jinghua; Wu, Xiaoqing; Yin, Yan; Zhao, Tianliang; Lu, Chunsong; Deng, Liping; Ding, HuiYang, K., J. Chen, X. Wu, Y. Yin, T. Zhao, C. Lu, L. Deng, H. Ding, 2024: Effects of the Indian summer monsoon on the cloud characteristics over the Eastern Tibetan Plateau: a simulation study. Climate Dynamics. doi: 10.1007/s00382-024-07219-w. As one of important large-scale systems in south Asia, the Indian summer monsoon (ISM) can affect the moisture budget and cloud processes over the Tibetan Plateau (TP). The influneces of ISM on cloud and precipitation of the Eastern TP (ETP) are discussed via a cloud-resolving model. The outbreak of ISM can activate the moisture transport between TP and the southern ocean in May, which reaches its annual most active period in July. The simulation results show that, compared to a normal ISM year, the moisture transport is intensified in pre-summer and is weakened in a strong ISM year, leading to more pre-summer deep clouds and rainfall. However, a weak ISM year exhibits weak pre-summer moisture transport and active summer moisture transport, resulting in few pre-summer deep clouds and rainfall. The summer moderate cloud cells are reduced in the strong ISM year while are promoted in the weak ISM year, taking responsibility for the summer precipitation variations. The ETP daily maximum precipitation appears at around 21:00 LST and increases after mid-April, reaches its maximum in summer. The model also suggests that the ETP warm season precipitation variation in the strong ISM year is closely related to deep convective cloud (DCC) properties (e.g. frequency and cloud water content). However, deep clouds (cloud depth > 4.0 km) rather than DCC contribute more to the precipitation diurnal variations during June and July in the weak ISM year. Cloud and precipitation; Indian summer monsoon; The Tibetan Plateau
Yarger, Drew; Wagman, Benjamin Moore; Chowdhary, Kenny; Shand, LyndsayYarger, D., B. M. Wagman, K. Chowdhary, L. Shand, 2024: Autocalibration of the E3SM Version 2 Atmosphere Model Using a PCA-Based Surrogate for Spatial Fields. Journal of Advances in Modeling Earth Systems, 16(4), e2023MS003961. doi: 10.1029/2023MS003961. Global Climate Model tuning (calibration) is a tedious and time-consuming process, with high-dimensional input and output fields. Experts typically tune by iteratively running climate simulations with hand-picked values of tuning parameters. Many, in both the statistical and climate literature, have proposed alternative calibration methods, but most are impractical or difficult to implement. We present a practical, robust, and rigorous calibration approach on the atmosphere-only model of the Department of Energy's Energy Exascale Earth System Model (E3SM) version 2. Our approach can be summarized into two main parts: (a) the training of a surrogate that predicts E3SM output in a fraction of the time compared to running E3SM, and (b) gradient-based parameter optimization. To train the surrogate, we generate a set of designed ensemble runs that span our input parameter space and use polynomial chaos expansions on a reduced output space to fit the E3SM output. We use this surrogate in an optimization scheme to identify values of the input parameters for which our model best matches gridded spatial fields of climate observations. To validate our choice of parameters, we run E3SMv2 with the optimal parameter values and compare prediction results to expertly-tuned simulations across 45 different output fields. This flexible, robust, and automated approach is straightforward to implement, and we demonstrate that the resulting model output matches present day climate observations as well or better than the corresponding output from expert tuned parameter values, while considering high-dimensional output and operating in a fraction of the time. climate; machine learning; calibration; tuning
Ye, Hanlin; Guo, Huadong; Liu, Guang; Huang, Jing; Liang, DongYe, H., H. Guo, G. Liu, J. Huang, D. Liang, 2024: Disk-Integrated Earth’s Outgoing Longwave Radiation Viewed From a Moon-Based Platform: Model Simulations. Journal of Geophysical Research: Atmospheres, 129(5), e2023JD038908. doi: 10.1029/2023JD038908. A Moon-based sensor can observe the Earth as a single point and achieve disk-integrated measurements of outgoing longwave radiation (OLR), which significantly differs from low orbital, geostationary, and Sun–Earth L1 point platforms. In this study, a scheme of determining the disk-integrated Earth’s OLR based on a Moon-based platform is proposed. The observational solid angle was theoretically derived based on the Earth’s ellipsoid model and the disk-integrated observational anisotropic factor was estimated to eliminate the effects of the Earth’s radiant anisotropy. The simulated disk-integrated Earth's OLR obtained from a Moon-based platform varies periodically, due to changes in the observation geometry and Earth's scene distribution within the observed Earth’s disk. Clouds, meteorological parameters, and the land cover distribution notably affect the disk-integrated Earth’s OLR. By analyzing the disk-integrated Earth’s OLR from a Moon-based platform, significant variabilities were investigated. Additionally, the Earth’s shape and radiant anisotropy that affecting the disk-integrated Earth’s OLR were estimated. In conclusion, a more realistic Earth’s shape, the latest version of the angular distribution model (ADM), and accurate land cover and meteorological datasets are needed when determining the disk-integrated Earth’s OLR. It is expected the unique variability captured by this platform and its ability to complement traditional satellite data make it a valuable tool for studying Earth’s radiation budget and energy cycle, and contributing to diagnostic of the climate General Circulation Models (GCM) performance. outgoing longwave radiation (OLR); disk-integrated measurement; Earth’s ellipsoid model; Earth’s radiant anisotropy; Moon-based platform
Yu, Lan; Zhang, Ming; Wang, Lunche; Li, Huaping; Li, JunliYu, L., M. Zhang, L. Wang, H. Li, J. Li, 2024: Characteristics of Aerosols and Clouds and Their Role in Earth’s Energy Budget. J. Climate, 37(3), 995-1014. doi: 10.1175/JCLI-D-23-0414.1. Abstract Clouds and aerosols provide the greatest uncertainty in estimating and interpreting Earth’s energy budget. This study not only focuses on surface brightening/dimming, but also explores Earth’s energy balance. The validation results of the CERES-SYN, ISCCP-FH, and GEWEX-SRB datasets with Baseline Surface Radiation Network (BSRN), Surface Radiation Budget Network (SURFRAD), and CMA observations show that CERES data have the highest accuracy and the longest temporal coverage. The role of clouds and aerosols in Earth’s energy budget was explained using CERES and MERRA-2 products. The results show that Earth’s energy increases at a rate of 0.63 W m−2 decade−1 in 2000–21. The global surface brightens at a rate of 0.57 W m−2 decade−1, with surface energy decreasing at a rate of 0.19 W m−2 decade−1. Brightening was found over Australia, central Asia, and southern Africa, mainly associated with cloud reduction, with aerosol emissions reductions contributing to the East Asian surface brightening. The surface brightening in South America and Southeast Asia is also due to the reduction of clouds. The increase of aerosols in South Asia is the main factor for its surface dimming, while we infer that the climatic effect from the increase of black carbon (BC) aerosols in South Asia is the inducing factor for the dimming in southern China. The surface darkening in West Asia is the result of the combined effect of clouds and aerosols, while in northern Africa it may be related to the increase of clouds caused by the decrease of dust aerosols. Surface energy increases only in Southeast Asia, South America, and Europe. Significance Statement Clouds and aerosols provide the greatest uncertainty in estimating and interpreting Earth’s changing energy budget. Moreover, the relative importance of clouds and aerosols is variable, depending on the regions and time scales of studies. This study shows that the energy inflow to the Earth system is greater than the energy outflow in 2000–21, with radiation on Earth increasing at a rate of 0.63 W m−2 decade−1 with the surface energy decreases at a rate of 0.19 W m−2 decade−1. Brightening was found over Southeast Asia, South America, Australia, and southern Africa, with the areas of surface darkening occurring mainly in Asia and northern Africa.
Yuan, Chang; Zhang, Hua; Jing, Xianwen; Zhao, Shuyun; Li, XiaohanYuan, C., H. Zhang, X. Jing, S. Zhao, X. Li, 2024: Impact of a New Radiation Scheme on Simulated Climate in the Global–Regional Integrated SysTem Model under Varying Physical Parameterization Schemes. Atmosphere, 15(4), 501. doi: 10.3390/atmos15040501. In this study, the radiation scheme BCC-RAD (Beijing Climate Center RADiative transfer model) developed for global climate models is implemented into the Global–Regional Integrated SysTem (GRIST) model as an alternative to the default RRTMG (general circulation model (GCM) version of the Rapid Radiative Transfer Model) scheme. Its impact on the simulated climate is comprehensively evaluated under different physics parametrization packages, in comparison with both the CERES (partly from ERA5 reanalysis) observations and multi-model results from CMIP6. The results indicate that under the default physics parameterization package of GRIST (PhysC), BCC-RAD improved the simulated global mean cloud cover by ~3% and the clear-sky outgoing longwave radiation by ~5.6 W/m2. Upon the inclusion of the PhysCN parameterization package, BCC-RAD exhibited further improvement in simulated cloud cover and radiative forcing (particularly longwave radiative forcing, the bias of which decreases from −9.2 W/m2 to −1.8 W/m2), leading it to be closer to observations than RRTMG. Additionally, BCC-RAD improved the simulation of atmospheric temperature and hence notably diminished the apparent overestimation of atmospheric humidity seen in RRTMG. This study demonstrates the advantages of BCC-RAD over RRTMG in certain aspects of the GRIST-simulated climate, verifying its capability for the climate-oriented configuration of GRIST. climate simulation; BCC-RAD; GRIST; radiation scheme evaluation
Yuan, Tianle; Song, Hua; Oreopoulos, Lazaros; Wood, Robert; Bian, Huisheng; Breen, Katherine; Chin, Mian; Yu, Hongbin; Barahona, Donifan; Meyer, Kerry; Platnick, StevenYuan, T., H. Song, L. Oreopoulos, R. Wood, H. Bian, K. Breen, M. Chin, H. Yu, D. Barahona, K. Meyer, S. Platnick, 2024: Abrupt reduction in shipping emission as an inadvertent geoengineering termination shock produces substantial radiative warming. Communications Earth & Environment, 5(1), 1-8. doi: 10.1038/s43247-024-01442-3. Human activities affect the Earth’s climate through modifying the composition of the atmosphere, which then creates radiative forcing that drives climate change. The warming effect of anthropogenic greenhouse gases has been partially balanced by the cooling effect of anthropogenic aerosols. In 2020, fuel regulations abruptly reduced the emission of sulfur dioxide from international shipping by about 80% and created an inadvertent geoengineering termination shock with global impact. Here we estimate the regulation leads to a radiative forcing of $$+0.2\pm 0.11$$Wm−2 averaged over the global ocean. The amount of radiative forcing could lead to a doubling (or more) of the warming rate in the 2020 s compared with the rate since 1980 with strong spatiotemporal heterogeneity. The warming effect is consistent with the recent observed strong warming in 2023 and expected to make the 2020 s anomalously warm. The forcing is equivalent in magnitude to 80% of the measured increase in planetary heat uptake since 2020. The radiative forcing also has strong hemispheric contrast, which has important implications for precipitation pattern changes. Our result suggests marine cloud brightening may be a viable geoengineering method in temporarily cooling the climate that has its unique challenges due to inherent spatiotemporal heterogeneity. Climate and Earth system modelling; Atmospheric chemistry
Yun, Misun; Kang, Jae-Joong; Jeong, Yubeen; Jo, Young-Heon; Sun, Jun; Lee, Sang-HeonYun, M., J. Kang, Y. Jeong, Y. Jo, J. Sun, S. Lee, 2024: Experimental Assessment of Ultraviolet Radiation Impact on the Primary Production of Phytoplankton in the East/Japan Sea. Journal of Marine Science and Engineering, 12(8), 1258. doi: 10.3390/jmse12081258. Solar radiation, particularly ultraviolet radiation (UVR, 280–400 nm), is known to play a significant role in driving primary production in marine ecosystems. However, our understanding of the specific effects of UVR on the primary production of natural phytoplankton communities is still limited. We utilized the 13C stable isotope to quantify primary production and conducted experiments using different types of incubation bottles (polycarbonate and quartz bottles) to compare the primary production in the absence and presence of UVR. Although we observed a weak inhibitory effect at the surface of the water column, UVR exposure resulted in an approximately 1.5-fold increase in primary production over the euphotic zone. The enhanced primary production during the study period can be attributed to the combined effect of low UVB (280–320 nm) dose and abundant nutrient conditions. Notably, our size-fractionated measurements revealed that UVR exposure led to a two-fold increase in primary production in large cells (>2 μm) compared to the exposure of solely photosynthetically active radiation (PAR). In contrast, there was no significant difference in the primary production of small cells ( phytoplankton; ultraviolet radiation; cell size; polycarbonate bottle; primary production; quartz bottle
Zhang, Bosong; Donner, Leo J.; Zhao, Ming; Tan, ZhihongZhang, B., L. J. Donner, M. Zhao, Z. Tan, 2024: Improved Precipitation Diurnal Cycle in GFDL Climate Models With Non-Equilibrium Convection. Journal of Advances in Modeling Earth Systems, 16(9), e2024MS004315. doi: 10.1029/2024MS004315. Most global climate models with convective parameterization have trouble in simulating the observed diurnal cycle of convection. Maximum precipitation usually happens too early during summertime, especially over land. Observational analyses indicate that deep convection over land cannot keep pace with rapid variations in convective available potential energy, which is largely controlled by boundary-layer forcing. In this study, a new convective closure in which shallow and deep convection interact strongly, out of equilibrium, is implemented in atmosphere-only and ocean-atmosphere coupled models. The diurnal cycles of convection in both simulations are significantly improved with small changes to their mean states. The new closure shifts maximum precipitation over land later by about three hours. Compared to satellite observations, the diurnal phase biases are reduced by half. Shallow convection to some extent equilibrates rapid changes in the boundary layer at subdiurnal time scales. Relaxed quasi-equilibrium for convective available potential energy holds in significant measure as a result. Future model improvement will focus on the remaining biases in the diurnal cycle, which may be further reduced by including stochastic entrainment and cold pools. deep convection; diurnal cycle of precipitation; shallow convection
Zhang, Chunyan; Wang, Donghai; Yao, Lebao; Wu, Zhenzhen; Ma, Qianhui; Li, Yongsheng; Wang, PeidongZhang, C., D. Wang, L. Yao, Z. Wu, Q. Ma, Y. Li, P. Wang, 2024: Contrasts of Large-Scale Moisture and Heat Budgets between Different Sea Areas of the South China Sea and the Adjacent Land. J. Appl. Meteor. Climatol., 63(1), 105-124. doi: 10.1175/JAMC-D-23-0084.1. Abstract This study investigates and compares large-scale moisture and heat budgets over the eastern rainy sea area around Dongsha, the western rainless sea area around Xisha, and the northern coastland of the South China Sea. Ten-year (2011–20) surface, balloon-sounding, satellite measurements, and ERA5 reanalysis are merged into the physically consistent data to study annual and vertical variations of the budgets. It shows that the surface and column-integrated heat and moisture budgets have the smallest annual evolution over the coastland. The latent heat as a key heat contributor in summer is mainly offset by total cold advection and partially offset by net radiative cooling. The horizontal moisture advection below 700 hPa presents moistening over the sea whereas drying over the coastland during rainy months, in which the vertical moisture advection presents moistening up to 250 hPa for all three subregions. The horizontal temperature advection is weak throughout the year over the sea but displays strong top warming and bottom cooling in summer and nearly the opposite in winter over the coastland. The diabatic cooling with a peak at ∼700 hPa in winter is largely due to the enhanced radiative cooling and latent cooling. While the diabatic heating with a peak at ∼500 hPa in summer is largely due to the enhanced latent heating. The earliest atmospheric heating and moistening occur in spring over the coastland, inducing the earliest precipitation increase. The enhanced heating and moistening over Xisha have a 1-month lag relative to Dongsha, resulting in lagging precipitation.
Zhang, Chunyan; Wang, Donghai; Zhang, Kaifeng; He, Wanwen; Zheng, Yanping; Xu, YanZhang, C., D. Wang, K. Zhang, W. He, Y. Zheng, Y. Xu, 2024: Differences in Precipitation and Related Wind Dynamics and Moisture and Heat Features in Separate Areas of the South China Sea before and after Summer Monsoon Onset. Advances in Atmospheric Sciences, 41(8), 1643-1660. doi: 10.1007/s00376-023-3141-3. Using surface and balloon-sounding measurements, satellite retrievals, and ERA5 reanalysis during 2011–20, this study compares the precipitation and related wind dynamics, moisture and heat features in different areas of the South China Sea (SCS) before and after SCS summer monsoon onset (SCSSMO). The rainy sea around Dongsha (hereafter simply referred to as Dongsha) near the north coast, and the rainless sea around Xisha (hereafter simply referred to as Xisha) in the western SCS, are selected as two typical research subregions. It is found that Dongsha, rather than Xisha, has an earlier and greater increase in precipitation after SCSSMO under the combined effect of strong low-level southwesterly winds, coastal terrain blocking and lifting, and northern cold air. When the 950-hPa southwesterly winds enhance and advance northward, accompanied by strengthened moisture flux, there is a strong convergence of wind and moisture in Dongsha due to a sudden deceleration and rear-end collision of wind by coastal terrain blocking. Moist and warm advection over Dongsha enhances early and deepens up to 200 hPa in association with the strengthened upward motion after SCSSMO, thereby providing ample moisture and heat to form strong precipitation. However, when the 950-hPa southwesterly winds weaken and retreat southward, Xisha is located in a wind-break area where strong convergence and upward motion centers move in. The vertical moistening and heating by advection in Xisha enhance later and appear far weaker compared to that in Dongsha, consistent with later and weaker precipitation. Dongsha; heat; moisture; precipitation; South China Sea summer monsoon onset; wind dynamics; Xisha; 东沙; 南海夏季风爆发; 水汽; 热量; 西沙; 降水; 风动
Zhang, Chunyan; Wang, Donghai; Zhou, Qinqiang; Yang, Yuhong; Hou, Ling; Yang, KunlinZhang, C., D. Wang, Q. Zhou, Y. Yang, L. Hou, K. Yang, 2024: Diabatic heating structures varying with convective and rainfall intensities in different areas of the pan-South China Sea region. Atmospheric Research, 306, 107474. doi: 10.1016/j.atmosres.2024.107474. This study investigates and compares diabatic heating structures related to vertical velocity, cloud types, and rainfall intensities in the northeast rainy sea subregion named Dongsha, the west rainless sea subregion named Xisha, and the north rainy land subregion named Coastland in the pan-SCS region. The diabatic heating rate of >2 K hr−1 over Dongsha and Coastland has a higher frequency and a deeper distribution than over Xisha where it requires stronger upward motion to achieve the same heating rate, indicating more frequent and deeper convection over the north coastal sea and land areas than the west sea area of the pan-SCS region. The deep convective Q1 profiles show a stronger peak at ∼500 hPa and a weaker peak at ∼700 hPa over two sea subregions while a single peak at ∼500 hPa over Coastland. The nimbostratus Q1 profile has a weakened heating peak at 350–550 hPa over Dongsha, 500–600 hPa over Xisha, and 425–575 hPa over Coastland. The shallow cumulus Q1 profile of Dongsha shows weak heating in the mid-to-lower troposphere while that of Xisha and Coastland has hardly heating. Latent heating and vertical turbulence significantly affect the diabatic heating structure related to deep convective clouds and nimbostratus but hardly affect that related to shallow cumulus. Despite cloud types, Dongsha has the strongest diabatic heating among the three subregions due to its geographical advantages. The no-rainfall Q1 profiles over three subregions have a similar shape with a weak cooling peak at ∼700 hPa due to boundary-layer evaporation and eddies. But the small-rainfall Q1 profiles present upper heating and lower cooling over sea subregions whereas the opposite over Coastland possibly due to stronger surface sensible heating on the land. From moderate to heavy rainfall, the Q1 profiles over three subregions are similar with a heating maximum at ∼500 hPa associated with deep convection, except for heating intensity which is much stronger over Xisha than the other two subregions. This suggests that Xisha presents stronger convection to achieve the same rainfall intensity as Dongsha and Coastland, which is closely due to a positive effect of coastal terrain blocking and uplifting on precipitation for Dongsha and Coastland whereas a negative effect of the Annam Mountains for Xisha. Cloud types; Diabatic heating; pan-SCS region; Profiles; Rainfall intensities
Zhang, Haipeng; Zheng, Youtong; Li, ZhanqingZhang, H., Y. Zheng, Z. Li, 2024: Improving Low-Cloud Fraction Prediction Through Machine Learning. Geophysical Research Letters, 51(15), e2024GL109735. doi: 10.1029/2024GL109735. In this study, we evaluated the performance of machine learning (ML) models (XGBoost) in predicting low-cloud fraction (LCF), compared to two generations of the community atmospheric model (CAM5 and CAM6) and ERA5 reanalysis data, each having a different cloud scheme. ML models show a substantial enhancement in predicting LCF regarding root mean squared errors and correlation coefficients. The good performance is consistent across the full spectrums of atmospheric stability and large-scale vertical velocity. Employing an explainable ML approach, we revealed the importance of including the amount of available moisture in ML models for representing spatiotemporal variations in LCF in the midlatitudes. Also, ML models demonstrated marked improvement in capturing the LCF variations during the stratocumulus-to-cumulus transition (SCT). This study suggests ML models' great potential to address the longstanding issues of “too few” low clouds and “too rapid” SCT in global climate models. cloud parameterization scheme; low-cloud fraction; machine learning; stratocumulus-to-cumulus transition
Zhang, Haipeng; Zheng, Youtong; Li, ZhanqingZhang, H., Y. Zheng, Z. Li, 2024: Evaluation of Stratocumulus Evolution Under Contrasting Temperature Advections in CESM2 Through a Lagrangian Framework. Geophysical Research Letters, 51(4), e2023GL106856. doi: 10.1029/2023GL106856. This study leveraged a Lagrangian framework to examine the evolution of stratocumulus clouds under cold and warm advections (CADV and WADV) in the Community Earth System Model 2 (CESM2) against observations. We found that CESM2 simulates a too rapid decline in low-cloud fraction (LCF) and cloud liquid water path (CLWP) under CADV conditions, while it better aligns closely with observed LCF under WADV conditions but overestimates the increase in CLWP. Employing an explainable machine learning approach, we found that too rapid decreases in LCF and CLWP under CADV conditions are related to overestimated drying effects induced by sea surface temperature, whereas the substantial increase in CLWP under WADV conditions is associated with the overestimated moistening effects due to free-tropospheric moisture and surface winds. Our findings suggest that overestimated drying effects of sea surface temperature on cloud properties might be one of crucial causes for the high equilibrium climate sensitivity in CESM2. equilibrium climate sensitivity; cloud simulation; explainable machine learning approach; horizontal temperature advection; stratocumulus evolution
Zhang, Haotian; Zhao, Chuanfeng; Xia, Yan; Chen, Annan; Yang, Yikun; Yang, Jie; Zhao, Xin; Chi, Yulei; Xu, Hongtao; Zhong, ShouyiZhang, H., C. Zhao, Y. Xia, A. Chen, Y. Yang, J. Yang, X. Zhao, Y. Chi, H. Xu, S. Zhong, 2024: Cloud Radiative Effects Slow Sea Ice Changes During Summer Arctic Dipole Anomaly. Geophysical Research Letters, 51(16), e2024GL111205. doi: 10.1029/2024GL111205. Over the past 30 years, the Arctic Dipole Anomaly (DA) has repeatedly led to record lows in summer sea ice extent, with cloud radiative effects (CRE) playing a crucial regulatory role. Here, we reveal the CRE variations between positive and negative DA events and elucidate the slowing impacts of CRE on sea ice thickness (SIT) changes. The DA triggers robust meridional winds and transpolar drift, markedly reducing SIT in the Beaufort Sea (BeS), Chukchi Sea (CS), and East Siberian Sea (ESS), while increasing it in the Greenland Sea (GS). CRE significantly slow SIT changes, contributing +14.4, +4.4, +16.4, and −26.7 cm to changes from June to August, against total changes of −55.9, −29.4, −39.8, and +42.8 cm in September over BeS, CS, ESS, and GS, respectively. This study underscores the key impacts of CRE on sea ice variation, emphasizing their significance in the polar climate system. Arctic dipole anomaly; cloud radiative effect; cloud variation; sea ice thickness
Zhang, Qian; Wang, Tijian; Wu, Hao; Qu, Yawei; Xie, Min; Li, Shu; Zhuang, Bingliang; Li, Mengmeng; Kilifarska, Natalya AndreevaZhang, Q., T. Wang, H. Wu, Y. Qu, M. Xie, S. Li, B. Zhuang, M. Li, N. A. Kilifarska, 2024: Radiative and Chemical Effects of Non-Homogeneous Methane on Terrestrial Carbon Fluxes in Asia. Journal of Geophysical Research: Atmospheres, 129(8), e2023JD040204. doi: 10.1029/2023JD040204. Methane (CH4) plays a crucial role in shaping terrestrial ecosystems due to its radiative effect and atmospheric photochemical reactions. In this study, we employed an enhanced regional climate-chemistry-ecosystem model (RegCM-Chem-YIBs) to comprehensively evaluate the impacts of both radiative and chemical effects of CH4 on terrestrial carbon fluxes across the East, South, and Southeast Asia (EA, SA, SEA) during the year 2010. Our findings showed that the radiative effects of CH4 yielded a positive influence on carbon fluxes. Specifically, the EA region experienced a significant increase in the gross primary production (GPP), reaching up to 0.515 Pg C Yr−1. In comparison, the SEA region exhibited a decrease in the net ecosystem exchange (NEE) of approximately −0.066 Pg C Yr−1. Further analysis revealed that alterations in radiation and vapor pressure deficit (VPD) were dominant drivers. Conversely, the chemical effects of CH4 lead to heightened regional surface ozone (O3) concentrations (2.704–3.115 ppb) and generate a negative response in carbon fluxes. Within the SEA region, GPP observed a decrease of up to −0.144 Pg C Yr−1, while NEE displayed a significant increase of 0.022 Pg C Yr−1. Taken together, the combined radiative and chemical effects of CH4 indicated a positive impact on regional carbon fluxes, with GPP increasing by 0.632 Pg C Yr−1 and NEE decreasing by −0.09 Pg C Yr−1. This holistic perspective is crucial for comprehending the intricate interactions linking climate change, atmospheric pollution, and the global carbon cycle.
Zhang, Taiping; Stackhouse, Paul W.; Macpherson, Bradley; Colleen Mikovitz, J.Zhang, T., P. W. Stackhouse, B. Macpherson, J. Colleen Mikovitz, 2024: A CERES-based dataset of hourly DNI, DHI and global tilted irradiance (GTI) on equatorward tilted surfaces: Derivation and comparison with the ground-based BSRN data. Solar Energy, 274, 112538. doi: 10.1016/j.solener.2024.112538. The NASA CERES SYN1deg(Ed4.1) satellite-based products include hourly global horizontal irradiance (GHI), diffuse horizontal irradiance (DHI) and direct horizontal irradiance (DirHI) as well as hourly solar zenith angle (SZA), and the direct normal irradiance (DNI) can thus be calculated by dividing the DirHI by cos(SZA). The spatial resolution of the dataset is 1° latitude by 1° longitude, and the time span is from March 2000 to near present (October 2023 as of this writing). While the GHI of the dataset agrees well with the ground-based Baseline Surface Radiation Network (BSRN) data, the DHI and DirHI, and thus DNI, show appreciable biases against the BSRN data. Nevertheless, the uncertainty of the DHI and DNI, as exhibited in the standard deviations of their differences from the BSRN data, are smaller than results from the DirIndex model, a global-to-beam model, applied to the CERES data, albeit the model is one of the two best out of 140 models according to a study. This means that the original CERES hourly DNI, though biased, renders the spatiotemporal variability better than does the DirIndex model. For this reason, we decided to perform a bias correction on the hourly DHI and DNI. With the corrected hourly DHI and DNI, we are able to use the isotropic model to calculate the global tilted irradiance (GTI) and the global tracker irradiance (GTrI) on an hourly basis. The BSRN DHI and DNI, on the other hand, are available on near-instantaneous time scales (1-, 2-, 3, or 5-minute intervals) and thus are more conducive to the isotropic model, and for the first time, we use the BSRN data to validate the GTI and GTrI, as opposed to GHI and DHI that have previously been used for validation purpose. For comparison and validation, we also use the monthly-mean-based LJCR method, an independent method as used by RETScreen®, which requires monthly mean GHI and DHI, to directly calculate the monthly mean DNI, GTI and, to extend the model, GTrI, and the results agree well with the BSRN data, which proves the LJCR method itself and corroborates the corrected DHI and DNI as well as the derived GTI and GTrI. The monthly mean DHI and DNI from the Whitlock Method, also monthly-mean-based, are evaluated as well, and we find that minor modification can dramatically improve the method. BSRN; POWER; CERES SYN1deg; DHI; DNI; Global tilted irradiance; GTI
Zhang, Tianyu; Letu, Husi; Dai, Tie; Shi, Chong; Lei, Yonghui; Peng, Yiran; Lin, Yanluan; Chen, Liangfu; Shi, Jiancheng; Tian, Wei; Shi, GuangyuZhang, T., H. Letu, T. Dai, C. Shi, Y. Lei, Y. Peng, Y. Lin, L. Chen, J. Shi, W. Tian, G. Shi, 2024: Estimating hourly surface shortwave radiation over northeast of the Tibetan Plateau by assimilating Himawari-8 cloud optical thickness. Geoscience Letters, 11(1), 1. doi: 10.1186/s40562-023-00312-8. To reduce the uncertainty estimation of clouds and improve the forecast of surface shortwave radiation (SSR) over the Tibetan Plateau, a new cloud assimilation system is proposed which is the first attempt to directly apply the four-dimensional local ensemble transform Kalman filter method to assimilate the cloud optical thickness (COT). The high-resolution spatial and temporal data assimilated from the next-generation geostationary satellite Himawari-8, with the high-assimilation frequency, realized an accurate estimation of the clouds and radiation forecasting. The COT and SSR were significantly improved after the assimilation by independent verification. The correlation coefficient (CORR) of the SSR was increased by 11.3%, and the root-mean-square error (RMSE) and mean bias error (MBE) were decreased by 28.5% and 58.9%, respectively. The 2-h cycle assimilation forecast results show that the overestimation of SSR has been effectively reduced using the assimilation system. These findings demonstrate the high potential of this assimilation technique in forecasting of SSR in numerical weather prediction. The ultimate goal that to improve the model forecast through the assimilation of cloud properties requires further studies to achieve.
Zhang, Wei; Chen, Yongzhe; Ji, Qinghua; Fan, Yuying; Zhang, Gong; Lu, Xi; Hu, Chengzhi; Liu, Huijuan; Qu, JiuhuiZhang, W., Y. Chen, Q. Ji, Y. Fan, G. Zhang, X. Lu, C. Hu, H. Liu, J. Qu, 2024: Assessing global drinking water potential from electricity-free solar water evaporation device. Nature Communications, 15(1), 6784. doi: 10.1038/s41467-024-51115-0. Universal and equitable access to affordable safely managed drinking water (SMDW) is a significant challenge and is highlighted by the United Nations’ Sustainable Development Goals-6.1. However, SMDW coverage by 2030 is estimated to reach only 81% of the global population. Solar water evaporation (SWE) represents one potential method to ensure decentralized water purification, but its potential for addressing the global SMDW challenge remains unclear. We use a condensation-enhanced strategy and develop a physics-guided machine learning model for assessing the global potential of SWE technology to meet SMDW demand for unserved populations without external electricity input. We find that a condensation-enhanced SWE device (1 m2) can supply enough drinking water (2.5 L day−1) to 95.8% of the population lacking SMDW. SWE can help fulfill universal SMDW coverage by 2030 with an annual cost of 10.4 billion U.S. dollars, saving 66.7% of the current investment and fulfilling the SDG-6.1 goal.
Zhang, Yanqing; Gao, Yi; Xu, Liren; Guan, Xu; Gong, Anbao; Zhang, MeigenZhang, Y., Y. Gao, L. Xu, X. Guan, A. Gong, M. Zhang, 2024: Assessment of future solar energy potential changes under the shared socio-economic pathways scenario 2–4.5 with WRF-chem: The roles of meteorology and emission. Atmospheric Environment, 318, 120232. doi: 10.1016/j.atmosenv.2023.120232. The 26th United Nations Climate Change Conference (COP26) proposes to limit global warming to WRF-Chem; Future emission reductions; Future meteorological conditions; Solar energy potential; SSP2–4.5 scenario
Zhang, Zhanjie; Wang, Yong; Zhang, Guang J.; Xing, Cheng; Xia, Wenwen; Yang, MengmiaoZhang, Z., Y. Wang, G. J. Zhang, C. Xing, W. Xia, M. Yang, 2024: Light rain exacerbates extreme humid heat. Nature Communications, 15(1), 7326. doi: 10.1038/s41467-024-51778-9. Humid heat waves pose significant risks to human health and the ecosystem. Intuitively, rainfall often alleviates extreme humid heat. However, here we show that light rain often accompanies extreme humid heat, exacerbating its frequency and intensity, especially over arid and semi-arid regions compared to no rain and moderate-to-heavy rain cases. This is because light rain does not dramatically reduce solar radiation but increases near-surface humidity through enhanced surface evaporation. The water replenishment from light rain as well as a shallower planetary boundary layer is crucial for consecutive extremes where there are commonly sporadic drizzle days amidst several rain-free days. These extremes last longer than rain-free extremes. Current global climate models (GCMs) overestimate light rain. After reducing this bias in a GCM, underestimations of humid heat waves in energy-limited regions and overestimations in water-limited regions are largely alleviated. These findings underscore the underappreciated impact of light rain on extreme humid heat. Atmospheric science; Hydrology
Zhang, Zhiding; Yue, Xu; Zhou, Hao; Zhu, Jun; Lei, Yadong; Tian, ChenguangZhang, Z., X. Yue, H. Zhou, J. Zhu, Y. Lei, C. Tian, 2024: Simulation of the Ecosystem Productivity Responses to Aerosol Diffuse Radiation Fertilization Effects over the Pan-Arctic during 2001–19. Advances in Atmospheric Sciences, 41(1), 84-96. doi: 10.1007/s00376-023-2329-x. The pan-Arctic is confronted with air pollution transported from lower latitudes. Observations have shown that aerosols help increase plant photosynthesis through the diffuse radiation fertilization effects (DRFEs). While such DRFEs have been explored at low to middle latitudes, the aerosol impacts on pan-Arctic ecosystems and the contributions by anthropogenic and natural emission sources remain less quantified. Here, we perform regional simulations at 0.2°×0.2° using a well-validated vegetation model (Yale Interactive terrestrial Biosphere, YIBs) in combination with multi-source of observations to quantify the impacts of aerosol DRFEs on the net primary productivity (NPP) in the pan-Arctic during 2001–19. Results show that aerosol DRFEs increase pan-Arctic NPP by 2.19 Pg C (12.8%) yr−1 under clear-sky conditions, in which natural and anthropogenic sources contribute to 8.9% and 3.9%, respectively. Under all-sky conditions, such DRFEs are largely dampened by cloud to only 0.26 Pg C (1.24%) yr−1, with contributions of 0.65% by natural and 0.59% by anthropogenic species. Natural aerosols cause a positive NPP trend of 0.022% yr−1 following the increased fire activities in the pan-Arctic. In contrast, anthropogenic aerosols induce a negative trend of −0.01% yr−1 due to reduced emissions from the middle latitudes. Such trends in aerosol DRFEs show a turning point in the year of 2007 with more positive NPP trends by natural aerosols but negative NPP trends by anthropogenic aerosols thereafter. Though affected by modeling uncertainties, this study suggests a likely increasing impact of aerosols on terrestrial ecosystems in the pan-Arctic under global warming. anthropogenic aerosols; diffuse radiation fertilization effects; natural aerosols; net primary productivity; pan-Arctic; 人为气溶胶; 净初级生产力; 散射辐射施肥效应; 泛北极; 自然气溶胶
Zhao, MingZhao, M., 2024: Cloud Radiative Effects Associated With Daily Weather Regimes. Geophysical Research Letters, 51(10), e2024GL109090. doi: 10.1029/2024GL109090. Using high temporal resolution satellite observations and reanalysis data, we classify daily weather into distinct regimes and quantify their associated cloud radiative effect (CRE) to better understand the roles of various weather systems in affecting Earth's top-of-atmosphere radiation budget. These regimes include non-precipitation, drizzle, wet non-storm, and storm days, which encompass atmospheric rivers (AR), tropical storms (TS), and mesoscale convection systems (MCS). We find that precipitation (wet) days account for roughly 80% (60%) of global longwave (LW) and shortwave (SW) CREs due to their large frequency and high intensity in CRE. Despite being rare globally (13%), AR, TS, and MCS days together account for 32% of global LW CRE and 27% of SW CRE due to their higher intensity in LW and SW CRE. These results enhance our understanding of how various weather systems, particularly severe storms, influence Earth's radiative balance, and will help to better constrain climate models. atmospheric rivers; cloud radiative effects; mesoscale convective systems; precipitation; tropical storms; weather regimes
Zheng, Mengzhe; Wu, Tongwen; Xin, Xiaoge; Liu, Xiangwen; Lu, Yixiong; Jie, Weihua; Xie, Chengjun; Zhou, YumengZheng, M., T. Wu, X. Xin, X. Liu, Y. Lu, W. Jie, C. Xie, Y. Zhou, 2024: Simulation of MJO with improved deep convection scheme in different resolutions of BCC-CSM2 models. Climate Dynamics, 62(3), 2161-2185. doi: 10.1007/s00382-023-07015-y. This study investigates the impacts of modifying the deep convection scheme on the ability to simulate the Madden–Julian Oscillation (MJO) in the Beijing Climate Center Climate System Model version 2 with a medium resolution (BCC-CSM2-T159) and a high resolution (BCC-CSM2-T382). On the basis of the original deep convection scheme, a modified scheme is suggested, which involves the transport processes of deep convective cloud water. The liquid cloud water that is detrained is transferred horizontally to its neighboring grids, and a portion of the cloud water that is horizontally transported is allowed to be transported downward into the lower troposphere. Both BCC-CSM2-T159 and BCC-CSM2-T382 with the modified deep convection scheme perform better than that used the original deep convection scheme in reproducing the major features of the MJO, such as its spectrum, period, intensity, eastward propagation and life cycle. Further analysis shows that those pronounced improvements in the MJO features in both BCC-CSM2-T159 and BCC-CSM2-T382 with the modified scheme are caused by transport processes of deep convective cloud water. The modified deep convection scheme enhances moisture and energy exchange from the lower troposphere to the upper troposphere around convective cloud, and promotes the convergence of moisture in the lower troposphere to the east of the MJO convection center, and then induces eastward propagation of the MJO. The comparisons between the coupled experiments and their corresponding experiments following Atmospheric Model Intercomparison Project (AMIP) simulations indicated that atmosphere–ocean interactions are also important to improve MJO simulations in the models. MJO; BCC-CSM2; Deep convection scheme; Improvement; MJO simulation
Zheng, Yueming; He, Tao; Liang, Shunlin; Ma, YichuanZheng, Y., T. He, S. Liang, Y. Ma, 2024: Deriving High Resolution Estimation of TOA Net Shortwave Radiation Over Global Land Using Data from Multiple-Geostationary Satellites. IEEE Transactions on Geoscience and Remote Sensing, 1-1. doi: 10.1109/TGRS.2024.3440329. Estimation of net shortwave radiation at the top-of-the atmosphere (Rns,TOA) at high spatial and temporal resolutions is essential for studying the Earth’s energy budget and its associated radiative forcing of natural or anthropogenic events on global or regional scales. Existing products typically use broadband sensors with coarse spatial resolution for the estimation. While narrowband sensors offer higher spatial resolution, they have a limited number of daily observations. Traditional estimation methods often necessitate atmospheric products as inputs, while inaccurate cloud and aerosol information can result in substantial estimation errors. Furthermore, geostationary satellites-based products are often developed for specific regions, with limited spatial coverage and varying accuracy due to the diverse range of satellites and algorithms used. To overcome these challenges and obtain global Rns,TOA with improved spatiotemporal resolution and accuracy, a universal approach was proposed in this study to derive hourly 3-km global Rns,TOA, which takes the advantages from radiative transfer model, machine learning algorithm, and dense observations from five geostationary satellites. Our Rns,TOA estimation shows reasonably good agreement with the Earth’s Radiant Energy System (CERES) product, with root mean square errors (RMSE) ranging from 53.43 W/m2 to 75.67 W/m2 and bias ranging from -12.78 W/m2 to -2.01 W/m2 on instantaneous scales, and the RMSE on daily scale improved by up to 6.7 W/m2 compared to those of the sinusoidal-integrated values. Our generated 3-km daily Rns,TOA exhibits highly consistency of spatial pattern with 1° CERES product at multiple temporal conditions, while providing much more spatial details. Furthermore, we find the diurnal patterns at 3km resolution differ significantly from the sinusoidal patterns at 1°, exhibiting greater variability. The difference in daytime Rns,TOA estimation between the two reaches up to 86W/m2. This significant difference reflects the unreliability of relying solely on sinusoidal pattern and the necessity of high frequency observations to estimate daily values at high spatial resolution. However, increasing the observation frequency beyond a certain point (120-min) yields only limited improvements in the accuracy of daily radiation estimates. Overall, the algorithms proposed in this study are reliable, and can be easily applied to any satellite equipped with MSG (Meteosat Second Generation)-like or more bands. This study demonstrates the feasibility of jointly using multiple geostationary satellites for, Rns,TOA estimation with high spatial and temporal resolutions. Accuracy; Atmospheric modeling; CERES; Estimation; geostationary satellite; Geostationary satellites; machine learning algorithm; Net shortwave radiation at TOA; radiative transfer model; Satellite broadcasting; Sensors; Spatial resolution
Zhong, Xiang; Dong, Xiquan; Xi, Baike; Brendecke, Jordann; Pilewskie, PeterZhong, X., X. Dong, B. Xi, J. Brendecke, P. Pilewskie, 2024: Tracing the physical signatures among the calculated global clear-sky spectral shortwave radiative flux distribution. Journal of Quantitative Spectroscopy and Radiative Transfer, 328, 109167. doi: 10.1016/j.jqsrt.2024.109167. This study utilized the high-spectral resolution radiative transfer model (MODerate resolution atmospheric TRANsmission, MODTRAN6.0.2.5) to compute global clear-sky shortwave (SW) radiative flux and compared it with NASA’s Clouds and the Earth’s Radiant Energy System (CERES) Synoptic Radiative Fluxes and Clouds (SYN1deg) product. The comparison revealed that the global distributions of clear-sky downwelling SW fluxes at the surface from the M6.0 calculations and SYN1 results are similar, with annual means of 246.51 Wm-2 and 242.42 Wm-2, respectively. Analysis further showed that most of the M6.0 calculations are slightly higher from low to mid-latitudes, particularly in the Northern Hemisphere (NH), but lower in higher latitudes compared to SYN1 results. However, these differences mostly fall within the CERES estimated uncertainty (6 Wm-2) of monthly mean clear-sky downwelling SW flux at the surface. The sensitivity of clear-sky SW/μ0 fluxes to changes in Precipitable Water Vapor (PWV), represented by the clear-sky water vapor radiative kernel, is about -0.7 Wm-2/(kgm-2) over oceans for both M6.0 and CERES SYN1 products, except for SYN1 results over the Southern Hemisphere (SH) ocean. Additionally, the zonal means of land coverage and SW/VIS/NIR albedos from M6.0 calculations indicate that VIS albedos are highest in polar regions (>60°), followed by SW and NIR albedos, while NIR albedos become highest from low to mid-latitudes ( Clear-sky shortwave flux at the surface; MODTRAN radiative transfer modeling; Water vapor radiative kernels
Ziar, HesanZiar, H., 2024: A global statistical assessment of designing silicon-based solar cells for geographical markets. Joule. doi: 10.1016/j.joule.2024.02.023. Here, we first visualize the achievable global efficiency for single-junction crystalline silicon cells and demonstrate how different regional markets have radically varied requirements for Si wafer thickness and injection level. Our findings showed that 219 g/kW of polysilicon can be conserved while producing slightly more electricity when c- Si cells are manufactured based on the global geographical market instead of standard test conditions. Then, we investigate the bifacial silicon cell and show that its optimal wafer thickness should be 1.67–2.89 times thicker than its monofacial counterpart, depending on the geographical region. Further, we study a double-junction two-terminal Si-based cell, reevaluate its theoretical limit as 42.8%, and illustrate that globally, tandem cells’ efficiency will only be slightly decreased when significantly reducing the bottom cell Si wafer thickness (−0.3%/mm). The outcomes of this study offer a blueprint to strategically design solar cells for target geographic markets, ensuring the conservation of substantial polysilicon volumes. bifacial; efficiency limit; global map; outdoor working condition; perovskite on silicon; polysilicon consumption; PV; silicon wafer thickness; single- and double-junction cells; solar photovoltaics
Akkermans, Tom; Clerbaux, NicolasAkkermans, T., N. Clerbaux, 2023: Validation of the CLARA-A3 Top-of-Atmosphere Radiative Fluxes Climate Data Record. J. Atmos. Oceanic Technol., 40(11), 1523-1539. doi: 10.1175/JTECH-D-23-0065.1. Abstract The third edition of the CM SAF Cloud, Albedo and Surface Radiation dataset from AVHRR data (CLARA-A3) contains for the first time the top-of-atmosphere products reflected solar flux (RSF) and outgoing longwave radiation (OLR), which are presented and validated using CERES, HIRS, and ERA5 reference data. The products feature an unprecedented resolution (0.25°) and time span (4 decades) and offer synergy and compatibility with other CLARA-A3 products. The RSF is relatively stable; its bias with respect to (w.r.t.) ERA5 remains mostly within ±2 W m−2. Deviations are predominantly caused by absence of either morning or afternoon satellite, mostly during the first decade. The radiative impact of the Pinatubo volcanic eruption is estimated at 3 W m−2. The OLR is stable w.r.t. ERA5 and HIRS, except during 1979–80. OLR regional uncertainty w.r.t. HIRS is quantified by the mean absolute bias (MAB) and correlates with observation density and time (satellite orbital configuration), which is optimal during 2002–16, with monthly and daily MAB of approximately 1.5 and 3.5 W m−2, respectively. Daily OLR uncertainty is higher (MAB +40%) during periods with only morning or only afternoon observations (1979–87). During the CERES era (2000–20), the OLR uncertainties w.r.t. CERES-EBAF, CERES-SYN, and HIRS are very similar. The RSF uncertainty achieves optimal results during 2002–16 with a monthly MAB w.r.t. CERES-EBAF of ∼2 W m−2 and a daily MAB w.r.t. CERES-SYN of ∼5 W m−2, and it is more sensitive to orbital configuration than is OLR. Overall, validation results are satisfactory for this first release of TOA flux products in the CLARA-A3 portfolio.
Amma, Michinari; Hayasaka, TadahiroAmma, M., T. Hayasaka, 2023: Interannual Variation in Top-of-Atmosphere Upward Shortwave Flux over the Arctic Related to Sea Ice, Snow Cover, and Land Cloud Cover in Spring and Summer. J. Climate, 36(15), 5163-5178. doi: 10.1175/JCLI-D-22-0440.1. Abstract We investigated the interannual variations in the annual mean and seasonal cycle of upward shortwave radiation at the top of the atmosphere (TOA SW↑) over the Arctic using the Clouds and the Earth’s Radiant Energy System (CERES) observation data during 2001–20. The annual mean TOA SW↑ over the Arctic showed a decreasing trend from 2001 to 2012 (−2.5 W m−2 decade−1) and had a large interannual variability after 2012. The standard deviation of detrended TOA SW↑ increased from 0.4 W m−2 in 2001–12 to 1.1 W m−2 in 2012–20. Over land, TOA SW↑ variation was related to snow cover in May; snow cover, cloud fraction, and cloud optical depth (COD) in June; and cloud fraction and COD in July. Over ocean, TOA SW↑ variation in June and July was linked to sea ice cover. TOA SW↑ variation over ocean in June and July after 2012 was highly related to the North Atlantic Oscillation (NAO). This study suggests that changes in the large annual mean TOA SW↑ variability after 2012 are explained by the timing of land snow and sea ice melt in spring and summer and cloud variability over land in summer.
Andersen, Hendrik; Cermak, Jan; Douglas, Alyson; Myers, Timothy A.; Nowack, Peer; Stier, Philip; Wall, Casey J.; Wilson Kemsley, SarahAndersen, H., J. Cermak, A. Douglas, T. A. Myers, P. Nowack, P. Stier, C. J. Wall, S. Wilson Kemsley, 2023: Sensitivities of cloud radiative effects to large-scale meteorology and aerosols from global observations. Atmospheric Chemistry and Physics, 23(18), 10775-10794. doi: 10.5194/acp-23-10775-2023. The radiative effects of clouds make a large contribution to the Earth's energy balance, and changes in clouds constitute the dominant source of uncertainty in the global warming response to carbon dioxide forcing. To characterize and constrain this uncertainty, cloud-controlling factor (CCF) analyses have been suggested that estimate sensitivities of clouds to large-scale environmental changes, typically in cloud-regime-specific multiple linear regression frameworks. Here, local sensitivities of cloud radiative effects to a large number of controlling factors are estimated in a regime-independent framework from 20 years (2001–2020) of near-global (60∘ N–60∘ S) satellite observations and reanalysis data using statistical learning. A regularized linear regression (ridge regression) is shown to skillfully predict anomalies of shortwave (R2=0.63) and longwave cloud radiative effects (CREs) (R2=0.72) in independent test data on the basis of 28 CCFs, including aerosol proxies. The sensitivity of CREs to selected CCFs is quantified and analyzed. CRE sensitivities to sea surface temperature and estimated inversion strength are particularly pronounced in low-cloud regions and generally in agreement with previous studies. The analysis of CRE sensitivities to three-dimensional wind field anomalies reflects the fact that CREs in tropical ascent regions are mainly driven by variability of large-scale vertical velocity in the upper troposphere. In the subtropics, CRE is sensitive to free-tropospheric zonal and meridional wind anomalies, which are likely to encapsulate information on synoptic variability that influences subtropical cloud systems by modifying wind shear and thus turbulence and dry-air entrainment in stratocumulus clouds, as well as variability related to midlatitude cyclones. Different proxies for aerosols are analyzed as CCFs, with satellite-derived aerosol proxies showing a larger CRE sensitivity than a proxy from an aerosol reanalysis, likely pointing to satellite aerosol retrieval biases close to clouds, leading to overestimated aerosol sensitivities. Sensitivities of shortwave CREs to all aerosol proxies indicate a pronounced cooling effect from aerosols in stratocumulus regions that is counteracted to a varying degree by a longwave warming effect. The analysis may guide the selection of CCFs in future sensitivity analyses aimed at constraining cloud feedback and climate forcings from aerosol–cloud interactions using data from both observations and global climate models.
Arsego, Vivian Bauce Machado; de Gonçalves, Luis Gustavo Gonçalves; Arsego, Diogo Alessandro; Figueroa, Silvio Nilo; Kubota, Paulo Yoshio; de Souza, Carlos RenatoArsego, V. B. M., L. G. G. de Gonçalves, D. A. Arsego, S. N. Figueroa, P. Y. Kubota, C. R. de Souza, 2023: Impact of Soil Moisture in the Monsoon Region of South America during Transition Season. Atmosphere, 14(5), 804. doi: 10.3390/atmos14050804. The land surface is an important component of numerical weather and climate forecast models due to their effect on energy–water balances and fluxes, and it is essential for forecasts on a seasonal scale. The present study aimed to understand the effects of land surface processes on initialization of seasonal forecasts in the austral spring, in particular soil moisture. We built forecasts with the Brazilian global Atmospheric Model hindcast from 2000 to 2010, with a configuration similar to those used in the operational environment. To improve it, we developed a new initial condition of the land surface using the Land Information System over South America and the Global Land Data Assimilation System for the rest of the globe and used it as the input in the forecast model. The results demonstrated that the model is sensitive to changes in soil moisture and that the new high–resolution soil moisture dataset can be used in model initialization, which resulted in an increase in the correlation of precipitation over part of South America. We also noticed an improvement in the representation of surface fluxes and an increase in soil moisture content and specific humidity at medium and low levels of the atmosphere. The analysis of the coupling between the land surface and the atmosphere showed that, for Central Brazil, the states of the continental surface define the surface fluxes. For the Amazon and La Plata Basins, the model did not correctly represent the coupling because it underestimated the soil moisture content. soil moisture; land surface; Brazilian global Atmospheric Model; initialization; seasonal forecast
Athulya, K.; Girishkumar, M. S.; McPhaden, M. J.; Kolukula, S. S.Athulya, K., M. S. Girishkumar, M. J. McPhaden, S. S. Kolukula, 2023: Seasonal Variation of the Land Breeze System in the Southwestern Bay of Bengal and Its Influence on Air-Sea Interactions. Journal of Geophysical Research: Oceans, 128(2), e2022JC019477. doi: 10.1029/2022JC019477. This study examines the seasonal variability of the Land Breeze System (LBS) in the Bay of Bengal (BoB) using hourly moored buoy data, coastal radar data, atmospheric reanalysis data, and 6-hourly satellite-based Cross-Calibrated Multi-Platform (CCMP) wind velocity data. We first provide an overview of the LBS for the entire BoB, then focus on the pronounced LBS in southwestern BoB and its impact on the near-surface current field and latent heat flux (LHF). We show that the LBS in the southwestern BoB exhibits a maximum diurnal wind speed amplitude of ∼2 m s−1 with seaward nearshore winds best developed in the morning hours. The geographical coverage is maximum in July and August and minimum in December and January. During its peak phase in July–August, the signature of the LBS in the southwestern BoB extends up to 600 km offshore, occupies ∼20% of the basin, and accounts for approximately 15% of the seasonal mean wind speed variance. The near-surface current field shows a rapid response to the diurnal wind speed variations, with an eastward current observed between 1000–1800 IST, a westward current between 1800–0800 IST, and a diurnal range of 12 cm s−1. LHF shows well-defined diurnal variability in response to diurnal LBS wind speed variability, with a morning maximum, evening minimum, and a diurnal range of 35 W m−2. We also find that the large-scale seasonal winds are the main factor in determining the annual variability in strength and geographical coverage of the LBS in the southwestern BoB. air-sea interaction; Bay of Bengal; land-sea breeze system; sub-daily variability
Ayyagari, Deepthi; Datta, Soumen; Das, Saurabh; Datta, AbhirupAyyagari, D., S. Datta, S. Das, A. Datta, 2023: Ionospheric response during Tropical Cyclones - A Brief Review on Amphan and Nisarga. Advances in Space Research, 71(6), 2799-2817. doi: 10.1016/j.asr.2022.11.026. Here, we explore the different characteristics of a possible coupling between tropospheric and ionospheric activities during the impact of tropical cyclones (TC) like Amphan and Nisarga in the Indian subcontinent. We have analyzed the effect of TCs Amphan and Nisarga on the low latitude ionosphere using the measurements from several IGS stations around India and a GPS + NavIC station in Indore, India. For the first time, this study assesses the impact of tropical cyclones on the equatorial ionosphere using both GPS and NavIC. After the landfall of TC Amphan, the VTEC analysis shows a significant drop from nominal values in both NavIC as well in GPS by 5.1 TECU and 3.6 TECU, respectively. In contrast to TC Amphan, Nisarga showed a rise in VTEC which ranged from 0.9 TECU in GPS to 1.7 - 5 TECU in NavIC satellites except for PRN6. The paper examines Outgoing Longwave Radiation as a proxy to the convective activity which may be responsible for the ionospheric variation through the generation of gravity waves. In addition, the horizontal neutral wind observations at the location of TC landfall confirm the presence of ionospheric disturbances. VTEC perturbation analysis using a band-pass filter reveals a variation in differential TEC values between ±0.4 and ±0.8 based on the IGS station measurements. This indicates that the gravity wave is one of the responsible mechanisms for the lower–upper atmospheric coupling during both cyclones. Gravity waves; Tropical cyclones; VTEC
Banerjee, Argha; Sarangi, Chandan; Rashid, Irfan; Vijay, Saurabh; Najar, Nadeem Ahmad; Chandel, Amit SinghBanerjee, A., C. Sarangi, I. Rashid, S. Vijay, N. A. Najar, A. S. Chandel, 2023: A Scaling Relation for Cryoconite Holes. Geophysical Research Letters, 50(22), e2023GL104942. doi: 10.1029/2023GL104942. Tiny cryoconite holes are commonly found on glacier surfaces. Despite a long history of research on them, their influence on glacier-scale mass balance and runoff are not well understood. We model the absorption of solar radiation at the bottom of cylindrical cryoconite holes, incorporating the three-dimensional geometry. The simulated holes achieve a limiting steady-state depth, where the daily melt rate at the bottom of the holes matches that at the glacier surface. This implies a feedback loop restricting the excess ice melt due to the presence of dark supraglacial impurities. The modeled steady-state depth scales approximately linearly with the radius, consistent with in situ observations at several glaciers across the world. Given the areal coverage and radius distribution of cryoconite holes on a glacier, this scaling yields first-order estimates of their melt contribution. cryoconite holes; glacier mass balance; glacier runoff; numerical modeling
Basso, Luana S.; Wilson, Chris; Chipperfield, Martyn P.; Tejada, Graciela; Cassol, Henrique L. G.; Arai, Egídio; Williams, Mathew; Smallman, T. Luke; Peters, Wouter; Naus, Stijn; Miller, John B.; Gloor, ManuelBasso, L. S., C. Wilson, M. P. Chipperfield, G. Tejada, H. L. G. Cassol, E. Arai, M. Williams, T. L. Smallman, W. Peters, S. Naus, J. B. Miller, M. Gloor, 2023: Atmospheric CO2 inversion reveals the Amazon as a minor carbon source caused by fire emissions, with forest uptake offsetting about half of these emissions. Atmospheric Chemistry and Physics, 23(17), 9685-9723. doi: 10.5194/acp-23-9685-2023. Tropical forests such as the Amazonian rainforests play an important role for climate, are large carbon stores and are a treasure of biodiversity. Amazonian forests have been exposed to large-scale deforestation and degradation for many decades. Deforestation declined between 2005 and 2012 but more recently has again increased with similar rates as in 2007–2008. The resulting forest fragments are exposed to substantially elevated temperatures in an already warming world. These temperature and land cover changes are expected to affect the forests, and an important diagnostic of their health and sensitivity to climate variation is their carbon balance. In a recent study based on CO2 atmospheric vertical profile observations between 2010 and 2018, and an air column budgeting technique used to estimate fluxes, we reported the Amazon region as a carbon source to the atmosphere, mainly due to fire emissions. Instead of an air column budgeting technique, we use an inverse of the global atmospheric transport model, TOMCAT, to assimilate CO2 observations from Amazon vertical profiles and global flask measurements. We thus estimate inter- and intra-annual variability in the carbon fluxes, trends over time and controls for the period of 2010–2018. This is the longest period covered by a Bayesian inversion of these atmospheric CO2 profile observations to date. Our analyses indicate that the Amazon is a small net source of carbon to the atmosphere (mean 2010–2018 = 0.13 ± 0.17 Pg C yr−1, where 0.17 is the 1σ uncertainty), with the majority of the emissions coming from the eastern region (77 % of total Amazon emissions). Fire is the primary driver of the Amazonian source (0.26 ± 0.13 Pg C yr−1), while forest carbon uptake removes around half of the fire emissions to the atmosphere (−0.13 ± 0.20 Pg C yr−1). The largest net carbon sink was observed in the western-central Amazon region (72 % of the fire emissions). We find larger carbon emissions during the extreme drought years (such as 2010, 2015 and 2016), correlated with increases in temperature, cumulative water deficit and burned area. Despite the increase in total carbon emissions during drought years, we do not observe a significant trend over time in our carbon total, fire and net biome exchange estimates between 2010 and 2018. Our analysis thus cannot provide clear evidence for a weakening of the carbon uptake by Amazonian tropical forests.
Bauer, Michael; Glenn, Tasha; Achtyes, Eric D.; Alda, Martin; Agaoglu, Esen; Altınbaş, Kürsat; Andreassen, Ole A.; Angelopoulos, Elias; Ardau, Raffaella; Aydin, Memduha; Ayhan, Yavuz; Baethge, Christopher; Bauer, Rita; Baune, Bernhard T.; Balaban, Ceylan; Becerra-Palars, Claudia; Behere, Aniruddh P.; Behere, Prakash B.; Belete, Habte; Belete, Tilahun; Belizario, Gabriel Okawa; Bellivier, Frank; Belmaker, Robert H.; Benedetti, Francesco; Berk, Michael; Bersudsky, Yuly; Bicakci, Şule; Birabwa-Oketcho, Harriet; Bjella, Thomas D.; Brady, Conan; Cabrera, Jorge; Cappucciati, Marco; Castro, Angela Marianne Paredes; Chen, Wei-Ling; Cheung, Eric Y. W.; Chiesa, Silvia; Crowe, Marie; Cuomo, Alessandro; Dallaspezia, Sara; Del Zompo, Maria; Desai, Pratikkumar; Dodd, Seetal; Etain, Bruno; Fagiolini, Andrea; Fellendorf, Frederike T.; Ferensztajn-Rochowiak, Ewa; Fiedorowicz, Jess G.; Fountoulakis, Kostas N.; Frye, Mark A.; Geoffroy, Pierre A.; Gitlin, Michael J.; Gonzalez-Pinto, Ana; Gottlieb, John F.; Grof, Paul; Haarman, Bartholomeus C. M.; Harima, Hirohiko; Hasse-Sousa, Mathias; Henry, Chantal; Hoffding, Lone; Houenou, Josselin; Imbesi, Massimiliano; Isometsä, Erkki T.; Ivkovic, Maja; Janno, Sven; Johnsen, Simon; Kapczinski, Flávio; Karakatsoulis, Gregory N.; Kardell, Mathias; Kessing, Lars Vedel; Kim, Seong Jae; König, Barbara; Kot, Timur L.; Koval, Michael; Kunz, Mauricio; Lafer, Beny; Landén, Mikael; Larsen, Erik R.; Lenger, Melanie; Licht, Rasmus W.; Lopez-Jaramillo, Carlos; MBauer, M., T. Glenn, E. D. Achtyes, M. Alda, E. Agaoglu, K. Altınbaş, O. A. Andreassen, E. Angelopoulos, R. Ardau, M. Aydin, Y. Ayhan, C. Baethge, R. Bauer, B. T. Baune, C. Balaban, C. Becerra-Palars, A. P. Behere, P. B. Behere, H. Belete, T. Belete, G. O. Belizario, F. Bellivier, R. H. Belmaker, F. Benedetti, M. Berk, Y. Bersudsky, Ş. Bicakci, H. Birabwa-Oketcho, T. D. Bjella, C. Brady, J. Cabrera, M. Cappucciati, A. M. P. Castro, W. Chen, E. Y. W. Cheung, S. Chiesa, M. Crowe, A. Cuomo, S. Dallaspezia, M. Del Zompo, P. Desai, S. Dodd, B. Etain, A. Fagiolini, F. T. Fellendorf, E. Ferensztajn-Rochowiak, J. G. Fiedorowicz, K. N. Fountoulakis, M. A. Frye, P. A. Geoffroy, M. J. Gitlin, A. Gonzalez-Pinto, J. F. Gottlieb, P. Grof, B. C. M. Haarman, H. Harima, M. Hasse-Sousa, C. Henry, L. Hoffding, J. Houenou, M. Imbesi, E. T. Isometsä, M. Ivkovic, S. Janno, S. Johnsen, F. Kapczinski, G. N. Karakatsoulis, M. Kardell, L. V. Kessing, S. J. Kim, B. König, T. L. Kot, M. Koval, M. Kunz, B. Lafer, M. Landén, E. R. Larsen, M. Lenger, R. W. Licht, C. Lopez-Jaramillo, . M, 2023: Exploratory study of ultraviolet B (UVB) radiation and age of onset of bipolar disorder. International Journal of Bipolar Disorders, 11(1), 22. doi: 10.1186/s40345-023-00303-w. Sunlight contains ultraviolet B (UVB) radiation that triggers the production of vitamin D by skin. Vitamin D has widespread effects on brain function in both developing and adult brains. However, many people live at latitudes (about > 40 N or S) that do not receive enough UVB in winter to produce vitamin D. This exploratory study investigated the association between the age of onset of bipolar I disorder and the threshold for UVB sufficient for vitamin D production in a large global sample.
Bazo, Elena; Granados-Muñoz, María J.; Román, Roberto; Bravo-Aranda, Juan Antonio; Cazorla, Alberto; Valenzuela, Antonio; González, Ramiro; Olmo, Francisco José; Alados-Arboledas, LucasBazo, E., M. J. Granados-Muñoz, R. Román, J. A. Bravo-Aranda, A. Cazorla, A. Valenzuela, R. González, F. J. Olmo, L. Alados-Arboledas, 2023: Evaluation of the vertically-resolved aerosol radiative effect on shortwave and longwave ranges using sun-sky photometer and ceilometer measurements. Atmospheric Research, 282, 106517. doi: 10.1016/j.atmosres.2022.106517. The aerosol radiative effect (ARE) is one of the atmospheric components still affected by large uncertainty. One of the causes is related to the fact that the longwave (LW) component is usually neglected, even though it is necessary for an accurate quantification of the ARE together with the shortwave component (SW). In this study we have developed a methodology based on the GAME (Global Atmospheric Model) radiative transfer model (RTM) that allows to obtain the radiative effect of the atmospheric aerosol for both spectral ranges in an automated way. The microphysical and optical properties necessary to feed the RTM have been obtained through the GRASP (Generalized Retrieval of Aerosol and Surface Properties) algorithm, with the combination of ceilometer and sun-sky photometer data. Data measured in Granada (Spain) during 2017 have been used for the evaluation and implementation of this methodology. According to the results, the ARE in the SW spectral range (ARESW) varies between 0 and − 50 Wm−2 for most of the data, whereas the ARE in the LW range (ARELW) varies between 0 and 5 Wm−2, at heights near the surface. In general, the obtained results agree with those found in the literature, with negative values in the SW range (cooling effect) and positive values in the LW (heating effect). The seasonal analysis shows that, for both components, the ARE is more important during the spring and summer seasons, when the aerosol load is greater, as expected. The analysis of the aerosol heating rate (AHR) shows positive values in the SW and negative values in the LW range. The majority of the AHRSW data varies between 0 and 1 Kd−1 during the year whereas the AHRLW does it between 0 and − 0.15 Kd−1. The seasonal analysis of the AHR shows that the greater monthly average values are found during spring, however there is not much variability along the year, with the exception of February, under the effects of an extreme dust intrusion. The mineral dust particles in this event cause an ARESW of −130 Wm−2 and an ARELW of 23 Wm−2 (ARELW/ARESW = 17%), thus pointing out that the LW component should not be neglected for coarse mode particles. Additionally, it is observed that the vertical distribution of the aerosol layers strongly influences the ARE and the AHR obtained profiles, affecting the way the atmospheric cooling/heating occurs in the vertical coordinate. Aerosol radiative properties; Ceilometer; GAME; GRASP; Longwave radiative effect; Sun-sky photometer
Braghiere, R. K.; Wang, Y.; Gagné-Landmann, A.; Brodrick, P. G.; Bloom, A. A.; Norton, A. J.; Ma, S.; Levine, P.; Longo, M.; Deck, K.; Gentine, P.; Worden, J. R.; Frankenberg, C.; Schneider, T.Braghiere, R. K., Y. Wang, A. Gagné-Landmann, P. G. Brodrick, A. A. Bloom, A. J. Norton, S. Ma, P. Levine, M. Longo, K. Deck, P. Gentine, J. R. Worden, C. Frankenberg, T. Schneider, 2023: The Importance of Hyperspectral Soil Albedo Information for Improving Earth System Model Projections. AGU Advances, 4(4), e2023AV000910. doi: 10.1029/2023AV000910. Earth system models (ESMs) typically simplify the representation of land surface spectral albedo to two values, which correspond to the photosynthetically active radiation (PAR, 400–700 nm) and the near infrared (NIR, 700–2,500 nm) spectral bands. However, the availability of hyperspectral observations now allows for a more direct retrieval of ecological parameters and reduction of uncertainty in surface reflectance. To investigate sensitivity and quantify biases of incorporating hyperspectral albedo information into ESMs, we examine how shortwave soil albedo affects surface radiative forcing and simulations of the carbon and water cycles. Results reveal that the use of two broadband values to represent soil albedo can introduce systematic radiative-forcing differences compared to a hyperspectral representation. Specifically, we estimate soil albedo biases of ±0.2 over desert areas, which can result in spectrally integrated radiative forcing divergences of up to 30 W m−2, primarily due to discrepancies in the blue (404–504 nm) and far-red (702–747 nm) regions. Furthermore, coupled land-atmosphere simulations indicate a significant difference in net solar flux at the top of the atmosphere (>3.3 W m−2), which can impact global energy fluxes, rainfall, temperature, and photosynthesis. Finally, simulations show that considering the hyperspectrally resolved soil reflectance leads to increased maximum daily temperatures under current and future CO2 concentrations. carbon cycle; Earth system models; radiative forcing; energy cycle; hyperspectral data; soil albedo
Cesana, Grégory V.; Ackerman, Andrew S.; de Guélis, Thibault Vaillant; Henderson, David S.Cesana, G. V., A. S. Ackerman, T. V. de Guélis, D. S. Henderson, 2023: Cloud-Radiation Interactions and Cloud-Climate Feedbacks From an Active-Sensor Satellite Perspective. Clouds and Their Climatic Impacts, 87-102. Clouds are ubiquitous in the troposphere. Their interactions with radiation may result in either a warming or a cooling of the Earth system and generate diverse climate feedbacks. The vertical structure of the radiative effects of clouds as well as the response of clouds to global warming (i.e., the cloud feedbacks) are inadequately constrained within the diversity of current climate models, which limits our ability to project the magnitude of future warming. In this chapter, we show how relatively recent active-sensor space-borne observations have narrowed constraints on cloud feedbacks. The value added beyond what can be retrieved from passive sensors is only just beginning to be exploited. climate sensitivity; climate models; radiation; cloud feedbacks; CloudSat-CALIPSO satellites
Cheng, Anning; Yang, FanglinCheng, A., F. Yang, 2023: Direct Radiative Effects of Aerosols on Numerical Weather Forecasts—A Comparison of Two Aerosol Datasets in the NCEP GFS. Wea. Forecasting, 38(5), 753-772. doi: 10.1175/WAF-D-22-0060.1. Abstract This study compares aerosol direct radiative effects on numerical weather forecasts made by the NCEP Global Forecast System (GFS) with two different aerosol datasets, the Optical Properties of Aerosols and Clouds (OPAC) and MERRA-2 aerosol climatologies. The underestimation of aerosol optical depth (AOD) by OPAC over northwest Africa, central to East Africa, the Arabian Peninsula, Southeast Asia, and the Indo-Gangetic Plain, and overestimation in the storm-track regions in both hemispheres are reduced by MERRA-2. Surface downward shortwave (SW) and longwave (LW) fluxes and the top-of-the-atmosphere SW and outgoing LW fluxes from model forecasts are compared with CERES satellite observations. Forecasts made with OPAC aerosols have large radiative flux biases, especially in northwest Africa and the storm-track regions. These biases are also reduced in the forecasts made with MERRA-2 aerosols. The improvements from MERRA-2 are most noticeable in the surface downward SW fluxes. GFS medium-range weather forecasts made with the MERRA-2 aerosols demonstrated slightly improved forecast accuracy of sea level pressure and precipitation over the Indian and East Asian summer monsoon region. A stronger Africa easterly jet is produced, associated with a low pressure over the east Atlantic Ocean and west of northwest Africa. Impacts on large-scale skill scores such as 500-hPa geopotential height anomaly correlation are generally positive in the Northern Hemisphere and the Pacific and North American regions in both the winter and summer seasons.
Christensen, Matthew W.; Ma, Po-Lun; Wu, Peng; Varble, Adam C.; Mülmenstädt, Johannes; Fast, Jerome D.Christensen, M. W., P. Ma, P. Wu, A. C. Varble, J. Mülmenstädt, J. D. Fast, 2023: Evaluation of aerosol–cloud interactions in E3SM using a Lagrangian framework. Atmospheric Chemistry and Physics, 23(4), 2789-2812. doi: 10.5194/acp-23-2789-2023. A Lagrangian framework is used to evaluate aerosol–cloud interactions in the U.S. Department of Energy's Energy Exascale Earth System Model (E3SM) version 1 (E3SMv1) for measurements taken at Graciosa Island in the Azores where a U.S. Department of Energy Atmosphere Radiation Measurement (ARM) site is located. This framework uses direct measurements of cloud condensation nuclei (CCN) concentration (instead of relying on satellite retrievals of aerosol optical depth) and incorporates a suite of ground-based ARM measurements, satellite retrievals, and meteorological reanalysis products that when applied to over a 1500 trajectories provides key insights into the evolution of low-level clouds and aerosol radiative forcing that is not feasible from a traditional Eulerian analysis framework. Significantly lower concentrations (40 %) of surface CCN concentration are measured when precipitation rates in 48 h back trajectories average above 1.2 mm d−1 in the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG) product. The depletion of CCN concentration when precipitation rates are elevated is nearly twice as large in the ARM observations compared to E3SMv1 simulations. The model CCN concentration bias remains significant despite modifying the autoconversion and accretion rates in warm clouds. As the clouds in trajectories associated with larger surface-based CCN concentration advect away from Graciosa Island, they maintain higher values of droplet number concentrations (Nd) over multiple days in observations and E3SM simulations compared to trajectories that start with lower CCN concentrations. The response remains robust even after controlling for meteorological factors such as lower troposphere stability, the degree of cloud coupling with the surface, and island wake effects. E3SMv1 simulates a multi-day aerosol effect on clouds and a Twomey radiative effect that is within 30 % of the ARM and satellite observations. However, the mean cloud droplet concentration is more than 2–3 times larger than in the observations. While Twomey radiative effects are similar amongst autoconversion and accretion sensitivity experiments, the liquid water path and cloud fraction adjustments are positive when using a regression model as opposed to negative when using the present-day minus pre-industrial aerosol emissions approach. This result suggests that tuning the autoconversion and accretion alone is unlikely to produce the desired aerosol susceptibilities in E3SMv1.
Chu, Wenchao; Lin, YanluanChu, W., Y. Lin, 2023: Description and Evaluation of a New Deep Convective Cloud Model Considering In-Cloud Inhomogeneity. Journal of Advances in Modeling Earth Systems, 15(2), e2022MS003119. doi: 10.1029/2022MS003119. Convections still need to be parameterized in general circulation models (GCMs) in the coming decades. Performances of GCMs are significantly influenced by the convection schemes used. In contrast to most conventional cloud models that ignore in-cloud inhomogeneities, a new convective cloud model explicitly considering in-cloud inhomogeneities is developed. The new model adopts a single bulk plume approach, but divides the plume into a series of interacting sub-plumes in order to mimic the transition from the plume core to its edges. We implemented the new cloud model in NCAR Community Atmosphere Model version 5.0 (CAM5) and evaluated its performance. Single-column tests show a stronger mass flux profile and low-level detrainment with the new model. In global simulations, the long-lasting wet bias in the tropical free troposphere of CAM5 is alleviated. Spatial pattern and intensity distribution of precipitation is improved, but the global hydrological cycle is over-enhanced. The diurnal cycle of tropical precipitation is also better captured though the precipitation peak still occurs earlier than the observations and the amplitude of the cycle tends to weaken. MJO simulation is slightly improved with the new scheme. In addition, the new cloud model generated more tropical cyclones, in better agreement with observations. CAM5; convection scheme; cloud inhomogeneity
Cordero, Raúl R.; Feron, Sarah; Damiani, Alessandro; Sepúlveda, Edgardo; Jorquera, Jose; Redondas, Alberto; Seckmeyer, Gunther; Carrasco, Jorge; Rowe, Penny; Ouyang, ZutaoCordero, R. R., S. Feron, A. Damiani, E. Sepúlveda, J. Jorquera, A. Redondas, G. Seckmeyer, J. Carrasco, P. Rowe, Z. Ouyang, 2023: Surface Solar Extremes in the Most Irradiated Region on Earth, Altiplano. Bull. Amer. Meteor. Soc., 104(6), E1206-E1221. doi: 10.1175/BAMS-D-22-0215.1. Abstract Satellites have consistently pointed to the Altiplano of the Atacama Desert as the place on Earth where the world’s highest surface irradiance occurs. This region, near the Tropic of Capricorn, is characterized by its high elevation, prevalent cloudless conditions, and relatively low concentrations of ozone, aerosols, and precipitable water. Aimed at studying the variability of the surface solar irradiance and detecting atmospheric composition changes in the Altiplano, an atmospheric observatory was set up in 2016 at the northwestern border of the Chajnantor Plateau (5,148 m MSL, 22.95°S, 67.78°W, Chile). Here, we report on the first 5 years of measurements at this observatory that establish the Altiplano as the region that receives the highest-known irradiation on Earth and illuminate the unique features of surface solar extremes at high-altitude locations. We found that the global horizontal shortwave (SW) irradiance on the plateau is on average 308 W m−2 (equivalent to an annual irradiation of 2.7 MWh m−2 yr−1, the highest worldwide). We also found that forward scattering by broken clouds often leads to intense bursts of SW irradiance; a record of 2,177 W m−2 was measured, equivalent to the extraterrestrial SW irradiance expected at approximately 0.79 astronomical units (AU) from the Sun. These cloud-driven surface solar extremes occur on the Chajnantor Plateau at a frequency, intensity, and duration not previously seen anywhere in the world, making the site an ideal location for studying the response of photovoltaic (PV) power plants to periods of enhanced SW variability.
Coss, Stephen; Durand, Michael T.; Shum, C. K.; Yi, Yuchan; Yang, Xiao; Pavelsky, Tamlin; Getirana, Augusto; Yamazaki, DaiCoss, S., M. T. Durand, C. K. Shum, Y. Yi, X. Yang, T. Pavelsky, A. Getirana, D. Yamazaki, 2023: Channel Water Storage Anomaly: A New Remotely Sensed Quantity for Global River Analysis. Geophysical Research Letters, 50(1), e2022GL100185. doi: 10.1029/2022GL100185. River channels store large volumes of water globally, critically impacting ecological and biogeochemical processes. Despite the importance of river channel storage, there is not yet an observational constraint on this quantity. We introduce a 26-year record of entirely remotely sensed volumetric channel water storage (CWS) change on 26 major world rivers. We find mainstem volumetric CWS climatology amplitude (CA) represents an appreciable amount of basin-wide terrestrial water storage variability (median 2.78%, range 0.04%–12.54% across world rivers), despite mainstem rivers themselves represent an average of just 0.2% of basin area. We find that two global river routing schemes coupled with land surface models reasonably approximate CA (within ±50%) in only 11.5% (CaMa-Flood) and 30.7% (HyMap) of rivers considered. These findings demonstrate volumetric CWS is a useful quantity for assessing global hydrological model performance, and for advancing understanding of spatial patterns in global hydrology. GRACE; hydrology; altimetery; river; storage; SWOT
Črnivec, Nina; Cesana, Grégory; Pincus, RobertČrnivec, N., G. Cesana, R. Pincus, 2023: Evaluating the Representation of Tropical Stratocumulus and Shallow Cumulus Clouds As Well As Their Radiative Effects in CMIP6 Models Using Satellite Observations. Journal of Geophysical Research: Atmospheres, 128(23), e2022JD038437. doi: 10.1029/2022JD038437. Low clouds over tropical oceans reflect a great proportion of solar radiation back to space and thereby cool the Earth, yet this phenomenon has been poorly simulated in several previous generations of climate models. The principal aim of the present study is to employ satellite observations to evaluate the representation of marine tropical low clouds and their radiative effect at the top of the atmosphere in a subset of latest climate models participating in CMIP6. We strive for regime-oriented model validation and hence introduce a qualitative approach to discriminate stratocumulus (Sc) from shallow cumulus (Cu). The novel Sc-Cu categorization has a conceptual advantage of being based on cloud properties, rather than relying on a model response to a cloud-controlling factor. We find that CMIP6 models underestimate low-cloud cover in both Sc-regions and Cu-regions of tropical oceans. A more detailed investigation of cloud biases reveals that most CMIP6 models underestimate the relative frequency of occurrence (RFO) of Sc and overestimate RFO of Cu. We further demonstrate that tropical low cloudiness in CMIP6 models remains too bright. The regime-oriented validation represents the basis for improving parameterizations of physical processes that determine the cloud cover and radiative impact of Sc and Cu, which are still misrepresented in current climate models. radiative effects; satellite observations; stratocumulus; climate model validation; marine tropical low clouds; shallow cumulus
Crueger, Traute; Schmidt, Hauke; Stevens, BjornCrueger, T., H. Schmidt, B. Stevens, 2023: Hemispheric Albedo Asymmetries across Three Phases of CMIP. J. Climate, 36(15), 5267-5280. doi: 10.1175/JCLI-D-22-0923.1. Abstract Earth’s planetary albedo shows a remarkable hemispheric symmetry. We assess to what extent CMIP models symmetrize the hemispheric clear-sky albedo asymmetry and what the role of clouds is for this. Following Voigt et al., we calculate a reference TOA reflected solar radiation considering the masking of clear-sky asymmetry by symmetric cloud contributions. We use the simple radiation model of Donohoe and Battisti to estimate this benchmark and to separate surface, aerosol, and cloud contributions to the compensation of this benchmark. In CERES, tropical clouds enhance the reference asymmetry while extratropical cloud asymmetries balance the reference asymmetry and the additional asymmetry introduced by tropical clouds. CMIP multimodel means show similar results as CERES. Clouds compensate reference asymmetries by 85% (CMIP3), 65% (CMIP5), and 78% (CMIP6) as compared with 98% for CERES. Spatial distributions of hemispheric differences indicate clear improvements across the CMIP phases. Remaining all-sky reflection asymmetries predominantly result from too-small, partly compensating cloud asymmetries: a too-weak enhancement of the reference asymmetry in the tropical Atlantic and eastern Pacific Oceans is accompanied by a too-weak compensation by extratropical clouds. Thus, tropical clouds and extratropical storm track regions are largely responsible for the compensation of hemispheric clear-sky asymmetries in CERES and CMIP, and for remaining biases in the GCMs. An unexpected result is the magnitude of model biases in the clear-sky asymmetries, which potentially condition systematic cloud biases. Experiments testing cloud-controlling factors influencing hemispheric asymmetry could help us to understand what drives hemispheric cloud differences.
Curasi, Salvatore R.; Melton, Joe R.; Humphreys, Elyn R.; Wang, Libo; Seiler, Christian; Cannon, Alex J.; Chan, Ed; Qu, BoCurasi, S. R., J. R. Melton, E. R. Humphreys, L. Wang, C. Seiler, A. J. Cannon, E. Chan, B. Qu, 2023: Evaluating the Performance of the Canadian Land Surface Scheme Including Biogeochemical Cycles (CLASSIC) Tailored to the Pan-Canadian Domain. Journal of Advances in Modeling Earth Systems, 15(4), e2022MS003480. doi: 10.1029/2022MS003480. Canada's boreal forests and tundra ecosystems are responding to unprecedented climate change with implications for the global carbon (C) cycle and global climate. However, our ability to model the response of Canada's terrestrial ecosystems to climate change is limited and there has been no comprehensive, process-based assessment of Canada's terrestrial C cycle. We tailor the Canadian Land Surface Scheme Including Biogeochemical Cycles (CLASSIC) to Canada and evaluate its C cycling performance against independent reference data. We utilize skill scores to assess model performance against reference data alongside benchmark scores that quantify the level of agreement between the reference data sets to aid in interpretation. Our results demonstrate CLASSIC's sensitivity to prescribed vegetation cover. They also show that the addition of five region-specific Plant functional types (PFTs) improves CLASSIC's skill at simulating the Canadian C cycle. CLASSIC performs well when tailored to Canada, falls within the range of the reference data sets, and meets or exceeds the benchmark scores for most C cycling processes. New region-specific land cover products, well-informed PFT parameterizations, and more detailed reference data sets will facilitate improvements to the representation of the terrestrial C cycle in regional and global land surface models. Incorporating a parameterization for boreal disturbance processes and explicitly representing peatlands and permafrost soils will improve CLASSIC's future performance in Canada and other boreal regions. This is an important step toward a comprehensive process-based assessment of Canada's terrestrial C cycle and evaluating Canada's net C balance under climate change. Arctic; boreal; Canada; carbon cycle; CLASSIC; land surface model
Das, Ripan; Chaturvedi, Rajiv Kumar; Roy, Adrija; Karmakar, Subhankar; Ghosh, SubimalDas, R., R. K. Chaturvedi, A. Roy, S. Karmakar, S. Ghosh, 2023: Warming inhibits increases in vegetation net primary productivity despite greening in India. Scientific Reports, 13(1), 21309. doi: 10.1038/s41598-023-48614-3. India is the second-highest contributor to the post-2000 global greening. However, with satellite data, here we show that this 18.51% increase in Leaf Area Index (LAI) during 2001–2019 fails to translate into increased carbon uptake due to warming constraints. Our analysis further shows 6.19% decrease in Net Primary Productivity (NPP) during 2001–2019 over the temporally consistent forests in India despite 6.75% increase in LAI. We identify hotspots of statistically significant decreasing trends in NPP over the key forested regions of Northeast India, Peninsular India, and the Western Ghats. Together, these areas contribute to more than 31% of the NPP of India (1274.8 TgC.year−1). These three regions are also the warming hotspots in India. Granger Causality analysis confirms that temperature causes the changes in net-photosynthesis of vegetation. Decreasing photosynthesis and stable respiration, above a threshold temperature, over these regions, as seen in observations, are the key reasons behind the declining NPP. Our analysis shows that warming has already started affecting carbon uptake in Indian forests and calls for improved climate resilient forest management practices in a warming world. Climate sciences; Ecology
de Ávila, Álvaro Vasconcellos Araujo; de Gonçalves, Luis Gustavo Gonçalves; Souza, Vanessa de Arruda; Alves, Laurizio Emanuel Ribeiro; Galetti, Giovanna Deponte; Maske, Bianca Muss; Getirana, Augusto; Ruhoff, Anderson; Biudes, Marcelo Sacardi; Machado, Nadja Gomes; Roberti, Débora Reginade Ávila, Á. V. A., L. G. G. de Gonçalves, V. d. A. Souza, L. E. R. Alves, G. D. Galetti, B. M. Maske, A. Getirana, A. Ruhoff, M. S. Biudes, N. G. Machado, D. R. Roberti, 2023: Assessing the Performance of the South American Land Data Assimilation System Version 2 (SALDAS-2) Energy Balance across Diverse Biomes. Atmosphere, 14(6), 959. doi: 10.3390/atmos14060959. Understanding the exchange of energy between the surface and the atmosphere is important in view of the climate scenario. However, it becomes a challenging task due to a sparse network of observations. This study aims to improve the energy balance estimates for the Amazon, Cerrado, and Pampa biomes located in South America using the radiation and precipitation forcing obtained from the Clouds and the Earth’s Radiant Energy System (CERES) and the precipitation CPTEC/MERGE datasets. We employed three surface models—Noah-MP, Community Land Model (CLSM), and Integrated Biosphere Simulator (IBIS)—and conducted modeling experiments, termed South America Land Data Assimilation System (SALDAS-2). The results showed that SALDAS-2 radiation estimates had the smallest errors. Moreover, SALDAS-2 precipitation estimates were better than the Global Land Data Assimilation System (GLDAS) in the Cerrado (MBE = −0.16) and Pampa (MBE = −0.19). Noah-MP presented improvements compared with CLSM and IBIS in 100% of towers located in the Amazon. CLSM tends to overestimate the latent heat flux and underestimate the sensible heat flux in the Amazon. Noah-MP and Ensemble outperformed GLDAS in terms latent and sensible heat fluxes. The potential of SALDAS-2 should be emphasized to provide more accurate estimates of surface energy balance. energy; modeling; surface; precipitation; balance
Devaliya, Sandeep; Bhate, Jyoti N.; Sunder Raman, Ramya; Muduchuru, Kaushik; Sharma, Arushi; Singh, Vikas; Kesarkar, Amit P.; Venkataraman, ChandraDevaliya, S., J. N. Bhate, R. Sunder Raman, K. Muduchuru, A. Sharma, V. Singh, A. P. Kesarkar, C. Venkataraman, 2023: Assessment of the impact of atmospheric aerosols and meteorological data assimilation on simulation of the weather over India during summer 2015. Atmospheric Environment, 297, 119586. doi: 10.1016/j.atmosenv.2023.119586. This study investigates the sensitivity of climate model-predicted surface radiation and surface meteorological parameters to atmospheric aerosols and meteorological data assimilation (meteorological initial and boundary conditions) utilizing the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). For this purpose, three sets of simulations including WRFChemCntrl (WRFChem without meteorological data assimilation), WRFChemDA (WRFChem with meteorological data assimilation) and WRFDA (WRF only with meteorological data assimilation) were performed over the South Asian domain. A 12-hourly cyclic 3-dimensional variational (3DVAR) meteorological data assimilation (DA) of in-situ meteorological observations was used to generate WRFChemDA and WRFDA reanalyses, during summer (March–May) 2015. The Carbon Bond Mechanism-Z (CBMZ) gas-phase chemistry with Model for Simulating Aerosol Interactions and Chemistry (MOSAIC) was selected for the chemistry simulations. A reduction in incoming shortwave radiation (∼10–60 W/m2) over the Indian landmass and a slight increase (∼10–20 W/m2) over the surrounding oceanic region due to the influence of aerosols in WRF-Chem simulations was observed, suggesting that aerosols effects, were simulated by the model successfully. These effects of aerosols were further evident in the model output of other parameters such as outgoing longwave radiation at the surface, 2-m temperature (T2), 2-m relative humidity (RH2), and planetary boundary layer height (PBLH). Our results also show that the inclusion of aerosols in the WRFDA simulations (i.e WRFChemDA) improved the prediction of incoming shortwave radiation but deteriorated some of the meteorological parameters. However, an improved agreement between model simulated radiation, T2, RH2 and PBLH and observations was evident in WRFChemDA output compared to WRFChemCntrl output, reinforcing DA induced improvements in meteorological parameters for a given model set-up. India; 3-Dimensional variational data assimilation (3DVAR); Aerosol-meteorology interactions; COALESCE project; WRF-Chem with CBMZ-MOSAIC
Devika, M. V.; Kottayil, Ajil; Koovekkallu, Prajwal; Xavier, Prince; John, VijuDevika, M. V., A. Kottayil, P. Koovekkallu, P. Xavier, V. John, 2023: Influence of monsoon extreme rainfall on the distribution of upper tropospheric humidity. International Journal of Climatology, 43(16), 7633-7645. doi: 10.1002/joc.8284. This study focuses on the changes in the upper tropospheric humidity (UTH) associated with two different extreme precipitation conditions for the period 2000–2019 over the Indian summer monsoon region. The analysis embodies UTH datasets derived from microwave sounders on-board NOAA and MetOp-A polar-orbiting satellites. The circulation characteristics in the upper troposphere are studied using the high-resolution ERA5 reanalysis data. The analysis of UTH variability over the Indian region shows a unique positive (negative) UTH anomaly patch extending from northwestern regions of India to the northern Arabian Sea for the enhanced (deficient) rainfall days over central India during the southwest monsoon period. The investigation reveals that deep convection alone does not impact the UTH variability. Rather the circulation in the upper troposphere also plays a crucial role in UTH distribution. The dynamics in the upper troposphere cause large-scale dispersal of both wet and dry air in the upper troposphere, which is linked to the strengthening/weakening of Asian monsoon anticyclone. The study indicates that monsoon extremes exhibit a distinct moisture distribution pattern in the upper troposphere, influenced by upper-level dynamics, which are associated with the intensity of the Asian monsoon anticyclone. Indian summer monsoon; extreme rainfall; Asian monsoon anticyclone; UTH
Diamond, Michael S.Diamond, M. S., 2023: Detection of large-scale cloud microphysical changes within a major shipping corridor after implementation of the International Maritime Organization 2020 fuel sulfur regulations. Atmospheric Chemistry and Physics, 23(14), 8259-8269. doi: 10.5194/acp-23-8259-2023. New regulations from the International Maritime Organization (IMO) limiting sulfur emissions from the shipping industry are expected to have large benefits in terms of public health but may come with an undesired side effect: acceleration of global warming as the climate-cooling effects of ship pollution on marine clouds are diminished. Previous work has found a substantial decrease in the detection of ship tracks in clouds after the IMO 2020 regulations went into effect, but changes in large-scale cloud properties have been more equivocal. Using a statistical technique that estimates counterfactual fields of what large-scale cloud and radiative properties within an isolated shipping corridor in the southeastern Atlantic would have been in the absence of shipping, we confidently detect a reduction in the magnitude of cloud droplet effective radius decreases within the shipping corridor and find evidence for a reduction in the magnitude of cloud brightening as well. The instantaneous radiative forcing due to aerosol–cloud interactions from the IMO 2020 regulations is estimated as O(1 W m−2) within the shipping corridor, lending credence to global estimates of O(0.1 W m−2). In addition to their geophysical significance, our results also provide independent evidence for general compliance with the IMO 2020 regulations.
Ding, Jiachen; Yang, Ping; Wang, Lifan; Oran, Elaine; Loeb, Norman G.; Smith Jr., William L.; Minnis, PatrickDing, J., P. Yang, L. Wang, E. Oran, N. G. Loeb, W. L. Smith Jr., P. Minnis, 2023: Quantification of Global Cloud Properties With Use of Spherical Harmonic Functions. Earth and Space Science, 10(3), e2022EA002718. doi: 10.1029/2022EA002718. Spherical harmonic (SH) expansion is a useful tool to study any variable that has valid values at all latitudes and longitudes. The variable can be quantified as a sum of different spherical harmonic components, which are the spherical harmonic functions multiplied by their expansion coefficients. We find that the SH components of cloud radiative effect (CRE) have correlations with El Niño-Southern Oscillation (ENSO) and the Hadley Circulation (HC). In particular, the expansion degree 2 () SH power spectrum component anomaly of CRE is strongly correlated with ENSO. The two dipole patterns appearing in the SH component anomaly map can be reasonably explained by a known mechanism of ENSO's impact on cloud properties. The and SH power spectrum components are correlated with HC intensity, whereas the and components are correlated with HC latitudinal widths. In ENSO warm and cold phases, the HC-correlated SH components have opposite anomalies, which suggests the impact of ENSO on HC. This study illustrates that the SH expansion technique provides a different perspective to study the impacts of large-scale atmospheric circulation on global cloud properties and radiative effects. cloud; cloud radiative effect; radiative transfer; spherical harmonic functions
Dommo, A.; Klutse, Nana Ama Browne; Fiedler, Stephanie; Koffi, Hubert Azoda; Vondou, Derbetini A.Dommo, A., N. A. B. Klutse, S. Fiedler, H. A. Koffi, D. A. Vondou, 2023: The seasonal cycle of cloud radiative effects over Congo Basin based on CERES observation and comparison to CMIP6 models. Atmospheric Research, 291, 106820. doi: 10.1016/j.atmosres.2023.106820. This study investigates the seasonal variability of the cloud radiative effects (CREs) over Congo Basin (CB) using 15-year observations from Clouds and the Earth's Radiant Energy System (CERES) Energy Budget and Filled (EBAF) Ed4.1 level 3b dataset involving CERES and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on board Terra and Aqua satellites. The relationships between CREs and cloud properties such as total cloud fraction (TCF), cloud top height (CTH), cloud top temperature (CTT) and cloud optical thickness (COT) are checked. An evaluation of Coupled Model Intercomparison Project (CMIP) Phase 6 in capturing the seasonal cycle of CREs as well as the magnitudes of the CREs along the seasonal cycle is also performed. This study shows a net cloud cooling effect of −8.4 W/m2 and − 43.9 W/m2 respectively at the top of the atmosphere (TOA) and at the surface, leading to a net warming effect of 35.67 W/m2 in the atmosphere. This value implies a large energy source over the Central Africa (CA) atmospheric column. The associated relationships between CREs and cloud properties show that the shortwave CRE is more sensitive to TCF and optical thickness whereas its longwave counterparts is more sensitive to CTH, CTT and COT at the TOA and in the atmosphere. All of the four CMIP6 models used in this study can capture the spatial pattern of CREs as well as their seasonal cycle but misrepresent intensity of CREs. Results also show that a better-simulated TCF considerably reduces the intensity of the annual mean underestimation in both longwave and shortwave CRE for some CMIP6 models, but not for models with overestimated shortwave CRE. Central Africa; CERES; Cloud radiative effect; CMIP6
Dong, Xiquan; Minnis, PatrickDong, X., P. Minnis, 2023: Stratus, Stratocumulus, and Remote Sensing. Fast Processes in Large-Scale Atmospheric Models, 141-199. Stratus and stratocumulus clouds comprise a critical component of the atmospheric system and have long been the subject of research from many perspectives. Observations from the surface, air, and space have provided the data necessary to quantify their occurrence, properties, and interactions with radiation, dynamics, and other atmospheric components. Such data have served to develop and improve parameterizations for characterizing these clouds in climate and weather prediction models. This chapter provides an overview of this cloud type and its role in climate with a focus upon what we have learned from ground-based and satellite remote sensing. The processes that determine the variations in these low-level cloud properties and govern where and when they occur are discussed along with factors, such as aerosols, radiation, and humidity, that influence their characteristics. Retrieval methods used to infer the properties of these stratiform clouds from satellite-based and ground-based sensors are also reviewed. Remote sensing is a critical means to further our understanding of these clouds and the processes involving them, as well as, for monitoring and predicting their role in a changing climate. Aerosol-cloud Interactions; Diurnal Variations; Remote Sensing; Stratus and Stratpcumulus clouds; Their macrophysical and Microphysical Properties
Dong, Zixiang; Ge, Jinming; Gao, Ang; Zhu, Zeen; Yan, Jialin; Mu, Qingyu; Su, Jing; Yang, Xuan; Hu, XiaoyuDong, Z., J. Ge, A. Gao, Z. Zhu, J. Yan, Q. Mu, J. Su, X. Yang, X. Hu, 2023: Comparisons of cirrus clouds and their linkages to meteorology at the SACOL and the SGP sites. Atmospheric Research, 281, 106467. doi: 10.1016/j.atmosres.2022.106467. Three-year of continuous observations collected by Ka-band zenith radars (KAZRs) at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) and the Atmospheric Radiation Measurement (ARM) Program Southern Great Plains (SGP) sites are used to explore and compare the midlatitude cirrus cloud macro-physical properties at distinct locations. Cirrus clouds over the two sites exhibit prominent differences of seasonal and diurnal variations with higher occurrence frequency and larger thickness over the SACOL than over the SGP. The linkages between the cirrus properties (e.g., frequency, thickness, height, and radiative effect) and the meteorological parameters in the upper troposphere are also examined. Cirrus clouds at the two sites have qualitatively similar relations with the meteorological factors. Large cirrus frequency and thickness are associated with large relative humidity, strong upward motion, low stability, cold temperature and positive vorticity advection in the upper troposphere. However, cirrus over the SACOL occurs more frequently than that over the SGP for a given constant meteorological condition, implying cirrus formation may be affected by different formation pathways. To explore the joint impact of atmospheric conditions on cirrus macrophysics, we combine four meteorological variables in the upper troposphere into a single factor that represents the largest atmospheric variability corresponding to the cirrus cloud development based on the principal component analysis (PCA) method. Most cirrus properties show better relations with the leading principal component (PC1) than any single meteorological indicator alone, and the changes of PC1 can well explain the annual and diurnal variations of cirrus occurrence. Meteorology; Cirrus cloud; Physical properties; Linkages；KAZR; Midlatitude sites
Du, Yihan; Wang, Tianxing; Zhou, Yu; Li, Dahui; Wang, Shiyao; Xian, YuyangDu, Y., T. Wang, Y. Zhou, D. Li, S. Wang, Y. Xian, 2023: Upscaling of longwave downward radiation from instantaneous to any temporal scale: Algorithms, validation, and comparison. International Journal of Applied Earth Observation and Geoinformation, 117, 103196. doi: 10.1016/j.jag.2023.103196. Surface longwave downward radiation (LWDR) is a key factor affecting the surface energy balance. The daily LWDR and the diurnal variations of LWDR are of great significance for studies of climate change and surface processes. How to obtain LWDR at an averaged temporal scale from instantaneous LWDR is one of the long-standing problems in the field of radiation budget from remote sensing. In this paper, two temporal upscaling methods are introduced, namely, a method based on the diurnal variations of LWDR (diurnal variation based, DVB) and a method based on random forest regression (RFR). The results reveal that: (1) The DVB method has a global hourly and daily LWDR root-mean-square error (RMSE) of less than 21 W/m2 and 15 W/m2, respectively, and the RMSE of the daily LWDR based on RFR is less than 7 W/m2; (2) When compared with four existing statistical interpolation methods, the DVB method can not only ensure the accuracy, but also can overcome the problem of missing samples and/or an abnormal samples during upscaling; (3) Except for directly predict daily LWDR, the DVB methods can also obtain more accurate LWDR diurnal variations such as hourly, half-hourly etc. The RFR method enables high-efficiency and accurate estimation of daily averaged LWDR from instantaneous measurements. Compared with existing methods and products, the proposed methods are not only efficient, but also have a superior applicability and reliable accuracy. The proposed strategies provide new ideas for the community in estimating LWDR at continuous temporal scales from remotely sensed measurements. Diurnal variation; Longwave downward radiation; Random forest regression; Statistical interpolation; Temporal upscaling
Duda, David P.; Smith Jr., William L.; Bedka, Sarah; Spangenberg, Douglas; Chee, Thad; Minnis, PatrickDuda, D. P., W. L. Smith Jr., S. Bedka, D. Spangenberg, T. Chee, P. Minnis, 2023: Impact of COVID-19-Related Air Traffic Reductions on the Coverage and Radiative Effects of Linear Persistent Contrails Over Conterminous United States and Surrounding Oceanic Routes. Journal of Geophysical Research: Atmospheres, 128(6), e2022JD037554. doi: 10.1029/2022JD037554. The radiative effects of the large-scale air traffic slowdown during April and May 2020 due to the international response to the COVID-19 pandemic are estimated by comparing the coverage (CC), optical properties, and radiative forcing of persistent linear contrails over the conterminous United States and two surrounding oceanic air corridors during the slowdown period and a similar baseline period during 2018 and 2019 when air traffic was unrestricted. The detected CC during the slowdown period decreased by an area-averaged mean of 41% for the three analysis boxes. The retrieved contrail optical properties were mostly similar for both periods. Total shortwave contrail radiative forcings (CRFs) during the slowdown were 34% and 42% smaller for Terra and Aqua, respectively. The corresponding differences for longwave CRF were 33% for Terra and 40% for Aqua. To account for the impact of any changes in the atmospheric environment between baseline and slowdown periods on detected CC amounts, the contrail formation potential (CFP) was computed from reanalysis data. In addition, a filtered CFP (fCFP) was also developed to account for factors that may affect contrail formation and visibility of persistent contrails in satellite imagery. The CFP and fCFP were combined with air traffic data to create empirical models that estimated CC during the baseline and slowdown periods and were compared to the detected CC. The models confirm that decreases in CC and radiative forcing during the slowdown period were mostly due to the reduction in air traffic, and partly due to environmental changes. contrail; COVID pandemic; radiative effects
Duffey, Alistair; Irvine, Peter; Tsamados, Michel; Stroeve, JulienneDuffey, A., P. Irvine, M. Tsamados, J. Stroeve, 2023: Solar Geoengineering in the Polar Regions: A Review. Earth's Future, 11(6), e2023EF003679. doi: 10.1029/2023EF003679. Solar geoengineering refers to proposals, including stratospheric aerosol injection (SAI), to slow or reverse climate change by reflecting away incoming sunlight. The rapid changes ongoing in the Arctic and Antarctic, and the risk of exceeding tipping points in the cryosphere within decades, make limiting such changes a plausible objective of solar geoengineering. Here, we review the impacts of SAI on polar climate and cryosphere, including the dependence of these impacts on the latitude(s) of injection, and make recommendations for future research directions. SAI would cool the polar regions and reduce many changes in polar climate under future warming scenarios. Some under-cooling of the polar regions relative to the global mean is expected under SAI without high latitude injection, due to latitudinal variation in insolation and CO2 forcing, the forcing dependence of the polar lapse rate feedback, and altered atmospheric dynamics. There are also potential limitations in the effectiveness of SAI to arrest changes in winter-time polar climate and to prevent sea-level rise from the Antarctic ice sheet. Finally, we also review the prospects for three other solar geoengineering proposals targeting the poles: marine cloud brightening, cirrus cloud thinning, and sea-ice albedo modification. Sea-ice albedo modification appears unlikely to be viable on pan-Arctic or Antarctic scales. Whether marine cloud brightening or cirrus cloud thinning would be effective in the polar regions remains uncertain. Solar geoengineering is an increasingly prominent proposal and a robust understanding of its consequences in the polar regions is needed to inform climate policy in the coming decades. climate change; polar climate; sea ice; solar geoengineering; solar radiation modification; stratospheric aerosol injection
Dunn, Robert J. H.; Miller, John B.; Willett, Kate M.; Gobron, Nadine; Ades, Melanie; Adler, Robert; Alexe, Mihai; Allan, Richard P.; Anderson, John; Anneville, Orlane; Aono, Yasuyuki; Arguez, Anthony; Arosio, Carlo; Augustine, John A.; Azorin-Molina, Cesar; Barichivich, Jonathan; Barnes, John E.; Beck, Hylke E.; Bellouin, Nicolas; Benedetti, Angela; Blagrave, Kevin; Blenkinsop, Stephen; Bock, Olivier; Bodin, Xavier; Bosilovich, Michael; Boucher, Olivier; Buechler, Dennis; Buehler, Stefan A.; Campos, Diego; Carrea, Laura; Chang, Kai-Lan; Christiansen, Hanne H.; Christy, John R.; Chung, Eui-Seok; Ciasto, Laura M.; Clingan, Scott; Coldewey-Egbers, Melanie; Cooper, Owen R.; Cornes, Richard C.; Covey, Curt; Créatux, Jean-François; Crimmins, Theresa; Cropper, Thomas; Crotwell, Molly; Culpepper, Joshua; Cusicanqui, Diego; Davis, Sean M.; Jeu, Richard A. M. de; Degenstein, Doug; Delaloye, Reynald; Dokulil, Martin T.; Donat, Markus G.; Dorigo, Wouter A.; Dugan, Hilary A.; Durre, Imke; Dutton, Geoff; Duveiller, Gregory; Estilow, Thomas W.; Estrella, Nicole; Fereday, David; Fioletov, Vitali E.; Flemming, Johannes; Foster, Michael J.; Franz, Bryan; Frith, Stacey M.; Froidevaux, Lucien; Füllekrug, Martin; Garforth, Judith; Garg, Jay; Gibbes, Badin; Goodman, Steven; Goto, Atsushi; Gruber, Alexander; Gu, Guojun; Hahn, Sebastian; Haimberger, Leopold; Hall, Bradley D.; Harris, Ian; Hemming, Deborah L.; Hirschi, Martin; Ho, Shu-peng (Ben); Holzworth, Robert; Hrbáček, Filip; Hu, Guojie; HDunn, R. J. H., J. B. Miller, K. M. Willett, N. Gobron, M. Ades, R. Adler, M. Alexe, R. P. Allan, J. Anderson, O. Anneville, Y. Aono, A. Arguez, C. Arosio, J. A. Augustine, C. Azorin-Molina, J. Barichivich, J. E. Barnes, H. E. Beck, N. Bellouin, A. Benedetti, K. Blagrave, S. Blenkinsop, O. Bock, X. Bodin, M. Bosilovich, O. Boucher, D. Buechler, S. A. Buehler, D. Campos, L. Carrea, K. Chang, H. H. Christiansen, J. R. Christy, E. Chung, L. M. Ciasto, S. Clingan, M. Coldewey-Egbers, O. R. Cooper, R. C. Cornes, C. Covey, J. Créatux, T. Crimmins, T. Cropper, M. Crotwell, J. Culpepper, D. Cusicanqui, S. M. Davis, R. A. M. d. Jeu, D. Degenstein, R. Delaloye, M. T. Dokulil, M. G. Donat, W. A. Dorigo, H. A. Dugan, I. Durre, G. Dutton, G. Duveiller, T. W. Estilow, N. Estrella, D. Fereday, V. E. Fioletov, J. Flemming, M. J. Foster, B. Franz, S. M. Frith, L. Froidevaux, M. Füllekrug, J. Garforth, J. Garg, B. Gibbes, S. Goodman, A. Goto, A. Gruber, G. Gu, S. Hahn, L. Haimberger, B. D. Hall, I. Harris, D. L. Hemming, M. Hirschi, S. Ho, R. Holzworth, F. Hrbáček, G. Hu, . H, 2023: Global Climate. Bull. Amer. Meteor. Soc., 104(9), S11-S145. doi: 10.1175/BAMS-D-23-0090.1. "Global Climate" published on 06 Sep 2023 by American Meteorological Society.
Ekman, Annica M. L.; Nygren, Eva; Pérez, Alejandro Baró; Schwarz, Matthias; Svensson, Gunilla; Bellouin, NicolasEkman, A. M. L., E. Nygren, A. B. Pérez, M. Schwarz, G. Svensson, N. Bellouin, 2023: Influence of horizontal resolution and complexity of aerosol–cloud interactions on marine stratocumulus and stratocumulus-to-cumulus transition in HadGEM3-GC3.1. Quarterly Journal of the Royal Meteorological Society, 149(755), 2049-2066. doi: 10.1002/qj.4494. Stratocumulus (Sc) clouds and stratocumulus-to-cumulus transitions (SCTs) are challenging to represent in global models and they contribute to a large spread in modeled subtropical cloud feedbacks. We evaluate the impact of increasing the horizontal model resolution (∼135, 60 and 25 km, respectively) and increasing the complexity of the aerosol–cloud interaction parameterization (interactive versus non-interactive at medium resolution) on springtime subtropical marine Sc properties and SCTs in the atmosphere-only version of HadGEM3-GC3.1. No significant impact on the spatial location of the SCT could be found between the different model versions. Increasing horizontal resolution led to small but significant increases in liquid water content and a stronger (more negative) shortwave (SW) cloud radiative effect (CRE), in particular over the southern-hemisphere Sc regions. However, for two out of the four studied regions, the stronger SW CRE also brought the model outside the range of satellite-derived values of the SW CRE. Applying non-interactive aerosols instead of interactive aerosols also led to significantly higher liquid water content and a stronger SW CRE over the southern-hemisphere Sc regions, while over the northern-hemisphere Sc regions, a competition between a substantial increase in the cloud droplet number concentration and small changes in the liquid water content resulted in a weaker SW CRE or non-significant changes. In general, using interactive instead of non-interactive aerosol–cloud interactions brought the model closer to satellite-retrieved mean values of the SW CRE. Our results suggest that increasing the horizontal resolution or the complexity of the aerosol–cloud parameterization has a small but statistically significant effect on the SW CRE of marine Sc, in particular over regions with high liquid water content. For these regions, the effect of introducing non-interactive versus interactive aerosol–cloud interactions is about as large as increasing the horizontal resolution from medium to high. general circulation model; stratocumulus; aerosol–cloud interaction; stratocumulus-to-cumulus transition
Fasullo, John; Golaz, Jean-Christophe; Caron, Julie; Rosenbloom, Nan; Meehl, Gerald; Strand, Warren; Glanville, Sasha; Stevenson, Samantha; Molina, Maria; Shields, Christine; Zhang, Chengzhu; Benedict, James; Bartoletti, TonyFasullo, J., J. Golaz, J. Caron, N. Rosenbloom, G. Meehl, W. Strand, S. Glanville, S. Stevenson, M. Molina, C. Shields, C. Zhang, J. Benedict, T. Bartoletti, 2023: An Overview of the E3SM version 2 Large Ensemble and Comparison to other E3SM and CESM Large Ensembles. EGUsphere, 1-32. doi: 10.5194/egusphere-2023-2310. Abstract. This work assesses a recently produced 21-member climate model large ensemble (LE) based on the U.S. Department of Energy’s Energy Exascale Earth System Model (E3SM) version 2 (E3SM2). The ensemble spans the historical era (1850 to 2014) and 21st Century (2015 to 2100), using the SSP370 pathway, allowing for an evaluation of the model’s forced response (FR). A companion 500-year preindustrial control simulation is used to initialize the ensemble and estimate drift. Characteristics of the LE are documented and compared against other recently produced ensembles using the E3SM version 1 (E3SM1) and Community Earth System Model (CESM) versions 1 and 2. Simulation drift is found to be smaller, and model agreement with observations is higher, in versions 2 of E3SM and CESM versus their version 1 counterparts. Shortcomings in E3SM2 include a lack of warming from the mid to late 20th Century likely due to excessive cooling influence of anthropogenic sulfate aerosols, an issue also evident in E3SM1. Associated impacts on the water cycle and energy budgets are also identified. Considerable model dependence in the FR associated with both aerosol and greenhouse gas responses is documented and E3SM2’s sensitivity to variable prescribed biomass burning emissions is demonstrated. Various E3SM2 and CESM2 model benchmarks are found to be on par with the highest performing recent generation of climate models, establishing the E3SM2 LE as an important resource for estimating climate variability and responses, though with various caveats as discussed herein. As an illustration of the usefulness of LEs in estimating the potential influence of internal variability, the observed CERES-era trend in net top-of-atmosphere flux is compared to simulated trends and found to be much larger than the FR in all LEs, with only a few members exhibiting trends as large as observed, thus motivating further study.
Feng, Taichen; Yuan, Tiangang; Cao, Jiahui; Wang, Zhikuan; Zhi, Rong; Hu, Zhiyuan; Huang, JianpingFeng, T., T. Yuan, J. Cao, Z. Wang, R. Zhi, Z. Hu, J. Huang, 2023: The influence of dust on extreme precipitation at a large city in North China. Science of The Total Environment, 901, 165890. doi: 10.1016/j.scitotenv.2023.165890. In recent decades, the Beijing-Tianjin-Hebei city cluster is experiencing rapid urbanization along with economic booming. Meanwhile, these cities are suffering the influence of extreme precipitation and dust storms. In this study, the impact of dust aerosol on extreme precipitation that occurred in Beijing during 19–21 July 2016 is investigated using both satellite retrievals and Weather Research and Forecasting model coupled to Chemistry (WRF-Chem) model simulations. Results reveal that the dust particles can increase extreme precipitation by promoting the formation of ice clouds and enhancing convections. The dust is lifted into the upper troposphere (>10 km) via strong convection and affects the physical process of precipitation after long-range transport. It further transforms the supercooled water into the middle and high levels of ice nuclei (IN). These promote the formation of ice clouds according to the decreased effective radius of IN and increased ice water path, respectively. Along with sufficient water vapor transport and strong convergence, the formation of IN could release more latent heat and further strengthen convection development. Thus, the precipitation amount in southern Beijing is almost enhanced by 40 % (>80 mm). This study will provide a deep insight into understanding the causes of urban extreme precipitation. WRF-Chem; Dust aerosol; Extreme precipitation; Urbanization
Fernández-Soler, Alejandro; González-Bárcena, David; Torralbo-Gimeno, Ignacio; Pérez-Grande, IsabelFernández-Soler, A., D. González-Bárcena, I. Torralbo-Gimeno, I. Pérez-Grande, 2023: Ascent phase convective heat transfer of a stratospheric-balloon-borne payload. Advances in Space Research. doi: 10.1016/j.asr.2023.04.010. Stratospheric ballooning flights are becoming more relevant due to these platforms can place payloads to an altitude above almost 99% of the atmosphere, where the environmental conditions are very similar to the space ones. From the thermal point of view, during the ascent phase convection is very relevant and, despite what a priori may be thought, depending on the element considered, convection may not be negligible at the float phase. With this in mind, the Thermal Analysis Support and Environment Characterization Laboratory (TASEC-Lab) was born. It is an experiment based on COTS, which consists in a 3U CubeSat-like experiment, that was launched onboard a stratospheric balloon in León (Spain) on 16th, July 2021. The upper unit of the 3U box contains a heated plate, with the aim of quantifying the relevance of convection during the flight. In this paper, the relevance of convection during the ascent phase is described, the correlation of in-flight temperature measurements with those provided by the thermal mathematical model developed in ESATAN-TMS is performed, using the air mass flow inside the cavity as a fitting parameter with a fitting error lower than 5°C during the ascent phase. ascent phase; Ballooning; convection; correlation; ESATAN-TMS; thermal control; thermal modelling
Field, Paul R.; Hill, Adrian; Shipway, Ben; Furtado, Kalli; Wilkinson, Jonathan; Miltenberger, Annette; Gordon, Hamish; Grosvenor, Daniel P.; Stevens, Robin; Van Weverberg, KwintenField, P. R., A. Hill, B. Shipway, K. Furtado, J. Wilkinson, A. Miltenberger, H. Gordon, D. P. Grosvenor, R. Stevens, K. Van Weverberg, 2023: Implementation of a double moment cloud microphysics scheme in the UK met office regional numerical weather prediction model. Quarterly Journal of the Royal Meteorological Society, n/a(n/a). doi: 10.1002/qj.4414. Cloud microphysics parametrizations control the transfer of water between phases and hydrometeor species in numerical weather prediction and climate models. As a fundamental component of weather modelling systems cloud microphysics can determine the intensity and timing of precipitation, the extent and longevity of cloud cover and its impact on radiative balance, and directly influence near surface weather metrics such as temperature and wind. In this paper we introduce and demonstrate the performance of a double moment cloud microphysical scheme (CASIM: Cloud AeroSol Interacting Microphysics) in both midlatitude and tropical settings using the same model configuration. Comparisons are made against a control configuration using the current operational single moment cloud microphysics, and CASIM configurations that use fixed in-cloud droplet number or compute cloud droplet number concentration from the aerosol environment. We demonstrate that configuring CASIM as a single moment scheme results in precipitation rate histograms that match the operational single moment microphysics. In the midlatitude setting, results indicate that CASIM performs as well as the single moment microphysics configuration, but improves certain aspects of the surface precipitation field such as greater extent of light ( CASIM; double moment microphysics; NWP
Flores, Hauke; Veyssière, Gaëlle; Castellani, Giulia; Wilkinson, Jeremy; Hoppmann, Mario; Karcher, Michael; Valcic, Lovro; Cornils, Astrid; Geoffroy, Maxime; Nicolaus, Marcel; Niehoff, Barbara; Priou, Pierre; Schmidt, Katrin; Stroeve, JulienneFlores, H., G. Veyssière, G. Castellani, J. Wilkinson, M. Hoppmann, M. Karcher, L. Valcic, A. Cornils, M. Geoffroy, M. Nicolaus, B. Niehoff, P. Priou, K. Schmidt, J. Stroeve, 2023: Sea-ice decline could keep zooplankton deeper for longer. Nature Climate Change, 1-9. doi: 10.1038/s41558-023-01779-1. As Arctic sea ice deteriorates, more light enters the ocean, causing largely unknown effects on the ecosystem. Using an autonomous biophysical observatory, we recorded zooplankton vertical distribution under Arctic sea ice from dusk to dawn of the polar night. Here we show that zooplankton ascend into the under-ice habitat during autumn twilight, following an isolume of 2.4 × 10−4 W m−2. We applied this trigger isolume to CMIP6 model outputs accounting for incoming radiation after sunset and before sunrise of the polar night. The models project that, in about three decades, the total time spent by zooplankton in the under-ice habitat could be reduced by up to one month, depending on geographic region. This will impact zooplankton winter survival, the Arctic foodweb, and carbon and nutrient fluxes. These findings highlight the importance of biological processes during the twilight periods for predicting change in high-latitude ecosystems. Cryospheric science; Phenology; Biooceanography; Marine biology
Fonseca, Ricardo; Francis, Diana; Nelli, Narendra; Cherif, CharfeddineFonseca, R., D. Francis, N. Nelli, C. Cherif, 2023: Regional atmospheric circulation patterns driving consecutive fog events in the United Arab Emirates. Atmospheric Research, 282, 106506. doi: 10.1016/j.atmosres.2022.106506. In this study, the link between the occurrence of consecutive fog days in the United Arab Emirates (UAE) and the associated synoptic-scale circulation is investigated. This is particularly pertinent, as such a link may provide an important predictive skill for a phenomenon that has a pronounced impact on road and air traffic but is still poorly simulated by numerical models. A cluster analysis of all consecutive fog days from January 1983 to December 2021 indicated that the positive phase of the East Atlantic/Western Russia teleconnection pattern, Eastern Pacific La Nina events, and the circumglobal wavenumber 5 pattern promote the occurrence of multiple fog days in the UAE. The fog's radiative impacts, as estimated from satellite data, revealed that the fog in the UAE is more optically thick than that observed elsewhere. A trend analysis over the period 1983 to 2021 revealed that consecutive fog events have become more frequent and longer-lasting but less intense (i.e., associated with higher values of visibility). The fog's spatial extent over the UAE at its mature stage has also decreased over time. An analysis of the trends in the surface and top of atmosphere (TOA) radiative fluxes indicated that over the period 2000–2021, the fog clouds have likely become less reflective, with a statistically significant decrease in the surface downward shortwave and TOA upward longwave radiation fluxes. Long-term measurements of fog microphysics in the region are needed to better understand the variability in the properties of the fog cloud droplets. Atmospheric circulation; Trends; Boreal winter; Fog; Radiative impact; Teleconnections
Francis, Diana; Fonseca, Ricardo; Nelli, Narendra; Bozkurt, Deniz; Cuesta, Juan; Bosc, EmmanuelFrancis, D., R. Fonseca, N. Nelli, D. Bozkurt, J. Cuesta, E. Bosc, 2023: On the Middle East's severe dust storms in spring 2022: Triggers and impacts. Atmospheric Environment, 296, 119539. doi: 10.1016/j.atmosenv.2022.119539. Large amounts of dust in the air can disrupt daily activities and pose a threat to human health. In May 2022, consecutive major dust storms occurred over the Middle East resulting in severe environmental, social and health impacts. In this study, we investigate the exceptional factors driving these storms and the effects of the dust clouds. Using a combination of satellite, in-situ and reanalysis datasets, we identify the atmospheric triggers for the occurrence of these severe dust storms, characterize their three-dimensional structure and evaluate the dust radiative impact. The dust emission was promoted by density currents emanating from deep convection over Turkey. The convective systems were triggered by cut-off lows from mid-latitudes fed by moisture from African atmospheric rivers. Data from the Infrared Atmospheric Sounding Interferometer (IASI) showed that the dust clouds were transported southward at 4 km in altitudes but sunk to ground levels when they reached the southern Arabian Peninsula due to strong subsidence. At a station in coastal UAE, the dust caused a 350 W m−2 drop in the surface downward shortwave flux and a 70 W m−2 increase in the longwave one during the dust episodes. This contributed to a 9 °C increase in nighttime temperatures which exacerbated the effects of the heat for the population. The newly highlighted mechanism for dust emission in the Middle East, in which a cut-off low interacts with an atmospheric river, as well as direct observations of the dust impact on the radiative budget can contribute to reducing associated uncertainties in climate models. Atmospheric rivers; Cut-off low; Density currents; Drylands; Dust storms; IASI
Franzke, Christian L. E.; Harnik, NiliFranzke, C. L. E., N. Harnik, 2023: Long-Term Trends of the Atmospheric Circulation and Moist Static Energy Budget in the JRA-55 Reanalysis. J. Climate, 36(9), 2959-2984. doi: 10.1175/JCLI-D-21-0724.1. Abstract The atmospheric circulation response to global warming is an important problem that is theoretically still not well understood. This is a particular issue since climate model simulations provide uncertain, and at times contradictory, projections of future climate. In particular, it is still unclear how a warmer and moister atmosphere will affect midlatitude eddies and their associated poleward transport of heat and moisture. Here we perform a trend analysis of three main components of the global circulation—the zonal-mean state, eddies, and the net energy input into the atmosphere—and examine how they relate in terms of a moist static energy budget for the JRA-55 reanalysis data. A particular emphasis is made on understanding the contribution of moisture to circulation trends. The observed trends are very different between the hemispheres. In the Southern Hemisphere there is an overall strengthening and during boreal summer, also a poleward shifting, of the jet stream, the eddies, and the meridional diabatic heating gradients. Correspondingly, we find an overall strengthening of the meridional gradients of the net atmospheric energy input. In the Northern Hemisphere, the trend patterns are more complex, with the dominant signal being a clear boreal winter Arctic amplification of positive trends in lower-tropospheric temperature and moisture, as well as a significant weakening of both bandpass and low-pass eddy heat and moisture fluxes. Consistently, surface latent and sensible heat fluxes, upward and downward longwave radiation, and longwave cloud radiative fluxes at high latitudes show significant trends. However, radiative fluxes and eddy fluxes are inconsistent, suggesting data assimilation procedures need to be improved. Significance Statement We use a long-term reanalysis dataset to get an overall view of the changes in the global circulation and its role in transporting moist static energy from the equator to the poles. We do this by examining the trends in its three main components—the zonal means, the eddies, and the net energy input into the atmosphere. We find that in the Southern Hemisphere, there is an overall strengthening of the eddies, their poleward energy fluxes, and correspondingly the meridional gradients of the net atmospheric energy input. In the Northern Hemisphere, though the pattern is more complex, there is an overall weakening of the eddies and poleward eddy fluxes, and of the meridional gradients of the net atmospheric energy input, consistent with Arctic warming.
Furtado, K.; Tsushima, Y.; Field, P. R.; Rostron, J.; Sexton, D.Furtado, K., Y. Tsushima, P. R. Field, J. Rostron, D. Sexton, 2023: The Relationship Between the Present-Day Seasonal Cycles of Clouds in the Mid-Latitudes and Cloud-Radiative Feedback. Geophysical Research Letters, 50(15), e2023GL103902. doi: 10.1029/2023GL103902. We show that the seasonal cycles of clouds over the mid-latitude oceans in the Northern Hemisphere are predictors of the responses of clouds to increasing sea-surface temperatures globally. These regions are therefore “natural laboratories” in which the processes responsible for low-cloud feedbacks on global scales are observed as seasonal changes in local cloud properties. We use an ensemble of configurations of a global-climate model to show that the sensitivities of cloud-radiative anomalies to surface temperature and lower-tropospheric stability in the “laboratory” regions predict the models' global cloud-radiative feedbacks. Models with greater changes in low-clouds between seasons are shown to have stronger negative feedbacks in the mid-latitudes, and stronger positive feedbacks from the subtropical stratocumulus. The biases in the simulated seasonal cycles, compared to observations, imply that both feedbacks are too weak in the model. The consequences of this for configuring our model to have a lower climate sensitivity are discussed.
Gao, Lu; Huang, Qian; Yao, Suxiang; Sun, TianleGao, L., Q. Huang, S. Yao, T. Sun, 2023: Numerical study of the precipitation diurnal variation and its relationship with cloud radiative heating during the Meiyu period in 2020. Meteorology and Atmospheric Physics, 136(1), 3. doi: 10.1007/s00703-023-01000-0. Based on hourly rain gauge observation, cloud amount, and radiative fluxes data from the Clouds and the Earth’s Radiant Energy System (CERES) and ECMWF Reanalysis v5 (ERA5) dataset, the precipitation process during the Meiyu period in the middle and lower reaches of the Yangtze River in 2020 was simulated in WRF to reveal the influence of cloud radiative heating process on the diurnal variation of precipitation using multiple cloud microphysical schemes. The statistical evaluation of three microphysical parameterization schemes shows that the two-moment scheme WDM6 is more reasonable than the other two schemes in simulating the precipitation distribution, central intensity, and cloud characteristic distribution. There are significant bimodal characteristics in the diurnal variation of precipitation during the Meiyu period by analyzing the observation data. The numerical experiment accurately simulated the time and magnitude of the early morning peak in the heavy rain area but failed to reproduce the peak in the late afternoon, resulting in a false weak rainfall accumulation. The comparison of simulation results with the observed cloud macroscale and microscale characteristics revealed that the reason for the deviation of precipitation simulation was closely related to the inaccurate description of cloud microphysical quantities. The lack of ice phase cloud droplets led to excessively strong radiative heating rate at 200–500 hPa, resulting in anomalous warming in the mid-upper troposphere. Meanwhile, the cold advection at 850 hPa led to anomalous cooling in the lower troposphere, increasing atmospheric stability and further inhibiting the development of the afternoon thermal convection process.
Gautam, Ritesh; Patel, Piyushkumar N.; Singh, Manoj K.; Liu, Tianjia; Mickley, Loretta J.; Jethva, Hiren; DeFries, Ruth S.Gautam, R., P. N. Patel, M. K. Singh, T. Liu, L. J. Mickley, H. Jethva, R. S. DeFries, 2023: Extreme Smog Challenge of India Intensified by Increasing Lower Tropospheric Stability. Geophysical Research Letters, 50(11), e2023GL103105. doi: 10.1029/2023GL103105. Extreme smog in India widely impacts air quality in late autumn and winter months. While the links between emissions, air quality and health impacts are well-recognized, the association of smog and its intensification with climatic trends in the lower troposphere, where aerosol pollution and its radiative effects manifest, are not understood well. Here we use long-term satellite data to show a significant increase in aerosol exceedances over northern India, resulting in sustained atmospheric warming and surface cooling trends over the last two decades. We find several lines of evidence suggesting these aerosol radiative effects have induced a multidecadal (1980–2019) strengthening of lower tropospheric stability and increase in relative humidity, leading to over fivefold increase in poor visibility days. Given this crucial aerosol-radiation-meteorological feedback driving the smog intensification, results from this study would help inform mitigation strategies supporting stronger region-wide measures, which are critical for solving the smog challenge in India. aerosols; India; meteorology; satellite data; smog
Gavrouzou, Maria; Hatzianastassiou, Nikos; Korras-Carraca, Marios-Bruno; Stamatis, Michalis; Lolis, Christos; Matsoukas, Christos; Michalopoulos, Nikos; Vardavas, IliasGavrouzou, M., N. Hatzianastassiou, M. Korras-Carraca, M. Stamatis, C. Lolis, C. Matsoukas, N. Michalopoulos, I. Vardavas, 2023: Three-Dimensional Distributions of the Direct Effect of anExtended and Intense Dust Aerosol Episode (16–18 June 2016) over the Mediterranean Basin on Regional Shortwave Radiation, Atmospheric Thermal Structure, and Dynamics. Applied Sciences, 13(12), 6878. doi: 10.3390/app13126878. In the present study, we used the FORTH deterministic spectral Radiation Transfer Model (RTM) to estimate detailed three-dimensional distributions of the Direct Radiative Effects (DREs) and their consequent modification of the thermal structure of the regional atmosphere during an intense dust episode that took place from 16 to 18 June 2016 over the Mediterranean Basin (MB). The RTM operated on a 3-hourly temporal and 0.5 × 0.625° spatial resolution, using 3-D aerosol optical properties (i.e., aerosol optical depth, single scattering albedo, and asymmetry parameter) and other surface and atmospheric properties from the MERRA-2 reanalysis and cloud properties (i.e., cloud amount, cloud optical depth, and cloud top height) from the ISCCP-H dataset. The model ran with and without dust aerosols, yielding the upwelling and downwelling solar fluxes at the top of the atmosphere, in the atmosphere, and at the Earth’s surface as well as at 50 levels in the atmosphere. The dust direct radiative effect (DDRE) was estimated as the difference between the two (one taking into account all aerosol types and one taking into account all except for dust aerosols) flux outputs. The atmospheric heating rates and subsequent convection induced by dust radiative absorption were calculated at 50 levels to determine how the DDRE affects the thermal structure and dynamics of the atmosphere. The results showed that such a great and intense dust transport event significantly reduces the net surface solar radiation over the MB (by up to 62 W/m2 on a daily mean basis, and up to 200 W/m2 on an hourly basis, at 12:00 UTC) while increasing the atmospheric solar absorption (by up to 72 W/m2 daily and 187 W/m2 hourly, at 12:00 UTC). At the top of the atmosphere, both heating (over desert areas) and cooling (over oceanic and other continental areas) are observed due to the significantly different surface albedos. Transported dust causes considerable heating of the region’s atmosphere, which becomes maximum at altitudes where the dust loadings are highest (0.14 K/3 h on 17 June 2016, 12:00 UTC, at 3–5 km above sea level). The dust solar absorption and heating induce a buoyancy as strong as 0.014 m/s2, resulting in considerable changes in vertical air motions and possibly contributing to the formation of middle- and high-level clouds over the Mediterranean Basin. radiative forcing; heating rates; buoyancy; dust episodes; Mediterranean Basin
Ge, Jun; Huang, Xin; Zan, Beilei; Qiu, Bo; Cao, Yipeng; Guo, WeidongGe, J., X. Huang, B. Zan, B. Qiu, Y. Cao, W. Guo, 2023: Local surface cooling from afforestation amplified by lower aerosol pollution. Nature Geoscience, 16(9), 781-788. doi: 10.1038/s41561-023-01251-x. Afforestation can play a key role in local climate mitigation by influencing local temperature through changes in land surface properties. Afforestation impacts depend strongly on the background climate, with contrasting effects observed across geographical locations, seasons and levels of greenhouse gas-induced warming. Meanwhile, atmospheric aerosols, which are a critical factor influencing regional climate, have varied substantially in recent decades and will continue to change. However, the impacts of aerosol changes on the local effects of afforestation remain unknown. Here, using multiple emissions scenario-based simulations, we show that lower anthropogenic emissions can modulate the local effects of afforestation through modifications in the surface energy balance. If current anthropogenic emissions are reduced to preindustrial levels, afforestation can produce additional cooling effects of up to 0.4 °C. The cooling effects of afforestation are projected to be most strongly affected in China if strict control measures on air pollution are adopted in the future. Our results demonstrate that the enhanced cooling effects of afforestation could partially counteract the warming effect of air quality control, with implications for countries that face the dual challenges of clean air and climate mitigation. Climate change; Environmental impact; Climate-change mitigation; Atmospheric chemistry
Ghausi, Sarosh Alam; Tian, Yinglin; Zehe, Erwin; Kleidon, AxelGhausi, S. A., Y. Tian, E. Zehe, A. Kleidon, 2023: Radiative controls by clouds and thermodynamics shape surface temperatures and turbulent fluxes over land. Proceedings of the National Academy of Sciences, 120(29), e2220400120. doi: 10.1073/pnas.2220400120. Land surface temperatures (LSTs) are strongly shaped by radiation but are modulated by turbulent fluxes and hydrologic cycling as the presence of water vapor in the atmosphere (clouds) and at the surface (evaporation) affects temperatures across regions. Here, we used a thermodynamic systems framework forced with independent observations to show that the climatological variations in LSTs across dry and humid regions are mainly mediated through radiative effects. We first show that the turbulent fluxes of sensible and latent heat are constrained by thermodynamics and the local radiative conditions. This constraint arises from the ability of radiative heating at the surface to perform work to maintain turbulent fluxes and sustain vertical mixing within the convective boundary layer. This implies that reduced evaporative cooling in dry regions is then compensated for by an increased sensible heat flux and buoyancy, which is consistent with observations. We show that the mean temperature variation across dry and humid regions is mainly controlled by clouds that reduce surface heating by solar radiation. Using satellite observations for cloudy and clear-sky conditions, we show that clouds cool the land surface over humid regions by up to 7 K, while in arid regions, this effect is absent due to the lack of clouds. We conclude that radiation and thermodynamic limits are the primary controls on LSTs and turbulent flux exchange which leads to an emergent simplicity in the observed climatological patterns within the complex climate system.
Ghosh, Sushovan; Kumar, Alok; Ganguly, Dilip; Dey, SagnikGhosh, S., A. Kumar, D. Ganguly, S. Dey, 2023: India's Photovoltaic Potential amidst Air Pollution and Land Constraints. iScience, 107856. doi: 10.1016/j.isci.2023.107856. India aims for ambitious solar energy goal to fulfil its climate commitment but limited studies on solar resource assessment considering both environmental and land availability constraints. Present work attempts to address this issue using satellite-derived air pollution, radiation, and land use data over the Indian region. Surface insolation over India has been decreasing at a rate of -0.29±0.19 Wm-2 y-1 between 2001 to 2018. Solar resources over nearly 98%, 40%, and 39% of the Indian landmass are significantly impacted by aerosols, clouds, and both aerosols and clouds respectively. Only 29.3% of the Indian landmass is presently suitable for effective solar photovoltaic harnessing, but this is further declining by -0.21% annually, causing a presumptive loss of 50 GW solar potential, translating 75 TWh power generation. Lowering two decades of aerosol burden can make 8% additional landmass apt for photovoltaic use. Alleviating aerosol-induced dimming can fast-track India's solar energy expansion. India; Global dimming and brightening; Global Human Settlement Layer (GHSL); Normalized Difference Vegetation Index (NDVI); Solar energy resources; Solar photovoltaic (SPV)
Goodwin, Philip; Williams, Richard G.Goodwin, P., R. G. Williams, 2023: On the Arctic Amplification of surface warming in a conceptual climate model. Physica D: Nonlinear Phenomena, 454, 133880. doi: 10.1016/j.physd.2023.133880. Over the last century Earth’s surface temperatures have warmed by order 1 K as a global average, but with significant variation in latitude: there has been most surface warming at high Northern latitudes, around 3 times more than in low latitude regions (termed Arctic Amplification), while there has been least warming over the Southern Ocean. Many contributing processes have been suggested to explain this asymmetrical latitudinal warming pattern, but quantification of the contributing factors responsible remains elusive. Complex general circulation climate models can reproduce similar asymmetrical patterns of warming, but it can be difficult to interpret the contributing processes. Meanwhile, idealised conceptual energy balance climate models have been able to reproduce a general polar amplification of warming whose origins can be interpreted, but this warming is often symmetrical across both hemispheres and may not be responsible for the real-world pattern. Here, we use a conceptual Energy Balance Model, with imposed closures for initial horizontal diffusivity and cloudiness drawing upon observational constraints and including temperature-dependent diffusivity and a sub-surface ocean heat reservoir, to show that the magnitude of present-day Arctic Amplification may arise through relatively simple thermodynamic (Clausius–Clapeyron) and radiative (climate feedback) processes. The current asymmetry between hemispheric warming may arise due to the transient heat transport up through the base of the surface ocean mixed layer from the slow-responding deep ocean to the fast-responding surface ocean being dominated by upwelling in the Southern Ocean. It should be noted that the processes identified here are not a unique in offering a potential solution, and so significant, or dominant, roles for dynamical processes remain plausible explanations for Arctic Amplification. Arctic amplification; Conceptual climate modelling; Energy balance climate models; Polar amplification
Gristey, Jake J.; Schmidt, K. Sebastian; Chen, Hong; Feldman, Daniel R.; Kindel, Bruce C.; Mauss, Joshua; van den Heever, Mathew; Hakuba, Maria Z.; Pilewskie, PeterGristey, J. J., K. S. Schmidt, H. Chen, D. R. Feldman, B. C. Kindel, J. Mauss, M. van den Heever, M. Z. Hakuba, P. Pilewskie, 2023: Angular sampling of a monochromatic, wide-field-of-view camera to augment next-generation Earth radiation budget satellite observations. Atmospheric Measurement Techniques, 16(15), 3609-3630. doi: 10.5194/amt-16-3609-2023. Earth radiation budget (ERB) satellite observations require conversion of the measured radiance, which is a remotely sensed quantity, to a derived irradiance, which is the relevant energy balance quantity routinely used in modeling and analysis of the climate system. The state-of-the-art approach for radiance-to-irradiance conversion taken by the Clouds and the Earth's Radiant Energy System (CERES) benefits from the exhaustive sampling of radiance anisotropy by multiple CERES instruments across many years. Unfortunately, the CERES approach is not easily extended to new ERB spectral channels that lack previous sampling, such as the “split-shortwave” planned to be part of the next-generation ERB mission Libera. As an alternative approach, the capability of a monochromatic, wide-field-of-view camera to provide dense angular sampling in a much shorter time frame is assessed. We present a general concept for how this can be achieved and quantify the proficiency of a camera to provide rapid angular distribution model (ADM) generation for the new Libera ultraviolet and visible (VIS) sub-band. A single mid-visible camera wavelength (555 nm) is shown to be ideal for representing the VIS sub-band, requiring only basic scene stratification for 555 nm to VIS conversion. Synthetic camera sampling with realistic operating constraints also demonstrates that the angular radiance field of various scenes can be well populated within a single day of sampling, a notable advance over existing approaches. These results provide a path for generating observationally based VIS ADMs with minimal lag time following Libera's launch. Coupled with efforts to utilize a camera for scene identification, this may also pave the way for future ERB satellite systems to develop stand-alone irradiance products for arbitrary sets of spectral channels, opening up new measurement and science possibilities.
Gupta, Mayank; Wild, Martin; Ghosh, SubimalGupta, M., M. Wild, S. Ghosh, 2023: Analytical framework based on thermodynamics to estimate spatially distributed surface energy fluxes from remotely sensed radiations. Remote Sensing of Environment, 295, 113659. doi: 10.1016/j.rse.2023.113659. The Limited surface observations of turbulent heat fluxes result in incomplete knowledge about the surface energy balance that drives the climate system. The highly parameterized surface energy balance models suffer from significant uncertainties. Remote sensing information of incoming and outgoing radiation fluxes are important input variables for turbulent heat flux models, though analytical solutions of surface energy budget from these variables are yet to be derived. Here, we developed a novel, purely physics-based analytical method grounded on the thermodynamic principle of maximum power. The approach derives the total turbulent heat flux only from the four inputs of incoming and outgoing longwave and shortwave radiations at the land surface, which are available from remotely sensed satellite data. The proposed approach does not use any parameterization, unlike the existing surface energy balance models, and hence does not suffer from uncertainty due to the same. We validated our methodology with 102 eddy covariance observation stations around the globe with different land use land covers from FLUXNET2015 and available urban datasets. Based on monthly averages of the total turbulent flux estimates for the eddy covariance sites, we observed root-mean-square error (RMSE) of 23.2 ± 10.9 Wm−2, a mean bias error (MBE) of 11.9 ± 13.1 Wm−2 and R2 value of 0.86 ± 0.15. Using the satellite observations of radiation fluxes from CERES at a spatial resolution of 10, we obtained the global flux field of total turbulent flux (QJ) and land surface heat storage (ΔQs) fluxes. On validation of QJ with FLUXNET sites for six grids for different land use land cover, we found RMSE of 20.1 ± 7 Wm−2, MBE of 14.4 ± 9 Wm−2 and R2 value of 0.96 ± 0.02. Further, from the evaporative stress factor of GLEAM, which is based on microwave remotely sensed vegetation optical depth and root zone soil moisture, we have obtained spatially distributed global estimates of Sensible(H) and latent heat (LE). In addition, our analytical estimates address the distribution of residual energy associated with the surface energy balance closure problem driven by the land use land cover. The theoretical estimates of all surface energy balance components from remote sensing based observations will improve our understanding of surface warming for different land use land covers across the globe. Radiation balance; Satellite based radiation; Surface eneregy balance; Thermodynamics
Hadas, Or; Datseris, George; Blanco, Joaquin; Bony, Sandrine; Caballero, Rodrigo; Stevens, Bjorn; Kaspi, YohaiHadas, O., G. Datseris, J. Blanco, S. Bony, R. Caballero, B. Stevens, Y. Kaspi, 2023: The role of baroclinic activity in controlling Earth’s albedo in the present and future climates. Proceedings of the National Academy of Sciences, 120(5), e2208778120. doi: 10.1073/pnas.2208778120. Clouds are one of the most influential components of Earth’s climate system. Specifically, the midlatitude clouds play a vital role in shaping Earth’s albedo. This study investigates the connection between baroclinic activity, which dominates the midlatitude climate, and cloud-albedo and how it relates to Earth’s existing hemispheric albedo symmetry. We show that baroclinic activity and cloud-albedo are highly correlated. By using Lagrangian tracking of cyclones and anticyclones and analyzing their individual cloud properties at different vertical levels, we explain why their cloud-albedo increases monotonically with intensity. We find that while for anticyclones, the relation between strength and cloudiness is mostly linear, for cyclones, in which clouds are more prevalent, the relation saturates with strength. Using the cloud-albedo strength relationships and the climatology of baroclinic activity, we demonstrate that the observed hemispheric difference in cloud-albedo is well explained by the difference in the population of cyclones and anticyclones, which counter-balances the difference in clear-sky albedo. Finally, we discuss the robustness of the hemispheric albedo symmetry in the future climate. Seemingly, the symmetry should break, as the northern hemisphere’s storm track response differs from that of the southern hemisphere due to Arctic amplification. However, we show that the saturation of the cloud response to storm intensity implies that the increase in the skewness of the southern hemisphere storm distribution toward strong storms will decrease future cloud-albedo in the southern hemisphere. This complex response explains how albedo symmetry might persist even with the predicted asymmetric hemispheric change in baroclinicity under climate change.
Hakuba, Maria Z.; Reynerson, Charles M.; Quadrelli, Marco B.; Wiese, David N.; Mccullough, Christopher; Landerer, Felix W.; Stephens, Graeme L.Hakuba, M. Z., C. M. Reynerson, M. B. Quadrelli, D. N. Wiese, C. Mccullough, F. W. Landerer, G. L. Stephens, 2023: Measuring Earth's Energy Imbalance via Radiation Pressure Accelerations Experienced in Orbit: Initial Simulations for “Space Balls”. 2023 IEEE Aerospace Conference, 1-10. doi: 10.1109/AERO55745.2023.10115678. The direct measurement of Earth's radiative Energy Imbalance (EEI) from space is a challenge for state-of-the-art radiometric observing systems. Current spaceborne radiometers measure the individual shortwave (Solar incoming and Earth reflected solar radiation) and longwave (Earth emitted thermal radiation) components of Earth's energy balance with unprecedented stability, but with calibration errors that are too large to determine the absolute magnitude of global mean EEI or net radiative flux, respectively, as the components' residual. Best estimates of multi-year (2005–2020) EEI are derived from temporal changes in planetary heat content, predominantly ocean heat content, and amount to 0.9 Wm−2. To monitor EEI directly from space, we propose an independent approach based on accelerometry that measures non-gravitational radial accelerations induced by radiation pressure. To provide requirements for a near-spherical “Space Balls” spacecraft and mission design, we develop a simulation environment using JPL's Mission Analysis, Operations, and Navigation Toolkit Environment (MONTE) software libraries and present-day radiative fluxes from the Clouds and Earth's Radiant Energy System (CERES). At its current initial stage, the toolset allows us to simulate accelerations acting on a spherical spacecraft due to solar radiation pressure, Earth's reflected shortwave (albedo) and emitted longwave radiation, as well as due to aerodynamic force. Induced accelerations as well as their sensitivity to mean orbit altitude and spacecraft absorptivity agree well with back-of the-envelope calculations and previous simulations that assess the role of radiation pressure accelerations for orbital drift. Future investigations will expand the MONTE-based simulation environment with additional shape and confounding force models. Preliminary simulations with an integrated spacecraft dynamics model suggest that the main confounding accelerations for a non-perfect, faceted sphere are related to Yarkovsky, aerodynamic force and relativistic effects, which will have to be mitigated to facilitate a high-accuracy EEI measurement from space. Earth; Extraterrestrial measurements; Sea measurements; Space vehicles; Energy measurement; Accelerometers; Force
Hao, Dalei; Bisht, Gautam; Gu, Yu; Leung, L. RubyHao, D., G. Bisht, Y. Gu, L. R. Leung, 2023: Regional and Teleconnected Impacts of Solar Radiation-Topography Interaction Over the Tibetan Plateau. Geophysical Research Letters, 50(23), e2023GL106293. doi: 10.1029/2023GL106293. Solar radiation-topography interaction plays an important role in surface energy balance over the Tibetan Plateau (TP). However, the impacts of such interaction over the TP on climate locally and in the Asian regions remain unclear. This study uses the Energy Exascale Earth System Model (E3SM) to evaluate the regional and teleconnected impacts of solar radiation-topography interaction over the TP. Land-atmosphere coupled experiments show that topography regulates the surface energy balance, snow processes, and surface climate over the TP across seasons. Accounting for solar radiation-topography interaction improves E3SM simulation of surface climate. The winter cold bias in air temperature decreases from −4.57 to −3.79 K, and the wet bias in summer precipitation is mitigated in southern TP. The TP's solar radiation-topography interaction further reduces the South and East Asian summer precipitation biases. Our results demonstrate the topographic roles in regional climate over the TP and highlight its teleconnected climate impacts. Tibetan Plateau; E3SM; East Asian summer monsoon; surface energy balance; radiation-topography interaction; teleconnected impacts
Heim, Christoph; Leutwyler, David; Schär, ChristophHeim, C., D. Leutwyler, C. Schär, 2023: Application of the Pseudo-Global Warming Approach in a Kilometer-Resolution Climate Simulation of the Tropics. Journal of Geophysical Research: Atmospheres, 128(5), e2022JD037958. doi: 10.1029/2022JD037958. Clouds over tropical oceans are an important factor in the Earth's response to increased greenhouse gas concentrations, but their representation in climate models is challenging due to the small-scale nature of the involved convective processes. We perform two 4-year-long simulations at kilometer-resolution (3.3 km horizontal grid spacing) with the limited-area model COSMO over the tropical Atlantic on a 9,000 × 7,000 km2 domain: A control simulation under current climate conditions driven by the ERA5 reanalysis, and a climate change scenario simulation using the Pseudo-Global Warming approach. We compare these results to the changes projected in the CMIP6 scenario ensemble. Validation shows a good representation of the annual cycle of albedo, in particular for trade-wind clouds, even compared to the ERA5 reanalysis. Also, the vertical structure and annual cycle of the intertropical convergence zone (ITCZ) is accurately simulated, and the simulation does not suffer from the double ITCZ problem commonly present in global climate models (GCMs). The response to global warming differs between the COSMO simulation and the analyzed GCMs. While both exhibit an overall weakening of the Hadley circulation, the narrowing of the ITCZ (known as the deep-tropics squeeze) is not so pronounced in the kilometer-resolution simulation, likely due to the absence of a double ITCZ bias. Also, there is a more pronounced intensification of the ITCZ at the equator in the kilometer-resolution COSMO simulation, and a stronger associated increase in the anvil cloud fraction. ITCZ; climate simulation; tropical clouds; Hadley cell; kilometer-resolution model; tropical low clouds
Hill, P. G.; Holloway, C. E.; Byrne, M. P.; Lambert, F. H.; Webb, M. J.Hill, P. G., C. E. Holloway, M. P. Byrne, F. H. Lambert, M. J. Webb, 2023: Climate Models Underestimate Dynamic Cloud Feedbacks in the Tropics. Geophysical Research Letters, 50(15), e2023GL104573. doi: 10.1029/2023GL104573. Cloud feedbacks are the leading cause of uncertainty in climate sensitivity. The complex coupling between clouds and the large-scale circulation in the tropics contributes to this uncertainty. To address this problem, the coupling between clouds and circulation in the latest generation of climate models is compared to observations. Significant biases are identified in the models. The implications of these biases are assessed by combining observations of the present day with future changes predicted by models to calculate observationally constrained feedbacks. For the dynamic cloud feedback (i.e., due to changes in circulation), the observationally constrained values are consistently larger than the model-only values. This is due to models failing to capture a nonlinear minimum in cloud brightness for weakly descending regimes. Consequently, while the models consistently predict that these regimes increase in frequency in association with a weakening tropical circulation, they underestimate the positive cloud feedback associated with this increase.
Horner, George; Gryspeerdt, EdwardHorner, G., E. Gryspeerdt, 2023: The evolution of deep convective systems and their associated cirrus outflows. Atmospheric Chemistry and Physics, 23(22), 14239-14253. doi: 10.5194/acp-23-14239-2023. Tropical deep convective clouds, particularly their large cirrus outflows, play an important role in modulating the energy balance of the Earth's atmosphere. Whilst the cores of these deep convective clouds have a significant short-wave (SW) cooling effect, they dissipate quickly. Conversely, the thin cirrus that flow from these cores can persist for days after the core has dissipated, reaching hundreds of kilometres in extent. These thin cirrus have a potential for large warming in the tropics. Understanding the evolution of air parcels from deep convection, clouds along these trajectories, and how they change in response to anthropogenic emissions is therefore important to understand past and future climate change. This work uses a novel approach to investigate the evolution of tropical convective clouds by introducing the concept of “time since convection” (TSC). This is used to build a composite picture of the lifecycle of air parcels from deep convection. Cloud properties are a strong function of TSC, showing decreases in the optical thickness, cloud-top height, and cloud fraction over time, thereby driving the latitudinal structure of cloudiness. After an initial dissipation of the convective core, changes in thin cirrus cloud amount were seen beyond 200 h from convection. Changes in cloud are shown to be a strong function of TSC and not simply reflective of latitudinal changes as air moves from the tropics to the extratropics. Finally, in the initial stages of convection there was a large net negative cloud radiative effect (CRE). However, once the convective core had dissipated, the sign of the CRE flipped and there was a sustained net warming CRE beyond 120 h from the convective event. Changes are present in the cloud properties long after the main convective activities have dissipated, signalling the need to continue further analysis at longer timescales than previously studied.
Horvath, Sean; Boisvert, Linette; Parker, Chelsea; Webster, Melinda; Taylor, Patrick; Boeke, Robyn; Fons, Steven; Stewart, J. ScottHorvath, S., L. Boisvert, C. Parker, M. Webster, P. Taylor, R. Boeke, S. Fons, J. S. Stewart, 2023: Database of daily Lagrangian Arctic sea ice parcel drift tracks with coincident ice and atmospheric conditions. Scientific Data, 10(1), 73. doi: 10.1038/s41597-023-01987-6. Since the early 2000s, sea ice has experienced an increased rate of decline in thickness, extent and age. This new regime, coined the ‘New Arctic’, is accompanied by a reshuffling of energy flows at the surface. Understanding of the magnitude and nature of this reshuffling and the feedbacks therein remains limited. A novel database is presented that combines satellite observations, model output, and reanalysis data with sea ice parcel drift tracks in a Lagrangian framework. This dataset consists of daily time series of sea ice parcel locations, sea ice and snow conditions, and atmospheric states, including remotely sensed surface energy budget terms. Additionally, flags indicate when sea ice parcels travel within cyclones, recording cyclone intensity and distance from the cyclone center. The quality of the ice parcel database was evaluated by comparison with sea ice mass balance buoys and correlations are high, which highlights the reliability of this database in capturing the seasonal changes and evolution of sea ice. This database has multiple applications for the scientific community; it can be used to study the processes that influence individual sea ice parcel time series, or to explore generalized summary statistics and trends across the Arctic. Cryospheric science; Physics
Hsu, Wei-Ching; Kooperman, Gabriel J.; Hannah, Walter M.; Reed, Kevin A.; Akinsanola, Akintomide A.; Pendergrass, Angeline G.Hsu, W., G. J. Kooperman, W. M. Hannah, K. A. Reed, A. A. Akinsanola, A. G. Pendergrass, 2023: Evaluating Mesoscale Convective Systems Over the US in Conventional and Multiscale Modeling Framework Configurations of E3SMv1. Journal of Geophysical Research: Atmospheres, 128(23), e2023JD038740. doi: 10.1029/2023JD038740. Organized mesoscale convective systems (MCSs) contribute a significant amount of precipitation in the Central and Eastern US during spring and summer, which impacts the availability of freshwater and flooding events. However, current global Earth system models cannot capture MCSs well and misrepresent the statistics of precipitation in the region. In this study, we investigate the representation of MCSs in three configurations of the Energy Exascale Earth System Model (E3SMv1) by tracking individual storms based on outgoing longwave radiation using a new application of TempestExtremes. Our results indicate that conventional parameterizations of convection, implemented in both low (LR; ∼150 km) and high (HR; ∼25 km) resolution configurations, fail to capture almost all MCS-like events, in-part because they underestimate high-level cloud ice associated with deep convection. On the other hand, the multiscale modeling framework (MMF; cloud-resolving models embedded in each grid-column of ∼150 km resolution E3SMv1) configuration represents MCSs and their annual cycle better. Nevertheless, relative to observations, the E3SMv1-MMF spatial distribution of MCSs and associated precipitation is shifted eastward, and the diurnal timing is lagged. A comparison between the large-scale environment in E3SMv1-MMF and ERA5 reanalysis suggests that the biases during the summer in E3SMv1-MMF are associated with biases in low-level humidity and meridional moisture transport within the low-level jet. The fact that conventional parameterizations of convection, even with high-resolution, cannot capture MCSs over the US suggests that methods with explicit representation of kilometer-scale convective organization, such as the MMF, may be necessary for improving the simulation of these convective systems. multiscale modeling framework; E3SMv1; mesoscale convection systems
Hu, Liang; Ritchie, Elizabeth A.; Scott Tyo, J.Hu, L., E. A. Ritchie, J. Scott Tyo, 2023: Quantifying the cooling effect of tropical cyclone clouds on the climate system. npj Climate and Atmospheric Science, 6(1), 1-10. doi: 10.1038/s41612-023-00433-z. The net effect on the upwelling radiation caused by tropical cyclone clouds is calculated over a 20-year global data set, and the corresponding contribution to the earth energy balance is analyzed. Tropical cyclone clouds are shown on average to increase the upwelling radiation at the top of the atmosphere compared with the background non-tropical-cyclone-cloud climatology. This increase in upwelling radiation provides an overall cooling effect on the climate system because the increased reflected shortwave radiation (cooling) outweighs the decreased emitted longwave radiation (warming). While the effect neglects the (likely considerable) contribution due to tropical cyclone drying, the amount of cooling by clouds alone represents a considerable fraction of the excess warming energy in the climate system. Thus, any future change in tropical cyclone activity has the potential to impact the overall energy balance if it substantially alters this total. The seasonal and geographic distribution of warming and cooling effects, and the diurnal dynamics that impact whether any particular cyclone is net cooling or net warming are discussed in this study. Climate change; Atmospheric dynamics
Hu, Wenting; Duan, Anmin; Wu, Guoxiong; Mao, Jiangyu; He, BianHu, W., A. Duan, G. Wu, J. Mao, B. He, 2023: Quasi-Biweekly Oscillation of Surface Sensible Heating over the Central-Eastern Tibetan Plateau and Its Relationship with Spring Rainfall in China. J. Climate, 36(19), 6917-6936. doi: 10.1175/JCLI-D-22-0892.1. Abstract This study examines the characteristics and phase evolution of the quasi-biweekly oscillation of surface sensible heating (SH) over the central-eastern Tibetan Plateau (CETP) during spring. The mechanism connecting CETP SH to spring rainfall in China on the quasi-biweekly time scale is further investigated. Results show that the dominant mode of quasi-biweekly CETP SH presents a monopole pattern, in which the peak leads the maximum of the quasi-biweekly rainfall in the middle and lower reaches of the Yangtze River (MLYR) and South China by approximately 5 and 7 days, respectively. As an upper-level Rossby wave train propagates eastward, an anomalous center of convergence moves to the CETP, which leads to a strong downdraft and reduced cloud cover. The resultant elevated shortwave radiation input and drier soil conditions are favorable for the CETP SH quasi-biweekly oscillation to enter a positive phase. When reaching its peak, the CETP SH efficiently heats the lower atmosphere, resulting in a local updraft. Due to the “SH-driven air pump” effect, abundant water vapor is transported from the oceans to China. A lower-layer southerly anomaly on the east side of the TP develops into an anomalous cyclonic circulation via the effect of topographic friction, which leads to the expansion of the positive potential vorticity anomaly and the maximum of the quasi-biweekly rainfall in the MLYR. Further southeastward propagation of the wave train leads to a shift in the rainfall anomaly center to South China. These findings suggest that the CETP monopole SH warming could be a good indicator for predicting intraseasonal variations in spring rainfall over China.
Huang, Han; Huang, YiHuang, H., Y. Huang, 2023: Diagnosing the Radiation Biases in Global Climate Models Using Radiative Kernels. Geophysical Research Letters, 50(13), e2023GL103723. doi: 10.1029/2023GL103723. Radiation energy balance at the top of the atmosphere (TOA) is a critical boundary condition for the Earth climate. It is essential to validate it in the global climate models (GCM) on both global and regional scales. However, the comparison of overall radiation field is known to conceal compensating errors. Here we use a new set of radiative kernels to diagnose the radiation biases caused by different geophysical variables in the GCMs of the Coupled Model Intercomparison Project. We find although clouds remain a primary cause of radiation biases, the radiation biases caused by non-cloud variables are of comparable magnitudes. Many GCMs have a cold air temperature bias and a moist tropospheric humidity bias, which lead to considerable biases in TOA radiation budget but are compensated by cloud biases. These findings signify the importance of validating the GCM simulations in terms of both the overall and component radiation biases. CMIP6; energy budget; radiation biases
Hulsman, P.; Keune, J.; Koppa, A.; Schellekens, J.; Miralles, D. G.Hulsman, P., J. Keune, A. Koppa, J. Schellekens, D. G. Miralles, 2023: Incorporating Plant Access to Groundwater in Existing Global, Satellite-Based Evaporation Estimates. Water Resources Research, 59(8), e2022WR033731. doi: 10.1029/2022WR033731. Groundwater is an important water source for evaporation, especially during dry conditions. Despite this recognition, plant access to groundwater is often neglected in global evaporation models. This study proposes a new, conceptual approach to incorporate plant access to groundwater in existing global evaporation models, and analyses the groundwater contribution to evaporation globally. To this end, the Global Land Evaporation Amsterdam Model (GLEAM) is used. The new GLEAM-Hydro model relies on the linear reservoir assumption for modeling groundwater flow, and introduces a transpiration partitioning approach to estimate groundwater contributions. Model estimates are validated globally against field observations of evaporation, soil moisture, discharge and groundwater level for the time period 2015–2021, and compared to a regional groundwater model. Representing groundwater access influences evaporation in 22% of the continental surface. Globally averaged, evaporation increases by 2.5 mm year−1 (0.5% of terrestrial evaporation), but locally, evaporation can increase up to 245.2 mm year−1 (149.7%). The groundwater contribution to transpiration is highest for tall vegetation under dry conditions due to more frequent groundwater access. The temporal dynamics of the simulated evaporation improve across 75% of the stations where groundwater is a relevant water source. The skill of the model for variables such as soil moisture and runoff remains similar to GLEAM v3. The proposed approach enables a more realistic process representation of evaporation under water-limited conditions in satellite-data driven models such as GLEAM, and sets the ground to assimilate satellite gravimetry data in the future. satellite observations; evaporation; GLEAM; groundwater
Ibrahim, Hamed D.; Sun, YunfangIbrahim, H. D., Y. Sun, 2023: Sea Surface Cooling by Rainfall Modulates Earth’s Heat Energy Flow. J. Climate, 36(15), 5125-5141. doi: 10.1175/JCLI-D-22-0735.1. Abstract Characterizing the physical processes that modulate the continuous partitioning of heat between the ocean and overlying atmosphere is important for monitoring the subsequent flow of the heat accumulating in the ocean because of anthropogenic climate change. Oceanic rainfall sensible heat flux (Qp), whereby rainwater cools the sea surface, is computed and compared to the sea surface heat energy balance in the 60°N–60°S region. Contrary to popular belief, the results show that Qp is large at both short and long time scales, accounting for up to 22.5% of sea surface net heat flux around the 5.8°N line of latitude, 10.1% in the tropical 20°N–20°S region, and 5.7% in the global 60°N–60°S region. In the mixed layer of these same regions, area-average temperature change owing to a 10-yr accumulated Qp is up to −2.6° and −1.4°C, respectively. Further analysis reveals a previously unspecified rainfall–evaporation negative feedback between successive evaporation–rainfall cycles at the sea surface. The Qp depresses sea surface temperature and thus inhibits evaporation (latent heat flux), which in turn inhibits rainfall owing to decrease in water vapor supply to the atmosphere. The decrease in sea surface temperature also inhibits heat conduction from the ocean to the atmosphere (sensible heat flux). To compensate for the weaker latent and sensible heat fluxes, sea surface upward longwave radiation flux strengthens. We conclude that Qp acts like a modulator of Earth’s heat energy flow by controlling the partition of upper-ocean heat energy and the cycle of heat flow in the ocean and between the ocean and the atmosphere. Significance Statement Upper-ocean heat energy is partitioned between the ocean and the overlying atmosphere. Characterizing the physical processes that modulate this continuous partitioning is important for monitoring the subsequent flow of the heat energy accumulating in the ocean because of anthropogenic climate change. Here, we identify sea surface cooling by rainwater (oceanic rainfall sensible heat flux) as a modulator of this partition: this cooling depresses sea surface temperature and thus inhibits evaporation (latent heat flux), which in turn inhibits rainfall owing to the decrease in water vapor supply to the atmosphere; depressing sea surface temperature also inhibits heat conduction from the ocean to the atmosphere (sensible heat flux). To compensate for the weaker latent and sensible heat fluxes, sea surface upward longwave radiation flux strengthens.
Ivanova, I. Yu.; Shakirov, V. A.; Khalgaeva, N. A.Ivanova, I. Y., V. A. Shakirov, N. A. Khalgaeva, 2023: Accuracy Analysis of Estimates of Total Solar Radiation in Databases and Regression Models for Eastern Russia. Geography and Natural Resources, 44(3), 278-283. doi: 10.1134/S1875372823030058. The efficient use of solar energy requires an accurate assessment of the incoming solar radiation. The study involves comparing the accuracy of monthly means of the global solar radiation flux from the ERA5 reanalysis database, the SYN1deg satellite-based observation database, climate reference data, and data of regression models for seven settlements in the east of Russia. The study employs two well-known regression models, including parameters of extraterrestrial solar radiation, total cloudiness, air humidity, minimum and maximum air temperature, atmospheric pressure, and a new regression model, which additionally includes parameters of low-level cloudiness and sun elevation angle. The accuracy of databases and regression models is evaluated by comparing their data with ground measurements of weather stations. The indices of the mean absolute error, root-mean-square error, and mean bias error are calculated. The comparison shows that the data of climate reference books for the period from 1937–1957 to 1980 have the smallest deviation from the estimates of the monthly mean flux of global solar radiation for 2006–2020 at most of the points discussed. The ERA5 monthly mean estimates of the global solar radiation flux are more accurate than the SYN1deg data at five of the seven points considered. The new regression model proposed in the study makes it possible to provide greater accuracy of monthly estimates of the global solar radiation flux compared to the data of SYN1deg and ERA5 for most of the points considered. satellite data; reanalysis; solar radiation; accuracy comparison; regression model
Jenkins, Matthew T.; Dai, Aiguo; Deser, ClaraJenkins, M. T., A. Dai, C. Deser, 2023: Seasonal Variations and Spatial Patterns of Arctic Cloud Changes in Association with Sea Ice Loss during 1950–2019 in ERA5. J. Climate, 37(2), 735-754. doi: 10.1175/JCLI-D-23-0117.1. Abstract The dynamic and thermodynamic mechanisms that link retreating sea ice to increased Arctic cloud amount and cloud water content are unclear. Using the fifth generation of the ECMWF Reanalysis (ERA5), the long-term changes between years 1950–79 and 1990–2019 in Arctic clouds are estimated along with their relationship to sea ice loss. A comparison of ERA5 to CERES satellite cloud fractions reveals that ERA5 simulates the seasonal cycle, variations, and changes of cloud fraction well over water surfaces during 2001–20. This suggests that ERA5 may reliably represent the cloud response to sea ice loss because melting sea ice exposes more water surfaces in the Arctic. Increases in ERA5 Arctic cloud fraction and water content are largest during October–March from ∼950 to 700 hPa over areas with significant (≥15%) sea ice loss. Further, regions with significant sea ice loss experience higher convective available potential energy (∼2–2.75 J kg−1), planetary boundary layer height (∼120–200 m), and near-surface specific humidity (∼0.25–0.40 g kg−1) and a greater reduction of the lower-tropospheric temperature inversion (∼3°–4°C) than regions with small (
Jiang, Xianan; Su, Hui; Jiang, Jonathan H.; Neelin, J. David; Wu, Longtao; Tsushima, Yoko; Elsaesser, GregoryJiang, X., H. Su, J. H. Jiang, J. D. Neelin, L. Wu, Y. Tsushima, G. Elsaesser, 2023: Muted extratropical low cloud seasonal cycle is closely linked to underestimated climate sensitivity in models. Nature Communications, 14(1), 5586. doi: 10.1038/s41467-023-41360-0. A large spread in model estimates of the equilibrium climate sensitivity (ECS), defined as the global mean near-surface air-temperature increase following a doubling of atmospheric CO2 concentration, leaves us greatly disadvantaged in guiding policy-making for climate change adaptation and mitigation. In this study, we show that the projected ECS in the latest generation of climate models is highly related to seasonal variations of extratropical low-cloud fraction (LCF) in historical simulations. Marked reduction of extratropical LCF from winter to summer is found in models with ECS > 4.75 K, in accordance with the significant reduction of extratropical LCF under a warming climate in these models. In contrast, a pronounced seasonal cycle of extratropical LCF, as supported by satellite observations, is largely absent in models with ECS Projection and prediction; Climate and Earth system modelling
Jiang, Xiaoyu; Wu, Chenglai; Chen, Bing; Wang, Weiyi; Liu, Xiaohong; Lin, Zhaohui; Han, ZhenyuJiang, X., C. Wu, B. Chen, W. Wang, X. Liu, Z. Lin, Z. Han, 2023: Exploring a variable-resolution approach for simulating the regional climate in Southwest China using VR-CESM. Atmospheric Research, 292, 106851. doi: 10.1016/j.atmosres.2023.106851. The complex terrain of Southwest China (SWC) leads to large spatial variations in its climate, which are challenging for climate models to accurately simulate. In this study, we perform a high-resolution simulation (∼0.125°) using the Variable-Resolution Community Earth System Model (VR-CESM) for SWC and evaluate the model's ability to simulate the spatiotemporal variations of precipitation and temperature in SWC. The VR-CESM results are compared with observations, as well as the simulation of the standard version of CESM at a quasi-uniform ∼1° resolution. We find that the high-resolution VR-CESM model better portrays the fine distribution of precipitation and temperature than the coarse resolution CESM model (∼1°). VR-CESM also shows some improvements in the seasonal variations of precipitation in SWC. VR-CESM reduces the overestimulation of precipitation in the Hengduan Mountains and surrounding areas. For heavy precipitation (daily precipitation >25 mm), VR-CESM better simulates its frequency than CESM (∼1°). Overall, VR-CESM has good simulation capabilities for the spatiotemporal evolution of precipitation and the occurrence frequency of extreme precipitation in SWC. Therefore, the VR-CESM model is a useful tool for understanding the mechanism driving the climate changes in SWC in the past and for projecting future climate changes in the region. High-resolution simulation; Precipitation; Southwest China; VR-CESM
Jiang, Yun; Tang, Bo-Hui; Zhang, HuanyuJiang, Y., B. Tang, H. Zhang, 2023: Estimation of downwelling surface longwave radiation for all-weather skies from FengYun-4A geostationary satellite data. International Journal of Remote Sensing, 1-14. doi: 10.1080/01431161.2023.2170194. Fengyun-4A (FY-4A) is the latest generation of China’s geostationary satellite. The Advanced Geosynchronous Radiation Imager (AGRI) onboard FY-4A can provide high-precision, high-frequency observation data, which makes a new possibility for estimating the downwelling surface longwave radiation (DSLR) with high spatial and temporal resolution. This work presents a new method for estimating DSLRs under all-sky conditions using a genetic algorithm–artificial neural network (GA-ANN) algorithm based on brightness temperature (BT) from the FY-4A AGRI infrared channels and near-surface air temperature and dew point temperature from ERA5 reanalysis data. Based on the verification results of two independent observation sites, it is shown that the bias and RMSE are - 4.31 W/m2 and 35.28 W/m2, respectively. Compared the CERES SYN all-sky DSLR product with the DSLR estimated by the new method, the bias and RMSE are 0.86 W/m2 and 26.87 W/m2, respectively, and the new method has a higher spatial resolution (4 km), which can display more details of spatial variation. all-sky; Downwelling surface longwave radiation; ERA5; FY-4A
Jin, Daeho; Kim, Daehyun; Son, Seok-Woo; Oreopoulos, LazarosJin, D., D. Kim, S. Son, L. Oreopoulos, 2023: QBO deepens MJO convection. Nature Communications, 14(1), 4088. doi: 10.1038/s41467-023-39465-7. The underlying mechanism that couples the Quasi-Biennial Oscillation (QBO) and the Madden-Julian oscillation (MJO) has remained elusive, challenging our understanding of both phenomena. A popular hypothesis about the QBO-MJO connection is that the vertical extent of MJO convection is strongly modulated by the QBO. However, this hypothesis has not been verified observationally. Here we show that the cloud-top pressure and brightness temperature of deep convection and anvil clouds are systematically lower in the easterly QBO (EQBO) winters than in the westerly QBO (WQBO) winters, indicating that the vertical growth of deep convective systems within MJO envelopes is facilitated by the EQBO mean state. Moreover, the deeper clouds during EQBO winters are more effective at reducing longwave radiation escaping to space and thereby enhancing longwave cloud-radiative feedback within MJO envelopes. Our results provide robust observational evidence of the enhanced MJO activity during EQBO winters by mean state changes induced by the QBO. Atmospheric dynamics; Climate and Earth system modelling
Jin, Daeho; Kramer, Ryan J.; Oreopoulos, Lazaros; Lee, DongminJin, D., R. J. Kramer, L. Oreopoulos, D. Lee, 2023: ENSO Disrupts Boreal Winter CRE Feedback. J. Climate, 37(2), 585-603. doi: 10.1175/JCLI-D-23-0282.1. Abstract Twenty years of satellite-based cloud and radiation observations allow us to examine the observed cloud radiative effect (CRE) feedback (i.e., CRE change per unit change in global mean surface temperature). By employing a decomposition method to separate the contribution of “internal changes” and “relative-frequency-of-occurrence (RFO) changes” of distinct cloud regime (CR) groups, notable seasonal contrasts of CRE feedback characteristics emerge. Boreal winter CRE feedback is dominated by the positive shortwave CRE (SWCRE) feedback of oceanic low-thick clouds, due to their decreasing RFO as temperature rises. This signal is most likely due to El Niño–Southern Oscillation (ENSO) activity. When ENSO signals are excluded, boreal winter CRE feedback becomes qualitatively similar to the boreal summer feedback, where several CR groups contribute to the total CRE feedback more evenly. Most CR groups’ CRE feedbacks largely come from changing RFO (e.g., the predominant transition from oceanic cumulus to broken clouds and more occurrences of higher convective clouds with warming temperature). At the same time, low-thick and broken clouds experience optical thinning and decreasing cloud fraction, and these features are more prominent in boreal summer than winter. Overall, the seasonally asymmetric patterns of CRE feedback, primarily due to ENSO, introduce complexity in assessments of CRE feedback.
Jin, Yubin; Hu, Shijie; Ziegler, Alan D.; Gibson, Luke; Campbell, J. Elliott; Xu, Rongrong; Chen, Deliang; Zhu, Kai; Zheng, Yan; Ye, Bin; Ye, Fan; Zeng, ZhenzhongJin, Y., S. Hu, A. D. Ziegler, L. Gibson, J. E. Campbell, R. Xu, D. Chen, K. Zhu, Y. Zheng, B. Ye, F. Ye, Z. Zeng, 2023: Energy production and water savings from floating solar photovoltaics on global reservoirs. Nature Sustainability, 1-10. doi: 10.1038/s41893-023-01089-6. Growing global energy use and the adoption of sustainability goals to limit carbon emissions from fossil fuel burning are increasing the demand for clean energy, including solar. Floating photovoltaic (FPV) systems on reservoirs are advantageous over traditional ground-mounted solar systems in terms of land conservation, efficiency improvement and water loss reduction. Here, based on multiple reservoir databases and a realistic climate-driven photovoltaic system simulation, we estimate the practical potential electricity generation for FPV systems with a 30% coverage on 114,555 global reservoirs is 9,434 ± 29 TWh yr−1. Considering the proximity of most reservoirs to population centres and the potential to develop dedicated local power systems, we find that 6,256 communities and/or cities in 124 countries, including 154 metropolises, could be self-sufficient with local FPV plants. Also beneficial to FPV worldwide is that the reduced annual evaporation could conserve 106 ± 1 km3 of water. Our analysis points to the huge potential of FPV systems on reservoirs, but additional studies are needed to assess the potential long-term consequences of large systems. Hydrology; Solar energy; Water resources
Johnson, G. C.; Lumpkin, R.; Atkinson, C.; Biló, Tiago; Boyer, Tim; Bringas, Francis; Carter, Brendan R.; Cetinić, Ivona; Chambers, Don P.; Chan, Duo; Cheng, Lijing; Chomiak, Leah; Cronin, Meghan F.; Dong, Shenfu; Feely, Richard A.; Franz, Bryan A.; Gao, Meng; Garg, Jay; Gilson, John; Goni, Gustavo; Hamlington, Benjamin D.; Hobbs, W.; Hu, Zeng-Zhen; Huang, Boyin; Ishii, Masayoshi; Jevrejeva, Svetlana; Johns, W.; Landschützer, Peter; Lankhorst, Matthias; Leuliette, Eric; Locarnini, Ricardo; Lyman, John M.; McPhaden, Michael J.; Merrifield, Mark A.; Mishonov, Alexey; Mitchum, Gary T.; Moat, Ben I.; Mrekaj, Ivan; Nerem, R. Steven; Purkey, Sarah G.; Qiu, Bo; Reagan, James; Sato, Katsunari; Schmid, Claudia; Sharp, Jonathan D.; Siegel, David A.; Smeed, David A.; Stackhouse, Paul W.; Sweet, William; Thompson, Philip R.; Triñanes, Joaquin A.; Volkov, Denis L.; Wanninkhof, Rik; Wen, Caihong; Westberry, Toby K.; Widlansky, Matthew J.; Willis, J.; Xie, Ping-Ping; Yin, Xungang; Zhang, Huai-min; Zhang, Li; Allen, Jessicca; Camper, Amy V.; Haley, Bridgette O.; Hammer, Gregory; Love-Brotak, S. Elizabeth; Ohlmann, Laura; Noguchi, Lukas; Riddle, Deborah B.; Veasey, Sara W.Johnson, G. C., R. Lumpkin, C. Atkinson, T. Biló, T. Boyer, F. Bringas, B. R. Carter, I. Cetinić, D. P. Chambers, D. Chan, L. Cheng, L. Chomiak, M. F. Cronin, S. Dong, R. A. Feely, B. A. Franz, M. Gao, J. Garg, J. Gilson, G. Goni, B. D. Hamlington, W. Hobbs, Z. Hu, B. Huang, M. Ishii, S. Jevrejeva, W. Johns, P. Landschützer, M. Lankhorst, E. Leuliette, R. Locarnini, J. M. Lyman, M. J. McPhaden, M. A. Merrifield, A. Mishonov, G. T. Mitchum, B. I. Moat, I. Mrekaj, R. S. Nerem, S. G. Purkey, B. Qiu, J. Reagan, K. Sato, C. Schmid, J. D. Sharp, D. A. Siegel, D. A. Smeed, P. W. Stackhouse, W. Sweet, P. R. Thompson, J. A. Triñanes, D. L. Volkov, R. Wanninkhof, C. Wen, T. K. Westberry, M. J. Widlansky, J. Willis, P. Xie, X. Yin, H. Zhang, L. Zhang, J. Allen, A. V. Camper, B. O. Haley, G. Hammer, S. E. Love-Brotak, L. Ohlmann, L. Noguchi, D. B. Riddle, S. W. Veasey, 2023: Global Oceans. Bull. Amer. Meteor. Soc., 104(9), S146-S206. doi: 10.1175/BAMS-D-23-0076.2. "Global Oceans" published on 06 Sep 2023 by American Meteorological Society.
Johnson, Gregory C.; Landerer, Felix W.; Loeb, Norman G.; Lyman, John M.; Mayer, Michael; Swann, Abigail L. S.; Zhang, JinlunJohnson, G. C., F. W. Landerer, N. G. Loeb, J. M. Lyman, M. Mayer, A. L. S. Swann, J. Zhang, 2023: Closure of Earth’s Global Seasonal Cycle of Energy Storage. Surveys in Geophysics. doi: 10.1007/s10712-023-09797-6. The global seasonal cycle of energy in Earth’s climate system is quantified using observations and reanalyses. After removing long-term trends, net energy entering and exiting the climate system at the top of the atmosphere (TOA) should agree with the sum of energy entering and exiting the ocean, atmosphere, land, and ice over the course of an average year. Achieving such a balanced budget with observations has been challenging. Disagreements have been attributed previously to sparse observations in the high-latitude oceans. However, limiting the local vertical integration of new global ocean heat content estimates to the depth to which seasonal heat energy is stored, rather than integrating to 2000 m everywhere as done previously, allows closure of the global seasonal energy budget within statistical uncertainties. The seasonal cycle of energy storage is largest in the ocean, peaking in April because ocean area is largest in the Southern Hemisphere and the ocean’s thermal inertia causes a lag with respect to the austral summer solstice. Seasonal cycles in energy storage in the atmosphere and land are smaller, but peak in July and September, respectively, because there is more land in the Northern Hemisphere, and the land has more thermal inertia than the atmosphere. Global seasonal energy storage by ice is small, so the atmosphere and land partially offset ocean energy storage in the global integral, with their sum matching time-integrated net global TOA energy fluxes over the seasonal cycle within uncertainties, and both peaking in April. Earth; Seasonal cycle; Climate; Global energy
Johnson, Richard H.; Szoeke, Simon P. de; Ciesielski, Paul E.; Brewer, W. AlanJohnson, R. H., S. P. d. Szoeke, P. E. Ciesielski, W. A. Brewer, 2023: The Atmospheric Boundary Layer and the Initiation of the MJO. J. Climate, 36(22), 7893-7903. doi: 10.1175/JCLI-D-23-0210.1. Abstract The Indian Ocean is a frequent site for the initiation of the Madden–Julian oscillation (MJO). The evolution of convection during MJO initiation is intimately linked to the subcloud atmospheric mixed layer (ML). Much of the air entering developing cumulus clouds passes through the cloud base; hence, the properties of the ML are critical in determining the nature of cloud development. The properties and depth of the ML are influenced by horizontal advection, precipitation-driven cold pools, and vertical motion. To address ML behavior during the initiation of the MJO, data from the 2011/12 Dynamics of the MJO Experiment (DYNAMO) are utilized. Observations from the research vessel Revelle are used to document the ML and its modification during the time leading up to the onset phase of the October MJO. The mixed layer depth increased from ∼500 to ∼700 m during the 1–12 October suppressed period, allowing a greater proportion of boundary layer thermals to reach the lifting condensation level and hence promote cloud growth. The ML heat budget defines an equilibrium mixed layer depth that accurately diagnoses the mixed layer depth over the DYNAMO convectively suppressed period, provided that horizontal advection is included. The advection at the Revelle is significantly influenced by low-level convective outflows from the southern ITCZ. The findings also demonstrate a connection between cirrus clouds and their remote impact on ML depth and convective development through a reduction in the ML radiative cooling rate. The emergent behavior of the equilibrium mixed layer has implications for simulating the MJO with models with parameterized cloud and turbulent-scale motions.
Karlowska, Eliza; Matthews, Adrian J.; Webber, Benjamin G. M.; Graham, Tim; Xavier, PrinceKarlowska, E., A. J. Matthews, B. G. M. Webber, T. Graham, P. Xavier, 2023: The effect of diurnal warming of sea-surface temperatures on the propagation speed of the Madden–Julian oscillation. Quarterly Journal of the Royal Meteorological Society, 150(758), 334-354. doi: 10.1002/qj.4599. The diurnal warm layer in the upper ocean develops during low surface winds and high incoming solar radiation conditions, often increasing sea-surface temperatures (SSTs) by up to 1°C. The suppressed phase of the Madden–Julian Oscillation (MJO) favours the formation of such a layer. Here, we analyse the coupled ocean–atmosphere and atmosphere-only numerical weather prediction systems of the UK Met Office to reveal that important differences arise from the representation of the diurnal warm layer in the coupled model. Though both models are skilful in predicting the MJO to at least a 7-day lead time, the coupled model predicts approximately 12% faster MJO RMM phase speed propagation than the atmosphere-only model due to the ability to resolve diurnal warming in the upper ocean that rectifies onto MJO-associated SST anomalies. The diurnal warming of SST (dSST) in the coupled model leads to an increase in daily mean SST compared with the atmosphere-only model persisted foundation SST. The strength of the dSST in the coupled model is modulated by MJO conditions. During suppressed MJO conditions on lead day 1, the dSST is enhanced, leading to 0.2°C warmer daily mean MJO-associated SST anomalies and increased convection in the coupled model by lead day 7. During active MJO convection, the dSST is suppressed, leading to 0.1°C colder MJO-associated SST anomalies in the coupled model and reduced convection by lead day 7. This variability in dSST further amplifies the MJO propagation speed, underlining the importance of the two-way feedback between the MJO and the diurnal cycle of SST and the need to accurately represent this process in coupled models. convection; diurnal warm layer; Madden–Julian Oscillation; ocean–atmosphere coupling
Kashtan Sundararaman, Harish Kumar; Shanmugam, Palanisamy; Nagamani, Pullaiahgari VenkataKashtan Sundararaman, H. K., P. Shanmugam, P. V. Nagamani, 2023: Robust extension of the simple sea-surface irradiance model to handle cloudy conditions for the global ocean using satellite remote sensing data. Advances in Space Research, 71(3), 1486-1509. doi: 10.1016/j.asr.2022.10.009. Sea-surface solar radiation (abbreviated as photosynthetically available radiation, PAR) in the visible wavelength (400–700 nm) is an essential parameter to estimate marine primary productivity and understanding phytoplankton dynamics, upper ocean physics and biogeochemical processes. Although many remote-sensing models were developed to estimate daily PAR (DPAR) from ocean colour data, these models often produce biases in the DPAR products under cloudy-sky and complex atmospheric conditions due to the lack of parameterization to deal with the cloud cover conditions and insufficient in-situ DPAR data. This study presents an Extended Sea-surface Solar Irradiance Model (ESSIM) for estimating DPAR over the global ocean. The ESSIM uses the direct and diffuse components from the Simple sea-surface Solar Irradiance Model (SSIM) along with a new parameter to handle cloudy conditions. The ESSIM produced DPAR products with greater accuracy under both clear and cloudy conditions. Its performance was tested on the time-series MODIS-Aqua images and compared with the concurrent in-situ data and the results from two global models. Results showed that the DPAR values produced by ESSIM agree with in-situ data better than the global models for all-sky conditions (with a mean relative error of 11.267 %; a root mean square error of 5.563 Em−2day−1; and a mean net bias of 2.917 Em−2day−1). The ESSIM performed slightly better than the SSIM for clear conditions and the Frouin's Operational Algorithm (FOA) for all-sky conditions. As the new parameterization accounts for cloudy conditions, the ESSIM produced more accurate results for cloud cover conditions across latitudes (up to 60°). The time-series Level-3 binned MODIS-Aqua data (global gridded) also demonstrated that the ESSIM improved the accuracy of DPAR products and produced spatially and temporally consistent DPAR products over the global ocean regardless of the seasons and sky conditions. Satellite observation; Cloudy condition; DPAR; ESSIM; Global Ocean; MODIS-Aqua
Kotsuki, Shunji; Terasaki, Koji; Satoh, Masaki; Miyoshi, TakemasaKotsuki, S., K. Terasaki, M. Satoh, T. Miyoshi, 2023: Ensemble-Based Data Assimilation of GPM DPR Reflectivity: Cloud Microphysics Parameter Estimation With the Nonhydrostatic Icosahedral Atmospheric Model (NICAM). Journal of Geophysical Research: Atmospheres, 128(5), e2022JD037447. doi: 10.1029/2022JD037447. Direct assimilation of Dual-frequency Precipitation Radar (DPR) data of the Global Precipitation Measurement (GPM) core satellite is challenging mainly due to its long revisiting intervals relative to the time scale of precipitation, and precipitation location errors. This study explores a method for improving precipitation forecasts using GPM DPR through model parameter estimation. We developed a 28 km mesh global atmospheric data assimilation system that integrates the Nonhydrostatic ICosahedral Atmospheric Model (NICAM) and Local Ensemble Transform Kalman Filter (LETKF) coupled with a satellite radar simulator. Using the NICAM-LETKF and GPM DPR observations, this study estimates a model cloud physics parameter corresponding to snowfall terminal velocity. To overcome the difficulties of long revisiting intervals and precipitation location errors, we propose a parameter estimation method based on a two-dimensional histogram known as the contoured frequency by temperature diagram (CFTD). Parameter estimation effectively mitigated the gap between simulated and observed CFTD, resulting in improved 6 hr precipitation forecasts. cloud microphysics; data assimilation; parameter estimation; GPM DPR; radar reflectivity
Kuma, Peter; Bender, Frida A.-M.; Schuddeboom, Alex; McDonald, Adrian J.; Seland, ØyvindKuma, P., F. A. Bender, A. Schuddeboom, A. J. McDonald, Ø. Seland, 2023: Machine learning of cloud types in satellite observations and climate models. Atmospheric Chemistry and Physics, 23(1), 523-549. doi: 10.5194/acp-23-523-2023. Uncertainty in cloud feedbacks in climate models is a major limitation in projections of future climate. Therefore, evaluation and improvement of cloud simulation are essential to ensure the accuracy of climate models. We analyse cloud biases and cloud change with respect to global mean near-surface temperature (GMST) in climate models relative to satellite observations and relate them to equilibrium climate sensitivity, transient climate response and cloud feedback. For this purpose, we develop a supervised deep convolutional artificial neural network for determination of cloud types from low-resolution (2.5∘×2.5∘) daily mean top-of-atmosphere shortwave and longwave radiation fields, corresponding to the World Meteorological Organization (WMO) cloud genera recorded by human observers in the Global Telecommunication System (GTS). We train this network on top-of-atmosphere radiation retrieved by the Clouds and the Earth’s Radiant Energy System (CERES) and GTS and apply it to the Coupled Model Intercomparison Project Phase 5 and 6 (CMIP5 and CMIP6) model output and the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis version 5 (ERA5) and the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) reanalyses. We compare the cloud types between models and satellite observations. We link biases to climate sensitivity and identify a negative linear relationship between the root mean square error of cloud type occurrence derived from the neural network and model equilibrium climate sensitivity (ECS), transient climate response (TCR) and cloud feedback. This statistical relationship in the model ensemble favours models with higher ECS, TCR and cloud feedback. However, this relationship could be due to the relatively small size of the ensemble used or decoupling between present-day biases and future projected cloud change. Using the abrupt-4×CO2 CMIP5 and CMIP6 experiments, we show that models simulating decreasing stratiform and increasing cumuliform clouds tend to have higher ECS than models simulating increasing stratiform and decreasing cumuliform clouds, and this could also partially explain the association between the model cloud type occurrence error and model ECS.
Leng, Wanchun; Wang, Tianxing; Wang, Gaofeng; Letu, Husi; Wang, Shiyao; Xian, Yuyang; Yan, Xuewei; Zhang, ZiqianLeng, W., T. Wang, G. Wang, H. Letu, S. Wang, Y. Xian, X. Yan, Z. Zhang, 2023: All-sky surface and top-of-atmosphere shortwave radiation components estimation: Surface shortwave radiation, PAR, UV radiation, and TOA albedo. Remote Sensing of Environment, 298, 113830. doi: 10.1016/j.rse.2023.113830. Surface and top-of-atmosphere (TOA) shortwave radiation components are key parameters in the energy budget of the Earth-atmosphere system, which influence the global climate, ecology, hydrology, etc. However, except for total surface shortwave downward radiation (SWDR), only a few satellite missions consistently release other radiation components such as solar direct/diffuse radiation, photosynthetically active radiation (PAR), ultraviolet radiation-A/B (UVA/UVB), as well as TOA albedo, although they are indispensable for many land and ocean applications. In this study, a unified framework by combining multi-band LUT inversion and classification of the atmospheric condition is proposed, which enables the simultaneous derivation of nine surface and TOA radiation variables and emphasizes the separation of direct and diffuse components. The estimated radiation variables include total and direct components of SWDR, PAR, UVA, UVB, as well as TOA albedo. The proposed method is easy-to-use with only a few inputs and works well with reasonable accuracy. Using Moderate Resolution Imaging Spectroradiometer (MODIS) raw resolution images as test data, the surface radiation variables are validated by 80 global sites from BSRN, SURFRAD, and FLUXNET, and the instantaneous RMSEs (biases) of SWDR, SWDRdir, PAR, PARdiff, and UVB are 103.6 (0.1), 114 (−1.7), 47.8 (6.8), 32.9 (5.7), and 0.14 (0.003) W/m2, respectively, demonstrating comparable or even better accuracy compared with existing products. In particular, the estimated SWDR behaves more accurate than CERES in polar regions. Due to the lack of in-situ measurements, TOA albedo is compared with CERES TOA products and shows good agreement with R2 of 0.9 and RMSE (bias) of 0.055 (−0.003). The unified framework reveals obvious advantages over existing studies in generating almost all physically consistent shortwave components in the same manner with simple inputs, implying the great potentials in globally mapping spatio-temporally continuous multiple components of shortwave radiation with a unified scheme. TOA albedo; Photosynthetically active radiation; Look-up table; Shortwave downward radiation; Ultraviolet radiation
Letu, Husi; Ma, Run; Nakajima, Takashi Y.; Shi, Chong; Hashimoto, Makiko; Nagao, Takashi M.; Baran, Anthony J.; Nakajima, Teruyuki; Xu, Jian; Wang, Tianxing; Tana, Gegen; Bilige, Sude; Shang, Huazhe; Chen, Liangfu; Ji, Dabin; Lei, Yonghui; Wei, Lesi; Zhang, Peng; Li, Jun; Li, Lei; Zheng, Yu; Khatri, Pradeep; Shi, JianchengLetu, H., R. Ma, T. Y. Nakajima, C. Shi, M. Hashimoto, T. M. Nagao, A. J. Baran, T. Nakajima, J. Xu, T. Wang, G. Tana, S. Bilige, H. Shang, L. Chen, D. Ji, Y. Lei, L. Wei, P. Zhang, J. Li, L. Li, Y. Zheng, P. Khatri, J. Shi, 2023: Surface Solar Radiation Compositions Observed from Himawari-8/9 and Fengyun-4 Series. Bull. Amer. Meteor. Soc., 104(10), E1772-E1789. doi: 10.1175/BAMS-D-22-0154.1. Abstract Surface downward solar radiation compositions (SSRC), including photosynthetically active radiation (PAR), ultraviolet-A (UVA), ultraviolet-B (UVB), and shortwave radiation (SWR), with high spatial–temporal resolutions and precision are essential for applications including solar power, vegetation photosynthesis, and environmental health. In this study, an optimal algorithm was developed to calculate SSRC, including their direct and diffuse components. Key features of the algorithm include combining the radiative transfer model with machine learning techniques, including full consideration of the effects of aerosol types, cloud phases, and gas components. A near-real-time monitoring system was developed based on this algorithm, with SSRC products generated from Himawari-8/9 and Fengyun-4 series data. Validation with ground-based data shows that the accuracy of the SWR and PAR compositions (daily mean RMSEs of 19.7 and 9.2 W m−2, respectively) are significantly better than those of state-of-the-art products from CERES, ERA5, and GLASS. The accuracy of UVA and UVB measurements is comparable with CERES. Characteristics of aerosols, clouds, gases, and their impacts on SSRC are investigated before, during, and post COVID-19; in particular, significant SSRC variations due to the reduction of aerosols and increase of ozone are identified in the Chinese central and eastern areas during that period. The spatial–temporal resolution of data products [up to 0.05° (10 min)−1 for the full-disk region] is one of the most important advantages. Data for the East Asia–Pacific region during 2016–20 is available from the CARE home page (www.slrss.cn/care/sp/pc/).
Li, Donghao; Folini, Doris; Wild, MartinLi, D., D. Folini, M. Wild, 2023: Assessment of Top of Atmosphere, Atmospheric and Surface Energy Budgets in CMIP6 Models on Regional Scales. Earth and Space Science, 10(4), e2022EA002758. doi: 10.1029/2022EA002758. We examine top of atmosphere (TOA), atmospheric, and surface energy budget components of 53 CMIP6 models for the period 2000–2009 on regional scales with respect to two reference data sets: the NASA Energy and Water cycle Study (NEWS), from which we adopt the regional decomposition, and the Clouds and the Earth's Radiant Energy System (CERES) Energy Balanced and Filled (EBAF). Focusing on regional scale, CMIP6 models tend to have more energy entering or less energy leaving the climate systems at TOA over the Northern Hemisphere land, Southern Hemisphere ocean and the polar regions compared to CERES EBAF, while the contrary applies in other regions. Atmospheric net shortwave and longwave fluxes both tend to be underestimated in CMIP6 models as compared to EBAF, with substantial regional differences. Regional surface radiative fluxes as reported by NEWS and EBAF can differ substantially. Nevertheless, robust regional biases exist in CMIP6. Surface upward shortwave radiation is overestimated by 43 (81%) models over Eurasia. For almost all surface radiative flux components over the North Atlantic and Indian Ocean, there are at least 21 (40%) models which fall outside the NEWS uncertainty range. Latent heat flux is overestimated over most of the land and ocean regions while firm conclusions for sensible heat flux remain elusive due to discrepancies between different reference data sets. Compared to CMIP5, there is an overall improvement in CMIP6 on regional scale. Still, substantial deficiencies and spreads on regional scale remain, which are potentially translated into an inadequate simulation of atmospheric dynamics or hydrological cycle.
Li, Jiandong; Geen, Ruth; Mao, Jiangyu; Song, Yajuan; Vallis, Geoffrey K.; Wu, GuoxiongLi, J., R. Geen, J. Mao, Y. Song, G. K. Vallis, G. Wu, 2023: Mechanical and Thermal Forcings of Asian Large-Scale Orography on Spring Cloud Amount and Atmospheric Radiation Budget over East Asia. J. Climate, 36(15), 5215-5232. doi: 10.1175/JCLI-D-22-0797.1. Abstract Asian large-scale orography profoundly influences circulation in the North Hemisphere. Considerable spring top-of-the-atmosphere (TOA) radiative cooling over Southeast China (SEC) is very likely related to upstream orography forcing. Here we investigate the mechanical and thermal forcings of Asian large-scale orography, particularly the Tibetan Plateau (TP), on downstream East Asian cloud amount and atmospheric radiation budget during March–April using the Global Monsoons Model Intercomparison Project simulations. The thermal forcing drives significant surface heating and a low-level cyclone over the TP, pumping low-level air to the middle troposphere. Ascent and water vapor convergence triggered by the thermal forcing favor air condensation, low–middle clouds, and resultant strong spring cloud radiative cooling over SEC. Moreover, the thermal forcing moves the position of cloud radiative cooling westward toward the TP. The TP’s blocking role weakens low-level westerlies over SEC, but its deflecting role increases downstream high-level westerlies, dynamically favoring cloud formation over SEC and the eastward ocean. In addition, the TP can force ascent and increase cloud amounts over the western and central TP. The thermal forcing contributes to 57.1% of total cloud amount and 47.6% of TOA cloud radiative cooling induced by the combined orography forcing over SEC while the mechanical one accounts for 79.4% and 95.8% of the counterparts over the ocean to the east of SEC. Our results indicate that Asian large-scale orography shapes the contemporary geographical distribution of spring East Asian cloud amount and atmospheric radiation budget to a large extent. Significance Statement Clouds tied to large-scale topography and circulation exhibit some remarkable geographical distributions. The global strongest cloud radiative cooling, with an intensity of up to −90 W m−2, occurs over Southeast China (SEC) during March–April. The primary purpose of this study is to understand the influences of Asian large-scale orography, particularly the Tibetan Plateau (TP), on this unique climatic phenomenon using the latest climate model simulations. Our results show that Asian large-scale orography forcing significantly increases ascent, low–middle cloud formation, and resultant strong spring cloud radiative cooling over SEC and downstream ocean. The sensible-heat-driven air pump induced by the TP’s thermal forcing maintains strong cloud radiative cooling over SEC. This study provides valuable insights that link Asian large-scale orography forcing to downstream cloud–radiation characteristics.
Li, Jiandong; Guo, Zhun; Chen, Guoxing; Zi, PengLi, J., Z. Guo, G. Chen, P. Zi, 2023: Seasonal and interannual characteristics of atmospheric cloud radiative effect over South China and neighbouring ocean regions. International Journal of Climatology, 43(15), 7412-7427. doi: 10.1002/joc.8271. Atmospheric cloud radiative effect (ACRE) is a critical heat source in the atmosphere, with pronounced regional distributions. Here, we investigate seasonal and interannual characteristics of ACRE over South China (SC) and neighbouring ocean regions using 2001–2020 satellite and reanalysis data. Annual mean net ACRE shows a warming role over most of SC, its eastern ocean (ESCO), and the South China Sea and western North Pacific (SWNP), with domain-mean values of 6.0, 14.9, and 32.8 W m−2, respectively. Over SC, the shortwave ACRE warming dominates annual mean net ACRE, and considerable low-middle clouds with small particle size and large water content reflect shortwave radiation and enhance shortwave absorption, especially in spring. Notably, winter longwave ACRE over SC, with a cooling role, strongly offsets its summer counterpart's warming role. In contrast, longwave ACRE mainly accounts for net ACRE over ESCO and SWNP, especially the latter where high clouds prevail. The Asian summer monsoon enhances summer high clouds and longwave (net) ACRE. Cloud types and complex vertical distribution associated with continental environments and the Tibetan Plateau's topography forcing enable seasonal behaviours of ACRE over SC to be different from the other two regions. Longwave ACRE dominates the interannual variation of net ACRE, with a larger interannual variability over SWNP, while a larger annual variability of shortwave ACRE occurs over SC. There are no significant interannual trends of ACRE except for annual and spring mean longwave (net) ACRE over SC. Moreover, the interannual variation of longwave (net) ACRE relates well to 500-hPa vertical velocity, indicating the strong influence of large-scale circulation on regional ACRE. cloud; interannual variation; seasonal variation; atmospheric radiative effect cloud; South China
Li, Na; Zhao, PingLi, N., P. Zhao, 2023: A Daily Land Surface Heat Flux Dataset in Tibetan Plateau During 2001–2016 Based on the Maximum Entropy Production Model and Multi-Source Datasets. doi: 10.2139/ssrn.4414712. The daily long-term land surface sensible (SH) and latent (LE) heat fluxes is important for understanding of energy and water cycle processes in the Tibetan Plateau (TP). In this study, the daily SH and LE at the horizontal resolution of 1° are first estimated using the maximum entropy production (MEP) model (hereinafter SHMEP and LEMEP) in the entire TP during 2001–2016. The MEP model is built on physical and statistical principles to simulate surface heat fluxes. The surface net radiation, soil moisture (SM), and land surface temperature (LST) are the main driving variables for MEP model. In order to select the relatively accurate MEP inputs, the merged surface net radiation (Rn–merged) under all-sky conditions are generated from CERES, ISCCP-FH, and ERA5 using the Bayesian Model Averaging scheme in the TP. Besides, the TP SM and LST from various sources are evaluated using the in-situ observations. Based on the daily Rn–merged, the ERA5 SM, and the CERES LST, the daily SH and LE are estimated in the entire TP. The results show that daily SHMEP and LEMEP perform well at all the TP measurement sites, with the correlation coefficient above 0.73, the root-mean-square error of less than 20.9 W m–2, and the absolute value of bias below 8.9 W m–2. The results are superior to the SH and LE in ERA5, ERA-Interim, and MERRA-2 reanalysis datasets and previous studies, especially for LE. Based on this new dataset, the spatial and temporal varying characteristics of SH and LE in the TP are analyzed. The annual SHMEP is high (small) in the western TP, the Qaidam Basin in the northern TP, and the Himalaya ranges (southeastern TP). The annual LEMEP has the minimum (maximum) value in the western TP and the Qaidam Basin (the southeastern TP). Meanwhile, the annual SHMEP and LEMEP over the entire TP are 35.76 W m–2 and 20.48 W m–2, with the increasing trends of 0.75 and 0.10 W m–2 decade–1 during the study period, respectively. Latent heat flux; Maximum entropy production model; Multi-Source datasets; Sensible heat flux; Tibetan Plateau
Li, Peizhen; Zhong, Lei; Ma, Yaoming; Fu, Yunfei; Cheng, Meilin; Wang, Xian; Qi, Yuting; Wang, ZixinLi, P., L. Zhong, Y. Ma, Y. Fu, M. Cheng, X. Wang, Y. Qi, Z. Wang, 2023: Estimation of 1 km downwelling shortwave radiation over the Tibetan Plateau under all-sky conditions. Atmospheric Chemistry and Physics, 23(16), 9265-9285. doi: 10.5194/acp-23-9265-2023. Downwelling shortwave radiation (DSR) is the basic driving force for the energy and water cycles of the Earth's climate system. Called the Third Pole of the Earth, the Tibetan Plateau (TP) absorbs a large amount of shortwave radiation and exerts important impacts on global weather and climate change. However, due to coarse spatial resolution and insufficient consideration of factors influencing radiative transfer processes, DSR parameterization schemes still need to be improved when applied to the TP. Based on satellite datasets and meteorological forcing data, all-sky DSR over the TP at a spatial resolution of 1 km was derived using an improved parameterization scheme. The influence of topography and different radiative attenuations were comprehensively taken into account. Specifically, the introduction of cloud multiscattering and topography factors further improves the DSR estimation accuracy. The validation results indicated that the developed parameterization scheme showed reasonable accuracy. By comparing with current, widely used DSR products based on the same in situ observations, the derived DSR performed much better on different spatial and temporal scales. On instantaneous, 10 d and monthly timescales, the root-mean-square errors (RMSEs) of the derived DSR are 132.8–158.2, 70.8–76.5 and 61.3–67.5 W m−2, respectively, which are much smaller than those of current DSR products. The derived DSR not only captured the temporal-variation characteristics that are more consistent with the in situ measurements, but also provided reasonable spatial patterns. Meanwhile, the proposed parameterization scheme demonstrated its superiority in characterizing more details and high dynamics of the spatial pattern of DSR due to its terrain correction and high resolution. Moreover, this parameterization scheme does not need any local correction in advance and has the potential to be extended to other regions in the world.
Li, Ruohan; Wang, Dongdong; Liang, ShunlinLi, R., D. Wang, S. Liang, 2023: Comparison between deep learning architectures for the 1 km, 10/15-min estimation of downward shortwave radiation from AHI and ABI. Remote Sensing of Environment, 295, 113697. doi: 10.1016/j.rse.2023.113697. The retrieval of downward shortwave radiation (DSR) with high spatiotemporal resolution and short latency is critical. It is the fundamental driving force of surface energy, carbon, and hydrological circulations, and a key energy source for photovoltaic electricity. However, existing methods face significant challenges owing to cloud heterogeneity and their reliance on other satellite-derived products, which hinder the retrieval of accurate and timely DSR with high spatiotemporal resolution. In addition to the spectral features used in traditional approaches, deep learning (DL) can incorporate the spatial and temporal features of satellite data. This study developed and compared three DL methods, namely the DenseNet, the bidirectional gated recurrent unit without surface albedo as inputs (BiGRUnor), and the convolutional neural network with gated recurrent unit without surface albedo as inputs (CNNGRUnor). These methods were used to estimate DSR at 1 km and 10/15 min resolutions directly from top-of-atmosphere reflectance over the Advanced Himawari Imager (AHI) onboard Himawari-8 and the Advanced Baseline Imager (ABI) onboard GOES-16 coverage, achieving high accuracies. The instantaneous root mean square error (RMSE) and relative RMSE for the three models were 68.4 (16.1%), 69.4 (16.3%), and 67.1 (15.7%) W/m2, respectively, which are lower than the baseline machine learning method, the multilayer perceptron model (MLP), with RMSE at 76.8 W/m2 (18.0%). Hourly accuracies for the three DL methods were 58.6 (14.1%), 57.8 (14.0%), and 57.3 (13.8%) W/m2, which are within the DSR RMSEs that we estimated for existing datasets of the Earth's Radiant Energy System (CERES) (88.8 W/m2, 21.4%) and GeoNEX (77.8 W/m2, 18.8%). The study illustrates that DL models that incorporate temporal information can eliminate the need for surface albedo as an input, which is crucial for timely monitoring and nowcasting of DSR. Incorporating spatial information can enhance retrieval accuracy in overcast conditions, and incorporating infrared bands can further improve the accuracy of DSR estimation. Solar radiation; Deep learning; Solar energy; AHI; Shortwave radiation; Geostationary; ABI; CNN; DeNET; GRU
Li, Xia; Tan, Zhihong; Zheng, Youtong; Bushuk, Mitchell; Donner, Leo J.Li, X., Z. Tan, Y. Zheng, M. Bushuk, L. J. Donner, 2023: Open Water in Sea Ice Causes High Bias in Polar Low-Level Clouds in GFDL CM4. Geophysical Research Letters, 50(24), e2023GL106322. doi: 10.1029/2023GL106322. Global climate models (GCMs) struggle to simulate polar clouds, especially low-level clouds that contain supercooled liquid and closely interact with both the underlying surface and large-scale atmosphere. Here we focus on GFDL's latest coupled GCM–CM4–and find that polar low-level clouds are biased high compared to observations. The CM4 bias is largely due to moisture fluxes that occur within partially ice-covered grid cells, which enhance low cloud formation in non-summer seasons. In simulations where these fluxes are suppressed, it is found that open water with an areal fraction less than 5% dominates the formation of low-level clouds and contributes to more than 50% of the total low-level cloud response to open water within sea ice. These findings emphasize the importance of accurately modeling open water processes (e.g., sea ice lead-atmosphere interactions) in the polar regions in GCMs.
Li, Zhengpeng; Bi, Jianrong; Hu, Zhiyuan; Ma, Junyang; Li, BowenLi, Z., J. Bi, Z. Hu, J. Ma, B. Li, 2023: Regional transportation and influence of atmospheric aerosols triggered by Tonga volcanic eruption. Environmental Pollution, 121429. doi: 10.1016/j.envpol.2023.121429. A cataclysmic submarine volcano at Hunga Tonga-HungaHa'apai (HTHH) near Tonga, erupted violently on 15 January 2022, which injected a plume of ash cloud soaring into the upper atmosphere. In this study, we examined the regional transportation and potential influence of atmospheric aerosols triggered by HTHH volcano, based on active and passive satellite products, ground-based observations, multi-source reanalysis datasets and radiation transfer model. The results indicated that about 0.7 Tg (1 Tg = 109 kg) sulfur dioxide (SO2) gas were emitted into stratosphere from the HTHH volcano, and were lifted to an altitude of 30 km. The regional averaged SO2 columnar content over western Tonga increased by 10–36 Dobson Units (DU), the mean aerosol optical thickness (AOT) retrieved from satellite products increased to 0.25–0.34. The stratospheric AOT values caused by HTHH emissions increased to 0.03, 0.20, and 0.23 on 16, 17, and 19 January, respectively, accounting for 1.5%, 21.9%, and 31.1% of total AOT. Ground-based observations also showed an AOT increase of 0.25–0.43, with the maximum daily average of 0.46–0.71 appeared on 17 January. The volcanic aerosols were remarkably dominated by fine-mode particles and posed strong light-scattering and hygroscopic abilities. Consequently, the mean downward surface net shortwave radiative flux was reduced by 2.45–11.9 Wm-2 on different regional scales, the surface temperature decreased by 0.16–0.42 K. The maximum aerosol extinction coefficient was 0.51 km−1 appeared at 27 km, which resulted in an instantaneous shortwave heating rate of 1.80 Khour−1. The volcanic materials were injected into the stratosphere and completed a circle around the earth in 15 days. This would exert a profound influence on the energy budget, water vapor and ozone exchange in the stratosphere, which deserves to be further studied. Volcanic aerosol; Shortwave heating rate; Tonga volcano
Liang, Hui; Jiang, Bo; Peng, Jianghai; Li, Shaopeng; Han, Jiakun; Yin, XiuwanLiang, H., B. Jiang, J. Peng, S. Li, J. Han, X. Yin, 2023: Estimating daily surface downward shortwave radiation over rugged terrain without bright surface at 30 m on clear-sky days using CERES data. International Journal of Digital Earth, 16(2), 4317-4345. doi: 10.1080/17538947.2023.2263421. In this study, the authors propose a model, called the Daily Downward Shortwave Radiation Random Forest Model over Rugged Terrain (DSRMT), to accurately calculate the downward shortwave radiation over a terrain without bright surface on clear days at a daily scale (DSRdaily−rugged). It was built by using the random forest method based on the comprehensive samples from CERES4_SYN1deg_Ed4A within 17 typical mountainous regions. DSRMT could directly estimate DSRdaily-rugged from the instantaneous direct and diffuse solar radiation on a flat surface during 10:30–14:30hrs on each day by comparing with the terrain factors from a digital elevation model, broadband albedo from the Global Land Surface Satellite, and ancillary information. The in-situ validation results showed that it generally delivered superior performance in estimating DSRdaily-rugged at any time during 10:30–14:30hrs, especially at noon, yielding a validated root mean-squared error (RMSE) of 24.90–29.22 Wm−2 and mean absolute error (MAE) of 19.16–22.94 Wm−2, and the average weighted DSRdaily-rugged were usually more accurate with the RMSE and MAE of 21.63 and 17.14 Wm−2. Overall, DSRMT was found to deliver satisfactory performance because of its high accuracy, robustness, ease of implementation, and efficiency, so it has the strong potential to be widely used in practice. remote sensing; modeling; CERES4; Daily downward shortwave radiation; DSRMT; estimation; rugged terrain
Liang, Kaixin; Wang, Jinfei; Luo, Hao; Yang, QinghuaLiang, K., J. Wang, H. Luo, Q. Yang, 2023: The Role of Atmospheric Rivers in Antarctic Sea Ice Variations. Geophysical Research Letters, 50(8), e2022GL102588. doi: 10.1029/2022GL102588. Antarctic sea ice variations are affected by moisture and heat from low- and mid-latitudes, more than 90% of which are transported by atmospheric rivers (ARs). This study employs the ERA5 reanalysis and satellite observations to detect all the ARs over the Antarctic sea ice and analyze the general contributions of ARs on sea ice changes from 1979 to 2020. Though AR frequency is low in all seasons, ARs give rise to intense sea ice reduction at a rate of more than 10%/day in marginal ice zone. Thermodynamic processes of sea ice dominate the AR-induced variations, associated with anomalous atmospheric conditions during ARs. Warm, moist and cloudy weather causes considerable melting by enhancing sensible heat flux in cold seasons but has restrictive influences in summer due to blocked solar radiation. Heavy precipitation during ARs is also nonnegligible, especially during the summer melt. sea ice; Antarctic; atmospheric river
Liang, Lusheng; Su, Wenying; Sejas, Sergio; Eitzen, Zachary A.; Loeb, Norman G.Liang, L., W. Su, S. Sejas, Z. A. Eitzen, N. G. Loeb, 2023: Next-generation radiance unfiltering process for the Clouds and Earth’s Radiant Energy System instrument. EGUsphere, 1-25. doi: 10.5194/egusphere-2023-1670. Abstract. The filtered radiances measured by the Clouds and the Earth’s Radiant Energy System (CERES) instruments are converted to shortwave (SW), longwave (LW), and window unfiltered radiances based on regressions developed from theoretical radiative transfer simulations to relate filtered and unfiltered radiances. This paper describes an update to the existing Edition 4 CERES unfiltering algorithm (Loeb et al., 2001), incorporating the most recent developments in radiative transfer modeling, ancillary input datasets, and increased computational and storage capabilities during the past 20 years. Simulations are performed with MODTRAN 5.4. Over land and snow, the surface Bidirectional Reflectance Distribution Function (BRDF) is characterized by a kernel-based representation in the simulations, instead of the Lambertian surface used in the Edition 4 unfiltering process. Radiance unfiltering is explicitly separated into 4 seasonally dependent land surface groups based on the spectral radiation similarities of different surface types (defined by International Geosphere-Biosphere Programme); over snow, it is separated into fresh snow, permanent snow, and sea ice. It contrasts to the Edition 4 unfiltering process that one set of regressions for land and snow, respectively. The instantaneous unfiltering errors are estimated with independent test cases generated from radiative transfer simulations in which the ‘true’ unfiltered radiances from radiative transfer simulations are compared with the unfiltered radiances calculated from the regressions. Overall, the relative errors are mostly within ±0.5 % for SW, within ±0.2 % for daytime LW, and within ±0.1 % for nighttime LW for both CERES Terra Flight Model 1 (FM1) and Aqua FM3 instruments. The unfiltered radiances are converted to fluxes and compared to CERES Edition 4 fluxes. The global mean instantaneous fluxes for Aqua FM3 are reduced by less than 0.42 Wm-2 for SW and increased by less than 0.47 Wm-2 for daytime LW; for Terra FM1, they are reduced by less than 0.31 Wm-2 for SW and increased by less than 0.29 Wm-2 for daytime LW, though regional differences can be as large as 2.0 Wm-2. Nighttime LW flux differences are nearly negligible for both instruments.
Liang, Mingjie; Han, Zhiwei; Li, Jiawei; Sun, Yele; Liang, Lin; Li, YueLiang, M., Z. Han, J. Li, Y. Sun, L. Liang, Y. Li, 2023: Radiative effects and feedbacks of anthropogenic aerosols on boundary layer meteorology and fine particulate matter during the COVID-19 lockdown over China. Science of The Total Environment, 862, 160767. doi: 10.1016/j.scitotenv.2022.160767. The COVID-19 epidemic has exerted significant impacts on human health, social and economic activities, air quality and atmospheric chemistry, and potentially on climate change. In this study, an online coupled regional climate–chemistry–aerosol model (RIEMS-Chem) was applied to explore the direct, indirect, and feedback effects of anthropogenic aerosols on radiation, boundary layer meteorology, and fine particulate matter during the COVID-19 lockdown period from 23 January to 8 April 2020 over China. Model performance was validated against a variety of observations for meteorological variables, PM2.5 and its chemical components, aerosol optical properties, as well as shortwave radiation flux, which demonstrated that RIEMS-Chem was able to reproduce the spatial distribution and temporal variation of the above variables reasonably well. During the study period, direct radiative effect (DRE) of anthropogenic aerosols was stronger than indirect radiative effect (IRE) in most regions north of the Yangtze River, whereas IRE dominated over DRE in the Yangtze River regions and South China. In North China, DRE induced larger changes in meteorology and PM2.5 than those induced by IRE, whereas in South China, the changes by IRE were remarkably larger than those by DRE. Emission reduction alone during the COVID-19 lockdown reduced PM2.5 concentration by approximately 32 % on average over East China. As a result, DRE at the surface was weakened by 15 %, whereas IRE changed little over East China, leading to a decrease in total radiative effect (TRE) by approximately 7 % in terms of domain average. The DRE-induced changes in meteorology and PM2.5 were weakened due to emission reduction, whereas the IRE-induced changes were almost the same between the cases with and without emission reductions. By aerosol radiative and feedback effects, the COVID-19 emission reductions resulted in 0.06 °C and 0.04 °C surface warming, 1.6 and 4.0 μg m−3 PM2.5 decrease, 0.4 and 1.3 mm precipitation increase during the lockdown period in 2020 in terms of domain average over North China and South China, respectively, whereas the lockdown caused negligible changes on average over East Asia. COVID-19; Indirect effect; Feedback; Anthropogenic aerosols; Boundary layer meteorology; Direct radiative effect
Liang, Yuanxin; Gui, Ke; Che, Huizheng; Li, Lei; Zheng, Yu; Zhang, Xutao; Zhang, Xindan; Zhang, Peng; Zhang, XiaoyeLiang, Y., K. Gui, H. Che, L. Li, Y. Zheng, X. Zhang, X. Zhang, P. Zhang, X. Zhang, 2023: Changes in aerosol loading before, during and after the COVID-19 pandemic outbreak in China: Effects of anthropogenic and natural aerosol. Science of The Total Environment, 857, 159435. doi: 10.1016/j.scitotenv.2022.159435. Anthropogenic emissions reduced sharply in the short-term during the coronavirus disease pandemic (COVID-19). As COVID-19 is still ongoing, changes in atmospheric aerosol loading over China and the factors of their variations remain unclear. In this study, we used multi-source satellite observations and reanalysis datasets to synergistically analyze the spring (February–May) evolution of aerosol optical depth (AOD) for multiple aerosol types over Eastern China (EC) before, during and after the COVID-19 lockdown period. Regional meteorological effects and the radiative response were also quantitatively assessed. Compared to the same period before COVID-19 (i.e., in 2019), a total decrease of −14.6 % in tropospheric TROPOMI nitrogen dioxide (NO2) and a decrease of −6.8 % in MODIS AOD were observed over EC during the lockdown period (i.e., in 2020). After the lockdown period (i.e., in 2021), anthropogenic emissions returned to previous levels and there was a slight increase (+2.3 %) in AOD over EC. Moreover, changes in aerosol loading have spatial differences. AOD decreased significantly in the North China Plain (−14.0 %, NCP) and Yangtze River Delta (−9.4 %) regions, where anthropogenic aerosol dominated the aerosol loading. Impacted by strong wildfires in Southeast Asia during the lockdown period, carbonaceous AOD increased by +9.1 % in South China, which partially offset the emission reductions. Extreme dust storms swept through the northern region in the period after COVID-19, with an increase of +23.5 % in NCP and + 42.9 % in Northeast China (NEC) for dust AOD. However, unfavorable meteorological conditions overwhelmed the benefits of emission reductions, resulting in a +20.1 % increase in AOD in NEC during the lockdown period. Furthermore, the downward shortwave radiative flux showed a positive anomaly due to the reduced aerosol loading in the atmosphere during the lockdown period. This study highlights that we can benefit from short-term controls for the improvement of air pollution, but we also need to seriously considered the cross-regional transport of natural aerosol and meteorological drivers. Aerosol optical depth; Anthropogenic aerosol; COVID-19 impacts over China; Meteorological drivers; Natural aerosol; Radiative flux
Lin, Lin; Liu, Xiaohong; Fu, Qiang; Shan, YunpengLin, L., X. Liu, Q. Fu, Y. Shan, 2023: Climate Impacts of Convective Cloud Microphysics in NCAR CAM5. J. Climate, 36(10), 3183-3202. doi: 10.1175/JCLI-D-22-0136.1. Abstract We improved the treatments of convective cloud microphysics in the NCAR Community Atmosphere Model version 5.3 (CAM5.3) by 1) implementing new terminal velocity parameterizations for convective ice and snow particles, 2) adding graupel microphysics, 3) considering convective snow detrainment, and 4) enhancing rain initiation and generation rate in warm clouds. We evaluated the impacts of improved microphysics on simulated global climate, focusing on simulated cloud radiative forcing, graupel microphysics, convective cloud ice amount, and tropical precipitation. Compared to CAM5.3 with the default convective microphysics, the too-strong cloud shortwave radiative forcing due primarily to excessive convective cloud liquid is largely alleviated over the tropics and midlatitudes after rain initiation and generation rate is enhanced, in better agreement with the CERES-EBAF estimates. Geographic distributions of graupel occurrence are reasonably simulated over continents; whereas the graupel occurrence remains highly uncertain over the oceanic storm-track regions. When evaluated against the CloudSat–CALIPSO estimates, the overestimation of convective ice mass is alleviated with the improved convective ice microphysics, among which adding graupel microphysics and the accompanying increase in hydrometeor fall speed play the most important role. The probability distribution function (PDF) of rainfall intensity is sensitive to warm rain processes in convective clouds, and enhancement in warm rain production shifts the PDF toward heavier precipitation, which agrees better with the TRMM observations. Common biases of overestimating the light rain frequency and underestimating the heavy rain frequency in GCMs are mitigated.
Liu, Huizeng; Li, Qingquan; Huang, Shaopeng; Qiu, Hong; Jiang, Huiping; Yang, Chao; Zhu, PingLiu, H., Q. Li, S. Huang, H. Qiu, H. Jiang, C. Yang, P. Zhu, 2023: Estimating the Angular Distribution of the Earth’s Longwave Radiation from Radiative Fluxes. IEEE Transactions on Geoscience and Remote Sensing, 1-1. doi: 10.1109/TGRS.2023.3269431. In recent years, several novel satellite platforms and sensors have been proposed for the Earth Radiation Budget (ERB). Simulating the sensor-measured signals could be helpful for optimizing the settings of sensors and exploring their potential in ERB. The anisotropic factor, depicting the anisotropy of Earth’s radiation, is essential in the simulation. However, developing angular distribution models involves complex procedures of data preparation, processing, and modeling. This study, targeting at simplifying the procedure of simulating the signals of ERB sensors, proposed a suit of models for estimating the longwave anisotropic factors directly from the Earth’s radiative fluxes. The models were developed with CERES/Terra data sensed in rotating azimuth plane (RAP) mode during 2000-2005 and the artificial neural network (ANN) algorithm, and tested with 12 monthly of CERES/Terra data collected in RAP and cross-track mode during 2021-2022, respectively. Models were developed for 10 scene types based on Earth’s surface types, and compared with the operational ANN ADMs. Results showed that the longwave anisotropic factors were accurately estimated with the correlation coefficient (r) varying between 0.84 and 0.98 and MAPE within 1.20% for the test dataset, and the approach proposed in this study had comparable performance with the ANN ADMs. With the estimated anisotropic factors, the sensor-measured radiances were accurately retrieved with r=1.00 and MAPE=0.53%. Therefore, the proposed approach is promising in accurate and efficient simulations of novel ERB platforms and sensors like the Moon-based Earth Radiation. CERES; Angular distribution models; Anisotropic factor; Artificial neural networks; Data models; Earth; Earth’s radiative budget; Extraterrestrial measurements; Instruments; Satellite broadcasting; Satellites; Top-of-atmosphere
Liu, Xue; Diao, Yina; Sun, Ruipeng; Gong, QinglongLiu, X., Y. Diao, R. Sun, Q. Gong, 2023: Impacts of Cyclones on Arctic Clouds during Autumn in the Early 21st Century. Atmosphere, 14(4), 689. doi: 10.3390/atmos14040689. Our study shows that, during 2001–2017, when the sea ice was melting rapidly, cyclone days accounted for more than 50% of the total autumn days at the sounding stations in the Arctic marginal seas north of the Eurasian continent and almost 50% of the total autumn days at the sounding station on the northern coast of Canada. It is necessary to investigate the influence of Arctic cyclones on the cloud fraction in autumn when the sea ice refreezes from its summer minimum and the infrared cloud radiative effect becomes increasingly important. Cyclones at the selected stations are characterized by a narrow maximum rising zone with vertically consistent high relative humidity (RH) and a broad region outside the high RH zone with low RH air from the middle troposphere covering the low troposphere’s high relative humidity air. Consequently, on approximately 40% of the cyclone days, the cloud formation condition was improved from the near surface to the upper troposphere due to the cooling of strong rising warm humid air. Therefore, cyclones lead to middle cloud increases and sometimes high cloud increases, since the climatological Arctic autumn clouds are mainly low clouds. On approximately 60% of the cyclone days, only low cloud formed, but the low cloud formation condition was suppressed due to the mixing ratio decrease induced by cold dry air sinking. As a result, cyclones generally lead to a decrease in low clouds. However, the correlation between the cyclones and low clouds is complex and varies with surface ice conditions. Arctic autumn clouds; Arctic cyclones; cloud change
Liu, Yawen; Wang, Minghuai; Yue, Man; Qian, YunLiu, Y., M. Wang, M. Yue, Y. Qian, 2023: Distinct Seasonality in Aerosol Responses to Emission Control Over Northern China. Journal of Geophysical Research: Atmospheres, 128(11), e2022JD038377. doi: 10.1029/2022JD038377. Despite intensive research exploring how aerosols respond to emission control over Northern China, efforts mostly focus on the environmental benefit, especially in winter. Here we found that unlike the most substantial PM2.5 concentration reduction in winter, aerosol optical depth (AOD) declines more than 2 times faster in summer, causing an increase in aerosol radiative effects of 1.2 (5.7)Wm−2 on all-sky (clear-sky) conditions over 2013–2019 and largely shaping the climate impact. Low-level aerosols are shown to be the prime contributor under the synergetic effects of aerosol composition and ambient relative humidity (RH). The dominance of the highly hygroscopic sulfate combined with high RH enables a strong extinction efficiency of the reduced summertime aerosols, while the insignificant AOD decline in wintertime result from the dominance of organic aerosols with weak hygroscopicity, and is further offset by the increased frequencies of extremely high RH. We show the environmental and climatic responses of aerosols to emission control exhibit distinctively different seasonality. aerosol response; climate effect; emission reduction; seasonality
Lu, Lu; Ma, QianLu, L., Q. Ma, 2023: Diurnal Cycle in Surface Incident Solar Radiation Characterized by CERES Satellite Retrieval. Remote Sensing, 15(13), 3217. doi: 10.3390/rs15133217. Surface incident solar radiation (Rs) plays an important role in climate change on Earth. Recently, the use of satellite-retrieved datasets to obtain global-scale Rs with high spatial and temporal resolutions has become an indispensable tool for research in related fields. Many studies were carried out for Rs evaluation based on the monthly satellite retrievals; however, few evaluations have been performed on their diurnal variation in Rs. This study used independently widely distributed ground-based data from the Baseline Surface Radiation Network (BSRN) to evaluate hourly Rs from the Clouds and the Earth’s Radiant Energy System Synoptic (CERES) SYN1deg–1Hour product through a detrended standardization process. Furthermore, we explored the influence of cloud cover and aerosols on the diurnal variation in Rs. We found that CERES-retrieved Rs performs better at midday than at 7:00–9:00 and 15:00–17:00. For spatial distribution, CERES-retrieved Rs performs better over the continent than over the island/coast and polar regions. The Bias, MAB and RMSE in CERES-retrieved Rs under clear-sky conditions are rather small, although the correlation coefficients are slightly lower than those under overcast-sky conditions from 9:00 to 15:00. In addition, the range in Rs bias caused by cloud cover is 1.97–5.38%, which is significantly larger than 0.31–2.52% by AOD. CERES; diurnal variation; BSRN; solar radiation
Luccini, Eduardo; Orte, Facundo; Lell, Julián; Nollas, Fernando; Carbajal, Gerardo; Wolfram, EliánLuccini, E., F. Orte, J. Lell, F. Nollas, G. Carbajal, E. Wolfram, 2023: The UV Index color palette revisited. Journal of Photochemistry and Photobiology, 15, 100180. doi: 10.1016/j.jpap.2023.100180. The UV Index (UVI), standardized by the World Health Organization (WHO) in 2002, is an internationally accepted reference for disseminating information on solar UV radiation levels with the purpose of preventing the harmful effects on human health by sun overexposure. The UVI is the erythemal irradiance expressed in a dimensionless unit, with numerical values adapted to a risk scale that considers the “Extreme” level from a UVI value equal to 11 upwards. This scale is linked to a color palette by health risk ranges, and to a graded color palette by units of UVI for more details. Both the numerical scale and its associated risk levels were universally adopted by the scientific community and by global information systems to the population. However, inconsistencies and limitations persist between both UVI color palettes, making their interpretation and application difficult. In the present work all these aspects are addressed, proposing a revised color palette for unit UVI values that resolves each of them. Based on the WHO risk-ranges UVI color palette, the new color palette for unit UVI values gives coherence to both color charts, allowing reliable identification of the risk level bands and of each unit UVI level within them, and solves the need to distinguish between units for numerical values of UVI higher than 11 that are registered daily in many regions of the world. Color codes; Color palettes; Public health; Risk scale; Solar radiation; UV Index
Luo, Hao; Quaas, Johannes; Han, YongLuo, H., J. Quaas, Y. Han, 2023: Examining cloud vertical structure and radiative effects from satellite retrievals and evaluation of CMIP6 scenarios. Atmospheric Chemistry and Physics, 23(14), 8169-8186. doi: 10.5194/acp-23-8169-2023. Clouds exhibit a wide range of vertical morphologies that are regulated by distinct atmospheric dynamics and thermodynamics and are related to a diversity of microphysical properties and radiative effects. In this study, the new CERES-CloudSat-CALIPSO-MODIS (CCCM) RelD1 dataset is used to investigate the morphology and spatial distribution of different cloud vertical structure (CVS) types during 2007–2010. The combined active and passive satellites provide a more precise CVS than those only based on passive imagers or microwave radiometers. We group the clouds into 12 CVS classes based on how they are located or overlapping in three standard atmospheric layers with pressure thresholds of 440 and 680 hPa. For each of the 12 CVS types, the global average cloud radiative effects (CREs) at the top of the atmosphere, within the atmosphere and at the surface, as well as the cloud heating rate (CHR) profiles are examined. The observations are subsequently used to evaluate the variations in total, high-, middle- and low-level cloud fractions in CMIP6 models. The “historical” experiment during 1850–2014 and two scenarios (ssp245 and ssp585) during 2015–2100 are analyzed. The observational results show a substantial difference in the spatial pattern among different CVS types, with the greatest contrast between high and low clouds. Single-layer cloud fraction is almost 4 times larger on average than multi-layer cloud fraction, with significant geographic differences associated with clearly distinguishable regimes, showing that overlapping clouds are regionally confined. The global average CREs reveal that four types of CVSs warm the planet, while eight of them cool it. The longwave component drives the net CHR profile, and the CHR profiles of multi-layer clouds are more curved and intricate than those of single-layer clouds, resulting in complex thermal stratifications. According to the long-term analysis from CMIP6, the projected total cloud fraction decreases faster over land than over the ocean. The high clouds over the ocean increase significantly, but other types of clouds over land and the ocean continue to decrease, helping to offset the decrease in oceanic total cloud fraction. Moreover, it is concluded that the spatial pattern of CVS types may not be significantly altered by climate change, and only the cloud fraction is influenced. Our findings suggest that long-term observed CVS should be emphasized in the future to better understand CVS responses to anthropogenic forcing and climate change.
Luo, Rui; Ding, Qinghua; Baxter, Ian; Chen, Xianyao; Wu, Zhiwei; Bushuk, Mitchell; Wang, HailongLuo, R., Q. Ding, I. Baxter, X. Chen, Z. Wu, M. Bushuk, H. Wang, 2023: Uncertain role of clouds in shaping summertime atmosphere-sea ice connections in reanalyses and CMIP6 models. Climate Dynamics. doi: 10.1007/s00382-023-06785-9. Downwelling longwave radiation (DLR) driven by the atmospheric and cloud conditions in the troposphere is suggested to be a dominant factor to determine the summertime net surface energy budget over the Arctic Ocean and thus plays a key role to shape the September sea ice. We use reanalyses and the self-organizing map (SOM) method to distinguish CMIP6 model performance in replicating the observed strong atmosphere-DLR connection. We find all models can reasonably simulate the linkage between key atmosphere variables and the clear sky DLR but behave differently in replicating the atmosphere-DLR connection due to cloud forcing. In ERA5 and strongly coupled models, tropospheric high pressure is associated with decreased clouds in the mid- and high-levels and increased clouds near the surface. This out-of-phase structure indicates that DLR cloud forcing is nearly neutral, making the clear sky DLR more important to bridge JJA circulation to late-summer sea ice. In MERRA-2 and weakly coupled models, tropospheric clouds display a vertically homogeneous reduction; the cloud DLR is thus strongly reduced due to the cooling effect, which partially cancels out the clear sky DLR and makes the total DLR less efficient to translate circulation forcing to sea ice. The differences of cloud vertical distribution in CMIP6 appear to be differentiated by circulation related relative humidity. Therefore, a better understanding of the discrepancy of different reanalyses and remote sensing products is critical to comprehensively evaluate simulated interactions among circulation, clouds, sea ice and energy budget at the surface in summer. CMIP6; Atmosphere-Sea ice connection; Clear-sky; Cloud; DLR
Luo, Run; Liu, Yuzhi; Luo, Min; Li, Dan; Tan, Ziyuan; Shao, Tianbin; Alam, KhanLuo, R., Y. Liu, M. Luo, D. Li, Z. Tan, T. Shao, K. Alam, 2023: Dust effects on mixed-phase clouds and precipitation during a super dust storm over northern China. Atmospheric Environment, 313, 120081. doi: 10.1016/j.atmosenv.2023.120081. Dust aerosols have been generally regarded as efficient ice nuclei (IN), but their influences on mixed-phase clouds and precipitation are poorly quantified. In this study, combining satellite observations, reanalysis data and the Weather Research and Forecasting (WRF) model, we investigate the impacts of dust aerosols on mixed-phase clouds and precipitation during a super dust storm over northern China. The Suomi National Polar-Orbiting Partnership (S-NPP) satellite observed a super dust storm from March 15–19, 2021 in northern China, followed by heavy precipitation between March 17 and 19. The results showed that the occurrence of super dust storms may play an important role in cloud formation and precipitation processes. Furthermore, numerical modeling revealed that dust aerosols can increase the ice crystal number concentration (QNi) and decrease the cloud droplet number concentration (QNc) in mixed-phase clouds through the Wegener–Bergeron–Findeisen (WBF) process, in which the maximum increase in QNi can reach 21%. Simultaneously, the mass mixing ratios of rain, graupel and snow increased due to dust aerosols. Consequently, precipitation could increase by up to 9.8% in northern China. This study could provide evidence for understanding the mechanisms of dust effects on mixed-phase clouds over northern China. Precipitation; Satellite observations; WRF model; Dust aerosols; Mixed-phase clouds
Lyapustin, Alexei; Wang, Yujie; Choi, Myungje; Xiong, Xiaoxiong; Angal, Amit; Wu, Aisheng; Doelling, David R.; Bhatt, Rajendra; Go, Sujung; Korkin, Sergey; Franz, Bryan; Meister, Gerhardt; Sayer, Andrew M.; Roman, Miguel; Holz, Robert E.; Meyer, Kerry; Gleason, James; Levy, RobertLyapustin, A., Y. Wang, M. Choi, X. Xiong, A. Angal, A. Wu, D. R. Doelling, R. Bhatt, S. Go, S. Korkin, B. Franz, G. Meister, A. M. Sayer, M. Roman, R. E. Holz, K. Meyer, J. Gleason, R. Levy, 2023: Calibration of the SNPP and NOAA 20 VIIRS sensors for continuity of the MODIS climate data records. Remote Sensing of Environment, 295, 113717. doi: 10.1016/j.rse.2023.113717. Accurate long-term sensor calibration and periodic re-processing to ensure consistency and continuity of atmospheric, land and ocean geophysical retrievals from space within the mission period and across different missions is a major requirement of climate data records. In this work, we applied the Multi-Angle Implementation of Atmospheric Correction (MAIAC)-based vicarious calibration technique over Libya-4 desert site to perform calibration analysis of Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi National Polar-orbiting Partnership (SNPP) and NOAA-20 satellites. For both VIIRS sensors we characterized residual linear calibration trends and cross-calibrated both sensors to MODerate resolution Imaging Spectroradiometer (MODIS) Aqua regarded as a calibration standard. The relative spectral response (RSR) differences were accounted for using the German Aerospace Center (DLR) Earth Sensing Imaging Spectrometer (DESIS) hyperspectral surface reflectance data. Our results agree with independent vicarious calibration results of both the MODIS/VIIRS Characterization Support Team as well as the CERES Imager and Geostationary Calibration Group within estimated uncertainty of 1–2%. Analysis of MAIAC geophysical products with the new calibration shows a high level of agreement of MAIAC aerosol, surface reflectance and NDVI records between MODIS and VIIRS. Excluding high aerosol optical depth (AOD), all three sensors agree in AOD with mean difference (MD) less than 0.01 and residual mean squared difference rmsd ∼ 0.04. Spectral geometrically normalized surface reflectance agrees within rmsd of 0.003–0.005 in the visible and 0.01–0.012 at longer wavelengths. The residual surface reflectance differences are fully explained by differences in spectral filter functions. Finally, difference in NDVI is characterized by rmsd ∼ 0.02 and MD less than 0.003 for NDVI based on VIIRS imagery bands I1/I2 and less than 0.01 for NDVI based on VIIRS radiometric bands M5/M7. In practical sense, these numbers indicate consistency and continuity in MAIAC records ensuring the smooth transition from MODIS to VIIRS. Calibration; MODIS; VIIRS; NDVI; MAIAC; Surface reflectance
Lyman, John M.; Johnson, Gregory C.Lyman, J. M., G. C. Johnson, 2023: Global High-Resolution Random Forest Regression Maps of Ocean Heat Content Anomalies Using In Situ and Satellite Data. J. Atmos. Oceanic Technol., 40(5), 575-586. doi: 10.1175/JTECH-D-22-0058.1. Abstract The ocean, with its low albedo and vast thermal inertia, plays key roles in the climate system, including absorbing massive amounts of heat as atmospheric greenhouse gas concentrations rise. While the Argo array of profiling floats has vastly improved sampling of ocean temperature in the upper half of the global ocean volume since the mid-2000s, they are not sufficient in number to resolve eddy scales in the oceans. However, satellite sea surface temperature (SST) and sea surface height (SSH) measurements do resolve these scales. Here we use random forest regressions to map ocean heat content anomalies (OHCA) using in situ training data from Argo and other sources on a 7-day × 1/4° × 1/4° grid with latitude, longitude, time, SSH, and SST as predictors. The maps display substantial patterns on eddy scales, resolving variations of ocean currents and fronts. During the well-sampled Argo period, global integrals of these maps reduce noise relative to estimates based on objective mapping of in situ data alone by roughly a factor of 3 when compared to time series of CERES (satellite data) top-of-the-atmosphere energy flux measurements and improve correlations of anomalies with CERES on annual time scales. Prior to and early on in the Argo period, when in situ data were sparser, global integrals of these maps retain low variance, and do not relax back to a climatological mean, avoiding potential deficiencies of various methods for infilling data-sparse regions with objective maps by exploiting temporal and spatial patterns of OHCA and its correlations with SST and SSH. Significance Statement We use a simple machine learning technique to improve maps of subsurface ocean warming by exploiting the relationships between subsurface ocean temperature both sea surface temperature and sea level. Mapping ocean warming is important because it contributes to sea level rise through thermal expansion; impacts marine life through marine heatwaves and changes in mixing, oxygen, and carbon dioxide levels; increases energy available to tropical cyclones; and stores most of the energy building up in Earth’s climate system owing to the accumulation of anthropogenic greenhouse gases in the atmosphere. Our new estimates generally have lower noise energy and higher correlations than other products when compared with global energy fluxes at the top of the atmosphere measured by satellite.
Ma, Qianrong; Sun, Yingxiao; Wan, Shiquan; Gu, Yu; Bai, Yang; Mu, JiayiMa, Q., Y. Sun, S. Wan, Y. Gu, Y. Bai, J. Mu, 2023: An ENSO Prediction Model Based on Backtracking Multiple Initial Values: Ordinary Differential Equations–Memory Kernel Function. Remote Sensing, 15(15), 3767. doi: 10.3390/rs15153767. This article presents a new prediction model, the ordinary differential equations–memory kernel function (ODE–MKF), constructed from multiple backtracking initial values (MBIV). The model is similar to a simplified numerical model after spatial dimension reduction and has both nonlinear characteristics and the low-cost advantage of a time series model. The ODE–MKF focuses on utilizing more temporal information and includes machine learning to solve complex mathematical inverse problems to establish a predictive model. This study first validates the feasibility of the ODE–MKF via experiments using the Lorenz system. The results demonstrate that the ODE–MKF prediction model could describe the nonlinear characteristics of complex systems and exhibited ideal predictive robustness. The prediction of the El Niño-Southern Oscillation (ENSO) index further demonstrates its effectiveness, as it achieved 24-month lead predictions and effectively improved nonlinear problems. Furthermore, the reliability of the model was also tested, and approximately 18 months of prediction were achieved, which was verified with the Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) radiation fluxes. The short-term memory index Southern Oscillation (SO) was further used to examine the applicability of ODE–MKF. A six-month lead prediction of the SO trend was achieved, indicating that the predictability of complex systems is related to their inherent memory scales. ENSO 3; multiple backtracking initial values 2; ordinary differential equations–memory kernel function 1; prediction 4
Mace, Gerald G.; Benson, Sally; Humphries, Ruhi; Gombert, Peter M.; Sterner, ElizabethMace, G. G., S. Benson, R. Humphries, P. M. Gombert, E. Sterner, 2023: Natural marine cloud brightening in the Southern Ocean. Atmospheric Chemistry and Physics, 23(2), 1677-1685. doi: 10.5194/acp-23-1677-2023. The number of cloud droplets per unit volume (Nd) is a fundamentally important property of marine boundary layer (MBL) liquid clouds that, at constant liquid water path, exerts considerable controls on albedo. Past work has shown that regional Nd has a direct correlation to marine primary productivity (PP) because of the role of seasonally varying, biogenically derived precursor gases in modulating secondary aerosol properties. These linkages are thought to be observable over the high-latitude oceans, where strong seasonal variability in aerosol and meteorology covary in mostly pristine environments. Here, we examine Nd variability derived from 5 years of MODIS Level 2-derived cloud properties in a broad region of the summer eastern Southern Ocean and adjacent marginal seas. We demonstrate latitudinal, longitudinal and temporal gradients in Nd that are strongly correlated with the passage of air masses over high-PP waters that are mostly concentrated along the Antarctic Shelf poleward of 60∘ S. We find that the albedo of MBL clouds in the latitudes south of 60∘ S is significantly higher than similar liquid water path (LWP) clouds north of this latitude.
Mall, Ankita; Singh, SachchidanandMall, A., S. Singh, 2023: Effects of Atmospheric Aerosol Types on Ultraviolet Flux at Different Stations in the Indo-Gangetic Plain. Environmental Sciences Proceedings, 27(1), 33. doi: 10.3390/ecas2023-15118. Atmospheric aerosols play a crucial role in the scattering and absorption of solar radiation, directly influencing the UV flux reaching the Earth’s surface. This study investigates the impact of different atmospheric aerosol types on the ultraviolet (UV) flux at four stations over the Indo-Gangetic plain (IGP). For this study, high-resolution 1° × 1° UVA and UVB data were obtained from Clouds and the Earth’s Radiant Energy System (CERES). Various aerosol types present in the atmosphere were categorized based upon their optical properties and their quantitative influence on UVA and UVB flux was examined. Ground-level aerosol products were obtained from the NASA-based Aerosol Robotic Network (AERONET) at four stations in the IGP. Based on the optical properties of aerosols (fine mode fraction, single scattering albedo, aerosol optical depth and angstrom exponent), four distinct atmospheric aerosol types were inferred, namely dust-dominant (DT), polluted-continental-dominant (PCD), black-carbon-dominant (BCD), and organic-carbon-dominant (OCD). It is observed that the AOD of different aerosol types when separated do not seem to have made significant effects on UVA/B radiation (except at Kanpur), possibly due to the statistically smaller data set. For the entire combined AOD, the effects on UVA/B became quite significant at all the stations, which shows that a unit rise in AOD leads to a reduction of 5–7 Wm−2 in UVA and 0.14–0.23 Wm−2 in UVB. CERES; AERONET; UVA; UVB; aerosol types
Masunaga, HirohikoMasunaga, H., 2023: The Edge Intensification of Eastern Pacific ITCZ Convection. J. Climate, 36(10), 3469-3480. doi: 10.1175/JCLI-D-22-0382.1. Abstract Tropical precipitation is climatologically most intense at the heart of the intertropical convergence zone (ITCZ), but this is not always true in instantaneous snapshots. Precipitation is amplified along the ITCZ edge rather than at its center from time to time. In this study, satellite observations of column water vapor, precipitation, and radiation as well as the thermodynamic field from reanalysis data are analyzed to investigate the behavior of ITCZ convection in light of the local atmospheric energy imbalance. The analysis is focused on the eastern Pacific ITCZ, defined as the areas where column water vapor exceeds 50 mm over a specified width (typically 400–600 km) in the domain of 20°S–20°N, 180°–90°W. The events with a precipitation maximum at the southern and northern edges of the ITCZ are each averaged into composite statistics and are contrasted against the reference case with peak precipitation at the ITCZ center. The key findings are as follows. When precipitation peaks at the ITCZ center, suppressed radiative cooling forms a prominent positive peak in the diabatic forcing to the atmosphere, counteracted by an export of moist static energy (MSE) owing to a deep vertical advection and a large horizontal export of MSE. When convection develops at the ITCZ edges, to the contrary, a positive peak of the diabatic forcing is only barely present. An import of MSE owing to a shallow ascent on the ITCZ edges presumably allows an edge intensification to occur despite the weak diabatic forcing.
Matsui, Toshi; Wolff, David B.; Lang, Stephen; Mohr, Karen; Zhang, Minghua; Xie, Shaocheng; Tang, Shuaiqi; Saleeby, Stephen M.; Posselt, Derek J.; Braun, Scott A.; Chern, Jiun-Dar; Dolan, Brenda; Pippitt, Jason L.; Loftus, Adrian M.Matsui, T., D. B. Wolff, S. Lang, K. Mohr, M. Zhang, S. Xie, S. Tang, S. M. Saleeby, D. J. Posselt, S. A. Braun, J. Chern, B. Dolan, J. L. Pippitt, A. M. Loftus, 2023: Systematic Validation of Ensemble Cloud-Process Simulations Using Polarimetric Radar Observations and Simulator Over the NASA Wallops Flight Facility. Journal of Geophysical Research: Atmospheres, 128(16), e2022JD038134. doi: 10.1029/2022JD038134. The BiLateral Operational Storm-Scale Observation and Modeling (BLOSSOM) project was initiated to establish a long-term supersite to improve understanding of cloud physical states and processes as well as to support satellite and climate model programs over the Wallops Flight Facility site via a bilateral approach of storm-scale observations and process modeling. This study highlights a noble systematic validation framework of the BLOSSOM ensemble cloud-process simulations through mixed-phase, light-rain, and deep-convective precipitation cases. The framework consists of creating a domain-shifted ensemble of large-scale forcing data sets, and configuring and performing cloud-process simulations with three different bulk microphysics schemes. Validation uses NASA S-band dual-POLarimetric radar observations in the form of statistical composites and skill scores via a polarimetric radar simulator and newly developed CfRad Data tool (CfRAD). While the simulations capture the overall structures of the reflectivity composites, polarimetric signals are still poorly simulated, mainly due to a lack of representation of ice microphysics diversity in shapes, orientation distributions, and their complex mixtures. Despite the limitation, this new ensemble-based validation framework demonstrates that (a) no particular forcing or microphysics scheme outperforms the rest and (b) the skill scores of coarse- and fine-resolution ensemble simulations with different domain-shifted forcing and microphysics schemes are highly correlated with each other with no clear improvement. On the other hand, this suggests that coarse-resolution ensemble simulations are relevant for selecting the best meteorological forcing and microphysics scheme before conducting computationally demanding large eddy simulations in support of aircraft and satellite instrument development as well as cloud-precipitation-convection parameterizations. validation; cloud-process model; ensemble simulations; polarimetric radar; radar simulator; Wallops Flight Facility
McCloskey, Kevin; Chen, Sixing; Meijer, Vincent R.; Ng, Joe Yue-Hei; Davis, Geoff; Elkin, Carl; Van Arsdale, Christopher; Geraedts, ScottMcCloskey, K., S. Chen, V. R. Meijer, J. Y. Ng, G. Davis, C. Elkin, C. Van Arsdale, S. Geraedts, 2023: Estimates of broadband upwelling irradiance from GOES-16 ABI. Remote Sensing of Environment, 285, 113376. doi: 10.1016/j.rse.2022.113376. Satellite-derived estimates of the Earth’s radiation budget are crucial for understanding and predicting the weather and climate. However, existing satellite products measuring broadband outgoing longwave radiation (OLR) and reflected shortwave radiation (RSR) have spatio-temporal resolutions that are too coarse to evaluate important radiative forcers like aircraft condensation trails. We present a neural network which estimates OLR and RSR based on narrowband radiances, using collocated Cloud and Earth’s Radiant Energy System (CERES) and GOES-16 Advanced Baseline Imager (ABI) data. The resulting estimates feature strong agreement with the CERES data products (R2 = 0.977 for OLR and 0.974 for RSR on CERES Level 2 footprints), and we provide open access to the collocated satellite data and model outputs on all available GOES-16 ABI data for the 4 years from 2018–2021. CERES; Artificial neural networks; Spatial resolution; OLR; Temporal resolution; GOES-16 ABI; RSR; Top of atmosphere flux
McCoy, Isabel L.; McCoy, Daniel T.; Wood, Robert; Zuidema, Paquita; Bender, Frida A.-M.McCoy, I. L., D. T. McCoy, R. Wood, P. Zuidema, F. A. Bender, 2023: The Role of Mesoscale Cloud Morphology in the Shortwave Cloud Feedback. Geophysical Research Letters, 50(2), e2022GL101042. doi: 10.1029/2022GL101042. A supervised neural network algorithm is used to categorize near-global satellite retrievals into three mesoscale cellular convective (MCC) cloud morphology patterns. At constant cloud amount, morphology patterns differ in brightness associated with the amount of optically thin cloud features. Environmentally driven transitions from closed MCC to other morphology patterns, typically accompanied by more optically thin cloud features, are used as a framework to quantify the morphology contribution to the optical depth component of the shortwave cloud feedback. A marine heat wave is used as an out-of-sample test of closed MCC occurrence predictions. Morphology shifts in optical depth between 65°S and 65°N under projected environmental changes (i.e., from an abrupt quadrupling of CO2) assuming constant cloud cover contributes between 0.04 and 0.07 W m−2 K−1 (aggregate of 0.06) to the global mean cloud feedback. climate change; cloud heterogeneity; boundary layer clouds; cloud organization; mesoscale cloud morphology; shortwave cloud feedback
Medeiros, Brian; Shaw, Jonah; Kay, Jennifer E.; Davis, IsaacMedeiros, B., J. Shaw, J. E. Kay, I. Davis, 2023: Assessing Clouds Using Satellite Observations Through Three Generations of Global Atmosphere Models. Earth and Space Science, 10(7), e2023EA002918. doi: 10.1029/2023EA002918. Clouds are parameterized in climate models using quantities on the model grid-scale to approximate the cloud cover and impact on radiation. Because of the complexity of processes involved with clouds, these parameterizations are one of the key challenges in climate modeling. Differences in parameterizations of clouds are among the main contributors to the spread in climate sensitivity across models. In this work, the clouds in three generations of an atmosphere model lineage are evaluated against satellite observations. Satellite simulators are used within the model to provide an appropriate comparison with individual satellite products. In some respects, especially the top-of-atmosphere cloud radiative effect, the models show generational improvements. The most recent generation, represented by two distinct branches of development, exhibits some regional regressions in the cloud representation; in particular the southern ocean shows a positive bias in cloud cover. The two branches of model development show how choices during model development, both structural and parametric, lead to different cloud climatologies. Several evaluation strategies are used to quantify the spatial errors in terms of the large-scale circulation and the cloud structure. The Earth mover's distance is proposed as a useful error metric for the passive satellite data products that provide cloud-top pressure-optical depth histograms. The cloud errors identified here may contribute to the high climate sensitivity in the Community Earth System Model, version 2 and in the Energy Exascale Earth System Model, version 1.
Meng, Xia; Hang, Yun; Lin, Xiuran; Li, Tiantian; Wang, Tijian; Cao, Junji; Fu, Qingyan; Dey, Sagnik; Huang, Kan; Liang, Fengchao; Kan, Haidong; Shi, Xiaoming; Liu, YangMeng, X., Y. Hang, X. Lin, T. Li, T. Wang, J. Cao, Q. Fu, S. Dey, K. Huang, F. Liang, H. Kan, X. Shi, Y. Liu, 2023: A satellite-driven model to estimate long-term particulate sulfate levels and attributable mortality burden in China. Environment International, 171, 107740. doi: 10.1016/j.envint.2023.107740. Ambient fine particulate matter (PM2.5) pollution is a major environmental and public health challenge in China. In the recent decade, the PM2.5 level has decreased mainly driven by reductions in particulate sulfate as a result of large-scale desulfurization efforts in coal-fired power plants and industrial facilities. Emerging evidence also points to the differential toxicity of particulate sulfate affecting human health. However, estimating the long-term spatiotemporal trend of sulfate is difficult because a ground monitoring network of PM2.5 constituents has not been established in China. Spaceborne sensors such as the Multi-angle Imaging SpectroRadiometer (MISR) instrument can provide complementary information on aerosol size and type. With the help of state-of-the-art machine learning techniques, we developed a sulfate prediction model under support from available ground measurements, MISR-retrieved aerosol microphysical properties, and atmospheric reanalysis data at a spatial resolution of 0.1°. Our sulfate model performed well with an out-of-bag cross-validationR2 of 0.68 at the daily level and 0.93 at the monthly level. We found that the national mean population-weighted sulfate concentration was relatively stable before the Air Pollution Prevention and Control Action Plan was enforced in 2013, ranging from 10.4 to 11.5 µg m−3. But the sulfate level dramatically decreased to 7.7 µg m−3 in 2018, with a change rate of −28.7 % from 2013 to 2018. Correspondingly, the annual mean total non-accidental and cardiopulmonary deaths attributed to sulfate decreased by 40.7 % and 42.3 %, respectively. The long-term, full-coverage sulfate level estimates will support future studies on evaluating air quality policies and understanding the adverse health effect of particulate sulfate. Air pollution; Machine learning; Atmospheric big data; Health impact assessment; Particulate sulfate; Spatiotemporal distribution
Meyssignac, Benoit; Ablain, Michael; Guérou, Adrien; Prandi, Pierre; Barnoud, Anne; Blazquez, Alejandro; Fourest, Sébastien; Rousseau, Victor; Bonnefond, Pascal; Cazenave, Anny; Chenal, Jonathan; Dibarboure, Gerald; Donlon, Craig; Benveniste, Jérôme; Sylvestre-Baron, Annick; Vinogradova, NadyaMeyssignac, B., M. Ablain, A. Guérou, P. Prandi, A. Barnoud, A. Blazquez, S. Fourest, V. Rousseau, P. Bonnefond, A. Cazenave, J. Chenal, G. Dibarboure, C. Donlon, J. Benveniste, A. Sylvestre-Baron, N. Vinogradova, 2023: How accurate is accurate enough for measuring sea-level rise and variability. Nature Climate Change, 13(8), 796-803. doi: 10.1038/s41558-023-01735-z. Sea-level measurements from radar satellite altimetry have reached a high level of accuracy and precision, which enables detection of global mean sea-level rise and attribution of most of the rate of rise to greenhouse gas emissions. This achievement is far beyond the original objectives of satellite altimetry missions. However, recent research shows that there is still room for improving the performance of satellite altimetry. Reduced uncertainties would enable regionalization of the detection and attribution of the anthropogenic signal in sea-level rise and provide new observational constraints on the water–energy cycle response to greenhouse gas emissions by improving the estimate of the ocean heat uptake and the Earth energy imbalance. Projection and prediction; Attribution; Physical oceanography
Minière, Audrey; von Schuckmann, Karina; Sallée, Jean-Baptiste; Vogt, LinusMinière, A., K. von Schuckmann, J. Sallée, L. Vogt, 2023: Robust acceleration of Earth system heating observed over the past six decades. Scientific Reports, 13(1), 22975. doi: 10.1038/s41598-023-49353-1. Global heating of the Earth system is unequivocal. However, detecting an acceleration of Earth heating has remained elusive to date, despite suggestive evidence of a potential increase in heating rates. In this study, we demonstrate that since 1960, the warming of the world ocean has accelerated at a relatively consistent pace of 0.15 ± 0.05 (W/m2)/decade, while the land, cryosphere, and atmosphere have exhibited an accelerated pace of 0.013 ± 0.003 (W/m2)/decade. This has led to a substantial increase in ocean warming, with a magnitude of 0.91 ± 0.80 W/m2 between the decades 1960–1970 and 2010–2020, which overlies substantial decadal-scale variability in ocean warming of up to 0.6 W/m2. Our findings withstand a wide range of sensitivity analyses and are consistent across different observation-based datasets. The long-term acceleration of Earth warming aligns qualitatively with the rise in CO2 concentrations and the decline in aerosol concentration during the same period, but further investigations are necessary to properly attribute these changes. Climate change; Climate sciences; Physical oceanography; Ocean sciences
Minnis, Patrick; Sun-Mack, Sunny; Smith, William L.; Trepte, Qing Z.; Hong, Gang; Chen, Yan; Yost, Christopher R.; Chang, Fu-Lung; Smith, Rita A.; Heck, Patrick W.; Yang, PingMinnis, P., S. Sun-Mack, W. L. Smith, Q. Z. Trepte, G. Hong, Y. Chen, C. R. Yost, F. Chang, R. A. Smith, P. W. Heck, P. Yang, 2023: VIIRS Edition 1 Cloud Properties for CERES, Part 1: Algorithm Adjustments and Results. Remote Sensing, 15(3), 578. doi: 10.3390/rs15030578. Cloud properties are essential for the Clouds and the Earth’s Radiant Energy System (CERES) Project, enabling accurate interpretation of measured broadband radiances, providing a means to understand global cloud-radiation interactions, and constituting an important climate record. Producing consistent cloud retrievals across multiple platforms is critical for generating a multidecadal cloud and radiation record. Techniques used by CERES for retrievals from measurements by the MODerate-Resolution Imaging Spectroradiometer (MODIS) on Terra and Aqua platforms are adapted for the application to radiances from the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership to continue the CERES record beyond the MODIS era. The algorithm adjustments account for spectral and channel differences, use revised reflectance models, and set new thresholds for detecting thin cirrus clouds at night. Cloud amounts from VIIRS are less than their MODIS counterparts by 0.016 during the day and 0.026 at night, but trend consistently over the 2012–2020 period. The VIIRS mean liquid water cloud fraction differs by ~0.01 from the MODIS amount. The average cloud heights from VIIRS differ from the MODIS heights by less than 0.2 km, except the VIIRS daytime ice cloud heights, which are 0.4 km higher. The mean VIIRS nonpolar optical depths are 17% (1%) larger (smaller) than those from MODIS for liquid (ice) clouds. The VIIRS cloud hydrometeor sizes are generally smaller than their MODIS counterparts. Discrepancies between the MODIS and VIIRS properties stem from spectral and spatial resolution differences, new tests at night, calibration inconsistencies, and new reflectance models. Many of those differences will be addressed in future editions. cloud; cloud height; cloud optical depth; cloud phase; cloud remote sensing; Clouds and the Earth’s Radiant Energy System (CERES); Visible Infrared Imaging Radiometer Suite (VIIRS); cloud amount; SNPP; Suomi National Polar-orbiting Partnership
Miyamoto, Ayumu; Nakamura, Hisashi; Xie, Shang-Ping; Miyasaka, Takafumi; Kosaka, YuMiyamoto, A., H. Nakamura, S. Xie, T. Miyasaka, Y. Kosaka, 2023: Radiative Impacts of Californian Marine Low Clouds on North Pacific Climate in a Global Climate Model. J. Climate, 36(24), 8443-8459. doi: 10.1175/JCLI-D-23-0153.1. Abstract The northeastern Pacific climate system features an extensive low-cloud deck off California on the southeastern flank of the subtropical high that accompanies intense northeasterly trades and relatively low sea surface temperatures (SSTs). This study assesses climatological impacts of the low-cloud deck and their seasonal differences by regionally turning on and off the low-cloud radiative effect in a fully coupled atmosphere–ocean model. The simulations demonstrate that the cloud radiative effect causes a local SST decrease of up to 3°C on an annual average with the response extending southwestward with intensified trade winds, indicative of the wind–evaporation–SST (WES) feedback. This nonlocal wind response is strong in summer, when the SST decrease peaks due to increased shortwave cooling, and persists into autumn. In these seasons when the background SST is high, the lowered SST suppresses deep-convective precipitation that would otherwise occur in the absence of the low-cloud deck. The resultant anomalous diabatic cooling induces a surface anticyclonic response with the intensified trades that promote the WES feedback. Such seasonal enhancement of the atmospheric response does not occur without air–sea couplings. The enhanced trades accompany intensified upper-tropospheric westerlies, strengthening the vertical wind shear that, together with the lowered SST, acts to shield Hawaii from powerful hurricanes. On the basin scale, the anticyclonic surface wind response accelerates the North Pacific subtropical ocean gyre to speed up the Kuroshio by as much as 30%. SST thereby increases along the Kuroshio and its extension, intensifying upward turbulent heat fluxes from the ocean to increase precipitation.
Mohamed, Marwa S.; Abdel Wahab, M. M.; El‐Metwally, Mossad; El-Nobi, Eman F.Mohamed, M. S., M. M. Abdel Wahab, M. El‐Metwally, E. F. El-Nobi, 2023: Validation of UV-Index retrieved from three satellites against Ground-Based measurements at different climates in Egypt. The Egyptian Journal of Remote Sensing and Space Science, 26(2), 361-367. doi: 10.1016/j.ejrs.2023.04.006. The UV Index is a useful tool to alert people with possible risks of exposure to solar UV radiation in Egypt. Ground UV-Index observation is a primary source to monitor solar UV levels, however the spatial coverage of the ground station is quite limited. The validation of available measurements were used frequently to define the possibility of using satellite data when measurements are not available, this was carried out for (leave area index and temperatures) for example (Ganguly et al., 2012) and (Laraby and Schott, 2018). In order to test the validity of the UV-index satellite products against ground observations, three satellite instruments (OMI, Terra + Aqua, and Terra + Npp) was performed at noontime in all sky conditions in the period 2012–2017 at three sites; Aswan, Cairo, and Matruh. The aforementioned sites were selected to represent different climates in Egypt. Annual intercomparison highlighted higher relative bias (rbias) at OMI (6.4 %) than both Terra + Aqua (2.3%) and Terra + Npp (2.8%). Also, Mean Absolute Percentage Error (MAPE), shows that OMI (10.6%) is relatively higher than both Terra + Aqua and Terra + Npp. (8.5 %). Based on these results, both Terra + Aqua and Terra + Npp have a better performance with respect to ground observations than OMI. This was due to OMI being more sensitive to dust and cloud than, Terra + Aqua and Terra + Npp. OMI/OMI/AURA; Terra+Aqua; Terra+Npp; UV-Index
Murray-Watson, Rebecca J.; Gryspeerdt, Edward; Goren, TomMurray-Watson, R. J., E. Gryspeerdt, T. Goren, 2023: Investigating the development of clouds within marine cold-air outbreaks. Atmospheric Chemistry and Physics, 23(16), 9365-9383. doi: 10.5194/acp-23-9365-2023. Marine cold-air outbreaks are important parts of the high-latitude climate system and are characterised by strong surface fluxes generated by the air–sea temperature gradient. These fluxes promote cloud formation, which can be identified in satellite imagery by the distinct transformation of stratiform cloud “streets” into a broken field of cumuliform clouds downwind of the outbreak. This evolution in cloud morphology changes the radiative properties of the cloud and therefore is of importance to the surface energy budget. While the drivers of stratocumulus-to-cumulus transitions, such as aerosols or the sea surface temperature gradient, have been extensively studied for subtropical clouds, the factors influencing transitions at higher latitudes are relatively poorly understood. This work uses reanalysis data to create a set of composite trajectories of cold-air outbreaks moving off the Arctic ice edge and co-locates these trajectories with satellite data to generate a unique view of liquid-dominated cloud development within cold-air outbreaks. The results of this analysis show that clouds embedded in cold-air outbreaks have distinctive properties relative to clouds following other trajectories in the region. The initial strength of the outbreak shows a lasting effect on cloud properties, with differences between clouds in strong and weak events visible over 30 h after the air has left the ice edge. However, while the strength (measured by the magnitude of the marine cold-air outbreak index) of the outbreak affects the magnitude of cloud properties, it does not affect the timing of the transition to cumuliform clouds or the top-of-atmosphere albedo. In contrast, the initial aerosol conditions do not strongly affect the magnitude of the cloud properties but are correlated to cloud break-up, leading to an enhanced cooling effect in clouds moving through high-aerosol conditions due to delayed break-up. Both the aerosol environment and the strength and frequency of marine cold-air outbreaks are expected to change in the future Arctic, and these results provide insight into how these changes will affect the radiative properties of the clouds. These results also highlight the need for information about present-day aerosol sources at the ice edge to correctly model cloud development.
Myers, Timothy A.; Zelinka, Mark D.; Klein, Stephen A.Myers, T. A., M. D. Zelinka, S. A. Klein, 2023: Observational Constraints on the Cloud Feedback Pattern Effect. J. Climate, 36(18), 6533-6545. doi: 10.1175/JCLI-D-22-0862.1. Abstract Model evidence for the “pattern effect” assumes that global climate models (GCMs) faithfully simulate how clouds respond to varying sea surface temperature (SST) patterns and associated meteorological perturbations. We exploit time-invariant satellite-based estimates of the sensitivity of marine low clouds to meteorological perturbations to estimate how these clouds responded to time-varying SST patterns and meteorology between 1870 and 2014. GCMs and reanalyses provide estimates of the historical meteorological changes. Observations suggest that increasing estimated inversion strength (EIS) between 1980 and 2014 produced a negative low cloud feedback, opposite to the positive feedback expected from increasing CO2. This indicates that the processes responsible for marine cloud changes from 1980 to the near present are distinct from those associated with an increase in CO2. We also observationally constrain the difference between the historical near-global marine low cloud feedback, λcloudhist, and that arising from increasing CO2, λcloud4xCO2. We find that this cloud feedback pattern effect depends strongly on time period and reanalysis dataset, and that varying changes in EIS and SST with warming explain much of its variability. Between 1980 and 2014, we estimate that λcloud4xCO2−λcloudhist=0.78±0.21 W m−2 K−1 (90% confidence) assuming meteorological changes from the Multiple Reanalysis Ensemble, implying a total pattern effect (that arising from all climate feedbacks) of 1.86 ± 0.45 W m−2 K−1. This observational evidence corroborates previous quantitative estimates of the pattern effect, which heretofore relied largely upon GCM-based cloud changes. However, disparate historical meteorological changes across individual reanalyses contribute to considerable uncertainty in its magnitude.
Nair, H. R. C. R.; Budhavant, Krishnakant; Manoj, M. R.; Andersson, August; Satheesh, S. K.; Ramanathan, V.; Gustafsson, ÖrjanNair, H. R. C. R., K. Budhavant, M. R. Manoj, A. Andersson, S. K. Satheesh, V. Ramanathan, Ö. Gustafsson, 2023: Aerosol demasking enhances climate warming over South Asia. npj Climate and Atmospheric Science, 6(1), 1-8. doi: 10.1038/s41612-023-00367-6. Anthropogenic aerosols mask the climate warming caused by greenhouse gases (GHGs). In the absence of observational constraints, large uncertainties plague the estimates of this masking effect. Here we used the abrupt reduction in anthropogenic emissions observed during the COVID-19 societal slow-down to characterize the aerosol masking effect over South Asia. During this period, the aerosol loading decreased substantially and our observations reveal that the magnitude of this aerosol demasking corresponds to nearly three-fourths of the CO2-induced radiative forcing over South Asia. Concurrent measurements over the northern Indian Ocean unveiled a ~7% increase in the earth’s surface-reaching solar radiation (surface brightening). Aerosol-induced atmospheric solar heating decreased by ~0.4 K d−1. Our results reveal that under clear sky conditions, anthropogenic emissions over South Asia lead to nearly 1.4 W m−2 heating at the top of the atmosphere during the period March–May. A complete phase-out of today’s fossil fuel combustion to zero-emission renewables would result in rapid aerosol demasking, while the GHGs linger on. Climate-change impacts; Atmospheric chemistry
Najarian, Hrag; Sakaeda, NaokoNajarian, H., N. Sakaeda, 2023: The Influence of Cloud Types on Cloud-Radiative Forcing During DYNAMO/AMIE. Journal of Geophysical Research: Atmospheres, 128(8), e2022JD038006. doi: 10.1029/2022JD038006. Cloud-radiative feedback is known to be an important process for the Madden-Julian Oscillation (MJO) and its accurate representation in general circulation models. The MJO is known to have a stronger cloud-radiative feedback compared to higher frequency convectively coupled equatorial waves (CCEW), for reasons that remain unclear. The objective of this study is to use data from the Dynamics of the MJO/Atmospheric Radiation Measurement MJO Investigation Experiment field campaign to investigate how cloud type evolution and their associated cloud-radiative forcing (CRF) differ between the MJO and CCEWs and their application to MJO dynamics under moisture mode theory. This study finds that the amplitude of CRF is the largest within the MJO compared to the higher frequency CCEWs, and CRF maximizes after the maximum precipitation (enhanced phase) of the MJO. We suggest this delay in the timing of maximum CRF occurs because most cloud types (congestus, deep, anvil, and cirrus) simultaneously maximize in frequency after the enhanced phase of the MJO, which is not seen for the higher frequency CCEWs. These specific cloud types help maintain the MJO through their radiatively-driven moistening which acts to prolong the enhanced phase of the MJO. The decomposition of radiatively-driven moistening by cloud types shows that simultaneous moistening by deep, anvil, and congestus clouds are particularly responsible for the maintenance of the MJO under moisture mode theory. This analysis suggests the importance of capturing the correct evolution of different cloud types and their associated radiative effects to better understand the thermodynamics of the MJO. cloud-radiative feedback; clouds; convectively-coupled equatorial waves; DYNAMO/AMIE; Madden-Julian Oscillation; moisture mode
Nguyen, Chuyen; Nachamkin, Jason E.; Sidoti, David; Gull, Jacob; Bienkowski, Adam; Bankert, Rich; Surratt, MelindaNguyen, C., J. E. Nachamkin, D. Sidoti, J. Gull, A. Bienkowski, R. Bankert, M. Surratt, 2023: Machine Learning–Based Cloud Forecast Corrections for Fusions of Numerical Weather Prediction Model and Satellite Data. Artificial Intelligence for the Earth Systems, 2(3). doi: 10.1175/AIES-D-22-0072.1. Abstract Given the diversity of cloud-forcing mechanisms, it is difficult to classify and characterize all cloud types through the depth of a specific troposphere. Importantly, different cloud families often coexist even at the same atmospheric level. The Naval Research Laboratory (NRL) is developing machine learning–based cloud forecast models to fuse numerical weather prediction model and satellite data. These models were built for the dual purpose of understanding numerical weather prediction model error trends as well as improving the accuracy and sensitivity of the forecasts. The framework implements a UNet convolutional neural network (UNet-CNN) with features extracted from clouds observed by the Geostationary Operational Environmental Satellite-16 (GOES-16) as well as clouds predicted by the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS). The fundamental idea behind this novel framework is the application of UNet-CNN for separate variable sets extracted from GOES-16 and COAMPS to characterize and predict broad families of clouds that share similar physical characteristics. A quantitative assessment and evaluation based on an independent dataset for upper-tropospheric (high) clouds suggests that UNet-CNN models capture the complexity and error trends of combined data from GOES-16 and COAMPS, and also improve forecast accuracy and sensitivity for different lead time forecasts (3–12 h). This paper includes an overview of the machine learning frameworks as well as an illustrative example of their application and a comparative assessment of results for upper-tropospheric clouds. Significance Statement Clouds are difficult to forecast because they require, in addition to spatial location, accurate height, depth, and cloud type. Satellite imagery is useful for verifying geographical location but is limited by 2D technology. Multiple cloud types can coexist at various heights within the same pixel. In this situation, cloud/no cloud verification does not convey much information about why the forecast went wrong. Sorting clouds by physical attributes such as cloud-top height, atmospheric stability, and cloud thickness contributes to a better understanding since very different physical mechanisms produce various types of clouds. Using a fusion of numerical model outputs and GOES-16 observations, we derive variables related to atmospheric conditions that form and move the clouds for our machine learning–based cloud forecast. The resulting verification over the U.S. mid-Atlantic region revealed our machine learning–based cloud forecast corrects systematic errors associated with high atmospheric clouds and provides accurate and consistent cloud forecasts from 3 to 12 h lead times.
Noda, Akira T.; Ohno, Tomoki; Kodama, Chihiro; Chen, Ying-Wen; Kuba, Naomi; Seiki, Tatsuya; Yamada, Yohei; Satoh, MasakiNoda, A. T., T. Ohno, C. Kodama, Y. Chen, N. Kuba, T. Seiki, Y. Yamada, M. Satoh, 2023: Recent global nonhydrostatic modeling approach without using a cumulus parameterization to understand the mechanisms underlying cloud changes due to global warming. Progress in Earth and Planetary Science, 10(1), 48. doi: 10.1186/s40645-023-00583-x. Clouds are the primary source of uncertainty in the prediction of climate change. To reduce the uncertainty of cloud simulations and overcome this difficulty in prediction, many climate modeling centers are now developing a new type of climate model, the global nonhydrostatic atmospheric model, which reduces the uncertainty arising from a cumulus parameterization by computing clouds explicitly using a cloud microphysics scheme. Among the global nonhydrostatic atmospheric models used in recent intercomparison studies, NICAM aims to project climate change by improving our understanding of cloud changes due to warming and related physical processes. NICAM is the first global nonhydrostatic model and was developed by our research team. This review summarizes the outcomes of a recent major five-year research program in Japan for studying climate using NICAM, as well as providing an overview of current issues regarding the use of global kilometer-scale simulations in high-resolution climate modeling. Clouds; Global nonhydrostatic model; Global warming; High-resolution climate simulation; Model improvement
Nuncio, M.; Athulya, R.; Nandanan, Naveen; Chatterjee, Sourav; Satheesan, K.; Acharya, Asutosh; Subeesh, M. P.; Vidya, P. J.Nuncio, M., R. Athulya, N. Nandanan, S. Chatterjee, K. Satheesan, A. Acharya, M. P. Subeesh, P. J. Vidya, 2023: Hails in Ny Alesund, Svalbard-atmospheric vertical structure and dependence on circulation. Natural Hazards, 117(2), 1365-1380. doi: 10.1007/s11069-023-05907-0. Hails observed at Ny Alesund, Svalbard in the Arctic during December–February 2018–19 is examined along with the atmospheric circulation patterns. When hail was noticed, surface warming and southwesterly—westerly winds were noticed. Atmospheric circulation pattern was characterised by high pressure anomaly over northwestern Europe. High clouds as well as excess liquid water were present when the high pressure systems were active over northwestern Europe. This is because winds blowing over ocean collect more moisture as well as transport nucleating particles to Svalbard. Also, hourly winds from ERA 5 reanalysis indicated vertical shear required for hail formation. When hails were observed, mixed precipitation types were recorded with the maximum intensities arising from the hails. The West Spitzbergen Current (WSC) induces a strong east west sea surface temperature (SST) gradient in the ocean west of Svalbard. A corresponding gradient in the atmospheric temperature is also maintained by the WSC in the west to east direction in the lower atmosphere. Moisture laden westerlies cross the SST gradient and induce strong frontal activity in the lower atmosphere resulting intense precipitation and hail. The upward vertical velocity noted in the lower troposphere supports the frontal activity. Human activities in the Arctic as elsewhere are bound to increase. Hence, there is a need to study the intense precipitation in the Arctic as well as its reasons as it can impact the Arctic environment and human activity. This calls for more continuous observations to clearly identify mechanisms and frequency of intense precipitation in the Arctic. Precipitation; Atmospheric circulation; Climate change; Hail; Seasurface temperature
Ouhechou, Amine; Philippon, Nathalie; Morel, Béatrice; Trentmann, Jörg; Graillet, Alexandre; Mariscal, Armand; Nouvellon, YannOuhechou, A., N. Philippon, B. Morel, J. Trentmann, A. Graillet, A. Mariscal, Y. Nouvellon, 2023: Inter-comparison and validation against in-situ measurements of satellite estimates of incoming solar radiation for Central Africa: From the annual means to the diurnal cycles. Atmospheric Research, 287, 106711. doi: 10.1016/j.atmosres.2023.106711. This study pictures for the first time incoming solar radiation mean evolution in Central Africa, intercomparing 8 gridded products (namely CERES-EBAF, CERES-SYN1deg, TPDC, CMSAF SARAH-2, CMSAF CLARA-A2, CAMS-JADE satellite products, as well as ERA5 reanalysis and WorldClim 2 interpolated measurements) and station-based estimations (FAOCLIM 2) or measurements. At the mean annual scale, all products picture low levels of global horizontal irradiance (GHI) to the west (SW Cameroon to SW Republic of Congo) and higher levels towards the north and south margins of the region. However, GHI levels in the CMSAF products are much higher than in CERES and TPDC. The mean annual cycles of GHI extracted for 6 sub-regions are bimodal, with two maxima during the two rainy seasons (March–May and September–November) and two minima during the two dry seasons (December–February and June–August). These seasonal cycles are well reproduced by most products except their amplitude which is dampened in TPDC. At the daily and sub-daily time-scales, products were compared with in-situ measurements from ten meteorological stations located in the western part of Central Africa. The products' performance is assessed through scores as bias and RMSE but also by considering the diurnal cycles' shape, amplitude and frequency of occurrence along the annual cycle. The products properly reproduce the shape of the four types of diurnal cycles with nonetheless noticeable differences in the cycle's frequencies of occurrence. Central Africa; Solar radiation; Diurnal cycle; Satellite estimates
Painemal, David; Chellappan, Seethala; Smith Jr., William L.; Spangenberg, Douglas; Park, J. Minnie; Ackerman, Andrew; Chen, Jingyi; Crosbie, Ewan; Ferrare, Richard; Hair, Johnathan; Kirschler, Simon; Li, Xiang-Yu; McComiskey, Allison; Moore, Richard H.; Sanchez, Kevin; Sorooshian, Armin; Tornow, Florian; Voigt, Christiane; Wang, Hailong; Winstead, Edward; Zeng, Xubin; Ziemba, Luke; Zuidema, PaquitaPainemal, D., S. Chellappan, W. L. Smith Jr., D. Spangenberg, J. M. Park, A. Ackerman, J. Chen, E. Crosbie, R. Ferrare, J. Hair, S. Kirschler, X. Li, A. McComiskey, R. H. Moore, K. Sanchez, A. Sorooshian, F. Tornow, C. Voigt, H. Wang, E. Winstead, X. Zeng, L. Ziemba, P. Zuidema, 2023: Wintertime synoptic patterns of midlatitude boundary layer clouds over the western North Atlantic: Climatology and insights from in-situ ACTIVATE observations. Journal of Geophysical Research: Atmospheres, n/a(n/a), e2022JD037725. doi: 10.1029/2022JD037725. The winter synoptic evolution of the western North Atlantic and its influence on the atmospheric boundary layer is described by means of a regime classification based on Self Organizing Maps applied to 12 year of data (2009-2020). The regimes are classified into categories according to daily 600-hPa geopotential height: dominant ridge, trough to ridge eastward transition (trough-ridge), dominant trough, and ridge to trough eastward transition (ridge-trough). A fifth synoptic regime resembles the winter climatological mean. Coherent changes in sea-level pressure and large-scale winds are in concert with the synoptic regimes: 1) the ridge regime is associated with a well-developed anticyclone; 2) the trough-ridge gives rise to a low pressure center over the ocean, ascents, and northerly winds over the coastal zone; 3) trough is associated with the eastward displacement of a cyclone, coastal subsidence, and northerly winds, all representative characteristics of cold-air outbreaks; 4) the ridge-trough regime features the development of an anticyclone and weak coastal winds. Low clouds are characteristic of the trough regime, with both trough and trough-ridge featuring synoptic maxima in cloud droplet number concentration (Nd). The Nd increase is primarily observed near the coast, concomitant with strong surface heat fluxes exceeding by more than 400 W m-2 compared to fluxes further east. Five consecutive days of aircraft observations collected during the ACTIVATE campaign corroborates the climatological characterization, confirming the occurrence of high Nd for days identified as trough. This study emphasizes the role of boundary-layer dynamics and aerosol activation and their roles in modulating cloud microphysics.
Pan, Yuying; Cheng, Lijing; Schuckmann, Karina von; Trenberth, Kevin E.; Li, Guancheng; Abraham, John; Liu, Yuanxin; Gouretski, Viktor; Yu, Yongqiang; Liu, Hailong; Liu, ChunleiPan, Y., L. Cheng, K. v. Schuckmann, K. E. Trenberth, G. Li, J. Abraham, Y. Liu, V. Gouretski, Y. Yu, H. Liu, C. Liu, 2023: Annual Cycle in Upper-Ocean Heat Content and the Global Energy Budget. J. Climate, 36(15), 5003-5026. doi: 10.1175/JCLI-D-22-0776.1. Abstract As a major component of Earth’s energy budget, ocean heat content (OHC) plays a vital role in buffering climate change. The annual cycle is the most prominent change in OHC but has always been removed to study variations and changes in Earth’s energy budget. Here, we investigate the annual cycle of the upper-2000-m OHC at regional to global scales and assess the robustness of the signals using the spread of multiple observational products. The potential drivers are also investigated by comparing the annual OHC signal with the corresponding change in top-of-atmosphere radiation, surface heat flux, ocean heat divergence, and meridional heat transport. Results show that the robust signal of annual OHC change is significant down to a 1000-m depth globally and can reach down to 1500 m in some areas such as the tropical ocean. The global OHC (0–1500 m) changes from positive anomalies within September–February to negative anomalies within March–August, mainly because of the larger ocean area in the Southern Hemisphere and the seasonal migration of solar irradiance. Owing to the huge ocean heat capacity, the annual cycle of OHC dominates that of the global energy budget. The difference among the OHC annual cycles in the three major ocean basins is mainly attributed to ocean heat transport, especially in the tropics. In the upper 1500 m at mid- and high latitudes and in the upper 50 m of the tropics, the net sea surface heat flux dominates the OHC annual cycle, while in the tropics below 50 m, wind-driven Ekman heat transport associated with the geostrophic flow is the main driver.
Pearce, F. A.; Bodas-Salcedo, A.Pearce, F. A., A. Bodas-Salcedo, 2023: Implied Heat Transport from CERES Data: Direct Radiative Effect of Clouds on Regional Patterns and Hemispheric Symmetry. J. Climate, 36(12), 4019-4030. doi: 10.1175/JCLI-D-22-0149.1. Abstract We calculate the implied horizontal heat transport due to the spatial anomalies of radiative fluxes at the top of the atmosphere (TOA). The regional patterns of implied heat transport for different components of the TOA fluxes are calculated by solving the Poisson equation with the flux components as source terms. The shortwave (SW) part of the spectrum governs the spatial patterns of the total implied heat transport. Using the cloud radiative effect (CRE) as source term, we show that the direct effect of clouds is to reduce the poleward heat transport in the majority of the Northern Hemisphere and at high southern latitudes. Clouds flatten the gradients of the clear-sky energy flux potential and hence reduce the implied heat transport with respect to clear skies. Clouds reduce the implied cross-equatorial heat transport with respect to clear sky through changes in the SW part of the spectrum. It changes from 0.83 PW in clear sky to −0.01 PW in all sky, equivalent to the hemispheric albedo symmetry reported in previous studies. We investigate hemispheric symmetry by introducing a metric that measures the symmetry of implied meridional heat transports at all latitudes. The direct effect of clouds is to increase the symmetry in the implied heat transport, and this is achieved through an increase in symmetry in the SW part of the spectrum in the tropics. Whether this is trivial or the result of a fundamental control in the climate system is still an open question.
Pei, Zhangcheng; Fiddes, Sonya L.; French, W. John R.; Alexander, Simon P.; Mallet, Marc D.; Kuma, Peter; McDonald, AdrianPei, Z., S. L. Fiddes, W. J. R. French, S. P. Alexander, M. D. Mallet, P. Kuma, A. McDonald, 2023: Assessing the cloud radiative bias at Macquarie Island in the ACCESS-AM2 model. Atmospheric Chemistry and Physics, 23(23), 14691-14714. doi: 10.5194/acp-23-14691-2023. As a long-standing problem in climate models, large positive shortwave radiation biases exist at the surface over the Southern Ocean, impacting the accurate simulation of sea surface temperature, atmospheric circulation, and precipitation. Underestimations of low-level cloud fraction and liquid water content are suggested to predominantly contribute to these radiation biases. Most model evaluations for radiation focus on summer and rely on satellite products, which have their own limitations. In this work, we use surface-based observations at Macquarie Island to provide the first long-term, seasonal evaluation of both downwelling surface shortwave and longwave radiation in the Australian Community Climate and Earth System Simulator Atmosphere-only Model version 2 (ACCESS-AM2) over the Southern Ocean. The capacity of the Clouds and the Earth’s Radiant Energy System (CERES) product to simulate radiation is also investigated. We utilize the novel lidar simulator, the Automatic Lidar and Ceilometer Framework (ALCF), and all-sky cloud camera observations of cloud fraction to investigate how radiation biases are influenced by cloud properties. Overall, we find an overestimation of +9.5±33.5 W m−2 for downwelling surface shortwave radiation fluxes and an underestimation of -2.3±13.5 W m−2 for downwelling surface longwave radiation in ACCESS-AM2 in all-sky conditions, with more pronounced shortwave biases of +25.0±48.0 W m−2 occurring in summer. CERES presents an overestimation of +8.0±18.0 W m−2 for the shortwave and an underestimation of -12.1±12.2 W m−2 for the longwave in all-sky conditions. For the cloud radiative effect (CRE) biases, there is an overestimation of +4.8±28.0 W m−2 in ACCESS-AM2 and an underestimation of -7.9±20.9 W m−2 in CERES. An overestimation of downwelling surface shortwave radiation is associated with an underestimated cloud fraction and low-level cloud occurrence. We suggest that modeled cloud phase is also having an impact on the radiation biases. Our results show that the ACCESS-AM2 model and CERES product require further development to reduce these radiation biases not just in shortwave and in all-sky conditions, but also in longwave and in clear-sky conditions.
Priestley, Matthew D. K.; Ackerley, Duncan; Catto, Jennifer L.; Hodges, Kevin I.Priestley, M. D. K., D. Ackerley, J. L. Catto, K. I. Hodges, 2023: Drivers of Biases in the CMIP6 Extratropical Storm Tracks. Part II: Southern Hemisphere. J. Climate, 36(5), 1469-1486. doi: 10.1175/JCLI-D-20-0977.1. Abstract The Southern Hemisphere storm tracks are commonly simulated too far equatorward in climate models for the historical period. In the latest generation of climate models from phase 6 of the Coupled Model Intercomparison Project (CMIP6), the equatorward bias that was present in CMIP5 models still persists, although it is reduced considerably. A further reduction of the equatorward bias is found in atmosphere-only simulations. Using diagnostic large-scale fields, we propose that an increase in the midlatitude temperature gradients contributes to the reduced equatorward bias in CMIP6 and AMIP6 models, reducing the biases relative to ERA5. These changes increase baroclinicity in the atmosphere and are associated with a storm track that is situated farther poleward. In CMIP6 models, the poleward shift of the storm tracks is associated with an amelioration of cold midlatitude SST biases in CMIP5 and not through a reduction of the long-standing warm Southern Ocean SST bias. We propose that increases in midlatitude temperature gradients in the atmosphere and ocean are connected to changes in the cloud radiative effect. Persistent track density biases to the south of Australia are shown to be connected to an apparent standing-wave pattern originating in the tropics, which modifies the split jet structure near Australia and subsequently the paths of cyclones.
Qin, Hongchen; Klein, Stephen A.; Ma, Hsi-Yen; Van Weverberg, Kwinten; Feng, Zhe; Chen, Xiaodong; Best, Martin; Hu, Huancui; Leung, L. Ruby; Morcrette, Cyril J.; Rumbold, Heather; Webster, StuartQin, H., S. A. Klein, H. Ma, K. Van Weverberg, Z. Feng, X. Chen, M. Best, H. Hu, L. R. Leung, C. J. Morcrette, H. Rumbold, S. Webster, 2023: Summertime Near-Surface Temperature Biases Over the Central United States in Convection-Permitting Simulations. Journal of Geophysical Research: Atmospheres, 128(22), e2023JD038624. doi: 10.1029/2023JD038624. Convection-Permitting Model (CPM) simulations of the Central United States climate for the summer of 2011 are studied to understand the causes of warm biases in 2-m air temperature (T2m) and related underestimates of precipitation including that from mesoscale convective systems (MCSs). Based on 10 CPM simulations and 9 coarser-resolution model simulations, we quantify contributions from evaporative fraction (EF) and radiation to the T2m bias with both types of models overestimating T2m largely because they underestimate EF. The performance of CPMs in capturing MCS characteristics (frequency, rainfall, propagation) varies. The pre-summer precipitation bias has large correlation with mean summertime T2m bias but the relationship between summertime MCS mean rainfall bias and T2m bias is non-monotonic. Analysis of lifting condensation level deficit and convective available potential energy suggests that models with T2m warm biases and low EF have too dry and stable boundary layers, inhibiting the formation of clouds, precipitation and MCSs. Among the CPMs with differing model formulations (e.g., transpiration, infiltration, cloud macrophysics and microphysics), evidence suggests that altering the land-surface model is more effective than altering the atmospheric model in reducing T2m biases. These results demonstrate that land-atmosphere interactions play a very important role in determining the summertime climate of the Central United States. warm bias; 2-m air temperature; central US; convection-permitting model; mesoscale convective systems
Raghuraman, Shiv Priyam; Paynter, David; Menzel, Raymond; Ramaswamy, V.Raghuraman, S. P., D. Paynter, R. Menzel, V. Ramaswamy, 2023: Forcing, Cloud Feedbacks, Cloud Masking, and Internal Variability in the Cloud Radiative Effect Satellite Record. J. Climate, 36(12), 4151-4167. doi: 10.1175/JCLI-D-22-0555.1. Abstract Satellite observations show a near-zero trend in the top-of-atmosphere global-mean net cloud radiative effect (CRE), suggesting that clouds did not further cool nor heat the planet over the last two decades. The causes of this observed trend are unknown and can range from effective radiative forcing (ERF) to cloud feedbacks, cloud masking, and internal variability. We find that the near-zero NetCRE trend is a result of a significant negative trend in the longwave (LW) CRE and a significant positive trend in the shortwave (SW) CRE, cooling and heating the climate system, respectively. We find that it is exceptionally unlikely (
Raghuraman, Shiv Priyam; Paynter, David; Ramaswamy, V.; Menzel, Raymond; Huang, XiangleiRaghuraman, S. P., D. Paynter, V. Ramaswamy, R. Menzel, X. Huang, 2023: Greenhouse Gas Forcing and Climate Feedback Signatures Identified in Hyperspectral Infrared Satellite Observations. Geophysical Research Letters, 50(24), e2023GL103947. doi: 10.1029/2023GL103947. Global greenhouse gas forcing and feedbacks are the primary causes of climate change but have limited direct observations. Here we show that continuous, stable, global, hyperspectral infrared satellite measurements (2003–2021) display decreases in outgoing longwave radiation (OLR) in the CO2, CH4, and N2O absorption bands and increases in OLR in the window band and H2O absorption bands. By conducting global line-by-line radiative transfer simulations with 2003–2021 meteorological conditions, we show that increases in CO2, CH4, and N2O concentrations caused an instantaneous radiative forcing and stratospheric cooling adjustment that decreased OLR. The climate response, comprising surface and atmospheric feedbacks to radiative forcings and unforced variability, increased OLR. The spectral trends predicted by our climate change experiments using our general circulation model identify three bedrock principles of the physics of climate change in the satellite record: an increasing greenhouse effect, stratospheric cooling, and surface-tropospheric warming. climate change; outgoing longwave radiation; satellite observations; spectral; climate model; radiation model
Ramachandran, S.; Rupakheti, Maheswar; Cherian, Ribu; Lawrence, Mark G.Ramachandran, S., M. Rupakheti, R. Cherian, M. G. Lawrence, 2023: Aerosols heat up the Himalayan climate. Science of The Total Environment, 894, 164733. doi: 10.1016/j.scitotenv.2023.164733. The impact of aerosols, especially the absorbing aerosols, in the Himalayan region is important for climate. We closely examine ground-based high-quality observations of aerosol characteristics including radiative forcing from several locations in the Indo-Gangetic Plain (IGP), the Himalayan foothills and the Tibetan Plateau, relatively poorly studied regions with several sensitive ecosystems of global importance, as well as highly vulnerable large populations. This paper presents a state-of-the-art treatment of the warming that arises from these particles, using a combination of new measurements and modeling techniques. This is a first-time analysis of its kind, including ground-based observations, satellite data, and model simulations, which reveals that the aerosol radiative forcing efficiency (ARFE) in the atmosphere is clearly high over the IGP and the Himalayan foothills (80–135 Wm−2 per unit aerosol optical depth (AOD)), with values being greater at higher elevations. AOD is >0.30 and single scattering albedo (SSA) is ∼0.90 throughout the year over this region. The mean ARFE is 2–4 times higher here than over other polluted sites in South and East Asia, owing to higher AOD and aerosol absorption (i.e., lower SSA). Further, the observed annual mean aerosol-induced atmospheric heating rates (0.5–0.8 Kelvin/day), which are significantly higher than previously reported values for the region, imply that the aerosols alone could account for >50 % of the total warming (aerosols + greenhouse gases) of the lower atmosphere and surface over this region. We demonstrate that the current state-of-the-art models used in climate assessments significantly underestimate aerosol-induced heating, efficiency and warming over the Hindu Kush – Himalaya – Tibetan Plateau (HKHTP) region, indicating a need for a more realistic representation of aerosol properties, especially of black carbon and other aerosols. The significant, regionally coherent aerosol-induced warming that we observe in the high altitudes of the region, is a significant factor contributing to increasing air temperature, observed accelerated retreat of the glaciers, and changes in the hydrological cycle and precipitation patterns over this region. Thus, aerosols are heating up the Himalayan climate, and will remain a key factor driving climate change over the region. Atmospheric aerosols; Himalayas; Model simulations; Observations; Radiative effects; South Asia
Ray, Sulagna; Stefanova, Lydia; Fu, Bing; Guan, Hong; Wang, Jiande; Meixner, Jessica; Mehra, Avichal; Zhu, YuejianRay, S., L. Stefanova, B. Fu, H. Guan, J. Wang, J. Meixner, A. Mehra, Y. Zhu, 2023: Improved forecast of 2015/16 El Niño event in an experimental coupled seasonal ensemble forecasting system. Climate Dynamics. doi: 10.1007/s00382-023-06746-2. To improve NOAA’s seasonal forecasting capabilities, a new coupled system within the Unified Forecast System (UFS) framework is being developed through a community-wide effort led by NOAA’s Environmental Modeling Center targeting the configuration of a future operational Seasonal Forecast System (SFS v1). An experimental version of this ensemble seasonal forecasting system is tested on forecasting the strong El Niño of 2015/16. The then-operational systems and NCEP real-time seasonal forecasts (CFSv2) underestimated its strength towards the end of 2015 and beginning of 2016. In addition to perturbing the atmospheric initial conditions, run-time stochastic physics-based perturbations are applied in both atmosphere and ocean components of this new coupled system to represent the model uncertainties. The UFS ensembles are initialized on June 1st, 2015 and run through a 9-month period. Compared to CFSv2, the forecast of Niño 3.4 SST and intra-seasonal zonal windstress for the 2015/16 El Niño in the UFS system are improved, as is the ensemble spread. A cold SST forecast error develops in the central equatorial Pacific, likely from excess evaporative cooling, shallower thermocline, and an excessively strong vertical current shear driven cooling. Near the eastern equatorial Pacific coast, on the other hand, warm surface and cool subsurface errors persist from initialization until the end of the forecast. The results suggest that further improvement in the seasonal forecast may be achieved by a combination of factors, including, but not limited to, improving the coupled system initialization, along with the atmospheric physics. El Niño; Ensemble prediction; Equatorial Kelvin waves; Equatorial ocean dynamics; Seasonal forecasts; Westerly wind bursts
Reed, K. A.; Stansfield, A. M.; Hsu, W.-C.; Kooperman, G. J.; Akinsanola, A. A.; Hannah, W. M.; Pendergrass, A. G.; Medeiros, B.Reed, K. A., A. M. Stansfield, W. Hsu, G. J. Kooperman, A. A. Akinsanola, W. M. Hannah, A. G. Pendergrass, B. Medeiros, 2023: Evaluating the Simulation of CONUS Precipitation by Storm Type in E3SM. Geophysical Research Letters, 50(12), e2022GL102409. doi: 10.1029/2022GL102409. Conventional low-resolution (LR) climate models, including the Energy Exascale Earth System Model (E3SMv1), have well-known biases in simulating the frequency, intensity, and timing of precipitation. Approaches to next-generation E3SM, whether the high-resolution (HR) or multiscale modeling framework (MMF) configuration, improve the simulation of the intensity and frequency of precipitation, but regional and seasonal deficiencies still exist. Here we apply a methodology to assess the contribution of tropical cyclones (TCs), extratropical cyclones (ETCs), and mesoscale convective systems (MCSs) to simulated precipitation in E3SMv1-HR and E3SMv1-MMF relative to E3SMv1-LR. Across the United States, E3SMv1-MMF provides the best simulation in terms of precipitation accumulation, frequency and intensity from MCSs and TCs compared to E3SMv1-LR and E3SMv1-HR. All E3SMv1 configurations overestimate precipitation amounts from and the frequency of ETCs over CONUS, with conventional E3SMv1-LR providing the best simulation compared to observations despite limitations in precipitation intensity within these events. Earth system model; precipitation; energy exascale earth system model; high resolution; extremes; multiscale modeling framework
Regayre, Leighton A.; Deaconu, Lucia; Grosvenor, Daniel P.; Sexton, David M. H.; Symonds, Christopher; Langton, Tom; Watson-Paris, Duncan; Mulcahy, Jane P.; Pringle, Kirsty J.; Richardson, Mark; Johnson, Jill S.; Rostron, John W.; Gordon, Hamish; Lister, Grenville; Stier, Philip; Carslaw, Ken S.Regayre, L. A., L. Deaconu, D. P. Grosvenor, D. M. H. Sexton, C. Symonds, T. Langton, D. Watson-Paris, J. P. Mulcahy, K. J. Pringle, M. Richardson, J. S. Johnson, J. W. Rostron, H. Gordon, G. Lister, P. Stier, K. S. Carslaw, 2023: Identifying climate model structural inconsistencies allows for tight constraint of aerosol radiative forcing. Atmospheric Chemistry and Physics, 23(15), 8749-8768. doi: 10.5194/acp-23-8749-2023. Aerosol radiative forcing uncertainty affects estimates of climate sensitivity and limits model skill in terms of making climate projections. Efforts to improve the representations of physical processes in climate models, including extensive comparisons with observations, have not significantly constrained the range of possible aerosol forcing values. A far stronger constraint, in particular for the lower (most-negative) bound, can be achieved using global mean energy balance arguments based on observed changes in historical temperature. Here, we show that structural deficiencies in a climate model, revealed as inconsistencies among observationally constrained cloud properties in the model, limit the effectiveness of observational constraint of the uncertain physical processes. We sample the uncertainty in 37 model parameters related to aerosols, clouds, and radiation in a perturbed parameter ensemble of the UK Earth System Model and evaluate 1 million model variants (different parameter settings from Gaussian process emulators) against satellite-derived observations over several cloudy regions. Our analysis of a very large set of model variants exposes model internal inconsistencies that would not be apparent in a small set of model simulations, of an order that may be evaluated during model-tuning efforts. Incorporating observations associated with these inconsistencies weakens any forcing constraint because they require a wider range of parameter values to accommodate conflicting information. We show that, by neglecting variables associated with these inconsistencies, it is possible to reduce the parametric uncertainty in global mean aerosol forcing by more than 50 %, constraining it to a range (around −1.3 to −0.1 W m−2) in close agreement with energy balance constraints. Our estimated aerosol forcing range is the maximum feasible constraint using our structurally imperfect model and the chosen observations. Structural model developments targeted at the identified inconsistencies would enable a larger set of observations to be used for constraint, which would then very likely narrow the uncertainty further and possibly alter the central estimate. Such an approach provides a rigorous pathway to improved model realism and reduced uncertainty that has so far not been achieved through the normal model development approach.
Ren, Tong; Yang, Ping; Loeb, Norman G.; Smith Jr., William L.; Minnis, PatrickRen, T., P. Yang, N. G. Loeb, W. L. Smith Jr., P. Minnis, 2023: On the Consistency of Ice Cloud Optical Models for Spaceborne Remote Sensing Applications and Broadband Radiative Transfer Simulations. Journal of Geophysical Research: Atmospheres, 128(20), e2023JD038747. doi: 10.1029/2023JD038747. Aqua satellite Moderate Resolution Imaging Spectroradiometer (MODIS) 1-km observations are collocated with Clouds and the Earth's Radiant Energy System (CERES) fields of view taken during July 2008 afternoon satellite passes over the equatorial western Pacific Ocean. Radiation simulations are compared with collocated CERES observations to better understand the sensitivity of computed fluxes to two ice cloud broadband radiation parameterization schemes and inferred ice cloud characteristics. In particular, the radiation computational schemes and ice cloud property retrievals are based on two respective ice particle models, the MODIS Collection 6 (MC6) aggregate model and a more microphysically consistent two-habit model (THM). The simulation results show that both MC6 and THM overestimate the shortwave (SW) and longwave (LW) cloud radiative effects at the top of the atmosphere, as compared to the CERES observations; the difference between the MC6 and THM-based ice cloud retrievals is too small to compensate for the differences between the two model-based radiation schemes. Therefore, the present finding suggests that broadband radiative simulations are more sensitive to the radiation parameterization scheme than to the input cloud properties retrieved using the corresponding ice cloud particle optical property model.
Rizza, Umberto; Avolio, Elenio; Morichetti, Mauro; Di Liberto, Luca; Bellini, Annachiara; Barnaba, Francesca; Virgili, Simone; Passerini, Giorgio; Mancinelli, EnricoRizza, U., E. Avolio, M. Morichetti, L. Di Liberto, A. Bellini, F. Barnaba, S. Virgili, G. Passerini, E. Mancinelli, 2023: On the Interplay between Desert Dust and Meteorology Based on WRF-Chem Simulations and Remote Sensing Observations in the Mediterranean Basin. Remote Sensing, 15(2), 435. doi: 10.3390/rs15020435. In this study, we investigate a series of Saharan dust outbreaks toward the Mediterranean basin that occurred in late June 2021. In particular, we analyze the effect of mineral dust aerosols on radiation and cloud properties (direct, semi-direct and indirect effects), and in turn, on meteorological parameters. This is achieved by running the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) over a domain covering North Africa and the Central Mediterranean Basin. The simulations were configured using a gradual coupling strategy between the GOCART aerosol model and the Goddard radiation and microphysics schemes available in the WRF-Chem package. A preliminary evaluation of the model performances was conducted in order to verify its capability to correctly reproduce the amount of mineral dust loaded into the atmosphere within the spatial domain considered. To this purpose, we used a suite of experimental data from ground- and space-based remote sensing measurements. This comparison highlighted a model over-estimation of aerosol optical properties to the order of 20%. The evaluation of the desert dust impact on the radiation budget, achieved by comparing the uncoupled and the fully coupled (aerosol–radiation–clouds) simulation, shows that mineral dust induces a net (shortwave–longwave) cooling effect to the order of −10 W m−2. If we consider the net dust radiative forcing, the presence of dust particles induces a small cooling effect at the top of the atmosphere (−1.2 W m−2) and a stronger cooling at the surface (−14.2 W m−2). At the same time, analysis of the perturbation on the surface energy budget yields a reduction of −7 W m−2 when considering the FULL-coupled simulation, a positive perturbation of +3 W m−2 when only considering microphysics coupling and −10.4 W m−2 when only considering radiation coupling. This last result indicates a sort of “superposition” of direct, indirect and semi-direct effects of dust on the radiation budget. This study shows that the presence of dust aerosols significantly influences radiative and cloud properties and specifically the surface energy budget. This suggests (i) that dust effects should be considered in climate models in order to increase the accuracy of climate predictions over the Mediterranean region and (ii) the necessity of performing fully coupled simulations including aerosols and their effects on meteorology at a regional scale. dust–radiation coupling; Mediterranean hot spot; WRF-Chem model
Roach, Lettie A.; Eisenman, Ian; Wagner, Till J. W.; Donohoe, AaronRoach, L. A., I. Eisenman, T. J. W. Wagner, A. Donohoe, 2023: Asymmetry in the Seasonal Cycle of Zonal-Mean Surface Air Temperature. Geophysical Research Letters, 50(10), e2023GL103403. doi: 10.1029/2023GL103403. At most latitudes, the seasonal cycle of zonal-mean surface air temperature is notably asymmetric: the length of the warming season is not equal to the length of the cooling season. The asymmetry varies spatially, with the cooling season being ∼40 days shorter than the warming season in the subtropics and the warming season being ∼100 days shorter than the cooling season at the poles. Furthermore, the asymmetry differs between the Northern Hemisphere and the Southern Hemisphere. Here, we show that these observed features are broadly captured in a simple model for the evolution of temperature forced by realistic insolation. The model suggests that Earth's orbital eccentricity largely determines the hemispheric contrast, and obliquity broadly dictates the meridional structure. Clouds, atmospheric heat flux convergence, and time-invariant effective surface heat capacity have minimal impacts on seasonal asymmetry. This simple, first-order picture has been absent from previous discussions of the surface temperature seasonal cycle. climate; energy balance model; idealized model; insolation; seasonal cycle; temperature
Roemer, Florian E.; Buehler, Stefan A.; Brath, Manfred; Kluft, Lukas; John, Viju O.Roemer, F. E., S. A. Buehler, M. Brath, L. Kluft, V. O. John, 2023: Direct observation of Earth’s spectral long-wave feedback parameter. Nature Geoscience, 1-6. doi: 10.1038/s41561-023-01175-6. The spectral long-wave feedback parameter represents how Earth’s outgoing long-wave radiation adjusts to temperature changes and directly impacts Earth’s climate sensitivity. Most research so far has focused on the spectral integral of the feedback parameter. Spectrally resolving the feedback parameter permits inferring information about the vertical distribution of long-wave feedbacks, thus gaining a better understanding of the underlying processes. However, investigations of the spectral long-wave feedback parameter have so far been limited mostly to model studies. Here we show that it is possible to directly observe the global mean all-sky spectral long-wave feedback parameter using satellite observations of seasonal and interannual variability. We find that spectral bands subject to strong water-vapour absorption exhibit a substantial stabilizing net feedback. We demonstrate that part of this stabilizing feedback is caused by the change of relative humidity with warming, the radiative fingerprints of which can be directly observed. Therefore, our findings emphasize the importance of better understanding processes affecting the present distribution and future trends in relative humidity. This observational constraint on the spectral long-wave feedback parameter can be used to evaluate the representation of long-wave feedbacks in global climate models and to better constrain Earth’s climate sensitivity. Climate change; Atmospheric dynamics; Projection and prediction
Rugenstein, Maria; Hakuba, MariaRugenstein, M., M. Hakuba, 2023: Connecting Hemispheric Asymmetries of Planetary Albedo and Surface Temperature. Geophysical Research Letters, 50(6), e2022GL101802. doi: 10.1029/2022GL101802. Satellite measurements show that the Northern and Southern hemispheres reflect equal amounts of shortwave radiation (“albedo symmetry”), but no theory exists on if, how, and why the symmetry is established and maintained. Ambiguously, climate models are strongly biased in albedo symmetry but agree in the sign of the response to CO2. We find that mean-state biases in albedo symmetry and hemispheric surface temperature asymmetry correlate negatively. Similarly, the response of albedo asymmetry to CO2 forcing correlates negatively with the magnitude of the asymmetry in surface warming. This is true across many and within single climate model simulations: a too warm or stronger warming hemisphere is darker or darkens more than its counterpart. In the 21 years of observations we find the same tendency and hypothesize (a) albedo symmetry is a function of the current climate state and (b) we will observe an evolution toward albedo asymmetry in coming decades.
Salmun, Haydee; Josephs, Holly; Molod, AndreaSalmun, H., H. Josephs, A. Molod, 2023: GRWP-PBLH: Global Radar Wind Profiler Planetary Boundary Layer Height Data. Bull. Amer. Meteor. Soc., 104(5), E1044-E1057. doi: 10.1175/BAMS-D-22-0002.1. Abstract The planetary boundary layer (PBL) is central to the exchange of heat and moisture between Earth’s surface and the atmosphere, to the turbulent transport of aerosol and chemical pollutants affecting air quality, and to near- and long-term climate prediction. Consequently, the PBL has become a major focus of atmospheric and climate science, particularly after its designation as a “targeted observable” by the 2018 National Academies of Science, Engineering, and Medicine Earth Science Decadal Survey. Information about the height of the PBL that is global in scope allows for wide geographical analysis of connections to seasonality, to latitude, proximity to oceans, and synoptic variability. Information about the PBL height at hourly resolution allows for the analysis of diurnal cycles and PBL height growth rates, both of which are critical to the study of near-surface transport processes. This manuscript describes the release of a new global dataset of PBL height estimates retrieved from radar wind profilers (RWPs), called Global Radar Wind Profiler Planetary Boundary Layer Height (GRWP-PBLH). Hourly PBL height estimates are retrieved using an existing algorithm applied to archived signal-to-noise ratio data from a series of networks located around the globe, specifically in Australia, Europe, and Japan. Information about the source data, details of data processing, and production of PBL height estimates are discussed here along with a description of supplementary data and the available software. The GRWP-PBLH dataset is now accessible to the community for ongoing and future research.
Saneev, B. G.; Ivanova, I. Yu.; Shakirov, V. A.Saneev, B. G., I. Y. Ivanova, V. A. Shakirov, 2023: Assessment of Indicators of Solar and Wind Energy Potential of the Republic of Sakha (Yakutia). Geography and Natural Resources, 43(1), S74-S79. doi: 10.1134/S187537282205016X. The potential of renewable energy sources varies over time and significantly depends on natural, climatic, and regional characteristics. This article evaluates a wide group of indicators of the potential of wind and solar energy in the Republic of Sakha (Yakutia) at 47 points to determine the most promising areas for wind power plants (WPPs) and solar power plants (SPPs). The characterization of the wind energy potential is carried out in two stages. At the first stage, a preliminary analysis of the territory is conducted according to the measurements of weather stations for 2018–2020. On the territory of the republic, the average wind speed for this period ranges from 2.8 to 6.1 m/s at a height of 10 m. The greatest wind energy potential is typical for the northern regions. At the second stage, a full set of indicators of wind energy potential for the ten most promising areas is evaluated according to ground-based measurements for 2006–2020. The highest indicators of wind energy potential are typical for points located in close proximity to the coast: Anabar, Ust-Olenek, Stolb Island, and Ambarchik Bay. Most of the criteria and signs of high wind energy potential are met in these areas. The assessment of solar energy potential indicators was carried out for 47 sites based on estimates from the CERES SYN1deg satellite observation database for 1984–2020. To characterize the solar energy potential, three indicators were used: the annual flux of total solar radiation to a horizontal surface, the annual flux of total solar radiation on a surface inclined at an angle of latitude, and the utilization factor of the installed capacity of photovoltaic converters. The receipt of total solar radiation on a horizontal surface is from 784 to 1128 kWh/m2/year. The greatest solar energy potential is observed in the southeastern part of the republic. ground-based measurements; potential of renewable energy sources; satellite observation data; solar energy; wind energy
Sarr, Alioune Badara; Sultan, BenjaminSarr, A. B., B. Sultan, 2023: Predicting crop yields in Senegal using machine learning methods. International Journal of Climatology, 43(4), 1817-1838. doi: 10.1002/joc.7947. Agriculture plays an important role in Senegalese economy and annual early warning predictions of crop yields are highly relevant in the context of climate change. In this study, we used three main machine learning methods (support vector machine, random forest, neural network) and one multiple linear regression method, namely Least Absolute Shrinkage and Selection Operator (LASSO), to predict yields of the main food staple crops (peanut, maize, millet and sorghum) in 24 departments of Senegal. Three combination of predictors (climate data, vegetation data or a combination of both) are used to compare the respective contribution of statistical methods and inputs in the predictive skill. Our results showed that the combination of climate and vegetation with the machine learning methods gives the best performance. The best prediction skill is obtained for peanut yield likely due to its high sensitivity to interannual climate variability. Although more research is needed to integrate the results of this study into an operational framework, this paper provides evidence of the promising performance machine learning methods. The development and operationalization of such prediction and their integration into operational early warning systems could increase resilience of Senegal to climate change and contribute to food security. climate change scenario; crop yield prediction; machine learning; Senegal
Schmidt, Gavin A.; Andrews, Timothy; Bauer, Susanne E.; Durack, Paul J.; Loeb, Norman G.; Ramaswamy, V.; Arnold, Nathan P.; Bosilovich, Michael G.; Cole, Jason; Horowitz, Larry W.; Johnson, Gregory C.; Lyman, John M.; Medeiros, Brian; Michibata, Takuro; Olonscheck, Dirk; Paynter, David; Raghuraman, Shiv Priyam; Schulz, Michael; Takasuka, Daisuke; Tallapragada, Vijay; Taylor, Patrick C.; Ziehn, TiloSchmidt, G. A., T. Andrews, S. E. Bauer, P. J. Durack, N. G. Loeb, V. Ramaswamy, N. P. Arnold, M. G. Bosilovich, J. Cole, L. W. Horowitz, G. C. Johnson, J. M. Lyman, B. Medeiros, T. Michibata, D. Olonscheck, D. Paynter, S. P. Raghuraman, M. Schulz, D. Takasuka, V. Tallapragada, P. C. Taylor, T. Ziehn, 2023: CERESMIP: a climate modeling protocol to investigate recent trends in the Earth's Energy Imbalance. Frontiers in Climate, 5. doi: 10.3389/fclim.2023.1202161. The Clouds and the Earth's Radiant Energy System (CERES) project has now produced over two decades of observed data on the Earth's Energy Imbalance (EEI) and has revealed substantive trends in both the reflected shortwave and outgoing longwave top-of-atmosphere radiation components. Available climate model simulations suggest that these trends are incompatible with purely internal variability, but that the full magnitude and breakdown of the trends are outside of the model ranges. Unfortunately, the Coupled Model Intercomparison Project (Phase 6) (CMIP6) protocol only uses observed forcings to 2014 (and Shared Socioeconomic Pathways (SSP) projections thereafter), and furthermore, many of the ‘observed' drivers have been updated substantially since the CMIP6 inputs were defined. Most notably, the sea surface temperature (SST) estimates have been revised and now show up to 50% greater trends since 1979, particularly in the southern hemisphere. Additionally, estimates of short-lived aerosol and gas-phase emissions have been substantially updated. These revisions will likely have material impacts on the model-simulated EEI. We therefore propose a new, relatively low-cost, model intercomparison, CERESMIP, that would target the CERES period (2000-present), with updated forcings to at least the end of 2021. The focus will be on atmosphere-only simulations, using updated SST, forcings and emissions from 1990 to 2021. The key metrics of interest will be the EEI and atmospheric feedbacks, and so the analysis will benefit from output from satellite cloud observation simulators. The Tier 1 request would consist only of an ensemble of AMIP-style simulations, while the Tier 2 request would encompass uncertainties in the applied forcing, atmospheric composition, single and all-but-one forcing responses. We present some preliminary results and invite participation from a wide group of models.
Schuddeboom, A. J.; McDonald, A. J.Schuddeboom, A. J., A. J. McDonald, 2023: Understanding Internal Cluster Variability Through Subcluster Metric Analysis in a Geophysical Context. Earth and Space Science, 10(1), e2022EA002373. doi: 10.1029/2022EA002373. Clustering algorithms are commonly used for inspecting the behavior of clouds in both model and satellite data sets. Often overlooked in cluster analysis is the variability that occurs within any clusters generated. This is particularly important in the geophysics where clusters are often generated with a focus on interpretability over mathematical optimization. Two metrics, the Davies-Bouldin index and the subsom entropy, are used to identify clusters with large internal variability. These metrics are applied to an example set of clusters from prior research that were generated using cloud top pressure-cloud optical thickness joint histograms from the Moderate Resolution Imaging Spectroradiometer data set. Applying these metrics to the clusters identifies one cluster in particular as a major outlier. Examining the calculations behind these metrics in more detail provides further information about the internal variability of the clusters. The clusters are also examined over several geographic regions showing mostly consistent behavior. There are, however, some large anomalies such as the behavior of the clear sky cluster or the behavior of several different clusters over the Arctic Ocean. To aide our interpretation of these results, two clusters are chosen for a detailed analysis of their subclusters. The geographic distributions and radiative properties of these subclusters are examined and clearly identify that subclusters have physically distinct behavior. This result illustrates that these metrics are capable of determining when a cluster contains physically distinct subclusters. This demonstrates the potential utility of these metrics if they were applied to other geophysical data sets. machine learning; cloud modeling; Clouds and the Earth's Radiant Energy System; Moderate Resolution Imaging Spectroradiometer; clustering; entropy
Schulz, Hauke; Stevens, BjornSchulz, H., B. Stevens, 2023: Evaluating Large-Domain, Hecto-Meter, Large-Eddy Simulations of Trade-Wind Clouds Using EUREC4A Data. Journal of Advances in Modeling Earth Systems, 15(10), e2023MS003648. doi: 10.1029/2023MS003648. The meso-scale variability in cloudiness of the marine trade-wind layer is explored with large-eddy simulations of regional extent and validated against observations of the EUREC4A field campaign. 41 days of realistically forced simulations present a representative, statistical view on shallow convection in the winter North Atlantic trades that includes a wide range of meso-scale variability including the four recently identified patterns of spatial organization: Sugar, Gravel, Flowers and Fish. The results show that cloud cover is on average captured well but with discrepancies in its vertical and spatial distribution. Cloudiness at the lifting condensation level depends on the model resolution with the finer one producing on average a more realistic cloud profile. Independent of the resolution, the variability in cloudiness below the trade inversion is not captured, leading to a lack of stratiform cloudiness with implications on the detectability of meso-scale patterns whose cloud patches are characterized by stratiform clouds. The simulations tend to precipitate more frequently than observed, with a narrower distribution of echo intensities. The observed co-variability between cloudiness and environmental conditions is well captured. marine boundary layer clouds; shallow convection; observations; convective organization; large eddy simulation
Sebastian, Dawn E.; Murtugudde, Raghu; Ghosh, SubimalSebastian, D. E., R. Murtugudde, S. Ghosh, 2023: Soil–vegetation moisture capacitor maintains dry season vegetation productivity over India. Scientific Reports, 13(1), 888. doi: 10.1038/s41598-022-27277-6. India receives more than 70% of its annual rainfall in the summer monsoon from June to September. The rainfall is scanty and scattered for the rest of the year. Combining satellite data and model simulations, we show that the soil-vegetation continuum works as a natural capacitor of water, storing the monsoon pulse and releasing the moisture to the atmosphere through evapotranspiration over approximately 135 days when the moisture supply from precipitation is less than the evapotranspiration losses. The total Gross Primary Productivity of vegetation in India during the capacitor period accounts for almost 35% of the total annual GPP value. It primarily depends on the soil moisture at the beginning of the period, a measure of moisture capacitance of soil, with a correlation of 0.6. Given that India is the second largest contributor to recent global greening, its soil-vegetation water capacitance plays a significant role in the global carbon balance. Hydrology; Climate sciences; Ecology
Seifert, Axel; Bachmann, Vanessa; Filipitsch, Florian; Förstner, Jochen; Grams, Christian M.; Hoshyaripour, Gholam Ali; Quinting, Julian; Rohde, Anika; Vogel, Heike; Wagner, Annette; Vogel, BernhardSeifert, A., V. Bachmann, F. Filipitsch, J. Förstner, C. M. Grams, G. A. Hoshyaripour, J. Quinting, A. Rohde, H. Vogel, A. Wagner, B. Vogel, 2023: Aerosol–cloud–radiation interaction during Saharan dust episodes: the dusty cirrus puzzle. Atmospheric Chemistry and Physics, 23(11), 6409-6430. doi: 10.5194/acp-23-6409-2023. Dusty cirrus clouds are extended optically thick cirrocumulus decks that occur during strong mineral dust events. So far they have mostly been documented over Europe associated with dust-infused baroclinic storms. Since today's global numerical weather prediction models neither predict mineral dust distributions nor consider the interaction of dust with cloud microphysics, they cannot simulate this phenomenon. We postulate that the dusty cirrus forms through a mixing instability of moist clean air with drier dusty air. A corresponding sub-grid parameterization is suggested and tested in the ICOsahedral Nonhydrostatic model with Aerosol and Reactive Trace gases (ICON-ART). Only with the help of this parameterization is ICON-ART able to simulate the formation of the dusty cirrus, which leads to substantial improvements in cloud cover and radiative fluxes compared to simulations without this parameterization. A statistical evaluation over six Saharan dust events with and without observed dusty cirrus shows robust improvements in cloud and radiation scores. The ability to simulate dusty cirrus formation removes the linear dependency on mineral dust aerosol optical depth from the bias of the radiative fluxes. For the six Saharan dust episodes investigated in this study, the formation of dusty cirrus clouds is the dominant aerosol–cloud–radiation effect of mineral dust over Europe.
Seo, Minji; Kim, Hyun-Cheol; Seong, Noh-Hun; Sim, Suyoung; Han, Kyung-SooSeo, M., H. Kim, N. Seong, S. Sim, K. Han, 2023: Variability of Surface Radiation Budget over Arctic during Two Recent Decades from Perspective of CERES and ERA5 Data. Remote Sensing, 15(3), 829. doi: 10.3390/rs15030829. This study focused on surface radiation budget, one of the essential factors for understanding climate change. Arctic surface radiation budget was summarized and explained using a satellite product, Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF), and reanalysis data, ERA5. Net radiation records indicated an increasing trend only in ERA5, with EBAF indicating a decreasing trend in the Arctic Circle (AC; poleward from 65°N) from 2000 to 2018. The differences in the net radiation trend between product types was due to longwave downward radiation. The extreme season was selected according to the seasonality of net radiation, surface air temperature, and sea ice extent. The surface radiation budget was synthesized for extreme season in the AC. Regardless of the data, net radiation tended to increase in the summer on an annual trend. By contrast, in the winter, trend of surface net radiation was observed in which ERA5 increased and EBAF decreased. The difference in surface radiation is represented in longwave of each data. This comprehensive information can be used to analyze and predict the surface energy budget, transport, and interaction between the atmosphere and surface in the Arctic. climate change; Arctic; cryosphere; surface radiation budget
Shan, Shuo; Wang, Yiye; Xie, Xiangying; Fan, Tao; Xiao, Yushun; Zhang, Kanjian; Wei, HaikunShan, S., Y. Wang, X. Xie, T. Fan, Y. Xiao, K. Zhang, H. Wei, 2023: Analysis of regional climate variables by using neural Granger causality. Neural Computing and Applications, 35(22), 16381-16402. doi: 10.1007/s00521-023-08506-z. In recent years, how to discover causality rather than correlation among climate variables and how to use causality to help in time-series tasks have received great concern. However, the high dimensionality and nonlinearity of climate variables are the main issues for causal inference based on historical large-scale climate time series. Therefore, a method based on neural Granger causality inference is proposed to study the interactions of climate variables, with focus on the variables commonly used in the energy field, especially in photovoltaics. Firstly, for each climate variable, the time-varying causality and global causality are, respectively, obtained on each time window and on the whole series by neural Granger causality inference. Secondly, the global causality is used as a feature selection map of the input variables in the prediction task. Finally, compared with some existing feature selection methods, the experiments determine that the proposed method not only reveals the appropriate causality rather than the correlation among climate variables, but also efficiently reduces the input dimensionality and improves the performance and interpretability of the predicting model. Climatic variables interaction; Feature selection; Multi-layer perceptron; Neural Granger causality; Time series prediction
Shankar, Mohan; Loeb, Norman G.; Smith, Nathaniel; Smith, Natividad; Daniels, Janet L.; Thomas, Susan; Walikainen, DaleShankar, M., N. G. Loeb, N. Smith, N. Smith, J. L. Daniels, S. Thomas, D. Walikainen, 2023: Evaluating the Radiometric Performance of the Clouds and the Earth’s Radiant Energy System (CERES) Instruments on Terra and Aqua Over 20 Years. IEEE Transactions on Geoscience and Remote Sensing, 61, 1-11. doi: 10.1109/TGRS.2023.3330398. Six Clouds and the Earth’s Radiant Energy System (CERES) instruments on four satellites are used to produce a global continuous multidecadal record of Earth’s radiation budget (ERB) at the top-of-atmosphere (TOA). Each CERES instrument was calibrated and characterized on the ground before launch, while postlaunch calibration was conducted using onboard calibration sources. The performance of the CERES instruments is verified using vicarious approaches involving both Earth and celestial targets. In this article, we describe the calibration and validation approach and demonstrate the performance of the CERES instruments on the Terra and Aqua spacecraft over the 20-year period since launch. Validation results demonstrate that after applying the appropriate calibration corrections, all four instruments are stable and perform consistently with each other. Comparisons of observations between instruments on the two spacecraft during orbital crossings further confirm the consistent performance across all instruments over the 20-year period. validation; Earth; Clouds and the Earth’s Radiant Energy System (CERES); calibration; Calibration; radiometry; Radiometry; Aqua; Terra; Space vehicles; Mirrors; Optical filters; Telescopes
Sharma, Arushi; Venkataraman, Chandra; Muduchuru, Kaushik; Singh, Vikas; Kesarkar, Amit; Ghosh, Sudipta; Dey, SagnikSharma, A., C. Venkataraman, K. Muduchuru, V. Singh, A. Kesarkar, S. Ghosh, S. Dey, 2023: Aerosol radiative feedback enhances particulate pollution over India: A process understanding. Atmospheric Environment, 298, 119609. doi: 10.1016/j.atmosenv.2023.119609. In this study, we investigate the role of aerosol direct radiative feedback on regional meteorological changes and subsequent distribution of air pollutant with the focus on particulate matter PM2.5 and ozone (O3) over India. WRF-Chem simulations have been applied for Baseline case with both aerosol direct and indirect effects and another simulation including only aerosol indirect effects. The aerosol direct radiative feedback on the meteorology and air quality were investigated by taking the differences between these two simulations. A comprehensive model evaluation showed the model had the capacity to reproduce the observations and well captured the temporal and spatial variation in meteorological and aerosol fields. We found that the reduction in incoming shortwave solar radiation, temperature at 2 m and planetary boundary layer height annually and across all the season due to aerosol radiation interaction (ARI). The concentration of PM2.5 and gaseous precursors like SO2 and NO2 showed enhancements, while O3 concentration mostly showed a reduction. Spatial and annual average PM2.5 concentration was increased by +6%, SO2 concentration was increased by +1.4%, NO2 concentration was increased by +3.4%, and O3 concentration was reduced by −1.4%. Largest regional increases of 40% in particulate pollution induced by ARI occurred over north-western Indian region. The increase in PM2.5 concentration was highly related to stabilisation induced through meteorological variables and increases in primary aerosol concentration. The decrease in O3 concentration was highly related increases in NO2 and SO2 concentration. In the most polluted regions of India, ARI significantly enhance surface-level particulate pollution and related premature mortality, of particular concern considering likely future increasing trends. This study highlights the importance of inclusion and better representations of ARI and for implementing effective mitigation plans. Meteorology; WRF-Chem; Atmospheric chemistry; Air quality simulations; Primary and secondary species
Sharma, Puneet; Ganguly, Dilip; Sharma, Amit Kumar; Kant, Sunny; Mishra, ShiwanshaSharma, P., D. Ganguly, A. K. Sharma, S. Kant, S. Mishra, 2023: Assessing the Aerosols, Clouds and Their Relationship Over the Northern Bay of Bengal Using a Global Climate Model. Earth and Space Science, 10(2), e2022EA002706. doi: 10.1029/2022EA002706. Comprehensive evaluation of aerosol-cloud interactions (ACI) simulated by climate models using observations is crucial for advancing model development. Here, we use Moderate Resolution Imaging Spectroradiometer (MODIS) data to evaluate aerosol and cloud properties obtained from Community Atmosphere Model 5 (CAM5) over northern Bay of Bengal during winter season. We conduct simulations for default model setup as well as for prescribed, and nudged meteorology using Goddard Earth Observing System (GEOS5) reanalysis dataset in order to study the impact of meteorological parameters on simulated ACI. CAM5 captures the spatial variability of cloud optical depth (τc), cloud droplet number concentration (Nc), and liquid water path (LWP), although the values are overestimated in the model. Default model strongly simulates observed negative cloud effective radius (re)-Nc susceptibility but fails to reproduce the observed positive LWP-Nc susceptibility possibly due to evaporative cooling of the large number of smaller droplets. Compared to default and prescribed meteorology simulations, nudging specific humidity (Q) at 6-hr relaxation time scale leads to a positive LWP-Nc susceptibility, and an overall improved simulation of aerosol indirect effects. Increasing the relaxation time scale beyond 6-hr degrade the simulation of indirect effects suggesting high sensitivity of indirect effects to Q and serious deficiencies in Q simulated by the model. Improvement in simulation of aerosol and cloud characteristics are also noted when winds (UV) are nudged but it worsens some of the simulated ACI sensitivities due to increased transport of absorbing aerosols over the study region and a dominant semi-direct effect in the model. aerosol indirect effect; CAM5; nudging; cloud susceptibility
Shaw, Jonah K.; Kay, Jennifer E.Shaw, J. K., J. E. Kay, 2023: Processes Controlling the Seasonally Varying Emergence of Forced Arctic Longwave Radiation Changes. J. Climate, 36(20), 7337-7354. doi: 10.1175/JCLI-D-23-0020.1. Abstract Most observed patterns of recent Arctic surface warming and sea ice loss lie outside of unforced internal climate variability. In contrast, human influence on related changes in outgoing longwave radiation has not been assessed. Outgoing longwave radiation captures the flow of thermal energy from the surface through the atmosphere to space, making it an essential indicator of Arctic change. Furthermore, satellites have measured pan-Arctic radiation for two decades while surface temperature observations remain spatially and temporally sparse. Here, two climate model initial-condition large ensembles and satellite observations are used to investigate when and why twenty-first-century Arctic outgoing longwave radiation changes emerge from unforced internal climate variability. Observationally, outgoing longwave radiation changes from 2001 to 2021 are within the range of unforced internal variability for all months except October. The model-predicted timing of Arctic longwave radiation emergence varies throughout the year. Specifically, fall emergence occurs a decade earlier than spring emergence. These large emergence timing differences result from seasonally dependent sea ice loss and surface warming. The atmosphere and clouds then widen these seasonal differences by delaying emergence more in the spring and winter than in the fall. Finally, comparison of the two ensembles shows that more sea ice and a more transparent atmosphere during the melt season led to an earlier emergence of forced longwave radiation changes. Overall, these findings demonstrate that attributing changes in Arctic outgoing longwave radiation to human influence requires understanding the seasonality of both forced change and internal climate variability.
Shen, Min-Hua; Yu, Jia-YuhShen, M., J. Yu, 2023: Changes in El Niño characteristics and air–sea feedback mechanisms under progressive global warming. Terrestrial, Atmospheric and Oceanic Sciences, 34(1), 19. doi: 10.1007/s44195-023-00051-5. In this study, we investigate the potential changes of El Niño characteristics, including intensity, frequency and CP/EP El Niño ratio, under progressive global warming based on the 140-year CMIP6 model simulation outputs with the 1pctCO2 experiment. Major air-sea feedback mechanisms attributing to the changes are also examined. The CMIP6 ensemble means project a slight enhancement of El Niño intensity by about 2% and a modest increase of El Niño frequency by about 4% from the first to the second 70-year periods. It is found that these small changes result from the opposite response to global warming between CP and EP El Niño, i.e., the intensity of EP El Niño is projected to weaken by nearly 4.6% while the intensity of CP El Niño is projected to increase by about 4.5%. Since CP El Niño occurs more frequently than EP El Niño in CMIP6 simulations, this leads to a slight enhancement of the total El Niño intensity if these two types of El Niño were not separated. A similar situation occurs in projecting the future change of El Niño frequency, i.e., the frequency of EP El Niño is projected to decrease by about 1.4% while the frequency of CP El Niño is projected to increase by about 2%, thereby leading to a modest increase of the total El Niño frequency. By comparing the variance explained by key air-sea feedback mechanism between the two 70-year periods, we also note that the increased CP/EP ratio can be explained by the enhanced role played by the SF (seasonal footprinting) mechanism in a warmer atmosphere. Our study also points out that, as long as a climate model can correctly produce the intensity (variance) of major air-sea feedback mechanisms, the relationship between changes in El Niño characteristics and changes in feedback mechanisms can be physically robust. El Niño; Global warming; Air–sea feedback mechanism
Shen, Pengke; Zhao, Shuqing; Ma, Yongjing; Liu, ShuguangShen, P., S. Zhao, Y. Ma, S. Liu, 2023: Urbanization-induced Earth's surface energy alteration and warming: A global spatiotemporal analysis. Remote Sensing of Environment, 284, 113361. doi: 10.1016/j.rse.2022.113361. As both drivers and first responders, urban areas are rapidly increasing in importance of shaping global climate change. The global imprint of urbanization on surface energy balance (SEB) remains, however, largely unknown. Here, we undertake a global spatiotemporal analysis on urbanization-induced Earth's surface energy alteration using annually dynamic maps of impervious surface and satellite-derived surface energy fluxes and land surface temperature (LST), alongside space-for-time (spatial) and time-for-time (temporal) approaches. Relying on space-for-time substitution, we estimate that global urbanization-driven surface warming of annual mean temperature has reached 0.054 °C (95% CI, −0.009–0.214 °C) between 2003 and 2018 (with temporal stability), especially pronounced in summer daytime (0.122 °C, −0.038–0.495 °C), largely attributed to decline in local latent heat cooling, enlarged long-wave heat dissipation and anthropogenic heat. Temporal quantification of urbanization effects demonstrates consistence with spatial gradient approach, implying that space can substitute time in understanding and predicting future urbanization imprint on SEB and temperature (i.e., cities as harbingers of climate change). We further predict that during the first 35 years of this century annual warming magnitude will be nearly double that of the period 1985–2018, and particularly, urbanization perturbation to SEB will be more intense across countries or regions in the arid and warm temperate climates under global warming. This research provides science-based foundation that can help inform the IPCC special report on cities and climate change, and emphasize urgency to develop tailored mitigation and adaptation strategies against rapidly warming based on SEB attribution and climate background. Surface energy balance; Climate background; Future prediction; Space-for-time substitution; Surface warming; Temporal analysis; Urbanization effects
Sherriff-Tadano, Sam; Abe-Ouchi, Ayako; Yoshimori, Masakazu; Ohgaito, Rumi; Vadsaria, Tristan; Chan, Wing-Le; Hotta, Haruka; Kikuchi, Maki; Kodama, Takanori; Oka, Akira; Suzuki, KentarohSherriff-Tadano, S., A. Abe-Ouchi, M. Yoshimori, R. Ohgaito, T. Vadsaria, W. Chan, H. Hotta, M. Kikuchi, T. Kodama, A. Oka, K. Suzuki, 2023: Southern Ocean Surface Temperatures and Cloud Biases in Climate Models Connected to the Representation of Glacial Deep Ocean Circulation. J. Climate, 36(11), 3849-3866. doi: 10.1175/JCLI-D-22-0221.1. Abstract Simulating and reproducing the past Atlantic meridional overturning circulation (AMOC) with comprehensive climate models are essential to understanding past climate changes as well as to testing the ability of the models in simulating different climates. At the Last Glacial Maximum (LGM), reconstructions show a shoaling of the AMOC compared to modern climate. However, almost all state-of-the-art climate models simulate a deeper LGM AMOC. Here, it is shown that this paleodata–model discrepancy is partly related to the climate model biases in modern sea surface temperatures (SST) over the Southern Ocean (70°–45°S). Analysis of model outputs from three phases of the Paleoclimate Model Intercomparison Project shows that models with warm Southern Ocean SST biases tend to simulate a deepening of the LGM AMOC, while the opposite is observed in models with cold SST biases. As a result, a positive correlation of 0.41 is found between SST biases and LGM AMOC depth anomalies. Using sensitivity experiments with a climate model, we show, as an example, that changes in parameters associated with the fraction of cloud thermodynamic phase in a climate model reduce the biases in the warm SST over the modern Southern Ocean. The less biased versions of the model then reproduce a colder Southern Ocean at the LGM, which increases formation of Antarctic Bottom Water and causes shoaling of the LGM AMOC, without affecting the LGM climate in other regions. The results highlight the importance of sea surface conditions and clouds over the Southern Ocean in simulating past and future global climates. Significance Statement To test the ability of comprehensive climate models, simulations of the Last Glacial Maximum (LGM) have been conducted. However, most models simulated a deeper Atlantic meridional overturning circulation (AMOC) in the LGM, which contradicts paleodata suggesting a shallower AMOC. Here, using multimodel analysis and sensitivity experiments with a climate model, we show that this paleodata–model discrepancy is partly related to model biases in the modern Southern Ocean. Improvements in Southern Ocean surface temperatures and clouds reproduce a colder climate over the Southern Ocean at the LGM, which causes an intense shoaling of the AMOC due to increased formation of Antarctic Bottom Water. These results demonstrate the important effect of model biases over the Southern Ocean on simulating past climates.
Shin, Jihoon; Baik, Jong-JinShin, J., J. Baik, 2023: Global Simulation of the Madden–Julian Oscillation With Stochastic Unified Convection Scheme. Journal of Advances in Modeling Earth Systems, 15(7), e2022MS003578. doi: 10.1029/2022MS003578. A new spectral convection scheme, the stochastic unified convection scheme (stochastic UNICON), is implemented in a general circulation model. The global climate simulation using stochastic UNICON is evaluated and compared with UNICON, focusing on the simulation of the Madden–Julian oscillation (MJO). Stochastic UNICON extends the original UNICON by randomly sampling convective updrafts from the joint probability density function constructed at the near-surface, generating a spectrum of convective updrafts in a physically based manner. The performances of UNICON and stochastic UNICON on simulating observed mean climates are comparable, while stochastic UNICON slightly reduces the mean bias of climate variables. For the simulation of intraseasonal variabilities, stochastic UNICON outperforms UNICON in many aspects. Stochastic UNICON improves the simulation of the intensity and propagation patterns of boreal winter MJO, which are too weakly simulated in UNICON. The coherency between MJO-related convection and large-scale circulation is also enhanced, which many climate models underestimate. The improvement of MJO simulation by stochastic UNICON is related to a better representation of the relationship between moisture and convection in the model. The increased frequency of shallow convection in stochastic UNICON leads to stronger moisture convergence that precedes convection activity peak and results in the more robust development of organized convection and more frequent intense precipitation. A precipitation budget analysis reveals that the moisture tendencies due to horizontal advection and convective process are consistently enhanced during MJO developing periods by stochastic UNICON. global climate model; shallow convection; stochastic parameterization; convection parameterization; Madden–Julian oscillation
Song, Xiaoliang; Zhang, Guang; Wan, Hui; Xie, ShaochengSong, X., G. Zhang, H. Wan, S. Xie, 2023: Incorporating the Effect of Large-Scale Vertical Motion on Convection Through Convective Mass Flux Adjustment in E3SMv2. Journal of Advances in Modeling Earth Systems, 15(10), e2022MS003553. doi: 10.1029/2022MS003553. Recent observational studies suggest that the large-scale dynamical forcing (vertical motion) plays important roles in deep convection development. In this study we propose a convective mass flux adjustment (MAdj) approach to represent the dynamical effects of large-scale vertical motion on convection in the Department of Energy's Energy Exascale Earth System Model version 2 (E3SMv2). With MAdj, convection is enhanced (suppressed) when there is large-scale ascending (descending) motion at the planetary boundary layer top. The coupling of convection with large-scale circulation significantly improves the simulation of climate variability in E3SMv2 across multiple scales from the diurnal cycle, convectively coupled equatorial waves, to the Madden-Julian Oscillation (MJO). The standard E3SMv2 tends to simulate overly weak diurnal amplitude of precipitation and overly weak variance of convectively coupled equatorial Kelvin and westward inertio-gravity (WIG) waves. It also fails to simulate the essential characteristics of the MJO: continuous eastward propagation. With MAdj, the amplitude of diurnal cycle of precipitation is systematically increased and its probability density distribution is much closer to observations. The MAdj can also simulate more realistic eastward propagation of the MJO and much stronger convectively coupled Kelvin and WIG waves. Moreover, the MAdj approach slightly improves the climatology simulations in precipitation, cloud, radiation, circulation, temperature, and moisture fields, with overall root-mean-square error (RMSE) of major climatological fields reduced by about 2%. The MAdj approach suppresses excessive grid-scale precipitation, reducing precipitation wet biases over South China Sea, Philippine Sea, Himalayas, and South Pacific Convergence Zone in western Pacific in summer. climate variability; diurnal cycle; convection parameterization; Madden-Julian oscillation; vertical velocity
Sreenath, A. V.; Abhilash, S.; Ajilesh, P. P.Sreenath, A. V., S. Abhilash, P. P. Ajilesh, 2023: Changes in the dynamical, thermodynamical and hydrometeor characteristics prior to extreme rainfall events along the southwest coast of India in recent decades. Atmospheric Research, 289, 106752. doi: 10.1016/j.atmosres.2023.106752. Extremes in rainfall have links with atmospheric dynamics, thermodynamics, and deep cloud properties. Employing station-based gridded rainfall data, analysis product of sea surface temperature (SST), reanalysis product of dynamic/thermodynamic parameters and remotely sensed cloud properties, we demonstrate the features and evolution of rainfall extremes over the southwest coast of India (8–14°N, 75–77.5°E) during monsoon season. Analysis of the frequency and total amount of extreme rainfall reveals that the northwest coast (14–20°N) typically serves as the central node for the precipitation extremes. However, linear trends in rainfall extremes are remarkably different across the northwest and southwest coasts of India. Specifically, we noted a marked decrease in extreme rain events between 14 and 16°N along the northwest coast, while at the same time, the southwest coast emerges as a hot spot for extreme rain events. Results suggest that the evolution of rainfall extremes on the southwest coast is linked to the warming of the south-central Arabian sea (AS), enhanced SST gradient between north and south AS, and low pressure over the Bay of Bengal (BoB) four days before the event day. Under the influence of these factors, moisture-laden winds shift from the northwest coast to the southwest coast of India. Three days before the extreme precipitation, the BoB low-pressure centre advances westward and eventually merges with the trough of low along the west coast on the event day and creates a considerable increase in the mid-tropospheric vorticity. Meteorological conditions on extreme rainfall days over the southwest coast are portrayed by a significant reduction of sea level pressure, an intense flow of low-level jets from the Arabian sea and a cyclonic vortex at mid-troposphere. These elements favour a substantial rise in moist static energy (MSE) throughout the troposphere, leading to deep convective clouds with copious ice content and extreme rainfall over the southwest coast. Cyclonic vortex; Deep convective clouds; MSE; Rainfall extremes; Southwest coast
Stamatis, Michael; Hatzianastassiou, Nikolaos; Korras-Carraca, Marios-Bruno; Matsoukas, Christos; Wild, Martin; Vardavas, IliasStamatis, M., N. Hatzianastassiou, M. Korras-Carraca, C. Matsoukas, M. Wild, I. Vardavas, 2023: An Assessment of Global Dimming and Brightening during 1984–2018 Using the FORTH Radiative Transfer Model and ISCCP Satellite and MERRA-2 Reanalysis Data. Atmosphere, 14(8), 1258. doi: 10.3390/atmos14081258. In this study, an assessment of the FORTH radiative transfer model (RTM) surface solar radiation (SSR) as well as its interdecadal changes (Δ(SSR)), namely global dimming and brightening (GDB), is performed during the 35-year period of 1984–2018. Furthermore, a thorough evaluation of SSR and (Δ(SSR)) is conducted against high-quality reference surface measurements from 1193 Global Energy Balance Archive (GEBA) and 66 Baseline Surface Radiation Network (BSRN) stations. For the first time, the FORTH-RTM Δ(SSR) was evaluated over an extended period of 35 years and with a spatial resolution of 0.5° × 0.625°. The RTM uses state-of-the-art input products such as MERRA-2 and ISCCP-H and computes 35-year-long monthly SSR and GDB, which are compared to a comprehensive dataset of reference measurements from GEBA and BSRN. Overall, the FORTH-RTM deseasonalized SSR anomalies correlate satisfactorily with either GEBA (R equal to 0.72) or BSRN (R equal to 0.80). The percentage of agreement between the sign of computed GEBA and FORTH-RTM Δ(SSR) is equal to 63.5% and the corresponding percentage for FORTH-RTM and BSRN is 54.5%. The obtained results indicate that a considerable and statistically significant increase in SSR (Brightening) took place over Europe, Mexico, Brazil, Argentina, Central and NW African areas, and some parts of the tropical oceans from the early 1980s to the late 2010s. On the other hand, during the same 35-year period, a strong and statistically significant decrease in SSR (Dimming) occurred over the western Tropical Pacific, India, Australia, Southern East China, Northern South America, and some parts of oceans. A statistically significant dimming at the 95% confidence level, equal to −0.063 Wm−2 year−1 (or −2.22 Wm−2) from 1984 to 2018 is found over the entire globe, which was more prevalent over oceanic than over continental regions (−0.07 Wm−2 year−1 and −0.03 Wm−2 year−1, statistically significant dimming at the 95% confidence level, respectively) in both hemispheres. Yet, this overall 35-year dimming arose from alternating decadal-scale changes, consisting of dimming during 1984–1989, brightening in the 1990s, turning into dimming over 2000–2009, and brightening during 2010–2018. climate; brightening; dimming; stations; surface solar radiation; radiative transfer model
Su, Hua; Wei, Yanan; Lu, Wenfang; Yan, Xiao-Hai; Zhang, HongshengSu, H., Y. Wei, W. Lu, X. Yan, H. Zhang, 2023: Unabated Global Ocean Warming Revealed by Ocean Heat Content from Remote Sensing Reconstruction. Remote Sensing, 15(3), 566. doi: 10.3390/rs15030566. As the most relevant indicator of global warming, the ocean heat content (OHC) change is tightly linked to the Earth’s energy imbalance. Therefore, it is vital to study the OHC and heat absorption and redistribution. Here we analyzed the characteristics of global OHC variations based on a previously reconstructed OHC dataset (named OPEN) with four other gridded OHC datasets from 1993 to 2021. Different from the other four datasets, the OPEN dataset directly obtains OHC through remote sensing, which is reliable and superior in OHC reconstruction, further verified by the Clouds and the Earth’s Radiant Energy System (CERES) radiation flux data. We quantitatively analyzed the changes in the upper 2000 m OHC of the oceans over the past three decades from a multisource and multilayer perspective. Meanwhile, we calculated the global ocean heat uptake to quantify and track the global ocean warming rate and combined it with the Oceanic Niño Index to analyze the global evolution of OHC associated with El Niño–Southern Oscillation variability. The results show that different datasets reveal a continuously increasing and non-decaying global ocean warming from multiple perspectives, with more heat being absorbed by the subsurface and deeper ocean over the past 29 years. The global OHC heating trend from 1993 to 2021 is 7.48 ± 0.17, 7.89 ± 0.1, 10.11 ± 0.16, 7.78 ± 0.17, and 12.8 ± 0.26 × 1022 J/decade according to OPEN, IAP, EN4, Ishii, and ORAS5, respectively, which shows that the trends of the OPEN, IAP, and Ishii datasets are generally consistent, while those of EN4 and ORAS5 datasets are much higher. In addition, the ocean warming characteristics revealed by different datasets are somewhat different. The OPEN OHC dataset from remote sensing reconstruction shows a unique remote sensing mapping advantage, presenting a distinctive warming pattern in the East Indian Ocean. Meanwhile, the OPEN dataset had the largest statistically significant area, with 85.6% of the ocean covered by significant positive trends. The significant and continuous increase in global ocean warming over the past three decades, revealed from remote sensing reconstruction, can provide an important reference for projecting ocean warming in the context of global climate change toward the United Nations Sustainable Development Goals. ENSO; global ocean warming; Ocean Heat Content (OHC); Ocean Heat Uptake (OHU); remote sensing reconstruction
Sun, Chao; Liang, Xin-ZhongSun, C., X. Liang, 2023: Understanding and Reducing Warm and Dry Summer Biases in the Central United States: Analytical Modeling to Identify the Mechanisms for CMIP Ensemble Error Spread. J. Climate, 36(7), 2035-2054. doi: 10.1175/JCLI-D-22-0255.1. Abstract Most climate models in phase 6 of the Coupled Model Intercomparison Project (CMIP6) still suffer pronounced warm and dry summer biases in the central United States (CUS), even in high-resolution simulations. We found that the cloud base definition in the cumulus parameterization was the dominant factor determining the spread of the biases among models and those defining cloud base at the lifting condensation level (LCL) performed the best. To identify the underlying mechanisms, we developed a physically based analytical bias model (ABM) to capture the key feedback processes of land–atmosphere coupling. The ABM has significant explanatory power, capturing 80% variance of temperature and precipitation biases among all models. Our ABM analysis via counterfactual experiments indicated that the biases are attributed mostly by surface downwelling longwave radiation errors and second by surface net shortwave radiation errors, with the former 2–5 times larger. The effective radiative forcing from these two errors as weighted by their relative contributions induces runaway temperature and precipitation feedbacks, which collaborate to cause CUS summer warm and dry biases. The LCL cumulus reduces the biases through two key mechanisms: it produces more clouds and less precipitable water, which reduce radiative energy input for both surface heating and evapotranspiration to cause a cooler and wetter soil; it produces more rainfall and wetter soil conditions, which suppress the positive evapotranspiration–precipitation feedback to damp the warm and dry bias coupling. Most models using non-LCL schemes underestimate both precipitation and cloud amounts, which amplify the positive feedback to cause significant biases.
Sun, Chunfa; Liu, Dongxia; Xiao, Xian; Chen, Yichen; Liu, Zirui; Sun, YangSun, C., D. Liu, X. Xiao, Y. Chen, Z. Liu, Y. Sun, 2023: The electrical activity of a thunderstorm under high dust circumstances over Beijing metropolis region. Atmospheric Research, 285, 106628. doi: 10.1016/j.atmosres.2023.106628. A rare dust-thunderstorm affected the Beijing area on April 15, 2021, generating frequent lightning, dirt precipitation, and gusting. Based on comprehensive data from satellite retrieval, in-situ observation, weather radar, and reanalysis data, this study investigated the electrical activity of this dust-thunderstorm. The results showed that dust aerosols from Mongolia were involved in the growth process of the thunderstorm. During the evolution of the thunderstorm, the ground electrical field always changed positively with the highest value of 9 kV, and PM2.5 and PM10 increased rapidly with the highest values of 1500 μg/m3 and 250 μg/m3. The positive cloud-to-ground (+CG) lightning accounted for a high percentage with an average ratio of >50%. The dust aerosols acting as effective ice nuclei (IN) and cloud condensation nuclei (CCN) invading the thunderstorm were likely to increase the content of ice-phase particles and supercooled water, resulting in a high proportion of +CG lightning. It is deduced that the dust-thunderstorm possibly presented an inverted charge structure. Dust aerosol; +CG lightning; Invert charge structure; Lightning activity
Sweeney, Aodhan; Fu, Qiang; Pahlavan, Hamid A.; Haynes, PeterSweeney, A., Q. Fu, H. A. Pahlavan, P. Haynes, 2023: Seasonality of the QBO Impact on Equatorial Clouds. Journal of Geophysical Research: Atmospheres, n/a(n/a), e2022JD037737. doi: 10.1029/2022JD037737. The Quasi-Biennial Oscillation (QBO) dominates the interannual variability in the tropical lower stratosphere and is characterized by the descent of alternating easterly and westerly zonal winds. The QBO impact on tropical clouds and convection has received great attention in recent years due to its implications for weather and climate. In this study, a 15-year record of high vertical resolution cloud observations from CALIPSO and a 50 hPa zonal wind QBO index from ERA5 are used to document the QBO impact on equatorial (10°S-10°N) clouds. Observations from radio occultations, the CERES instrument, and the ERA5 reanalysis are also used to document the QBO impact on temperature, cloud radiative effect, and zonal wind, respectively. It is shown that the QBO impact on zonal mean equatorial cloud fraction has a strong seasonality. The strongest cloud fraction response to the QBO occurs in boreal spring and early summer, which extends from above the mean tropopause to ∼12.5 km and results in a significant longwave cloud radiative effect anomaly of 1 W/m2. The seasonality of the QBO impact on cloud fraction is synchronized with the QBO impacts on temperature and zonal wind in the tropical upper troposphere. Cirrus Clouds; Quasi-Biennial Oscillation; Seasonality
Szewczyk, Z. Peter; Smith, G. Louis; Daniels, Janet L.; Priestley, Kory J.Szewczyk, Z. P., G. L. Smith, J. L. Daniels, K. J. Priestley, 2023: Comparison of unfiltered CERES shortwave radiances measured in the minor plane over snow/ice of Greenland during summer solstices. Remote Sensing of Clouds and the Atmosphere XXVIII, 12730, 83-93. doi: 10.1117/12.2678565. A purpose of this paper is to present comparison of unfiltered radiances measured by CERES scanners when their scanning is aligned in the plane orthogonal to the solar plane and targeting Greenland around the time of summer solstice. Since the summer solstice in 2002, FM1 on Terra and FM4/FM3 on Aqua have been scanning in the minor plane for the month of June to collect comparison data. Measurements of FM5 on S-NPP and FM6 on NOAA20 have been added to this dataset starting in 2012 and 2018, respectively, with the data collection extended from May to July due to orbit characteristics. This unique dataset presents one-of-a-kind opportunity to compare radiances measured from four different platforms to assess CERES calibrations, particularly the consistency of their shortwave channel, as the solar zenith angles are the smallest for high latitudes producing relatively strong SW signal over ice/snow/clouds of Greenland. Results of comparison reported in this paper will be used in work to release new and updated versions, Edition 5, of ERBE-like (ES8) data products, for Terra and Aqua scanners.
Takahashi, Naoya; Richards, Kelvin J.; Schneider, Niklas; Stuecker, Malte F.; Annamalai, Hariharasubramanian; Nonaka, MasamiTakahashi, N., K. J. Richards, N. Schneider, M. F. Stuecker, H. Annamalai, M. Nonaka, 2023: Observed Relative Contributions of Anomalous Heat Fluxes and Effective Heat Capacity to Sea Surface Temperature Variability. Geophysical Research Letters, 50(17), e2023GL103165. doi: 10.1029/2023GL103165. Sea surface temperatures (SSTs) vary not only due to heat exchange across the air-sea interface but also due to changes in effective heat capacity as primarily determined by mixed layer depth (MLD). Here, we investigate seasonal and regional characteristics of the contribution of MLD anomalies to the month-to-month variability of SST using observational datasets. First, we propose a metric called Flux Divergence Angle, which can quantify the relative contributions of surface heat fluxes and MLD anomalies to SST variability. Using this metric, we find that MLD anomalies tend to amplify SST anomalies in the extra-tropics, especially in the eastern ocean basins, during spring and summer. In contrast, MLD anomalies tend to suppress SST anomalies in the eastern tropical Pacific during December-January-February. This paper provides the first global picture of the observed importance of MLD anomalies to the local SST variability.
Talib, Joshua; Müller, Omar V.; Barton, Emma J.; Taylor, Christopher M.; Vidale, Pier LuigiTalib, J., O. V. Müller, E. J. Barton, C. M. Taylor, P. L. Vidale, 2023: The Representation of Soil Moisture-Atmosphere Feedbacks across the Tibetan Plateau in CMIP6. Advances in Atmospheric Sciences, 40(11), 2063-2081. doi: 10.1007/s00376-023-2296-2. Thermal processes on the Tibetan Plateau (TP) influence atmospheric conditions on regional and global scales. Given this, previous work has shown that soil moisture–driven surface flux variations feed back onto the atmosphere. Whilst soil moisture is a source of atmospheric predictability, no study has evaluated soil moisture–atmosphere coupling on the TP in general circulation models (GCMs). In this study, we use several analysis techniques to assess soil moisture-atmosphere coupling in CMIP6 simulations including: instantaneous coupling indices; analysis of flux and atmospheric behaviour during dry spells; and a quantification of the preference for convection over drier soils. Through these metrics we partition feedbacks into their atmospheric and terrestrial components. Tibetan Plateau; model evaluation; precipitation; surface energy balance; land–atmosphere feedbacks; 模式评估; 表面能量平衡; 陆-气反馈; 降水; 青藏高原
Talib, Joshua; Taylor, Christopher M.; Harris, Bethan L.; Wainwright, Caroline M.Talib, J., C. M. Taylor, B. L. Harris, C. M. Wainwright, 2023: Surface-driven amplification of Madden–Julian oscillation circulation anomalies across East Africa and its influence on the Turkana jet. Quarterly Journal of the Royal Meteorological Society, 149(754), 1890-1912. doi: 10.1002/qj.4487. In semi-arid environments, rainfall-driven soil moisture fluctuations exert a strong influence on surface turbulent fluxes. Intraseasonal rainfall variability can therefore impact low-level atmospheric temperatures and influence regional circulations. Using satellite observations and an atmospheric reanalysis, we investigate whether rainfall variability induced by the Madden–Julian oscillation (MJO) triggers land–atmosphere feedbacks across East Africa. We identify that surface fluxes during the East African wet seasons (March–May and October–December) are sensitive to MJO-induced precipitation variations across low-lying regions of South Sudan and highland regions of Uganda and southwest Kenya. For example, during MJO phases 6 to 8, when rainfall is suppressed, surface temperatures and sensible heat fluxes increase, whilst evapotranspiration decreases. Spatial variations in the surface flux response to rainfall variability feed back onto the atmosphere through amplifying MJO-associated pressure anomalies. During dry MJO events for instance, surface warming across the exit region of the Turkana channel increases the low-tropospheric along-channel pressure gradient and intensifies the Turkana jet. We conclude that average surface-driven temperature fluctuations during a single day are responsible for approximately 12% of MJO-associated variability of the Turkana jet speed. However, we expect that the accumulation of heat over multiple days to the west of the East African Highlands further amplifies anomalies in the pressure gradient and jet intensity. Modelling experiments are required to quantify the accumulated impact of the surface forcing. Surface-driven Turkana jet variations influence the East African moisture budget and affect the intensity and inland propagation of coastal convection. Not only is this the first study to investigate the importance of intraseasonal land–atmosphere feedbacks across East Africa, but it is also the first to show that Turkana jet characteristics are partly driven by surface conditions. This work motivates an investigation into whether subseasonal forecast models fully harness the predictability from surface-induced jet variations. convection; intraseasonal variability; East Africa; land surface; soil moisture–atmosphere feedbacks
Tana, Gegen; Ri, Xu; Shi, Chong; Ma, Run; Letu, Husi; Xu, Jian; Shi, JianchengTana, G., X. Ri, C. Shi, R. Ma, H. Letu, J. Xu, J. Shi, 2023: Retrieval of cloud microphysical properties from Himawari-8/AHI infrared channels and its application in surface shortwave downward radiation estimation in the sun glint region. Remote Sensing of Environment, 290, 113548. doi: 10.1016/j.rse.2023.113548. Satellite remote sensing of cloud property retrieval and shortwave downward radiation (SWDR) estimation is essential for global radiation budget and climate change studies. Sun glint areas remain a challenge for the existing cloud and SWDR algorithms based on the visible channel since surface specular reflection has a significant impact on satellite retrieval. In this study, a set of algorithms for cloud detection and cloud microphysical parameter estimation were developed using infrared multichannel data from the new generation geostationary satellite Himawari-8 based on the random forest method. The results indicated that the cloud retrieval algorithm exhibited better performance in the sun glint areas where the official Himawari-8 products (cloud detection and cloud optical thickness) were overestimated. We developed a new SWDR estimation algorithm combining the radiative transfer model and machine learning techniques by considering the cloud properties from the cloud retrieval algorithm. The results indicated that the SWDR and cloud radiative forcing derived by the new algorithm were more consistent with those of the well-known radiation products Cloud and the Earth's Radiant Energy System than those estimated using the official-based cloud product, with decreases in the root mean square error of approximately 22% and 41%, respectively. The new algorithms effectively addressed sun glint contamination by providing more data coverage and exhibiting stable performance on a spatiotemporal scale. Cloud; AHI/Himawari-8; Infrared bands; Sun glint; Surface solar radiation
Tang, Chenqian; Shi, Chong; Letu, Husi; Ma, Run; Yoshida, Mayumi; Kikuchi, Maki; Xu, Jian; Li, Nan; Zhao, Mengjie; Chen, Liangfu; Shi, GuangyuTang, C., C. Shi, H. Letu, R. Ma, M. Yoshida, M. Kikuchi, J. Xu, N. Li, M. Zhao, L. Chen, G. Shi, 2023: Evaluation and uncertainty analysis of Himawari-8 hourly aerosol product version 3.1 and its influence on surface solar radiation before and during the COVID-19 outbreak. Science of The Total Environment, 892, 164456. doi: 10.1016/j.scitotenv.2023.164456. The hourly Himawari-8 version 3.1 (V31) aerosol product has been released and incorporates an updated Level 2 algorithm that uses forecast data as an a priori estimate. However, there has not been a thorough evaluation of V31 data across a full-disk scan, and V31 has yet to be applied in the analysis of its influence on surface solar radiation (SSR). This study firstly investigates the accuracy of V31 aerosol products, which includes three categories of aerosol optical depth (AOD) (AODMean, AODPure, and AODMerged) as well as the corresponding Ångström exponent (AE), using ground-based measurements from the AERONET and SKYNET. Results indicate that V31 AOD products are more consistent with ground-based measurements compared to previous products (V30). The highest correlation and lowest error were seen in the AODMerged, with a correlation coefficient of 0.8335 and minimal root mean square error of 0.1919. In contrast, the AEMerged shows a larger discrepancy with measurements unlike the AEMean and AEPure. Error analysis reveals that V31 AODMerged has generally stable accuracy across various ground types and geometrical observation angles, however, there are higher uncertainties in areas with high aerosol loading, particularly for fine aerosols. The temporal analysis shows that V31 AODMerged performs better compared to V30, particularly in the afternoon. Finally, the impacts of aerosols on SSR based on the V31 AODMerged are investigated through the development of a sophisticated SSR estimation algorithm in the clear sky. Results demonstrate that the estimated SSR is significant consistency with those of well-known CERES products, with preservation of 20 times higher spatial resolution. The spatial analysis reveals a significant reduction of AOD in the North China Plain before and during the COVID-19 outbreak, resulting in an average 24.57 W m−2 variation of the surface shortwave radiative forcing in clear sky daytime. AERONET and SKYNET; Aerosol optical depth; Aerosol type; COVID-19; Himawari-8; Surface shortwave radiative forcing
Taylor, Patrick C.; Monroe, EmilyTaylor, P. C., E. Monroe, 2023: Isolating the Surface Type Influence on Arctic Low-Clouds. Journal of Geophysical Research: Atmospheres, 128(16), e2022JD038098. doi: 10.1029/2022JD038098. Interactions between sea ice and clouds represent a mechanism through which sea ice influences climate. We composite cloud properties for ice-free, marginal ice zone (MIZ), and ice-covered surfaces during MIZ crossing events to analyze the cloud property differences between surface types. Restricting the analysis to MIZ crossing events enables the isolation of the sea ice effect on clouds from meteorological factors. We find larger cloud fraction (CF) and total water concentration below ∼1.5 km over ice-free relative to ice-covered surfaces during non-summer months. During summer, the results suggest larger CF and total water concentration over ice-free surfaces, however differences do not exceed observational uncertainty. Cloud property differences are linked to atmospheric thermodynamic profile differences, namely ice-free surfaces are warmer, moister, less stable, and have more positive surface turbulent fluxes than ice-covered surfaces. Ice-free minus ice-covered cloud property differences scale with surface temperature differences and are only found in the presence of a surface temperature difference. Our results suggest a 0.02 CF and 0.005 g m−3 total water concentration increase (∼5%) at the level of maximum CF between 2000 and 2021 due to the observed Arctic sea ice decline in fall, corresponding to ∼2 W m−2 increase in the net surface radiative flux. Our results support a positive sea ice-cloud radiative feedback in fall and winter and a negative sea ice-cloud radiative feedback in spring. We propose an updated conceptual model where the average surface type influence on cloud properties is mediated by surface temperature differences between ice-free and ice-covered surfaces.
Thandlam, Venugopal; Rutgersson, Anna; Rahaman, Hasibur; Yabaku, Mounika; Kaagita, Venkatramana; Sakirevupalli, Venkatramana ReddyThandlam, V., A. Rutgersson, H. Rahaman, M. Yabaku, V. Kaagita, V. R. Sakirevupalli, 2023: Quantifying Uncertainties in CERES/MODIS Downwelling Radiation Fluxes in the Global Tropical Oceans. Ocean-Land-Atmosphere Research, 2, 0003. doi: 10.34133/olar.0003. The Clouds and the Earth's Radiant Energy System program, which uses the Moderate Resolution Imaging Spectroradiometer (CM), has been updated with the launch of new satellites and the availability of newly upgraded radiation data. The spatial and temporal variability of daily averaged synoptic 1-degree CM version 3 (CMv3) (old) and version 4 (CMv4) (new) downwelling shortwave (QS) and longwave radiation (QL) data in the global tropical oceans spanning 30°S–30°N from 2000 to 2017 is investigated. Daily in situ data from the Global Tropical Moored Buoy Array were used to validate the CM data from 2000 to 2015. When compared to CMv3, both QS and QL in CMv4 show significant improvements in bias, root-mean-square error, and standard deviations. Furthermore, a long-term trend analysis shows that QS has been increasing by 1 W m−2 per year in the Southern Hemisphere. In contrast, the Northern Hemisphere has a −0.7 W m−2 annual decreasing trend. QS and QL exhibit similar spatial trend patterns. However, in the Indian Ocean, Indo-Pacific warm pool region, and Southern Hemisphere, QL spatial patterns in CMv3 and CMv4 differ with an opposite trend (0.5 W m−2). These annual trends in QS and QL could cause the sea surface temperature to change by −0.2 to 0.3 °C per year in the tropical oceans. These results stress the importance of accurate radiative flux data, and CMv4 can be an alternative to reanalysis or other model-simulated data.
Tian, Yinglin; Zhong, Deyu; Ghausi, Sarosh Alam; Wang, Guangqian; Kleidon, AxelTian, Y., D. Zhong, S. A. Ghausi, G. Wang, A. Kleidon, 2023: Understanding variations in downwelling longwave radiation using Brutsaert's equation. EGUsphere, 1-17. doi: 10.5194/egusphere-2023-451. Abstract. A dominant term in the surface energy balance and central to global warming is downwelling longwave radiation (Rld). It is influenced by radiative properties of the atmospheric column, in particular by greenhouse gases, water vapour, clouds and differences in atmospheric heat storage. We use the semi-empirical equation derived by Brutsaert (1975) to identify the leading terms responsible for the spatio-temporal climatological variations in Rld. This equation requires only near-surface observations of air temperature and humidity. We first evaluated this equation and its extension by Crawford and Duchon (1999) with observations from FLUXNET, the NASA-CERES dataset , and the ERA5 reanalysis. We found a strong agreement with r2 ranging from 0.87 to 0.99 across the datasets for clear-sky and all-sky conditions. We then used the equations to show that diurnal and seasonal variations in Rld are predominantly controlled by changes in atmospheric heat storage. Variations in the emissivity of the atmosphere form a secondary contribution to the variation in Rld, and are mainly controlled by anomalies in cloud cover. We also found that as aridity increases, the contributions from changes in emissivity and atmospheric heat storage tend to offset each other (−40 W m−2 and 20−30 W m−2, respectively), explaining the relatively small decrease in Rld with aridity (−(10−20) W/m−2). These equations thus provide a solid physical basis for understanding the spatio-temporal variability of surface downwelling longwave radiation. This should help to better understand and interpret climatological changes, such as those associated with extreme events and global warming.
Tomassini, Lorenzo; Willett, Martin; Sellar, Alistair; Lock, Adrian; Walters, David; Whitall, Michael; Sanchez, Claudio; Heming, Julian; Earnshaw, Paul; Rodriguez, José M.; Ackerley, Duncan; Xavier, Prince; Franklin, Charmaine; Senior, Catherine A.Tomassini, L., M. Willett, A. Sellar, A. Lock, D. Walters, M. Whitall, C. Sanchez, J. Heming, P. Earnshaw, J. Rodriguez, . M., D. Ackerley, P. Xavier, C. Franklin, C. A. Senior, 2023: Confronting the Convective Gray Zone in the Global Configuration of the Met Office Unified Model. Journal of Advances in Modeling Earth Systems, 15(5), e2022MS003418. doi: 10.1029/2022MS003418. In atmospheric models with kilometer-scale grids the resolution approaches the scale of convection. As a consequence the most energetic eddies in the atmosphere are partially resolved and partially unresolved. The modeling challenge to represent convection partially explicitly and partially as a subgrid process is called the convective gray zone problem. The gray zone issue has previously been discussed in the context of regional models, but the evolution in regional models is constrained by the lateral boundary conditions. Here we explore the convective gray zone starting from a defined global configuration of the Met Office Unified Model using initialized forecasts and comparing different model formulations to observations. The focus is on convection and turbulence, but some aspects of the model dynamics are also considered. The global model is run at nominal 5 km resolution and thus contributions from both resolved and subgrid turbulent and convective fluxes are non-negligible. The main conclusion is that in the present assessment, the configurations which include scale-aware turbulence and a carefully reduced and simplified mass-flux convection scheme outperform both the configuration with fully parameterized convection as well as a configuration in which the subgrid convection parameterization is switched off completely. The results are more conclusive with regard to convective organization and tropical variability than extratropical predictability. The present study thus endorses the strategy to further develop scale-aware physics schemes and to pursue an operational implementation of the global 5 km-resolution model to be used alongside other ensemble forecasts to allow researchers and forecasters to further assess these simulations. atmospheric variability and predictability; convection-circulation interaction; convective gray zone; kilometer-scale global atmospheric modeling
Valkenborg, Bram; De Lannoy, Gabriëlle J. M.; Gruber, Alexander; Miralles, Diego G.; Köhler, Philipp; Frankenberg, Christian; Desai, Ankur R.; Humphreys, Elyn; Klatt, Janina; Lohila, Annalea; Nilsson, Mats B.; Tuittila, Eeva-Stiina; Bechtold, MichelValkenborg, B., G. J. M. De Lannoy, A. Gruber, D. G. Miralles, P. Köhler, C. Frankenberg, A. R. Desai, E. Humphreys, J. Klatt, A. Lohila, M. B. Nilsson, E. Tuittila, M. Bechtold, 2023: Drought and Waterlogging Stress Regimes in Northern Peatlands Detected Through Satellite Retrieved Solar-Induced Chlorophyll Fluorescence. Geophysical Research Letters, 50(19), e2023GL105205. doi: 10.1029/2023GL105205. The water table depth (WTD) in peatlands determines the soil carbon decomposition rate and influences vegetation growth, hence the above-ground carbon assimilation. Here, we used satellite-observed Solar-Induced chlorophyll Fluorescence (SIF) as a proxy of Gross Primary Production (GPP) to investigate water-related vegetation stress over northern peatlands. A linear model with interaction effects was used to relate short- and long-term anomalies in SIF with WTD anomalies and the absolute WTD. Most locations showed the occurrence of drought and waterlogging stress though regions with exclusively waterlogging or drought stress were also detected. As a spatial median, minimal water-related vegetation stress was found for a WTD of −0.22 m (short-term) and −0.20 m (long-term) (±0.01 m, 95% confidence interval of statistical uncertainty). The stress response observed with SIF is supported by an analysis of in situ GPP data. Our findings provide insight into how changes in WTD of northern peatlands could affect GPP under climate change. carbon cycle; drought; hydrology; gross primary production; peatlands; solar induced chlorophyll fluorescence
Wall, Casey J.; Storelvmo, Trude; Possner, AnnaWall, C. J., T. Storelvmo, A. Possner, 2023: Global observations of aerosol indirect effects from marine liquid clouds. Atmospheric Chemistry and Physics, 23(20), 13125-13141. doi: 10.5194/acp-23-13125-2023. Interactions between aerosols and liquid clouds are one of the largest sources of uncertainty in the historical radiative forcing of climate. One widely shared goal to reduce this uncertainty is to decompose radiative anomalies arising from aerosol–cloud interactions into components associated with changes in cloud-droplet number concentration (Twomey effect), liquid-water-path adjustments, and cloud-fraction adjustments. However, there has not been a quantitative foundation for simultaneously estimating these components with global satellite observations. Here we present a method for assessing shortwave radiative flux anomalies from the Twomey effect and cloud adjustments over ocean between 55∘ S and 55∘ N. We find that larger aerosol concentrations are associated with widespread cloud brightening from the Twomey effect, a positive radiative adjustment from decreasing liquid water path in subtropical stratocumulus regions, and a negative radiative adjustment from increasing cloud fraction in the subtropics and midlatitudes. The Twomey effect and total cloud adjustment have contributed −0.77 ± 0.25 and −1.02 ± 0.43 W m−2, respectively, to the effective radiative forcing since 1850 over the domain (95 % confidence). Our findings reduce uncertainty in these components of aerosol forcing and suggest that cloud adjustments make a larger contribution to the forcing than is commonly believed.
Wang, Meihua; Su, Jing; Xu, Ying; Han, Xinyi; Peng, Nan; Ge, JinmingWang, M., J. Su, Y. Xu, X. Han, N. Peng, J. Ge, 2023: Radiative contributions of different cloud types to regional energy budget over the SACOL site. Climate Dynamics. doi: 10.1007/s00382-022-06651-0. Different cloud types have distinct radiative effects on the energy budget of the earth–atmosphere system. To better understand the cloud radiative impacts, it is necessary to distinguish the effects of different cloud types, which can be achieved through the cloud radar data that can provide cloud profiles for both day-to-day and diurnal variations. In this study, we use 6-year high-temporal resolution data from the Ka-Band Zenith Radar (KAZR) at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) site to analyze the physical properties and radiative effects of main cloud types. The three types of clouds that occur most frequently at the SACOL site are single-layer ice clouds, single-layer water clouds, and double-layer clouds with the annual occurrence frequencies being 29.1%, 3.4%, and 8.3%, respectively. By using the Fu–Liou radiative transfer model simulation, it is found that the distinct diurnal variations of both the occurrence frequency and their macro- and micro-physical properties significantly affect the cloud-radiation. On annual mean, the single-layer ice clouds have a positive radiative forcing of 7.4 W/m2 to heat the system, which is a result of reflecting 12.9 W/m2 shortwave (SW) radiation and retaining 20.3 W/m2 longwave (LW) radiation; while the single-layer water clouds and double-layer clouds have much stronger SW cooling effect than LW warming effect, causing a net negative forcing of 8.5 W/m2. Although all these clouds have an overall small cooling effect of 1.1 W/m2 on the annual radiative energy budget, the significant differences of the diurnal and seasonal distributions for different type clouds can lead to distinct radiative forcing. Especially the LW warming effect induced by the exclusive ice clouds in the cold season may have an important contribution to the rapid winter warming over the semi-arid regions.
Wang, Shaoyin; Liu, Jiping; Cheng, Xiao; Greatbatch, Richard J.; Wei, Zixin; Chen, Zhuoqi; Li, HuaWang, S., J. Liu, X. Cheng, R. J. Greatbatch, Z. Wei, Z. Chen, H. Li, 2023: Separation of Atmospheric Circulation Patterns Governing Regional Variability of Arctic Sea Ice in Summer. Advances in Atmospheric Sciences, 40(12), 2344-2361. doi: 10.1007/s00376-022-2176-1. In recent decades, Arctic summer sea ice extent (SIE) has shown a rapid decline overlaid with large interannual variations, both of which are influenced by geopotential height anomalies over Greenland (GL-high) and the central Arctic (CA-high). In this study, SIE along coastal Siberia (Sib-SIE) and Alaska (Ala-SIE) is found to account for about 65% and 21% of the Arctic SIE interannual variability, respectively. Variability in Ala-SIE is related to the GL-high, whereas variability in Sib-SIE is related to the CA-high. A decreased Ala-SIE is associated with decreased cloud cover and increased easterly winds along the Alaskan coast, promoting ice—albedo feedback. A decreased Sib-SIE is associated with a significant increase in water vapor and downward longwave radiation (DLR) along the Siberian coast. The years 2012 and 2020 with minimum recorded ASIE are used as examples. Compared to climatology, summer 2012 is characterized by a significantly enhanced GL-high with major sea ice loss along the Alaskan coast, while summer 2020 is characterized by an enhanced CA-high with sea ice loss focused along the Siberian coast. In 2012, the lack of cloud cover along the Alaskan coast contributed to an increase in incoming solar radiation, amplifying ice-albedo feedback there; while in 2020, the opposite occurs with an increase in cloud cover along the Alaskan coast, resulting in a slight increase in sea ice there. Along the Siberian coast, increased DLR in 2020 plays a dominant role in sea ice loss, and increased cloud cover and water vapor both contribute to the increased DLR. Arctic sea ice; water vapor; shortwave and longwave radiation; cloud cover; Arctic circulation patterns; 云量; 北极海冰; 北极环流型; 水汽; 短波和长波辐射
Wang, Youcun; Li, Min; Jiang, Kecai; Li, Wenwen; Zhao, Qile; Fang, Rongxin; Wei, Na; Mu, RenhaiWang, Y., M. Li, K. Jiang, W. Li, Q. Zhao, R. Fang, N. Wei, R. Mu, 2023: Improving Precise Orbit Determination of LEO Satellites Using Enhanced Solar Radiation Pressure Modeling. Space Weather, 21(1), e2022SW003292. doi: 10.1029/2022SW003292. Precise orbit knowledge is a fundamental requirement for low Earth orbit (LEO) satellites. High-precision non-gravitational force modeling directly improves the overall quality of LEO precise orbit determination (POD). To address the potential systematic errors in solar radiation pressure (SRP), we introduce observed radiation data and modeled physical effects to describe the real in-flight environment of satellites. Time-dependent solar irradiance data and a highly physical shadow model are considered for SRP modeling. We develop an advanced thermal reradiation model for satellite solar panels. A set of improved non-gravitational force models is performed for LEO POD, and we discuss the benefits of the enhanced dynamic models on orbit quality and dependence on empirical parameters. The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO), Jason-3, and Haiyang-2B missions are selected for the POD process. Estimated empirical acceleration and scale parameters and independent satellite laser ranging (SLR) are used to validate the final orbit solutions. The magnitude of empirical acceleration estimated in POD is reduced by 19% with the enhanced dynamic modeling, and the estimated scale factor for the SRP converges to stable and reasonable level. Furthermore, the steady-state temperature model used in thermal reradiation can effectively reduce mismodeled effects in the SRP, and the systematic linear dependency revealed by the SLR residuals is significantly reduced for the GRACE-C and Jason-3 satellites, with improvements of approximately 61% and 49%, respectively. Overall, advances are made in the explicit modeling of non-gravitational forces to pursue superior satellite orbits, suggesting a more dynamic orbit solution.
Weaver, Clark Jay; Herman, Jay; Marshak, Alexander; Lorentz, Steven R.; Yu, Yinan; Smith, Allan W.; Szabo, AdamWeaver, C. J., J. Herman, A. Marshak, S. R. Lorentz, Y. Yu, A. W. Smith, A. Szabo, 2023: Shortwave reflected energy from NISTAR and the Earth Polychromatic Imaging Camera onboard the DSCOVR spacecraft. EGUsphere, 1-18. doi: 10.5194/egusphere-2023-638. Abstract. We describe a new method for estimating the total reflected shortwave energy from the Earth Polychromatic Imaging Camera (EPIC) and compare it with direct measurements from the NIST Advanced Radiometer (NISTAR) instrument (Electrical substitution radiometer) – both are onboard the Lagrange-1 orbiting Deep Space Climate Observatory (DSCOVR). The 6 narrow-band wavelength channels (340 to 780 nm) available from EPIC provide a framework for estimating the integrated spectral energy for each EPIC pixel. The Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and the SCIAMACHY instrument provide spectral information away from the EPIC wavelengths, particularly for wavelengths longer than 780 nm. The total area-weighted reflected shortwave energy from an entire EPIC image is compared with co-temporal Band B Shortwave reflected energy observed by NISTAR. Our analysis from March to December 2017 shows the two are highly correlated with differences ranging from -10 to 10 Watts m-2. The offset bias over the entire period is less than 0.2 Watts m-2. We also compare our EPIC energy maps with the Clouds and the Earth’s Radiant Energy System (CERES) Single Scanner Footprint (SSF) Shortwave (SW) reflected energy observed within 3 hours of an EPIC image. Our EPIC-AVIRIS SW estimate is 5–20 % higher near the EPIC image center and 5–20 % lower near the image edges compared with the CERES SSF.
Wei, Jian; Ren, Tong; Yang, Ping; DiMarco, Steven F.; Huang, XiangleiWei, J., T. Ren, P. Yang, S. F. DiMarco, X. Huang, 2023: Sensitivity of Arctic Surface Temperature to Including a Comprehensive Ocean Interior Reflectance to the Ocean Surface Albedo Within the Fully Coupled CESM2. Journal of Advances in Modeling Earth Systems, 15(12), e2023MS003702. doi: 10.1029/2023MS003702. Almost all current climate models simplify the ocean surface albedo (OSA) by assuming the reflected solar energy without the ocean interior contribution. In this study, an improved ocean surface albedo scheme is incorporated into the Community Earth System Model version 2 (CESM2) to assess the sensitivity of Arctic surface temperature to including ocean interior reflectance to the OSA. Fully coupled CESM2 simulations with and without ocean interior reflectance are subsequently performed, we focus on the analysis of Arctic surface temperature responses. Incorporating ocean interior reflectance increases absorbed solar radiation and warms the ocean, enhancing seasonal heat storage and release across the Arctic Ocean, and increasing sea ice reduction and positive climate feedbacks that elevates Arctic surface temperature. Seasonal variations in air-surface temperature differences induce changes in turbulent heat flux patterns, concurrently modifying dynamic advection and moisture processes that affect boundary layer humidity and low clouds, especially in winter. Based on partitioning physical processes in the thermodynamic energy equation, surface air warming is induced primarily through positive heating anomalies of vertical advection, latent heat release, and longwave radiative forcing. Through an examination of the surface energy budget, skin temperature warming is driven predominantly by increased downward longwave radiation, positive surface albedo feedback in summer, and increased conductive heat transport from the ocean particularly in winter. Significant effects of ocean interior reflectance on the Arctic Ocean, including sea surface warming and sea ice reduction, justify the importance of ocean interior reflectance in climate models for better understanding of ongoing Arctic climate changes. ocean surface albedo; Arctic surface temperature; fully coupled climate model simulation; ocean interior reflectance
Wei, Jiangfeng; Lu, Boyan; Song, Yuanyuan; Chen, Haishan; Weng, ZhimeiWei, J., B. Lu, Y. Song, H. Chen, Z. Weng, 2023: Anthropogenic Aerosols Weaken Land–Atmosphere Coupling Over North China. Geophysical Research Letters, 50(20), e2023GL105685. doi: 10.1029/2023GL105685. North China, characterized by its strong land–atmosphere coupling, also has a high concentration of atmospheric aerosols from anthropogenic emissions. However, the impact of aerosols on land–atmosphere coupling in this region remains partially unclear. Here, we use Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) experiments to show that the aerosol radiative effect weakens land–atmosphere coupling in North China. This weakening occurs across all five indexes used to measure different aspects of land–atmosphere coupling. Notably, the weakening is more pronounced for indexes that describe surface coupling compared to the index that characterizes the coupling between the planetary boundary layer (PBL) and clouds. The mechanisms underlying the aerosol influence can be primarily attributed to the reduction of land surface fluxes and their sensitivities to soil moisture, while the weakened entrainment of moisture at the upper boundary of the PBL may also contribute to the effects.
Wen, Guoyong; Marshak, AlexanderWen, G., A. Marshak, 2023: Effect of scattering angle on DSCOVR/EPIC observations. Frontiers in Remote Sensing, 4. doi: 10.3389/frsen.2023.1188056. The Earth Polychromatic Imaging Camera (EPIC) on the Deep Space Climate Observatory (DSCOVR) routinely captures reflected radiation from the whole sunlit side of the Earth in the near backward direction to monitor the changing planet. The instrument had routinely operated until 27 June 2019, when the spacecraft was placed in an extended safe hold due to degradation of an inertial navigation unit. DSCOVR returned to full operations on 2 March 2020. Since then, the range of scattering angles between the incident sunlight and sensor direction has been larger than before and the largest scattering angle reaches ∼178°, only 2° from perfect backscattering, proving a unique opportunity to study the top-of-atmosphere (TOA) reflectance under such extreme conditions. In the paper, we compare EPIC global spectral reflectances in 2021–2016. We found that there are four occasions when the scattering angle reaches about 178° and associated with them enhanced global daily average spectral reflectances in 2021. The scattering angle related reflectance enhancements are not found in 2016 data when the maximum scattering angle is about 174.5°. CERES data do not show such occasions in global daily reflected shortwave flux. As a result, those enhanced reflectance occasions are primarily due to the change in scattering angle. The enhancement due to changes in scattering angle depends strongly on wavelength, primarily because of wavelength dependence of cloud scattering phase function. Radiative transfer calculations show that the change in scattering angles has the largest impact on reflectance in the red and NIR channels at 680 nm and 780 nm and the smallest influence on reflectance in the UV channel at 388 nm, consistent with EPIC observations. The change of global average cloud amount also plays an important role in the reflectance enhancement. The influence of the cloud effect depends on whether the change is in phase or not with the change of scattering angle.
Windler, Grace; Tierney, Jessica E.; deMenocal, Peter B.Windler, G., J. E. Tierney, P. B. deMenocal, 2023: Hydroclimate Variability in the Equatorial Western Indian Ocean for the Last 250,000 Years. Paleoceanography and Paleoclimatology, 38(2), e2022PA004530. doi: 10.1029/2022PA004530. Indian Ocean sea surface temperatures impact precipitation across the basin through coupled ocean-atmosphere responses to changes in climate. To understand the hydroclimate response over the western Indian Ocean and equatorial east Africa to different forcing mechanisms, we present four new proxy reconstructions from core VM19-193 (2.98°N, 51.47°E) that span the last 250 ky. Sub-surface water temperatures (Sub-T; TEX86) show strong precessional (23 ky) variability that is primarily influenced by maximum incoming solar radiation (insolation) during the Northern Hemisphere spring season, likely indicating that local insolation dominates the upper water column at this tropical location over time. Leaf waxes, on the other hand, reflect two different precipitation signals: δ13Cwax (in phase with boreal fall insolation) is likely reflecting vegetation changes in response to local rainfall over east Africa, whereas δDprecip (primarily driven by boreal summer insolation) represents changes in regional circulation associated with the summer monsoon. Glacial-interglacial changes in ocean temperatures support glacial shelf exposure over the Maritime Continent in the eastern Indian Ocean and the subsequent weakening of the Indian Walker Circulation as a mechanism driving 100 ky climate variability across the tropical Indo-Pacific. Additionally, the 100 ky spectral power in δDprecip supports a basin-wide weakening of summer monsoon circulation in response to glacial climates. Overall, the proxy records from VM19-193 indicate that both precession and glacial-interglacial cycles exert control over hydroclimate at this tropical location. Indian Ocean; alkenone; leaf wax; Pleistocene paleoclimate; TEX86
Wong, Vox Kalai; Zhang, Chujun; Zhang, Zhuoqiong; Hao, Mingwei; Zhou, Yuanyuan; So, Shu KongWong, V. K., C. Zhang, Z. Zhang, M. Hao, Y. Zhou, S. K. So, 2023: 0.01 to 0.5 Sun is a Realistic and Alternative Irradiance Window to Analyze Urban Outdoor Photovoltaic Cells. Materials Today Energy, 101347. doi: 10.1016/j.mtener.2023.101347. Solar cells have penetrated many cities as Building Integrated Photovoltaic (BIPV) or the energy source for standalone Internet of Things (IoT) devices. Traditionally, photovoltaic (PV) cells are evaluated using 1 sun irradiance. However, in a city, factors such as air pollution, cloudiness and cell installation orientation may attenuate the receivable solar energy. Also, the power conversion efficiency (PCE) of a PV cell is highly irradiance-dependent. Evaluating urban outdoor PV cells using 1 sun irradiance could lead to inaccurate prediction of PCE and overestimated output power in actual usage. Herein, we analyzed daytime irradiances of 11 cities located across the globe. Our results show that realistic irradiances (RI) in most cities are between 0.01 and 0.5 sun, reflecting the irradiance under a cloudy to mostly sunny sky. Under such an RI window, the PCEs of 9 different PV technologies were compared. 7 PV technologies have compromised performance. 2 PV technologies, organic and perovskite PVs, show enhanced PCE under the RI window and are favorable for urban outdoor applications. The potential of powering IoT devices by these PV technologies under sub-optimal irradiance conditions in cities is also highlighted.
Wu, Jie; Pallé, Enric; Guo, Huadong; Ding, YixingWu, J., E. Pallé, H. Guo, Y. Ding, 2023: Long-term trends in albedo as seen from a lunar observatory. Advances in Space Research. doi: 10.1016/j.asr.2023.06.028. The Earth’s albedo is the fraction of short-wave solar radiation that is reflected back to space, and is key to understand the observed trends in climate change. Although there have been many observational approaches to estimate the Earth’s albedo, different methods have their own drawbacks, for example, artificial satellites have a finite life time, and are operating in a hard environment that could quickly degrade the detectors. The Moon, the only natural satellite of Earth, offers an additional platform for monitoring the Earth’s albedo. In this paper, we calculate the global TOA (top-of-atmosphere) albedo that would be observed by a theoretical observatory on the Moon, and compare it with long-term trends derived from CERES (Clouds and the Earth’s Radiant Energy System, 2000-2020) and earthshine data (1999-2017). We find that the global hourly mean albedo observed in the direction of the Moon is more variable because of the orbital movement of the Moon. However, the regional and long-term global mean albedo anomalies that would be observed by CERES and has a good general agreement by a lunar observer over 20 years the data spans. Similarly, earthshine data show a steady decline during two decades of about 0.7 W/m2 which is in line with the decline of 0.5 W/m2 that would be observed from the Moon. Besides, to compare the regional changes of albedo with CERES, the spatially-resolved decadal anomalies in the albedo are also calculated for analysis. We find that a lunar-based observatory would be capable of detecting similar changes seen from CERES. Thus, it is a a practical option to monitor the long-term trends in albedo from the point of view of capturing the variability in the TOA fluxes of the Earth’s atmosphere. CERES; earthshine; Albedo; lunar observatory
Wu, S.-N.; Soden, B. J.; Alaka Jr., G. J.Wu, S., B. J. Soden, G. J. Alaka Jr., 2023: The Influence of Radiation on the Prediction of Tropical Cyclone Intensification in a Forecast Model. Geophysical Research Letters, 50(2), e2022GL099442. doi: 10.1029/2022GL099442. This study examines the influence of radiative heating on the prediction of tropical cyclone (TC) intensification in the Hurricane Weather Research and Forecasting (HWRF) model. Previous idealized modeling and observational studies demonstrated that radiative heating can substantially modulate the evolution of TC intensity. However, the relevance of this process under realistic conditions remains unclear. Here, we use observed longwave radiative heating to explore the performance of TC forecasts in HWRF simulations. The performance of TC intensity forecasts is then investigated in the context of radiative heating forecasts. In observations and HWRF forecasts, high clouds near the TC center increase the convergence of radiative fluxes. A sharp spatial gradient (≥60 W/m2) in the flux convergence from the TC center outward toward the environment is associated with subsequent TC intensification. More accurate simulation of the spatial structure of longwave radiative heating is associated with more accurate TC intensity forecasts. radiation; radiative feedback; tropical cyclone; hurricane forecasting; hurricane model
Xia, Yan; Hu, Yongyun; Huang, Yi; Bian, Jianchun; Zhao, Chuanfeng; Lin, Jintai; Xie, Fei; Zhou, ChunjiangXia, Y., Y. Hu, Y. Huang, J. Bian, C. Zhao, J. Lin, F. Xie, C. Zhou, 2023: Stratospheric Ozone Loss Enhances Summer Precipitation Over the Southern Slope of the Tibetan Plateau. Geophysical Research Letters, 50(15), e2023GL103742. doi: 10.1029/2023GL103742. Heavy summer precipitation over the southern slope of the Tibetan Plateau has dramatic influences on water resources and hydrological disasters in South Asia. It experienced increasing trends over 1979–1996 and decreasing trends over 1996–2022, which are not yet well understood. Here we show observational and numerical evidence that stratospheric ozone has significant impacts on long-term trends of summer precipitation in this strong convection area. It is found that stratospheric ozone depletion, by modulating the lower stratospheric temperature and upper-tropospheric static stability, enhances deep convection and precipitation over the southern slope of the Tibetan Plateau. The results suggest that the ozone recovery in the future may reduce the summer precipitation over the southern slope of the Tibetan Plateau in the first half of the 21st century, which would be imperative for future water resource management in South Asia. South Asia; Tibetan Plateau; deep convection; stratospheric ozone; precipitation; long-term changes
Xiang, Baoqiang; Xie, Shang-Ping; Kang, Sarah M.; Kramer, Ryan J.Xiang, B., S. Xie, S. M. Kang, R. J. Kramer, 2023: An emerging Asian aerosol dipole pattern reshapes the Asian summer monsoon and exacerbates northern hemisphere warming. npj Climate and Atmospheric Science, 6(1), 1-10. doi: 10.1038/s41612-023-00400-8. Since the early 2010s, anthropogenic aerosols have started decreasing in East Asia (EA) while have continued to increase in South Asia (SA). Yet the climate impacts of this Asian aerosol dipole (AAD) pattern remain largely unknown. Using a state-of-the-art climate model, we demonstrate that the climate response is distinctly different between the SA aerosol increases and EA aerosol decreases. The SA aerosol increases lead to ~2.7 times stronger land summer precipitation change within the forced regions than the EA aerosol decreases. Contrastingly, the SA aerosol increases, within the tropical monsoon regime, produce weak and tropically confined responses, while the EA aerosol decreases yield a pronounced northern hemisphere warming aided by extratropical mean westerly and positive air-sea feedbacks over the western North Pacific. By scaling the observed instantaneous shortwave radiative forcing, we reveal that the recent AAD induces a pronounced northern hemisphere extratropical (beyond 30°N) warming (0.024 ± 0.010 °C decade−1), particularly over Europe (0.049 ± 0.009 °C decade−1). These findings highlight the importance of the pattern effect of forcings in driving global climate and have important implications for decadal prediction. Atmospheric dynamics; Climate and Earth system modelling
Xu, Jianglei; Liang, Shunlin; He, Tao; Ma, Han; Zhang, Yufang; Zhang, Guodong; Liang, HuiXu, J., S. Liang, T. He, H. Ma, Y. Zhang, G. Zhang, H. Liang, 2023: Variability and trends in land surface longwave radiation fluxes from six satellite and reanalysis products. International Journal of Digital Earth, 16(1), 2912-2940. doi: 10.1080/17538947.2023.2239795. Earth surface longwave radiation (SLR), including downward (DLR), upward (ULR), and net longwave radiation (NLR), significantly impacts the surface radiation budget and global climate evolution. However, the spatiotemporal variation in SLR remains poorly understood. In this study, three satellite products (GLASS-MODIS V40, GLASS-AVHRR, and CERES-SYN) and three reanalysis datasets (ERA5, MERRA-2, and GLDAS) were validated using ground measurements from 288 sites at seven observation networks. The mean biases and root mean square errors of the monthly DLR (ULR, NLR) estimates from the six products were −6.36 (−3.56, −2.86) Wm-2 and 16.63 (14.33, 13.38) Wm-2, respectively. Large differences in the spatial distribution of the SLR were mainly observed at high-latitude, high-altitude and desert/barren-covered regions. Large interannual variability was detected at high latitudes. GLASS-AVHRR and ERA5 better captured the long-term variability in DLR and ULR, whereas GLASS-AVHRR and MERRA-2 better detected trends in NLR. An increasing trend in DLR and ULR was observed between 1982 and 2015, followed by a decreasing trend from 2016 to 2021; the NLR flux did not exhibit a significant trend. Overall, the GLASS-AVHRR and ERA5 SLR estimates were more accurate and stable than those of the other products in accuracy, spatiotemporal distribution, and trend analysis. satellite remote sensing; annual mean value; long-term variability; spatiotemporal distributions; Surface longwave radiation
Xu, Jianglei; Liang, Shunlin; Ma, Han; He, Tao; Zhang, Yufang; Zhang, GuodongXu, J., S. Liang, H. Ma, T. He, Y. Zhang, G. Zhang, 2023: A daily 5-km all-sky sea-surface longwave radiation product based on statistically modified deep neural network and spatiotemporal analysis for 1981–2018. Remote Sensing of Environment, 290, 113550. doi: 10.1016/j.rse.2023.113550. Longwave radiation components, including downward, upward, and net longwave radiation (DLR, ULR, and NLR, respectively), are essential parameters in heat flux exchange across the ocean–atmosphere interface. However, few long-term, high-resolution, and accurate sea–surface longwave radiation (SSLR) products are available. We generated the first high-resolution (5-km) all-sky daily SSLR product from Advanced Very High-Resolution Radiometer (AVHRR) top-of-atmosphere observations, combined with the European Center for Medium-Range Weather Forecasts Reanalysis V5 near-surface meteorological variables and National Oceanic and Atmospheric Administration sea–surface temperatures from 1981 to 2018. We coupled the densely connected convolutional neural network and bidirectional long short-term memory neural network as a retrieval algorithm. The training dataset was generated using integrated SSLR samples from 2002 to 2012 at 437 globally distributed locations. The archived product, SSLR_AVHRR, showed a high accuracy against 81,546 buoy-based observations from eight observation networks, with an R2 of 0.96 (1.00, 0.77), root mean square error of 10.27 (4.51, 9.27) Wm−2, and mean bias error of −1.30 (0.30, −0.72) Wm−2 for DLR (ULR, NLR) retrievals. Based on SSLR_AVHRR, the global DLR (ULR) flux exhibited a significantly (p-value Climate change; AVHRR; Deep learning; Longwave radiation; Spatiotemporal variations; Trend analysis
Xu, Kuan-Man; Zhou, Yaping; Sun, Moguo; Kato, Seiji; Hu, YongxiangXu, K., Y. Zhou, M. Sun, S. Kato, Y. Hu, 2023: Observed Cloud Type-Sorted Cloud Property and Radiative Flux Changes with the Degree of Convective Aggregation from CERES Data. Journal of Geophysical Research: Atmospheres, n/a(n/a), e2023JD039152. doi: 10.1029/2023JD039152. Cloud-radiation interactions are a critical mechanism for convective self-aggregation, especially the longwave radiative cooling of low clouds and environments. In this study, two data products from CERES observations combined with MERRA-2 reanalysis are used to understand the changes of cloud properties and radiative fluxes by cloud type with the degree of convective aggregation at the 1000-km scale, which is represented by the number of cloud objects (N), simple convective aggregation index (SCAI), modified SCAI (MCAI) or convective organization potential (COP). The changes with SCAI are similar to those with N as an index, agreeing with previous studies using grid-averaged properties. For changes from weak to strong degrees of aggregation using N and SCAI, area fractions of middle- and high-level cloud types decrease by up to 4% but those of low-level cloud types increase by up to 2%, and more infrared radiation is emitted to space (2 8 W m-2) from optically thin cloud types but more solar radiation is reflected (2 4 W m-2) from optically-thick cloud types. However, using COP (MCAI to lesser extent), area fractions of optically-thick cloud types increase, which emit less infrared radiation and reflect more solar radiation, whereas the area fractions of low-level clouds decrease. These results can be explained by greater expansion of cloud object sizes for COP than MCAI/SCAI as the degree of convective aggregation increases, which also explains the difference between SCAI and MCAI pertaining to the opposite changes of optically-thick high-level clouds. These results can have implications for understanding convective self-aggregation. CERES; Radiative fluxes; Cloud properties; Convective aggregation; Flux by cloud type; Observational Analysis
Xun, Lina; Liu, Xue; Lu, Hui; Zhang, Jingjing; Yan, QingXun, L., X. Liu, H. Lu, J. Zhang, Q. Yan, 2023: Screening Approach of the Langley Calibration Station for Sun Photometers in China. Atmosphere, 14(11), 1641. doi: 10.3390/atmos14111641. A sun photometer is a type of photometer that points at the sun, and it has been playing an increasingly important role in characterizing aerosols across the world. As long as the solar photometer is accurately calibrated, the optical thickness of the aerosol can be obtained from the measured value of this device. When the calibration of a single instrument is not accurate, the inversion quantity varies greatly. The calibration constant of the sun photometer changes during its use process; thus, calibrations are frequently needed in order to ensure the accuracy of the measured value. The calibration constant of the solar photometer is usually determined using the Langley method. Internationally, AERONET has two Langley calibration stations: the Mauna Loa observatory in the United States and the Izaña observatory in Spain. So far, the International Comparison and Calibration System has been established in Beijing, similar to AERONET at GSFC, but the Langley calibration system has not yet been established. Therefore, it is necessary to select a suitable calibration station in China. This paper studies the requirements of the calibration station using the Langley method. We used long-term records of satellite-derived measurements and survey data belonging to the aerosol optical thickness data of SNPP/VIIRS, CERES, MERRA-2, etc., in order to gain a better understanding of whether these stations are suitable for calibration. From the existing astronomical observation stations, meteorological stations, and the Sun–Sky Radiometer Observation Network (SONET) observation stations in China, the qualified stations were selected. According to the statistical data from the Ali observatory, the monthly average of clear sky is 20.21 days, and it is always greater than 15 days. The monthly average of aerosol is not more than 0.15 and is less than 0.3. We believe that the atmosphere above the Ali observatory is stable, and the results show that the Ali observatory has excellent weather conditions. This study can provide a selection of calibration sites for solar photometer calibrations in China that may need to be further characterized and evaluated, and at the same time provide a method to exclude unsuitable calibration sites. calibration; atmospheric stability; boundary layer depth; langley plot method; sun photometer
Yang, Shuyue; Zhang, Xiaotong; Guan, Shikang; Zhao, Wenbo; Duan, Yanjun; Yao, Yunjun; Jia, Kun; Jiang, BoYang, S., X. Zhang, S. Guan, W. Zhao, Y. Duan, Y. Yao, K. Jia, B. Jiang, 2023: A review and comparison of surface incident shortwave radiation from multiple data sources: satellite retrievals, reanalysis data and GCM simulations. International Journal of Digital Earth, 16(1), 1332-1357. doi: 10.1080/17538947.2023.2198262. Surface incident shortwave radiation (Rs) can promote the circulation of substance and energy, and the accuracy of its estimation is of great significance for climate studies. The Rs can be acquired from satellite retrievals, reanalysis predictions and general circulation model (GCM) simulations. Although Rs estimates have been evaluated and compared in previous studies, most of them focus on evaluating the Rs estimates over specific regions using ground measurements from limited stations. Therefore, it is essential to comprehensively validate Rs estimates from multiple data sources. In this study, ground measurements of 690 stations from BSRN, GEBA, CMA, GC-NET and buoys were employed to validate the Rs estimates from seven representative products (GLASS, GEWEX-SRB, CERES-EBAF, ERA5, MERRA2, CFSR and CMIP6). The validation results indicated that the selected products overestimated Rs globally, with biases ranged from 0.48 to 21.27 W/m2. The satellite retrievals showed relatively better accuracy among seven datasets compared to ground measurements at the selected stations. Moreover, the selected seven products were all in poor accuracy at high-latitude regions with RMSEs greater than 50 W/m2. The long-term variation trends were also analyzed in this study. Downward shortwave radiation; general circulation model; reanalysis; satellite
Ye, Jiacheng; Wang, Zhuo; Yang, Fanglin; Harris, Lucas; Jensen, Tara; Miller, Douglas E.; Kalb, Christina; Adriaansen, Daniel; Li, WeiweiYe, J., Z. Wang, F. Yang, L. Harris, T. Jensen, D. E. Miller, C. Kalb, D. Adriaansen, W. Li, 2023: Evaluation and Process-Oriented Diagnosis of the GEFSv12 Reforecasts. J. Climate, 36(12), 4255-4274. doi: 10.1175/JCLI-D-22-0772.1. Abstract Three levels of process-oriented model diagnostics are applied to evaluate the Global Ensemble Forecast System version 12 (GEFSv12) reforecasts. The level-1 diagnostics are focused on model systematic errors, which reveals that precipitation onset over tropical oceans occurs too early in terms of column water vapor accumulation. Since precipitation acts to deplete water vapor, this results in prevailing negative biases of precipitable water in the tropics. It is also associated with overtransport of moisture into the mid- and upper troposphere, leading to a dry bias in the lower troposphere and a wet bias in the mid–upper troposphere. The level-2 diagnostics evaluate some major predictability sources on the extended-range time scale: the Madden–Julian oscillation (MJO) and North American weather regimes. It is found that the GEFSv12 can skillfully forecast the MJO up to 16 days ahead in terms of the Real-time Multivariate MJO indices (bivariate correlation ≥ 0.6) and can reasonably represent the MJO propagation across the Maritime Continent. The weakened and less coherent MJO signals with increasing forecast lead times may be attributed to humidity biases over the Indo-Pacific warm pool region. It is also found that the weather regimes can be skillfully predicted up to 12 days ahead with persistence comparable to the observation. In the level-3 diagnostics, we examined some high-impact weather systems. The GEFSv12 shows reduced mean biases in tropical cyclone genesis distribution and improved performance in capturing tropical cyclone interannual variability, and midlatitude blocking climatology in the GEFSv12 also shows a better agreement with the observations than in the GEFSv10. Significance Statement The latest U.S. operational weather prediction model—Global Ensemble Forecast System version 12—is evaluated using a suite of physics-based diagnostic metrics from a climatic perspective. The foci of our study consist of three levels: 1) systematic biases in physical processes, 2) tropical and extratropical extended-range predictability sources, and 3) high-impact weather systems like hurricanes and blockings. Such process-oriented diagnostics help us link the model performance to the deficiencies of physics parameterization and thus provide useful information on future model improvement.
Yost, Christopher R.; Minnis, Patrick; Sun-Mack, Sunny; Smith, William L.; Trepte, Qing Z.Yost, C. R., P. Minnis, S. Sun-Mack, W. L. Smith, Q. Z. Trepte, 2023: VIIRS Edition 1 Cloud Properties for CERES, Part 2: Evaluation with CALIPSO. Remote Sensing, 15(5), 1349. doi: 10.3390/rs15051349. The decades-long Clouds and Earth’s Radiant Energy System (CERES) Project includes both cloud and radiation measurements from instruments on the Aqua, Terra, and Suomi National Polar-orbiting Partnership (SNPP) satellites. To build a reliable long-term climate data record, it is important to determine the accuracies of the parameters retrieved from the sensors on each satellite. Cloud amount, phase, and top height derived from radiances taken by the Visible Infrared Imaging Radiometer Suite (VIIRS) on the SNPP are evaluated relative to the same quantities determined from measurements by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) spacecraft. The accuracies of the VIIRS cloud fractions are found to be as good as or better than those for the CERES amounts determined from Aqua MODerate-resolution Imaging Spectroradiometer (MODIS) data and for cloud fractions estimated by two other operational algorithms. Sensitivities of cloud fraction bias to CALIOP resolution, matching time window, and viewing zenith angle are examined. VIIRS cloud phase biases are slightly greater than their CERES MODIS counterparts. A majority of cloud phase errors are due to multilayer clouds during the daytime and supercooled liquid water clouds at night. CERES VIIRS cloud-top height biases are similar to those from CERES MODIS, except for ice clouds, which are smaller than those from CERES MODIS. CERES VIIRS cloud phase and top height uncertainties overall are very similar to or better than several operational algorithms, but fail to match the accuracies of experimental machine learning techniques. The greatest errors occur for multilayered clouds and clouds with phase misclassification. Cloud top heights can be improved by relaxing tropopause constraints, improving lapse-rate to model temperature profiles, and accounting for multilayer clouds. Other suggestions for improving the retrievals are also discussed. validation; cloud; CALIPSO; cloud height; cloud optical depth; cloud phase; cloud remote sensing; Clouds and the Earth’s Radiant Energy System (CERES); Suomi National Polar-orbiting Partnership (SNPP); Visible Infrared Imaging Radiometer Suite (VIIRS)
Yousufzai, Usama Ayub; Iqbal, Dr Javed; Afridi, FaisalYousufzai, U. A., D. J. Iqbal, F. Afridi, 2023: Analysis and Evaluation of Infrared Radiations from Top of the Atmosphere. doi: 10.2139/ssrn.4597712. The purpose of this study is to forecast infrared radiations coming from top of the atmosphere and approaches for the upper atmospheric region over 6 cities of Pakistan collected over 10 years from the Synoptic TOA and surface fluxes and clouds (SYN) Ed4A, which is the data product of Clouds and the Earth’s Radiant Energy System (CERES) used for collection of daily ten-year local weather data. This study is an attempt to investigate quantification of infrared radiations using exploratory data analysis. To predict average daily infrared variation, Artificial neural network has been used for Karachi, Thatta, Mirpurkhas, Gilgit, Kalam and Astore, cities in Pakistan. The network was trained, validated and tested for seven years with infrared flux recorded from 2011-2018. The average daily infrared flux was predicted and with the help of training and validation parameters of the hidden layer. A study of this nature will allow us to explore the shifts in the Earth's climate over time, which are influenced by several factors. For the validation of the statistical errors, Mean Squared Error (MSE), Mean Absolute Percentage Error (MAPE), correlation coefficient (R), Root Mean Square Error (RMSE), and Mean Bias Error (MBE) are determined. The statistical errors show that neural network model provide good prediction of infrared radiations for Thatta city and average predictions are made for Mirpurkhas city and Astore, Gilgit and Kalam respectively. Best fitting for correlation can be seen for Astore while Thatta, Karachi, Kalam, Gilgit and Mispurkhas come afterward. ANN Modeling; Infrared Radiations; IR Evaluation; Top of the Atmosphere; Upper Atmosphere
Yu, Laibo; Liu, Guoxiang; Zhang, RuiYu, L., G. Liu, R. Zhang, 2023: Differences Evaluation among Three Global Remote Sensing SDL Products. Remote Sensing, 15(17), 4244. doi: 10.3390/rs15174244. At present, a variety of global remote sensing surface downwelling longwave radiation (SDL) products are used for atmospheric science research; however, there are few studies on the quantitative evaluation of differences among different SDL products. In order to evaluate the differences among different SDL products quantitatively, we have selected three commonly used SDL products—Clouds and the Earth’s Radiant Energy System-Synoptic Radiative Fluxes and Clouds (CERES-SYN), the European Centre for Medium Range Weather Forecasts-Surface Radiation Budget (ECMWF-SRB) and the Global Energy and Water Exchanges Project-Surface Radiation Budget (GEWEX-SRB)—to comprehensively study in this paper. The results show that there are significant differences among the three SDL products in some areas, such as in the Arctic, the Antarctic, the Sahara, the Tibet Plateau, and Greenland. The maximum absolute root mean square error (RMSEab) in these areas is greater than 20 Wm−2, the maximum relative root mean square error (RMSEre) is greater than 20%, the maximum and minimum absolute mean bias error (MBEab) are about 20 Wm−2 and −20 Wm−2, respectively, and the maximum and minimum relative mean bias error (MBEre) are about 10% and −10%, respectively. Among the three SDL products, the difference between the ECMWF-SRB and GEWEX-SRB is the most significant. In addition, this paper also analyzed the differences among different SDL products based on three aspects. Firstly, the differences among the three SDL products show that there is significant seasonality, and the differences among different months may vary greatly. However, the differences are not sensitive to years. Secondly, there are some differences in cloud-forcing radiative fluxes (CFRFs) of different SDL products, which is also an important factor affecting the difference between different SDL products. Finally, in the process of converting high temporal resolution SDL products into monthly SDL products, data processing also affects the difference between different SDL products. CERES-SYN; GEWEX-SRB; ECMWF-SRB; surface downwelling longwave radiation
Zeng, Qi; Cheng, Jie; Guo, MengfeiZeng, Q., J. Cheng, M. Guo, 2023: A Comprehensive Evaluation of Three Global Surface Longwave Radiation Products. Remote Sensing, 15(12), 2955. doi: 10.3390/rs15122955. Surface longwave radiation is sensitive to climate change on Earth. This study first comprehensively evaluates the accuracies of surface longwave upward radiation (SLUR) and surface longwave downward radiation (SLDR) among the mainstream surface longwave (LW) radiation products (GLASS, CERES SYN and ERA5); then, the global annual mean values of surface LW radiation as well as its temporal variations from 2003 to 2020 are quantified. The ERA5 SLUR and SLDR show the best accuracies by direct validation, with biases/Stds/RMSEs of −1.05/18.34/18.37 W/m2 and −9.41/24.15/25.92 W/m2, respectively. The GLASS SLUR has the best accuracy under clear-sky conditions with a bias/Std/RMSE of −6.73/14.21/15.72 W/m2. The accuracy of the GLASS SLDR is comparable to CERES SYN. The merit of the GLASS LW radiation is that it can provide rich spatial details due to its high spatial resolution. The global annual mean SLUR is 399.77/398.92/398.19 W/m2, and that of the SLDR is 342.64/347.98/340.47 W/m2 for GLASS, CERES SYN and ERA5, respectively. The interannual variation trends for the three products produce substantially growing long-term trends for the global mean SLUR and SDLR over the globe and land, while there are almost no trends over the ocean. The long-term trends of the seasonal mean SLUR and SDLR in the Northern and Southern Hemispheres are asymmetrical. Our comprehensive evaluation and trend analysis of the mainstream surface LW radiation products can aid in understanding the global energy balance and climate change. ERA5; surface radiation budget; GLASS; surface longwave downward radiation (SLDR); CERES SYN; surface longwave upward radiation (SLUR)
Zhan, Chuan; Liang, ShunlinZhan, C., S. Liang, 2023: Generation of global 1-km daily top-of-atmosphere outgoing longwave radiation product from 2000 to 2021 using machine learning. International Journal of Digital Earth, 16(1), 2002-2012. doi: 10.1080/17538947.2023.2220611. Top-of-atmosphere (TOA) outgoing longwave radiation (OLR), a key component of the Earth’s energy budget, serves as a diagnostic of the Earth’s climate system response to incoming solar radiation. However, existing products are typically estimated using broadband sensors with coarse spatial resolutions. This paper presents a machine learning method to estimate TOA OLR by directly linking Moderate Resolution Imaging Spectroradiometer (MODIS) TOA radiances with TOA OLR determined by Clouds and the Earth’s Radiant Energy System (CERES) and other information, such as the viewing geometry, land surface temperature and cloud top temperature determined by Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). Models are built separately under clear- and cloudy-sky conditions using a gradient boosting regression tree. Independent test results show that the root mean square errors (RMSEs) of the clear-sky and cloudy-sky models for estimating instantaneous values are 4.1 and 7.8 W/m2, respectively. Real-time conversion ratios derived from CERES daily and hourly OLR data are used to convert the instantaneous MODIS OLR to daily results. Inter-comparisons of the daily results show that the RMSE of the estimated MODIS OLR is 8.9 W/m2 in East Asia. The developed high resolution dataset will be beneficial in analyzing the regional energy budget. CERES; machine learning; MODIS; Earth’s energy budget; TOA outgoing longwave radiation
Zhan, Chuan; Yang, Jing; Li, Yan; Chen, Yong; Miao, Zuohua; Zeng, Xiangyang; Li, JunZhan, C., J. Yang, Y. Li, Y. Chen, Z. Miao, X. Zeng, J. Li, 2023: Evaluation of Five Global Top-of-Atmosphere Outgoing Longwave Radiation Products. Remote Sensing, 15(15), 3722. doi: 10.3390/rs15153722. Five global monthly top-of-atmosphere (TOA) outgoing longwave radiation (OLR) products are evaluated in this study, including the products derived from the High-Resolution Infrared Radiation Sounder (HIRS), Clouds and the Earth’s Radiant Energy System (CERES), Advanced Very High Resolution Radiometer (AVHRR), the CM SAF cLoud, Albedo and surface RAdiation dataset from AVHRR data (CLARA), and the Global Energy and Water Cycle EXchanges (GEWEX) project. Results show that overall there is good consistency among these five products. Larger differences are found between GEWEX and CERES (HIRS) after (before) 2000 (RMSE ~ 5 W/m2), particularly in the tropical regions. In terms of global mean values, GEWEX shows large differences with the other products from the year 1992 to 2002, and CLARA shows large differences from the year 1979 to 1981, which are more obvious in the global ocean values. Large discrepancies among these products exist at low latitudinal bands, particularly before the year 2000. Australia and Asia (mid–low latitude part) are two typical regions in which larger differences are found. CERES; AVHRR; outgoing longwave radiation; evaluation; HIRS; CLARA; GEWEX
Zhang, Haotian; Zhao, Chuanfeng; Xia, Yan; Yang, YikunZhang, H., C. Zhao, Y. Xia, Y. Yang, 2023: North Atlantic Oscillation–Associated Variation in Cloud Phase and Cloud Radiative Forcing over the Greenland Ice Sheet. J. Climate, 36(10), 3203-3215. doi: 10.1175/JCLI-D-22-0718.1. Abstract The Greenland ice sheet (GrIS) has been losing mass at an accelerating rate in recent decades due to warming, and understanding the underlying mechanisms, such as the impacts of clouds, is essential. Using spaceborne data, this study investigates the spatial distribution of ice clouds and liquid-bearing clouds (LBCs) over the GrIS and their surface radiative forcing effects during summer daytime from 2006 to 2017, along with their characteristics during the North Atlantic Oscillation (NAO) events. Due to the perennial high-albedo surface, both ice and LBCs have a less important shortwave radiative cooling effect than in other environments. Based on the spatial variation pattern of clouds with the NAO index, the GrIS can be divided into three regions: the western, central, and eastern GrIS. During the positive NAO, the westerly wind strengthens in the western region, which causes the fraction of both ice clouds and LBCs to increase, and the cloud radiative effect at the surface increases by 2.07 W m−2; the temperature decreases in the central region, the fraction of ice clouds increases, the fraction of LBCs decreases, and the net radiative forcing is −2.05 W m−2; and sinking airflow is generated in the eastern region, both ice cloud and LBCs decrease, and the net cloud radiative effect at the surface is −1.34 W m−2. The spatial and temporal variations in clouds in different phases over the GrIS are closely related to the NAO, and the response of clouds to changes in the atmospheric circulation field during the NAO varies in different regions of the GrIS. Significance Statement This study investigates the associations between the North Atlantic Oscillation and the spatiotemporal variations in clouds, including both cloud fraction and cloud phases, and further examines the impacts of these changes on the surface radiation balance. The findings can help us improve our understanding of cloud variability and the corresponding influence on surface radiation over the GrIS, which are essential for better prediction of ice coverage over this region and for more efficient protection of ecosystems located there.
Zhang, Hua; Wang, Haibo; Liu, Yangang; Jing, Xianwen; Liu, YiZhang, H., H. Wang, Y. Liu, X. Jing, Y. Liu, 2023: Influences of Cloud Vertical Overlapping on the Calculated Cloud Albedo and Their Validation with Satellite Observations. J. Atmos. Sci., 81(1), 65-76. doi: 10.1175/JAS-D-22-0219.1. Abstract Cloud albedo is expected to influence cloud radiative forcing in addition to cloud fraction, and inadequate description of the cloud overlapping effects on the cloud fraction may influence the simulated cloud fraction, and thus the relative cloud radiative forcing (RCRF) and cloud albedo. In this study, we first present a new formula by extending that presented previously to consider multilayer clouds directly in the relationship between cloud albedo, cloud fraction, and RCRF, and then quantitatively evaluate the effects of different cloud vertical overlapping structures, represented by the decorrelation length scales (Lcf), on the simulated cloud albedos. We use the BCC_AGCM2.0_CUACE/Aero model with simultaneous validation by observations from the Clouds and the Earth’s Radiation Energy System (CERES) satellite. When Lcf < 4 km (i.e., the cloud overlap is closer to the random overlap), the simulated cloud albedos are generally in good agreement with the satellite-based albedos for December–February and June–August; when Lcf ≥ 4 km (i.e., the cloud vertical overlap is closer to the maximum overlap), the difference between simulated and observed cloud albedos became larger, due mainly to significant differences in cloud fractions and RCRF. Further quantitative analysis shows that the relative Euclidean distance, which represents the degree of overall model–observation disagreement, increases with the Lcf for all three variables (cloud albedo, cloud fraction, and RCRF), indicating the importance of cloud vertical overlapping in determining the accuracy of the calculated cloud albedo for multilayer clouds. Significance Statement The purpose of this study is presenting a new formula to consider multilayer clouds directly in the relationship between cloud albedo, cloud fraction, and relative cloud radiative forcing (RCRF). This is important because the effects of different cloud vertical overlapping structures, represented by the decorrelation length scales (Lcf), can affect the simulated cloud albedos. Our results provide a guide on the importance of cloud vertical overlapping in determining the accuracy of the calculated cloud albedo for multilayer clouds.
Zhang, Jiahui; You, Wei; Yu, Biao; Fan, DongmingZhang, J., W. You, B. Yu, D. Fan, 2023: GRACE-FO accelerometer performance analysis and calibration. GPS Solutions, 27(4), 158. doi: 10.1007/s10291-023-01487-5. As a crucial payload on dedicated gravity satellites, the accelerometer (ACC) measures the non-gravitational force acting on the satellite. The unknown scale and bias contaminate the raw ACC data, preventing the direct use in precise orbit determination (POD) and gravity recovery, and thus ACC data need to be calibrated. We analyze the performance of GRACE-FO ACC and calibrate the ACC data from 2018 to 2021 based on a step-by-step calibration method. First, we give an overview of temperature records and ACC operational modes, which reflect the operational status of the ACC. The calibration method consists of four steps: pre-calibration, two POD processes with different parameterizations, and bias fitting. Low-degree/order (10 × 10) spherical harmonic coefficients (SHCs) are estimated with scale, bias, and other dynamic parameters in POD. As an assessment, we compare the calibrated ACC data and the modeled non-gravitational force products. The average differences between them are less than 5 nm/s2 in the SRF-X direction and 6 nm/s2 in other directions. The obtained orbits based on ACC data and GPS observations are compared with precise science orbits. Furthermore, six tests show that introducing low-order/degree SHCs could effectively improve the consistency of the calibrated ACC data with non-gravitational force models and enhance orbit determination. Otherwise, empirical accelerations should be estimated with loose constraints to ensure POD results. Accelerometer calibration; GRACE-FO; Non-gravitational force; Precise orbit determination; Spaceborne GNSS
Zhang, Jianhao; Feingold, GrahamZhang, J., G. Feingold, 2023: Distinct regional meteorological influences on low-cloud albedo susceptibility over global marine stratocumulus regions. Atmospheric Chemistry and Physics, 23(2), 1073-1090. doi: 10.5194/acp-23-1073-2023. Marine stratocumuli cool the Earth effectively due to their high reflectance of incoming solar radiation and persistent occurrence. The susceptibility of cloud albedo to droplet number concentration perturbations depends strongly on large-scale meteorological conditions. Studies focused on the meteorological dependence of cloud adjustments often overlook the covariability among meteorological factors and their geographical and temporal variability. We use 8 years of satellite observations sorted by day and geographical location to show the global distribution of marine low-cloud albedo susceptibility. We find an overall cloud brightening potential for most marine warm clouds, which is more pronounced over subtropical coastal regions. A weak cloud darkening potential in the annual mean is evident over the remote SE Pacific and SE Atlantic. We show that large-scale meteorological fields from the ERA5 reanalysis data, including lower-tropospheric stability, free-tropospheric relative humidity, sea surface temperature, and boundary layer depth, have distinct covariabilities over each of the eastern subtropical ocean basins where marine stratocumuli prevail. This leads to a markedly different annual cycle in albedo susceptibility over each basin. Moreover, we find that basin-specific regional relationships between key meteorological factors and albedo susceptibilities are absent in a global analysis. Our results stress the importance of considering the geographical distinctiveness of temporal meteorological covariability when scaling up the local-to-global response of cloud albedo to aerosol perturbations.
Zhang, Pengfei; Chen, Gang; Ting, Mingfang; Ruby Leung, L.; Guan, Bin; Li, LaifangZhang, P., G. Chen, M. Ting, L. Ruby Leung, B. Guan, L. Li, 2023: More frequent atmospheric rivers slow the seasonal recovery of Arctic sea ice. Nature Climate Change, 13(3), 266-273. doi: 10.1038/s41558-023-01599-3. In recent decades, Arctic sea-ice coverage underwent a drastic decline in winter, when sea ice is expected to recover following the melting season. It is unclear to what extent atmospheric processes such as atmospheric rivers (ARs), intense corridors of moisture transport, contribute to this reduced recovery of sea ice. Here, using observations and climate model simulations, we find a robust frequency increase in ARs in early winter over the Barents–Kara Seas and the central Arctic for 1979–2021. The moisture carried by more frequent ARs has intensified surface downward longwave radiation and rainfall, caused stronger melting of thin, fragile ice cover and slowed the seasonal recovery of sea ice, accounting for 34% of the sea-ice cover decline in the Barents–Kara Seas and central Arctic. A series of model ensemble experiments suggests that, in addition to a uniform AR increase in response to anthropogenic warming, tropical Pacific variability also contributes to the observed Arctic AR changes. Climate change; Cryospheric science
Zhang, Yuan; Dewitte, Steven; Bi, ShengshanZhang, Y., S. Dewitte, S. Bi, 2023: A Model for Estimating the Earth’s Outgoing Radiative Flux from A Moon-Based Radiometer. Remote Sensing, 15(15), 3773. doi: 10.3390/rs15153773. A Moon-based radiometer can provide continuous measurements for the Earth’s full-disk broadband irradiance, which is useful for studying the Earth’s Radiation Budget (ERB) at the height of the Top of the Atmosphere (TOA). The ERB describes how the Earth obtains solar energy and emits energy to space through the outgoing broadband Short-Wave (SW) and emitted thermal Long-Wave (LW) radiation. In this work, a model for estimating the Earth’s outgoing radiative flux from the measurements of a Moon-based radiometer is established. Using the model, the full-disk LW and SW outgoing radiative flux are gained by converting the unfiltered entrance pupil irradiances (EPIs) with the help of the anisotropic characteristics of the radiances. Based on the radiative transfer equation, the unfiltered EPI time series is used to validate the established model. By comparing the simulations for a Moon-based radiometer with the satellite-based data from the National Institute of Standards and Technology Advanced Radiometer (NISTAR) and the Clouds and the Earth’s Radiant Energy System (CERES) datasets, the simulations show that the daytime SW fluxes from the Moon-based measurements are expected to vary between 194 and 205 Wm−2; these simulations agree well with the CERES data. The simulations are about 5 to 20 Wm−2 smaller than the NISTAR data. For the simulated Moon-based LW fluxes, the range is 251~287 Wm−2. The Moon-based and NISTAR fluxes are consistently 5~15 Wm−2 greater than CERES LW fluxes, and both of them also show larger diurnal variations compared with the CERES fluxes. The correlation coefficients of SW fluxes for Moon-based data and NISTAR data are 0.97, 0.63, and 0.53 for the months of July, August, and September, respectively. Compared with the SW flux, the correlation of LW fluxes is more stable for the same period and the correlation coefficients are 0.87, 0.69, and 0.61 for July to September 2017. CERES; radiation budget; radiometer; Earth observation; Moon-based; NISTAR
Zhang, Yuan; Dewitte, Steven; Bi, ShengshanZhang, Y., S. Dewitte, S. Bi, 2023: The Uncertainty Analysis of the Entrance Pupil Irradiance for a Moon-Based Earth Radiation Observation Instrument. Remote Sensing, 15(17), 4132. doi: 10.3390/rs15174132. Moon-Based Earth Radiation Observation (MERO) is expected to improve and enrich the current Earth radiation budget (ERB). For the design of MERO’s instrument and the interpretation of Moon-based data, evaluating the uncertainty of the instrument’s Entrance Pupil Irradiance (EPI) is an important part. In this work, by analyzing the effect of the Angular Distribution Models (ADMs), Earth’s Top of Atmosphere (TOA) flux, and the Earth–Moon distance on the EPI, the uncertainty of EPI is finally studied with the help of the theory of errors. Results show that the ADMs have a stronger influence on the Short-Wave (SW) EPI than those from the Long-Wave (LW). For the change of TOA flux, the SW EPI could keep the attribute of varying hourly time scales, but the LW EPI will lose its hourly-scale variability. The variation in EPI caused by the hourly change of the Moon–Earth distance does not exceed 0.13 mW∙m−2 (1σ). The maximum hourly combined uncertainty reveals that the SW and LW combined uncertainties are about 5.18 and 1.08 mW∙m−2 (1σ), respectively. The linear trend extraction of the EPI demonstrates that the Moon-based data can effectively capture the overall linear change trend of Earth’s SW and LW outgoing radiation, and the uncertainty does not change the linear trend of data. The variation of SW and LW EPIs in the long term are 0.16 mW∙m−2 (SW) and 0.23 mW∙m−2 (LW) per decade, respectively. Based on the constraint of the uncertainty, a simplified dynamic response model is built for the cavity radiometer, a kind of MERO instrument, and the results illuminate that the Cassegrain optical system and electrical substitution principle can realize the detection of Earth’s outing radiation with the sensitivity design goal 1 mW∙m−2. radiation budget; uncertainty analysis; irradiance; moon-based earth observation
Zhang, Yuanchong; Rossow, William B.Zhang, Y., W. B. Rossow, 2023: Global Radiative Flux Profile Data Set: Revised and Extended. Journal of Geophysical Research: Atmospheres, 128(5), e2022JD037340. doi: 10.1029/2022JD037340. The third generation of the radiative flux profile data product, called ISCCP-FH, is described. The revisions over the previous generation (called ISCCP-FD) include improvements in the radiative model representation of gaseous and aerosol effects, as well as a refined statistical model of cloud vertical layer variations with cloud types, and increased spatial resolution. The new product benefits from the changes in the new H-version of the ISCCP cloud products (called ISCCP-H): higher spatial resolution, revised radiance calibration and treatment of ice clouds, treatment of aerosol effects, and revision of all the ancillary atmosphere and surface property products. The ISCCP-FH product is evaluated against more direct measurements from the Clouds and the Earth’s Radiant Energy System and the Baseline Surface Radiation Network products, showing some small, overall reductions in average flux uncertainties; but the main results are similar to ISCCP-FD: the ISCCP-FH uncertainties remain ≲10 Wm−2 at the top-of-atmosphere (TOA) and ≲15 Wm−2 at surface for monthly, regional averages. The long-term variations of TOA, surface and in-atmosphere net fluxes are documented and the possible transient cloud feedback implications of a long-term change of clouds are investigated. The cloud and flux variations from 1998 to 2012 suggest a positive cloud-radiative feedback on the oceanic circulation and a negative feedback on the atmospheric circulation. This example demonstrates that the ISCCP-FH product can provide useful diagnostic information about weather-to-interannual scale variations of radiation induced by changes in cloudiness as well as atmospheric and surface properties. cloud feedback; ISCCP-FH; cloud trends; ISCCP-H; radiative flux profile; radiative flux trends
Zhao, Pengfei; Bai, Yang; Zhang, Zhaoyang; Wang, Lijun; Guo, Jianzhong; Wang, JiayaoZhao, P., Y. Bai, Z. Zhang, L. Wang, J. Guo, J. Wang, 2023: Differences in diffuse photosynthetically active radiation effects on cropland light use efficiency calculated via contemporary remote sensing and crop production models. Ecological Informatics, 73, 101948. doi: 10.1016/j.ecoinf.2022.101948. Diffuse photosynthetically active radiation (PARdiff) is instrumental to the light use efficiency (LUE) of vegetation. Accurately assessing the impact of PARdiff on crop LUE can better our understanding of the carbon cycle in cropland ecosystems. LUE estimates from six remote sensing models (including four big-leaf models and two two-leaf models) and two crop production models were compared with measured FLUXNET LUE data from cropland sites under different PARdiff fraction (FDIFFPAR) intervals. Compared with the FLUXNET observations, the Eddy Covariance-Light Use Efficiency (EC-LUEa) model exhibited the best LUE estimation (R2 = 0.250, RMSE = 0.868 gC·MJ−1, and Bias = −0.005 gC·MJ−1) owing to the use of more accurate calculation scheme of environmental stress factors. LUEs calculated from FLUXNET observational data were positively correlated with FDIFFPAR, but only LUEs simulated by the Moderate Resolution Imaging Spectroradiometer Photosynthesis (MOD17) and Two-Leaf Light Use Efficiency (TL-LUE) models increased with increasing FDIFFPAR. This is attributed to the fact that the MOD17 model divides the crop growth types into cereal and broadleaf, while the TL-LUE model considers the change of light interception with increased FDIFFPAR. Furthermore, the maximum LUE (LUEmax) increased with FDIFFPAR at FLUXNET observational sites, but the eight models could not capture the effects of PARdiff on the crop LUEmax. Among the eight models, the LUEmax–FDIFFPAR relationship simulated by the two-leaf models fluctuated because the crops were divided into sunlit and shaded leaves, while the big-leaf and crop production models used a constant LUEmax and showed a constant LUEmax–FDIFFPAR relationship. Additionally, big-leaf models performed better than two-leaf models for gross primary production (GPP) simulation in the cropland ecosystem, which is related to the planting density and vegetation structure. These results demonstrate the importance of considering the impact of FDIFFPAR on LUEmax in LUE modeling. Cropland ecosystem; Diffuse radiation fraction; Gross primary production; Light use efficiency; Maximum light use efficiency
Zhao, Xu; Yue, Xu; Tian, Chenguang; Zhou, Hao; Wang, Bin; Chen, Yuwen; Zhao, Yuan; Fu, Weijie; Hu, YihanZhao, X., X. Yue, C. Tian, H. Zhou, B. Wang, Y. Chen, Y. Zhao, W. Fu, Y. Hu, 2023: Multimodel ensemble projection of photovoltaic power potential in China by the 2060s. Atmospheric and Oceanic Science Letters, 100403. doi: 10.1016/j.aosl.2023.100403. China's demand for solar energy has been growing rapidly to meet energy transformation targets. However, the potential of solar energy is affected by weather conditions and is expected to change under climate warming. Here, the authors project the photovoltaic (PV) power potential over China under low and high emission scenarios by the 2060s, taking advantage of meteorological variables from 24 CMIP6 models and 4 PV models with varied formats. The ensemble mean of these models yields an average PV power of 277.2 KWh m−2 yr−1 during 2004–2014, with a decreasing tendency from the west to east. By 2054–2064, the national average PV power potential is projected to increase by 2.29% under a low emission scenario but decrease by 0.43% under a high emission scenario. The emission control in the former scenario significantly enhances surface solar radiation and promotes PV power in the east. On the contrary, strong warming causes inhibitions to PV power generation under the high emission scenario. Extreme warming events on average decrease the PV power potential by 0.28% under the low emission scenario and 0.44% under the high emission scenario, doubling and tripling the present-day loss, respectively. The projections reveal large benefits of controlling emissions for the future solar energy in China due to both the clean atmosphere and the moderate warming. 摘要 为了实现能源转型的目标, 中国对太阳能的需求一直在极速增长. 然而, 太阳能发电潜力受到天气条件的影响并预期在气候变暖背景下发生改变. 本文中, 作者利用第六次国际耦合模式比较计划 (CMIP6) 24个气候模式的气象变量以及4个不同形式的光伏模型, 预估了在2060年代低排放或高排放情况下中国的光伏发电潜力. 多模式集合平均光伏功率在2004–2014年为277.2 KWh m−2 yr−1, 并呈现出从西到东的下降趋势. 到2054–2064年, 在低排放情景下, 全国平均光伏发电潜力将增加2.29%, 而在高排放情景下则减少0.43%. 低排放情景的排放控制大大增强了地表太阳辐射, 促进了东部的光伏发电. 相反, 在高排放情景下, 强烈的变暖对光伏发电产生了抑制作用. 极端暖事件使光伏发电潜力在低排放情景下降低0.28%, 而高排放情景下降低0.44%, 分别相当于当代损失量的两倍和三倍. 预估表明排放控制带来的清洁空气和适度变暖对中国未来的太阳能利用是有益的. CMIP6; Climate change; Ensemble projection; Photovoltaic power; Warming extremes; 光伏发电; 极端暖事件; 气候变化; 第六次国际耦合模式比较计划; 集合预估
Zhi Xiang, Jonas Koh; Bairoliya, Sakcham; Cho, Zin Thida; Cao, BinZhi Xiang, J. K., S. Bairoliya, Z. T. Cho, B. Cao, 2023: Plastic-microbe interaction in the marine environment: Research methods and opportunities. Environment International, 171, 107716. doi: 10.1016/j.envint.2022.107716. Approximately 9 million metric tons of plastics enters the ocean annually, and once in the marine environment, plastic surfaces can be quickly colonised by marine microorganisms, forming a biofilm. Studies on plastic debris-biofilm associations, known as plastisphere, have increased exponentially within the last few years. In this review, we first briefly summarise methods and techniques used in exploring plastic-microbe interactions. Then we highlight research gaps and provide future research opportunities for marine plastisphere studies, especially, on plastic characterisation and standardised biodegradation tests, the fate of “environmentally friendly” plastics, and plastisphere of coastal habitats. Located in the tropics, Southeast Asian (SEA) countries are significant contributors to marine plastic debris. However, plastisphere studies in this region are lacking and therefore, we discuss how the unique environmental conditions in the SEA seas may affect plastic-microbe interaction and why there is an imperative need to conduct plastisphere studies in SEA marine environments. Finally, we also highlight the lack of understanding of the pathogenicity and ecotoxicological effects of plastisphere on marine ecosystems. Biofilm; Marine debris; Plastic-microbe interaction; Plastisphere
Zhi-Lun, Z. H. A. N. G.; Feng-Ming, H. U. I.; Vihma, Timo; Granskog, Mats A.; Cheng, Bin; Zhuo-Qi, C. H. E. N.; Cheng, XiaoZhi-Lun, Z. H. A. N. G., H. U. I. Feng-Ming, T. Vihma, M. A. Granskog, B. Cheng, C. H. E. N. Zhuo-Qi, X. Cheng, 2023: On the turbulent heat fluxes: A comparison among satellite-based estimates, atmospheric reanalyses, and in-situ observations during the winter climate over Arctic sea ice. Advances in Climate Change Research. doi: 10.1016/j.accre.2023.04.004. The surface energy budget is crucial for Arctic sea ice mass balance calculation and climate systems, among which turbulent heat fluxes significantly affect the air–sea exchanges of heat and moisture in the atmospheric boundary layer. Satellite observations (e.g. CERES and APP-X) and atmospheric reanalyses (e.g., ERA5) are often used to represent components of the energy budget at regional and pan-Arctic scales. However, the uncertainties of the satellite-based turbulent heat fluxes are largely unknown, and cross-comparisons with reanalysis data and in-situ observations are limited. In this study, satellite-based turbulent heat fluxes were assessed against in-situ observations from the N-ICE2015 drifting ice station (north of Svalbard, January–June 2015) and ERA5 reanalysis. The turbulent heat fluxes were calculated by two approaches using the satellite-based ice surface temperature and radiative fluxes, surface atmospheric parameters from ERA5, and snow/sea ice thickness from the pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS). We found that the bulk-aerodynamic formula based results could better capture the variations of turbulent heat fluxes, while the maximum entropy production based estimates are comparable with ERA5 in terms of root-mean-square error (RMSE). CERES-based estimates outperform the APP-X-based ones but ERA5 performs the best in all seasons (RMSE of 18 and 7 W m−2 for sensible and latent heat flux, respectively). The air–ice temperature/humidity differences and the surface radiation budget were found the primary driving factors in the bulk-formula method and maximum entropy production (MEP) method, respectively. Furthermore, errors in the surface and near-surface temperature and humidity explain almost 50% of the uncertainties in the estimates based on the bulk-formula, whereas errors in the net radiative fluxes explain more than 50% of the uncertainties in the MEP-based results. Arctic sea ice; Bulk-aerodynamic formula; Maximum entropy production; Reanalysis; Satellite observation; Surface energy budget; Turbulent heat flux
Zhong, Ziqian; He, Bin; Chen, Hans W.; Chen, Deliang; Zhou, Tianjun; Dong, Wenjie; Xiao, Cunde; Xie, Shang-ping; Song, Xiangzhou; Guo, Lanlan; Ding, Ruiqiang; Zhang, Lixia; Huang, Ling; Yuan, Wenping; Hao, Xingming; Ji, Duoying; Zhao, XiangZhong, Z., B. He, H. W. Chen, D. Chen, T. Zhou, W. Dong, C. Xiao, S. Xie, X. Song, L. Guo, R. Ding, L. Zhang, L. Huang, W. Yuan, X. Hao, D. Ji, X. Zhao, 2023: Reversed asymmetric warming of sub-diurnal temperature over land during recent decades. Nature Communications, 14(1), 7189. doi: 10.1038/s41467-023-43007-6. In the latter half of the twentieth century, a significant climate phenomenon “diurnal asymmetric warming” emerged, wherein global land surface temperatures increased more rapidly during the night than during the day. However, recent episodes of global brightening and regional droughts and heatwaves have brought notable alterations to this asymmetric warming trend. Here, we re-evaluate sub-diurnal temperature patterns, revealing a substantial increase in the warming rates of daily maximum temperatures (Tmax), while daily minimum temperatures have remained relatively stable. This shift has resulted in a reversal of the diurnal warming trend, expanding the diurnal temperature range over recent decades. The intensified Tmax warming is attributed to a widespread reduction in cloud cover, which has led to increased solar irradiance at the surface. Our findings underscore the urgent need for enhanced scrutiny of recent temperature trends and their implications for the wider earth system. Environmental impact; Climate-change mitigation
Zhou, Lu; Heuzé, Céline; Mohrmann, MartinZhou, L., C. Heuzé, M. Mohrmann, 2023: Sea Ice Production in the 2016 and 2017 Maud Rise Polynyas. Journal of Geophysical Research: Oceans, 128(2), e2022JC019148. doi: 10.1029/2022JC019148. Sea ice production within polynyas, an outcome of the atmosphere-ice-ocean interaction, is a major source of dense water and hence key to the global overturning circulation, but is poorly quantified over open-ocean polynyas. Using the two recent extensive open-ocean polynyas within the wider Maud Rise region of the Weddell Sea in 2016 and 2017, we here explore the sea ice energy budget and estimate their sea ice production based on satellite retrievals, in-situ hydrographic observations and the Japanese 55-year Reanalysis. We find that the oceanic heat flux amounts to 36.1 and 30.7 W m−2 within the 2016 and 2017 polynyas, respectively. Especially the 2017 open-ocean polynya produced nearly 200 km3 of new sea ice, which is comparable to the production in the largest Antarctic coastal polynyas. Finally, we determine that ice production is highly correlated with and sensitive to skin temperature and wind speed, which affect the turbulent fluxes. It is also strongly sensitive to uncertainties in the sea ice concentration and 1,000 hPa temperature, which all urgently need to be better monitored at high latitudes. Lastly, more process-oriented campaigns are required to further elucidate the role of open-ocean polynya on the local and global ocean circulations. energy budget; Maud Rise polynya; ocean heat flux; sea ice production
Zhou, Wenyu; Leung, L. Ruby; Siler, Nicholas; Lu, JianZhou, W., L. R. Leung, N. Siler, J. Lu, 2023: Future precipitation increase constrained by climatological pattern of cloud effect. Nature Communications, 14(1), 6363. doi: 10.1038/s41467-023-42181-x. The fractional increase in global mean precipitation ($$\triangle \bar{P}/\bar{P}$$) is a first-order measure of the hydrological cycle intensification under anthropogenic warming. However, $$\triangle \bar{P}/\bar{P}$$varies by a factor of more than three among model projections, hindering credible assessments of the associated climate impacts. The uncertainty in $$\triangle \bar{P}/\bar{P}$$stems from uncertainty in both hydrological sensitivity (global mean precipitation increase per unit warming) and climate sensitivity (global mean temperature increase per forcing). Here, by investigating hydrological and climate sensitivities in a unified surface-energy-balance perspective, we find that both sensitivities are significantly correlated with surface shortwave cloud feedback, which is further linked to the climatological pattern of cloud shortwave effect. The observed pattern of cloud effect thus constrains both sensitivities and consequently constrains $$\triangle \bar{P}/\bar{P}$$. The 5%-95% uncertainty range of $$\triangle \bar{P}/\bar{P}$$from 1979-2005 to 2080-2100 under the high-emission (moderate-emission) scenario is constrained from 6.34$$\pm$$3.53% (4.19$$\pm$$2.28%) in the raw ensemble-model projection to 7.03$$\pm$$2.59% (4.63$$\pm$$1.71%). The constraint thus suggests a higher most-likely $$\triangle \bar{P}/\bar{P}$$and reduces the uncertainty by ~25%, providing valuable information for impact assessments. Atmospheric dynamics; Projection and prediction; Hydrology
Zhou, Xiaoli; Feingold, GrahamZhou, X., G. Feingold, 2023: Impacts of Mesoscale Cloud Organization on Aerosol-Induced Cloud Water Adjustment and Cloud Brightness. Geophysical Research Letters, 50(13), e2023GL103417. doi: 10.1029/2023GL103417. The role of mesoscale cellular convection (MCC) in regulating aerosol-induced cloud brightness remains unaddressed. Using 7 years of satellite-based observations of cloud water adjustment to aerosol-induced perturbations for closed MCCs across different sizes (8, 16, 32, and 64 km) over the North Atlantic Ocean, we show that MCC cell-size plays a nontrivial role in regulating aerosol-induced cloud brightness via cloud water adjustment. In cells that are primarily non-precipitating, the adjustment in small-scale MCCs can be 10 times more negative than in large-scale MCCs, consistent with stronger evaporation via cloud top entrainment. Consequently, the response of cloud brightness is significantly stronger for large-scale MCCs. We also find notable intra-cell co-variability between cloud liquid water path (LWP) and drop concentration (Nd) within MCCs that varies with cell size. Erroneously considering such co-variability as a LWP response to Nd can lead to a significant positive bias, especially for small scale MCCs.
Zo, Il-Sung; Jee, Joon-Bum; Lee, Kyu-Tae; Lee, Kwon-Ho; Lee, Mi-Young; Kwon, Yong-SoonZo, I., J. Jee, K. Lee, K. Lee, M. Lee, Y. Kwon, 2023: Radiative Energy Budget for East Asia Based on GK-2A/AMI Observation Data. Remote Sensing, 15(6), 1558. doi: 10.3390/rs15061558. The incident and emitted radiative energy data for the top of the atmosphere (TOA) are essential in climate research. Since East Asia (11–61°N, 80–175°E) is complexly composed of land and ocean, real-time satellite data are used importantly for analyzing the detailed energy budget or climate characteristics of this region. Therefore, in this study, the radiative energy budget for East Asia, during the year 2021, was analyzed using GEO-KOMPSAT-2A/Advanced Metrological Imager (GK-2A/AMI) and the European Centre for Medium-range Weather Forecasts reanalysis (ERA5) data. The results showed that the net fluxes for the TOA and surface were −4.09 W·m−2 and −8.24 W·m−2, respectively. Thus, the net flux difference of 4.15 W·m−2 between TOA and surface implied atmospheric warming. These results, produced by GK-2A/AMI, were well-matched with the ERA5 data. However, they varied with surface characteristics; the atmosphere over ocean areas warmed because of the large amounts of longwave radiation emitted from surfaces, while the atmosphere over the plain area was relatively balanced and the atmosphere over the mountain area was cooled because large amount of longwave radiation was emitted to space. Although the GK2A/AMI radiative products used for this study have not yet been sufficiently compared with surface observation data, and the period of data used was only one year, they were highly correlated with the CERES (Clouds and the Earth’s Radiant Energy System of USA), HIMAWARI/AHI (Geostationary Satellite of Japan), and ERA5 data. Therefore, if more GK-2A/AMI data are accumulated and analyzed, it could be used for the analysis of radiant energy budget and climate research for East Asia, and it will be an opportunity to greatly increase the utilization of total meteorological products of 52 types, including radiative products. ERA5; East Asia; European center for medium-range weather forecasts reanalysis data; Geo-KOMPSAT-2A; geostationary-Korean multi-purpose satellite-2A; GK-2A/AMI; radiative energy budget
Andersen, Hendrik; Cermak, Jan; Zipfel, Lukas; Myers, Timothy A.Andersen, H., J. Cermak, L. Zipfel, T. A. Myers, 2022: Attribution of Observed Recent Decrease in Low Clouds Over the Northeastern Pacific to Cloud-Controlling Factors. Geophysical Research Letters, 49(3), e2021GL096498. doi: 10.1029/2021GL096498. Marine low clouds cool the Earth's climate, with their coverage (LCC) being controlled by their environment. Here, an observed significant decrease of LCC in the northeastern Pacific over the past two decades is linked quantitatively to changes in cloud-controlling factors. In a comparison of different statistical and machine learning methods, a decrease in the inversion strength and near-surface winds, and an increase in sea surface temperatures (SSTs) are unanimously shown to be the main causes of the LCC decrease. While the decreased inversion strength leads to more entrainment of dry free-tropospheric air, the increasing SSTs are shown to lead to an increased vertical moisture gradient that enhances evaporation when entrainment takes place. While the LCC trend is likely driven by natural variability, the trend-attribution framework developed here can be used with any method in future analyses. We find the choice of predictors is more important than the method. satellite data; machine learning; low clouds; trend analysis; cloud-controlling factors
Andrews, Timothy; Bodas-Salcedo, Alejandro; Gregory, Jonathan M.; Dong, Yue; Armour, Kyle C.; Paynter, David; Lin, Pu; Modak, Angshuman; Mauritsen, Thorsten; Cole, Jason N. S.; Medeiros, Brian; Benedict, James J.; Douville, Hervé; Roehrig, Romain; Koshiro, Tsuyoshi; Kawai, Hideaki; Ogura, Tomoo; Dufresne, Jean-Louis; Allan, Richard P.; Liu, ChunleiAndrews, T., A. Bodas-Salcedo, J. M. Gregory, Y. Dong, K. C. Armour, D. Paynter, P. Lin, A. Modak, T. Mauritsen, J. N. S. Cole, B. Medeiros, J. J. Benedict, H. Douville, R. Roehrig, T. Koshiro, H. Kawai, T. Ogura, J. Dufresne, R. P. Allan, C. Liu, 2022: On the Effect of Historical SST Patterns on Radiative Feedback. Journal of Geophysical Research: Atmospheres, 127(18), e2022JD036675. doi: 10.1029/2022JD036675. We investigate the dependence of radiative feedback on the pattern of sea-surface temperature (SST) change in 14 Atmospheric General Circulation Models (AGCMs) forced with observed variations in SST and sea-ice over the historical record from 1871 to near-present. We find that over 1871–1980, the Earth warmed with feedbacks largely consistent and strongly correlated with long-term climate sensitivity feedbacks (diagnosed from corresponding atmosphere-ocean GCM abrupt-4xCO2 simulations). Post 1980, however, the Earth warmed with unusual trends in tropical Pacific SSTs (enhanced warming in the west, cooling in the east) and cooling in the Southern Ocean that drove climate feedback to be uncorrelated with—and indicating much lower climate sensitivity than—that expected for long-term CO2 increase. We show that these conclusions are not strongly dependent on the Atmospheric Model Intercomparison Project (AMIP) II SST data set used to force the AGCMs, though the magnitude of feedback post 1980 is generally smaller in nine AGCMs forced with alternative HadISST1 SST boundary conditions. We quantify a “pattern effect” (defined as the difference between historical and long-term CO2 feedback) equal to 0.48 ± 0.47 [5%–95%] W m−2 K−1 for the time-period 1871–2010 when the AGCMs are forced with HadISST1 SSTs, or 0.70 ± 0.47 [5%–95%] W m−2 K−1 when forced with AMIP II SSTs. Assessed changes in the Earth's historical energy budget agree with the AGCM feedback estimates. Furthermore satellite observations of changes in top-of-atmosphere radiative fluxes since 1985 suggest that the pattern effect was particularly strong over recent decades but may be waning post 2014. climate sensitivity; climate models; observations; climate feedback; pattern effect; historical record
Aparna, A. R.; Girishkumar, M. S.Aparna, A. R., M. S. Girishkumar, 2022: Mixed layer heat budget in the eastern equatorial Indian Ocean during the two consecutive positive Indian Ocean dipole events in 2018 and 2019. Climate Dynamics. doi: 10.1007/s00382-021-06099-8. The Indian Ocean hosted a strong positive Indian Ocean Dipole (pIOD) event in 2019–2020, and a weak event in 2018–2019, such as the magnitude of the cold sea surface temperature anomaly (SSTA) during June-December in the former case is a factor of two higher (~ − 1.5 °C) than the latter (~ − 0.75 °C) at the western periphery of the eastern IOD zone at 5° S, 95° E. The plausible mechanisms responsible for this difference in the SSTA between these two events are examined using the mixed layer heat budget estimate using the moored buoy measurements. It is found that the enhanced cooling during June-December in 2019–2020 is determined primarily by the anomalous cooling due to the vertical processes associated with the combined effect of the anomalous thin barrier layer (BL), shallow thermocline, weak near-surface stratification, and strong wind speed induced vertical mixing, and secondarily by the enhancement in the latent heat flux (LHF) loss from the ocean. Conversely, the magnitude of cooling due to the vertical processes is much smaller in 2018–2019 due to the near-climatological states such as a thick BL, deep thermocline, and weak wind speed. During these events, the warming tendency by the horizontal advection dampens the cooling tendency associated with the vertical processes and LHF. These characteristics are distinct from the past study that suggested that the horizontal advection was responsible for the cool SSTA at the exact location during an extreme pIOD event in 2006–2007.
Atlas, R.l.; Bretherton, C.s.; Khairoutdinov, M.f.; Blossey, P.n.Atlas, R., C. Bretherton, M. Khairoutdinov, P. Blossey, 2022: Hallett-Mossop rime splintering dims cumulus clouds over the Southern Ocean: New insight from nudged global storm-resolving simulations. AGU Advances, n/a(n/a), e2021AV000454. doi: 10.1029/2021AV000454. In clouds containing both liquid and ice with temperatures between − 3°C and − 8°C, liquid droplets collide with large ice crystals, freeze, and shatter, producing a plethora of small ice splinters. This process, known as Hallett-Mossop rime splintering, and other forms of secondary ice production, can cause clouds to reflect less sunlight and to have shorter lifetimes. We show its impact on Southern Ocean shallow cumuli using a novel suite of five global storm-resolving simulations, which partition the Earth’s atmosphere into 2-4 km wide columns. We evaluate simulated clouds and radiation over the Southern Ocean with aircraft observations from the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES), and satellite observations from Clouds and the Earth’s Radiant Energy System (CERES) and Himawari. Simulations with large concentrations of ice crystals in boundary layer clouds, which agree better with SOCRATES observations, have reduced mixed-phase cumulus cloud cover and weaker shortwave cloud radiative effects that are less biased compared with CERES. Using a pair of simulations differing only in their treatment of Hallett-Mossop rime splintering, we show that including this process increases ice crystal concentrations in cumulus clouds and weakens shortwave cloud radiative effects over the Southern Ocean by 10 W m−2. We also demonstrate the key role that global storm-resolving models can play in detangling the effects of clouds on Earth’s climate across scales, making it possible to trace the impact of changes in individual cumulus cloud anvils (10 km2) on the radiative budget of the massive Southern Ocean basin (108 km2). Boundary layer; Southern Ocean; Global cloud-resolving simulations; Hallett-Mossop rime splintering; Open cell cumuli; Secondary ice production
Atmoko, Dwi; Lin, Tang-HuangAtmoko, D., T. Lin, 2022: Sea Salt Aerosol Identification Based on Multispectral Optical Properties and Its Impact on Radiative Forcing over the Ocean. Remote Sensing, 14(13), 3188. doi: 10.3390/rs14133188. The ground-based measurement of sea salt (SS) aerosol over the ocean requires the massive utilization of satellite-derived aerosol products. In this study, n-order spectral derivatives of aerosol optical depth (AOD) based on wavelength were examined to characterize SS and other aerosol types in terms of their spectral dependence related to their optical properties such as particle size distributions and complex refractive indices. Based on theoretical simulations from the second simulation of a satellite signal in the solar spectrum (6S) model, AOD spectral derivatives of SS were characterized along with other major types including mineral dust (DS), biomass burning (BB), and anthropogenic pollutants (APs). The approach (normalized derivative aerosol index, NDAI) of partitioning aerosol types with intrinsic values of particle size distribution and complex refractive index from normalized first- and second-order derivatives was applied to the datasets from a moderate resolution imaging spectroradiometer (MODIS) as well as by the ground-based aerosol robotic network (AERONET). The results after implementation from multiple sources of data indicated that the proposed approach could be highly effective for identifying and segregating abundant SS from DS, BB, and AP, across an ocean. Consequently, each aerosol’s shortwave radiative forcing and its efficiency could be further estimated in order to predict its impact on the climate. particle size; sea salt aerosol; aerosol optical depth (AOD); complex refractive index; normalized derivative aerosol index (NDAI); spectral derivatives
Bai, Jianhui; Zong, Xuemei; Lanconelli, Christian; Lupi, Angelo; Driemel, Amelie; Vitale, Vito; Li, Kaili; Song, TaoBai, J., X. Zong, C. Lanconelli, A. Lupi, A. Driemel, V. Vitale, K. Li, T. Song, 2022: Long-Term Variations of Global Solar Radiation and Its Potential Effects at Dome C (Antarctica). International Journal of Environmental Research and Public Health, 19(5), 3084. doi: 10.3390/ijerph19053084. An empirical model to predict hourly global solar irradiance under all-sky conditions as a function of absorbing and scattering factors has been applied at the Dome C station in the Antarctic, using measured solar radiation and meteorological variables. The calculated hourly global solar irradiance agrees well with measurements at the ground in 2008–2011 (the model development period) and at the top of the atmosphere (TOA). This model is applied to compute global solar irradiance at the ground and its extinction in the atmosphere caused by absorbing and scattering substances during the 2006–2016 period. A sensitivity study shows that the responses of global solar irradiance to changes in water vapor and scattering factors (expressed by water vapor pressure and S/G, respectively; S and G are diffuse and global solar irradiance, respectively) are nonlinear and negative, and that global solar irradiance is more sensitive to changes in scattering than to changes in water vapor. Applying this empirical model, the albedos at the TOA and the surface in 2006–2016 are estimated and found to agree with the satellite-based retrievals. During 2006–2016, the annual mean observed and estimated global solar exposures decreased by 0.05% and 0.09%, respectively, and the diffuse exposure increased by 0.68% per year, associated with the yearly increase of the S/G ratio by 0.57% and the water vapor pressure by 1.46%. The annual mean air temperature increased by about 1.80 °C over the ten years, and agrees with the warming trends for all of Antarctica. The annual averages were 316.49 Wm−2 for the calculated global solar radiation, 0.332 for S/G, −46.23 °C for the air temperature and 0.10 hPa for the water vapor pressure. The annual mean losses of solar exposure due to absorbing and scattering substances and the total loss were 4.02, 0.19 and 4.21 MJ m−2, respectively. The annual mean absorbing loss was much larger than the scattering loss; their contributions to the total loss were 95.49% and 4.51%, respectively, indicating that absorbing substances are dominant and play essential roles. The annual absorbing, scattering and total losses increased by 0.01%, 0.39% and 0.28% per year, respectively. The estimated and satellite-retrieved annual albedos increased at the surface. The mechanisms of air-temperature change at two pole sites, as well as a mid-latitude site, are discussed. albedo; energy balance; air temperature; climate and climate change; absorbing and scattering substances
Bai, Jianhui; Zong, Xuemei; Ma, Yaoming; Wang, Binbin; Zhao, Chuanfeng; Yang, Yikung; Guang, Jie; Cong, Zhiyuan; Li, Kaili; Song, TaoBai, J., X. Zong, Y. Ma, B. Wang, C. Zhao, Y. Yang, J. Guang, Z. Cong, K. Li, T. Song, 2022: Long-Term Variations in Global Solar Radiation and Its Interaction with Atmospheric Substances at Qomolangma. International Journal of Environmental Research and Public Health, 19(15), 8906. doi: 10.3390/ijerph19158906. An empirical model to estimate global solar radiation was developed at Qomolangma Station using observed solar radiation and meteorological parameters. The predicted hourly global solar radiation agrees well with observations at the ground in 2008–2011. This model was used to calculate global solar radiation at the ground and its loss in the atmosphere due to absorbing and scattering substances in 2007–2020. A sensitivity analysis shows that the responses of global solar radiation to changes in water vapor and scattering factors (expressed as water-vapor pressure and the attenuation factor, AF, respectively) are nonlinear, and global solar radiation is more sensitive to changes in scattering than to changes in absorption. Further applying this empirical model, the albedos at the top of the atmosphere (TOA) and the surface in 2007–2020 were computed and are in line with satellite-based retrievals. During 2007–2020, the mean estimated annual global solar radiation increased by 0.22% per year, which was associated with a decrease in AF of 1.46% and an increase in water-vapor pressure of 0.37% per year. The annual mean air temperature increased by about 0.16 °C over the 14 years. Annual mean losses of solar radiation caused by absorbing and scattering substances and total loss were 2.55, 0.64, and 3.19 MJ m−2, respectively. The annual average absorbing loss was much larger than the scattering loss; their contributions to the total loss were 77.23% and 22.77%, indicating that absorbing substances play significant roles. The annual absorbing loss increased by 0.42% per year, and scattering and total losses decreased by 2.00% and 0.14% per year, respectively. The estimated and satellite-derived annual albedos increased at the TOA and decreased at the surface. This study shows that solar radiation and its interactions with atmospheric absorbing and scattering substances have played key but different roles in regional climate and climate change at the three poles. energy; air temperature; absorbing and scattering; climate and climate change; wind speed
Barrientos-Velasco, Carola; Deneke, Hartwig; Hünerbein, Anja; Griesche, Hannes J.; Seifert, Patric; Macke, AndreasBarrientos-Velasco, C., H. Deneke, A. Hünerbein, H. J. Griesche, P. Seifert, A. Macke, 2022: Radiative closure and cloud effects on the radiation budget based on satellite and ship-borne observations during the Arctic summer research cruise PS106. Atmospheric Chemistry and Physics Discussions, 1-71. doi: 10.5194/acp-2021-1004. Abstract. For understanding Arctic climate change, it is critical to quantify and address uncertainties in climate data records on clouds and radiative fluxes derived from long-term passive satellite observations. A unique set of observations collected during the research vessel Polarstern PS106 expedition (28 May to 16 July 2017) by the OCEANET facility is exploited here for this purpose and compared with the CERES SYN1deg Ed. 4.1 satellite remote sensing products. Mean cloud fraction (CF) of 86.7 % for CERES and 76.1 % for OCEANET were found for the entire cruise. The difference of CF between both data sets is due to different spatial resolution and momentary data gaps due to technical limitations of the set of ship-borne instruments. A comparison of radiative fluxes during clear-sky conditions enables radiative closure for CERES products by means of independent radiative transfer simulations. Several challenges were encountered to accurately represent clouds in radiative transfer under cloudy conditions, especially for ice-containing clouds and low-level stratus (LLS) clouds. During LLS conditions, the OCEANET retrievals were in particular compromised by the altitude detection limit of 155 m of the cloud radar. Radiative fluxes from CERES show a good agreement with ship observations, having a bias (standard deviation) of −6.0 (14.6) W m−2 and 23.1 (59.3) W m−2 for the downward longwave (LW) and shortwave (SW) fluxes, respectively. Based on CERES products, mean values of the radiation budget and the cloud radiative effect (CRE) were determined for the PS106 cruise track and the central Arctic region (70°–90° N). For the period of study, the results indicate a strong influence of the SW flux in the radiation budget, which is reduced by clouds leading to a net surface CRE of −8.8 W m−2 and −9.3 W m−2 along the PS106 cruise and for the entire Arctic, respectively. The similarity of local and regional CRE supports that the PS106 cloud observations can be considered to be representative of Arctic cloudiness during early summer.
Baxter, Ian; Ding, QinghuaBaxter, I., Q. Ding, 2022: An Optimal Atmospheric Circulation Mode in the Arctic Favoring Strong Summertime Sea Ice Melting and Ice–Albedo Feedback. J. Climate, 35(20), 3027-3045. doi: 10.1175/JCLI-D-21-0679.1. Abstract The rapid decline of summer Arctic sea ice over the past few decades has been driven by a combination of increasing greenhouse gases and internal variability of the climate system. However, uncertainties remain regarding spatial and temporal characteristics of the optimal internal atmospheric mode that most favors summer sea ice melting on low-frequency time scales. To pinpoint this mode, we conduct a suite of simulations in which atmospheric circulation is constrained by nudging tropospheric Arctic (60°–90°N) winds within the Community Earth System Model, version 1 (CESM1), to those from reanalysis. Each reanalysis year is repeated for over 10 model years using fixed greenhouse gas concentrations and the same initial conditions. Composites show the strongest September sea ice losses are closely preceded by a common June–August (JJA) barotropic anticyclonic circulation in the Arctic favoring shortwave absorption at the surface. Successive years of strong wind-driven melting also enhance declines in Arctic sea ice through enhancement of the ice–albedo feedback, reaching a quasi-equilibrium response after repeated wind forcing for over 5–6 years, as the effectiveness of the wind-driven ice–albedo feedback becomes saturated. Strong melting favored by a similar wind pattern as observations is detected in a long preindustrial simulation and 400-yr paleoclimate reanalysis, suggesting that a summer barotropic anticyclonic wind pattern represents the optimal internal atmospheric mode maximizing sea ice melting in both the model and natural world over a range of time scales. Considering strong contributions of this mode to changes in Arctic climate, a better understanding of its origin and maintenance is vital to improving future projections of Arctic sea ice.
Bhattarai, Santosh; Ziebart, Marek; Springer, Tim; Gonzalez, Francisco; Tobias, GuillermoBhattarai, S., M. Ziebart, T. Springer, F. Gonzalez, G. Tobias, 2022: High-precision physics-based radiation force models for the Galileo spacecraft. Advances in Space Research, 69(12), 4141-4154. doi: 10.1016/j.asr.2022.04.003. We present two new high-precision physics-based radiation force models for the In-Orbit Validation (IOV) and Full Operational Capability (FOC) spacecraft (s/c) of the Galileo Global Navigation Satellite System (GNSS). In both cases, the s/c bus surfaces are covered in material types, i.e., Laser Retro-reflector Array (LRA), Optical Surface Reflector (OSR) and Single-Layer Insulation (SLI) coverings, that were either not encountered or not specifically dealt with in earlier work. To address this, a number of modelling enhancements were proposed and tested, including: a specific model to account for the direct and reflected solar radiation force for LRA surfaces; a design update of the bus model computation process to allow for more than one insulation material; a specific thermal force model for OSR surfaces; a thermal force model for the Navigation Antenna (NAVANT) surface that includes a temperature model derived from on-orbit temperature measurements; and force models to account for thermal emissions from radiator panels on the +X and ±Y surfaces for both IOV and FOC, and on the -Z surface for FOC only. In the UCL2+ model each of these effects are accounted for. The theoretical impact of each modelling concept introduced is assessed, individually, by considering the magnitude of its effect in acceleration-space. The impact on orbit accuracy is confirmed through a rigorous set of Precise Orbit Determination (POD) validation tests, in which observations from all active Galileo s/c over two full years, 2017 and 2018, including during eclipsing periods, are included in the analysis. The UCL2+ approach results in day boundary discontinuities of 22 mm, 17 mm and 27 mm in the radial, across-track and along-track components, respectively. Analysis of the one-way Satellite Laser Ranging (SLR) residuals suggests that radial accuracy at better than 1 cm (3.7 mm mean residuals) and precision at better than 2 cm (17 mm root mean square (rms) error) is achievable with the UCL2+ model. Precise orbit determination; Full operational capability; Galileo; Global Navigation Satellite Systems (GNSS); In-orbit validation; Radiation force modelling
Blanchard-Wrigglesworth, Edward; Webster, Melinda; Boisvert, Linette; Parker, Chelsea; Horvat, ChristopherBlanchard-Wrigglesworth, E., M. Webster, L. Boisvert, C. Parker, C. Horvat, 2022: Record Arctic Cyclone of January 2022: Characteristics, Impacts, and Predictability. Journal of Geophysical Research: Atmospheres, 127(21), e2022JD037161. doi: 10.1029/2022JD037161. Arctic cyclones are a fundamental component of Arctic climate, influencing atmospheric heat and moisture transport into the region and surface energy, moisture, and momentum fluxes. Arctic cyclones can also drive changes in sea ice and energize ocean waves. Here we investigate a record low sea level pressure (SLP) Arctic cyclone which formed in East Greenland and tracked NE over the Barents and Kara seas between 21 and 27 January 2022. At its peak intensity on 24 January, the cyclone reached an estimated depth of 932.2 mb at 79.5°N 20°E. North of 70°N, this is the lowest SLP in the ERA-5 reanalysis over 1979 to present. The cyclone resulted in a record (over the period 1979–2022) weekly loss of regional sea ice area and surface wind speeds, and generated ocean waves exceeding 8 m that impinged on sea ice in the Barents sea, observed via satellite altimetry as large waves-in-sea ice up to 2 m in amplitude more than 100 km into the ice pack. Surface heat fluxes were strongly impacted by the cyclone, with record atmosphere-to-surface turbulent fluxes. However, the direct atmospheric thermodynamic impact on sea ice loss was modest, and the record sea ice changes were likely mainly driven by dynamical and/or ocean processes. While the storm was well predicted up to 8 days in advance, subsequent changes in sea ice cover were not, likely due to biases in the forecasts' sea ice initial conditions and missing physics in the forecast model such as wave-sea ice interaction.
Boudala, Faisal S.; Milbrandt, Jason A.; Isaac, George A.Boudala, F. S., J. A. Milbrandt, G. A. Isaac, 2022: Evaluation of CanESM Cloudiness, Cloud Type and Cloud Radiative Forcing Climatologies Using the CALIPSO-GOCCP and CERES Datasets. Remote Sensing, 14(15), 3668. doi: 10.3390/rs14153668. In this study, the annual and seasonal climatology of cloud fraction (CF) and cloud type simulated by the Canadian Environmental System Models (CanESMs) version 5 (CanESM5) and version 2 (CanESM2) at their fully coupled and AMIP configurations were validated against the CALIPSO-GOCCP-based CF. The CFs produced using the CALIPSO-COSP simulator based on the CanESMs data at their atmospheric (AMIP) configuration are also evaluated. The simulated shortwave, longwave, and net cloud radiative forcing using the AMIP version of the CanESM5 were also validated against satellite observations based on the recent CERES radiation satellite products. On average, all models have a negative bias in the total CF with global mean biases (MBs) of 2%, 2.4%, 3.9%, 6.4%, 5.6%, and 7.1% for the coupled-CanESM5, AMIP-CanESM5, COSP-AMIP-CanESM5, coupled-CanESM2, AMIP-CanESM2, and COSP-AMIP-CanESM2, respectively, indicating that the CanESM5 has a smaller MB. There were no significant differences between AMIP and coupled versions of the model, but the COSP-based model-simulated data showed larger biases. Although the models captured well the climatological features of CF, they also exhibited a significant bias in CF reaching up to 40% over some geographical locations. This is particularly prevalent over the low level (LL) marine stratocumulus/cumulus, convectively active tropical latitudes that are normally dominated by high level (HL) clouds and at the polar regions where all models showed negative, positive, and positive bias corresponding to these locations, respectively. The AMIP-CanESM5 model performed reasonably well simulating the global mean cloud radiative forcing (CRF) with slight negative biases in the NetCRF at the TOA and surface that would be expected if the model has a positive bias in CF. This inconsistent result may be attributed to the parameterization of the optical properties in the model. The geographical distributions of the model bias in the NetCRF, however, can be significant reaching up to ±40 Wm−2 depending on the location and atmospheric level. The Pearson correlation showed that there is a strong correlation between the global distribution of model bias in NetCRF and CF and it is significantly influenced by the LL and HL clouds. satellite data; cloud radiative forcing; cloud fraction; GCM model evaluation
Cao, Qimeng; Liu, Yan; Sun, Xue; Yang, LiuCao, Q., Y. Liu, X. Sun, L. Yang, 2022: Country-level evaluation of solar radiation data sets using ground measurements in China. Energy, 241, 122938. doi: 10.1016/j.energy.2021.122938. Solar radiation is a crucial parameter that affects the thermal environment in buildings. The spatial and temporal distributions of solar radiation data are important for energy-efficient building design. Models that correlate solar radiation with other parameters can address the lack of solar radiation data. Satellite-derived products and reanalysis data sets have been produced using solar radiation models. The accuracy of these products directly affects building thermal environment design. To choose the most appropriate data set, it is necessary to evaluate the deviation in different data sets based on ground measurements. We used data acquired between 2001 and 2016 from 98 solar radiation measurement stations in China to verify two satellite-derived products (SARAH-E and CERES-SYN1deg) and two reanalysis data sets (ERA5 and MERRA-2). The CERES-SYN1deg and SARAH-E products performed better than the ERA5 and MERRA-2 data sets at estimating the daily global solar radiation. The daily global radiation products were more accurate than direct, diffuse, and hourly global solar radiation products. The models merged ground measurements show good performance. Further improvement in solar radiation estimation especially direct and diffuse in areas where there are no ground measurements and taking into account the effect of inadequate weather conditions on the hourly solar radiation is required. These findings may provide the basis for solar radiation models and products, especially applications in the building industry. Global solar radiation; Direct solar radiation; Reanalysis data set; Satellite-derived product
Cao, Yunfeng; Li, Manyao; Zhang, YuzhenCao, Y., M. Li, Y. Zhang, 2022: Estimating the Clear-Sky Longwave Downward Radiation in the Arctic from FengYun-3D MERSI-2 Data. Remote Sensing, 14(3), 606. doi: 10.3390/rs14030606. Surface longwave downward radiation (LWDR) plays a key role in determining the Arctic surface energy budget, especially in insolation-absent boreal winter. A reliable LWDR product is essential for understanding the intrinsic physical mechanisms of the rapid changes in the Arctic climate. The Medium-Resolution Spectral Imager (MERSI-2), a major payload of the Chinese second-generation polar-orbiting meteorological satellite, FengYun-3D (FY-3D), was designed similar to the NASA Moderate-Resolution Imaging Spectroradiometer (MODIS) in terms of the spectral bands. Although significant progress has been made in estimating clear-sky LWDR from MODIS observations using a variety of methods, few studies have focused on the retrieval of clear-sky LWDR from FY-3D MERSI-2 observations. In this study, we propose an advanced method to directly estimate the clear-sky LWDR in the Arctic from the FY-3D MERSI-2 thermal infrared (TIR) top-of-atmosphere (TOA) radiances and auxiliary information using the extremely randomized trees (ERT) machine learning algorithm. The retrieval accuracy of RMSE and bias, validated with the Baseline Surface Radiation Network (BSRN) in situ measurements, are 14.14 W/m2 and 4.36 W/m2, respectively, which is comparable and even better than previous studies. The scale effect in retrieval accuracy evaluation was further analyzed and showed that the validating window size could significantly influence the retrieval accuracy of the MERSI-2 clear-sky LWDR dataset. After aggregating to a spatial resolution of 9 km, the RMSE and bias of MERSI-2 retrievals can be reduced to 9.43 W/m2 and −0.14 W/m2, respectively. The retrieval accuracy of MERSI-2 clear-sky LWDR at the CERES SSF FOV spatial scale (approximately 20 km) can be further reduced to 8.64 W/m2, which is much higher than the reported accuracy of the CERES SSF products. This study demonstrates the feasibility of producing LWDR datasets from Chinese FY-3D MERSI-2 observations using machine learning methods. machine learning; satellite observation; Arctic region; surface downward longwave radiation; FengYun-3D; MERSI-2
Cesana, Grégory V.; Khadir, Théodore; Chepfer, Hélène; Chiriaco, MarjolaineCesana, G. V., T. Khadir, H. Chepfer, M. Chiriaco, 2022: Southern Ocean Solar Reflection Biases in CMIP6 Models Linked to Cloud Phase and Vertical Structure Representations. Geophysical Research Letters, 49(22), e2022GL099777. doi: 10.1029/2022GL099777. Over the Southern Ocean (SO, 40°S–70°S), climate models have consistently underestimated solar reflection. Here we evaluate the relationship between cloud profiles, cloud phase and radiation over the SO in Coupled Model Intercomparison Project Phase 6 (CMIP6) models against Clouds and the Earth's Radiant Energy System and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations. We find that the lack of solar reflection is slightly improved in CMIP6 models compared to CMIP5's, attributable to a better representation of cloud fraction and phase. We show that clouds have a different vertical structure and radiative effect south and north of where the 0°C isotherm meets the surface (∼55°S). Although the models capture the greater vertical extent of clouds south of 55°S, they fail to reproduce the observed increase in solar reflection, which we pinpoint to cloud phase biases. Increasing CMIP6 supercooled liquid cloud opacity should help reduce their persistent shortwave biases. cloud phase; climate models; radiation; evaluation; CALIPSO-GOCCP; southern ocean
Chakraborty, T.; Lee, X.; Lawrence, D. M.Chakraborty, T., X. Lee, D. M. Lawrence, 2022: Diffuse Radiation Forcing Constraints on Gross Primary Productivity and Global Terrestrial Evapotranspiration. Earth's Future, 10(8), e2022EF002805. doi: 10.1029/2022EF002805. The diffuse radiation fertilization effect—the increase in plant productivity in the presence of higher diffuse radiation (K↓,d)—is an important yet understudied aspect of atmosphere-biosphere interactions and can modify the terrestrial carbon, energy, and water budgets. The K↓,d fertilization effect links the carbon cycle with clouds and aerosols, all of which are large sources of uncertainties for our current understanding of the Earth system and for future climate projections. Here we establish to what extent observational and modeling uncertainty in sunlight's diffuse fraction (kd) affects simulated gross primary productivity (GPP) and terrestrial evapotranspiration (λE). We find only 48 eddy covariance sites with simultaneous sufficient measurements of K↓,d with none in the tropical climate zone, making it difficult to constrain this mechanism globally using observations. Using a land modeling framework based on the latest version of the Community Land Model, we find that global GPP ranges from 114 Pg C year−1 when using kd forcing from the Modern-Era Retrospective analysis for Research and Applications, version 2 reanalysis to a ∼7% higher value of 122 Pg C year−1 when using the Clouds and the Earth's Radiant Energy System satellite product, with especially strong differences apparent over the tropical region (mean increase ∼9%). The differences in λE, although smaller (−0.4%) due to competing changes in shaded and sunlit leaf transpiration, can be greater than regional impacts of individual forcing agents like aerosols. Our results demonstrate the importance of comprehensively and systematically validating the simulated kd by atmosphere modules as well as the response to differences in kd within land modules across Earth System Models. evapotranspiration; atmosphere-biosphere interactions; diffuse radiation fertilization effect; gross primary productivity; land-surface models
Chan, Man-Yau; Chen, Xingchao; Leung, L. RubyChan, M., X. Chen, L. R. Leung, 2022: A High-Resolution Tropical Mesoscale Convective System Reanalysis (TMeCSR). Journal of Advances in Modeling Earth Systems, 14(9), e2021MS002948. doi: 10.1029/2021MS002948. Modern global reanalysis products have greatly accelerated meteorological research in synoptic-to-planetary-scale phenomena. However, their use in studying tropical mesoscale convective systems (MCSs) and their regional-to-global impact has mostly been limited to supplying initial and boundary conditions for MCS-resolving simulations and providing information about the large-scale environments of MCSs. These limitations are due to difficulties in resolving tropical MCS dynamics in the relatively low-resolution global models and that tropical MCSs often occur over poorly observed regions. In this work, a Tropical MCS-resolving Reanalysis product (TMeCSR) was created over a region with frequent tropical MCSs. This region spans the tropical Indian Ocean, tropical continental Asia, Maritime Continent, and Western Pacific. TMeCSR is produced by assimilating all-sky infrared radiances from geostationary satellites and other conventional observations into an MCS-resolving regional model using the Ensemble Kalman Filter. The resulting observation-constrained high-resolution (9-km grid spacing) data set is available hourly during the boreal summer (June-August) of 2017, during which widespread severe flooding occurred. Comparisons of TMeCSR and European Center for Medium Range Weather Forecast Reanalysis version 5 (ERA5) against independent satellite retrievals indicate that TMeCSR's cloud and multiscale rain fields are better than those of ERA5. Furthermore, TMeCSR better captured the diurnal variability of rainfall and the statistical characteristics of MCSs. Forecasts initialized from TMeCSR also have more accurate rain and clouds than those initialized from ERA5. The TMeCSR and ERA5 forecasts have similar performances with respect to sounding and surface observations. These results indicate that TMeCSR is a promising MCS-resolving data set for tropical MCS studies. reanalysis; data assimilation; mesoscale convective system
Chao, Li-Wei; Muller, Jacob C.; Dessler, Andrew E.Chao, L., J. C. Muller, A. E. Dessler, 2022: Impacts of the Unforced Pattern Effect on the Cloud Feedback in CERES Observations and Climate Models. Geophysical Research Letters, 49(2), e2021GL096299. doi: 10.1029/2021GL096299. The equilibrium climate sensitivity estimated from different sources is inconsistent due to its dependence on the surface warming pattern. Cloud feedbacks have been identified as the major contributor to this so-called pattern effect. We find a large unforced pattern effect in CERES data, with cloud feedback estimated from two consecutive 125-month periods (March 2000–July 2010 and August 2010–December 2020) changing from −0.45 ± 0.85 to +1.2 ± 0.78 W/m2/K. When comparing to models, 27% of consecutive 10-year segments in CMIP6 control runs have differences similar to the observations. We also compare the spatial patterns in the CERES data to those in climate models and find they are similar, with the East Pacific playing a key role. This suggests that the impact of the unforced pattern effect can be significant and that models are capable of reproducing its global-average magnitude. cloud feedback; climate models; pattern effect
Chen, Annan; Zhao, Chuanfeng; Fan, TianyiChen, A., C. Zhao, T. Fan, 2022: Spatio-temporal distribution of aerosol direct radiative forcing over mid-latitude regions in north hemisphere estimated from satellite observations. Atmospheric Research, 266, 105938. doi: 10.1016/j.atmosres.2021.105938. An empirical method is used to estimate the aerosol direct radiative forcing (ADRF) over 20oN − 40oN regions from March 2000 to March 2019. The ADRF is calculated as the difference between the cloud-free sky and clean-sky (non-aerosol) radiative fluxes, which are fitted to an exponential function of the aerosol optical depth (AOD). The regional averaged ADRFs are negative (cooling effect) at the surface (SUR) and the top of atmosphere (TOA) and positive (warming effect) in the atmosphere (ATM). The spatial and temporal distributions of ADRF are closely linked to the spatio-temporal distributions of AOD. Higher AOD and stronger ADRF are found in spring (March to May) and summer (June to August). ADRFs are larger in regions with frequent sandstorm outbreaks and rapid economic growth since 2000 than other regions. The uncertainty of ADRF due to data source is 1.12 W/m2 at the surface and 0.91 W/m2 at the TOA according to the stochastic error propagation function. The ADRFs in our study regions show statistically significant but different changes of −0.074 W/m2 /year and 0.1 W/m2 /year at the surface during 2000 to 2009 and 2010 to 2019, respectively. Recent trend analysis also shows that the reduced aerosol contributes to the increasing short-wave flux about 0.32 W/m2 under the background of the global warming during the period from 2000 to 2019 in our study area, which indicates that it may alter the pattern of atmospheric circulation or enhance the global warming effect. Aerosol optical depth; Aerosol direct radiative forcing; Anthropogenic activity; Mid-latitude region; Sandstorm
Chen, Guangcan; Zhang, Xiangdong; Fu, YunfeiChen, G., X. Zhang, Y. Fu, 2022: Diurnal Variation in Clouds and Radiative Budgets Over the Tibetan Plateau During Summer Using CERES Data. Journal of Geophysical Research: Atmospheres, 127(16), e2021JD036329. doi: 10.1029/2021JD036329. Diurnal variations in clouds and radiation budgets over four subareas of the Tibetan Plateau (TP) during summer (June–August) are analyzed using the Clouds and the Earth's Radiant Energy System (CERES) synoptic 1° (SYN1deg) data from 2000 to 2020. The results show that the total cloud amount decreases from southeast to northwest and is larger during daytime (71.1%) than nighttime (67.2%) over the entire TP. High-clouds develop in the afternoon, persist during nighttime, and dissipate after sunrise. Low clouds develop after sunrise and dissipate in the afternoon over the entire TP, but show opposite temporal variation over the Kunlun Mountains. The net radiation budget at the top-of-atmosphere reaches its maximum at noon. The surface net radiation budget is positive in the daytime and negative at nighttime. These features are mainly adjusted by the cloud distribution. The diurnal variations in heating rate over the four subareas are similar in the upper atmosphere but different in the lower layer. The low-atmosphere heating rate shows a maximum value over the center-south (CS) subarea, while it is lowest over the west (W) subarea. Internal cloud forcing has distinct regional differences over the four subareas: it shows a heating effect in the low atmosphere and a cooling effect in the middle atmosphere over the CS subarea, whereas over the W subarea it shows a radiative cooling effect in the low atmosphere and no significant radiative effect in the middle layer. The findings of this study help toward improving our understanding of the TP's energy cycle. diurnal variation; heating rate; cloud cover; internal cloud forcing; Tibet Plateau
Chen, Jiang; He, Tao; Liang, ShunlinChen, J., T. He, S. Liang, 2022: Estimation of Daily All-wave Surface Net Radiation with Multispectral and Multitemporal Observations from GOES-16 ABI. IEEE Transactions on Geoscience and Remote Sensing, 1-1. doi: 10.1109/TGRS.2022.3140335. As a vital parameter describing the Earth surface energy budget, surface all-wave net radiation (Rn) drives many physical and biological processes. Remote estimation of Rn using satellite data is an effective approach to monitor the spatial and temporal dynamics of Rn. Accurate daily Rn estimation typically depends on the spatio-temporal resolutions of satellite data. There are currently few high-spatial-resolution daily Rn products from polar-orbiting satellite data, and they exhibit limited accuracy due to sparse diurnal observations. In addition, traditional estimation approaches typically require cloud mask and clear-sky albedo as inputs and ignore the length ratio of daytime (LRD), which may lead to large errors. To overcome these challenges and obtain Rn data with improved spatial resolution and accuracy, an operational approach was proposed in this study to derive daily 1-km Rn, which takes the advantages from a radiative transfer model, a machine learning algorithm, and multispectral and dense diurnal temporal information of geostationary satellite observations. An improved all-sky hybrid model (AHM) coupling radiative transfer simulations with a random forest (RF) model was first developed to estimate the shortwave net radiation (Rns). Then, another RF model was developed to estimate the daily Rn from Rns, incorporating the LRD, which is called extended hybrid model (EHM). Data from the Advanced Baseline Imager (ABI) onboard the new-generation Geostationary Operational Environmental Satellite (GOES)-16 with a 5-min temporal resolution and a 1-km spatial resolution were used to test the proposed method. Compared to traditional look-up table (LUT) algorithms, the results show that AHM not only makes the process of Rns estimation simple and efficient, but also has high accuracy in estimating instantaneous all-sky Rns. Benefiting from high spatio-temporal resolutions, our daily Rns estimates using GOSE-16 data exhibited superior performance compared to using the 1-km Moderate Resolution Imaging Spectroradiometer (MODIS) and 1° Clouds and the Earth’s Radiant Energy System (CERES) product. Using accurate daily Rns estimates and LRD as inputs, the EHM model shows reasonably good results for estimating Rn (R2, RMSE, and bias of 0.91, 20.95 W/m2, and -0.05 W/m2, respectively). Maps of 1-km Rns and Rn exhibit similar spatial patterns to those from the 1° CERES product, but with substantially more spatial details. Overall, the proposed Rn retrieval scheme can accurately estimate all-sky 1-km Rns and Rn at mid- to low-latitudes and can be easily adapted and applied to other GOES-16-like satellites, such as Himawari-8, METEOSAT Third Generation (MTG) and Fenyun-4. This study demonstrates the advantages of estimating Rn using geostationary satellites with improved accuracy and resolutions. Atmospheric modeling; Clouds; Estimation; Spatial resolution; MODIS; Remote sensing; geostationary satellite; all-sky hybrid model; daily net radiation; extended hybrid model; Geostationary satellites; length ratio of daytime
Chen, Jingyi; Wang, Hailong; Li, Xiangyu; Painemal, David; Sorooshian, Armin; Thornhill, Kenneth Lee; Robinson, Claire; Shingler, TaylorChen, J., H. Wang, X. Li, D. Painemal, A. Sorooshian, K. L. Thornhill, C. Robinson, T. Shingler, 2022: Impact of Meteorological Factors on the Mesoscale Morphology of Cloud Streets during a Cold-Air Outbreak over the Western North Atlantic. J. Atmos. Sci., 79(11), 2863-2879. doi: 10.1175/JAS-D-22-0034.1. Abstract Postfrontal clouds (PFC) are ubiquitous in the marine boundary layer, and their morphology is essential to estimating the radiation budget in weather and climate models. Here we examine the roles of sea surface temperature (SST) and meteorological factors in controlling the mesoscale morphology and evolution of shallow clouds associated with a cold-air outbreak that occurred on 1 March 2020 during phase I of the Aerosol Cloud Meteorology Interactions over the Western Atlantic Experiment (ACTIVATE). Our results show that the simulated PFC structure and ambient conditions by the Weather Research and Forecasting (WRF) Model are generally consistent with observations from GOES-16 and dropsonde measurements. We also examine the thermodynamical and dynamical influences in the cloud mesoscale morphology using WRF sensitivity experiments driven by two meteorological forcing datasets with different domain-mean SST and spatial gradients, which lead to dissimilar values of hydrometeor water path and cloud core fraction. The SST from ERA5 leads to weaker stability and higher inversion height than the SST from FNL does. In addition, the use of large-scale meteorological forcings from ERA5 yields a distinctive time evolution of wind direction shear in the inner domain, which favors the formation and persistence of longer cloud rolls. Both factors contribute to a change in the time evolution of domain-mean water path and cloud core fraction of cloud streets. Our study takes advantage of the simulation driven by the differences between two large-scale forcing datasets to illustrate the importance of SST and wind direction shear in the cloud street morphology in a realistic scenario.
Chen, Xingan; Huang, Yuefei; Nie, Chong; Zhang, Shuo; Wang, Guangqian; Chen, Shiliu; Chen, ZhichaoChen, X., Y. Huang, C. Nie, S. Zhang, G. Wang, S. Chen, Z. Chen, 2022: A long-term reconstructed TROPOMI solar-induced fluorescence dataset using machine learning algorithms. Scientific Data, 9(1), 427. doi: 10.1038/s41597-022-01520-1. Photosynthesis is a key process linking carbon and water cycles, and satellite-retrieved solar-induced chlorophyll fluorescence (SIF) can be a valuable proxy for photosynthesis. The TROPOspheric Monitoring Instrument (TROPOMI) on the Copernicus Sentinel-5P mission enables significant improvements in providing high spatial and temporal resolution SIF observations, but the short temporal coverage of the data records has limited its applications in long-term studies. This study uses machine learning to reconstruct TROPOMI SIF (RTSIF) over the 2001–2020 period in clear-sky conditions with high spatio-temporal resolutions (0.05° 8-day). Our machine learning model achieves high accuracies on the training and testing datasets (R2 = 0.907, regression slope = 1.001). The RTSIF dataset is validated against TROPOMI SIF and tower-based SIF, and compared with other satellite-derived SIF (GOME-2 SIF and OCO-2 SIF). Comparing RTSIF with Gross Primary Production (GPP) illustrates the potential of RTSIF for estimating gross carbon fluxes. We anticipate that this new dataset will be valuable in assessing long-term terrestrial photosynthesis and constraining the global carbon budget and associated water fluxes. Phenology; Ecosystem ecology
Chen, Zhe; Wang, Minghuai; Zhang, Haipeng; Lin, Shuheng; Guo, Zhun; Jiang, Yiquan; Zhou, ChenChen, Z., M. Wang, H. Zhang, S. Lin, Z. Guo, Y. Jiang, C. Zhou, 2022: Long-term change in low-cloud cover in Southeast China during cold seasons. Atmospheric and Oceanic Science Letters, 15(6), 100222. doi: 10.1016/j.aosl.2022.100222. Southeast China has comparable stratus cloud to that over the oceans, especially in the cold seasons (winter and spring), and this cloud has a substantial impact on energy and hydrological cycles. However, uncertainties remain across datasets and simulation results about the long-term trend in low-cloud cover in Southeast China, making it difficult to understand climate change and related physical processes. In this study, multiple datasets and numerical simulations were applied to show that low-cloud cover in Southeast China has gone through two stages since 1980—specifically, a decline and then a rise, with the turning point around 2008. The regional moisture transport plays a crucial role in low-cloud cover changes in the cold seasons and is mainly affected by the Hadley Cell in winter and the Walker Circulation in spring, respectively. The moisture transport was not well simulated in CMIP6 climate models, leading to poor simulation of the low-cloud cover trend in these models. This study provides insights into further understanding the regional climate changes in Southeast China. 摘要 中国东南地区在冬春冷季节盛行低云, 对局地能量平衡和水文循环有重要的作用. 本研究使用多套数据和数值模拟结果, 分析这一地区冷季节内低云云量在1980年至2017年的长期变化. 结果表明, 低云云量经历了先下降后上升的趋势变化, 转折点出现在2008年左右. 局地水汽通量输送在影响低云云量的变化中起着至关重要的作用, 其在冬季和春季分别受到哈德莱环流和沃克环流的影响. CMIP6中的气候模式对水汽通量输送的模拟能力欠佳, 影响了对低云云量的模拟结果. Hadley cell; Large-scale circulation; Low-cloud cover; Pacific walker circulation; 低云云量; 关键词:; 哈德莱环流; 大尺度环流场; 沃克环流
Cheng, Anning; Yan, FanglinCheng, A., F. Yan, 2022: Direct Radiative Effects of Aerosols on Numerical Weather Forecast -- A Comparison of Two Aerosol Datasets in the NCEP GFS. doi: 10.25923/RB1N-ZA92. This study compares aerosol direct radiative effects on numerical weather forecasts made by the NCEP Global Forecast Systems (GFS) with two different aerosol datasets, the OPAC and MERRA2 aerosol climatologies. The OPAC overestimates the aerosol loading from sea salt in storm track regions over the Northern and Southern Hemisphere ocean and underestimates the aerosol loading over most continents. The experiments made with MERRA2 aerosols showed improvements in GFS forecasts of aerosol optical depth (AOD) over the globe when verified against satellite retrievals. The experiment made with the OPAC aerosols largely underestimated the AOD over northwest Africa, central to east Africa, southeast Asia, and the Indo-Gangetic Plain, and overestimated the AOD in the storm track regions in both hemispheres. Surface downward short-wave (SW) and long- wave (LW) fluxes and the top of the atmosphere SW and outgoing LW fluxes from model forecasts are compared with CERES satellite observations. Forecasts made with OPAC aerosols have large AOD biases, especially in northwest Africa and the storm track regions. These biases are reduced in the forecasts made with MERRA2 aerosols. The improvements are most noticeable in the surface downward SW fluxes. GFS medium-range weather forecasts made with the MERRA2 aerosols demonstrated improved forecast accuracy of circulation and precipitation over the India and East Asian summer monsoon region. Forecasts of Africa easterly jets are also improved. Impacts on large-scale skill scores such as 500hPa geopotential height anomaly correlation are generally positive in the Northern Hemisphere and the Pacific and North American regions in the winter and summer seasons.
Chtirkova, Boriana; Folini, Doris; Correa, Lucas Ferreira; Wild, MartinChtirkova, B., D. Folini, L. F. Correa, M. Wild, 2022: Internal Variability of All-Sky and Clear-Sky Surface Solar Radiation on Decadal Timescales. Journal of Geophysical Research: Atmospheres, 127(12), e2021JD036332. doi: 10.1029/2021JD036332. Internal variability comprises all processes that occur within the climate system without any natural or anthropogenic forcing. Climate-driving variables like the surface solar radiation (SSR) are shown to exhibit unforced trends (i.e., trends due to internal variability) of magnitudes comparable to the magnitude of the forced signal even on decadal timescales. We use annual mean data from 50 models participating in the preindustrial control experiment (piControl) of the Coupled Model Intercomparison Project-Phase 6 (CMIP6) to give quantitative grid-box specific estimates of the magnitudes of unforced trends. To characterize a trend distribution, symmetrical around 0, we use the 75th percentile of all possible values, which corresponds to a positive trend with 25% chance of occurrence. For 30-year periods and depending on geographical location, this trend has a magnitude between 0.15 and 2.1 W m−2/decade for all-sky and between 0.04 and 0.38 W m−2/decade for clear-sky SSR. The corresponding area-weighted medians are 0.69 W m−2/decade for all-sky trends and 0.17 W m−2/decade for clear-sky trends. The influence of internal variability is on average six times smaller in clear-sky, compared to all-sky SSR. The relative uncertainties in the physical representation, derived from the CMIP6 inter-model spread, are ±32% for all-sky and ±43% for clear-sky SSR trends. Reasons for differences between models like horizontal resolution, aerosol handling, and the representation of atmospheric and oceanic phenomena are investigated. The results can be used in the analysis of observational time series by attributing a probability for a trend to be caused by internal variability, given its magnitude, length, and location. CMIP6; surface solar radiation; dimming and brightening; internal variability; unforced trends
Chu, Wenchao; Lin, Yanluan; Zhao, MingChu, W., Y. Lin, M. Zhao, 2022: Implementation and Evaluation of a Double-Plume Convective Parameterization in NCAR CAM5. J. Climate, 35(2), 617-637. doi: 10.1175/JCLI-D-21-0267.1. Abstract Performance of global climate models (GCMs) is strongly affected by the cumulus parameterization (CP) used. Similar to the approach in GFDL AM4, a double-plume CP, which unifies the deep and shallow convection in one framework, is implemented and tested in the NCAR Community Atmospheric Model version 5 (CAM5). Based on the University of Washington (UW) shallow convection scheme, an additional plume was added to represent the deep convection. The shallow and deep plumes share the same cloud model, but use different triggers, fractional mixing rates, and closures. The scheme was tested in single-column, short-term hindcast, and AMIP simulations. Compared with the default combination of the Zhang–McFarlane scheme and UW scheme in CAM5, the new scheme tends to produce a top-heavy mass flux profile during the active monsoon period in the single-column simulations. The scheme increases the intensity of tropical precipitation, closer to TRMM observations. The new scheme increased subtropical marine boundary layer clouds and high clouds over the deep tropics, both in better agreement with observations. Sensitivity tests indicate that regime-dependent fractional entrainment rates of the deep plume are desired to improve tropical precipitation distribution and upper troposphere temperature. This study suggests that a double-plume approach is a promising way to combine shallow and deep convections in a unified framework.
Cui, Jiangpeng; Lian, Xu; Huntingford, Chris; Gimeno, Luis; Wang, Tao; Ding, Jinzhi; He, Mingzhu; Xu, Hao; Chen, Anping; Gentine, Pierre; Piao, ShilongCui, J., X. Lian, C. Huntingford, L. Gimeno, T. Wang, J. Ding, M. He, H. Xu, A. Chen, P. Gentine, S. Piao, 2022: Global water availability boosted by vegetation-driven changes in atmospheric moisture transport. Nature Geoscience, 15(12), 982-988. doi: 10.1038/s41561-022-01061-7. Surface-water availability, defined as precipitation minus evapotranspiration, can be affected by changes in vegetation. These impacts can be local, due to the modification of evapotranspiration and precipitation, or non-local, due to changes in atmospheric moisture transport. However, the teleconnections of vegetation changes on water availability in downwind regions remain poorly constrained by observations. By linking measurements of local precipitation to a new hydrologically weighted leaf area index that accounts for both local and upwind vegetation contributions, we demonstrate that vegetation changes have increased global water availability at a rate of 0.26 mm yr−2 for the 2001–2018 period. Critically, this increase has attenuated about 15% of the recently observed decline in global water availability. The water availability increase is due to a greater rise in precipitation relative to evapotranspiration for over 53% of the global land surface. We also quantify the potential hydrological impacts of regional vegetation increases at any given location across global land areas. We find that enhanced vegetation is beneficial to both local and downwind water availability for ~45% of the land surface, whereas it is adverse elsewhere, primarily in water-limited or high-elevation regions. Our results highlight the potential strong effects of deliberate vegetation changes, such as afforestation programmes, on water resources beyond local and regional scales. Climate change; Atmospheric dynamics; Hydrology; Climate sciences; Environmental impact
Cutler, Lauren; Brunke, Michael A.; Zeng, XubinCutler, L., M. A. Brunke, X. Zeng, 2022: Re-Evaluation of Low Cloud Amount Relationships With Lower-Tropospheric Stability and Estimated Inversion Strength. Geophysical Research Letters, 49(12), e2022GL098137. doi: 10.1029/2022GL098137. Lower-tropospheric stability (LTS) and estimated inversion strength (EIS) have a widely accepted relationship with low cloud amount and are key observational foundations for understanding and modeling low-level stratiform clouds. Using the updated surface-based and satellite cloud data, we find that low cloud amount is not as strongly correlated with LTS, and not as sensitive to LTS, as established in the past. EIS does not provide a stronger correlation with low cloud amount than LTS over all eight regions (including the midlatitudes). Further analyzing the relationships between LTS and EIS with different types of low clouds, we find that there is a strong correlation of LTS and EIS with stratocumulus only. This explains the weaker correlation of low cloud fraction (including cumulus, stratocumulus, and stratus) to both LTS and EIS. These results also suggest the need to re-evaluate these relationships in Earth system models.
Dadashazar, Hossein; Corral, Andrea F.; Crosbie, Ewan; Dmitrovic, Sanja; Kirschler, Simon; McCauley, Kayla; Moore, Richard; Robinson, Claire; Schlosser, Joseph S.; Shook, Michael; Thornhill, K. Lee; Voigt, Christiane; Winstead, Edward; Ziemba, Luke; Sorooshian, ArminDadashazar, H., A. F. Corral, E. Crosbie, S. Dmitrovic, S. Kirschler, K. McCauley, R. Moore, C. Robinson, J. S. Schlosser, M. Shook, K. L. Thornhill, C. Voigt, E. Winstead, L. Ziemba, A. Sorooshian, 2022: Organic enrichment in droplet residual particles relative to out of cloud over the northwestern Atlantic: analysis of airborne ACTIVATE data. Atmospheric Chemistry and Physics, 22(20), 13897-13913. doi: 10.5194/acp-22-13897-2022. Cloud processing is known to generate aerosol species such as sulfate and secondary organic aerosol, yet there is a scarcity of airborne data to examine this issue. The NASA Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) was designed to build an unprecedented dataset relevant to aerosol–cloud interactions with two coordinated aircraft over the northwestern Atlantic, with aerosol mass spectrometer data used from four deployments between 2020–2021 to contrast aerosol composition below, in (using a counterflow virtual impactor) and above boundary layer clouds. Consistent features in all time periods of the deployments (January–March, May–June, August–September) include the mass fraction of organics and relative amount of oxygenated organics (m/z 44) relative to total organics (f44) increasing in droplet residuals relative to below and above cloud. Detailed analysis comparing data below and in cloud suggests a possible role for in-cloud aqueous processing in explaining such results; an intriguing aspect though requiring more attention is that only approximately a quarter of the cloud cases (29 of 110) showed higher organic mass fractions either below or above cloud. Of those 29 cases, the majority (25) showed higher organic mass fraction below cloud base where the cloud processing signature is presumably more evident as compared to above cloud. These results are consistent with the few past studies analyzing droplet residuals pointing to higher organic enrichment than in adjacent cloud-free areas. The data findings are important as other datasets (e.g., reanalysis) suggest that sulfate is both more abundant than organics (in contrast to this work) and more closely related to drop number concentrations in the winter when aerosol–cloud interactions are strongest. Here we show that organics are more abundant than sulfate in the droplet residuals and that aerosol interaction with clouds potentially decreases particle hygroscopicity due to the increase in organic:sulfate ratio for droplet residuals relative to surrounding cloud-free air. These results are important in light of the growing importance of organics over the northwestern Atlantic in recent decades relative to sulfate owing to the success of regulatory activity over the eastern United States to cut sulfur dioxide emissions.
Dasari, Hari Prasad; Viswanadhapalli, Yesubabu; Langodan, Sabique; Abualnaja, Yasser; Desamsetti, Srinivas; Vankayalapati, Koteswararao; Thang, Luong; Hoteit, IbrahimDasari, H. P., Y. Viswanadhapalli, S. Langodan, Y. Abualnaja, S. Desamsetti, K. Vankayalapati, L. Thang, I. Hoteit, 2022: High-resolution climate characteristics of the Arabian Gulf based on a validated regional reanalysis. Meteorological Applications, 29(5), e2102. doi: 10.1002/met.2102. The regional climate of the Arabian Gulf (AG) and its variability are examined based on a 40-year (1980–2019), 5-km regional reanalysis of the Arabian Peninsula (AP reanalysis). The AP reanalysis fields were first validated against the available observations over the AG, suggesting that this high-resolution reanalysis well reproduces the spatio-temporal features of the AG atmospheric circulations. The validated AP reanalysis fields were then analysed to examine the climatic characteristics over the AG including the monthly mean, maximum and minimum temperatures, and the seasonal variations in winds, relative humidity and rainfall over the AG. The AG climate is mostly dry between May and October, and experiences moderate rainfall between December and January. The higher (lower) pressure difference between the northwest and southeast AG during summer (winter) generates the northwesterly Shamal winds over the north (central) AG. The mean Shamal winds are relatively stronger (weaker) and prolonged (shorter) during summer (winter); however, the short lived Shamal jet events in winter can be occasionally stronger than summer. In terms of interannual variability, the Shamal winds are stronger and more persistent in summer during El Niño years and in winter during La Niña years. These differences are mainly associated with changes in temperature gradients between the eastern AG and northwestern AP. temperature; Arabian Gulf; climate variability; regional reanalysis; Shamal winds
Datseris, George; Blanco, Joaquin; Hadas, Or; Bony, Sadrine; Caballero, Rodrigo; Kaspi, Yohai; Stevens, BjornDatseris, G., J. Blanco, O. Hadas, S. Bony, R. Caballero, Y. Kaspi, B. Stevens, 2022: Minimal Recipes for Global Cloudiness. Geophysical Research Letters, 49(20), e2022GL099678. doi: 10.1029/2022GL099678. Clouds are primary modulators of Earth's energy balance. It is thus important to understand the links connecting variabilities in cloudiness to variabilities in other state variables of the climate system, and also describe how these links would change in a changing climate. A conceptual model of global cloudiness can help elucidate these points. In this work we derive simple representations of cloudiness, that can be useful in creating a theory of global cloudiness. These representations illustrate how both spatial and temporal variability of cloudiness can be expressed in terms of basic state variables. Specifically, cloud albedo is captured by a nonlinear combination of pressure velocity and a measure of the low-level stability, and cloud longwave effect is captured by surface temperature, pressure velocity, and standard deviation of pressure velocity. We conclude with a short discussion on the usefulness of this work in the context of global warming response studies. energy balance; cloud controlling factors; global cloudiness
Dauhut, Thibaut; Hohenegger, CathyDauhut, T., C. Hohenegger, 2022: The Contribution of Convection to the Stratospheric Water Vapor: The First Budget Using a Global Storm-Resolving Model. Journal of Geophysical Research: Atmospheres, 127(5), e2021JD036295. doi: 10.1029/2021JD036295. The deepest convection on Earth injects water in the tropical stratosphere, but its contribution to the global stratospheric water budget remains uncertain. The Global Storm-Resolving Model ICOsahedral Non-hydrostatic is used to simulate the moistening of the lower stratosphere for 40 days during boreal summer. The decomposition of the water vapor budget in the tropical lower stratosphere (TLS, 10°S–30°N, and 17–20 km altitude) indicates that the average moistening (+21 Tg) over the simulated 40-day period is the result of the combined effect of the vertical water vapor transport from the troposphere (+27 Tg), microphysical phase changes and subgrid-scale transport (+2 Tg), partly compensated by horizontal water vapor export (−8 Tg). The very deep convective systems, explicitly represented thanks to the employed 2.5 km grid spacing of the model, are identified using the very low Outgoing Longwave Radiation of their cold cloud tops. The water vapor budget reveals that the vertical transport, the sublimation and the subgrid-scale transport at their top contribute together to 11% of the water vapor mass input into the TLS. convection; water vapor; budget; global storm-resolving model; ICON; stratosphere
Devi, Archana; Satheesh, Sreedharan K.Devi, A., S. K. Satheesh, 2022: Global maps of aerosol single scattering albedo using combined CERES-MODIS retrieval. Atmospheric Chemistry and Physics, 22(8), 5365-5376. doi: 10.5194/acp-22-5365-2022. Abstract. Single scattering albedo (SSA) is a leading contributor to the uncertainty in aerosol radiative impact assessments. Therefore accurate information on aerosol absorption is required on a global scale. In this study, we have applied a multi-satellite algorithm to retrieve SSA (550 nm) using the concept of critical optical depth. Global maps of SSA were generated following this approach using spatially and temporally collocated data from Clouds and the Earth's Radiant Energy System (CERES) and Moderate Resolution Imaging Spectroradiometer (MODIS) sensors on board Terra and Aqua satellites. Limited comparisons against airborne observations over India and surrounding oceans were generally in agreement within ±0.03. Global mean SSA estimated over land and ocean is 0.93 and 0.97, respectively. Seasonal and spatial distribution of SSA over various regions are also presented. Sensitivity analysis to various parameters indicate a mean uncertainty around ±0.044 and shows maximum sensitivity to changes in surface albedo. The global maps of SSA, thus derived with improved accuracy, provide important input to climate models for assessing the climatic impact of aerosols on regional and global scales.
Diamond, Michael S.; Gristey, Jake J.; Kay, Jennifer E.; Feingold, GrahamDiamond, M. S., J. J. Gristey, J. E. Kay, G. Feingold, 2022: Anthropogenic aerosol and cryosphere changes drive Earth’s strong but transient clear-sky hemispheric albedo asymmetry. Communications Earth & Environment, 3(1), 1-10. doi: 10.1038/s43247-022-00546-y. A striking feature of the Earth system is that the Northern and Southern Hemispheres reflect identical amounts of sunlight. This hemispheric albedo symmetry comprises two asymmetries: The Northern Hemisphere is more reflective in clear skies, whereas the Southern Hemisphere is cloudier. Here we show that the hemispheric reflection contrast from differences in continental coverage is offset by greater reflection from the Antarctic than the Arctic, allowing the net clear-sky asymmetry to be dominated by aerosol. Climate model simulations suggest that historical anthropogenic aerosol emissions drove a large increase in the clear-sky asymmetry that would reverse in future low-emission scenarios. High-emission scenarios also show decreasing asymmetry, instead driven by declines in Northern Hemisphere ice and snow cover. Strong clear-sky hemispheric albedo asymmetry is therefore a transient feature of Earth’s climate. If all-sky symmetry is maintained, compensating cloud changes would have uncertain but important implications for Earth’s energy balance and hydrological cycle. Cryospheric science; Climate and Earth system modelling; Atmospheric chemistry
Ding, Qinghua; Schweiger, Axel; Baxter, IanDing, Q., A. Schweiger, I. Baxter, 2022: Nudging Observed Winds in the Arctic to Quantify Associated Sea Ice Loss from 1979 to 2020. J. Climate, 35(20), 3197-3213. doi: 10.1175/JCLI-D-21-0893.1. Abstract Over the past decades, Arctic climate has exhibited significant changes characterized by strong pan-Arctic warming and a large-scale wind shift trending toward an anticyclonic anomaly centered over Greenland and the Arctic Ocean. Recent work has suggested that this wind change is able to warm the Arctic atmosphere and melt sea ice through dynamically driven warming, moistening, and ice drift effects. However, previous examination of this linkage lacks a capability to fully consider the complex nature of the sea ice response to the wind change. In this study, we perform a more rigorous test of this idea by using a coupled high-resolution modeling framework with observed winds nudged over the Arctic that allows for a comparison of these wind-induced effects with observations and simulated effects forced by anthropogenic forcing. Our nudging simulation can well capture observed variability of atmospheric temperature, sea ice, and the radiation balance during the Arctic summer and appears to simulate around 30% of Arctic warming and sea ice melting over the whole period (1979–2020) and more than 50% over the period 2000–12, which is the fastest Arctic warming decade in the satellite era. In particular, in the summer of 2020, a similar wind pattern reemerged to induce the second-lowest sea ice extent since 1979, suggesting that large-scale wind changes in the Arctic are essential in shaping Arctic climate on interannual and interdecadal time scales and may be critical to determine Arctic climate variability in the coming decades. Significance Statement This work conducts a set of new CESM1 nudging simulations to quantify the impact of the observed evolution of large-scale high-latitude atmospheric winds on Arctic climate variability over the past four decades. Variations in climate parameters, including sea ice, radiation, and atmospheric temperatures are well replicated in the model when observed winds are imposed in the Arctic. By investigating simulated sea ice melting processes in the simulation, we illustrate and estimate how large-scale winds in the Arctic help melt sea ice in summer. The nudging method has the potential to make Arctic climate attribution more tangible and to unravel the important physical processes underlying recent abrupt climate change in the Arctic.
Dodson, J. Brant; Robles, Marilé Colón; Rogerson, Tina M.; Taylor, Jessica E.Dodson, J. B., M. Robles, . Colón, T. M. Rogerson, J. E. Taylor, 2022: Do citizen science Intense Observation Periods increase data usability? A deep dive of the NASA GLOBE Clouds data set with satellite comparisons. Earth and Space Science, n/a(n/a), e2021EA002058. doi: 10.1029/2021EA002058. The Global Learning and Observations to Benefit the Environment (GLOBE) citizen science program has recently conducted a series of month-long intensive observation periods (IOPs), asking the public to submit daily reports on cloud and sky conditions from all regions of Earth. This provides a wealth of crowdsourced observations from the ground, which complements other conventional scientific cloud data. In addition, the GLOBE reports are matched in space and time with geostationary and low Earth orbit satellites, which allows for a straightforward comparison of cloud properties, and minimizes the biases associated with mismatched sampling between participants and satellites. The matched GLOBE dataset is used to calculate the mean observed cloud cover by atmospheric level both worldwide and by region. The overall magnitudes of cloud cover between the GLOBE participants and the matched satellites agree within 10%, which is notable given the distinctly different natures of the data sources. The mean vertical cloud profiles show GLOBE reporting more low-level clouds and fewer high-level clouds than satellites. The low cloud disagreement is likely related to satellites missing low clouds when high clouds block their view. Conversely, the high cloud disagreement is related primarily to cloud opacity, as satellites may miss some optically thin clouds. Monte Carlo testing shows the results to be robust, and the tripled amount of IOP data reduces uncertainty by half. These findings also highlight ways in which citizen science IOP data may be used to support scientific research while accounting for their unique properties. Monte Carlo; citizen science; cloud cover; global data set; satellite validation; vertical cloud structure
Doelling, David R.; Haney, Conor; Bhatt, Rajendra; Scarino, Benjamin; Gopalan, ArunDoelling, D. R., C. Haney, R. Bhatt, B. Scarino, A. Gopalan, 2022: Daily monitoring algorithms to detect geostationary imager visible radiance anomalies. Journal of Applied Remote Sensing, 16(1), 014502. doi: 10.1117/1.JRS.16.014502. The NASA Clouds and the Earth’s Radiant Energy System (CERES) project provides observed flux and cloud products for the climate science community. Geostationary satellite (GEO) imager measured clouds and broadband derived fluxes are incorporated in the CERES SYN1deg product to provide regional diurnal information in between Sun-synchronous Terra and Aqua CERES measurements. The recently launched GEO imagers with onboard calibration systems have active calibration teams that incrementally update the calibration in order to mitigate calibration drifts. However, short-term L1B radiance anomalies and calibration adjustment discontinuities may still exist in the record. To avoid any GEO cloud and flux artifacts in the CERES SYN1deg product, these calibration events must be addressed while scaling the GEO imagers to the Aqua-moderate resolution imaging spectroradiometer (MODIS) calibration reference. All-sky tropical ocean ray-matching (ATO-RM) and deep convective cloud invariant target (DCC-IT)-based monitoring algorithms are presented to detect calibration-driven daily anomalies in the GOES-16 Advanced Baseline Imager L1B visible (0.65 μm) radiance measurements. Sufficient daily ATO-RM sampling was obtained both by ray-matching GOES-16 with multiple MODIS and visible-infrared imaging radiometer suite imagers as well as by increasing the grid resolution. Optimized angular matching and outlier filtering were most effective in reducing the ATO-RM daily gain algorithm noise. The DCC-IT daily calibration algorithm utilized a larger domain and included more GOES-16 scan times. The DCC-IT daily gain uncertainty was reduced by normalizing the DCC regional reflectance on a regional, seasonal, and diurnal basis. The combination of ATO-RM and DCC-IT daily monitoring algorithms is shown to detect, with a high degree of confidence, daily GOES-16 L1B calibration-driven radiance anomalies >2.4 % , while keeping false positives at a minimum. Remarkably, the ATO-RM and DCC-IT daily gains are mostly within 0.5%. The ATO-RM and DCC-IT daily monitoring algorithms can be easily adapted to other GEO imagers and visible channels.
Duan, Wentao; Jin, ShuanggenDuan, W., S. Jin, 2022: An improved methodology for quantifying pixel-scale entrance pupil irradiance of a Moon-based Earth radiation observatory. ISPRS Journal of Photogrammetry and Remote Sensing, 183, 389-402. doi: 10.1016/j.isprsjprs.2021.11.019. The establishment of a Moon-based Earth Radiation Observatory (MERO) is expected to improve current Earth radiation budget observations. In terms of the MERO instrument design, the pixel-scale entrance pupil irradiance (EPI), which acts as the true input radiation to the MERO detector unit, is essential to judge the detector optimization and systematic parameter adjustment. The primary motivation of this study is to improve the pixel-scale EPI quantification quality by proposing a modified methodology. Evaluations indicated that the new pixel ground field of view (GFOV) positioning method would bring accuracy improvements of 7.79% and 3.84% for pixel-scale shortwave (SW) EPI and longwave (LW) EPI quantifications respectively; while the accuracy enhancements result from the newly proposed Earth top of atmosphere (TOA) radiant anisotropy method in this study are about 20.67% and 12.15% for the pixel-scale SW EPI and LW EPI estimations respectively. Following this modified methodology, an 18.6-year pixel-scale EPI variability prediction was accomplished to facilitate the MERO instrument design coping with change in future decades. This prediction fully considers the influences from the MERO-Earth geometry evolution, Earth TOA radiant anisotropic factor temporal change, the Earth TOA flux temporal variation and MERO location change. Results showed that the SW EPI would vary from approximately 3.32 × 10−6 to 2.16 × 10−4 W/m2 over the future 18.6-year period (March 2019 to November 2037); while the LW EPI would change between 4.43 × 10–6 and 4.91 × 10−4 W/m2. Earth radiation budget; Moon-based Earth Radiation Observatory; Pixel-scale entrance pupil irradiance
Erfani, Ehsan; Blossey, Peter; Wood, Robert; Mohrmann, Johannes; Doherty, Sarah J.; Wyant, Matthew; O, Kuan-TingErfani, E., P. Blossey, R. Wood, J. Mohrmann, S. J. Doherty, M. Wyant, K. O, 2022: Simulating Aerosol Lifecycle Impacts on the Subtropical Stratocumulus-to-Cumulus Transition Using Large-Eddy Simulations. Journal of Geophysical Research: Atmospheres, 127(21), e2022JD037258. doi: 10.1029/2022JD037258. Observed stratocumulus to cumulus transitions (SCTs) and their sensitivity to aerosols are studied using a large-eddy simulation (LES) model that simulates the aerosol lifecycle, including aerosol sources and sinks. To initialize, force, and evaluate the LES, we used a combination of reanalysis, satellite, and aircraft data from the 2015 Cloud System Evolution in the Trades field campaign over the Northeast Pacific. The simulations follow two Lagrangian trajectories from initially overcast stratocumulus (Sc) to the tropical shallow cumulus region near Hawaii. The first trajectory is characterized by an initially clean, well-mixed Sc-topped marine boundary layer (MBL), then continuous MBL deepening and precipitation onset followed by a clear SCT and a consistent reduction of aerosols that ultimately leads to an ultra-clean layer in the upper MBL. The second trajectory is characterized by an initially polluted and decoupled MBL, weak precipitation, and a late SCT. Overall, the LES simulates the observed general MBL features. Sensitivity studies with different aerosol initial and boundary conditions reveal aerosol-induced changes in the transition, and albedo changes are decomposed into the Twomey effect and adjustments of cloud liquid water path and cloud fraction. Impacts on precipitation play a key role in the sensitivity to aerosols: for the first case, runs with enhanced aerosols exhibit distinct changes in microphysics and macrophysics such as enhanced cloud droplet number concentration, reduced precipitation, and delayed SCT. Cloud adjustments are dominant in this case. For the second case, enhancing aerosols does not affect cloud macrophysical properties significantly, and the Twomey effect dominates. aerosols; clouds; marine boundary layer; large eddy simulations; stratocumulus to cumulus transition
Espinoza, Jhan-Carlo; Marengo, José Antonio; Schongart, Jochen; Jimenez, Juan CarlosEspinoza, J., J. Marengo, . Antonio, J. Schongart, J. C. Jimenez, 2022: The new historical flood of 2021 in the Amazon River compared to major floods of the 21st century: Atmospheric features in the context of the intensification of floods. Weather and Climate Extremes, 35, 100406. doi: 10.1016/j.wace.2021.100406. In June 2021 a new extreme flood was reported in the Amazon Basin, the largest hydrological system on Earth. During this event water level was above 29 m (the emergency threshold) for 91 days at Manaus station (Brazil), surpassing even the previous historical flood of 2012. Since the late 1990s, 9 extreme floods occurred, while only 8 events were reported from 1903 to 1998. Here we report that the 2021 flood is associated with an intensification of the atmospheric upward motion in the northern Amazonia (5°S-5°N), which is related to an intensification of the Walker circulations. This atmospheric feature is associated with an enhanced of deep convective clouds and intense rainfall over the northern Amazonia that produce positive anomalies of terrestrial water storage over northern Amazonia in the 2021 austral summer. The intensification of Walker circulation is associated with La Niña conditions that characterize the major floods observed in Amazonia during the 21st century (2009, 2012 and 2021). However, during the 2021 an intensification of the continental Hadley circulation is also observed. This feature produces simultaneous dry conditions over southern and southeastern Amazonia, where negative rainfall anomalies, low frequency of deep convective clouds and negative anomalies of terrestrial water storage are observed.
Fasullo, J. T.; Lamarque, Jean-Francois; Hannay, Cecile; Rosenbloom, Nan; Tilmes, Simone; DeRepentigny, Patricia; Jahn, Alexandra; Deser, ClaraFasullo, J. T., J. Lamarque, C. Hannay, N. Rosenbloom, S. Tilmes, P. DeRepentigny, A. Jahn, C. Deser, 2022: Spurious Late Historical-Era Warming in CESM2 Driven by Prescribed Biomass Burning Emissions. Geophysical Research Letters, 49(2), e2021GL097420. doi: 10.1029/2021GL097420. A spurious increase in the interannual variability of prescribed biomass burning (BB) emissions in the CMIP6 forcing database during the satellite era of wildfire monitoring (1997–2014) is found to lead to warming in the Northern Hemisphere extratropics in simulations with the Community Earth System Model version 2 (CESM2). Using targeted sensitivity experiments with the CESM2 in which prescribed BB emissions are homogenized and variability is removed, we show that the warming is specifically attributable to BB variability from 40° to 70°N and arises from a net thinning of the cloud field and an associated increase in absorbed solar radiation. Our results also demonstrate the potential pitfalls of introducing discontinuities in climate forcing data sets when trying to incorporate novel observations. global climate models; land/atmosphere interactions; aerosol/cloud interactions; global change
Feng, Chunjie; Zhang, Xiaotong; Xu, Jiawen; Yang, Shuyue; Guan, Shikang; Jia, Kun; Yao, YunjunFeng, C., X. Zhang, J. Xu, S. Yang, S. Guan, K. Jia, Y. Yao, 2022: Comprehensive assessment of global atmospheric downward longwave radiation in the state-of-the-art reanalysis using satellite and flux tower observations. Climate Dynamics. doi: 10.1007/s00382-022-06366-2. The atmospheric downward longwave radiation at the Earth’s surface (Ld) is an important parameter for investigating greenhouse effects and global climate changes. Reanalysis data have been widely applied to obtain surface radiation components. Since new generation reanalysis data have been released, a comprehensive evaluation of the Ld predictions from the latest reanalysis data using ground measurements is still necessary. In this study, the Ld estimates of four representative reanalysis data (CFSR, JRA-55, ERA5, and MERRA2) were evaluated using ground observations at 383 stations from the AmeriFlux, AsiaFlux, BSRN, Buoy, FLUXNET, and SURFEAD networks. The evaluation results manifested that the overall root mean square errors (mean bias errors) of daily mean Ld values over the global surface were 21.1 (− 1.8) W m−2, 22.4 (− 3.9) W m−2, 19.3 (− 3.6) W m−2, 25.2 (− 12.6) W m−2, and 20.5 (3.1) W m−2 for CFSR, JRA-55, ERA5, MERAA2, and CERES-SYN, respectively. Compared with the CERES-SYN satellite retrievals, the ERA5 (CFSR) daily mean Ld estimates had relatively smaller overall root mean square errors (mean bias errors) over the global land surface. Over the global ocean surface, the JRA-55 daily mean Ld estimates had comparable mean bias errors (MBEs) with CERES-SYN. After removing the MBEs, the best annual mean Ld estimate was 344.0 (± 3) W m−2 over the global surface of 2001 to 2020. The spatial distributions and long-term trends of Ld for the selected four reanalysis data and CERES-SYN were also investigated in this study. The comprehensive assessment of the Ld products from reanalysis data and satellite retrievals in this study would be helpful for climate change studies. Reanalysis; CERES-SYN; Surface downward longwave radiation; Ground observation
Feng, Huihui; Xiong, Jian; Ye, Shuchao; Zou, Bin; Wang, WeiFeng, H., J. Xiong, S. Ye, B. Zou, W. Wang, 2022: Vegetation change enhanced the positive global surface radiation budget. Advances in Space Research, 70(2), 324-335. doi: 10.1016/j.asr.2022.04.038. Surface radiation budget was an important variable for global climate and eco-environment change. Vegetation exerted significant influences on the budget by altering the surface thermal properties and land-atmospheric interactions, while the sign and magnitude remained unclear. With the aid of satellite observations, this study estimated the vegetation influences through a semi-physical approach. Methodologically, a physical model of the total surface radiation budget (Rnet) was firstly built. Then, the empirical regressions between vegetation with radiation albedo and thermal emissivity were adopted. Finally, the vegetation influences were estimated by measuring the response of budgets (Rsnet, Rlnet and subsequently Rnet) to vegetation perturbance. Our results demonstrated that the global Rnet presented a positive budget (73.20 W/m2) over the past two decades (2001–2020), which was dominated by the positive Rsnet (135.52 W/m2). In contrast, the Rlnet showed a negative value (−60.92 W/m2), which helped to mitigate the warming trend. Vegetation tended to enhance the positive surface radiation budgets. Overall, the vegetation influences on Rsnet, Rlnet and Rnet were 56.20 W/m2, −6.65 W/m2, and 50.29 W/m2, accounting for 41.47 %, 10.92 % and 68.70 % of the total budgets. Temporally, the vegetation influences showed increasing trends of 0.019 W/m2/yr (Rsnet), 0.007 W/m2/yr (Rlnet) and 0.031 W/m2/yr (Rnet). Physically, temporal variations of the vegetation influences were strongly affected by the interactions of atmospheric factors, particularly of the cloud, aerosol, and greenhouse gases (GHGs). Results of this study help to capture characteristics of surface radiation budgets and corresponding mechanism, which could support the climatic adaption and eco-environment management. Climate change; Satellite; Radiation budget; Globe; Vegetation change
Ferris, Laur; Gong, Donglai; Clayson, Carol Anne; Merrifield, Sophia; Shroyer, Emily L.; Smith, Madison; Laurent, Louis StFerris, L., D. Gong, C. A. Clayson, S. Merrifield, E. L. Shroyer, M. Smith, L. S. Laurent, 2022: Shear Turbulence in the High-Wind Southern Ocean Using Direct Measurements. J. Phys. Oceanogr., 52(10), 2325-2341. doi: 10.1175/JPO-D-21-0015.1. Abstract The ocean surface boundary layer is a gateway of energy transfer into the ocean. Wind-driven shear and meteorologically forced convection inject turbulent kinetic energy into the surface boundary layer, mixing the upper ocean and transforming its density structure. In the absence of direct observations or the capability to resolve subgrid-scale 3D turbulence in operational ocean models, the oceanography community relies on surface boundary layer similarity scalings (BLS) of shear and convective turbulence to represent this mixing. Despite their importance, near-surface mixing processes (and ubiquitous BLS representations of these processes) have been undersampled in high-energy forcing regimes such as the Southern Ocean. With the maturing of autonomous sampling platforms, there is now an opportunity to collect high-resolution spatial and temporal measurements in the full range of forcing conditions. Here, we characterize near-surface turbulence under strong wind forcing using the first long-duration glider microstructure survey of the Southern Ocean. We leverage these data to show that the measured turbulence is significantly higher than standard shear-convective BLS in the shallower parts of the surface boundary layer and lower than standard shear-convective BLS in the deeper parts of the surface boundary layer; the latter of which is not easily explained by present wave-effect literature. Consistent with the CBLAST (Coupled Boundary Layers and Air Sea Transfer) low winds experiment, this bias has the largest magnitude and spread in the shallowest 10% of the actively mixing layer under low-wind and breaking wave conditions, when relatively low levels of turbulent kinetic energy (TKE) in surface regime are easily biased by wave events. Significance Statement Wind blows across the ocean, turbulently mixing the water close to the surface and altering its properties. Without the ability to measure turbulence in remote locations, oceanographers use approximations called boundary layer scalings (BLS) to estimate the amount of turbulence caused by the wind. We compared turbulence measured by an underwater robot to turbulence estimated from wind speed to determine how well BLS performs in stormy places. We found that in both calm and stormy conditions, estimates are 10 times too large closest to the surface and 10 times too small deeper within the turbulently mixed surface ocean.
Fiddes, Sonya L.; Protat, Alain; Mallet, Marc D.; Alexander, Simon P.; Woodhouse, Matthew T.Fiddes, S. L., A. Protat, M. D. Mallet, S. P. Alexander, M. T. Woodhouse, 2022: Southern Ocean cloud and shortwave radiation biases in a nudged climate model simulation: does the model ever get it right?. Atmospheric Chemistry and Physics, 22(22), 14603-14630. doi: 10.5194/acp-22-14603-2022. The Southern Ocean radiative bias continues to impact climate and weather models, including the Australian Community Climate and Earth System Simulator (ACCESS). The radiative bias, characterised by too much shortwave radiation reaching the surface, is attributed to the incorrect simulation of cloud properties, including frequency and phase. To identify cloud regimes important to the Southern Ocean, we use k-means cloud histogram clustering, applied to a satellite product and then fitted to nudged simulations of the latest-generation ACCESS atmosphere model. We identify instances when the model correctly or incorrectly simulates the same cloud type as the satellite product for any point in time or space. We then evaluate the cloud and radiation biases in these instances. We find that when the ACCESS model correctly simulates the cloud type, cloud property and radiation biases of equivalent, or in some cases greater, magnitude remain compared to when cloud types are incorrectly simulated. Furthermore, we find that even when radiative biases appear small on average, cloud property biases, such as liquid or ice water paths or cloud fractions, remain large. Our results suggest that simply getting the right cloud type (or the cloud macrophysics) is not enough to reduce the Southern Ocean radiative bias. Furthermore, in instances where the radiative bias is small, it may be so for the wrong reasons. Considerable effort is still required to improve cloud microphysics, with a particular focus on cloud phase.
Francis, Diana; Fonseca, Ricardo; Nelli, Narendra; Bozkurt, Deniz; Picard, Ghislain; Guan, BinFrancis, D., R. Fonseca, N. Nelli, D. Bozkurt, G. Picard, B. Guan, 2022: Atmospheric rivers drive exceptional Saharan dust transport towards Europe. Atmospheric Research, 266, 105959. doi: 10.1016/j.atmosres.2021.105959. This study highlights the occurrence of atmospheric rivers (ARs) over northwest Africa towards Europe, which were accompanied by intense episodes of Saharan dust transport all the way to Scandinavia, in the winter season. Using a combination of observational and reanalysis data, we investigate two extreme dusty AR events in February 2021 and assess their impact on snow melt in the Alps. The warm, moist, and dusty air mass (spatially-averaged 2-meter temperature and water vapour mixing ratio anomalies of up to 8 K and 3 g kg−1, and aerosol optical depths and dust loadings of up to 0.85 and 11 g m−2, respectively) led to a 50% and 40% decrease in snow depth and surface albedo, respectively, in less than one month during the winter season. ARs over northwest Africa show increasing trends over the past 4 decades, with 78% of AR events associated with severe dust episodes over Europe. Dust aerosols; Atmospheric rivers; European Alps; Sahara Desert; Snow melting; Water vapour
Francis, Diana; Fonseca, Ricardo; Nelli, Narendra; Teixido, Oriol; Mohamed, Ruqaya; Perry, RichardFrancis, D., R. Fonseca, N. Nelli, O. Teixido, R. Mohamed, R. Perry, 2022: Increased Shamal winds and dust activity over the Arabian Peninsula during the COVID-19 lockdown period in 2020. Aeolian Research, 55, 100786. doi: 10.1016/j.aeolia.2022.100786. While anthropogenic pollutants have decreased during the lockdown imposed as an effort to contain the spread of the Coronavirus disease 2019 (COVID-19), changes in particulate matter (PM) do not necessarily exhibit the same tendency. This is the case for the eastern Arabian Peninsula, where in March–June 2020, and with respect to the same period in 2016–2019, a 30 % increase in PM concentration is observed. A stronger than normal nocturnal low-level jet and subtropical jet over parts of Saudi Arabia, in response to anomalous convection over the tropical Indian Ocean, promoted enhanced and more frequent episodes of Shamal winds over the Arabian Peninsula. Increased surface winds associated with the downward mixing of momentum to the surface fostered, in turn, dust lifting and increased PM concentrations. The stronger low-level winds also favoured long-range transport of aerosols, changing the PM values downstream. The competing effects of reduced anthropogenic and increased dust concentrations leave a small positive signal (20 W m−2 with respect to the baseline period, owing to a clearer environment and weaker winds. It is concluded that a reduction in anthropogenic emissions due to the lockdown does not necessarily go hand in hand with lower particulate matter concentrations. Therefore, emissions reduction strategies need to account for feedback effects in order to reach the planned long-term outcomes. Arabian Peninsula; Low-level jet; Particulate Matter; Rossby Wavetrain; Shamal Winds; Surface Radiation Budget
Francis, Diana; Nelli, Narendra; Fonseca, Ricardo; Weston, Michael; Flamant, Cyrille; Cherif, CharfeddineFrancis, D., N. Nelli, R. Fonseca, M. Weston, C. Flamant, C. Cherif, 2022: The dust load and radiative impact associated with the June 2020 historical Saharan dust storm. Atmospheric Environment, 268, 118808. doi: 10.1016/j.atmosenv.2021.118808. In June 2020, a major dust outbreak occurred in the Sahara that impacted the tropical Atlantic Ocean. In this study, the dust load and radiative forcing of the dust plumes on both the atmosphere and ocean surface is investigated by means of observations and modelling. We estimated dust loadings in excess of 8 Tg over the eastern tropical Atlantic, comparable to those observed over the desert during major Saharan dust storms. The dust induced an up to 1.1 K net warming of the ocean surface and a 1.8K warming of the air temperature (i.e., two to three times the respective climatological standard deviations), with a +14 W m−2 (∼28% of the mean value) increase in the surface net radiation flux at night. As the dust plumes extended all the way to the Caribbean, it is possible that this historical dust event helped fuel the record-breaking 2020 Atlantic hurricane season. Dust aerosols; Radiative forcing; WRF-Chem; Sahara; Tropical Atlantic
Gao, Zhibo; Zhao, Chuanfeng; Yan, Xiaodong; Guo, Yan; Liu, Sichang; Luo, Neng; Song, Shuaifeng; Zhao, ZihuiGao, Z., C. Zhao, X. Yan, Y. Guo, S. Liu, N. Luo, S. Song, Z. Zhao, 2022: Effects of cumulus and radiation parameterization on summer surface air temperature over eastern China. Climate Dynamics. doi: 10.1007/s00382-022-06601-w. Cloud-radiation process has a strong impact on surface air temperature (SAT). Using the Weather Research and Forecasting (WRF) model, this study investigates the effects of cumulus and radiation parameterization on SAT simulation over Eastern China (EC) during the summer season from 2001 to 2020. Four experiments are performed at a 30 km resolution using the combination of two cumulus schemes (KF and KF-CUP) and two radiation schemes (CAM and RRTMG). The results indicate that the KF and RRTMG scheme can produce warmer SAT than KF-CUP and CAM, respectively. By decomposing the differences in SAT simulation, it is found that KF and RRTMG have greater surface downward shortwave radiation (DSR), and the DSR shows a significant positive correlation with SAT in most parts of EC. Further analysis reveals that low-level cloud (LC) can strongly reflect the DSR, and the LC fraction (LCF) of KF and RRTMG is less than that of KF-CUP and CAM, respectively. The reason for this phenomenon is that the sub-grid cumulus heating rate is higher in KF and RRTMG, resulting in their higher air temperature (T) and greater differences between T and dew point (Td), which is not conducive to the formation of large-scale stratiform cloud and the increase of LCF. As a result, KF and RRTMG have more DSR and higher SAT than KF-CUP and CAM, respectively. The same mechanism can also explain the differences in the sub-seasonal cycle simulations between the four experiments. By comparing the SAT error in each subregion, this study can also provide a reference for future dynamic downscaling over the EC region.
García Pedreros, Julián Guillermo; Ospina-Noreña, Jesús EfrénGarcía Pedreros, J. G., J. E. Ospina-Noreña, 2022: Spatial distribution model of terrestrial radiation imbalance measured by means of orbiting radiometers. Remote Sensing Applications: Society and Environment, 28, 100857. doi: 10.1016/j.rsase.2022.100857. A spatial distribution model was applied to net radiation levels in central Colombia obtained from remote sensing data; this model was based on the use of spatial interpolation geostatistical techniques and consists of three essential phases: an evaluation of the quality of the spectral scenes, the application of spatial interpolation techniques and the statistical evaluation of the model. These procedures allowed a more accurate analysis of the variables that influence the spatial patterns of terrestrial radiation imbalance (T.R.I) in specific areas of the country. The input data used in this model are called FlashFlux Time Integrated and Spatially Averaged (TISA) and come from observations of the Terra and Aqua satellites of the CERES (Clouds and the Earths Radiant Energy System) and MODIS (Moderate-Resolution Imaging Spectroradiometer) projects. In summary, the way in which this research was carried out was initially with an evaluation of the image quality, to analyse the potential and statistical characteristics of the FlashFlux TISA data; subsequently, a kriging interpolation method was applied adapting the radiometric data for a correct analysis and the patterns of terrestrial radiation imbalance in the centre of the country were analysed, trying to explore variables that influence these spatial dynamics. Finally, an evaluation of the spatial distribution model of terrestrial radiation imbalance was established, where the virtues, relevance and limitations of the techniques used in it were validated. This research was able to implement statistical methods of spatial interpolation, specifically the Ordinary Kriging technique, allowing the modelling of the recent situation of terrestrial radiation imbalance in central Colombia, identifying some processes and factors that are closely related to this atmospheric phenomenon responsible for the effects of regional warming. Remote sensing; Kriging interpolation; Spatial modelling; Terrestrial radiation
Ghate, Virendra P.; Carlton, Annmarie G.; Surleta, Thomas; Burns, Alyssa MarieGhate, V. P., A. G. Carlton, T. Surleta, A. M. Burns, 2022: Changes in Aerosols, Meteorology, and Radiation in the Southeastern U.S. Warming Hole Region during 2000 to 2019. J. Climate, 35(23), 4125-4137. doi: 10.1175/JCLI-D-22-0073.1. Abstract Surface air temperatures in the southeastern United States that did not change from the climatological mean from 1900 to 2000 have increased since the year 2000. Analyzed herein are factors modulating the surface air temperatures in the region for a 20-yr period (2000–19) using space- and surface-based observations, and output from a reanalysis model. The 20-yr period is segregated into two decades, 2000–09 and 2010–19, corresponding to different tropospheric chemical regimes. Changes in seasonal and decadal averages are examined. The later decade experienced higher average surface air temperatures with significant warming during summer and fall seasons. Decadal and seasonal averages of cloud properties, column water vapor, rain rates, and top-of-atmosphere outgoing longwave radiation did not exhibit statistically significant differences between the two decades. The region experienced strong warm and moist advection during the winter months and very weak advection during the summer months. The later decade exhibited higher low-level moisture advection during the winter months than the earlier decade with insignificant changes in the temperature advection between the two decades. The later decade had significantly lower aerosol dry and liquid water mass during all seasons, along with lower aerosol optical depth, higher single scattering albedo, and lower top-of-the-atmosphere outgoing shortwave radiation during cloud-free conditions in the summer season. Collectively, these results suggest that changes in the aerosol direct radiative forcing are responsible for warming during summer months that experience weak advection and highlight seasonal differences in the temperature controlling mechanisms in the region.
Ghayas, Humaira; Radhakrishnan, S. R.; Sehgal, Vinay Kumar; Singh, SachchidanandGhayas, H., S. R. Radhakrishnan, V. K. Sehgal, S. Singh, 2022: Measurement and comparison of photosynthetically active radiation by different methods at Delhi. Theoretical and Applied Climatology, 150(3), 1559-1571. doi: 10.1007/s00704-022-04252-9. Photosynthetically active radiation (PAR) received at the earth surface is the primary driver of plant growth and biomass production. The absence of a dedicated sensor network for regular measurements of PAR over the Indian region poses a challenge to the crop modelers and the decision makers. In the absence of any long-term study of PAR from this region, the present study from Delhi provides 4 years (2013–2016) of dedicated PAR measurements and also compares it with three other different methods of PAR estimation. PAR has been measured at the surface using Kipp and Zonen PQS1 PAR sensor and the data has been compared with the remotely sensed CERES-derived all-sky PAR values. It was also compared with the PAR estimated by fractional method using shortwave (SW) flux measured by pyranometer and the ratio of PAR/SW fraction using long-term satellite data for Delhi. It was further compared with the TUV radiative transfer model–derived PAR on clear-sky days. The daily mean PAR observed at Delhi is in the range 7.9 to 185.3 Wm−2 (average 94.5 ± 1.1 Wm−2) which nearly matched with the CERES-derived PAR in the range 10.8 to 144.3 Wm−2 (average 89.4 ± 0.8 Wm−2) and PAR derived by fractional method range 8.9 to 187 Wm−2 (with average 88.1 ± 0.8 Wm−2). The TUV model–estimated PAR on clear-sky days was found in the range 39.1–154.9 Wm−2 (average 96.8 ± 1.4 Wm−2) which showed a strong correlation of 0.82 with the observed PAR values on concurrent days. PAR estimated by all the three methods showed a good correlation with the observations (> 0.80). It may be concluded that in the absence of a regular PAR measurements, any of the three above methods of PAR estimation can give fairy accurate value at a point but CERES gives added advantage of providing PAR over large spatial area in the region. CERES; PAR; Radiation; TUV model
Giraldo, Jorge A.; del Valle, Jorge I.; González-Caro, Sebastián; Sierra, Carlos A.Giraldo, J. A., J. I. del Valle, S. González-Caro, C. A. Sierra, 2022: Intra-annual isotope variations in tree rings reveal growth rhythms within the least rainy season of an ever-wet tropical forest. Trees, 36(3), 1039-1052. doi: 10.1007/s00468-022-02271-7. Isotope variation (δ18O) in wood suggests new insights on growth rhythms in trees growing in tropical forest with extremely high precipitation, without seasonal droughts or flooding. Biogeographical Chocó region; C isotopes; Dendrochronology; O isotopes; Tropical trees
Golaz, Jean-Christophe; Van Roekel, Luke P.; Zheng, Xue; Roberts, Andrew F.; Wolfe, Jonathan D.; Lin, Wuyin; Bradley, Andrew M.; Tang, Qi; Maltrud, Mathew E.; Forsyth, Ryan M.; Zhang, Chengzhu; Zhou, Tian; Zhang, Kai; Zender, Charles S.; Wu, Mingxuan; Wang, Hailong; Turner, Adrian K.; Singh, Balwinder; Richter, Jadwiga H.; Qin, Yi; Petersen, Mark R.; Mametjanov, Azamat; Ma, Po-Lun; Larson, Vincent E.; Krishna, Jayesh; Keen, Noel D.; Jeffery, Nicole; Hunke, Elizabeth C.; Hannah, Walter M.; Guba, Oksana; Griffin, Brian M.; Feng, Yan; Engwirda, Darren; Di Vittorio, Alan V.; Dang, Cheng; Conlon, LeAnn M.; Chen, Chih-Chieh-Jack; Brunke, Michael A.; Bisht, Gautam; Benedict, James J.; Asay-Davis, Xylar S.; Zhang, Yuying; Zhang, Meng; Zeng, Xubin; Xie, Shaocheng; Wolfram, Phillip J.; Vo, Tom; Veneziani, Milena; Tesfa, Teklu K.; Sreepathi, Sarat; Salinger, Andrew G.; Reeves Eyre, J. E. Jack; Prather, Michael J.; Mahajan, Salil; Li, Qing; Jones, Philip W.; Jacob, Robert L.; Huebler, Gunther W.; Huang, Xianglei; Hillman, Benjamin R.; Harrop, Bryce E.; Foucar, James G.; Fang, Yilin; Comeau, Darin S.; Caldwell, Peter M.; Bartoletti, Tony; Balaguru, Karthik; Taylor, Mark A.; McCoy, Renata B.; Leung, L. Ruby; Bader, David C.Golaz, J., L. P. Van Roekel, X. Zheng, A. F. Roberts, J. D. Wolfe, W. Lin, A. M. Bradley, Q. Tang, M. E. Maltrud, R. M. Forsyth, C. Zhang, T. Zhou, K. Zhang, C. S. Zender, M. Wu, H. Wang, A. K. Turner, B. Singh, J. H. Richter, Y. Qin, M. R. Petersen, A. Mametjanov, P. Ma, V. E. Larson, J. Krishna, N. D. Keen, N. Jeffery, E. C. Hunke, W. M. Hannah, O. Guba, B. M. Griffin, Y. Feng, D. Engwirda, A. V. Di Vittorio, C. Dang, L. M. Conlon, C. Chen, M. A. Brunke, G. Bisht, J. J. Benedict, X. S. Asay-Davis, Y. Zhang, M. Zhang, X. Zeng, S. Xie, P. J. Wolfram, T. Vo, M. Veneziani, T. K. Tesfa, S. Sreepathi, A. G. Salinger, J. E. J. Reeves Eyre, M. J. Prather, S. Mahajan, Q. Li, P. W. Jones, R. L. Jacob, G. W. Huebler, X. Huang, B. R. Hillman, B. E. Harrop, J. G. Foucar, Y. Fang, D. S. Comeau, P. M. Caldwell, T. Bartoletti, K. Balaguru, M. A. Taylor, R. B. McCoy, L. R. Leung, D. C. Bader, 2022: The DOE E3SM Model Version 2: Overview of the Physical Model and Initial Model Evaluation. Journal of Advances in Modeling Earth Systems, 14(12), e2022MS003156. doi: 10.1029/2022MS003156. This work documents version two of the Department of Energy's Energy Exascale Earth System Model (E3SM). E3SMv2 is a significant evolution from its predecessor E3SMv1, resulting in a model that is nearly twice as fast and with a simulated climate that is improved in many metrics. We describe the physical climate model in its lower horizontal resolution configuration consisting of 110 km atmosphere, 165 km land, 0.5° river routing model, and an ocean and sea ice with mesh spacing varying between 60 km in the mid-latitudes and 30 km at the equator and poles. The model performance is evaluated with Coupled Model Intercomparison Project Phase 6 Diagnosis, Evaluation, and Characterization of Klima simulations augmented with historical simulations as well as simulations to evaluate impacts of different forcing agents. The simulated climate has many realistic features of the climate system, with notable improvements in clouds and precipitation compared to E3SMv1. E3SMv1 suffered from an excessively high equilibrium climate sensitivity (ECS) of 5.3 K. In E3SMv2, ECS is reduced to 4.0 K which is now within the plausible range based on a recent World Climate Research Program assessment. However, a number of important biases remain including a weak Atlantic Meridional Overturning Circulation, deficiencies in the characteristics and spectral distribution of tropical atmospheric variability, and a significant underestimation of the observed warming in the second half of the historical period. An analysis of single-forcing simulations indicates that correcting the historical temperature bias would require a substantial reduction in the magnitude of the aerosol-related forcing. climate modeling; DOE E3SM
González-Bárcena, David; Bermejo-Ballesteros, Juan; Pérez-Grande, Isabel; Sanz-Andrés, ÁngelGonzález-Bárcena, D., J. Bermejo-Ballesteros, I. Pérez-Grande, Á. Sanz-Andrés, 2022: Selection of time-dependent worst-case thermal environmental conditions for Low Earth Orbit spacecrafts. Advances in Space Research, 70(7), 1847-1868. doi: 10.1016/j.asr.2022.06.060. When facing the thermal analysis of a Low Earth Orbit satellite, selecting the worst-case orbit where the minimum and maximum temperatures are reached is essential for ensuring the success of the mission. Typical orbits have a non-constant Solar Beta Angle throughout the year providing a wide range of orbits with different heat loads and eclipses. It is possible to focus the analysis on a single orbit configuration by a rough analysis using a simple model. In order to achieve this, every potential orbit with their corresponding thermal environmental parameters must be analysed based on real data. The direct solar radiation, the albedo and the Earth Outgoing Longwave Radiation (OLR) characterize the thermal environment to be taken into account. However, their values have a wide variability which depend on many parameters. Based on the characteristics of the orbit and the system thermo-optical properties and characteristic time, it is possible to obtain particularized profiles of albedo and OLR that would lead the system to its maximum and minimum temperatures. The conventional criteria, which is studied here in depth, provides two constant values of albedo and OLR as the hot and cold worst-cases. This is suitable for massive system or cases in which the characteristics times of the system are high. For lighter elements or low characteristic times, temperatures throughout the orbit deviate considerably from the real behaviour. In contrast, the methodology here proposed provides a time-dependant profile that allows for the determination of a system temperature response closer to the real one, together with the potential minimum and maximum temperatures of the orbit, in order to optimize the design and avoid the oversizing. OLR; Albedo; Thermal environment; LEO; Thermal analysis; Worst-case
Guo, Huan; Ming, Yi; Fan, Songmiao; Wittenberg, Andrew T.; Zhang, Rong; Zhao, Ming; Zhou, LinjiongGuo, H., Y. Ming, S. Fan, A. T. Wittenberg, R. Zhang, M. Zhao, L. Zhou, 2022: Performance of Two-Moment Stratiform Microphysics With Prognostic Precipitation in GFDL's CM4.0. Journal of Advances in Modeling Earth Systems, 14(12), e2022MS003111. doi: 10.1029/2022MS003111. We describe the model performance of a new global coupled climate model configuration, CM4-MG2. Beginning with the Geophysical Fluid Dynamics Laboratory's fourth-generation physical climate model (CM4.0), we incorporate a two-moment Morrison-Gettelman bulk stratiform microphysics scheme with prognostic precipitation (MG2), and a mineral dust and temperature-dependent cloud ice nucleation scheme. We then conduct and analyze a set of fully coupled atmosphere-ocean-land-sea ice simulations, following Coupled Model Intercomparison Project Phase 6 protocols. CM4-MG2 generally captures CM4.0's baseline simulation characteristics, but with several improvements, including better marine stratocumulus clouds off the west coasts of Africa and North and South America, a reduced bias toward “double” Intertropical Convergence Zones south of the equator, and a stronger Madden-Julian Oscillation (MJO). Some degraded features are also identified, including excessive Arctic sea ice extent and a stronger-than-observed El Nio-Southern Oscillation. Compared to CM4.0, the climate sensitivity is reduced by about 10% in CM4-MG2. GCM; coupled; GFDL; CM4.0; MG2
Haghighatnasab, Mahnoosh; Kretzschmar, Jan; Block, Karoline; Quaas, JohannesHaghighatnasab, M., J. Kretzschmar, K. Block, J. Quaas, 2022: Impact of Holuhraun volcano aerosols on clouds in cloud-system-resolving simulations. Atmospheric Chemistry and Physics, 22(13), 8457-8472. doi: 10.5194/acp-22-8457-2022. Abstract. Increased anthropogenic aerosols result in an enhancement in cloud droplet number concentration (Nd), which consequently modifies the cloud and precipitation process. It is unclear how exactly the cloud liquid water path (LWP) and cloud fraction respond to aerosol perturbations. A volcanic eruption may help to better understand and quantify the cloud response to external perturbations, with a focus on the short-term cloud adjustments. The goal of the present study is to understand and quantify the response of clouds to a selected volcanic eruption and to thereby advance the fundamental understanding of the cloud response to external forcing. In this study we used the ICON (ICOsahedral Non-hydrostatic) model in its numerical weather prediction setup at a cloud-system-resolving resolution of 2.5 km horizontally, to simulate the region around the Holuhraun volcano for 1 week (1–7 September 2014). A pair of simulations, with and without the volcanic aerosol plume, allowed us to assess the simulated effective radiative forcing and its mechanisms, as well as its impact on adjustments of LWP and cloud fraction to the perturbations of Nd. In comparison to MODIS (Moderate Resolution Imaging Spectroradiometer) satellite retrievals, a clear enhancement of Nd due to the volcanic aerosol is detected and attributed. In contrast, no changes in either LWP or cloud fraction could be attributed. The on average almost unchanged LWP is a result of some LWP enhancement for thick clouds and a decrease for thin clouds.
Ham, Seung-Hee; Kato, Seiji; Rose, Fred G.; Sun-Mack, Sunny; Chen, Yan; Miller, Walter F.; Scott, Ryan C.Ham, S., S. Kato, F. G. Rose, S. Sun-Mack, Y. Chen, W. F. Miller, R. C. Scott, 2022: Combining Cloud Properties from CALIPSO, CloudSat, and MODIS for Top-of-Atmosphere (TOA) Shortwave Broadband Irradiance Computations: Impact of Cloud Vertical Profiles. J. Appl. Meteor. Climatol., 61(10), 1449-1471. doi: 10.1175/JAMC-D-21-0260.1. Abstract Cloud vertical profile measurements from the CALIPSO and CloudSat active sensors are used to improve top-of-atmosphere (TOA) shortwave (SW) broadband (BB) irradiance computations. The active sensor measurements, which occasionally miss parts of the cloud columns because of the full attenuation of sensor signals, surface clutter, or insensitivity to a certain range of cloud particle sizes, are adjusted using column-integrated cloud optical depth derived from the passive MODIS sensor. Specifically, we consider two steps in generating cloud profiles from multiple sensors for irradiance computations. First, cloud extinction coefficient and cloud effective radius (CER) profiles are merged using available active and passive measurements. Second, the merged cloud extinction profiles are constrained by the MODIS visible scaled cloud optical depth, defined as a visible cloud optical depth multiplied by (1 − asymmetry parameter), to compensate for missing cloud parts by active sensors. It is shown that the multisensor-combined cloud profiles significantly reduce positive TOA SW BB biases, relative to those with MODIS-derived cloud properties only. The improvement is more pronounced for optically thick clouds, where MODIS ice CER is largely underestimated. Within the SW BB (0.18–4 μm), the 1.04–1.90-μm spectral region is mainly affected by the CER, where both the cloud absorption and solar incoming irradiance are considerable. Significance Statement The purpose of this study is to improve shortwave irradiance computations at the top of the atmosphere by using combined cloud properties from active and passive sensor measurements. Relative to the simulation results with passive sensor cloud measurements only, the combined cloud profiles provide more accurate shortwave simulation results. This is achieved by more realistic profiles of cloud extinction coefficient and cloud particle effective radius. The benefit is pronounced for optically thick clouds composed of large ice particles.
Hartmann, Dennis L.; Dygert, Brittany D.Hartmann, D. L., B. D. Dygert, 2022: Global Radiative Convective Equilibrium With a Slab Ocean: SST Contrast, Sensitivity and Circulation. Journal of Geophysical Research: Atmospheres, 127(12), e2021JD036400. doi: 10.1029/2021JD036400. Warming experiments with a uniformly insolated, non-rotating climate model with a slab ocean are conducted by increasing the solar irradiance. As the global mean surface temperature is varied across the range from 289 to 319K, the sea surface temperature (SST) contrast at first declines, then increases then declines again. Increasing SST contrast with global warming is associated with reduced climate sensitivity, while decreasing SST contrast is associated with enhanced climate sensitivity. The changing SST contrast and climate sensitivity are both related fundamentally to the effect of water vapor on clear-sky radiative cooling. The clouds in the convective region are always more reflective than those in the subsiding region and so always act to reduce the SST contrast. At lower temperatures between 289 and 297 K the shortwave suppression of SST contrast increases faster than the longwave enhancement of SST contrast. At warmer temperatures between 297 and 309 K the longwave enhancement of SST contrast with warming is stronger than the shortwave suppression of SST contrast, so that the SST contrast increases. Above 309 K the greenhouse effect in the subsiding region begins to grow, the SST contrast declines and the climate sensitivity increases. The transitions at 297 and 309 K can be related to the increasing vapor pressure path with warming. The mass circulation rate between warm and cool regions consists of shallow and deep cells. Both cells increase in strength with SST contrast. The lower cell remains connected to the surface, while the upper cell rises to maintain a roughly constant temperature. climate change; climate model; climate feedbacks
Heidinger, Andrew K.; Foster, Michael J.; Knapp, Kenneth R.; Schmit, Timothy J.Heidinger, A. K., M. J. Foster, K. R. Knapp, T. J. Schmit, 2022: Using GOES-R ABI Full-Disk Reflectance as a Calibration Source for the GOES Imager Visible Channels. Remote Sensing, 14(15), 3630. doi: 10.3390/rs14153630. The availability of onboard calibration for solar reflectance channels on recently launched advanced geostationary imagers provides an opportunity to revisit the calibration of the visible channels on past geostationary imagers, which lacked onboard calibration systems. This study used the data from the Advanced Baseline Imager (ABI) on GOES-16 and GOES-17 to calibrate the visible channels on the GOES-IP (GOES-8, -9, -10, -11, -12, -13, and -15) sensors (1994–2021). The visible channels are dominant sources of information for many of the essential climate variables from these sensors. The technique developed uses the stability of the integrated full-disk reflectance to define a calibration target that is applied to past sensors to generate new calibration equations. These equations are found to be stable and agree well with other established techniques. Given the lack of assumptions and ease of application, this technique offers a new calibration method that can be used to complement existing techniques used by the operational space agencies with the GSICS Project. In addition, its simplicity allows for its application to data that existed prior to many of the reference data employed in current calibration methods. climate; calibration; GOES
Herrington, Adam R.; Lauritzen, Peter H.; Lofverstrom, Marcus; Lipscomb, William H.; Gettelman, Andrew; Taylor, Mark A.Herrington, A. R., P. H. Lauritzen, M. Lofverstrom, W. H. Lipscomb, A. Gettelman, M. A. Taylor, 2022: Impact of grids and dynamical cores in CESM2.2 on the surface mass balance of the Greenland Ice Sheet. Journal of Advances in Modeling Earth Systems, n/a(n/a), e2022MS003192. doi: 10.1029/2022MS003192. Six different configurations, a mixture of grids and atmospheric dynamical cores available in the Community Earth System Model, version 2.2 (CESM2.2), are evaluated for their skill in representing the climate of the Arctic and the surface mass balance of the Greenland Ice Sheet (GrIS). The finite-volume dynamical core uses structured, latitude-longitude grids, whereas the spectral-element dynamical core is built on unstructured meshes, permitting grid flexibility such as quasi-uniform grid spacing globally. The 1° − 2° latitude-longitude and quasi-uniform unstructured grids systematically overestimate both accumulation and ablation over the GrIS. Of these 1° − 2° grids, the latitude-longitude grids outperform the quasi-uniform unstructured grids because they have more degrees of freedom to represent the GrIS. Two Arctic-refined meshes, with 1/4° and 1/8° refinement over Greenland, were developed for the spectral-element dynamical core and are documented here as newly supported configurations in CESM2.2. The Arctic meshes substantially improve the simulated clouds and precipitation rates in the Arctic. Over Greenland, these meshes skillfully represent accumulation and ablation processes, leading to a more realistic GrIS surface mass balance. As CESM is in the process of transitioning away from conventional latitude-longitude grids, these new Arctic-refined meshes improve the representation of polar processes in CESM by recovering resolution lost in the transition to quasi-uniform grids, albeit at increased computational cost.
Hu, Zhiyuan; Jin, Qinjian; Ma, Yuanyuan; Ji, Zhenming; Zhu, Xian; Dong, WenjieHu, Z., Q. Jin, Y. Ma, Z. Ji, X. Zhu, W. Dong, 2022: How Does COVID-19 Lockdown Impact Air Quality in India?. Remote Sensing, 14(8), 1869. doi: 10.3390/rs14081869. Air pollution is a severe environmental problem in the Indian subcontinent. Largely caused by the rapid growth of the population, industrialization, and urbanization, air pollution can adversely affect human health and environment. To mitigate such adverse impacts, the Indian government launched the National Clean Air Programme (NCAP) in January 2019. Meanwhile, the unexpected city-lockdown due to the COVID-19 pandemic in March 2020 in India greatly reduced human activities and thus anthropogenic emissions of gaseous and aerosol pollutants. The NCAP and the lockdown could provide an ideal field experiment for quantifying the extent to which various levels of human activity reduction impact air quality in the Indian subcontinent. Here, we study the improvement in air quality due to COVID-19 and the NCAP in the India subcontinent by employing multiple satellite products and surface observations. Satellite data shows significant reductions in nitrogen dioxide (NO2) by 17% and aerosol optical depth (AOD) by 20% during the 2020 lockdown with reference to the mean levels between 2005–2019. No persistent reduction in NO2 nor AOD is detectable during the NCAP period (2019). Surface observations show consistent reductions in PM2.5 and NO2 during the 2020 lockdown in seven cities across the Indian subcontinent, except Mumbai in Central India. The increase in relative humidity and the decrease in the planetary boundary layer also play an important role in influencing air quality during the 2020 lockdown. With the decrease in aerosols during the lockdown, net radiation fluxes show positive anomalies at the surface and negative anomalies at the top of the atmosphere over most parts of the Indian subcontinent. The results of this study could provide valuable information for policymakers in South Asia to adjust the scientific measures proposed in the NCAP for efficient air pollution mitigation. COVID-19; air quality; AOD; India subcontinent; NO2; PM2.5
Huang, Xianglei; Chen, Xiuhong; Fan, Chongxing; Kato, Seiji; Loeb, Norman; Bosilovich, Michael; Ham, Seung-Hee; Rose, Fred G.; Strow, Lawrence L.Huang, X., X. Chen, C. Fan, S. Kato, N. Loeb, M. Bosilovich, S. Ham, F. G. Rose, L. L. Strow, 2022: A Synopsis of AIRS Global-Mean Clear-Sky Radiance Trends From 2003 to 2020. Journal of Geophysical Research: Atmospheres, 127(24), e2022JD037598. doi: 10.1029/2022JD037598. Atmospheric Infrared Sounder (AIRS) aboard the National Aeronautics and Space Administration (NASA) Aqua satellite has been operating since September 2002. Its information content, superb instrument performance, and dense sampling pattern make the AIRS radiances an invaluable data set for climate studies. The trends of global-mean, nadir-view, clear-sky AIRS radiances from 2003 to 2020 are studied here, together with the counterparts of synthetic radiances based on two reanalyzes, European Centre for Medium-Range Weather Forecasts Reanalysis V5 (ECMWF ERA5) and NASA Goddard Earth Observing System V5.4.1 (GEOS-5.4.1; a reanalysis product without assimilation of hyperspectral radiances such as AIRS). The AIRS observation shows statistically significant negative trends in most of its CO2 channels, positive but non-significant trends in the channels over the window regions, and statistically significant positive trends in some of its H2O channels. The best agreements between observed and simulated radiance trends are seen over the CO2 tropospheric channels, while the observed and simulated trends over the CO2 stratospheric channels are opposite. ERA5 results largely agree with the AIRS observation over the H2O channels. The comparison in the H2O channels helps reveal a data continuity issue in the GEOS-5.4.1. Contributions from individual variables to the radiance trends are also assessed by performing separate simulations. This study provides the first synopsis of the global-mean trend of AIRS radiances over all its thermal-IR channels. reanalysis; infrared radiation; linear trend; spectral radiance
Huang, Yiyi; Taylor, Patrick C.; Rose, Fred G.; Rutan, David A.; Shupe, Matthew D.; Webster, Melinda A.; Smith, Madison M.Huang, Y., P. C. Taylor, F. G. Rose, D. A. Rutan, M. D. Shupe, M. A. Webster, M. M. Smith, 2022: Toward a more realistic representation of surface albedo in NASA CERES-derived surface radiative fluxes: A comparison with the MOSAiC field campaign: Comparison of CERES and MOSAiC surface radiation fluxes. Elementa: Science of the Anthropocene, 10(1), 00013. doi: 10.1525/elementa.2022.00013. Accurate multidecadal radiative flux records are vital to understand Arctic amplification and constrain climate model uncertainties. Uncertainty in the NASA Clouds and the Earth’s Radiant Energy System (CERES)-derived irradiances is larger over sea ice than any other surface type and comes from several sources. The year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition in the central Arctic provides a rare opportunity to explore uncertainty in CERES-derived radiative fluxes. First, a systematic and statistically robust assessment of surface shortwave and longwave fluxes was conducted using in situ measurements from MOSAiC flux stations. The CERES Synoptic 1degree (SYN1deg) product overestimates the downwelling shortwave flux by +11.40 Wm–2 and underestimates the upwelling shortwave flux by –15.70 Wm–2 and downwelling longwave fluxes by –12.58 Wm–2 at the surface during summer. In addition, large differences are found in the upwelling longwave flux when the surface approaches the melting point (approximately 0°C). The biases in downwelling shortwave and longwave fluxes suggest that the atmosphere represented in CERES is too optically thin. The large negative bias in upwelling shortwave flux can be attributed in large part to lower surface albedo (–0.15) in satellite footprint relative to surface sensors. Additionally, the results show that the spectral surface albedo used in SYN1deg overestimates albedo in visible and mid-infrared bands. A series of radiative transfer model perturbation experiments are performed to quantify the factors contributing to the differences. The CERES-MOSAiC broadband albedo differences (approximately 20 Wm–2) explain a larger portion of the upwelling shortwave flux difference than the spectral albedo shape differences (approximately 3 Wm–2). In addition, the differences between perturbation experiments using hourly and monthly MOSAiC surface albedo suggest that approximately 25% of the sea ice surface albedo variability is explained by factors not correlated with daily sea ice concentration variability. Biases in net shortwave and longwave flux can be reduced to less than half by adjusting both albedo and cloud inputs toward observed values. The results indicate that improvements in the surface albedo and cloud data would substantially reduce the uncertainty in the Arctic surface radiation budget derived from CERES data products.
Ito, Masato; Masunaga, HirohikoIto, M., H. Masunaga, 2022: Process-level Assessment of the Iris Effect over Tropical Oceans. Geophysical Research Letters, n/a(n/a), e2022GL097997. doi: 10.1029/2022GL097997. The iris hypothesis suggests a cloud feedback mechanism that a reduction in the tropical anvil cloud fraction (CF) in a warmer climate may act to mitigate the warming by enhanced outgoing longwave radiation. Two different physical processes, one involving precipitation efficiency and the other focusing on upper-tropospheric stability, have been argued in the literature to be responsible for the iris effect. In this study, A-Train observations and reanalysis data are analyzed to assess these two processes. Major findings are as follows: (1) the anvil CF changes evidently with upper-tropospheric stability as expected from the stability iris theory, (2) precipitation efficiency is unlikely to have control on the anvil CF but is related to mid- and low-level CFs, and (3) the day and nighttime cloud radiative effects are expected to largely cancel out when integrated over a diurnal cycle, suggesting a neutral cloud feedback.
J.-L. F, Li; Xu, Kuan-Man; Lee, Wei-Liang; Jiang, J. H.; Fetzer, Eric; Stephens, Graeme; Wang, Yi-Hui; Yu, Jia-YuhJ.-L. F, L., K. Xu, W. Lee, J. H. Jiang, E. Fetzer, G. Stephens, Y. Wang, J. Yu, 2022: Exploring Radiation Biases over the Tropical and Subtropical Oceans Based on Treatments of Frozen Hydrometeor Radiative Properties in CMIP6 Models. Journal of Geophysical Research: Atmospheres, n/a(n/a), e2021JD035976. doi: 10.1029/2021JD035976. To explore the impacts of hydrometeor radiative effects over subtropical and tropical Pacific and Atlantic Oceans, we quantify the mean radiation biases in historical climate simulations based on how frozen hydrometeors radiative properties are calculated in CMIP6 models. CMIP6 models are divided with cloud ice only (NOS), with combined (SON1), and with separate treatments (SON2) of cloud ice and falling ice (snow) radiative properties. Over the deep convective regions, NOS models overestimate outgoing longwave radiation (RLUT) and surface shortwave irradiance (RSDS), while underestimate top-of-atmosphere reflected shortwave radiation (RSUT). SON2 models reduce these biases by 4—14 W m-2. However, this improvement is not seen in SON1 against NOS. Spatially-averaged absolute biases in radiative fluxes for SON1 models are larger than those of NOS, suggesting that the SON1 approach of falling ice radiative effects may not produce the expected hydrometeor-radiation interactions. Over the south Pacific trade-wind regions, both SON2 and SON1 show similar improvements in RLUT, RSUT and RSDS with positive absolute bias differences up to 20 W m-2 against NOS, leading to improvement of CMIP6 over CMIP5 ensembles. The seasonal cycles are consistent with the annual means over these two regions except with larger differences between subsets of models during January–May than during June–December. In general, improvement from CMIP5 to CMIP6 due to more participating SON2 models is limited because of offset by SON1. These results suggest that a separate treatment of frozen-hydrometeor radiative properties may be critical for reducing the spread of CMIP models. CMIP6; GCM; cloud radiations; frozen hydrometeors; tropical oceans
Jahani, Babak; Andersen, Hendrik; Calbó, Josep; González, Josep-Abel; Cermak, JanJahani, B., H. Andersen, J. Calbó, J. González, J. Cermak, 2022: Longwave radiative effect of the cloud–aerosol transition zone based on CERES observations. Atmospheric Chemistry and Physics, 22(2), 1483-1494. doi: 10.5194/acp-22-1483-2022. Abstract. This study presents an approach for the quantification of cloud–aerosol transition-zone broadband longwave radiative effects at the top of the atmosphere (TOA) during daytime over the ocean, based on satellite observations and radiative transfer simulation. Specifically, we used several products from MODIS (MODerate Resolution Imaging Spectroradiometer) and CERES (Clouds and the Earth's Radiant Energy System) sensors for the identification and selection of CERES footprints with a horizontally homogeneous transition-zone and clear-sky conditions. For the selected transition-zone footprints, radiative effect was calculated as the difference between the instantaneous CERES TOA upwelling broadband longwave radiance observations and corresponding clear-sky radiance simulations. The clear-sky radiances were simulated using the Santa Barbara DISORT (DIScrete Ordinates Radiative Transfer program for a multi-Layered plane-parallel medium) Atmospheric Radiative Transfer model fed by the hourly ERA5 reanalysis (fifth generation ECMWF ReAnalysis) atmospheric and surface data. The CERES radiance observations corresponding to the clear-sky footprints detected were also used for validating the simulated clear-sky radiances. We tested this approach using the radiative measurements made by the MODIS and CERES instruments on board the Aqua platform over the southeastern Atlantic Ocean during August 2010. For the studied period and domain, transition-zone radiative effect (given in flux units) is on average equal to 8.0 ± 3.7 W m−2 (heating effect; median: 5.4 W m−2), although cases with radiative effects as large as 50 W m−2 were found.
Jenkins, Stuart; Povey, Adam; Gettelman, Andrew; Grainger, Roy; Stier, Philip; Allen, MylesJenkins, S., A. Povey, A. Gettelman, R. Grainger, P. Stier, M. Allen, 2022: Is Anthropogenic Global Warming Accelerating?. J. Climate, 35(24), 4273-4290. doi: 10.1175/JCLI-D-22-0081.1. Abstract Estimates of the anthropogenic effective radiative forcing (ERF) trend have increased by 50% since 2000 (from +0.4 W m−2 decade−1 in 2000–09 to +0.6 W m−2 decade−1 in 2010–19), the majority of which is driven by changes in the aerosol ERF trend, as a result of aerosol emissions reductions. Here we study the extent to which observations of the climate system agree with these ERF assumptions. We use a large ERF ensemble from the IPCC’s Sixth Assessment Report (AR6) to attribute the anthropogenic contributions to global mean surface temperature (GMST), top-of-atmosphere radiative flux, and we use aerosol optical depth observations. The GMST trend has increased from +0.18°C decade−1 in 2000–09 to +0.35°C decade−1 in 2010–19, coinciding with the anthropogenic warming trend rising from +0.19°C decade−1 in 2000–09 to +0.24°C decade−1 in 2010–19. This, as well as observed trends in top-of-atmosphere radiative fluxes and aerosol optical depths, supports the claim of an aerosol-induced temporary acceleration in the rate of warming. However, all three observation datasets additionally suggest that smaller aerosol ERF trend changes are compatible with observations since 2000, since radiative flux and GMST trends are significantly influenced by internal variability over this period. A zero-trend-change aerosol ERF scenario results in a much smaller anthropogenic warming acceleration since 2000 but is poorly represented in AR6’s ERF ensemble. Short-term ERF trends are difficult to verify using observations, so caution is required in predictions or policy judgments that depend on them, such as estimates of current anthropogenic warming trend, and the time remaining to, or the outstanding carbon budget consistent with, 1.5°C warming. Further systematic research focused on quantifying trends and early identification of acceleration or deceleration is required.
Jia, Aolin; Liang, Shunlin; Wang, DongdongJia, A., S. Liang, D. Wang, 2022: Generating a 2-km, all-sky, hourly land surface temperature product from Advanced Baseline Imager data. Remote Sensing of Environment, 278, 113105. doi: 10.1016/j.rse.2022.113105. By characterizing high-frequency surface thermal dynamics at a medium spatial scale, hourly land surface temperatures (LST), retrieved from geostationary satellite thermal infrared (TIR) observations, shows great potential to be used across a range of scientific applications; however, cloud cover typically leads to data gaps and degraded retrieval accuracy in TIR LST products, such as the official Advanced Baseline Imager (ABI) LST product. Studies have focused on the LST gap reconstruction; however, most interpolation-based methods only work for a short-term cloud duration and are unable to adequately compensate for cloud effects, and traditional surface energy balance (SEB)-based methods are able to handle cloud coverage while they are not feasible for use at night. Moreover, few studies have concentrated on recovering the abnormal retrievals of partial cloud pixels. In this study, an all-sky diurnal, hourly LST estimation method based on SEB theory was proposed; the proposed method involved three major steps: 1) an original spatiotemporal dynamic model of LST was constructed from ECMWF Reanalysis v.5 (ERA5); 2) clear-sky ABI LST was then assimilated to the dynamic model to generate a continuous LST series; 3) the diurnal cloud effects were superimposed on cloudy time estimated by an innovative optimization method from satellite radiation products. A 2-km, all-sky, hourly LST product was produced over the contiguous US and Mexico from July 2017 to June 2021. Validation was conducted using ground measurements at 18 sites from Surface Radiation (SURFRAD) and core AmeriFlux networks, and produced an overall root-mean-square error (RMSE) of 2.44 K, a bias of −0.19 K, and an R2 of 0.97 based on 408,300 samples. For clear-sky samples, the RMSE values were 2.37 and 2.24 K for day and nighttime, respectively, which was a notable improvement over the corresponding values of the official ABI LST product (2.73 and 2.86 K, respectively). The RMSE values on cloudy-sky were 2.78 and 2.23 K for day and nighttime, respectively. The daily mean LST by aggregating all-sky, hourly LST had an RMSE of 1.13 K and R2 of 0.99. Overall, this product showed reliability under consistent cloud durations, although it was slightly affected by surface elevation. The diurnal temperature cycle climatology of major land cover types was also characterized. The product is freely available at: http://glass.umd.edu/allsky_LST/ABI/. Data assimilation; Surface energy balance; Land surface temperature; ABI; All-sky; Diurnal temperature cycle
Jia, Aolin; Wang, Dongdong; Liang, Shunlin; Peng, Jingjing; Yu, YunyueJia, A., D. Wang, S. Liang, J. Peng, Y. Yu, 2022: Global daily actual and snow-free blue-sky land surface albedo climatology from 20-year MODIS products. Journal of Geophysical Research: Atmospheres, n/a(n/a), e2021JD035987. doi: 10.1029/2021JD035987. Land surface albedo plays a critical role in climate, hydrological and biogeochemical modeling, and weather forecasting. It is often assigned in models and satellite retrievals by albedo climatology look-up tables using land cover type and other variables; however, there are considerable differences in albedo simulations among models, which partially result from uncertainty in obsolete albedo climatology. Therefore, this study introduces a new global 500 m daily blue-sky land surface albedo climatology dataset under both actual and snow-free surface conditions utilizing 20-year Moderate Resolution Imaging Spectroradiometer (MODIS) products from Google Earth Engine. In situ measurements from 38 long-term-maintained sites were utilized to validate the accuracies of different albedo climatology datasets. The root-mean-square error, bias, and correlation coefficient of the new climatology are 0.031, -0.003, and 0.96, respectively, which are more accurate than the GLASS, GlobAlbedo, and 16 model datasets. Data intercomparison suggests that ERA5 exhibits better performance than MERRA2 and 14 CMIP6 models. However, it contains positive biases in the snow-free season, while MERRA2 underestimates the snow albedo. Global albedo variation associated with basic surface plant functional types was also characterized, and snow impact was considered separately. Temporal variability analysis indicates that traditional climatology datasets with coarser temporal resolutions (≥8 days) cannot capture albedo variation over areas with distinct snow seasons, especially in central Eurasia and boreal regions. These results confirm the high reliability and robustness of the new albedo climatology in model assessment, data assimilation, and satellite product retrievals. MODIS; climatology; satellite retrieval; land surface albedo; model assessment
Jiang, Shuyi; Zhao, Chuanfeng; Xia, YanJiang, S., C. Zhao, Y. Xia, 2022: Distinct response of near surface air temperature to clouds in North China. Atmospheric Science Letters, n/a(n/a), e1128. doi: 10.1002/asl.1128. Using the daily 2 m maximum temperature (Tmax), 2 m minimum temperature (Tmin) and cloud cover data measured at ground sites of the China Meteorological Administration in North China from 2000 to 2017, this study investigates the influence of clouds on the daily temperature range (DTR) defined as the difference between Tmax and Tmin. As expected, the cloud cover shows the similar averaged spatial distribution and monthly variation with Tmin. Surprisingly, it also shows the similar average spatial distribution and monthly variation with Tmax, suggesting the more important roles of regions (latitude) and seasons associated with the variations of land surface temperature, which is further related to solar radiation absorbed and surface heat capacity. By comparing monthly variations of temperature between cloudy and clear skies, we find that clouds can weaken Tmax and increase Tmin, and thus decrease DTR. As a result, the spatial distribution of DTR is opposite to the cloud cover. The clouds have relatively stronger impact on Tmin and DTR over mountain region, which is most likely caused by the stronger longwave cloud radiative forcing associated with higher cloud tops over the mountain region. cloud cover; cloud top; daily temperature range; spatial distribution; temporal variation
Jiao, Zhong-Hu; Mu, XihanJiao, Z., X. Mu, 2022: Single-footprint retrieval of clear-sky surface longwave radiation from hyperspectral AIRS data. International Journal of Applied Earth Observation and Geoinformation, 110, 102802. doi: 10.1016/j.jag.2022.102802. Surface longwave radiation (SLR) derived from remotely sensed data facilitates understanding of the SLR in global climate change. Hyperspectral infrared sounders aboard space platforms provide information on the surface and vertical structure of Earth’s atmosphere. However, currently, SLR products estimated from these observations are unavailable, which hampers their application potential for Earth’s radiation budget in the context of global warming. To address this issue, we developed simple and effective SLR model under clear-sky conditions using at-sensor spectral radiances from Atmospheric Infrared Sounder (AIRS). The model was found to be insensitive to AIRS instrument noise, and showed good performances based on a simulation dataset. The AIRS footprint geometrical model was proposed to match the AIRS and Moderate Resolution Imaging Spectroradiometer (MODIS) data to estimate the cloud fraction. Validation against ground-based measurements found that the surface upward longwave radiation model has a bias of 3.18 W/m2, root-mean-square error (RMSE) of 30.51 W/m2, and R2 of 0.84; the surface downward longwave radiation model has a bias of 0.77 W/m2, RMSE of 29.09 W/m2, and R2 of 0.78. The large validation biases at two ground sites reflect the limited spatial representativeness for AIRS footprints. Terrain-induced altitude differences and spatial inhomogeneity can redistribute the spatial distributions of SLR. Moreover, the model performances were weakly dependent on seasonal variation. The results indicate that the proposed model provides a foundation for the further development of operational SLR products. Surface radiation budget; Surface longwave radiation; Atmospheric Infrared Sounder (AIRS); Hybrid method; Hyperspectral infrared remote sensing; Spatial representativeness
Jin, Daeho; Oreopoulos, Lazaros; Lee, Dongmin; Tan, Jackson; Kim, Kyu-myongJin, D., L. Oreopoulos, D. Lee, J. Tan, K. Kim, 2022: A New Organization Metric for Synoptic Scale Tropical Convective Aggregation. Journal of Geophysical Research: Atmospheres, 127(13), e2022JD036665. doi: 10.1029/2022JD036665. Organization metrics were originally developed to measure how densely convective clouds are arranged at mesoscales. In this work, we apply organization metrics to describe tropical synoptic scale convective activity. Such activity is identified by cloud-precipitation (hybrid) regimes defined at 1-degree and 1-hourly resolution. Existing metrics were found to perform inadequately for such convective regime aggregates because the large domain size and co-existence of sparse aggregate occurrences with noisy isolated convection often violate assumptions inherent in these metrics. In order to capture these characteristics, in this study the existing “convective organization potential” (COP) metric was modified so as to focus on local organization and provide increased weight to aggregate size. The resulting “area-based COP” (ABCOP) follows the principle that the more numerous the objects, the higher the chance of organization. It is thus optimized to capture large-scale convective events occurring during phenomena such as ENSO and MJO, while also performs as well as existing metrics for small domain sizes. tropical convection; cloud-precipitation regime; organization metric
Johnson, Richard H.; Ciesielski, Paul E.; Schubert, Wayne H.Johnson, R. H., P. E. Ciesielski, W. H. Schubert, 2022: Hydrometeor Storage and Advection Effects in DYNAMO Budget Analyses. J. Atmos. Sci., 80(1), 181-188. doi: 10.1175/JAS-D-21-0266.1. Abstract The Dynamics of the Madden–Julian Oscillation (MJO) (DYNAMO) field campaign over the central Indian Ocean captured three strong MJO events during October–December 2011. Using the conventional budget approach of Yanai et al. surface rainfall P0 is computed as a residual from the vertically integrated form of the moisture budget equation. This budget-derived P0 is spatially averaged over the Gan Island NCAR S-PolKa radar domain and compared with rainfall estimates from the radar itself. To isolate the MJO signal, these rainfall time series are low-pass (LP) filtered and a three-MJO composite is created based on the time of maximum LP-filtered S-PolKa rainfall for each event. A comparison of the two composite rainfall estimates shows that the budget rainfall overestimates the radar rainfall by ∼15% in the MJO buildup stage and underestimates radar rainfall by ∼8% in the MJO decay stage. These rainfall differences suggest that hydrometeor (clouds and rain) storage and advection effects, which are neglected in the budget approach, are likely significant. Satellite and ground-based observations are used to investigate these hydrometeor storage and advection effects. While the findings are qualitatively consistent with expectations from theory, they fall short of explaining their full magnitude, suggesting even more refined experimental designs and measurements will be needed to adequately address this issue.
Jönsson, Aiden; Bender, Frida A.-M.Jönsson, A., F. A. Bender, 2022: Corrigendum. J. Climate, 35(15), 5233-5234. doi: 10.1175/JCLI-D-22-0128.1. "Corrigendum" published on 01 Aug 2022 by American Meteorological Society.
Jönsson, Aiden; Bender, Frida A.-M.Jönsson, A., F. A. Bender, 2022: Persistence and Variability of Earth’s Interhemispheric Albedo Symmetry in 19 Years of CERES EBAF Observations. J. Climate, 35(1), 249-268. doi: 10.1175/JCLI-D-20-0970.1. Abstract Despite the unequal partitioning of land and aerosol sources between the hemispheres, Earth’s albedo is observed to be persistently symmetric about the equator. This symmetry is determined by the compensation of clouds to the clear-sky albedo. Here, the variability of this interhemispheric albedo symmetry is explored by decomposing observed radiative fluxes in the CERES EBAF satellite data record into components reflected by the atmosphere, clouds, and the surface. We find that the degree of interhemispheric albedo symmetry has not changed significantly throughout the observational record. The variability of the interhemispheric difference in reflected solar radiation (asymmetry) is strongly determined by tropical and subtropical cloud cover, particularly those related to nonneutral phases of El Niño–Southern Oscillation (ENSO). As ENSO is the most significant source of interannual variability in reflected radiation on a global scale, this underscores the interhemispheric albedo symmetry as a robust feature of Earth’s current annual mean climate. Comparing this feature in observations with simulations from coupled models reveals that the degree of modeled albedo symmetry is mostly dependent on biases in reflected radiation in the midlatitudes, and that models that overestimate its variability the most have larger biases in reflected radiation in the tropics. The degree of model albedo symmetry is improved when driven with historical sea surface temperatures, indicating that the degree of symmetry in Earth’s albedo is dependent on the representation of cloud responses to coupled ocean–atmosphere processes.
Jungclaus, J.h.; Lorenz, S.j.; Schmidt, H.; Brovkin, V.; Brüggemann, N.; Chegini, F.; Crüger, T.; De-Vrese, P.; Gayler, V.; Giorgetta, M.a; Gutjahr, O.; Haak, H.; Hagemann, S.; Hanke, M.; Ilyina, T.; Korn, P.; Kröger, J.; Linardakis, L.; Mehlmann, C.; Mikolajewicz, U.; Müller, W.a.; Nabel, J.e.m.s; Notz, D.; Pohlmann, H.; Putrasahan, D.a.; Raddatz, T.; Ramme, L.; Redler, R.; Reick, C.h.; Riddick, T.; Sam, T.; Schneck, R.; Schnur, R.; Schupfner, M.; Storch, J.-S. von; Wachsmann, F.; Wieners, K.-H.; Ziemen, F.; Stevens, B.; Marotzke, J.; Claussen, M.Jungclaus, J., S. Lorenz, H. Schmidt, V. Brovkin, N. Brüggemann, F. Chegini, T. Crüger, P. De-Vrese, V. Gayler, M. Giorgetta, O. Gutjahr, H. Haak, S. Hagemann, M. Hanke, T. Ilyina, P. Korn, J. Kröger, L. Linardakis, C. Mehlmann, U. Mikolajewicz, W. Müller, J. Nabel, D. Notz, H. Pohlmann, D. Putrasahan, T. Raddatz, L. Ramme, R. Redler, C. Reick, T. Riddick, T. Sam, R. Schneck, R. Schnur, M. Schupfner, J. v. Storch, F. Wachsmann, K. Wieners, F. Ziemen, B. Stevens, J. Marotzke, M. Claussen, 2022: The ICON Earth System Model Version 1.0. Journal of Advances in Modeling Earth Systems, n/a(n/a), e2021MS002813. doi: 10.1029/2021MS002813. This work documents the ICON-Earth System Model (ICON-ESM V1.0), the first coupled model based on the ICON (ICOsahedral Non-hydrostatic) framework with its unstructured, icosahedral grid concept. The ICON-A atmosphere uses a nonhydrostatic dynamical core and the ocean model ICON-O builds on the same ICON infrastructure, but applies the Boussinesq and hydrostatic approximation and includes a sea-ice model. The ICON-Land module provides a new framework for the modelling of land processes and the terrestrial carbon cycle. The oceanic carbon cycle and biogeochemistry are represented by the Hamburg Ocean Carbon Cycle module. We describe the tuning and spin-up of a base-line version at a resolution typical for models participating in the Coupled Model Intercomparison Project (CMIP). The performance of ICON-ESM is assessed by means of a set of standard CMIP6 simulations. Achievements are well-balanced top-of-atmosphere radiation, stable key climate quantities in the control simulation, and a good representation of the historical surface temperature evolution. The model has overall biases, which are comparable to those of other CMIP models, but ICON-ESM performs less well than its predecessor, the Max Planck Institute Earth System Model. Problematic biases are diagnosed in ICON-ESM in the vertical cloud distribution and the mean zonal wind field. In the ocean, sub-surface temperature and salinity biases are of concern as is a too strong seasonal cycle of the sea-ice cover in both hemispheres. ICON-ESM V1.0 serves as a basis for further developments that will take advantage of ICON-specific properties such as spatially varying resolution, and configurations at very high resolution. Earth; Model; System
Kelleher, Mitchell K.; Grise, Kevin M.Kelleher, M. K., K. M. Grise, 2022: Varied midlatitude shortwave cloud radiative responses to Southern Hemisphere circulation shifts. Atmospheric Science Letters, 23(1), e1068. doi: 10.1002/asl.1068. Changes in midlatitude clouds as a result of shifts in general circulation patterns are widely thought to be a potential source of radiative feedbacks onto the climate system. Previous work has suggested that two general circulation shifts anticipated to occur in a warming climate, poleward shifts in the midlatitude jet streams and a poleward expansion of the Hadley circulation, are associated with differing effects on midlatitude clouds. This study examines two dynamical cloud-controlling factors, mid-tropospheric vertical velocity, and the estimated inversion strength (EIS) of the marine boundary layer temperature inversion, to explain why poleward shifts in the Southern Hemisphere midlatitude jet and Hadley cell edge have varying shortwave cloud-radiative responses at midlatitudes. Changes in vertical velocity and EIS occur further equatorward for poleward shifts in the Hadley cell edge than they do for poleward shifts of the midlatitude jet. Because the sensitivity of shortwave cloud radiative effects (SWCRE) to variations in vertical velocity and EIS is a function of latitude, the SWCRE anomalies associated with jet and Hadley cell shifts differ. The dynamical changes associated with a poleward jet shift occur further poleward in a regime where the sensitivities of SWCRE to changes in vertical velocity and EIS balance, leading to a near-net zero change in SWCRE in midlatitudes with a poleward jet shift. Conversely, the dynamical changes associated with Hadley cell expansion occur further equatorward at a latitude where the sensitivity of SWCRE is more strongly associated with changes in mid-tropospheric vertical velocity, leading to a net shortwave cloud radiative warming effect in midlatitudes. Hadley cell expansion; midlatitude jet shifts; shortwave cloud radiative effects
Kenny, Darragh; Fiedler, StephanieKenny, D., S. Fiedler, 2022: Which gridded irradiance data is best for modelling photovoltaic power production in Germany?. Solar Energy, 232, 444-458. doi: 10.1016/j.solener.2021.12.044. Model estimates of expected photovoltaic (PV) power production rely on accurate irradiance data. Reanalysis and satellite products freely provide irradiance data with a high temporal and spatial resolution including locations for which no ground-based measurements are available. We assess differences in such gridded irradiance data and quantify the subsequent bias propagation from individual radiation components to capacity factors in a contemporary PV model. PV power production is simulated based on four reanalysis (ERA5, COSMO-REA6, COSMO-REA6pp, COSMO-REA2) and three satellite products (CAMS, SARAH-2, CERES Syn1Deg). The results are compared against simulations using measurements from 30 weather stations of the German Weather Service. We compute metrics characterizing biases in seasonal and annual means, day-to-day variability and extremes in PV power. Our results highlight a bias of −1.4% (COSMO-REA6) to ＋8.2% (ERA5) in annual and spatial means of PV power production for Germany. No single data set is best in all metrics, although SARAH-2 and the postprocessed COSMO-REA6 data (COSMO-REA6pp) outperform the other products for many metrics. SARAH-2 yields good results in summer, but overestimates PV output in winter by 16% averaged across all stations. COSMO-REA6pp represents day-to-day variability in the PV power production of a simulated PV fleet best and has a particularly small bias of 0.5% in annual means. This is at least in parts due to compensating biases in local and seasonal means. Our results imply that gridded irradiance data should be used with caution for site assessments and ideally be complemented by local measurements. Satellite; Data evaluation; Irradiance data; PV power model; Re-analysis; Station observations
Khairoutdinov, Marat F.; Blossey, Peter N.; Bretherton, Christopher S.Khairoutdinov, M. F., P. N. Blossey, C. S. Bretherton, 2022: Global System for Atmospheric Modeling: Model Description and Preliminary Results. Journal of Advances in Modeling Earth Systems, 14(6), e2021MS002968. doi: 10.1029/2021MS002968. The extension of a cloud-resolving model, the System for Atmospheric Modeling (SAM), to global domains is described. The resulting global model, gSAM, is formulated on a latitude-longitude grid. It uses an anelastic dynamical core with a single reference profile (as in SAM), but its governing equations differ somewhat from other anelastic models. For quasihydrostatic flows, they are isomorphic to the primitive equations (PE) in pressure coordinates but with the globally uniform reference pressure playing the role of actual pressure. As a result, gSAM can exactly maintain steady zonally symmetric baroclinic flows that have been specified in pressure coordinates, produces accurate simulations when initialized or nudged with global reanalyses, and has a natural energy conservation equation despite the drawbacks of using the anelastic system to model global scales. gSAM employs a novel treatment of topography using a type of immersed boundary method, the Quasi-Solid Body Method, where the instantaneous flow velocity is forced to stagnate in grid cells inside a prescribed terrain. The results of several standard tests designed to evaluate the accuracy of global models with and without topography as well as results from real Earth simulations are presented. model description; global cloud-resolving model; anelastic dynamical core; global storm-resolving model; system for atmospheric modeling
Knippertz, Peter; Gehne, Maria; Kiladis, George N.; Kikuchi, Kazuyoshi; Rasheeda Satheesh, Athul; Roundy, Paul E.; Yang, Gui-Ying; Žagar, Nedjeljka; Dias, Juliana; Fink, Andreas H.; Methven, John; Schlueter, Andreas; Sielmann, Frank; Wheeler, Matthew C.Knippertz, P., M. Gehne, G. N. Kiladis, K. Kikuchi, A. Rasheeda Satheesh, P. E. Roundy, G. Yang, N. Žagar, J. Dias, A. H. Fink, J. Methven, A. Schlueter, F. Sielmann, M. C. Wheeler, 2022: The intricacies of identifying equatorial waves. Quarterly Journal of the Royal Meteorological Society, 148(747), 2814-2852. doi: 10.1002/qj.4338. Equatorial waves (EWs) are synoptic- to planetary-scale propagating disturbances at low latitudes with periods from a few days to several weeks. Here, this term includes Kelvin waves, equatorial Rossby waves, mixed Rossby–gravity waves, and inertio-gravity waves, which are well described by linear wave theory, but it also other tropical disturbances such as easterly waves and the intraseasonal Madden–Julian Oscillation with more complex dynamics. EWs can couple with deep convection, leading to a substantial modulation of clouds and rainfall. EWs are amongst the dynamic features of the troposphere with the longest intrinsic predictability, and models are beginning to forecast them with an exploitable level of skill. Most of the methods developed to identify and objectively isolate EWs in observations and model fields rely on (or at least refer to) the adiabatic, frictionless linearized primitive equations on the sphere or the shallow-water system on the equatorial β$$ \beta $$-plane. Common ingredients to these methods are zonal wave-number–frequency filtering (Fourier or wavelet) and/or projections onto predefined empirical or theoretical dynamical patterns. This paper gives an overview of six different methods to isolate EWs and their structures, discusses the underlying assumptions, evaluates the applicability to different problems, and provides a systematic comparison based on a case study (February 20–May 20, 2009) and a climatological analysis (2001–2018). In addition, the influence of different input fields (e.g., winds, geopotential, outgoing long-wave radiation, rainfall) is investigated. Based on the results, we generally recommend employing a combination of wave-number–frequency filtering and spatial-projection methods (and of different input fields) to check for robustness of the identified signal. In cases of disagreement, one needs to carefully investigate which assumptions made for the individual methods are most probably not fulfilled. This will help in choosing an approach optimally suited to a given problem at hand and avoid misinterpretation of the results. convection; equatorial Rossby waves; Kelvin waves; mixed Rossby–gravity waves; spatial projection; time–space filtering; tropical rainfall
Kooperman, G. J.; Akinsanola, A. A.; Hannah, W. M.; Pendergrass, A. G.; Reed, K. A.Kooperman, G. J., A. A. Akinsanola, W. M. Hannah, A. G. Pendergrass, K. A. Reed, 2022: Assessing Two Approaches for Enhancing the Range of Simulated Scales in the E3SMv1 and the Impact on the Character of Hourly US Precipitation. Geophysical Research Letters, 49(4), e2021GL096717. doi: 10.1029/2021GL096717. Improving the representation of precipitation in Earth system models is essential for understanding and projecting water cycle changes across scales. Progress has been hampered by persistent deficiencies in representing precipitation frequency, intensity, and timing in current models. Here, we analyze simulated US precipitation in the low-resolution (LR) configuration of the Energy Exascale Earth System Model (E3SMv1) and assess the effect of two approaches to enhance the range of explicitly resolved scales: high-resolution (HR) and multiscale modeling framework (MMF), which incur similar computational expense. Both E3SMv1-MMF and E3SMv1-HR capture more intense and less frequent precipitation on hourly and daily timescales relative to E3SMv1-LR. E3SMv1-HR improves the intensity over the Eastern and Northwestern US during winter, while E3SMv1-MMF improves the intensity over the Eastern US and summer diurnal timing over the Central US. These results indicate that both methods may be needed to improve simulations of different storm types, seasons, and regions. earth system model; United States; precipitation; energy exascale earth system model; high resolution; multiscale modelling framework
Koppa, Akash; Rains, Dominik; Hulsman, Petra; Poyatos, Rafael; Miralles, Diego G.Koppa, A., D. Rains, P. Hulsman, R. Poyatos, D. G. Miralles, 2022: A deep learning-based hybrid model of global terrestrial evaporation. Nature Communications, 13(1), 1912. doi: 10.1038/s41467-022-29543-7. Terrestrial evaporation (E) is a key climatic variable that is controlled by a plethora of environmental factors. The constraints that modulate the evaporation from plant leaves (or transpiration, Et) are particularly complex, yet are often assumed to interact linearly in global models due to our limited knowledge based on local studies. Here, we train deep learning algorithms using eddy covariance and sap flow data together with satellite observations, aiming to model transpiration stress (St), i.e., the reduction of Et from its theoretical maximum. Then, we embed the new St formulation within a process-based model of E to yield a global hybrid E model. In this hybrid model, the St formulation is bidirectionally coupled to the host model at daily timescales. Comparisons against in situ data and satellite-based proxies demonstrate an enhanced ability to estimate St and E globally. The proposed framework may be extended to improve the estimation of E in Earth System Models and enhance our understanding of this crucial climatic variable. Hydrology; Ecological modelling
Kuwano, A.; Evan, A.Kuwano, A., A. Evan, 2022: A Method to Account for the Impact of Water Vapor on Observation-Based Estimates of the Clear-Sky Shortwave Direct Radiative Effect of Mineral Dust. Journal of Geophysical Research: Atmospheres, 127(17), e2022JD036620. doi: 10.1029/2022JD036620. The shortwave direct radiative effect of dust, the difference between net shortwave radiative flux in a cloud free and cloud and aerosol free atmosphere, is typically estimated using forward calculations made with a radiative transfer model. However, estimates of the direct radiative effect made via this initial method can be highly uncertain due to difficultly in accurately describing the relevant optical and physical properties of dust used in these calculations. An alternative approach to estimate this effect is to determine the forcing efficiency, or the direct radiative effect normalized by aerosol optical depth. While this approach avoids the uncertainties associated with the initial method for calculating the direct effect, random errors and biases associated with this approach have not been thoroughly examined in literature. Here we explore biases in this observation-based approach that are related to atmospheric water vapor. We use observations to show that over the Sahara Desert dust optical depth and column-integrated atmospheric water vapor are positively correlated. We use three idealized radiative models of varying complexity to demonstrate that a positive correlation between dust and water vapor produces a positive bias in the dust forcing efficiency estimated via the observation-based method. We describe a simple modification to the observation-based method that correctly accounts for the correlation between dust and water vapor when estimating the forcing efficiency and use this method to estimate the instantaneous forcing efficiency of dust over the Sahara Desert using satellite data, obtaining −12.3 ± 6.68 to 20.9 ± 11.9 W m−2 per unit optical depth. satellite data; radiative transfer; dust; shortwave; observations; forcing efficiency
Lauer, Axel; Bock, Lisa; Hassler, Birgit; Schröder, Marc; Stengel, MartinLauer, A., L. Bock, B. Hassler, M. Schröder, M. Stengel, 2022: Cloud Climatologies from Global Climate Models—A Comparison of CMIP5 and CMIP6 Models with Satellite Data. J. Climate, 36(2), 281-311. doi: 10.1175/JCLI-D-22-0181.1. Abstract Simulating clouds with global climate models is challenging as the relevant physics involves many nonlinear processes covering a wide range of spatial and temporal scales. As key components of the hydrological cycle and the climate system, an evaluation of clouds from models used for climate projections is an important prerequisite for assessing the confidence in the results from these models. Here, we compare output from models contributing to phase 6 of the Coupled Model Intercomparison Project (CMIP6) with satellite data and with results from their predecessors (CMIP5). We use multiproduct reference datasets to estimate the observational uncertainties associated with different sensors and with internal variability on a per-pixel basis. Selected cloud properties are also analyzed by region and by dynamical regime and thermodynamic conditions. Our results show that for parameters such as total cloud cover, cloud water path, and cloud radiative effect, the CMIP6 multimodel mean performs slightly better than the CMIP5 ensemble mean in terms of mean bias, pattern correlation, and relative root-mean square deviation. The intermodel spread in CMIP6, however, is not reduced compared to CMIP5. Compared with CALIPSO-ICECLOUD data, the CMIP5/6 models overestimate cloud ice, particularly in the lower and middle troposphere, partly due to too high ice fractions for given temperatures. This bias is reduced in the CMIP6 multimodel mean. While many known biases such as an underestimation in cloud cover in stratocumulus regions remain in CMIP6, we find that the CMIP5 problem of too few but too reflective clouds over the Southern Ocean is significantly improved.
Lee, Jae N.; Wu, Dong L.Lee, J. N., D. L. Wu, 2022: Non-Gaussian Distributions of TOA SW Flux as Observed by MISR and CERES. Journal of Geophysical Research: Atmospheres, 127(14), e2022JD036636. doi: 10.1029/2022JD036636. The Top of Atmosphere (TOA) shortwave (SW) flux, converted from Terra Multi-angle Imaging SpectroRadiometer (MISR) narrow band albedos, is compared with that measured from Clouds and the Earth's Radiant Energy System (CERES). We describe the probability density function (PDF) of the monthly TOA SW flux and how the statistical third moment, skewness, can impact the quantification of the flux. The PDF of the SW flux is not normally distributed but positively skewed. In both sets of observations, the near-global (80 S–80 N) median value of the SW flux is ∼3 W/m2 less than the mean value, due to the positive skewness of the distribution. The near-global mean TOA SW flux converted from MISR is about 7 W/m2 (∼7%) less than CERES measured flux during the last two decades. Surprisingly, a hemispheric asymmetry exists with TOA SW observations from the Terra platform. SH reflects 3.92 and 1.15 W/m2 more mean SW flux than NH, from MISR and CERES Single Scanner Footprint products, respectively. We can infer that the offsetting by morning clouds in the SH is greater than the effect of hemispheric imbalance of SW flux caused by different land masses in two hemispheres. While the characteristics of the two SW fluxes broadly agree with each other, differences in the regional PDF from two different SW fluxes are substantial over high cloud regions and high altitude regions. Our analysis shows that some parts of the different skewness from the two measurements may be attributed to the different calibration of the radiance anisotropy over high cloud scenes. CERES; MISR; hemispheric asymmetry; non-Gaussian; TOA SW flux
Lee, Jiheun; Kang, Sarah M.; Kim, Hanjun; Xiang, BaoqiangLee, J., S. M. Kang, H. Kim, B. Xiang, 2022: Disentangling the effect of regional SST bias on the double-ITCZ problem. Climate Dynamics. doi: 10.1007/s00382-021-06107-x. This study investigates the causes of the double intertropical convergence zone (ITCZ) bias, characterized by too northward northern Pacific ITCZ, too dry equatorial Pacific, and too zonally elongated southern Pacific rainband. While the biases within one fully coupled model GFDL CM2.1 are examined, the large-scale bias patterns are broadly common to CMIP5/6 models. We disentangle the individual contribution of regional sea surface temperature (SST) biases to the double-ITCZ bias pattern using a series of slab ocean model experiments. A previously suggested Southern Ocean warm bias effect in displacing the zonal-mean ITCZ southward is manifested in the northern Pacific ITCZ while having little contribution to the zonally elongated wet bias south of the equatorial Pacific. The excessive southern Pacific precipitation is instead induced by the warm bias along the west coast of South America. The Southern Ocean bias effect on the zonal-mean ITCZ position is diminished by the neighboring midlatitude bias of opposite sign in GFDL CM2.1. As a result, the northern extratropical cold bias turns out to be most responsible for a southward-displaced zonal-mean ITCZ. However, this southward ITCZ displacement results from the northern Pacific branch, so ironically fixing the extratropical biases only deteriorates the northern Pacific precipitation bias. Thus, we emphasize that the zonal-mean diagnostics poorly represent the spatial pattern of the tropical Pacific response. Examination of longitude-latitude structure indicates that the overall tropical precipitation bias is mostly locally driven from the tropical SST bias. While our model experiments are idealized with no ocean dynamics, the results shed light on where preferential foci should be applied in model development to improve particular features of tropical precipitation bias.
Leng, Song; Huete, Alfredo; Cleverly, Jamie; Gao, Sicong; Yu, Qiang; Meng, Xianyong; Qi, Junyu; Zhang, Rongrong; Wang, QianfengLeng, S., A. Huete, J. Cleverly, S. Gao, Q. Yu, X. Meng, J. Qi, R. Zhang, Q. Wang, 2022: Assessing the Impact of Extreme Droughts on Dryland Vegetation by Multi-Satellite Solar-Induced Chlorophyll Fluorescence. Remote Sensing, 14(7), 1581. doi: 10.3390/rs14071581. Satellite-estimated solar-induced chlorophyll fluorescence (SIF) is proven to be an effective indicator for dynamic drought monitoring, while the capability of SIF to assess the variability of dryland vegetation under water and heat stress remains challenging. This study presents an analysis of the responses of dryland vegetation to the worst extreme drought over the past two decades in Australia, using multi-source spaceborne SIF derived from the Global Ozone Monitoring Experiment-2 (GOME-2) and TROPOspheric Monitoring Instrument (TROPOMI). Vegetation functioning was substantially constrained by this extreme event, especially in the interior of Australia, in which there was hardly seasonal growth detected by neither satellite-based observations nor tower-based flux measurements. At a 16-day interval, both SIF and enhanced vegetation index (EVI) can timely capture the reduction at the onset of drought over dryland ecosystems. The results demonstrate that satellite-observed SIF has the potential for characterizing and monitoring the spatiotemporal dynamics of drought over water-limited ecosystems, despite coarse spatial resolution coupled with high-retrieval noise as compared with EVI. Furthermore, our study highlights that SIF retrieved from TROPOMI featuring substantially enhanced spatiotemporal resolution has the promising capability for accurately tracking the drought-induced variation of heterogeneous dryland vegetation. SIF; EVI; dryland; extreme drought; TROPOMI
Leng, Song; Huete, Alfredo; Cleverly, Jamie; Yu, Qiang; Zhang, Rongrong; Wang, QianfengLeng, S., A. Huete, J. Cleverly, Q. Yu, R. Zhang, Q. Wang, 2022: Spatiotemporal Variations of Dryland Vegetation Phenology Revealed by Satellite-Observed Fluorescence and Greenness across the North Australian Tropical Transect. Remote Sensing, 14(13), 2985. doi: 10.3390/rs14132985. Accurate characterization of spatial patterns and temporal variations in dryland vegetation is of great importance for improving our understanding of terrestrial ecosystem functioning under changing climates. Here, we explored the spatiotemporal variability of dryland vegetation phenology using satellite-observed Solar-Induced chlorophyll Fluorescence (SIF) and the Enhanced Vegetation Index (EVI) along the North Australian Tropical Transect (NATT). Substantial impacts of extreme drought and intense wetness on the phenology and productivity of dryland vegetation are observed by both SIF and EVI, especially in the arid/semiarid interior of Australia without detectable seasonality in the dry year of 2018–2019. The greenness-based vegetation index (EVI) can more accurately capture the seasonal and interannual variation in vegetation production than SIF (EVI r2: 0.47~0.86, SIF r2: 0.47~0.78). However, during the brown-down periods, the rate of decline in EVI is evidently slower than that in SIF and in situ measurement of gross primary productivity (GPP), due partially to the advanced seasonality of absorbed photosynthetically active radiation. Over 70% of the variability of EVI (except for Hummock grasslands) and 40% of the variability of SIF (except for shrublands) can be explained by the water-related drivers (rainfall and soil moisture). By contrast, air temperature contributed to 25~40% of the variability of the effective fluorescence yield (SIFyield) across all biomes. In spite of high retrieval noises and variable accuracy in phenological metrics (MAE: 8~60 days), spaceborne SIF observations, offsetting the drawbacks of greenness-based phenology products with a potentially lagged end of the season, have the promising capability of mapping and characterizing the spatiotemporal dynamics of dryland vegetation phenology. SIF; EVI; NATT; phenology
Letu, Husi; Nakajima, Takashi Y.; Wang, Tianxing; Shang, Huazhe; Ma, Run; Yang, Kun; Baran, Anthony J.; Riedi, Jerome; Ishimoto, Hiroshi; Yoshida, Mayumi; Shi, Chong; Khatri, Pradeep; Du, Yihan; Chen, Liangfu; Shi, JianchengLetu, H., T. Y. Nakajima, T. Wang, H. Shang, R. Ma, K. Yang, A. J. Baran, J. Riedi, H. Ishimoto, M. Yoshida, C. Shi, P. Khatri, Y. Du, L. Chen, J. Shi, 2022: A New Benchmark for Surface Radiation Products over the East Asia–Pacific Region Retrieved from the Himawari-8/AHI Next-Generation Geostationary Satellite. Bull. Amer. Meteor. Soc., 103(3), E873-E888. doi: 10.1175/BAMS-D-20-0148.1. Abstract Surface downward radiation (SDR), including shortwave downward radiation (SWDR) and longwave downward radiation (LWDR), is of great importance to energy and climate studies. Considering the lack of reliable SDR data with a high spatiotemporal resolution in the East Asia–Pacific (EAP) region, we derived SWDR and LWDR at 10-min and 0.05° resolutions for this region from 2016 to 2020 based on the next-generation geostationary satellite Himawari-8 (H-8). The SDR product is unique in terms of its all-sky features, high accuracy, and high-resolution levels. The cloud effect is fully considered in the SDR product, and the influence of high aerosol loadings and topography on the SWDR are considered. Compared to benchmark products of the radiation, such as Clouds and the Earth’s Radiant Energy System (CERES) and the European Centre for Medium-Range Weather Forecasts (ECMWF) next-generation reanalysis (ERA5), and the Global Land Surface Satellite (GLASS), not only is the resolution of the new SDR product notably much higher, but the product accuracy is also higher than that of those products. In particular, hourly and daily root-mean-square errors of the new SWDR are 104.9 and 31.5 W m−2, respectively, which are much smaller than those of CERES (at 121.6 and 38.6 W m−2, respectively), ERA5 (at 176.6 and 39.5 W m−2, respectively), and GLASS (daily of 36.5 W m−2). Meanwhile, RMSEs of hourly and daily values of the new LWDR are 19.6 and 14.4 W m−2, respectively, which are comparable to that of CERES and ERA5, and even better over high-altitude regions.
Li, JianDong; Wang, Wei-Chyung; Chen, GuoXing; You, QingLongLi, J., W. Wang, G. Chen, Q. You, 2022: Characteristics of top-of-atmosphere radiation budget over the Tibetan Plateau and its bias sources in climate models. Atmospheric Research, 276, 106256. doi: 10.1016/j.atmosres.2022.106256. Observations indicate that the Tibetan Plateau (TP) has an annual-mean ~9.3 W m−2 positive radiation budget (RT) at the top of the atmosphere, the largest at the same continental latitudes. This unique radiative heating is critical to the TP's thermal forcing and hydrological cycle. Here we use satellite and reanalyzed data to investigate the characteristics of RT over the TP in the observation and 28 CMIP6 models. The positive observational RT is mainly caused by low surface temperature associated with high elevation. Most models underestimate annual mean RT over the whole TP, with a multimodel average of 2.0 W m−2. This RT bias results mainly from weaker absorbed shortwave radiation (ASR) that exhibits substantial seasonal and regional differences. Serious RT, ASR, and surface albedo biases appear over the western TP. For instance, their wintertime multimodel-mean biases of −44.9 W m−2, −53.3 W m−2, and 0.23 are larger than the eastern TP's counterparts (−38.6 W m−2, −40.6 W m−2, and 0.15). Simulated RT also shows a large intermodel spread. In the models with worse RT's performance, weaker ASR is primarily attributed to higher surface albedo that coincides well with lower surface temperature. In contrast, the models that reproduce well the RT have less surface albedo bias but somewhat overestimate surface temperature. Weaker simulated cloud radiative cooling reduces reflected shortwave radiation that alleviates the RT bias, especially over the springtime eastern TP. This study highlights the importance of land surface states and clouds in modeling the TP's climate. Significance statement Observations indicate that the Tibetan Plateau (TP) has an annual-mean ~ 9.3 W m−2 positive radiation budget (RT) at the top of the atmosphere, the largest among land regions in the same latitudes. This study aims to investigate the characteristics of RT over the TP in the observation and CMIP6 models. Most models underestimate annual mean RT over the whole TP, with a multimodel average of 2.0 W m−2. This bias results mainly from weaker absorbed shortwave radiation, exhibiting substantial seasonal and regional differences. CMIP6 simulations show a large multimodel spread, especially over the wintertime and springtime western TP. This study highlights the importance of land surface states (e.g., surface temperature and albedo) and clouds in modeling the TP's climate. Tibetan Plateau; Cloud; Radiation budget; CMIP6 models
Li, Liang; Liu, Minxia; Qi, Yuhan; Zhang, Guojuan; Yu, RuixinLi, L., M. Liu, Y. Qi, G. Zhang, R. Yu, 2022: Spatiotemporal variations and relationships of absorbing aerosol-radiation-gross primary productivity over China. Environmental Monitoring and Assessment, 195(1), 169. doi: 10.1007/s10661-022-10775-5. High-load carbonaceous and dust aerosols can significantly reduce direct radiation (DIRR), which would affect photosynthesis in terrestrial ecosystems, thereby further affecting the productivity of vegetation. Based on this, a variety of remote sensing data were used to study the spatiotemporal distributions and changing tendencies of the absorbing aerosols, CO, DIRR, and gross primary productivity (GPP) in China during 2005–2019; then, the relationships were analyzed between different types of absorbing aerosols and DIRR as well as GPP. The results showed that the annual mean absorbing aerosols index (AAI) in China during 2005–2019 was 0.39, with a slow growth rate of 0.02 year−1, and the emission of CO showed a decreasing trend with each passing year, especially in North China Plain and Sichuan Basin. Carbonaceous and dust aerosols were predominantly bounded by Hu line. The east of Hu line was the dominant area of carbonaceous aerosols, and the west of Hu line was the topographical region of dust aerosols. Near the Hu line was the dominant area of carbonaceous-dust aerosols. However, the Karamay–Urumqi–Hami area and Northeast China Plain were exceptional. During the vegetation growing season, different types of absorbing aerosols significantly negatively affected GPP. From a perspective of regional scale variation pattern, the negative effect of absorbing aerosols on vegetation productivity was the most significant in Northeast China; from the perspective of the effects of different vegetation types, the negative effect of absorbing aerosols on grasslands was greater than that of woodlands; from the perspective of the composition characteristics of aerosols, the negative effect of dust aerosols on GPP was greater than that of carbonaceous aerosols. Spatiotemporal variations; Aerosol classification; Correlation; Direct radiation; GPP
Li, Lingfeng; Qiu, Bo; Guo, Weidong; Zhang, Yiping; Song, Qinghai; Chen, JiuyiLi, L., B. Qiu, W. Guo, Y. Zhang, Q. Song, J. Chen, 2022: Phenological and physiological responses of the terrestrial ecosystem to the 2019 drought event in Southwest China: Insights from satellite measurements and the SSiB2 model. International Journal of Applied Earth Observation and Geoinformation, 111, 102832. doi: 10.1016/j.jag.2022.102832. Understanding plant phenological and physiological changes in response to drought will provide key insight into the response of terrestrial ecosystems to climate change, but is still limited due to the increased drought severity and frequency in recent decades. Here, we combine solar-induced chlorophyll fluorescence (SIF) along with SSiB2 (Simplified Simple Biosphere Model) simulations to investigate the plant phenological and physiological responses to the 2019 drought in southwestern China. Our results show that this 2019 drought had substantial impacts on vegetation phenology and photosynthesis due to the soil moisture deficit in spring, while the rewatering process in July alleviated the water deficit and reduced drought damage to plants. Moreover, SIF observations provide a physiology-related vegetation response, as the recovery of plant photosynthesis indicated by fluorescence yield (SIFyield) is much stronger than the recovery of greenness described by vegetation indices during the rewatering in July. The SSiB2 simulations captured the physiological response of plants to moisture deficit during drought period, while the lack of realistic energy dissipation mechanisms under stressed conditions may lead to discrepancies in the timing of peak response to drought. Our findings highlight the prospective application of remote sensing SIF measurements in monitoring the timely response of plant physiology to changes in water conditions and to provide important information for model evaluation and improvement. Drought; Solar-induced chlorophyll fluorescence; Water stress; Plant physiological response
Li, Meng; Chu, Ronghao; Sha, Xiuzhu; Xie, Pengfei; Ni, Feng; Wang, Chao; Jiang, Yuelin; Shen, Shuanghe; Islam, Abu Reza Md TowfiqulLi, M., R. Chu, X. Sha, P. Xie, F. Ni, C. Wang, Y. Jiang, S. Shen, A. R. M. T. Islam, 2022: Monitoring 2019 Drought and Assessing Its Effects on Vegetation Using Solar-Induced Chlorophyll Fluorescence and Vegetation Indexes in the Middle and Lower Reaches of Yangtze River, China. Remote Sensing, 14(11), 2569. doi: 10.3390/rs14112569. Monitoring drought precisely and evaluating drought effects quantitatively can establish a scientific foundation for understanding drought. Although solar-induced chlorophyll fluorescence (SIF) can detect the drought stress in advance, the performance of SIF in monitoring drought and assessing drought-induced gross primary productivity (GPP) losses from lush to senescence remains to be further studied. Taking the 2019 drought in the middle and lower reaches of the Yangtze River (MLRYR) as an example, this study aims to monitor and assess this drought by employing a new global, OCO-2-based SIF (GOSIF) and vegetation indexes (VIs). Results showed that the GPP, GOSIF, and VIs all exhibited significant increasing trends during 2000–2020. GOSIF was most consistent with GPP in spatial distribution and was most correlated with GPP in both annual (linear correlation, R2 = 0.87) and monthly (polynomial correlation, R2 = 0.976) time scales by comparing with VIs. During July–December 2019, the precipitation (PPT), soil moisture, and standardized precipitation evapotranspiration index (SPEI) were generally below the averages during 2011–2020 and reached their lowest point in November, while those of air temperature (Tem), land surface temperature (LST), and photosynthetically active radiation (PAR) were the contrary. For drought monitoring, the spatial distributions of standardized anomalies of GOSIF and VIs were consistent during August–October 2019. In November and December, however, considering vegetation has entered the senescence stage, SIF had an obvious early response in vegetation physiological state monitoring compared with VIs, while VIs can better indicate meteorological drought conditions than SIF. For drought assessment, the spatial distribution characteristics of GOSIF and its standardized anomaly were both most consistent with that of GPP, especially the standardized anomaly in November and December. All the above phenomena verified the good spatial consistency between SIF and GPP and the superior ability of SIF in capturing and quantifying drought-induced GPP losses. Results of this study will improve the understanding of the prevention and reduction in agrometeorological disasters and can provide an accurate and timely method for drought monitoring. drought; solar-induced chlorophyll fluorescence; gross primary productivity; the middle and lower reaches of Yangtze River; vegetation indexes
Li, Ming; Letu, Husi; Peng, Yiran; Ishimoto, Hiroshi; Lin, Yanluan; Nakajima, Takashi Y.; Baran, Anthony J.; Guo, Zengyuan; Lei, Yonghui; Shi, JianchengLi, M., H. Letu, Y. Peng, H. Ishimoto, Y. Lin, T. Y. Nakajima, A. J. Baran, Z. Guo, Y. Lei, J. Shi, 2022: Investigation of ice cloud modeling capabilities for the irregularly shaped Voronoi ice scattering models in climate simulations. Atmospheric Chemistry and Physics, 22(7), 4809-4825. doi: 10.5194/acp-22-4809-2022. Abstract. Both weather–climate models and ice cloud remote sensing applications need to obtain effective ice crystal scattering (ICS) properties and the parameterization scheme. An irregularly shaped Voronoi ICS model has been suggested to be effective in remote sensing applications for several satellite programs, e.g., Himawari-8, GCOM-C (Global Change Observation Mission–Climate) and EarthCARE (Earth Cloud Aerosol and Radiation Explorer). As continuation work of Letu et al. (2016), an ice cloud optical property parameterization scheme (Voronoi scheme) of the Voronoi ICS model is employed in the Community Integrated Earth System Model (CIESM) to simulate the optical and radiative properties of ice clouds. We utilized the single-scattering properties (extinction efficiency, single-scattering albedo and asymmetry factor) of the Voronoi model from the ultraviolet to the infrared, combined with 14 408 particle size distributions obtained from aircraft measurements to complete the Voronoi scheme. The Voronoi scheme and existing schemes (Fu, Mitchell, Yi and Baum-yang05) are applied to the CIESM to simulate 10-year global cloud radiative effects during 2001–2010. Simulated globally averaged cloud radiative forcings at the top of the atmosphere (TOA) for Voronoi and the other four existing schemes are compared to the Clouds and the Earth's Radiant Energy System Energy Balanced and Filled (EBAF) product. The results show that the differences in shortwave and longwave globally averaged cloud radiative forcing at the TOA between the Voronoi scheme simulations and EBAF products are 1.1 % and 1.4 %, which are lower than those of the other four schemes. Particularly for regions (from 30∘ S to 30∘ N) where ice clouds occur frequently, the Voronoi scheme provides the closest match with EBAF products compared with the other four existing schemes. The results in this study fully demonstrated the effectiveness of the Voronoi ICS model in the simulation of the radiative properties of ice clouds in the climate model.
Li, Ruohan; Wang, Dongdong; Liang, Shunlin; Jia, Aolin; Wang, ZhihaoLi, R., D. Wang, S. Liang, A. Jia, Z. Wang, 2022: Estimating global downward shortwave radiation from VIIRS data using a transfer-learning neural network. Remote Sensing of Environment, 274, 112999. doi: 10.1016/j.rse.2022.112999. In recent years, machine learning (ML) has been successfully used in estimating downward shortwave radiation (DSR). To achieve global estimations, traditional ML models need sufficient ground measurements covering various atmospheric and surface conditions globally, which is difficult to accomplish. Training on the simulated data of a radiative transfer model (RTM) is a possible solution, but widely used RTMs ignore some complex cloud conditions which brings bias to simulations. In this study, a neural network applied with the transfer-learning (TL) concept is introduced to utilize both radiative transfer simulations and ground measurement data, achieving global DSR estimation with only top-of-atmosphere and surface albedo at local solar noon as inputs. The proposed method estimates both instantaneous and daily DSR from Visible Infrared Imaging Radiometer Suite (VIIRS) data at 750-m resolution, and both the estimates are validated by 40 independent stations globally. The root mean-square error and relative root mean square error of instantaneous DSR validation over 25 Baseline Surface Radiation Network, seven Surface Radiation Network, and eight Greenland Climate Network stations in 2013 were 91.2 (16.1%), 106.3 (18.3%), 75.0 (24.2%) W/m2, respectively, and the daily validation achieved 30.8 (15.5%), 33.5 (17.6%), and 31.3 (14.4) W/m2, respectively. The proposed method presents significant high accuracy over polar regions and similar performances over other areas compared with traditional ML models, physics models (e.g., look-up tables and direct estimations), and existing DSR products. The algorithm is also applied to VIIRS swath data to test its global efficacy. Instantaneous mapping captures the spatial pattern of the cloud-mask product, and daily mapping shows spatial patterns similar to the Clouds and the Earth's Radiant Energy System Synoptic TOA and surface fluxes and clouds product, but with more detail. Further analysis indicates that model performance is less sensitive to the quantity of training data after TL has been incorporated. This study demonstrates the advantages of TL on boosting both the generality and accuracy of DSR estimation, which can potentially be applied to other variable retrievals. Downward shortwave radiation; Solar energy; VIIRS; Radiative transfer; Machine learning; Transfer learning
Li, Shaopeng; Jiang, Bo; Peng, Jianghai; Liang, Hui; Han, Jiakun; Yao, Yunjun; Zhang, Xiaotong; Cheng, Jie; Zhao, Xiang; Liu, Qiang; Jia, KunLi, S., B. Jiang, J. Peng, H. Liang, J. Han, Y. Yao, X. Zhang, J. Cheng, X. Zhao, Q. Liu, K. Jia, 2022: Estimation of the All-Wave All-Sky Land Surface Daily Net Radiation at Mid-Low Latitudes from MODIS Data Based on ERA5 Constraints. Remote Sensing, 14(1), 33. doi: 10.3390/rs14010033. The surface all-wave net radiation (Rn) plays an important role in the energy and water cycles, and most studies of Rn estimations have been conducted using satellite data. As one of the most commonly used satellite data sets, Moderate Resolution Imaging Spectroradiometer (MODIS) data have not been widely used for radiation calculations at mid-low latitudes because of its very low revisit frequency. To improve the daily Rn estimation at mid-low latitudes with MODIS data, four models, including three models built with random forest (RF) and different temporal expansion models and one model built with the look-up-table (LUT) method, are used based on comprehensive in situ radiation measurements collected from 340 globally distributed sites, MODIS top-of-atmosphere (TOA) data, and the fifth generation of European Centre for Medium-Range Weather Forecasts Reanalysis 5 (ERA5) data from 2000 to 2017. After validation against the in situ measurements, it was found that the RF model based on the constraint of the daily Rn from ERA5 (an RF-based model with ERA5) performed the best among the four proposed models, with an overall validated root-mean-square error (RMSE) of 21.83 Wm−2, R2 of 0.89, and a bias of 0.2 Wm−2. It also had the best accuracy compared to four existing products (Global LAnd Surface Satellite Data (GLASS), Clouds and the Earth’s Radiant Energy System Edition 4A (CERES4A), ERA5, and FLUXCOM_RS) across various land cover types and different elevation zones. Further analyses illustrated the effectiveness of the model by introducing the daily Rn from ERA5 into a “black box” RF-based model for Rn estimation at the daily scale, which is used as a physical constraint when the available satellite observations are too limited to provide sufficient information (i.e., when the overpass time is less than twice per day) or the sky is overcast. Overall, the newly-proposed RF-based model with ERA5 in this study shows satisfactory performance and has strong potential to be used for long-term accurate daily Rn global mapping at finer spatial resolutions (e.g., 1 km) at mid-low latitudes. modeling; MODIS; net radiation; energy balance; ERA5; constraint; mid-low latitude; random forest; temporal expansion
Li, Shuping; Sørland, Silje Lund; Wild, Martin; Schär, ChristophLi, S., S. L. Sørland, M. Wild, C. Schär, 2022: Aerosol sensitivity simulations over East Asia in a convection-permitting climate model. Climate Dynamics. doi: 10.1007/s00382-022-06620-7. The parameterization of deep convection is one of the primary sources of uncertainties in regional climate simulations. Due to computational constraints, long-term kilometer-scale simulations with explicit deep convection have been limited, especially over East Asia. We here conduct a pair of 10-years (2001–2010) reference simulations, one convection-parameterizing simulation at 12 km (0.11$$^{\circ }$$) resolution covering the CORDEX East Asia domain, and one 4.4-km (0.04$$^{\circ }$$) convection-permitting simulation over a subdomain. The two simulations are driven by the ERA5 reanalysis and the coarser-resolution simulation, respectively. The 4.4-km convection-permitting simulation noticeably improves the representation of the top-of-atmosphere outgoing longwave and shortwave radiation as well as precipitation intensity. In addition, sensitivity simulations are performed with perturbed sulfate and black carbon aerosols, considering the direct and semi-direct aerosol radiative effects. For the simulations with sulfate aerosol perturbations, the cloud radiative effect partly offsets the aerosol radiative effects. Decreasing sulfate aerosols leads to low-level warming, destabilizing the atmospheric stratification and thereby increasing mean precipitation and the frequency of wet days. Increasing sulfate aerosols leads to an approximately opposite response. For the simulations with black carbon aerosol perturbations, there is some near-surface warming for both increases and decreases in aerosol concentration. Also, there are significant changes in cloud cover, but changes in precipitation are comparatively weak. While for sulfate aerosol perturbations the response is approximately linear (in the sense that positive and negative perturbations yield approximately opposite effects), the response to black carbon aerosol perturbations is more complex and shows some nonlinearity, regardless of the treatment of deep convection in the simulations. We present a simple interpretation for this surprising result. Black carbon; COSMO; East Asia; Regional climate model; Sulfate
Li, Te; Wang, Minghuai; Guo, Zhun; Yang, Ben; Xu, Yifei; Han, Xiaomen; Sun, JianningLi, T., M. Wang, Z. Guo, B. Yang, Y. Xu, X. Han, J. Sun, 2022: An Updated CLUBB PDF Closure Scheme to Improve Low Cloud Simulation in CAM6. Journal of Advances in Modeling Earth Systems, 14(12), e2022MS003127. doi: 10.1029/2022MS003127. Cloud Layers Unified By Binormals (CLUBB) adopts the joint probability density function (PDF) to close higher-order turbulence and diagnose the cloud fraction. CLUBB assumes the equal PDF width of vertical velocity () as the default closure scheme, called Analytic Double Gaussian 1 (ADG1). In this study, a new unequal width PDF closure scheme is adopted in CLUBB, in which the PDF width of is assumed to be associated with skewness and kurtosis of vertical velocity. Offline calculation shows that the updated closure scheme improves the tail in the joint PDF and produces the saturation area from the joint PDF of the total water and liquid water potential temperature closer to that derived from large-eddy simulations than ADG1. The new PDF scheme implemented in Community Atmosphere Model Version 6 is shown to increase low cloud fraction by 20%–30% in most stratocumulus-to-cumulus transition regions. The updated closure scheme is found to improve the low cloud simulation by simulating more symmetric turbulence in stratocumulus and stronger turbulent transport in shallow cumulus. Furthermore, the updated closure scheme enhances the cloud fraction near the cloud base by interacting with the microphysical scheme. Our work indicates the importance of continuous improvement in the PDF closures for higher-order turbulence schemes. low clouds; cloud parameterization; climate model; higher-order turbulence closure; sub-grid processes
Li, Xiaohan; Zhang, Yi; Peng, Xindong; Chu, Wenchao; Lin, Yanluan; Li, JianLi, X., Y. Zhang, X. Peng, W. Chu, Y. Lin, J. Li, 2022: Improved Climate Simulation by Using a Double-Plume Convection Scheme in a Global Model. Journal of Geophysical Research: Atmospheres, 127(11), e2021JD036069. doi: 10.1029/2021JD036069. Convective parameterization can drastically regulate the mean climate and tropical transient activity of a General circulation model (GCM). In this study, the physics suite of the NCAR Community Atmosphere Model, version 5 (CAM5) was first ported to the Global-to-Regional Integrated Forecast System model. Then, the original convective parameterization of CAM5—with a separate representation of deep convection Zhang–Mcfarlane (ZM) and shallow convection University of Washington (UW)—was replaced by a double-plume (DP) scheme. This DP scheme adopts a quasi-unified representation of shallow and deep convection within a single framework. Results demonstrate that the new scheme brings about several improvements in the modeled climate. The differences in the trigger and closure assumptions, lateral mixing rate, and cloud model for the deep convection result in systematic regional differences in the simulated precipitation pattern, cloud vertical structure, and the associated radiative forcing. Compared with ZM-UW, DP reduces the biases in precipitation over the Indian Ocean, ameliorates the “high-frequency and low-intensity” problem of tropical precipitation, and leads to an improved representation of tropical variability, including the Madden–Julian Oscillation. Double-plume reduces low clouds and increases high clouds in the tropics, due to its internal parallel-split convective processes and smaller cumulus cloud fraction. Discussions related to parametric tuning of convective parameterization are also presented.
Liang, Hui; Jiang, Bo; Liang, Shunlin; Peng, Jianghai; Li, Shaopeng; Han, Jiakun; Yin, Xiuwan; Cheng, Jie; Jia, Kun; Liu, Qiang; Yao, Yunjun; Zhao, Xiang; Zhang, XiaotongLiang, H., B. Jiang, S. Liang, J. Peng, S. Li, J. Han, X. Yin, J. Cheng, K. Jia, Q. Liu, Y. Yao, X. Zhao, X. Zhang, 2022: A global long-term ocean surface daily/0.05° net radiation product from 1983–2020. Scientific Data, 9(1), 337. doi: 10.1038/s41597-022-01419-x. The all-wave net radiation (Rn) on the ocean surface characterizes the available radiative energy balance and is important to understand the Earth’s climate system. Considering the shortcomings of available ocean surface Rn datasets (e.g., coarse spatial resolutions, discrepancy in accuracy, inconsistency, and short duration), a new long-term global daily Rn product at a spatial resolution of 0.05° from 1983 to 2020, as part of the Global High Resolution Ocean Surface Energy (GHOSE) products suite, was generated in this study by fusing several existing datasets including satellite and reanalysis products based on the comprehensive in situ measurements from 68 globally distributed moored buoy sites. Evaluation against in-situ measurements shows the root mean square difference, mean bias error and correlation coefficient squared of 23.56 Wm−2, 0.88 Wm−2 and 0.878. The global average ocean surface Rn over 1983–2020 is estimated to be 119.71 ± 2.78 Wm−2 with a significant increasing rate of 0.16 Wm−2 per year. GHOSE Rn product can be valuable for oceanic and climatic studies. Physical oceanography
Lim, Won-Il; Park, Hyo-Seok; Petty, Alek A.; Seo, Kyong-HwanLim, W., H. Park, A. A. Petty, K. Seo, 2022: The Role of Summer Snowstorms on Seasonal Arctic Sea Ice Loss. Journal of Geophysical Research: Oceans, 127(12), e2021JC018066. doi: 10.1029/2021JC018066. In the Arctic, short-lived summer snowstorms can provide snow cover that can increase surface reflectivity and heat capacity. Despite their potential importance, little research has been done to understand the impact of summer snowstorms on basin-scale Arctic sea ice cover. Our observational analysis shows that a summer snowstorm event is accompanied by cyclonic ice drift, increases in surface albedo and surface air cooling that can persist for up to ∼2 weeks, dampening sea ice loss. Specifically, multiple snowstorm events in a summer, on average, results in net increase in sea ice extent of ∼0.2 × 106 km2 by early September. Experiments with a sophisticated ice-ocean model framework indicate that the initial expansion of sea ice extent is driven by cyclonic wind-driven ice drifts driving sea ice southwards and increasing albedo around the summer ice edge, however the thermal effects from the associated snowfall and atmospheric conditions result in a stronger overall impact on basin-averaged sea ice extent at seasonal scales. Additional model experiments were carried out to isolate the physical processes contributing to the thermal response of Arctic sea ice to summer snowstorms. Our results show the impact of surface air cooling on sea ice extent is about 3.5 times larger than the snowfall/albedo response. However, our simulated albedo response is weaker than the observed response, likely due to the negligible difference in surface albedo between old snow and freshly fallen snow—a limiting factor in our analysis and a topic worthy of future focus. Arctic sea ice; albedo; snowfall
Lin, Qiao-Jun; Yu, Jia-YuhLin, Q., J. Yu, 2022: The potential impact of model horizontal resolution on the simulation of atmospheric cloud radiative effect in CMIP6 models. Terrestrial, Atmospheric and Oceanic Sciences, 33(1), 21. doi: 10.1007/s44195-022-00021-3. The simulations of atmospheric cloud-radiative effect (ACRE) from 54 Coupled Model Intercomparison Project phase 6 (CMIP6) models during the historical period of 2000/03–2014/12 are compared and evaluated against the satellite-based Clouds and the Earth’s Radiant Energy System (CERES) products. For ease of comparison, all CMIP6 models are divided into high-, medium-, and low-resolution groups to examine the potential impact of model horizontal resolution change on the simulations of ACRE distribution over the tropical oceans. The results show that ACRE is positive inside the ITCZs but negative in the subtropics and cold tongue areas, owing to the very different radiative forcing between deep and shallow clouds. Simulations of ACRE are sensitive to the model horizontal resolution used and the finer resolution models generally produce a better performance of ACRE simulations against the CERES observations. The reduced ACRE biases in finer resolution models are mainly contributed by the improved longwave ACRE (i.e., LWACRE) simulations, especially over the Pacific and Atlantic cold tongue areas where shallow stratocumulus clouds prevail. CMIP6; Atmospheric cloud-radiative effect; Model horizontal resolution
Lindzen, Richard S.; Choi, Yong-SangLindzen, R. S., Y. Choi, 2022: The Iris Effect: A Review. Asia-Pacific Journal of Atmospheric Sciences, 58(1), 159-168. doi: 10.1007/s13143-021-00238-1. This study reviews the research of the past 20-years on the role of anvil cirrus in the Earth’s climate – research initiated by Lindzen et al. (Bull. Am. Meteor. Soc. 82:417-432, 2001). The original study suggested that the anvil cirrus would shrink with warming, which was estimated to induce longwave cooling for the Earth. This is referred to as the iris effect since the areal change hypothetically resembles the light control by the human eye’s iris. If the effect is strong enough, it exerts a significant negative climate feedback which stabilizes tropical temperatures and limits climate sensitivity. Initial responses to Lindzen et al. (Bull. Am. Meteor. Soc. 82:417-432, 2001) denied the existence and effectiveness of the iris effect. Assessment of the debatable issues in these responses will be presented later in this review paper. At this point, the strong areal reduction of cirrus with warming appears very clearly in both climate models and satellite observations. Current studies found that the iris effect may not only come from the decreased cirrus outflow due to increased precipitation efficiency, but also from concentration of cumulus cores over warmer areas (the so-called aggregation effect). Yet, different opinions remain as to the radiative effect of cirrus clouds participating in the iris effect. For the iris effect to be most important, it must involve cirrus clouds that are not as opaque for visible radiation as they are for infrared radiation. However, current climate models often simulate cirrus clouds that are opaque in both visible and infrared radiation. This issue requires thorough examination as it seems to be opposed to conventional wisdom based on explicit observations. This paper was written in the hope of stimulating more effort to carefully evaluate these important issues.
Lipzig, Nicole P. M. van; Walle, Jonas Van de; Belušić, Danijel; Berthou, Ségolène; Coppola, Erika; Demuzere, Matthias; Fink, Andreas H.; Finney, Declan L.; Glazer, Russell; Ludwig, Patrick; Marsham, John H.; Nikulin, Grigory; Pinto, Joaquim G.; Rowell, David P.; Wu, Minchao; Thiery, WimLipzig, N. P. M. v., J. V. d. Walle, D. Belušić, S. Berthou, E. Coppola, M. Demuzere, A. H. Fink, D. L. Finney, R. Glazer, P. Ludwig, J. H. Marsham, G. Nikulin, J. G. Pinto, D. P. Rowell, M. Wu, W. Thiery, 2022: Representation of precipitation and top-of-atmosphere radiation in a multi-model convection-permitting ensemble for the Lake Victoria Basin (East-Africa). Climate Dynamics. doi: 10.1007/s00382-022-06541-5. The CORDEX Flagship Pilot Study ELVIC (climate Extremes in the Lake VICtoria basin) was recently established to investigate how extreme weather events will evolve in this region of the world and to provide improved information for the climate impact community. Here we assess the added value of the convection-permitting scale simulations on the representation of moist convective systems over and around Lake Victoria. With this aim, 10 year present-day model simulations were carried out with five regional climate models at both PARameterized (PAR) scales (12–25 km) and Convection-Permitting (CP) scales (2.5–4.5 km), with COSMO-CLM, RegCM, AROME, WRF and UKMO. Most substantial systematic improvements were found in metrics related to deep convection. For example, the timing of the daily maximum in precipitation is systematically delayed in CP compared to PAR models, thereby improving the agreement with observations. The large overestimation in the total number of rainy events is alleviated in the CP models. Systematic improvements were found in the diurnal cycle in Top-Of-Atmosphere (TOA) radiation and in some metrics for precipitation intensity. No unanimous improvement nor deterioration was found in the representation of the spatial distribution of total rainfall and the seasonal cycle when going to the CP scale. Furthermore, some substantial biases in TOA upward radiative fluxes remain. Generally our analysis indicates that the representation of the convective systems is strongly improved in CP compared to PAR models, giving confidence that the models are valuable tools for studying how extreme precipitation events may evolve in the future in the Lake Victoria basin and its surroundings. Convection permitting simulations; CORDEX Flagship Pilot Study; Equatorial Africa; Extreme weather events; Kilometer-scale resolution; Lake Victoria basin; Regional climate models; Tropical deep convection
Liu, Chunlei; Chen, Ni; Long, Jingchao; Cao, Ning; Liao, Xiaoqing; Yang, Yazhu; Ou, Niansen; Jin, Liang; Zheng, Rong; Yang, Ke; Su, QianyeLiu, C., N. Chen, J. Long, N. Cao, X. Liao, Y. Yang, N. Ou, L. Jin, R. Zheng, K. Yang, Q. Su, 2022: Review of the Observed Energy Flow in the Earth System. Atmosphere, 13(10), 1738. doi: 10.3390/atmos13101738. The energy budget imbalance at the top of the atmosphere (TOA) and the energy flow in the Earth’s system plays an essential role in climate change over the global and regional scales. Under the constraint of observations, the radiative fluxes at TOA have been reconstructed prior to CERES (Clouds and the Earth’s Radiant Energy System) between 1985 and 2000. The total atmospheric energy divergence has been mass corrected based on ERA5 (the fifth generation ECMWF ReAnalysis) atmospheric reanalysis by a newly developed method considering the enthalpy removing of the atmospheric water vapor, which avoids inconsistencies due to the residual lateral total mass flux divergence in the atmosphere, ensuring the balances of the freshwater fluxes at the surface. The net surface energy flux (Fs) has been estimated using the residual method based on energy conservation, which is the difference between the net TOA radiative flux and the atmospheric energy tendency and divergence. The Fs is then verified directly and indirectly with observations, and results show that the estimated Fs in North Atlantic is superior to those from model simulations. This paper gives a brief review of the progress in the estimation of the observed energy flow in the Earth system, discusses some caveats of the existing method, and provides some suggestions for the improvements of the aforementioned data sets. energy transport; mass corrected atmospheric energy divergence; net surface energy flux; TOA radiative flux
Liu, Chunlei; Yang, Yazhu; Liao, Xiaoqing; Cao, Ning; Liu, Jimmy; Ou, Niansen; Allan, Richard P.; Jin, Liang; Chen, Ni; Zheng, RongLiu, C., Y. Yang, X. Liao, N. Cao, J. Liu, N. Ou, R. P. Allan, L. Jin, N. Chen, R. Zheng, 2022: Discrepancies in Simulated Ocean Net Surface Heat Fluxes over the North Atlantic. Advances in Atmospheric Sciences. doi: 10.1007/s00376-022-1360-7. The change in ocean net surface heat flux plays an important role in the climate system. It is closely related to the ocean heat content change and ocean heat transport, particularly over the North Atlantic, where the ocean loses heat to the atmosphere, affecting the AMOC (Atlantic Meridional Overturning Circulation) variability and hence the global climate. However, the difference between simulated surface heat fluxes is still large due to poorly represented dynamical processes involving multiscale interactions in model simulations. In order to explain the discrepancy of the surface heat flux over the North Atlantic, datasets from nineteen AMIP6 and eight highresSST-present climate model simulations are analyzed and compared with the DEEPC (Diagnosing Earth’s Energy Pathways in the Climate system) product. As an indirect check of the ocean surface heat flux, the oceanic heat transport inferred from the combination of the ocean surface heat flux, sea ice, and ocean heat content tendency is compared with the RAPID (Rapid Climate Change-Meridional Overturning Circulation and Heat flux array) observations at 26°N in the Atlantic. The AMIP6 simulations show lower inferred heat transport due to less heat loss to the atmosphere. The heat loss from the AMIP6 ensemble mean north of 26°N in the Atlantic is about 10 W m−2 less than DEEPC, and the heat transport is about 0.30 PW (1 PW = 1015 W) lower than RAPID and DEEPC. The model horizontal resolution effect on the discrepancy is also investigated. Results show that by increasing the resolution, both surface heat flux north of 26°N and heat transport at 26°N in the Atlantic can be improved. observations; ocean heat transport; discrepancy; ocean net surface heat flux; simulations
Liu, Le; Wu, Bingyi; Ding, ShuoyiLiu, L., B. Wu, S. Ding, 2022: On the Association of the Summertime Shortwave Cloud Radiative Effect in Northern Russia With Atmospheric Circulation and Climate Over East Asia. Geophysical Research Letters, 49(2), e2021GL096606. doi: 10.1029/2021GL096606. This study employs ERA5 reanalysis and CERES/EBAF Ed4.1 data to evaluate the dominant features of summer shortwave cloud radiative effect (SWCRE) variability and associated atmospheric circulation anomalies. Our findings suggest that the greatest variability in summer SWCRE occurs over the Barents, Kara, and Laptev seas and northern Eurasia. We also observe a close relationship between summertime SWCRE, particularly in northern Russia, and atmospheric circulation variability over East Asia. Significant positive SWCRE anomalies over northern Russia favor the generation of the Ural blocking, and dynamically trigger the emergence of positive Eurasian (EU) pattern, resulting in positive (negative) precipitation anomalies in northern (southeastern) China and persistent East Asian heatwaves between 20°N and 40°N. In contrast to previous work, which has focused mainly on local atmospheric responses to SWCRE, this study provides a broader perspective, thereby helping bridge summertime circulation between high latitudes and East Asia. shortwave cloud radiative effect; East Asian atmospheric circulation variability; Eurasian teleconnection; Ural blocking
Liu, Xinyan; He, Tao; Sun, Lin; Xiao, Xiongxin; Liang, Shunlin; Li, SiweiLiu, X., T. He, L. Sun, X. Xiao, S. Liang, S. Li, 2022: Analysis of Daytime Cloud Fraction Spatiotemporal Variation over the Arctic from 2000 to 2019 from Multiple Satellite Products. J. Climate, 35(23), 3995-4023. doi: 10.1175/JCLI-D-22-0007.1. Abstract Insufficient understanding of complex Arctic cloud properties introduced large errors in estimating radiant energy balance parameters at the regional and global scales. Comprehensive and reliable cloud information is necessary for improving the accuracy of flux inversion. This study evaluated daytime cloud fraction (CF) uncertainties from 16 available satellite products and estimated the spatiotemporal distributions of Arctic daytime CF during 2000–19. Our results show that the differences among multiple products had significant temporal and spatial heterogeneities. Temporally, the maximum and minimum interproduct discrepancies occurred in April and the summer months, respectively. Spatially, the largest uncertainties were seen over Greenland. Substantial inconsistency also occurred on the central and Pacific sides of the Arctic Ocean. The active satellite product tended to capture more clouds in these two regions. We found that the inconsistencies caused by sensor differences were smaller than those caused by algorithm differences; that is, for MODIS based CF products, the inconsistencies caused by different sensors and different algorithms are ±2% and ±5%, while for AVHRR-based products, these inconsistencies are ±6% and ±15%, respectively. The annual average daytime CF in sunlit months was 70.9% ± 2.93% and increased over the Arctic during study periods. These upward trends might cool the Arctic by approximately 0.05–0.5 W m−2 decade−1. In terms of the spatiotemporal distributions, the CF over the ocean is higher than that over the land, and the former increased significantly while the latter decreased; the CF trends of most products are positive in June and July but are opposite in other months. From this study, the findings based on multiple products would be more robust than that based on a single or few datasets. Significance Statement This study aimed to comprehensively understand and obtain more robust general characteristics of the temporal and spatial distributions of Arctic daytime cloud fraction by comparing and analyzing the consistencies and discrepancies of multisource satellite products. It is important because the cloud fraction is a nonnegligible modulator of Earth’s energy budget and climate change. Although the Arctic is the most climate-sensitive region, existing studies lack a comprehensive assessment of the cloud fraction over the entire Arctic. We analyzed 16 different cloud products and found that although the inconsistencies were inevitable, most products showed similar spatiotemporal distribution and trend distribution of daytime CF. This study provided a new idea for Arctic CF research under the existing conditions.
Liu, Yansong; Ren, Qiang; Yu, Fei; Wang, Jianfeng; Wang, Ran; Nan, Feng; Ding, Yanan; Zheng, Tongtong; Zhang, Chuanzheng; Zhao, Ruixiang; Zheng, Hua; Zhu, Xiao-HuaLiu, Y., Q. Ren, F. Yu, J. Wang, R. Wang, F. Nan, Y. Ding, T. Zheng, C. Zhang, R. Zhao, H. Zheng, X. Zhu, 2022: Observed Taylor cap around a seamount intensified by a surface mesoscale eddy in the Northwest Pacific. Climate Dynamics. doi: 10.1007/s00382-022-06570-0. Observations from 4 current and pressure-recording inverted echo sounders (CPIESs) deployed in the northwest Pacific from 2018 to 2019 reveal an anticyclonic cap around a seamount. Significant increases in velocity can be found from mid-November 2018 to January 2019 and verified the coexistence with the “cold dome” combined with numerical model data. The Taylor cap induced by the impinging flow toward the seamount plays a primary role in the anticyclonic current structure compared with tide rectification. The relationship between the impinging flow and surface mesoscale eddy in the northwest Pacific was further analyzed by combining the satellite altimeter data. When the surface cyclonic eddy moved to the center of the seamount in November 2018, the absolute sea level anomaly (SLA) increased, the temperature at the summit decreased, and the deep velocity impinging toward the seamount decreased and then intensified the Taylor cap around the seamount. CPIES; Northwest Pacific; Seamount; Surface mesoscale eddy; Taylor cap
Liu, Yawen; Wang, Minghuai; Qian, Yun; Ding, AijunLiu, Y., M. Wang, Y. Qian, A. Ding, 2022: A Strong Anthropogenic Black Carbon Forcing Constrained by Pollution Trends Over China. Geophysical Research Letters, 49(10), e2022GL098965. doi: 10.1029/2022GL098965. Estimates of the effective radiative forcing from aerosol-radiation interaction (ERFari) of anthropogenic Black Carbon (BC) have been disputable and require better constraints. Here we find a substantial decline in atmospheric absorption of −5.79Wm−2decade−1 over eastern central China (ECC) responding to recent anthropogenic BC emission reductions. By combining the observational finding with advances from Coupled Model Intercomparison Project phase6 (CMIP6), we identify an emergent constraint on the ERFari of anthropogenic BC. We show that across CMIP6 models the simulated trends correlate well with simulated annual mean shortwave atmospheric absorption by anthropogenic BC over China. Making use of this emergent relationship allows us to constrain the aerosol absorption optical depth of anthropogenic BC and further provide a constrained range of 2.4–3.0 Wm−2 for its top-of-atmosphere ERFari over China, higher than existing estimates. Our work supports a strong warming effect of BC over China, and highlights the need to improve BC simulations over source regions. CMIP6 models; anthropogenic black carbon; effective radiative forcing from aerosol-radiation interaction; long-term trend; observational constraint
Liu, Yuzhi; Huang, Jianping; Wang, Tianhe; Li, Jiming; Yan, Hongru; He, YongliLiu, Y., J. Huang, T. Wang, J. Li, H. Yan, Y. He, 2022: Aerosol-cloud interactions over the Tibetan Plateau: An overview. Earth-Science Reviews, 234, 104216. doi: 10.1016/j.earscirev.2022.104216. This paper reviews progress in the study of aerosol-cloud interactions over the Tibetan Plateau (TP) in the past decade. Clarifying the aerosol-cloud-precipitation interactions over the TP is an important issue for both local and downstream precipitation forecasts. By exerting a “dynamic pump” effect due to the elevated heat source in summer, the TP acts as a “transfer station” for aerosols and water vapor, possessing abundant water vapor and enough cloud condensation nuclei (CCN) and ice nuclei (IN) in cloud physical processes. We found that mixtures of aerosols and clouds are frequently observed over the margin areas of the TP, especially the mixture between aerosols and ice clouds. The convective clouds over the TP could be affected by the Taklimakan dusts lifted from the north slope of the TP, inducing higher and more invigorated convective clouds locally. Furthermore, the dust-polluted convective clouds can continuously move eastward and merge with the convective cloud clusters along their motion paths, inducing more intensive rainfall over the downstream regions of the TP. Finally, challenges to further understanding aerosol-cloud interactions over the TP in the future are discussed. Precipitation; Tibetan Plateau; Cloud; Aerosol; Interaction
Loeb, Norman G.; Mayer, Michael; Kato, Seiji; Fasullo, John T.; Zuo, Hao; Senan, Retish; Lyman, John M.; Johnson, Gregory C.; Balmaseda, MagdalenaLoeb, N. G., M. Mayer, S. Kato, J. T. Fasullo, H. Zuo, R. Senan, J. M. Lyman, G. C. Johnson, M. Balmaseda, 2022: Evaluating Twenty-Year Trends in Earth's Energy Flows From Observations and Reanalyses. Journal of Geophysical Research: Atmospheres, 127(12), e2022JD036686. doi: 10.1029/2022JD036686. Satellite, reanalysis, and ocean in situ data are analyzed to evaluate regional, hemispheric and global mean trends in Earth's energy fluxes during the first 20 years of the twenty-first century. Regional trends in net top-of-atmosphere (TOA) radiation from the Clouds and the Earth's Radiant Energy System (CERES), ECMWF Reanalysis 5 (ERA5), and a model similar to ERA5 with prescribed sea surface temperature (SST) and sea ice differ markedly, particularly over the Eastern Pacific Ocean, where CERES observes large positive trends. Hemispheric and global mean net TOA flux trends for the two reanalyses are smaller than CERES, and their climatological means are half those of CERES in the southern hemisphere (SH) and more than nine times larger in the northern hemisphere (NH). The regional trend pattern of the divergence of total atmospheric energy transport (TEDIV) over ocean determined using ERA5 analyzed fields is similar to that inferred from the difference between TOA and surface fluxes from ERA5 short-term forecasts. There is also agreement in the trend pattern over ocean for surface fluxes inferred as a residual between CERES net TOA flux and ERA5 analysis TEDIV and surface fluxes obtained directly from ERA5 forecasts. Robust trends are observed over the Gulf Stream associated with enhanced surface-to-atmosphere transfer of heat. Within the ocean, larger trends in ocean heating rate are found in the NH than the SH after 2005, but the magnitude of the trend varies greatly among datasets.
Lv, Mingzhu; Song, Yan; Li, Xijia; Wang, Mengsi; Qu, YingLv, M., Y. Song, X. Li, M. Wang, Y. Qu, 2022: Spatiotemporal characteristics and driving factors of global planetary albedo: an analysis using the Geodetector method. Theoretical and Applied Climatology, 147(1), 737-752. doi: 10.1007/s00704-021-03858-9. As an important parameter of the Earth’s energy budget, the planetary albedo of Earth varies with the dynamics of atmospheric and surface variables. In this study, we investigated the spatiotemporal characteristics and driving factors of the global planetary albedo using the Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) dataset and the Geodetector method. The results revealed that the planetary albedo can be decomposed into atmospheric and surface contributions, and the planetary albedo in the middle and low latitudes was predominantly affected by the atmospheric contribution. The global planetary albedo and the atmospheric and surface contributions exhibited decreasing trends of − 0.0020, − 0.0015, and − 0.0004/decade from 2001 to 2018, respectively, which were closely related to the variations of atmospheric and surface variables. The cloud fraction was the driving factor of the atmospheric contribution in the middle and low latitudes, and its influence was further enhanced by the aerosol optical thickness (AOT), ice water path (IWP), and liquid water path (LWP). The snow/ice coverage and normalized difference vegetation index (NDVI) were the driving factors of the surface contribution in the snow/ice-covered and vegetated areas, respectively. The interaction relationships between the surface variables were mainly bi-enhanced and nonlinearly enhanced. These results provide useful information about the driving factors of the planetary albedo and are benefit for improving the parametrization of the planetary albedo.
Ma, Mengnan; Ou, Tinghai; Liu, Dongqing; Wang, Shuyu; Fang, Juan; Tang, JianpingMa, M., T. Ou, D. Liu, S. Wang, J. Fang, J. Tang, 2022: Summer regional climate simulations over Tibetan Plateau: from gray zone to convection permitting scale. Climate Dynamics. doi: 10.1007/s00382-022-06314-0. The Tibetan Plateau (TP) is often referred to as ‘the Third Pole’ and plays an essential role in the global climate. However, it remains challenging for most global and regional models to realistically simulate the characteristics of climate over the TP. In this study, two Weather Research and Forecasting model (WRF) experiments using spectral nudging with gray-zone (GZ9) and convection-permitting (CP3) resolution are conducted for summers from 2009 to 2018. The surface air temperature (T2m) and precipitation from the two simulations and the global reanalysis ERA5 are evaluated against in-situ observations. The results show that ERA5 has a general cold bias over southern TP, especially in maximum T2m (Tmax), and wet bias over whole TP. Both experiments can successfully capture the spatial pattern and daily variation of T2m and precipitation, though cold bias for temperature and dry bias for precipitation exist especially over the regions south of 35° N. Compared with ERA5, the added value of the two WRF experiments is mainly reflected in the reduced cold bias especially for Tmax with more improvement found in CP3 and the reduced wet bias. However, the ability of the convection-permitting WRF experiment in improving the simulation of precipitation seems limited when compared to the gray-zone WRF experiment, which may be related to the biases in physical parameterization and lack of representativeness of station observation. Further investigation into surface radiation budget reveals that the underestimation of net shortwave radiation contributes a lot to the cold bias of T2m over the southeastern TP in GZ9 which is improved in CP3. Compared with GZ9, CP3 shows that larger specific humidity at low-level (mid-high level) coexists with more precipitation (clouds) over the southern TP. This improvement is achieved by better depiction of topographic details, underlying surface and atmospheric processes, land–atmosphere interactions and so on, leading to stronger northward water vapor transport (WVT) in CP3, providing more water vapor for precipitation at surface and much wetter condition in the mid-high level. Tibetan Plateau; Convection permitting; Gray zone; Spectral nudging; Summer precipitation; Surface air temperature
Ma, Wen; Ding, Jianli; Wang, Jinlong; Zhang, JunyongMa, W., J. Ding, J. Wang, J. Zhang, 2022: Effects of aerosol on terrestrial gross primary productivity in Central Asia. Atmospheric Environment, 288, 119294. doi: 10.1016/j.atmosenv.2022.119294. Aerosols significantly contribute to global and regional climate change by altering the surface solar radiation, thereby affecting plant productivity. Central Asia is a primary source of global dust aerosols. However, the mechanisms of how aerosols affect terrestrial gross primary productivity (GPP), especially in Central Asia, are not clearly understood. In this study, we investigated the spatial variation in aerosol optical depth (AOD) and GPP and the relationship between them during the growing season (April–October) from 2001 to 2018 using remote sensing data from several sources. We created a GWR-SEM model consisting of a geographically weighted model (GWR) coupled with a structural equation model (SEM) to quantify and analyze the effects of AOD on GPP. The results show that AOD decreased slightly at a rate of −0.0002 y−1 during the study period and that there was a tendency towards spatial aggregation. The extent of AOD pollution in the northwest region (around the Aral Sea) was slightly greater than that in the southeast. GPP increased significantly at a rate of 7.2965 g C m−2 y−2, especially in the northern region. There were some differences in the effects of AOD on GPP between different vegetation types; the highest AOD–GPP correlation was found in shrublands and croplands. Analysis of the GWR-SEM model suggested that AOD and two forms of radiation (surface net radiation, SNR, and photosynthetically active radiation, PAR) explained 72.4% (63.4% for 2001, 66.8% for 2018) of the spatial variation in GPP. SNR had the greatest effect on GPP, followed by AOD. Diffuse PAR had the greatest indirect effect on GPP. The findings of this study highlight the importance of aerosol pollution on spatial variation in gross primary productivity, and they provide a methodological framework for investigating the relationship between AOD and GPP in arid areas. GPP; Aerosol optional depth; Central Asia; SEM
Maity, Suman; Nayak, Sridhara; Nayak, Hara Prasad; Bhatla, R.Maity, S., S. Nayak, H. P. Nayak, R. Bhatla, 2022: Comprehensive assessment of RegCM4 towards interannual variability of Indian Summer Monsoon using multi-year simulations. Theoretical and Applied Climatology. doi: 10.1007/s00704-022-03961-5. In this study, the interannual variability (IAV) of Indian Summer Monsoon (ISM) is investigated using multi-year (1982‒2016) seasonal scale simulations (May‒September) of the regional climate model RegCM4. Model-simulated fields such as surface temperature, wind and rainfall are validated initially to testify the climatological behaviour of ISM. Subsequently, different aspects of IAV associated with ISM are discussed primarily focusing on model simulated rainfall and are verified against high-resolution rainfall analysis from India Meteorological Department (IMD). Analysis indicated that RegCM4 shows reasonable accuracy in simulating major large-scale features, however, has cold bias over entire India and wet (dry) bias over northwest and peninsular (central) India. Easterly (westerly) bias is noticed in the model simulated low (upper) level wind that affects regional Hadley circulation. The cold bias is found to be associated with the feedback cycle of land–atmosphere interaction. Surface evaporative cooling likely affects the static instability in the atmospheric column, thereby limiting the convection and thus reducing rainfall. While categorizing, it is noticed that the efficacy of the model is found to be better in simulating normal monsoon as compared to contrasting monsoon (deficit and excess) year, thereby reducing the simulation skill for the entire period. EOF analysis revealed that first two leading modes of IMD rainfall are linked with large-scale variabilities, viz. El-Nino Southern Oscillation and Indian Ocean Dipole, respectively, but RegCM4 could not well reproduce these relationships. The spectral analysis showed 2–7 year periodicity in the model. However, the associated spectral peaks are close to the red noise spectrum due to their weak power suggesting limited model skill to capture large-scale variability. Overall, this study advocates that the RegCM4 could capture the climatological features of ISM fairly well, but needs further improvement in representing the IAV more accurately.
Maloney, Christopher; Toon, Brian; Bardeen, Charles; Yu, Pengfei; Froyd, Karl; Kay, Jennifer; Woods, SarahMaloney, C., B. Toon, C. Bardeen, P. Yu, K. Froyd, J. Kay, S. Woods, 2022: The balance between heterogeneous and homogeneous nucleation of ice clouds using CAM5/CARMA. Journal of Geophysical Research: Atmospheres, e2021JD035540. doi: 10.1029/2021JD035540. We present a modification to the Community Aerosol and Radiation model for Atmospheres (CARMA) sectional ice microphysical model where we have added interactive nucleation of sulfates and heterogeneous nucleation onto dust in order to create a more comprehensive representation of ice nucleation within the CARMA sectional ice model. The convective wet removal fix has also been added in order to correctly transport aerosol within the Community Atmosphere Model version 5 (CAM5) and the 3-mode Modal Aerosols Model (MAM3). In CARMA, the balance of homogeneous and heterogeneous nucleation is controlled by the presence of temperatures below 240 °K, supersaturation, and the availability of heterogeneous nuclei. Due to a paucity of dust at altitudes above about 7 km, where temperatures over most of the Earth fall below 240 °K, cirrus clouds above 7 km nucleate primarily via homogeneous nucleation on aqueous sulfate aerosols in our simulations. Over mid-latitudes of the Northern Hemisphere, dust is more common above 7 km during spring through fall, and both heterogeneous nucleation and homogenous freezing occur in our model. Below 7 km heterogeneous nucleation dominates in situ formation of ice. Furthermore, we find an improvement of the representation of in-cloud ice within mixed phase clouds in CAM5/CARMA when compared to simulations with only homogeneous ice nucleation. Other modes of nucleation such as contact nucleation of liquid cloud droplets or liquid cloud droplet freezing on immersion nuclei, were not directly compared with classical depositional heterogeneous nucleation in this study. Cloud modeling; Dust Aerosol; Heterogeneous nucleation; Homogeneous nucleation; Ice nucleation
Matthews, G.Matthews, G., 2022: Direct Solar Viewing Calibration Concept for Future CERES-, GERB-, or Libera-Type Earth Orbital Climate Missions. J. Atmos. Oceanic Technol., 39(7), 1085-1091. doi: 10.1175/JTECH-D-21-0002.1. Abstract Better predictions of global warming can be enabled by tuning legacy and current computer simulations to Earth radiation budget (ERB) measurements. Since the 1970s, such orbital results exist, and the next-generation instruments such as one called “Libera” are in production. Climate communities have requested that new ERB observing system missions like these have calibration accuracy obtaining significantly improved calibration SI traceability and stability. This is to prevent untracked instrument calibration drifts that could lead to false conclusions on climate change. Based on experience from previous ERB missions, the alternative concept presented here utilizes directly viewing solar calibration, for cloud-size Earth measurement resolution at
Matthews, GrantMatthews, G., 2022: Assessment of Terra/Aqua MODIS and Deep Convective Cloud Albedo Solar Calibration Accuracies and Stabilities Using Lunar Calibrated MERBE Results. Remote Sensing, 14(11), 2517. doi: 10.3390/rs14112517. Moon calibrated radiometrically stable and relatively accurate Earth reflected solar measurements from the Moon and Earth Radiation Budget Experiment (MERBE) are compared here to primary channels of coaligned Terra/Aqua MODIS instruments. A space-based climate observing system immune to untracked drifts due to varying instrument calibration is a key priority for climate science. Measuring these changes in radiometers such as MODIS and compensating for them is critical to such a system. The independent MERBE project using monthly lunar scans has made a proven factor of ten improvement in calibration stability and relative accuracy of measurements by all devices originally built for another project called ‘CERES’, also on the Terra and Aqua satellites. The MERBE comparison shown here uses spectrally invariant Deep Convective Cloud or DCC targets as a transfer, with the objective of detecting possible unknown MODIS calibration trends or errors. Most MODIS channel 1–3 collection 5 calibrations are shown to be correct and stable within stated accuracies of 3% relative to the Moon, much in line with changes made for MODIS collection 6. Stable lunar radiance standards are then separately compared to the sometimes used calibration metric of the coldest DCCs as standalone calibration targets, when also located by MODIS. The analysis overall for the first time finds such clouds can serve as an absolute solar target on the order of 1% accuracy and are stable to ±0.3% decade−1 with two sigma confidences, based on the Moon from 2000–2015. Finally, time series analysis is applied to potential DCC albedo corrected Terra data. This shows it is capable of beginning the narrowing of cloud climate forcing uncertainty before 2015; some twenty five years sooner than previously calculated elsewhere, for missions yet to launch. earth radiation budget; MODIS; earth observation; lunar calibration; MERBE; climate observing system; deep convective cloud (DCC) albedo; solar forcing
Mayer, Johannes; Mayer, Michael; Haimberger, Leopold; Liu, ChunleiMayer, J., M. Mayer, L. Haimberger, C. Liu, 2022: Comparison of Surface Energy Fluxes from Global to Local Scale. J. Climate, 35(14), 4551-4569. doi: 10.1175/JCLI-D-21-0598.1. Abstract This study uses the ECMWF ERA5 reanalysis and observationally constrained top-of-the-atmosphere radiative fluxes to infer net surface energy fluxes covering 1985–2018, which can be further adjusted to match the observed mean land heat uptake. Various diagnostics are applied to provide error estimates of inferred fluxes on different spatial scales. For this purpose, adjusted as well as unadjusted inferred surface fluxes are compared with other commonly used flux products. On a regional scale, the oceanic energy budget of the North Atlantic between the RAPID array at 26.5°N and moorings located farther north (e.g., at the Greenland–Scotland Ridge) is evaluated. On the station scale, a comprehensive comparison of inferred and buoy-based fluxes is presented. Results indicate that global land and ocean averages of unadjusted inferred surface fluxes agree with the observed heat uptake to within 1 W m−2, while satellite-derived and model-based fluxes show large global mean biases. Furthermore, the oceanic energy budget of the North Atlantic is closed to within 2.7 (−0.2) W m−2 for the period 2005–09 when unadjusted (adjusted) inferred surface fluxes are employed. Indirect estimates of the 2004–16 mean oceanic heat transport at 26.5°N are 1.09 PW (1.17 PW with adjusted fluxes), which agrees well with observed RAPID transports. On the station scale, inferred fluxes exhibit a mean bias of −20.1 W m−2 when using buoy-based fluxes as reference, which confirms expectations that biases increase from global to local scales. However, buoy-based fluxes as reference are debatable, and are likely positively biased, suggesting that the station-scale bias of inferred fluxes is more likely on the order of −10 W m−2.
Mazhar, Usman; Jin, Shuanggen; Hu, Ting; Bilal, Muhammad; Ali, MD Arfan; Atique, LuqmanMazhar, U., S. Jin, T. Hu, M. Bilal, M. A. Ali, L. Atique, 2022: Long-time Variation and Mechanism of Surface Energy Budget over Diverse Geographical Regions in Pakistan. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 1-13. doi: 10.1109/JSTARS.2022.3185177. Earth's Energy budget is a major force that drives global climate. The long-term pattern of land surface energy budget with pronounced biophysical effects on climate was normally ignored at a regional scale, particularly in Pakistan. In this paper, the land surface energy budget from 2001 to 2018 was estimated and analyzed from Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud and the Earth's Radiant Energy System (CERES) observations over three geographical regions (Northern highlands, Indus plains and Baluchistan plateau) in Pakistan. Biophysical and energy budget parameters such as Land Surface Temperature (LST), albedo, emissivity, and Normalized Difference Vegetation Index (NDVI) were obtained from MODIS, while the downward shortwave solar and longwave thermal radiation were obtained from CERES satellite data. Spatiotemporal trends of three energy budget parameters: net radiation, latent heat flux and sensible heat flux, and three biophysical parameters, albedo, NDVI and LST, were investigated from 2001 to 2018. The latent heat flux showed a significant increase with a trend of 0.24, while a decrease in sensible heat flux with a trend of−0.21 was observed over Pakistan. Net radiation showed an ignorable increase with a trend of 0.054 over whole Pakistan. A significant negative relation was found between net radiation and sensible heat flux with albedo while a significant positive relation was found between latent heat flux and NDVI. Biophysical parameters such as NDVI, albedo and LST successively explain the trends of radiative and non-radiative fluxes. This study comprehensively explains the mechanism and patterns of the regional energy budget. CERES; Land surface; Net radiation; Meteorology; MODIS; Land surface temperature; Heating systems; and Pakistan; IP networks; Land surface Energy budget; Spatiotemporal phenomena
McCoy, Daniel T.; Field, Paul; Frazer, Michelle E.; Zelinka, Mark D.; Elsaesser, Gregory S; Mülmenstädt, Johannes; Tan, Ivy; Myers, Timothy A.; Lebo, Zachary J.McCoy, D. T., P. Field, M. E. Frazer, M. D. Zelinka, G. S. Elsaesser, J. Mülmenstädt, I. Tan, T. A. Myers, Z. J. Lebo, 2022: Extratropical shortwave cloud feedbacks in the context of the global circulation and hydrological cycle. Geophysical Research Letters, n/a(n/a), e2021GL097154. doi: 10.1029/2021GL097154. Shortwave (SW) cloud feedback (SWFB) is the primary driver of uncertainty in the effective climate sensitivity (ECS) predicted by global climate models (GCMs). ECS for several GCMs participating in the sixth assessment report exceed 5K, above the fifth assessment report ‘likely’ maximum (4.5K) due to extratropical SWFB’s that are more positive than those simulated in the previous generation of GCMs. Here we show that across 57 GCMs Southern Ocean SWFB can be predicted from the sensitivity of column-integrated liquid water mass (LWP) to moisture convergence and to surface temperature. The response of LWP to moisture convergence and the response of albedo to LWP anti-correlate across GCMs. This is because GCMs that simulate a larger response of LWP to moisture convergence tend to have higher mean-state LWPs, which reduces the impact of additional LWP on albedo. Observational constraints suggest a modestly negative Southern Ocean SWFB— inconsistent with extreme ECS. Clouds; Feedback; Moisture; Climate; Simulations
Miyamoto, Ayumu; Nakamura, Hisashi; Miyasaka, Takafumi; Kosaka, YuMiyamoto, A., H. Nakamura, T. Miyasaka, Y. Kosaka, 2022: Wintertime Weakening of Low-Cloud Impacts on the Subtropical High in the South Indian Ocean. J. Climate, 35(1), 323-334. doi: 10.1175/JCLI-D-21-0178.1. Abstract To elucidate the unique seasonality in the coupled system of the subtropical Mascarene high and low-level clouds, the present study compares wintertime cloud radiative impacts on the high with their summertime counterpart through coupled and atmospheric general circulation model simulations. A comparison of a fully coupled control simulation with another simulation in which the radiative effects of low-level clouds are artificially switched off demonstrates that the low-cloud effect on the formation of the Mascarene high is much weaker in winter. Background climatology plays an important role in this seasonality of the Mascarene high reinforcement. Relative to summer, the suppression of deep convection due to low-level clouds that acts to reinforce the high is much weaker in winter. This arises from 1) seasonally lower sea surface temperature in concert with the smaller sea surface temperature reduction due to the deeper ocean mixed layer and the weaker cloud radiative effect under weaker insolation and 2) seasonally stronger subtropical subsidence associated with the Hadley circulation in winter. As verified through atmospheric dynamical model experiments, enhanced cloud-top radiative cooling by low-level clouds acts to reinforce the wintertime Mascarene high in comparable magnitude as in summer. The present study reveals that the self-sustaining feedback with low-level clouds alone is insufficient for replenishing the full strength of the wintertime Mascarene high. This implies that another internal feedback pathway and/or external driver must be operative in maintaining the wintertime high.
Nasihati Gourabi, Forough; Kiani, Maryam; Pourtakdoust, Seid H.Nasihati Gourabi, F., M. Kiani, S. H. Pourtakdoust, 2022: Satellite pose estimation using Earth radiation modeled by artificial neural networks. Advances in Space Research, 70(8), 2195-2207. doi: 10.1016/j.asr.2022.07.009. The thermal energy received by each surface of an Earth-orbiting satellite strongly depends on its position and orientation. In this sense, simultaneous orbit and attitude estimation (SOAE) using the surface temperature data has been focused in the present study. The Earth infrared (IR) radiation and the Earth’s top-of-atmosphere (TOA) albedo are two key sources of radiation affecting the satellite surface temperature rate. The Earth’s radiation information has been monitored for the past two decades by the Clouds and the Earth’s Radiant Energy System (CERES) project, producing a comprehensive set of Earth radiation budget (ERB) data for climate, weather and applied science research. The current study utilizes the ERB data to forecast the IR radiation flux (IRF) and the TOA albedo factor (AF) via an artificial neural network (ANN). In this respect, the satellite longitude, latitude and time constitute the input vector of the learning set, while the AF and IRF are considered as the output. The ANN is then employed to model the satellite surface temperature rate in the radiation-based SOAE process. The feasibility of the proposed pose estimation approach has been addressed and verified via Monte Carlo simulation. Obtained results demonstrate suitability of the algorithm in sunlight intervals with good accuracy. Artificial neural network; Albedo radiation; Attitude estimation; Infrared radiation; Orbit estimation
Niu, Xiaoying; Pu, Wei; Fu, Pingqing; Chen, Yang; Xing, Yuxuan; Wu, Dongyou; Chen, Ziqi; Shi, Tenglong; Zhou, Yue; Wen, Hui; Wang, XinNiu, X., W. Pu, P. Fu, Y. Chen, Y. Xing, D. Wu, Z. Chen, T. Shi, Y. Zhou, H. Wen, X. Wang, 2022: Fluorescence characteristics, absorption properties, and radiative effects of water-soluble organic carbon in seasonal snow across northeastern China. Atmospheric Chemistry and Physics, 22(21), 14075-14094. doi: 10.5194/acp-22-14075-2022. Water-soluble organic carbon (WSOC) in the cryosphere can significantly influence the global carbon cycle and radiation budget. However, WSOC in the snowpack has received little scientific attention to date. This study reports the fluorescence characteristics, absorption properties, and radiative effects of WSOC based on 34 snow samples collected from sites in northeastern China. A significant degree of regional WSOC variability is found, with concentrations ranging from 0.5±0.2 to 5.7±3.7 µg g−1 (average concentration: 3.6±3.2 µg g−1). The three principal fluorescent components of WSOC are identified as (1) the high-oxygenated humic-like substances (HULIS-1) of terrestrial origin, (2) the low-oxygenated humic-like substances (HULIS-2) of mixed origin, and (3) the protein-like substances (PRLIS) derived from autochthonous microbial activity. In southeastern Inner Mongolia (SEIM), a region dominated by desert and exposed soils, the WSOC exhibits the highest humification index (HIX) but the lowest fluorescence (FI) and biological (BIX) indices; the fluorescence signal is mainly attributed to HULIS-1 and thus implicates soil as the primary source. By contrast, the HIX (FI and BIX) value is the lowest (highest), and the percentage of PRLIS is the highest in the remote area of northeastern Inner Mongolia (NEIM), suggesting a primarily biological source. For south and north of northeastern China (SNC and NNC), both of which are characterized by intensive agriculture and industrial activity, the fluorescence signal is dominated by HULIS-2, and the HIX, FI, and BIX values are all moderate, indicating the mixed origins for WSOC (anthropogenic activity, microbial activity, and soil). We also observe that, throughout northeastern China, the light absorption of WSOC is dominated by HULIS-1, followed by HULIS-2 and PRLIS. The contribution of WSOC to albedo reduction (average concentration: 3.6 µg g−1) in the ultraviolet–visible (UV–Vis) band is approximately half that of black carbon (BC average concentration: 0.6 µg g−1). Radiative forcing is 3.8 (0.8) W m−2 in old (fresh) snow, equating to 19 % (17 %) of the radiative forcing of BC. These results indicate that WSOC has a profound impact on snow albedo and the solar radiation balance.
Nugent, J. M.; Turbeville, S. M.; Bretherton, C. S.; Blossey, P. N.; Ackerman, T. P.Nugent, J. M., S. M. Turbeville, C. S. Bretherton, P. N. Blossey, T. P. Ackerman, 2022: Tropical Cirrus in Global Storm-Resolving Models: 1. Role of Deep Convection. Earth and Space Science, 9(2), e2021EA001965. doi: 10.1029/2021EA001965. Pervasive cirrus clouds in the upper troposphere and tropical tropopause layer (TTL) influence the climate by altering the top-of-atmosphere radiation balance and stratospheric water vapor budget. These cirrus are often associated with deep convection, which global climate models must parameterize and struggle to accurately simulate. By comparing high-resolution global storm-resolving models from the Dynamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) intercomparison that explicitly simulate deep convection to satellite observations, we assess how well these models simulate deep convection, convectively generated cirrus, and deep convective injection of water into the TTL over representative tropical land and ocean regions. The DYAMOND models simulate deep convective precipitation, organization, and cloud structure fairly well over land and ocean regions, but with clear intermodel differences. All models produce frequent overshooting convection whose strongest updrafts humidify the TTL and are its main source of frozen water. Intermodel differences in cloud properties and convective injection exceed differences between land and ocean regions in each model. We argue that, with further improvements, global storm-resolving models can better represent tropical cirrus and deep convection in present and future climates than coarser-resolution climate models. To realize this potential, they must use available observations to perfect their ice microphysics and dynamical flow solvers. convection; microphysics; cirrus; tropical tropopause layer; DYAMOND; global storm-resolving models
Nuncio, M.; Satheesan, K.; Acharya, Asutosh; Chatterjee, Sourav; Subeesh, M. P.; Athulya, R.Nuncio, M., K. Satheesan, A. Acharya, S. Chatterjee, M. P. Subeesh, R. Athulya, 2022: A southerly wind event and precipitation in Ny Ålesund, Arctic. Journal of Atmospheric and Solar-Terrestrial Physics, 231, 105869. doi: 10.1016/j.jastp.2022.105869. Precipitation in the Arctic is expected to increase with implications to ecosystems and changes to atmospheric circulation. In the Arctic strong southerly wind, often known as atmospheric rivers, supply enormous moisture and heat into the Arctic and is expected to increase in future warming scenarios. The impact of these events on Arctic climate change is not yet understood fully. In this study precipitation associated with such an event is studied for Ny Ålesund, Svalbard for 2016 March. During the event, the high precipitation was noticed between 22 and 23 UTC and 6–9 UTC on 12th March and 13th March respectively. It has been shown that during these two time periods, downwelling longwave radiation increased due to clouds. The enhanced downwelling longwave radiation increased the surface temperature locally. Above the shallow planetary boundary, advection dominated the temperature changes and initiated a shallow convection in the atmosphere leading to intensified precipitation in the lower layers during the event. Enhanced vertical velocity in MRR could be a result of this convection. Thus, the largescale southerly winds, that developed into an atmospheric river has not only contributed to the supply of heat and moisture but also enhanced cloud radiative effects and resulted in local warming. The moisture sources for this event appears to be Norwegian Sea and the east coast of Greenland. The scenario we have investigated was characterised by a warm Arctic with southerly warm winds. Studies suggest that convective scale precipitation is increasing in Eurasia under warm conditions. Our study points to the change in precipitation regime that Arctic may characterise as the warming continues. Cloud radiative effects; Arctic precipitation; Atmospheric river
Ojo, Olusola SamuelOjo, O. S., 2022: Validation of net radiation from multi-models and satellite retrieval over Nigeria. Modeling Earth Systems and Environment. doi: 10.1007/s40808-022-01647-5. In this study, net radiation obtained from the three reanalysis models and a satellite product coded ERA-5, MERRA-2, NCAR/NCEP, and CERES were compared with ground measurement (in situ) from Nigerian Meteorological Agency (NIMET) using the comparative statistical analytic metrics. Atmospheric radiation data such as the shortwave and longwave radiative fluxes spanned a period of 13 years (2000–2013) across the four climatic regions viz the Sahel, Guinea savannah, Rainforest, and Coastal regions over Nigeria were used to evaluate net radiation. The correlation, similarity, and bias analyses between the in situ and the remote sensing net radiation were performed using the correlation coefficient (R) metric and Taylor Skill Scores. Analyses showed that net radiation from the National Centers for Environmental Prediction and the National Center for Atmospheric Research model (NCAR/NCEP) showed best agreement with the in situ net radiation across all the climatic zones in Nigeria. The correlations between NCAR/NCEP and in situ net radiation data have highest R-value of 0.8629 in the Sahel region, 0.6252 in the Guinea Savannah region, 0.7996 in the Rainforest region, and 0.7852 in the Coastal region for the annual timescale. Similar spatial patterns were observed from other analytical metrics for the dry and wet seasons across the four climatic zones. It can be concluded from the results that although all the four remote sensing data show similar patterns of variations but those of ERA-5 revealed significant departure to their in situ counterpart. Assessment; Net radiation; Nigeria; Reanalysis product; Satellite product
Oreopoulos, Lazaros; Cho, Nayeong; Lee, Dongmin; Lebsock, Matthew; Zhang, ZhiboOreopoulos, L., N. Cho, D. Lee, M. Lebsock, Z. Zhang, 2022: Assessment of Two Stochastic Cloud Subcolumn Generators Using Observed Fields of Vertically Resolved Cloud Extinction. J. Atmos. Oceanic Technol., 39(8), 1229-1244. doi: 10.1175/JTECH-D-21-0166.1. Abstract We evaluate two stochastic subcolumn generators used in GCMs to emulate subgrid cloud variability enabling comparisons with satellite observations and simulations of certain physical processes. Our evaluation necessitated the creation of a reference observational dataset that resolves horizontal and vertical cloud variability. The dataset combines two CloudSat cloud products that resolve two-dimensional cloud optical depth variability of liquid, ice, and mixed-phase clouds when blended at ∼200 m vertical and ∼2 km horizontal scales. Upon segmenting the dataset to individual “scenes,” mean profiles of the cloud fields are passed as input to generators that produce scene-level cloud subgrid variability. The assessment of generator performance at the scale of individual scenes and in a mean sense is largely based on inferred joint histograms that partition cloud fraction within predetermined combinations of cloud-top pressure–cloud optical thickness ranges. Our main finding is that both generators tend to underestimate optically thin clouds, while one of them also tends to overestimate some cloud types of moderate and high optical thickness. Associated radiative flux errors are also calculated by applying a simple transformation to the cloud fraction histogram errors, and are found to approach values almost as high as 3 W m−2 for the cloud radiative effect in the shortwave part of the spectrum. Significance Statement The purpose of the paper is to assess the realism of relatively simple ways of producing fine-scale cloud variability in global models from coarsely resolved cloud properties. The assessment is achieved via comparisons to observed cloud fields where the fine-scale variability is known in both the horizontal and vertical directions. Our results show that while the generators have considerable skill, they still suffer from consistent deficiencies that need to be addressed with further development guided by appropriate observations.
Paca, Victor Hugo da Motta; Espinoza-Dávalos, Gonzalo E.; da Silva, Rodrigo; Tapajós, Raphael; dos Santos Gaspar, Avner BrasileiroPaca, V. H. d. M., G. E. Espinoza-Dávalos, R. da Silva, R. Tapajós, A. B. dos Santos Gaspar, 2022: Remote Sensing Products Validated by Flux Tower Data in Amazon Rain Forest. Remote Sensing, 14(5), 1259. doi: 10.3390/rs14051259. This work compares methods of climate measurements, such as those used to measure evapotranspiration, precipitation, net radiation, and temperature. The satellite products used were compared and evaluated against flux tower data. Evapotranspiration was validated against the SSEBop monthly and GLEAM daily and monthly products, respectively, and the results were RMSE = 24.144 mm/month, NRMSE = 0.223, r2 = 0.163, slope = 0.411; RMSE = 1.781 mm/day, NRMSE = 0.599, r2 = 0.000, slope = 0.006; RMSE = 36.17 mm/month, NRMSE = 0.401, r2 = 0.002, and slope = 0.026. Precipitation was compared with the CHIRPS data, K67 was not part of the CHIRPS station correction. The results for both the daily and monthly comparisons were RMSE = 18.777 mm/day, NRMSE = 1.027, r2 = 0.086, slope = 0.238 and RMSE = 130.713 mm/month, NRMSE = 0.706, r2 = 0.402, and slope = 0.818. The net radiation validated monthly with CERES was RMSE = 75.357 W/m2, NRMSE = 0.383, r2 = 0.422, and slope = 0.867. The temperature results, as compared to MOD11C3, were RMSE = 2.829 °C, NRMSE = 0.116, r2 = 0.153, and slope = 0.580. Comparisons between the remote sensing products and validation against the ground data were performed on a monthly basis. GLEAM and CHIRPS daily were the data sets with considerable discrepancy. comparison and validation; hydro-meteorological variables; remote sensing products
Parkinson, Claire L.Parkinson, C. L., 2022: The Earth-Observing Aqua Satellite Mission: 20 Years and Counting. Earth and Space Science, n/a(n/a), e2022EA002481. doi: 10.1029/2022EA002481. The Earth-observing Aqua spacecraft was launched on May 4, 2002 and has now completed 20 years collecting and transmitting data regarding the Earth’s radiation budget, atmosphere, oceans, land, and ice. Although launched with a design life of 6 years, four of its instruments continue to operate and provide high-quality data streams more than 20 years after launch. The Aqua data are readily available to users worldwide and have been used in thousands of scientific publications and in numerous practical applications, including weather forecasting, air-quality assessments, and monitoring of forest fires, dust storms, volcanic ash plumes, oil spills, and crop yields. This article is protected by copyright. All rights reserved. Remote sensing; Earth Observing System; Aqua satellite; Satellite Earth observations
Peng, Liran; Pritchard, Michael; Hannah, Walter M.; Blossey, Peter N.; Worley, Patrick H; Bretherton, Christopher S.Peng, L., M. Pritchard, W. M. Hannah, P. N. Blossey, P. H. Worley, C. S. Bretherton, 2022: Load-balancing intense physics calculations to embed regionalized high-resolution cloud resolving models in the E3SM and CESM climate models. Journal of Advances in Modeling Earth Systems, n/a(n/a), e2021MS002841. doi: 10.1029/2021MS002841. We design a new strategy to load-balance high-intensity sub-grid atmospheric physics calculations restricted to a small fraction of a global climate simulation’s domain. We show why the current parallel load balancing infrastructure of CESM and E3SM cannot efficiently handle this scenario at large core counts. As an example, we study an unusual configuration of the E3SM Multiscale Modeling Framework (MMF) that embeds a binary mixture of two separate cloud-resolving model grid structures that is attractive for low cloud feedback studies. Less than a third of the planet uses high-resolution (MMF-HR; sub-km horizontal grid spacing) relative to standard low-resolution (MMF-LR) cloud superparameterization elsewhere. To enable MMF runs with Multi-Domain CRMs, our load balancing theory predicts the most efficient computational scale as a function of the high-intensity work’s relative overhead and its fractional coverage. The scheme successfully maximizes model throughput and minimizes model cost relative to precursor infrastructure, effectively by devoting the vast majority of the processor pool to operate on the few high-intensity (and rate-limiting) HR grid columns. Two examples prove the concept, showing that minor artifacts can be introduced near the HR/LR CRM grid transition boundary on idealized aquaplanets, but are minimal in operationally relevant real-geography settings. As intended, within the high (low) resolution area, our Multi-Domain CRM simulations exhibit cloud fraction and shortwave reflection convergent to standard baseline tests that use globally homogenous MMF-LR and MMF-HR. We suggest this approach can open up a range of creative multi-resolution climate experiments without requiring unduly large allocations of computational resources.
Quaas, Johannes; Jia, Hailing; Smith, Chris; Albright, Anna Lea; Aas, Wenche; Bellouin, Nicolas; Boucher, Olivier; Doutriaux-Boucher, Marie; Forster, Piers M.; Grosvenor, Daniel; Jenkins, Stuart; Klimont, Zig; Loeb, Norman G.; Ma, Xiaoyan; Naik, Vaishali; Paulot, Fabien; Stier, Philip; Wild, Martin; Myhre, Gunnar; Schulz, MichaelQuaas, J., H. Jia, C. Smith, A. L. Albright, W. Aas, N. Bellouin, O. Boucher, M. Doutriaux-Boucher, P. M. Forster, D. Grosvenor, S. Jenkins, Z. Klimont, N. G. Loeb, X. Ma, V. Naik, F. Paulot, P. Stier, M. Wild, G. Myhre, M. Schulz, 2022: Robust evidence for reversal in the aerosol effective climate forcing trend. Atmospheric Chemistry and Physics Discussions, 1-25. doi: 10.5194/acp-2022-295. Abstract. Anthropogenic aerosols exert a cooling influence that offsets part of the greenhouse gas warming. Due to their short tropospheric lifetime of only up to several days, the aerosol forcing responds quickly to emissions. Here we present and discuss the evolution of the aerosol forcing since 2000. There are multiple lines of evidence that allow to robustly conclude that the anthropogenic aerosol effective radiative forcing – both aerosol-radiation and aerosol-cloud interactions – has become globally less negative, i.e. that the trend in aerosol effective radiative forcing changed sign from negative to positive. Bottom-up inventories show that anthropogenic primary aerosol and aerosol precursor emissions declined in most regions of the world; observations related to aerosol burden show declining trends, in particular of the fine-mode particles that make up most of the anthropogenic aerosols; satellite retrievals of cloud droplet numbers show trends consistent in sign, as do observations of top-of-atmosphere radiation. Climate model results, including a revised set that is constrained by observations of the ocean heat content evolution show a consistent sign and magnitude for a positive forcing relative to 2000 due to reduced aerosol effects. This reduction leads to an acceleration of the forcing of climate change, i.e. an increase in forcing by 0.1 to 0.3 W m-2, up to 12 % of the total climate forcing in 2019 compared to 1750 according to IPCC.
Ramesh, Nandini; Boos, William R.Ramesh, N., W. R. Boos, 2022: The Unexpected Oceanic Peak in Energy Input to the Atmosphere and Its Consequences for Monsoon Rainfall. Geophysical Research Letters, 49(12), e2022GL099283. doi: 10.1029/2022GL099283. Monsoons have historically been understood to be caused by the low thermal inertia of land, allowing more energy from summer insolation to be transferred to the overlying atmosphere than over adjacent ocean. Here, we show that during boreal summer, the global maximum net energy input (NEI) to the atmosphere unexpectedly lies over the Indian Ocean, not over land. Observed radiative fluxes suggest that cloud-radiative effects (CRE) almost double the NEI over ocean, shifting the NEI peak from land to ocean. Global climate model experiments with both land and interactive sea surface temperatures confirm that CRE create the oceanic NEI maximum. Interactions between CRE, NEI, circulation, and land-sea contrast in surface heat capacity shift precipitation from Southeast to South Asia. CRE thus alter the global partitioning of precipitation between land and ocean and the spatial structure of Earth's strongest monsoon, in ways that can be understood through the NEI. monsoons; cloud radiative effects; atmospheric dynamics; land-sea contrast; tropical climate
Ramos, R. D.; LeGrande, A. N.; Griffiths, M. L.; Elsaesser, G. S.; Litchmore, D. T.; Tierney, J. E.; Pausata, F. S. R.; Nusbaumer, J.Ramos, R. D., A. N. LeGrande, M. L. Griffiths, G. S. Elsaesser, D. T. Litchmore, J. E. Tierney, F. S. R. Pausata, J. Nusbaumer, 2022: Constraining Clouds and Convective Parameterizations in a Climate Model Using Paleoclimate Data. Journal of Advances in Modeling Earth Systems, 14(8), e2021MS002893. doi: 10.1029/2021MS002893. Cloud and convective parameterizations strongly influence uncertainties in equilibrium climate sensitivity. We provide a proof-of-concept study to constrain these parameterizations in a perturbed parameter ensemble of the atmosphere-only version of the Goddard Institute for Space Studies Model E2.1 simulations by evaluating model biases in the present-day runs using multiple satellite climatologies and by comparing simulated δ18O of precipitation (δ18Op), known to be sensitive to parameterization schemes, with a global database of speleothem δ18O records covering the Last Glacial Maximum (LGM), mid-Holocene (MH) and pre-industrial (PI) periods. Relative to modern interannual variability, paleoclimate simulations show greater sensitivity to parameter changes, allowing for an evaluation of model uncertainties over a broader range of climate forcing and the identification of parts of the world that are parameter sensitive. Certain simulations reproduced absolute δ18Op values across all time periods, along with LGM and MH δ18Op anomalies relative to the PI, better than the default parameterization. No single set of parameterizations worked well in all climate states, likely due to the non-stationarity of cloud feedbacks under varying boundary conditions. Future work that involves varying multiple parameter sets simultaneously with coupled ocean feedbacks will likely provide improved constraints on cloud and convective parameterizations. PPE; cloud and convective parameterization; paleoclimate model; proxy-model comparison; speleothem; water isotopes
Ren, Tong; Yang, Ping; Wei, Jian; Huang, Xianglei; Sang, HuiyanRen, T., P. Yang, J. Wei, X. Huang, H. Sang, 2022: Performance of Cloud 3D Solvers in Ice Cloud Shortwave Radiation Closure Over the Equatorial Western Pacific Ocean. Journal of Advances in Modeling Earth Systems, 14(2), e2021MS002754. doi: 10.1029/2021MS002754. For retrieving cloud optical properties from satellite images or computing these properties from climate model output, computationally efficient treatments of cloud horizontal inhomogeneity include the Monte Carlo Independent Column Approximation (McICA) and the Tripleclouds method. Computationally efficient treatment of cloud horizontal radiation exchanges includes the SPeedy Algorithm for Radiative TrAnsfer through CloUd Sides (SPARTACUS). As a test to derive properties from satellite images, we collocate Moderate Resolution Imaging Spectroradiometer (MODIS) cloud retrievals with near-nadir Cloud and the Earth's Radiant Energy System (CERES) footprints in July 2008 over an equatorial western Pacific Ocean region to compare the performance of the McICA, Tripleclouds, and SPARTACUS solvers to the conventional plane-parallel homogeneous (PPH) treatment. PPH overestimates cloud albedo, and the three solvers effectively reduce overestimation with root mean square error of shortwave upwelling irradiance decreasing between 15.72 and 18.53 W m−2, or about 22%–25%. Although cloud top variability does not get fed into the simulations, all three solvers also reduce the effect of cloud top variability on cloud albedo. Entrapment (energy reflected downward from clouds) and horizontal radiation transfer have opposite effects on the SPARTACUS cloud albedo simulation. The net effect depends on the cloud vertical extent, the unawareness of which limits the performance of the SPARTACUS solver. cloud 3D effect; cloud top variability; cloud vertical extent
Rosário, Nilton Évora do; Sena, Elisa Thomé; Yamasoe, Marcia AkemiRosário, N. É. d., E. T. Sena, M. A. Yamasoe, 2022: South American 2020 regional smoke plume: intercomparison with previous years, impact on solar radiation, and the role of Pantanal biomass burning season. Atmospheric Chemistry and Physics, 22(22), 15021-15033. doi: 10.5194/acp-22-15021-2022. The 2020 biomass burning season in Brazil was marked by an atypical amount of fire across the Pantanal biome, which led to high levels of smoke within the biome and downwind areas. The present study analyzes fire counts and smoke over Pantanal in 2020, comparing this particular year's data with those from the previous 17 years (2003–2019). Taking as reference the most-polluted years in this period, the regional smoke plume and its impact on surface solar radiation were also evaluated. In 2020, the regional smoke plume core covered an area of ∼ 2.6×106 km2 at the peak of the burning season, an area well above that of the previous 6 years but smaller than areas observed in a more remote past, as in 2007 and 2010 (> 5.0×106 km2). The smoke loading was lower (mean aerosol optical depth, AOD, of 550 nm; ∼ 0.7) than that of 2007 and 2010 (mean AOD 550 nm; ∼ 1.0). The plume radiation absorption efficiency, when compared with the previous year's plumes, did not present significant differences. Regarding the Pantanal burning season, it revealed some atypical features. Fire counts were up to 3.0 times higher than for the years from 2003 to 2019. Smoke loading over Pantanal, which is typically a fraction of that over Amazonia, was higher in 2020 than that over Amazonia, an indication that local smoke surpassed the smoke advection from upwind regions. The observed intraseasonal variability in smoke over Pantanal revealed to be largely driven by the nature of the burned areas in the biome. From September on, there was a significant increase in fire count in conservation and indigenous areas, where higher biomass density is present, which would explain the larger smoke plumes over Pantanal, even during October when the fire count was reduced. In October, the biome was covered by a thick smoke layer, which resulted in a mean deficit of surface solar radiation up to 200 W m−2. Despite the Pantanal biomes' massive burning in 2020, the regional smoke plume was not far from its climatological features. Nevertheless, the Pantanal 2020 burning season represents the worst combination of a climate extreme applied to a fire-prone environment, coupled with inadequately enforced environmental regulations, from which there is much to be learned.
Russotto, Rick D.; Strong, Jeffrey D. O.; Camargo, Suzana J.; Sobel, Adam; Elsaesser, Gregory S.; Kelley, Maxwell; Del Genio, Anthony; Moon, Yumin; Kim, DaehyunRussotto, R. D., J. D. O. Strong, S. J. Camargo, A. Sobel, G. S. Elsaesser, M. Kelley, A. Del Genio, Y. Moon, D. Kim, 2022: Evolution of Tropical Cyclone Properties Across the Development Cycle of the GISS-E3 Global Climate Model. Journal of Advances in Modeling Earth Systems, 14(1), e2021MS002601. doi: 10.1029/2021MS002601. The next-generation global climate model from the NASA Goddard Institute for Space Studies, GISS-E3, contains many improvements to resolution and physics that allow for improved representation of tropical cyclones (TCs) in the model. This study examines the properties of TCs in two different versions of E3 at different points in its development cycle, run for 20 years at 0.5° resolution, and compares these TCs with observations, the previous generation GISS model, E2, and other climate models. E3 shares many TC biases common to global climate models, such as having too few tropical cyclones, but is much improved from E2. E3 produces strong enough TCs that observation-based wind speed thresholds can now be used to detect and track them, and some storms now reach hurricane intensity; neither of these was true of E2. Model development between the first and second versions of E3 further increased the number and intensity of TCs and reduced TC count biases globally and in most regions. One-year sensitivity tests to changes in various microphysical and dynamical tuning parameters are also examined. Increasing the entrainment rate for the more strongly entraining plume in the convection scheme increases the number of TCs (though also affecting other climate variables, and in some cases increasing biases). Variations in divergence damping did not have a strong effect on simulated TC properties, contrary to expectations based on previous studies. Overall, the improvements in E3 make it more credible for studies of TC activity and its relationship to climate. tropical meteorology; climate model; tropical cyclones; hurricanes
Săftoiu, G; Stefan, Sabina; Antonescu, B; Iorga, Gabriela; Belegante, LSăftoiu, G., S. Stefan, B. Antonescu, G. Iorga, L. Belegante, 2022: CHARACTERISTICS OF STRATOCUMULUS CLOUDS OVER BUCHAREST-MĂGURELE. Romanian Reports in Physics, 74. Stratocumulus clouds represent one of the key components of the Earth's radiative balance because it generally reflects incident solar radiation. The aim of the study is to understand the occurrence and characteristics of stratocumulus clouds using satellite data collected from Dec 2019 to Feb 2021. A series of macrophysically and microphysical cloud parameters (cloud cover fraction, cloud types, cloud geometrical depth, cloud top temperature, cloud top pressure, cloud height, cloud optical depth, liquid water path) were extracted from the Clouds and the Earth's Radiant Energy System (CERES) database for a region in south west Bucharest, were the Măgurele Center for Atmosphere and Radiation Studies (MARS) is located.
Salazar-Martínez, Diego; Holwerda, Friso; Holmes, Thomas R. H.; Yépez, Enrico A.; Hain, Christopher R.; Alvarado-Barrientos, Susana; Ángeles-Pérez, Gregorio; Arredondo-Moreno, Tulio; Delgado-Balbuena, Josué; Figueroa-Espinoza, Bernardo; Garatuza-Payán, Jaime; González del Castillo, Eugenia; Rodríguez, Julio C.; Rojas-Robles, Nidia E.; Uuh-Sonda, Jorge M.; Vivoni, Enrique R.Salazar-Martínez, D., F. Holwerda, T. R. H. Holmes, E. A. Yépez, C. R. Hain, S. Alvarado-Barrientos, G. Ángeles-Pérez, T. Arredondo-Moreno, J. Delgado-Balbuena, B. Figueroa-Espinoza, J. Garatuza-Payán, E. González del Castillo, J. C. Rodríguez, N. E. Rojas-Robles, J. M. Uuh-Sonda, E. R. Vivoni, 2022: Evaluation of remote sensing-based evapotranspiration products at low-latitude eddy covariance sites. Journal of Hydrology, 610, 127786. doi: 10.1016/j.jhydrol.2022.127786. Remote sensing-based evapotranspiration (ET) products have been evaluated primarily using data from northern middle latitudes; therefore, little is known about their performance at low latitudes. To address this bias, an evaluation dataset was compiled using eddy covariance data from 40 sites between latitudes 30° S and 30° N. The flux data were obtained from the emerging network in Mexico (MexFlux) and from openly available databases of FLUXNET, AsiaFlux, and OzFlux. This unique reference dataset was then used to evaluate remote sensing-based ET products in environments that have been underrepresented in earlier studies. The evaluated products were: MODIS ET (MOD16, both the discontinued collection 5 (C5) and the latest collection (C6)), Global Land Evaporation Amsterdam Model (GLEAM) ET, and Atmosphere-Land Exchange Inverse (ALEXI) ET. Products were compared with unadjusted fluxes (ETorig) and with fluxes corrected for the lack of energy balance closure (ETebc). Three common statistical metrics were used: coefficient of determination (R2), root mean square error (RMSE), and percent bias (PBIAS). The effect of a vegetation mismatch between pixel and site on product evaluation results was investigated by examining the relationship between the statistical metrics and product-specific vegetation match indexes. Evaluation results of this study and those published in the literature were used to examine the performance of the products across latitudes. Differences between the MOD16 collection 5 and 6 datasets were generally smaller than differences with the other products. Performance and ranking of the evaluated products depended on whether ETorig or ETebc was used. When using ETorig, GLEAM generally had the highest R2, smallest PBIAS, and best RMSE values across the studied land cover types and climate zones. Neither MOD16 nor ALEXI performed consistently better than the other. When using ETebc, none of the products stood out in terms of both low bias and strong correlations. The use of ETebc instead of ETorig affected the biases more than the correlations. The product evaluation results showed no significant relationship with the degree of match between the vegetation at the pixel and site scale. The latitudinal comparison showed tendencies of lower R2 (all products) but better PBIAS and normalized RMSE values (MOD16 and GLEAM) for forests at low latitudes than for forests at northern middle latitudes. For non-forest vegetation, the products showed no clear latitudinal differences in performance. Subtropics; MOD16; GLEAM; ALEXI; Tropics
Salzmann, M.; Ferrachat, S.; Tully, C.; Münch, S.; Watson-Parris, D.; Neubauer, D.; Siegenthaler-Le Drian, C.; Rast, S.; Heinold, B.; Crueger, T.; Brokopf, R.; Mülmenstädt, J.; Quaas, J.; Wan, H.; Zhang, K.; Lohmann, U.; Stier, P.; Tegen, I.Salzmann, M., S. Ferrachat, C. Tully, S. Münch, D. Watson-Parris, D. Neubauer, C. Siegenthaler-Le Drian, S. Rast, B. Heinold, T. Crueger, R. Brokopf, J. Mülmenstädt, J. Quaas, H. Wan, K. Zhang, U. Lohmann, P. Stier, I. Tegen, 2022: The Global Atmosphere-aerosol Model ICON-A-HAM2.3–Initial Model Evaluation and Effects of Radiation Balance Tuning on Aerosol Optical Thickness. Journal of Advances in Modeling Earth Systems, 14(4), e2021MS002699. doi: 10.1029/2021MS002699. The Hamburg Aerosol Module version 2.3 (HAM2.3) from the ECHAM6.3-HAM2.3 global atmosphere-aerosol model is coupled to the recently developed icosahedral nonhydrostatic ICON-A (icon-aes-1.3.00) global atmosphere model to yield the new ICON-A-HAM2.3 atmosphere-aerosol model. The ICON-A and ECHAM6.3 host models use different dynamical cores, parameterizations of vertical mixing due to sub-grid scale turbulence, and parameter settings for radiation balance tuning. Here, we study the role of the different host models for simulated aerosol optical thickness (AOT) and evaluate impacts of using HAM2.3 and the ECHAM6-HAM2.3 two-moment cloud microphysics scheme on several meteorological variables. Sensitivity runs show that a positive AOT bias over the subtropical oceans is remedied in ICON-A-HAM2.3 because of a different default setting of a parameter in the moist convection parameterization of the host models. The global mean AOT is biased low compared to MODIS satellite instrument retrievals in ICON-A-HAM2.3 and ECHAM6.3-HAM2.3, but the bias is larger in ICON-A-HAM2.3 because negative AOT biases over the Amazon, the African rain forest, and the northern Indian Ocean are no longer compensated by high biases over the sub-tropical oceans. ICON-A-HAM2.3 shows a moderate improvement with respect to AOT observations at AERONET sites. A multivariable bias score combining biases of several meteorological variables into a single number is larger in ICON-A-HAM2.3 compared to standard ICON-A and standard ECHAM6.3. In the tropics, this multivariable bias is of similar magnitude in ICON-A-HAM2.3 and in ECHAM6.3-HAM2.3. In the extra-tropics, a smaller multivariable bias is found for ICON-A-HAM2.3 than for ECHAM6.3-HAM2.3. aerosol; modeling
Sathiyamoorthy, V.Sathiyamoorthy, V., 2022: A study on the anomalous TOA net radiative warming by clouds in a sub-region within the Indian summer monsoon region. Advances in Space Research. doi: 10.1016/j.asr.2022.08.018. Indian summer monsoon clouds generally exert a net radiative cooling at top of atmosphere. In contrast, clouds over a sub-region comprising parts of South peninsular India, Sri Lanka and adjoining Bay of Bengal (SISB) inside the Indian monsoon region exert a net radiative warming. In this work, an attempt is made to understand the reasons behind the anomalous radiative warming found over SISB. Ten-year (2000–2009) top of atmosphere radiative flux data from Clouds and the Earth’s Radiant Energy System payloads onboard Aqua and Terra satellites and cloud data from International Satellite Cloud Climatology Project during the peak Indian summer monsoon season of July–August are analyzed to understand the underlying causes. Top of Atmosphere net radiative forcing is positive and as high as ∼15 Wm−2 over SISB during the peak Indian summer monsoon season. Cloud cover amounts over SISB with net radiative warming and north Bay of Bengal with net radiative cooling are compared. Cloud cover amounts of high-level cirrostratus and deep convective cumulonimbus clouds are less by 65% and 87% respectively over SISB when compared to north Bay of Bengal. SISB is located on the leeward side of the Western Ghats mountain chain with descending motion. Adiabatic compression and associated warming of descending air leads to dehydration of air parcel. The upper tropospheric tropical easterly jet sweeps the deep convective cloud tops of the Indian monsoon and advect them to large distance as upper level thin cirrus family of clouds. When these clouds reach SISB with descending motion, they thin out by melting and evaporation or sublimation as the air mass is compressed and heated adiabatically. Over SISB, pressure vertical velocity at 500 hPa is moderately inversely correlated to cloud cover amount of cirrostratus and cumulonimbus clouds. Cloud cover amount of these two clouds is significantly correlated to shortwave cloud radiative forcing and longwave cloud radiative forcing over SISB. When cloud cover amount of cirrostratus and cumulonimbus clouds are low ( Indian summer monsoon; Cloud radiative forcing; Tropical easterly jet
Scott, Ryan C.; Rose, Fred G.; Stackhouse, Paul W.; Loeb, Norman G.; Kato, Seiji; Doelling, David R.; Rutan, David A.; Taylor, Patrick C.; Smith, William L.Scott, R. C., F. G. Rose, P. W. Stackhouse, N. G. Loeb, S. Kato, D. R. Doelling, D. A. Rutan, P. C. Taylor, W. L. Smith, 2022: Clouds and the Earth’s Radiant Energy System (CERES) Cloud Radiative Swath (CRS) Edition 4 Data Product. J. Atmos. Oceanic Technol., 39(11), 1781-1797. doi: 10.1175/JTECH-D-22-0021.1. Abstract Satellite observations from Clouds and the Earth’s Radiant Energy System (CERES) radiometers have produced over two decades of world-class data documenting time–space variations in Earth’s top-of-atmosphere (TOA) radiation budget. In addition to energy exchanges among Earth and space, climate studies require accurate information on radiant energy exchanges at the surface and within the atmosphere. The CERES Cloud Radiative Swath (CRS) data product extends the standard Single Scanner Footprint (SSF) data product by calculating a suite of radiative fluxes from the surface to TOA at the instantaneous CERES footprint scale using the NASA Langley Fu–Liou radiative transfer model. Here, we describe the CRS flux algorithm and evaluate its performance against a network of ground-based measurements and CERES TOA observations. CRS all-sky downwelling broadband fluxes show significant improvements in surface validation statistics relative to the parameterized fluxes on the SSF product, including a ∼30%–40% (∼20%) reduction in SW↓ (LW↓) root-mean-square error (RMSΔ), improved correlation coefficients, and the lowest SW↓ bias over most surface types. RMSΔ and correlation statistics improve over five different surface types under both overcast and clear-sky conditions. The global mean computed TOA outgoing LW radiation (OLR) remains within
Seifert, Axel; Bachmann, Vanessa; Filipitsch, Florian; Förstner, Jochen; Grams, Christian; Hoshyaripour, Gholam Ali; Quinting, Julian; Rohde, Anika; Vogel, Heike; Wagner, Annette; Vogel, BernhardSeifert, A., V. Bachmann, F. Filipitsch, J. Förstner, C. Grams, G. A. Hoshyaripour, J. Quinting, A. Rohde, H. Vogel, A. Wagner, B. Vogel, 2022: Aerosol-cloud-radiation interaction during Saharan dust episodes: The dusty cirrus puzzle. Atmospheric Chemistry and Physics Discussions, 1-35. doi: 10.5194/acp-2022-746. Abstract. Dusty cirrus clouds are extended optically thick cirrocumulus decks that occur during strong mineral dust events. So far they have been mostly documented over Europe associated with dust-infused baroclinic storms. Since today's numerical weather prediction models neither predict mineral dust distributions nor consider the interaction of dust with cloud microphysics, they cannot simulate this phenomenon. We postulate that the dusty cirrus forms through a mixing instability of moist clean air with drier dusty air. A corresponding sub-grid parameterization is suggested and tested in the ICON-ART model. Only with help of this parameterization ICON-ART is able to simulate the formation of the dusty cirrus, which leads to substantial improvements in cloud cover and radiative fluxes compared to simulations without this parameterization. A statistical evaluation over six Saharan dust events with and without observed dusty cirrus shows robust improvements in cloud and radiation scores. The ability to simulate dusty cirrus formation removes the linear dependency on mineral dust aerosol optical depth from the bias of the radiative fluxes. This suggests that the formation of dusty cirrus clouds is the dominant aerosol-cloud-radiation effect of mineral dust over Europe.
Seiki, Tatsuya; Ohno, TomokiSeiki, T., T. Ohno, 2022: Improvements of the Double-Moment Bulk Cloud Microphysics Scheme in the Nonhydrostatic Icosahedral Atmospheric Model (NICAM). J. Atmos. Sci., 80(1), 111-127. doi: 10.1175/JAS-D-22-0049.1. Abstract This study revises the collisional growth, heterogeneous ice nucleation, and homogeneous ice nucleation processes in a double-moment bulk cloud microphysics scheme implemented in the Nonhydrostatic Icosahedral Atmospheric Model (NICAM). The revised cloud microphysical processes are tested by 10-day global simulations with a horizontal resolution of 14 km. It is found that both the aggregation of cloud ice with smaller diameters and the graupel production by riming are overestimated in the current schemes. A new method that numerically integrates the collection kernel solves this issue, and consequently, the lifetime of cloud ice is reasonably extended in reference to satellite observations. In addition, the results indicate that a reduction in graupel modulates the convective intensity, particularly in intense rainfall systems. The revision of both heterogeneous and homogeneous ice nucleation significantly increases the production rate of cloud ice number concentration. With these revisions, the new version of the cloud microphysics scheme successfully improves outgoing longwave radiation, particularly over the intertropical convergence zone, in reference to satellite observations. Therefore, the revisions are beneficial for both long-term climate simulations and representing the structure of severe storms. Significance Statement Very high-resolution global atmospheric models have been developed to simultaneously address global climate and regional weather. In general, cloud microphysics schemes used in such global models are introduced from regional weather forecasting models to realistically represent mesoscale cloud systems. However, a cloud microphysics scheme that was originally developed with the aim of weather forecasting can cause unexpected errors in global climate simulations because such a cloud microphysics scheme is not designed for interdisciplinary usage across spatiotemporal scales. This study focuses on systematic model biases in evaluating the terminal velocity of ice cloud particles and proposes a method to accurately calculate the growth rate of ice cloud particles. Improvements in ice cloud modeling successfully reduce model biases in the global energy budget. In addition, the internal structure of intense rainfall systems is modified using the new cloud model. Therefore, improvements in ice cloud modeling could further increase the reliability of weather forecasting, seasonal prediction, and climate projection.
Seo, Minji; Kim, Hyun-Cheol; Seong, Noh-Hun; Sim, Suyoung; Han, Kyung-SooSeo, M., H. Kim, N. Seong, S. Sim, K. Han, 2022: Variability of Surface Radiation Budget Over Arctic During Recent Two Decades from Perspective of CERES and ERA5 Data. doi: 10.2139/ssrn.4145705. Extreme weather events, such as cold waves and droughts, have occurred recently in the mid-latitudes. Arctic climate change is a key parameter that determines the weather in these regions. It is therefore necessary to understand exactly how the Arctic climate is changing. This study focused on surface radiation budget, one of the essential factors for understanding climate change. Arctic surface radiative fluxes were summarized and explained using a satellite product, Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF), and reanalysis data, ERA5. Net radiation records indicated an increasing trend only in ERA5, with EBAF indicating a decreasing trend in the Arctic Circle from 2000 to 2018. The EBAF results differed from the general ice-albedo feedback. The differences in the net radiation trend between product types was due to longwave downward radiation. When the measurement periods were determined using surface air temperature (SAT) different results were obtained. In the maximum temperature period, all data displayed an increasing trend. The surface radiation budget was synthesized for extreme months in the Arctic Circle. Regardless of the data source, net radiation tended to increase in the maximum temperature period on an annual basis. By contrast, in the minimum temperature period, a net radiation tendency was observed in which ERA5 values increased and EBAF values decreased. It is possible to determine the average values and trends of radiative fluxes according to the characteristics of the Arctic temperature. This comprehensive information can be used to analyze and predict the surface energy budget, transport, and interaction between the atmosphere and surface in the Arctic. Climate change; Arctic; Surface radiation budget
Shaw, J.; McGraw, Z.; Bruno, O.; Storelvmo, T.; Hofer, S.Shaw, J., Z. McGraw, O. Bruno, T. Storelvmo, S. Hofer, 2022: Using Satellite Observations to Evaluate Model Microphysical Representation of Arctic Mixed-Phase Clouds. Geophysical Research Letters, 49(3), e2021GL096191. doi: 10.1029/2021GL096191. Mixed-phase clouds play an important role in determining Arctic warming, but are parametrized in models and difficult to constrain with observations. We use two satellite-derived cloud phase metrics to investigate the vertical structure of Arctic clouds in two global climate models that use the Community Atmosphere Model version 6 (CAM6) atmospheric component. We report a model error limiting ice nucleation, produce a set of Arctic-constrained model runs by adjusting model microphysical variables to match the cloud phase metrics, and evaluate cloud feedbacks for all simulations. Models in this small ensemble uniformly overestimate total cloud fraction in the summer, but have variable representation of cloud fraction and phase in the winter and spring. By relating modeled cloud phase metrics and changes in low-level liquid cloud amount under warming to longwave cloud feedback, we show that mixed-phase processes mediate the Arctic climate by modifying how wintertime and springtime clouds respond to warming. satellite; cloud feedback; climate models; ice nucleation; Arctic amplificantion
Shaw, Tiffany A.; Miyawaki, Osamu; Donohoe, AaronShaw, T. A., O. Miyawaki, A. Donohoe, 2022: Stormier Southern Hemisphere induced by topography and ocean circulation. Proceedings of the National Academy of Sciences, 119(50), e2123512119. doi: 10.1073/pnas.2123512119. A defining feature of Earth’s present-day climate is that the Southern Hemisphere is stormier than the Northern Hemisphere. Consistently, the Southern Hemisphere has a stronger jet stream and more extreme weather events than the Northern Hemisphere. Understanding the relative importance of land–ocean contrast, including topography, radiative processes, and ocean circulation for determining this storminess asymmetry is important and may be helpful for interpreting projections of future storminess. Here, we show that the stormier Southern Hemisphere is induced by nearly equal contributions from topography and the ocean circulation, which moves energy from the Southern to Northern Hemisphere. These findings are based on 1) diagnostic energetic analyses applied to observations and climate model simulations and 2) modifying surface (land and ocean) boundary conditions in climate model simulations. Flattening topography and prescribing hemispherically symmetric surface energy fluxes (the manifestation of ocean energy transport on the atmosphere) in a climate model reduce the storminess asymmetry from 23 to 12% and 11%, respectively. Finally, we use the energetic perspective to interpret storminess trends since the beginning of the satellite era. We show that the Southern Hemisphere has become stormier, consistent with implied ocean energy transport changes in the Southern Ocean. In the Northern Hemisphere, storminess has not changed significantly consistent with oceanic and radiative (increased absorption of sunlight due to the loss of sea ice and snow) changes opposing one another. The trends are qualitatively consistent with climate model projections.
Shi, Yang; Liu, Xiaohong; Wu, Mingxuan; Zhao, Xi; Ke, Ziming; Brown, HunterShi, Y., X. Liu, M. Wu, X. Zhao, Z. Ke, H. Brown, 2022: Relative importance of high-latitude local and long-range-transported dust for Arctic ice-nucleating particles and impacts on Arctic mixed-phase clouds. Atmospheric Chemistry and Physics, 22(4), 2909-2935. doi: 10.5194/acp-22-2909-2022. Abstract. Dust particles, serving as ice-nucleating particles (INPs), may impact the Arctic surface energy budget and regional climate by modulating the mixed-phase cloud properties and lifetime. In addition to long-range transport from low-latitude deserts, dust particles in the Arctic can originate from local sources. However, the importance of high-latitude dust (HLD) as a source of Arctic INPs (compared to low-latitude dust, LLD) and its effects on Arctic mixed-phase clouds are overlooked. In this study, we evaluate the contribution to Arctic dust loading and INP population from HLD and six LLD source regions by implementing a source-tagging technique for dust aerosols in version 1 of the US Department of Energy's Energy Exascale Earth System Model (E3SMv1). Our results show that HLD is responsible for 30.7 % of the total dust burden in the Arctic, whereas LLD from Asia and North Africa contributes 44.2 % and 24.2 %, respectively. Due to its limited vertical transport as a result of stable boundary layers, HLD contributes more in the lower troposphere, especially in boreal summer and autumn when the HLD emissions are stronger. LLD from North Africa and East Asia dominates the dust loading in the upper troposphere with peak contributions in boreal spring and winter. The modeled INP concentrations show better agreement with both ground and aircraft INP measurements in the Arctic when including HLD INPs. The HLD INPs are found to induce a net cooling effect (−0.24 W m−2 above 60∘ N) on the Arctic surface downwelling radiative flux by changing the cloud phase of the Arctic mixed-phase clouds. The magnitude of this cooling is larger than that induced by North African and East Asian dust (0.08 and −0.06 W m−2, respectively), mainly due to different seasonalities of HLD and LLD. Uncertainties of this study are discussed, which highlights the importance of further constraining the HLD emissions.
Shukla, Abhivyakti; Pattnaik, Sandeep; Trivedi, DhananjayShukla, A., S. Pattnaik, D. Trivedi, 2022: Study of Mesoscale Convective System and its Associated Cloud Structure over Indian Region Using Satellite Observations and Model Simulations. Journal of the Indian Society of Remote Sensing. doi: 10.1007/s12524-022-01573-0. The present study has discussed the identification of mesoscale convective systems (MCS) events using Cloud top temperatures from Cloud and the Earth’s Radiant Energy System and INSAT 3D imageries over the Indian region. The parameters such as height, areal extent, and vertical depth are considered as the criteria for identifying these intense rain-bearing MCS. High equivalent potential temperature, pronounced warm advection, low-level convergence, and local maximum in relative vorticity is associated with large-scale environments are the key indicators in identifying MCS. A total of five heavy rainfall events associated with MCS are simulated using the Weather Research and forecasting at a horizontal resolution of 3 km with a lead time of up to 96 h. In addition, the performance of two cumulus and four cloud microphysical parameterizations and their optimized combination are investigated for these MCS systems causing heavy rainfall over the region. The Betts–Miller–Janjic–Thompson combination simulated the best results in terms of rainfall, convective available potential energy, vertical updrafts, and reflectivity and its pre-formation environment of MCS. Further, this optimized combination is able to accurately represent the dominant hydrometeors (i.e., rain, graupel and snow), which have played a key role in simulating the MCS. Large-scale forcing such as moisture advection, convergence, relative vorticity, and equivalent potential temperature play a dominant role in the evolution and sustenance of MCS. Finally, a more robust (weaker) intensity MCS is better (poorly) predicted by the model. The findings of this study will further augment our understanding for better prediction of MCS associated with heavy rainfall events over the Indian region. Hydrometeors; Mesoscale convective system (MCS); WRF-ARW
Simonetti, Paolo; Vladilo, Giovanni; Silva, Laura; Maris, Michele; Ivanovski, Stavro L.; Biasiotti, Lorenzo; Malik, Matej; Hardenberg, Jost vonSimonetti, P., G. Vladilo, L. Silva, M. Maris, S. L. Ivanovski, L. Biasiotti, M. Malik, J. v. Hardenberg, 2022: EOS: Atmospheric Radiative Transfer in Habitable Worlds with HELIOS. The Astrophysical Journal, 925(2), 105. doi: 10.3847/1538-4357/ac32ca. We present EOS, a procedure for determining the outgoing longwave radiation (OLR) and top-of-atmosphere (TOA) albedo for a wide range of conditions expected to be present in the atmospheres of rocky planets with temperate conditions. EOS is based on HELIOS and HELIOS-K, which are novel and publicly available atmospheric radiative transfer (RT) codes optimized for fast calculations with GPU processors. These codes were originally developed for the study of giant planets. In this paper we present an adaptation for applications to terrestrial-type, habitable planets, adding specific physical recipes for the gas opacity and vertical structure of the atmosphere. To test the reliability of the procedure, we assessed the impact of changing line opacity profile, continuum opacity model, atmospheric lapse rate, and tropopause position prescriptions on the OLR and the TOA albedo. The results obtained with EOS are in line with those of other RT codes running on traditional CPU processors, while being at least one order of magnitude faster. The adoption of OLR and TOA albedo data generated with EOS in a zonal and seasonal climate model correctly reproduces the fluxes of the present-day Earth measured by the CERES spacecraft. The results of this study disclose the possibility to incorporate fast RT calculations in climate models aimed at characterizing the atmospheres of habitable exoplanets.
Singh, Sachchidanand; Mishra, Amit Kumar; Jose, Sandhya; Lodhi, Neelesh K.Singh, S., A. K. Mishra, S. Jose, N. K. Lodhi, 2022: Chapter 7 - Atmospheric pollution and solar ultraviolet radiation in Asia. Asian Atmospheric Pollution, 129-146. This chapter deals with atmospheric pollution, particularly the aerosol optical depth (AOD) and its impact on ultraviolet radiation flux reaching the Earth's surface, and its subsequent effect on vitamin D levels observed in the Asian region. It begins with the mean distribution during the last 16 years (2001–2016) of AOD, UVA, and UVB fluxes over Asia along with their trends on a 1°×1° grid scale. The Clouds and Earth Radiant Energy System (CERES) is the main source of data supported by data from MISR. High AOD values over Asia are well anticorrelated with the UVA and UVB fluxes reaching the surface. The reducing trend in UVB due to an increasing trend in AOD is a matter of concern, as UVB has a direct relation with the level of vitamin D prevalent in the Asian population, particularly in the South, Southeast Asian region. The accelerated economic development during the last two decades in Asia has led to an enhancement in AOD leading to a decrease in UVB reaching the surface and possibly reducing the production of vitamin D on a huge population in the region. Further targeted studies are however required to quantify the amount of reduction in vitamin D due to enhanced air pollution and AOD. CERES; Aerosol optical depth; MISR; Air pollution; UVA flux; UVB flux; Vitamin D
Sismanidis, Panagiotis; Bechtel, Benjamin; Perry, Mike; Ghent, DarrenSismanidis, P., B. Bechtel, M. Perry, D. Ghent, 2022: The Seasonality of Surface Urban Heat Islands across Climates. Remote Sensing, 14(10), 2318. doi: 10.3390/rs14102318. In this work, we investigate how the seasonal hysteresis of the Surface Urban Heat Island Intensity (SUHII) differs across climates and provide a detailed typology of the daytime and nighttime SUHII hysteresis loops. Instead of the typical tropical/dry/temperate/continental grouping, we describe Earth’s climate using the Köppen–Geiger system that empirically maps Earth’s biome distribution into 30 climate classes. Our thesis is that aggregating multi-city data without considering the biome of each city results in temporal means that fail to reflect the actual SUHII characteristics. This is because the SUHII is a function of both urban and rural features and the phenology of the rural surroundings can differ considerably between cities, even in the same climate zone. Our investigation covers all the densely populated areas of Earth and uses 18 years (2000–2018) of land surface temperature and land cover data from the European Space Agency’s Climate Change Initiative. Our findings show that, in addition to concave-up and -down shapes, the seasonal hysteresis of the SUHII also exhibits twisted, flat, and triangle-like patterns. They also suggest that, in wet climates, the daytime SUHII hysteresis is almost universally concave-up, but they paint a more complex picture for cities in dry climates. MODIS; LST; land surface temperature; ESA-CCI; Köppen–Geiger climate zones; seasonal hysteresis; SUHI; surface urban heat island
Södergren, A. H.; McDonald, A. J.Södergren, A. H., A. J. McDonald, 2022: Quantifying the Role of Atmospheric and Surface Albedo on Polar Amplification Using Satellite Observations and CMIP6 Model Output. Journal of Geophysical Research: Atmospheres, 127(12), e2021JD035058. doi: 10.1029/2021JD035058. Understanding polar amplification (PA) and its underlying processes is key to accurately predicting the climate system's response to increasing anthropogenic forcings. We examine the amplified warming in the Arctic and Antarctic in 17 global climate models from the Coupled Model Intercomparison Project 6 (CMIP6) against satellite data. Large hemispheric differences in PA strength was found in the CMIP6 models. Changes in surface temperature and strength of PA is closely coupled to changes in albedo. The planetary albedo of Earth (αp) is partitioned into a component associated with surface albedo (defined as surface contribution to planetary albedo, ), and a component associated with atmospheric albedo (atmospheric contribution to planetary albedo, ). To assess the hemispheric differences in PA strengths, the relative importance of and were investigated. The surface reflection looks different as seen at the surface (defined as surface albedo, αsurf) compared to (as seen at the top of the atmosphere). We find a stronger correlation between surface temperature and αsurf in the Arctic than in the Antarctic, with correlation coefficients of −0.94 and −0.88, respectively. Interestingly, the correlation for surface temperature and is stronger in the Antarctic than in the Arctic with correlation coefficients of −0.93 and −0.90, respectively. In the southern high latitudes, albedo changes at the surface are more important than changes in the atmosphere, while the opposite applies in the northern high latitudes. Surface temperature changes in the low- and mid-latitudes are strongly associated with changes in , dominated by changes in cloud properties. climate change; climate models; albedo; cmip6; polar amplification
Song, Yajuan; Qiao, Fangli; Liu, Jiping; Shu, Qi; Bao, Ying; Wei, Meng; Song, ZhenyaSong, Y., F. Qiao, J. Liu, Q. Shu, Y. Bao, M. Wei, Z. Song, 2022: Effects of Sea Spray on Large-Scale Climatic Features over the Southern Ocean. J. Climate, 35(14), 4645-4663. doi: 10.1175/JCLI-D-21-0608.1. Abstract The Southern Ocean, characterized by strong westerly winds and a rough sea state, exhibits the most pronounced sea spray effects. Sea spray ejected by ocean surface waves enhances heat and water exchange at the air–sea interface. However, this process has not been considered in current climate models, and the influence of sea spray on the coupled air–sea system remains largely unknown. This study incorporated a parameterization of the sea spray influence on latent and sensible heat fluxes into the First Institute of Oceanography Earth System Model version 2.0 (FIO-ESM v2.0), a climate model coupled with an ocean surface waves component. The results indicate that the spray-mediated enthalpy flux accounted for over 20%–50% of the total value. Sea spray promoted ocean evaporation and heat transport, resulting in air and ocean surface cooling and strengthened westerly winds. Furthermore, a moist and stable atmosphere favored an increase in cloud fraction over the Southern Ocean, particularly low-level clouds. Increased clouds reflected downward shortwave radiation and reduced solar radiation absorption at the surface. At present, the climate models participating in phase 6 of the Coupled Model Intercomparison Project (CMIP6) still suffer notable deficiencies in reasonably reproducing the climatological features of the Southern Ocean, including warm SST and underestimated clouds biases with more absorbed shortwave radiation. Our results suggest that consideration of sea spray effects is a feasible solution to mitigate these common biases and enhance the confidence in simulations and predictions with climate models.
Song, Zhen; Liang, Shunlin; Zhou, HongminSong, Z., S. Liang, H. Zhou, 2022: Top-of-Atmosphere Clear-Sky Albedo Estimation Over Ocean: Preliminary Framework for MODIS. IEEE Transactions on Geoscience and Remote Sensing, 60, 1-9. doi: 10.1109/TGRS.2021.3116620. Top-of-atmosphere (TOA) albedo is a significant factor of earth energy budget, climate change, and environmental change. As tremendous regional and global changes are happening over ocean, more details are needed to monitor the ocean environment. However, there were still no high-spatial resolution TOA albedo products over ocean. In this study, a new algorithm for clear-sky TOA albedo estimation over ocean was proposed, based on Moderate Resolution Imaging Spectroradiometer (MODIS) data. Instead of building angular distribution models, direct retrieval models between TOA reflectance and TOA albedo were developed based on extensive radiative transfer (RT) simulations, covering thousands of ocean and atmosphere types. Three-component ocean water albedo model was involved to take account for the ocean surface anisotropy at different wind speed, wind direction, and chlorophyll concentration, while Modtran 5 was utilized to simulate different atmospheric conditions. Our results showed good agreement with the Clouds and the Earth’s Radiant Energy System (CERES) based on a global comparison on August 4, 2011, with RMSE = 0.015 and bias = 0.002. And our MODIS-based products provide more spatial details due to higher spatial resolution (1 km), which will be a good data source for regional environmental and climatic research and will also enhance the understanding of Earth’s radiation budget. Earth; Oceans; Wind speed; MODIS; Atmospheric modeling; energy budget; Moderate Resolution Imaging Spectroradiometer (MODIS); Sea surface; Climate change; Broadband communication; ocean bidirectional reflectance distribution function (BRDF); radiative transfer (RT) simulations; top-of-atmosphere (TOA) albedo
Sreenath, A. V.; Abhilash, S.; Vijaykumar, P.; Mapes, B. E.Sreenath, A. V., S. Abhilash, P. Vijaykumar, B. E. Mapes, 2022: West coast India’s rainfall is becoming more convective. npj Climate and Atmospheric Science, 5(1), 1-7. doi: 10.1038/s41612-022-00258-2. A disastrous cloudburst and associated floods in Kerala during the 2019 monsoon season raise the hypothesis that rainfall over the west coast of India, much of which is stratiform, may be trending towards being more convective. As a first exploration, we sought statistically significant differences in monthly ERA-5 reanalysis data for the monsoon season between two epochs, 1980–1999 and 2000–2019. Results suggest a more convective (deeper, ice-rich) cloud population in recent decades, with patterns illustrated in ERA-5 spatial maps. Deepening of convection, above and beyond its trend in amount, is also indicated by the steeper regression slope of outgoing longwave radiation trends against precipitation than that exhibited in interannual variability. Our reanalysis results are strengthened by related trends manifested in more direct observations from satellite and gauge-based rainfall and a CAPE index from balloon soundings data. Attribution; Climate-change impacts
Srinivasan, Ashwanth; Chin, T. M.; Chassignet, E. P.; Iskandarani, M.; Groves, N.Srinivasan, A., T. M. Chin, E. P. Chassignet, M. Iskandarani, N. Groves, 2022: A Statistical Interpolation Code for Ocean Analysis and Forecasting. J. Atmos. Oceanic Technol., 39(3), 367-386. doi: 10.1175/JTECH-D-21-0033.1. Abstract We present a data assimilation package for use with ocean circulation models in analysis, forecasting, and system evaluation applications. The basic functionality of the package is centered on a multivariate linear statistical estimation for a given predicted/background ocean state, observations, and error statistics. Novel features of the package include support for multiple covariance models, and the solution of the least squares normal equations either using the covariance matrix or its inverse—the information matrix. The main focus of this paper, however, is on the solution of the analysis equations using the information matrix, which offers several advantages for solving large problems efficiently. Details of the parameterization of the inverse covariance using Markov random fields are provided and its relationship to finite-difference discretizations of diffusion equations are pointed out. The package can assimilate a variety of observation types from both remote sensing and in situ platforms. The performance of the data assimilation methodology implemented in the package is demonstrated with a yearlong global ocean hindcast with a 1/4° ocean model. The code is implemented in modern Fortran, supports distributed memory, shared memory, multicore architectures, and uses climate and forecasts compliant Network Common Data Form for input/output. The package is freely available with an open source license from www.tendral.com/tsis/.
Stamatis, Michael; Hatzianastassiou, Nikolaos; Korras-Carraca, Marios Bruno; Matsoukas, Christos; Wild, Martin; Vardavas, IliasStamatis, M., N. Hatzianastassiou, M. B. Korras-Carraca, C. Matsoukas, M. Wild, I. Vardavas, 2022: Interdecadal Changes of the MERRA-2 Incoming Surface Solar Radiation (SSR) and Evaluation against GEBA & BSRN Stations. Applied Sciences, 12(19), 10176. doi: 10.3390/app121910176. This study assesses and evaluates the 40-year (1980–2019) Modern-Era Retrospective Analysis for Research and Applications v.2 (MERRA-2) surface solar radiation (SSR) as well as its interdecadal changes (Δ(SSR)) against high quality reference surface measurements from 1397 Global Energy Balance Archive (GEBA) and 73 Baseline Surface Radiation Network (BSRN) stations. The study is innovative since MERRA-2 (Δ(SSR)) has never been evaluated in the past, while the MERRA-2 SSR fluxes themselves have not been evaluated in such large spatial scale, which is global here, and temporal basis, which counts 40-years. Other novelties of the study are the use of the highest quality BSRN stations, done for the first time in such an evaluation, as well as the use of a greater number of reference-GEBA stations than in other studies. Moreover, the assessment and evaluation in this study are largely based on SSR anomalies, while being done in depth, at spatial scales ranging from the local to global/hemispherical, and separately for land and ocean areas, and at temporal scales spanning intervals from decadal sub-periods to 40 years. Overall, the MERRA-2 deseasonalized SSR anomalies correlate well with either GEBA (R equal to 0.61) and BSRN (R equal to 0.62). The percentage of agreement between the sign of computed GEBA and MERRA-2 Δ(SSR) is equal to 63.4% and the corresponding percentage for MERRA-2 and BSRN is 50%. According to MERRA-2, strong and statistically significant positive Δ(SSR) (Brightening) is found over Europe, Central Africa, Mongolia, Mexico, Brazil, Argentina and some parts of the tropical oceans. In contrast, large and statistically significant negative Δ(SSR) (Dimming) occurs over the western Tropical Warm Pool, India, Southern East China, Amazonia, stratocumulus covered areas and some parts of oceans. MERRA-2 yields a dimming equal to −0.158 ± 0.005 W/m2/year over the globe from 1980 to 2019. This 40-year dimming, which occurred in both hemispheres, more over ocean than continental areas (−0.195 ± 0.006 and −0.064 ± 0.006 W/m2/year, respectively), underwent decadal scale variations. climate; reanalysis; brightening; dimming; model; stations; surface solar radiation
Storto, Andrea; Cheng, Lijing; Yang, ChunxueStorto, A., L. Cheng, C. Yang, 2022: Revisiting the 2003–18 Deep Ocean Warming through Multiplatform Analysis of the Global Energy Budget. J. Climate, 35(14), 4701-4717. doi: 10.1175/JCLI-D-21-0726.1. Abstract Recent estimates of the global warming rates suggest that approximately 9% of Earth’s excess heat has been cumulated in the deep and abyssal oceans (below 2000-m depth) during the last two decades. Such estimates assume stationary trends deducted as long-term rates. To reassess the deep ocean warming and potentially shed light on its interannual variability, we formulate the balance between Earth’s energy imbalance (EEI), the steric sea level, and the ocean heat content (OHC), at yearly time scales during the 2003–18 period, as a variational problem. The solution is achieved through variational minimization, merging observational data from top-of-atmosphere EEI, inferred from Clouds and the Earth’s Radiant Energy System (CERES), steric sea level estimates from altimetry minus gravimetry, and upper-ocean heat content estimates from in situ platforms (mostly Argo floats). Global ocean reanalyses provide background-error covariances for the OHC analysis. The analysis indicates a 2000-m–bottom warming of 0.08 ± 0.04 W m−2 for the period 2003–18, equal to 13% of the total ocean warming (0.62 ± 0.08 W m−2), slightly larger than previous estimates but consistent within the error bars. The analysis provides a fully consistent optimized solution also for the steric sea level and EEI. Moreover, the simultaneous use of the different heat budget observing networks is able to decrease the analysis uncertainty with respect to the observational one, for all observation types and especially for the 0–700-m OHC and steric sea level (more than 12% reduction). The sensitivity of the analysis to the choice of the background time series proved insignificant. Significance Statement Several observing networks provide complementary information about the temporal evolution of the global energy budget. Here, satellite observations of Earth’s energy imbalance (EEI) and steric sea level and in situ–derived estimates of ocean heat content anomalies are combined in a variational analysis framework, with the goal of assessing the deep ocean warming. The optimized solution accounts for the uncertainty of the different observing networks. Furthermore, it provides fully consistent analyses of global ocean heat content, steric sea level, and EEI, which show smaller uncertainty than the original observed time series. The deep ocean (below 2000-m depth) exhibits a significant warming of 0.08 ± 0.04 W m−2 for the period 2003–18, equal to the 13% of the total ocean warming.
Su, Shixiang; Wang, Jinyan; Yin, Zelun; Wang, Tianyu; Yasheng, Dilinuer; Xie, Xiangshan; Sun, Caixia; Yang, YiSu, S., J. Wang, Z. Yin, T. Wang, D. Yasheng, X. Xie, C. Sun, Y. Yang, 2022: Understanding the Daytime and Nighttime Impacts of Dust Aerosols on Surface Energy and Meteorological Fields in Northwest China. Journal of Geophysical Research: Atmospheres, 127(24), e2022JD037619. doi: 10.1029/2022JD037619. Dust aerosols pose non-negligible impacts on regional and global climate, particularly over northwest China (NWC), where dust events frequently occur. Here, six dust events with different intensities occurred from 2014 to 2019 in NWC were simulated by the Weather Research and Forecasting model coupled to Chemistry (WRF-Chem) to quantitatively evaluate the contributions of dust aerosols to radiation fluxes, surface energy, and meteorology, with specific consideration to the distinctions between daytime and nighttime. The results show that the contributions of dust aerosols to surface energy and meteorology were significantly affected by dust concentrations and dust layer heights and exhibited diurnal variation. In the case with high dust concentration and low dust layer height, dust aerosols increased the surface energy during the nighttime but decreased in the daytime, and the increase was much greater than the decrease. As a result, dust aerosols increase surface energy (0.06 W/m2 in the dust source region; 0.13 W/m2 in the dust affected region (DAR)) and surface temperature (0.0088°C in the DSR; 0.0781°C in the DAR) and decrease surface relative humidity (−0.053% in the DSR; −0.205% in the DAR) throughout the whole day. In contrast, dust causes opposite impacts on surface meteorology throughout the whole day due to the nighttime warming effect from the dust events with low dust concentration and high dust layer height is lesser than the daytime cooling effect. The study provides scientific insights for improving our understanding of dust aerosols-regional meteorology interaction. meteorology; energy budget; dust aerosol; WRF-chem
Subba, Tamanna; Gogoi, Mukunda M.; Moorthy, K. Krishna; Bhuyan, Pradip K.; Pathak, Binita; Guha, Anirban; Srivastava, Manoj Kumar; Vyas, B. M.; Singh, Karamjit; Krishnan, Jayabala; Lakshmi Kumar, T. V.; Babu, S. SureshSubba, T., M. M. Gogoi, K. K. Moorthy, P. K. Bhuyan, B. Pathak, A. Guha, M. K. Srivastava, B. M. Vyas, K. Singh, J. Krishnan, T. V. Lakshmi Kumar, S. S. Babu, 2022: New estimates of aerosol radiative effects over India from surface and satellite observations. Atmospheric Research, 276, 106254. doi: 10.1016/j.atmosres.2022.106254. Multi-year measurements of surface-reaching solar (shortwave) radiation fluxes across a network of aerosol observatories (ARFINET) are combined with concurrent satellite (CERES)-based top of the atmosphere (TOA) fluxes to estimate regional aerosol direct radiative forcing (ARF) over the Indian region. The synergistic approach improves the accuracy of ARF estimates, which otherwise results in an overestimation or underestimation of the atmospheric forcing. During summer, an overestimation of ~5 W m−2 (corresponding heating rate ~ 0.15 K day−1) is noticed. The regional average ARF from the synergistic approach reveals the surface forcing reaching −49 W m−2 over the Indo Gangetic Plains, −45 W m−2 over northeast India, −34 W m−2 over the southern Peninsula, and − 16 W m−2 in the oceanic regions of the Bay of Bengal. The ARF over the northern half of the Indian subcontinent is influenced mainly by anthropogenic sulfate and carbonaceous aerosols. Dust is dominant in the western region of India during MAM and JJAS. Overall, the clear sky surface reaching solar radiation fluxes is reduced by 3–22% due to the abundance of aerosols in the atmosphere, with the highest reduction over the IGP during autumn and winter. CERES; MERRA-2; Heating rate; ARFINET; SW-radiation; Aerosol composition; Aerosol radiative forcing
Sun, Moguo; Doelling, David R.; Loeb, Norman G.; Scott, Ryan C.; Wilkins, Joshua; Nguyen, Le Trang; Mlynczak, PamelaSun, M., D. R. Doelling, N. G. Loeb, R. C. Scott, J. Wilkins, L. T. Nguyen, P. Mlynczak, 2022: Clouds and the Earth’s Radiant Energy System (CERES) FluxByCldTyp Edition 4 Data Product. J. Atmos. Oceanic Technol., 39(3), 303-318. doi: 10.1175/JTECH-D-21-0029.1. Abstract The Clouds and the Earth’s Radiant Energy System (CERES) project has provided the climate community 20 years of globally observed top of the atmosphere (TOA) fluxes critical for climate and cloud feedback studies. The CERES Flux By Cloud Type (FBCT) product contains radiative fluxes by cloud type, which can provide more stringent constraints when validating models and also reveal more insight into the interactions between clouds and climate. The FBCT product provides 1° regional daily and monthly shortwave (SW) and longwave (LW) cloud-type fluxes and cloud properties sorted by seven pressure layers and six optical depth bins. Historically, cloud-type fluxes have been computed using radiative transfer models based on observed cloud properties. Instead of relying on radiative transfer models, the FBCT product utilizes Moderate Resolution Imaging Spectroradiometer (MODIS) radiances partitioned by cloud type within a CERES footprint to estimate the cloud-type broadband fluxes. The MODIS multichannel derived broadband fluxes were compared with the CERES observed footprint fluxes and were found to be within 1% and 2.5% for LW and SW, respectively, as well as being mostly free of cloud property dependencies. These biases are mitigated by constraining the cloud-type fluxes within each footprint with the CERES Single Scanner Footprint (SSF) observed flux. The FBCT all-sky and clear-sky monthly averaged fluxes were found to be consistent with the CERES SSF1deg product. Several examples of FBCT data are presented to highlight its utility for scientific applications.
Sun, Yuanheng; Knyazikhin, Yuri; She, Xiaojun; Ni, Xiangnan; Chen, Chi; Ren, Huazhong; Myneni, Ranga B.Sun, Y., Y. Knyazikhin, X. She, X. Ni, C. Chen, H. Ren, R. B. Myneni, 2022: Seasonal and long-term variations in leaf area of Congolese rainforest. Remote Sensing of Environment, 268, 112762. doi: 10.1016/j.rse.2021.112762. It is important to understand temporal and spatial variations in the structure and photosynthetic capacity of tropical rainforests in a world of changing climate, increased disturbances and human appropriation. The equatorial rainforests of Central Africa are the second largest and least disturbed of the biodiversly-rich and highly productive rainforests on Earth. Currently, there is a dearth of knowledge about the phenological behavior and long-term changes that these forests are experiencing. Thus, this study reports on leaf area seasonality and its time trend over the past two decades as assessed from multiple remotely sensed datasets. Seasonal variations of leaf area in Congolese forests derived from MODIS data co-vary with the bimodal precipitation pattern in this region, with higher values during the wet season. Independent observational evidence derived from MISR and EPIC sensors in the form of angular reflectance signatures further corroborate this seasonal behavior of leaf area. The bimodal patterns vary latitudinally within this large region. Two sub-seasonal cycles, each consisting of a dry and wet season, could be discerned clearly. These exhibit different sensitivities to changes in precipitation. Contrary to a previous published report, no widespread decline in leaf area was detected across the entire extent of the Congolese rainforests over the past two decades with the latest MODIS Collection 6 dataset. Long-term precipitation decline did occur in some localized areas, but these had minimal impacts on leaf area, as inferred from MODIS and MISR multi-angle observations. Remote sensing; MODIS; Phenology; MISR; Congolese rainforests; DSCOVR EPIC; Leaf area; Long-term trends
Tan, Ivy; Barahona, DonifanTan, I., D. Barahona, 2022: The Impacts of Immersion Ice Nucleation Parameterizations on Arctic Mixed-Phase Stratiform Cloud Properties and the Arctic Radiation Budget in GEOS-5. J. Climate, 35(13), 4049-4070. doi: 10.1175/JCLI-D-21-0368.1. Abstract The influence of four different immersion freezing parameterizations on Arctic clouds and the top-of-the atmosphere (TOA) and surface radiation fluxes is investigated in the fifth version of the National Aeronautics and Space Administration (NASA) Goddard Earth Observing System (GEOS-5) with sea surface temperature, sea ice fraction, and aerosol emissions held fixed. The different parameterizations were derived from a variety of sources, including classical nucleation theory and field and laboratory measurements. Despite the large spread in the ice-nucleating particle (INP) concentrations in the parameterizations, the cloud properties and radiative fluxes had a tendency to form two groups, with the lower INP concentration category producing larger water path and low-level cloud fraction during winter and early spring, whereas the opposite occurred during the summer season. The stability of the lower troposphere was found to strongly correlate with low-cloud fraction and, along with the effect of ice nucleation, ice sedimentation, and melting rates, appears to explain the spring-to-summer reversal pattern in the relative magnitude of the cloud properties between the two categories of simulations. The strong modulation effect of the liquid phase on immersion freezing led to the successful simulation of the characteristic Arctic cloud structure, with a layer rich in supercooled water near cloud top and ice and snow at lower levels. Comparison with satellite retrievals and in situ data suggest that simulations with low INP concentrations more realistically represent Arctic clouds and radiation.
Taylor, Patrick C.; Itterly, Kyle F.; Corbett, Joe; Bucholtz, Anthony; Sejas, Sergio; Su, Wenying; Doelling, Dave; Kato, SeijiTaylor, P. C., K. F. Itterly, J. Corbett, A. Bucholtz, S. Sejas, W. Su, D. Doelling, S. Kato, 2022: A Comparison of Top-Of-Atmosphere Radiative Fluxes From CERES and ARISE. Journal of Geophysical Research: Atmospheres, 127(24), e2022JD037573. doi: 10.1029/2022JD037573. Uncertainty in Arctic top-of-atmosphere (TOA) radiative flux observations stems from the low sun angles and the heterogeneous scenes. Advancing our understanding of the Arctic climate system requires improved TOA radiative fluxes. We compare Cloud and Earth's Radiant Energy System (CERES) TOA radiative fluxes with Arctic Radiation-IceBridge Sea and Ice Experiment (ARISE) airborne measurements using two approaches: grid box averages and instantaneously matched footprints. Both approaches indicate excellent agreement in the longwave and good agreement in the shortwave (SW), within 2σ uncertainty considering all error sources (CERES and airborne radiometer calibration, inversion, and sampling). While the SW differences are within 2σ uncertainty, both approaches show a ∼−10 W m−2 average CERES-aircraft flux difference. Investigating the source of this negative difference, we find a substantial sensitivity of the flux differences to the sea ice concentration data set. Switching from imager-based to passive microwave-based sea ice data in the CERES inversion process reduces the differences in the grid box average fluxes and in the sea ice partly cloudy scene anisotropy in the matched footprints. In the long-term, more accurate sea ice concentration data are needed to reduce CERES TOA SW flux uncertainties. Switching from imager to passive microwave sea ice data, in the short-term, could improve CERES TOA SW fluxes in polar regions, additional testing is required. Our analysis indicates that calibration and sampling uncertainty limit the ability to place strong constraints ( CERES; sea ice; remote sensing; ARISE; polar energy budget; TOA radiative fluxes
Tezaur, Irina; Peterson, Kara; Powell, Amy; Jakeman, John; Roesler, ErikaTezaur, I., K. Peterson, A. Powell, J. Jakeman, E. Roesler, 2022: Global Sensitivity Analysis Using the Ultra-Low Resolution Energy Exascale Earth System Model. Journal of Advances in Modeling Earth Systems, 14(8), e2021MS002831. doi: 10.1029/2021MS002831. For decades, Arctic temperatures have increased twice as fast as average global temperatures. As a first step toward quantifying parametric uncertainty in Arctic climate, we performed a variance-based global sensitivity analysis (GSA) using a fully coupled, ultra-low resolution (ULR) configuration of version 1 of the U.S. Department of Energy's Energy Exascale Earth System Model (E3SMv1). Specifically, we quantified the sensitivity of six quantities of interests (QOIs), which characterize changes in Arctic climate over a 75 year period, to uncertainties in nine model parameters spanning the sea ice, atmosphere, and ocean components of E3SMv1. Sensitivity indices for each QOI were computed with a Gaussian process emulator using 139 random realizations of the random parameters and fixed preindustrial forcing. Uncertainties in the atmospheric parameters in the Cloud Layers Unified by Binormals (CLUBB) scheme were found to have the most impact on sea ice status and the larger Arctic climate. Our results demonstrate the importance of conducting sensitivity analyses with fully coupled climate models. The ULR configuration makes such studies computationally feasible today due to its low computational cost. When advances in computational power and modeling algorithms enable the tractable use of higher-resolution models, our results will provide a baseline that can quantify the impact of model resolution on the accuracy of sensitivity indices. Moreover, the confidence intervals provided by our study, which we used to quantify the impact of the number of model evaluations on the accuracy of sensitivity estimates, have the potential to inform the computational resources needed for future sensitivity studies. Arctic climate state; Energy Exascale Earth System Model (E3SM); fully coupled; global sensitivity analysis (GSA); ultra-low resolution (ULR); uncertainty quantification (UQ)
Thompson, Chelsea R.; Wofsy, Steven C.; Prather, Michael J.; Newman, Paul A.; Hanisco, Thomas F.; Ryerson, Thomas B.; Fahey, David W.; Apel, Eric C.; Brock, Charles A.; Brune, William H.; Froyd, Karl; Katich, Joseph M.; Nicely, Julie M.; Peischl, Jeff; Ray, Eric; Veres, Patrick R.; Wang, Siyuan; Allen, Hannah M.; Asher, Elizabeth; Bian, Huisheng; Blake, Donald; Bourgeois, Ilann; Budney, John; Bui, T. Paul; Butler, Amy; Campuzano-Jost, Pedro; Chang, Cecilia; Chin, Mian; Commane, Róisín; Correa, Gus; Crounse, John D.; Daube, Bruce; Dibb, Jack E.; DiGangi, Joshua P.; Diskin, Glenn S.; Dollner, Maximilian; Elkins, James W.; Fiore, Arlene M.; Flynn, Clare M.; Guo, Hao; Hall, Samuel R.; Hannun, Reem A.; Hills, Alan; Hintsa, Eric J.; Hodzic, Alma; Hornbrook, Rebecca S.; Huey, L. Greg; Jimenez, Jose L.; Keeling, Ralph F.; Kim, Michelle J.; Kupc, Agnieszka; Lacey, Forrest; Lait, Leslie R.; Lamarque, Jean-Francois; Liu, Junhua; McKain, Kathryn; Meinardi, Simone; Miller, David O.; Montzka, Stephen A.; Moore, Fred L.; Morgan, Eric J.; Murphy, Daniel M.; Murray, Lee T.; Nault, Benjamin A.; Neuman, J. Andrew; Nguyen, Louis; Gonzalez, Yenny; Rollins, Andrew; Rosenlof, Karen; Sargent, Maryann; Schill, Gregory; Schwarz, Joshua P.; Clair, Jason M. St; Steenrod, Stephen D.; Stephens, Britton B.; Strahan, Susan E.; Strode, Sarah A.; Sweeney, Colm; Thames, Alexander B.; Ullmann, Kirk; Wagner, Nicholas; Weber, Rodney; Weinzierl, Bernadett; Wennberg, Paul O.; Williamson, Christina J.; Wolfe, GlenThompson, C. R., S. C. Wofsy, M. J. Prather, P. A. Newman, T. F. Hanisco, T. B. Ryerson, D. W. Fahey, E. C. Apel, C. A. Brock, W. H. Brune, K. Froyd, J. M. Katich, J. M. Nicely, J. Peischl, E. Ray, P. R. Veres, S. Wang, H. M. Allen, E. Asher, H. Bian, D. Blake, I. Bourgeois, J. Budney, T. P. Bui, A. Butler, P. Campuzano-Jost, C. Chang, M. Chin, R. Commane, G. Correa, J. D. Crounse, B. Daube, J. E. Dibb, J. P. DiGangi, G. S. Diskin, M. Dollner, J. W. Elkins, A. M. Fiore, C. M. Flynn, H. Guo, S. R. Hall, R. A. Hannun, A. Hills, E. J. Hintsa, A. Hodzic, R. S. Hornbrook, L. G. Huey, J. L. Jimenez, R. F. Keeling, M. J. Kim, A. Kupc, F. Lacey, L. R. Lait, J. Lamarque, J. Liu, K. McKain, S. Meinardi, D. O. Miller, S. A. Montzka, F. L. Moore, E. J. Morgan, D. M. Murphy, L. T. Murray, B. A. Nault, J. A. Neuman, L. Nguyen, Y. Gonzalez, A. Rollins, K. Rosenlof, M. Sargent, G. Schill, J. P. Schwarz, J. M. S. Clair, S. D. Steenrod, B. B. Stephens, S. E. Strahan, S. A. Strode, C. Sweeney, A. B. Thames, K. Ullmann, N. Wagner, R. Weber, B. Weinzierl, P. O. Wennberg, C. J. Williamson, G. Wolfe, 2022: The NASA Atmospheric Tomography (ATom) Mission: Imaging the Chemistry of the Global Atmosphere. Bull. Amer. Meteor. Soc., 103(3), E761-E790. doi: 10.1175/BAMS-D-20-0315.1. Abstract This article provides an overview of the NASA Atmospheric Tomography (ATom) mission and a summary of selected scientific findings to date. ATom was an airborne measurements and modeling campaign aimed at characterizing the composition and chemistry of the troposphere over the most remote regions of the Pacific, Southern, Atlantic, and Arctic Oceans, and examining the impact of anthropogenic and natural emissions on a global scale. These remote regions dominate global chemical reactivity and are exceptionally important for global air quality and climate. ATom data provide the in situ measurements needed to understand the range of chemical species and their reactions, and to test satellite remote sensing observations and global models over large regions of the remote atmosphere. Lack of data in these regions, particularly over the oceans, has limited our understanding of how atmospheric composition is changing in response to shifting anthropogenic emissions and physical climate change. ATom was designed as a global-scale tomographic sampling mission with extensive geographic and seasonal coverage, tropospheric vertical profiling, and detailed speciation of reactive compounds and pollution tracers. ATom flew the NASA DC-8 research aircraft over four seasons to collect a comprehensive suite of measurements of gases, aerosols, and radical species from the remote troposphere and lower stratosphere on four global circuits from 2016 to 2018. Flights maintained near-continuous vertical profiling of 0.15–13-km altitudes on long meridional transects of the Pacific and Atlantic Ocean basins. Analysis and modeling of ATom data have led to the significant early findings highlighted here.
Tian, Lei; Zhang, Baoqing; Wang, Xuejin; Chen, Shuoyu; Pan, BaotianTian, L., B. Zhang, X. Wang, S. Chen, B. Pan, 2022: Large-Scale Afforestation Over the Loess Plateau in China Contributes to the Local Warming Trend. Journal of Geophysical Research: Atmospheres, 127(1), e2021JD035730. doi: 10.1029/2021JD035730. Afforestation is a major anthropogenic forcing to the global and regional climate. However, the biophysical impacts of large-scale afforestation on local temperature in temperate regions remain unclear, due to the closely matched but compensating radiative and non-radiative effects. The Grain for Green Program (GFGP) is a large-scale afforestation program implemented over the Loess Plateau (LP) in China. The GFGP thus provides an ideal platform to explore the temperature effect of afforestation. This study investigated such a temperature effect through long-term, high-resolution simulations incorporating satellite observations in a coupled land-atmosphere model. With an optimal combination of physical schemes proposed by this study, we greatly improved the accuracy of regional climate modeling. The results reveal that the afforestation caused a significant decline (−0.50% yr−1) in albedo. An increment in net shortwave radiation mainly led to an increment in net radiation (7.95 W m−2). The afforestation also led to an increment in sensible heat flux (3.78 W m−2). Consequently, the afforestation caused a warming effect (0.36°C) in 2-meter air temperature at the inter-annual scale. At the intra-annual scale, there was a cooling effect in July and August, while other months demonstrated a warming effect. The radiative effect dominated local temperature change induced by the afforestation over the LP. Therefore, the large-scale afforestation contributed to the local warming trend. Our findings highlight the temperature effect of afforestation, and imply that more attention should be paid to future revegetation to carefully assess its potential influence on regional climate. temperature; regional climate; evapotranspiration; afforestation; energy and water cycle; land-atmosphere model
Tomasini, M.; Guichard, F.; Couvreux, F.; Roehrig, R.; Barbier, J.Tomasini, M., F. Guichard, F. Couvreux, R. Roehrig, J. Barbier, 2022: Spurious effects of the deep convection parameterization on the simulation of a Sahelian heatwave. Quarterly Journal of the Royal Meteorological Society, n/a(n/a). doi: 10.1002/qj.4365. A severe heatwave occurred in April 2010 over West Africa. It was characterised by a particularly high daily minimum temperature reaching more than 35°C locally and a high water vapour content. In this study we analyse the ability of a mesoscale limited area model to represent such an event and investigate the advantage of using an explicit representation of deep convection for such a case associated with very limited precipitation amounts. Two high-resolution simulations (5 km x 5 km horizontal grid) have been performed from 10 to 19 April 2010; they are identical except that one uses a deep convection parameterization (simulation PARAM) and the other does not (simulation EXPL). These simulations are evaluated with different observational datasets including gridded products as well as local meteorological measurements and radiosoundings. Overall, both simulations display a negative temperature bias in the low levels but this bias is much more pronounced in PARAM, mainly due to evaporative cooling of spurious precipitation. Indeed, in PARAM, precipitation is too frequently triggered (around mid-day, i.e. several hours too early) and too strong; the Inter-Tropical Discontinuity (ITD) propagates too far north during this 10-day sequence. Conversely, in EXPL, the observed northward shift of the ITD is correctly simulated and precipitation displays a better timing, variability, intensity and latitudinal extent. It thus appears that the representation of deep convection affects the atmospheric circulation associated with the heatwave event. The mechanisms involved in this humid heatwave are further investigated with thermodynamic and dynamic budgets which also underline the main differences between the two simulations. A proper representation of deep convection on sub-diurnal time scale turns out to be necessary for the simulation of this heatwave episode, which points to the interest of convection-permitting simulations for the study of heatwaves even though they are generally characterised by very little precipitation. This article is protected by copyright. All rights reserved. Convection-permitting model; Deep convection parameterization; Heatwave; Inter-Tropical Discontinuity; Monsoon Surge; Sahel; Thermodynamic and dynamic budgets
Topál, Dániel; Ding, Qinghua; Ballinger, Thomas J.; Hanna, Edward; Fettweis, Xavier; Li, Zhe; Pieczka, IldikóTopál, D., Q. Ding, T. J. Ballinger, E. Hanna, X. Fettweis, Z. Li, I. Pieczka, 2022: Discrepancies between observations and climate models of large-scale wind-driven Greenland melt influence sea-level rise projections. Nature Communications, 13(1), 6833. doi: 10.1038/s41467-022-34414-2. While climate models project that Greenland ice sheet (GrIS) melt will continue to accelerate with climate change, models exhibit limitations in capturing observed connections between GrIS melt and changes in high-latitude atmospheric circulation. Here we impose observed Arctic winds in a fully-coupled climate model with fixed anthropogenic forcing to quantify the influence of the rotational component of large-scale atmospheric circulation variability over the Arctic on the temperature field and the surface mass/energy balances through adiabatic processes. We show that recent changes involving mid-to-upper-tropospheric anticyclonic wind anomalies – linked with tropical forcing – explain half of the observed Greenland surface warming and ice loss acceleration since 1990, suggesting a pathway for large-scale winds to potentially enhance sea-level rise by ~0.2 mm/year per decade. We further reveal fingerprints of this observed teleconnection in paleo-reanalyses spanning the past 400 years, which heightens concern about model limitations to capture wind-driven adiabatic processes associated with GrIS melt. Atmospheric dynamics; Cryospheric science; Climate and Earth system modelling
Truong, Son C. H.; Huang, Yi; Siems, Steven T.; Manton, Michael J.; Lang, FranciscoTruong, S. C. H., Y. Huang, S. T. Siems, M. J. Manton, F. Lang, 2022: Biases in the thermodynamic structure over the Southern Ocean in ERA5 and their radiative implications. International Journal of Climatology, n/a(n/a). doi: 10.1002/joc.7672. The thermodynamic structure of the lower troposphere in the 37 standard levels ERA5 reanalysis has been evaluated against 2,186 high-resolution upper air soundings collected over the Southern Ocean (SO). The reanalysis, which incorporated these soundings, was found to be skilled in depicting the general synoptic meteorology and thermodynamic structure as defined by the cluster analysis of Truong et al. (2020) Journal of Geophysical Research: Atmospheres, 125, e2020JD033214. Using dew-point depression as a proxy for cloud, however, we found a significant reduction in the number of inferred cloud layers, which is inherited from a bias in the specific humidity in the ERA5 reanalysis, most notably over the high latitudes of the SO, where a multilayer cloud structure is frequently observed. The reanalysis was also found to have thinner inferred cloud geometric layer and shallower cloud top heights. Further analysis showed that the reanalysis displays a greater percentage of soundings having no inversion with this bias being more pronounced at high latitudes that tends to be associated with the colder sea surface temperature. While the statistics of the main inversion height are largely consistent, the average inversion strength in the ERA5 reanalysis is found to be weaker than the observations. We anticipate the 137-level ERA5 reanalysis simulation yields a smoothed vertical structure, from which the 37 standard levels ERA5 reanalysis is linearly interpolated. An examination of the sensitivity of the radiative transfer to cloud macrophysics suggests that the correct representation of thin multiple cloud layers can help reduce the amount of downward shortwave surface radiation over the SO. Southern Ocean; marine atmospheric boundary layer; inversion; multilayer clouds; radiation bias
Turbeville, S. M.; Nugent, J. M.; Ackerman, T. P.; Bretherton, C. S.; Blossey, P. N.Turbeville, S. M., J. M. Nugent, T. P. Ackerman, C. S. Bretherton, P. N. Blossey, 2022: Tropical Cirrus in Global Storm-Resolving Models: 2. Cirrus Life Cycle and Top-of-Atmosphere Radiative Fluxes. Earth and Space Science, 9(2), e2021EA001978. doi: 10.1029/2021EA001978. Cirrus clouds of various thicknesses and radiative characteristics extend over much of the tropics, especially around deep convection. They are difficult to observe due to their high altitude and sometimes small optical depths. They are also difficult to simulate in conventional global climate models, which have coarse grid spacings and simplified parameterizations of deep convection and cirrus formation. We investigate the representation of tropical cirrus in global storm-resolving models (GSRMs), which have higher spatial resolution and explicit convection and could more accurately represent cirrus cloud processes. This study uses GSRMs from the DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) project. The aggregate life cycle of tropical cirrus is analyzed using joint albedo and outgoing longwave radiation (OLR) histograms to assess the fidelity of models in capturing the observed cirrus cloud populations over representative tropical ocean and land regions. The proportions of optically thick deep convection, anvils, and cirrus vary across models and are portrayed in the vertical distribution of cloud cover and top-of-atmosphere radiative fluxes. Model differences in cirrus populations, likely driven by subgrid processes such as ice microphysics, dominate over regional differences between convectively active tropical land and ocean locations. cirrus; life cycle; tropical tropopause layer; model comparison; DYAMOND; global storm-resolving models
Uribe, Alejandro; Bender, Frida A.-M.; Mauritsen, ThorstenUribe, A., F. A. Bender, T. Mauritsen, 2022: Observed and CMIP6 Modeled Internal Variability Feedbacks and Their Relation to Forced Climate Feedbacks. Geophysical Research Letters, 49(24), e2022GL100075. doi: 10.1029/2022GL100075. Inter model variations in global temperature response to increasing atmospheric carbon dioxide stem mostly from uncertainties in modeled climate feedbacks. To study potential reductions in model feedback uncertainties, we estimate observed feedbacks in response to internal variability using changes in Top Of the Atmosphere energy balance with temperature. We compare those observations with internal variability feedbacks from historical simulations of coupled and atmosphere-only experiments from the sixth phase of the Coupled Model Intercomparison Project (CMIP6) to identify that simulated feedbacks exhibit biases in the tropics, subtropics, and the Southern Ocean. Furthermore, we find a relation between simulated longwave and shortwave internal variability feedbacks and those where atmospheric carbon dioxide is abruptly quadrupled. In the model range of internal variability feedbacks, the observations are more consistent with moderately negative longwave feedback, and weak shortwave feedback, but the observations can't be used to rule out any models or their long-term feedback.
Volvach, Alexandr; Kurbasova, Galina; Volvach, LarisaVolvach, A., G. Kurbasova, L. Volvach, 2022: Time series analysis of temperatures and insolation of the Earth's surface at Kara-Dag using satellite observation. Advances in Space Research, 69(12), 4228-4239. doi: 10.1016/j.asr.2022.04.016. This article discusses the results of a numerical analysis of the time series of the surface temperature, air temperature at a height of 2 m, as well as the total insolation falling to the earth at the Kara-Dag point over the past 38 years. Statistical analysis of observations and continuous time-frequency wavelet analysis are performed. Models of seasonal fluctuations in three time series of observations are compared. Coherent fluctuations were established between variations in total insolation data and data variations: of length of the day (LOD) (the period of variations is 11.8 years, the square of the coherence modulus is 0.85); of solar activity (the period of variations is 10.5 years, the squared modulus of coherence is 0.8; and the period of variations is 3.6 years, the squared modulus of coherence is 0.85); of global temperature indices (the period of variations is 2.3 years, the squared modulus of coherence is 0.7; and the period of variations is 3.5 years, the squared modulus of coherence is 0.9), respectively. The time evolution of observations in order to detect signs of chaotic oscillations is discussed. Earth; Insolation; Chaotic oscillations; Global temperature; POWER
Wall, Casey J.; Lutsko, Nicholas J.; Vishny, David N.Wall, C. J., N. J. Lutsko, D. N. Vishny, 2022: Revisiting Cloud Radiative Heating and the Southern Annular Mode. Geophysical Research Letters, n/a(n/a), e2022GL100463. doi: 10.1029/2022GL100463. Cloud-circulation interactions have a potentially large but uncertain influence on regional climate. Here we use satellite observations to investigate relationships between atmospheric cloud radiative heating and hemispheric-scale shifts in the Southern Hemisphere extratropical jet stream, as represented by the Southern Annular Mode. In contrast to a previous study, we find that poleward jet shifts cause bottom-heavy heating anomalies. The heating anomalies arise from two distinct mechanisms: First, poleward jet shifts promote anomalous large-scale subsidence equatorward of the mean jet latitude. This increases the fraction of low clouds that are exposed to space, thereby enhancing lower-tropospheric radiative cooling. Second, deep and multi-layer clouds in extratropical cyclones shift poleward with the jet, causing radiative heating anomalies throughout the troposphere. The bottom-heavy structure of the heating anomalies occurs because low clouds strongly emit radiation. These results establish new observational benchmarks for understanding extratropical cloud-circulation interactions. Cloud Radiative Effects; Annular Modes; Cloud-Circulation Interactions
Wall, Casey J.; Norris, Joel R.; Possner, Anna; McCoy, Daniel T.; McCoy, Isabel L.; Lutsko, Nicholas J.Wall, C. J., J. R. Norris, A. Possner, D. T. McCoy, I. L. McCoy, N. J. Lutsko, 2022: Assessing effective radiative forcing from aerosol–cloud interactions over the global ocean. Proceedings of the National Academy of Sciences, 119(46), e2210481119. doi: 10.1073/pnas.2210481119. How clouds respond to anthropogenic sulfate aerosols is one of the largest sources of uncertainty in the radiative forcing of climate over the industrial era. This uncertainty limits our ability to predict equilibrium climate sensitivity (ECS)—the equilibrium global warming following a doubling of atmospheric CO2. Here, we use satellite observations to quantify relationships between sulfate aerosols and low-level clouds while carefully controlling for meteorology. We then combine the relationships with estimates of the change in sulfate concentration since about 1850 to constrain the associated radiative forcing. We estimate that the cloud-mediated radiative forcing from anthropogenic sulfate aerosols is −1.11±0.43 − 1.11 ± 0.43 W m−2 over the global ocean (95% confidence). This constraint implies that ECS is likely between 2.9 and 4.5 K (66% confidence). Our results indicate that aerosol forcing is less uncertain and ECS is probably larger than the ranges proposed by recent climate assessments.
Wall, Casey J.; Storelvmo, Trude; Norris, Joel R.; Tan, IvyWall, C. J., T. Storelvmo, J. R. Norris, I. Tan, 2022: Observational Constraints on Southern Ocean Cloud-Phase Feedback. J. Climate, 35(15), 5087-5102. doi: 10.1175/JCLI-D-21-0812.1. Abstract Shortwave radiative feedbacks from Southern Ocean clouds are a major source of uncertainty in climate projections. Much of this uncertainty arises from changes in cloud scattering properties and lifetimes that are caused by changes in cloud thermodynamic phase. Here we use satellite observations to infer the scattering component of the cloud-phase feedback mechanism and determine its relative importance by comparing it with an estimate of the overall temperature-driven cloud feedback. The overall feedback is dominated by an optical thinning of low-level clouds. In contrast, the scattering component of cloud-phase feedback is an order of magnitude smaller and is primarily confined to free-tropospheric clouds. The small magnitude of this feedback component is a consequence of counteracting changes in albedo from cloud optical thickening and enhanced forward scattering by cloud particles. These results indicate that shortwave cloud feedback is likely positive over the Southern Ocean and that changes in cloud scattering properties arising from phase changes make a small contribution to the overall feedback. The feedback constraints shift the projected 66% confidence range for the global equilibrium temperature response to doubling atmospheric CO2 by about +0.1 K relative to a recent consensus estimate of cloud feedback. Significance Statement Understanding how clouds respond to global warming is a key challenge of climate science. One particularly uncertain aspect of the cloud response involves a conversion of ice particles to liquid droplets in extratropical clouds. Here we use satellite data to infer how cloud-phase conversions affect climate by changing cloud albedo. We find that ice-to-liquid conversions increase cloud optical thickness and shift the scattering angles of cloud particles toward the forward direction. These changes in optical properties have offsetting effects on cloud albedo. This finding provides new insight about how changes in cloud phase affect climate change.
Wang, Fei; Zhang, Hua; Wang, Qiuyan; Xie, Bing; Zhou, Xixun; Liu, QingquanWang, F., H. Zhang, Q. Wang, B. Xie, X. Zhou, Q. Liu, 2022: An Assessment of Short-term Global and East Asian Local Climate Feedbacks using New Radiative Kernels. Climate Dynamics. doi: 10.1007/s00382-022-06369-z. This study estimates short-term climate feedbacks by using a new set of radiative kernels applied to observations and the Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations. The new kernels are generated based on multiyear satellite observations, and they can well reproduce the top-of-atmosphere (TOA) radiation budget. The choice of radiative kernels influences the feedback estimation, especially the surface albedo feedback and cloud feedback in the Arctic and the Southern Ocean. Observational estimates show that tropospheric water vapor feedback makes the largest contribution to global warming, while lapse rate feedback is the largest contributor to local warming over East Asia. Compared to the observations, biases occur but differ when simulating global and East Asian local climate feedbacks. CMIP6 models overestimate global mean Planck, lapse rate, stratospheric temperature and water vapor, and cloud feedbacks, but underestimate global mean tropospheric water vapor and surface albedo feedbacks. Over East Asia, local Planck and lapse rate feedbacks are underestimated, while tropospheric water vapor, stratospheric temperature, and cloud feedbacks are overestimated. The simulation biases in local longwave (LW) and shortwave (SW) cloud feedbacks over East Asia are considerable, probably due to the failure in simulating cloud fraction response of marine cirrostratus, deep convective cloud, and stratus. The intermodel spread of cloud feedback is the largest for both global and East Asian local feedback processes. Our results suggest that contemporary climate models are still difficult to accurately simulate global and local climate feedback processes. Observations; East Asia; CMIP6 models; Radiative kernels; Short-term climate feedback
Wang, Hao; Wang, Minghuai; Zhang, Zhibo; Larson, Vincent E.; Griffin, Brian M.; Guo, Zhun; Zhu, Yannian; Rosenfeld, Daniel; Cao, Yang; Bai, HemingWang, H., M. Wang, Z. Zhang, V. E. Larson, B. M. Griffin, Z. Guo, Y. Zhu, D. Rosenfeld, Y. Cao, H. Bai, 2022: Improving the treatment of subgrid cloud variability in warm rain simulation in CESM2. Journal of Advances in Modeling Earth Systems, n/a(n/a), e2022MS003103. doi: 10.1029/2022MS003103. Representing subgrid variability of cloud properties has always been a challenge in global climate models (GCMs). In many cloud microphysics schemes, the warm rain non-linear process rates calculated based on grid-mean cloud properties are usually scaled by an enhancement factor (EF) to account for the effects of subgrid cloud variability. In our study, we find that the EF derived from Cloud Layers Unified by Binormals (CLUBB) in Community Atmosphere Model version 6 (CAM6) is severely overestimated in most of the cloudy oceanic areas, which leads to strong overestimation of the autoconversion rate. We improve the EF in warm rain simulation by developing a new formula for in-cloud subgrid cloud water variance. With the updated subgrid cloud water variance and EF treatment, the liquid cloud fraction (LCF) and cloud optical thickness (COT) increases noticeably for marine stratocumulus, and the shortwave cloud forcing (SWCF) matches better with observations. The updated formula improves the relationship between autoconversion rate and cloud droplet number concentration (CDNC), and it decreases the sensitivity of autoconversion rate to aerosols. The sensitivity of liquid water path (LWP) to aerosols decreases noticeably and is in better agreement with that in MODIS. Although the sensitivity of COT is similar to that in MODIS, CAM6 underestimates the sensitivity of grid-mean SWCF to aerosols because of the underestimation in the sensitivities of LCF and in-cloud SWCF. Our results indicate the importance of representing reasonable subgrid cloud variability in the simulation of cloud properties and aerosol-cloud interaction in GCMs. aerosol-cloud interaction; marine boundary layer clouds; CLUBB; CAM6; subgrid variability
Wang, Meihua; Su, Jing; Peng, Nan; Xu, Ying; Ge, JinmingWang, M., J. Su, N. Peng, Y. Xu, J. Ge, 2022: Diurnal cycle of cirrus cloud and its associated radiative effects at the SACOL site. Atmospheric Research, 265, 105887. doi: 10.1016/j.atmosres.2021.105887. Diurnal cycle of cirrus cloud (DCCci) can affect cloud interactions with both the solar radiation and terrestrial radiation. However, evaluation on how DCCci influences the radiative effects is relatively few, especially in the semi-arid region, which is one of the most sensitive areas in response to global climate change. In this study, we investigate the physical properties and associated radiative effects of DCCci using two-year, high-resolution Ka-band Zenith Radar (KZAR) observations at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) site in Northwest China. We find that cirrus clouds occur more frequently during nighttime than during daytime, with a maximum occurrence frequency of 48% at midnight and a minimum occurrence frequency of 35% at midday, which drastically influences the diurnal variation of cirrus radiative effects. The diurnal variation of cirrus cloud radiative forcing (CRF) is calculated using the Fu-Liou model, involving 96 cirrus profiles per day to represent DCCci accurately. In each season, the diurnal cycle amplitude of CRF is more than 40 W/m2 for shortwave (SW), and less than 16 W/m2 for longwave (LW). During daytime, the net CRF at the top of the atmosphere (TOA) ranges from −16 to 30 W/m2; during nighttime, it varies from 30 to 33 W/m2. Based on the accurate simulation of CRF with DCCci, we then calculate the daily-mean CRF and compare it with the simulated results derived from different averaged cirrus profiles that do not fully represent the diurnal cycle, to evaluate the radiative biases induced by not having accurate DCCci. We find that the absolute bias of net CRF at the TOA can reach 11 W/m2 at the SACOL site when only one daily averaged cirrus property profile is used in the simulation, demonstrating that neglecting DCCci in the model will result in significant bias of cirrus net CRF. This evaluation suggests that DCCci need to be well considered in climate models to reduce the uncertainty of cirrus radiative effects. Radiative effect; Cirrus cloud; Diurnal cycle; KAZR observations; Physical properties; Semi-arid region
Wang, Qiuyan; Zhang, Hua; Yang, Su; Chen, Qi; Zhou, Xixun; Xie, Bing; Wang, Yuying; Shi, Guangyu; Wild, MartinWang, Q., H. Zhang, S. Yang, Q. Chen, X. Zhou, B. Xie, Y. Wang, G. Shi, M. Wild, 2022: An assessment of land energy balance over East Asia from multiple lines of evidence and the roles of the Tibet Plateau, aerosols, and clouds. Atmospheric Chemistry and Physics, 22(24), 15867-15886. doi: 10.5194/acp-22-15867-2022. With high emissions of aerosols and the known world's “Third Pole” of the Tibet Plateau (TP) in East Asia, knowledge on the energy budget over this region has been widely concerned. This study first attempts to estimate the present-day land energy balance over East Asia by combining surface and satellite observations as well as the atmospheric reanalysis and Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations. Compared to the global land budget, a substantially larger fraction of atmospheric shortwave radiation of 5.2 % is reflected, highly associated with the higher aerosol loadings and more clouds over East Asian land. While a slightly smaller fraction of atmospheric shortwave absorption of 0.6 % is unexpectedly estimated, possibly related to the lower water vapor content effects due to the thinner air over the TP to overcompensate for the aerosol and cloud effects over East Asian land. The weaker greenhouse effect and fewer low clouds due to the TP are very likely the causes of the smaller fraction of East Asian land surface downward longwave radiation. Hence, high aerosol loadings, clouds, and the TP over East Asia play vital roles in the shortwave budgets, while the TP is responsible for the longwave budgets during this regional energy budget assessment. The further obtained cloud radiative effects suggest that the presence of clouds results in a larger cooling effect on the climate system over East Asian land than that over the globe. This study provides a perspective to understand fully the roles of potential factors in influencing the different energy budget assessments over regions.
Wang, Shiyao; Wang, Tianxing; Leng, Wanchun; Wang, Gaofeng; Letu, HusiWang, S., T. Wang, W. Leng, G. Wang, H. Letu, 2022: Toward an Improved Global Longwave Downward Radiation Product by Fusing Satellite and Reanalysis Data. IEEE Transactions on Geoscience and Remote Sensing, 60, 1-16. doi: 10.1109/TGRS.2022.3179017. Surface longwave downward radiation (LWDR) plays an important role in modulating greenhouse effect and climate change. Constructing a global longtime series LWDR dataset is greatly necessary to systematically and in-depth study the LWDR effect on the climate. However, the current multisource LWDR products (satellite and reanalysis) show large differences in terms of both spatiotemporal resolutions and accuracy in various regions. Therefore, it is necessary to fuse multisource datasets to generate more accurate LWDR with high spatiotemporal resolution on a global scale. To this end, a downscaling strategy is first proposed to generate LWDR dataset with 0.25° resolution from CERES-SYN data with 1° scale, by incorporating the land surface temperature (LST), total column water vapor (TCWV), and elevation. Then, a machine learning-based fusion method is provided to generate a global hourly LWDR dataset with a spatial resolution of 0.25° by combining three products (CERES-SYN, ERA5, and GLDAS). Compared with ground measurements, the performance of generated LWDR product reveals that the correlation coefficient ( $R$ ), mean bias error (BIAS), and root-mean-square error (RMSE) were 0.97, −0.95 W/m2, and 22.38 W/m2 over the land and 0.99, −0.88 W/m2, and 10.96 W/m2 over the ocean, respectively. In particular, it shows improved accuracy in the low and middle latitude regions compared with other LWDR products. Considering its better accuracy and higher spatiotemporal resolution, the new LWDR product can provide essential data for deeply understanding the global energy balance and even the global warming. Moreover, the proposed fusion strategy can be enlightening for readers in the fields of multisource data combination and big data analysis. Data models; ERA5; Ocean temperature; Spatial resolution; machine learning; CERES-SYN; Remote sensing; data fusion; Land surface temperature; GLDAS; Machine learning; Fuses; surface longwave downward radiation (LWDR)
Wang, Yipu; Li, Rui; Hu, Jiheng; Fu, Yuyun; Duan, Jiawei; Cheng, Yuanxi; Song, BinbinWang, Y., R. Li, J. Hu, Y. Fu, J. Duan, Y. Cheng, B. Song, 2022: Evaluation of evapotranspiration estimation under cloud impacts over China using ground observations and multiple satellite optical and microwave measurements. Agricultural and Forest Meteorology, 314, 108806. doi: 10.1016/j.agrformet.2021.108806. Evapotranspiration (ET) is an important component of the hydrological cycle and energy balance in a land-atmosphere system. Satellite remote sensing has been widely used to estimate regional and global ET, but most previous methods depend on optical measurements that are limited to cloud-free conditions. This makes ET estimation challenging under cloudy sky. Currently, evaluations of satellite ET estimation under various cloud conditions remain lacking at the regional scale. Owing to the ability to penetrate clouds, satellite passive microwave measurements are powerful tools for retrieving ET under clouds. This study evaluated a satellite microwave-based daily ET method under all sky conditions over the part of China between 18°N and 50°N from 2003 to 2010, using microwave emissivity difference vegetation index (EDVI) as the proxy of vegetation water content (VWC). Validations using the surface water balance method found that the estimated ET (EDVI-ET) had an overall small bias (6.18%) in eight river basins. EDVI-ET displayed consistent spatiotemporal patterns with global MOD16 ET, with high spatial correlation (R>0.71) and monthly temporal correlation (R>0.82) throughout four seasons. Their differences were also small ( cloudy sky; Evapotranspiration (ET); microwave Emissivity Difference Vegetation Index (EDVI); MOD16
Wang, Yong; Xia, Wenwen; Zhang, Guang J.; Wang, Bin; Lin, GuangxingWang, Y., W. Xia, G. J. Zhang, B. Wang, G. Lin, 2022: Impacts of Suppressing Excessive Light Rain on Aerosol Radiative Effects and Health Risks. Journal of Geophysical Research: Atmospheres, 127(9), e2021JD036204. doi: 10.1029/2021JD036204. Global climate models (GCMs) have been used widely to study radiative forcing and health risks of aerosols. A recent study using two GCMs found that light rain plays a dominant role in controlling aerosol loading. However, “too much light rain and too little heavy rain” is a longstanding bias in GCMs. It is unclear how much light rain affects aerosol-cloud-radiation interactions and health risks from air pollution. Here we show that, with the correction of the rainfall intensity spectrum in the National Center for Atmospheric Research Community Atmosphere Model version 5.3 by introducing a stochastic deep convection scheme, the reduced frequency of light rain (1–20 mm d−1) results in changes of aerosol direct radiative effects (DRE) of up to −0.5 ± 0.03 W/m2 and aerosol cloud radiative effects (CRE) of up to −0.9 ± 0.03 W/m2. The total (CRE + DRE) radiative effects of light rain-mediated aerosol changes exceed the present-day anthropogenic forcing of aerosols relative to preindustrial levels from the Coupled Model Intercomparison Project (CMIP5&6) models. However, the correction of the rainfall intensity spectrum has little effect on anthropogenic aerosol forcing (defined as the radiative perturbation due to changes in aerosol concentrations between the industrial era and preindustrial levels). Due to increased exposure to fine particulates (PM2.5), the estimated global total premature mortality is much higher than previously estimated, by 300,000 ± 60,000 deaths per year, and is more severe in populous regions such as India and China. The findings in this study highlight the need to understand uncertainties in radiative effects and health risks of aerosols due to simulation biases of precipitation in GCMs. aerosol health risks; aerosol radiative effects; light rainfall; stochastic deep convection parameterization
Wang, Zhenquan; Ge, Jinming; Yan, Jialin; Li, Wenxue; Yang, Xuan; Wang, Meihua; Hu, XiaoyuWang, Z., J. Ge, J. Yan, W. Li, X. Yang, M. Wang, X. Hu, 2022: Interannual shift of tropical high cloud diurnal cycle under global warming. Climate Dynamics. doi: 10.1007/s00382-022-06273-6. This research focuses on the observed tropical oceanic high clouds above the 300 hPa level, to investigate their diurnal cycles and radiative effects at the top of atmosphere. The diurnal centroid is used to quantify the diurnal cycle based on circular statistics to indicate the daily peaking time of cloud cover. It is found that the diurnal cycle of the tropical oceanic high clouds can significantly impact their cloud radiative effects, with a correlation coefficient of − 0.63 at the 95% significant level and a slope of − 14.5 Wm−2 h−1 between the net cloud radiative effects and the diurnal centroid shifting from midnight towards noon. This implies that the changes of the diurnal cycle can strongly influence the Earth radiative budget, and thus possibly impose radiative feedbacks to affect atmospheric circulations under global climate warming. It is also found that the strength of convection and the cold point temperature are two major environmental factors in influencing the diurnal-cycle centroid of the tropical oceanic high clouds. Furthermore, according to observations, the correlation coefficient between the diurnal-cycle centroid of the tropical oceanic high clouds and the global mean temperature is 0.75 at the 95% significant level, indicating a 2-h shift of the tropical oceanic high clouds towards noon with 1℃ increases of the global mean temperature.
Wang, Zhili; Wang, Chense; Yang, Su; Lei, Yadong; Che, Huizheng; Zhang, Xiaoye; Wang, QiuyanWang, Z., C. Wang, S. Yang, Y. Lei, H. Che, X. Zhang, Q. Wang, 2022: Evaluation of surface solar radiation trends over China since the 1960s in the CMIP6 models and potential impact of aerosol emissions. Atmospheric Research, 268, 105991. doi: 10.1016/j.atmosres.2021.105991. Accurate representation of surface solar radiation (SSR) trends is an important indicator for global climate models (GCMs) to correctly reproducing the historical climate evolution. This study examines the annual mean SSR trends in China under all-sky and clear-sky conditions for the period 1961–2014 in 34 Coupled Model Intercomparison Project Phase 6 (CMIP6) models using the latest homogenized in-situ SSR dataset. The site-observed annual mean SSR over China shows a significant decadal decline during 1961–2005 but an uptrend during 2006–2014, with the trends being −6.4 (−8.6) W m−2 and + 2.5 (+5.9) W m−2 per decade under all-sky (clear-sky) condition, respectively. All CMIP6 models simulate the sustained decline in SSR over China for the period 1961–2005 but significantly underestimate the dimming. The model results show trends of −1.9 ± 0.5 W m−2 and -2.5 ± 0.7 W m−2 per decade during 1961–2005 under all-sky and clear-sky conditions, respectively, which are around one third of the observed results. Furthermore, the models fail to capture the reversal of SSR trends in China during 2006–2014, with the trends being −1.1 ± 1.7 W m−2 and -2.2 ± 0.9 W m−2 per decade under all-sky and clear-sky conditions, respectively. We infer that the underestimation of anthropogenic aerosol emissions, especially absorbing black carbon emissions cause the underestimated simulation of SSR in dimming period over China. After 2005, the unseasonal increase in carbonaceous aerosol emissions and the weaker decline of sulfur dioxide emissions in China in the models result in an opposite SSR trends relative to the trends based on the site-observations. Our results suggest that improving the anthropogenic aerosol emissions inventory will be useful for generating a more accurate reproduction of the regional SSR evolution over China in GCMs. Surface solar radiation; CMIP6; Aerosol emissions; Black carbon
Wei, Linyi; Lu, Zheng; Wang, Yong; Liu, Xiaohong; Wang, Weiyi; Wu, Chenglai; Zhao, Xi; Rahimi, Stefan; Xia, Wenwen; Jiang, YiquanWei, L., Z. Lu, Y. Wang, X. Liu, W. Wang, C. Wu, X. Zhao, S. Rahimi, W. Xia, Y. Jiang, 2022: Black carbon-climate interactions regulate dust burdens over India revealed during COVID-19. Nature Communications, 13(1), 1839. doi: 10.1038/s41467-022-29468-1. India as a hotspot for air pollution has heavy black carbon (BC) and dust (DU) loadings. BC has been identified to significantly impact the Indian climate. However, whether BC-climate interactions regulate Indian DU during the premonsoon season is unclear. Here, using long-term Reanalysis data, we show that Indian DU is positively correlated to northern Indian BC while negatively correlated to southern Indian BC. We further identify the mechanism of BC-dust-climate interactions revealed during COVID-19. BC reduction in northern India due to lockdown decreases solar heating in the atmosphere and increases surface albedo of the Tibetan Plateau (TP), inducing a descending atmospheric motion. Colder air from the TP together with warmer southern Indian air heated by biomass burning BC results in easterly wind anomalies, which reduces dust transport from the Middle East and Sahara and local dust emissions. The premonsoon aerosol-climate interactions delay the outbreak of the subsequent Indian summer monsoon. Climate change; Atmospheric science
Wong, T.; Stackhouse Jr, PW; Sawaengphokhai, P.; Garg, J.; Loeb, N. G.Wong, T., P. Stackhouse Jr, P. Sawaengphokhai, J. Garg, N. G. Loeb, 2022: Earth Radiation Budget at Top-Of-Atmosphere [in “State of the Climate in 2021”]. Bull. Amer. Meteor. Soc., 103(8), S75-S77. doi: https://doi.org/10.1175/2022BAMSStateoftheClimate.1.
Wu, Jie; Guo, Huadong; Ding, Yixing; Shang, Haolu; Li, Tong; Li, Lei; Lv, MingyangWu, J., H. Guo, Y. Ding, H. Shang, T. Li, L. Li, M. Lv, 2022: The Influence of Anisotropic Surface Reflection on Earth’s Outgoing Shortwave Radiance in the Lunar Direction. Remote Sensing, 14(4), 887. doi: 10.3390/rs14040887. The variation in the radiation budget at Earth’s top of the atmosphere (TOA) represents the most fundamental metric defining the status of global climate change. The accurate estimation of Earth’s shortwave radiant exitance is of critical importance to study Earth’s radiation budget (ERB) at TOA. Measuring Earth’s outgoing shortwave radiance (OSR) is a key point to estimate Earth’s shortwave radiant exitance. Compared with space-borne satellite systems, Moon-based sensors (MS) could provide large-scale, continuous, and long-term data for Earth radiation observations, bringing a new perspective on ERB. However, the factors affecting the estimation of Earth’s OSR in the lunar direction have not yet been fully explored, for example, anisotropic surface reflection and the effects of clouds and aerosols on radiation budget. In this work, we only focused on the influence of anisotropic surface reflection. To evaluate the extent of this influence, we constructed a model to estimate Earth’s OSR in the lunar direction (EOSRiLD), integrating the variables of anisotropic surface reflection (scene types, solar zenith angles, viewing zenith angles, and relative azimuth angles) and radiant flux in Moon-viewed sunlit regions. Then, we discussed it over three time periods (Earth’s rotation, revolution period, and synodic month cycle) and analyzed the impact of three variables (area of the Moon-viewed sunlit region, scene types, and incident-viewing angular bins) on anisotropic EOSRiLD. Our results indicate that EOSRiLD based on the assumptions of anisotropic and isotropic reflection is different but they all show the same monthly cycle change, which is related to the area of the Moon-viewed sunlit region. At the beginning and end of the lunar month, the differences between anisotropy and isotropy are greatest in each cycle; when it is close to the first half of each cycle, there is a small difference peak. Both anisotropy and isotropy are caused by the relative azimuth angles between the Sun and Moon. In conclusion, even if the Moon-based platform has a wider scope than space-borne satellites, the difference is still large between anisotropy and isotropy. Therefore, we still need to consider the anisotropic surface reflection based on the Moon-based observation. Earth’s radiation budget; anisotropic surface reflection; Moon-based observation; outgoing shortwave radiance
Wu, Jinyang; Fang, Hejin; Qin, Wenmin; Wang, Lunche; Song, Yan; Su, Xin; Zhang, YujieWu, J., H. Fang, W. Qin, L. Wang, Y. Song, X. Su, Y. Zhang, 2022: Constructing High-Resolution (10 km) Daily Diffuse Solar Radiation Dataset across China during 1982–2020 through Ensemble Model. Remote Sensing, 14(15), 3695. doi: 10.3390/rs14153695. Diffuse solar radiation is an essential component of surface solar radiation that contributes to carbon sequestration, photovoltaic power generation, and renewable energy production in terrestrial ecosystems. We constructed a 39-year (1982–2020) daily diffuse solar radiation dataset (CHSSDR), using ERA5 and MERRA_2 reanalysis data, with a spatial resolution of 10 km through a developed ensemble model (generalized additive models, GAM). The validation results, with ground-based measurements, showed that GAM had a high and stable performance with the correlation coefficient (R), root-mean-square error (RMSE), and mean absolute error (MAE) for the sample-based cross-validations of 0.88, 19.54 Wm−2, and 14.87 Wm−2, respectively. CHSSDR had the highest consistency with ground-based measurements among the four diffuse solar radiation products (CERES, ERA5, JiEA, and CHSSDR), with the least deviation (MAE = 15.06 Wm−2 and RMSE = 20.22 Wm−2) and highest R value (0.87). The diffuse solar radiation values in China range from 59.13 to 104.65 Wm−2, with a multi-year average value of 79.39 Wm−2 from 1982 to 2020. Generally, low latitude and low altitude regions have larger diffuse solar radiation than high latitude and high altitude regions, and eastern China has less diffuse solar radiation than western China. This dataset would be valuable for analyzing regional climate change, photovoltaic applications, and solar energy resources. The dataset is freely available from figshare. machine learning; China; reanalysis data; diffuse solar radiation; ensemble model
Wu, Wen-Ying; Yang, Zong-LiangWu, W., Z. Yang, 2022: Aridity-Dependent Land Surface Skin Temperature Biases in CMIP5/6. Geophysical Research Letters, 49(15), e2022GL098952. doi: 10.1029/2022GL098952. Land surface skin temperature, a critical indicator of climate change, connects the water and energy cycles between the land and the atmosphere. Here, we evaluate the simulations of land surface skin temperature from the Coupled Model Intercomparison Project Phase 5 (CMIP5) and CMIP6 models with satellite-based datasets and reanalysis. We find systematic cold skin temperature biases over arid regions in CMIP5/CMIP6 simulations. Over arid and semi-arid regions, latent heat biases drive skin temperature biases by evaporative cooling. Over humid regions, surface downward shortwave and albedo biases are relatively more critical. Spatial patterns of biases remain similar in the latest CMIP6 simulations, suggesting systematic biases in land-atmosphere interactions. These biases need to be corrected or considered while using models for future projections. CMIP; land surface temperature; land-atmosphere interaction
Xie, Xiaoming; He, Bin; Guo, Lanlan; Huang, Ling; Hao, Xingming; Zhang, Yafeng; Liu, Xuebang; Tang, Rui; Wang, SifanXie, X., B. He, L. Guo, L. Huang, X. Hao, Y. Zhang, X. Liu, R. Tang, S. Wang, 2022: Revisiting dry season vegetation dynamics in the Amazon rainforest using different satellite vegetation datasets. Agricultural and Forest Meteorology, 312, 108704. doi: 10.1016/j.agrformet.2021.108704. There has been a debate regarding whether the Amazon rainforest is greening during the dry season. This is partially because of the great uncertainty associated with the ability of different vegetation indices to accurately assess tropical vegetation status. This paper, revisit this issue by comprehensively examining the seasonal variations in vegetation recorded in various satellite-based vegetation datasets, namely, the leaf area index (LAI), contiguous solar-induced fluorescence (CSIF), enhanced vegetation index (EVI), and vegetation optical depth (VOD). All four of these vegetation datasets show an increase in vegetation during the dry season in most parts of the Amazon; however, the vegetation changes are not only spatially variable, but also differ among the datasets. This may be attributable in part to the different physical characteristics captured by each of the datasets. For example, the seasonal maximum value occurs first in the LAI, followed by the CSIF, EVI, and VOD, in that order. The seasonal cycle of the LAI agrees reasonably well with in-situ observations of leaf flush and leaf fall. As new leaf production offsets senescence and abscission, the dry-season vegetation increases in most parts of the Amazon rainforest. Partial correlation analysis was used to further investigate the potential climatic cues (i.e., precipitation, temperature and radiation) associated with the seasonal changes recorded in the vegetation data. We found that precipitation and radiation were the dominant potential cues for seasonal VOD (48%) and LAI (59%) changes, respectively. However, CSIF appears to be associated more closely with temperature and precipitation, with significant correlations observed across ∼x223C 37% of the Amazon rainforest area for both with CSIF. Finally, variations in the EVI showed similar sensitivity to all three climatic variables considered. The findings presented here will greatly improve our understanding of vegetation dynamics and the carbon cycle in the Amazon rainforest ecosystem. Amazon; Dry season; Greening; Rainforest; Vegetation data
Xin, Xiaozhou; Yu, Shanshan; Sun, Daozhong; Zhang, Hailong; Li, Li; Zhong, BoXin, X., S. Yu, D. Sun, H. Zhang, L. Li, B. Zhong, 2022: Assessment of Three Satellite-Derived Surface Downward Longwave Radiation Products in Polar Regions. Atmosphere, 13(10), 1602. doi: 10.3390/atmos13101602. The radiation budget in polar regions plays an important role in global climate change study. This study investigates the performance of downward longwave radiation (DLR) of three satellite radiation products in polar regions, including GEWEX-SRB, ISCCP-FD, and CERES-SYN. The RMSEs are 35.8, 40.5, and 26.9 W/m2 at all polar sites for GEWEX-SRB, ISCCP-FD, and CERES-SYN. The results in the Arctic are much better than those in the Antarctic, RMSEs of the three products are 34.7 W/m2, 36.0 W/m2, and 26.2 W/m2 in the Arctic and are 38.8 W/m2 and 54.8 W/m2, and 28.6 W/m2 in the Antarctic. Both GEWEX-SRB and CERES-SYN underestimate DLRs at most sites, while ISCCP-FD overestimates DLRs at most sites. CERES-SYN and GEWEX-SRB DLR products can capture most of the DLR seasonal variation in both the Antarctic and Arctic. Though CERES-SYN has the best results that RMSE within 30 W/m2 in most polar sites, the accuracy of satellite products in polar regions still cannot meet the requirement of climate research. The improvement of satellite DLR products in polar regions mainly depends on the quality of improving input atmospheric parameters, the accuracy of improving cloud detection over the snow and ice surface and cloud parameters, and better consideration of spatial resolution and heterogeneity. CERES-SYN; downward longwave radiation; GEWEX-SRB; ISCCP-FD; polar regions
Xu, Jianglei; Liang, Shunlin; Ma, Han; He, TaoXu, J., S. Liang, H. Ma, T. He, 2022: Generating 5 km resolution 1981–2018 daily global land surface longwave radiation products from AVHRR shortwave and longwave observations using densely connected convolutional neural networks. Remote Sensing of Environment, 280, 113223. doi: 10.1016/j.rse.2022.113223. Surface longwave radiation (SLWR) components, including downward longwave radiation (DLR), upward longwave radiation (ULR), and net longwave radiation (NLR), are major contributors to the Earth's surface radiation budget and play important roles in ecological, hydrological, and atmospheric processes. Previous SLWR products have different drawbacks, such as being temporally short (after 2000), spatially coarse (≥ 25 km), and instantaneous values, which hinder their in-depth applications in land surface process modeling and climate trends analysis. Here, we reported the Advanced Very High-Resolution Radiometer (AVHRR)-based Global LAnd Surface Satellites (GLASS-AVHRR) SLWR products over the global land surface at a 5 km spatial resolution and 1 day temporal resolution between 1981 and 2018. These products were generated using multiple densely connected convolutional neural networks (DesCNNs) from the AVHRR top-of-atmosphere (TOA) reflected and emitted observations and European Centre for Medium-Range Weather Forecasts (ECMWF) fifth generation reanalysis (ERA5) near-surface meteorological data. DesCNNs were trained using integrated SLWR samples derived from the Moderate Resolution Imaging Spectroradiometer (MODIS)-based GLASS, Clouds and the Earth's Radiant Energy System Synoptic (CERES-SYN), and ERA5 SLWR products. In situ measurements from 231 globally distributed sites were used to evaluate the GLASS-AVHRR SLWR estimates. The results illustrated the overall high accuracies of GLASS-AVHRR SLWR products with root-mean-square-errors (RMSEs) of 18.66, 14.92, and 16.29 Wm−2, and mean bias errors (MBEs) of −2.69, −3.77, and 0.49 Wm−2 for all-sky DLR, ULR, and NLR, respectively. We found good correlation and consistency between GLASS-AVHRR and both CERES-SYN and ERA5 in terms of spatial patterns, latitudinal gradient, and temporal evolution. Our results revealed the significant contribution of shortwave observations to SLWR estimation owing to the high amounts of clouds over polar regions and water vapor and clouds in tropical areas, which was not previously widely recognized by the remote sensing community. GLASS-AVHRR SLWR products were updated, documented, and made available to the public at www.glass.umd.edu and www.geodata.cn. AVHRR; Surface longwave radiation; Deep neural network; Long time series; Shortwave observation
Xu, Jiawen; Zhang, Xiaotong; Zhang, Weiyu; Hou, Ning; Feng, Chunjie; Yang, Shuyue; Jia, Kun; Yao, Yunjun; Xie, Xianhong; Jiang, Bo; Cheng, Jie; Zhao, Xiang; Liang, ShunlinXu, J., X. Zhang, W. Zhang, N. Hou, C. Feng, S. Yang, K. Jia, Y. Yao, X. Xie, B. Jiang, J. Cheng, X. Zhao, S. Liang, 2022: Assessment of surface downward longwave radiation in CMIP6 with comparison to observations and CMIP5. Atmospheric Research, 270, 106056. doi: 10.1016/j.atmosres.2022.106056. Surface downward longwave radiation (SDLR) plays an important role in understanding the greenhouse effect and global warming. The simulated SDLR from 47 coupled models in the Coupled Model Intercomparison Project (CMIP6) general circulation models (GCMs) was evaluated by comparing them with ground measurements and CMIP5 results. The estimated SDLR using all CMIP6 GCMs based on the multimodel ensemble (MME) methods was validated as well. The bias values of the SDLR simulations from individual CMIP6 GCMs averaged over the selected 183 sites around the world varied from −10 to 10 W m−2, while the root mean squared error (RMSE) values ranged from 20 to 26 W m−2. Compared to CMIP5 models, the CMIP6 GCMs did not show a significant tendency to underestimate SDLR. However, the SDLR from CMIP6 GCMs exhibited the relatively better precision at low altitude and low latitude sites compared to that at high altitude and high latitude sites. Moreover, the Bayesian model averaging (BMA) method increased the correlation coefficient (R) by approximately 0.02 and reduced the RMSE by approximately 5 W m−2 on average compared to the individual CMIP6 GCMs. The trend in SDLR was also investigated in this study, which has been related to the changes in air temperature (SAT), and water vapor pressure (WVP). CMIP6; CMIP5; GCMs; Bayesian model averaging; Multimodel ensemble; Surface downward longwave radiation (SDLR)
Yadav, Ramashray; Giri, R. K.; Bhan, S. C.Yadav, R., R. K. Giri, S. C. Bhan, 2022: High-resolution outgoing long wave radiation data (2014–2020) of INSAT-3D Imager and its comparison with Clouds and Earth’s Radiant Energy System (CERES) data. Advances in Space Research, 70(4), 976-991. doi: 10.1016/j.asr.2022.05.053. As a proxy of convection INSAT-3D satellite-derived product Outgoing Long Wave Radiation (OLR) data is available in both high temporal and spatial ranges over 40°N–40°S & 35°E–135°E. Daily gridded data set of 7 years of data (2014–2020) has been generated at 10 km × 10 km resolution and the same is compared with Clouds and Earth’s Radiant Energy System (CERES) instrument data taken from CERES as reference. Almost all the INSAT-3D data set generated is Global Space-based Inter-Calibration System (GSICS) corrected. The spatiotemporal consistency of the data set was statistically analyzed and found to be reasonably good agreement having a bias of ∼±5–6 W/m2 over above said domain. This inter-comparison is essential to get confidence in the data sets and release it further in the public domain for any scientific study. Again, this data set will be very useful in diagnosing the variations of convection at different scales (daily, weekly, monthly, annual, seasonal, intra-seasonal, etc.) & an important repository of Daily Climate Data Records (DCDR) for future studies. The specified domain of the present study is affected throughout the year with variable (weak, moderate, intense, or severe) spatiotemporal Inter-Tropical Convergence Zone (ITCZ) convection streams due to different types of weather activities (winter, pre-monsoon, monsoon, and post-monsoon) throughout the year. To visualize the importance of this high-resolution OLR data set a case study of Cyclone Amphan and Vayu is presented. The extremely severe intense convection (OLR departure −112 W/m2 with INSAT-3D new data set whereas −104 W/m2 in CERES data) was observed in both the data sets on 18th May-2020 at 13.7–16°N & 86.2–86.8°E during the super cyclonic stage of Amphan. A similar type of variation in the OLR has been noticed for Vayu Cyclone (OLR departure −94 W/m2 with INSAT-3D new data set whereas −86 W/m2 in CERES data). This information is very useful in impact-based forecasting and further future actions for disaster managers/decision-makers. The localized convective features during cyclone activity over the Indian Ocean region both in the Arabian Sea and the Bay of Bengal are well captured with this new data set and the difference in OLR of INSAT -3D and CERES -9 W/m2 and -12 W/m2 respectively. CERES; OLR; ITCZ; GSICS & DCDR; INSAT-3D; Spatiotemporal
Yang, Jiangyan; Yi, Bingqi; Wang, Shuai; Liu, Yushan; Li, YuxiaoYang, J., B. Yi, S. Wang, Y. Liu, Y. Li, 2022: Diverse cloud and aerosol impacts on solar photovoltaic potential in southern China and northern India. Scientific Reports, 12(1), 19671. doi: 10.1038/s41598-022-24208-3. Cloud and aerosol are two important modulators that influence the solar radiation reaching the earth’s surface. It is intriguing to find diverse impacts of clouds and aerosols over Southern China (SC) and Northern India (NI) which result in remarkable differences in the plane-of-array irradiance (POAI) that signifies the maximum available solar photovoltaic potential by combining the latest satellite retrieval results and modeling tools. By separating the impacts of cloud and aerosol on the POAI, it is found that clouds are responsible for the most reduction of POAI in the SC, while aerosols and clouds are equally important for the NI region. The frequent occurrences of low and middle level clouds with high optical depth in the SC, as compared with the much lower occurrences of all levels of clouds with lower optical depth in the NI, is regarded as the major reason for the differences in the POAI. The differences in the main compositions of aerosols in the SC (sulfate) and the NI (dust) could be essential to answer the question of why higher aerosol optical depth in the SC whereas leads to weaker reduction in the POAI than that in the NI. The mitigation measures targeting on the controls of different types of aerosols should be considered for different regions. Atmospheric science; Photovoltaics
Yang, Jie; Zhao, Chuanfeng; Sun, Yue; Chi, Yulei; Yang, YikunYang, J., C. Zhao, Y. Sun, Y. Chi, Y. Yang, 2022: Aerosol first indirect effect over narrow longitude regions of North Pacific and same-latitude lands. Atmospheric Environment, 277, 119081. doi: 10.1016/j.atmosenv.2022.119081. Aerosol first indirect effect (FIE), which causes variations of cloud droplet effective radius (re) and then cloud radiative effect (CRE), is one of the critical factors leading to uncertainties in climate model simulations. Different from most previous studies over continental regions, using 10-year observation data from CERES, this study investigates the statistical relationships between aerosol optical depth (AOD) and non-precipitating single-layer liquid phase cloud re and surface shortwave CRE (CRESW) over narrow longitude regions of North Pacific and its eastern and western lands at equal latitudes, along with the estimation of aerosol FIE. Both surface CRESW and cloud re are highly affected by aerosols. When AOD is less than 0.3–0.4 and liquid water path (LWP) is greater than 30 g/m2, positive AOD-CRESW and negative AOD-cloud re relationships are found over both ocean and land. With the increase of AOD, the sensitivity of CRESW and cloud re to aerosol is weakened, but both have greater fluctuations. The latitude dependence of the CRESW and cloud re variations with AOD are weak. The increases in liquid water path (LWP) when LWP is in a certain range (30–120 g/m2 over ocean and 30–90 g/m2 over land) can highly increase CRESW and promote the growth of cloud droplets. We also find that FIE values are positive under clean condition, while negative under polluted condition. Associated with the much less aerosol amount and more sufficient water supply, the FIE values over the ocean are distinctly larger than that over the land. Ocean; Liquid water path; Aerosol first indirect effect; Cloud droplet effective radius; Land; Shortwave cloud radiative effect
Yi, BingqiYi, B., 2022: Diverse cloud radiative effects and global surface temperature simulations induced by different ice cloud optical property parameterizations. Scientific Reports, 12(1), 10539. doi: 10.1038/s41598-022-14608-w. The representation of ice cloud optical properties in climate models has long been a difficult problem. Very different ice cloud optical property parameterization schemes developed based on very different assumptions of ice particle shape habits, particle size distributions, and surface roughness conditions, are used in various models. It is not clear as to how simulated climate variables are affected by the ice cloud optical property parameterizations. A total of five ice cloud optical property parameterization schemes, including three based on the ice habit mixtures suitable for general ice clouds, mid-latitude synoptic ice clouds, and tropical deep convective ice clouds, and the other two based on single ice habits (smooth hexagonal column and severely roughened column aggregate), are developed under a same framework and are implemented in the National Center for Atmospheric Research Community Atmospheric Model version 5. A series of atmosphere-only climate simulations are carried out for each of the five cases with different ice parameterizations. The differences in the simulated top of the atmosphere shortwave and longwave cloud radiative effects (CREs) are evaluated, and the global averaged net CRE differences among different cases range from − 1.93 to 1.03 Wm−2. The corresponding changes in simulated surface temperature are found to be most prominent on continental regions which amount to several degrees in Kelvin. Our results indicate the importance of choosing a reasonable ice cloud optical property parameterization in climate simulations. Climate sciences; Environmental sciences
Zeppetello, Lucas R. Vargas; Battisti, David S.; Baker, Marcia B.Zeppetello, L. R. V., D. S. Battisti, M. B. Baker, 2022: The Physics of Heat Waves: What Causes Extremely High Summertime Temperatures?. J. Climate, 35(7), 2231-2251. doi: 10.1175/JCLI-D-21-0236.1. Abstract We analyze observations and develop a hierarchy of models to understand heat waves—long-lived, high temperature anomalies—and extremely high daily temperatures during summertime in the continental extratropics. Throughout the extratropics, the number of extremely hot days found in the three hottest months is much greater than expected from a random, single-process model. Furthermore, in many locations the temperature skewness switches from negative on daily time scales to positive on monthly time scales (or shifts from positive on daily time scales to higher positive values on monthly time scales) in ways that cannot be explained by averaging alone. These observations motivate a hierarchy of models of the surface energy and moisture budgets that we use to illuminate the physics responsible for daily and monthly averaged temperature variability. Shortwave radiation fluctuations drive much of the variance and the negative skewness found in daily temperature observations. On longer time scales, precipitation-induced soil moisture anomalies are important for temperature variability and account for the shift toward positive skewness in monthly averaged temperature. Our results demonstrate that long-lived heat waves are due to (i) the residence time of soil moisture anomalies and (ii) a nonlinear feedback between temperature and evapotranspiration via the impact of temperature on vapor pressure deficit. For most climates, these two processes give rise to infrequent, long-lived heat waves in response to randomly distributed precipitation forcing. Combined with our results concerning high-frequency variability, extremely hot days are seen to be state-independent filigree driven by shortwave variability acting on top of longer-lived, moisture-driven heat waves.
Zhan, Chuan; Jiang, Yazhen; Chen, Yong; Miao, Zuohua; Zeng, Xiangyang; Li, JunZhan, C., Y. Jiang, Y. Chen, Z. Miao, X. Zeng, J. Li, 2022: A Direct Method for the Estimation of Top-of-Atmosphere Outgoing Longwave Radiation from Himawari-8/AHI Data. Remote Sensing, 14(22), 5696. doi: 10.3390/rs14225696. Top-of-atmosphere (TOA) outgoing longwave radiation (OLR), a key component of the Earth’s energy budget, serves as a diagnostic of the Earth’s climate system response to incoming solar radiation. However, existing products are typically estimated using the traditional two-step method, which may bring extra uncertainties. This paper presents a direct machine learning method to estimate TOA OLR by directly linking Himawari-8/Advanced Himawari Imager (AHI) TOA radiances with TOA OLR determined by Clouds and the Earth’s Radiant Energy System (CERES) and other information, such as the viewing geometry. Models are built separately under clear- and cloudy-sky conditions using a gradient-boosting regression tree. Independent test results show that the root mean square errors (RMSEs) of the clear-sky and cloudy-sky models for estimating instantaneous values are 7.46 W/m2 (3.0%) and 11.61 W/m2 (5.8%), respectively. Daily results are obtained by averaging all the instantaneous results in one day. Intercomparisons of the daily results with CERES TOA OLR data show that the RMSE of the estimated AHI OLR is ~6 W/m2 (3%). The developed high-resolution AHI TOA OLR dataset will be beneficial in analyzing the regional energy budget. CERES; machine learning; AHI; earth’s energy budget; outgoing longwave radiation
Zhan, Chuan; Liang, ShunlinZhan, C., S. Liang, 2022: Improved estimation of the global top-of-atmosphere albedo from AVHRR data. Remote Sensing of Environment, 269, 112836. doi: 10.1016/j.rse.2021.112836. The top-of-atmosphere (TOA) albedo, a key component of the earth's energy balance, can be monitored regularly by satellite observations. Compared to the previous study Song et al. (2018), this paper estimates TOA albedo by directly linking Advanced Very High Resolution Radiometer (AVHRR) narrowband reflectance with TOA broadband albedo determined by NASA's Clouds and the Earth's Radiant Energy System (CERES) instead of Moderate Resolution Imaging Spectroradiometer (MODIS). The TOA albedo product developed in this study has an increased spatial resolution, from 1° to 0.05°, and its starting year has been extended from 2000 to 1981, compared to the CERES TOA albedo product. Models of lands and oceans are established separately under different atmospheric and surface conditions using gradient boosting regression tree (GBRT) method instead of the linear regression models in the previous study. The root mean square errors (RMSEs) of the cloudy-sky, clear-sky and snow-cover models over land are 11.2%, 9.2% and 2.3%, respectively; over oceans they are 14.6%, 10.6% and 5.6%, respectively. Compared to Song et al. (2018), the improvements of the three models over land are 28.8%, 29.2% and 68.6%, respectively. Compared to the CERES product, the new product is much more accurate than that from our previous study. The global monthly mean differences of the TOA albedo obtained with the GBRT product and CERES from 2001 to 2014 are mostly less than 5%. CERES; AVHRR; TOA albedo; Earth's energy budget; Machine learning
Zhang, Honghai; Seager, Richard; Xie, Shang-PingZhang, H., R. Seager, S. Xie, 2022: How Does Sea Surface Temperature Drive the Intertropical Convergence Zone in the Southern Indian Ocean?. J. Climate, 35(16), 5415-5432. doi: 10.1175/JCLI-D-21-0870.1. Abstract The Indian Ocean has an intriguing intertropical convergence zone (ITCZ) south of the equator year-round, which remains largely unexplored. Here we investigate this Indian Ocean ITCZ and the mechanisms for its origin. With a weak semiannual cycle, this ITCZ peaks in January–February with the strongest rainfall and southernmost location and a northeast–southwest orientation from the Maritime Continent to Madagascar, reaches a minimum around May with a zonal orientation, grows until its secondary maximum around September with a northwest–southeast orientation, weakens slightly until December, and then regains its mature phase in January. During austral summer, the Indian Ocean ITCZ exists over maximum surface moist static energy (MSE), consistent with convective quasi-equilibrium theory. This relationship breaks up during boreal summer when the surface MSE maximizes in the northern monsoon region. The position and orientation of the Indian Ocean ITCZ can be simulated well in both a linear dynamical model and the state-of-the-art Community Atmosphere Model version 6 (CAM6) when driven by observed sea surface temperature (SST). To quantify the contributions of the planetary boundary layer (PBL) and free-atmosphere processes to this ITCZ, we homogenize the free-atmosphere diabatic heating over the Indian Ocean in CAM6. In response, the ITCZ weakens significantly, owing to a weakened circulation and deep convection. Therefore, in CAM6, the SST drives the Indian Ocean ITCZ directly through PBL processes and indirectly via free-atmosphere diabatic heating. Their contributions are comparable during most seasons, except during the austral summer when the free-atmosphere diabatic heating dominates the mature-phase ITCZ. Significance Statement The intertropical convergence zone (ITCZ) is the globe-encircling band where trade winds converge and strong rainfall occurs in the tropics. Its rains provide life-supporting water to billions of people. Its associated latent heating invigorates the tropical atmospheric circulation and influences climate and weather across the planet. The ITCZ is located north of the equator in most tropical oceans, except in the Indian Ocean where it sits south of the equator year-around. In contrast to the well-known northern ITCZs, the origin of the southern ITCZ in the Indian Ocean remains unknown. This work provides the first explanation for how ocean surface temperature works together with processes in the lower and upper atmosphere to shape the unique ITCZ in the Indian Ocean.
Zhang, Jianhao; Zhou, Xiaoli; Goren, Tom; Feingold, GrahamZhang, J., X. Zhou, T. Goren, G. Feingold, 2022: Albedo susceptibility of northeastern Pacific stratocumulus: the role of covarying meteorological conditions. Atmospheric Chemistry and Physics, 22(2), 861-880. doi: 10.5194/acp-22-861-2022. Abstract. Quantification of the radiative adjustment of marine low clouds to aerosol perturbations, regionally and globally, remains the largest source of uncertainty in assessing current and future climate. One of the important steps towards quantifying the role of aerosol in modifying cloud radiative properties is to quantify the susceptibility of cloud albedo and liquid water path (LWP) to perturbations in cloud droplet number concentration (Nd). We use 10 years of spaceborne observations from the polar-orbiting Aqua satellite to quantify the albedo susceptibility of marine low clouds to Nd perturbations over the northeast (NE) Pacific stratocumulus (Sc) region. Mutual information analysis reveals a dominating control of cloud state (e.g., LWP and Nd) on low-cloud albedo susceptibility, relative to the meteorological states that drive these cloud states. Through a LWP–Nd space decomposition of albedo susceptibilities, we show clear separation among susceptibility regimes (brightening or darkening), consistent with previously established mechanisms through which aerosol modulates cloud properties. These regimes include (i) thin non-precipitating clouds (LWP < 55 g m−2) that exhibit brightening (occurring 37 % of the time), corresponding to the Twomey effect; (ii) thicker non-precipitating clouds, corresponding to entrainment-driven negative LWP adjustments that manifest as a darkening regime (36 % of the time); and (iii) another brightening regime (22 % of the time) consisting of mostly precipitating clouds, corresponding to precipitation-suppression LWP positive adjustments. Overall, we find an annual-mean regional low-cloud brightening potential of 20.8±2.68 W m−2 ln(Nd)−1, despite an overall negative LWP adjustment for non-precipitating marine stratocumulus, owing to the high occurrence of the Twomey–brightening regime. Over the NE Pacific, clear seasonal covariabilities among meteorological factors related to the large-scale circulation are found to play an important role in grouping conditions favorable for each susceptibility regime. When considering the covarying meteorological conditions, our results indicate that for the northeastern Pacific stratocumulus, clouds that exhibit the strongest brightening potential occur most frequently within shallow marine boundary layers over a cool ocean surface with a stable atmosphere and a dry free troposphere above. Clouds that exhibit a darkening potential associated with negative LWP adjustments occur most frequently within deep marine boundary layers in which the atmospheric instability and the ocean surface are not strong and warm enough to produce frequent precipitation. Cloud brightening associated with warm-rain suppression is found to preferably occur either under unstable atmospheric conditions or humid free-tropospheric conditions that co-occur with a warm ocean surface.
Zhang, Ke; Zhao, Long; Tang, Wenjun; Yang, Kun; Wang, JingZhang, K., L. Zhao, W. Tang, K. Yang, J. Wang, 2022: Global and Regional Evaluation of the CERES Edition-4A Surface Solar Radiation and Its Uncertainty Quantification. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 15, 2971-2985. doi: 10.1109/JSTARS.2022.3164471. This article presents a comprehensive evaluation of the 2000–2018 Clouds and Earth's Radiant Energy System Synoptic 1° Ed4A (CERES SYN1deg Edition 4A) surface solar radiation (SSR) product. In particular, the global assessment is conducted over different temporal scales (i.e., hourly, daily, and monthly-average) with special attention given to the impact of clouds, and a regional evaluation is further implemented over the Mainland of China (MC) using SSR measurements from a denser observational network provided by the China Meteorological Administration. Evaluation across all valid station-grid pairs yields mixed performance with |MBE|≤2.8 (6.2) W m−2, RMSE≤89.5 (31.6) W m−2, and R≥0.95 (0.93) over the globe (MC) for different temporal scales, and the monthly CERES SSR, with RMSE≤20 W m−2, is found to hold promise for global numerical weather prediction and climate monitoring. In addition, CERES is found to generally underestimate and overestimate SSR over land and ocean, respectively. Comparison between year-round and cloudy-season suggests that the presence of clouds may potentially impact the SSR retrievals, especially at the hourly temporal scales, with an increase in RMSE values larger than 10 W m−2 for most stations. Further investigation of subgrid heterogeneity suggests that most in situ SSR measurements can reasonably represent the 1° grid average except for some stations with specific geographic deployments, which may raise significant spatial representativeness issues and, therefore, need to be used with great caution. Solar radiation; Earth; Satellites; cloud; Clouds; surface solar radiation; Sea measurements; uncertainty quantification; Sea surface; Cloud computing; Clouds and Earth's radiant energy system synoptic (CERES); spatial representativeness
Zhang, Kun; Zhu, Gaofeng; Ma, Ning; Chen, Huiling; Shang, ShashaZhang, K., G. Zhu, N. Ma, H. Chen, S. Shang, 2022: Improvement of evapotranspiration simulation in a physically based ecohydrological model for the groundwater–soil–plant–atmosphere continuum. Journal of Hydrology, 613, 128440. doi: 10.1016/j.jhydrol.2022.128440. Accurate quantification of terrestrial evapotranspiration (ET) is essential to understanding the interaction between land and atmosphere, as well as the feedback response of vegetation dynamics. In our previous work, a physically based ecohydrological model called the simple terrestrial hydrosphere (SiTH) model was developed to estimate ET and the other ET-related variables based on the groundwater–soil–plant–atmosphere continuum (GSPAC). However, the SiTH model (SiTHv1) still has some deficiencies in the model structure and parameters, which can result in potential uncertainty in the estimation of terrestrial ET. In this study, we aimed to address these limitations by developing a new version of the SiTH model (SiTHv2). The main modifications of the SiTHv2 model include: (1) the vegetation moisture constraint module is updated with vegetation optical depth observations; (2) the critical model parameters associated with root distribution are constrained using flux observations; (3) the soil module is extended to a three-layer module with 5 m of total depth; (4) an irrigation input water strategy is applied in the cropland areas; and (5) the latest ERA5-Land reanalysis data with a finer spatial resolution are used as the meteorological forcing data. The estimated ET of the SiTHv2 model was validated/compared at multiple scales (i.e., site/plot, basin, and global) with flux data, basin water balance data, and other mainstream global ET products, respectively. The results demonstrate that the SiTHv2 model performs better than the SiTHv1 model, with an improvement in the overall model root-mean-square error of 0.66 mm day−1 (plot scale) and 98.58 mm year−1 (basin scale), representing 27% and 22% improvements over the SiTHv1 model in the same circumstances, respectively. In addition, the performance of the SiTHv2 model ranks well when compared to the existing terrestrial ET models and products. The improvements to the SiTH model should allow improved estimation of terrestrial ET and provide support to potential studies in water transfer within the GSPAC. Evapotranspiration; Multi-scale verification; SiTH model; Water stress
Zhang, Wanchun; Liu, Jian; Zhang, Peng; Sun, Ling; Xu, Hanlie; Wang, Yanjiao; Chen, LinZhang, W., J. Liu, P. Zhang, L. Sun, H. Xu, Y. Wang, L. Chen, 2022: Evaluation of Reprocessed Fengyun-3B Global Outgoing Longwave Radiation Data: Comparison with CERES OLR. Journal of Meteorological Research, 36(3), 417-428. doi: 10.1007/s13351-022-1132-4. Outgoing longwave radiation (OLR) at the top of the atmosphere (TOA) is a key parameter for understanding and interpreting the relationship between clouds, radiation, and climate interactions. It has been one of the operational products of the Fengyun (FY) meteorological satellites. OLR accuracy has gradually improved with advancements in satellite payload performance and the OLR retrieval algorithm. Supported by the National Key R&D Program Retrospective Calibration of Historical Chinese Earth Observation Satellite data (Richceos) project, a long-term OLR climate data record (CDR) was reprocessed based on the recalibrated Level 1 data of FY series satellites using the latest OLR retrieval algorithm. In this study, Fengyun-3B (FY-3B)’s reprocessed global OLR data from 2010 to 2018 were evaluated by using the Clouds and the Earth’s Radiant Energy System (CERES) global daily OLR data. The results showed that there was a high consistency between the FY-3B instantaneous OLR and CERES Single Scanner Footprint (SSF) OLR. Globally, between the two CDR datasets, the correlation coefficient reached 0.98, and the root-mean-square error (RMSE) was approximately 8–9 W m−2. The bias mainly came from the edge regions of the satellite orbit, which may be related to the satellite zenith angle and cloud cover distribution. It was shown that the long-term FY-3B OLR had temporal stability compared to CERES OLR long-term data. In terms of spatial distribution, the mean deviations showed zonal and seasonal characteristics, although seasonal fluctuations were observed in the differences between the two datasets. Effects of FY-3B OLR application to the South China Sea monsoon region and ENSO were demonstrated and analyzed, and the results showed that the seasonal deviation of FY-3B’s OLR comes mainly from the retrieval algorithm. However, it has little effect on the analysis of climate events. Clouds and the Earth’s Radiant Energy System (CERES); El Niño—Southern Oscillation (ENSO); Fengyun-3B (FY-3B); outgoing longwave radiation (OLR); South China Sea monsoon
Zhang, Xiyue; Schneider, Tapio; Shen, Zhaoyi; Pressel, Kyle G.; Eisenman, IanZhang, X., T. Schneider, Z. Shen, K. G. Pressel, I. Eisenman, 2022: Seasonal Cycle of Idealized Polar Clouds: Large Eddy Simulations Driven by a GCM. Journal of Advances in Modeling Earth Systems, 14(1), e2021MS002671. doi: 10.1029/2021MS002671. The uncertainty in polar cloud feedbacks calls for process understanding of the cloud response to climate warming. As an initial step toward improved process understanding, we investigate the seasonal cycle of polar clouds in the current climate by adopting a novel modeling framework using large eddy simulations (LES), which explicitly resolve cloud dynamics. Resolved horizontal and vertical advection of heat and moisture from an idealized general circulation model (GCM) are prescribed as forcing in the LES. The LES are also forced with prescribed sea ice thickness, but surface temperature, atmospheric temperature, and moisture evolve freely without nudging. A semigray radiative transfer scheme without water vapor and cloud feedbacks allows the GCM and LES to achieve closed energy budgets more easily than would be possible with more complex schemes. This enables the mean states in the two models to be consistently compared, without the added complications from interaction with more comprehensive radiation. We show that the LES closely follow the GCM seasonal cycle, and the seasonal cycle of low-level clouds in the LES resembles observations: maximum cloud liquid occurs in late summer and early autumn, and winter clouds are dominated by ice in the upper troposphere. Large-scale advection of moisture provides the main source of water vapor for the liquid-containing clouds in summer, while a temperature advection peak in winter makes the atmosphere relatively dry and reduces cloud condensate. The framework we develop and employ can be used broadly for studying cloud processes and the response of polar clouds to climate warming. cloud; GCM; Arctic; mixed-phase cloud; LES; seasonal cycle
Zhang, Yanqing; Gao, Yi; Xu, Liren; Zhang, MeigenZhang, Y., Y. Gao, L. Xu, M. Zhang, 2022: Quantification of aerosol and cloud effects on solar energy over China using WRF-Chem. Atmospheric Research, 275, 106245. doi: 10.1016/j.atmosres.2022.106245. The promotion of renewable energy as a substitute for fossil fuels is the key solution to achieve the goals established during the United Nations Climate Change Conference in Glasgow (COP26) based on which member countries agreed to phase down coal power and achieve net-zero carbon emissions. Among various renewable energy sources, solar energy is an attractive option that will have a significant effect on the future energy supply and energy use. Therefore, we selected the period of 2016–2020 during which the aerosol concentration gradually decreased due to strict pollutant control measures to evaluate solar energy simulations based on the Weather Research Forecast-Chemistry (WRF-Chem) model. We also analyzed the contributions of the aerosol direct effect (ADE), aerosol indirect effect (AIE), and cloud radiation effect (CRE) to solar energy trends by conducting sensitivity experiments. The results show that the WRF-Chem model performs well for the 2 m temperature (T2), cloud fraction, PM2.5, solar energy trends during 2016–2020. There are regional and seasonal differences in the contributions of ADE, AIE, and CRE to solar energy trends, with a decrease in ADE contributions and an increase in CRE contributions from north to south in China, and the AIE contribution being relatively slight. On an annual scale, ADE is the main contributor to the increase in solar energy trends in the Beijing-Tianjin-Hebei (89%) and Fenwei Plains (83.9%) from 2016 to 2020, which is related to the horizontal distribution of PM2.5. In the Yangtze River Delta and other regions, ADE and CRE contributed equally to the increase in solar energy trends, about 40%. In the Pearl River Delta and Sichuan Basin, the contribution of CRE is larger than that of AIE and ADE, the Pearl River Delta region is the largest contributor of CRE to the annual solar energy trends among the five major urban agglomerations, with a contribution of 78.4%, and Sichuan basin is the only region where CRE has a negative contribution to the annual solar energy trends (−59.1%). On the seasonal scale, the contribution of CRE is dominant except for the greater positive contribution of ADE to the solar energy trends in spring, summer, and autumn in Beijing-Tianjin-Hebei and in autumn in Fenwei Plain. Aerosol direct effect; WRF-Chem; Aerosol indirect effect; Cloud radiation effect
Zhang, Yi; Li, Xiaohan; Liu, Zhuang; Rong, Xinyao; Li, Jian; Zhou, Yihui; Chen, SuyangZhang, Y., X. Li, Z. Liu, X. Rong, J. Li, Y. Zhou, S. Chen, 2022: Resolution Sensitivity of the GRIST Nonhydrostatic Model from 120 to 5 km (3.75 km) during the DYAMOND winter. Earth and Space Science, n/a(n/a), e2022EA002401. doi: 10.1029/2022EA002401. We investigated the resolution sensitivity of the GRIST global nonhydrostatic model characterized by explicit dynamics–microphysics coupling using varying uniform resolutions (120, 60, 30, 15 and 5 km). The experiments followed the DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) winter protocol, which covers a 40-day integration. These simulations did not activate parameterized convection. One 120 km test with parameterized convection was performed as a coarse-resolution reference. Other model configurations for different simulations were kept as consistent as possible. Our results showed that the model gradually improved its representation of the fine-scale features as the resolution increased. The 5 km simulation was overall close to a 3.75 km simulation during the first 12 days of the DYAMOND winter. With respect to the mean climate, the 5 km simulation had a more realistic rainfall distribution than the lower resolution explicit convection simulations. Cloud water and the related physical fields (e.g., shortwave cloud radiative forcing) had a large resolution sensitivity. The tropical rainfall frequency–intensity spectra became more realistic in the 5 km explicit convection simulation, but the 120 km run with parameterized convection showed a more realistic mean climate. As the resolution increases, the mean bulk effect of finely resolved model convection gradually converges to that of parameterized convection. The mean climate of this storm-resolving model has slightly higher rainfall biases than a parameterized convection coarse-resolution model, highlighting the importance of balancing resolved- and under-resolved model convection for developing a unified multiscale global model. This article is protected by copyright. All rights reserved.
Zhang, Yuan; Bi, Shengshan; Wu, JiangtaoZhang, Y., S. Bi, J. Wu, 2022: The influence of lunar surface position on irradiance of moon-based earth radiation observation. Frontiers of Earth Science. doi: 10.1007/s11707-021-0937-2. As a platform for longer-term continuous moon-based earth radiation observation (MERO) which includes reflected solar short-wave (SW) radiation and long-wave infrared (LW) radiation, the huge lunar surface space can provide multiple location choices. It is important to analyze the influence of lunar surface position on irradiance which is the aim of the present work based on a radiation heat transfer model. To compare the differences caused by positions, the site of 0°E 0°N was selected as the reference site and a good agreement of the calculation results was verified by the comparison with the NISTAR’s actual detected data. By analyzing the spatial characteristics of the irradiance, the results showed that the irradiance on the lunar surface was of circular distribution and the instrument that was placed in the region of 65°W–65°E and 65°S–65°N could detect the irradiance most effectively. The relative deviation between the reference site and the marginal area (region of > 65°S or 65°N or > 65°W or 65°E) was less than 0.9 mW·m−2 and the small regional differences make a small-scale network conducive to radiometric calibration between instruments. To achieve accurate measurement of the irradiance, the sensitivity design goal of the MERO instrument should be better than 1 mW·m−2 in a future actual design. Because the lunar polar region is the priority region for future exploration, the irradiance at the poles has also been analyzed. The results show that the irradiance changes periodically and exhibits complementary characteristics of time. The variation range of irradiance for short-wave radiation is greater than long-wave radiation and the irradiance of SW reaches the maximum at different times. The MERO at the polar region will provide valuable practical experiment for the follow-up study of the moon-based earth observation in low latitudes. earth observation; irradiance; NISTAR; lunar surface position; moon-based
Zhao, Guangyu; Yang, Muqun; Gao, Yizhao; Zhan, Yizhe; Lee, H. Joe; Di Girolamo, LarryZhao, G., M. Yang, Y. Gao, Y. Zhan, H. J. Lee, L. Di Girolamo, 2022: PYTAF: A Python Tool for Spatially Resampling Earth Observation Data. Earth Science Informatics, 15(3), 1443-1448. doi: 10.1007/s12145-020-00461-w. Earth observation data have revolutionized Earth science and significantly enhanced the ability to forecast weather, climate and natural hazards. The storage format of the majority of Earth observation data can be classified into swath, grid or point structures. Earth science studies frequently involve resampling between swath, grid and point data when combining measurements from multiple instruments, which can provide more insights into geophysical processes than using any single instrument alone. As the amount of Earth observation data increases each day, the demand for a high computational efficient tool to resample and fuse Earth observation data has never been greater. We present a software tool, called pytaf, that resamples Earth observation data stored in swath, grid or point structures using a novel block indexing algorithm. This tool is specially designed to process large scale datasets. The core functions of pytaf were implemented in C with OpenMP to enable parallel computations in a shared memory environment. A user-friendly python interface was also built. The tool has been extensively tested on supercomputers and successfully used to resample the data from five instruments on the EOS-Terra platform at a mission-wide scale. Grid; Nearest Neighbor; Pytaf; Python; Resample; Swath
Zhao, Lijun; Wang, Yuan; Zhao, Chuanfeng; Dong, Xiquan; Yung, Yuk L.Zhao, L., Y. Wang, C. Zhao, X. Dong, Y. L. Yung, 2022: Compensating Errors in Cloud Radiative and Physical Properties over the Southern Ocean in the CMIP6 Climate Models. Advances in Atmospheric Sciences. doi: 10.1007/s00376-022-2036-z. The Southern Ocean is covered by a large amount of clouds with high cloud albedo. However, as reported by previous climate model intercomparison projects, underestimated cloudiness and overestimated absorption of solar radiation (ASR) over the Southern Ocean lead to substantial biases in climate sensitivity. The present study revisits this long-standing issue and explores the uncertainty sources in the latest CMIP6 models. We employ 10-year satellite observations to evaluate cloud radiative effect (CRE) and cloud physical properties in five CMIP6 models that provide comprehensive output of cloud, radiation, and aerosol. The simulated longwave, shortwave, and net CRE at the top of atmosphere in CMIP6 are comparable with the CERES satellite observations. Total cloud fraction (CF) is also reasonably simulated in CMIP6, but the comparison of liquid cloud fraction (LCF) reveals marked biases in spatial pattern and seasonal variations. The discrepancies between the CMIP6 models and the MODIS satellite observations become even larger in other cloud macro- and micro-physical properties, including liquid water path (LWP), cloud optical depth (COD), and cloud effective radius, as well as aerosol optical depth (AOD). However, the large underestimation of both LWP and cloud effective radius (regional means ∼20% and 11%, respectively) results in relatively smaller bias in COD, and the impacts of the biases in COD and LCF also cancel out with each other, leaving CRE and ASR reasonably predicted in CMIP6. An error estimation framework is employed, and the different signs of the sensitivity errors and biases from CF and LWP corroborate the notions that there are compensating errors in the modeled shortwave CRE. Further correlation analyses of the geospatial patterns reveal that CF is the most relevant factor in determining CRE in observations, while the modeled CRE is too sensitive to LWP and COD. The relationships between cloud effective radius, LWP, and COD are also analyzed to explore the possible uncertainty sources in different models. Our study calls for more rigorous calibration of detailed cloud physical properties for future climate model development and climate projection. cloud radiative effect; global climate models; cloud physics; the Southern Ocean
Zheng, Cheng; Ting, Mingfang; Wu, Yutian; Kurtz, Nathan; Orbe, Clara; Alexander, Patrick; Seager, Richard; Tedesco, MarcoZheng, C., M. Ting, Y. Wu, N. Kurtz, C. Orbe, P. Alexander, R. Seager, M. Tedesco, 2022: Turbulent Heat Flux, Downward Longwave Radiation, and Large-Scale Atmospheric Circulation Associated with Wintertime Barents–Kara Sea Extreme Sea Ice Loss Events. J. Climate, 35(12), 3747-3765. doi: 10.1175/JCLI-D-21-0387.1. Abstract We investigate wintertime extreme sea ice loss events on synoptic to subseasonal time scales over the Barents–Kara Sea, where the largest sea ice variability is located. Consistent with previous studies, extreme sea ice loss events are associated with moisture intrusions over the Barents–Kara Sea, which are driven by the large-scale atmospheric circulation. In addition to the role of downward longwave radiation associated with moisture intrusions, which is emphasized by previous studies, our analysis shows that strong turbulent heat fluxes are associated with extreme sea ice melting events, with both turbulent sensible and latent heat fluxes contributing, although turbulent sensible heat fluxes dominate. Our analysis also shows that these events are connected to tropical convective anomalies. A dipole pattern of convective anomalies with enhanced convection over the Maritime Continent and suppressed convection over the central to eastern Pacific is consistently detected about 6–10 days prior to extreme sea ice loss events. This pattern is associated with either the Madden–Julian oscillation (MJO) or El Niño–Southern Oscillation (ENSO). Composites show that extreme sea ice loss events are connected to tropical convection via Rossby wave propagation in the midlatitudes. However, tropical convective anomalies alone are not sufficient to trigger extreme sea ice loss events, suggesting that extratropical variability likely modulates the connection between tropical convection and extreme sea ice loss events.
Zhou, Chen; Liu, Yincheng; Wang, QuanZhou, C., Y. Liu, Q. Wang, 2022: Calculating the Climatology and Anomalies of Surface Cloud Radiative Effect Using Cloud Property Histograms and Cloud Radiative Kernels. Advances in Atmospheric Sciences. doi: 10.1007/s00376-021-1166-z. Cloud radiative kernels (CRK) built with radiative transfer models have been widely used to analyze the cloud radiative effect on top of atmosphere (TOA) fluxes, and it is expected that the CRKs would also be useful in the analyses of surface radiative fluxes, which determines the regional surface temperature change and variability. In this study, CRKs at the surface and TOA were built using the Rapid Radiative Transfer Model (RRTM). Longwave cloud radiative effect (CRE) at the surface is primarily driven by cloud base properties, while TOA CRE is primarily decided by cloud top properties. For this reason, the standard version of surface CRK is a function of latitude, longitude, month, cloud optical thickness (τ) and cloud base pressure (CBP), and the TOA CRK is a function of latitude, longitude, month, τ and cloud top pressure (CTP). Considering that the cloud property histograms provided by climate models are functions of CTP instead of CBP at present, the surface CRKs on CBP-τ histograms were converted to CTP-τ fields using the statistical relationship between CTP, CBP and τ obtained from collocated CloudSat and MODIS observations. For both climate model outputs and satellites observations, the climatology of surface CRE and cloud-induced surface radiative anomalies calculated with the surface CRKs and cloud property histograms are well correlated with those calculated from surface radiative fluxes. The cloud-induced surface radiative anomalies reproduced by surface CRKs and MODIS cloud property histograms are not affected by spurious trends that appear in Clouds and the Earth’s Radiant Energy System (CERES) surface irradiances products.
Zhou, Hao; Yue, Xu; Lei, Yadong; Tian, Chenguang; Zhu, Jun; Ma, Yimian; Cao, Yang; Yin, Xixi; Zhang, ZhidingZhou, H., X. Yue, Y. Lei, C. Tian, J. Zhu, Y. Ma, Y. Cao, X. Yin, Z. Zhang, 2022: Distinguishing the impacts of natural and anthropogenic aerosols on global gross primary productivity through diffuse fertilization effect. Atmospheric Chemistry and Physics, 22(1), 693-709. doi: 10.5194/acp-22-693-2022. Abstract. Aerosols can enhance ecosystem productivity by increasing diffuse radiation. Such diffuse fertilization effects (DFEs) vary among different aerosol compositions and sky conditions. Here, we apply a suite of chemical, radiation, and vegetation models in combination with ground- and satellite-based measurements to assess the impacts of natural and anthropogenic aerosol species on gross primary productivity (GPP) through DFE from 2001–2014. Globally, aerosols enhance GPP by 8.9 Pg C yr−1 under clear-sky conditions but only 0.95 Pg C yr−1 under all-sky conditions. Anthropogenic aerosols account for 41 % of the total GPP enhancement, though they contribute only 25 % to the increment of diffuse radiation. Sulfate/nitrate aerosols from anthropogenic sources make dominant contributions of 33 % (36 %) to aerosol DFE under all-sky (clear-sky) conditions, followed by the fraction of 18 % (22 %) by organic carbon aerosols from natural sources. In contrast to other species, black carbon aerosols reduce global GPP by 0.28 (0.12) Pg C yr−1 under all-sky (clear-sky) conditions. Long-term simulations show that aerosol DFE increases 2.9 % yr−1 under all-sky conditions mainly because of a downward trend in cloud amount. This study suggests that the impacts of aerosols and cloud should be considered in projecting future changes of ecosystem productivity under varied emission scenarios.
Zhou, Wenyu; Leung, L. Ruby; Lu, JianZhou, W., L. R. Leung, J. Lu, 2022: Linking Large-Scale Double-ITCZ Bias to Local-Scale Drizzling Bias in Climate Models. J. Climate, 35(24), 4365-4379. doi: 10.1175/JCLI-D-22-0336.1. Abstract Tropical precipitation in climate models presents significant biases in both the large-scale pattern (i.e., double intertropical convergence zone bias) and local-scale characteristics (i.e., drizzling bias with too frequent drizzle/convection and reduced occurrences of no and heavy precipitation). By untangling the coupled system and analyzing the biases in precipitation, cloud, and radiation, this study shows that local-scale drizzling bias in atmospheric models can lead to large-scale double-ITCZ bias in coupled models by inducing convective-regime-dependent biases in precipitation and cloud radiative effects (CRE). The double-ITCZ bias consists of a hemispherically asymmetric component that arises from the asymmetric SST bias and a nearly symmetric component that exists in atmospheric models without the SST bias. By increasing light rain but reducing heavy rain, local-scale drizzling bias induces positive (negative) precipitation bias in the moderate (strong) convective regime, leading to the nearly symmetric wet bias in atmospheric models. By affecting the cloud profile, local-scale drizzling bias induces positive (negative) CRE bias in the stratocumulus (convective) regime in atmospheric models. Because the stratocumulus (convective) region is climatologically more pronounced in the southern (northern) tropics, the CRE bias is deemed to be hemispherically asymmetric and drives warm and wet (cold and dry) biases in the southern (northern) tropics when coupled to ocean. Our results suggest that correcting local-scale drizzling bias is critical for fixing large-scale double-ITCZ bias. The drizzling and double-ITCZ biases are not alleviated in models with mesoscale (0.25°–0.5°) or even storm-resolving (∼3 km) resolution, implying that either large-eddy simulation or fundamental improvement in small-scale subgrid parameterizations is needed.
Zhou, Xingyu; Chen, Hua; Jiang, Weiping; Chen, Yan; Jin, Taoyong; Liu, Tianjun; Gao, YangZhou, X., H. Chen, W. Jiang, Y. Chen, T. Jin, T. Liu, Y. Gao, 2022: A new ambiguity resolution method for LEO precise orbit determination. Journal of Geodesy, 96(7), 49. doi: 10.1007/s00190-022-01629-6. Ambiguity resolution (AR) is an effective approach to improve the orbit accuracy of the low Earth orbit satellites using the Global Navigation Satellite System (GNSS). The most commonly used single-difference (SD) AR requires prior knowledge of the GNSS hardware biases, while the potential unavailability of the bias products may hinder the AR process for users. The track-to-track (T2T) AR can work as an alternative without the GNSS bias products, but the performance may be degraded by the receiver hardware biases. To provide a better alternative in this condition, a new AR method called SD T2T (SDT2T) is proposed in this study, where the GNSS and receiver biases can be greatly eliminated without external knowledge. The performance of the SD AR, SDT2T AR, and T2T AR methods are assessed based on the gravity recovery and climate experiment follow on and SWARM data. The results show that the improvements contributed by the SDT2T AR are comparable to the SD AR. The multiple iterations required by the T2T AR can be avoided by the SDT2T AR, and the accuracy of the T2T AR can be further improved with the preprocessed ambiguities of the SDT2T AR. Considering the efficiency and stable performance, the SDT2T AR is recommended as the preferred alternative single-receiver AR method in the absence of the GNSS hardware bias products. Precise orbit determination; LEO; Ambiguity resolution; K-band range validation; SLR orbit validation
Zhu, Jiang; Otto-Bliesner, Bette L.; Brady, Esther C.; Gettelman, Andrew; Bacmeister, Julio T.; Neale, Richard B.; Poulsen, Christopher J.; Shaw, Jonah K.; McGraw, Zachary S.; Kay, Jennifer E.Zhu, J., B. L. Otto-Bliesner, E. C. Brady, A. Gettelman, J. T. Bacmeister, R. B. Neale, C. J. Poulsen, J. K. Shaw, Z. S. McGraw, J. E. Kay, 2022: LGM paleoclimate constraints inform cloud parameterizations and equilibrium climate sensitivity in CESM2. Journal of Advances in Modeling Earth Systems, n/a(n/a), e2021MS002776. doi: 10.1029/2021MS002776. The Community Earth System Model version 2 (CESM2) simulates a high equilibrium climate sensitivity (ECS > 5°C) and a Last Glacial Maximum (LGM) that is substantially colder than proxy temperatures. In this study, we examine the role of cloud parameterizations in simulating the LGM cooling in CESM2. Through substituting different versions of cloud schemes in the atmosphere model, we attribute the excessive LGM cooling to the new CESM2 schemes of cloud microphysics and ice nucleation. Further exploration suggests that removing an inappropriate limiter on cloud ice number (NoNimax) and decreasing the time-step size (substepping) in cloud microphysics largely eliminate the excessive LGM cooling. NoNimax produces a more physically consistent treatment of mixed-phase clouds, which leads to an increase in cloud ice content and a weaker shortwave cloud feedback over mid-to-high latitudes and the Southern Hemisphere subtropics. Microphysical substepping further weakens the shortwave cloud feedback. Based on NoNimax and microphysical substepping, we have developed a paleoclimate-calibrated CESM2 (PaleoCalibr), which simulates well the observed 20th century warming and spatial characteristics of key cloud and climate variables. PaleoCalibr has a lower ECS (∼4°C) and a 20% weaker aerosol-cloud interaction than CESM2. PaleoCalibr represents a physically more consistent treatment of cloud microphysics than CESM2 and is a valuable tool in climate change studies, especially when a large climate forcing is involved. Our study highlights the unique value of paleoclimate constraints in informing the cloud parameterizations and ultimately the future climate projection. Cloud parameterizations; Cloud feedback; Community Earth System Model version 2; Equilibrium Climate Sensitivity; Last Glacial Maximum
Akkermans, Tom; Clerbaux, NicolasAkkermans, T., N. Clerbaux, 2021: Retrieval of Daily Mean Top-of-Atmosphere Reflected Solar Flux Using the Advanced Very High Resolution Radiometer (AVHRR) Instruments. Remote Sensing, 13(18), 3695. doi: 10.3390/rs13183695. The records of the Advanced Very High Resolution Radiometer (AVHRR) instrument observations can resolve the current lack of a long global climate data record of Reflected Solar Flux (RSF), by transforming these measurements into broadband flux at the top-of-atmosphere. This paper presents a methodology for obtaining daily mean RSF (Wm−2) from AVHRR. First, the narrowband reflectances are converted to broadband reflectance using empirical regressions with the Clouds and the Earth’s Radiant Energy System (CERES) observations. Second, the anisotropy is corrected by applying Angular Distribution Models (ADMs), which convert directional reflectance into a hemispherical albedo. Third, the instantaneous albedos are temporally interpolated by a flexible diurnal cycle model, capable of ingesting any number of observations at any time of day, making it suitable for any orbital configuration of NOAA and MetOp satellites. Finally, the twilight conditions prevailing near sunrise and sunset are simulated with an empirical model. The entire day is then integrated into a single daily mean RSF. This paper furthermore demonstrates the methodology by validating a full year (2008) of RSF daily means with the CERES SYN1deg data record, both on daily and subdaily scale. Several configurations are tested, each excluding particular satellites from the constellation in order to mimic orbital changes (e.g., orbital drift), and to assess their relative importance to the daily mean RSF. The best performance is obtained by the combination of at least one mid-morning (NOAA-17 or MetOp-A) and one early afternoon (NOAA-18) orbit. In this case, the RMS difference with CERES is about 7 Wm−2. Removing NOAA-18 degrades the performance to an RMS difference of 12 Wm−2, thereby providing an estimate of the impact of NOAA-19’s orbital drift between 2016 and 2020. Very early or late observations (NOAA-15, NOAA-16) provide little added value, and both mid-morning orbits turn out to be almost interchangeable given their close temporal proximity. broadband; radiation; diurnal cycle; AVHRR; flux; TOA; daily mean
Aldhaif, Abdulmonam M.; Lopez, David H.; Dadashazar, Hossein; Painemal, David; Peters, Andrew J.; Sorooshian, ArminAldhaif, A. M., D. H. Lopez, H. Dadashazar, D. Painemal, A. J. Peters, A. Sorooshian, 2021: An Aerosol Climatology and Implications for Clouds at a Remote Marine Site: Case Study Over Bermuda. Journal of Geophysical Research: Atmospheres, 126(9), e2020JD034038. doi: https://doi.org/10.1029/2020JD034038. Aerosol characteristics and aerosol–cloud interactions remain uncertain in remote marine regions. We use over a decade of data (2000–2012) from the NASA AErosol RObotic NETwork, aerosol and wet deposition samples, satellite remote sensors, and models to examine aerosol and cloud droplet number characteristics at a representative open ocean site (Bermuda) over the Western North Atlantic Ocean (WNAO). Annual mean values were as follows: aerosol optical depth (AOD) = 0.12, Ångström Exponent (440/870 nm) = 0.95, fine mode fraction = 0.51, asymmetry factor = 0.72 (440 nm) and 0.68 (1020 nm), and Aqua-MODIS cloud droplet number concentrations = 51.3 cm−3. The winter season (December–February) was characterized by high sea salt optical thickness and the highest aerosol extinction in the lowest 2 km. Extensive precipitation over the WNAO in winter helps contribute to the low FMFs in winter (∼0.40–0.50) even though air trajectories often originate over North America. Spring and summer had more pronounced influence from sulfate, dust, organic carbon, and black carbon. Volume size distributions were bimodal with a dominant coarse mode (effective radii: 1.85–2.09 µm) and less pronounced fine mode (0.14–0.16 µm), with variability in the coarse mode likely due to different characteristic sizes for transported dust (smaller) versus regional sea salt (larger). Extreme pollution events highlight the sensitivity of this site to long-range transport of urban emissions, dust, and smoke. Differing annual cycles are identified between AOD and cloud droplet number concentrations, motivating a deeper look into aerosol–cloud interactions at this site. aerosol; ACTIVATE; sea salt; African dust; Bermuda; EVS-3
Alexandri, Georgia; Georgoulias, Aristeidis K.; Balis, DimitrisAlexandri, G., A. K. Georgoulias, D. Balis, 2021: Effect of Aerosols, Tropospheric NO2 and Clouds on Surface Solar Radiation over the Eastern Mediterranean (Greece). Remote Sensing, 13(13), 2587. doi: 10.3390/rs13132587. In this work, the effect that two basic air quality indexes, aerosols and tropospheric NO2, exert on surface solar radiation (SSR) is studied, along with the effect of liquid and ice clouds over 16 locations in Greece, in the heart of the Eastern Mediterranean. State-of-the-art satellite-based observations and climatological data for the 15-year period 2005–2019, and a radiative transfer system based on a modified version of the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model are used. Our SSR simulations are in good agreement with ground observations and two satellite products. It is shown that liquid clouds dominate, with an annual radiative effect (RE) of −36 W/m2, with ice clouds (−19 W/m2) and aerosols (−13 W/m2) following. The radiative effect of tropospheric NO2 is smaller by two orders of magnitude (−0.074 W/m2). Under clear skies, REaer is about 3–4 times larger than for liquid and ice cloud-covered skies, while RENO2 doubles. The radiative effect of all the parameters exhibits a distinct seasonal cycle. An increase in SSR is observed for the period 2005–2019 (positive trends ranging from 0.01 to 0.52 W/m2/year), which is mostly related to a decrease in the aerosol optical depth and the liquid cloud fraction. clouds; aerosols; CERES; MODIS; surface solar radiation; CALIPSO; CM SAF; SBDART; Greece; tropospheric NO2
Arouf, Assia; Chepfer, Hélène; Vaillant de Guélis, Thibault; Chiriaco, Marjolaine; Shupe, Matthew D.; Guzman, Rodrigo; Feofilov, Artem; Raberanto, Patrick; L’Ecuyer, Tristan S.; Kato, Seiji; Gallagher, Michael R.Arouf, A., H. Chepfer, T. Vaillant de Guélis, M. Chiriaco, M. D. Shupe, R. Guzman, A. Feofilov, P. Raberanto, T. S. L’Ecuyer, S. Kato, M. R. Gallagher, 2021: The Surface Longwave Cloud Radiative Effect derived from Space Lidar Observations. Atmospheric Measurement Techniques Discussions, 1-54. doi: 10.5194/amt-2021-392. Abstract. Clouds warm the surface in the longwave (LW) and this warming effect can be quantified through the surface LW cloud radiative effect (CRE). The global surface LW CRE is estimated using long-term observations from space-based radiometers (2000–2021) but has some bias over continents and icy surfaces. It is also estimated globally using the combination of radar, lidar and space-based radiometer over the 5–year period ending in 2011. To develop a more reliable long time series of surface LW CRE over continental and icy surfaces, we propose new estimates of the global surface LW CRE from space-based lidar observations. We show from 1D atmospheric column radiative transfer calculations, that surface LW CRE linearly decreases with increasing cloud altitude. These computations allow us to establish simple relationships between surface LW CRE, and five cloud properties that are well observed by the CALIPSO space-based lidar: opaque cloud cover and altitude, and thin cloud cover, altitude, and emissivity. We use these relationships to retrieve the surface LW CRE at global scale over the 2008–2020 time period (27 Wm−2). We evaluate this new surface LW CRE product by comparing it to existing satellite-derived products globally on instantaneous collocated data at footprint scale and on global averages, as well as to ground-based observations at specific locations. Our estimate appears to be an improvement over others as it appropriately capture the surface LW CRE annual variability over bright polar surfaces and it provides a dataset of more than 13 years long.
Arya, V. B.; Surendran, Sajani; Rajendran, KavirajanArya, V. B., S. Surendran, K. Rajendran, 2021: On the build-up of dust aerosols and possible indirect effect during Indian summer monsoon break spells using recent satellite observations of aerosols and cloud properties. Journal of Earth System Science, 130(1), 42. doi: 10.1007/s12040-020-01526-6. Association of higher (lower) rainfall with lower (higher) Aerosol Optical Depth (AOD) is consistent with the understanding that increased washout (build-up) and shorter (longer) life-time of aerosols occur in wetter (drier) conditions. Given the life-time of aerosols, it is imperative to examine how aerosols impact active/break (wetter/drier than normal) spells, prominent intraseasonal variability (ISV) of Indian summer monsoon (ISM), through their composite analysis using recent satellite observations of aerosols and cloud properties, circulation and rainfall. Dust aerosols can act as CCN and participate efficiently in cloud processes during active phase. During breaks, build-up of desert dust transported by prevalent circulation, is associated with lower cloud effective radius implying aerosols’ indirect effect where they can inhibit cloud growth in the presence of reduced moisture and decrease precipitation efficiency/rainfall. Correspondingly, correlation albeit small, between intraseasonal anomalies of AOD and rainfall is negative, when AOD leads rainfall by 3–5 days implying that indirect aerosols impact is effective during breaks, though it is not the dominant responsible factor. During breaks, lower shortwave flux at top of atmosphere hints at dust-induced semi-direct effect. As breaks are permanent features of ISM, incorporation of dust-induced feedbacks in models, is essential for improved ISV simulation and ISM prediction.
Attada, Raju; Kunchala, Ravi Kumar; Dasari, Hari Prasad; Sivareddy, Sanikommu; Yesubabu, Viswanadhapalli; Knio, Omar; Hoteit, IbrahimAttada, R., R. K. Kunchala, H. P. Dasari, S. Sivareddy, V. Yesubabu, O. Knio, I. Hoteit, 2021: Representation of Arabian Peninsula summer climate in a regional atmospheric model using spectral nudging. Theoretical and Applied Climatology, 145(1), 13-30. doi: 10.1007/s00704-021-03617-w. This study assesses the performance of the Weather Research and Forecasting (WRF) model in simulating the Arabian Peninsula summer climate for the period 2001–2016. The European Centre for Medium range Weather Forecast (ECMWF) reanalysis is downscaled using WRF without (CTRL) and with the Spectral Nudging (SPN) method. Our results suggest that the noticeable cold biases in surface temperatures (mean, minimum, and maximum) over the Arabian Peninsula in CTRL are significantly reduced in SPN. The seasonal patterns of surface pressure, cloud cover, lower and upper tropospheric circulation, and mid-tropospheric anticyclone are also simulated more realistically with SPN. The evaluation of mean vertical profiles of dynamical and thermo-dynamical features over the Arabian Peninsula further confirms the enhanced simulations with SPN with respect to CTRL. Though SPN captures better the observed evolution of rainfall compared to that of CTRL, it produces a positive rainfall bias over the Southwestern Arabian Peninsula. Stronger vertical motions associated with the local topography enhance the higher water vapor loading, condenses in the upper layers, and results in excess amount of rainfall in SPN. Furthermore, with SPN, WRF is further able to better simulate the synoptic features of heat waves. Overall, SPN enhances WRF simulation skill of the horizontal structures and vertical profiles of the Arabian Peninsula summer climate by enforcing a better balance between the small and large scale features and associated feedbacks.
Baba, YuyaBaba, Y., 2021: Improved intraseasonal variability in the initialization of SINTEX-F2 using a spectral cumulus parameterization. International Journal of Climatology, 41(15), 6690-6712. doi: 10.1002/joc.7220. A newly developed spectral cumulus parameterization (spectral scheme) was implemented in the Scale Interaction Experiment-Frontier version 2 (SINTEX-F2) seasonal prediction system to improve intraseasonal variability in the system initialization. A simple sea surface temperature (SST) nudging scheme using different SST data and restoring times was used to initialize the system, and the initialized atmosphere obtained from both the original convection scheme (Tiedtke scheme) and the new spectral scheme was evaluated against observational data. It was found that that climatology and variability simulated by the spectral scheme were comparable to those simulated by the original scheme. In addition, the intraseasonal variability represented by the Madden–Julian oscillation (MJO) was better simulated by the spectral scheme than the original scheme. An analysis of the structure of the organized convection revealed the successful simulation of low-level shallow convection before the peak of the organized convection by the spectral scheme when compared with the observation, a result lacking in the original scheme simulation. In addition to the positive qualitative results, a statistical and quantitative analysis showed that the spectral scheme captured the MJO-related variability better than the original scheme. In conclusion, the prediction system using the spectral scheme is expected to improve seasonal predictions for seasonal variability whose evolution is affected by intraseasonal variations. atmosphere; convection; tropics; climate; general circulation model experiments; seasonal prediction
Bai, Jianhui; Zong, XuemeiBai, J., X. Zong, 2021: Global Solar Radiation Transfer and Its Loss in the Atmosphere. Applied Sciences, 11(6), 2651. doi: 10.3390/app11062651. Based on the analysis of solar radiation and meteorological parameters measured at a subtropical forest in China during 2013–2016, a new empirical model of global solar irradiance has been developed. It can calculate global solar irradiance at the ground and at the top of the atmosphere (TOA); both are in agreement with the observations. This model is used to calculate the extinction of global solar irradiance in the atmosphere and the contributions from absorbing and scattering substances. The loss of global solar irradiance is dominated by absorbing and absorbing substances. The results show clear seasonal and interannual variations during the observation period. Sensitivity analysis indicates that global solar irradiance is more sensitive to changes in scattering, quantified by the S/G factor (S and G are diffuse and global solar radiation, respectively), than to changes in absorption. The relationships between the extinction factor (AF) of G and S/G and between the AF and the aerosol optical depth (AOD) are determined and used to estimate S/G and the AOD from the measured AF. This empirical model is applied to calculate the albedos at the TOA and the ground. This empirical model is useful to study global solar radiation and the energy–atmosphere interactions. climate; aerosol optical depth; absorbing and scattering factors; global solar radiation; OH radicals
Balaguru, Karthik; Roekel, Luke P. Van; Leung, L. Ruby; Veneziani, MilenaBalaguru, K., L. P. V. Roekel, L. R. Leung, M. Veneziani, 2021: Subtropical Eastern North Pacific SST Bias in Earth System Models. Journal of Geophysical Research: Oceans, 126(8), e2021JC017359. doi: 10.1029/2021JC017359. This study systematically evaluates the warm sea surface temperature (SST) bias in the Subtropical Eastern North Pacific, a problem plaguing most Coupled Model Intercomparison Project Phase 6 models, using the Energy Exascale Earth System Model version 1 (E3SM). In the model at its standard resolution (1° atmosphere, 30–60 km ocean), the SST bias, exceeding several degrees, is mainly concentrated along the coast between 25°N and 40°N. In the high-resolution (0.25° atmosphere, 18–6 km ocean) version of the model, the nearshore SST bias improves considerably with a better representation of coastal upwelling. However, the offshore SST bias, approximately centered at 125°W and 25°N, is relatively stronger in the high-resolution version. To better understand the offshore warm bias in the model, a mixed-layer heat budget analysis is performed. While errors in surface radiative fluxes occur at both resolutions, positive biases in horizontal heat advection also play a role in the SST bias at high-resolution. Analysis of HighResMIP models indicates that the shift in the location of the prominent SST bias from nearshore to offshore with an increase in model spatial resolution, is not native to E3SM alone. CMIP6; coupled climate models; Eastern Pacific; large-scale circulation; mixed-layer heat budget; SST biases
Benjamin, Stanley G.; James, Eric P.; Hu, Ming; Alexander, Curtis R.; Ladwig, Therese T.; Brown, John M.; Weygandt, Stephen S.; Turner, David D.; Minnis, Patrick; Smith, William L.; Heidinger, Andrew K.Benjamin, S. G., E. P. James, M. Hu, C. R. Alexander, T. T. Ladwig, J. M. Brown, S. S. Weygandt, D. D. Turner, P. Minnis, W. L. Smith, A. K. Heidinger, 2021: Stratiform Cloud-Hydrometeor Assimilation for HRRR and RAP Model Short-Range Weather Prediction. Mon. Wea. Rev., 149(8), 2673-2694. doi: 10.1175/MWR-D-20-0319.1. AbstractAccurate cloud and precipitation forecasts are a fundamental component of short-range data assimilation/model prediction systems such as the NOAA 3-km High-Resolution Rapid Refresh (HRRR) or the 13-km Rapid Refresh (RAP). To reduce cloud and precipitation spinup problems, a nonvariational assimilation technique for stratiform clouds was developed within the Gridpoint Statistical Interpolation (GSI) data assimilation system. One goal of this technique is retention of observed stratiform cloudy and clear 3D volumes into the subsequent model forecast. The cloud observations used include cloud-top data from satellite brightness temperatures, surface-based ceilometer data, and surface visibility. Quality control, expansion into spatial information content, and forward operators are described for each observation type. The projection of data from these observation types into an observation-based cloud-information 3D gridded field is accomplished via identification of cloudy, clear, and cloud-unknown 3D volumes. Updating of forecast background fields is accomplished through clearing and building of cloud water and cloud ice with associated modifications to water vapor and temperature. Impact of the cloud assimilation on short-range forecasts is assessed with a set of retrospective experiments in warm and cold seasons using the RAPv5 model. Short-range (1–9 h) forecast skill is improved in both seasons for cloud ceiling and visibility and for 2-m temperature in daytime and with mixed results for other measures. Two modifications were introduced and tested with success: use of prognostic subgrid-scale cloud fraction to condition cloud building (in response to a high bias) and removal of a WRF-based rebalancing.
Bhatt, Rajendra; Doelling, David R.; Coddington, Odele; Scarino, Benjamin; Gopalan, Arun; Haney, ConorBhatt, R., D. R. Doelling, O. Coddington, B. Scarino, A. Gopalan, C. Haney, 2021: Quantifying the Impact of Solar Spectra on the Inter-Calibration of Satellite Instruments. Remote Sensing, 13(8), 1438. doi: 10.3390/rs13081438. In satellite-based remote sensing applications, the conversion of the sensor recorded top-of-atmosphere reflectance to radiance, or vice-versa, is carried out using a reference spectral solar irradiance (SSI) dataset. The choice of reference SSI spectrum has consistently changed over the past four decades with the increasing availability of more accurate SSI measurements with greater spectral coverage. Considerable differences (up to 15% at certain wavelengths) exist between the numerous SSI spectra that are currently being used in satellite ground processing systems. The aim of this study is to quantify the absolute differences between the most commonly used SSI datasets and investigate their impact in satellite inter-calibration and environmental retrievals. It was noted that if analogous SNPP and NOAA-20 VIIRS channel reflectances were perfectly inter-calibrated, the derived channel radiances can still differ by up to 3% due to the utilization of differing SSI datasets by the two VIIRS instruments. This paper also highlights a TSIS-1 SIM-based Hybrid Solar Reference Spectrum (HSRS) with an unprecedented absolute accuracy of 0.3% between 460 and 2365 nm, and recommends that the remote sensing community use it as a common reference SSI in satellite retrievals. calibration; solar spectra; VIIRS; solar constant; TSIS-1 SIM
Biagio, C. Di; Pelon, J.; Blanchard, Y.; Loyer, L.; Hudson, S. R.; Walden, V. P.; Raut, J.-C.; Kato, S.; Mariage, V.; Granskog, M. A.Biagio, C. D., J. Pelon, Y. Blanchard, L. Loyer, S. R. Hudson, V. P. Walden, J. Raut, S. Kato, V. Mariage, M. A. Granskog, 2021: Towards a better surface radiation budget analysis over sea ice in the high Arctic Ocean: a comparative study between satellite, reanalysis, and local‒scale observations. Journal of Geophysical Research: Atmospheres, (In press). doi: https://doi.org/10.1029/2020JD032555. AbstractReanalysis datasets from atmospheric models and satellite products are often used for Arctic surface shortwave (SW) and longwave (LW) radiative budget analyses, but they suffer from limitations and require validation against local‒scale observations. These are rare in the high Arctic, especially for longer periods that include seasonal transitions. In this study, radiation and meteorological observations acquired during the Norwegian Young Sea Ice Cruise (N‒ICE2015) campaign over sea ice north of Svalbard (80‒83°N, 5‒25°E) from January to June 2015, cloud lidar observations from the Ice‒Atmosphere‒Ocean Observing System (IAOOS) and the Cloud and Aerosol Lidar with Orthogonal Polarization (CALIOP) are compared to daily and monthly satellite retrievals from the Clouds and the Earth's Radiant Energy System (CERES) and ERA‒Interim and ERA5 reanalyses. Results indicate that surface temperature is a significant driver for winter LW radiation biases in both satellite and reanalysis data, along with cloud optical depth in CERES. In May the SW and LW downwelling irradiances are close to observations and cloud properties are well captured (except for ERA-Interim), while SW upward irradiances are biased low due to surface albedo biases in all datasets. Net SW and LW radiation biases are comparable (⁓20‒30 Wm‒2) but opposite in sign for ERA‒Interim and CERES in May, which allows for error compensation. Biases reduce to ±10 Wm‒2 in ERA5. In June downward LW remains biased low (8‒10 Wm‒2) in all datasets suggesting unsettled cloud representation issues. Surface albedo always differs by more than 0.1 between datasets, leading to significant SW and total flux differences.This article is protected by copyright. All rights reserved. clouds; surface albedo; sea ice; temperature; reanalysis; radiation; satellite data; high Arctic Ocean
Blanchard, Yann; Pelon, Jacques; Cox, Christopher J.; Delanoë, Julien; Eloranta, Edwin W.; Uttal, TanielBlanchard, Y., J. Pelon, C. J. Cox, J. Delanoë, E. W. Eloranta, T. Uttal, 2021: Comparison of TOA and BOA LW Radiation Fluxes Inferred From Ground-Based Sensors, A-Train Satellite Observations and ERA Reanalyzes at the High Arctic Station Eureka Over the 2002–2020 Period. Journal of Geophysical Research: Atmospheres, 126(11), e2020JD033615. doi: 10.1029/2020JD033615. This study focuses on the accuracy of longwave radiation flux retrievals at the top and bottom of the atmosphere at Eureka station, Canada, in the high Arctic. We report comparisons between seven products derived from (a) calculations based on a combination of ground-based and space-based lidar and radar observations, (b) standard radiometric observations from the CERES sensor, (c) direct observations at the surface from a broadband radiation station, and (d) the ERA-Interim and ERA5 reanalyzes. Statistical, independent analyses are first performed to look at recurring bias and trends in fluxes at Top and Bottom of the Atmosphere (TOA, BOA). The analysis is further refined by comparing fluxes derived from coincident observations decomposed by scene types. Results show that radiative transfer calculations using ground-based lidar-radar profiles derived at Eureka agree well with TOA LW fluxes observed by CERES and with BOA LW fluxes reference. CloudSat-CALIPSO also shows good agreement with calculations from ground-based sensor observations, with a relatively small bias. This bias is shown to be largely due to low and thick cloud occurrences that the satellites are insensitive to owing to attenuation from clouds above and surface clutter. These conditions of opaque low clouds, cause an even more pronounced bias for CERES BOA flux calculation in winter, due to the deficit of low clouds identified by MODIS. ERA-I and ERA5 fluxes behave differently, the large positive bias observed with ERA-I is much reduced in ERA5. ERA5 is closer to reference observations due to better behavior of low and mid-level clouds and surface temperature. clouds; radiation; satellite data; intercomparison; high Arctic; re-analyses
Blossey, Peter N.; Bretherton, Christopher S.; Mohrmann, JohannesBlossey, P. N., C. S. Bretherton, J. Mohrmann, 2021: Simulating Observed Cloud Transitions in the Northeast Pacific during CSET. Mon. Wea. Rev., 149(8), 2633-2658. doi: 10.1175/MWR-D-20-0328.1. AbstractThe goal of this study is to challenge a large-eddy simulation model with a range of observations from a modern field campaign and to develop case studies useful to other modelers. The 2015 Cloud System Evolution in the Trades (CSET) field campaign provided a wealth of in situ and remote sensing observations of subtropical cloud transitions in the summertime northeast Pacific. Two Lagrangian case studies based on these observations are used to validate the thermodynamic, radiative, and microphysical properties of large-eddy simulations (LES) of the stratocumulus to cumulus transition. The two cases contrast a relatively fast cloud transition in a clean, initially well-mixed boundary layer versus a slower transition in an initially decoupled boundary layer with higher aerosol concentrations and stronger mean subsidence. For each case, simulations of two neighboring trajectories sample mesoscale variability and the coherence of the transition in adjacent air masses. In both cases, LES broadly reproduce satellite and aircraft observations of the transition. Simulations of the first case match observations more closely than for the second case, where simulations underestimate cloud cover early in the simulations and overestimate cloud top height later. For the first case, simulated cloud fraction and liquid water path increase if a larger cloud droplet number concentration is prescribed. In the second case, precipitation onset and inversion cloud breakup occur earlier when the LES domain is chosen to be large enough to support strong mesoscale organization.
Bloxam, Kevin; Huang, YiBloxam, K., Y. Huang, 2021: Radiative Relaxation Time Scales Quantified from Sudden Stratospheric Warmings. Journal of Atmospheric Sciences, 78(1), 269-286. doi: 10.1175/JAS-D-20-0015.1. AbstractSudden stratospheric warmings (SSWs) are impressive events that occur in the winter hemisphere’s polar stratosphere and are capable of producing temperature anomalies upward of +50 K within a matter of days. While much work has been dedicated toward determining how SSWs occur and their ability to interact with the underlying troposphere, one underexplored aspect is the role of radiation, especially during the recovery phase of SSWs. Using a radiative transfer model and a heating rate analysis for distinct layers of the stratosphere averaged over the 60°–90°N polar region, this paper accounts for the radiative contribution to the removal of the anomalous temperatures associated with SSWs. In total 17 events are investigated over the 1979–2016 period. This paper reveals that in the absence of dynamical heating following major SSWs, longwave radiative cooling dominates and often results in a strong negative temperature anomaly. The polar winter stratospheric temperature change driven by the radiative cooling is characterized by an exponential decay of temperature with an increasing e-folding time of 5.7 ± 2.0 to 14.6 ± 4.4 days from the upper to middle stratosphere. The variability of the radiative relaxation rates among the SSWs was determined to be most impacted by the initial temperature of the stratosphere and the combined dynamic and solar heating rates following the onset of the events. We also found that trace-gas anomalies have little impact on the radiative heating rates and the temperature evolution during the SSWs in the mid- to upper stratosphere.
Bogenschutz, Peter A.; Yamaguchi, Takanobu; Lee, Hsiang-HeBogenschutz, P. A., T. Yamaguchi, H. Lee, 2021: The Energy Exascale Earth System Model Simulations With High Vertical Resolution in the Lower Troposphere. Journal of Advances in Modeling Earth Systems, 13(6), e2020MS002239. doi: 10.1029/2020MS002239. General circulation models (GCMs) are typically run with coarse vertical resolution. For example, the Energy Exascale Earth System Model (E3SM) has a vertical resolution of about 200 m in the boundary layer, which is far too coarse to resolve sharp gradients often found in the thermodynamic fields capping subtropical marine stratocumulus. In this article, we present a series of multiyear atmosphere only simulations of E3SM version 1 where we progressively increase the vertical resolution in the lower troposphere to scales approaching those often used in large eddy simulation (LES). We report marginal impacts in regards to the simulation of boundary layer clouds when vertical resolution is moderately increased, yet find significant positive impacts when the vertical resolution approaches that typically used in LES (∼10 m). In these experiments, there is a marked change in the simulated turbulence and thermodynamics which leads to more abundant marine stratocumulus. However, these simulations are burdened with excessive computational cost. They are also subject to degradations in overall climate metrics due to time step sensitivities and because some processes and parameterizations are sensitive to changes in the vertical resolution.
Boudala, Faisal S.; Milbrandt, Jason A.Boudala, F. S., J. A. Milbrandt, 2021: Evaluations of the Climatologies of Three Latest Cloud Satellite Products Based on Passive Sensors (ISCCP-H, Two CERES) against the CALIPSO-GOCCP. Remote Sensing, 13(24), 5150. doi: 10.3390/rs13245150. In this study, the climatologies of three different satellite cloud products, all based on passive sensors (CERES Edition 4.1 [EBAF4.1 and SYN4.1] and ISCCP–H), were evaluated against the CALIPSO-GOCCP (GOCCP) data, which are based on active sensors and, hence, were treated as the reference. Based on monthly averaged data (ocean + land), the passive sensors underestimated the total cloud cover (TCC) at lower (TCC < 50%), but, overall, they correlated well with the GOCCP data (r = 0.97). Over land, the passive sensors underestimated the TCC, with a mean difference (MD) of −2.6%, followed by the EBAF4.1 and ISCCP-H data with a MD of −2.0%. Over the ocean, the CERES-based products overestimated the TCC, but the SYN4.1 agreed better with the GOCCP data. The ISCCP-H data on average underestimated the TCC both over oceanic and continental regions. The annual mean TCC distribution over the globe revealed that the passive sensors generally underestimated the TCC over continental dry regions in northern Africa and southeastern South America as compared to the GOCCP, particularly over the summer hemisphere. The CERES datasets overestimated the TCC over the Pacific Islands between the Indian and eastern Pacific Oceans, particularly during the winter hemisphere. The ISCCP-H data also underestimated the TCC, particularly over the southern hemisphere near 60° S where the other datasets showed a significantly enhanced TCC. The ISCCP data also showed less TCC when compared against the GOCCP data over the tropical regions, particularly over the southern Pacific and Atlantic Oceans near the equator and also over the polar regions where the satellite retrieval using the passive sensors was generally much more challenging. The calculated global mean root meant square deviation value for the ISCCP-H data was 6%, a factor of 2 higher than the CERES datasets. Based on these results, overall, the EBAF4.1 agreed better with the GOCCP data. CERES; satellite remote sensing; ISCCP; CALIPSO; active and passive sensors; cloud cover 2
Bouniol, D.; Guichard, F.; Barbier, J.; Couvreux, F.; Roehrig, R.Bouniol, D., F. Guichard, J. Barbier, F. Couvreux, R. Roehrig, 2021: Sahelian Heat Wave Characterization From Observational Data Sets. Journal of Geophysical Research: Atmospheres, 126(11), e2020JD034465. doi: 10.1029/2020JD034465. This paper makes use of spaceborne observational data sets in order to characterize radiative processes involved in spring time heat waves in the Sahel. Spring corresponds to the hottest period of the year, with a high aerosol load, a gradual moistening, and the presence of clouds contributing to greenhouse effect. Heat waves are defined as synoptic events that have a large spatial extent and a duration longer than 3 days. Two types of heat waves are studied: daytime heat waves, detected with the daily maximum temperature and nighttime heat waves, detected with the daily minimum temperature. Daytime heat waves correspond to situations where cloud optical thickness is lower than the climatology and a large number of these situations are also associated with a lower aerosol load and a drier atmosphere. Nighttime heat waves correspond to a moister atmosphere compared to the climatology. In a large fraction of them, an increase in aerosol loading is also observed. This study, only based on observational data sets, highlights the subtle but different radiative balance at play in both types of events. radiation budget; observations; West Africa; heat wave
Caldwell, P. M.; Terai, C. R.; Hillman, B.; Keen, N. D.; Bogenschutz, P.; Lin, W.; Beydoun, H.; Taylor, M.; Bertagna, L.; Bradley, A. M.; Clevenger, T. C.; Donahue, A. S.; Eldred, C.; Foucar, J.; Golaz, J.-C.; Guba, O.; Jacob, R.; Johnson, J.; Krishna, J.; Liu, W.; Pressel, K.; Salinger, A. G.; Singh, B.; Steyer, A.; Ullrich, P.; Wu, D.; Yuan, X.; Shpund, J.; Ma, H.-Y.; Zender, C. S.Caldwell, P. M., C. R. Terai, B. Hillman, N. D. Keen, P. Bogenschutz, W. Lin, H. Beydoun, M. Taylor, L. Bertagna, A. M. Bradley, T. C. Clevenger, A. S. Donahue, C. Eldred, J. Foucar, J. Golaz, O. Guba, R. Jacob, J. Johnson, J. Krishna, W. Liu, K. Pressel, A. G. Salinger, B. Singh, A. Steyer, P. Ullrich, D. Wu, X. Yuan, J. Shpund, H. Ma, C. S. Zender, 2021: Convection-Permitting Simulations With the E3SM Global Atmosphere Model. Journal of Advances in Modeling Earth Systems, 13(11), e2021MS002544. doi: 10.1029/2021MS002544. This paper describes the first implementation of the Δx = 3.25 km version of the Energy Exascale Earth System Model (E3SM) global atmosphere model and its behavior in a 40-day prescribed-sea-surface-temperature simulation (January 20 through February 28, 2020). This simulation was performed as part of the DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) Phase 2 model intercomparison. Effective resolution is found to be the horizontal dynamics grid resolution despite using a coarser grid for physical parameterizations. Despite this new model being in an immature and untuned state, moving to 3.25 km grid spacing solves several long-standing problems with the E3SM model. In particular, Amazon precipitation is much more realistic, the frequency of light and heavy precipitation is improved, agreement between the simulated and observed diurnal cycle of tropical precipitation is excellent, and the vertical structure of tropical convection and coastal stratocumulus look good. In addition, the new model is able to capture the frequency and structure of important weather events (e.g., tropical cyclones, extratropical cyclones including atmospheric rivers, and cold air outbreaks). Interestingly, this model does not get rid of the erroneous southern branch of the intertropical convergence zone nor the tendency for strongest convection to occur over the Maritime Continent rather than the West Pacific, both of which are classic climate model biases. Several other problems with the simulation are identified, underscoring the fact that this model is a work in progress. general circulation model; E3SM; cloud resolving model; convection permitting model; storm resolving model
Campbell, James R.; Dolinar, Erica K.; Lolli, Simone; Fochesatto, Gilberto J.; Gu, Yu; Lewis, Jasper R.; Marquis, Jared W.; McHardy, Theodore M.; Ryglicki, David R.; Welton, Ellsworth J.Campbell, J. R., E. K. Dolinar, S. Lolli, G. J. Fochesatto, Y. Gu, J. R. Lewis, J. W. Marquis, T. M. McHardy, D. R. Ryglicki, E. J. Welton, 2021: Cirrus Cloud Top-of-the-Atmosphere Net Daytime Forcing in the Alaskan Subarctic from Ground-Based MPLNET Monitoring. J. Appl. Meteor. Climatol., (In Press). doi: 10.1175/JAMC-D-20-0077.1. AbstractCirrus cloud daytime top-of-the-atmosphere radiative forcing (TOA CRF) is estimated for a two-year NASA Micro-Pulse Lidar Network (532 nm; MPLNET) dataset collected at Fairbanks, Alaska. Two-year averaged daytime TOA CRF is estimated at between -1.08 and 0.78 W·m-2 (-0.49 to 1.10 W·m-2 in 2017, and -1.67 to 0.47 W·m-2 in 2018). This subarctic study completes a now trilogy of MPLNET ground-based cloud forcing investigations, following midlatitude and tropical studies by Campbell et al. (2016; C16) at Greenbelt, Maryland and Lolli et al. (2017) at Singapore. C16 hypothesize a global meridional daytime TOA CRF gradient that begins positive at the equator (2.20 – 2.59 W·m-2 over land and -0.46 – 0.42 W·m-2 over ocean at Singapore), becomes neutral in the midlatitudes (0.03 – 0.27 W·m-2 over land in Maryland) and turns negative moving poleward. This study does not completely confirm C16, as values are not found as exclusively negative. Evidence in historical reanalysis data suggests that daytime cirrus forcing in and around the subarctic likely once was exclusively negative. Increasing tropopause heights, inducing higher and colder cirrus, have likely increased regional forcing over the last forty years. We hypothesize that subarctic inter-annual cloud variability is likely a considerable influence on global cirrus cloud forcing sensitivity, given the irregularity of polar versus midlatitude synoptic weather intrusions. This study and hypothesis lays basis for an extrapolation of these MPLNET experiments to satellite-based lidar cirrus cloud datasets.
Ceppi, Paulo; Fueglistaler, StephanCeppi, P., S. Fueglistaler, 2021: The El Niño–Southern Oscillation Pattern Effect. Geophysical Research Letters, 48(21), e2021GL095261. doi: 10.1029/2021GL095261. El Niño–Southern Oscillation (ENSO) variability is accompanied by out-of-phase anomalies in the top-of-atmosphere tropical radiation budget, with anomalous downward flux (i.e., net radiative heating) before El Niño and anomalous upward flux thereafter (and vice versa for La Niña). Here, we show that these radiative anomalies result mainly from a sea surface temperature (SST) “pattern effect,” mediated by changes in tropical-mean tropospheric stability. These stability changes are caused by SST anomalies migrating from climatologically cool to warm regions over the ENSO cycle. Our results are suggestive of a two-way coupling between SST variability and radiation, where ENSO-induced radiative changes may in turn feed back onto SST during ENSO. clouds; climate change; radiation budget; ENSO; climate feedbacks; climate variability
Ceppi, Paulo; Nowack, PeerCeppi, P., P. Nowack, 2021: Observational evidence that cloud feedback amplifies global warming. Proceedings of the National Academy of Sciences, 118(30). doi: 10.1073/pnas.2026290118. Global warming drives changes in Earth’s cloud cover, which, in turn, may amplify or dampen climate change. This “cloud feedback” is the single most important cause of uncertainty in Equilibrium Climate Sensitivity (ECS)—the equilibrium global warming following a doubling of atmospheric carbon dioxide. Using data from Earth observations and climate model simulations, we here develop a statistical learning analysis of how clouds respond to changes in the environment. We show that global cloud feedback is dominated by the sensitivity of clouds to surface temperature and tropospheric stability. Considering changes in just these two factors, we are able to constrain global cloud feedback to 0.43 ± 0.35 W⋅m−2⋅K−1 (90% confidence), implying a robustly amplifying effect of clouds on global warming and only a 0.5% chance of ECS below 2 K. We thus anticipate that our approach will enable tighter constraints on climate change projections, including its manifold socioeconomic and ecological impacts. clouds; climate change; climate feedbacks; climate modeling; climate sensitivity
Cerasoli, Sara; Yin, Jun; Porporato, AmilcareCerasoli, S., J. Yin, A. Porporato, 2021: Cloud cooling effects of afforestation and reforestation at midlatitudes. Proceedings of the National Academy of Sciences, 118(33). doi: 10.1073/pnas.2026241118. Because of the large carbon sequestration potential, reforestation and afforestation (R&A) are among the most prominent natural climate solutions. However, while their effectiveness is well established for wet tropics, it is often argued that R&A are less advantageous or even detrimental at higher latitudes, where the reduction of forest albedo (the amount of reflected solar radiation by a surface) tends to nullify or even overcome the carbon benefits. Here, we carefully analyze the situation for R&A at midlatitudes, where the warming effects due to vegetation albedo are regarded to be almost balanced by the cooling effects from an increased carbon storage. Using both satellite data and atmospheric boundary-layer models, we show that by including cloud–albedo effects due to land–atmosphere interactions, the R&A cooling at midlatitudes becomes prevalent. This points to a much greater potential of R&A for wet temperate regions than previously considered. cloud feedback; afforestation; carbon mitigation
Cesana, Grégory V.; Del Genio, Anthony D.Cesana, G. V., A. D. Del Genio, 2021: Observational constraint on cloud feedbacks suggests moderate climate sensitivity. Nature Climate Change, 11(3), 213-218. doi: 10.1038/s41558-020-00970-y. Global climate models predict warming in response to increasing GHG concentrations, partly due to decreased tropical low-level cloud cover and reflectance. We use satellite observations that discriminate stratocumulus from shallow cumulus clouds to separately evaluate their sensitivity to warming and constrain the tropical contribution to low-cloud feedback. We find an observationally inferred low-level cloud feedback two times smaller than a previous estimate. Shallow cumulus clouds are insensitive to warming, whereas global climate models exhibit a large positive cloud feedback in shallow cumulus regions. In contrast, stratocumulus clouds show sensitivity to warming and the tropical inversion layer strength, controlled by the tropical Pacific sea surface temperature gradient. Models fail to reproduce the historical sea surface temperature gradient trends and therefore changes in inversion strength, generating an overestimate of the positive stratocumulus cloud feedback. Continued weak east Pacific warming would therefore produce a weaker low-cloud feedback and imply a more moderate climate sensitivity (3.47 ± 0.33 K) than many models predict.
Chakraborty, T. C.; Lee, XuhuiChakraborty, T. C., X. Lee, 2021: Using supervised learning to develop BaRAD, a 40-year monthly bias-adjusted global gridded radiation dataset. Scientific Data, 8(1), 238. doi: 10.1038/s41597-021-01016-4. Diffuse solar radiation is an important, but understudied, component of the Earth’s surface radiation budget, with most global climate models not archiving this variable and a dearth of ground-based observations. Here, we describe the development of a global 40-year (1980–2019) monthly database of total shortwave radiation, including its diffuse and direct beam components, called BaRAD (Bias-adjusted RADiation dataset). The dataset is based on a random forest algorithm trained using Global Energy Balance Archive (GEBA) observations and applied to the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) dataset at the native MERRA-2 resolution (0.5° by 0.625°). The dataset preserves seasonal, latitudinal, and long-term trends in the MERRA-2 data, but with reduced biases than MERRA-2. The mean bias error is close to 0 (root mean square error = 10.1 W m−2) for diffuse radiation and −0.2 W m−2 (root mean square error = 19.2 W m−2) for the total incoming shortwave radiation at the surface. Studies on atmosphere-biosphere interactions, especially those on the diffuse radiation fertilization effect, can benefit from this dataset. Atmospheric science; Hydrology
Chakraborty, T.; Lee, X.Chakraborty, T., X. Lee, 2021: Large Differences in Diffuse Solar Radiation Among Current-Generation Reanalysis and Satellite-Derived Products. J. Climate, -1(aop), 1-52. doi: 10.1175/JCLI-D-20-0979.1. AbstractThough the partitioning of shortwave radiation (K↓) at the surface into its diffuse (K↓,d) and direct beam (K↓,b) components is relevant for, among other things, the terrestrial energy and carbon budgets, there is a dearth of large-scale comparisons of this partitioning across reanalysis and satellite-derived products. Here we evaluate K↓, K↓,d, and K↓,b, as well as the diffuse fraction (kd) of solar radiation in four current-generation reanalysis (NOAA-CIRES-DOE, NCEP/NCAR, MERRA-2, ERA5) datasets and one satellite-derived product (CERES) using ≈1400 site years of observations. Although the systematic positive biases in K↓ is consistent with previous studies, the biases in gridded K↓,d and K↓,b vary in direction and magnitude, both annually and across seasons. The inter-model variability in cloud cover strongly explains the biases in both K↓,d and K↓,b. Over Europe and China, the long-term (10-year plus) trends in K↓,d in the gridded products are noticeably differ from corresponding observations and the grid-averaged 35-year trends show an order of magnitude variability. In the MERRA-2 reanalysis, which includes both clouds and assimilated aerosols, the reduction in both clouds and aerosols reinforce each other to establish brightening trends over Europe, while the effect of increasing aerosols overwhelm the effect of decreasing cloud cover over China. The inter-model variability in kd seen here (0.27 to 0.50 from CERES to MERRA-2) suggests substantial differences in shortwave parameterization schemes and their inputs in climate models and can contribute to inter-model variability in coupled simulations. Based on these results, we call for systematic evaluations of K↓,d and K↓,b in CMIP6 models.
Chang, Chiao-Wei; Chen, Wei-Ting; Chen, Yi-ChunChang, C., W. Chen, Y. Chen, 2021: Susceptibility of East Asian Marine Warm Clouds to Aerosols in Winter and Spring from Co-Located A-Train Satellite Observations. Remote Sensing, 13(24), 5179. doi: 10.3390/rs13245179. We constructed the A-Train co-located aerosol and marine warm cloud data from 2006 to 2010 winter and spring over East Asia and investigated the sensitivities of single-layer warm cloud properties to aerosols under different precipitation statuses and environmental regimes. The near-surface stability (NSS), modulated by cold air on top of a warm surface, and the estimated inversion strength (EIS) controlled by the subsidence are critical environmental parameters affecting the marine warm cloud structure over East Asia and, thus, the aerosols–cloud interactions. Based on our analysis, precipitating clouds revealed higher cloud susceptibility to aerosols as compared to non-precipitating clouds. The cloud liquid water path (LWP) increased with aerosols for precipitating clouds, yet decreased with aerosols for non-precipitating clouds, consistent with previous studies. For precipitating clouds, the cloud LWP and albedo increased more under higher NSS as unstable air promotes more moisture flux from the ocean. Under stronger EIS, the cloud albedo response to aerosols was lower than that under weaker EIS, indicating that stronger subsidence weakens the cloud susceptibility due to more entrainment drying. Our study suggests that the critical environmental factors governing the aerosol–cloud interactions may vary for different oceanic regions, depending on the thermodynamic conditions. aerosol–cloud interaction; cloud susceptibility; co-located data
Chao, Li-Wei; Dessler, Andrew E.Chao, L., A. E. Dessler, 2021: An Assessment of Climate Feedbacks in Observations and Climate Models Using Different Energy Balance Frameworks. J. Climate, 34(24), 9763-9773. doi: 10.1175/JCLI-D-21-0226.1. Abstract This study evaluates the performance of models from phase 5 and phase 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6) by comparing feedbacks in models with those inferred from observations. Overall, we find no systematic disagreements between the feedbacks in the model ensembles and feedbacks inferred from observations, although there is a wide range in the ability of individual models to reproduce the observations. In particular, 40 of 52 models have best estimates that fall within the uncertainty of the observed total feedback. We quantify two sources of uncertainty in the model ensembles: 1) the structural difference, due to the differences in model parameterizations, and 2) the unforced pattern effect, due to unforced variability, and find that both are important when comparing with an 18-yr observational dataset. We perform the comparison using two energy balance frameworks: the traditional energy balance framework, in which it is assumed that changes in energy balance are controlled by changes in global average surface temperatures, and an alternative framework that assumes the changes in energy balance are controlled by tropical atmospheric temperatures. We find that the alternative framework provides a more robust way of comparing the models with observations, with both smaller structural differences and smaller unforced pattern effect. However, when considering the relation of feedbacks in response to interannual variability and long-term warming, the traditional framework has advantages. There are no great differences between the CMIP5 and CMIP6 ensembles’ ability to reproduce the observed feedbacks.
Chen, Hong; Schmidt, Sebastian; King, Michael D.; Wind, Galina; Bucholtz, Anthony; Reid, Elizabeth A.; Segal-Rozenhaimer, Michal; Smith, William L.; Taylor, Patrick C.; Kato, Seiji; Pilewskie, PeterChen, H., S. Schmidt, M. D. King, G. Wind, A. Bucholtz, E. A. Reid, M. Segal-Rozenhaimer, W. L. Smith, P. C. Taylor, S. Kato, P. Pilewskie, 2021: The effect of low-level thin arctic clouds on shortwave irradiance: evaluation of estimates from spaceborne passive imagery with aircraft observations. Atmospheric Measurement Techniques, 14(4), 2673-2697. doi: 10.5194/amt-14-2673-2021. Abstract. Cloud optical properties such as optical thickness along with surface albedo are important inputs for deriving the shortwave radiative effects of clouds from spaceborne remote sensing. Owing to insufficient knowledge about the snow or ice surface in the Arctic, cloud detection and the retrieval products derived from passive remote sensing, such as from the Moderate Resolution Imaging Spectroradiometer (MODIS), are difficult to obtain with adequate accuracy – especially for low-level thin clouds, which are ubiquitous in the Arctic. This study aims at evaluating the spectral and broadband irradiance calculated from MODIS-derived cloud properties in the Arctic using aircraft measurements collected during the Arctic Radiation-IceBridge Sea and Ice Experiment (ARISE), specifically using the upwelling and downwelling shortwave spectral and broadband irradiance measured by the Solar Spectral Flux Radiometer (SSFR) and the BroadBand Radiometer system (BBR). This starts with the derivation of surface albedo from SSFR and BBR, accounting for the heterogeneous surface in the marginal ice zone (MIZ) with aircraft camera imagery, followed by subsequent intercomparisons of irradiance measurements and radiative transfer calculations in the presence of thin clouds. It ends with an attribution of any biases we found to causes, based on the spectral dependence and the variations in the measured and calculated irradiance along the flight track. The spectral surface albedo derived from the airborne radiometers is consistent with prior ground-based and airborne measurements and adequately represents the surface variability for the study region and time period. Somewhat surprisingly, the primary error in MODIS-derived irradiance fields for this study stems from undetected clouds, rather than from the retrieved cloud properties. In our case study, about 27 % of clouds remained undetected, which is attributable to clouds with an optical thickness of less than 0.5. We conclude that passive imagery has the potential to accurately predict shortwave irradiances in the region if the detection of thin clouds is improved. Of at least equal importance, however, is the need for an operational imagery-based surface albedo product for the polar regions that adequately captures its temporal, spatial, and spectral variability to estimate cloud radiative effects from spaceborne remote sensing.
Chen, Jiang; Zhu, Weining; Yu, QianChen, J., W. Zhu, Q. Yu, 2021: Estimating half-hourly solar radiation over the Continental United States using GOES-16 data with iterative random forest. Renewable Energy, 178, 916-929. doi: 10.1016/j.renene.2021.06.129. To reduce carbon emissions, using more solar energy is a feasible solution. Many meteorological-based models can estimate global downward solar radiation (DSR), but they are with limited applications due to the point-based estimation and low temporal resolution. Satellite remote sensing-based models can estimate DSR with better spatial coverage. However, most previous models are restricted to estimate clear-sky or monthly scale DSR at several sites, limiting the solar energy monitoring of nationwide scale. In this study, using high spatiotemporal resolution Geostationary Operational Environmental Satellites (GOES)-16 satellite data, an iterative random forest (RF) model was developed to estimate and map half-hourly DSR at 1-km spatial resolution over the Continental United States (CONUS). The results show that the iterative RF model performed better than multiple linear regression (MLR) and traditional RF models. The accuracy of estimating half-hourly DSR is that R2 = 0.95, root-mean-square-error (RMSE) = 66.92 W/m2, and mean-bias-error (MBE) = 0.06 W/m2. Half-hourly and daily DSR with spatial resolution 1-km over the CONUS were mapped. The GOES-16 estimated DSR showed the similar spatial patterns with the results from the Clouds and the Earth's Radiant Energy System (CERES) DSR product. This study demonstrated the potential of GOES-16 data for mapping DSR over the CONUS, and hence can be further used in solar energy related applications. Global solar radiation; Satellite remote sensing; Solar energy; Half-hourly; Iterative random forest
Chen, Shiliu; McColl, Kaighin A.; Berg, Alexis; Huang, YuefeiChen, S., K. A. McColl, A. Berg, Y. Huang, 2021: Surface Flux Equilibrium Estimates of Evapotranspiration at Large Spatial Scales. J. Hydrometeor., 22(4), 765-779. doi: 10.1175/JHM-D-20-0204.1. AbstractA recent theory proposes that inland continental regions are in a state of surface flux equilibrium (SFE), in which tight coupling between the land and atmosphere allow estimation of the Bowen ratio at daily to monthly time scales solely from atmospheric measurements, without calibration, even when the land surface strongly constrains the surface energy budget. However, since the theory has only been evaluated at quasi-point spatial scales using eddy covariance measurements with limited global coverage, it is unclear if it is applicable to the larger spatial scales relevant to studies of global climate. In this study, SFE estimates of the Bowen ratio are combined with satellite observations of surface net radiation to obtain large-scale estimates of latent heat flux λE. When evaluated against multiyear mean annual λE obtained from catchment water balance estimates from 221 catchments across the United States, the resulting error statistics are comparable to those in the catchment water balance estimates themselves. The theory is then used to diagnostically estimate λE using historical simulations from 26 CMIP6 models. The resulting SFE estimates are typically at least as accurate as the CMIP6 model’s simulated λE, when compared with catchment water balance estimates. Globally, there is broad spatial and temporal agreement between CMIP6 model SFE estimates and the CMIP6 model’s simulated λE, although SFE likely overestimates λE in some arid regions. We conclude that SFE applies reasonably at large spatial scales relevant to climate studies, and is broadly reproduced in climate models.
Chen, Yao-Sheng; Yamaguchi, Takanobu; Bogenschutz, Peter A.; Feingold, GrahamChen, Y., T. Yamaguchi, P. A. Bogenschutz, G. Feingold, 2021: Model Evaluation and Intercomparison of Marine Warm Low Cloud Fractions With Neural Network Ensembles. Journal of Advances in Modeling Earth Systems, 13(11), e2021MS002625. doi: 10.1029/2021MS002625. Low cloud fractions (LCFs) and meteorological factors (MFs) over an oceanic region containing multiple cloud regimes are examined for three data sets: one Energy Exascale Earth System Model (E3SM) simulation with the default 72-layer vertical grid (E3SM72), another one with 8-times vertical resolution via the Framework for Improvement by Vertical Enhancement (E3SM8), and one with MFs from ERA5 reanalysis and LCFs from the CERES SSF product (ERA5-SSF). Neural networks (NNs) are trained to capture the relationship between MFs and LCF and to select the best-performing MF subsets for predicting LCF. NN ensembles are used to (a) confirm the performance of selected MF subsets, (b) to serve as proxy models for each data set to predict LCFs for MFs from all data sets, and (c) to classify MFs into those in shared and uniquely occupied MF subspaces. Overall, E3SM72 and E3SM8 have large fractions of MFs in shared MF subspace, but less so near the Californian and Peruvian stratocumulus decks. E3SM8 and ERA5 have small fractions of MFs in shared MF subspace but greater than E3SM72 and ERA5, especially in the Southeast Pacific. The differences in LCFs between three pairs of data sets are decomposed into those associated with the differences in the LCF-MF relationship and those involving different MFs. Given the same MFs, LCFs produced by E3SM8 are greater than those produced by E3SM72 but are still different from those in ERA5-SSF. In general, the shift in MFs dominates the difference in the LCFs. E3SM; shallow clouds; machine learning; cloud controlling factors; high resolution modeling
Ciesielski, Paul E.; Johnson, Richard H.; Tang, Shuaiqi; Zhang, Yunyan; Xie, ShaochengCiesielski, P. E., R. H. Johnson, S. Tang, Y. Zhang, S. Xie, 2021: Comparison of Conventional and Constrained Variational Methods for Computing Large-Scale Budgets and Forcing Fields. Journal of Geophysical Research: Atmospheres, 126(16), e2021JD035183. doi: 10.1029/2021JD035183. Analyses of atmospheric heat and moisture budgets serve as an effective tool to study convective characteristics over a region and to provide large-scale forcing fields for various modeling applications. This paper examines two popular methods for computing large-scale atmospheric budgets: the conventional budget method (CBM) using objectively gridded analyses based primarily on radiosonde data and the constrained variational analysis (CVA) approach which supplements vertical profiles of atmospheric fields with measurements at the top of the atmosphere and at the surface to conserve mass, water, energy, and momentum. Successful budget computations are dependent on accurate sampling and analyses of the thermodynamic state of the atmosphere and the divergence field associated with convection and the large-scale circulation that influences it. Utilizing analyses generated from data taken during Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign conducted over the central Indian Ocean from October to December 2011, we evaluate the merits of these budget approaches and examine their limitations. While many of the shortcomings of the CBM, in particular effects of sampling errors in sounding data, are effectively minimized with CVA, accurate large-scale diagnostics in CVA are dependent on reliable background fields and rainfall constraints. For the DYNAMO analyses examined, the operational model fields used as the CVA background state provided wind fields that accurately resolved the vertical structure of convection in the vicinity of Gan Island. However, biases in the model thermodynamic fields were somewhat amplified in CVA resulting in a convective environment much weaker than observed. DYNAMO; forcing fields; large-scale atmospheric budgets; limitations; methodologies; strengths
Coelho, Caio A. S.; de Souza, Dayana C.; Kubota, Paulo Y.; Costa, Simone M. S.; Menezes, Layrson; Guimarães, Bruno S.; Figueroa, Silvio N.; Bonatti, José P.; Cavalcanti, Iracema F. A.; Sampaio, Gilvan; Klingaman, Nicholas P.; Baker, Jessica C. A.Coelho, C. A. S., D. C. de Souza, P. Y. Kubota, S. M. S. Costa, L. Menezes, B. S. Guimarães, S. N. Figueroa, J. Bonatti, . P., I. F. A. Cavalcanti, G. Sampaio, N. P. Klingaman, J. C. A. Baker, 2021: Evaluation of climate simulations produced with the Brazilian global atmospheric model version 1.2. Climate Dynamics, 56(3), 873-898. doi: 10.1007/s00382-020-05508-8. This paper presents an evaluation of climate simulations produced by the Brazilian Global Atmospheric Model version 1.2 (BAM-1.2) of the Center for Weather Forecast and Climate Studies (CPTEC). The model was run over the 1975–2017 period at two spatial resolutions, corresponding to ~ 180 and ~ 100 km, both with 42 vertical levels, following most of the Atmospheric Model Intercomparison Project (AMIP) protocol. In this protocol, observed sea surface temperatures (SSTs) are used as boundary conditions for the atmospheric model. Four ensemble members were run for each of the two resolutions. A series of diagnostics was computed for assessing the model’s ability to represent the top of the atmosphere (TOA) radiation, atmospheric temperature, circulation and precipitation climatological features. The representation of precipitation interannual variability, El Niño-Southern Oscillation (ENSO) precipitation teleconnections, the Madden and Julian Oscillation (MJO) and daily precipitation characteristics was also assessed. The model at both resolutions reproduced many observed temperature, atmospheric circulation and precipitation climatological features, despite several identified biases. The model atmosphere was found to be more transparent than the observations, leading to misrepresentation of cloud-radiation interactions. The net cloud radiative forcing, which produces a cooling effect on the global mean climate at the TOA, was well represented by the model. This was found to be due to the compensation between both weaker longwave cloud radiative forcing (LWCRF) and shortwave cloud radiative forcing (SWCRF) in the model compared to the observations. The model capability to represent inter-annual precipitation variability at both resolutions was found to be linked to the adequate representation of ENSO teleconnections. However, the model produced weaker than observed convective activity associated with the MJO. Light daily precipitation over the southeast of South America and other climatologically similar regions was diagnosed to be overestimated, and heavy daily precipitation underestimated by the model. Increasing spatial resolution helped to slightly reduce some of the diagnosed biases. The performed evaluation identified model aspects that need to be improved. These include the representation of polar continental surface and sea ice albedo, stratospheric ozone, low marine clouds, and daily precipitation features, which were found to be larger and last longer than the observed features.
Dai, Ni; Kramer, Ryan J.; Soden, Brian J.; L’Ecuyer, Tristan S.Dai, N., R. J. Kramer, B. J. Soden, T. S. L’Ecuyer, 2021: Evaluation of CloudSat Radiative Kernels Using ARM and CERES Observations and ERA5 Reanalysis. Journal of Geophysical Research: Atmospheres, 126(23), e2020JD034510. doi: 10.1029/2020JD034510. Despite the widespread use of the radiative kernel technique for studying radiative feedbacks and radiative forcings, there has not been any systematic, observation-based validation of the radiative kernel method. Here, we utilize observed and reanalyzed radiative fluxes and atmospheric profiles from the Atmospheric Radiation Measurement (ARM) program and ERA5 reanalysis to assess a set of observation-based radiative kernels from CloudSat for six ARM sites. The CloudSat radiative kernels, convoluted with the ERA5 state variables, can almost perfectly reconstruct the monthly anomalies of shortwave (SW) and longwave (LW) radiative fluxes in ERA5 at the surface (SFC) and top-of-atmosphere (TOA) with correlations significantly being greater than 0.95. The biases of kernel-estimated flux anomalies calculated using the ARM-observed state variables can be more than twice as large when compared with the ARM-observed surface flux anomalies and Clouds and Earth's Radiant Energy System observed anomalies at the TOA. Generally, clouds contribute to most (>60%) of the variance of flux anomalies at Southern Great Plain (SGP), Tropical Western Pacific (TWP), and Eastern North Atlantic (ENA), and surface albedo dominates (>69%) the variance of SW flux anomalies at North Slope of Alaska. The radiative kernels exhibit the lowest correlation (r∼[0.55,0.85]) when reconstructing SFC LW flux anomalies at SGP, TWP, and ENA, whose biases are related to the possibility that the kernels may not fully capture the characteristics associated with Madden-Julian oscillation and El Niño-Southern Oscillation at TWP and the presence of clouds at SGP and ENA.
Datseris, George; Stevens, BjornDatseris, G., B. Stevens, 2021: Earth’s Albedo and Its Symmetry. AGU Advances, 2(3), e2021AV000440. doi: 10.1029/2021AV000440. The properties of Earth's albedo and its symmetries are analyzed using twenty years of space-based Energy Balanced And Filled product of Clouds and the Earth's Radiant Energy System measurements. Despite surface asymmetries, top of the atmosphere temporally & hemispherically averaged reflected solar irradiance R appears symmetric over Northern/Southern hemispheres. This is confirmed with the use of surrogate time-series, which provides margins of 0.1±0.28Wm−2 for possible hemispheric differences supported by Clouds and Earth's Radiant System data. R time-series are further analyzed by decomposition into a seasonal (yearly and half yearly) cycle and residuals. Variability in the reflected solar irradiance is almost entirely (99%) due to the seasonal variations, mostly due to seasonal variations in insolation. The residuals of hemispherically averaged R are not only small, but also indistinguishable from noise, and thus not correlated across hemispheres. This makes yearly and sub-yearly timescales unlikely as the basis for a symmetry-establishing mechanism. The residuals however contain a global trend that is large, as compared to expected albedo feedbacks. It is also hemispherically symmetric, and thus indicates the possibility of a symmetry enforcing mechanism at longer timescales. To pinpoint precisely which parts of the Earth system establish the hemispheric symmetry, we create an energetically consistent cloud-albedo field from the data. We show that the surface albedo asymmetry is compensated by asymmetries between clouds over extra-tropical oceans, with southern hemispheric storm-tracks being 11% cloudier than their northern hemisphere counterparts. This again indicates that, assuming the albedo symmetry is not a result of chance, its mechanism likely operates on large temporal and spatial scales. CERES; albedo; energy balance; cloud albedo; hemispheric symmetry
de Freitas, Pedro Paulo; Paiva, Afonso de Moraes; Cirano, Mauro; Mill, Guilherme Nogueira; da Costa, Vladimir Santos; Gabioux, Mariela; França, Bruna Reis Leitede Freitas, P. P., A. d. M. Paiva, M. Cirano, G. N. Mill, V. S. da Costa, M. Gabioux, B. R. L. França, 2021: Coastal trapped waves propagation along the Southwestern Atlantic Continental Shelf. Continental Shelf Research, 226, 104496. doi: 10.1016/j.csr.2021.104496. This study investigates the propagation of coastal trapped waves (CTWs) along the Brazilian continental shelf between 34°S and 11°S using in situ data combined with the outputs from a high-resolution ocean simulation with HYCOM. The CTWs generation area covers a wide region ranging from the Patagonian shelf to the southern Brazilian shelf. The spectral analysis of coastal sea level series between 54°S and 10.5°S shows three bands of high energy associated with periods from 5 to 12 days, 15–22 days, and 25–40 days. The energy of the CTWs decreases along their propagation for all frequency bands, showing a drastic reduction north of 22°S, due to abrupt variations in the width and depth of the continental shelf between Tubarão Bight and Abrolhos Bank. Their phase speed propagation varies along the coast, being faster (>25 m/s) in the southernmost region (between 42°S and 41°S), reaching ~11 m/s north of 41°S, and reducing to ~3 m/s further north (equatorward of 24°S). The free Continental Shelf Wave theory supports the notion that the intense deceleration north of 24°S can be explained by the narrowing of the continental shelf. The stratification parameter indicates that the Brazilian continental shelf has a barotropic response to wind-generated disturbances. Air-sea interaction; Brazilian continental shelf; Coastal sea level; Continental Shelf Waves; Observing systems
Devi, N. S. M. P. LathaDevi, N. S. M. P. L., 2021: Recent Climatology and Environmental Impacts of Aerosols Observed from Satellite Data Over Yangtze River Delta Region. Research Trends and Challenges in Physical Science Vol. 4, 40-54. doi: 10.9734/bpi/rtcps/v4/12884D. The important elements of the climate system are aerosols and clouds, significantly affecting the radiation budget. They play an important role in modifying the hydrological cycle and chemistry of the atmosphere. The authors have analyzed and examined the optical and radiative effects of aerosols and clouds on the radiative forcing. This has been achieved through the investigation of aerosol optical depth (AOD), absorbing aerosol index (AAI), and vertically distributed aerosol types. The work reported in this paper demonstrates the spatiotemporal changes and climatology of aerosols and clouds over the urban agglomeration domain in East China, namely the Yangtze River Delta region during 2002-2020. The results revealed a strong spatiotemporal heterogeneity in AOD and AAI values over East China during the study period. The study also presents the impact of fire counts to understand the impact of forest fires and burning on the urban atmosphere. Further, we presented the vertical structure of aerosol distribution and their classification retrieved from the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) over the area during 2007-2020. Finally, the short-wave and long-wave cloud radiative forcing are investigated with the data obtained from the CERES (Clouds and the Earth’s Radiant Energy System) satellite over the domain. short- and long-wave radiation
Doelling, David R.; Cao, Changyong; Xiong, JDoelling, D. R., C. Cao, J. Xiong, 2021: GSICS recommends NOAA-20 VIIRS as reflective solar band (RSB) calibration reference. GSICS Quarterly Vol. 14 No. 4, 14(4), 2-4. doi: 10.25923/JMBT-D994.
Dong, Wenhao; Zhao, Ming; Ming, Yi; Ramaswamy, V.Dong, W., M. Zhao, Y. Ming, V. Ramaswamy, 2021: Representation of Tropical Mesoscale Convective Systems in a General Circulation Model: Climatology and Response to Global Warming. J. Climate, 34(14), 5657-5671. doi: 10.1175/JCLI-D-20-0535.1. AbstractThe characteristics of tropical mesoscale convective systems (MCSs) simulated with a finer-resolution (~50 km) version of the Geophysical Fluid Dynamics Laboratory (GFDL) AM4 model are evaluated by comparing with a comprehensive long-term observational dataset. It is shown that the model can capture the various aspects of MCSs reasonably well. The simulated spatial distribution of MCSs is broadly in agreement with the observations. This is also true for seasonality and interannual variability over different land and oceanic regions. The simulated MCSs are generally longer-lived, weaker, and larger than observed. Despite these biases, an event-scale analysis suggests that their duration, intensity, and size are strongly correlated. Specifically, longer-lived and stronger events tend to be bigger, which is consistent with the observations. The same model is used to investigate the response of tropical MCSs to global warming using time-slice simulations forced by prescribed sea surface temperatures and sea ice. There is an overall decrease in occurrence frequency, and the reduction over land is more prominent than over ocean.
Dong, Xiquan; Wu, Peng; Wang, Yuan; Xi, Baike; Huang, YiyiDong, X., P. Wu, Y. Wang, B. Xi, Y. Huang, 2021: New Observational Constraints on Warm Rain Processes and Their Climate Implications. Geophysical Research Letters, 48(6), e2020GL091836. doi: https://doi.org/10.1029/2020GL091836. Low stratiform clouds have profound impacts on the hydrological cycle and the Earth’s radiation budget. However, realistic simulation of low clouds in climate models presents a major challenge. Here we employ the newly retrieved cloud and drizzle microphysical properties to improve the autoconversion and accretion parameterizations in a microphysical scheme. We find that the new autoconversion (accretion) rate contributes 14% lower (greater) to total drizzle water content than the original scheme near the cloud top. Compared to satellite results, the simulated cloud liquid water path (LWP) and shortwave cloud radiative effect using the original scheme in a climate model agree well on global average but with large regional differences. Simulations using the updated scheme show a 7.3% decrease in the light rain frequency, and a 10% increase in LWP. The updated microphysics scheme alleviates the long-lasting problem in most climate models, that is “too frequent and too light precipitation.”
Duan, Wentao; Liu, Jiandong; Yan, Qingyun; Ruan, Haibing; Jin, ShuanggenDuan, W., J. Liu, Q. Yan, H. Ruan, S. Jin, 2021: The Effect of Spatial Resolution and Temporal Sampling Schemes on the Measurement Error for a Moon-Based Earth Radiation Observatory. Remote Sensing, 13(21), 4432. doi: 10.3390/rs13214432. The Moon-Based Earth Radiation Observatory (MERO) is a new platform, which is expected to advance current Earth radiation budget (ERB) research with better observations. For the instrument design of a MERO system, ascertaining the spatial resolution and sampling scheme is important. However, current knowledge about this is still limited. Here we proposed a simulation method for the MERO-measured Earth top of atmosphere (TOA) outgoing shortwave radiation (OSR) and outgoing longwave radiation (OLR) fluxes and constructed the “true” Earth TOA OSR and OLR fluxes based on the Clouds and Earth’s Radiant Energy System (CERES) data. Then we used them to reveal the effects of spatial resolution and temporal scheme (sampling interval and the temporal sampling sequence) on the measurement error of a MERO. Our results indicate that the spatial sampling error in the unit of percentage reduces linearly as the spatial resolution varies from 1000 km to 100 km; the rate is 2.5%/100 km for the Earth TOA OSR flux, which is higher than that (1%/100 km) of the TOA OLR flux. Besides, this rate becomes larger when the spatial resolution is finer than 40 km. It is also demonstrated that a sampling temporal sequence of starting time of 64 min with a sampling interval of 90 min is the optimal sampling scheme that results in the least temporal sampling error for the MERO system with a 40 km spatial resolution, note that this conclusion depends on the temporal resolution and quality of the data used to construct the “true” Earth TOA OSR and OLR fluxes. The proposed method and derived results in this study could facilitate the ascertainment of the optimal spatial resolution and sampling scheme of a MERO system under certain manufacturing budget and measurement error limit. spatial resolution; measurement error; Moon-Based Earth Radiation Observatory (MERO); temporal sampling scheme
Dübal, Hans-Rolf; Vahrenholt, FritzDübal, H., F. Vahrenholt, 2021: Radiative Energy Flux Variation from 2001–2020. Atmosphere, 12(10), 1297. doi: 10.3390/atmos12101297. Radiative energy flux data, downloaded from CERES, are evaluated with respect to their variations from 2001 to 2020. We found the declining outgoing shortwave radiation to be the most important contributor for a positive TOA (top of the atmosphere) net flux of 0.8 W/m2 in this time frame. We compare clear sky with cloudy areas and find that changes in the cloud structure should be the root cause for the shortwave trend. The radiative flux data are compared with ocean heat content data and analyzed in the context of a longer-term climate system enthalpy estimation going back to the year 1750. We also report differences in the trends for the Northern and Southern hemisphere. The radiative data indicate more variability in the North and higher stability in the South. The drop of cloudiness around the millennium by about 1.5% has certainly fostered the positive net radiative flux. The declining TOA SW (out) is the major heating cause (+1.42 W/m2 from 2001 to 2020). It is almost compensated by the growing chilling TOA LW (out) (−1.1 W/m2). This leads together with a reduced incoming solar of −0.17 W/m2 to a small growth of imbalance of 0.15 W/m2. We further present surface flux data which support the strong influence of the cloud cover on the radiative budget. CERES; shortwave flux; cloud thinning; longwave flux; radiative energy flux
Espinoza, Jhan-Carlo; Arias, Paola A.; Moron, Vincent; Junquas, Clementine; Segura, Hans; Sierra-Pérez, Juan Pablo; Wongchuig, Sly; Condom, ThomasEspinoza, J., P. A. Arias, V. Moron, C. Junquas, H. Segura, J. P. Sierra-Pérez, S. Wongchuig, T. Condom, 2021: Recent Changes in the Atmospheric Circulation Patterns during the Dry-to-Wet Transition Season in South Tropical South America (1979–2020): Impacts on Precipitation and Fire Season. J. Climate, 34(22), 9025-9042. doi: 10.1175/JCLI-D-21-0303.1. Abstract We analyze the characteristics of atmospheric variations over tropical South America using the pattern recognition framework of weather typing or atmospheric circulation patterns (CPs). During 1979–2020, nine CPs are defined in the region, using a k-means algorithm based on daily unfiltered 850-hPa winds over 10°N–30°S, 90°–30°W. CPs are primarily interpreted as stages of the annual cycle of the low-level circulation. We identified three “winter” CPs (CP7, CP8, and CP9), three “summer” CPs (CP3, CP4, and CP5), and three “transitional” CPs (CP1, CP2, and CP6). Significant long-term changes are detected during the dry-to-wet transition season (July–October) over southern tropical South America (STSA). One of the wintertime patterns (CP9) increases from 20% in the 1980s to 35% in the last decade while the “transitional” CP2 decreases from 13% to 7%. CP9 is characterized by enhancement of the South American low-level jet and increasing atmospheric subsidence over STSA. CP2 is characterized by southerly cold-air incursions and anomalous convective activity over STSA. The years characterized by high frequency of CP9 and low frequency of CP2 during the dry-to-wet transition season are associated with a delayed South American monsoon onset and anomalous dry conditions over STSA. Consistently, a higher frequency of CP9 intensifies the fire season over STSA (1999–2020). Over the Brazilian states of Maranhão, Tocantins, Goiás, and São Paulo, the seasonal frequency of CP9 explains around 35%–44% of the interannual variations of fire counts.
Feldman, D. R.; Su, W.; Minnis, P.Feldman, D. R., W. Su, P. Minnis, 2021: Subdiurnal to Interannual Frequency Analysis of Observed and Modeled Reflected Shortwave Radiation From Earth. Geophysical Research Letters, 48(4), e2020GL089221. doi: https://doi.org/10.1029/2020GL089221. Estimates of global top-of-atmosphere radiation on monthly, seasonal, annual, and longer time-scales require estimates of the diurnal variability in both insolation and surface and atmospheric reflection. We compare Earth Polychromatic Imaging Camera (EPIC) and National Institute of Standards and Technology Advanced Radiometer (NISTAR) observations from the Deep Space Climate Observatory (DSCOVR) satellite with Clouds and Earth’s Radiant Energy System (CERES) hourly synoptic fluxes, which are diurnally filled through geostationary observations, and find that their power spectral density functions substantially agree, showing strong relative power at subdiurnal, diurnal, seasonal, and annual time-scales, and power growing from diurnal to seasonal time-scales. Frequency analysis of fluxes from several coupled model intercomparison project 5 model (CMIP5) and CMIP6 models shows that they distribute too much power over periods greater than 1 day but less than one year, indicating that a closer look is needed into how models achieve longer-term stability in reflected shortwave radiation. Model developers can consider using these datasets for time-varying energetic constraints, since tuning parameter choices will impact modeled planetary shortwave radiation across timescales ranging from subdiurnal to decadal. diurnal cycle; Albedo; DSCOVR; shortwave radiative energy budget
Feng, Chunjie; Zhang, Xiaotong; Wei, Yu; Zhang, Weiyu; Hou, Ning; Xu, Jiawen; Yang, Shuyue; Xie, Xianhong; Jiang, BoFeng, C., X. Zhang, Y. Wei, W. Zhang, N. Hou, J. Xu, S. Yang, X. Xie, B. Jiang, 2021: Estimation of Long-Term Surface Downward Longwave Radiation over the Global Land from 2000 to 2018. Remote Sensing, 13(9), 1848. doi: 10.3390/rs13091848. It is of great importance for climate change studies to construct a worldwide, long-term surface downward longwave radiation (Ld, 4–100 μm) dataset. Although a number of global Ld datasets are available, their low accuracies and coarse spatial resolutions limit their applications. This study generated a daily Ld dataset with a 5-km spatial resolution over the global land surface from 2000 to 2018 using atmospheric parameters, which include 2-m air temperature (Ta), relative humidity (RH) at 1000 hPa, total column water vapor (TCWV), surface downward shortwave radiation (Sd), and elevation, based on the gradient boosting regression tree (GBRT) method. The generated Ld dataset was evaluated using ground measurements collected from AmeriFlux, AsiaFlux, baseline surface radiation network (BSRN), surface radiation budget network (SURFRAD), and FLUXNET networks. The validation results showed that the root mean square error (RMSE), mean bias error (MBE), and correlation coefficient (R) values of the generated daily Ld dataset were 17.78 W m−2, 0.99 W m−2, and 0.96 (p < 0.01). Comparisons with other global land surface radiation products indicated that the generated Ld dataset performed better than the clouds and earth’s radiant energy system synoptic (CERES-SYN) edition 4.1 dataset and ERA5 reanalysis product at the selected sites. In addition, the analysis of the spatiotemporal characteristics for the generated Ld dataset showed an increasing trend of 1.8 W m−2 per decade (p < 0.01) from 2003 to 2018, which was closely related to Ta and water vapor pressure. In general, the generated Ld dataset has a higher spatial resolution and accuracy, which can contribute to perfect the existing radiation products. air temperature; relative humidity; surface downward longwave radiation; gradient boosting regression tree; surface downward shortwave radiation; total column water vapor
Feng, Fei; Wang, KaicunFeng, F., K. Wang, 2021: Merging High-Resolution Satellite Surface Radiation Data with Meteorological Sunshine Duration Observations over China from 1983 to 2017. Remote Sensing, 13(4), 602. doi: 10.3390/rs13040602. Surface solar radiation (Rs) is essential to climate studies. Thanks to long-term records from the Advanced Very High-Resolution Radiometers (AVHRR), the recent release of International Satellite Cloud Climatology Project (ISCCP) HXG cloud products provide a promising opportunity for building long-term Rs data with high resolutions (3 h and 10 km). In this study, we compare three satellite Rs products based on AVHRR cloud products over China from 1983 to 2017 with direct observations of Rs and sunshine duration (SunDu)-derived Rs. The results show that SunDu-derived Rs have higher accuracy than the direct observed Rs at time scales of a month or longer by comparing with the satellite Rs products. SunDu-derived Rs is available from the 1960s at more than 2000 stations over China, which provides reliable decadal estimations of Rs. However, the three AVHRR-based satellite Rs products have significant biases in quantifying the trend of Rs from 1983 to 2016 (−4.28 W/m2/decade to 2.56 W/m2/decade) due to inhomogeneity in satellite cloud products and the lack of information on atmospheric aerosol optical depth. To adjust the inhomogeneity of the satellite Rs products, we propose a geographically weighted regression fusion method (HGWR) to merge ISCCP-HXG Rs with SunDu-derived Rs. The merged Rs product over China from 1983 to 2017 with a spatial resolution of 10 km produces nearly the same trend as that of the SunDu-derived Rs. This study makes a first attempt to adjust the inhomogeneity of satellite Rs products and provides the merged high-resolution Rs product from 1983 to 2017 over China, which can be downloaded freely. surface solar radiation; data fusion; AVHRR; sunshine duration
Fillmore, David; Rutan, David; Kato, Seiji; Rose, Fred; Caldwell, ThomasFillmore, D., D. Rutan, S. Kato, F. Rose, T. Caldwell, 2021: Evaluation of aerosol optical depths and clear-sky radiative fluxes of the CERES Edition 4.1 SYN1deg data product. Atmospheric Chemistry and Physics Discussions, 1-50. doi: 10.5194/acp-2021-283. Abstract. Aerosol optical depths (AOD) used for the Edition 4.1 Clouds and the Earth’s Radiant Energy System (CERES) Synoptic (SYN1deg) are evaluated. AODs are derived from Moderate Resolution Imaging Spectroradiometer (MODIS) observations and assimilated by an aerosol transport model (MATCH). As a consequence, clear-sky AODs closely match with those derived from MODIS instruments. AODs under all-sky conditions are larger than AODs under clear-sky conditions, which is supported by ground-based AERONET observations. When all-sky MATCH AODs are compared with Modern-Era Retrospective Analysis for Research and Applications (MERRA2) AODs, MATCH AODs are generally larger than MERRA2 AODS especially over convective regions (e.g. Amazon, central Africa, and eastern Asia). The difference is largely caused by MODIS AODs used for assimilation. Including AODs with larger retrieval uncertainty makes AODs over the convective regions larger. When AODs are used for clear-sky irradiance computations and computed downward shortwave irradiances are compared with ground- based observations, the computed instantaneous irradiances are 1 % to 2 % larger than observed irradiances. The comparison of top-of-atmosphere clear-sky irradiances with those derived from CERES observations suggests that AODs used for surface radiation observation sites are larger by 0.01 to 0.03, which is within the uncertainty of instantaneous MODIS AODs. However, the comparison with AERONET AOD suggests AODs used for computations over desert sites are 0.08 larger. The cause of positive biases of downward shortwave irradiance and AODs for the desert sites are unknown.
Freese, Lyssa M.; Cronin, Timothy W.Freese, L. M., T. W. Cronin, 2021: Antarctic Radiative and Temperature Responses to a Doubling of CO2. Geophysical Research Letters, 48(17), e2021GL093676. doi: 10.1029/2021GL093676. Greenhouse gases (GHGs), including carbon dioxide (), impact global and local outgoing longwave radiation (OLR). The Antarctic is known for its near-surface temperature inversion, where the addition of GHGs can lead to increased OLR during all but the winter months. These changes in OLR, however, are unable to explain modeled surface warming due to changes in GHGs across central Antarctica. Here we develop a simple explanation showing why adding always warms the surface, and allowing an estimation of the change in surface temperature due to a change in concentration based on the initial surface temperature. We develop a radiative-advective-turbulent single-column model based on observed temperatures for explicit comparisons between our estimations and model equilibrium behavior. We confirm that Antarctic surface temperatures warm as GHG concentrations increase, and find that this response is best explained through the surface greenhouse effect rather than that of the top of atmosphere (TOA). climate; temperature; radiation; Antarctic; GHG
Gasparini, Blaž; Rasch, Philip J.; Hartmann, Dennis L.; Wall, Casey J.; Dütsch, MarinaGasparini, B., P. J. Rasch, D. L. Hartmann, C. J. Wall, M. Dütsch, 2021: A Lagrangian Perspective on Tropical Anvil Cloud Lifecycle in Present and Future Climate. Journal of Geophysical Research: Atmospheres, 126(4), e2020JD033487. doi: https://doi.org/10.1029/2020JD033487. The evolution of tropical anvil clouds from their origin in deep convective cores to their slow decay determines the climatic effects of clouds in tropical convective regions. Despite the relevance of anvil clouds for climate and responses of clouds to global warming, processes dominating their evolution are not well understood. Currently available observational data reveal instantaneous snapshots of anvil cloud properties, but cannot provide a process-based perspective on anvil evolution. We therefore conduct simulations with the high resolution version of the exascale earth system model in which we track mesoscale convective systems over the tropical Western Pacific and compute trajectories that follow air parcels detrained from peaks of convective activity. With this approach we gain new insight into the anvil cloud evolution both in present day and future climate. Comparison with geostationary satellite data shows that the model is able to simulate maritime mesoscale convective systems reasonably well. Trajectory results indicate that anvil cloud lifetime is about 15 h with no significant change in a warmer climate. The anvil ice mixing ratio is larger in a warmer climate due to a larger source of ice by detrainment and larger depositional growth leading to a more negative net cloud radiative effect along detrained trajectories. However, the increases in sources are counteracted by increases in sinks of ice, particularly snow formation and sedimentation. Furthermore, we find that the mean anvil cloud feedback along trajectories is positive and consistent with results from more traditional cloud feedback calculation methods. cirrus clouds; cloud feedbacks; radiative effects; tropical convection; anvil clouds; convective life cycle
Ge, Jinming; Wang, Zhenquan; Wang, Chen; Yang, Xuan; Dong, Zixiang; Wang, MeihuaGe, J., Z. Wang, C. Wang, X. Yang, Z. Dong, M. Wang, 2021: Diurnal variations of global clouds observed from the CATS spaceborne lidar and their links to large-scale meteorological factors. Climate Dynamics. doi: 10.1007/s00382-021-05829-2. Diurnal cycle of cloud (DCC), referring to the diurnal variation of cloud macro- and micro-physical properties, thus largely determining the strength of net cloud radiative forcing (CRF), is a critical feature of clouds’ variation and is important for weather and climate evolutions. Nevertheless, neither the DCC vertical structures and their links to meteorology are well understood, nor the DCCs for different cloud type are accurately represented in current climate models. With unique orbit of the international space station, Cloud-Aerosol Transport System (CATS) lidar onboard the international space station (ISS) can sample cloud profiles at different local times and provide DCC vertical structures. In this study, we analyzed 2-year CATS data and found that the amplitude of diurnal cycle is significantly correlated with the mean frequency of occurrence. High clouds and oceanic low clouds have strong vertical development during nighttime, and continental low clouds tend to develop in daytime. These DCC features can impact the strength and the direction of CRF. Overall, large cloud cover and amplitude can amplify net cloud cooling effects, and high cloud nighttime (18:00 PM–06:00 AM) occurrence frequency can strengthen the cloud warming effects. To explain the DCC phenomenon, the instantaneous links between cloud vertical structure and lower-tropospheric stability (LTS), vertical velocity and cold point temperature (CPT) are discussed individually to show the evidence of their controls on cloud properties from tropics to midlatitude. Our results confirm that tropical water clouds and cirrus are more affected by LTS and CPT, respectively. Towards midlatitude from tropics, vertical velocity gradually plays a more important role in cloud development and dissipation. According to the diurnal cycles of these factors, temperature and static stability have the largest daily amplitude in the boundary layer of tropics and subtropics, which can explain the diurnal cycle of relative humidity and low clouds evolution, whereas vertical velocity has the largest daily amplitude in midlatitude, which is more related to the diurnal cycle of relative humidity and clouds in upper level of troposphere.
Gettelman, A.; Gagne, D. J.; Chen, C.-C.; Christensen, M. W.; Lebo, Z. J.; Morrison, H.; Gantos, G.Gettelman, A., D. J. Gagne, C. Chen, M. W. Christensen, Z. J. Lebo, H. Morrison, G. Gantos, 2021: Machine Learning the Warm Rain Process. Journal of Advances in Modeling Earth Systems, 13(2), e2020MS002268. doi: https://doi.org/10.1029/2020MS002268. Clouds are critical for weather and climate prediction. The multiple scales of cloud processes make simulation difficult. Often models and measurements are used to develop empirical relationships for large-scale models to be computationally efficient. Machine learning provides another potential tool to improve our empirical parameterizations of clouds. To explore these opportunities, we replace the warm rain formation process in a General Circulation Model (GCM) with a detailed treatment from a bin microphysical model that causes a 400% slowdown in the GCM. We analyze the changes in climate that result from the use of the bin microphysical calculation and find improvements in the rain onset and frequency of light rain compared to high resolution process models and observations. We also find a resulting change in the cloud feedback response of the model to warming, which will significantly impact the climate sensitivity. We then replace the bin microphysical model with several neural networks designed to emulate the autoconversion and accretion rates produced by the bin microphysical model. The neural networks are organized into two stages: the first stage identifies where tendencies will be nonzero (and the sign of the tendency), and the second stage predicts the magnitude of the autoconversion and accretion rates. We describe the risks of overfitting, extrapolation, and linearization by using perfect model experiments with and without the emulator. We can recover the solutions with the emulators in almost all respects, and get simulations that perform as the detailed model, but with the computational cost of the control simulation. clouds; microphysics; machine learning
Ghiz, Madison L.; Scott, Ryan C.; Vogelmann, Andrew M.; Lenaerts, Jan T. M.; Lazzara, Matthew; Lubin, DanGhiz, M. L., R. C. Scott, A. M. Vogelmann, J. T. M. Lenaerts, M. Lazzara, D. Lubin, 2021: Energetics of surface melt in West Antarctica. The Cryosphere, 15(7), 3459-3494. doi: 10.5194/tc-15-3459-2021. Abstract. We use reanalysis data and satellite remote sensing of cloud properties to examine how meteorological conditions alter the surface energy balance to cause surface melt that is detectable in satellite passive microwave imagery over West Antarctica. This analysis can detect each of the three primary mechanisms for inducing surface melt at a specific location: thermal blanketing involving sensible heat flux and/or longwave heating by optically thick cloud cover, all-wave radiative enhancement by optically thin cloud cover, and föhn winds. We examine case studies over Pine Island and Thwaites glaciers, which are of interest for ice shelf and ice sheet stability, and over Siple Dome, which is more readily accessible for field work. During January 2015 over Siple Dome we identified a melt event whose origin is an all-wave radiative enhancement by optically thin clouds. During December 2011 over Pine Island and Thwaites glaciers, we identified a melt event caused mainly by thermal blanketing from optically thick clouds. Over Siple Dome, those same 2011 synoptic conditions yielded a thermal-blanketing-driven melt event that was initiated by an impulse of sensible heat flux and then prolonged by cloud longwave heating. The December 2011 synoptic conditions also generated föhn winds at a location on the Ross Ice Shelf adjacent to the Transantarctic Mountains, and we analyze this case with additional support from automatic weather station data. In contrast, a late-summer thermal blanketing period over Pine Island and Thwaites glaciers during February 2013 showed surface melt initiated by cloud longwave heating and then prolonged by enhanced sensible heat flux. One limitation thus far with this type of analysis involves uncertainties in the cloud optical properties. Nevertheless, with improvements this type of analysis can enable quantitative prediction of atmospheric stress on the vulnerable Antarctic ice shelves in a steadily warming climate.
Ghosh, Sudipta; Riemer, Nicole; Giuliani, Graziano; Giorgi, Filippo; Ganguly, Dilip; Dey, SagnikGhosh, S., N. Riemer, G. Giuliani, F. Giorgi, D. Ganguly, S. Dey, 2021: Sensitivity of Carbonaceous Aerosol Properties to the Implementation of a Dynamic Aging Parameterization in the Regional Climate Model RegCM. Journal of Geophysical Research: Atmospheres, 126(17), e2020JD033613. doi: 10.1029/2020JD033613. Freshly emitted soot is hydrophobic, but condensation of secondary aerosols and coagulation with other particles modify its hygroscopic optical properties. This conversion is referred to as “aerosol aging.” Many climate models represent this aging process with a fixed aging time scale, whereas in reality, it is a dynamic process that depends on environmental conditions. Here, we implement a dynamic aging parameterization scheme in the regional climate model RegCM4 in place of the fixed aging timescale of 1.15 days (∼27.6 h) and examine its impact on the aerosol life cycle over the Indian subcontinent. The conversion from hydrophobic to hydrophilic aerosol is usually lower than 27.6 h over the entire landmass and lower than 10 h over the polluted Indo-Gangetic Basin (IGB), with seasonal variability. Due to the implementation of the dynamic aging scheme, the column burden and surface mass concentration of carbonaceous aerosols increase during the drier season (December–February) when washout is negligible. The burden is reduced during the wet season (June–September) due to a more efficient washout except over the IGB, where a reduction in precipitation as a result of radiative feedbacks increases the aerosol concentrations. Over the polluted IGB, surface dimming increases due to the dynamic aging scheme, with the top of the atmosphere forcing remaining mostly unchanged. As a result, atmospheric heating increases by at least 1.2 W/m2. Our results suggest that climate models should incorporate dynamic aging for a more realistic representation of aerosol simulations, especially in highly polluted regions. climate; black carbon; regional climate model; dynamic aging; feedback; India
Gibbins, Goodwin; Haigh, Joanna D.Gibbins, G., J. D. Haigh, 2021: Comments on “Global and Regional Entropy Production by Radiation Estimated from Satellite Observations”. J. Climate, 34(9), 3721-3728. doi: 10.1175/JCLI-D-20-0685.1. AbstractA recent paper by Kato and Rose reports a negative correlation between the annual mean entropy production rate of the climate and the absorption of solar radiation in the CERES SYN1deg dataset, using the simplifying assumption that the system is steady in time. It is shown here, however, that when the nonsteady interannual storage of entropy is accounted for, the dataset instead implies a positive correlation; that is, global entropy production rates increase with solar absorption. Furthermore, this increase is consistent with the response demonstrated by an energy balance model and a radiative–convective model. To motivate this updated analysis, a detailed discussion of the conceptual relationship between entropy production, entropy storage, and entropy flows is provided. The storage-corrected estimate for the mean global rate of entropy production in the CERES dataset from all irreversible transfer processes is 81.9 mW m−2 K−1 and from only nonradiative processes is 55.2 mW m−2 K−1 (observations from March 2000 to February 2018).
Girishkumar, M. S.; Joseph, Jofia; McPhaden, M. J.; Pattabhi Ram Rao, E.Girishkumar, M. S., J. Joseph, M. J. McPhaden, E. Pattabhi Ram Rao, 2021: Atmospheric Cold Pools and Their Influence on Sea Surface Temperature in the Bay of Bengal. Journal of Geophysical Research: Oceans, 126(9), e2021JC017297. doi: 10.1029/2021JC017297. Recent observations show that atmospheric cold pool (ACP) events are plentiful in the Bay of Bengal (BoB) during summer (May–September) and fall (October–November) and that these events can significantly modify local air-sea interaction processes on sub-daily time scales. In this study, we examine whether the magnitude of sea surface temperature (SST) drop associated with ACP events shows any diurnal variability during summer and fall. For this purpose, we use moored buoy data with a 10-min temporal resolution at 8°, 12°, and 15°N along 90°E and a one-dimensional mixed layer (ML) model. The analysis shows a reduction in SST (ΔSST) due to ACPs in the BoB during summer and fall, with a maximum magnitude of ΔSST during the afternoon (1200–1600 LST). However, the maximum magnitude of ΔSST during the afternoon is a factor of two higher during fall (∼−0.14°C) than summer (∼−0.07°C). Analysis based on observations and ACP sensitivity experiments indicates that the shallow daytime thermocline and associated thin surface ML is the primary factor regulating the day to night difference in ΔSST associated with ACPs. The presence of this shallow daytime thermocline and thin ML amplifies the effects on SST of net surface heat loss and entrainment of cold sub-surface water associated with enhanced ACP wind speeds. sea surface temperature; Bay of Bengal; air-sea interaction; mixed layer processes; atmospheric cold pool
Goode, P. R.; Pallé, E.; Shoumko, A.; Shoumko, S.; Montañes-Rodriguez, P.; Koonin, S. E.Goode, P. R., E. Pallé, A. Shoumko, S. Shoumko, P. Montañes-Rodriguez, S. E. Koonin, 2021: Earth's Albedo 1998–2017 as Measured From Earthshine. Geophysical Research Letters, 48(17), e2021GL094888. doi: 10.1029/2021GL094888. The reflectance of the Earth is a fundamental climate parameter that we measured from Big Bear Solar Observatory between 1998 and 2017 by observing the earthshine using modern photometric techniques to precisely determine daily, monthly, seasonal, yearly and decadal changes in terrestrial albedo from earthshine. We find the inter-annual fluctuations in albedo to be global, while the large variations in albedo within individual nights and seasonal wanderings tend to average out over each year. We measure a gradual, but climatologically significant 0.5 decline in the global albedo over the two decades of data. We found no correlation between the changes in the terrestrial albedo and measures of solar activity. The inter-annual pattern of earthshine fluctuations are in good agreement with those measured by CERES (data began in 2001) even though the satellite observations are sensitive to retroflected light while earthshine is sensitive to wide-angle reflectivity. The CERES decline is about twice that of earthshine. atmospheres; methods; observational; planetary systems; planets and satellites; spectroscopic techniques; stars: low mass
Grise, Kevin M.; Kelleher, Mitchell K.Grise, K. M., M. K. Kelleher, 2021: Midlatitude Cloud Radiative Effect Sensitivity to Cloud Controlling Factors in Observations and Models: Relationship with Southern Hemisphere Jet Shifts and Climate Sensitivity. J. Climate, 34(14), 5869-5886. doi: 10.1175/JCLI-D-20-0986.1. AbstractAn effective method to understand cloud processes and to assess the fidelity with which they are represented in climate models is the cloud controlling factor framework, in which cloud properties are linked with variations in large-scale dynamical and thermodynamical variables. This study examines how midlatitude cloud radiative effects (CRE) over oceans covary with four cloud controlling factors—midtropospheric vertical velocity, estimated inversion strength (EIS), near-surface temperature advection, and sea surface temperature (SST)—and assesses their representation in CMIP6 models with respect to observations and CMIP5 models. CMIP5 and CMIP6 models overestimate the sensitivity of midlatitude CRE to perturbations in vertical velocity and underestimate the sensitivity of midlatitude shortwave CRE to perturbations in EIS and temperature advection. The largest improvement in CMIP6 models is a reduced sensitivity of CRE to vertical velocity perturbations. As in CMIP5 models, many CMIP6 models simulate a shortwave cloud radiative warming effect associated with a poleward shift in the Southern Hemisphere (SH) midlatitude jet stream, an effect not present in observations. This bias arises because most models’ shortwave CRE are too sensitive to vertical velocity perturbations and not sensitive enough to EIS perturbations, and because most models overestimate the SST anomalies associated with SH jet shifts. The presence of this bias directly impacts the transient surface temperature response to increasing greenhouse gases over the Southern Ocean, but not the global-mean surface temperature. Instead, the models’ climate sensitivity is correlated with their shortwave CRE sensitivity to surface temperature advection perturbations near 40°S, with models with more realistic values of temperature advection sensitivity generally having higher climate sensitivity.
Gristey, Jake J.; Su, Wenying; Loeb, Norman G.; Vonder Haar, Thomas H.; Tornow, Florian; Schmidt, K. Sebastian; Hakuba, Maria Z.; Pilewskie, Peter; Russell, Jacqueline E.Gristey, J. J., W. Su, N. G. Loeb, T. H. Vonder Haar, F. Tornow, K. S. Schmidt, M. Z. Hakuba, P. Pilewskie, J. E. Russell, 2021: Shortwave Radiance to Irradiance Conversion for Earth Radiation Budget Satellite Observations: A Review. Remote Sensing, 13(13), 2640. doi: 10.3390/rs13132640. Observing the Earth radiation budget (ERB) from satellites is crucial for monitoring and understanding Earth’s climate. One of the major challenges for ERB observations, particularly for reflected shortwave radiation, is the conversion of the measured radiance to the more energetically relevant quantity of radiative flux, or irradiance. This conversion depends on the solar-viewing geometry and the scene composition associated with each instantaneous observation. We first outline the theoretical basis for algorithms to convert shortwave radiance to irradiance, most commonly known as empirical angular distribution models (ADMs). We then review the progression from early ERB satellite observations that applied relatively simple ADMs, to current ERB satellite observations that apply highly sophisticated ADMs. A notable development is the dramatic increase in the number of scene types, made possible by both the extended observational record and the enhanced scene information now available from collocated imager information. Compared with their predecessors, current shortwave ADMs result in a more consistent average albedo as a function of viewing zenith angle and lead to more accurate instantaneous and mean regional irradiance estimates. One implication of the increased complexity is that the algorithms may not be directly applicable to observations with insufficient accompanying imager information, or for existing or new satellite instruments where detailed scene information is not available. Recent advances that complement and build on the base of current approaches, including machine learning applications and semi-physical calculations, are highlighted. angular distribution model; shortwave radiation; irradiance; radiance
Gryspeerdt, Edward; McCoy, Daniel T.; Crosbie, Ewan; Moore, Richard H.; Nott, Graeme J.; Painemal, David; Small-Griswold, Jennifer; Sorooshian, Armin; Ziemba, LukeGryspeerdt, E., D. T. McCoy, E. Crosbie, R. H. Moore, G. J. Nott, D. Painemal, J. Small-Griswold, A. Sorooshian, L. Ziemba, 2021: The impact of sampling strategy on the cloud droplet number concentration estimated from satellite data. Atmospheric Measurement Techniques Discussions, 1-25. doi: 10.5194/amt-2021-371. Abstract. Cloud droplet number concentration (Nd) is of central importance to observation-based estimates of aerosol indirect effects, being used to quantify both the cloud sensitivity to aerosol and the base state of the cloud. However, the derivation of Nd from satellite data depends on a number of assumptions about the cloud and the accuracy of the retrievals of the cloud properties from which it is derived, making it prone to systematic biases. A number of sampling strategies have been proposed to address these biases by selecting the most accurate Nd retrievals in the satellite data. This work compares the impact of these strategies on the accuracy of the satellite retrieved Nd, using a selection of insitu measurements. In stratocumulus regions, the MODIS Nd retrieval is able to achieve a high precision (r2 of 0.5–0.8). This is lower in other cloud regimes, but can be increased by appropriate sampling choices. Although the Nd sampling can have significant effects on the Nd climatology, it produces only a 20 % variation in the implied radiative forcing from aerosol-cloud interactions, with the choice of aerosol proxy driving the overall uncertainty. The results are summarised into recommendations for using MODIS Nd products and appropriate sampling.
Guigma, Kiswendsida H.; Guichard, Françoise; Todd, Martin; Peyrille, Philippe; Wang, YiGuigma, K. H., F. Guichard, M. Todd, P. Peyrille, Y. Wang, 2021: Atmospheric tropical modes are important drivers of Sahelian springtime heatwaves. Climate Dynamics, 56(5), 1967-1987. doi: 10.1007/s00382-020-05569-9. Heatwaves pose a serious threat to human health worldwide but remain poorly documented over Africa. This study uses mainly the ERA5 dataset to investigate their large-scale drivers over the Sahel region during boreal spring, with a focus on the role of tropical modes of variability including the Madden–Julian Oscillation (MJO) and the equatorial Rossby and Kelvin waves. Heatwaves were defined from daily minimum and maximum temperatures using a methodology that retains only intraseasonal scale events of large spatial extent. The results show that tropical modes have a large influence on the occurrence of Sahelian heatwaves, and, to a lesser extent, on their intensity. Depending on their convective phase, they can either increase or inhibit heatwave occurrence, with the MJO being the most important of the investigated drivers. A certain sensitivity to the geographic location and the diurnal cycle is observed, with nighttime heatwaves more impacted by the modes over the eastern Sahel and daytime heatwaves more affected over the western Sahel. The examination of the physical mechanisms shows that the modulation is made possible through the perturbation of regional circulation. Tropical modes thus exert a control on moisture and the subsequent longwave radiation, as well as on the advection of hot air. A detailed case study of a major event, which took place in April 2003, further supports these findings. Given the potential predictability offered by tropical modes at the intraseasonal scale, this study has key implications for heatwave risk management in the Sahel.
Guo, Huan; Ming, Yi; Fan, Songmiao; Zhou, Linjiong; Harris, Lucas; Zhao, MingGuo, H., Y. Ming, S. Fan, L. Zhou, L. Harris, M. Zhao, 2021: Two-Moment Bulk Cloud Microphysics With Prognostic Precipitation in GFDL's Atmosphere Model AM4.0: Configuration and Performance. Journal of Advances in Modeling Earth Systems, 13(6), e2020MS002453. doi: 10.1029/2020MS002453. A two-moment Morrison-Gettelman bulk cloud microphysics with prognostic precipitation (MG2), together with a mineral dust and temperature-dependent ice nucleation scheme, have been implemented into the Geophysical Fluid Dynamics Laboratory's Atmosphere Model version 4.0 (AM4.0). We refer to this configuration as AM4-MG2. This paper describes the configuration of AM4-MG2, evaluates its performance, and compares it with AM4.0. It is shown that the global simulations with AM4-MG2 compare favorably with observations and reanalyses. The model skill scores are close to AM4.0. Compared to AM4.0, improvements in AM4-MG2 include (a) better coastal marine stratocumulus and seasonal cycles, (b) more realistic ice fraction, and (c) dominant accretion over autoconversion. Sensitivity tests indicate that nucleation and sedimentation schemes have significant impacts on cloud liquid and ice water fields, but higher horizontal resolution (about 50 km instead of 100 km) does not.
Guo, Zhun; Zhou, Tianjun; Wang, Minghuai; Yang, Ben; Wu, BoGuo, Z., T. Zhou, M. Wang, B. Yang, B. Wu, 2021: The role of Tibetan summer low clouds in the simulation of the East Asian summer monsoon rain belt. International Journal of Climatology, 1-13. doi: 10.1002/joc.7405. It has been challenging to simulate the East Asian summer monsoon (EASM) using general circulation models. By evaluating the cloud layers unified by binormals (CLUBB) model and its revised version in the version-5 Community Atmosphere Model, we find that EASM simulations benefit from improving the reproduction of low clouds over the Tibetan Plateau. When a cloud-top radiative cooling scheme (RAD) is coupled with CLUBB, it significantly improves the resulting EASM rain belt and western Pacific subtropical high (WPSH) simulations compared to the default simulations without RAD; in these default simulations, the low-level southwesterlies, WPSH ridge, and EASM rain belt are displaced northward. The moisture budget analyses indicate that the improvements in EASM simulations are mainly contributed to by the improved presentation of low-level stationary eddy meridional flow convergence over East Asia; this convergence shifts northward during the default model runs. Because the RAD scheme enables the model to better represent the subgrid radiation–turbulence interaction, the model produces stronger turbulent fluxes and lower clouds but reduces incoming solar radiation over the Tibetan Plateau. It thus shifts the Tibetan High southward, ultimately resulting in an improved simulation of the low-level southwesterlies. These improvements in CLUBB_RAD highlight the importance of improving the representation of low clouds when simulating EASM rainfall. Tibetan Plateau; low clouds; cloud-top radiative cooling scheme; EASM rain belt; low-level southwesterlies
Hakuba, M. Z.; Frederikse, T.; Landerer, F. W.Hakuba, M. Z., T. Frederikse, F. W. Landerer, 2021: Earth's Energy Imbalance From the Ocean Perspective (2005–2019). Geophysical Research Letters, 48(16), e2021GL093624. doi: 10.1029/2021GL093624. Earth's energy imbalance (EEI) represents the rate of global energy accumulation in response to radiative forcings and feedbacks. Ocean heat uptake (OHU) poses a vital constraint on EEI and its uncertainty. Considering recent geodetic observations, geophysical corrections, and new estimates of the ocean's expansion efficiency of heat, we translate steric sea-level change, the difference of total sea-level and ocean-mass change, into an OHU of 0.86 [0.62, 1.10, 5%–95%] Wm−2 for the period 2005–2019. Adding components of non-oceanic heat uptake, we obtain an EEI of 0.94 [0.70, 1.19] Wm−2, which is at the upper end of previous assessments, but agrees within uncertainty. Interannual geodetic OHU variability exhibits a higher correlation with top-of-the-atmosphere net radiative flux than hydrographic-only data, but has a three times larger standard deviation. The radiation fluxes and the geodetic approach suggest an increase in heat uptake since 2005, most markedly in recent years. ocean heat uptake; Earth's energy imbalance; Geodesy; sea level budget; thermal expansion
Ham, Seung-Hee; Kato, Seiji; Rose, Fred G.; Loeb, Norman G.; Xu, Kuan-Man; Thorsen, Tyler; Bosilovich, Michael G.; Sun-Mack, Sunny; Chen, Yan; Miller, Walter F.Ham, S., S. Kato, F. G. Rose, N. G. Loeb, K. Xu, T. Thorsen, M. G. Bosilovich, S. Sun-Mack, Y. Chen, W. F. Miller, 2021: Examining Cloud Macrophysical Changes over the Pacific for 2007–17 Using CALIPSO, CloudSat, and MODIS Observations. J. Appl. Meteor. Climatol., 60(8), 1105-1126. doi: 10.1175/JAMC-D-20-0226.1. AbstractCloud macrophysical changes over the Pacific Ocean from 2007 to 2017 are examined by combining CALIPSO and CloudSat (CALCS) active-sensor measurements, and these are compared with MODIS passive-sensor observations. Both CALCS and MODIS capture well-known features of cloud changes over the Pacific associated with meteorological conditions during El Niño–Southern Oscillation (ENSO) events. For example, midcloud (cloud tops at 3–10 km) and high cloud (cloud tops at 10–18 km) amounts increase with relative humidity (RH) anomalies. However, a better correlation is obtained between CALCS cloud volume and RH anomalies, confirming more accurate CALCS cloud boundaries than MODIS. Both CALCS and MODIS show that low cloud (cloud tops at 0–3 km) amounts increase with EIS and decrease with SST over the eastern Pacific, consistent with earlier studies. It is also further shown that the low cloud amounts do not increase with positive EIS anomalies if SST anomalies are positive. While similar features are found between CALCS and MODIS low cloud anomalies, differences also exist. First, relative to CALCS, MODIS shows stronger anticorrelation between low and mid/high cloud anomalies over the central and western Pacific, which is largely due to the limitation in detecting overlapping clouds from passive MODIS measurements. Second, relative to CALCS, MODIS shows smaller impacts of mid- and high clouds on the low troposphere (<3 km). The differences are due to the underestimation of MODIS cloud layer thicknesses of mid- and high clouds.
He, Haozhe; Kramer, Ryan J.; Soden, Brian J.He, H., R. J. Kramer, B. J. Soden, 2021: Evaluating Observational Constraints on Intermodel Spread in Cloud, Temperature, and Humidity Feedbacks. Geophysical Research Letters, 48(17), e2020GL092309. doi: 10.1029/2020GL092309. Uncertainty in climate feedbacks is the primary source of the spread in projected surface temperature responses to anthropogenic forcing. Cloud feedback persistently appears as the main source of disagreement in future projections while the combined lapse-rate plus water vapor (LR + WV) feedback is a smaller (30%), but non-trivial source of uncertainty in climate sensitivity. Here we attempt to observationally constrain the feedbacks in an effort to reduce their intermodel uncertainties. The observed interannual variation provides a useful constraint on the long-term cloud feedback, as evidenced by the consistency of global-mean values and regional contributions to the intermodel spread on both interannual and long-term timescales. However, interannual variability does not serve to constrain the long-term LR + WV feedback spread, which we find is dominated by the varying tropical relative humidity (RH) response to interhemispheric warming differences under clear-sky conditions and the RH-fixed LR feedback under all-sky conditions. cloud feedback; emergent constraint; intermodel spread; lapse-rate plus water vapor feedback
Henry, Matthew; Merlis, Timothy M.; Lutsko, Nicholas J.; Rose, Brian E. J.Henry, M., T. M. Merlis, N. J. Lutsko, B. E. J. Rose, 2021: Decomposing the Drivers of Polar Amplification with a Single-Column Model. J. Climate, 34(6), 2355-2365. doi: 10.1175/JCLI-D-20-0178.1. AbstractThe precise mechanisms driving Arctic amplification are still under debate. Previous attribution methods compute the vertically uniform temperature change required to balance the top-of-atmosphere energy imbalance caused by each forcing and feedback, with any departures from vertically uniform warming collected into the lapse-rate feedback. We propose an alternative attribution method using a single-column model that accounts for the forcing dependence of high-latitude lapse-rate changes. We examine this method in an idealized general circulation model (GCM), finding that, even though the column-integrated carbon dioxide (CO2) forcing and water vapor feedback are stronger in the tropics, they contribute to polar-amplified surface warming as they produce bottom-heavy warming in high latitudes. A separation of atmospheric temperature changes into local and remote contributors shows that, in the absence of polar surface forcing (e.g., sea ice retreat), changes in energy transport are primarily responsible for the polar-amplified pattern of warming. The addition of surface forcing substantially increases polar surface warming and reduces the contribution of atmospheric dry static energy transport to the warming. This physically based attribution method can be applied to comprehensive GCMs to provide a clearer view of the mechanisms behind Arctic amplification.
Hourdin, Frédéric; Williamson, Daniel; Rio, Catherine; Couvreux, Fleur; Roehrig, Romain; Villefranque, Najda; Musat, Ionela; Fairhead, Laurent; Diallo, F. Binta; Volodina, VictoriaHourdin, F., D. Williamson, C. Rio, F. Couvreux, R. Roehrig, N. Villefranque, I. Musat, L. Fairhead, F. B. Diallo, V. Volodina, 2021: Process-based climate model development harnessing machine learning: II. model calibration from single column to global. Journal of Advances in Modeling Earth Systems, (In Press). doi: https://doi.org/10.1029/2020MS002225. AbstractWe demonstrate a new approach for climate model tuning in a realistic situation. Our approach, the mathematical foundations and technical details of which are given in Part I, systematically uses a single-column configuration of a global atmospheric model on test cases for which reference large-eddy-simulations are available. The space of free parameters is sampled running the single-column model from which metrics are estimated in the full parameter space using emulators. The parameter space is then reduced by retaining only the values for which the emulated metrics match large eddy simulations within a given tolerance to error. The approach is applied to the 6A version of the LMDZ model which results from a long investment in the development of physics parameterizations and by-hand tuning. The boundary layer is revisited by increasing the vertical resolution and varying parameters that were kept fixed so far, which improves the representation of clouds at process scale. The approach allows us to automatically reach a tuning of this modified configuration as good as that of the 6A version. We show how this approach helps accelerate the introduction of new parameterizations. It allows us to maintain the physical foundations of the model and to ensure that the improvement of global metrics is obtained for a reasonable behavior at process level, reducing the risk of error compensations that may arise from over-fitting some climate metrics. That is, we get things right for the right reasons.
Hu, Zhiyuan; Jin, Qinjian; Ma, Yuanyuan; Pu, Bing; Ji, Zhenming; Wang, Yonghong; Dong, WenjieHu, Z., Q. Jin, Y. Ma, B. Pu, Z. Ji, Y. Wang, W. Dong, 2021: Temporal evolution of aerosols and their extreme events in polluted Asian regions during Terra's 20-year observations. Remote Sensing of Environment, 263, 112541. doi: 10.1016/j.rse.2021.112541. Aerosol pollution is an acute environmental issue in developing countries. Asia has been experiencing rapid changes in anthropogenic aerosols during the past two decades due to fast growth in population and economy. It is still an open question how aerosol loadings, represented by aerosol optical depth (AOD), have evolved in this century, particularly during the past decade when China and India implemented a clean air act aiming to improve air quality. Based on Terra aerosol retrievals and aerosol reanalysis, a change point of AOD trend is detected at 2010 in East China versus a persistent increasing AOD trend in the Indian subcontinent with no detectable change point from 2000 to 2019. In East China, positive AOD trend (+0.11 ± 0.022 decade−1) is confirmed from 2000 to 2010 (hereinafter the former period) yet negative trend (−0.26 ± 0.027 decade−1) is identified from 2011 to 2019 (hereinafter the later period). In the Indian subcontinent, persistent positive trend (+0.04 ± 0.001) is detected from 2000 to 2019 (hereinafter the whole period). All of these trends are attributed mainly to changes in sulfate aerosols. Further analysis of the aerosol pollution extreme events (APEE; defined as daily AOD over the long-term local 90th AOD percentile) manifest a positive trend (+0.16 ± 0.029 decade−1) of the APEEs' magnitude in East China during the former period yet a negative trend (−0.11 ± 0.020 decade−1) during the latter period; the Indian subcontinent demonstrates a positive trend (+0.02 ± 0.004 decade−1) during the whole period due to increasing sulfate aerosols. The APEEs have become more frequent (+3.5 ± 0.53 day month−1 decade−1) in East China during the former period yet less frequent (−3.6 ± 0.39 day month−1 decade−1) during the latter period; in the Indian subcontinent, more frequent APEEs (+1.1 ± 0.25 day month−1 decade−1) have been detected during the whole period. Consistent with the AOD trends, clear-sky radiation in East China shows a negative trend at the surface (−3.2 ± 0.67 W m−2 decade−1), a positive trend in the atmosphere (+1.4 ± 0.68 decade−1), and a negative trend at the top of the atmosphere (−1.8 ± 0.43 decade−1) during the former period, respectively; opposite trends with much larger magnitude are seen during the latter period. In the Indian subcontinent, the clear-sky radiation trends during the whole period are −1.4 ± 0.38, +1.7 ± 0.31, and + 0.5 ± 0.16 W m−2 decade−1 at the surface, in the atmosphere, and at the top of the atmosphere, respectively. Comparison of radiation trends at clear-sky and all-sky conditions suggests that absorbing aerosols dominate the radiation budget in the atmosphere and the aerosol reanalysis of the Modern-Era Retrospective Analysis for Research ans Applications version 2 (MERRA-2) might overestimate the radiation response to clouds. This study provides an up-to-date analysis of the long-term trends in aerosols and their extreme events and radiation in two of the world's heavily polluted regions and the results have important implications for assessment of the environmental and climatic impacts of the ongoing clean air acts in Asia. Terra; Aerosol; Asia; Radiation; MERRA-2; Air pollution; Extreme events; Trend
Huang, Han; Huang, Yi; Hu, YongyunHuang, H., Y. Huang, Y. Hu, 2021: Quantifying the energetic feedbacks in ENSO. Climate Dynamics, 56(1), 139-153. doi: 10.1007/s00382-020-05469-y. Energetic feedbacks play important roles during the El Niño-Southern Oscillation (ENSO). Here we conduct a thorough analysis of the radiative and non-radiative vertical fluxes and compare them to horizontal energy transport to provide a complete view of the energetics of ENSO. Our analyses affirm that cloud feedbacks are the most important radiative feedbacks, with cloud shortwave (SW) and longwave (LW) feedbacks dominating at the surface and in the atmosphere respectively. Oceanic energy transport dominates the oceanic heat content change in the developing phase and has significant effects on the sea surface temperature (SST) about 6 months earlier than vertical fluxes. Atmospheric horizontal energy transport is also important, acting to quickly remove the surplus of energy provided by the convergence of vertical energy fluxes in the atmosphere. The differential diabatic heating between the Central Pacific and the Warm Pool, induced by the latent heat release as well as LW radiation, strengthens the anomalous circulation and reinforces the Bjerknes positive feedback to strengthen the SST anomaly. This work reveals that the differential heating is more strongly correlated with the SST anomaly in the Central Pacific than the local SW negative feedback of clouds and supports the idea that the overall atmospheric effect is likely a positive feedback that acts to strengthen ENSO.
Huang, Xin; Ding, AijunHuang, X., A. Ding, 2021: Aerosol as a critical factor causing forecast biases of air temperature in global numerical weather prediction models. Science Bulletin. doi: 10.1016/j.scib.2021.05.009. Weather prediction is essential to the daily life of human beings. Current numerical weather prediction models such as the Global Forecast System (GFS) are still subject to substantial forecast biases and rarely consider the impact of atmospheric aerosol, despite the consensus that aerosol is one of the most important sources of uncertainty in the climate system. Here we demonstrate that atmospheric aerosol is one of the important drivers biasing daily temperature prediction. By comparing observations and the GFS prediction, we find that the monthly-averaged bias in the 24-h temperature forecast varies between ± 1.5 °C in regions influenced by atmospheric aerosol. The biases depend on the properties of aerosol, the underlying land surface, and aerosol–cloud interactions over oceans. It is also revealed that forecast errors are rapidly magnified over time in regions featuring high aerosol loadings. Our study provides direct “observational” evidence of aerosol’s impacts on daily weather forecast, and bridges the gaps between the weather forecast and climate science regarding the understanding of the impact of atmospheric aerosol. Aerosol–cloud interactions; Aerosol–radiation interactions; Atmospheric aerosol; Temperature forecast errors; Weather prediction
Huang, Yiyi; Ding, Qinghua; Dong, Xiquan; Xi, Baike; Baxter, IanHuang, Y., Q. Ding, X. Dong, B. Xi, I. Baxter, 2021: Summertime low clouds mediate the impact of the large-scale circulation on Arctic sea ice. Communications Earth & Environment, 2(1), 1-10. doi: 10.1038/s43247-021-00114-w. The rapid Arctic sea ice retreat in the early 21st century is believed to be driven by several dynamic and thermodynamic feedbacks, such as ice-albedo feedback and water vapor feedback. However, the role of clouds in these feedbacks remains unclear since the causality between clouds and these processes is complex. Here, we use NASA CERES satellite products and NCAR CESM model simulations to suggest that summertime low clouds have played an important role in driving sea ice melt by amplifying the adiabatic warming induced by a stronger anticyclonic circulation aloft. The upper-level high pressure regulates low clouds through stronger downward motion and increasing lower troposphere relative humidity. The increased low clouds favor more sea ice melt via emitting stronger longwave radiation. Then decreased surface albedo triggers a positive ice-albedo feedback, which further enhances sea ice melt. Considering the importance of summertime low clouds, accurate simulation of this process is a prerequisite for climate models to produce reliable future projections of Arctic sea ice.
Huang, Yiyi; Dong, Xiquan; Kay, Jennifer E.; Xi, Baike; McIlhattan, Elin A.Huang, Y., X. Dong, J. E. Kay, B. Xi, E. A. McIlhattan, 2021: The climate response to increased cloud liquid water over the Arctic in CESM1: a sensitivity study of Wegener–Bergeron–Findeisen process. Climate Dynamics. doi: 10.1007/s00382-021-05648-5. The surface radiative imbalance has large impacts on the long-term trends and year-to-year variability of Arctic sea ice. Clouds are believed to be a key factor in regulating this radiative imbalance, whose underlying processes and mechanisms, however, are not well understood. Compared with observations, the Community Earth System Model version 1 (CESM1) is known to underestimate Arctic cloud liquid water. Here, the following hypothesis is proposed and tested: this underestimation is caused by an overactive Wegener–Bergeron–Findeisen (WBF) process in model as too many supercooled liquid droplets are scavenged by ice crystals via deposition. In this study, the efficiency of the WBF process in CESM1 was reduced to investigate the Arctic climate response, and differentiate the responses induced by atmosphere–ocean–sea ice coupling and global warming. By weakening the WBF process, CESM1 simulated liquid cloud fractions increased, especially in winter and spring. The cloud response resulted in increased downwelling longwave flux and decreased shortwave flux at the surface. Arctic clouds and radiation in simulations with reduced WBF efficiency show a better agreement with satellite retrievals. In addition, both coupling and global warming amplify the cloud response to a less efficient WBF process, due to increased relative humidity and enhanced evaporation, respectively. As a response, the sea ice tends to melt over the North Atlantic Ocean, most likely caused by a positive feedback process between clouds, radiation and sea ice during non-summer months. These results improve our understanding of large-scale effects of the WBF process and the role of cloud liquid water in the Arctic climate system.
Itterly, Kyle; Taylor, Patrick; Roberts, J. BrentItterly, K., P. Taylor, J. B. Roberts, 2021: Satellite Perspectives of Sea Surface Temperature Diurnal Warming on Atmospheric Moistening and Radiative Heating During MJO. J. Climate, (In Press). doi: 10.1175/JCLI-D-20-0350.1.
Jadala, Nirmala Bai; Sridhar, Miriyala; Dutta, Gopa; Yousuf, Mohammed; Reddy, Y. K.Jadala, N. B., M. Sridhar, G. Dutta, M. Yousuf, Y. K. Reddy, 2021: Integrated water vapor during active and break spells of monsoon and its relationship with temperature, precipitation and precipitation efficiency over a tropical site. Geodesy and Geodynamics. doi: 10.1016/j.geog.2021.09.008. Global Positioning System (GPS) measurements of integrated water vapor (IWV) for two years (2014 and 2015) are presented in this paper. Variation of IWV during active and break spells of Indian summer monsoon has been studied for a tropical station Hyderabad (17.4° N, 78.46° E). The data is validated with ECMWF Re-Analysis (ERA) 91 level data. Relationships of IWV with other atmospheric variables like surface temperature, rain, and precipitation efficiency have been established through cross-correlation studies. A positive correlation coefficient is observed between IWV and surface temperature over two years. But the coefficient becomes negative when only summer monsoon months (June, July, August, and September) are considered. Rainfall during these months cools down the surface and could be the reason for this change in the correlation coefficient. Correlation studies between IWV- precipitation, IWV- precipitation efficiency (P.E), and precipitation-P.E show that coefficients are −0.05, −0.10 and 0.983 with 95% confidence level respectively, which proves that the efficacy of rain does not depend only on the level of water vapor. A proper dynamic mechanism is necessary to convert water vapor into the rain. The diurnal variations of IWV during active and break spells have been analyzed. The amplitudes of diurnal oscillation and its harmonics of individual spell do not show clear trends but the mean amplitudes of the break spells are approximately double than those of the active spells. The amplitudes of diurnal, semi-diurnal and ter-diurnal components during break spells are 1.08 kg/m2, 0.52 kg/m2 and 0.34 kg/m2 respectively. The corresponding amplitudes during active spells are 0.68 kg/m2, 0.41 kg/m2 and 0.23 kg/m2. Correlation coefficient; Diurnal oscillation; Precipitation efficiency
Jahani, Babak; Andersen, Hendrik; Calbó, Josep; González, Josep-Abel; Cermak, JanJahani, B., H. Andersen, J. Calbó, J. González, J. Cermak, 2021: Longwave Radiative Effect of the Cloud-Aerosol Transition Zone Based on CERES Observations. Atmospheric Chemistry and Physics Discussions, 1-17. doi: 10.5194/acp-2021-421. Abstract. This study presents an approach for quantification of cloud-aerosol transition zone broadband longwave radiative effects at the top of the atmosphere (TOA) during daytime over the ocean, based on satellite observations and radiative transfer simulation. Specifically, we used several products from MODIS (Moderate Resolution Imaging Spectroradiometer) and CERES (Clouds and the Earth’s Radiant Energy System) sensors for identification and selection of CERES footprints with horizontally homogeneous transition zone and clear-sky conditions. For the selected transition zone footprints, radiative effect was calculated as the difference between the instantaneous CERES TOA upwelling broadband longwave radiance observations and corresponding clear-sky radiance simulations. The clear-sky radiances were simulated using the Santa Barbara DISORT Atmospheric Radiative Transfer model fed by the hourly ERA5 reanalysis (fifth generation ECMWF reanalysis) atmospheric and surface data. The CERES radiance observations corresponding to the clear-sky footprints detected were also used for validating the simulated clear-sky radiances. We tested this approach using the radiative measurements made by the MODIS and CERES instruments onboard Aqua platform over the south-eastern Atlantic Ocean during August 2010. For the studied period and domain, transition zone radiative effect (given in flux units) is on average equal to 8.0 ± 3.7 W m−2 (heating effect; median: 5.4 W m−2), although cases with radiative effects as large as 50 W m−2 were found.
Jensen, Michael P.; Ghate, Virendra P.; Wang, Dié; Apoznanski, Diana K.; Bartholomew, Mary J.; Giangrande, Scott E.; Johnson, Karen L.; Thieman, Mandana M.Jensen, M. P., V. P. Ghate, D. Wang, D. K. Apoznanski, M. J. Bartholomew, S. E. Giangrande, K. L. Johnson, M. M. Thieman, 2021: Contrasting characteristics of open- and closed-cellular stratocumulus cloud in the eastern North Atlantic. Atmospheric Chemistry and Physics, 21(19), 14557-14571. doi: 10.5194/acp-21-14557-2021. Abstract. Extensive regions of marine boundary layer cloud impact the radiative balance through their significant shortwave albedo while having little impact on outgoing longwave radiation. Despite this importance, these cloud systems remain poorly represented in large-scale models due to difficulty in representing the processes that drive their life cycle and coverage. In particular, the mesoscale organization and cellular structure of marine boundary clouds have important implications for the subsequent cloud feedbacks. In this study, we use long-term (2013–2018) observations from the Atmospheric Radiation Measurement (ARM) Facility's Eastern North Atlantic (ENA) site on Graciosa Island, Azores, Portugal, to identify cloud cases with open- or closed-cellular organization. More than 500 h of each organization type are identified. The ARM observations are combined with reanalysis and satellite products to quantify the cloud, precipitation, aerosol, thermodynamic, and large-scale synoptic characteristics associated with these cloud types. Our analysis shows that both cloud organization populations occur during similar sea surface temperature conditions, but the open-cell cases are distinguished by stronger cold-air advection and large-scale subsidence compared to the closed-cell cases, consistent with their formation during cold-air outbreaks. We also find that the open-cell cases were associated with deeper boundary layers, stronger low-level winds, and higher rain rates compared to their closed-cell counterparts. Finally, raindrops with diameters larger than 1 mm were routinely recorded at the surface during both populations, with a higher number of large drops during the open-cellular cases. The similarities and differences noted herein provide important insights into the environmental and cloud characteristics during varying marine boundary layer cloud mesoscale organization and will be useful for the evaluation of model simulations for ENA marine clouds.
Jia, Aolin; Ma, Han; Liang, Shunlin; Wang, DongdongJia, A., H. Ma, S. Liang, D. Wang, 2021: Cloudy-sky land surface temperature from VIIRS and MODIS satellite data using a surface energy balance-based method. Remote Sensing of Environment, 263, 112566. doi: 10.1016/j.rse.2021.112566. Land surface temperature (LST) has been effectively retrieved from thermal infrared (TIR) satellite measurements under clear-sky conditions. However, TIR satellite data are often severely contaminated by clouds, which cause spatiotemporal discontinuities and low retrieval accuracy in the LST products. Several solutions have been proposed to fill the “gaps”; however, a majority of these possess constraints. For example, fusion methods with microwave data suffer from coarse spatial resolution and diverse land cover types while spatial-temporal interpolation methods neglect cloudy cooling effects. We developed a novel method to estimate cloudy-sky LST from polar-orbiting satellite data based on the surface energy balance (SEB) principle. First, the hypothetical clear-sky LST of missing or likely cloud-contaminated pixels was reconstructed by assimilating high-quality satellite retrievals into a time-evolving model built from reanalysis data using a Kalman filter data assimilation algorithm. Second, clear-sky LST was hypothetically corrected by accounting for cloud cooling based on SEB theory. The proposed method was applied to Visible Infrared Imaging Radiometer Suite (VIIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS) data, and further validated using ground measurements of fourteen sites from SURFRAD, BSRN, and AmeriFlux in 2013. VIIRS LST recovered from cloud gaps exhibited a root mean square error (RMSE) of 3.54 K, a bias of −0.36 K, R2 of 0.94, and sample size (N) of 2411, comparable to the accuracy of clear-sky LST products and cloudy-sky LST estimation from MODIS (RMSE of 3.69 K, bias of −0.45 K, R2 of 0.93, and N of 2398). Thus, the proposed method performs well across different sensors, seasons, and land cover types. The abnormal retrieval values caused by cloud contamination were also corrected in the proposed method. The overall accuracy was better than the downscaled cloudy-sky LST retrieved from passive microwave (PMW) observations and former SEB-based cloudy-sky LST estimation methods. Validation using time-series measurements showed that the all-sky LST time series, including both clear- and cloudy-sky retrievals, can capture realistic variability without sudden abruptions or discontinuities. RMSE values for the all-sky LST varied from 2.54 to 4.15 K at the fourteen sites. Spatially continuous LST maps over the Contiguous United States were compared with corresponding maps from PMW data in the winter and summer of 2018, exhibiting similar spatial patterns but with additional spatial details. Moreover, sensitivity analysis suggested that the reconstruction of clear-sky LST dominantly impacts the accuracy of cloudy-sky LST estimation. The proposed method can be potentially implemented in similar satellite sensors for global real-time production. Data assimilation; Land surface temperature; Cloudy-sky; Surface energy balance principle; VIIRS and MODIS
Jia, Hailing; Ma, Xiaoyan; Yu, Fangqun; Quaas, JohannesJia, H., X. Ma, F. Yu, J. Quaas, 2021: Significant underestimation of radiative forcing by aerosol–cloud interactions derived from satellite-based methods. Nature Communications, 12(1), 3649. doi: 10.1038/s41467-021-23888-1. Satellite-based estimates of radiative forcing by aerosol–cloud interactions (RFaci) are consistently smaller than those from global models, hampering accurate projections of future climate change. Here we show that the discrepancy can be substantially reduced by correcting sampling biases induced by inherent limitations of satellite measurements, which tend to artificially discard the clouds with high cloud fraction. Those missed clouds exert a stronger cooling effect, and are more sensitive to aerosol perturbations. By accounting for the sampling biases, the magnitude of RFaci (from −0.38 to −0.59 W m−2) increases by 55 % globally (133 % over land and 33 % over ocean). Notably, the RFaci further increases to −1.09 W m−2 when switching total aerosol optical depth (AOD) to fine-mode AOD that is a better proxy for CCN than AOD. In contrast to previous weak satellite-based RFaci, the improved one substantially increases (especially over land), resolving a major difference with models.
Jian, Bida; Li, Jiming; Wang, Guoyin; Zhao, Yuxin; Li, Yarong; Wang, Jing; Zhang, Min; Huang, JianpingJian, B., J. Li, G. Wang, Y. Zhao, Y. Li, J. Wang, M. Zhang, J. Huang, 2021: Evaluation of the CMIP6 marine subtropical stratocumulus cloud albedo and its controlling factors. Atmospheric Chemistry and Physics Discussions, 1-29. doi: https://doi.org/10.5194/acp-2020-1245. Abstract. The cloud albedo at the subtropical marine subtropical stratocumulus regions has a key role in regulating the regional energy budget. Based on 12 years of monthly data from multiple satellite datasets, the long-term, monthly and seasonal cycle averaged cloud albedo at five stratocumulus regions were investigated to inter-compare the atmosphere-only simulations of Phase 5 and 6 of the Coupled Model Inter-comparison Project (AMIP5 and AMIP6). Statistical results showed that the long-term regressed cloud albedos were underestimated in most AMIP6 models compared with the satellite-driven cloud albedos, and the AMIP6 models produced a similar spread of AMIP5 at all regions. The monthly mean and seasonal cycle of cloud albedo of AMIP6 ensemble mean showed better correlation with the satellite-driven observation than that of AMIP5 ensemble mean, however, fail to reproduce the values and amplitude in some regions. By employing the Modern-Era Retrospective Analysis for Research and Applications Version 2 data, this study estimated the relative contributions of different aerosols and meteorological factors on the marine stratocumulus cloud albedo under different cloud liquid water path (LWP) conditions. The multiple regression models can explain ~60 % of the changes in the cloud albedo. Under the monthly mean LWP ≤ 60 g m−2, dust and black carbon dominantly contributed to the changes in the cloud albedo, while sulfate aerosol contributed the most under the condition of 60 g m−2
Joseph, Jofia; Girishkumar, M. S.; McPhaden, M. J.; Rao, E. Pattabhi RamaJoseph, J., M. S. Girishkumar, M. J. McPhaden, E. P. R. Rao, 2021: Diurnal variability of atmospheric cold pool events and associated air-sea interactions in the Bay of Bengal during the summer monsoon. Climate Dynamics, 56(3), 837-853. doi: 10.1007/s00382-020-05506-w. Atmospheric cold pools generated from convective downdrafts can significantly modulate air-sea interaction processes, though the variability in cold pool events is not yet documented in the Bay of Bengal (BoB). In this study, the seasonal and diurnal variability of cold pool events (defined as a drop in air temperature greater than 1 °C within 30 min) in the BoB is examined using moored buoy measurements with 10-min temporal resolution at 8°N, 12°N, and 15°N along 90°E. The analysis shows that cold pools are plentiful and frequent during summer (May–September) and fall (October–November) compared to winter (December-February) and spring (March–April). Results also indicate a significant diurnal variability at 15°N and 12°N (but not at 8°N) during summer, with more frequent and intense cold pool events in the afternoon. Cold pools lead to an intensification of turbulent heat exchange between the ocean and atmosphere, with increased latent heat loss (~ 80 Wm−2) through both an increase in wind speed and reduction in air specific humidity and increased sensible heat loss (~ 40 Wm−2) due primarily to air temperature drops. There is also a significant diurnal variability in these air-sea exchanges during the summer, with a twofold enhancement in latent and sensible heat fluxes associated with afternoon vs nighttime cold pools events. Finally, we establish the connection between the enhancement of afternoon cold pool events and southeastward propagating synoptic-scale rainfall activity on diurnal time scales from the western BoB.
Joseph, Jofia; Girishkumar, M. S.; Varikoden, Hamza; Thangaprakash, V. P.; Shivaprasad, S.; Rama Rao, E. PattabhiJoseph, J., M. S. Girishkumar, H. Varikoden, V. P. Thangaprakash, S. Shivaprasad, E. P. Rama Rao, 2021: Observed sub-daily variability of latent and sensible heat fluxes in the Bay of Bengal during the summer. Climate Dynamics, 56(3), 917-934. doi: 10.1007/s00382-020-05512-y. The sub-daily variability of latent (LHF) and sensible heat flux (SHF) in the Bay of Bengal (BoB) during the summer (May–September) is examined using moored buoys data at 8° N (2008 and 2011), 12° N (2010, 2011, 2012, 2013, 2014, and 2015), and 15° N (2009, 2013, 2014, and 2015) along 90° E. In the weak wind regime ( 6 ms−1) with a range of ~ 13 Wm−2 at 8° N and ~ 17 Wm−2 at 12° N and 15° N. In the strong wind regime, SHF shows heat gain by the ocean with a maximum (minimum) value during the daytime (night), while it shows heat loss from the ocean in the weak wind regime with maximum (minimum) value during the night (daytime). The diurnal range of SHF does not show significant meridional variation in the strong (~ 3.5 Wm−2) and weak (~ 2 Wm−2) wind regime. The difference in sub-daily evolution of air-temperature, air-specific humidity, and wind speed determines distinct evolutions of LHF and SHF in different wind regimes, which appears to be driven by atmospheric boundary layer processes and eastward propagating land-sea breeze signals over the BoB. Finally, we also establish the relationship between sub-daily evolutions of turbulent heat fluxes in the different wind regimes with synoptic conditions associated with the active and break phases of the Indian summer monsoon.
Kang, Litai; Marchand, Roger; Smith, WilliamKang, L., R. Marchand, W. Smith, 2021: Evaluation of MODIS and Himawari-8 Low Clouds Retrievals Over the Southern Ocean With In Situ Measurements From the SOCRATES Campaign. Earth and Space Science, 8(3), e2020EA001397. doi: https://doi.org/10.1029/2020EA001397. Aircraft observations collected during the Southern Ocean Cloud Radiation Aerosol Transport Experimental Study in January-February of 2018 are used to evaluate cloud properties from three satellite-imager datasets: (1) the Moderate Resolution Imaging Spectroradiometer level 2 (collection 6.1) cloud product, (2) the CERES-MODIS Edition 4 cloud product, and (3) the NASA SatCORPS Himawari-8 cloud product. Overall the satellite retrievals compare well with the in situ observations, with little bias and modest to good correlation coefficients when considering all aircraft profiles for which there are coincident MODIS observations. The Himawari-8 product does, however, show a statistically significant mean bias of about 1.2 μm for effective radius (re) and 2.6 for optical depth (τ) when applied to a larger set of profiles with coincident Himawari-8 observations. The low overall mean-bias in the re retrievals is due in part to compensating errors between cases that are non- or lightly precipitating, with cases that have heavier precipitation. re is slightly biased high (by about 0.5–1.0 μm) for non- and lightly precipitating cases and biased low by about 3–4 μm for heavily precipitating cases when precipitation exits near cloud top. The bias in non- and lightly precipitating conditions is due to (at least in part) having assumed a drop size distribution in the retrieval that is too broad. These biases in the re ultimately propagate into the retrieved liquid water path and number concentration. clouds; MODIS; remote sensing; southern ocean; himawari-8; SOCRATES
Kato, Seiji; Loeb, Norman G.; Fasullo, John T.; Trenberth, Kevin E.; Lauritzen, Peter H.; Rose, Fred G.; Rutan, David A.; Satoh, MasakiKato, S., N. G. Loeb, J. T. Fasullo, K. E. Trenberth, P. H. Lauritzen, F. G. Rose, D. A. Rutan, M. Satoh, 2021: Regional Energy and Water Budget of a Precipitating Atmosphere over Ocean. J. Climate, 34(11), 4189-4205. doi: 10.1175/JCLI-D-20-0175.1. AbstractEffects of water mass imbalance and hydrometeor transport on the enthalpy flux and water phase on diabatic heating rate in computing the regional energy and water budget of the atmosphere over ocean are investigated. Equations of energy and water budget of the atmospheric column that explicitly consider the velocity of liquid and ice cloud particles, and rain and snow are formulated by separating water variables from dry air. Differences of energy budget equations formulated in this study from those used in earlier studies are that 1) diabatic heating rate depends on water phase, 2) diabatic heating due to net condensation of nonprecipitating hydrometeors is included, and 3) hydrometeors can be advected with a different velocity from the dry-air velocity. Convergence of water vapor associated with phase change and horizontal transport of hydrometeors is to increase diabatic heating in the atmospheric column where hydrometeors are formed and exported and to reduce energy where hydrometeors are imported and evaporated. The process can improve the regional energy and water mass balance when energy data products are integrated. Effects of enthalpy transport associated with water mass transport through the surface are cooling to the atmosphere and warming to the ocean when the enthalpy is averaged over the global ocean. There is no net effect to the atmosphere and ocean columns combined. While precipitation phase changes the regional diabatic heating rate up to 15 W m−2, the dependence of the global mean value on the temperature threshold of melting snow to form rain is less than 1 W m−2.
Kato, Seiji; Rose, Fred G.Kato, S., F. G. Rose, 2021: Reply to “Comments on ‘Global and Regional Entropy Production by Radiation Estimated from Satellite Observations’”. J. Climate, 34(9), 3729-3731. doi: 10.1175/JCLI-D-20-0950.1. AbstractThis reply addresses a comment on the study by Kato and Rose (herein referred to as KR2020). The comment raises four points of criticism. These are 1) on notations used, 2) on a steady-state assumption made, 3) on the result of entropy production change with Earth’s albedo, and 4) disputing the statement that a simple energy balance model cannot produce absorption temperature change with Earth’s albedo. We concur on points 2 and 3 raised by the comment and recognize the significance of entropy storage due to ocean heating in the analysis of how entropy production changes with the shortwave absorptivity of Earth. Once entropy storage is considered, the results of KR2020 indicate that the increase of entropy production rate by irreversible processes, including by radiative processes, is smaller than the increase of entropy storage when absorptivity is increased. This is a manifestation of the primary contribution of positive top-of-atmosphere net irradiances (i.e., energy input to Earth) to heating the ocean and is consistent with an energy budget perspective. Once entropy storage is separated, the entropy production by irreversible processes increases with the shortwave absorptivity.
Kato, Seiji; Rose, Fred G.; Chang, Fu-Lung; Painemal, David; Smith, William L.Kato, S., F. G. Rose, F. Chang, D. Painemal, W. L. Smith, 2021: Evaluation of Regional Surface Energy Budget Over Ocean Derived From Satellites. Frontiers in Marine Science, 8, 1264. doi: 10.3389/fmars.2021.688299. The energy balance equation of an atmospheric column indicates that two approaches are possible to compute regional net surface energy flux. The first approach is to use the sum of surface energy flux components Fnet,c and the second approach is to use net top-of-atmosphere (TOA) irradiance and horizontal energy transport by the atmosphere Fnet,t. When regional net energy flux is averaged over the global ocean, Fnet,c and Fnet,t are, respectively, 16 and 2 Wm–2, both larger than the ocean heating rate derived from ocean temperature measurements. The difference is larger than the estimated uncertainty of Fnet,t of 11 Wm–2. Larger regional differences between Fnet,c and Fnet,t exist over tropical ocean. The seasonal variability of energy flux components averaged between 45°N and 45°S ocean reveals that the surface provides net energy to the atmosphere from May to July. These two examples demonstrates that the energy balance can be used to assess the quality of energy flux data products.
Kawai, Hideaki; Koshiro, Tsuyoshi; Yukimoto, SeijiKawai, H., T. Koshiro, S. Yukimoto, 2021: Relationship between shortwave radiation bias over the Southern Ocean and the double-intertropical convergence zone problem in MRI-ESM2. Atmospheric Science Letters, 22(12), e1064. doi: 10.1002/asl.1064. The relationship between improvements in the radiation bias over the Southern Ocean and the alleviation of the double-intertropical convergence zone (ITCZ) problem in the actual updates of our climate models is investigated. The radiation bias in MRI-CGCM3 that was used for CMIP5 simulations, particularly over the Southern Ocean, is significantly reduced in MRI-ESM2 that is used for CMIP6 simulations. Each modification that contributed to the reduction of the radiation bias was progressively reverted to the corresponding older treatment in order to examine their individual impacts on the ITCZ representation. Results show the double-ITCZ problem worsens almost monotonically when the excessive shortwave insolation over the Southern Ocean increases. The contribution of the atmosphere is about one third of the impact on the total northward energy transport and the corresponding response of the Hadley cell is related to the change in the double-ITCZ. However, our results also imply that the ITCZ bias cannot be completely resolved by the improvements of radiative flux alone and that there are other causes of the problem. cloud; ITCZ; climate model; Southern Ocean
Kim, Rachel; Tremblay, L. Bruno; Brunette, Charles; Newton, RobertKim, R., L. B. Tremblay, C. Brunette, R. Newton, 2021: A Regional Seasonal Forecast Model of Arctic Minimum Sea Ice Extent: Reflected Solar Radiation versus Late Winter Coastal Divergence. J. Climate, 34(15), 6097-6113. doi: 10.1175/JCLI-D-20-0846.1. AbstractThinning sea ice cover in the Arctic is associated with larger interannual variability in the minimum sea ice extent (SIE). The current generation of forced or fully coupled models, however, has difficulty predicting SIE anomalies from the long-term trend, highlighting the need to better identify the mechanisms involved in the seasonal evolution of sea ice cover. One such mechanism is coastal divergence (CD), a proxy for ice thickness anomalies based on late winter ice motion, quantified using Lagrangian ice tracking. CD gains predictive skill through the positive feedback of surface albedo anomalies, mirrored in reflected solar radiation (RSR), during melt season. Exploring the dynamic and thermodynamic contributions to minimum SIE predictability, RSR, initial SIE (iSIE), and CD are compared as predictors using a regional seasonal sea ice forecast model for 1 July, 1 June, and 1 May forecast dates for all Arctic peripheral seas. The predictive skill of June RSR anomalies mainly originates from open water fraction at the surface; that is, June iSIE and June RSR have equal predictive skill for most seas. The finding is supported by the surprising positive correlation found between June melt pond fraction (MPF) and June RSR in all peripheral seas: MPF anomalies indicate the presence of ice or open water, which is key to creating minimum SIE anomalies. This contradicts models that show correlation between melt onset, MPF, and the minimum SIE. A hindcast model shows that for a 1 May forecast, CD anomalies have better predictive skill than RSR anomalies for most peripheral seas.
Koppa, Akash; Alam, Sarfaraz; Miralles, Diego G.; Gebremichael, MekonnenKoppa, A., S. Alam, D. G. Miralles, M. Gebremichael, 2021: Budyko-Based Long-Term Water and Energy Balance Closure in Global Watersheds From Earth Observations. Water Resources Research, 57(5), e2020WR028658. doi: https://doi.org/10.1029/2020WR028658. Earth observations offer potential pathways for accurately closing the water and energy balance of watersheds, a fundamental challenge in hydrology. However, previous attempts based on purely satellite-based estimates have focused on closing the water and energy balances separately. They are hindered by the lack of estimates of key components, such as runoff. Here, we posit a novel approach based on Budyko’s water and energy balance constraints. The approach is applied to quantify the degree of long-term closure at the watershed scale, as well as its associated uncertainties, using an ensemble of global satellite data sets. We find large spatial variability across aridity, elevation, and other environmental gradients. Specifically, we find a positive correlation between elevation and closure uncertainty, as derived from the Budyko approach. In mountainous watersheds the uncertainty in closure is 3.9 ± 0.7 (dimensionless). Our results show that uncertainties in terrestrial evaporation contribute twice as much as precipitation uncertainties to errors in the closure of water and energy balance. Moreover, our results highlight the need for improving satellite-based precipitation and evaporation data in humid temperate forests, where the closure error in the Budyko space is as high as 1.1 ± 0.3, compared to only 0.2 ± 0.03 in tropical forests. Comparing the results with land surface model-based data sets driven by in situ precipitation, we find that Earth observation-based data sets perform better in regions where precipitation gauges are sparse. These findings have implications for improving the understanding of global hydrology and regional water management and can guide the development of satellite remote sensing-based data sets and Earth system models. precipitation; remote sensing; water balance; evapotranspiration; Budyko hypothesis; energy Balance
Kottayil, Ajil; Xavier, Anu; Xavier, Prince; Koovekkallu, Prajwal; Mohanakumar, KesavapillaiKottayil, A., A. Xavier, P. Xavier, P. Koovekkallu, K. Mohanakumar, 2021: Evolution of large-scale factors influencing extreme rainfall over south western coast of India. International Journal of Climatology, 1-15. doi: 10.1002/joc.7455. The life cycle and the large-scale factors driving extreme heavy rainfall events over the south west coast of India are studied. The extreme rainfall events are linked to the development of monsoon depressions and the associated large-scale dynamics. Strengthening of these parameters intensifies the monsoon low-level circulation over the Arabian Sea and the west coast via steepened meridional pressure gradient. The intensification of the low-level jet stream speed and its extension in the vertical causes an increase in the humidity flux in the lower and midtroposphere. The consequent ascending motion is from the midtroposphere to the upper troposphere, resulting in the formation of deep convective cloud clusters over the west coast and eastern parts of the Arabian Sea. This results in the incidence of extreme heavy rainfall over the south west coast of India. It is observed that during days of extreme rainfall, the direction of wind in the lower troposphere tends to be almost perpendicular to the Western Ghats favouring a strong orographic lift. The extreme rainfall events over the south west coast do not necessarily occur during the active cycle of monsoon intraseasonal oscillation, but are linked to the north westwards propagating monsoon depressions. We show that the signatures of extreme rainfall can be observed in several meteorological variables developing over different parts of the monsoon region. A synergistic analysis of these variables may help in the accurate and timely prediction of these events. monsoon; extreme rainfall; low-level jet; moisture flux; Western Ghats
Kramer, Ryan J.; He, Haozhe; Soden, Brian J.; Oreopoulos, Lazaros; Myhre, Gunnar; Forster, Piers M.; Smith, Christopher J.Kramer, R. J., H. He, B. J. Soden, L. Oreopoulos, G. Myhre, P. M. Forster, C. J. Smith, 2021: Observational evidence of increasing global radiative forcing. Geophysical Research Letters, n/a(n/a), e2020GL091585. doi: https://doi.org/10.1029/2020GL091585. Changes in atmospheric composition, such as increasing greenhouse gases, cause an initial radiative imbalance to the climate system, quantified as the instantaneous radiative forcing. This fundamental metric has not been directly observed globally and previous estimates have come from models. In part, this is because current space-based instruments cannot distinguish the instantaneous radiative forcing from the climate’s radiative response. We apply radiative kernels to satellite observations to disentangle these components and find all-sky instantaneous radiative forcing has increased 0.53±0.11 W/m2 from 2003 through 2018, accounting for positive trends in the total planetary radiative imbalance. This increase has been due to a combination of rising concentrations of well-mixed greenhouse gases and recent reductions in aerosol emissions. These results highlight distinct fingerprints of anthropogenic activity in Earth’s changing energy budget, which we find observations can detect within 4 years. aerosols; radiative forcing; greenhouse gases; radiative kernels
Lang, Simon T. K.; Dawson, Andrew; Diamantakis, Michail; Dueben, Peter; Hatfield, Samuel; Leutbecher, Martin; Palmer, Tim; Prates, Fernando; Roberts, Christopher D.; Sandu, Irina; Wedi, NilsLang, S. T. K., A. Dawson, M. Diamantakis, P. Dueben, S. Hatfield, M. Leutbecher, T. Palmer, F. Prates, C. D. Roberts, I. Sandu, N. Wedi, 2021: More accuracy with less precision. Quarterly Journal of the Royal Meteorological Society, 147(741), 4358-4370. doi: 10.1002/qj.4181. Reducing the numerical precision of the forecast model of the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF) from double to single precision results in significant computational savings without negatively affecting forecast accuracy. The computational savings allow to increase the vertical resolution of the operational ensemble forecasts from 91 to 137 levels earlier than anticipated and before the next upgrade of ECMWF's high-performance computing facility. This upgrade to 137 levels harmonises the vertical resolution of the medium-range deterministic forecasts and the medium-range and extended-range ensemble forecasts. Increasing the vertical resolution of the ensemble forecasts substantially improves forecast skill for all lead times as well as the mean of the model climate. ECMWF's ensemble and deterministic forecasts will run operationally at single precision from IFS model cycle 47R2 onwards. ensemble forecasting; reduced precision
Lang, Simon T. K.; Lock, Sarah-Jane; Leutbecher, Martin; Bechtold, Peter; Forbes, Richard M.Lang, S. T. K., S. Lock, M. Leutbecher, P. Bechtold, R. M. Forbes, 2021: Revision of the Stochastically Perturbed Parametrisations model uncertainty scheme in the Integrated Forecasting System. Quarterly Journal of the Royal Meteorological Society, 147(735), 1364-1381. doi: https://doi.org/10.1002/qj.3978. The Stochastically Perturbed Parametrisations scheme (SPP) represents model uncertainty in numerical weather prediction by introducing stochastic perturbations into the physical parametrisation schemes. The perturbations are constructed in such a way that the internal consistency of the physical parametrisation schemes is preserved. We developed a revised version of SPP for the Integrated Forecasting System of the European Centre for Medium-Range Weather Forecasts (ECMWF). The revised version introduces perturbations to additional quantities and modifies the probability distributions sampled by the scheme. Medium-range ensemble forecasts with the revised SPP are considerably more skilful than ensemble forecasts with the original implementation of SPP. The revised version of SPP is similar, in terms of forecast skill, to the Stochastically Perturbed Parametrisation Tendency scheme (SPPT), which is currently used to represent model uncertainty in the operational ECMWF ensemble forecasts. stochastic physics; ensemble forecasting; ensemble perturbation methods; SPP; SPPT
Lee, Hsiang-He; Bogenschutz, Peter; Yamaguchi, TakanobuLee, H., P. Bogenschutz, T. Yamaguchi, 2021: The Implementation of Framework for Improvement by Vertical Enhancement Into Energy Exascale Earth System Model. Journal of Advances in Modeling Earth Systems, 13(6), e2020MS002240. doi: 10.1029/2020MS002240. The low cloud bias in global climate models (GCMs) remains an unsolved problem. Coarse vertical resolution in GCMs has been suggested to be a significant cause of low cloud bias because planetary boundary layer parameterizations cannot resolve sharp temperature and moisture gradients often found at the top of subtropical stratocumulus layers. This work aims to ameliorate the low cloud problem by implementing a new computational method, the Framework for Improvement by Vertical Enhancement (FIVE), into the Energy Exascale Earth System Model (E3SM). Three physics schemes representing microphysics, radiation, and turbulence as well as vertical advection are interfaced to vertically enhanced physics (VEP), which allows for these processes to be computed on a higher vertical resolution grid compared to the rest of the E3SM model. We demonstrate the better representation of subtropical boundary layer clouds with FIVE while limiting additional computational cost from the increased number of levels. When the vertical resolution approaches the large eddy simulation-like vertical resolution in VEP, the climatological low cloud amount shows a significant increase of more than 30% in the southeastern Pacific Ocean. Using FIVE to improve the representation of low-level clouds does not come with any negative side effects associated with the simulation of mid- and high-level cloud and precipitation, that can occur when running the full model at higher vertical resolution. marine boundary layer; E3SM; vertical resolution; stratocumulus cloud; FIVE; low-level cloud
Lee, Jiwoo; Planton, Yann Y.; Gleckler, Peter J.; Sperber, Kenneth R.; Guilyardi, Eric; Wittenberg, Andrew T.; McPhaden, Michael J.; Pallotta, GiulianaLee, J., Y. Y. Planton, P. J. Gleckler, K. R. Sperber, E. Guilyardi, A. T. Wittenberg, M. J. McPhaden, G. Pallotta, 2021: Robust Evaluation of ENSO in Climate Models: How Many Ensemble Members Are Needed?. Geophysical Research Letters, 48(20), e2021GL095041. doi: 10.1029/2021GL095041. Large ensembles of model simulations require considerable resources, and thus defining an appropriate ensemble size for a particular application is an important experimental design criterion. We estimate the ensemble size (N) needed to assess a model’s ability to capture observed El Niño-Southern Oscillation (ENSO) behavior by utilizing the recently developed International CLIVAR ENSO Metrics Package. Using the larger ensembles available from CMIP6 and the US CLIVAR Large Ensemble Working Group, we find that larger ensembles are needed to robustly capture baseline ENSO characteristics (N > 50) and physical processes (N > 50) than the background climatology (N ≥ 12) and remote ENSO teleconnections (N ≥ 6). While these results vary somewhat across metrics and models, our study quantifies how larger ensembles are required to robustly evaluate simulated ENSO behavior, thereby providing some guidance for the design of model ensembles. ENSO; CMIP6; large ensemble; CLIVAR ENSO metrics; Monte-Carlo sampling; PCMDI metrics package (PMP)
Li, Jiandong; Sun, Zhian; Liu, Yimin; You, Qinglong; Chen, Guoxing; Bao, QingLi, J., Z. Sun, Y. Liu, Q. You, G. Chen, Q. Bao, 2021: Top-of-Atmosphere Radiation Budget and Cloud Radiative Effects Over the Tibetan Plateau and Adjacent Monsoon Regions From CMIP6 Simulations. Journal of Geophysical Research: Atmospheres, 126(9), e2020JD034345. doi: 10.1029/2020JD034345. This study investigates the top-of-atmosphere (TOA) radiation budget (RT) and cloud radiative effects (CREs) over the Tibetan Plateau (TP) and adjacent Asian monsoon regions including Eastern China (EC) and South Asia (SA) using the Coupled Model Intercomparison Project 6 (CMIP6) simulations. Considerable simulation biases occur but specific causes differ in these regions. Most models underestimate the intensity of annual mean RT and cloud radiative cooling effect over the TP, and the RT during the cold-warm transition period is hard to capture. The biases in surface temperature and cloud fractions substantially contribute to cloud-radiation biases over the western and eastern TP, respectively. Over EC, the intensity of RT and cloud radiative cooling effect is seriously underestimated especially in the springtime when the model spread is large, and their biases are closely related to less low-middle cloud fractions and weaker ascending motion. Over SA, simulation biases mainly arise from longwave radiative components associated with less high cloud fraction and weaker convection, with the large model spread in the summertime. The annual cycles of RT and CREs over EC and SA can be well reproduced by most models, while the summertime peak of the net CRE over the TP occurs later than the observation. The RT and its simulation bias strongly depend on the cloud radiative cooling effect over EC and SA. Our results demonstrate that contemporary climate models still have obvious difficulties in representing various complex cloud-radiation processes in Asian monsoon regions. radiation budget; Tibetan Plateau; cloud radiative effects; CMIP6; Asian monsoon regions
Li, Jianduo; Miao, Chiyuan; Wei, Wei; Zhang, Guo; Hua, Lijuan; Chen, Yueli; Wang, XiaoxiaoLi, J., C. Miao, W. Wei, G. Zhang, L. Hua, Y. Chen, X. Wang, 2021: Evaluation of CMIP6 Global Climate Models for Simulating Land Surface Energy and Water Fluxes During 1979–2014. Journal of Advances in Modeling Earth Systems, 13(6), e2021MS002515. doi: 10.1029/2021MS002515. This study examined the overall performance of the climate models in Phase 6 of the Coupled Model Intercomparison Project (CMIP6) in simulating the key energy and water fluxes over land. For this purpose, this study selected multiple land flux products as reference data sets and assessed the global spatial means, patterns, trends, seasonal cycles, and regional mean estimates of the sensible heat (SH), latent heat (LH), net radiation (RN), runoff (RF), and precipitation (PR) simulated by 32 CMIP6 models in recent decades. The global (Antarctica, Greenland, and hot deserts are not included) mean SH, LH, RN, RF, and PR simulated by the CMIP6 models are 37.55 ± 4.81 W m−2, 49.88 ± 5.31 W m−2, 89.10 ± 4.45 W m−2, 351.31 ± 95.28 mm yr−1, and 948.35 ± 88.77 mm yr−1, respectively. The ensemble median of CMIP6 simulations (CMIP6-MED) can provide robust estimates of global and regional land fluxes, which are within the ranges given by the reference data sets, and highly consistent spatiotemporal patterns of these fluxes. The comparison of CMIP6-MED with the first preferred reference data sets shows that CMIP6-MED generally overestimates the water and energy fluxes over land, except for the simulated RF and PR in the Amazon region. The most disagreements between CMIP6-MED and the reference data sets occur in South America (particularly the Amazon region) and the Tibetan Plateau. Finally, the sources of model biases are discussed. It is suggested that current land flux products should be widely used to optimize the structures and parameters of climate models in future work. model evaluation; CMIP6; land surface model; energy flux; water flux
Li, Jui-Lin F.; Xu, Kuan-Man; Richardson, Mark; Jiang, Jonathan H.; Stephens, Graeme; Lee, Wei-Liang; Fetzer, Eric; Yu, Jia-Yuh; Wang, Yi-Hui; Wang, F.-J.Li, J. F., K. Xu, M. Richardson, J. H. Jiang, G. Stephens, W. Lee, E. Fetzer, J. Yu, Y. Wang, F. Wang, 2021: Improved ice content, radiation, precipitation and low-level circulation over the tropical pacific from ECMWF ERA-interim to ERA5. Environmental Research Communications, 3(8), 081006. doi: 10.1088/2515-7620/ac1bfe. This study evaluates changes in simulated Pacific climate between two ECMWF re-analyses; the ERA Interim (ERAI) and the newest ERA5. Changes in the Integrated Forecasting System (IFS) and possibly sea surface temperature result in greatly reduced discrepancies in ERA5’s ice water path (IWP), radiative fluxes and precipitation relative to satellite-based observational products. IWP shows the largest percentage change, increasing by over 300% from ERAI to ERA5, due to inclusion of falling ice (snow) that impacts radiative calculation. ERAI to ERA5 changes in high-cloud fraction are generally anticorrelated as expected with outgoing longwave radiation, with ERA5 having smaller longwave discrepancies versus CERES observations compared with ERAI. Reflected shortwave discrepancies are similarly reduced from ERAI to ERA5, which appears to be due to changes in both cloud fraction and optical depth. Finally, ERA5 also reduces a longstanding precipitation excess relative to the GPCP observational product in the southern trade winds region between the Southern Pacific and intertropical convergence zones. This appears to be related to cooler prescribed sea surface temperatures, thereby reducing local moisture supply via suppressing net latent heat flux and stronger surface trade-winds. Compared with GPCP and CERES, ERA5 shows similar geographic patterns of discrepancies to ERAI in terms of precipitation and top-of-atmosphere radiation, but their magnitudes are greatly reduced in ERA5.
Li, Ming; Letu, Husi; Peng, Yiran; Ishimoto, Hiroshi; Lin, Yanluan; Nakajima, Takashi; Baran, Anthony; Guo, Zengyuan; Lei, Yonghui; Shi, JianchengLi, M., H. Letu, Y. Peng, H. Ishimoto, Y. Lin, T. Nakajima, A. Baran, Z. Guo, Y. Lei, J. Shi, 2021: Assessment of ice cloud modeling capabilities for the irregularly shaped Voronoi models in climate simulations with CAM5. Atmospheric Chemistry and Physics Discussions, 1-32. doi: 10.5194/acp-2021-208. Abstract. Climate models and satellite remote sensing applications require accurate descriptions of ice cloud optical and radiative properties through parameterization of their scattering properties. While abundant irregularly shaped ice particle habits present a challenge for modelling ice clouds. An irregularly shaped ice particle habit (Voronoi model) has been developed and recently suggested to be effective in inferring the microphysical and radiative properties of ice clouds from Himawari-8 and GCOM-C satellite measurements. As a continuation of previous work by Letu et al. (2016), in this study, we develop a broadband ice cloud scheme based on the Voronoi model through parameterization for use in the Community Atmosphere Model, Version 5 (CAM5). With single scattering properties of Voronoi model, ice cloud bulk scattering properties are integrate over particle size distributions of 11 field campaigns and are parameterized over particle effective diameter. The new ice cloud scheme is compared with four ice cloud schemes (the Yi, Mitchell, Baum-yang and Fu scheme), and is evaluated through the General circulation model version of the Rapid Radiative Transfer Model (RRTMG), and simulations of the top of atmosphere (TOA) shortwave and longwave cloud forcing (SWCF and LWCF) in CAM5. The Clouds and the Earth's Radiant Energy System (CERES) satellite data was selected as validation data. Results indicated that the Voronoi scheme can minimize differences between the satellite-based measurements and CAM5 simulations of global TOA SWCF compared to other four schemes, but performance is not significant for TOA LWCF. For tropical ice clouds, Voronoi scheme has advantages of ice cloud modelling capabilities for shortwave (SW) and longwave (LW) spectrum over other four schemes. In general, it is found that the Voronoi model has advantages over conventional ice cloud schemes and is sufficient for ice cloud modelling in climate simulations with CAM5.
Li, Ruohan; Wang, Dongdong; Liang, ShunlinLi, R., D. Wang, S. Liang, 2021: Comprehensive assessment of five global daily downward shortwave radiation satellite products. Science of Remote Sensing, 4, 100028. doi: 10.1016/j.srs.2021.100028. The downward shortwave radiation (DSR) is a critical parameter of the surface radiation budget. Several DSR satellite products have been developed in recent years. In this study, five updated global satellite daily DSR products were evaluated using in situ measurements from 142 global sites with a special focus on high latitudes in 2004. These five products are Clouds and the Earth's Radiant Energy System Synoptic TOA and surface fluxes and clouds (CERES), Clouds, Albedo and Radiation Edition 2 data (CLARA), Global Land Surface Satellite Downward Shortwave Radiation (GLASS), Breathing Earth System Simulator (BESS) shortwave radiation product, and Moderate Resolution Imaging Spectroradiometer land surface Downward Shortwave Radiation (MCD18) with a spatial resolution of 100, 25, 5, 5, and 1 km, respectively. The CERES, BESS, and MCD18 provide full global coverage throughout the year, whereas CLARA and GLASS present different levels of seasonal data loss over high-latitude areas. The products were aggregated and compared at various spatial resolutions over different subareas. The overall accuracy increased after the products were aggregated to 100 km. However, the highest accuracy was achieved at a resolution of 25 km over high-latitude areas for GLASS and MCD18. When all products were evaluated at a resolution of 100 km, the global root-mean-square error of CERES, CLARA, GLASS, BESS, and MCD18 was 27.6, 29.1, 30.3, 29.6, and 31.6 W/m2, respectively, and the mean bias difference was 2.2, −1.5, −1.8, −3.4, and −8.0 W/m2. The accuracies of most products are ~7 W/m2 lower over high-latitude areas. A seasonal variation of the accuracies was observed for all products. It is particularly pronounced over high-latitude areas. With respect to the long term, both in situ data, BESS, and CERES show insignificant trends, while CLARA and GLASS present dimming trend. Besides, CLARA and GLASS exhibit slight annual changes of −0.250 and −0.387 W/m2 in the bias and 0.357 and 0.310 Wm−2 in the RMSE in the past two decades. GLASS and MCD18 exhibit a superior performance over coastal regions but degrade over snow-covered areas. Potential refinements of current high-resolution DSR retrieval algorithms are suggested, which will improve the retrieval accuracy. Highly accurate products with a long-term stability, especially over high-latitude areas, are required for future climate change analyses. Downward shortwave radiation; High spatial resolution; High latitude; Satellite products validation
Liang, Shunlin; Cheng, Jie; Jia, Kun; Jiang, Bo; Liu, Qiang; Xiao, Zhiqiang; Yao, Yunjun; Yuan, Wenping; Zhang, Xiaotong; Zhao, Xiang; Zhou, JiLiang, S., J. Cheng, K. Jia, B. Jiang, Q. Liu, Z. Xiao, Y. Yao, W. Yuan, X. Zhang, X. Zhao, J. Zhou, 2021: The Global LAnd Surface Satellite (GLASS) product suite. Bull. Amer. Meteor. Soc., (In Press). doi: 10.1175/BAMS-D-18-0341.1.
Lim, Young-Kwon; Wu, Dong L.; Kim, Kyu-Myong; Lee, Jae N.Lim, Y., D. L. Wu, K. Kim, J. N. Lee, 2021: An Investigation on Seasonal and Diurnal Cycles of TOA Shortwave Radiations from DSCOVR/EPIC, CERES, MERRA-2, and ERA5. Remote Sensing, 13(22), 4595. doi: 10.3390/rs13224595. Reflected shortwave (SW) solar radiations at the top of atmosphere from Clouds and the Earth’s Radiant Energy System (CERES), Modern Era-Retrospective analysis for Research and Applications version 2 (MERRA-2), and ECMWF Reanalysis 5th Generation (ERA5) are examined to better understand their differences in spatial and temporal variations (seasonal and diurnal cycle timescale) with respect to the observations from the Earth Polychromatic Imaging Camera (EPIC) on the Deep Space Climate Observatory (DSCOVR) satellite. Comparisons between two reanalyses (MERRA-2 and ERA5) and EPIC reveal that MERRA-2 has a generally larger deviation from EPIC than ERA5 in terms of the SW radiance and diurnal variability in all seasons, which can be attributed to larger cloud biases in MERRA-2. MERRA-2 produces more ice/liquid water content than ERA5 over the tropical warm pool, leading to positive SW biases in cloud and radiance, while both reanalyses underestimate the observed SW radiance from EPIC in the stratus-topped region off the western coast of US/Mexico in the boreal summer. Himalaya/Tibet region in the boreal spring/summer and the midlatitude Southern Hemisphere in the boreal winter are the regions where MERRA-2 and ERA5 deviate largely from EPIC, but their deviations have the opposite sign. Vertical structures of cloud ice/liquid water content explain reasonably well these contrasting differences between the two reanalyses. As two independent observations, CERES and EPIC agree well with each other in terms of the SW radiance maps, showing 2–3% mean absolute errors over the tropical midlatitudes. The CERES-EPIC consistency further confirms that the reanalyses still have challenges in representing the SW flux and its global distribution. In the CERES-EPIC observation differences, CERES slightly overestimates the diurnal cycle (as a function of local solar time) of the observed EPIC irradiance in the morning and underestimates it in the afternoon, while the opposite is the case in the reanalyses. CERES; cloud; reanalysis; DSCOVR; EPIC; irradiance; reflected shortwave radiance
Liu, Lingling; Li, Yuanlong; Wang, FanLiu, L., Y. Li, F. Wang, 2021: MJO-Induced Intraseasonal Mixed Layer Depth Variability in the Equatorial Indian Ocean and Impacts on Subsurface Water Obduction. J. Phys. Oceanogr., 51(4), 1247-1263. doi: 10.1175/JPO-D-20-0179.1. AbstractChange of oceanic surface mixed layer depth (MLD) is critical for vertical exchanges between the surface and subsurface oceans and modulates surface temperature variabilities on various time scales. In situ observations have documented prominent intraseasonal variability (ISV) of MLD with 30–105-day periods in the equatorial Indian Ocean (EIO) where the Madden–Julian oscillation (MJO) initiates. Simulation of Hybrid Coordinate Ocean Model (HYCOM) reveals a regional maximum of intraseasonal MLD variability in the EIO (70°–95°E, 3°S–3°N) with a standard deviation of ~14 m. Sensitivity experiments of HYCOM demonstrate that, among all of the MJO-related forcing effects, the wind-driven downwelling and mixing are primary causes for intraseasonal MLD deepening and explain 83.7% of the total ISV. The ISV of MLD gives rise to high-frequency entrainments of subsurface water, leading to an enhancement of the annual entrainment rate by 34%. However, only a small fraction of these entrainment events (<20%) can effectively contribute to the annual obduction rate of 1.36 Sv, a quantification for the amount of resurfacing thermocline water throughout a year that mainly (84.6%) occurs in the summer monsoon season (May–October). The ISV of MLD achieves the maximal intensity in April–May and greatly affects the subsequent obduction. Estimation based on our HYCOM simulations suggests that MJOs overall reduce the obduction rate in the summer monsoon season by as much as 53%. A conceptual schematic is proposed to demonstrate how springtime intraseasonal MLD deepening events caused by MJO winds narrow down the time window for effective entrainment and thereby suppress the obduction of thermocline water.
Liu, Qiaozhen; Zhang, Zhaoyang; Fan, Meng; Wang, QuanLiu, Q., Z. Zhang, M. Fan, Q. Wang, 2021: The Divergent Estimates of Diffuse Radiation Effects on Gross Primary Production of Forest Ecosystems Using Light-Use Efficiency Models. Geophysical Research Letters, 48(19), e2021GL093864. doi: 10.1029/2021GL093864. Diffuse radiation can promote the vegetation photosynthesis. Radiation use efficiency (RUE = GPP/PAR) simulated by Terrestrial Ecosystem Carbon Flux GPP Model (TEC), Vegetation Photosynthesis Model (VPM), Eddy Covariance Light Use Efficiency Model (EC-LUE), and Diffuse Fraction-Based Two-Leaf Terrestrial Ecosystem Carbon Flux Model (DTEC) models were against the measured radiation-use efficiency (RUE) from FLUXNET under different bins of diffuse photosynthetically active radiation fraction (FDIFFPAR) in this study. Our results showed that the observed RUE increased linearly with FDIFFPAR. The differences of RUE between the first bin and other bin (RUEbin) from two big-leaf models were underestimated when the FDIFFPAR is higher than 0.5 except in evergreen broadleaf forests and RUEbin from the DTEC model was overestimated when the FDIFFPAR is higher than 0.7. The role of temperature and vapor pressure deficit in the diffuse radiation effects on vegetation photosynthesis was underestimated in EC-LUE, TEC, VPM. Although many studies applied LUE models to assess the effects of diffuse radiation on vegetation photosynthesis, our results suggested that these models were needed to be improved. diffuse fertilization effects (DFE); LUE models; Diffuse radiation fraction
Liu, Ziwei; Yang, HanboLiu, Z., H. Yang, 2021: Estimation of Water Surface Energy Partitioning With a Conceptual Atmospheric Boundary Layer Model. Geophysical Research Letters, 48(9), e2021GL092643. doi: 10.1029/2021GL092643. Open water surface evaporation (E) or the latent heat flux (λE) is of great importance to surface water and energy budget. However, partitioning of the available energy into sensible heat flux (H) and λE, quantified as the Bowen ratio (), is implicitly discrepant between models and observations. In this study, an explicit equation for the estimation of Bo (thus for the λE) is derived based on an atmospheric boundary layer model combined with the potential vapor pressure deficit budget. Derived equation only requires the air temperature (Ta) and specific humidity (Q) as inputs, and performs well in λE estimation with a relative error of
Loeb, Norman G.; Johnson, Gregory C.; Thorsen, Tyler J.; Lyman, John M.; Rose, Fred G.; Kato, SeijiLoeb, N. G., G. C. Johnson, T. J. Thorsen, J. M. Lyman, F. G. Rose, S. Kato, 2021: Satellite and Ocean Data Reveal Marked Increase in Earth’s Heating Rate. Geophysical Research Letters, 48(13), e2021GL093047. doi: 10.1029/2021GL093047. Earth's Energy Imbalance (EEI) is a relatively small (presently ∼0.3%) difference between global mean solar radiation absorbed and thermal infrared radiation emitted to space. EEI is set by natural and anthropogenic climate forcings and the climate system's response to those forcings. It is also influenced by internal variations within the climate system. Most of EEI warms the ocean; the remainder heats the land, melts ice, and warms the atmosphere. We show that independent satellite and in situ observations each yield statistically indistinguishable decadal increases in EEI from mid-2005 to mid-2019 of 0.50 ± 0.47 W m−2 decade−1 (5%–95% confidence interval). This trend is primarily due to an increase in absorbed solar radiation associated with decreased reflection by clouds and sea-ice and a decrease in outgoing longwave radiation (OLR) due to increases in trace gases and water vapor. These changes combined exceed a positive trend in OLR due to increasing global mean temperatures. CERES; Earth energy imbalance; planetary heat uptake
Loeb, Norman G.; Su, Wenying; Bellouin, Nicolas; Ming, YiLoeb, N. G., W. Su, N. Bellouin, Y. Ming, 2021: Changes in Clear-Sky Shortwave Aerosol Direct Radiative Effects Since 2002. Journal of Geophysical Research: Atmospheres, 126(5), e2020JD034090. doi: https://doi.org/10.1029/2020JD034090. A new method for determining clear-sky shortwave aerosol direct radiative effects (ADRE) from the Clouds and the Earth's Radiant Energy System is used to examine changes in ADRE since 2002 alongside changes in aerosol optical depth (AOD) from the Moderate Resolution Spectroradiometer. At global scales, neither ADRE nor AOD show a significant trend. Over the northern hemisphere (NH), ADRE increases by 0.18 ± 0.17 Wm−2 per decade (less reflection to space) but shows no significant change over the southern hemisphere. The increase in the NH is primarily due to emission reductions in China, the United States, and Europe. The COVID-19 shutdown shows no noticeable impact on either global ADRE or AOD, but there is a substantial influence over northeastern China in March 2020. In contrast, February 2020 anomalies in ADRE and AOD are within natural variability even though the impact of the shutdown on industry was more pronounced in February than March. The reason is because February 2020 was exceptionally hot and humid over China, which compensated for reduced emissions. After accounting for meteorology and normalizing by incident solar flux, February ADRE anomalies increase substantially, exceeding the climatological mean ADRE by 23%. February and March 2020 correspond to the only period in which adjusted anomalies exceed the 95% confidence interval for 2 consecutive months. Distinct water-land differences over northeastern China are observed in ADRE but not in AOD. This is likely due to the influence of surface albedo on ADRE in the presence of absorbing aerosols.
Lu, Tianwei; Zhang, Jing; Xue, Wenhao; Qiao, Yan; Zhou, Lihua; Che, YunfeiLu, T., J. Zhang, W. Xue, Y. Qiao, L. Zhou, Y. Che, 2021: Impacts of aerosol direct radiative forcing on terrestrial ecosystem respiration in China from 2001 to 2014. Atmospheric Research, 260, 105713. doi: 10.1016/j.atmosres.2021.105713. Aerosol direct radiative forcing (ADRF) has complex effects on vegetation and ecosystems by altering environmental conditions. Based on the Fu-Liou radiation transfer model and Community Land Model (CLM4.5), this study simulated the ecosystem processes under scenarios with and without ADRF in China from 2001 to 2014, analysed the respiration changes in different ecosystems, and evaluated the relationship between the ADRF-induced changes in soil hydrothermal conditions and respiration changes in the vegetation growing season (Jun-Jul-Aug). During the study period, ADRF changed the total ecosystem respiration (ER) in the farm, forest and grass ecosystems by 25.14, −6.84 and 5.03 g C m−2 yr−1, respectively, and this difference was related to the canopy structure and aerosol loadings in the three ecosystems. Moreover, ADRF had the greatest impact on ecosystem respiration in summer. In addition, ADRF had significant promoting effects on autotrophic respiration (AR) and significant inhibitory effects on heterotrophic respiration (HR) by reducing the soil temperature at 10 cm below the surface (TS). ADRF-induced changes in soil hydrothermal conditions further affected the nitrogen content in plants, especially N in fine roots and leaves. N is closely related to proteins associated with respiration; thus, changes in N had a nonnegligible impact on respiration. The increased soil volume water content (HS) alleviated the drought stress in the north of China, which may be the reason for the increased HR there. In addition, changes in CO2 fixation and CH4 and N2O emissions were also observed, and the results showed that ADRF had a greater influence on carbonaceous greenhouse gases (GHGs). In China, ADRF aggravated the greenhouse effects in the farm, forest and grass ecosystems, of which the GWPs were 1.22*1010, 7.27*1010 and 2.42*1010 kg CO2 equivalent yr−1, respectively. Our study highlights the serious effects of aerosol-induced radiation perturbations on biogeochemical processes, especially respiration, in terrestrial ecosystems, which ultimately have feedback effects on the climate. Aerosol; Aerosol direct radiative forcing; CLM4.5 model; Fu-Liou model; Greenhouse effects; Respiration fluxes
Luo, Rui; Ding, Qinghua; Wu, Zhiwei; Baxter, Ian; Bushuk, Mitchell; Huang, Yiyi; Dong, XiquanLuo, R., Q. Ding, Z. Wu, I. Baxter, M. Bushuk, Y. Huang, X. Dong, 2021: Summertime atmosphere–sea ice coupling in the Arctic simulated by CMIP5/6 models: Importance of large-scale circulation. Climate Dynamics, 56(5), 1467-1485. doi: 10.1007/s00382-020-05543-5. Summertime barotropic high pressure in the Arctic and its induced warmer and wetter atmosphere over sea ice are suggested to be important contributors to September sea ice loss on interannual and interdecadal time scales in the past decades. Using ERA5 and other reanalysis data, we find that atmospheric warming and moistening in the Arctic, synchronized by high latitude atmospheric circulation variability, work in tandem to melt sea ice through increasing downwelling longwave radiation at the surface. To what extent this atmosphere-longwave radiation-sea ice relationship can be captured in CMIP5 and 6 remains unknown and thus addressing this question is the objective of this study. To achieve this goal, we construct a process-oriented metric emphasizing the statistical relationship between atmospheric temperature and humidity with sea ice, which can effectively rank and differentiate the performance of 30 CMIP5 climate models in reproducing the observed connection. Based on our evaluation, we suggest that most available models in CMIP5 and 6 have a limitation in reproducing the full strength of the observed atmosphere–sea ice connection. This limitation likely stems from a weak impact of downwelling longwave radiation in linking sea ice with circulation associated with the weak sensitivity of the temperature and humidity fields to circulation variability in the Arctic. Thus, further efforts should be devoted to understanding the sources of these models’ limitations and improve skill in simulating the effects of atmospheric circulation in coupling temperature, humidity, surface radiation and sea ice together during Arctic summer.
Lutsko, Nicholas J.; Popp, Max; Nazarian, Robert H.; Albright, Anna LeaLutsko, N. J., M. Popp, R. H. Nazarian, A. L. Albright, 2021: Emergent Constraints on Regional Cloud Feedbacks. Geophysical Research Letters, 48(10), e2021GL092934. doi: 10.1029/2021GL092934. Low-cloud based emergent constraints have the potential to substantially reduce uncertainty in Earth’s equilibrium climate sensitivity, but recent work has shown that previously developed constraints fail in the latest generation of climate models, suggesting that new approaches are needed. Here, we investigate the potential for emergent constraints to reduce uncertainty in regional cloud feedbacks, rather than the global-mean cloud feedback. Strong relationships are found between the monthly and interannual variability of tropical clouds, and the tropical net cloud feedback. These relationships are combined with observations to substantially narrow the uncertainty in the tropical cloud feedback and demonstrate that the tropical cloud feedback is likely >0Wm−2K−1. Promising relationships are also found in the 90°–60°S and 30°–60°N regions, though these relationships are not robust across model generations and we have not identified the associated physical mechanisms. Climate sensitivity; cloud feedbacks; emergent constraint; tropical clouds
Ma, Hsi-Yen; Zhang, Kai; Tang, Shuaiqi; Xie, Shaocheng; Fu, RongMa, H., K. Zhang, S. Tang, S. Xie, R. Fu, 2021: Evaluation of the Causes of Wet-Season Dry Biases Over Amazonia in CAM5. Journal of Geophysical Research: Atmospheres, 126(11), e2020JD033859. doi: 10.1029/2020JD033859. This study investigates the causes of pronounced low precipitation bias over Amazonia in the Community Atmosphere Model version 5 (CAM5), a common feature in many global climate models. Our analysis is based on a suite of 3-day long hindcasts starting every day at 00Z from 1997 to 2012 and an AMIP simulation for the same period. The Amazonia dry bias appears by the second day in the hindcasts and is very robust for all the seasons with the largest bias magnitude during the wet season (December–February). The bias pattern and magnitude do not change much during different dynamical wind regimes on sub-seasonal time scales. We further classify the diurnal cycle of precipitation near the LBA sites from observations and hindcasts into three convective regimes: no precipitation, late afternoon deep convection, and nighttime deep convection. CAM5 can only simulate the late afternoon convective regime and completely fails to simulate the nighttime convection, which is mostly from propagating convective systems originating from remote locations. CAM5 mainly underestimates precipitation in the late afternoon and nighttime convective regimes, which occur during ∼67% of wet season days and account for ∼75% of accumulated precipitation amount in observations. The persistent warm temperature bias and slightly higher moisture below 850 mb likely trigger deep convection too frequently, resulting in an earlier but weaker rainfall peak in the diurnal cycle. Furthermore, shallow convection may not effectively transport moisture from boundary layer to the free atmosphere, which also leads to weaker deep convection events.
Ma, Qianrong; You, Qinglong; Ma, Yujun; Cao, Yu; Zhang, Jie; Niu, Miaomiao; Zhang, YuqingMa, Q., Q. You, Y. Ma, Y. Cao, J. Zhang, M. Niu, Y. Zhang, 2021: Changes in cloud amount over the Tibetan Plateau and impacts of large-scale circulation. Atmospheric Research, 249, 105332. doi: 10.1016/j.atmosres.2020.105332. Using the Clouds and Earth's Radiant Energy System (CERES) Edition 4 dataset, characteristics and variations of cloud amounts over the Tibetan Plateau (Tibet) during 2001–2019 was analyzed. Our results reveal that the mid–high cloud cover (MHCC) constitutes the major proportion and shows similar seasonal variations and annual cycle to the total cloud cover (TCC). The high cloud cover (HCC) has the greatest seasonal variation, whereas the mid–low cloud cover (MLCC) has the least variation. TCC, MHCC, and HCC exhibit the largest values in summer. The summer TCC, MHCC and MLCC exhibited decreasing trends and MHCC is more significant. The summer HCC shows increasing trend. Clouds at different heights show different correlations with skin temperature, and decreased TCC likely influences recent warming over the Tibet. The increased skin temperature is mainly adjusted by the decreased cloud amount especially MHCC. Cloud amounts are highly responsible for the precipitation, and the summer precipitation over the Tibet is mainly influenced by HCC, followed by MHCC. The decreasing TCC is related to two Rossby wave trains over Eurasia, corresponding to the Eurasian teleconnection pattern and Silk Road pattern. They induce an anomalous anti-cyclone in north Tibet and restrain ascending motions. Meanwhile, the South Asia High weakens and further enhances the sinking movements. Precipitation; Cloud amounts; Rossby wave trains; South Asia High; Surface temperature
Mackie, Anna; Brindley, Helen E.; Palmer, Paul I.Mackie, A., H. E. Brindley, P. I. Palmer, 2021: Contrasting observed atmospheric responses to tropical SST warming patterns. Journal of Geophysical Research: Atmospheres, n/a(n/a), e2020JD033564. doi: https://doi.org/10.1029/2020JD033564. Equilibrium climate sensitivity (ECS) is a theoretical concept which describes the change in global mean surface temperature that results from a sustained doubling of atmospheric CO2. Current ECS estimates range from ∼1.8–5.6K, reflecting uncertainties in climate feedbacks. The sensitivity of the lower (1000-700 hPa) and upper (500-200 hPa) troposphere to changes in spatial patterns of tropical sea surface temperature (SST) have been proposed by recent model studies as key feedbacks controlling climate sensitivity. We examine empirical evidence for these proposed mechanisms using 14 years of satellite data. We examine the response of temperature and humidity profiles, clouds and top-of-the-atmosphere (TOA) radiation to relative warming in tropical ocean regions when there is either strong convection or subsidence. We find warmer SSTs in regions of strong subsidence are coincident with a decrease in lower tropospheric stability (-0.9±0.4 KK−1) and low cloud cover ( ∼-6 %K−1). This leads to a warming associated with the weakening in the shortwave cooling effect of clouds (4.2±1.9 Wm−2K−1), broadly consistent with model calculations. In contrast, warmer SSTs in regions of strong convection are coincident with an increase in upper tropospheric humidity (3.2±1.5 %K−1). In this scenario, the dominant effect is the enhancement of the warming longwave cloud radiative effect (3.8±3.0 Wm−2K−1 ) from an increase in high cloud cover ( ∼7 %K−1), though changes in the net (longwave and shortwave) effect are not statistically significant (p < 0.003). Our observational evidence supports the existence of mechanisms linking contrasting atmospheric responses to patterns in SST, mechanisms which have been linked to climate sensitivity. Climate sensitivity; Satellite observations; SST warming patterns; Tropical atmosphere
Marcianesi, F.; Aulicino, G.; Wadhams, P.Marcianesi, F., G. Aulicino, P. Wadhams, 2021: Arctic sea ice and snow cover albedo variability and trends during the last three decades. Polar Science, (In Press). doi: 10.1016/j.polar.2020.100617. The aim of the present study is to assess the full effect on the albedo of both sea ice extent decrease and snowline retreat in the Arctic during the last three decades. Averaged over the globe, the overall warming effect due to Arctic land and ocean albedo change corresponds to adding about 44% to the direct effect of human CO2 emissions during the same period. In fact, the area and thickness of Arctic sea ice have both been declining in this time frame. This has caused feedbacks affecting the whole global climate system. One such is albedo feedback of sea ice shrinking which was previously estimated (Pistone et al., 2014) to add about 25% to the direct warming effect of anthropogenic CO2 emissions. In this study, we demonstrate that the role of snowline retreat in albedo decrease is comparable to that of sea ice shrinking. To this aim, we estimate the radiative forcing (W/m2) due to snow and ice decrease during 34 years (1982–2015) from the analysis of changes of observed albedo based on the Clouds and the Earth's Radiant Energy System Energy Balanced And Filled (CERES EBAF) dataset, paired with sea ice and snow cover data from the US National Snow & Ice Data Center (NSIDC). Arctic; Albedo change; Global climate; Sea ice decrease; Snowline retreat
Mardi, Ali Hossein; Dadashazar, Hossein; Painemal, David; Shingler, Taylor; Seaman, Shane T.; Fenn, Marta A.; Hostetler, Chris A.; Sorooshian, ArminMardi, A. H., H. Dadashazar, D. Painemal, T. Shingler, S. T. Seaman, M. A. Fenn, C. A. Hostetler, A. Sorooshian, 2021: Biomass Burning Over the United States East Coast and Western North Atlantic Ocean: Implications for Clouds and Air Quality. Journal of Geophysical Research: Atmospheres, 126(20), e2021JD034916. doi: 10.1029/2021JD034916. Biomass burning (BB) aerosol events were characterized over the U.S. East Coast and Bermuda over the western North Atlantic Ocean (WNAO) between 2005 and 2018 using a combination of ground-based observations, satellite data, and model outputs. Days with BB influence in an atmospheric column (BB days) were identified using criteria biased toward larger fire events based on anomalously high AERONET aerosol optical depth (AOD) and MERRA-2 black carbon (BC) column density. BB days are present year-round with more in June–August (JJA) over the northern part of the East Coast, in contrast to more frequent events in March–May (MAM) over the southeast U.S. and Bermuda. BB source regions in MAM are southern Mexico and by the Yucatan, Central America, and the southeast U.S. JJA source regions are western parts of North America. Less than half of the BB days coincide with anomalously high PM2.5 levels in the surface layer, according to data from 14 IMPROVE sites over the East Coast. Profiles of aerosol extinction suggest that BB particles can be found in the boundary layer and into the upper troposphere with the potential to interact with clouds. Higher cloud drop number concentration and lower drop effective radius are observed during BB days. In addition, lower liquid water path is found during these days, especially when BB particles are present in the boundary layer. While patterns are suggestive of cloud-BB aerosol interactions over the East Coast and the WNAO, additional studies are needed for confirmation. ACTIVATE; smoke; aerosol-cloud interaction; EVS-3; biomass burning; HSRL
Markowicz, Krzysztof M.; Zawadzka-Manko, Olga; Posyniak, MichalMarkowicz, K. M., O. Zawadzka-Manko, M. Posyniak, 2021: A large reduction of direct aerosol cooling over Poland in the last decades. International Journal of Climatology, 1-18. doi: 10.1002/joc.7488. This paper presents an analysis of the long-term (1982–2015) variability of aerosol optical properties, as well as aerosol and greenhouse gases (GHG) direct radiative forcing (RF) in central Europe on the basis of MERRA-2 reanalysis and ground-based observation. Calculations of longwave (LW) and shortwave (SW) RF were made with the use of the off-line Fu-Liou radiative transfer model and were preceded by the sensitivity study of the code's input parameters. Then, the long-term mean as well as the annual variability for selected regions of aerosol optical properties and radiative forcing were analysed. The mean AOD trend was −0.056 ± 9% per decade and AOD was reduced by 48% between 1982 and 2015. While for 1982–1990 the trend per decade was −0.12 ± 20%, for 1991–2000 it was −0.17 ± 17% and only −0.02 ± 31% in the last 15 years (2001–2015). The trend of the aerosol radiative forcing (ARF) was 1.52 ± 0.12 W·m−2/10 year and 1.21 ± 0.19 W·m−2/10 year at top of the atmosphere (TOA) and at Earth's surface, respectively. The trend for GHG was significantly smaller and it equalled 0.27 ± 0.01 W·m−2/10 year at TOA and 0.17 ± 0.01 W·m−2/10 year at the surface. Changes in GHG and aerosol direct effect produced additional 3.2 ± 0.2 W·m−2 at TOA, which could be associated with the observed regional climate warming. The change of the direct aerosol effect was about 4 times the GHG RF. The influence of aerosol loading reduction on the radiation budget was significantly higher in the 1990s of the 20th century in comparison to the first decades of the 21st. The effect of aerosol reduction has significant impact on air temperature changes during warm season and negligible during winter. aerosol; radiative forcing; aerosol optical depth; absorbing particles; aerosol direct effect; climate warming; single scattering albedo
Marti, Florence; Blazquez, Alejandro; Meyssignac, Benoit; Ablain, Michaël; Barnoud, Anne; Fraudeau, Robin; Jugier, Rémi; Chenal, Jonathan; Larnicol, Gilles; Pfeffer, Julia; Restano, Marco; Benveniste, JérômeMarti, F., A. Blazquez, B. Meyssignac, M. Ablain, A. Barnoud, R. Fraudeau, R. Jugier, J. Chenal, G. Larnicol, J. Pfeffer, M. Restano, J. Benveniste, 2021: Monitoring the ocean heat content change and the Earth energy imbalance from space altimetry and space gravimetry. Earth System Science Data Discussions, 1-32. doi: 10.5194/essd-2021-220. Abstract. The Earth energy imbalance (EEI) at the top of the atmosphere is responsible for the accumulation of heat in the climate system. Monitoring the EEI is therefore necessary to better understand the Earth’s warming climate. Measuring the EEI is challenging as it is a globally integrated variable whose variations are small (0.5–1 W m−2) compared to the amount of energy entering and leaving the climate system (~ 340 W m−2). Since the ocean absorbs more than 90 % of the excess energy stored by the Earth system, estimating the ocean heat content (OHC) provides an accurate proxy of the EEI. This study provides a space geodetic estimation of the OHC changes at global and regional scales based on the combination of space altimetry and space gravimetry measurements. From this estimate, the global variations in the EEI are derived with realistic estimates of its uncertainty. The mean EEI value is estimated at +0.74 ± 0.22 W m−2 (90 % confidence level) between August 2002 and August 2016. Comparisons against independent estimates based on Argo data and on CERES measurements show good agreement within the error bars of the global mean and the time variations in EEI. Further improvements are needed to reduce uncertainties and to improve the time series especially at interannual and smaller time scales. The space geodetic OHC-EEI product is freely available at https://doi.org/10.24400/527896/a01-2020.003.
Matthews, G.Matthews, G., 2021: CERES Replacement “Libera” SI Traceable Measurement Spectral Calibration Concept using Direct Solar Views by High Resolution Earth Telescopes. J. Atmos. Oceanic Technol., -1(aop). doi: 10.1175/JTECH-D-21-0002.1. AbstractBetter predictions of global warming can be enabled by tuning legacy and current computer simulations to Earth Radiation Budget (ERB) measurements. Since the 1970’s, such orbital results exist, and the next generation instruments called “Libera” are in design. Climate communities have requested that ERB observing system calibration accuracy obtain significantly better SI traceability and stability improvements. This is to prevent untracked instrument calibration drifts, that could lead to false conclusions on climate change. Based on experience from previous ERB missions, the concept presented here utilizes solar calibration for cloud size Earth measurement resolution, at ≪1% accuracy. However it neglects shown to be unsuccessful calibration technology like solar diffusers and on-board lights, as used by ERBE, ScaRaB, CERES, GERB & other Libera designs etc. New spectral characterizing concepts are therefore introduced. This allows in-flight wavelength dependent calibration of Earth observing Libera telescopes using direct solar views, through narrow-band filters continuously characterized on-orbit.
Matthews, GrantMatthews, G., 2021: NASA CERES Spurious Calibration Drifts Corrected by Lunar Scans to Show the Sun Is not Increasing Global Warming and Allow Immediate CRF Detection. Geophysical Research Letters, 48(15), e2021GL092994. doi: 10.1029/2021GL092994. Orbital Earth Radiation Budget measurement comparisons to models, are critical for climate prediction confidence. Satellite systems must reduce calibration drifts for this purpose. NASA Clouds and the Earth's Radiant Energy System (CERES) measures Earth albedo reductions that if correct, would increase solar forcing and suggest greater sunlight absorption is driving much of recent temperature increases. Such results are presented, alongside those from the Moon and Earth Radiation Budget Experiment (MERBE). MERBE uses constant lunar reflectivity for tracking and compensation of instrument telescope degradation, undetectable by CERES. MERBE finds Earth albedo constant compared to that of the Moon, because Arctic solar warming effects are balanced by solar cooling elsewhere, likely due to negative feedbacks. Contrary to NASA, this shows the Sun is not increasing warming and that CERES results are not as stable as claimed and assumed. Furthermore, MERBE can actually resolve Cloud Radiative Forcing (CRF) signals from the existing record, rather than in decades with official observations. earth radiation budget; CERES; climate; Albedo; solar; MERBE
Matthews, GrantMatthews, G., 2021: New satellite results further confirming that Earth reflectivity changes are not driving Global Warming. Earth and Space Science Open Archive. Measurements of solar energy entering Earth are critical for comparison/validation of model simulated climate signals run in the present, for confidence in their predictions. Satellite systems detect
Mayer, Johannes; Mayer, Michael; Haimberger, LeopoldMayer, J., M. Mayer, L. Haimberger, 2021: Consistency and Homogeneity of Atmospheric Energy, Moisture, and Mass Budgets in ERA5. J. Climate, 34(10), 3955-3974. doi: 10.1175/JCLI-D-20-0676.1. AbstractThis study uses advanced numerical and diagnostic methods to evaluate the atmospheric energy budget with the fifth major global reanalysis produced by ECMWF (ERA5) in combination with observed and reconstructed top of the atmosphere (TOA) energy fluxes for the period 1985–2018. We assess the meridional as well as ocean–land energy transport and perform internal consistency checks using mass-balanced data. Furthermore, the moisture and mass budgets in ERA5 are examined and compared with previous budget evaluations using ERA-Interim as well as observation-based estimates. Results show that peak annual mean meridional atmospheric energy transports in ERA5 (4.58 ± 0.07 PW in the Northern Hemisphere) are weaker compared to ERA-Interim (4.74 ± 0.09 PW), where the higher spatial and temporal resolution of ERA5 can be excluded as a possible reason. The ocean–land energy transport in ERA5 is reliable at least from 2000 onward (~2.5 PW) such that the imbalance between net TOA fluxes and lateral energy fluxes over land are on the order of ~1 W m−2. Spinup and spindown effects as revealed from inconsistencies between analyses and forecasts are generally smaller and temporally less variable in ERA5 compared to ERA-Interim. Evaluation of the moisture budget shows that the ocean–land moisture transport and parameterized freshwater fluxes agree well in ERA5, while there are large inconsistencies in ERA-Interim. Overall, the quality of the budgets derived from ERA5 is demonstrably better than estimates from ERA-Interim. Still some particularly sensitive budget quantities (e.g., precipitation, evaporation, and ocean–land energy transport) show apparent inhomogeneities, especially in the late 1990s, which warrant further investigation and need to be considered in studies of interannual variability and trends.
Mazhar, Usman; Jin, Shuanggen; Bilal, Muhammad; Arfan Ali, Md.; Khan, RehanaMazhar, U., S. Jin, M. Bilal, M. Arfan Ali, R. Khan, 2021: Reduction of surface radiative forcing observed from remote sensing data during global COVID-19 lockdown. Atmospheric Research, 261, 105729. doi: 10.1016/j.atmosres.2021.105729. The calamity of the COVID-19 pandemic during the early half of 2020 not only caused a huge physical and economic loss but altered the social behavior of the whole world. The social and economic stagnation imposed in many countries and served as a major cause of perturbation in atmospheric composition. This paper utilized the relation between atmospheric composition and surface radiation and analyzed the impact of global COVID-19 lockdown on land surface solar and thermal radiation. Top of atmosphere (TOA) and surface radiation are obtained from the Clouds and Earth's Radiant Energy System (CERES) and European Reanalysis product (ERA5) reanalysis product. Aerosol Optical Depth (AOD) is obtained from Moderate Resolution Imaging Spectroradiometer (MODIS) while Nitrogen dioxide (NO2), and sulfur dioxide (SO2) are obtained from Ozone Monitoring Instrument (OMI). Observations of all mentioned parameters are studied for the global lockdown period of 2020 (from January to July) and compared with the corresponding months of the previous four years (2016–19) observations. Regarding surface radiation, April 2020 is the most affected month during the pandemic in which 0.2% increased net solar radiation (NSR), while 3.45% and 4.8% decreased net thermal radiation (NTR) and net radiation (NR) respectively was observed. Average radiative forcing during March–May 2020 was observed as 1.09 Wm−2, −2.19 Wm−2 and −1.09 Wm−2 for NSR, NTR and NR, respectively. AOD was reduced by 0.2% in May 2020 while NO2 and SO2 were reduced by 5.4% and 8.8%, respectively, in April 2020. It was observed that NO2 kept on reducing since January 2020 while SO2 kept on reducing since February 2020 which were the pre-lockdown months. These results suggest that a more sophisticated analysis is needed to explain the atmosphere-radiation relation. Air pollution; COVID-19; Economic and social lockdown; Land surface radiation
Mazhar, Usman; Jin, Shuanggen; Duan, Wentao; Bilal, Muhammad; Ali, Md Arfan; Farooq, HasnainMazhar, U., S. Jin, W. Duan, M. Bilal, M. A. Ali, H. Farooq, 2021: Spatio-Temporal Trends of Surface Energy Budget in Tibet from Satellite Remote Sensing Observations and Reanalysis Data. Remote Sensing, 13(2), 256. doi: 10.3390/rs13020256. Being the highest and largest land mass of the earth, the Tibetan Plateau has a strong impact on the Asian climate especially on the Asian monsoon. With high downward solar radiation, the Tibetan Plateau is a climate sensitive region and the main water source for many rivers in South and East Asia. Although many studies have analyzed energy fluxes in the Tibetan Plateau, a long-term detailed spatio-temporal variability of all energy budget parameters is not clear for understanding the dynamics of the regional climate change. In this paper, satellite remote sensing and reanalysis data are used to quantify spatio-temporal trends of energy budget parameters, net radiation, latent heat flux, and sensible heat flux over the Tibetan Plateau from 2001 to 2019. The validity of both data sources is analyzed from in situ ground measurements of the FluxNet micrometeorological tower network, which verifies that both datasets are valid and reliable. It is found that the trend of net radiation shows a slight increase. The latent heat flux increases continuously, while the sensible heat flux decreases continuously throughout the study period over the Tibetan Plateau. Varying energy fluxes in the Tibetan plateau will affect the regional hydrological cycle. Satellite LE product observation is limited to certain land covers. Thus, for larger spatial areas, reanalysis data is a more appropriate choice. Normalized difference vegetation index proves a useful indicator to explain the latent heat flux trend. Despite the reduction of sensible heat, the atmospheric temperature increases continuously resulting in the warming of the Tibetan Plateau. The opposite trend of sensible heat flux and air temperature is an interesting and explainable phenomenon. It is also concluded that the surface evaporative cooling is not the indicator of atmospheric cooling/warming. In the future, more work shall be done to explain the mechanism which involves the complete heat cycle in the Tibetan Plateau. surface energy budget; ERA5; energy flux trends; optical remote sensing; tibetan plateau
Meftah, Mustapha; Boutéraon, Thomas; Dufour, Christophe; Hauchecorne, Alain; Keckhut, Philippe; Finance, Adrien; Bekki, Slimane; Abbaki, Sadok; Bertran, Emmanuel; Damé, Luc; Engler, Jean-Luc; Galopeau, Patrick; Gilbert, Pierre; Lapauw, Laurent; Sarkissian, Alain; Vieau, André-Jean; Lacroix, Patrick; Caignard, Nicolas; Arrateig, Xavier; Hembise Fanton d’Andon, Odile; Mangin, Antoine; Carta, Jean-Paul; Boust, Fabrice; Mahé, Michel; Mercier, ChristopheMeftah, M., T. Boutéraon, C. Dufour, A. Hauchecorne, P. Keckhut, A. Finance, S. Bekki, S. Abbaki, E. Bertran, L. Damé, J. Engler, P. Galopeau, P. Gilbert, L. Lapauw, A. Sarkissian, A. Vieau, P. Lacroix, N. Caignard, X. Arrateig, O. Hembise Fanton d’Andon, A. Mangin, J. Carta, F. Boust, M. Mahé, C. Mercier, 2021: The UVSQ-SAT/INSPIRESat-5 CubeSat Mission: First In-Orbit Measurements of the Earth’s Outgoing Radiation. Remote Sensing, 13(8), 1449. doi: 10.3390/rs13081449. UltraViolet & infrared Sensors at high Quantum efficiency onboard a small SATellite (UVSQ-SAT) is a small satellite at the CubeSat standard, whose development began as one of the missions in the International Satellite Program in Research and Education (INSPIRE) consortium in 2017. UVSQ-SAT is an educational, technological and scientific pathfinder CubeSat mission dedicated to the observation of the Earth and the Sun. It was imagined, designed, produced and tested by LATMOS in collaboration with its academic and industrial partners, and the French-speaking radioamateur community. About the size of a Rubik’s Cube and weighing about 2 kg, this satellite was put in orbit in January 2021 by the SpaceX Falcon 9 launch vehicle. After briefly introducing the UVSQ-SAT mission, this paper will present the importance of measuring the Earth’s radiation budget and its energy imbalance and the scientific objectives related to its various components. Finally, the first in-orbit observations will be shown (maps of the solar radiation reflected by the Earth and of the outgoing longwave radiation at the top of the atmosphere during February 2021). UVSQ-SAT is one of the few CubeSats worldwide with a scientific goal related to climate studies. It represents a research in remote sensing technologies for Climate observation and monitoring. earth radiation budget; climate observation and monitoring; IPCC; nanosatellite
Miao, Hao; Wang, Xiaocong; Liu, Yimin; Wu, GuoxiongMiao, H., X. Wang, Y. Liu, G. Wu, 2021: A Regime-Based Investigation Into the Errors of CMIP6 Simulated Cloud Radiative Effects Using Satellite Observations. Geophysical Research Letters, 48(18), e2021GL095399. doi: 10.1029/2021GL095399. Using a variety of CloudSat/CALIPSO products, this study synergistically examines the performance of clouds and their radiative effects (CRE) for models participating in CMIP6. Results show virtually all models overestimate the net cooling effect of clouds, which is caused by the overestimation of shortwave CRE and the underestimation of longwave CRE. By dividing clouds into regimes jointly sorted by cloud water path and cloud cover, we found models commonly underestimate the relative frequency of occurrence (RFO) for clouds that are geometrically thick, and the bias of RFO is dominant over that of within-regime CRE in an error decomposition of total CRE. This results in underestimations of CRE in geometrically thick clouds, which are partially offset by overestimations in the remaining cloud regimes, leading to the globally averaged CRE being less biased. The consideration of regime-based CRE gives important information that could be used for correction of cloud parameterization in models.
Ming, Yi; Loeb, Norman G.; Lin, Pu; Shen, Zhaoyi; Naik, Vaishali; Singer, Clare E.; Ward, Ryan X.; Paulot, Fabien; Zhang, Zhibo; Bellouin, Nicolas; Horowitz, Larry W.; Ginoux, Paul A.; Ramaswamy, V.Ming, Y., N. G. Loeb, P. Lin, Z. Shen, V. Naik, C. E. Singer, R. X. Ward, F. Paulot, Z. Zhang, N. Bellouin, L. W. Horowitz, P. A. Ginoux, V. Ramaswamy, 2021: Assessing the Influence of COVID-19 on the Shortwave Radiative Fluxes Over the East Asian Marginal Seas. Geophysical Research Letters, 48(3), e2020GL091699. doi: https://doi.org/10.1029/2020GL091699. The Coronavirus Disease 2019 (COVID-19) pandemic led to a widespread reduction in aerosol emissions. Using satellite observations and climate model simulations, we study the underlying mechanisms of the large decreases in solar clear-sky reflection (3.8 W m−2 or 7%) and aerosol optical depth (0.16 W m−2 or 32%) observed over the East Asian Marginal Seas in March 2020. By separating the impacts from meteorology and emissions in the model simulations, we find that about one-third of the clear-sky anomalies can be attributed to pandemic-related emission reductions, and the rest to weather variability and long-term emission trends. The model is skillful at reproducing the observed interannual variations in solar all-sky reflection, but no COVID-19 signal is discerned. The current observational and modeling capabilities will be critical for monitoring, understanding, and predicting the radiative forcing and climate impacts of the ongoing crisis.
Miyamoto, Ayumu; Nakamura, Hisashi; Miyasaka, Takafumi; Kosaka, YuMiyamoto, A., H. Nakamura, T. Miyasaka, Y. Kosaka, 2021: Radiative Impacts of Low-Level Clouds on the Summertime Subtropical High in the South Indian Ocean Simulated in a Coupled General Circulation Model. J. Climate, 34(10), 3991-4007. doi: 10.1175/JCLI-D-20-0709.1. AbstractOver the south Indian Ocean, the coupled system of the subtropical Mascarene high and low-level clouds exhibits marked seasonality. To investigate this seasonality, the present study assesses radiative impacts of low-level clouds on the summertime Mascarene high with a coupled general circulation model. Comparison between a fully coupled control simulation and a “no-low-cloud simulation,” where the radiative effects of low-level clouds are artificially turned off, demonstrates that they act to reinforce the Mascarene high. Their impacts are so significant that the summertime Mascarene high almost disappears in the no-low-cloud experiment, suggesting their essential role in the existence of the summertime Mascarene high. As the primary mechanism, lowered sea surface temperature by the cloud albedo effect suppresses deep convective precipitation, inducing a Matsuno–Gill type response that reinforces the high, as verified through an atmospheric dynamical model diagnosis. Associated reduction of high-top clouds, as well as increased low-level clouds, augments in-atmosphere radiative cooling, which further reinforces the high. The present study reveals that low-level clouds constitute a tight positive feedback system with the subtropical high via sea surface temperature over the summertime south Indian Ocean.
Monroe, Emily E.; Taylor, Patrick C.; Boisvert, Linette N.Monroe, E. E., P. C. Taylor, L. N. Boisvert, 2021: Arctic Cloud Response to a Perturbation in Sea Ice Concentration: The North Water Polynya. Journal of Geophysical Research: Atmospheres, 126(16), e2020JD034409. doi: 10.1029/2020JD034409. Surface and atmosphere energy exchanges play an important role in the Arctic climate system by influencing the lower atmospheric stability and humidity, sea ice melt and growth, and surface temperature. Sea ice significantly alters the character of these energy exchanges relative to ice-free ocean. The observed decline in Arctic sea ice since 1979 motivates questions related to the evolving role of surface-atmosphere coupling and potential feedbacks on the Arctic system. Due to the strong wintertime cloud warming effect, a critical question concerns the potential response of low clouds to Arctic sea ice decline. Previous approaches relied on interannual variability to investigate the cloud response to sea ice decline. However, the covariation between atmospheric conditions and sea ice makes it difficult to define an observational control when using interannual variability. To circumvent this difficulty, we exploit the recurring North Water polynya, an episodic opening in the northern Baffin Bay sea ice, as a natural laboratory to isolate the cloud response to a rapid, near-step perturbation in sea ice. Our results show that during the event, (a) low-cloud cover is 10%–33% larger over the polynya than nearby sea ice, (b) cloud liquid water content is up to 400% larger over the polynya than nearby sea ice, and (c) the surface cloud radiative effect is 18 W m−2 larger over the polynya than nearby sea ice. Our results provide evidence that the low-cloud response during a polynya is a positive feedback lengthening the event. sea ice; cloud radiative effects; Arctic clouds; North Water; polynya; surface turbulent flux
Myers, Timothy A.; Scott, Ryan C.; Zelinka, Mark D.; Klein, Stephen A.; Norris, Joel R.; Caldwell, Peter M.Myers, T. A., R. C. Scott, M. D. Zelinka, S. A. Klein, J. R. Norris, P. M. Caldwell, 2021: Observational constraints on low cloud feedback reduce uncertainty of climate sensitivity. Nature Climate Change, 11(6), 501-507. doi: 10.1038/s41558-021-01039-0. Marine low clouds strongly cool the planet. How this cooling effect will respond to climate change is a leading source of uncertainty in climate sensitivity, the planetary warming resulting from CO2 doubling. Here, we observationally constrain this low cloud feedback at a near-global scale. Satellite observations are used to estimate the sensitivity of low clouds to interannual meteorological perturbations. Combined with model predictions of meteorological changes under greenhouse warming, this permits quantification of spatially resolved cloud feedbacks. We predict positive feedbacks from midlatitude low clouds and eastern ocean stratocumulus, nearly unchanged trade cumulus and a near-global marine low cloud feedback of 0.19 ± 0.12 W m−2 K−1 (90% confidence). These constraints imply a moderate climate sensitivity (~3 K). Despite improved midlatitude cloud feedback simulation by several current-generation climate models, their erroneously positive trade cumulus feedbacks produce unrealistically high climate sensitivities. Conversely, models simulating erroneously weak low cloud feedbacks produce unrealistically low climate sensitivities.
Needham, Michael R.; Randall, David A.Needham, M. R., D. A. Randall, 2021: Linking Atmospheric Cloud Radiative Effects and Tropical Precipitation. Geophysical Research Letters, 48(14), e2021GL094004. doi: 10.1029/2021GL094004. Studies in recent decades have demonstrated a robust relationship between tropical precipitation and column relative humidity (CRH). The present study identifies a similar relationship between CRH and the atmospheric cloud radiative effect (ACRE) calculated from satellite observations. Like precipitation, the ACRE begins to increase rapidly when CRH exceeds a critical value near 70%. We show that the ACRE can be estimated from CRH, similar to the way that CRH has been used to estimate precipitation. Our method reproduces the annual mean spatial structure of the ACRE in the tropics, and skillfully estimates the mean ACRE on monthly and daily time scales in six regions of the tropics. We propose that the exponential dependence of precipitation on CRH may be partially explained by cloud-longwave feedbacks, which facilitate a shift from convective to stratiform conditions. tropical precipitation; atmospheric cloud radiative effect; cloud longwave feedback; column relative humidity
Nga, Pham Thi Thanh; Ha, Pham Thanh; Hang, Vu ThanhNga, P. T. T., P. T. Ha, V. T. Hang, 2021: Satellite-Based Regionalization of Solar Irradiation in Vietnam by k-Means Clustering. J. Appl. Meteor. Climatol., 60(3), 391-402. doi: 10.1175/JAMC-D-20-0070.1. AbstractThis study presents the application of k-means clustering to satellite-based solar irradiation in different regions of Vietnam. The solar irradiation products derived from the Himawari-8 satellite, named AMATERASS by the solar radiation consortium under the Japan Science and Technology Agency (JST), are validated with observations recorded at five stations in the period from October 2017 to September 2018 before their use for clustering. High correlations among them enable the use of satellite-based daily global horizontal irradiation for spatial variability analysis and regionalization. With respect to the climate regime in Vietnam, the defined 6-cluster groups demonstrate better agreement with the conventionally classified seven climatic zones rather than the four climatic zones of the Köppen classification. The spatial distribution and seasonal variation in the regionalized solar irradiation reflect interchangeable influences of large-scale atmospheric circulation in terms of the East Asian winter monsoon and the South Asian summer monsoon as well as the effect of local topography. Higher daily averaged solar radiation and its weaker seasonal variation were found in two clusters in the southern region where the South Asian summer monsoon dominates in the rainy season. Pronounced seasonal variability in solar irradiation in four clusters in the northern region is associated with the influence of the East Asian monsoon, resulting in its clear reduction during the winter months.
Noda, Akira T.; Seiki, Tatsuya; Roh, Woosub; Satoh, Masaki; Ohno, TomokiNoda, A. T., T. Seiki, W. Roh, M. Satoh, T. Ohno, 2021: Improved Representation of Low-Level Mixed-Phase Clouds in a Global Cloud-System-Resolving Simulation. Journal of Geophysical Research: Atmospheres, 126(17), e2021JD035223. doi: 10.1029/2021JD035223. Low-level mixed-phase clouds are important for Earth's climate but are poorly represented in climate models. A one-moment microphysics scheme from Seiki and Roh (2020, https://doi.org/10.1175/JAS-D-19-0266.1) improves the representation of supercooled water and verifies it with a single-column model. We evaluate the performance of this scheme using a global cloud-system-resolving simulation. We show that the scheme has several major improvements over the original scheme on which it is based, which underestimated the generation of supercooled droplets. The new scheme suppresses the original scheme's tendency to overestimate the conversion of cloud water to rain, vapor to cloud ice, and cloud water to cloud ice. It greatly improves the previously underestimated production of low-level mixed-phase clouds at middle-to-high latitudes, particularly over the ocean at the middle latitudes of the Southern Hemisphere. It also increases the lifetime of liquid clouds, thus improving the simulation of low-level liquid clouds in western coastal regions of the tropics. The temperature dependency of the ratio of mass fraction of liquid cloud to the sum of ice and liquid clouds, F, reveals that mixed-phase clouds statistically develop in a much wider range of temperature (−30°C ∼ 0°C), which supports the development of more mixed-phase clouds in our simulation. The change to a wider range of F at given temperature is expected to be important, because it allows more complex feedback processes to arise from different cloud phase regimes. An improved simulation in seasonal variation of shortwave radiation and its cloud radiative effect are also identified. cloud microphysics; mixed-phase clouds; global cloud-resolving model; supercooled water; seasonal variation
Obregón, María Ángeles; Serrano, Antonio; Costa, Maria João; Silva, Ana MariaObregón, M. Á., A. Serrano, M. J. Costa, A. M. Silva, 2021: Global Spatial and Temporal Variation of the Combined Effect of Aerosol and Water Vapour on Solar Radiation. Remote Sensing, 13(4), 708. doi: 10.3390/rs13040708. This study aims to calculate the combined and individual effects of the optical thickness of aerosols (AOT) and precipitable water vapour (PWV) on the solar radiation reaching the Earth’s surface at a global scale and to analyse its spatial and temporal variation. For that purpose, a novel but validated methodology is applied to CERES SYN1deg products for the period 2000–2019. Spatial distributions of AOT and PWV effects, both individually and combined, show a close link with the spatial distributions of AOT and PWV. The spatially averaged combined effect results in a −13.9% reduction in irradiance, while the average AOT effect is −2.3%, and the PWV effect is −12.1%. The temporal analysis focuses on detecting trends in the anomalies. The results show overall positive trends for AOT and PWV. Consequently, significant negative overall trends are found for the effects. However, significant positive trends for the individual AOT and the combined AOT-PWV effects are found in specific regions, such as the eastern United States, Europe or Asia, indicating successful emission control policies in these areas. This study contributes to a better understanding of the individual and combined effects of aerosols and water vapour on solar radiation at a global scale. CERES; aerosol optical depth; precipitable water vapour; combined effects; global radiative effects
Okamoto, Kozo; Hayashi, Masahiro; Hashino, Tempei; Nakagawa, Masayuki; Okuyama, ArataOkamoto, K., M. Hayashi, T. Hashino, M. Nakagawa, A. Okuyama, 2021: Examination of all-sky infrared radiance simulation of Himawari-8 for global data assimilation and model verification. Quarterly Journal of the Royal Meteorological Society, 147(740), 3611-3627. doi: 10.1002/qj.4144. The systematic difference between observations and simulation from weather forecast model hampers effective data assimilation and model improvement. The purpose of this study is to identify the characteristics and cause of the systematic difference or observation-minus-background (O − B) bias for all-sky infrared radiances of the Himawari-8 satellite, and propose data assimilation preprocessings and model verification. The O − B bias in cloudy scenes showed substantial negative values because of the shortage of high-altitude clouds generated in the forecast model. Additionally, a positive bias appeared for thin ice clouds because of the excessive absorption of radiative transfer models (RTMs). These biases were traced based on a bottom-up approach investigating individual uncertainty of RTMs, observation calibration, and the forecast model using two RTMs, reference hyperspectral sounders and synergetic measurements of CloudSat and CALIPSO. Based on these findings, data assimilation preprocessing such as quality-control procedures excluding samples that models poorly reproduced was developed. Although the quality controls reduced the number of biased samples, non-negligible O − B biases remained. Possible problems and treatments for the biases were discussed, including bias correction, observation error inflation, and correction of the cloud effect parameter. The O–B statistics also suggested insufficient representation of the diurnal variation in the cloud fraction in the tropics. Modified physical processes in the forecast model to increase ice clouds were tested to help improve the model bias and develop data assimilation. This trial indicated the difficulty in improving both O − B bias and variance and the necessity of adjusting the cloud effect parameters in data assimilation. cloud; data assimilation; bias; Himawari-8; radiative transfer model; all-sky infrared radiance
Painemal, David; Corral, Andrea F.; Sorooshian, Armin; Brunke, Michael A.; Chellappan, Seethala; Gorooh, Vesta Afzali; Ham, Seung-Hee; O'Neill, Larry; Smith, William L.; Tselioudis, George; Wang, Hailong; Zeng, Xubin; Zuidema, PaquitaPainemal, D., A. F. Corral, A. Sorooshian, M. A. Brunke, S. Chellappan, V. A. Gorooh, S. Ham, L. O'Neill, W. L. Smith, G. Tselioudis, H. Wang, X. Zeng, P. Zuidema, 2021: An Overview of Atmospheric Features Over the Western North Atlantic Ocean and North American East Coast—Part 2: Circulation, Boundary Layer, and Clouds. Journal of Geophysical Research: Atmospheres, 126(6), e2020JD033423. doi: https://doi.org/10.1029/2020JD033423. The Western North Atlantic Ocean (WNAO) is a complex land-ocean-atmosphere system that experiences a broad range of atmospheric phenomena, which in turn drive unique aerosol transport pathways, cloud morphologies, and boundary layer variability. This work, Part 2 of a 2-part paper series, provides an overview of the atmospheric circulation, boundary layer variability, three-dimensional cloud structure, and precipitation over the WNAO; the companion paper (Part 1) focused on chemical characterization of aerosols, gases, and wet deposition. Seasonal changes in atmospheric circulation and sea surface temperature explain a clear transition in cloud morphologies from small shallow cumulus clouds, convective clouds, and tropical storms in summer, to stratus/stratocumulus and multilayer cloud systems associated with winter storms. Synoptic variability in cloud fields is estimated using satellite-based weather states, and the role of postfrontal conditions (cold-air outbreaks) in the development of stratiform clouds is further analyzed. Precipitation is persistent over the ocean, with a regional peak over the Gulf Stream path, where offshore sea surface temperature gradients are large and surface fluxes reach a regional peak. Satellite data show a clear annual cycle in cloud droplet number concentration with maxima (minima) along the coast in winter (summer), suggesting a marked annual cycle in aerosol-cloud interactions. Compared with satellite cloud retrievals, four climate models qualitatively reproduce the annual cycle in cloud cover and liquid water path, but with large discrepancies across models, especially in the extratropics. The paper concludes with a summary of outstanding issues and recommendations for future work. air-sea interactions; atmospheric boundary layer; climate model evaluation; stratiform clouds; Western North Atlantic
Painemal, David; Spangenberg, Douglas; Smith Jr., William L.; Minnis, Patrick; Cairns, Brian; Moore, Richard H.; Crosbie, Ewan; Robinson, Claire; Thornhill, Kenneth L.; Winstead, Edward L.; Ziemba, LukePainemal, D., D. Spangenberg, W. L. Smith Jr., P. Minnis, B. Cairns, R. H. Moore, E. Crosbie, C. Robinson, K. L. Thornhill, E. L. Winstead, L. Ziemba, 2021: Evaluation of satellite retrievals of liquid clouds from the GOES-13 Imager and MODIS over the midlatitude North Atlantic during NAAMES campaign. Atmospheric Measurement Techniques Discussions, 1-23. doi: 10.5194/amt-2021-7. Abstract. Satellite retrievals of cloud droplet effective radius (re) and optical depth (t) from the Thirteenth Geostationary Operational Environmental Satellite (GOES-13), and the MOderate resolution Imaging Spectroradiometer (MODIS) onboard Aqua and Terra are evaluated with airborne data collected over the midlatitude boundary layer during the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES). The airborne dataset comprises in-situ re from the Cloud Droplet Probe (CDP) and remotely sensed re and t from the airborne Research Scanning Polarimeter (RSP). GOES-13 and MODIS (Aqua and Terra) re values are systematically greater than those from the CDP and RSP by at least 4.8 um (GOES-13) and 1.7 um (MODIS) despite relatively high linear correlations coefficients (r = 0.52–0.68). In contrast, the satellite t underestimates its RSP counterpart by −3.0, with r = 0.76–077. Overall, MODIS yields better agreement with airborne data than GOES-13, with biases consistent with those reported for subtropical stratocumulus clouds. While the negative bias in satellite t is mostly due to the retrievals having been collected in highly heterogeneous cloud scenes, the causes for the positive bias in satellite re, especially for GOES-13, are more complex. Although the high viewing zenith angle (~65°) and coarser pixel resolution for GOES-13 could explain a re bias of at least 0.7 um, the higher GOES-13 re bias relative to that from MODIS is likely rooted in other factors. In this regard, a near monotonic increase was also observed in GOES-13 re up to 1.0 um with satellite scattering angle (ϴ) over the angular range 116°–165°, that is, re increases toward the backscattering direction. Understanding the variations of re with ϴ will require the combined use of theoretical computations along with inter-comparisons of satellite retrievals derived from sensors with dissimilar viewing geometry.
Pan, Sijie; Gao, Jidong; Jones, Thomas A.; Wang, Yunheng; Wang, Xuguang; Li, JunPan, S., J. Gao, T. A. Jones, Y. Wang, X. Wang, J. Li, 2021: The Impact of Assimilating Satellite-Derived Layered Precipitable Water, Cloud Water Path, and Radar Data on Short-Range Thunderstorm Forecasts. Mon. Wea. Rev., 149(5), 1359-1380. doi: 10.1175/MWR-D-20-0040.1. AbstractWith the launch of GOES-16 in November 2016, effective utilization of its data in convective-scale numerical weather prediction (NWP) has the potential to improve high-impact weather (HIWeather) forecasts. In this study, the impact of satellite-derived layered precipitable water (LPW) and cloud water path (CWP) in addition to NEXRAD observations on short-term convective-scale NWP forecasts are examined using three severe weather cases that occurred in May 2017. In each case, satellite-derived CWP and LPW products and radar observations are assimilated into the Advanced Research Weather Research and Forecasting (WRF-ARW) Model using the NSSL hybrid Warn-on-Forecast (WoF) analysis and forecast system. The system includes two components: the GSI-EnKF system and a deterministic 3DEnVAR system. This study examines deterministic 0–6-h forecasts launched from the hybrid 3DEnVAR analyses for the three severe weather events. Three types of experiments are conducted and compared: (i) the control experiment (CTRL) without assimilating any data, (ii) the radar experiment (RAD) with the assimilation of radar and surface observations, and (iii) the satellite experiment (RADSAT) with the assimilation of all observations including surface-, radar-, and satellite-derived CWP and LPW. The results show that assimilating additional GOES products improves short-range forecasts by providing more accurate initial conditions, especially for moisture and temperature variables.
Pathak, Raju; Sahany, Sandeep; Mishra, Saroj KantaPathak, R., S. Sahany, S. K. Mishra, 2021: Impact of Stochastic Entrainment in the NCAR CAM Deep Convection Parameterization on the Simulation of South Asian Summer Monsoon. Climate Dynamics. doi: 10.1007/s00382-021-05870-1. Model simulations are highly sensitive to the formulation of the atmospheric mixing process or entrainment in the deep convective parameterizations used in their atmospheric component. In this paper, we have implemented stochastic entrainment in the deep convection scheme of NCAR CAM5 and analyzed the improvements in model simulation, focusing on the South Asian Summer Monsoon (SASM), as compared to the deterministic entrainment formulation in the default version of the model. Simulations using stochastic entrainment (StochCAM5) outperformed default model simulations (DefCAM5), as inferred from multiple metrics associated with the SASM. StochCAM5 significantly alleviated some of the longstanding SASM biases seen in DefCAM5, such as precipitation pattern and magnitude over the Arabian Sea and western Equatorial Indian ocean, early monsoon withdrawal, and the overestimation in the frequency of light precipitation and the underestimation in the frequency of large-to-extreme precipitation. Related SASM dynamical and thermodynamical features, such as Somali Jet, low-level westerly winds, and meridional tropospheric temperature gradient (MTTG), are improved in StochCAM5. Further, the simulation of monsoon intra-seasonal oscillation (MISO), Madden Julian Oscillation (MJO), and equatorial Kelvin waves are improved in StochCAM5. Many essential climate variables, such as shortwave and longwave cloud forcing, cloud cover, relative and specific humidity, and precipitable water, show significant improvement in StochCAM5.
Payez, Alexandre; Dewitte, Steven; Clerbaux, NicolasPayez, A., S. Dewitte, N. Clerbaux, 2021: Dual View on Clear-Sky Top-of-Atmosphere Albedos from Meteosat Second Generation Satellites. Remote Sensing, 13(9), 1655. doi: 10.3390/rs13091655. Geostationary observations offer the unique opportunity to resolve the diurnal cycle of the Earth’s Radiation Budget at the top of the atmosphere (TOA), crucial for climate-change studies. However, a drawback of the continuous temporal coverage of the geostationary orbit is the fixed viewing geometry. As a consequence, imperfections in the angular distribution models (ADMs) used in the radiance-to-flux conversion process or residual angular-dependent narrowband-to-broadband conversion errors can result in systematic errors of the estimated radiative fluxes. In this work, focusing on clear-sky reflected TOA observations, we compare the overlapping views from Meteosat Second Generation satellites at 0° and 41.5°E longitude which enable a quantification of viewing-angle-dependent differences. Using data derived from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI), we identify some of the main sources of discrepancies, and show that they can be significantly reduced at the level of one month. This is achieved, separately for each satellite, via a masking procedure followed by an empirical fit at the pixel-level that takes into account all the clear-sky data from that satellite, calculated separately per timeslot of the day, over the month of November 2016. The method is then applied to each month of 2017, and gives a quadratic mean of the albedo root-mean squared difference over the dual-view region which is comparable from month to month, with a 2017 average value of 0.01. Sources of discrepancies include the difficulty to estimate the flux over the sunglint ocean region close to the limbs, the fact that the data processing does not include dedicated angular distribution models for the aerosol-over-ocean case, and the existence of an observer-dependent diurnal-asymmetry artefact affecting the clear-sky-albedo dependence on the solar zenith angle particularly over land areas. angular distribution models; SEVIRI; geostationary satellites; top-of-atmosphere albedo; reflected solar radiation; diurnal-asymmetry artefact
Pei, Suyang; Shinoda, Toshiaki; Steffen, John; Seo, HyodaePei, S., T. Shinoda, J. Steffen, H. Seo, 2021: Substantial Sea Surface Temperature Cooling in the Banda Sea Associated With the Madden-Julian Oscillation in the Boreal Winter of 2015. Journal of Geophysical Research: Oceans, 126(6), e2021JC017226. doi: 10.1029/2021JC017226. Substantial (∼2°C) basin averaged sea surface temperature (SST) cooling in the Banda Sea occurred in less than a 14-day period during the 2015 boreal winter Madden-Julian Oscillation (MJO). Such rapid and large cooling associated with the MJO has not been reported at least in the last two decades. Processes that control the substantial cooling during the 2015 MJO event are examined using high-resolution ocean reanalysis and one-dimensional (1-D) ocean model simulations. Previous studies suggest that MJO-induced SST variability in the Banda Sea is primarily controlled by surface heat flux. However, heat budget analysis of the model indicates that entrainment cooling produced by vertical mixing contributes more than surface heat flux for driving the basin-wide SST cooling during the 2015 event. Analysis of the ocean reanalysis further demonstrates that the prominent coastal upwelling around islands in the southern basin occurs near the end of the cooling period. The upwelled cold waters are advected by MJO-induced surface currents to a large area within the Banda Sea, which further maintains the basin-wide cold SST. These results are compared with another MJO-driven substantial cooling event during the boreal winter of 2007 in which the cooling is mostly driven by surface heat flux. Sensitivity experiments, in which initial temperature conditions for the two events are replaced by each other, demonstrate that the elevated thermocline associated with the 2015 strong El Niño is largely responsible for the intensified cooling generated by the vertical mixing with colder subsurface waters. sea surface temperature; Banda Sea; El Niño-Southern Oscillation (ENSO); Madden-Julian Oscillation (MJO); Maritime Continent; mixed layer processes
Peng, Jianghai; Jiang, Bo; Chen, Hongkai; Liang, Shunlin; Liang, Hui; Li, Shaopeng; Han, Jiakun; Liu, Qiang; Cheng, Jie; Yao, Yunjun; Jia, Kun; Zhang, XiaotongPeng, J., B. Jiang, H. Chen, S. Liang, H. Liang, S. Li, J. Han, Q. Liu, J. Cheng, Y. Yao, K. Jia, X. Zhang, 2021: A New Empirical Estimation Scheme for Daily Net Radiation at the Ocean Surface. Remote Sensing, 13(20), 4170. doi: 10.3390/rs13204170. Ocean surface net radiation (Rn) is significant in research on the Earth’s heat balance systems, air–sea interactions, and other applications. However, there have been few studies on Rn until now. Based on radiative and meteorological measurements collected from 66 globally distributed moored buoys, it was found that Rn was dominated by downward shortwave radiation (Rg↓) when the length ratio of daytime (LRD) was greater than 0.4 but dominated by downward longwave radiation (Rl↓) for the other cases (LRD ≤ 0.4). Therefore, an empirical scheme that includes two conditional models named Case 1 (LRD > 0.4) utilizing Rg↓ as a major input and Case 2 (LRD ≤ 0.4) utilizing Rl↓ as a major input for Rn estimation was successfully developed. After validation against in situ Rn, the performance of the empirical scheme was satisfactory with an overall R2 value of 0.972, an RMSE of 9.768 Wm−2, and a bias of −0.092 Wm−2. Specifically, the accuracies of the two conditional models were also very good, with RMSEs of 9.805 and 2.824 Wm−2 and biases of −0.095 and 0.346 Wm−2 for the Case 1 and Case 2 models, respectively. However, due to the limited number of available samples, the performances of these new models were poor in coastal and high-latitude areas, and the models did not work when the LRD was too small (i.e., LRD < 0.3). Overall, the newly developed empirical scheme for Rn estimation has strong potential to be widely used in practical use because of its simple format and high accuracy. CERES; longwave radiation; net radiation; shortwave radiation; buoy data; empirical model; sea surface
Perpina, Miguel; Noel, Vincent; Chepfer, Helene; Guzman, Rodrigo; Feofilov, Artem G.Perpina, M., V. Noel, H. Chepfer, R. Guzman, A. G. Feofilov, 2021: Link Between Opaque Cloud Properties and Atmospheric Dynamics in Observations and Simulations of Current Climate in the Tropics, and Impact on Future Predictions. Journal of Geophysical Research: Atmospheres, 126(17), e2020JD033899. doi: 10.1029/2020JD033899. Using spaceborne lidar observations and reanalyzes (2008–2014), we relate the vertical wind speed at 500 hPa (ω500), indicator of atmospheric circulation, to properties of opaque clouds (altitude and cover) and to the Cloud Radiative Effect (CRE) in the Tropics. We confront those observations with simulations by IPSL-CM6 and CESM1 climate models using early 21st century emissions. Both models overestimate the average opaque cloud cover. IPSL-CM6 puts high opaque clouds too high (+2 km), especially in ascendance. CESM1 overestimates the intermediate opaque cloud cover and underestimates small and large opaque cloud covers. Both models agree that cloud properties behave differently at wind speed above (strong subsidence) or below (weak subsidence and ascendance) 20 hPa/day. In future climate (2089–2095), variables affected by biases in current climate are affected by notable changes: IPSL-CM6 puts high opaque clouds even higher (+2 km) while opaque cloud cover above 30% decreases and below 30% increases in CESM1. Both models predict very little change in the average net CRE in the future. We find that predicted changes of cloud properties can be regionally driven by dynamic or thermodynamic changes, depending on the relationship between opaque cloud altitude and ω500 in the model. Overall, most changes are due to thermodynamic changes in the relationship between cloud property and atmospheric dynamics.
Peters, Ian Marius; Buonassisi, TonioPeters, I. M., T. Buonassisi, 2021: How changes in worldwide operating conditions affect solar cell performance. Solar Energy, 220, 671-679. doi: 10.1016/j.solener.2021.01.017. In field operation, solar cells are exposed to constantly changing operating conditions. These changing conditions have an impact on energy yield. Present-day yield predictions mostly use linear correction coefficients derived from lab experiments. These corrections neglect interactions between meteorological parameters like temperature and humidity. In this study, we reverse this approach by analyzing simulated solar cell performance under varying conditions worldwide. We use meteorological data measured between 2006 and 2015 to establish trends in the development of meteorological conditions and solar cell performance. From these two trends, we obtain linear correlation coefficients. The obtained implied temperature coefficient, on average, has a value of −0.52 ± 0.03%/K. This value is 15% higher than the tabulated temperature coefficient (−0.45%/K) used in the simulation, demonstrating the impact of coinciding meteorological factors. Light absorption due to elevated humidity levels is likely the strongest contributor to the deviation. One application of these findings is a projection of how today's crystalline silicon solar panels would perform due to rising temperature at the end of the 21st century. Using the established implied temperature coefficient, we project performance reductions of between 0.7% and 2.5%, depending on the warming scenario. The effect is reduced in higher efficient, upcoming photovoltaic technologies, providing further motivation to develop and improve these solar cells. Modelling; Performance ratio; Silicon solar cell; Temperature dependence
Pi, Chia-Jung; Chen, Jen-PingPi, C., J. Chen, 2021: Integrated cloud macro- and micro-physics schemes with kinetic treatment of condensation processes for global models. Atmospheric Research, 261, 105745. doi: 10.1016/j.atmosres.2021.105745. A new parameterization scheme was developed to remove the saturation adjustment assumption and resolve the condensation process in the grid-scale cloud macrophysics scheme to build an integrated cloud microphysics scheme for global climate models. By applying a saturation prediction equation with calculations based on cloud hydrometeor properties, supersaturation or subsaturation can be determined within the macrophysics scheme. This treatment provides the basis for condensation calculation and allows the Wegener–Bergeron–Findeisen process to be resolved explicitly to render a realistic liquid–ice partition in mixed-phase clouds. The cloud fraction scheme was modified based on physics principles to complement the condensation scheme. The new scheme's performance was examined by incorporating it into the Community Atmosphere Model version 5 (CAM5) single-column model to simulate a Tropical Warm Pool–International Cloud Experiment (TWP–ICE) case. The results revealed that grid-scale cloud properties are sensitive to the condensation process's treatment, and the new scheme can produce a more reasonable cloud fraction and liquid–ice partition than the original CAM5. The theory-based scheme developed in this study may provide insight for addressing consistency between the macrophysical and microphysical schemes in global climate models. Cloud microphysics; Cloud macrophysics; Liquid-ice partition; Mixed-phase supersaturation; Wegener–Bergeron–Findeisen process
Pinker, Rachel T.; Ma, Yingtao; Chen, Wen; Laszlo, Istvan; Liu, Hongqing; Kim, Hye-Yun; Daniels, JaimePinker, R. T., Y. Ma, W. Chen, I. Laszlo, H. Liu, H. Kim, J. Daniels, 2021: Top of the Atmosphere Reflected Shortwave Radiative Fluxes from GOES-R. Atmospheric Measurement Techniques Discussions, 1-45. doi: 10.5194/amt-2021-289. Abstract. Under the GOES-R activity, new algorithms are being developed at the National Oceanic and Atmospheric Administration (NOAA)/Center for Satellite Applications and Research (STAR) to derive surface and Top of the Atmosphere (TOA) shortwave (SW) radiative fluxes from the Advanced Baseline Imager (ABI), the primary instrument on GOES-R. This paper describes a support effort in the development and evaluation of the ABI instrument capabilities to derive such fluxes. Specifically, scene dependent narrow-to-broadband (NTB) transformations are developed to facilitate the use of observations from ABI at the TOA. Simulations of NTB transformations have been performed with MODTRAN4.3 using an updated selection of atmospheric profiles as implemented with the final ABI specifications. These are combined with Angular Distribution Models (ADMs), which are a synergy of ADMs from the Clouds and the Earth's Radiant Energy System (CERES) and from simulations. Surface condition at the scale of the ABI products as needed to compute the TOA radiative fluxes come from the International Geosphere-Biosphere Programme (IGBP). Land classification at 1/6° resolution for 18 surface types are converted to the ABI 2-km grid over the (CONtiguous States of the United States) (CONUS) and subsequently re-grouped to 12 IGBP types to match the classification of the CERES ADMs. In the simulations, default information on aerosols and clouds is based on the ones used in MODTRAN. Comparison of derived fluxes at the TOA is made with those from the CERES and/or the Fast Longwave and Shortwave Radiative Flux (FLASHFlux) data. A satisfactory agreement between the fluxes was observed and possible reasons for differences have been identified; the agreement of the fluxes at the TOA for predominantly clear sky conditions was found to be better than for cloudy sky due to possible time shift in observation times between the two observing systems that might have affected the position of the clouds during such periods.
Prijith, S. S.; Lima, C. B.; Ramana, M. V.; Sai, M. V. R. SeshaPrijith, S. S., C. B. Lima, M. V. Ramana, M. V. R. S. Sai, 2021: Intra-seasonal contrasting trends in clouds due to warming induced circulation changes. Scientific Reports, 11(1), 16985. doi: 10.1038/s41598-021-96246-2. Quantification of long term changes in cloud distribution and properties is critical for the proper assessment of future climate. We show contrasting trends in cloud properties and cloud radiative effects over Northwest Indian Ocean (NWIO) in south Asian summer monsoon. Cloud top height (CTH) decreases in June (− 69 ± 3 myr−1) and July (− 44 ± 3 myr−1), whereas it increases in August (106 ± 2 myr−1) and September (37 ± 1 myr−1). These contrasting trends are investigated to be due to the changes in upper tropospheric winds and atmospheric circulation pattern. Strengthening of upper tropospheric easterlies and changes in vertical wind dampen the vertical development of clouds in June and July. In contrast, weakening of upper tropospheric winds over NWIO and strengthening of updraft favour the vertical growth of clouds in August. Further, changes in horizontal winds at 450–350 hPa and strengthening of Indian Ocean Walker cell favour the westward spread of high level clouds, contributing to the increase in CTH over NWIO in August. Decrease of cloud cover and altitude in June and July and increase of the same in subsequent months would affect the monsoon rainfall over the Indian region. Proper representation of these intra-seasonal contrasting trends of clouds in climate models is important for the better prediction of regional weather.
Pu, Wei; Cui, Jiecan; Wu, Dongyou; Shi, Tenglong; Chen, Yang; Xing, Yuxuan; Zhou, Yue; Wang, XinPu, W., J. Cui, D. Wu, T. Shi, Y. Chen, Y. Xing, Y. Zhou, X. Wang, 2021: Unprecedented snow darkening and melting in New Zealand due to 2019–2020 Australian wildfires. Fundamental Research. doi: 10.1016/j.fmre.2021.04.001. Wildfire events have recently shown a rapid increase in frequency and scale due to the warmer present-day climate; however, their potential effects on the cryosphere are difficult to assess. Catastrophic wildfires in Australia during 2019–2020 emitted large amounts of light-absorbing particles (LAPs) to the atmosphere. Satellite observations indicate that these LAPs caused unprecedented snow-darkening of glaciers in New Zealand through long-range transport and deposition, with their effects lasting for up to three months in January–March 2020, influencing >90% of total glacier/snow and leading to a mean broadband snow-reflectance reduction of 0.08 ± 0.03. This snow darkening accelerated snowmelt by ~0.41 ± 0.2 cm day–1 during the southern summer, equivalent to that caused by a ~1.8 °C increase in air temperature. This indicates the significant impact of the 2019–2020 Australian wildfires on the hydrologic cycle in New Zealand, exceeding that of the local climate warming of ~1.5 °C since the preindustrial period. Wildfire-induced snow darkening is not limited to New Zealand. Future projections of wildfire incidence indicate widespread effects of snow darkening on the global cryosphere. Remote sensing; Australian wildfire; Glacier; Light-absorbing particles; Snow darkening
Raghuraman, Shiv Priyam; Paynter, David; Ramaswamy, V.Raghuraman, S. P., D. Paynter, V. Ramaswamy, 2021: Anthropogenic forcing and response yield observed positive trend in Earth’s energy imbalance. Nature Communications, 12(1), 4577. doi: 10.1038/s41467-021-24544-4. The observed trend in Earth’s energy imbalance (TEEI), a measure of the acceleration of heat uptake by the planet, is a fundamental indicator of perturbations to climate. Satellite observations (2001–2020) reveal a significant positive globally-averaged TEEI of 0.38 ± 0.24 Wm−2decade−1, but the contributing drivers have yet to be understood. Using climate model simulations, we show that it is exceptionally unlikely (
Ren, Tong; Li, Dongchen; Muller, Jake; Yang, PingRen, T., D. Li, J. Muller, P. Yang, 2021: Sensitivity of Radiative Flux Simulations to Ice Cloud Parameterization over the Equatorial Western Pacific Ocean Region. J. Atmos. Sci., 78(8), 2549-2571. doi: 10.1175/JAS-D-21-0017.1. AbstractPrevious studies suggest explanations of the observed cancellation of shortwave (SW) and longwave (LW) cloud radiative effects (CREs) at the top of the atmosphere over tropical oceans where deep convection prevails, such as interactions among cloud microphysics, radiation, and dynamics. However, simulations based on general circulation models (GCMs) show disagreement in terms of the net (SW + LW) CREs over tropical deep convective ocean regions. One of the GCM uncertainty sources is the parameterization of ice cloud bulk optical properties. In this study, a combination of active and passive satellite daytime cloud retrievals is used to study the sensitivity of radiation flux calculations to ice cloud parameterization over the equatorial western Pacific Ocean region. Three ice cloud schemes are tested. The first is a widely used scheme that assumes hexagonal column ice particles. The second scheme treats ice particles as aggregates of surface-roughened hexagonal columns. The third scheme best matches the cloud ice mass–dimension relation in the cloud microphysics scheme by assuming a mixture of two ice particle habits. The results show that the hexagonal-column-based scheme has the weakest SW CRE but strongest LW CRE among the three. In addition, cloud optical thickness and effective radius are used to cluster cold-top single-layer ice clouds into three types, which resemble thin cirrus, detrained anvil clouds, and deep convective cores, respectively. In agreement with previous studies, cloud SW heating overwhelms LW cooling in the upper portion of anvil-like clouds.
Renner, Maik; Kleidon, Axel; Clark, Martyn; Nijssen, Bart; Heidkamp, Marvin; Best, Martin; Abramowitz, GabRenner, M., A. Kleidon, M. Clark, B. Nijssen, M. Heidkamp, M. Best, G. Abramowitz, 2021: How well can land-surface models represent the diurnal cycle of turbulent heat fluxes?. J. Hydrometeor., 22(1), 77-94. doi: 10.1175/JHM-D-20-0034.1. Abstract The diurnal cycle of solar radiation represents the strongest energetic forcing and dominates the exchange of heat and mass of the land surface with the atmosphere. This diurnal heat redistribution represents a core of land-atmosphere coupling that should be accurately represented in Land-Surface Models (LSM) which are critical parts of weather and climate models. We employ a diagnostic model evaluation approach using a signature-based metric which describes the diurnal variation of heat fluxes. The metric is obtained by decomposing the diurnal variation of surface heat fluxes into their direct response and the phase lag to incoming solar radiation. We employ the output of 13 different LSMs driven with meteorological forcing of 20 FLUXNET sites (PLUMBER dataset by Best et al., 2015). All LSMs show a poor representation of the evaporative fraction and thus the diurnal magnitude of the sensible and latent heat ux under cloud-free conditions. In addition, we find that the diurnal phase of both heat fluxes is poorly represented. The best performing model only reproduces 33% of the evaluated evaporative conditions across the sites. The poor performance of the diurnal cycle of turbulent heat exchange appears to be linked to how models solve for the surface energy balance and redistribute heat into the subsurface. We conclude that a systematic evaluation of diurnal signatures is likely to help to improve the simulated diurnal cycle, better represent land-atmosphere interactions and therefore improve simulations of the near-surface climate.
Richards, Benjamin D. G.; Koll, Daniel D. B.; Cronin, Timothy W.Richards, B. D. G., D. D. B. Koll, T. W. Cronin, 2021: Seasonal Loops Between Local Outgoing Longwave Radiation and Surface Temperature. Geophysical Research Letters, 48(17), e2021GL092978. doi: 10.1029/2021GL092978. The relationship between outgoing longwave radiation (OLR) and the surface temperature has a major influence on Earth's climate sensitivity. Studies often assume that this relationship is approximately linear, but it is unclear whether the approximation always holds. Here we show that, on seasonal timescales, clear-sky OLR is a multivalued function of local surface temperature. In many places, the OLR-temperature relationship is better approximated by a loop than a line and we quantify the resulting “OLR loopiness”, that is, how much clear-sky OLR varies between different seasons with the same surface temperature. Based on offline radiative calculations, in the tropics OLR loops are mainly caused by seasonal variations in relative humidity that are out of phase with surface temperature; in the extratropics, OLR loops are mainly due to variations in lapse rates. Our work provides a mechanism through which Earth's climate feedback can differ between seasonal and long-term time scales.
Ridout, James A.; Barton, Neil P.; Janiga, Matthew A.; Reynolds, Carolyn A.; May, Jackie C.; Rowley, Clark; Bishop, Craig H.Ridout, J. A., N. P. Barton, M. A. Janiga, C. A. Reynolds, J. C. May, C. Rowley, C. H. Bishop, 2021: Surface Radiative Flux Bias Reduction through Regionally Varying Cloud Fraction Parameter Nudging in a Global Coupled Forecast System. Journal of Advances in Modeling Earth Systems, (In Press). doi: 10.1029/2019MS002006. Key Points: A method is presented to nudge a cloud fraction parameter in a global coupled forecast system to reduce surface net shortwave flux biases. Results from a series of 45-day test forecasts are presented demonstrating the efficacy of the approach. Further tests are required to determine operational applicability using a suitable near real-time source of surface radiative flux data. cloud parameterization; coupled modelling; parameter adjustment; surface radiation budget
Riihelä, Aku; Bright, Ryan M.; Anttila, KatiRiihelä, A., R. M. Bright, K. Anttila, 2021: Recent strengthening of snow and ice albedo feedback driven by Antarctic sea-ice loss. Nature Geoscience, 14(11), 832-836. doi: 10.1038/s41561-021-00841-x. The decline of the Arctic cryosphere during recent decades has lowered the region’s surface albedo, reducing its ability to reflect solar radiation back to space. It is not clear what role the Antarctic cryosphere plays in this regard, but new remote-sensing-based techniques and datasets have recently opened the possibility to investigate its role. Here, we leverage these to show that the surface albedo reductions from sustained post-2000 losses in Arctic snow and ice cover equate to increasingly positive snow and ice albedo feedback relative to a 1982–1991 baseline period, with a decadal trend of +0.08 ± 0.04 W m–2 decade–1 between 1992 and 2015. During the same period, the expansion of the Antarctic sea-ice pack generated a negative feedback, with a decadal trend of −0.06 ± 0.02 W m–2 decade–1. However, substantial Antarctic sea-ice losses during 2016–2018 completely reversed the trend, increasing the three-year mean combined Arctic and Antarctic snow and ice albedo feedback to +0.26 ± 0.15 W m–2. This reversal highlights the importance of Antarctic sea-ice loss to the global snow and ice albedo feedback. The 1992–2018 mean feedback is equivalent to approximately 10% of anthropogenic CO2 emissions over the same period; the share may rise markedly should 2016–2018 snow and ice conditions become common, although increasing long-wave emissions will probably mediate the impact on the total radiative-energy budget. Climate-change impacts; Cryospheric science
Roy, Kumar; Mukhopadhyay, Parthasarathi; Krishna, R. P. M.; Khouider, B.; Goswami, B. B.Roy, K., P. Mukhopadhyay, R. P. M. Krishna, B. Khouider, B. B. Goswami, 2021: Evaluation of Mean State in NCEP Climate Forecast System (Version 2) Simulation Using a Stochastic Multicloud Model Calibrated With DYNAMO RADAR Data. Earth and Space Science, 8(8), e2020EA001455. doi: 10.1029/2020EA001455. Stochastic parameterizations are continuously providing promising simulations of unresolved atmospheric processes for global climate models (GCMs). One of the stochastic multi-cloud model (SMCM) features is to mimic the life cycle of the three most common cloud types (congestus, deep, and stratiform) in tropical convective systems. To better represent organized convection in the Climate Forecast System version 2 (CFSv2), the SMCM parameterization is adopted in CFSv2 (SMCM-CTRL) in lieu of the pre-existing revised simplified Arakawa–Schubert (RSAS) cumulus scheme and has shown essential improvements in different large-scale features of tropical convection. But the sensitivity of the SMCM parameterization from the observations is yet to be ascertained. Radar data during the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign is used to tune the SMCM in the present manuscript. The DYNAMO radar observations have been used to calibrate the SMCM using a Bayesian inference procedure to generate key time scale parameters for the transition probabilities of the underlying Markov chains of the SMCM as implemented in CFS (hereafter SMCM-DYNAMO). SMCM-DYNAMO improves many aspects of the mean state climate compared to RSAS, and SMCM-CTRL. Significant improvement is noted in the rainfall probability distribution function over the global tropics. The global distribution of different types of clouds, particularly low-level clouds, is also improved. The convective and large-scale rainfall simulations are investigated in detail. Atmospheric mean state; DYNAMO constrained SMCM used in CFSv2; DYNAMO RADAR data for constraining the SMCM; stochastic multi-cloud model
Rybka, Harald; Burkhardt, Ulrike; Köhler, Martin; Arka, Ioanna; Bugliaro, Luca; Görsdorf, Ulrich; Horváth, Ákos; Meyer, Catrin I.; Reichardt, Jens; Seifert, Axel; Strandgren, JohanRybka, H., U. Burkhardt, M. Köhler, I. Arka, L. Bugliaro, U. Görsdorf, Á. Horváth, C. I. Meyer, J. Reichardt, A. Seifert, J. Strandgren, 2021: The behavior of high-CAPE (convective available potential energy) summer convection in large-domain large-eddy simulations with ICON. Atmospheric Chemistry and Physics, 21(6), 4285-4318. doi: 10.5194/acp-21-4285-2021. Abstract. Current state-of-the-art regional numerical weather prediction (NWP) models employ kilometer-scale horizontal grid resolutions, thereby simulating convection within the grey zone. Increasing resolution leads to resolving the 3D motion field and has been shown to improve the representation of clouds and precipitation. Using a hectometer-scale model in forecasting mode on a large domain therefore offers a chance to study processes that require the simulation of the 3D motion field at small horizontal scales, such as deep summertime moist convection, a notorious problem in NWP. We use the ICOsahedral Nonhydrostatic weather and climate model in large-eddy simulation mode (ICON-LEM) to simulate deep moist convection and distinguish between scattered, large-scale dynamically forced, and frontal convection. We use different ground- and satellite-based observational data sets, which supply information on ice water content and path, ice cloud cover, and cloud-top height on a similar scale as the simulations, in order to evaluate and constrain our model simulations. We find that the timing and geometric extent of the convectively generated cloud shield agree well with observations, while the lifetime of the convective anvil was, at least in one case, significantly overestimated. Given the large uncertainties of individual ice water path observations, we use a suite of observations in order to better constrain the simulations. ICON-LEM simulates a cloud ice water path that lies between the different observational data sets, but simulations appear to be biased towards a large frozen water path (all frozen hydrometeors). Modifications of parameters within the microphysical scheme have little effect on the bias in the frozen water path and the longevity of the anvil. In particular, one of our convective days appeared to be very sensitive to the initial and boundary conditions, which had a large impact on the convective triggering but little impact on the high frozen water path and long anvil lifetime bias. Based on this limited set of sensitivity experiments, the evolution of locally forced convection appears to depend more on the uncertainty of the large-scale dynamical state based on data assimilation than of microphysical parameters. Overall, we judge ICON-LEM simulations of deep moist convection to be very close to observations regarding the timing, geometrical structure, and cloud ice water path of the convective anvil, but other frozen hydrometeors, in particular graupel, are likely overestimated. Therefore, ICON-LEM supplies important information for weather forecasting and forms a good basis for parameterization development based on physical processes or machine learning.
Sato, Kazutoshi; Inoue, JunSato, K., J. Inoue, 2021: Seasonal Change in Satellite-Retrieved Lower-Tropospheric Ice-Cloud Fraction Over the Southern Ocean. Geophysical Research Letters, 48(23), e2021GL095295. doi: 10.1029/2021GL095295. This study investigated the temperature and fraction of lower-tropospheric ice cloud over Antarctica and the Southern Ocean (SO) using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation satellite data. Over the SO, the maximum low-level ice-cloud fraction below 2 km is observed at cold temperatures (−7.5°C (>−17.5°C) during summer (winter). High fractions of low-level ice cloud observed at higher temperatures over near-coastal Antarctic sea ice areas in summer, coincident with the highest chlorophyll-a concentrations, and over coastal Antarctic ice-covered areas in winter, suggest that marine aerosols act as ice-nucleating particles for ice-cloud formation during summer and winter. ice cloud; Antarctica; CALIPSO; Southern Ocean; chlorophyll
Schuddeboom, A. J.; McDonald, A. J.Schuddeboom, A. J., A. J. McDonald, 2021: The Southern Ocean Radiative Bias, Cloud Compensating Errors, and Equilibrium Climate Sensitivity in CMIP6 Models. Journal of Geophysical Research: Atmospheres, 126(22), e2021JD035310. doi: 10.1029/2021JD035310. Coupled Model Intercomparison Project Phase 6 (CMIP6) models are analyzed using an established cloud clustering methodology. This enables a comparison of cloud representation in models and observations. The simulation of stratocumulus clouds over the Southern Ocean is shown to have changed substantially from earlier generation models. The CMIP6 models analyzed show stratocumulus clouds now occur more often in simulations than in International Satellite Cloud Climatology Project (ISCCP) observations, but are not bright enough compared to Clouds and the Earth's Radiant Energy System (CERES) data. This is in contrast to the “too few, too bright” problem, which has characterized prior model simulations of stratocumulus clouds, particularly over the Southern Ocean. The cloud clusters also enable the calculation of mean and compensating shortwave cloud radiative effect (SW CRE) errors from model data. The compensating errors are shown to be much larger than mean errors suggesting the CMIP6 models still have much to improve in their cloud representation. A statistically significant negative relationship between the mean and compensating errors in SW CRE over the Southern Ocean is identified. This relationship is observed elsewhere, but is only significant over the Southern Ocean. This implies model tuning efforts are hiding biases in the representation of clouds in this region. CMIP6 models have been shown to have a higher equilibrium climate sensitivity (ECS) relative to CMIP5 simulations. The link between ECS and SW CRE mean and compensating errors is investigated but no evidence of a relationship between these variables was found. Southern Ocean; CMIP6; cloud radiative bias; compensating errors; ECS; model comparison
Shang, Haolu; Ding, Yixing; Guo, Huadong; Liu, Guang; Liu, Xiaoyu; Wu, Jie; Liang, Lei; Jiang, Hao; Chen, GuoqiangShang, H., Y. Ding, H. Guo, G. Liu, X. Liu, J. Wu, L. Liang, H. Jiang, G. Chen, 2021: Simulation of Earth’s Outward Radiative Flux and Its Radiance in Moon-Based View. Remote Sensing, 13(13), 2535. doi: 10.3390/rs13132535. To study the Earth’s energy balance and to extend exoplanet research, the Earth’s outward radiative flux and its radiance in the Moon-based view were simulated according to the Earth–Sun–Moon geometry model, with the help of ERA5. A framework was developed to identify the angular distribution model (ADM) of Earth’s surface and its scene types, according to the surface and atmospheric data from ERA5. Our simulation shows that the specific viewing geometry controls the periodical variations in the Moon-based view radiative flux and its radiance, which reflect the orbital period of the Moon. The seasonal variations in shortwave and longwave radiative flux follow the energy balance in general, which is probably influenced by the Earth albedo. The derived global ADM would help to identify the anisotropic factor of observations at DSCOVR. Our simulations prove that Moon-based observation is a valuable source for Earth observation and that the orbital information of exoplanets could be derived from the radiance observation. earth energy balance; earth radiation; exoplanet; moon-based observation
Shen, Lixing; Zhao, Chuanfeng; Yang, XingchuanShen, L., C. Zhao, X. Yang, 2021: Insight Into the Seasonal Variations of the Sea-Land Breeze in Los Angeles With Respect to the Effects of Solar Radiation and Climate Type. Journal of Geophysical Research: Atmospheres, 126(6), e2020JD033197. doi: https://doi.org/10.1029/2020JD033197. This study uses 20 years of observation data to analyze the long-term trend of the sea-land breeze (SLB) in the city of Los Angeles. The focus of the study is on the seasonal variation of the SLB and the main influencing factors both regionally and at a large scale. A new method which is suitable for automatic processing is introduced to analyze the SLB and determine the specific characteristics of the local SLB. The results show the sea wind speed has an obvious seasonal variation with peak value in summer and minimum value in winter. Note the sea wind speed is generally positively related to the in situ solar radiation. In contrast, the seasonal variation of the land wind speed is much weaker. Two main factors are responsible for this phenomenon. First, the response of the temperature difference between land and sea (TDLS) to the season is much more insensitive during nighttime than during daytime, and the TDLS is the direct driver of SLB. Second, the magnitude of the upper layer westerlies has an obvious seasonal variation under the local climate background, which is called the Mediterranean climate. During winter, the stronger upper westerlies enhance the land wind circulation, which further offsets the seasonal gap, and this even causes the fact that there is no corresponding relationship between the season and wind speed. In contrast, the seasonal variation of the westerlies has little effect on the sea wind speed, and the in situ solar radiation remains the determinant factor. solar radiation; Mediterranean climate; sea-land breeze; westerlies
Shen, Pengke; Zhao, Shuqing; Ma, YongjingShen, P., S. Zhao, Y. Ma, 2021: Perturbation of Urbanization to Earth's Surface Energy Balance. Journal of Geophysical Research: Atmospheres, 126(8), e2020JD033521. doi: https://doi.org/10.1029/2020JD033521. Urbanization, one of the most dramatic forms of land conversion, modifies local climatic environments and threatens human life and health. Here we use the space-for-time approach combined with satellite data to quantify the potential perturbation of surface energy balance and land surface temperature (LST) caused by urbanization at global scale. We estimate that collectively +2.4°C, +0.9°C, and +1.7°C potential changes for annual daytime, nighttime, and mean LST could be triggered when land surface converted from natural area to urban use, due primarily to the decline of latent heat during months from April to October (−23.9–−3.2 W m−2), and the reduced sensible heat and ground heat storage in other months (−5.2–−2.4 W m−2). Urbanization perturbation to surface energy balance and temperature exhibit conspicuous spatial heterogeneity (i.e., varying with latitude and climate zones) and temporal asymmetries (i.e., diurnal and seasonal: strong in summer daytime and weak in winter nighttime). These spatial-temporal variations are interrelated closely with local background climate-vegetation regimes, as indicated by strong correlations between urbanization perturbation to surface biophysical effects and precipitation, temperature, vegetation index across regions and months. Our findings provide empirical evidence that biophysical mechanisms of urbanization need to be considered in predicting future trajectories of climate change and local susceptibility of surface energy balance should be accounted for when evaluating urbanization effects and mitigating urban heat. land surface temperature; surface energy balance; background climate; global change; urbanization
Shi, Hongrong; Zhang, Jinqiang; Zhao, Bin; Xia, Xiangao; Hu, Bo; Chen, Hongbin; Wei, Jing; Liu, Mengqi; Bian, Yuxuan; Fu, Disong; Gu, Yu; Liou, Kuo-NanShi, H., J. Zhang, B. Zhao, X. Xia, B. Hu, H. Chen, J. Wei, M. Liu, Y. Bian, D. Fu, Y. Gu, K. Liou, 2021: Surface Brightening in Eastern and Central China Since the Implementation of the Clean Air Action in 2013: Causes and Implications. Geophysical Research Letters, 48(3), e2020GL091105. doi: https://doi.org/10.1029/2020GL091105. Surface brightening has been observed in China since 2005. However, it remains unclear whether the brightening has accelerated recently in response to the strictest ever air pollution control policies since 2013. By combining intensive surface and satellite observations, we find an unprecedented rapid increasing trend in surface solar radiation (SSR) of 0.70–1.16 W m−2 yr−1 over the eastern and central China for 2014–2019. Using a novel method to identify the relative contributions of aerosol and cloud radiative effects to the SSR trends, we find that the strongly declining aerosol radiative effect due to the strict air pollution controls is the main cause of the upward SSR trends; cloud variations should not be the main reason. Distinction exists in seasonal trends of SSR, with decreasing trends in winter and increasing trends in other seasons. Air pollution controls play an important role in regulating SSR, which has valuable implications for photovoltaic power generation. aerosol radiative effect; air pollutant control; eastern and central China; surface solar radiation brightening
Si, Yuwen; Wang, Hongqiang; Wang, Yujia; Yang, Honghai; Chen, Yonghang; Liu, Qiong; Chen, Shuyi; Zheng, NingSi, Y., H. Wang, Y. Wang, H. Yang, Y. Chen, Q. Liu, S. Chen, N. Zheng, 2021: Effects of single-layer low clouds on the surface solar radiation in East Asia. Solar Energy, 224, 1099-1106. doi: 10.1016/j.solener.2021.06.047. The earth surface solar radiation is largely influenced by the physical properties of low clouds, which need to be investigated for effectively utilizing the solar energy. In this paper, four different regions in East Asia were selected and NASA CERES (Clouds and the Earth's Radiant Energy System) SSF (Single Satellite Footprint) Aqua Edition 3A data from the year 2003 to 2016 were used to analyze the annual and inter-annual variations in the low cloud coverage, ice water path and liquid water path of the single-layer low clouds. Results showed that these three physical property parameters achieved their maximums in December or January for most regions. For the past 14 years, both the low cloud coverage and liquid water path achieved their highest multi-year averages and largest fluctuation ranges in the southern region, while the ice water path achieved its highest multi-year average and largest fluctuation range in the northwestern region. The cooling effect of single-layer low clouds on the solar radiation depended on the regions and seasons. For the past 14 years, the cooling effect of single-layer low clouds showed an overall weakening tendency in the northwestern region, but an overall strengthening tendency in the other three regions, and especially, in the southern region. Regarding the correlation to the surface shortwave radiation, the liquid water path was a closer factor for most regions, while the ice water path was an insignificant factor, especially in the northwestern region. East Asia; Cloud physical properties; Shortwave radiative forcing; Single-layer low clouds
Sledd, A.; L’Ecuyer, T. S.Sledd, A., T. S. L’Ecuyer, 2021: Emerging Trends in Arctic Solar Absorption. Geophysical Research Letters, 48(24), e2021GL095813. doi: 10.1029/2021GL095813. Recent satellite observations confirm that the Arctic is absorbing more solar radiation now than at the start of this century in response to declining Arctic sea ice and snow covers. Trends in the solar radiation input to Arctic ocean and land surfaces now each exceed interannual variability at the 95% confidence level, although all-sky trends have taken 20%–40% longer to emerge compared to clear-sky conditions. Clouds reduce mean solar absorption and secular trends over both land and ocean, but the effect of clouds on natural variability depends on the underlying surface. While clouds increase the time needed to unambiguously identify trends in nearly all Arctic regions, their masking effects are strongest over oceans. Clouds have extended the time to emergence of already observed clear-sky trends beyond the existing 21 years Clouds and Earth's Radiant Energy System record in half of eight Arctic seas, supporting the need for continued satellite-based radiative flux observations over the Arctic. clouds; climate change; Arctic; solar radiation; trend detection
Sledd, Anne; L'Ecuyer, TristanSledd, A., T. L'Ecuyer, 2021: Uncertainty in Forced and Natural Arctic Solar Absorption Variations in CMIP6 Models. J. Climate, 34(3), 931-948. doi: 10.1175/JCLI-D-20-0244.1.
Su, Wenying; Liang, Lusheng; Myhre, Gunnar; Thorsen, Tyler J.; Loeb, Norman G.; Schuster, Gregory L.; Ginoux, Paul; Paulot, Fabien; Neubauer, David; Checa-Garcia, Ramiro; Matsui, Hitoshi; Tsigaridis, Kostas; Skeie, Ragnhild B.; Takemura, Toshihiko; Bauer, Susanne E.; Schulz, MichaelSu, W., L. Liang, G. Myhre, T. J. Thorsen, N. G. Loeb, G. L. Schuster, P. Ginoux, F. Paulot, D. Neubauer, R. Checa-Garcia, H. Matsui, K. Tsigaridis, R. B. Skeie, T. Takemura, S. E. Bauer, M. Schulz, 2021: Understanding Top-of-Atmosphere Flux Bias in the AeroCom Phase III Models: A Clear-Sky Perspective. Journal of Advances in Modeling Earth Systems, 13(9), e2021MS002584. doi: 10.1029/2021MS002584. Biases in aerosol optical depths (AOD) and land surface albedos in the AeroCom models are manifested in the top-of-atmosphere (TOA) clear-sky reflected shortwave (SW) fluxes. Biases in the SW fluxes from AeroCom models are quantitatively related to biases in AOD and land surface albedo by using their radiative kernels. Over ocean, AOD contributes about 25% to the S–N mean SW flux bias for the multi-model mean (MMM) result. Over land, AOD and land surface albedo contribute about 40% and 30%, respectively, to the S–N mean SW flux bias for the MMM result. Furthermore, the spatial patterns of the SW flux biases derived from the radiative kernels are very similar to those between models and CERES observation, with the correlation coefficient of 0.6 over ocean and 0.76 over land for MMM using data of 2010. Satellite data used in this evaluation are derived independently from each other, consistencies in their bias patterns when compared with model simulations suggest that these patterns are robust. This highlights the importance of evaluating related variables in a synergistic manner to provide an unambiguous assessment of the models, as results from single parameter assessments are often confounded by measurement uncertainty. Model biases in land surface albedos can and must be corrected to accurately calculate TOA flux. We also compare the AOD trend from three models with the observation-based counterpart. These models reproduce all notable trends in AOD except the decreasing trend over eastern China and the adjacent oceanic regions due to limitations in the emission data set. aerosols; radiative flux; surface albedo
Subba, Tamanna; Gogoi, Mukunda M.; Moorthy, K. Krishna; Bhuyan, Pradip K.; Pathak, Binita; Guha, Anirban; Srivastava, Manoj Kumar; Vyas, Brij Mohan; Singh, Karamjit; Krishnan, Jayabala; Lakshmikumar, T. V. S.; Babu, S. SureshSubba, T., M. M. Gogoi, K. K. Moorthy, P. K. Bhuyan, B. Pathak, A. Guha, M. K. Srivastava, B. M. Vyas, K. Singh, J. Krishnan, T. V. S. Lakshmikumar, S. S. Babu, 2021: Aerosol Radiative Effects Over India from Direct Radiation Measurements and Model Estimates. Multi-year measurements of surface-reaching solar (shortwave) radiation fluxes across a network of aerosol observatories (ARFINET) are combined, for the first time, with concurrent satellite (CERES)-based retrieval of top of the atmosphere (TOA) fluxes and radiative transfer simulations to estimate regional aerosol direct radiative forcing (ARF) over the Indian region. We observed that the synergistic approach improves the accuracy of ARF estimates, which is otherwise differed by as high as 9% (in the atmosphere) in the independent model (radiative transfer and aerosol model constraining measured values spectral aerosol optical properties) simulations. Especially, the model simulated TOA fluxes are found to differ significantly, which leads to the overestimation/ underestimation in the atmospheric forcing. During JJAS, an overestimation of ~ 2 W m-2 (corresponding heating rate ~ 0.15 K day-1) is noticed. The ARF estimated from the synergistic approach revealed significant spatial heterogeneity across distinct geographic regions of India, with surface (SUR) forcing as high as -48.5 W m-2 over the Indo Gangetic Plains, -45.1 W m-2 over northeast India and -34.4 W m-2 over the southern Peninsula and as low as -15.8 W m-2 in the oceanic regions of the Bay of Bengal. The influence of dust and anthropogenic sulfate and carbonaceous aerosols are crucial in modulating ARF over the northern part of India, which contributes up to 60% during their high emission periods. The effect of anthropogenic aerosols on ARF is also significant (~ 50%) over the peninsular and oceanic regions. In terms of clear sky surface reaching solar radiation fluxes (SWin), the reduction in SWin due to the effect of aerosols in the atmosphere is found to vary between 3 to 22%, being highest over the IGP during ON and DJF. CERES; aerosol radiative forcing; heating rate; MERRA-2; aerosol composition; aerosol sources; ARFINET; SW-radiation
Sullivan, Sylvia C.; Voigt, AikoSullivan, S. C., A. Voigt, 2021: Ice microphysical processes exert a strong control on the simulated radiative energy budget in the tropics. Communications Earth & Environment, 2(1), 1-8. doi: 10.1038/s43247-021-00206-7. Simulations of the global climate system at storm-resolving resolutions of 2 km are now becoming feasible and show promising realism in clouds and precipitation. However, shortcomings in their representation of microscale processes, like the interaction of cloud droplets and ice crystals with radiation, can still restrict their utility. Here, we illustrate how changes to the ice microphysics scheme dramatically alter both the vertical profile of cloud-radiative heating and top-of-atmosphere outgoing longwave radiation (terrestrial infrared cooling) in storm-resolving simulations over the Asian monsoon region. Poorly-constrained parameters in the ice nucleation scheme, overactive conversion of ice to snow, and inconsistent treatment of ice crystal effective radius between microphysics and radiation alter cloud-radiative heating by a factor of four and domain-mean infrared cooling by 30 W m−2. Vertical resolution, on the other hand, has a very limited impact. Even in state-of-the-art models then, uncertainties in microscale cloud properties exert a strong control on the radiative budget that propagates to both atmospheric circulation and regional climate. These uncertainties need to be reduced to realize the full potential of storm-resolving models.
Suselj, Kay; Teixeira, Joao; Kurowski, Marcin J.; Molod, AndreaSuselj, K., J. Teixeira, M. J. Kurowski, A. Molod, 2021: Improving the Representation of Subtropical Boundary Layer Clouds in the NASA GEOS Model with the Eddy-Diffusivity/Mass-Flux Parameterization. Mon. Wea. Rev., 149(3), 793-809. doi: 10.1175/MWR-D-20-0183.1. AbstractA systematic underestimation of subtropical planetary boundary layer (PBL) stratocumulus clouds by the GEOS model has been significantly improved by a new eddy-diffusivity/mass-flux (EDMF) parameterization. The EDMF parameterization represents the subgrid-scale transport in the dry and moist parts of the PBL in a unified manner and it combines an adjusted eddy-diffusivity PBL scheme from GEOS with a stochastic multiplume mass-flux model. The new EDMF version of the GEOS model is first compared against the CONTROL version in a single-column model (SCM) framework for two benchmark cases representing subtropical stratocumulus and shallow cumulus clouds, and validated against large-eddy simulations. Global simulations are performed and compared against observations and reanalysis data. The results show that the EDMF version of the GEOS model produces more realistic subtropical PBL clouds. The EDMF improvements first detected in the SCM framework translate into similar improvements of the global GEOS model.
Svensmark, Henrik; Svensmark, Jacob; Enghoff, Martin Bødker; Shaviv, Nir J.Svensmark, H., J. Svensmark, M. B. Enghoff, N. J. Shaviv, 2021: Atmospheric ionization and cloud radiative forcing. Scientific Reports, 11(1), 19668. doi: 10.1038/s41598-021-99033-1. Atmospheric ionization produced by cosmic rays has been suspected to influence aerosols and clouds, but its actual importance has been questioned. If changes in atmospheric ionization have a substantial impact on clouds, one would expect to observe significant responses in Earth’s energy budget. Here it is shown that the average of the five strongest week-long decreases in atmospheric ionization coincides with changes in the average net radiative balance of 1.7 W/m$$^2$$(median value: 1.2 W/m$$^2$$) using CERES satellite observations. Simultaneous satellite observations of clouds show that these variations are mainly caused by changes in the short-wave radiation of low liquid clouds along with small changes in the long-wave radiation, and are almost exclusively located over the pristine areas of the oceans. These observed radiation and cloud changes are consistent with a link in which atmospheric ionization modulates aerosol's formation and growth, which survive to cloud condensation nuclei and ultimately affect cloud formation and thereby temporarily the radiative balance of Earth. Astronomy and planetary science; Climate sciences
Takahashi, Naoya; Hayasaka, Tadahiro; Qiu, Bo; Yamaguchi, RyoheiTakahashi, N., T. Hayasaka, B. Qiu, R. Yamaguchi, 2021: Observed response of marine boundary layer cloud to the interannual variations of summertime Oyashio extension SST front. Climate Dynamics. doi: 10.1007/s00382-021-05649-4. Active roles of both sea surface temperature (SST) and its frontal characteristics to the atmosphere in the mid-latitudes have been investigated around the western boundary current regions, and most studies have focused on winter season. The present study investigated the influence of the variation of the summertime Oyashio extension SST front (SSTF) in modulating low-level cloud properties (i.e., low-level cloud cover [LCC], cloud optical thickness [COT], and shortwave cloud radiative effect [SWCRE]) on inter-annual timescales, based on available satellite and Argo float datasets during 2003–2016. First, we examined the mechanism of summertime SSTF variability itself. The strength of the SSTF (SSSTF), defined as the maximum horizontal gradient of SST, has clear inter-annual variations. Frontogenesis equation analysis and regression analysis for subsurface temperature indicated that the inter-annual variations of the summertime SSSTF in the western North Pacific are closely related to the variations of not surface heat flux, but western boundary currents, particularly the Oyashio Extensions. The response of low-level cloud to intensified SSSTF is that negative SWCRE with positive COT anomaly in the northern flank of the SSTF can be induced by cold SST anomalies. The spatial scale of the low-level cloud response was larger than the SST frontal scale, and the spatial distribution of the response was mainly constrained by the pathways of Kuroshio and Oyashio Extensions. Multi-linear regression analysis revealed that the local SST anomaly played largest role in modulating the SWCRE and COT anomalies among the cloud controlling factors (e.g., estimated inversion strength, air-temperature advection) accounting for more than 50% of the variation. This study provides an observational evidence of the active role of local SST anomalies in summertime associated with the western boundary currents to the oceanic low-level cloud.
Takahashi, Naoya; Richards, Kelvin J.; Schneider, Niklas; Annamalai, H.; Hsu, Wei-Ching; Nonaka, MasamiTakahashi, N., K. J. Richards, N. Schneider, H. Annamalai, W. Hsu, M. Nonaka, 2021: Formation Mechanism of Warm SST Anomalies in 2010s Around Hawaii. Journal of Geophysical Research: Oceans, 126(11), e2021JC017763. doi: 10.1029/2021JC017763. Warm sea surface temperature (SST) anomalies have been observed in the subtropical North Pacific around Hawaii in the recent decade, appearing from 2013. We examined the formation mechanisms of the warm SST anomalies in terms of relative contribution of atmospheric surface forcing and oceanic dynamics, using the latest reanalysis products from ECMWF (ERA5 for atmosphere and ORAS5 for ocean). Results of the mixed layer temperature budget diagnosis in the target area (10–20°N and 180°–160°W) indicates that contributions from anomalous latent heat fluxes to the subtropical SST anomalies are dominant. Oceanic advective contributions play a secondary role, dampen the SST anomalies, and are negatively correlated (r = −0.38) with the latent heat fluxes. For example, the +1.0 K SST increased from 2011 to 2015 results from +1.5 K contributions from sum of surface heat flux and −0.5 K from meridional oceanic advection. The anti-correlation between atmospheric forcing and oceanic meridional advection reflects co-variations of wind-driven latent heat flux and meridional Ekman advection due to the weakening of the zonal component of the surface winds.
Talib, Joshua; Taylor, Christopher M.; Duan, Anmin; Turner, Andrew G.Talib, J., C. M. Taylor, A. Duan, A. G. Turner, 2021: Intraseasonal soil moisture-atmosphere feedbacks on the Tibetan Plateau circulation. J. Climate, (In Press). doi: 10.1175/JCLI-D-20-0377.1.
Tang, Wenjun; Qin, Jun; Yang, Kun; Zhu, Fuxin; Zhou, XuTang, W., J. Qin, K. Yang, F. Zhu, X. Zhou, 2021: Does ERA5 outperform satellite products in estimating atmospheric downward longwave radiation at the surface?. Atmospheric Research, 252, 105453. doi: 10.1016/j.atmosres.2021.105453. Atmospheric downward longwave radiation (DLR) is a key component of the surface energy budget in the Earth system. Satellite retrievals and atmospheric reanalysis estimates are the two typical approaches to obtaining a spatio-temporally continuous DLR product. In this study, we evaluated the DLR product from the latest ERA5 atmospheric reanalysis and the well-known Clouds and Earth's Radiant Energy System (CERES) satellite retrievals, against high-quality observations collected at 46 Baseline Surface Radiation Network (BSRN) stations over land surfaces and at 9 Global Tropical Moored Buoy Array (GTMBA) buoy stations. The accuracy of the ERA5 DLR product over land was found to be higher on average than that of CERES at hourly to monthly time scales. Conversely, ERA5 performed slightly worse than CERES-SYN when estimating DLR over the ocean surface. This is the first time that atmospheric reanalysis has performed better than satellite retrievals in estimating DLR over the land surface, demonstrating the potentially extensive application prospects for ERA5 as well as setting new challenges for quantitative remote sensing research. CERES; ERA5; Accuracy; Evaluation; Longwave radiation
Tang, Wenjun; Yang, Kun; Qin, Jun; Li, Jun; Ye, JiangangTang, W., K. Yang, J. Qin, J. Li, J. Ye, 2021: How Accurate Are Satellite-Derived Surface Solar Radiation Products over Tropical Oceans?. J. Atmos. Oceanic Technol., 38(2), 283-291. doi: 10.1175/JTECH-D-20-0099.1. AbstractSurface solar radiation (SSR) over the ocean is essential for studies of ocean–atmosphere interactions and marine ecology, and satellite remote sensing is a major way to obtain the SSR over ocean. A new high-resolution (10 km; 3 h) SSR product has recently been developed, mainly based on the newly released cloud product of the International Satellite Cloud Climatology Project H series (ISCCP-HXG), and is available for the period from July 1983 to December 2018. In this study, we compared this SSR product with in situ observations from 70 buoy sites in the Global Tropical Moored Buoy Array (GTMBA) and also compared it with another well-known satellite-derived SSR product from the Clouds and the Earth’s Radiant Energy System (CERES; edition 4.1), which has a spatial resolution of approximately 100 km. The results show that the ISCCP-HXG SSR product is generally more accurate than the CERES SSR product for both ocean and land surfaces. We also found that the accuracy of both satellite-derived SSR products (ISCCP-HXG and CRERS) was higher over ocean than over land and that the accuracy of ISCCP-HXG SSR improves greatly when the spatial resolution of the product is coarsened to ≥ 30 km.
Tornow, F.; Domenech, C.; Cole, J. N. S.; Madenach, N.; Fischer, J.Tornow, F., C. Domenech, J. N. S. Cole, N. Madenach, J. Fischer, 2021: Changes in TOA SW Fluxes over Marine Clouds When Estimated via Semiphysical Angular Distribution Models. J. Atmos. Oceanic Technol., 38(3), 669-684. doi: 10.1175/JTECH-D-20-0107.1. AbstractTop-of-atmosphere (TOA) shortwave (SW) angular distribution models (ADMs) approximate—per angular direction of an imagined upward hemisphere—the intensity of sunlight scattered back from a specific Earth–atmosphere scene. ADMs are, thus, critical when converting satellite-borne broadband radiometry into estimated radiative fluxes. This paper applies a set of newly developed ADMs with a more refined scene definition and demonstrates tenable changes in estimated fluxes compared to currently operational ADMs. Newly developed ADMs use a semiphysical framework to consider cloud-top effective radius (R¯e) and above-cloud water vapor (ACWV), in addition to accounting for surface wind speed and clouds’ phase, fraction, and optical depth. In effect, instantaneous TOA SW fluxes for marine liquid-phase clouds had the largest flux differences (of up to 25 W m−2) for lower solar zenith angles and cloud optical depth greater than 10 due to extremes in R¯e or ACWV. In regions where clouds had persistently extreme levels of R¯e (here mostly for R¯e<7 μm and R¯e>15 μm) or ACWV, instantaneous fluxes estimated from Aqua, Terra, Meteosat-8, and Meteosat-9 satellites using the two ADMs differed systematically, resulting in significant deviations in daily mean fluxes (up to ±10 W m−2) and monthly mean fluxes (up to ±5 W m−2). Flux estimates using newly developed, semiphysical ADMs may contribute to a better understanding of solar fluxes over low-level clouds. It remains to be seen whether aerosol indirect effects are impacted by these updates.
Tselioudis, George; Rossow, William B.; Jakob, Christian; Remillard, Jasmine; Tropf, Derek; Zhang, YuanchongTselioudis, G., W. B. Rossow, C. Jakob, J. Remillard, D. Tropf, Y. Zhang, 2021: Evaluation of Clouds, Radiation, and Precipitation in CMIP6 Models Using Global Weather States Derived from ISCCP-H Cloud Property Data. J. Climate, 34(17), 7311-7324. doi: 10.1175/JCLI-D-21-0076.1. AbstractA clustering methodology is applied to cloud optical depth (τ)–cloud top pressure (TAU-PC) histograms from the new 1° resolution ISCCP-H dataset to derive an updated global weather state (WS) dataset. Then, TAU-PC histograms from current-climate CMIP6 model simulations are assigned to the ISCCP-H WSs along with their concurrent radiation and precipitation properties to evaluate model cloud, radiation, and precipitation properties in the context of the weather states. The new ISCCP-H analysis produces WSs that are very similar to those previously found in the lower-resolution ISCCP-D dataset. The main difference lies in the splitting of the ISCCP-D thin stratocumulus WS between the ISCCP-H shallow cumulus and stratocumulus WSs, which results in the reduction by one of the total WS number. The evaluation of the CMIP6 models against the ISCCP-H weather states shows that, in the ensemble mean, the models are producing an adequate representation of the frequency and geographical distribution of the WSs, with measurable improvements compared to the WSs derived for the CMIP5 ensemble. However, the frequency of shallow cumulus clouds continues to be underestimated, and, in some WSs the good agreement of the ensemble mean with observations comes from averaging models that significantly overpredict and underpredict the ISCCP-H WS frequency. In addition, significant biases exist in the internal cloud properties of the model WSs, such as the model underestimation of cloud fraction in middle-top clouds and secondarily in midlatitude storm and stratocumulus clouds, that result in an underestimation of cloud SW cooling in those regimes.
Tucker, Simon O.; Kendon, Elizabeth J.; Bellouin, Nicolas; Buonomo, Erasmo; Johnson, Ben; Murphy, James M.Tucker, S. O., E. J. Kendon, N. Bellouin, E. Buonomo, B. Johnson, J. M. Murphy, 2021: Evaluation of a new 12 km regional perturbed parameter ensemble over Europe. Climate Dynamics. doi: 10.1007/s00382-021-05941-3. We evaluate a 12-member perturbed parameter ensemble of regional climate simulations over Europe at 12 km resolution, carried out as part of the UK Climate Projections (UKCP) project. This ensemble is formed by varying uncertain parameters within the model physics, allowing uncertainty in future projections due to climate modelling uncertainty to be explored in a systematic way. We focus on present day performance both compared to observations, and consistency with the driving global ensemble. Daily and seasonal temperature and precipitation are evaluated as two variables commonly used in impacts assessments. For precipitation we find that downscaling, even whilst within the convection-parameterised regime, generally improves daily precipitation, but not everywhere. In summer, the underestimation of dry day frequency is worse in the regional ensemble than in the driving simulations. For temperature we find that the regional ensemble inherits a large wintertime cold bias from the global model, however downscaling reduces this bias. The largest bias reduction is in daily winter cold temperature extremes. In summer the regional ensemble is cooler and wetter than the driving global models, and we examine cloud and radiation diagnostics to understand the causes of the differences. We also use a low-resolution regional simulation to determine whether the differences are a consequence of resolution, or due to other configuration differences, with the predominant configuration difference being the treatment of aerosols. We find that use of the EasyAerosol scheme in the regional model, which aims to approximate the aerosol effects in the driving model, causes reduced temperatures by around 0.5 K over Eastern Europe in Summer, and warming of a similar magnitude over France and Germany in Winter, relative to the impact of interactive aerosol in the global runs. Precipitation is also increased in these regions. Overall, we find that the regional model is consistent with the global model, but with a typically better representation of daily extremes and consequently we have higher confidence in its projections of their future change.
Uribe, M. R.; Sierra, C. A.; Dukes, J. S.Uribe, M. R., C. A. Sierra, J. S. Dukes, 2021: Seasonality of Tropical Photosynthesis: A Pantropical Map of Correlations With Precipitation and Radiation and Comparison to Model Outputs. Journal of Geophysical Research: Biogeosciences, 126(11), e2020JG006123. doi: 10.1029/2020JG006123. Tropical ecosystems strongly influence Earth's climate and weather patterns. Most tropical ecosystems remain warm year-round; nonetheless, their plants undergo seasonal cycles of carbon and water exchange. Previous research has shown the importance of precipitation and radiation as drivers of the seasonality of photosynthetic activity in the tropics. Although data are scarce, field-based studies have found that seasonal cycles at a handful of tropical sites do not match those in the land surface model (LSM) simulations. A comprehensive understanding and model comparison of how seasonal variations in tropical photosynthetic activity relate to climate is lacking. Here, we identify the relationships of precipitation and radiation with satellite-based proxies for photosynthetic activity (e.g., GOME-2 SIF, MAIAC EVI) for the pantropical region. Three dominant and spatially distinct seasonal relationships emerge: photosynthetic activity that is positively correlated with both drivers (36% of tropical pixels), activity that increases following rain but decreases with radiation (28%), and activity that increases following bright seasons but decreases with rain (14%). We compare distributions of these observed relationships with those from LSMs. In general, compared to satellite-based proxies of photosynthetic activity, model simulations of gross primary productivity (GPP) overestimate the extent of positive correlations of photosynthetic activity with water and underestimate positive correlations with radiation. The largest discrepancies between simulations and observations are in the representation of regions where photosynthetic activity increases with radiation and decreases with rain. Our clear scheme for representing the relationship between climate and photosynthetic activity can be used to benchmark tropical seasonality of GPP in LSMs. climate; seasonality; models; photosynthetic activity; solar induced fluorescence; tropical ecosystems
Valdivieso, Maria; Peatman, Simon C.; Klingaman, Nicholas P.Valdivieso, M., S. C. Peatman, N. P. Klingaman, 2021: The influence of air-sea coupling on forecasts of the 2016 Indian summer monsoon and its intraseasonal variability. Quarterly Journal of the Royal Meteorological Society, (In Press). doi: 10.1002/qj.3914. Daily initialized coupled and uncoupled numerical weather prediction (NWP) forecasts from the global Met Office Unified Model (MetUM) are compared for the 2016 Indian summer monsoon. Three MetUM configurations are used: atmosphere-only (ATM), coupled to a mixed-layer ocean model (KPP), and coupled to a dynamical ocean model (NEMO). The analysis focuses on the impact of air-sea coupling, particularly in the Bay of Bengal (BoB), on NWP for monsoon rainfall. Seasonal-mean biases in all three configurations are highly consistent and driven by errors in atmospheric processes. Rainfall is initially overestimated over India, but underestimated over the BoB, the latter associated with too much shortwave radiation and too little cloud cover in MetUM. The excess shortwave radiation (>40 Wm -2 over the northwest BoB) is partially compensated by additional latent cooling, primarily due to overestimated surface wind speeds. In NEMO and KPP, coupling improves the timing of intraseasonal active and break phases over India, primarily the end of these phases, which are systematically too late in ATM. NEMO and KPP show a more realistic intraseasonal local phase relationship between sea surface temperature (SST) and rainfall throughout the BoB, but no configuration reproduces the observed significant lagged relationship between BoB SST and Indian rainfall. The lack of this relationship may be partly attributed to weak heat flux feedbacks to northern BoB SST, with the forecast shortwave feedback having systematically the wrong sign (positive) compared to satellite radiation, and thus contributing to SST warming at all lead times. Based on these MetUM forecasts, there is a limited impact of coupling on NWP for monsoon rainfall, both for the mean rainfall and intraseasonal variability. Further research to improve NWP for monsoon rainfall should focus on reducing MetUM atmospheric systematical biases. air–sea coupling; atmospheric convection; Bay of Bengal; Indian monsoon; intraseasonal variability; weather forecasting
Volodin, E.Volodin, E., 2021: The Mechanisms of Cloudiness Evolution Responsible for Equilibrium Climate Sensitivity in Climate Model INM-CM4-8. Geophysical Research Letters, 48(24), e2021GL096204. doi: 10.1029/2021GL096204. Current climate models demonstrate large discrepancy in equilibrium climate sensitivity (ECS). The effects of cloudiness parameterization changes on the ECS of the INM-CM4-8 climate model were investigated. This model shows the lowest ECS among CMIP6 models. Reasonable changes in the parameterization of the degree of cloudiness yielded ECS variability of 1.8–4.1 K in INM-CM4-8, which was more than half of the interval for the CMIP6 models. The three principal mechanisms responsible for the increased ECS were increased cloudiness dissipation in warmer climates due to the increased water vapor deficit in the non-cloud fraction of a cell, decreased cloudiness generation in the atmospheric boundary layer in warm climates, and the instantaneous cloud response to CO2 increases due to stratification changes. Climate sensitivity; parameterization; cloudiness; radiation forcing
Wan, Xiaozhong; Qin, Fang; Cui, Fang; Chen, Weidong; Ding, Huang; Li, ChaohuiWan, X., F. Qin, F. Cui, W. Chen, H. Ding, C. Li, 2021: Correlation between the distribution of solar energy resources and the cloud cover in Xinjiang. IOP Conference Series: Earth and Environmental Science, 675(1), 012060. doi: 10.1088/1755-1315/675/1/012060. In order to study the influence of cloud cover on solar energy resources, it provides scientific basis for the development and utilization of solar radiation resources. Based on the Cloud and the Earth’s Radiant Energy System (CERES) and European Centre for Medium-Range Weather Forecasts (ECWMF) data from 2014-2018, the correlation between the temporal and spatial distribution of solar energy resources and the cloud cover in Xinjiang was studied and analyzed. The results show that solar energy resources have generally shown an upward trend in the past five years, with an average annual radiation of 7206.5 MJ/m2 and very stable. The overall distribution of solar radiation is mainly dominated by latitude, decreasing from south to north, and the change is relatively uniform. The maximum value of annual total radiation in the southern area of Xinjiang is about 9000 MJ/m2, which is 1.5 times of that in the northern area. The maximum daily total radiation is 28.88 MJ/m2 in July, which is 3.3 times of that in December. The total radiation in summer can reach up to 2200 MJ/m2, which is 2.2 times of that in winter. Summer radiation is high but fluctuating, and winter radiation is small but relatively stable. The autumn is the period with the least amount of total cloud during the year, the cloud cover in the northern area is about 40%, and the winter in the northern area is the highest along the foothills of the Tianshan Mountain, up to 70%. The fitting effect of radiation attenuation and cloud cover in the northern area is higher than that in the southern area, and the maximum correlation coefficient is 0.98 in summer and the minimum is 0.571 in winter. The fitting effect of radiation attenuation and cloud cover in the northern area is higher than that in the southern area, and the maximum correlation coefficient is 0.98 in summer and the minimum is 0.571 in winter. The solar radiation is mainly affected by clouds in summer, while in winter, there are other factors such as aerosols.
Wang, Gaofeng; Wang, Tianxing; Xue, HuazhuWang, G., T. Wang, H. Xue, 2021: Validation and comparison of surface shortwave and longwave radiation products over the three poles. International Journal of Applied Earth Observation and Geoinformation, 104, 102538. doi: 10.1016/j.jag.2021.102538. Global warming has currently become a great concern to the international community, among which the three poles (the Arctic, Antarctic, and Qinghai-Tibet Plateau) are the most serious. In this paper, in order to improve the understanding of the matter and energy cycle in the three poles and even the world, eleven shortwave products, (namely, CERES-SYN, ERA5, MERRA-2, NCEP-CFSR, JRA-55, GLDAS, BESS_Rad, MCD18A1, ISCCP-HXG-SSR, GLASS and APP-x), and seven longwave products, (CERES-SYN, ERA5, MERRA-2, NCEP-CFSR, JRA-55, GLDAS, and APP-x) are evaluated and inter-compared in terms of accuracy. During the assessment, the ground measurements collected from four independent ground observation networks (BSRN, CEOP, TPDC, and NMC) are used as reference, and the being compared products are aggregated to the same spatial and temporal scales to make them comparable. To better examine their performance, the eleven radiation products are comprehensively compared in multiple spatial (original scale and 1°×1°) and temporal scales (1-hourly, 3-hourly, daily, and monthly means, and instantaneous). The results show that in the three poles, CERES-SYN and ERA5 show overall better accuracy, at daily, 1°×1° resolutions. The (r)bias and (r)RMSE are less than (3%)5 W/m2 and (23%)40 W/m2 for SWDR, and less than (3%)7 W/m2 and (15%)25 W/m2 for LWDR, respectively, over the polar regions (the Arctic and Antarctic), which are generally better than that of the Qinghai-Tibet Plateau for most products. The remote sensing products and reanalysis products have their own advantages and disadvantages at different regions. In addition, with the spatio-temporal resolution decreasing, the accuracy of radiation products will gradually increase, except for the products of MCD18A1, ISCCP-HXG-SSR, NCEP-CFSR and GLDAS. Shortwave radiation; Arctic; GLASS; ERA5; Longwave radiation; Antarctic; CERES-SYN; MCD18A1; Qinghai-Tibet Plateau; Three poles
Wang, Haibo; Zhang, Hua; Xie, Bing; Jing, Xianwen; He, Jingyi; Liu, YiWang, H., H. Zhang, B. Xie, X. Jing, J. He, Y. Liu, 2021: Evaluating the Impacts of Cloud Microphysical and Overlap Parameters on Simulated Clouds in Global Climate Models. Advances in Atmospheric Sciences. doi: 10.1007/s00376-021-0369-7. The improvement of the accuracy of simulated cloud-related variables, such as the cloud fraction, in global climate models (GCMs) is still a challenging problem in climate modeling. In this study, the influence of cloud microphysics schemes (one-moment versus two-moment schemes) and cloud overlap methods (observation-based versus a fixed vertical decorrelation length) on the simulated cloud fraction was assessed in the BCC_AGCM2.0_CUACE/Aero. Compared with the fixed decorrelation length method, the observation-based approach produced a significantly improved cloud fraction both globally and for four representative regions. The utilization of a two-moment cloud microphysics scheme, on the other hand, notably improved the simulated cloud fraction compared with the one-moment scheme; specifically, the relative bias in the global mean total cloud fraction decreased by 42.9%–84.8%. Furthermore, the total cloud fraction bias decreased by 6.6% in the boreal winter (DJF) and 1.64% in the boreal summer (JJA). Cloud radiative forcing globally and in the four regions improved by 0.3%–1.2% and 0.2%–2.0%, respectively. Thus, our results showed that the interaction between clouds and climate through microphysical and radiation processes is a key contributor to simulation uncertainty.
Wang, Jingyu; Fan, Jiwen; Feng, Zhe; Zhang, Kai; Roesler, Erika; Hillman, Benjamin; Shpund, Jacob; Lin, Wuyin; Xie, ShaochengWang, J., J. Fan, Z. Feng, K. Zhang, E. Roesler, B. Hillman, J. Shpund, W. Lin, S. Xie, 2021: Impact of a New Cloud Microphysics Parameterization on the Simulations of Mesoscale Convective Systems in E3SM. Journal of Advances in Modeling Earth Systems, 13(11), e2021MS002628. doi: 10.1029/2021MS002628. Mesoscale convective systems (MCSs) are one of the most climatically significant forms of convection because of their large role in water and energy cycles. The mesoscale features associated with MCS are difficult to represent in climate models because the relevant dynamics and physics are absent or poorly represented with coarse model resolution (∼100 km). Using a regionally refined model (RRM) with 0.25° grid spacing embedded in the Energy Exascale Earth System Model (E3SM), we explore the impact of cloud microphysics parameterizations on the simulation of precipitation, particularly MCS precipitation over the contiguous United States. The Predicted Particle Properties (P3) cloud microphysics scheme has been modified and implemented into E3SM to overcome the limitations of the default Morrison and Gettelman (MG2) scheme in which rimed precipitating ice particles (graupel/hail) are absent and frozen particles are artificially partitioned into cloud ice and snow. We show that P3 improves the simulation of precipitation statistics including frequency distribution compared with MG2 with a limited effect on the diurnal cycle. P3 predicts higher hourly rain rates, resulting in 20% more MCSs and a higher total MCS precipitation (4.4%) compared to MG2, agreeing better with observations. The improvements with P3 mainly result from improved representations of ice microphysics, which not only produces higher rain rates through melting but also leads to a stronger large-scale ascending motion by releasing more latent heating. This study suggests that improving microphysics parameterization is important for simulating MCS precipitation as future climate model resolutions continue to increase. microphysics parameterization; energy exascale Earth system model; MCS tracking; mesoscale convective system; predicted particle properties; regionally refined model
Wang, Kai; Zhang, Yang; Yahya, KhairunnisaWang, K., Y. Zhang, K. Yahya, 2021: Decadal application of WRF/Chem over the continental U.S.: Simulation design, sensitivity simulations, and climatological model evaluation. Atmospheric Environment, 118331. doi: 10.1016/j.atmosenv.2021.118331. The WRF/Chem v3.7 is applied to 2001-2010 over the continental U.S. using the National Emission Inventory (NEI). This study will provide the baseline simulation for a future work to investigate the impacts of both climate and emission changes on the future regional air quality and human health. This paper focuses on the current year simulation design, comprehensive model evaluation, and sensitivity simulations that demonstrate the impacts of different reinitialization setup, cloud physical schemes, and emission inventories on the model predictions. Nine one-month sensitivity simulations by using different reinitialization setup and cloud microphysics and cumulus parameterizations are first conducted to provide the optimal model configurations. The model performance in predicting the regional meteorology and air quality on a decadal scale is further evaluated against available surface, satellite, and reanalysis data. The decadal WRF/Chem simulation by using NEI emissions (referred to as simulation NEI) performs well for major meteorological variables such as T2, RH2, WS10, and precipitation and shows good performance for major radiation variables such as SWDOWN, OLR, and SWCF. Large model biases still exist for cloud variables due to limitations of cloud dynamics/thermodynamics treatments and uncertainties associated with satellite retrievals. The simulation NEI also predicts O3 and PM2.5 well in terms of spatiotemporal distribution. Compared to a previous study using the Representative Concentration Pathway (RCP8.5) emissions, the simulation NEI performs better for most of variables, especially for precipitation and cloud radiative forcing due to better representation of cloud processes and also for O3 and PM2.5 in terms of spatiotemporal variations due to more accurate emission inventory. The evaluation results in this work are within the range or better than other previous studies using the WRF/Chem model and lay the foundation for more realistic projection of future climate and air quality in the future work. WRF/Chem; Climatological evaluation; Continental U.S.; Decadal simulation; NEI; RCP
Wang, Mingcheng; Fu, QiangWang, M., Q. Fu, 2021: Stratosphere-Troposphere Exchange of Air Masses and Ozone Concentrations Based on Reanalyses and Observations. Journal of Geophysical Research: Atmospheres, 126(18), e2021JD035159. doi: 10.1029/2021JD035159. This study estimates the stratosphere–troposphere exchange (STE) of air masses and ozone concentrations averaged over 2007 to 2010 using the Modern Era Retrospective-Analyses for Research and Applications 2 (MERRA2) and ERA5 reanalyses, and observations. The latter includes Microwave Limb Sounder (MLS) for ozone, MLS and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) for temperatures, and A-Train measurements for diabatic heating. The extratropical downward ozone fluxes are 538 Tg year−1 from the ERA5 reanalysis, 543 Tg year−1 from the MERRA2 reanalysis, and 528–539 Tg year−1 from the observations, consistent with previous studies. Previous studies, however, did not consider tropical upward ozone flux. Here we show that the tropical upward ozone flux is 183–193 Tg year−1, which compensates about 35% of the extratropical downward ozone fluxes and should not be neglected. After considering the tropical upward ozone flux, the global ozone STE is 346 Tg year−1 from the ERA5 reanalysis, 360 Tg year−1 from the MERRA2 reanalysis, and 336–346 Tg year−1 from the observations. Those estimates (347 ± 12 Tg year−1) can be used as the contribution of ozone STE to the tropospheric ozone budget. We also investigate cloud radiative effects on the STE of air mass and ozone. At 380 K, cloud radiative effects enhance downward fluxes in the extratropics from both reanalyses and observation, but reduce and enhance upward fluxes in the tropics from reanalyses and observation, respectively. The discrepancy in the tropics is related to the tropical tropopause layer thin cirrus that is missing in the reanalyses. We find that cloud radiative effects enhance the global ozone STE by about 21%–29%. CloudSat; CALIPSO; MERRA2; cloud radiative effects; MLS; ERA5; ozone; stratosphere-troposphere exchange
Wang, Qiuyan; Zhang, Hua; Yang, Su; Chen, Qi; Zhou, Xixun; Shi, Guangyu; Cheng, Yueming; Wild, MartinWang, Q., H. Zhang, S. Yang, Q. Chen, X. Zhou, G. Shi, Y. Cheng, M. Wild, 2021: Potential Driving Factors on Surface Solar Radiation Trends over China in Recent Years. Remote Sensing, 13(4), 704. doi: 10.3390/rs13040704. The annual mean surface solar radiation (SSR) trends under all-sky, clear-sky, all-sky-no-aerosol, and clear-sky-no-aerosol conditions as well as their possible causes are analyzed during 2005–2018 across China based on different satellite-retrieved datasets to determine the major drivers of the trends. The results confirm clouds and aerosols as the major contributors to such all-sky SSR trends over China but play differing roles over sub-regions. Aerosol variations during this period result in a widespread brightening, while cloud effects show opposite trends from south to north. Moreover, aerosols contribute more to the increasing all-sky SSR trends over northern China, while clouds dominate the SSR decline over southern China. A radiative transfer model is used to explore the relative contributions of cloud cover from different cloud types to the all-types-of-cloud-cover-induced (ACC-induced) SSR trends during this period in four typical sub-regions over China. The simulations point out that the decreases in low-cloud-cover (LCC) over the North China Plain are the largest positive contributor of all cloud types to the marked annual and seasonal ACC-induced SSR increases, and the positive contributions from both high-cloud-cover (HCC) and LCC declines in summer and winter greatly contribute to the ACC-induced SSR increases over East China. The contributions from medium-low-cloud-cover (mid-LCC) and LCC variations dominate the ACC-caused SSR trends over southwestern and South China all year round, except for the larger HCC contribution in summer. radiative transfer model; cloud and aerosols; different types of cloud cover; relative contributions; SSR trends under different conditions
Wang, Tao; Wu, Dong L.; Gong, Jie; Wang, ChenxiWang, T., D. L. Wu, J. Gong, C. Wang, 2021: Long-Term Observations of Upper-Tropospheric Cloud Ice From the MLS. Journal of Geophysical Research: Atmospheres, 126(9), e2020JD034058. doi: 10.1029/2020JD034058. Upper tropospheric cloud ice varies across different timescales and plays an important role in regulating Earth's climate, but knowledge of the abundances and the variability of cloud ice has been limited for decades. The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) provides an unprecedented record of cloud ice measurements since its launch in April 2006. However, CALIPSO has left the A-Train in September 2018 and entered the C-Train orbit which follows a slightly different ground track with a different local crossing time. This orbit change challenges the continuation of a long-term record of cloud ice since ice is subject to stronger diurnal cycle. Fortunately, the Aura Microwave Limb Sounder (MLS), still as a member of the A-Train, has a consistent local crossing time and has measured high quality radiance since launch in 2004, and will probably continue beyond 2024. We present the use of MLS 640-GHz cloud-induced radiance (Tcir) to build a robust upper tropospheric partial ice water path (pIWP) product due to its high dynamical range to different sizes of ice particles. The MLS rebuilt pIWP, which extends nearly two decades, captures the spatial and temporal variabilities of upper tropospheric cloud ice that CALIOP is capable of measuring. This provides valuable alternative for studying the upper tropospheric cloud ice and possibly provides a more consistent input to climate studies. cloud; ice water path; ice water content; caliop; enso; mls
Wang, Tianyuan; Zhou, Lihang; Tan, Changyi; Divakarla, Murty; Pryor, Ken; Warner, Juying; Wei, Zigang; Goldberg, Mitch; Nalli, Nicholas R.Wang, T., L. Zhou, C. Tan, M. Divakarla, K. Pryor, J. Warner, Z. Wei, M. Goldberg, N. R. Nalli, 2021: Validation of Near-Real-Time NOAA-20 CrIS Outgoing Longwave Radiation with Multi-Satellite Datasets on Broad Timescales. Remote Sensing, 13(19), 3912. doi: 10.3390/rs13193912. The Outgoing Longwave Radiation (OLR) package was first developed as a stand-alone application, and then integrated into the National Oceanic and Atmospheric Administration (NOAA) Unique Combined Atmospheric Processing System (NUCAPS) hyperspectral sounding retrieval system. An objective of this package is to provide near-real-time OLR products derived from the Cross Track Infrared Sounder (CrIS) onboard the Joint Polar Satellite System (JPSS) satellites. It was initially developed and validated with CrIS onboard the Suomi National Polar-orbiting Partnership (SNPP) satellite, and has been expanded to JPSS-1 (renamed NOAA-20 after launch) datasets that are currently available to the public. In this paper, we provide the results of detailed validation tests with NOAA-20 CrIS for large and wide representative conditions at a global scale. In our validation tests, the observations from Clouds and Earth’s Radiant Energy System (CERES) on Aqua were treated as the absolute reference or “truth”, and those from SNPP CrIS OLR were used as the transfer standard. The tests were performed on a 1°×1° global spatial grid over daily, monthly, and yearly timescales. We find that the CrIS OLR products from NOAA-20 agree exceptionally well with those from Aqua CERES and SNPP CrIS OLR products in all conditions: the daily bias is within ±0.6 Wm−2, and the standard deviation (STD) ranges from 4.88 to 9.1 Wm−2. The bias and the STD of OLR monthly mean are better, within 0.3 and 2.0 Wm−2, respectively. These findings demonstrate the consistency between NOAA-20 and SNPP CrIS OLR up to annual scales, and the robustness of NUCAPS CrIS OLR products. radiation budget; validation; outgoing longwave radiation; OLR; NOAA-20; CrIS; NUCAPS
Wang, Tongxin; Zhang, Hongyan; Zhao, Jianjun; Guo, Xiaoyi; Xiong, Tao; Wu, RihanWang, T., H. Zhang, J. Zhao, X. Guo, T. Xiong, R. Wu, 2021: Shifting Contribution of Climatic Constraints on Evapotranspiration in the Boreal Forest. Earth's Future, 9(8), e2021EF002104. doi: 10.1029/2021EF002104. The global evapotranspiration (ET) shows an increasing trend with global warming in recent decades, while ET variation in different regions is still uncertain. Boreal forest ecosystem, as one of the most sensitive regions to climate change, are still poorly understood due to the sparse observation and the changing of ET in the boreal forest has been covered up for lower values compared to lower-latitude regions. Based on the PT-JPL model, we estimated the ET in the boreal forest during 1982–2015. The annual ET showed an increasing trend (0.5073 mm year−1). Seventy percentage of the boreal forest area is increasing which mainly occurred in Central Canada, Alaska, Central Siberia and Northern Europe, while 24% is decreasing, which occurred in the southern Siberia, Northern Mongolia and Northern Canada. The quantification of basic climatic factors shows that atmospheric demand is the main factor with an increasing trend which is accordance with the (a) increasing temperature; (b) annual precipitation is increasing providing increasing water supply for boreal forest. Factorial experiments were also conducted and showed that the climatic constraints that contribute mainly to ET have gradually shifted from net radiation to moisture restriction in the boreal forest. The moisture control tendency indicated that ET in the boreal forest was gradually controlled by humidity rather than energy, suggesting a limited water supply and an intensifying water cycle in the boreal forest. climate change; PT-JPL model; evapotranspiration; boreal forest
Wang, Wei; Chakraborty, T. C.; Xiao, Wei; Lee, XuhuiWang, W., T. C. Chakraborty, W. Xiao, X. Lee, 2021: Ocean surface energy balance allows a constraint on the sensitivity of precipitation to global warming. Nature Communications, 12(1), 2115. doi: 10.1038/s41467-021-22406-7. Climate models generally predict higher precipitation in a future warmer climate. Whether the precipitation intensification occurred in response to historical warming continues to be a subject of debate. Here, using observations of the ocean surface energy balance as a hydrological constraint, we find that historical warming intensified precipitation at a rate of 0.68 ± 0.51% K−1, which is slightly higher than the multi-model mean calculation for the historical climate (0.38 ± 1.18% K−1). The reduction in ocean surface albedo associated with melting of sea ice is a positive contributor to the precipitation temperature sensitivity. On the other hand, the observed increase in ocean heat storage weakens the historical precipitation. In this surface energy balance framework, the incident shortwave radiation at the ocean surface and the ocean heat storage exert a dominant control on the precipitation temperature sensitivity, explaining 91% of the inter-model spread and the spread across climate scenarios in the Intergovernmental Panel on Climate Change Fifth Assessment Report.
Wang, Xuejia; Chen, Deliang; Pang, Guojin; Anwar, Samy A.; Ou, Tinghai; Yang, MeixueWang, X., D. Chen, G. Pang, S. A. Anwar, T. Ou, M. Yang, 2021: Effects of cumulus parameterization and land-surface hydrology schemes on Tibetan Plateau climate simulation during the wet season: insights from the RegCM4 model. Climate Dynamics. doi: 10.1007/s00382-021-05781-1. Dynamical downscaling generally performs poorly on the Tibetan Plateau (TP), due to the region’s complex topography and several aspects of model physics, especially convection and land surface processes. This study investigated the effects of the cumulus parameterization scheme (CPS) and land-surface hydrology scheme (LSHS) on TP climate simulation during the wet season using the RegCM4 regional climate model. To address these issues and seek an optimal simulation, we conducted four experiments at a 20 km resolution using various combinations of two CPSs (Grell and MIT-Emanuel), two LSHSs (the default TOPMODEL [TOP], and Variable Infiltration Capacity [VIC]). The simulations in terms of 2-m air temperature, precipitation (including large-scale precipitation [LSP] and convective precipitation [CP]), surface energy-water balance, as well as atmospheric moisture flux transport and vertical motion were compared with surface and satellite-based observations as well as the ERA5 reanalysis dataset for the period 2006–2016. The results revealed that the model using the Grell and TOP schemes better reproduced air temperature but with a warm bias, part of which could be significantly decreased by the MIT scheme. All schemes simulated a reasonable spatial distribution of precipitation, with the best performance in the experiment using the MIT and VIC schemes. Excessive precipitation was produced by the Grell scheme, mainly due to overestimated LSP, while the MIT scheme largely reduced the overestimation, and the simulated contribution of CP to total precipitation was in close agreement with the ERA5 data. The RegCM4 model satisfactorily captured diurnal cycles of precipitation amount and frequency, although there remained some differences in phase and magnitude, which were mainly caused by the CPSs. Relative to the Grell scheme, the MIT scheme yielded a weaker surface heating by reducing net radiation fluxes and the Bowen ratio. Consequently, anomalous moisture flux transport was substantially reduced over the southeastern TP, leading to a decrease in precipitation. The VIC scheme could also help decrease the wet bias by reducing surface heating. Further analysis indicated that the high CP in the MIT simulations could be attributed to destabilization in the low and mid-troposphere, while the VIC scheme tended to inhibit shallow convection, thereby decreasing CP. This study’s results also suggest that CPS interacts with LSHS to affect the simulated climate over the TP.
Wang, Yi-Chi; Hsu, Huang-Hsiung; Chen, Chao-An; Tseng, Wan-Ling; Hsu, Pei-Chun; Lin, Cheng-Wei; Chen, Yu-Luen; Jiang, Li-Chiang; Lee, Yu-Chi; Liang, Hsin-Chien; Chang, Wen-Ming; Lee, Wei-Liang; Shiu, Chein-JungWang, Y., H. Hsu, C. Chen, W. Tseng, P. Hsu, C. Lin, Y. Chen, L. Jiang, Y. Lee, H. Liang, W. Chang, W. Lee, C. Shiu, 2021: Performance of the Taiwan Earth System Model in Simulating Climate Variability Compared With Observations and CMIP6 Model Simulations. Journal of Advances in Modeling Earth Systems, 13(7), e2020MS002353. doi: 10.1029/2020MS002353. This study evaluates the performance of the Taiwan Earth System Model version 1 (TaiESM1) in simulating the observed climate variability in the historical simulation of the Coupled Model Intercomparison Phase 6 (CMIP6). TaiESM1 is developed on the basis of the Community Earth System Model version 1.2.2, with the inclusion of several new physical schemes and improvements in the atmosphere model. The new additions include an improved triggering function in the cumulus convection scheme, a revised distribution-based formula in the cloud fraction scheme, a new aerosol scheme, and a unique scheme for three-dimensional surface absorption of shortwave radiation that accounts for the influence of complex terrains. In contrast to the majority of model evaluation processes, which focus mainly on the climatological mean, this evaluation focuses on climate variability parameters, including the diurnal rainfall cycle, precipitation extremes, synoptic eddy activity, intraseasonal fluctuation, monsoon evolution, and interannual and multidecadal atmospheric and oceanic teleconnection patterns. A series of intercomparisons between the simulations of TaiESM1 and CMIP6 models and observations indicate that TaiESM1, a participating model in CMIP6, can realistically simulate the observed climate variability at various time scales and are among the leading CMIP6 models in terms of many key climate features. model evaluation; CMIP6; climate variability; TaiESM
Wang, Yipu; Li, Rui; Hu, Jiheng; Wang, Xuewen; Kabeja, Crispin; Min, Qilong; Wang, YuWang, Y., R. Li, J. Hu, X. Wang, C. Kabeja, Q. Min, Y. Wang, 2021: Evaluations of MODIS and microwave based satellite evapotranspiration products under varied cloud conditions over East Asia forests. Remote Sensing of Environment, 264, 112606. doi: 10.1016/j.rse.2021.112606. Satellite remote sensing is an important tool to retrieve terrestrial evapotranspiration (ET). Widely-used MOD16 ET product (MOD-ET) is a representative of Penman-Monteith method coupled with MODerate Resolution Imaging Spectroradiometer (MODIS) optic observations. Although MOD-ET has been extensively evaluated over the world, its accuracy under various cloud conditions remains unevaluated. Combining MODIS-observed cloud cover (Frc) and in-situ measurements at sixteen forests sites in East Asia, we evaluated 8-day MOD-ET and its primary MODIS inputs (i.e. LAI, FPAR and albedo) from clear to cloudy sky. A new satellite microwave ET method based on microwave Emissivity Difference Vegetation Index (EDVI-ET) was also compared with MOD-ET. Results showed that the accuracy of MOD-ET was highly variable under the changing Frc over the forests. The largest bias (>30%) in MOD-ET was found under Frc 30%) deteriorated the bias in MOD-ET (20%–30%). In contrast, EDVI-ET performed stably with lower bias (0.81) under other sky conditions. Further investigation found that MOD-ET over four tropical coastal forests contributed most to the bias, especially under least cloudy sky. A case study at a tropical forest showed that MODIS LAI/FPAR and surface albedo products were overestimated, which could directly cause the overestimation of canopy-scale conductance and the underestimation of net solar radiation in MOD-ET method, respectively. Analysis showed that the bias in MOD-ET was significantly related to the bias in MODIS LAI under various Frc, but it was weakly related to that in MODIS albedo, suggesting that LAI-based conductance might dominate the overestimation of MOD-ET. During a consecutive cloud cover period when fewer reliable MODIS pixels are available, slight increase of clouds partly reduced MODIS-observed signals of LAI/FPAR and increased those of albedo over the tropical forest, resulting in the lower bias in MOD-ET. More clouds reduced surface MODIS albedo and might increase the uncertainty in all-sky shortwave radiation from reanalysis data, which deteriorated MOD-ET accuracy under overcast sky. Our study highlighted the importance of cloud impacts on the satellite ET estimation. Emissivity difference vegetation index (EDVI); Cloudy effects; Evapotranspiration (ET); Forest; MODIS ET
Wang, Yonglin; Zhou, Lei; Zhuang, Jie; Sun, Leigang; Chi, YonggangWang, Y., L. Zhou, J. Zhuang, L. Sun, Y. Chi, 2021: The spatial heterogeneity of the relationship between gross primary production and sun-induced chlorophyll fluorescence regulated by climate conditions during 2007–2018. Global Ecology and Conservation, 29, e01721. doi: 10.1016/j.gecco.2021.e01721. The strong relationship between gross primary productivity (GPP) and sun-induced chlorophyll fluorescence (SIF) provided a novel perspective to estimate the terrestrial GPP based on satellite SIF. However, the influence of environmental conditions on the relationship between GPP and SIF is still unclear. In this study, we synthesized GOME-2 SIF and FLUXCOM GPP coupled with climate data to explore the spatial pattern of the GPP-SIF relationship and its sensitivity to climate conditions at global scale during 2007–2018. The slope (GPP/SIF) of the intercept-free linear regression, which contained information about the allocation of light energy for fluorescence and photosynthesis, was used to represent the GPP-SIF relationship. Our study found that the slope and R2 of the GPP-SIF relationship were spatially heterogeneous, with high slope mainly distributed in the tropical regions and boreal regions and the high R2 mainly concentrated in temperate ecosystems of the Northern Hemisphere. In climate regimes, we found that the GPP-SIF relationship was jointly constrained by environmental variables and the slope had a significant decreasing trend in climate regions from high mean annual temperature (MAT) and low mean annual photosynthetically active radiation (MAR) to low MAT and high MAR. Furthermore, the slope and mean annual precipitation (MAP) have a positive correlation, which indicated the GPP-SIF relationship was climate-dependent. Environmental stress may destroy the relationship between fluorescence and photosynthesis by increasing non-photochemical quenching (NPQ). Our research showed that environmental conditions regulated the light energy distribution for fluorescence and photosynthesis, so accurate estimation of terrestrial ecosystem productivity based on SIF should consider the constraints of climate variables. Climate-dependent; GPP/SIF; Seasonality; Spatial pattern; The GPP-SIF relationship
Wang, Yu; Zhao, Xueshang; Mamtimin, Ali; Sayit, Hajigul; Abulizi, Simayi; Maturdi, Amina; Yang, Fan; Huo, Wen; Zhou, Chenglong; Yang, Xinghua; Liu, XinchunWang, Y., X. Zhao, A. Mamtimin, H. Sayit, S. Abulizi, A. Maturdi, F. Yang, W. Huo, C. Zhou, X. Yang, X. Liu, 2021: Evaluation of Reanalysis Datasets for Solar Radiation with In Situ Observations at a Location over the Gobi Region of Xinjiang, China. Remote Sensing, 13(21), 4191. doi: 10.3390/rs13214191. Solar radiation is the most important source of energy on the Earth. The Gobi area in the eastern Xinjiang region, due to its geographic location and climate characteristics, has abundant solar energy resources. In order to provide detailed scientific data supporting solar energy development in this area, we used ground-based data to evaluate the applicability of the five reanalysis data sources: the Clouds and the Earth’s Radiant Energy System (CERES), the European Center for Medium-Range Weather Forecasts Reanalysis version 5 (ERA5), the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA2), and the Japanese 55-year Reanalysis (JRA-55). Our results indicated that the CERES data show underestimated short-wave radiation and overestimated long-wave radiation. The correlation coefficients (r) between the ERA5 dataset and the net long-wave and short-wave radiation in observation were 0.92 and 0.91, respectively, and the r between the MERRA2 dataset and the net long-wave and short-wave radiation in observation were both 0.88. The JRA-55 dataset overestimated the long-wave radiation flux and underestimated the short-wave radiation flux. The clearness index (kt) of all datasets was poor during autumn and winter, the ERA5 estimates were cloudy when the actual condition was sunny, while the JRA-55 estimates were sunny when the actual condition was cloudy. Overall, the radiation flux in the ERA5 dataset had the highest applicability in the Gobi region. CERES; solar radiation; Gobi region; reanalysis datasets
Wei, Jian; Ren, Tong; Yang, Ping; DiMarco, Steven F.; Mlawer, EliWei, J., T. Ren, P. Yang, S. F. DiMarco, E. Mlawer, 2021: An Improved Ocean Surface Albedo Computational Scheme: Structure and Performance. Journal of Geophysical Research: Oceans, 126(8), e2020JC016958. doi: 10.1029/2020JC016958. Ocean surface albedo (OSA) is an important factor for the transfer of radiation in the coupled atmosphere-ocean system. By resolving the spectral variations of the reflective properties for incident direct and diffuse solar radiation, we develop an OSA computational scheme to study the impact of ocean biogeochemistry on the air-sea boundary condition of solar radiative transfer in the atmosphere. The new scheme is implemented for the General Circulation Model applications of the shortwave rapid radiative transfer model RRTMG_SW, a radiative transfer model used extensively in regional and global models. We show that a number of OSA schemes lead to underestimated results in comparison with in-situ measurements obtained at a site 25 km east of Virginia Beach. The scheme developed in this study considers multiple influential factors and is robust in terms of the mean absolute percentage error (MAPE) and the root mean square error in comparison with in-situ measurements. Furthermore, the new simulations are highly consistent with the Clouds and the Earth's Radiant Energy System (CERES) OSA distribution on a global scale. However, the theoretical results show slight differences compared with the CERES OSA under all sky conditions and overestimate the OSA in the subpolar Southern Ocean under clear sky conditions. The assumption of a uniform phase function, which neglects the spatial variability of the optical properties of oceanic particles, is largely responsible for the primary source of uncertainties in an OSA scheme. climate model; ocean surface albedo; shortwave radiative transfer
Wei, Jianfen; Wang, Zhaomin; Gu, Mingyi; Luo, Jing-Jia; Wang, YunheWei, J., Z. Wang, M. Gu, J. Luo, Y. Wang, 2021: An evaluation of the Arctic clouds and surface radiative fluxes in CMIP6 models. Acta Oceanologica Sinica, 40(1), 85-102. doi: 10.1007/s13131-021-1705-6. To assess the performances of state-of-the-art global climate models on simulating the Arctic clouds and surface radiation balance, the 2001–2014 Arctic Basin surface radiation budget, clouds, and the cloud radiative effects (CREs) in 22 coupled model intercomparison project 6 (CMIP6) models are evaluated against satellite observations. For the results from CMIP6 multi-model mean, cloud fraction (CF) peaks in autumn and is lowest in winter and spring, consistent with that from three satellite observation products (CloudSat-CALIPSO, CERES-MODIS, and APP-x). Simulated CF also shows consistent spatial patterns with those in observations. However, almost all models overestimate the CF amount throughout the year when compared to CERES-MODIS and APP-x. On average, clouds warm the surface of the Arctic Basin mainly via the longwave (LW) radiation cloud warming effect in winter. Simulated surface energy loss of LW is less than that in CERES-EBAF observation, while the net surface shortwave (SW) flux is underestimated. The biases may result from the stronger cloud LW warming effect and SW cooling effect from the overestimated CF by the models. These two biases compensate each other, yielding similar net surface radiation flux between model output (3.0 W/m2) and CERES-EBAF observation (6.1 W/m2). During 2001–2014, significant increasing trend of spring CF is found in the multi-model mean, consistent with previous studies based on surface and satellite observations. Although most of the 22 CMIP6 models show common seasonal cycles of CF and liquid water path/ice water path (LWP/IWP), large inter-model spreads exist in the amounts of CF and LWP/IWP throughout the year, indicating the influences of different cloud parameterization schemes used in different models. Cloud Feedback Model Intercomparison Project (CFMIP) observation simulator package (COSP) is a great tool to accurately assess the performance of climate models on simulating clouds. More intuitive and credible evaluation results can be obtained based on the COSP model output. In the future, with the release of more COSP output of CMIP6 models, it is expected that those inter-model spreads and the model-observation biases can be substantially reduced. Longer term active satellite observations are also necessary to evaluate models’ cloud simulations and to further explore the role of clouds in the rapid Arctic climate changes.
Wei, Yu; Zhang, Xiaotong; Li, Wenhong; Hou, Ning; Zhang, Weiyu; Xu, Jiawen; Feng, Chunjie; Jia, Kun; Yao, Yunjun; Cheng, Jie; Jiang, Bo; Wang, Kaicun; Liang, ShunlinWei, Y., X. Zhang, W. Li, N. Hou, W. Zhang, J. Xu, C. Feng, K. Jia, Y. Yao, J. Cheng, B. Jiang, K. Wang, S. Liang, 2021: Trends and Variability of Atmospheric Downward Longwave Radiation Over China From 1958 to 2015. Earth and Space Science, 8(2), e2020EA001370. doi: https://doi.org/10.1029/2020EA001370. Surface downward longwave radiation (SDLR) is a major component of the energy budget. Although studies have reported the spatiotemporal variations of SDLR in China, the spatiotemporal coverage of the situ measurements used is always limited. In this study, the gradient boosting regression tree (GBRT) was developed to reconstruct SDLR based on air temperature (Ta), relative humidity (RH), and downward shortwave radiation (DSR). Ground measurements collected at the Baseline Surface Radiation Network (BSRN) and the Arid and Semi-arid Region Collaborative Observation Project (ASRCOP) were used to build and evaluate the GBRT model. The evaluation results showed that the daily SDLR estimates are correlated well with the SDLR in situ, with an overall root mean square errors (RMSE) of 16.5 Wm−2 and a correlation coefficient (R) value of 0.91 for the validation data set. Comparison with existing SDLR products showed that accuracy and trends of the SDLR estimates based on the GBRT method are reasonable. To obtain long-term SDLR data for spatiotemporal analysis over China, densely distributed reconstructed DSR and ground measured Ta and RH collected at 756 Chinese Meteorological Administration (CMA) stations were used as input to estimate the SDLR based on the GBRT method over China during 1958–2015. The long-term estimated SDLRs at the selected 563 stations showed that SDLR increased at an average rate of 1.3 Wm−2 per decade over China from 1958 to 2015. The trend of SDLR is positively correlated with the trend in Ta and water vapor pressure, whereas negatively correlated with the trend in DSR. downward longwave radiation; GBRT; CMA; MK trend test
Wu, S.-N.; Soden, B. J.; Nolan, D. S.Wu, S., B. J. Soden, D. S. Nolan, 2021: Examining the Role of Cloud Radiative Interactions in Tropical Cyclone Development Using Satellite Measurements and WRF Simulations. Geophysical Research Letters, 48(15), e2021GL093259. doi: 10.1029/2021GL093259. This study examines the role of cloud-radiative interactions in the development of tropical cyclones using satellite measurements and model simulations. Previous modeling studies have found that the enhanced cloud radiative heating from longwave radiation in the convective region plays a key role in promoting the development of tropical convective systems. Here, we use satellite measurements and Weather Research and Forecasting Model (WRF) simulations to further investigate how critical cloud radiative interactions are to the development of tropical cyclones (TCs). Clouds and the Earth's Radiant Energy System measurements show that intensifying TCs have greater radiative heating from clouds within the TC area than weakening ones. Based on this result, idealized WRF simulations are performed to examine the importance of the enhanced radiative heating to TC intensification. Sensitivity experiments demonstrate that removing cloud-radiative interactions often inhibits tropical cyclogenesis, suggesting that cloud-radiative interactions play a critical role. cloud; radiation; hurricane; cloud-radiative heating; tropical cyclone
Wu, Yuxuan; Xi, Yi; Feng, Maoyuan; Peng, ShushiWu, Y., Y. Xi, M. Feng, S. Peng, 2021: Wetlands Cool Land Surface Temperature in Tropical Regions but Warm in Boreal Regions. Remote Sensing, 13(8), 1439. doi: 10.3390/rs13081439. Wetlands play a critical role in global hydrological and biogeochemical cycles. Regulating the regional climate is one of the most important ecosystem services of natural wetlands. However, the impact of wetlands on local temperature on the global scale and the attribution is still unclear. This study utilizes the satellite-based products (land surface temperature (LST), albedo, and evapotranspiration (ET)) to evaluate the difference in LST between wetlands and their adjacent landcover types and the possible drivers. Here we show that on average for the whole year, wetlands have a cooling effect in tropical regions, but have a warming effect in boreal regions. The impacts of wetlands on LST show great seasonality in the boreal regions; i.e., the wetlands have a warming effect in winter but a cooling effect in summer. The difference in albedo and ET between wetlands and the other landcover types only interprets 30% of temporal variation of the difference in LST. Due to the large water storage in wetlands, the ground heat flux (G) may interpret the rest of the impact, absorbing energy in summer and releasing energy in winter in wetlands, which has often been neglected in previous studies. Our results indicate that it is critical to comprehensively consider the effects of wetland restoration in different regions to realize potential climatic benefits in the future. albedo; remote sensing; land surface temperature; evapotranspiration; surface energy balance; wetlands
Xia, Yan; Hu, Yongyun; Huang, Yi; Zhao, Chuanfeng; Xie, Fei; Yang, YikunXia, Y., Y. Hu, Y. Huang, C. Zhao, F. Xie, Y. Yang, 2021: Significant Contribution of Severe Ozone Loss to the Siberian-Arctic Surface Warming in Spring 2020. Geophysical Research Letters, 48(8), e2021GL092509. doi: https://doi.org/10.1029/2021GL092509. Severe ozone loss and significant surface warming anomalies in the Siberian Arctic were observed in spring 2020. Here, we show that the anomalous surface warming was likely related to the ozone loss. The dramatic Arctic ozone loss in March was shifted to Siberia in April and May, which largely cools the lower stratosphere and leads to an increase of high clouds by modifying the static stability in the upper troposphere. This further results in an increase of longwave radiation at surface which likely contributes to surface warming. Multiple linear regression demonstrates that ozone loss contributes most of the surface warming in April, while the Arctic Oscillation and ice-albedo feedback play a minor role. In May, both ozone loss and ice-albedo feedback contribute to the surface warming. These results support that surface warming in the Siberian Arctic could occur in April and May when severe ozone loss occurs in March. cloud radiative effect; ice-albedo feedback; stratospheric ozone; Arctic warming; the Siberian Arctic
Xu, Hui; Guo, Jianping; Li, Jian; Liu, Lin; Chen, Tianmeng; Guo, Xiaoran; Lyu, Yanmin; Wang, Ding; Han, Yi; Chen, Qi; Zhang, YongXu, H., J. Guo, J. Li, L. Liu, T. Chen, X. Guo, Y. Lyu, D. Wang, Y. Han, Q. Chen, Y. Zhang, 2021: The Significant Role of Radiosonde-measured Cloud-base Height in the Estimation of Cloud Radiative Forcing. Advances in Atmospheric Sciences. doi: 10.1007/s00376-021-0431-5. The satellite-based quantification of cloud radiative forcing remains poorly understood, due largely to the limitation or uncertainties in characterizing cloud-base height (CBH). Here, we use the CBH data from radiosonde measurements over China in combination with the collocated cloud-top height (CTH) and cloud properties from MODIS/Aqua to quantify the impact of CBH on shortwave cloud radiative forcing (SWCRF). The climatological mean SWCRF at the surface (SWCRFSUR), at the top of the atmosphere (SWCRFTOA), and in the atmosphere (SWCRFATM) are estimated to be −97.14, −84.35, and 12.79 W m−2, respectively for the summers spanning 2010 to 2018 over China. To illustrate the role of the cloud base, we assume four scenarios according to vertical profile patterns of cloud optical depth (COD). Using the CTH and cloud properties from MODIS alone results in large uncertainties for the estimation of SWCRFATM, compared with those under scenarios that consider the CBH. Furthermore, the biases of the CERES estimation of SWCRFATM tend to increase in the presence of thick clouds with low CBH. Additionally, the discrepancy of SWCRFATM relative to that calculated without consideration of CBH varies according to the vertical profile of COD. When a uniform COD vertical profile is assumed, the largest SWCRF discrepancies occur during the early morning or late afternoon. By comparison, the two-point COD vertical distribution assumption has the largest uncertainties occurring at noon when the solar irradiation peaks. These findings justify the urgent need to consider the cloud vertical structures when calculating the SWCRF which is otherwise neglected.
Xu, Jianglei; Jiang, Bo; Liang, Shunlin; Li, Xiuxia; Wang, Yezhe; Peng, Jianghai; Chen, Hongkai; Liang, Hui; Li, ShaopengXu, J., B. Jiang, S. Liang, X. Li, Y. Wang, J. Peng, H. Chen, H. Liang, S. Li, 2021: Generating a High-Resolution Time-Series Ocean Surface Net Radiation Product by Downscaling J-OFURO3. IEEE Transactions on Geoscience and Remote Sensing, (In Press). doi: 10.1109/TGRS.2020.3021585. The ocean surface net radiation (Rn) characterizing ocean surface radiation budget is a key variable in ocean climate modeling and analysis. In this study, a downscaling scheme was developed to generate a high-resolution (0.05°) time-series (2002-2013) daily ocean surface Rn from the third-generation Japanese Ocean Flux Data Sets with Use of Remote-Sensing Observations (J-OFURO3) at 0.25° based on the Advanced Very-High-Resolution Radiometer (AVHRR) top-of-atmosphere (TOA) observations (AVH021C) and other ancillary information (Clearness Index and cloud mask). This downscaling scheme includes the statistical downscaling models and the residual correction post-processing. A series of angle-dependent downscaling statistical models were established between the daily ocean surface Rn in J-OFURO3 and the AVHRR TOA data, and then, the residual correction was conducted to the model estimates Rn_AVHRR_est to obtain the final downscaled data set Rn_AVHRR. Validation against the measurements from 57 moored buoy sites in six ocean observing networks shows the high accuracy of the downscaled estimates Rn_AVHRR_est with a R² of 0.88, RMSE of 23.44 W·m⁻², and bias of -0.14 W·m⁻² under all-sky condition. The results of the spatio-temporal analysis in Rn_AVHRR and intercomparison with Cloud and the Earth's Radiant Energy System (CERES) and the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim) products also indicated that the superior of the Rn_AVHRR with more detailed information especially in the hot spot regions, such as central tropical Pacific (warming pool), Atlantic and Equatorial Eastern Indian Ocean (EIO). Land surface; Remote sensing; Meteorology; Sea surface; net radiation; Advanced Very-High-Resolution Radiometer (AVHRR); downscaling; ocean surface; Ocean temperature; remote sensing.; Spatial resolution
Xu, Jianglei; Liang, Shunlin; Jiang, BoXu, J., S. Liang, B. Jiang, 2021: A global long term (1981–2019) daily land surface radiation budget product from AVHRR satellite data using a residual convolutional neural network. Earth System Science Data Discussions, 1-36. doi: 10.5194/essd-2021-250. Abstract. The surface radiation budget, also known as all-wave net radiation (Rn), is a key parameter for various land surface processes including hydrological, ecological, agricultural, and biogeochemical processes. Satellite data can be effectively used to estimate Rn, but existing satellite products have coarse spatial resolutions and limited temporal coverage. In this study, a point-surface matching estimation (PSME) method is proposed to estimate surface Rn using a residual convolutional neural network (RCNN) integrating spatially adjacent information to improve the accuracy of retrievals. A global high-resolution (0.05°) long-term (1981–2019) Rn product was subsequently generated from Advanced Very High-Resolution Radiometer (AVHRR) data. Specifically, the RCNN was employed to establish a nonlinear relationship between globally distributed ground measurements from 537 sites and AVHRR top of atmosphere (TOA) observations. Extended triplet collocation (ETC) technology was applied to address the spatial scale mismatch issue resulting from the low spatial support of ground measurements within the AVHRR footprint by selecting reliable sites for model training. The overall independent validation results show that the generated AVHRR Rn product is highly accurate, with R2, root-mean-square error (RMSE), and bias of 0.84, 26.66 Wm−2 (31.66 %), and 1.59 Wm−2 (1.89 %), respectively. Inter-comparisons with three other Rn products, i.e., the 5 km Global Land Surface Satellite (GLASS), the 1° Clouds and the Earth's Radiant Energy System (CERES), and the 0.5° × 0.625° Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA2), illustrate that our AVHRR Rn retrievals have the best accuracy under all of the considered surface and atmospheric conditions, especially thick cloud or hazy conditions. The spatiotemporal analyses of these four Rn datasets indicate that the AVHRR Rn product reasonably replicates the spatial pattern and temporal evolution trends of Rn observations. This dataset is freely available at https://doi.org/10.5281/zenodo.5509854 for 1981–2019 (Xu et al., 2021).
Xu, Jiawen; Zhang, Xiaotong; Feng, Chunjie; Yang, Shuyue; Guan, Shikang; Jia, Kun; Yao, Yunjun; Xie, Xianhong; Jiang, Bo; Cheng, Jie; Zhao, XiangXu, J., X. Zhang, C. Feng, S. Yang, S. Guan, K. Jia, Y. Yao, X. Xie, B. Jiang, J. Cheng, X. Zhao, 2021: Evaluation of Surface Upward Longwave Radiation in the CMIP6 Models with Ground and Satellite Observations. Remote Sensing, 13(21), 4464. doi: 10.3390/rs13214464. Surface upward longwave radiation (SULR) is an indicator of thermal conditions over the Earth’s surface. In this study, we validated the simulated SULR from 51 Coupled Model Intercomparison Project (CMIP6) general circulation models (GCMs) through a comparison with ground measurements and satellite-retrieved SULR from the Clouds and the Earth’s Radiant Energy System, Energy Balanced and Filled (CERES EBAF). Moreover, we improved the SULR estimations by a fusion of multiple CMIP6 GCMs using multimodel ensemble (MME) methods. Large variations were found in the monthly mean SULR among the 51 CMIP6 GCMs; the bias and root mean squared error (RMSE) of the individual CMIP6 GCMs at 133 sites ranged from −3 to 24 W m−2 and 22 to 38 W m−2, respectively, which were higher than those found between the CERES EBAF and GCMs. The CMIP6 GCMs did not improve the overestimation of SULR compared to the CMIP5 GCMs. The Bayesian model averaging (BMA) method showed better performance in simulating SULR than the individual GCMs and simple model averaging (SMA) method, with a bias of 0 W m−2 and an RMSE of 19.29 W m−2 for the 133 sites. In terms of the global annual mean SULR, our best estimation for the CMIP6 GCMs using the BMA method was 392 W m−2 during 2000–2014. We found that the SULR varied between 386 and 393 W m−2 from 1850 to 2014, exhibiting an increasing tendency of 0.2 W m−2 per decade (p < 0.05). CMIP5; GCMs; CMIP6; Bayesian model averaging; multimodel ensemble; surface upward longwave radiation (SULR)
Xu, Lingxuan; Sun, Shanlei; Chen, Haishan; Chai, Rongfan; Wang, Jiazhi; Zhou, Yang; Ma, Qianrong; Chotamonsak, Chakrit; Wangpakapattanawong, PrasitXu, L., S. Sun, H. Chen, R. Chai, J. Wang, Y. Zhou, Q. Ma, C. Chotamonsak, P. Wangpakapattanawong, 2021: Changes in the reference evapotranspiration and contributions of climate factors over the Indo–China Peninsula during 1961–2017. International Journal of Climatology, 41(15), 6511-6529. doi: 10.1002/joc.7209. Given the key roles of the Indo–China Peninsula (ICP) in weather and climate systems, hydrometeorology, and ecology, the annual and monthly changes in the Food and Agriculture Organization-56 Penman–Monteith reference evapotranspiration (ET0), which was calculated based on the Climatic Research Unit datasets, were investigated in ICP during 1961–2017. The annual ICP ET0 significantly (p < .05) increased, with different increasing tendencies in most months. In particular, larger and more significant (p < .05) ET0 values were found during October–December. The annual and monthly ET0 changes showed evident spatial differences, characterized by increases in more than 50% of the ICP area except for decreases in around 70% of that area during March–May. A sensitivity experiment-based separation method was utilized to evaluate the contribution of each influential factor, and the corresponding determinants were identified by comparing the contributions. Results showed that the annual ICP ET0 increase was attributed to the increased vapour pressure deficit (Vpd). However, the annual determinants varied spatially, with net solar radiation (Rn) in the southern region of ICP, wind speed (Wnd) in the northeast, and Vpd in the remaining regions. The monthly ICP determinant was Wnd in January, March–May and December, and Vpd for the remaining months. Despite different spatial patterns of monthly dominants, Vpd and Wnd were the determinants with the most extensive distributions over ICP (>75% of ICP in total). The results of this study can significantly fulfil the research gap regarding the ICP ET0 changes and the underlying mechanisms. Meanwhile, this study provides fundamental and necessary information for protecting biodiversity and understanding hydrometeorological extreme events, thus promoting specific measures to sustain the ICP development. reference evapotranspiration; Indo–China Peninsula; quantitative analysis; separation method; trends
Yamazaki, Kuniko; Sexton, David M. H.; Rostron, John W.; McSweeney, Carol F.; Murphy, James M.; Harris, Glen R.Yamazaki, K., D. M. H. Sexton, J. W. Rostron, C. F. McSweeney, J. M. Murphy, G. R. Harris, 2021: A perturbed parameter ensemble of HadGEM3-GC3.05 coupled model projections: part 2: global performance and future changes. Climate Dynamics, 56(11), 3437-3471. doi: 10.1007/s00382-020-05608-5. This paper provides a quantitative assessment of large-scale features in a perturbed parameter ensemble (PPE) of Met Office Unified Model HadGEM-GC3.05 in coupled global historical and future simulations. The main motivation for the simulations is to provide a major component of the UK Climate Projections 2018 (UKCP18), but they will also be used to make worldwide projections and inform future model development. Initially, a 25-member PPE, with 25 different parameter combinations, was simulated. Five members were subsequently dropped because either their simulated climate was unrealistically cool by 1970 or they suffered from numerical instabilities. The remaining 20 members were evaluated after completing the historical phase (1900–2005) against 13 separately selected Climate Model Intercomparison Project Phase 5 (CMIP5) models, and five more members were dropped. The final product is a combined projection system of 15 PPE members and 13 CMIP5 models, which has a number of benefits. In particular, the range of outcomes available from the combined set of 28 is often larger than from either of the two constituent ensembles, thus providing users with a more complete picture of plausible impacts. Here we mainly describe the evaluation process of the 20 PPE members. We evaluate biases in a number of important properties of the global coupled system, including assessment of climatological averages, coupled modes of internal variability and historical and future changes. The parameter combinations yielded plausible yet diverse atmosphere and ocean model behaviours. The range of global temperature changes is narrow, largely driven by use of different CO2 pathways. The range of global warming is seemingly not linked to range of feedbacks estimated from atmosphere-only runs, though we caution that the range of the latter is narrow relative to CMIP5, and therefore this result is not unexpected. This is the second of two papers describing the generation of the PPE for UKCP18 projections. Part 1 (Sexton et al. 2021) describes the selection of 25 parameter combinations of 47 atmosphere and land surface parameters, using a set of cheap atmosphere-only runs at a coarser resolution from nearly 3000 samples of parameter space.
Yang, Feng; Cheng, Jie; Zeng, QiYang, F., J. Cheng, Q. Zeng, 2021: Validation of a Cloud-Base Temperature-Based Single-Layer Cloud Model for Estimating Surface Longwave Downward Radiation. IEEE Geoscience and Remote Sensing Letters, 1-5. doi: 10.1109/LGRS.2021.3083502. As one of the four components of surface radiation balance, surface longwave downward radiation (SLDR) greatly affects the accurate characterization of hydrological, ecological, and biochemical processes. Since cloud-base temperature (CBT)-based single-layer cloud models (SLCMs) have advantages in both their strong physical mechanisms and abilities to produce high spatial resolution SLDR products, this study validated a CBT-based SLCM developed at the global scale using in situ observations collected by the baseline surface radiation network (BSRN) in conjunction with Aqua and Terra Moderate Resolution Imaging Spectroradiometer (MODIS) cloud products and Modern-Era Retrospective Analysis For Research And Applications, Version 2 (MERRA-2) reanalysis data. Overall, the CBT-based SLCM achieved a relatively high SLDR estimation accuracy for the Terra and Aqua satellites, with biases better than -1.2 W/m² and root-mean-squared error (RMSE) values better than 29.9 W/m². However, its random RMSE was slightly worse than those of two Clouds and the Earth's Radiant Energy System (CERES) Single Scanner Footprint (SSF) SLDR products due to the larger spatial variability that exists at the Earth's surface when it is quantified at a high spatial resolution (1 km). Additionally, the CBT-based SLCM outperformed two existing cloud-top temperature (CTT)-based SLCMs. In the future, we will continue to improve the performance of the CBT-based SLCM and will update the Global LAnd Surface Satellite (GLASS) SLDR product under cloudy sky conditions. Land surface; Satellites; Spatial resolution; Land surface temperature; remote sensing; Clouds; Cloud computing; validation.; Cloud-base temperature (CBT); single-layer cloud model (SLCM); surface longwave downward radiation (SLDR); Temperature distribution
Yarahmadi, Mehran; Mahan, J. Robert; Kowsary, FarshadYarahmadi, M., J. R. Mahan, F. Kowsary, 2021: A New Approach to Inverse Boundary Design in Radiation Heat Transfer. Advances in Heat Transfer and Thermal Engineering, 377-383. doi: 10.1007/978-981-33-4765-6_65. Inverse boundary design problems in surface-to-surface radiation heat transfer occur when both the temperature and net heat flux are prescribed on some of the surfaces while neither is known on the remaining surfaces. The problem is to find the unknown surface temperatures required to produce the prescribed temperatures and net heat fluxes. This chapter presents a novel approach in which a transcendental function of position—in this case a Fourier cosine series—is used to represent the spatial distribution of the unknown fourth power of surface temperature. The problem then becomes one of the findings the Fourier coefficients and fundamental angular frequency that minimize the difference between the prescribed and calculated surface temperature distributions. The approach is shown to produce more accurate results than the classical optimization approach in a fraction of the execution time for the example of an industrial processing oven.
Ye, Shuchao; Feng, Huihui; Zou, Bin; Ding, Ying; Zhu, Sijia; Li, Feng; Dong, GuotaoYe, S., H. Feng, B. Zou, Y. Ding, S. Zhu, F. Li, G. Dong, 2021: Satellite-Based Estimation of the Influence of Land Use and Cover Change on the Surface Shortwave Radiation Budget in a Humid Basin. Remote Sensing, 13(8), 1447. doi: 10.3390/rs13081447. The surface shortwave radiation budget (Rsn) is one of the main drivers of Earth’s ecosystems and varies with atmospheric and surface conditions. Land use and cover change (LUCC) alters radiation through biogeophysical effects. However, due to the complex interactions between atmospheric and surface factors, it is very challenging to quantify the sole impacts of LUCC. Based on satellite data from the Global Land Surface Satellite (GLASS) Product and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments, this study introduces an observation-based approach for detecting LUCC influences on the Rsn by examining a humid basin over the Dongting Lake Basin, China from 2001 to 2015. Our results showed that the Rsn of the study area presented a decreasing trend due to the combined effects of LUCC and climate change. Generally, LUCC contributed −0.45 W/m2 to Rsn at the basin scale, which accounted for 2.53% of the total Rsn change. Furthermore, the LUCC contributions reached −0.69 W/m2, 0.21 W/m2, and −0.41 W/m2 in regions with land transitions of forest→grass, grass→forest, and grass→farmland, which accounted for 5.38%, −4.68%, and 2.40% of the total Rsn change, respectively. Physically, LUCC affected surface radiation by altering the surface properties. Specifically, LUCC induced albedo changes of +0.0039 at the basin scale and +0.0061, −0.0020, and +0.0036 in regions with land transitions of forest→grass, grass→forest, and grass→farmland, respectively. Our findings revealed the impact and process of LUCC on the surface radiation budget, which could support the understanding of the physical mechanisms of LUCC’s impact on ecosystems. albedo; satellite; Dongting Lake Basin; land-use and cover change; surface shortwave radiation budget
You, Cheng; Tjernström, Michael; Devasthale, AbhayYou, C., M. Tjernström, A. Devasthale, 2021: Eulerian and Lagrangian views of warm and moist air intrusions into summer Arctic. Atmospheric Research, 256, 105586. doi: 10.1016/j.atmosres.2021.105586. In this study, warm and moist air intrusions (WaMAI) over the sea sectors of Kara, Laptev, East Siberian and Beaufort from 1979 to 2018 are identified in ERA5 reanalysis and their air-mass transformation is analysed using interpolation in ERA5 and satellite products along trajectories. The analysis shows that WaMAIs, driven by blocking high-pressure systems over the respective ocean sectors, induce surface warming (11–18 W m−2) and sea ice melt from positive anomalies of net longwave radiation (5–8 W m−2) and turbulent flux (8–13 W m−2) to the surface, although the anomaly of net shortwave radiation (−9 ~ +1 W m−2) is negative. From a Lagrangian perspective, the surface energy-budget anomaly decreases linearly, while total column cloud liquid water (TCLW) increases linearly with the downstream distance from the sea-ice edge. However, the cloud radiative effects of both longwave and shortwave radiation reach an equilibrium as TCLW increases in a much lower rate beyond 7 degrees north of the sea ice edge. The boundary-layer energy-budget pattern can be categorized into two classes: radiation-dominated and turbulence-dominated, comprised of 26% and 62% WaMAIs respectively. Statistically, turbulence-dominated cases occur with 3 times stronger large-scale subsidence, and also feature a larger anomaly in net shortwave radiation. In radiation-dominated WaMAIs, stratocumulus develops more strongly and hence exerts larger longwave and shortwave forcing to the surface. In both categories, a well-mixed boundary layer deepens by 500 m along the trajectories, from the continuous turbulent mixing. Arctic climate; Boundary-layer; Trajectories; Warm and moist air intrusion
Zeitler, Lea; Corbin, Armin; Vielberg, Kristin; Rudenko, Sergei; Löcher, Anno; Bloßfeld, Mathis; Schmidt, Michael; Kusche, JürgenZeitler, L., A. Corbin, K. Vielberg, S. Rudenko, A. Löcher, M. Bloßfeld, M. Schmidt, J. Kusche, 2021: Scale Factors of the Thermospheric Density: A Comparison of Satellite Laser Ranging and Accelerometer Solutions. Journal of Geophysical Research: Space Physics, 126(12), e2021JA029708. doi: 10.1029/2021JA029708. A major problem in the precise orbit determination (POD) of satellites at altitudes below 1,000 km is the modeling of the aerodynamic drag which mainly depends on the thermospheric density and causes the largest non-gravitational acceleration. Typically, empirical thermosphere models are used to calculate density values at satellite positions but current thermosphere models cannot provide the required accuracy. Thus, unaccounted variations in the thermospheric density may lead to significantly incorrect satellite positions. For the first time, we bring together thermospheric density corrections for the NRLMSISE-00 model in terms of scale factors with a temporal resolution of 12 hr derived from satellite laser ranging (SLR) and accelerometer measurements. Whereas, the latter are in situ information given along the satellite orbit, SLR results have to be interpreted as mean values along the orbit within the underlying time interval. From their comparison, we notice a rather similar behavior with correlations of up to 80% and more depending on altitude. During high solar activity, scale factors vary around 30% at low solar activity and up to 70% at high solar activity from the value one. In addition, we found the scaled thermospheric density decreasing stronger as the modeled density of NRLMSISE-00. To check the reliability of the SLR-derived scale factors, we compare the POD result of two different software packages, namely DOGS-OC from DGFI-TUM and GROOPS from IGG Bonn. Furthermore, a validation of our estimated scale factors with respect to an external data set proofs the high quality of the obtained results.
Zhang, Caijin; Long, Di; Zhang, Yucui; Anderson, Martha C.; Kustas, William P.; Yang, YangZhang, C., D. Long, Y. Zhang, M. C. Anderson, W. P. Kustas, Y. Yang, 2021: A decadal (2008–2017) daily evapotranspiration data set of 1 km spatial resolution and spatial completeness across the North China Plain using TSEB and data fusion. Remote Sensing of Environment, 262, 112519. doi: 10.1016/j.rse.2021.112519. Daily continuous evapotranspiration (ET) estimates of 1 km spatial resolution can benefit agricultural water resources management at regional scales. Thermal infrared remote sensing-derived land surface temperature (LST) is a critical variable for ET estimation using energy balance-based models. However, missing LST information under cloudy conditions remains a long-standing barrier for spatiotemporally continuous monitoring of daily ET at regional scales. In this study, LST data of 1 km spatial resolution at 11:00 local solar time under all-weather conditions across the North China Plain (NCP) were first generated using a data fusion approach developed previously. Second, combined with the generated LST data, MODIS products, and meteorological forcing from the China Land Data Assimilation System, the Two-Source Energy Balance model (TSEB) and a temporal upscaling method were jointly used to estimate daily ET at 1 km spatial resolution across the NCP for a decade from 2008 to 2017. In particular, to better incorporate the impact of crop phenology on ET and improve the ET estimation, the fraction of greenness in TSEB was determined in terms of a leaf area index threshold during the crop growth period. Compared with observed instantaneous latent heat flux (LE) corrected for energy balance closure, the estimated LE reasonably captures inter- and intra-annual variations in LE measured at the Huailai, Daxing, Weishan, and Guantao flux towers, with R2 of 0.63–0.79. Estimated daily ET against in situ ET measurements with energy balance closure at the Huailai, Daxing, and Guantao sites showed good performance in terms of R2 greater than 0.70 and RMSE below 0.91 mm/d. These accuracies are comparable with published results, with our ET data set validated by many more observations than previous studies and featuring spatiotemporal continuity and high spatial resolution across the entire NCP for a decade. Furthermore, seasonal ET variations reflected by our product outperform two widely used global products in capturing water consumption characteristics in the winter wheat-summer maize rotation system. In terms of temporal trends, annual ET estimates across the NCP show a decreasing and then increasing trend over the past decade, which is attributed to the increased cropping intensity over the recent years reflected by an increase in leaf area index. Evapotranspiration; Land surface temperature; Data fusion; Two-source energy balance
Zhang, Chunyan; Wang, Donghai; Pang, Zihao; Zhang, Yu; Jiang, Xiaoling; Zeng, Zhilin; Wu, ZhenzhenZhang, C., D. Wang, Z. Pang, Y. Zhang, X. Jiang, Z. Zeng, Z. Wu, 2021: Large-scale dynamic, heat and moisture structures of monsoon-influenced precipitation in the East Asian monsoon rainy area. Quarterly Journal of the Royal Meteorological Society, 147(735), 1007-1030. doi: https://doi.org/10.1002/qj.3956. This study investigated large-scale dynamic structures along with heat and moisture budgets associated with monsoon-influenced precipitation over a typical rainy domain in the East Asian monsoon region. Large-scale dynamically and thermodynamically consistent forcing data based on multiple measurements were produced by a one-dimensional constrained variational analysis method. Using the forcing data, distinct characteristics of large-scale states were documented for cases of notable pre-monsoon rainfall before the South China Sea monsoon onset (SCSMO), extreme rainfall during SCSMO, and persistent strong rainfall after SCSMO. The pre-monsoon period mainly resulted from weak and discrete cloud regimes. The extreme-rain period was associated with a severe deep convective system moving from the west, and the persistent-rain period was related to moderate convective cells separated from the strong convective system over the northern South China Sea. Large-scale features including vertical velocity, wind convergence, and diabatic heating and drying were the strongest (weakest) during the extreme-rain (pre-monsoon) period. For the pre-monsoon and persistent-rain periods, the period-averaged profiles of vertical velocity and diabatic heating and drying showed a one-peak structure. However, during the extreme-rain period, a leap-forward mutation was seen in the vertical structure and magnitude of these large-scale states. The multiple peaks shown in the vertical profiles of vertical velocity and diabatic heating during the extreme-rain period may indicate various convective cloud systems co-existed. The diabatic heating profiles of extreme rainfall indicated that the first rainfall peak was related to the successive occurrence of stratiform anvils and convective clouds, while the second rainfall peak, which was most intense, was associated with shallow convective clouds, severe deep convective clouds, and detraining stratiform anvils. constrained variational analysis; heating profile; large-scale structures; monsoon-influenced precipitation; upward motion
Zhang, Jishi; Lin, Yanluan; Ma, ZhanhongZhang, J., Y. Lin, Z. Ma, 2021: Footprint of Tropical Cyclone Cold Wakes on Top-of-Atmosphere Radiation. Geophysical Research Letters, 48(19), e2021GL094705. doi: 10.1029/2021GL094705. A recent study noted reduced rainfall and cloud fraction over cold wakes induced by tropical cyclones, but a quantification of top-of-atmosphere (TOA) radiation change due to these cold wakes has not been attempted. Based on global TOA radiative flux observations, we show that TOA shortwave and longwave radiations increase by 0.76 W m−2 (0.2%) and 0.74 W m−2 (0.3%) over the cold wake area relative to local climatology, respectively. Due to the cancelation between the shortwave and longwave components, daily average TOA net radiation is only marginally modulated by cold wakes, but stands out in the day and night time average. In addition, the seasonal basin-wide regulation of TOA net radiation by cold wakes can be up to 1.0 W m−2, locally comparable to the magnitude of radiative forcing due to man-made aerosols. The regional impact of cold wakes on TOA radiations is therefore highly relevant and potentially important. diurnal cycle; tropical cyclone; cold wake; radiative budget
Zhang, Rudong; Wang, Hailong; Fu, Qiang; Rasch, Philip J.; Wu, Mingxuan; Maslowski, WieslawZhang, R., H. Wang, Q. Fu, P. J. Rasch, M. Wu, W. Maslowski, 2021: Understanding the Cold Season Arctic Surface Warming Trend in Recent Decades. Geophysical Research Letters, 48(19), e2021GL094878. doi: 10.1029/2021GL094878. Whether sea-ice loss or lapse-rate feedback dominates the Arctic amplification (AA) remains an open question. Analysis of data sets based upon observations reveals a 1.11 K per decade surface warming trend in the Arctic (70°–90°N) during 1979–2020 cold season (October–February) that is five times higher than the corresponding global mean. Based on surface energy budget analysis, we show that the largest contribution (∼82%) to this cold season warming trend is attributed to changes in clear-sky downward longwave radiation. In contrast to that in Arctic summer and over tropics, a reduction in lower-tropospheric inversions plays a unique role in explaining the reduction of the downward longwave radiation associated with atmospheric nonuniform temperature and corresponding moisture changes. Our analyses also suggest that Arctic lower-tropospheric stability should be considered in conjunction with sea-ice decline during the preceding warm season to explain AA. reanalysis; energy budget; Arctic amplification; radiative feedback; Arctic inversion; sea ice loss
Zhang, Taiping; Stackhouse, Paul W.; Cox, Stephen J.; Mikovitz, J. Colleen; Long, Charles N.Zhang, T., P. W. Stackhouse, S. J. Cox, J. C. Mikovitz, C. N. Long, 2021: Addendum to figs. 10 and 11 in “Clear-sky shortwave downward flux at the earth's surface: Ground-based data vs. satellite-based data” [J. Quant. Spec. and Rad. Tran. 224 (2019) 247-260]. Journal of Quantitative Spectroscopy and Radiative Transfer, 261, 107487. doi: 10.1016/j.jqsrt.2020.107487. While the CERES input aerosol optical depth and precipitable water data are continuously available, the same parameters derived from BSRN site measurements are available only intermittently. Cloudiness disrupts the aerosol optical depth (AOD) retrieval and precipitable water (w) observation sampling. Irregularly sampled records, such as these, can cause systematic biases if the averages of the continuous data are not sampled at the same times as the observed data, as shown by high biases in Fig. 10 in our original paper. This, however, does not suggest that the CERES input aerosol optical depth and precipitable water are systematically significantly higher than ground-based observations. In this addendum, we show that when the monthly means are computed from only those CERES hourly means that have a BSRN match, then the resulting monthly means differ from BSRN-derived parameters to a much lesser extent. To be precise, the biases in the original Fig. 10 decrease 82%, 69% and 52%, respectively; the magnitudes of slopes in the original Fig. 11 decrease by 69% and 65%, respectively. Imposing a cloud fraction less than or equal to 5% further reduces AOD and w mean values but not biases. Nevertheless, the flux bias reduces from -16.9 W m−2 to -4.2 W m−2 after imposing the cloud fraction restraint relative to the RADFlux clear-sky fluxes which appear to represent the driest and clearest conditions. CERES; Solar radiation; Satellite; GEWEX SRB; RadFlux
Zhang, Yuanchong; Jin, Zhonghai; Sikand, MonikaZhang, Y., Z. Jin, M. Sikand, 2021: The Top-of-Atmosphere, Surface and Atmospheric Cloud Radiative Kernels Based on ISCCP-H Datasets: Method and Evaluation. Journal of Geophysical Research: Atmospheres, 126(24), e2021JD035053. doi: 10.1029/2021JD035053. This study aims to create observation-based cloud radiative kernel (CRK) datasets and evaluate them by direct comparison of CRK and the CRK-derived cloud feedback datasets. Based on the International Satellite Cloud Climatology Project (ISCCP) H datasets, we calculate CRKs (called ISCCP-FH or FH CRKs) as 2D joint function/histogram of cloud optical depth and cloud top pressure for shortwave (SW), longwave (LW), and their sum, Net, at the top of atmosphere (TOA), as well as, for the first time, at the surface (SFC) and in the atmosphere (ATM). With cloud fraction change (CFC) datasets from doubled-CO2 simulation and short-term observational anomalies, we derive all the TOA, SFC and ATM cloud feedback for SW, LW and Net using our CRKs.The direct comparison with modeled and observed CRKs (or cloud radiative effects), cloud feedback from previous model results and the Clouds and the Earth's Radiant Energy System products show that our CRKs and CRK-derived cloud feedback are reasonably well validated. We estimate the uncertainty for the CRK-derived cloud feedback and show that the CFC-associated uncertainty contributes >98.5% of the total cloud feedback uncertainty while CRK's is very small. Our preliminary evaluation also shows that some near-zero/small cloud feedback in the TOA-alone feedback indeed results from the compensation of sizable cloud feedback of the SFC and ATM feedback and reveals some significant surface and atmospheric cloud feedback whose sum appears insignificant in TOA-alone feedback. In addition, the atmospheric longwave cloud feedback seems to play a role in enhancing meridional atmospheric energy transport. CERES; cloud feedback; cloud radiative effects; cloud radiative kernel; cloud-type based decomposition; ISCCP-FH
Zhao, Xi; Liu, XiaohongZhao, X., X. Liu, 2021: Global Importance of Secondary Ice Production. Geophysical Research Letters, 48(11), e2021GL092581. doi: 10.1029/2021GL092581. Measured ice crystal number concentrations are often orders of magnitude higher than the number concentrations of ice nucleating particles, indicating the existence of secondary ice production (SIP) in clouds. Here, we present the first study to examine the global importance of SIP through the droplet shattering during freezing of rain, ice-ice collision fragmentation, and rime splintering, using a global climate model. Our results show that SIP happens quite uniformly in the two hemispheres and dominates the ice formation in the moderately cold clouds with temperatures warmer than −15°C. SIP decreases the global annual average liquid water path by −14.6 g m−2 (−22%), increases the ice water path by 8.7 g m−2 (23%), improving the model agreement with observations. SIP changes the global annual average shortwave, longwave, and net cloud forcing by 2.1, −1.0, and 1.1 W m−2, respectively, highlighting the importance of SIP on cloud properties on the global scale. cloud forcing; global climate model; cloud microphysics; secondary ice production
Zhao, Yang; Zhao, Yuxin; Li, Jiming; Wang, Yang; Jian, Bida; Zhang, Min; Huang, JianpingZhao, Y., Y. Zhao, J. Li, Y. Wang, B. Jian, M. Zhang, J. Huang, 2021: Evaluating cloud radiative effect from CMIP6 and two satellite datasets over the Tibetan Plateau based on CERES observation. Climate Dynamics. doi: 10.1007/s00382-021-05991-7. Based on 12 years (March 2000–February 2012) of monthly data from Clouds and the Earth’s Radiant Energy System energy balanced and filled (CERES-EBAF), this study systematically evaluates the applicability of Advanced Very High Resolution Radiometer (AVHRR) and second Along-Track Scanning Radiometer and advanced ATSR (AATSR) flux products at the top-of-the-atmosphere (TOA), and the ability of atmosphere-only simulations of the Coupled Model Intercomparison Project Phase6 (CMIP6/AMIP) model in reproducing the observed spatial–temporal patterns of TOA cloud radiative effect (CRE) over the Tibetan Plateau (TP). Results show that TOA radiative fluxes from AVHRR and AATSR can be used to analyze their spatial/temporal characteristics over TP region, especially for AVHRR, but none of them can capture the observed CRE trend since 2000. In particular, when using AATSR TOA radiative flux in clear-sky of TP, the large bias of SW flux (regional mean about 30.48 Wm−2) compared with CERES-EBAF must be taken seriously. The multimodel ensemble mean (MEM) can sufficiently reproduce the temporal changes of CREs, particularly the shortwave CRE. Regarding the geographical pattern of CREs of MEM, the annual mean deviations of longwave CRE are very small, while obvious underestimations can be found in the southeastern TP for shortwave CRE. Additionally, the spatial distribution of CREs is difficult to reproduce for many individual models due to albedo and temperature biases of surface. Our results also demonstrated that MEM still has evident difficulties to capture realistic CRE trends in TP due to poor simulations in surface and cloud properties (particularly cloud fraction).
Zhao, Zhe; Li, Wei; Ciais, Philippe; Santoro, Maurizio; Cartus, Oliver; Peng, Shushi; Yin, Yi; Yue, Chao; Yang, Hui; Yu, Le; Zhu, Lei; Wang, JingmengZhao, Z., W. Li, P. Ciais, M. Santoro, O. Cartus, S. Peng, Y. Yin, C. Yue, H. Yang, L. Yu, L. Zhu, J. Wang, 2021: Fire enhances forest degradation within forest edge zones in Africa. Nature Geoscience, 14(7), 479-483. doi: 10.1038/s41561-021-00763-8. African forests suffer from severe fragmentation that further causes forest degradation near forest edges. The impact of fires used for slash-and-burn on forest edge effects remains unclear. Here, using high-resolution satellite-based forest-cover and biomass datasets, we find that edge effects extend a median distance and an interquartile range of $$0.11_{ - 0.04}^{ + 0.06}\,{\mathrm{km}}$$and $$0.15_{ - 0.05}^{ + 0.09}\,{\mathrm{km}}$$into moist and dry forests, and biomass within the forest edge zones has a carbon deficit of 4.1 PgC. Fires occurred in 52% of the forest edges and increased the carbon deficit by $$5.5_{ - 2.9}^{ + 4.3}\,{\mathrm{MgC}}\,{\mathrm{ha}^{{-1}}}$$, compared with non-fire edges, through both the direct impact of fires intruding into forests and the indirect impact of changes in the local atmospheric circulations increasing canopy dryness. If small-scale slash-and-burn practices continue, increased fragmentation during 2010–2100 will result in a carbon loss from edge effects of 0.54–4.6 PgC. Fragmentation-caused forest degradation could be avoided by implementing dedicated forest protection policies supported by satellite monitoring of forest edges.
Zhong, Bo; Ma, Yingbo; Yang, Aixia; Wu, JunjunZhong, B., Y. Ma, A. Yang, J. Wu, 2021: Radiometric Performance Evaluation of FY-4A/AGRI Based on Aqua/MODIS. Sensors, 21(5), 1859. doi: 10.3390/s21051859. Fengyun-4A (FY-4A) is the first satellite of the Chinese second-generation geostationary orbit meteorological satellites (FY-4). The Advanced Geostationary Radiation Imager (AGRI), onboard FY-4A does not load with high-precision calibration facility in visible and near infrared (VNIR) channel. As a consequence, it is necessary to comprehensively evaluate its radiometric performance and quantitatively describe the attenuation while using its VNIR data. In this paper, the radiometric performance at VNIR channels of FY-4A/AGRI is evaluated based on Aqua/MODIS data using the deep convective cloud (DCC) target. In order to reduce the influence of view angle and spectral response difference, the bi-directional reflectance distribution function (BRDF) correction and spectral matching have been performed. The evaluation result shows the radiometric performance of FY-4A/AGRI: (1) is less stable and with obvious fluctuations; (2) has a lower radiation level because of 24.99% lower compared with Aqua/MODIS; 3) has a high attenuation with 9.11% total attenuation over 2 years and 4.0% average annual attenuation rate. After the evaluation, relative radiometric normalization between AGRI and MODIS in VNIR channel is performed and the procedure is proved effective. This paper proposed a more reliable reference for the quantitative applications of FY-4A data. DCC; Aqua/MODIS; FY-4A/AGRI; radiometric performance; VNIR
Zhou, Chen; Zelinka, Mark D.; Dessler, Andrew E.; Wang, MinghuaiZhou, C., M. D. Zelinka, A. E. Dessler, M. Wang, 2021: Greater committed warming after accounting for the pattern effect. Nature Climate Change, 11(2), 132-136. doi: 10.1038/s41558-020-00955-x. Our planet’s energy balance is sensitive to spatial inhomogeneities in sea surface temperature and sea ice changes, but this is typically ignored in climate projections. Here, we show the energy budget during recent decades can be closed by combining changes in effective radiative forcing, linear radiative damping and this pattern effect. The pattern effect is of comparable magnitude but opposite sign to Earth’s net energy imbalance in the 2000s, indicating its importance when predicting the future climate on the basis of observations. After the pattern effect is accounted for, the best-estimate value of committed global warming at present-day forcing rises from 1.31 K (0.99–2.33 K, 5th–95th percentile) to over 2 K, and committed warming in 2100 with constant long-lived forcing increases from 1.32 K (0.94–2.03 K) to over 1.5 K, although the magnitude is sensitive to sea surface temperature dataset. Further constraints on the pattern effect are needed to reduce climate projection uncertainty.
Zhou, Xiaoli; Atlas, Rachel; McCoy, Isabel L.; Bretherton, Christopher S.; Bardeen, Charles; Gettelman, Andrew; Lin, Pu; Ming, YiZhou, X., R. Atlas, I. L. McCoy, C. S. Bretherton, C. Bardeen, A. Gettelman, P. Lin, Y. Ming, 2021: Evaluation of cloud and precipitation simulations in CAM6 and AM4 using observations over the Southern Ocean. Earth and Space Science, (In Press). doi: https://doi.org/10.1029/2020EA001241. This study uses cloud and radiative properties collected from in-situ and remote sensing instruments during two coordinated campaigns over the Southern Ocean between Tasmania and Antarctica in January-February 2018 to evaluate the simulations of clouds and precipitation in nudged-meteorology simulations with the CAM6 and AM4 global climate models sampled at the times and locations of the observations. Fifteen SOCRATES research flights sampled cloud water content, cloud droplet number concentration, and particle size distributions in mixed-phase boundary-layer clouds at temperatures down to -25 C. The six-week CAPRICORN2 research cruise encountered all cloud regimes across the region. Data from vertically-pointing 94 GHz radars deployed was compared with radar-simulator output from both models. Satellite data was compared with simulated top-of-atmosphere (TOA) radiative fluxes. Both models simulate observed cloud properties fairly well within the variability of observations. Cloud base and top in both models are generally biased low. CAM6 overestimates cloud occurrence and optical thickness while cloud droplet number concentrations are biased low, leading to excessive TOA reflected shortwave radiation. In general, low clouds in CAM6 precipitate at the same frequency but are more homogeneous compared to observations. Deep clouds are better simulated but produce snow too frequently. AM4 underestimates cloud occurrence but overestimates cloud optical thickness even more than CAM6, causing excessive outgoing longwave radiation fluxes but comparable reflected shortwave radiation. AM4 cloud droplet number concentrations match observations better than CAM6. Precipitating low and deep clouds in AM4 have too little snow. Further investigation of these microphysical biases is needed for both models.
Zhou, Xiaoli; Zhang, Jianhao; Feingold, GrahamZhou, X., J. Zhang, G. Feingold, 2021: On the Importance of Sea Surface Temperature for Aerosol-Induced Brightening of Marine Clouds and Implications for Cloud Feedback in a Future Warmer Climate. Geophysical Research Letters, 48(24), e2021GL095896. doi: 10.1029/2021GL095896. Marine low clouds are one of the greatest sources of uncertainty for climate projection. We present an observed climatology of cloud albedo susceptibility to cloud droplet number concentration perturbations (S0) with changing sea surface temperature (SST) and estimated inversion strength for single-layer warm clouds over the North Atlantic Ocean, using eight years of satellite and reanalysis data. The key findings are that SST has a dominant control on S0 in the presence of co-varying synoptic conditions and aerosol perturbations. Regions conducive to aerosol-induced darkening (brightening) clouds occur with high (low) local SST. Higher SST significantly hastens cloud-top evaporation with increasing aerosol loading, by accelerating entrainment and facilitating entrainment drying. In a global-warming-like scenario where aerosol loading is reduced, less cloud darkening is expected, mainly as a result of reduced entrainment drying. Our results imply a less positive low-cloud liquid water path feedback in a warmer climate with decreasing aerosol loading. Climatology; North Atlantic Ocean; marine boundary layer clouds; A-Train satellite measurements; Cloud aerosol interaction; low-cloud liquid water path feedback
Zhu, Fuxin; Li, Xin; Qin, Jun; Yang, Kun; Cuo, Lan; Tang, Wenjun; Shen, ChaopengZhu, F., X. Li, J. Qin, K. Yang, L. Cuo, W. Tang, C. Shen, 2021: Integration of Multisource Data to Estimate Downward Longwave Radiation Based on Deep Neural Networks. IEEE Transactions on Geoscience and Remote Sensing, 1-15. doi: 10.1109/TGRS.2021.3094321. Downward longwave radiation (DLR) at the surface is a key variable of interest in fields, such as hydrology and climate research. However, existing DLR estimation methods and DLR products are still problematic in terms of both accuracy and spatiotemporal resolution. In this article, we propose a deep convolutional neural network (DCNN)-based method to estimate hourly DLR at 5-km spatial resolution from top of atmosphere (TOA) brightness temperature (BT) of the Himawari-8/Advanced Himawari Imager (AHI) thermal channels, combined with near-surface air temperature and dew point temperature of ERA5 and elevation data. Validation results show that the DCNN-based method outperforms popular random forest and multilayer perceptron-based methods and that our proposed scheme integrating multisource data outperforms that only using remote sensing TOA observations or surface meteorological data. Compared with state-of-the-art CERES-SYN and ERA5-land DLR products, the estimated DLR by our proposed DCNN-based method with physical multisource inputs has higher spatiotemporal resolution and accuracy, with correlation coefficient (CC) of 0.95, root-mean-square error (RMSE) of 17.2 W/m², and mean bias error (MBE) of -0.8 W/m² in the testing period on the Tibetan Plateau. Atmospheric modeling; Clouds; Deep convolutional neural network (DCNN); downward longwave radiation (DLR); Estimation; Himawari-8; Land surface; Ocean temperature; Spatial resolution; Temperature distribution; Tibetan Plateau (TP); Tibetan Plateau (TP).
Zhu, Yingli; Mitchum, Gary T.; Thompson, Philip R.; Lagerloef, Gary S. E.Zhu, Y., G. T. Mitchum, P. R. Thompson, G. S. E. Lagerloef, 2021: Diagnosis of Large-Scale, Low-Frequency Sea Level Variability in the Northeast Pacific Ocean. Journal of Geophysical Research: Oceans, 126(5), e2020JC016682. doi: https://doi.org/10.1029/2020JC016682. Earlier studies in the Northeast Pacific (NEP) suggest that the local and remote sea level responses are important for the large-scale, low-frequency sea level variability, but the relative importance of the two processes remains unclear. In this study, we develop a novel sea level model driven by wind, buoyancy and eddy forcing to examine their relative roles in the NEP. Based on the new model, a diagnostic equation for sea level that is an alternative to the conventional method of characteristics is formed. The wind, buoyancy and eddy forcing account for the sea level variability in different regions. Sea level variability is primarily controlled by the wind forcing in the central to the northeast of the NEP, by the local buoyancy forcing in the southeast region between 210°E and 230°E, and by the eddy forcing in the southwest of the NEP. In addition, the diagnosis demonstrates that the local sea level response is more important than the remote response over most of the NEP, while the remote sea level response could play an important role in the southwest portion of the NEP. wind forcing; Northeast Pacific; buoyancy forcing; eddy forcing; local sea level response; remote sea level response
Zou, Xun; Bromwich, David H.; Montenegro, Alvaro; Wang, Sheng-Hung; Bai, LeshengZou, X., D. H. Bromwich, A. Montenegro, S. Wang, L. Bai, 2021: Major surface melting over the Ross Ice Shelf part II: Surface energy balance. Quarterly Journal of the Royal Meteorological Society, 147(738), 2895-2916. doi: 10.1002/qj.4105. The West Antarctic climate is under the combined impact of synoptic and regional drivers. Regional factors have contributed to more frequent surface melting with a similar pattern recently, which accelerates ice loss and favors global sea-level rise. Part I of this research identified and quantified the two leading drivers of Ross Ice Shelf (RIS) melting, viz. foehn effect and direct marine air advection, based on Polar WRF (PWRF) simulations. In this article (Part II), the impact of clouds and the pattern of surface energy balance (SEB) during melting are analyzed, as well as the relationship among these three factors. In general, net shortwave radiation dominates the surface melting with a daily mean value above 100 W·m−2. Foehn clearance and decreasing surface albedo respectively increase the downward shortwave radiation and increase the absorbed shortwave radiation, significantly contributing to surface melting in areas such as western Marie Byrd Land. Also, extensive downward longwave radiation caused by low-level liquid cloud favors the melting expansion over the middle and coastal RIS. With significant moisture transport occurring over more than 40% of the time during the melting period, the impact from net radiation can be amplified. Moreover, frequent foehn cases can enhance the turbulent mixing on the leeside. With a Froude number (Fr) around 1 or slightly larger, fast downdrafts or reversed wind flows can let the warm foehn air penetrate down to the surface with up to 20 W·m−2 in sensible heat flux transfer to the ground. However, when the Froude number is close to infinity with breaking waves on the leeside, the contribution of turbulence to the surface warming is reduced. With better understanding of the regional factors for the surface melting, prediction of the future stability of West Antarctic ice shelves can be improved. clouds; surface energy balance; polar WRF; West Antarctic surface melting
Abera, Temesgen Alemayehu; Heiskanen, Janne; Pellikka, Petri K. E.; Maeda, Eduardo EijiAbera, T. A., J. Heiskanen, P. K. E. Pellikka, E. E. Maeda, 2020: Impact of rainfall extremes on energy exchange and surface temperature anomalies across biomes in the Horn of Africa. Agricultural and Forest Meteorology, 280, 107779. doi: 10.1016/j.agrformet.2019.107779. Precipitation extremes have a strong influence on the exchange of energy and water between the land surface and the atmosphere. Although the Horn of Africa has faced recurrent drought and flood events in recent decades, it is still unclear how these events impact energy exchange and surface temperature across different ecosystems. Here, we analyzed the impact of precipitation extremes on spectral albedo (total shortwave, visible, and near-infrared (NIR) broadband albedos), energy balance, and surface temperature in four natural vegetation types: forest, savanna, grassland, and shrubland. We used remotely sensed observations of surface biophysical properties and climate from 2001 to 2016. Our results showed that, in forests and savannas, precipitation extremes led to divergent spectral changes in visible and NIR albedos, which cancelled each other limiting shortwave albedo changes. An exception to this pattern was observed in shrublands and grasslands, where both visible and NIR albedo increased during drought events. Given that shrublands and grasslands occupy a large fraction of the Horn of Africa (52%), our results unveil the importance of these ecosystems in driving the magnitude of shortwave radiative forcing in the region. The average regional shortwave radiative forcing during drought events (−0.64 W m−2, SD 0.11) was around twice that of the extreme wet events (0.33 W m−2, SD 0.09). Such shortwave forcing, however, was too small to influence the surface–atmosphere coupling. In contrast, the surface feedback through turbulent flux changes was strong across vegetation types and had a significant (P CERES; MODIS; Albedo; Energy exchange; Land surface temperature; Precipitation extremes
Ahmad, Maqbool; Tariq, Shahina; Alam, Khan; Anwar, Sajid; Ikram, MuhammadAhmad, M., S. Tariq, K. Alam, S. Anwar, M. Ikram, 2020: Long-term variation in aerosol optical properties and their climatic implications over major cities of Pakistan. Journal of Atmospheric and Solar-Terrestrial Physics, 210(15), 105419. doi: 10.1016/j.jastp.2020.105419. The present study investigates long-term variation in aerosol optical properties (AOP) and their associated climatic implications over selected cities of Chitral, Gwadar, Karachi, Lahore, Peshawar and Quetta in Pakistan for the period 2005–2018. For this purpose, aerosol optical depth (AOD) and aerosol index (AI) are retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) and Ozone Monitoring Instrument (OMI). Results revealed annual increasing trend of AOD with maximum values in summer during the study period over all study regions, except for Chitral. Similar annual trend was observed for AI but with minimum values in summer. Further, temperature and relative humidity (RH) showed significant relationships with AOD along with evidences of precipitation influences. In addition, the trajectory analysis of Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) Model confirmed the arrival of both short and long-range air masses to the receptor sites. Similarly, the direct aerosol radiative forcing (DARF) and direct aerosol radiative forcing efficiency (DARFE) were calculated using Cloud's and the Earth's Radiant Energy System (CERES) data. The multiyear mean monthly atmospheric DARF of 8.80, 16.32, 10.74, 21.64, 9.10 and 10.94 W/m2 was observed over Chitral, Gwadar, Karachi, Lahore, Peshawar and Quetta, respectively. Consequently, the maximum heating rate (HR) of 0.48 K/day (Chitral), 0.93 K/day (Gwadar), 0.51 K/day (Karachi), 1.23 K/day (Lahore), 0.44 K/day (Peshawar) and 0.56 K/day (Quetta) showed a net warming effect during 2005–2018. These results can give an insight into aerosol concentration and can form the basis for aerosol-induced climatic implications in the study area. CERES; MODIS; AOD; Radiative forcing; Heating rate; AI; HYSPLIT
Ajoku, Osinachi; Norris, Joel R.; Miller, Arthur J.Ajoku, O., J. R. Norris, A. J. Miller, 2020: Observed monsoon precipitation suppression caused by anomalous interhemispheric aerosol transport. Climate Dynamics, 54(1), 1077-1091. doi: 10.1007/s00382-019-05046-y. This study uses observations and atmospheric reanalysis products in order to understand the impacts of smoke aerosols advected from the Southern Hemisphere on the dynamics of the West African monsoon. Seasonal biomass burning and resulting aerosol emissions have been well documented to affect regional weather patterns, especially low-level convection. Out of all monsoon months, precipitation shows the most variability over land during August, in which anomalous smoke aerosol values can increase (decrease) by 33% (29%) in the Northern Gulf of Guinea and precipitation can decrease (increase) by up to ~ 2.5 mm day−1 (~ 3 mm day−1) along the West African monsoon region accounting for a 17% (18%) change in precipitation. Smoke aerosols produced by biomass burning occurring near Central Africa are advected towards the Gulf of Guinea at elevations around the 850 hPa level. Satellite observations show an increase (decrease) in cloud fraction and optical depth below (above) the 300-hPa level in the Gulf of Guinea and along the West African coastline along with concurrent decreases (increases) in cloud droplet radius during dirty (clean) aerosol episodes. Additional observations of shortwave radiation quantify changes in cloud coverage and monsoon dynamics. On average, reductions in surface shortwave radiation of ~ 10–15 W m−2 occur over the Gulf of Guinea during increased aerosol transport, with aerosols accounting for ~ 33–50% of that reduction. Reductions in shortwave radiation are associated with decreased convective available potential energy (CAPE). This demonstrates that increased transport of aerosols perturbs surface radiation, convection in the lower troposphere and eventually cloud coverage, potentially leading to the observed monsoon precipitation suppression. In a broader social context, this region houses 200 million people and thus understanding these climate patterns may carry great importance.
Akkermans, Tom; Clerbaux, NicolasAkkermans, T., N. Clerbaux, 2020: Narrowband-to-Broadband Conversions for Top-of-Atmosphere Reflectance from the Advanced Very High Resolution Radiometer (AVHRR). Remote Sensing, 12(2), 305. doi: 10.3390/rs12020305. The current lack of a long, 30+ year, global climate data record of reflected shortwave top-of-atmosphere (TOA) radiation could be tackled by relying on existing narrowband records from the Advanced Very High Resolution Radiometer (AVHRR) instruments, and transform these measurements into broadband quantities like provided by the Clouds and the Earth’s Radiant Energy System (CERES). This paper presents the methodology of an AVHRR-to-CERES narrowband-to-broadband conversion for shortwave TOA reflectance, including the ready-to-use results in the form of scene-type dependent regression coefficients, allowing a calculation of CERES-like shortwave broadband reflectance from AVHRR channels 1 and 2. The coefficients are obtained using empirical relations in a large data set of collocated, coangular and simultaneous AVHRR-CERES observations, requiring specific orbital conditions for the AVHRR- and CERES-carrying satellites, from which our data analysis uses all available data for an unprecedented observation matching between both instruments. The multivariate linear regressions were found to be robust and well-fitting, as demonstrated by the regression statistics on the calibration subset (80% of data): adjusted R 2 higher than 0.9 and relative RMS residual mostly below 3%, which is a significant improvement compared to previous regressions. Regression models are validated by applying them on a validation subset (20% of data), indicating a good performance overall, roughly similar to the calibration subset, and a negligible mean bias. A second validation approach uses an expanded data set with global coverage, allowing regional analyses. In the error analysis, instantaneous accuracy is quantified at regional scale between 1.8 Wm − 2 and 2.3 Wm − 2 (resp. clear-sky and overcast conditions) at 1 standard deviation (RMS bias). On daily and monthly time scales, these errors correspond to 0.7 and 0.9 Wm − 2 , which is compliant with the GCOS requirement of 1 Wm − 2 . shortwave; broadband; CERES; radiation; AVHRR; narrowband
Alkama, Ramdane; Taylor, Patrick C.; Garcia-San Martin, Lorea; Douville, Herve; Duveiller, Gregory; Forzieri, Giovanni; Swingedouw, Didier; Cescatti, AlessandroAlkama, R., P. C. Taylor, L. Garcia-San Martin, H. Douville, G. Duveiller, G. Forzieri, D. Swingedouw, A. Cescatti, 2020: Clouds damp the radiative impacts of polar sea ice loss. The Cryosphere, 14(8), 2673-2686. doi: 10.5194/tc-14-2673-2020. Abstract. Clouds play an important role in the climate system: (1) cooling Earth by reflecting incoming sunlight to space and (2) warming Earth by reducing thermal energy loss to space. Cloud radiative effects are especially important in polar regions and have the potential to significantly alter the impact of sea ice decline on the surface radiation budget. Using CERES (Clouds and the Earth's Radiant Energy System) data and 32 CMIP5 (Coupled Model Intercomparison Project) climate models, we quantify the influence of polar clouds on the radiative impact of polar sea ice variability. Our results show that the cloud short-wave cooling effect strongly influences the impact of sea ice variability on the surface radiation budget and does so in a counter-intuitive manner over the polar seas: years with less sea ice and a larger net surface radiative flux show a more negative cloud radiative effect. Our results indicate that 66±2% of this change in the net cloud radiative effect is due to the reduction in surface albedo and that the remaining 34±1 % is due to an increase in cloud cover and optical thickness. The overall cloud radiative damping effect is 56±2 % over the Antarctic and 47±3 % over the Arctic. Thus, present-day cloud properties significantly reduce the net radiative impact of sea ice loss on the Arctic and Antarctic surface radiation budgets. As a result, climate models must accurately represent present-day polar cloud properties in order to capture the surface radiation budget impact of polar sea ice loss and thus the surface albedo feedback.
Amos, Helen M.; Starke, Matthew J.; Rogerson, Tina M.; Robles, Marilé Colón; Andersen, Travis; Boger, Rebecca; Campbell, Brian A.; Low, Russanne D.; Nelson, Peder; Overoye, David; Taylor, Jessica E.; Weaver, Kristen L.; Ferrell, Trena M.; Kohl, Holli; Schwerin, Theresa G.Amos, H. M., M. J. Starke, T. M. Rogerson, M. Robles, . Colón, T. Andersen, R. Boger, B. A. Campbell, R. D. Low, P. Nelson, D. Overoye, J. E. Taylor, K. L. Weaver, T. M. Ferrell, H. Kohl, T. G. Schwerin, 2020: GLOBE Observer Data: 2016–2019. Earth and Space Science, 7(8), e2020EA001175. doi: 10.1029/2020EA001175. This technical report summarizes the GLOBE Observer data set from 1 April 2016 to 1 December 2019. GLOBE Observer is an ongoing NASA-sponsored international citizen science project that is part of the larger Global Learning and Observations to Benefit the Environment (GLOBE) Program, which has been in operation since 1995. GLOBE Observer has the greatest number of participants and geographic coverage of the citizen science projects in the Earth Science Division at NASA. Participants use the GLOBE Observer mobile app (launched in 2016) to collect atmospheric, hydrologic, and terrestrial observations. The app connects participants to satellite observations from Aqua, Terra, CALIPSO, GOES, Himawari, and Meteosat. Thirty-eight thousand participants have contributed 320,000 observations worldwide, including 1,000,000 georeferenced photographs. It would take an individual more than 13 years to replicate this effort. The GLOBE Observer app has substantially increased the spatial extent and sampling density of GLOBE measurements and more than doubled the number of measurements collected through the GLOBE Program. GLOBE Observer data are publicly available (at observer.globe.gov). cloud cover; citizen science; global data set; land cover; mosquitoes; tree height
Annamalai, H.Annamalai, H., 2020: ENSO Precipitation Anomalies along the Equatorial Pacific: Moist Static Energy Framework Diagnostics. J. Climate, 33(21), 9103-9127. doi: 10.1175/JCLI-D-19-0374.1.
Attada, Raju; Dasari, Hari Prasad; Kunchala, Ravi Kumar; Langodan, Sabique; Niranjan Kumar, Kondapalli; Knio, Omar; Hoteit, IbrahimAttada, R., H. P. Dasari, R. K. Kunchala, S. Langodan, K. Niranjan Kumar, O. Knio, I. Hoteit, 2020: Evaluating Cumulus Parameterization Schemes for the Simulation of Arabian Peninsula Winter Rainfall. J. Hydrometeor., 21(5), 1089-1114. doi: 10.1175/JHM-D-19-0114.1. This study investigates the sensitivity of winter seasonal rainfall over the Arabian Peninsula (AP) to different convective physical parameterization schemes using a high-resolution WRF Model. Three different parameterization schemes, Kain–Fritch (KF), Betts–Miller–Janjić (BMJ), and Grell–Freitas (GF), are used in winter simulations from 2001 to 2016. Results from seasonal simulations suggest that simulated AP winter rainfall with KF is in best agreement with observed rainfall in terms of spatial distribution and intensity. Higher spatial correlation coefficients and fewer biases with observations are also obtained with KF. In addition, the regional moisture transport, cloud distribution, and cloud microphysical responses are better simulated by KF. The AP low-level circulation, characterized by the Arabian anticyclone, is well captured by KF and BMJ, but its position is displaced in GF. KF is furthermore successful at simulating the moisture distribution in the lower atmosphere and atmospheric water plumes in the middle troposphere. The higher skill of rainfall simulation with the KF (and to some extent BMJ) is attributed to a better representation of the Arabian anticyclone and subtropical westerly jet, which guides the upper tropospheric synoptic transients and moisture. In addition, the vertical profile of diabatic heating from KF is in better agreement with the observations. Discrepancies in representing the diabatic heating profile by BMJ and GF show discrepancies in instability and in turn precipitation biases. Our results indicate that the selection of subgrid convective parameterization in a high-resolution atmospheric model over the AP is an important factor for accurate regional rainfall simulations.
Avtar, Ram; Komolafe, Akinola Adesuji; Kouser, Asma; Singh, Deepak; Yunus, Ali P.; Dou, Jie; Kumar, Pankaj; Gupta, Rajarshi Das; Johnson, Brian Alan; Thu Minh, Huynh Vuong; Aggarwal, Ashwani Kumar; Kurniawan, Tonni AgustionoAvtar, R., A. A. Komolafe, A. Kouser, D. Singh, A. P. Yunus, J. Dou, P. Kumar, R. D. Gupta, B. A. Johnson, H. V. Thu Minh, A. K. Aggarwal, T. A. Kurniawan, 2020: Assessing sustainable development prospects through remote sensing: A review. Remote Sensing Applications: Society and Environment, 20, 100402. doi: 10.1016/j.rsase.2020.100402. The Earth's ecosystems face severe environmental stress from unsustainable socioeconomic development linked to population growth, urbanization, and industrialization. Governments worldwide are interested in sustainability measures to address these issues. Remote sensing allows for the measurement, integration, and presentation of useful information for effective decision-making at various temporal and spatial scales. Scientists and decision-makers have endorsed extensive use of remote sensing to bridge gaps among disciplines and achieve sustainable development. This paper presents an extensive review of remote sensing technology used to support sustainable development efforts, with a focus on natural resource management and assessment of natural hazards. We further explore how remote sensing can be used in a cross-cutting, interdisciplinary manner to support decision-making aimed at addressing sustainable development challenges. Remote sensing technology has improved significantly in terms of sensor resolution, data acquisition time, and accessibility over the past several years. This technology has also been widely applied to address key issues and challenges in sustainability. Furthermore, an evaluation of the suitability and limitations of various satellite-derived indices proposed in the literature for assessing sustainable development goals showed that these older indices still perform reasonably well. Nevertheless, with advancements in sensor radiometry and resolution, they were less exploited and new indices are less explored. Decision support system; Indices; Natural hazards; Natural resource management; Sustainability
Baba, YuyaBaba, Y., 2020: Shallow convective closure in a spectral cumulus parameterization. Atmospheric Research, 233, 104707. doi: 10.1016/j.atmosres.2019.104707. A shallow convective closure (shallow closure) was introduced in a spectral cumulus parameterization (spectral scheme), and the validity was evaluated using an atmospheric general circulation model (AGCM) and Atmospheric Model Intercomparison Project (AMIP) experiments. The spectral scheme with shallow closure improved model simulated climatology and variability as compared with the spectral scheme only. The shallow closure enhanced shallow convection, leading to an improvements in dry bias in the tropics and cold bias in the extratropics. The simulated interannual variabilities were comparable regardless of the shallow closure; however, intraseasonal variability was greatly improved with the shallow closure. This is because detrainment from shallow convection during development of the Madden-Julian oscillation (MJO) contributes to supplying moisture in organized convection, and the spectral scheme with shallow closure was able to simulate this contribution well. Climatology; Atmospheric variability; Convection scheme; Convective closure; Shallow convection
Baba, Yuya; Giorgetta, Marco A.Baba, Y., M. A. Giorgetta, 2020: Tropical Variability Simulated in ICON-A With a Spectral Cumulus Parameterization. Journal of Advances in Modeling Earth Systems, 12(1), e2019MS001732. doi: 10.1029/2019MS001732. We implemented a spectral cumulus parameterization based on a cloud-resolving model (SC scheme) in the icosahedral nonhydrostatic atmospheric model (ICON-A). We compared the resulting simulated climatology and tropical variability with results from the standard version of ICON-A using a variant of the Tiedtke-Nordeng scheme (TK scheme) using observational and reanalysis data. The climatological errors of the SC scheme were similar to those of the TK scheme, but several biases, such as properties of meridional winds and precipitation pattern in the western Pacific, were much improved. For tropical variability, we found that the SC scheme improved the interannual response of the precipitation in the western Pacific and was able to simulate Madden-Julian oscillation (MJO) features much better than the TK scheme. We investigated the reason for the better simulation of the MJO using composite analysis and column process analysis for moisture. Our results suggest that the entrainment parameterization of the SC scheme is necessary to reproduce the MJO; however, spectral representation and improved convective closure are also found to contribute for better MJO simulation. These parameterizations improved moisture supply from low-level clouds and cloud mass flux which were needed to sustain the MJO. atmospheric general circulation model; convection scheme; tropical variability
Back, Seung-Yoon; Han, Ji-Young; Son, Seok-WooBack, S., J. Han, S. Son, 2020: Modeling Evidence of QBO-MJO Connection: A Case Study. Geophysical Research Letters, 47(20), e2020GL089480. doi: 10.1029/2020GL089480. The boreal winter Madden-Julian Oscillation (MJO) is modulated by the Quasi-Biennial Oscillation (QBO). The MJO becomes relatively strong during the easterly QBO (EQBO) winters but weak during the westerly QBO (WQBO) winters. To better understand their relationship, a set of WRF model experiments is conducted with varying lateral boundary conditions. The MJO event in December 2007, during EQBO winter, is chosen as a reference case. The control experiment qualitatively reproduces the observed MJO. When the lateral boundary conditions are switched with those of WQBO or strong WQBO winters, the MJO becomes weak over the Maritime Continent. All eight ensemble members exhibit enhanced outgoing longwave radiation and reduced precipitation from EQBO to WQBO, and to strong WQBO conditions, although the magnitude of changes is smaller than observations. This result, one of the first mesoscale modeling evidences of the QBO-MJO connection, suggests that the MJO is at least partly modulated by the QBO. tropics; Madden-Julian Oscillation; Quasi-Biennial Oscillation
Baek, Eun-Hyuk; Kim, Joo-Hong; Park, Sungsu; Kim, Baek-Min; Jeong, Jee-HoonBaek, E., J. Kim, S. Park, B. Kim, J. Jeong, 2020: Impact of poleward heat and moisture transports on Arctic clouds and climate simulation. Atmospheric Chemistry and Physics, 20(5), 2953-2966. doi: 10.5194/acp-20-2953-2020. Abstract. Many general circulation models (GCMs) have difficulty simulating Arctic clouds and climate, causing substantial inter-model spread. To address this issue, two Atmospheric Model Intercomparison Project (AMIP) simulations from the Community Atmosphere Model version 5 (CAM5) and Seoul National University (SNU) Atmosphere Model version 0 (SAM0) with a unified convection scheme (UNICON) are employed to identify an effective mechanism for improving Arctic cloud and climate simulations. Over the Arctic, SAM0 produced a larger cloud fraction and cloud liquid mass than CAM5, reducing the negative Arctic cloud biases in CAM5. The analysis of cloud water condensation rates indicates that this improvement is associated with an enhanced net condensation rate of water vapor into the liquid condensate of Arctic low-level clouds, which in turn is driven by enhanced poleward transports of heat and moisture by the mean meridional circulation and transient eddies. The reduced Arctic cloud biases lead to improved simulations of surface radiation fluxes and near-surface air temperature over the Arctic throughout the year. The association between the enhanced poleward transports of heat and moisture and increase in liquid clouds over the Arctic is also evident not only in both models, but also in the multi-model analysis. Our study demonstrates that enhanced poleward heat and moisture transport in a model can improve simulations of Arctic clouds and climate.
Bai, Heming; Wang, Minghuai; Zhang, Zhibo; Liu, YawenBai, H., M. Wang, Z. Zhang, Y. Liu, 2020: Synergetic Satellite Trend Analysis of Aerosol and Warm Cloud Properties ver Ocean and Its Implication for Aerosol-Cloud Interactions. Journal of Geophysical Research: Atmospheres, 125(6), e2019JD031598. doi: 10.1029/2019JD031598. Decadal-scale trends in aerosol and cloud properties provide important ways for understanding aerosol-cloud interactions. In this paper, by using MODIS products (2003–2017), we analyze synergetic trends in aerosol properties and warm cloud properties over global ocean. Cloud droplet number concentration (CDNC) and aerosol parameters (aerosol optical depth, angstrom exponent, and aerosol index) show consistent decreasing trend over East Coast of the United States (EUS), west coast of Europe (WEU), and east coast of China (EC), and no significant trend in liquid water path is found over these regions during the period 2003–2017. Over regions with significant long-term trends of aerosol loading and CDNC (e.g., EUS and WEU), the sensitivity of CDNC to aerosol loading based on the long-term trend is closer to those derived from ground and aircraft observations and larger than those derived from instantaneous satellite observations, providing an alternative way for quantifying aerosol-cloud interactions. A clear shift in the normalized probability density function of CDNC between the first 5 years (2003–2007) and the last 5 years (2013–2017) is found, with a decrease of around 50% in the occurrence frequency of high CDNC (>400 cm−3) over EUS and WEU. The relative variances of cloud droplet effective radius generally decrease with decreasing aerosol loading, providing large-scale evidence for the effects of anthropogenic aerosols on the dispersion of cloud droplet size distribution. The long-term satellite data sets provide great opportunities for quantifying aerosol-cloud interactions and further confronting these interactions in climate models in the future.
Bao, Shanhu; Letu, Husi; Zhao, Jun; Lei, Yonghui; Zhao, Chuanfeng; Li, Jiming; Tana, Gegen; Liu, Chao; Guo, Enliang; Zhang, Jie; He, Jie; Bao, YuhaiBao, S., H. Letu, J. Zhao, Y. Lei, C. Zhao, J. Li, G. Tana, C. Liu, E. Guo, J. Zhang, J. He, Y. Bao, 2020: Spatiotemporal distributions of cloud radiative forcing and response to cloud parameters over the Mongolian Plateau during 2003–2017. International Journal of Climatology, 40(9), 4082-4101. doi: 10.1002/joc.6444. The Mongolian Plateau (MP) is among the most sensitive areas to global climate change, and the clouds over the MP have a greater impact on regional and global radiation budgets by altering the atmospheric and surface radiative forcing. In this study, daily Cloud and Earth Radiation Energy System data are used to investigate spatiotemporal variation of cloud radiative forcing (CRF) at the top of atmosphere (TOA), surface and atmosphere over the MP from 2003 to 2017 and then combined with Moderate Resolution Imaging Spectroradiometer level 2 atmospheric data during the same period to analyse the cloud parameter impacts on CRF over the MP. At the TOA and surface, net radiative forcing (NRF) and shortwave radiative forcing (SRF) have cooling effects and longwave radiative forcing (LRF) have heating effects in all four seasons, and the NRF cooling effect in most areas of the MP decreases in summer and autumn and increases in spring and winter. In the atmosphere, SRF in spring and summer and NRF in summer reach larger values and heat the atmosphere, and LRF plays a strong cooling role in winter. The NRF change trend in the atmosphere over Mongolia is noteworthy in spring, its reduction slope is large, and most areas of Mongolia passed a significance test. As expected, a significant negative correlation was observed between cloud cover and NRF (as well as SRF) at the TOA and surface and a positive correlation was observed with NRF/SRF in the atmosphere and all LRF. With the increase in cloud optical thickness and cloud water path, the NRF and SRF cooling effects at the TOA and surface, the LRF cooling effect in the atmosphere, the LRF heating effect at the surface, and the SRF heating effect in the atmosphere all become stronger. cloud radiative forcing; cloud classification; cloud parameters; Mongolian Plateau; radiation validation
Barpanda, Pragallva; Shaw, Tiffany A.Barpanda, P., T. A. Shaw, 2020: Surface fluxes modulate the seasonality of zonal-mean storm tracks. J. Atmos. Sci., 77(2), 753–779. doi: 10.1175/JAS-D-19-0139.1. The observed zonal-mean extratropical storm tracks exhibit distinct hemispheric seasonality. Previously, the moist static energy (MSE) framework was used diagnostically to show that shortwave absorption (insolation) dominates seasonality but surface heat fluxes damp seasonality in the Southern Hemisphere (SH) and amplify it in the Northern Hemisphere (NH). Here we establish the causal role of surface fluxes (ocean energy storage), which affect surface heat fluxes, by varying the mixed layer depth (d) in zonally-symmetric 1) slab-ocean aquaplanet simulations with zero ocean energy transport and 2) Energy Balance Model (EBM) simulations. Using a scaling analysis we define a critical mixed layer depth (dc) and hypothesize 1) large mixed layer depths (d > dc) produce surface heat fluxes that are out of phase with shortwave absorption resulting in small storm track seasonality and 2) small mixed layer depths (d < dc) produce surface heat fluxes that are in phase with shortwave absorption resulting in large storm track seasonality. The aquaplanet simulations confirm the large mixed layer depth hypothesis and yield a useful idealization of the SH storm track. However, the small mixed layer depth hypothesis fails to account for the large contribution of the Ferrel cell and atmospheric storage. The small mixed layer limit does not yield a useful idealization of the NH storm track because the seasonality of the Ferrel cell contribution is opposite to the stationary eddy contribution in the NH. Varying the mixed layer depth in an EBM qualitatively supports the aquaplanet results.
Bauer, Susanne E.; Tsigaridis, Kostas; Faluvegi, Greg; Kelley, Maxwell; Lo, Ken K.; Miller, Ron L.; Nazarenko, Larissa; Schmidt, Gavin A.; Wu, JingboBauer, S. E., K. Tsigaridis, G. Faluvegi, M. Kelley, K. K. Lo, R. L. Miller, L. Nazarenko, G. A. Schmidt, J. Wu, 2020: Historical (1850-2014) aerosol evolution and role on climate forcing using the GISS ModelE2.1 contribution to CMIP6. Journal of Advances in Modeling Earth Systems, 12(8), e2019MS001978. doi: 10.1029/2019MS001978. The Earth’s climate is rapidly changing. Over the past centuries, aerosols, via their ability to absorb or scatter solar radiation and alter clouds, played an important role in counterbalancing some of the greenhouse gas (GHG) caused global warming. The multi-century anthropogenic aerosol cooling effect prevented present-day climate from reaching even higher surface air temperatures and subsequent more dramatic climate impacts. Trends in aerosol concentrations and optical depth show that in many polluted regions such as Europe and the United States of America, aerosol precursor emissions decreased back to levels of the 1950s. More recent polluting countries such as China may have reached a turning point in recent years as well, while India still follows an upward trend. Here we study aerosol trends in the CMIP6 simulations of the GISS ModelE2.1 climate model using a fully coupled atmosphere composition configuration, including interactive gas-phase chemistry, and either an aerosol microphysical (MATRIX) or a mass-based (OMA) aerosol module. Results show that whether global aerosol radiative forcing is already declining depends on the aerosol scheme used. Using the aerosol microphysical scheme, where the aerosol system reacts more strongly to the trend in sulfur dioxide (SO2) emissions, global peak direct aerosol forcing was reached in the 1980’s, whereas the mass-based scheme simulates peak direct aerosol forcing around 2010. aerosol microphysics; Aerosol Forcing; CMIP6 historical simulation; GISS model
Bellouin, N.; Quaas, J.; Gryspeerdt, E.; Kinne, S.; Stier, P.; Watson‐Parris, D.; Boucher, O.; Carslaw, K. S.; Christensen, M.; Daniau, A.-L.; Dufresne, J.-L.; Feingold, G.; Fiedler, S.; Forster, P.; Gettelman, A.; Haywood, J. M.; Lohmann, U.; Malavelle, F.; Mauritsen, T.; McCoy, D. T.; Myhre, G.; Mülmenstädt, J.; Neubauer, D.; Possner, A.; Rugenstein, M.; Sato, Y.; Schulz, M.; Schwartz, S. E.; Sourdeval, O.; Storelvmo, T.; Toll, V.; Winker, D.; Stevens, B.Bellouin, N., J. Quaas, E. Gryspeerdt, S. Kinne, P. Stier, D. Watson‐Parris, O. Boucher, K. S. Carslaw, M. Christensen, A. Daniau, J. Dufresne, G. Feingold, S. Fiedler, P. Forster, A. Gettelman, J. M. Haywood, U. Lohmann, F. Malavelle, T. Mauritsen, D. T. McCoy, G. Myhre, J. Mülmenstädt, D. Neubauer, A. Possner, M. Rugenstein, Y. Sato, M. Schulz, S. E. Schwartz, O. Sourdeval, T. Storelvmo, V. Toll, D. Winker, B. Stevens, 2020: Bounding global aerosol radiative forcing of climate change. Reviews of Geophysics, 58(1), e2019RG000660. doi: 10.1029/2019RG000660. Aerosols interact with radiation and clouds. Substantial progress made over the past 40 years in observing, understanding, and modeling these processes helped quantify the imbalance in the Earth's radiation budget caused by anthropogenic aerosols, called aerosol radiative forcing, but uncertainties remain large. This review provides a new range of aerosol radiative forcing over the industrial era based on multiple, traceable and arguable lines of evidence, including modelling approaches, theoretical considerations, and observations. Improved understanding of aerosol absorption and the causes of trends in surface radiative fluxes constrain the forcing from aerosol-radiation interactions. A robust theoretical foundation and convincing evidence constrain the forcing caused by aerosol-driven increases in liquid cloud droplet number concentration. However, the influence of anthropogenic aerosols on cloud liquid water content and cloud fraction is less clear, and the influence on mixed-phase and ice clouds remains poorly constrained. Observed changes in surface temperature and radiative fluxes provide additional constraints. These multiple lines of evidence lead to a 68% confidence interval for the total aerosol effective radiative forcing of -1.60 to -0.65 W m-2, or -2.0 to -0.4 W m-2 with a 90% likelihood. Those intervals are of similar width to the last Intergovernmental Panel on Climate Change assessment but shifted towards more negative values. The uncertainty will narrow in the future by continuing to critically combine multiple lines of evidence, especially those addressing industrial-era changes in aerosol sources and aerosol effects on liquid cloud amount and on ice clouds. Aerosol; Aerosol-cloud interaction; Aerosol-radiation interaction; Climate change; Radiative forcing
Berry, Elizabeth; Mace, Gerald G.; Gettelman, AndrewBerry, E., G. G. Mace, A. Gettelman, 2020: Using A-Train Observations to Evaluate East Pacific Cloud Occurrence and Radiative Effects in the Community Atmosphere Model. J. Climate, 33(14), 6187-6203. doi: 10.1175/JCLI-D-19-0870.1.
Bhatt, Rajendra; Doelling, David R.; Angal, Amit; Xiong, Xiaoxiong; Haney, Conor; Scarino, Benjamin R.; Wu, Aisheng; Gopalan, ArunBhatt, R., D. R. Doelling, A. Angal, X. Xiong, C. Haney, B. R. Scarino, A. Wu, A. Gopalan, 2020: Response Versus Scan-Angle Assessment of MODIS Reflective Solar Bands in Collection 6.1 Calibration. IEEE Transactions on Geoscience and Remote Sensing, 58(4), 2276-2289. doi: 10.1109/TGRS.2019.2946963. The Moderate Resolution Imaging Spectroradiometer (MODIS) instruments onboard the Aqua and Terra satellites have been operated for nearly two decades, producing high-quality earth observation data sets suitable for a broad range of scientific studies regarding the earth's land, ocean, and atmospheric processes. The high radiometric accuracy of MODIS reflective solar band (RSB) calibration has also served as benchmark measurements for on-orbit cross-calibration studies. As the two MODIS instruments have operated well beyond their design lifespan of six years, the measurements from the onboard calibrators alone become inadequate to characterize the sensor's response at all scan angles, as evinced by long-term drifts observed at certain scan positions of the Aqua-MODIS 0.64- and 0.86-μm bands in Collection 6 (C6) data set. The latest MODIS Level 1B C6.1 data set incorporates earth-view response trending from invariant desert sites as supplemental inputs to characterize the scan-angle calibration dependencies for all RSB. This article presents a deep convective cloud (DCC)-based calibration approach for an independent evaluation of the MODIS RSB response versus scan-angle (RVS) performance in C6.1. The long-term calibration stability and RVS differences in C6.1 have been significantly improved for Aqua-MODIS RSB. The observed RVS differences of more than 2% in Aqua-MODIS C6 bands 1 and 2 have been reduced to within 1% in C6.1. Some RSBs of Terra-MODIS have suffered temporal drifts up to 2% and calibration shifts up to 3%, particularly around 2016 when the Terra satellite entered into safe mode. The DCC approach has been found very effective in tracking the on-orbit RVS changes over time. calibration; clouds; Earth; radiometry; deep convective cloud; Moderate Resolution Imaging Spectroradiometer; MODIS; Moderate Resolution Imaging Spectroradiometer (MODIS); Terra satellite; remote sensing; VIIRS; Clouds and the Earth’s Radiant Energy System (CERES); Calibration; Cloud computing; Aqua satellites; Aqua-MODIS RSB; deep convective cloud (DCC); Earth Polychromatic Imaging Camera (EPIC); high-quality earth observation datasets; Mirrors; MODIS instruments; MODIS level 1B C6.1 dataset; MODIS reflective solar band calibration; onboard calibrators; radiometric calibration; response versus scan-angle (RVS); scan-angle calibration; Terra-MODIS
Bhatt, Rajendra; Doelling, David R.; Haney, Conor O.; Spangenberg, Douglas A.; Scarino, Benjamin R.; Gopalan, ArunBhatt, R., D. R. Doelling, C. O. Haney, D. A. Spangenberg, B. R. Scarino, A. Gopalan, 2020: Clouds and the Earth’s Radiant Energy System strategy for intercalibrating the new-generation geostationary visible imagers. Journal of Applied Remote Sensing, 14(3), 032410. doi: 10.1117/1.JRS.14.032410. The advanced baseline imager (ABI) instrument onboard Geostationary Operational Environmental Satellite (GOES)-16 is the first of National Oceanic and Atmospheric Administration (NOAA’s) new-generation geostationary earth orbiting (GEO) imagers that provides high-quality calibrated and geolocated Earth observations in six reflective solar bands (RSBs). The spectral similarity between the Visible Infrared Imaging Radiometer Suite (VIIRS) and ABI RSB offers an opportunity for deriving VIIRS-quality cloud retrievals from the ABI radiances. NASA’s Clouds and the Earth’s Radiant Energy System (CERES) project utilizes GEO imager (including ABI) radiances to retrieve clouds and derive broadband fluxes that are used to account for the regional diurnal flux variation between the CERES measurements and to convert the CERES observed radiances into fluxes. In order to derive a seamless cloud and flux datasets for CERES, it is important that the GEO, MODIS, and VIIRS imagers are all placed on the same radiometric scale. We describe an absolute radiometric intercomparison between the NOAA-20 VIIRS and GOES-16 ABI RSB using ray-matched radiance/reflectance pairs over all-sky tropical ocean scenes as well as a deep convective cloud invariant target calibration algorithm. Results indicate that the ABI and VIIRS RSB calibration are within 5%, except for the 0.47-μm band, for which the radiometric inconsistency is found to be ∼7 % . The GOES-16 radiometric scaling factors referenced to NOAA-20 VIIRS were computed from the two independent calibration methods to agree within 1% for ABI bands 1 to 4, and within 3% for bands 5 and 6. Results from this study were used to propose a future CERES GEO intercalibration algorithm referenced to NOAA-20 VIIRS, given the eventual demise of the Terra and Aqua satellites.
Bock, L.; Lauer, A.; Schlund, M.; Barreiro, M.; Bellouin, N.; Jones, C.; Meehl, G. A.; Predoi, V.; Roberts, M. J.; Eyring, V.Bock, L., A. Lauer, M. Schlund, M. Barreiro, N. Bellouin, C. Jones, G. A. Meehl, V. Predoi, M. J. Roberts, V. Eyring, 2020: Quantifying Progress Across Different CMIP Phases With the ESMValTool. Journal of Geophysical Research: Atmospheres, 125(21), e2019JD032321. doi: 10.1029/2019JD032321. More than 40 model groups worldwide are participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6), providing a new and rich source of information to better understand past, present, and future climate change. Here, we use the Earth System Model Evaluation Tool (ESMValTool) to assess the performance of the CMIP6 ensemble compared to the previous generations CMIP3 and CMIP5. While CMIP5 models did not capture the observed pause in the increase in global mean surface temperature between 1998 and 2013, the historical CMIP6 simulations agree well with the observed recent temperature increase, but some models have difficulties in reproducing the observed global mean surface temperature record of the second half of the twentieth century. While systematic biases in annual mean surface temperature and precipitation remain in the CMIP6 multimodel mean, individual models and high-resolution versions of the models show significant reductions in many long-standing biases. Some improvements are also found in the vertical temperature, water vapor, and zonal wind speed distributions, and root-mean-square errors for selected fields are generally smaller with reduced intermodel spread and higher average skill in the correlation patterns relative to observations. An emerging property of the CMIP6 ensemble is a higher effective climate sensitivity with an increased range between 2.3 and 5.6 K. A possible reason for this increase in some models is improvements in cloud representation resulting in stronger shortwave cloud feedbacks than in their predecessor versions. climate model; evaluation; CMIP
Bony, S.; Semie, A.; Kramer, R. J.; Soden, B.; Tompkins, A. M.; Emanuel, K. A.Bony, S., A. Semie, R. J. Kramer, B. Soden, A. M. Tompkins, K. A. Emanuel, 2020: Observed Modulation of the Tropical Radiation Budget by Deep Convective Organization and Lower-Tropospheric Stability. AGU Advances, 1(3), e2019AV000155. doi: 10.1029/2019AV000155. This study analyzes the observed monthly deseasonalized and detrended variability of the tropical radiation budget and suggests that variations of the lower-tropospheric stability and of the spatial organization of deep convection both strongly contribute to this variability. Satellite observations show that on average over the tropical belt, when deep convection is more aggregated, the free troposphere is drier, the deep convective cloud coverage is less extensive, and the emission of heat to space is increased; an enhanced aggregation of deep convection is thus associated with a radiative cooling of the tropics. An increase of the tropical-mean lower-tropospheric stability is also coincident with a radiative cooling of the tropics, primarily because it is associated with more marine low clouds and an enhanced reflection of solar radiation, although the free-tropospheric drying also contributes to the cooling. The contributions of convective aggregation and lower-tropospheric stability to the modulation of the radiation budget are complementary, largely independent of each other, and equally strong. Together, they account for more than sixty percent of the variance of the tropical radiation budget. Satellite observations are thus consistent with the suggestion from modeling studies that the spatial organization of deep convection substantially influences the radiative balance of the Earth. This emphasizes the importance of understanding the factors that control convective organization and lower-tropospheric stability variations, and the need to monitor their changes as the climate warms. radiation budget; tropical variability; convective organization; tropospheric stability
Bony, Sandrine; Schulz, Hauke; Vial, Jessica; Stevens, BjornBony, S., H. Schulz, J. Vial, B. Stevens, 2020: Sugar, Gravel, Fish and Flowers: Dependence of Mesoscale Patterns of Trade-wind Clouds on Environmental Conditions. Geophysical Research Letters, 47(7), e2019GL085988. doi: 10.1029/2019GL085988. Trade-wind clouds exhibit a large diversity of spatial organizations at the mesoscale. Over the tropical western Atlantic, a recent study has visually identified four prominent mesoscale patterns of shallow convection, referred to as Flowers, Fish, Gravel and Sugar. We show that these four patterns can be identified objectively from satellite observations by analyzing the spatial distribution of infrared brightness temperatures. By applying this analysis to 19 years of data, we examine relationships between cloud patterns and large-scale environmental conditions. This investigation reveals that on daily and interannual timescales, the near-surface wind speed and the strength of the lower-tropospheric stability discriminate the occurrence of the different organization patterns. These results, combined with the tight relationship between cloud patterns, low-level cloud amount and cloud-radiative effects, suggest that the mesoscale organization of shallow clouds might change under global warming. The role of shallow convective organization in determining low-cloud feedback should thus be investigated. low-cloud feedback; mesoscale organization; shallow convection; tradewind clouds
Bosilovich, Michael G.; Robertson, Franklin R.; Stackhouse, Paul W.Bosilovich, M. G., F. R. Robertson, P. W. Stackhouse, 2020: El Niño–Related Tropical Land Surface Water and Energy Response in MERRA-2. J. Climate, 33(3), 1155-1176. doi: 10.1175/JCLI-D-19-0231.1. Although El Niño events each have distinct evolutionary character, they typically provide systematic large-scale forcing for warming and increased drought frequency across the tropical continents. We assess this response in the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), reanalysis and in a 10-member-model Atmospheric Model Intercomparison Project (AMIP) ensemble. The lagged response (3–4 months) of mean tropical land temperature to El Niño warming in the Pacific Ocean is well represented. MERRA-2 reproduces the patterns of precipitation in the tropical regions, and the AMIP ensemble reproduces some regional responses that are similar to those observed and some regions that are not simulating the response well. Model skill is dependent on event forcing strength and temporal proximity to the peak of the sea surface warming. A composite approach centered on maximum Niño-3.4 SSTs and lag relationships to energy fluxes and transports is used to identify mechanisms supporting tropical land warming. The composite necessarily moderates weather-scale variability of the individual events while retaining the systematic features across all events. We find that reduced continental upward motions lead to reduced cloudiness and more shortwave radiation at the surface, as well as reduced precipitation. The increased shortwave heating at the land surface, along with reduced soil moisture, leads to warmer surface temperature, more sensible heating, and warming of the lower troposphere. The composite provides a broad picture of the mechanisms governing the hydrologic response to El Niño forcing, but the regional and temporal responses can vary substantially for any given event. The 2015/16 El Niño, one of the strongest events, demonstrates some of the forced response noted in the composite, but with shifts in the evolution that depart from the composite, demonstrating the limitations of the composite and individuality of El Niño.
Boucher, Olivier; Servonnat, Jérôme; Albright, Anna Lea; Aumont, Olivier; Balkanski, Yves; Bastrikov, Vladislav; Bekki, Slimane; Bonnet, Rémy; Bony, Sandrine; Bopp, Laurent; Braconnot, Pascale; Brockmann, Patrick; Cadule, Patricia; Caubel, Arnaud; Cheruy, Frédérique; Codron, Francis; Cozic, Anne; Cugnet, David; D'Andrea, Fabio; Davini, Paolo; Lavergne, Casimir de; Denvil, Sébastien; Deshayes, Julie; Devilliers, Marion; Ducharne, Agnès; Dufresne, Jean-Louis; Dupont, Eliott; Éthé, Christian; Fairhead, Laurent; Falletti, Lola; Flavoni, Simona; Foujols, Marie-Alice; Gardoll, Sébastien; Gastineau, Guillaume; Ghattas, Josefine; Grandpeix, Jean-Yves; Guenet, Bertrand; Guez, Lionel; Guilyardi, Éric; Guimberteau, Matthieu; Hauglustaine, Didier; Hourdin, Frédéric; Idelkadi, Abderrahmane; Joussaume, Sylvie; Kageyama, Masa; Khodri, Myriam; Krinner, Gerhard; Lebas, Nicolas; Levavasseur, Guillaume; Lévy, Claire; Li, Laurent; Lott, François; Lurton, Thibaut; Luyssaert, Sebastiaan; Madec, Gurvan; Madeleine, Jean-Baptiste; Maignan, Fabienne; Marchand, Marion; Marti, Olivier; Mellul, Lidia; Meurdesoif, Yann; Mignot, Juliette; Musat, Ionela; Ottlé, Catherine; Peylin, Philippe; Planton, Yann; Polcher, Jan; Rio, Catherine; Rochetin, Nicolas; Rousset, Clément; Sepulchre, Pierre; Sima, Adriana; Swingedouw, Didier; Thiéblemont, Rémi; Traore, Abdoul Khadre; Vancoppenolle, Martin; Vial, Jessica; Vialard, Jérôme; Viovy, Nicolas; Vuichard, NicolasBoucher, O., J. Servonnat, A. L. Albright, O. Aumont, Y. Balkanski, V. Bastrikov, S. Bekki, R. Bonnet, S. Bony, L. Bopp, P. Braconnot, P. Brockmann, P. Cadule, A. Caubel, F. Cheruy, F. Codron, A. Cozic, D. Cugnet, F. D'Andrea, P. Davini, C. d. Lavergne, S. Denvil, J. Deshayes, M. Devilliers, A. Ducharne, J. Dufresne, E. Dupont, C. Éthé, L. Fairhead, L. Falletti, S. Flavoni, M. Foujols, S. Gardoll, G. Gastineau, J. Ghattas, J. Grandpeix, B. Guenet, L. Guez, É. Guilyardi, M. Guimberteau, D. Hauglustaine, F. Hourdin, A. Idelkadi, S. Joussaume, M. Kageyama, M. Khodri, G. Krinner, N. Lebas, G. Levavasseur, C. Lévy, L. Li, F. Lott, T. Lurton, S. Luyssaert, G. Madec, J. Madeleine, F. Maignan, M. Marchand, O. Marti, L. Mellul, Y. Meurdesoif, J. Mignot, I. Musat, C. Ottlé, P. Peylin, Y. Planton, J. Polcher, C. Rio, N. Rochetin, C. Rousset, P. Sepulchre, A. Sima, D. Swingedouw, R. Thiéblemont, A. K. Traore, M. Vancoppenolle, J. Vial, J. Vialard, N. Viovy, N. Vuichard, 2020: Presentation and evaluation of the IPSL-CM6A-LR climate model. Journal of Advances in Modeling Earth Systems, 12(7), e2019MS002010. doi: 10.1029/2019MS002010. keypoints The IPSL-CM6A-LR model climatology is much improved over the previous version although some systematic biases and shortcomings persist. A long pre-industrial control and a large number of historical and scenario simulations have been performed as part of CMIP6. The effective climate sensitivity of the IPSL model increases from 4.1 to 4.8 K between IPSL-CM5A-LR and IPSL-CM6A-LR. climate model; CMIP6; climate sensitivity; climate metrics; IPSL-CM6A-LR
Brunner, Lukas; McSweeney, Carol; Ballinger, Andrew P.; Hegerl, Gabriele C.; Befort, Daniel J.; O’Reilly, Chris; Benassi, Marianna; Booth, Ben; Harris, Glen; Lowe, Jason; Coppola, Erika; Nogherotto, Rita; Knutti, Reto; Lenderink, Geert; de Vries, Hylke; Qasmi, Saïd; Ribes, Aurélien; Stocchi, Paolo; Undorf, SabineBrunner, L., C. McSweeney, A. P. Ballinger, G. C. Hegerl, D. J. Befort, C. O’Reilly, M. Benassi, B. Booth, G. Harris, J. Lowe, E. Coppola, R. Nogherotto, R. Knutti, G. Lenderink, H. de Vries, S. Qasmi, A. Ribes, P. Stocchi, S. Undorf, 2020: Comparing methods to constrain future European climate projections using a consistent framework. J. Climate, 33(20), 8671–8692. doi: 10.1175/JCLI-D-19-0953.1. Political decisions, adaptation planning, and impact assessments need reliable estimates of future climate change and related uncertainties. In order to provide these estimates, different approaches to constrain, filter, or weight climate model projections into probabilistic distributions have been proposed. However, an assessment of multiple such methods to, for example, expose cases of agreement or disagreement, is often hindered by a lack of coordination, with methods focusing on a variety of variables, time periods, regions, or model pools. Here, a consistent framework is developed to allow a quantitative comparison of eight different methods; focus is given to summer temperature and precipitation change in three spatial regimes in Europe in 2041-2060 relative to 1995-2014. The analysis draws on projections from several large ensembles, the CMIP5 multi-model ensemble, and perturbed physics ensembles, all using the high-emission scenario RCP8.5. The methods’ key features are summarized, assumptions are discussed and resulting constrained distributions are presented. Method agreement is found to be dependent on the investigated region but is generally higher for median changes than for the uncertainty ranges. This study, therefore, highlights the importance of providing clear context about how different methods affect the assessed uncertainty, particularly the upper and lower percentiles that are of interest to risk-averse stakeholders. The comparison also exposes cases where diverse lines of evidence lead to diverging constraints; additional work is needed to understand how the underlying differences between methods lead to such disagreements and to provide clear guidance to users.
Brutsaert, Wilfried; Cheng, Lei; Zhang, Lu; Brutsaert, Wilfried; Cheng, Lei; Zhang, LuBrutsaert, W., L. Cheng, L. Zhang, W. Brutsaert, L. Cheng, L. Zhang, 2020: Spatial Distribution of Global Landscape Evaporation in the Early Twenty-First Century by Means of a Generalized Complementary Approach. J. Hydrometeor., 21(2), 551–581. doi: 10.1175/JHM-D-19-0208.1. AbstractA generalized implementation of the complementary principle was applied to estimate global land surface evaporation and its spatial distribution. The single parameter in the method was cali...
Burgdorf, Martin J.; Müller, Thomas G.; Buehler, Stefan A.; Prange, Marc; Brath, ManfredBurgdorf, M. J., T. G. Müller, S. A. Buehler, M. Prange, M. Brath, 2020: Characterization of the High-Resolution Infrared Radiation Sounder Using Lunar Observations. Remote Sensing, 12(9), 1488. doi: 10.3390/rs12091488. The High-Resolution Infrared Radiation Sounder (HIRS) has been operational since 1975 on different satellites. In spite of this long utilization period, the available information about some of its basic properties is incomplete or contradictory. We have approached this problem by analyzing intrusions of the Moon in the deep space view of HIRS/2 through HIRS/4. With this method we found: (1) The diameters of the field of view of HIRS/2, HIRS/3, and HIRS/4 have the relative proportions of 1.4 ° to 1.3 ° to 0.7 ° with all channels; (2) the co-registration differs by up to 0.031 ° among the long-wave and by up to 0.015 ° among the shortwave spectral channels in the along-track direction; (3) the photometric calibration is consistent within 0.7% or less for channels 2–7 (1.2% for HIRS/2), similar values were found for channels 13–16; (4) the non-linearity of the short-wavelength channels is negligible; and (5) the contribution of reflected sunlight to the flux in the short-wavelength channels can be determined in good approximation, if the emissivity of the surface is known. calibration; surface; infrared sounder; moon
Butler, John C.Butler, J. C., 2020: CERES Gimbal Performance on Terra. Lubricants, 8(8), 79. doi: 10.3390/lubricants8080079. The Terra satellite has been operating in orbit for 20 years. The Terra satellite is also called the flagship earth-observing satellite. The two Clouds and the Earth’s Radiant Energy System CERES instruments on board continue to function nominally. Their expected mission lifetime was 7 years. Critical to their performance is the longevity of the scanning gimbals. This can be traced to the performance of the fluid-lubricated bearings. Two metrics are used to estimate their lifetime and health. Both lend themselves to readily available data and ease of interpretation. One is predicting the evaporative lubricant loss. This analysis indicates that the lubricant supply is adequate for the continual life of the gimbals. The second is trending the torque with time. Torque precursors are sampled quarterly. These data are converted to torque. Two types of torque behavior were examined. Contrasting torque data have supported the conclusion that the gimbals are operating nominally. This can be partially attributed to the design choices for the bearings and lubricant. The aim of this paper is to quantitatively describe the present health and expected life of the CERES gimbals on the Terra satellite. space vehicles; bearings; lubricant; torque
Cao, Yunfeng; Liang, Shunlin; Yu, MengCao, Y., S. Liang, M. Yu, 2020: Observed low-frequency linkage between Northern Hemisphere tropical expansion and polar vortex weakening from 1979 to 2012. Atmospheric Research, 243, 105034. doi: 10.1016/j.atmosres.2020.105034. In recent decades, the northern hemisphere (NH) atmospheric meridional circulation has experienced unprecedented changes. The NH tropical belt is significantly expanding toward high latitudes, and the Arctic polar vortex is continually weakening. Both phenomena have led to severe consequences on the Earth's surface, such as more frequent droughts in the subtropics and accelerated sea ice loss in the Arctic. However, the potential linkage between these phenomena and the underlying mechanisms have rarely been discussed. In this study, we report strong observational evidence that the NH tropical boundary and tropospheric polar vortex are synchronously changing, based on analysis of long-term satellite records from 1979 to 2012. Our investigation suggests that both the variance of the NH tropical boundary and tropospheric polar vortex from 1979 to 2012 are associated to the natural anomaly of NH mid-latitude sea surface temperature. The low-frequency sea surface temperature anomalies over the North Pacific (i.e., the Pacific Decadal Oscillation, PDO) and Atlantic (i.e., the Atlantic Multidecadal Oscillation, AMO) could explain 61% of the NH tropical boundary variance and 56% of the polar vortex variance from 1979 to 2012. Atlantic Multidecadal Oscillation; Low-frequency linkage; NH tropical expansion; Pacific Decadal Oscillation; Polar vortex weakening
Chen, Jiang; He, Tao; Jiang, Bo; Liang, ShunlinChen, J., T. He, B. Jiang, S. Liang, 2020: Estimation of all-sky all-wave daily net radiation at high latitudes from MODIS data. Remote Sensing of Environment, 245, 111842. doi: 10.1016/j.rse.2020.111842. Surface all-wave net radiation (Rn) plays an important role in various land surface processes, such as agricultural, ecological, hydrological, and biogeochemical processes. Recently, remote sensing of Rn at regional and global scales has attracted considerable attention and has achieved significant advances. However, there are many issues in estimating all-sky daily average Rn at high latitudes, such as posing greater uncertainty by surface and atmosphere satellite products at high latitudes, and unavailability of real-time and accurate cloud base height and temperature parameters. In this study, we developed the LRD (length ratio of daytime) classification model using the genetic algorithm-artificial neural network (GA-ANN) to estimate all-sky daily average Rn at high latitudes. With a very high temporal repeating frequency (~6 to 20 times per day) at high latitudes, data from the Moderate Resolution Imaging Spectroradiometer (MODIS) were used to test the proposed method. Rn measurements at 82 sites and top-of-atmosphere (TOA) data of MODIS from 2000 to 2017 were matched for model training and validation. Two models for estimating daily average Rn were developed: model I based on instantaneous daytime MODIS observation and model II based on instantaneous nighttime MODIS observation. Validation results of model I showed an R2 of 0.85, an RMSE of 23.66 W/m2, and a bias of 0.27 W/m2, whereas these values were 0.51, 15.04 W/m2, and −0.08 W/m2 for model II, respectively. Overall, the proposed machine learning algorithm with the LRD classification can accurately estimate the all-sky daily average Rn at high latitudes. Mapping of Rn over the high latitudes at 1 km spatial resolution showed a similar spatial distribution to Rn estimates from the Clouds and the Earth's Radiant Energy System (CERES) product. This method has the potential for operational monitoring of spatio-temporal change of Rn at high latitudes with a long-term coverage of MODIS observations. MODIS; Net radiation; High latitudes; High spatial resolution; Length ratio of daytime
Chen, Liang; Dirmeyer, Paul A.Chen, L., P. A. Dirmeyer, 2020: Reconciling the disagreement between observed and simulated temperature responses to deforestation. Nature Communications, 11(1), 1-10. doi: 10.1038/s41467-019-14017-0. Models show a cooler surface temperature response to deforestation than observations which has been attributed to uncertainties in the models. A comparison of satellite observations and model experiments shows that the disagreement is due to the role of atmospheric feedbacks, which are not well captured in the observational space-for-time approach.
Cherian, Ribu; Quaas, JohannesCherian, R., J. Quaas, 2020: Trends in AOD, Clouds, and Cloud Radiative Effects in Satellite Data and CMIP5 and CMIP6 Model Simulations Over Aerosol Source Regions. Geophysical Research Letters, 47(9), e2020GL087132. doi: 10.1029/2020GL087132. Several regions worldwide have seen significant trends in anthropogenic aerosol emissions during the period of detailed satellite observations since 2001. Over Europe (EUR) and North America (NAM) there were strong declines, over China increases then declines and over India, strong increases. Regional trends in model-simulated aerosol optical depth (AOD) and cloud radiative effects in both the Fifth and Sixth Coupled Model Intercomparison Projects (CMIP5 and CMIP6) are broadly consistent with the ones from satellite retrievals in most parts of EUR, NAM and India. CMIP6 models better match satellite-derived AOD trend in western NAM (increasing) and eastern China (decreasing), where CMIP5 models failed, pointing to improved anthropogenic aerosol emissions. Drop concentration trends in both observations and models qualitatively match AOD trends. The result for solar cloud radiative effect in models, however, is due to compensating errors: Models fail to reproduce observed liquid water path trends and show, in turn, opposite trends in cloud fraction. climate models; cloud radiative effects; aerosol optical depth; aerosol emission trend; aerosol source regions; CDNC
Cheruy, Frédérique; Ducharne, Agnés; Hourdin, Frédéric; Musat, Ionela; Vignon, Etienne; Gastineau, Guillaume; Bastrikov, Vladislav; Vuichard, Nicolas; Diallo, Binta; Dufresne, Jean-Louis; Ghattas, Josefine; Grandpeix, Jean-Yves; Idelkadi, Abderrahmane; Mellul, Lidia; Maignan, Fabienne; Menegoz, Martin; Ottlé, Catherine; Peylin, Philippe; Servonnat, Jérôme; Wang, Fuxing; Zhao, YanfengCheruy, F., A. Ducharne, F. Hourdin, I. Musat, E. Vignon, G. Gastineau, V. Bastrikov, N. Vuichard, B. Diallo, J. Dufresne, J. Ghattas, J. Grandpeix, A. Idelkadi, L. Mellul, F. Maignan, M. Menegoz, C. Ottlé, P. Peylin, J. Servonnat, F. Wang, Y. Zhao, 2020: Improved near surface continental climate in IPSL-CM6A-LR by combined evolutions of atmospheric and land surface physics. Journal of Advances in Modeling Earth Systems, 12(10), e2019MS002005. doi: 10.1029/2019MS002005. keypoints The representation of the land-atmosphere coupled system by the IPSL model is thoroughly evaluated. Improvements with respect to previous versions are documented in the context of the Coupled Model Intercomparison Project, CMIP. Advanced parameterization of land surface and atmospheric processes, tuning of the radiation and the turbulent mixing yielded many improvements. hydrology; climate modelling; atmosphere-land surface interactions; soil moisture; stable boundary layer; temperature bias
Cho, Heeje; Jun, Sang-Yoon; Ho, Chang-Hoi; McFarquhar, GregCho, H., S. Jun, C. Ho, G. McFarquhar, 2020: Simulations of Winter Arctic Clouds and Associated Radiation Fluxes Using Different Cloud Microphysics Schemes in the Polar WRF: Comparisons With CloudSat, CALIPSO, and CERES. Journal of Geophysical Research: Atmospheres, 125(2), e2019JD031413. doi: 10.1029/2019JD031413. Key Points Winter Arctic clouds simulated by the polar version of the Weather Research and Forecasting model are compared with satellite retrievals The cloud amount and cloud top height of model simulations agree well with those of satellite retrievals The downward longwave radiation at the surface shows realistic temporal variations, but is sensitive to the cloud microphysics scheme choice cloud microphysics; Polar WRF; satellite observation; surface radiation; winter Arctic cloud
Choi, Yong-Sang; Hwang, Jiwon; Ok, Jung; Park, Doo-Sun R.; Su, Hui; Jiang, Jonathan H.; Huang, Lei; Limpasuvan, TyChoi, Y., J. Hwang, J. Ok, D. R. Park, H. Su, J. H. Jiang, L. Huang, T. Limpasuvan, 2020: Effect of Arctic clouds on the ice-albedo feedback in midsummer. International Journal of Climatology, 40(10), 4707-4714. doi: 10.1002/joc.6469. The Arctic clouds should be an important factor that affects the summertime sea ice. By reflecting the incoming solar radiation before it reaches the surface, the Arctic clouds may prevent the surface from absorbing tremendous solar radiation due to the reduced sea ice. This cloud effect will lead to intervene the feedback relation between the solar radiation and the sea ice change. However, few studies have quantitatively investigated the Arctic cloud effect on the ice-albedo feedback. This study found that the Arctic clouds regulate the melting speed of sea ice in midsummer months (June to August) based on the data from multiple sources, that is, satellite, reanalysis, and climate models. During this period, the fraction of Arctic clouds with the net radiative cooling effect is almost invariable with sea ice reduction. However, despite of the steady cloud fraction in the midsummer months, the shortwave cloud radiative effect (total-sky minus clear-sky absorbed shortwave radiation) was found to significantly increase with the reduced sea ice concentration (0.64 W m−2%−1 in CERES, 0.73 W m−2%−1 in ERA5). This is because the clouds present more contrast of albedo with the sea ice-free ocean than the sea ice-covered ocean. Finally, our analyses show that the Arctic clouds are nearly halving the strength of the ice-albedo feedback in the midsummer months. These results imply that the sea ice reduction could have been much faster in the past decades in the absence of the cloud effect found here. Arctic clouds; Arctic Sea ice; cloud effect; ice-albedo feedback; midsummer
Christensen, Matthew W.; Jones, William K.; Stier, PhilipChristensen, M. W., W. K. Jones, P. Stier, 2020: Aerosols enhance cloud lifetime and brightness along the stratus-to-cumulus transition. Proceedings of the National Academy of Sciences, 117(30), 17591-17598. doi: 10.1073/pnas.1921231117. Anthropogenic aerosols are hypothesized to enhance planetary albedo and offset some of the warming due to the buildup of greenhouse gases in Earth’s atmosphere. Aerosols can enhance the coverage, reflectance, and lifetime of warm low-level clouds. However, the relationship between cloud lifetime and aerosol concentration has been challenging to measure from polar orbiting satellites. We estimate two timescales relating to the formation and persistence of low-level clouds over 1○×1○1○×1○1○×1○ spatial domains using multiple years of geostationary satellite observations provided by the Clouds and Earth’s Radiant Energy System (CERES) Synoptic (SYN) product. Lagrangian trajectories spanning several days along the classic stratus-to-cumulus transition zone are stratified by aerosol optical depth and meteorology. Clouds forming in relatively polluted trajectories tend to have lighter precipitation rates, longer average lifetime, and higher cloud albedo and cloud fraction compared with unpolluted trajectories. While liquid water path differences are found to be negligible, we find direct evidence of increased planetary albedo primarily through increased drop concentration (NdNdNd) and cloud fraction, with the caveat that the aerosol influence on cloud fraction is positive only for stable atmospheric conditions. While the increase in cloud fraction can be large typically in the beginning of trajectories, the Twomey effect accounts for the bulk (roughly 3/4) of the total aerosol indirect radiative forcing estimate. clouds; aerosols; radiative forcing
Clerbaux, Nicolas; Akkermans, Tom; Baudrez, Edward; Velazquez Blazquez, Almudena; Moutier, William; Moreels, Johan; Aebi, ChristineClerbaux, N., T. Akkermans, E. Baudrez, A. Velazquez Blazquez, W. Moutier, J. Moreels, C. Aebi, 2020: The Climate Monitoring SAF Outgoing Longwave Radiation from AVHRR. Remote Sensing, 12(6), 929. doi: 10.3390/rs12060929. Data from the Advanced Very High Resolution Radiometer (AVHRR) have been used to create several long-duration data records of geophysical variables describing the atmosphere and land and water surfaces. In the Climate Monitoring Satellite Application Facility (CM SAF) project, AVHRR data are used to derive the Cloud, Albedo, and Radiation (CLARA) climate data records of radiation components (i.a., surface albedo) and cloud properties (i.a., cloud cover). This work describes the methodology implemented for the additional estimation of the Outgoing Longwave Radiation (OLR), an important Earth radiation budget component, that is consistent with the other CLARA variables. A first step is the estimation of the instantaneous OLR from the AVHRR observations. This is done by regressions on a large database of collocated observations between AVHRR Channel 4 (10.8 µm) and 5 (12 µm) and the OLR from the Clouds and Earth’s Radiant Energy System (CERES) instruments. We investigate the applicability of this method to the first generation of AVHRR instrument (AVHRR/1) for which no Channel 5 observation is available. A second step concerns the estimation of daily and monthly OLR from the instantaneous AVHRR overpasses. This step is especially important given the changes in the local time of the observations due to the orbital drift of the NOAA satellites. We investigate the use of OLR in the ERA5 reanalysis to estimate the diurnal variation. The developed approach proves to be valuable to model the diurnal change in OLR due to day/night time warming/cooling over clear land. Finally, the resulting monthly mean AVHRR OLR product is intercompared with the CERES monthly mean product. For a typical configuration with one morning and one afternoon AVHRR observation, the Root Mean Square (RMS) difference with CERES monthly mean OLR is about 2 Wm−2 at 1° × 1° resolution. We quantify the degradation of the OLR product when only one AVHRR instrument is available (as is the case for some periods in the 1980s) and also the improvement when more instruments are available (e.g., using METOP-A, NOAA-15, NOAA-18, and NOAA-19 in 2012). The degradation of the OLR product from AVHRR/1 instruments is also quantified, which is done by “masking” the Channel 5 observations. broadband; CERES; AVHRR; outgoing longwave radiation; flux; OLR; TOA
Colón Robles, Marilé; Amos, Helen M.; Dodson, J. Brant; Bouwman, Jeffrey; Rogerson, Tina; Bombosch, Annette; Farmer, Lauren; Burdick, Autumn; Taylor, Jessica; Chambers, Lin H.Colón Robles, M., H. M. Amos, J. B. Dodson, J. Bouwman, T. Rogerson, A. Bombosch, L. Farmer, A. Burdick, J. Taylor, L. H. Chambers, 2020: Clouds around the World: How a Simple Citizen Science Data Challenge Became a Worldwide Success. Bull. Amer. Meteor. Soc., 101(7), E1201-E1213. doi: 10.1175/BAMS-D-19-0295.1.
Danabasoglu, G.; Lamarque, J.-F.; Bacmeister, J.; Bailey, D. A.; DuVivier, A. K.; Edwards, J.; Emmons, L. K.; Fasullo, J.; Garcia, R.; Gettelman, A.; Hannay, C.; Holland, M. M.; Large, W. G.; Lauritzen, P. H.; Lawrence, D. M.; Lenaerts, J. T. M.; Lindsay, K.; Lipscomb, W. H.; Mills, M. J.; Neale, R.; Oleson, K. W.; Otto‐Bliesner, B.; Phillips, A. S.; Sacks, W.; Tilmes, S.; Kampenhout, L. van; Vertenstein, M.; Bertini, A.; Dennis, J.; Deser, C.; Fischer, C.; Fox‐Kemper, B.; Kay, J. E.; Kinnison, D.; Kushner, P. J.; Larson, V. E.; Long, M. C.; Mickelson, S.; Moore, J. K.; Nienhouse, E.; Polvani, L.; Rasch, P. J.; Strand, W. G.Danabasoglu, G., J. Lamarque, J. Bacmeister, D. A. Bailey, A. K. DuVivier, J. Edwards, L. K. Emmons, J. Fasullo, R. Garcia, A. Gettelman, C. Hannay, M. M. Holland, W. G. Large, P. H. Lauritzen, D. M. Lawrence, J. T. M. Lenaerts, K. Lindsay, W. H. Lipscomb, M. J. Mills, R. Neale, K. W. Oleson, B. Otto‐Bliesner, A. S. Phillips, W. Sacks, S. Tilmes, L. v. Kampenhout, M. Vertenstein, A. Bertini, J. Dennis, C. Deser, C. Fischer, B. Fox‐Kemper, J. E. Kay, D. Kinnison, P. J. Kushner, V. E. Larson, M. C. Long, S. Mickelson, J. K. Moore, E. Nienhouse, L. Polvani, P. J. Rasch, W. G. Strand, 2020: The Community Earth System Model Version 2 (CESM2). Journal of Advances in Modeling Earth Systems, 12(2), e2019MS001916. doi: 10.1029/2019MS001916. An overview of the Community Earth System Model Version 2 (CESM2) is provided, including a discussion of the challenges encountered during its development and how they were addressed. In addition, an evaluation of a pair of CESM2 long preindustrial control and historical ensemble simulations is presented. These simulations were performed using the nominal 1° horizontal resolution configuration of the coupled model with both the “low-top” (40 km, with limited chemistry) and “high-top” (130 km, with comprehensive chemistry) versions of the atmospheric component. CESM2 contains many substantial science and infrastructure improvements and new capabilities since its previous major release, CESM1, resulting in improved historical simulations in comparison to CESM1 and available observations. These include major reductions in low-latitude precipitation and shortwave cloud forcing biases; better representation of the Madden-Julian Oscillation; better El Niño-Southern Oscillation-related teleconnections; and a global land carbon accumulation trend that agrees well with observationally based estimates. Most tropospheric and surface features of the low- and high-top simulations are very similar to each other, so these improvements are present in both configurations. CESM2 has an equilibrium climate sensitivity of 5.1–5.3 °C, larger than in CESM1, primarily due to a combination of relatively small changes to cloud microphysics and boundary layer parameters. In contrast, CESM2's transient climate response of 1.9–2.0 °C is comparable to that of CESM1. The model outputs from these and many other simulations are available to the research community, and they represent CESM2's contributions to the Coupled Model Intercomparison Project Phase 6. Community Earth System Model (CESM); coupled model development and evaluation; global coupled Earth system modeling; preindustrial and historical simulations
Devasthale, Abhay; Sedlar, Joseph; Tjernström, Michael; Kokhanovsky, AlexanderDevasthale, A., J. Sedlar, M. Tjernström, A. Kokhanovsky, 2020: A Climatological Overview of Arctic Clouds. Physics and Chemistry of the Arctic Atmosphere, 331-360. The Arctic climate system is complex and clouds are one of its least understood components. Since cloud processes occur from micrometer to synoptic scales, their couplings with the other components of the Arctic climate system and their overall role in modulating the energy budget at different spatio-temporal scales is challenging to quantify. The in-situ measurements, as limited in space and time as they are, still reveal the complex nature of cloud microphysical and thermodynamical processes in the Arctic. However, the synoptic scale variability of cloud systems can only be obtained from the satellite observations. A considerable progress has been made in the last decade in understanding cloud processes in the Arctic due to the availability of valuable data from the multiple campaigns in the Central Arctic and due to the advances in the satellite remote sensing. This chapter provides an overview of this progress.First an overview of the lessons learned from the recent in-situ measurement campaigns in the Arctic is provided. In particular, the importance of supercooled liquid water clouds, their role in the radiation budget and their interaction with the vertical thermodynamical structure is discussed. In the second part of the chapter, a climatological overview of cloud properties using the state-of-the-art satellite based cloud climate datasets is provided. The agreements and disagreements in these datasets are highlighted. The third and the fourth parts of the chapter highlight two most important processes that are currently being researched, namely cloud response to the rapidly changing sea-ice extent and the role of moisture transport in to the Arctic in governing cloud variability. Both of these processes have implications for the cloud feedback in the Arctic. Arctic clouds; Arctic sea-ice; Climate data records; Cloud properties; Cloud variability; Moisture transport; Satellite remote sensing; Supercooled liquid clouds; Surface radiation budget; Thermodynamic structure
Diamond, Michael S.; Director, Hannah M.; Eastman, Ryan; Possner, Anna; Wood, RobertDiamond, M. S., H. M. Director, R. Eastman, A. Possner, R. Wood, 2020: Substantial Cloud Brightening From Shipping in Subtropical Low Clouds. AGU Advances, 1(1), e2019AV000111. doi: 10.1029/2019AV000111. The influence of aerosol particles on cloud reflectivity remains one of the largest sources of uncertainty in our understanding of anthropogenic climate change. Commercial shipping constitutes a large and concentrated aerosol perturbation in a meteorological regime where clouds have a disproportionally large effect on climate. Yet, to date, studies have been unable to detect climatologically relevant cloud radiative effects from shipping, despite models indicating that the cloud response should produce a sizable negative radiative forcing (perturbation to Earth's energy balance). We attribute a significant increase in cloud reflectivity to enhanced cloud droplet number concentrations within a major shipping corridor in the southeast Atlantic. Prevailing winds constrain emissions around the corridor, which cuts through a climatically important region of expansive low cloud cover. We use universal kriging, a classic geostatistical method, to estimate what cloud properties would have been in the absence of shipping. In the morning, cloud brightening is consistent with changes in microphysics alone, whereas in the afternoon, increases in cloud brightness from microphysical changes are offset by decreases in the total amount of cloud water. We calculate an effective radiative forcing within the southeast Atlantic shipping corridor of approximately −2 W/m2. Several years of data are required to identify a clear signal. Extrapolating our results globally, we calculate an effective radiative forcing due to aerosol-cloud interactions in low clouds of −1.0 W/m2 (95% confidence interval: −1.6 to −0.4 W/m2). The unique setup in the southeast Atlantic could be an ideal test for the representation of aerosol-cloud interactions in climate models. cloud; aerosol; radiative forcing; climate; shipping
Dolinar, Erica K.; Campbell, James R.; Lolli, Simone; Ozog, Scott C.; Yorks, John E.; Camacho, Christopher; Gu, Yu; Bucholtz, Anthony; McGill, Matthew J.Dolinar, E. K., J. R. Campbell, S. Lolli, S. C. Ozog, J. E. Yorks, C. Camacho, Y. Gu, A. Bucholtz, M. J. McGill, 2020: Sensitivities in Satellite Lidar-derived Estimates of Daytime Top-of-the-Atmosphere Optically-Thin Cirrus Cloud Radiative Forcing: A Case Study. Geophysical Research Letters, 47(17), e2020GL088871. doi: 10.1029/2020GL088871. An optically-thin cirrus cloud was profiled concurrently with nadir-pointing 1064 nm lidars on 11 August 2017 over eastern Texas, including NASA's airborne Cloud Physics Lidar (CPL) and space-borne Clouds and Aerosol Transport System (CATS) instruments. Despite resolving fewer (37% vs 94%) and denser (i.e., more emissive) clouds (average cloud optical depth of 0.10 vs 0.03, respectively), CATS data render a near-equal estimate of the top-of-atmosphere (TOA) net cloud radiative forcing (CRF) versus CPL. The sample-relative TOA net CRF solved from CPL is 1.39 W/m2, which becomes 1.32 W/m2 after normalizing by occurrence frequency. Since CATS overestimates extinction for this case, the sample-relative TOA net forcing is 3.0 W/m2 larger than CPL, with the absolute value reduced to within 0.3 W/m2 of CPL due its underestimation of cloud occurrence. We discuss the ramifications of thin cirrus cloud detectability from satellite and its impact on attempts at TOA CRF closure. cloud radiative forcing; cirrus cloud; radiative transfer model; cirrus cloud detection and retrieval; satellite lidar
Donohoe, Aaron; Armour, Kyle C.; Roe, Gerard H.; Battisti, David S.; Hahn, LilyDonohoe, A., K. C. Armour, G. H. Roe, D. S. Battisti, L. Hahn, 2020: The Partitioning of Meridional Heat Transport from the Last Glacial Maximum to CO2 Quadrupling in Coupled Climate Models. J. Climate, 33(10), 4141-4165. doi: 10.1175/JCLI-D-19-0797.1. Meridional heat transport (MHT) is analyzed in ensembles of coupled climate models simulating climate states ranging from the Last Glacial Maximum (LGM) to quadrupled CO2. MHT is partitioned here into atmospheric (AHT) and implied oceanic (OHT) heat transports. In turn, AHT is partitioned into dry and moist energy transport by the meridional overturning circulation (MOC), transient eddy energy transport (TE), and stationary eddy energy transport (SE) using only monthly averaged model output that is typically archived. In all climate models examined, the maximum total MHT (AHT + OHT) is nearly climate-state invariant, except for a modest (4%, 0.3 PW) enhancement of MHT in the Northern Hemisphere (NH) during the LGM. However, the partitioning of MHT depends markedly on the climate state, and the changes in partitioning differ considerably among different climate models. In response to CO2 quadrupling, poleward implied OHT decreases, while AHT increases by a nearly compensating amount. The increase in annual-mean AHT is a smooth function of latitude but is due to a spatially inhomogeneous blend of changes in SE and TE that vary by season. During the LGM, the increase in wintertime SE transport in the NH midlatitudes exceeds the decrease in TE resulting in enhanced total AHT. Total AHT changes in the Southern Hemisphere (SH) are not significant. These results suggest that the net top-of-atmosphere radiative constraints on total MHT are relatively invariant to climate forcing due to nearly compensating changes in absorbed solar radiation and outgoing longwave radiation. However, the partitioning of MHT depends on detailed regional and seasonal factors.
Donohoe, Aaron; Blanchard-Wrigglesworth, Ed; Schweiger, Axel; Rasch, Philip J.Donohoe, A., E. Blanchard-Wrigglesworth, A. Schweiger, P. J. Rasch, 2020: The Effect of Atmospheric Transmissivity on Model and Observational Estimates of the Sea Ice Albedo Feedback. J. Climate, 33(13), 5743-5765. doi: 10.1175/JCLI-D-19-0674.1.
Donohoe, Aaron; Dawson, Eliza; McMurdie, Lynn; Battisti, David S.; Rhines, AndyDonohoe, A., E. Dawson, L. McMurdie, D. S. Battisti, A. Rhines, 2020: Seasonal Asymmetries in the Lag between Insolation and Surface Temperature. J. Climate, 33(10), 3921-3945. doi: 10.1175/JCLI-D-19-0329.1. We analyze the temporal structure of the climatological seasonal cycle in surface air temperature across the globe. We find that, over large regions of Earth, the seasonal cycle of surface temperature departs from an annual harmonic: the duration of fall and spring differ by as much as 2 months. We characterize this asymmetry by the metric ASYM, defined as the phase lag of the seasonal maximum temperature relative to the summer solstice minus the phase lag of the seasonal minimum temperature relative to winter solstice. We present a global analysis of ASYM from weather station data and atmospheric reanalysis and find that ASYM is well represented in the reanalysis. ASYM generally features positive values over land and negative values over the ocean, indicating that spring has a longer duration over the land domain whereas fall has a longer duration over the ocean. However, ASYM also features more positive values over North America compared to Europe and negative values in the polar regions over ice sheets and sea ice. Understanding the root cause of the climatological ASYM will potentially further our understanding of controls on the seasonal cycle of temperature and its future/past changes. We explore several candidate mechanisms to explain the spatial structure of ASYM including 1) modification of the seasonal cycle of surface solar radiation by the seasonal evolution of cloud thickness, 2) differences in the seasonal cycle of the atmospheric boundary layer depth over ocean and over land, and 3) temperature advection by the seasonally evolving atmospheric circulation.
Duncan, Bryan N.; Ott, Lesley E.; Abshire, James B.; Brucker, Ludovic; Carroll, Mark L.; Carton, James; Comiso, Josefino C.; Dinnat, Emmanuel P.; Forbes, Bruce C.; Gonsamo, Alemu; Gregg, Watson W.; Hall, Dorothy K.; Ialongo, Iolanda; Jandt, Randi; Kahn, Ralph A.; Karpechko, Alexey; Kawa, Stephan R.; Kato, Seiji; Kumpula, Timo; Kyrölä, Erkki; Loboda, Tatiana V.; McDonald, Kyle C.; Montesano, Paul M.; Nassar, Ray; Neigh, Christopher S. R.; Parkinson, Claire L.; Poulter, Benjamin; Pulliainen, Jouni; Rautiainen, Kimmo; Rogers, Brendan M.; Rousseaux, Cecile S.; Soja, Amber J.; Steiner, Nicholas; Tamminen, Johanna; Taylor, Patrick C.; Tzortziou, Maria A.; Virta, Henrik; Wang, James S.; Watts, Jennifer D.; Winker, David M.; Wu, Dong L.Duncan, B. N., L. E. Ott, J. B. Abshire, L. Brucker, M. L. Carroll, J. Carton, J. C. Comiso, E. P. Dinnat, B. C. Forbes, A. Gonsamo, W. W. Gregg, D. K. Hall, I. Ialongo, R. Jandt, R. A. Kahn, A. Karpechko, S. R. Kawa, S. Kato, T. Kumpula, E. Kyrölä, T. V. Loboda, K. C. McDonald, P. M. Montesano, R. Nassar, C. S. R. Neigh, C. L. Parkinson, B. Poulter, J. Pulliainen, K. Rautiainen, B. M. Rogers, C. S. Rousseaux, A. J. Soja, N. Steiner, J. Tamminen, P. C. Taylor, M. A. Tzortziou, H. Virta, J. S. Wang, J. D. Watts, D. M. Winker, D. L. Wu, 2020: Space-Based Observations for Understanding Changes in the Arctic-Boreal Zone. Reviews of Geophysics, 58(1), e2019RG000652. doi: 10.1029/2019RG000652. Observations taken over the last few decades indicate that dramatic changes are occurring in the Arctic-Boreal Zone (ABZ), which are having significant impacts on ABZ inhabitants, infrastructure, flora and fauna, and economies. While suitable for detecting overall change, the current capability is inadequate for systematic monitoring and for improving process-based and large-scale understanding of the integrated components of the ABZ, which includes the cryosphere, biosphere, hydrosphere, and atmosphere. Such knowledge will lead to improvements in Earth system models, enabling more accurate prediction of future changes and development of informed adaptation and mitigation strategies. In this article, we review the strengths and limitations of current space-based observational capabilities for several important ABZ components and make recommendations for improving upon these current capabilities. We recommend an interdisciplinary and stepwise approach to develop a comprehensive ABZ Observing Network (ABZ-ON), beginning with an initial focus on observing networks designed to gain process-based understanding for individual ABZ components and systems that can then serve as the building blocks for a comprehensive ABZ-ON. Arctic; satellite; Arctic-Boreal Zone; Boreal; Observing Strategy
Dunne, J. P.; Horowitz, L. W.; Adcroft, A. J.; Ginoux, P.; Held, I. M.; John, J. G.; Krasting, J. P.; Malyshev, S.; Naik, V.; Paulot, F.; Shevliakova, E.; Stock, C. A.; Zadeh, N.; Balaji, V.; Blanton, C.; Dunne, K. A.; Dupuis, C.; Durachta, J.; Dussin, R.; Gauthier, P. P. G.; Griffies, S. M.; Guo, H.; Hallberg, R. W.; Harrison, M.; He, J.; Hurlin, W.; McHugh, C.; Menzel, R.; Milly, P. C. D.; Nikonov, S.; Paynter, D. J.; Ploshay, J.; Radhakrishnan, A.; Rand, K.; Reichl, B. G.; Robinson, T.; Schwarzkopf, D. M.; Sentman, L. T.; Underwood, S.; Vahlenkamp, H.; Winton, M.; Wittenberg, A. T.; Wyman, B.; Zeng, Y.; Zhao, M.Dunne, J. P., L. W. Horowitz, A. J. Adcroft, P. Ginoux, I. M. Held, J. G. John, J. P. Krasting, S. Malyshev, V. Naik, F. Paulot, E. Shevliakova, C. A. Stock, N. Zadeh, V. Balaji, C. Blanton, K. A. Dunne, C. Dupuis, J. Durachta, R. Dussin, P. P. G. Gauthier, S. M. Griffies, H. Guo, R. W. Hallberg, M. Harrison, J. He, W. Hurlin, C. McHugh, R. Menzel, P. C. D. Milly, S. Nikonov, D. J. Paynter, J. Ploshay, A. Radhakrishnan, K. Rand, B. G. Reichl, T. Robinson, D. M. Schwarzkopf, L. T. Sentman, S. Underwood, H. Vahlenkamp, M. Winton, A. T. Wittenberg, B. Wyman, Y. Zeng, M. Zhao, 2020: The GFDL Earth System Model version 4.1 (GFDL-ESM 4.1): Overall coupled model description and simulation characteristics. Journal of Advances in Modeling Earth Systems, 12(11), e2019MS002015. doi: 10.1029/2019MS002015. Key Points: A new coupled chemistry-carbon-climate Earth system model has been developed at the Geophysical Fluid Dynamics Laboratory. This model unifies component advances in chemistry, carbon, and ecosystem comprehensiveness within a single coupled climate framework. This model features much improved climate mean patterns and variability from previous chemistry and carbon coupled models. Earth System Model; Biogeochemistry; Climate Model
Feng, Huihui; Ye, Shuchao; Zou, BinFeng, H., S. Ye, B. Zou, 2020: Contribution of vegetation change to the surface radiation budget: A satellite perspective. Global and Planetary Change, 192, 103225. doi: 10.1016/j.gloplacha.2020.103225. The surface radiation budget is of crucial importance to ecosystem evolution but varies with complex atmospheric and surface conditions. Vegetation change alters the surface thermal properties and the subsequent radiation budget; however, the vegetation contribution is difficult to isolate from mixed influences. Based on satellite observations, we apply a novel trajectory-based approach to detect the impact of vegetation change on the global surface radiation variation in recent decades (2001–2016). Satellite data on radiation and vegetation available from the Clouds and the Earth's Radiant Energy System (CERES) and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments are adopted for this investigation. Methodologically, the surface net radiation (Rn) in the nonchanged vegetation trajectory represents the synthetic result of atmospheric influences and serves as a reference for isolating Rn variations due to vegetation change. The results demonstrate that the multiyear mean of global Rn is 71.57 W·m−2 with an increasing trend of 0.053 W·m−2·yr−1. Vegetation change contributes an additional 0.047 W·m−2·yr−1 of radiation in greening regions, accounting for 53.36% of the total increase in Rn. Spatially, the contribution of vegetation presents significant variability, with positive contributions located mainly in western Europe and southern Africa and negative contributions located mainly in parts of Asia and eastern Australia. Physically, the influence of vegetation change on the surface radiation budget originates from its alteration of albedo and emissivity, particularly the former. Specifically, a 1% increase in the normalized difference vegetation index (NDVI) is expected to reduce albedo by −0.003 and increase surface net shortwave radiation by 0.86 W·m−2. It can be concluded that the change in albedo by vegetation change has a nonnegligible influence on the surface radiation budget in different regions. These results help capture the physical mechanism responsible for the evolution of Earth's radiation and support environmental management. Satellite; Surface radiation budget; Climate; Globe; Vegetation change
Fiedler, Stephanie; Crueger, Traute; D’Agostino, Roberta; Peters, Karsten; Becker, Tobias; Leutwyler, David; Paccini, Laura; Burdanowitz, Jörg; Buehler, Stefan A.; Cortes, Alejandro Uribe; Dauhut, Thibaut; Dommenget, Dietmar; Fraedrich, Klaus; Jungandreas, Leonore; Maher, Nicola; Naumann, Ann Kristin; Rugenstein, Maria; Sakradzija, Mirjana; Schmidt, Hauke; Sielmann, Frank; Stephan, Claudia; Timmreck, Claudia; Zhu, Xiuhua; Stevens, BjornFiedler, S., T. Crueger, R. D’Agostino, K. Peters, T. Becker, D. Leutwyler, L. Paccini, J. Burdanowitz, S. A. Buehler, A. U. Cortes, T. Dauhut, D. Dommenget, K. Fraedrich, L. Jungandreas, N. Maher, A. K. Naumann, M. Rugenstein, M. Sakradzija, H. Schmidt, F. Sielmann, C. Stephan, C. Timmreck, X. Zhu, B. Stevens, 2020: Simulated Tropical Precipitation Assessed Across Three Major Phases of the Coupled Model Intercomparison Project (CMIP). Mon. Wea. Rev., 148(9), 3653–368. doi: 10.1175/MWR-D-19-0404.1. The representation of tropical precipitation is evaluated across three generations of models participating in the Coupled Model Intercomparison Project (CMIP), phases 3, 5 and 6. Compared to state-of-the-art observations, improvements in tropical precipitation in the CMIP6 models are identified for some metrics, but we find no general improvement in tropical precipitation on different temporal and spatial scales. Our results indicate overall little changes across the CMIP phases for the summer monsoons, the double-ITCZ bias and the diurnal cycle of tropical precipitation. We find a reduced amount of drizzle events in CMIP6, but tropical precipitation occurs still too frequently. Continuous improvements across the CMIP phases are identified for the number of consecutive dry days, the representation of modes of variability, namely the Madden-Julian Oscillation and the El Niño Southern Oscillation, as well as the trends in dry months in the 20th century. The observed positive trend in extreme wet months is, however, not captured by any of the CMIP phases, which simulate negative trends for extremely wet months in the 20th century. The regional biases are larger than a climate-change signal one hopes to use the models to identify. Given the pace of climate change as compared to the pace of model improvements to simulate tropical precipitation, we question the past strategy of the development of the present class of global climate models as the mainstay of the scientific response to climate change. We suggest to explore alternative approaches such as high-resolution storm-resolving models that can offer better prospects to inform us about how tropical precipitation might change with anthropogenic warming.
Fielding, Mark D.; Schäfer, Sophia A. K.; Hogan, Robin J.; Forbes, Richard M.Fielding, M. D., S. A. K. Schäfer, R. J. Hogan, R. M. Forbes, 2020: Parameterizing cloud geometry and its application in a subgrid cloud edge erosion scheme. Quarterly Journal of the Royal Meteorological Society, 146(729), 1651-1667. doi: 10.1002/qj.3758. To represent the effects of unresolved cloud processes in numerical weather prediction and climate models, parameterizations of the subgrid properties of clouds are required. In this paper, we describe a method for specifying the ‘cloud edge length’ within a model grid-box, which is an important parameter for approximating the subgrid mixing of air at cloud boundaries. We begin by proposing three conceptual models that predict the cloud edge length using the grid-box cloud fraction and a length scale to be derived empirically. The conceptual models are then evaluated using a wide range of observations and cloud-resolving models. Based on the finding that the ‘effective cloud spacing’ approach fits both these data best, we parameterize the effective cloud spacing as a function of pressure and model resolution. An application of this parameterization to the cloud erosion scheme in the ECMWF forecast model is then demonstrated. The effective cloud spacing approach is compared to the ‘effective cloud scale’ approach and is shown to increase cloud fraction in stratocumulus regions, while decreasing cloud fraction in cumulus regions. These cloud changes have the overall effect of decreasing the error of the modelled top-of-atmosphere net shortwave irradiance when compared to CERES observations by around 3%. Additionally, the cloud edge length is an important parameter for approximating subgrid radiative transfer and it is hoped that this parameterization will be useful to quantify the effect of representing 3D cloud radiative transfer in global models. This article is protected by copyright. All rights reserved. cloud perimeter; cloud structure; subgrid parameterization; turbulent mixing
Fiolleau, Thomas; Roca, Rémy; Cloché, Sophie; Bouniol, Dominique; Raberanto, PatrickFiolleau, T., R. Roca, S. Cloché, D. Bouniol, P. Raberanto, 2020: Homogenization of Geostationary Infrared Imager Channels for Cold Cloud Studies Using Megha-Tropiques/ScaRaB. IEEE Transactions on Geoscience and Remote Sensing, 58(9), 6609-6622. doi: 10.1109/TGRS.2020.2978171. Infrared (IR) observations from the fleet of multiagencies meteorological geostationary satellites have a great potential to support scientific and operational investigations at a quasi-global scale. In particular, such a data record, defined as the GEOring data set, is well suited to document the tropical convective systems life cycles by applying cloud tracking algorithms. Yet, this GEOring data set is far from being homogeneous, preventing the realization of its potential. A number of sources of inhomogeneities are identified ranging from spatiotemporal resolutions to spectral characteristics of the IR channels and calibration methodologies. While previous efforts have attempted to correct such issues, the adjustment of the cold part of the IR spectrum remains unfit for cold cloud studies. Here, a processing method is introduced to minimize the inhomogeneities against a reference observational data set from the Scanner for Radiation Budget (ScaRaB) instrument onboard the Megha-Tropiques satellite. The method relies on the collocations between the geostationary observations and the reference. The techniques exhibit significant sensitivity to the selection of the relevant pairs of observations requiring a dedicated filtering of the data. A second effort is then proposed to account for the limb-darkening effect and a method is developed to correct the brightness temperature (BT) dependence on the geostationary viewing zenith angle (VZA). Overall, results show a residual after the processing of 0 K between any of the geostationary data and the ScaRaB reference. The final calibrated and limb-adjusted IR observations are then homogeneous for cold BT lower than 240 K with a standard deviation lower than 1.5 K throughout the GEOring. calibration; clouds; infrared imaging; Satellites; atmospheric radiation; atmospheric techniques; Instruments; atmospheric measuring apparatus; convection; geostationary satellites; Temperature measurement; Spatial resolution; Satellite broadcasting; remote sensing; Clouds; atmospheric humidity; Calibration; Calibration and spectral corrections; cloud tracking algorithms; cold cloud studies; data record; final calibrated limb-adjusted IR observations; GEOring data set; geostationary data; geostationary infrared imager channels; geostationary observations; geostationary viewing zenith angle; homogenization; infrared (IR) image sensors; inhomogeneities; IR channels; IR spectrum; limb-darkening corrections; Megha-Tropiques satellite; meteorology; multiagencies meteorological geostationary satellites; operational investigations; quasiglobal scale; Radiation Budget instrument; reference observational data; ScaRaB reference; scientific investigations; tropical convective systems life cycles
Foster, M. J.; Di Girolamo, L.; Frey, R. A.; Heidinger, A. K.; Phillips, C.; Menzel, W.P.; Zhao, G.Foster, M. J., L. Di Girolamo, R. A. Frey, A. K. Heidinger, C. Phillips, W. Menzel, G. Zhao, 2020: Global Cloudiness [in “State of the Climate in 2019”].. Bull. Amer. Meteor. Soc, 101(8), S51-53. doi: 10.1175/2020BAMSStateoftheClimate.1..
Fountoukis, Christos; Harshvardhan, Harshvardhan; Gladich, Ivan; Ackermann, Luis; Ayoub, Mohammed A.Fountoukis, C., H. Harshvardhan, I. Gladich, L. Ackermann, M. A. Ayoub, 2020: Anatomy of a severe dust storm in the middle east: Impacts on aerosol optical properties and radiation budget. Aerosol and Air Quality Research, 20(1), 155-165. doi: 10.4209/aaqr.2019.04.0165.
Fowler, Laura D.; Barth, Mary C.; Alapaty, KiranFowler, L. D., M. C. Barth, K. Alapaty, 2020: Impact of scale-aware deep convection on the cloud liquid and ice water paths and precipitation using the Model for Prediction Across Scales (MPAS-v5.2). Geoscientific Model Development, 13(6), 2851-2877. doi: https://doi.org/10.5194/gmd-13-2851-2020. Abstract. The cloud liquid water path (LWP), ice water path (IWP), and precipitation simulated with uniform- and variable-resolution numerical experiments using the Model for Prediction Across Scales (MPAS) are compared against Clouds and the Earth's Radiant Energy System (CERES) and Tropical Rainfall Measuring Mission data. Our comparison between monthly-mean model diagnostics and satellite data focuses on the convective activity regions of the tropical Pacific Ocean, extending from the Tropical Eastern Pacific Basin where trade wind boundary layer clouds develop to the Western Pacific Warm Pool characterized by deep convective updrafts capped with extended upper-tropospheric ice clouds. Using the scale-aware Grell–Freitas (GF) and Multi-scale Kain–Fritsch (MSKF) convection schemes in conjunction with the Thompson cloud microphysics, uniform-resolution experiments produce large biases between simulated and satellite-retrieved LWP, IWP, and precipitation. Differences in the treatment of shallow convection lead the LWP to be strongly overestimated when using GF, while being in relatively good agreement when using MSKF compared to CERES data. Over areas of deep convection, uniform- and variable-resolution experiments overestimate the IWP with both MSKF and GF, leading to strong biases in the top-of-the-atmosphere longwave and shortwave radiation relative to satellite-retrieved data. Mesh refinement over the Western Pacific Warm Pool does not lead to significant improvement in the LWP, IWP, and precipitation due to increased grid-scale condensation and upward vertical motions. Results underscore the importance of evaluating clouds, their optical properties, and the top-of-the-atmosphere radiation budget in addition to precipitation when performing mesh refinement global simulations.
Francis, Diana; Chaboureau, Jean-Pierre; Nelli, Narendra; Cuesta, Juan; Alshamsi, Noor; Temimi, Marouane; Pauluis, Olivier; Xue, LulinFrancis, D., J. Chaboureau, N. Nelli, J. Cuesta, N. Alshamsi, M. Temimi, O. Pauluis, L. Xue, 2020: Summertime dust storms over the Arabian Peninsula and impacts on radiation, circulation, cloud development and rain. Atmospheric Research, 105364. doi: 10.1016/j.atmosres.2020.105364. This study investigates the underlying atmospheric dynamics associated with intense dust storms in summer 2018 over the Arabian Peninsula (AP); a major dust source at global scale. It reports, for the first time, on the formation of cyclone over the Empty Quarter Desert as important mechanism for intense dust storms over this source region. The dust direct and semi-direct radiative forcings are observed, for the first time over this source region, using high-resolution in-situ and CERES-SYN satellite observational data. The three-dimensional structure and evolution of the dust storms are inferred from state-of-the-art satellite products such as SEVIRI, AEROIASI and CALIPSO. The dynamics and thermodynamics of the boundary layer during this event are thoroughly analyzed using ERA5 reanalysis and ground based observations. We found that a large dust storm by Shamal winds led up, through radiative forcing, to cyclone development over the Empty Quarter Desert, subsequent dust emissions, development of convective clouds and rain. The cyclogenesis over this region initiated a second intense dust storm which developed and impacted the AP for 3 consecutive days. The uplifted dust by the cyclone reached 5 km in altitude and altered the radiative budget at the surface, inducing both significant warming during night and cooling during day. The dust load uplifted by the cyclone was estimated by the mesoscale model Meso-NH to be in the order of 20 Tg, and the associated aerosol optical depth was higher than 3. The model simulates reasonably the radiative impact of the dust in the shortwave but highly underestimated its impact in the LW. Our study stresses the importance of the dust radiative forcing in the longwave and that it should be accurately accounted for in models to properly represent the impact of dust on the Earth system especially near source areas. Missing the warming effect of dust aerosols would impact both the weather and air quality forecast, and the regional climate projections. SEVIRI; Dust aerosols; CALIPSO; Radiative forcing; Convective clouds; AEROIASI; Cyclogenesis; Meso-NH; Southwest Asia
Francis, Timmy; Jayakumar, A.; Mohandas, Saji; Sethunadh, Jisesh; Reddy, M. Venkatarami; Arulalan, T.; Rajagopal, E. N.Francis, T., A. Jayakumar, S. Mohandas, J. Sethunadh, M. V. Reddy, T. Arulalan, E. N. Rajagopal, 2020: Simulation of a mesoscale convective system over Northern India: Sensitivity to convection partitioning in a regional NWP model. Dynamics of Atmospheres and Oceans, 92, 101162. doi: 10.1016/j.dynatmoce.2020.101162. Simulations of a mesoscale convective system (MCS), which propagated across Northern India on 2nd May 2018 - leading to many fatalities when the gust front knocked down homes and tore apart building roofs - have been performed using the National Centre for Medium Range Weather Forecasting (NCMRWF) Unified Model – Regional (4 km horizontal grid spacing), to evaluate the model’s convective treatments. Though the model captures many of the qualitative and quantitative features, it slightly lags behind the observed MCS organisation and movement, produces lesser precipitation, and lacks the spatial separation between two adjacent organised convective systems in the satellite observations – leading to a faintly offset MCS track. Sensitivity simulations are then performed, for this non-equilibrium MCS case, with different partitioning between parametrized and explicit convection to assess the reliance of the convective treatments on the large-scale environment, as well as to test the notion of a breakdown of convective parametrization at the mesoscale model resolution. Fully parametrized (FP) convection produces even lesser rainfall and are dominated by orographic precipitations along the foot hills of Himalayas with no any trace of the MCS. Fully explicit (FE) convection realistically simulates most of the prominent convective cells and enhance precipitation along the MCS track that agree better with the observations, though the ‘two lobes’ of intense precipitation are not resolved; instead it produces a squall line of precipitation. The FE configuration generates the most vigorous convective updraft, along with a vertical shear that is tilted westward. The simulation with partially parametrized and partially explicit convection resembles the fashion in the FP and FE scenarios, with a transition over the duration of the run from parametrized to explicit precipitation. The results are in line with the notion from previous studies; that the majority of successful explicit simulations of mesoscale organisation are those associated with strong large-scale forcing for convection, wherein resolved vertical motions are sufficient to minimise delays in onset. Mesoscale convective systems; NWP; Thunderstorms; Unified model
Freitas, Saulo R.; Putman, William M.; Arnold, Nathan P.; Adams, David K.; Grell, Georg A.Freitas, S. R., W. M. Putman, N. P. Arnold, D. K. Adams, G. A. Grell, 2020: Cascading Toward a Kilometer-Scale GCM: Impacts of a Scale-Aware Convection Parameterization in the Goddard Earth Observing System GCM. Geophysical Research Letters, 47(17), e2020GL087682. doi: 10.1029/2020GL087682. The National Aeronautics and Space Administration (NASA) Goddard Earth Observing System global circulation model (GCM) is evaluated through a cascade of simulations with increasing horizontal resolution. This model employs a nonhydrostatic dynamical core and includes a scale-aware, deep convection parameterization (DPCP). The 40-day simulations at six resolutions (100 km to 3 km) with unvarying model formulation were produced. At the highest resolution, extreme experiments were carried out: one with no DPCP and one with its scale awareness eliminated. Simulated precipitation, radiative balance, and atmospheric thermodynamic and dynamical variables are well reproduced with respect to both observational and reanalysis data. As model resolution increases, the convective precipitation smoothly transitions from being mostly produced by the convection parameterization to the cloud microphysics parameterization. However, contrary to current thought, these extreme cases argue for maintaining, to some extent, the scale-aware DPCP even at 3-km scale, as the run relying solely on explicit grid-scale production of rainfall performs more poorly at this resolution. model evaluation; global circulation models; convection parameterization; convection-permitting GCM; GEOS GCM
Gettelman, A.; Bardeen, C. G.; McCluskey, C. S.; Järvinen, E.; Stith, J.; Bretherton, C.; McFarquhar, G.; Twohy, C.; D'Alessandro, J.; Wu, W.Gettelman, A., C. G. Bardeen, C. S. McCluskey, E. Järvinen, J. Stith, C. Bretherton, G. McFarquhar, C. Twohy, J. D'Alessandro, W. Wu, 2020: Simulating Observations of Southern Ocean Clouds and Implications for Climate. Journal of Geophysical Research: Atmospheres, 125(21), e2020JD032619. doi: 10.1029/2020JD032619. Southern Ocean (S. Ocean) clouds are important for climate prediction. Yet, previous global climate models failed to accurately represent cloud phase distributions in this observation-sparse region. In this study, data from the Southern Ocean Clouds, Radiation, Aerosol, Transport Experimental Study (SOCRATES) experiment is compared to constrained simulations from a global climate model (the Community Atmosphere Model, CAM). Nudged versions of CAM are found to reproduce many of the features of detailed in-situ observations, such as cloud location, cloud phase and boundary layer structure. The simulation in CAM6 has improved its representation of S. Ocean clouds with adjustments to the ice nucleation and cloud microphysics schemes that permit more supercooled liquid. Comparisons between modeled and observed hydrometeor size distributions suggest that the modeled hydrometeor size distributions represent the dual peaked shape and form of observed distributions, which is remarkable given the scale difference between model and observations. Comparison to satellite observations of cloud physics is difficult due to model assumptions that do not match retrieval assumptions. Some biases in the model's representation of S. Ocean clouds and aerosols remain, but the detailed cloud physical parameterization provides a basis for process level improvement and direct comparisons to observations. This is crucial because cloud feedbacks and climate sensitivity are sensitive to the representation of Southern Ocean clouds. clouds; observations; southern ocean; supercooled water
Gonçalves, Nathan Borges; Lopes, Aline Pontes; Dalagnol, Ricardo; Wu, Jin; Pinho, Davieliton Mesquita; Nelson, Bruce WalkerGonçalves, N. B., A. P. Lopes, R. Dalagnol, J. Wu, D. M. Pinho, B. W. Nelson, 2020: Both near-surface and satellite remote sensing confirm drought legacy effect on tropical forest leaf phenology after 2015/2016 ENSO drought. Remote Sensing of Environment, 237, 111489. doi: 10.1016/j.rse.2019.111489. Amazon forest leaf phenology patterns have often been inferred from the Moderate Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index (EVI). But reliable MODIS detection of seasonal and interannual leaf phenology patterns has also been questioned and is generally not validated with field observation. Here we compare inter-annual patterns of local-scale upper canopy leaf phenology and demography derived from tower-mounted phenocams at two upland forest sites in the Central Amazon, to corresponding satellite vegetation indices retrieved from MODIS-MAIAC (Multi-Angle Implementation of Atmospheric Correction). We focus on forest response to an unprecedented drought caused by the El Niño of 2015-16. At both sites, multi-year phenocam data showed post-drought shifts in leaf demography. These were consistent with MODIS-MAIAC anomalies in two vegetation indices. Specifically, a precocious leaf flush at both sites during the first two post-drought months, Feb-Mar 2016, caused (1) an anomalous decrease in flushing trees in Jun–Jul of 2016 and (2) an increase of trees with early mature stage leaves (2-4 mo age) in Apr-May-Jun of 2016. At both sites, these two phenological anomalies showed up in MODIS-MAIAC as, respectively, (1) a strong negative anomaly in Gcc (Green chromatic coordinate), which prior work has shown to be sensitive to the abundance of leaves 0-1 mo old, and (2) a strong positive anomaly in EVI, which is sensitive to abundance of leaves 2-4 mo age. A shift to sub-optimal seasonal leaf age mix is expected to change the ecosystem-scale intrinsic photosynthetic capacity for ~18 month after the drought. El Niño; Amazon green-up; EVI seasonality; Leaf demography; MODIS-MAIAC; Phenocam
González-Bárcena, David; Fernández-Soler, Alejandro; Pérez-Grande, Isabel; Sanz-Andrés, ÁngelGonzález-Bárcena, D., A. Fernández-Soler, I. Pérez-Grande, Á. Sanz-Andrés, 2020: Real data-based thermal environment definition for the ascent phase of Polar-Summer Long Duration Balloon missions from Esrange (Sweden). Acta Astronautica, 170, 235-250. doi: 10.1016/j.actaastro.2020.01.024. Long Duration Balloon missions are key platforms for scientific research and space technology development. Thermal analyses of this kind of systems are crucial for the success of the mission. Even though the science is usually performed at float altitude, the ascent phase, usually non-operational, is where the extreme cold conditions occur, due to the convective effects caused by relative wind speed together with the low temperatures found in the tropopause, making this scenario a dimensioning case. In this paper, a thorough study of the thermal environmental conditions during the ascent is carried out, in particular winds, temperature, and radiative thermal loads have been obtained as a function of the altitude. The study is based on real data obtained from different sources, including atmospheric soundings, radar and satellite, and a meticulous statistical treatment. The study is focussed on one of the main stratospheric balloon launch sites in Europe, Esrange (Sweden), a center of the Swedish Space Corporation, and the analyses are performed for the summer period. However, the methodology can be extended to any other location and epoch. As an example, the convective effect of the horizontal winds on a plate has been studied, and the heat transfer during the ascent phase has been quantified. A subcooling of around 7 °C was found in this case, which make worth the dedicated analysis. Albedo; Ascent phase; Convection; Long duration balloon (LDB); Thermal environment; Winds
Gupta, Ashok Kumar; Rajeev, K.; Davis, Edwin V.; Mishra, Manoj Kumar; Nair, Anish Kumar M.Gupta, A. K., K. Rajeev, E. V. Davis, M. K. Mishra, A. K. M. Nair, 2020: Direct observations of the multi-year seasonal mean diurnal variations of TOA cloud radiative forcing over tropics using Megha-Tropiques-ScaRaB/3. Climate Dynamics, 55(11), 3289-3306. doi: 10.1007/s00382-020-05441-w. Diurnal variation of cloud radiative forcing (CRF) is a major factor that controls the global radiation balance. This study presents multi-year seasonal mean diurnal variations of longwave cloud radiative forcing (LWCRF) and daytime shortwave cloud radiative forcing (SWCRF) at the top of atmosphere over tropics, derived from the broadband radiation measurements made by ScaRaB/3 onboard the low-inclination Megha-Tropiques satellite. The largest LWCRF (60–80 Wm−2) occurs over the oceanic regions of the east equatorial Indian Ocean and the western Pacific during all seasons, as well as the South Pacific Convergence Zone, the northeast Bay of Bengal, Amazon region, central and southern Africa and north Indian landmass (monsoon trough) during the local summer. Diurnal variations of 15–25 Wm−2 in LWCRF (20–35% of the mean) are observed with peak values occurring at 18–21 local time (LT) over continents and 00–06 LT over oceans. The minimum LWCRF occurs at 09–12 LT throughout the tropics. Over convective regions, SWCRF maximizes at 12–15 LT (− 220 to − 300 Wm−2) and has a higher magnitude over continents due to early convection occurrence, indicating the importance of diurnal phase. Certain specific features including the CRF associated with the double inter-tropical convergence zone, day-night changes in net CRF, and the effect of El Ni$$\stackrel{\sim }{\mathrm{n}}$$n∼o on CRF are also presented. The net CRF and its zonal variations are strikingly similar during the normal and El Ni$$\stackrel{\sim }{\mathrm{n}}$$n∼o periods because the changes in LWCRF and SWCRF are mutually compensated.
Hahn, L. C.; Storelvmo, T.; Hofer, S.; Parfitt, R.; Ummenhofer, C. C.Hahn, L. C., T. Storelvmo, S. Hofer, R. Parfitt, C. C. Ummenhofer, 2020: Importance of Orography for Greenland Cloud and Melt Response to Atmospheric Blocking. J. Climate, 33(10), 4187-4206. doi: 10.1175/JCLI-D-19-0527.1. More frequent high pressure conditions associated with atmospheric blocking episodes over Greenland in recent decades have been suggested to enhance melt through large-scale subsidence and cloud dissipation, which allows more solar radiation to reach the ice sheet surface. Here we investigate mechanisms linking high pressure circulation anomalies to Greenland cloud changes and resulting cloud radiative effects, with a focus on the previously neglected role of topography. Using reanalysis and satellite data in addition to a regional climate model, we show that anticyclonic circulation anomalies over Greenland during recent extreme blocking summers produce cloud changes dependent on orographic lift and descent. The resulting increased cloud cover over northern Greenland promotes surface longwave warming, while reduced cloud cover in southern and marginal Greenland favors surface shortwave warming. Comparison with an idealized model simulation with flattened topography reveals that orographic effects were necessary to produce area-averaged decreasing cloud cover since the mid-1990s and the extreme melt observed in the summer of 2012. This demonstrates a key role for Greenland topography in mediating the cloud and melt response to large-scale circulation variability. These results suggest that future melt will depend on the pattern of circulation anomalies as well as the shape of the Greenland Ice Sheet.
Ham, Seung-Hee; Kato, Seiji; Rose, Fred G.Ham, S., S. Kato, F. G. Rose, 2020: Examining Biases in Diurnally-Integrated Shortwave Irradiances due to Two- and Four-Stream Approximations in Cloudy Atmosphere. J. Atmos. Sci., 77(2), 551–581. doi: 10.1175/JAS-D-19-0215.1. Shortwave irradiance biases due to two- and four-stream approximations have been studied for the last couple of decades, but biases in estimating Earth’s radiation budget have not been examined in earlier studies. In order to quantify biases in diurnally-averaged irradiances, we integrate the two- and four-stream biases using realistic diurnal variations of cloud properties from Clouds and the Earth’s Radiant Energy System (CERES) synoptic (SYN) hourly product. Three approximations are examined in this study, delta-two-stream-Eddington (D2strEdd), delta-two-stream-quadrature (D2strQuad), and delta-four-stream-quadrature (D4strQuad). Irradiances computed by the Discrete Ordinates Radiative Transfer (DISORT) and Monte Carlo (MC) methods are used as references. The MC noises are further examined by comparing with DISORT results. When the biases are integrated with a one-day of solar zenith angle variation, regional biases of D2strEdd and D2strQuad reach up to 8 W m−2, while biases of D4strQuad reach up to 2 W m−2. When the biases are further averaged monthly or annually, regional biases of D2strEdd and D2strQuad can reach –1.5 W m−2 in SW top-of-atmosphere (TOA) upward irradiances and +3 W m−2 in surface downward irradiances. In contrast, regional biases of D4strQuad are within +0.9 for TOA irradiances and –1.2 W m−2 for surface irradiances. Except for polar regions, monthly and annual global mean biases are similar, suggesting that the biases are nearly independent to season. Biases in SW heating rate profiles are up to –0.008 Kd−1 for D2strEdd and –0.016 K d−1 for D2strQuad, while the biases of the D4strQuad method are negligible.
Han, Ji-Young; Hong, Song-You; Kwon, Young CheolHan, J., S. Hong, Y. C. Kwon, 2020: The Performance of a Revised Simplified Arakawa–Schubert (SAS) Convection Scheme in the Medium-Range Forecasts of the Korean Integrated Model (KIM). Wea. Forecasting, 35(3), 1113-1128. doi: 10.1175/WAF-D-19-0219.1. The Korea Institute of Atmospheric Prediction Systems (KIAPS) has developed a new global numerical weather prediction model, named the Korean Integrated Model (KIM). This paper presents the cumulus parameterization scheme (CPS) used in KIM, which originates from the simplified Arakawa–Schubert (SAS) convection scheme in the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) and has undergone numerous modifications in an effort to improve the medium-range forecast skill for precipitation and large-scale fields. The modifications include the following: 1) the threshold of the trigger condition is updated to consider the dependency on the environmental relative humidity (RH) averaged over the subcloud layer in order to suppress the trigger of convection in dry low-level environments; 2) the entrainment rate is modified to increase the sensitivity to environmental humidity, so that enhanced entrainment under lower RH conditions leads to a greater decrease in the strength of the convection that develops in drier environments; 3) the autoconversion parameter from cloud condensate to convective precipitation is changed to have a temperature dependency above the freezing level; 4) the closure is modified to consider rapidly varying boundary layer forcing; 5) the effect of the convection-induced pressure gradient force in convective momentum transport is enhanced in the upper part of the convective updrafts; and 6) scale awareness that enables a mass-flux CPS to work seamlessly at various grid sizes across gray-zone resolutions is addressed. The evaluation of medium-range forecasts with the KIM CPS reveals higher forecast skill, especially over the tropics, in comparison with its original version.
Hayashi, Michiya; Jin, Fei-Fei; Stuecker, Malte F.Hayashi, M., F. Jin, M. F. Stuecker, 2020: Dynamics for El Niño-La Niña asymmetry constrain equatorial-Pacific warming pattern. Nature Communications, 11(1), 4230. doi: 10.1038/s41467-020-17983-y. The El Niño-Southern Oscillation (ENSO) results from the instability of and also modulates the strength of the tropical-Pacific cold tongue. While climate models reproduce observed ENSO amplitude relatively well, the majority still simulates its asymmetry between warm (El Niño) and cold (La Niña) phases very poorly. The causes of this major deficiency and consequences thereof are so far not well understood. Analysing both reanalyses and climate models, we here show that simulated ENSO asymmetry is largely proportional to subsurface nonlinear dynamical heating (NDH) along the equatorial Pacific thermocline. Most climate models suffer from too-weak NDH and too-weak linear dynamical ocean-atmosphere coupling. Nevertheless, a sizeable subset (about 1/3) having relatively realistic NDH shows that El Niño-likeness of the equatorial-Pacific warming pattern is linearly related to ENSO amplitude change in response to greenhouse warming. Therefore, better simulating the dynamics of ENSO asymmetry potentially reduces uncertainty in future projections.
Hinkelman, Laura M.; Marchand, RogerHinkelman, L. M., R. Marchand, 2020: Evaluation of CERES and CloudSat Surface Radiative Fluxes over Macquarie Island, the Southern Ocean. Earth and Space Science, 7(9), e2020EA001224. doi: 10.1029/2020EA001224. Many studies involving surface radiative fluxes rely on surface fluxes retrieved by the Clouds and the Earth's Radiant Energy System (CERES) project, or derived from spaceborne cloud radar and lidar observations (CloudSat-CALIPSO). In particular, most climate models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) were found to have too little shortwave radiation being reflected back to space and excessive shortwave radiation reaching the surface over the Southern Ocean – an error with significant consequences for predicting both regional and global climate. There have been few evaluations of CERES or CloudSat retrievals over the Southern Ocean. In this article, CERES and CloudSat retrieved surface shortwave (SW) and longwave (LW) downwelling fluxes are evaluated using surface observations collected over the Southern Ocean during the Macquarie Island Cloud and Radiation Experiment (MICRE). Overall, biases (CERES – surface observations) in the CERES- surface fluxes are found to be slightly larger over Macquarie Island than most other regions, approximately +10 Wm-2 for the SW and -10 Wm-2 for the LW in the annual mean, but with significant seasonal and diurnal variations. If the Macquarie observations are representative of the larger SO, these results imply that CMIP5 model errors in SW surface fluxes are (if anything) somewhat larger than previous evaluation studies suggest. The bias in LW surface flux shows a marked increase at night, which explains most of the total LW bias. The nighttime bias is due to poor representation of cloud base associated with low clouds. Southern Ocean; Macquarie Island; MICRE; Surface Radiative Fluxes
Hobeichi, Sanaa; Abramowitz, Gab; Contractor, Steefan; Evans, JasonHobeichi, S., G. Abramowitz, S. Contractor, J. Evans, 2020: Evaluating Precipitation Datasets Using Surface Water and Energy Budget Closure. J. Hydrometeor., 21(5), 989-1009. doi: 10.1175/JHM-D-19-0255.1. Evaluation of global gridded precipitation datasets typically entails using the in situ or satellite-based data used to derive them, so that out-of-sample testing is usually not possible. Here we detail a methodology that incorporates the physical balance constraints of the surface water and energy budgets to evaluate gridded precipitation estimates, providing the capacity for out-of-sample testing. Performance conclusions are determined by the ability of precipitation products to achieve closure of the linked budgets using adjustments that are within their prescribed uncertainty bounds. We evaluate and compare five global gridded precipitation datasets: IMERG, GPCP, GPCC, REGEN, and MERRA-2. At the spatial level, we show that precipitation is best estimated by GPCC over the high latitudes, by GPCP over the tropics, and by REGEN over North Africa and the Middle East. IMERG and REGEN appear best over Australia and South Asia. Furthermore, our results give insight into the adequacy of prescribed uncertainties of these products and shows that MERRA-2, while being less competent than the other four products in estimating precipitation, has the best representation of uncertainties in its precipitation estimates. The spatial extent of our results is not only limited to grid cells with in situ observations. Therefore, the approach enables a robust evaluation of precipitation estimates and goes some way to addressing the challenge of validation over observation scarce regions.
Hobeichi, Sanaa; Abramowitz, Gab; Evans, JasonHobeichi, S., G. Abramowitz, J. Evans, 2020: Conserving Land–Atmosphere Synthesis Suite (CLASS). J. Climate, 33(5), 1821-1844. doi: 10.1175/JCLI-D-19-0036.1. Accurate estimates of terrestrial water and energy cycle components are needed to better understand climate processes and improve models’ ability to simulate future change. Various observational estimates are available for the individual budget terms; however, these typically show inconsistencies when combined in a budget. In this work, a Conserving Land–Atmosphere Synthesis Suite (CLASS) of estimates of simultaneously balanced surface water and energy budget components is developed. Individual CLASS variable datasets, where possible, 1) combine a range of existing variable product estimates, and hence overcome the limitations of estimates from a single source; 2) are observationally constrained with in situ measurements; 3) have uncertainty estimates that are consistent with their agreement with in situ observations; and 4) are consistent with each other by being able to solve the water and energy budgets simultaneously. First, available datasets of a budget variable are merged by implementing a weighting method that accounts both for the ability of datasets to match in situ measurements and the error covariance between datasets. Then, the budget terms are adjusted by applying an objective variational data assimilation technique (DAT) that enforces the simultaneous closure of the surface water and energy budgets linked through the equivalence of evapotranspiration and latent heat. Comparing component estimates before and after applying the DAT against in situ measurements of energy fluxes and streamflow showed that modified estimates agree better with in situ observations across various metrics, but also revealed some inconsistencies between water budget terms in June over the higher latitudes. CLASS variable estimates are freely available via https://doi.org/10.25914/5c872258dc183.
Hogikyan, Allison; Cronin, Meghan F.; Zhang, Dongxiao; Kato, SeijiHogikyan, A., M. F. Cronin, D. Zhang, S. Kato, 2020: Uncertainty in Net Surface Heat Flux due to Differences in Commonly Used Albedo Products. J. Climate, 33(1), 303-315. doi: 10.1175/JCLI-D-18-0448.1. The ocean surface albedo is responsible for the distribution of solar (shortwave) radiant energy between the atmosphere and ocean and therefore is a key parameter in Earth’s surface energy budget. In situ ocean observations typically do not measure upward reflected solar radiation, which is necessary to compute net solar radiation into the ocean. Instead, the upward component is computed from the measured downward component using an albedo estimate. At two NOAA Ocean Climate Station buoy sites in the North Pacific, the International Satellite Cloud Climatology Project (ISCCP) monthly climatological albedo has been used, while for the NOAA Global Tropical Buoy Array a constant albedo is used. This constant albedo is also used in the Coupled Ocean–Atmosphere Response Experiment (COARE) bulk flux algorithm. This study considers the impacts of using the more recently available NASA Cloud and the Earth’s Radiant Energy System (CERES) albedo product for these ocean surface heat flux products. Differences between albedo estimates in global satellite products like these imply uncertainty in the net surface solar radiation heat flux estimates that locally exceed the target uncertainty of 1.0 W m−2 for the global mean, set by the Global Climate Observing System (GCOS) of the World Meteorological Organization (WMO). Albedo has large spatiotemporal variability on hourly, monthly, and interannual time scales. Biases in high-resolution SWnet (the difference between surface downwelling and upwelling shortwave radiation) can arise if the albedo diurnal cycle is unresolved. As a result, for periods when satellite albedo data are not available it is recommended that an hourly climatology be used when computing high-resolution net surface shortwave radiation.
Horowitz, Larry W.; Naik, Vaishali; Paulot, Fabien; Ginoux, Paul A.; Dunne, John P.; Mao, Jingqiu; Schnell, Jordan; Chen, Xi; He, Jian; John, Jasmin G.; Lin, Meiyun; Lin, Pu; Malyshev, Sergey; Paynter, David; Shevliakova, Elena; Zhao, MingHorowitz, L. W., V. Naik, F. Paulot, P. A. Ginoux, J. P. Dunne, J. Mao, J. Schnell, X. Chen, J. He, J. G. John, M. Lin, P. Lin, S. Malyshev, D. Paynter, E. Shevliakova, M. Zhao, 2020: The GFDL Global Atmospheric Chemistry-Climate Model AM4.1: Model Description and Simulation Characteristics. Journal of Advances in Modeling Earth Systems, 12(10), e2019MS002032. doi: 10.1029/2019MS002032. We describe the baseline model configuration and simulation characteristics of GFDL's Atmosphere Model version 4.1 (AM4.1), which builds on developments at GFDL over 2013–2018 for coupled carbon-chemistry-climate simulation as part of the sixth phase of the Coupled Model Intercomparison Project. In contrast with GFDL's AM4.0 development effort, which focused on physical and aerosol interactions and which is used as the atmospheric component of CM4.0, AM4.1 focuses on comprehensiveness of Earth system interactions. Key features of this model include doubled horizontal resolution of the atmosphere ( 200 km to 100 km) with revised dynamics and physics from GFDL's previous-generation AM3 atmospheric chemistry-climate model. AM4.1 features improved representation of atmospheric chemical composition, including aerosol and aerosol precursor emissions, key land-atmosphere interactions, comprehensive land-atmosphere-ocean cycling of dust and iron, and interactive ocean-atmosphere cycling of reactive nitrogen. AM4.1 provides vast improvements in fidelity over AM3, captures most of AM4.0's baseline simulations characteristics and notably improves on AM4.0 in the representation of aerosols over the Southern Ocean, India, and China—even with its interactive chemistry representation—and in its manifestation of sudden stratospheric warmings in the coldest months. Distributions of reactive nitrogen and sulfur species, carbon monoxide, and ozone are all substantially improved over AM3. Fidelity concerns include degradation of upper atmosphere equatorial winds and of aerosols in some regions. Aerosols; Ozone; Earth System Model; Atmospheric Chemistry; Chemistry-Climate Model
Hotta, Haruka; Suzuki, Kentaroh; Goto, Daisuke; Lebsock, MatthewHotta, H., K. Suzuki, D. Goto, M. Lebsock, 2020: Climate Impact of Cloud Water Inhomogeneity through Microphysical Processes in a Global Climate Model. J. Climate, 33(12), 5195-5212. doi: 10.1175/JCLI-D-19-0772.1. This study investigates how subgrid cloud water inhomogeneity within a grid spacing of a general circulation model (GCM) links to the global climate through precipitation processes. The effect of the cloud inhomogeneity on autoconversion rate is incorporated into the GCM as an enhancement factor using a prognostic cloud water probability density function (PDF), which is assumed to be a truncated skewed-triangle distribution based on the total water PDF originally implemented. The PDF assumption and the factor are evaluated against those obtained by global satellite observations and simulated by a global cloud-system-resolving model (GCRM). Results show that the factor implemented exerts latitudinal variations, with higher values at low latitudes, qualitatively consistent with satellite observations and the GCRM. The GCM thus validated for the subgrid cloud inhomogeneity is then used to investigate how the characteristics of the enhancement factor affect global climate through sensitivity experiments with and without the factor incorporated. The latitudinal variation of the factor is found to have a systematic impact that reduces the cloud water and the solar reflection at low latitudes in the manner that helps mitigate the too-reflective cloud bias common among GCMs over the tropical oceans. Due to the limitation of the factor arising from the PDF assumption, however, no significant impact is found in the warm rain formation process. Finally, it is shown that the functional form for the PDF in a GCM is crucial to properly characterize the observed cloud water inhomogeneity and its relationship with precipitation.
Hou, Ning; Zhang, Xiaotong; Zhang, Weiyu; Wei, Yu; Jia, Kun; Yao, Yunjun; Jiang, Bo; Cheng, JieHou, N., X. Zhang, W. Zhang, Y. Wei, K. Jia, Y. Yao, B. Jiang, J. Cheng, 2020: Estimation of Surface Downward Shortwave Radiation over China from Himawari-8 AHI Data Based on Random Forest. Remote Sensing, 12(1), 181. doi: 10.3390/rs12010181. Downward shortwave radiation (RS) drives many processes related to atmosphere–surface interactions and has great influence on the earth’s climate system. However, ground-measured RS is still insufficient to represent the land surface, so it is still critical to generate high accuracy and spatially continuous RS data. This study tries to apply the random forest (RF) method to estimate the RS from the Himawari-8 Advanced Himawari Imager (AHI) data from February to May 2016 with a two-km spatial resolution and a one-day temporal resolution. The ground-measured RS at 86 stations of the Climate Data Center of the Chinese Meteorological Administration (CDC/CMA) are collected to evaluate the estimated RS data from the RF method. The evaluation results indicate that the RF method is capable of estimating the RS well at both the daily and monthly time scales. For the daily time scale, the evaluation results based on validation data show an overall R value of 0.92, a root mean square error (RMSE) value of 35.38 (18.40%) Wm−2, and a mean bias error (MBE) value of 0.01 (0.01%) Wm−2. For the estimated monthly RS, the overall R was 0.99, the RMSE was 7.74 (4.09%) Wm−2, and the MBE was 0.03 (0.02%) Wm−2 at the selected stations. The comparison between the estimated RS data over China and the Clouds and Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) RS dataset was also conducted in this study. The comparison results indicate that the RS estimates from the RF method have comparable accuracy with the CERES-EBAF RS data over China but provide higher spatial and temporal resolution. downward shortwave radiation; Himawari-8 AHI; machine learning methods; multi-channel; Random Forest
Hourdin, Frédéric; Rio, Catherine; Grandpeix, Jean-Yves; Madeleine, Jean-Baptiste; Cheruy, Frédérique; Rochetin, Nicolas; Jam, Arnaud; Musat, Ionela; Idelkadi, Abderrahmane; Fairhead, Laurent; Foujols, Marie-Alice; Mellul, Lidia; Traore, Abdoul-Khadre; Dufresne, Jean-Louis; Boucher, Olivier; Lefebvre, Marie-Pierre; Millour, Ehouarn; Vignon, Etienne; Jouhaud, Jean; Diallo, F. Binta; Lott, François; Gastineau, Guillaume; Caubel, Arnaud; Meurdesoif, Yann; Ghattas, JosefineHourdin, F., C. Rio, J. Grandpeix, J. Madeleine, F. Cheruy, N. Rochetin, A. Jam, I. Musat, A. Idelkadi, L. Fairhead, M. Foujols, L. Mellul, A. Traore, J. Dufresne, O. Boucher, M. Lefebvre, E. Millour, E. Vignon, J. Jouhaud, F. B. Diallo, F. Lott, G. Gastineau, A. Caubel, Y. Meurdesoif, J. Ghattas, 2020: LMDZ6A: the atmospheric component of the IPSL climate model with improved and better tuned physics. Journal of Advances in Modeling Earth Systems, 12(7), e2019MS001892. doi: 10.1029/2019MS001892. This study presents the version of the LMDZ global atmospheric model used as the atmospheric component of the Institut Pierre Simon Laplace coupled model (IPSL-CM6A-LR) to contribute to the 6th phase of the international Coupled Model Intercomparison Project (CMIP6). This LMDZ6A version includes original convective parameterizations that define the LMDZ 'New Physics’: a mass flux parameterization of the organized structures of the convective boundary layer, the 'thermal plume model', and a parameterization of the cold pools created by reevaporation of convective rainfall. The vertical velocity associated with thermal plumes and gust fronts of cold pools are used to control the triggering and intensity of deep convection. Because of several shortcomings, the early version 5B of this ‘New Physics’ was worse than the previous 'Standard Physics' version 5A regarding several classical climate metrics. To overcome these deficiencies, version 6A includes new developments: a stochastic triggering of deep convection, a modification of the thermal plume model that allows the representation of stratocumulus and cumulus clouds in a unified framework, an improved parameterization of very stable boundary layers, and the modification of the gravity waves scheme targeting the quasi biennal oscillation in the stratosphere. These improvements to the physical content and a more well-defined tuning strategy led to major improvements in the LMDZ6A version model climatology. Beyond the presentation of this particular model version and documentation of its climatology, the present paper underlines possible methodological pathways toward model improvement that can be shared across modeling groups. Climate model development; tuning
Hourdin, Frédéric; Rio, Catherine; Jam, Arnaud; Traore, Abdoul-Khadre; Musat, IonelaHourdin, F., C. Rio, A. Jam, A. Traore, I. Musat, 2020: Convective Boundary Layer Control of the Sea Surface Temperature in the Tropics. Journal of Advances in Modeling Earth Systems, 12(6), e2019MS001988. doi: 10.1029/2019MS001988. Using successive versions of a global climate model, we show how convective transport to the free troposphere of the humidity evaporated at the surface or, reciprocally, entrainment of dry air from the free troposphere into the mixed layer, controls surface evaporative cooling and then sea surface temperature. This control is as important as the radiative effect of boundary layer clouds on radiation. Those aspects are shown to be improved when activating a mass flux representation of the organized structures of the convective boundary layer coupled to eddy diffusion, the so-called “thermal plume model,” leading to an increased near-surface drying compared to the use of turbulent diffusion alone. Controlling detrainment by air properties from just above the boundary layer allows the thermal plume model to be valid for both cumulus and stratocumulus regimes, improving the contrast in near-surface humidity between the trade winds region and East Tropical oceans. Using pairs of stand-alone atmospheric simulations forced by sea surface temperature and of coupled atmosphere-ocean simulations, we show how the improvement of the surface fluxes that arise from this improved physics projects into an improvement of the representation of sea surface temperature patterns in the coupled model, and in particular into a reduction of the East Tropical Ocean warm bias. The work presented here led to the bias reduction in sea surface temperature in the Institute Pierre Simon Laplace coupled model, IPSL-CM6A, developed recently for the 6th phase of the Coupled Model Intercomparison Project, CMIP6. convective boundary layer; SST warm biases; stratocumulus clouds
Hua, Shan; Liu, Yuzhi; Luo, Run; Shao, Tianbin; Zhu, QingzheHua, S., Y. Liu, R. Luo, T. Shao, Q. Zhu, 2020: Inconsistent aerosol indirect effects on water clouds and ice clouds over the Tibetan Plateau. International Journal of Climatology, 40(8), 3832-3848. doi: 10.1002/joc.6430. Recently, satellites have observed that dust events are occurring more frequently over the Tibetan Plateau (TP), which implies a new issue of aerosols influencing cloud properties and presents a new challenge in research on the role of the TP in climate change. In this study, combining satellite observations with Climate Model Intercomparison Project Phase 5 (CMIP5) model simulations, the inconsistent aerosol indirect effects on the properties of water clouds and ice clouds over the TP are compared and quantified. Analyses of satellite observations show that, compared with water clouds, ice clouds are observed more frequently and are more significantly correlated with aerosols over the TP. Correspondingly, the aerosol effect on the radiative forcing of ice clouds is more significant than that on the forcing of water clouds, in which the aerosol indirect effect is dominated by the effect on the shortwave radiative forcing of ice clouds. Both observations and CMIP5 model simulation results show that, due to the variation of aerosols, changes in the ice cloud radiative forcing cover most of the TP, while changes in the water cloud radiative forcing mainly appear over the southern edge of the TP. The CMIP5 simulation results suggest that the aerosol indirect effect on the total radiative forcing of water clouds over the TP is −0.34 (±0.03) W⋅m−2, while that on the forcing of ice clouds is −0.73 (±0.03) W⋅m−2. Overall, both the model simulations and satellite results show that the indirect effect of aerosols on ice clouds is more pronounced than that on water clouds. cloud; aerosol; indirect effect; Tibetan Plateau
Huang, Guan; Liu, Qiong; Wang, Yanyu; He, Qianshan; Chen, Yonghang; Jin, Lili; Liu, Tongqiang; He, Qing; Gao, Jiacheng; Zhao, Keming; Liu, PingpingHuang, G., Q. Liu, Y. Wang, Q. He, Y. Chen, L. Jin, T. Liu, Q. He, J. Gao, K. Zhao, P. Liu, 2020: The accuracy improvement of clear-sky surface shortwave radiation derived from CERES SSF dataset with a simulation analysis. Science of The Total Environment, 749, 141671. doi: 10.1016/j.scitotenv.2020.141671. Towards the Xiaotang region along the northern margin of the China's largest desert, a quantitative assessment of the precision of clear-sky satellite observations (the Single Scanner Footprint TOA/Surface Fluxes and Clouds downward surface shortwave radiation product of Clouds and the Earth's Radiant Energy System (CERES), DSSRCER) is conducted, the localized inversion mode of “absolutely clear-sky” downward surface shortwave radiation (DSSR) is established, and the “absolutely clear-sky” DSSR in Xiaotang during 2005–2018 is simulated by the Santa Barbara Discrete Atmospheric Radiative Transfer (SBDART) model. In general, under the “absolutely clear-sky” condition of Xiaotang region, there is a significant error in DSSRCER, and the simulated results of SBDART (DSSRSBD) with same input parameters as DSSRCER is better and more comparable. Single scattering albedo (SSA), asymmetry parameter (ASY) and aerosol optical depth (AOD) play crucial roles in deciding the accuracy of DSSR, and after parameter adjustment, the DSSRSBD is better than the initial, which is improved remarkably with all indexes of the fitting results greatly improved. The temporal variation of the DSSR during 2005–2018 indicates that the highest annual average value is found in 2008 (770.00 W·m−2), while the lowest appears in 2010 (600.97 W·m−2). Besides, the highest seasonal mean DSSR appears in summer, which between 860.6 and 935.07 W·m−2, while reaches the lowest in winter (403.79–587.53 W·m−2). Moreover, the monthly average DSSR changes as a curve with a single peak and is close to normal distribution, the highest appears in June (934.61 W·m−2), while the minimum with the value of 390.34 W·m−2 is found in December. All of the solar elevation angle, the characteristics of climate and aerosol particles in different seasons may contribute to the temporal variation. CERES; Correction; Downward surface shortwave radiation; LPSA; SBDART; Xiaotang
Hulswar, Shrivardhan; Menon, Harilal B.; Anilkumar, N.Hulswar, S., H. B. Menon, N. Anilkumar, 2020: Physical-chemical characteristics of composite aerosols in the Indian Ocean sector of the Southern Ocean and its associated effect on insolation: A climate perspective. Deep Sea Research Part II: Topical Studies in Oceanography, 104801. doi: 10.1016/j.dsr2.2020.104801. Aerosol optical depth (AOD), black carbon (BC) mass concentration, aerosol size, along with wind parameters, were derived during Southern Ocean expeditions (SOE) 7 and 8 carried out in austral summer of 2013 and 2015, with an aim to analyse the effect of aerosol on incoming solar radiation. The data were complemented with trace metals from aerosol samples of SOE-6 conducted in 2012. The AOD spectra north of 40oS followed Angstrom turbidity formulae while those in the south deviated from it. A statistically significant correlation (R2) of 0.79 (P « 0.0001) between the differences of AOD440 estimated from an Optical Properties of Aerosol and Cloud (OPAC) model and measured in situ and chlorophyll-a concentration revealed phytoplankton as a significant source of fine mode aerosols. Analysis of ten years of MODIS derived fine mode particle concentration indicated an increase as season advanced from winter to summer and a subsequent decrease towards the following winter, clearly showing a contribution from phytoplankton. BC mass concentration was found to be around 80 ng m−3. Prevalence of trace metals such as Cu, Cd and Zn and the anions SO4−4-2 and NO3−3-1 were observed in this part of the world ocean. An inverse relation was observed between Cu and phytoplankton derived SO4−4-2, indicating the detrimental effect of Cu on fine mode sulphate aerosols which are as significant as cloud condensation nuclei (CCN). The aerosol radiative forcing was found to be between 25 and –28 W m−2 to the north of the ITCZ while it was around 2–6 W m−2 in the south. The associated heating rate was from 0.05 to –0.09 and from 0.01 to –0.02 K day−1, respectively. The study revealed an increase in black carbon due to ship emissions. An increase in BC over the Southern Ocean atmosphere may have a far-reaching effect on the cloud formation and regional albedo.
Hwang, Jiwon; Choi, Yong-Sang; Su, Hui; Jiang, Jonathan H.Hwang, J., Y. Choi, H. Su, J. H. Jiang, 2020: Invariability of Arctic top-of-atmosphere radiative response to surface temperature changes. Earth and Space Science, 7(11), e2020EA001316. doi: 10.1029/2020EA001316. Recent studies have used satellite data to estimate the response of top-of-atmosphere (TOA) radiative fluxes to surface temperature changes in the Arctic. The satellite-observed radiative response is indicative of Arctic climate sensitivity that determines future Arctic warming. However, it remains ambiguous whether the satellite-observed radiative response is invariable because the time period covered by satellite data reflects a rapidly changing transient Arctic climate state with considerable sea ice loss. Using NASA’s CERES observations from 2000 to 2018, this study evaluates the invariability of the radiative response by comparing the radiative response of high sea ice concentrations (SICs) period to that of low SIC period. The results show that the net radiative response remains approximately unchanged regardless of the SIC (–0.19 ± 0.44 W m-2K-1 and 0.15 ± 0.16 W m-2K-1 for high and low SIC periods, respectively). In addition, seven of the eleven models from the CMIP6 demonstrated that the modeled radiative responses are stable. The ERA-interim reanalysis estimates show that regionally confined changes in individual radiative feedbacks such as albedo, lapse rate, water vapor, and clouds do not vary considerably. Consequently, we infer that the radiative response in the Arctic may remain stable even under rapid Arctic climate change. Hence, the Arctic climate sensitivity can be quantified with present satellite observations.
Janisková, Marta; Fielding, Mark D.Janisková, M., M. D. Fielding, 2020: Direct 4D-Var assimilation of space-borne cloud radar and lidar observations. Part II: Impact on analysis and subsequent forecast. Quarterly Journal of the Royal Meteorological Society, 146(733), 3900-3916. doi: 10.1002/qj.3879. Observations related to cloud, such as radiances from microwave imagers, have been at the forefront of recent developments in data assimilation for numerical weather prediction (NWP). While they offer unrivalled spatial coverage, they contain limited information on the vertical structure of clouds. In contrast, active observations from profiling instruments such as cloud radar and lidar contain a wealth of information on the structure of clouds and precipitation, providing the much-needed vertical context of clouds, but have never been assimilated directly in global NWP models. To explore the potential benefits of these profiling observations, the European Centre for Medium-Range Weather Forecasts (ECMWF) Four-Dimensional Variational (4D-Var) data assimilation system has been recently adapted to allow direct assimilation of cloud profile observations from space-borne radar and lidar instruments. In this paper, in conjunction with its companion paper, the first-time direct assimilation of cloud radar and lidar observations into a global NWP model is demonstrated. Using CloudSat radar reflectivity and CALIPSO attenuated backscatter shows that the assimilation brings the analysis closer to these observations and has a mainly neutral affect on other assimilated observations. Some improvements in the forecast skill are also observed when verified against the experiment's own analysis, with the largest positive impact noticed for temperature at the lowest model levels and for vector wind above 500 hPa, but longer experiments are required to reach 95% statistical significance of the results. The potential improvements in the model radiation budget is explored by verifying with Clouds and the Earth's Radiation Energy System (CERES) observations. Sensitivity of the results to observation error and to the observation reduction by increased averaging is also discussed. The demonstration of statistically significant improvements to forecast skill in some metrics without any significant degredation in others shows great promise for the future use of cloud radar and lidar observations in NWP. cloud radar reflectivity; lidar backscatter; variational technique
Ji, Peng; Yuan, Xing; Li, DanJi, P., X. Yuan, D. Li, 2020: Atmospheric Radiative Processes Accelerate Ground Surface Warming over the Southeastern Tibetan Plateau during 1998–2013. J. Climate, 33(5), 1881-1895. doi: 10.1175/JCLI-D-19-0410.1. The Tibetan Plateau (TP), known as the world’s “Third Pole,” plays a vital role in regulating the regional and global climate and provides freshwater for about 1.5 billion people. Observations show an accelerated ground surface warming trend over the southeastern TP during the global warming slowdown period of 1998–2013, especially in the summer and winter seasons. The processes responsible for such acceleration are under debate as contributions from different radiative processes are still unknown. Here we estimate for the first time the contributions of each radiative component to the ground surface warming trend before and after 1998 by analyzing multisource datasets under an energy balance framework. Results show that declining cloud cover caused by the weakening of both the South Asian summer monsoon and local-scale atmospheric upward motion mainly led to the accelerated ground surface warming during the summers of 1998–2013, whereas the decreased surface albedo caused by the snow melting was the major warming factor in winter. Moreover, increased clear-sky longwave radiation induced by the warming middle and upper troposphere was the second largest factor, contributing to about 21%–48% of the ground surface warming trend in both the summer and winter seasons. Our results unravel the key processes driving the ground surface warming over the southeastern TP and have implications for the development of climate and Earth system models in simulating ground surface temperature change and other related complex cryosphere–hydrosphere–atmosphere interactions over high-altitude land areas.
Jian, Bida; Li, Jiming; Zhao, Yuxin; He, Yongli; Wang, Jing; Huang, JianpingJian, B., J. Li, Y. Zhao, Y. He, J. Wang, J. Huang, 2020: Evaluation of the CMIP6 planetary albedo climatology using satellite observations. Climate Dynamics, 54(11), 5145-5161. doi: 10.1007/s00382-020-05277-4. The Earth’s planetary albedo (PA) has an essential impact on the global radiation budget. Based on 14 years of monthly data from the Clouds and the Earth’s Radiant Energy System energy balanced and filled (CERES-EBAF) Ed4.1 dataset and atmosphere-only simulations of the Coupled Model Intercomparison Project Phase6 (CMIP6/AMIP), this study investigates the ability of CMIP6/AMIP model in reproducing the observed inter-month changes, annual cycle and trend of PA at near-global and regional scales. Statistical results indicate that some persistent biases in the previous models continue to exist in the CMIP6 models; however, some progresses have been made. In CMIP6/AMIP, large negative correlations for PA between the model ensemble mean and observation are addressed over the subtropical stratocumulus regions. In addition, the simulation of PA in drylands and tropical oceans remains a challenge in CMIP6 models. Over the most regions, PA biases are governed by cloud albedo forcing biases. These results demonstrate the importance of improving cloud process simulations for accurately representing the PA in models. For the annual cycles, the model ensemble mean captures the difference in amplitude between the two peak values of PA (June and December), as well as the phase of the seasonal cycle, despite PA is systematically overestimated. The differences between different terrestrial climatic regions are also examined. Results indicate that the relative biases of PA are greatest in semi-arid (2.2%) and semi-humid (2.8%) regions, whereas the minimum relative bias occurs in arid regions (0.3%) due to compensating errors.
Jin, Qinjian; Pryor, S. C.Jin, Q., S. C. Pryor, 2020: Long-term trends of high aerosol pollution events and their climatic impacts in North America using multiple satellite retrievals and MERRA-2. Journal of Geophysical Research: Atmospheres, 125(4), e2019JD031137. doi: 10.1029/2019JD031137. Mean magnitudes and temporal trends in Aerosol Optical Depth (AOD) from satellite observations and an aerosol reanalysis exhibit a negative-positive east-northwest dipole across the contiguous US with large magnitude negative trends over the eastern US while small magnitude positive trends over the northwestern states. Based on analyses of MERRA-2, the AOD reduction over the eastern US appears to be largely attributable to reductions in aerosol-sulfate, while there have been marked increases in aerosol-organic and elemental carbon over almost all of the contiguous US and particularly the northwestern states. Long-term trends of high aerosol pollution events (HAPE; days with AOD over the long-term local 90th daily AOD percentile) during 2000-2017 also indicate that over the eastern US, both the frequency and spatial scale of summer HAPEs exhibit significant negative trends, while those of moderate aerosol events (days with AOD between the local 30th and 70th AOD percentiles) exhibit weak upward trends. Opposing trends, of smaller magnitude, are derived in the north-western US and southwestern Canada. Net and shortwave solar radiation show positive trends at the surface and top of atmosphere under clear-sky conditions over the eastern US consistent with the reduction in AOD. However, skin temperatures do not indicate significant trends during all days or HAPEs, indicating that the aerosol-induced radiation trends are not sufficient to manifest trends in surface temperature. Precipitation during HAPEs appears to have increased during 2000-2017 over the eastern and central US, indicating that the reduction in aerosol may already be enhancing the precipitation through aerosol-cloud interactions. CERES; aerosol-precipitation interaction; extreme aerosol trend; MERRA2; North America; satellite retrieval
Johnson, Richard H.; Ciesielski, Paul E.Johnson, R. H., P. E. Ciesielski, 2020: Potential Vorticity Generation by West African Squall Lines. Mon. Wea. Rev., 148(4), 1691-1715. doi: 10.1175/MWR-D-19-0342.1. The West African summer monsoon features multiple, complex interactions between African easterly waves (AEWs), moist convection, variable land surface properties, dust aerosols, and the diurnal cycle. One aspect of these interactions, the coupling between convection and AEWs, is explored using observations obtained during the 2006 African Monsoon Multidisciplinary Analyses (AMMA) field campaign. During AMMA, a research weather radar operated at Niamey, Niger, where it surveilled 28 squall-line systems characterized by leading convective lines and trailing stratiform regions. Nieto Ferreira et al. found that the squall lines were linked with the passage of AEWs and classified them into two tracks, northerly and southerly, based on the position of the African easterly jet (AEJ). Using AMMA sounding data, we create a composite of northerly squall lines that tracked on the cyclonic shear side of the AEJ. Latent heating within the trailing stratiform regions produced a midtropospheric positive potential vorticity (PV) anomaly centered at the melting level, as commonly observed in such systems. However, a unique aspect of these PV anomalies is that they combined with a 400–500-hPa positive PV anomaly extending southward from the Sahara. The latter feature is a consequence of the deep convective boundary layer over the hot Saharan Desert. Results provide evidence of a coupling and merging of two PV sources—one associated with the Saharan heat low and another with latent heating—that ends up creating a prominent midtropospheric positive PV maximum to the rear of West African squall lines.
Jose, Subin; Nair, Vijayakumar S.; Babu, S. SureshJose, S., V. S. Nair, S. S. Babu, 2020: Anthropogenic emissions from South Asia reverses the aerosol indirect effect over the northern Indian Ocean. Scientific Reports, 10(1), 18360. doi: 10.1038/s41598-020-74897-x. Atmospheric aerosols play an important role in the formation of warm clouds by acting as efficient cloud condensation nuclei (CCN) and their interactions are believed to cool the Earth-Atmosphere system (‘first indirect effect or Twomey effect’) in a highly uncertain manner compared to the other forcing agents. Here we demonstrate using long-term (2003–2016) satellite observations (NASA’s A-train satellite constellations) over the northern Indian Ocean, that enhanced aerosol loading (due to anthropogenic emissions) can reverse the first indirect effect significantly. In contrast to Twomey effect, a statistically significant increase in cloud effective radius (CER, µm) is observed with respect to an increase in aerosol loading for clouds having low liquid water path (LWP
Jouan, Caroline; Milbrandt, Jason A.; Vaillancourt, Paul A.; Chosson, Frédérick; Morrison, HughJouan, C., J. A. Milbrandt, P. A. Vaillancourt, F. Chosson, H. Morrison, 2020: Adaptation of the Predicted Particles Properties (P3) microphysics scheme for large-scale numerical weather prediction. Wea. Forecasting, 35(6), 2541-2565. doi: 10.1175/WAF-D-20-0111.1.
Jung, Hyun-Seok; Lee, Kyu-Tae; Zo, Il-SungJung, H., K. Lee, I. Zo, 2020: Calculation Algorithm of Upward Longwave Radiation Based on Surface Types. Asia-Pacific Journal of Atmospheric Sciences, 56(2), 291-306. doi: 10.1007/s13143-020-00175-5. Upward longwave radiation (ULR) is an important element for climate change analysis. We calculated ULR using land surface temperature (LST), sea surface temperature (SST), and downward longwave radiation (DLR) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud and the Earth’s Radiant Energy System (CERES), along with broadband emissivity calculated using four multiple linear regression models designed to consider specific land-cover categories along with MODIS data and reflectivity data for 241 materials from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Our broadband emissivity values were compared with those of Wang et al. Journal of Geophysical Research: Atmospheres, 110(D11), (2005); all correlation coefficients were higher than 0.90 for the period from January to December 2016, and the root mean square error (RMSE) was 0.00750–0.00825. We then calculated ULR using the broadband emissivity and compared the results with CERES data, resulting in smaller errors relative to CERES than found by Wang et al. (2005). Furthermore, the calculated ULR compared with the observational data of Baseline Surface Radiation Network (BSRN) and the resultant statistical values of R(correlation coefficient), RMSE, and bias were 0.93, 21.22 W m−2, and 0.29 respectively.
Kang, Hyoji; Choi, Yong-Sang; Hwang, Jiwon; Kim, Hye-SilKang, H., Y. Choi, J. Hwang, H. Kim, 2020: On the cloud radiative effect for tropical high clouds overlying low clouds. Geoscience Letters, 7(1), 7. doi: 10.1186/s40562-020-00156-6. Since high and low clouds ubiquitously overlie the Tropical Western Pacific (TWP) region, the cloud radiative effect (CRE) cannot be influenced by either high or low clouds, but by combinations of the clouds. This study investigates the CRE of multi-layered clouds in TWP via a radiative transfer model, Streamer. We assumed that multi-layered clouds are composed of full coverage of high clouds overlying low clouds with fractional coverage. The simulation results show that low clouds readily change CREs from positive to negative in the case of optically thin high clouds, even if the fraction of low clouds takes 10% of that of high clouds. Also, various combinations of physical properties of multi-layered high and low clouds allow more CRE variability (− 253.76 to 93.10 W m−2) than single-layered clouds do (− 101.62 to 96.95 W m−2). Even in the same conditions (total column cloud optical thickness = 15 and high cloud top pressure = 200 hPa), the multi-layer clouds have various CREs from − 180.55 to 45.64 W m−2, while the single-layer high clouds − 2.00 W m−2. These findings are also comparable with satellite observations from CERES and CALIPSO. The present study suggests that considerable uncertainty of radiative effects of high clouds over TWP can attribute to low clouds below high clouds.
Kato, Seiji; Loeb, Norman G.; Rutan, David A.; Rose, Fred G.Kato, S., N. G. Loeb, D. A. Rutan, F. G. Rose, 2020: Effects of electromagnetic wave interference on observations of the Earth radiation budget. Journal of Quantitative Spectroscopy and Radiative Transfer, 253, 107157. doi: 10.1016/j.jqsrt.2020.107157. This paper investigates conditions necessary to match the irradiance derived by integrating radiances measured by a narrow field of view scanning radiometer with the irradiance measured by a hemispherical radiometer, both placed at a satellite altitude for Earth radiation budget estimates. When all sources are similar and they are spatially distributed randomly, then integrating radiance for the irradiance does not introduce a bias. Although the exact magnitude of the bias in other conditions is unknown, a finite area of the aperture that is much larger than the coherence area of radiation contributing to the Earth radiation budget, and a finite time to take a single measurement that is longer than the coherence time are likely to make the difference of the irradiance integrated from radiances and the irradiance measured by a hemispherical instrument insignificant. This conclusion does not contradict the existence of spatial coherence of light from incoherent sources. Therefore, electromagnetic energy absorbed by Earth is derivable from radiances measured by a scanning radiometer integrated over the Earth-viewing hemisphere and then averaging across all locations on the satellite orbital sphere when combined with solar irradiance measurements. Comparisons made in earlier studies show that the difference is less than 1%. In addition, when surface irradiances computed by a radiative transfer model constrained by top-of-atmosphere irradiances derived from radiance measurements are compared with downward shortwave irradiances taken by combinations of a pyreheliometer and a shaded pyranometer, or pyranometers, and with longwave irradiances taken by pyrgeometers, the biases in monthly mean irradiances are less than the uncertainties in the surface observations.
Kato, Seiji; Rose, Fred G.Kato, S., F. G. Rose, 2020: Global and Regional Entropy Production by Radiation Estimated from Satellite Observations. J. Climate, 33(8), 2985-3000. doi: 10.1175/JCLI-D-19-0596.1. Vertical profiles of shortwave and longwave irradiances computed with satellite-derived cloud properties and temperature and humidity profiles from reanalysis are used to estimate entropy production. Entropy production by shortwave radiation is computed by the absorbed irradiance within layers in the atmosphere and by the surface divided by their temperatures. Similarly, entropy production by longwave radiation is computed by emitted irradiance to space from layers in the atmosphere and surface divided by their temperatures. Global annual mean entropy production by shortwave absorption and longwave emission to space are, respectively, 0.852 and 0.928 W m−2 K−1. With a steady-state assumption, entropy production by irreversible processes within the Earth system is estimated to be 0.076 W m−2 K−1 and by nonradiative irreversible processes to be 0.049 W m−2 K−1. Both global annual mean entropy productions by shortwave absorption and longwave emission to space increase with increasing shortwave absorption (i.e., with decreasing the planetary albedo). The increase of entropy production by shortwave absorption is, however, larger than the increase of entropy production by longwave emission to space. The result implies that global annual mean entropy production by irreversible processes decreases with increasing shortwave absorption. Input and output temperatures derived by dividing the absorbed shortwave irradiance and emitted longwave irradiance to space by respective entropy production are, respectively, 282 and 259 K, which give the Carnot efficiency of the Earth system of 8.5%.
Kato, Seiji; Rutan, David A.; Rose, Fred G.; Caldwell, Thomas E.; Ham, Seung-Hee; Radkevich, Alexander; Thorsen, Tyler J.; Viudez-Mora, Antonio; Fillmore, David; Huang, XiangleiKato, S., D. A. Rutan, F. G. Rose, T. E. Caldwell, S. Ham, A. Radkevich, T. J. Thorsen, A. Viudez-Mora, D. Fillmore, X. Huang, 2020: Uncertainty in Satellite-Derived Surface Irradiances and Challenges in Producing Surface Radiation Budget Climate Data Record. Remote Sensing, 12(12), 1950. doi: 10.3390/rs12121950. The Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) Edition 4.1 data product provides global surface irradiances. Uncertainties in the global and regional monthly and annual mean all-sky net shortwave, longwave, and shortwave plus longwave (total) irradiances are estimated using ground-based observations. Error covariance is derived from surface irradiance sensitivity to surface, atmospheric, cloud and aerosol property perturbations. Uncertainties in global annual mean net shortwave, longwave, and total irradiances at the surface are, respectively, 5.7 Wm−2, 6.7 Wm−2, and 9.7 Wm−2. In addition, the uncertainty in surface downward irradiance monthly anomalies and their trends are estimated based on the difference derived from EBAF surface irradiances and observations. The uncertainty in the decadal trend suggests that when differences of decadal global mean downward shortwave and longwave irradiances are, respectively, greater than 0.45 Wm−2 and 0.52 Wm−2, the difference is larger than 1σ uncertainties. However, surface irradiance observation sites are located predominately over tropical oceans and the northern hemisphere mid-latitude. As a consequence, the effect of a discontinuity introduced by using multiple geostationary satellites in deriving cloud properties is likely to be excluded from these trend and decadal change uncertainty estimates. Nevertheless, the monthly anomaly timeseries of radiative cooling in the atmosphere (multiplied by −1) agrees reasonably well with the anomaly time series of diabatic heating derived from global mean precipitation and sensible heat flux with a correlation coefficient of 0.46. surface radiation budget; variability; regional monthly mean
Kelley, Maxwell; Schmidt, Gavin A.; Nazarenko, Larissa S.; Bauer, Susanne E.; Ruedy, Reto; Russell, Gary L.; Ackerman, Andrew S.; Aleinov, Igor; Bauer, Michael; Bleck, Rainer; Canuto, Vittorio; Cesana, Grégory; Cheng, Ye; Clune, Thomas L.; Cook, Ben I.; Cruz, Carlos A.; Genio, Anthony D. Del; Elsaesser, Gregory S.; Faluvegi, Greg; Kiang, Nancy Y.; Kim, Daehyun; Lacis, Andrew A.; Leboissetier, Anthony; LeGrande, Allegra N.; Lo, Ken K.; Marshall, John; Matthews, Elaine E.; McDermid, Sonali; Mezuman, Keren; Miller, Ron L.; Murray, Lee T.; Oinas, Valdar; Orbe, Clara; García‐Pando, Carlos Pérez; Perlwitz, Jan P.; Puma, Michael J.; Rind, David; Romanou, Anastasia; Shindell, Drew T.; Sun, Shan; Tausnev, Nick; Tsigaridis, Kostas; Tselioudis, George; Weng, Ensheng; Wu, Jingbo; Yao, Mao-SungKelley, M., G. A. Schmidt, L. S. Nazarenko, S. E. Bauer, R. Ruedy, G. L. Russell, A. S. Ackerman, I. Aleinov, M. Bauer, R. Bleck, V. Canuto, G. Cesana, Y. Cheng, T. L. Clune, B. I. Cook, C. A. Cruz, A. D. D. Genio, G. S. Elsaesser, G. Faluvegi, N. Y. Kiang, D. Kim, A. A. Lacis, A. Leboissetier, A. N. LeGrande, K. K. Lo, J. Marshall, E. E. Matthews, S. McDermid, K. Mezuman, R. L. Miller, L. T. Murray, V. Oinas, C. Orbe, C. P. García‐Pando, J. P. Perlwitz, M. J. Puma, D. Rind, A. Romanou, D. T. Shindell, S. Sun, N. Tausnev, K. Tsigaridis, G. Tselioudis, E. Weng, J. Wu, M. Yao, 2020: GISS-E2.1: Configurations and Climatology. Journal of Advances in Modeling Earth Systems, 12(8), e2019MS002025. doi: 10.1029/2019MS002025. This paper describes the GISS-E2.1 contribution to the Coupled Model Intercomparison Project, Phase 6 (CMIP6). This model version differs from the predecessor model (GISS-E2) chiefly due to parameterization improvements to the atmospheric and ocean model components, while keeping atmospheric resolution the same. Model skill when compared to modern era climatologies is significantly higher than in previous versions. Additionally, updates in forcings have a material impact on the results. In particular, there have been specific improvements in representations of modes of variability (such as the Madden-Julian Oscillation and other modes in the Pacific) and significant improvements in the simulation of the climate of the Southern Oceans, including sea ice. The effective climate sensitivity to 2 × CO2 is slightly higher than previously at 2.7–3.1°C (depending on version) and is a result of lower CO2 radiative forcing and stronger positive feedbacks. climate change; CMIP6; General Circulation Model; NASA GISS
Kim, Siyun; Park, Sungsu; Shin, JihoonKim, S., S. Park, J. Shin, 2020: Impact of Subgrid Variation of Water Vapor on Longwave Radiation in a General Circulation Model. Journal of Advances in Modeling Earth Systems, 12(4), e2019MS001926. doi: 10.1029/2019MS001926. Most general circulation models compute radiation fluxes by assuming that water vapor is uniform within individual grid layers, which leads to an underestimation of satellite-observed longwave (LW) cloud radiative forcing (LWCF). To fix this problem, we calculated water vapor content separately for clear and cloudy portions and used them to compute LW radiation. The impacts of this modification were examined by comparing two global simulations with and without the modification (NEW and OLD, respectively). Global-annual mean LWCF from NEW was 1.8 W m−2 higher than that of OLD, thus remedying a long-standing negative bias of LWCF. This improvement is a combined result of more clear-sky and less all-sky upward LW flux at the top of the atmosphere than OLD. Large increases in LWCF and clear-sky LW flux occurred in the tropical deep convection and midlatitude storm track regions where upper- and middle-level clouds are abundant. Although only the LW radiation scheme was modified, global-annual mean shortwave cloud radiative forcing also increased, particularly in the vicinity of the eastern subtropical marine stratocumulus decks through radiative feedback processes. With this improved treatment, it may be possible to tune general circulation models in a more flexible and physical way without introducing compensating errors. longwave radiation; GCM; longwave cloud radiative forcing; water vapor inhomogeneity
Kotsuki, Shunji; Sato, Yousuke; Miyoshi, TakemasaKotsuki, S., Y. Sato, T. Miyoshi, 2020: Data Assimilation for Climate Research: Model Parameter Estimation of Large-Scale Condensation Scheme. Journal of Geophysical Research: Atmospheres, 125(1), e2019JD031304. doi: 10.1029/2019JD031304. This study proposes using data assimilation (DA) for climate research as a tool for optimizing model parameters objectively. Mitigating radiation bias is very important for climate change assessments with general circulation models. With the Nonhydrostatic ICosahedral Atmospheric Model (NICAM), this study estimated an autoconversion parameter in a large-scale condensation scheme. We investigated two approaches to reducing radiation bias: examining useful satellite observations for parameter estimation and exploring the advantages of estimating spatially varying parameters. The parameter estimation accelerated autoconversion speed when we used liquid water path, outgoing longwave radiation, or outgoing shortwave radiation (OSR). Accelerated autoconversion reduced clouds and mitigated overestimated OSR bias of the NICAM. An ensemble-based DA with horizontal localization can estimate spatially varying parameters. When liquid water path was used, the local parameter estimation resulted in better cloud representations and improved OSR bias in regions where shallow clouds are dominant. radiation; data assimilation; global climate model; large-scale condensation; liquid water path; parameter estimation
Kratz, David P.; Gupta, Shashi K.; Wilber, Anne C.; Sothcott, Victor E.Kratz, D. P., S. K. Gupta, A. C. Wilber, V. E. Sothcott, 2020: Validation of the CERES Edition-4A Surface-Only Flux Algorithms. J. Appl. Meteor. Climatol., 59(2), 281-295. doi: 10.1175/JAMC-D-19-0068.1. Surface radiative fluxes have been derived with the objective of supplementing top-of-atmosphere (TOA) radiative fluxes being measured under NASA’s Clouds and the Earth’s Radiant Energy System (CERES) project. This has been accomplished by using combinations of CERES TOA measurements, parameterized radiative transfer algorithms, and high-quality meteorological datasets available from reanalysis projects. Current CERES footprint-level products include surface fluxes derived from two shortwave (SW) and three longwave (LW) algorithms designated as SW models A and B and LW models A, B, and C. The SW and LW models A work for clear conditions only; the other models work for both clear and cloudy conditions. The current CERES Edition-4A computed surface fluxes from all models are validated against ground-based flux measurements from high-quality surface networks like the Baseline Surface Radiation Network and NOAA’s Surface Radiation Budget Network (SURFRAD). Validation results as systematic and random errors are provided for all models, separately for five different surface types and combined for all surface types as tables and scatterplots. Validation of surface fluxes is now a part of CERES processing and is used to continually improve the above algorithms. Since both models B work for clear and cloudy conditions alike and meet the accuracy requirement, their results are considered to be the most reliable and most likely to be retained for future work. Both models A have limited use given that they work for clear skies only. Models B will continue to undergo further improvement as more validation results become available.
Kuma, P.; McDonald, A. J.; Morgenstern, O.; Alexander, S. P.; Cassano, J. J.; Garrett, S.; Halla, J.; Hartery, S.; Harvey, M. J.; Parsons, S.; Plank, G.; Varma, V.; Williams, J.Kuma, P., A. J. McDonald, O. Morgenstern, S. P. Alexander, J. J. Cassano, S. Garrett, J. Halla, S. Hartery, M. J. Harvey, S. Parsons, G. Plank, V. Varma, J. Williams, 2020: Evaluation of Southern Ocean cloud in the HadGEM3 general circulation model and MERRA-2 reanalysis using ship-based observations. Atmospheric Chemistry and Physics, 20(11), 6607–6630. doi: 10.5194/acp-20-6607-2020.
Kumar, Siddharth; Phani, R.; Mukhopadhyay, P.; Balaji, C.Kumar, S., R. Phani, P. Mukhopadhyay, C. Balaji, 2020: An assessment of radiative flux biases in the climate forecast system model CFSv2. Climate Dynamics. doi: 10.1007/s00382-020-05546-2. An extensive analysis of radiative flux biases in the Climate Forecast System Model Version 2 (CFSv2) is done. Annual mean and seasonal variations of biases at the surface and top of the atmosphere (TOA) are reported in the global domain. Large regional biases in shortwave (SW) and longwave (LW) radiation are observed over convectively active zones in the tropics. The relative contribution of various processes responsible for the reported biases is quantified. The poor simulation of clouds and inadequate representation of surface properties seem to be major contributors. Over certain regions, errors due to different processes add up, whereas, over other regions, errors tend to nullify each other. Surface and atmospheric variables taken as input parameters in the radiative transfer modules are compared with satellite-based observations. The maximum biases in SW and LW radiation are observed over the regions of persistent low clouds. The magnitude of the SW and LW biases at the TOA is in phase with the biases in cloud fraction by and large. However, the error in the radiative fluxes due to errors in surface radiative properties is of equal importance. The cold bias in near-surface air temperature reported in other studies may partly be attributed to an underestimation in the net SW radiation at the surface. In the present study, a plausible prescription is also provided to correct the source of the biases.
Largeron, Yann; Guichard, Françoise; Roehrig, Romain; Couvreux, Fleur; Barbier, JessicaLargeron, Y., F. Guichard, R. Roehrig, F. Couvreux, J. Barbier, 2020: The April 2010 North African heatwave: when the water vapor greenhouse effect drives nighttime temperatures. Climate Dynamics, 54(9), 3879-3905. doi: 10.1007/s00382-020-05204-7. North Africa experienced a severe heatwave in April 2010 with daily maximum temperatures ($$T_{max}$$Tmax) frequently exceeding $$40\,^{\circ }\mathrm{C}$$40∘Cand daily minimum temperatures ($$T_{min}$$Tmin) over $$27\,^{\circ }\mathrm{C}$$27∘Cfor more than five consecutive days in extended Saharan and Sahelian areas. Observations show that areas and periods affected by the heatwave correspond to strong positive anomalies of surface incoming longwave fluxes ($$LW_{in}$$LWin) and negative anomalies of incoming shortwave fluxes ($$SW_{in}$$SWin). The latter are explained by clouds in the Sahara, and by both clouds and dust loadings in the Sahel. However, the strong positive anomalies of $$LW_{in}$$LWinare hardly related to cloud or aerosol radiative effects. An analysis based on climate-model simulations (CNRM-AM) complemented by a specially-designed conceptual soil-atmospheric surface layer model (SARAWI) shows that this positive anomaly of $$LW_{in}$$LWinis mainly due to a water vapor greenhouse effect. SARAWI, which represents the two processes driving temperatures, namely turbulence and longwave radiative transfer between the soil and the atmospheric surface layer, points to the crucial impact of synoptic low-level advection of water vapor on $$T_{min}$$Tmin. By increasing the atmospheric infrared emissivity, the advected water vapor dramatically increases the nocturnal radiative warming of the soil surface, then in turn reducing the nocturnal cooling of the atmospheric surface layer, which remains warm throughout the night. Over Western Sahel, this advection is related to an early northward incursion of the monsoon flow. Over Sahara, the anomalously high precipitable water is due to a tropical plume event. Both observations and simulations support this major influence of the low-level water vapor radiative effect on $$T_{min}$$Tminduring this spring heatwave.
Laszlo, Istvan; Liu, Hongqing; Kim, Hye-Yun; Pinker, Rachel T.Laszlo, I., H. Liu, H. Kim, R. T. Pinker, 2020: Chapter 15 - Shortwave Radiation from ABI on the GOES-R Series. The GOES-R Series, 179-191. Two components of SRB, solar radiation reflected to space and solar radiation reaching the surface, are retrieved from the Advanced Baseline Imager (ABI). Physical algorithms are used that combine forward and inverse methods to estimate reflection and transmission and account for all major interactions of the radiation with the atmosphere and the surface. Owing to the improved upstream ABI cloud and aerosol product inputs, and because of availability of calibrated solar reflective bands on ABI, the two products represent an improvement in quality over legacy radiation products. Preliminary evaluation of the two products with reference data indicates that they meet expectations. Satellite; Advanced Baseline Imager (ABI); Clear-sky composite; Direct path; GOES (Geostationary Operational Environmental Satellite); Indirect path; Narrow-to-broadband transformation; Radiation budget; Shortwave; Surface; Top of atmosphere
Lehmann, Peter; Bickel, Samuel; Wei, Zhongwang; Or, DaniLehmann, P., S. Bickel, Z. Wei, D. Or, 2020: Physical Constraints for Improved Soil Hydraulic Parameter Estimation by Pedotransfer Functions. Water Resources Research, 56(4), e2019WR025963. doi: 10.1029/2019WR025963. Global land surface models use spatially distributed soil information for the parameterization of soil hydraulic properties (SHP). Parameters of measured SHP are correlated with easy-to-measure soil properties to construct general pedotransfer functions (PTFs) used to predict SHP from spatial soil information. Global PTFs are based on a limited number of samples yielding highly variable and poorly constrained SHP. The study implements a physical constraint, soil-specific capillary length, to reduce unphysical combinations of SHP. The procedure fits concurrently soil water retention and capillary length using the same parameters. Results suggest that meeting the capillary length constraint has minor effects on the goodness of fit to soil water retention data. Constrained SHP were applied to represent 4 years of lysimeter fluxes yielding evapotranspiration values in close agreement with measurements relative to slight overestimation by unconstrained SHP. The procedure was applied for testing constraint SHP at a regional scale in New Zealand using the surface evaporation capacitance model and Noah-MP for detailed simulations of land surface processes. The use of constrained SHP in both models yields higher surface runoff in agreement with observations (unconstrained SHP severely underestimated runoff generation). The concept of constrained SHP could be extended to include other physical constraints to improve PTFs, for example, by consideration of vegetation cover and soil structure effects on infiltration. characteristic length; pedotransfer function; soil hydraulic properties; soil water characteristics
León, José Andrés PérezLeón, J., . Andrés Pérez, 2020: Progress towards assimilating cloud radar and lidar observations. ECMWF. Successful weather forecasts start from accurate estimates of the current state of the Earth system. Such estimates are obtained by combining model information with Earth system observations in a process called data assimilation. Recent work at ECMWF has demonstrated for the first time that assimilating cloud observations from satellite radar and lidar instruments into a global, operational forecasting system using a 4D-Var data assimilation system is feasible and improves weather forecasts.
Letu, Husi; Shi, Jiancheng; Li, Ming; Wang, Tianxing; Shang, Huazhe; Lei, Yonghui; Ji, Dabin; Wen, Jianguang; Yang, Kun; Chen, LiangfuLetu, H., J. Shi, M. Li, T. Wang, H. Shang, Y. Lei, D. Ji, J. Wen, K. Yang, L. Chen, 2020: A review of the estimation of downward surface shortwave radiation based on satellite data: Methods, progress and problems. Science China Earth Sciences, 63(6), 774-789. doi: 10.1007/s11430-019-9589-0. The estimation of downward surface shortwave radiation (DSSR) is important for the Earth’s energy budget and climate change studies. This review was organised from the perspectives of satellite sensors, algorithms and future trends, retrospects and summaries of the satellite-based retrieval methods of DSSR that have been developed over the past 10 years. The shortwave radiation reaching the Earth’s surface is affected by both atmospheric and land surface parameters. In recent years, studies have given detailed considerations to the factors which affect DSSR. It is important to improve the retrieval accuracy of cloud microphysical parameters and aerosols and to reduce the uncertainties caused by complex topographies and high-albedo surfaces (such as snow-covered areas) on DSSR estimation. This review classified DSSR retrieval methods into four categories: empirical, parameterisation, look-up table and machine-learning methods, and evaluated their advantages, disadvantages and accuracy. Further efforts are needed to improve the calculation accuracy of atmospheric parameters such as cloud, haze, water vapor and other land surface parameters such as albedo of complex terrain and bright surface, organically combine machine learning and other methods, use the new-generation geostationary satellite and polar orbit satellite data to produce high-resolution DSSR products, and promote the application of radiation products in hydrological and climate models.
Li, J.-L. F.; Xu, K.-M.; Jiang, J. H.; Lee, Wei-Liang; Wang, Li-Chiao; Yu, Jia-Yuh; Stephens, G.; Fetzer, Eric; Wang, Yi-HuiLi, J. F., K. Xu, J. H. Jiang, W. Lee, L. Wang, J. Yu, G. Stephens, E. Fetzer, Y. Wang, 2020: An Overview of CMIP5 and CMIP6 Simulated Cloud Ice, Radiation Fields, Surface Wind Stress, Sea Surface Temperatures, and Precipitation Over Tropical and Subtropical Oceans. Journal of Geophysical Research: Atmospheres, 125(15), e2020JD032848. doi: 10.1029/2020JD032848. Abstract The potential links between ice water path (IWP), radiation, circulation, sea surface temperature (SST), and precipitation over the Pacific and Atlantic Oceans resulting from the falling ice radiative effects (FIREs) are examined from Coupled Model Intercomparison Project phase 5 (CMIP5) and phase 6 (CMIP6) historical simulations. The latter is divided into two subsets with (SON6) and without FIREs (NOS6) in CMIP6. Improvement in nonfalling cloud ice (~20 g m?2) is noticeable over convective regions in CMIP6 relative to CMIP5. The inclusion of FIREs in SON6 subset may contribute to reduce biases of overestimated outgoing longwave radiation and downward surface shortwave and underestimated reflected shortwave at the top of the atmosphere (TOA) by magnitudes of ~8 W m?2 over convective regions against CERES, compared to NOS6 subset. The reduced biases in radiative fluxes in convective regions stabilize the atmosphere and lead to circulation, SST, cloud, and precipitation changes over the trade wind regions, as seen from improved radiative fluxes (~15 W m?2), surface wind stress biases, SST (~0.8 K), and precipitation (1 mm day?1) biases. The significant improvement from NOS6 to SON6 leads to improved multimodel means for CMIP6 relative to CMIP5 for radiation fields over the trade wind regions but the degradation over convective zones is attributed to NOS6 subset. The results suggest that other sources of uncertainty and deficiencies in climate models may play significant roles for reducing discrepancies although FIREs, via radiation-circulation coupling, may be one of the factors that help to reduce regional biases.
Li, Jiandong; You, Qinglong; He, BianLi, J., Q. You, B. He, 2020: Distinctive spring shortwave cloud radiative effect and its inter-annual variation over southeastern China. Atmospheric Science Letters, 21(6), e970. doi: 10.1002/asl.970. The shortwave cloud radiative effect (SWCRE) plays a critical role in the earth's radiation balance, and its global mean magnitude is much larger than the warming effect induced by greenhouse gases. This study investigates the SWCRE at the top of the atmosphere and its inter-annual variation over southeastern China (SEC) using satellite retrievals and ERA-Interim reanalysis data. The results show that in this region the largest SWCRE with the maximum intensity up to −120 W·m−2 occurs in spring and is also the strongest between 60°S and 60°N. The domain-averaged intensity of SWCRE is much larger than the longwave cloud radiative effect (LWCRE), suggesting the dominant cooling role of SWCRE in the regional atmosphere–surface system. The spring SWCRE over SEC shows a weak increasing trend and its anomalies in most years exceed those of LWCRE during 2000–2017. This means that SWCRE also plays a dominant role in the inter-annual variation of regional cloud radiative effects. Over SEC, low- to mid-level ascending motion and water vapor convergence during spring favor the generation and maintenance of cloud water, leading to strong SWCRE. Statistical analysis shows that the spatial pattern and intensity of the spring SWCRE are well correlated with the low- to mid-level ascending motion and water vapor convergence. The temporal correlation coefficient between domain-averaged spring SWCRE and 850–500-hPa vertical velocity is .76 during 2000–2017. The long-term variation in spring SWCRE over SEC can be inferred to some extent from regional ascending motion and associated large-scale circulations. southeastern China; ascending motion; inter-annual variation; shortwave cloud radiative effect; spring
Li, Lijuan; Dong, Li; Xie, Jinbo; Tang, Yanli; Xie, Feng; Guo, Zhun; Liu, Hongbo; Feng, Tao; Wang, Lu; Pu, Ye; Sun, Wenqi; Xia, Kun; Liu, Li; Xie, Zhenghui; Wang, Yan; Wang, Longhuan; Shi, Xiangjun; Jia, Binghao; Liu, Juanjuan; Wang, BinLi, L., L. Dong, J. Xie, Y. Tang, F. Xie, Z. Guo, H. Liu, T. Feng, L. Wang, Y. Pu, W. Sun, K. Xia, L. Liu, Z. Xie, Y. Wang, L. Wang, X. Shi, B. Jia, J. Liu, B. Wang, 2020: The GAMIL3: Model Description and Evaluation. Journal of Geophysical Research: Atmospheres, 125(15), e2020JD032574. doi: 10.1029/2020JD032574. The Grid-point Atmospheric Model of the IAP LASG version 3 (GAMIL3) has been developed by upgrading the horizontal resolution, methods of parallel computation, boundary layer scheme, aerosol parameterization, convective parameterization, stratocumulus cloud fraction scheme, land component, and coupler, as well as tuning some moist physical parameters with large uncertainties. Its performance is evaluated, and the results show significant improvements compared with the previous version, GAMIL2. The simulated performance of mean states is notably enhanced, including the energy budget terms at the top of the atmosphere (TOA) and surface, shortwave/longwave cloud radiative forcing (SWCF/LWCF), precipitation, zonal wind, low-level temperature, 500-hPa geopotential height, and snow cover fraction in the Northern Hemisphere. The characteristics of internal variability are captured well, such as the frequency band and active areas of quasi-biweekly (QBW) oscillation, spectral power of convectively coupled equatorial waves (CCEWs), Madden-Julian Oscillation (MJO) eastward propagation, and heat flux response to El Niño-Southern Oscillation (ENSO), and these variabilities are generally strengthened in GAMIL3. In addition, the anthropogenic aerosol climate effects are weakened when using the forcings recommended by CMIP6.
Li, Xia; Krueger, Steven K.; Strong, Courtenay; Mace, Gerald G.Li, X., S. K. Krueger, C. Strong, G. G. Mace, 2020: Relationship Between Wintertime Leads and Low Clouds in the Pan-Arctic. Journal of Geophysical Research: Atmospheres, 125(18), e2020JD032595. doi: 10.1029/2020JD032595. Wintertime leads play an important role in the Arctic boundary layer as they promote turbulent flux exchanges from the warm exposed water to the cold atmosphere, thereby affecting the boundary layer cloudiness and structure. Recent work suggests that less (more) low-level cloud occurrence is found in higher (lower) lead fraction periods, yet the analysis efforts were limited to a peripheral sea north of Barrow, Alaska. Here, we extend the previous study to examine this relationship between wintertime Arctic leads and low clouds in the context of a longer time series (November–March, 2006–2011) and greater spatial coverage (pan-Arctic), based on cloud products from CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellites and lead area fraction derived from Advanced Microwave Scanning Radiometer for EOS (AMSR-E) observations. We focus on the east side of high-pressure systems to isolate lead impacts on boundary layer clouds. Using a k-means cluster-analysis algorithm, low-level cloud regimes are categorized on the basis of occurrence frequency of low-level clouds. We find that, in the pan-Arctic, less (more) low-level cloud occurrence is associated with higher (lower) large-scale lead flux, in agreement with the previous study. This lead-low cloud association exhibits strong regional variation; it is enhanced over the Beaufort Sea where the variability of large-scale meteorological conditions is decreased. These results suggest that a higher lead fraction might have important impacts on the Arctic surface energy budget by decreasing downwelling longwave radiation through reduced low-level cloudiness.
Li, Xiaoyuan; Mauzerall, Denise L.; Bergin, Mike H.Li, X., D. L. Mauzerall, M. H. Bergin, 2020: Global reduction of solar power generation efficiency due to aerosols and panel soiling. Nature Sustainability, 3(9), 720-727. doi: 10.1038/s41893-020-0553-2. Air pollution and dust prevail over many regions that have rapid growth of solar photovoltaic (PV) electricity generation, potentially reducing PV generation. Here we combine solar PV performance modelling with long-term satellite-observation-constrained surface irradiance, aerosol deposition and precipitation rates to provide a global picture of the impact of particulate matter (PM) on PV generation. We consider attenuation caused by both atmospheric PM and PM deposition on panels (soiling) in calculating the overall effect of PM on PV generation, and include precipitation removal of soiling and the benefits of panel cleaning. Our results reveal that, with no cleaning and precipitation-only removal, PV generation in heavily polluted and desert regions is reduced by more than 50% by PM, with soiling accounting for more than two-thirds of the total reduction. Our findings highlight the benefit of cleaning panels in heavily polluted regions with low precipitation and the potential to increase PV generation through air-quality improvements.
Li, Xin; Liang, Hongyu; Cheng, WeimingLi, X., H. Liang, W. Cheng, 2020: Spatio-Temporal Variation in AOD and Correlation Analysis with PAR and NPP in China from 2001 to 2017. Remote Sensing, 12(6), 976. doi: 10.3390/rs12060976. Atmospheric aerosols can elicit variations in how much solar radiation reaches the ground surface due to scattering and absorption, which may affect plant photosynthesis and carbon uptake in terrestrial ecosystems. In this study, the spatio-temporal variations in aerosol optical depth (AOD) are compared with that in photosynthetically active radiation (PAR) and net primary productivity (NPP) during 2001–2017 in China using multiple remote sensing data. The correlations between them are analyzed at different scales. Overall, the AOD exhibited a northeast-to-southwest decreasing pattern in space. A national increasing trend of 0.004 year−1 and a declining trend of −0.007 year−1 of AOD are observed during 2001–2008 and 2009–2017. The direct PAR (PARdir) and diffuse PAR (PARdif) present consistent and opposite tendency with AOD during two periods, respectively. The total PAR (PARtotal) shows a similar variation pattern with PARdir. In terms of annual variation, the peaks of AOD coincide with the peaks of PARdif and the troughs of PARdir, indicating that aerosols have a significant positive impact on PARdir and a negative impact on PARdif. Furthermore, the PARdir has a stronger negative association with AOD than the positive correlation between PARdif and AOD at national and regional scales, indicating that PARdir is more sensitive to aerosol changes. The NPP has higher values in the east than in the west and exhibits a significant increasing trend of 0.035 gCm−2day−1 after 2008. The NPP has a negative correlation (−0.4–0) with AOD and PARdif and a positive correlation (0–0.4) with PARdir in most areas of China. The area covered by forests has the highest NPP-PAR correlation, indicating that NPP in forests is more sensitive to the PAR than is the NPP in grasslands and croplands. This study is beneficial for interpreting the aerosol-induced PAR impact on plant growth and for predicting plant production on haze days. AOD; PAR; correlation; NPP; spatio-temporal variation
Li, Zhujun; Xu, Kuan-ManLi, Z., K. Xu, 2020: Arctic Clouds Simulated by a Multiscale Modeling Framework and Comparisons With Observations and Conventional GCMs. Journal of Geophysical Research: Atmospheres, 125(1), e2019JD030522. doi: 10.1029/2019JD030522. Clouds are an important component of the Arctic climate system through their regulation of the surface energy budget; however, Arctic clouds are poorly simulated in global climate models (GCMs). In this study, we evaluate the Arctic clouds simulated by a multiscale modeling framework (MMF). The results are compared against a merged CloudSat-CALIPSO radar-lidar cloud product and contrasted with an atmospheric reanalysis and conventional GCMs. The comparisons focus on the annual cycle of cloud covers, vertical structures of cloud fraction, and condensate mixing ratio, as well as the relationships between low-cloud cover and atmospheric static stability. The MMF is found to represent Arctic boundary layer clouds slightly more realistically than the reanalysis and GCMs in both the annual cycle and vertical distribution except that middle- and high-cloud covers are underestimated and the amplitude of annual cycle of total cloud cover is larger. The relationship between low-cloud cover and near-surface atmospheric stability produced by MMF is remarkably similar to the satellite observation during autumn, winter, and early spring, as low-cloud cover decreases with colder surface and stronger stability. Such relationships over the annual cycle are not reproduced by other modeling approaches. Lastly, MMF yields a positive correlation between low-cloud cover and atmospheric stability over the Arctic ocean from May to August, opposite to the satellite observation, implying stronger control of horizontal advection on low-cloud formation. This modeled relationship is contributed by cloud fraction near the surface, which is known to be underestimated due to radar's surface clutter.
Lin, Yanluan; Huang, Xiaomeng; Liang, Yishuang; Qin, Yi; Xu, Shiming; Huang, Wenyu; Xu, Fanghua; Liu, Li; Wang, Yong; Peng, Yiran; Wang, Lanning; Xue, Wei; Fu, Haohuan; Zhang, Guang Jun; Wang, Bin; Li, Ruizhe; Zhang, Cheng; Lu, Hui; Yang, Kun; Luo, Yong; Bai, Yuqi; Song, Zhenya; Wang, Minqi; Zhao, Wenjie; Zhang, Feng; Xu, Jingheng; Zhao, Xi; Lu, Chunsong; Chen, Yizhao; Luo, Yiqi; Hu, Yong; Tang, Qiang; Chen, Dexun; Yang, Guangwen; Gong, PengLin, Y., X. Huang, Y. Liang, Y. Qin, S. Xu, W. Huang, F. Xu, L. Liu, Y. Wang, Y. Peng, L. Wang, W. Xue, H. Fu, G. J. Zhang, B. Wang, R. Li, C. Zhang, H. Lu, K. Yang, Y. Luo, Y. Bai, Z. Song, M. Wang, W. Zhao, F. Zhang, J. Xu, X. Zhao, C. Lu, Y. Chen, Y. Luo, Y. Hu, Q. Tang, D. Chen, G. Yang, P. Gong, 2020: Community Integrated Earth System Model (CIESM): Description and Evaluation. Journal of Advances in Modeling Earth Systems, 12(8), e2019MS002036. doi: 10.1029/2019MS002036. A team effort to develop a Community Integrated Earth System Model (CIESM) was initiated in China in 2012. The model was based on NCAR Community Earth System Model (Version 1.2.1) with several novel developments and modifications aimed to overcome some persistent systematic biases, such as the double Intertropical Convergence Zone problem and underestimated marine boundary layer clouds. Aerosols' direct and indirect effects are prescribed using the MACv2-SP approach and data sets. The spin-up of a 500-year preindustrial simulation and three historical simulations are described and evaluated. Prominent improvements include alleviated double Intertropical Convergence Zone problem, increased marine boundary layer clouds, and better El Niño Southern Oscillation amplitude and periods. One deficiency of the model is the significantly underestimated Arctic and Antarctic sea ice in warm seasons. The historical warming is about 0.55 °C greater than observations toward 2014. CIESM has an equilibrium climate sensitivity of 5.67 K, mainly resulted from increased positive shortwave cloud feedback. Our efforts on porting and redesigning CIESM for the heterogeneous Sunway TaihuLight supercomputer are also introduced, including some ongoing developments toward a future version of the model. preindustrial and historical simulations; Community Integrated Earth System Model; coupled model evaluation
Liu, Xin; Kang, Yanming; Liu, Qiong; Guo, Zijia; Chen, Yonghang; Huang, Dizhi; Chen, Chunmei; Zhang, HuaLiu, X., Y. Kang, Q. Liu, Z. Guo, Y. Chen, D. Huang, C. Chen, H. Zhang, 2020: Evaluation of net shortwave radiation over China with a regional climate model. Climate Research, 80(2), 147-163. doi: 10.3354/cr01598. The regional climate model RegCM version 4.6, developed by the European Centre for Medium-Range Weather Forecasts Reanalysis, was used to simulate the radiation budget over China. Clouds and the Earth’s Radiant Energy System (CERES) satellite data were utilized to evaluate the simulation results based on 4 radiative components: net shortwave (NSW) radiation at the surface of the earth and top of the atmosphere (TOA) under all-sky and clear-sky conditions. The performance of the model for low-value areas of NSW was superior to that for high-value areas. NSW at the surface and TOA under all-sky conditions was significantly underestimated; the spatial distribution of the bias was negative in the north and positive in the south, bounded by 25°N for the annual and seasonal averaged difference maps. Compared with the all-sky condition, the simulation effect under clear-sky conditions was significantly better, which indicates that the cloud fraction is the key factor affecting the accuracy of the simulation. In particular, the bias of the TOA NSW under the clear-sky condition was China; Net shortwave radiation; RegCM4.6; Regional climate mode
Loeb, Norman G.; Doelling, David R.Loeb, N. G., D. R. Doelling, 2020: CERES Energy Balanced and Filled (EBAF) from Afternoon-Only Satellite Orbits. Remote Sensing, 12(8), 1280. doi: 10.3390/rs12081280. The Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) data product uses a diurnal correction methodology to produce a shortwave (SW) top-of-atmosphere (TOA) radiative flux time series that accounts for diurnal cycle changes between CERES observation times while ensuring that the stability of the EBAF record is tied as closely as possible to CERES instrument calibration stability. The current EBAF Ed4.1 data product combines observations from Terra and Aqua after July 2002. However, the Terra satellite will start to drift in Mean Local Time (MLT) in early 2021, and Aqua’s MLT will start to drift in 2022. To ensure the EBAF record remains temporally stable, we explore the feasibility of using only CERES instruments from afternoon satellite orbits with a tight 1330 MLT after July 2002. We test this approach by directly comparing SW TOA fluxes generated after applying diurnal corrections to Aqua-only and to Terra + Aqua for 07/2002–06/2019. We find that global climatological mean SW TOA fluxes for these two cases are within 0.01 Wm−2 and the trend of the difference is < is 0.03 Wm−2 per decade. climate; radiation budget; diurnal
Loeb, Norman G.; Rose, Fred G.; Kato, Seiji; Rutan, David A.; Su, Wenying; Wang, Hailan; Doelling, David R.; Smith, William L.; Gettelman, AndrewLoeb, N. G., F. G. Rose, S. Kato, D. A. Rutan, W. Su, H. Wang, D. R. Doelling, W. L. Smith, A. Gettelman, 2020: Toward a Consistent Definition between Satellite and Model Clear-Sky Radiative Fluxes. J. Climate, 33(1), 61-75. doi: 10.1175/JCLI-D-19-0381.1. A new method of determining clear-sky radiative fluxes from satellite observations for climate model evaluation is presented. The method consists of applying adjustment factors to existing satellite clear-sky broadband radiative fluxes that make the observed and simulated clear-sky flux definitions more consistent. The adjustment factors are determined from the difference between observation-based radiative transfer model calculations of monthly mean clear-sky fluxes obtained by ignoring clouds in the atmospheric column and by weighting hourly mean clear-sky fluxes with imager-based clear-area fractions. The global mean longwave (LW) adjustment factor is −2.2 W m−2 at the top of the atmosphere and 2.7 W m−2 at the surface. The LW adjustment factors are pronounced at high latitudes during winter and in regions with high upper-tropospheric humidity and cirrus cloud cover, such as over the west tropical Pacific, and the South Pacific and intertropical convergence zones. In the shortwave (SW), global mean adjustment is 0.5 W m−2 at TOA and −1.9 W m−2 at the surface. It is most pronounced over sea ice off of Antarctica and over heavy aerosol regions, such as eastern China. However, interannual variations in the regional SW and LW adjustment factors are small compared to those in cloud radiative effect. After applying the LW adjustment factors, differences in zonal mean cloud radiative effect between observations and climate models decrease markedly between 60°S and 60°N and poleward of 65°N. The largest regional improvements occur over the west tropical Pacific and Indian Oceans. In contrast, the impact of the SW adjustment factors is much smaller.
Loeb, Norman G.; Wang, Hailan; Allan, Richard P.; Andrews, Timothy; Armour, Kyle; Cole, Jason N. S.; Dufresne, Jean-Louis; Forster, Piers; Gettelman, Andrew; Guo, Huan; Mauritsen, Thorsten; Ming, Yi; Paynter, David; Proistosescu, Cristian; Stuecker, Malte F.; Willén, Ulrika; Wyser, KlausLoeb, N. G., H. Wang, R. P. Allan, T. Andrews, K. Armour, J. N. S. Cole, J. Dufresne, P. Forster, A. Gettelman, H. Guo, T. Mauritsen, Y. Ming, D. Paynter, C. Proistosescu, M. F. Stuecker, U. Willén, K. Wyser, 2020: New Generation of Climate Models Track Recent Unprecedented Changes in Earth's Radiation Budget Observed by CERES. Geophysical Research Letters, 47(5), e2019GL086705. doi: 10.1029/2019GL086705. We compare top-of-atmosphere (TOA) radiative fluxes observed by the Clouds and the Earth's Radiant Energy System (CERES) and simulated by seven general circulation models forced with observed sea-surface temperature (SST) and sea-ice boundary conditions. In response to increased SSTs along the equator and over the eastern Pacific (EP) following the so-called global warming “hiatus” of the early 21st century, simulated TOA flux changes are remarkably similar to CERES. Both show outgoing shortwave and longwave TOA flux changes that largely cancel over the west and central tropical Pacific, and large reductions in shortwave flux for EP low-cloud regions. A model's ability to represent changes in the relationship between global mean net TOA flux and surface temperature depends upon how well it represents shortwave flux changes in low-cloud regions, with most showing too little sensitivity to EP SST changes, suggesting a “pattern effect” that may be too weak compared to observations.
Ma, Han; Liang, Shunlin; Shi, Hanyu; Zhang, YiMa, H., S. Liang, H. Shi, Y. Zhang, 2020: An Optimization Approach for Estimating Multiple Land Surface and Atmospheric Variables From the Geostationary Advanced Himawari Imager Top-of-Atmosphere Observations. IEEE Transactions on Geoscience and Remote Sensing, 1-21. doi: 10.1109/TGRS.2020.3007118. Since a new generation of geostationary satellite data has incredibly high temporal, spatial, and spectral resolutions, new methodologies are now needed to take advantage of both the temporal and spectral signatures of them for accurate estimation of Earth's environmental variables. This article describes a novel optimization method to estimate a suite of 11 physically consistent land surface and atmospheric variables under all-sky conditions from the geostationary advanced Himawari imager (AHI) top-of-atmosphere (TOA) observations. This method is based on a coupled soil, snow, vegetation, and atmospheric radiative transfer (RT) model from 0.28 to 14 μm. The inversion algorithm consists of three major steps. First, the “clearest” observations at each moment during a temporal window were determined and then the essential variables that characterize surface RT models, such as leaf area index (LAI), leaf chlorophyll concentration, and soil parameters were estimated. Second, the atmospheric variables, including aerosol optical depth (AOD) under clear-sky conditions, and cloud optical thickness (COT) and cloud effective particle radius (CER) under cloudy-sky conditions, were inverted given surface reflectance calculated by the surface RT models. Finally, the inverted atmospheric and land surface variables were fed into the coupled RT model to calculate the remaining set of variables, including spectral directional reflectance, surface broadband albedo, thermal emissivity, incident shortwave radiation (ISR), photosynthetically active radiation (PAR), fraction of absorbed PAR by green vegetation (FAPAR), and TOA shortwave albedo. The retrieved variables were validated using in-situ measurements from Ozflux network sites and compared with the other existing satellite products. Intercomparisons demonstrate that the AHI-retrieved atmospheric variables (AOD, CER, and COT) and surface variables (surface reflectance, LAI, FAPAR, PAR, and surface emissivity) are well correlated with the corresponding JAXA released AHI, NASA Moderate Resolution Imaging Spectroradiometer (MODIS) and Clouds and the Earth's Radiant Energy System (CERES), and the Global LAnd Surface Satellite (GLASS) products. Direct validation using in-situ measurements indicates that the retrieved ISR achieves higher accuracy than the CERES ISR product (with R² values of 0.95 and 0.89, and root-mean-square error (RMSE) of 20.3 and 29.6 W/m² for the AHI-retrieved and CERES daily ISR, respectively). Validation also shows that the estimated daily surface albedo has an accuracy comparable to the MODIS daily albedo product (RMSE = 0.03). Both the direct validation and product comparisons have demonstrated that this proposed inversion framework works very well for the AHI data. Unlike other algorithms that are usually used for estimating an individual parameter and rely heavily on a separate atmospheric correction, this inversion framework can effectively estimate a group of atmospheric and land surface variables and be easily applied to other similar multispectral geostationary satellite data. A comprehensive sensitivity and validation study is still needed to quantify the uncertainties of the retrieval variables. Land surface; MODIS; Atmospheric modeling; remote sensing.; Clouds; Advanced Himawari imager (AHI); coupled radiative transfer (RT) model; geostationary satellite; inversion; optimization; Soil
Ma, Libin; Yang, ShuangyanMa, L., S. Yang, 2020: Impacts of the stochastic multicloud parameterization on the simulation of Western North Pacific summer rainfall. Atmospheric Research, 244, 105067. doi: 10.1016/j.atmosres.2020.105067. This study investigated the sensitivity of the western North Pacific (WNP) summer precipitation to the convection schemes and discussed the associated dynamical processes. Two convection schemes were compared: one is the default mass-flux convection scheme used in the state-of-the-art ECHAM6.3 atmosphere model and the other incorporates the Stochastic Multicloud Model (SMCM) into ECHAM6.3. Incorporation of the SMCM reduces the bias of cloud cover and shortwave and longwave radiation by regulating the shortwave and longwave cloud radiative forcing over the WNP. Compared to the default model, the modified model with the SMCM alleviates the dry bias in the WNP, which is associated with enhanced ascending motion. The moist static energy balance revealed that improved simulation of precipitation in the modified model is contributed by enhanced horizontal advection of moist enthalpy and increased net energy in the atmosphere, which is attributed to increased total cloud cover, over the WNP. Additionally, intensified latent energy advection over the WNP dominates enhanced horizontal advection of moist enthalpy in the modified model. On the other hand, the moisture budget analysis of the WNP demonstrated that strengthened convergence of moisture flux in the modified model plays the most influential role in reducing precipitation bias. Further analysis unraveled that enhanced zonal-mean moisture transported by the stationary eddy zonal flow convergence in the WNP dominates intensified zonal moisture convergence, thus increased horizontal convergence of moist flux in the modified model. ECHAM6.3 atmosphere model; Moist static energy balance; Moisture budget analysis; The Stochastic Multicloud Model; The western North Pacific precipitation
Ma, Qianrong; Zhang, Jie; Gu, Yu; Ma, Yujun; Cao, YuMa, Q., J. Zhang, Y. Gu, Y. Ma, Y. Cao, 2020: Seasonal and Regional Variability of Long-Wave Effective Radiation in China and Associated Modulating Factors. Advances in Meteorology, 2020, 1689431. doi: 10.1155/2020/1689431. Variations in all-sky and clear-sky long-wave effective radiation (LER) in China during the period 2001–2016 were determined using monthly radiative datasets from the Clouds and the Earth’s Radiant Energy System (CERES). Annual and seasonal spatial distributions are found to be quite similar and show a decreasing trend from northwest to southeast, although highest values are found in spring. Mean LER under clear-sky conditions is approximately 20–30 Wm−2 higher than that under all-sky conditions. There is a consistent downward trend in annual and seasonal variations of LER under different weather conditions in China especially after 2007. In northwest China, the eastern Tibetan Plateau, and southeast and northeast China, LER is significantly reduced in two weather conditions and this is more pronounced in spring. However, decreases in clear-sky LER are more obvious. Empirical orthogonal function (EOF) results for LER differences between all-sky conditions and clear-sky conditions were used to analyze regional characteristics and modulating factors. The first mode shows that the LER differences of two weather conditions over China become larger and significant after 2007. The second mode reflects the spatial characteristics, and four climate regions are divided according to the second pattern. According to the definition of LER, regression analysis shows that downward long-wave radiation has a greater influence on LER. When considering cloud effects and other modulating factors, LER has higher correlation with relative humidity in climate regions 3 and 4. However, there are higher negative correlations with middle and high clouds in regions 1 and 2, which are modulated by cloud characteristics. When these factors influence LER together, their correlation is significant in all regions (correlation coefficients are on average higher than 0.7). In summary, changes of LER can well reflect the change of climate system.
Mackie, Anna; Wild, Martin; Brindley, Helen; Folini, Doris; Palmer, Paul I.Mackie, A., M. Wild, H. Brindley, D. Folini, P. I. Palmer, 2020: Observed and CMIP5-Simulated Radiative Flux Variability Over West Africa. Earth and Space Science, 7(5), e2019EA001017. doi: 10.1029/2019EA001017. We explore the ability of general circulation models in the Coupled Model Intercomparison Project (CMIP5) to recreate observed seasonal variability in top-of-the-atmosphere and surface radiation fluxes over West Africa. This tests CMIP5 models' ability to describe the radiative energy partitioning, which is fundamental to our understanding of the current climate and its future changes. We use 15 years of the monthly Clouds and the Earth's Radiant Energy System Energy Balanced and Filled (EBAF) product, alongside other satellite, reanalysis, and surface station products. We find that the CMIP5 multimodel mean is generally within the reference product range, with annual mean CMIP5 multimodel mean—EBAF of −0.5 W m−2 for top-of-the-atmosphere reflected shortwave radiation, and 4.6 W m−2 in outgoing longwave radiation over West Africa. However, the range in annual mean of the model seasonal cycles is large (37.2 and 34.0 W m−2 for reflected shortwave radiation and outgoing longwave radiation, respectively). We use seasonal and regional contrasts in all-sky fluxes to infer that the representation of the West African monsoon in numerical models affects radiative energy partitioning. Using clear-sky surface fluxes, we find that the models tend to have more downwelling shortwave and less downwelling longwave radiation than EBAF, consistent with past research. We find models that are drier and have lower aerosol loading tend to show the largest differences. We find evidence that aerosol variability has a larger effect in modulating downwelling shortwave radiation than water vapor in EBAF, while the opposite effect is seen in the majority of CMIP5 models. aerosols; water vapor; CMIP5; TOA radiation flux; West African monsoon
Madeleine, Jean-Baptiste; Hourdin, Frédéric; Grandpeix, Jean-Yves; Rio, Catherine; Dufresne, Jean-Louis; Vignon, Etienne; Boucher, Olivier; Konsta, Dimitra; Cheruy, Frédérique; Musat, Ionela; Idelkadi, Abderrahmane; Fairhead, Laurent; Millour, Ehouarn; Lefebvre, Marie-Pierre; Mellul, Lidia; Rochetin, Nicolas; Lemonnier, Florentin; Touzé‐Peiffer, Ludovic; Bonazzola, MarineMadeleine, J., F. Hourdin, J. Grandpeix, C. Rio, J. Dufresne, E. Vignon, O. Boucher, D. Konsta, F. Cheruy, I. Musat, A. Idelkadi, L. Fairhead, E. Millour, M. Lefebvre, L. Mellul, N. Rochetin, F. Lemonnier, L. Touzé‐Peiffer, M. Bonazzola, 2020: Improved representation of clouds in the atmospheric component LMDZ6A of the IPSL Earth system model IPSL-CM6A. Journal of Advances in Modeling Earth Systems, 12(10), e2020MS002046. doi: 10.1029/2020MS002046. The cloud parameterizations of the LMDZ6A climate model (the atmospheric component of the IPSL-CM6 Earth system model) are entirely described and the global cloud distribution and cloud radiative effects are evaluated against the CALIPSO-CloudSat and CERES observations. The cloud parameterizations in recent versions of LMDZ favor an object-oriented approach for convection, with two distinct parameterizations for shallow and deep convection, and a coupling between convection and cloud description through the specification of the subgrid scale distribution of water. Compared to the previous version of the model (LMDZ5A), LMDZ6A better represents the low-level cloud distribution in the tropical belt, and low-level cloud reflectance and cover are closer to the PARASOL and CALIPSO-GOCCP observations. Mid-level clouds, which were mostly missing in LMDZ5A, are now better represented globally. The distribution of cloud liquid and ice in mixed-phase clouds is also in better agreement with the observations. Among identified deficiencies, low-level cloud covers are too high in mid-to high-latitude regions and high-level cloud covers are biased low globally. However, the cloud global distribution is significantly improved and progress has been made in the tuning of the model, resulting in a radiative balance in close agreement with the CERES observations. Improved tuning also revealed structural biases in LMDZ6A, which are currently being addressed through a series of new physical and radiative parameterizations for the next version of LMDZ. cloud radiative effect; global climate model; mixed-phase clouds; CMIP6; climate model tuning; subgrid-scale parameterization
Mantsis, Damianos F.; Sherwood, Steven; Dixit, Vishal; Morrison, Hugh; Thompson, GregMantsis, D. F., S. Sherwood, V. Dixit, H. Morrison, G. Thompson, 2020: Mid-level clouds over the Sahara in a convection-permitting regional model. Climate Dynamics, 54(7), 3425-3439. doi: 10.1007/s00382-020-05188-4. The simulation of Saharan mid tropospheric clouds is investigated with the weather research and forecasting (WRF) regional atmospheric model at convection permitting (4 km) horizontal grid-spacing. We identify two potential problems in such simulations: one that affects cloud cover, and another that affects the mean and geographic patterns of both cloud and precipitation. Our simulations show that using a vertical grid typical of GCMs (38 levels) inhibits the formation of Saharan mid-level clouds. In particular, it underestimates the supercooled water content that often resides at the top of these clouds, in favour of ice which falls out of the cloud quickly. When the vertical resolution becomes high enough to allow layers of supercooled water and ice to exist separately, the simulation of the Saharan mid-level clouds improves significantly. Additional improvement is achieved by using realistic high resolution surface albedo, which also shows that low albedo areas favour the formation of mid-level clouds much more than high albedo ones. The simulation of precipitation on the northern edge of the Sahel is also improved with the use of realistic surface albedo. Overall, despite the disagreement of the simulated and the observed clouds, our results show that using increased resolution and realistic surface albedo seems to fully reproduce their observed radiative effect.
Marchand, Roger T; Hinkelman, Laura M.Marchand, R. T., L. M. Hinkelman, 2020: Evaluation of CERES and CloudSat Surface Radiative Fluxes over the Southern Ocean. Earth and Space Science Open Archive, 32. doi: 10.1002/essoar.10502814.1. Many studies involving surface radiative fluxes rely on surface fluxes retrieved by the Clouds and the Earth’s Radiant Energy System (CERES) project, or derived from spaceborne cloud radar and lidar observations (CloudSat-CALIPSO). In particular, most climate models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) were found to have too little shortwave radiation being reflected back to space and excessive shortwave radiation reaching the surface over the Southern Ocean – an error with significant consequences for predicting both regional and global climate. There have been few evaluations of CERES or CloudSat retrievals over the Southern Ocean. In this article, CERES and CloudSat retrieved surface shortwave (SW) and longwave (LW) downwelling fluxes are evaluated using surface observations collected over the Southern Ocean during the Macquarie Island Cloud and Radiation Experiment (MICRE). Overall, biases (CERES – surface observations) in the CERES- surface fluxes are found to be slightly larger over Macquarie Island than most other regions, approximately +10 Wm for the SW and -10 Wm for the LW in the annual mean, but with significant seasonal and diurnal variations. If the Macquarie observations are representative of the larger SO, these results imply that CMIP5 model errors in SW surface fluxes are (if anything) somewhat larger than previous evaluation studies suggest. The bias in LW surface flux shows a marked increase at night, which explains most of the total LW bias. The nighttime bias is due to poor representation of cloud base associated with low clouds.
McCoy, Daniel T.; Field, Paul; Bodas-Salcedo, Alejandro; Elsaesser, Gregory S.; Zelinka, Mark D.McCoy, D. T., P. Field, A. Bodas-Salcedo, G. S. Elsaesser, M. D. Zelinka, 2020: A regime-oriented approach to observationally constraining extratropical shortwave cloud feedbacks. J. Climate, 33(23), 9967–9983. doi: 10.1175/JCLI-D-19-0987.1.
McGraw, Zachary; Storelvmo, Trude; David, Robert O.; Sagoo, NavjitMcGraw, Z., T. Storelvmo, R. O. David, N. Sagoo, 2020: Global Radiative Impacts of Mineral Dust Perturbations Through Stratiform Clouds. Journal of Geophysical Research: Atmospheres, 125(23), e2019JD031807. doi: https://doi.org/10.1029/2019JD031807. Airborne mineral dust influences cloud occurrence and optical properties, which may provide a pathway for recent and future changes in dust concentration to alter the temperature at Earth's surface. However, despite prior suggestions that dust-cloud interactions are an important control on the Earth's radiation balance, we find global mean cloud radiative effects to be insensitive to widespread dust changes. Here we simulate uniformly applied shifts in dust amount in a present-day atmosphere using a version of the CAM5 atmosphere model (within CESM v1.2.2) modified to incorporate laboratory-based ice nucleation parameterizations in stratiform clouds. Increasing and decreasing dustiness from current levels to paleoclimate extremes caused effective radiative forcings through clouds of +0.02 ± 0.01 and −0.05 ± 0.02 W/m2, respectively, with ranges of −0.26 to +0.13 W/m2 and −0.21 to +0.39 W/m2 from sensitivity tests. Our simulations suggest that these forcings are limited by several factors. Longwave and shortwave impacts largely cancel, particularly in mixed-phase clouds, while in warm and cirrus clouds opposite responses between regions further reduce each global forcing. Additionally, changes in dustiness cause opposite forcings through aerosol indirect effects in mixed-phase clouds as in cirrus, while in warm clouds indirect effects are weak at nearly all locations. Nevertheless, regional forcings and global impacts on longwave and shortwave radiation were found to be nonnegligible, suggesting that cloud-mediated dust effects have significance in simulations of present and future climate. cirrus clouds; mineral dust; aerosol indirect effects; mixed-phase clouds; climate modeling; ice nucleation
Meftah, Mustapha; Damé, Luc; Keckhut, Philippe; Bekki, Slimane; Sarkissian, Alain; Hauchecorne, Alain; Bertran, Emmanuel; Carta, Jean-Paul; Rogers, David; Abbaki, Sadok; Dufour, Christophe; Gilbert, Pierre; Lapauw, Laurent; Vieau, André-Jean; Arrateig, Xavier; Muscat, Nicolas; Bove, Philippe; Sandana, Éric; Teherani, Ferechteh; Li, Tong; Pradel, Gilbert; Mahé, Michel; Mercier, Christophe; Paskeviciute, Agne; Segura, Kevin; Berciano Alba, Alicia; Aboulila, Ahmed; Chang, Loren; Chandran, Amal; Dahoo, Pierre-Richard; Bui, AlainMeftah, M., L. Damé, P. Keckhut, S. Bekki, A. Sarkissian, A. Hauchecorne, E. Bertran, J. Carta, D. Rogers, S. Abbaki, C. Dufour, P. Gilbert, L. Lapauw, A. Vieau, X. Arrateig, N. Muscat, P. Bove, É. Sandana, F. Teherani, T. Li, G. Pradel, M. Mahé, C. Mercier, A. Paskeviciute, K. Segura, A. Berciano Alba, A. Aboulila, L. Chang, A. Chandran, P. Dahoo, A. Bui, 2020: UVSQ-SAT, a Pathfinder CubeSat Mission for Observing Essential Climate Variables. Remote Sensing, 12(1), 92. doi: 10.3390/rs12010092. The UltraViolet and infrared Sensors at high Quantum efficiency onboard a small SATellite (UVSQ-SAT) mission aims to demonstrate pioneering technologies for broadband measurement of the Earth’s radiation budget (ERB) and solar spectral irradiance (SSI) in the Herzberg continuum (200–242 nm) using high quantum efficiency ultraviolet and infrared sensors. This research and innovation mission has been initiated by the University of Versailles Saint-Quentin-en-Yvelines (UVSQ) with the support of the International Satellite Program in Research and Education (INSPIRE). The motivation of the UVSQ-SAT mission is to experiment miniaturized remote sensing sensors that could be used in the multi-point observation of Essential Climate Variables (ECV) by a small satellite constellation. UVSQ-SAT represents the first step in this ambitious satellite constellation project which is currently under development under the responsibility of the Laboratory Atmospheres, Environments, Space Observations (LATMOS), with the UVSQ-SAT CubeSat launch planned for 2020/2021. The UVSQ-SAT scientific payload consists of twelve miniaturized thermopile-based radiation sensors for monitoring incoming solar radiation and outgoing terrestrial radiation, four photodiodes that benefit from the intrinsic advantages of Ga 2 O 3 alloy-based sensors made by pulsed laser deposition for measuring solar UV spectral irradiance, and a new three-axis accelerometer/gyroscope/compass for satellite attitude estimation. We present here the scientific objectives of the UVSQ-SAT mission along the concepts and properties of the CubeSat platform and its payload. We also present the results of a numerical simulation study on the spatial reconstruction of the Earth’s radiation budget, on a geographical grid of 1 ° × 1 ° degree latitude-longitude, that could be achieved with UVSQ-SAT for different observation periods. carbon nanotubes; earth’s radiation budget; Ga2O3; nanosatellite remote sensing; photodiodes; solar–terrestrial relations; thermopiles; UV solar spectral irradiance
Minnis, Patrick; Sun-Mack, Szedung; Chen, Yan; Chang, Fu-Lung; Yost, Christopher R.; Smith, William L.; Heck, Patrick W.; Arduini, Robert F.; Bedka, Sarah T.; Yi, Yuhong; Hong, Gang; Jin, Zhonghai; Painemal, David; Palikonda, Rabindra; Scarino, Benjamin R.; Spangenberg, Douglas A.; Smith, Rita A.; Trepte, Qing Z.; Yang, Ping; Xie, YuMinnis, P., S. Sun-Mack, Y. Chen, F. Chang, C. R. Yost, W. L. Smith, P. W. Heck, R. F. Arduini, S. T. Bedka, Y. Yi, G. Hong, Z. Jin, D. Painemal, R. Palikonda, B. R. Scarino, D. A. Spangenberg, R. A. Smith, Q. Z. Trepte, P. Yang, Y. Xie, 2020: CERES MODIS Cloud Product Retrievals for Edition 4–Part I: Algorithm Changes. IEEE Transactions on Geoscience and Remote Sensing, 1-37. doi: 10.1109/TGRS.2020.3008866. The Edition 2 (Ed2) cloud property retrieval algorithm system was upgraded and applied to the MODerate-resolution Imaging Spectroradiometer (MODIS) data for the Clouds and the Earth's Radiant Energy System (CERES) Edition 4 (Ed4) products. New calibrations for solar channels and the use of the 1.24-μm channel for cloud optical depth (COD) over snow improve the daytime consistency between Terra and Aqua MODIS retrievals. Use of additional spectral channels and revised logic enhanced the cloud-top phase retrieval accuracy. A new ice crystal reflectance model and a CO₂-channel algorithm retrieved higher ice clouds, while a new regional lapse rate technique produced more accurate water cloud heights than in Ed2. Ice cloud base heights are more accurate due to a new cloud thickness parameterization. Overall, CODs increased, especially over the polar (PO) regions. The mean particle sizes increased slightly for water clouds, but more so for ice clouds in the PO areas. New experimental parameters introduced in Ed4 are limited in utility, but will be revised for the next CERES edition. As part of the Ed4 retrieval evaluation, the average properties are compared with those from other algorithms and the differences between individual reference data and matched Ed4 retrievals are explored. Part II of this article provides a comprehensive, objective evaluation of selected parameters. More accurate interpretation of the CERES radiation measurements has resulted from the use of the Ed4 cloud properties. cloud; Meteorology; MODIS; Optical imaging; Integrated optics; Clouds; Ice; Climate; Cloud computing; cloud height; cloud optical depth (COD); cloud phase; validation.; cloud particle size; cloud remote sensing MODerate-resolution Imaging Spectroradiometer (MODIS); clouds and the Earth's radiant energy system (CERES)
Muench, Steffen; Lohmann, UlrikeMuench, S., U. Lohmann, 2020: Developing a Cloud Scheme with Prognostic Cloud Fraction and Two Moment Microphysics for ECHAM-HAM. Journal of Advances in Modeling Earth Systems, 12(8), e2019MS001824. doi: 10.1029/2019MS001824. We present a new cloud scheme for the ECHAM-HAM global climate model (GCM) that includes prognostic cloud fraction, and allows for sub- and supersaturation with respect to ice separately in the cloud-free and cloudy air. Stratiform clouds form by convective detrainment, turbulent vertical diffusion, and large-scale ascent. For each process, the corresponding cloud fraction is calculated and the individual updraft velocities are used to determine cloud droplet/ice crystal number concentrations. Further, convective condensate is always detrained as supercooled cloud droplets at mixed-phase temperatures (between 235 and 273 K), and convectively detrained ice crystal number concentrations are calculated based on the updraft velocity. Finally, the new scheme explicitly calculates condensation/evaporation and deposition/sublimation rates for phase-change calculations. The new cloud scheme simulates a reasonable present-day climate, reduces the previously overestimated cirrus cloud fraction, and in general improves the simulation of ice clouds. The model simulates the observed in-cloud supersaturation for cirrus clouds, and it allows for a better representation of the tropical to extra-tropical ratio of the longwave cloud radiative effect. Further, the ice water path, the ice crystal number concentrations, and the supercooled liquid fractions in mixed-phase clouds agree better with observations in the new model than in the reference model. Ice crystal formation is dominated by the liquid-origin processes of convective detrainment and homogeneous freezing of cloud droplets. The simulated ice clouds strongly depend on model tuning choices, in particular, the enhancement of the aggregation rate of ice crystals. Cloud microphysics; Cloud cover; Clouds; Ice clouds; Climate model
Myers, Timothy A.; Mechoso, Carlos R.Myers, T. A., C. R. Mechoso, 2020: Relative Contributions of Atmospheric, Oceanic, and Coupled Processes to North Pacific and North Atlantic Variability. Geophysical Research Letters, 47(5), e2019GL086321. doi: 10.1029/2019GL086321. Patterns of sea surface temperature (SST) variability over the northern oceans arise from a combination of atmospheric, oceanic, and coupled processes. Here we use a novel methodology and a suite of observations to quantify the processes contributing to the dominant patterns of interannual SST variability over these regions. We decompose the upper ocean heat content tendency associated with such dominant patterns into contributions from different heat fluxes: (a) atmospherically driven, (b) surface feedbacks, and (c) oceanic. We find that in the subtropics, cloud radiative flux, turbulent heat flux, and residual oceanic processes each contributes substantially to North Pacific SST variability, whereas turbulent heat flux primarily induces North Atlantic SST variability. Cloud radiative fluxes therefore provide a major source of interannual SST variability in the North Pacific but not in the North Atlantic. In midlatitudes, SST fluctuations over the northern oceans are driven by the combination of turbulent and oceanic heat fluxes.
Niyogi, Dev; Jamshidi, Sajad; Smith, David; Kellner, OliviaNiyogi, D., S. Jamshidi, D. Smith, O. Kellner, 2020: Evapotranspiration Climatology of Indiana Using In Situ and Remotely Sensed Products. J. Appl. Meteor. Climatol., 59(12), 2093-2111. doi: 10.1175/JAMC-D-20-0024.1. AbstractAn intercomparison of multiresolution evapotranspiration (ET) datasets with reference to ground-based measurements for the development of regional reference (ETref) and actual (ETa) evapotranspiration maps over Indiana is presented. A representative ETref equation for the state is identified by evaluating 10 years of in situ measurements (2009–19). A statewide ETref climatology is developed using the ETref equation and high-resolution surface meteorological data from the gridded surface meteorological dataset (gridMET). For ETa analyses, MODIS, Simplified Surface Energy Balance Operational dataset (SSEBop), Global Land Evaporation Amsterdam Model (GLEAM) (versions 3.3a and 3.3b), and NLDAS (Noah and VIC) datasets are evaluated using AmeriFlux data. Thirty years of rainfall data from Climate Hazards Group Infrared Precipitation with Station Data Rainfall (CHIRPS) are used with the ET datasets to develop effective precipitation fields. Results show that the standardized Penman–Monteith equation performs as the best ETref equation with median symmetric accuracy (MSA) of 0.37, Taylor’s skill score (TSC) of 0.89, and r2 = 0.83. The analysis shows that the gridMET dataset overestimates wind speed and requires adjustment before a series of statewide ETref climatology maps are generated (1990–2020). For ETa, the MODIS and GLEAM (3.3b) datasets outperform the rest, with MSA = 0.5, TSC = 0.8, and r2 = 0.8. The state ETa dataset is generated using all MODIS data from 2003 and blending the MODIS data with GLEAM (3.3b) to cover data unavailability. Using the top-performing datasets, annual ETref for Indiana is computed as 1110 mm, ETa as 708 mm, and precipitation as 1091 mm. A marginal increasing climatological trend is found for Indiana’s ETref (0.013 mm yr−1) while ETa is found to be relatively stable. The state’s water availability, defined as rainfall minus ETa, has remained positive and stable at 0.99 mm day−1 (annual magnitude of +3820 mm).
Obregón, Maria A.; Costa, Maria João; Silva, Ana Maria; Serrano, AntonioObregón, M. A., M. J. Costa, A. M. Silva, A. Serrano, 2020: Spatial and Temporal Variation of Aerosol and Water Vapour Effects on Solar Radiation in the Mediterranean Basin during the Last Two Decades. Remote Sensing, 12(8), 1316. doi: 10.3390/rs12081316. This study aims to calculate and analyse the spatial and temporal variation of aerosol optical thickness (AOT) and precipitable water vapour (PWV) and their effects on solar radiation at the surface in the Mediterranean basin, one of the maritime areas with the largest aerosol loads in the world. For the achievement of this objective, a novel and validated methodology was applied. Satellite data, specifically CERES (Clouds and the Earth’s Radiant Energy System) SYN1deg products during the period 2000–2018, were used. Results show that the spatial distribution of AOT and PWV are closely linked to the spatial distributions of its effects on solar radiation. These effects are negative, indicating a reduction of solar radiation reaching the surface due to aerosol and water vapour effects. This reduction ranges between 2% and 8% for AOT, 11.5% and 15% for PWV and 14% and 20% for the combined effect. The analysis of the temporal distribution has focused on the detection of trends from their anomalies. This study has contributed to a better understanding of AOT and PWV effects on solar radiation over the Mediterranean basin, one of the most climatically sensitive regions of the planet, and highlighted the importance of water vapour. CERES; radiative effects; aerosol optical depth; Mediterranean basin; precipitable water vapour
Ollila, AnteroOllila, A., 2020: The Pause End and Major Temperature Impacts during Super El Niños are Due to Shortwave Radiation Anomalies. Physical Science International Journal, 1-20. doi: 10.9734/psij/2020/v24i230174. climate change; El Niño; ENSO; hiatus; Pause; shortwave changes
Oreopoulos, Lazaros; Cho, Nayeong; Lee, DongminOreopoulos, L., N. Cho, D. Lee, 2020: A Global Survey of Apparent Aerosol-Cloud Interaction Signals. Journal of Geophysical Research: Atmospheres, 125(1), e2019JD031287. doi: 10.1029/2019JD031287. We update and expand analysis of the apparent responses to aerosol variations of the planet's cloud regimes seen by the Moderate Resolution Imaging Spectroradiometer (MODIS). We distinguish between morning aerosol loadings and afternoon clouds and consider local scales explicitly. Aerosol loading is represented by gridded aerosol optical depth (AOD) from either MODIS or a reanalysis data set, while cloud information comes exclusively from MODIS. The afternoon cloud affected quantities (CAQs) examined in conjunction with morning AOD include precipitation and cloud radiative effect, in addition to cloud properties. One analysis thrust focuses on calculating global means distinguished by morning cloud regime, of afternoon CAQs, for distinct percentiles of grid cell seasonal morning AOD distributions. When the dependence of these global means on AOD is examined, we find persistent increases in cloud radiative fluxes with AOD as predicted by classic aerosol-cloud interaction paradigms, and also deviations from expected cloud responses, especially for precipitation. The other analysis thrust involves calculations at 1° scales of logarithmic CAQ sensitivities to AOD perturbations, approximated by linear regression slopes for distinct morning cloud regime groups. While the calculations are fundamentally local, we concentrate on the prevailing sensitivity signs in statistics of the slopes at global scales. Results from this second analysis approach indicate CAQ directions of change with AOD that are largely consistent with the first approach. When using a rather simple methodology where meteorological variables are treated as if they were CAQs, no conclusive results on the potential influence of meteorology on our findings are inferred. clouds; aerosol; MODIS; indirect effects; MERRA; satellite
Painemal, David; Chang, Fu-Lung; Ferrare, Richard; Burton, Sharon; Li, Zhujun; Smith Jr., William L.; Minnis, Patrick; Feng, Yan; Clayton, MarianPainemal, D., F. Chang, R. Ferrare, S. Burton, Z. Li, W. L. Smith Jr., P. Minnis, Y. Feng, M. Clayton, 2020: Reducing uncertainties in satellite estimates of aerosol–cloud interactions over the subtropical ocean by integrating vertically resolved aerosol observations. Atmospheric Chemistry and Physics, 20(12), 7167-7177. doi: https://doi.org/10.5194/acp-20-7167-2020. Abstract. Satellite quantification of aerosol effects on clouds relies on aerosol optical depth (AOD) as a proxy for aerosol concentration or cloud condensation nuclei (CCN). However, the lack of error characterization of satellite-based results hampers their use for the evaluation and improvement of global climate models. We show that the use of AOD for assessing aerosol–cloud interactions (ACIs) is inadequate over vast oceanic areas in the subtropics. Instead, we postulate that a more physical approach that consists of matching vertically resolved aerosol data from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite at the cloud-layer height with Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua cloud retrievals reduces uncertainties in satellite-based ACI estimates. Combined aerosol extinction coefficients (σ) below cloud top (σBC) from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and cloud droplet number concentrations (Nd) from MODIS Aqua yield high correlations across a broad range of σBC values, with σBC quartile correlations ≥0.78. In contrast, CALIOP-based AOD yields correlations with MODIS Nd of 0.54–0.62 for the two lower AOD quartiles. Moreover, σBC explains 41 % of the spatial variance in MODIS Nd, whereas AOD only explains 17 %, primarily caused by the lack of spatial covariability in the eastern Pacific. Compared with σBC, near-surface σ weakly correlates in space with MODIS Nd, accounting for a 16 % variance. It is concluded that the linear regression calculated from ln(Nd)–ln(σBC) (the standard method for quantifying ACIs) is more physically meaningful than that derived from the Nd–AOD pair.
Palchetti, L.; Brindley, H.; Bantges, R.; Buehler, S. A.; Camy-Peyret, C.; Carli, B.; Cortesi, U.; Bianco, S. Del; Natale, G. Di; Dinelli, B. M.; Feldman, D.; Huang, X. L.; C.-Labonnote, L.; Libois, Q.; Maestri, T.; Mlynczak, M. G.; Murray, J. E.; Oetjen, H.; Ridolfi, M.; Riese, M.; Russell, J.; Saunders, R.; Serio, C.Palchetti, L., H. Brindley, R. Bantges, S. A. Buehler, C. Camy-Peyret, B. Carli, U. Cortesi, S. D. Bianco, G. D. Natale, B. M. Dinelli, D. Feldman, X. L. Huang, L. C.-Labonnote, Q. Libois, T. Maestri, M. G. Mlynczak, J. E. Murray, H. Oetjen, M. Ridolfi, M. Riese, J. Russell, R. Saunders, C. Serio, 2020: FORUM: Unique Far-Infrared Satellite Observations to Better Understand How Earth Radiates Energy to Space. Bull. Amer. Meteor. Soc., 101(12), E2030-E2046. doi: 10.1175/BAMS-D-19-0322.1. AbstractThe outgoing longwave radiation (OLR) emitted to space is a fundamental component of the Earth’s energy budget. There are numerous, entangled physical processes that contribute to OLR and that are responsible for driving, and responding to, climate change. Spectrally resolved observations can disentangle these processes, but technical limitations have precluded accurate space-based spectral measurements covering the far infrared (FIR) from 100 to 667 cm−1 (wavelengths between 15 and 100 µm). The Earth’s FIR spectrum is thus essentially unmeasured even though at least half of the OLR arises from this spectral range. The region is strongly influenced by upper-tropospheric–lower-stratospheric water vapor, temperature lapse rate, ice cloud distribution, and microphysics, all critical parameters in the climate system that are highly variable and still poorly observed and understood. To cover this uncharted territory in Earth observations, the Far-Infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission has recently been selected as ESA’s ninth Earth Explorer mission for launch in 2026. The primary goal of FORUM is to measure, with high absolute accuracy, the FIR component of the spectrally resolved OLR for the first time with high spectral resolution and radiometric accuracy. The mission will provide a benchmark dataset of global observations which will significantly enhance our understanding of key forcing and feedback processes of the Earth’s atmosphere to enable more stringent evaluation of climate models. This paper describes the motivation for the mission, highlighting the scientific advances that are expected from the new measurements.
Pan, Fang; Kato, Seiji; Rose, Fred G.; Radkevich, Alexander; Liu, Xu; Huang, XiangleiPan, F., S. Kato, F. G. Rose, A. Radkevich, X. Liu, X. Huang, 2020: An Algorithm to Derive Temperature and Humidity Profile Changes Using Spatially and Temporally Averaged Spectral Radiance Differences. J. Atmos. Oceanic Technol., 37(7), 1173-1187. doi: 10.1175/JTECH-D-19-0143.1.
Pan, Zengxin; Mao, Feiyue; Lu, Xin; Gong, Wei; Shen, Huanfeng; Mao, QingzhouPan, Z., F. Mao, X. Lu, W. Gong, H. Shen, Q. Mao, 2020: Enhancement of vertical cloud-induced radiative heating in East Asian monsoon circulation derived from CloudSat-CALIPSO observations. International Journal of Remote Sensing, 41(2), 595-614. doi: 10.1080/01431161.2019.1646935. Improving the understanding of cloud–radiation–monsoon interactions is difficult due to the limited knowledge regarding the impacts of vertical cloud radiative forcing on monsoon circulation. Here, we focus on the annual cycle of the vertical structure of cloud-induced radiative heating (CRH) to evaluate further their impacts on the East Asian monsoon circulation (100°–140° E, 20°–45° N) derived from satellite observations and reanalysis datasets. Entire troposphere and lower stratosphere are heated by vertical CRH, with the peak reaching 1 K day−1 at the mid-level troposphere (4–10 km) during summer. Although radiative warming occurs below 3 km from the prevailing stratocumulus, widespread weak radiative cooling (approximately −0.2 K day−1) occurs at a wide vertical range above 3 km during winter. Consequently, the wind vector variations resulting from vertical CRH highly coincide with the monsoon circulation, leading to the increase in wind speeds by 1.8 and 0.5 m s−1 during summer and winter, respectively, while a weakly negative influence (about 0.3 m s−1) occurs at the low-level troposphere below 3 km during winter. Although high clouds, stratiform clouds, and stratocumulus dominate these wind vector variations, deep convective clouds generate the strongest updraft (up to 7 m s−1) amongst all cloud categories despite their low occurrence frequency. Results highlight the important enhancement of vertical CRH to East Asian monsoon circulation by perturbing the vertical structure of heating rate.
Pandey, Satyendra Kumar; Vinoj, V.; Panwar, AnnuPandey, S. K., V. Vinoj, A. Panwar, 2020: The short-term variability of aerosols and their impact on cloud properties and radiative effect over the Indo-Gangetic Plain. Atmospheric Pollution Research, 11(3), 630-638. doi: 10.1016/j.apr.2019.12.017. Anthropogenic activities have been shown to have a significant effect on weather and hence climate. However, discerning them from various observations over a certain region including India has been a challenge due to the large role played by natural variability. We show that anthropogenic signals in terms of sub-weekly scale are quite significant (of the order of 20%) in aerosol loading over the Indo-Gangetic Plains. These, in turn, clouds become thinner and less reflective with weekly variations of aerosol, which indicate the possible effect of aerosol on clouds. In terms of changes to Short Wave (SW) and Long Wave (LW) radiation fluxes, we find that change in aerosol direct effect is larger during cloudy sky conditions than clear sky conditions showing that aerosol induced changes to dynamics and hence clouds are dominant factors. This is also manifested in changes to cloud macro physical properties such as cloud optical depth (COD), cloud top temperature (CTT), cloud top pressure (CTP) and liquid water path (LWP). The changes in clear-sky and all-sky top of the atmosphere aerosol direct radiative effect (DRE) and cloud radiative effect (CRE) using CERES derived fluxes were found to be ~7–10% different during weekends with respect to weekly means. Similarly, the change in longwave cloud radiative effect is double that of the shortwave CRE. Aerosol direct effect; Anthropogenic aerosols; Cloud radiative effect; Indo-Gangetic plain
Papavasileiou, Georgios; Voigt, Aiko; Knippertz, PeterPapavasileiou, G., A. Voigt, P. Knippertz, 2020: The role of observed cloud-radiative anomalies for the dynamics of the North Atlantic Oscillation on synoptic time-scales. Quarterly Journal of the Royal Meteorological Society, 146(729), 1822-1841. doi: 10.1002/qj.3768. Clouds shape weather and climate by regulating the latent and radiative heating in the atmosphere. Recent work has demonstrated the importance of cloud-radiative effects (CRE) for the mean circulation of the extratropical atmosphere and its response to global warming. In contrast, little research has been done regarding the impact of CRE on internal variability. Here, we study how clouds and the North Atlantic Oscillation (NAO) couple on synoptic time-scales during Northern Hemisphere winter via CRE within the atmosphere (ACRE). A regression analysis based on 5-day mean data from CloudSat/CALIPSO, CERES and GERB satellite observations and ERA-Interim short-term forecast data reveals a robust dipole of high-level and low-level cloud-incidence anomalies during a positive NAO, with increased high-level cloud incidence along the storm track (near 45°N) and the subpolar Atlantic, and decreased high-level cloud incidence poleward and equatorward of this track. Opposite changes occur for low-level cloud incidence. The cloud anomalies lead to an anomalous column-mean heating from ACRE over the region of the Iceland low, and to a cooling over the region of the Azores high. To quantify the impact of the ACRE anomalies on the NAO, and to thereby test the hypothesis of a cloud-radiative feedback on the NAO persistence, we apply the surface pressure tendency equation for ERA-Interim short-term forecast data. The NAO-generated ACRE anomalies amplify the NAO-related surface pressure anomalies over the Azores high but have no area-averaged impact on the Iceland low. In contrast, diabatic processes as a whole, including latent heating and clear-sky radiation, strongly amplify the NAO-related surface pressure anomalies over both the Azores high and the Iceland low, and their impact is much more spatially coherent. This suggests that, while atmospheric cloud-radiative effects lead to an increase in NAO persistence on synoptic time-scales, their impact is relatively minor and much smaller than other diabatic processes. latent heating; atmospheric cloud-radiative effects (ACRE); cloud–circulation coupling; diabatic processes; North Atlantic Oscillation (NAO)
Pasut, Chiara; Tang, Fiona H. M.; Maggi, FedericoPasut, C., F. H. M. Tang, F. Maggi, 2020: A Mechanistic Analysis of Wetland Biogeochemistry in Response to Temperature, Vegetation, and Nutrient Input Changes. Journal of Geophysical Research: Biogeosciences, 125(4), e2019JG005437. doi: 10.1029/2019JG005437. Wetlands represent the most significant natural greenhouse gas (GHG) source and their annual emissions tightly depend on climatic and anthropogenic factors. Biogeochemical processes occurring in wetlands are still poorly described by mechanistic models and hence their dynamic response to environmental changes are weakly predicted. We investigated wetland GHG emissions, relevant electron acceptors and donors concentrations, and microbial composition resulting from changes in temperature, CH4 plant uptake efficiency, and SO deposition using a mechanistic biogeochemical model (here called BAMS3) that integrates the carbon (C), nitrogen (N), and sulfur (S) cycles. Parameters constraining the coupled C-N-S cycles were retrieved from controlled experiments and were validated against independent field data of CH4 emissions, and CH4(aq) and SO concentration profiles in a wetland in southern Michigan, USA (Shannon & White, 1994, http://hdl.handle.net/102.100.100/236252?index=1). We found that +1.75 °C increase in temperature leads to 22% and 30% increment in CH4 and N2O emissions, respectively. A decrease in the CH4 plant uptake efficiency causes the prevalent CH4 emission pathway to become diffusion mediated and resulted in 50% increase in the daily average CH4 emissions. Finally, a decreasing SO deposition rate can increase CH4 emissions up to 5%. We conclude that the increasing GHG emissions from wetlands is a result of both environmental and anthropogenic causes rather than global warming alone. An increase in model complexity does not necessary improve the estimation of GHG emissions but it aids interpretation of intermediate processes to a greater detail. modeling; nutrients; wetland
Pathak, Harshavardhana Sunil; Satheesh, Sreedharan Krishnakumari; Moorthy, Krishnaswamy Krishna; Nanjundiah, Ravi ShankarPathak, H. S., S. K. Satheesh, K. K. Moorthy, R. S. Nanjundiah, 2020: Assessment of Regional Aerosol Radiative Effects under SWAAMI Campaign – PART 2: Clear-sky Direct Shortwave Radiative Forcing using Multi-year Assimilated Data. Atmospheric Chemistry and Physics Discussions, 1-31. doi: https://doi.org/10.5194/acp-2020-454. Abstract. Clear-sky, direct shortwave Aerosol Radiative Forcing (ARF) has been estimated over the Indian region, for the first time employing multi-year (2009–2013) gridded, assimilated aerosol products. The aerosol datasets have been constructed following statistical assimilation of concurrent data from a dense network of ground-based observatories, and multi-satellite products, as described in Part-1 of this two-part paper. The ARF, thus estimated, are assessed for their superiority or otherwise over other ARF estimates based on satellite-retrieved aerosol products, over the Indian region, by comparing the radiative fluxes (upward) at Top of Atmosphere (TOA) estimated using assimilated products with spatio-temporally matched radiative flux values provided by CERES (Clouds and Earth's Radiant Energy System) Single Scan Footprint (SSF) product. This clearly demonstrated improved accuracy of the forcing estimates using the assimilated vis-a-vis satellite-based aerosol datasets; at regional, sub-regional and seasonal scales. The regional distribution of diurnally averaged ARF estimates has revealed (a) significant differences from similar estimates made using currently available satellite data, not only in terms of magnitude but also sign of TOA forcing; (b) largest magnitudes of surface cooling and atmospheric warming over IGP and arid regions from north-western India; and (c) negative TOA forcing over most parts of the Indian region, except for three sub-regions – the Indo-Gangetic plains (IGP), north-western India and eastern parts of peninsular India where the TOA forcing changes to positive during pre-monsoon season. Aerosol induced atmospheric warming rates, estimated using the assimilated data, demonstrate substantial spatial heterogeneities (~ 0.2 to 2.0 K day−1) over the study domain with the IGP demonstrating relatively stronger atmospheric heating rates (~ 0.6 to 2.0 K day−1). There exists a strong seasonality as well; with atmospheric warming being highest during pre-monsoon and lowest during winter seasons. It is to be noted that the present ARF estimates demonstrate substantially smaller uncertainties than their satellite counterparts, which is a natural consequence of reduced uncertainties in assimilated vis-a-vis satellite aerosol properties. The results demonstrate the potential application of the assimilated datasets and ARF estimates for improving accuracies of climate impact assessments at regional and sub-regional scales.
Pendergrass, A. G.Pendergrass, A. G., 2020: The Global-Mean Precipitation Response to CO2-Induced Warming in CMIP6 Models. Geophysical Research Letters, 47(17), e2020GL089964. doi: 10.1029/2020GL089964. We examine the response of globally averaged precipitation to global warming—the hydrologic sensitivity (HS)—in the Coupled Model Intercomparison Project phase 6 (CMIP6) multi-model ensemble. Multi-model mean HS is 2.5% K−1 (ranging from 2.1–3.1% K−1 across models), a modest decrease compared to CMIP5 (where it was 2.6% K−1). This new set of simulations is used as an out-of-sample test for observational constraints on HS proposed based on CMIP5. The constraint based on clear-sky shortwave absorption sensitivity to water vapor has weakened, and it is argued that a proposed constraint based on surface low cloud longwave radiative effects does not apply to HS. Finally, while a previously proposed mechanism connecting HS and climate sensitivity via low clouds is present in the CMIP6 ensemble, it is not an important factor for variations in HS. This explains why HS is uncorrelated with climate sensitivity across the CMIP5 and CMIP6 ensembles. climate change; climate models; precipitation; CMIP; climate sensitivity; emergent constraints
Perdigão, João; Canhoto, Paulo; Salgado, Rui; Costa, Maria JoãoPerdigão, J., P. Canhoto, R. Salgado, M. J. Costa, 2020: Assessment of Direct Normal Irradiance Forecasts Based on IFS/ECMWF Data and Observations in the South of Portugal. Forecasting, 2(2), 130-150. doi: 10.3390/forecast2020007. Direct Normal Irradiance (DNI) predictions obtained from the Integrated Forecasting System of the European Centre for Medium-Range Weather Forecast (IFS/ECMWF) were compared against ground-based observational data for one location at the south of Portugal (Évora). Hourly and daily DNI values were analyzed for different temporal forecast horizons (1 to 3 days ahead) and results show that the IFS/ECMWF slightly overestimates DNI for the period of analysis (1 August 2018 until 31 July 2019) with a fairly good agreement between model and observations. Hourly basis evaluation shows relatively high errors, independently of the forecast day. Root mean square error increases as the forecast time increases with a relative error of ~45% between the first and the last forecast. Similar patterns are observed in the daily analysis with comparable magnitude errors. The correlation coefficients between forecast and observed data are above 0.7 for both hourly and daily data. A methodology based on a new DNI attenuation Index (DAI) was developed to estimate cloud fraction from hourly values integrated over a day and, with that, to correlate the accuracy of the forecast with sky conditions. This correlation with DAI reveals that in IFS/ECMWF model, the atmosphere as being more transparent than reality since cloud cover is underestimated in the majority of the months of the year, taking the ground-based measurements as a reference. The use of the DAI estimator confirms that the errors in IFS/ECMWF are larger under cloudy skies than under clear sky. The development and application of a post-processing methodology improves the DNI predictions from the IFS/ECMWF outputs, with a decrease of error of the order of ~30%, when compared with raw data. evaluation; bias correction; Direct Normal Irradiance (DNI); DNI attenuation Index (DAI); forecast; IFS/ECMWF
Poulsen, Caroline A.; McGarragh, Gregory R.; Thomas, Gareth E.; Stengel, Martin; Christensen, Matthew W.; Povey, Adam C.; Proud, Simon R.; Carboni, Elisa; Hollmann, Rainer; Grainger, Roy G.Poulsen, C. A., G. R. McGarragh, G. E. Thomas, M. Stengel, M. W. Christensen, A. C. Povey, S. R. Proud, E. Carboni, R. Hollmann, R. G. Grainger, 2020: Cloud_cci ATSR-2 and AATSR data set version 3: a 17-year climatology of global cloud and radiation properties. Earth System Science Data, 12(3), 2121-2135. doi: https://doi.org/10.5194/essd-12-2121-2020. Abstract. We present version 3 (V3) of the Cloud_cci Along-Track Scanning Radiometer (ATSR) and Advanced ATSR (AATSR) data set. The data set was created for the European Space Agency (ESA) Cloud_cci (Climate Change Initiative) programme. The cloud properties were retrieved from the second ATSR (ATSR-2) on board the second European Remote Sensing Satellite (ERS-2) spanning 1995–2003 and the AATSR on board Envisat, which spanned 2002–2012. The data are comprised of a comprehensive set of cloud properties: cloud top height, temperature, pressure, spectral albedo, cloud effective emissivity, effective radius, and optical thickness, alongside derived liquid and ice water path. Each retrieval is provided with its associated uncertainty. The cloud property retrievals are accompanied by high-resolution top- and bottom-of-atmosphere shortwave and longwave fluxes that have been derived from the retrieved cloud properties using a radiative transfer model. The fluxes were generated for all-sky and clear-sky conditions. V3 differs from the previous version 2 (V2) through development of the retrieval algorithm and attention to the consistency between the ATSR-2 and AATSR instruments. The cloud properties show improved accuracy in validation and better consistency between the two instruments, as demonstrated by a comparison of cloud mask and cloud height with co-located CALIPSO data. The cloud masking has improved significantly, particularly in its ability to detect clear pixels. The Kuiper Skill score has increased from 0.49 to 0.66. The cloud top height accuracy is relatively unchanged. The AATSR liquid water path was compared with the Multisensor Advanced Climatology of Liquid Water Path (MAC-LWP) in regions of stratocumulus cloud and shown to have very good agreement and improved consistency between ATSR-2 and AATSR instruments. The correlation with MAC-LWP increased from 0.4 to over 0.8 for these cloud regions. The flux products are compared with NASA Clouds and the Earth's Radiant Energy System (CERES) data, showing good agreement within the uncertainty. The new data set is well suited to a wide range of climate applications, such as comparison with climate models, investigation of trends in cloud properties, understanding aerosol–cloud interactions, and providing contextual information for co-located ATSR-2/AATSR surface temperature and aerosol products. The following new digital identifier has been issued for the Cloud_cci ATSR-2/AATSRv3 data set: https://doi.org/10.5676/DWD/ESA_Cloud_cci/ATSR2-AATSR/V003 (Poulsen et al., 2019).
Qin, Boxiong; Cao, Biao; Li, Hua; Bian, Zunjian; Hu, Tian; Du, Yongming; Yang, Yingpin; Xiao, Qing; Liu, QinhuoQin, B., B. Cao, H. Li, Z. Bian, T. Hu, Y. Du, Y. Yang, Q. Xiao, Q. Liu, 2020: Evaluation of Six High-Spatial Resolution Clear-Sky Surface Upward Longwave Radiation Estimation Methods with MODIS. Remote Sensing, 12(11), 1834. doi: 10.3390/rs12111834. Surface upward longwave radiation (SULR) is a critical component in the calculation of the Earth’s surface radiation budget. Multiple clear-sky SULR estimation methods have been developed for high-spatial resolution satellite observations. Here, we comprehensively evaluated six SULR estimation methods, including the temperature-emissivity physical methods with the input of the MYD11/MYD21 (TE-MYD11/TE-MYD21), the hybrid methods with top-of-atmosphere (TOA) linear/nonlinear/artificial neural network regressions (TOA-LIN/TOA-NLIN/TOA-ANN), and the hybrid method with bottom-of-atmosphere (BOA) linear regression (BOA-LIN). The recently released MYD21 product and the BOA-LIN—a newly developed method that considers the spatial heterogeneity of the atmosphere—is used initially to estimate SULR. In addition, the four hybrid methods were compared with simulated datasets. All the six methods were evaluated using the Moderate Resolution Imaging Spectroradiometer (MODIS) products and the Surface Radiation Budget Network (SURFRAD) in situ measurements. Simulation analysis shows that the BOA-LIN is the best one among four hybrid methods with accurate atmospheric profiles as input. Comparison of all the six methods shows that the TE-MYD21 performed the best, with a root mean square error (RMSE) and mean bias error (MBE) of 14.0 and −0.2 W/m2, respectively. The RMSE of BOA-LIN, TOA-NLIN, TOA-LIN, TOA-ANN, and TE-MYD11 are equal to 15.2, 16.1, 17.2, 21.2, and 18.5 W/m2, respectively. TE-MYD21 has a much better accuracy than the TE-MYD11 over barren surfaces (NDVI < 0.3) and a similar accuracy over non-barren surfaces (NDVI ≥ 0.3). BOA-LIN is more stable over varying water vapor conditions, compared to other hybrid methods. We conclude that this study provides a valuable reference for choosing the suitable estimation method in the SULR product generation. MODIS; SURFRAD; temperature-emissivity method; hybrid method; method evaluation; surface upward longwave radiation
Rampal, Neelesh; Davies, RogerRampal, N., R. Davies, 2020: On the Factors That Determine Boundary Layer Albedo. Journal of Geophysical Research: Atmospheres, 125(15), e2019JD032244. doi: 10.1029/2019JD032244. This study investigates the factors that control marine boundary layer cloud albedo measured by the Multiangle Imaging SpectroRadiometer (MISR) over domains of (200 km)2. We use three key metrics to investigate domain albedo: cloud fraction, cloud heterogeneity, and cloud morphology. Cloud heterogeneity is quantified at the domain level with a unified heterogeneity index. Cloud morphology is determined from a cloud classification algorithm using an Artificial Neural Network (ANN) to classify each domain into one of four categories: (i) closed-cell Mesoscale Cellular Convection (MCC); (ii) open-cell MCC; (iii) disorganized MCC; and (iv) No MCC. These different types of MCC are usefully defined as low clouds of different morphologies. Classifications from the ANN are also combined with the satellite observations of MISR to develop relationships between cloud morphology, domain albedo, cloud fraction, and cloud heterogeneity. Cloud morphology is found to play an essential role in modulating these relationships. The cloud fraction-albedo relationships are found to be directly a function of cloud morphology. Relationships between domain albedo and cloud heterogeneity are also found to be a function of MCC type. Our results indicate that the albedo has a strong dependence on cloud morphology and cloud heterogeneity. Understanding both the physical properties and the meteorological controls on MCC has important implications for understanding low cloud behavior and improving their representation in General Circulation Models. albedo; MISR; mesoscale cellular convection; boundary layer cloud; heterogeneity
Rehbein, Amanda; Rugna, Martín; Hobouchian, M. Paula; Moral, Anna del; Goodman, Steven J.; Lindsey, Daniel T.; Thomas, JanelRehbein, A., M. Rugna, M. P. Hobouchian, A. d. Moral, S. J. Goodman, D. T. Lindsey, J. Thomas, 2020: A Workshop on the Next-Generation Environmental Satellite Constellations. Bull. Amer. Meteor. Soc., 101(6), E763-E770. doi: 10.1175/BAMS-D-19-0349.1.
Ren, Tong; Yang, Ping; Schumacher, Courtney; Huang, Xianglei; Lin, WuyinRen, T., P. Yang, C. Schumacher, X. Huang, W. Lin, 2020: Impact of Cloud Longwave Scattering on Radiative Fluxes Associated With the Madden-Julian Oscillation in the Indian Ocean and Maritime Continent. Journal of Geophysical Research: Atmospheres, 125(13), e2020JD032591. doi: 10.1029/2020JD032591. Previous studies suggested that cloud longwave radiation contributes to the development and maintenance of the Madden-Julian Oscillation (MJO) and model-based convection is highly sensitive to the radiation scheme. However, currently used radiation schemes do not take cloud longwave scattering into account, resulting in an overestimation of the outgoing longwave radiation (OLR) and an underestimation of the downward longwave flux at the surface. We use combined active and passive satellite cloud property retrievals to quantify the one-layer cloud OLR and heating rate (HR) biases introduced by neglecting cloud longwave scattering in the Indian Ocean and Maritime Continent in the context of MJO, with a focus on its phases 3, 5, and 6. The results show that the satellite-detected one-layer cloud area consists primarily of ice clouds, particularly during the boreal winter in the 4-year study period. An increased ice cloud area fraction of one-layer cloud groups is present up to 5 days before the onset of MJO events. If longwave scattering is neglected, the composite mean OLR overestimation over the one-layer ice cloud area from 5 days before to 4 days after the MJO passage is approximately 3.5 to 5.0 W m−2. Neglecting longwave scattering also leads to a HR underestimation at cloud base and an overestimation at cloud top, making the base-to-top heating gradient less sharp at the cloud-resolving scale.
Righi, Mattia; Andela, Bouwe; Eyring, Veronika; Lauer, Axel; Predoi, Valeriu; Schlund, Manuel; Vegas-Regidor, Javier; Bock, Lisa; Brötz, Björn; Mora, Lee de; Diblen, Faruk; Dreyer, Laura; Drost, Niels; Earnshaw, Paul; Hassler, Birgit; Koldunov, Nikolay; Little, Bill; Loosveldt Tomas, Saskia; Zimmermann, KlausRighi, M., B. Andela, V. Eyring, A. Lauer, V. Predoi, M. Schlund, J. Vegas-Regidor, L. Bock, B. Brötz, L. d. Mora, F. Diblen, L. Dreyer, N. Drost, P. Earnshaw, B. Hassler, N. Koldunov, B. Little, S. Loosveldt Tomas, K. Zimmermann, 2020: Earth System Model Evaluation Tool (ESMValTool) v2.0 – technical overview. Geoscientific Model Development, 13(3), 1179-1199. doi: 10.5194/gmd-13-1179-2020. Abstract. This paper describes the second major release of the Earth System Model Evaluation Tool (ESMValTool), a community diagnostic and performance metrics tool for the evaluation of Earth system models (ESMs) participating in the Coupled Model Intercomparison Project (CMIP). Compared to version 1.0, released in 2016, ESMValTool version 2.0 (v2.0) features a brand new design, with an improved interface and a revised preprocessor. It also features a significantly enhanced diagnostic part that is described in three companion papers. The new version of ESMValTool has been specifically developed to target the increased data volume of CMIP Phase 6 (CMIP6) and the related challenges posed by the analysis and the evaluation of output from multiple high-resolution or complex ESMs. The new version takes advantage of state-of-the-art computational libraries and methods to deploy an efficient and user-friendly data processing. Common operations on the input data (such as regridding or computation of multi-model statistics) are centralized in a highly optimized preprocessor, which allows applying a series of preprocessing functions before diagnostics scripts are applied for in-depth scientific analysis of the model output. Performance tests conducted on a set of standard diagnostics show that the new version is faster than its predecessor by about a factor of 3. The performance can be further improved, up to a factor of more than 30, when the newly introduced task-based parallelization options are used, which enable the efficient exploitation of much larger computing infrastructures. ESMValTool v2.0 also includes a revised and simplified installation procedure, the setting of user-configurable options based on modern language formats, and high code quality standards following the best practices for software development.
Righi, Mattia; Hendricks, Johannes; Lohmann, Ulrike; Beer, Christof Gerhard; Hahn, Valerian; Heinold, Bernd; Heller, Romy; Krämer, Martina; Ponater, Michael; Rolf, Christian; Tegen, Ina; Voigt, ChristianeRighi, M., J. Hendricks, U. Lohmann, C. G. Beer, V. Hahn, B. Heinold, R. Heller, M. Krämer, M. Ponater, C. Rolf, I. Tegen, C. Voigt, 2020: Coupling aerosols to (cirrus) clouds in the global EMAC-MADE3 aerosol–climate model. Geoscientific Model Development, 13(3), 1635-1661. doi: 10.5194/gmd-13-1635-2020. Abstract. A new cloud microphysical scheme including a detailed parameterization for aerosol-driven ice formation in cirrus clouds is implemented in the global ECHAM/MESSy Atmospheric Chemistry (EMAC) chemistry–climate model and coupled to the third generation of the Modal Aerosol Dynamics model for Europe adapted for global applications (MADE3) aerosol submodel. The new scheme is able to consistently simulate three regimes of stratiform clouds – liquid, mixed-, and ice-phase (cirrus) clouds – considering the activation of aerosol particles to form cloud droplets and the nucleation of ice crystals. In the cirrus regime, it allows for the competition between homogeneous and heterogeneous freezing for the available supersaturated water vapor, taking into account different types of ice-nucleating particles, whose specific ice-nucleating properties can be flexibly varied in the model setup. The new model configuration is tuned to find the optimal set of parameters that minimizes the model deviations with respect to observations. A detailed evaluation is also performed comparing the model results for standard cloud and radiation variables with a comprehensive set of observations from satellite retrievals and in situ measurements. The performance of EMAC-MADE3 in this new coupled configuration is in line with similar global coupled models and with other global aerosol models featuring ice cloud parameterizations. Some remaining discrepancies, namely a high positive bias in liquid water path in the Northern Hemisphere and overestimated (underestimated) cloud droplet number concentrations over the tropical oceans (in the extratropical regions), which are both a common problem in these kinds of models, need to be taken into account in future applications of the model. To further demonstrate the readiness of the new model system for application studies, an estimate of the anthropogenic aerosol effective radiative forcing (ERF) is provided, showing that EMAC-MADE3 simulates a relatively strong aerosol-induced cooling but within the range reported in the Intergovernmental Panel on Climate Change (IPCC) assessments.
Rind, D.; Orbe, C.; Jonas, J.; Nazarenko, L.; Zhou, T.; Kelley, M.; Lacis, A.; Shindell, D.; Faluvegi, G.; Romanou, A.; Russell, G.; Tausnev, N.; Bauer, M.; Schmidt, G.Rind, D., C. Orbe, J. Jonas, L. Nazarenko, T. Zhou, M. Kelley, A. Lacis, D. Shindell, G. Faluvegi, A. Romanou, G. Russell, N. Tausnev, M. Bauer, G. Schmidt, 2020: GISS Model E2.2: A Climate Model Optimized for the Middle Atmosphere—Model Structure, Climatology, Variability, and Climate Sensitivity. Journal of Geophysical Research: Atmospheres, 125(10), e2019JD032204. doi: 10.1029/2019JD032204. We introduce a new climate model (GISS E2.2) that has been specially optimized for the middle atmosphere and whose output is being contributed to the CMIP6 archive. The top of the model is at a geopotential altitude of 89 km, and parameterizations of moist convection and various forms of gravity wave drag based on tropospheric processes are chosen specifically for this optimization. We first evaluate the model in its configuration as a coupled atmosphere-chemistry model with respect to its simulation of the mean state of the middle atmosphere, from the mesosphere down through the upper troposphere/lower stratosphere. Then we assess its use as a coupled atmosphere-ocean climate model by exploring its mean ocean climatology. To evaluate its variability, we report on its simulation of the primary modes in the troposphere, stratosphere, and ocean. Two climate change simulations are presented, the responses to instantaneous increases of 2xCO2 and 4xCO2, run with two different ocean models. Sensitivity studies are performed to illustrate the effect of parameterizations on the model results. We compare these results to the lower vertical resolution/top GISS Model E2.1, whose output has also been submitted to CMIP6. The different choices made for these models are explored. It is shown that important improvements in the circulation above and below the tropopause can be obtained when attention is paid to representation of middle atmosphere processes in climate model development. climate model; model development; middle atmosphere
Rivoire, Louis; Birner, Thomas; Knaff, John A.; Tourville, NatalieRivoire, L., T. Birner, J. A. Knaff, N. Tourville, 2020: Quantifying the Radiative Impact of Clouds on Tropopause Layer Cooling in Tropical Cyclones. J. Climate, 33(15), 6361-6376. doi: 10.1175/JCLI-D-19-0813.1.
Robson, Jon; Aksenov, Yevgeny; Bracegirdle, Thomas J.; Dimdore‐Miles, Oscar; Griffiths, Paul T.; Grosvenor, Daniel P.; Hodson, Daniel L. R.; Keeble, James; MacIntosh, Claire; Megann, Alex; Osprey, Scott; Povey, Adam C.; Schröder, David; Yang, Mingxi; Archibald, Alexander T.; Carslaw, Ken S.; Gray, Lesley; Jones, Colin; Kerridge, Brian; Knappett, Diane; Kuhlbrodt, Till; Russo, Maria; Sellar, Alistair; Siddans, Richard; Sinha, Bablu; Sutton, Rowan; Walton, Jeremy; Wilcox, Laura J.Robson, J., Y. Aksenov, T. J. Bracegirdle, O. Dimdore‐Miles, P. T. Griffiths, D. P. Grosvenor, D. L. R. Hodson, J. Keeble, C. MacIntosh, A. Megann, S. Osprey, A. C. Povey, D. Schröder, M. Yang, A. T. Archibald, K. S. Carslaw, L. Gray, C. Jones, B. Kerridge, D. Knappett, T. Kuhlbrodt, M. Russo, A. Sellar, R. Siddans, B. Sinha, R. Sutton, J. Walton, L. J. Wilcox, 2020: The Evaluation of the North Atlantic Climate System in UKESM1 Historical Simulations for CMIP6. Journal of Advances in Modeling Earth Systems, 12(9), e2020MS002126. doi: 10.1029/2020MS002126. Earth system models enable a broad range of climate interactions that physical climate models are unable to simulate. However, the extent to which adding Earth system components changes or improves the simulation of the physical climate is not well understood. Here we present a broad multivariate evaluation of the North Atlantic climate system in historical simulations of the UK Earth System Model (UKESM1) performed for CMIP6. In particular, we focus on the mean state and the decadal time scale evolution of important variables that span the North Atlantic climate system. In general, UKESM1 performs well and realistically simulates many aspects of the North Atlantic climate system. Like the physical version of the model, we find that changes in external forcing, and particularly aerosol forcing, are an important driver of multidecadal change in UKESM1, especially for Atlantic Multidecadal Variability and the Atlantic Meridional Overturning Circulation. However, many of the shortcomings identified are similar to common biases found in physical climate models, including the physical climate model that underpins UKESM1. For example, the summer jet is too weak and too far poleward; decadal variability in the winter jet is underestimated; intraseasonal stratospheric polar vortex variability is poorly represented; and Arctic sea ice is too thick. Forced shortwave changes may be also too strong in UKESM1, which, given the important role of historical aerosol forcing in shaping the evolution of the North Atlantic in UKESM1, motivates further investigation. Therefore, physical model development, alongside Earth system development, remains crucial in order to improve climate simulations. model evaluation; CMIP6; Earth system model; North Atlantic
Roehrig, Romain; Beau, Isabelle; Saint‐Martin, David; Alias, Antoinette; Decharme, Bertrand; Guérémy, Jean-Francois; Voldoire, Aurore; Younous, Abdel-Lathif Ahmat; Bazile, Eric; Belamari, Sophie; Blein, Sébastien; Bouniol, Dominique; Bouteloup, Yves; Cattiaux, Julien; Chauvin, Fabrice; Chevallier, Matthieu; Colin, Jeanne; Douville, Hervé; Marquet, Pascal; Michou, Martine; Nabat, Pierre; Oudar, Thomas; Peyrillé, Philippe; Piriou, Jean-Marcel; Melia, David Salas y; Séférian, Roland; Sénési, StéphaneRoehrig, R., I. Beau, D. Saint‐Martin, A. Alias, B. Decharme, J. Guérémy, A. Voldoire, A. A. Younous, E. Bazile, S. Belamari, S. Blein, D. Bouniol, Y. Bouteloup, J. Cattiaux, F. Chauvin, M. Chevallier, J. Colin, H. Douville, P. Marquet, M. Michou, P. Nabat, T. Oudar, P. Peyrillé, J. Piriou, D. S. y. Melia, R. Séférian, S. Sénési, 2020: The CNRM global atmosphere model ARPEGE-Climat 6.3: description and evaluation. Journal of Advances in Modeling Earth Systems, 12(7), e2020MS002075. doi: 10.1029/2020MS002075. keypoints The version 6.3 of the ARPEGE-Climat atmospheric model includes an increased vertical resolution and a major update of the moist physics Improvements include radiation, cloud and precipitation climatology, daily rainfall distribution and water discharge at major river outlets Weaknesses still include biases in low clouds and some dynamical fields, while the West African monsoon is a new model deficiency
Saidou Chaibou, Abdoul Aziz; Ma, Xiaoyan; Sha, TongSaidou Chaibou, A. A., X. Ma, T. Sha, 2020: Dust radiative forcing and its impact on surface energy budget over West Africa. Scientific Reports, 10(1), 12236. doi: 10.1038/s41598-020-69223-4. Dust is the dominant aerosol type over West Africa (WA), and therefore accurate simulation of dust impact is critical for better prediction of weather and climate change. The dust radiative forcing (DRF) is estimated using two sets of experiments in this study: one without and the other with dust aerosol and its feedbacks with the Weather Research and Forecasting with Chemistry model (WRF-Chem). Results show that DRF presents a net warming effect at the top-of-atmosphere (TOA) and in the atmosphere (ATM), and cooling at the surface (SFC). The net DRF over WA is estimated to be 9 W/m2 at the TOA, 23 W/m2 in the ATM, and − 13 W/m2 at the SFC. Furthermore, dust-induced a reduction of sensible heat up to 24 W/m2 and SFC temperature up to 2 °C cooling over WA, an increase of latent heat up to 12 W/m2 over Sahara, a decrease up to 24 W/m2 over the vegetated surfaces and an increase in the surface energy balance up to 12 W/m2 over WA. The presence of dust significantly influences the surface energy budget over WA, suggesting that dust effects should be considered in more climate studies to improve the accuracy of climate predictions.
Salazar, Germán; Gueymard, Christian; Galdino, Janis Bezerra; de Castro Vilela, Olga; Fraidenraich, NaumSalazar, G., C. Gueymard, J. B. Galdino, O. de Castro Vilela, N. Fraidenraich, 2020: Solar irradiance time series derived from high-quality measurements, satellite-based models, and reanalyses at a near-equatorial site in Brazil. Renewable and Sustainable Energy Reviews, 117, 109478. doi: 10.1016/j.rser.2019.109478. This study analyzes five years of 1-min solar global horizontal irradiance (GHI) and direct normal irradiance (DNI) observations obtained at Petrolina (northeast Brazil). Quality-assured hourly and daily averages are obtained after applying filters and methodologies based on a Baseline Solar Radiation Network (BSRN) quality-control procedure. To calculate correct hourly averages, a minimum fraction of 20% of valid GHI or DNI minutely data is needed, as well as at least 60% of valid days to calculate correct daily-mean monthly values. An asymmetric diurnal pattern is found in GHI and DNI during all months, attributed to consistently higher cloudiness in the morning. The quality-assured hourly and monthly-mean GHI and DNI time series are compared to estimates from 11 solar databases regularly used in solar resource assessment studies: CAMS, CERES, ERA5, INPE, MERRA-2, Meteonorm, NASA-POWER, NSRDB, SARAH, SWERA-BR, and SWERA-US. For hourly GHI values, a range of RMS differences is found between the best (CAMS, 17.3%) and the worst (MERRA-2, 38.9%) results. The latter database is also affected by a larger bias (18.7%) than CAMS (4%). Larger RMS differences are found with hourly DNI, in a range extending from 37% (CAMS) to 63.4% (ERA5). Biases are all above 12%, except for CERES (−1%). For long-term mean-monthly GHI results, low biases of less than 1% are obtained with CAMS, CERES and NASA-POWER, whereas MERRA-2 overestimates (13%). Larger biases are found for mean-monthly DNI, spanning between CAMS (3%) and Meteonorm (−18.4%). Overall, CAMS appears the most consistent solar database for long-term irradiance time series at Petrolina. The significant differences found here between modeled databases are larger than expected, and underline the importance of regional validation studies like this one to decrease the incidence of uncertainties in solar resource assessments on the design and performance of solar energy projects. Data gaps; Data quality control; Solar irradiance; Solar resource assessment; Validation
Sayago, Silvina; Ovando, Gustavo; Almorox, Javier; Bocco, MónicaSayago, S., G. Ovando, J. Almorox, M. Bocco, 2020: Daily solar radiation from NASA-POWER product: assessing its accuracy considering atmospheric transparency. International Journal of Remote Sensing, 41(3), 897-910. doi: 10.1080/01431161.2019.1650986. Satellite remote sensing in estimating solar energy budget components at the top of the atmosphere (TOA) level and at the terrestrial level plays a very important role in various types of applications. Solar radiation data are especially problematic because of a quite generalized lack of sufficient data in quantity and quality. Satellite images allow solving the problem of continuity or lack of solar radiation data. The objective of this work was to fit daily solar radiation from NASA-POWER (National Aeronautics and Space Administration – Prediction Of Worldwide Energy Resources), considering different intervals of atmospheric transparency index. The accuracy was assessed from the analysis of voluminous data-sets registered by meteorological ground stations, 31 in number, located in whole Spain, during the period from 2000 to 2017. Clearness index (KT) was calculated to define nine classes of cloud cover conditions. The study reveals that the degree of correlation between the satellite data and observatory data depends upon atmospheric conditions and the correlation accuracy improves for higher values of KT. The coefficients of determination (R2), considering all KT values, were between 0.85 and 0.96; particularly for clear days R2 = 0.96 and root-mean-square error equal to 1.78 MJ m−2 d−1 were obtained. Geographically, the better statistic values were located in the central region of the country. NASA-POWER shows potential to estimate solar radiation and that it is an important information resource for different applications.
Scarino, Benjamin R.; Bedka, Kristopher; Bhatt, Rajendra; Khlopenkov, Konstantin; Doelling, David R.; Smith Jr., William L.Scarino, B. R., K. Bedka, R. Bhatt, K. Khlopenkov, D. R. Doelling, W. L. Smith Jr., 2020: A kernel-driven BRDF model to inform satellite-derived visible anvil cloud detection. Atmospheric Measurement Techniques, 13(10), 5491-5511. doi: https://doi.org/10.5194/amt-13-5491-2020. Abstract. Satellites routinely observe deep convective clouds across the world. The cirrus outflow from deep convection, commonly referred to as anvil cloud, has a ubiquitous appearance in visible and infrared (IR) wavelength imagery. Anvil clouds appear as broad areas of highly reflective and cold pixels relative to the darker and warmer clear sky background, often with embedded textured and colder pixels that indicate updrafts and gravity waves. These characteristics would suggest that creating automated anvil cloud detection products useful for weather forecasting and research should be straightforward, yet in practice such product development can be challenging. Some anvil detection methods have used reflectance or temperature thresholding, but anvil reflectance varies significantly throughout a day as a function of combined solar illumination and satellite viewing geometry, and anvil cloud top temperature varies as a function of convective equilibrium level and tropopause height. This paper highlights a technique for facilitating anvil cloud detection based on visible observations that relies on comparative analysis with expected cloud reflectance for a given set of angles, thereby addressing limitations of previous methods. A 1-year database of anvil-identified pixels, as determined from IR observations, from several geostationary satellites was used to construct a bidirectional reflectance distribution function (BRDF) model to quantify typical anvil reflectance across almost all expected viewing, solar, and azimuth angle configurations, in addition to the reflectance uncertainty for each angular bin. Application of the BRDF model for cloud optical depth retrieval in deep convection is described as well.
Scarino, Benjamin; Doelling, David R.; Bhatt, Rajendra; Gopalan, Arun; Haney, ConorScarino, B., D. R. Doelling, R. Bhatt, A. Gopalan, C. Haney, 2020: Evaluating the Magnitude of VIIRS Out-of-Band Response for Varying Earth Spectra. Remote Sensing, 12(19), 3267. doi: 10.3390/rs12193267. Prior evaluations of Visible Infrared Imaging Radiometer Suite (VIIRS) out-of-band (OOB) contribution to total signal revealed specification exceedance for multiple key solar reflective and infrared bands that are of interest to the passive remote-sensing community. These assessments are based on laboratory measurements, and although highly useful, do not necessarily translate to OOB contribution with consideration of true Earth-reflected or Earth-emitted spectra, especially given the significant spectral variation of Earth targets. That is, although the OOB contribution of VIIRS is well known, it is not a uniform quantity applicable across all scene types. As such, this article quantifies OOB contribution for multiple relative spectral response characterization versions across the S-NPP, NOAA-20, and JPSS-2 VIIRS sensors as a function of varied SCIAMACHY- and IASI-measured hyperspectral Earth-reflected and Earth-emitted scenes. For instance, this paper reveals measured radiance variations of nearly 2% for the S-NPP VIIRS M5 (~0.67 μm) band, and up to 5.7% for certain VIIRS M9 (~1.38 μm) and M13 (~4.06 μm) bands that are owed solely to the truncation of OOB response for a set of spectrally distinct Earth scenes. If unmitigated, e.g., by only considering the published extended bandpass, such variations may directly translate to scene-dependent scaling discrepancies or subtle errors in vegetative index determinations. Therefore, knowledge of OOB effects is especially important for inter-calibration or environmental retrieval efforts that rely on specific or multiple categories of Earth scene spectra, and also to researchers whose products rely on the impacted channels. Additionally, instrument teams may find this evaluation method useful for pre-launch characterization of OOB contribution with specific Earth targets in mind rather than relying on general models. VIIRS; S-NPP; hyperspectral; in-band; JPSS-2; NOAA-20; out-of-band; spectral response
Schifano, Luca; Smeesters, Lien; Berghmans, Francis; Dewitte, StevenSchifano, L., L. Smeesters, F. Berghmans, S. Dewitte, 2020: Optical System Design of a Wide Field-of-View Camera for the Characterization of Earth’s Reflected Solar Radiation. Remote Sensing, 12(16), 2556. doi: 10.3390/rs12162556. We report on the conceptual design of a new wide field-of-view shortwave camera, for measuring Earth’s reflected solar radiation. The camera comprises a commercial-off-the-shelf CMOS sensor, and a custom-designed wide field-of-view lens system with an opening angle of 140°. The estimated effective nadir resolution is 2.2 km. The simulated stand-alone random error of the broadband albedo is 3%. The camera is suited for integration within 1U of a CubeSat. earth radiation budget; radiative transfer; aspherical optical design; earth energy imbalance; reflected solar radiation; refractive imaging system; space instrumentation; wide field-of-view
Schifano, Luca; Smeesters, Lien; Geernaert, Thomas; Berghmans, Francis; Dewitte, StevenSchifano, L., L. Smeesters, T. Geernaert, F. Berghmans, S. Dewitte, 2020: Design and Analysis of a Next-Generation Wide Field-of-View Earth Radiation Budget Radiometer. Remote Sensing, 12(3), 425. doi: 10.3390/rs12030425. Climate on Earth is determined by the Earth Radiation Budget (ERB), which quantifies the incoming and outgoing radiative energy fluxes. The ERB can be monitored by non-scanning wide field-of-view radiometers, or by scanning narrow field-of-view radiometers. We propose an enhanced design for the wide field-of-view radiometer, with as key features the use of a near-spherical cavity to obtain a uniform angular sensitivity and the integration of the shuttered electrical substitution principle, eliminating long term drifts of the radiometer and improving its time response. The target absolute accuracy is 1 W/m 2 and the target stability is 0.1 W/m 2 per decade for the measurement of the total outgoing Earth’s radiation. In order to increase the spatial resolution and to separate the total outgoing radiation into reflected Solar and emitted thermal radiation, we propose the joint use of the radiometer with wide field-of-view Shortwave (400–900 nm) and Longwave (8–14 μm) cameras. This paper presents the concept and design of the novel wide field-of-view radiometer, including simulations and analyses of its expected performance. We focus on mechanical design and the measurement characteristics based on optical and thermal analyses. In combination with the cameras, we obtain an estimated accuracy of 0.44 W/m 2 . radiometer; Earth Radiation Budget; Earth Energy Imbalance; space instrumentation; optical modelling; thermal modelling
Schwarz, M.; Folini, D.; Yang, S.; Allan, R. P.; Wild, M.Schwarz, M., D. Folini, S. Yang, R. P. Allan, M. Wild, 2020: Changes in atmospheric shortwave absorption as important driver of dimming and brightening. Nature Geoscience, 13(2), 110-115. doi: 10.1038/s41561-019-0528-y. Changes in the atmospheric absorption of shortwave radiation, probably through cloud and aerosol effects, is the main reason for the dimming and brightening over China and Europe in past decades, according to co-located surface and space observations.
Scott, Ryan C.; Myers, Timothy A.; Norris, Joel R.; Zelinka, Mark D.; Klein, Stephen A.; Sun, Moguo; Doelling, David R.Scott, R. C., T. A. Myers, J. R. Norris, M. D. Zelinka, S. A. Klein, M. Sun, D. R. Doelling, 2020: Observed Sensitivity of Low-Cloud Radiative Effects to Meteorological Perturbations over the Global Oceans. J. Climate, 33(18), 7717-7734. doi: 10.1175/JCLI-D-19-1028.1.
Semmler, Tido; Danilov, Sergey; Gierz, Paul; Goessling, Helge F.; Hegewald, Jan; Hinrichs, Claudia; Koldunov, Nikolay; Khosravi, Narges; Mu, Longjiang; Rackow, Thomas; Sein, Dmitry V.; Sidorenko, Dmitry; Wang, Qiang; Jung, ThomasSemmler, T., S. Danilov, P. Gierz, H. F. Goessling, J. Hegewald, C. Hinrichs, N. Koldunov, N. Khosravi, L. Mu, T. Rackow, D. V. Sein, D. Sidorenko, Q. Wang, T. Jung, 2020: Simulations for CMIP6 With the AWI Climate Model AWI-CM-1-1. Journal of Advances in Modeling Earth Systems, 12(9), e2019MS002009. doi: 10.1029/2019MS002009. The Alfred Wegener Institute Climate Model (AWI-CM) participates for the first time in the Coupled Model Intercomparison Project (CMIP), CMIP6. The sea ice-ocean component, FESOM, runs on an unstructured mesh with horizontal resolutions ranging from 8 to 80 km. FESOM is coupled to the Max Planck Institute atmospheric model ECHAM 6.3 at a horizontal resolution of about 100 km. Using objective performance indices, it is shown that AWI-CM performs better than the average of CMIP5 models. AWI-CM shows an equilibrium climate sensitivity of 3.2°C, which is similar to the CMIP5 average, and a transient climate response of 2.1°C which is slightly higher than the CMIP5 average. The negative trend of Arctic sea-ice extent in September over the past 30 years is 20–30% weaker in our simulations compared to observations. With the strongest emission scenario, the AMOC decreases by 25% until the end of the century which is less than the CMIP5 average of 40%. Patterns and even magnitude of simulated temperature and precipitation changes at the end of this century compared to present-day climate under the strong emission scenario SSP585 are similar to the multi-model CMIP5 mean. The simulations show a 11°C warming north of the Barents Sea and around 2°C to 3°C over most parts of the ocean as well as a wetting of the Arctic, subpolar, tropical, and Southern Ocean. Furthermore, in the northern middle latitudes in boreal summer and autumn as well as in the southern middle latitudes, a more zonal atmospheric flow is projected throughout the year. climate change; global climate model; AWI climate model; Coupled Model Intercomparison Project; unstructured mesh
Seo, Minji; Kim, Hyun-Cheol; Lee, Kyeong-Sang; Seong, Noh-Hun; Lee, Eunkyung; Kim, Jinsoo; Han, Kyung-SooSeo, M., H. Kim, K. Lee, N. Seong, E. Lee, J. Kim, K. Han, 2020: Characteristics of the Reanalysis and Satellite-Based Surface Net Radiation Data in the Arctic. Journal of Sensors. In this study, we compared four net radiation products: the fifth generation of European Centre for Medium-Range Weather Forecasts atmospheric reanalysis of the global climate (ERA5), National Centers for Environmental Prediction (NCEP), Clouds and the Earth’s Radiant Energy System Energy Balanced and Filled (EBAF), and Global Energy and Water Exchanges (GEWEX), based on ground observation data and intercomparison data. ERA5 showed the highest accuracy, followed by EBAF, GEWEX, and NCEP. When analyzing the validation grid, ERA5 showed the most similar data distribution to ground observation data. Different characteristics were observed between the reanalysis data and satellite data. In the case of satellite-based data, the net radiation value tended to increase at high latitudes. Compared with the reanalysis data, Greenland and the central Arctic appeared to be overestimated. All data were highly correlated, with a difference of 6–21 W/m2 among the products examined in this study. Error was attributed mainly to difficulties in predicting long-term climate change and having to combine net radiation data from several sources. This study highlights criteria that may be helpful in selecting data for future climate research models of this region.
Shankar, Mohan; Su, Wenying; Manalo-Smith, Natividad; Loeb, Norman G.Shankar, M., W. Su, N. Manalo-Smith, N. G. Loeb, 2020: Generation of a Seamless Earth Radiation Budget Climate Data Record: A New Methodology for Placing Overlapping Satellite Instruments on the Same Radiometric Scale. Remote Sensing, 12(17), 2787. doi: 10.3390/rs12172787. The Clouds and the Earth’s Radiant Energy System (CERES) instruments have enabled the generation of a multi-decadal Earth radiation budget (ERB) climate data record (CDR) at the top of the Earth’s atmosphere, within the atmosphere, and at the Earth’s surface. Six CERES instruments have been launched over the course of twenty years, starting in 1999. To seamlessly continue the data record into the future, there is a need to radiometrically scale observations from newly launched instruments to observations from the existing data record. In this work, we describe a methodology to place the CERES Flight Model (FM) 5 instrument on the Suomi National Polar-orbiting Partnership (SNPP) spacecraft on the same radiometric scale as the FM3 instrument on the Aqua spacecraft. We determine the required magnitude of radiometric scaling by using spatially and temporally matched observations from these two instruments and describe the process to radiometrically scale SNPP/FM5 to Aqua/FM3 through the instrument spectral response functions. We also present validation results after application of this radiometric scaling and demonstrate the long-term consistency of the SNPP/FM5 record in comparison with the CERES instruments on Aqua and Terra. calibration; radiation budget; radiometric scaling
Shell, Karen M.; de Szoeke, Simon P.; Makiyama, Michael; Feng, ZheShell, K. M., S. P. de Szoeke, M. Makiyama, Z. Feng, 2020: Vertical Structure of Radiative Heating Rates of the MJO during DYNAMO. J. Climate, 33(12), 5317-5335. doi: 10.1175/JCLI-D-19-0519.1. The vertical structure of radiative heating rates over the region of the tropical Indian Ocean associated with the MJO during the DYNAMO/ARM MJO Investigation Experiment is presented. The mean and variability of heating rates during active, suppressed, and disturbed phases are determined from the Pacific Northwest National Laboratory Combined Remote Sensing Retrieval (CombRet) from Gan Island, Maldives (0.69°S, 73.15°E). TOA and surface fluxes from the CombRet product are compared with collocated 3-hourly CERES SYN1deg Ed4A satellite retrievals. The fluxes are correlated in time with correlation coefficients around 0.9, yet CombRet time-mean OLR is 15 W m−2 larger. Previous work has suggested that CombRet undersamples high clouds, due to signal attenuation by low-level clouds and reduced instrument sensitivity with altitude. However, mean OLR differs between CombRet and CERES for all values of OLR, not just the lowest values corresponding to widespread high clouds. The discrepancy peaks for midrange OLR, suggestive of precipitating, towering cumulus convective clouds, rather than stratiform cirrus clouds. Low biases in the cloud-top height of thick clouds substantially contribute to the overestimate of OLR by CombRet. CombRet data are used to generate composite shortwave and longwave atmospheric heating rate profiles as a function of the local OLR. Although there is considerable variability in CombRet not directly related to OLR, the time–height structure of mean heating rate composites generated using OLR as the interpolant is broadly representative of tropical convective variability on intraseasonal time scales.
Sherwood, S.; Webb, M. J.; Annan, J. D.; Armour, K. C.; Forster, P. M.; Hargreaves, J. C.; Hegerl, G.; Klein, S. A.; Marvel, K. D.; Rohling, E. J.; Watanabe, M.; Andrews, T.; Braconnot, P.; Bretherton, C. S.; Foster, G. L.; Hausfather, Z.; Heydt, A. S. von der; Knutti, R.; Mauritsen, T.; Norris, J. R.; Proistosescu, C.; Rugenstein, M.; Schmidt, G. A.; Tokarska, K. B.; Zelinka, M. D.Sherwood, S., M. J. Webb, J. D. Annan, K. C. Armour, P. M. Forster, J. C. Hargreaves, G. Hegerl, S. A. Klein, K. D. Marvel, E. J. Rohling, M. Watanabe, T. Andrews, P. Braconnot, C. S. Bretherton, G. L. Foster, Z. Hausfather, A. S. v. d. Heydt, R. Knutti, T. Mauritsen, J. R. Norris, C. Proistosescu, M. Rugenstein, G. A. Schmidt, K. B. Tokarska, M. D. Zelinka, 2020: An assessment of Earth's climate sensitivity using multiple lines of evidence. Reviews of Geophysics, 58(4), e2019RG000678. doi: 10.1029/2019RG000678. We assess evidence relevant to Earth's equilibrium climate sensitivity per doubling of atmospheric CO2, characterized by an effective sensitivity S. This evidence includes feedback process understanding, the historical climate record, and the paleoclimate record. An S value lower than 2 K is difficult to reconcile with any of the three lines of evidence. The amount of cooling during the Last Glacial Maximum provides strong evidence against values of S greater than 4.5 K. Other lines of evidence in combination also show that this is relatively unlikely. We use a Bayesian approach to produce a probability density (PDF) for S given all the evidence, including tests of robustness to difficult-to-quantify uncertainties and different priors. The 66% range is 2.6-3.9 K for our Baseline calculation, and remains within 2.3-4.5 K under the robustness tests; corresponding 5-95% ranges are 2.3-4.7 K, bounded by 2.0-5.7 K (although such high-confidence ranges should be regarded more cautiously). This indicates a stronger constraint on S than reported in past assessments, by lifting the low end of the range. This narrowing occurs because the three lines of evidence agree and are judged to be largely independent, and because of greater confidence in understanding feedback processes and in combining evidence. We identify promising avenues for further narrowing the range in S, in particular using comprehensive models and process understanding to address limitations in the traditional forcing-feedback paradigm for interpreting past changes. Bayesian methods; global warming; climate sensitivity; Climate
Shi, Tenglong; Pu, Wei; Zhou, Yue; Cui, Jiecan; Zhang, Daizhou; Wang, XinShi, T., W. Pu, Y. Zhou, J. Cui, D. Zhang, X. Wang, 2020: Albedo of Black Carbon-Contaminated Snow Across Northwestern China and the Validation With Model Simulation. Journal of Geophysical Research: Atmospheres, 125(9), e2019JD032065. doi: 10.1029/2019JD032065. Light-absorbing particles in snow can significantly reduce the snow albedo. Quantification of the influence of black carbon (BC), one of the most important light-absorbing particles, on snow albedo is essential for understanding the budgets of solar radiation on snow-covered areas. We measured BC concentration in snow at 28 sites and snow albedo at 18 sites in a vast region across northwestern China in January 2018. The BC concentration was in a wide range of 40–1,850 ng g−1. The presence of the BC reduced the snow albedo by 0.01–0.20 at the visible wavelength band (400–750 nm). The reduction differed from sites to sites with large values close to industrial areas that are characterized by high pollutants emission. Albedos simulated with a Snow, Ice, and Aerosol Radiation model based on the measured BC agreed well with the measured albedos, with the deviation within ±0.03 and the average underestimation of
Shi, Yifan; Zhang, Ming; Ma, Yingying; Gong, Wei; Chen, Shihua; Jin, Shikuan; Liu, BomingShi, Y., M. Zhang, Y. Ma, W. Gong, S. Chen, S. Jin, B. Liu, 2020: A novel simplified method for surface albedo together with a look-up table to get an 18-year assessment of surface aerosol direct radiative effect in Central and East China. Atmospheric Environment, 243, 117858. doi: 10.1016/j.atmosenv.2020.117858. Calculating the aerosol direct radiative effect (ADRE) is significance for estimating the influence of aerosols. However, calculating ADRE through the radiative transfer model at large scales and for long periods is time-consuming. In this paper, a linear relationship between surface albedo and surface shortwave ADRE (ADRESW) was proposed together with a look-up table to simplify the calculation. The linear relationship is tested and remains reliable as atmospheric properties vary. Validation that compared the results calculated with and without simplifications shows high coefficient of determination (0.97). The time required for calculation with the simplification is only 1/2630th of the unsimplified calculation, which reveals that our method greatly simplified the calculation and maintains high accuracy. Based on the simplification, daily surface ADRESW under clear-sky conditions over Central and East China from 2001 to 2018 is calculated and analyzed. Central and East China has a regional average aerosol optical depth (AOD) of 0.66 and surface ADREsw of −34.33 W/m2. The North China Plain (0.83, −41.42 W/m2), The Jianghan Plain (0.79, −40.33 W/m2) and the Yangtze River Delta City Agglomeration (0.90, −46.50 W/m2) feature heavy aerosol loading and a strong cooling effect. The inter-annual AOD and cooling effect decreased by 37.60% and 33.21%, respectively, after the 2011 accord to decrease anthropogenic emissions, proving the success of efforts by the Chinese government to protect environment. A study of daily shortwave aerosol radiative effect efficiency found that sunshine duration is the primary controlling factor. Aerosol radiative effect; Look-up table; Surface albedo simplification
Shukla, Ravi P.; Huang, BohuaShukla, R. P., B. Huang, 2020: Cumulative Influence of Summer Subsurface Soil Temperature on North America Surface Temperature in the CFSv2. Journal of Geophysical Research: Atmospheres, 125(6), e2019JD031899. doi: 10.1029/2019JD031899. Analyzing a long simulation and a set of seasonal reforecasts of the Climate Forecast System version 2 (CFSv2), this study demonstrates a large model cold bias in the deep soil layer (100–200 cm) over most of North America continent during summer due to weaker seasonal change in summer. The summer subsurface temperature (SUBT) cold bias influences the land surface temperature (LST) during the summer and subsequent seasons in different ways over different geographical regions in North America: West of the Rocky Mountains, the SUBT's effect on LST is largely overruled by the stronger upstream marine influence from the Pacific. Over the central Great Plains, however, it is a major cause for severe cold LST bias during summer in the model simulation and reforecasts. As a result, model underestimates sensible heat flux into the atmosphere but overestimates latent heat flux. The latter may contribute to an excessive summer rainfall in the region. Over the northeast region, the SUBT cold bias persists to August and September, which causes an additional surface cooling in the fall and helps to bring LST to the freezing point early. This sets up the stage for a prolonged snow-albedo feedback. In particular, the model long simulation that passes through previous summer and fall demonstrates longer persistence of snow cover over the northeast region than reforecasts initialized in late winter and spring do. A cold bias of the water temperature in the North Atlantic seems also to play a role to prolong cold bias in the northeast region. deep soil layer (100–200 cm); NCEP CFSv2; North America continent; simulation and seasonal reforecasts; snow-albedo feedback; subsurface soil temperature
Sorooshian, Armin; Corral, Andrea F.; Braun, Rachel A.; Cairns, Brian; Crosbie, Ewan; Ferrare, Richard; Hair, Johnathan; Kleb, Mary M.; Mardi, Ali Hossein; Maring, Hal; McComiskey, Allison; Moore, Richard; Painemal, David; Scarino, Amy Jo; Schlosser, Joseph; Shingler, Taylor; Shook, Michael; Wang, Hailong; Zeng, Xubin; Ziemba, Luke; Zuidema, PaquitaSorooshian, A., A. F. Corral, R. A. Braun, B. Cairns, E. Crosbie, R. Ferrare, J. Hair, M. M. Kleb, A. H. Mardi, H. Maring, A. McComiskey, R. Moore, D. Painemal, A. J. Scarino, J. Schlosser, T. Shingler, M. Shook, H. Wang, X. Zeng, L. Ziemba, P. Zuidema, 2020: Atmospheric Research Over the Western North Atlantic Ocean Region and North American East Coast: A Review of Past Work and Challenges Ahead. Journal of Geophysical Research: Atmospheres, 125(6), e2019JD031626. doi: 10.1029/2019JD031626. Decades of atmospheric research have focused on the Western North Atlantic Ocean (WNAO) region because of its unique location that offers accessibility for airborne and ship measurements, gradients in important atmospheric parameters, and a range of meteorological regimes leading to diverse conditions that are poorly understood. This work reviews these scientific investigations for the WNAO region, including the East Coast of North America and the island of Bermuda. Over 50 field campaigns and long-term monitoring programs, in addition to 715 peer-reviewed publications between 1946 and 2019 have provided a firm foundation of knowledge for these areas. Of particular importance in this region has been extensive work at the island of Bermuda that is host to important time series records of oceanic and atmospheric variables. Our review categorizes WNAO atmospheric research into eight major categories, with some studies fitting into multiple categories (relative %): Aerosols (25%), Gases (24%), Development/Validation of Techniques, Models, and Retrievals (18%), Meteorology and Transport (9%), Air-Sea Interactions (8%), Clouds/Storms (8%), Atmospheric Deposition (7%), and Aerosol-Cloud Interactions (2%). Recommendations for future research are provided in the categories highlighted above. ACTIVATE; Aerosol; Atlantic Ocean; Cloud; Deposition; Gas
Steffen, John; Bourassa, MarkSteffen, J., M. Bourassa, 2020: Upper-Ocean Response to Precipitation Forcing in an Ocean Model Hindcast of Hurricane Gonzalo. J. Phys. Oceanogr., 50(11), 3219-3234. doi: 10.1175/JPO-D-19-0277.1.
Stengel, Martin; Stapelberg, Stefan; Sus, Oliver; Finkensieper, Stephan; Würzler, Benjamin; Philipp, Daniel; Hollmann, Rainer; Poulsen, Caroline; Christensen, Matthew; McGarragh, GregoryStengel, M., S. Stapelberg, O. Sus, S. Finkensieper, B. Würzler, D. Philipp, R. Hollmann, C. Poulsen, M. Christensen, G. McGarragh, 2020: Cloud_cci Advanced Very High Resolution Radiometer post meridiem (AVHRR-PM) dataset version 3: 35-year climatology of global cloud and radiation properties. Earth System Science Data, 12(1), 41-60. doi: 10.5194/essd-12-41-2020. Abstract. We present version 3 of the Cloud_cci Advanced Very High Resolution Radiometer post meridiem (AVHRR-PM) dataset, which contains a comprehensive set of cloud and radiative flux properties on a global scale covering the period of 1982 to 2016. The properties were retrieved from AVHRR measurements recorded by the afternoon (post meridiem – PM) satellites of the National Oceanic and Atmospheric Administration (NOAA) Polar Operational Environmental Satellite (POES) missions. The cloud properties in version 3 are of improved quality compared with the precursor dataset version 2, providing better global quality scores for cloud detection, cloud phase and ice water path based on validation results against A-Train sensors. Furthermore, the parameter set was extended by a suite of broadband radiative flux properties. They were calculated by combining the retrieved cloud properties with thermodynamic profiles from reanalysis and surface properties. The flux properties comprise upwelling and downwelling and shortwave and longwave broadband fluxes at the surface (bottom of atmosphere – BOA) and top of atmosphere (TOA). All fluxes were determined at the AVHRR pixel level for all-sky and clear-sky conditions, which will particularly facilitate the assessment of the cloud radiative effect at the BOA and TOA in future studies. Validation of the BOA downwelling fluxes against the Baseline Surface Radiation Network (BSRN) shows a very good agreement. This is supported by comparisons of multi-annual mean maps with NASA's Clouds and the Earth's Radiant Energy System (CERES) products for all fluxes at the BOA and TOA. The Cloud_cci AVHRR-PM version 3 (Cloud_cci AVHRR-PMv3) dataset allows for a large variety of climate applications that build on cloud properties, radiative flux properties and/or the link between them. For the presented Cloud_cci AVHRR-PMv3 dataset a digital object identifier has been issued: https://doi.org/10.5676/DWD/ESA_Cloud_cci/AVHRR-PM/V003 (Stengel et al., 2019).
Su, Wenying; Liang, Lusheng; Wang, Hailan; Eitzen, Zachary A.Su, W., L. Liang, H. Wang, Z. A. Eitzen, 2020: Uncertainties in CERES Top-of-Atmosphere Fluxes Caused by Changes in Accompanying Imager. Remote Sensing, 12(12), 2040. doi: 10.3390/rs12122040. The Clouds and the Earth’s Radiant Energy System (CERES) project provides observations of Earth’s radiation budget using measurements from CERES instruments on board the Terra, Aqua, Suomi National Polar-orbiting Partnership (S-NPP), and NOAA-20 satellites. The CERES top-of-atmosphere (TOA) fluxes are produced by converting radiance measurements using empirical angular distribution models, which are functions of cloud properties that are retrieved from imagers flying with the CERES instruments. As the objective is to create a long-term climate data record, not only calibration consistency of the six CERES instruments needs to be maintained for the entire time period, it is also important to maintain the consistency of other input data sets used to produce this climate data record. In this paper, we address aspects that could potentially affect the CERES TOA flux data quality. Discontinuities in imager calibration can affect cloud retrieval which can lead to erroneous flux trends. When imposing an artificial 0.6 per decade decreasing trend to cloud optical depth, which is similar to the trend difference between CERES Edition 2 and Edition 4 cloud retrievals, the decadal SW flux trend changed from − 0.3 5 ± 0.18 Wm − 2 to 0.61 ± 0.18 Wm − 2 . This indicates that a 13% change in cloud optical depth results in about 1% change in the SW flux. Furthermore, different CERES instruments provide valid fluxes at different viewing zenith angle ranges, and including fluxes derived at the most oblique angels unique to S-NPP (>66 ∘ ) can lead to differences of 0.8 Wm − 2 and 0.3 Wm − 2 in global monthly mean instantaneous SW flux and LW flux. To ensure continuity, the viewing zenith angle ranges common to all CERES instruments (<66 ∘ ) are used to produce the long-term Earth’s radiation budget climate data record. The consistency of cloud properties retrieved from different imagers also needs to be maintained to ensure the TOA flux consistency. cloud properties; angular distribution model; climate data record; Earth’s radiation budget
Su, Wenying; Minnis, Patrick; Liang, Lusheng; Duda, David P.; Khlopenkov, Konstantin; Thieman, Mandana M.; Yu, Yinan; Smith, Allan; Lorentz, Steven; Feldman, Daniel; Valero, Francisco P. J.Su, W., P. Minnis, L. Liang, D. P. Duda, K. Khlopenkov, M. M. Thieman, Y. Yu, A. Smith, S. Lorentz, D. Feldman, F. P. J. Valero, 2020: Determining the daytime Earth radiative flux from National Institute of Standards and Technology Advanced Radiometer (NISTAR) measurements. Atmospheric Measurement Techniques, 13(2), 429-443. doi: https://doi.org/10.5194/amt-13-429-2020. Abstract. The National Institute of Standards and Technology Advanced Radiometer (NISTAR) onboard the Deep Space Climate Observatory (DSCOVR) provides continuous full-disk global broadband irradiance measurements over most of the sunlit side of the Earth. The three active cavity radiometers measure the total radiant energy from the sunlit side of the Earth in shortwave (SW; 0.2–4 µm), total (0.4–100 µm), and near-infrared (NIR; 0.7–4 µm) channels. The Level 1 NISTAR dataset provides the filtered radiances (the ratio between irradiance and solid angle). To determine the daytime top-of-atmosphere (TOA) shortwave and longwave radiative fluxes, the NISTAR-measured shortwave radiances must be unfiltered first. An unfiltering algorithm was developed for the NISTAR SW and NIR channels using a spectral radiance database calculated for typical Earth scenes. The resulting unfiltered NISTAR radiances are then converted to full-disk daytime SW and LW flux by accounting for the anisotropic characteristics of the Earth-reflected and emitted radiances. The anisotropy factors are determined using scene identifications determined from multiple low-Earth orbit and geostationary satellites as well as the angular distribution models (ADMs) developed using data collected by the Clouds and the Earth's Radiant Energy System (CERES). Global annual daytime mean SW fluxes from NISTAR are about 6 % greater than those from CERES, and both show strong diurnal variations with daily maximum–minimum differences as great as 20 Wm−2 depending on the conditions of the sunlit portion of the Earth. They are also highly correlated, having correlation coefficients of 0.89, indicating that they both capture the diurnal variation. Global annual daytime mean LW fluxes from NISTAR are 3 % greater than those from CERES, but the correlation between them is only about 0.38.
Subba, Tamanna; Gogoi, Mukunda M.; Pathak, Binita; Bhuyan, Pradip K.; Babu, S. SureshSubba, T., M. M. Gogoi, B. Pathak, P. K. Bhuyan, S. S. Babu, 2020: Recent trend in the global distribution of aerosol direct radiative forcing from satellite measurements. Atmospheric Science Letters, 21(11), e975. doi: 10.1002/asl.975. Global distribution of aerosol direct radiative forcing (DRF) is estimated using Clouds and Earth's Radiant Energy System (CERES) synoptic (SYN) 1° datasets. During 2001–2017, a statistically significant change of global DRFs is revealed with a general decreasing trend (i.e., a reduced cooling effect) at the top of the atmosphere (DRFTOA 0.017 W⋅m−2⋅year−1) and at the surface (DRFSFC 0.033 W⋅m−2⋅year−1) with rapid change over the land compared to the global ocean. South Asia and Africa/Middle East regions depict significant increasing trend of atmospheric warming by 0.025 and 0.002 W·m−2⋅year−1 whereas, the rest of the regions show a decline. These regional variations significantly modulate the global mean DRF (−5.36 ± 0.04 W·m−2 at the TOA and − 9.64 ± 0.07 W·m−2 at the surface during the study period). The observed DRF trends are coincident with the change in the underlying aerosol properties, for example, aerosol optical depth, Ångström exponent and partly due to the increasing columnar burden of SO2 over some of the regions. This indicates that increasing industrialization and urbanization have caused prominent change in the DRF during recent decades. trend; angstrom exponent; aerosol optical depth; global aerosol radiative forcing
Suseno, Dwi Prabowo Yuga; Yamada, Tomohito J.Suseno, D. P. Y., T. J. Yamada, 2020: Simulating Flash Floods Using Geostationary Satellite-Based Rainfall Estimation Coupled with a Land Surface Model. Hydrology, 7(1), 9. doi: 10.3390/hydrology7010009. Clarifying hydrologic behavior, especially behavior related to extreme events such as flash floods, is vital for flood mitigation and management. However, discharge and rainfall measurement data are scarce, which is a major obstacle to flood mitigation. This study: (i) simulated flash floods on a regional scale using three types of rainfall forcing implemented in a land surface model; and (ii) evaluated and compared simulated flash floods with the observed discharge. The three types of rainfall forcing were those observed by the Automated Meteorological Data Acquisition System (AMeDAS) (Simulation I), the observed rainfall from the Ministry of Land, Infrastructure and Transportation (MLIT) (Simulation II), and the estimated rainfall from the Multi-purpose Transport Satellite (MTSAT), which was downscaled by AMeDAS rainfall (Simulation III). MLIT rainfall observations have a denser station network over the Ishikari River basin (spacing of approximately 10 km) compared with AMeDAS (spacing of approximately 20 km), so they are expected to capture the rainfall spatial distribution more accurately. A land surface model, the Minimal Advance Treatments of Surface Interaction and Runoff (MATSIRO), was implemented for the flash flood simulation. The river flow simulations were run over the Ishikari river basin at a 1-km grid resolution and a 1-h temporal resolution during August 2010. The statistical performance of the river flow simulations during a flash flood event on 23 and 24 August 2010 demonstrated that Simulation I was reasonable compared with Simulation III. The findings also suggest that the advantages of the MTSAT-based estimated rainfall (i.e., good spatial distribution) can be coupled with the benefit of direct AMeDAS observations (i.e., representation of the true rainfall). MTSAT; flash flood; heavy rainfall; LSM
Takahashi, Naoya; Hayasaka, TadahiroTakahashi, N., T. Hayasaka, 2020: Air–Sea Interactions among Oceanic Low-Level Cloud, Sea Surface Temperature, and Atmospheric Circulation on an Intraseasonal Time Scale in the Summertime North Pacific Based on Satellite Data Analysis. J. Climate, 33(21), 9195-9212. doi: 10.1175/JCLI-D-19-0670.1.
Terai, C. R.; Pritchard, M. S.; Blossey, P.; Bretherton, C. S.Terai, C. R., M. S. Pritchard, P. Blossey, C. S. Bretherton, 2020: The impact of resolving sub-kilometer processes on aerosol-cloud interactions of low-levels clouds in global model simulations. Journal of Advances in Modeling Earth Systems, 12(11), e2020MS002274. doi: 10.1029/2020MS002274. Sub-kilometer processes are critical to the physics of aerosol-cloud interaction but have been dependent on parameterizations in global model simulations. We thus report the strength of aerosol-cloud interaction in the Ultra-Parameterized Community Atmosphere Model (UPCAM), a multiscale climate model that uses coarse exterior resolution to embed explicit cloud resolving models with enough resolution (250-m horizontal, 20-m vertical) to quasi-resolve sub-kilometer eddies. To investigate the impact on aerosol-cloud interactions, UPCAM’s simulations are compared to a coarser multi-scale model with 4 km horizontal resolution. UPCAM produces cloud droplet number concentrations (Nd) and cloud liquid water path (LWP) values that are higher than the coarser model but equally plausible compared to observations. Our analysis focuses on the Northern Hemisphere (20° - 50°N) oceans, where historical aerosol increases have been largest. We find similarities in the overall radiative forcing from aerosol-cloud interactions in the two models, but this belies fundamental underlying differences. The radiative forcing from increases in LWP is weaker in UPCAM, whereas the forcing from increases in Nd is larger. Surprisingly, the weaker LWP increase is not due to a weaker increase in LWP in raining clouds, but a combination of weaker increase in LWP in non-raining clouds and a smaller fraction of raining clouds in UPCAM. The implication is that as global modeling moves towards finer than storm-resolving grids, nuanced model validation of ACI statistics conditioned on the existence of precipitation and good observational constraints on the baseline probability of precipitation will become key for tighter constraints and better conceptual understanding. clouds; climate change; GCM; aerosol-cloud interaction; multi-scale model
Thomas, Christopher M.; Dong, Bo; Haines, KeithThomas, C. M., B. Dong, K. Haines, 2020: Inverse modelling of global and regional energy and water cycle fluxes using Earth observation data. J. Climate, 33(5), 1707–1723. doi: 10.1175/JCLI-D-19-0343.1. The NASA Energy and Water Cycle Study (NEWS) climatology is a self–consistent coupled annual and seasonal cycle solution for radiative, turbulent and water fluxes over the Earth’s surface using Earth observation data covering 2000–2009. Here we seek to improve the NEWS solution, particularly over the ocean basins, by considering spatial covariances in the observation errors (some evidence for which is found by comparing five turbulent flux products over the oceans) and by introducing additional horizontal transports from ocean reanalyses as weak constraints. By explicitly representing large error covariances between surface heat flux components over the major ocean basins we retain the flux contrasts present in the original data and infer additional heat losses over the North Atlantic, more consistent with a strong Atlantic overturning. This change does not alter the global flux balance but if only the errors in evaporation and precipitation are correlated then those fluxes experience larger adjustments (e.g. the surface latent heat flux increases to 85±2 Wm−2). Replacing SeaFlux v1 with J-OFURO v3 ocean fluxes also leads to a considerable increase in the global latent heat loss as well as a larger North Atlantic heat loss. Furthermore, including a weak constraint on the horizontal transports of heat and freshwater from high-resolution ocean reanalyses improves the net fluxes over the North Atlantic, Caribbean and Arctic Oceans, without any impact on the global flux balances. These results suggest that better characterised flux uncertainties can greatly improve the quality of the optimised flux solution.
Thorsen, Tyler J.; Ferrare, Richard A.; Kato, Seiji; Winker, David M.Thorsen, T. J., R. A. Ferrare, S. Kato, D. M. Winker, 2020: Aerosol Direct Radiative Effect Sensitivity Analysis. J. Climate, 33(14), 6119-6139. doi: 10.1175/JCLI-D-19-0669.1.
Thorsen, Tyler J.; Winker, David M.; Ferrare, Richard A.Thorsen, T. J., D. M. Winker, R. A. Ferrare, 2020: Uncertainty in Observational Estimates of the Aerosol Direct Radiative Effect and Forcing. J. Climate, 34(1), 195-214. doi: 10.1175/JCLI-D-19-1009.1. AbstractA lower bound on the uncertainty in observational estimates of the aerosol direct radiative effect (DRE; the direct interaction with solar radiation by all aerosols) and the aerosol direct radiative forcing [DRF; the radiative effect of just anthropogenic aerosols (RFari)] is quantified by making the optimistic assumption that global aerosol observations can be made with the accuracy found in the Aerosol Robotic Network (AERONET) sun photometer retrievals. The global-mean all-sky aerosol DRE uncertainty was found to be 1.1 W m−2 (one standard deviation). The global-mean all-sky aerosol DRF (RFari) uncertainty was determined to be 0.31 W m−2. The total uncertainty in both quantities is dominated by contributions from the aerosol single scattering albedo uncertainty. These uncertainty estimates were compared to a literature survey of mostly satellite-based aerosol DRE/DRF values. Comparisons to previous studies reveal that most have significantly underestimated the aerosol DRE uncertainty. Past estimates of the aerosol DRF uncertainty are smaller (on average) than our optimistic observational estimates, including the aerosol DRF uncertainty given in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5). This disconnect between our observation-based uncertainty and that found in past aerosol DRF studies that rely, at least in part, on modeling is discussed. Also quantified is a potential reduction in the current observational uncertainty possible with a future generation of satellite observations that would leverage aerosol typing and more refined vertical information.
Tian, Jingjing; Dong, Xiquan; Xi, Baike; Feng, ZheTian, J., X. Dong, B. Xi, Z. Feng, 2020: Characteristics of Ice Cloud–Precipitation of Warm Season Mesoscale Convective Systems over the Great Plains. J. Hydrometeor., 21(2), 317-334. doi: 10.1175/JHM-D-19-0176.1. In this study, the mesoscale convective systems (MCSs) are tracked using high-resolution radar and satellite observations over the U.S. Great Plains during April–August from 2010 to 2012. The spatiotemporal variability of MCS precipitation is then characterized using the Stage IV product. We found that the spatial variability and nocturnal peaks of MCS precipitation are primarily driven by the MCS occurrence rather than the precipitation intensity. The tracked MCSs are further classified into convective core (CC), stratiform rain (SR), and anvil clouds regions. The spatial variability and diurnal cycle of precipitation in the SR regions of MCSs are not as significant as those of MCS precipitation. In the SR regions, the high-resolution, long-term ice cloud microphysical properties [ice water content (IWC) and ice water paths (IWPs)] are provided. The IWCs generally decrease with height. Spatially, the IWC, IWP, and precipitation are all higher over the southern Great Plains than over the northern Great Plains. Seasonally, those ice and precipitation properties are all higher in summer than in spring. Comparing the peak timings of MCS precipitation and IWPs from the diurnal cycles and their composite evolutions, it is found that when using the peak timing of IWPSR as a reference, the heaviest precipitation in the MCS convective core occurs earlier, while the strongest SR precipitation occurs later. The shift of peak timings could be explained by the stratiform precipitation formation process. The IWP and precipitation relationships are different at MCS genesis, mature, and decay stages. The relationships and the transition processes from ice particles to precipitation also depend on the low-level humidity.
Tomasi, Claudio; Petkov, Boyan H.; Lupi, Angelo; Mazzola, Mauro; Lanconelli, Christian; Gultepe, IsmailTomasi, C., B. H. Petkov, A. Lupi, M. Mazzola, C. Lanconelli, I. Gultepe, 2020: Radiation in the Arctic Atmosphere and Atmosphere – Cryosphere Feedbacks. Physics and Chemistry of the Arctic Atmosphere, 591-672. Arctic surface temperature has been increasing at a rate 2–3 times that of the global average in the last half century. Enhanced warming of the Arctic, or Arctic Amplification, is a climatic response to external forcing. Despite good results obtained by climatic models for the globe, the largest intermodel differences in surface temperature warming are found in the Arctic. The magnitude of this warming drives many different processes and determines the evolution of many climatic parameters such as clouds, sea ice extent, and land ice sheet mass. The Arctic Amplification can be attributed to the peculiar feedback processes that are triggered in the Arctic. Most of these processes include radiation interaction with the atmosphere and with the surface, all of them contributing to the radiation budget. It is then mandatory to correctly evaluate this budget both at the surface and at the top of the atmosphere and in the solar and thermal spectra. This can be done using both direct observations, from ground and from space, and model simulation via radiation transfer codes. This last approach need many observed input parameters anyhow.In this contribution results on the evaluation of the radiation budget in the Arctic are first reviewed. Follows a detailed description of the effects of the most important atmospheric gases (carbon dioxide, methane, ozone etc.) on both shortwave and longwave radiation ranges. The same is illustrated for aerosol loading in the Arctic, based on a large dataset of aerosol radiative properties measured by means of sun-photometers in numerous Arctic stations. Finally, the effect of the surface reflectivity characteristics on the radiation budget is illustrated by means of albedo models specific for the Arctic. Albedo; Radiation budget; Aerosols; Arctic amplification; Feedback processes; Greenhouse gas; Reflectivity
Tornow, Florian; Domenech, Carlos; Barker, Howard W.; Preusker, René; Fischer, JürgenTornow, F., C. Domenech, H. W. Barker, R. Preusker, J. Fischer, 2020: Using two-stream theory to capture fluctuations of satellite-perceived TOA SW radiances reflected from clouds over ocean. Atmospheric Measurement Techniques, 13(7), 3909-3922. doi: https://doi.org/10.5194/amt-13-3909-2020. Abstract. Shortwave (SW) fluxes estimated from broadband radiometry rely on empirically gathered and hemispherically resolved fields of outgoing top-of-atmosphere (TOA) radiances. This study aims to provide more accurate and precise fields of TOA SW radiances reflected from clouds over ocean by introducing a novel semiphysical model predicting radiances per narrow sun-observer geometry. This model was statistically trained using CERES-measured radiances paired with MODIS-retrieved cloud parameters as well as reanalysis-based geophysical parameters. By using radiative transfer approximations as a framework to ingest the above parameters, the new approach incorporates cloud-top effective radius and above-cloud water vapor in addition to traditionally used cloud optical depth, cloud fraction, cloud phase, and surface wind speed. A two-stream cloud albedo – serving to statistically incorporate cloud optical thickness and cloud-top effective radius – and Cox–Munk ocean reflectance were used to describe an albedo over each CERES footprint. Effective-radius-dependent asymmetry parameters were obtained empirically and separately for each viewing-illumination geometry. A simple equation of radiative transfer, with this albedo and attenuating above-cloud water vapor as inputs, was used in its log-linear form to allow for statistical optimization. We identified the two-stream functional form that minimized radiance residuals calculated against CERES observations and outperformed the state-of-the-art approach for most observer geometries outside the sun-glint and solar zenith angles between 20 and 70∘, reducing the median SD of radiance residuals per solar geometry by up to 13.2 % for liquid clouds, 1.9 % for ice clouds, and 35.8 % for footprints containing both cloud phases. Geometries affected by sun glint (constituting between 10 % and 1 % of the discretized upward hemisphere for solar zenith angles of 20 and 70∘, respectively), however, often showed weaker performance when handled with the new approach and had increased residuals by as much as 60 % compared to the state-of-the-art approach. Overall, uncertainties were reduced for liquid-phase and mixed-phase footprints by 5.76 % and 10.81 %, respectively, while uncertainties for ice-phase footprints increased by 0.34 %. Tested for a variety of scenes, we further demonstrated the plausibility of scene-wise predicted radiance fields. This new approach may prove useful when employed in angular distribution models and may result in improved flux estimates, in particular dealing with clouds characterized by small or large droplet/crystal sizes.
Unglaub, Claudia; Block, Karoline (ORCID:0000000244582327); Mülmenstädt, Johannes (ORCID:0000000311056678); Sourdeval, Odran (ORCID:0000000228225303); Quaas, Johannes (ORCID:000000017057194X)Unglaub, C., K. Block, J. Mülmenstädt, O. Sourdeval, J. Quaas, 2020: A new classification of satellite-derived liquid water cloud regimes at cloud scale. Atmospheric Chemistry and Physics (Online), 20(4). doi: 10.5194/acp-20-2407-2020. The U.S. Department of Energy's Office of Scientific and Technical Information
Vargas Zeppetello, Lucas R.; Battisti, David S.; Baker, Marcia B.Vargas Zeppetello, L. R., D. S. Battisti, M. B. Baker, 2020: A New Look at the Variance of Summertime Temperatures over Land. J. Climate, 33(13), 5465-5477. doi: 10.1175/JCLI-D-19-0887.1. The increasing frequency of very high summertime temperatures has motivated growing interest in the processes determining the probability distribution of surface temperature over land. Here, we show that on monthly time scales, temperature anomalies can be modeled as linear responses to fluctuations in shortwave radiation and precipitation. Our model contains only three adjustable parameters, and, surprisingly, these can be taken as constant across the globe, notwithstanding large spatial variability in topography, vegetation, and hydrological processes. Using observations of shortwave radiation and precipitation from 2000 to 2017, the model accurately reproduces the observed pattern of temperature variance throughout the Northern Hemisphere midlatitudes. In addition, the variance in latent heat flux estimated by the model agrees well with the few long-term records that are available in the central United States. As an application of the model, we investigate the changes in the variance of monthly averaged surface temperature that might be expected due to anthropogenic climate change. We find that a climatic warming of 4°C causes a 10% increase in temperature variance in parts of North America.
Vielberg, Kristin; Kusche, JürgenVielberg, K., J. Kusche, 2020: Extended forward and inverse modeling of radiation pressure accelerations for LEO satellites. Journal of Geodesy, 94(4), 43. doi: 10.1007/s00190-020-01368-6. For low Earth orbit (LEO) satellites, activities such as precise orbit determination, gravity field retrieval, and thermospheric density estimation from accelerometry require modeled accelerations due to radiation pressure. To overcome inconsistencies and better understand the propagation of modeling errors into estimates, we here suggest to extend the standard analytical LEO radiation pressure model with emphasis on removing systematic errors in time-dependent radiation data products for the Sun and the Earth. Our extended unified model of Earth radiation pressure accelerations is based on hourly CERES SYN1deg data of the Earth’s outgoing radiation combined with angular distribution models. We apply this approach to the GRACE (Gravity Recovery and Climate Experiment) data. Validations with 1 year of calibrated accelerometer measurements suggest that the proposed model extension reduces RMS fits between 5 and 27%, depending on how measurements were calibrated. In contrast, we find little changes when implementing, e.g., thermal reradiation or anisotropic reflection at the satellite’s surface. The refined model can be adopted to any satellite, but insufficient knowledge of geometry and in particular surface properties remains a limitation. In an inverse approach, we therefore parametrize various combinations of possible systematic errors to investigate estimability and understand correlations of remaining inconsistencies. Using GRACE-A accelerometry data, we solve for corrections of material coefficients and CERES fluxes separately over ocean and land. These results are encouraging and suggest that certain physical radiation pressure model parameters could indeed be determined from satellite accelerometry data.
Wall, Casey J.; Norris, Joel R.; Gasparini, Blaž; Smith, William L.; Thieman, Mandana M.; Sourdeval, OdranWall, C. J., J. R. Norris, B. Gasparini, W. L. Smith, M. M. Thieman, O. Sourdeval, 2020: Observational Evidence that Radiative Heating Modifies the Life Cycle of Tropical Anvil Clouds. J. Climate, 33(20), 8621–8640. doi: 10.1175/JCLI-D-20-0204.1.
Wan, Hui; Woodward, Carol S.; Zhang, Shixuan; Vogl, Christopher J.; Stinis, Panos; Gardner, David J.; Rasch, Philip J.; Zeng, Xubin; Larson, Vincent E.; Singh, BalwinderWan, H., C. S. Woodward, S. Zhang, C. J. Vogl, P. Stinis, D. J. Gardner, P. J. Rasch, X. Zeng, V. E. Larson, B. Singh, 2020: Improving time-step convergence in an atmosphere model with simplified physics: the impacts of closure assumption and process coupling. Journal of Advances in Modeling Earth Systems, (In Press). doi: 10.1029/2019MS001982. Convergence testing is a common practice in the development of dynamical cores of atmospheric models but is not as often exercised for the parameterization of sub-grid physics. An earlier study revealed that the stratiform cloud parameterizations in several predecessors of the Energy Exascale Earth System Model (E3SM) showed strong time-step sensitivity and slower-than-expected convergence when the model's time step was systematically refined. In this work, a simplified atmosphere model is configured that consists of the spectral-element dynamical core of the E3SM atmosphere model coupled with a large-scale condensation parameterization based on commonly used assumptions. This simplified model also resembles E3SM and its predecessors in the numerical implementation of process coupling and shows poor time-step convergence in short ensemble tests. We present a formal error analysis to reveal the expected time-step convergence rate and the conditions for obtaining such convergence. Numerical experiments are conducted to investigate the root causes of convergence problems. We show that revisions in the process coupling and closure assumption help to improve convergence in short simulations using the simplified model; the same revisions applied to a full atmosphere model lead to significant changes in the simulated long-term climate. This work demonstrates that causes of convergence issues in atmospheric simulations can be understood by combining analyses from physical and mathematical perspectives. Addressing convergence issues can help to obtain a discrete model that is more consistent with the intended representation of the physical phenomena. Parameterization; Atmospheric model; Convergence; Time stepping
Wang, Dongdong; Liang, Shunlin; Zhang, Yi; Gao, Xueyuan; Brown, Meredith G. L.; Jia, AolinWang, D., S. Liang, Y. Zhang, X. Gao, M. G. L. Brown, A. Jia, 2020: A New Set of MODIS Land Products (MCD18): Downward Shortwave Radiation and Photosynthetically Active Radiation. Remote Sensing, 12(1), 168. doi: 10.3390/rs12010168. Surface downward shortwave radiation (DSR) and photosynthetically active radiation (PAR), its visible component, are key parameters needed for many land process models and terrestrial applications. Most existing DSR and PAR products were developed for climate studies and therefore have coarse spatial resolutions, which cannot satisfy the requirements of many applications. This paper introduces a new global high-resolution product of DSR (MCD18A1) and PAR (MCD18A2) over land surfaces using the MODIS data. The current version is Collection 6.0 at the spatial resolution of 5 km and two temporal resolutions (instantaneous and three-hour). A look-up table (LUT) based retrieval approach was chosen as the main operational algorithm so as to generate the products from the MODIS top-of-atmosphere (TOA) reflectance and other ancillary data sets. The new MCD18 products are archived and distributed via NASA’s Land Processes Distributed Active Archive Center (LP DAAC). The products have been validated based on one year of ground radiation measurements at 33 Baseline Surface Radiation Network (BSRN) and 25 AmeriFlux stations. The instantaneous DSR has a bias of −15.4 W/m2 and root mean square error (RMSE) of 101.0 W/m2, while the instantaneous PAR has a bias of −0.6 W/m2 and RMSE of 45.7 W/m2. RMSE of daily DSR is 32.3 W/m2, and that of the daily PAR is 13.1 W/m2. The accuracy of the new MODIS daily DSR data is higher than the GLASS product and lower than the CERES product, while the latter incorporates additional geostationary data with better capturing DSR diurnal variability. MCD18 products are currently under reprocessing and the new version (Collection 6.1) will provide improved spatial resolution (1 km) and accuracy. MODIS; validation; downward shortwave radiation; photosynthetically active radiation; satellite product; solar radiation
Wang, Minqi; Peng, Yiran; Liu, Yangang; Liu, Yu; Xie, Xiaoning; Guo, ZengyuanWang, M., Y. Peng, Y. Liu, Y. Liu, X. Xie, Z. Guo, 2020: Understanding cloud droplet spectral dispersion effect using empirical and semi-analytical parameterizations in NCAR CAM5.3. Earth and Space Science, 7(8), e2020EA001276. doi: 10.1029/2020EA001276. Five parameterizations of cloud droplet spectral shape are implemented in a global climate model to investigate the dispersion effect and aerosol indirect effect (AIE). We design a series of experiments by modifying the microphysical cloud scheme of NCAR CAM5.3 (Community Atmospheric Model Version 5.3). We employ four empirical (Martin94, RLiu03, PengL03, Liu08) and one semi-analytical (LiuLi15) expressions for cloud droplet spectral shape parameters. Analysis focuses on the instantaneous differences in the simulated cloud microphysical properties and the comparison between model output and satellite data. The results show that RLiu03, PengL03 and LiuLi15 produce wider droplet spectrum and faster autoconversion rate, but Liu08 has a narrower droplet spectrum and slower autoconversion rate than the default parameterization (Martin94) in CAM5.3. Global dispersion effects caused by the five parameterizations modify the aerosol indirect effect by -10% (counteract) to 13% (strengthen). The simulated AIEs and dispersion effects exhibit noticeably spatial inhomogeneity. In the sensitive regions of AIE (Southeast Asia, North Pacific and west coast of South America), we decompose the response of shortwave cloud forcing to the change in droplet number for analysis. The varying dispersion effects can be explained by different responses of cloud properties in different spectral parameterizations.
Wang, Tianxing; Shi, Jiancheng; Ma, Ya; Letu, Husi; Li, XingcaiWang, T., J. Shi, Y. Ma, H. Letu, X. Li, 2020: All-sky longwave downward radiation from satellite measurements: General parameterizations based on LST, column water vapor and cloud top temperature. ISPRS Journal of Photogrammetry and Remote Sensing, 161, 52-60. doi: 10.1016/j.isprsjprs.2020.01.011. Remotely sensed surface longwave downward radiation (LWDR) plays an essential role in studying the surface energy budget and greenhouse effect. Most existing satellite-based methods or products depend on variables that are not readily available from space such as, liquid water path, air temperature, vapor pressure and/or cloud-base temperature etc., which seriously restrict the wide applications of satellite data. In this paper, new nonlinear parameterizations and a machine learning-based model for deriving all-sky LWDR are proposed based only on land surface temperature (LST), column water vapor and cloud-top temperature (CTT), that are relatively readily available day and night for most satellite missions. It is the first time to incorporate the CTT in the parameterizations for estimating LWDR under the cloudy-sky conditions. The results reveal that the new models work well and can derive all-sky global LWDR with reasonable accuracies (RMSE CERES; Land surface temperature; Cloud-top temperature; Cloudy-sky; Column water vapor; Surface longwave downward radiation
Wang, Yanyu; Lyu, Rui; Xie, Xin; Meng, Ze; Huang, Meijin; Wu, Junshi; Mu, Haizhen; Yu, Qiu-Run; He, Qianshan; Cheng, TiantaoWang, Y., R. Lyu, X. Xie, Z. Meng, M. Huang, J. Wu, H. Mu, Q. Yu, Q. He, T. Cheng, 2020: Retrieval of gridded aerosol direct radiative forcing based on multiplatform datasets. Atmospheric Measurement Techniques, 13(2), 575-592. doi: 10.5194/amt-13-575-2020. Abstract. Atmospheric aerosols play a crucial role in regional radiative budgets. Previous studies on clear-sky aerosol direct radiative forcing (ADRF) have mainly been limited to site-scale observations or model simulations for short-term cases, and long-term distributions of ADRF in China have not been portrayed yet. In this study, an accurate fine-resolution ADRF estimate at the surface was proposed. Multiplatform datasets, including satellite (MODIS aboard Terra and Aqua) and reanalysis datasets, served as inputs to the Santa Barbara Discrete Atmospheric Radiative Transfer (SBDART) model for ADRF simulation with consideration of the aerosol vertical profile over eastern China during 2000–2016. Specifically, single-scattering albedo (SSA) from the Modern-Era Retrospective Analysis for Research and Application, Version 2 (MERRA-2) was validated with sun photometers over eastern China. The gridded asymmetry parameter (ASY) was then simulated by matching the calculated top-of-atmosphere (TOA) radiative fluxes from the radiative transfer model with satellite observations (Clouds and the Earth's Radiant Energy System, CERES). The high correlation and small discrepancy (6–8 W m−2) between simulated and observed radiative fluxes at three sites (Baoshan, Fuzhou, and Yong'an) indicated that ADRF retrieval is feasible and has high accuracy over eastern China. Then this method was applied in each grid of eastern China, and the overall picture of ADRF distributions over eastern China during 2000–2016 was displayed. ADRF ranges from −220 to −20 W m−2, and annual mean ADRF is −100.21 W m−2, implying that aerosols have a strong cooling effect at the surface in eastern China. With the economic development and rapid urbanization, the spatiotemporal changes of ADRF during the past 17 years are mainly attributed to the changes of anthropogenic emissions in eastern China. Our method provides the long-term ADRF distribution over eastern China for the first time, highlighting the importance of aerosol radiative impact under climate change.
Weaver, Clark J.; Wu, Dong L.; Bhartia, Pawan K.; Labow, Gordon J.; Haffner, David P.Weaver, C. J., D. L. Wu, P. K. Bhartia, G. J. Labow, D. P. Haffner, 2020: A Long-Term Cloud Albedo Data Record Since 1980 from UV Satellite Sensors. Remote Sensing, 12(12), 1982. doi: 10.3390/rs12121982. Black-sky cloud albedo (BCA) is derived from satellite UV 340 nm observations from NOAA and NASA satellites to infer long-term (1980–2018) shortwave cloud albedo variations induced by volcano eruptions, the El Niño–Southern Oscillation, and decadal warming. While the UV cloud albedo has shown no long-term trend since 1980, there are statistically significant reductions over the North Atlantic and over the marine stratocumulus decks off the coast of California; increases in cloud albedo can be seen over Southeast Asia and over cloud decks off the coast of South America. The derived BCA assumes a C-1 water cloud model with varying cloud optical depths and a Cox–Munk surface BRDF over the ocean, using radiances calibrated over the East Antarctic Plateau and Greenland ice sheets during summer. ENSO; diurnal cycle; cloud feedback; cloud albedo; OMPS; SBUV; volcanoes
Whitburn, Simon; Clarisse, Lieven; Bauduin, Sophie; George, Maya; Hurtmans, Daniel; Safieddine, Sarah; Coheur, Pierre François; Clerbaux, CathyWhitburn, S., L. Clarisse, S. Bauduin, M. George, D. Hurtmans, S. Safieddine, P. F. Coheur, C. Clerbaux, 2020: Spectrally Resolved Fluxes from IASI Data: Retrieval Algorithm for Clear-Sky Measurements. J. Climate, 33(16), 6971-6988. doi: 10.1175/JCLI-D-19-0523.1.
Wild, MartinWild, M., 2020: The global energy balance as represented in CMIP6 climate models. Climate Dynamics, 55(3), 553-577. doi: 10.1007/s00382-020-05282-7. A plausible simulation of the global energy balance is a first-order requirement for a credible climate model. Here I investigate the representation of the global energy balance in 40 state-of-the-art global climate models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6). In the CMIP6 multi-model mean, the magnitudes of the energy balance components are often in better agreement with recent reference estimates compared to earlier model generations on a global mean basis. However, the inter-model spread in the representation of many of the components remains substantial, often on the order of 10–20 Wm−2 globally, except for aspects of the shortwave clear-sky budgets, which are now more consistently simulated by the CMIP6 models. The substantial inter-model spread in the simulated global mean latent heat fluxes in the CMIP6 models, exceeding 20% (18 Wm−2), further implies also large discrepancies in their representation of the global water balance. From a historic perspective of model development over the past decades, the largest adjustments in the magnitudes of the simulated present-day global mean energy balance components occurred in the shortwave atmospheric clear-sky absorption and the surface downward longwave radiation. Both components were gradually adjusted upwards over several model generations, on the order of 10 Wm−2, to reach 73 and 344 Wm−2, respectively in the CMIP6 multi-model means. Thereby, CMIP6 has become the first model generation that largely remediates long-standing model deficiencies related to an overestimation in surface downward shortwave and compensational underestimation in downward longwave radiation in its multi-model mean.
Williams, K. D.; Hewitt, A. J.; Bodas‐Salcedo, A.Williams, K. D., A. J. Hewitt, A. Bodas‐Salcedo, 2020: Use of Short-Range Forecasts to Evaluate Fast Physics Processes Relevant for Climate Sensitivity. Journal of Advances in Modeling Earth Systems, 12(4), e2019MS001986. doi: 10.1029/2019MS001986. The configuration of the Met Office Unified Model being submitted to CMIP6 has a high climate sensitivity. Previous studies have suggested that the impact of model changes on initial tendencies in numerical weather prediction (NWP) should be used to guide their suitability for inclusion in climate models. In this study we assess, using NWP experiments, the atmospheric model changes which lead to the increased climate sensitivity in the CMIP6 configuration, namely, the replacement of the aerosol scheme with GLOMAP-mode and the introduction of a scheme for representing the turbulent production of liquid water within mixed-phase cloud. Overall, the changes included in this latest configuration were found to improve the initial tendencies of the model state variables over the first 6 hr of the forecast, this timescale being before significant dynamical feedbacks are likely to occur. The reduced model drift through the forecast appears to be the result of increased cloud liquid water, leading to enhanced radiative cooling from cloud top and contributing to a stronger shortwave cloud radiative effect. These changes improve the 5-day forecast in traditional metrics used for numerical weather prediction. This study was conducted after the model was frozen and the climate sensitivity of the model determined; hence, it provides an independent test of the model changes contributing to the higher climate sensitivity. The results, along with the large body process-orientated evaluation conducted during the model development process, provide reassurance that these changes are improving the physical processes simulated by the model.
Wolf, Kevin; Ehrlich, André; Mech, Mario; Hogan, Robin J.; Wendisch, ManfredWolf, K., A. Ehrlich, M. Mech, R. J. Hogan, M. Wendisch, 2020: Evaluation of ECMWF Radiation Scheme Using Aircraft Observations of Spectral Irradiance above Clouds. J. Atmos. Sci., 77(8), 2665-2685. doi: 10.1175/JAS-D-19-0333.1.
Wong, T.; Stackhouse, P. W.; Kratz, D. P.; Sawaengphokhai, Parnchai; Wilber, A. C.; Gupta, S. K.; Loeb, N. GWong, T., P. W. Stackhouse, D. P. Kratz, P. Sawaengphokhai, A. C. Wilber, S. K. Gupta, N. G. Loeb, 2020: Earth Radiation Budget at Top-Of-Atmosphere [in “State of the Climate in 2019”].. Bull. Amer. Meteor. Soc, 101(8), S68-69. doi: 10.1175/BAMS-D-20-0104.1.
Wright, J. S.; Sun, X.; Konopka, P.; Krüger, K.; Legras, B.; Molod, A. M.; Tegtmeier, S.; Zhang, G. J.; Zhao, X.Wright, J. S., X. Sun, P. Konopka, K. Krüger, B. Legras, A. M. Molod, S. Tegtmeier, G. J. Zhang, X. Zhao, 2020: Differences in tropical high clouds among reanalyses: origins and radiative impacts. Atmospheric Chemistry and Physics, 20(14), 8989–9030. doi: 10.5194/acp-20-8989-2020.
Wu, Dong L.; Lee, Jae Nyung; Kim, Kyu-Myong; Lim, Young-KwonWu, D. L., J. N. Lee, K. Kim, Y. Lim, 2020: Interannual Variations of TOA Albedo over the Arctic, Antarctic and Tibetan Plateau in 2000–2019. Remote Sensing, 12(9), 1460. doi: 10.3390/rs12091460. Recent changes in Earth’s climate system have significantly affected the radiation budget and its year-to-year variations at top of the atmosphere (TOA). Observing high-latitude TOA fluxes is still challenging from space, because spatial inhomogeneity of surface/atmospheric radiative processes and spectral variability can reflect sunlight very differently. In this study we analyze the 20-year TOA flux and albedo data from CERES and MISR over the Arctic, the Antarctic, and Tibetan Plateau (TP), and found overall great consistency in the TOA albedo trend and interannual variations. The observations reveal a lagged correlation between the Arctic and subarctic albedo fluctuations. The observed year-to-year variations are further used to evaluate the reanalysis data, which exhibit substantial shortcomings in representing the polar TOA flux variability. The observed Arctic flux variations are highly correlated with cloud fraction (CF), except in the regions where CF > 90% or where the surface is covered by ice. An empirical orthogonal function (EOF) analysis shows that the first five EOFs can account for ~50% of the Arctic TOA variance, whereas the correlation with climate indices suggests that Sea Ice Extent (SIE), North Atlantic Oscillation (NAO) and 55°N–65°N cloudiness are the most influential processes in driving the TOA flux variabilities. albedo; shortwave radiation; 4-year oscillation; interannual variations; lagged correlation; top of the atmosphere
Wunderling, Nico; Willeit, Matteo; Donges, Jonathan F.; Winkelmann, RicardaWunderling, N., M. Willeit, J. F. Donges, R. Winkelmann, 2020: Global warming due to loss of large ice masses and Arctic summer sea ice. Nature Communications, 11(1), 5177. doi: 10.1038/s41467-020-18934-3. Several large-scale cryosphere elements such as the Arctic summer sea ice, the mountain glaciers, the Greenland and West Antarctic Ice Sheet have changed substantially during the last century due to anthropogenic global warming. However, the impacts of their possible future disintegration on global mean temperature (GMT) and climate feedbacks have not yet been comprehensively evaluated. Here, we quantify this response using an Earth system model of intermediate complexity. Overall, we find a median additional global warming of 0.43 °C (interquartile range: 0.39−0.46 °C) at a CO2 concentration of 400 ppm. Most of this response (55%) is caused by albedo changes, but lapse rate together with water vapour (30%) and cloud feedbacks (15%) also contribute significantly. While a decay of the ice sheets would occur on centennial to millennial time scales, the Arctic might become ice-free during summer within the 21st century. Our findings imply an additional increase of the GMT on intermediate to long time scales.
Xu, Xiaoqi; Lu, Chunsong; Liu, Yangang; Gao, Wenhua; Wang, Yuan; Cheng, Yueming; Luo, Shi; Weverberg, Kwinten VanXu, X., C. Lu, Y. Liu, W. Gao, Y. Wang, Y. Cheng, S. Luo, K. V. Weverberg, 2020: Effects of Cloud Liquid-Phase Microphysical Processes in Mixed-Phase Cumuli Over the Tibetan Plateau. Journal of Geophysical Research: Atmospheres, 125(19), e2020JD033371. doi: 10.1029/2020JD033371. Numerical simulations often overpredict precipitation over the Tibetan Plateau (TP). To examine the factors causing precipitation overprediction, different parameterizations of liquid-phase microphysical processes (accretion, autoconversion, and entrainment mixing) are implemented into the Morrison microphysics scheme to simulate a TP precipitation event in summer with the Weather Research and Forecasting (WRF) model. The general spatial distribution and temporal trend of precipitation are captured by all simulations, but the precipitation rate is overpredicted. The results from sensitivity experiments suggest that compared to other examined liquid-phase processes, the accretion process is more important in precipitation simulation over the TP region. Further investigation with the Heidke skill scores reveals that accretion parameterization that takes into account the raindrop size produces the most accurate results in terms of the total surface precipitation. This parameterization suppresses spurious accretion and does not produce liquid-phase precipitation until cloud droplets are big enough. It is also confirmed that increasing the model resolution can reduce precipitation overprediction. Results from the case study are confirmed by the use of a 1-month simulation. Tibetan Plateau; cloud microphysics; precipitation; warm rain processes
Yang, DazhiYang, D., 2020: Quantifying the spatial scale mismatch between satellite-derived solar irradiance and in situ measurements: A case study using CERES synoptic surface shortwave flux and the Oklahoma Mesonet. Journal of Renewable and Sustainable Energy, 12(5), 056104. doi: 10.1063/5.0025771.
Yang, Dazhi; Bright, Jamie M.Yang, D., J. M. Bright, 2020: Worldwide validation of 8 satellite-derived and reanalysis solar radiation products: A preliminary evaluation and overall metrics for hourly data over 27 years. Solar Energy, 210, 3-19. doi: 10.1016/j.solener.2020.04.016. Gridded solar radiation products, namely satellite-derived irradiance and reanalysis irradiance, are key to the next-generation solar resource assessment and forecasting. Since their accuracies are generally lower than that of the ground-based measurements, providing validation of the gridded solar radiation products is necessary in order to understand their qualities and characteristics. This article delivers a worldwide validation of hourly global horizontal irradiance derived from satellite imagery and reanalysis. The accuracies of 6 latest satellite-derived irradiance products (CAMS-RAD, NSRDB, SARAH-2, SARAH-E, CERES-SYN1deg, and Solcast) and 2 latest global reanalysis irradiance products (ERA5 and MERRA-2) are verified against the complete records from 57 BSRN stations, over 27 years (1992–2018). This scope of validation is unprecedented in the field of solar energy. Moreover, the importance of using distribution-oriented verification approaches is emphasized. Such approaches go beyond the traditional measure-oriented verification approach, and thus can offer additional insights and flexibility to the verification problem. Reanalysis; Satellite-derived irradiance; Solar resources; Verification; Worldwide validation
Yang, Feng; Cheng, JieYang, F., J. Cheng, 2020: A framework for estimating cloudy sky surface downward longwave radiation from the derived active and passive cloud property parameters. Remote Sensing of Environment, 248, 111972. doi: 10.1016/j.rse.2020.111972. The cloud-base temperature (CBT) is one of the parameters that dominates the cloudy sky surface downward longwave radiation (SDLR). However, CBT is rarely available at regional and global scales, and its application in estimating cloud sky SDLR is limited. In this study, a framework to globally estimate cloud sky SDLR during both daytime and nighttime is proposed. This framework is composed of three parts. First, a global cloudy property database was constructed by combing the extracted cloud vertical structure (CVS) parameters from the active CloudSat data and cloud properties from passive MODIS data. Second, the empirical methods for estimating cloud thickness (CT) under ISCCP cloud classification system and MODIS cloud classification system were developed. Additionally, the coefficients of CERES CT estimate models were refitted using the constructed cloud property database. With the estimated CT and reanalysis data, calculating the CBT is straightforward. The accuracy of the estimated CT for ISCCP cloud type is compared with the existing studies that were conducted at local scales. Our CT estimate accuracy is comparable to that of the existing studies. According to the validation results at ARM NSA and SGP stations, the CT estimated by the developed CT model for MODIS cloud type is better than that estimated by the original CERES CT model. Finally, the cloudy sky SDLR values were derived by feeding the estimated CBT and other parameters to the single-layer cloud model (SLCM). When validated by the ground measured SDLR collected from the SURFRAD network, the bias and RMSE are 5.42 W∙m−2 and 30.3 W∙m−2, respectively. This accuracy is comparable to the evaluation results of the mainstream SDLR products (Gui et al. 2010), the new evaluation results of SLCMs (Yu et al. 2018), and the accuracy of a new cloudy sky SDLR estimate method (Wang et al. 2018). All the derived CBTs improve the SDLR estimate accuracy more than the SLCM that directly uses cloud-top temperature (CTT). We will collect more ground measurements and continue to validate the developed framework in the future. Remote sensing; Cloud-top temperature; Cloud thickness; Cloud-base temperature; Single-layer cloud model; Surface downward longwave radiation
Yang, Qiguang; Liu, Xu; Wu, WanYang, Q., X. Liu, W. Wu, 2020: A Hyperspectral Bidirectional Reflectance Model for Land Surface. Sensors, 20(16), 4456. doi: 10.3390/s20164456. A hyperspectral bidirectional reflectance (HSBR) model for land surface has been developed in this work. The HSBR model includes a very diverse land surface bidirectional reflectance distribution function (BRDF) database with ~40,000 spectra. The BRDF database is saved as Ross-Li parameters, which can generate hyperspectral reflectance spectra at different sensor and solar observation geometries. The HSBR model also provides an improved method for generating hyperspectral surface reflectance using multiband satellite measurements. It is shown that the land surface reflective spectrum can be easily simulated using BRDF parameters or reflectance at few preselected wavelengths. The HSBR model is validated using the U.S. Geological Survey (USGS) vegetation database and the AVIRIS reflectance product. The simulated reflective spectra fit the measurements very well with standard deviations normally smaller than 0.01 in the unit of reflectivity. The HSBR model could be used to significantly improve the quality of the reflectance products of satellite and airborne sensors. It also plays important role for intercalibration among space-based instruments and other land surface related applications. remote sensing; BRDF; hyperspectral bidirectional reflectance model; land surface; Ross-Li model
Yang, Quan; Zhang, Feng; Zhang, Hua; Wang, Zhili; Iwabuchi, Hironobu; Li, JiangnanYang, Q., F. Zhang, H. Zhang, Z. Wang, H. Iwabuchi, J. Li, 2020: Impact of δ-Four-Stream Radiative Transfer Scheme on global climate model simulation. Journal of Quantitative Spectroscopy and Radiative Transfer, 243, 106800. doi: 10.1016/j.jqsrt.2019.106800. The impact of radiative transfer scheme on global climate model (GCM) simulation is presented in this paper by comparing the difference between δ-two-stream adding method (δ-2DDA) and adding algorithm of the δ-four-stream discrete ordinates method (δ-4DDA) radiation schemes in the Atmospheric General Circulation Model of the Beijing Climate Center (BCC_AGCM). Only consider the effects of the calculation method itself, the δ-4DDA reduces the negative shortwave cloud radiative effect (CRE) in the areas with a significant fraction of low cloud, while enhances the negative shortwave CRE in the areas with the large fraction of high cloud. For the longwave CRE, the δ-4DDA enhances the longwave CRE drastically in the regions with a significant fraction of the high cloud. The feedback of clouds results in more interesting results. The δ-4DDA produces more accurate shortwave CRE in the region over the land and ocean in the middle and high latitude areas. The longwave CRE simulated by δ-4DDA is better than that affected by δ-2DDA over the ground in Africa, South America, and Atlantic. The change of radiation scheme affects the simulation of other meteorological variables. The simulation of global humidity by δ-4DDA is improved obviously. The δ-4DDA simulates more accurate temperature in continents of the northern hemisphere and precipitation in North America, Africa, northern Indian Ocean and western Pacific. Although the improvement of every physical process is required to develop the models, implementing δ-4DDA scheme into GCM and evaluating the effect of it are necessary and meaningful. Global climate model; Radiative transfer scheme; δ-4DDA
Yarahmadi, Mehran; Mahan, J. Robert; McFall, Kevin; Ashraf, Anum BarkiYarahmadi, M., J. R. Mahan, K. McFall, A. B. Ashraf, 2020: Numerical Focusing of a Wide-Field-Angle Earth Radiation Budget Imager Using an Artificial Neural Network. Remote Sensing, 12(1), 176. doi: 10.3390/rs12010176. Narrow field-of-view scanning thermistor bolometer radiometers have traditionally been used to monitor the earth’s radiant energy budget from low earth orbit (LEO). Such instruments use a combination of cross-path scanning and along-path spacecraft motion to obtain a patchwork of punctual observations which are ultimately assembled into a mosaic. Monitoring has also been achieved using non-scanning instruments operating in a push-broom mode in LOE and imagers operating in geostationary orbit. The current contribution considers a fourth possibility, that of an imager operating in LEO. The system under consideration consists of a Ritchey-Chrétien telescope illuminating a plane two-dimensional microbolometer array. At large field angles, the focal length of the candidate instrument is field-angle dependent, resulting in a blurred image in the readout plane. Presented is a full-field focusing algorithm based on an artificial neural network (ANN). Absorbed power distributions on the microbolometer array produced by discretized scenes are obtained using a high-fidelity Monte Carlo ray-trace (MCRT) model of the imager. The resulting readout array/scene pairs are then used to train an ANN. We demonstrate that a properly trained ANN can be used to convert the readout power distribution into an accurate image of the corresponding discretized scene. This opens the possibility of using an ANN based on a high-fidelity imager model for numerical focusing of an actual imager. artificial neural networks; earth radiation budget monitoring; image deblurring; numerical focusing
Yin, Jun; Molini, Annalisa; Porporato, AmilcareYin, J., A. Molini, A. Porporato, 2020: Impacts of solar intermittency on future photovoltaic reliability. Nature Communications, 11(1), 4781. doi: 10.1038/s41467-020-18602-6. As photovoltaic power is expanding rapidly worldwide, it is imperative to assess its promise under future climate scenarios. While a great deal of research has been devoted to trends in mean solar radiation, less attention has been paid to its intermittent character, a key challenge when compounded with uncertainties related to climate variability. Using both satellite data and climate model outputs, we characterize solar radiation intermittency to assess future photovoltaic reliability. We find that the relation between the future power supply and long-term mean solar radiation trends is spatially heterogeneous, showing power reliability is more sensitive to the fluctuations of mean solar radiation in hot arid regions. Our results highlight how reliability analysis must account simultaneously for the mean and intermittency of solar inputs when assessing the impacts of climate change on photovoltaics.
Yin, Jun; Porporato, AmilcareYin, J., A. Porporato, 2020: Radiative effects of daily cycle of cloud frequency in past and future climates. Climate Dynamics, 54(3), 1625-1637. doi: 10.1007/s00382-019-05077-5. The daily cloud cycle or diurnal cloud cycle (DCC) and its response to global warming are critical to the Earth’s energy budget, but their radiative effects have not been systematically quantified. Toward this goal, here we analyze the radiation at the top of the atmosphere and propose a measure of the DCC radiative effect (DCCRE) as the difference between the total radiative fluxes with the full cloud cycle and its uniformly distributed cloud counterpart. When applied to the frequency of cloud occurrence, DCCRE is linked to the covariance between DCC and cloud radiative effects. Satellite observations show that the daily cloud cycle is strongly linked to pacific decadal oscillation (PDO) and climate hiatus, revealing its potential role in controlling climate variability. Climate model outputs show large inter-model spreads of DCCRE, accounting for approximately 20% inter-model spread of the cloud radiative effects. Climate models also suggest that while DCCRE is not sensitive to rising temperatures at the global scale, it can be important in certain regions. Such a framework can be used to conduct a more systematic evaluation of the DCC in climate models and observations with the goal to understand climate variability and reduce uncertainty in climate projections.
Yost, Christopher R.; Minnis, Patrick; Sun-Mack, Sunny; Chen, Yan; Smith, William L.Yost, C. R., P. Minnis, S. Sun-Mack, Y. Chen, W. L. Smith, 2020: CERES MODIS Cloud Product Retrievals for Edition 4–Part II: Comparisons to CloudSat and CALIPSO. IEEE Transactions on Geoscience and Remote Sensing, 1-30. doi: 10.1109/TGRS.2020.3015155. Assessments of the Clouds and the Earth's Radiant Energy System Edition 4 (Ed4) cloud retrievals are critical for climate studies. Ed4 cloud parameters are evaluated using instruments in the A-Train Constellation. Cloud-Aerosol LiDAR with Orthogonal Polarization (CALIOP) and Cloud Profiling Radar (CPR) retrievals are compared with Ed4 retrievals from the Aqua Moderate-Resolution Imaging Spectroradiometer (MODIS) as a function of the CALIOP horizontal averaging (HA) scale. Regardless of the HA scale, MODIS daytime (nighttime) water cloud fraction (CF) is greater (less) than that from CALIOP. MODIS ice CF is less than CALIOP overall, with the largest differences in polar regions. Ed4 and CALIOP retrieve the same cloud phase in 70%-98% of simultaneous observations depending on the time of day, surface conditions, HA scales, and type of cloud vertical structure. Mean cloud top height (CTH) differences for single-layer water clouds over snow-/ice-free surfaces are less than 100 m. Base altitude positive biases of 170-460 m may be impacted by CPR detection limitations. Average MODIS ice CTHs are underestimated by 70 m for some deep convective clouds and up to 2.2 km for thin cirrus. Ice cloud base altitudes are typically underestimated (overestimated) during daytime (nighttime). MODIS and CALIOP cirrus optical depths over oceans are within 46% and 5% for daytime and nighttime observations, respectively. Ice water path differences depend on the CALIOP retrieval version and warrant further investigation. Except for daytime cirrus optical depth, Ed4 cloud property retrievals are at least as accurate as other long-term operational cloud property retrieval systems. cloud; Clouds and the Earth's Radiant Energy System (CERES); cloud remote sensing; Climate; cloud height; cloud optical depth (COD); cloud phase; Cloud-Aerosol LiDAR and Infrared Pathfinder Satellite Observation (CALIPSO); MODerate-resolution Imaging Spectroradiometer (MODIS); validation.
You, Cheng; Tjernström, Michael; Devasthale, AbhayYou, C., M. Tjernström, A. Devasthale, 2020: Warm-Air Advection Over Melting Sea-Ice: A Lagrangian Case Study. Boundary-Layer Meteorology. doi: 10.1007/s10546-020-00590-1. Observations from the 2014 Arctic Clouds in Summer Experiment indicate that, in summer, warm-air advection over melting sea-ice results in a strong surface melting feedback forced by a very strong surface-based temperature inversion and fog formation exerting additional heat flux on the surface. Here, we analyze this case further using a combination of reanalysis dataset and satellite products in a Lagrangian framework, thereby extending the view spatially from the local icebreaker observations into a Langrangian perspective. The results confirm that warm-air advection induces a positive net surface-energy-budget anomaly, exerting positive longwave radiation and turbulent heat flux on the surface. Additionally, as warm and moist air penetrates farther into the Arctic, cloud-top cooling and surface mixing eventually erode the surface inversion downstream. The initial surface inversion splits into two elevated inversions while the air columns below the elevated inversions transform into well-mixed layers.
You, Qinglong; Chen, Deliang; Wu, Fangying; Pepin, Nick; Cai, Ziyi; Ahrens, Bodo; Jiang, Zhihong; Wu, Zhiwei; Kang, Shichang; AghaKouchak, AmirYou, Q., D. Chen, F. Wu, N. Pepin, Z. Cai, B. Ahrens, Z. Jiang, Z. Wu, S. Kang, A. AghaKouchak, 2020: Elevation dependent warming over the Tibetan Plateau: Patterns, mechanisms and perspectives. Earth-Science Reviews, 210, 103349. doi: 10.1016/j.earscirev.2020.103349. The Tibetan Plateau (TP) is also known as the “Third Pole”. Elevation dependent warming (EDW), the phenomenon that warming rate changes systematically with elevation, is of high significance for realistically estimating warming rates and their impacts over the TP. This review summarizes studies of characteristics and mechanisms behind EDW over the TP based on multiple observed datasets and model simulations. Spatial expression of EDW and explanatory mechanisms are still largely unknown because of the lack of suitable data over the TP. The focus is on the roles played by known mechanisms such as snow/ice-albedo feedback, cloud feedback, atmospheric water vapor feedback, aerosol feedback, and changes in land use, ozone and vegetation. At present, there is limited consensus on the main mechanisms controlling EDW. Finally, new perspectives and unresolved issues are outlined, including quantification of EDW in climate model simulations, explanation of the long-term EDW reconstructed from proxies, interaction between the Asian summer monsoon and EDW, importance of EDW for future environmental changes and water resources, and current gaps in understanding EDW over extremely high elevations. Further progress requires a more comprehensive ground observation network, greater use of remote sensing data, and high-resolution climate modeling with better representation of both atmospheric and cryospheric processes. Tibetan Plateau; Elevation dependent warming; Patterns and trends; Physical mechanisms
Young, Cindy L.; Lukashin, Constantine; Taylor, Patrick C.; Swanson, Rand; Kirk, William S.; Cooney, Michael; Swartz, William H.; Goldberg, Arnold; Stone, Thomas; Jackson, Trevor; Doelling, David R.; Shaw, Joseph A.; Buleri, ChristineYoung, C. L., C. Lukashin, P. C. Taylor, R. Swanson, W. S. Kirk, M. Cooney, W. H. Swartz, A. Goldberg, T. Stone, T. Jackson, D. R. Doelling, J. A. Shaw, C. Buleri, 2020: Trutinor: A Conceptual Study for a Next-Generation Earth Radiant Energy Instrument. Remote Sensing, 12(20), 3281. doi: 10.3390/rs12203281. Uninterrupted and overlapping satellite instrument measurements of Earth’s radiation budget from space are required to sufficiently monitor the planet’s changing climate, detect trends in key climate variables, constrain climate models, and quantify climate feedbacks. The Clouds and Earth’s Radiant Energy System (CERES) instruments are currently making these vital measurements for the scientific community and society, but with modern technologies, there are more efficient and cost-effective alternatives to the CERES implementation. We present a compact radiometer concept, Trutinor (meaning “balance” in Latin), with two broadband channels, shortwave (0.2–3 μm) and longwave (5–50 μm), capable of continuing the CERES record by flying in formation with an existing imager on another satellite platform. The instrument uses a three-mirror off-axis anastigmat telescope as the front optics to image these broadband radiances onto a microbolometer array coated with gold black, providing the required performance across the full spectral range. Each pixel of the sensor has a field of view of 0.6°, which was chosen so the shortwave band can be efficiently calibrated using the Moon as an on-orbit light source with the same angular extent, thereby reducing mass and improving measurement accuracy, towards the goal of a gap-tolerant observing system. The longwave band will utilize compact blackbodies with phase-change cells for an absolute calibration reference, establishing a clear path for SI-traceability. Trutinor’s instrument breadboard has been designed and is currently being built and tested. earth radiation budget; CERES; climate change; carbon nanotubes; ARCSTONE; lunar calibration; microbolometer array; phase change cells; RAVAN; small satellite constellation
Yu, Lan; Zhang, Ming; Wang, Lunche; Qin, Wenmin; Lu, Yunbo; Li, JunliYu, L., M. Zhang, L. Wang, W. Qin, Y. Lu, J. Li, 2020: Clear-sky solar radiation changes over arid and semi-arid areas in China and their determining factors during 2001–2015. Atmospheric Environment, 223, 117198. doi: 10.1016/j.atmosenv.2019.117198. In the study, we investigated the clear-sky solar radiation at the surface and their determining factors over the arid and semi-arid (ASA) areas in China using the simulations by Mesoscale Atmospheric Global Irradiance Code (MAGIC) radiation code with satellite remote sensing aerosol data and reanalysis data as input. The coefficient of determination (R2) between ground-based measurements and simulations was 0.959, and the average relative error was 6.33%. Stations with an average relative error of less than 10% accounted for 100%, confirming the reliability of simulations. The distribution of clear-sky solar radiation showed low values in regions with high latitudes and low altitudes, and high ones in regions with low latitudes and high altitudes. The monthly average of water vapour radiative effects (WVRE) was higher than the monthly average of aerosol direct radiative effects (ADRE) for each month. WVRE were even more than six times that of ADRE in July, August, September, indicating that water vapour has stronger weakening of clear-sky solar radiation than aerosols. The annual trend indicated increases in clear-sky solar radiation in most part of ASA areas. Central Inner Mongolia (0.389 W m−2 year−1) has the significant increase. There was an interesting finding that the area where the clear-sky solar radiation decreased/increased has a good match with the area where ADRE enhanced/weakened. The R2 between clear-sky solar radiation trend and ADRE trend was 0.957, indicating that the ADRE trends were the determining factor of the clear-sky solar radiation trends. Central Inner Mongolia (0.345 Wm-2 year−1) has the significant weakening of ADRE. Aerosol radiative effects; Arid and semi-arid areas; Clear-sky solar radiation at the surface; Liner trends; MAGIC; Water vapour radiative effects
Yu, Lisan; Stackhouse, P. W.; Wilber, A. C.; Weller, R.Yu, L., P. W. Stackhouse, A. C. Wilber, R. Weller, 2020: Global ocean heat, freshwater, and momentum fluxes.[in "State of the Climate in 2019"]. Bull. Amer. Meteor. Soc, 101(8), S149-152. doi: 10.1175/BAMS-D-20-0105.1.
Zapadka, Tomasz; Ostrowska, Mirosława; Stoltmann, Damian; Krężel, AdamZapadka, T., M. Ostrowska, D. Stoltmann, A. Krężel, 2020: A satellite system for monitoring the radiation budget at the Baltic Sea surface. Remote Sensing of Environment, 240, 111683. doi: 10.1016/j.rse.2020.111683. The paper discusses the possibilities and limitations of using satellite data to determine the radiation budget NET and its components at the Baltic Sea surface in near real time using a newly established SBRB system (SatBałtyk Radiation Budget). The system enables determination of daily radiation fluxes over the entire Baltic Sea employing data from satellites in combination with data from numerical prognostic models. Data from satellite radiometers like SEVIRI, AVHRR are used together with algorithms that take into account the specificity of this sea and are developed based on large empirical data sets collected in this region. A verification of the system has been carried out based on separate, empirical data collected in 2015 on the oil rig Plat placed on the Baltic Sea and Svenska Högarna station. The analysis showed that daily average NET had been calculated with RMSD of 15 Wm−2 and R2 = 0.95 for the South Baltic. For downward radiation fluxes in the solar wavelength range (SW) and the terrestrial, thermal wavelength range (LW) RMSD is respectively 11.9 Wm−2 and 9.6 Wm−2 and in both cases increase with latitude. The NET components estimated using SBRB were also compared with the corresponding magnitudes OSI -303-a and OSI 304-a from OSI SAF, EBAF surface Edition 4.0 from CERES and ERA-interim data from ECMWF systems. The main reasons for the discrepancies are discussed. The analyses confirmed the advisability of using local solutions which ensure high accuracy and spatial resolution. SBRB was developed and implemented as part of the comprehensive SatBałtyk System designed to monitor the Baltic Sea environment. The maps together with instantaneous values of the radiation components measured at actinometric stations employed at SatBałtyk System are accessible at www.satbaltyk.iopan.gda.pl. The scheme, algorithms and the way of the SBRB operation are described in detail.
Zeng, Qi; Cheng, Jie; Dong, LixinZeng, Q., J. Cheng, L. Dong, 2020: Assessment of the Long-Term High-Spatial-Resolution Global LAnd Surface Satellite (GLASS) Surface Longwave Radiation Product Using Ground Measurements. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 13, 2032-2055. doi: 10.1109/JSTARS.2020.2992472. In this article, we comprehensively assessed the newly released long-term high-spatial-resolution Global LAnd Surface Satellite (GLASS) surface longwave (LW) radiation product using site measurements of LW fluxes. In total, three years of ground-measured LW fluxes (surface longwave upward radiation (LWUP), surface longwave downward radiation (LWDN), and surface longwave net radiation (LWNR) collected from 141 sites in six independent networks (AmeriFlux, AsiaFlux, BSRN, CEOP, HiWATER-MUSOEXE, and TIPEX-III) are used to evaluate the GLASS LW radiation product. These sites cover various land cover types, surface elevations, and climatic types. According to the evaluation results, the biases are -4.33, -3.77, and 0.70 W/m2 and the RMSEs are 18.15, 26.94, and 26.70 W/m2 for clear-sky LWUP, LWDN, and LWNR, respectively. The GLASS LW radiation product performs well in climate-change-sensitive areas such as poleward areas, semiarid areas, and the “third pole”, namely, the Tibetan Plateau. The accuracy of the GLASS LW product is higher or comparable to that of available LW products and studies but has a high-spatial-resolution of 1 km and a time span of 19 years. In conclusion, the overall accuracy of the clear-sky GLASS LW radiation product can satisfy the requirements of the hydrological, meteorological, and agricultural research communities on a global scale. We will continue to improve the retrieval algorithms and update the products accordingly. Land surface; atmospheric radiation; atmospheric techniques; Atmospheric modeling; surface radiation budget (SRB); Sea surface; Tibetan Plateau; Ocean temperature; Land surface temperature; remote sensing; Clouds; Glass; Global LAnd Surface Satellite (GLASS); Global LAnd Surface Satellite; hybrid method; clear-sky GLASS surface longwave radiation product; ground-measured surface longwave fluxes; high-spatial-resolution GLASS; land cover types; longwave downward (LWDN); longwave net radiation (LWNR); longwave upward (LWUP); surface elevations; surface longwave (LW) radiation; surface longwave net radiation
Zhang, Baichao; Guo, Zhun; Zhang, Lixia; Zhou, Tianjun; Hayasaya, TadahiroZhang, B., Z. Guo, L. Zhang, T. Zhou, T. Hayasaya, 2020: Cloud Characteristics and Radiation Forcing in the Global Land Monsoon Region From Multisource Satellite Data Sets. Earth and Space Science, 7(3), e2019EA001027. doi: 10.1029/2019EA001027. The global land monsoon region has the highest land cloud amount in the world affecting two thirds of the world's population. Understanding the characteristics of cloud-radiation relies heavily on satellite data set, while few studies have addressed the advantages and weaknesses of current existing satellite data sets in estimating the cloud-radiation characteristics over global land monsoon regions. Multisource satellite data sets are used in this study to show the cloud characteristics in different monsoon regions. We find that all satellite data sets consistently show a peak of cloud fraction, cloud top height and cloud radiation forcing during summer over the global land monsoon regions. A regional difference in cloud characteristics is observed from multisource data sets. The seasonal cycle of cloud amount in the North American monsoon region is relatively smaller than that of the other monsoon regions. High-level clouds dominate the North African monsoon, while Low-level clouds dominate the Asian monsoon. The cloud properties and their radiative forcings revealed by four cloud-parameter data sets with multispectral imagers, that is, International Satellite Cloud Climatology Project (ISCCP)-D2, ISCCP-H, Moderate Resolution Imaging Spectroradiometer (MODIS)-MYD, and MODIS-MOD, are similar to one another, except stronger short-wave cloud radiative forcing in ISCCP-FD. Multidata comparison confirmed the climate and seasonal cycles of cloud characteristics in this study, demonstrating a better representation of cloud vertical structure in CloudSat over global land monsoon region. cloud; satellite data; global monsoon; multidata comparison
Zhang, He; Zhang, Minghua; Jin, Jiangbo; Fei, Kece; Ji, Duoying; Wu, Chenglai; Zhu, Jiawen; He, Juanxiong; Chai, Zhaoyang; Xie, Jinbo; Dong, Xiao; Zhang, Dongling; Bi, Xunqiang; Cao, Hang; Chen, Huansheng; Chen, Kangjun; Chen, Xueshun; Gao, Xin; Hao, Huiqun; Jiang, Jinrong; Kong, Xianghui; Li, Shigang; Li, Yangchun; Lin, Pengfei; Lin, Zhaohui; Liu, Hailong; Liu, Xiaohong; Shi, Ying; Song, Mirong; Wang, Huijun; Wang, Tianyi; Wang, Xiaocong; Wang, Zifa; Wei, Ying; Wu, Baodong; Xie, Zhenghui; Xu, Yongfu; Yu, Yongqiang; Yuan, Liang; Zeng, Qingcun; Zeng, Xiaodong; Zhao, Shuwen; Zhou, Guangqing; Zhu, JiangZhang, H., M. Zhang, J. Jin, K. Fei, D. Ji, C. Wu, J. Zhu, J. He, Z. Chai, J. Xie, X. Dong, D. Zhang, X. Bi, H. Cao, H. Chen, K. Chen, X. Chen, X. Gao, H. Hao, J. Jiang, X. Kong, S. Li, Y. Li, P. Lin, Z. Lin, H. Liu, X. Liu, Y. Shi, M. Song, H. Wang, T. Wang, X. Wang, Z. Wang, Y. Wei, B. Wu, Z. Xie, Y. Xu, Y. Yu, L. Yuan, Q. Zeng, X. Zeng, S. Zhao, G. Zhou, J. Zhu, 2020: CAS-ESM 2: Description and Climate Simulation Performance of the Chinese Academy of Sciences (CAS) Earth System Model (ESM) Version 2. Journal of Advances in Modeling Earth Systems, 12(12), e2020MS002210. doi: 10.1029/2020MS002210. The second version of Chinese Academy of Sciences Earth System Model (CAS-ESM 2) is described with emphasis on the development process, strength and weakness, and climate sensitivities in simulations of the Coupled Model Intercomparison Project (CMIP6) DECK experiments. CAS-ESM 2 was built as a numerical model to simulate both the physical climate system as well as atmospheric chemistry and carbon cycle. It is a newcomer in the international modeling community to provide sufficiently independent solutions of climate simulations from those of other models. Performances of the model in simulating the basic states of the radiation budget of the atmosphere and ocean, precipitation, circulations, variabilities, and the 20th Century warming are presented. Model biases and their possible causes are discussed. Strength includes horizontal heat transport in the atmosphere and oceans, vertical profile of the Atlantic Meridional Overturning Circulation; weakness includes the double Inter-Tropical Convergence Zone (ITCZ) and stronger amplitude of the El Niño-Southern Oscillation (ENSO) that are also common in many other models. The simulated the 20th Century warming shares a similar discrepancy with observations as in several other models—less warming in the 1920s and stronger cooling in the 1960s than in observation—at the time when there was a steep increase of anthropogenic aerosols. As a result, the 20th Century warming is about 60% of the observed warming despite that the model simulated a similar slope of warming trend after 1980 to observation. The model has an equilibrium climate sensitivity of 3.4 K with a positive cloud feedback from the shortwave radiation. climate sensitivity; Earth System Model; CAS-ESM; DECK experiments; Model calibration
Zhang, Taiping; Stackhouse, Paul W.; Cox, Stephen J.; Mikovitz, J. ColleenZhang, T., P. W. Stackhouse, S. J. Cox, J. C. Mikovitz, 2020: The uncertainty of the BSRN monthly mean Global 1 and Global 2 fluxes due to missing hourly means with and without quality-control and an examination through validation of the NASA GEWEX SRB datasets. Journal of Quantitative Spectroscopy and Radiative Transfer, 255, 107272. doi: 10.1016/j.jqsrt.2020.107272. The Baseline Surface Radiation Network (BSRN) is a project of the Data and Assessments Panel from the Global Energy and Water Exchanges (GEWEX) under the umbrella of the World Climate Research Programme (WCRP). Currently in the archive there are data from 67 sites located in all seven continents spanning from 1992 to the present. The original BSRN records are at 1-, 2-, 3- or 5-minute intervals, and sophisticated quality-control procedures have been developed to eliminate erroneous records before hourly, daily and monthly means are computed. The resulting gaps from quality-control, however, give rise to uncertainties in computed temporal averages on various scales. There are two types of total shortwave downward fluxes: The Global 1 which is the sum of direct horizontal and diffuse irradiances, observed using the pyrheliometer and radiometer, respectively, and is recommended by the BSRN committee for its higher precision, and the Global 2 which is observed using the pyranometer. It has been found that, compared to Global 2, Global 1 is more susceptible to errors, thus resulting in more gaps in the original records. Here we examine the effect of quality-control on the monthly mean Global 1 and Global 2 and attempt to quantify the resulting uncertainties through analysis of the quality-control procedure and averaging algorithm and comparison with the NASA GEWEX Surface Radiation Budget (SRB) dataset. The SRB project is now making progress toward its Release 4.0 Integrated Products (Rel. 4.0-IP or V4.0-IP) with changes in both algorithm and inputs on the basis of its Release 3.0 (Rel. 3.0 or V3.0) products. The preliminary results from Rel. 4.0-IP span 34 years continuously from July 1983 to June 2017 on a 1° by 1° quasi-equal-area grid system in the form of 3-hourly, daily and monthly means. It is found that Global 2 generally has fewer missing records and is less affected by the quality-check procedure; on average, the monthly mean Global 1 and Global 2 differ by less than 1 W m−2; the GEWEX SRB preliminary GSW(V4.0-IP) monthly mean shortwave downward fluxes agree the best with the BSRN Global 1 monthly means computed from observational records that are nearly complete and that survive the quality-check nearly completely. BSRN; GEWEX SRB; Global 1; Global 2; Uncertainty
Zhang, Xiaotong; Liang, ShunlinZhang, X., S. Liang, 2020: Chapter 5 - Solar radiation. Advanced Remote Sensing (Second Edition), 157-191.
Zhang, Xingxing; Lu, Ning; Jiang, Hou; Yao, LingZhang, X., N. Lu, H. Jiang, L. Yao, 2020: Evaluation of Reanalysis Surface Incident Solar Radiation Data in China. Scientific Reports, 10(1), 1-20. doi: 10.1038/s41598-020-60460-1. Surface incident solar radiation (Rs) of reanalysis products is widely used in ecological conservation, agricultural production, civil engineering and various solar energy applications. It is of great importance to have a good knowledge of the uncertainty of reanalysis Rs products. In this study, we evaluated the Rs estimates from two representative global reanalysis (ERA-Interim and MERRA-2) using quality- controlled surface measurements from China Meteorological Administration (CMA) and Multi-layer Simulation and Data Assimilation Center of the Tibetan Plateau (DAM) from 2000 to 2009. Error causes are further analyzed in combination radiation products from the Earth’s Radiant Energy System (CERES) EBAF through time series estimation, hotspot selection and Geodetector methods. Both the ERA-Interim and MERRA-2 products overestimate the Rs in China, and the MERRA-2 overestimation is more pronounced. The errors of the ERA-Interim are greater in spring and winter, while that of the MERRA-2 are almost the same in all seasons. As more quality-controlled measurements were used for validation, the conclusions seem more reliable, thereby providing scientific reference for rational use of these datasets. It was also found that the main causes of errors are the cloud coverage in the southeast coastal area, aerosol optical depth (AOD) and water vapor content in the Sichuan Basin, and cloud coverage and AOD in the northeast and middle east of China.
Zhou, Zhigao; Lin, Aiwen; Wang, Lunche; Qin, Wenmin; Zhong, Yang; He, LijieZhou, Z., A. Lin, L. Wang, W. Qin, Y. Zhong, L. He, 2020: Trends in downward surface shortwave radiation from multi-source data over China during 1984–2015. International Journal of Climatology, 40(7), 3467-3485. doi: 10.1002/joc.6408. The clear knowledge of decadal variability of surface solar radiation (SSR) is of vitally significant for understanding hydrological and biological processes and climate prediction. However, existing studies have shown observed SSR over China may have large discrepancies and inhomogeneity in decadal variability due to sensitivity drift, inaccurate calibrations and instrument replacement. Therefore, a new procedure of station selection was proposed to eliminate errors and to derive “true” SSR values in this study. Afterward, two satellite retrieves of SSR, including Clouds and the Earth's Radiant Energy System-energy balanced and filled product (CERES-EBAF) (edition 4) and Global Energy and Water Cycle Experiment-Surface Radiation Budget (GEWEX-SRB) (Version 3.0), and three reanalysis products, including National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR), national centers for environmental prediction-/department of energy (NCEP-DOE) and Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) were evaluated using “true” SSR values at 39 homogeneous stations from the China Meteorological Administration and it was found that although all five products overestimated SSR, two satellite retrieves showed better accuracy with an overall R of 0.95, an root mean squared error (RMSE) of 20.4 W m−2 and mean absolute bias error (MAE) of 14.9 W m−2 for CERES-EBAF and an overall R of 0.92, an RMSE of 27.7 W m−2 and MAE of 21.2 W m−2 for GEWEX-SRB across China. Meanwhile, inter-comparisons between trends of observations and trends of two satellite retrieves in this study showed that the new trends derived from two satellite retrieves (+0.78 W m−2 decade−1) were good agreement with trends of observation (+0.92 W m−2 decade−1) from 1994 to 2015. However, trends of SSR (+5.8 W m−2 decade−1) in situ measurements were still in disagreement with the trends of SSR (−3.7 W m−2 decade−1) derived from two satellite retrieves from 1984 to 1993 because of the sensitivity drift and instrument replacement in this period. The possible reasons for decadal variability of SSR in China were detected and it was found that variations in aerosol optical depth (AOD) and aerosol-cloud interaction, rather than cloud, were suggested to be likely the main influencing factor of decadal variability of SSR across China from 1984 to 2015. Aerosol optical depth; China; Decadal variability; Reanalyses; Satellite retrievals; Surface solar radiation
Zou, Cheng-Zhi; Zhou, Lihang; Lin, Lin; Sun, Ninghai; Chen, Yong; Flynn, Lawrence E.; Zhang, Bin; Cao, Changyong; Iturbide-Sanchez, Flavio; Beck, Trevor; Yan, Banghua; Kalluri, Satya; Bai, Yan; Blonski, Slawomir; Choi, Taeyoung; Divakarla, Murty; Gu, Yalong; Hao, Xianjun; Li, Wei; Liang, Ding; Niu, Jianguo; Shao, Xi; Strow, Larrabee; Tobin, David C.; Tremblay, Denis; Uprety, Sirish; Wang, Wenhui; Xu, Hui; Yang, Hu; Goldberg, Mitchell D.Zou, C., L. Zhou, L. Lin, N. Sun, Y. Chen, L. E. Flynn, B. Zhang, C. Cao, F. Iturbide-Sanchez, T. Beck, B. Yan, S. Kalluri, Y. Bai, S. Blonski, T. Choi, M. Divakarla, Y. Gu, X. Hao, W. Li, D. Liang, J. Niu, X. Shao, L. Strow, D. C. Tobin, D. Tremblay, S. Uprety, W. Wang, H. Xu, H. Yang, M. D. Goldberg, 2020: The Reprocessed Suomi NPP Satellite Observations. Remote Sensing, 12(18), 2891. doi: 10.3390/rs12182891. The launch of the National Oceanic and Atmospheric Administration (NOAA)/ National Aeronautics and Space Administration (NASA) Suomi National Polar-orbiting Partnership (S-NPP) and its follow-on NOAA Joint Polar Satellite Systems (JPSS) satellites marks the beginning of a new era of operational satellite observations of the Earth and atmosphere for environmental applications with high spatial resolution and sampling rate. The S-NPP and JPSS are equipped with five instruments, each with advanced design in Earth sampling, including the Advanced Technology Microwave Sounder (ATMS), the Cross-track Infrared Sounder (CrIS), the Ozone Mapping and Profiler Suite (OMPS), the Visible Infrared Imaging Radiometer Suite (VIIRS), and the Clouds and the Earth’s Radiant Energy System (CERES). Among them, the ATMS is the new generation of microwave sounder measuring temperature profiles from the surface to the upper stratosphere and moisture profiles from the surface to the upper troposphere, while CrIS is the first of a series of advanced operational hyperspectral sounders providing more accurate atmospheric and moisture sounding observations with higher vertical resolution for weather and climate applications. The OMPS instrument measures solar backscattered ultraviolet to provide information on the concentrations of ozone in the Earth’s atmosphere, and VIIRS provides global observations of a variety of essential environmental variables over the land, atmosphere, cryosphere, and ocean with visible and infrared imagery. The CERES instrument measures the solar energy reflected by the Earth, the longwave radiative emission from the Earth, and the role of cloud processes in the Earth’s energy balance. Presently, observations from several instruments on S-NPP and JPSS-1 (re-named NOAA-20 after launch) provide near real-time monitoring of the environmental changes and improve weather forecasting by assimilation into numerical weather prediction models. Envisioning the need for consistencies in satellite retrievals, improving climate reanalyses, development of climate data records, and improving numerical weather forecasting, the NOAA/Center for Satellite Applications and Research (STAR) has been reprocessing the S-NPP observations for ATMS, CrIS, OMPS, and VIIRS through their life cycle. This article provides a summary of the instrument observing principles, data characteristics, reprocessing approaches, calibration algorithms, and validation results of the reprocessed sensor data records. The reprocessing generated consistent Level-1 sensor data records using unified and consistent calibration algorithms for each instrument that removed artificial jumps in data owing to operational changes, instrument anomalies, contaminations by anomaly views of the environment or spacecraft, and other causes. The reprocessed sensor data records were compared with and validated against other observations for a consistency check whenever such data were available. The reprocessed data will be archived in the NOAA data center with the same format as the operational data and technical support for data requests. Such a reprocessing is expected to improve the efficiency of the use of the S-NPP and JPSS satellite data and the accuracy of the observed essential environmental variables through either consistent satellite retrievals or use of the reprocessed data in numerical data assimilations. climate change monitoring; fundamental climate data records; satellite recalibration; satellite reprocessing; suomi NPP and JPSS satellite instruments
Ackerman, S. A.; Platnick, S.; Bhartia, P. K.; Duncan, B.; L’Ecuyer, T.; Heidinger, A.; Skofronick-Jackson, G.; Loeb, N.; Schmit, T.; Smith, N.Ackerman, S. A., S. Platnick, P. K. Bhartia, B. Duncan, T. L’Ecuyer, A. Heidinger, G. Skofronick-Jackson, N. Loeb, T. Schmit, N. Smith, 2019: Satellites see the World’s Atmosphere. Meteorological Monographs, 59, 4.1–4.53. doi: 10.1175/AMSMONOGRAPHS-D-18-0009.1. Satellite meteorology is a relatively new branch of the atmospheric sciences. The field emerged in the late 1950’s during the Cold War and built on the advances in rocketry after World War II. In less than seventy years, satellite observations have transformed the way scientists observe and study Earth. This paper discusses some of the key advances in our understanding of the energy and water cycles, weather forecasting and atmospheric composition enabled by satellite observations. While progress truly has been an international achievement, in accord with a monograph observing the centennial of the American Meteorological Society, as well as limited space, the emphasis of this chapter is on the U.S. satellite effort.
Albrecht, Bruce; Ghate, Virendra; Mohrmann, Johannes; Wood, Robert; Zuidema, Paquita; Bretherton, Christopher; Schwartz, Christian; Eloranta, Edwin; Glienke, Susanne; Donaher, Shaunna; Sarkar, Mampi; McGibbon, Jeremy; Nugent, Alison D.; Shaw, Raymond A.; Fugal, Jacob; Minnis, Patrick; Paliknoda, Robindra; Lussier, Louis; Jensen, Jorgen; Vivekanandan, J.; Ellis, Scott; Tsai, Peisang; Rilling, Robert; Haggerty, Julie; Campos, Teresa; Stell, Meghan; Reeves, Michael; Beaton, Stuart; Allison, John; Stossmeister, Gregory; Hall, Samuel; Schmidt, SebastianAlbrecht, B., V. Ghate, J. Mohrmann, R. Wood, P. Zuidema, C. Bretherton, C. Schwartz, E. Eloranta, S. Glienke, S. Donaher, M. Sarkar, J. McGibbon, A. D. Nugent, R. A. Shaw, J. Fugal, P. Minnis, R. Paliknoda, L. Lussier, J. Jensen, J. Vivekanandan, S. Ellis, P. Tsai, R. Rilling, J. Haggerty, T. Campos, M. Stell, M. Reeves, S. Beaton, J. Allison, G. Stossmeister, S. Hall, S. Schmidt, 2019: Cloud System Evolution in the Trades—CSET Following the Evolution of Boundary Layer Cloud Systems with the NSF/NCAR GV. Bull. Amer. Meteor. Soc., 100(1), 93–12. doi: 10.1175/BAMS-D-17-0180.1. The evolution of the boundary layer aerosol, cloud, precipitation, and thermodynamic structures along trajectories within the north-Pacific trade-winds was investigated using the NSF NCAR Gulfstream V.
Ali, Md. Arfan; Islam, Md. Monirul; Islam, Md. Nazrul; Almazroui, MansourAli, M. A., M. M. Islam, M. N. Islam, M. Almazroui, 2019: Investigations of MODIS AOD and cloud properties with CERES sensor based net cloud radiative effect and a NOAA HYSPLIT Model over Bangladesh for the period 2001–2016. Atmospheric Research, 215, 268-283. doi: 10.1016/j.atmosres.2018.09.001. The present study investigates the spatiotemporal characteristics of aerosol optical depth (AOD), cloud properties, and TOA (Top Of Atmosphere) Net Cloud Radiative Effect (Net CRE) using MODIS (Moderate Resolution Imaging Spectroradiometer) Terra and CERES (Clouds and the Earth's Radiant Energy System) products over Bangladesh for the period 2001–2016. This study also explores the backward trajectory using a HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory) model from the National Oceanic and Atmospheric Administration (NOAA) to discover the origins of air masses. Results show annual values of AOD (0.55), Cloud Fraction (CF, 0.66), CER (Cloud Effective Radius, 14.89), COT (Cloud Optical Thickness, 15.25), CTP (Cloud Top Pressure, 639.17), CTT (Cloud Top Temperature, 262.52), WV (Water Vapor, 4.48), and Net CRE (−13.06) over Bangladesh. A seasonally peak is recorded for AOD (0.64) in MAM while for CF (0.96), CER (17.24), COT (21.12), WV (6.86), and Net CRE (−34.44) the peak is in JJA, and for CTP (884.06) and CTT (284.17) it is in DJF. By monthly the peak is recorded in June for AOD (0.73) and COT (24.86); for CER (17.87), WV (7.26), and Net CRE (−45.38) it is in July; for CF (0.97) it is in July/August; CTP (900.89) and for CTT (285.75) it is in February. Regression analysis shows annual increasing trends for AOD, CF, WV, COT, CTP, and CTT with negative trends for CER and Net CRE. AOD shows increasing trends in all seasons, whereas CF, CER and COT show increasing trends in DJF and MAM only. CTP and CTT show increasing trends in JJA and SON. WV shows an increasing trend in MAM, JJA, and DJF, whereas Net CRE shows an increasing trend in MAM and SON. Relationship study provides a better conclusion of AOD and cloud interaction based on the analysis of positive and negative correlation values over the study region. The backward trajectory indicated that the air masses originated from the Bay of Bengal, India, Nepal, Pakistan, and Iran. This study may be considered as a base document for further study on aerosols over Bangladesh using climate model simulation for the projection period. CERES; MODIS; A HYSPLIT Model; AOD; Bangladesh
Anderson, Martha; Diak, George; Gao, Feng; Knipper, Kyle; Hain, Christopher; Eichelmann, Elke; Hemes, Kyle S.; Baldocchi, Dennis; Kustas, William; Yang, YunAnderson, M., G. Diak, F. Gao, K. Knipper, C. Hain, E. Eichelmann, K. S. Hemes, D. Baldocchi, W. Kustas, Y. Yang, 2019: Impact of Insolation Data Source on Remote Sensing Retrievals of Evapotranspiration over the California Delta. Remote Sensing, 11(3), 216. doi: 10.3390/rs11030216. The energy delivered to the land surface via insolation is a primary driver of evapotranspiration (ET)—the exchange of water vapor between the land and atmosphere. Spatially distributed ET products are in great demand in the water resource management community for real-time operations and sustainable water use planning. The accuracy and deliverability of these products are determined in part by the characteristics and quality of the insolation data sources used as input to the ET models. This paper investigates the practical utility of three different insolation datasets within the context of a satellite-based remote sensing framework for mapping ET at high spatiotemporal resolution, in an application over the Sacramento–San Joaquin Delta region in California. The datasets tested included one reanalysis product: The Climate System Forecast Reanalysis (CFSR) at 0.25° spatial resolution, and two remote sensing insolation products generated with geostationary satellite imagery: a product for the continental United States at 0.2°, developed by the University of Wisconsin Space Sciences and Engineering Center (SSEC) and a coarser resolution (1°) global Clouds and the Earth’s Radiant Energy System (CERES) product. The three insolation data sources were compared to pyranometer data collected at flux towers within the Delta region to establish relative accuracy. The satellite products significantly outperformed CFSR, with root-mean square errors (RMSE) of 2.7, 1.5, and 1.4 MJ·m−2·d−1 for CFSR, CERES, and SSEC, respectively, at daily timesteps. The satellite-based products provided more accurate estimates of cloud occurrence and radiation transmission, while the reanalysis tended to underestimate solar radiation under cloudy-sky conditions. However, this difference in insolation performance did not translate into comparable improvement in the ET retrieval accuracy, where the RMSE in daily ET was 0.98 and 0.94 mm d−1 using the CFSR and SSEC insolation data sources, respectively, for all the flux sites combined. The lack of a notable impact on the aggregate ET performance may be due in part to the predominantly clear-sky conditions prevalent in central California, under which the reanalysis and satellite-based insolation data sources have comparable accuracy. While satellite-based insolation data could improve ET retrieval in more humid regions with greater cloud-cover frequency, over the California Delta and climatologically similar regions in the western U.S., the CFSR data may suffice for real-time ET modeling efforts. data fusion; California Delta; evapotranspiration; insolation; surface energy balance; water resource management
Armour, Kyle C.; Siler, Nicholas; Donohoe, Aaron; Roe, Gerard H.Armour, K. C., N. Siler, A. Donohoe, G. H. Roe, 2019: Meridional Atmospheric Heat Transport Constrained by Energetics and Mediated by Large-Scale Diffusion. J. Climate, 32(12), 3655–3680. doi: 10.1175/JCLI-D-18-0563.1. Meridional atmospheric heat transport (AHT) has been investigated through three broad perspectives: a dynamic perspective, linking AHT to the poleward flux of moist static energy (MSE) by atmospheric motions; an energetic perspective, linking AHT to energy input to the atmosphere by top-of-atmosphere radiation and surface heat fluxes; and a diffusive perspective, representing AHT in terms down-gradient energy transport. It is shown here that the three perspectives provide complementary diagnostics of meridional AHT and its changes under greenhouse-gas forcing. When combined, the energetic and diffusive perspectives offer prognostic insights: anomalous AHT is constrained to satisfy the net energetic demands of radiative forcing, radiative feedbacks, and ocean heat uptake; in turn, the meridional pattern of warming must adjust to produce those AHT changes, and does so approximately according to diffusion of anomalous MSE. The relationship between temperature and MSE exerts strong constraints on the warming pattern, favoring polar amplification. These conclusions are supported by use of a diffusive moist energy balance model (EBM) that accurately predicts zonal-mean warming and AHT changes within comprehensive general circulation models (GCMs). A dry diffusive EBM predicts similar AHT changes in order to satisfy the same energetic constraints, but does so through tropically-amplified warming – at odds with the GCMs’ polar-amplified warming pattern. The results suggest that polar-amplified warming is a near-inevitable consequence of a moist, diffusive atmosphere’s response to greenhouse-gas forcing. In this view, atmospheric circulations must act to satisfy net AHT as constrained by energetics.
Bae, S. Y.; Park, R.-S.Bae, S. Y., R. Park, 2019: Consistency between the cloud and radiation processes in a numerical forecasting model. Meteorology and Atmospheric Physics, 131(5), 1429-1436. doi: 10.1007/s00703-018-0647-9. In this study, the radiation process in the Korean Integrated Model (KIM) is modified to calculate the cloud radiative forcing keeping a physical consistency with the microphysics, convection, and cloudiness schemes in an aspect of hydrometeor. A formula to calculate effective radii of cloud water in radiation scheme of the KIM is modified to be consistent with that in the microphysics scheme and the radiative effect of a subgrid-scale hydrometeor is considered along with convective parameterization and cloudiness schemes. The impacts of these modifications on radiation and precipitation are diagnosed via an observation comparison, and a detailed analysis of these impacts is conducted. Especially, the contrasting feedback of the subgrid-scale hydrometeor on precipitation over the land and the ocean is separately discussed.
Beucler, Tom; Abbott, Tristan H.; Cronin, Timothy W.; Pritchard, Michael S.Beucler, T., T. H. Abbott, T. W. Cronin, M. S. Pritchard, 2019: Comparing Convective Self-Aggregation in Idealized Models to Observed Moist Static Energy Variability Near the Equator. Geophysical Research Letters, 46(17-18), 10589-10598. doi: 10.1029/2019GL084130. Idealized convection-permitting simulations of radiative-convective equilibrium have become a popular tool for understanding the physical processes leading to horizontal variability of tropical water vapor and rainfall. However, the applicability of idealized simulations to nature is still unclear given that important processes are typically neglected, such as lateral water vapor advection by extratropical intrusions, or interactive ocean coupling. Here, we exploit spectral analysis to compactly summarize the multiscale processes supporting convective aggregation. By applying this framework to high-resolution reanalysis data and satellite observations in addition to idealized simulations, we compare convective-aggregation processes across horizontal scales and data sets. The results affirm the validity of the radiative-convective equilibrium simulations as an analogy to the real world. Column moist static energy tendencies share similar signs and scale selectivity in convection-permitting models and observations: Radiation increases variance at wavelengths above 1,000 km, while advection damps variance across wavelengths, and surface fluxes mostly reduce variance between 1,000 and 10,000 km. convection; water vapor; radiation; cloud physics; aggregation; spectral analysis
Blunden, Jessica; Arndt, Derek S.Blunden, J., D. S. Arndt, 2019: State of the Climate in 2018. Bull. Amer. Meteor. Soc., 100(9), Si-S306. doi: 10.1175/2019BAMSStateoftheClimate.1. Editor’s note: For easy download the posted pdf of the State of the Climate for 2019 is a low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.
Bodas‐Salcedo, A.; Mulcahy, J. P.; Andrews, T.; Williams, K. D.; Ringer, M. A.; Field, P. R.; Elsaesser, G. S.Bodas‐Salcedo, A., J. P. Mulcahy, T. Andrews, K. D. Williams, M. A. Ringer, P. R. Field, G. S. Elsaesser, 2019: Strong Dependence of Atmospheric Feedbacks on Mixed-Phase Microphysics and Aerosol-Cloud Interactions in HadGEM3. Journal of Advances in Modeling Earth Systems, 11(6), 1735-1758. doi: 10.1029/2019MS001688. We analyze the atmospheric processes that explain the large changes in radiative feedbacks between the two latest climate configurations of the Hadley Centre Global Environmental model. We use a large set of atmosphere-only climate change simulations (amip and amip-p4K) to separate the contributions to the differences in feedback parameter from all the atmospheric model developments between the two latest model configurations. We show that the differences are mostly driven by changes in the shortwave cloud radiative feedback in the midlatitudes, mainly over the Southern Ocean. Two new schemes explain most of the differences: the introduction of a new aerosol scheme and the development of a new mixed-phase cloud scheme. Both schemes reduce the strength of the preexisting shortwave negative cloud feedback in the midlatitudes. The new aerosol scheme dampens a strong aerosol-cloud interaction, and it also suppresses a negative clear-sky shortwave feedback. The mixed-phase scheme increases the amount of cloud liquid water path (LWP) in the present day and reduces the increase in LWP with warming. Both changes contribute to reducing the negative radiative feedback of the increase of LWP in the warmer climate. The mixed-phase scheme also enhances a strong, preexisting, positive cloud fraction feedback. We assess the realism of the changes by comparing present-day simulations against observations and discuss avenues that could help constrain the relevant processes. cloud feedbacks; HadGEM3
Bretherton, Christopher (ORCID:0000000267128856)Bretherton, C., 2019: Expanding the computational frontier of multi-scale atmospheric simulation to advance understanding of low cloud / climate feedbacks: Final Technical Report. The U.S. Department of Energy's Office of Scientific and Technical Information
Bright, Jamie M.; Gueymard, Christian A.Bright, J. M., C. A. Gueymard, 2019: Climate-specific and global validation of MODIS Aqua and Terra aerosol optical depth at 452 AERONET stations. Solar Energy, 183, 594-605. doi: 10.1016/j.solener.2019.03.043. Aerosol optical depth (AOD) is a highly influential variable in solar resource assessment and clear-sky radiation modelling. Hence, the accuracy of solar energy estimates ultimately depends on the accuracy of the measured or assumed AOD. Gridded satellite information is often used for solar modelling due to its geographical coverage, and so a global validation of commonly utilised AOD products is imperative. Here, all Level-3 Moderate Resolution Imaging Spectroradiometer (MODIS) daily observations of AOD (at 470, 550 and 660 nm, noted AOD470, AOD550 and AOD660, respectively) from the Aqua and Terra satellites (of 1° × 1° spatial resolution) from 2000 to 02/2018 are compared and validated against all of NASA’s ground sensing Aerosol Robotic NETwork (AERONET) V3 Level 2 AOD daily averages from sites that reported at least one year of observations during 2000–2018 (452 sites representing at least 653,000 observations per variable). Furthermore, sub-categorisation by Köppen-Geiger climate regions enables a novel climate-specific validation to ascertain any distinct climatic influence. The results demonstrate significant climatological influences that impact the derived AOD product at all three wavelengths. It is found that blending the two Aqua and Terra products results in a higher accuracy of daily estimates of all AOD products. Each AOD product is validated similarly and separately. AOD550, which is most commonly used in solar resource assessment, is found worst in the equatorial climate (absolute root mean square error (RMSE) of 0.194) and best in the temperate climate (RMSE of 0.126). Globally, the combined Aqua + Terra AOD550 experiences an absolute RMSE of 0.106 and a mean absolute error of 0.109. The most common MODIS AOD retrievals are between 0.01 and 0.25, suggesting that the MODIS daily AOD products may introduce a significant source of uncertainty in modelled irradiance estimates, and that other sources of input data should be used instead whenever their applications demand high accuracy. Aerosol optical depth; MODIS; AERONET; Global validation; Irradiance modelling
Bright, Ryan M.; O'Halloran, Thomas L.Bright, R. M., T. L. O'Halloran, 2019: Developing a monthly radiative kernel for surface albedo change from satellite climatologies of Earth's shortwave radiation budget: CACK v1.0. Geoscientific Model Development, 12(9), 3975-3990. doi: https://doi.org/10.5194/gmd-12-3975-2019. Abstract. Due to the potential for land-use–land-cover change (LULCC) to alter surface albedo, there is need within the LULCC science community for simple and transparent tools for predicting radiative forcings (ΔF) from surface albedo changes (Δαs). To that end, the radiative kernel technique – developed by the climate modeling community to diagnose internal feedbacks within general circulation models (GCMs) – has been adopted by the LULCC science community as a tool to perform offline ΔF calculations for Δαs. However, the codes and data behind the GCM kernels are not readily transparent, and the climatologies of the atmospheric state variables used to derive them vary widely both in time period and duration. Observation-based kernels offer an attractive alternative to GCM-based kernels and could be updated annually at relatively low costs. Here, we present a radiative kernel for surface albedo change founded on a novel, simplified parameterization of shortwave radiative transfer driven with inputs from the Clouds and the Earth's Radiant Energy System (CERES) Energy Balance and Filled (EBAF) products. When constructed on a 16-year climatology (2001–2016), we find that the CERES-based albedo change kernel – or CACK – agrees remarkably well with the mean kernel of four GCMs (rRMSE = 14 %). When the novel parameterization underlying CACK is applied to emulate two of the GCM kernels using their own boundary fluxes as input, we find even greater agreement (mean rRMSE = 7.4 %), suggesting that this simple and transparent parameterization represents a credible candidate for a satellite-based alternative to GCM kernels. We document and compute the various sources of uncertainty underlying CACK and include them as part of a more extensive dataset (CACK v1.0) while providing examples showcasing its application.
Caldwell, Peter M.; Mametjanov, Azamat; Tang, Qi; Roekel, Luke P. Van; Golaz, Jean-Christophe; Lin, Wuyin; Bader, David C.; Keen, Noel D.; Feng, Yan; Jacob, Robert; Maltrud, Mathew E.; Roberts, Andrew F.; Taylor, Mark A.; Veneziani, Milena; Wang, Hailong; Wolfe, Jonathan D.; Balaguru, Karthik; Cameron‐Smith, Philip; Dong, Lu; Klein, Stephen A.; Leung, L. Ruby; Li, Hong-Yi; Li, Qing; Liu, Xiaohong; Neale, Richard B.; Pinheiro, Marielle; Qian, Yun; Ullrich, Paul A.; Xie, Shaocheng; Yang, Yang; Zhang, Yuying; Zhang, Kai; Zhou, TianCaldwell, P. M., A. Mametjanov, Q. Tang, L. P. V. Roekel, J. Golaz, W. Lin, D. C. Bader, N. D. Keen, Y. Feng, R. Jacob, M. E. Maltrud, A. F. Roberts, M. A. Taylor, M. Veneziani, H. Wang, J. D. Wolfe, K. Balaguru, P. Cameron‐Smith, L. Dong, S. A. Klein, L. R. Leung, H. Li, Q. Li, X. Liu, R. B. Neale, M. Pinheiro, Y. Qian, P. A. Ullrich, S. Xie, Y. Yang, Y. Zhang, K. Zhang, T. Zhou, 2019: The DOE E3SM Coupled Model Version 1: Description and Results at High Resolution. Journal of Advances in Modeling Earth Systems, 11(12), 4095-4146. doi: 10.1029/2019MS001870. This study provides an overview of the coupled high-resolution Version 1 of the Energy Exascale Earth System Model (E3SMv1) and documents the characteristics of a 50-year-long high-resolution control simulation with time-invariant 1950 forcings following the HighResMIP protocol. In terms of global root-mean-squared error metrics, this high-resolution simulation is generally superior to results from the low-resolution configuration of E3SMv1 (due to resolution, tuning changes, and possibly initialization procedure) and compares favorably to models in the CMIP5 ensemble. Ocean and sea ice simulation is particularly improved, due to better resolution of bathymetry, the ability to capture more variability and extremes in winds and currents, and the ability to resolve mesoscale ocean eddies. The largest improvement in this regard is an ice-free Labrador Sea, which is a major problem at low resolution. Interestingly, several features found to improve with resolution in previous studies are insensitive to resolution or even degrade in E3SMv1. Most notable in this regard are warm bias and associated stratocumulus deficiency in eastern subtropical oceans and lack of improvement in El Niño. Another major finding of this study is that resolution increase had negligible impact on climate sensitivity (measured by net feedback determined through uniform +4K prescribed sea surface temperature increase) and aerosol sensitivity. Cloud response to resolution increase consisted of very minor decrease at all levels. Large-scale patterns of precipitation bias were also relatively unaffected by grid spacing.
Carlson, Barbara; Lacis, Andrew; Colose, Christopher; Marshak, Alexander; Su, Wenying; Lorentz, StevenCarlson, B., A. Lacis, C. Colose, A. Marshak, W. Su, S. Lorentz, 2019: Spectral Signature of the Biosphere: NISTAR Finds It in Our Solar System From the Lagrangian L-1 Point. Geophysical Research Letters, 46(17-18), 10679-10686. doi: 10.1029/2019GL083736. NISTAR, aboard the DSCOVR spacecraft, is one of the National Aeronautics and Space Administration's energy budget instruments designed to measure the seasonal changes in Earth's total outgoing radiation from a unique vantage point at the Lagrangian L-1 point a million miles from Earth. Global radiation energy balance measurements are important constraints for climate models, but are difficult measurements to quantify. CERES data offer the best current observational constraints, but need extensive modeling to get global energy. NISTAR observes the entire dayside hemisphere of the Earth as a single pixel, splitting the shortwave radiation into broadband visible and near-infrared components (analogous to the narrowband spectral ratios used to define vegetation indices). This spectral partitioning at the 0.7-μm vegetation red edge offers unique constraints on climate model spectral treatment of cloud and surface albedos. Moreover, NISTAR's unique viewing geometry amounts to observing the Earth as an exoplanet, which opens a new perspective on exoplanet observations. satellite data; diurnal cycle; global energy budget; remote sensing; climate model validation; exoplanet studies
Carrer, Dominique; Ceamanos, Xavier; Moparthy, Suman; Vincent, Chloé; C. Freitas, Sandra; Trigo, Isabel F.Carrer, D., X. Ceamanos, S. Moparthy, C. Vincent, S. C. Freitas, I. F. Trigo, 2019: Satellite Retrieval of Downwelling Shortwave Surface Flux and Diffuse Fraction under All Sky Conditions in the Framework of the LSA SAF Program (Part 1: Methodology). Remote Sensing, 11(21), 2532. doi: 10.3390/rs11212532. Several studies have shown that changes in incoming solar radiation and variations of the diffuse fraction can significantly modify the vegetation carbon uptake. Hence, monitoring the incoming solar radiation at large scale and with high temporal frequency is crucial for this reason along with many others. The European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) Satellite Application Facility for Land Surface Analysis (LSA SAF) has operationally disseminated in near real time estimates of the downwelling shortwave radiation at the surface since 2005. This product is derived from observations provided by the SEVIRI instrument onboard the Meteosat Second Generation series of geostationary satellites, which covers Europe, Africa, the Middle East, and part of South America. However, near real time generation of the diffuse fraction at the surface level has only recently been initiated. The main difficulty towards achieving this goal was the general lack of accurate information on the aerosol particles in the atmosphere. This limitation is less important nowadays thanks to the improvements in atmospheric numerical models. This study presents an upgrade of the LSA SAF operational retrieval method, which provides the simultaneous estimation of the incoming solar radiation and its diffuse fraction from the satellite every 15 min. The upgrade includes a comprehensive representation of the influence of aerosols based on physical approximations of the radiative transfer within an atmosphere-surface associated medium. This article explains the retrieval method, discusses its limitations and differences with the previous method, and details the characteristics of the output products. A companion article will focus on the evaluation of the products against independent measurements of solar radiation. Finally, the access to the source code is provided through an open access platform in order to share the expertise on the satellite retrieval of this variable with the community. aerosols; solar radiation; diffuse; LSA SAF; MSG SEVIRI; open source code
Cesana, G.; Waliser, D. E.; Henderson, D.; L’Ecuyer, T. S.; Jiang, X.; Li, J-L. F.Cesana, G., D. E. Waliser, D. Henderson, T. S. L’Ecuyer, X. Jiang, J. F. Li, 2019: The Vertical Structure Of Radiative Heating Rates: A Multimodel Evaluation Using A-Train Satellite Observations. J. Climate, 32, 1573–1590. doi: 10.1175/JCLI-D-17-0136.1. We assess the vertical distribution of radiative heating rates (RHR) in climate models using a model experiment and A-train satellite observations, for the first time. As RHR relies on the representation of cloud amount and properties, we first compare the modeled vertical distribution of clouds directly against lidar-radar combined cloud observations (i.e., without simulator). On a near-global scale (50°S/N), two systematic differences arise: an excess of high-level clouds around 200hPa in the tropics, and a general lack of middle- and low-level clouds compared to the observations. Then, using RHR profiles calculated with constraints from A-train and reanalysis data, along with their associated maximum uncertainty estimates, we show that the excess clouds and ice water content in the upper troposphere results in excess infrared heating in the vicinity and below the clouds as well as a lack of solar heating below the clouds. In the lower troposphere, the smaller cloud amount and the underestimation of cloud-top height is coincident with a shift of the infrared cooling to lower levels, substantially reducing the greenhouse effect, that is slightly compensated for by an erroneous excess absorption of solar radiation. Clear sky RHR differences between the observations and the models mitigate cloudy RHR biases in the low levels while they enhance them in the high levels. Finally, our results indicate that a better agreement between observed and modeled cloud profiles could substantially improve the RHR profiles. However, more work is needed to precisely quantify modeled cloud errors and their subsequent effect on RHR.
Cesana, Grégory; Genio, Anthony D. Del; Ackerman, Andrew S.; Kelley, Maxwell; Elsaesser, Gregory; Fridlind, Ann M.; Cheng, Ye; Yao, Mao-SungCesana, G., A. D. D. Genio, A. S. Ackerman, M. Kelley, G. Elsaesser, A. M. Fridlind, Y. Cheng, M. Yao, 2019: Evaluating models' response of tropical low clouds to SST forcings using CALIPSO observations. Atmospheric Chemistry and Physics, 19(5), 2813-2832. doi: 10.5194/acp-19-2813-2019. Abstract. Recent studies have shown that, in response to a surface warming, the marine tropical low-cloud cover (LCC) as observed by passive-sensor satellites substantially decreases, therefore generating a smaller negative value of the top-of-the-atmosphere (TOA) cloud radiative effect (CRE). Here we study the LCC and CRE interannual changes in response to sea surface temperature (SST) forcings in the GISS model E2 climate model, a developmental version of the GISS model E3 climate model, and in 12 other climate models, as a function of their ability to represent the vertical structure of the cloud response to SST change against 10 years of CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) observations. The more realistic models (those that satisfy the observational constraint) capture the observed interannual LCC change quite well (ΔLCC/ΔSST=-3.49±1.01 % K−1 vs. ΔLCC/ΔSSTobs=-3.59±0.28 % K−1) while the others largely underestimate it (ΔLCC/ΔSST=-1.32±1.28 % K−1). Consequently, the more realistic models simulate more positive shortwave (SW) feedback (ΔCRE/ΔSST=2.60±1.13 W m−2 K−1) than the less realistic models (ΔCRE/ΔSST=0.87±2.63
Chang, Kai-Wei; L'Ecuyer, Tristan S.Chang, K., T. S. L'Ecuyer, 2019: Role of Latent Heating Vertical Distribution in the Formation of the Tropical Cold Trap. Journal of Geophysical Research: Atmospheres, 124(14), 7836-7851. doi: 10.1029/2018JD030194. This study examines the role of latent heating (LH) vertical distribution in tropical tropopause layer (TTL) cooling and upper-tropospheric warming associated with equatorial wave responses using LH from the Tropical Rainfall Measurement Mission and temperature from radio occultation observations. We distinguish the effects of convective and stratiform LH in tropical convection on temperature in the upper troposphere and lower stratosphere. Cross-spectral analysis of time series of temperature and LH shows that stratiform LH exhibits higher coherence with temperature throughout most of the upper troposphere and lower stratosphere, especially in the equatorial Rossby wave response. Coherence between total LH and temperature tends to increase with the altitude of heating. Highest coherences occur almost exclusively at time scales of the Madden-Julian Oscillation, suggesting the importance of mesoscale convective activity in TTL cooling and subsequent dehydration processes. These results demonstrate that TTL and upper-tropospheric temperature perturbations depend on the vertical distribution of LH and that stratiform LH release has strong relationship with the formation of the horseshoe-shaped cold trap over the Maritime Continent and West Pacific. Madden-Julian Oscillation; tropical tropopause layer; equatorial waves; latent heating; stratosphere-troposphere coupling
Chen, Gengxin; Han, Weiqing; Li, Yuanlong; Yao, Jinglong; Wang, DongxiaoChen, G., W. Han, Y. Li, J. Yao, D. Wang, 2019: Intraseasonal Variability of the Equatorial Undercurrent in the Indian Ocean. J. Phys. Oceanogr., 49(1), 85-101. doi: 10.1175/JPO-D-18-0151.1. By analyzing in situ observations and conducting a series of ocean general circulation model experiments, this study investigates the physical processes controlling intraseasonal variability (ISV) of the Equatorial Undercurrent (EUC) of the Indian Ocean. ISV of the EUC leads to time-varying water exchanges between the western and eastern equatorial Indian Ocean. For the 2001–14 period, standard deviations of the EUC transport variability are 1.92 and 1.77 Sv (1 Sv ≡ 106 m3 s−1) in the eastern and western basins, respectively. The ISV of the EUC is predominantly caused by the wind forcing effect of atmospheric intraseasonal oscillations (ISOs) but through dramatically different ocean dynamical processes in the eastern and western basins. The stronger ISV in the eastern basin is dominated by the reflected Rossby waves associated with intraseasonal equatorial zonal wind forcing. It takes 20–30 days to set up an intraseasonal EUC anomaly through the Kelvin and Rossby waves associated with the first and second baroclinic modes. In the western basin, the peak intraseasonal EUC anomaly is generated by the zonal pressure gradient force, which is set up by radiating equatorial Kelvin and Rossby waves induced by the equatorial wind stress. Directly forced and reflected Rossby waves from the eastern basin propagate westward, contributing to intraseasonal zonal current near the surface but having weak impact on the peak ISV of the EUC.
Chen, Jinghua; Wu, Xiaoqing; Yin, Yan; Lu, Chunsong; Xiao, Hui; Huang, Qian; Deng, LipingChen, J., X. Wu, Y. Yin, C. Lu, H. Xiao, Q. Huang, L. Deng, 2019: Thermal Effects of the Surface Heat Flux on Cloud Systems over the Tibetan Plateau in Boreal Summer. J. Climate, 32(15), 4699-4714. doi: 10.1175/JCLI-D-18-0604.1. The influence of surface heat fluxes on the generation and development of cloud and precipitation and its relative importance to the large-scale circulation patterns are investigated via cloud-resolving model (CRM) simulations over the Tibetan Plateau (TP) during boreal summer. Over the lowland (e.g., along the middle and lower reaches of the Yangtze River), the dynamical and thermal properties of the atmosphere take more responsibility than the surface heat fluxes for the triggering of heavy rainfall events. However, the surface thermal driving force is a necessary criterion for the triggering of heavy rainfall in the eastern and western TP (ETP and WTP). Strong surface heat fluxes can trigger shallow convections in the TP. Furthermore, moisture that is mainly transported from the southern tropical ocean has a greater influence on the heavy rainfall events of the WTP than those of the ETP. Cloud microphysical processes are substantially less active and heavy rainfall cannot be produced when surface heat fluxes are weakened by half in magnitude over the TP. In addition, surface heating effects are largely responsible for the high occurrence frequency of convection during the afternoon, and the cloud tops of convective systems show a positive relationship with the intensity of surface heat fluxes.
Chen, Yi-Hsuan; Huang, Xianglei; Chen, Xiuhong; Flanner, MarkChen, Y., X. Huang, X. Chen, M. Flanner, 2019: The Effects of Surface Longwave Spectral Emissivity on Atmospheric Circulation and Convection over the Sahara and Sahel. J. Climate, 32(15), 4873-4890. doi: 10.1175/JCLI-D-18-0615.1. This study quantifies the impact of the inclusion of realistic surface spectral emissivity in the Sahara and Sahel on the simulated local climate and beyond. The surface emissivity in these regions can be as low as 0.6–0.7 over the infrared window band while close to unity in other spectral bands, but such spectral dependence has been ignored in current climate models. Realistic surface spectral emissivities over the Sahara and Sahel are incorporated into the Community Earth System Model (CESM) version 1.1.1, while treatments of surface emissivity for the rest of the globe remain unchanged. Both the modified and standard CESM are then forced with prescribed climatological SSTs and fixed present-day forcings for 35-yr simulations. The outputs from the last 30 years are analyzed. Compared to the standard CESM, the modified CESM has warmer surface air temperature, as well as a warmer and wetter planetary boundary layer over the Sahara and Sahel. The modified CESM thus favors more convection in these regions and has more convective rainfall, especially in the Sahara. The moisture convergence induced by such inclusion of surface spectral emissivity also contributes to the differences in simulated precipitation in the Sahel and the region south to it. Compared to observations, inclusion of surface spectral emissivity reduces surface temperature biases in the Sahara and precipitation biases in the Gulf of Guinea but exacerbates the wet biases in the Sahara. Such realistic representation of surface spectral emissivity can help unmask other factors contributing to regional biases in the original CESM.
Chen, Yilun; Chong, Kezhen; Fu, YunfeiChen, Y., K. Chong, Y. Fu, 2019: Impacts of distribution patterns of cloud optical depth on the calculation of radiative forcing. Atmospheric Research, 218, 70-77. doi: 10.1016/j.atmosres.2018.11.007. The gridding process applied to satellite-retrieved cloud properties results in the loss of certain information. In this study, we analyzed the error associated with using gridded cloud optical depth (τ) in calculating radiative forcing from the perspective of the distribution pattern of τ. Utilizing the simulated results from SBDART (Santa Babara DISORT Atmospheric Radiative Transfer), we calculated this error in ideal probability distribution functions (PDFs) of τ while keeping the average τ constant, and then used the τ retrieved from MODIS (Moderate Resolution Imaging Spectroradiometer) pixel-level observations to simulate real case studies. The results from both the ideal experiments and real case studies indicate that there is a large dependence of the error caused by gridding process on the PDF of τ. The greatest relative error occurs in the cases when τ fits a two-point or uniform distribution, reaching 10–20%, while this error is below 5% when τ follows a binomial distribution. From the analysis of MODIS pixel-level data from June 2016, we found that the PDFs of τ within one grid point (1° × 1°) could not be simply described by a normal distribution. Although using the logarithmic mean of τ controls the error effectively, the error can still be up to 4%. Our study suggests that using gridded data (especially the arithmetic mean) to calculate radiative forcing may result in uncertainty to a certain extent, which depends strongly on the distribution pattern of cloud properties within the grid point. The PDF of cloud properties should be comprehensively considered in the gridding process in the future. Cloud optical depth; MODIS; Radiative forcing; Distribution pattern; Grid
Choi, In-Jin; Park, Rae-Seol; Lee, JoonsukChoi, I., R. Park, J. Lee, 2019: Impacts of a newly-developed aerosol climatology on numerical weather prediction using a global atmospheric forecasting model. Atmospheric Environment, 197, 77-91. doi: 10.1016/j.atmosenv.2018.10.019. New four-dimensional aerosol climatology for global weather forecasting model is developed to take aerosol direct effect into account and its impacts on numerical weather prediction are investigated. The proposed aerosol climatology provides the global distribution of monthly-varying species-wise aerosol optical depths with more realistic aerosol vertical profiles. Including aerosol climatology enhances vertical stratification by surface cooling and atmospheric heating through the lower atmosphere by affecting radiation budget. Weakened vertical mixing and reduced surface fluxes related to aerosol loading result in decreased cloud fraction, particularly in the lower atmosphere. Evaluation of medium-range forecasts using the proposed aerosol climatology shows the overall improvement statistically for large-scale variable with reducing their biases, and the alleviation of systematic biases of overestimated light precipitation over the northern hemisphere. Aerosol climatology; Forecast skill; Global NWP; MACC; MOZART
Cronin, Meghan F.; Gentemann, Chelle L.; Edson, James; Ueki, Iwao; Bourassa, Mark; Brown, Shannon; Clayson, Carol Anne; Fairall, Chris W.; Farrar, J. Thomas; Gille, Sarah T.; Gulev, Sergey; Josey, Simon A.; Kato, Seiji; Katsumata, Masaki; Kent, Elizabeth; Krug, Marjolaine; Minnett, Peter J.; Parfitt, Rhys; Pinker, Rachel T.; Stackhouse, Paul W.; Swart, Sebastiaan; Tomita, Hiroyuki; Vandemark, Douglas; Weller, A. Robert; Yoneyama, Kunio; Yu, Lisan; Zhang, DongxiaoCronin, M. F., C. L. Gentemann, J. Edson, I. Ueki, M. Bourassa, S. Brown, C. A. Clayson, C. W. Fairall, J. T. Farrar, S. T. Gille, S. Gulev, S. A. Josey, S. Kato, M. Katsumata, E. Kent, M. Krug, P. J. Minnett, R. Parfitt, R. T. Pinker, P. W. Stackhouse, S. Swart, H. Tomita, D. Vandemark, A. R. Weller, K. Yoneyama, L. Yu, D. Zhang, 2019: Air-Sea Fluxes With a Focus on Heat and Momentum. Frontiers in Marine Science, 6, 430. doi: 10.3389/fmars.2019.00430. Turbulent and radiative exchanges of heat between the ocean and atmosphere (hereafter heat fluxes), ocean surface wind stress, and state variables used to estimate them, are Essential Ocean Variables (EOVs) and Essential Climate Variables (ECVs) influencing weather and climate. This paper describes an observational strategy for producing 3-hourly, 25-km (and an aspirational goal of hourly at 10-km) heat flux and wind stress fields over the global, ice-free ocean with breakthrough 1-day random uncertainty of 15 W m–2 and a bias of less than 5 W m–2. At present this accuracy target is met only for OceanSITES reference station moorings and research vessels (RVs) that follow best practices. To meet these targets globally, in the next decade, satellite-based observations must be optimized for boundary layer measurements of air temperature, humidity, sea surface temperature, and ocean wind stress. In order to tune and validate these satellite measurements, a complementary global in situ flux array, built around an expanded OceanSITES network of time series reference station moorings, is also needed. The array would include 500–1000 measurement platforms, including autonomous surface vehicles, moored and drifting buoys, RVs, the existing OceanSITES network of 22 flux sites, and new OceanSITES expanded in 19 key regions. This array would be globally distributed, with 1–3 measurement platforms in each nominal 10° by 10° box. These improved moisture and temperature profiles and surface data, if assimilated into Numerical Weather Prediction (NWP) models, would lead to better representation of cloud formation processes, improving state variables and surface radiative and turbulent fluxes from these models. The in situ flux array provides globally distributed measurements and metrics for satellite algorithm development, product validation, and for improving satellite-based, NWP and blended flux products. In addition, some of these flux platforms will also measure direct turbulent fluxes, which can be used to improve algorithms for computation of air-sea exchange of heat and momentum in flux products and models. With these improved air-sea fluxes, the ocean’s influence on the atmosphere will be better quantified and lead to improved long-term weather forecasts, seasonal-interannual-decadal climate predictions, and regional climate projections.
Cui, Wenjun; Dong, Xiquan; Xi, Baike; Fan, Jiwen; Tian, Jingjing; Wang, Jingyu; McHardy, Theodore M.Cui, W., X. Dong, B. Xi, J. Fan, J. Tian, J. Wang, T. M. McHardy, 2019: Understanding Ice Cloud-Precipitation Properties of Three Modes of Mesoscale Convective Systems During PECAN. Journal of Geophysical Research: Atmospheres, 124(7), 4121-4140. doi: 10.1029/2019JD030330. This study analyzes the precipitation and ice cloud microphysical features of three common modes of linear mesoscale convective systems during the Plains Elevated Convection at Night (PECAN) campaign. Three cases, one for each linear mesoscale convective system archetype (trailing stratiform, leading stratiform, and parallel stratiform precipitation), are selected. We focus primarily on analyzing ice cloud microphysical properties and precipitation rates (PRs) over the classified convective core (CC) and stratiform rain (SR) regions, as well as the two stratiform regions that developed behind (SR1) and ahead (SR2) of the convective line relative to the storm motion. In the three selected cases, the ice water path (IWP) and PR have strong correlations in the CC, but not in the SR. In terms of the temporal evolution of the mean IWPs and PRs, both CC and SR IWPs, as well as CC PRs, reach peaks quickly but take a longer time to dissipate than the increase period. For all the three cases, both SR1 and SR2 IWPs are 20–70% of their corresponding CC values in both the leading stratiform and parallel stratiform cases and up to 95% for the trailing stratiform case, while all of their PRs are only 7–25% of their CC values. These values suggest not only that the SR PRs may depend on IWPs but also that the microphysical properties of ice particles such as habit and size distribution may play an important role. Utilizing cloud-resolving simulations of these systems may provide better understanding of the physical meanings behind the results in the future.
Danso, Derrick Kwadwo; Anquetin, Sandrine; Diedhiou, Arona; Lavaysse, Christophe; Kobea, Arsène; Touré, N'Datchoh EvelyneDanso, D. K., S. Anquetin, A. Diedhiou, C. Lavaysse, A. Kobea, N. E. Touré, 2019: Spatio-temporal variability of cloud cover types in West Africa with satellite-based and reanalysis data. Quarterly Journal of the Royal Meteorological Society, 145(725), 3715-3731. doi: 10.1002/qj.3651. This study aims to understand and document the occurrence and variability of cloud cover types in West Africa (WA). Investigations are carried out with a 10-year hourly record of two cloud data products: CERES passive satellite observations and ERA5 reanalysis. The seasonal evolutions of high (HCC), middle (MCC), low (LCC) and total (TCC) cloud cover are examined. Both products agree on the seasonal and spatial occurrence of cloud cover, although CERES presents lower values of cloud fraction than ERA5 which is partly attributed to the inability of the satellite sensor to detect optically thin clouds in the atmosphere. Southern WA is found to be cloudier than other parts of the region in all seasons with mean TCC fractions of 70 and 80% for CERES and ERA5 respectively during the monsoon season. In all seasons, the presence of LCC over large areas of the Sahel/Sahara region is noted in the CERES product. This could be due to a possible misinterpretation of Saharan dust as low clouds which may have thus, caused it to overestimate the occurrences and fractions of LCC over this region. Northern WA is associated with higher frequencies of no cloud occurrence events, unlike the south where cloudless skies are rarely observed. Furthermore, in southern WA, overcast conditions of LCC are observed for a significant number of times (up to 20% of the time during the rainy season in CERES and 40% in ERA5). The climatology of cloud cover presented in this study could be useful for the planning of solar energy projects. CERES; West Africa; cloud cover; ERA5; occurrence frequency; variability
Dewitte, Steven; Clerbaux, Nicolas; Cornelis, JanDewitte, S., N. Clerbaux, J. Cornelis, 2019: Decadal Changes of the Reflected Solar Radiation and the Earth Energy Imbalance. Remote Sensing, 11(6), 663. doi: 10.3390/rs11060663. Decadal changes of the Reflected Solar Radiation (RSR) as measured by CERES from 2000 to 2018 are analysed. For both polar regions, changes of the clear-sky RSR correlate well with changes of the Sea Ice Extent. In the Arctic, sea ice is clearly melting, and as a result the earth is becoming darker under clear-sky conditions. However, the correlation between the global all-sky RSR and the polar clear-sky RSR changes is low. Moreover, the RSR and the Outgoing Longwave Radiation (OLR) changes are negatively correlated, so they partly cancel each other. The increase of the OLR is higher then the decrease of the RSR. Also the incoming solar radiation is decreasing. As a result, over the 2000–2018 period the Earth Energy Imbalance (EEI) appears to have a downward trend of −0.16 ± 0.11 W/m2dec. The EEI trend agrees with a trend of the Ocean Heat Content Time Derivative of −0.26 ± 0.06 (1 σ ) W/m2dec. Earth Radiation Budget; Earth Energy Imbalance; Reflected Solar Radiation
Dolinar, Erica K.; Dong, Xiquan; Xi, Baike; Jiang, Jonathan H.; Loeb, Norman G.; Campbell, James R.; Su, HuiDolinar, E. K., X. Dong, B. Xi, J. H. Jiang, N. G. Loeb, J. R. Campbell, H. Su, 2019: A global record of single-layered ice cloud properties and associated radiative heating rate profiles from an A-Train perspective. Climate Dynamics, 1-20. doi: 10.1007/s00382-019-04682-8. A record of global single-layered ice cloud properties has been generated using the CloudSat and CALIPSO Ice Cloud Property Product (2C-ICE) during the period 2007–2010. These ice cloud properties are used as inputs for the NASA Langley modified Fu–Liou radiative transfer model to calculate cloud radiative heating rate profiles and are compared with the NASA CERES observed top-of-atmosphere fluxes. The radiative heating rate profiles calculated in the CloudSat/CALIPSO 2B-FLXHR-LIDAR and CCCM_CC products are also examined to assess consistency and uncertainty of their properties using independent methods. Based on the methods and definitions used herein, single-layered ice clouds have a global occurrence frequency of ~ 18%, with most of them occurring in the tropics above 12 km. Zonal mean cloud radiative heating rate profiles from the three datasets are similar in their patterns of SW warming and LW cooling with small differences in magnitude; nevertheless, all three datasets show that the strongest net heating (> + 1.0 K day−1) occurs in the tropics (latitude < 30°) near the cloud-base while cooling occurs at higher latitudes (> ~ 50°). Differences in radiative heating rates are also assessed based on composites of the 2C-ICE ice water path (IWP) and total column water vapor (TCWV) mixing ratio to facilitate model evaluation and guide ice cloud parameterization improvement. Positive net cloud radiative heating rates are maximized in the upper troposphere for large IWPs and large TCWV, with an uncertainty of 10–25% in the magnitude and vertical structure of this heating. Satellite remote sensing; Radiative heating rate profiles; Single-layered ice cloud properties
Douglas, Alyson; L'Ecuyer, TristanDouglas, A., T. L'Ecuyer, 2019: Quantifying variations in shortwave aerosol–cloud–radiation interactions using local meteorology and cloud state constraints. Atmospheric Chemistry and Physics, 19(9), 6251-6268. doi: 10.5194/acp-19-6251-2019. Abstract. While many studies have tried to quantify the sign and the magnitude of the warm marine cloud response to aerosol loading, both remain uncertain, owing to the multitude of factors that modulate microphysical and thermodynamic processes within the cloud. Constraining aerosol–cloud interactions using the local meteorology and cloud liquid water may offer a way to account for covarying influences, potentially increasing our confidence in observational estimates of warm cloud indirect effects. A total of 4 years of collocated satellite observations from the NASA A-Train constellation, combined with reanalysis from MERRA-2, are used to partition marine warm clouds into regimes based on stability, the free atmospheric relative humidity, and liquid water path. Organizing the sizable number of satellite observations into regimes is shown to minimize the covariance between the environment or liquid water path and the indirect effect. Controlling for local meteorology and cloud state mitigates artificial signals and reveals substantial variance in both the sign and magnitude of the cloud radiative response, including regions where clouds become systematically darker with increased aerosol concentration in dry, unstable environments. A darkening effect is evident even under the most stringent of constraints. These results suggest it is not meaningful to report a single global sensitivity of cloud radiative effect to aerosol. To the contrary, we find the sensitivity can range from −0.46 to 0.11 Wm−2 ln(AI)−1 regionally.
Duan, Wentao; Huang, Shaopeng; Nie, ChenweiDuan, W., S. Huang, C. Nie, 2019: Entrance Pupil Irradiance Estimating Model for a Moon-Based Earth Radiation Observatory Instrument. Remote Sensing, 11(5), 583. doi: 10.3390/rs11050583. A Moon-based Earth radiation observatory (MERO) could provide a longer-term continuous measurement of radiation exiting the Earth system compared to current satellite-based observatories. In order to parameterize the detector for such a newly-proposed MERO, the evaluation of the instrument’s entrance pupil irradiance (EPI) is of great importance. The motivation of this work is to build an EPI estimating model for a simplified single-pixel MERO instrument. The rationale of this model is to sum the contributions of every location in the MERO-viewed region on the Earth’s top of atmosphere (TOA) to the MERO sensor’s EPI, taking into account the anisotropy in the longwave radiance at the Earth TOA. Such anisotropy could be characterized by the TOA anisotropic factors, which can be derived from the Clouds and the Earth’s Radiant Energy System (CERES) angular distribution models (ADMs). As an application, we estimated the shortwave (SW) (0.3–5 µm) and longwave (LW) (5–200 µm) EPIs for a hypothetic MERO instrument located at the Apollo 15 landing site. Results show that the SW EPI varied from 0 to 0.065 W/m2, while the LW EPI ranged between 0.061 and 0.075 W/m2 from 1 to 29 October, 2017. We also utilized this model to predict the SW and LW EPIs for any given location within the MERO-deployable region (region of 80.5°W–80.5°E and 81.5°S–81.5°N on the nearside of the Moon) for the future 18.6 years from October 2017 to June 2036. Results suggest that the SW EPI will vary between 0 and 0.118 W/m2, while the LW EPI will range from 0.056 to 0.081 W/m2. Though the EPI estimating model in this study was built for a simplistic single-pixel instrument, it could eventually be extended and improved in order to estimate the EPI for a multi-pixel MERO sensor. CERES; ADMs; Earth radiation; entrance pupil irradiance; MERO; TOA anisotropy
Duda, David P.; Bedka, Sarah T.; Minnis, Patrick; Spangenberg, Douglas; Khlopenkov, Konstantin; Chee, Thad; Smith Jr., William L.Duda, D. P., S. T. Bedka, P. Minnis, D. Spangenberg, K. Khlopenkov, T. Chee, W. L. Smith Jr., 2019: Northern Hemisphere contrail properties derived from Terra and Aqua MODIS data for 2006 and 2012. Atmospheric Chemistry and Physics, 19(8), 5313-5330. doi: 10.5194/acp-19-5313-2019. Abstract. Linear contrail coverage, optical property, and radiative forcing data over the Northern Hemisphere (NH) are derived from a year (2012) of Terra and Aqua Moderate-resolution Imaging Spectroradiometer (MODIS) imagery and compared with previously published 2006 results (Duda et al., 2013; Bedka et al., 2013; Spangenberg et al., 2013) using a consistent retrieval methodology. Differences in the observed Terra-minus-Aqua screened contrail coverage and patterns in the 2012 annual-mean air traffic estimated with respect to satellite overpass time suggest that most contrails detected by the contrail detection algorithm (CDA) form approximately 2 h before overpass time. The 2012 screened NH contrail coverage (Mask B) shows a relative 3 % increase compared to 2006 data for Terra and increases by almost 7 % for Aqua, although the differences are not expected to be statistically significant. A new post-processing algorithm added to the contrail mask processing estimated that the total contrail cirrus coverage visible in the MODIS imagery may be 3 to 4 times larger than the linear contrail coverage detected by the CDA. This estimate is similar in magnitude to the spreading factor estimated by Minnis et al. (2013). Contrail property retrievals of the 2012 data indicate that both contrail optical depth and contrail effective diameter decreased approximately 10 % between 2006 and 2012. The decreases may be attributed to better background cloudiness characterization, changes in the waypoint screening, or changes in contrail temperature. The total mean contrail radiative forcings (TCRFs) for all 2012 Terra observations were −6.3, 14.3, and 8.0 mW m−2 for the shortwave (SWCRF), longwave (LWCRF), and net forcings, respectively. These values are approximately 20 % less than the corresponding 2006 Terra estimates. The decline in TCRF results from the decrease in normalized CRF, partially offset by the 3 % increase in overall contrail coverage in 2012. The TCRFs for 2012 Aqua are similar, −6.4, 15.5, and 9.0 mW m−2 for shortwave, longwave, and net radiative forcing. The strong correlation between the relative changes in both total SWCRF and LWCRF between 2006 and 2012 and the corresponding relative changes in screened contrail coverage over each air traffic region suggests that regional changes in TCRF from year to year are dominated by year-to-year changes in contrail coverage over each area.
El Masri, Bassil; Rahman, Abdullah F.; Dragoni, DaniloEl Masri, B., A. F. Rahman, D. Dragoni, 2019: Evaluating a new algorithm for satellite-based evapotranspiration for North American ecosystems: Model development and validation. Agricultural and Forest Meteorology, 268, 234-248. doi: 10.1016/j.agrformet.2019.01.025. We introduce a different operational approach to estimate 8-day average daily evapotranspiration (ET) using both routinely available data and the Penman-Monteith (P-M) equation for canopy transpiration and evaporation of intercepted water and Priestley and Taylor for soil evaporation. Our algorithm considered the environmental constraints on canopy resistance and ET by (1) including vapor pressure deficit (VPD), incoming solar radiation, soil moisture, and temperature constraints on stomatal conductance; (2) using leaf area index (LAI) to scale from the leaf to canopy conductance; and (3) calculating canopy resistance as a function of environmental variables such as net radiation and VPD. Remote sensing data from the Moderate Resolution Spectroradiometer (MODIS) and satellite soil moisture data were used to derive the ET model. The algorithm was calibrated and evaluated using measured ET data from 20 AmeriFlux Eddy covariance flux sites for the period of 2003–2012. We found good agreements between our 8-day ET estimates and observations with mean absolute error (MAE) ranges from 0.17 mm/day to 0.94 mm/day compared with MAE ranging from 0.28 mm/day to 1.50 mm/day for MODIS ET. Compared to MODIS ET, our proposed algorithm has higher correlations and higher Willmott’s index of agreement with observations for the majority of the Ameriflux sites. The strong relationship between the model estimated ET and the flux tower observations implies that our model has the potential to be applied to different ecosystems and at different temporal scales. Remote sensing; MODIS; Evapotranspiration; Eddy covariance flux; Penman-Monteith
Feng, Fei; Wang, KaicunFeng, F., K. Wang, 2019: Does the modern-era retrospective analysis for research and applications-2 aerosol reanalysis introduce an improvement in the simulation of surface solar radiation over China?. International Journal of Climatology, 39(3), 1305-1318. doi: 10.1002/joc.5881. Surface incident solar radiation (Rs) is a key parameter of energy and water cycles of the Earth. Reanalyses represent important sources of information on Rs. However, reanalyses Rs may have important bias due to their imperfect parameterizations and input errors of cloud and aerosol. NASA's Global Modelling and Assimilation Office has recently released Version 2 of the Modern-Era Retrospective Analysis for Research and Applications (MERRA2), which incorporates a reanalysis of atmospheric optical depth for the first time. In this study, we evaluate Rs from MERRA2 and its predecessor (MERRA) in China from 1980 to 2014. We first compare three possible reference data sources: (a) observed Rs at 122 stations, (b) satellite retrievals of Rs and (c) Rs values derived from sunshine durations measured at 2,400 weather stations. We find sunshine duration derived Rs is a reliable reference and use it to evaluate MERRA and MERRA2. Our results show that both MERRA and MERRA2 have a high mean bias of 38.63 and 43.86 W/m2 over China due to their underestimation of cloud fraction, which is greater in southern China. MERRA2 displays improved capability in reproducing monthly and annual variability, and national mean trend of Rs. MERRA overestimates the trend of Rs by 3.23 W/m2 in eastern China. MERRA2 reduced this trend bias over the North China Plain likely due to its aerosol assimilation. However, MERRA2 show a negative bias in trend of Rs (?3.44 W/m2) in the south China likely due to its overestimation of atmospheric aerosols loading and aerosol-cloud interaction. The results provide guidance for future development of reanalysis and its scientific applications for ecological and hydrological models. cloud; aerosol; MERRA2; surface incident solar radiation
Feng, Fei; Wang, KaicunFeng, F., K. Wang, 2019: Determining Factors of Monthly to Decadal Variability in Surface Solar Radiation in China: Evidences From Current Reanalyses. Journal of Geophysical Research: Atmospheres, 124(16), 9161-9182. doi: 10.1029/2018JD030214. Clouds and aerosols play essential roles in regulating surface incident solar radiation (Rs). It has been suggested that the increased aerosol loading over China is a key factor for the decadal variability in Rs and can explain the bias in its trend from reanalyses because the reanalyses do not include the interannual variability of aerosols. In this study, we compare the Rs derived from sunshine duration at 2,400 weather stations in China and that from five reanalyses from 1980 to 2014. The determining factors for the biases in the mean values and trends of Rs from the reanalyses are examined, with the help of Rs and the cloud fraction (CF), from satellite and 2,400 weather stations. Our results show that all reanalyses overestimate the multiyear Rs by 24.10–40.00 W/m2 due to their underestimations of CF, which is more obvious in southern China. The biases in the simulated CF in the reanalyses can explain the biases in Rs by 55–41%, and the bias in clear-sky surface solar radiation (Rc), which is primarily due to biases in aerosol loading, can explain 32–9% of the bias in Rs. The errors in the trend of the simulated CF can explain the errors in the Rs trends in the reanalyses by 73–12%, and the trend errors in the Rc can explain 43–30% of the trend error in Rs. Our study suggests that more work is needed to improve the simulation of aerosols, clouds, and aerosol-cloud-radiation interactions in the reanalyses. radiation; surface; solar
Feng, Huihui; Zou, BinFeng, H., B. Zou, 2019: Satellite-based estimation of the aerosol forcing contribution to the global land surface temperature in the recent decade. Remote Sensing of Environment, 232, 111299. doi: 10.1016/j.rse.2019.111299. The aerosol forcing is an essential factor of global climate change, which can be estimated by various models. However, the model results ranging from −2.8 to 2.2 K remain controversial because of unavoidable uncertainty, leaving a great gap for global change prediction. This study aims to evaluate the forcing on the land surface temperature (Ts) using satellite-based observations. Based on the Blackbody radiation and surface radiation budget, first, a semi-physical framework is developed to estimate the Ts. Subsequently, the aerosol forcing is calculated by measuring the Ts difference between the changing aerosol scenario and baseline scenario with a fixed aerosol amount. Results show that the framework simulates Ts with acceptable accuracy (R = 0.62 and RMSE = 1.48 K), which supports the estimation of aerosol forcing. Generally, the change in the aerosol contributes 0.005 ± 0.237 K to the global Ts, which presents significant temporal and spatial variabilities. Temporally, the forcing shows a decreasing trend of −0.0006 K/year (R2 = 0.29, p = 0.031). Spatially, the forcing tends to warm the surface in regions with arid climate, low-cloud fraction, and moderate vapor or in sparsely vegetated and cool regions because of the potential interactions with climatic and environmental factors. The result of this study helps to reduce the uncertainty and validate the model results, which further supports the research on global climatic and environmental change. Satellite; Aerosol forcing; Land surface temperature; Radiation budget; Global change
Feng, Jiaojiao; Wang, Weizhen; Li, JingFeng, J., W. Wang, J. Li, 2019: An LM-BP Neural Network Approach to Estimate Monthly-Mean Daily Global Solar Radiation Using MODIS Atmospheric Products. Energies, 11(12), 3510. doi: 10.3390/en11123510. Solar energy is one of the most widely used renewable energy sources in the world and its development and utilization are being integrated into people’s lives. Therefore, accurate solar radiation data are of great significance for site-selection of photovoltaic (PV) power generation, design of solar furnaces and energy-efficient buildings. Practically, it is challenging to get accurate solar radiation data because of scarce and uneven distribution of ground-based observation sites throughout the country. Many artificial neural network (ANN) estimation models are therefore developed to estimate solar radiation, but the existing ANN models are mostly based on conventional meteorological data; clouds, aerosols, and water vapor are rarely considered because of a lack of instrumental observations at the conventional meteorological stations. Based on clouds, aerosols, and precipitable water-vapor data from Moderate Resolution Imaging Spectroradiometer (MODIS), along with conventional meteorological data, back-propagation (BP) neural network method was developed in this work with Levenberg-Marquardt (LM) algorithm (referred to as LM-BP) to simulate monthly-mean daily global solar radiation (M-GSR). Comparisons were carried out among three M-GSR estimates, including the one presented in this study, the multiple linear regression (MLR) model, and remotely-sensed radiation products by Cloud and the Earth’s radiation energy system (CERES). The validation results indicate that the accuracy of the ANN model is better than that of the MLR model and CERES radiation products, with a root mean squared error (RMSE) of 1.34 MJ·m−2 (ANN), 2.46 MJ·m−2 (MLR), 2.11 MJ·m−2 (CERES), respectively. Finally, according to the established ANN-based method, the M-GSR of 36 conventional meteorological stations for 12 months was estimated in 2012 in the study area. Solar radiation data based on the LM-BP method of this study can provide some reference for the utilization of solar and heat energy. clouds; aerosols; solar radiation; precipitable water vapor; LM-BP neural network
Fueglistaler, S.Fueglistaler, S., 2019: Observational Evidence for Two Modes of Coupling Between Sea Surface Temperatures, Tropospheric Temperature Profile, and Shortwave Cloud Radiative Effect in the Tropics. Geophysical Research Letters, 46(16), 9890-9898. doi: 10.1029/2019GL083990. Tropical average shortwave cloud radiative effect (SWCRE) anomalies observed by CERES/EBAF v4 are explained by observed average sea surface temperature ( ) and the difference between the warmest 30% where deep convection occurs and ). Observed tropospheric temperatures show variations in boundary layer capping strength over time consistent with the evolution of SST#. The CERES/EBAF v4 data confirm that associated cloud fraction changes over the colder waters dominate SWCRE. This observational evidence for the “pattern effect” noted in General Circulation Model simulations suggests that SST# captures much of this effect. The observed sensitivities (dSWCRE/d W·m−2·K−1, dSWCRE/dSST#≈−4.8W·m−2·K−1) largely reflect El Niño–Southern Oscillation. As El Niño develops, increases and SST# decreases (both increasing SWCRE). Only after the El Niño peak, SST# increases and SWCRE decreases. SST# is also relevant for the tropical temperature trend profile controversy and the discrepancy between observed and modeled equatorial Pacific SST trends. Causality and implications for future climates are discussed. ENSO; tropical convection; climate sensitivity; cloud albedo; sea surface temperatures
Furtado, Kalli; Field, Paul; Luo, Yali; Zhou, Tianjun; Hill, AdrianFurtado, K., P. Field, Y. Luo, T. Zhou, A. Hill, 2019: The effects of cloud-aerosol-interaction complexity on simulations of presummer rainfall over southern China. Atmospheric Chemistry and Physics Discussions, 1-19. doi: https://doi.org/10.5194/acp-2019-596. Abstract. Convection-permitting simulations are used to understand the effects of cloud-aerosol interactions on a case of heavy rainfall over south China. The simulations are evaluated using radar observations from the South China Monsoon Rainfall Experiment and remotely sensed estimates of precipitation, clouds and radiation. We focus on the effects of complexity in cloud-aerosol interactions, especially processing and transport of dissolved material inside clouds. In particular, simulations with aerosol concentrations held constant are compared with a fully coupled cloud-aerosol-interacting system to isolate the effects of processing on a line of organised-deep convection. It is shown that in-cloud processing of aerosols can change the vertical structure of squall lines thereby inducing changes in the statistics of surface rainfall. These effects are shown to be consistent with a modulation by aerosol of the timescale of the converting cloud-droplets to rain.
Gasparini, Blaž; Blossey, Peter N.; Hartmann, Dennis L.; Lin, Guangxing; Fan, JiwenGasparini, B., P. N. Blossey, D. L. Hartmann, G. Lin, J. Fan, 2019: What Drives the Life Cycle of Tropical Anvil Clouds?. Journal of Advances in Modeling Earth Systems, 11(8), 2586-2605. doi: 10.1029/2019MS001736. The net radiative effects of tropical clouds are determined by the evolution of thick, freshly detrained anvil clouds into thin anvil clouds. Thick anvil clouds reduce Earth's energy balance and cool the climate, while thin anvil clouds warm the climate. To determine role of these clouds in climate change we need to understand how interactions of their microphysical and macrophysical properties control their radiative properties. We explore anvil cloud evolution using a cloud-resolving model in three-simulation setups of increasing complexity to disentangle the impacts of the various components of diabatic heating and their interaction with cloud-scale motions. The first phase of evolution and rapid cloud spreading is dominated by latent heating within convective updrafts. After the convective detrainment stops, most of the spreading and thinning of the anvil cloud is driven by cloud radiative processes and latent heating. The combination of radiative cooling at cloud top, latent cooling due to sublimation at cloud base, latent heating due to deposition and radiative heating in between leads to a sandwich-like, cooling-heating-cooling structure. The heating sandwich promotes the development of two within-anvil convective layers and a double cell circulation, dominated by strong outflow at 12-km altitude with inflow above and below. Our study reveals how small-scale processes including convective, microphysical processes, latent and radiative heating interact within the anvil cloud system. The absence or a different representation of only one component results in a significantly different cloud evolution with large impacts on cloud radiative effects. radiative effects; circulation; anvil cloud; convective life cycle; high clouds; tropical cirrus
Ge, Jinming; Wang, Zhenquan; Liu, Yuanyong; Su, Jing; Wang, Chen; Dong, ZixiangGe, J., Z. Wang, Y. Liu, J. Su, C. Wang, Z. Dong, 2019: Linkages between mid-latitude cirrus cloud properties and large-scale meteorology at the SACOL site. Climate Dynamics, 53(7), 5035-5046. doi: 10.1007/s00382-019-04843-9. The linkages between midlatitude cirrus properties and large-scale meteorology are investigated in this study by using 2-year observations from a ground Ka-band Zenith Radar (KAZR) and the Earth’s Radiant Energy System (CERES) SYN1deg satellite product over the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). Four atmospheric parameters (i.e. upward motion, relative humidity, stability and temperature at upper atmosphere) are used to examine the cirrus dependence on these factors. It is found that cirrus properties significantly depend on the changes of the four parameters and are most linearly correlated with upper atmosphere temperature. Cirrus infrared (IR) emissivity and ice water path (IWP) are sensitive to the strength of upward motions (ω), while cirrus thickness and albedo are more sensitive to relative humidity. An Empirical Orthogonal Function (EOF) is used to combine the four meteorological factors into a single variable and isolate the irrelevant synoptic noise to cirrus development and dissipation from the structure strongly associated with cirrus variations. The first leading principle component (PC1) is much better correlated with cirrus properties than any one of the four parameters. We further apply the EOF analysis to all 37 vertical levels of the four parameters. It is found that a negative area of the main structure between 6 and 10 km above ground level (AGL) is well collocated with the cirrus distribution from the KAZR observations on a diurnal time scale, indicating a robust relationship between cirrus and the combined meteorological fields.
Geiss, Andrew; Marchand, RogerGeiss, A., R. Marchand, 2019: Cloud responses to climate variability over the extratropical oceans as observed by MISR and MODIS. Atmospheric Chemistry and Physics Discussions, 1-30. doi: 10.5194/acp-2018-520. Abstract. Linear temporal trends in cloud fraction over the extratropical oceans, observed by NASA's Multiangle Imaging Spectro-Radiometer (MISR) during the period 2000–2013, are examined in the context of coincident ECMWF reanalysis data using a maximum covariance analysis. Changes in specific cloud types defined with respect to cloud top height and cloud optical depth are related to trends in reanalysis variables. A pattern of reduced high altitude optically thick cloud and increased low altitude cloud of moderate optical depth is found to be associated with increased temperatures, geopotential heights, and anticyclonicity over the extratropical oceans. These and other trends in cloud occurrence are shown to be correlated with changes in the El Niño Southern Oscillation, the Pacific Decadal Oscillation, the North Pacific Index, and the Southern Annular Mode.
Gettelman, A.; Mills, M. J.; Kinnison, D. E.; Garcia, R. R.; Smith, A. K.; Marsh, D. R.; Tilmes, S.; Vitt, F.; Bardeen, C. G.; McInerny, J.; Liu, H.-L.; Solomon, S. C.; Polvani, L. M.; Emmons, L. K.; Lamarque, J.-F.; Richter, J. H.; Glanville, A. S.; Bacmeister, J. T.; Phillips, A. S.; Neale, R. B.; Simpson, I. R.; DuVivier, A. K.; Hodzic, A.; Randel, W. J.Gettelman, A., M. J. Mills, D. E. Kinnison, R. R. Garcia, A. K. Smith, D. R. Marsh, S. Tilmes, F. Vitt, C. G. Bardeen, J. McInerny, H. Liu, S. C. Solomon, L. M. Polvani, L. K. Emmons, J. Lamarque, J. H. Richter, A. S. Glanville, J. T. Bacmeister, A. S. Phillips, R. B. Neale, I. R. Simpson, A. K. DuVivier, A. Hodzic, W. J. Randel, 2019: The Whole Atmosphere Community Climate Model Version 6 (WACCM6). Journal of Geophysical Research: Atmospheres, 124(23), 12380-12403. doi: 10.1029/2019JD030943. The Whole Atmosphere Community Climate Model version 6 (WACCM6) is a major update of the whole atmosphere modeling capability in the Community Earth System Model (CESM), featuring enhanced physical, chemical and aerosol parameterizations. This work describes WACCM6 and some of the important features of the model. WACCM6 can reproduce many modes of variability and trends in the middle atmosphere, including the quasi-biennial oscillation, stratospheric sudden warmings, and the evolution of Southern Hemisphere springtime ozone depletion over the twentieth century. WACCM6 can also reproduce the climate and temperature trends of the 20th century throughout the atmospheric column. The representation of the climate has improved in WACCM6, relative to WACCM4. In addition, there are improvements in high-latitude climate variability at the surface and sea ice extent in WACCM6 over the lower top version of the model (CAM6) that comes from the extended vertical domain and expanded aerosol chemistry in WACCM6, highlighting the importance of the stratosphere and tropospheric chemistry for high-latitude climate variability.
Golaz, Jean-Christophe; Caldwell, Peter M.; Roekel, Luke P. Van; Petersen, Mark R.; Tang, Qi; Wolfe, Jonathan D.; Abeshu, Guta; Anantharaj, Valentine; Asay‐Davis, Xylar S.; Bader, David C.; Baldwin, Sterling A.; Bisht, Gautam; Bogenschutz, Peter A.; Branstetter, Marcia; Brunke, Michael A.; Brus, Steven R.; Burrows, Susannah M.; Cameron‐Smith, Philip J.; Donahue, Aaron S.; Deakin, Michael; Easter, Richard C.; Evans, Katherine J.; Feng, Yan; Flanner, Mark; Foucar, James G.; Fyke, Jeremy G.; Griffin, Brian M.; Hannay, Cécile; Harrop, Bryce E.; Hoffman, Mattthew J.; Hunke, Elizabeth C.; Jacob, Robert L.; Jacobsen, Douglas W.; Jeffery, Nicole; Jones, Philip W.; Keen, Noel D.; Klein, Stephen A.; Larson, Vincent E.; Leung, L. Ruby; Li, Hong-Yi; Lin, Wuyin; Lipscomb, William H.; Ma, Po-Lun; Mahajan, Salil; Maltrud, Mathew E.; Mametjanov, Azamat; McClean, Julie L.; McCoy, Renata B.; Neale, Richard B.; Price, Stephen F.; Qian, Yun; Rasch, Philip J.; Eyre, J. E. Jack Reeves; Riley, William J.; Ringler, Todd D.; Roberts, Andrew F.; Roesler, Erika L.; Salinger, Andrew G.; Shaheen, Zeshawn; Shi, Xiaoying; Singh, Balwinder; Tang, Jinyun; Taylor, Mark A.; Thornton, Peter E.; Turner, Adrian K.; Veneziani, Milena; Wan, Hui; Wang, Hailong; Wang, Shanlin; Williams, Dean N.; Wolfram, Phillip J.; Worley, Patrick H.; Xie, Shaocheng; Yang, Yang; Yoon, Jin-Ho; Zelinka, Mark D.; Zender, Charles S.; Zeng, Xubin; Zhang, Chengzhu; Zhang, Kai; Zhang, Yuying; Zheng, Xue; Zhou, Tian; Zhu, QingGolaz, J., P. M. Caldwell, L. P. V. Roekel, M. R. Petersen, Q. Tang, J. D. Wolfe, G. Abeshu, V. Anantharaj, X. S. Asay‐Davis, D. C. Bader, S. A. Baldwin, G. Bisht, P. A. Bogenschutz, M. Branstetter, M. A. Brunke, S. R. Brus, S. M. Burrows, P. J. Cameron‐Smith, A. S. Donahue, M. Deakin, R. C. Easter, K. J. Evans, Y. Feng, M. Flanner, J. G. Foucar, J. G. Fyke, B. M. Griffin, C. Hannay, B. E. Harrop, M. J. Hoffman, E. C. Hunke, R. L. Jacob, D. W. Jacobsen, N. Jeffery, P. W. Jones, N. D. Keen, S. A. Klein, V. E. Larson, L. R. Leung, H. Li, W. Lin, W. H. Lipscomb, P. Ma, S. Mahajan, M. E. Maltrud, A. Mametjanov, J. L. McClean, R. B. McCoy, R. B. Neale, S. F. Price, Y. Qian, P. J. Rasch, J. E. J. R. Eyre, W. J. Riley, T. D. Ringler, A. F. Roberts, E. L. Roesler, A. G. Salinger, Z. Shaheen, X. Shi, B. Singh, J. Tang, M. A. Taylor, P. E. Thornton, A. K. Turner, M. Veneziani, H. Wan, H. Wang, S. Wang, D. N. Williams, P. J. Wolfram, P. H. Worley, S. Xie, Y. Yang, J. Yoon, M. D. Zelinka, C. S. Zender, X. Zeng, C. Zhang, K. Zhang, Y. Zhang, X. Zheng, T. Zhou, Q. Zhu, 2019: The DOE E3SM Coupled Model Version 1: Overview and Evaluation at Standard Resolution. Journal of Advances in Modeling Earth Systems, 11(7), 2089-2129. doi: 10.1029/2018MS001603. This work documents the first version of the U.S. Department of Energy (DOE) new Energy Exascale Earth System Model (E3SMv1). We focus on the standard resolution of the fully coupled physical model designed to address DOE mission-relevant water cycle questions. Its components include atmosphere and land (110-km grid spacing), ocean and sea ice (60 km in the midlatitudes and 30 km at the equator and poles), and river transport (55 km) models. This base configuration will also serve as a foundation for additional configurations exploring higher horizontal resolution as well as augmented capabilities in the form of biogeochemistry and cryosphere configurations. The performance of E3SMv1 is evaluated by means of a standard set of Coupled Model Intercomparison Project Phase 6 (CMIP6) Diagnosis, Evaluation, and Characterization of Klima simulations consisting of a long preindustrial control, historical simulations (ensembles of fully coupled and prescribed SSTs) as well as idealized CO2 forcing simulations. The model performs well overall with biases typical of other CMIP-class models, although the simulated Atlantic Meridional Overturning Circulation is weaker than many CMIP-class models. While the E3SMv1 historical ensemble captures the bulk of the observed warming between preindustrial (1850) and present day, the trajectory of the warming diverges from observations in the second half of the twentieth century with a period of delayed warming followed by an excessive warming trend. Using a two-layer energy balance model, we attribute this divergence to the model's strong aerosol-related effective radiative forcing (ERFari+aci = −1.65 W/m2) and high equilibrium climate sensitivity (ECS = 5.3 K).
Granados-Muñoz, Maria José; Sicard, Michaël; Papagiannopoulos, Nikolaos; Barragán, Rubén; Bravo-Aranda, Juan Antonio; Nicolae, DoinaGranados-Muñoz, M. J., M. Sicard, N. Papagiannopoulos, R. Barragán, J. A. Bravo-Aranda, D. Nicolae, 2019: 2-D mineral dust radiative forcing calculations from CALIPSO observations over Europe. Atmospheric Chemistry and Physics Discussions, 1-40. doi: 10.5194/acp-2019-440. Abstract. A demonstration study to examine the feasibility to retrieve dust radiative effects based on combined satellite data from MODIS (Moderate Resolution Imaging Spectroradiometer), CERES (Clouds and the Earth’s Radiant Energy System) and CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) li-dar vertical profiles along their orbit is presented. The radiative transfer model GAME (Global Atmos-pheric Model) is used to estimate the shortwave and longwave dust radiative effects below the CALIP-SO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite) orbit assuming an aerosol parameterization based on CALIOP vertical distribution at a horizontal resolution of 5 km and additional AERONET (Aerosol Robotic Network) data. Two study cases are analysed; a strong long-range transport mineral dust event (AOD = 0.52) originated in the Sahara Desert and reaching the United Kingdom and a weaker event (AOD = 0.16) affecting Eastern Europe. The obtained radiative fluxes are first validated in terms of radiative forcing efficiency at a single point with space-time co-located lidar ground-based measurements from EARLINET (European Aerosol Research Lidar Network) stations below the orbit. The methodology is then applied to the full orbit. The obtained results indicate that the radiative effects show a strong dependence on the aerosol load, highlighting the need of accurate AOD measurements for forcing studies, and on the surface albedo. The calculated dust radiative effects and heating rates below the orbits are in good agreement with previous studies of mineral dust, with the forcing efficiency obtained at the surface ranging between −80.3 and −63.0 W m−2 for the weaker event and −119.1 and −79.3 W m−2 for the strong one. Results thus demonstrate the validity of the presented method to retrieve 2-D accurate radiative properties with large spatial and temporal coverage.
Granados-Muñoz, María José; Sicard, Michael; Román, Roberto; Benavent-Oltra, Jose Antonio; Barragán, Rubén; Brogniez, Gerard; Denjean, Cyrielle; Mallet, Marc; Formenti, Paola; Torres, Benjamín; Alados-Arboledas, LucasGranados-Muñoz, M. J., M. Sicard, R. Román, J. A. Benavent-Oltra, R. Barragán, G. Brogniez, C. Denjean, M. Mallet, P. Formenti, B. Torres, L. Alados-Arboledas, 2019: Impact of mineral dust on shortwave and longwave radiation: evaluation of different vertically resolved parameterizations in 1-D radiative transfer computations. Atmospheric Chemistry and Physics, 19(1), 523-542. doi: 10.5194/acp-19-523-2019. Abstract. Aerosol radiative properties are investigated in southeastern Spain during a dust event on 16–17 June 2013 in the framework of the ChArMEx/ADRIMED (Chemistry-Aerosol Mediterranean Experiment/Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region) campaign. Particle optical and microphysical properties from ground-based sun/sky photometer and lidar measurements, as well as in situ measurements on board the SAFIRE ATR 42 French research aircraft, are used to create a set of different levels of input parameterizations, which feed the 1-D radiative transfer model (RTM) GAME (Global Atmospheric ModEl). We consider three datasets: (1) a first parameterization based on the retrievals by an advanced aerosol inversion code (GRASP; Generalized Retrieval of Aerosol and Surface Properties) applied to combined photometer and lidar data, (2) a parameterization based on the photometer columnar optical properties and vertically resolved lidar retrievals with the two-component Klett–Fernald algorithm, and (3) a parameterization based on vertically resolved optical and microphysical aerosol properties measured in situ by the aircraft instrumentation. Once retrieved, the outputs of the RTM in terms of both shortwave and longwave radiative fluxes are compared against ground and in situ airborne measurements. In addition, the outputs of the model in terms of the aerosol direct radiative effect are discussed with respect to the different input parameterizations. Results show that calculated atmospheric radiative fluxes differ no more than 7% from the measured ones. The three parameterization datasets produce a cooling effect due to mineral dust both at the surface and the top of the atmosphere. Aerosol radiative effects with differences of up to 10Wm−2 in the shortwave spectral range (mostly due to differences in the aerosol optical depth) and 2Wm−2 for the longwave spectral range (mainly due to differences in the aerosol optical depth but also to the coarse mode radius used to calculate the radiative properties) are obtained when comparing the three parameterizations. The study reveals the complexity of parameterizing 1-D RTMs as sizing and characterizing the optical properties of mineral dust is challenging. The use of advanced remote sensing data and processing, in combination with closure studies on the optical and microphysical properties from in situ aircraft measurements when available, is recommended.
Gristey, Jake J.; Chiu, J. Christine; Gurney, Robert J.; Shine, Keith P.; Havemann, Stephan; Thelen, Jean-Claude; Hill, Peter G.Gristey, J. J., J. C. Chiu, R. J. Gurney, K. P. Shine, S. Havemann, J. Thelen, P. G. Hill, 2019: Shortwave Spectral Radiative Signatures and Their Physical Controls. J. Climate, 32(15), 4805-4828. doi: 10.1175/JCLI-D-18-0815.1. The spectrum of reflected solar radiation emerging at the top of the atmosphere is rich with Earth system information. To identify spectral signatures in the reflected solar radiation and directly relate them to the underlying physical properties controlling their structure, over 90 000 solar reflectance spectra are computed over West Africa in 2010 using a fast radiation code employing the spectral characteristics of the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). Cluster analysis applied to the computed spectra reveals spectral signatures related to distinct surface properties, and cloud regimes distinguished by their spectral shortwave cloud radiative effect (SWCRE). The cloud regimes exhibit a diverse variety of mean broadband SWCREs, and offer an alternative approach to define cloud type for SWCRE applications that does not require any prior assumptions. The direct link between spectral signatures and distinct physical properties extracted from clustering remains robust between spatial scales of 1, 20, and 240 km, and presents an excellent opportunity to understand the underlying properties controlling real spectral reflectance observations. Observed SCIAMACHY spectra are assigned to the calculated spectral clusters, showing that cloud regimes are most frequent during the active West African monsoon season of June–October in 2010, and all cloud regimes have a higher frequency of occurrence during the active monsoon season of 2003 compared with the inactive monsoon season of 2004. Overall, the distinct underlying physical properties controlling spectral signatures show great promise for monitoring evolution of the Earth system directly from solar spectral reflectance observations.
Guo, Zhun; Wang, Minghuai; Larson, Vincent E.; Zhou, TianjunGuo, Z., M. Wang, V. E. Larson, T. Zhou, 2019: A Cloud Top Radiative Cooling Model Coupled With CLUBB in the Community Atmosphere Model: Description and Simulation of Low Clouds. Journal of Advances in Modeling Earth Systems, 11(4), 979-997. doi: 10.1029/2018MS001505. In this study, a higher-order closure scheme known as Cloud Layers Unified By Binormals (CLUBB) is coupled with a cloud top radiative cooling scheme (RAD). The cloud top radiative cooling scheme treats the buoyancy flux generated near the top of the boundary layer which helps the CLUBB scheme to better represent the radiation-turbulence interaction on the condition of coarse vertical resolution. CLUBB with RAD is found to improve subtropical low-cloud simulations, and the improvement is particularly evident for nocturnal stratocumulus. The improvements are caused by the stronger and more symmetric vertical turbulent mixing in the boundary layer, as CLUBB with RAD increases the variance of vertical velocity and vertical turbulent transports and reduces the skewness of vertical velocity by enhancing the radiative cooling effects and buoyancy fluxes at the cloud layer. The pumping effect related to the stronger vertical turbulent transports further cools and dries the lower boundary layer, which increases the local surface heating fluxes and further improves the low-cloud simulations. buoyancy flux; cloud top radiative cooling; higher-order closure scheme; low cloud
Hahn, Gregory G.; Adoram-Kershner, Lauren Andrea; Cantin, Heather P.; Shafer, Michael W.Hahn, G. G., L. A. Adoram-Kershner, H. P. Cantin, M. W. Shafer, 2019: Assessing Solar Power for Globally Migrating Marine and Submarine Systems. IEEE Journal of Oceanic Engineering, 44(3), 693-706. doi: 10.1109/JOE.2018.2835178. Remote marine sensing systems, such as autonomous underwater vehicles or telemetry tags, can be limited in data collection and deployment duration due to the finite energy of the onboard battery. With these technologies migrating vast distances over long-term deployments, maintaining high data resolution is difficult and often yields nonideal data sets. Furthermore, electronics systems used in telemetry tags are often potted in epoxy, which makes replacing or recharging the battery impractical. The implementation of solar energy harvesting on these technologies could increase the fidelity of collected data and/or tag longevity. This paper presents an assessment model that estimates the energy output of a stationary or migrating solar cell above or below the ocean's surface. The theory and assumptions behind the model are explained, including a review of established concepts for the purpose of consolidation and variable consistency. The model is then compared to benchmark data for verification. Finally, a preliminary analysis is conducted on the previously collected time, depth, and global location data from a northern elephant seal deployment to demonstrate the resulting model outputs and how they can be used for analysis in future works. solar energy; oceanographic equipment; oceanographic techniques; Sea surface; Ocean temperature; solar power; assessing solar power; assessment model; autonomous underwater vehicles; benchmark data; collected time; data collection; deployment duration; electronics systems; energy harvesting; energy output; global location data; globally migrating marine; high data resolution; long-term deployments; Marine technology; migrating solar cell; model outputs; nonideal data sets; northern elephant seal deployment; onboard battery; Photovoltaic cells; predictive models; radiotelemetry; remote marine sensing systems; remotely operated vehicles; Solar energy; solar energy harvesting; stationary cell; submarine systems; Sun; tag longevity; telemetry; Telemetry; telemetry tags; underwater equipment; underwater vehicles; Underwater vehicles; wireless sensor networks
Hakuba, Maria Z.; Stephens, Graeme L.; Christophe, Bruno; Nash, Alfred E.; Foulon, Bernard; Bettadpur, Srinivas V.; Tapley, Byron D.; Webb, Frank H.Hakuba, M. Z., G. L. Stephens, B. Christophe, A. E. Nash, B. Foulon, S. V. Bettadpur, B. D. Tapley, F. H. Webb, 2019: Earth’s Energy Imbalance Measured From Space. IEEE Transactions on Geoscience and Remote Sensing, 57(1), 32-45. doi: 10.1109/TGRS.2018.2851976. The direct measurement of earth's energy imbalance (EEI) is one of the greatest challenges in climate research. The global mean EEI represents the integrated value of global warming and is tightly linked to changes in hydrological cycle and the habitability of our planet. Current space-born radiometers measure the individual radiative components of the energy balance with unprecedented stability, but with calibration errors too large to determine the absolute magnitude of global mean EEI as the components' residual. Best estimates of the long-term EEI are currently derived from temporal changes in ocean heat content at 0.7 Wm-2. To monitor EEI directly from space, we propose an independent approach based on accelerometry that measures nongravitational forces, such as radiation pressure, acting on earth-orbiting spacecrafts. The concept of deriving EEI from radiation pressure has been considered in the past, and we provide analysis that shows today's capabilities are sufficiently accurate to answer the question: At what rate is our planet warming? To measure global mean EEI to within at least ±0.3 Wm-2 requires spacecraft(s) of near-spherical shape and well-characterized surface properties to reduce confounding effects. The proposed concept may provide the basis for a data record of global and zonal mean EEI on annual and potentially monthly timescales. It is not meant to replace the existing concepts designed to measure energy balance components or ocean heat storage, but to complement these by providing an independent estimate of EEI for comparison and to anchor data products and climate models that lack energy balance closure. Earth; Extraterrestrial measurements; atmospheric radiation; Space vehicles; radiometry; Oceans; hydrological cycle; hydrology; Sea measurements; global warming; atmospheric temperature; Accelerometer; climate research; climatology; current space-born radiometers; earth-orbiting spacecrafts; earth’s energy imbalance; energy balance closure; energy balance components; global EEI; global mean EEI; Heating systems; individual radiative components; long-term EEI; low earth orbit satellites; Pressure measurement; radiation pressure; remote sensing; space vehicles; zonal mean EEI
Ham, Seung-Hee; Kato, Seiji; Rose, Fred G.Ham, S., S. Kato, F. G. Rose, 2019: Impacts of Partly Cloudy Pixels on Shortwave Broadband Irradiance Computations. J. Atmos. Oceanic Technol., 36(3), 369-386. doi: 10.1175/JTECH-D-18-0153.1. Because of the limitation of the spatial resolution of satellite sensors, satellite pixels identified as cloudy are often partly cloudy. For the first time, this study demonstrates the bias in shortwave (SW) broadband irradiances for partly cloudy pixels when the cloud optical depths are retrieved with an overcast and homogeneous assumption, and subsequently, the retrieved values are used for the irradiance computations. The sign of the SW irradiance bias is mainly a function of viewing geometry of the cloud retrieval. The bias in top-of-atmosphere (TOA) upward SW irradiances is positive for small viewing zenith angles (VZAs) ~60°. For a given solar zenith angle and viewing geometry, the magnitude of the bias increases with the cloud optical depth and reaches a maximum at the cloud fraction between 0.2 and 0.8. The sign of the SW surface net irradiance bias is opposite of the sign of TOA upward irradiance bias, with a similar magnitude. As a result, the bias in absorbed SW irradiances by the atmosphere is smaller than the biases in both TOA and surface irradiances. The monthly mean biases in SW irradiances due to partly cloudy pixels are
Hang, Yun; L’Ecuyer, Tristan S.; Henderson, David S.; Matus, Alexander V.; Wang, ZhienHang, Y., T. S. L’Ecuyer, D. S. Henderson, A. V. Matus, Z. Wang, 2019: Reassessing the Effect of Cloud Type on Earth’s Energy Balance in the Age of Active Spaceborne Observations. Part II: Atmospheric Heating. J. Climate, 32(19), 6219-6236. doi: 10.1175/JCLI-D-18-0754.1. The role of clouds in modulating vertically integrated atmospheric heating is investigated using CloudSat’s multisensor radiative flux dataset. On the global mean, clouds are found to induce a net atmospheric heating of 0.07 ± 0.08 K day−1 that derives largely from 0.06 ± 0.07 K day−1 of enhanced shortwave absorption and a small, 0.01 ± 0.04 K day−1 reduction of longwave cooling. However, this small global average longwave effect results from the near cancellation of much larger regional warming by multilayered cloud systems in the tropics and cooling from stratocumulus clouds in subtropical oceans. Clouds are observed to warm the tropical atmosphere by 0.23 K day−1 and cool the polar atmosphere by −0.13 K day−1 enhancing required zonal heat redistribution by the meridional overturning circulation. Zonal asymmetries in the occurrence of multilayered clouds that are more frequent in the Northern Hemisphere and stratocumulus that occur more frequently over the southern oceans also leads to 3 times as much cloud heating in the Northern Hemisphere (0.1 K day−1) than the Southern Hemisphere (0.04 K day−1). These findings suggest that clouds very likely make the strongest contribution to the annual mean atmospheric energy imbalance between the hemispheres (2.0 ± 3.5 PW).
Hao, Dalei; Asrar, Ghassem R.; Zeng, Yelu; Zhu, Qing; Wen, Jianguang; Xiao, Qing; Chen, MinHao, D., G. R. Asrar, Y. Zeng, Q. Zhu, J. Wen, Q. Xiao, M. Chen, 2019: Estimating hourly land surface downward shortwave and photosynthetically active radiation from DSCOVR/EPIC observations. Remote Sensing of Environment, 232, 111320. doi: 10.1016/j.rse.2019.111320. The direct and diffuse components of downward shortwave radiation (SW), and photosynthetically active radiation (PAR) at the Earth surface play an essential role in biochemical (e.g. photosynthesis) and physical (e.g. energy balance) processes that control weather and climate conditions, and many ecological processes. Space-based observations have the unique advantage of providing reliable estimates of SW and PAR globally with sufficient accuracy for constructing Earth's radiation budget and estimating land-surface fluxes that control these processes. However, most existing space-based SW and PAR estimations from sensors onboard polar-orbiting and geostationary satellites have inherently low temporal resolution and/or limited spatial coverage of the entire Earth surface. The unique location/orbit of Earth Polychromatic Imaging Camera (EPIC) onboard the Deep Space Climate Observatory (DSCOVR) provides an unprecedented opportunity to obtain global estimates of SW and PAR accurately at a high temporal resolution of about 1–2 h. In this study, we developed and used a model (random forest, RF) to estimate global hourly SW and PAR at 0.1° × 0.1° (about 10 km at equator) spatial resolution based on EPIC measurements. We used a combination of EPIC Level-2 products, including solar zenith angle, aerosol optical depth, cloud optical thickness, cloud fraction, total column ozone and surface pressure with their associated quality flags to drive the RF model for estimating SW and PAR. We evaluated the model results against in situ observations from the Baseline Surface Radiation Network (BSRN) and Surface Radiation Budget Network (SURFRAD). We found the EPIC SW and PAR estimates at both hourly and daily time scales to be highly correlated and consistent with these independently obtained in situ measurements. The RMSEs for estimated daily diffuse SW, direct SW, total SW, and total PAR were 19.10, 38.47, 33.52, and 14.09 W/m2, respectively, and the biases for these estimates were 1.71, −0.77, 1.04 and 4.11 W/m2, respectively. We further compared the estimated SW and PAR with the Clouds and the Earth's Radiant Energy System Synoptic 1° × 1° (CERES SYN1deg) products and found a good correlation and consistency in their accuracy, spatial patterns and latitudinal gradient. The EPIC SW and PAR estimates provide a unique dataset (i.e. observations from single instrument from pole-to-pole for the entire sunlit portion of Earth) for characterizing their diurnal cycles and their potential impact on photosynthesis and evapotranspiration processes. Shortwave radiation; BSRN; Diffuse PAR; PAR; SURFRAD; DSCOVR; EPIC
Hayatbini, Negin; Hsu, Kuo-lin; Sorooshian, Soroosh; Zhang, Yunji; Zhang, FuqingHayatbini, N., K. Hsu, S. Sorooshian, Y. Zhang, F. Zhang, 2019: Effective Cloud Detection and Segmentation Using a Gradient-Based Algorithm for Satellite Imagery: Application to Improve PERSIANN-CCS. J. Hydrometeor., 20(5), 901-913. doi: 10.1175/JHM-D-18-0197.1. The effective identification of clouds and monitoring of their evolution are important toward more accurate quantitative precipitation estimation and forecast. In this study, a new gradient-based cloud-image segmentation algorithm is developed using image processing techniques. This method integrates morphological image gradient magnitudes to separate cloud systems and patches boundaries. A varying scale kernel is implemented to reduce the sensitivity of image segmentation to noise and to capture objects with various finenesses of the edges in remote sensing images. The proposed method is flexible and extendable from single to multispectral imagery. Case studies were carried out to validate the algorithm by applying the proposed segmentation algorithm to synthetic radiances for channels of the Geostationary Operational Environmental Satellite (GOES-16) simulated by a high-resolution weather prediction model. The proposed method compares favorably with the existing cloud-patch-based segmentation technique implemented in the Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks–Cloud Classification System (PERSIANN-CCS) rainfall retrieval algorithm. Evaluation of event-based images indicates that the proposed algorithm has potentials comparing to the conventional segmentation technique used in PERSIANN-CCS to improve rain detection and estimation skills with an accuracy rate of up to 98% in identifying cloud regions.
He, Min; Hu, Yongxiang; Chen, Nan; Wang, Donghai; Huang, Jianping; Stamnes, KnutHe, M., Y. Hu, N. Chen, D. Wang, J. Huang, K. Stamnes, 2019: High cloud coverage over melted areas dominates the impact of clouds on the albedo feedback in the Arctic. Scientific Reports, 9(1), 1-11. doi: 10.1038/s41598-019-44155-w. Warming in the Arctic is larger than the global average. A primary reason for this Arctic Amplification is the albedo feedback. The contrasting albedo of sea ice and dark melted surface areas is the key component of albedo feedback. Cloud coverage over the changing surface and the response of the clouds to the changing surface conditions will modify the change in planetary albedo when sea ice melts. Space-based lidar measurements provide a unique opportunity for cloud measurements in the Arctic. The response of clouds to the changing sea ice concentration was directly observed. Based on CALIPSO satellite observations of cloud properties, this study found that cloud coverage in ice-free regions in the Arctic linearly increased with the area of ice-free water during the melt seasons in the past 10 years, while sea ice coverage varies significantly year-to-year. The observations suggest that when sea-ice retreats, cloud fraction of the ice-free region remains fixed at nearly 81%. The high cloud coverage over melted areas significantly reduces the albedo feedback. These results indicate that space-based lidar cloud and surface observations of the Arctic can help constrain and improve climate models.
Hecht, Matthew; Veneziani, Milena; Weijer, Wilbert; Kravitz, Ben; Burrows, Susannah; Comeau, Darin; Hunke, Elizabeth; Jeffery, Nicole; Urrego‐Blanco, Jorge; Wang, Hailong; Wang, Shanlin; Zhang, Jiaxu; Bailey, David; Mills, Catrin; Rasch, Philip; Urban, NathanHecht, M., M. Veneziani, W. Weijer, B. Kravitz, S. Burrows, D. Comeau, E. Hunke, N. Jeffery, J. Urrego‐Blanco, H. Wang, S. Wang, J. Zhang, D. Bailey, C. Mills, P. Rasch, N. Urban, 2019: E3SMv0-HiLAT: A Modified Climate System Model Targeted for the Study of High-Latitude Processes. Journal of Advances in Modeling Earth Systems, 11(8), 2814-2843. doi: 10.1029/2018MS001524. We document the configuration, tuning, and evaluation of a modified version of the Community Earth System Model version 1 (Hurrell et al., 2013, https://doi.org/10.1175/BAMS-D-12), introduced here as E3SMv0-HiLAT, intended for study of high-latitude processes. E3SMv0-HiLAT incorporates changes to the atmospheric model affecting aerosol transport to high northern latitudes and to reduce shortwave cloud bias over the Southern Ocean. An updated sea ice model includes biogeochemistry that is coupled to an extended version of the ocean model's biogechemistry. This enables cloud nucleation to depend on the changing marine emissions of aerosol precursors, which may be expected in scenarios with strongly changing sea ice extent, oceanic stratification and associated nutrient availability, and atmospheric state. An evaluation of the basic preindustrial state of E3SMv0-HiLAT is presented in order to ensure that its climate is adequate to support future experimentation. Additional capability is not achieved without some cost, relative to the extraordinarily well-tuned model from which it was derived. In particular, a reduction of bias in cloud forcing achieved over the Southern Hemisphere also allows for greater Southern Ocean sea ice extent, a tendency that has been partially but not fully alleviated through experimentation and tuning. The most interesting change in the behavior of the model may be its response to greenhouse gas forcing: While the climate sensitivity is found to be essentially unchanged from that of Community Earth System Model version 1, the adjusted radiative forcing has increased from within one standard deviation above that of Coupled Model Intercomparison Project Phase 5 models to nearly two standard deviations. clouds; CESM; Earth System Model; high latitudes
Held, I. M.; Guo, H.; Adcroft, A.; Dunne, J. P.; Horowitz, L. W.; Krasting, J.; Shevliakova, E.; Winton, M.; Zhao, M.; Bushuk, M.; Wittenberg, A. T.; Wyman, B.; Xiang, B.; Zhang, R.; Anderson, W.; Balaji, V.; Donner, L.; Dunne, K.; Durachta, J.; Gauthier, P. P. G.; Ginoux, P.; Golaz, J.-C.; Griffies, S. M.; Hallberg, R.; Harris, L.; Harrison, M.; Hurlin, W.; John, J.; Lin, P.; Lin, S.-J.; Malyshev, S.; Menzel, R.; Milly, P. C. D.; Ming, Y.; Naik, V.; Paynter, D.; Paulot, F.; Rammaswamy, V.; Reichl, B.; Robinson, T.; Rosati, A.; Seman, C.; Silvers, L. G.; Underwood, S.; Zadeh, N.Held, I. M., H. Guo, A. Adcroft, J. P. Dunne, L. W. Horowitz, J. Krasting, E. Shevliakova, M. Winton, M. Zhao, M. Bushuk, A. T. Wittenberg, B. Wyman, B. Xiang, R. Zhang, W. Anderson, V. Balaji, L. Donner, K. Dunne, J. Durachta, P. P. G. Gauthier, P. Ginoux, J. Golaz, S. M. Griffies, R. Hallberg, L. Harris, M. Harrison, W. Hurlin, J. John, P. Lin, S. Lin, S. Malyshev, R. Menzel, P. C. D. Milly, Y. Ming, V. Naik, D. Paynter, F. Paulot, V. Rammaswamy, B. Reichl, T. Robinson, A. Rosati, C. Seman, L. G. Silvers, S. Underwood, N. Zadeh, 2019: Structure and Performance of GFDL's CM4.0 Climate Model. Journal of Advances in Modeling Earth Systems, 11(11), 3691-3727. doi: 10.1029/2019MS001829. We describe the Geophysical Fluid Dynamics Laboratory's CM4.0 physical climate model, with emphasis on those aspects that may be of particular importance to users of this model and its simulations. The model is built with the AM4.0/LM4.0 atmosphere/land model and OM4.0 ocean model. Topics include the rationale for key choices made in the model formulation, the stability as well as drift of the preindustrial control simulation, and comparison of key aspects of the historical simulations with observations from recent decades. Notable achievements include the relatively small biases in seasonal spatial patterns of top-of-atmosphere fluxes, surface temperature, and precipitation; reduced double Intertropical Convergence Zone bias; dramatically improved representation of ocean boundary currents; a high-quality simulation of climatological Arctic sea ice extent and its recent decline; and excellent simulation of the El Niño-Southern Oscillation spectrum and structure. Areas of concern include inadequate deep convection in the Nordic Seas; an inaccurate Antarctic sea ice simulation; precipitation and wind composites still affected by the equatorial cold tongue bias; muted variability in the Atlantic Meridional Overturning Circulation; strong 100 year quasiperiodicity in Southern Ocean ventilation; and a lack of historical warming before 1990 and too rapid warming thereafter due to high climate sensitivity and strong aerosol forcing, in contrast to the observational record. Overall, CM4.0 scores very well in its fidelity against observations compared to the Coupled Model Intercomparison Project Phase 5 generation in terms of both mean state and modes of variability and should prove a valuable new addition for analysis across a broad array of applications. climate; model; CM4; CMIP6; coupled; GFDL
Hinkelman, Laura M.Hinkelman, L. M., 2019: The global radiative energy budget in MERRA Version 1 and Version 2: Evaluation with respect to CERES EBAF data. J. Climate, 32(6), 1973–1994. doi: 10.1175/JCLI-D-18-0445.1. The representation of the long-term radiative energy budgets in NASA’s MERRA and MERRA-2 reanalyses has been evaluated, emphasizing changes associated with the reanalysis system update. Data from the CERES EBAF Edition 2.8 satellite product over 2001-2015 were used as a reference. For both MERRA and MERRA-2, the climatological global means of most TOA radiative flux terms agree to within ∼3 Wm-2 of EBAF. However, MERRA-2’s all-sky reflected shortwave flux is ∼7 Wm-2 higher than either MERRA or EBAF’s, resulting in a net TOA flux imbalance of -4 Wm-2. At the surface, all-sky downward longwave fluxes are problematic for both reanalyses while high clear-sky downward shortwave fluxes indicate that their atmospheres are too transmissive. Although MERRA-2’s individual all-sky flux terms agree better with EBAF, its net flux agreement is worse (-8.3 Wm-2 vs -3.3 Wm-2 for MERRA) because MERRA benefits from cancellation of errors. Analysis by region and surface type gives mixed outcomes. The results consistently indicate that clouds are over-represented over the tropical oceans in both reanalyses, particularly MERRA-2, and somewhat under-represented in marine stratocumulus areas. MERRA-2 also exhibits signs of excess cloudiness in the Southern Ocean. Notable discrepancies occur in the polar regions, where the effects of snow and ice cover are important. In most cases, MERRA-2 better represents variability and trends in the global mean radiative fluxes over the period of analysis. Overall, the performance of MERRA-2 relative to MERRA is mixed; there is still room for improvement in the radiative fluxes in this family of reanalysis products.
Hourdin, Frédéric; Jam, Arnaud; Rio, Catherine; Couvreux, Fleur; Sandu, Irina; Lefebvre, Marie-Pierre; Brient, Florent; Idelkadi, AbderrahmaneHourdin, F., A. Jam, C. Rio, F. Couvreux, I. Sandu, M. Lefebvre, F. Brient, A. Idelkadi, 2019: Unified Parameterization of Convective Boundary Layer Transport and Clouds With the Thermal Plume Model. Journal of Advances in Modeling Earth Systems, 11(9), 2910-2933. doi: 10.1029/2019MS001666. The representation of stratocumulus clouds, and of the stratocumulus to cumulus transitions which are ubiquitous features of marine boundary layer clouds, remains a challenge for climate models. We show how a mass flux representation of boundary layer convective structures combined with an eddy diffusivity scheme, the “thermal plume model,” first developed to represent cumulus clouds, can also adequately simulate stratocumulus and the stratocumulus to cumulus transition in a climate model. To achieve this, the detrainment formulation, in which detrainment increases for increasing negative buoyancy, has to be slightly modified: the buoyancy of a thermal plume parcel of air is computed by comparing the virtual potential temperature θv,th of the parcel with that of the surrounding environment θv,env at a given distance above instead of at the same level. This is consistent with the picture of detrained air parcels that experience some overshoot and reach a final destination at a level lower than the one at which they effectively leave the cloud or organized convective plume. The impacts of this modification are documented both for selected cases of stratocumulus, in comparison with large-eddy simulations, and in full 3-D climate simulations, in comparison with satellite observations of cloud cover. The modified scheme provides a uniform treatment of the dry convective boundary layer, of cumulus clouds, of stratocumulus, and of the transition from stratocumulus to cumulus. It is included in the most recent version of the LMDZ atmospheric general circulation model. global climate model; convective boundary layer; mass flux scheme; stratocumulus
Huang, Guanghui; Li, Zhanqing; Li, Xin; Liang, Shunlin; Yang, Kun; Wang, Dongdong; Zhang, YiHuang, G., Z. Li, X. Li, S. Liang, K. Yang, D. Wang, Y. Zhang, 2019: Estimating surface solar irradiance from satellites: Past, present, and future perspectives. Remote Sensing of Environment, 233, 111371. doi: 10.1016/j.rse.2019.111371. Surface Solar Irradiance (SSI) is a key parameter dictating surface-atmosphere interactions, driving radiative, hydrological, and land surface processes, and can thus impinge greatly upon weather and climate. It is thereby a prerequisite of many studies and applications. Estimating SSI from satellites began in the 1960s, and is currently the principal way to map SSI spatiotemporal distributions from regional to global scales. Starting from an overview of historical studies carried out in the past several decades, this paper reviews the progresses made in methodology, validation, and products over these years. First, the requirements of SSI in various studies or applications are presented along with the theoretical background of SSI satellite estimation. Methods to estimate SSI from satellites are then summarized as well as their advantages and limitations. Validations of satellite-based SSI on two typical spatial scales are discussed followed by a brief description of existing products and their accuracies. Finally, the challenges faced by current SSI satellite estimation are analyzed, and possible improvements to implement in the future are suggested. This review not only updates the review paper by Pinker et al. (1995) on satellite methods to derive SSI but also offers a more comprehensive summary of the related studies and applications. Remote sensing; Satellites; Radiation budget; Review; Surface solar irradiance
Huang, Xianglei; Chen, Xiuhong; Yue, QingHuang, X., X. Chen, Q. Yue, 2019: Band-by-Band Contributions to the Longwave Cloud Radiative Feedbacks. Geophysical Research Letters, 46(12), 6998-7006. doi: 10.1029/2019GL083466. Cloud radiative feedback is central to our projection of future climate change. It can be estimated using the cloud radiative kernel (CRK) method or adjustment method. This study, for the first time, examines the contributions of each spectral band to the longwave (LW) cloud radiative feedbacks (CRFs). Simulations of three warming scenarios are analyzed, including +2 K sea surface temperature, 2 × CO2, and 4 × CO2 experiments. While the LW broadband CRFs derived from the CRK and adjustment methods agree with each other, they disagree on the relative contributions from the far-infrared and window bands. The CRK method provides a consistent band-by-band decomposition of LW CRF for different warming scenarios. The simulated and observed short-term broadband CRFs for the 2003–2013 period are similar to the long-term counterparts, but their band-by-band decompositions are different, which can be further related to the cloud fraction changes in respective simulations and observation. climate model; cloud radiative feedback; radiative kernel; spectral longwave radiation
Huang, Yi; Chou, Gina; Xie, Yan; Soulard, NicholasHuang, Y., G. Chou, Y. Xie, N. Soulard, 2019: Radiative Control of the Interannual Variability of Arctic Sea Ice. Geophysical Research Letters, 46(16), 9899-9908. doi: 10.1029/2019GL084204. On top of a declining trend driven by global warming, the Arctic sea ice extent (SIE) exhibits considerable interannual variations. In this study, we analyze the interannual anomalies of September SIE in relation to the surface radiation anomalies. We find that the accumulation of radiation energy in the early months (June, July, and August) very well explains the September SIE variability (R2 = 0.81). In Particular, strong correlations are found between September SIE and June radiation anomalies, which in the shortwave is due to cloud and surface albedo changes and in the longwave due to atmospheric warming. The results show that monitoring the radiation anomalies affords a potential means to improve the prediction of the late summer sea ice. cloud; sea ice; radiative forcing; Arctic; interannual variability; NAO
Huang, Yiyi; Dong, Xiquan; Bailey, David A.; Holland, Marika M.; Xi, Baike; DuVivier, Alice K.; Kay, Jennifer E.; Landrum, Laura L.; Deng, YiHuang, Y., X. Dong, D. A. Bailey, M. M. Holland, B. Xi, A. K. DuVivier, J. E. Kay, L. L. Landrum, Y. Deng, 2019: Thicker Clouds and Accelerated Arctic Sea Ice Decline: The Atmosphere-Sea Ice Interactions in Spring. Geophysical Research Letters, 46(12), 6980-6989. doi: 10.1029/2019GL082791. Observations show that increased Arctic cloud cover in the spring is linked with sea ice decline. As the atmosphere and sea ice can influence each other, which one plays the leading role in spring remains unclear. Here we demonstrate, through observational data diagnosis and numerical modeling, that there is active coupling between the atmosphere and sea ice in early spring. Sea ice melting and thus the presence of more open water lead to stronger evaporation and promote cloud formation that increases downward longwave flux, leading to even more ice melt. Spring clouds are a driving force in the disappearance of sea ice and displacing the mechanism of atmosphere-sea ice coupling from April to June. These results suggest the need to accurately model interactions of Arctic clouds and radiation in Earth System Models in order to improve projections of the future of the Arctic. Arctic sea ice retreat; atmosphere-sea ice coupling; atmospheric physical processes; cloud and radiation impact
Huang, Yiyi; Dong, Xiquan; Xi, Baike; Deng, YiHuang, Y., X. Dong, B. Xi, Y. Deng, 2019: A survey of the atmospheric physical processes key to the onset of Arctic sea ice melt in spring. Climate Dynamics, 52(7), 4907-4922. doi: 10.1007/s00382-018-4422-x. September sea ice concentration (SIC) is found to be most sensitive to the early melt onset over the East Siberian Sea and Laptev Sea (73°–84°N, 90°–155°) in the Arctic, a region defined here as the area of focus (AOF). The areal initial melt date for a given year is marked when sea ice melting extends beyond 10% of the AOF size. With this definition, four early melting years (1990, 2012, 2003, 1991) and four late melting years (1996, 1984, 1983, 1982) were selected. The impacts and feedbacks of atmospheric physical and dynamical variables on the Arctic SIC variations were investigated for the selected early and late melting years based on the NASA MERRA-2 reanalysis. The sea ice melting tends to happen in a shorter period of time with larger magnitude in late melting years, while the melting lasts longer and tends to be more temporally smooth in early melting years. The first major melting event in each year has been further investigated and compared. In the early melting years, the positive Arctic Oscillation (AO) phase is dominant during springtime, which is accompanied by intensified atmospheric transient eddy activities in the Arctic and enhanced moisture flux convergence in the AOF and consequently enhanced northward transport of moist and warm air. As a result, positive anomalies of air temperature, precipitable water vapor (PWV) and/or cloud fraction and cloud water path were found over the AOF, increasing downward longwave radiative flux at the surface. The associated warming effect further contributes to the initial melt of sea ice. In contrast, the late melt onset is usually linked to the negative AO phase in spring accompanied with negative anomalies of PWV and downward longwave flux at the surface. The increased downward shortwave radiation during middle to late June plays a more important role in triggering the melting, aided further by the stronger than normal cloud warming effects. Arctic sea ice melt onset; Arctic September sea ice minimum retreat; Atmospheric physical processes; Cloud and radiation impact; Moisture and heat transport
Hwang, Jiwon; Choi, Yong-Sang; Yoo, Changhyun; Wang, Yuan; Su, Hui; Jiang, Jonathan H.Hwang, J., Y. Choi, C. Yoo, Y. Wang, H. Su, J. H. Jiang, 2019: Interpretation of the Top-of-Atmosphere Energy Flux for Future Arctic Warming. Scientific Reports, 9(1), 1-10. doi: 10.1038/s41598-019-49218-6. With the trend of amplified warming in the Arctic, we examine the observed and modeled top-of-atmosphere (TOA) radiative responses to surface air-temperature changes over the Arctic by using TOA energy fluxes from NASA’s CERES observations and those from twelve climate models in CMIP5. Considerable inter-model spreads in the radiative responses suggest that future Arctic warming may be determined by the compensation between the radiative imbalance and poleward energy transport (mainly via transient eddy activities). The poleward energy transport tends to prevent excessive Arctic warming: the transient eddy activities are weakened because of the reduced meridional temperature gradient under polar amplification. However, the models that predict rapid Arctic warming do not realistically simulate the compensation effect. This role of energy compensation in future Arctic warming is found only when the inter-model differences in cloud radiative effects are considered. Thus, the dynamical response can act as a buffer to prevent excessive Arctic warming against the radiative response of 0.11 W m−2 K−1 as measured from satellites, which helps the Arctic climate system retain an Arctic climate sensitivity of 4.61 K. Therefore, if quantitative analyses of the observations identify contribution of atmospheric dynamics and cloud effects to radiative imbalance, the satellite-measured radiative response will be a crucial indicator of future Arctic warming.
Jakob, C.; Singh, M. S.; Jungandreas, L.Jakob, C., M. S. Singh, L. Jungandreas, 2019: Radiative Convective Equilibrium and Organized Convection: An Observational Perspective. Journal of Geophysical Research: Atmospheres, 124(10), 5418-5430. doi: 10.1029/2018JD030092. Radiative convective equilibrium (RCE) describes a balance between the cooling of the atmosphere by radiation and the heating through latent heat release and surface heat fluxes. While RCE is known to provide an energetic constraint on the atmosphere at the global scale, little is known about the proximity of the atmosphere to RCE at smaller spatial and temporal scales, despite the common use of RCE in idealized modeling studies. Here we provide the first observational evaluation of the scales at which the atmosphere is near RCE. We further use observations of cloud characteristics to investigate the role played by organized convection in the RCE state. While the tropical atmosphere as a whole is near RCE on daily time scales and longer, this is not the case for any given location. Rather, areas in excess of 5,000 × 5,000 km2 must be considered to ensure the atmosphere remains near RCE at least 80% of the time, even for monthly averaged conditions. We confirm that RCE is established through the interplay of regions of active deep convection with high precipitation and weak radiative cooling and regions of subsiding motions leading to shallow cloud states that allow strong radiative cooling with no precipitation. The asymmetry in the maximum amount of radiative cooling and latent heating leads to the well-known ratio of small areas of precipitation and large regions of subsidence observed in the tropics. Finally, we show that organized deep convection does not occur when regions smaller than 1,000 × 1,000 km2 are near RCE. convection; tropics; climate; radiation
Jia, Hailing; Ma, Xiaoyan; Quaas, Johannes; Yin, Yan; Qiu, TomJia, H., X. Ma, J. Quaas, Y. Yin, T. Qiu, 2019: Is positive correlation between cloud droplet effective radius and aerosol optical depth over land due to retrieval artifacts or real physical processes?. Atmospheric Chemistry and Physics, 19(13), 8879-8896. doi: https://doi.org/10.5194/acp-19-8879-2019. Abstract. The Moderate Resolution Imaging Spectroradiometer (MODIS) C6 L3, Clouds and the Earth's Radiant Energy System (CERES) Edition-4 L3 products, and the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis data are employed to systematically study aerosol–cloud correlations over three anthropogenic aerosol regions and their adjacent oceans, as well as explore the effect of retrieval artifacts and underlying physical mechanisms. This study is confined to warm phase and single-layer clouds without precipitation during the summertime (June, July, and August). Our analysis suggests that cloud effective radius (CER) is positively correlated with aerosol optical depth (AOD) over land (positive slopes), but negatively correlated with aerosol index (AI) over oceans (negative slopes) even with small ranges of liquid water path (quasi-constant). The changes in albedo at the top of the atmosphere (TOA) corresponding to aerosol-induced changes in CER also lend credence to the authenticity of this opposite aerosol–cloud correlation between land and ocean. It is noted that potential artifacts, such as the retrieval biases of both cloud (partially cloudy and 3-D-shaped clouds) and aerosol, can result in a serious overestimation of the slope of CER–AOD/AI. Our results show that collision–coalescence seems not to be the dominant cause for positive slope over land, but the increased CER caused by increased aerosol might further increase CER by initializing collision–coalescence, generating a positive feedback. By stratifying data according to the lower tropospheric stability and relative humidity near cloud top, it is found that the positive correlations more likely occur in the case of drier cloud top and stronger turbulence in clouds, while negative correlations occur in the case of moister cloud top and weaker turbulence in clouds, which implies entrainment mixing might be a possible physical interpretation for such a positive CER–AOD slope.
Jiang, Bo; Liang, Shunlin; Jia, Aolin; Xu, Jianglei; Zhang, Xiaotong; Xiao, Zhiqiang; Zhao, Xiang; Jia, Kun; Yao, YunjunJiang, B., S. Liang, A. Jia, J. Xu, X. Zhang, Z. Xiao, X. Zhao, K. Jia, Y. Yao, 2019: Validation of the Surface Daytime Net Radiation Product From Version 4.0 GLASS Product Suite. IEEE Geoscience and Remote Sensing Letters, 16(4), 509-513. doi: 10.1109/LGRS.2018.2877625. The daytime surface net radiation (Rn) product from version 4.0 Global LAnd Surface Satellite (GLASS) product suite was recently generated from Moderate Resolution Imaging Spectroradiometer data. It is the daytime average product of Rn derived from 2000 to 2015 at a spatial resolution of 0.05°. This letter describes the results of validation of this new Rn product using ground measurements collected from 142 sites distributed worldwide. The overall accuracy of the GLASS daytime Rn product was satisfactory, with an R2 of 0.80, root-mean-square error of 51.35 Wm-2, and mean bias error of 0.11 Wm-2. Its accuracy and quality were highly consistent for different land cover classes and elevation zones. Land surface; Satellites; atmospheric radiation; atmospheric techniques; Atmospheric modeling; net radiation; Spatial resolution; remote sensing; 4.0 Global LAnd Surface Satellite product suite; Clouds; daytime average product; daytime surface net radiation; Glass; GLASS daytime R; Global LAnd Surface Satellite (GLASS); Ice; mean square error methods; Moderate Resolution Imaging Spectroradiometer data; product; Rn; Rn product; spatial resolution; Surface daytime net radiation product; version 4.0 GLASS product
Jing, Xianwen; Suzuki, Kentaroh; Michibata, TakuroJing, X., K. Suzuki, T. Michibata, 2019: The Key Role of Warm Rain Parameterization in Determining the Aerosol Indirect Effect in a Global Climate Model. J. Climate, 32(14), 4409-4430. doi: 10.1175/JCLI-D-18-0789.1. Global climate models (GCMs) have been found to share the common too-frequent bias in the warm rain formation process. In this study, five different autoconversion schemes are incorporated into a single GCM, to systematically evaluate the warm rain formation processes in comparison with satellite observations and investigate their effects on aerosol indirect effect (AIE). It is found that some schemes generate warm rain less efficiently under polluted conditions in the manner closer to satellite observations, while the others generate warm rain too frequently. Large differences in AIE are found among these schemes. It is remarkable that the schemes with more observation-like warm rain formation processes exhibit larger AIEs that far exceed the uncertainty range reported in IPCC AR5, to an extent that can cancel much of the warming trend in the past century, whereas schemes with too-frequent rain formations yield AIEs that are well bounded by the reported range. The power-law dependence of autoconversion rate on cloud droplet number concentration (β) is found to affect substantially the susceptibility of rain formation to aerosols: the more negative β is, the more difficult for rain to be triggered in polluted clouds, leading to larger AIE through substantial contributions from the wet scavenging feedback. The appropriate use of droplet size threshold can mitigate the effect of a less negative β. The role of the warm rain formation process on AIE in this particular model has broad implications for others that share the too-frequent rain-formation bias.
Joos, HannaJoos, H., 2019: Warm Conveyor Belts and Their Role for Cloud Radiative Forcing in the Extratropical Storm Tracks. J. Climate, 32(16), 5325-5343. doi: 10.1175/JCLI-D-18-0802.1. The link between cloud radiative forcing (CRF) and warm conveyor belts (WCBs), which are strongly ascending airstreams in extratropical cyclones, is investigated based on ERA-Interim reanalysis from 1979 to 2011. Clouds associated with WCBs can be liquid, mixed phase, or ice clouds. They interact with the longwave and shortwave radiation in different ways and thus strongly influence Earth’s radiative budget in the extratropical storm tracks in a complex way. In this study, WCBs are identified with a Lagrangian method, where WCBs are represented by trajectories that rise at least 600 hPa in 48 h in the vicinity of an extratropical cyclone, and CRF is traced along all WCB trajectories during the considered 30-yr period. The results show that due to the poleward ascent of WCBs, they exhibit negative net cloud forcing (NetCRF) in the southern part of the associated cloud band, whereas in their northern part, NetCRF gets positive due to the lack of sunlight in the winter months. This nonuniform CRF along WCBs from low to high latitudes increases the meridional NetCRF gradient. Furthermore, in their outflow regions in the North Atlantic, where WCBs are mainly associated with ice clouds, WCBs contribute up to 10 W m−2 to the global climatological NetCRF maximum in winter. The results highlight the importance of WCBs in modulating the radiative budget in the extratropics. Furthermore, the results emphasize the need for a correct representation of WCBs in climate models to correctly simulate the cloud–circulation coupling.
Kacenelenbogen, Meloë S.; Vaughan, Mark A.; Redemann, Jens; Young, Stuart A.; Liu, Zhaoyan; Hu, Yongxiang; Omar, Ali H.; LeBlanc, Samuel; Shinozuka, Yohei; Livingston, John; Zhang, Qin; Powell, Kathleen A.Kacenelenbogen, M., . S., M. A. Vaughan, J. Redemann, S. A. Young, Z. Liu, Y. Hu, A. H. Omar, S. LeBlanc, Y. Shinozuka, J. Livingston, Q. Zhang, K. A. Powell, 2019: Estimations of Global Shortwave Direct Aerosol Radiative Effects Above Opaque Water Clouds Using a Combination of A-Train Satellite Sensors. Atmospheric Chemistry and Physics Discussions, 1-96. doi: 10.5194/acp-2018-1090. Abstract. All-sky Direct Aerosol Radiative Effects (DARE) play a significant yet still uncertain role in climate. This is partly due to poorly quantified radiative properties of Aerosol Above Clouds (AAC). We compute global estimates of short-wave top-of-atmosphere DARE over Opaque Water Clouds (OWC), DAREOWC, using observation-based aerosol and cloud radiative properties from a combination of A-Train satellite sensors and a radiative transfer model. There are three major differences between our DAREOWC calculations and previous studies: (1) we use the Depolarization Ratio method (DR) on CALIOP (Cloud Aerosol LIdar with Orthogonal Polarization) Level 1 measurements to compute the AAC frequencies of occurrence and the AAC Aerosol Optical Depths (AOD), thus introducing fewer uncertainties compared to using the CALIOP standard product; (2) we apply our calculations globally, instead of focusing exclusively on regional AAC hotspots such as the southeast Atlantic; and (3) instead of the traditional look-up table approach, we use a combination of satellite-based sensors to obtain AAC intensive radiative properties. Our results agree with previous findings on the dominant locations of AAC (South and North East Pacific, Tropical and South East Atlantic, northern Indian Ocean and North West Pacific), the season of maximum occurrence, aerosol optical depths (a majority in the 0.01–0.02 range and that can exceed 0.2 at 532nm) and aerosol extinction-to-backscatter ratios (a majority in the 40–50sr range at 532nm which is typical of dust aerosols) over the globe. We find positive averages of global seasonal DAREOWC between 0.13 and 0.26W·m−2 (i.e., a warming effect on climate). Regional seasonal DAREOWC values range from −0.06W·m−2 in the Indian Ocean, offshore from western Australia (in March–April–May) to 2.87W·m−2 in the South East Atlantic (in September–October–November). High positive values are usually paired with high aerosol optical depths (>0.1) and low single scattering albedos (
Kant, Sunny; Panda, Jagabandhu; Gautam, RiteshKant, S., J. Panda, R. Gautam, 2019: A seasonal analysis of aerosol-cloud-radiation interaction over Indian region during 2000–2017. Atmospheric Environment, 201, 212-222. doi: 10.1016/j.atmosenv.2018.12.044. The present study uses 18 years (March 2000–May 2017) of satellite–derived relevant parameters to examine the impact of aerosols on cloud properties, radiative fluxes and ACI (aerosol-cloud interaction) over Indian region. The study includes consideration of shortwave cloud radiative forcing (SWCRF), longwave cloud radiative forcing (LWCRF) and net cloud radiative forcing (NetCRF) from CERES (Clouds and Earth's Radiant Energy System). Also, aerosol optical depth (AOD) and cloud properties such as ice/liquid CER (Cloud Effective Radius), CF (Cloud Fraction), COD (Cloud Optical Depth), CTP (Cloud Top Pressure) and ice/liquid CWP (Cloud Water Path; i.e., ICWP and LCWP) are also considered. Moderate to high aerosol loading and the significant increasing trend of AOD is observed over several parts of Indian region depending upon the seasons. CF is found to be moderate to higher during monsoon months with increasing trend over several parts of the country. Optically thicker high-level clouds have low SWCRF value; whereas, middle-level and low-level clouds have low to moderate SWCRF value. In the majority of cases, Twomey effect is observed whereas in some scenarios Anti-Twomey effect is seen. Aerosol; Cloud; Cloud properties; Cloud radiative forcing
Kato, Seiji; Rose, Fred G.; Ham, Seung Hee; Rutan, David A.; Radkevich, Alexander; Caldwell, Thomas E.; Sun‐Mack, Sunny; Miller, Walter F.; Chen, YanKato, S., F. G. Rose, S. H. Ham, D. A. Rutan, A. Radkevich, T. E. Caldwell, S. Sun‐Mack, W. F. Miller, Y. Chen, 2019: Radiative Heating Rates Computed with Clouds Derived from Satellite-based Passive and Active Sensors and their Effects on Generation of Available Potential Energy. Journal of Geophysical Research: Atmospheres, 124(3), 1720-1740. doi: 10.1029/2018JD028878. Radiative heating rates computed with cloud properties derived from passive and active sensors are investigated. Zonal monthly radiative heating rate anomalies computed using both active and passive sensors show that larger variability in longwave cooling exists near the tropical tropopause and near the top of the boundary layer between 50°N to 50°S. Aerosol variability contributes to increases in shortwave heating rate variability. When zonal monthly mean cloud effects on the radiative heating rate computed with both active and passive sensors and those computed with passive sensor only are compared, the latter shows cooling and heating peaks corresponding to cloud top and base height ranges used for separating cloud types. The difference of these two sets of cloud radiative effect on heating rates in the middle to upper troposphere is larger than the radiative heating rate uncertainty estimated based on the difference of two active sensor radiative heating rate profile data products. In addition, radiative heating rate contribution to generation of eddy available potential energy is also investigated. Although radiation contribution to generation of eddy available potential energy averaged over a year and the entire globe is small, radiation increases the eddy available potential energy in the northern hemisphere during summer. Two key elements that longwave radiation contribute to the generation of eddy potential energy are 1) longitudinal temperature gradient in the atmosphere associated with land and ocean surface temperatures contrasts and absorption of longwave radiation emitted by the surface and 2) cooling near the cloud top of stratocumulus clouds. clouds; Available potential energy; Heating rate; Radiation
Kelleher, Mitchell K.; Grise, Kevin M.Kelleher, M. K., K. M. Grise, 2019: Examining Southern Ocean cloud controlling factors on daily timescales and their connections to midlatitude weather systems. J. Climate, 32(16), 5145–5160. doi: 10.1175/JCLI-D-18-0840.1. Clouds and their associated radiative effects are a large source of uncertainty in global climate models. One region with particularly large model biases in shortwave cloud radiative effects (CRE) is the Southern Ocean. Previous research has shown that many dynamical “cloud controlling factors” influence shortwave CRE on monthly timescales, and that two important cloud controlling factors over the Southern Ocean are mid-tropospheric vertical velocity and estimated inversion strength (EIS). Model errors may thus arise from biases in representing cloud controlling factors (atmospheric dynamics), representing how clouds respond to those cloud controlling factors (cloud parametrizations), or some combination thereof.This study extends previous work by examining cloud controlling factors over the Southern Ocean on daily timescales in both observations and global climate models. This allows the cloud controlling factors to be examined in the context of transient weather systems. Composites of EIS and mid-tropospheric vertical velocity are constructed around extratropical cyclones and anticyclones to examine how the different dynamical cloud controlling factors influence shortwave CRE around midlatitude weather systems and to assess how models compare to observations. On average, models tend to produce a realistic cyclone and anticyclone, when compared to observations, in terms of the dynamical cloud controlling factors. The difference between observations and models instead lies in how the models’ shortwave CRE respond to the dynamics. In particular, the models’ shortwave CRE are too sensitive to perturbations in mid-tropospheric vertical velocity and, thus, they tend to produce clouds that excessively brighten in the frontal region of the cyclone and excessively dim in the center of the anticyclone.
Khazaei, Bahram; Khatami, Sina; Alemohammad, Seyed Hamed; Rashidi, Lida; Wu, Changshan; Madani, Kaveh; Kalantari, Zahra; Destouni, Georgia; Aghakouchak, AmirKhazaei, B., S. Khatami, S. H. Alemohammad, L. Rashidi, C. Wu, K. Madani, Z. Kalantari, G. Destouni, A. Aghakouchak, 2019: Climatic or regionally induced by humans? Tracing hydro-climatic and land-use changes to better understand the Lake Urmia tragedy. Journal of Hydrology, 569, 203-217. doi: 10.1016/j.jhydrol.2018.12.004. Lake Urmia—a shallow endemic hypersaline lake in northwest Iran—has undergone a dramatic decline in its water level (WL), by about 8 m, since 1995. The primary cause of the WL decline in Lake Urmia has been debated in the scientific literature, regarding whether it has been predominantly driven by atmospheric climate change or by human activities in the watershed landscape. Using available climate, hydrological, and vegetation data for the period 1981–2015, this study analyzes and aims to explain the lake desiccation based on other observed hydro-climatic and vegetation changes in the Lake Urmia watershed and classical exploratory statistical methods. The analysis accounts for the relationships between atmospheric climate change (precipitation P, temperature T), and hydrological (soil moisture SM, and WL) and vegetation cover (VC; including agricultural crops and other vegetation) changes in the landscape. Results show that P, T, and SM changes cannot explain the sharp decline in lake WL since 2000. Instead, the agricultural increase of VC in the watershed correlates well with the lake WL change, indicating this human-driven VC and associated irrigation expansion as the dominant human driver of the Lake Urmia desiccation. Specifically, the greater transpiration from the expanded and increasingly irrigated agricultural crops implies increased total evapotranspiration and associated consumptive use of water (inherently related to the irrigation and water diversion and storage developments in the watershed). Thereby the runoff from the watershed into the lake has decreased, and the remaining smaller inflow to the lake has been insufficient for keeping up the previous lake WL, causing the observed WL drop to current conditions. Climate change; Vegetation; Anthropogenic change; Lake Urmia; Land-use change; Water resources management
Kim, Bu-Yo; Lee, Kyu-TaeKim, B., K. Lee, 2019: Using the Himawari-8 AHI Multi-Channel to Improve the Calculation Accuracy of Outgoing Longwave Radiation at the Top of the Atmosphere. Remote Sensing, 11(5), 589. doi: 10.3390/rs11050589. In this study, Himawari-8 Advanced Himawari Imager (AHI) longwave channel data that is sensitive to clouds and absorption gas were used to improve the accuracy of the algorithm used to calculate outgoing longwave radiation (OLR) at the top of the atmosphere. A radiative transfer model with a variety of atmospheric conditions was run using Garand vertical profile data as input data. The results of the simulation showed that changes in AHI channels 8, 12, 15, and 16, which were used to calculate OLR, were sensitive to changes in cloud characteristics (cloud optical thickness and cloud height) and absorption gases (water vapor, O3, CO2, aerosol optical thickness) in the atmosphere. When compared to long-term analysis OLR data from 2017, as recorded by the Cloud and Earth’s Radiant Energy System (CERES), the OLR calculated in this study had an annual mean bias of 2.28 Wm−2 and a root mean square error (RMSE) of 11.03 Wm−2. The new calculation method mitigated the problem of overestimations in OLR in mostly cloudy and overcast regions and underestimated OLR in cloud-free desert regions. It is also an improvement over the result from the existing OLR calculation algorithm, which uses window and water vapor channels. multi-channel; algorithm improvement; Cloud and Earth’s Radiant Energy System (CERES); Himawari-8 Advanced Himawari Imager (AHI); outgoing longwave radiation at the top of the atmosphere (TOA OLR); radiative transfer model
Kim, Jiwon; Kim, Kwangjin; Cho, Jaeil; Kang, Yong Q.; Yoon, Hong-Joo; Lee, Yang-WonKim, J., K. Kim, J. Cho, Y. Q. Kang, H. Yoon, Y. Lee, 2019: Satellite-Based Prediction of Arctic Sea Ice Concentration Using a Deep Neural Network with Multi-Model Ensemble. Remote Sensing, 11(1), 19. doi: 10.3390/rs11010019. Warming of the Arctic leads to a decrease in sea ice, and the decrease of sea ice, in turn, results in warming of the Arctic again. Several microwave sensors have provided continuously updated sea ice data for over 30 years. Many studies have been conducted to investigate the relationships between the satellite-derived sea ice concentration (SIC) of the Arctic and climatic factors associated with the accelerated warming. However, linear equations using the general circulation model (GCM) data, with low spatial resolution, cannot sufficiently cope with the problem of complexity or non-linearity. Time-series techniques are effective for one-step-ahead forecasting, but are not appropriate for future prediction for about ten or twenty years because of increasing uncertainty when forecasting multiple steps ahead. This paper describes a new approach to near-future prediction of Arctic SIC by employing a deep learning method with multi-model ensemble. We used the regional climate model (RCM) data provided in higher resolution, instead of GCM. The RCM ensemble was produced by Bayesian model averaging (BMA) to minimize the uncertainty which can arise from a single RCM. The accuracies of RCM variables were much improved by the BMA2 method, which took into consideration temporal and spatial variations to minimize the uncertainty of individual RCMs. A deep neural network (DNN) method was used to deal with the non-linear relationships between SIC and climate variables, and to provide a near-future prediction for the forthcoming 10 to 20 years. We adjusted the DNN model for optimized SIC prediction by adopting best-fitted layer structure, loss function, optimizer algorithm, and activation function. The accuracy was much improved when the DNN model was combined with BMA2 ensemble, showing the correlation coefficient of 0.888. This study provides a viable option for monitoring Arctic sea ice change of the near future. regional climate model; Bayesian model averaging; deep neural network; sea ice concentration
Kim, So-Young; Bae, Soo Ya; Park, Rae-Seol; Hong, Song-YouKim, S., S. Y. Bae, R. Park, S. Hong, 2019: Effects of Partial Cloudiness in a Cloud Microphysics Scheme on Simulated Precipitation Processes During a Boreal Summer. Journal of Geophysical Research: Atmospheres, 124(6), 3476-3491. doi: 10.1029/2018JD029519. The effect of partial cloudiness is included in a cloud microphysics scheme, and its impact on precipitation processes is examined through global-model simulations for a boreal summer. An excessive precipitation rate in the simulations is reduced by considering the partial cloudiness effect in microphysical processes, especially in the tropical western Pacific region where convective activity is strong. The reduction of the precipitation rate in this region is mainly due to a decrease in convective precipitation, as the partial cloudiness effect in cloud microphysical processes modulates the convective activity by interacting with radiative processes. Cloud radiative forcings are weaker in the simulations including the partial cloudiness effect, as more cloud water and ice are converted to rain and snow mainly due to enhanced accretion rates. This leads to a decrease in cloud radiative forcing for both shortwave and longwave fluxes, which is overestimated overall over the ocean in the simulations. Temperature is lowered overall as increased longwave radiative cooling overcompensates increased shortwave radiative heating. This reduces the convective available potential energy and results in a decrease in convective precipitation. The weakened instability and upward motion over the tropical western Pacific region due to the partial cloudiness effect not only affect the local precipitation processes in this region but also suppress the downward motion over the tropical eastern Pacific regions by modulating the large-scale zonal circulation over the tropical Pacific ocean.
Kniffka, Anke; Knippertz, Peter; Fink, Andreas H.Kniffka, A., P. Knippertz, A. H. Fink, 2019: The role of low-level clouds in the West African monsoon system. Atmospheric Chemistry and Physics, 19(3), 1623-1647. doi: 10.5194/acp-19-1623-2019. Abstract. Realistically simulating the West African monsoon system still poses a substantial challenge to state-of-the-art weather and climate models. One particular issue is the representation of the extensive and persistent low-level clouds over southern West Africa (SWA) during boreal summer. These clouds are important in regulating the amount of solar radiation reaching the surface, but their role in the local energy balance and the overall monsoon system has never been assessed. Based on sensitivity experiments using the ICON model for July 2006, we show for the first time that rainfall over SWA depends logarithmically on the optical thickness of low clouds, as these control the diurnal evolution of the planetary boundary layer, vertical stability and finally convection. In our experiments, the increased precipitation over SWA has a small direct effect on the downstream Sahel, as higher temperatures due to increased surface radiation are accompanied by decreases in low-level moisture due to changes in advection, leading to almost unchanged equivalent potential temperatures in the Sahel. A systematic comparison of simulations with and without convective parameterization reveals agreement in the direction of the precipitation signal but larger sensitivity for explicit convection. For parameterized convection the main rainband is too far south and the diurnal cycle shows signs of unrealistic vertical mixing, leading to a positive feedback on low clouds. The results demonstrate that relatively minor errors, variations or trends in low-level cloudiness over SWA can have substantial impacts on precipitation. Similarly, they suggest that the dimming likely associated with an increase in anthropogenic emissions in the future would lead to a decrease in summer rainfall in the densely populated Guinea coastal area. Future work should investigate longer-term effects of the misrepresentation of low clouds in climate models, e.g. moderated through effects on rainfall, soil moisture and evaporation.
Kramer, Ryan J.; Matus, Alexander V.; Soden, Brian J.; L'Ecuyer, Tristan S.Kramer, R. J., A. V. Matus, B. J. Soden, T. S. L'Ecuyer, 2019: Observation-Based Radiative Kernels From CloudSat/CALIPSO. Journal of Geophysical Research: Atmospheres, 124(10), 5431-5444. doi: 10.1029/2018JD029021. Radiative kernels describe the differential response of radiative fluxes to small perturbations in state variables and are widely used to quantify radiative feedbacks on the climate system. Radiative kernels have traditionally been generated using simulated data from a global climate model, typically sourced from the model's base climate. Consequently, these radiative kernels are subject to model bias from the climatological fields used to produce them. Here, we introduce the first observation-based temperature, water vapor, and surface albedo radiative kernels, developed from CloudSat's fluxes and heating rates data set, 2B-FLXHR-LIDAR, which is supplemented with cloud information from the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). We compare the radiative kernels to a previously published set generated from the Geophysical Fluid Dynamics Laboratory (GFDL) model and find general agreement in magnitude and structure. However, several key differences illustrate the sensitivity of radiative kernels to the distribution of clouds. The radiative kernels are used to quantify top-of-atmosphere and surface cloud feedbacks in an ensemble of global climate models from the Climate Model Intercomparison Project Phase 5, showing that biases in the GFDL low clouds likely cause the GFDL kernel to underestimate longwave surface cloud feedback. Since the CloudSat kernels are free of model bias in the base state, they will be ideal for future analysis of radiative feedbacks and forcing in both models and observations and for evaluating biases in model-derived radiative kernels. cloud feedback; remote sensing; cloud distribution; cloud masking; radiative kernel
Kubar, Terence L.; Jiang, Jonathan H.Kubar, T. L., J. H. Jiang, 2019: Net Cloud Thinning, Low-Level Cloud Diminishment, and Hadley Circulation Weakening of Precipitating Clouds with Tropical West Pacific SST Using MISR and Other Satellite and Reanalysis Data. Remote Sensing, 11(10), 1250. doi: 10.3390/rs11101250. Daily gridded Multi-Angle Imaging Spectroradiometer (MISR) satellite data are used in conjunction with CERES, TRMM, and ERA-Interim reanalysis data to investigate horizontal and vertical high cloud structure, top-of-atmosphere (TOA) net cloud forcing and albedo, and dynamics relationships against local SST and precipitation as a function of the mean Tropical West Pacific (TWP; 120°E to 155°W; 30°S–30°N) SST. As the TWP warms, the SST mode (~29.5 °C) is constant, but the area of the mode grows, indicating increased kurtosis of SSTs and decreased SST gradients overall. This is associated with weaker low-level convergence and mid-tropospheric ascent (ω500) over the highest SSTs as the TWP warms, but also a broader area of weak ascent away from the deepest convection, albeit stronger when compared to when the mean TWP is cooler. These associated dynamics changes are collocated with less anvil and thick cloud cover over the highest SSTs and similar thin cold cloud fraction when the TWP is warmer, but broadly more anvil and cirrus clouds over lower local SSTs (SST < 27 °C). For all TWP SST quintiles, anvil cloud fraction, defined as clouds with tops > 9 km and TOA albedos between 0.3–0.6, is closely associated with rain rate, making it an excellent proxy for precipitation; but for a given heavier rain rate, cirrus clouds are more abundant with increasing domain-mean TWP SST. Clouds locally over SSTs between 29–30 °C have a much less negative net cloud forcing, up to 25 W m−2 greater, when the TWP is warm versus cool. When the local rain rate increases, while the net cloud fraction with tops < 9 km decreases, mid-level clouds (4 km < Ztop < 9 km) modestly increase. In contrast, combined low-level and mid-level clouds decrease as the domain-wide SST increases (−10% deg−1). More cirrus clouds for heavily precipitating systems exert a stronger positive TOA effect when the TWP is warmer, and anvil clouds over a higher TWP SST are less reflective and have a weaker cooling effect. For all precipitating systems, total high cloud cover increases modestly with higher TWP SST quintiles, and anvil + cirrus clouds are more expansive, suggesting more detrainment when TWP SSTs are higher. Total-domain anvil cloud fraction scales mostly with domain-mean ω500, but cirrus clouds mostly increase with domain-mean SST, invoking an explanation other than circulation. The overall thinning and greater top-heaviness of clouds over the TWP with warming are possible TWP positive feedbacks not previously identified. cloud fraction; cloud radiative forcing; cloud feedbacks; precipitation; remote sensing; tropical convection
Kumar, Amit; Singh, Virendra; Mukherjee, Sunil; Singh, RandhirKumar, A., V. Singh, S. Mukherjee, R. Singh, 2019: Quality assessment of Outgoing Longwave Radiation (OLR) derived from INSAT-3D Imager: Impact of GSICS correction. Mausam, 70(2), 309-320. The INSAT-3D Outgoing longwave radiation (OLR), a fast-delivery level-2 product at pixel resolution, is being generated operationally from every half hourly acquisition of Imager Payload of INSAT-3D. In addition to this, binned daily and monthly OLR products are also generated. The OLR is estimated from the radiance observations in the infrared windows (TIR1: 10.3-11.3 mu m, TIR2: 11.5-12.5 mu m) and water vapor (WV: 6.5-7.1 mu m) channels of INSAT-3D Imager. In the present study, OLR estimated using the INSAT-3D Imager radiance observation is validated with the CERES (Cloud and Earth's Radiant Energy System; on board NPP satellite) from February, 2014 to December, 2017. For the uniform scenes, OLR estimated using INSAT-3D Imager radiance is of good quality with mean CC 0.93, bias -5.03 Wm(-2) & RMSD 10.39 Wm(-)(2) and it could be used in the various applications studies. validation; Validation; assimilation; ceres; diurnal-variation; erbe; insat-3d; olr
Lee, Wei-Liang; Li, Jui-Lin Frank; Xu, Kuan-Man; Suhas, Ettamal; Jiang, Jonathan H.; Wang, Yi-Hui; Stephens, Graeme; Fetzer, Eric; Yu, Jia-YuhLee, W., J. F. Li, K. Xu, E. Suhas, J. H. Jiang, Y. Wang, G. Stephens, E. Fetzer, J. Yu, 2019: Relating Precipitating Ice Radiative Effects to Surface Energy Balance and Temperature Biases Over the Tibetan Plateau in Winter. Journal of Geophysical Research: Atmospheres, 124(23), 12455-12467. doi: 10.1029/2018JD030204. Key Points Surface temperature bias is primarily determined by biases of surface radiative fluxes Underestimated ice water path in models is related to radiation deficiency and cold bias over the Tibetan Plateau in winter Precipitating ice radiative effects are responsible for some reduction of biases in surface radiative fluxes and temperature Tibetan Plateau; CMIP5; snow radiative effect
Lee, Wei-Liang; Liou, Kuo-Nan; Wang, Chia-chi; Gu, Yu; Hsu, Huang-Hsiung; Li, Jui-Lin F.Lee, W., K. Liou, C. Wang, Y. Gu, H. Hsu, J. F. Li, 2019: Impact of 3-D Radiation-Topography Interactions on Surface Temperature and Energy Budget Over the Tibetan Plateau in Winter. Journal of Geophysical Research: Atmospheres, 24(3), 1537-1549. doi: 10.1029/2018JD029592. We incorporate a parameterization to quantify the effect of three-dimensional (3-D) radiation-topography interactions on the solar flux absorbed by the surfaces, including multiple reflections between surfaces and differences in sunward/shaded slopes, in the Community Climate System Model version 4 (CCSM4). A sensitivity experiment is carried out using CCSM4 with the prescribed sea surface temperature for year 2000 to investigate its impact on energy budget and surface temperature over the Tibetan Plateau (TP). The results show that the topographic effect reduces the upward surface shortwave flux and, at the same time, enhance snowmelt rate over the central and southern parts of TP. Comparing to observations and the ensemble of Coupled Model Intercomparison Project Phase 5 (CMIP5), we found that CMIP5 models have a strong cold bias of 3.9 K over TP, partially induced by the strong reflection of shortwave fluxes. We show that the inclusion of topographic effect reduces the substantial biases of upward shortwave fluxes and surface air temperatures over TP by 13% in the CCSM4 model. Tibetan Plateau; CMIP5; 3-D radiative transfer; topographic effect
Lehmann, Peter; Berli, Markus; Koonce, Jeremy E.; Or, DaniLehmann, P., M. Berli, J. E. Koonce, D. Or, 2019: Surface Evaporation in Arid Regions: Insights From Lysimeter Decadal Record and Global Application of a Surface Evaporation Capacitor (SEC) Model. Geophysical Research Letters, 46(16), 9648-9657. doi: 10.1029/2019GL083932. Surface evaporation in arid regions determines the fraction of rainfall that remains to support vegetation and recharge. The surface evaporation capacitor approach was used to estimate rainfall partitioning to surface evaporation and leakage into deeper layers. The surface evaporation capacitor estimates a soil-specific surface evaporation depth and critical storage capacitance that defines rainfall events that exceed local capacitance and result in leakage into deeper layers protected from surface evaporation. A decade-long record of hydrologic observations in deep and barren lysimeters near Las Vegas revealed the dominance of a few large rainfall events in generating leakage and increasing interannual soil water storage. The surface evaporation capacitor was used to estimate mean annual surface evaporation and leakage protected from surface evaporation in all arid regions globally. About 13% of arid region rainfall contributes to soil water storage (in the absence of vegetation), similar to 11% found in the lysimeter study. water balance; evaporation; aridity; redistribution
Lemburg, Alexander; Bader, Jürgen; Claussen, MartinLemburg, A., J. Bader, M. Claussen, 2019: Sahel rainfall – Tropical Easterly Jet relationship on synoptic to intraseasonal time scales. Mon. Wea. Rev., 147, 1733–1752. doi: 10.1175/MWR-D-18-0254.1. The Tropical Easterly Jet (TEJ) is a characteristic upper-level feature of the West African Monsoon (WAM) circulation. Moreover, the TEJ over West Africa is significantly correlated with summer Sahel rainfall on interannual and decadal time scales. In contrast, the relationship between Sahel rainfall and the regional TEJ on synoptic to intraseasonal time scales is unclear. Therefore, this relationship is investigated by means of multiple statistical analyses using temporally highly resolved measurement and reanalysis data. It is shown that average correlations between convective activity and regional TEJ intensity remain below 0.3 for all synoptic to intraseasonal time scales. Especially on the synoptic time scale, the TEJ significantly lags anomalies in convective activity by one or two days which indicates that convection anomalies are more likely to drive changes in the regional TEJ than vice versa. To further shed light on the role of the TEJ for rainfall over West Africa, a previously proposed effect of TEJ-induced upper-level divergence on the development of mesoscale convective systems (MCS) is examined more closely. An analysis of nearly 300 Sahelian MCSs shows that their initiation is generally not associated with significant TEJ anomalies or jet-induced upper-level divergence. Furthermore, no statistically significant evidence is found that preexisting TEJ-related upper-level divergence anomalies affect intensity, size and lifetime of MCSs. A limiting factor of this study is the focus on TEJinduced upper-level divergence. Therefore, a possible effect of the TEJ on Sahel rainfall via other mechanisms cannot be ruled out and should be subject to future studies.
Li, Jiandong; Wang, Wei-Chyung; Mao, Jiangyu; Wang, Ziqian; Zeng, Gang; Chen, GuoxingLi, J., W. Wang, J. Mao, Z. Wang, G. Zeng, G. Chen, 2019: Persistent Spring Shortwave Cloud Radiative Effect and the Associated Circulations over Southeastern China. J. Climate, 32(11), 3069-3087. doi: 10.1175/JCLI-D-18-0385.1. Clouds strongly modulate regional radiation balance and their evolution is profoundly influenced by circulations. This study uses 2001–16 satellite and reanalysis data together with regional model simulations to investigate the spring shortwave cloud radiative effect (SWCRE) and the associated circulations over southeastern China (SEC). Strong SWCRE, up to −110 W m−2, persists throughout springtime in this region and its spring mean is the largest among the same latitudes of the Northern Hemisphere. SWCRE exhibits pronounced subseasonal variation and is closely associated with persistent regional ascending motion and moisture convergence, which favor large amounts of cloud liquid water and resultant strong SWCRE. Around pentad 12 (late February), SWCRE abruptly increases and afterward remains stable between 22° and 32°N. The thermal and dynamic effects of Tibetan Plateau and westerly jet provide appropriate settings for the maintenance of ascending motion, while water vapor, as cloud water supply, stably comes from the southern flank of the Tibetan Plateau and South China Sea. During pentads 25–36 (early May to late June), SWCRE is further enhanced by the increased water vapor transport caused by the march of East Asian monsoon systems, particularly after the onset of the South China Sea monsoon. After pentad 36, these circulations quickly weaken and the SWCRE decreases accordingly. Individual years with spring strong and weak rainfall are chosen to highlight the importance of the strength of the ascending motion. The simulation broadly reproduced the observed results, although biases exist. Finally, the model biases in SWCRE–circulation associations are discussed.
Li, Jui-Lin Frank; Richardson, Mark; Lee, Wei-Liang; Fetzer, Eric; Stephens, Graeme; Jiang, Jonathan; Hong, Yulan; Wang, Yi-Hui; Yu, Jia-Yuh; Liu, YinghuiLi, J. F., M. Richardson, W. Lee, E. Fetzer, G. Stephens, J. Jiang, Y. Hong, Y. Wang, J. Yu, Y. Liu, 2019: Potential faster Arctic sea ice retreat triggered by snowflakes' greenhouse effect. The Cryosphere, 13(3), 969-980. doi: https://doi.org/10.5194/tc-13-969-2019. Abstract. Recent Arctic sea ice retreat has been quicker than in most general circulation model (GCM) simulations. Internal variability may have amplified the observed retreat in recent years, but reliable attribution and projection requires accurate representation of relevant physics. Most current GCMs do not fully represent falling ice radiative effects (FIREs), and here we show that the small set of Coupled Model Intercomparison Project Phase 5 (CMIP5) models that include FIREs tend to show faster observed retreat. We investigate this using controlled simulations with the CESM1-CAM5 model. Under 1pctCO2 simulations, including FIREs results in the first occurrence of an “ice-free” Arctic (monthly mean extent <1×106 km2) at 550 ppm CO2, compared with 680 ppm otherwise. Over 60–90∘ N oceans, snowflakes reduce downward surface shortwave radiation and increase downward surface longwave radiation, improving agreement with the satellite-based CERES EBAF-Surface dataset. We propose that snowflakes' equivalent greenhouse effect reduces the mean sea ice thickness, resulting in a thinner pack whose retreat is more easily triggered by global warming. This is supported by the CESM1-CAM5 surface fluxes and a reduced initial thickness in perennial sea ice regions by approximately 0.3 m when FIREs are included. This explanation does not apply across the CMIP5 ensemble in which inter-model variation in the simulation of other processes likely dominates. Regardless, we show that FIRE can substantially change Arctic sea ice projections and propose that better including falling ice radiative effects in models is a high priority.
Li, R. L.; Storelvmo, T.; Fedorov, A. V.; Choi, Y.-S.Li, R. L., T. Storelvmo, A. V. Fedorov, Y. Choi, 2019: A Positive Iris Feedback: Insights from Climate Simulations with Temperature-Sensitive Cloud–Rain Conversion. J. Climate, 32(16), 5305-5324. doi: 10.1175/JCLI-D-18-0845.1. Estimates for equilibrium climate sensitivity from current climate models continue to exhibit a large spread, from 2.1 to 4.7 K per carbon dioxide doubling. Recent studies have found that the treatment of precipitation efficiency in deep convective clouds—specifically the conversion rate from cloud condensate to rain Cp—may contribute to the large intermodel spread. It is common for convective parameterization in climate models to carry a constant Cp, although its values are model and resolution dependent. In this study, we investigate how introducing a potential iris feedback, the cloud–climate feedback introduced by parameterizing Cp to increase with surface temperature, affects future climate simulations within a slab ocean configuration of the Community Earth System Model. Progressively stronger dependencies of Cp on temperature unexpectedly increase the equilibrium climate sensitivity monotonically from 3.8 to up to 4.6 K. This positive iris feedback puzzle, in which a reduction in cirrus clouds increases surface temperature, is attributed to changes in the opacity of convectively detrained cirrus. Cirrus clouds reduced largely in ice content and marginally in horizontal coverage, and thus the positive shortwave cloud radiative feedback dominates. The sign of the iris feedback is robust across different cloud macrophysics schemes, which control horizontal cloud cover associated with detrained ice. These results suggest a potentially strong but highly uncertain connection among convective precipitation, detrained anvil cirrus, and the high cloud feedback in a climate forced by increased atmospheric carbon dioxide concentrations.
Liu, Yuzhi; Hua, Shan; Jia, Rui; Huang, JianpingLiu, Y., S. Hua, R. Jia, J. Huang, 2019: Effect of Aerosols on the Ice Cloud Properties Over the Tibetan Plateau. Journal of Geophysical Research: Atmospheres, 124(16), 9594-9608. doi: 10.1029/2019JD030463. With the highlight of environmental problems over the Tibetan Plateau (TP), aerosol pollution and the influence of this pollution on cloud properties are becoming a new area of research. Based on the aerosol index and cloud property parameters derived from satellite observations, in this study, the inconsistent effects of aerosols on ice cloud properties between daytime and nighttime over the TP are investigated. The results indicate that ice clouds are mainly distributed over the TP margin area, especially over the north slope, during both daytime and nighttime. The occurrence frequency of ice cloud is higher during the daytime than during the nighttime over the margin areas of the TP. Similarly, aerosols are mainly concentrated over the northern margin of the TP. A potential relationship may exist between the aerosol index and ice cloud properties. When the aerosol index increases from 0.05 to 0.17, the ice cloud droplet radius (ICDR) during the daytime decreases from 32.1 to 27.9 μm, while the ICDR during the nighttime remains almost constant (approximately 25 μm); furthermore, the ice water path (IWP) during the daytime decreases slightly due to the saturation effect, while the nocturnal IWP increases significantly. The changes in ice cloud optical depth (ICOD) during daytime and nighttime show significant and completely opposite trends. The removal of the influence of meteorological factors showed that aerosols have a more dominant influence than meteorological conditions on ice cloud properties (except for the nocturnal ICDR and IWP during the daytime). aerosol; ice cloud; Tibetan Plateau; cloud droplet radius; cloud optical property
Liu, Yuzhi; Tang, Yuhan; Hua, Shan; Luo, Run; Zhu, QingzheLiu, Y., Y. Tang, S. Hua, R. Luo, Q. Zhu, 2019: Features of the Cloud Base Height and Determining the Threshold of Relative Humidity over Southeast China. Remote Sensing, 11(24), 2900. doi: 10.3390/rs11242900. Clouds play a critical role in adjusting the global radiation budget and hydrological cycle; however, obtaining accurate information on the cloud base height (CBH) is still challenging. In this study, based on Lidar and aircraft soundings, we investigated the features of the CBH and determined the thresholds of the environmental relative humidity (RH) corresponding to the observed CBHs over Southeast China from October 2017 to September 2018. During the observational period, the CBHs detected by Lidar/aircraft were commonly higher in cold months and lower in warm months; in the latter, 75.91% of the CBHs were below 2000 m. Overall, the RHs at the cloud base were mainly distributed between 70 and 90% for the clouds lower than 1000 m, in which the most concentrated RH was approximately 80%. In addition, for the clouds with a cloud base higher than 1000 m, the RH thresholds decreased dramatically with increasing CBH, where the RH thresholds at cloud bases higher than 2000 m could be lower than 60%. On average, the RH thresholds for determining the CBHs were the highest (72.39%) and lowest (63.56%) in the summer and winter, respectively, over Southeast China. Therefore, to determine the CBH, a specific threshold of RH is needed. Although the time period covered by the collected CBH data from Lidar/aircraft is short, the above analyses can provide some verification and evidence for using the RH threshold to determine the CBH. cloud base height; ground-based observations; relative humidity profile; threshold
Liu, Yuzhi; Zhu, Qingzhe; Huang, Jianping; Hua, Shan; Jia, RuiLiu, Y., Q. Zhu, J. Huang, S. Hua, R. Jia, 2019: Impact of dust-polluted convective clouds over the Tibetan Plateau on downstream precipitation. Atmospheric Environment, 209, 67-77. doi: 10.1016/j.atmosenv.2019.04.001. Based on satellite observations and reanalysis datasets, this study focuses on the effect of aerosols on clouds over the Tibetan Plateau (TP) and the impact of dust-polluted convective clouds on precipitation over downstream regions. A heavy dust event is detected by Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) over the northern slope of the TP on 16 July and 17 July 2016. The high aerosol optical depth (AOD) values are mainly distributed over the northern slope of the TP. Simultaneously, the CloudSat satellite observes deep convective clouds over the northern slope area of the TP, in which convective clouds and dust mix at the same height. With the AOD increasing from 16 July to its peak on 17 July, the ice particle size decreases to a minimum, and convective clouds develop at higher heights because of the prolonged cloud life. Accordingly, a larger ice water path (IWP) is induced by the development of convective clouds that move eastwardly from 16 to 17 July. In the following days, under favorable meteorological conditions, some of the developed convective clouds continuously move eastward and merge with the convective cloud clusters along the motion path, which induces significant precipitation over the Yangtze River basin on 17 July. Furthermore, driven by the northward wind, some developed convective cloud clusters move northward and induce strong precipitation over North China on 19 July. The indirect effect of dust aerosols over the TP could enhance the plateau's cloud development and potentially contribute to downstream precipitation, which is a meaningful factor for weather forecasting. Precipitation; Aerosols; Tibetan plateau; Convective clouds
Loeb, Norman G.; Wang, Hailan; Rose, Fred G.; Kato, Seiji; Smith, William L.; Sun-Mack, SunnyLoeb, N. G., H. Wang, F. G. Rose, S. Kato, W. L. Smith, S. Sun-Mack, 2019: Decomposing Shortwave Top-of-Atmosphere and Surface Radiative Flux Variations in Terms of Surface and Atmospheric Contributions. J. Climate, 32(16), 5003–501. doi: 10.1175/JCLI-D-18-0826.1. A diagnostic tool for determining surface and atmospheric contributions to interannual variations in top-of-atmosphere (TOA) reflected shortwave (SW) and net downward SW surface radiative fluxes is introduced. The method requires only upward and downward radiative fluxes at the TOA and surface as input and therefore can readily be applied to both satellite-derived and model-generated radiative fluxes. Observations from the Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) Ed4.0 product show that 81% of the monthly variability in global mean reflected SW TOA flux anomalies is associated with atmospheric variations (mainly clouds), 6% is from surface variations, and 13% is from atmosphere-surface covariability. Over the Arctic Ocean, most of the variability in both reflected SW TOA flux and net downward SW surface flux anomalies is explained by variations in sea-ice and cloud fraction alone (r2=0.94). Compared to CERES, variability in two reanalyses—ECMWF Interim Reanalysis (ERA-Interim) and NASA’s Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2)—show large differences in the regional distribution of variance for both the atmospheric and surface contributions to anomalies in net downward SW surface flux. For MERRA-2 the atmospheric contribution is 17% too large compared to CERES while ERA-Interim underestimates the variance by 15%. The difference is mainly due to how cloud variations are represented in the reanalyses. The overall surface contribution in both ERA-Interim and MERRA- 2 is smaller than CERES EBAF by 15% for ERA-Interim and 58% for MERRA-2, highlighting limitations of the reanalyses in representing surface albedo variations and their influence on SW radiative fluxes.
L’Ecuyer, Tristan S.; Hang, Yun; Matus, Alexander V.; Wang, ZhienL’Ecuyer, T. S., Y. Hang, A. V. Matus, Z. Wang, 2019: Reassessing the Effect of Cloud Type on Earth’s Energy Balance in the Age of Active Spaceborne Observations. Part I: Top of Atmosphere and Surface. J. Climate, 32(19), 6197-6217. doi: 10.1175/JCLI-D-18-0753.1. This study revisits the classical problem of quantifying the radiative effects of unique cloud types in the era of spaceborne active observations. The radiative effects of nine cloud types, distinguished based on their vertical structure defined by CloudSat and CALIPSO observations, are assessed at both the top of the atmosphere and the surface. The contributions from single- and multilayered clouds are explicitly diagnosed. The global, annual mean net cloud radiative effect at the top of the atmosphere is found to be −17.1 ± 4.2 W m−2 owing to −44.2 ± 2 W m−2 of shortwave cooling and 27.1 ± 3.7 W m−2 of longwave heating. Leveraging explicit cloud base and vertical structure information, we further estimate the annual mean net cloud radiative effect at the surface to be −24.8 ± 8.7 W m−2 (−51.1 ± 7.8 W m−2 in the shortwave and 26.3 ± 3.8 W m−2 in the longwave). Multilayered clouds are found to exert the strongest influence on the top-of-atmosphere energy balance. However, a strong asymmetry in net cloud radiative cooling between the hemispheres (8.6 W m−2) is dominated by enhanced cooling from stratocumulus over the southern oceans. It is found that there is no corresponding asymmetry at the surface owing to enhanced longwave emission by southern ocean clouds in winter, which offsets a substantial fraction of their impact on solar absorption in summer. Thus the asymmetry in cloud radiative effects is entirely realized as an atmosphere heating imbalance between the hemispheres.
Maher, Nicola; Milinski, Sebastian; Suarez‐Gutierrez, Laura; Botzet, Michael; Dobrynin, Mikhail; Kornblueh, Luis; Kröger, Jürgen; Takano, Yohei; Ghosh, Rohit; Hedemann, Christopher; Li, Chao; Li, Hongmei; Manzini, Elisa; Notz, Dirk; Putrasahan, Dian; Boysen, Lena; Claussen, Martin; Ilyina, Tatiana; Olonscheck, Dirk; Raddatz, Thomas; Stevens, Bjorn; Marotzke, JochemMaher, N., S. Milinski, L. Suarez‐Gutierrez, M. Botzet, M. Dobrynin, L. Kornblueh, J. Kröger, Y. Takano, R. Ghosh, C. Hedemann, C. Li, H. Li, E. Manzini, D. Notz, D. Putrasahan, L. Boysen, M. Claussen, T. Ilyina, D. Olonscheck, T. Raddatz, B. Stevens, J. Marotzke, 2019: The Max Planck Institute Grand Ensemble: Enabling the Exploration of Climate System Variability. Journal of Advances in Modeling Earth Systems, 11(7), 2050-2069. doi: 10.1029/2019MS001639. The Max Planck Institute Grand Ensemble (MPI-GE) is the largest ensemble of a single comprehensive climate model currently available, with 100 members for the historical simulations (1850–2005) and four forcing scenarios. It is currently the only large ensemble available that includes scenario representative concentration pathway (RCP) 2.6 and a 1% CO2 scenario. These advantages make MPI-GE a powerful tool. We present an overview of MPI-GE, its components, and detail the experiments completed. We demonstrate how to separate the forced response from internal variability in a large ensemble. This separation allows the quantification of both the forced signal under climate change and the internal variability to unprecedented precision. We then demonstrate multiple ways to evaluate MPI-GE and put observations in the context of a large ensemble, including a novel approach for comparing model internal variability with estimated observed variability. Finally, we present four novel analyses, which can only be completed using a large ensemble. First, we address whether temperature and precipitation have a pathway dependence using the forcing scenarios. Second, the forced signal of the highly noisy atmospheric circulation is computed, and different drivers are identified to be important for the North Pacific and North Atlantic regions. Third, we use the ensemble dimension to investigate the time dependency of Atlantic Meridional Overturning Circulation variability changes under global warming. Last, sea level pressure is used as an example to demonstrate how MPI-GE can be utilized to estimate the ensemble size needed for a given scientific problem and provide insights for future ensemble projects. internal variability; forced response; large ensemble; MPI-GE
Maldonado, Walter; Valeriano, Taynara Tuany Borges; de Souza Rolim, GlaucoMaldonado, W., T. T. B. Valeriano, G. de Souza Rolim, 2019: EVAPO: A smartphone application to estimate potential evapotranspiration using cloud gridded meteorological data from NASA-POWER system. Computers and Electronics in Agriculture, 156, 187-192. doi: 10.1016/j.compag.2018.10.032. In this study a new android app for smartphones to estimate potential evapotranspuration (PET) in real time, using gridded data from NASA-POWER, to any location in the world, would result in a more efficient irrigation and increase irrigation water conservation. The smartphone app called EVAPO uses meteorological data to calculate PET using the Penman–Monteith (FAO56) method. To evaluate performance of the proposed method, we compared PET estimated by the EVAPO with that estimated from climatic data from conventional surface meteorological stations. The accuracy, tendency and precision of the models were determined using the Willmott et al. (1985) concordance index (d), systematic root mean square error (RMSEs) and determination index (R2), respectively. The results obtained were satisfactory for all studied locations whit mean values of 0.67, 0.95 (mm) and 0.72 for d, RMSEs and R2, respectively. The app can be accessed in the Play Store (free): https://play.google.com/store/apps/details?id=br.com.maldonado.instantet0. Big data; Internet of things; Irrigation; Rational use of water
Maloney, Christopher; Bardeen, Charles; Toon, Owen Brian; Jensen, Eric; Woods, Sarah; Thornberry, Troy; Pfister, Leonhard; Diskin, Glenn; Bui, Thao PaulMaloney, C., C. Bardeen, O. B. Toon, E. Jensen, S. Woods, T. Thornberry, L. Pfister, G. Diskin, T. P. Bui, 2019: An Evaluation of the Representation of Tropical Tropopause Cirrus in the CESM/CARMA Model Using Satellite and Aircraft Observations. Journal of Geophysical Research: Atmospheres, 124(15), 8659-8687. doi: 10.1029/2018JD029720. Observations from the third campaign of the National Aeronautics and Space Administration Airborne Tropical Tropopause Experiment (ATTREX 3) field mission and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations satellite mission are used to evaluate simulations of tropical tropopause layer (TTL) cirrus clouds in the Community Earth System Model's (CESM) Community Atmosphere Model, CAM5. In this study, CAM5 is coupled with a sectional ice cloud model, the Community Aerosol and Radiation Model for Atmospheres (CARMA). We find that both model variants underrepresent cloud frequency along the ATTREX 3 flight path and both poorly represent relative humidity in the TTL. Furthermore, simulated in-cloud ice size distributions contained erroneous amounts of ice crystals throughout the distribution. In response, we present a modified ice cloud fraction scheme that boosts the cloud fraction within the TTL. Due to coarse vertical model resolution in the TTL, we also prescribe a 2-K decrease in cold point tropopause temperatures to better align with observed temperatures. Our modifications improve both CAM5 and CAM5/CARMA's in-cloud ice size and mass distributions. However, only CAM5/CARMA has a significant improvement in cloud frequency and relative humidity. An investigation of cloud extinction in the ATTREX 3 region found that each model variant struggles to reproduce observed extinctions. As a first-order approximation, we introduce randomly generated temperature perturbations to simulate the effect of gravity waves into the CAM5/CARMA simulation. These gravity waves significantly increase the incidence of low extinction ( ice clouds; CARMA; cirrus; CESM; ATTREX; tropical tropopause layer
Mauritsen, Thorsten; Bader, Jürgen; Becker, Tobias; Behrens, Jörg; Bittner, Matthias; Brokopf, Renate; Brovkin, Victor; Claussen, Martin; Crueger, Traute; Esch, Monika; Fast, Irina; Fiedler, Stephanie; Fläschner, Dagmar; Gayler, Veronika; Giorgetta, Marco; Goll, Daniel S.; Haak, Helmuth; Hagemann, Stefan; Hedemann, Christopher; Hohenegger, Cathy; Ilyina, Tatiana; Jahns, Thomas; Jimenéz‐de‐la‐Cuesta, Diego; Jungclaus, Johann; Kleinen, Thomas; Kloster, Silvia; Kracher, Daniela; Kinne, Stefan; Kleberg, Deike; Lasslop, Gitta; Kornblueh, Luis; Marotzke, Jochem; Matei, Daniela; Meraner, Katharina; Mikolajewicz, Uwe; Modali, Kameswarrao; Möbis, Benjamin; Müller, Wolfgang A.; Nabel, Julia E. M. S.; Nam, Christine C. W.; Notz, Dirk; Nyawira, Sarah-Sylvia; Paulsen, Hanna; Peters, Karsten; Pincus, Robert; Pohlmann, Holger; Pongratz, Julia; Popp, Max; Raddatz, Thomas Jürgen; Rast, Sebastian; Redler, Rene; Reick, Christian H.; Rohrschneider, Tim; Schemann, Vera; Schmidt, Hauke; Schnur, Reiner; Schulzweida, Uwe; Six, Katharina D.; Stein, Lukas; Stemmler, Irene; Stevens, Bjorn; Storch, Jin-Song von; Tian, Fangxing; Voigt, Aiko; Vrese, Philipp; Wieners, Karl-Hermann; Wilkenskjeld, Stiig; Winkler, Alexander; Roeckner, ErichMauritsen, T., J. Bader, T. Becker, J. Behrens, M. Bittner, R. Brokopf, V. Brovkin, M. Claussen, T. Crueger, M. Esch, I. Fast, S. Fiedler, D. Fläschner, V. Gayler, M. Giorgetta, D. S. Goll, H. Haak, S. Hagemann, C. Hedemann, C. Hohenegger, T. Ilyina, T. Jahns, D. Jimenéz‐de‐la‐Cuesta, J. Jungclaus, T. Kleinen, S. Kloster, D. Kracher, S. Kinne, D. Kleberg, G. Lasslop, L. Kornblueh, J. Marotzke, D. Matei, K. Meraner, U. Mikolajewicz, K. Modali, B. Möbis, W. A. Müller, J. E. M. S. Nabel, C. C. W. Nam, D. Notz, S. Nyawira, H. Paulsen, K. Peters, R. Pincus, H. Pohlmann, J. Pongratz, M. Popp, T. J. Raddatz, S. Rast, R. Redler, C. H. Reick, T. Rohrschneider, V. Schemann, H. Schmidt, R. Schnur, U. Schulzweida, K. D. Six, L. Stein, I. Stemmler, B. Stevens, J. v. Storch, F. Tian, A. Voigt, P. Vrese, K. Wieners, S. Wilkenskjeld, A. Winkler, E. Roeckner, 2019: Developments in the MPI-M Earth System Model version 1.2 (MPI-ESM1.2) and Its Response to Increasing CO2. Journal of Advances in Modeling Earth Systems, 11(4), 998-1038. doi: 10.1029/2018MS001400. A new release of the Max Planck Institute for Meteorology Earth System Model version 1.2 (MPI-ESM1.2) is presented. The development focused on correcting errors in and improving the physical processes representation, as well as improving the computational performance, versatility, and overall user friendliness. In addition to new radiation and aerosol parameterizations of the atmosphere, several relatively large, but partly compensating, coding errors in the model's cloud, convection, and turbulence parameterizations were corrected. The representation of land processes was refined by introducing a multilayer soil hydrology scheme, extending the land biogeochemistry to include the nitrogen cycle, replacing the soil and litter decomposition model and improving the representation of wildfires. The ocean biogeochemistry now represents cyanobacteria prognostically in order to capture the response of nitrogen fixation to changing climate conditions and further includes improved detritus settling and numerous other refinements. As something new, in addition to limiting drift and minimizing certain biases, the instrumental record warming was explicitly taken into account during the tuning process. To this end, a very high climate sensitivity of around 7 K caused by low-level clouds in the tropics as found in an intermediate model version was addressed, as it was not deemed possible to match observed warming otherwise. As a result, the model has a climate sensitivity to a doubling of CO2 over preindustrial conditions of 2.77 K, maintaining the previously identified highly nonlinear global mean response to increasing CO2 forcing, which nonetheless can be represented by a simple two-layer model. model development; climate sensitivity; coupled climate model
Mayer, Michael; Tietsche, Steffen; Haimberger, Leopold; Tsubouchi, Takamasa; Mayer, Johannes; Zuo, HaoMayer, M., S. Tietsche, L. Haimberger, T. Tsubouchi, J. Mayer, H. Zuo, 2019: An Improved Estimate of the Coupled Arctic Energy Budget. J. Climate, 32(22), 7915-7934. doi: 10.1175/JCLI-D-19-0233.1. This study combines state-of-the-art reanalyses such as the fifth-generation European Re-Analysis (ERA5) and the Ocean Reanalysis System 5 (ORAS5) with novel observational products to present an updated estimate of the coupled atmosphere–ocean–sea ice Arctic energy budget, including flux and storage terms covering 2001–17. Observational products provide independent estimates of crucial budget terms, including oceanic heat transport from unique mooring-derived data, radiative fluxes from satellites, and sea ice volume from merged satellite data. Results show that the time averages of independent estimates of radiative, atmospheric, and oceanic energy fluxes into the Arctic Ocean domain are remarkably consistent in the sense that their sum closely matches the observed rate of regional long-term oceanic heat accumulation of ~1 W m−2. Atmospheric and oceanic heat transports are found to be stronger compared to earlier assessments (~100 and ~16 W m−2, respectively). Data inconsistencies are larger when considering the mean annual cycle of the coupled energy budget, with RMS values of the monthly budget residual between 7 and 15 W m−2, depending on the employed datasets. This nevertheless represents an average reduction of ~72% of the residual compared to earlier work and demonstrates the progress made in data quality and diagnostic techniques. Finally, the budget residual is eliminated using a variational approach to provide a best estimate of the mean annual cycle. The largest remaining sources of uncertainty are ocean heat content and latent heat associated with sea ice melt and freeze, which both suffer from the lack of observational constraints. More ocean in situ observations and reliable sea ice thickness observations and their routinely assimilation into reanalyses are needed to further reduce uncertainty.
McTaggart‐Cowan, R.; Vaillancourt, P. A.; Zadra, A.; Chamberland, S.; Charron, M.; Corvec, S.; Milbrandt, J. A.; Paquin‐Ricard, D.; Patoine, A.; Roch, M.; Separovic, L.; Yang, J.McTaggart‐Cowan, R., P. A. Vaillancourt, A. Zadra, S. Chamberland, M. Charron, S. Corvec, J. A. Milbrandt, D. Paquin‐Ricard, A. Patoine, M. Roch, L. Separovic, J. Yang, 2019: Modernization of Atmospheric Physics Parameterization in Canadian NWP. Journal of Advances in Modeling Earth Systems, 11(11), 3593-3635. doi: 10.1029/2019MS001781. Atmospheric physics is represented in numerical models by parameterizations that use resolved-scale information to estimate the effects of physical processes on the atmospheric state. Over time, our understanding of these processes improves, new techniques are introduced to represent physics in a numerical model, and increased resolution changes the relative importance of different parameterizations within the system. As a result, the physical parameterization packages of numerical weather prediction (NWP) models undergo regular updates as older schemes are replaced with newer ones that offer an improved, and often more complex, depiction of relevant physical processes. Such changes are typically combined with a rebalancing of the physics suite because of strong interactions between parameterization schemes and the presence of compensating errors in the system. In this study, a major update to the package of physical parameterizations used in Canadian operational NWP is introduced. The primary goals of this effort were to improve the global energy budget and to facilitate an increase in the vertical resolution of operational configurations. Both of these objectives were achieved, along with a significant improvement in guidance quality for global and regional prediction systems. atmospheric physics; forecast evaluation; numerical weather prediction; physical parameterization; physical processes
Meyssignac, Benoit; Boyer, Tim; Zhao, Zhongxiang; Hakuba, Maria Z.; Landerer, Felix W.; Stammer, Detlef; Köhl, Armin; Kato, Seiji; L’Ecuyer, Tristan; Ablain, Michael; Abraham, John Patrick; Blazquez, Alejandro; Cazenave, Anny; Church, John A.; Cowley, Rebecca; Cheng, Lijing; Domingues, Catia M.; Giglio, Donata; Gouretski, Viktor; Ishii, Masayoshi; Johnson, Gregory C.; Killick, Rachel E.; Legler, David; Llovel, William; Lyman, John; Palmer, Matthew Dudley; Piotrowicz, Steve; Purkey, Sarah G.; Roemmich, Dean; Roca, Rémy; Savita, Abhishek; Schuckmann, Karina von; Speich, Sabrina; Stephens, Graeme; Wang, Gongjie; Wijffels, Susan Elisabeth; Zilberman, NathalieMeyssignac, B., T. Boyer, Z. Zhao, M. Z. Hakuba, F. W. Landerer, D. Stammer, A. Köhl, S. Kato, T. L’Ecuyer, M. Ablain, J. P. Abraham, A. Blazquez, A. Cazenave, J. A. Church, R. Cowley, L. Cheng, C. M. Domingues, D. Giglio, V. Gouretski, M. Ishii, G. C. Johnson, R. E. Killick, D. Legler, W. Llovel, J. Lyman, M. D. Palmer, S. Piotrowicz, S. G. Purkey, D. Roemmich, R. Roca, A. Savita, K. v. Schuckmann, S. Speich, G. Stephens, G. Wang, S. E. Wijffels, N. Zilberman, 2019: Measuring Global Ocean Heat Content to Estimate the Earth Energy Imbalance. Frontiers in Marine Science, 6, 432. doi: 10.3389/fmars.2019.00432. The energy radiated by the Earth towards space does not compensate the incoming radiation from the Sun leading to a small positive energy imbalance at the top of the atmosphere (0.4-1.Wm-2). This imbalance is coined Earth’s Energy Imbalance (EEI). It is mostly caused by anthropogenic greenhouse gases emissions and is driving the current warming of the planet. Precise monitoring of EEI is critical to assess the current status of climate change and the future evolution of climate. But the monitoring of EEI is challenging as EEI is two order of magnitude smaller than the radiation fluxes in and out of the Earth. Over 93% of the excess energy that is gained by the Earth in response to the positive EEI accumulates into the ocean in the form of heat. This accumulation of heat can be tracked with the ocean observing system such that today, the monitoring of Ocean Heat Content (OHC) and its long-term change provide the most efficient approach to estimate EEI. In this community paper we review the current four state-of-the-art methods to estimate global OHC changes and evaluate their relevance to derive EEI estimate on different time scales. These four methods make use of : 1) direct observations of in situ temperature; 2) satellite-based measurements of the ocean surface net heat fluxes; 3) satellite-based estimates of the thermal expansion of the ocean and 4) ocean reanalyses that assimilate observations from both satellite and in situ instruments. For each method we review the potential and the uncertainty of the method to estimate global OHC changes. We also analyze gaps in the current capability of each method and identify ways of progress for the future to fulfill the requirements of EEI monitoring. Achieving the observation of EEI with sufficient accuracy will depend on merging the remote sensing techniques with in situ measurements of key variables as an integral part of the Ocean Observing System. CERES; altimetry; Earth Energy Imbalance; ARGO; GRACE (Gravity recovery and climate experiment); internal tide tomography; ocean heat content (OHC); Ocean mass; Ocean surface fluxes; Sea level
Michibata, Takuro; Suzuki, Kentaroh; Sekiguchi, Miho; Takemura, ToshihikoMichibata, T., K. Suzuki, M. Sekiguchi, T. Takemura, 2019: Prognostic Precipitation in the MIROC6-SPRINTARS GCM: Description and Evaluation Against Satellite Observations. Journal of Advances in Modeling Earth Systems, 11(3), 839-860. doi: 10.1029/2018MS001596. A comprehensive two-moment microphysics scheme is incorporated into the MIROC6-SPRINTARS general circulation model (GCM). The new scheme includes prognostic precipitation for both rain and snow and considers their radiative effects. To evaluate the impacts of applying different treatments of precipitation and the associated radiative effect, we perform climate simulations employing both the traditional diagnostic and new prognostic precipitation schemes, the latter also being tested with and without incorporating the radiative effect of snow. The prognostic precipitation, which maintains precipitation in the atmosphere across multiple time steps, models the ratio of accretion to autoconversion as being approximately an order of magnitude higher than that for the diagnostic scheme. Such changes in microphysical process rates tend to reduce the cloud water susceptibility as the autoconversion process is the only pathway through which aerosols can influence rain formation. The resultant anthropogenic aerosol effect is reduced by approximately 21% in the prognostic precipitation scheme. Modifications to the microphysical process rates also change the vertical distribution of hydrometeors in the manner that increases the fractional occurrence of single-layered warm clouds by 38%. The new scheme mitigates the excess of supercooled liquid water produced by the previous scheme and increases the total mass of ice hydrometeors. Both characteristics are consistent with CloudSat/CALIPSO retrievals. The radiative effect of snow is significant at both longwave and shortwave (6.4 and 5.1 W/m2 in absolute values, respectively) and can alter the precipitation fields via energetic controls on precipitation. These results suggest that the prognostic precipitation scheme, with its radiative effects incorporated, makes an indispensable contribution to improving the reliability of climate modeling. microphysics; climate; GCM; aerosol-cloud-precipitation interactions; prognostic precipitation
Middlemas, Eleanor A.; Clement, Amy C.; Medeiros, Brian; Kirtman, BenMiddlemas, E. A., A. C. Clement, B. Medeiros, B. Kirtman, 2019: Cloud radiative feedbacks and El Niño Southern Oscillation. J. Climate, 32(15), 4661-4680. doi: 10.1175/JCLI-D-18-0842.1. Cloud radiative feedbacks are disabled via “cloud-locking” in the Community Earth System Model, version 1.2, (CESM1.2) to result in a shift in El Niño Southern Oscillation (ENSO) periodicity from 2-7 years to decadal timescales. We hypothesize that cloud radiative feedbacks may impact the periodicity in three ways: by (1) modulating heat flux locally into the equatorial Pacific subsurface through negative shortwave cloud feedback on sea surface temperature anomalies (SSTA), (2) damping the persistence of subtropical Southeast Pacific SSTA such that the South Pacific Meridional Mode impacts the duration of ENSO events, or (3) controlling the meridional width of off-equatorial westerly winds, which impact the periodicity of ENSO by initiating longer Rossby waves. The result of cloud-locking in CESM1.2 contrasts that of another study which found that cloud-locking in a different global climate model led to decreased ENSO magnitude across all timescales due to a lack of positive longwave feedback on the anomalous Walker circulation. CESM1.2 contains this positive longwave feedback on the anomalous Walker circulation, but either its influence on the surface is decoupled from ocean dynamics or the feedback is only active on interannual timescales. The role of cloud radiative feedbacks in ENSO in other global climate models are additionally considered. In particular, it is shown that one cannot predict the role of cloud radiative feedbacks in ENSO through a multimodel diagnostic analysis. Instead, they must be directly altered.
Mohino, Elsa; Rodríguez-Fonseca, Belén; Mechoso, C. Roberto; Losada, Teresa; Polo, IreneMohino, E., B. Rodríguez-Fonseca, C. R. Mechoso, T. Losada, I. Polo, 2019: Relationships Among Inter-model Spread and Biases in Tropical Atlantic Sea Surface Temperatures. J. Climate, 32(12), 3615–3635. doi: 10.1175/JCLI-D-18-0846.1. State-of-the-art general circulation models show important systematic errors in their simulation of sea surface temperatures (SST), especially in the Tropical Atlantic. In this work the spread in the simulation of climatological SST in the Tropical Atlantic by 24 CMIP5 models is examined, and its relationship with the mean systematic biases in the region is explored. The modes of inter-model variability are estimated by applying Principal Component (PC) analysis to the SSTs in the region 70°W-20°E, 20°S-20°N. The inter-model variability is approximately explained by the first three modes. The first mode is related to warmer SSTs in the basin, shows worldwide connections with same-signed loads over most of the tropics and is connected with lower low cloud cover over the eastern parts of the subtropical oceans. The second mode is restricted to the Atlantic, where it shows negative and positive loads to the north and south of the equator, respectively, and is connected to a too weak Atlantic Meridional Overturning Circulation (AMOC). The third mode is related to the double Intertropical Convergence Zone bias in the Pacific and to an interhemispheric asymmetry in the net radiation at the top of the atmosphere. The structure of second mode is closer to the mean bias than that of the others in the Tropical Atlantic, suggesting that model difficulties with the AMOC contribute to the regional biases.
Mohrmann, Johannes; Bretherton, Christopher S.; McCoy, Isabel L.; McGibbon, Jeremy; Wood, Robert; Ghate, Virendra; Albrecht, Bruce; Sarkar, Mampi; Zuidema, Paquita; Palikonda, RabindraMohrmann, J., C. S. Bretherton, I. L. McCoy, J. McGibbon, R. Wood, V. Ghate, B. Albrecht, M. Sarkar, P. Zuidema, R. Palikonda, 2019: Lagrangian Evolution of the Northeast Pacific Marine Boundary Layer Structure and Cloud during CSET. Mon. Wea. Rev., 147(12), 4681-4700. doi: 10.1175/MWR-D-19-0053.1. Flight data from the Cloud System Evolution over the Trades (CSET) campaign over the Pacific stratocumulus-to-cumulus transition are organized into 18 Lagrangian cases suitable for study and future modeling, made possible by the use of a track-and-resample flight strategy. Analysis of these cases shows that 2-day Lagrangian coherence of long-lived species (CO and O3) is high (r = 0.93 and 0.73, respectively), but that of subcloud aerosol, MBL depth, and cloud properties is limited. Although they span a wide range in meteorological conditions, most sampled air masses show a clear transition when considering 2-day changes in cloudiness (−31% averaged over all cases), MBL depth (+560 m), estimated inversion strength (EIS; −2.2 K), and decoupling, agreeing with previous satellite studies and theory. Changes in precipitation and droplet number were less consistent. The aircraft-based analysis is augmented by geostationary satellite retrievals and reanalysis data along Lagrangian trajectories between aircraft sampling times, documenting the evolution of cloud fraction, cloud droplet number concentration, EIS, and MBL depth. An expanded trajectory set spanning the summer of 2015 is used to show that the CSET-sampled air masses were representative of the season, with respect to EIS and cloud fraction. Two Lagrangian case studies attractive for future modeling are presented with aircraft and satellite data. The first features a clear Sc–Cu transition involving MBL deepening and decoupling with decreasing cloud fraction, and the second undergoes a much slower cloud evolution despite a greater initial depth and decoupling state. Potential causes for the differences in evolution are explored, including free-tropospheric humidity, subsidence, surface fluxes, and microphysics.
Naegele, A. C.; Randall, D. A.Naegele, A. C., D. A. Randall, 2019: Geographical and Seasonal Variability of Cloud-Radiative Feedbacks on Precipitation. Journal of Geophysical Research: Atmospheres, 124(2), 684-699. doi: 10.1029/2018JD029186. We have used observations to study the temporal covariability of precipitation and atmospheric radiative cooling (ARC, defined as positive when the atmosphere is radiatively cooled) on seasonal and longer time scales. Clouds act to decrease the globally averaged ARC, but their radiative effect on the ARC varies with latitude. Clouds decrease the ARC in the tropics, mainly by reducing the outgoing longwave radiation, but they increase the ARC in higher latitudes, primarily by increasing the downwelling longwave radiation at the surface. The temporal correlation of the zonally averaged precipitation rate and the zonally averaged ARC is about -0.7 in the tropics and +0.5 in higher latitudes, and it changes sign almost discontinuously toward the poles at approximately 30° N and 30° S. This suggests that changes in the ARC feed back negatively on precipitating tropical systems, and positively on precipitating systems at higher latitudes. cloud feedback; precipitation; cloud radiative effects; convective aggregation; hydrologic cycle
Nascimento, Gláucia dos Santos; Ruhoff, Anderson; Cavalcanti, J. Rafael; Marques, David da Motta; Roberti, Débora Regina; da Rocha, Humberto Ribeiro; Munar, Andrés Maurício; Fragoso, Carlos Ruberto; de Oliveira, Maria Betânia LealNascimento, G. d. S., A. Ruhoff, J. R. Cavalcanti, D. d. M. Marques, D. R. Roberti, H. R. da Rocha, A. M. Munar, C. R. Fragoso, M. B. L. de Oliveira, 2019: Assessing CERES Surface Radiation Components for Tropical and Subtropical Biomes. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 12(10), 3826-3840. doi: 10.1109/JSTARS.2019.2939382. An adequate estimate of the radiation components on the earth's surface may help reveal many important interactions between the earth's surface and the atmosphere. In-situ measurements of radiation components are sparse, and remote sensing is one way to overcome this limitation. The clouds and the earth's radiant energy system (CERES) provides a long-term estimate of shortwave and longwave radiation over the entire globe. This article compared and evaluated all components of the surface radiation, estimated using CERES SYN1deg Ed3A and SYN1deg Ed4A data (shortwave up and down, longwave up and down, and photosynthetically active radiation) against measurements for 15 sites located in Brazil. Our results indicated that CERES SYN1deg estimates are accurate for all variables evaluated, with the SYN1deg Ed4A version increasing the 2$ and decreasing the RMSE from the SYN1deg Ed3A version. We also evaluated the main driving factors controlling the variability of the surface radiation components, using cluster analysis and multiple linear regression. The results showed that surface temperature and total precipitable water vapor are the main driving factors affecting the variability of the different radiation components. The results also highlighted the influence of climate conditions and biome features on the estimates of surface radiation components by CERES. The radiation data provided by CERES SYN1deg Ed4A proved to be a promising alternative for large regions where meteorological information is unavailable or sparse. Earth; Remote sensing; Meteorology; Monitoring; Atmospheric measurements; longwave radiation; Atmospheric modeling; Clouds; shortwave radiation; Amazon rain forest; clouds and the earth's radiant energy system (CERES) validation
Naud, Catherine M.; Booth, James F.; Jeyaratnam, Jeyavinoth; Donner, Leo J.; Seman, Charles J.; Zhao, Ming; Guo, Huan; Ming, YiNaud, C. M., J. F. Booth, J. Jeyaratnam, L. J. Donner, C. J. Seman, M. Zhao, H. Guo, Y. Ming, 2019: Extratropical Cyclone Clouds in the GFDL Climate Model: Diagnosing Biases and the Associated Causes. J. Climate, 32(20), 6685-6701. doi: 10.1175/JCLI-D-19-0421.1. The clouds in Southern Hemisphere extratropical cyclones generated by the GFDL climate model are analyzed against MODIS, CloudSat, and CALIPSO cloud and precipitation observations. Two model versions are used: one is a developmental version of “AM4,” a model GFDL that will utilize for CMIP6, and the other is the same model with a different parameterization of moist convection. Both model versions predict a realistic top-of-atmosphere cloud cover in the southern oceans, within 5% of the observations. However, an examination of cloud cover transects in extratropical cyclones reveals a tendency in the models to overestimate high-level clouds (by differing amounts) and underestimate cloud cover at low levels (again by differing amounts), especially in the post–cold frontal (PCF) region, when compared with observations. In focusing only on the models, it is seen that their differences in high and midlevel clouds are consistent with their differences in convective activity and relative humidity (RH), but the same is not true for the PCF region. In this region, RH is higher in the model with less cloud fraction. These seemingly contradictory cloud and RH differences can be explained by differences in the cloud-parameterization tuning parameters that ensure radiative balance. In the PCF region, the model cloud differences are smaller than either of the model biases with respect to observations, suggesting that other physics changes are needed to address the bias. The process-oriented analysis used to assess these model differences will soon be automated and shared.
Or, D.; Lehmann, P.Or, D., P. Lehmann, 2019: Surface Evaporative Capacitance: How Soil Type and Rainfall Characteristics Affect Global-Scale Surface Evaporation. Water Resources Research, 55(1), 519-539. doi: 10.1029/2018WR024050. The separation of evapotranspiration (ET) into its surface evaporation (E) and transpiration (T) components remains a challenge despite its importance for linking water and carbon cycles, for water management, and for attribution of hydrologic isotope fractionation. Regional and global estimates of surface evaporation often rely on estimates of ET (e.g., Penman-Monteith) where E is deduced as a residual or as a fraction of potential evaporation. We propose a novel and direct method for estimating E from soil properties considering regional rainfall characteristics and accounting for internal drainage dynamics. A soil-dependent evaporative characteristic length defines an active surface evaporative capacitor depth below which soil water is sheltered from capillary pull to the evaporating surface. A site-specific evaporative capacitor is periodically recharged by rainfall and discharges at rates determined by interplay between internal drainage and surface evaporation. The surface evaporative capacitor concept was tested using field measurements and subsequently applied to generate a global map of climatic surface evaporation. Latitudinal comparisons with estimates from other global models (e.g., Penman-Monteith method modified by Leuning et al., 2008, https://doi.org/10.1029/2007WR006562 [PML]; Moderate Resolution Imaging Spectroradiometer [MODIS]; and Global Land-surface Evaporation: the Amsterdam Methodology [GLEAM]) show good agreement but also point to potential shortcomings of present estimates of surface evaporation. Interestingly, the ratio of surface evaporation (E) to potential evapotranspiration (ET0) is relatively constant across climates, biomes, and soil types with E/ET0 < 0.15 for 60% of all terrestrial surfaces, in agreement with recent studies. evapotranspiration; evaporation; global data; soil physics
Pagán, Brianna R.; Maes, Wouter H.; Gentine, Pierre; Martens, Brecht; Miralles, Diego G.Pagán, B. R., W. H. Maes, P. Gentine, B. Martens, D. G. Miralles, 2019: Exploring the Potential of Satellite Solar-Induced Fluorescence to Constrain Global Transpiration Estimates. Remote Sensing, 11(4), 413. doi: 10.3390/rs11040413. The opening and closing of plant stomata regulates the global water, carbon and energy cycles. Biophysical feedbacks on climate are highly dependent on transpiration, which is mediated by vegetation phenology and plant responses to stress conditions. Here, we explore the potential of satellite observations of solar-induced chlorophyll fluorescence (SIF)—normalized by photosynthetically-active radiation (PAR)—to diagnose the ratio of transpiration to potential evaporation (‘transpiration efficiency’, τ). This potential is validated at 25 eddy-covariance sites from seven biomes worldwide. The skill of the state-of-the-art land surface models (LSMs) from the eartH2Observe project to estimate τ is also contrasted against eddy-covariance data. Despite its relatively coarse (0.5°) resolution, SIF/PAR estimates, based on data from the Global Ozone Monitoring Experiment 2 (GOME-2) and the Clouds and Earth’s Radiant Energy System (CERES), correlate to the in situ τ significantly (average inter-site correlation of 0.59), with higher correlations during growing seasons (0.64) compared to decaying periods (0.53). In addition, the skill to diagnose the variability of in situ τ demonstrated by all LSMs is on average lower, indicating the potential of SIF data to constrain the formulations of transpiration in global models via, e.g., data assimilation. Overall, SIF/PAR estimates successfully capture the effect of phenological changes and environmental stress on natural ecosystem transpiration, adequately reflecting the timing of this variability without complex parameterizations. eddy-covariance; GOME-2; solar-induced chlorophyll fluorescence; transpiration; transpiration efficiency
Park, Sungsu; Oh, Eunsil; Kim, Siyun; Shin, JihoonPark, S., E. Oh, S. Kim, J. Shin, 2019: Impact of Interactive Vertical Overlap of Cumulus and Stratus on Global Aerosol, Precipitation, and Radiation Processes in the Seoul National University Atmosphere Model Version 0 With a Unified Convection Scheme (SAM0-UNICON). Journal of Advances in Modeling Earth Systems, 11(12), 4016-4043. doi: 10.1029/2019MS001643. The previously proposed parameterization for the integrated vertical overlap of cumulus and stratus is generalized to handle both conventional exponential-random stratus overlap and nonconventional (i.e., other than exponential-random) cumulus overlap in a simultaneous way. With the parameterization of the decorrelation length scale of stratus as a function of vertical wind shear, our parameterization simulates various interactive feedback between vertical cloud overlap and other physical processes. This interactive vertical overlap parameterization of cumulus and stratus was implemented into all relevant physics parameterizations (i.e., convection, stratus microphysics, radiation, aerosol wet deposition, and aerosol activation at the base of stratus) of the Seoul National University Atmosphere Model version 0 with a Unified Convection Scheme (SAM0-UNICON) in a fully consistent way. It is shown that the overall performance of the interactive cloud overlap parameterization to simulate the observed mean climate is similar to that of the original overlap parameterization. Given that an intensive tuning has not yet been performed with the new overlap parameterization, this result is quite encouraging. cloud; overlap; parameterization
Park, Sungsu; Shin, Jihoon; Kim, Siyun; Oh, Eunsil; Kim, YoonjaePark, S., J. Shin, S. Kim, E. Oh, Y. Kim, 2019: Global Climate Simulated by the Seoul National University Atmosphere Model Version 0 with a Unified Convection Scheme (SAM0-UNICON). J. Climate, 32(10), 2917-2949. doi: 10.1175/JCLI-D-18-0796.1. As a contribution to phase 6 of the Coupled Model Intercomparison Project (CMIP6), the global climate simulated by an atmospheric general circulation model (GCM), the Seoul National University Atmosphere Model version 0 with a Unified Convection Scheme (SAM0-UNICON), is compared with observation and climates simulated by the Community Atmosphere Model version 5 (CAM5) and Community Earth System Model version 1 (CESM1), on which SAM0-UNICON is based. Both SAM0-UNICON and CESM1 successfully reproduce observed global warming after 1970. The global mean climate simulated by SAM0-UNICON is roughly similar to that of CAM5/CESM1. However, SAM0-UNICON improves the simulations of the double intertropical convergence zone, shortwave cloud forcing, near-surface air temperature, aerosol optical depth, sea ice fraction, and sea surface temperature (SST), but is slightly poorer for the simulation of tropical relative humidity, Pacific surface wind stress, and ocean rainfall. Two important biases in the simulated mean climate in both models are a set of horseshoe-shaped biases of SST, sea level pressure, precipitation, and cloud radiative forcings in the central equatorial Pacific and a higher sea ice fraction in the Arctic periphery and Southern Hemispheric circumpolar regions. Both SAM0-UNICON and CESM1 simulate the observed El Niño–Southern Oscillation (ENSO) reasonably well. However, compared with CAM5/CESM1, SAM0-UNICON performs better in simulating the Madden–Julian oscillation (MJO), diurnal cycle of precipitation, and tropical cyclones. The aerosol indirect effect (AIE) simulated by SAM0-UNICON is similar to that from CAM5 but the magnitudes of the individual shortwave and longwave AIEs are substantially reduced.
Patel, Piyushkumar N.; Gautam, Ritesh; Michibata, Takuro; Gadhavi, HarishPatel, P. N., R. Gautam, T. Michibata, H. Gadhavi, 2019: Strengthened Indian Summer Monsoon Precipitation Susceptibility Linked to Dust-Induced Ice Cloud Modification. Geophysical Research Letters, 46(14), 8431-8441. doi: 10.1029/2018GL081634. A growing body of research has underscored the radiative impact of mineral dust in influencing Indian summer monsoon rainfall variability. However, the various aerosol-cloud-precipitation interaction mechanisms remain poorly understood. Here we analyze multisatellite observations to examine dust-induced modification in ice clouds and precipitation susceptibility. We show contrasting dust-induced changes in ice cloud regimes wherein despite a 25% reduction in ice particle radius in thin ice clouds, we find 40% increase in ice particle radius and ice water path in thick ice clouds resulting in the cloud deepening and subsequently strengthened precipitation susceptibility, under strong updraft regimes. The observed dust-ice cloud-precipitation interactions are supported by a strong correlation between the interannual monsoon rainfall variability and dust frequency. This microphysical-dynamical coupling appears to provide negative feedback to aerosol-cloud interactions, which acts to buffer enhanced aerosol wet scavenging. Our results underscore the importance of incorporating meteorological regime-dependent dust-ice cloud-precipitation interactions in climate simulations. satellite remote sensing; aerosol-cloud-precipitation interactions; cloud invigoration; dust-ice cloud interactions; dynamical feedback; Indian Monsoon
Peterson, Colten A.; Chen, Xiuhong; Yue, Qing; Huang, XiangleiPeterson, C. A., X. Chen, Q. Yue, X. Huang, 2019: The Spectral Dimension of Arctic Outgoing Longwave Radiation and Greenhouse Efficiency Trends From 2003 to 2016. Journal of Geophysical Research: Atmospheres, 124(15), 8467-8480. doi: 10.1029/2019JD030428. Fourteen years of spectral fluxes derived from collocated Atmospheric Infrared Sounder (AIRS) and Clouds and the Earth's Radiant Energy System (CERES) observations are used in conjunction with AIRS retrievals to examine the trends of zonal mean spectral outgoing longwave radiation (OLR) and greenhouse efficiency (GHE) in the Arctic. AIRS retrieved profiles are fed into a radiative transfer model to generate synthetic clear-sky spectral OLR. Trends are derived from the simulated clear-sky spectral OLR and GHE and then compared with their counterparts derived from collocated observations. Spectral trends in different seasons are distinctively different. March and September exhibit positive trends in spectral OLR over the far-IR dirty window and mid-IR window region for most of the Arctic. In contrast, spectral OLR trends in July are negative over the far-IR dirty window and can be positive or negative in the mid-IR window depending on the latitude. Sensitivity studies reveal that surface temperature contributes much more than atmospheric temperature and humidity to the spectral OLR and GHE trends, while the contributions from the latter two are also discernible over many spectral regions (e.g., trends in the far-IR dirty window in March). The largest increase of spectral GHE is seen north of 80°N in March across the water vapor v2 band and far-IR. When the secular fractional change of spectral OLR is less than that of surface spectral emission, an increase of spectral GHE can be expected. Spectral trend analyses reveal more information than broadband trend analyses alone. outgoing longwave radiation; Arctic climate; greenhouse efficiency; spectral flux
Pistone, Kristina; Eisenman, Ian; Ramanathan, VeerabhadranPistone, K., I. Eisenman, V. Ramanathan, 2019: Radiative Heating of an Ice-Free Arctic Ocean. Geophysical Research Letters, 46, 7474-7480. doi: 10.1029/2019GL082914. During recent decades, there has been dramatic Arctic sea ice retreat. This has reduced the top-of-atmosphere albedo, adding more solar energy to the climate system. There is substantial uncertainty regarding how much ice retreat and associated solar heating will occur in the future. This is relevant to future climate projections, including the timescale for reaching global warming stabilization targets. Here we use satellite observations to estimate the amount of solar energy that would be added in the worst-case scenario of a complete disappearance of Arctic sea ice throughout the sunlit part of the year. Assuming constant cloudiness, we calculate a global radiative heating of 0.71 W/m2 relative to the 1979 baseline state. This is equivalent to the effect of one trillion tons of CO2 emissions. These results suggest that the additional heating due to complete Arctic sea ice loss would hasten global warming by an estimated 25 years.
Popp, Max; Bony, SandrinePopp, M., S. Bony, 2019: Stronger zonal convective clustering associated with a wider tropical rain belt. Nature Communications, 10(1), 1-12. doi: 10.1038/s41467-019-12167-9. How the spatial patterns of deep convection affect the large-scale dynamics of the atmosphere remains an open question. Here, it is shown that if convection along the equator is clustered, the tropical rain belt widens and exhibits a double peak structure.
Posselt, Derek J.; Wu, Longtao; Mueller, Kevin; Huang, Lei; Irion, Fredrick W.; Brown, Shannon; Su, Hui; Santek, David; Velden, Christopher S.Posselt, D. J., L. Wu, K. Mueller, L. Huang, F. W. Irion, S. Brown, H. Su, D. Santek, C. S. Velden, 2019: Quantitative Assessment of State-Dependent Atmospheric Motion Vector Uncertainties. J. Appl. Meteor. Climatol., 58(11), 2479-2495. doi: 10.1175/JAMC-D-19-0166.1. This study examines the error characteristics of atmospheric motion vectors (AMVs) obtained by tracking the movement of water vapor features. A high-resolution numerical simulation of a dynamic weather event is used as a baseline, and AMVs tracked from retrieved water vapor fields are compared with the “true” winds produced by the model. The sensitivity of AMV uncertainty to time interval, AMV tracking window size, water vapor content, horizontal gradient, and wind structure is examined. AMVs are derived from the model water vapor field at a specific height and also from water vapor fields vertically blurred using smoothing functions consistent with high-spectral-resolution infrared (IR) and high-frequency microwave (MW) water vapor sounders. Uncertainties in water vapor AMVs are state dependent and are largest for regions with small water vapor content and small water vapor spatial gradient and in places where the flow runs parallel to contours of constant water vapor content. Smoothing of water vapor consistent with IR and MW retrievals does not increase AMV uncertainty; however, the yield of AMVs from IR sounders is much lower than from MW sounders because of the inability of IR sounders to retrieve water vapor below clouds. The yield and error are similar for AMVs in the lower and upper troposphere, even though the water vapor content in the upper troposphere is much smaller. The results have implications for the design of new observing systems, as well as the specification of errors when AMVs are ingested in data assimilation systems.
Qiu, Yun; Han, Weiqing; Lin, Xinyu; West, B. Jason; Li, Yuanlong; Xing, Wen; Zhang, Xiaolin; Arulananthan, K.; Guo, XiaogangQiu, Y., W. Han, X. Lin, B. J. West, Y. Li, W. Xing, X. Zhang, K. Arulananthan, X. Guo, 2019: Upper-Ocean Response to the Super Tropical Cyclone Phailin (2013) over the Freshwater Region of the Bay of Bengal. J. Phys. Oceanogr., 49(5), 1201-1228. doi: 10.1175/JPO-D-18-0228.1. This study investigates the impact of salinity stratification on the upper-ocean response to a category 5 tropical cyclone, Phailin, that crossed the northern Bay of Bengal (BOB) from 8 to 13 October 2013. A drastic increase of up to 5.0 psu in sea surface salinity (SSS) was observed after Phailin’s passage, whereas a weak drop of below 0.5°C was observed in sea surface temperature (SST). Rightward biases were apparent in surface current and SSS but not evident in SST. Phailin-induced SST variations can be divided into the warming and cooling stages, corresponding to the existence of the thick barrier layer (BL) and temperature inversion before and erosion after Phailin’s passage, respectively. During the warming stage, SST increased due to strong entrainment of warmer water from the BL, which overcame the cooling induced by surface heat fluxes and horizontal advection. During the cooling stage, the entrainment and upwelling dominated the SST decrease. The preexistence of the BL, which reduced entrainment cooling by ~1.09°C day−1, significantly weakened the overall Phailin-induced SST cooling. The Hybrid Coordinate Ocean Model (HYCOM) experiments confirm the crucial roles of entrainment and upwelling in the Phailin-induced dramatic SSS increase and weak SST decrease. Analyses of upper-ocean stratification associated with 16 super TCs that occurred in the BOB during 1980–2015 show that intensifications of 13 TCs were associated with a thick isothermal layer, and 5 out of the 13 were associated with a thick BL. The calculation of TC intensity with and without considering subsurface temperature demonstrates the importance of large upper-ocean heat storage in TC growth.
Quast, Ralf; Giering, Ralf; Govaerts, Yves; Rüthrich, Frank; Roebeling, RobQuast, R., R. Giering, Y. Govaerts, F. Rüthrich, R. Roebeling, 2019: Climate Data Records from Meteosat First Generation Part II: Retrieval of the In-Flight Visible Spectral Response. Remote Sensing, 11(5), 480. doi: 10.3390/rs11050480. How can the in-flight spectral response functions of a series of decades-old broad band radiometers in Space be retrieved post-flight? This question is the key to developing Climate Data Records from the Meteosat Visible and Infrared Imager on board the Meteosat First Generation (MFG) of geostationary satellites, which acquired Earth radiance images in the Visible (VIS) broad band from 1977 to 2017. This article presents a new metrologically sound method for retrieving the VIS spectral response from matchups of pseudo-invariant calibration site (PICS) pixels with datasets of simulated top-of-atmosphere spectral radiance used as reference. Calibration sites include bright desert, open ocean and deep convective cloud targets. The absolute instrument spectral response function is decomposed into generalised Bernstein basis polynomials and a degradation function that is based on plain physical considerations and able to represent typical chromatic ageing characteristics. Retrieval uncertainties are specified in terms of an error covariance matrix, which is projected from model parameter space into the spectral response function domain and range. The retrieval method considers target type-specific biases due to errors in, e.g., the selection of PICS target pixels and the spectral radiance simulation explicitly. It has been tested with artificial and well-comprehended observational data from the Spinning Enhanced Visible and Infrared Imager on-board Meteosat Second Generation and has retrieved meaningful results for all MFG satellites apart from Meteosat-1, which was not available for analysis. remote sensing; algorithmic differentiation; Climate Data Record; Earth Observation; Fundamental Climate Data Record; instrument degradation; instrument spectral response function; Meteosat Visible and Infrared Imager (MVIRI); metrology; uncertainty propagation
Raghuraman, Shiv Priyam; Paynter, David; Ramaswamy, V.Raghuraman, S. P., D. Paynter, V. Ramaswamy, 2019: Quantifying the Drivers of the Clear Sky Greenhouse Effect, 2000–2016. Journal of Geophysical Research: Atmospheres, 124(21), 11354-11371. doi: 10.1029/2019JD031017. The clear sky greenhouse effect (G) is defined as the trapping of infrared radiation by the atmosphere in the absence of clouds. The magnitude and variability of G is an important element in the understanding of Earth's energy balance; yet the quantification of the governing factors of G is poor. The global mean G averaged over 2000 to 2016 is 130–133 W m−2 across data sets. We use satellite observations from Clouds and the Earth's Radiant Energy System Energy Balance and Filled (CERES EBAF) to calculate the monthly anomalies in the clear sky greenhouse effect (ΔG). We quantify the contributions to ΔG due to changes in surface temperature, atmospheric temperature, and water vapor by performing partial radiation perturbation experiments using ERA-Interim and Geophysical Fluid Dynamics Laboratory's Atmospheric Model 4.0 climatological data. Water vapor in the middle troposphere and upper troposphere is found to contribute equally to the global mean and tropical mean ΔG. Holding relative humidity (RH) fixed in the radiative transfer calculations captures the temporal variability of global mean ΔG while variations in RH control the regional ΔG signal. The variations in RH are found to help generate the clear sky super greenhouse effect (SGE). Thirty-six percent of Earth's area exhibits SGE, and this disproportionately contributes to 70% of the globally averaged magnitude of ΔG. In the global mean, G's sensitivity to surface temperature is 3.1–4.0 W m−2 K−1, and the clear sky longwave feedback parameter is 1.5–2.0 W m−2 K−1. Observations from CERES EBAF lie at the more sensitive ends of these ranges and the spread arises from its cloud removal treatment, suggesting that it is difficult to constrain clear sky feedbacks. water vapor; relative humidity; climate feedback; greenhouse effect; middle troposphere; super greenhouse effect
Rasch, P. J.; Xie, S.; Ma, P.-L.; Lin, W.; Wang, H.; Tang, Q.; Burrows, S. M.; Caldwell, P.; Zhang, K.; Easter, R. C.; Cameron‐Smith, P.; Singh, B.; Wan, H.; Golaz, J.-C.; Harrop, B. E.; Roesler, E.; Bacmeister, J.; Larson, V. E.; Evans, K. J.; Qian, Y.; Taylor, M.; Leung, L. R.; Zhang, Y.; Brent, L.; Branstetter, M.; Hannay, C.; Mahajan, S.; Mametjanov, A.; Neale, R.; Richter, J. H.; Yoon, J.-H.; Zender, C. S.; Bader, D.; Flanner, M.; Foucar, J. G.; Jacob, R.; Keen, N.; Klein, S. A.; Liu, X.; Salinger, A. G.; Shrivastava, M.; Yang, Y.Rasch, P. J., S. Xie, P. Ma, W. Lin, H. Wang, Q. Tang, S. M. Burrows, P. Caldwell, K. Zhang, R. C. Easter, P. Cameron‐Smith, B. Singh, H. Wan, J. Golaz, B. E. Harrop, E. Roesler, J. Bacmeister, V. E. Larson, K. J. Evans, Y. Qian, M. Taylor, L. R. Leung, Y. Zhang, L. Brent, M. Branstetter, C. Hannay, S. Mahajan, A. Mametjanov, R. Neale, J. H. Richter, J. Yoon, C. S. Zender, D. Bader, M. Flanner, J. G. Foucar, R. Jacob, N. Keen, S. A. Klein, X. Liu, A. G. Salinger, M. Shrivastava, Y. Yang, 2019: An Overview of the Atmospheric Component of the Energy Exascale Earth System Model. Journal of Advances in Modeling Earth Systems, 11(8), 2377-2411. doi: 10.1029/2019MS001629. The Energy Exascale Earth System Model Atmosphere Model version 1, the atmospheric component of the Department of Energy's Energy Exascale Earth System Model is described. The model began as a fork of the well-known Community Atmosphere Model, but it has evolved in new ways, and coding, performance, resolution, physical processes (primarily cloud and aerosols formulations), testing and development procedures now differ significantly. Vertical resolution was increased (from 30 to 72 layers), and the model top extended to 60 km ( 0.1 hPa). A simple ozone photochemistry predicts stratospheric ozone, and the model now supports increased and more realistic variability in the upper troposphere and stratosphere. An optional improved treatment of light-absorbing particle deposition to snowpack and ice is available, and stronger connections with Earth system biogeochemistry can be used for some science problems. Satellite and ground-based cloud and aerosol simulators were implemented to facilitate evaluation of clouds, aerosols, and aerosol-cloud interactions. Higher horizontal and vertical resolution, increased complexity, and more predicted and transported variables have increased the model computational cost and changed the simulations considerably. These changes required development of alternate strategies for tuning and evaluation as it was not feasible to “brute force” tune the high-resolution configurations, so short-term hindcasts, perturbed parameter ensemble simulations, and regionally refined simulations provided guidance on tuning and parameterization sensitivity to higher resolution. A brief overview of the model and model climate is provided. Model fidelity has generally improved compared to its predecessors and the CMIP5 generation of climate models. climate change; climate; climate modeling; atmospheric model; Earth system; general circulation modeling
Renner, M.; Wild, M.; Schwarz, M.; Kleidon, A.Renner, M., M. Wild, M. Schwarz, A. Kleidon, 2019: Estimating Shortwave Clear-Sky Fluxes From Hourly Global Radiation Records by Quantile Regression. Earth and Space Science, 6(8), 1532-1546. doi: 10.1029/2019EA000686. Estimates of radiative fluxes under cloud-free conditions (“clear-sky”) are required in many fields, from climatic analyses of solar transmission to estimates of solar energy potential for electricity generation. Ideally, these fluxes can be obtained directly from measurements of solar fluxes at the surface. However, common standard methods to identify clear-sky conditions require observations of both the total and the diffuse radiative fluxes at very high temporal resolution of minutes, which restricts these methods to a few, well-equipped sites. Here we propose a simple method to estimate clear-sky fluxes only from typically available global radiation measurements (Rsd) at (half-)hourly resolution. Plotting a monthly sample of observed Rsd against the corresponding incoming solar radiation at the top of atmosphere (potential solar radiation) reveals a typical triangle shape with clear-sky conditions forming a distinct, linear slope in the upper range of observations. This upper slope can be understood as the fractional transmission of solar radiation representative for cloud-free conditions of the sample period. We estimate this upper slope through quantile regression. We employ data of 42 stations of the worldwide Baseline Surface Radiation Network to compare our monthly estimates with the standard clear-sky identification method developed by Long and Ackerman (2000, https://doi.org/10.1029/2000JD900077). We find very good agreement of the derived fractional solar transmission (R2 = 0.73) across sites. These results thus provide confidence in applying the proposed method to the larger set of global radiation measurements to obtain further observational constraints on clear-sky fluxes and cloud radiative effects. clear-sky; global radiation; cloud-free; quantile regression; transmission
Rizvi, Shahnilla Haider; Alam, Khan; Iqbal, Muhammad JawedRizvi, S. H., K. Alam, M. J. Iqbal, 2019: Spatio -temporal variations in urban heat island and its interaction with heat wave. Journal of Atmospheric and Solar-Terrestrial Physics, 185, 50-57. doi: 10.1016/j.jastp.2019.02.001. Most of the urban localities are facing the effects of Urban Heat Island (UHI) and extreme heat wave (HW) events. It is expected that these HW events are likely to be intensified by the effect of UHI in the future. As these events project to increase in both severity and frequency therefore, it is crucial to assess the intensity of UHI and examine the relationship between HW and UHI. In this study, observations for different coastal areas are used to quantify the impacts of UHI during the HW events. The spatial and temporal variability patterns of UHI in the metropolitan city of Karachi were also investigated using hourly temperature observations for a period of 10 years in two phases (a) from 1998 to 2002 (b) from 2012 to 2016. During the first phase (1998–2001), the maximum Urban Heat Island Intensity (UHII) for night time in summer was 1.9 °C, while during the second phase (2012–2016), it increased by 0.6 °C. Despite the fact that both phases have shown similar pattern for seasonal UHII, urban-rural temperature difference was found to be significant in summer especially in the night time. Temporal distribution of UHII for winter shows that average intensity of UHI during daytime varies between 0.1 °C and 3.2 °C, considering the overall time duration. The results indicate that UHII increased significantly during the HW period which caused more than 800 deaths in Karachi between 17th June and 24th June 2015. Heat index; Heat stroke; Heat wave; Urban heat island intensity
Rodríguez, José Antonio SobrinoRodríguez, J., . Antonio Sobrino, 2019: Fifth recent advances in quantitative remote sensing. The Fifth International Symposium on Recent Advances in Quantitative Remote Sensing was held in Torrent, Spain from 18 to 22 September 2018. It was sponsored and organized by the Global Change Unit (GCU) from the Image Processing Laboratory (IPL), University of Valencia (UVEG), Spain. This Symposium addressed the scientific advances in quantitative remote sensing in connection with real applications. Its main goal was to assess the state of the art of both theory and applications in the analysis of remote sensing data, as well as to provide a forum for researcher in this subject area to exchange views and report their latest results. In this book 89 of the 262 contributions presented in both plenary and poster sessions are arranged according to the scientific topics selected. The papers are ranked in the same order as the final programme. Science / Mechanics / Thermodynamics
Rowell, David P.Rowell, D. P., 2019: An Observational Constraint on CMIP5 Projections of the East African Long Rains and Southern Indian Ocean Warming. Geophysical Research Letters, 46(11), 6050-6058. doi: 10.1029/2019GL082847. Two outlying projections of the East African Long Rains suggest the seasonal rainfall may double by the late 21st century. Previous work has linked these extremes—found in the IPSL-CM5A model—to an exceptional March to May warming of the southern Indian Ocean. The current study shows a strong feedback between sea surface temperature (SST) increases and reduced low-level cloud cover (with similar behavior in other southern subtropical oceans). An observational constraint is developed by demonstrating a correlation across 28 models between the strength of present-day interannual SST-cloud sensitivity and future SST response. Verification of the present-day sensitivity finds that IPSL-CM5A's feedbacks are very likely overestimated. It is therefore suggested its projections should be discounted for the March to May southern Indian Ocean and East African Long Rains. This narrows the CMIP5 plausible range of Long Rains totals by a third. climate change; Indian Ocean; CMIP5; cloud feedbacks; East Africa; emergent constraint
Ruan, Ruomei; Chen, Xianyao; Zhao, Jinping; Perrie, William; Mottram, Ruth; Zhang, Minghong; Diao, Yina; Du, Ling; Wu, LixinRuan, R., X. Chen, J. Zhao, W. Perrie, R. Mottram, M. Zhang, Y. Diao, L. Du, L. Wu, 2019: Decelerated Greenland Ice Sheet Melt Driven by Positive Summer North Atlantic Oscillation. Journal of Geophysical Research: Atmospheres, 124(14), 7633-7646. doi: 10.1029/2019JD030689. The abrupt deceleration of accelerated Greenland Ice Sheet (GrIS) melting since 2013, after a period of acceleration previously noted, is studied here. It is shown that the deceleration of GrIS melting since 2013 is due to the reduction in short-wave solar radiation in the presence of increasing total cloud cover, which is driven by a more persistent positive summer North Atlantic Oscillation on the decadal time scale. By presenting the coherence with the temperature variability at the weather stations in Greenland, which have century-long records, we deduce that the acceleration of GrIS melting during the early 2000s and the subsequent deceleration since 2013 will reoccur frequently on decadal time scales, with the amplitude nearly half of the multidecadal warming trend of the GrIS melt. It can reduce the mass loss from the GrIS on short to medium time scales but is unlikely to halt mass loss related to climate change in the future. This finding highlights the importance of internal climate variability on the mass budget of the GrIS and therefore on predictions of future global sea level change and may help to assist planning for associated social and economic consequences. Greenland Ice Sheet; mass balance; summer North Atlantic Oscillation; time scale
Ruosteenoja, Kimmo; Räisänen, Petri; Devraj, Sarvesh; Garud, Shirish S; Lindfors, Anders V.Ruosteenoja, K., P. Räisänen, S. Devraj, S. S. Garud, A. V. Lindfors, 2019: Future changes in incident surface solar radiation and contributing factors in India in CMIP5 climate model simulations. J. Appl. Meteor. Climatol., 58(1), 19-35. doi: 10.1175/JAMC-D-18-0013.1. To support the planning of future solar energy production in India, forthcoming changes in incoming surface solar radiation and the main physical factors contributing to the change were inferred from simulations performed with 27 global CMIP5 climate models. According to the multi-model mean response, radiation diminishes by a few percent during the early decades of the 21st century, in tandem with strengthening aerosol and water vapour dimming. The largest reduction is anticipated for Northern India. The evolution of incident radiation in mid- and late 21st century depends substantially on the emission scenario. According to the Representative Concentration Pathways RCP2.6 and RCP4.5, solar radiation would gradually recover close to the level that prevailed in late 20th century. This results from the peaking of aerosol loading before mid-century, while the water vapour content continuously increases somewhat. Conversely, under RCP8.5, incident radiation would still decline, even though more slowly than during the early century. This coincides with a substantial increase in atmospheric water vapour content and a modest decrease in aerosol forcing. In cloud forcing, multi-model mean changes are minor but divergence among the model simulations is substantial. Moreover, cloud forcing proved to be the factor that correlates most strongly with intermodel differences in the solar radiation response. Multi-model mean changes in solar radiation are rather small and would not crucially affect the conditions of solar energy production. Nevertheless, some individual models simulate far more substantial reductions, up to ~ 10%.
Saito, Masanori; Yang, Ping; Hu, Yongxiang; Liu, Xu; Loeb, Norman; Smith, William L.; Minnis, PatrickSaito, M., P. Yang, Y. Hu, X. Liu, N. Loeb, W. L. Smith, P. Minnis, 2019: An Efficient Method for Microphysical Property Retrievals in Vertically Inhomogeneous Marine Water Clouds Using MODIS-CloudSat Measurements. Journal of Geophysical Research: Atmospheres, 124(4), 2174-2193. doi: 10.1029/2018JD029659. An efficient method is developed to infer cloud optical thickness (COT) and cloud droplet effective radius (CDER) of marine water clouds from Moderate Resolution Imaging Spectroradiometer (MODIS) and CloudSat measurements, incorporating droplet size vertical inhomogeneity. Empirical orthogonal function (EOF) analysis is employed to reduce the degrees of freedom of the droplet size profile. The first two EOFs can explain 94% of the variability in the droplet size profile. Compared to the existing bispectral CDER retrieval from MODIS assuming plane parallel vertically homogeneous clouds, the new retrieval produces smaller CDER values in clouds in which the adiabatic growth process is dominant and larger CDER values in clouds in which the collision-coalescence process is dominant. To evaluate the performance of the retrieval algorithm, we compare retrieved COT and CDER in this study with their MODIS and CloudSat counterparts on a pixel-by-pixel basis. CDER retrieval based on the vertically homogeneous assumption may be underestimated by 30% due to droplet size vertical inhomogeneity when COT is large and the collision-coalescence process is dominant in the cloud. Retrieved CDER in conjunction with the two scores for EOFs can reconstruct the vertical profile of CDER, which is useful for cloud microphysical process studies. Furthermore, potential expansion of this algorithm to MODIS pixels without CloudSat collocations is discussed. remote sensing; droplet size; EOF; marine water clouds
Saito, Masanori; Yang, Ping; Loeb, Norman G.; Kato, SeijiSaito, M., P. Yang, N. G. Loeb, S. Kato, 2019: A Novel Parameterization of Snow Albedo Based on a Two-Layer Snow Model with a Mixture of Grain Habits. J. Atmos. Sci., 76(5), 1419-1436. doi: 10.1175/JAS-D-18-0308.1. Snow albedo plays a critical role in the surface energy budget in snow-covered regions and is subject to large uncertainty due to variable physical and optical characteristics of snow. We develop an optically and microphysically consistent snow grain habit mixture (SGHM) model, aiming at an improved representation of bulk snow properties in conjunction with considering the particle size distribution, particle shape, and internally mixed black carbon (BC). Spectral snow albedos computed with two snow layers with the SGHM model implemented in an adding–doubling radiative transfer model agree with observations. Top-snow-layer optical properties essentially determine spectral snow albedo when the top-layer snow water equivalent (SWE) is large. When the top-layer SWE is less than 1 mm, the second-snow-layer optical properties have nonnegligible impacts on the albedo of the snow surface. Snow albedo enhancement with increasing solar zenith angle (SZA) largely depends on snow particle effective radius and also internally mixed BC. Based on the SGHM model and various sensitivity studies, single- and two-layer snow albedos are parameterized for six spectral bands used in NASA Langley Research Center’s modified Fu–Liou broadband radiative transfer model. Parameterized albedo is expressed as a function of snow particle effective radii of the two layers, SWE in the top layer, internally mixed BC mass fraction in both layers, and SZA. Both single-layer and two-layer parameterizations provide band-mean snow albedo consistent with rigorous calculations, achieving correlation coefficients close to 0.99 for all bands.
Schmeisser, Lauren; Bond, Nicholas A.; Siedlecki, Samantha A.; Ackerman, Thomas P.Schmeisser, L., N. A. Bond, S. A. Siedlecki, T. P. Ackerman, 2019: The Role of Clouds and Surface Heat Fluxes in the Maintenance of the 2013–2016 Northeast Pacific Marine Heatwave. Journal of Geophysical Research: Atmospheres, 124(20), 10772-10783. doi: 10.1029/2019JD030780. Starting in late 2013, the Northeast (NE) Pacific Ocean experienced anomalously warm sea surface temperatures (SSTs) that persisted for over 2 years. This marine heatwave, known as “the Blob,” produced many devastating ecological impacts with socioeconomic implications for coastal communities. The warm waters observed during the NE Pacific 2013/2016 marine heatwave altered the surface energy balance and disrupted ocean–atmosphere interactions in the region. In principle, ocean–atmosphere interactions following the formation of the marine heatwave could have perpetuated warm SSTs through a positive SST-cloud feedback. The actual situation was more complicated. While reanalysis data show a decrease in boundary layer cloud fraction and an increase in downward shortwave radiative flux at the surface coincident with warm SSTs, this was accompanied by an increase in longwave radiative fluxes at the surface, as well as an increase in sensible and latent heat fluxes out of the ocean mixed layer. The result is a small negative net heat flux anomaly (compared to the anomalies of the individual terms contributing to the net heat flux). This provides new information about the midlatitude ocean–atmosphere system while it was in a perturbed state. More specifically, a mixed layer heat budget reveals that anomalies in both the atmospheric and oceanic processes offset each other such that the anomalously warm SSTs persisted for multiple years. The results show how the atmosphere–ocean system in the NE Pacific is able to maintain itself in an anomalous state for an extended period of time. cloud feedback; marine heatwave; atmosphere–ocean interactions; extreme event; midlatitude; surface heat fluxes
Schuddeboom, Alex; Varma, Vidya; McDonald, Adrian J.; Morgenstern, Olaf; Harvey, Mike; Parsons, Simon; Field, Paul; Furtado, KalliSchuddeboom, A., V. Varma, A. J. McDonald, O. Morgenstern, M. Harvey, S. Parsons, P. Field, K. Furtado, 2019: Cluster-based Evaluation of Model Compensating Errors: A Case Study of Cloud Radiative Effect in the Southern Ocean. Geophysical Research Letters, 46(6), 3446-3453. doi: 10.1029/2018GL081686. Model evaluation is difficult and generally relies on analysis which can mask compensating errors. This paper defines new metrics, using clusters generated from a machine learning algorithm, to estimate mean and compensating errors in different model runs. As a test case, we investigate the Southern Ocean shortwave radiative bias using clusters derived by applying self-organizing maps to satellite data. In particular, the effects of changing cloud phase parameterizations in the MetOffice Unified Model are examined. Differences in cluster properties show that the regional radiative biases are substantially different than the global bias, with two distinct regions identified within the Southern Ocean, each with a different signed bias. Changing cloud phase parameterizations can reduce errors at higher latitudes, but increase errors at lower latitudes of the Southern Ocean. Ranking the parameterizations often shows a contrast in mean and compensating errors, notably in all cases large compensating errors remain. Southern Ocean; Cloud simulation; Compensating errors; Model Evaluation
Schwarz, M.; Folini, D.; Yang, S.; Wild, M.Schwarz, M., D. Folini, S. Yang, M. Wild, 2019: The Annual Cycle of Fractional Atmospheric Shortwave Absorption in Observations and Models: Spatial Structure, Magnitude, and Timing. J. Climate, 32(20), 6729-6748. doi: 10.1175/JCLI-D-19-0212.1. We use the best currently available in situ and satellite-derived surface and top-of-the-atmosphere (TOA) shortwave radiation observations to explore climatological annual cycles of fractional (i.e., normalized by incoming radiation at the TOA) atmospheric shortwave absorption a˜a˜a˜ on a global scale. The analysis reveals that a˜a˜a˜ is a rather regional feature where the reported nonexisting a˜a˜a˜ in Europe is an exception rather than the rule. In several regions, large and distinctively different a˜a˜a˜ are apparent. The magnitudes of a˜a˜a˜ reach values up to 10% in some regions, which is substantial given that the long-term global mean atmospheric shortwave absorption is roughly 23%. Water vapor and aerosols are identified as major drivers for a˜a˜a˜ while clouds seem to play only a minor role for a˜a˜a˜. Regions with large annual cycles in aerosol emissions from biomass burning also show the largest a˜a˜a˜. As biomass burning is generally related to human activities, a˜a˜a˜ is likely also anthropogenically intensified or forced in the respective regions. We also test if climate models are able to simulate the observed pattern of a˜a˜a˜. In regions where a˜a˜a˜ is driven by the annual cycle of natural aerosols or water vapor, the models perform well. In regions with large a˜a˜a˜ induced by biomass-burning aerosols, the models’ performance is very limited.
Sellar, Alistair A.; Jones, Colin G.; Mulcahy, Jane P.; Tang, Yongming; Yool, Andrew; Wiltshire, Andy; O'Connor, Fiona M.; Stringer, Marc; Hill, Richard; Palmieri, Julien; Woodward, Stephanie; Mora, Lee de; Kuhlbrodt, Till; Rumbold, Steven T.; Kelley, Douglas I.; Ellis, Rich; Johnson, Colin E.; Walton, Jeremy; Abraham, Nathan Luke; Andrews, Martin B.; Andrews, Timothy; Archibald, Alex T.; Berthou, Ségolène; Burke, Eleanor; Blockley, Ed; Carslaw, Ken; Dalvi, Mohit; Edwards, John; Folberth, Gerd A.; Gedney, Nicola; Griffiths, Paul T.; Harper, Anna B.; Hendry, Maggie A.; Hewitt, Alan J.; Johnson, Ben; Jones, Andy; Jones, Chris D.; Keeble, James; Liddicoat, Spencer; Morgenstern, Olaf; Parker, Robert J.; Predoi, Valeriu; Robertson, Eddy; Siahaan, Antony; Smith, Robin S.; Swaminathan, Ranjini; Woodhouse, Matthew T.; Zeng, Guang; Zerroukat, MohamedSellar, A. A., C. G. Jones, J. P. Mulcahy, Y. Tang, A. Yool, A. Wiltshire, F. M. O'Connor, M. Stringer, R. Hill, J. Palmieri, S. Woodward, L. d. Mora, T. Kuhlbrodt, S. T. Rumbold, D. I. Kelley, R. Ellis, C. E. Johnson, J. Walton, N. L. Abraham, M. B. Andrews, T. Andrews, A. T. Archibald, S. Berthou, E. Burke, E. Blockley, K. Carslaw, M. Dalvi, J. Edwards, G. A. Folberth, N. Gedney, P. T. Griffiths, A. B. Harper, M. A. Hendry, A. J. Hewitt, B. Johnson, A. Jones, C. D. Jones, J. Keeble, S. Liddicoat, O. Morgenstern, R. J. Parker, V. Predoi, E. Robertson, A. Siahaan, R. S. Smith, R. Swaminathan, M. T. Woodhouse, G. Zeng, M. Zerroukat, 2019: UKESM1: Description and Evaluation of the U.K. Earth System Model. Journal of Advances in Modeling Earth Systems, 11(12), 4513-4558. doi: 10.1029/2019MS001739. We document the development of the first version of the U.K. Earth System Model UKESM1. The model represents a major advance on its predecessor HadGEM2-ES, with enhancements to all component models and new feedback mechanisms. These include a new core physical model with a well-resolved stratosphere; terrestrial biogeochemistry with coupled carbon and nitrogen cycles and enhanced land management; tropospheric-stratospheric chemistry allowing the holistic simulation of radiative forcing from ozone, methane, and nitrous oxide; two-moment, five-species, modal aerosol; and ocean biogeochemistry with two-way coupling to the carbon cycle and atmospheric aerosols. The complexity of coupling between the ocean, land, and atmosphere physical climate and biogeochemical cycles in UKESM1 is unprecedented for an Earth system model. We describe in detail the process by which the coupled model was developed and tuned to achieve acceptable performance in key physical and Earth system quantities and discuss the challenges involved in mitigating biases in a model with complex connections between its components. Overall, the model performs well, with a stable pre-industrial state and good agreement with observations in the latter period of its historical simulations. However, global mean surface temperature exhibits stronger-than-observed cooling from 1950 to 1970, followed by rapid warming from 1980 to 2014. Metrics from idealized simulations show a high climate sensitivity relative to previous generations of models: Equilibrium climate sensitivity is 5.4 K, transient climate response ranges from 2.68 to 2.85 K, and transient climate response to cumulative emissions is 2.49 to 2.66 K TtC−1.
Seviour, W. J. M.; Codron, F.; Doddridge, E. W.; Ferreira, D.; Gnanadesikan, A.; Kelley, M.; Kostov, Y.; Marshall, J.; Polvani, L. M.; Thomas, J. L.; Waugh, D. W.Seviour, W. J. M., F. Codron, E. W. Doddridge, D. Ferreira, A. Gnanadesikan, M. Kelley, Y. Kostov, J. Marshall, L. M. Polvani, J. L. Thomas, D. W. Waugh, 2019: The Southern Ocean sea surface temperature response to ozone depletion: A multi-model comparison. J. Climate, 32(16), 5107–5121. doi: 10.1175/JCLI-D-19-0109.1. The effect of the Antarctic ozone hole extends downwards from the stratosphere, with clear signatures in surface weather patterns including a positive trend in the Southern Annular Mode (SAM). Several recent studies have used coupled climate models to investigate the impact of these changes on Southern Ocean sea surface temperature (SST), notably motivated by the observed cooling from the late 1970s. Here we examine the robustness of these model results through comparison of both previously published and new simulations. We focus on the calculation of ‘climate response functions’ (CRFs), transient responses to an instantaneous step-change in ozone concentrations. The CRF for most models consists of a rapid cooling of SST, followed by a slower warming trend. However, inter-model comparison reveals large uncertainties, such that even the sign of the impact of ozone depletion on historical SST, when reconstructed from the CRF, remains unconstrained. Comparison of these CRFs with SST responses to a hypothetical step-change in the SAM, inferred through lagged linear regression, shows broadly similar results. Causes of uncertainty are explored by examining relationships between model climatologies and their CRFs. The inter-model spread in CRFs can be reproduced by varying a single subgrid-scale mixing parameter within a single model. Antarctic sea-ice CRFs are also calculated: these do not generally exhibit the two-time-scale behavior of SST, suggesting a complex relationship between the two. Finally, by constraining model climatology-response relationships with observational values, we conclude that ozone depletion in unlikely to have been the primary driver of the observed SST cooling trend.
Shrestha, A. K.; Kato, S.; Wong, T.; Stackhouse, P.; Loughman, R. P.Shrestha, A. K., S. Kato, T. Wong, P. Stackhouse, R. P. Loughman, 2019: New Temporal and Spectral Unfiltering Technique for ERBE/ERBS WFOV Nonscanner Instrument Observations. IEEE Transactions on Geoscience and Remote Sensing, 1-12. doi: 10.1109/TGRS.2019.2891748. Earth Radiation Budget Experiment (ERBE) Wide-Field-of-View (WFOV) nonscanner instrument onboard Earth Radiation Budget Satellite (ERBS) provided critical 15-year outgoing broadband irradiances at the top of atmosphere (TOA) from 1985 to 1999 for studying Earth's climate. However, earlier studies show that the uncertainty in this radiation data set (Ed3) is significantly higher after the Mt. Pinatubo eruption in 1991 and satellite battery issue in 1993. Furthermore, Lee et al. showed that the transmission of ERBS WFOV shortwave dome degraded due to exposure to direct sunlight. To account for this degradation, a simple time-dependent but spectral-independent correction model was implemented in the past. This simple spectral-independent model did not completely remove the shortwave sensor artifact as seen in the temporal growth of the tropical mean day-minus-night longwave irradiance. A new temporal-spectral-dependent correction model of shortwave dome transmissivity loss similar to that used in the Clouds and the Earth's Radiant Energy System (CERES) project is developed and applied to the 15-year ERBS WFOV data. This model is constrained by the solar transmission obtained from ERBS WFOV shortwave nonscanner instrument observations of the Sun during biweekly in-flight solar calibration events. This new model is able to reduce the reported tropical day-minus-night longwave irradiance trend by ≈34%. In addition, the slope of this new trend is observed to be consistent over different regions. The remaining trend is accounted using a postprocess Ed3Rev1 correction. Furthermore, the time series analysis of these data over the Libya-4 desert site showed that the shortwave data are stable to within 0.7%. Earth; Instruments; Meteorology; Satellite broadcasting; Radiometry; Data models; Calibration; Data conversion; earth; energy measurements.
Shukla, Ravi P.; Huang, Bohua; Dirmeyer, Paul A.; Kinter, James L.Shukla, R. P., B. Huang, P. A. Dirmeyer, J. L. Kinter, 2019: The Influence of Summer Deep Soil Temperature on Early Winter Snow Conditions in Eurasia in the NCEP CFSv2 Simulation. Journal of Geophysical Research: Atmospheres, 124(16), 9062-9077. doi: 10.1029/2019JD030279. The National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2) has a large cold bias in the model's deep soil temperature during summer. This study explores the potential triggering effect of that bias on excessive Eurasian snow cover in early winter. Snow cover appears erroneously early in the fall, especially in western Eurasia, in long simulations with CFSv2. The seasonal transition may be too early because the model land surface temperature (LST) reaches its freezing point earlier than observed, so that new snow cannot melt. This process initiates snow-albedo feedback too early. The early cooling of LST is partially influenced by a seasonal resurfacing of the cold bias in the deep soil layer. From winter to early spring, a cold bias prevails in LST and upper soil temperature as snow cover remains. During this season, the temperature in the deep soil is generally warmer than in the upper soil and has relatively little bias. From spring to summer, the cold bias in the upper soil becomes smaller as it warms up in response to solar heating. On the other hand, the deep soil temperature has a noticeably smaller seasonal change than observed, resulting in a severe cold bias during summer. As the solar radiation declines quickly in early fall, the cold deep soil temperature causes additional cooling in the upper soil layer and helps to bring LST to the freezing point early in the western Eurasia, which leads to enhanced bias in the snow properties. NCEP CFSv2; snow-albedo feedback; subsurface soil temperature; deep soil temperature; Eurasia; seasonal transition
Sicard, MichaëlSicard, M., 2019: Validation of AERONET-Estimated Upward Broadband Solar Fluxes at the Top-Of-The-Atmosphere with CERES Measurements. Remote Sensing, 11(18), 2168. doi: 10.3390/rs11182168. The AERONET (Aerosol Robotic Network) global network provides estimations of broadband solar radiative fluxes at the surface and at the TOA (Top-Of-the-Atmosphere). This paper reports on the validation of AERONET flux estimations at the TOA with the CERES (Clouds and the Earth’s Radiant Energy System) instrument. The validation was made at eight AERONET sites worldwide with at least seven years of Level 2.0 and Version 3 data and representatives of mineral dust, biomass burning, background continental, and urban-industrial aerosol regimes. To co-locate in time and space the AERONET and CERES fluxes, several criteria based on time and distance differences and cloud coverage were defined. When the strictest criterion was applied to all sites, the linear relationship between the observed and estimated fluxes (y = 1.04x – 3.67 Wm−2) was very close to the 1:1 ideal line. The correlation coefficient was 0.96 and nearly all points were contained in the ±15% region around the 1:1 line. The average flux difference was –2.52 Wm−2 (–0.84% in relative terms). AERONET overestimations were observed at two sites and were correlated with large aerosol optical depth (AOD) (>0.2) Underestimations were observed at one desert site and were correlated with large surface albedos (>0.2). CERES; AERONET; flux comparison; Top-Of-the-Atmosphere (TOA) upward solar fluxes
Siegel, EthanSiegel, E., 2019: The Simplest Explanation Of Global Warming Ever. Forbes. The Earth is getting warmer, and humans are the cause. This is why.
Silber, Israel; Fridlind, Ann M.; Verlinde, Johannes; Ackerman, Andrew S.; Chen, Yao-Sheng; Bromwich, David H.; Wang, Sheng-Hung; Cadeddu, Maria; Eloranta, Edwin W.Silber, I., A. M. Fridlind, J. Verlinde, A. S. Ackerman, Y. Chen, D. H. Bromwich, S. Wang, M. Cadeddu, E. W. Eloranta, 2019: Persistent Supercooled Drizzle at Temperatures Below −25 °C Observed at McMurdo Station, Antarctica. Journal of Geophysical Research: Atmospheres, 124(20), 10878-10895. doi: 10.1029/2019JD030882. The rarity of reports in the literature of brief and spatially limited observations of drizzle at temperatures below −20 °C suggest that riming and other temperature-dependent cloud microphysical processes such as heterogeneous ice nucleation and ice crystal depositional growth prevent drizzle persistence in cold environments. In this study, we report on a persistent drizzle event observed by ground-based remote sensing measurements at McMurdo Station, Antarctica. The temperatures in the drizzle-producing cloud were below −25 °C and the drizzle persisted for a period exceeding 7.5 hr. Using ground-based, satellite, and reanalysis data, we conclude that drizzle was likely present in parts of a widespread cloud field, which stretched more than 1,000 km along the Ross Ice Shelf coast. Parameter space sensitivity tests using two-moment bulk microphysics in large eddy simulations constrained by the observations suggest that activated ice freezing nuclei and accumulation-mode aerosol number concentrations aloft during this persistent drizzle period were likely on the order of 0.2 L−1 and 20 cm−3, respectively. In such constrained simulations, the drizzle moisture flux through cloud base exceeds that of ice. The simulations also indicate that drizzle can lead to the formation of multiple peaks in cloud water content profiles. This study suggests that persistent drizzle at these low temperatures may be common at the low aerosol concentrations typical of the Antarctic and Southern Ocean atmospheres. Antarctica; mixed-phase clouds; LES; McMurdo Station; Persistent drizzle; Supercooled drizzle
Sindhu, Kapil Dev; Sahany, SandeepSindhu, K. D., S. Sahany, 2019: Long-term cloud fraction biases in CMIP5 GCMs over India during monsoon season. Theoretical and Applied Climatology, 137(3-4), 2559–2571. doi: 10.1007/s00704-018-02760-1. Using 24 years of cloud fraction (CF) data from the International Satellite Cloud Climatology Project (ISCCP) observations and their corresponding simulators in general circulation models (GCMs) from the Coupled Model Intercomparison Project phase 5 (CMIP5), we have analyzed cloud biases and their role on radiation over the Indian region (65–100° E and 5–40° N) for the monsoon season of June to September. The present study reports the spatial patterns of CFs and their biases in GCMs compared to observations. It is found that the simulated CFs are highly underestimated up to ~ 40%. Mean of total CF from ISCCP observations is 75% with at least 10% difference with simulated CFs. For high-topped clouds, this difference is about 3–4%. Except for high-topped clouds, other cloud types are not simulated realistically by CMIP5 models used in this study. Further, we investigated the individual cloud types classified based on cloud optical depth and cloud top pressure. We found that, in general, individual cloud types are poorly simulated by models, although some (Max Planck Institute Earth System Model, Low Resolution and Hadley Centre Global Environmental Model, version 2, Earth System) models convincingly simulate high-topped thin clouds. To assess the impact of cloud biases on the simulated radiative forcings, we studied shortwave and longwave cloud radiative forcings from CERES (Clouds and the Earth’s Radiant Energy System) observations and CMIP5 GCMs. It is noticed that the spatial patterns of biases in radiative forcings are similar to the patterns of biases in CFs for high-topped clouds, specifically over the oceanic regions. We find that the biases in cloud radiative forcings could potentially be caused due to the inefficacy of CMIP5 models in simulating high-topped anvil clouds (high-topped cirrus/stratocirrus clouds). The present study confirms that the uncertainty in simulating cloud fractions over the Indian region is still a prominent issue to be addressed in general circulation models.
Sivan, C.; Manoj, M. G.Sivan, C., M. G. Manoj, 2019: Aerosol and cloud radiative forcing over various hot spot regions in India. Advances in Space Research, 64(8), 1577-1591. doi: 10.1016/j.asr.2019.07.028. Twelve years of NASA CERES (Clouds and Earth’s Radiant Energy System) data have been used to examine the spatio-temporal variability of aerosol– and cloud– induced shortwave radiative forcing over selected hot spot regions in India. Four regions (northern semiarid – R1; monsoon trough – R2; densely populated urban – R3; and southern peninsula – R4) are selected with different surface characteristics and notable difference in meteorological and geographical features. The analysis shows that three out of the four regions (viz. R1, R2, and R3) experience high aerosol loading and forcing in the monsoon season followed by moderate forcing in pre-monsoon season. While all the seasons except the post-monsoon period show a positive linear relation between cloud optical depth and aerosol optical depth for all the regions, the post-monsoon season shows a negative relation. However, the relation between aerosol forcing and cloud forcing shows adequate non-linearity owing to the numerous factors that control cloud radiative effect. The estimated aerosol induced heating rate shows exponential decrease with height, but with high variability during each season. Irrespective of any region, the maximum heating rate is observed in the pre-monsoon season (2.86 ± 0.78, 2.49 ± 0.78, 1.89 ± 0.57, and 0.88 ± 0.28 K/day for R1, R2, R3, and R4, respectively). Plausible reasons for the variation in the above parameters are discussed. The results suggest that increased anthropogenic activities affect the thermodynamics and hence the dynamics through retention and exchange of heat, and it could affect the precipitation pattern adversely. Aerosol optical depth; CERES data; Cloud; Radiative forcing; Heating rate
Sledd, Anne; L’Ecuyer, TristanSledd, A., T. L’Ecuyer, 2019: How Much Do Clouds Mask the Impacts of Arctic Sea Ice and Snow Cover Variations? Different Perspectives from Observations and Reanalyses. Atmosphere, 10(1), 12. doi: 10.3390/atmos10010012. Decreasing sea ice and snow cover are reducing the surface albedo and changing the Arctic surface energy balance. How these surface albedo changes influence the planetary albedo is a more complex question, though, that depends critically on the modulating effects of the intervening atmosphere. To answer this question, we partition the observed top of atmosphere (TOA) albedo into contributions from the surface and atmosphere, the latter being heavily dependent on clouds. While the surface albedo predictably declines with lower sea ice and snow cover, the TOA albedo decreases approximately half as much. This weaker response can be directly attributed to the fact that the atmosphere contributes more than 70% of the TOA albedo in the annual mean and is less dependent on surface cover. The surface accounts for a maximum of 30% of the TOA albedo in spring and less than 10% by the end of summer. Reanalyses (ASR versions 1 and 2, ERA-Interim, MERRA-2, and NCEP R2) represent the annual means of surface albedo fairly well, but biases are found in magnitudes of the TOA albedo and its contributions, likely due to their representations of clouds. Reanalyses show a wide range of TOA albedo sensitivity to changing sea ice concentration, 0.04–0.18 in September, compared to 0.11 in observations. sea ice; ice-albedo feedback; arctic clouds; reanalyses
Smalley, Mark; Suselj, Kay; Lebsock, Matthew; Teixeira, JoaoSmalley, M., K. Suselj, M. Lebsock, J. Teixeira, 2019: A novel framework for evaluating and improving parameterized subtropical marine boundary layer cloudiness. Mon. Wea. Rev., 147(9), 3241–3260. doi: 10.1175/MWR-D-18-0394.1. A Single Column Model (SCM) is used to simulate a variety of environmental conditions between Los Angeles and Hawaii in order to identify physical elements of parameterizations that are required to reproduce the observed behavior of marine boundary layer (MBL) cloudiness. The SCM is composed of the JPL Eddy-Diffusivity/Mass-Flux mixing formulation and the RRTM-G radiation model. Model forcings are provided by the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA2). Simulated low cloud cover (LCC), rain rate, albedo, and liquid water path are compared to co-located pixel-level observations from A-Train satellites. This framework ensures that the JPL EDMF is able to simulate a continuum of real-world conditions.First, the JPL EDMF is shown to reproduce the observed mean LCC as a function of lower tropospheric stability. Joint probability distributions of lower-tropospheric cloud fraction, height, and LTS show that the JPL EDMF improves upon its MERRA2 input but struggles to match the frequency of observed intermediate-range LCC.We then illustrate the physical roles of plume lateral entrainment and eddy-diffusivity mixing length in producing a realistic behavior of LCC as a function of LTS. In low-LTS conditions, LCC is mostly sensitive to the ability of convection to mix moist air out of the MBL. In high-LTS conditions, LCC is also sensitive to the turbulent mixing of free-tropospheric air into the MBL. In the intermediate LTS regime typical of stratocumulus-cumulus transition there is proportional sensitivity to both mixing mechanisms, emphasizing the utility of a combined Eddy-Diffusivity/Mass-Flux approach for representing mixing processes.
Smith, Samantha A.; Field, Paul R.; Vosper, Simon B.; Derbyshire, Steve H.Smith, S. A., P. R. Field, S. B. Vosper, S. H. Derbyshire, 2019: Verification of a seeder–feeder orographic precipitation enhancement scheme accounting for low-level blocking. Quarterly Journal of the Royal Meteorological Society, 145(724), 2909-2932. doi: 10.1002/qj.3584. A subgrid parametrization scheme representing the enhancement of precipitation due to subgrid orography via the seeder–feeder (SF) effect has been modified to account for flow blocking in small Froude number situations. The scheme was validated in a set of limited-area model simulations with a 1.5 km grid spacing, in which the orography was degraded by varying amounts. For simulations in which the largest orographic scales are still fairly well represented, the SF scheme was able to reduce the precipitation deficit by 30 to 70%. For simulations where the hills were completely subgrid, the SF scheme was still able to reduce the precipitation deficit by 10 to 30%. As well as increasing the integrated precipitation in global simulations with various grid spacings, some of the precipitation production was shifted from the convection scheme, with its very simple microphysical representation, to the microphysics scheme. In a long-duration climate simulation, the SF scheme enhancements of orographic precipitation perturb the large-scale hydrological cycle, as evidenced by the far-field changes in both microphysical and convective precipitation. Changes over major mountain ranges were similar to those described for the case-studies, so long as the upstream precipitation impinging on the mountains was not reduced by these changes in the global hydrological cycle. Increased atmospheric drying reduces column-integrated resolved cloud water mixing ratios over mountains, reducing a positive bias in the amount of optically thick cloud with low- to mid-level tops compared to ISCCP satellite observations. The associated reductions in cloud albedo slightly reduced the RMS error in the top-of-atmosphere outgoing short-wave radiative fluxes over mountains compared to CERES satellite observations. parametrization; climate simulation; low-level flow blocking; orographic precipitation enhancement; precipitation forecasting; seeder–feeder mechanism
Soldatenko, Sergei; Colman, RobertSoldatenko, S., R. Colman, 2019: Climate variability from annual to multi-decadal timescales in a two-layer stochastic energy balance model: analytic solutions and implications for general circulation models. Tellus A: Dynamic Meteorology and Oceanography, 71(1), 1-15. doi: 10.1080/16000870.2018.1554421. A low-order stochastically forced two-layer global energy balance model (EBM) admitting an analytical solution is developed for studying natural inter-annual, decadal and multi-decadal climate variability, and ultimately to better understand forced climate change. The EBM comprises upper and lower oceanic layers with a diffusive coupling, a radiative damping term including feedbacks and stochastic atmospheric forcing. The EBM is used to analyse the influence of radiative forcing, feedbacks and climate system inertia on the global mean surface temperature variance (climate variability) and to understand why Coupled Model Intercomparison Project, Phase 5 (CMIP5) models exhibit such a wide range in the level of variability in globally averaged surface air temperature. We examine the influence of the model parameters on the climate variability on different timescales. To this end, we derive the Fokker–Planck equation for the EBM and then obtain the analytical expression that quantifies the sensitivity coefficients for all model parameters. For all timescales, the most influential factors are as follows: (1) the magnitude of the stochastic forcing, (2) the feedback mechanisms, (3) the upper layer depth, (4) the diffusion parameter and (5) the lower ocean depth. Results from the EBM imply that the range of stochastic forcing in the CMIP5 climate models is around twice as important as the strength of radiative feedback or upper layer depth in causing the model-to-model spread in the magnitude of globally averaged climate model variability. sensitivity analysis; climate variability; climate sensitivity; radiative feedbacks
Sorooshian, Armin; Anderson, Bruce; Bauer, Susanne E.; Braun, Rachel A.; Cairns, Brian; Crosbie, Ewan; Dadashazar, Hossein; Diskin, Glenn; Ferrare, Richard; Flagan, Richard C.; Hair, Johnathan; Hostetler, Chris; Jonsson, Haflidi H.; Kleb, Mary M.; Liu, Hongyu; MacDonald, Alexander B.; McComiskey, Allison; Moore, Richard; Painemal, David; Russell, Lynn M.; Seinfeld, John H.; Shook, Michael; Smith, William L.; Thornhill, Kenneth; Tselioudis, George; Wang, Hailong; Zeng, Xubin; Zhang, Bo; Ziemba, Luke; Zuidema, PaquitaSorooshian, A., B. Anderson, S. E. Bauer, R. A. Braun, B. Cairns, E. Crosbie, H. Dadashazar, G. Diskin, R. Ferrare, R. C. Flagan, J. Hair, C. Hostetler, H. H. Jonsson, M. M. Kleb, H. Liu, A. B. MacDonald, A. McComiskey, R. Moore, D. Painemal, L. M. Russell, J. H. Seinfeld, M. Shook, W. L. Smith, K. Thornhill, G. Tselioudis, H. Wang, X. Zeng, B. Zhang, L. Ziemba, P. Zuidema, 2019: Aerosol–Cloud–Meteorology Interaction Airborne Field Investigations: Using Lessons Learned from the U.S. West Coast in the Design of ACTIVATE off the U.S. East Coast. Bull. Amer. Meteor. Soc., 100(8), 1511-1528. doi: 10.1175/BAMS-D-18-0100.1. We report on a multiyear set of airborne field campaigns (2005–16) off the California coast to examine aerosols, clouds, and meteorology, and how lessons learned tie into the upcoming NASA Earth Venture Suborbital (EVS-3) campaign: Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE; 2019–23). The largest uncertainty in estimating global anthropogenic radiative forcing is associated with the interactions of aerosol particles with clouds, which stems from the variability of cloud systems and the multiple feedbacks that affect and hamper efforts to ascribe changes in cloud properties to aerosol perturbations. While past campaigns have been limited in flight hours and the ability to fly in and around clouds, efforts sponsored by the Office of Naval Research have resulted in 113 single aircraft flights (>500 flight hours) in a fixed region with warm marine boundary layer clouds. All flights used nearly the same payload of instruments on a Twin Otter to fly below, in, and above clouds, producing an unprecedented dataset. We provide here i) an overview of statistics of aerosol, cloud, and meteorological conditions encountered in those campaigns and ii) quantification of model-relevant metrics associated with aerosol–cloud interactions leveraging the high data volume and statistics. Based on lessons learned from those flights, we describe the pragmatic innovation in sampling strategy (dual-aircraft approach with combined in situ and remote sensing) that will be used in ACTIVATE to generate a dataset that can advance scientific understanding and improve physical parameterizations for Earth system and weather forecasting models, and for assessing next-generation remote sensing retrieval algorithms.
Stackhouse, P. W.; Wong, T.; Kratz, D. P.; Sawaengphokhai, Parnchai; Wilber, A. C.; Gupta, S. K.; Loeb, N. GStackhouse, P. W., T. Wong, D. P. Kratz, P. Sawaengphokhai, A. C. Wilber, S. K. Gupta, N. G. Loeb, 2019: Earth Radiation Budget at Top-Of-Atmosphere [in “State of the Climate in 2018”].. Bull. Amer. Meteor. Soc, 100(9), S46-48. doi: 10.1175/2019BAMSStateoftheClimate.1.
Stackhouse, P. W.; Wong, T.; Kratz, D. P.; Sawaengphokhai, Parnchai; Wilber, A. C.; Gupta, S. K.; Loeb, N. GStackhouse, P. W., T. Wong, D. P. Kratz, P. Sawaengphokhai, A. C. Wilber, S. K. Gupta, N. G. Loeb, 2019: Earth Radiation Budget at Top-Of-Atmosphere [in “State of the Climate in 2018”].. Bull. Amer. Meteor. Soc, 100(9), S46-48. doi: 10.1175/2019BAMSStateoftheClimate.1.
Stengel, Martin; Stapelberg, Stefan; Sus, Oliver; Finkensieper, Stephan; Würzler, Benjamin; Philipp, Daniel; Hollmann, Rainer; Poulsen, Caroline; Christensen, Matthew; McGarragh, GregoryStengel, M., S. Stapelberg, O. Sus, S. Finkensieper, B. Würzler, D. Philipp, R. Hollmann, C. Poulsen, M. Christensen, G. McGarragh, 2019: Cloud_cci AVHRR-PM dataset version 3: 35 year climatology of global cloud and radiation properties. Earth System Science Data Discussions, 1-29. doi: 10.5194/essd-2019-104. Abstract. We present version 3 of the Cloud_cci AVHRR-PM dataset which contains a comprehensive set of cloud and radiative flux properties on a global scale covering the period of 1982 to 2016. The properties were retrieved from Advanced Very High Resolution Radiometer (AVHRR) measurements recorded by the afternoon (post meridiem, PM) satellites of the National Oceanic and Atmospheric Administration (NOAA) Polar Operational Environmental Satellites (POES) missions. The cloud properties in version 3 are of improved quality compared with the precursor dataset version 2, providing better global quality scores for cloud detection, cloud phase and ice water path based on validation results against A-Train sensors. Furthermore, the parameter set was extended by a suite of broadband radiative flux properties. They were calculated by combining the retrieved cloud properties with thermodynamic profiles from reanalysis and surface properties. The flux properties comprise upwelling and downwelling, shortwave and longwave broadband fluxes at the surface (bottom-of-atmosphere - BOA) and top-of-atmosphere (TOA). All fluxes were determined at AVHRR pixel level for all-sky and clear-sky conditions, which will particularly facilitate the assessment of the cloud radiative effect at BOA and TOA in future studies. Validation of the BOA downwelling fluxes against the Baseline Surface Radiation Network (BSRN) show a very good agreement. This is supported by comparisons of multi-annual mean maps with NASA's Clouds and the Earth's Radiant Energy System (CERES) products for all fluxes at BOA and TOA. The Cloud_cci AVHRR-PM version 3 dataset allows for a large variety of climate applications that build on cloud properties, radiative flux properties and/or the link between them. For the presented Cloud_cci AVHRR-PMv3 dataset a Digital Object Identifier has been issued: https://doi.org/10.5676/DWD/ESA_Cloud_cci/AVHRR-PM/V003 (Stengel et al., 2019).
Stephens, Benjamin A.; Jackson, Charles S.; Wagman, Benjamin M.Stephens, B. A., C. S. Jackson, B. M. Wagman, 2019: Effect of Tropical Nonconvective Condensation on Uncertainty in Modeled Projections of Rainfall. J. Climate, 32(19), 6571-6588. doi: 10.1175/JCLI-D-18-0833.1. We find that part of the uncertainty in the amplitude and pattern of the modeled precipitation response to CO2 forcing traces to tropical condensation not directly involved with parameterized convection. The fraction of tropical rainfall associated with large-scale condensation can vary from a few percent to well over half depending on model details and parameter settings. In turn, because of the coupling between condensation and tropical circulation, the different ways model assumptions affect the large-scale rainfall fraction also affect the patterns of the response within individual models. In two single-model ensembles based on the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM), versions 3.1 and 5.3, we find strong correlations between the fraction of tropical large-scale rain and both climatological rainfall and circulation and the response to CO2 forcing. While the effects of an increasing tropical large-scale rain fraction are opposite in some ways in the two ensembles—for example, the Hadley circulation weakens with the large-scale rainfall fraction in the CAM3.1 ensemble while strengthening in the CAM5.3 ensemble—we can nonetheless understand these different effects in terms of the relationship between latent heating and circulation, and we propose explanations for each ensemble. We compare these results with data from phase 5 of the Coupled Model Intercomparison Project (CMIP5), for which some of the same patterns hold. Given the importance of this partitioning, there is a need for constraining this source of uncertainty using observations. However, since a “large-scale rainfall fraction” is a modeling construct, it is not clear how observations may be used to test various modeling assumptions determining this fraction.
Stephens, Graeme L.; Christensen, Matthew; Andrews, Timothy; Haywood, James; Malavelle, Florent F.; Suzuki, Kentaroh; Jing, Xianwen; Lebsock, Mathew; Li, Jui-Lin F.; Takahashi, Hanii; Sy, OusmaneStephens, G. L., M. Christensen, T. Andrews, J. Haywood, F. F. Malavelle, K. Suzuki, X. Jing, M. Lebsock, J. F. Li, H. Takahashi, O. Sy, 2019: Cloud physics from space. Quarterly Journal of the Royal Meteorological Society, 145(724), 2854-2875. doi: 10.1002/qj.3589. A review of the progression of cloud physics from a subdiscipline of meteorology into the global science it is today is described. The discussion briefly touches on the important post-war contributions of three key individuals who were instrumental in developing cloud physics into a global science. These contributions came on the heels of the post-war weather modification efforts that influenced much of the early development of cloud physics. The review is centred on the properties of warm clouds primarily to limit the scope of the article and the connection between the early contributions to cloud physics and the current vexing problem of aerosol effects on cloud albedo is underlined. Progress toward estimating cloud properties from space and insights on warm cloud processes are described. Measurements of selected cloud properties, such as cloud liquid water path are now mature enough that multi-decadal time series of these properties exist and this climatology is used to compare to analogous low-cloud properties taken from global climate models. The too-wet (and thus too bright) and the too-dreary biases of models are called out underscoring the challenges we still face in representing warm clouds in Earth system models. We also provide strategies for using observations to constrain the indirect radiative forcing of the climate system. atmosphere; clouds; microphysics; climate; observations; remote sensing
Su, Chun-Yian; Wu, Chien-Ming; Chen, Wei-Ting; Chen, Jen-HerSu, C., C. Wu, W. Chen, J. Chen, 2019: Object-based precipitation system bias in grey zone simulation: the 2016 South China Sea summer monsoon onset. Climate Dynamics, 53(1), 617-630. doi: 10.1007/s00382-018-04607-x. This study aims to evaluate the precipitation bias in the grey zone simulation (~ 15 km) using the Central Weather Bureau Global Forecast System (CWBGFS). We develop a new evaluation method using the object-based precipitation system (OPS) to examine the bias associated with the degree of convection organization. The 2016 South China Sea (SCS) Summer Monsoon onset is selected to evaluate the model’s performance due to its sharp transition of large-scale circulation, which contributes to the complexity of precipitation pattern. The results based on OPS show that the observed precipitation tends to aggregate toward the central part of SCS during the post-onset period, while the precipitation in the model distributes more sparsely over the ocean. The observed precipitation intensity increases with the size of OPS especially for the extremes; however, the model underrepresents the relationship between the precipitation spectrum and the size of OPS. Moreover, the model simulates earlier diurnal peak time of precipitation over land in the organized systems than observation. The results also suggest that the convection scheme is insensitive to column moisture during the pre-onset period which seems to be one of the key factors to the excessive precipitation in the model. Using high horizontal resolution, however, does not improve the simulation of precipitation much in the model. The current study suggests that the precipitation bias related to aggregation of the convective systems should be regarded as an essential objective of model evaluation and improvement.
Sujith, K.; Saha, Subodh Kumar; Rai, Archana; Pokhrel, Samir; Chaudhari, Hemantkumar S.; Hazra, Anupam; Murtugudde, Raghu; Goswami, B.n.Sujith, K., S. K. Saha, A. Rai, S. Pokhrel, H. S. Chaudhari, A. Hazra, R. Murtugudde, B. Goswami, 2019: Effects of a Multilayer Snow Scheme on the Global Teleconnections of the Indian Summer Monsoon. Quarterly Journal of the Royal Meteorological Society, 145(720), 1102-1117. doi: 10.1002/qj.3480. Eurasian snow is one of the slowly varying boundary forcings, that is known to have significant influences on the mean and variability of the Indian summer monsoon rainfall (ISMR). A multilayer complex snow scheme, incorporated into the state-of-the-art coupled Climate Forecast System version 2 (CFSv2) showed significant improvements in the simulation of mean ISMR, snow, northern hemisphere surface and tropospheric temperature. Here we show that a realistic simulation of high latitude snow decreases the north-south temperature gradient, which in turn decreases the meridional transport of energy from the equator to the pole, consequently affecting the tropical sea surface temperature (SST) and air-sea interactions. The global teleconnections of the ISMR with SST and 2m temperature over land are also improved considerably in association with improved simulation of the oceanic natural modes of variability. Our findings provide new insights for the relationship between the winter Eurasian snow and the following ISMR, namely that the same relationship may be understood through a framework of meridional atmospheric energy transport and its effects on the tropical air-sea interactions. The improvements in the global teleconnection in the modified version of CFSv2 may have implications in the ISMR predictability and prediction skill. air-sea interactions; Eurasian Snow; Monsoon; teleconnections
Sun, Jian; Zhang, Kai; Wan, Hui; Ma, Po-Lun; Tang, Qi; Zhang, ShixuanSun, J., K. Zhang, H. Wan, P. Ma, Q. Tang, S. Zhang, 2019: Impact of Nudging Strategy on the Climate Representativeness and Hindcast Skill of Constrained EAMv1 Simulations. Journal of Advances in Modeling Earth Systems, 11(12), 3911-3933. doi: 10.1029/2019MS001831. Nudging is a simulation technique widely used in sensitivity studies and in the evaluation of atmosphere models. Care is needed in the experimental setup in order to achieve the desired constraint on the simulated atmospheric processes without introducing undue intervention. In this study, sensitivity experiments are conducted with the Energy Exascale Earth System Model (E3SM) Atmosphere Model Version 1 (EAMv1) to identify setups that can give results representative of the model's long-term climate and meanwhile reasonably capture characteristics of the observed meteorological conditions to facilitate the comparison of model results with measurements. We show that when the prescribed meteorological conditions are temporally interpolated to the model time to constrain EAM's horizontal winds at each time step, a nudged simulation can reproduce the characteristic evolution of the observed weather events (especially in middle and high latitudes) as well as the model's long-term climatology, although nudging also leads to nonnegligible regional changes in wind-driven aerosol emissions, low-level clouds in the stratocumulus regime, and cloud and precipitation near the maritime continent. Compared to its predecessor model used in an earlier study, EAMv1 is less sensitive to temperature nudging, although significant impacts on the cloud radiative effects still exist. EAMv1 remains very sensitive to humidity nudging. Constraining humidity substantially improves the correlation between the simulated and observed tropical precipitation but also leads to large changes in the long-term statistics of the simulated precipitation, clouds, and aerosol lifecycle. E3SM; EAMv1; hindcast; nudging
Tan, J.; Frouin, R.Tan, J., R. Frouin, 2019: Seasonal and Interannual Variability of Satellite-Derived Photosynthetically Available Radiation Over the Tropical Oceans. Journal of Geophysical Research: Oceans, 124(5), 3073-3088. doi: 10.1029/2019JC014942. The seasonal and interannual variability of photosynthetically available radiation (PAR) over the tropical oceans is examined using satellite imagery acquired from 1997 to 2017. Spatial and temporal biases between monthly PAR estimates from different instruments are determined and corrected, resulting in a consistent time series over the 20-year record. Uncertainty is evaluated in comparisons with in situ measurements at various sites. Empirical orthogonal function (EOF) analysis is performed with both seasonal and nonseasonal PAR signals, and linear trends are quantified. Seasonal cycles dominate PAR variability, with the first three seasonal EOF modes explaining 84.7% of the total variance. The seasonal patterns are related to solar position and monsoon. Canonical El Niño–Southern Oscillation (ENSO) and Modoki ENSO are related to the two leading nonseasonal EOF modes, with a correlation coefficient of 0.84 between the first mode and the multivariate ENSO index and of 0.48 between the second mode and the El Niño Modoki index. Trend analysis reveals that PAR tends to decrease by 0.2%/year in the central Pacific north of the equator and to increase by 0.2%/year in the central Pacific around 5°S. The tendency is also for PAR to increase west of Central and South America. These changes are consistent with patterns of cloud change evidenced in the satellite cloud record and predicted by global climate models. The long-term satellite PAR data set, together with information of nutrient availability and temperature, enables further studies to elucidate the causes of phytoplankton variability in the tropical oceans.
Tang, Wenjun; Yang, Kun; Qin, Jun; Li, Xin; Niu, XiaoleiTang, W., K. Yang, J. Qin, X. Li, X. Niu, 2019: A 16-year dataset (2000–2015) of high-resolution (3 h, 10 km) global surface solar radiation. Earth System Science Data, 11(4), 1905-1915. doi: https://doi.org/10.5194/essd-11-1905-2019. Abstract. The recent release of the International Satellite Cloud Climatology Project (ISCCP) HXG cloud products and new ERA5 reanalysis data enabled us to produce a global surface solar radiation (SSR) dataset: a 16-year (2000–2015) high-resolution (3 h, 10 km) global SSR dataset using an improved physical parameterization scheme. The main inputs were cloud optical depth from ISCCP-HXG cloud products; the water vapor, surface pressure and ozone from ERA5 reanalysis data; and albedo and aerosol from Moderate Resolution Imaging Spectroradiometer (MODIS) products. The estimated SSR data were evaluated against surface observations measured at 42 stations of the Baseline Surface Radiation Network (BSRN) and 90 radiation stations of the China Meteorological Administration (CMA). Validation against the BSRN data indicated that the mean bias error (MBE), root mean square error (RMSE) and correlation coefficient (R) for the instantaneous SSR estimates at 10 km scale were −11.5 W m−2, 113.5 W m−2 and 0.92, respectively. When the estimated instantaneous SSR data were upscaled to 90 km, its error was clearly reduced, with RMSE decreasing to 93.4 W m−2 and R increasing to 0.95. For daily SSR estimates at 90 km scale, the MBE, RMSE and R at the BSRN were −5.8 W m−2, 33.1 W m−2 and 0.95, respectively. These error metrics at the CMA radiation stations were 2.1 W m−2, 26.9 W m−2 and 0.95, respectively. Comparisons with other global satellite radiation products indicated that our SSR estimates were generally better than those of the ISCCP flux dataset (ISCCP-FD), the global energy and water cycle experiment surface radiation budget (GEWEX-SRB), and the Earth's Radiant Energy System (CERES). Our SSR dataset will contribute to the land-surface process simulations and the photovoltaic applications in the future. The dataset is available at https://doi.org/10.11888/Meteoro.tpdc.270112 (Tang, 2019).
Taylor, Patrick C.; Boeke, Robyn C.; Li, Ying; Thompson, David W. J.Taylor, P. C., R. C. Boeke, Y. Li, D. W. J. Thompson, 2019: Arctic cloud annual cycle biases in climate models. Atmospheric Chemistry and Physics, 19(13), 8759-8782. doi: 10.5194/acp-19-8759-2019. Abstract. Arctic clouds exhibit a robust annual cycle with maximum cloudiness in fall and minimum cloudiness in winter. These variations affect energy flows in the Arctic with a large influence on the surface radiative fluxes. Contemporary climate models struggle to reproduce the observed Arctic cloud amount annual cycle and significantly disagree with each other. The goal of this analysis is to quantify the cloud-influencing factors that contribute to winter–summer cloud amount differences, as these seasons are primarily responsible for the model discrepancies with observations. We find that differences in the total cloud amount annual cycle are primarily caused by differences in low, rather than high, clouds; the largest differences occur between the surface and 950 hPa. Grouping models based on their seasonal cycles of cloud amount and stratifying cloud amount by cloud-influencing factors, we find that model groups disagree most under strong lower tropospheric stability, weak to moderate mid-tropospheric subsidence, and cold lower tropospheric air temperatures. Intergroup differences in low cloud amount are found to be a function of lower tropospheric thermodynamic characteristics. Further, we find that models with a larger low cloud amount in winter have a larger ice condensate fraction, whereas models with a larger low cloud amount in summer have a smaller ice condensate fraction. Stratifying model output by the specifics of the cloud microphysical scheme reveals that models treating cloud ice and liquid condensate as separate prognostic variables simulate a larger ice condensate fraction than those that treat total cloud condensate as a prognostic variable and use a temperature-dependent phase partitioning. Thus, the cloud microphysical parameterization is the primary cause of inter-model differences in the Arctic cloud annual cycle, providing further evidence of the important role that cloud ice microphysical processes play in the evolution and modeling of the Arctic climate system.
Thandlam, Venugopal; Rahaman, HasiburThandlam, V., H. Rahaman, 2019: Evaluation of surface shortwave and longwave downwelling radiations over the global tropical oceans. SN Applied Sciences, 1(10), 1171. doi: 10.1007/s42452-019-1172-2. In the present study, daily downwelling shortwave (QS) and longwave radiation (QL) data from one satellite and two hybrid products have been evaluated using Global Tropical Moored Buoy Array during 2001–2009 in the tropical oceans. Daily satellite data are used from the Clouds and Earth’s Radiant Energy System (CERES) program. Data are obtained using Moderate Resolution Imaging Spectroradiometer (MODIS) (CM) aboard the Terra and Aqua satellites. Coordinated Ocean Research Experiments (CORE-II) and Tropical Flux data (TropFlux) are the other two hybrid products used in this study. The analysis shows that majority of QS observations as well as derived products lie in 200–300 Wm−2 range in all the three tropical oceans. Both QS and QL in all products overestimated the majority of the observations. Yet, they underestimated the lower (0–100 Wm−2) values in QS and higher (300–440 Wm−2) values in QL. Majority of the QL observations lie within 390–420 Wm−2 range, and CM slightly overestimated this observed distribution in the Pacific and the Atlantic Oceans. But, majority of the observations in the Indian Ocean lie within 420–450 Wm−2 range. This implies that the tropical Indian Ocean receives 30 Wm−2 more energy as compared to the tropical Pacific and the Atlantic in the form of downwelling longwave radiation. Daily observed QS shows dominant seasonal cycle over the central, the eastern Pacific and the eastern Atlantic. On the other hand, the western Pacific, the central Atlantic and the Indian Oceans show intraseasonal variations. All products show this variation with high root-mean-square error (RMSE) values (QS and QL) over the Indian Ocean than in the Pacific and the Atlantic Oceans. Downwelling radiation from CORE-II shows highest RMSE (for both QS and QL) with least correlation coefficient (CC), and TropFlux has lowest RMSE and highest CC among all products in all three tropical oceans. CM has intermediate values of standard deviation, CC and RMSE. These results are not seasonally dependent, since the seasonal statistics are consistent with seasonal changes. Assuming that the SST is only driven by the downwelling shortwave and longwave fluxes, the errors associated with monthly SST can be as large as 0.2–0.3 (0.1–0.2) °C associated with errors in QS (QL). Both QS and QL in CORE-II have lower spatial variability as compared to other datasets. QL in the tropical oceans shows seasonal spatial variability determined by intertropical convergence zone positions. This variability does not change significantly over the Pacific and the Atlantic Oceans. The summer and winter monsoon patterns in the Indian Ocean guide the QL variability. Opposite to QS, higher QL values have lower variability. Thus, this study aims at finding better radiation dataset to use in the numerical models and deduce that satellite data could be an alternative to existing reanalysis products.
Thomas, Manu Anna; Devasthale, Abhay; Koenigk, Torben; Wyser, Klaus; Roberts, Malcolm; Roberts, Christopher; Lohmann, KatjaThomas, M. A., A. Devasthale, T. Koenigk, K. Wyser, M. Roberts, C. Roberts, K. Lohmann, 2019: A statistical and process-oriented evaluation of cloud radiative effects in high-resolution global models. Geoscientific Model Development, 12(4), 1679-1702. doi: 10.5194/gmd-12-1679-2019. Abstract. This study evaluates the impact of atmospheric horizontal resolution on the representation of cloud radiative effects (CREs) in an ensemble of global climate model simulations following the protocols of the High Resolution Model Intercomparison Project (HighResMIP). We compare results from four European modelling centres, each of which provides data from “standard”- and “high”-resolution model configurations. Simulated radiative fluxes are compared with observation-based estimates derived from the Clouds and Earth's Radiant Energy System (CERES) dataset. Model CRE biases are evaluated using both conventional statistics (e.g. time and spatial averages) and after conditioning on the phase of two modes of internal climate variability, namely the El Niño–Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO). Simulated top-of-atmosphere (TOA) and surface CREs show large biases over the polar regions, particularly over regions where seasonal sea-ice variability is strongest. Increasing atmospheric resolution does not significantly improve these biases. The spatial structure of the cloud radiative response to ENSO and NAO variability is simulated reasonably well by all model configurations considered in this study. However, it is difficult to identify a systematic impact of atmospheric resolution on the associated CRE errors. Mean absolute CRE errors conditioned on the ENSO phase are relatively large (5–10 W m−2) and show differences between models. We suggest this is a consequence of differences in the parameterization of SW radiative transfer and the treatment of cloud optical properties rather than a result of differences in resolution. In contrast, mean absolute CRE errors conditioned on the NAO phase are generally smaller (0–2 W m−2) and more similar across models. Although the regional details of CRE biases show some sensitivity to atmospheric resolution within a particular model, it is difficult to identify patterns that hold across all models. This apparent insensitivity to increased atmospheric horizontal resolution indicates that physical parameterizations play a dominant role in determining the behaviour of cloud–radiation feedbacks. However, we note that these results are obtained from atmosphere-only simulations and the impact of changes in atmospheric resolution may be different in the presence of coupled climate feedbacks.
Tian, Jingjing; Dong, Xiquan; Xi, Baike; Williams, Christopher R.; Wu, PengTian, J., X. Dong, B. Xi, C. R. Williams, P. Wu, 2019: Estimation of liquid water path below the melting layer in stratiform precipitation systems using radar measurements during MC3E. Atmospheric Measurement Techniques, 12(7), 3743-3759. doi: 10.5194/amt-12-3743-2019. Abstract. In this study, the liquid water path (LWP) below the melting layer in stratiform precipitation systems is retrieved, which is a combination of rain liquid water path (RLWP) and cloud liquid water path (CLWP). The retrieval algorithm uses measurements from the vertically pointing radars (VPRs) at 35 and 3 GHz operated by the US Department of Energy Atmospheric Radiation Measurement (ARM) and National Oceanic and Atmospheric Administration (NOAA) during the field campaign Midlatitude Continental Convective Clouds Experiment (MC3E). The measured radar reflectivity and mean Doppler velocity from both VPRs and spectrum width from the 35 GHz radar are utilized. With the aid of the cloud base detected by a ceilometer, the LWP in the liquid layer is retrieved under two different situations: (I) no cloud exists below the melting base, and (II) cloud exists below the melting base. In (I), LWP is primarily contributed from raindrops only, i.e., RLWP, which is estimated by analyzing the Doppler velocity differences between two VPRs. In (II), cloud particles and raindrops coexist below the melting base. The CLWP is estimated using a modified attenuation-based algorithm. Two stratiform precipitation cases (20 and 11 May 2011) during MC3E are illustrated for two situations, respectively. With a total of 13 h of samples during MC3E, statistical results show that the occurrence of cloud particles below the melting base is low (9 %); however, the mean CLWP value can be up to 0.56 kg m−2, which is much larger than the RLWP (0.10 kg m−2). When only raindrops exist below the melting base, the average RLWP value is larger (0.32 kg m−2) than the with-cloud situation. The overall mean LWP below the melting base is 0.34 kg m−2 for stratiform systems during MC3E.
Tian, Lin; Zhang, Peng; Chen, LinTian, L., P. Zhang, L. Chen, 2019: Estimation of the Dust Aerosol Shortwave Direct Forcing Over Land Based on an Equi-albedo Method From Satellite Measurements. Journal of Geophysical Research: Atmospheres, 124(15), 8793-8807. doi: 10.1029/2019JD030974. It is important but difficult to measure the shortwave radiative forcing of the dust aerosols over land from satellite-observed radiance because the inhomogeneous surface albedo varies in a large dynamic range. In this study, we proposed a satellite-based equi-albedo method to derive the dust aerosol shortwave direct forcing over land. In the method, an equal radiance at the top of atmosphere was assumed for the region with the similar surface albedo and the similar solar zenith angle. The aerosol optical depth (AOD) from Moderate Resolution Imaging Spectroradiometer and the shortwave radiance product from Clouds and Earth's Radiant Energy System were used to derive the dust aerosol radiative forcing. The dust storm events outbroken on 9 and 24 April 2010 in Taklimakan desert were selected as study cases. The mean dust shortwave direct forcing efficiency is −35.08 W/m2 per unit of dust AOD during the dust storm events. The results were validated with the calculated radiative forcing from Moderate Resolution Imaging Spectroradiometer AOD product by the radiative transfer model. It shows that the derived radiative forcing is well correlated with the simulated one. The mean difference is 10.57 and the standard deviation is 1.35. Moreover, uncertainty has been estimated. The regional mean-directed radiative forcing due to dust are −28.98 ± 7.99 and −35.76 ± 10.61 W/m2 of these two cases directly from satellite observations. This research indicates that the proposed method is reliable and effective, which can be used to estimate the shortwave direct radiative forcing of the dust storm event.
Tornow, F.; Domenech, C.; Fischer, J.Tornow, F., C. Domenech, J. Fischer, 2019: On the Use of Geophysical Parameters for the Top-of-Atmosphere Shortwave Clear-Sky Radiance-to-Flux Conversion in EarthCARE. J. Atmos. Oceanic Technol., 36(4), 717-732. doi: 10.1175/JTECH-D-18-0087.1. We have investigated whether differences across Clouds and the Earth’s Radiant Energy System (CERES) top-of-atmosphere (TOA) clear-sky angular distribution models, estimated separately over regional (1° × 1° longitude–latitude) and temporal (monthly) bins above land, can be explained by geophysical parameters from Max Planck Institute Aerosol Climatology, version 1 (MAC-v1), ECMWF twentieth-century reanalysis (ERA-20C), and a MODIS bidirectional reflectance distribution function (BRDF)/albedo/nadir BRDF-adjusted reflectance (NBAR) Climate Modeling Grid (CMG) gap-filled products (MCD43GF) climatology. Our research aimed to dissolve binning and to isolate inherent properties or indicators of such properties, which govern the TOA radiance-to-flux conversion in the absence of clouds. We collocated over seven million clear-sky footprints from CERES Single Scanner Footprint (SSF), edition 4, data with above geophysical auxiliary data. Looking at data per surface type and per scattering direction—as perceived by the broadband radiometer (BBR) on board Earth Clouds, Aerosol and Radiation Explorer (EarthCARE)—we identified optimal subsets of geophysical parameters using two different methods: random forest regression followed by a permutation test and multiple linear regression combined with the genetic algorithm. Using optimal subsets, we then trained artificial neural networks (ANNs). Flux error standard deviations on unseen test data were on average 2.7–4.0 W m−2, well below the 10 W m−2 flux accuracy threshold defined for the mission, with the exception of footprints containing fresh snow. Dynamic surface types (i.e., fresh snow and sea ice) required simpler ANN input sets to guarantee mission-worthy flux estimates, especially over footprints consisting of several surface types.
Trenberth, Kevin E.; Zhang, YongxinTrenberth, K. E., Y. Zhang, 2019: Observed inter-hemispheric meridional heat transports and the role of the Indonesian Throughflow in the Pacific Ocean. J. Climate, 32(24), 8523–8536. doi: 10.1175/JCLI-D-19-0465.1. The net surface energy flux is computed as a residual of the energy budget using top-of-atmosphere radiation combined with the divergence of the column-integrated atmospheric energy transports, and then used with the vertically-integrated ocean heat content tendencies to compute the ocean meridional heat transports (MHTs). The mean annual cycles, and 12-month running mean MHTs as a function of latitude are presented for 2000-2016. Effects of the Indonesian Throughflow (ITF), associated with a net volume flow around Australia accompanied by a heat transport are fully included. Because the ITF-related flow necessitates a return current northward in the Tasman Sea that relaxes during El Niño, the reduced ITF during El Niño may contribute to warming in the south Tasman Sea by allowing the East Australian current to push farther south even as it gains volume from the tropical waters not flowing through the ITF. Although evident in 2015-16, when a major marine heat wave occurred, these effects can be overwhelmed by changes in the atmospheric circulation. Large interannual MHT variability in the Pacific is four times that of the Atlantic. Strong relationships reveal influences from the southern subtropics on ENSO for this period. At the equator, northward ocean MHT arises mainly in the Atlantic (0.75 PW), offset by the Pacific (-0.33 PW) and Indian Oceans (-0.20 PW) while the atmosphere transports energy southward (-0.35 PW). The net equatorial MHT southward (-0.18 PW) is enhanced by -0.1 PW that contributes to the greater warming of the southern (vs northern) oceans.
Trenberth, Kevin E.; Zhang, Yongxin; Fasullo, John T.; Cheng, LijingTrenberth, K. E., Y. Zhang, J. T. Fasullo, L. Cheng, 2019: Observation-based estimate of global and basin ocean meridional heat transport time series. J. Climate, 32(14), 4567–4583. doi: 10.1175/JCLI-D-18-0872.1. Ocean meridional heat transports (MHTs) are deduced as a residual using energy budgets to produce latitude vs time series for the globe, Indo-Pacific and Atlantic. The top-of-atmosphere (TOA) radiation is combined with the vertically-integrated atmospheric energy divergence from atmospheric reanalyses to produce the net surface energy fluxes everywhere. The latter is then combined with estimates of the vertically-integrated ocean heat content (OHC) tendency to produce estimates of the ocean heat divergence. Because seasonal sea-ice and land runoff effects are not fully considered, the mean annual cycle is incomplete, but those effects are small for interannual variability. However, there is a mismatch between 12-month inferred surface flux and the corresponding OHC changes globally, requiring adjustments to account for the Earth’s global energy imbalance. Estimates are greatly improved by building in the constraint that MHT must go to zero at the northern and southern extents of the ocean basin at all times, enabling biases between the TOA and OHC data to be reconciled. Zonal mean global, Indo-Pacific and Atlantic basin ocean MHTs are computed and presented as 12-month running means and for the mean annual cycle for 2000 to 2016. For the Indo-Pacific, the tropical and subtropical MHTs feature a strong relationship with El Niño-Southern Oscillation (ENSO), and in the Atlantic, MHT interannual variability is significantly affected by and likely influences the North Atlantic Oscillation (NAO). However, Atlantic and Pacific changes are linked, suggesting that the Northern Annular Mode (versus NAO) is predominant. There is also evidence of decadal variability or trends.
Trepte, Q. Z.; Minnis, P.; Sun-Mack, S.; Yost, C. R.; Chen, Y.; Jin, Z.; Hong, G.; Chang, F.; Smith, W. L.; Bedka, K. M.; Chee, T. L.Trepte, Q. Z., P. Minnis, S. Sun-Mack, C. R. Yost, Y. Chen, Z. Jin, G. Hong, F. Chang, W. L. Smith, K. M. Bedka, T. L. Chee, 2019: Global Cloud Detection for CERES Edition 4 Using Terra and Aqua MODIS Data. IEEE Transactions on Geoscience and Remote Sensing, 1-40. doi: 10.1109/TGRS.2019.2926620. The Clouds and Earth's Radiant Energy System (CERES) has been monitoring clouds and radiation since 2000 using algorithms developed before 2002 for CERES Edition 2 (Ed2) products. To improve cloud amount accuracy, CERES Edition 4 (Ed4) applies revised algorithms and input data to Terra and Aqua MODerate-resolution Imaging Spectroradiometer (MODIS) radiances. The Ed4 cloud mask uses 5-7 additional channels, new models for clear-sky ocean and snow/ice-surface radiances, and revised Terra MODIS calibrations. Mean Ed4 daytime and nighttime cloud amounts exceed their Ed2 counterparts by 0.035 and 0.068. Excellent consistency between average Aqua and Terra cloud fraction is found over nonpolar regions. Differences over polar regions are likely due to unresolved calibration discrepancies. Relative to Ed2, Ed4 cloud amounts agree better with those from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). CALIPSO comparisons indicate that Ed4 cloud amounts are more than or as accurate as other available cloud mask systems. The Ed4 mask correctly identifies cloudy or clear areas 90%-96% of the time during daytime over nonpolar areas depending on the CALIPSO-MODIS averaging criteria. At night, the range is 88%-95%. Accuracy decreases over land. The polar day and night accuracy ranges are 90%-91% and 80%-81%, respectively. The mean Ed4 cloud fractions slightly exceed the average for seven other imager cloud masks. Remaining biases and uncertainties are mainly attributed to errors in Ed4 predicted clear-sky radiances. The resulting cloud fractions should help CERES produce a more accurate radiation budget and serve as part of a cloud property climate data record. Satellites; cloud; Meteorology; MODIS; Clouds and the Earth's Radiant Energy System (CERES); cloud remote sensing; Clouds; Broadband communication; Calibration; Climate; Cloud computing; cloud mask; MODerate-resolution Imaging Spectroradiometer (MODIS).
Vargas Zeppetello, Lucas R.; Battisti, David S.; Baker, Marcia B.Vargas Zeppetello, L. R., D. S. Battisti, M. B. Baker, 2019: The Origin of Soil Moisture Evaporation “Regimes”. J. Climate, 32(20), 6939-6960. doi: 10.1175/JCLI-D-19-0209.1. Evaporation plays an extremely important role in determining summertime surface temperature variability over land. Observations show the relationship between evaporation and soil moisture generally conforms to the Budyko “two regime” framework; namely, that evaporation is limited by available soil moisture in dry climates and by radiation in wet climates. This framework has led climate models to different parameterizations of the relationship between evaporation and soil moisture in wet and dry regions. We have developed the Simple Land–Atmosphere Model (SLAM) as a tool for studying land–atmosphere interaction in general, and summertime temperature variability in particular. We use the SLAM to show that a negative feedback between evaporation and surface temperature gives rise to the two apparent evaporation “regimes” and provide analytic solutions for evaporative cooling anomalies that demonstrate the nonlinear impact of soil moisture perturbations. Stemming from the temperature dependence of vapor pressure deficit, the feedback we identify has important implications for how transitions between wet and dry land surfaces may impact temperature variability as the climate warms. We also elucidate the impacts of surface moisture and insolation perturbations on latent and sensible heat fluxes and on surface temperature variability.
Várnai, Tamás; Gatebe, Charles; Gautam, Ritesh; Poudyal, Rajesh; Su, WenyingVárnai, T., C. Gatebe, R. Gautam, R. Poudyal, W. Su, 2019: Developing an Aircraft-Based Angular Distribution Model of Solar Reflection from Wildfire Smoke to Aid Satellite-Based Radiative Flux Estimation. Remote Sensing, 11(13), 1509. doi: 10.3390/rs11131509. This study examines the angular distribution of scattered solar radiation associated with wildfire smoke aerosols observed over boreal forests in Canada during the ARCTAS (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites) campaign. First, it estimates smoke radiative parameters (550 nm optical depth of 3.9 and single scattering albedo of 0.90) using quasi-simultaneous multiangular and multispectral airborne measurements by the Cloud Absorption Radiometer (CAR). Next, the paper estimates the broadband top-of-atmosphere radiances that a satellite instrument such as the Clouds and the Earth’s Radiant Energy System (CERES) could have observed, given the narrowband CAR measurements made from an aircraft circling about a kilometer above the smoke layer. This estimation includes both an atmospheric correction that accounts for the atmosphere above the aircraft and a narrowband-to-broadband conversion. The angular distribution of estimated radiances is found to be substantially different than the angular model used in the operational data processing of CERES observations over the same area. This is because the CERES model is a monthly average model that was constructed using observations taken under smoke-free conditions. Finally, a sensitivity analysis shows that the estimated angular distribution remains accurate for a fairly wide range of smoke and underlying surface parameters. Overall, results from this work suggest that airborne CAR measurements can bring some substantial improvements in the accuracy of satellite-based radiative flux estimates. aerosol; angular distribution model; smoke; wildfire; Cloud Absorption Radiometer
Voldoire, A.; Saint‐Martin, D.; Sénési, S.; Decharme, B.; Alias, A.; Chevallier, M.; Colin, J.; Guérémy, J.-F.; Michou, M.; Moine, M.-P.; Nabat, P.; Roehrig, R.; Mélia, D. Salas y; Séférian, R.; Valcke, S.; Beau, I.; Belamari, S.; Berthet, S.; Cassou, C.; Cattiaux, J.; Deshayes, J.; Douville, H.; Ethé, C.; Franchistéguy, L.; Geoffroy, O.; Lévy, C.; Madec, G.; Meurdesoif, Y.; Msadek, R.; Ribes, A.; Sanchez‐Gomez, E.; Terray, L.; Waldman, R.Voldoire, A., D. Saint‐Martin, S. Sénési, B. Decharme, A. Alias, M. Chevallier, J. Colin, J. Guérémy, M. Michou, M. Moine, P. Nabat, R. Roehrig, D. S. y. Mélia, R. Séférian, S. Valcke, I. Beau, S. Belamari, S. Berthet, C. Cassou, J. Cattiaux, J. Deshayes, H. Douville, C. Ethé, L. Franchistéguy, O. Geoffroy, C. Lévy, G. Madec, Y. Meurdesoif, R. Msadek, A. Ribes, E. Sanchez‐Gomez, L. Terray, R. Waldman, 2019: Evaluation of CMIP6 DECK Experiments With CNRM-CM6-1. Journal of Advances in Modeling Earth Systems, 11(7), 2177-2213. doi: 10.1029/2019MS001683. This paper describes the main characteristics of CNRM-CM6-1, the fully coupled atmosphere-ocean general circulation model of sixth generation jointly developed by Centre National de Recherches Météorologiques (CNRM) and Cerfacs for the sixth phase of the Coupled Model Intercomparison Project 6 (CMIP6). The paper provides a description of each component of CNRM-CM6-1, including the coupling method and the new online output software. We emphasize where model's components have been updated with respect to the former model version, CNRM-CM5.1. In particular, we highlight major improvements in the representation of atmospheric and land processes. A particular attention has also been devoted to mass and energy conservation in the simulated climate system to limit long-term drifts. The climate simulated by CNRM-CM6-1 is then evaluated using CMIP6 historical and Diagnostic, Evaluation and Characterization of Klima (DECK) experiments in comparison with CMIP5 CNRM-CM5.1 equivalent experiments. Overall, the mean surface biases are of similar magnitude but with different spatial patterns. Deep ocean biases are generally reduced, whereas sea ice is too thin in the Arctic. Although the simulated climate variability remains roughly consistent with CNRM-CM5.1, its sensitivity to rising CO2 has increased: the equilibrium climate sensitivity is 4.9 K, which is now close to the upper bound of the range estimated from CMIP5 models. climate model; CMIP6 DECK; CNRM-CM6-1
Wall, Casey J.; Hartmann, Dennis L.; Norris, Joel R.Wall, C. J., D. L. Hartmann, J. R. Norris, 2019: Is the Net Cloud Radiative Effect Constrained to be Uniform Over the Tropical Warm Pools?. Geophysical Research Letters, 46(21), 12495-12503. doi: 10.1029/2019GL083642. Global radiative-convective equilibrium simulations are used to investigate the hypothesis that mutual interactions among cloud albedo, sea surface temperature gradients, and atmospheric circulation constrain the net cloud radiative effect (CRE) to be similar in convective and nonconvective regions over the tropical warm pools. We perform an experiment in which convective clouds interact naturally with the ocean and atmosphere by forming over the warmest water and shading it and an experiment in which this interaction is removed by randomizing cloud shading of the ocean. Removing the cloud shading interaction enhances sea surface temperature gradients, lateral atmospheric heat transport, and large-scale convective aggregation and produces convective clouds with much more negative net CRE. These findings support the hypothesis that feedbacks between sea surface temperature and convection are critical to obtaining similar net CRE in convective and nonconvective regions over the tropical warm pools. Cloud Radiative Effects; Ocean-Atmosphere Interactions; Tropical Convection
Walther, Sophia; Duveiller, Gregory; Jung, Martin; Guanter, Luis; Cescatti, Alessandro; Camps‐Valls, GustauWalther, S., G. Duveiller, M. Jung, L. Guanter, A. Cescatti, G. Camps‐Valls, 2019: Satellite Observations of the Contrasting Response of Trees and Grasses to Variations in Water Availability. Geophysical Research Letters, 46(3), 1429-1440. doi: 10.1029/2018GL080535. Interannual variations in ecosystem primary productivity are dominated by water availability. Until recently, characterizing the photosynthetic response of different ecosystems to soil moisture anomalies was hampered by observational limitations. Here, we use a number of satellite-based proxies for productivity, including spectral indices, sun-induced chlorophyll fluorescence, and data-driven estimates of gross primary production, to reevaluate the relationship between terrestrial photosynthesis and water. In contrast to nonwoody vegetation, we find a resilience of forested ecosystems to reduced soil moisture. Sun-induced chlorophyll fluorescence and data-driven gross primary production indicate an increase in photosynthesis as a result of the accompanying higher amounts of light and temperature despite lowered light-use-efficiency. Conversely, remote sensing indicators of greenness reach their detection limit and largely remain stable. Our study thus highlights the differential responses of ecosystems along a tree cover gradient and illustrates the importance of differentiating photosynthesis indicators from those of greenness for the monitoring and understanding of ecosystems. satellite; forest; GPP; photosynthesis; SIF; water effects
Wang, Jianjie; Liu, Chao; Yao, Bin; Min, Min; Letu, Husi; Yin, Yan; Yung, Yuk L.Wang, J., C. Liu, B. Yao, M. Min, H. Letu, Y. Yin, Y. L. Yung, 2019: A multilayer cloud detection algorithm for the Suomi-NPP Visible Infrared Imager Radiometer Suite (VIIRS). Remote Sensing of Environment, 227, 1-11. doi: 10.1016/j.rse.2019.02.024. A new multilayer (ML) cloud detection algorithm based on three shortwave infrared (SWIR) and two longwave infrared (LWIR) channels is developed and applied to the Visible Infrared Imager Radiometer Suite (VIIRS) onboard the Suomi-NPP satellite. The algorithm identifies ML clouds, i.e., ice clouds overlying water clouds, based on satellite multispectral observations in the 1.38, 1.6, 2.25, 8.5, and 11 μm channels. We perform synthetic radiative transfer simulations to understand the sensitivities of the aforementioned channels on ML and single-layer (SL) clouds. Active CALIOP observations are used to evaluate the algorithm. Compared with the collocated CALIOP results, the algorithm can determine SL and ML clouds correctly with success rates of approximately 80% and 60%, respectively, and has similar performance to that of the current MODIS operational ML cloud detection algorithm. The misclassification of ML clouds as SL clouds is primarily caused by thin ice clouds that are practically undetectable using LWIR tests. Furthermore, the algorithm is extended to analyze data from radiometers onboard the geostationary Himawari-8 and FengYun-4A satellites, and results similar to those of VIIRS are obtained. VIIRS; Radiometer; Longwave infrared; Multilayer clouds; Shortwave infrared
Wang, Qian; Zhang, Su-Ping; Xie, Shang-Ping; Norris, Joel R.; Sun, Jian-Xiang; Jiang, Yu-XiWang, Q., S. Zhang, S. Xie, J. R. Norris, J. Sun, Y. Jiang, 2019: Observed Variations of the Atmospheric Boundary Layer and Stratocumulus over a Warm Eddy in the Kuroshio Extension. Mon. Wea. Rev., 147(5), 1581-1591. doi: 10.1175/MWR-D-18-0381.1. A research vessel sailing across a warm eddy in the Kuroshio Extension on 13 April 2016 captured an abrupt development of stratocumulus under synoptic high pressure. Shipboard observations and results from regional atmospheric model simulations indicate that increased surface heat flux over the ocean eddy lowered surface pressure and thereby accelerated southeasterly winds. The southeasterly winds transported moisture toward the low pressure and enhanced the air–sea interface heat flux, which in turn deepened the low pressure and promoted low-level convergence and rising motion over the warm eddy. The lifting condensation level lowered and the top of the marine atmospheric boundary layer (MABL) rose, thereby aiding the development of the stratocumulus. Further experiments showed that 6°C sea surface temperature anomalies associated with the 400-km-diameter warm eddy accounted for 80% of the total ascending motion and 95% of total cloud water mixing ratio in the marine atmospheric boundary layer during the development of stratocumulus. The synthesis of in situ soundings and modeling contributes to understanding of the mechanism by which the MABL and marine stratocumulus respond to ocean eddies.
Wang, Tao; Wu, Dong L.; Gong, Jie; Tsai, VictoriaWang, T., D. L. Wu, J. Gong, V. Tsai, 2019: Tropopause Laminar Cirrus and Its Role in the Lower Stratosphere Total Water Budget. Journal of Geophysical Research: Atmospheres, 124(13), 7034-7052. doi: 10.1029/2018JD029845. Laminar cirrus are thin, extensive, isolated layers of ice clouds frequently observed in the tropical tropopause layer. Widespread laminar cirrus significantly affects tropical tropopause layer total water and thermal budget. In this study, we extract laminar cirrus from the Cloud-Aerosol Lidar with Orthogonal Polarization Level 1 attenuated total backscatter images for January 2009, in order to characterize statistical properties of laminar cirrus cloud length, base, thickness, optical depth, and layer partial ice water path. These characteristics are used to develop an algorithm identifying laminar cirrus automatically from the Cloud-Aerosol Lidar with Orthogonal Polarization Level 2 layer product for 2008–2017. The nearly 10-year records reveal that tropopause laminar cirrus occurrence (30–40% of total cirrus) is strongly anticorrelated with the tropopause temperatures in that colder tropopause in frequent (super)saturation during boreal winter favors in situ formation of clouds. Interannually, anomalously warmer troposphere temperature (ΔT), easterly shear of the quasi-biennial oscillation, and stronger upwelling branch of the Brewer-Dobson circulation enhance laminar cirrus formation via cooling of the tropopause. The tropopause laminar cirrus carries 0.05 mg/m3 ( 0.5 ppmv) of ice water content during boreal winter and tropopause; TTL; ice water content (IWC); laminar cirrus; total water budget; water vapor (H2O)
Wang, Wenshan; Zender, Charles S.; van As, Dirk; Miller, Nathaniel B.Wang, W., C. S. Zender, D. van As, N. B. Miller, 2019: Spatial distribution of melt-season cloud radiative effects over Greenland: Evaluating satellite observations, reanalyses, and model simulations against in situ measurements. Journal of Geophysical Research: Atmospheres, 124(1), 57-71. doi: 10.1029/2018JD028919. Arctic clouds can profoundly influence surface radiation and thus surface melt. Over Greenland, these cloud radiative effects (CRE) vary greatly with the diverse topography. To investigate the ability of assorted platforms to reproduce heterogeneous CRE, we evaluate CRE spatial distributions from a satellite product, reanalyses, and a global climate model against estimates from 21 automatic weather stations (AWS). Net CRE estimated from AWS generally decreases with elevation, forming a “warm center” distribution. CRE areal averages from the five large-scale data sets we analyze are all around 10 W m−2. MERRA-2, ERA-Interim, and CERES CRE estimates agree with AWS and reproduce the “warm center” distribution. However, the NCAR Arctic System Reanalysis (ASR) and the CESM Large ENSemble community project (LENS) show strong warming in the south and northwest, forming a “warm L-shape” distribution. Discrepancies are mainly caused by longwave CRE in the accumulation zone. MERRA-2, ERA-Interim, and CERES successfully reproduce cloud fraction and its dominant positive influence on longwave CRE in this region. On the other hand, longwave CRE from ASR and LENS correlates strongly with ice water path instead of with cloud fraction or liquid water path. Moreover, ASR overestimates cloud fraction and LENS underestimates liquid water path substantially, both with limited spatial variability. MERRA-2 best captures the observed inter-station changes, captures most of the observed cloud-radiation physics, and largely reproduces both albedo and cloud properties. The “warm center” CRE spatial distribution indicates that clouds enhance surface melt in the higher accumulation zone and reduce surface melt in the lower ablation zone. Cloud; Radiation; Greenland; Automatic weather stations
Wang, Yipu; Li, Rui; Min, Qilong; Zhang, Leiming; Yu, Guirui; Bergeron, YvesWang, Y., R. Li, Q. Min, L. Zhang, G. Yu, Y. Bergeron, 2019: Estimation of Vegetation Latent Heat Flux over Three Forest Sites in ChinaFLUX using Satellite Microwave Vegetation Water Content Index. Remote Sensing, 11(11), 1359. doi: 10.3390/rs11111359. Latent heat flux (LE) and the corresponding water vapor lost from the Earth’s surface to the atmosphere, which is called Evapotranspiration (ET), is one of the key processes in the water cycle and energy balance of the global climate system. Satellite remote sensing is the only feasible technique to estimate LE over a large-scale region. While most of the previous satellite LE methods are based on the optical vegetation index (VI), here we propose a microwave-VI (EDVI) based LE algorithm which can work for both day and night time, and under clear or non-raining conditions. This algorithm is totally driven by multiple-sensor satellite products of vegetation water content index, solar radiation, and cloud properties, with some aid from a reanalysis dataset. The satellite inputs and the performance of this algorithm are validated with in situ measurements at three ChinaFLUX forest sites. Our results show that the selected satellite observations can indeed serve as the inputs for the purpose of estimating ET. The instantaneous estimations of LE (LEcal) from this algorithm show strong positive temporal correlations with the in situ measured LE (LEobs) with the correlation coefficients (R) of 0.56–0.88 in the study years. The mean bias is kept within 16.0% (23.0 W/m2) across the three sites. At the monthly scale, the correlations between the retrieval and the in situ measurements are further improved to an R of 0.84–0.95 and the bias is less than 14.3%. The validation results also indicate that EDVI-based LE method can produce stable LEcal under different cloudy skies with good accuracy. Being independent of any in situ measurements as inputs, this algorithm shows great potential for estimating ET under both clear and cloudy skies on a global scale for climate study. satellite remote sensing; cloudy sky; ChinaFLUX; clouds and earth’s radiation energy system (CERES); evapotranspiration (ET); Microwave emissivity difference vegetation index (EDVI)
Wehrli, Kathrin; Guillod, Benoit P.; Hauser, Mathias; Leclair, Matthieu; Seneviratne, Sonia I.Wehrli, K., B. P. Guillod, M. Hauser, M. Leclair, S. I. Seneviratne, 2019: Identifying Key Driving Processes of Major Recent Heat Waves. Journal of Geophysical Research: Atmospheres, 124(22), 11746-11765. doi: 10.1029/2019JD030635. Heat waves lead to major impacts on human health, food production, and ecosystems. To assess their predictability and how they are projected to change under global warming, it is crucial to improve our understanding of the underlying processes affecting their occurrence and intensity under present-day climate conditions. Beside greenhouse gas forcing, processes in the different components of the climate system—in particular the land surface, atmospheric circulation, and the oceans—may play a key role in changing the odds for a particular event. This study aims to identify the role of the individual drivers for five heat waves (and, in some cases, of concurrent droughts) in the recent decade. Simulations are performed with the Community Earth System Model using nudging of horizontal atmospheric circulation and prescription of soil moisture. The fully constrained model accurately reproduces how anomalous an event was. Factorial experiments, which force the model toward observations for one or several key components at a time, allow us to identify how much of the observed temperature anomaly of each event can be attributed to each driver. Considering all analyzed events, atmospheric circulation and soil moisture play similarly important roles, each contributing between 20% and 70% to the events' anomalies. This highlights that the role of thermodynamics can be just as important as that of the dynamics for temperature extremes, a possibly underestimated feature. In addition, recent climate change amplified the events and contributed between 10% and 40% of the events' anomalies. atmospheric nudging; extreme events; global climate models; heat waves; soil moisture prescription
Wei, Yu; Zhang, Xiaotong; Hou, Ning; Zhang, Weiyu; Jia, Kun; Yao, YunjunWei, Y., X. Zhang, N. Hou, W. Zhang, K. Jia, Y. Yao, 2019: Estimation of surface downward shortwave radiation over China from AVHRR data based on four machine learning methods. Solar Energy, 177, 32-46. doi: 10.1016/j.solener.2018.11.008. Downward shortwave radiation (DSR) is one of the major driving forces of climate system. Knowledge of the Earth’s radiation budget is essential for improving our understanding of the Earth’s climate. Therefore, accurate estimation of DSR has great significance. Satellite remote sensing is a practical way to derive DSR with high spatial resolution and coverage. In this study, four machine learning methods, including gradient boosting regression tree (GBRT), random forest (RF), multivariate adaptive regression spline (MARS), and artificial neural network (ANN), were applied to estimate DSR at a spatial resolution of 5 km and a temporal resolution of 1 day using Advanced Very High Resolution Radiometer (AVHRR) data. The DSR estimates based on four machine learning methods were evaluated using ground measurements at 96 sites over China. The measurements were collected from the Climate Data Center of the Chinese Meteorological Administration (CDC/CMA) from 2001 to 2003. The evaluation results showed that the GBRT method performed best at both daily and monthly time scales under both clear and cloudy sky conditions. The validation results at the daily time scale showed an overall root mean square error (RMSE) of 30.34 W m−2 and an R value of 0.90 under clear sky conditions, whereas these values were 42.03 W m−2 and 0.86, respectively, under cloudy sky conditions. The DSR estimates had an overall RMSE value of 16.93 W m−2 and an R value of 0.97 at the monthly time scale. The Clouds and Earth's Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) data sets were also used for comparison with the DSR estimates based on the GBRT method. The DSR estimates based on the GBRT method exhibited similar spatial distributions with those of the CERES-EBAF DSR product. Moreover, the DSR estimates based on the GBRT method did not show a clear overestimation tendency, as the CERES-EBAF DSR product did, at the CDC/CMA sites. AVHRR; Downward shortwave radiation; GBRT; Machine learning methods
Wild, Martin; Hakuba, Maria Z.; Folini, Doris; Dorig-Ott, Patricia; Schar, Christoph; Kato, Seiji; Long, Charles N.Wild, M., M. Z. Hakuba, D. Folini, P. Dorig-Ott, C. Schar, S. Kato, C. N. Long, 2019: The cloud-free global energy balance and inferred cloud radiative effects: an assessment based on direct observations and climate models.. Climate dynamics, 52(7), 4787-4812. doi: 10.1007/s00382-018-4413-y. In recent studies we quantified the global mean Earth energy balance based on direct observations from surface and space. Here we infer complementary referenceestimates for its components specifically under cloud-free conditions. While the clear-sky fluxes at the top of atmosphere (TOA) are accurately known from satellite measurements, the corresponding fluxes at the Earth's surface are not equally well established, as they cannot be directly measured from space. This is also evident in 38 global climate models from CMIP5, which are shown to greatly vary in their clear-sky surface radiation budgets. To better constrain the latter, we established new clear-sky reference climatologies of surface downward shortwave and longwave radiative fluxes from worldwide distributed Baseline Surface Radiation Network sites. 33 out of the 38 CMIP5 models overestimate the clear-sky downward shortwave reference climatologies, whereas both substantial overestimations and underestimations are found in the longwave counterparts in some of the models. From the bias structure of the CMIP5 models we infer best estimates for the global mean surface downward clear-sky shortwave and longwave radiation, at 247 and 314 Wm-2, respectively. With a global mean surface albedo of 13.5% and net shortwave clear-sky flux of 287 Wm-2 at the TOA this results in a global mean clear-sky surface and atmospheric shortwave absorption of 214 and 73 Wm-2, respectively. From the newly-established diagrams of the global energy balance under clear-sky and all-sky conditions, we quantify the cloud radiative effects not only at the TOA, but also within the atmosphere and at the surface.
Woelfle, M. D.; Bretherton, C. S.; Hannay, C.; Neale, R.Woelfle, M. D., C. S. Bretherton, C. Hannay, R. Neale, 2019: Evolution of the Double-ITCZ Bias Through CESM2 Development. Journal of Advances in Modeling Earth Systems, 11(7), 1873-1893. doi: 10.1029/2019MS001647. The structure of the east Pacific Intertropical Convergence Zone (ITCZ) as simulated in the Community Earth System Model version 2 (CESM2) is greatly improved as compared to its previous version, CESM version 1. Examination of intermediate model versions created as part of the development process for CESM2 shows the improvement in the ITCZ is well correlated with a reduction in the relative warmth of southeast Pacific sea surface temperatures (SSTs) as compared to the broader tropical mean. Cooling SST in this region enhances the zonal SST and surface pressure gradients and reduces the anomalously southward SST gradient present in boreal spring in early version of CESM2. The improvements in southeast Pacific SST are attributed to increases in low cloud cover and the associated shortwave cloud forcing over the southeast. Sensitivity tests using fixed SST simulations demonstrate the increase in cloud cover between two intermediate model versions, 119 and 125, to be driven by removal of the dependence of autoconversion and accretion rates on cloud water variance as well as the removal of a secondary condensation scheme. Both of these changes reduce drizzle rates in warm clouds increasing cloud lifetime and cloud fraction in the stratocumulus to trade cumulus transition region. The improvements in southeast Pacific shortwave cloud forcing and ITCZ climatology persist through subsequent changes to the cloud microphysics parameterizations. Despite improvements in the east Pacific ITCZ, the global mean ITCZ position and Pacific cold tongue bias strength do not exhibit a systematic improvement across the development simulations. ITCZ; climate model; CESM; double ITCZ; model bias; Pacific rainfall
Wu, M.; Lee, J.-E.Wu, M., J. Lee, 2019: Thresholds for Atmospheric Convection in Amazonian Rainforests. Geophysical Research Letters, 46(16), 10024-10033. doi: 10.1029/2019GL082909. The Amazon rainforest is known as the “Green Ocean” for its maritime-like convection and cloud microphysics during the wet season. Although previous studies suggest the dominant thermodynamic processes involved in deep convection may differ between land and ocean, a comprehensive understanding of the thermodynamics of Amazonian convection is lacking. Using 404,971 daytime precipitating cloud profiles from the CloudSat satellite, we observe a regime transition from congestus dominance to cumulonimbus dominance when convective available potential energy exceeds a threshold in Amazonia and also in shrublands, but not in oceanic regions. In addition, the cloud regime transition is linked to boundary layer moisture in the two continental regions, while it is linked to lower-free-tropospheric moisture in the oceanic region. As the dry season progresses in Amazonia and modifies the free-tropospheric stability, a moderate plant water stress and increased incoming solar energy facilitate the initiation of deep convection and the onset of the wet season. CloudSat; atmospheric convection; tropical rainforest
Xia, Youlong; Hao, ZengchaoXia, Y., Z. Hao, 2019: Regional and Global Land Data Assimilation Systems: Innovations, Challenges, and Prospects. Journal of Meteorological Research, 33(2), 159-189. doi: 10.1007/s13351-019-8172-4.
Xie, Yuanyu; Wang, Yuxuan; Dong, Wenhao; Wright, Jonathon S.; Shen, Lu; Zhao, ZijianXie, Y., Y. Wang, W. Dong, J. S. Wright, L. Shen, Z. Zhao, 2019: Evaluating the Response of Summertime Surface Sulfate to Hydroclimate Variations in the Continental United States: Role of Meteorological Inputs in the GEOS-Chem Model. Journal of Geophysical Research: Atmospheres, 124(3), 1662-1679. doi: 10.1029/2018JD029693. Understanding the response of sulfate to climate change is crucial given tight couplings between sulfate and the hydrological cycle. As the sources and sinks of sulfate are sensitive to cloud and precipitation processes, the accuracy of model simulations depends on the accuracy of these meteorological inputs. In this study, we evaluate the GEOS-Chem model in simulating summertime surface sulfate concentrations in the continental United States across different levels of dryness and compare the model performance based on two sets of meteorological fields: Modern Era Retrospective Analysis for Research and Applications (MERRA) and MERRA-2. Both simulations fail to reproduce observed increases in sulfate during drought, as indicated by negative correlation slopes between surface sulfate concentrations and the standardized precipitation evapotranspiration index (SPEI). This deficiency can be largely attributed to too large a decrease in clouds and hence aqueous phase sulfate production as conditions shift from wet to dry. MERRA-2-driven GEOS-Chem (M2GC) shows improvements in cloud and precipitation fields relative to the MERRA-driven GEOS-Chem, hence eliminating approximately half of the bias in the simulated sulfate-SPEI slope. However, M2GC still underestimates boundary layer cloud fraction, overestimates liquid water content, and overestimates the rates of the decrease in both quantities as conditions become drier. Explicitly correcting these cloud biases in M2GC results in a 60–80% reduction of the bias in the simulated sulfate-SPEI slope. The strong sensitivity of simulated sulfate to prescribed cloud fields suggests the need for more comprehensive assessment of cloud inputs for sulfate simulations under current and future climate change scenarios. clouds; aqueous phase production; hydrological cycles; precipitation; sulfate
Xie, Zhiling; Wang, BinXie, Z., B. Wang, 2019: Summer atmospheric heat sources over the western-central Tibetan Plateau: An integrated analysis of multiple reanalysis and satellite datasets. J. Climate, 32(4), 1181–1202. doi: 10.1175/JCLI-D-18-0176.1. Multiple bias-corrected top-quality reanalysis datasets, gauge-based observations, and selected satellite products are synthetically employed to revisit the climatology and variability of the summer atmospheric heat sources over the Tibetan Plateau (TP). Verification-based selection and ensemble-mean methods are utilized to combine various datasets. Different from previous works, this study pays special attention to estimating the total heat source (TH) and its components over the data-void western plateau (70° - 85°E), including the surface sensible heat (SH), latent heat released by precipitation (LH), and net radiation flux (RD).Consistent with previous studies, the climatology of summer SH (LH) typically increases (decreases) from southeast to northwest. Generally, LH dominates TH over most of the TP. A notable new finding is a minimum TH area over the high-altitude region of the northwestern TP, where the Karakoram Mountain Range is located. We find that during the period of 1984-2006, TH shows insignificant trends over the eastern and central TP, whereas exhibits an evident increasing trend over the western TP that is attributed to the rising tendency of LH before 1996 and that of RD after 1996. The year-to-year variation of TH over the central-eastern TP is highly correlated with that of LH, but that’s not the case over the western TP. It is also worth noting that the variations of TH in each summer month are not significantly correlated with each other, hence study of the interannual variation of the TP heat sources should consider the remarkable subseasonal variations.
Xu, Donghui; Agee, Elizabeth; Wang, Jingfeng; Ivanov, Valeriy Y.Xu, D., E. Agee, J. Wang, V. Y. Ivanov, 2019: Estimation of Evapotranspiration of Amazon Rainforest Using the Maximum Entropy Production Method. Geophysical Research Letters, 46(3), 1402-1412. doi: 10.1029/2018GL080907. Energy budget of Amazonian forests has a large influence on regional and global climate, but relevant data are scarce. A novel energy partition method based on the maximum entropy production (MEP) theory is applied to simulate evapotranspiration in Amazonia. Using site-level eddy flux data, the MEP method shows high skill at the hourly, daily, and monthly scales. Consistent performance under different levels of land surface dryness is revealed, hinting that drought signal is appropriately resolved. The site-level MEP-based estimates outperform the estimates of the Moderate Resolution Imaging Spectroradiometer evapotranspiration product, which is commonly used for large-scale assessments. At the Amazon basin scale, the two series yield similar averages but exhibit spatial differences. The parameter parsimony and demonstrated skill of the MEP method make it an attractive approach for environments with diverse strategies of water flux control. remote sensing; evapotranspiration; Amazon rainforest; maximum entropy production; water stress
Xu, Kuan-Man; Hu, Yongxiang; Wong, TakmengXu, K., Y. Hu, T. Wong, 2019: Convective Aggregation and Indices Examined from CERES Cloud Object Data. Journal of Geophysical Research: Atmospheres, 124(24), 13604-13624. doi: 10.1029/2019JD030816. Convective aggregation is a self-aggregation phenomenon appearing in idealized radiative-convective equilibrium simulations under constant, uniform sea surface temperature (SST). To gain an understanding of observed convective aggregation or organization, three metrics, i.e., simple convective aggregation index (SCAI), modified SCAI (MCAI), and convective organization potential (COP), are evaluated with cloud object data from CERES. MCAI is related to object sizes through a modified inter-object distance (IOD). It is found that large-size object groups are less aggregated according to SCAI but more organized according to COP, compared to small-size object groups. The opposite sensitivities to object-group size can be explained by the dominant roles of the IOD in SCAI and the sum of object radii in COP as object-group sizes increase. However, large-size object groups are slightly more aggregated than small-size ones according to MCAI. Both SCAI and MCAI increase with the number of cloud objects (N) in an object group but COP has a weak dependency on N. Further sorting by object-group total area shows that sensitivity of MCAI to object-group area agrees with that of SCAI for small-area ranges but with that of COP for large-area ranges, which is related to the weak sensitivity of the modified IOD to object-group area, as compared to that of the original IOD. Finally, the three metrics show the similar contrasts between continental and oceanic convection and the same weak sensitivity to SST. The latter suggests that self-aggregation is weaker at higher SSTs than at lower SSTs, in contrast to the findings of many simulations. Cloud object; Convective aggregation; Convective aggregation index
Yang, Quan; Zhang, Feng; Zhang, Hua; Wang, Zhili; Li, Jiangnan; Wu, Kun; Shi, Yining; Peng, YiranYang, Q., F. Zhang, H. Zhang, Z. Wang, J. Li, K. Wu, Y. Shi, Y. Peng, 2019: Assessment of two-stream approximations in a climate model. Journal of Quantitative Spectroscopy and Radiative Transfer, 225, 25-34. doi: 10.1016/j.jqsrt.2018.12.016. The accuracies of the two-stream discrete-ordinate-method (DOM) and Eddington approximation schemes are systematically compared using the BCC_RAD radiative transfer scheme used in a general circulation model (GCM). It is found that the two-stream DOM produces more accurate results for the upward radiative flux, downward radiative flux and heating rate under clear-sky conditions in an offline radiation model, whereas the Eddington approximation is more accurate under all-sky conditions. An experiment using satellite data as the approximation of cloud properties confirms the superiority of the Eddington approximation under cloudy-sky conditions. Experiments using the GCM of the Beijing Climate Center (BCC_AGCM2.0.1) show that, compared to the two-stream DOM, the Eddington approximation can enhance the fraction of low cloud, and this increased cloud fraction can affect the differences in radiative fluxes between these schemes. This study suggests that the more suitable approach in GCMs is to use the Eddington approximation. General circulation model; Radiative transfer; Two-stream approximation
Yang, Yuting; Roderick, Michael L.Yang, Y., M. L. Roderick, 2019: Radiation, surface temperature and evaporation over wet surfaces. Quarterly Journal of the Royal Meteorological Society, 145(720), 1118-1129. doi: 10.1002/qj.3481. Predicting evaporation from wet surfaces (water, wet soil and canopy surfaces) has long been of major interest in hydrological, meteorological and agricultural communities. In practical applications of the existing models/theories of wet surface evaporation (e.g., the Priestley-Taylor model), net radiation (Rn) and/or surface temperature (Ts; or near-surface air temperature) are considered to be independent external forcings that determine the evaporation rate. However, neither Rn nor Ts are independent of evaporation, since Rn directly depends on Ts via the outgoing longwave radiation. In this study, we use monthly data for the global ocean to investigate the relation between radiation, evaporation and surface temperature. We use a new theoretical formulation to show that as Ts increases, a greater fraction of Rn is partitioned to evaporation (i.e., higher evaporative fraction) but Rn declines because of an increase in outgoing longwave radiation. The consequence is that a maximum evaporation rate emerges naturally from that trade-off. We find that this maximum corresponds to the actual evaporation over global ocean surfaces at both local and global scales. In addition, the maximum in evaporation defines a Ts that corresponds to independent estimates of sea surface temperature. These results suggest that the concept of maximum evaporation reported here is a natural attribute of a wet evaporating surface. Evaporation; Radiation; Surface temperature; Bowen ratio; Ocean surfaces
Yang, Zesu; Zhang, Qiang; Hao, Xiaocui; Yue, PingYang, Z., Q. Zhang, X. Hao, P. Yue, 2019: Changes in Evapotranspiration Over Global Semiarid Regions 1984–2013. Journal of Geophysical Research: Atmospheres, 124(6), 2946-2963. doi: 10.1029/2018JD029533. Global mean evapotranspiration (ET) has been increasing in recent decades under climate warming. Yet the magnitude and spatial distribution of ET variation remain highly uncertain. ET changes in different regions are still poorly understood due to limitations in observation records, especially in semiarid regions with undeveloped economic systems and sparse observations. Based on the Priestley-Taylor Jet Propulsion Laboratory model, ET was estimated over global typical semiarid regions for 1984–2013. All of these regions show a decreasing ET trend, which is opposite to the trend in global mean ET. In particular, North Africa has the fastest decreasing trend, 8.6 mm/year, while South Africa has the slowest decreasing trend, 0.7 mm/year. North America, South America, northern Africa, and Australia have declining trends in ET during both warm and cold seasons, while the Loess Plateau, East Asia, central Asia, and South Africa have declining trends in ET only during warm seasons. Accounting for basic factors controlling ET, three important results are identified: First, atmospheric demand is increasing over all semiarid regions due to climate warming; second, the effect of atmospheric composition and cloud weakening radiation is strengthening over all semiarid regions; and finally, annual precipitation is decreasing over all semiarid regions except for South Africa. Factorial experiments indicate that the remarkable declining trend in relative air humidity forces the decreasing trend in ET over all semiarid regions. These results imply a slowing water cycle in global semiarid regions. climate change; evapotranspiration trend; global semiarid areas; PT-JPL model
Yin, Jun; Calabrese, Salvatore; Daly, Edoardo; Porporato, AmilcareYin, J., S. Calabrese, E. Daly, A. Porporato, 2019: The Energy Side of Budyko: Surface-Energy Partitioning From Hydrological Observations. Geophysical Research Letters, 46(13), 7456-7463. doi: 10.1029/2019GL083373. Land-surface partitioning of net radiation into sensible and latent heat fluxes is critical for hydroclimatic processes but remains highly uncertain due to limited observations. We show that a suitable extension of the Budyko's curve, a well-known framework in hydrology for water balance estimation, can be utilized effectively to partition the surface energy fluxes by expressing the long-term evaporative fraction (EF) as a function of the dryness index only. The combination of this energy partitioning method with hydrological observations allows us to estimate the surface energy components at watershed and continental scales. Using this new framework, we show that North American Regional Reanalysis data overestimate surface evaporation, likely influencing the modeling of atmospheric convection. The obtained hydrologic constrains on energy partitioning can be used to provide more accurate estimations of surface energy fluxes for hydroclimatic predictions. Budyko's curve; Budyko's energy curve; hydrological observations; MOPEX; NARR; surface energy partitioning
Yu, LisanYu, L., 2019: Global Air–Sea Fluxes of Heat, Fresh Water, and Momentum: Energy Budget Closure and Unanswered Questions. Annual Review of Marine Science, 11(1), 227-248. doi: 10.1146/annurev-marine-010816-060704. The ocean interacts with the atmosphere via interfacial exchanges of momentum, heat (via radiation and convection), and fresh water (via evaporation and precipitation). These fluxes, or exchanges, constitute the oceansurface energy and water budgets and define the ocean’s role in Earth’s climate and its variability on both short and long timescales. However, direct flux measurements are available only at limited locations. Air–sea fluxes are commonly estimated from bulk flux parameterization using flux-related near-surface meteorological variables (winds, sea and air temperatures, and humidity) that are available from buoys, ships, satellite remote sensing, numerical weather prediction models, and/or a combination of any of these sources. Uncertainties in parameterization-based flux estimates are large, and when they are integrated over the ocean basins, they cause a large imbalance in the global-ocean budgets. Despite the significant progress that has been made in quantifying surface fluxes in the past 30 years, achieving a global closure of ocean-surface energy and water budgets remains a challenge for flux products constructed from all data sources. This review provides a personal perspective on three questions: First, to what extent can time-series measurements from air–sea buoys be used as benchmarks for accuracy and reliability in the context of the budget closures? Second, what is the dominant source of uncertainties for surface flux products, the flux-related variables or the bulk flux algorithms? And third, given the coupling between the energy and water cycles, precipitation and surface radiation can act as twin budget constraints—are the community-standard precipitation and surface radiation products pairwise compatible? Expected final online publication date for the Annual Review of Marine Science Volume 11 is January 3, 2019. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
Yu, Lisan; Jin, X.; Stackhouse, P. W.; Wilber, A. C.; Kato, S.; Loeb, N. G; Weller, R.Yu, L., X. Jin, P. W. Stackhouse, A. C. Wilber, S. Kato, N. G. Loeb, R. Weller, 2019: Global ocean heat, freshwater, and momentum fluxes.[in "State of the Climate in 2018"]. Bull. Amer. Meteor. Soc, 100(9), S81-84. doi: 10.1175/2019BAMSStateoftheClimate.1.
Yu, Shanshan; Xin, Xiaozhou; Liu, Qinhuo; Zhang, Hailong; Li, LiYu, S., X. Xin, Q. Liu, H. Zhang, L. Li, 2019: An Improved Parameterization for Retrieving Clear-Sky Downward Longwave Radiation from Satellite Thermal Infrared Data. Remote Sensing, 11(4), 425. doi: 10.3390/rs11040425. Surface downward longwave radiation (DLR) is a crucial component in Earth’s surface energy balance. Yu et al. (2013) developed a parameterization for retrieving clear-sky DLR at high spatial resolution by combined use of satellite thermal infrared (TIR) data and column integrated water vapor (IWV). We extended the Yu2013 parameterization to Moderate Resolution Imaging Spectroradiometer (MODIS) data based on atmospheric radiative simulation, and we modified the parameterization to decrease the systematic negative biases at large IWVs. The new parameterization improved DLR accuracy by 1.9 to 3.1 W/m2 for IWV ≥3 cm compared to the Yu2013 algorithm. We also compared the new parameterization with four algorithms, including two based on Top-of-Atmosphere (TOA) radiance and two using near-surface meteorological parameters and water vapor. The algorithms were first evaluated using simulated data and then applied to MODIS data and validated using surface measurements at 14 stations around the globe. The results suggest that the new parameterization outperforms the TOA-radiance based algorithms in the regions where ground temperature is substantially different (enough that the difference between them is as large as 20 K) from skin air temperature. The parameterization also works well at high elevations where atmospheric parameter-based algorithms often have large biases. Furthermore, comparing different sources of atmospheric input data, we found that using the parameters interpolated from atmospheric reanalysis data improved the DLR estimation by 7.8 W/m2 for the new parameterization and 19.1 W/m2 for other algorithms at high-altitude sites, as compared to MODIS atmospheric products. MODIS; downward longwave radiation; parameterization; brightness temperature; ground-air temperature difference; water vapor content
Yu, Y.; Shi, J.; Wang, T.; Letu, H.; Yuan, P.; Zhou, W.; Hu, L.Yu, Y., J. Shi, T. Wang, H. Letu, P. Yuan, W. Zhou, L. Hu, 2019: Evaluation of the Himawari-8 Shortwave Downward Radiation (SWDR) Product and its Comparison With the CERES-SYN, MERRA-2, and ERA-Interim Datasets. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 12(2), 519-532. doi: 10.1109/JSTARS.2018.2851965. The land surface shortwave downward radiation (SWDR), also known as surface incident solar radiation, is usually defined as the total solar spectral energy between 300 nm and 3000 nm that arrives at the earth's surface. The SWDR is an essential variable for numerous land models and thus need to be accurately mapped using various approaches. Although numerous efforts have been made to assess the applicability and accuracy of the SWDR datasets produced by satellite and numeric models, few studies have evaluated the performance of the SWDR products from Himawari-8. In this paper, the Himawari-8 SWDR products with both 1 km and 5 km spatial scales were evaluated using ground measurements. The validation results indicate that both of the Himawari-8 SWDR products are in close agreement with ground measurements, even though obvious biases are found. Also, an in-depth intercomparison between the Himawari-8 SWDR product at a 5 km resolution and three other SWDR radiation datasets (CERES-SYN, MERRA-2, and ERA-Interim) was conducted. Here, the Himawari-8 showed the highest levels of accuracy among the four SWDR datasets. Considering its higher temporal and spatial resolutions, the Himawari-8 SWDR products are more detailed and provide the unprecedented potential to improve land surface modeling and reveal the cloud-radiation interactions, even at a 10-min temporal scale. clouds; Earth; Land surface; Remote sensing; atmospheric radiation; atmospheric techniques; Atmospheric modeling; Sea surface; Spatial resolution; evaluation; ERA-Interim; Himawari-8; solar radiation; Clouds; Earth surface; Clouds and the Earth's Radiant Energy System Synoptic (CERES-SYN); land surface shortwave downward radiation (SWDR); Modern-Era Retrospective Analysis for Research and Applications; Version 2 (MERRA-2); CERES-SYN dataset; cloud-radiation interactions; ERA-Interim dataset; ground measurements; Himawari-8 shortwave downward radiation product; Himawari-8 SWDR product; land models; land surface shortwave downward radiation; MERRA-2 dataset; numeric model; satellite model; size 1.0 km; size 5.0 km; surface incident solar radiation; SWDR datasets; SWDR products; SWDR radiation datasets; total solar spectral energy; wavelength 300.0 nm to 3000.0 nm
Yu, Yueyue; Taylor, Patrick C.; Cai, MingYu, Y., P. C. Taylor, M. Cai, 2019: Seasonal variations of Arctic low-level clouds and its linkage to sea ice seasonal variations. Journal of Geophysical Research: Atmospheres, 124(22), 12206-12226. doi: 10.1029/2019JD031014. Using CALIPSO-CloudSat-Clouds and the Earth's Radiant Energy System (CERES)-Moderate Resolution Imaging Spectrometer (MODIS) (C3M) dataset, this study documents the seasonal variation of sea ice, cloud, and atmospheric properties in the Arctic (70°N–82°N) for 2007–2010. A surface type stratification—consisting Permanent Ocean, Land, Permanent Ice, and Transient Sea Ice—is used to investigate the influence of surface type on low-level Arctic cloud liquid water path (LWP) seasonality. The results show significant variations in the Arctic low-level cloud LWP by surface type linked to differences in thermodynamic state. Subdividing the Transient Ice region (seasonal sea ice zone) by melt/freeze season onset dates reveals a complex influence of sea ice variations on low cloud LWP seasonality. We find that lower tropospheric stability (LTS) is the primary factor affecting the seasonality of cloud LWP. Our results suggest that variations in sea ice melt/freeze onset have a significant influence on the seasonality of low-level cloud LWP by modulating the lower tropospheric thermal structure and not by modifying the surface evaporation rate in late spring and mid-summer. We find no significant dependence of the May low-level cloud LWP peak on the melt/freeze onset dates, whereas and September/October low-level cloud LWP maximum shifts later in the season for earlier melt/later freeze onset regions. The Arctic low cloud LWP seasonality is controlled by several surface-atmosphere interaction processes; the importance of each varies seasonally due to the thermodynamic properties of sea ice. Our results demonstrate that when analyzing Arctic cloud-sea ice interactions, a seasonal perspective is critical. Arctic cloud; atmosphere-surface interactions; cloud-sea ice interactions; seasonal cycle
Yue, Qing; Kahn, Brian H.; Fetzer, Eric J.; Wong, Sun; Huang, Xianglei; Schreier, MathiasYue, Q., B. H. Kahn, E. J. Fetzer, S. Wong, X. Huang, M. Schreier, 2019: Temporal and Spatial Characteristics of Short-term Cloud Feedback on Global and Local Interannual Climate Fluctuations from A-Train Observations. J. Climate, 32(6), 1875–1893. doi: 10.1175/JCLI-D-18-0335.1. Observations from multiple sensors on the NASA Aqua satellite are used to estimate the temporal and spatial variability of short-term cloud responses (CR) and cloud feedbacks (λ) for different cloud types, with respect to the interannual variability within the A-Train era (July 2002-June 2017). Short-term cloud feedbacks by cloud type are investigated both globally and locally by three different definitions in the literature: (1) the global mean cloud feedback parameter λGG from regressing the global mean cloud-induced TOA radiation anomaly ΔRG with the global mean surface temperature change ΔTGS; (2) the local feedback parameter λLL from regressing the local ΔR with the local surface temperature change ΔTS; and (3) the local feedback parameter λGL from regressing global ΔRG with local ΔTS. Observations show significant temporal variability in the magnitudes and spatial patterns in λGG and λGL, whereas λLL remains essentially time invariant for different cloud types. The global mean net λGG exhibits a gradual transition from negative to positive in the A-Train era due to a less negative λGG from low clouds and an increased positive λGG from high clouds over the Warm Pool Region associated with the 2015-2016 strong El Niño event. Strong temporal variability in λGL is intrinsically linked to its dependence on global ΔRG, and the scaling of λGL with surface temperature change patterns to obtain global feedback λGG does not hold. Despite the shortness of the A-Train record, statistically robust signals can be obtained for different cloud types and regions of interest.
Zeng, Linglin; Hu, Shun; Xiang, Daxiang; Zhang, Xiang; Li, Deren; Li, Lin; Zhang, TingqiangZeng, L., S. Hu, D. Xiang, X. Zhang, D. Li, L. Li, T. Zhang, 2019: Multilayer Soil Moisture Mapping at a Regional Scale from Multisource Data via a Machine Learning Method. Remote Sensing, 11(3), 284. doi: 10.3390/rs11030284. Soil moisture mapping at a regional scale is commonplace since these data are required in many applications, such as hydrological and agricultural analyses. The use of remotely sensed data for the estimation of deep soil moisture at a regional scale has received far less emphasis. The objective of this study was to map the 500-m, 8-day average and daily soil moisture at different soil depths in Oklahoma from remotely sensed and ground-measured data using the random forest (RF) method, which is one of the machine-learning approaches. In order to investigate the estimation accuracy of the RF method at both a spatial and a temporal scale, two independent soil moisture estimation experiments were conducted using data from 2010 to 2014: a year-to-year experiment (with a root mean square error (RMSE) ranging from 0.038 to 0.050 m3/m3) and a station-to-station experiment (with an RMSE ranging from 0.044 to 0.057 m3/m3). Then, the data requirements, importance factors, and spatial and temporal variations in estimation accuracy were discussed based on the results using the training data selected by iterated random sampling. The highly accurate estimations of both the surface and the deep soil moisture for the study area reveal the potential of RF methods when mapping soil moisture at a regional scale, especially when considering the high heterogeneity of land-cover types and topography in the study area. remote sensing; ground monitoring; multilayer soil moisture mapping; RF method
Zhan, Chuan; Allan, Richard P.; Liang, Shunlin; Wang, Dongdong; Song, ZhenZhan, C., R. P. Allan, S. Liang, D. Wang, Z. Song, 2019: Evaluation of Five Satellite Top-of-Atmosphere Albedo Products over Land. Remote Sensing, 11(24), 2919. doi: 10.3390/rs11242919. Five satellite top-of-atmosphere (TOA) albedo products over land were evaluated in this study including global products from the Advanced Very High Resolution Radiometer (AVHRR) (TAL-AVHRR), Moderate Resolution Imaging Spectroradiometer (MODIS) (TAL-MODIS), and Clouds and the Earth’s Radiant Energy System (CERES); one regional product from the Climate Monitoring Satellite Application Facility (CM SAF); and one harmonized product termed Diagnosing Earth’s Energy Pathways in the Climate system (DEEP-C). Results showed that overall, there is good consistency among these five products, particularly after the year 2000. The differences among these products in the high-latitude regions were relatively larger. The percentage differences among TAL-AVHRR, TAL-MODIS, and CERES were generally less than 20%, while the differences between TAL-AVHRR and DEEP-C before 2000 were much larger. Except for the obvious decrease in the differences after 2000, the differences did not show significant changes over time, but varied among different regions. The differences between TAL-AVHRR and the other products were relatively large in the high-latitude regions of North America, Asia, and the Maritime Continent, while the differences between DEEP-C and CM SAF in Europe and Africa were smaller. Interannual variability was consistent between products after 2000, before which the differences among the three products were much larger. CERES; evaluation; CM SAF; TOA albedo; DEEP-C; TAL-AVHRR; TAL-MODIS
Zhang, Bosong; Kramer, Ryan J.; Soden, Brian J.Zhang, B., R. J. Kramer, B. J. Soden, 2019: Radiative Feedbacks Associated with the Madden–Julian Oscillation. J. Climate, 32(20), 7055-7065. doi: 10.1175/JCLI-D-19-0144.1. Radiative kernels derived from CloudSat/CALIPSO measurements are used to diagnose radiative feedbacks induced by the Madden–Julian oscillation (MJO). Over the Indo-Pacific warm pool, positive cloud and water vapor feedbacks are coincident with the convective envelope of the MJO during its active phases, whereas the lapse rate feedback shows faster eastward propagation than the convective envelope. During phase 2/3, when the convective envelope is over the Indian Ocean, water vapor exhibits a vertically coherent response, with the largest anomalies and strongest feedback in the midtroposphere. Though spatial structures of the feedbacks vary, the most prominent difference lies in the magnitude. Cloud changes induce the largest radiative perturbations associated with the MJO. It is also found that the strength of the cloud feedback per unit of precipitation is greater for strong MJO events, suggesting that the strength of individual MJO events is largely dictated by the magnitude of cloud radiative heating of the atmosphere. In addition, stronger radiative heating due to water vapor and clouds helps the MJO survive the barrier effect of the Maritime Continent, leading to farther eastward propagation. These results offer process-oriented metrics that could help to improve model simulations and predictions of the MJO in the future.
Zhang, Guang J.; Song, Xiaoliang; Wang, YongZhang, G. J., X. Song, Y. Wang, 2019: The double ITCZ syndrome in GCMs: A coupled feedback problem among convection, clouds, atmospheric and ocean circulations. Atmospheric Research, 229, 255-268. doi: 10.1016/j.atmosres.2019.06.023. The appearance of a spurious double ITCZ south of the equator in coupled general circulation models has been a stubborn problem ever since the beginning of coupled model development. This article reviews the past research in this area, with a focus on three possible major contributors to the double ITCZ biases: 1) the southeastern Pacific marine stratus clouds and associated warm sea surface temperature (SST) biases; 2) the extratropical shortwave absorption biases over Southern Ocean; and 3) convective parameterization. The negative biases in marine boundary layer clouds in the southeastern Pacific lead to warm SST biases. Through coupled atmosphere-ocean interactions, it contributes to the double ITCZ bias. Positive shortwave absorption biases over Southern Ocean is believed to be an extratropical contributor to the double ITCZ biases in models. Since the heat from excess shortwave absorption must be transported to the northern hemisphere by the Hadley circulation, the position of the ITCZ must shift southward. However, later research finds that reducing the extratropical shortwave absorption has little effect on the ITCZ position. One possibility is that some feedback mechanism involving subtropical low-level clouds as intermediary is missing. For convective parameterization, changes in various elements in convection schemes can have large impacts on the ITCZ simulation. It involves a complex chain of interactions among convection, large-scale atmospheric circulation, SST, and upper ocean circulation. In one scheme, changes in the scheme lead to the elimination of double ITCZ in all seasons, giving hope that we can finally take on the double ITCZ problem.
Zhang, Shuhua; Li, Xingong; She, Jiangfeng; Peng, XiaominZhang, S., X. Li, J. She, X. Peng, 2019: Assimilating remote sensing data into GIS-based all sky solar radiation modeling for mountain terrain. Remote Sensing of Environment, 231, 111239. doi: 10.1016/j.rse.2019.111239. Solar radiation is the ultimate energy resource of earth surface energy balance and the main driving force of atmospheric, ecological and hydrological processes. Solar radiation over complex terrain has large spatial and temporal variation because of terrain shading and high cloud heterogeneity. While most existing GIS-based solar radiation models only work under clear sky condition, this research presents a solar radiation model which considers both terrain shading and anisotropic cloud attenuation and diffuse radiation using MODIS atmospheric products. Specifically, we use skyshed map, sky cloud maps, and sky weight map to represent angular distribution of sky obstruction, anisotropic cloud properties, and diffuse radiance over hemispherical sky, respectively. Combining skyshed map, sky weight map and sky cloud maps, we develop a solar radiation model where 3D geometrical relationships among sun, cloud, and terrain are considered and anisotropic diffuse radiance and cloud attenuation are modeled. Model results are evaluated using field observations in the Kunlun Mountains of western China. At Terra and Aqua overpass time, our model performs well with a mean relative bias (MRB) of −0.2%. It underestimates in clear and partly cloudy sky with a MRB of −5.86% and −4.79% and has a mean absolute relative bias (MARB) of 8.11% and 21.59% respectively. It overestimates under overcast sky with a MRB of 1.68% and has a MARB of 31.71%. Our model performs better when compared with existing instantaneous solar radiation products. For daily solar radiation, our model shows good performance with a MRB of 1.43% and MARB of 17.02%. Our model shows significant spatial variation of solar radiation within the study area with the influences from terrain and cloud. Our research provides a novel and improved approach to assimilating remote sensing data into GIS-based solar radiation modeling in mountainous terrain where observations are sparse and difficult to obtain. Solar radiation; Cloud attenuation; Sky cloud map; Terrain shadow
Zhang, Taiping; Stackhouse, Paul W.; Cox, Stephen J.; Mikovitz, J. Colleen; Long, Charles N.Zhang, T., P. W. Stackhouse, S. J. Cox, J. C. Mikovitz, C. N. Long, 2019: Clear-sky shortwave downward flux at the Earth's surface: Ground-based data vs. satellite-based data. Journal of Quantitative Spectroscopy and Radiative Transfer, 224, 247-260. doi: 10.1016/j.jqsrt.2018.11.015. The radiative flux data and other meteorological data in the BSRN archive start in 1992, but the RadFlux data, the clear-sky radiative fluxes at the BSRN sites empirically inferred through regression analyses of actually observed clear-sky fluxes, did not come into existence until the early 2000s, and at first, they were limited to the 7 NOAA SURFRAD and 4 DOE ARM sites, a subset of the BSRN sites. Recently, the RadFlux algorithm was applied more extensively to the BSRN sites for the production of clear-sky ground-based fluxes. At the time of this writing, there are 7119 site-months of clear-sky fluxes at 42 BSRN sites spanning from 1992 to late 2017. These data provide an unprecedented opportunity to validate the satellite-based clear-sky fluxes. In this paper, the GEWEX SRB GSW(V3.0) clear-sky shortwave downward fluxes spanning 24.5 years from July 1983 to December 2007, the CERES SYN1deg(Ed4A) and EBAF(Ed4.0) clear-sky shortwave fluxes spanning March 2000 to mid-2017 are compared with their RadFlux counterparts on the hourly, 3-hourly, daily and monthly time scales. All the three datasets show reasonable agreement with their ground-based counterparts. Comparison of the satellite-based surface shortwave clear-sky radiative fluxes to the BSRN RadFlux analysis shows negative biases (satellite-based minus RadFlux). Further analysis shows that the satellite-based atmosphere contains greater aerosol loading as well as more precipitable water than RadFlux analysis estimates. CERES; Solar radiation; Satellite; GEWEX SRB; RadFlux
Zhang, Weiyu; Zhang, Xiaotong; Li, Wenhong; Hou, Ning; Wei, Yu; Jia, Kun; Yao, Yunjun; Cheng, JieZhang, W., X. Zhang, W. Li, N. Hou, Y. Wei, K. Jia, Y. Yao, J. Cheng, 2019: Evaluation of Bayesian Multimodel Estimation in Surface Incident Shortwave Radiation Simulation over High Latitude Areas. Remote Sensing, 11(15), 1776. doi: 10.3390/rs11151776. Surface incident shortwave radiation (SSR) is crucial for understanding the Earth’s climate change issues. Simulations from general circulation models (GCMs) are one of the most practical ways to produce long-term global SSR products. Although previous studies have comprehensively assessed the performance of the GCMs in simulating SSR globally or regionally, studies assessing the performance of these models over high-latitude areas are sparse. This study evaluated and intercompared the SSR simulations of 48 GCMs participating in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) using quality-controlled SSR surface measurements at 44 radiation sites from three observation networks (GC-NET, BSRN, and GEBA) and the SSR retrievals from the Clouds and the Earth’s Radiant Energy System, Energy Balanced and Filled (CERES EBAF) data set over high-latitude areas from 2000 to 2005. Furthermore, this study evaluated the performance of the SSR estimations of two multimodel ensemble methods, i.e., the simple model averaging (SMA) and the Bayesian model averaging (BMA) methods. The seasonal performance of the SSR estimations of individual GCMs, the SMA method, and the BMA method were also intercompared. The evaluation results indicated that there were large deficiencies in the performance of the individual GCMs in simulating SSR, and these GCM SSR simulations did not show a tendency to overestimate the SSR over high-latitude areas. Moreover, the ensemble SSR estimations generated by the SMA and BMA methods were superior to all individual GCM SSR simulations over high-latitude areas, and the estimations of the BMA method were the best compared to individual GCM simulations and the SMA method-based estimations. Compared to the CERES EBAF SSR retrievals, the uncertainties of the SSR estimations of the GCMs, the SMA method, and the BMA method are relatively large during summer. CMIP5; Bayesian model averaging; general circulation models; high-latitude areas; multimodel ensembles; surface incident shortwave radiation
Zhang, Xiaotong; Wang, Dongdong; Liu, Qiang; Yao, Yunjun; Jia, Kun; He, Tao; Jiang, Bo; Wei, Yu; Ma, Han; Zhao, Xiang; Li, Wenhong; Liang, ShunlinZhang, X., D. Wang, Q. Liu, Y. Yao, K. Jia, T. He, B. Jiang, Y. Wei, H. Ma, X. Zhao, W. Li, S. Liang, 2019: An Operational Approach for Generating the Global Land Surface Downward Shortwave Radiation Product From MODIS Data. IEEE Transactions on Geoscience and Remote Sensing, 57(7), 4636-4650. doi: 10.1109/TGRS.2019.2891945. Surface shortwave net radiation (SSNR) and surface downward shortwave radiation (DSR) are the two surface shortwave radiation components in earth's radiation budget and the fundamental quantities of energy available at the earth's surface. Although several global radiation products from global circulation models, global reanalyses, and satellite observations have been released, their coarse spatial resolutions and low accuracies limit their application. In this paper, the Global LAnd Surface Satellite (GLASS) DSR product was generated from the Moderate Resolution Imaging Spectroradiometer top-of-atmosphere (TOA) spectral reflectance based on a direct-estimation method. First, the TOA reflectances were derived based on the atmospheric radiative transfer simulations under different solar/view geometries; second, a linear regression relationship between the TOA reflectance and SSNR was developed under various atmospheric conditions and surface properties for different solar/view geometries; third, the coefficients derived from the linear regression were used to compute the SSNR; and finally, the DSR was estimated using the SSNR estimates and broadband albedo at the surface. A 13-year (2003-2015) GLASS DSR product was generated at a 5-km spatial resolution and 1-day temporal resolution. Compared with the ground measurements collected from 525 stations from 2003 to 2005 around the world, the model-computed SSNR (DSR) had an overall bias of 8.82 (3.72) W/m2 and a root mean square error of 28.83 (32.84) W/m2 at the daily time scale. Moreover, the global land annual mean of the DSR was determined to be 184.8 W/m2 with a standard deviation of 0.8 W/m2 over a 13-year (2003-2015) period. Earth; Land surface; Remote sensing; Satellites; atmospheric radiation; atmospheric techniques; radiometry; radiative transfer; MODIS; Atmospheric modeling; Ocean temperature; remote sensing; atmospheric radiative transfer simulations; coarse spatial resolutions; Earth radiation budget; Earth surface; GLASS DSR product; global circulation models; global land annual mean; global land surface downward shortwave radiation product; Global LAnd Surface Satellite; global radiation products; global reanalyses; Globalirradiance; incident shortwave radiation; model-computed SSNR; solar-view geometries; SSNR estimates; surface shortwave net radiation; surface shortwave radiation components; TOA reflectance; top-of-atmosphere spectral reflectance
Zhang, Xiaoyan; Zhang, BaoqingZhang, X., B. Zhang, 2019: The responses of natural vegetation dynamics to drought during the growing season across China. Journal of Hydrology, 574, 706-714. doi: 10.1016/j.jhydrol.2019.04.084. Knowledge of vegetative responses to drought across hydroclimatic zones is crucial for understanding ecohydrologic cycles. Based on monthly self-calibrated Palmer drought severity index (PDSI), standardized precipitation evapotranspiration index (SPEI) at different time scales (1–48 month scales), and normalized difference vegetation index (NDVI), this study examined the relationship between natural vegetation dynamics and drought in the growing season during 1982–2012 at 293 sites over China. Pearson correlations between NDVI and drought indices (PDSI and SPEI) were employed to quantify the association between vegetation and drought. The results show that the Pearson correlations between PDSI and NDVI in growing season (CNP) ranged from −0.47 to 0.84, and the maximum correlation between SPEI and NDVI in growing season (MaxSPEI) ranged from −0.31 to 0.86, within which the negative correlations were mainly observed in the areas dominated by forest in south China. Moreover, the CNP was highly and nonlinearly related to the aridity index (∅) (MaxSPEI showed a similar trend). The relationship between CNP and ∅ indicated that, water stress was not the limiting factor for natural vegetation in humid regions (∅4.68; in extreme arid regions, the natural vegetation exhibited less sensitivity to drought. These tendencies could be seen worldwide. The varied physiological properties of plants and the response of photosynthesis to energy processes probably explain some discernible variation. Drought assessment; Drought impacts; Hydroclimatic zones; Vegetation variations; Water availability
Zhang, Yang; Jena, Chinmay; Wang, Kai; Paton-Walsh, Clare; Guérette, Élise-Andrée; Utembe, Steven; Silver, Jeremy David; Keywood, MelitaZhang, Y., C. Jena, K. Wang, C. Paton-Walsh, É. Guérette, S. Utembe, J. D. Silver, M. Keywood, 2019: Multiscale Applications of Two Online-Coupled Meteorology-Chemistry Models during Recent Field Campaigns in Australia, Part I: Model Description and WRF/Chem-ROMS Evaluation Using Surface and Satellite Data and Sensitivity to Spatial Grid Resolutions. Atmosphere, 10(4), 189. doi: 10.3390/atmos10040189. Air pollution and associated human exposure are important research areas in Greater Sydney, Australia. Several field campaigns were conducted to characterize the pollution sources and their impacts on ambient air quality including the Sydney Particle Study Stages 1 and 2 (SPS1 and SPS2), and the Measurements of Urban, Marine, and Biogenic Air (MUMBA). In this work, the Weather Research and Forecasting model with chemistry (WRF/Chem) and the coupled WRF/Chem with the Regional Ocean Model System (ROMS) (WRF/Chem-ROMS) are applied during these field campaigns to assess the models’ capability in reproducing atmospheric observations. The model simulations are performed over quadruple-nested domains at grid resolutions of 81-, 27-, 9-, and 3-km over Australia, an area in southeastern Australia, an area in New South Wales, and the Greater Sydney area, respectively. A comprehensive model evaluation is conducted using surface observations from these field campaigns, satellite retrievals, and other data. This paper evaluates the performance of WRF/Chem-ROMS and its sensitivity to spatial grid resolutions. The model generally performs well at 3-, 9-, and 27-km resolutions for sea-surface temperature and boundary layer meteorology in terms of performance statistics, seasonality, and daily variation. Moderate biases occur for temperature at 2-m and wind speed at 10-m in the mornings and evenings due to the inaccurate representation of the nocturnal boundary layer and surface heat fluxes. Larger underpredictions occur for total precipitation due to the limitations of the cloud microphysics scheme or cumulus parameterization. The model performs well at 3-, 9-, and 27-km resolutions for surface O3 in terms of statistics, spatial distributions, and diurnal and daily variations. The model underpredicts PM2.5 and PM10 during SPS1 and MUMBA but overpredicts PM2.5 and underpredicts PM10 during SPS2. These biases are attributed to inaccurate meteorology, precursor emissions, insufficient SO2 conversion to sulfate, inadequate dispersion at finer grid resolutions, and underprediction in secondary organic aerosol. The model gives moderate biases for net shortwave radiation and cloud condensation nuclei but large biases for other radiative and cloud variables. The performance of aerosol optical depth and latent/sensible heat flux varies for different simulation periods. Among all variables evaluated, wind speed at 10-m, precipitation, surface concentrations of CO, NO, NO2, SO2, O3, PM2.5, and PM10, aerosol optical depth, cloud optical thickness, cloud condensation nuclei, and column NO2 show moderate-to-strong sensitivity to spatial grid resolutions. The use of finer grid resolutions (3- or 9-km) can generally improve the performance for those variables. While the performance for most of these variables is consistent with that over the U.S. and East Asia, several differences along with future work are identified to pinpoint reasons for such differences. WRF/Chem; model evaluation; air quality; satellite retrievals; MUMBA; SPS1; SPS2; Sydney; WRF/Chem-ROMS
Zhang, Yuxiang; Li, Rui; Min, Qilong; Bo, Haixu; Fu, Yuyun; Wang, Yipu; Gao, ZongtingZhang, Y., R. Li, Q. Min, H. Bo, Y. Fu, Y. Wang, Z. Gao, 2019: The Controlling Factors of Atmospheric Formaldehyde (HCHO) in Amazon as Seen From Satellite. Earth and Space Science, 6(6), 959-971. doi: 10.1029/2019EA000627. To understand the relative importance of biogenic emission, biomass burning emission on volatile organic compounds in Amazon, the spatial and temporal correlations between atmospheric column-integrated formaldehyde (HCHO) and fire count, vegetation hydrological states index, surface solar radiation flux, near-surface air temperature are studied using synergized satellite products and reanalysis data. A recently developed microwave-based vegetation index (emissivity difference vegetation index, EDVI) with high temporal resolution is used for the linkages between vegetation and HCHO at daily scale with and without fire contaminations. At large regional scale, EDVI shows highest spatial correlation with HCHO indicating the important controlling effect of biogenic emission. In given subregions with frequent fires, the temporal variations of monthly HCHO show much stronger correlations with fire count. The temporal correlations between monthly HCHO and EDVI are vague and even negative in some subregions. Radiation and temperature show stable positive temporal correlations with HCHO, particularly in areas with few fires. After excluding the samples contaminated by fires, the daily temporal correlation between vegetation (EDVI) and HCHO becomes significant and positive in most areas except the northern rainforest with weak temporal variations of EDVI. We proposed a bilinear model of biogenic-emission-induced HCHO (B-HCHO) using radiation and EDVI as inputs. The bias between modeled long-term mean B-HCHO and satellite observation is less than 20%. And the daily time series of modeled B-HCHO matches observations as well. It is the first time to provide satellite observational evidences of the relative importance of biogenic emission and biomass burning emission on HCHO, the proxy of atmospheric volatile organic compounds concentration.
Zhang, Yuying; Xie, Shaocheng; Lin, Wuyin; Klein, Stephen A.; Zelinka, Mark; Ma, Po-Lun; Rasch, Philip J.; Qian, Yun; Tang, Qi; Ma, Hsi-YenZhang, Y., S. Xie, W. Lin, S. A. Klein, M. Zelinka, P. Ma, P. J. Rasch, Y. Qian, Q. Tang, H. Ma, 2019: Evaluation of Clouds in Version 1 of the E3SM Atmosphere Model with Satellite Simulators. Journal of Advances in Modeling Earth Systems, 11, 1253-1268. doi: 10.1029/2018MS001562. This study systematically evaluates clouds simulated by the Energy Exascale Earth System Model (E3SM) Atmosphere Model version one (EAMv1) against satellite cloud observations. Both low (1°) and high (0.25°) resolution EAMv1 configurations generally underestimate clouds in low and midlatitudes and overestimate clouds in the Arctic although the error is smaller in the high-resolution model. The underestimate of clouds is due to the underestimate of optically thin to intermediate clouds, as EAMv1 generally overestimates optically intermediate to thick clouds. Other model errors include the largely under-predicted marine stratocumulus along the coasts and high clouds over the tropical deep convection regions. The underestimate of thin clouds results in too much LW radiation being emitted to space and too little SW radiation being reflected back to space while the overestimate of optically intermediate and thick clouds leads to too little LW radiation being emitted to space and too much SW radiation being reflected back to space. EAMv1 shows better skill in reproducing the observed distribution of clouds and their properties and has smaller radiatively relevant errors in the distribution of clouds than most of the CFMIP1 and CFMIP2 models. It produces more supercooled liquid cloud fraction than CAM5 and most CMIP5 models primarily due to a new ice nucleation scheme and secondarily due to a reduction of the ice deposition growth rate.
Zheng, Lei; Zhao, Guosong; Dong, Jinwei; Ge, Quansheng; Tao, Jian; Zhang, Xuezhen; Qi, Youcun; Doughty, Russell B.; Xiao, XiangmingZheng, L., G. Zhao, J. Dong, Q. Ge, J. Tao, X. Zhang, Y. Qi, R. B. Doughty, X. Xiao, 2019: Spatial, temporal, and spectral variations in albedo due to vegetation changes in China’s grasslands. ISPRS Journal of Photogrammetry and Remote Sensing, 152, 1-12. doi: 10.1016/j.isprsjprs.2019.03.020. Changes in Earth’s albedo due to vegetation dynamics, snow cover, and land cover change have attracted much attention. However, the effects of vegetation dynamics on albedo have not been comprehensively documented according to its spatial (regional), temporal (within growing season), and spectral (visible, near-infrared, and shortwave) characteristics. This study examined the effects of vegetation greenness on albedo from 2000 to 2014 in China’s grasslands, which have considerable intra- and inter-annual variations, using remote sensing-based albedo and two-band Enhanced Vegetation Index (EVI2) data. Generally, we found an insignificant negative correlation between the shortwave (SW) albedo and EVI2 for grasslands in China. However, the visible (VIS) albedo was more sensitive to changes in vegetation greenness than near-infrared (NIR) albedo in China’s grasslands. The relationship between the NIR albedo and EVI2 was more complicated, especially in the Tibetan Plateau (TP), where the correlation was negative in the early growing season and positive in the late growing season; while the correlation between the NIR albedo and EVI2 was always negative in main part of Inner Mongolia (IM). The different albedo-EVI2 relationships in IM and TP may be related to differences in soil albedos. The higher sensitivity of the SW albedo to vegetation greenness change in IM, the stronger effect on land surface radiation budget. Our finding about vegetation-induced changes in albedo differ in space, time and spectral bands is expected to contribute to the improvement of land surface models. Albedo; Climate change; China; Grassland; Greenness
Zhong, Lei; Zou, Mijun; Ma, Yaoming; Huang, Ziyu; Xu, Kepiao; Wang, Xian; Ge, Nan; Cheng, MeilinZhong, L., M. Zou, Y. Ma, Z. Huang, K. Xu, X. Wang, N. Ge, M. Cheng, 2019: Estimation of Downwelling Shortwave and Longwave Radiation in the Tibetan Plateau Under All-Sky Conditions. Journal of Geophysical Research: Atmospheres, 124(21), 11086-11102. doi: 10.1029/2019JD030763. Downwelling shortwave radiation (DSWR) and downwelling longwave radiation (DLWR) are two important components of the Earth's surface radiation balance. In this study, the Heliosat method and the parameterization of Crawford and Duchon (1999, https://doi.org/10.1175/1520-0450(1999)0382.0.CO;2, hereafter CD99) were calibrated to make them suitable for estimation of DSWR and DLWR over the Tibetan Plateau (TP). Based on meteorological data, forcing data, and observations from polar-orbiting satellites, the cloud albedo was calculated, and the clear-sky index estimation scheme of the Heliosat method was improved. These improvements were then applied to derive 10-day DSWR under all-sky conditions over the TP by combining the clear-sky shortwave radiation scheme with a clear-sky index. The coefficient of the CD99 parameterization scheme clear-sky DLWR was also calibrated, and 10-day all-sky DLWR was then determined and validated using ground-based measurements. The spatiotemporal distributions of DSWR and DLWR were analyzed in detail. The results showed that the modified methods are efficient and applicable for downward radiation retrieval under all-sky conditions over the TP with a reasonable accuracy. The mean percentage errors for DSWR and DLWR were −4.75% and 0.11%, respectively. The variation in the monthly DSWR (DLWR) showed a convex shape, with a maximum appearing in May (July). The spatial distributions of DLWR showed a southeast-high and northwest-low pattern. As the subsolar point moves northward, DSWR increases gradually and is clearly influenced by the Asian summer monsoon.
Zou, Xun; Bromwich, David H.; Nicolas, Julien P.; Montenegro, Alvaro; Wang, Sheng-HungZou, X., D. H. Bromwich, J. P. Nicolas, A. Montenegro, S. Wang, 2019: West Antarctic Surface Melt Event of January 2016 Facilitated by Foehn Warming. Quarterly Journal of the Royal Meteorological Society, 145(719), 687-704. doi: 10.1002/qj.3460. The Ross Ice Shelf (RIS) buttresses ice streams from the Antarctic continent and restrains the grounded ice sheet from flowing into the ocean, which is important for the stability of the ice sheet. In recent decades, West Antarctic ice shelves, including the RIS, have experienced more frequent surface melting during summer. We investigated the role of warm, descending foehn winds in a major melt event that occurred on the RIS in January 2016. Only a few summer melt events of this magnitude have been observed since 1979. Backward trajectories from the area of earliest melting were constructed using the Antarctic Mesoscale Prediction System (AMPS) to investigate the dominant mechanisms at the beginning of the melt event, mainly from 10 to 13 January. Analysis was conducted over two distinct areas. The foehn effect contributed around 2-4 °C to the surface temperature increase over the coastal mountains of Marie Byrd Land (MBL) and around 1 °C over the much lower Edward VII Peninsula. Most of the foehn warming was caused by isentropic drawdown of air aloft. On 10 January, the second-most important contributor for both mountain ranges was the thermodynamic mechanism. On 11 January, the second-most important mechanism was the sensible and radiative heat flux. This study contributes to a better understanding of surface melt events over the RIS and benefits research associated with the stability of West Antarctic ice shelves. foehn warming; Ross Ice Shelf; surface melting; West Antarctic warming
Abdel-Lathif, Ahmat Younous; Roehrig, Romain; Beau, Isabelle; Douville, HervéAbdel-Lathif, A. Y., R. Roehrig, I. Beau, H. Douville, 2018: Single-Column Modeling of Convection During the CINDY2011/DYNAMO Field Campaign With the CNRM Climate Model Version 6. Journal of Advances in Modeling Earth Systems, 45(5), 2404-2412. doi: 10.1002/2017MS001077. A single-column model (SCM) approach is used to assess the CNRM climate model (CNRM-CM) version 6 ability to represent the properties of the apparent heat source (Q1) and moisture sink (Q2) as observed during the 3 month CINDY2011/DYNAMO field campaign, over its Northern Sounding Array (NSA). The performance of the CNRM SCM is evaluated in a constrained configuration in which the latent and sensible heat surface fluxes are prescribed, as, when forced by observed sea surface temperature, the model is strongly limited by the underestimate of the surface fluxes, most probably related to the SCM forcing itself. The model exhibits a significant cold bias in the upper troposphere, near 200 hPa, and strong wet biases close to the surface and above 700 hPa. The analysis of the Q1 and Q2 profile distributions emphasizes the properties of the convective parameterization of the CNRM-CM physics. The distribution of the Q2 profile is particularly challenging. The model strongly underestimates the frequency of occurrence of the deep moistening profiles, which likely involve misrepresentation of the shallow and congestus convection. Finally, a statistical approach is used to objectively define atmospheric regimes and construct a typical convection life cycle. A composite analysis shows that the CNRM SCM captures the general transition from bottom-heavy to mid-heavy to top-heavy convective heating. Some model errors are shown to be related to the stratiform regimes. The moistening observed during the shallow and congestus convection regimes also requires further improvements of this CNRM-CM physics. statistical analysis; 3371 Tropical convection; 3365 Subgrid-scale (SGS) parameterization; tropical convection; CINDY2011/DYNAMO field campaign; single-column modeling; subgrid-scale (SGS) parameterization
Ahlgrimm, Maike; Forbes, Richard M.; Hogan, Robin J.; Sandu, IrinaAhlgrimm, M., R. M. Forbes, R. J. Hogan, I. Sandu, 2018: Understanding global model systematic shortwave radiation errors in subtropical marine boundary layer cloud regimes. Journal of Advances in Modeling Earth Systems, 10(8), 2042-2060. doi: 10.1029/2018MS001346. Global numerical weather prediction and climate models are subject to long-standing systematic shortwave radiation errors due to deficiencies in the representation of boundary layer clouds over the ocean. In the subtropics, clouds are typically too reflective in the cumulus regime and not reflective enough in the stratocumulus regime. Potential sources of error include cloud cover, liquid water path, effective radius and subgrid heterogeneity, but diagnosing the absolute contributions of each to the radiation bias is hampered by uncertainties and sometimes contradictory information from different observational products. This paper draws on a set of ship-based observations of boundary layer clouds obtained during the ARM MAGIC campaign along a north-east Pacific Ocean transect, crossing both stratocumulus and shallow cumulus cloud regimes. The surface-based observations of cloud properties are compared with various satellite products, taking account of the diurnal cycle, to provide an improved quantitative assessment of the deficiencies in the ECMWF global numerical weather prediction model. A series of offline radiation calculations are then performed to assess the impact on the shortwave radiation bias of “correcting” each of the model's deficiencies in cloud characteristics along the transect. A reduction in the bias is achieved by improving the agreement between modelled and observed in-cloud LWP frequency distributions. In the cumulus regime, this is accomplished primarily by reducing the all-sky water path, while for the stratocumulus regime, an underestimate of cloud cover and liquid water and an overestimate in effective radius and subgrid heterogeneity all contribute to a lack of reflected shortwave radiation. cloud properties; marine boundary layer clouds; shortwave bias
Ahn, Seo-Hee; Lee, Kyu-Tae; Rim, Se-Hun; Zo, Il-Sung; Kim, Bu-YoAhn, S., K. Lee, S. Rim, I. Zo, B. Kim, 2018: Surface Downward Longwave Radiation Retrieval Algorithm for GEO-KOMPSAT-2A/AMI. Asia-Pacific Journal of Atmospheric Sciences, 54(2), 237-251. doi: 10.1007/s13143-018-0007-1. This study contributes to the development of an algorithm to retrieve the Earth’s surface downward longwave radiation (DLR) for 2nd Geostationary Earth Orbit KOrea Multi-Purpose SATellite (GEO-KOMPSAT-2A; GK-2A)/Advanced Meteorological Imager (AMI). Regarding simulation data for algorithm development, we referred to Clouds and the Earth’s Radiant Energy System (CERES), and the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-interim reanalysis data. The clear sky DLR calculations were in good agreement with the Gangneung-Wonju National University (GWNU) Line-By-Line (LBL) model. Compared with CERES data, the Root Mean Square Error (RMSE) was 10.14Wm−2. In the case of cloudy sky DLR, we estimated the cloud base temperature empirically by utilizing cloud liquid water content (LWC) according to the cloud type. As a result, the correlation coefficients with CERES all sky DLRs were greater than 0.99. However, the RMSE between calculated DLR and CERES data was about 16.67Wm−2, due to ice clouds and problems of mismatched spatial and temporal resolutions for input data. This error may be reduced when GK-2A is launched and its products can be used as input data. Accordingly, further study is needed to improve the accuracy of DLR calculation by using high-resolution input data. In addition, when compared with BSRN surface-based observational data and retrieved DLR for all sky, the correlation coefficient was 0.86 and the RMSE was 31.55 Wm−2, which indicates relatively high accuracy. It is expected that increasing the number of experimental Cases will reduce the error.
Alamirew, N. K.; Todd, M. C.; Ryder, C. L.; Marsham, J. H.; Wang, Y.Alamirew, N. K., M. C. Todd, C. L. Ryder, J. H. Marsham, Y. Wang, 2018: The early summertime Saharan heat low: sensitivity of the radiation budget and atmospheric heating to water vapour and dust aerosol. Atmos. Chem. Phys., 18(2), 1241-1262. doi: 10.5194/acp-18-1241-2018. The Saharan heat low (SHL) is a key component of the west African climate system and an important driver of the west African monsoon across a range of timescales of variability. The physical mechanisms driving the variability in the SHL remain uncertain, although water vapour has been implicated as of primary importance. Here, we quantify the independent effects of variability in dust and water vapour on the radiation budget and atmospheric heating of the region using a radiative transfer model configured with observational input data from the Fennec field campaign at the location of Bordj Badji Mokhtar (BBM) in southern Algeria (21.4° N, 0.9° E), close to the SHL core for June 2011. Overall, we find dust aerosol and water vapour to be of similar importance in driving variability in the top-of-atmosphere (TOA) radiation budget and therefore the column-integrated heating over the SHL (∼ 7 W m−2 per standard deviation of dust aerosol optical depth – AOD). As such, we infer that SHL intensity is likely to be similarly enhanced by the effects of dust and water vapour surge events. However, the details of the processes differ. Dust generates substantial radiative cooling at the surface (∼ 11 W m−2 per standard deviation of dust AOD), presumably leading to reduced sensible heat flux in the boundary layer, which is more than compensated by direct radiative heating from shortwave (SW) absorption by dust in the dusty boundary layer. In contrast, water vapour invokes a radiative warming at the surface of ∼ 6 W m−2 per standard deviation of column-integrated water vapour in kg m−2. Net effects involve a pronounced net atmospheric radiative convergence with heating rates on average of 0.5 K day−1 and up to 6 K day−1 during synoptic/mesoscale dust events from monsoon surges and convective cold-pool outflows (haboobs). On this basis, we make inferences on the processes driving variability in the SHL associated with radiative and advective heating/cooling. Depending on the synoptic context over the region, processes driving variability involve both independent effects of water vapour and dust and compensating events in which dust and water vapour are co-varying. Forecast models typically have biases of up to 2 kg m−2 in column-integrated water vapour (equivalent to a change in 2.6 W m−2 TOA net flux) and typically lack variability in dust and thus are expected to poorly represent these couplings. An improved representation of dust and water vapour and quantification of associated radiative impact in models is thus imperative to further understand the SHL and related climate processes.
Almeida, Cláudia M. de; Feitosa, Raul Q.; Hernandez, Jaime; Scavuzzo, Carlos M.; Aragão, Luiz E. O. C. deAlmeida, C. M. d., R. Q. Feitosa, J. Hernandez, C. M. Scavuzzo, L. E. O. C. d. Aragão, 2018: Coping with environmental challenges in Latin America. ISPRS Journal of Photogrammetry and Remote Sensing, 145, 211-212. doi: 10.1016/j.isprsjprs.2018.10.001.
Angal, A.; Xiong, X.; Mu, Q.; Doelling, D. R.; Bhatt, R.; Wu, A.Angal, A., X. Xiong, Q. Mu, D. R. Doelling, R. Bhatt, A. Wu, 2018: Results From the Deep Convective Clouds-Based Response Versus Scan-Angle Characterization for the MODIS Reflective Solar Bands. IEEE Transactions on Geoscience and Remote Sensing, 56(2), 1115-1128. doi: 10.1109/TGRS.2017.2759660. The Terra and Aqua Moderate-Resolution Imaging Spectroradiometer (MODIS) scan mirror reflectance is a function of the angle of incidence (AOI) and was characterized prior to launch by the instrument vendor. The relative change of the prelaunch response versus scan angle (RVS) is tracked and linearly scaled on-orbit using observations at two AOIs of 11.2° and 50.2° corresponding to the moon view and solar diffuser, respectively. As the missions continue to operate well beyond their design life of six years, the assumption of linear scaling between the two AOIs is known to be inadequate in accurately characterizing the RVS, particularly at short wavelengths. Consequently, an enhanced approach of supplementing the on-board measurements with response trends from desert pseudoinvariant calibration sites (PICS) was formulated in MODIS Collection 6 (C6). An underlying assumption for the continued effectiveness of this approach is the long-term (multiyear) and short-term (month to month) stability of the PICS. Previous work has shown that the deep convective clouds (DCC) can also be used to monitor the on-orbit RVS performance with less trend uncertainties compared with desert sites. In this paper, the raw sensor response to the DCC is used to characterize the on-orbit RVS on a band and mirror-side basis. These DCC-based RVS results are compared with those of C6 PICS-based RVS, showing an agreement within 2% observed in most cases. The pros and cons of using a DCC-based RVS approach are also discussed in this paper. Although this reaffirms the efficacy of the C6 PICS-based RVS, the DCC-based RVS approach presents itself as an effective alternative for future considerations. Potential applications of this approach to other instruments, such as Suomi National Polar-orbiting Partnership, Joint Polar Satellite Systems, and Visible Infrared Imaging Radiometer Suite, are also discussed.
Bair, Edward H.; Abreu Calfa, Andre; Rittger, Karl; Dozier, JeffBair, E. H., A. Abreu Calfa, K. Rittger, J. Dozier, 2018: Using machine learning for real-time estimates of snow water equivalent in the watersheds of Afghanistan. The Cryosphere Discussions, 1-21. doi: 10.5194/tc-2017-196. In the mountains, snowmelt often provides most of the runoff. Operational estimates use imagery from optical and passive microwave sensors, but each has its limitations. An accurate approach, which we validate in Afghanistan and the Sierra Nevada USA, reconstructs spatially distributed snow water equivalent (SWE) by calculating snowmelt backward from a remotely sensed date of disappearance. However, reconstructed SWE estimates are available only retrospectively; they do not provide a forecast. To estimate SWE throughout the snowmelt season, we consider physiographic and remotely sensed information as predictors and reconstructed SWE as the target. The period of analysis matches the AMSR-E radiometer’s lifetime from 2003 to 2011, for the months of April through June. The spatial resolution of the predictions is 3.125 km, to match the resolution of a microwave brightness temperature product. Two machine learning techniques – bagged regression trees and feed-forward neural networks – produced similar mean results, with 0–14 % bias and 46–48 mm RMSE on average. Nash–Sutcliffe efficiencies averaged 0.68 for all years. Daily SWE climatology and fractional snow-covered area are the most important predictors. We conclude that these methods can accurately estimate SWE during the snow season in remote mountains, and thereby provide an independent estimate to forecast runoff and validate other methods to assess the snow resource.
Balsamo, Gianpaolo; Agustì-Parareda, Anna; Albergel, Clément; Arduini, Gabriele; Beljaars, Anton; Bidlot, Jean; Bousserez, Nicolas; Boussetta, Souhail; Brown, Andy; Buizza, Roberto; Buontempo, Carlo; Chevallier, Frédéric; Choulga, Margarita; Cloke, Hannah; Cronin, Meghan F.; Dahoui, Mohamed; De Rosnay, Patricia; Dirmeyer, Paul A.; Drusch, Matthias; Dutra, Emanuel; Ek, Michael B.; Gentine, Pierre; Hewitt, Helene; Keeley, Sarah P. E.; Kerr, Yann; Kumar, Sujay; Lupu, Cristina; Mahfouf, Jean-François; McNorton, Joe; Mecklenburg, Susanne; Mogensen, Kristian; Muñoz-Sabater, Joaquín; Orth, Rene; Rabier, Florence; Reichle, Rolf; Ruston, Ben; Pappenberger, Florian; Sandu, Irina; Seneviratne, Sonia I.; Tietsche, Steffen; Trigo, Isabel F.; Uijlenhoet, Remko; Wedi, Nils; Woolway, R. Iestyn; Zeng, XubinBalsamo, G., A. Agustì-Parareda, C. Albergel, G. Arduini, A. Beljaars, J. Bidlot, N. Bousserez, S. Boussetta, A. Brown, R. Buizza, C. Buontempo, F. Chevallier, M. Choulga, H. Cloke, M. F. Cronin, M. Dahoui, P. De Rosnay, P. A. Dirmeyer, M. Drusch, E. Dutra, M. B. Ek, P. Gentine, H. Hewitt, S. P. E. Keeley, Y. Kerr, S. Kumar, C. Lupu, J. Mahfouf, J. McNorton, S. Mecklenburg, K. Mogensen, J. Muñoz-Sabater, R. Orth, F. Rabier, R. Reichle, B. Ruston, F. Pappenberger, I. Sandu, S. I. Seneviratne, S. Tietsche, I. F. Trigo, R. Uijlenhoet, N. Wedi, R. I. Woolway, X. Zeng, 2018: Satellite and In Situ Observations for Advancing Global Earth Surface Modelling: A Review. Remote Sensing, 10(12), 2038. doi: 10.3390/rs10122038. In this paper, we review the use of satellite-based remote sensing in combination with in situ data to inform Earth surface modelling. This involves verification and optimization methods that can handle both random and systematic errors and result in effective model improvement for both surface monitoring and prediction applications. The reasons for diverse remote sensing data and products include (i) their complementary areal and temporal coverage, (ii) their diverse and covariant information content, and (iii) their ability to complement in situ observations, which are often sparse and only locally representative. To improve our understanding of the complex behavior of the Earth system at the surface and sub-surface, we need large volumes of data from high-resolution modelling and remote sensing, since the Earth surface exhibits a high degree of heterogeneity and discontinuities in space and time. The spatial and temporal variability of the biosphere, hydrosphere, cryosphere and anthroposphere calls for an increased use of Earth observation (EO) data attaining volumes previously considered prohibitive. We review data availability and discuss recent examples where satellite remote sensing is used to infer observable surface quantities directly or indirectly, with particular emphasis on key parameters necessary for weather and climate prediction. Coordinated high-resolution remote-sensing and modelling/assimilation capabilities for the Earth surface are required to support an international application-focused effort. direct and inverse methods; earth system modelling; earth-observations
Beer, Tom; Li, Jianping; Alverson, KeithBeer, T., J. Li, K. Alverson, 2018: Global Change and Future Earth: The Geoscience Perspective. Global Change and Future Earth is derived from the work of several programs of the International Union of Geodesy and Geophysics (IUGG). It demonstrates how multi- and inter-disciplinary research outputs from the geoscience community can be applied to tackle the physical and societal impacts of climate change and contribute to the Future Earth programme of the International Council for Science. The volume brings together an international team of eminent researchers to provide authoritative reviews on the wide-ranging ramifications of climate change spanning eight key themes: planetary issues; geodetic issues; the Earth's fluid environment; regions of the Earth; urban environments; food security; and risk, safety and security; and climate change and global change. Covering the challenges faced by urban and rural areas, and in both developed and developing counties, this volume provides an important resource for a global audience of graduate students and researchers from a broad range of disciplines, as well as policy advisors and practitioners. Science / Earth Sciences / Meteorology & Climatology; Technology & Engineering / Agriculture / Agronomy / Soil Science; Science / Earth Sciences / Geology; Science / Earth Sciences / Hydrology; Science / Environmental Science; Science / Physics / Geophysics
Bender, F. A.-M.; Frey, L.; McCoy, D. T.; Grosvenor, D. P.; Mohrmann, J. K.Bender, F. A., L. Frey, D. T. McCoy, D. P. Grosvenor, J. K. Mohrmann, 2018: Assessment of aerosol–cloud–radiation correlations in satellite observations, climate models and reanalysis. Climate Dynamics, 1-22. doi: 10.1007/s00382-018-4384-z. Representing large-scale co-variability between variables related to aerosols, clouds and radiation is one of many aspects of agreement with observations desirable for a climate model. In this study such relations are investigated in terms of temporal correlations on monthly mean scale, to identify points of agreement and disagreement with observations. Ten regions with different meteorological characteristics and aerosol signatures are studied and correlation matrices for the selected regions offer an overview of model ability to represent present day climate variability. Global climate models with different levels of detail and sophistication in their representation of aerosols and clouds are compared with satellite observations and reanalysis assimilating meteorological fields as well as aerosol optical depth from observations. One example of how the correlation comparison can guide model evaluation and development is the often studied relation between cloud droplet number and water content. Reanalysis, with no parameterized aerosol–cloud coupling, shows weaker correlations than observations, indicating that microphysical couplings between cloud droplet number and water content are not negligible for the co-variations emerging on larger scale. These observed correlations are, however, not in agreement with those expected from dominance of the underlying microphysical aerosol–cloud couplings. For instance, negative correlations in subtropical stratocumulus regions show that suppression of precipitation and subsequent increase in water content due to aerosol is not a dominating process on this scale. Only in one of the studied models are cloud dynamics able to overcome the parameterized dependence of rain formation on droplet number concentration, and negative correlations in the stratocumulus regions are reproduced. Aerosol–cloud–radiation interaction; GCM-evaluation; Reanalysis; Satellite observations; Volcanic aerosol
Bhatt, Rajendra; Doelling, David; Haney, Conor; Scarino, Benjamin; Gopalan, Arun; Bhatt, Rajendra; Doelling, David; Haney, Conor; Scarino, Benjamin; Gopalan, ArunBhatt, R., D. Doelling, C. Haney, B. Scarino, A. Gopalan, R. Bhatt, D. Doelling, C. Haney, B. Scarino, A. Gopalan, 2018: Consideration of Radiometric Quantization Error in Satellite Sensor Cross-Calibration. Remote Sensing, 10(7), 1131. doi: 10.3390/rs10071131. The radiometric resolution of a satellite sensor refers to the smallest increment in the spectral radiance that can be detected by the imaging sensor. The fewer bits that are used for signal discretization, the larger the quantization error in the measured radiance. In satellite inter-calibration, a difference in radiometric resolution between a reference and a target sensor can induce a calibration bias, if not properly accounted for. The effect is greater for satellites with a quadratic count response, such as the Geostationary Meteorological Satellite-5 (GMS-5) visible imager, where the quantization difference can introduce non-linearity in the inter-comparison datasets, thereby affecting the cross-calibration slope and offset. This paper describes a simulation approach to highlight the importance of considering the radiometric quantization in cross-calibration and presents a correction method for mitigating its impact. The method, when applied to the cross-calibration of GMS-5 and Terra Moderate Resolution Imaging Spectroradiometer (MODIS) sensors, improved the absolute calibration accuracy of the GMS-5 imager. This was validated via radiometric inter-comparison of GMS-5 and Multifunction Transport Satellite-2 (MTSAT-2) imager top-of-atmosphere (TOA) measurements over deep convective clouds (DCC) and Badain Desert invariant targets. The radiometric bias between GMS-5 and MTSAT-2 was reduced from 1.9% to 0.5% for DCC, and from 7.7% to 2.3% for Badain using the proposed correction method. calibration; MODIS; GMS-5; quantization
Bran, Sherin Hassan; Jose, Subin; Srivastava, RohitBran, S. H., S. Jose, R. Srivastava, 2018: Investigation of optical and radiative properties of aerosols during an intense dust storm: A regional climate modeling approach. Journal of Atmospheric and Solar-Terrestrial Physics, 168, 21-31. doi: 10.1016/j.jastp.2018.01.003. The dynamical and optical properties of aerosols during an intense dust storm event over the Arabian Sea have been studied using Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) and space borne instruments such as MODIS, MISR, CALIPSO and CERES during the period 17 to 24 March, 2012. The model captures the spatio-temporal and vertical variations of meteorological and optical parameters, however an overestimation in simulated aerosol optical parameters are observed when compared to satellite retrievals. The correlation coefficients (R) between simulated and observed AOD from MODIS and MISR are found to be 0.54 and 0.32 respectively. Model simulated AOD on dusty days (20 and 21 March 2012) increased by 2–3 times compared to non-dusty days (17 and 24 March 2012) and the single scattering albedo (SSA) and the asymmetry parameter increased from 0.96 to 0.99 and from 0.56 to 0.66, respectively. The R between simulated shortwave (SW) radiation at top of the atmosphere (TOA) and TOA SW radiation obtained from CERES is found to be 0.43, however the model simulated SW radiation at the TOA showed an underestimation with respect to CERES. The shortwave aerosol radiative forcing (SWARF) during the event over surface and TOA are ∼ -19.3 and ∼ -14.2 Wm-2 respectively, which is about 2–5 times higher when compared to the respective forcing values during non-dust days. Estimated net radiative forcing was in the range of −13 to −21 Wm-2 at TOA and −12 to −20 Wm-2 at the surface. The heating rate during event days within the lower atmosphere near 850 hPa is found to 0.32 − 0.4 K day−1 and 0.18 − 0.22 K day−1 on dusty and non-dusty days, respectively. Results of this study may be useful for a better modeling of atmospheric aerosols and its optical and radiative properties over oceanic region. AOD; Heating rate; Arabian Sea; Dust storm; SWARF; WRF-Chem
Bright, Ryan M.; Eisner, Stephanie; Lund, Marianne T.; Majasalmi, Titta; Myhre, Gunnar; Astrup, RasmusBright, R. M., S. Eisner, M. T. Lund, T. Majasalmi, G. Myhre, R. Astrup, 2018: Inferring Surface Albedo Prediction Error Linked to Forest Structure at High Latitudes. Journal of Geophysical Research: Atmospheres, 123(10), 4910-4925. doi: 10.1029/2018JD028293.
Bromwich, D. H.; Wilson, A. B.; Bai, L.; Liu, Z.; Barlage, M.; Shih, C.-F.; Maldonado, S.; Hines, K. M.; Wang, S.-H.; Woollen, J.; Kuo, B.; Lin, H.-C.; Wee, T.-K.; Serreze, M. C.; Walsh, J. E.Bromwich, D. H., A. B. Wilson, L. Bai, Z. Liu, M. Barlage, C. Shih, S. Maldonado, K. M. Hines, S. Wang, J. Woollen, B. Kuo, H. Lin, T. Wee, M. C. Serreze, J. E. Walsh, 2018: The Arctic System Reanalysis Version 2. Bull. Amer. Meteor. Soc., 99(4), 805–828. doi: 10.1175/BAMS-D-16-0215.1. The new regional-15 km Arctic System Reanalysis version 2 provides the accuracy and details necessary for many Arctic climate studies over the period 2000–2012.
Carmona, F.; Holzman, M.; Rivas, R.; Degano, M.F.; Kruse, E.; Bayala, M.Carmona, F., M. Holzman, R. Rivas, M. Degano, E. Kruse, M. Bayala, 2018: Evaluation of two models using CERES data for reference evapotranspiration estimation. Revista de Teledetección, 51, 87-98. doi: 10.4995/raet.2018.9259. Evapotranspiration is the most important variable in the Pampas plain. Information provided by sensors onboard satellite missions allows represent the spatial and temporal variability of evapotranspiration, which cannot be achieved using only measurements of weather stations. In this work, the Priestley and Taylor (PT) and FAO Penman Monteith (FAO PM) equations were adapted to estimate the reference evapotranspiration, ET 0 , using only CERES satellite products (SYN1 and CldTypHist). In order to evaluate the reference evapotranspiration from CERES, a comparison with in situ measurements was conducted. We used ET data provided by the Oficina de Riesgo Agropecuario, corresponding to 24 stations placed in the Pampean Region of Argentina (2001-2016). Results showed very good agreement between the estimates with CERES products and in situ values, with errors between ±0.8 and ±1.1 mm d– 1 and r 2 greater than 0.75 at daily scale, and errors between ±14 and ±19 mm month –1 and r 2 greater than 0.9, at monthly scale better results were obtained with adapted model FAO PM than PT. Finally, ET 0 monthly maps for the Pampean Region of Argentina were elaborated, which allowed knowing the temporal-spatial variation in the validation area. In conclusion, the methods presented here are a suitable alternative to estimate the reference evapotranspiration without requiring ground measurements.
Carmona, Facundo; Orte, P. Facundo; Rivas, Raúl; Wolfram, Elian; Kruse, EduardoCarmona, F., P. F. Orte, R. Rivas, E. Wolfram, E. Kruse, 2018: Development and Analysis of a New Solar Radiation Atlas for Argentina from Ground-Based Measurements and CERES_SYN1deg data. The Egyptian Journal of Remote Sensing and Space Science, 21(3), 211-217. doi: 10.1016/j.ejrs.2017.11.003. Currently, quantifying global solar radiation at surface in Argentina is crucial for the development of projects related to solar energy, calculation of evapotranspiration and eco-sustainability architecture, among other environmental issues. In recent years, several models have been developed to estimate the solar energy resources by means of various techniques, e.g. satellite imaging, kriging, or Artificial Neural Networks. The use of satellite data allows for a better spatial representation, being of great relevance in areas with lack of terrain measurements. In this paper, we use the CERES_SYN1deg to develop a new Global Solar Radiation Atlas for Argentina. In this study, we developed maps of annual and monthly mean daily global solar radiation using CERES_SYN1deg data between 2000 and 2016. In order to validate the global solar radiation data provided by CERES_SYN1deg, they were compared with ground-based measurements in the time overlap of both instruments, in four monitoring sites of the SAVER-Net project and an additional site in Tandil, which belongs to the Remote Sensing Group of IHLLA. The maps show the spatial and temporal variation of global solar radiation in Argentina. Comparisons with ground-based pyranometers reveal relative differences of around 3% at a monthly scale for all sites, while the biases can be neglected. Therefore, it is possible to conclude that the maps could be very useful for different technical and scientific purposes, and the comparison with ground-based data demonstrates CERES_SYN1deg’s reliability. Remote sensing; CERES_SYN1deg product; Global solar radiation; SAVER-Net
Chen, Dong; Loboda, Tatiana V.; He, Tao; Zhang, Yi; Liang, ShunlinChen, D., T. V. Loboda, T. He, Y. Zhang, S. Liang, 2018: Strong cooling induced by stand-replacing fires through albedo in Siberian larch forests. Scientific Reports, 8(1), 4821. doi: 10.1038/s41598-018-23253-1. The Siberian larch forests, taking up about a fifth of the global boreal biome, are different from the North American boreal forests in that they generally do not undergo a secondary succession. While wildfires in the boreal forests in North America have been shown to exert a cooling effect on the climate system through a sharp increase in surface albedo associated with canopy removal and species composition change during succession, the magnitude of the surface forcing resulting from fire-induced albedo change and its longevity in Siberia have not been previously quantified. Here we show that in contrast to previous expectations, stand-replacing fires exert a strong cooling effect similar in magnitude to that in North America. This cooling effect is attributable to the increase in surface albedo during snow-on periods. However, the observed earlier snowmelt in the region, and subsequently a longer snow-free season, has resulted in a warming effect which has the potential to offset the fire-induced cooling. The net albedo-induced forcing of the Siberian larch forests in the future would hinge on the interaction between the fire-induced cooling effect and the climate-induced warming effect, both of which will be impacted by the expected further warming in the region.
Chen, Xiuhong; Huang, Xianglei; Dong, Xiquan; Xi, Baike; Dolinar, Erica K.; Loeb, Norman G.; Kato, Seiji; Stackhouse, Paul W.; Bosilovich, Michael G.Chen, X., X. Huang, X. Dong, B. Xi, E. K. Dolinar, N. G. Loeb, S. Kato, P. W. Stackhouse, M. G. Bosilovich, 2018: Using AIRS and ARM SGP Clear-Sky Observations to Evaluate Meteorological Reanalyses: A Hyperspectral Radiance Closure Approach. Journal of Geophysical Research: Atmospheres, 123(20), 11,720-11,734. doi: 10.1029/2018JD028850. Using the ground-based measurements from the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site and spectral radiance from the Atmospheric Infrared Sounder (AIRS) on National Aeronautics and Space Administration Aqua, we evaluate the temperature and humidity profiles from European Center for Medium Range Weather Forecasting ERA-Interim and Modern-Era Retrospective analysis for Research and Applications Version 2 reanalyses. Four sets of synthetic AIRS spectra are calculated using 51 clear-sky sounding profiles from the ARM SGP observations, the collocated AIRS L2 retrievals and the two reanalyses, respectively. A subset of AIRS channels sensitive to temperature, CO2, or H2O but not to other trace gases is chosen and further categorized into different groups according to the peak altitudes of their weighting functions. Synthetic radiances are then compared to the observed AIRS radiances for each group. For all groups, the observed AIRS radiances agree well with the synthetic ones based on the ARM SGP soundings or the AIRS L2 retrievals. The brightness temperature (BT) differences are within ±0.5 K. For two reanalyses, BT differences in all temperature-sensitive groups are generally within ±0.5 K; but the mean BT differences in all groups sensitive to both T and H2O are negative. Together, they suggest a wet bias in the free troposphere in both reanalyses. Moreover, such BT differences can be seen in the analysis of AIRS clear-sky radiances over the entire 30–40°N zone. A grid-search retrieval suggests that 9–30% reduction for reanalysis humidity between 200 and 800 hPa is needed to correct such wet bias. AIRS radiances; ARM soundings; reanalysis bias correction
Chen, Ying-Wen; Seiki, Tatsuya; Kodama, Chihiro; Satoh, Masaki; Noda, Akira T.Chen, Y., T. Seiki, C. Kodama, M. Satoh, A. T. Noda, 2018: Impact of Precipitating Ice Hydrometeors on Longwave Radiative Effect Estimated by a Global Cloud-System Resolving Model. Journal of Advances in Modeling Earth Systems, 10(2), 284-296. doi: 10.1002/2017MS001180. Satellite observation and general circulation model (GCM) studies suggest that precipitating ice makes nonnegligible contributions to the radiation balance of the Earth. However, in most GCMs, precipitating ice is diagnosed and its radiative effects are not taken into account. Here we examine the longwave radiative impact of precipitating ice using a global nonhydrostatic atmospheric model with a double-moment cloud microphysics scheme. An off-line radiation model is employed to determine cloud radiative effects according to the amount and altitude of each type of ice hydrometeor. Results show that the snow radiative effect reaches 2 W m−2 in the tropics, which is about half the value estimated by previous studies. This effect is strongly dependent on the vertical separation of ice categories and is partially generated by differences in terminal velocities, which are not represented in GCMs with diagnostic precipitating ice. Results from sensitivity experiments that artificially change the categories and altitudes of precipitating ice show that the simulated longwave heating profile and longwave radiation field are sensitive to the treatment of precipitating ice in models. This study emphasizes the importance of incorporating appropriate treatments for the radiative effects of precipitating ice in cloud and radiation schemes in GCMs in order to capture the cloud radiative effects of upper level clouds. 1620 Climate dynamics; 0321 Cloud/radiation interaction; global cloud-system resolving modeling; longwave radiation impact; precipitating ice hydrometeors
Chepfer, H.; Noel, V.; Chiriaco, M.; Wielicki, B.; Winker, D.; Loeb, N.; Wood, R.Chepfer, H., V. Noel, M. Chiriaco, B. Wielicki, D. Winker, N. Loeb, R. Wood, 2018: The Potential of a Multidecade Spaceborne Lidar Record to Constrain Cloud Feedback. Journal of Geophysical Research: Atmospheres, 123(10), 5433-5454. doi: 10.1002/2017JD027742. Synthetic multidecadal spaceborne lidar records are used to examine when a cloud response to anthropogenic forcing would be detectable from spaceborne lidar observations. The synthetic records are generated using long-term cloud changes predicted by two Coupled Model Intercomparison Program 5 models seen through the COSP/lidar (CFMIP, Cloud Feedback Model Intercomparison Project, Observation Simulators Package) and cloud interannual variability observed by the CALIPSO (Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations) spaceborne lidar during the past decade. CALIPSO observations do not show any significant trend yet. Our analysis of the synthetic time series suggests that the tropical cloud longwave feedback and the Southern Ocean cloud shortwave feedback might be constrained with 70% confidence with, respectively, a 20-year and 29-year uninterrupted lidar-in-space record. A 27-year record might be needed to separate the two different model predictions in the tropical subsidence clouds. Assuming that combining the CALIPSO and Earth-CARE (Earth Clouds, Aerosols and Radiation Explorer) missions will lead to a spaceborne lidar record of at least 16 years, we examine the impact of gaps and calibration offsets between successive missions. A 2-year gap between Earth-CARE and the following spaceborne lidar would have no significant impact on the capability to constrain the cloud feedback if all the space lidars were perfectly intercalibrated. Any intercalibration shift between successive lidar missions would delay the capability to constrain the cloud feedback mechanisms, larger shifts leading to longer delays. clouds; climate; space lidar
Ciesielski, Paul E.; Johnson, Richard H.; Schubert, Wayne H.; Ruppert, James H.Ciesielski, P. E., R. H. Johnson, W. H. Schubert, J. H. Ruppert, 2018: Diurnal Cycle of the ITCZ in DYNAMO. J. Climate, 31(11), 4543–4562. doi: 10.1175/JCLI-D-17-0670.1. During the 2011 special observing period of the Dynamics of the Madden-Julian Oscillation (DYNAMO; MJO) field experiment, two sounding arrays were established over the central Indian Ocean, one north and one south of the equator, referred to here as the NSA and SSA, respectively. Three-hourly soundings from these arrays augmented by observations of radiation and rainfall are used to investigate the diurnal cycle of ITCZ convection during the MJO suppressed phase. During the first half of October when convection was suppressed over the NSA but prominent over the SSA, the circulation over the sounding arrays could be characterized as a local Hadley cell. Strong rising motion was present within the ITCZ extending across the SSA with compensating subsidence over the NSA. A prominent diurnal pulsing of this cell was observed, impacting conditions on both sides of the equator, with the cell running strongest in the early morning hours (05-08 LT) and notably weakening later in the day (17-20LT). The declining daytime subsidence over the NSA may have assisted the moistening of the low to mid-troposphere there during the pre-onset stage of the MJO. Apparent heating Q1 within the ITCZ exhibited a diurnal evolution from early morning bottom-heavy profiles to weaker daytime top-heavy profiles, indicating a progression from convective to stratiform precipitation. Making use of the weak temperature gradient approximation, results suggest that both horizontal radiative heating gradients and direct cloud radiative forcing have an important influence on diurnal variations of vertical motion and convection within the ITCZ.
Collier, Nathan; Hoffman, Forrest M.; Lawrence, David M.; Keppel‐Aleks, Gretchen; Koven, Charles D.; Riley, William J.; Mu, Mingquan; Randerson, James T.Collier, N., F. M. Hoffman, D. M. Lawrence, G. Keppel‐Aleks, C. D. Koven, W. J. Riley, M. Mu, J. T. Randerson, 2018: The International Land Model Benchmarking (ILAMB) System: Design, Theory, and Implementation. Journal of Advances in Modeling Earth Systems, 10(11), 2731-2754. doi: 10.1029/2018MS001354. The increasing complexity of Earth system models (ESMs) has inspired efforts to quantitatively assess model fidelity through rigorous comparison with best-available measurements and observational data products. ESMs exhibit a high degree of spread in predictions of land biogeochemistry, biogeophysics, and hydrology, which are sensitive to forcing from other model components. Based on insights from prior land model evaluation studies and community workshops, the authors developed an open source model benchmarking software package that generates graphical diagnostics and scores model performance in support of the International Land Model Benchmarking (ILAMB) project. Employing a suite of in situ, remote sensing, and reanalysis datasets, the ILAMB package performs comprehensive model assessment across a wide range of land variables and generates a hierarchical set of webpages containing statistical analyses and figures designed to provide the user insights into strengths and weaknesses of multiple models or model versions. Described here is the benchmarking philosophy and mathematical methodology embodied in the most recent implementation of the ILAMB package. Comparison methods unique to a few specific datasets are presented, and guidelines for configuring an ILAMB analysis and interpreting resulting model performance scores are discussed. ILAMB is being adopted by modeling teams and centers during model development and for model intercomparison projects, and community engagement is sought for extending evaluation metrics and adding new observational datasets to the benchmarking framework. model evaluation; benchmarking; earth system model
Crueger, T.; Giorgetta, M. A.; Brokopf, R.; Esch, M.; Fiedler, S.; Hohenegger, C.; Kornblueh, L.; Mauritsen, T.; Nam, C.; Naumann, A. K.; Peters, K.; Rast, S.; Roeckner, E.; Sakradzija, M.; Schmidt, H.; Vial, J.; Vogel, R.; Stevens, B.Crueger, T., M. A. Giorgetta, R. Brokopf, M. Esch, S. Fiedler, C. Hohenegger, L. Kornblueh, T. Mauritsen, C. Nam, A. K. Naumann, K. Peters, S. Rast, E. Roeckner, M. Sakradzija, H. Schmidt, J. Vial, R. Vogel, B. Stevens, 2018: ICON-A, The Atmosphere Component of the ICON Earth System Model: II. Model Evaluation. Journal of Advances in Modeling Earth Systems, 10(7), 1638-1662. doi: 10.1029/2017MS001233. We evaluate the new icosahedral nonhydrostatic atmospheric (ICON-A) general circulation model of the Max Planck Institute for Meteorology that is flexible to be run at grid spacings from a few tens of meters to hundreds of kilometers. A simulation with ICON-A at a low resolution (160 km) is compared to a not-tuned fourfold higher-resolution simulation (40 km). Simulations using the last release of the ECHAM climate model (ECHAM6.3) are also presented at two different resolutions. The ICON-A simulations provide a compelling representation of the climate and its variability. The climate of the low-resolution ICON-A is even slightly better than that of ECHAM6.3. Improvements are obtained in aspects that are sensitive to the representation of orography, including the representation of cloud fields over eastern-boundary currents, the latitudinal distribution of cloud top heights, and the spatial distribution of convection over the Indian Ocean and the Maritime Continent. Precipitation over land is enhanced, in particular at high-resolution ICON-A. The response of precipitation to El Niño sea surface temperature variability is close to observations, particularly over the eastern Indian Ocean. Some parameterization changes lead to improvements, for example, with respect to rain intensities and the representation of equatorial waves, but also imply a warmer troposphere, which we suggest leads to an unrealistic poleward mass shift. Many biases familiar to ECHAM6.3 are also evident in ICON-A, namely, a too zonal SPCZ, an inadequate representation of north hemispheric blocking, and a relatively poor representation of tropical intraseasonal variability. model; circulation; general
Dai, Z.; Weisenstein, D. K.; Keith, D. W.Dai, Z., D. K. Weisenstein, D. W. Keith, 2018: Tailoring meridional and seasonal radiative forcing by sulfate aerosol solar geoengineering. Geophysical Research Letters, 45(2), 1030-1039. doi: 10.1002/2017GL076472. We study the possibility of designing solar radiation management schemes to achieve a desired meridional radiative forcing (RF) profile using a two-dimensional chemistry-transport-aerosol model. Varying SO2 or H2SO4 injection latitude, altitude, and season, we compute RF response functions for a broad range of possible injection schemes, finding that linear combinations of these injection cases can roughly achieve RF profiles that have been proposed to accomplish various climate objectives. Globally averaged RF normalized by the sulfur injection rate (the radiative efficacy) is largest for injections at high altitudes, near the equator, and using emission of H2SO4 vapor into an aircraft wake to produce accumulation-mode particles. There is a trade-off between radiative efficacy and control as temporal and spatial control is best achieved with injections at lower altitudes and higher latitudes. These results may inform studies using more realistic models that couple aerosol microphysics, chemistry, and stratospheric dynamics. 0305 Aerosols and particles; Solar geoengineering; Stratospheric H2SO4 injection; Stratospheric SO2 injection
Dessler, A. E.; Forster, P. M.Dessler, A. E., P. M. Forster, 2018: An estimate of equilibrium climate sensitivity from interannual variability. Journal of Geophysical Research: Atmospheres, 123(16), 8634-8645. doi: 10.1029/2018JD028481. Estimating the equilibrium climate sensitivity (ECS; the equilibrium warming in response to a doubling of CO2) from observations is one of the big problems in climate science. Using observations of interannual climate variations covering the period 2000 to 2017 and a model-derived relationship between interannual variations and forced climate change, we estimate ECS is likely 2.4-4.6 K (17-83% confidence interval), with a mode and median value of 2.9 and 3.3 K, respectively. This analysis provides no support for low values of ECS (below 2 K) suggested by other analyses. The main uncertainty in our estimate is not observational uncertainty, but rather uncertainty in converting observations of short-term, mainly unforced climate variability to an estimate of the response of the climate system to long-term forced warming. equilibrium climate sensitivity; interannual variability
Dessler, A. E.; Mauritsen, T.; Stevens, B.Dessler, A. E., T. Mauritsen, B. Stevens, 2018: The influence of internal variability on Earth's energy balance framework and implications for estimating climate sensitivity. Atmos. Chem. Phys., 18(7), 5147-5155. doi: 10.5194/acp-18-5147-2018.
Dewey, M.; Goldblatt, C.Dewey, M., C. Goldblatt, 2018: Evidence for Radiative-Convective Bistability in Tropical Atmospheres. Geophysical Research Letters, 45(19), 10,673-10,681. doi: 10.1029/2018GL078903. Earth's energy balance requires that energy absorbed and emitted at the top of the atmosphere be equal; to first order this balance is maintained via the Planck feedback: outgoing longwave radiation increases as surface temperature increases. Failure of the Planck feedback to stabilize the climate is described by three generally independent phenomena: the super-greenhouse effect, the runaway greenhouse, and multiple equilibria of radiative-convective atmospheres. Here we use satellite observations and models to show that the existence of the super-greenhouse gives rise to a radiative-convective instability which is relevant to Earth's tropics. The super-greenhouse is caused by the low troposphere becoming optically thick, causing a positive feedback on near surface temperature and moisture, driving deep convection, column moistening, and reduced outgoing longwave radiation. Aspects of the runaway greenhouse physics are implicated, but a local runaway greenhouse is avoided. These results have implications for understanding the response of the tropics to a warming world. clouds; convection; tropics; satellite observations; super-greenhouse effect; runaway greenhouse
Dewitte, Steven; Clerbaux, NicolasDewitte, S., N. Clerbaux, 2018: Decadal Changes of Earth’s Outgoing Longwave Radiation. Remote Sensing, 10(10), 1539. doi: 10.3390/rs10101539. The Earth Radiation Budget (ERB) at the top of the atmosphere quantifies how the earth gains energy from the sun and loses energy to space. Its monitoring is of fundamental importance for understanding ongoing climate change. In this paper, decadal changes of the Outgoing Longwave Radiation (OLR) as measured by the Clouds and Earth’s Radiant Energy System from 2000 to 2018, the Earth Radiation Budget Experiment from 1985 to 1998, and the High-resolution Infrared Radiation Sounder from 1985 to 2018 are analysed. The OLR has been rising since 1985, and correlates well with the rising global temperature. An observational estimate of the derivative of the OLR with respect to temperature of 2.93 +/− 0.3 W/m 2 K is obtained. The regional patterns of the observed OLR change from 1985–2000 to 2001–2017 show a warming pattern in the Northern Hemisphere in particular in the Arctic, as well as tropical cloudiness changes related to a strengthening of La Niña. earth radiation budget; outgoing longwave radiation
Doelling, David; Haney, Conor; Bhatt, Rajendra; Scarino, Benjamin; Gopalan, ArunDoelling, D., C. Haney, R. Bhatt, B. Scarino, A. Gopalan, 2018: Geostationary Visible Imager Calibration for the CERES SYN1deg Edition 4 Product. Remote Sensing, 10(2), 288. doi: 10.3390/rs10020288. The Clouds and the Earth’s Radiant Energy System (CERES) project relies on geostationary (GEO) imager derived TOA broadband fluxes and cloud properties to account for the regional diurnal fluctuations between the Terra and Aqua CERES and MODIS measurements. Anchoring the GEO visible calibration to the MODIS reference calibration and stability is critical for consistent fluxes and cloud retrievals across the 16 GEO imagers utilized in the CERES record. The CERES Edition 4A used GEO and MODIS ray-matched radiance pairs over all-sky tropical ocean (ATO-RM) to transfer the MODIS calibration to the GEO imagers. The primary GEO ATO-RM calibration was compared with the deep convective cloud (DCC) ray-matching and invariant desert/DCC target calibration methodologies, which are all tied to the same Aqua-MODIS calibration reference. Results indicate that most GEO record mean calibration method biases are within 1% with respect to ATO-RM. Most calibration method temporal trends were within 0.5% relative to ATO-RM. The monthly gain trend standard errors were mostly within 1% for all methods and GEOs. The close agreement amongst the independent calibration techniques validates all methodologies, and verifies that the coefficients are not artifacts of the methodology but rather adequately represent the true GEO visible imager degradation. calibration; MODIS; DCC; Earth invariant targets; geostationary; ray-matching
Donahue, Aaron S.; Caldwell, Peter M.Donahue, A. S., P. M. Caldwell, 2018: Impact of Physics Parameterization Ordering in A Global Atmosphere Model. Journal of Advances in Modeling Earth Systems, 10(2), 481–499. doi: 10.1002/2017MS001067. Because weather and climate models must capture a wide variety of spatial and temporal scales, they rely heavily on parameterizations of sub-grid scale processes. The goal of this study is to demonstrate that the assumptions used to couple these parameterizations have an important effect on the climate of version 0 of the Energy Exascale Earth System Model (E3SM) General Circulation Model (GCM), a close relative of version 1 of the Community Earth System Model (CESM1). Like most GCMs, parameterizations in E3SM are sequentially split in the sense that parameterizations are called one after another with each subsequent process feeling the effect of the preceding processes. This coupling strategy is non-commutative in the sense that the order in which processes are called impacts the solution. By examining a suite of 24 simulations with deep convection, shallow convection, macrophysics/microphysics, and radiation parameterizations reordered, process order is shown to have a big impact on predicted climate. In particular, reordering of processes induces differences in net climate feedback that are as big as the inter-model spread in phase 5 of the Coupled Model Inter-comparison Project. One reason why process ordering has such a large impact is that the effect of each process is influenced by the processes preceding it. Where output is written is therefore an important control on apparent model behavior. Application of K-means clustering demonstrates that the positioning of macro-/micro- physics and shallow convection plays a critical role on the model solution. 3305 Climate change and variability; 3337 Global climate models; 3336 Numerical approximations and analyses; 3365 Subgrid-scale (SGS) parameterization; 3367 Theoretical modeling; Global Climate Models; Net Climate Feedback; Physics Parameterizations; Sequential Time Splitting
Douglas, Alyson; L'Ecuyer, TristanDouglas, A., T. L'Ecuyer, 2018: Understanding Aerosol-Cloud-Radiation Interactions Using Local Meteorology and Cloud State Constraints. Atmospheric Chemistry and Physics Discussions, 1-25. doi: 10.1029/2018GL078903. Abstract. While many studies have tried to quantify the sign and the magnitude of the warm cloud response to aerosol loading, both remain uncertain owing to the multitude of factors that modulate microphysical and thermodynamic processes within the cloud. Constraining aerosol-cloud interactions using the local meteorology and cloud liquid water may offer a way to account for covarying influences, potentially increasing our confidence in observational estimates of warm cloud indirect effects. Four years of collocated satellite observations from the NASA A-Train constellation, combined with reanalaysis from MERRA-2, are used to partition warm clouds into regimes based on stability, the free atmospheric relative humidity, and liquid water path. Organizing the sizable number of satellite observations into regimes is shown to minimize the covariance between the environment or liquid water path and the indirect effect. Controlling for local meteorology and cloud state mitigates artificial signals and reveals substantial variance in both the sign and magnitude of the cloud radiative response, including regions where clouds become systematically darker with increased aerosol concentration in dry, unstable environments. The reverse Twomey effect, as it has been called, is evident even under the most stringent of constraints, confirming it is not an artificial signal or an isolated phenomenon. These results suggest it is not meaningful to report a single global sensitivity of cloud radiative effect to aerosol. To the contrary, we find the sensitivity can range from −.46 to .11 Wm−2ln(AI) regionally.
Draper, Clara S.; Reichle, Rolf H.; Koster, Randal D.Draper, C. S., R. H. Reichle, R. D. Koster, 2018: Assessment of MERRA-2 Land Surface Energy Flux Estimates. J. Climate, 31(2), 671–691. doi: 10.1175/JCLI-D-17-0121.1. In the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) system the land is forced by replacing the model-generated precipitation with observed precipitation before it reaches the surface. This approach is motivated by the expectation that the resultant improvements in soil moisture will lead to improved land surface latent heating (LH). Here we assess aspects of the MERRA-2 land surface energy budget and 2 m air temperatures (T2m). For global land annual averages, MERRA-2 appears to overestimate the LH (by 5 Wm−2 ), the sensible heating (by 6 Wm−2), and the downwelling shortwave radiation (by 14 Wm−2), while underestimating the downwelling and upwelling (absolute) longwave radiation (by 10-15 Wm−2 each). These results differ only slightly from those for NASA’s previous reanalysis, MERRA. Comparison to various gridded reference data sets over Boreal summer (June-July-August) suggests that MERRA-2 has particularly large positive biases (>20 Wm−2) where LH is energy-limited, and that these biases are associated with evaporative fraction biases rather than radiation biases. For time series of monthly means during Boreal summer, the globally averaged anomaly correlations (Ranom) with reference data were improved from MERRA to MERRA-2, for LH (from 0.39 to 0.48 vs. GLEAM data) and the daily maximum T2m (from 0.69 to 0.75 vs. CRU data). In regions where T2m is particularly sensitive to the precipitation corrections (including the central US, the Sahel, and parts of south Asia), the changes in the T2m Ranom are relatively large, suggesting that the observed precipitation influenced the T2m performance.
Duda, David P.; Bedka, Sarah T.; Minnis, Patrick; Spangenberg, Douglas; Khlopenkov, Konstantin; Chee, Thad; Smith Jr., William L.Duda, D. P., S. T. Bedka, P. Minnis, D. Spangenberg, K. Khlopenkov, T. Chee, W. L. Smith Jr., 2018: Northern Hemisphere Contrail Properties Derived from Terra and Aqua MODIS Data for 2006 and 2012. Atmospheric Chemistry and Physics Discussions, 1-30. doi: 10.5194/acp-2018-993. Abstract. Linear contrail coverage, optical property, and radiative forcing data over the Northern Hemisphere (NH) are derived from a year (2012) of Terra and Aqua Moderate-resolution Imaging Spectroradiometer (MODIS) imagery, and are compared with previously published 2006 results (Duda et al., 2013; Bedka et al., 2013; Spangenberg et al., 2013) using a consistent retrieval methodology. Differences in the observed Terra-minus-Aqua screened contrail coverage and patterns in the 2012 annual-mean air traffic estimated with respect to satellite overpass time suggest that most contrails detected by the contrail detection algorithm (CDA) form approximately 2h before overpass time. The 2012 screened NH contrail coverage (Mask B) shows a relative 3% increase (from 0.136% to 0.140%) compared to 2006 data for Terra and increased by almost 7% (0.134% to 0.143%) for Aqua. A new post-processing algorithm added to the contrail mask processing estimated that the total contrail cirrus coverage visible in the MODIS imagery may be three to four times larger than the linear contrail coverage detected by the CDA. This estimate is similar in magnitude to the spreading factor estimated by Minnis et al. (2013). Contrail property retrievals of the 2012 data indicate that both contrail optical depth and contrail effective diameter decreased approximately 10% between 2006 and 2012. The decreases may be attributed to better background cloudiness characterization, changes in the waypoint screening, or changes in contrail temperature. The total mean contrail radiative forcing (TCRF) for all 2012 Terra observations were −6.3, 14.3, and 8.0mWm−2 for the shortwave (SWCRF), longwave (LWCRF), and net forcings, respectively. These values are approximately 20% less than the corresponding 2006 Terra estimates. The decline in TCRF results from the decrease in normalized CRF, partially offset by the 3% increase in overall contrail coverage in 2012. The TCRFs for 2012 Aqua are similar, −6.4, 15.5, and 9.0mWm−2 for shortwave, longwave, and net radiative forcing. The strong correlation between the relative changes in both total SWCRF and LWCRF between 2006 and 2012 and the corresponding relative changes in screened contrail coverage over each air traffic region suggests that regional changes in TCRF from year to year are dominated by interannual changes in contrail coverage over each area.
Duveiller, Gregory; Hooker, Josh; Cescatti, AlessandroDuveiller, G., J. Hooker, A. Cescatti, 2018: A dataset mapping the potential biophysical effects of vegetation cover change. Scientific Data, 5, 180014. doi: 10.1038/sdata.2018.14. Changing the vegetation cover of the Earth has impacts on the biophysical properties of the surface and ultimately on the local climate. Depending on the specific type of vegetation change and on the background climate, the resulting competing biophysical processes can have a net warming or cooling effect, which can further vary both spatially and seasonally. Due to uncertain climate impacts and the lack of robust observations, biophysical effects are not yet considered in land-based climate policies. Here we present a dataset based on satellite remote sensing observations that provides the potential changes i) of the full surface energy balance, ii) at global scale, and iii) for multiple vegetation transitions, as would now be required for the comprehensive evaluation of land based mitigation plans. We anticipate that this dataset will provide valuable information to benchmark Earth system models, to assess future scenarios of land cover change and to develop the monitoring, reporting and verification guidelines required for the implementation of mitigation plans that account for biophysical land processes.
Duveiller, Gregory; Hooker, Josh; Cescatti, AlessandroDuveiller, G., J. Hooker, A. Cescatti, 2018: The mark of vegetation change on Earth’s surface energy balance. Nature Communications, 9(1), 679. doi: 10.1038/s41467-017-02810-8. Depending on where and when it occurs, vegetation cover change can affect local climate by altering the surface energy balance. Based on satellite data, this study provides the first data-driven assessment of such effects for multiple vegetation transitions at global scale.
Feng, Fei; Wang, KaicunFeng, F., K. Wang, 2018: Merging Satellite Retrievals and Reanalyses to Produce Global Long-Term and Consistent Surface Incident Solar Radiation Datasets. Remote Sensing, 10(1), 115. doi: 10.3390/rs10010115. Surface incident solar radiation (Rs) is a key parameter in many climatic and ecological processes. The data from satellites and reanalysis have been widely used. However, for reanalysis, Rs data has been shown to have substantial spatial bias, and the time span of reliable satellite Rs is too short for climatic and ecological studies. Combining reanalysis and satellite data would be an effective method for generating long-term and consistent Rs datasets. Here, we apply a cumulative probability density function-based (CPDF) method to merge eight reanalyses with the latest available satellite Rs data from Clouds and Earth’s Radiant Energy System Energy Balanced and Filled (CERES EBAF) surface retrievals. The CPDF method not only reduces the spatial bias of the reanalysis Rs data, but also makes the Rs datasets in a global, long-term and consistent way. The observed Rs data collected at 54 Baseline Surface Radiation Network (BSRN) stations from 1992 to 2016 are used to evaluate the method. Results show that the CPDF method could reduce the mean absolute biases (MAB) of the reanalysis Rs effectively by 21.24–64.36%. The European Centre for Medium-Range Weather Forecasts Re-Analysis interim (ERA-interim) reanalysis Rs data, which are available for 1979 onward, perform the best before MAB = 13.20 W·m−2 and after MAB = 10.40 W·m−2 merging. This small post-merging MAB of the ERA-interim reanalysis is caused by the MAB of 9.90 W·m−2 in the satellite Rs retrievals. The Japanese 55-year reanalysis provides Rs values back to 1958, and CPDF can reduce its MAB by 32.87%, to 11.17 W·m−2. The National Oceanic and Atmospheric Administration (NOAA)-CIRES twentieth-century reanalysis (CIRES) and the ECMWF twentieth-century reanalysis (ERA20CM) provide century-long Rs estimates. CIRES performs better after merging. The MAB of CIRES can be reduced by 32.10%, to 12.99 W·m−2, while ERA20CM’s can be reduced by 12.51%, to 16.40 W·m−2. data fusion; CERES EBAF; surface incident solar radiation; reanalyses; bias correction
Forzieri, Giovanni; Duveiller, Gregory; Georgievski, Goran; Li, Wei; Robertson, Eddy; Kautz, Markus; Lawrence, Peter; Martin, Lorea Garcia San; Anthoni, Peter; Ciais, Philippe; Pongratz, Julia; Sitch, Stephen; Wiltshire, Andy; Arneth, Almut; Cescatti, AlessandroForzieri, G., G. Duveiller, G. Georgievski, W. Li, E. Robertson, M. Kautz, P. Lawrence, L. G. S. Martin, P. Anthoni, P. Ciais, J. Pongratz, S. Sitch, A. Wiltshire, A. Arneth, A. Cescatti, 2018: Evaluating the Interplay Between Biophysical Processes and Leaf Area Changes in Land Surface Models. Journal of Advances in Modeling Earth Systems, 10(5), 1102-1126. doi: 10.1002/2018MS001284.
Foster, M. J.; Ackerman, S. A.; Bedka, Kristopher; Di Girolamo, L.; Frey, R. A.; Heidinger, A. K.; Sun-Mack, S.; Phillips, C.; Menzel, W. P.; Stengal, M; Zhao, GFoster, M. J., S. A. Ackerman, K. Bedka, L. Di Girolamo, R. A. Frey, A. K. Heidinger, S. Sun-Mack, C. Phillips, W. P. Menzel, M. Stengal, G. Zhao, 2018: Cloudiness [in “State of the Climate in 2017”].. Bull. Amer. Meteor. Soc, 99(8), S31-32. doi: 10.1175/2018BAMSStateoftheClimate.1.
Frey, W. R.; Morrison, A. L.; Kay, J. E.; Guzman, R.; Chepfer, H.Frey, W. R., A. L. Morrison, J. E. Kay, R. Guzman, H. Chepfer, 2018: The combined influence of observed Southern Ocean clouds and sea ice on top‐of‐atmosphere albedo. Journal of Geophysical Research: Atmospheres, 123(9), 4461-4475. doi: 10.1029/2018JD028505.
Fu, Yuyun; Li, Rui; Huang, Jianguo; Bergeron, Yves; Fu, Yunfei; Wang, Yu; Gao, ZongtingFu, Y., R. Li, J. Huang, Y. Bergeron, Y. Fu, Y. Wang, Z. Gao, 2018: Satellite-Observed Impacts of Wildfires on Regional Atmosphere Composition and the Shortwave Radiative Forcing: A Multiple Case Study. Journal of Geophysical Research: Atmospheres, 123(15), 8326-8343. doi: 10.1029/2017JD027927. Emissions of aerosols and trace gases from wildfires and their direct shortwave radiative forcing (DSRF) at the top of atmosphere were studied using satellite observations from Moderate-Resolution Imaging Spectroradiometer, Atmospheric Infrared Sounder, Clouds and Earth Radiant Energy System on Aqua, and Ozone Monitoring Instrument on Aura. The dominant fuel types of the selected fire cases in the northeast of China (NEC), Siberia (Russia), and California (USA) are cropland, mixed forest, and needle-leaf forest, respectively. For the cropland fire case in NEC, the fire radiative power-based emission coefficients (Ce) of aerosol is 20.51 ± 2.55 g/MJ, half that of the forest fire cases in Siberia (40.01 ± 9.21 g/MJ) and California (45.23 ± 8.81 g/MJ), and the carbon monoxide (CO) Ce (23.94 ± 11.83 g/MJ) was about one third and half that of the forest fire cases in Siberia and California, respectively. However, the NOx (NO2 + NO) Ce (2.76 ± 0.25g MJ−1) of the cropland fire in NEC was nearly 3 times that of those forest fire cases. Ratios of NOx to aerosol, HCHO, and CO in the cropland case in NEC show much higher values than those in the forest fire cases. Despite the differences of the Ce and the composition ratios, the DSRF efficiency of smoke aerosol at the top of atmosphere showed similar values among those fire cases. Our results highlight the large variability of emission rate and relative chemical composition but similar DSRF efficiencies among wildfires, which would provide valuable information for understanding the impact of fire on air quality and climate. satellite remote sensing; direct shortwave radiative forcing; emission rate; fire radiative power; wildfire
Furtado, KalliFurtado, K., 2018: Chapter 8 - Subgrid Representation of Mixed-Phase Clouds in a General Circulation Model A2 - Andronache, Constantin. Mixed-Phase Clouds, 185-214. Abstract The ubiquity and longevity of supercooled liquid-water and mixed-phase clouds in nature is at odds with the relative lack of these cloud types in numerical models of cloudy atmospheres when compared to observations. Amongst the mechanisms proposed for the longevity of mixed-phase conditions in nature is that small-scale turbulent motions compete with ice microphysical processes to maintain a statistical steady state in which a constant amount of liquid water exists for a long of period time. In this chapter we review previous work on understanding this mechanism and show how it can be developed into a parametrization of mixed-phase clouds. The parametrization is based on exact, steady-state solutions for the statistics of supersaturation fluctuations in a turbulent cloud layer from which expressions for the liquid-cloud properties can be derived. We review the implementation of the parametrization in a general circulation model and discuss implications of the parametrization for long-standing biases in the radiative properties of simulated mid- and high-latitude cloud-systems.
Furtado, Kalli; Field, Paul R.; Luo, Yali; Liu, Xi; Guo, Zhun; Zhou, Tianjun; Shipway, Benjamin J.; Hill, Adrian A.; Wilkinson, Jonathan M.Furtado, K., P. R. Field, Y. Luo, X. Liu, Z. Guo, T. Zhou, B. J. Shipway, A. A. Hill, J. M. Wilkinson, 2018: Cloud-microphysical factors affecting simulations of deep convection during the presummer rainy-season in southern China. Journal of Geophysical Research: Atmospheres, 123(18), 10,477-10,505. doi: 10.1029/2017JD028192. The sensitivity of subtropical deep-convection to the parametrization of cloud microphysics is elucidated through high-resolution modelling of extreme presummer-rainfall over southern China. An ensemble of physics-configuration experiments is used to identify several drivers of model errors in comparison to radar observations from the South China Monsoon Rainfall Experiment (SCMREX), and remotely-sensed estimates of cloud, precipitation and radiation from satellites in the A-train constellation. The benefits of increasing the number of prognostic variables in the microphysics scheme is assessed, relative to the effects of the parametrization of cloud microphysical-properties and cloud-fraction diagnosis. By matching individual parametrizations between the microphysical configurations, it is shown that a small subset of the parametrization changes can reproduce most of the dependence of model performance on physics configuration. In particular, biases that are due to the low-level clouds and rain are strongly influenced by cloud-fraction diagnosis and rain-drop size distribution, whereas variations in the effects of high clouds are strongly influenced by differences in the parametrization of ice-crystal sedimentation. Hence, for the case studied here, these parametrizations give more insight into the causes of variability in model performance than does the number of model prognostics per se. clouds; microphysics; observations; China; modelling; monsoons
Garimella, S.; Rothenberg, D. A.; Wolf, M. J.; Wang, C.; Cziczo, D. J.Garimella, S., D. A. Rothenberg, M. J. Wolf, C. Wang, D. J. Cziczo, 2018: How Uncertainty in Field Measurements of Ice Nucleating Particles Influences Modeled Cloud Forcing. J. Atmos. Sci., 75(1), 179-187. doi: 10.1175/JAS-D-17-0089.1. Field and laboratory measurements using continuous flow diffusion chambers (CFDCs) have been used to construct parameterizations of the number of ice nucleating particles (INPs) in mixed-phase and completely glaciated clouds in weather and climate models. Because of flow nonidealities, CFDC measurements are subject to systematic low biases. Here, the authors investigate the effects of this undercounting bias on simulated cloud forcing in a global climate model. The authors assess the influence of measurement variability by constructing a stochastic parameterization framework to endogenize measurement uncertainty. The authors find that simulated anthropogenic longwave ice-bearing cloud forcing in a global climate model can vary up to 0.8 W m−2 and can change sign from positive to negative within the experimentally constrained bias range. Considering the variability in the undercounting bias, in a range consistent with recent experiments, leads to a larger negative cloud forcing than that when the variability is ignored and only a constant bias is assumed.
George, Geet; Sarangi, Chandan; Tripathi, Sachchida Nand; Chakraborty, Tirthankar; Turner, AndrewGeorge, G., C. Sarangi, S. N. Tripathi, T. Chakraborty, A. Turner, 2018: Vertical Structure and Radiative Forcing of Monsoon Clouds over Kanpur during the 2016 INCOMPASS field campaign. Journal of Geophysical Research: Atmospheres, 123(4), 2152–2174. doi: 10.1002/2017JD027759. An overview of cloud vertical structure (CVS) and cloud radiative forcing (CRF) during Indian summer monsoon is obtained over Kanpur, through observations made during the Interaction of Convective Organisation and Monsoon Precipitation, Atmosphere, Surface and Sea (INCOMPASS) field campaign of 2016. Associations of CVS parameters with CRF at surface and top of atmosphere (TOA) are also investigated. 137 radiosondes were launched at Indian Institute of Technology Kanpur (IITK), between 5th and 28th July, 2016. CVS is determined using an algorithm that identifies cloud layers from vertical profiles of relative humidity (RH), with altitude-dependent RH thresholds. CVS is analysed by separating the campaign period on the basis of presence and absence of depressions/low-pressure systems. Compared to non-depression periods, low-pressure events showed significant difference in all CVS and CRF parameters except cloud-top height. CVS was multi-layered in ∼75% launches, with deep, mixed-phase clouds being present in ∼70% launches. CRF was calculated from clear-sky measurements and TOA observations from Clouds and the Earth's Radiant Energy System (CERES) satellite retrievals, and surface measurements. A net cooling effect was found overall, with instantaneous shortwave forcing (SWCRF) (mean values of -95.92 and -101.89 W/m2 at surface and TOA, respectively) dominating longwave forcing (LWCRF) (mean values of 15.33 and 66.55 W/m2 at surface and TOA, respectively). Results suggest that SWCRF depends on total depth of cloud layers, and is independent of cloud altitude, whereas LWCRF depends on both depth and vertical location of cloud layers, with base and top heights regulating LWCRF at surface and TOA, respectively. 0321 Cloud/radiation interaction; 3374 Tropical meteorology; 3310 Clouds and cloud feedbacks; 3329 Mesoscale meteorology; cloud base top height depth; cloud forcing surface TOA; cloud multi layers; india monsoon indo gangetic plain; monsoon depression low pressure; radiosondes weather balloons
Giardina, Francesco; Konings, Alexandra G.; Kennedy, Daniel; Alemohammad, Seyed Hamed; Oliveira, Rafael S.; Uriarte, Maria; Gentine, PierreGiardina, F., A. G. Konings, D. Kennedy, S. H. Alemohammad, R. S. Oliveira, M. Uriarte, P. Gentine, 2018: Tall Amazonian forests are less sensitive to precipitation variability. Nature Geoscience, 11(6), 405-409. doi: 10.1038/s41561-018-0133-5. Tall trees are less sensitive to variation in precipitation than short trees, according to analyses of photosynthetic sensitivity to drought in tall and short Amazon forests. The results demonstrate higher resilience of tall trees to drought.
Giorgetta, M. A.; Brokopf, R.; Crueger, T.; Esch, M.; Fiedler, S.; Helmert, J.; Hohenegger, C.; Kornblueh, L.; Köhler, M.; Manzini, E.; Mauritsen, T.; Nam, C.; Raddatz, T.; Rast, S.; Reinert, D.; Sakradzija, M.; Schmidt, H.; Schneck, R.; Schnur, R.; Silvers, L.; Wan, H.; Zängl, G.; Stevens, B.Giorgetta, M. A., R. Brokopf, T. Crueger, M. Esch, S. Fiedler, J. Helmert, C. Hohenegger, L. Kornblueh, M. Köhler, E. Manzini, T. Mauritsen, C. Nam, T. Raddatz, S. Rast, D. Reinert, M. Sakradzija, H. Schmidt, R. Schneck, R. Schnur, L. Silvers, H. Wan, G. Zängl, B. Stevens, 2018: ICON-A, the Atmosphere Component of the ICON Earth System Model: I. Model Description. Journal of Advances in Modeling Earth Systems, 10(7), 1613-1637. doi: 10.1029/2017MS001242. ICON-A is the new icosahedral nonhydrostatic (ICON) atmospheric general circulation model in a configuration using the Max Planck Institute physics package, which originates from the ECHAM6 general circulation model, and has been adapted to account for the changed dynamical core framework. The coupling scheme between dynamics and physics employs a sequential updating by dynamics and physics, and a fixed sequence of the physical processes similar to ECHAM6. To allow a meaningful initial comparison between ICON-A and the established ECHAM6-LR model, a setup with similar, low resolution in terms of number of grid points and levels is chosen. The ICON-A model is tuned on the base of the Atmospheric Model Intercomparison Project (AMIP) experiment aiming primarily at a well balanced top-of atmosphere energy budget to make the model suitable for coupled climate and Earth system modeling. The tuning addresses first the moisture and cloud distribution to achieve the top-of-atmosphere energy balance, followed by the tuning of the parameterized dynamic drag aiming at reduced wind errors in the troposphere. The resulting version of ICON-A has overall biases, which are comparable to those of ECHAM6. Problematic specific biases remain in the vertical distribution of clouds and in the stratospheric circulation, where the winter vortices are too weak. Biases in precipitable water and tropospheric temperature are, however, reduced compared to the ECHAM6. ICON-A will serve as the basis of further development and as the atmosphere component to the coupled model, ICON-Earth system model (ESM). model tuning; atmospheric GCM; ICON-A; model description
Girihagama, Lakshika; Nof, DoronGirihagama, L., D. Nof, 2018: Why is the ocean surface slightly warmer than the atmosphere?. Journal of Marine Research, 76(1), 23-46. doi: 10.1357/002224018824082007. How much warmer is the ocean surface than the atmosphere directly above it? The present study offers a means to quantify this temperature difference using a conceptual nonlinear one-dimensional global energy balance coupled ocean–atmosphere model ("Aqua Planet"). The significance of our idealized model, which is of intermediate complexity, is its ability to obtain an analytical solution for the global average temperatures. Our analytical model results show that, for the present climate, predicted global mean ocean temperature is 291.1 K whereas surface atmospheric temperature above the ocean surface is 287.4 K. Thus, the modeled surface ocean is 3.7 K warmer than the atmosphere above it. Temporal perturbation of the global mean solution obtained for "Aqua Planet" showed a stable system. Oscillation amplitude of the atmospheric temperature anomaly is greater in magnitude than those found in the ocean. There is a phase shift (a lag in the ocean), which is caused by oceanic thermal inertia. Climate feedbacks due to selected climate parameters such as incoming radiation, cloud cover, and CO2 are discussed. Warming obtained with our model compares well with Intergovernmental Panel on Climate Change's (IPCC) estimations. Application of our model to local regions illuminates the importance of evaporative cooling in determining derived air–sea temperature offsets, where an increase in the latter increases the systems overall sensitivity to evaporative cooling. ATMOSPHERE INTERACTION; CONCEPTUAL CLIMATE MODELS; OCEAN–; TEMPERATURE DIFFERENCE
Grosvenor, Daniel P.; Sourdeval, Odran; Zuidema, Paquita; Ackerman, Andrew; Alexandrov, Mikhail D.; Bennartz, Ralf; Boers, Reinout; Cairns, Brian; Chiu, J. Christine; Christensen, Matthew; Deneke, Hartwig M.; Diamond, Michael S.; Feingold, Graham; Fridlind, Ann; Hünerbein, Anja; Knist, Christine L.; Kollias, Pavlos; Marshak, Alexander; McCoy, Daniel; Merk, Daniel; Painemal, David; Rausch, John; Rosenfeld, Daniel; Russchenberg, Herman; Seifert, Patric; Sinclair, Kenneth; Stier, Philip; van Diedenhoven, Bastiaan; Wendisch, Manfred; Werner, Frank; Wood, Robert; Zhang, Zhibo; Quaas, JohannesGrosvenor, D. P., O. Sourdeval, P. Zuidema, A. Ackerman, M. D. Alexandrov, R. Bennartz, R. Boers, B. Cairns, J. C. Chiu, M. Christensen, H. M. Deneke, M. S. Diamond, G. Feingold, A. Fridlind, A. Hünerbein, C. L. Knist, P. Kollias, A. Marshak, D. McCoy, D. Merk, D. Painemal, J. Rausch, D. Rosenfeld, H. Russchenberg, P. Seifert, K. Sinclair, P. Stier, B. van Diedenhoven, M. Wendisch, F. Werner, R. Wood, Z. Zhang, J. Quaas, 2018: Remote sensing of droplet number concentration in warm clouds: A review of the current state of knowledge and perspectives. Reviews of Geophysics, 56(2), 409-453. doi: 10.1029/2017RG000593.
Gryspeerdt, Edward; Quaas, Johannes; Goren, Tom; Klocke, Daniel; Brueck, MatthiasGryspeerdt, E., J. Quaas, T. Goren, D. Klocke, M. Brueck, 2018: An automated cirrus classification. Atmospheric Chemistry and Physics, 18(9), 6157-6169. doi: 10.5194/acp-18-6157-2018. Cirrus clouds play an important role in determining the radiation budget of the earth, but many of their properties remain uncertain, particularly their response to aerosol variations and to warming. Part of the reason for this uncertainty is the dependence of cirrus cloud properties on the cloud formation mechanism, which itself is strongly dependent on the local meteorological conditions.
Hanea, A. M.; Nane, G. F.; Wielicki, B. A.; Cooke, R. M.Hanea, A. M., G. F. Nane, B. A. Wielicki, R. M. Cooke, 2018: Bayesian networks for identifying incorrect probabilistic intuitions in a climate trend uncertainty quantification context. Journal of Risk Research, 1-16. doi: 10.1080/13669877.2018.1437059. Probabilistic thinking can often be unintuitive. This is the case even for simple problems, let alone the more complex ones arising in climate modelling, where disparate information sources need to be combined. The physical models, the natural variability of systems, the measurement errors and their dependence upon the observational period length should be modelled together in order to understand the intricacies of the underlying processes. We use Bayesian networks (BNs) to connect all the above-mentioned pieces in a climate trend uncertainty quantification framework. Inference in such models allows us to observe some seemingly nonsensical outcomes. We argue that they must be pondered rather than discarded until we understand how they arise. We would like to stress that the main focus of this paper is the use of BNs in complex probabilistic settings rather than the application itself.
Haney, C.; Doelling, D.; Bhatt, R.; Scarino, B.; Gopalan, ArunHaney, C., D. Doelling, R. Bhatt, B. Scarino, A. Gopalan, 2018: Advances in utilizing deep convective cloud targets to inter-calibrate geostationary reflective solar band imagers with well calibrated imagers.
Hartmann, Dennis L.; Gasparini, Blaž; Berry, Sara E.; Blossey, Peter N.Hartmann, D. L., B. Gasparini, S. E. Berry, P. N. Blossey, 2018: The Life Cycle and Net Radiative Effect of Tropical Anvil Clouds. Journal of Advances in Modeling Earth Systems, 10(12), 3012-3029. doi: 10.1029/2018MS001484. We explore the importance of the life cycle of detrained tropical anvil clouds in producing a weak net cloud radiative effect (NCRE) by tropical convective systems. We simulate a horizontally homogeneous elevated ice cloud in a 2-D framework using the System for Atmospheric Modeling cloud-resolving model. The initially thick cloud produces a negative NCRE, which is later canceled by a positive NCRE as the cloud thins and rises. Turning off interactive cloud radiation reveals that cloud radiative heating and in-cloud convection are fundamental in driving net radiative neutrality. In-cloud convection acts to thin initially thick anvil clouds and loft and maintain thin cirrus. The maintenance of anvil clouds is tied to the recycling of water vapor and cloud ice through sublimation, nucleation, and deposition as air parcels circulate vertically within the cloud layer. Without interactive radiation, the cloud sediments and sublimates away, producing a large negative NCRE. The specification of cloud microphysics substantially influences the cloud's behavior and life cycle , but the tendency of the life cycle to produce compensating cloud radiative effects is robust to substantial changes in the microphysics. Our study shows that small-scale processes within upper level ice clouds likely have a strong influence on the NCRE associated with tropical convective cloud systems. cirrus clouds; tropical convection; anvil clouds; climate sensitivity
He, Jian; He, Ruoying; Zhang, YangHe, J., R. He, Y. Zhang, 2018: Impacts of Air-sea Interactions on Regional Air Quality Predictions Using a Coupled Atmosphere-ocean Model in Southeastern U.S.. Aerosol and Air Quality Research, 18(4), 1044-1067. doi: 10.4209/aaqr.2016.12.0570. Air-sea interactions have significant impacts on coastal convection and surface fluxes exchange. They are important for the spatial and vertical distributions of air pollutants that affect public health, particularly in densely populated coastal areas. To understand the impacts of air-sea interactions on coastal air quality predictions, sensitivity simulations with different atmosphere-ocean coupling are conducted in this work over southeastern U.S. in July 2010 using the Weather Research and Forecasting Model with Chemistry (WRF/Chem). The results show that comparing to WRF/Chem without air-sea interactions, WRF/Chem with a 1-D ocean mixed layer model (WRF/Chem-OML) and WRF/Chem coupled with a 3-D Regional Ocean Modeling System (WRF/Chem-ROMS) predict the domain averaged changes in the sea surface temperature of 0.06°C and 0.94°C, respectively for July average. The simulated differences in the surface concentrations of O3 and PM2.5 between WRF/Chem-ROMS and WRF/Chem can be as large as 17.3 ppb and 7.9 µg m–3, respectively, with the largest changes occurring not only along coast and remote ocean, but also over some inland areas. Extensive validations against observations show that WRF/Chem-ROMS improves the predictions of most cloud and radiative variables, and surface concentrations of some chemical species such as SO2, NO2, maximum 1-h and 8-h O3, SO42–, NH4+, NO3–, and PM10. This illustrates the benefits and needs of using coupled atmosphere-ocean model with advanced model representations of air-sea interactions for regional air quality modeling.
He, Lijie; Wang, Lunche; Lin, Aiwen; Zhang, Ming; Xia, Xiangao; Tao, Minghui; Zhou, HaoHe, L., L. Wang, A. Lin, M. Zhang, X. Xia, M. Tao, H. Zhou, 2018: What drives changes in aerosol properties over the Yangtze River Basin in past four decades？. Atmospheric Environment, 190, 269-283. doi: 10.1016/j.atmosenv.2018.07.034. Since the Reform and Opening up in China, aerosols increasingly affect the country's climate change and human health. However, remote sensing studies have been inconclusive as to long-term trends in Chinese aerosol emissions. The newly-released MERRA-2 product provides a long-term (1980 onward) aerosol reanalysis dataset, and thus is used in this study for identifying trends in aerosol optical depth (AOD) and aerosol direct radiative effect (ADRE) in clear sky over the Yangtze River Basin (YRB) based on the MK nonparametric method. Results reveal that there is a notable turning point in AOD trends around 2008, i.e., significantly increasing by 0.0201 year−1 before 2008 and then deceasing by −0.0185 year−1. The reason may be the decreases of S02, NOx and soot (dust) emissions from major cities in the YRB since 2006. Likewise, the cooling (warming) effects at the top of atmosphere (TOA), surface (SFC) and atmosphere (ATM) strongly increase by −0.3744 and −0.5652 (0.2935) wm−2 year−1 before 2008, and then significantly decrease by 0.2731 and 0.5868 (−0.3145) wm−2 year−1. Trend analyses confirm that changes in AOD dominate ADRE trends. Furthermore, AOD is significantly negatively (positively) associated with NDVI and precipitation (GDP and Population density) over most areas of the YRB. Besides, similar spatial trends with AOD are also identified in GDP and NDVI. This indicates that increases in GDP and decreases in NDVI caused by rapid urbanization partly lead to the growth of AOD over the middle and lower reaches of the YRB. However, changes in precipitation and Population density alone may not be the main factors for the increasing AOD. Aerosol optical depth; Aerosol direct radiative effect; Impact factor analysis; Trend analysis; Yangtze river basin
Hegyi, Bradley M.; Taylor, Patrick C.Hegyi, B. M., P. C. Taylor, 2018: The unprecedented 2016-17 Arctic sea ice growth season: the crucial role of atmospheric rivers and longwave fluxes. Geophysical Research Letters, 45(10), 5204-5212. doi: 10.1029/2017GL076717. The 2016-17 Arctic sea ice growth season (October-March) exhibited one of the lowest end-of-season sea ice volume and extent of any year since 1979. An analysis of MERRA2 atmospheric reanalysis data and CERES radiative flux data reveals that a record warm and moist Arctic atmosphere supported the reduced sea ice growth. Numerous regional episodes of increased atmospheric temperature and moisture, transported from lower latitudes, increased the cumulative energy input from downwelling longwave surface fluxes. In those same episodes, the efficiency of the atmosphere cooling radiatively to space was reduced, increasing the amount of energy retained in the Arctic atmosphere and reradiated back toward the surface. Overall, the Arctic radiative cooling efficiency shows a decreasing trend since 2000. The results presented highlight the increasing importance of atmospheric forcing on sea ice variability demonstrating that episodic Arctic atmospheric rivers, regions of elevated poleward water vapor transport, and the subsequent surface energy budget response is a critical mechanism actively contributing to the evolution of Arctic sea ice. Arctic sea ice growth; Atmospheric water vapor; Longwave fluxes
Hill, Peter G.; Allan, Richard P.; Chiu, J. Christine; Bodas-Salcedo, Alejandro; Knippertz, PeterHill, P. G., R. P. Allan, J. C. Chiu, A. Bodas-Salcedo, P. Knippertz, 2018: Quantifying the contribution of different cloud types to the radiation budget in southern West Africa. J. Climate, 31(13), 5273–5291. doi: 10.1175/JCLI-D-17-0586.1. The contribution of cloud to the radiation budget of southern West Africa (SWA) is poorly understood yet is important for understanding regional monsoon evolution and for evaluating and improving climate models, which have large biases in this region. Radiative transfer calculations applied to atmospheric profiles obtained from the CERES-CloudSat-CALIPSO-MODIS (CCCM) dataset are used to investigate the effects of 12 different cloud types (defined by their vertical structure) on the regional energy budget of SWA (5–10 °N, 8 °W-8 °E) during June-September. We show that the large regional mean cloud radiative effect in SWA is due to non-negligible contributions from many different cloud types; 8 cloud types have a cloud fraction larger than 5 % and contribute at least 5 % of the regional mean shortwave cloud radiative effect at the top of atmosphere. Low-clouds, which are poorly observed by passive satellite measurements, were found to cause net radiative cooling of the atmosphere, which reduces the heating from other cloud types by approximately 10 %. The sensitivity of the radiation budget to underestimating low-cloud cover is also investigated. The radiative effect of missing low-cloud is found to be up to approximately –25 W m-2 for upwelling shortwave irradiance at the top of atmosphere and 35 W m-2 for downwelling shortwave irradiance at the surface.
Hill, Spencer A.; Ming, Yi; Zhao, MingHill, S. A., Y. Ming, M. Zhao, 2018: Robust Responses of the Sahelian Hydrological Cycle to Global Warming. J. Climate, 31(24), 9793-9814. doi: 10.1175/JCLI-D-18-0238.1. How the globally uniform component of sea surface temperature (SST) warming influences rainfall in the African Sahel remains insufficiently studied, despite mean SST warming being among the most robustly simulated and theoretically grounded features of anthropogenic climate change. A prior study using the NOAA Geophysical Fluid Dynamics Laboratory (GFDL) AM2.1 atmospheric general circulation model (AGCM) demonstrated that uniform SST warming strengthens the prevailing northerly advection of dry Saharan air into the Sahel. The present study uses uniform SST warming simulations performed with 7 GFDL and 10 CMIP5 AGCMs to assess the robustness of this drying mechanism across models and uses observations to assess the physical credibility of the severe drying response in AM2.1. In all 17 AGCMs, mean SST warming enhances the free-tropospheric meridional moisture gradient spanning the Sahel and with it the Saharan dry-air advection. Energetically, this is partially balanced by anomalous subsidence, yielding decreased precipitation in 14 of the 17 models. Anomalous subsidence and precipitation are tightly linked across the GFDL models but not the CMIP5 models, precluding the use of this relationship as the start of a causal chain ending in an emergent observational constraint. For AM2.1, cloud–rainfall covariances generate radiative feedbacks on drying through the subsidence mechanism and through surface hydrology that are excessive compared to observations at the interannual time scale. These feedbacks also act in the equilibrium response to uniform warming, calling into question the Sahel’s severe drying response to warming in all coupled models using AM2.1.
Holzman, Mauro E.; Carmona, Facundo; Rivas, Raúl; Niclòs, RaquelHolzman, M. E., F. Carmona, R. Rivas, R. Niclòs, 2018: Early assessment of crop yield from remotely sensed water stress and solar radiation data. ISPRS Journal of Photogrammetry and Remote Sensing, 145, 297-308. doi: 10.1016/j.isprsjprs.2018.03.014. Soil moisture (SM) available for evapotranspiration is crucial for food security, given the significant interannual yield variability of rainfed crops in large agricultural regions. Also, incoming solar radiation (Rs) influences the photosynthetic rate of vegetated surfaces and can affect productivity. The aim of this work is to evaluate the ability of crop water stress and Rs remotely sensed data to forecast yield at regional scale. Temperature Vegetation Dryness Index (TVDI) was computed as an indicator of crop water stress and soil moisture availability. TVDI during critical growth stage of crops was calculated from MODIS products: MODIS/AQUA 8-day composite LST at 1 km and 16-day composite vegetation index at 1 km. Rs data were obtained from Clouds and the Earth’s Radiant Energy System (CERES). The relationship between TVDI, Rs and yield of wheat, corn and soybean was analyzed. High R2 values (0.55–0.82, depending on crop and region) were found in different agro-climatic regions of Argentine Pampas. Validation results showed the suitability of the model RMSE = 330–1300 kg ha−1, Relative Error = 13–34%. However, results were significantly improved considering the most important factor affecting yield. Rs proved to be important for winter crops in humid areas, where incoming radiation can be a limiting factor. In semi-arid regions, soils with low water retention capacity and summer crops, crop water stress showed the best results. Overall, results reflected that the proposed approach is suitable for crop yield forecasting at regional scale several weeks previous to harvest. Evapotranspiration; Crop water stress; Food security; Yield estimation
Hu, Zeyuan; Cronin, Timothy W.; Tziperman, EliHu, Z., T. W. Cronin, E. Tziperman, 2018: Suppression of Cold Weather Events over High-Latitude Continents in Warm Climates. J. Climate, 31(23), 9625-9640. doi: 10.1175/JCLI-D-18-0129.1. Recent studies, using Lagrangian single-column atmospheric models, have proposed that in warmer climates more low clouds would form as maritime air masses advect into Northern Hemisphere high-latitude continental interiors during winter (DJF). This increase in low cloud amount and optical thickness could reduce surface radiative cooling and suppress Arctic air formation events, partly explaining both the warm winter high-latitude continental interior climate and frost-intolerant species found there during the Eocene and the positive lapse-rate feedback in future Arctic climate change scenarios. Here the authors examine the robustness of this low-cloud mechanism in a three-dimensional atmospheric model that includes large-scale dynamics. Different warming scenarios are simulated under prescribed CO2 and sea surface temperature, and the sensitivity of winter temperatures and clouds over high-latitude continental interior to mid- and high-latitude sea surface temperatures is examined. Model results show that winter 2-m temperatures on extreme cold days increase about 50% faster than the winter mean temperatures and the prescribed SST. Low cloud fraction and surface longwave cloud radiative forcing also increase in both the winter mean state and on extreme cold days, consistent with previous Lagrangian air-mass studies, but with cloud fraction increasing for different reasons than proposed by previous work. At high latitudes, the cloud longwave warming effect dominates the shortwave cooling effect, and the net cloud radiative forcing at the surface tends to warm high-latitude land but cool midlatitude land. This could contribute to the reduced meridional temperature gradient in warmer climates and help explain the greater warming of winter cold extremes relative to winter mean temperatures.
Hua, Shan; Liu, Yuzhi; Jia, Rui; Chang, Shuting; Wu, Chuqiao; Zhu, Qingzhe; Shao, Tianbin; Wang, BingHua, S., Y. Liu, R. Jia, S. Chang, C. Wu, Q. Zhu, T. Shao, B. Wang, 2018: Role of clouds in accelerating cold-season warming during 2000–2015 over the Tibetan Plateau. International Journal of Climatology, 38(13), 4950-4966. doi: 10.1002/joc.5709. With the global warming slowdown in the twenty-first century, a huge discrepancy in regional climate warming has been identified over the main region of the Tibetan Plateau (TP). Compared with the +0.04 °C/decade warming from 1961 to 1999, the warming greatly accelerated for the period 2000–2015 at a rate of +0.30 °C/decade. During the same period, warming in the cold season (November to March) was more pronounced than in the warm season (May to September) over the TP. The results also indicated that the middle-level cloud (middle cloud) decreased (−0.359%/year), while the high-level cloud (high cloud) increased (+0.241%/year) over almost all the TP during the cold season. Further analysis showed positive net cloud radiative forcing over the western TP from 2000–2015, that is, a heating effect of clouds, especially in the cold season. Combining the trends of the increase in high cloud and the decrease in middle cloud over most parts of the TP, the decreased albedo effect of middle cloud and the increased longwave greenhouse effect of high cloud may have partially contributed to the sustained warming, especially in the cold season from 2000 to 2015. Meanwhile, the results showed that the warming rate and cloud area fraction changes were significantly amplified with elevation. The analysis based on a model of Coupled Model Intercomparison Project Phase 5 shows that the decreased middle cloud plays more important role than the increased high cloud in modulating the enhanced warming over the TP, especially in the cold season. cloud; warming; cloud radiative forcing; Tibetan plateau
Hwang, Jiwon; Choi, Yong-Sang; Kim, WonMoo; Su, Hui; Jiang, Jonathan H.Hwang, J., Y. Choi, W. Kim, H. Su, J. H. Jiang, 2018: Observational estimation of radiative feedback to surface air temperature over Northern High Latitudes. Climate Dynamics, 50(1-2), 615-628. doi: 10.1007/s00382-017-3629-6. The high-latitude climate system contains complicated, but largely veiled physical feedback processes. Climate predictions remain uncertain, especially for the Northern High Latitudes (NHL; north of 60°N), and observational constraint on climate modeling is vital. This study estimates local radiative feedbacks for NHL based on the CERES/Terra satellite observations during March 2000–November 2014. The local shortwave (SW) and longwave (LW) radiative feedback parameters are calculated from linear regression of radiative fluxes at the top of the atmosphere on surface air temperatures. These parameters are estimated by the de-seasonalization and 12-month moving average of the radiative fluxes over NHL. The estimated magnitudes of the SW and the LW radiative feedbacks in NHL are 1.88 ± 0.73 and 2.38 ± 0.59 W m−2 K−1, respectively. The parameters are further decomposed into individual feedback components associated with surface albedo, water vapor, lapse rate, and clouds, as a product of the change in climate variables from ERA-Interim reanalysis estimates and their pre-calculated radiative kernels. The results reveal the significant role of clouds in reducing the surface albedo feedback (1.13 ± 0.44 W m−2 K−1 in the cloud-free condition, and 0.49 ± 0.30 W m−2 K−1 in the all-sky condition), while the lapse rate feedback is predominant in LW radiation (1.33 ± 0.18 W m−2 K−1). However, a large portion of the local SW and LW radiative feedbacks were not simply explained by the sum of these individual feedbacks.
Hyder, Patrick; Edwards, John M.; Allan, Richard P.; Hewitt, Helene T.; Bracegirdle, Thomas J.; Gregory, Jonathan M.; Wood, Richard A.; Meijers, Andrew J. S.; Mulcahy, Jane; Field, Paul; Furtado, Kalli; Bodas-Salcedo, Alejandro; Williams, Keith D.; Copsey, Dan; Josey, Simon A.; Liu, Chunlei; Roberts, Chris D.; Sanchez, Claudio; Ridley, Jeff; Thorpe, Livia; Hardiman, Steven C.; Mayer, Michael; Berry, David I.; Belcher, Stephen E.Hyder, P., J. M. Edwards, R. P. Allan, H. T. Hewitt, T. J. Bracegirdle, J. M. Gregory, R. A. Wood, A. J. S. Meijers, J. Mulcahy, P. Field, K. Furtado, A. Bodas-Salcedo, K. D. Williams, D. Copsey, S. A. Josey, C. Liu, C. D. Roberts, C. Sanchez, J. Ridley, L. Thorpe, S. C. Hardiman, M. Mayer, D. I. Berry, S. E. Belcher, 2018: Critical Southern Ocean climate model biases traced to atmospheric model cloud errors. Nature Communications, 9(1), 3625. doi: 10.1038/s41467-018-05634-2. The Southern Ocean is critically important for global climate yet poorly represented by climate models. Here the authors trace sea surface temperature biases in this region to cloud-related errors in atmospheric-model simulated surface heat fluxes and provide a pathway to improve the models.
Itterly, Kyle F.; Taylor, Patrick C.; Dodson, Jason BrantItterly, K. F., P. C. Taylor, J. B. Dodson, 2018: Sensitivity of the Amazonian convective diurnal cycle to its environment in observations and reanalysis. Journal of Geophysical Research: Atmospheres, 123(22), 12,621-12,646. doi: 10.1029/2018JD029251. Atmospheric model parameterizations of tropical deep convection struggle to reproduce the observed diurnal variability of convection in the Amazon leading to climatological biases in the energy budget and water cycle. To identify the physical process contributions to these biases, we analyze the relationships between the convective diurnal cycle and atmosphere state variables relevant to convection in the Amazon using satellite observations and reanalysis data sets for wet and dry seasons between 2002-2016 and two GOAmazon periods. The analysis first stratifies the diurnal cycle into convective and non-convective days using a daily maximum rain rate threshold of 0.5 mm hour-1. Secondly, the population of days is constrained by requiring reanalysis and observations to agree on the occurrence of convective rain rates, controlling for frequency-dependent biases in convection. The model-generated precipitation phase in MERRA-2 is closer to observations than ERA during 2002-2016, which exhibits a systematic noontime bias and exaggerated diurnal amplitude. Despite the systematic noontime precipitation bias, ERA produces better agreement with GOAmazon observations due to the frequent midmorning arrival of the coastal front acting to shift the observed diurnal cycle closer to noon. Model disagreement between middle-tropospheric vertical velocity is largest overnight during the dissipation stage of convection; acting to sustain biases through radiative effects. Specifically, the slower dissipation of convection in MERRA-2 acts to reduce morning surface fluxes and increase convective inhibition whereas enhanced nocturnal mid-tropospheric subsidence and higher boundary layer humidity in ERA reduces morning convective inhibition leading to an earlier initiation of afternoon deep convection. Amazonian Convection; Convective Diurnal Cycle; GoAmazon Diurnal Cycle; Humidity and Convection; Reanalysis Model Evaluation; Sensitivity to Environment
Jia, Aolin; Liang, Shunlin; Jiang, Bo; Zhang, Xiaotong; Wang, GuoxinJia, A., S. Liang, B. Jiang, X. Zhang, G. Wang, 2018: Comprehensive Assessment of Global Surface Net Radiation Products and Uncertainty Analysis. Journal of Geophysical Research: Atmospheres, 123(4), 1970-1989. doi: 10.1002/2017JD027903. Earth surface net radiation (Rn) characterizes the surface radiation budget and plays a critical role in ecological, biogeochemical, and hydrological processes. The Rn products from remote sensing and reanalysis have not been validated comprehensively. In this study, four Rn products (CERES, ERA-Interim, MERRA2, and JRA-55) were validated using global ground measurements on monthly (255 sites) and annual (172 sites) timescales. These products have similar accuracies, with average root-mean-square error ranges of 5.35 Wm-2 (monthly) and 2.30 Wm-2 (annually). However, varying accuracies and systemic biases exist across different climatic zones. The annual land Rn intercomparison illustrates that large uncertainty exists over polar regions and deserts. A significantly negative annual anomaly in the CERES product for the 2001–2008 period is identified when examining annual Rn anomalies over the global land surface. Detailed uncertainty analysis indicates that the global CERES Rn anomaly is mainly due to different versions of input data such as aerosol optical thickness and atmospheric profiles (in 2006 and 2008) and cloud properties (in 2002). This work demonstrates that temporal analysis provides powerful quality control for global time series satellite products when the validation using ground measurements fails to capture potential issues. 1640 Remote sensing; CERES; 0321 Cloud/radiation interaction; 1814 Energy budgets; 1873 Uncertainty assessment; 1988 Temporal analysis and representation; Assessment; global products; net radiation; uncertainty analysis
Jia, Rui; Liu, Yuzhi; Hua, Shan; Zhu, Qingzhe; Shao, TianbinJia, R., Y. Liu, S. Hua, Q. Zhu, T. Shao, 2018: Estimation of the Aerosol Radiative Effect over the Tibetan Plateau Based on the Latest CALIPSO Product. Journal of Meteorological Research, 32(5), 707-722. doi: 10.1007/s13351-018-8060-3. Based on the CALIPSO (Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation) Version 4.10 products released on 8 November 2016, the Level 2 (L2) aerosol product over the Tibetan Plateau (TP) is evaluated and the aerosol radiative effect is also estimated in this study. As there are still some missing aerosol data points in the daytime CALIPSO Version 4.10 L2 product, this study re-calculated the aerosol extinction coefficient to explore the aerosol radiative effect over the TP based on the CALIPSO Level 1 (L1) and CloudSat 2B-CLDCLASS-LIDAR products. The energy budget estimation obtained by using the AODs (aerosol optical depths) from calculated aerosol extinction coefficient as an input to a radiative transfer model shows better agreement with the Earth’s Radiant Energy System (CERES) and CloudSat 2B-FLXHR-LIDAR observations than that with the input of AODs from aerosol extinction coefficient from CALIPSO Version 4.10 L2 product. The radiative effect and heating rate of aerosols over the TP are further simulated by using the calculated aerosol extinction coefficient. The dust aerosols may heat the atmosphere by retaining the energy in the layer. The instantaneous heating rate can be as high as 5.5 K day–1 depending on the density of the dust layers. Overall, the dust aerosols significantly affect the radiative energy budget and thermodynamic structure of the air over the TP, mainly by altering the shortwave radiation budget. The significant influence of dust aerosols over the TP on the radiation budget may have important implications for investigating the atmospheric circulation and future regional and global climate. Tibetan Plateau; aerosol radiative effect; Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) Version 4.10 product
Jian, Bida; Li, Jiming; Wang, Guoyin; He, Yongli; Han, Ying; Zhang, Min; Huang, JianpingJian, B., J. Li, G. Wang, Y. He, Y. Han, M. Zhang, J. Huang, 2018: The impacts of atmospheric and surface parameters on long-term variations in the planetary albedo. J. Climate, 31(21), 8705–8718. doi: 10.1175/JCLI-D-17-0848.1. Planetary albedo (PA, shortwave broadband albedo) and its long-term variations, which are controlled in a complex way by various atmospheric and surface properties, play a key role in controlling the global and regional energy budget. This study investigates the contributions of different atmospheric and surface properties on the long-term variations of PA based on 13 years (2003–2015) of albedo, cloud and ice coverage datasets from the Clouds and the Earth’s Radiant Energy System (CERES) Single Scanner Footprint (SSF) Edition4A product, vegetation product from Moderate Resolution Imaging Spectroradiometer (MODIS) and surface albedo product from the CLARA-A2 (Cloud, Albedo, and Radiation dataset, version 2). According to the temporal correlation analysis, statistical results indicate that variations in PA are closely related to the variations of cloud properties (e.g., cloud fraction, ice water path and liquid water path) and surface parameters (e.g., ice/snow percent coverage and normalized difference vegetation index), but their temporal relationships vary among the different regions. Generally, the stepwise multiple linear regression models can capture the observed PA anomalies for most regions. Based on the contribution calculation, cloud fraction dominates the variability of PA in the mid and low latitudes while ice/snow percent coverage (or surface albedo) dominate the variability in the mid high and latitudes. Changes in cloud liquid water path and ice water path are the secondary dominant factor over most regions whereas change in vegetation cover is the least important factor over land. These results verify the effects of atmospheric and surface factors on planetary albedo changes, thus may be of benefit for improving the parameterization of the PA and determining the climate feedbacks.
Joiner, Joanna; Yoshida, Yasuko; Anderson, Martha; Holmes, Thomas; Hain, Christopher; Reichle, Rolf; Koster, Randal; Middleton, Elizabeth; Zeng, Fan-WeiJoiner, J., Y. Yoshida, M. Anderson, T. Holmes, C. Hain, R. Reichle, R. Koster, E. Middleton, F. Zeng, 2018: Global relationships among traditional reflectance vegetation indices (NDVI and NDII), evapotranspiration (ET), and soil moisture variability on weekly timescales. Remote Sensing of Environment, 219, 339-352. doi: 10.1016/j.rse.2018.10.020. Monitoring the effects of water availability on vegetation globally using satellites is important for applications such as drought early warning, precision agriculture, and food security as well as for more broadly understanding relationships between water and carbon cycles. In this global study, we examine how quickly several satellite-based indicators, assumed to have relationships with water availability, respond, on timescales of days to weeks, in comparison with variations in root-zone soil moisture (RZM) that extends to about 1 m depth. The satellite indicators considered are the normalized difference vegetation and infrared indices (NDVI and NDII, respectively) derived from reflectances obtained with moderately wide (20–40 nm) spectral bands in the visible and near-infrared (NIR) and evapotranspiration (ET) estimated from thermal infrared observations and normalized by a reference ET. NDVI is primarily sensitive to chlorophyll contributions and vegetation structure while NDII may contain additional information on water content in leaves and canopy. ET includes both the loss of root zone soil water through transpiration (modulated by stomatal conductance) as well as evaporation from bare soil. We find that variations of these satellite-based drought indicators on time scales of days to weeks have significant correlations with those of RZM in the same water-limited geographical locations that are dominated by grasslands, shrublands, and savannas whose root systems are generally contained within the 1 m RZM layer. Normalized ET interannual variations show generally a faster response to water deficits and enhancements as compared with those of NDVI and NDII, particularly in sparsely vegetated regions. Evapotranspiration; Drought; Root zone soil moisture; Vegetation; Vegetation index
Kato, Seiji; Rose, Fred G.; Rutan, David A.; Thorsen, Tyler J.; Loeb, Norman G.; Doelling, David R.; Huang, Xianglei; Smith, William L.; Su, Wenying; Ham, Seung HeeKato, S., F. G. Rose, D. A. Rutan, T. J. Thorsen, N. G. Loeb, D. R. Doelling, X. Huang, W. L. Smith, W. Su, S. H. Ham, 2018: Surface Irradiances of Edition 4.0 Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) Data Product. J. Climate, 31(11), 4501–4527. doi: 10.1175/JCLI-D-17-0523.1. The algorithm to produce the Clouds and the Earth’s Energy System (CERES) Ed4.0 Energy Balanced and Filled (EBAF)-surface data product is explained. The algorithm forces computed top-of-atmosphere (TOA) irradiances to match with Ed4.0 EBAF-TOA irradiances by adjusting surface, cloud and atmospheric properties. Surface irradiances are subsequently adjusted using radiative kernels. The adjustment process is composed of two parts, bias correction and Lagrange multiplier. The bias in temperature and specific humidity between 200 hPa and 500 hPa used for the irradiance computation is corrected based on observations by Atmospheric Infrared Sounder (AIRS). Similarly, the bias in the cloud fraction is corrected based on observations by Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), and CloudSat. Remaining errors in surface, cloud and atmospheric properties are corrected in the Lagrange multiplier process. Ed4.0 global annual mean (January 2005 thorough December 2014) surface net shortwave (SW) and longwave (LW) irradiances, respectively, increases by 1.3 Wm-2 and decreases by 0.2 Wm-2 compared to EBAF Ed2.8 counterparts (the previous version), resulting increasing in net SW+LW surface irradiance by 1.1 Wm-2. The uncertainty in surface irradiances over ocean, land and polar regions at various spatial scales are estimated. The uncertainties in all-sky global annual mean upward and downward shortwave irradiance are, respectively, 3 Wm-2 and 4 Wm-2, and the uncertainties in upward and downward longwave irradiance are respectively, 3 Wm-2 and 6 Wm-2. With an assumption of all errors being independent the uncertainty in the global annual mean surface LW+SW net irradiance is 8 Wm-2.
Katsumata, Masaki; Mori, Shuichi; Hamada, Jun-Ichi; Hattori, Miki; Syamsudin, Fadli; Yamanaka, Manabu D.Katsumata, M., S. Mori, J. Hamada, M. Hattori, F. Syamsudin, M. D. Yamanaka, 2018: Diurnal cycle over a coastal area of the Maritime Continent as derived by special networked soundings over Jakarta during HARIMAU2010. Progress in Earth and Planetary Science, 5(1), 64. doi: 10.1186/s40645-018-0216-3. This study investigates the nature and mechanisms of the diurnal precipitation system over a coastal area of the Maritime Continent (MC) by utilizing the data from a field campaign, HARIMAU2010. During the 1-month campaign, diurnal cycles over Jakarta were well identified by special networked soundings and a C-band radar. Radar and satellites captured the convective-type heavy rains that appeared in the afternoon over the array, which were followed by stratiform-type precipitation during the night. Thermodynamic budget analyses were also performed using sounding data. The period-averaged vertical profiles of Q1 and Q2 indicate that diurnal precipitation acted as deep convection in the diabatic heating and drying. The diurnal composite of the obtained parameters revealed key processes such as (1) just before the onset of the afternoon convective rain, the lower troposphere was moistened by subarray-scale processes; (2) moistening of the troposphere continued during the convective heavy precipitation; (3) the stratiform rains during the night were partly maintained by consuming the pre-existing hydrometeor aloft; and (4) in the early morning, the clouds redeveloped over the ocean to produce precipitation as well as hydrometeor aloft. The possible physical processes promoting lower-tropospheric moistening before onset of the convective rain are also discussed.
Kim, Bu-Yo; Lee, Kyu-Tae; Jee, Joon-Bum; Zo, Il-SungKim, B., K. Lee, J. Jee, I. Zo, 2018: Retrieval of outgoing longwave radiation at top-of-atmosphere using Himawari-8 AHI data. Remote Sensing of Environment, 204(Supplement C), 498-508. doi: 10.1016/j.rse.2017.10.006. This study proposes an algorithm to retrieve the outgoing longwave radiation at the top of the atmosphere (TOA OLR) using the advanced Himawari imager (AHI) unit that is a narrowband sensor installed in Himawari-8, a geostationary satellite providing window and water vapor imagery. The outgoing longwave radiation at the top of the atmosphere (TOA OLR) was retrieved by an empirical method where a radiative transfer model (RTM) was used to simulate various atmospheric conditions, such as the surface temperature, water vapor, and cloud characteristics (e.g., cloud optical thickness and cloud height). The results of an algorithm using a single channel (OLR12.4) and two channels (OLR6.2+12.4) were converted into Terra Cloud and Earth's Radiant Energy System (CERES) TOA OLR for the daytime (0105–0135 UTC) and nighttime (1325–1355 UTC) cases of a scene analysis (typhoon Goni on August 18, 2015). Long-term analysis (August 2015–July 2016) and statistical analysis (i.e., mean, bias, root mean square error (RMSE), and correlation coefficient) were conducted. The analysis results showed that the largest error was produced in the cloudy areas (overcast areas), and the minimum RMSE and a high correlation coefficient were observed over an ocean area. In the scene analysis, however, the daytime and nighttime average RMSE of the CERES TOA OLR and OLR6.2+12.4 was 12.21Wm−2 and showed the correlation coefficient of 0.971. It was an improved result over the RMSE (12.33Wm−2) and correlation coefficient (0.967) shown in the analysis of OLR12.4. In the long-term analysis, the average RMSE was 11.83Wm−2 and showed a correlation coefficient of 0.972 (OLR12.4 showed 12.17Wm−2 and 0.969). Furthermore, to minimize the difference in the cloud area that had the largest error, the study analyzed TOA OLR at the significance level of 95% (±2 RMSE). As a result, the scene analysis showed an RMSE of 10.54Wm−2 and correlation coefficient of 0.977, and the long-term data showed an RMSE of 10.23Wm−2 and correlation coefficient of 0.979. Clouds and the Earth's Radiant Energy System; Radiative transfer model; Advanced Himawari imager; Himawari-8; Narrowband; Outgoing longwave radiation
Kim, Bu-Yo; Lee, Kyu-Tae; Kim, Bu-Yo; Lee, Kyu-TaeKim, B., K. Lee, B. Kim, K. Lee, 2018: Radiation Component Calculation and Energy Budget Analysis for the Korean Peninsula Region. Remote Sensing, 10(7), 1147. doi: 10.3390/rs10071147. In this study, a radiation component calculation algorithm was developed using channel data from the Himawari-8 Advanced Himawari Imager (AHI) and meteorological data from the Unified Model (UM) Local Data Assimilation and Prediction System (LDAPS). In addition, the energy budget of the Korean Peninsula region in 2016 was calculated and its regional differences were analyzed. Radiation components derived using the algorithm were calibrated using the broadband radiation component data from the Clouds and the Earth’s Radiant Energy System (CERES) to improve their accuracy. The calculated radiation components and the CERES data showed an annual mean percent bias of less than 3.5% and a high correlation coefficient of over 0.98. The energy budget of the Korean Peninsula region was −2.4 Wm−2 at the top of the atmosphere (RT), −14.5 Wm−2 at the surface (RS), and 12.1 Wm−2 in the atmosphere (RA), with regional energy budget differences. The Seoul region had a high surface temperature (289.5 K) and a RS of −33.4 Wm−2 (surface emission), whereas the Sokcho region had a low surface temperature (284.7 K) and a RS of 5.0 Wm−2 (surface absorption), for a difference of 38.5 Wm−2. In short, regions with relatively high surface temperatures tended to show energy emission, and regions with relatively low surface temperatures tended to show energy absorption. Such regional energy imbalances can cause weather and climate changes and bring about meteorological disasters, and thus research on detecting energy budget changes must be continued. energy budget; Himawari-8 AHI; energy imbalance; Korean Peninsula region; UM LDAPS
Kim, Ji-Eun; Zhang, Chidong; Kiladis, George N.; Bechtold, PeterKim, J., C. Zhang, G. N. Kiladis, P. Bechtold, 2018: Heating and Moistening of the MJO during DYNAMO in ECMWF Reforecasts. J. Atmos. Sci., 75(5), 1429–1452. doi: 10.1175/JAS-D-17-0170.1. Reforecasts produced by the ECMWF Integrated Forecasting System (IFS) were used to study heating and moistening processes associated with three MJO events over the equatorial Indian Ocean during the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign. Variables produced by and derived from the IFS reforecast (IFS-RF) agree reasonably well with observations over the DYNAMO sounding arrays, and they vary smoothly from western to eastern equatorial Indian Ocean. This lends confidence towards using IFS-RF as a surrogate of observations over the equatorial Indian Ocean outside the DYNAMO arrays. The apparent heat source Q1 and apparent moisture sink Q2 produced by IFS are primarily generated by parameterized cumulus convection, followed by microphysics and radiation. The vertical growth of positive Q1 and Q2 associated with the progression of MJO convection can be gradual, stepwise, or rapid depending on the event and its location over the broader equatorial Indian Ocean. The time for convective heating and drying to progress from shallow (800 hPa) to deep (400 hPa) can be
Kolly, A.; Huang, Y.Kolly, A., Y. Huang, 2018: The radiative feedback during the ENSO cycle: Observations vs. Models. Journal of Geophysical Research: Atmospheres, 123(17), 9097-9108. doi: 10.1029/2018JD028401. Observational and model data are used to study the radiative feedbacks during the El Niño Southern Oscillation (ENSO) cycle. We extend the previous works by analyzing the feedbacks with respect to not only top-of-atmosphere (TOA) but also the surface and atmospheric radiation budgets, using a newly developed set of radiation kernels. We find that the tropical radiative budgets undergo distinctive variations during ENSO. The radiative perturbation is especially significant for the atmospheric energy budget. We find that the cloud feedback during the developing phase of ENSO heats the atmosphere over the west and central Pacific differentially, which acts to strengthen the development. We also find that a prominent cloud feedback bias persists in the newer version global climate models. This bias results from wrong extent of compensation between longwave and shortwave effects, which points to the importance of validating the radiative sensitivity of clouds in the GCMs. radiative forcing; ENSO; cloud radiative feedback; energetics of ENSO
Lacour, A.; Chepfer, H.; Miller, N. B.; Shupe, M. D.; Noel, V.; Fettweis, X.; Gallee, H.; Kay, J. E.; Guzman, R.; Cole, J.Lacour, A., H. Chepfer, N. B. Miller, M. D. Shupe, V. Noel, X. Fettweis, H. Gallee, J. E. Kay, R. Guzman, J. Cole, 2018: How Well Are Clouds Simulated over Greenland in Climate Models? Consequences for the Surface Cloud Radiative Effect over the Ice Sheet. J. Climate, 31(22), 9293-9312. doi: 10.1175/JCLI-D-18-0023.1. Using lidar and radiative flux observations from space and ground, and a lidar simulator, we evaluate clouds simulated by climate models over the Greenland ice sheet, including predicted cloud cover, cloud fraction profile, cloud opacity, and surface cloud radiative effects. The representation of clouds over Greenland is a central concern for the models because clouds impact ice sheet surface melt. We find that over Greenland, most of the models have insufficient cloud cover during summer. In addition, all models create too few nonopaque, liquid-containing clouds optically thin enough to let direct solar radiation reach the surface (−1% to −3.5% at the ground level). Some models create too few opaque clouds. In most climate models, the cloud properties biases identified over all Greenland also apply at Summit, Greenland, proving the value of the ground observatory in model evaluation. At Summit, climate models underestimate cloud radiative effect (CRE) at the surface, especially in summer. The primary driver of the summer CRE biases compared to observations is the underestimation of the cloud cover in summer (−46% to −21%), which leads to an underestimated longwave radiative warming effect (CRELW = −35.7 to −13.6 W m−2 compared to the ground observations) and an underestimated shortwave cooling effect (CRESW = +1.5 to +10.5 W m−2 compared to the ground observations). Overall, the simulated clouds do not radiatively warm the surface as much as observed.
Lee, Sang-Ho; Kim, Bu-Yo; Lee, Kyu-Tae; Zo, Il-Sung; Jung, Hyun-Seok; Rim, Se-HunLee, S., B. Kim, K. Lee, I. Zo, H. Jung, S. Rim, 2018: Retrieval of Reflected Shortwave Radiation at the Top of the Atmosphere Using Himawari-8/AHI Data. Remote Sensing, 10(2), 213. doi: 10.3390/rs10020213. This study developed a retrieval algorithm for reflected shortwave radiation at the top of the atmosphere (RSR). This algorithm is based on Himawari-8/AHI (Advanced Himawari Imager) whose sensor characteristics and observation area are similar to the next-generation Geostationary Korea Multi-Purpose Satellite/Advanced Meteorological Imager (GK-2A/AMI). This algorithm converts the radiance into reflectance for six shortwave channels and retrieves the RSR with a regression coefficient look-up-table according to geometry of the solar-viewing (solar zenith angle, viewing zenith angle, and relative azimuth angle) and atmospheric conditions (surface type and absence/presence of clouds), and removed sun glint with high uncertainty. The regression coefficients were calculated using numerical experiments from the radiative transfer model (SBDART), and ridge regression for broadband albedo at the top of the atmosphere (TOA albedo) and narrowband reflectance considering anisotropy. The retrieved RSR were validated using Terra, Aqua, and S-NPP/CERES data on the 15th day of every month from July 2015 to February 2017. The coefficient of determination (R2) between AHI and CERES for scene analysis was higher than 0.867 and the Bias and root mean square error (RMSE) were −21.34–5.52 and 51.74–59.28 Wm−2. The R2, Bias, and RMSE for the all cases were 0.903, −2.34, and 52.12 Wm−2, respectively. broadband albedo at the top of the atmosphere (TOA albedo); Clouds and the Earth Radiant Energy System (CERES); Geostationary Korea Multi-Purse Satellite/Advanced Meteorological Imager (GK-2A/AMI); Himawari-8/Advanced Meteorological Imager (Himawari-8/AHI); reflected shortwave radiation at the top of the atmosphere (RSR)
Lee, Sang-Ho; Lee, Kyu-Tae; Kim, Bu-Yo; Zo, ll-Sung; Jung, Hyun-Seok; Rim, Se-HunLee, S., K. Lee, B. Kim, l. Zo, H. Jung, S. Rim, 2018: Retrieval Algorithm for Broadband Albedo at the Top of the Atmosphere. Asia-Pacific Journal of Atmospheric Sciences, 54(2), 165-178. doi: 10.1007/s13143-018-0001-7. The objective of this study is to develop an algorithm that retrieves the broadband albedo at the top of the atmosphere (TOA albedo) for radiation budget and climate analysis of Earth’s atmosphere using Geostationary Korea Multi-Purse Satellite/Advanced Meteorological Imager (GK-2A/AMI) data. Because the GK-2A satellite will launch in 2018, we used data from the Japanese weather satellite Himawari-8 and onboard sensor Advanced Himawari Imager (AHI), which has similar sensor properties and observation area to those of GK-2A. TOA albedo was retrieved based on reflectance and regression coefficients of shortwave channels 1 to 6 of AHI. The regression coefficient was calculated using the results of the radiative transfer model (SBDART) and ridge regression. The SBDART used simulations of the correlation between TOA albedo and reflectance of each channel according to each atmospheric conditions (solar zenith angle, viewing zenith angle, relative azimuth angle, surface type, and absence/presence of clouds). The TOA albedo from Himawari-8/AHI were compared to that from the National Aeronautics and Space Administration (NASA) satellite Terra with onboard sensor Clouds and the Earth’s Radiant Energy System (CERES). The correlation coefficients between the two datasets from the week containing the first day of every month between 1st August 2015 and 1st July 2016 were high, ranging between 0.934 and 0.955, with the root mean square error in the 0.053-0.068 range.
Li, J.-L. F.; Suhas, E.; Richardson, Mark; Lee, Wei-Liang; Wang, Yi-Hui; Yu, Jia-Yuh; Lee, Tong; Fetzer, Eric; Stephens, Graeme; Shen, Min-HuaLi, J. F., E. Suhas, M. Richardson, W. Lee, Y. Wang, J. Yu, T. Lee, E. Fetzer, G. Stephens, M. Shen, 2018: The Impacts of Bias in Cloud-Radiation-Dynamics Interactions on Central-Pacific Seasonal and El Nino Simulations in Contemporary GCMs. Earth and Space Science, 5(2), 50-60. doi: 10.1002/2017EA000304. Most of the global climate models (GCMs) in the Coupled Model Intercomparison Project, phase 5 (CMIP5) do not include precipitating ice (a.k.a. falling snow) in their radiation calculations. We examine the importance of the radiative effects of precipitating ice on simulated surface wind stress and sea surface temperatures (SSTs) in terms of seasonal variation and in the evolution of Central Pacific El Nino (CP-El Nino) events. Using controlled simulations with the CESM1 model, we show that the exclusion of precipitating ice radiative effects generates a persistent excessive upper-level radiative cooling and an increasingly unstable atmosphere over convective regions such as the western Pacific and tropical convergence zones. The invigorated convection leads to persistent anomalous low-level outflows which weaken the easterly trade winds, reducing upper-ocean mixing and leading to a positive SST bias in the model mean state. In CP-El Nino events, this means that outflow from the modeled convection in the central Pacific reduces winds to the east, allowing unrealistic eastward propagation of warm SST anomalies following the peak in CP-El Nino activity. Including the radiative effects of precipitating ice reduces these model biases and improves the simulated life cycle of the CP-El Nino. Improved simulations of present day tropical seasonal variations and CP-El Nino events would increase the confidence in simulating their future behaviour. cloud; 0321 Cloud/radiation interaction; radiation; GCM; 4522 ENSO; ENSO; 3371 Tropical convection; 1627 Coupled models of the climate system; 3373 Tropical dynamics
Liu, Chunlei; Allan, Richard P.Liu, C., R. P. Allan, 2018: Unrealistic increases in wind speed explain reduced eastern Pacific heat flux in reanalyses. J. Climate, 31(8), 2981–2993. doi: 10.1175/JCLI-D-17-0642.1. Tropical eastern Pacific sea surface temperature plays a pivotal role in mechanisms that determine global mean surface temperature variability. In this study, the surface flux contribution to recent cooling of the tropical eastern Pacific is investigated using data from three atmospheric reanalyses with full assimilation of observations, an observations-based net surface energy flux reconstruction and fifteen atmospheric-only climate model simulations. For the ERA-Interim reanalysis, 78% of the decrease in net surface flux (-0.65 Wm-2yr-1 over 1988-2008) is explained by the latent heat flux variability. Latent heat flux variability differs between datasets and this is investigated using a bulk formula. We find that discrepancies in wind speed change explain contrasting latent heat flux trends across datasets. The significant increase of 0.26 ms-1decade-1 in wind speed over the tropical eastern Pacific in the ERA-Interim reanalysis is not reproduced by satellite or buoy observations and atmospheric-only climate model simulations, casting questions on the reliability of reanalysis-based surface fluxes over the tropical eastern Pacific.
Liu, Dongqing; Yang, Ben; Zhang, Yaocun; Qian, Yun; Huang, Anning; Zhou, Yang; Zhang, LujunLiu, D., B. Yang, Y. Zhang, Y. Qian, A. Huang, Y. Zhou, L. Zhang, 2018: Combined impacts of convection and microphysics parameterizations on the simulations of precipitation and cloud properties over Asia. Atmospheric Research, 212, 172-185. doi: 10.1016/j.atmosres.2018.05.017. Convection and microphysics parameterization schemes (i.e. CPS and MPS) are two important components related to the precipitation and cloud simulations in climate models, and one parameterization's impacts on the results can be dependent on the treatments in the other one. This study investigates the individual and combined impacts of CPS and MPS on the precipitation and cloud simulations over Asia based on nine regional model experiments using combinations of three CPSs of the Kain–Fritsch (KF), Zhang–McFarlane (ZM), and Grell 3D ensemble (G3), and three MPSs of the WRF double-moment 5-class (WDM5), WRF double-moment 6-class (WDM6), and Morrison double-moment (MORR). We first evaluate the simulated precipitation and find the experiment configured with the ZM CPS and MORR MPS performs the best when considering both the precipitation mean magnitude and spatial pattern. The sensitivity analysis results show that enhanced convection due to changing the CPS can cause strengthened or weakened stratiform processes, depending on the height of convective detrainments relative to that of convective drying, which is different among CPSs. In general, the CPS impacts on precipitation and clouds are larger when associating with the MORR MPS than with the other two MPSs as the former simulates more clouds and exhibits larger sensitivity of stratiform-type drying to convective detrainments. The MPS impacts on the precipitation and cloud simulations are also highly related to the CPS's behavior in simulating ice detrainments. Compared to the sum of the individual effects of CPS and MPS, simultaneously changing the two parameterizations causes considerably larger impacts on the precipitation and cloud simulations, suggesting the strong nonlinear interaction between the CPS and MPS. WRF model; Asia; Convection and microphysics parameterizations; Nonlinear combined impacts; Precipitation and cloud simulations
Liu, Dongyang; Liu, Qi; Liu, Guosheng; Wei, Junbo; Deng, Shumei; Fu, YunfeiLiu, D., Q. Liu, G. Liu, J. Wei, S. Deng, Y. Fu, 2018: Multiple factors explaining the deficiency of Cloud Profiling Radar on detecting oceanic warm clouds. Journal of Geophysical Research: Atmospheres, 123(15), 8135-8158. doi: 10.1029/2017JD028053. The CPR detecting efficiency on low-level clouds is affected by many situations, including surface clutter, spatial resolution, and radar sensitivity. These factors can uniquely or jointly result in missed detections of oceanic single-layer warm clouds. 57% of missed detections are attributed to a single factor and the rest are attributed to two or more factors that are indistinguishable. For missed warm clouds above 1 km, 30% result from the non-overcast effect, while the CPR range resolution is the major cause for the overcast ones. In particular, 18.4% are attributed exclusively to specific cloud microphysics, which is characterized by droplet effective radius (DER) and cloud optical thickness (COT). Compared to COT, the CPR detection is more dependent on DER, with a critical value standing around 10 μm. It is only for larger DER that the effects from COT turn to arise. Given LWP, clouds with larger DER and smaller COT are more likely to generate sufficient reflectivity and be detected than their counterpart. For clouds with the same DER and COT, opposite detecting results are primarily determined by the different droplet size distributions that lead to a variable reflectivity across the CPR detecting limit. Over global oceans, total miss rate of cloud occurrences approaches 0.73, while the loss rate of cloud water mass is 0.42 due to the smaller LWP of CPR-missed clouds. The CPR missed detections also lead to uncertainties in cloud radiative forcing estimations. A notable overestimation of shortwave cloud forcingat160% is found at BOA and TOA. Cloud microphysics; CPR missed detection; Miss rate; Radar reflectivity; Single-layer warm clouds
Liu, Meixian; Xu, Xianli; Sun, Alexander Y.; Luo, Wei; Wang, KelinLiu, M., X. Xu, A. Y. Sun, W. Luo, K. Wang, 2018: Why do karst catchments exhibit higher sensitivity to climate change? Evidence from a modified Budyko model. Advances in Water Resources, 122, 238-250. doi: 10.1016/j.advwatres.2018.10.013. Karst landscape, covers more than 10% of the global land surface and plays an important role in supporting ecosystems and human society, may be strongly influenced by climate change. Vegetation available water (VAW) is a key variable impacting the sensitivity of ecosystems to a changing environment. However, VAW in karst region is difficult to determine and remains uncertain. This study improved a dynamic Budyko-type water balance model, by introducing a nonlinear equation linking climate, vegetation and Budyko-type water balance. This model was calibrated using evolutionary algorithm based on monthly runoff. Comparison results in the Pearl, Yangtze and 12 karst catchments in south China, suggested high effectiveness of this improved model in simulating monthly runoff and evapotranspiration. Furthermore, in the 12 karst catchments, the max VAW was negatively correlated to the portion of karst landscape of the catchment (POK, r = −0.63, α = 0.027) and the elasticity of evapotranspiration to precipitation (r = −0.60, α = 0.04). These implied that karst catchments with higher POK had lower VAW, making the ecosystems rely more on precipitation. Climate sensitivity; Budyko framework; Ecohydrology; Hydrological modeling; Water balance
Liu, Yi Y.; van Dijk, Albert I. J. M.; Miralles, Diego G.; McCabe, Matthew F.; Evans, Jason P.; de Jeu, Richard A. M.; Gentine, Pierre; Huete, Alfredo; Parinussa, Robert M.; Wang, Lixin; Guan, Kaiyu; Berry, Joe; Restrepo-Coupe, NataliaLiu, Y. Y., A. I. J. M. van Dijk, D. G. Miralles, M. F. McCabe, J. P. Evans, R. A. M. de Jeu, P. Gentine, A. Huete, R. M. Parinussa, L. Wang, K. Guan, J. Berry, N. Restrepo-Coupe, 2018: Enhanced canopy growth precedes senescence in 2005 and 2010 Amazonian droughts. Remote Sensing of Environment, 211, 26-37. doi: 10.1016/j.rse.2018.03.035. Unprecedented droughts hit southern Amazonia in 2005 and 2010, causing a sharp increase in tree mortality and carbon loss. To better predict the rainforest's response to future droughts, it is necessary to understand its behavior during past events. Satellite observations provide a practical source of continuous observations of Amazonian forest. Here we used a passive microwave-based vegetation water content record (i.e., vegetation optical depth, VOD), together with multiple hydrometeorological observations as well as conventional satellite vegetation measures, to investigate the rainforest canopy dynamics during the 2005 and 2010 droughts. During the onset of droughts in the wet-to-dry season (May–July) of both years, we found large-scale positive anomalies in VOD, leaf area index (LAI) and enhanced vegetation index (EVI) over the southern Amazonia. These observations are very likely caused by enhanced canopy growth. Concurrent below-average rainfall and above-average radiation during the wet-to-dry season can be interpreted as an early arrival of normal dry season conditions, leading to enhanced new leaf development and ecosystem photosynthesis, as supported by field observations. Our results suggest that further rainfall deficit into the subsequent dry season caused water and heat stress during the peak of 2005 and 2010 droughts (August–October) that exceeded the tolerance limits of the rainforest, leading to widespread negative VOD anomalies over the southern Amazonia. Significant VOD anomalies were observed mainly over the western part in 2005 and mainly over central and eastern parts in 2010. The total area with significant negative VOD anomalies was comparable between these two drought years, though the average magnitude of significant negative VOD anomalies was greater in 2005. This finding broadly agrees with the field observations indicating that the reduction in biomass carbon uptake was stronger in 2005 than 2010. The enhanced canopy growth preceding drought-induced senescence should be taken into account when interpreting the ecological impacts of Amazonian droughts. Satellite; Surface temperature; Amazonian droughts; Canopy water content; Passive microwave; Soil water deficit; Vapor pressure deficit
Liu, Zhihua; Ballantyne, Ashley P.; Cooper, L. AnnieLiu, Z., A. P. Ballantyne, L. A. Cooper, 2018: Increases in Land Surface Temperature in Response to Fire in Siberian Boreal Forests and Their Attribution to Biophysical Processes. Geophysical Research Letters, 45(13), 6485-6494. doi: 10.1029/2018GL078283. Wildfire is the most prevalent natural disturbance in boreal forests and impacts climate through biogeochemical (e.g., greenhouse gas emission from biomass burning) and biophysical (e.g., albedo [α], evapotranspiration [ET], and roughness) processes. We used satellite observations to investigate the immediate (i.e., 1 year after fire) biophysical effects of fire in Siberian boreal forests. We found that boreal forest fires have a net annual warming effect (0.0728 to 0.325 K) due to strong summer warming and weak winter cooling. Fires also increased the diurnal temperature range and seasonal amplitude. These effects are strongest in summer and significantly higher in evergreen than in deciduous coniferous forests. Decreases in ET contributed to warming effects in summer, and increases in α contributed to cooling in winter. Our results suggest that the increase in observed land surface temperature immediately following fires in boreal ecosystems is most likely due to reduced ET leading to a strong positive feedback on the surface radiative budget. climate; forest; remote sensing; boreal fire; disturbance; land surface temperature
Loeb, Norman G.; Doelling, David R.; Wang, Hailan; Su, Wenying; Nguyen, Cathy; Corbett, Joseph G.; Liang, Lusheng; Mitrescu, Cristian; Rose, Fred G.; Kato, SeijiLoeb, N. G., D. R. Doelling, H. Wang, W. Su, C. Nguyen, J. G. Corbett, L. Liang, C. Mitrescu, F. G. Rose, S. Kato, 2018: Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) Top-of-Atmosphere (TOA) Edition 4.0 Data Product. J. Climate, 31(2), 895–918. doi: 10.1175/JCLI-D-17-0208.1. The Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) top-of-atmosphere (TOA) Ed4.0 data product is described. EBAF Ed4.0 is an update to EBAF Ed2.8, incorporating all of the Ed4.0 suite of CERES data product algorithm improvements and consistent input datasets throughout the record. A one-time adjustment to SW and LW TOA fluxes is made to ensure that global mean net TOA flux for July 2005-June 2015 is consistent with the in-situ value of 0.71 W m–2. While global mean all-sky TOA flux differences between Ed4.0 and Ed2.8 are within 0.5 Wm-2, appreciable SW regional differences occur over marine stratocumulus and snow/sea-ice regions. Marked regional differences in SW clear-sky TOA flux occur in polar regions and dust areas over ocean. Clear-sky LW TOA fluxes in EBAF Ed4.0 exceed Ed2.8 in regions of persistent high cloud cover. Owing to substantial differences in global mean clear-sky TOA fluxes, the net cloud radiative effect in EBAF Ed4.0 is -18 Wm-2 compared to -21 Wm-2 in EBAF Ed2.8. We estimate the overall uncertainty in 1°x1° latitude-longitude regional monthly all-sky TOA flux to be 3 Wm-2 (1σ) for the Terra-only period and 2.5 Wm-2 for the Terra-Aqua period both for SW and LW. The SW clear-sky regional monthly uncertainty is estimated to be 6 Wm-2 for the Terra-only period and 5 Wm-2 for the Terra-Aqua period. The LW clear-sky regional monthly uncertainty is 5 Wm-2 for Terra-only and 4.5 Wm-2 for Terra-Aqua.
Loeb, Norman G.; Thorsen, Tyler J.; Norris, Joel R.; Wang, Hailan; Su, WenyingLoeb, N. G., T. J. Thorsen, J. R. Norris, H. Wang, W. Su, 2018: Changes in Earth’s Energy Budget during and after the “Pause” in Global Warming: An Observational Perspective. Climate, 6(3), 62. doi: 10.3390/cli6030062. This study examines changes in Earth’s energy budget during and after the global warming “pause” (or “hiatus”) using observations from the Clouds and the Earth’s Radiant Energy System. We find a marked 0.83 ± 0.41 Wm−2 reduction in global mean reflected shortwave (SW) top-of-atmosphere (TOA) flux during the three years following the hiatus that results in an increase in net energy into the climate system. A partial radiative perturbation analysis reveals that decreases in low cloud cover are the primary driver of the decrease in SW TOA flux. The regional distribution of the SW TOA flux changes associated with the decreases in low cloud cover closely matches that of sea-surface temperature warming, which shows a pattern typical of the positive phase of the Pacific Decadal Oscillation. Large reductions in clear-sky SW TOA flux are also found over much of the Pacific and Atlantic Oceans in the northern hemisphere. These are associated with a reduction in aerosol optical depth consistent with stricter pollution controls in China and North America. A simple energy budget framework is used to show that TOA radiation (particularly in the SW) likely played a dominant role in driving the marked increase in temperature tendency during the post-hiatus period. clouds; energy budget; global warming hiatus
Loeb, Norman G.; Yang, Ping; Rose, Fred G.; Hong, Gang; Sun-Mack, Sunny; Minnis, Patrick; Kato, Seiji; Ham, Seung-Hee; Smith, William L.; Hioki, Souichiro; Tang, GuanglinLoeb, N. G., P. Yang, F. G. Rose, G. Hong, S. Sun-Mack, P. Minnis, S. Kato, S. Ham, W. L. Smith, S. Hioki, G. Tang, 2018: Impact of Ice Cloud Microphysics on Satellite Cloud Retrievals and Broadband Flux Radiative Transfer Model Calculations. J. Climate, 31(5), 1851–1864. doi: 10.1175/JCLI-D-17-0426.1. Ice cloud particles exhibit a range of shapes and sizes affecting a cloud’s single-scattering properties. Because they cannot be inferred from passive visible/infrared imager measurements, assumptions about the bulk single-scattering properties of ice clouds are fundamental to satellite cloud retrievals and broadband radiative flux calculations. To examine the sensitivity to ice particle model assumptions, three sets of models are used in satellite imager retrievals of ice cloud fraction, thermodynamic phase, optical depth, effective height and particle size, and in top-of-atmosphere and surface broadband radiative flux calculations. The three ice particle models include smooth hexagonal ice columns (SMOOTH), roughened hexagonal ice columns, and a two-habit model (THM) comprised of an ensemble of hexagonal columns and 20-element aggregates. While the choice of ice particle model has a negligible impact on daytime cloud fraction and thermodynamic phase, the global mean ice cloud optical depth retrieved from THM is smaller than SMOOTH by 2.3 (28%), and the regional root-mean-square-difference (RMSD) is 2.8 (32%). Effective radii derived from THM are 3.9 μm (16%) smaller than SMOOTH values and the RMSD is 5.2 μm (21%). In contrast, the regional RMSD in top-of-atmosphere (TOA) and surface flux between the THM and SMOOTH is only 1% in the SW and 0.3% in the LW when a consistent ice particle model is assumed in the cloud property retrievals and forward radiative transfer model calculations. Consequently, radiative fluxes derived using a consistent ice particle model assumption throughout provide a more robust reference for climate model evaluation compared to ice cloud property retrievals.
Lohmann, Ulrike; Neubauer, DavidLohmann, U., D. Neubauer, 2018: The importance of mixed-phase and ice clouds for climate sensitivity in the global aerosol–climate model ECHAM6-HAM2. Atmospheric Chemistry and Physics, 18(12), 8807-8828. doi: 10.5194/acp-18-8807-2018. How clouds change in a warmer climate remains one of the largest uncertainties for the equilibrium climate sensitivity (ECS). While a large spread in the cloud feedback arises from low-level clouds, it was recently shown that mixed-phase clouds are also important for ECS. If mixedphase clouds in the current climate contain too few supercooled cloud droplets, too much ice will change to liquid water in a warmer climate. As shown by Tan et al. (2016), this overestimates the negative cloud-phase feedback and underestimates ECS in the CAM global climate model (GCM). Here we use the newest version of the ECHAM6-HAM2 GCM to investigate the importance of mixed-phase and ice clouds for ECS.
Lorenz, Ruth; Herger, Nadja; Sedláček, Jan; Eyring, Veronika; Fischer, Erich M.; Knutti, RetoLorenz, R., N. Herger, J. Sedláček, V. Eyring, E. M. Fischer, R. Knutti, 2018: Prospects and caveats of weighting climate models for summer maximum temperature projections over North America. Journal of Geophysical Research: Atmospheres, 23(9), 4509-4526. doi: 10.1029/2017JD027992.
Lutsko, Nicholas J.; Takahashi, KenLutsko, N. J., K. Takahashi, 2018: What Can the Internal Variability of CMIP5 Models Tell Us About Their Climate Sensitivity?. J. Climate, 31(3), 5051–5069. doi: 10.1175/JCLI-D-17-0736.1. The relationship between climate models’ internal variability and their response to external forcings is investigated. Frequency-dependent regressions are performed between the outgoing top-of-atmosphere (TOA) energy fluxes and the global-mean surface temperature in the pre-industrial control simulations of the CMIP5 archive. Two distinct regimes are found. At sub-decadal frequencies the surface temperature and the outgoing short-wave flux are in quadrature, while the outgoing long-wave flux is linearly related to temperature and acts as a negative feedback on temperature perturbations. On longer time-scales the outgoing short-wave and long-wave fluxes are both linearly related to temperature, with the long-wave continuing to act as a negative feedback and the short-wave acting as a positive feedback on temperature variability. In addition to the different phase relationships, the two regimes can also be seen in estimates of the coherence and of the frequency-dependent regression co-efficients. The frequency-dependent regression co-efficients for the total cloudy-sky flux on time-scales of 2.5 to 3 years are found to be strongly (r2 >0.6) related to the models’ equilibrium climate sensitivities (ECSs), suggesting a potential “emergent constraint” for Earth’s ECS. However, O(100) years of data are required for this relationship to become robust. A simple model for Earths surface temperature variability and its relationship to the TOA fluxes is used to provide a physical explanation of these results.
Ma, H.-Y.; Klein, S. A.; Xie, S.; Zhang, C.; Tang, S.; Tang, Q.; Morcrette, C. J.; Van Weverberg, K.; Petch, J.; Ahlgrimm, M.; Berg, L. K.; Cheruy, F.; Cole, J.; Forbes, R.; Gustafson, W. I.; Huang, M.; Liu, Y.; Merryfield, W.; Qian, Y.; Roehrig, R.; Wang, Y.-C.Ma, H., S. A. Klein, S. Xie, C. Zhang, S. Tang, Q. Tang, C. J. Morcrette, K. Van Weverberg, J. Petch, M. Ahlgrimm, L. K. Berg, F. Cheruy, J. Cole, R. Forbes, W. I. Gustafson, M. Huang, Y. Liu, W. Merryfield, Y. Qian, R. Roehrig, Y. Wang, 2018: CAUSES: On the Role of Surface Energy Budget Errors to the Warm Surface Air Temperature Error Over the Central United States. Journal of Geophysical Research: Atmospheres, 123(5), 2888-2909. doi: 10.1002/2017JD027194.
Ma, Po-Lun; Rasch, Philip J.; Chepfer, Hélène; Winker, David M.; Ghan, Steven J.Ma, P., P. J. Rasch, H. Chepfer, D. M. Winker, S. J. Ghan, 2018: Observational constraint on cloud susceptibility weakened by aerosol retrieval limitations. Nature Communications, 9(1), 2640. doi: 10.1038/s41467-018-05028-4. Cloud susceptibility to aerosols in models frequently exceeds satellite estimates. Here the authors show that the discrepancy can be explained by retrieval limitations especially in clean environments, suggesting that conventional comparison strategies may lead to misunderstanding.
Ma, Zhanshan; Liu, Qijun; Zhao, Chuanfeng; Shen, Xueshun; Wang, Yuan; Jiang, Jonathan H.; Li, Zhe; Yung, YukMa, Z., Q. Liu, C. Zhao, X. Shen, Y. Wang, J. H. Jiang, Z. Li, Y. Yung, 2018: Application and Evaluation of an Explicit Prognostic Cloud-Cover Scheme in GRAPES Global Forecast System. Journal of Advances in Modeling Earth Systems, 10(3), 652-667. doi: 10.1002/2017MS001234. An explicit prognostic cloud-cover scheme (PROGCS) is implemented into the Global/Regional Assimilation and Prediction System (GRAPES) for global middle-range numerical weather predication system (GRAPES_GFS) to improve the model performance in simulating cloud cover and radiation. Unlike the previous diagnostic cloud-cover scheme (DIAGCS), PROGCS considers the formation and dissipation of cloud cover by physically connecting it to the cumulus convection and large-scale stratiform condensation processes. Our simulation results show that clouds in mid-high latitudes arise mainly from large-scale stratiform condensation processes, while cumulus convection and large-scale condensation processes jointly determine cloud cover in low latitudes. Compared with DIAGCS, PROGCS captures more consistent vertical distributions of cloud cover with the observations from Atmospheric Radiation Measurements (ARM) program at the Southern Great Plains (SGP) site and simulates more realistic diurnal cycle of marine stratocumulus with the ERA-Interim reanalysis data. The low, high, and total cloud covers that are determined via PROGCS appear to be more realistic than those simulated via DIAGCS when both are compared with satellite retrievals though the former maintains slight negative biases. In addition, the simulations of outgoing longwave radiation (OLR) at the top of the atmosphere (TOA) from PROGCS runs have been considerably improved as well, resulting in less biases in radiative heating rates at heights below 850 hPa and above 400 hPa of GRAPES_GFS. Our results indicate that a prognostic method of cloud-cover calculation has significant advantage over the conventional diagnostic one, and it should be adopted in both weather and climate simulation and forecast. 0320 Cloud physics and chemistry; radiative flux; 0321 Cloud/radiation interaction; 1622 Earth system modeling; cloud cover; diagnostic cloud-cover scheme; GRAPES_GFS; prognostic cloud-cover scheme
Mao, Feiyue; Pan, Zengxin; Henderson, David S.; Wang, Wei; Gong, WeiMao, F., Z. Pan, D. S. Henderson, W. Wang, W. Gong, 2018: Vertically resolved physical and radiative response of ice clouds to aerosols during the Indian summer monsoon season. Remote Sensing of Environment, 216, 171-182. doi: 10.1016/j.rse.2018.06.027. Changes in aerosol loading affect cloud albedo and emission and Earth's radiative balance with a low level of scientific understanding. In this study, we investigate the vertical response of ice clouds to aerosols within the Indian subcontinent during monsoon season (2006–2010) based on multiple satellite observations. As a function of aerosol loading, we find that the cloud optical depth, cloud geometrical depth and ice water path decrease by 0.23 (from 0.39 to 0.16), 0.8 km (from 2.6 to 1.8 km), 5.1 g/m2 (from 7.9 to 2.8 g/m2), respectively, and that ice particles possibly decrease in size and become more spherical in shape as aerosol optical depth (AOD) increases from 0.1 to 1; these changes tend to plateau as AOD increases beyond 1. The absolute negative response between ice clouds and aerosols under moist and unstable atmospheric conditions is stronger than that under drier and stable atmospheric conditions, and vice versa. Moreover, the negative impact of smoke on ice clouds is stronger than dust and polluted dust, which is likely related to the strong absorption properties and poor ice nucleation efficiency of smoke. Aerosol impacts on ice clouds lead to a decrease in the net cloud radiative effect of 7.3 W/m2 (from 18.5 to 11.2 W/m2) as AOD increases from 0.1 to 1. This change in ice cloud properties mainly results in the decrease in downwelling LW radiation to the surface and consequently weakened radiative forcing of ice clouds during the Indian summer monsoon season. Indian summer monsoon; Ice clouds; Indirect effect; Semi-direct effect; Three dimension observations
Matthews, GrantMatthews, G., 2018: Signal Processing Enhancements to Improve Instantaneous Accuracy of a Scanning Bolometer: Application to MERBE. IEEE Transactions on Geoscience and Remote Sensing, 56(6), 3421-3431. doi: 10.1109/TGRS.2018.2799823.
Matthews, GrantMatthews, G., 2018: First decadal lunar results from the Moon and Earth Radiation Budget Experiment. Applied Optics, 57(7), 1594. doi: 10.1364/AO.57.001594.
Matthews, GrantMatthews, G., 2018: Real-Time Determination of Earth Radiation Budget Spectral Signatures for Nonlinear Unfiltering of Results from MERBE. J. Appl. Meteor. Climatol., 57(2), 273-294. doi: 10.1175/JAMC-D-16-0406.1. AbstractAmong the best ways to gain more certainty in climate model prediction is to compare and constrain simulations with worldwide satellite measurements of the Earth radiation budget (ERB) short- and longwave radiant fluxes (SW and LW), which drive climate processes. Recent calls to ensure orbital ERB measurements track true climate, rather than instrument changes, led to the creation of the Moon and Earth Radiation Budget Experiment (MERBE). This independent project is recalibrating multiple existing ERB devices from different international space agencies so they adhere to common SI-traceable radiometric standards, by regularly sampling the unaltering constants of lunar reflectivity/emissivity, thus ensuring no artificial trends exist. This work details the use of MODTRAN to give an instantaneous SW and LW Earth spectrum for all scenes viewed by devices in the project, to then be used with instrument spectral responses for unfiltering radiances. In the majority of cases when data from a collocated imager are available, a dual-layer unfiltering is also performed separately on cloudy and cloud-free areas, yielding clear and overcast ERB spectral results. Additionally, use is made of improved in-flight methods to derive spectral responses from a previous American Meteorological Society study, and comparisons between Earth MERBE radiances from two identical devices operating on Terra/Aqua are shown along with results from the CERES project. These demonstrate an order of magnitude improvement in relative accuracy for edition 1 MERBE results over CERES and show that the latest CERES data are less accurate and stable than claimed.
Mayer, Michael; Balmaseda, Magdalena Alonso; Haimberger, LeopoldMayer, M., M. A. Balmaseda, L. Haimberger, 2018: Unprecedented 2015/16 Indo-Pacific heat transfer speeds up Tropical Pacific heat recharge. Geophysical Research Letters, 45(7), 3274-3284. doi: 10.1002/2018GL077106. El Nino events are characterized by anomalously warm tropical Pacific surface waters and concurrent ocean heat discharge, a precursor of subsequent cold La Nina conditions. Here we show that El Nino 2015/16 departed from this norm: despite extreme peak surface temperatures, Tropical Pacific (30N-30S) upper ocean heat content (OHC) increased by 9.6±1.7 ZJ (1ZJ=1021J), in stark contrast to the previous strong El Nino in 1997/98 (-11.5±2.9 ZJ). Unprecedented reduction of Indonesian Throughflow volume and heat transport played a key role in the anomalous 2015/16 event. We argue that this anomaly is linked with the previously documented intensified warming and associated rising sea levels in the Indian Ocean during the last decade. Additionally, increased absorption of solar radiation acted to dampen Pacific OHC discharge. These results explain the weak and short-lived La Nina conditions in 2016/17 and indicate the need for realistic representation of Indo-Pacific energy transfers for skilful seasonal-to-decadal predictions. 3359 Radiative processes; 4522 ENSO; 3339 Ocean/atmosphere interactions; 4215 Climate and interannual variability; 4260 Ocean data assimilation and reanalysis; 3339; 3359; 4215; 4260; 4522
McCoy, Daniel T.; Field, Paul R.; Schmidt, Anja; Grosvenor, Daniel P.; Bender, Frida A.-M.; Shipway, Ben J.; Hill, Adrian A.; Wilkinson, Jonathan M.; Elsaesser, Gregory S.McCoy, D. T., P. R. Field, A. Schmidt, D. P. Grosvenor, F. A. Bender, B. J. Shipway, A. A. Hill, J. M. Wilkinson, G. S. Elsaesser, 2018: Aerosol midlatitude cyclone indirect effects in observations and high-resolution simulations. Atmospheric Chemistry and Physics, 18(8), 5821-5846. doi: 10.5194/acp-18-5821-2018.
McHardy, Theodore M.; Dong, Xiquan; Xi, Baike; Thieman, Mandana M.; Minnis, Patrick; Palikonda, RabindraMcHardy, T. M., X. Dong, B. Xi, M. M. Thieman, P. Minnis, R. Palikonda, 2018: Comparison of Daytime Low-Level Cloud Properties Derived from GOES and ARM SGP Measurements. Journal of Geophysical Research: Atmospheres, 123(15), 8221-8237. doi: 10.1029/2018JD028911. Large-scale satellite data are critical for both verifying and improving general circulation model (GCM) parameterizations of clouds and radiation for climate prediction. For reliable application of satellite datasets in cloud processes and climate models, it is important to have a reasonable estimate of the errors in the derived cloud properties. The daytime single-layered low-level cloud properties retrieved by the Geostationary Operational Environmental Satellite system (GOES) are compared with ground-based observations and retrievals over the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) Central Facility (SCF) from June 1998 through December 2006. The GOES retrievals are made via the Visible-Infrared Solar-infrared Split-window technique (VISST). They are spatially averaged within a 0.15° x 0.15° box centered on the ARM SGP site and the ARM surface observations are temporally averaged ± 15 minutes around the GOES scans to produce collocated pairs. Comparisons are made for monthly means, diurnal means, and one-to-one GOES and ARM collocated pairs. GOES Teff is highly correlated with ARM Ttop cloud temperature, having an R2 value of 0.75, though GOES exhibits a cold bias. GOES retrieved τ and LWP have very good agreement with ARM retrievals with R2s of 0.45 and 0.47, while re (GOES), on average, is about 2 μm greater than ARM re. An examination of solar and viewing geometry has shown that GOES retrieved mean re and τ values are impacted by solar zenith angle (SZA) and especially scattering angle (SCA), which is not unexpected and needs to be accounted for by users. GOES; ARM SGP; Microphysics; Stratocumulus
Miyakawa, Tomoki; Noda, Akira T.; Kodama, ChihiroMiyakawa, T., A. T. Noda, C. Kodama, 2018: The Impact of Hybrid Usage of a Cumulus Parameterization Scheme on Tropical Convection and Large-Scale Circulations in a Global Cloud-System Resolving Model. Journal of Advances in Modeling Earth Systems, 10(11), 2952-2970. doi: 10.1029/2018MS001302. The impact of activating a cumulus parameterization scheme in the global nonhydrostatic icosahedral atmospheric model (NICAM) coupled with a one-dimensional (1-D) mixed-layer ocean model is assessed using a cloud-system-resolving, 14-km mesh. The Chikira-Sugiyama (CS) scheme, which employs an entrainment rate sensitive to the humidity of the environment, can consider congestus clouds in the tropics when used in conventional global climate models. Congestus clouds are underresolved in the default 14-km mesh NICAM. In the present study, boreal summer NICAM simulations are performed with and without the CS scheme, and several different scheme parameters are evaluated. The results show that the horizontal scale of convection and precipitable water increased in the tropics when using the CS scheme. Model adjustments were apparent at two different timescales: a rapid adjustment within the first week and a slower adjustment at 1 to 2 months. Both effects were magnified in the simulations that employed smaller values for the parameter that defines the fractional of loss of buoyancy-generated energy in parameterized convection. The upward branch of the Hadley circulation shifted northward, and the Walker circulation was enhanced when the CS scheme was activated. These large-scale adjustments suggested that increased midtropospheric moisture in the tropics tends to favor larger organized convective activities, which require an abundant supply of moisture, which, in this case, is available to the north of the equatorial West Pacific Ocean. cumulus parameterization; convective aggregation; general circulation; global cloud-system-resolving model
Moch, Jonathan M.; Dovrou, Eleni; Mickley, Loretta J.; Keutsch, Frank N.; Cheng, Yuan; Jacob, Daniel J.; Jiang, Jingkun; Li, Meng; Munger, J. William; Qiao, Xiaohui; Zhang, QiangMoch, J. M., E. Dovrou, L. J. Mickley, F. N. Keutsch, Y. Cheng, D. J. Jacob, J. Jiang, M. Li, J. W. Munger, X. Qiao, Q. Zhang, 2018: Contribution of hydroxymethane sulfonate to ambient particulate matter: A potential explanation for high particulate sulfur during severe winter haze in Beijing. Geophysical Research Letters, 45(21), 11,969-11,979. doi: 10.1029/2018GL079309. PM2.5 during severe winter haze in Beijing, China, has reached levels as high as 880 μg m-3, with sulfur compounds contributing significantly to PM2.5 composition. This sulfur has been traditionally assumed to be sulfate, although atmospheric chemistry models are unable to account for such large sulfate enhancements under dim winter conditions. Using a 1-D model, we show that well characterized but previously overlooked chemistry of aqueous-phase HCHO and S (IV) in cloud droplets to form a S (IV)-HCHO adduct, hydroxymethane sulfonate (HMS), may explain high particulate sulfur in wintertime Beijing. We also demonstrate in the laboratory that methods of ion chromatography typically used to measure ambient particulates easily misinterpret HMS as sulfate. Our findings suggest that HCHO and not SO2 has been the limiting factor in many haze events in Beijing and that to reduce severe winter pollution in this region, policymakers may need to address HCHO sources such as transportation. sulfate; China; Air pollution; formaldehyde; hydroxymethane sulfonate; PM2.5
Mulcahy, J. P.; Jones, C.; Sellar, A.; Johnson, B.; Boutle, I. A.; Jones, A.; Andrews, T.; Rumbold, S. T.; Mollard, J.; Bellouin, N.; Johnson, C. E.; Williams, K. D.; Grosvenor, D. P.; McCoy, D. T.Mulcahy, J. P., C. Jones, A. Sellar, B. Johnson, I. A. Boutle, A. Jones, T. Andrews, S. T. Rumbold, J. Mollard, N. Bellouin, C. E. Johnson, K. D. Williams, D. P. Grosvenor, D. T. McCoy, 2018: Improved aerosol processes and effective radiative forcing in HadGEM3 and UKESM1. Journal of Advances in Modeling Earth Systems, 10(11), 2786-2805. doi: 10.1029/2018MS001464. Abstract Aerosol processes and, in particular, aerosol-cloud interactions cut across the traditional physical-Earth system boundary of coupled Earth system models and remain one of the key uncertainties in estimating anthropogenic radiative forcing of climate. Here, we calculate the historical aerosol effective radiative forcing (ERF) in the HadGEM3-GA7 climate model in order to assess the suitability of this model for inclusion in the UK Earth system model, UKESM1. The aerosol ERF, calculated for the year 2000 relative to 1850, is large and negative in the standard GA7 model leading to an unrealistic negative total anthropogenic forcing over the 20th century. We show how underlying assumptions and missing processes in both the physical model and aerosol parameterizations lead to this large aerosol ERF. A number of model improvements are investigated to assess their impact on the aerosol ERF. These include; an improved representation of cloud droplet spectral dispersion, updates to the aerosol activation scheme and black carbon optical properties. One of the largest contributors to the aerosol forcing uncertainty is insufficient knowledge of the pre-industrial aerosol climate. We evaluate the contribution of uncertainties in the natural marine emissions of dimethyl sulphide (DMS) and organic aerosol to the ERF. The combination of model improvements derived from these studies weaken the aerosol ERF by up to 50% of the original value and lead to a total anthropogenic historical forcing more in-line with assessed values. climate models; aerosol forcing; effective radiative forcing; model development
Müller, W. A.; Jungclaus, J. H.; Mauritsen, T.; Baehr, J.; Bittner, M.; Budich, R.; Bunzel, F.; Esch, M.; Ghosh, R.; Haak, H.; Ilyina, T.; Kleine, T.; Kornblueh, L.; Li, H.; Modali, K.; Notz, D.; Pohlmann, H.; Roeckner, E.; Stemmler, I.; Tian, F.; Marotzke, J.Müller, W. A., J. H. Jungclaus, T. Mauritsen, J. Baehr, M. Bittner, R. Budich, F. Bunzel, M. Esch, R. Ghosh, H. Haak, T. Ilyina, T. Kleine, L. Kornblueh, H. Li, K. Modali, D. Notz, H. Pohlmann, E. Roeckner, I. Stemmler, F. Tian, J. Marotzke, 2018: A Higher-resolution Version of the Max Planck Institute Earth System Model (MPI-ESM1.2-HR). Journal of Advances in Modeling Earth Systems, 10(7), 1383-1413. doi: 10.1029/2017MS001217. The MPI-ESM1.2 is the latest version of the Max Planck Institute Earth System Model and is the baseline for the Coupled Model Intercomparison Project Phase 6 and current seasonal and decadal climate predictions. This paper evaluates a coupled higher-resolution version (MPI-ESM1.2-HR) in comparison with its lower-resolved version (MPI-ESM1.2-LR). We focus on basic oceanic and atmospheric mean states and selected modes of variability, the El Niño/Southern Oscillation and the North Atlantic Oscillation. The increase in atmospheric resolution in MPI-ESM1.2-HR reduces the biases of upper-level zonal wind and atmospheric jet stream position in the northern extratropics. This results in a decrease of the storm track bias over the northern North Atlantic, for both winter and summer season. The blocking frequency over the European region is improved in summer, and North Atlantic Oscillation and related storm track variations improve in winter. Stable Atlantic meridional overturning circulations are found with magnitudes of 16 Sv for MPI-ESM1.2-HR and 20 Sv for MPI-ESM1.2-LR at 26°N. A strong sea surface temperature bias of 5°C along with a too zonal North Atlantic current is present in both versions. The sea surface temperature bias in the eastern tropical Atlantic is reduced by 1°C due to higher-resolved orography in MPI-ESM-HR, and the region of the cold-tongue bias is reduced in the tropical Pacific. MPI-ESM1.2-HR has a well-balanced radiation budget and its climate sensitivity is explicitly tuned to 3 K. Although the obtained reductions in long-standing biases are modest, the improvements in atmospheric dynamics make this model well suited for prediction and impact studies. climate variability; Earth System Modeling
Myers, Timothy A.; Mechoso, Carlos R.; Cesana, Gregory V.; DeFlorio, Michael J.; Waliser, Duane E.Myers, T. A., C. R. Mechoso, G. V. Cesana, M. J. DeFlorio, D. E. Waliser, 2018: Cloud feedback key to marine heatwave off Baja California. Geophysical Research Letters, 45(9), 4345-4352. doi: 10.1029/2018GL078242.
Myers, Timothy A.; Mechoso, Carlos R.; DeFlorio, Michael J.Myers, T. A., C. R. Mechoso, M. J. DeFlorio, 2018: Coupling between marine boundary layer clouds and summer-to-summer sea surface temperature variability over the North Atlantic and Pacific. Climate Dynamics, 50(3-4), 955-969. doi: 10.1007/s00382-017-3651-8. Climate modes of variability over the Atlantic and Pacific may be amplified by a positive feedback between sea-surface temperature (SST) and marine boundary layer clouds. However, it is well known that climate models poorly simulate this feedback. Does this deficiency contribute to model-to-model differences in the representation of climate modes of variability? Over both the North Atlantic and Pacific, typical summertime interannual to interdecadal SST variability exhibits horseshoe-like patterns of co-located anomalies of shortwave cloud radiative effect (CRE), low-level cloud fraction, SST, and estimated inversion strength over the subtropics and midlatitudes that are consistent with a positive cloud feedback. During winter over the midlatitudes, this feedback appears to be diminished. Models participating in the Coupled Model Intercomparison Project phase 5 that simulate a weak feedback between subtropical SST and shortwave CRE produce smaller and less realistic amplitudes of summertime SST and CRE variability over the northern oceans compared to models with a stronger feedback. The change in SST amplitude per unit change in CRE amplitude among the models and observations may be understood as the temperature response of the ocean mixed layer to a unit change in radiative flux over the course of a season. These results highlight the importance of boundary layer clouds in interannual to interdecadal atmosphere–ocean variability over the northern oceans during summer. The results also suggest that deficiencies in the simulation of these clouds in coupled climate models contribute to underestimation in their simulation of summer-to-summer SST variability.
Osipov, Sergey; Stenchikov, GeorgiyOsipov, S., G. Stenchikov, 2018: Simulating the Regional Impact of Dust on the Middle East Climate and the Red Sea. Journal of Geophysical Research: Oceans, 123(2), 1032-1047. doi: 10.1002/2017JC013335. The Red Sea is located between North Africa and the Arabian Peninsula, the largest sources of dust in the world. Satellite retrievals show very high aerosol optical depth in the region, which increases during the summer season, especially over the southern Red Sea. Previously estimated and validated radiative effect from dust is expected to have a profound thermal and dynamic impact on the Red Sea, but that impact has not yet been studied or evaluated. Due to the strong dust radiative effect at the sea surface, uncoupled ocean modeling approaches with prescribed atmospheric boundary conditions result in an unrealistic ocean response. Therefore, to study the impact of dust on the regional climate of the Middle East and the Red Sea, we employed the Regional Ocean Modeling System fully coupled with the Weather Research and Forecasting model. We modified the atmospheric model to account for the radiative effect of dust. The simulations show that, in the equilibrium response, dust cools the Red Sea, reduces the surface wind speed, and weakens both the exchange at the Bab-el-Mandeb strait and the overturning circulation. The salinity distribution, freshwater, and heat budgets are significantly altered. A validation of the simulations against satellite products indicates that accounting for radiative effect from dust almost completely removes the bias and reduces errors in the top of the atmosphere fluxes and sea surface temperature. Our results suggest that dust plays an important role in the energy balance, thermal, and circulation regimes in the Red Sea. 0305 Aerosols and particles; 4504 Air/sea interactions; radiative forcing; 1616 Climate variability; dust; 3355 Regional modeling; 4845 Nutrients and nutrient cycling; biological productivity; energy balance; overturning circulation; Red Sea
Ottaviani, Matteo; Foster, Robert; Gilerson, Alexander; Ibrahim, Amir; Carrizo, Carlos; El-Habashi, Ahmed; Cairns, Brian; Chowdhary, Jacek; Hostetler, Chris; Hair, Johnathan; Burton, Sharon; Hu, Yongxiang; Twardowski, Michael; Stockley, Nicole; Gray, Deric; Slade, Wayne; Cetinic, IvonaOttaviani, M., R. Foster, A. Gilerson, A. Ibrahim, C. Carrizo, A. El-Habashi, B. Cairns, J. Chowdhary, C. Hostetler, J. Hair, S. Burton, Y. Hu, M. Twardowski, N. Stockley, D. Gray, W. Slade, I. Cetinic, 2018: Airborne and shipborne polarimetric measurements over open ocean and coastal waters: Intercomparisons and implications for spaceborne observations. Remote Sensing of Environment, 206, 375-390. doi: 10.1016/j.rse.2017.12.015. Comprehensive polarimetric closure is demonstrated using observations from two in-situ polarimeters and Vector Radiative Transfer (VRT) modeling. During the Ship-Aircraft Bio-Optical Research (SABOR) campaign, the novel CCNY HyperSAS-POL polarimeter was mounted on the bow of the R/V Endeavor and acquired hyperspectral measurements from just above the surface of the ocean, while the NASA GISS Research Scanning Polarimeter was deployed onboard the NASA LaRC's King Air UC-12B aircraft. State-of-the-art, ancillary measurements were used to characterize the atmospheric and marine contributions in the VRT model, including those of the High Spectral Resolution Lidar (HSRL), the AErosol RObotic NETwork for Ocean Color (AERONET-OC), a profiling WETLabs ac-9 spectrometer and the Multi-spectral Volume Scattering Meter (MVSM). An open-ocean and a coastal scene are analyzed, both affected by complex aerosol conditions. In each of the two cases, it is found that the model is able to accurately reproduce the Stokes components measured simultaneously by each polarimeter at different geometries and viewing altitudes. These results are mostly encouraging, considering the different deployment strategies of RSP and HyperSAS-POL, which imply very different sensitivities to the atmospheric and ocean contributions, and open new opportunities in above-water polarimetric measurements. Furthermore, the signal originating from each scene was propagated to the top of the atmosphere to explore the sensitivity of polarimetric spaceborne observations to changes in the water type. As expected, adding polarization as a measurement capability benefits the detection of such changes, reinforcing the merits of the full-Stokes treatment in modeling the impact of atmospheric and oceanic constituents on remote sensing observations.
Ovando, Gustavo; Sayago, Silvina; Bocco, MónicaOvando, G., S. Sayago, M. Bocco, 2018: Evaluating accuracy of DSSAT model for soybean yield estimation using satellite weather data. ISPRS Journal of Photogrammetry and Remote Sensing, 138, 208-217. doi: 10.1016/j.isprsjprs.2018.02.015. Crop models allow simulating the development and yield of the crops, to represent and to evaluate the influence of multiple factors. The DSSAT cropping system model is one of the most widely used and contains CROPGRO module for soybean. This crop has a great importance for many southern countries of Latin America and for Argentina. Solar radiation and rainfall are necessary variables as inputs for crop models; however these data are not as readily available. The satellital products from Clouds and Earth's Radiant Energy System (CERES) and Tropic Rainfall Measurement Mission (TRMM) provide continuous spatial and temporal information of solar radiation and precipitation, respectively. This study evaluates and quantifies the uncertainty in estimating soybean yield using a DSSAT model, when recorded weather data are replaced with CERES and TRMM ones. Different percentages of data replacements, soybean maturity groups and planting dates are considered, for 2006–2016 period in Oliveros (Argentina). Results show that CERES and TRMM products can be used for soybean yield estimation with DSSAT considering that: percentage of data replacement, campaign, planting date and maturity group, determine the amounts and trends of yield errors. Replacements with CERES data up to 30% result in %RMSE lower than 10% in 87% of the cases; while the replacement with TRMM data presents the best statisticals in campaigns with high yields. Simulations based entirely on CERES solar radiation give better results than those with TRMM. In general, similar percentages of replacement show better performance in the estimation of soybean yield for solar radiation than the replacement of precipitation values. CERES; TRMM; Argentina; Crop models
Painemal, DavidPainemal, D., 2018: Global Estimates of Changes in Shortwave Low-Cloud Albedo and Fluxes Due to Variations in Cloud Droplet Number Concentration Derived From CERES-MODIS Satellite Sensors. Geophysical Research Letters, 45(17), 9288-9296. doi: 10.1029/2018GL078880. Fifteen years of Aqua Clouds and the Earth's Radiant Energy Systems (CERES) and MOderate resolution Imaging Spectroradiometer (MODIS) observations are combined to derive nearly global maps of shortwave albedo (A) and flux (F) response to changes in cloud droplet number concentration (Nd). Absolute ( ) and relative ( ) albedo susceptibilities are computed by exploiting the linear relationship between A and ln (Nd) for shallow liquid clouds. Subtropical stratiform clouds over the eastern Pacific, eastern Atlantic, and off the coast of eastern Asia yield the highest Sr, followed by the extratropical oceans during their hemispheric summer. When Sr is cast in terms of F, the eastern Pacific clouds dominate Sr. Sa is mainly governed by Nd, with offshore clouds producing high Sa. While both Sa and Sr are advantageous for understanding radiative aspects of the aerosol indirect effect, Sr is more suitable for calculating changes in A and F due to the linearity of the A-ln (Nd) relationship.
Pan, X; Yang, Y; Liu, Y; Fan, X; Shan, L; Zhang, XPan, X., Y. Yang, Y. Liu, X. Fan, L. Shan, X. Zhang, 2018: Quantifying the contributions of environmental parameters to CERES surface net radiation error in China. International Archives of the Photogrammetry, Remote Sensing & Spatial Information Sciences, 42(3), 1339-1345. doi: 10.5194/isprs-archives-XLII-3-1339-2018. Error source analyses are critical for the satellite-retrieved surface net radiation (Rn) products. In this study, we evaluate the Rn error sources in the Clouds and the Earth's Radiant Energy System (CERES) project at 43 sites from July in 2007 to December in 2007 in China. The results show that cloud fraction (CF), land surface temperature (LST), atmospheric temperature (AT) and algorithm error dominate the Rn error, with error contributions of ~-20, ~15, ~10 and ~10 W/m2 (net shortwave (NSW)/longwave (NLW) radiation), respectively. For NSW, the dominant error source is algorithm error (more than 10 W/m2), particularly in spring and summer with abundant cloud. For NLW, due to the high sensitivity of algorithm and large LST/CF error, LST and CF are the largest error sources, especially in northern China. The AT influences the NLW error large in southern China because of the large AT error in there. The total precipitable water has weak influence on Rn error even with the high sensitivity of algorithm. In order to improve Rn quality, CF and LST (AT) error in northern (southern) China should be decreased.
Pan, Zengxin; Mao, Feiyue; Wang, Wei; Logan, Timothy; Hong, JiaPan, Z., F. Mao, W. Wang, T. Logan, J. Hong, 2018: Examining Intrinsic Aerosol-Cloud Interactions in South Asia Through Multiple Satellite Observations. Journal of Geophysical Research: Atmospheres, 23(19), 11,210-11,224. doi: 10.1029/2017JD028232. Changes in anthropogenic aerosol loading affect cloud albedo and the Earth's radiative balance with a low level of scientific understanding. Aerosol-cloud interaction and its effects on climate are mainly evaluated using passive observations in a global scale. Here this study estimated the intrinsic response of clouds to aerosols by combining active and passive satellite observations from July 2006 to February 2011 in South Asia. We evaluate the average radiative forcing by the intrinsic aerosol-cloud interaction for warm liquid clouds as 0.63 ± 0.19, −0.34 ± 0.40, and 1.11 ± 0.08 W/m2 during the annual, monsoon, and nonmonsoon periods in South Asia, respectively. Relationships derived among liquid water path, cloud droplet number concentration, and consequent cloud albedo are assessed as a function of aerosol concentration. The intensity of the aerosol-cloud interaction gradually weakens with increasing cloud base height above ground level in South Asia, is associated with aerosol vertical distribution and vertical atmospheric upward motion. Moreover, distinct regional and seasonal variations in the aerosol-cloud interaction are observed for liquid water path, cloud droplet number concentration, and the resulting cloud albedo in South Asia. These variations are associated with water vapor and aerosol absorption levels. Results contribute to the understanding and modeling of aerosol-cloud interactions and determining their effects on radiative forcing and climate in South Asia. aerosol-cloud interaction; South Asia; vertical variations
Pan, Zengxin; Mao, Feiyue; Wang, Wei; Zhu, Bo; Lu, Xin; Gong, WeiPan, Z., F. Mao, W. Wang, B. Zhu, X. Lu, W. Gong, 2018: Impacts of 3D Aerosol, Cloud, and Water Vapor Variations on the Recent Brightening during the South Asian Monsoon Season. Remote Sensing, 10(4), 651. doi: 10.3390/rs10040651. South Asia is experiencing a levelling-off trend in solar radiation and even a transition from dimming to brightening. Any change in incident solar radiation, which is the only significant energy source of the global ecosystem, profoundly affects our habitats. Here, we use multiple observations of the A-Train constellation to evaluate the impacts of three-dimensional (3D) aerosol, cloud, and water vapor variations on the changes in surface solar radiation during the monsoon season (June–September) in South Asia from 2006 to 2015. Results show that surface shortwave radiation (SSR) has possibly increased by 16.2 W m−2 during this period. However, an increase in aerosol loading is inconsistent with the SSR variations. Instead, clouds are generally reduced and thinned by approximately 8.8% and 280 m, respectively, with a decrease in both cloud water path (by 34.7 g m−2) and particle number concentration under cloudy conditions. Consequently, the shortwave cloud radiative effect decreases by approximately 45.5 W m−2 at the surface. Moreover, precipitable water in clear-sky conditions decreases by 2.8 mm (mainly below 2 km), and related solar brightening increases by 2.5 W m−2. Overall, the decreases in 3D water vapor and clouds distinctly result in increased absorption of SSR and subsequent surface brightening. cloud; aerosol; water vapor; South Asia; A-Train; brightening
Parishani, Hossein; Pritchard, Michael S.; Bretherton, Christopher S.; Terai, Christopher R.; Wyant, Matthew C.; Khairoutdinov, Marat; Singh, BalwinderParishani, H., M. S. Pritchard, C. S. Bretherton, C. R. Terai, M. C. Wyant, M. Khairoutdinov, B. Singh, 2018: Insensitivity of the Cloud Response to Surface Warming Under Radical Changes to Boundary Layer Turbulence and Cloud Microphysics: Results From the Ultraparameterized CAM. Journal of Advances in Modeling Earth Systems, 10(12), 3139-3158. doi: 10.1029/2018MS001409. Abstract We study the cloud response to a +4K surface warming in a new multiscale climate model that uses enough interior resolution to begin explicitly resolving boundary layer turbulence (i.e., ultraparameterization or UP). UP's predictions are compared against those from standard superparameterization (SP). The mean cloud radiative effect feedback turns out to be remarkably neutral across all of our simulations, despite some radical changes in both cloud microphysical parameter settings and cloud-resolving model grid resolution. The overall low cloud response to warming is a positive low cloud feedback over land, a negative feedback (driven by cloud optical depth increase) at high latitudes, and weak feedback over the low-latitude oceans. The most distinct effects of UP result from tuning decisions impacting high-latitude cloud feedback. UP's microphysics is tuned to optimize the model present-day, top-of-atmosphere radiation fluxes against CERES observations, by lowering the cloud ice-liquid phase shift temperature ramp, adjusting the ice/liquid autoconversion rate, and increasing the ice fall speed. This reduces high-latitude low cloud amounts and damps the optical depth feedback at high latitudes, leading to a slightly more positive global cloud feedback compared to SP. A sensitivity test that isolates these microphysical impacts from UP's grid resolution confirms that the microphysical settings are mostly responsible for the differences between SP and UP cloud feedback. cloud feedback; model tuning; low clouds; ultraparameterization; boundary layer; surface warming
Park, R.-S.; Kwon, Y. C.Park, R., Y. C. Kwon, 2018: The Implications for radiative cloud forcing via the link between shallow convection and planetary boundary layer mixing. Journal of Geophysical Research: Atmospheres, 123(23), 13,203-13,218. doi: 10.1029/2018JD028678. In this study, the role of shallow convection and its links with planetary boundary layer (PBL) mixing is analyzed using a global atmospheric model. All of the simulations are conducted with the Korean Integrated Model (KIM), which is a next-generation operational global model for Korea Meteorological Administration (KMA). The simulation results show that the direct effect of shallow convection enhances additional vertical mixing inside the shallow convective layer whereas its indirect effect reduces vertical mixing inside the PBL by changing the PBL height, thus vertical mixing strength. It is also found that the impact of shallow convection on low-level clouds is tightly related to the overlapping between PBL and shallowing convection. When the PBL height is located in the relatively higher (lower) part of the shallow convective layer, the mixing across the top of the PBL becomes smaller (larger). Therefore, the diffusivity profile of KIM shallow convection scheme is modified according to the overlapping pattern of PBL mixing and shallow convection. The systematic bias of downward solar radiation at the surface of KIM is improved with the revised diffusivity profile of the shallow convection scheme proposed in this study. Radiation; Shallow convection; Clouds; PBL mixing; vertical transport
Park, SungsuPark, S., 2018: An Economical Analytical Equation for the Integrated Vertical Overlap of Cumulus and Stratus. Journal of Advances in Modeling Earth Systems, 10(3), 826-841. doi: 10.1002/2017MS001190. By extending the previously proposed heuristic parameterization, the author derived an analytical equation computing the overlap areas between the precipitation (or radiation) areas and the cloud areas in a cloud system consisting of cumulus and stratus. The new analytical equation is accurate and much more efficient than the previous heuristic equation, which suffers from the truncation error in association with the digitalization of the overlap areas. Global test simulations with the new analytical formula in an offline mode showed that the maximum cumulus overlap simulates more surface precipitation flux than the random cumulus overlap. On the other hand, the maximum stratus overlap simulates less surface precipitation flux than random stratus overlap, which is due to the increase in the evaporation rate of convective precipitation from the random to maximum stratus overlap. The independent precipitation approximation (IPA) marginally decreases the surface precipitation flux, implying that IPA works well with other parameterizations. In contrast to the net production rate of precipitation and surface precipitation flux that increase when the cumulus and stratus are maximally and randomly overlapped, respectively, the global mean net radiative cooling and longwave cloud radiative forcing (LWCF) increase when the cumulus and stratus are randomly overlapped. On the global average, the vertical cloud overlap exerts larger impacts on the precipitation flux than on the radiation flux. The radiation scheme taking the subgrid variability of water vapor between the cloud and clear portions into account substantially increases the global mean LWCF in tropical deep convection and midlatitude storm track regions. 3311 Clouds and aerosols; 3337 Global climate models; 3354 Precipitation; 3336 Numerical approximations and analyses; 3367 Theoretical modeling; cumulus and stratus; Economical Overlap Equation; Parameterization; Vertical cloud overlap
Paulot, Fabien; Paynter, David; Ginoux, Paul; Naik, Vaishali; Horowitz, Larry W.Paulot, F., D. Paynter, P. Ginoux, V. Naik, L. W. Horowitz, 2018: Changes in the aerosol direct radiative forcing from 2001 to 2015: observational constraints and regional mechanisms. Atmospheric Chemistry and Physics, 18(17), 13265-13281. doi: 10.5194/acp-18-13265-2018. Abstract. We present estimates of changes in the direct aerosol effects (DRE) and its anthropogenic component (DRF) from 2001 to 2015 using the GFDL chemistry–climate model AM3 driven by CMIP6 historical emissions. AM3 is evaluated against observed changes in the clear-sky shortwave direct aerosol effect (DREswclr) derived from the Clouds and the Earth's Radiant Energy System (CERES) over polluted regions. From 2001 to 2015, observations suggest that DREclrsw increases (i.e., less radiation is scattered to space by aerosols) over western Europe (0.7–1Wm−2decade−1) and the eastern US (0.9–1.4Wm−2decade−1), decreases over India (−1 to −1.6Wm−2decade−1), and does not change significantly over eastern China. AM3 captures these observed regional changes in DREclrsw well in the US and western Europe, where they are dominated by the decline of sulfate aerosols, but not in Asia, where the model overestimates the decrease of DREclrsw. Over India, the model bias can be partly attributed to a decrease of the dust optical depth, which is not captured by our model and offsets some of the increase of anthropogenic aerosols. Over China, we find that the decline of SO2 emissions after 2007 is not represented in the CMIP6 emission inventory. Accounting for this decline, using the Modular Emission Inventory for China, and for the heterogeneous oxidation of SO2 significantly reduces the model bias. For both India and China, our simulations indicate that nitrate and black carbon contribute more to changes in DREclrsw than in the US and Europe. Indeed, our model suggests that black carbon (+0.12Wm−2) dominates the relatively weak change in DRF from 2001 to 2015 (+0.03Wm−2). Over this period, the changes in the forcing from nitrate and sulfate are both small and of the same magnitude (−0.03Wm−2 each). This is in sharp contrast to the forcing from 1850 to 2001 in which forcings by sulfate and black carbon largely cancel each other out, with minor contributions from nitrate. The differences between these time periods can be well understood from changes in emissions alone for black carbon but not for nitrate and sulfate; this reflects non-linear changes in the photochemical production of nitrate and sulfate associated with changes in both the magnitude and spatial distribution of anthropogenic emissions.
Penner, Joyce E.; Zhou, Cheng; Garnier, Anne; Mitchell, David L.Penner, J. E., C. Zhou, A. Garnier, D. L. Mitchell, 2018: Anthropogenic Aerosol Indirect Effects in Cirrus Clouds. Journal of Geophysical Research: Atmospheres, 123(20), 11,652-11,677. doi: 10.1029/2018JD029204. We have implemented a parameterization for forming ice in large-scale cirrus clouds that accounts for the changes in updrafts associated with a spectrum of waves acting within each time step in the model. This allows us to account for the frequency of homogeneous and heterogenous freezing events that occur within each time step of the model and helps to determine more realistic ice number concentrations as well as changes to ice number concentrations. The model is able to fit observations of ice number at the lowest temperatures in the tropical tropopause, but is still somewhat high in tropical latitudes with temperatures between 195 °K and 215 °K. The climate forcings associated with different representations of heterogeneous ice nuclei (IN or INPs) are primarily negative unless large additions of IN are made, such as when we assumed that all aircraft soot acts as an IN. However, they can be close to zero if it is assumed that all background dust can act as an INP irrespective of how much sulfate is deposited on these particles. Our best estimate for the forcing of anthropogenic aircraft soot in this model is -0.2 ± 0.06 Wm-2 while that from anthropogenic fossil/bio-fuel soot is -0.093± 0.033 Wm-2. Natural and anthropogenic open biomass burning leads to a net forcing of -0.057 ± 0.05 Wm-2. Cirrus cloud formation; Climate forcing; Gravity waves; heterogeneous ice nuclei
Peters, Ian Marius; Liu, Haohui; Reindl, Thomas; Buonassisi, TonioPeters, I. M., H. Liu, T. Reindl, T. Buonassisi, 2018: Global Prediction of Photovoltaic Field Performance Differences Using Open-Source Satellite Data. Joule, 2(2), 307-322. doi: 10.1016/j.joule.2017.11.012. Summary Accurate field-performance prediction is essential for the calculation of return-on-investment for photovoltaic projects. Leading software predicting field performance was developed for traditional technologies and markets. Yet emerging markets are projected to install over half of all solar cells by the end of this decade, with persisting interest in new technologies. In this study, we map photovoltaic system performance over the entire planet, for standard and emerging technologies, using open-source satellite data. We validate results using time-resolved field-performance data of cadmium telluride and silicon modules in temperate (Perrysburg, OH, USA) and hot-humid (Singapore) climates. Watt for watt, we find that CdTe produces up to 6% more energy than Si in tropical regions. This result emphasizes the significance of local performance evaluation to complement standard testing condition efficiencies. We extend our model to emerging materials including lead-halide perovskites and III-V thin films, and demonstrate that larger band gaps have performance advantages in hot and humid environments. CdTe; energy yield; performance calculations; photovoltaics; silicon; solar cell performance
Pettorelli, Nathalie; Bühne, Henrike Schulte to; Tulloch, Ayesha; Dubois, Grégoire; Macinnis‐Ng, Cate; Queirós, Ana M.; Keith, David A.; Wegmann, Martin; Schrodt, Franziska; Stellmes, Marion; Sonnenschein, Ruth; Geller, Gary N.; Roy, Shovonlal; Somers, Ben; Murray, Nicholas; Bland, Lucie; Geijzendorffer, Ilse; Kerr, Jeremy T.; Broszeit, Stefanie; Leitão, Pedro J.; Duncan, Clare; Serafy, Ghada El; He, Kate S.; Blanchard, Julia L.; Lucas, Richard; Mairota, Paola; Webb, Thomas J.; Nicholson, EmilyPettorelli, N., H. S. t. Bühne, A. Tulloch, G. Dubois, C. Macinnis‐Ng, A. M. Queirós, D. A. Keith, M. Wegmann, F. Schrodt, M. Stellmes, R. Sonnenschein, G. N. Geller, S. Roy, B. Somers, N. Murray, L. Bland, I. Geijzendorffer, J. T. Kerr, S. Broszeit, P. J. Leitão, C. Duncan, G. E. Serafy, K. S. He, J. L. Blanchard, R. Lucas, P. Mairota, T. J. Webb, E. Nicholson, 2018: Satellite remote sensing of ecosystem functions: opportunities, challenges and way forward. Remote Sensing in Ecology and Conservation, 4(2), 71-93. doi: 10.1002/rse2.59. Societal, economic and scientific interests in knowing where biodiversity is, how it is faring and what can be done to efficiently mitigate further biodiversity loss and the associated loss of ecosystem services are at an all-time high. So far, however, biodiversity monitoring has primarily focused on structural and compositional features of ecosystems despite growing evidence that ecosystem functions are key to elucidating the mechanisms through which biological diversity generates services to humanity. This monitoring gap can be traced to the current lack of consensus on what exactly ecosystem functions are and how to track them at scales beyond the site level. This contribution aims to advance the development of a global biodiversity monitoring strategy by proposing the adoption of a set of definitions and a typology for ecosystem functions, and reviewing current opportunities and potential limitations for satellite remote sensing technology to support the monitoring of ecosystem functions worldwide. By clearly defining ecosystem processes, functions and services and their interrelationships, we provide a framework to improve communication between ecologists, land and marine managers, remote sensing specialists and policy makers, thereby addressing a major barrier in the field. satellite remote sensing; Biodiversity loss; biodiversity monitoring; ecosystem functions; ecosystem services
Pinker, R. T.; Zhang, B. Z.; Weller, R. A.; Chen, W.Pinker, R. T., B. Z. Zhang, R. A. Weller, W. Chen, 2018: Evaluating Surface Radiation Fluxes Observed From Satellites in the Southeastern Pacific Ocean. Geophysical Research Letters, 45(5), 2404-2412. doi: 10.1002/2017GL076805. This study is focused on evaluation of current satellite and reanalysis estimates of surface radiative fluxes in a climatically important region. It uses unique observations from the STRATUS Ocean Reference Station buoy in a region of persistent marine stratus clouds 1,500 km off northern Chile during 2000–2012. The study shows that current satellite estimates are in better agreement with buoy observations than model outputs at a daily time scale and that satellite data depict well the observed annual cycle in both shortwave and longwave surface radiative fluxes. Also, buoy and satellite estimates do not show any significant trend over the period of overlap or any interannual variability. This verifies the stability and reliability of the satellite data and should make them useful to examine El Niño–Southern Oscillation variability influences on surface radiative fluxes at the STRATUS site for longer periods for which satellite record is available. 4504 Air/sea interactions; satellite; 3307 Boundary layer processes; surface radiation; flux; 4247 Marine meteorology; buoy; comparison; stratus
Potter, Gerald L.; Carriere, Laura; Hertz, Judy; Bosilovich, Michael; Duffy, Daniel; Lee, Tsengdar; Williams, Dean N.Potter, G. L., L. Carriere, J. Hertz, M. Bosilovich, D. Duffy, T. Lee, D. N. Williams, 2018: Enabling Reanalysis Research Using the Collaborative REAnalysis Technical Environment (CREATE). Bull. Amer. Meteor. Soc., 99, 677–687. doi: 10.1175/BAMS-D-17-0174.1. This paper describes repackaging and consistent distribution of the world’s major atmospheric and oceanic reanalyses. It also presents examples of the usefulness of examining multiple reanalyses. This service will make it much easier for anybody using reanalysis to access multiple data sets using an approach similar to that of the Coupled Model Intercomparison Project Phase 5 (CMIP5) data. Experienced users as well as students will find the standardized formatted data convenient to use.
Priestley, Kory J.; Thomas, Susan; Smith, Nathaniel; Daniels, Janet; Wilson, Robert; Walikainen, Dale; Ashraf, AnumPriestley, K. J., S. Thomas, N. Smith, J. Daniels, R. Wilson, D. Walikainen, A. Ashraf, 2018: Ensuring continuity of earth radiation budget observations initial results of CERES FM-6 on NOAA-20 (Conference Presentation). Earth Observing Systems XXIII, 10764, 107640Q. doi: 10.1117/12.2321645. The Clouds and Earth Radiant Energy System (CERES) program has the objective of producing a multi-decadal Climate Data Record (CDR) of Earth Radiation Budget (ERB) measurements. CERES Flight Model 6 was placed in orbit in November 2017 aboard the NOAA-20 spacecraft. FM-6 joined the FM-1 and FM-2 aboard the Terra, FM-3 and -4 aboard the Aqua, and FM-5 aboard the S-NPP spacecraft to seamlessly continue the Earth radiation budget CDR. FM-6 is the most highly calibrated CERES instrument due to improvements in the extensive pre-launch ground calibration campaign. Operations in orbit began with functional check-outs followed immediately by a period of intensive calibrations and validation checks and then transition to the long-term Cal/Val protocol. Initial results demonstrate agreement with ground calibrations within 0.5%. Operations to inter-calibrate with other CERES instruments will commence in the Spring of 2018. The current effort will document the results of the intensive post launch cal/val campaign completed in early 2018 as well as continued radiometric performance and including intercomparisons with other CERES instruments already on orbit.
Proistosescu, Cristian; Donohoe, Aaron; Armour, Kyle C.; Roe, Gerard H.; Stuecker, Malte F.; Bitz, Cecilia M.Proistosescu, C., A. Donohoe, K. C. Armour, G. H. Roe, M. F. Stuecker, C. M. Bitz, 2018: Radiative feedbacks from stochastic variability in surface temperature and radiative imbalance. Geophysical Research Letters, 45(10), 5082-5094. doi: 10.1029/2018GL077678. Estimates of radiative feedbacks obtained by regressing fluctuations in top-of-atmosphere (TOA) energy imbalance and surface temperature depend critically on the sampling interval and on assumptions about the nature of the stochastic forcing driving internal variability. Here we develop an energy-balance framework that allows us to model the different contributions of stochastic atmospheric and oceanic forcing on feedback estimates. The contribution of different forcing components are parsed based on their impacts on the covariance structure of temperature and TOA energy fluxes, and the framework is validated in a hierarchy of climate model simulations that span a range of oceanic configurations and reproduce the key features seen in observations. We find that at least three distinct forcing sources, feedbacks, and time scales are needed to explain the full covariance structure. Atmospheric and oceanic forcings drive modes of variability with distinct relationships between near-surface air temperature and TOA radiation, leading to an effect akin to regression dilution. The net regression-based feedback estimate is found to be a weighted average of the distinct feedbacks associated with each mode. Moreover, the estimated feedback depends on whether surface temperature and TOA energy fluxes are sampled at monthly or annual timescales. The results suggest that regression-based feedback estimates reflect contributions from a combination of stochastic forcings, and should not be interpreted as providing an estimate of the radiative feedback governing the climate response to greenhouse gas forcing. Climate Sensitivity; Natural Variability; Radiative Feedbacks; Stochastic Processes
Qian, Yun; Wan, Hui; Yang, Ben; Golaz, Jean-Christophe; Harrop, Bryce; Hou, Zhangshuan; Larson, Vincent E.; Leung, L. Ruby; Lin, Guangxing; Lin, Wuyin; Ma, Po-Lun; Ma, Hsi-Yen; Rasch, Phil; Singh, Balwinder; Wang, Hailong; Xie, Shaocheng; Zhang, KaiQian, Y., H. Wan, B. Yang, J. Golaz, B. Harrop, Z. Hou, V. E. Larson, L. R. Leung, G. Lin, W. Lin, P. Ma, H. Ma, P. Rasch, B. Singh, H. Wang, S. Xie, K. Zhang, 2018: Parametric sensitivity and uncertainty quantification in the version 1 of E3SM Atmosphere Model based on short Perturbed Parameters Ensemble simulations. Journal of Geophysical Research: Atmospheres, 123(23), 13,046-13,073. doi: 10.1029/2018JD028927. The atmospheric component of Energy Exascale Earth System Model (E3SM) version 1 (EAMv1) has included many new features in the physics parameterizations compared to its predecessors. Potential complex nonlinear interactions among the new features create a significant challenge for understanding the model behaviors and parameter tuning. Using the one-at-a-time method, the benefit of tuning one parameter may offset the benefit of tuning another parameter, or improvement in one target variable may lead to degradation in another target variable. To better understand the EAMv1 model behaviors and physics, we conducted a large number of short simulations (3 days) in which 18 parameters carefully selected from parameterizations of deep convection, shallow convection and cloud macrophysics and microphysics were perturbed simultaneously using the Latin Hypercube sampling method. From the Perturbed Parameters Ensemble (PPE) simulations and use of different skill score functions, we identified the most sensitive parameters, quantified how the model responds to changes of the parameters for both global mean and spatial distribution, and estimated the maximum likelihood of model parameter space for a number of important fidelity metrics. Comparison of the parametric sensitivity using simulations of two different lengths suggests that PPE using short simulations has some bearing on understanding parametric sensitivity of longer simulations. Results from this analysis provide a more comprehensive picture of the EAMv1 behavior. The difficulty in reducing biases in multiple variables simultaneously highlights the need of characterizing model structural uncertainty (so-called embedded errors) to inform future development efforts. E3SM; Parametric sensitivity; PPE; sensitivity analysis; short simulations; uncertainty quantification
Qin, Yi; Lin, Yanluan; Xu, Shiming; Ma, Hsi-Yen; Xie, ShaochengQin, Y., Y. Lin, S. Xu, H. Ma, S. Xie, 2018: A Diagnostic PDF Cloud Scheme to Improve Subtropical Low Clouds in NCAR Community Atmosphere Model (CAM5). Journal of Advances in Modeling Earth Systems, 10(2), 320-341. doi: 10.1002/2017MS001095. Low clouds strongly impact the radiation budget of the climate system, but their simulation in most GCMs has remained a challenge, especially over the subtropical stratocumulus region. Assuming a Gaussian distribution for the subgrid-scale total water and liquid water potential temperature, a new statistical cloud scheme is proposed and tested in NCAR Community Atmospheric Model version 5 (CAM5). The subgrid-scale variance is diagnosed from the turbulent and shallow convective processes in CAM5. The approach is able to maintain the consistency between cloud fraction and cloud condensate and thus alleviates the adjustment needed in the default relative humidity-based cloud fraction scheme. Short-term forecast simulations indicate that low cloud fraction and liquid water content, including their diurnal cycle, are improved due to a proper consideration of subgrid-scale variance over the southeastern Pacific Ocean region. Compared with the default cloud scheme, the new approach produced the mean climate reasonably well with improved shortwave cloud forcing (SWCF) due to more reasonable low cloud fraction and liquid water path over regions with predominant low clouds. Meanwhile, the SWCF bias over the tropical land regions is also alleviated. Furthermore, the simulated marine boundary layer clouds with the new approach extend further offshore and agree better with observations. The new approach is able to obtain the top of atmosphere (TOA) radiation balance with a slightly alleviated double ITCZ problem in preliminary coupled simulations. This study implies that a close coupling of cloud processes with other subgrid-scale physical processes is a promising approach to improve cloud simulations. parameterization; 3365 Subgrid-scale (SGS) parameterization; CAM5; marine low clouds; PDF cloud scheme
Qiu, Shaoyue; Xi, Baike; Dong, XiquanQiu, S., B. Xi, X. Dong, 2018: Influence of Wind Direction on Thermodynamic Properties and Arctic Mixed-Phase Clouds in Autumn at Utqiaġvik, Alaska. Journal of Geophysical Research: Atmospheres, 123(17), 9589-9603. doi: 10.1029/2018JD028631. Seven years of autumnal ground-based observations (September–November 2002–2008) at the U.S. Department of Energy Atmospheric Radiation Measurement North Slope of Alaska site have been analyzed for addressing the occurrence frequency and macrophysical and microphysical properties of Arctic mixed-phase clouds (AMC), as well as the relationship between environmental parameters and AMC properties. In September and October, AMC occurrence frequency is 20–30% lower during a southerly wind when compared to the other wind directions; in November, the variation of AMC occurrence frequency with wind direction is small. The mean liquid water path in November is about half of that in October and September. When the surface is snow free, temperature (T) and specific humidity (q) profiles during a northerly wind are warmer and moister than those for the southerly wind. Northerly wind profiles have a higher relative humidity to ice (RHi) and lower atmosphere stability. Furthermore, the AMC occurrence frequency has a positive relationship with RHi and a negative relationship with stability. These two points may explain the lower AMC occurrence frequency during a southerly wind. During a northerly wind, AMCs have larger radar reflectivity, wider spectrum width, and larger Doppler velocity signatures. The stronger precipitation for AMC during a northerly wind is possibly due to the cleaner air masses from the ocean (north). With the same amount of q, the radar spectrum width has a higher frequency in the larger bins during a northerly wind. Both T, q, and radar reflectivity, radar spectrum width profiles show evidence of deposition in the sub-cloud layer in September and October. cloud vertical structure; Arctic mixed-phase cloud; cloud microphysical processes; cloud occurrence frequency; thermodynamic profile; wind direction
Rai, Archana; Saha, Subodh KumarRai, A., S. K. Saha, 2018: Evaluation of energy fluxes in the NCEP climate forecast system version 2.0 (CFSv2). Climate Dynamics, 50(1-2), 101-114. doi: 10.1007/s00382-017-3587-z. The energy fluxes at the surface and top of the atmosphere (TOA) from a long free run by the NCEP climate forecast system version 2.0 (CFSv2) are validated against several observation and reanalysis datasets. This study focuses on the annual mean energy fluxes and tries to link it with the systematic cold biases in the 2 m air temperature, particularly over the land regions. The imbalance in the long term mean global averaged energy fluxes are also evaluated. The global averaged imbalance at the surface and at the TOA is found to be 0.37 and 6.43 Wm−2, respectively. It is shown that CFSv2 overestimates the land surface albedo, particularly over the snow region, which in turn contributes to the cold biases in 2 m air temperature. On the other hand, surface albedo is highly underestimated over the coastal region around Antarctica and that may have contributed to the warm bias over that oceanic region. This study highlights the need for improvements in the parameterization of snow/sea-ice albedo scheme for a realistic simulation of surface temperature and that may have implications on the global energy imbalance in the model.
Regayre, Leighton; Johnson, Jill; Yoshioka, Masaru; Pringle, Kirsty; Sexton, David; Booth, Ben; Lee, Lindsay; Bellouin, Nicolas; Carslaw, KennethRegayre, L., J. Johnson, M. Yoshioka, K. Pringle, D. Sexton, B. Booth, L. Lee, N. Bellouin, K. Carslaw, 2018: Aerosol and physical atmosphere model parameters are both important sources of uncertainty in aerosol ERF. Atmospheric Chemistry and Physics Discussions, 18, 9975-10006. doi: 10.5194/acp-2018-175.
Revelli, Roberto; Porporato, AmilcareRevelli, R., A. Porporato, 2018: Ecohydrological model for the quantification of ecosystem services provided by urban street trees. Urban Ecosystems, 1-16. doi: 10.1007/s11252-018-0741-2. Urban green spaces have been recognized as an important source of ecosystem services, whose quantification requires the determination of quantities related to energy, water, carbon and soil nutrient content. In this paper we propose a stochastic ecohydrological model that couples two existing models for water and nutrients in urban soil at the single street-tree scale. The model input are rainfall and irrigation, for water, and deposition and fertilization, for nitrogen, while the output are evapotranspiration, runoff and deep percolation, for water, and plant uptake and leaching, for nitrogen. The various terms are related to the amount of paved and impervious surfaces that surround the tree trunk and regulate the water and nutrient fluxes in and out the soil. Particular attention is paid to the effects of seasonal variations on plant water and nutrients through a temporal variation of the hydrologic variables (i.e., temperature and rainfall intensity and frequencies). The average model outputs are preliminarily compared with the scant existing literature data, supporting the model application to cities with different climatic conditions. The model results are used to estimate the potential for ecosystem services like tree cooling effects, soil carbon sequestration or storm-water management. Because of the minimal structure of the proposed model, it requires a very low amount of data, while accounting for the stochastic input of rainfall. In the context of climate change and increasing urbanization, the model may offer useful indications to urban planners to enhance ecosystem services while minimizing irrigation, fertilization and their related costs.
Rozenhaimer, Michal Segal; Barton, Neil; Redemann, Jens; Schmidt, Sebastian; LeBlanc, Samuel; Anderson, Bruce; Winstead, Edward; Corr, Chelsea A.; Moore, Richard; Thornhill, K. Lee; Cullather, Richard I.Rozenhaimer, M. S., N. Barton, J. Redemann, S. Schmidt, S. LeBlanc, B. Anderson, E. Winstead, C. A. Corr, R. Moore, K. L. Thornhill, R. I. Cullather, 2018: Bias and Sensitivity of Boundary Layer Clouds and Surface Radiative Fluxes in MERRA-2 and Airborne Observations Over the Beaufort Sea During the ARISE Campaign. Journal of Geophysical Research: Atmospheres, 123(2), 6565-6580. doi: 10.1029/2018JD028349. The representation of Arctic surface radiative fluxes in atmospheric models and reanalyses is integral to understanding relevant physical processes, yet testing of these models is confounded by a scarcity of in situ observations of near-surface atmospheric state profiles, cloud vertical structure, cloud phase, and surface properties. Here, airborne measurements obtained from the Arctic Radiation IceBridge Sea&Ice Experiment (ARISE) during fall 2014 are compared with concurrent products from the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2). Both data sets are then used as input to a radiative transfer model to produce surface radiative fluxes over multiple locations in the Beaufort Sea under the various conditions observed during ARISE. The sensitivity of the simulated fluxes is assessed and compared between these two data sets. Then, the relative contribution of atmospheric state, boundary layer clouds, and their properties to the sensitivity of the simulated surface fluxes is assessed. In our comparisons with ARISE observations we found that MERRA-2 has a warm temperature bias near the surface and it underestimates near-surface clouds and cloud liquid and ice water content. These prevail over both open water and sea ice surfaces. Our sensitivity analysis showed that boundary layer cloud vertical structure and water content account for more than 70% of the difference between MERRA-2 and the radiative fluxes calculated from airborne observations and that differences in boundary layer atmospheric state parameters contribute about 10–20% to the positive bias in the longwave surface flux. Arctic Ocean; boundary layer clouds; airborne observations; marginal ice zone; surface fluxes
Ryu, Youngryel; Jiang, Chongya; Kobayashi, Hideki; Detto, MatteoRyu, Y., C. Jiang, H. Kobayashi, M. Detto, 2018: MODIS-derived global land products of shortwave radiation and diffuse and total photosynthetically active radiation at 5km resolution from 2000. Remote Sensing of Environment, 204(Supplement C), 812-825. doi: 10.1016/j.rse.2017.09.021. Incident shortwave radiation (SW), photosynthetically active radiation (PAR), and diffuse PAR (PARdif) at the land surface drive a multitude of processes related to biosphere-atmosphere interactions and play a critical role in the Earth climate system. Previous global solar radiation products were spatially coarse (>50-km resolution) or temporally short (a few years), which hindered scaling-up ground based observations of the land surface processes into regional, continental, and global scales across multiple time scales. Here, we report Breathing Earth System Simulator (BESS) SW, PAR, and PARdif products over the global land surface at a 5km resolution with 4day intervals between 2000 and 2016. We combined an atmospheric radiative transfer model with an artificial neural network (ANN) to compute SW, PAR, and PARdif. A series of MODerate Resolution Imaging Spectroradiometer (MODIS) atmosphere and land products were used as inputs to run the ANN. We test the performance of the products using data from 158 (SW), 77 (PAR), and 22 (PARdif) stations collected in the Baseline Surface Radiation Network (BSRN) and flux tower networks, which covered a range of climatic zones from polar to tropical zones. BESS had strong linear relationships with in-situ SW data (R2=0.95, relative bias=−2.3%), PAR (R2=0.94, relative bias=1.7%), and PARdif (R2=0.84, relative bias=0.2%). BESS captured the interannual variability of SW at both the site (a majority of long-term BSRN sites) and continental levels. Over the study period, global annual SW, PAR, and PARdif values did not show any dimming or brightening trends, although these trends appeared at regional levels, e.g. dimming in India. Mean annual SW over the global land surface was 184.8Wm−2 (875ZJyr−1, zetta=1021); 46% of SW was partitioned to PAR, which was further split into direct (59%) and diffuse (41%) components. The developed products will be useful in solar energy harvesting research and will improve water, carbon, and energy flux estimates of terrestrial ecosystems from local to the global scales. Solar radiation; MODIS; BSRN; BESS; Diffuse PAR; FLUXNET; PAR
Sarangi, Chandan; Kanawade, Vijay P.; Tripathi, Sachchida N.; Thomas, Abin; Ganguly, DilipSarangi, C., V. P. Kanawade, S. N. Tripathi, A. Thomas, D. Ganguly, 2018: Aerosol-induced intensification of cooling effect of clouds during Indian summer monsoon. Nature Communications, 9(1), 3754. doi: 10.1038/s41467-018-06015-5. The invigoration of deep convective clouds in the Indian summer monsoon region is associated with high aerosol loading. Here the authors show that convective clouds from high aerosol loads in the Indian Summer Monsoon region have a cooling effect.
Schmeisser, Lauren; Hinkelman, Laura M.; Ackerman, Thomas P.Schmeisser, L., L. M. Hinkelman, T. P. Ackerman, 2018: Evaluation of Radiation and Clouds From Five Reanalysis Products in the Northeast Pacific Ocean. Journal of Geophysical Research: Atmospheres, 123(14), 7238-7253. doi: 10.1029/2018JD028805. Atmospheric reanalyses are valuable tools for studying the atmosphere, as they provide temporally and spatially complete coverage of atmospheric variables. However, some regions are susceptible to large biases in reanalysis products due to the scarce data available to assimilate into the reanalyses. Consequently, evaluation of reanalyses using available measurements is essential for quantifying regional errors. Here we use NASA's CERES satellite estimates to evaluate surface radiative fluxes and total cloud fraction in the Northeast Pacific from five reanalysis products—ERA-Interim, MERRA2, JRA-55, NCEP2, and CFSR—from years 2001 to 2015. Results show that biases of surface incident shortwave radiative flux in reanalyses compared to satellite estimates range from 3.8 (CFSR) to 21.2 Wm-2 (NCEP2), with significant biases in JRA-55 and NCEP2. Mean surface downward longwave radiative flux in the reanalysis products is biased by −8.9 (MERRA2) to 3.9 Wm−2 (JRA-55), with significant biases in MERRA2 and NCEP2. Errors in the surface radiative fluxes are partially linked to differences in total cloud fraction in the satellite estimates and reanalyses, which show significant negative biases ranging from −8% (CFSR) to −21.7% (NCEP2). There is not one reanalysis that outperforms the rest in the NE Pacific. The most appropriate data set depends on the variables of interest, subregion of the NE Pacific being studied, time period of interest, and whether the reanalysis data will be used to study long-term or short-term climate processes. Using the errors presented for each reanalysis data set can help guide appropriate use and bound uncertainty for the five reanalysis products analyzed. cloud fraction; surface radiative fluxes; atmospheric reanalysis; CERES EBAF; Northeast Pacific
Schmidt, Anja; Mills, Michael J.; Ghan, Steven; Gregory, Jonathan M.; Allan, Richard P.; Andrews, Timothy; Bardeen, Charles G.; Conley, Andrew; Forster, Piers M.; Gettelman, Andrew; Portmann, Robert W.; Solomon, Susan; Toon, Owen B.Schmidt, A., M. J. Mills, S. Ghan, J. M. Gregory, R. P. Allan, T. Andrews, C. G. Bardeen, A. Conley, P. M. Forster, A. Gettelman, R. W. Portmann, S. Solomon, O. B. Toon, 2018: Volcanic radiative forcing from 1979 to 2015. Journal of Geophysical Research: Atmospheres, 123(22), 12,491-12,508. doi: 10.1029/2018JD028776. Using volcanic sulfur dioxide emissions in an aerosol-climate model we derive a time-series of global-mean volcanic effective radiative forcing (ERF) from 1979 to 2015. For 2005-2015, we calculate a global multi-annual mean volcanic ERF of -0.08 W m-2 relative to the volcanically quiescent 1999-2002 period, due to a high frequency of small-to-moderate-magnitude explosive eruptions after 2004. For eruptions of large magnitude such as 1991 Mt. Pinatubo, our model-simulated volcanic ERF, which accounts for rapid adjustments including aerosol perturbations of clouds, is less negative than that reported in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) that only accounted for stratospheric temperature adjustments. We find that, when rapid adjustments are considered, the relation between volcanic forcing and volcanic stratospheric optical depth (SAOD) is 13-21% weaker than reported in IPCC AR5 for large-magnitude eruptions. Further, our analysis of the recurrence frequency of eruptions reveals that sulfur-rich small-to-moderate-magnitude eruptions with column heights ≥10 km occur frequently, with periods of volcanic quiescence being statistically rare. Small-to-moderate-magnitude eruptions should therefore be included in climate model simulations, given the >50% chance of one or two eruptions to occur in any given year. Not all of these eruptions affect the stratospheric aerosol budget, but those that do increase the non-volcanic background SAOD by 0.004 on average, contributing 50% to the total SAOD in the absence of large-magnitude eruptions. This equates to a volcanic ERF of about -0.10 W m-2, which is about two-thirds of the ERF from ozone changes induced by ozone-depleting substances. climate change; aerosol-cloud interactions; volcanic aerosol; volcanic emissions; volcanic eruptions; volcanic radiative forcing
Schuddeboom Alex; McDonald Adrian J.; Morgenstern Olaf; Harvey Mike; Parsons SimonSchuddeboom Alex, ., . McDonald Adrian J., . Morgenstern Olaf, . Harvey Mike, . Parsons Simon, 2018: Regional Regime‐Based Evaluation of Present‐Day General Circulation Model Cloud Simulations Using Self‐Organizing Maps. Journal of Geophysical Research: Atmospheres, 123(8), 4259-4272. doi: 10.1002/2017JD028196. Abstract Global clusters are derived by applying the self?organizing map technique to the Moderate Resolution Imaging Spectroradiometer cloud top pressure?cloud optical thickness joint histograms. These cloud clusters are then used to classify Cloud Feedback Model Intercomparison Project Observation Simulator Package output from the HadGEM3 (Global Atmosphere version 7) atmosphere?only climate model. Discrepancies in the Global Atmosphere version 7 representation of particular clusters can be established by examining the two sets of cluster's occurrence rate and radiative effect. The overall differences in the occurrence rates show major discrepancies in several of the clusters, resulting in a shift from five dominant clusters in Moderate Resolution Imaging Spectroradiometer (above 10% occurrence rate) to two dominant clusters in the model. A comparison of the geographic distributions of occurrence rate shows that the differences are strongly regional and unique to each cluster. While comparisons of the global mean longwave and shortwave cloud radiative effect (CRE) show strong agreement, examination of the CRE of individual cloud types reveals larger errors that highlight the role of compensating errors in masking model deficiencies. CRE data for each of the clusters is further partitioned into regions. This establishes that the bias associated with a cluster is highly variable globally, with no clusters showing consistent biases across all regions. Therefore, regional level phenomena likely play an important role in the creation of these errors. clouds; MODIS; radiation; climate models; model evaluation; self‐organizing maps
Schwartz, Stephen E.Schwartz, S. E., 2018: Resource Letter GECC-1: The Greenhouse Effect and Climate Change: Earth's Natural Greenhouse Effect. American Journal of Physics, 86(8), 565-576. doi: 10.1119/1.5045574. Earth's greenhouse effect is manifested as the difference between thermal infrared radiation emitted at the Earth surface and that emitted to space at the top of the atmosphere. This difference, which is due mainly to absorption and downward emission of radiant energy by atmospheric trace gases, results in global mean surface temperature about 32 K greater than what it would otherwise be for the same planetary absorption of solar radiation, and is thus of enormous importance to Earth's climate. This Resource Letter introduces the physics of the greenhouse effect and more broadly of Earth's climate system and provides resources for further study. A companion Resource Letter (GECC-2), planned for the following issue, examines the increase in the greenhouse effect due to human activities over the past 200 years and its consequences for Earth's climate system.
Schwarz, M.; Folini, D.; Hakuba, M. Z.; Wild, M.Schwarz, M., D. Folini, M. Z. Hakuba, M. Wild, 2018: From point to area: worldwide assessment of the representativeness of monthly surface solar radiation records. Journal of Geophysical Research: Atmospheres, 123(24), 13,857-13,874. doi: 10.1029/2018JD029169. The representativeness of surface solar radiation (SSR) point observations is an important issue when using them in combination with gridded data. We conduct a comprehensive near-global (50°S-55°N) analysis on the representativeness of SSR point observations on the monthly mean time scale. Thereto, we apply the existing concepts of decorrelation lengths (δ), spatial sampling biases (β), and spatial sampling errors (ϵ) to three high-resolution gridded monthly mean SSR data sets (CLARA, SARAH-P, and SARAH-E) provided by the Satellite Application Facility on Climate Monitoring. While δ quantifies the area for which a point observation is representative, β and ϵ are uncertainty estimates with respect to the one-degree reference grid (G). For this grid we find a near-global average δG = 3.4°, βG = 1.4Wm−2, and ϵG = 7.6Wm−2 with substantial regional differences. Disregarding tropical, mountainous, and some coastal regions, monthly SSR point observations can largely be considered representative of a one-degree grid. Since ϵ is an uncorrectable error the total uncertainty when combining point with one-degree gridded data is roughly 40% higher than the uncertainty of station-based SSR measurements alone if a rigorous bias correction is applied. Cloud cover and terrain data can at maximum explain 50% of the patterns of the representativeness metrics. We apply our methodology to the stations of the Baseline Surface Radiation Network. Overall, this study shows that representativeness is strongly dependent on local conditions and that all three metrics (δ, β, and ϵ) must be considered for a comprehensive assessment of representativeness. surface solar radiation; representativeness; decorrelation lentgh; near-global assessment; spatial sampling bias; spatial sampling error
Sedlar, JosephSedlar, J., 2018: Spring Arctic Atmospheric Preconditioning: Do Not Rule Out Shortwave Radiation Just Yet. J. Climate, 31, 4225–4240,. doi: 10.1175/JCLI-D-17-0710.1. Springtime atmospheric preconditioning of Arctic sea ice for enhanced or buffered sea ice melt during the subsequent melt year has received considerable research focus. Studies have identified enhanced poleward atmospheric transport of moisture and heat during spring, leading to increased emission of longwave radiation to the surface. Simultaneously, these studies ruled out the role of shortwave radiation as an effective preconditioning mechanism because of relatively weak incident solar radiation, high surface albedo from sea ice and snow, and increased clouds during spring. These conclusions are derived primarily from atmospheric reanalysis, which may not always accurately represent the Arctic climate system. Here, top-of-atmosphere shortwave radiation observations from a state-of-the-art satellite sensor are compared with ERA-Interim reanalysis to examine similarities and differences in the springtime absorbed shortwave radiation (ASR) over the Arctic Ocean. Distinct biases in regional location and absolute magnitude of ASR anomalies are found between satellite-based measurements and reanalysis. Observations indicate separability between ASR anomalies in spring corresponding to anomalously low and high ice extents in September; the reanalysis fails to capture the full extent of this separability. The causes for difference in ASR anomalies between observations and reanalysis are considered in terms of the variability in surface albedo and cloud presence. Additionally, biases in reanalysis cloud water during spring are presented and are considered for their impact on overestimating spring downwelling longwave anomalies. Taken together, shortwave radiation should not be overlooked as a contributing mechanism to springtime Arctic atmospheric preconditioning.
Séférian, R.; Baek, S.; Boucher, O.; Dufresne, J.-L.; Decharme, B.; Saint-Martin, D.; Roehrig, R.Séférian, R., S. Baek, O. Boucher, J. Dufresne, B. Decharme, D. Saint-Martin, R. Roehrig, 2018: An interactive ocean surface albedo scheme (OSAv1.0): formulation and evaluation in ARPEGE-Climat (V6.1) and LMDZ (V5A). Geosci. Model Dev., 11(1), 321-338. doi: 10.5194/gmd-11-321-2018. Ocean surface represents roughly 70 % of the Earth's surface, playing a large role in the partitioning of the energy flow within the climate system. The ocean surface albedo (OSA) is an important parameter in this partitioning because it governs the amount of energy penetrating into the ocean or reflected towards space. The old OSA schemes in the ARPEGE-Climat and LMDZ models only resolve the latitudinal dependence in an ad hoc way without an accurate representation of the solar zenith angle dependence. Here, we propose a new interactive OSA scheme suited for Earth system models, which enables coupling between Earth system model components like surface ocean waves and marine biogeochemistry. This scheme resolves spectrally the various contributions of the surface for direct and diffuse solar radiation. The implementation of this scheme in two Earth system models leads to substantial improvements in simulated OSA. At the local scale, models using the interactive OSA scheme better replicate the day-to-day distribution of OSA derived from ground-based observations in contrast to old schemes. At global scale, the improved representation of OSA for diffuse radiation reduces model biases by up to 80 % over the tropical oceans, reducing annual-mean model–data error in surface upwelling shortwave radiation by up to 7 W m−2 over this domain. The spatial correlation coefficient between modeled and observed OSA at monthly resolution has been increased from 0.1 to 0.8. Despite its complexity, this interactive OSA scheme is computationally efficient for enabling precise OSA calculation without penalizing the elapsed model time.
Shaw, Tiffany A.; Barpanda, Pragallva; Donohoe, AaronShaw, T. A., P. Barpanda, A. Donohoe, 2018: A moist static energy framework for zonal-mean storm track intensity. J. Atmos. Sci., 75(6), 1979–1994. doi: 10.1175/JAS-D-17-0183.1. A moist static energy (MSE) framework for zonal-mean storm track intensity, defined as the extremum of zonal-mean transient eddy MSE flux, is derived and applied across a range of timescales. According to the framework storm track intensity can be decomposed into contributions from net energy input (sum of shortwave absorption and surface heat fluxes into the atmosphere minus outgoing longwave radiation (OLR) and atmospheric storage) integrated poleward of the storm track position and MSE flux by the mean meridional circulation or stationary eddies at the storm track position. The framework predicts storm tracks decay in spring and amplify in fall in response to seasonal insolation. When applied diagnostically the framework shows shortwave absorption and land turbulent surface heat fluxes account for the seasonal evolution of Northern Hemisphere (NH) intensity, however they are partially compensated by OLR (Planck feedback) and stationary eddy MSE flux. The negligible amplitude of Southern Hemisphere (SH) seasonal intensity is consistent with the compensation of shortwave absorption by OLR and oceanic turbulent surface heat fluxes (ocean energy storage). On interannual timescales, El Nino minus La Nina conditions amplify the NH storm track consistent with decreased subtropical stationary eddy MSE flux. Finally, on centennial timescales, the CO2 indirect effect (sea surface temperature warming) amplifies the NH summertime storm track whereas the direct effect weakens it consistent with opposing turbulent surface heat flux responses over land and ocean.
Shi, Xiangjun; Liu, Xiaohong; Shi, Xiangjun; Liu, XiaohongShi, X., X. Liu, X. Shi, X. Liu, 2018: Sensitivity Study of Anthropogenic Aerosol Indirect Forcing through Cirrus Clouds with CAM5 using Three Ice Nucleation Parameterizations. Journal of Meteorological Research, 32(5), 693-706. doi: 10.1007/s13351-018-8011-z.
Shin, Hyeyum Hailey; Ming, Yi; Zhao, Ming; Golaz, Jean-Christophe; Xiang, Baoqiang; Guo, HuanShin, H. H., Y. Ming, M. Zhao, J. Golaz, B. Xiang, H. Guo, 2018: Evaluation of Planetary Boundary Layer Simulation in GFDL Atmospheric General Circulation Models. J. Climate, 31(13), 5071-5087. doi: 10.1175/JCLI-D-17-0543.1. This study describes the performance of two Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric general circulation models (AGCMs) in simulating the climatologies of planetary boundary layer (PBL) parameters, with a particular focus on the diurnal cycles. The two models differ solely in the PBL parameterization: one uses a prescribed K-profile parameterization (KPP) scheme with an entrainment parameterization, and the other employs a turbulence kinetic energy (TKE) scheme. The models are evaluated through comparison with the reanalysis ensemble, which is generated from European Centre for Medium-Range Weather Forecasts (ECMWF) twentieth-century reanalysis (ERA-20C), ERA-Interim, NCEP CFSR, and NASA MERRA, and the following systematic biases are identified. The models exhibit widespread cold biases in the high latitudes, and the biases are smaller when the KPP scheme is used. The diurnal cycle amplitudes are underestimated in most dry regions, and the model with the TKE scheme simulates larger amplitudes. For the near-surface winds, the models underestimate both the daily means and the diurnal amplitudes; the differences between the models are relatively small compared to the biases. The role of the PBL schemes in simulating the PBL parameters is investigated through the analysis of vertical profiles. The Sahara, which is suitable for focusing on the role of vertical mixing in dry PBLs, is selected for a detailed analysis. It reveals that compared to the KPP scheme, the heat transport is weaker with the TKE scheme in both convective and stable PBLs as a result of weaker vertical mixing, resulting in larger diurnal amplitudes. Lack of nonlocal momentum transport from the nocturnal low-level jets to the surfaces appears to explain the underestimation of the near-surface winds in the models.
Siler, Nicholas; Po-Chedley, Stephen; Bretherton, Christopher S.Siler, N., S. Po-Chedley, C. S. Bretherton, 2018: Variability in modeled cloud feedback tied to differences in the climatological spatial pattern of clouds. Climate Dynamics, 50(3-4), 1209-1220. doi: 10.1007/s00382-017-3673-2. Despite the increasing sophistication of climate models, the amount of surface warming expected from a doubling of atmospheric CO22_2 (equilibrium climate sensitivity) remains stubbornly uncertain, in part because of differences in how models simulate the change in global albedo due to clouds (the shortwave cloud feedback). Here, model differences in the shortwave cloud feedback are found to be closely related to the spatial pattern of the cloud contribution to albedo (αα\alpha) in simulations of the current climate: high-feedback models exhibit lower (higher) αα\alpha in regions of warm (cool) sea-surface temperatures, and therefore predict a larger reduction in global-mean αα\alpha as temperatures rise and warm regions expand. The spatial pattern of αα\alpha is found to be strongly predictive (r=0.84r=0.84r=0.84) of a model’s global cloud feedback, with satellite observations indicating a most-likely value of 0.58±0.310.58±0.310.58\pm 0.31 Wm−2−2^{-2} K−1−1^{-1} (90% confidence). This estimate is higher than the model-average cloud feedback of 0.43 Wm−2−2^{-2} K−1−1^{-1}, with half the range of uncertainty. The observational constraint on climate sensitivity is weaker but still significant, suggesting a likely value of 3.68 ± 1.30 K (90% confidence), which also favors the upper range of model estimates. These results suggest that uncertainty in model estimates of the global cloud feedback may be substantially reduced by ensuring a realistic distribution of clouds between regions of warm and cool SSTs in simulations of the current climate.
Singh, Sachchidanand; Lodhi, Neelesh K.; Mishra, Amit Kumar; Jose, Sandhya; Kumar, S. Naresh; Kotnala, R. K.Singh, S., N. K. Lodhi, A. K. Mishra, S. Jose, S. N. Kumar, R. K. Kotnala, 2018: Assessment of satellite-retrieved surface UVA and UVB radiation by comparison with ground-measurements and trends over Mega-city Delhi. Atmospheric Environment, 188, 60-70. doi: 10.1016/j.atmosenv.2018.06.027. Solar UV radiation reaching the Earth's surface is known to have various effects on human health and on the ecosystem. Ground-based measurements of surface UV radiation are spatially sparse and in many cases do not provide long time series. Higher spatial coverage can be provided by measurements from satellite based instruments, but these measurements need to be compared to ground-based measurements of sufficient quality before they can be used in health and ecosystem applications. Here, we compare the measurements of surface solar UV radiation in UVA (315–400 nm) and UVB (280–315 nm) bands with the satellite retrievals (CERES) and validate the latter at an urban location, Delhi, India. We have also used MODIS-retrieved aerosol optical depth (AOD) and cloud optical depth (COD) data to see the effect of atmospheric opacity on UV radiation. Ground-based measurements of UVA and UVB were performed from 01 October, 2012 to 30 September, 2015. Correlations between daily surface measurements and CERES-derived surface UV fluxes showed very good agreement (r ∼ 0.92–0.93) over Delhi. We found a negative correlation between UV fluxes and AOD over Delhi during all seasons. A unit increase in AOD leads to a decrease of ∼4–5 Wm-2 in UVA and ∼0.09–0.14 Wm-2 in UVB over Delhi. The trend analysis from monthly mean CERES-derived UV fluxes for 17 years data reveals that UVA and UVB are decreasing ∼0.07 Wm-2 yr−1 and 0.003 Wm-2 yr−1, respectively with AOD increase (∼0.005 yr−1) over Delhi. The simultaneous increase in aerosol loading with decrease in UV fluxes at the surface may be explained as a masking effect of ever increasing pollution on surface UV radiation over Delhi. Our results show ∼10% and ∼20% decrease (with respect to mean) in UVA and UVB surface fluxes, respectively during last 17 years. CERES; AOD; Radiometer; UVA; UVB
Skinner, Patrick S.; Wheatley, Dustan M.; Knopfmeier, Kent H.; Reinhart, Anthony E.; Choate, Jessica J.; Jones, Thomas A.; Creager, Gerald J.; Dowell, David C.; Alexander, Curtis R.; Ladwig, Therese T.; Wicker, Louis J.; Heinselman, Pamela L.; Minnis, Patrick; Palikonda, RabindraSkinner, P. S., D. M. Wheatley, K. H. Knopfmeier, A. E. Reinhart, J. J. Choate, T. A. Jones, G. J. Creager, D. C. Dowell, C. R. Alexander, T. T. Ladwig, L. J. Wicker, P. L. Heinselman, P. Minnis, R. Palikonda, 2018: Object-based verification of a prototype Warn-on-Forecast system. Wea. Forecasting, 33, 1225–1250. doi: 10.1175/WAF-D-18-0020.1. An object-based verification methodology for the NSSL Experimental Warn-on-Forecast System for ensembles (NEWS-e) has been developed and applied to 32 cases between December 2015 and June 2017. NEWS-e forecast objects of composite reflectivity and 30-minute updraft helicity swaths are matched to corresponding reflectivity and rotation track objects in Multi-Radar Multi-Sensor data on space and time scales typical of a National Weather Service warning. Object matching allows contingency table-based verification statistics to be used to establish baseline performance metrics for NEWS-e thunderstorm and mesocyclone forecasts.NEWS-e Critical Success Index (CSI) scores of reflectivity (updraft helicity) forecasts decrease from approximately 0.7 (0.4) to 0.4 (0.2) over 3 hours of forecast time. CSI scores decrease through the forecast period, indicating that errors do not saturate during the 3-hour forecast. Lower verification scores for rotation track forecasts are primarily a result of a high frequency bias. Comparison of different system configurations used in 2016 and 2017 show an increase in skill for 2017 reflectivity forecasts, attributable mainly to improvements in the forecast initial condition. A small decrease in skill in 2017 rotation track forecasts is likely a result of sample differences between 2016 and 2017. Although large case-to-case variation is present, evidence is found that NEWS-e forecast skill improves with increasing object size and intensity.
Smith, N.; Wilson, R.; Szewczyk, Z.; Thomas, S.; Priestley, K.Smith, N., R. Wilson, Z. Szewczyk, S. Thomas, K. Priestley, 2018: Early trends on the Clouds and the Earth's Radiant Energy System (CERES) Flight Model 6 (FM6) instrument's performance. doi: 10.1117/12.2322712.
Smith, Natividad; Thomas, Susan; Shankar, Mohan; Priestley, Kory; Loeb, Norman; Walikainen, DaleSmith, N., S. Thomas, M. Shankar, K. Priestley, N. Loeb, D. Walikainen, 2018: Assessment of on-orbit variations of the Clouds and the Earth's Radiant Energy System (CERES) FM5 instrument. Earth Observing Missions and Sensors: Development, Implementation, and Characterization V, 10781, 1078119. doi: 10.1117/12.2324739. The Clouds and the Earth’s Radiant Energy System (CERES) mission is instrumental in monitoring changes in the Earth’s radiant energy and cloud systems. The CERES project is critical in guaranteeing the continuation of highly accurate Earth radiation budget Climate Data Records (CDRs). The CERES Flight Model-5 (FM-5) instrument, integrated onto the Suomi-National Polar-Orbiting Partnership (NPP) spacecraft, joined a suite of four CERES instruments deployed aboard NASA’s Earth Observing System (EOS) satellites Terra and Aqua. Each CERES instrument consists of scanning thermistor bolometer sensors that measure broadband radiances in the shortwave (0.3 to 5μm), total (0.3 to < 200 μm) and water vapor window (8 to 12 μm) regions. In order to ensure the consistency and accuracy of instrument radiances, needed for generating higher-level climate data products, the CERES project implements rigorous and comprehensive radiometric calibration and validation procedures. This paper briefly describes the trends observed in Edition-1 FM5 flux data products that are corrected for inflight gain changes derived from on-board calibration sources. The strategy to detect artifacts and correct for any sensor spectral response changes is discussed. Improvements and validation results of preliminary FM5 Edition-2 products will be compared with Terra and Aqua data products.
Song, Hua; Zhang, Zhibo; Ma, Po-Lun; Ghan, Steven J.; Wang, MinghuaiSong, H., Z. Zhang, P. Ma, S. J. Ghan, M. Wang, 2018: An Evaluation of Marine Boundary Layer Cloud Property Simulations in the Community Atmosphere Model Using Satellite Observations: Conventional Subgrid Parameterization versus CLUBB. J. Climate, 31(6), 2299-2320. doi: 10.1175/JCLI-D-17-0277.1. This paper presents a satellite-observation-based evaluation of the marine boundary layer (MBL) cloud properties from two Community Atmosphere Model, version 5 (CAM5), simulations, one with the standard parameterization schemes (CAM5–Base) and the other with the Cloud Layers Unified by Binormals scheme (CAM5–CLUBB). When comparing the direct model outputs, the authors find that CAM5–CLUBB produces more MBL clouds, a smoother transition from stratocumulus to cumulus, and a tighter correlation between in-cloud water and cloud fraction than CAM5–Base. In the model-to-observation comparison using the COSP satellite simulators, the authors find that both simulations capture the main features and spatial patterns of the observed cloud fraction from MODIS and shortwave cloud radiative forcing (SWCF) from CERES. However, CAM5–CLUBB suffers more than CAM5–Base from a problem that can be best summarized as “undetectable” clouds (i.e., a significant fraction of simulated MBL clouds are thinner than the MODIS detection threshold). This issue leads to a smaller COSP–MODIS cloud fraction and a weaker SWCF in CAM5–CLUBB than the observations and also CAM5–Base in the tropical descending regions. Finally, the authors compare modeled radar reflectivity with CloudSat observations and find that both simulations, especially CAM5–CLUBB, suffer from an excessive drizzle problem. Further analysis reveals that the subgrid precipitation enhancement factors in CAM5–CLUBB are unrealistically large, which makes MBL clouds precipitate too excessively, and in turn results in too many undetectable thin clouds.
Song, Qianqian; Zhang, Zhibo; Yu, Hongbin; Kato, Seiji; Yang, Ping; Colarco, Peter; Remer, Lorraine A.; Ryder, Claire L.Song, Q., Z. Zhang, H. Yu, S. Kato, P. Yang, P. Colarco, L. A. Remer, C. L. Ryder, 2018: Net radiative effects of dust in the tropical North Atlantic based on integrated satellite observations and in situ measurements. Atmospheric Chemistry and Physics, 18(15), 11303-11322. doi: 10.5194/acp-18-11303-2018. In this study, we integrate recent in situ measurements with satellite retrievals of dust physical and radiative properties to quantify dust direct radiative effects on shortwave (SW) and longwave (LW) radiation (denoted as DRESW and DRELW, respectively) in the tropical North Atlantic during the summer months from 2007 to 2010. Through linear regression of the CERES-measured top-of-atmosphere (TOA) flux versus satellite aerosol optical depth (AOD) retrievals, we estimate the instantaneous DRESW efficiency at the TOA to be -49.7 +/- 7.1 W m(-2) AOD(-1) and -36.5 +/- 4.8 W m(-2) AOD(-1) based on AOD from MODIS and CALIOP, respectively. We then perform various sensitivity studies based on recent measurements of dust particle size distribution (PSD), refractive index, and particle shape distribution to determine how the dust microphysical and optical properties affect DRE estimates and its agreement with the above-mentioned satellite-derived DREs. Our analysis shows that a good agreement with the observation-based estimates of instantaneous DRESW and DRELW can be achieved through a combination of recently observed PSD with substantial presence of coarse particles, a less absorptive SW refractive index, and spheroid shapes. Based on this optimal combination of dust physical properties we further estimate the diurnal mean dust DRESW in the region of -10 W m(-2) at TOA and -26 W m(-2) at the surface, respectively, of which similar to 30% is canceled out by the positive DRELW. This yields a net DRE of about -6.9 and -18.3 W m(-2) at TOA and the surface, respectively. Our study suggests that the LW flux contains useful information on dust particle size, which could be used together with SW observations to achieve a more holistic understanding of the dust radiative effect. desert dust; airborne mineral aerosols; atmospheric transport; boundary-layer; climate response; infrared optical depth; modis; refractive-index; saharan dust; size distribution
Song, Xiaoliang; Zhang, Guang J.Song, X., G. J. Zhang, 2018: The Roles of Convection Parameterization in the Formation of Double ITCZ Syndrome in the NCAR CESM: I. Atmospheric Processes. Journal of Advances in Modeling Earth Systems, 10(3), 842-866. doi: 10.1002/2017MS001191. Abstract Several improvements are implemented in the Zhang‐McFarlane (ZM) convection scheme to investigate the roles of convection parameterization in the formation of double intertropical convergence zone (ITCZ) bias in the NCAR CESM1.2.1. It is shown that the prominent double ITCZ biases of precipitation, sea surface temperature (SST), and wind stress in the standard CESM1.2.1 are largely eliminated in all seasons with the use of these improvements in convection scheme. This study for the first time demonstrates that the modifications of convection scheme can eliminate the double ITCZ biases in all seasons, including boreal winter and spring. Further analysis shows that the elimination of the double ITCZ bias is achieved not by improving other possible contributors, such as stratus cloud bias off the west coast of South America and cloud/radiation biases over the Southern Ocean, but by modifying the convection scheme itself. This study demonstrates that convection scheme is the primary contributor to the double ITCZ bias in the CESM1.2.1, and provides a possible solution to the long‐standing double ITCZ problem. The atmospheric model simulations forced by observed SST show that the original ZM convection scheme tends to produce double ITCZ bias in high SST scenario, while the modified convection scheme does not. The impact of changes in each core component of convection scheme on the double ITCZ bias in atmospheric model is identified and further investigated.
Song, Zhen; Liang, Shunlin; Wang, Dongdong; Zhou, Yuan; Jia, AolinSong, Z., S. Liang, D. Wang, Y. Zhou, A. Jia, 2018: Long-term record of top-of-atmosphere albedo over land generated from AVHRR data. Remote Sensing of Environment, 211, 71-88. doi: 10.1016/j.rse.2018.03.044. Top-of-atmosphere (TOA) albedo is a fundamental component of Earth's energy budget. To date, long-term global land TOA albedo products with spatial resolution higher than 20-km are not available. In this study, we propose a novel algorithm to retrieve TOA albedo from multispectral imager observations acquired by Advanced Very High Resolution Radiometer (AVHRR), which provides the longest continuous record of global satellite observations since 1981. Direct estimation models were established first to derive instantaneous TOA broadband albedo under various atmospheric and surface conditions, including cloudy-sky, clear-sky (snow-free) and snow-cover conditions. To perform long-term series analysis, the instantaneous TOA albedo were then converted to daily/monthly mean values based on the diurnal curves from multi-year Clouds and the Earth's Radiant Energy System (CERES) 3-hourly flux dataset. Calibration differences between sequential AVHRR sensors were further mitigated by invariant targets normalization. The retrieved TOA albedo at 0.05° × 0.05° was validated against two TOA albedo datasets, CM SAF (Climate Monitoring Satellite Application Facility) flux data and CERES flux data, at spatial resolutions of 0.05° × 0.05°, 20 km × 20 km and 1° × 1°. The instantaneous TOA albedo had an overall Root-Mean-Square-Error (RMSE) of 0.047 when compared with 20-km CERES fluxes, whereas the 1° by 1° monthly mean TOA albedo showed closer agreements with both CM SAF and CERES, with RMSE ranging from 0.029 to 0.040 and from 0.022 to 0.031, respectively. Moreover, our product was found to be highly consistent with both CERES and CM SAF at long-term trend detection. The extensive validation indicated the robustness of our algorithm and subsequently, comparable data quality with existing datasets. With global coverage and long time series (1981–2017), our product is expected to provide valuable information for climate change studies. CERES; Climate change; AVHRR; CM SAF; TOA albedo; Earth's energy budget
Stephens, Graeme L.; Hakuba, Maria Z.; Webb, Mark; Lebsock, Matthew; Yue, Qing; Kahn, Brian H.; Hristova‐Veleva, Svetla; Rapp, Anita; Stubenrauch, Claudia; Elsaesser, Gregory S.; Slingo, JuliaStephens, G. L., M. Z. Hakuba, M. Webb, M. Lebsock, Q. Yue, B. H. Kahn, S. Hristova‐Veleva, A. Rapp, C. Stubenrauch, G. S. Elsaesser, J. Slingo, 2018: Regional intensification of the tropical hydrological cycle during ENSO. Geophysical Research Letters, 45(9), 4361-4370. doi: 10.1029/2018GL077598.
Stratton, Rachel A.; Senior, Catherine A.; Vosper, Simon B.; Folwell, Sonja S.; Boutle, Ian A; Earnshaw, Paul D; Kendon, Elizabeth; Lock, Adrian P.; Malcolm, Andrew; Manners, James; Morcrette, Cyril J.; Short, Christopher; Stirling, Alison J.; Taylor, Christopher M.; Tucker, Simon; Webster, Stuart; Wilkinson, Jonathan M.Stratton, R. A., C. A. Senior, S. B. Vosper, S. S. Folwell, I. A. Boutle, P. D. Earnshaw, E. Kendon, A. P. Lock, A. Malcolm, J. Manners, C. J. Morcrette, C. Short, A. J. Stirling, C. M. Taylor, S. Tucker, S. Webster, J. M. Wilkinson, 2018: A pan-Africa convection-permitting regional climate simulation with the Met Office Unified Model: CP4-Africa. J. Climate, 31(9), 3485–3508. doi: 10.1175/JCLI-D-17-0503.1. A convection-permitting multi-year regional climate simulation using the Met Office Unified Model has been run for the first time on an Africa-wide domain. The model has been run as part of the Future Climate for Africa (FCFA) IMPALA (Improving Model Processes for African cLimAte) project and its configuration, domain and forcing data are described here in detail. The model (CP4-Africa) uses a 4.5km horizontal grid spacing at the equator and is run without a convection parametrization, nested within a global atmospheric model driven by observations at the sea-surface which does include a convection scheme. An additional regional simulation, with identical resolution and physical parametrizations to the global model, but with the domain, land surface and aerosol climatologies of the CP4-Africa model, has been run to aid understanding of the differences between the CP4-Africa and global model, in particular to isolate the impact of the convection parametrization and resolution. The effect of enforcing moisture conservation in the CP4-Africa model is described and its impact on reducing extreme precipitation values is assessed. Preliminary results from the first 5 years of the CP4-Africa simulation show substantial improvements in JJA average rainfall compared to the parameterized convection models, with most notably a reduction in the persistent dry bias in West Africa - giving an indication of the benefits to be gained from running a convection-permitting simulation over the whole African continent.
Su, Wenying; Liang, Lusheng; Doelling, David R.; Minnis, Patrick; Duda, David P.; Khlopenkov, Konstantin V.; Thieman, Mandana M.; Loeb, Norman G.; Kato, Seiji; Valero, Francisco P. J.; Wang, Hailan; Rose, Fred G.Su, W., L. Liang, D. R. Doelling, P. Minnis, D. P. Duda, K. V. Khlopenkov, M. M. Thieman, N. G. Loeb, S. Kato, F. P. J. Valero, H. Wang, F. G. Rose, 2018: Determining the Shortwave Radiative Flux from Earth Polychromatic Imaging Camera. Journal of Geophysical Research: Atmospheres, 123(20), 11,479-11,491. doi: 10.1029/2018JD029390. The Earth Polychromatic Imaging Camera (EPIC) onboard Deep Space Climate Observatory (DSCOVR) provides 10 narrowband spectral images of the sunlit side of the Earth. The blue (443 nm), green (551 nm), and red (680 nm) channels are used to derive EPIC broadband radiances based upon narrowband-to-broadband regressions developed using collocated MODIS equivalent channels and CERES broadband measurements. The pixel-level EPIC broadband radiances are averaged to provide global daytime means at all applicable EPIC times. They are converted to global daytime mean shortwave (SW) fluxes by accounting for the anisotropy characteristics using a cloud property composite based on lower Earth orbiting satellite imager retrievals and the CERES angular distribution models (ADMs). Global daytime mean SW fluxes show strong diurnal variations with daily maximum-minimum differences as great as 20 Wm−2 depending on the conditions of the sunlit portion of the Earth. The EPIC SW fluxes are compared against the CERES SYN1deg hourly SW fluxes. The global monthly mean differences (EPIC-SYN) between them range from 0.1 Wm−2 in July to -4.1 Wm−2 in January, and the RMS errors range from 3.2 Wm−2 to 5.2 Wm−2. Daily mean EPIC and SYN fluxes calculated using concurrent hours agree with each other to within 2% and both show a strong annual cycle. The SW flux agreement is within the calibration and algorithm uncertainties, which indicates that the method developed to calculate the global anisotropic factors from the CERES ADMs is robust and that the CERES ADMs accurately account for the Earth's anisotropy in the near-backscatter direction. CERES; angular distribution model; radiation; DSCOVR; EPIC; Lagrange-1 point
Sun, Daozhong; Ji, Changdong; Sun, Wenxiao; Yang, Yikun; Wang, HaosenSun, D., C. Ji, W. Sun, Y. Yang, H. Wang, 2018: Accuracy assessment of three remote sensing shortwave radiation products in the Arctic. Atmospheric Research, 212, 296-308. doi: 10.1016/j.atmosres.2018.01.003. In this study, the shortwave radiation data in 2007 from GEWEX-SRB, ISCCP-FD and CERES-SYN radiation products were evaluated against ground observations from BSRN, CEOP and GC-Net in the Arctic. The evaluation result shows that the accuracy of the three shortwave radiation products in the Arctic is low. In the Arctic Region, CERES-SYN radiation product quality is superior to GEWEX-SRB and ISCCP-FD. The RMSEs and MAEs of the three shortwave radiation products are > 20 W/m2 at most sites. The mean RMSE and MAE of the downward shortwave radiation data of CERES-SYN are 54.4 W/m2 (42.9%) and 28.4 W/m2 (23.0%), respectively, the mean RMSE and MAE of the upward shortwave radiation data are 50.8 W/m2 (80.4%), 28.4 W/m2 (41.3%). The indexes values of the other two products are greater than CERES-SYN. Through accuracy analysis, it can be concluded that there are seasonal shortwave differences between satellite-estimates and ground measurements. The error sources are mainly systematic errors, rather than random errors. The main factors that affect the accuracy of the flux data include the spatial heterogeneity of the surface, the influence of the cloud, the accuracy of input inversion parameters and the low spatial resolution of the radiation products.
Sun, Wenbo; Baize, Rosemary R.; Videen, Gorden; Hu, YongxiangSun, W., R. R. Baize, G. Videen, Y. Hu, 2018: Chapter 7 - Polarimetric Technique for Satellite Remote Sensing of Superthin Clouds. Remote Sensing of Aerosols, Clouds, and Precipitation, 153-174. Superthin clouds with optical depths smaller than ~ 0.3 exist globally and can seriously affect the remote sensing of aerosols, surface temperature, and atmospheric composition. Failing to detect these clouds, the sea-surface temperature retrieved from NASA's Atmospheric Infrared Sounder (AIRS) satellite data is ~ 5–10 K lower than true values at tropical and midlatitude regions, where these clouds frequently exist. Unfortunately, superthin clouds generally cannot be detected by passive satellite instruments that use only total intensity for measurements. Long-term global surveys of superthin clouds using space-borne lidars are limited by the large operational cost and narrow field of view of these active instruments. This chapter reviews the algorithm for remote sensing of superthin clouds based on our previous study results (Sun et al., 2014, 2015), which show that superthin clouds can be well detected by a polarimetric imager facing toward the backscattering direction of sunlight, exploiting a distinct, characterizing feature of the angle of linear polarization of the backscattered solar radiation (NASA Technology GSC-17392-1). If implemented for satellite remote sensing of the Earth-atmosphere system, this technology will greatly improve the detection of superthin clouds and tremendously impact the remote sensing of clouds, aerosols, surface temperature, atmospheric composition gases, and thus significantly improving data for climate modeling. Remote sensing; Satellite; ice clouds; Angle of linear polarization; Backscattered light; parasol; Polarization of light; Radiative transfer model; Superthin clouds; Water clouds
Sun-Mack, S.; Minnis, P.; Chen, Y.; Doelling, D. R.; Scarino, B. R.; Haney, C. O.; Smith, W. L.Sun-Mack, S., P. Minnis, Y. Chen, D. R. Doelling, B. R. Scarino, C. O. Haney, W. L. Smith, 2018: Calibration Changes to Terra MODIS Collection-5 Radiances for CERES Edition 4 Cloud Retrievals. IEEE Transactions on Geoscience and Remote Sensing, 1-17. doi: 10.1109/TGRS.2018.2829902. Previous research has revealed inconsistencies between the Collection 5 (C5) calibrations of certain channels common to the Terra and Aqua Moderate Resolution Imaging Spectroradiometers (MODISs). To achieve consistency between the Terra and Aqua MODIS radiances used in the Clouds and the Earth's Radiant Energy System (CERES) Edition 4 (Ed4) cloud property retrieval system, adjustments were developed and applied to the Terra C5 calibrations for channels 1-5, 7, 20, and 26. These calibration corrections, developed independently of those used for the later MODIS Collection 6 (C6), ranged from -3.0% for channel 5 to +4.3% for channel 26. For channel 20, the Terra C5 brightness temperatures were decreased nonlinearly by 0.55 K at 300-10 K or more at 220 K. The corrections were applied to the Terra C5 data for CERES Ed4 and resulted in Terra-Aqua radiance consistency that is as good as or better than that of the C6 data sets. The C5 adjustments led to more consistent Aqua and Terra cloud property retrievals than seen in the previous CERES edition. After Ed4 began processing, other calibration artifacts were found in some corrected channels and in some of the uncorrected thermal channels. Because no corrections were developed or applied for those artifacts, some anomalies or false trends could have been introduced into the Ed4 cloud property record. Thus, despite the much improved consistency achieved for the Terra and Aqua data sets in Ed4, the CERES Ed4 cloud property data sets should be used cautiously for cloud trend studies due to those remaining calibration artifacts. Earth; Satellites; cloud; Meteorology; climate; MODIS; Clouds and the Earth's Radiant Energy System (CERES); Moderate Resolution Imaging Spectroradiometer (MODIS); Market research; Clouds; Calibration
Swapna, P.; Krishnan, R.; Sandeep, N.; Prajeesh, A. G.; Ayantika, D. C.; Manmeet, S.; Vellore, R.Swapna, P., R. Krishnan, N. Sandeep, A. G. Prajeesh, D. C. Ayantika, S. Manmeet, R. Vellore, 2018: Long‐Term Climate Simulations Using the IITM Earth System Model (IITM‐ESMv2) With Focus on the South Asian Monsoon. Journal of Advances in Modeling Earth Systems, 10(5), 1127-1149. doi: 10.1029/2017MS001262.
Swift, LukeSwift, L., 2018: A New Radiative Model Derived from Solar Insolation, Albedo, and Bulk Atmospheric Emissivity: Application to Earth and Other Planets. Climate, 6(2), 52. doi: 10.3390/cli6020052. This study develops an equilibrium radiative model based on a quasi-adiabatic atmosphere that quantifies the average surface flux of a planetary body as a function of absorbed solar radiation P and the bulk emissivity of the atmosphere with respect to surface radiation ε. The surface flux is then given by P/(1−ε), and I define the scaling term 1/(1−ε) as the greenhouse factor. The model is applied to all of the rocky planets in the solar system to determine their greenhouse factors, and accounts for the diversity of planetary surface fluxes. The model is modified to allow for a top of atmosphere non-equilibrium state, which when compared with a recent observation-based model of the Earth energy budget, predicts the Earth’s radiative fluxes to within the uncertainty ranges of that model. The model developed in this study is able to quantify the changes in Earth’s surface flux caused by changes in bond albedo and atmospheric bulk emissivity by using the surface temperature, ocean heat content, incoming solar radiation and outgoing longwave radiation records. The model indicates an increase in absorbed solar radiation over the time period from 1979–2015 of the order of 3 W/m2, which was caused by a decrease in planetary bond albedo. The time-series albedo generated by the model is in agreement with Clouds and Earth’s Radiant Energy System (CERES) derived albedo over the period from 2000–2015. The model also indicates a slight decrease in atmospheric bulk emissivity over the same period. Since atmospheric bulk emissivity is a function of the sum of all of the greenhouse gas species, a simultaneous decrease in atmospheric water vapor may offset the effect of the well-documented increase in the non-condensing greenhouse gases over the period, and result in an overall net decrease in bulk emissivity. Atmospheric water vapor datasets partially support the conclusion, with the International Satellite Cloud Climatology Project (ISCCP) data supporting a decrease. The NASA Water Vapor Project (NVAP-M) data supports a decrease in atmospheric water content over the period 1998–2008, but not over the longer period of 1988–2008. The model indicates that the decrease in planetary albedo was the driver for the increased surface flux over the stated period. greenhouse effect; atmospheric energy budget; adiabatic radiative model; greenhouse factor; planetary surface temperature
Szewczyk, Z.; Thomas, Susan; Priestley, Kory J.Szewczyk, Z., S. Thomas, K. J. Priestley, 2018: Strategies for shortwave radiances comparison of CERES instruments aboard the JPSS1 and Terra/Aqua satellites. doi: 10.1117/12.2323131.
Talla Fotsing, Cyrille; Njomo, Donatien; Cornet, Céline; Dubuisson, Philippe; Akana Nguimdo, LeonardTalla Fotsing, C., D. Njomo, C. Cornet, P. Dubuisson, L. Akana Nguimdo, 2018: ECMWF Atmospheric Profiles in Maroua, Cameroon: Analysis and Overview of the Simulation of Downward Global Solar Radiation. Atmosphere, 9(2), 44. doi: 10.3390/atmos9020044. Atmospheric analysis data from the European Center for Medium-Range Weather Forecasts (ECMWF) have been acquired and are used to characterize the meteorological situation in Maroua, Cameroon ( 10.614 ∘ N, 14.361 ∘ E) at 12:00 UTC. These are then used to simulate downward global solar radiation (DGSR) with the moderate-resolution transmittance (MODTRAN) radiative transfer code (RTC). In comparison with meteorological data measured during the year 2014 in Maroua, ECMWF atmospheric quantities at ground level, in general, showed good correlation coefficients and slight differences. It is shown that ECMWF atmospheric profiles can thus be used to complete the scarce atmospheric data and to study the atmosphere state and dynamics, such as the African monsoon phenomenon detected in this region, which regulates the rainy season. In addition, they are more suitable to simulate clear-sky DGSR compared to MODTRAN standard atmospheric profiles. The causes and effects of the substantial bias and weak correlation coefficient observed with ECMWF wind data and the constant underestimation of simulated DGSR in comparison with ground-based measurements are investigated. The paper emphasizes the need for a better characterization of the Maroua atmosphere state and dynamics as well as the simulation of more accurate and reliable DGSR under any atmospheric conditions. solar radiation; MODTRAN; African monsoon; ECMWF atmospheric profiles; meteorological data
Tang, Guanglin; Yang, Ping; Kattawar, George W.; Huang, Xianglei; Mlawer, Eli J.; Baum, Bryan A.; King, Michael D.Tang, G., P. Yang, G. W. Kattawar, X. Huang, E. J. Mlawer, B. A. Baum, M. D. King, 2018: Improvement of the Simulation of Cloud Longwave Scattering in Broadband Radiative Transfer Models. J. Atmos. Sci., 75(7), 2217-2233. doi: 10.1175/JAS-D-18-0014.1. Cloud longwave scattering is generally neglected in general circulation models (GCMs), but it plays a significant and highly uncertain role in the atmospheric energy budget as demonstrated in recent studies. To reduce the errors caused by neglecting cloud longwave scattering, two new radiance adjustment methods are developed that retain the computational efficiency of broadband radiative transfer simulations. In particular, two existing scaling methods and the two new adjustment methods are implemented in the Rapid Radiative Transfer Model (RRTM). The results are then compared with those based on the Discrete Ordinate Radiative Transfer model (DISORT) that explicitly accounts for multiple scattering by clouds. The two scaling methods are shown to improve the accuracy of radiative transfer simulations for optically thin clouds but not effectively for optically thick clouds. However, the adjustment methods reduce computational errors over a wide range, from optically thin to thick clouds. With the adjustment methods, the errors resulting from neglecting cloud longwave scattering are reduced to less than 2 W m−2 for the upward irradiance at the top of the atmosphere and less than 0.5 W m−2 for the surface downward irradiance. The adjustment schemes prove to be more accurate and efficient than a four-stream approximation that explicitly accounts for multiple scattering. The neglect of cloud longwave scattering results in an underestimate of the surface downward irradiance (cooling effect), but the errors are almost eliminated by the adjustment methods (warming effect).
Taylor, Patrick C.; Boeke, Robyn C.; Li, Ying; Thompson, David W. J.Taylor, P. C., R. C. Boeke, Y. Li, D. W. J. Thompson, 2018: Arctic cloud annual cycle biases in climate models. Atmospheric Chemistry and Physics Discussions, 1-35. doi: 10.5194/acp-2018-1159. Abstract. Arctic clouds exhibit a robust annual cycle with maximum cloudiness in fall and minimum in winter. These variations affect energy flows in the Arctic with a large influence on the surface radiative fluxes. Contemporary climate models struggle to reproduce the observed Arctic cloud amount annual cycle and significantly disagree with each other. The goal of this analysis is to quantify the cloud influencing factors that contribute to winter-summer cloud amount differences, as these seasons are primarily responsible for the model discrepancies with observations. We find that differences in the total cloud amount annual cycle are primarily caused by differences in low, not high, clouds; the largest differences occur between the surface and 950hPa. Stratifying cloud amount by cloud influencing factors, we find that model groups disagree most under strong lower tropospheric stability, weak to moderate mid-tropospheric subsidence, and cold lower tropospheric air temperatures. Inter-group differences in low cloud amount are found to be a function of the dependence of low cloud amount on the lower tropospheric thermodynamic characteristics. We find that models with a larger low cloud amount in winter produce more cloud ice, whereas models with a larger low cloud amount in summer produce more cloud liquid. Thus, the parameterization of ice microphysics, specifically the ice formation mechanism (deposition vs. immersion freezing) and cloud liquid and ice partitioning, contributes to the inter-model differences in the Arctic cloud annual cycle and provides further evidence of the important role that cloud ice microphysical processes play in the evolution and modeling of the Arctic climate system.
Thomas, Manu Anna; Devasthale, Abhay; Koenigk, Torben; Wyser, Klaus; Roberts, Malcolm; Roberts, Christopher; Lohmann, KatjaThomas, M. A., A. Devasthale, T. Koenigk, K. Wyser, M. Roberts, C. Roberts, K. Lohmann, 2018: A statistical and process oriented evaluation of cloud radiative effects in high resolution global models. Geoscientific Model Development Discussions, 1-30. doi: 10.5194/gmd-2018-221. Abstract. This study evaluates the impact of atmospheric horizontal resolution on the representation of cloud radiative effects (CREs) in an ensemble of global climate model simulations following the protocols of the High Resolution Model Intercomparison Project (HighResMIP). We compare results from four European modelling centres, each of which provides data from "standard" and "high" resolution model configurations. Simulated radiative fluxes are compared with observation-based estimates derived from the Clouds and Earth's Radiant Energy System (CERES) dataset. Model CRE biases are evaluated using both conventional statistics (e.g. time and spatial averages) and after conditioning on the phase of two modes of internal climate variability, namely the El Niño and Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO). Simulated top-of-atmosphere (TOA) and surface CREs show large biases over the polar regions, particularly over regions where seasonal sea-ice variability is strongest. Increasing atmospheric resolution does not significantly improve these biases. The spatial structure of the cloud radiative response to ENSO and NAO variability is simulated reasonably well by all model configurations considered in this study. However, it is difficult to identify a systematic impact of atmospheric resolution on the associated CRE errors. Mean absolute CRE errors conditioned on ENSO phase are relatively large (5–10W/m2) and show differences between models. We suggest this is a consequence of differences in the parameterization of SW radiative transfer and the treatment of cloud optical properties rather than a result of differences in resolution. In contrast, mean absolute CRE errors conditioned on NAO phase are generally smaller (0–2W/m2) and more similar across models. Although the regional details of CRE biases show some sensitivity to atmospheric resolution within a particular model, it is difficult to identify patterns that hold across all models. This apparent insensitivity to increased atmospheric horizontal resolution indicates that physical parameterizations play a dominant role in determining the behaviour of cloud-radiation feedbacks. However, we note that these results are obtained from atmosphere-only simulations and the impact of changes in atmospheric resolution may be different in the presence of coupled climate feedbacks.
Thomas, S.; Priestley, K. J.; Smith, N. P.; Wilson, R. S.; Walikainen, D. R.; Smith, N. M.Thomas, S., K. J. Priestley, N. P. Smith, R. S. Wilson, D. R. Walikainen, N. M. Smith, 2018: Performance Stability Evaluation of Clouds and the Earth'S Radiant Energy System (CERES) Flight Model S(FMS) Instrument on S-NPP. IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 3292-3295. doi: 10.1109/IGARSS.2018.8518588. Clouds and the Earth's Radiant Energy System (CERES) Flight Model 5 (FM5) instrument is designed to continue the long-term monitoring of the Earth's radiation budget. Flight Model 5, the sixth of the CERES instrument was launched aboard the NPP spacecraft on October 2011 and it has started the Earth-viewing measurements on January 26, 2012. The CERES instrument with the three scanning sensors measure radiances in 0.3 to 5.0 micron region with Shortwave sensor, 0.3 to > 100 microns with Total sensor and 8 to 12 micron region with Window sensor. The prelaunch accuracy goal for the CERES instrument measurements is to have the emitted longwave radiances within 0.5% and the shortwave radiances within 1.0%. An accurate determination of the radiometric gains and spectral responsivity of CERES FM5 sensors was accomplished through rigorous calibrations using the primary sources. Post-launch evaluation of the sensor performance consists of sensor calibrations with the on-board sources and the solar diffuser called Mirror Attenuator Mosaic (MAM). Several validation studies utilising targets such as tropical ocean and deep convective clouds are performed as part of the CallVal protocol. This paper covers the overall performance of the CERES-FM5 instrument. The post-launch calibration and the validation results from the instrument are presented. calibration; clouds; Earth; atmospheric radiation; atmospheric techniques; CERES; Instruments; atmospheric measuring apparatus; radiometry; Sea measurements; Temperature measurement; Sensors; Market research; remote sensing; Radiometry; Calibration; CERES FM5 sensors; CERES instrument measurements; CERES-FM5 instrument; deep convective clouds; Earth radiation Budget; Earth-viewing measurements; Earth's Radiant Energy System; Earth's radiation budget; emitted longwave radiances; Flight Model 5; long-term monitoring; Mirror Attenuator Mosaic; NPP spacecraft; performance stability evaluation; post-launch calibration; post-launch evaluation; S-NPP; scanning sensors measure radiances; sensor calibrations; sensor performance; shortwave radiances; Shortwave sensor; solar diffuser; Total sensor; wavelength 0.3 micron to 5.0 micron; wavelength 8.0 micron to 12.0 micron; Window sensor
Thorsen, Tyler J.; Kato, Seiji; Loeb, Norman G.; Rose, Fred G.Thorsen, T. J., S. Kato, N. G. Loeb, F. G. Rose, 2018: Observation-Based Decomposition of Radiative Perturbations and Radiative Kernels. J. Climate, 31(24), 10039-10058. doi: 10.1175/JCLI-D-18-0045.1. The Clouds and the Earth’s Radiant Energy System (CERES)–partial radiative perturbation [PRP (CERES-PRP)] methodology applies partial-radiative-perturbation-like calculations to observational datasets to directly isolate the individual cloud, atmospheric, and surface property contributions to the variability of the radiation budget. The results of these calculations can further be used to construct radiative kernels. A suite of monthly mean observation-based inputs are used for the radiative transfer, including cloud properties from either the diurnally resolved passive-sensor-based CERES synoptic (SYN) data or the combination of the CloudSat cloud radar and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar. The CloudSat/CALIPSO cloud profiles are incorporated via a clustering method that obtains monthly mean cloud properties suitable for accurate radiative transfer calculations. The computed fluxes are validated using the TOA fluxes observed by CERES. Applications of the CERES-PRP methodology are demonstrated by computing the individual contributions to the variability of the radiation budget over multiple years and by deriving water vapor radiative kernels. The calculations for the former are used to show that an approximately linear decomposition of the total flux anomalies is achieved. The observation-based water vapor kernels were used to investigate the accuracy of the GCM-based NCAR CAM3.0 water vapor kernel. Differences between our observation-based kernel and the NCAR one are marginally larger than those inferred by previous comparisons among different GCM kernels.
Tian, Jingjing; Dong, Xiquan; Xi, Baike; Minnis, Patrick; Smith, William L.; Sun-Mack, Sunny; Thieman, Mandana; Wang, JingyuTian, J., X. Dong, B. Xi, P. Minnis, W. L. Smith, S. Sun-Mack, M. Thieman, J. Wang, 2018: Comparisons of Ice Water Path in Deep Convective Systems Among Ground-Based, GOES, and CERES-MODIS Retrievals. Journal of Geophysical Research: Atmospheres, 123(3), 1708-1723. doi: 10.1002/2017JD027498. Retrievals of convective cloud microphysical properties based on passive satellite imagery are difficult. To help quantify their uncertainties, ice water paths (IWPs) retrieved from the NASA Clouds and the Earth's Radiant Energy System project using Geostationary Operational Environmental Satellite (GOES) and Terra/Aqua MODerate-resolution Imaging Spectroradiometer observations are compared with IWPs retrieved from Next-Generation Radar (NEXRAD) observations over a large domain (32°N to 40°N and 105°W to 91°W) during the 2011 Midlatitude Continental Convective Clouds Experiment field campaign. Based on comparisons of pixel-level (4 km × 4 km) daytime IWP retrievals from NEXRAD and GOES, it is found that NEXRAD- and GOES-retrieved mean IWPs are 2.03 and 1.83 kg m−2, respectively, for ice-phase cloud in thick anvil area. Their mean difference of 0.20 kg m−2 (with 95% confidence interval: 0.14–0.26 kg m−2) is within the uncertainty of NEXRAD retrievals. However, the low correlation between pixel-to-pixel comparisons indicates a large variation in GOES-retrieved IWP. For mixed-phase clouds in thick anvil areas, in addition to IWPs, total water paths (TWPs, sum of ice and liquid water path) are estimated with aid of aircraft measurements for NEXRAD retrievals and corrected using a TWP parameterization for GOES retrievals. The mean values of estimated TWPs from NEXRAD (corrected using aircraft in situ measurements) and GOES are similar. GOES and Clouds and the Earth's Radiant Energy System-MODerate-resolution Imaging Spectroradiometer-retrieved IWPs/TWPs generally do not exceed 5 kg m−2. Large differences and low correlations exist between satellite and NEXRAD retrievals in stratiform rain areas. Possible reasons for the differences between retrievals are discussed. 0320 Cloud physics and chemistry; satellite remote sensing; 3314 Convective processes; ice particles; deep convection; 3360 Remote sensing; 0319 Cloud optics; cloud microphysics retrieval
Tornow, F.; Barker, H. W.; Blázquez, A. Velázquez; Domenech, C.; Fischer, J.Tornow, F., H. W. Barker, A. V. Blázquez, C. Domenech, J. Fischer, 2018: EarthCARE’s Broadband Radiometer: Uncertainties Associated with Cloudy Atmospheres. J. Atmos. Oceanic Technol., 35(11), 2201–2211. doi: 10.1175/JTECH-D-18-0083.1. The EarthCARE satellite’s Broadband Radiometer (BBR) consists of three telescopes and a rotating chopper drum (CD). Together they yield alternating measurements of totalwave (TW) (0.25 - >50 µm) and shortwave (SW) (0.25 - 4 µm) radiances with point-spread functions that translate to ∼0.6 km diameter pixels. The mission requires that SW and TW radiances be averaged over ∼100 km2 domains. Corresponding average longwave (LW) radiances are differences between TW and SW averages. It is shown that impacts on domain-average nadir radiances due to alternating samples of TW and SW signals for realistic cloudy atmospheres are sensitive to: variance of cloudy-sky radiances; CD rotation rate; and along-track length of averaging domains. Over 5 × 21 km domains and at 50% rotation rate, uncertainties reached up to 3.2 W m−2 sr−1 and 4.1 W m−2 sr−1 for SW and TW radiances, respectively. The BBR’s design allows for in-flight alteration of CD rate. An approximate method is provided for estimating SW and LW uncertainties due to CD rate. While the nominal rotation rate meets EarthCARE’s mission requirements, reducing below ∼75% of that rate will lead to uncertainties for domain-average LW radiances that will often exceed mission requirements. This could be mitigated by increasing the size of averaging domains, but that would compromise the BBR’s role in EarthCARE’s radiative closure assessment programme. Uncertainties for off-nadir radiances are largely free of impacts arising from changes to CD rotation rate.
Tornow, Florian; Preusker, René; Domenech, Carlos; Carbajal Henken, Cintia; Testorp, Sören; Fischer, Jürgen; Tornow, Florian; Preusker, René; Domenech, Carlos; Carbajal Henken, Cintia K.; Testorp, Sören; Fischer, JürgenTornow, F., R. Preusker, C. Domenech, C. Carbajal Henken, S. Testorp, J. Fischer, F. Tornow, R. Preusker, C. Domenech, C. K. Carbajal Henken, S. Testorp, J. Fischer, 2018: Top-of-Atmosphere Shortwave Anisotropy over Liquid Clouds: Sensitivity to Clouds’ Microphysical Structure and Cloud-Topped Moisture. Atmosphere, 9(7), 256. doi: 10.3390/atmos9070256. We investigated whether Top-of-Atmosphere Shortwave (TOA SW) anisotropy—essential to convert satellite-based instantaneous TOA SW radiance measurements into TOA SW fluxes—is sensitive to cloud-top effective radii and cloud-topped water vapor. Using several years of CERES SSF Edition 4 data—filtered for overcast, horizontally homogeneous, low-level and single-layer clouds of cloud optical thickness 10—as well as broadband radiative transfer simulations, we built refined empirical Angular Distribution Models (ADMs). The ADMs showed that anisotropy fluctuated particularly around the cloud bow and cloud glory (up to 2.9–8.0%) for various effective radii and at highest and lowest viewing zenith angles under varying amounts of cloud-topped moisture (up to 1.3–6.4%). As a result, flux estimates from refined ADMs differed from CERES estimates by up to 20 W m−2 at particular combinations of viewing and illumination geometry. Applied to CERES cross-track observation of January and July 2007—utilized to generate global radiation budget climatologies for benchmark comparisons with global climate models—we found that such differences between refined and CERES ADMs introduced large-scale biases of 1–2 W m−2 and on regional levels of up to 10 W m−2. Such biases could be attributed in part to low cloud-top effective radii (about 8 μm) and low cloud-topped water vapor (1.7 kg m−2) and in part to an inopportune correlation of viewing and illumination conditions with temporally varying effective radii and cloud-topped moisture, which failed to compensate towards vanishing flux bias. This work may help avoid sampling biases due to discrepancies between individual samples and the median cloud-top effective radii and cloud-top moisture conditions represented in current ADMs. CERES; energy budget; broadband radiative transfer simulations; cloud effective radius; upper-tropospheric humidity
Tozuka, Tomoki; Oettli, PascalTozuka, T., P. Oettli, 2018: Asymmetric Cloud-Shortwave Radiation-Sea Surface Temperature Feedback of Ningaloo Niño/Niña. Geophysical Research Letters, 45(18), 9870-9879. doi: 10.1029/2018GL079869. Using observational and reanalysis data, the cloud-shortwave radiation-sea surface temperature (SST) feedback in the Ningaloo Niño/Niña region off the west coast of Australia is examined. It is found that this feedback operates as a negative feedback for positive SST anomalies and as a positive feedback for negative SST anomalies. This asymmetry is due to variation in the dominant cloud amount with SST. For positive SST anomalies, a decrease in the shortwave radiation resulting from an increase in high cloud amount associated with deep convection prevails, because SSTs in this region are relatively high compared to other eastern boundary regions and close to the convective threshold. Conversely, the region is under the influence of the subtropical high, and a decrease in the surface shortwave radiation associated with an increase in low cloud amount is dominant for negative SST anomalies. sea surface temperature; cloud amount; marine heatwave; Ningaloo Niño/Niña; ocean-atmosphere interaction; shortwave radiation
Trenberth, Kevin E.; Cheng, Lijing; Jacobs, Peter; Zhang, Yongxin; Fasullo, JohnTrenberth, K. E., L. Cheng, P. Jacobs, Y. Zhang, J. Fasullo, 2018: Hurricane Harvey Links to Ocean Heat Content and Climate Change Adaptation. Earth's Future, 6, 730-744. doi: 10.1029/2018EF000825. While hurricanes occur naturally, human-caused climate change is supercharging them and exacerbating the risk of major damage. Here using ocean and atmosphere observations, we demonstrate links between increased upper ocean heat content due to global warming with the extreme rainfalls from recent hurricanes. Hurricane Harvey provides an excellent case study as it was isolated in space and time. We show that prior to the beginning of northern summer of 2017, ocean heat content was the highest on record both globally and in the Gulf of Mexico, but the latter sharply decreased with hurricane Harvey via ocean evaporative cooling. The lost ocean heat was realized in the atmosphere as moisture, and then as latent heat in record-breaking heavy rainfalls. Accordingly, record high ocean heat values not only increased the fuel available to sustain and intensify Harvey but also increased its flooding rains on land. Harvey could not have produced so much rain without human-induced climate change. Results have implications for the role of hurricanes in climate. Proactive planning for the consequences of human-caused climate change is not happening in many vulnerable areas, making the disasters much worse. rainfall; climate change; extreme events; adaptation; hurricane; ocean heat content
Trenberth, Kevin E.; Fasullo, John T.Trenberth, K. E., J. T. Fasullo, 2018: Applications of an updated atmospheric energetics formulation. J. Climate, 31(16), 6263–6279. doi: 10.1175/JCLI-D-17-0838.1. As observations and atmospheric reanalyses have improved, the diagnostics that can be computed with confidence also increase. Accordingly, a new formulation of the energetics of the atmosphere is laid out with a view to advancing diagnostic studies of the Earth’s energy budget and flows. It is utilized to produce assessments of the vertically-integrated divergences in both the atmosphere and ocean. Careful conservation of mass is required, with special attention to the hydrological cycle and redistribution of mass associated with precipitation and evaporation, and a new method for ensuring this is developed. It guarantees that the atmospheric divergence is associated with moisture and precipitation, unlike previous methods. A new term, identified as associated with the enthalpy of precipitation, is included in a preliminary way. It is sensitive to the formulation, and use of temperature in degrees Celsius instead of Kelvin greatly reduces errors and produces the extra term with values up to about ±5 W m-2. New results for 2000 to 2016 are presented for the vertical mean and annual mean diabatic atmospheric heating, atmospheric moistening, and total atmospheric energy divergence. Results for the atmospheric divergence are combined with top-of-atmosphere radiation observations to deduce total surface energy fluxes. Along with estimates of changes in ocean heat content, the Atlantic Ocean meridional heat transports are re-computed for March 2000 through 2013. The new results are compared with previous estimates and an assessment is made of the effects of the new mass balance, change in temperature scale, and the extra precipitation enthalpy term.
Trishchenko, Alexander P.; Wang, ShusenTrishchenko, A. P., S. Wang, 2018: Variations of climate, surface energy budget and minimum snow/ice extent over Canadian Arctic landmass for 2000-2016. J. Climate, 31(3), 1155–1172. doi: 10.1175/JCLI-D-17-0198.1. Snow and ice over land are important hydrological resources and sensitive indicators of climate change. The Moderate Resolution Imaging Spectroradiometer (MODIS) dataset at 250m spatial resolution generated at the Canada Centre for Remote Sensing (CCRS) is used to derive the annual minimum snow and ice (MSI) extent over the Canadian Arctic landmass over a 17-year time span (2000-2016). The smallest MSI extent 1.53×105 km2 was observed in 2012, the largest 2.09×105 km2 was observed in 2013, while the average value was 1.70×105 km2. Several re-analyses and observational datasets are assessed to explain the derived MSI variations: ERA-Interim reanalysis, North American Regional Reanalysis (NARR), Clouds and the Earth’s Radiant Energy System (CERES) radiative fluxes, and European Space Agency’s GlobSnow dataset. Comparison with the Randolph Glacier Inventory (RGI) showed two important facts: 1) the semi-permanent snowpack in the Canadian Arctic which persists through the entire melting season is a significant component relative to the ice caps and glacier-covered areas (up to 36% or 5.58×104 km2); 2) the MSI variations are related to variations in the local climate dynamics such as warm season average temperature, energy fluxes and snow cover. The correlation coefficients (absolute values) can be as high as 0.77. The reanalysis-based MSI estimates agree with satellite MSI results (the average bias of 2.2·103km2 or 1.3% of the mean value).
Tsujino, Hiroyuki; Urakawa, Shogo; Nakano, Hideyuki; Small, R. Justin; Kim, Who M.; Yeager, Stephen G.; Danabasoglu, Gokhan; Suzuki, Tatsuo; Bamber, Jonathan L.; Bentsen, Mats; Böning, Claus W.; Bozec, Alexandra; Chassignet, Eric P.; Curchitser, Enrique; Boeira Dias, Fabio; Durack, Paul J.; Griffies, Stephen M.; Harada, Yayoi; Ilicak, Mehmet; Josey, Simon A.; Kobayashi, Chiaki; Kobayashi, Shinya; Komuro, Yoshiki; Large, William G.; Le Sommer, Julien; Marsland, Simon J.; Masina, Simona; Scheinert, Markus; Tomita, Hiroyuki; Valdivieso, Maria; Yamazaki, DaiTsujino, H., S. Urakawa, H. Nakano, R. J. Small, W. M. Kim, S. G. Yeager, G. Danabasoglu, T. Suzuki, J. L. Bamber, M. Bentsen, C. W. Böning, A. Bozec, E. P. Chassignet, E. Curchitser, F. Boeira Dias, P. J. Durack, S. M. Griffies, Y. Harada, M. Ilicak, S. A. Josey, C. Kobayashi, S. Kobayashi, Y. Komuro, W. G. Large, J. Le Sommer, S. J. Marsland, S. Masina, M. Scheinert, H. Tomita, M. Valdivieso, D. Yamazaki, 2018: JRA-55 based surface dataset for driving ocean–sea-ice models (JRA55-do). Ocean Modelling, 130, 79-139. doi: 10.1016/j.ocemod.2018.07.002. We present a new surface-atmospheric dataset for driving ocean–sea-ice models based on Japanese 55-year atmospheric reanalysis (JRA-55), referred to here as JRA55-do. The JRA55-do dataset aims to replace the CORE interannual forcing version 2 (hereafter called the CORE dataset), which is currently used in the framework of the Coordinated Ocean-ice Reference Experiments (COREs) and the Ocean Model Intercomparison Project (OMIP). A major improvement in JRA55-do is the refined horizontal grid spacing ( ∼ 55 km) and temporal interval (3 hr). The data production method for JRA55-do essentially follows that of the CORE dataset, whereby the surface fields from an atmospheric reanalysis are adjusted relative to reference datasets. To improve the adjustment method, we use high-quality products derived from satellites and from several other atmospheric reanalysis projects, as well as feedback on the CORE dataset from the ocean modelling community. Notably, the surface air temperature and specific humidity are adjusted using multi-reanalysis ensemble means. In JRA55-do, the downwelling radiative fluxes and precipitation, which are affected by an ambiguous cloud parameterisation employed in the atmospheric model used for the reanalysis, are based on the reanalysis products. This approach represents a notable change from the CORE dataset, which imported independent observational products. Consequently, the JRA55-do dataset is more self-contained than the CORE dataset, and thus can be continually updated in near real-time. The JRA55-do dataset extends from 1958 to the present, with updates expected at least annually. This paper details the adjustments to the original JRA-55 fields, the scientific rationale for these adjustments, and the evaluation of JRA55-do. The adjustments successfully corrected the biases in the original JRA-55 fields. The globally averaged features are similar between the JRA55-do and CORE datasets, implying that JRA55-do can suitably replace the CORE dataset for use in driving global ocean–sea-ice models. Surface fluxes; COREs; JRA55-do; Ocean model forcing; OMIP
Van Weverberg K.; Morcrette C. J.; Petch J.; Klein S. A.; Ma H.‐Y.; Zhang C.; Xie S.; Tang Q.; Gustafson W. I.; Qian Y.; Berg L. K.; Liu Y.; Huang M.; Ahlgrimm M.; Forbes R.; Bazile E.; Roehrig R.; Cole J.; Merryfield W.; Lee W.‐S.; Cheruy F.; Mellul L.; Wang Y.‐C.; Johnson K.; Thieman M. M.Van Weverberg K., ., . Morcrette C. J., . Petch J., . Klein S. A., . Ma H.‐Y., . Zhang C., . Xie S., . Tang Q., . Gustafson W. I., . Qian Y., . Berg L. K., . Liu Y., . Huang M., . Ahlgrimm M., . Forbes R., . Bazile E., . Roehrig R., . Cole J., . Merryfield W., . Lee W.‐S., . Cheruy F., . Mellul L., . Wang Y.‐C., . Johnson K., . Thieman M. M., 2018: CAUSES: Attribution of Surface Radiation Biases in NWP and Climate Models near the U.S. Southern Great Plains. Journal of Geophysical Research: Atmospheres, 123(7), 3612-3644. doi: 10.1002/2017JD027188. Abstract Many Numerical Weather Prediction (NWP) and climate models exhibit too warm lower tropospheres near the midlatitude continents. The warm bias has been shown to coincide with important surface radiation biases that likely play a critical role in the inception or the growth of the warm bias. This paper presents an attribution study on the net radiation biases in nine model simulations, performed in the framework of the CAUSES project (Clouds Above the United States and Errors at the Surface). Contributions from deficiencies in the surface properties, clouds, water vapor, and aerosols are quantified, using an array of radiation measurement stations near the Atmospheric Radiation Measurement Southern Great Plains site. Furthermore, an in?depth analysis is shown to attribute the radiation errors to specific cloud regimes. The net surface shortwave radiation is overestimated in all models throughout most of the simulation period. Cloud errors are shown to contribute most to this overestimation, although nonnegligible contributions from the surface albedo exist in most models. Missing deep cloud events and/or simulating deep clouds with too weak cloud radiative effects dominate in the cloud?related radiation errors. Some models have compensating errors between excessive occurrence of deep cloud but largely underestimating their radiative effect, while other models miss deep cloud events altogether. Surprisingly, even the latter models tend to produce too much and too frequent afternoon surface precipitation. This suggests that rather than issues with the triggering of deep convection, cloud radiative deficiencies are related to too weak convective cloud detrainment and too large precipitation efficiencies. clouds; radiation; warm bias; attribution; CAUSES
Vinayachandran, P. N.; Matthews, Adrian J.; Vijay Kumar, K.; Sanchez-Franks, Alejandra; Thushara, V.; George, Jenson; Vijith, V.; Webber, Benjamin G. M.; Queste, Bastien Y.; Roy, Rajdeep; Sarkar, Amit; Baranowski, Dariusz B.; Bhat, G. S.; Klingaman, Nicholas P.; Peatman, Simon C.; Parida, C.; Heywood, Karen J.; Hall, Robert; King, Brian; Kent, Elizabeth C.; Nayak, Anoop A.; Neema, C. P.; Amol, P.; Lotliker, A.; Kankonkar, A.; Gracias, D. G.; Vernekar, S.; D.Souza, A. C.; Valluvan, G.; Pargaonkar, Shrikant M.; Dinesh, K.; Giddings, Jack; Joshi, ManojVinayachandran, P. N., A. J. Matthews, K. Vijay Kumar, A. Sanchez-Franks, V. Thushara, J. George, V. Vijith, B. G. M. Webber, B. Y. Queste, R. Roy, A. Sarkar, D. B. Baranowski, G. S. Bhat, N. P. Klingaman, S. C. Peatman, C. Parida, K. J. Heywood, R. Hall, B. King, E. C. Kent, A. A. Nayak, C. P. Neema, P. Amol, A. Lotliker, A. Kankonkar, D. G. Gracias, S. Vernekar, A. C. D.Souza, G. Valluvan, S. M. Pargaonkar, K. Dinesh, J. Giddings, M. Joshi, 2018: BoBBLE (Bay of Bengal Boundary Layer Experiment): Ocean–atmosphere interaction and its impact on the South Asian monsoon. Bull. Amer. Meteor. Soc., 99(8), 1569–1587. doi: 10.1175/BAMS-D-16-0230.1. A field experiment in the southern Bay of Bengal to generate new high-quality in situ observational data sets of the ocean, air–sea interface and atmosphere during the summer monsoon.
Voosen, PaulVoosen, P., 2018: NASA climate mission Trump tried to kill moves forward. Science | AAAS. After 1.5-year delay, agency revives the Climate Absolute Radiance and Refractivity Observatory Pathfinder
Wall, Casey J.; Hartmann, Dennis L.Wall, C. J., D. L. Hartmann, 2018: Balanced cloud radiative effects across a range of dynamical conditions over the tropical west Pacific. Geophysical Research Letters, 45(20), 11,490-11,498. doi: 10.1029/2018GL080046. Instantaneous relationships between clouds and large-scale vertical motion are used to study the impact of circulation on the near-cancellation of cloud radiative effects that is observed over the tropical west Pacific Ocean. The coverage of deep-convective clouds increases with stronger upward motion, but the proportion of thick, medium, and thin anvil cloud remains nearly constant. Thus, when averaging over scales larger than individual storms, the top-of-atmosphere net radiation is only weakly sensitive to the large-scale flow. The balance in cloud radiative effects is therefore maintained across a wide range of large-scale circulations. The ability of the Community Atmosphere Model Version 5 (CAM5) to reproduce the observed cloud-circulation relationships is investigated. The simulated convective clouds substantially overestimate the proportion of deep and optically thick cloud, and underestimate the proportion of anvil cirrus. These results demonstrate that simulating key properties of deep-convective clouds remains challenging for some state-of-the-art climate models. Clouds; Tropical Convection
Wall, Casey J.; Hartmann, Dennis L.; Thieman, Mandana M.; Smith, William L.; Minnis, PatrickWall, C. J., D. L. Hartmann, M. M. Thieman, W. L. Smith, P. Minnis, 2018: The Life Cycle of Anvil Clouds and the Top-of-Atmosphere Radiation Balance over the Tropical West Pacific. J. Climate, 31(24), 10059-10080. doi: 10.1175/JCLI-D-18-0154.1. Observations from a geostationary satellite are used to study the life cycle of mesoscale convective systems (MCS), their associated anvil clouds, and their effects on the radiation balance over the warm pool of the tropical western Pacific Ocean. In their developing stages, MCS primarily consist of clouds that are optically thick and have a negative net cloud radiative effect (CRE). As MCS age, ice crystals in the anvil become larger, the cloud top lowers somewhat, and cloud radiative effects decrease in magnitude. Shading from anvils causes cool anomalies in the underlying sea surface temperature (SST) of up to −0.6°C. MCS often occur in clusters that are embedded within large westward-propagating disturbances, and therefore shading from anvils can cool SSTs over regions spanning hundreds of kilometers. Triggering of convection is more likely to follow a warm SST anomaly than a cold SST anomaly on a time scale of several days. This information is used to evaluate hypotheses for why, over the warm pool, the average shortwave and longwave CRE are individually large but nearly cancel. The results are consistent with the hypothesis that the cancellation in CRE is caused by feedbacks among cloud albedo, large-scale circulation, and SST.
Wang, Fang; Yang, SongWang, F., S. Yang, 2018: Can CFMIP2 models reproduce the leading modes of cloud vertical structure in the CALIPSO-GOCCP observations?. Theoretical and Applied Climatology, 131(3-4), 1465-1477. doi: 10.1007/s00704-017-2051-7. Using principal component (PC) analysis, three leading modes of cloud vertical structure (CVS) are revealed by the GCM-Oriented CALIPSO Cloud Product (GOCCP), i.e. tropical high, subtropical anticyclonic and extratropical cyclonic cloud modes (THCM, SACM and ECCM, respectively). THCM mainly reflect the contrast between tropical high clouds and clouds in middle/high latitudes. SACM is closely associated with middle-high clouds in tropical convective cores, few-cloud regimes in subtropical anticyclonic clouds and stratocumulus over subtropical eastern oceans. ECCM mainly corresponds to clouds along extratropical cyclonic regions. Models of phase 2 of Cloud Feedback Model Intercomparison Project (CFMIP2) well reproduce the THCM, but SACM and ECCM are generally poorly simulated compared to GOCCP. Standardized PCs corresponding to CVS modes are generally captured, whereas original PCs (OPCs) are consistently underestimated (overestimated) for THCM (SACM and ECCM) by CFMIP2 models. The effects of CVS modes on relative cloud radiative forcing (RSCRF/RLCRF) (RSCRF being calculated at the surface while RLCRF at the top of atmosphere) are studied in terms of principal component regression method. Results show that CFMIP2 models tend to overestimate (underestimated or simulate the opposite sign) RSCRF/RLCRF radiative effects (REs) of ECCM (THCM and SACM) in unit global mean OPC compared to observations. These RE biases may be attributed to two factors, one of which is underestimation (overestimation) of low/middle clouds (high clouds) (also known as stronger (weaker) REs in unit low/middle (high) clouds) in simulated global mean cloud profiles, the other is eigenvector biases in CVS modes (especially for SACM and ECCM). It is suggested that much more attention should be paid on improvement of CVS, especially cloud parameterization associated with particular physical processes (e.g. downwelling regimes with the Hadley circulation, extratropical storm tracks and others), which may be crucial to reduce the CRF biases in current climate models.
Wang, Kai; Zhang, Yang; Zhang, Xin; Fan, Jiwen; Leung, L. Ruby; Zheng, Bo; Zhang, Qiang; He, KebinWang, K., Y. Zhang, X. Zhang, J. Fan, L. R. Leung, B. Zheng, Q. Zhang, K. He, 2018: Fine-scale application of WRF-CAM5 during a dust storm episode over East Asia: Sensitivity to grid resolutions and aerosol activation parameterizations. Atmospheric Environment, 176, 1-20. doi: 10.1016/j.atmosenv.2017.12.014. An advanced online-coupled meteorology and chemistry model WRF-CAM5 has been applied to East Asia using triple-nested domains at different grid resolutions (i.e., 36-, 12-, and 4-km) to simulate a severe dust storm period in spring 2010. Analyses are performed to evaluate the model performance and investigate model sensitivity to different horizontal grid sizes and aerosol activation parameterizations and to examine aerosol-cloud interactions and their impacts on the air quality. A comprehensive model evaluation of the baseline simulations using the default Abdul-Razzak and Ghan (AG) aerosol activation scheme shows that the model can well predict major meteorological variables such as 2-m temperature (T2), water vapor mixing ratio (Q2), 10-m wind speed (WS10) and wind direction (WD10), and shortwave and longwave radiation across different resolutions with domain-average normalized mean biases typically within ±15%. The baseline simulations also show moderate biases for precipitation and moderate-to-large underpredictions for other major variables associated with aerosol-cloud interactions such as cloud droplet number concentration (CDNC), cloud optical thickness (COT), and cloud liquid water path (LWP) due to uncertainties or limitations in the aerosol-cloud treatments. The model performance is sensitive to grid resolutions, especially for surface meteorological variables such as T2, Q2, WS10, and WD10, with the performance generally improving at finer grid resolutions for those variables. Comparison of the sensitivity simulations with an alternative (i.e., the Fountoukis and Nenes (FN) series scheme) and the default (i.e., AG scheme) aerosol activation scheme shows that the former predicts larger values for cloud variables such as CDNC and COT across all grid resolutions and improves the overall domain-average model performance for many cloud/radiation variables and precipitation. Sensitivity simulations using the FN series scheme also have large impacts on radiations, T2, precipitation, and air quality (e.g., decreasing O3) through complex aerosol-radiation-cloud-chemistry feedbacks. The inclusion of adsorptive activation of dust particles in the FN series scheme has similar impacts on the meteorology and air quality but to lesser extent as compared to differences between the FN series and AG schemes. Compared to the overall differences between the FN series and AG schemes, impacts of adsorptive activation of dust particles can contribute significantly to the increase of total CDNC (∼45%) during dust storm events and indicate their importance in modulating regional climate over East Asia. East Asia; Dust storm; WRF-CAM5; Adsorptive activation; Aerosol activation; Nested simulations
Wang, Tianxing; Shi, Jiancheng; Yu, Yuechi; Husi, Letu; Gao, Bo; Zhou, Wang; Ji, Dabin; Zhao, Tianjie; Xiong, Chuan; Chen, LingWang, T., J. Shi, Y. Yu, L. Husi, B. Gao, W. Zhou, D. Ji, T. Zhao, C. Xiong, L. Chen, 2018: Cloudy-sky land surface longwave downward radiation (LWDR) estimation by integrating MODIS and AIRS/AMSU measurements. Remote Sensing of Environment, 205, 100-111. doi: 10.1016/j.rse.2017.11.011. Longwave downward radiation (LWDR) is another major energy source received by the earth's surface apart from solar radiation. Its importance in regulating air temperature and balancing surface energy is enlarged especially under cloudy-sky conditions. Unfortunately, to date, a large number of efforts have been made to derive LWDR from space under only clear-sky conditions leading to difficulty in utilizing space-based LWDR in most models due to its spatio-temporal discontinuity. Currently, only a few studies are focused on LWDR estimation under cloudy skies, while their global application is still questionable. In this paper, an alternative strategy is proposed aiming to derive high-resolution (1 km) cloudy-sky LWDR by fusing collocated satellite multi-sensor measurements. The results show that the newly developed method works well and can derive LWDR at a better accuracy with RMSE < 27 W/m2 and bias < 10 W/m2 even under cloudy skies and at 1 km scales. By comparing the CCCM and SSF products of CERES, MERRA, ERA-interim and NCEP-CSFR over the Tibetan Plateau region, the new approach demonstrates its superiority in terms of accuracy, temporal variation and spatial distribution patterns of LWDR. Comprehensive comparison analysis also reveals that, except for the proposed product, the other four products (CERES, MERRA, ERA-interim and NCEP-CSFR) show a big difference from each other in the LWDR spatio-temporal distribution pattern and magnitude. The difference between these products can still be up to 60 W/m2 even at the monthly scale, implying that large uncertainties exist in current LWDR estimations. More importantly, besides the higher accuracy of the proposed method, it provides unprecedented possibilities for jointly generating high-resolution global LWDR datasets by connecting the NASA's Earth Observing System-(EOS) mission (MODIS-AIRS/AMSU) and the Suomi National Polar-orbiting Partnership-(NPP) mission (VIIRS-CrIS/ATMS). Meanwhile, the scheme proposed in this study also gives some clues towards multiple data fusing in the remote sensing community. MODIS; AIRS/AMSU; Cloudy sky; Land surface longwave downward radiation; The Tibetan Plateau
Wang, Yawen; Trentmann, Jörg; Yuan, Wenping; Wild, MartinWang, Y., J. Trentmann, W. Yuan, M. Wild, 2018: Validation of CM SAF CLARA-A2 and SARAH-E Surface Solar Radiation Datasets over China. Remote Sensing, 10(12), 1977. doi: 10.3390/rs10121977. To achieve high-quality surface solar radiation (SSR) data for climate monitoring and analysis, the two satellite-derived monthly SSR datasets of CM SAF CLARA-A2 and SARAH-E have been validated against a homogenized ground-based dataset covering 59 stations across China for 1993–2015 and 1999–2015, respectively. The satellite products overestimate surface solar irradiance by 10.0 W m−2 in CLARA-A2 and 7.5 W m−2 in SARAH-E on average. A strong urbanization effect has been noted behind the large positive bias in China. The bias decreased after 2004, possibly linked to a weakened attenuating effect of aerosols on radiation in China. Both satellite datasets can reproduce the monthly anomalies of SSR, indicated by a significant correlation around 0.8. Due to the neglection of temporal aerosol variability in the satellite algorithms, the discrepancy between the satellite-estimated and ground-observed SSR trends slightly increases in 1999–2015 as compared to 1993–2015. The seasonal performance of the satellite products shows a better accuracy during warm than cold seasons. With respect to the spatial performance, the effects from anthropogenic aerosols, dust aerosols and high elevation and snow-covered surfaces should be well considered in the satellite SSR retrievals to further improve the performance in the eastern, northwestern and southwestern parts of China, respectively. validation; surface solar radiation; satellite; China; solar brightening
Wang, Yong; Zhang, Guang J.; Jiang, YiquanWang, Y., G. J. Zhang, Y. Jiang, 2018: Linking Stochasticity of Convection to Large-Scale Vertical Velocity to Improve Indian Summer Monsoon Simulation in the NCAR CAM5. J. Climate, 31(17), 6985-7002. doi: 10.1175/JCLI-D-17-0785.1. The Plant–Craig (PC) stochastic convective parameterization scheme is modified by linking the stochastic generation of convective clouds to the change of large-scale vertical pressure velocity at 500 hPa with time so as to better account for the relationship between convection and the large-scale environment. Three experiments using the National Center for Atmospheric Research (NCAR) Community Atmosphere Model, version 5 (CAM5), are conducted: one with the default Zhang–McFarlane deterministic convective scheme, another with the original PC stochastic scheme, and a third with the modified PC stochastic scheme. Evaluation is focused on the simulation of the Indian summer monsoon (ISM), which is a long-standing challenge for all current global circulation models. Results show that the modified stochastic scheme better represents the annual cycle of the climatological mean rainfall over central India and the mean onset date of ISM compared to other simulations. Also, for the simulations of ISM intraseasonal variability for quasi-biweekly and 30–60-day modes, the modified stochastic parameterization produces more realistic propagation and magnitude, especially for the observed northeastward movement of the 30–60-day mode, for which the other two simulations show the propagation in the opposite direction. Causes are investigated through a moisture budget analysis. Compared to the other two simulations, the modified stochastic scheme with an appropriate representation of convection better represents the patterns and amplitudes of large-scale dynamical convergence and moisture advection and thus corrects the monsoon cycle associated with their covariation during the peaks and troughs of intraseasonal oscillation.
Weatherhead, Betsy; Wielicki, Bruce A.; Ramaswamy, V.; Abbott, Mark; Ackerman, Thomas; Atlas, Robert; Brasseur, Guy; Bruhwiler, Lori; Busalacchi, Antonio; Butler, James H.; Clack, Christopher T. M.; Cooke, Roger; Cucurull, Lidia; Davis, Sean; English, Jason M.; Fahey, David W.; Fine, Steven S.; Lazo, Jeffrey K.; Liang, Shunlin; Loeb, Norman G.; Rignot, Eric; Soden, Brian; Stanitski, Diane; Stephens, Graeme; Tapley, Byron; Thompson, Anne M.; Trenberth, Kevin E.; Wuebbles, DonaldWeatherhead, B., B. A. Wielicki, V. Ramaswamy, M. Abbott, T. Ackerman, R. Atlas, G. Brasseur, L. Bruhwiler, A. Busalacchi, J. H. Butler, C. T. M. Clack, R. Cooke, L. Cucurull, S. Davis, J. M. English, D. W. Fahey, S. S. Fine, J. K. Lazo, S. Liang, N. G. Loeb, E. Rignot, B. Soden, D. Stanitski, G. Stephens, B. Tapley, A. M. Thompson, K. E. Trenberth, D. Wuebbles, 2018: Designing the Climate Observing System of the Future. Earth's Future, 6(1), 80-102. doi: 10.1002/2017EF000627. Climate observations are needed to address a large range of important societal issues including sea level rise, droughts, floods, extreme heat events, food security, and fresh water availability in the coming decades. Past, targeted investments in specific climate questions have resulted in tremendous improvements in issues important to human health, security, and infrastructure. However, the current climate observing system was not planned in a comprehensive, focused manner required to adequately address the full range of climate needs. A potential approach to planning the observing system of the future is presented in this paper. First, this paper proposes that priority be given to the most critical needs as identified within the World Climate Research Program as Grand Challenges. These currently include seven important topics: Melting Ice and Global Consequences; Clouds, Circulation and Climate Sensitivity; Carbon Feedbacks in the Climate System; Understanding and Predicting Weather and Climate Extremes; Water for the Food Baskets of the World; Regional Sea-Level Change and Coastal Impacts; and Near-term Climate Prediction. For each Grand Challenge, observations are needed for long-term monitoring, process studies and forecasting capabilities. Second, objective evaluations of proposed observing systems, including satellites, ground-based and in situ observations as well as potentially new, unidentified observational approaches, can quantify the ability to address these climate priorities. And third, investments in effective climate observations will be economically important as they will offer a magnified return on investment that justifies a far greater development of observations to serve society's needs. 1699 General or miscellaneous; climate observations; Climate Observing System Simulation Experiments; Economic Value; Grand Challenges; Value of Information
Wehrli, Kathrin; Guillod, Benoit P.; Hauser, Mathias; Leclair, Matthieu; Seneviratne, Sonia I.Wehrli, K., B. P. Guillod, M. Hauser, M. Leclair, S. I. Seneviratne, 2018: Assessing the Dynamic Versus Thermodynamic Origin of Climate Model Biases. Geophysical Research Letters, 45(16), 8471-8479. doi: 10.1029/2018GL079220. Global climate models present systematic biases, among others, a tendency to overestimate hot and dry summers in midlatitude regions. Here we investigate the origin of such biases in the Community Earth System Model. To disentangle the contribution of dynamics and thermodynamics, we perform simulations that include nudging of horizontal wind and compare them to simulations with a free atmosphere. Prescribing the observed large-scale circulation improves the modeled weather patterns as well as many related fields. However, the larger part of the temperature and precipitation biases of the free atmosphere configuration remains after nudging, in particular, for extremes. Our results suggest that thermodynamical processes, including land-atmosphere coupling and atmospheric parameterizations, drive the errors present in Community Earth System Model. Our result may apply to other climate models and highlight the importance of distinguishing thermodynamic and dynamic sources of biases in present-day global climate models. atmospheric nudging; global climate models; Earth system models; climate model biases; dynamics versus thermodynamics; systematic biases
Wei, Wei; Li, Wenhong; Deng, Yi; Yang, Song; Jiang, Jonathan H.; Huang, Lei; Liu, W. TimothyWei, W., W. Li, Y. Deng, S. Yang, J. H. Jiang, L. Huang, W. T. Liu, 2018: Dynamical and thermodynamical coupling between the North Atlantic subtropical high and the marine boundary layer clouds in boreal summer. Climate Dynamics, 50(7), 2457-2469. doi: 10.1007/s00382-017-3750-6. This study investigates dynamical and thermodynamical coupling between the North Atlantic subtropical high (NASH), marine boundary layer (MBL) clouds, and the local sea surface temperatures (SSTs) over the North Atlantic in boreal summer for 1984–2009 using NCEP/DOE Reanalysis 2 dataset, various cloud data, and the Hadley Centre sea surface temperature. On interannual timescales, the summer mean subtropical MBL clouds to the southeast of the NASH is actively coupled with the NASH and local SSTs: a stronger (weaker) NASH is often accompanied with an increase (a decrease) of MBL clouds and abnormally cooler (warmer) SSTs along the southeast flank of the NASH. To understand the physical processes between the NASH and the MBL clouds, the authors conduct a data diagnostic analysis and implement a numerical modeling investigation using an idealized anomalous atmospheric general circulation model (AGCM). Results suggest that significant northeasterly anomalies in the southeast flank of the NASH associated with an intensified NASH tend to induce stronger cold advection and coastal upwelling in the MBL cloud region, reducing the boundary surface temperature. Meanwhile, warm advection associated with the easterly anomalies from the African continent leads to warming over the MBL cloud region at 700 hPa. Such warming and the surface cooling increase the atmospheric static stability, favoring growth of the MBL clouds. The anomalous diabatic cooling associated with the growth of the MBL clouds dynamically excites an anomalous anticyclone to its north and contributes to strengthening of the NASH circulation in its southeast flank. The dynamical and thermodynamical couplings and their associated variations in the NASH, MBL clouds, and SSTs constitute an important aspect of the summer climate variability over the North Atlantic.
Williams, K. D.; Copsey, D.; Blockley, E. W.; Bodas-Salcedo, A.; Calvert, D.; Comer, R.; Davis, P.; Graham, T.; Hewitt, H. T.; Hill, R.; Hyder, P.; Ineson, S.; Johns, T. C.; Keen, A. B.; Lee, R. W.; Megann, A.; Milton, S. F.; Rae, J. G. L.; Roberts, M. J.; Scaife, A. A.; Schiemann, R.; Storkey, D.; Thorpe, L.; Watterson, I. G.; Walters, D. N.; West, A.; Wood, R. A.; Woollings, T.; Xavier, P. K.Williams, K. D., D. Copsey, E. W. Blockley, A. Bodas-Salcedo, D. Calvert, R. Comer, P. Davis, T. Graham, H. T. Hewitt, R. Hill, P. Hyder, S. Ineson, T. C. Johns, A. B. Keen, R. W. Lee, A. Megann, S. F. Milton, J. G. L. Rae, M. J. Roberts, A. A. Scaife, R. Schiemann, D. Storkey, L. Thorpe, I. G. Watterson, D. N. Walters, A. West, R. A. Wood, T. Woollings, P. K. Xavier, 2018: The Met Office Global Coupled Model 3.0 and 3.1 (GC3.0 & GC3.1) Configurations. Journal of Advances in Modeling Earth Systems, 10(2), 357-380. doi: 10.1002/2017MS001115. The Global Coupled 3 (GC3) configuration of the Met Office Unified Model is presented. Amongst other applications, GC3 is the basis of the United Kingdom's submission to the Coupled Model Intercomparison Project 6 (CMIP6). This paper documents the model components that make up the configuration (although the scientific description of these components are in companion papers), and details the coupling between them. The performance of GC3 is assessed in terms of mean biases and variability in long climate simulations using present-day forcing. The suitability of the configuration for predictability on shorter timescales (weather and seasonal forecasting) is also briefly discussed. The performance of GC3 is compared against GC2, the previous Met Office coupled model configuration, and against an older configuration (HadGEM2-AO) which was the submission to CMIP5. In many respects, the performance of GC3 is comparable with GC2, however there is a notable improvement in the Southern Ocean warm sea surface temperature bias which has been reduced by 75%, and there are improvements in cloud amount and some aspects of tropical variability. Relative to HadGEM2-AO, many aspects of the present-day climate are improved in GC3 including tropospheric and stratospheric temperature structure, most aspects of tropical and extra-tropical variability and top-of-atmosphere & surface fluxes. A number of outstanding errors are identified including a residual asymmetric sea surface temperature bias (cool northern hemisphere, warm Southern Ocean), an overly strong global hydrological cycle and insufficient European blocking. 0360 Radiation: transmission and scattering; 0321 Cloud/radiation interaction; 0319 Cloud optics; Model description; Model evaluation
Wittenberg, Andrew T.; Vecchi, Gabriel A.; Delworth, Thomas L.; Rosati, Anthony; Anderson, Whit G.; Cooke, William F.; Underwood, Seth; Zeng, Fanrong; Griffies, Stephen M.; Ray, SulagnaWittenberg, A. T., G. A. Vecchi, T. L. Delworth, A. Rosati, W. G. Anderson, W. F. Cooke, S. Underwood, F. Zeng, S. M. Griffies, S. Ray, 2018: Improved Simulations of Tropical Pacific Annual-Mean Climate in the GFDL FLOR and HiFLOR Coupled GCMs. Journal of Advances in Modeling Earth Systems, 10(12), 3176-3220. doi: 10.1029/2018MS001372. Abstract The National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory has recently developed two global coupled general circulation models, the Forecast-oriented Low Ocean Resolution (FLOR) model and the High atmospheric resolution Forecast-oriented Low Ocean Resolution (HiFLOR) model, which are now being utilized for climate research and seasonal predictions. Compared to their predecessor Coupled Model version 2.1 (CM2.1), the new versions have improved ocean/atmosphere physics and numerics and refinement of the atmospheric horizontal grid from 220 km (CM2.1) to 55 km (FLOR) and 26 km (HiFLOR). Both FLOR and HiFLOR demonstrate greatly improved simulations of the tropical Pacific annual-mean climatology, with FLOR practically eliminating any equatorial cold bias in sea surface temperature. An additional model experiment (Low Ocean Atmosphere Resolution version 1) using FLOR's ocean/atmosphere physics, but with the atmospheric grid coarsened toward that of CM2.1, is used to further isolate the impacts of the refined atmospheric grid versus the improved physics and numerics. The improved ocean/atmosphere formulations are found to produce more realistic tropical Pacific patterns of sea surface temperature and rainfall, surface heat fluxes, ocean mixed layer depths, surface currents, and tropical instability wave activity; enhance the near-surface equatorial upwelling; and reduce the intercentennial warm drift of the tropical Pacific upper ocean. The atmospheric grid refinement further improves these features and also improves the tropical Pacific surface wind stress, implied Ekman and Sverdrup transports, subsurface temperature and salinity structure, and heat advection in the equatorial upper ocean. The results highlight the importance of nonlocal air-sea interactions in the tropical Pacific climate system, including the influence of off-equatorial surface fluxes on the equatorial annual-mean state. Implications are discussed for improving future simulations, observations, and predictions of tropical Pacific climate. air-sea interactions; coupled models of the climate system; El Niño Southern Oscillation (ENSO); tropical Pacific climate; upper ocean and mixed layer processes
Wong, T.; Kratz, D. P.; Stackhouse, P. W.; Sawaengphokhai, Parnchai; Wilber, A. C.; Gupta, S. K.; Loeb, N. GWong, T., D. P. Kratz, P. W. Stackhouse, P. Sawaengphokhai, A. C. Wilber, S. K. Gupta, N. G. Loeb, 2018: Earth Radiation Budget at Top-Of-Atmosphere [in “State of the Climate in 2017”].. Bull. Amer. Meteor. Soc, 99(8), S45-46. doi: 10.1175/2018BAMSStateoftheClimate.1.
Wong, T.; Smith, G. L.; Kato, S.; Loeb, N. G.; Kopp, G.; Shrestha, A. K.Wong, T., G. L. Smith, S. Kato, N. G. Loeb, G. Kopp, A. K. Shrestha, 2018: On the Lessons Learned From the Operations of the ERBE Nonscanner Instrument in Space and the Production of the Nonscanner TOA Radiation Budget Data Set. IEEE Transactions on Geoscience and Remote Sensing, 56(10), 5936-5947. doi: 10.1109/TGRS.2018.2828783. Monitoring the flow of radiative energy at top of atmosphere (TOA) is essential for understanding Earth's climate and how it is changing with time. The determination of TOA global net radiation budget using broadband nonscanner instruments has received renewed interest recently due to advances in both instrument technology and the availability of small satellite platforms. The use of such instruments for monitoring Earth's radiation budget was attempted in the past from satellite missions such as the Nimbus-7 and the Earth Radiation Budget Experiment (ERBE). This paper discusses the important lessons learned from the operation of the ERBE nonscanner instrument and the production of the ERBE nonscanner TOA radiation budget data set that have direct relevance to current nonscanner instrument efforts. Earth; Extraterrestrial measurements; atmospheric radiation; atmospheric techniques; Instruments; Meteorology; atmospheric measuring apparatus; Atmospheric measurements; uncertainty; Sea measurements; Satellite broadcasting; Data conversion; broadband nonscanner instruments; current nonscanner instrument efforts; Earth Radiation Budget Experiment; Earth's climate; energy measurement; ERBE nonscanner instrument; ERBE nonscanner TOA radiation budget data; important lessons; instrument technology; monitoring Earth's radiation budget; Nimbus-7; nonscanner TOA Radiation Budget data set; radiative energy; small satellite platforms; TOA global net radiation budget
Wood, Robert; O, Kuan-Ting; Bretherton, Christopher S.; Mohrmann, Johannes; Albrecht, Bruce. A.; Zuidema, Paquita; Ghate, Virendra; Schwartz, Chris; Eloranta, Ed; Glienke, Susanne; Shaw, Raymond A.; Fugal, Jacob; Minnis, PatrickWood, R., K. O, C. S. Bretherton, J. Mohrmann, B. A. Albrecht, P. Zuidema, V. Ghate, C. Schwartz, E. Eloranta, S. Glienke, R. A. Shaw, J. Fugal, P. Minnis, 2018: Ultraclean Layers and Optically Thin Clouds in the Stratocumulus-to-Cumulus Transition. Part I: Observations. J. Atmos. Sci., 75(5), 1631-1652. doi: 10.1175/JAS-D-17-0213.1. A common feature of the stratocumulus-to-cumulus transition (SCT) is the presence of layers in which the concentration of particles larger than 0.1 μm is below 10 cm−3. These ultraclean layers (UCLs) are explored using aircraft observations from 14 flights of the NSF–NCAR Gulfstream V (G-V) aircraft between California and Hawaii. UCLs are commonly located in the upper part of decoupled boundary layers, with coverage increasing from less than 5% within 500 km of the California coast to ~30%–60% west of 130°W. Most clouds in UCLs are thin, horizontally extensive layers containing drops with median volume radii ranging from 15 to 30 μm. Many UCL clouds are optically thin and do not fully attenuate the G-V lidar and yet are frequently detected with a 94-GHz radar with a sensitivity of around −30 dBZ. Satellite data indicate that UCL clouds have visible reflectances of ~0.1–0.2 and are often quasi laminar, giving them a veil-like appearance. These optically thin veil clouds exist for 1–3 h or more, are associated with mesoscale cumulus clusters, and likely grow by spreading under strong inversions. Active updrafts in cumulus (Cu) clouds have droplet concentrations of ~25–50 cm−3. Collision–coalescence in the Cu and later sedimentation in the thinner UCL clouds are likely the key processes that remove droplets in UCL clouds. UCLs are relatively quiescent, and a lack of mixing with dry air above and below the cloud may help to explain their longevity. The very low and highly variable droplet concentrations in UCL clouds, together with their low geometrical and optical thickness, make these clouds particularly challenging to represent in large-scale models.
Xiang, Baoqiang; Zhao, Ming; Ming, Yi; Yu, Weidong; Kang, Sarah M.Xiang, B., M. Zhao, Y. Ming, W. Yu, S. M. Kang, 2018: Contrasting Impacts of radiative forcing in the Southern Ocean versus Southern Tropics on ITCZ position and energy transport in one GFDL climate model. J. Climate, 31, 5609–5628. doi: 10.1175/JCLI-D-17-0566.1. Most current climate models suffer from pronounced cloud and radiation biases in the Southern Ocean (SO) and in the tropics. Using one GFDL climate model, this study investigates the migration of the Inter-tropical Convergence Zone (ITCZ) with prescribed Top of Atmosphere (TOA) shortwave radiative heating in the SO (50°S-80°S) versus the Southern Tropics (ST, 0-20°S). Results demonstrate that the ITCZ position response to the ST forcing is twice as strong as the SO forcing, which is primarily driven by the contrasting sea surface temperature (SST) gradient over the tropics; however, the mechanism for the formation of the SST pattern remains elusive.Energy budget analysis reveals that the conventional energetic constraint framework is inadequate in explaining the ITCZ shift in these two perturbed experiments. For both cases, the anomalous Hadley circulation does not contribute to transport the imposed energy from the Southern Hemisphere to the Northern Hemisphere, given a positive mean gross moist stability in the equatorial region. Changes in the cross-equatorial atmospheric energy are primarily transported by atmospheric transient eddies when the anomalous ITCZ shift is most pronounced during December-May.The partitioning of energy transport between the atmosphere and ocean shows latitudinal dependence: the atmosphere and ocean play an overall equivalent role in transporting the imposed energy for the extratropical SO forcing, while for the ST forcing, the imposed energy is nearly completely transported by the atmosphere. This contrast originates from the different ocean heat uptake and also the different meridional scale of the anomalous ocean circulation.
Xie, Shaocheng; Lin, Wuyin; Rasch, Philip J.; Ma, Po-Lun; Neale, Richard; Larson, Vincent E.; Qian, Yun; Bogenschutz, Peter A.; Caldwell, Peter; Cameron‐Smith, Philip; Golaz, Jean-Christophe; Mahajan, Salil; Singh, Balwinder; Tang, Qi; Wang, Hailong; Yoon, Jin-Ho; Zhang, Kai; Zhang, YuyingXie, S., W. Lin, P. J. Rasch, P. Ma, R. Neale, V. E. Larson, Y. Qian, P. A. Bogenschutz, P. Caldwell, P. Cameron‐Smith, J. Golaz, S. Mahajan, B. Singh, Q. Tang, H. Wang, J. Yoon, K. Zhang, Y. Zhang, 2018: Understanding Cloud and Convective Characteristics in Version 1 of the E3SM Atmosphere Model. Journal of Advances in Modeling Earth Systems, 10(10), 2618-2644. doi: 10.1029/2018MS001350. This study provides comprehensive insight into the notable differences in clouds and precipitation simulated by the Energy Exascale Earth System Model (E3SM) atmosphere model version 0 (EAMv0) and version 1 (EAMv1). Several sensitivity experiments are conducted to isolate the impact of changes in model physics, resolution, and parameter choices on these differences. The overall improvement in EAMv1 clouds and precipitation is primarily attributed to the introduction of a simplified third-order turbulence parameterization (CLUBB; Cloud Layers Unified By Binormals) (along with the companion changes) for a unified treatment of boundary layer turbulence, shallow convection, and cloud macrophysics, though it also leads to a reduction in subtropical coastal stratocumulus clouds (Sc). This lack of Sc is considerably improved by increasing vertical resolution from 30 to 72 layers, but the gain is unfortunately subsequently offset by other retuning to reach the top-of-atmosphere (TOA) energy balance. Increasing vertical resolution also results in a considerable underestimation of high clouds over the Tropical Warm Pool, primarily due to the selection for numerical stability of a higher air parcel launch level in the deep convection scheme. Increasing horizontal resolution from 1° to 0.25° without retuning leads to considerable degradation in cloud and precipitation fields, with much weaker tropical and subtropical short- and longwave cloud radiative forcing and much stronger precipitation in the intertropical convergence zone, indicating poor scale-awareness of the cloud parameterizations. To avoid this degradation, significantly different parameter settings for the low-resolution (1°) and high-resolution (0.25°) were required to achieve optimal performance in EAMv1. Global climate model; E3SM; EAMv1; Cloud and convection; Model resolution; Model tuning
Xu, Chen; Duan, Junyan; Wang, Yanyu; Li, Mei; Cheng, Tiantao; Wang, Hua; Zhu, Hailin; Xie, Xin; Liu, Yuehui; Ling, Yan; Li, Xiang; Kong, Lingdong; He, Qianshan; Wang, Hongli; Zhang, RenjianXu, C., J. Duan, Y. Wang, M. Li, T. Cheng, H. Wang, H. Zhu, X. Xie, Y. Liu, Y. Ling, X. Li, L. Kong, Q. He, H. Wang, R. Zhang, 2018: Effects of Wintertime Polluted Aerosol on Clouds over the Yangtze River Delta: Case Study. Aerosol and Air Quality Research, 18(7), 1799-1816. doi: 10.4209/aaqr.2017.09.0322.
Yamauchi, Akira; Kawamoto, Kazuaki; Manda, Atsuyoshi; Li, JimingYamauchi, A., K. Kawamoto, A. Manda, J. Li, 2018: Assessing the impact of the Kuroshio Current on vertical cloud structure using CloudSat data. Atmospheric Chemistry and Physics Discussions, 18, 7657–7667. doi: 10.5194/acp-2017-1134. This study analyzed CloudSat satellite data to determine how the warm ocean Kuroshio Current affects the vertical structure of clouds. Rainfall intensity around the middle troposphere (6 km in height) over the Kuroshio was greater than that over surrounding areas. The drizzle clouds over the Kuroshio have a higher frequency of occurrence of geometrically thin (0.5–3 km) clouds and thicker (7–10 km) clouds compared to those around the Kuroshio. Moreover, the frequency of occurrence of precipitating clouds with a geometric thickness of 7 to 10 km increased over the Kuroshio. Stronger updrafts over the Kuroshio maintain large droplets higher in the upper part of the cloud layer, and the maximum radar reflectivity within a cloud layer in non-precipitating and drizzle clouds over the Kuroshio is higher than that around the Kuroshio.
Yang, Jia; Tian, Hanqin; Pan, Shufen; Chen, Guangsheng; Zhang, Bowen; Dangal, ShreeYang, J., H. Tian, S. Pan, G. Chen, B. Zhang, S. Dangal, 2018: Amazon drought and forest response: Largely reduced forest photosynthesis but slightly increased canopy greenness during the extreme drought of 2015/2016. Global Change Biology, 24(5), 1919-1934. doi: 10.1111/gcb.14056. Amazon droughts have impacted regional ecosystem functioning as well as global carbon cycling. The severe dry-season droughts in 2005 and 2010, driven by Atlantic sea surface temperature (SST) anomaly, have been widely investigated in terms of drought severity and impacts on ecosystems. Although the influence of Pacific SST anomaly on wet-season precipitation has been well recognized, it remains uncertain to what extent the droughts driven by Pacific SST anomaly could affect forest greenness and photosynthesis in the Amazon. Here, we examined the monthly and annual dynamics of forest greenness and photosynthetic capacity when Amazon ecosystems experienced an extreme drought in 2015/2016 driven by a strong El Niño event. We found that the drought during August 2015–July 2016 was one of the two most severe meteorological droughts since 1901. Due to the enhanced solar radiation during this drought, overall forest greenness showed a small increase, and 21.6% of forests even greened up (greenness index anomaly ≥1 standard deviation). In contrast, solar-induced chlorophyll fluorescence (SIF), an indicator of vegetation photosynthetic capacity, showed a significant decrease. Responses of forest greenness and photosynthesis decoupled during this drought, indicating that forest photosynthesis could still be suppressed regardless of the variation in canopy greenness. If future El Niño frequency increases as projected by earth system models, droughts would result in persistent reduction in Amazon forest productivity, substantial changes in tree composition, and considerable carbon emissions from Amazon. satellite observations; drought; El Niño-Southern Oscillation; forest productivity; tropical forests
Yang, Liu; Liu, Jing-Wu; Ren, Zhao-Peng; Xie, Shang-Ping; Zhang, Su-Ping; Gao, Shan-HongYang, L., J. Liu, Z. Ren, S. Xie, S. Zhang, S. Gao, 2018: Atmospheric Conditions for Advection-Radiation Fog Over the Western Yellow Sea. Journal of Geophysical Research: Atmospheres, 123(10), 5455-5468. doi: 10.1029/2017JD028088. Advection fog occurs usually when warm and moist air flows over cold sea surface. It is occasionally reported that the fog air temperature falls below sea surface temperature (called here the sea fog with sea surface heating [ssH]) due to longwave radiation cooling at fog top. Using 8-year buoy observations, this study reveals that about 33% of the time, the advection fog is with ssH in the western Yellow Sea. By synthesizing long-term observations from meteorological stations, atmospheric soundings, and offshore buoys, this study further investigates the marine atmospheric boundary layer (MABL) structure and atmospheric circulation associated with the ssH sea fog. Composite analysis shows that a local anomalous high pressure favors widespread formation of the ssH sea fog. The subsidence in the high pressure intensifies the thermal and moist stratification between the MABL and free atmosphere through adiabatic warming. The dry air above helps cool the fog layer by enhancing the longwave radiative cooling at the fog top and the vertical mixing beneath, causing air temperature to drop below sea surface temperature. The ratio of sea fog with ssH to total sea fog decreases from spring to summer as the descending motion and MABL stratification both weaken. This study highlights the importance of longwave radiative cooling at the advection fog top and suggests a way to improve sea fog forecast in the Yellow Sea. advection fog; boundary layer; longwave radiative cooling; Yellow Sea
Yang, Lu; Zhang, Xiaotong; Liang, Shunlin; Yao, Yunjun; Jia, Kun; Jia, AolinYang, L., X. Zhang, S. Liang, Y. Yao, K. Jia, A. Jia, 2018: Estimating Surface Downward Shortwave Radiation over China Based on the Gradient Boosting Decision Tree Method. Remote Sensing, 10(2), 185. doi: 10.3390/rs10020185. Downward shortwave radiation (DSR) is an essential parameter in the terrestrial radiation budget and a necessary input for models of land-surface processes. Although several radiation products using satellite observations have been released, coarse spatial resolution and low accuracy limited their application. It is important to develop robust and accurate retrieval methods with higher spatial resolution. Machine learning methods may be powerful candidates for estimating the DSR from remotely sensed data because of their ability to perform adaptive, nonlinear data fitting. In this study, the gradient boosting regression tree (GBRT) was employed to retrieve DSR measurements with the ground observation data in China collected from the China Meteorological Administration (CMA) Meteorological Information Center and the satellite observations from the Advanced Very High Resolution Radiometer (AVHRR) at a spatial resolution of 5 km. The validation results of the DSR estimates based on the GBRT method in China at a daily time scale for clear sky conditions show an R2 value of 0.82 and a root mean square error (RMSE) value of 27.71 W·m−2 (38.38%). These values are 0.64 and 42.97 W·m−2 (34.57%), respectively, for cloudy sky conditions. The monthly DSR estimates were also evaluated using ground measurements. The monthly DSR estimates have an overall R2 value of 0.92 and an RMSE of 15.40 W·m−2 (12.93%). Comparison of the DSR estimates with the reanalyzed and retrieved DSR measurements from satellite observations showed that the estimated DSR is reasonably accurate but has a higher spatial resolution. Moreover, the proposed GBRT method has good scalability and is easy to apply to other parameter inversion problems by changing the parameters and training data. downward shortwave radiation; AVHRR; CMA; gradient boosting regression tree; machine learning
Yang, Ping; Hioki, Souichiro; Saito, Masanori; Kuo, Chia-Pang; Baum, Bryan A.; Liou, Kuo-NanYang, P., S. Hioki, M. Saito, C. Kuo, B. A. Baum, K. Liou, 2018: A Review of Ice Cloud Optical Property Models for Passive Satellite Remote Sensing. Atmosphere, 9(12), 499. doi: 10.3390/atmos9120499. The current wealth of spaceborne passive and active measurements from ultraviolet to the infrared wavelengths provides an unprecedented opportunity to construct ice cloud bulk optical property models that lead to consistent ice cloud property retrievals across multiple sensors and platforms. To infer the microphysical and radiative properties of ice clouds from these satellite measurements, the general approach is to assume an ice cloud optical property model that implicitly assumes the habit (shape) and size distributions of the ice particles in these clouds. The assumption is that this ice optical property model will be adequate for global retrievals. In this review paper, we first summarize the key optical properties of individual particles and then the bulk radiative properties of their ensemble, followed by a review of the ice cloud models developed for application to satellite remote sensing. We illustrate that the random orientation condition assumed for ice particles is arguably justified for passive remote sensing applications based on radiometric measurements. The focus of the present discussion is on the ice models used by the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Clouds and Earth’s Radiant Energy System (CERES) science teams. In addition, we briefly review the ice cloud models adopted by the Polarization and Directionality of the Earth’s Reflectance (POLDER) and the Himawari-8 Advanced Himawari Imager (AHI) for ice cloud retrievals. We find that both the MODIS Collection 6 ice model and the CERES two-habit model result in spectrally consistent retrievals. satellite; remote sensing; ice cloud model; single-scattering properties
Yosef, Gil; Walko, Robert; Avisar, Roni; Tatarinov, Fedor; Rotenberg, Eyal; Yakir, DanYosef, G., R. Walko, R. Avisar, F. Tatarinov, E. Rotenberg, D. Yakir, 2018: Large-scale semi-arid afforestation can enhance precipitation and carbon sequestration potential. Scientific Reports, 8(1), 996. doi: 10.1038/s41598-018-19265-6. Afforestation is an important approach to mitigate global warming. Its complex interactions with the climate system, however, makes it controversial. Afforestation is expected to be effective in the tropics where biogeochemical and biogeophysical effects act in concert; however, its potential in the large semi-arid regions remains insufficiently explored. Here, we use a Global Climate Model to provide a process-based demonstration that implementing measured characteristics of a successful semi-arid afforestation system (2000 ha, ~300 mm mean annual precipitation) over large areas (~200 million ha) of similar precipitation levels in the Sahel and North Australia leads to the weakening and shifting of regional low-level jets, enhancing moisture penetration and precipitation (+0.8 ± 0.1 mm d−1 over the Sahel and +0.4 ± 0.1 mm d−1 over North Australia), influencing areas larger than the original afforestation. These effects are associated with increasing root depth and surface roughness and with decreasing albedo. This results in enhanced evapotranspiration, surface cooling and the modification of the latitudinal temperature gradient. It is estimated that the carbon sequestration potential of such large-scale semi-arid afforestation can be on the order of ~10% of the global carbon sink of the land biosphere and would overwhelm any biogeophysical warming effects within ~6 years.
Yu, Han; Zhang, Jie; Bai, HanbingYu, H., J. Zhang, H. Bai, 2018: The Variation of Effective Radiation in Qinghai-Tibetan Plateau Based on the CERES Satellite Data, The Variation of Effective Radiation in Qinghai-Tibetan Plateau Based on the CERES Satellite Data. Plateau Meteorology, 37(1), 106-122. doi: 10.7522/j.issn.1000-0534.2017.00045.
Yu, L.; Jin, X; Kato, S.; Loeb, N. G; Stackhouse, P. W.; Weller, R. A.; Wilber, A. C.Yu, L., X. Jin, S. Kato, N. G. Loeb, P. W. Stackhouse, R. A. Weller, A. C. Wilber, 2018: Global ocean heat, freshwater, and momentum fluxes [in “State of the Climate in 2017”].. Bull. Amer. Meteor. Soc, 99(8), S81-84. doi: 10.1175/2018BAMSStateoftheClimate.1.
Yu, Shanshan; Xin, Xiaozhou; Liu, Qinhuo; Zhang, Hailong; Li, LiYu, S., X. Xin, Q. Liu, H. Zhang, L. Li, 2018: Comparison of Cloudy-Sky Downward Longwave Radiation Algorithms Using Synthetic Data, Ground-Based Data, and Satellite Data. Journal of Geophysical Research: Atmospheres, 123(10), 5397-5415. doi: 10.1029/2017JD028234. Cloud plays a crucial role in surface downward longwave radiation (DLR). To determine optimal algorithms for cloud-sky DLR calculation under various climates, three types of algorithms were assessed, (i) four empirical algorithms determining cloudy DLR by simple cloud correction using the cloud fraction, (ii) three parameterized algorithms determining the cloud contribution by cloud temperature, and (iii) a semiempirical algorithm, Zhou-Cess, parameterized by the cloud water path. A sensitivity study was conducted using a Moderate Resolution Transmittance (MODTRAN) code to first determine the sensitive cloud parameters of DLR. Then, these algorithms were validated using synthetic data simulated by MODTRAN, ground-observed data, and satellite-observed data. When all the input parameters were accurate, the cloud-correction algorithms showed poor performance. Cloud-temperature-based algorithms showed much better results but exhibited positive systematic biases. The Zhou-Cess algorithm performed best but could not precisely describe the effect caused by cloud variations. When these algorithms were applied to ground- and satellite-based data, the accuracies of DLR calculations were affected by the uncertainty in the atmospheric and cloud parameters. The simple empirical algorithms showed the poorest results. The cloud-temperature-based algorithms were greatly influenced by the uncertainty in cloud base temperature and cloud fraction and showed acceptable results when cloud fractions were accurate. The Zhou-Cess algorithm revealed the best results at most sites and was less impacted by cloud parameter uncertainties; therefore, this algorithm is suggested for cloudy-sky DLR calculation with poor-quality cloud parameters. surface downward longwave radiation; cloud base temperature; cloud correction; cloud water path; cloudy sky
Zelinka, Mark D.; Grise, Kevin M.; Klein, Stephen A.; Zhou, Chen; DeAngelis, Anthony M.; Christensen, Matthew W.Zelinka, M. D., K. M. Grise, S. A. Klein, C. Zhou, A. M. DeAngelis, M. W. Christensen, 2018: Drivers of the Low Cloud Response to Poleward Jet Shifts in the North Pacific in Observations and Models. J. Climate, 31(19), 7925–7947. doi: 10.1175/JCLI-D-18-0114.1. The long-standing expectation that poleward shifts of the midlatitude jet under global warming will lead to poleward shifts of clouds and a positive radiative feedback on the climate system has been shown to be misguided by several recent studies. On interannual timescales, free tropospheric clouds are observed to shift along with the jet, but low clouds increase across a broad expanse of the North Pacific Ocean basin, resulting in negligible changes in total cloud fraction and top-of-atmosphere radiation. Here it is shown that this low cloud response is consistent across eight independent satellite-derived cloud products. Using multiple linear regression, it is demonstrated that the spatial pattern and magnitude of the low cloud coverage response is primarily driven by anomalous surface temperature advection. In the Eastern North Pacific, anomalous cold advection by anomalous northerly surface winds enhances sensible and latent heat fluxes from the ocean into the boundary layer, resulting in large increases in low cloud coverage. Local increases in low-level stability make a smaller contribution to this low cloud increase. Despite closely capturing the observed response of large-scale meteorology to jet shifts, global climate models largely fail to capture the observed response of clouds and radiation to interannual jet shifts because they systematically underestimate how sensitive low clouds are to surface temperature advection, and to a lesser extent, low-level stability. More realistic model simulations of cloud-radiation-jet interactions require that parameterizations more accurately capture the sensitivity of low clouds to surface temperature advection.
Zhan, Yizhe; Di Girolamo, Larry; Davies, Roger; Moroney, CatherineZhan, Y., L. Di Girolamo, R. Davies, C. Moroney, 2018: Instantaneous Top-of-Atmosphere Albedo Comparison between CERES and MISR over the Arctic. Remote Sensing, 10(12), 1882. doi: 10.3390/rs10121882. The top-of-atmosphere (TOA) albedo is one of the key parameters in determining the Arctic radiation budget, with continued validation of its retrieval accuracy still required. Based on three years (2007, 2015, 2016) of summertime (May–September) observations from the Clouds and the Earth’s Radiant Energy System (CERES) and the Multi-angle Imaging SpectroRadiometer (MISR), collocated instantaneous albedos for overcast ocean and snow/ice scenes were compared within the Arctic. For samples where both instruments classified the scene as overcast, the relative root-mean-square (RMS) difference between the sample albedos grew as the solar zenith angle (SZA) increased. The RMS differences that were purely due to differential Bidirectional Reflectance Factor (BRF) anisotropic corrections ( σ A D M ) were estimated to be less than 4% for overcast ocean and overcast snow/ice when the SZA ≤ 70°. The significant agreement between the CERES and MISR strongly increased our confidence in using the instruments overcast cloud albedos in Arctic studies. Nevertheless, there was less agreement in the cloud albedos for larger solar zenith angles, where the RMS differences of σ A D M reached 13.5% for overcast ocean scenes when the SZA > 80°. Additionally, inconsistencies between the CERES and MISR scene identifications were examined, resulting in an overall recommendation for improvements to the MISR snow/ice mask and a rework of the MISR Albedo Cloud Designation (ACD) field by incorporating known strengths of the standard MISR cloud masks. CERES; Arctic; MISR; top-of-atmosphere albedo
Zhang, Chengzhu; Xie, Shaocheng; Klein, Stephen A.; Ma, Hsi-yen; Tang, Shuaiqi; Van Weverberg, Kwinten; Morcrette, Cyril J.; Petch, JonZhang, C., S. Xie, S. A. Klein, H. Ma, S. Tang, K. Van Weverberg, C. J. Morcrette, J. Petch, 2018: CAUSES: Diagnosis of the Summertime Warm Bias in CMIP5 Climate Models at the ARM Southern Great Plains Site. Journal of Geophysical Research: Atmospheres, 123(6), 2968-2992. doi: 10.1002/2017JD027200. All the weather and climate models participating in the Clouds Above the United States and Errors at the Surface (CAUSES) project show a summertime surface air temperature (T2m) warm bias in the region of the central United States. To understand the warm bias in long-term climate simulations, we assess the Atmospheric Model Intercomparison Project (AMIP) simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5), with long-term observations mainly from the Atmospheric Radiation Measurement program (ARM) Southern Great Plains (SGP) site. Quantities related to the surface energy and water budget, and large-scale circulation are analyzed to identify possible factors and plausible links involved in the warm bias. The systematic warm season bias is characterized by an overestimation of T2m and underestimation of surface humidity, precipitation, and precipitable water. Accompanying the warm bias is an overestimation of absorbed solar radiation at the surface, which is due to a combination of insufficient cloud reflection and clear-sky shortwave absorption by water vapor and an underestimation in surface albedo. The bias in cloud is shown to contribute most to the radiation bias. The surface layer soil moisture impacts T2m through its control on evaporative fraction (EF). The error in EF is another important contributor to T2m. Similar sources of error are found in hindcast from other CAUSES studies. In AMIP simulations, biases in meridional wind velocity associated with the low-level jet and the 500-hPa vertical velocity may also relate to T2m bias through their control on the surface energy and water budget. 1655 Water cycles; 0321 Cloud/radiation interaction; ARM; CMIP5; 1631 Land/atmosphere interactions; 1626 Global climate models; 0550 Model verification and validation; CAUSES; SGP; Surface temperature bias; Systematic error
Zhang, Lei; Han, Weiqing; Li, Yuanlong; Maloney, Eric D.Zhang, L., W. Han, Y. Li, E. D. Maloney, 2018: Role of North Indian Ocean Air-Sea Interaction in Summer Monsoon Intraseasonal Oscillation. J. Climate, 31(19), 7885–7908. doi: 10.1175/JCLI-D-17-0691.1. Air-sea coupling processes over the North Indian Ocean associated with the Indian summer monsoon intraseasonal oscillation (MISO) are investigated. Observations show that MISO convection anomalies affect underlying sea surface temperature (SST) through changes in surface shortwave radiation and surface latent heat flux. In turn, SST anomalies may also affect the MISO precipitation tendency (dP/dt). In particular, warm (cold) SST anomalies can contribute to increasing (decreasing) precipitation rate through enhanced (suppressed) surface convergence associated with boundary layer pressure gradients. These air-sea interaction processes are manifest in a quadrature relation between MISO precipitation and SST anomalies.A local air-sea coupling model (LACM) is formulated based on these observed physical processes. The period of the LACM is proportional to the square root of seasonal mixed layer depth H, assuming other physical parameters remain unchanged. Hence, LACM predicts a relatively short (long) MISO period over the North Indian Ocean during the May-June monsoon developing (July-August monsoon mature) phase when H is shallow (deep). This result is consistent with observed MISO characteristics.A 30-day period oscillating external forcing is also added to the LACM, representing intraseasonal oscillations propagating from the equatorial Indian Ocean to the North Indian Ocean. It is found that resonance will occur when H is close to 25 m, which significantly enhances the MISO amplitude. This process may contribute to the higher MISO amplitude during the monsoon developing phase compared to the mature phase, which is associated with the seasonal cycle of H.
Zhang, Rudong; Wang, Hailong; Fu, Qiang; Pendergrass, Angeline G.; Wang, Minghuai; Yang, Yang; Ma, Po-Lun; Rasch, Philip J.Zhang, R., H. Wang, Q. Fu, A. G. Pendergrass, M. Wang, Y. Yang, P. Ma, P. J. Rasch, 2018: Local Radiative Feedbacks Over the Arctic Based on Observed Short-Term Climate Variations. Geophysical Research Letters, 45(11), 5761-5770. doi: 10.1029/2018GL077852. We compare various radiative feedbacks over the Arctic (60–90°N) estimated from short-term climate variations occurring in reanalysis, satellite, and global climate model data sets using the combined Kernel-Gregory approach. The lapse rate and surface albedo feedbacks are positive, and their magnitudes are comparable. Relative to the tropics (30°S–30°N), the lapse rate feedback is the largest contributor to Arctic amplification among all feedbacks, followed by surface albedo feedback and Planck feedback deviation from its global mean. Both shortwave and longwave water vapor feedbacks are positive, leading to a significant positive net water vapor feedback over the Arctic. The net cloud feedback has large uncertainties including its sign, which strongly depends on the data used for all-sky and clear-sky radiative fluxes at the top of the atmosphere, the time periods considered, and the methods used to estimate the cloud feedback. surface albedo; satellite data; Arctic amplification; climate modeling; radiative feedback; reanalysis data
Zhao, Long; Yang, Zong-LiangZhao, L., Z. Yang, 2018: Multi-sensor land data assimilation: Toward a robust global soil moisture and snow estimation. Remote Sensing of Environment, 216, 13-27. doi: 10.1016/j.rse.2018.06.033. Global monitoring of soil moisture and snow is now available through various satellite observations from optical, microwave, and gravitational sensors. However, very few modeling frameworks exist that conjointly use the above sensors to produce mutually and physically consistent earth system records. To this goal, a prototype of multi-sensor land data assimilation system is developed by linking the Community Land Model version 4 (CLM4) and a series of forward models with the Data Assimilation Research Testbed (DART). The deterministic Ensemble Adjustment Kalman Filter (EAKF) within the DART is utilized to estimate global soil moisture and snow by assimilating brightness temperature, snow cover fraction, and daily total water storage observations from the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E), Moderate Resolution Imaging Spectroradiometer (MODIS), and Gravity Recovery and Climate Experiment (GRACE), respectively. A 40-member of Community Atmosphere Model version 4 (CAM4) reanalysis is adopted to introduce ensemble spread in CLM4 land states and some methods are used to reduce the computational load. Data assimilation with different combinations of sensors is implemented for 2003–2009 to investigate individual contributions from different satellite observations. Evaluation results and cross-comparison of open-loop and data assimilation cases suggest that 1) assimilation of MODIS snow cover fraction slightly improves snow estimation in mid and high latitudes; 2) lower and higher frequencies of AMSR-E brightness temperature play complementary roles in improving global soil moisture and snow estimation; 3) assimilation of GRACE tends to degrade soil moisture estimation but poses potential in improving snow depth estimation in most high-latitude regions. Generally, the combination of MODIS, GRACE, and AMSR-E observations with regard to spatial locations holds promise to provide a robust global soil moisture and snow estimation through the multi-sensor land data assimilation system. MODIS; AMSR-E; GRACE; Soil moisture; Snow; Land data assimilation
Zhao, M.; Golaz, J.-C.; Held, I. M.; Guo, H.; Balaji, V.; Benson, R.; Chen, J.-H.; Chen, X.; Donner, L. J.; Dunne, J. P.; Dunne, K.; Durachta, J.; Fan, S.-M.; Freidenreich, S. M.; Garner, S. T.; Ginoux, P.; Harris, L. M.; Horowitz, L. W.; Krasting, J. P.; Langenhorst, A. R.; Liang, Z.; Lin, P.; Lin, S.-J.; Malyshev, S. L.; Mason, E.; Milly, P. C. D.; Ming, Y.; Naik, V.; Paulot, F.; Paynter, D.; Phillipps, P.; Radhakrishnan, A.; Ramaswamy, V.; Robinson, T.; Schwarzkopf, D.; Seman, C. J.; Shevliakova, E.; Shen, Z.; Shin, H.; Silvers, L. G.; Wilson, J. R.; Winton, M.; Wittenberg, A. T.; Wyman, B.; Xiang, B.Zhao, M., J. Golaz, I. M. Held, H. Guo, V. Balaji, R. Benson, J. Chen, X. Chen, L. J. Donner, J. P. Dunne, K. Dunne, J. Durachta, S. Fan, S. M. Freidenreich, S. T. Garner, P. Ginoux, L. M. Harris, L. W. Horowitz, J. P. Krasting, A. R. Langenhorst, Z. Liang, P. Lin, S. Lin, S. L. Malyshev, E. Mason, P. C. D. Milly, Y. Ming, V. Naik, F. Paulot, D. Paynter, P. Phillipps, A. Radhakrishnan, V. Ramaswamy, T. Robinson, D. Schwarzkopf, C. J. Seman, E. Shevliakova, Z. Shen, H. Shin, L. G. Silvers, J. R. Wilson, M. Winton, A. T. Wittenberg, B. Wyman, B. Xiang, 2018: The GFDL Global Atmosphere and Land Model AM4.0/LM4.0: 1. Simulation Characteristics With Prescribed SSTs. Journal of Advances in Modeling Earth Systems, 10(3), 691-734. doi: 10.1002/2017MS001208. In this two-part paper, a description is provided of a version of the AM4.0/LM4.0 atmosphere/land model that will serve as a base for a new set of climate and Earth system models (CM4 and ESM4) under development at NOAA's Geophysical Fluid Dynamics Laboratory (GFDL). This version, with roughly 100 km horizontal resolution and 33 levels in the vertical, contains an aerosol model that generates aerosol fields from emissions and a “light” chemistry mechanism designed to support the aerosol model but with prescribed ozone. In Part 1, the quality of the simulation in AMIP (Atmospheric Model Intercomparison Project) mode—with prescribed sea surface temperatures (SSTs) and sea-ice distribution—is described and compared with previous GFDL models and with the CMIP5 archive of AMIP simulations. The model's Cess sensitivity (response in the top-of-atmosphere radiative flux to uniform warming of SSTs) and effective radiative forcing are also presented. In Part 2, the model formulation is described more fully and key sensitivities to aspects of the model formulation are discussed, along with the approach to model tuning. 3311 Clouds and aerosols; 3305 Climate change and variability; 3337 Global climate models; 3371 Tropical convection; 3365 Subgrid-scale (SGS) parameterization; atmospheric variability; climate simulation; cloud and aerosol effect; convection and clouds; global atmospheric model; global climate model development
Zhao, M.; Golaz, J.-C.; Held, I. M.; Guo, H.; Balaji, V.; Benson, R.; Chen, J.-H.; Chen, X.; Donner, L. J.; Dunne, J. P.; Dunne, K.; Durachta, J.; Fan, S.-M.; Freidenreich, S. M.; Garner, S. T.; Ginoux, P.; Harris, L. M.; Horowitz, L. W.; Krasting, J. P.; Langenhorst, A. R.; Liang, Z.; Lin, P.; Lin, S.-J.; Malyshev, S. L.; Mason, E.; Milly, P. C. D.; Ming, Y.; Naik, V.; Paulot, F.; Paynter, D.; Phillipps, P.; Radhakrishnan, A.; Ramaswamy, V.; Robinson, T.; Schwarzkopf, D.; Seman, C. J.; Shevliakova, E.; Shen, Z.; Shin, H.; Silvers, L. G.; Wilson, J. R.; Winton, M.; Wittenberg, A. T.; Wyman, B.; Xiang, B.Zhao, M., J. Golaz, I. M. Held, H. Guo, V. Balaji, R. Benson, J. Chen, X. Chen, L. J. Donner, J. P. Dunne, K. Dunne, J. Durachta, S. Fan, S. M. Freidenreich, S. T. Garner, P. Ginoux, L. M. Harris, L. W. Horowitz, J. P. Krasting, A. R. Langenhorst, Z. Liang, P. Lin, S. Lin, S. L. Malyshev, E. Mason, P. C. D. Milly, Y. Ming, V. Naik, F. Paulot, D. Paynter, P. Phillipps, A. Radhakrishnan, V. Ramaswamy, T. Robinson, D. Schwarzkopf, C. J. Seman, E. Shevliakova, Z. Shen, H. Shin, L. G. Silvers, J. R. Wilson, M. Winton, A. T. Wittenberg, B. Wyman, B. Xiang, 2018: The GFDL Global Atmosphere and Land Model AM4.0/LM4.0: 2. Model Description, Sensitivity Studies, and Tuning Strategies. Journal of Advances in Modeling Earth Systems, 10(3), 652-667. doi: 10.1002/2017MS001209. In Part 2 of this two-part paper, documentation is provided of key aspects of a version of the AM4.0/LM4.0 atmosphere/land model that will serve as a base for a new set of climate and Earth system models (CM4 and ESM4) under development at NOAA's Geophysical Fluid Dynamics Laboratory (GFDL). The quality of the simulation in AMIP (Atmospheric Model Intercomparison Project) mode has been provided in Part 1. Part 2 provides documentation of key components and some sensitivities to choices of model formulation and values of parameters, highlighting the convection parameterization and orographic gravity wave drag. The approach taken to tune the model's clouds to observations is a particular focal point. Care is taken to describe the extent to which aerosol effective forcing and Cess sensitivity have been tuned through the model development process, both of which are relevant to the ability of the model to simulate the evolution of temperatures over the last century when coupled to an ocean model. 3311 Clouds and aerosols; 3305 Climate change and variability; 3337 Global climate models; 3371 Tropical convection; 3365 Subgrid-scale (SGS) parameterization; atmospheric variability; climate simulation; cloud and aerosol effect; convection and clouds; global atmospheric model; global climate model development
Abhik, S.; Krishna, R. P. M.; Mahakur, M.; Ganai, Malay; Mukhopadhyay, P.; Dudhia, J.Abhik, S., R. P. M. Krishna, M. Mahakur, M. Ganai, P. Mukhopadhyay, J. Dudhia, 2017: Revised cloud processes to improve the mean and intraseasonal variability of Indian summer monsoon in climate forecast system: Part 1. Journal of Advances in Modeling Earth Systems, 9(2), 1002–1029. doi: 10.1002/2016MS000819. The National Centre for Environmental Prediction (NCEP) Climate Forecast System (CFS) is being used for operational monsoon prediction over the Indian region. Recent studies indicate that the moist convective process in CFS is one of the major sources of uncertainty in monsoon predictions. In this study, the existing simple cloud microphysics of CFS is replaced by the six-class Weather Research Forecasting (WRF) single moment (WSM6) microphysical scheme. Additionally, a revised convective parameterization is employed to improve the performance of the model in simulating the boreal summer mean climate and intraseasonal variability over the Indian summer monsoon (ISM) region. The revised version of the model (CFSCR) exhibits a potential to improve shortcomings in the seasonal mean precipitation distribution relative to the standard CFS (CTRL), especially over the ISM region. Consistently, notable improvements are also evident in other observed ISM characteristics. These improvements are found to be associated with a better simulation of spatial and vertical distributions of cloud hydrometeors in CFSCR. A reasonable representation of the subgrid-scale convective parameterization along with cloud hydrometeors helps to improve the convective and large-scale precipitation distribution in the model. As a consequence, the simulated low-frequency boreal summer intraseasonal oscillation (BSISO) exhibits realistic propagation and the observed northwest-southeast rainband is well reproduced in CFSCR. Additionally, both the high and low-frequency BSISOs are better captured in CFSCR. The improvement of low and high-frequency BSISOs in CFSCR is shown to be related to a realistic phase relationship of clouds. Indian summer monsoon; 0429 Climate dynamics; 3365 Subgrid-scale (SGS) parameterization; boreal summer intraseasonal oscillation; climate forecast system; tropical cloud processes
Adam, Ori; Schneider, Tapio; Brient, FlorentAdam, O., T. Schneider, F. Brient, 2017: Regional and seasonal variations of the double-ITCZ bias in CMIP5 models. Climate Dynamics, 1-17. doi: 10.1007/s00382-017-3909-1. Current climate models represent the zonal- and annual-mean intertropical convergence zone (ITCZ) position in a biased way, with an unrealistic double precipitation peak straddling the equator in the ensemble mean over the models. This bias is seasonally and regionally localized. It results primarily from two regions: the eastern Pacific and Atlantic (EPA), where the ITCZ in boreal winter and spring is displaced farther south than is observed; and the western Pacific (WP), where a more pronounced and wider than observed double ITCZ straddles the equator year-round. Additionally, the precipitation associated with the ascending branches of the zonal overturning circulations (e.g., Walker circulation) in the Pacific and Atlantic sectors is shifted westward. We interpret these biases in light of recent theories that relate the ITCZ position to the atmospheric energy budget. WP biases are associated with the well known Pacific cold tongue bias, which, in turn, is linked to atmospheric net energy input biases near the equator. In contrast, EPA biases are shown to be associated with a positive bias in the cross-equatorial divergent atmospheric energy transport during boreal winter and spring, with two potential sources: tropical biases associated with equatorial sea surface temperatures (SSTs) and tropical low clouds, and extratropical biases associated with Southern Ocean clouds and north Atlantic SST. The distinct seasonal and regional characteristics of WP and EPA biases and the differences in their associated energy budget biases suggest that the biases in the two sectors involve different mechanisms and potentially different sources.
Alexandri, G.; Georgoulias, A. K.; Meleti, C.; Balis, D.; Kourtidis, K. A.; Sanchez-Lorenzo, A.; Trentmann, J.; Zanis, P.Alexandri, G., A. K. Georgoulias, C. Meleti, D. Balis, K. A. Kourtidis, A. Sanchez-Lorenzo, J. Trentmann, P. Zanis, 2017: A high resolution satellite view of surface solar radiation over the climatically sensitive region of Eastern Mediterranean. Atmospheric Research, 188, 107–121. doi: 10.1016/j.atmosres.2016.12.015. In this work, the spatiotemporal variability of surface solar radiation (SSR) is examined over the Eastern Mediterranean region for a 31-year period (1983–2013). The CM SAF SARAH (Satellite Application Facility on Climate Monitoring Solar surfAce RAdiation Heliosat) satellite-based product was found to be homogeneous (based on relative Standard Normal Homogeneity Tests — SNHTs, 95% confidence level) as compared to ground-based observations, and hence appropriate for climatological studies. Specifically, the dataset shows good agreement with monthly observations from five quality assured stations in the region with a mean bias of 7.1 W/m2 or 3.8% and a strong correlation. This high resolution (0.05° × 0.05°) product is capable of revealing various local features. Over land, the SSR levels are highly dependent on the topography, while over the sea, they exhibit a smooth latitudinal variability. SSR varies significantly over the region on a seasonal basis being three times higher in summer (309.6 ± 26.5 W/m2) than in winter (100.2 ± 31.4 W/m2). The CM SAF SARAH product was compared against three satellite-based and one reanalysis products. The satellite-based data from CERES (Cloud and the Earth's Radiant Energy System), GEWEX (Global Energy and Water Cycle Experiment) and ISCCP (International Satellite Cloud Climatology Project) underestimate SSR while the reanalysis data from the ERA-Interim overestimate SSR compared to CM SAF SARAH. Using a radiative transfer model and a set of ancillary data, these biases are attributed to the atmospheric parameters that drive the transmission of solar radiation in the atmosphere, namely, clouds, aerosols and water vapor. It is shown that the bias between CERES and CM SAF SARAH SSR can be explained through the cloud fractional cover and aerosol optical depth biases between these datasets. The CM SAF SARAH SSR trend was found to be positive (brightening) and statistically significant at the 95% confidence level (0.2 ± 0.05 W/m2/year or 0.1 ± 0.02%/year) being almost the same over land and sea. The CM SAF SARAH SSR trends are closer to the ground-based ones than the CERES, GEWEX, ISCCP and ERA-Interim trends. The use of an aerosol climatology for the production of CM SAF SARAH, that neglects the trends of aerosol loads, leads to an underestimation of the SSR trends. It is suggested here, that the inclusion of changes of the aerosol load and composition within CM SAF SARAH would allow for a more accurate reproduction of the SSR trends. clouds; aerosols; surface solar radiation; CM SAF; Dimming-brightening; Eastern Mediterranean
Alexandri, G.; Georgoulias, A. K.; Zanis, P.; Katragkou, E.; Tsikerdekis, A.; Kourtidis, K.; Meleti, C.Alexandri, G., A. K. Georgoulias, P. Zanis, E. Katragkou, A. Tsikerdekis, K. Kourtidis, C. Meleti, 2017: Evaluation of Regional Climate Model Surface Solar Radiation Patterns Over Europe Using Satellite-Based Observations and Radiative Transfer Calculations. Perspectives on Atmospheric Sciences, 701-706. The ability of RegCM4 regional climate model to simulate surface solar radiation (SSR) patterns over Europe is assessed through an evaluation of a decadal simulation against satellite-based observations from the Satellite Application Facility on Climate Monitoring (CM SAF). The model simulates adequately the SSR patterns over the region slightly overestimating SSR (bias of ~+2.5 % for the period 2000–2009). Cloud macrophysical and microphysical properties from RegCM4 such as cloud fractional cover (CFC), cloud optical thickness (COT) and cloud effective radius (Re) are evaluated against data from CM SAF. The same is done for aerosol optical properties such as aerosol optical depth (AOD), asymmetry factor (ASY), and single scattering albedo (SSA) using data from the MACv1 aerosol climatology, and other parameters, such as surface broadband albedo (ALB) using data from the CERES satellite sensors, and water vapor amount (WV) using data from the ERA-Interim reanalysis. The good agreement between RegCM4 and satellite-based SSR observations is a result of counterbalancing effects of these parameters. The contribution of each parameter to the RegCM4-CM SAF SSR deviations is estimated with the combined use of the aforementioned data and a radiative transfer model (SBDART). CFC, COT and AOD are the major determinants of these deviations.
Alfaro-Contreras, R.; Zhang, J.; Reid, J. S.; Christopher, S.Alfaro-Contreras, R., J. Zhang, J. S. Reid, S. Christopher, 2017: A study of 15-year aerosol optical thickness and direct shortwave aerosol radiative effect trends using MODIS, MISR, CALIOP and CERES. Atmos. Chem. Phys., 17(22), 13849-13868. doi: 10.5194/acp-17-13849-2017. By combining Collection 6 Moderate Resolution and Imaging Spectroradiometer (MODIS) and Version 22 Multi-angle Imaging Spectroradiometer (MISR) aerosol products with Cloud and Earth's Radiant Energy System (CERES) flux products, the aerosol optical thickness (AOT, at 0.55 µm) and shortwave (SW) aerosol radiative effect (SWARE) trends are studied over ocean for the near-full Terra (2000–2015) and Aqua (2002–2015) data records. Despite differences in sampling methods, regional SWARE and AOT trends are highly correlated with one another. Over global oceans, weak SWARE (cloud-free SW flux) and AOT trends of 0.5–0.6 W m−2 (−0.5 to −0.6 W m−2) and 0.002 AOT decade−1 are found using Terra data. Near-zero AOT and SWARE trends are also found for using Aqua data, regardless of the angular distribution models (ADMs) used. Regionally, positive AOT and cloud-free SW flux (negative SWARE) trends are found over the Bay of Bengal, the Arabian Sea, the Arabian/Persian Gulf and the Red Sea, while statistically significant negative trends are derived over the Mediterranean Sea and the eastern US coast. In addition, the global mean instantaneous SW aerosol direct forcing efficiencies are found to be ∼ −60 W m−2 AOT−1, with corresponding SWARE values of ∼ −7 W m−2 from both Aqua and Terra data, again regardless of CERES ADMs used. Regionally, SW aerosol direct forcing efficiency values of ∼ −40 W m−2 AOT−1 are found over the southwest coast of Africa where smoke aerosol particles dominate in summer. Larger (in magnitude) SW aerosol direct forcing efficiency values of −50 to −80 W m−2 AOT−1 are found over several other dust- and pollutant-aerosol-dominated regions. Lastly, the AOT and SWARE trends from this study are also intercompared with aerosol trends (such as active-based ones) from several previous studies. Findings suggest that a cohesive understanding of the changing aerosol skies can be achieved through the analysis of observations from both passive- and active-based analyses, as well as from both narrowband and broadband datasets.
Almorox, Javier; Ovando, Gustavo; Sayago, Silvina; Bocco, MónicaAlmorox, J., G. Ovando, S. Sayago, M. Bocco, 2017: Assessment of surface solar irradiance retrieved by CERES. International Journal of Remote Sensing, 38(12), 3669-3683. doi: 10.1080/01431161.2017.1302111. This study compared and evaluated the monthly global solar radiation generated by Clouds and the Earth’s Radiant Energy System (CERES) with the surface radiation registered in 232 meteorological stations located in whole Spain, for the period of July 2006–July 2015. Results showed strong correlations between CERES and registered data with R2 values greater than 0.96, for all stations considered. When the temporal evolution of recorded and provided by CERES solar radiation was analysed, a systematic overestimation by CERES was detected from July 2011, although the shapes of both curves were respected in the whole period. This finding led us to propose a linear adjustment model since July 2011. After applying the developed model to rescale CERES data for the whole period, an improvement in solar radiation fit was observed. Our finding offers an insight into error patterns of CERES solar radiation, since July 2011, and proposes a model for improving accuracy allowing therefore a reliable use of this product. Moreover, our study on radiation data of Spain provides a case example for worldwide validation.
Annamalai, H.; Taguchi, Bunmei; McCreary, Julian P.; Nagura, Motoki; Miyama, ToruAnnamalai, H., B. Taguchi, J. P. McCreary, M. Nagura, T. Miyama, 2017: Systematic Errors in South Asian Monsoon Simulation: Importance of Equatorial Indian Ocean Processes. J. Climate, 30(20), 8159-8178. doi: 10.1175/JCLI-D-16-0573.1. Forecasting monsoon rainfall using dynamical climate models has met with little success, partly due to models’ inability to represent the monsoon climatological state accurately. In this article the nature and dynamical causes of their biases are investigated. The approach is to analyze errors in multimodel-mean climatological fields determined from CMIP5, and to carry out sensitivity experiments using a coupled model [the Coupled Model for the Earth Simulator (CFES)] that does represent the monsoon realistically. Precipitation errors in the CMIP5 models persist throughout the annual cycle, with positive (negative) errors occurring over the near-equatorial western Indian Ocean (South Asia). Model errors indicate that an easterly wind stress bias Δτ along the equator begins during April–May and peaks during November; the severity of the Δτ is that the Wyrtki jets, eastward-flowing equatorial currents during the intermonsoon seasons (April–May and October–November), are almost eliminated. An erroneous east–west SST gradient (warm west and cold east) develops in June. The structure of the model errors indicates that they arise from Bjerknes feedback in the equatorial Indian Ocean (EIO). Vertically integrated moisture and moist static energy budgets confirm that warm SST bias in the western EIO anchors moist processes that cause the positive precipitation bias there. In CFES sensitivity experiments in which Δτ or warm SST bias over the western EIO is artificially introduced, errors in the EIO are similar to those in the CMIP5 models; moreover, precipitation over South Asia is reduced. An overall implication of these results is that South Asian rainfall errors in CMIP5 models are linked to errors of coupled processes in the western EIO, and in coupled models correct representation of EIO coupled processes (Bjerknes feedback) is a necessary condition for realistic monsoon simulation.
Bannon, Peter; Lee, SukyoungBannon, P., S. Lee, 2017: Towards Quantifying the Climate Heat Engine: Solar Absorption and Terrestrial Emission Temperatures and Material Entropy Production. J. Atmos. Sci., 74(6), 1721–1734. doi: 10.1175/JAS-D-16-0240.1. A heat engine analysis of a climate system requires the determination of the solar absorption temperature and the terrestrial emission temperature. These temperatures are entropically defined as the ratio of the energy exchanged to the entropy produced. The emission temperature, shown here to be greater than or equal to the effective emission temperature, is relatively well known. In contrast, the absorption temperature requires radiative transfer calculations for its determination and is poorly known.The maximum material (i.e., nonradiative) entropy production of a planet’s steady-state climate system is a function of the absorption and emission temperatures. Because a climate system does no work, the material entropy production measures the system’s activity. The sensitivity of this production to changes in the emission and absorption temperatures is quantified. If Earth’s albedo does not change, material entropy production would increase by about five percent per one-degree increase in absorption temperature. If the absorption temperature does not change, entropy production would decrease by about four percent for a one percent decrease in albedo. We show that, as a planet’s emission temperature becomes more uniform, its entropy production tends to increase. Conversely, as a planet’s absorption temperature or albedo becomes more uniform, its entropy production tends to decrease. These findings underscore the need to monitor the absorption temperature and albedo both in nature and in climate models.
Bender, Frida; Engström, Anders; Wood, Robert; Charlson, RobertBender, F., A. Engström, R. Wood, R. Charlson, 2017: Evaluation of hemispheric asymmetries in marine cloud radiative properties. J. Climate, 30(11), 4131–4147. doi: 10.1175/JCLI-D-16-0263.1. The hemispheric symmetry of albedo and its contributing factors in satellite observations and global climate models is evaluated. The analysis is performed on the annual mean time scale, on which a bimodality in the joint distribution of albedo and cloud fraction is evident, resulting from tropical/ subtropical and mid-latitude clouds respectively. Hemispheric albedo symmetry is not found in individual ocean-only latitude bands; comparing the Northern and Southern Hemisphere (NH and SH), regional mean albedo is higher in the NH tropics, and lower in the NH subtropics and mid-latitudes, than in the SH counterparts. This follows the hemispheric asymmetry of cloud fraction. In mid-latitudes and tropics the hemispheric asymmetry in cloud albedo also contributes to the asymmetry in total albedo, whereas in the subtropics the cloud albedo is more hemispherically symmetric. According to the observations, cloud-contributions to compensation for higher clear-sky albedo in the NH come primarily from cloud albedo in mid-latitudes and cloud amount in the subtropics. Current-generation climate models diverge in their representation of these relations, but common features of the model-to-data comparison include weaker than observed asymmetry in cloud fraction and cloud albedo in the tropics, weaker or reversed cloud fraction asymmetry in the subtropics and agreement with observed cloud albedo asymmetry in the mid-latitudes. Models on average reproduce the NH/SH asymmetry in total albedo over the 60°S–60°N ocean, but more than observations show higher occurrence of brighter clouds in the SH. The albedo bias in both hemispheres is reinforced by over-estimated clear-sky albedo in the models.
Bhatt, Rajendra; Doelling, David R.; Angal, Amit; Xiong, Xiaoxiong; Scarino, Benjamin; Gopalan, Arun; Haney, Conor; Wu, AishengBhatt, R., D. R. Doelling, A. Angal, X. Xiong, B. Scarino, A. Gopalan, C. Haney, A. Wu, 2017: Characterizing response versus scan-angle for MODIS reflective solar bands using deep convective clouds. Journal of Applied Remote Sensing, 11(1), 016014-016014. doi: 10.1117/1.JRS.11.016014. Abstract. MODIS consists of a cross-track, two-sided scan mirror, whose reflectance is not uniform but is a function of angle of incidence (AOI). This feature, known as response versus scan-angle (RVS), was characterized for all reflective solar bands of both MODIS instruments prior to launch. The RVS characteristic has changed on orbit, which must be tracked precisely over time to ensure the quality of MODIS products. The MODIS characterization support team utilizes the onboard calibrators and the earth view responses from multiple pseudoinvariant desert sites to track the RVS changes at different AOIs. The drawback of using deserts is the assumption that these sites are radiometrically stable during the monitoring period. In addition, the 16-day orbit repeat cycle of MODIS allows for only a limited set of AOIs over a given desert. We propose a novel and robust approach of characterizing the MODIS RVS using tropical deep convective clouds (DCC). The method tracks the monthly DCC response at specified sets of AOIs to compute the temporal RVS changes. Initial results have shown that the Aqua-MODIS collection 6 band 1 level 1B radiances show considerable residual RVS dependencies, with long-term drifts up to 2.3% at certain AOIs.
Bhatt, Rajendra; Doelling, David R.; Scarino, Benjamin; Haney, Conor; Gopalan, ArunBhatt, R., D. R. Doelling, B. Scarino, C. Haney, A. Gopalan, 2017: Development of Seasonal BRDF Models to Extend the Use of Deep Convective Clouds as Invariant Targets for Satellite SWIR-Band Calibration. Remote Sensing, 9(10), 1061. doi: 10.3390/rs9101061. Tropical deep convective clouds (DCC) are an excellent invariant target for vicarious calibration of satellite visible (VIS) and near-infrared (NIR) solar bands. The DCC technique (DCCT) is a statistical approach that collectively analyzes all identified DCC pixels on a monthly basis. The DCC reflectance in VIS and NIR spectrums is mainly a function of cloud optical depth, and provides a stable monthly statistical mode. However, for absorption shortwave infrared (SWIR) bands, the monthly DCC response is found to exhibit large seasonal cycles that make the implementation of the DCCT more challenging at these wavelengths. The seasonality assumption was tested using the SNPP-VIIRS SWIR bands, with up to 50% of the monthly DCC response temporal variation removed through deseasonalization. In this article, a monthly DCC bidirectional reflectance distribution function (BRDF) approach is proposed, which is found to be comparable to or can outperform the effects of deseasonalization alone. To demonstrate that the SNPP-VIIRS DCC BRDF can be applied to other JPSS VIIRS imagers in the same 13:30 sun-synchronous orbit, the VIIRS DCC BRDF was applied to Aqua-MODIS. The Aqua-MODIS SWIR band DCC reflectance natural variability is reduced by up to 45% after applying the VIIRS-based monthly DCC BRDFs. calibration; MODIS; VIIRS; BRDF; DCC; JPSS; SWIR bands
Biswas, Jhuma; Pathak, Binita; Patadia, Falguni; Bhuyan, Pradip K.; Gogoi, Mukunda M.; Babu, S. SureshBiswas, J., B. Pathak, F. Patadia, P. K. Bhuyan, M. M. Gogoi, S. S. Babu, 2017: Satellite-retrieved direct radiative forcing of aerosols over North-East India and adjoining areas: climatology and impact assessment. International Journal of Climatology, 37, 298-317. doi: 10.1002/joc.5004. In order to understand the climatic implications of atmospheric aerosols, top of atmosphere (TOA) shortwave (SW, 0.3–5 µm) fluxes and aerosol optical depth (AOD) at 550 nm retrieved simultaneously by clouds and the earth's radiant energy system (CERES) and moderate resolution imaging spectroradiometer (MODIS) instruments, respectively, are analysed over North-East India and its adjoining areas for the period July 2002–December 2013. The aerosol-free TOA flux obtained by establishing the linear regression between CERES SW TOA fluxes and MODIS AODs exhibits strong seasonality with peak values in monsoon and minimum in winter. Same seasonality is captured by the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model, but with difference in absolute values. SBDART code is used to extend instantaneous radiative forcing estimates into 24-h averages. AOD over the North East India region with complex terrain shows altitudinal variation with maximum value at the lowest elevation site Dhaka and minimum value at the high-altitude locations Shillong and Aizwal. In general, strong seasonality in AOD is observed with a peak in pre-monsoon (March–May) and dip in post-monsoon (October–November) at all the locations. The direct instantaneous TOA shortwave aerosol radiative forcing (SWARF) shows maximum values in pre-monsoon over all the locations except at Guwahati, Banmauk, Aizawl, and Shillong. The lowest value of instantaneous SWARF is observed in post-monsoon except at Banmauk and Shillong. Climatologically TOA diurnally averaged SWARF varies between −6.95 W m−2 in Aizawl to −20.39 W m−2 in Shillong. In general, the TOA SW forcing efficiency is highest in monsoon at all the locations. The radiative forcing efficiency is found to be less negative when surface reflectance increases. CERES; aerosol radiative forcing; remote sensing; aerosol optical depth; regional air quality
Bright, Ryan M.; Davin, Edouard; O’Halloran, Thomas; Pongratz, Julia; Zhao, Kaiguang; Cescatti, AlessandroBright, R. M., E. Davin, T. O’Halloran, J. Pongratz, K. Zhao, A. Cescatti, 2017: Local temperature response to land cover and management change driven by non-radiative processes. Nature Climate Change, 7(4), 296-302. doi: 10.1038/nclimate3250. Following a land cover and land management change (LCMC), local surface temperature responds to both a change in available energy and a change in the way energy is redistributed by various non-radiative mechanisms. However, the extent to which non-radiative mechanisms contribute to the local direct temperature response for different types of LCMC across the world remains uncertain. Here, we combine extensive records of remote sensing and in situ observation to show that non-radiative mechanisms dominate the local response in most regions for eight of nine common LCMC perturbations. We find that forest cover gains lead to an annual cooling in all regions south of the upper conterminous United States, northern Europe, and Siberia—reinforcing the attractiveness of re-/afforestation as a local mitigation and adaptation measure in these regions. Our results affirm the importance of accounting for non-radiative mechanisms when evaluating local land-based mitigation or adaptation policies. Climate and Earth system modelling; Climate-change mitigation
Brown, Patrick T.; Caldeira, KenBrown, P. T., K. Caldeira, 2017: Greater future global warming inferred from Earth’s recent energy budget. Nature, 552(7683), 45. doi: 10.1038/nature24672. Models show that several aspects of Earth’s top-of-atmosphere energy budget and the magnitude of projected global warming are correlated, enabling us to infer that future warming has been underestimated.
Burgman, Robert J.; Kirtman, Ben P.; Clement, Amy C.; Vazquez, HeatherBurgman, R. J., B. P. Kirtman, A. C. Clement, H. Vazquez, 2017: Model evidence for low-level cloud feedback driving persistent changes in atmospheric circulation and regional hydroclimate. Geophysical Research Letters, 44(1), 428–437. doi: 10.1002/2016GL071978. Recent studies suggest that low clouds in the Pacific play an important role in the observed decadal climate variability and future climate change. In this study, we implement a novel modeling experiment designed to isolate how interactions between local and remote feedbacks associated with low cloud, SSTs, and the large-scale circulation play a significant role in the observed persistence of tropical Pacific SST and associated North American drought. The modeling approach involves the incorporation of observed patterns of satellite-derived shortwave cloud radiative effect (SWCRE) into the coupled model framework and is ideally suited for examining the role of local and large-scale coupled feedbacks and ocean heat transport in Pacific decadal variability. We show that changes in SWCRE forcing in eastern subtropical Pacific alone reproduces much of the observed changes in SST and atmospheric circulation over the past 16 years, including the observed changes in precipitation over much of the Western Hemisphere. Feedback; 3310 Clouds and cloud feedbacks; 1616 Climate variability; drought; cloud radiative effect; hiatus; 1812 Drought; 3344 Paleoclimatology; Pacific; 4513 Decadal ocean variability; decadal
Burls, Natalie J.; Muir, Leslie; Vincent, Emmanuel M.; Fedorov, AlexeyBurls, N. J., L. Muir, E. M. Vincent, A. Fedorov, 2017: Extra-tropical origin of equatorial Pacific cold bias in climate models with links to cloud albedo. Climate Dynamics, 49(5-6), 2093-2113. doi: 10.1007/s00382-016-3435-6. General circulation models frequently suffer from a substantial cold bias in equatorial Pacific sea surface temperatures (SSTs). For instance, the majority of the climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) have this particular problem (17 out of the 26 models evaluated in the present study). Here, we investigate the extent to which these equatorial cold biases are related to mean climate biases generated in the extra-tropics and then communicated to the equator via the oceanic subtropical cells (STCs). With an evident relationship across the CMIP5 models between equatorial SSTs and upper ocean temperatures in the extra-tropical subduction regions, our analysis suggests that cold SST biases within the extra-tropical Pacific indeed translate into a cold equatorial bias via the STCs. An assessment of the relationship between these extra-tropical SST biases and local surface heat flux components indicates a link to biases in the simulated shortwave fluxes. Further sensitivity studies with a climate model (CESM) in which extra-tropical cloud albedo is systematically varied illustrate the influence of cloud albedo perturbations, not only directly above the oceanic subduction regions but across the extra-tropics, on the equatorial bias. The CESM experiments reveal a quadratic relationship between extra-tropical Pacific albedo and the root-mean-square-error in equatorial SSTs—a relationship with which the CMIP5 models generally agree. Thus, our study suggests that one way to improve the equatorial cold bias in the models is to improve the representation of subtropical and mid-latitude cloud albedo.
Cao, Wen; Duan, Chunfeng; Shen, Shuanghe; Yao, YunCao, W., C. Duan, S. Shen, Y. Yao, 2017: Evaluation and Parameter Optimization of Monthly Net Long-Wave Radiation Climatology Methods in China. Atmosphere, 8(6), 94. doi: 10.3390/atmos8060094. Based on surface radiation balance data and meteorological observations at 19 radiation stations in China from 1993 to 2012, we assessed the applicability of seven empirical formulas for the estimation of monthly surface net long-wave radiation (Rnl). We then established a revised method applicable to China by re-fitting the formula using new observational data. The iterative solution method and the multivariate regression analysis method with the minimum root mean square error (RMSE) were used as the objective functions in the revised method. Meanwhile, the accuracy of the CERES (Clouds and the Earth’s Radiant Energy System) estimated Rnl was also evaluated. Results show that monthly Rnl over China was underestimated by the seven formulas and the CERES data. The Tong Hongliang formula with lowest errors was the best among the seven formulas for estimating Rnl over China as a whole, followed by the Penman and the Deng Genyun formulas. The estimated Rnl based on the CERES data also showed relatively higher precision in accordance with the three formulas mentioned above. The FAO56-PM formula (Penman–Monteith formula recommended in the No. 56 report of the Food and Agriculture Organization) without calibration was not applicable to China due to its low accuracy. For individual stations, the Deng Genyun formula was the most accurate in the eastern plain area, while the Tong Hongliang formula was suitable for the plateau. Regional formulas were established based on the geographical distribution of water vapor pressure and elevation over China. The revised national and regional formulas were more accurate than the seven original formulas and the CERES data. Furthermore, the regional formulas produced smaller errors than the national formula at most of the stations. The regional formulas were clearly more accurate than the Deng Genyun formula at stations in Northwestern China and on the Tibetan Plateau. They were also more accurate than the Tong Hongliang formula at the stations located in the eastern area. Therefore, the regional formulas developed in this study are recommended as the standard climatology formulas to calculate monthly Rnl over China. evaluation; China; method; net long-wave radiation; Optimization
Cao, Yunfeng; Liang, Shunlin; Chen, Xiaona; He, Tao; Wang, Dongdong; Cheng, XiaoCao, Y., S. Liang, X. Chen, T. He, D. Wang, X. Cheng, 2017: Enhanced wintertime greenhouse effect reinforcing Arctic amplification and initial sea-ice melting. Scientific Reports, 7(1), 8462. doi: 10.1038/s41598-017-08545-2. The speeds of both Arctic surface warming and sea-ice shrinking have accelerated over recent decades. However, the causes of this unprecedented phenomenon remain unclear and are subjects of considerable debate. In this study, we report strong observational evidence, for the first time from long-term (1984–2014) spatially complete satellite records, that increased cloudiness and atmospheric water vapor in winter and spring have caused an extraordinary downward longwave radiative flux to the ice surface, which may then amplify the Arctic wintertime ice-surface warming. In addition, we also provide observed evidence that it is quite likely the enhancement of the wintertime greenhouse effect caused by water vapor and cloudiness has advanced the time of onset of ice melting in mid-May through inhibiting sea-ice refreezing in the winter and accelerating the pre-melting process in the spring, and in turn triggered the positive sea-ice albedo feedback process and accelerated the sea ice melting in the summer.
Cassano, John J.; DuVivier, Alice; Roberts, Andrew; Hughes, Mimi; Seefeldt, Mark; Brunke, Michael; Craig, Anthony; Fisel, Brandon; Gutowski, William; Hamman, Joseph; Higgins, Matthew; Maslowski, Wieslaw; Nijssen, Bart; Osinski, Robert; Zeng, XubinCassano, J. J., A. DuVivier, A. Roberts, M. Hughes, M. Seefeldt, M. Brunke, A. Craig, B. Fisel, W. Gutowski, J. Hamman, M. Higgins, W. Maslowski, B. Nijssen, R. Osinski, X. Zeng, 2017: Development of the Regional Arctic System Model (RASM): Near-Surface Atmospheric Climate Sensitivity. J. Climate, 30(15), 5729-5753. doi: 10.1175/JCLI-D-15-0775.1. The near-surface climate, including the atmosphere, ocean, sea ice, and land state and fluxes, in the initial version of the Regional Arctic System Model (RASM) are presented. The sensitivity of the RASM near-surface climate to changes in atmosphere, ocean, and sea ice parameters and physics is evaluated in four simulations. The near-surface atmospheric circulation is well simulated in all four RASM simulations but biases in surface temperature are caused by biases in downward surface radiative fluxes. Errors in radiative fluxes are due to biases in simulated clouds with different versions of RASM simulating either too much or too little cloud radiative impact over open ocean regions and all versions simulating too little cloud radiative impact over land areas. Cold surface temperature biases in the central Arctic in winter are likely due to too few or too radiatively thin clouds. The precipitation simulated by RASM is sensitive to changes in evaporation that were linked to sea surface temperature biases. Future work will explore changes in model microphysics aimed at minimizing the cloud and radiation biases identified in this work.
Chambers, Lin H.Chambers, L. H., 2017: Clouds. International Encyclopedia of Geography: People, the Earth, Environment and Technology.
Chambers, Lin H.; McKeown, Megan A.; McCrea, Sarah A.; Martin, Ann M.; Rogerson, Tina M.; Bedka, Kristopher M.Chambers, L. H., M. A. McKeown, S. A. McCrea, A. M. Martin, T. M. Rogerson, K. M. Bedka, 2017: CERES S’COOL Project Update: The Evolution and Value of a Long-Running Education Project With a Foundation in NASA Earth Science Missions. Bull. Amer. Meteor. Soc., 98(3), 473–483. doi: 10.1175/BAMS-D-15-00248.1. Since 1997, S’COOL has engaged interested participants worldwide in observing clouds and comparing data from ground and satellite sources to inform validation efforts for several NASA Earth science missions.
Chen, Jinghua; Wu, Xiaoqing; Yin, Yan; Huang, Qian; Xiao, HuiChen, J., X. Wu, Y. Yin, Q. Huang, H. Xiao, 2017: Characteristics of Cloud Systems over the Tibetan Plateau and East China during Boreal Summer. J. Climate, 30(9), 3117-3137. doi: 10.1175/JCLI-D-16-0169.1. Constrained by ERA-Interim, a cloud-resolving model is employed to characterize cloud systems over the Tibetan Plateau (TP) and east China. The authors focus on analyzing the role of different physical processes on cloud macro- and microscale properties of the cloud systems, especially convective cloud systems between east China and the TP. It is found that convective clouds over the TP are thinner than over east China. This difference is also reflected in the albedo at the top of the atmosphere, where smaller albedos are found for the clouds over the TP. Furthermore, the lifetimes of the deep cloud systems over the TP are shorter than over east China. For the entire simulated period, the latent heat released by phase transitions contributes the most to the total heating and moisture budget, followed by eddy transport over all regions. In addition, radiative heating also plays a nonnegligible role in the total heating effects over the TP. These results also suggest that the influence of ice phase processes is more important over the TP than east China, especially during deep convective periods. Affected by strong surface heat flux, the cloud-top height of convective clouds over the TP exhibits a diurnal cycle, leading to a diurnal cycle of rainfall.
Chen, Xiaona; Long, Di; Hong, Yang; Liang, Shunlin; Hou, AizhongChen, X., D. Long, Y. Hong, S. Liang, A. Hou, 2017: Observed radiative cooling over the Tibetan Plateau for the past three decades driven by snow cover-induced surface albedo anomaly. Journal of Geophysical Research: Atmospheres, 122(12), 6170–6185. doi: 10.1002/2017JD026652. Seasonal snow cover on the Tibetan Plateau (TP) is a sensitive indicator of climate change. Unlike the decreasing snow cover extent and associated weakening of radiative cooling effects for the Northern Hemisphere during recent decades reported by previous studies, snow cover variability over the TP and its impact on the energy budget remain largely unknown. We defined the snow cover-induced radiative forcing (SnRF) as the instantaneous perturbation to Earth's shortwave radiation at the top of the atmosphere (TOA) induced by the presence of snow cover. Here using satellite observations and a radiative kernel approach, we found slightly enhanced SnRF, i.e., a radiative cooling effect on the TP during the past three decades (1982–2014). However, this cooling effect weakened during 2001–2014 because of reduced snow cover at a rate of −0.61% decade−1 and land surface albedo at a rate of −0.72% decade−1. Changes in snow cover fraction are highly correlated with anomalies in land surface albedo (as) over the TP both spatially and temporally. Moreover, the SnRF is closely related to the direct observation of TOA shortwave flux anomalies (R2 = 0.54, p = 0.004) over the TP during 2001–2014. Despite the insignificant interannual variability in SnRF, its intra-annual variability has intensified driven mostly by enhanced SnRF during the snow accumulation season but weakened SnRF during the melt season, indicating greater energy release during the transition between accumulation and melt seasons. This may pose a great challenge to snow meltwater use and flood prediction for transboundary rivers originating from the TP, such as the Brahmaputra River basin. albedo; Snow cover; radiation; Tibetan Plateau; 0736 Snow; 0764 Energy balance; 4908 Albedo; 1807 Climate impacts; radiative cooling
Cheng, Jie; Liang, Shunlin; Wang, Wenhui; Guo, YaminCheng, J., S. Liang, W. Wang, Y. Guo, 2017: An efficient hybrid method for estimating clear-sky surface downward longwave radiation from MODIS data. Journal of Geophysical Research: Atmospheres, 122(5), 2616–2630. doi: 10.1002/2016JD026250. This paper proposes an efficient hybrid method for estimating 1 km instantaneous clear-sky surface downward longwave radiation (LWDN) from Moderate Resolution Imaging Spectroradiometer (MODIS) thermal infrared observations and the MODIS near-infrared column water vapor (CWV) data product. The LWDN was formulated as a nonlinear function of surface upwelling longwave radiation estimated from the MODIS top-of-atmosphere (TOA) radiance of channels 29, 31, and 32, as well as CWV and the MODIS TOA radiance of channel 29. Ground measurements collected at 62 globally distributed sites from six networks were used to develop and validate the proposed hybrid method. The validation results showed that the bias and root-mean-square error (RMSE) were 0.0597 W/m2 and 21.008 W/m2. These results demonstrate that the performance of our method is superior to that of other studies reported in the literature. The drawback of our method is that LWDN is overestimated over high-elevation areas with extremely low CWV ( MODIS; 1814 Energy budgets; surface energy budget; CWV; hybrid method; surface downward longwave radiation; surface upwelling longwave radiation
Choi, Yong-Sang; Kim, Won Moo; Yeh, Sang-Wook; Masunaga, Hirohiko; Kwon, Min-Jae; Jo, Hyun-Su; Huang, LeiChoi, Y., W. M. Kim, S. Yeh, H. Masunaga, M. Kwon, H. Jo, L. Huang, 2017: Revisiting the Iris Effect of Tropical Cirrus Clouds with TRMM and A-train Satellite Data. Journal of Geophysical Research: Atmospheres, 122(11), 5917–5931. doi: 10.1002/2016JD025827. Just as the iris of human eye controls the light influx (iris effect), tropical anvil cirrus clouds may regulate the Earth's surface warming by controlling outgoing longwave radiation. This study examines this possible effect with monthly satellite observations such as TRMM precipitation, MODIS cirrus fraction, and CERES top-of-the-atmosphere radiative fluxes averaged over different tropical domains from March 2000 to October 2014. To confirm that high-level cirrus is relevant to this study, CALIOP high cloud observations were also analyzed from June 2006 to December 2015. Our analysis revealed that the increase in sea surface temperature in the tropical western Pacific tends to concentrate convective cloud systems. This concentration effect very likely induces the significant reduction of both stratiform rain rate and cirrus fraction, without appreciable change in the convective rain rate. This reduction of stratiform rain rate and cirrus fraction cannot be found over its sub-region or the tropical eastern Pacific, where the concentration effect of anvil cirrus is weak. Consistently, over the tropical western Pacific, the higher ratio of convective rain rate to total rain rate (i.e., precipitation efficiency) significantly correlates with warmer sea surface temperature and lower cirrus fraction. The reduced cirrus eventually increased outgoing longwave radiation to a greater degree than absorbed solar radiation. Finally, the negative relationship between precipitation efficiency and cirrus fraction tends to correspond to a low global equilibrium climate sensitivity in the models in the CMIP5. This suggests that tropical anvil cirrus clouds exert a negative climate feedback in strong association with precipitation efficiency. 3305 Climate change and variability; 3337 Global climate models; 3310 Clouds and cloud feedbacks; Climate sensitivity; 3371 Tropical convection; cloud feedback; cirrus; iris effect; tropical cloud
Christensen, H. M.; Lock, S.-J; Moroz, I. M.; Palmer, T. N.Christensen, H. M., S. Lock, I. M. Moroz, T. N. Palmer, 2017: Introducing Independent Patterns into the Stochastically Perturbed Parametrisation Tendencies (SPPT) scheme. Quarterly Journal of the Royal Meteorological Society, 143(706), 2168–2181. doi: 10.1002/qj.3075. The Stochastically Perturbed Parametrisation Tendencies (SPPT) scheme is used at weather and climate forecasting centres worldwide to represent model uncertainty that arises from simplifications involved in the parametrisation process. It uses spatio-temporally correlated multiplicative noise to perturb the sum of the parametrised tendencies. However, SPPT does not distinguish between different parametrisation schemes, which do not necessarily have the same error characteristics. A generalisation to SPPT is proposed, whereby the tendency from each parametrisation scheme can be perturbed using an independent stochastic pattern. This acknowledges that the forecast errors arising from different parametrisations are not perfectly correlated. Two variations of this ‘independent SPPT’ (iSPPT) approach are tested in the Integrated Forecasting System (IFS). The first perturbs all parametrised tendencies independently while the second groups tendencies before perturbation. The iSPPT schemes lead to statistically significant improvements in forecast reliability in the tropics in medium range weather forecasts. This improvement can be attributed to a large, beneficial increase in ensemble spread in regions with significant convective activity. The iSPPT schemes also lead to improved forecast skill in the extra tropics for a set of cases in which the synoptic initial conditions were more likely to result in European ‘forecast busts’. Longer 13-month simulations are also considered to indicate the effect of iSPPT on the mean climate of the IFS. ensemble forecasts; independent SPPT (iSPPT); medium-range forecasts; model uncertainty; multiplicative noise; stochastic parametrisation
Ciesielski, Paul E.; Johnson, Richard H.; Jiang, Xianan; Zhang, Yunyan; Xie, ShaochengCiesielski, P. E., R. H. Johnson, X. Jiang, Y. Zhang, S. Xie, 2017: Relationships Between Radiation, Clouds, and Convection During DYNAMO. Journal of Geophysical Research: Atmospheres, 122(5), 2529–2548. doi: 10.1002/2016JD025965. The relationships between radiation, clouds, and convection on an intraseasonal time scale are examined with data taken during the Dynamics of the MJO (DYNAMO) field campaign. Specifically, column-net, as well as vertical profiles of radiative heating rates, computed over Gan Island in the central Indian Ocean (IO) are used along with an objective analysis of large-scale fields to examine three MJO events that occurred during the 3-month period (October to December 2011) over this region. Longwave (LW) and shortwave (SW) radiative heating rates exhibit tilted structures, reflecting radiative effects associated with the prevalence of shallow cumulus during the dry, suppressed MJO phase followed by increasing deep convection leading into the active phase. As the convection builds going into the MJO active phase, there are increasingly top-heavy anomalous radiative heating rates while the column-net radiative cooling rate progressively decreases. Temporal fluctuations in the cloud radiative forcing (CRF), being quite sensitive to changes in high cloudiness, are dominated by LW effects with an intraseasonal variation of ~0.4-0.6 K/day. While both the water vapor and cloud fields are inextricably linked, it appears that the tilted radiative structures are more related to water vapor effects. The intraseasonal variation of column-net radiative heating enhances the convective signal in the mean by ~20% with a minimum in this enhancement ~10 days prior to peak MJO rainfall and maximum ~7 days after. This suggests that as MJO convective envelope weakens over the central IO, cloud-radiative feedbacks help maintain the mature MJO as it moves eastward. clouds; convection; 3359 Radiative processes; 3314 Convective processes; radiation; 3371 Tropical convection; DYNAMO; MJO
Cusworth, D. H.; Mickley, L. J.; Leibensperger, E. M.; Iacono, M. J.Cusworth, D. H., L. J. Mickley, E. M. Leibensperger, M. J. Iacono, 2017: Aerosol trends as a potential driver of regional climate in the central United States: evidence from observations. Atmos. Chem. Phys., 17(22), 13559-13572. doi: 10.5194/acp-17-13559-2017. In situ surface observations show that downward surface solar radiation (SWdn) over the central and southeastern United States (US) has increased by 0.58–1.0 Wm−2 a−1 over the 2000–2014 time frame, simultaneously with reductions in US aerosol optical depth (AOD) of 3.3–5.0 × 10−3 a−1. Establishing a link between these two trends, however, is challenging due to complex interactions between aerosols, clouds, and radiation. Here we investigate the clear-sky aerosol–radiation effects of decreasing US aerosols on SWdn and other surface variables by applying a one-dimensional radiative transfer to 2000–2014 measurements of AOD at two Surface Radiation Budget Network (SURFRAD) sites in the central and southeastern United States. Observations characterized as clear-sky may in fact include the effects of thin cirrus clouds, and we consider these effects by imposing satellite data from the Clouds and Earth's Radiant Energy System (CERES) into the radiative transfer model. The model predicts that 2000–2014 trends in aerosols may have driven clear-sky SWdn trends of +1.35 Wm−2 a−1 at Goodwin Creek, MS, and +0.93 Wm−2 a−1 at Bondville, IL. While these results are consistent in sign with observed trends, a cross-validated multivariate regression analysis shows that AOD reproduces 20–26 % of the seasonal (June–September, JJAS) variability in clear-sky direct and diffuse SWdn at Bondville, IL, but none of the JJAS variability at Goodwin Creek, MS. Using in situ soil and surface flux measurements from the Ameriflux network and Illinois Climate Network (ICN) together with assimilated meteorology from the North American Land Data Assimilation System (NLDAS), we find that sunnier summers tend to coincide with increased surface air temperature and soil moisture deficits in the central US. The 1990–2015 trends in the NLDAS SWdn over the central US are also of a similar magnitude to our modeled 2000–2014 clear-sky trends. Taken together, these results suggest that climate and regional hydrology in the central US are sensitive to the recent reductions in aerosol concentrations. Our work has implications for severely polluted regions outside the US, where improvements in air quality due to reductions in the aerosol burden could inadvertently pose an enhanced climate risk.
Dang, Cheng; Warren, Stephen G.; Fu, Qiang; Doherty, Sarah J.; Sturm, MatthewDang, C., S. G. Warren, Q. Fu, S. J. Doherty, M. Sturm, 2017: Measurements of light-absorbing particles in snow across the Arctic, North America, and China: effects on surface albedo. Journal of Geophysical Research: Atmospheres, 122(19), 10,149–10,168. doi: 10.1002/2017JD027070. Using field observation, we perform radiative transfer calculations on snowpacks in the Arctic, China, and North America to quantify the impact of light-absorbing particles (LAPs) on snow albedo and its sensitivity to different factors. For new snow, the regional-averaged albedo reductions caused by all LAPs in the Arctic, North America, and China are 0.009, 0.012, and 0.077, respectively, of which the albedo reductions caused by black carbon (BC) alone are 0.005, 0.005, and 0.031, corresponding to a positive radiative forcing of 0.06, 0.3, and 3 Wm-2. The albedo reduction for old melting snow is larger than that of new snow by a factor of 2, for the same particulate concentrations; this leads to 3 – 8 times larger radiative forcing, in part due to higher solar irradiance in the melting season. These calculations used ambient snowpack properties; if all snowpacks were instead assumed to be optically thick, the albedo reduction would be 20-50% larger for new snow in the Arctic and North America and 120-300% larger for old snow. Accounting for non-BC LAPs reduces the albedo reduction by BC in the Arctic, North America, and China by 32%, 29% and 70% respectively for new snow and 11%, 7% and 51% for old snow. BC-in-snow albedo reduction computed using two-layer model agrees reasonably with that computed using multi-layer model. Biases in BC concentration or snow depth often lead to nonlinear biases in BC-induced albedo reduction. 0305 Aerosols and particles; 3305 Climate change and variability; black carbon; 0736 Snow; snow albedo; light-absorbing particles; observation; radiative transfer calculation
de Guélis, T. V.; Chepfer, H.; Noel, V.; Guzman, R.; Dubuisson, P.; Winker, D. M.; Kato, S.de Guélis, T. V., H. Chepfer, V. Noel, R. Guzman, P. Dubuisson, D. M. Winker, S. Kato, 2017: The link between outgoing longwave radiation and the altitude at which a spaceborne lidar beam is fully attenuated. Atmos. Meas. Tech., 10(12), 4659-4685. doi: 10.5194/amt-10-4659-2017. According to climate model simulations, the changing altitude of middle and high clouds is the dominant contributor to the positive global mean longwave cloud feedback. Nevertheless, the mechanisms of this longwave cloud altitude feedback and its magnitude have not yet been verified by observations. Accurate, stable, and long-term observations of a metric-characterizing cloud vertical distribution that are related to the longwave cloud radiative effect are needed to achieve a better understanding of the mechanism of longwave cloud altitude feedback. This study shows that the direct measurement of the altitude of atmospheric lidar opacity is a good candidate for the necessary observational metric. The opacity altitude is the level at which a spaceborne lidar beam is fully attenuated when probing an opaque cloud. By combining this altitude with the direct lidar measurement of the cloud-top altitude, we derive the effective radiative temperature of opaque clouds which linearly drives (as we will show) the outgoing longwave radiation. We find that, for an opaque cloud, a cloud temperature change of 1 K modifies its cloud radiative effect by 2 W m−2. Similarly, the longwave cloud radiative effect of optically thin clouds can be derived from their top and base altitudes and an estimate of their emissivity. We show with radiative transfer simulations that these relationships hold true at single atmospheric column scale, on the scale of the Clouds and the Earth's Radiant Energy System (CERES) instantaneous footprint, and at monthly mean 2° × 2° scale. Opaque clouds cover 35 % of the ice-free ocean and contribute to 73 % of the global mean cloud radiative effect. Thin-cloud coverage is 36 % and contributes 27 % of the global mean cloud radiative effect. The link between outgoing longwave radiation and the altitude at which a spaceborne lidar beam is fully attenuated provides a simple formulation of the cloud radiative effect in the longwave domain and so helps us to understand the longwave cloud altitude feedback mechanism.
de Guélis, Thibault Vaillant; Chepfer, Hélène; Noel, Vincent; Guzman, Rodrigo; Winker, David M.; Plougonven, Riwalde Guélis, T. V., H. Chepfer, V. Noel, R. Guzman, D. M. Winker, R. Plougonven, 2017: Using space lidar observations to decompose Longwave Cloud Radiative Effect variations over the last decade. Geophysical Research Letters, 44(23), 11,994–12,003. doi: 10.1002/2017GL074628. Measurements of the longwave cloud radiative effect (LWCRE) at the top of the atmosphere assess the contribution of clouds to the Earth warming, but do not quantify the cloud property variations that are responsible for the LWCRE variations. The CALIPSO space-lidar observes directly the detailed profile of cloud, cloud opacity, and cloud cover. Here we use these observations to quantify the influence of cloud properties on the variations of the LWCRE observed between 2008 and 2015 in the tropics and at global scale. At global scale, the method proposed here gives good results except over the Southern Ocean. We find that the global LWCRE variations observed over ocean are mostly due to variations in the opaque cloud properties (82 %); transparent cloud columns contributed 18 %. Variation of opaque cloud cover is the first contributor to the LWCRE evolution (58 %); opaque cloud temperature is the second contributor (28 %). 1640 Remote sensing; 0321 Cloud/radiation interaction; 3310 Clouds and cloud feedbacks; cloud radiative effect; cloud profile; decomposition; space-lidar
Dewitte, Steven; Clerbaux, NicolasDewitte, S., N. Clerbaux, 2017: Measurement of the Earth Radiation Budget at the Top of the Atmosphere—A Review. Remote Sensing, 9(11), 1143. doi: 10.3390/rs9111143. The Earth Radiation Budget at the top of the atmosphere quantifies how the Earth gains energy from the Sun and loses energy to space. It is of fundamental importance for climate and climate change. In this paper, the current state-of-the-art of the satellite measurements of the Earth Radiation Budget is reviewed. Combining all available measurements, the most likely value of the Total Solar Irradiance at a solar minimum is 1362 W/m 2, the most likely Earth albedo is 29.8%, and the most likely annual mean Outgoing Longwave Radiation is 238 W/m 2. We highlight the link between long-term changes of the Outgoing Longwave Radiation, the strengthening of El Nino in the period 1985–1997 and the strengthening of La Nina in the period 2000–2009. Satellite remote sensing; Earth Radiation Budget; Total Solar irradiance
Dieng, H. B.; Cazenave, A.; Meyssignac, B.; von Schuckmann, K.; Palanisamy, H.Dieng, H. B., A. Cazenave, B. Meyssignac, K. von Schuckmann, H. Palanisamy, 2017: Sea and land surface temperatures, ocean heat content, Earth's energy imbalance and net radiative forcing over the recent years. International Journal of Climatology, 37(S1), 218–229. doi: 10.1002/joc.4996. We investigate the global mean and regional change of sea surface and land surface temperature over 2003–2013, using a large number of different data sets, and compare with changes observed over the past few decades (starting in 1950). We find that over 2003–2013, both global land surface temperature and global sea surface temperature have increased at a rate significantly lower than over the previous decades. While confirming cooling of eastern tropical Pacific during the last decade as reported in several recent studies, our results show that the reduced rate of change of the 2003–2013 time span is a global phenomenon. GMST short-term trends since 1950 computed over successive 11-year windows with 1-year overlap show important decadal variability that highly correlates with 11-year trends of the Atlantic Multidecadal Oscillation index. The GMST 11-year trend distribution is well fitted by a Gaussian function, confirming an unforced origin related to internal climate variability. We evaluate the time derivative of full-depth ocean heat content to determine the planetary energy imbalance with different approaches: in situ measurements, ocean reanalysis and global sea level budget. For 2003–2013, it amounts to 0.5 +/− 0.1 W m−2, 0.68 +/− 0.1 W m−2 and 0.65 +/− 0.1 W m−2, respectively for the three approaches. Comparing with the Energy Balanced and Filled (EBAF) data of the Clouds and Earth's Radiant Energy Systems (CERES) project, we find significant agreement at interannual scales. Finally, using 15-year averages of GMST and total ocean heat content rate, we compute the net radiative forcing since 1970 (this start date being constrained by availability of ocean temperature data). Although the uncertainty is quite large because of considerable errors in the climate sensitivity parameter, we find no evidence of decrease in net radiative forcing in the recent years, but rather an increase compared to the previous decades. Ocean heat content; Earth's energy imbalance; Global mean Earth's temperature
Eidhammer, Trude; Morrison, Hugh; Mitchell, David; Gettelman, Andrew; Erfani, EhsanEidhammer, T., H. Morrison, D. Mitchell, A. Gettelman, E. Erfani, 2017: Improvements in global climate model microphysics using a consistent representation of ice particle properties. J. Climate, 30(2), 609–629. doi: 10.1175/JCLI-D-16-0050.1. This paper describes a new approach for representing ice microphysics in climate models. In contrast with most previous schemes, this approach does not include separate categories for cloud and precipitating ice and instead uses a single two-moment category to represent all solid hydrometeors. Thus, there is no need for an ice “autoconversion” size threshold parameter, which has a critical impact on simulated climate in the Community Atmosphere Model (CAM5), yet is poorly constrained by theory or observations. Further, in the new treatment, all ice microphysical processes and parameters, including ice effective radius and mean fallspeed, are formulated self-consistently and flexibly based on empirical ice particle mass-size and projected area-size relationships. This means that the scheme can represent the physical coupling between bulk particle density, mean fallspeed, and effective radius, which is not possible in current schemes. Two different methods for specifying these relationships based on observations are proposed. The new scheme is tested in global simulations using CAM5. Differences in simulations using the two methods for specifying the mass- and projected-area size relationships, particularly the cloud radiative forcing, are attributable mainly to the effects on mean ice particle fallspeed, impacting sedimentation and ice water path. With some tuning of parameters involved in calculating homogeneous freezing it produces a similar climate compared to the simulations using the original CAM5 microphysics. Thus, it can produce a comparable climate while improving the physical basis and self-consistency of ice particle properties and parameters.
Eitzen, Zachary A.; Su, Wenying; Xu, Kuan-Man; Loeb, Norman; Sun, Moguo; Doelling, David; Rose, Fred; Bodas-Salcedo, AlejandroEitzen, Z. A., W. Su, K. Xu, N. Loeb, M. Sun, D. Doelling, F. Rose, A. Bodas-Salcedo, 2017: Evaluation of a general circulation model by the CERES Flux-by-cloud type simulator. Journal of Geophysical Research: Atmospheres, 122(20), 10,655–10,668. doi: 10.1002/2017JD027076. In this work, we use the CERES FluxByCloudTyp data product (FBCTObs), which calculates TOA shortwave and longwave fluxes for cloud types defined by cloud optical depth (τ) and cloud top pressure (pc), and the CERES Flux-by-cloud type simulator (FBCTSim) to evaluate the HadGEM2-A model. FBCTSim is comprised of a cloud generator that produces subcolumns with profiles of binary cloud fraction, a cloud property simulator that determines the cloud type (τ, pc) for each subcolumn, and a radiative transfer model that calculates TOA fluxes. The identification of duplicate subcolumns greatly reduces the number of radiative transfer calculations required. In the Southern Great Plains region in January, February, and December (JFD) 2008, FBCTSim shows that HadGEM2-A cloud tops are higher in altitude than in FBCTObs, but also have higher values of OLR than in FBCTObs, leading to a compensating error that results in an average value of OLR that is close to observed. When FBCTSim is applied to the Southeast Pacific stratocumulus region in JJA 2008, the cloud tops are primarily low in altitude; however, the clouds tend to be less numerous, and have higher optical depths than are observed. In addition, the HadGEM2-A albedo is higher than that of FBCTObs for those cloud types that occur most frequently. FBCTSim is also applied to the entire 60° N to 60° S region, and it is found that there are both fewer clouds and higher albedos than observed for most cloud types, which represents a compensating error in terms of the shortwave radiative budget. CERES; 0321 Cloud/radiation interaction; 3337 Global climate models; 3394 Instruments and techniques; 3360 Remote sensing; model evaluation; Instrument simulator
Fan, Yongzhen; Li, Wei; Gatebe, Charles K.; Jamet, Cédric; Zibordi, Giuseppe; Schroeder, Thomas; Stamnes, KnutFan, Y., W. Li, C. K. Gatebe, C. Jamet, G. Zibordi, T. Schroeder, K. Stamnes, 2017: Atmospheric correction over coastal waters using multilayer neural networks. Remote Sensing of Environment, 199(Supplement C), 218-240. doi: 10.1016/j.rse.2017.07.016. Standard atmospheric correction (AC) algorithms work well in open ocean areas where the water inherent optical properties (IOPs) are correlated with pigmented particles. However, the IOPs of turbid coastal waters may independently vary with pigmented particles, suspended inorganic particles, and colored dissolved organic matter (CDOM). In turbid coastal waters standard AC algorithms often exhibit large inaccuracies that may lead to negative water-leaving radiances (Lw) or remote sensing reflectance (Rrs). We introduce a new atmospheric correction algorithm for coastal waters based on a multilayer neural network (MLNN) method. We use a coupled atmosphere-ocean radiative transfer model to simulate the Rayleigh-corrected radiance (Lrc) at the top of the atmosphere (TOA) and the Rrs just above the surface simultaneously, and train a MLNN to derive the aerosol optical depth (AOD) and Rrs directly from the TOA Lrc. The method is validated using both a synthetic dataset and Aerosol Robotic Network – Ocean Color (AERONET–OC) measurements. The SeaDAS NIR algorithm, the SeaDAS NIR/SWIR algorithm, and the MODIS version of the Case 2 regional water - CoastColour (C2RCC) algorithm are also included in the comparison with AERONET–OC measurements. The performance of the AC algorithms is evaluated with four statistical metrics: the Pearson correlation coefficient (R), the average percentage difference (APD), the mean percentage bias, and the root mean square difference (RMSD). The comparison with AERONET–OC measurements shows that the MLNN algorithm significantly improves retrieval of normalized Lw in blue bands (412nm and 443nm) and yields minor improvements in green and red bands compared with the other three algorithms. On a global scale, the MLNN algorithm reduces APD in normalized Lw by up to 13% in blue bands and by 2–7% in green and red bands when compared with the standard SeaDAS NIR algorithm. In highly absorbing coastal waters, such as the Baltic Sea, the MLNN algorithm reduces APD in normalized Lw by more than 60% in blue bands compared to the standard SeaDAS NIR algorithm, while in highly scattering coastal waters, such as the Black Sea, the MLNN algorithm reduces APD by more than 25%. These results indicate that the MLNN algorithm is suitable for application in turbid coastal waters. Application of the MLNN algorithm to MODIS Aqua images in several coastal areas also shows that it is robust and resilient to contamination due to sunglint or adjacency effects of land and cloud edges. The MLNN algorithm is very fast once the neural network has been properly trained and is therefore suitable for operational use. A significant advantage of the MLNN algorithm is that it does not need SWIR bands. Remote sensing; MODIS; Ocean color; AERONET-OC; Atmosphere correction; Coastal area; Multilayer neural network; SeaDAS
Fasullo, J. T.; Tomas, R.; Stevenson, S.; Otto-Bliesner, B.; Brady, E.; Wahl, E.Fasullo, J. T., R. Tomas, S. Stevenson, B. Otto-Bliesner, E. Brady, E. Wahl, 2017: The amplifying influence of increased ocean stratification on a future year without a summer. Nature Communications, 8(1), 1236. doi: 10.1038/s41467-017-01302-z. The 1815 eruption of Mt. Tambora caused one of the strongest climate perturbations in the modern record; the 1816 year without a summer. Here, the authors show that climate change, through its impact on ocean stratification, strengthens the surface response to such an eruption.
Fiedler, S.; Stevens, B.; Mauritsen, T.Fiedler, S., B. Stevens, T. Mauritsen, 2017: On the sensitivity of anthropogenic aerosol forcing to model-internal variability and parameterizing a Twomey effect. Journal of Advances in Modeling Earth Systems, 9(2), 1325–1341. doi: 10.1002/2017MS000932. Despite efforts to accurately quantify the effective radiative forcing (ERF) of anthropogenic aerosol, the historical evolution of ERF remains uncertain. As a further step towards a better understanding of ERF uncertainty, the present study systematically investigates the sensitivity of the shortwave ERF at the top of the atmosphere to model-internal variability and spatial distributions of the monthly mean radiative effects of anthropogenic aerosol. For this, ensembles are generated with the atmospheric model ECHAM6.3 that uses monthly prescribed optical properties and changes in cloud-droplet number concentrations designed to mimic that associated with the anthropogenic aerosol using the new parameterization MACv2-SP. The results foremost highlight the small change in our best estimate of the global averaged all-sky ERF associated with a substantially different pattern of anthropogenic aerosol radiative effects from the mid-1970s (-0.51 Wm−2) and present day (-0.50 Wm−2). Such a small change in ERF is difficult to detect when model-internal year-to-year variability (0.32 Wm−2 standard deviation) is considered. A stable estimate of all-sky ERF requires ensemble simulations, the size of which depends on the targeted precision, confidence level, and the magnitude of model-internal variability. A larger effect of the pattern of the anthropogenic aerosol radiative effects on the globally averaged all-sky ERF (15%) occurs with a strong Twomey effect through lowering the background aerosol optical depth in regions downstream of major pollution sources. It suggests that models with strong aerosol-cloud interactions could show a moderate difference in the global mean ERF associated with the mid-1970s to present-day change in the anthropogenic aerosol pattern. 0305 Aerosols and particles; 3311 Clouds and aerosols; 3305 Climate change and variability; 3337 Global climate models; radiative forcing; CMIP6; 3320 Idealized model; anthropogenic aerosol; ECHAM; natural variability; Twomey effect
Folini, D.; Dallafior, T. N.; Hakuba, M. Z.; Wild, M.Folini, D., T. N. Dallafior, M. Z. Hakuba, M. Wild, 2017: Trends of surface solar radiation in unforced CMIP5 simulations. Journal of Geophysical Research: Atmospheres, 122(1), 469–484. doi: 10.1002/2016JD025869. We consider decadal scale trends of annual mean all-sky surface solar radiation (SSR) that occur solely because of internal variability of the climate system. We give statistical estimates of their magnitude and probability of occurrence. The estimates are based on 43 preindustrial control (piControl) experiments of the Coupled Model Intercomparison Project phase 5 (CMIP5). Trends are found to depend strongly on geographical region and on whether they are quantified in absolute units or relative to the long-term mean SSR. We find it to be sufficient to provide one map for absolute and one for relative trends, as approximate analytical relations are shown to hold between trends of different length and likelihood and the standard deviation of the underlying SSR time series. We estimate that a positive trend over 30 years and with 25% chance of occurrence (75th percentile of all possible trends) has a magnitude between 0.15 and 1.7 W/m2/decade or 0.11 and 1.4% of long-term mean SSR per decade, depending on geographical location. Comparison with present-day observations and intermodel spread suggests an average uncertainty of these estimates of about 30%. Intermodel spread suggests that regional uncertainties can be up to about 3 times larger or smaller. We give examples of how these results may be used to obtain statistical estimates of how (un)likely it is that observed SSR trends or part thereof are due to internal variability alone. 3311 Clouds and aerosols; 3305 Climate change and variability; 3337 Global climate models; 3354 Precipitation; 1627 Coupled models of the climate system; decadal scale trends; internal variability; surface solar radiation
Foster, M.; Ackerman, S.; Bedka, K.; Di Girolmao, L.; Frey, R.; Heidinger, A.; Sun-Mack, S.; Phillips, C.; Menzel, W.; Minnis, P.; Zhao, G.Foster, M., S. Ackerman, K. Bedka, L. Di Girolmao, R. Frey, A. Heidinger, S. Sun-Mack, C. Phillips, W. Menzel, P. Minnis, G. Zhao, 2017: Cloudiness [in “State of the Climate in 2016"]. Bull. Amer. Meteor. Soc., 96(8), S27-S30. doi: 10.1175/2017BAMSStateoftheClimate.1.
Fu, Yunfei; Chen, Yilun; Li, Rui; Qin, Fang; Xian, Tao; Yu, Lu; Zhang, Aoqi; Liu, Guosheng; Zhang, XiangdongFu, Y., Y. Chen, R. Li, F. Qin, T. Xian, L. Yu, A. Zhang, G. Liu, X. Zhang, 2017: Lateral Boundary of Cirrus Cloud from CALIPSO Observations. Scientific Reports, 7(1), 14221. doi: 10.1038/s41598-017-14665-6. Due to the thinness and small scale of cirrus clouds, its lateral boundary may be missed by conventional passive remote-sensing techniques and climate models. Here, using satellite observations in June–August from 2006 to 2011, a global dataset for the cirrus cloud lateral boundary (CCLB) was established. The results indicate that the optical properties, such as the lidar backscatter, the depolarization ratio and the optical depth, sharply decrease from cloudy regions to clear-sky regions. There are significant regional differences in optical properties and height and thickness of the CCLB. Based on a quantitative estimation, the strongest longwave warming effects (>0.3 W m−2) are found near the Equator and over tropical continents. The global average longwave warming effect of the CCLB is at least 0.07 W m−2, which is much larger than some of the radiative forcings considered in the Intergovernmental Panel on Climate Change (IPCC) reports. Specifically, the CCLB in traditional “clear-sky” region may be totally missed by current models and IPCC reports, which contributes 28.25% (~0.02 W m−2) of the whole CCLB radiative effect, twice greater than contrail effect. It is recommended that the CCLB effect should be taken account in future climate models and the next IPCC reports.
Furtado, Kalli; Field, PaulFurtado, K., P. Field, 2017: The role of ice-microphysics parametrizations in determining the prevalence of supercooled liquid water in high-resolution simulations of a Southern Ocean midlatitude cyclone. J. Atmos. Sci., 74(6), 2001–2021. doi: 10.1175/JAS-D-16-0165.1. High-resolution simulations of a Southern Ocean cyclone are compared to satellite-derived observations of liquid water path, cloud-top properties and top-of-atmosphere radiative fluxes. We focus on the cold-air outflow region, where there are contributions to the hydrological budget from the microphysical growth of ice particles by riming and vapor-deposition and transport by turbulent mixing. The sensitivity of the simulation to the parametrization of these processes is tested and the relative importance of ice-nucleation temperature is identified. It is shown that ice-phase microphysics is a key factor determining the phase composition of Southern Ocean clouds and physically-reasonable parametrization changes are identified that affect the liquid water content of these clouds. The information gained from the sensitivity tests is applied to global-model development, where it is shown that a modification to the riming parametrization improves climate mean-state biases in the Southern Ocean region.
Ge, Xuyang; Wang, Wanqiu; Kumar, Arun; Zhang, YingGe, X., W. Wang, A. Kumar, Y. Zhang, 2017: Importance of the Vertical Resolution in Simulating SST Diurnal and Intraseasonal Variability in an Oceanic General Circulation Model. J. Climate, 30(11), 3963-3978. doi: 10.1175/JCLI-D-16-0689.1. In this paper, the influence of high vertical resolution near the surface in an oceanic general circulation model in simulating the observed sea surface temperature (SST) variability is investigated. In situ observations of vertical temperature profiles are first used to quantify temperature variability with depth near the ocean surface. The analysis shows that there is a sharp vertical temperature gradient within the top 10 m of the ocean. Both diurnal and intraseasonal variabilities of the ocean temperatures are largest near the surface and decrease with the ocean depth. Numerical experiments with an oceanic general circulation model are next carried out with 1- and 10-m vertical resolutions for the upper ocean to study the dependence of the simulated SST and vertical temperature structure on the vertical resolution. It is found that the simulated diurnal and intraseasonal variabilities, as well as the associated vertical temperature gradient near the surface, are strongly influenced by the oceanic vertical resolution, with the 1-m vertical resolution producing a stronger vertical temperature gradient and temporal variability than the 10-m vertical resolution. These results suggest that a realistic representation of SST variability with a high vertical resolution in the upper ocean is required for a coupled atmosphere–ocean model to correctly simulate the observed tropical intraseasonal oscillations, including the Madden–Julian oscillation and the boreal summer monsoon intraseasonal oscillation, which are strongly linked with the underlying SST.
Glotfelty, Timothy; Zhang, YangGlotfelty, T., Y. Zhang, 2017: Impact of future climate policy scenarios on air quality and aerosol-cloud interactions using an advanced version of CESM/CAM5: Part II. Future trend analysis and impacts of projected anthropogenic emissions. Atmospheric Environment, 152, 531-552. doi: 10.1016/j.atmosenv.2016.12.034. Following a comprehensive evaluation of the Community Earth System Model modified at the North Carolina State University (CESM-NCSU), Part II describes the projected changes in the future state of the atmosphere under the representative concentration partway scenarios (RCP4.5 and 8.5) by 2100 for the 2050 time frame and examine the impact of climate change on future air quality under both scenarios, and the impact of projected emission changes under the RCP4.5 scenario on future climate through aerosol direct and indirect effects. Both the RCP4.5 and RCP8.5 simulations predict similar changes in air quality by the 2050 period due to declining emissions under both scenarios. The largest differences occur in O3, which decreases by global mean of 1.4 ppb under RCP4.5 but increases by global mean of 2.3 ppb under RCP8.5 due to differences in methane levels, and PM10, which decreases by global mean of 1.2 μg m−3 under RCP4.5 and increases by global mean of 0.2 μg m−3 under RCP8.5 due to differences in dust and sea-salt emissions under both scenarios. Enhancements in cloud formation in the Arctic and Southern Ocean and increases of aerosol optical depth (AOD) in central Africa and South Asia dominate the change in surface radiation in both scenarios, leading to global average dimming of 1.1 W m−2 and 2.0 W m−2 in the RCP4.5 and RCP8.5 scenarios, respectively. Declines in AOD, cloud formation, and cloud optical thickness from reductions of emissions of primary aerosols and aerosol precursors under RCP4.5 result in near surface warming of 0.2 °C from a global average increase of 0.7 W m−2 in surface downwelling solar radiation. This warming leads to a weakening of the Walker Circulation in the tropics, leading to significant changes in cloud and precipitation that mirror a shift in climate towards the negative phase of the El Nino Southern Oscillation. climate change; CESM/CAM5; Emission changes; Future air quality; Global climate change; Representative concentration pathways
Green, Julia K.; Konings, Alexandra G.; Alemohammad, Seyed Hamed; Berry, Joseph; Entekhabi, Dara; Kolassa, Jana; Lee, Jung-Eun; Gentine, PierreGreen, J. K., A. G. Konings, S. H. Alemohammad, J. Berry, D. Entekhabi, J. Kolassa, J. Lee, P. Gentine, 2017: Regionally strong feedbacks between the atmosphere and terrestrial biosphere. Nature Geoscience, 10(6), 410-414. doi: 10.1038/ngeo2957. The terrestrial biosphere and atmosphere interact through a series of feedback loops. Variability in terrestrial vegetation growth and phenology can modulate fluxes of water and energy to the atmosphere, and thus affect the climatic conditions that in turn regulate vegetation dynamics. Here we analyse satellite observations of solar-induced fluorescence, precipitation, and radiation using a multivariate statistical technique. We find that biosphere–atmosphere feedbacks are globally widespread and regionally strong: they explain up to 30% of precipitation and surface radiation variance in regions where feedbacks occur. Substantial biosphere–precipitation feedbacks are often found in regions that are transitional between energy and water limitation, such as semi-arid or monsoonal regions. Substantial biosphere–radiation feedbacks are often present in several moderately wet regions and in the Mediterranean, where precipitation and radiation increase vegetation growth. Enhancement of latent and sensible heat transfer from vegetation accompanies this growth, which increases boundary layer height and convection, affecting cloudiness, and consequently incident surface radiation. Enhanced evapotranspiration can increase moist convection, leading to increased precipitation. Earth system models underestimate these precipitation and radiation feedbacks mainly because they underestimate the biosphere response to radiation and water availability. We conclude that biosphere–atmosphere feedbacks cluster in specific climatic regions that help determine the net CO2 balance of the biosphere. hydrology; Atmospheric science; Carbon cycle; Environmental impact
Gristey, Jake J.; Chiu, J. Christine; Gurney, Robert J.; Han, Shin-Chan; Morcrette, Cyril J.Gristey, J. J., J. C. Chiu, R. J. Gurney, S. Han, C. J. Morcrette, 2017: Determination of global Earth outgoing radiation at high temporal resolution using a theoretical constellation of satellites. Journal of Geophysical Research: Atmospheres, 122(2), 1114–1131. doi: 10.1002/2016JD025514. New, viable, and sustainable observation strategies from a constellation of satellites have attracted great attention across many scientific communities. Yet the potential for monitoring global Earth outgoing radiation using such a strategy has not been explored. To evaluate the potential of such a constellation concept and to investigate the configuration requirement for measuring radiation at a time resolution sufficient to resolve the diurnal cycle for weather and climate studies, we have developed a new recovery method and conducted a series of simulation experiments. Using idealized wide field-of-view broadband radiometers as an example, we find that a baseline constellation of 36 satellites can monitor global Earth outgoing radiation reliably to a spatial resolution of 1000 km at an hourly time scale. The error in recovered daily global mean irradiance is 0.16 W m−2 and −0.13 W m−2, and the estimated uncertainty in recovered hourly global mean irradiance from this day is 0.45 W m−2 and 0.15 W m−2, in the shortwave and longwave spectral regions, respectively. Sensitivity tests show that addressing instrument-related issues that lead to systematic measurement error remains of central importance to achieving similar accuracies in reality. The presented error statistics therefore likely represent the lower bounds of what could currently be achieved with the constellation approach, but this study demonstrates the promise of an unprecedented sampling capability for better observing the Earth's radiation budget. 0360 Radiation: transmission and scattering; 1610 Atmosphere; 0394 Instruments and techniques; 3359 Radiative processes; 3360 Remote sensing; Earth outgoing radiation; satellite constellation; spherical harmonic analysis
Gupta, Ashok Kumar; Rajeev, K.; Sijikumar, S.Gupta, A. K., K. Rajeev, S. Sijikumar, 2017: Day-night changes in the altitude distribution, physical properties and radiative impact of low-altitude clouds over the stratocumulus-dominated subtropical oceans. Journal of Atmospheric and Solar-Terrestrial Physics, 161, 118-126. doi: 10.1016/j.jastp.2017.06.021. Properties of low-altitude clouds, their radiative impact and day-night changes over the subtropical oceans of prominent stratocumulus occurrence (the Northeast and the Southeast Pacific, the Southeast Atlantic, and the South Indian Ocean) are investigated using multi-year (2006–2010) CloudSat, CALIPSO and radiative flux observations. In all these regions, the occurrence, thickness and longwave radiative impact of clouds are enhanced during the nighttime, while the altitude of peak cloud occurrence (960–1200 m) remains steady. The observed features provide evidence for the physical mechanisms proposed earlier for the coupling between marine boundary layer and low-level clouds and their day-night variations over these regions. cloud properties; cloud radiative forcing; Subtropics; Cloud occurrence frequency; Low-altitude clouds; Marine stratocumulus clouds
Guzman, R.; Chepfer, H.; Noel, V.; de Guélis, T. Vaillant; Kay, J. E.; Raberanto, P.; Cesana, G.; Vaughan, M. A.; Winker, D. M.Guzman, R., H. Chepfer, V. Noel, T. V. de Guélis, J. E. Kay, P. Raberanto, G. Cesana, M. A. Vaughan, D. M. Winker, 2017: Direct atmosphere opacity observations from CALIPSO provide new constraints on cloud-radiation interactions. Journal of Geophysical Research: Atmospheres, 122(2), 1066–1085. doi: 10.1002/2016JD025946. The spaceborne lidar CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) directly measures atmospheric opacity. In eight years of CALIPSO observations, we find that 69% of vertical profiles penetrate through the complete atmosphere. The remaining 31% do not reach the surface, due to opaque clouds. The global mean altitude of full attenuation of the lidar beam (z_opaque) is 3.2 km, but there are large regional variations in this altitude. Of relevance to cloud-climate studies, the annual zonal mean longwave cloud radiative effect and annual zonal mean z_opaque weighted by opaque cloud cover are highly correlated (0.94). The annual zonal mean shortwave cloud radiative effect and annual zonal mean opaque cloud cover are also correlated (-0.95). The new diagnostics introduced here are implemented within a simulator framework to enable scale-aware and definition-aware evaluation of the LMDZ5B global climate model. The evaluation shows the model overestimates opaque cloud cover (31% obs. vs. 38% model) and z_opaque (3.2 km obs. vs. 5.1 km model). In contrast, the model underestimates thin cloud cover (35% obs. vs. 14% model). Further assessment shows reasonable agreement between modeled and observed longwave cloud radiative effects results from compensating errors between insufficient warming by thin clouds and excessive warming due to overestimating both z_opaque and opaque cloud cover. This work shows the power of spaceborne lidar observations to directly constrain cloud-radiation interactions in both observations and models. 0321 Cloud/radiation interaction; 3309 Climatology; 3359 Radiative processes; 3310 Clouds and cloud feedbacks; 3360 Remote sensing; CALIPSO; COSP; Climate model constraint; GOCCP; Opaque cloud altitude; Opaque cloud cover
Ham, Seung-Hee; Kato, Seiji; Rose, Fred G.Ham, S., S. Kato, F. G. Rose, 2017: Examining impacts of mass-diameter (m-D) and area-diameter (A-D) relationships of ice particles on retrievals of effective radius and ice water content from radar and lidar measurements. Journal of Geophysical Research: Atmospheres, 122(6), 3396–3420. doi: 10.1002/2016JD025672. Mass-diameter (m-D) and projected area-diameter (A-D) relations are often used to describe the shape of nonspherical ice particles. This study analytically investigates how retrieved effective radius (reff) and ice water content (IWC) from radar and lidar measurements depend on the assumption of m-D [m(D) = a Db] and A-D [A(D) = γ Dδ] relationships. We assume that unattenuated reflectivity factor (Z) and visible extinction coefficient (kext) by cloud particles are available from the radar and lidar measurements, respectively. A sensitivity test shows that reff increases with increasing a, decreasing b, decreasing γ, and increasing δ. It also shows that a 10% variation of a, b, γ, and δ induces more than a 100% change of reff. In addition, we consider both gamma and lognormal particle size distributions (PSDs) and examine the sensitivity of reff to the assumption of PSD. It is shown that reff increases by up to 10% with increasing dispersion (μ) of the gamma PSD by 2, when large ice particles are predominant. Moreover, reff decreases by up to 20% with increasing the width parameter (ω) of the lognormal PSD by 0.1. We also derive an analytic conversion equation between two effective radii when different particle shapes and PSD assumptions are used. When applying the conversion equation to nine types of m-D and A-D relationships, reff easily changes up to 30%. The proposed reff conversion method can be used to eliminate the inconsistency of assumptions that made in a cloud retrieval algorithm and a forward radiative transfer model. 0360 Radiation: transmission and scattering; 6952 Radar atmospheric physics; 0321 Cloud/radiation interaction; Lidar; radar; 0480 Remote sensing; 0317 Chemical kinetic and photochemical properties; area-diameter (A-D); effective radius; ice particle shape; mass-diameter (m-D)
Ham, Seung-Hee; Kato, Seiji; Rose, Fred G.; Winker, David; L'Ecuyer, Tristan; Mace, Gerald G.; Painemal, David; Sun-Mack, Sunny; Chen, Yan; Miller, Walter F.Ham, S., S. Kato, F. G. Rose, D. Winker, T. L'Ecuyer, G. G. Mace, D. Painemal, S. Sun-Mack, Y. Chen, W. F. Miller, 2017: Cloud Occurrences and Cloud Radiative Effects (CREs) from CERES-CALIPSO-CloudSat-MODIS (CCCM) and CloudSat Radar-Lidar (RL) Products. Journal of Geophysical Research: Atmospheres, 122(16), 8852–8884. doi: 10.1002/2017JD026725. Two kinds of cloud products obtained from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), CloudSat, and Moderate Resolution Imaging Spectroradiometer (MODIS) are compared and analyzed in this study; Clouds and the Earth's Radiant Energy System (CERES)-CALIPSO-CloudSat-MODIS (CCCM) product and CloudSat radar-lidar (RL) products such as GEOPROF-LIDAR and FLXHR-LIDAR. Compared to GEOPROF-LIDAR, low-level (< 1 km) cloud occurrences in CCCM are larger over tropical oceans because the CCCM algorithm uses a more relaxed threshold of Cloud-Aerosol Discrimination (CAD) score for CALIPSO vertical feature mask (VFM) product. In contrast, mid-level (1–8 km) cloud occurrences in GEOPROF-LIDAR are larger than CCCM at high latitudes (> 40°). The difference occurs when hydrometeors are detected by CALIPSO lidar but are undetected by CloudSat radar. In the comparison of cloud radiative effects (CREs), global mean differences between CCCM and FLXHR-LIDAR are mostly smaller than 5 W m-2, while noticeable regional differences are found. For example, CCCM shortwave (SW) and longwave (LW) CREs are larger than FXLHR-LIDAR along the west coasts of Africa and America because the GEOPROF-LIDAR algorithm misses shallow marine boundary layer clouds. In addition, FLXHR-LIDAR SW CREs are larger than CCCM counterpart over tropical oceans away from the west coasts of America. Over midlatitude storm-track regions, CCCM SW and LW CREs are larger than FLXHR-LIDAR counterpart. 0360 Radiation: transmission and scattering; 6952 Radar atmospheric physics; CERES; 0321 Cloud/radiation interaction; 7847 Radiation processes; 8040 Remote sensing; CCCM; cloud occurence; CRE; FLXHR-LIDAR; GEOPROF-LIDAR
Hartmann, Dennis L.; Berry, Sara E.Hartmann, D. L., S. E. Berry, 2017: The balanced radiative effect of tropical anvil clouds. Journal of Geophysical Research: Atmospheres, 122(9), 5003–5020. doi: 10.1002/2017JD026460. Coincident instantaneous broadband radiation budget measurements from Clouds and Earth's Radiant Energy System and cloud vertical structure information from CloudSat-Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations radar-lidar observations are combined to study the relationship of cloud vertical structure to top-of-atmosphere energy balance fluctuations. Varying optical and physical thickness of high ice clouds produces most of the covariation between albedo and outgoing longwave radiation in regions of tropical convection. Rainy cores of tropical convective clouds have a negative impact on the radiation balance, while nonprecipitating anvil clouds have a positive effect. The effect of anvil clouds on the radiative heating profile is to warm near cloud base and cool near cloud top, and to reduce the radiative cooling rate in the clear air below the cloud. The cooling rate in the clear air below the anvil is reduced to small values for moderately thick anvils, and the driving of instability in the anvil itself also saturates for relatively thin clouds. It is hypothesized that the dependence of radiative heating on cloud thickness may be important in driving the distribution of tropical cloud structures toward one that produces net neutrality of the cloud radiative effect at the top-of-the-atmosphere, as is found in regions of deep convection over ocean areas with high and relatively uniform surface temperatures. This idea is tested with a single-column model, which indicates that cloud-radiation interactions affect anvil cloud properties, encouraging further investigation of the hypothesis. clouds; 1640 Remote sensing; 0321 Cloud/radiation interaction; 3310 Clouds and cloud feedbacks; radiation balance; 3371 Tropical convection; cloud feedback; tropical convection
Hawcroft, Matt; Haywood, Jim M.; Collins, Mat; Jones, Andy; Jones, Anthony C.; Stephens, GraemeHawcroft, M., J. M. Haywood, M. Collins, A. Jones, A. C. Jones, G. Stephens, 2017: Southern Ocean albedo, inter-hemispheric energy transports and the double ITCZ: global impacts of biases in a coupled model. Climate Dynamics, 48(7-8), 2279-2295. doi: 10.1007/s00382-016-3205-5. A causal link has been invoked between inter-hemispheric albedo, cross-equatorial energy transport and the double-Intertropical Convergence Zone (ITCZ) bias in climate models. Southern Ocean cloud biases are a major determinant of inter-hemispheric albedo biases in many models, including HadGEM2-ES, a fully coupled model with a dynamical ocean. In this study, targeted albedo corrections are applied in the Southern Ocean to explore the dynamical response to artificially reducing these biases. The Southern Hemisphere jet increases in strength in response to the increased tropical-extratropical temperature gradient, with increased energy transport into the mid-latitudes in the atmosphere, but no improvement is observed in the double-ITCZ bias or atmospheric cross-equatorial energy transport, a finding which supports other recent work. The majority of the adjustment in energy transport in the tropics is achieved in the ocean, with the response further limited to the Pacific Ocean. As a result, the frequently argued teleconnection between the Southern Ocean and tropical precipitation biases is muted. Further experiments in which tropical longwave biases are also reduced do not yield improvement in the representation of the tropical atmosphere. These results suggest that the dramatic improvements in tropical precipitation that have been shown in previous studies may be a function of the lack of dynamical ocean and/or the simplified hemispheric albedo bias corrections applied in that work. It further suggests that efforts to correct the double ITCZ problem in coupled models that focus on large-scale energetic controls will prove fruitless without improvements in the representation of atmospheric processes.
He, Jian; Zhang, Yang; Wang, Kai; Chen, Ying; Leung, L. Ruby; Fan, Jiwen; Li, Meng; Zheng, Bo; Zhang, Qiang; Duan, Fengkui; He, KebinHe, J., Y. Zhang, K. Wang, Y. Chen, L. R. Leung, J. Fan, M. Li, B. Zheng, Q. Zhang, F. Duan, K. He, 2017: Multi-year application of WRF-CAM5 over East Asia-Part I: Comprehensive evaluation and formation regimes of O3 and PM2.5. Atmospheric Environment, 165, 122-142. doi: 10.1016/j.atmosenv.2017.06.015. Accurate simulations of air quality and climate require robust model parameterizations on regional and global scales. The Weather Research and Forecasting model with Chemistry version 3.4.1 has been coupled with physics packages from the Community Atmosphere Model version 5 (CAM5) (WRF-CAM5) to assess the robustness of the CAM5 physics package for regional modeling at higher grid resolutions than typical grid resolutions used in global modeling. In this two-part study, Part I describes the application and evaluation of WRF-CAM5 over East Asia at a horizontal resolution of 36-km for six years: 2001, 2005, 2006, 2008, 2010, and 2011. The simulations are evaluated comprehensively with a variety of datasets from surface networks, satellites, and aircraft. The results show that meteorology is relatively well simulated by WRF-CAM5. However, cloud variables are largely or moderately underpredicted, indicating uncertainties in the model treatments of dynamics, thermodynamics, and microphysics of clouds/ices as well as aerosol-cloud interactions. For chemical predictions, the tropospheric column abundances of CO, NO2, and O3 are well simulated, but those of SO2 and HCHO are moderately overpredicted, and the column HCHO/NO2 indicator is underpredicted. Large biases exist in the surface concentrations of CO, NOx, and PM10 due to uncertainties in the emissions as well as vertical mixing. The underpredictions of NO lead to insufficient O3 titration, thus O3 overpredictions. The model can generally reproduce the observed O3 and PM indicators. These indicators suggest to control NOx emissions throughout the year, and VOCs emissions in summer in big cities and in winter over North China Plain, North/South Korea, and Japan to reduce surface O3, and to control SO2, NH3, and NOx throughout the year to reduce inorganic surface PM. East Asia; WRF-CAM5; Multi-year evaluation; O3 and PM indicators; Regional air quality; Regional climate change
He, Lijie; Wang, Lunche; Lin, Aiwen; Zhang, Ming; Bilal, Muhammad; Tao, MinghuiHe, L., L. Wang, A. Lin, M. Zhang, M. Bilal, M. Tao, 2017: Aerosol Optical Properties and Associated Direct Radiative Forcing over the Yangtze River Basin during 2001–2015. Remote Sensing, 9(7), 746. doi: 10.3390/rs9070746. The spatiotemporal variation of aerosol optical depth at 550 nm (AOD550), Ångström exponent at 470–660 nm (AE470–660), water vapor content (WVC), and shortwave (SW) instantaneous aerosol direct radiative effects (IADRE) at the top-of-atmosphere (TOA) in clear skies obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Clouds and the Earth’s Radiant Energy System (CERES) are quantitatively analyzed over the Yangtze River Basin (YRB) in China during 2001–2015. The annual and seasonal frequency distributions of AE470–660 and AOD550 reveal the dominance of fine aerosol particles over YRB. The regional average AOD550 is 0.49 ± 0.31, with high value in spring (0.58 ± 0.35) and low value in winter (0.42 ± 0.29). The higher AOD550 (≥0.6) is observed in midstream and downstream regions of YRB and Sichuan Basin due to local anthropogenic emissions and long-distance transport of dust particles, while lower AOD550 (≤0.3) is in high mountains of upstream regions. The IADRE is estimated using a linear relationship between SW upward flux and coincident AOD550 from CERES and MODIS at the satellite passing time. The regional average IADRE is −35.60 ± 6.71 Wm−2, with high value (−40.71 ± 6.86 Wm−2) in summer and low value (−29.19 ± 7.04 Wm−2) in winter, suggesting a significant cooling effect at TOA. The IADRE at TOA is lower over Yangtze River Delta (YRD) (≤−30 Wm−2) and higher in midstream region of YRB, Sichuan Basin and the source area of YRB (≥−45 Wm−2). The correlation coefficient between the 15-year monthly IADRE and AOD550 values is 0.63, which confirms the consistent spatiotemporal variation patterns over most of the YRB. However, a good agreement between IADRE and AOD is not observed in YRD and the source area of YRB, which is probably due to the combined effects of aerosol and surface properties. Aerosol direct radiative forcing; aerosol optical properties; spatiotemporal distribution; Yangtze River Basin
He, Zhuoqi; Wu, Renguang; Wang, Weiqiang; Wen, Zhiping; Wang, DongxiaoHe, Z., R. Wu, W. Wang, Z. Wen, D. Wang, 2017: Contributions of surface heat fluxes and oceanic processes to tropical SST changes: Seasonal and regional dependence. J. Climate, 30(11), 4185–4205. doi: 10.1175/JCLI-D-16-0500.1. The present study employs six surface heat flux datasets and three ocean assimilation products to assess the relative contributions of surface heat fluxes and oceanic processes to the sea surface temperature (SST) change in the tropical oceans. Large differences are identified in the major terms of the heat budget equation. The largest discrepancies among different datasets appear in the contribution of vertical advection. The heat budget is nearly balanced in the shortwave radiation and horizontal advection-dominant cases, but not balanced in some of the latent heat flux and vertical advection-dominant cases. The contributions of surface heat fluxes and ocean advections to the SST tendency display remarkable seasonal and regional dependence. The contribution of surface heat fluxes covers a large geographical area. The oceanic processes dominate the SST tendency in the near-equatorial regions with large values but small spatial scales. In the Pacific and Atlantic Ocean, the SST tendency is governed by the dynamic and thermodynamic processes respectively, while a wide variety of processes contributes to the SST tendency in the Indian Ocean. Several regions have been selected to illustrate the dominant contributions of individual terms to the SST tendency in different seasons. The seasonality and regionality of the interannual air-sea relationship indicates a physical connection with the mean state.
Hedemann, Christopher; Mauritsen, Thorsten; Jungclaus, Johann; Marotzke, JochemHedemann, C., T. Mauritsen, J. Jungclaus, J. Marotzke, 2017: The subtle origins of surface-warming hiatuses. Nature Climate Change, 7(5), 336-339. doi: 10.1038/nclimate3274. During the first decade of the twenty-first century, the Earth’s surface warmed more slowly than climate models simulated. This surface-warming hiatus is attributed by some studies to model errors in external forcing, while others point to heat rearrangements in the ocean caused by internal variability, the timing of which cannot be predicted by the models. However, observational analyses disagree about which ocean region is responsible. Here we show that the hiatus could also have been caused by internal variability in the top-of-atmosphere energy imbalance. Energy budgeting for the ocean surface layer over a 100-member historical ensemble reveals that hiatuses are caused by energy-flux deviations as small as 0.08 W m−2, which can originate at the top of the atmosphere, in the ocean, or both. Budgeting with existing observations cannot constrain the origin of the recent hiatus, because the uncertainty in observations dwarfs the small flux deviations that could cause a hiatus. The sensitivity of these flux deviations to the observational dataset and to energy budget choices helps explain why previous studies conflict, and suggests that the origin of the recent hiatus may never be identified. climate change; Climate and Earth system modelling; Ocean sciences
Hegyi, Bradley M.; Deng, YiHegyi, B. M., Y. Deng, 2017: Dynamical and Thermodynamical Impacts of High and Low Frequency Atmospheric Eddies on the Initial Melt of Arctic Sea Ice. J. Climate, 30(3), 865–883. doi: 10.1175/JCLI-D-15-0366.1. The role of high-frequency and low-frequency eddies in the melt onset of Arctic sea ice is investigated through an examination of eddy effects on lower tropospheric (1000-500mb) meridional heat transport into the Arctic and local surface downwelling shortwave and longwave radiation. Total and eddy components of the meridional heat transport into the Arctic from 1979-2012 are calculated from reanalysis data, and surface radiation data is acquired from the NASA Clouds and the Earth’s Radiant Energy System (CERES) project dataset. There is a significant positive correlation between the mean initial melt date and the September sea ice minimum extent, with each quantity characterized by a negative trend. Spatially, the earlier mean melt onset date is primarily found in a region bounded by 90°E and 130°W longitude. The decline in this region is step-like and not associated with an increase in meridional heat transport but with an earlier appearance of above-freezing temperatures in the troposphere. In most years, discrete short-duration episodes of melt onset over a large area occur. In an investigation of two of these melt episodes, a positive total meridional heat transport is associated with the peak melt, with the product of high-frequency eddy wind and mean temperature fields the most important contributor. Additionally there is a key positive anomaly in surface downwelling longwave radiation immediately preceding the peak melt that is associated with increased cloud cover and precipitable water. These results suggest the importance of carefully considering and properly representing atmospheric eddies when modeling the melt onset of Arctic sea ice.
Hegyi, Bradley M.; Taylor, Patrick C.Hegyi, B. M., P. C. Taylor, 2017: The regional influence of the Arctic Oscillation and Arctic Dipole on the wintertime Arctic surface radiation budget and sea ice growth. Geophysical Research Letters, 44(9), 4341–4350. doi: 10.1002/2017GL073281. An analysis of 2000–2015 monthly Clouds and the Earth's Radiant Energy System-Energy Balanced and Filled (CERES-EBAF) and Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA2) data reveals statistically significant fall and wintertime relationships between Arctic surface longwave (LW) radiative flux anomalies and the Arctic Oscillation (AO) and Arctic Dipole (AD). Signifying a substantial regional imprint, a negative AD index corresponds with positive downwelling clear-sky LW flux anomalies (>10 W m−2) north of western Eurasia (0°E–120°E) and reduced sea ice growth in the Barents and Kara Seas in November–February. Conversely, a positive AO index coincides with negative clear-sky LW flux anomalies and minimal sea ice growth change in October–November across the Arctic. Increased (decreased) atmospheric temperature and water vapor coincide with the largest positive (negative) clear-sky flux anomalies. Positive surface LW cloud radiative effect anomalies also accompany the negative AD index in December–February. The results highlight a potential pathway by which Arctic atmospheric variability influences the regional surface radiation budget over areas of Arctic sea ice growth. 3359 Radiative processes; 3310 Clouds and cloud feedbacks; 1616 Climate variability; 0750 Sea ice; cloud radiative effect; 3349 Polar meteorology; Arctic sea ice; large-scale atmospheric variability; longwave surface fluxes; winter
Hinkelman, Laura M.; Schaeffer, NevinHinkelman, L. M., N. Schaeffer, 2017: Relating solar resource and its variability to weather and climate across the northwestern United States. Solar Energy, 157(Supplement C), 966-978. doi: 10.1016/j.solener.2017.07.060. The spatiotemporal variability of the solar resource has implications for every stage in the development and operation of a photovoltaic power plant from siting and design through grid integration and day-to-day operation. The irregular and relatively unpredictable portion of this variability is primarily caused by the passage of clouds and large-scale weather systems. In this study, we examine the variability of solar irradiance at five locations in the northwestern US at temporal scales ranging from 5min to 9days in the context of local and regional weather patterns. The total solar resource in this area exceeded expectations, with values as high as 4.5kWh/m2/day. The magnitude of the seasonal cycle of the solar resource at these locations was found to be greater than in other regions of the US due to the strong seasonality of cloudiness. Seasonal differences were also seen in the variability of measured solar irradiance down to sub-hourly time scales. Site-to-site differences in the magnitude of irradiance fluctuations could be traced to local meteorological differences, but also depended on temporal scale, reflecting the contrasting influences of overall cloudiness and the smaller scale spatial characteristics of cloud structure. The degree to which combining irradiance time series from pairs or groups of diverse locations smoothed temporal irradiance variability mainly depended on the magnitude of the variability of the original data at short time scales but on the separation of the sites for daily averages. This distinction can be traced to the negligible/appreciable correlation of sub-hourly/daily irradiance fluctuations measured at these widely separated (250–850km) sites, which again reflects differences between the spatial and temporal extent of weather systems as opposed to their underlying cloud structure. Each of these results demonstrates how knowledge of local and regional meteorology can provide insights into the character of the solar resource at a particular location. Irradiance; Variability; Clear-sky index; Northwestern USA; solar resource; Weather
Hourdin, Frederic; Mauritsen, Thorsten; Gettelman, Andrew; Golaz, Jean-Christophe; Balaji, Venkatramani; Duan, Qingyun; Folini, Doris; Ji, Duoying; Klocke, Daniel; Qian, Yun; Rauser, Florian; Rio, Cathrine; Tomassini, Lorenzo; Watanabe, Masahiro; Williamson, DanielHourdin, F., T. Mauritsen, A. Gettelman, J. Golaz, V. Balaji, Q. Duan, D. Folini, D. Ji, D. Klocke, Y. Qian, F. Rauser, C. Rio, L. Tomassini, M. Watanabe, D. Williamson, 2017: The art and science of climate model tuning. Bull. Amer. Meteor. Soc., 98(3), 589–602. doi: 10.1175/BAMS-D-15-00135.1. We survey the rationale and diversity of approaches for tuning, a fundamental aspect of climate modeling which should be more systematically documented and taken into account in multi-model analysis.
Huang, Andrew; Li, Hui; Sriver, Ryan L.; Fedorov, Alexey V.; Brierley, Chris M.Huang, A., H. Li, R. L. Sriver, A. V. Fedorov, C. M. Brierley, 2017: Regional variations in the ocean response to tropical cyclones: Ocean mixing versus low cloud suppression. Geophysical Research Letters, 44(4), 1947–1955. doi: 10.1002/2016GL072023. Tropical cyclones (TCs) tend to cool sea surface temperature (SST) via enhanced vertical mixing and evaporative fluxes. This cooling is substantially reduced in the subtropics, especially in the northeastern Pacific where the occurrence of TCs can warm the ocean surface. Here we investigate the cause of this anomalous warming by analyzing the local oceanic features and TC-induced anomalies of SST, surface fluxes, and cloud fraction using satellite and in situ data. We find that TCs tend to suppress low-clouds at the margins of the tropical ocean warm pool, enhancing shortwave radiative surface fluxes within the first week following storm passage, which combined with spatial variations in ocean thermal structure, can produce a ~1 °C near-surface warming in the northeastern Pacific. These findings, supported by high-resolution Earth system model simulations, point to potential connections between TCs, ocean temperature, and low-cloud distributions that can influence tropical surface heat budgets. 3310 Clouds and cloud feedbacks; 1627 Coupled models of the climate system; 3372 Tropical cyclones; 0429 Climate dynamics; Tropical Climate; Earth system model; Ocean-atmosphere interactions; tropical cyclones
Huang, Jianping; Yu, Haipeng; Dai, Aiguo; Wei, Yun; Kang, LitaiHuang, J., H. Yu, A. Dai, Y. Wei, L. Kang, 2017: Drylands face potential threat under 2 °C global warming target. Nature Climate Change, 7(6), 417-422. doi: 10.1038/nclimate3275. The Paris Agreement aims to limit global mean surface warming to less than 2 °C relative to pre-industrial levels. However, we show this target is acceptable only for humid lands, whereas drylands will bear greater warming risks. Over the past century, surface warming over global drylands (1.2–1.3 °C) has been 20–40% higher than that over humid lands (0.8–1.0 °C), while anthropogenic CO2 emissions generated from drylands (~230 Gt) have been only ~30% of those generated from humid lands (~750 Gt). For the twenty-first century, warming of 3.2–4.0 °C (2.4–2.6 °C) over drylands (humid lands) could occur when global warming reaches 2.0 °C, indicating ~44% more warming over drylands than humid lands. Decreased maize yields and runoff, increased long-lasting drought and more favourable conditions for malaria transmission are greatest over drylands if global warming were to rise from 1.5 °C to 2.0 °C. Our analyses indicate that ~38% of the world’s population living in drylands would suffer the effects of climate change due to emissions primarily from humid lands. If the 1.5 °C warming limit were attained, the mean warming over drylands could be within 3.0 °C; therefore it is necessary to keep global warming within 1.5 °C to prevent disastrous effects over drylands. Projection and prediction; Climate-change impacts; Water resources
Huang, Yiyi; Dong, Xiquan; Xi, Baike; Dolinar, Erica K.; Stanfield, Ryan E.; Qiu, ShaoyueHuang, Y., X. Dong, B. Xi, E. K. Dolinar, R. E. Stanfield, S. Qiu, 2017: Quantifying the Uncertainties of Reanalyzed Arctic Cloud and Radiation Properties Using Satellite Surface Observations. J. Climate, 30(19), 8007-8029. doi: 10.1175/JCLI-D-16-0722.1. Reanalyses have proven to be convenient tools for studying the Arctic climate system, but their uncertainties should first be identified. In this study, five reanalyses (JRA-55, 20CRv2c, CFSR, ERA-Interim, and MERRA-2) are compared with NASA CERES–MODIS (CM)-derived cloud fractions (CFs), cloud water paths (CWPs), top-of-atmosphere (TOA) and surface longwave (LW) and shortwave (SW) radiative fluxes over the Arctic (70°–90°N) over the period of 2000–12, and CloudSat–CALIPSO (CC)-derived CFs from 2006 to 2010. The monthly mean CFs in all reanalyses except JRA-55 are close to or slightly higher than the CC-derived CFs from May to September. However, wintertime CF cannot be confidently evaluated until instrument simulators are implemented in reanalysis products. The comparison between CM and CC CFs indicates that CM-derived CFs are reliable in summer but not in winter. Although the reanalysis CWPs follow the general seasonal variations of CM CWPs, their annual means are only half or even less than the CM-retrieved CWPs (126 g m−2). The annual mean differences in TOA and surface SW and LW fluxes between CERES EBAF and reanalyses are less than 6 W m−2 for TOA radiative fluxes and 16 W m−2 for surface radiative fluxes. All reanalyses show positive biases along the northern and eastern coasts of Greenland as a result of model elevation biases or possible CM clear-sky retrieval issues. The correlations between the reanalyses and CERES satellite retrievals indicate that all five reanalyses estimate radiative fluxes better than cloud properties, and MERRA-2 and JRA-55 exhibit comparatively higher correlations for Arctic cloud and radiation properties.
Huang, Yiyi; Dong, Xiquan; Xi, Baike; Dolinar, Erica; Stanfield, RyanHuang, Y., X. Dong, B. Xi, E. Dolinar, R. Stanfield, 2017: The footprints of 16-year trends of Arctic springtime cloud and radiation properties on September sea-ice retreat. Journal of Geophysical Research: Atmospheres, 122(4), 2179–2193. doi: 10.1002/2016JD026020. The most prominent September Arctic sea-ice decline over the period of 2000-2015 occurs over the Siberian Sea, Laptev Sea, and Kara Sea. The satellite observed and retrieved sea-ice concentration (SIC) and cloud/radiation properties over the Arctic (70°-90°N) have been used to investigate the impact of springtime cloud and radiation properties on September SIC variation. Positive trends of cloud fractions, cloud water paths and surface downward longwave flux at the surface over the September sea-ice retreat areas are found over the period of March 1st to May 14th, while negative trends are found over the period of May 15th to June 28th. The spatial distributions of correlations between springtime cloud/radiation properties and September SIC have been calculated, indicating that increasing cloud fractions and downward longwave flux during springtime tend to enhance sea-ice melting due to strong cloud warming effects. Surface downward and upward shortwave fluxes play an important role from May to June when the onset of sea-ice melting occurs. The comparison between linearly detrended and non-detrended of each parameter indicates that significant impact of cloud and radiation properties on September sea-ice retreat occurs over the Chukchi/Beaufort Sea at interannual time-scale, especially over the period of March 31st to April 29th, while strongest climatological trends are found over the Laptev/Siberian Sea. satellite remote sensing; 0321 Cloud/radiation interaction; 0758 Remote sensing; 0750 Sea ice; Arctic sea-ice trend; cloud and radiation feedbacks
Javadnia, Eslam; Abkar, Ali Akbar; Schubert, PerJavadnia, E., A. A. Abkar, P. Schubert, 2017: Estimation of High-Resolution Surface Shortwave Radiative Fluxes Using SARA AOD over the Southern Great Plains. Remote Sensing, 9(11), 1146. doi: 10.3390/rs9111146. Atmospheric aerosol optical depth (AOD) plays a determinant role in estimations of surface shortwave (SW) radiative fluxes. Therefore, this study aims to develop a hybrid scheme to produce surface SW fluxes, based on AOD at 1-km spatial resolution retrieved from the Simplified Aerosol Retrieval Algorithm (SARA) and several Terra MODIS land and atmospheric products (i.e., geolocation properties, water vapor amount, total ozone column, surface reflectance, and top-of-atmosphere (TOA) radiance). Estimations based on SARA were made over the Southern Great Plains (SGP) under cloud-free conditions in 2014 and compared with estimations based on the latest Terra MODIS AOD product at 3-km resolution. Validation against ground-based measurements showed that SARA-based fluxes obtain lower RMSE and bias values compared with MODIS-based estimations. MODIS-based downward and net fluxes are satisfactory, while the direct and diffuse components are less reliable. The results demonstrate that the SARA-based scheme produces better surface SW radiative fluxes than the MODIS-based estimates provided in this and other similar studies and that these fluxes are comparable to existing CERES data products which have been tested over the SGP. Southern Great Plains; MODIS; AOD; SARA; shortwave radiative fluxes
Jeong, Su-Jong; Schimel, David; Frankenberg, Christian; Drewry, Darren T.; Fisher, Joshua B.; Verma, Manish; Berry, Joseph A.; Lee, Jung-Eun; Joiner, JoannaJeong, S., D. Schimel, C. Frankenberg, D. T. Drewry, J. B. Fisher, M. Verma, J. A. Berry, J. Lee, J. Joiner, 2017: Application of satellite solar-induced chlorophyll fluorescence to understanding large-scale variations in vegetation phenology and function over northern high latitude forests. Remote Sensing of Environment, 190, 178-187. doi: 10.1016/j.rse.2016.11.021. This study evaluates the large-scale seasonal phenology and physiology of vegetation over northern high latitude forests (40°–55°N) during spring and fall by using remote sensing of solar-induced chlorophyll fluorescence (SIF), normalized difference vegetation index (NDVI) and observation-based estimate of gross primary productivity (GPP) from 2009 to 2011. Based on GPP phenology estimation in GPP, the growing season determined by SIF time-series is shorter in length than the growing season length determined solely using NDVI. This is mainly due to the extended period of high NDVI values, as compared to SIF, by about 46 days (± 11 days), indicating a large-scale seasonal decoupling of physiological activity and changes in greenness in the fall. In addition to phenological timing, mean seasonal NDVI and SIF have different responses to temperature changes throughout the growing season. We observed that both NDVI and SIF linearly increased with temperature increases throughout the spring. However, in the fall, although NDVI linearly responded to temperature increases, SIF and GPP did not linearly increase with temperature increases, implying a seasonal hysteresis of SIF and GPP in response to temperature changes across boreal ecosystems throughout their growing season. Seasonal hysteresis of vegetation at large-scales is consistent with the known phenomena that light limits boreal forest ecosystem productivity in the fall. Our results suggest that continuing measurements from satellite remote sensing of both SIF and NDVI can help to understand the differences between, and information carried by, seasonal variations vegetation structure and greenness and physiology at large-scales across the critical boreal regions. Phenology; GPP; SIF; Large-scale; NDVI; Solar-induced chlorophyll fluorescence
Jin, Qinjian; Wang, ChienJin, Q., C. Wang, 2017: A revival of Indian summer monsoon rainfall since 2002. Nature Clim. Change, 7(8), 587-594. doi: 10.1038/nclimate3348. A significant reduction in summer monsoon rainfall has been observed in northern central India during the second half of the twentieth century, threatening water security and causing widespread socio-economic impacts. Here, using various observational data sets, we show that monsoon rainfall has increased in India at 1.34[thinsp]mm[thinsp]d-1[thinsp]decade-1 since 2002. This apparent revival of summer monsoon precipitation is closely associated with a favourable land-ocean temperature gradient, driven by a strong warming signature over the Indian subcontinent and slower rates of warming over the Indian Ocean. The continental Indian warming is attributed to a reduction of low cloud due to decreased ocean evaporation in the Arabian Sea, and thus decreased moisture transport to India. Global climate models fail to capture the observed rainfall revival and corresponding trends of the land-ocean temperature gradient, with implications for future projections of the Indian monsoon.
Jin, Zhonghai; Sun, MoguoJin, Z., M. Sun, 2017: Errors in spectral fingerprints and their effects on climate fingerprinting accuracy in the solar spectrum. Journal of Quantitative Spectroscopy and Radiative Transfer, 188, 165–175. doi: 10.1016/j.jqsrt.2016.06.029. Using the Earth׳s reflected solar spectrum for climate change fingerprinting is an emerging research area. The spectral fingerprinting approach directly retrieves the changes in climate variables from the mean spectral data averaged across large space and time scales. To investigate this fingerprinting concept, we use ten years of satellite data to simulate the monthly and annual mean reflected solar spectra and the associated spectral fingerprints for different regions over the ocean. The interannual variations in the spectral data are derived and attributed to the interannual variations in the relevant climate variables. The fingerprinting retrieved changes in climate variables are then compared with the actual underlying variable changes from the observational data to evaluate the fingerprinting retrieval accuracy. Two important errors related to the fingerprinting approach, the nonlinearity error and the averaging error in the mean fingerprints, and their impact on the retrieval accuracy, are investigated. It is found that the averaging error increases but the nonlinearity error decreases as the region size increases. The averaging error has minimal effect on the fingerprinting retrieval accuracy in small regions but has more of an impact in large regions. In comparison, the effect of nonlinearity error on the retrieval accuracy decreases as the region size increases. It is also found that the fingerprinting retrieval accuracy is more sensitive to the nonlinearity error than to the averaging error. In addition, we compare the fingerprinting accuracy between using the monthly mean data and the annual mean data. The results show that on average higher retrieval accuracy is achieved when the annual mean data are used for the fingerprinting retrieval. radiative transfer; Climate change fingerprinting; Spectral fingerprint
Johnson, Gregory C.; Birnbaum, Abigail N.Johnson, G. C., A. N. Birnbaum, 2017: As El Niño builds, Pacific Warm Pool expands, ocean gains more heat. Geophysical Research Letters, 44(1), 438–445. doi: 10.1002/2016GL071767. El Niño–Southern Oscillation (ENSO) effects substantial redistributions of ocean temperature, both horizontal and vertical, on interannual time scales, especially in the Pacific Ocean. Analyses of monthly Argo-based ocean temperature maps illustrate large-scale ocean heat content redistributions with ENSO. They quantify a globally averaged sea surface temperature warming of ~0.1°C with a 1°C increase of the Niño3.4 index (a moderate El Niño), a substantial perturbation to the 0.13°C decade−1 trend in sea surface temperature. Monthly satellite-based estimates of Earth's energy imbalance suggest that a 1°C increase of the Niño3.4 index corresponds to an increase of ~3.4 ZJ in Earth's energy storage, more gently modulating the longer-term ~114 ZJ decade−1 trend. Yearly global ocean heat content estimates based on ocean temperature data, with their reduced uncertainties compared to monthly maps, reveal interannual variations in Earth's energy storage that correspond well with satellite-based estimates. CERES; 3359 Radiative processes; 1616 Climate variability; Ocean heat content; 4522 ENSO; 1635 Oceans; 4215 Climate and interannual variability; Argo; Earth's energy imbalance
Jose, Subin and Gharai, Biswadip and Rao, Pamaraju Venkata NarasimhaJose, S. a. G., 2017: Cross-Sectional View of Atmospheric Aerosols over an Urban Location in Central India. Aerosol and Air Quality Research, 17(3), 761-775. doi: 10.4209/aaqr.2016.04.0154.
Khanna, Jaya; Medvigy, David; Fueglistaler, Stephan; Walko, RobertKhanna, J., D. Medvigy, S. Fueglistaler, R. Walko, 2017: Regional dry-season climate changes due to three decades of Amazonian deforestation. Nature Climate Change, 7(3), 200-204. doi: 10.1038/nclimate3226. More than 20% of the Amazon rainforest has been cleared in the past three decades, triggering important hydroclimatic changes. Small-scale (a few kilometres) deforestation in the 1980s has caused thermally triggered atmospheric circulations that increase regional cloudiness and precipitation frequency. However, these circulations are predicted to diminish as deforestation increases. Here we use multi-decadal satellite records and numerical model simulations to show a regime shift in the regional hydroclimate accompanying increasing deforestation in Rondônia, Brazil. Compared with the 1980s, present-day deforested areas in downwind western Rondônia are found to be wetter than upwind eastern deforested areas during the local dry season. The resultant precipitation change in the two regions is approximately ±25% of the deforested area mean. Meso-resolution simulations robustly reproduce this transition when forced with increasing deforestation alone, showing that large-scale climate variability plays a negligible role. Furthermore, deforestation-induced surface roughness reduction is found to play an essential role in the present-day dry-season hydroclimate. Our study illustrates the strong scale sensitivity of the climatic response to Amazonian deforestation and suggests that deforestation is sufficiently advanced to have caused a shift from a thermally to a dynamically driven hydroclimatic regime. hydrology; Atmospheric dynamics; Attribution
Khlopenkov, Konstantin; Duda, David; Thieman, Mandana; Minnis, Patrick; Su, Wenying; Bedka, KristopherKhlopenkov, K., D. Duda, M. Thieman, P. Minnis, W. Su, K. Bedka, 2017: Development of multi-sensor global cloud and radiance composites for earth radiation budget monitoring from DSCOVR. doi: 10.1117/12.2278645. The Deep Space Climate Observatory (DSCOVR) enables analysis of the daytime Earth radiation budget via the onboard Earth Polychromatic Imaging Camera (EPIC) and National Institute of Standards and Technology Advanced Radiometer (NISTAR). Radiance observations and cloud property retrievals from low earth orbit and geostationary satellite imagers have to be co-located with EPIC pixels to provide scene identification in order to select anisotropic directional models needed to calculate shortwave and longwave fluxes. A new algorithm is proposed for optimal merging of selected radiances and cloud properties derived from multiple satellite imagers to obtain seamless global hourly composites at 5-km resolution. An aggregated rating is employed to incorporate several factors and to select the best observation at the time nearest to the EPIC measurement. Spatial accuracy is improved using inverse mapping with gradient search during reprojection and bicubic interpolation for pixel resampling. The composite data are subsequently remapped into EPIC-view domain by convolving composite pixels with the EPIC point spread function defined with a half-pixel accuracy. PSF-weighted average radiances and cloud properties are computed separately for each cloud phase. The algorithm has demonstrated contiguous global coverage for any requested time of day with a temporal lag of under 2 hours in over 95% of the globe.
Klein, Stephen A.; Hall, Alex; Norris, Joel R.; Pincus, RobertKlein, S. A., A. Hall, J. R. Norris, R. Pincus, 2017: Low-Cloud Feedbacks from Cloud-Controlling Factors: A Review. Surveys in Geophysics, 38(6), 1307-1329. doi: 10.1007/s10712-017-9433-3. The response to warming of tropical low-level clouds including both marine stratocumulus and trade cumulus is a major source of uncertainty in projections of future climate. Climate model simulations of the response vary widely, reflecting the difficulty the models have in simulating these clouds. These inadequacies have led to alternative approaches to predict low-cloud feedbacks. Here, we review an observational approach that relies on the assumption that observed relationships between low clouds and the “cloud-controlling factors” of the large-scale environment are invariant across time-scales. With this assumption, and given predictions of how the cloud-controlling factors change with climate warming, one can predict low-cloud feedbacks without using any model simulation of low clouds. We discuss both fundamental and implementation issues with this approach and suggest steps that could reduce uncertainty in the predicted low-cloud feedback. Recent studies using this approach predict that the tropical low-cloud feedback is positive mainly due to the observation that reflection of solar radiation by low clouds decreases as temperature increases, holding all other cloud-controlling factors fixed. The positive feedback from temperature is partially offset by a negative feedback from the tendency for the inversion strength to increase in a warming world, with other cloud-controlling factors playing a smaller role. A consensus estimate from these studies for the contribution of tropical low clouds to the global mean cloud feedback is 0.25 ± 0.18 W m−2 K−1 (90% confidence interval), suggesting it is very unlikely that tropical low clouds reduce total global cloud feedback. Because the prediction of positive tropical low-cloud feedback with this approach is consistent with independent evidence from low-cloud feedback studies using high-resolution cloud models, progress is being made in reducing this key climate uncertainty.
Kratz, D. P.; Stackhouse, P.W.; Wong, T; Sawaengphokhai, P.; Wilber, A. C.; Gupta, S. K.; Loeb, N. G.Kratz, D. P., P. Stackhouse, T. Wong, P. Sawaengphokhai, A. C. Wilber, S. K. Gupta, N. G. Loeb, 2017: Earth radiation Budget at Top-of-Atmosphere [in “State of the Climate in 2016"]. Bull. Amer. Meteor. Soc., 97(8), S41-S42. doi: 10.1175/2017BAMSStateoftheClimate.1.
Kucharski, D.; Kirchner, G.; Bennett, J. C.; Lachut, M.; Sośnica, K.; Koshkin, N.; Shakun, L.; Koidl, F.; Steindorfer, M.; Wang, P.; Fan, C.; Han, X.; Grunwaldt, L.; Wilkinson, M.; Rodríguez, J.; Bianco, G.; Vespe, F.; Catalán, M.; Salmins, K.; del Pino, J. R.; Lim, H.-C.; Park, E.; Moore, C.; Lejba, P.; Suchodolski, T.Kucharski, D., G. Kirchner, J. C. Bennett, M. Lachut, K. Sośnica, N. Koshkin, L. Shakun, F. Koidl, M. Steindorfer, P. Wang, C. Fan, X. Han, L. Grunwaldt, M. Wilkinson, J. Rodríguez, G. Bianco, F. Vespe, M. Catalán, K. Salmins, J. R. del Pino, H. Lim, E. Park, C. Moore, P. Lejba, T. Suchodolski, 2017: Photon Pressure Force on Space Debris TOPEX/Poseidon Measured by Satellite Laser Ranging. Earth and Space Science, 4(10), 661–668. doi: 10.1002/2017EA000329. The (TOPography EXperiment) TOPEX/Poseidon (T/P) altimetry mission operated for 13 years before the satellite was decommissioned in January 2006, becoming a large space debris object at an altitude of 1,340 km. Since the end of the mission, the interaction of T/P with the space environment has driven the satellite's spin dynamics. Satellite laser ranging (SLR) measurements collected from June 2014 to October 2016 allow for the satellite spin axis orientation to be determined with an accuracy of 1.7°. The spin axis coincides with the platform yaw axis (formerly pointing in the nadir direction) about which the body rotates in a counterclockwise direction. The combined photometric and SLR data collected over the 11 year time span indicates that T/P has continuously gained rotational energy at an average rate of 2.87 J/d and spins with a period of 10.73 s as of 19 October 2016. The satellite attitude model shows a variation of the cross-sectional area in the Sun direction between 8.2 m2 and 34 m2. The direct solar radiation pressure is the main factor responsible for the spin-up of the body, and the exerted photon force varies from 65 μN to 228 μN around the mean value of 138.6 μN. Including realistic surface force modeling in orbit propagation algorithms will improve the prediction accuracy, giving better conjunction warnings for scenarios like the recent close approach reported by the ILRS Space Debris Study Group—an approximate 400 m flyby between T/P and Jason-2 on 20 June 2017. 7538 Solar irradiance; 1299 General or miscellaneous; 7934 Impacts on technological systems; 7969 Satellite drag; 7984 Space radiation environment; photometry; satellite laser ranging; satellite spin; solar radiation pressure; space debris
Kuo, Chia-Pang; Yang, Ping; Huang, Xianglei; Feldman, Daniel; Flanner, Mark; Kuo, Chaincy; Mlawer, Eli J.Kuo, C., P. Yang, X. Huang, D. Feldman, M. Flanner, C. Kuo, E. J. Mlawer, 2017: Impact of Multiple Scattering on Longwave Radiative Transfer Involving Clouds. Journal of Advances in Modeling Earth Systems, 9(8), 3082-3098. doi: 10.1002/2017MS001117. General circulation models (GCMs) are extensively used to estimate the influence of clouds on the global energy budget and other aspects of climate. Because radiative transfer computations involved in GCMs are costly, it is typical to consider only absorption but not scattering by clouds in longwave (LW) spectral bands. In this study, the flux and heating rate biases due to neglecting the scattering of LW radiation by clouds are quantified by using advanced cloud optical property models, and satellite data from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), CloudSat, Clouds and the Earth's Radiant Energy System (CERES), and Moderate Resolution Imaging Spectrometer (MODIS) merged products (CCCM). From the products, information about the atmosphere and clouds (microphysical and buck optical properties, and top and base heights) is used to simulate fluxes and heating rates. One-year global simulations for 2010 show that the LW scattering decreases top-of-atmosphere (TOA) upward flux and increases surface downward flux by 2.6 and 1.2 W/m2, respectively, or approximately 10% and 5% of the TOA and surface LW cloud radiative effect, respectively. Regional TOA upward flux biases are as much as 5% of global averaged outgoing longwave radiation (OLR). LW scattering causes approximately 0.018 K/d cooling at the tropopause and about 0.028 K/d heating at the surface. Furthermore, over 40% of the total OLR bias for ice clouds is observed in 350–500 cm−1. Overall, the radiative effects associated with neglecting LW scattering are comparable to the counterpart due to doubling atmospheric CO2 under clear-sky conditions. 0360 Radiation: transmission and scattering; 0321 Cloud/radiation interaction; radiative transfer; 0319 Cloud optics; outgoing longwave radiation; doubling CO2; longwave scattering; radiative effect of clouds; simulation biases
L'Ecuyer, Tristan S.L'Ecuyer, T. S., 2017: Earth's Energy Balance. International Encyclopedia of Geography: People, the Earth, Environment and Technology. The Earth's weather and climate are driven by exchanges of energy between the sun, the atmosphere, and the surface. Globally, the Earth receives 123.5 PW (1 PW = 1 petaWatt = 1015 Watts) of radiation from the sun. Of this, 29.4% is reflected back to space while the remainder is absorbed, heating the planet. The warm Earth, in turn, emits thermal radiation to space, ultimately reaching equilibrium at an effective blackbody temperature of −18°C. Energy surpluses at lower latitudes and deficits at higher latitudes are balanced by large circulations in the atmosphere and oceans that transport an enormous 350 exaJoules (1018 J) of energy daily from the equator to the poles. These circulations drive global weather patterns, moderate regional climates, and make the Earth habitable. Current observations suggest that the Earth currently receives 0.3 PW more energy than it emits, owing primarily to increased concentrations of greenhouse gases and associated climate feedbacks. The oceans absorb most of this excess energy while the remainder heats the atmosphere and melts the ice sheets. clouds; satellite observations; climate; Atmospheric circulation; radiation; global warming; earth observation; human impacts
Lacagnina, Carlo; Hasekamp, Otto P.; Torres, OmarLacagnina, C., O. P. Hasekamp, O. Torres, 2017: Direct radiative effect of aerosols based on PARASOL and OMI satellite observations. Journal of Geophysical Research: Atmospheres, 122(4), 2366–2388. doi: 10.1002/2016JD025706. Accurate portrayal of the aerosol characteristics is crucial to determine aerosol contribution to the Earth's radiation budget. We employ novel satellite retrievals to make a new measurement-based estimate of the shortwave direct radiative effect of aerosols (DREA), both over land and ocean. Global satellite measurements of aerosol optical depth (AOD), single-scattering albedo (SSA) and phase function from PARASOL (Polarization & Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) are used in synergy with OMI (Ozone Monitoring Instrument) SSA. Aerosol information is combined with land-surface Bi-directional Reflection Distribution Function (BRDF) and cloud characteristics from MODIS (Moderate Resolution Imaging Spectrometer) satellite products. Eventual gaps in observations are filled with the state-of-art global aerosol model ECHAM5-HAM2. It is found that our estimate of DREA is largely insensitive to model choice.Radiative transfer calculations show that DREA at top-of-atmosphere is -4.6 ± 1.5 W/m2 for cloud-free and -2.1 ± 0.7 W/m2 for all-sky conditions, during year 2006. These fluxes are consistent with, albeit generally less negative over ocean than, former assessments. Unlike previous studies, our estimate is constrained by retrievals of global coverage SSA, which may justify different DREA values. Remarkable consistency is found in comparison with DREA based on CERES (Clouds and the Earth's Radiant Energy System) and MODIS observations. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; climate; 0368 Troposphere: constituent transport and chemistry; parasol; 3360 Remote sensing; 4321 Climate impact; aerosol absorption; aerosol radiative effect; OMI; Single Scattering Albedo (SSA)
Lacour, Adrien; Chepfer, Helene; Shupe, Matthew D.; Miller, Nathaniel B.; Noel, Vincent; Kay, Jennifer; Turner, David D.; Guzman, RodrigoLacour, A., H. Chepfer, M. D. Shupe, N. B. Miller, V. Noel, J. Kay, D. D. Turner, R. Guzman, 2017: Greenland clouds observed in CALIPSO-GOCCP: comparison with ground-based Summit observations.. J. Climate, 30, 6065–6083. doi: 10.1175/JCLI-D-16-0552.1. Spaceborne lidar observations from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) provide the first-ever observations of cloud vertical structure and phase over the entire Greenland icesheet. This study leverages CALIPSO observations over Greenland to pursue two investigations. First, the GCM-Oriented-CALIPSO Cloud Product (CALIPSO-GOCCP) observations are compared with collocated ground-based radar and lidar observations at Summit, Greenland. The liquid cloud cover agrees well between the spaceborne and ground-based observations. In contrast, ground satellite differences reach 30% in total cloud cover and 40% in cloud fraction below 2 km Above Ground Level, due to optically very thin ice clouds (IWC < 2.5×10-3 g m-3) missed by CALIPSO-GOCCP. Those results are compared with satellite cloud climatologies from the GEWEX cloud assessment. Most passive sensors detect fewer clouds than CALIPSO-GOCCP and the Summit ground observations, due to different detection methods. Second, the distribution of clouds over the Greenland is analyzed using CALIPSO-GOCCP. The central Greenland is the cloudiest area in summer: +7% and +4% above Greenland-wide average for respectively total and liquid cloud cover. South Greenland contains free troposphere thin ice clouds all seasons, and liquid clouds in summer. In northern Greenland, fewer ice clouds are detected than in other areas, but the liquid cloud cover seasonal cycle in that region drives the total Greenland cloud annual variability with a maximum in summer. In 2010 and 2012, large ice-sheet melting events have positive liquid cloud cover anomaly (+1 to 2%). In contrast, less clouds (-7%) are observed during low ice-sheet melt years (e.g., 2009).
Langenbrunner, B.; Neelin, J. D.Langenbrunner, B., J. D. Neelin, 2017: Multiobjective constraints for climate model parameter choices: Pragmatic Pareto fronts in CESM1. Journal of Advances in Modeling Earth Systems, 9(5), 2008-2026. doi: 10.1002/2017MS000942. Global climate models (GCMs) are examples of high-dimensional input-output systems, where model output is a function of many variables, and an update in model physics commonly improves performance in one objective function (i.e., measure of model performance) at the expense of degrading another. Here concepts from multiobjective optimization in the engineering literature are used to investigate parameter sensitivity and optimization in the face of such trade-offs. A metamodeling technique called cut high-dimensional model representation (cut-HDMR) is leveraged in the context of multiobjective optimization to improve GCM simulation of the tropical Pacific climate, focusing on seasonal precipitation, column water vapor, and skin temperature. An evolutionary algorithm is used to solve for Pareto fronts, which are surfaces in objective function space along which trade-offs in GCM performance occur. This approach allows the modeler to visualize trade-offs quickly and identify the physics at play. In some cases, Pareto fronts are small, implying that trade-offs are minimal, optimal parameter value choices are more straightforward, and the GCM is well-functioning. In all cases considered here, the control run was found not to be Pareto-optimal (i.e., not on the front), highlighting an opportunity for model improvement through objectively informed parameter selection. Taylor diagrams illustrate that these improvements occur primarily in field magnitude, not spatial correlation, and they show that specific parameter updates can improve fields fundamental to tropical moist processes—namely precipitation and skin temperature—without significantly impacting others. These results provide an example of how basic elements of multiobjective optimization can facilitate pragmatic GCM tuning processes. 1622 Earth system modeling; 1626 Global climate models; global climate model; 3365 Subgrid-scale (SGS) parameterization; 1854 Precipitation; CESM1; multiobjective optimization; parameter optimization; tropical pacific climate
Lapo, Karl E.; Hinkelman, Laura M.; Sumargo, Edwin; Hughes, Mimi; Lundquist, Jessica D.Lapo, K. E., L. M. Hinkelman, E. Sumargo, M. Hughes, J. D. Lundquist, 2017: A critical evaluation of modeled solar irradiance over California for hydrologic and land surface modeling. Journal of Geophysical Research: Atmospheres, 122(1), 299–317. doi: 10.1002/2016JD025527. Studies of land surface processes in complex terrain often require estimates of meteorological variables, i.e., the incoming solar irradiance (Qsi), to force land surface models. However, estimates of Qsi are rarely evaluated within mountainous environments. We evaluated four methods of estimating Qsi: the CERES Synoptic Radiative Fluxes and Clouds (SYN) product, MTCLIM, a regional reanalysis product derived from a long-term Weather Research and Forecast simulation, and Mountain Microclimate Simulation Model (MTCLIM). These products are evaluated over the Central Valley and Sierra Nevada mountains in California, a region with meteorology strongly impacted by complex topography. We used a spatially dense network of Qsi observations (n = 70) to characterize the spatial characteristics of Qsi uncertainty. Observation sites were grouped into five subregions, and Qsi estimates were evaluated against observations in each subregion. Large monthly biases (up to 80 W m−2) outside the observational uncertainty were found for all estimates in all subregions examined, typically reaching a maximum in the spring. We found that MTCLIM and SYN generally perform the best across all subregions. Differences between Qsi estimates were largest over the Sierra Nevada, with seasonal differences exceeding 50 W m−2. Disagreements in Qsi were especially pronounced when averaging over high-elevation basins, with monthly differences up to 80 W m−2. Biases in estimated Qsi predominantly occurred with darker than normal conditions associated with precipitation (a proxy for cloud cover), while the presence of aerosols and water vapor was unable to explain the biases. Users of Qsi estimates in regions of complex topography, especially those estimating Qsi to force land surface models, need to be aware of this source of uncertainty. 0360 Radiation: transmission and scattering; Solar radiation; 1814 Energy budgets; Mountain meteorology; surface energy budget; 1843 Land/atmosphere interactions
Lauer, Axel; Eyring, Veronika; Righi, Mattia; Buchwitz, Michael; Defourny, Pierre; Evaldsson, Martin; Friedlingstein, Pierre; de Jeu, Richard; de Leeuw, Gerrit; Loew, Alexander; Merchant, Christopher J.; Müller, Benjamin; Popp, Thomas; Reuter, Maximilian; Sandven, Stein; Senftleben, Daniel; Stengel, Martin; Van Roozendael, Michel; Wenzel, Sabrina; Willén, UlrikaLauer, A., V. Eyring, M. Righi, M. Buchwitz, P. Defourny, M. Evaldsson, P. Friedlingstein, R. de Jeu, G. de Leeuw, A. Loew, C. J. Merchant, B. Müller, T. Popp, M. Reuter, S. Sandven, D. Senftleben, M. Stengel, M. Van Roozendael, S. Wenzel, U. Willén, 2017: Benchmarking CMIP5 models with a subset of ESA CCI Phase 2 data using the ESMValTool. Remote Sensing of Environment, 203, 9-39. doi: 10.1016/j.rse.2017.01.007. The Coupled Model Intercomparison Project (CMIP) is now moving into its sixth phase and aims at a more routine evaluation of the models as soon as the model output is published to the Earth System Grid Federation (ESGF). To meet this goal the Earth System Model Evaluation Tool (ESMValTool), a community diagnostics and performance metrics tool for the systematic evaluation of Earth system models (ESMs) in CMIP, has been developed and a first version (1.0) released as open source software in 2015. Here, an enhanced version of the ESMValTool is presented that exploits a subset of Essential Climate Variables (ECVs) from the European Space Agency's Climate Change Initiative (ESA CCI) Phase 2 and this version is used to demonstrate the value of the data for model evaluation. This subset includes consistent, long-term time series of ECVs obtained from harmonized, reprocessed products from different satellite instruments for sea surface temperature, sea ice, cloud, soil moisture, land cover, aerosol, ozone, and greenhouse gases. The ESA CCI data allow extending the calculation of performance metrics as summary statistics for some variables and add an important alternative data set in other cases where observations are already available. The provision of uncertainty estimates on a per grid basis for the ESA CCI data sets is used in a new extended version of the Taylor diagram and provides important additional information for a more objective evaluation of the models. In our analysis we place a specific focus on the comparability of model and satellite data both in time and space. The ESA CCI data are well suited for an evaluation of results from global climate models across ESM compartments as well as an analysis of long-term trends, variability and change in the context of a changing climate. The enhanced version of the ESMValTool is released as open source software and ready to support routine model evaluation in CMIP6 and at individual modeling centers. Model evaluation; Aerosols; Clouds; Soil moisture; Earth system models; Ozone; CMIP; Sea ice; Climate; CO2; ESA CCI; ESMValTool; Greenhouse gases; Land cover; Sea surface temperature
Lebsock, Matthew D.; L’Ecuyer, Tristan S.; Pincus, RobertLebsock, M. D., T. S. L’Ecuyer, R. Pincus, 2017: An Observational View of Relationships Between Moisture Aggregation, Cloud, and Radiative Heating Profiles. Surveys in Geophysics, 38(6), 1237-1254. doi: 10.1007/s10712-017-9443-1. Data from several coincident satellite sensors are analyzed to determine the dependence of cloud and precipitation characteristics of tropical regions on the variance in the water vapor field. Increased vapor variance is associated with decreased high cloud fraction and an enhancement of low-level radiative cooling in dry regions of the domain. The result is found across a range of sea surface temperatures and rain rates. This suggests the possibility of an enhanced low-level circulation feeding the moist convecting areas when vapor variance is large. These findings are consistent with idealized models of self-aggregation, in which the aggregation of convection is maintained by a combination of low-level radiative cooling in dry regions and mid-to-upper-level radiative warming in cloudy regions.
Lee, KwonhoLee, K., 2017: Effects of Aerosol Optical Properties on Upward Shortwave Flux in the Presence of Aerosol and Cloud layers. Korean Journal of Remote Sensing, 33(3), 301-311. Aerosol optical properties as well as vertical location of layer can alter the radiative balance of the Earth by reflecting and absorbing solar radiation. In this study, radiative transfer model (RTM) and satellite-based analysis have been used to quantify the top-of-atmosphere (TOA) radiative effect of aerosol layers in the cloudy atmosphere of the northeast Asia. RTM simulation results show that the atmospheric warming effect of aerosols increases with their height in the presence of underlying cloud layer. This relationship is higher for stronger absorbing aerosols and higher surface albedo condition. Over study region (20-50 ˚N, 110-140 ˚E) and aerosol event cases, it is possible to qualitatively identify absorbing aerosol effects in the presence of clouds by combining the UV Absorbing Aerosol Index (AAI) derived from Total Ozone Mapping Spectrometer (TOMS), cloud parameters derived from the Moderate Resolution Imaging Spectro-radiometer (MODIS), with TOA Upward Shortwave Flux (USF) from the Clouds and the Earth’s Radiant Energy System (CERES). As the regional-mean radiative effect of aerosols, 6 - 26 % lower the USF between aerosols and cloud cover is taken into account. These results demonstrate the importance of estimation for the accurate quantification of aerosol’s direct and indirect effect. Aerosol; Cloud; Optical property; Radiative effect; Shortwave flux
Lenaerts, Jan T. M.; Tricht, Kristof van; Lhermitte, Stef; L'Equyer, TristanLenaerts, J. T. M., K. v. Tricht, S. Lhermitte, T. L'Equyer, 2017: Polar clouds and radiation in satellite observations, reanalyses, and climate models. Geophysical Research Letters, 44(7), 3355–3364. doi: 10.1002/2016GL072242. Clouds play a pivotal role in the surface energy budget of the Polar regions. Here we use two largely independent datasets of cloud and surface downwelling radiation observations derived by satellite remote sensing (2007-2010) to evaluate simulated clouds and radiation over both Polar ice sheets and oceans in state-of-the-art atmospheric reanalyses (ERA-Interim and MERRA-2) and the CMIP5 climate model ensemble. Firstly, we show that, compared to CERES-EBAF, CloudSat-CALIPSO better represents cloud liquid and ice water path over high latitudes, owing to its recent explicit determination of cloud phase that will be part of its new R05 release. The reanalyses and climate models disagree widely on the amount of cloud liquid and ice in the Polar regions. Compared to the observations, we find significant but inconsistent biases in the model simulations of cloud liquid and ice water, as well as in the downwelling radiation components. The CMIP5 models display a wide range of cloud characteristics of the Polar regions, especially with regard to cloud liquid water, limiting the representativeness of the multi-model mean. A few CMIP5 models (CNRM, GISS, GFDL, and IPSL_CM5b) clearly outperform the others, which enhances credibility in their projected future cloud and radiation changes over high latitudes. Given the rapid changes in Polar regions and global feedbacks involved, future climate model developments should target improved representation of Polar clouds. To that end, remote sensing observations are crucial, in spite of large remaining observational uncertainties, which is evidenced by the substantial differences between the two datasets. clouds; satellite observations; 3310 Clouds and cloud feedbacks; reanalysis; radiation; 0758 Remote sensing; 1626 Global climate models; 3349 Polar meteorology; 0764 Energy balance; polar regions; climate modelling
Leutbecher, Martin; Lock, Sarah-Jane; Ollinaho, Pirkka; Lang, Simon T. K.; Balsamo, Gianpaolo; Bechtold, Peter; Bonavita, Massimo; Christensen, H. M.; Diamantakis, Michail; Dutra, Emanuel; English, Stephen; Fisher, Michael; Forbes, Richard M.; Goddard, Jacqueline; Haiden, Thomas; Hogan, Robin J.; Juricke, Stephan; Lawrence, Heather; MacLeod, Dave; Magnusson, Linus; Malardel, Sylvie; Massart, Sebastien; Sandu, Irina; Smolarkiewicz, Piotr K.; Subramanian, Aneesh; Vitart, Frédéric; Wedi, Nils; Weisheimer, AntjeLeutbecher, M., S. Lock, P. Ollinaho, S. T. K. Lang, G. Balsamo, P. Bechtold, M. Bonavita, H. M. Christensen, M. Diamantakis, E. Dutra, S. English, M. Fisher, R. M. Forbes, J. Goddard, T. Haiden, R. J. Hogan, S. Juricke, H. Lawrence, D. MacLeod, L. Magnusson, S. Malardel, S. Massart, I. Sandu, P. K. Smolarkiewicz, A. Subramanian, F. Vitart, N. Wedi, A. Weisheimer, 2017: Stochastic representations of model uncertainties at ECMWF: State of the art and future vision. Quarterly Journal of the Royal Meteorological Society, 143(707), 2315–2339. doi: 10.1002/qj.3094. Members in ensemble forecasts differ due to the representations of initial uncertainties and model uncertainties. The inclusion of stochastic schemes to represent model uncertainties has improved the probabilistic skill of the ECMWF ensemble by increasing reliability and reducing the error of the ensemble mean. Recent progress, challenges and future directions regarding stochastic representations of model uncertainties at ECMWF are described in this paper. The coming years are likely to see a further increase in the use of ensemble methods in forecasts and assimilation. This will put increasing demands on the methods used to perturb the forecast model. An area that is receiving a greater attention than 5 to 10 years ago is the physical consistency of the perturbations. Other areas where future efforts will be directed are the expansion of uncertainty representations to the dynamical core and to other components of the Earth system as well as the overall computational efficiency of representing model uncertainty. Earth system model; ensemble forecasts; model uncertainty; dynamical core; ensemble data assimilation; Numerical weather prediction; stochastic parametrization; weak-constraint 4D-Var
Levine, Xavier J.; Boos, William R.Levine, X. J., W. R. Boos, 2017: Land surface albedo bias in climate models and its association with tropical rainfall. Geophysical Research Letters, 44(12), 6363–6372. doi: 10.1002/2017GL072510. The influence of surface albedo on tropical precipitation is widely appreciated, but albedo bias over snow-free areas in climate models has been studied little. Here, historical CMIP5 simulations are shown to exhibit large multi-model mean bias and intermodel variability in boreal summer mean surface broadband shortwave albedo. Intermodel variability in this albedo is globally coherent over vegetated regions, and correlates with intermodel tropical precipitation variability. Evidence supports the hypothesis that these spatially coherent albedo variations cause precipitation variations. Specifically, the spatial structure of albedo and precipitation variations are distinct, suggesting the latter do not cause the former by darkening soil. Furthermore, simulated interannual albedo variance is small compared to intermodel albedo variance, while the ratio of interannual to intermodel precipitation variance is much larger. Finally, imposing the dominant pattern of intermodel albedo variability in one climate model causes a precipitation change with structure similar to that of the intermodel variability. 1610 Atmosphere; 1640 Remote sensing; albedo; 1630 Impacts of global change; 1631 Land/atmosphere interactions; 1626 Global climate models; model bias; Boreal Summer; CMIP5 Archive; Intermodel Variability; Tropical Rainfall
Li, J.-L. F.; Richardson, Mark; Hong, Yulan; Lee, Wei-Liang; Wang, Yi-Hui; Yu, Jia-Yuh; Fetzer, Eric; Graeme Stephens; Liu, YinghuiLi, J. F., M. Richardson, Y. Hong, W. Lee, Y. Wang, J. Yu, E. Fetzer, . Graeme Stephens, Y. Liu, 2017: Improved simulation of Antarctic sea ice due to the radiative effects of falling snow. Environmental Research Letters, 12(8), 084010. doi: 10.1088/1748-9326/aa7a17. Southern Ocean sea-ice cover exerts critical control on local albedo and Antarctic precipitation, but simulated Antarctic sea-ice concentration commonly disagrees with observations. Here we show that the radiative effects of precipitating ice (falling snow) contribute substantially to this discrepancy. Many models exclude these radiative effects, so they underestimate both shortwave albedo and downward longwave radiation. Using two simulations with the climate model CESM1, we show that including falling-snow radiative effects improves the simulations relative to cloud properties from CloudSat-CALIPSO, radiation from CERES-EBAF and sea-ice concentration from passive microwave sensors. From 50–70°S, the simulated sea-ice-area bias is reduced by 2.12 × 10 6 km 2 (55%) in winter and by 1.17 × 10 6 km 2 (39%) in summer, mainly because increased wintertime longwave heating restricts sea-ice growth and so reduces summer albedo. Improved Antarctic sea-ice simulations will increase confidence in projected Antarctic sea level contributions and changes in global warming driven by long-term changes in Southern Ocean feedbacks.
Li, Jiandong; Wang, Tianhe; Habib, AmmaraLi, J., T. Wang, A. Habib, 2017: Observational characteristics of cloud radiative effects over three arid regions in the Northern Hemisphere. Journal of Meteorological Research, 31(4), 654-664. doi: 10.1007/s13351-017-6166-7. Cloud–radiation processes play an important role in regional energy budgets and surface temperature changes over arid regions. Cloud radiative effects (CREs) are used to quantitatively measure the aforementioned climatic role. This study investigates the characteristics of CREs and their temporal variations over three arid regions in central Asia (CA), East Asia (EA), and North America (NA), based on recent satellite datasets. Our results show that the annual mean shortwave (SW) and net CREs (SWCRE and NCRE) over the three arid regions are weaker than those in the same latitudinal zone of the Northern Hemisphere. In most cold months (November–March), the longwave (LW) CRE is stronger than the SWCRE over the three arid regions, leading to a positive NCRE and radiative warming in the regional atmosphere–land surface system. The cold-season mean NCRE at the top of the atmosphere (TOA) averaged over EA is 4.1 W m–2, with a positive NCRE from November to March, and the intensity and duration of the positive NCRE is larger than that over CA and NA. The CREs over the arid regions of EA exhibit remarkable annual cycles due to the influence of the monsoon in the south. The TOA LWCRE over arid regions is closely related to the high-cloud fraction, and the SWCRE relates well to the total cloud fraction. In addition, the relationship between the SWCRE and the low-cloud fraction is good over NA because of the considerable occurrence of low cloud. Further results show that the interannual variation of TOA CREs is small over the arid regions of CA and EA, but their surface LWCREs show certain decreasing trends that correspond well to their decreasing total cloud fraction. It is suggested that combined studies of more observational cloud properties and meteorological elements are needed for indepth understanding of cloud–radiation processes over arid regions of the Northern Hemisphere.
Li, Jiandong; Wang, Wei-Chyung; Dong, Xiquan; Mao, JiangyuLi, J., W. Wang, X. Dong, J. Mao, 2017: Cloud-radiation-precipitation associations over the Asian monsoon region: an observational analysis. Climate Dynamics, 1-19. doi: 10.1007/s00382-016-3509-5. This study uses 2001–2014 satellite observations and reanalyses to investigate the seasonal characteristics of Cloud Radiative Effects (CREs) and their associations with cloud fraction (CF) and precipitation over the Asian monsoon region (AMR) covering Eastern China (EC) and South Asia (SA). The CREs exhibit strong seasonal variations but show distinctly different relationships with CFs and precipitation over the two regions. For EC, the CREs is dominated by shortwave (SW) cooling, with an annual mean value of − 40 W m− 2 for net CRE, and peak in summer while the presence of extensive and opaque low-level clouds contributes to large Top-Of-Atmosphere (TOA) albedo (>0.5) in winter. For SA, a weak net CRE exists throughout the year due to in-phase compensation of SWCRE by longwave (LW) CRE associated with the frequent occurrence of high clouds. For the entire AMR, SWCRE strongly correlates with the dominant types of CFs, although the cloud vertical structure plays important role particularly in summer. The relationships between CREs and precipitation are stronger in SA than in EC, indicating the dominant effect of monsoon circulation in the former region. SWCRE over EC is only partly related to precipitation and shows distinctive regional variations. Further studies need to pay more attention to vertical distributions of cloud micro- and macro-physical properties, and associated precipitation systems over the AMR.
Li, Xiaoyuan; Wagner, Fabian; Peng, Wei; Yang, Junnan; Mauzerall, Denise L.Li, X., F. Wagner, W. Peng, J. Yang, D. L. Mauzerall, 2017: Reduction of solar photovoltaic resources due to air pollution in China. Proceedings of the National Academy of Sciences, 114(45), 11867-11872. doi: 10.1073/pnas.1711462114. Solar photovoltaic (PV) electricity generation is expanding rapidly in China, with total capacity projected to be 400 GW by 2030. However, severe aerosol pollution over China reduces solar radiation reaching the surface. We estimate the aerosol impact on solar PV electricity generation at the provincial and regional grid levels in China. Our approach is to examine the 12-year (2003–2014) average reduction in point-of-array irradiance (POAI) caused by aerosols in the atmosphere. We apply satellite-derived surface irradiance data from the NASA Clouds and the Earth’s Radiant Energy System (CERES) with a PV performance model (PVLIB-Python) to calculate the impact of aerosols and clouds on POAI. Our findings reveal that aerosols over northern and eastern China, the most polluted regions, reduce annual average POAI by up to 1.5 kWh/m2 per day relative to pollution-free conditions, a decrease of up to 35%. Annual average reductions of POAI over both northern and eastern China are about 20–25%. We also evaluate the seasonal variability of the impact and find that aerosols in this region are as important as clouds in winter. Furthermore, we find that aerosols decrease electricity output of tracking PV systems more than those with fixed arrays: over eastern China, POAI is reduced by 21% for fixed systems at optimal angle and 34% for two-axis tracking systems. We conclude that PV system performance in northern and eastern China will benefit from improvements in air quality and will facilitate that improvement by providing emission-free electricity. aerosols; renewable energy; China; air pollution; solar photovoltaic
Li, Yuanlong; Han, Weiqing; Ravichandran, M.; Wang, Wanqiu; Shinoda, Toshiaki; Lee, TongLi, Y., W. Han, M. Ravichandran, W. Wang, T. Shinoda, T. Lee, 2017: Bay of Bengal salinity stratification and Indian summer monsoon intraseasonal oscillation: 1. Intraseasonal variability and causes. Journal of Geophysical Research: Oceans, 122(5), 4291–4311. doi: 10.1002/2017JC012691. The huge freshwater flux of the Indian summer monsoon (ISM; May–October) gives rise to strong salinity stratification in the Bay of Bengal (BoB), causing a shallow mixed layer and a thick barrier layer, which potentially affects intraseasonal oscillations of the monsoon (MISOs). In this study, intraseasonal variability of the mixed-layer depth (MLD) and barrier layer thickness (BLT) is investigated using in situ observations from Argo floats and moored buoys and an ocean general circulation model (OGCM). The average MLD in the BoB is typically 20–30 m during the ISM, while the BLT increases from ∼10 m in May–June to 20–40 m in September–October. MISOs induce in-phase variations in MLD and isothermal layer depth (ILD), both of which are deepened by 8–15 m during MISO active phase, while the change of BLT is small and within the error range of Argo data sampling. In the northern (southern) bay, BLT increases by ∼5 m (2 m) during MISOs owing to a larger deepening of ILD than MLD. OGCM experiments are performed to understand the underlying mechanism. In the BoB intraseasonal variations of MLD, ILD and BLT arise largely from ocean internal instability, whereas those induced by MISOs are weaker. The in-phase variations of MLD and ILD during MISOs are induced by different processes. The MLD deepening is primarily caused by wind stress forcing, while the ILD deepening is driven by surface heat fluxes via surface cooling. The limited variability of BLT is due to the offsetting of different forcing processes. 4572 Upper ocean and mixed layer processes; 4504 Air/sea interactions; Indian summer monsoon; barrier layer; bay of bengal; intraseasonal oscillation; ocean mixed layer
Li, Zhujun; Xu, Kuan-Man; Cheng, AnningLi, Z., K. Xu, A. Cheng, 2017: The Response of Simulated Arctic Mixed-Phase Stratocumulus to Sea Ice Cover Variability in the Absence of Large-Scale Advection. Journal of Geophysical Research: Atmospheres, 122(12), 12,335–12,352. doi: 10.1002/2017JD027086. This study examines the responses of Arctic Mixed-Phase Stratocumulus (AMPS) boundary layer to sea ice cover variability near the sea ice margins using large eddy simulations. The simulations are conducted for two different atmospheric conditions, based on observations from the Surface Heat Budget of the Arctic Ocean Experiment (SHEBA) (100% sea ice-covered) and the Mixed-Phase Arctic Cloud Experiment (M-PACE) (open ocean). The effect of sea ice cover variability is investigated for both atmospheric conditions by conducting a series of simulations prescribed with varying amounts of sea ice cover and no large-scale advection. As sea ice cover amount decreases, the SHEBA boundary layer deepens and becomes decoupled. The relative strength of turbulence driven by surface heating to that driven by cloud top radiative cooling increases. Cloud ice and snow grow more efficiently than cloud liquid with moisture transported from the lower boundary layer. On the other hand, as sea ice cover amount increases, the M-PACE boundary layer becomes shallower and more coupled with the surface as turbulence mainly driven by cloud top radiative cooling. Moisture supply from the surface is reduced while cloud droplets are generated from turbulence at cloud top with little ice formation. In both atmospheric conditions, the boundary layer turbulence structure is modified according to change in the relative strength of boundary-layer turbulent sources as sea ice amount changes, resulting in the growth/decay of the cloud layer. Simulations with smaller sea ice cover amounts are associated with more cloud ice but not necessarily more cloud liquid. 0320 Cloud physics and chemistry; sea ice; Arctic; Surface fluxes; boundary layer clouds; large eddy simulation
Liu, Chunlei; Allan, Richard P.; Mayer, Michael; Hyder, Patrick; Loeb, Norman G.; Roberts, Chris D.; Valdivieso, Maria; Edwards, John M.; Vidale, Pier-LuigiLiu, C., R. P. Allan, M. Mayer, P. Hyder, N. G. Loeb, C. D. Roberts, M. Valdivieso, J. M. Edwards, P. Vidale, 2017: Evaluation of satellite and reanalysis-based global net surface energy flux and uncertainty estimates. Journal of Geophysical Research: Atmospheres, 122(12), 6250–6272. doi: 10.1002/2017JD026616. The net surface energy flux is central to the climate system yet observational limitations lead to substantial uncertainty. A combination of satellite-derived radiative fluxes at the top of atmosphere (TOA) adjusted using the latest estimation of the net heat uptake of the Earth system, and the atmospheric energy tendencies and transports from the ERA-Interim reanalysis are used to estimate surface energy flux globally. To consider snowmelt and improve regional realism, land surface fluxes are adjusted through a simple energy balance approach at each grid point. This energy adjustment is redistributed over the oceans to ensure energy conservation and maintain realistic global ocean heat uptake, using a weighting function to avoid meridional discontinuities. Calculated surface energy fluxes are evaluated through comparison to ocean reanalyses. Derived turbulent energy flux variability is compared with the OAFLUX product and inferred meridional energy transports in the global ocean and the Atlantic are also evaluated using observations. Uncertainties in surface fluxes are investigated using a variety of approaches including comparison with a range of atmospheric reanalysis products. Decadal changes in the global mean and the inter-hemispheric energy imbalances are quantified and present day cross-equator heat transports are reevaluated at 0.22 ± 0.15 PW southward by the atmosphere and 0.32 ± 0.16 PW northward by the ocean considering the observed ocean heat sinks. 0300 Atmospheric Composition and Structure; 0399 General or miscellaneous; uncertainty; inter-hemispheric energy imbalance; land surface flux constraint; mass correction; net surface energy flux
Liu, Run; Liou, Kuo-Nan; Su, Hui; Gu, Yu; Zhao, Bin; Jiang, Jonathan H.; Liu, Shaw ChenLiu, R., K. Liou, H. Su, Y. Gu, B. Zhao, J. H. Jiang, S. C. Liu, 2017: High cloud variations with surface temperature from 2002 to 2015: Contributions to atmospheric radiative cooling rate and precipitation changes. Journal of Geophysical Research: Atmospheres, 122(10), 5457–5471. doi: 10.1002/2016JD026303. The global mean precipitation is largely constrained by atmospheric radiative cooling rates (Qr), which are sensitive to changes in high cloud fraction. We investigate variations of high cloud fraction with surface temperature (Ts) from July 2002 to June 2015 and compute their radiative effects on Qr using the Fu-Liou-Gu plane-parallel radiation model. We find that the tropical mean (30°S–30°N) high cloud fraction decreases with increasing Ts at a rate of about −1.0 ± 0.34% K−1 from 2002 to 2015, which leads to an enhanced atmospheric cooling around 0.86 W m−2 K−1. On the other hand, the northern midlatitudes (30°N–60°N) high cloud fraction increases with surface warming at a rate of 1.85 ± 0.65% K−1 and the near-global mean (60°S–60°N) high cloud fraction shows a statistically insignificant decreasing trend with increasing Ts over the analysis period. Dividing high clouds into cirrus, cirrostratus, and deep convective clouds, we find that cirrus cloud fraction increases with surface warming at a rate of 0.32 ± 0.11% K−1 (0.01 ± 0.17% K−1) for the near-global mean (tropical mean), while cirrostratus and deep convective clouds decrease with surface warming at a rate of −0.02 ± 0.18% K−1 and −0.33 ± 0.18% K−1 for the near-global mean and −0.64 ± 0.23% K−1 and −0.37 ± 0.13% K−1 for the tropical mean, respectively. High cloud fraction response to feedback to Ts accounts for approximately 1.9 ± 0.7% and 16.0 ± 6.1% of the increase in precipitation per unit surface warming over the period of 2002–2015 for the near-global mean and the tropical mean, respectively. radiative flux; 0321 Cloud/radiation interaction; Precipitation; high cloud; atmospheric radiative cooling; Fu-Liou-Gu plane-parallel radiation model
Loeb, Norman G.; Wang, Hailan; Liang, Lusheng; Kato, Seiji; Rose, Fred G.Loeb, N. G., H. Wang, L. Liang, S. Kato, F. G. Rose, 2017: Surface energy budget changes over Central Australia during the early 21st century drought. International Journal of Climatology, 37(1), 159–168. doi: 10.1002/joc.4694. Satellite observations are used to investigate surface energy budget variability over central Australia during the early 21st century drought. Over a large expanse of open shrubland and savanna, surface albedo exhibits a multiyear increase of 0.06 during the drought followed by a sharp decline of 0.08 after heavy rainfall in 2010 broke the drought. The surface albedo variations are associated with increased normalized difference vegetation index (NDVI) during wet years before and after the drought and decreased NDVI during drought years. During the worst drought years (2002–2009), the surface albedo increase is most pronounced in the shortwave infrared region (wavelengths between 1 and 3 µm), implying soil moisture content variability is the likely cause of the albedo changes. At interannual timescales, surface albedo variability is associated with near-surface soil moisture, controlled by episodic precipitation events, whereas the multiyear increase in surface albedo is more closely linked with decreases in soil moisture in deeper surface layers. In addition to a higher surface albedo and lower soil moisture content during the drought, the observations show less evaporation, enhanced reflected shortwave radiation, increased upward emission of thermal infrared radiation, lower downwelling longwave (LW) radiation, reduced net total downward radiation, and higher sensible heating compared with the rainy period following the drought. Upward emission of thermal infrared radiation decreases sharply after the drought with increased surface evaporation. However, the surface energy budget changes during the worst drought years show a stronger relationship between upward emission of thermal radiation and reflected shortwave flux. During this period, evaporative fraction is extremely low and surface albedo is steadily increasing. In such extreme conditions, the surface albedo appears to modulate surface upward LW radiation, preventing it from getting too high. The change in upward LW radiation thus represents a negative feedback as it offsets further decreases in surface net radiation. albedo; radiation; energy budget; Precipitation; drought; Latent heat; Sensible heat
Lu, Xiaomei; Hu, Yongxiang; Liu, Zhaoyan; Rodier, Sharon; Vaughan, Mark; Lucker, Patricia; Trepte, Charles; Pelon, JacquesLu, X., Y. Hu, Z. Liu, S. Rodier, M. Vaughan, P. Lucker, C. Trepte, J. Pelon, 2017: Observations of Arctic snow and sea ice cover from CALIOP lidar measurements. Remote Sensing of Environment, 194(Supplement C), 248-263. doi: 10.1016/j.rse.2017.03.046. This paper describes the development and validation of a method to accurately identify snow/ice cover, surface melting, land surface and open water in polar regions using polar-orbiting Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) lidar measurements from the Cloud and Aerosol Lidar and Infrared Pathfinder Observation (CALIPSO) mission. The technique is based on the relationship between integrated attenuated backscatter color ratio and integrated depolarization ratio, and is proven to efficiently separate snow/ice cover and surface melting from open water and land surfaces. The method has been applied to 10years (2006–2016) of CALIOP data to study the seasonal and inter-annual variability of Arctic sea ice cover and its declining trend. Results show that the area fraction of snow cover over land at latitudes >60°N varied between 0.9 during winter and 0.1 in summer. The CALIOP observations of Arctic sea ice cover exhibit a strong seasonal cycle and significant inter-annual variability, which are consistent with the passive microwave-based sea ice results. The >10years of CALIOP continuous observations of the snow/ice cover will benefit the communities modeling snow/ice melting and climate change. CALIOP; Sea ice; Snow; Surface type identification
Ma, Wei; Jia, Gensuo; Zhang, AnzhiMa, W., G. Jia, A. Zhang, 2017: Multiple satellite-based analysis reveals complex climate effects of temperate forests and related energy budget. Journal of Geophysical Research: Atmospheres, 122(7), 3806–3820. doi: 10.1002/2016JD026278. Forest conversion driven biophysical processes have been examined in various case studies that largely depend on sensitivity analysis of climate modeling. However, much remains unknown in real world due to the complicated process and uncertainty in magnitude, especially in the temperate bio-climate regions. This study applied satellite based observation to investigate the biophysical climate response to potential forest conversion in China, especially on the spatial and temporal patterns and underlying mechanisms. We evaluated the differences of land surface temperature (∆LST) between adjacent forest and cropland, in terms of the latitudinal and seasonal patterns. Compared to cropland, the temperate forest to the south of 40°N showed the cooling effect of -0.61 ±0.02°C (95% confidence interval, and hereafter), and it presented the warming effect of 0.48±0.06°C to the north of 48°N (the transition zone was between 40°N and 48°N). Seasonal analysis further demonstrated that the cooling effects of temperate forest in China in spring (MAM), summer (JJA) and autumn (SON) were -0.53±0.02°C, -0.55±0.02°C, -0.30±0.02°C, respectively, while the forest caused the warming effect of 0.10±0.04°C in winter (DJF). However, the biophysical climate response to forest conversion in temperate regions was complex and showed highly spatial and temporal heterogeneity. We further assessed the role of two major biophysical processes, i.e., albedo and evapotranspiration (ET), in shaping land surface temperature from surface energy budget perspective. Results showed that the latitudinal, seasonal and spatio-temporal patterns of ∆LST was determined by the net effect of ET induced latent heat changes and albedo induced solar radiation absorption changes. Land surface temperature; surface energy budget; 1818 Evapotranspiration; 4908 Albedo; biophysical climate effects; biophysical properties; latitudinal; satellite-based observations; seasonal; temperate forest conversion
Mao, Yuna; Wang, KaicunMao, Y., K. Wang, 2017: Comparison of evapotranspiration estimates based on the surface water balance, modified Penman-Monteith model, and reanalysis data sets for continental China. Journal of Geophysical Research: Atmospheres, 122(6), 3228–3244. doi: 10.1002/2016JD026065. Evapotranspiration (ET) combines the land-atmosphere water, energy, and carbon cycles and plays a critical role in climate studies. However, ET is difficult to quantify accurately. This study compares three 1982–2013 ET data sets for China based on surface water balance values, a modified Penman-Monteith (MPM) model and reanalysis data. Water balance ET data, which have been widely used as benchmark data for regional ET, were calculated with and without considering reservoir water storage. MPM ET values were calculated from combinations of input data from different sources, including solar radiation and meteorological data. The MPM model is primarily energy determined, although the impacts of vegetation, soil moisture, air temperature, and wind speed on ET are also considered. The reanalysis ET data used in this study are derived from atmospheric and off-line land reanalyses. We examined their spatial patterns, interannual variabilities, trends, and key drivers. We found that MPM ET is consistent with water balance ET in detecting ET trends for 1997 to 2013, whereas reanalysis ET is not. The trends and interannual variabilities of ET found via reanalyses are primarily determined by precipitation patterns. However, the precipitation data derived from the atmospheric reanalyses present significant uncertainties. Off-line land reanalyses correct these biases but do not consider terrestrial water storage changes resulting from reservoir construction and interannual variability in vegetation. Both omissions may produce unreliable trends of ET in reanalyses for China. This study will help improve current ET simulations and contribute to further extending climate studies. 1655 Water cycles; 1616 Climate variability; 1637 Regional climate change; 1631 Land/atmosphere interactions; Evapotranspiration; 1818 Evapotranspiration
Martin, G. M.; Peyrillé, P.; Roehrig, R.; Rio, C.; Caian, M.; Bellon, G.; Codron, F.; Lafore, J.-P.; Poan, D. E.; Idelkadi, A.Martin, G. M., P. Peyrillé, R. Roehrig, C. Rio, M. Caian, G. Bellon, F. Codron, J. Lafore, D. E. Poan, A. Idelkadi, 2017: Understanding the West African Monsoon from the analysis of diabatic heating distributions as simulated by climate models. Journal of Advances in Modeling Earth Systems, 9(1), 239–270. doi: 10.1002/2016MS000697. Vertical and horizontal distributions of diabatic heating in the West African monsoon (WAM) region as simulated by four model families are analyzed in order to assess the physical processes that affect the WAM circulation. For each model family, atmosphere-only runs of their CMIP5 configurations are compared with more recent configurations which are on the development path toward CMIP6. The various configurations of these models exhibit significant differences in their heating/moistening profiles, related to the different representation of physical processes such as boundary layer mixing, convection, large-scale condensation and radiative heating/cooling. There are also significant differences in the models' simulation of WAM rainfall patterns and circulations. The weaker the radiative cooling in the Saharan region, the larger the ascent in the rainband and the more intense the monsoon flow, while the latitude of the rainband is related to heating in the Gulf of Guinea region and on the northern side of the Saharan heat low. Overall, this work illustrates the difficulty experienced by current climate models in representing the characteristics of monsoon systems, but also that we can still use them to understand the interactions between local subgrid physical processes and the WAM circulation. Moreover, our conclusions regarding the relationship between errors in the large-scale circulation of the WAM and the structure of the heating by small-scale processes will motivate future studies and model development. 1620 Climate dynamics; 3337 Global climate models; 3374 Tropical meteorology; monsoon; 9305 Africa; model; 3365 Subgrid-scale (SGS) parameterization; diabatic; West Africa
Masiri, I.; Janjai, S.; Nunez, M.; Anusasananan, P.Masiri, I., S. Janjai, M. Nunez, P. Anusasananan, 2017: A technique for mapping downward longwave radiation using satellite and ground-based data in the tropics. Renewable Energy, 103, 171-179. doi: 10.1016/j.renene.2016.11.018. This paper presents a technique for mapping monthly average hourly downward longwave (LW↓) irradiance using ground- and satellite-based data. A model relating LW↓ irradiance to a satellite derived-brightness temperature of the earth-atmospheric system, relative humidity and ambient air temperature was formulated. This model was validated against LW↓ irradiance obtained from measurements at 4 sites in the tropics and discrepancy in terms of root mean square errors and mean bias errors was found to be 1.89% and −0.69%, respectively. After the validation, the model was used to calculate monthly average hourly LW↓ irradiance over Thailand and the results were displayed as LW↓ maps. These maps reveal the influence of various factors on LW↓ irradiance. tropics; satellite data; downward longwave radiation
Masunaga, Hirohiko; Sumi, YukariMasunaga, H., Y. Sumi, 2017: A toy model of tropical convection with a moisture storage closure. Journal of Advances in Modeling Earth Systems, 9(1), 647–667. doi: 10.1002/2016MS000855. A time-dependent, zero-dimensional toy model is constructed to study the large-scale variability in association with tropical moist convection. Case studies from sounding-array observations are analyzed as a benchmark to test the model performance. The model predicts the vertical integral of vertical moisture advection decomposed into the deep convective and congestus/stratiform modes. A closure representing the consumption efficiency of water vapor into precipitation is introduced using the moisture storage ratio, or the degree to which the vertical moisture advection associated with each vertical mode accounts for moisture storage. The observations suggest that this moisture consumption is highly inefficient for the convective/stratiform mode while efficient for the deep convective mode. The model solution is interpreted as a delayed response to the diabatic forcing, unless the sum of the moisture storage ratio and gross moist stability is negative, in which case the system is unstable. Baseline experiments with a fixed moisture storage closure overall reproduce the vertical moisture advection and precipitation as observed, but fail to simulate a sharp pickup of precipitation in the well-known moisture-rainfall curve. This deficiency is eliminated when the moisture storage ratio is allowed to vary as convection intensifies and dissipates. 3371 Tropical convection; 3373 Tropical dynamics; 3320 Idealized model; conceptual model; tropical convection
Matus, Alexander V.; L'Ecuyer, Tristan S.Matus, A. V., T. S. L'Ecuyer, 2017: The role of cloud phase in Earth's radiation budget. Journal of Geophysical Research: Atmospheres, 122(5), 2559–2578. doi: 10.1002/2016JD025951. The radiative impact of clouds strongly depends on their partitioning between liquid and ice phases. Until recently, however, it has been challenging to unambiguously discriminate cloud phase in a number of important global regimes. CloudSat and CALIPSO supply vertically-resolved measurements necessary to identify clouds composed of both liquid and ice that are not easily detected using conventional passive sensors. The capability of these active sensors to discriminate cloud phase has been incorporated into the fifth generation of CloudSat's 2B-FLXHR-LIDAR algorithm. Comparisons with CERES fluxes at the TOA reveal that an improved representation of cloud phase leads to better agreement compared to earlier versions of the algorithm. The RMS differences in annual mean OLR gridded at 2.5° resolution are 4.9 Wm−2 while RMS differences in outgoing SW are slightly larger at 8.9 Wm−2 due to the larger diurnal range of solar insolation. This study documents the relative contributions of clouds composed of only liquid, only ice, and a combination of both phases to global and regional radiation budgets. It is found that mixed-phase clouds exert a global net cloud radiative effect of −3.4 Wm−2, with contributions of −8.1 Wm−2 and 4.7 Wm−2 from SW and LW radiation, respectively. When compared with the effects of warm liquid clouds (−11.8 Wm−2), ice clouds (3.5 Wm−2), and multi-layered clouds consisting of distinct liquid and ice layers (−4.6 Wm−2), these results reinforce the notion that accurate representation of mixed-phase clouds is essential for quantifying cloud feedbacks in future climate scenarios. 1640 Remote sensing; satellite remote sensing; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; 3359 Radiative processes; CloudSat; Cloud radiative effects; Cloud Phase; 0429 Climate dynamics; global energy budget; mixed-phase clouds
May, Jackie C.; Rowley, Clark; Barron, Charlie N.May, J. C., C. Rowley, C. N. Barron, 2017: NFLUX satellite-based surface radiative heat fluxes. Part I: Swath-level products. J. Appl. Meteor. Climatol., 56(4), 1043–1057. doi: 10.1175/JAMC-D-16-0282.1. The Naval Research Laboratory (NRL) ocean surface flux (NFLUX) system originally provided operational near-real time satellite-based surface state parameter and turbulent heat flux fields over the global ocean. This study extends the NFLUX system to include the production of swath-level shortwave and longwave radiative heat fluxes at the ocean surface. A companion paper presents the production of the satellite-based global gridded radiative heat flux analysis fields. The swath-level radiative heat fluxes are produced using the Rapid Radiative Transfer Model for Global Circulation Models (RRTMG), with the primary inputs of satellite-derived atmospheric temperature and moisture profiles and cloud information retrieved from the Microwave Integrated Retrieval System (MIRS). This study uses MIRS data provided for 6 polar orbiting satellite platforms. Additional inputs to the RRTMG include sea surface temperature, aerosol optical depths, atmospheric gas concentrations, ocean surface albedo, and ocean surface emissivity. Swath-level shortwave flux estimates are converted into clearness index values, which are used in data assimilation since the clearness index values are less dependent on the solar zenith angle. The NFLUX swath-level shortwave flux, longwave flux, and clearness index estimates are produced for 1 May 2013 through 30 April 2014 and validated against observations from research vessel and moored buoy platforms. Each of the flux parameters compares well among the various satellites.
Mayer, Michael; Haimberger, Leopold; Edwards, John M.; Hyder, PatrickMayer, M., L. Haimberger, J. M. Edwards, P. Hyder, 2017: Towards consistent diagnostics of the coupled atmosphere and ocean energy budgets. J. Climate, 30(22), 9225–9246. doi: 10.1175/JCLI-D-17-0137.1. The widely used diagnostic vertically integrated total energy budget equations of atmosphere and ocean contain inconsistencies that should no longer be disregarded. The neglect of enthalpy fluxes associated with precipitation and evaporation leads to a spurious dependence on reference temperature. This seemingly small inconsistency is amplified because enthalpy of water vapor implicitly included in lateral atmospheric energy transports usually is computed on Kelvin scale, leading to inconsistencies which, though zero when globally averaged, attain values on the order of 20Wm-2 in the tropics. A more consistent energy budget framework is presented, which is independent of reference temperature and takes full account of enthalpy fluxes associated with mass transfer through the surface. The latter include effects of snowfall and additional non-latent contributions, which have a net cooling effect on the Earth’s surface (-1.3Wm-2). In addition to these diagnostic issues, comparatively small inconsistencies in the energetic formulations of current weather and climate models are highlighted. Using the energy budget formulation presented here, instead of that commonly used, yields enhanced self-consistency of diagnosed atmospheric energy budgets and substantially improved spatial agreement between fields of net surface energy flux inferred from the divergence of lateral atmospheric energy transports in conjunction with satellite-based radiative fluxes and independent surface flux products.Results imply that previous estimates of radiative plus turbulent surface fluxes over the ocean, balancing the observed ocean warming, are biased low by ~1.3Wm-2. Moreover, previous studies seriously underestimated cross-equatorial atmospheric and oceanic energy transports.Overall, the presented framework allows for unambiguous coupled energy budget diagnostics and yields more reliable benchmark values for validation purposes.
McCoy, D. T.; Bender, F. a.-M.; Mohrmann, J. K. C.; Hartmann, D. L.; Wood, R.; Grosvenor, D. P.McCoy, D. T., F. a. Bender, J. K. C. Mohrmann, D. L. Hartmann, R. Wood, D. P. Grosvenor, 2017: The global aerosol-cloud first indirect effect estimated using MODIS, MERRA, and AeroCom. Journal of Geophysical Research: Atmospheres, 122(3), 1779–1796. doi: 10.1002/2016JD026141. Aerosol-cloud interactions (ACI) represent a significant source of forcing uncertainty in global climate models (GCMs). Estimates of radiative forcing due to ACI in Fifth Assessment Report range from −0.5 to −2.5 W m−2. A portion of this uncertainty is related to the first indirect, or Twomey, effect whereby aerosols act as nuclei for cloud droplets to condense upon. At constant liquid water content this increases the number of cloud droplets (Nd) and thus increases the cloud albedo. In this study we use remote-sensing estimates of Nd within stratocumulus regions in combination with state-of-the-art aerosol reanalysis from Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA2) to diagnose how aerosols affect Nd. As in previous studies, Nd is related to sulfate mass through a power law relationship. The slope of the log-log relationship between Nd and SO4 in maritime stratocumulus is found to be 0.31, which is similar to the range of 0.2–0.8 from previous in situ studies and remote-sensing studies in the pristine Southern Ocean. Using preindustrial emissions models, the change in Nd between preindustrial and present day is estimated. Nd is inferred to have more than tripled in some regions. Cloud properties from Moderate Resolution Imaging Spectroradiometer (MODIS) are used to estimate the radiative forcing due to this change in Nd. The Twomey effect operating in isolation is estimated to create a radiative forcing of −0.97 ± 0.23 W m−2 relative to the preindustrial era. 1610 Atmosphere; 1640 Remote sensing; 0320 Cloud physics and chemistry; 0305 Aerosols and particles; 0345 Pollution: urban and regional; cloud; aerosol; microphysics; climate
McCoy, Isabel L.; Wood, Robert; Fletcher, Jennifer K.McCoy, I. L., R. Wood, J. K. Fletcher, 2017: Identifying Meteorological Controls on Open and Closed Mesoscale Cellular Convection Associated with Marine Cold Air Outbreaks. Journal of Geophysical Research: Atmospheres, 122(21), 11,678–11,702. doi: 10.1002/2017JD027031. Mesoscale cellular convective (MCC) clouds occur in large-scale patterns over the ocean and have important radiative effects on the climate system. An examination of time-varying meteorological conditions associated with satellite-observed open and closed MCC clouds is conducted to illustrate the influence of large-scale meteorological conditions. Marine cold air outbreaks (MCAO) influence the development of open MCC clouds and the transition from closed to open MCC clouds. MCC neural network classifications on Moderate Resolution Imaging Spectroradiometer (MODIS) data for 2008 are collocated with Clouds and the Earth's Radiant Energy System (CERES) data and ERA-Interim reanalysis to determine the radiative effects of MCC clouds and their thermodynamic environments. Closed MCC clouds are found to have much higher albedo on average than open MCC clouds for the same cloud fraction. Three meteorological control metrics are tested: sea-air temperature difference (ΔT), estimated inversion strength (EIS), and a MCAO index (M). These predictive metrics illustrate the importance of atmospheric surface forcing and static stability for open and closed MCC cloud formation. Predictive sigmoidal relations are found between M and MCC cloud frequency globally and regionally: negative for closed MCC cloud and positive for open MCC cloud. The open MCC cloud seasonal cycle is well correlated with M, while the seasonality of closed MCC clouds is well correlated with M in the midlatitudes and EIS in the tropics and subtropics. M is found to best distinguish open and closed MCC clouds on average over shorter time scales. The possibility of a MCC cloud feedback is discussed. 3309 Climatology; 3310 Clouds and cloud feedbacks; climate; radiation; 3364 Synoptic-scale meteorology; 3360 Remote sensing; 3307 Boundary layer processes; marine low clouds; boundary layer clouds; marine cold air outbreak; mesoscale cellular convection
Mishra, M. K.; Gupta, A. K.; Rajeev, K.Mishra, M. K., A. K. Gupta, K. Rajeev, 2017: Spaceborne Observations of the Diurnal Variation of Shortwave Aerosol Direct Radiative Effect at Top of Atmosphere Over the Dust-Dominated Arabian Sea and the Atlantic Ocean. IEEE Transactions on Geoscience and Remote Sensing, 55(11), 6610-6616. doi: 10.1109/TGRS.2017.2730758. The ScaRaB payload onboard the low-inclination Megha-Tropiques (MT) satellite has been making observations of radiative fluxes at the top of the atmosphere (TOA) for different local times (LTs) of the day over the tropics since October 2011. This provides a unique opportunity to investigate the diurnal variation of the regional instantaneous aerosol direct radiative effect efficiency (IADREE) at TOA, which is otherwise not possible using the available long-term satellite observations carried out using similar sensors onboard polar sun-synchronous satellites. In this paper, the diurnal variations of the IADREE over the Arabian Sea and the Atlantic Ocean during June-September, when both these regions are engulfed by large-scale mineral dust plumes transported from the adjoining deserts, are investigated using collocated multiyear (2012-2014) observations of the MT-ScaRaB measured shortwave fluxes and MODIS-derived aerosol optical depth. The estimates of the IADREE made using the MT-ScaRaB data at 13:30 LT are found to be in agreement with those derived from the Cloud and the Earth's Radiant Energy System data at this LT, at which the latter observations are carried out. The IADREE derived from the MT-ScaRaB shows diurnal peak value of -53 ± 10 Wm-2τ550-1 and -40 ± 3 Wm-2τ550-1 at solar zenith angle of 40° over the Arabian Sea and the Atlantic Ocean, respectively. Diurnal mean aerosol direct radiative effect efficiency at TOA during June-September is -22 ± 4.5 Wm-2τ550-1 over the Arabian Sea and -18 ± 3.6 Wm-2τ550-1 over the Atlantic Ocean. clouds; Satellites; atmospheric radiation; aerosols; radiative flux; Oceans; atmospheric optics; radiative transfer; Sea measurements; dust; AD 2011 10; Atlantic Ocean; atmospheric composition; Arabian Sea; sunlight; Aerosols; solar radiation; Clouds; aerosol optical depth; B; Earth radiant energy system data; IADREE estimate; large-scale mineral dust; long-term satellite observation; low-inclination Megha-Tropiques satellite; mineral dust plume; Minerals; MT-ScaRaB data; onboard polar sun-synchronous satellite sensor; regional instantaneous aerosol direct radiative effect efficiency; ScaRaB payload; shortwave aerosol direct radiative effect; spaceborne observation; Wavelength measurement
Molina, Alejandra; Falvey, Mark; Rondanelli, RobertoMolina, A., M. Falvey, R. Rondanelli, 2017: A solar radiation database for Chile. Scientific Reports, 7(1), 14823. doi: 10.1038/s41598-017-13761-x. Chile hosts some of the sunniest places on earth, which has led to a growing solar energy industry in recent years. However, the lack of high resolution measurements of solar irradiance becomes a critical obstacle for both financing and design of solar installations. Besides the Atacama Desert, Chile displays a large array of “solar climates” due to large latitude and altitude variations, and so provides a useful testbed for the development of solar irradiance maps. Here a new public database for surface solar irradiance over Chile is presented. This database includes hourly irradiance from 2004 to 2016 at 90 m horizontal resolution over continental Chile. Our results are based on global reanalysis data to force a radiative transfer model for clear sky solar irradiance and an empirical model based on geostationary satellite data for cloudy conditions. The results have been validated using 140 surface solar irradiance stations throughout the country. Model mean percentage error in hourly time series of global horizontal irradiance is only 0.73%, considering both clear and cloudy days. The simplicity and accuracy of the model over a wide range of solar conditions provides confidence that the model can be easily generalized to other regions of the world.
Myers, Timothy A.; Mechoso, Carlos R.; DeFlorio, Michael J.Myers, T. A., C. R. Mechoso, M. J. DeFlorio, 2017: Importance of positive cloud feedback for tropical Atlantic interhemispheric climate variability. Climate Dynamics, 1-11. doi: 10.1007/s00382-017-3978-1. Over the tropical Atlantic during boreal spring, average interhemispheric differences in sea-surface temperature (SST) coincide with a coherent pattern of interannual climate variability often referred to as the Atlantic Meridional Mode. This includes anomalous SST and sea-level pressure roughly anti-symmetric about the equator, as well as cross-equatorial near-surface winds directed toward the warmer hemisphere. Within subtropical marine boundary layer cloud regions in both hemispheres, enhanced cloudiness associated with this variability is co-located with cool SST, a strong temperature inversion, and cold horizontal surface temperature advection, while reduced cloudiness is associated with the opposite meteorological conditions. This is indicative a positive cloud feedback that reinforces the underlying SST anomalies. The simulation of this feedback varies widely among models participating in phase 5 of the Coupled Model Intercomparison Project. Models that fail to simulate this feedback substantially underestimate the amplitudes of typical tropical Atlantic interhemispheric variability in cloudiness off of the equator, SST, and atmospheric circulation. Models that correctly reproduce a positive cloud feedback generally produce higher and more realistic amplitudes of variability, but with substantial scatter. Marine boundary layer clouds therefore appear to be a key element of springtime coupled atmosphere–ocean variability over the tropical Atlantic. A markedly more successful simulation of this variability in climate models may be obtained by better representing boundary layer cloud processes.
Nachamkin, Jason E.; Jin, Yi; Grasso, Lewis D.; Richardson, KimNachamkin, J. E., Y. Jin, L. D. Grasso, K. Richardson, 2017: Using Synthetic Brightness Temperatures to Address Uncertainties in Cloud-Top-Height Verification. J. Appl. Meteor. Climatol., 56(2), 283-296. doi: 10.1175/JAMC-D-16-0240.1. Cloud-top verification is inherently difficult because of large uncertainties in the estimates of observed cloud-top height. Misplacement of cloud top associated with transmittance through optically thin cirrus is one of the most common problems. Forward radiative models permit a direct comparison of predicted and observed radiance, but uncertainties in the vertical position of clouds remain. In this work, synthetic brightness temperatures are compared with forecast cloud-top heights so as to investigate potential errors and develop filters to remove optically thin ice clouds. Results from a statistical analysis reveal that up to 50% of the clouds with brightness temperatures as high as 280 K are actually optically thin cirrus. The filters successfully removed most of the thin ice clouds, allowing for the diagnosis of very specific errors. The results indicate a strong negative bias in midtropospheric cloud cover in the model, as well as a lack of land-based convective cumuliform clouds. The model also predicted an area of persistent stratus over the North Atlantic Ocean that was not apparent in the observations. In contrast, high cloud tops associated with deep convection were well simulated, as were mesoscale areas of enhanced trade cumulus coverage in the Sargasso Sea.
Neubauer, D.; Christensen, M. W.; Poulsen, C. A.; Lohmann, U.Neubauer, D., M. W. Christensen, C. A. Poulsen, U. Lohmann, 2017: Unveiling aerosol–cloud interactions – Part 2: Minimising the effects of aerosol swelling and wet scavenging in ECHAM6-HAM2 for comparison to satellite data. Atmos. Chem. Phys., 17(21), 13165-13185. doi: 10.5194/acp-17-13165-2017. Aerosol–cloud interactions (ACIs) are uncertain and the estimates of the ACI effective radiative forcing (ERFaci) magnitude show a large variability. Within the Aerosol_cci project the susceptibility of cloud properties to changes in aerosol properties is derived from the high-resolution AATSR (Advanced Along-Track Scanning Radiometer) data set using the Cloud–Aerosol Pairing Algorithm (CAPA) (as described in our companion paper) and compared to susceptibilities from the global aerosol climate model ECHAM6-HAM2 and MODIS–CERES (Moderate Resolution Imaging Spectroradiometer – Clouds and the Earth's Radiant Energy System) data. For ECHAM6-HAM2 the dry aerosol is analysed to mimic the effect of CAPA. Furthermore the analysis is done for different environmental regimes. The aerosol–liquid water path relationship in ECHAM6-HAM2 is systematically stronger than in AATSR–CAPA data and cannot be explained by an overestimation of autoconversion when using diagnostic precipitation but rather by aerosol swelling in regions where humidity is high and clouds are present. When aerosol water is removed from the analysis in ECHAM6-HAM2 the strength of the susceptibilities of liquid water path, cloud droplet number concentration and cloud albedo as well as ERFaci agree much better with those of AATSR–CAPA or MODIS–CERES. When comparing satellite-derived to model-derived susceptibilities, this study finds it more appropriate to use dry aerosol in the computation of model susceptibilities. We further find that the statistical relationships inferred from different satellite sensors (AATSR–CAPA vs. MODIS–CERES) as well as from ECHAM6-HAM2 are not always of the same sign for the tested environmental conditions. In particular the susceptibility of the liquid water path is negative in non-raining scenes for MODIS–CERES but positive for AATSR–CAPA and ECHAM6-HAM2. Feedback processes like cloud-top entrainment that are missing or not well represented in the model are therefore not well constrained by satellite observations. In addition to aerosol swelling, wet scavenging and aerosol processing have an impact on liquid water path, cloud albedo and cloud droplet number susceptibilities. Aerosol processing leads to negative liquid water path susceptibilities to changes in aerosol index (AI) in ECHAM6-HAM2, likely due to aerosol-size changes by aerosol processing. Our results indicate that for statistical analysis of aerosol–cloud interactions the unwanted effects of aerosol swelling, wet scavenging and aerosol processing need to be minimised when computing susceptibilities of cloud variables to changes in aerosol.
Oreopoulos, Lazaros; Cho, Nayeong; Lee, DongminOreopoulos, L., N. Cho, D. Lee, 2017: Using MODIS cloud regimes to sort diagnostic signals of aerosol-cloud-precipitation interactions. Journal of Geophysical Research: Atmospheres, 122(10), 5416–5440. doi: 10.1002/2016JD026120. Coincident multiyear measurements of aerosol, cloud, precipitation, and radiation at near-global scales are analyzed to diagnose their apparent relationships as suggestive of interactions previously proposed based on theoretical, observational, and model constructs. Specifically, we examine whether differences in aerosol loading in separate observations go along with consistently different precipitation, cloud properties, and cloud radiative effects. Our analysis uses a cloud regime (CR) framework to dissect and sort the results. The CRs come from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor and are defined as distinct groups of cloud systems with similar covariations of cloud top pressure and cloud optical thickness. Aerosol optical depth used as proxy for aerosol loading comes from two sources, MODIS observations and the MERRA-2 reanalysis, and its variability is defined with respect to local seasonal climatologies. The choice of aerosol data set impacts our results substantially. We also find that the responses of the marine and continental component of a CR are frequently quite disparate. Overall, CRs dominated by warm clouds tend to exhibit less ambiguous signals but also have more uncertainty with regard to precipitation changes. Finally, we find weak, but occasionally systematic covariations of select meteorological indicators and aerosol, which serve as a sober reminder that ascribing changes in cloud and cloud-affected variables solely to aerosol variations is precarious. cloud; 3311 Clouds and aerosols; 3359 Radiative processes; aerosol; 3310 Clouds and cloud feedbacks; Satellite; radiation; Precipitation; 3354 Precipitation; indirect effects; 3355 Regional modeling
Oueslati, Boutheina; Pohl, Benjamin; Moron, Vincent; Rome, Sandra; Janicot, SergeOueslati, B., B. Pohl, V. Moron, S. Rome, S. Janicot, 2017: Characterisation of Heat Waves in the Sahel and Associated Physical Mechanisms. J. Climate, 30(9), 3095–3115. doi: 10.1175/JCLI-D-16-0432.1. Large efforts are made to address Heat Waves (HWs) in developed countries because of their devastating impacts on society, economy and environment. However, HWs are still understudied over developing countries. This is particularly true in West Africa, and especially in the Sahel, where temperatures recurrently reach critical values, such as during the 2010 HW event in Western Sahel. Our work aims at characterizing the Sahelian HWs during boreal spring seasons (April-May-June) and understanding the mechanisms associated with such extreme events. Over the last three decades, Sahelian HWs have been becoming more frequent, lasting longer, covering larger areas and reaching higher intensities. The physical mechanisms associated with HWs are examined to assess the respective roles of atmospheric dynamics, radiative and turbulent fluxes by analysing the surface energy budget. Results suggest that the greenhouse effect of water vapour is the main driver of HWs in western Sahel, increasing minimum temperatures by enhanced downward longwave radiation. Atmospheric circulation plays an important role in sustaining these warm anomalies by advecting moisture from the Atlantic Ocean and the Guinean coasts into the Sahel. Maximum temperature anomalies are mostly explained by increased downward shortwave radiation due to a reduction in cloud cover. Interannual variability of HWs is affected by the delayed impact of El Nino Southern Oscillation (ENSO), with anomalous temperature warming following warm ENSO events, resulting from an amplified water vapour feedback.
Painemal, David; Chiu, J.-Y. Christine; Minnis, Patrick; Yost, Christopher; Zhou, Xiaoli; Cadeddu, Maria; Eloranta, Edwin; Lewis, Ernie R.; Ferrare, Richard; Kollias, PavlosPainemal, D., J. C. Chiu, P. Minnis, C. Yost, X. Zhou, M. Cadeddu, E. Eloranta, E. R. Lewis, R. Ferrare, P. Kollias, 2017: Aerosol and cloud microphysics co-variability in the northeast Pacific boundary layer estimated with ship-based and satellite remote sensing observations. Journal of Geophysical Research: Atmospheres, 122(4), 2403–2418. doi: 10.1002/2016JD025771. Ship measurements collected over the northeast Pacific along transects between the port of Los Angeles (33.7°N, 118.2°W) and Honolulu (21.3°N, 157.8°W) during May to August 2013 were utilized to investigate the co-variability between marine low cloud microphysical and aerosol properties. Ship-based retrievals of cloud optical depth (τ) from a sun-photometer and liquid water path (LWP) from a microwave radiometer were combined to derive cloud droplet number concentration Nd or compute a cloud-aerosol-interaction (ACI) metric defined as ACICCN = ∂ ln(Nd)/∂ ln(CCN), with CCN denoting the cloud condensation nuclei concentration measured at 0.4% (CCN0.4) and 0.3% (CCN0.3) supersaturation. Analysis of CCN0.4, accumulation mode aerosol concentration (Na), and extinction coefficient (σext) indicates that Na and σext can be used as CCN0.4 proxies for estimating ACI. ACICCN derived from 10-min averaged Nd and CCN0.4 and CCN0.3, and CCN0.4 regressions using Na and σext, produce high ACICCN: near 1.0, that is, a fractional change in aerosols is associated with an equivalent fractional change in Nd. ACICCN computed in deep boundary layers was small (ACICCN =0.60), indicating that surface aerosol measurements inadequately represent the aerosol variability below clouds. Satellite cloud retrievals from MODIS and GOES-15 data were compared against ship-based retrievals and further analyzed to compute a satellite-based ACICCN. Satellite data correlated well with their ship-based counterparts with linear correlation coefficients equal to or greater than 0.78. Combined satellite Nd and ship-based CCN0.4 and Na yielded a maximum ACICCN =0.88-0.92, a value slightly less than the ship-based ACICCN, but still consistent with aircraft-based studies in the eastern Pacific. 0305 Aerosols and particles; 3311 Clouds and aerosols; 3310 Clouds and cloud feedbacks; 3307 Boundary layer processes; cloud remote sensing; cloud-aerosol interactions; marine atmospheric boundary layer
Painemal, David; Xu, Kuan-Man; Palikonda, Rabindra; Minnis, PatrickPainemal, D., K. Xu, R. Palikonda, P. Minnis, 2017: Entrainment rate diurnal cycle in marine stratiform clouds estimated from geostationary satellite retrievals and a meteorological forecast model. Geophysical Research Letters, 44(14), 7482–7489. doi: 10.1002/2017GL074481. The mean diurnal cycle of cloud entrainment rate (we) over the northeast Pacific region is for the first time computed by combining, in a mixed-layer model framework, the hourly-composited GOES-15 satellite-based cloud top height (HT) tendency, advection, and large-scale vertical velocity (w) during May to September 2013, with horizontal winds and w taken from the ECMWF forecast model. The tendency term dominates the magnitude and phase of the we diurnal cycle, with a secondary role of w, and a modest advective contribution. The peak and minimum in we occur between 20:00-22:00 LT and 9:00-11:00 LT, respectively, in close agreement with the diurnal cycle of turbulence driven by cloud-top longwave cooling. Uncertainties in HT and ECMWF fields are assessed with in-situ observations and three meteorological reanalysis datasets. This study provides the basis for constructing nearly-global climatologies of we by combining a suite of well-calibrated geostationary satellites. 3310 Clouds and cloud feedbacks; 3360 Remote sensing; 3307 Boundary layer processes; Stratiform clouds; entrainment rate; satellite retrievals
Palmer, Matthew D.Palmer, M. D., 2017: Reconciling Estimates of Ocean Heating and Earth’s Radiation Budget. Current Climate Change Reports, 1-9. doi: 10.1007/s40641-016-0053-7. Purpose of reviewThe purpose of this review is to summarise the recent literature and scientific challenges on the topic of reconciling estimates of ocean heating rates with satellite-based monitoring of Earth’s radiation budget (ERB), including discussion of the satellite record and in situ ocean observing system.Recent findingsState-of-the-art climate model simulations suggest that the global ocean becomes the dominant term the planetary heat budget on annual and longer timescales. Therefore, we expect to see a close correspondence between year-to-year variations in ocean heating rates and satellite measurements of ERB. Recent comparisons of satellite ERB time series and ocean heating rates show a marked improvement over earlier studies in terms of consistency and specification of uncertainties. Contemporary research has also emphasised the utility of these independent data sets for cross validation of the climate record and their fundamental importance for monitoring the rate of climate change.SummaryAnthropogenic greenhouse gas emissions have brought about an imbalance in Earth’s radiation budget that is driving global climate change. Our primary means for monitoring this energy imbalance is via direct satellite measurements of ERB and through estimates of global ocean heat content (OHC) change. CERES satellite measurements of ERB offer high spatiotemporal resolution and uncertainties on annual time series of order 0.1 Wm-2 but cannot provide absolute monitoring of Earth’s energy imbalance due to limitations in sensor calibration. The Argo array of autonomous profiling floats has revolutionised the ocean observing system and our ability to estimate absolute ocean heating rates with current uncertainties estimated to be 0.5/0.1 Wm-2 on annual/decadal timescales. These ocean observations are essential to “anchor” the time series of ERB and can be used to mitigate satellite sensor drifts. Sustaining these highly complementary elements of the climate observing system is essential for improved understanding of climate variability and change. Improvements in satellite sensor calibration, estimates of total solar irradiance and more comprehensive sampling of the global oceans (e.g. Deep Argo) are key aspects to reducing uncertainties in future observations of Earth’s energy imbalance.
Parishani, Hossein; Pritchard, Michael S.; Bretherton, Christopher S.; Wyant, Matthew C.; Khairoutdinov, MaratParishani, H., M. S. Pritchard, C. S. Bretherton, M. C. Wyant, M. Khairoutdinov, 2017: Toward low-cloud-permitting cloud superparameterization with explicit boundary layer turbulence. Journal of Advances in Modeling Earth Systems, 9(3), 1542-1571. doi: 10.1002/2017MS000968. Systematic biases in the representation of boundary layer (BL) clouds are a leading source of uncertainty in climate projections. A variation on superparameterization (SP) called “ultraparameterization” (UP) is developed, in which the grid spacing of the cloud-resolving models (CRMs) is fine enough (250 × 20 m) to explicitly capture the BL turbulence, associated clouds, and entrainment in a global climate model capable of multiyear simulations. UP is implemented within the Community Atmosphere Model using 2° resolution (∼14,000 embedded CRMs) with one-moment microphysics. By using a small domain and mean-state acceleration, UP is computationally feasible today and promising for exascale computers. Short-duration global UP hindcasts are compared with SP and satellite observations of top-of-atmosphere radiation and cloud vertical structure. The most encouraging improvement is a deeper BL and more realistic vertical structure of subtropical stratocumulus (Sc) clouds, due to stronger vertical eddy motions that promote entrainment. Results from 90 day integrations show climatological errors that are competitive with SP, with a significant improvement in the diurnal cycle of offshore Sc liquid water. Ongoing concerns with the current UP implementation include a dim bias for near-coastal Sc that also occurs less prominently in SP and a bright bias over tropical continental deep convection zones. Nevertheless, UP makes global eddy-permitting simulation a feasible and interesting alternative to conventionally parameterized GCMs or SP-GCMs with turbulence parameterizations for studying BL cloud-climate and cloud-aerosol feedback. 3305 Climate change and variability; 3337 Global climate models; 3310 Clouds and cloud feedbacks; 3319 General circulation; 3307 Boundary layer processes; general circulation model; marine boundary layer; superparameterization; cloud-resolving model; shallow clouds; ultraparameterization
Park, SungsuPark, S., 2017: A Heuristic Parameterization for the Integrated Vertical Overlap of Cumulus and Stratus. Journal of Advances in Modeling Earth Systems, 9(6), 2437–2465. doi: 10.1002/2017MS001055. The author developed a heuristic parameterization to handle the contrasting vertical overlap structures of cumulus and stratus in an integrated way. The parameterization assumes that cumulus is maximum-randomly overlapped with adjacent cumulus; stratus is maximum-randomly overlapped with adjacent stratus; and radiation and precipitation areas at each model interface are grouped into four categories, that is, convective, stratiform, mixed, and clear areas. For simplicity, thermodynamic scalars within individual portions of cloud, radiation, and precipitation areas are assumed to be internally homogeneous. The parameterization was implemented into the Seoul National University Atmosphere Model version 0 (SAM0) in an offline mode and tested over the globe. The offline control simulation reasonably reproduces the online surface precipitation flux and longwave cloud radiative forcing (LWCF). Although the cumulus fraction is much smaller than the stratus fraction, cumulus dominantly contributes to precipitation production in the tropics. For radiation, however, stratus is dominant. Compared with the maximum overlap, the random overlap of stratus produces stronger LWCF and, surprisingly, more precipitation flux due to less evaporation of convective precipitation. Compared with the maximum overlap, the random overlap of cumulus simulates stronger LWCF and weaker precipitation flux. Compared with the control simulation with separate cumulus and stratus, the simulation with a single-merged cloud substantially enhances the LWCF in the tropical deep convection and midlatitude storm track regions. The process-splitting treatment of convective and stratiform precipitation with an independent precipitation approximation (IPA) simulates weaker surface precipitation flux than the control simulation in the tropical region. 3311 Clouds and aerosols; 3337 Global climate models; 3354 Precipitation; parameterization; 3336 Numerical approximations and analyses; 3367 Theoretical modeling; cumulus and stratus; vertical cloud overlap
Perdigão, João; Salgado, Rui; Magarreiro, Clarisse; Soares, Pedro M. M.; Costa, Maria João; Dasari, Hari PrasadPerdigão, J., R. Salgado, C. Magarreiro, P. M. M. Soares, M. J. Costa, H. P. Dasari, 2017: An Iberian climatology of solar radiation obtained from WRF regional climate simulations for 1950–2010 period. Atmospheric Research, 198, 151-162. doi: 10.1016/j.atmosres.2017.08.016. The mesoscale Weather Research and Forecasting (WRF) Model is used over the Iberian Peninsula to generate 60years (1950–2010) of climate data, at 5km resolution, in order to evaluate and characterize the incident shortwave downward radiation at the surface (SW↓), in present climate. The simulated values of SW↓ in the period 2000–2009 were compared with data measured in Spanish and Portuguese meteorological stations before and a statistical BIAS correction was applied using data from Clouds and the Earth's Radiant Energy System (CERES), on board four different satellites. The spatial and temporal comparison between WRF results and observations show a good agreement for the analyzed period, although the model overestimates observations. This overestimation has a mean normalized bias of about 7% after BIAS correction (or 17% for original WRF output). Additionally, the present simulation was confronted against another previously validated WRF simulation performed with different resolution and set of parametrizations, showing comparable results. WRF adequately reproduces the observational features of SW↓ with correlation coefficients above 0.8 in annual and seasonal basis. 60years of simulated SW↓ over the Iberian Peninsula were produced, which showed annual mean values that range from 130W/m2, in the northern regions, to a maximum of around 230W/m2 in the southeast of the Iberian Peninsula (IP). SW↓ over IP shows a positive gradient from north to south and from west to east, with local effects influenced by topography and distance to the coast. The analysis of the simulated cloud fraction indicates that clear sky days are found in >30% of the period at the southern area of IP, particularly in the Algarve (Portugal) and Andalusia (Spain), and this value increases significantly in the summer season for values above 80%. WRF model; Cloud fractions; Downscaling climatology; Downward solar radiation; Iberian peninsula
Platnick, S.; Meyer, K. G.; King, M. D.; Wind, G.; Amarasinghe, N.; Marchant, B.; Arnold, G. T.; Zhang, Z.; Hubanks, P. A.; Holz, R. E.; Yang, P.; Ridgway, W. L.; Riedi, J.Platnick, S., K. G. Meyer, M. D. King, G. Wind, N. Amarasinghe, B. Marchant, G. T. Arnold, Z. Zhang, P. A. Hubanks, R. E. Holz, P. Yang, W. L. Ridgway, J. Riedi, 2017: The MODIS Cloud Optical and Microphysical Products: Collection 6 Updates and Examples From Terra and Aqua. IEEE Transactions on Geoscience and Remote Sensing, 55(1), 502-525. doi: 10.1109/TGRS.2016.2610522. The Moderate-Resolution Imaging Spectroradiometer (MODIS) level-2 (L2) cloud product (earth science data set names MOD06 and MYD06 for Terra and Aqua MODIS, respectively) provides pixel-level retrievals of cloud top properties (day and night pressure, temperature, and height) and cloud optical properties (optical thickness, effective particle radius, and water path for both liquid water and ice cloud thermodynamic phases-daytime only). Collection 6 (C6) reprocessing of the product was completed in May 2014 and March 2015 for MODIS Aqua and Terra, respectively. Here we provide an overview of major C6 optical property algorithm changes relative to the previous Collection 5 (C5) product. Notable C6 optical and microphysical algorithm changes include: 1) new ice cloud optical property models and a more extensive cloud radiative transfer code lookup table (LUT) approach; 2) improvement in the skill of the shortwave-derived cloud thermodynamic phase; 3) separate cloud effective radius retrieval data sets for each spectral combination used in previous collections; 4) separate retrievals for partly cloudy pixels and those associated with cloud edges; 5) failure metrics that provide diagnostic information for pixels having observations that fall outside the LUT solution space; and 6) enhanced pixel-level retrieval uncertainty calculations. The C6 algorithm changes can collectively result in significant changes relative to C5, though the magnitude depends on the data set and the pixel's retrieval location in the cloud parameter space. Example L2 granule and level-3 gridded data set differences between the two collections are shown. While the emphasis is on the suite of cloud optical property data sets, other MODIS cloud data sets are discussed when relevant. clouds; atmospheric radiation; Terrestrial atmosphere; radiometry; atmospheric optics; MODIS; Aqua; Terra; Moderate Resolution Imaging Spectroradiometer (MODIS); Ocean temperature; Optical imaging; AD 2014 05 to 2015 03; air height; air temperature; Aqua MODIS; atmospheric pressure; atmospheric temperature; atmospheric thermodynamics; C6 microphysical algorithm; C6 optical property algorithm; cloud edges; cloud effective radius retrieval data sets; cloud optical thickness; cloud parameter space; cloud radiative transfer code lookup table approach; cloud remote sensing; cloud top optical properties; cloudy pixels; day pressure; effective particle radius; ice; ice cloud optical property models; ice cloud thermodynamic; Integrated optics; liquid water; LUT approach; MOD06; moderate-resolution imaging spectroradiometer; MODIS cloud microphysical product; MODIS cloud optical product; MYD06; night pressure; Optical sensors; pixel-level retrieval uncertainty calculations; pixel-level retrieva
Qian, Yitian; Hsu, Pang-Chi; Cheng, Chi-HanQian, Y., P. Hsu, C. Cheng, 2017: Changes in surface energy partitioning in China over the past three decades. Advances in Atmospheric Sciences, 34(5), 635-649. doi: 10.1007/s00376-016-6194-8. Surface energy balance and the partitioning of sensible heat flux (SHF) and latent heat flux (LHF) play key roles in land–atmosphere feedback. However, the lack of long-term observations of surface energy fluxes, not to mention spatially extensive ones, limits our understanding of how the surface energy distribution has responded to a warming climate over recent decades (1979–2009) at the national scale in China. Using four state-of-the-art reanalysis products with long-term surface energy outputs, we identified robust changes in surface energy partitioning, defined by the Bowen ratio (BR = SHF/LHF), over different climate regimes in China. Over the past three decades, the net radiation showed an increasing trend over almost the whole of China. The increase in available radiative energy flux, however, was balanced by differential partitioning of surface turbulent fluxes, determined by local hydrological conditions. In semi-arid areas, such as Northeast China, the radiative energy was transferred largely into SHF. A severe deficiency in near-surface and soil moistures led to a significant decreasing trend in LHF. The combined effect of increased SHF and decreased LHF resulted in significant upward trends in the BR and surface warming over Northeast China. In contrast, in the wet monsoon regions, such as southern China, increased downward net radiation favored a rise in LHF rather than in SHF, leading to a significant decreasing trend in the BR. Meanwhile, the increased LHF partly cancelled out the surface warming. The warming trend in southern China was smaller than that in Northeast China. In addition to impacts on heat-related events, the changes in the BR also reflected recent cases of extreme drought in China. Our results indicate that information regarding the BR may be valuable for drought monitoring, especially in regions prone to such conditions.
Quetin, Gregory R.; Swann, Abigail L. S.Quetin, G. R., A. L. S. Swann, 2017: Empirically Derived Sensitivity of Vegetation to Climate across Global Gradients of Temperature and Precipitation. J. Climate, 30(15), 5835-5849. doi: 10.1175/JCLI-D-16-0829.1. The natural composition of terrestrial ecosystems can be shaped by climate to take advantage of local environmental conditions. Ecosystem functioning (e.g., interaction between photosynthesis and temperature) can also acclimate to different climatological states. The combination of these two factors thus determines ecological–climate interactions. A global empirical map of the sensitivity of vegetation to climate is derived using the response of satellite-observed greenness to interannual variations in temperature and precipitation. Mechanisms constraining ecosystem functioning are inferred by analyzing how the sensitivity of vegetation to climate varies across climate space. Analysis yields empirical evidence for multiple physical and biological mediators of the sensitivity of vegetation to climate at large spatial scales. In hot and wet locations, vegetation is greener in warmer years despite temperatures likely exceeding thermally optimum conditions. However, sunlight generally increases during warmer years, suggesting that the increased stress from higher atmospheric water demand is offset by higher rates of photosynthesis. The sensitivity of vegetation transitions in sign (greener when warmer or drier to greener when cooler or wetter) along an emergent line in climate space with a slope of about 59 mm yr−1 °C−1, twice as steep as contours of aridity. The mismatch between these slopes is evidence at a global scale of the limitation of both water supply due to inefficiencies in plant access to rainfall and plant physiological responses to atmospheric water demand. This empirical pattern can provide a functional constraint for process-based models, helping to improve predictions of the global-scale response of vegetation to a changing climate.
Riihelä, Aku; Key, Jeffrey R.; Meirink, Jan Fokke; Kuipers Munneke, Peter; Palo, Timo; Karlsson, Karl-GöranRiihelä, A., J. R. Key, J. F. Meirink, P. Kuipers Munneke, T. Palo, K. Karlsson, 2017: An intercomparison and validation of satellite-based surface radiative energy flux estimates over the Arctic. Journal of Geophysical Research: Atmospheres, 122(9), 4829–4848. doi: 10.1002/2016JD026443. Accurate determination of radiative energy fluxes over the Arctic is of crucial importance for understanding atmosphere-surface interactions, melt and refreezing cycles of the snow and ice cover, and the role of the Arctic in the global energy budget. Satellite-based estimates can provide comprehensive spatiotemporal coverage, but the accuracy and comparability of the existing data sets must be ascertained to facilitate their use. Here we compare radiative flux estimates from Clouds and the Earth's Radiant Energy System (CERES) Synoptic 1-degree (SYN1deg)/Energy Balanced and Filled, Global Energy and Water Cycle Experiment (GEWEX) surface energy budget, and our own experimental FluxNet / Satellite Application Facility on Climate Monitoring cLoud, Albedo and RAdiation (CLARA) data against in situ observations over Arctic sea ice and the Greenland Ice Sheet during summer of 2007. In general, CERES SYN1deg flux estimates agree best with in situ measurements, although with two particular limitations: (1) over sea ice the upwelling shortwave flux in CERES SYN1deg appears to be underestimated because of an underestimated surface albedo and (2) the CERES SYN1deg upwelling longwave flux over sea ice saturates during midsummer. The Advanced Very High Resolution Radiometer-based GEWEX and FluxNet-CLARA flux estimates generally show a larger range in retrieval errors relative to CERES, with contrasting tendencies relative to each other. The largest source of retrieval error in the FluxNet-CLARA downwelling shortwave flux is shown to be an overestimated cloud optical thickness. The results illustrate that satellite-based flux estimates over the Arctic are not yet homogeneous and that further efforts are necessary to investigate the differences in the surface and cloud properties which lead to disagreements in flux retrievals. Remote sensing; 0321 Cloud/radiation interaction; Radiative fluxes; 3359 Radiative processes; Satellite; validation; 0758 Remote sensing; Arctic; 0764 Energy balance; Comparison
Roberts, C. D.; Palmer, M. D.; Allan, R. P.; Desbruyeres, D.g.; Hyder, P.; Liu, C.; Smith, D.Roberts, C. D., M. D. Palmer, R. P. Allan, D. Desbruyeres, P. Hyder, C. Liu, D. Smith, 2017: Surface flux and ocean heat transport convergence contributions to seasonal and interannual variations of ocean heat content. Journal of Geophysical Research: Oceans, 122(1), 726–744. doi: 10.1002/2016JC012278. We present an observation-based heat budget analysis for seasonal and interannual variations of ocean heat content (H) in the mixed layer (Hmld) and full-depth ocean (Htot). Surface heat flux and ocean heat content estimates are combined using a novel Kalman smoother-based method. Regional contributions from ocean heat transport convergences are inferred as a residual and the dominant drivers of Hmld and Htot are quantified for seasonal and interannual time scales. We find that non-Ekman ocean heat transport processes dominate Hmld variations in the equatorial oceans and regions of strong ocean currents and substantial eddy activity. In these locations, surface temperature anomalies generated by ocean dynamics result in turbulent flux anomalies that drive the overlying atmosphere. In addition, we find large regions of the Atlantic and Pacific oceans where heat transports combine with local air-sea fluxes to generate mixed layer temperature anomalies. In all locations, except regions of deep convection and water mass transformation, interannual variations in Htot are dominated by the internal rearrangement of heat by ocean dynamics rather than the loss or addition of heat at the surface. Our analysis suggests that, even in extratropical latitudes, initialization of ocean dynamical processes could be an important source of skill for interannual predictability of Hmld and Htot. Furthermore, we expect variations in Htot (and thus thermosteric sea level) to be more predictable than near surface temperature anomalies due to the increased importance of ocean heat transport processes for full-depth heat budgets. 1616 Climate variability; Variability; Interannual; Surface fluxes; heat budget; heat content; heat transports
Roh, Woosub; Satoh, Masaki; Nasuno, TomoeRoh, W., M. Satoh, T. Nasuno, 2017: Improvement of a Cloud Microphysics Scheme for a Global Nonhydrostatic Model Using TRMM and a Satellite Simulator. J. Atmos. Sci., 74(1), 167-184. doi: 10.1175/JAS-D-16-0027.1. The cloud and precipitation simulated by a global nonhydrostatic model with a 3.5-km horizontal resolution, the Nonhydrostatic Icosahedral Atmospheric Model (NICAM), are evaluated using the Tropical Rainfall Measuring Mission (TRMM) and a satellite simulator. A previous study by Roh and Satoh evaluated the single-moment bulk microphysics and established the modified microphysics scheme for the specific tropical open ocean using a regional version of NICAM. In this study, the authors expanded the evaluation over the entire tropics and parts of the midlatitude areas (20°–36°S, 20°–36°N) using a joint histogram of the cloud-top temperature and precipitation echo-top heights and contoured frequency by altitude diagrams of the deep convective systems. The modified microphysics simulation improves the joint probability density functions of the cloud-top temperatures and precipitation cloud-top heights over not only the tropical ocean but also the land and midlatitude areas. Compared with the default microphysics simulation, the modified microphysics simulation shows a clearer distinction between the land and ocean in the tropics, which is related to the contrast between the shallow and the deep clouds. In addition, the two microphysics simulation methods were also compared over the tropics using joint histograms of the cloud-top and precipitation cloud-top heights on the basis of CloudSat measurements. It was found that the microphysics scheme that was modified for the tropical ocean displayed general cloud and precipitation improvements in the global domain over the tropics.
Ryu, Young-Hee; Hodzic, Alma; Descombes, Gael; Hall, Samuel; Minnis, Patrick; Spangenberg, Douglas; Ullmann, Kirk; Madronich, SashaRyu, Y., A. Hodzic, G. Descombes, S. Hall, P. Minnis, D. Spangenberg, K. Ullmann, S. Madronich, 2017: Improved modeling of cloudy-sky actinic flux using satellite cloud retrievals. Geophysical Research Letters, 44(3), 1592–1600. doi: 10.1002/2016GL071892. Clouds play a critical role in modulating tropospheric radiation and thus photochemistry. We develop a methodology for calculating the vertical distribution of tropospheric ultraviolet (300–420 nm) actinic fluxes using satellite cloud retrievals and a radiative transfer model. We demonstrate that our approach can accurately reproduce airborne-measured actinic fluxes from the 2013 Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign as a case study. The results show that the actinic flux is reduced below moderately thick clouds with increasing cloud optical depth and can be enhanced by a factor of 2 above clouds. Inside clouds, the actinic flux can be enhanced by up to 2.4 times in the upper part of clouds or reduced up to 10 times in the lower parts of clouds. Our study suggests that the use of satellite-derived actinic fluxes as input to chemistry-transport models can improve the accuracy of photochemistry calculations. clouds; 0360 Radiation: transmission and scattering; 0321 Cloud/radiation interaction; Satellite; Radiative transfer model; 0317 Chemical kinetic and photochemical properties; actinic flux; photolysis
Salzmann, M.Salzmann, M., 2017: The polar amplification asymmetry: role of Antarctic surface height. Earth Syst. Dynam., 8(2), 323-336. doi: 10.5194/esd-8-323-2017.
Samson, Guillaume; Masson, Sébastien; Durand, Fabien; Terray, Pascal; Berthet, Sarah; Jullien, SwenSamson, G., S. Masson, F. Durand, P. Terray, S. Berthet, S. Jullien, 2017: Roles of land surface albedo and horizontal resolution on the Indian summer monsoon biases in a coupled ocean–atmosphere tropical-channel model. Climate Dynamics, 48(5-6), 1571-1594. doi: 10.1007/s00382-016-3161-0. The Indian summer monsoon (ISM) simulated over the 1989–2009 period with a new 0.75° ocean–atmosphere coupled tropical-channel model extending from 45°S to 45°N is presented. The model biases are comparable to those commonly found in coupled global climate models (CGCMs): the Findlater jet is too weak, precipitations are underestimated over India while they are overestimated over the southwestern Indian Ocean, South-East Asia and the Maritime Continent. The ISM onset is delayed by several weeks, an error which is also very common in current CGCMs. We show that land surface temperature errors are a major source of the ISM low-level circulation and rainfall biases in our model: a cold bias over the Middle-East (ME) region weakens the Findlater jet while a warm bias over India strengthens the monsoon circulation over the southern Bay of Bengal. A surface radiative heat budget analysis reveals that the cold bias is due to an overestimated albedo in this desertic ME region. Two new simulations using a satellite-observed land albedo show a significant and robust improvement in terms of ISM circulation and precipitation. Furthermore, the ISM onset is shifted back by 1 month and becomes in phase with observations. Finally, a supplementary set of simulations at 0.25°-resolution confirms the robustness of our results and shows an additional reduction of the warm and dry bias over India. These findings highlight the strong sensitivity of the simulated ISM rainfall and its onset timing to the surface land heating pattern and amplitude, especially in the ME region. It also illustrates the key-role of land surface processes and horizontal resolution for improving the ISM representation, and more generally the monsoons, in current CGCMs.
Scarino, B. R.; Minnis, P.; Chee, T.; Bedka, K. M.; Yost, C. R.; Palikonda, R.Scarino, B. R., P. Minnis, T. Chee, K. M. Bedka, C. R. Yost, R. Palikonda, 2017: Global clear-sky surface skin temperature from multiple satellites using a single-channel algorithm with angular anisotropy corrections. Atmos. Meas. Tech., 10(1), 351-371. doi: 10.5194/amt-10-351-2017. Surface skin temperature (Ts) is an important parameter for characterizing the energy exchange at the ground/water–atmosphere interface. The Satellite ClOud and Radiation Property retrieval System (SatCORPS) employs a single-channel thermal-infrared (TIR) method to retrieve Ts over clear-sky land and ocean surfaces from data taken by geostationary Earth orbit (GEO) and low Earth orbit (LEO) satellite imagers. GEO satellites can provide somewhat continuous estimates of Ts over the diurnal cycle in non-polar regions, while polar Ts retrievals from LEO imagers, such as the Advanced Very High Resolution Radiometer (AVHRR), can complement the GEO measurements. The combined global coverage of remotely sensed Ts, along with accompanying cloud and surface radiation parameters, produced in near-realtime and from historical satellite data, should be beneficial for both weather and climate applications. For example, near-realtime hourly Ts observations can be assimilated in high-temporal-resolution numerical weather prediction models and historical observations can be used for validation or assimilation of climate models. Key drawbacks to the utility of TIR-derived Ts data include the limitation to clear-sky conditions, the reliance on a particular set of analyses/reanalyses necessary for atmospheric corrections, and the dependence on viewing and illumination angles. Therefore, Ts validation with established references is essential, as is proper evaluation of Ts sensitivity to atmospheric correction source.This article presents improvements on the NASA Langley GEO satellite and AVHRR TIR-based Ts product that is derived using a single-channel technique. The resulting clear-sky skin temperature values are validated with surface references and independent satellite products. Furthermore, an empirically adjusted theoretical model of satellite land surface temperature (LST) angular anisotropy is tested to improve satellite LST retrievals. Application of the anisotropic correction yields reduced mean bias and improved precision of GOES-13 LST relative to independent Moderate-resolution Imaging Spectroradiometer (MYD11_L2) LST and Atmospheric Radiation Measurement Program ground station measurements. It also significantly reduces inter-satellite differences between LSTs retrieved simultaneously from two different imagers. The implementation of these universal corrections into the SatCORPS product can yield significant improvement in near-global-scale, near-realtime, satellite-based LST measurements. The immediate availability and broad coverage of these skin temperature observations should prove valuable to modelers and climate researchers looking for improved forecasts and better understanding of the global climate model.
Schneider, TapioSchneider, T., 2017: Feedback of Atmosphere-Ocean Coupling on Shifts of the Intertropical Convergence Zone. Geophysical Research Letters, 44(22), 2017GL075817. doi: 10.1002/2017GL075817. It is well known that the Intertropical Convergence Zone (ITCZ) shifts in response to remote perturbations in the atmospheric energy balance, with shifts roughly in proportion to changes in the cross-equatorial atmospheric energy flux. However, atmospheric and oceanic energy fluxes in low latitudes are mechanically coupled, and the oceanic energy flux dominates the atmospheric energy flux. Here a quantitative framework is derived that shows how Ekman coupling of atmospheric and oceanic energy fluxes damps the perturbation response of the atmospheric energy flux, energy flux equator (EFE), and ITCZ. To first order, Ekman coupling alone mutes the response of EFE and ITCZ in the coupled atmosphere-ocean system by a factor γ = 1+O0/NEI0, where O0 is the ocean energy uptake and NEI0 is the net energy input into the atmosphere at the equator. In the current climate in the zonal and annual mean, this factor is about γ≈3. 3305 Climate change and variability; ITCZ; 3319 General circulation; 3339 Ocean/atmosphere interactions; energy balance; 3367 Theoretical modeling; 3320 Idealized model; atmosphere-ocean coupling
Schwarz, M.; Folini, D.; Hakuba, M. Z.; Wild, M.Schwarz, M., D. Folini, M. Z. Hakuba, M. Wild, 2017: Spatial Representativeness of Surface-Measured Variations of Downward Solar Radiation. Journal of Geophysical Research: Atmospheres, 122(24), 2017JD027261. doi: 10.1002/2017JD027261. When using time series of ground-based surface solar radiation (SSR) measurements in combination with gridded data, the spatial and temporal representativeness of the point observations must be considered. We use SSR data from surface observations and high-resolution (0.05°) satellite-derived data to infer the spatiotemporal representativeness of observations for monthly and longer time scales in Europe. The correlation analysis shows that the squared correlation coefficients (R2) between SSR times series decrease linearly with increasing distance between the surface observations. For deseasonalized monthly mean time series, R2 ranges from 0.85 for distances up to 25 km between the stations to 0.25 at distances of 500 km. A decorrelation length (i.e., the e-folding distance of R2) on the order of 400 km (with spread of 100–600 km) was found. R2 from correlations between point observations and colocated grid box area means determined from satellite data were found to be 0.80 for a 1° grid. To quantify the error which arises when using a point observation as a surrogate for the area mean SSR of larger surroundings, we calculated a spatial sampling error (SSE) for a 1° grid of 8 (3) W/m2 for monthly (annual) time series. The SSE based on a 1° grid, therefore, is of the same magnitude as the measurement uncertainty. The analysis generally reveals that monthly mean (or longer temporally aggregated) point observations of SSR capture the larger-scale variability well. This finding shows that comparing time series of SSR measurements with gridded data is feasible for those time scales. 3359 Radiative processes; 3305 Climate change and variability; surface solar radiation; 1988 Temporal analysis and representation; 1990 Uncertainty; 1980 Spatial analysis and representation; spatiotemporal representativeness
Schwingshackl, Clemens; Hirschi, Martin; Seneviratne, Sonia I.Schwingshackl, C., M. Hirschi, S. I. Seneviratne, 2017: Quantifying Spatiotemporal Variations of Soil Moisture Control on Surface Energy Balance and Near-Surface Air Temperature. J. Climate, 30(18), 7105-7124. doi: 10.1175/JCLI-D-16-0727.1. AbstractSoil moisture plays a crucial role for the energy partitioning at Earth?s surface. Changing fractions of latent and sensible heat fluxes caused by soil moisture variations can affect both near-surface air temperature and precipitation. In this study, a simple framework for the dependence of evaporative fraction (the ratio of latent heat flux over net radiation) on soil moisture is used to analyze spatial and temporal variations of land?atmosphere coupling and its effect on near-surface air temperature. Using three different data sources (two reanalysis datasets and one combination of different datasets), three key parameters for the relation between soil moisture and evaporative fraction are estimated: 1) the frequency of occurrence of different soil moisture regimes, 2) the sensitivity of evaporative fraction to soil moisture in the transitional soil moisture regime, and 3) the critical soil moisture value that separates soil moisture- and energy-limited evapotranspiration regimes. The results show that about 30%?60% (depending on the dataset) of the global land area is in the transitional regime during at least half of the year. Based on the identification of transitional regimes, the effect of changes in soil moisture on near-surface air temperature is analyzed. Typical soil moisture variations (standard deviation) can impact air temperature by up to 1.1?1.3 K, while changing soil moisture over its full range in the transitional regime can alter air temperature by up to 6?7 K. The results emphasize the role of soil moisture for atmosphere and climate and constitute a useful benchmark for the evaluation of the respective relationships in Earth system models.
Scott, Ryan C.; Lubin, Dan; Vogelmann, Andrew M.; Kato, SeijiScott, R. C., D. Lubin, A. M. Vogelmann, S. Kato, 2017: West Antarctic Ice Sheet cloud cover and surface radiation budget from NASA A-Train satellites. J. Climate, 30(16), 6151–6170. doi: 10.1175/JCLI-D-16-0644.1. Clouds are an essential parameter of the surface energy budget influencing the West Antarctic Ice Sheet (WAIS) response to atmospheric warming and net contribution to global sea-level rise. A four-year record of NASA A-Train cloud observations is combined with surface radiation measurements to quantify the WAIS radiation budget and constrain the three-dimensional occurrence frequency, thermodynamic phase partitioning, and surface radiative effect of clouds over West Antarctica (WA). The skill of satellite-modeled radiative fluxes is confirmed through evaluation against measurements at four Antarctic sites (WAIS Divide Ice Camp, Neumayer, Syowa, and Concordia Stations). Due to perennial high-albedo snow and ice cover, cloud infrared emission dominates over cloud solar reflection/absorption leading to a positive net all-wave cloud radiative effect (CRE) at the surface, with all monthly means and 99.15% of instantaneous CRE values exceeding zero. The annual-mean CRE at theWAIS surface is 34 W m−2, representing a significant cloud-induced warming of the ice sheet. Low-level liquid-containing clouds, including thin liquid water clouds implicated in radiative contributions to surface melting, are widespread and most frequent in WA during the austral summer. In summer, clouds warm the WAIS by 26 W m−2, on average, despite maximum offsetting shortwave CRE. Glaciated cloud systems are strongly linked to orographic forcing, with maximum incidence on the WAIS continuing downstream along the Transantarctic Mountains.
Sedlar, Joseph; Tjernström, MichaelSedlar, J., M. Tjernström, 2017: Clouds, warm air, and a climate cooling signal over the summer Arctic. Geophysical Research Letters, 44(2), 1095–1103. doi: 10.1002/2016GL071959. While the atmospheric greenhouse effect always results in a warming at the surface, outgoing longwave radiation (OLR) to space always represents a cooling. During events of heat and moisture advection into the Arctic, increases in tropospheric temperature and moisture impact clouds, in turn impacting longwave (LW) radiation. State-of-the-art satellite measurements and atmospheric reanalysis consistently reveal an enhancement of summer Arctic monthly OLR cooling ranging 1.5–4 W m−2 during months with anomalously high thermodynamic advection. This cooling anomaly is found to be of the same magnitude or slightly larger than associated downwelling LW surface warming anomalies. We identify a relationship between large-scale circulation variability and changing cloud properties permitting LW radiation at both the surface and top of the atmosphere to respond to variability in atmospheric thermodynamics. Driven by anomalous advection of warm air, the corresponding enhanced OLR cooling signal on monthly time scales represents an important buffer to regional Arctic warming. clouds; 3359 Radiative processes; 3310 Clouds and cloud feedbacks; radiation; Arctic; 3307 Boundary layer processes; Thermodynamics; advection
Shea, Yolanda L.; Wielicki, Bruce A.; Sun-Mack, Sunny; Minnis, PatrickShea, Y. L., B. A. Wielicki, S. Sun-Mack, P. Minnis, 2017: Quantifying the Dependence of Satellite Cloud Retrievals on Instrument Uncertainty. J. Climate, 30(17), 6959-6976. doi: 10.1175/JCLI-D-16-0429.1. Cloud response to Earth’s changing climate is one of the largest sources of uncertainty among global climate model (GCM) projections. Two of the largest sources of uncertainty are the spread in equilibrium climate sensitivity (ECS) and uncertainty in radiative forcing due to uncertainty in the aerosol indirect effect. Satellite instruments with sufficient accuracy and on-orbit stability to detect climate change–scale trends in cloud properties will improve confidence in the understanding of the relationship between observed climate change and cloud property trends, thus providing information to better constrain ECS and radiative forcing. This study applies a climate change uncertainty framework to quantify the impact of measurement uncertainty on trend detection times for cloud fraction, effective temperature, optical thickness, and water cloud effective radius. Although GCMs generally agree that the total cloud feedback is positive, disagreement remains on its magnitude. With the climate uncertainty framework, it is demonstrated how stringent measurement uncertainty requirements for reflected solar and infrared satellite measurements enable improved constraint of SW and LW cloud feedbacks and the ECS by significantly reducing trend uncertainties for cloud fraction, optical thickness, and effective temperature. The authors also demonstrate improved constraint on uncertainty in the aerosol indirect effect by reducing water cloud effective radius trend uncertainty.
Smith, Nathaniel P.; Szewczyk, Z. Peter; Hess, Phillip C.; Priestley, Kory J.Smith, N. P., Z. P. Szewczyk, P. C. Hess, K. J. Priestley, 2017: A strategy to assess the pointing accuracy of the CERES FM1-FM5 scanners. doi: 10.1117/12.2271644. The Clouds and the Earth’s Radiant Energy System (CERES) scanning radiometer is designed to measure the solar radiation reflected by the Earth and thermal radiation emitted by the Earth. Five CERES instruments are currently in service; two aboard the Terra spacecraft, launched in 1999; two aboard the Aqua spacecraft, launched in 2002; and one instrument about the NPP spacecraft, launched in 2011. Verifying the pointing accuracy of the CERES instruments is required to assure that all earth viewing data is correctly geolocated. The CERES team has developed an on-orbit technique for assessing the pointing accuracy of the CERES sensors that relies on a rapid gradient change of measurements taken over a well-defined and known Earth target, such as a coastline, where a strong contrast in brightness and temperature exists. The computed coastline is then compared with World Bank II map to verify the accuracy of the measurement location. This paper briefly restates the algorithm used in the study, describes collection of coastline data, and summarizes the results of the study the CERES FM1, FM2, FM3, and FM5 instruments.
Smith, William L.; Hansen, Christy; Bucholtz, Anthony; Anderson, Bruce E.; Beckley, Matthew; Corbett, Joseph G.; Cullather, Richard I.; Hines, Keith M.; Hofton, Michelle; Kato, Seiji; Lubin, Dan; Moore, Richard H.; Segal Rosenhaimer, Michal; Redemann, Jens; Schmidt, Sebastian; Scott, Ryan; Song, Shi; Barrick, John D.; Blair, J. Bryan; Bromwich, David H.; Brooks, Colleen; Chen, Gao; Cornejo, Helen; Corr, Chelsea A.; Ham, Seung-Hee; Kittelman, A. Scott; Knappmiller, Scott; LeBlanc, Samuel; Loeb, Norman G.; Miller, Colin; Nguyen, Louis; Palikonda, Rabindra; Rabine, David; Reid, Elizabeth A.; Richter-Menge, Jacqueline A.; Pilewskie, Peter; Shinozuka, Yohei; Spangenberg, Douglas; Stackhouse, Paul; Taylor, Patrick; Thornhill, K. Lee; van Gilst, David; Winstead, EdwardSmith, W. L., C. Hansen, A. Bucholtz, B. E. Anderson, M. Beckley, J. G. Corbett, R. I. Cullather, K. M. Hines, M. Hofton, S. Kato, D. Lubin, R. H. Moore, M. Segal Rosenhaimer, J. Redemann, S. Schmidt, R. Scott, S. Song, J. D. Barrick, J. B. Blair, D. H. Bromwich, C. Brooks, G. Chen, H. Cornejo, C. A. Corr, S. Ham, A. S. Kittelman, S. Knappmiller, S. LeBlanc, N. G. Loeb, C. Miller, L. Nguyen, R. Palikonda, D. Rabine, E. A. Reid, J. A. Richter-Menge, P. Pilewskie, Y. Shinozuka, D. Spangenberg, P. Stackhouse, P. Taylor, K. L. Thornhill, D. van Gilst, E. Winstead, 2017: Arctic Radiation-IceBridge Sea and Ice Experiment: The Arctic Radiant Energy System during the Critical Seasonal Ice Transition. Bull. Amer. Meteor. Soc., 98(7), 1399-1426. doi: 10.1175/BAMS-D-14-00277.1. AbstractThe National Aeronautics and Space Administration (NASA)?s Arctic Radiation-IceBridge Sea and Ice Experiment (ARISE) acquired unique aircraft data on atmospheric radiation and sea ice properties during the critical late summer to autumn sea ice minimum and commencement of refreezing. The C-130 aircraft flew 15 missions over the Beaufort Sea between 4 and 24 September 2014. ARISE deployed a shortwave and longwave broadband radiometer (BBR) system from the Naval Research Laboratory; a Solar Spectral Flux Radiometer (SSFR) from the University of Colorado Boulder; the Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) from the NASA Ames Research Center; cloud microprobes from the NASA Langley Research Center; and the Land, Vegetation and Ice Sensor (LVIS) laser altimeter system from the NASA Goddard Space Flight Center. These instruments sampled the radiant energy exchange between clouds and a variety of sea ice scenarios, including prior to and after refreezing began. The most critical and unique aspect of ARISE mission planning was to coordinate the flight tracks with NASA Cloud and the Earth?s Radiant Energy System (CERES) satellite sensor observations in such a way that satellite sensor angular dependence models and derived top-of-atmosphere fluxes could be validated against the aircraft data over large gridbox domains of order 100?200 km. This was accomplished over open ocean, over the marginal ice zone (MIZ), and over a region of heavy sea ice concentration, in cloudy and clear skies. ARISE data will be valuable to the community for providing better interpretation of satellite energy budget measurements in the Arctic and for process studies involving ice?cloud?atmosphere energy exchange during the sea ice transition period.
Song, Xiangzhou; Yu, LisanSong, X., L. Yu, 2017: Air-Sea heat flux climatologies in the Mediterranean Sea: Surface energy balance and its consistency with ocean heat storage. Journal of Geophysical Research: Oceans, 122(5), 4068–4087. doi: 10.1002/2016JC012254. This study provides an analysis of the Mediterranean Sea surface energy budget using nine surface heat flux climatologies. The ensemble mean estimation shows that the net downward shortwave radiation (192±19 Wm−2) is balanced by latent heat flux (-98±10 Wm−2), followed by net longwave radiation (-78±13 Wm−2) and sensible heat flux (-13±4 Wm−2). The resulting net heat budget (Qnet) is 2±12 Wm−2 into the ocean, which appears to be warm biased. The annual-mean Qnet should be -5.6±1.6 Wm−2 when estimated from the observed net transport through the Strait of Gibraltar. To diagnose the uncertainty in nine Qnet climatologies, we constructed Qnet from the heat budget equation by using historic hydrological observations to determine the heat content changes and advective heat flux. We also used the Qnet from a data-assimilated global ocean state estimation as an additional reference. By comparing with the two reference Qnet estimates, we found that seven products (NCEP 1, NCEP 2, CFSR, ERA-Interim, MERRA, NOCSv2.0 and OAFlux+ISCCP) overestimate Qnet, with magnitude ranging from 6 to 27 Wm−2, while two products underestimate Qnet by -6 Wm−2 (JRA55) and -14 Wm−2 (CORE.2). Together with the previous warm pool work of Song and Yu, [2013], we show that CFSR, MERRA, NOCSv2.0, and OAFlux+ISCCP are warm biased not only in the western Pacific warm pool but also in the Mediterranean Sea, whilst CORE.2 is cold biased in both regions. The NCEP 1, 2 and ERA-Interim are cold biased over the warm pool but warm biased in the Mediterranean Sea. This article is protected by copyright. All rights reserved. 4572 Upper ocean and mixed layer processes; 4504 Air/sea interactions; heat budget analysis; 4243 Marginal and semi-enclosed seas; Air-sea heat flux; Heat content changes; Mediterranean Sea
Stevens, Bjorn; Fiedler, StephanieStevens, B., S. Fiedler, 2017: Reply to “Comment on ‘Rethinking the Lower Bound on Aerosol Radiative Forcing’”. J. Climate, 30(16), 6585-6589. doi: 10.1175/JCLI-D-17-0034.1. AbstractKretzschmar et al., in a comment in 2017, use the spread in the output of aerosol?climate models to argue that the models refute the hypothesis (presented in a paper by Stevens in 2015) that for the mid-twentieth-century warming to be consistent with observations, then the present-day aerosol forcing, must be less negative than ?1 W m?2. The main point of contention is the nature of the relationship between global SO2 emissions and In contrast to the concave (log-linear) relationship used by Stevens and in earlier studies, whereby becomes progressively less sensitive to SO2 emissions, some models suggest a convex relationship, which would imply a less negative lower bound. The model that best exemplifies this difference, and that is most clearly in conflict with the hypothesis of Stevens, does so because of an implausible aerosol response to the initial rise in anthropogenic aerosol precursor emissions in East and South Asia?already in 1975 this model?s clear-sky reflectance from anthropogenic aerosol over the North Pacific exceeds present-day estimates of the clear-sky reflectance by the total aerosol. The authors perform experiments using a new (observationally constrained) climatology of anthropogenic aerosols to further show that the effects of changing patterns of aerosol and aerosol precursor emissions during the late twentieth century have, for the same global emissions, relatively little effect on These findings suggest that the behavior Kretzschmar et al. identify as being in conflict with the lower bound in Stevens arises from an implausible relationship between SO2 emissions and and thus provides little basis for revising this lower bound.
Storto, Andrea; Yang, Chunxue; Masina, SimonaStorto, A., C. Yang, S. Masina, 2017: Constraining the Global Ocean Heat Content Through Assimilation of CERES-Derived TOA Energy Imbalance Estimates. Geophysical Research Letters, 44(20), 10,520–10,529. doi: 10.1002/2017GL075396. The Earth's energy imbalance (EEI) is stored in the oceans for the most part. Thus, estimates of its variability can be ingested in ocean retrospective analyses to constrain the global ocean heat budget. Here we propose a scheme to assimilate top of the atmosphere global radiation imbalance estimates from Clouds and the Earth's Radiant Energy System (CERES) in a coarse-resolution variational ocean reanalysis system (2000–2014). The methodology proves able to shape the heat content tendencies according to the EEI estimates, without compromising the reanalysis accuracy. Spurious variability and underestimation (overestimation) present in experiments with in situ (no) data assimilation disappear when EEI data are assimilated. The warming hiatus present without the assimilation of EEI data is mitigated, inducing ocean warming at depths below 1,500 m and slightly larger in the Southern Hemisphere, in accordance with recent studies. Furthermore, the methodology may be applied to Earth System reanalyses and climate simulations to realistically constrain the global energy budget. 1622 Earth system modeling; net radiation; 1635 Oceans; 4260 Ocean data assimilation and reanalysis; heat budget; 1910 Data assimilation, integration and fusion; variational assimilation; warming hiatus
Su, Hui; Jiang, Jonathan H.; Neelin, J. David; Shen, T. Janice; Zhai, Chengxing; Yue, Qing; Wang, Zhien; Huang, Lei; Choi, Yong-Sang; Stephens, Graeme L.; Yung, Yuk L.Su, H., J. H. Jiang, J. D. Neelin, T. J. Shen, C. Zhai, Q. Yue, Z. Wang, L. Huang, Y. Choi, G. L. Stephens, Y. L. Yung, 2017: Tightening of tropical ascent and high clouds key to precipitation change in a warmer climate. Nature Communications, 30(15), 5835–5849. doi: doi:10.1038/ncomms15771.
Su, W.; Liang, L.; Miller, W. F.; Sothcott, V. E.Su, W., L. Liang, W. F. Miller, V. E. Sothcott, 2017: The effects of different footprint sizes and cloud algorithms on the top-of-atmosphere radiative flux calculation from the Clouds and Earth's Radiant Energy System (CERES) instrument on Suomi National Polar-orbiting Partnership (NPP). Atmos. Meas. Tech., 10(10), 4001-4011. doi: 10.5194/amt-10-4001-2017. Only one Clouds and Earth's Radiant Energy System (CERES) instrument is onboard the Suomi National Polar-orbiting Partnership (NPP) and it has been placed in cross-track mode since launch; it is thus not possible to construct a set of angular distribution models (ADMs) specific for CERES on NPP. Edition 4 Aqua ADMs are used for flux inversions for NPP CERES measurements. However, the footprint size of NPP CERES is greater than that of Aqua CERES, as the altitude of the NPP orbit is higher than that of the Aqua orbit. Furthermore, cloud retrievals from the Visible Infrared Imaging Radiometer Suite (VIIRS) and the Moderate Resolution Imaging Spectroradiometer (MODIS), which are the imagers sharing the spacecraft with NPP CERES and Aqua CERES, are also different. To quantify the flux uncertainties due to the footprint size difference between Aqua CERES and NPP CERES, and due to both the footprint size difference and cloud property difference, a simulation is designed using the MODIS pixel-level data, which are convolved with the Aqua CERES and NPP CERES point spread functions (PSFs) into their respective footprints. The simulation is designed to isolate the effects of footprint size and cloud property differences on flux uncertainty from calibration and orbital differences between NPP CERES and Aqua CERES. The footprint size difference between Aqua CERES and NPP CERES introduces instantaneous flux uncertainties in monthly gridded NPP CERES measurements of less than 4.0 W m−2 for SW (shortwave) and less than 1.0 W m−2 for both daytime and nighttime LW (longwave). The global monthly mean instantaneous SW flux from simulated NPP CERES has a low bias of 0.4 W m−2 when compared to simulated Aqua CERES, and the root-mean-square (RMS) error is 2.2 W m−2 between them; the biases of daytime and nighttime LW flux are close to zero with RMS errors of 0.8 and 0.2 W m−2. These uncertainties are within the uncertainties of CERES ADMs. When both footprint size and cloud property (cloud fraction and optical depth) differences are considered, the uncertainties of monthly gridded NPP CERES SW flux can be up to 20 W m−2 in the Arctic regions where cloud optical depth retrievals from VIIRS differ significantly from MODIS. The global monthly mean instantaneous SW flux from simulated NPP CERES has a high bias of 1.1 W m−2 and the RMS error increases to 5.2 W m−2. LW flux shows less sensitivity to cloud property differences than SW flux, with uncertainties of about 2 W m−2 in the monthly gridded LW flux, and the RMS errors of global monthly mean daytime and nighttime fluxes increase only slightly. These results highlight the importance of consistent cloud retrieval algorithms to maintain the accuracy and stability of the CERES climate data record.
Su, Wenying; Loeb, Norman G.; Liang, Lusheng; Liu, Nana; Liu, ChuntaoSu, W., N. G. Loeb, L. Liang, N. Liu, C. Liu, 2017: The El Niño-Southern Oscillation Effect on Tropical Outgoing Longwave Radiation: A Daytime Versus Nighttime Perspective. Journal of Geophysical Research: Atmospheres, 122(15), 7820–7833. doi: 10.1002/2017JD027002. Trends of tropical (30° N-30° S) mean daytime and nighttime outgoing longwave radiation (OLR) from CERES and AIRS are analyzed using data from 2003 to 2013. Both the daytime and nighttime OLR from these instruments show decreasing trends because of El Niño conditions early in the period and La Niña conditions at the end. However, the daytime and nighttime OLR decrease at different rates with the OLR decreasing faster during daytime than nighttime. The daytime-nighttime OLR trend is consistent across CERES Terra, Aqua observations, and computed OLR based upon AIRS and MODIS retrievals. To understand the cause of the differing decreasing rates of daytime and nighttime OLR, high cloud fraction and effective temperature are examined using cloud retrievals from MODIS and AIRS. Unlike the very consistent OLR trends between CERES and AIRS, the trends in cloud properties are not as consistent, which is likely due to the different cloud retrieval methods used. When MODIS and AIRS cloud properties are used to compute OLR, the daytime and nighttime OLR trends based upon MODIS cloud properties are approximately half as large as the trends from AIRS cloud properties, but their daytime-nighttime OLR trends are in agreement. This demonstrates that though the current cloud retrieval algorithms lack the accuracy to pinpoint the changes of daytime and nighttime clouds in the tropics, they do provide a radiatively-consistent view for daytime and nighttime OLR changes. The causes for the larger decreasing daytime OLR trend than that for nighttime OLR are not clear and further studies are needed. clouds; 0321 Cloud/radiation interaction; ENSO; outgoing longwave radiation
Swann, Abigail L. S.; Koven, Charles D.Swann, A. L. S., C. D. Koven, 2017: A Direct Estimate of the Seasonal Cycle of Evapotranspiration over the Amazon Basin. J. Hydrometeor., 18(8), 2173-2185. doi: 10.1175/JHM-D-17-0004.1. AbstractEvapotranspiration (ET) is a critical term in the surface energy budget as well as the water cycle. There are few direct measurements of ET, and thus the magnitude and variability are poorly constrained at large spatial scales. Estimates of the annual cycle of ET over the Amazon are critical because they influence predictions of the seasonal cycle of carbon fluxes, as well as atmospheric dynamics and circulation. The authors estimate ET for the Amazon basin using a water budget approach by differencing rainfall, discharge, and time-varying storage from the Gravity Recovery and Climate Experiment. It is found that the climatological annual cycle of ET over the Amazon basin upstream of ?bidos shows suppression of ET during the wet season and higher ET during the dry season, consistent with flux-tower-based observations in seasonally dry forests. They also find a statistically significant decrease in ET over the time period 2002?15 of ?1.46 mm yr?1. The direct estimate of the seasonal cycle of ET is largely consistent with previous indirect estimates, including energy-budget-based approaches, an upscaled station-based estimate, and land surface model estimates, but suggests that suppression of ET during the wet season is underestimated by existing products.
Szewczyk, Z. Peter; Walikainen, Dale R.; Smith, Nitchie; Thomas, Susan; Priestley, Kory J.Szewczyk, Z. P., D. R. Walikainen, N. Smith, S. Thomas, K. J. Priestley, 2017: Improving consistency of the ERB record measured by CERES scanners aboard Terra/Aqua/S-NPP satellites. doi: 10.1117/12.2278457. A purpose of this paper is to present verification of the consistency of unfiltered radiances measured by CERES instruments over their mission 2000-2016. The FM1 scanner on Terra, designated as the climate instrument, is used as a benchmark. The degradation modeling while the instruments on Terra and Aqua were operating in the RAPS mode is being revised, and the rate of the monthly degradation is shown to be 0.03%. The focus of this paper is on consistency between Terra CERES scanners, and it is a part of a broader investigation. Results of comparing FM2 and FM1 are reported for all-sky condition and selected scene types for shortwave and long-wave radiances based on Edition 4 ERBE-like (ES8) data product. Some scene type based results are also verified using an SSF product that contains imager (MODIS) information.
Tan, Zeli; Zhuang, Qianlai; Shurpali, Narasinha J.; Marushchak, Maija E.; Biasi, Christina; Eugster, Werner; Walter Anthony, KateyTan, Z., Q. Zhuang, N. J. Shurpali, M. E. Marushchak, C. Biasi, W. Eugster, K. Walter Anthony, 2017: Modeling CO2 emissions from Arctic lakes: Model development and site-level study. Journal of Advances in Modeling Earth Systems, 9(5), 2190-2213. doi: 10.1002/2017MS001028. Recent studies indicated that Arctic lakes play an important role in receiving, processing, and storing organic carbon exported from terrestrial ecosystems. To quantify the contribution of Arctic lakes to the global carbon cycle, we developed a one-dimensional process-based Arctic Lake Biogeochemistry Model (ALBM) that explicitly simulates the dynamics of organic and inorganic carbon in Arctic lakes. By realistically modeling water mixing, carbon biogeochemistry, and permafrost carbon loading, the model can reproduce the seasonal variability of CO2 fluxes from the study Arctic lakes. The simulated area-weighted CO2 fluxes from yedoma thermokarst lakes, nonyedoma thermokarst lakes, and glacial lakes are 29.5, 13.0, and 21.4 g C m−2 yr−1, respectively, close to the observed values (31.2, 17.2, and 16.5 ± 7.7 g C m−2 yr−1, respectively). The simulations show that the high CO2 fluxes from yedoma thermokarst lakes are stimulated by the biomineralization of mobilized labile organic carbon from thawing yedoma permafrost. The simulations also imply that the relative contribution of glacial lakes to the global carbon cycle could be the largest because of their much larger surface area and high biomineralization and carbon loading. According to the model, sunlight-induced organic carbon degradation is more important for shallow nonyedoma thermokarst lakes but its overall contribution to the global carbon cycle could be limited. Overall, the ALBM can simulate the whole-lake carbon balance of Arctic lakes, a difficult task for field and laboratory experiments and other biogeochemistry models. 9315 Arctic region; 0428 Carbon cycling; 0414 Biogeochemical cycles, processes, and modeling; 0708 Thermokarst; 0746 Lakes; Arctic lake biogeochemistry; CO2 fluxes; glacial lakes; lake biogeochemistry model; thermokarst lakes; yedoma lakes
Tang, Wenjun; Qin, Jun; Yang, Kun; Niu, Xiaolei; Min, Min; Liang, ShunlinTang, W., J. Qin, K. Yang, X. Niu, M. Min, S. Liang, 2017: An efficient algorithm for calculating photosynthetically active radiation with MODIS products. Remote Sensing of Environment, 194, 146-154. doi: 10.1016/j.rse.2017.03.028. Photosynthetically active radiation (PAR) is the critical forcing data in ecological and agricultural fields. Remote sensing can be utilized to derive spatiotemporally continuous PAR. Empirical algorithms can be used to quickly retrieve surface PAR data sets, but their accuracy cannot be guaranteed in regions without local calibration. Physical algorithms generally incorporate all relevant physical processes and can be used globally, but their computational efficiency is often low. In this paper, an efficient algorithm is developed to calculate surface PAR by combining a clear-sky PAR model and the parameterizations for cloud transmittances. In the algorithm, the transmittances for water vapor, ozone, Rayleigh, aerosol, and cloud are each handled across the whole PAR band (400–700 nm). In addition, the contribution of the multiple reflections between surface ground and the atmosphere are also expressly considered. The new algorithm is applied to estimate instantaneous PAR with inputs from Moderate Resolution Imaging Spectroradiometer (MODIS) products onboard both Terra and Aqua platforms. The daily PAR is estimated from these two instantaneous values by an upscaling method. The instantaneous and daily PAR estimates were validated with in situ data collected in the USA and China. The results indicate that the new algorithm, based on MODIS products, can effectively retrieve PAR with root mean square errors (RMSE) of about 40 W m− 2 and 15 W m− 2 at instantaneous and daily-mean time scales, respectively. These performances are generally better than those of previous studies. algorithm; radiative transfer; MODIS; Photosynthetically active radiation
Thampi, Bijoy; Wong, Takmeng; Lukashin, Constantin; Loeb, Norman GThampi, B., T. Wong, C. Lukashin, N. G. Loeb, 2017: Determination of CERES TOA fluxes using Machine learning algorithms. Part I: Classification and retrieval of CERES cloudy and clear scenes. J. Atmos. Oceanic Technol., 34(10), 2329–2345. doi: 10.1175/JTECH-D-16-0183.1. Continuous monitoring of the Earth radiation budget (ERB) is critical to our understanding of the Earth’s climate and its variability with time. The Clouds and the Earth’s Radiant Energy System (CERES) instrument is able to provide a long record of ERB for such scientific studies. This manuscript, which is first of a two-part paper, describes the new CERES algorithm for improving the clear/cloudy scene classification without the use of coincident cloud imager data. This new CERES algorithm is based on a subset of modern artificial intelligence (AI) paradigm called Machine Learning (ML) algorithms. This paper describes development and application of the ML algorithm known as Random Forests (RF) which is used to classify CERES broadband footprint measurements into clear and cloudy scenes. Results from the RF analysis carried using the CERES Single Scanner Footprint (SSF) data for the months of January and July are presented in the manuscript. The daytime RF misclassification rate (MCR) shows relatively large values (>30%) for snow, sea ice and bright desert surface types while lower values of (
Tollenaar, Matthijs; Fridgen, Jon; Tyagi, Priyanka; Stackhouse Jr, Paul W.; Kumudini, SarathaTollenaar, M., J. Fridgen, P. Tyagi, P. W. Stackhouse Jr, S. Kumudini, 2017: The contribution of solar brightening to the US maize yield trend. Nature Clim. Change, 7(4), 275-278. doi: 10.1038/nclimate3234.
Trenberth, Kevin E.; Fasullo, John T.Trenberth, K. E., J. T. Fasullo, 2017: Atlantic meridional heat transports computed from balancing Earth's energy locally. Geophysical Research Letters, 44(4), 1919–1927. doi: 10.1002/2016GL072475. The Atlantic Meridional Overturning Circulation (AMOC) plays a major role in moving heat and carbon around in the ocean. A new estimate of ocean heat transports for 2000 through 2013 throughout the Atlantic is derived. Top-of-atmosphere radiation is combined with atmospheric reanalyses to estimate surface heat fluxes, and combined with vertically-integrated ocean heat content to estimate ocean heat transport divergence as a residual. Atlantic peak northward ocean heat transports average 1.18 ± 0.13 PW (1-sigma) at 15°N but vary considerably in latitude and time. Results agree well with observational estimates at 26.5°N from the RAPID array but for 2004-13 the meridional heat transport is 1.00 ± 0.11 vs 1.23 ± 0.11 PW for RAPID. In addition, these results have no hint of a trend, unlike the RAPID results. Strong westerlies north of a meridian drive ocean currents and an ocean heat loss into the atmosphere that is exacerbated by a decrease in ocean heat transport northwards. energy budgets; 1620 Climate dynamics; 3305 Climate change and variability; 3319 General circulation; 3339 Ocean/atmosphere interactions; 4532 General circulation; AMOC variability; atmospheric energy; climate dynamics; ocean heat transport; RAPID array
Ullman, D. J.; Schmittner, A.Ullman, D. J., A. Schmittner, 2017: A cloud feedback emulator (CFE, version 1.0) for an intermediate complexity model. Geosci. Model Dev., 10(2), 945-958. doi: 10.5194/gmd-10-945-2017.
Urbain, Manon; Clerbaux, Nicolas; Ipe, Alessandro; Tornow, Florian; Hollmann, Rainer; Baudrez, Edward; Velazquez Blazquez, Almudena; Moreels, JohanUrbain, M., N. Clerbaux, A. Ipe, F. Tornow, R. Hollmann, E. Baudrez, A. Velazquez Blazquez, J. Moreels, 2017: The CM SAF TOA Radiation Data Record Using MVIRI and SEVIRI. Remote Sensing, 9(5), 466. doi: 10.3390/rs9050466. The CM SAF Top of Atmosphere (TOA) Radiation MVIRI/SEVIRI Data Record provides a homogenised satellite-based climatology of TOA Reflected Solar (TRS) and Emitted Thermal (TET) radiation in all-sky conditions over the Meteosat field of view. The continuous monitoring of these two components of the Earth Radiation Budget is of prime importance to study climate variability and change. Combining the Meteosat MVIRI and SEVIRI instruments allows an unprecedented temporal (30 min/15 min) and spatial (2.5 km/3 km) resolution compared to, e.g., the CERES products. It also opens the door to the generation of a long data record covering a 32 years time period and extending from 1 February 1983 to 30 April 2015. The retrieval method used to process the CM SAF TOA Radiation MVIRI/SEVIRI Data Record is discussed. The overlap between the MVIRI and GERB instruments in the period 2004–2006 is used to derive empirical narrowband to broadband regressions. The CERES TRMM angular dependency models and theoretical models are respectively used to compute the TRS and TET fluxes from the broadband radiances. The TOA radiation products are issued as daily means, monthly means and monthly averages of the hourly integrated values (diurnal cycle). The data is provided on a regular grid at a spatial resolution of 0.05 degrees and covers the region 70 ∘ N–70 ∘ S and 70 ∘ W–70 ∘ E. The quality of the data record has been evaluated by intercomparison with several references. In general, the stability in time of the data record is found better than 4 Wm − 2 and most products fulfill the predefined accuracy requirements. earth radiation budget; SEVIRI; Meteosat; climate data record; emitted thermal; MVIRI; reflected solar; top-of-atmosphere radiation
Usinowicz, Jacob; Chang-Yang, Chia-Hao; Chen, Yu-Yun; Clark, James S.; Fletcher, Christine; Garwood, Nancy C.; Hao, Zhanqing; Johnstone, Jill; Lin, Yiching; Metz, Margaret R.; Masaki, Takashi; Nakashizuka, Tohru; Sun, I.-Fang; Valencia, Renato; Wang, Yunyun; Zimmerman, Jess K.; Ives, Anthony R.; Wright, S. JosephUsinowicz, J., C. Chang-Yang, Y. Chen, J. S. Clark, C. Fletcher, N. C. Garwood, Z. Hao, J. Johnstone, Y. Lin, M. R. Metz, T. Masaki, T. Nakashizuka, I. Sun, R. Valencia, Y. Wang, J. K. Zimmerman, A. R. Ives, S. J. Wright, 2017: Temporal coexistence mechanisms contribute to the latitudinal gradient in forest diversity. Nature, 550(7674), 105. doi: 10.1038/nature24038. High tree species diversity in tropical forests is driven by reduced interspecific competition relative to intraspecific competition, as a result of the asynchronous timing of tree recruitment permitted by long and stable growing seasons.
Ussiri, David A. N.; Lal, RattanUssiri, D. A. N., R. Lal, 2017: Introduction: Climate Overview. Carbon Sequestration for Climate Change Mitigation and Adaptation, 1-25. Energy exchange between Sun, Earth, and space controls the global climate. Earth is in dynamic equilibrium such that it receives the radiation from the Sun and emits the same amount of heat as infrared (IR) energy to space. Earth’s energy imbalance is the difference between the incoming solar radiation absorbed by the Earth and the amount of heat the Earth radiates to the space. If positive imbalance occurs, such that the incoming radiation from the Sun is more than outgoing heat from the Earth, Earth becomes warmer. In contrast, if the imbalance is negative, such that more energy is going out than it receives, then Earth will cool. Earth’s energy imbalance is the single most important measure of the status of the Earth’s climate system which defines the expectations of future global climate change resulting from the anthropogenic perturbation or the greenhouse effect. The energy budget of the Earth’s climate system is discussed in this chapter. The processes that Earth retains more electromagnetic radiation energy than it receives are also explained. In addition, the role of greenhouse gases (GHGs) in regulating the energy balance is discussed with the emphasis on carbon dioxide (CO2). The concentrations of GHGs have increased significantly since the Industrial Revolution ~ circa 1750. Most notable is the increase in concentration of CO2 which have played a significant role in the current and future global temperature increases. infrared radiation; climate change; energy budget; ultraviolet radiation; greenhouse gases; global warming; Agriculture; Climate system; Soil Science & Conservation
Valenzuela, A.; Costa, M. J.; Guerrero-Rascado, J. L.; Bortoli, D.; Olmo, F. J.Valenzuela, A., M. J. Costa, J. L. Guerrero-Rascado, D. Bortoli, F. J. Olmo, 2017: Solar and thermal radiative effects during the 2011 extreme desert dust episode over Portugal. Atmospheric Environment, 148, 16-29. doi: 10.1016/j.atmosenv.2016.10.037. This paper analyses the influence of the extreme Saharan desert dust (DD) event on shortwave (SW) and longwave (LW) radiation at the EARLINET/AERONET Évora station (Southern Portugal) from 4 up to 7 April 2011. There was also some cloud occurrence in the period. In this context, it is essential to quantify the effect of cloud presence on aerosol radiative forcing. A radiative transfer model was initialized with aerosol optical properties, cloud vertical properties and meteorological atmospheric vertical profiles. The intercomparison between the instantaneous TOA shortwave and longwave fluxes derived using CERES and those calculated using SBDART, which was fed with aerosol extinction coefficients derived from the CALIPSO and lidar-PAOLI observations, varying OPAC dataset parameters, was reasonably acceptable within the standard deviations. The dust aerosol type that yields the best fit was found to be the mineral accumulation mode. Therefore, SBDART model constrained with the CERES observations can be used to reliably determine aerosol radiative forcing and heating rates. Aerosol radiative forcings and heating rates were derived in the SW (ARFSw, AHRSw) and LW (ARFLw, AHRLw) spectral ranges, considering a cloud-aerosol free reference atmosphere. We found that AOD at 440 nm increased by a factor of 5 on 6 April with respect to the lower dust load on 4 April. It was responsible by a strong cooling radiative effect pointed out by the ARFSw value (−99 W/m2 for a solar zenith angle of 60°) offset by a warming radiative effect according to ARFLw value (+21.9 W/m2) at the surface. Overall, about 24% and 12% of the dust solar radiative cooling effect is compensated by its longwave warming effect at the surface and at the top of the atmosphere, respectively. Hence, larger aerosol loads could enhance the response between the absorption and re-emission processes increasing the ARFLw with respect to those associated with moderate and low aerosol loads. The unprecedented results derived from this work complement the findings in other regions on the modifications of radiative energy budget by the dust aerosols, which could have relevant influences on the regional climate and will be topics for future investigations. forcing; dust; AERONET; Aerosol vertical profiles; EARLINET
Váňa, Filip; Düben, Peter; Lang, Simon; Palmer, Tim; Leutbecher, Martin; Salmond, Deborah; Carver, GlennVáňa, F., P. Düben, S. Lang, T. Palmer, M. Leutbecher, D. Salmond, G. Carver, 2017: Single precision in weather forecasting models: An evaluation with the IFS. Mon. Wea. Rev., 145(2), 495–502. doi: 10.1175/MWR-D-16-0228.1. Earth’s climate is a nonlinear dynamical system with scale-dependent Lyapunov exponents. As such, an important theoretical question for modelling weather and climate is how much real information is carried in a model’s physical variables as a function of scale and variable type. Answering this question is of crucial practical importance given that the development of weather and climate models is strongly constrained by available supercomputer power. As a starting point for answering this question, the impact of limiting almost all real-number variables in the forecasting mode of ECMWF Integrated Forecast System (IFS) from 64 to 32 bits is investigated. Results for annual integrations and medium-range ensemble forecasts indicate no noticeable reduction in accuracy, and an average gain in computational efficiency by approximately 40%. This study provides the motivation for more scale-selective reductions in numerical precision.
Wall, Casey J.; Hartmann, Dennis L.; Ma, Po-LunWall, C. J., D. L. Hartmann, P. Ma, 2017: Instantaneous Linkages between Clouds and Large-Scale Meteorology over the Southern Ocean in Observations and a Climate Model. J. Climate, 30(23), 9455-9474. doi: 10.1175/JCLI-D-17-0156.1. Instantaneous, coincident, footprint-level satellite observations of cloud properties and radiation taken during austral summer over the Southern Ocean are used to study relationships between clouds and large-scale meteorology. Cloud properties are very sensitive to the strength of vertical motion in the midtroposphere, and low-cloud properties are sensitive to estimated inversion strength, low-level temperature advection, and sea surface temperature. These relationships are quantified. An index for the meteorological anomalies associated with midlatitude cyclones is presented, and it is used to reveal the sensitivity of clouds to the meteorology within the warm and cold sectors of cyclones.The observed relationships between clouds and meteorology are compared to those in the Community Atmosphere Model, version 5 (CAM5), using satellite simulators. Low clouds simulated by CAM5 are too few, are too bright, and contain too much ice. In the cold sector of cyclones, the low clouds are also too sensitive to variations in the meteorology. When CAM5 is coupled with an updated boundary layer parameterization known as Cloud Layers Unified by Binormals (CLUBB), bias in the ice content of low clouds is dramatically reduced. More generally, this study demonstrates that examining the instantaneous time scale is a powerful approach to understanding the physical processes that control clouds and how they are represented in climate models. Such an evaluation goes beyond the cloud climatology and exposes model bias under various meteorological conditions.
Wang, Chunlei; Tang, Bo-Hui; Wu, Hua; Tang, Ronglin; Li, Zhao-LiangWang, C., B. Tang, H. Wu, R. Tang, Z. Li, 2017: Estimation of Downwelling Surface Longwave Radiation under Heavy Dust Aerosol Sky. Remote Sensing, 9(3), 207. doi: 10.3390/rs9030207. The variation of aerosols, especially dust aerosol, in time and space plays an important role in climate forcing studies. Aerosols can effectively reduce land surface longwave emission and re-emit energy at a colder temperature, which makes it difficult to estimate downwelling surface longwave radiation (DSLR) with satellite data. Using the latest atmospheric radiative transfer code (MODTRAN 5.0), we have simulated the outgoing longwave radiation (OLR) and DSLR under different land surface types and atmospheric profile conditions. The results show that dust aerosol has an obvious “warming” effect to longwave radiation compared with other aerosols; that aerosol longwave radiative forcing (ALRF) increased with the increasing of aerosol optical depth (AOD); and that the atmospheric water vapor content (WVC) is critical to the understanding of ALRF. A method is proposed to improve the accuracy of DSLR estimation from satellite data for the skies under heavy dust aerosols. The AOD and atmospheric WVC under cloud-free conditions with a relatively simple satellite-based radiation model yielding the high accurate DSLR under heavy dust aerosol are used explicitly as model input to reduce the effects of dust aerosol on the estimation of DSLR. Validations of the proposed model with satellites data and field measurements show that it can estimate the DSLR accurately under heavy dust aerosol skies. The root mean square errors (RMSEs) are 20.4 W/m2 and 24.2 W/m2 for Terra and Aqua satellites, respectively, at the Yingke site, and the biases are 2.7 W/m2 and 9.6 W/m2, respectively. For the Arvaikheer site, the RMSEs are 23.2 W/m2 and 19.8 W/m2 for Terra and Aqua, respectively, and the biases are 7.8 W/m2 and 10.5 W/m2, respectively. The proposed method is especially applicable to acquire relatively high accurate DSLR under heavy dust aerosol using MODIS data with available WVC and AOD data. MODIS; dust aerosol; aerosol optical depth (AOD); downwelling surface longwave radiation (DSLR)
Wang, D.; Liang, S.Wang, D., S. Liang, 2017: Estimating Top-of-Atmosphere Daily Reflected Shortwave Radiation Flux Over Land From MODIS Data. IEEE Transactions on Geoscience and Remote Sensing, 55(7), 4022-4031. doi: 10.1109/TGRS.2017.2686599. High-spatial resolution data of the top-of-atmosphere (TOA) reflected shortwave radiation flux are needed to understand the effects of local-scale anthropogenic and natural processes on earth’s radiation budget. A previous study developed an algorithm to estimate the TOA instantaneous shortwave component from polar-orbiting Moderate Resolution Imaging Spectroradiometer (MODIS) data. This paper presents a temporal scaling approach to predict daily values of TOA reflected shortwave radiation flux from temporally sparse MODIS observations. Radiative transfer simulation and statistical regression are used to establish the relationship between daily shortwave flux and MODIS spectral reflectance. A comparison between the Terra and Aqua combined MODIS computed data and the Clouds and the Earth’s Radiant Energy System SYN1deg product of 1° regional daily shortwave fluxes have a bias of 3.8 W/ $\textm^2$ with a root-mean-square error (RMSE) of 13.3 W/ $\textm^2$ using data from 2009 over eight subsets across various latitudes. Comparing the regional monthly shortwave fluxes reduces the RMSE to 6.9 W/ $\textm^2$ . The longer the averaging period the lower the uncertainty is self-explanatory. clouds; Earth; Satellites; MODIS; Shortwave radiation; Atmospheric modeling; radiation budget; Moderate Resolution Imaging Spectroradiometer (MODIS); Sensors; Clouds and the Earth’s Radiant Energy System (CERES); top-of-atmosphere (TOA) flux
Wang, Gongjie; Cheng, Lijing; Abraham, John; Li, ChongyinWang, G., L. Cheng, J. Abraham, C. Li, 2017: Consensuses and discrepancies of basin-scale ocean heat content changes in different ocean analyses. Climate Dynamics, 1-17. doi: 10.1007/s00382-017-3751-5. Inconsistent global/basin ocean heat content (OHC) changes were found in different ocean subsurface temperature analyses, especially in recent studies related to the slowdown in global surface temperature rise. This finding challenges the reliability of the ocean subsurface temperature analyses and motivates a more comprehensive inter-comparison between the analyses. Here we compare the OHC changes in three ocean analyses (Ishii, EN4 and IAP) to investigate the uncertainty in OHC in four major ocean basins from decadal to multi-decadal scales. First, all products show an increase of OHC since 1970 in each ocean basin revealing a robust warming, although the warming rates are not identical. The geographical patterns, the key modes and the vertical structure of OHC changes are consistent among the three datasets, implying that the main OHC variabilities can be robustly represented. However, large discrepancies are found in the percentage of basinal ocean heating related to the global ocean, with the largest differences in the Pacific and Southern Ocean. Meanwhile, we find a large discrepancy of ocean heat storage in different layers, especially within 300–700 m in the Pacific and Southern Oceans. Furthermore, the near surface analysis of Ishii and IAP are consistent with sea surface temperature (SST) products, but EN4 is found to underestimate the long-term trend. Compared with ocean heat storage derived from the atmospheric budget equation, all products show consistent seasonal cycles of OHC in the upper 1500 m especially during 2008 to 2012. Overall, our analyses further the understanding of the observed OHC variations, and we recommend a careful quantification of errors in the ocean analyses.
Wang, Hailan; Su, Wenying; Loeb, Norman G.; Achuthavarier, Deepthi; Schubert, Siegfried D.Wang, H., W. Su, N. G. Loeb, D. Achuthavarier, S. D. Schubert, 2017: The Role of DYNAMO In-situ Observations in Improving NASA CERES-like Daily Surface and Atmospheric Radiative Flux Estimates. Earth and Space Science, 4(4), 164–183. doi: 10.1002/2016EA000248. The daily surface and atmospheric radiative fluxes from NASA Clouds and the Earth's Radiant Energy System (CERES) SYN1deg Ed3A are among the most widely used data to study cloud-radiative feedback. The CERES SYN1deg data are based on Fu-Liou radiative transfer computations that use specific humidity (Q) and air temperature (T) from NASA Global Modeling and Assimilation Office (GMAO) reanalyses as inputs, and are therefore subject to the quality of those fields. This study uses in-situ Q and T observations collected during the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign to augment the input stream used in the NASA GMAO reanalysis and assess the impact on the CERES daily surface and atmospheric longwave estimates. The results show that the assimilation of DYNAMO observations considerably improves the vertical profiles of analyzed Q and T over and near DYNAMO stations by moistening and warming the lower troposphere and upper troposphere and drying and cooling the mid-upper troposphere. As a result of these changes in Q and T, the computed CERES daily surface downward longwave flux increases by about 5 Wm-2, due mainly to the warming and moistening in the lower troposphere; the computed daily top-of-atmosphere (TOA) outgoing longwave radiation increases by 2-3 Wm-2 during dry periods only. Correspondingly, the estimated local atmospheric longwave radiative cooling enhances by about 5 Wm-2 (7-8 Wm-2) during wet (dry) periods. These changes reduce the bias in the CERES SYN1deg-like daily longwave estimates at both the TOA and surface, and represent an improvement over the DYNAMO region. This article is protected by copyright. All rights reserved. 1616 Climate variability; 3315 Data assimilation; 0434 Data sets; 7847 Radiation processes; CERES surface and atmospheric radiation estimation; DYNAMO in-situ observations; NASA GMAO reanalysis
Wang, Lei-Di; LÜ, Da-RenWang, L., D. LÜ, 2017: Downward surface shortwave radiation over the subtropical Asia–Pacific region simulated by CMIP5 models. Atmospheric and Oceanic Science Letters, 10(2), 130-137. doi: 10.1080/16742834.2017.1259541. The downward surface shortwave radiation (DSSR) over the subtropical Asia–Pacific region simulated by the historical experiments of 15 CMIP5 models is evaluated in this study. The simulated DSSR is compared against two satellite observational datasets, and the possible causes for the DSSR bias of the models are further investigated by dividing the subtropical Asia–Pacific region into five areas. Most of the CMIP5 models underestimate DSSR over the oceans, but overestimate DSSR over land. Aside from the Mediterranean–West Asia (MWA) and Central Asia (CA) areas, both the biases in annual and seasonal mean DSSR are well explained by the bias in surface shortwave cloud radiative forcing (CRF), with an overestimation of the CRF effect over the subtropical North Pacific but an underestimation over other land regions. The effect of cloud plays a dominant role over the subtropical Asia–Pacific region, with relatively weaker influences over MWA and CA in boreal summer and fall. CMIP5; cloud radiative forcing; surface shortwave radiation; 云辐射强迫; 太阳总辐射
Wei, Jiangfeng; Jin, Qinjian; Yang, Zong-Liang; Zhou, LimingWei, J., Q. Jin, Z. Yang, L. Zhou, 2017: Land–atmosphere–aerosol coupling in North China during 2000–2013. International Journal of Climatology, 37(S1), 1297–1306. doi: 10.1002/joc.4993. North China is one of the most densely populated regions in the world. To its west, north, and northwest, the world's largest afforestation project has been going on for decades. At the same time, North China has been suffering from air pollution because of its large fossil fuel consumption. Here we show that the changes in land cover and aerosol concentration are coupled with the variations of land surface temperature, cloud cover, and surface solar radiation during the summer 2000–2013. Model experiments show that the interannual variation of aerosol concentration in North China is mainly a result of the varying atmospheric circulation. The increasing vegetation cover due to afforestation has enhanced surface evapotranspiration (ET) and cooled the local surface, and precipitation is observed to be increasing with ET. The model with prescribed increasing vegetation cover can simulate the increasing ET but cannot reproduce the increasing precipitation. Although this may be caused by model biases, the lack of aerosol processes in the model could also be a potential cause. aerosol; vegetation; China; land
Wei, Nan; Zhou, Liming; Dai, Yongjiu; Xia, Geng; Hua, WenjianWei, N., L. Zhou, Y. Dai, G. Xia, W. Hua, 2017: Observational Evidence for Desert Amplification Using Multiple Satellite Datasets. Scientific Reports, 7(1), 2043. doi: 10.1038/s41598-017-02064-w. Desert amplification identified in recent studies has large uncertainties due to data paucity over remote deserts. Here we present observational evidence using multiple satellite-derived datasets that desert amplification is a real large-scale pattern of warming mode in near surface and low-tropospheric temperatures. Trend analyses of three long-term temperature products consistently confirm that near-surface warming is generally strongest over the driest climate regions and this spatial pattern of warming maximizes near the surface, gradually decays with height, and disappears in the upper troposphere. Short-term anomaly analyses show a strong spatial and temporal coupling of changes in temperatures, water vapor and downward longwave radiation (DLR), indicating that the large increase in DLR drives primarily near surface warming and is tightly associated with increasing water vapor over deserts. Atmospheric soundings of temperature and water vapor anomalies support the results of the long-term temperature trend analysis and suggest that desert amplification is due to comparable warming and moistening effects of the troposphere. Likely, desert amplification results from the strongest water vapor feedbacks near the surface over the driest deserts, where the air is very sensitive to changes in water vapor and thus efficient in enhancing the longwave greenhouse effect in a warming climate.
Williams, Ian N.; Pierrehumbert, Raymond T.Williams, I. N., R. T. Pierrehumbert, 2017: Observational evidence against strongly stabilizing tropical cloud feedbacks. Geophysical Research Letters, 44(3), 1503–1510. doi: 10.1002/2016GL072202. We present a method to attribute cloud radiative feedbacks to convective processes, using subcloud layer buoyancy as a diagnostic of stable and deep convective regimes. Applying this approach to tropical remote sensing measurements over years 2000–2016 shows that an inferred negative short-term cloud feedback from deep convection was nearly offset by a positive cloud feedback from stable regimes. The net cloud feedback was within statistical uncertainty of the National Center for Atmospheric Research Community Atmosphere Model (CAM5) with historical forcings, with discrepancies in the partitioning of the cloud feedback into convective regimes. Compensation between high-cloud responses to tropics-wide warming in stable and unstable regimes resulted in smaller net changes in high-cloud fraction with warming. In addition, deep convection and associated high clouds set in at warmer temperatures in response to warming, as a consequence of nearly invariant subcloud buoyancy. This invariance further constrained the magnitude of cloud radiative feedbacks and is consistent with climate model projections. Remote sensing; cloud; Feedback; 3305 Climate change and variability; 3337 Global climate models; 3310 Clouds and cloud feedbacks; 3371 Tropical convection; deep convection; tropical; tropical circulation
Wolf, Sebastian; Yin, Dongqin; Roderick, Michael L.Wolf, S., D. Yin, M. L. Roderick, 2017: Using radiative signatures to diagnose the cause of warming during the 2013–2014 Californian Drought. Journal of Hydrology, 553, 408-418. doi: 10.1016/j.jhydrol.2017.07.015. California recently experienced among the worst droughts of the last century, with exceptional precipitation deficits and co-occurring record high temperatures. The dry conditions caused severe water shortages in one of the economically most important agricultural regions of the US. It has recently been hypothesized that anthropogenic warming is increasing the likelihood of such extreme droughts in California, or more specifically, that warmer temperatures from the enhanced greenhouse effect intensify drought conditions. However, separating the cause and effect is difficult because the dry conditions lead to a reduction in evaporative cooling that contributes to the warming. Here we investigate and compare the forcing of long-term greenhouse-induced warming with the short-term warming during the 2013–2014 Californian drought. We use the concept of radiative signatures to investigate the source of the radiative perturbation during the drought, relate the signatures to expected changes due to anthropogenic warming, and assess the cause of warming based on observed changes in the surface energy balance compared to the period 2001–2012. We found that the recent meteorological drought based on precipitation deficits was characterised by an increase in incoming shortwave radiation coupled with a decline in incoming longwave radiation, which contributed to record warm temperatures. In contrast, climate models project that anthropogenic warming is accompanied by little change in incoming shortwave but a large increase in incoming longwave radiation. The warming during the drought was associated with increased incoming shortwave radiation in combination with reduced evaporative cooling from water deficits, which enhanced surface temperatures and sensible heat transfer to the atmosphere. Our analyses demonstrate that radiative signatures are a powerful tool to differentiate the source of perturbations in the surface energy balance at monthly to seasonal time scales. drought; Greenhouse effect; Anthropogenic warming; California; Land-surface feedbacks; Radiative signature
Wu, Peng; Dong, Xiquan; Xi, Baike; Liu, Yangang; Thieman, Mandana; Minnis, PatrickWu, P., X. Dong, B. Xi, Y. Liu, M. Thieman, P. Minnis, 2017: Effects of environment forcing on marine boundary layer cloud-drizzle processes. Journal of Geophysical Research: Atmospheres, 122(8), 4463–4478. doi: 10.1002/2016JD026326. Determining the factors affecting drizzle formation in marine boundary layer (MBL) clouds remains a challenge for both observation and modeling communities. To investigate the roles of vertical wind shear and buoyancy (static instability) in drizzle formation, ground-based observations from the Atmospheric Radiation Measurement Program at the Azores are analyzed for two types of conditions. The type I clouds should last for at least 5 h and more than 90% time must be nondrizzling and then followed by at least 2 h of drizzling periods, while the type II clouds are characterized by mesoscale convection cellular structures with drizzle occur every 2 to 4 h. By analyzing the boundary layer wind profiles (direction and speed), it was found that either directional or speed shear is required to promote drizzle production in the type I clouds. Observations and a recent model study both suggest that vertical wind shear helps the production of turbulent kinetic energy (TKE), stimulates turbulence within cloud layer, and enhances drizzle formation near the cloud top. The type II clouds do not require strong wind shear to produce drizzle. The small values of lower tropospheric stability (LTS) and negative Richardson number (Ri) in the type II cases suggest that boundary layer instability plays an important role in TKE production and cloud-drizzle processes. By analyzing the relationships between LTS and wind shear for all cases and all time periods, a stronger connection was found between LTS and wind directional shear than that between LTS and wind speed shear. 0320 Cloud physics and chemistry; 3311 Clouds and aerosols; 3360 Remote sensing; 3354 Precipitation; 3307 Boundary layer processes; boundary layer static instability; drizzle formation; vertical wind shear
Xiang, Baoqiang; Zhao, Ming; Held, Isaac M.; Golaz, Jean-ChristopheXiang, B., M. Zhao, I. M. Held, J. Golaz, 2017: Predicting the severity of spurious “double ITCZ” problem in CMIP5 coupled models from AMIP simulations. Geophysical Research Letters, 44(3), 1520–1527. doi: 10.1002/2016GL071992. The severity of the double Intertropical Convergence Zone (DI) problem in climate models can be measured by a tropical precipitation asymmetry index (PAI), indicating whether tropical precipitation favors the Northern Hemisphere or the Southern Hemisphere. Examination of 19 Coupled Model Intercomparison Project phase 5 models reveals that the PAI is tightly linked to the tropical sea surface temperature (SST) bias. As one of the factors determining the SST bias, the asymmetry of tropical net surface heat flux in Atmospheric Model Intercomparison Project (AMIP) simulations is identified as a skillful predictor of the PAI change from an AMIP to a coupled simulation, with an intermodel correlation of 0.90. Using tropical top-of-atmosphere (TOA) fluxes, the correlations are lower but still strong. However, the extratropical asymmetries of surface and TOA fluxes in AMIP simulations cannot serve as useful predictors of the PAI change. This study suggests that the largest source of the DI bias is from the tropics and from atmospheric models. CMIP5; 1627 Coupled models of the climate system; 3373 Tropical dynamics; 1854 Precipitation; double ITCZ; precipitation asymmetry index; SST bias; surface heat flux bias
Xu, Kuan-Man; Li, Zhujun; Cheng, Anning; Blossey, Peter N.; Stan, CristianaXu, K., Z. Li, A. Cheng, P. N. Blossey, C. Stan, 2017: Differences in the hydrological cycle and sensitivity between multiscale modeling frameworks with and without a higher-order turbulence closure. Journal of Advances in Modeling Earth Systems, 9(5), 2120-2137. doi: 10.1002/2017MS000970. Current conventional global climate models (GCMs) produce a weak increase in global-mean precipitation with anthropogenic warming in comparison with the lower tropospheric moisture increases. The motive of this study is to understand the differences in the hydrological sensitivity between two multiscale modeling frameworks (MMFs) that arise from the different treatments of turbulence and low clouds in order to aid to the understanding of the model spread among conventional GCMs. We compare the hydrological sensitivity and its energetic constraint from MMFs with (SPCAM-IPHOC) or without (SPCAM) an advanced higher-order turbulence closure. SPCAM-IPHOC simulates higher global hydrological sensitivity for the slow response but lower sensitivity for the fast response than SPCAM. Their differences are comparable to the spreads of conventional GCMs. The higher sensitivity in SPCAM-IPHOC is associated with the higher ratio of the changes in latent heating to those in net atmospheric radiative cooling, which is further related to a stronger decrease in the Bowen ratio with warming than in SPCAM. The higher sensitivity of cloud radiative cooling resulting from the lack of low clouds in SPCAM is another major factor in contributing to the lower precipitation sensitivity. The two MMFs differ greatly in the hydrological sensitivity over the tropical lands, where the simulated sensitivity of surface sensible heat fluxes to surface warming and CO2 increase in SPCAM-IPHOC is weaker than in SPCAM. The difference in divergences of dry static energy flux simulated by the two MMFs also contributes to the difference in land precipitation sensitivity between the two models. 3337 Global climate models; 3310 Clouds and cloud feedbacks; 3314 Convective processes; 3354 Precipitation; 3307 Boundary layer processes; low clouds; MMF; energetic constraint; higher-order turbulence closure; hydrological sensitivity; precipitation change
Xu, Kuan-Man; Wong, Takmeng; Dong, Shengtao; Chen, Feng; Kato, Seiji; Taylor, Patrick C.Xu, K., T. Wong, S. Dong, F. Chen, S. Kato, P. C. Taylor, 2017: Cloud object analysis of CERES Aqua observations of tropical and subtropical cloud regimes: Evolution of cloud object size distributions during the Madden–Julian Oscillation. Journal of Quantitative Spectroscopy and Radiative Transfer, 188, 148–158. doi: 10.1016/j.jqsrt.2016.06.008. In this study, we analyze cloud object data from the Aqua satellite between July 2006 and June 2010 that are matched with the real-time multivariate Madden–Julian Oscillation (MJO) index to examine the impact of MJO evolution on the evolutions of the size distributions of cloud object types. These types include deep convective (DC), cirrostratus, shallow cumulus, stratocumulus and overcast-stratus. A cloud object is a contiguous region of the earth with a single dominant cloud-system type. It is found that the cloud object size distributions of some phases depart greatly from the 8-phase combined distribution at large cloud-object diameters. The large-size group of cloud objects contributes to most of the temporal variations during the MJO evolution. For deep convective and cirrostratus cloud objects, there is a monotonic increase in both the number and footprint of large objects from the depressed to mature phases, which is attributed to the development and maturing of deep convection and anvils. The largest increase in the mean diameter during the mature phases that lasts to the early dissipating phase is related to growth of anvil clouds and is accompanied by moderate decreases in small-size objects. For shallow cumulus, the large objects decrease in number at the mature phases, but increase in number for both sizes before the mature phase. The opposite is true for the large overcast-stratus objects. The temporal evolution of large stratocumulus objects is similar to that of deep convective and cirrostratus object types except for peaking slightly earlier. CERES; Aqua observations; cloud regimes; Cloud size distribution; Madden-Julian Oscillation
Yahya, Khairunnisa; Wang, Kai; Campbell, Patrick; Chen, Ying; Glotfelty, Timothy; He, Jian; Pirhalla, Michael; Zhang, YangYahya, K., K. Wang, P. Campbell, Y. Chen, T. Glotfelty, J. He, M. Pirhalla, Y. Zhang, 2017: Decadal application of WRF/Chem for regional air quality and climate modeling over the U.S. under the representative concentration pathways scenarios. Part 1: Model evaluation and impact of downscaling. Atmospheric Environment, 152, 562-583. doi: 10.1016/j.atmosenv.2016.12.029. An advanced online-coupled meteorology-chemistry model, i.e., the Weather Research and Forecasting Model with Chemistry (WRF/Chem), is applied for current (2001–2010) and future (2046–2055) decades under the representative concentration pathways (RCP) 4.5 and 8.5 scenarios to examine changes in future climate, air quality, and their interactions. In this Part I paper, a comprehensive model evaluation is carried out for current decade to assess the performance of WRF/Chem and WRF under both scenarios and the benefits of downscaling the North Carolina State University's (NCSU) version of the Community Earth System Model (CESM_NCSU) using WRF/Chem. The evaluation of WRF/Chem shows an overall good performance for most meteorological and chemical variables on a decadal scale. Temperature at 2-m is overpredicted by WRF (by ∼0.2–0.3 °C) but underpredicted by WRF/Chem (by ∼0.3–0.4 °C), due to higher radiation from WRF. Both WRF and WRF/Chem show large overpredictions for precipitation, indicating limitations in their microphysics or convective parameterizations. WRF/Chem with prognostic chemical concentrations, however, performs much better than WRF with prescribed chemical concentrations for radiation variables, illustrating the benefit of predicting gases and aerosols and representing their feedbacks into meteorology in WRF/Chem. WRF/Chem performs much better than CESM_NCSU for most surface meteorological variables and O3 hourly mixing ratios. In addition, WRF/Chem better captures observed temporal and spatial variations than CESM_NCSU. CESM_NCSU performance for radiation variables is comparable to or better than WRF/Chem performance because of the model tuning in CESM_NCSU that is routinely made in global models. Air quality-climate interactions; CESM; Decadal evaluation; The continental U.S.; WRF; WRF/Chem
Yang, Yang; Russell, Lynn M.; Lou, Sijia; Liao, Hong; Guo, Jianping; Liu, Ying; Singh, Balwinder; Ghan, Steven J.Yang, Y., L. M. Russell, S. Lou, H. Liao, J. Guo, Y. Liu, B. Singh, S. J. Ghan, 2017: Dust-wind interactions can intensify aerosol pollution over eastern China. Nature Communications, 8, 15333. doi: 10.1038/ncomms15333. Anthropogenic aerosol and calm conditions give rise to winter haze episodes in eastern China. Yang et al. show that these weak winds also decrease natural dust emissions, reducing the land–ocean temperature difference and associated winds, enhancing air stagnation…
Yu, L.; Adler, R.; Huffman, G.; Jin, X.; Kato, S.; Loeb, N.; Stackhouse, P.; Weller, R.; Wilber, A.Yu, L., R. Adler, G. Huffman, X. Jin, S. Kato, N. Loeb, P. Stackhouse, R. Weller, A. Wilber, 2017: Ocean surface heat and momentum fluxes [In "State of the Climate in 2016"]. Bull. Amer. Meteor. Soc., 97(8), S75-S79. doi: 10.1175/2017BAMSStateoftheClimate.1.
Yue, Qing; Kahn, Brian H.; Fetzer, Eric J.; Wong, Sun; Frey, Richard; Meyer, Kerry G.Yue, Q., B. H. Kahn, E. J. Fetzer, S. Wong, R. Frey, K. G. Meyer, 2017: On the response of MODIS cloud coverage to global mean surface air temperature. Journal of Geophysical Research: Atmospheres, 122(2), 966–979. doi: 10.1002/2016JD025174. The global surface temperature change (ΔTs) mediated cloud cover response is directly related to cloud-climate feedback. Using satellite remote sensing data to relate cloud and climate requires a well-calibrated, stable, and consistent long-term cloud data record. The Collection 5.1 (C5) Moderate Resolution Imaging Spectroradiometer (MODIS) cloud observations have been widely used for this purpose. However, the MODIS data quality varies greatly with the surface type, spectral region, cloud type, and time periods of study, which calls for additional caution when applying such data to studies on cloud cover temporal trends and variability. Using 15 years of cloud observations made by Terra and Aqua MODIS, we analyze the ΔTs-mediated cloud cover response for different cloud types by linearly regressing the monthly anomaly of cloud cover (ΔC) with the monthly anomaly of global Ts. The Collection 6 (C6) Aqua data exhibit a similar cloud response to the long-term counterpart simulated by advanced climate models. A robust increase in altitude with increasing ΔTs is found for high clouds, while a robust decrease of ΔC is noticed for optically thick low clouds. The large differences between C5 and C6 results are from improvements in calibration and cloud retrieval algorithms. The large positive cloud cover responses with data after 2010 and the strong sensitivity to time period obtained from the Terra (C5 and C6) data are likely due to calibration drift that has not been corrected, suggesting that the previous estimate of the short-term cloud cover response from the these data should be revisited. 3309 Climatology; 3305 Climate change and variability; 3310 Clouds and cloud feedbacks; MODIS; 3360 Remote sensing; short-term cloud feedback; temperature-mediated cloud cover response
Zelinka, Mark D.; Randall, David A.; Webb, Mark J.; Klein, Stephen A.Zelinka, M. D., D. A. Randall, M. J. Webb, S. A. Klein, 2017: Clearing clouds of uncertainty. Nature Climate Change, 7, 674–678. doi: doi:10.1038/nclimate3402.
Zhan, Yizhe; Davies, RogerZhan, Y., R. Davies, 2017: September Arctic sea-ice extent indicated by June reflected solar radiation. Journal of Geophysical Research: Atmospheres, 122(4), 2194–2202. doi: 10.1002/2016JD025819. The predictability of the minimum sea-ice extent (SIE) in the Arctic in September, especially for large anomaly years, is of strong current interest given the rapid decline in sea-ice amount. Our results show that June reflected solar radiation (RSR) is closely related to the underlying sea-ice condition in that month, and can be used to achieve September SIE predictions with good accuracy. The correlation coefficient between detrended June RSR and September SIE reaches 0.91 based on 16-yr satellite observations, and the relatively high forecast skill using MERRA2 reanalysis data is similar to or better than other complex prediction models. The results confirm the particular importance of the early summer sea-ice state and help to explain the abrupt declines of September SIE in the 21st century (2007, 2012). 0312 Air/sea constituent fluxes; CERES; 0758 Remote sensing; 0750 Sea ice; MISR; TOA albedo; 0766 Thermodynamics; 3238 Prediction; Sea-Ice Prediction
Zhang, Kai; Fu, Rong; Shaikh, Muhammad J.; Ghan, Steven; Wang, Minghuai; Leung, L. Ruby; Dickinson, Robert E.; Marengo, JoseZhang, K., R. Fu, M. J. Shaikh, S. Ghan, M. Wang, L. R. Leung, R. E. Dickinson, J. Marengo, 2017: Influence of Superparameterization and a Higher-Order Turbulence Closure on Rainfall Bias Over Amazonia in Community Atmosphere Model Version 5. Journal of Geophysical Research: Atmospheres, 122(18), 9879–9902. doi: 10.1002/2017JD026576. We evaluate the Community Atmosphere Model Version 5 (CAM5) with a higher-order turbulence closure scheme, named Cloud Layers Unified By Binomials (CLUBB), and a Multiscale Modeling Framework, referred to as the “superparameterization” (SP) with two different microphysics configurations to investigate their influences on rainfall simulations over southern Amazonia. The two different microphysics configurations in SP are the one-moment cloud microphysics without aerosol treatment (SP1) and two-moment cloud microphysics coupled with aerosol treatment (SP2). Results show that both SP2 and CLUBB effectively reduce the low biases of rainfall, mainly during the wet season, and reduce low biases of humidity in the lower troposphere with further reduced shallow clouds and increased surface solar flux. These changes increase moist static energy in the lower atmosphere and contribute to stronger convection and more rainfall. SP2 appears to realistically capture the observed increase of relative humidity prior to deep convection, and it significantly increases rainfall in the afternoon; CLUBB significantly delays the afternoon peak rainfall and produces more precipitation in the early morning, due to more gradual transition between shallow and deep convection. In CAM5 and CAM5 with CLUBB, occurrence of more deep convection appears to be a result of stronger heating rather than higher relative humidity. 0320 Cloud physics and chemistry; rainfall; 0321 Cloud/radiation interaction; Amazon; superparameterization; convective and cloud parameterizations
Zhang, Kexin; Goldberg, Mitchell D.; Sun, Fengying; Zhou, Lihang; Wolf, Walter W.; Tan, Changyi; Nalli, Nicholas R.; Liu, QuanhuaZhang, K., M. D. Goldberg, F. Sun, L. Zhou, W. W. Wolf, C. Tan, N. R. Nalli, Q. Liu, 2017: Estimation of Near Real-time Outgoing Longwave Radiation from Cross-track Infrared Sounder (CrIS) Radiance Measurements. J. Atmos. Oceanic Technol., 34(3), 643–655. doi: 10.1175/JTECH-D-15-0238.1. This study describes the algorithm for deriving near real-time Outgoing Longwave Radiation (OLR) from Cross-track Infrared Sounder (CrIS) hyperspectral infrared sounder radiance measurements. The estimation of OLR on a near real-time basis provides a unique perspective for studying the variability of the Earth’s current atmospheric radiation budget. CrIS derived OLR values are estimated as a weighted linear combination of CrIS adjusted “pseudo-channel” radiances. The algorithm uses Atmospheric Infrared Sounder (AIRS) as the transfer instrument, and a least-squares regression algorithm is applied to generate two sets of regression coefficients. The first set of regression coefficients is derived from collocated Clouds and the Earth’s Radiant Energy System (CERES) OLR on Aqua and pseudo-channel radiances calculated from AIRS radiances. The second set of coefficients is derived to adjust the CrIS pseudo-channel radiance to account for the differences in pseudo-channel radiances between AIRS and CrIS. The CrIS-derived OLR is then validated by using a limited set of available CERES S-NPP OLR observations over 1° × 1° global grids, as well as monthly OLR mean and interannual differences against CERES OLR data sets from S-NPP and Aqua. The results show that the bias of global CrIS OLR estimation is within ±2 Wm−2, and the standard deviation is within 5 Wm−2 for all conditions, and ±1 Wm−2 and 3 Wm−2 for homogeneous scenes. The interannual CrIS derived OLR differences agree well with Aqua CERES interannual OLR differences on a 1° by 1° spatial scale, with only a small drift of the global mean of these two data sets of around 0.004 Wm−2.
Zhang, Zhibo; Dong, Xiquan; Xi, Baike; Song, Hua; Ma, Po-Lun; Ghan, Steven J.; Platnick, Steven; Minnis, PatrickZhang, Z., X. Dong, B. Xi, H. Song, P. Ma, S. J. Ghan, S. Platnick, P. Minnis, 2017: Inter-comparisons of marine boundary layer cloud properties from the ARM CAP-MBL campaign and two MODIS cloud products. Journal of Geophysical Research: Atmospheres, 122(4), 2351–2365. doi: 10.1002/2016JD025763. From April 2009 to December 2010, the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program carried out an observational field campaign on Graciosa Island, targeting the marine boundary layer (MBL) clouds over the Azores region. In this paper, we present an inter-comparison of the MBL cloud properties, namely, cloud liquid water path (LWP), cloud optical thickness (COT) and cloud-droplet effective radius (CER), among retrievals from the ARM mobile facility (AMF) and two Moderate Resolution Spectroradiometer (MODIS) cloud products (GSFC-MODIS and CERES-MODIS). A total of 63 daytime single-layer MBL cloud cases are selected for inter-comparison. Comparison of collocated retrievals indicates that the two MODIS cloud products agree well on both COT and CER retrievals, with the correlation coefficient R > 0.95. despite their significant difference in spatial sampling. In both MODIS products, the CER retrievals based on the 2.1 µm band (CER2.1) are significantly larger than those based on the 3.7 µm band (CER3.7). The GSFC-MODIS cloud product is collocated and compared with ground-based ARM observations at several temporal-spatial scales. In general, the correlation increases with more precise collocation. For the 63 selected MBL cloud cases, the GSFC-MODIS LWP and COT retrievals agree reasonably well with the ground-based observations with no apparent bias and correlation coefficient R around 0.85 and 0.70, respectively. However, GSFC-MODIS CER3.7 and CER2.1 retrievals have a lower correlation (R ~ 0.5) with the ground-based retrievals. For the 63 selected cases, they are on average larger than ground observations by about 1.5 µm and 3.0 µm, respectively. Taking into account that the MODIS CER retrievals are only sensitive to cloud top reduces the bias only by 0.5 µm. cloud; 0321 Cloud/radiation interaction; ARM; 3337 Global climate models; MODIS; 3360 Remote sensing; 1622 Earth system modeling; Azores
Zhao, Xi; Lin, Yanluan; Peng, Yiran; Wang, Bin; Morrison, Hugh; Gettelman, AndrewZhao, X., Y. Lin, Y. Peng, B. Wang, H. Morrison, A. Gettelman, 2017: A single ice approach using varying ice particle properties in global climate model microphysics. Journal of Advances in Modeling Earth Systems, 9(5), 2138-2157. doi: 10.1002/2017MS000952. Ice and mixed-phase cloud representation and simulation in global climate models are challenging with large uncertainties and biases. Sharing similar growth paths, no distinct separation exists in nature between cloud ice and snow. Different from conventional microphysics schemes separating cloud ice from snow, a single prognostic category is used to represent the whole spectrum of solid hydrometeors. Instead of using fixed physical properties for separate ice classes, e.g., the mass, area, and fall velocity, we consider the particle shape and riming impacts on ice properties. This approach simplifies several ice-related microphysical processes and eliminates the ambiguity and uncertainty associated with parameterizing cloud ice to snow conversion. The modifications were implemented in the Morrison-Gettelman (MG08) scheme and tested in Community Atmosphere Model. Evaluation using single column simulations indicated that the new approach increased the ice water content (IWC) in high clouds during dry period, which is improved compared to available retrievals. Global atmospheric simulations using the new approach give an overall comparable mean climate with notable improvement in terms of clouds and their radiative forcing. Both longwave and shortwave cloud forcing are closer to observations due to more realistic IWC, liquid water content, and cloud top height. Furthermore, the new approach yields slightly better representation of mixed-phase clouds when a smaller capacitance for nonspherical particles is used in the ice depositional growth parameterization. Overall, the physically based single-ice approach is a promising direction for future GCM microphysics development given its simplified representation of microphysical processes and flexible description of ice particle properties. 0320 Cloud physics and chemistry; 0321 Cloud/radiation interaction; Cloud microphysics; cloud forcing; 1626 Global climate models; parameterization; CAM5; total ice
Zhou, Chen; Zelinka, Mark D.; Klein, Stephen A.Zhou, C., M. D. Zelinka, S. A. Klein, 2017: Analyzing the dependence of global cloud feedback on the spatial pattern of sea surface temperature change with a Green's function approach. Journal of Advances in Modeling Earth Systems, 9(5), 2174–2189. doi: 10.1002/2017MS001096. The spatial pattern of sea surface temperature (SST) changes has a large impact on the magnitude of cloud feedback. In this study, we seek a basic understanding of the dependence of cloud feedback on the spatial pattern of warming. Idealized experiments are carried out with an AGCM to calculate the change in global mean cloud-induced radiation anomalies (ΔRcloud) in response to imposed surface warming/cooling in 74 individual localized oceanic “patches”. Then the cloud feedback in response to a specific warming pattern can be approximated as the superposition of global cloud feedback in response to a temperature change in each region, weighted by the magnitude of the local temperature changes. When there is a warming in the tropical subsidence or extratropical regions, the local decrease of LCC results in a positive change in Rcloud. Conversely, warming in tropical ascent regions increases the free-tropospheric temperature throughout the tropics, thereby enhancing the inversion strength over remote regions and inducing positive global low-cloud cover (LCC) anomalies and negative Rcloud anomalies. The Green's function approach performs reasonably well in predicting the response of global mean ΔLCC and net ΔRcloud, but poorly for shortwave and longwave components of ΔRcloud due to its ineffectiveness in predicting middle and high cloud cover changes. The approach successfully captures the change of cloud feedback in response to time-evolving CO2-induced warming and captures the interannual variations in ΔRcloud observed by CERES. The results highlight important nonlocal influences of SST changes on cloud feedback. 0321 Cloud/radiation interaction; 3305 Climate change and variability; 3310 Clouds and cloud feedbacks; cloud feedback; 1626 Global climate models; 3373 Tropical dynamics; Green's function approach; spatial pattern of warming
Adam, Ori; Bischoff, Tobias; Schneider, TapioAdam, O., T. Bischoff, T. Schneider, 2016: Seasonal and interannual variations of the energy flux equator and ITCZ. Part I: Zonally averaged ITCZ position. J. Climate, 29(9), 3219–3230. doi: 10.1175/JCLI-D-15-0512.1. In the zonal mean, the ITCZ lies at the foot of the ascending branch of the tropical mean meridional circulation, close to where the near-surface meridional mass flux vanishes. The ITCZ also lies near the energy flux equator (EFE), where the column-integrated meridional energy flux vanishes. This latter observation makes it possible to relate the ITCZ position to the energy balance, specifically, the atmospheric net energy input near the equator and the cross-equatorial energy flux. Here the validity of the resulting relations between the ITCZ position and energetic quantities is examined with reanalysis data for the years 1979-2014. In the reanalysis data, the EFE and ITCZ position indeed co-vary on timescales of seasons and longer. Consistent with theory, the ITCZ position is proportional to the cross-equatorial atmospheric energy flux and inversely proportional to atmospheric net energy input at the equator. Variations of the cross-equatorial energy flux dominate seasonal variations of the ITCZ position. By contrast, variations of the equatorial net energy input, driven by ocean energy uptake variations, dominate interannual variations of the ITCZ position, e.g., those associated with ENSO.
Adam, Ori; Schneider, Tapio; Brient, Florent; Bischoff, TobiasAdam, O., T. Schneider, F. Brient, T. Bischoff, 2016: Relation of the double-ITCZ bias to the atmospheric energy budget in climate models. Geophysical Research Letters, 43(14), 7670–7677. doi: 10.1002/2016GL069465. We examine how tropical zonal-mean precipitation biases in current climate models relate to the atmospheric energy budget. Both hemispherically symmetric and antisymmetric tropical precipitation biases contribute to the well known double-intertropical convergence zone (ITCZ) bias; however, they have distinct signatures in the energy budget. Hemispherically symmetric biases in tropical precipitation are proportional to biases in the equatorial net energy input; hemispherically antisymmetric biases are proportional to the atmospheric energy transport across the equator. Both relations can be understood within the framework of recently developed theories. Atmospheric net energy input biases in the deep tropics shape both the symmetric and antisymmetric components of the double-ITCZ bias. Potential causes of these energetic biases and their variation across climate models are discussed. 1620 Climate dynamics; 3374 Tropical meteorology; 3310 Clouds and cloud feedbacks; ITCZ; 3319 General circulation; 1853 Precipitation-radar; atmospheric energy budget; double-ITCZ bias
Adebiyi, Adeyemi A.; Zuidema, PaquitaAdebiyi, A. A., P. Zuidema, 2016: The role of the southern African easterly jet in modifying the southeast Atlantic aerosol and cloud environments. Quarterly Journal of the Royal Meteorological Society, 142(697), 1574-1589. doi: 10.1002/qj.2765. The westward transport of biomass-burning (BB) aerosols by mid-tropospheric winds over the southeast Atlantic stratocumulus deck has long been recognized, but the coupling to the large-scale circulation has yet to be investigated fully. This goal is furthered here using satellite observations and reanalysis datasets spanning 2001–2012, as well as 10 day forward trajectory calculations of satellite-detected smoke emissions. The results highlight the important role of a mid-tropospheric zonal wind maximum, the Southern African Easterly Jet (AEJ-S), in transporting BB aerosol west off the African continent. The AEJ-S, defined through daily-mean 600 hPa easterly wind speeds exceeding 6 m s−1 between 5°S and 15°S and centred zonally on the coastline, is most pronounced during September–October. The AEJ-S is part of a meridional circulation that is diabatically forced by the temperature–moisture gradient between the southern hot–dry and northern cool–moist convective structures over land. 45% of 24 264 total identified smoke trajectories exit the continent to its west between 5°S and 15°S. These thereafter follow three major pathways: northwestward (8%), directly westward (55%) and anticyclonically recirculated (37%). The AEJ-S induces an upward motion directly below the jet that enhances prevailing updraughts over land, lifting emissions and transporting aerosols more efficiently over the southeast Atlantic. Offshore, the prevailing large-scale mean subsidence is reduced, with an associated increase in the nearby cloud-top heights and reduction in the nearby marine low-level cloud fraction. Further from the jet, increased warm continental temperature advection at 800 hPa associated with the strengthened land-based anticyclone decreases mean low-level cloud heights. aerosols; Subsidence; ageostrophic circulation; large-scale dynamics; Southern African easterly jet; stratocumulus cloud
Ahlgrimm, Maike; Forbes, Richard M.Ahlgrimm, M., R. M. Forbes, 2016: Regime dependence of cloud condensate variability observed at the Atmospheric Radiation Measurement Sites. Quarterly Journal of the Royal Meteorological Society, 142(697), 1605-1617. doi: 10.1002/qj.2783. Microphysical processes and cloud–radiation interaction occur on spatial scales of variability smaller than those represented explicitly in global weather forecasting and climate models. It is therefore necessary to parametrize the unresolved heterogeneity of humidity and cloud condensate in order to predict process rates accurately. Ground-based observations from the Atmospheric Radiation Measurement sites located in various climatic regions of the world provide a source of high-temporal-resolution observations of cloud condensate. A number of different retrieval products for cloud condensate are assessed for the different geographical regions, years and seasons. The retrieval reliability varies with cloud type, but for cloud categories largely unaffected by precipitation a comparison across sites and longer time periods is possible. These observations confirm previously documented variability behaviour as a function of cloud fraction, but also reveal a systematic regime dependence that is not captured by existing parametrizations. Condensate variability measured as a fractional standard deviation (FSD) in warm boundary-layer clouds is greater in the Tropics than in mid and high latitudes for scenes with comparable cloud type and fraction, with the observed FSD varying from 1.2 in the Tropics to 0.4 in the Arctic. A parametrization of the FSD of cloud liquid condensate based on the grid-box mean total water amount and cloud fraction is formulated and shown to capture the observed range of FSD values better across different geographical sites and different seasons. The regime dependence of FSD for cirrus cloud is less pronounced than that for liquid clouds and is found largely to agree with FSD values previously derived from satellite observations. cloud heterogeneity; condensate variability; regime dependence
Ahlgrimm, Maike; Forbes, Richard M.; Morcrette, Jean-Jacques; Neggers, Roel A. J.Ahlgrimm, M., R. M. Forbes, J. Morcrette, R. A. J. Neggers, 2016: ARM’s Impact on Numerical Weather Prediction at ECMWF. Meteorological Monographs, 57, 28.1-28.13. doi: 10.1175/AMSMONOGRAPHS-D-15-0032.1.
Baker, Noel C.; Taylor, Patrick C.Baker, N. C., P. C. Taylor, 2016: A Framework for Evaluating Climate Model Performance Metrics. J. Climate, 29(5), 1773-1782. doi: 10.1175/JCLI-D-15-0114.1. Given the large amount of climate model output generated from the series of simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5), a standard set of performance metrics would facilitate model intercomparison and tracking performance improvements. However, no framework exists for the evaluation of performance metrics. The proposed framework systematically integrates observations into metric assessment to quantitatively evaluate metrics. An optimal metric is defined in this framework as one that measures a behavior that is strongly linked to model quality in representing mean-state present-day climate. The goal of the framework is to objectively and quantitatively evaluate the ability of a performance metric to represent overall model quality. The framework is demonstrated, and the design principles are discussed using a novel set of performance metrics, which assess the simulation of top-of-atmosphere (TOA) and surface radiative flux variance and probability distributions within 34 CMIP5 models against Clouds and the Earth’s Radiant Energy System (CERES) observations and GISS Surface Temperature Analysis (GISTEMP). Of the 44 tested metrics, the optimal metrics are found to be those that evaluate global-mean TOA radiation flux variance.
Bantges, R. J.; Brindley, H. E.; Chen, X. H.; Huang, X. L.; Harries, J. E.; Murray, J. E.Bantges, R. J., H. E. Brindley, X. H. Chen, X. L. Huang, J. E. Harries, J. E. Murray, 2016: On the detection of robust multi-decadal changes in the Earth’s Outgoing Longwave Radiation spectrum.. J. Climate, 29(13), 4939–4947. doi: 10.1175/JCLI-D-15-0713.1. Differences between the Earth’s global mean all-sky outgoing longwave radiation spectrum as observed in 1970 (IRIS), 1997 (IMG) and 2012 (IASI) are presented. These differences are evaluated to determine whether these are robust signals of multi-decadal radiative forcing and hence whether there is the potential for evaluating feedback-type responses. IASI-IRIS differences range from +2K in the atmospheric window (800-1000 cm-1) to -5.5 K in the 1304 cm-1 CH4 band centre. Corresponding IASI-IMG differences are much smaller, at 0.2 K and - 0.8 K, respectively. More noticeably, IASI-IRIS differences show a distinct step-change across the 1042 cm-1 O3 band that is not seen in IASI-IMG comparisons. This step-change is a consequence of a difference in behaviour when moving from colder to warmer scenes in the IRIS data compared to IASI and IMG. Matched simulations for the relevant periods using ERA-reanalyses mimic the spectral behaviour shown by IASI and IMG rather than by IRIS. These findings suggest that uncertainties in the spectral response of IRIS preclude the use of these data for quantitative assessments of forcing and feedback processes.
Baran, Anthony J.; Hill, Peter; Walters, David; Hardiman, Steven C.; Furtado, Kalli; Field, Paul R.; Manners, JamesBaran, A. J., P. Hill, D. Walters, S. C. Hardiman, K. Furtado, P. R. Field, J. Manners, 2016: The Impact of Two Coupled Cirrus Microphysics-Radiation Parameterizations on the Temperature and Specific Humidity Biases in the Tropical Tropopause Layer in a Climate Model. J. Climate, 29(14), 5299–5316. doi: 10.1175/JCLI-D-15-0821.1. The impact of two different coupled cirrus microphysics-radiation parameterizations on the zonally averaged temperature and humidity biases in the tropical tropopause layer (TTL) of a Met Office climate model configuration is assessed. One parameterization is based on a linear coupling between a model prognostic variable, the ice mass mixing ratio, qi, and the integral optical properties. The second is based on the integral optical properties being parameterized as functions of qi and temperature, Tc, where the mass coefficients (i.e. scattering and extinction) are parameterized as nonlinear functions of the ratio between qi and Tc. The cirrus microphysics parameterization is based on a moment estimation parameterization of the particle size distribution (PSD), which relates the mass moment (i.e. second moment if mass is proportional to size raised to the power of 2 ) of the PSD to all other PSD moments through the magnitude of the second moment and Tc. This same microphysics PSD parameterization is applied to calculate the integral optical properties used in both radiation parameterizations and, thus, ensures PSD and mass consistency between the cirrus microphysics and radiation schemes.In this paper, the temperature-non-dependent and temperature-dependent parameterizations are shown to increase and decrease the zonally averaged temperature biases in the TTL by about 1 K, respectively. The temperature-dependent radiation parameterization is further demonstrated to have a positive impact on the specific humidity biases in the TTL, as well as decreasing the shortwave and longwave biases in the cloudy radiative effect. The temperature-dependent radiation parameterization is shown to be more consistent with TTL and global radiation observations.
Barragan, Ruben; Romano, Salvatore; Sicard, Michaël; Burlizzi, Pasquale; Perrone, Maria Rita; Comeron, AdolfoBarragan, R., S. Romano, M. Sicard, P. Burlizzi, M. R. Perrone, A. Comeron, 2016: Estimation of mineral dust direct radiative forcing at the European Aerosol Research Lidar NETwork site of Lecce, Italy, during the ChArMEx/ADRIMED summer 2013 campaign: Impact of radiative transfer model spectral resolutions. Journal of Geophysical Research: Atmospheres, 121(17), 10,237–10,261. doi: 10.1002/2016JD025016. A field campaign took place in the western and central Mediterranean basin on June–July 2013 in the framework of the ChArMEx (Chemistry-Aerosol Mediterranean Experiment, http://charmex.lsce.ipsl.fr/)/ADRIMED (Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region, http://adrimed.sedoo.fr/) project to characterize the aerosol direct radiative forcing (DRF) over the Mediterranean. This work focuses on the aerosol DRF estimations at Lecce (40.33°N; 18.11°E; 30 m above sea level) during the Saharan dust outbreak that affected southern Italy from 20 to 24 June 2013. The Global Atmospheric Model (GAME) and the Two-Stream (TS) model were used to calculate the instantaneous aerosol DRF in the short-wave (SW) and long-wave (LW) spectral ranges, at the surface and at the top of the atmosphere (TOA). The main differences between the two models were due to the different numerical methods to solve the radiative transfer (RT) equations and to the more detailed spectral resolution of GAME compared to that of TS. 167 and 115 subbands were used by GAME in the 0.3–4 and 4–37 µm spectral ranges, respectively. Conversely, the TS model used 8 and 11 subbands in the same spectral ranges, respectively. We found on 22 June that the SW-DRFs from the two models were in good agreement, both at the TOA and at the surface. The instantaneous SW-DRFs at the surface and at the TOA varied from −50 to −34 W m−2 and from −6 to +8 W m−2, respectively, while the surface and TOA LW-DRFs ranged between +3.5 and +8.0 W m−2 and between +1.7 and +6.9 W m−2, respectively. In particular, both models provided positive TOA SW-DRFs at solar zenith angles smaller than 25° because of the mixing of the desert dust with anthropogenic pollution during its transport to the study site. In contrast, the TS model overestimated the GAME LW-DRF up to about 5 and 7.5 times at the surface and at the TOA, respectively, when the dust particle contribution was largest. The low spectral resolution of the real (n) and imaginary (k) refractive index values was mainly responsible for the LW-DRF overestimates of the TS model. However, we found that the “optimization” of the n and k values at 8.75 and 11.5 µm was sufficient in this study to obtain a satisfactory agreement between the LW-DRFs from the two models, both at the TOA and at the surface. The impact of the spectral dependence of the water vapor absorption coefficients on the estimation of the flux without aerosol has also been addressed. Paper results did not reveal any significant impact due to the different numerical methods used by the two models to solve the RT equations. 0305 Aerosols and particles; 3359 Radiative processes; 3337 Global climate models; mineral dust; Aerosol direct radiative forcing; radiative flux measurements; radiative transfer model spectral resolution
Bates, Ray J.Bates, R. J., 2016: Estimating Climate Sensitivity Using Two-zone Energy Balance Models. Earth and Space Science, 3(5), 207–225. doi: 10.1002/2015EA000154. Estimates of 2×CO2 equilibrium climate sensitivity (EqCS) derive from running global climate models (GCMs) to equilibrium. Estimates of effective climate sensitivity (EfCS) are the corresponding quantities obtained using transient GCM output or observations. The EfCS approach uses an accompanying energy balance model (EBM), the zero-dimensional model (ZDM) being standard. GCM values of EqCS and EfCS vary widely [IPCC range: (1.5, 4.5)°C] and have failed to converge over the past 35 years. Recently, attempts have been made to refine the EfCS approach by using two-zone (tropical/extratropical) EBMs. When applied using satellite radiation data, these give low and tightly-constrained EfCS values, in the neighbourhood of 1 °C. These low observational EfCS/two-zone EBM values have been questioned because (a) they disagree with higher observational EfCS/ZDM values, and (b) the EfCS/two-zone EBM values given by GCMs are poorly correlated with the standard GCM sensitivity estimates. The validity of the low observational EfCS/two-zone EBM values is here explored, with focus on the limitations of the observational EfCS/ZDM approach, the disagreement between the GCM and observational radiative responses to surface temperature perturbations in the tropics, and on the modified EfCS values provided by an extended two-zone EBM that includes an explicit parameterization of dynamical heat transport. The results support the low observational EfCS/two-zone EBM values, indicating that objections (a) and (b) to these values both need to be reconsidered. It is shown that in the EBM with explicit dynamical heat transport the traditional formulism of climate feedbacks can break down because of lack of additivity. ©2016. American Geophysical Union. All Rights Reserved. 1620 Climate dynamics; Climate sensitivity; 1626 Global climate models; additivity of climate feedbacks; energy balance models; heat transport and climate sensitivity; observational climate sensitivity
Bellomo, Katinka; Clement, Amy C.; Murphy, Lisa N.; Polvani, Lorenzo M.; Cane, Mark A.Bellomo, K., A. C. Clement, L. N. Murphy, L. M. Polvani, M. A. Cane, 2016: New Observational Evidence for a Positive Cloud Feedback that Amplifies the Atlantic Multidecadal Oscillation. Geophysical Research Letters, 43(18), 9852–9859. doi: 10.1002/2016GL069961. The Atlantic Multidecadal Oscillation (AMO) affects climate variability in the North Atlantic basin and adjacent continents with potential societal impacts. Previous studies based on model simulations and short-term satellite retrievals hypothesized an important role for cloud radiative forcing in modulating the persistence of the AMO in the tropics, but this mechanism remains to be tested with long-term observational records. Here we analyze datasets that span multiple decades and present new observational evidence for a positive feedback between total cloud amount, sea-surface temperature (SST), and atmospheric circulation that can strengthen the persistence and amplitude of the tropical branch of the AMO. In addition, we estimate cloud amount feedback from observations and quantify its impact on SST with idealized modeling experiments. From these experiments we conclude that cloud feedbacks can account for 10% to 31% of the observed SST anomalies associated with the AMO over the tropics. 3310 Clouds and cloud feedbacks; 1616 Climate variability; 4513 Decadal ocean variability; 9325 Atlantic Ocean; atlantic multidecadal oscillation
Bender, Frida; Engström, Anders; Karlsson, JohannesBender, F., A. Engström, J. Karlsson, 2016: Factors controlling cloud albedo in marine subtropical stratocumulus regions in climate models and satellite observations. J. Climate, 29(9), 3559–3587. doi: 10.1175/JCLI-D-15-0095.1. This study focuses on the radiative properties of five subtropical marine stratocumulus cloud regions, on monthly mean scale. Through examination of the relation between total albedo and cloud fraction, and its variability and relation to other parameters, some of the factors controlling the reflectivity, or albedo, of the clouds in these regions are investigated. It is found that the main part of the variability in albedo at a given cloud fraction can be related to temporal, rather than spatial variability, indicating spatial homogeneity in cloud radiative properties in the studied regions. This is seen most clearly in satellite observations, but also in an ensemble of climate models. Further comparison between satellite data and output from climate models shows that there is good agreement with respect to the role of liquid water path, the parameter that can be assumed to be the primary source of variability in cloud reflectivity for a given cloud fraction. On the other hand, the influence of aerosol loading on cloud albedo differs between models and observations. The cloud-albedo effect, or cloud brightening caused by aerosol through its coupling to cloud droplet number concentration and droplet size, is found not to dominate in the satellite observations on monthly mean scale, as it appears to do on this scale in the climate models. The disagreement between models and observations is particularly strong in regions with frequent occurrence of absorbing aerosols above clouds, where satellite data contrary to the climate models indicate a scene darkening with increasing aerosol loading.
Blanc, Elodie; Strobl, EricBlanc, E., E. Strobl, 2016: Assessing the impact of typhoons on rice production in the philippines. J. Appl. Meteor. Climatol., 55(4), 993-1007. doi: 10.1175/JAMC-D-15-0214.1. We quantify the impact of typhoons on rice production in the Philippines. To this end we use satellite derived reflectance data to detect the location of rice fields at the 500m resolution. Utilizing typhoon track data within a wind field model and satellite derived precipitation measures, we then employ fragility curves to proxy damages of storms on rice production within each rice field. Our results from a panel spatial regression model show that typhoons substantially reduced local provincial production in the quarter of the strike, having caused losses of up to 12.5 million tons since 2001. Using extreme value theory to predict future losses, our results suggest that a typhoon like the recent Haiyan, which is estimated to have caused losses of around 260,000 tons, has a return period of 13 years. Our methodology can provide a relatively timely tool for rice damage assessments after tropical cyclones in the region.
Blunden, Jessica; Arndt, Derek S.Blunden, J., D. S. Arndt, 2016: State of the Climate in 2015. Bull. Amer. Meteor. Soc., 97(8), Si-S275. doi: 10.1175/2016BAMSStateoftheClimate.1. Editor’s note: For easy download the posted pdf of the State of the Climate for 2016 is a very low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.
Bodas-Salcedo, A.; Andrews, T.; Karmalkar, A. V.; Ringer, M. A.Bodas-Salcedo, A., T. Andrews, A. V. Karmalkar, M. A. Ringer, 2016: Cloud liquid water path and radiative feedbacks over the Southern Ocean. Geophysical Research Letters, 43(20), 10,938–10,946. doi: 10.1002/2016GL070770. Climate models show a robust shortwave negative feedback in the midlatitude oceans in climate change simulations. This feedback is commonly attributed to an increase in cloud optical depth due to ice to liquid phase change as the climate warms. Here we use a cyclone compositing technique to show that the models' cloud liquid water path (LWP) response is strongly dependent on cloud regime. The radiative and LWP responses are not as tightly coupled as a zonal-mean analysis would suggest, implying that the physical mechanisms that control the overall LWP response are not necessarily responsible for the radiative response. The area of the cyclone dominated by low-level stratiform and shallow convective clouds plays dominant role in the radiative response. Since these are mostly supercooled liquid clouds, the strength of a negative cloud-phase feedback in the real world should be smaller than the one predicted by current models. 3337 Global climate models; 3310 Clouds and cloud feedbacks; cloud feedbacks
Bodas-Salcedo, A.; Hill, P. G.; Furtado, K.; Williams, K. D.; Field, P. R.; Manners, J. C.; Hyder, P.; Kato, S.Bodas-Salcedo, A., P. G. Hill, K. Furtado, K. D. Williams, P. R. Field, J. C. Manners, P. Hyder, S. Kato, 2016: Large contribution of supercooled liquid clouds to the solar radiation budget of the Southern Ocean. J. Climate, 29(11), 4213–4228. doi: 10.1175/JCLI-D-15-0564.1. The Southern ocean is a critical region for global climate, yet large cloud and solar radiation biases over the Southern Ocean are a long-standing problem in climate models and are poorly understood, leading to biases in simulated sea-surface-temperatures. In this study we show that supercooled liquid clouds are central to understanding and simulating the Southern Ocean environment. We use a combination of satellite observational data and detailed radiative transfer calculations to quantify the impact of cloud phase and cloud vertical structure on the reflected solar radiation in the southern hemisphere summer. We find that clouds with supercooled liquid tops dominate the population of liquid clouds. The observations show that clouds with supercooled liquid tops contribute between 27% and 38% to the total reflected solar radiation between 40°S and 70°S, and climate models are found to poorly simulate these clouds. Our results quantify the importance of supercooled liquid clouds in the Southern Ocean environment, and highlight the need to improve our understanding of the physical processes that control these clouds in order to improve their simulation in numerical models. This is not only important for improving the simulation of present-day climate and climate variability, but also relevant for increasing our confidence in climate feedback processes and future climate projections.
Boeke, Robyn C.; Taylor, Patrick C.Boeke, R. C., P. C. Taylor, 2016: Evaluation of the Arctic surface radiation budget in CMIP5 models. Journal of Geophysical Research: Atmospheres, 121(14), 8525–8548. doi: 10.1002/2016JD025099. The Arctic region is warming at a rate more than double the global average, a trend predicted to continue by all Coupled Model Intercomparison Project 5 (CMIP5) climate models. Despite this consistency, significant inter-model spread exists in the simulated Arctic climate related to differences in the Arctic surface radiation budget. Building upon previous work to characterize and understand surface radiation budget biases in climate models, the annual mean and seasonal cycle of the Arctic surface radiation budget in 17 CMIP5 models using the Historical-forcing scenario is evaluated against state-of-the-art Cloud and Earth's Radiant Energy System SFC-EBAF data. The CMIP5 multi-model ensemble is found to simulate longwave surface fluxes well during the sunlit months (~1 W m-2 differences in July) but exhibits significant wintertime biases (up to -19 W m-2). Shortwave fluxes show substantial across-model spread during summer; the model standard deviation approaches 20 W m-2 in July. Applying a decomposition analysis to the cloud radiative effect (CRE) seasonal cycles, an unrealistic compensation is uncovered between the model-simulated seasonal cycles of cloud fraction, all sky-clear sky flux differences, and surface albedo that enables models to simulate realistic CRE seasonal cycles with unrealistic individual contributions. This unrealistic behavior in models must be constrained to improve Arctic climate simulation; observational uncertainty is sufficient to do so. Lastly, biases in all and clear-sky longwave downwelling fluxes positively correlate with model surface temperature in winter, while in summer surface temperature is most strongly related to clear-sky upwelling radiation biases from surface albedo errors. 0321 Cloud/radiation interaction; 3359 Radiative processes; 3310 Clouds and cloud feedbacks; radiation; CMIP5; Arctic; cloud radiative effect; surface
Boos, William R.; Korty, Robert L.Boos, W. R., R. L. Korty, 2016: Regional energy budget control of the intertropical convergence zone and application to mid-Holocene rainfall. Nature Geoscience, 9(12), 892-897. doi: 10.1038/ngeo2833. Shifts in the latitude of the intertropical convergence zone—a region of intense tropical rainfall—have often been explained through changes in the atmospheric energy budget, specifically through theories that tie rainfall to meridional energy fluxes. These quantitative theories can explain shifts in the zonal mean, but often have limited relevance for regional climate shifts, such as a period of enhanced precipitation over Saharan Africa during the mid-Holocene. Here we present a theory for regional tropical rainfall shifts that utilizes both zonal and meridional energy fluxes. We first identify a qualitative link between zonal and meridional energy fluxes and rainfall variations associated with the seasonal cycle and the El Niño/Southern Oscillation. We then develop a quantitative theory based on these fluxes that relates atmospheric energy transport to tropical rainfall. When applied to the orbital configuration of the mid-Holocene, our theory predicts continental rainfall shifts over Africa and Southeast Asia that are consistent with complex model simulations. However, the predicted rainfall over the Sahara is not sufficient to sustain vegetation at a level seen in the palaeo-record, which instead requires an additional large energy source such as that due to reductions in Saharan surface albedo. We thus conclude that additional feedbacks, such as those involving changes in vegetation or soil type, are required to explain changes in rainfall over Africa during the mid-Holocene. Atmospheric dynamics; Climate and Earth system modelling; Palaeoclimate
Bouniol, Dominique; Roca, Rémy; Fiolleau, Thomas; Poan, D. EmmanuelBouniol, D., R. Roca, T. Fiolleau, D. E. Poan, 2016: Macrophysical, microphysical and radiative properties of tropical Mesocale Convective Systems over their life cycle.. J. Climate, 29(9), 3353–3371. doi: 10.1175/JCLI-D-15-0551.1. Mesoscale convective systems (MCS) are important drivers of the atmospheric large-scale circulation through their associated diabatic heating profile. Taking advantage of recent tracking techniques, this study investigates the evolution of macrophysical, microphysical and radiative properties over the MCS life cycle by merging geostationary and polar orbiting satellite data. These observations are performed in three major convective areas: the West Africa continent, the adjacent Atlantic ocean, and the open Indian ocean. MCS properties are also investigated according to internal sub-regions (convective, stratiform and non-precipitating anvil).Continental MCSs show a specific life cycle, with more intense convection at the beginning. Larger and denser hydrometeors are thus found at higher altitudes, as well as up to the cirriform sub-region. Oceanic MCSs have more constant reflectivity values, suggesting a less intense convective updraft, but more persistent intensity. A layer of small crystals is found in all sub-regions, but with a depth that varies according to the MCS sub-region and life cycle.Radiative properties are also examined. It appears that the evolution of large and dense hydrometeors tends to control the evolution of the cloud albedo and the outgoing longwave radiation. The impact of dense hydrometeors, detrained from the convective towers, is also seen in the radiative heating profiles, in particular in the shortwave domain. A dipole of cooling near the cloud top and heating near the cloud base is found in the longwave; this cooling intensifies near the end of the life cycle.
Brient, Florent; Schneider, TapioBrient, F., T. Schneider, 2016: Constraints on climate sensitivity from space-based measurements of low-cloud reflection. J. Climate, 29(16), 5821–5835. doi: 10.1175/JCLI-D-15-0897.1. Physical uncertainties in global-warming projections are dominated by uncertainties about how the fraction of incoming shortwave radiation that clouds reflect will change as greenhouse gas concentrations rise. Differences in the shortwave reflection by low clouds over tropical oceans alone account for more than half of the variance of the equilibrium climate sensitivity (ECS) among climate models, which ranges from 2.1 to 4.7 K. Space-based measurements now provide an opportunity to assess how well models reproduce temporal variations of this shortwave reflection on seasonal to interannual timescales. Here such space-based measurements are used to show that shortwave reflection by low clouds over tropical oceans decreases robustly when the underlying surface warms, for example, by −(0.96±0.22)%/K (90% confidence level) for deseasonalized variations. Additionally, the temporal covariance of low-cloud reflection with temperature in historical simulations with current climate models correlates strongly (r = −0.67) with the models’ ECS. Therefore, measurements of temporal low-cloud variations can be used to constrain ECS estimates based on climate models. An information-theoretic weighting of climate models by how well they reproduce the measured deseasonalized covariance of shortwave cloud reflection with temperature yields a most likely ECS estimate around 4.0 K; an ECS below 2.3 K becomes very unlikely (90% confidence).
Brown, Patrick T.; Li, Wenhong; Jiang, Jonathan H.; Su, HuiBrown, P. T., W. Li, J. H. Jiang, H. Su, 2016: Unforced Surface Air Temperature Variability and Its Contrasting Relationship with the Anomalous TOA Energy Flux at Local and Global Spatial Scales. J. Climate, 29(3), 925-940. doi: 10.1175/JCLI-D-15-0384.1. Unforced global mean surface air temperature () is stable in the long term primarily because warm anomalies are associated with enhanced outgoing longwave radiation () to space and thus a negative net radiative energy flux (, positive downward) at the top of the atmosphere (TOA). However, it is shown here that, with the exception of high latitudinal and specific continental regions, warm unforced surface air temperature anomalies at the local spatial scale [T(θ, ϕ), where (θ, ϕ) = (latitude, longitude)] tend to be associated with anomalously positive N(θ, ϕ). It is revealed that this occurs mainly because warm T(θ, ϕ) anomalies are accompanied by anomalously low surface albedo near sea ice margins and over high altitudes, low cloud albedo over much of the middle and low latitudes, and a large water vapor greenhouse effect over the deep Indo-Pacific.It is shown here that the negative versus relationship arises because warm anomalies are associated with large divergence of atmospheric energy transport over the tropical Pacific [where the N(θ, ϕ) versus T(θ, ϕ) relationship tends to be positive] and convergence of atmospheric energy transport at high latitudes [where the N(θ, ϕ) versus T(θ, ϕ) relationship tends to be negative]. Additionally, the characteristic surface temperature pattern contains anomalously cool regions where a positive local N(θ, ϕ) versus T(θ, ϕ) relationship helps induce negative . Finally, large-scale atmospheric circulation changes play a critical role in the production of the negative versus relationship as they drive cloud reduction and atmospheric drying over large portions of the tropics and subtropics, which allows for greatly enhanced . surface temperature; Feedback; longwave radiation; Cloud radiative effects; Interannual variability; Physical Meteorology and Climatology; Variability; Atm/Ocean Structure/ Phenomena; el nino
Cao, Y.; Liang, S.; He, T.; Chen, X.Cao, Y., S. Liang, T. He, X. Chen, 2016: Evaluation of Four Reanalysis Surface Albedo Data Sets in Arctic Using a Satellite Product. IEEE Geoscience and Remote Sensing Letters, 13(3), 384-388. doi: 10.1109/LGRS.2016.2515159. Surface albedo has been widely used in studying energy budgets and climate dynamics in the Arctic region. Previous efforts have focused on using reanalysis albedo data, but their uncertainties remain unknown. In this letter, we evaluated four popularly used reanalysis surface albedo products, namely, the European Centre for Medium-Range Weather Forecasts Interim Reanalysis (ERA-Interim), the Modern-Era Retrospective Analysis for Research and Applications (MERRA), the National Centers for Environmental Prediction Climate Forecast System Reanalysis (CFSR), and the Japanese 55-Year Reanalysis (JRA-55), over the Arctic Ocean using satellite-retrieved product (CLARA-SAL) from 1982 to 2009. Owing to the flawed parameterization scheme or problematic model inputs, reanalysis products are unable to capture both the interannual variation and long-term reduction of surface albedo in the Arctic. This results in a large bias in the decline of shortwave radiative forcing at both surface (from -11.74 to -38.25 W m-2) and top of atmosphere (from -5.35 to -20.19 W m-2). The most significant underestimation occurred in the melt season and after sea-ice melting acceleration started since 1996, in the central Arctic Basin north of 80° N, which is likely due to the failure in simulating the influence of thinning ice and decreasing snow depth. The JRA-55 albedo product outperformed the other three products, which is likely due to the employment of observed sea-ice concentration on the parameterization scheme. On the other hand, the other three reanalysis products, namely, ERA-Interim, MERRA, and CFSR, are unable to effectively track the interannual variation of surface albedo and significantly underestimate (from -0.016 to -0.021 relative to -0.048, by one-third to half) the decreasing surface albedo. Satellites; Meteorology; albedo; surface albedo; sea ice; Atmospheric modeling; energy budget; Sea surface; Arctic; climate dynamics; MERRA; Ocean temperature; shortwave radiative forcing; ERA-Interim; satellite product; AD 1982 to 2009; Arctic region; CFSR; CLARA-SAL; European centre-for-medium-range weather forecasts interim reanalysis; evaluation and assessment; four reanalysis surface albedo data set; interannual surface albedo variation; interannual variation; JRA-55; oceanographic regions; parameterization scheme; reanalysis product; satellite application; satellite-retrieved product; sea-ice concentration; sea-ice melting acceleration; underwater optics
Ceppi, Paulo; McCoy, Daniel T.; Hartmann, Dennis L.Ceppi, P., D. T. McCoy, D. L. Hartmann, 2016: Observational evidence for a negative shortwave cloud feedback in mid to high latitudes. Geophysical Research Letters, 43(3), 1331–1339. doi: 10.1002/2015GL067499. Exploiting the observed robust relationships between temperature and optical depth in extratropical clouds, we calculate the shortwave cloud feedback from historical data, by regressing observed and modeled cloud property histograms onto local temperature in mid to high Southern latitudes. In this region, all CMIP5 models and observational data sets predict a negative cloud feedback, mainly driven by optical thickening. Between 45∘ and 60∘ S, the mean observed shortwave feedback (−0.91 ± 0.82 W m−2 K−1, relative to local rather than global-mean warming) is very close to the multi-model mean feedback in RCP8.5 (−0.98 W m−2 K−1), despite differences in the meridional structure. In models, historical temperature–cloud property relationships reliably predict the forced RCP8.5 response. Because simple theory predicts this optical thickening with warming, and cloud amount changes are relatively small, we conclude that the shortwave cloud feedback is very likely negative in the real world at mid to high latitudes. clouds; climate change; 3305 Climate change and variability; 3337 Global climate models; 3310 Clouds and cloud feedbacks; climate; 3360 Remote sensing; climate feedbacks
Cesana, G.; Chepfer, H.; Winker, D.; Getzewich, B.; Cai, X.; Jourdan, O.; Mioche, G.; Okamoto, H.; Hagihara, Y.; Noel, V.; Reverdy, M.Cesana, G., H. Chepfer, D. Winker, B. Getzewich, X. Cai, O. Jourdan, G. Mioche, H. Okamoto, Y. Hagihara, V. Noel, M. Reverdy, 2016: Using in-situ airborne measurements to evaluate three cloud phase products derived from CALIPSO. Journal of Geophysical Research: Atmospheres, 121(10), 5788–5808. doi: 10.1002/2015JD024334. We compare the cloud detection and cloud phase determination of three independent climatologies based on Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) to airborne in-situ measurements. Our analysis of the cloud detection shows that the differences between the satellite and in-situ measurements mainly arise from three factors. Firstly, averaging CALIPSO Level-l data along-track before cloud detection increases the estimate of high- and low-level cloud fractions. Secondly, the vertical averaging of Level-1 data before cloud detection tends to artificially increase the cloud vertical extent. Thirdly, the differences in classification of fully attenuated pixels among the CALIPSO climatologies lead to differences in the low-level Arctic cloud fractions. In another section, we compare the cloudy pixels detected by co-located in-situ and satellite observations to study the cloud phase determination. At mid-latitudes, retrievals of homogeneous high ice clouds by CALIPSO datasets are very robust (more than 94.6% of agreement with in-situ). In the Arctic, where the cloud phase vertical variability is larger within a 480 m-pixel, all climatologies show disagreements with the in-situ measurements and CALIPSO-General Circulation Models-Oriented Cloud Product (GOCCP) report significant undefined-phase clouds, which likely correspond to mixed-phase clouds. In all CALIPSO products, the phase determination is dominated by the cloud-top phase. Finally, we use global statistics to demonstrate that main differences between the CALIPSO cloud phase products stem from the cloud detection (horizontal averaging, fully attenuated pixels) rather than the cloud phase determination procedures. 0320 Cloud physics and chemistry; cloud; validation; 0480 Remote sensing; CALIPSO; Cloud Phase; in-situ
Chen, Gengxin; Han, Weiqing; Li, Yuanlong; Wang, DongxiaoChen, G., W. Han, Y. Li, D. Wang, 2016: Interannual Variability of Equatorial Eastern Indian Ocean Upwelling: Local versus Remote Forcing. J. Phys. Oceanogr., 46(3), 789-807. doi: 10.1175/JPO-D-15-0117.1. The equatorial eastern Indian Ocean (EIO) upwelling occurs in the Indian Ocean warm pool, differing from the equatorial Pacific and Atlantic upwelling that occurs in the cold tongue. By analyzing observations and performing ocean model experiments, this paper quantifies the remote versus local forcing in causing interannual variability of the equatorial EIO upwelling from 2001 to 2011 and elucidates the associated processes. For all seasons, interannual variability of thermocline depth in the EIO, as an indicator of upwelling, is dominated by remote forcing from equatorial Indian Ocean winds, which drive Kelvin waves that propagate along the equator and subsequently along the Sumatra–Java coasts. Upwelling has prominent signatures in sea surface temperature (SST) and chlorophyll-a concentration but only in boreal summer–fall (May–October). Local forcing plays a larger role than remote forcing in producing interannual SST anomaly (SSTA). During boreal summer–fall, when the mean thermocline is relatively shallow, SSTA is primarily driven by the upwelling process, with comparable contributions from remote and local forcing effects. In contrast, during boreal winter–spring (November–April), when the mean thermocline is relatively deep, SSTA is controlled by surface heat flux and decoupled from thermocline variability. Advection affects interannual SSTA in all cases. The remote and local winds that drive the interannual variability of the equatorial EIO upwelling are closely associated with Indian Ocean dipole events and to a lesser degree with El Niño–Southern Oscillation.
Chen, Guoxing; Wang, Wei-ChyungChen, G., W. Wang, 2016: Aerosol-stratocumulus-radiation interactions over the southeast Pacific: Implications to the underlying air-sea coupling. J. Atmos. Sci., 73(7), 2759–2771. doi: 10.1175/JAS-D-15-0277.1. Recently, Chen et al. used a combination of observations and WRF simulations to illustrate that the anthropogenic aerosol-cloud microphysics-radiation interactions over the southeast Pacific can potentially reduce the excessive shortwave radiation reaching the sea surface, a common bias identified in CMIP5 models. Here, with the aid of a mixed-layer ocean we further study the implications of the shortwave radiation reduction to the underlying air-sea coupling, focusing on the SST sensitivity to the changes. Results show that responses of the air-sea coupling include two negative feedbacks (a large decrease in the latent heat flux and a small decrease in the sensible heat flux, both associated with the surface cooling) and a positive feedback (an increase in the cloud cover, caused by the increase in the relative humidity within the boundary layer, especially during the daytime). The 0.1 °C /(W m-2) SST sensitivity is about half that documented in CMIP5 models. In addition, an effective daytime cloud fraction weighted with the solar diurnal cycle is proposed to facilitate diagnosing the intensity of cloud-radiation interactions in general circulation models.
Chen, X.; Huang, X.Chen, X., X. Huang, 2016: Deriving clear-sky longwave spectral flux from spaceborne hyperspectral radiance measurements: a case study with AIRS observations. Atmos. Meas. Tech., 9(12), 6013-6023. doi: 10.5194/amt-9-6013-2016. Previous studies have shown that longwave (LW) spectral fluxes have unique merit in climate studies. Using Atmospheric Infrared Sounder (AIRS) radiances as a case study, this study presents an algorithm to derive the entire LW clear-sky spectral fluxes from spaceborne hyperspectral observations. No other auxiliary observations are needed in the algorithm. A clear-sky scene is identified using a three-step detection method. The identified clear-sky scenes are then categorized into different sub-scene types using information about precipitable water, lapse rate and surface temperature inferred from the AIRS radiances at six selected channels. A previously established algorithm is then used to invert AIRS radiances to spectral fluxes over the entire LW spectrum at 10 cm−1 spectral interval. Accuracy of the algorithms is evaluated against collocated Clouds and the Earth's Radiant Energy System (CERES) observations. For nadir-view observations, the mean difference between outgoing longwave radiation (OLR) derived by this algorithm and the collocated CERES OLR is 1.52 Wm−2 with a standard deviation of 2.46 Wm−2. When the algorithm is extended for viewing zenith angle up to 45°, the performance is comparable to that for nadir-view results.
Cheng, J.; Liang, S.Cheng, J., S. Liang, 2016: Global Estimates for High-Spatial-Resolution Clear-Sky Land Surface Upwelling Longwave Radiation From MODIS Data. IEEE Transactions on Geoscience and Remote Sensing, 54(7), 4115-4129. doi: 10.1109/TGRS.2016.2537650. Surface upwelling longwave radiation (LWUP) is a vital component in calculating the Earth's surface radiation budget. Under the general framework of the hybrid method, we developed linear and dynamic learning neural network (DLNN) models for estimating the global 1-km instantaneous clear-sky LWUP from the top-of-atmosphere radiance of Moderate Resolution Imaging Spectroradiometer thermal infrared channels 29, 31, and 32. Extensive radiative transfer simulations were conducted to produce a large number of representative samples, from which the linear model and DLNN model were derived. These two hybrid models were evaluated using ground measurements collected at 19 sites from three networks (SURFRAD, ASRCOP, and GAME-AAN). According to the validation results, the linear model was more accurate than the DLNN model, with a bias and root-mean-square error (RMSE) of -0.31 W/m2 and 19.92 W/m2 obtained by averaging the mean bias and RMSE for the three networks. Additionally, the computational efficiency of the linear model was much higher than that of the DLNN model. We also compared our linear model to a hybrid method developed by a previous study and found ours to perform better. atmosphere; Land surface; Remote sensing; Satellites; atmospheric radiation; Atmospheric measurements; radiative transfer; neural nets; MODIS; surface radiation budget (SRB); Moderate Resolution Imaging Spectroradiometer (MODIS); ground measurement; Land surface temperature; MODIS data; radiative transfer simulation; surface upwelling longwave radiation (LWUP); Biological system modeling; ASRCOP network; clear-sky land surface upwelling longwave radiation; DLNN model; dynamic learning neural network; Earth surface radiation budget; GAME-AAN network; linear model; Moderate Resolution Imaging Spectroradiometer thermal infrared channel; SURFRAD network
Chern, Jiun-Dar; Tao, Wei-Kuo; Lang, Stephen E.; Matsui, Toshihisa; Li, J.-L. F.; Mohr, Karen I.; Skofronick-Jackson, Gail M.; Peters-Lidard, Christa D.Chern, J., W. Tao, S. E. Lang, T. Matsui, J. F. Li, K. I. Mohr, G. M. Skofronick-Jackson, C. D. Peters-Lidard, 2016: Performance of the Goddard multiscale modeling framework with Goddard ice microphysical schemes. Journal of Advances in Modeling Earth Systems, 8(1), 66–95. doi: 10.1002/2015MS000469. The multiscale modeling framework (MMF), which replaces traditional cloud parameterizations with cloud-resolving models (CRMs) within a host atmospheric general circulation model (GCM), has become a new approach for climate modeling. The embedded CRMs make it possible to apply CRM-based cloud microphysics directly within a GCM. However, most such schemes have never been tested in a global environment for long-term climate simulation. The benefits of using an MMF to evaluate rigorously and improve microphysics schemes are here demonstrated. Four one-moment microphysical schemes are implemented into the Goddard MMF and their results validated against three CloudSat/CALIPSO cloud ice products and other satellite data. The new four-class (cloud ice, snow, graupel, and frozen drops/hail) ice scheme produces a better overall spatial distribution of cloud ice amount, total cloud fractions, net radiation, and total cloud radiative forcing than earlier three-class ice schemes, with biases within the observational uncertainties. Sensitivity experiments are conducted to examine the impact of recently upgraded microphysical processes on global hydrometeor distributions. Five processes dominate the global distributions of cloud ice and snow amount in long-term simulations: (1) allowing for ice supersaturation in the saturation adjustment, (2) three additional correction terms in the depositional growth of cloud ice to snow, (3) accounting for cloud ice fall speeds, (4) limiting cloud ice particle size, and (5) new size-mapping schemes for snow and graupel. Despite the cloud microphysics improvements, systematic errors associated with subgrid processes, cyclic lateral boundaries in the embedded CRMs, and momentum transport remain and will require future improvement. 3337 Global climate models; 3310 Clouds and cloud feedbacks; microphysics; CloudSat; superparameterization; MMF
Christensen, Matthew W.; Behrangi, Ali; L’Ecuyer, Tristan; Wood, Norman B.; Lebsock, Matthew D.; Stephens, Graeme L.Christensen, M. W., A. Behrangi, T. L’Ecuyer, N. B. Wood, M. D. Lebsock, G. L. Stephens, 2016: Arctic Observation and Reanalysis Integrated System: A New Data Product for Validation and Climate Study. Bull. Amer. Meteor. Soc., 97(6), 907–915. doi: 10.1175/BAMS-D-14-00273.1. Over recent decades sea ice and snow cover extent has significantly declined across the Arctic. The melting has been confirmed using numerous observational tools. While climate models also tend to predict melting trends a wide range of projections manifest due to uncertainties in Arctic processes. Causes for the rapid loss of sea ice are complex and linked to the surface radiation budget through cloud and sea-ice feedbacks. To improve assessments of the Arctic energy budget for validation and scientific study we have developed the Arctic Observation and Reanalysis Integrated System (ArORIS). ArOIS merges together numerous state-of-the-art satellite, reanalysis, and in-situ datasets from peer-reviewed products using a conventional grid (2.5° spatial resolution averaged over a monthly timescale interval) and name-labeling framework. Primary variables include state-of-the art satellite retrieved cloud properties, radiation fluxes (top and bottom of atmosphere), surface precipitation rates, and snow and sea ice extents. The dataset is geared for scientific inquiry, product validation, and assessment of the radiation and moisture budgets in the Arctic.
Christensen, Matthew W.; Chen, Yi-Chun; Stephens, Graeme L.Christensen, M. W., Y. Chen, G. L. Stephens, 2016: Aerosol indirect effect dictated by liquid clouds. Journal of Geophysical Research: Atmospheres, 121(24), 14,636–14,650. doi: 10.1002/2016JD025245. Anthropogenic aerosols have been shown to enhance the solar reflection from warm liquid clouds and mask part of the warming due to the buildup of greenhouse gases. However, very little is known about the effects of aerosol on mixed-phase stratiform clouds as well as other cloud regimes including cumulus, altocumulus, nimbostratus, deep convection, and anvil cirrus. These additional cloud categories are ubiquitous and typically overlooked in satellite-based assessments of the global aerosol indirect forcing. Here we provide their contribution to the aerosol indirect forcing estimate using satellite data collected from several colocated sensors in the A-train for the period 2006–2010. Cloud type is determined according to the 2B-CLDCLASS-LIDAR CloudSat product, and the observations are matched to the radiative flux measurements from CERES (Clouds and the Earth's Radiant Energy System) and aerosol retrievals from MODIS (MODerate resolution Imaging Spectroradiometer). The oceanic mean aerosol indirect forcing is estimated to be −0.20 ± 0.31 W m−2 with warm low-level cloud largely dictating the strength of the response (−0.36 ± 0.21 W m−2) due to their abundance and strong cloud albedo effect. Contributions from mixed-phase low-level cloud (0.01 ± 0.06 W m−2) and convective cloud (0.15 ± 0.23 W m−2) are positive and buffer the system due to strong aerosol-cloud feedbacks that reduce the cloud albedo effect and/or lead to convective invigoration causing a countering positive longwave warming response. By combining all major cloud categories together, aerosol indirect forcing decreases and now contains positive values in the uncertainty estimate. 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; MODIS; CloudSat; CALIPSO; aerosol-cloud interactions; aerosol indirect forcing; 2B-CLDCLASS-LIDAR
Collow, Allison B. Marquardt; Miller, Mark A.Collow, A. B. M., M. A. Miller, 2016: The Seasonal Cycle of the Radiation Budget and Cloud Radiative Effect in the Amazon Rainforest of Brazil. J. Climate, 29(21), 7703–7722. doi: 10.1175/JCLI-D-16-0089.1. Changes in the climate system of the Amazon Rainforest of Brazil can impact factors that influence the radiation budget such as clouds, atmospheric moisture, and the surface albedo. This study examines the relationships between clouds and radiation in this region using surface observations from the first year of the deployment of the Atmospheric Radiation Measurement Program’s Mobile Facility #1 (AMF1) in Manacapuru, Brazil and satellite measurements from the Clouds and the Earth’s Radiant Energy System (CERES). The seasonal cycles of the radiation budget and Cloud Radiative Effects (CREs) are evaluated at the top of the atmosphere (TOA), surface, and within the atmospheric column using these observations and are placed into a regional context using the Modern Era Retrospective Analysis for Research and Applications – Version 2 (MERRA-2). Water vapor and clouds are abundant throughout the year though slight decreases are observed in the dry season. The column water vapor load is large enough that the longwave radiative flux divergence is nearly constant throughout the year. Clouds produce a significant shortwave CRE at the surface and TOA, exceeding 200 W m-2 during the wet season. Discrepancies, especially in column SW absorption, between the observations and MERRA-2 are demonstrated that warrant additional analysis of the microphysical and macrophysical cloud properties in MERRA-2. More trustworthy fields in the MERRA-2 product suggest that the expansive nearby river system impacts the regional radiation budget and thereby renders AMF1 observations potentially biased relative to regions further removed from rivers within the Amazon Rainforest.
Collow, Allison B.; Ghate, Virendra P.; Miller, Mark A.; Trabachino, Lynne C.Collow, A. B., V. P. Ghate, M. A. Miller, L. C. Trabachino, 2016: A one-year study of the diurnal cycle of meteorology, clouds and radiation in the West African Sahel region. Quarterly Journal of the Royal Meteorological Society, 142(694), 16-29. doi: 10.1002/qj.2623. The diurnal cycles of meteorological and radiation variables are analysed during the wet and dry seasons over the Sahel region of West Africa during 2006 using surface data collected by the Atmospheric Radiation Measurement (ARM) programme's Mobile Facility, satellite radiation measurements from the Geostationary Earth Radiation Budget (GERB) instrument aboard Meteosat 8, and reanalysis products from the National Centers for Environmental Prediction (NCEP). The meteorological analysis builds upon past studies of the diurnal cycle in the region by incorporating diurnal cycles of lower tropospheric wind profiles, thermodynamic profiles, integrated water vapour and liquid water measurements, and cloud radar measurements of frequency and location. These meteorological measurements are complemented by 3 h measurements of the diurnal cycles of the top-of-atmosphere (TOA) and surface short-wave (SW) and long-wave (LW) radiative fluxes and cloud radiative effects (CREs), and the atmospheric radiative flux divergence (RFD) and atmospheric CREs. Cirrus cloudiness during the dry season is shown to peak in coverage in the afternoon, while convective clouds during the wet season are shown to peak near dawn and have an afternoon minimum related to the rise of the lifting condensation level into the Saharan Air Layer. The LW and SW RFDs and CREs exhibit diurnal cycles during both seasons, but there is a relatively small difference in the LW cycles during the two seasons (10 − 30 W m−2 depending on the variable and time of day). Small differences in the TOA CREs during the two seasons are overwhelmed by large differences in the surface SW CREs, which exceed 100 W m−2. A significant surface SW CRE during the wet season combined with a negligible TOA SW CRE produces a diurnal cycle in the atmospheric CRE that is modulated primarily by the SW surface CRE, peaks at midday at ∼150 W m−2, and varies widely from day to day. radiation budget; diurnal cycle; cloud radiative effect; lifting condensation level; radiative flux divergence; Saharan Air Layer; West African Monsoon
Collow, Allison Marquardt; Miller, Mark A.; Trabachino, Lynne C.Collow, A. M., M. A. Miller, L. C. Trabachino, 2016: Cloudiness over the Amazon Rainforest: Meteorology and Thermodynamics. Journal of Geophysical Research: Atmospheres, 121(13), 7990–8005. doi: 10.1002/2016JD024848. Comprehensive meteorological observations collected during GOAmazon2014/15 using the Atmospheric Radiation Measurement Mobile Facility #1 (AMF1) and assimilated observations from the Modern Era Retrospective Analysis for Research and Applications -Version 2 (MERRA-2) are used to document the seasonal cycle of cloudiness, thermodynamics, and precipitation above the Amazon Rainforest. The reversal of synoptic scale vertical motions modulates the transition between a wet and dry season. Ascending moist air during the wet season originates near the surface of the Atlantic Ocean and is advected into the Amazon Rainforest where it experiences convergence and, ultimately, precipitates. The dry season is characterized by weaker winds and synoptic scale subsidence with little or no moisture convergence accompanying moisture advection. This combination results in the drying of the mid-troposphere during June through October as indicated by a decrease in liquid water path, integrated water, and the vertical profile of water vapor mixing ratio. The vertical profile of cloud fraction exhibits a relatively consistent decline in cloud fraction from the LCL to the freezing level where a minimum is observed, unlike many other tropical regions. Coefficients of determination between the Lifting Condensation Level (LCL) and cloud fractional coverage suggest a relatively robust relationship between the LCL and cloudiness beneath 5 km during the dry season (R2 = 0.42), but a weak relationship during the wet season (0.12). 3374 Tropical meteorology; 3310 Clouds and cloud feedbacks; 3354 Precipitation; 3322 Land/atmosphere interactions; Thermodynamics; GoAmazon; lifting condensation level
Crétat, Julien; Masson, Sébastien; Berthet, Sarah; Samson, Guillaume; Terray, Pascal; Dudhia, Jimy; Pinsard, Françoise; Hourdin, ChristopheCrétat, J., S. Masson, S. Berthet, G. Samson, P. Terray, J. Dudhia, F. Pinsard, C. Hourdin, 2016: Control of shortwave radiation parameterization on tropical climate SST-forced simulation. Climate Dynamics, 1-20. doi: 10.1007/s00382-015-2934-1. SST-forced tropical-channel simulations are used to quantify the control of shortwave (SW) parameterization on the mean tropical climate compared to other major model settings (convection, boundary layer turbulence, vertical and horizontal resolutions), and to pinpoint the physical mechanisms whereby this control manifests. Analyses focus on the spatial distribution and magnitude of the net SW radiation budget at the surface (SWnet_SFC), latent heat fluxes, and rainfall at the annual timescale. The model skill and sensitivity to the tested settings are quantified relative to observations and using an ensemble approach. Persistent biases include overestimated SWnet_SFC and too intense hydrological cycle. However, model skill is mainly controlled by SW parameterization, especially the magnitude of SWnet_SFC and rainfall and both the spatial distribution and magnitude of latent heat fluxes over ocean. On the other hand, the spatial distribution of continental rainfall (SWnet_SFC) is mainly influenced by convection parameterization and horizontal resolution (boundary layer parameterization and orography). Physical understanding of the control of SW parameterization is addressed by analyzing the thermal structure of the atmosphere and conducting sensitivity experiments to O3 absorption and SW scattering coefficient. SW parameterization shapes the stability of the atmosphere in two different ways according to whether surface is coupled to atmosphere or not, while O3 absorption has minor effects in our simulations. Over SST-prescribed regions, increasing the amount of SW absorption warms the atmosphere only because surface temperatures are fixed, resulting in increased atmospheric stability. Over land–atmosphere coupled regions, increasing SW absorption warms both atmospheric and surface temperatures, leading to a shift towards a warmer state and a more intense hydrological cycle. This turns in reversal model behavior between land and sea points, with the SW scheme that simulates greatest SW absorption producing the most (less) intense hydrological cycle over land (sea) points. This demonstrates strong limitations for simulating land/sea contrasts in SST-forced simulations. rainfall; Climatology; Oceanography; Geophysics/Geodesy; Latent heat fluxes; Physical parameterizations; Radiative budget; Shortwave radiation schemes; Tropical-channel simulations
Daniels, J. L.; Smith, G. L.; Priestley, K. J.; Thomas, S.Daniels, J. L., G. L. Smith, K. J. Priestley, S. Thomas, 2016: Using Lunar Observations to Validate Clouds and the Earth's Radiant Energy System Pointing Accuracy. IEEE Transactions on Geoscience and Remote Sensing, 54(1), 65-73. doi: 10.1109/TGRS.2015.2450182. To make measurements of the Earth's radiation budget, a pair of Clouds and the Earth's Radiant Energy System (CERES) instruments, i.e., Flight Models (FM) 1 and 2, have flown on the Terra spacecraft since December 1999, and a pair, i.e., FM-3 and FM-4, have flown on the Aqua spacecraft since June 2002. To produce accurate radiation fluxes at the top of the atmosphere and at various levels within the atmosphere and at the surface, CERES data are combined with higher resolution imager data. Validation is necessary to ensure that the accuracy with which the CERES footprints are located on the Earth will be adequate to use the imager data. The Moon provides a useful target for determining the pointing accuracy of the three channels of CERES. Near full moon, the CERES instruments can be turned to look at the Moon as the host spacecraft passes near the pole. The instrument scans the Moon in a raster-like pattern for a few minutes during the orbit when the Moon is in position. A technique has been developed by which these data can be used to compute accurately the direction in which the instrument is pointed in terms of azimuth and elevation angles when it views the Moon. The difference between this direction and the computed direction of the Moon is taken to be the pointing error of the instrument. The technique has been applied to each of the three channels of all four CERES instruments using lunar observation data from 2006 to present. The maximum error was found to be 0.05° in azimuth and 0.03° in elevation angle. This corresponds to an error in geolocation of 0.37 km near nadir. These results agree with those from the coastline detection method within one standard deviation for all but one case, where the difference was one-and-a-half standard deviations. The lunar and coastline techniques supplement each other for computing pixel location errors away from nadir. The alignment of the three channels in each instrument is evaluated as the differences of- azimuth and elevation angles of the shortwave and window channels from those of the total channel. The alignment was within 0.1° for all cases and within 0.02° for most cases. earth radiation budget; Remote sensing; atmospheric radiation; atmospheric techniques; Instruments; Space vehicles; Detectors; validation; Aqua; Terra; oceanographic techniques; CERES data; Clouds and the Earth's Radiant Energy System (CERES); Aqua spacecraft; Orbits; Terra spacecraft; Moon; accuracy; CERES instruments; Clouds and the Earth Radiant Energy System; lunar observations; AD 1999 12; AD 2002 06; Alignment; Azimuth; CERES footprints; coastline detection method; computing pixel location errors; elevation angle; one-and-a-half standard deviations; pointing accuracy; radiation fluxes; raster-like pattern; top-of-the-atmosphere; window channels
de Szoeke, Simon P.; Verlinden, Kathryn L.; Yuter, Sandra E.; Mechem, David B.de Szoeke, S. P., K. L. Verlinden, S. E. Yuter, D. B. Mechem, 2016: The time scales of variability of marine low clouds. J. Climate, 29, 6463–6481. doi: 10.1175/JCLI-D-15-0460.1. Multi-decade global regressions of inversion strength, vertical velocity, and sea surface temperature (SST) on low cloud amount, from sub-daily to multi-year time scales, refute the dominance of seasonal inversion strength on marine low cloud variability. Multi-day low cloud variance averaged over the eastern Pacific and Atlantic stratocumulus regions (5×10−2 cloud amount2) is twice the sub-daily variance and 5 times larger than the multi-month variance. The broad multi-day band contains most (60%) of the variance, despite strong seasonal (annual) and diurnal spectral peaks. Multi-day low cloud amount over the eastern tropical and midlatitude Oceans is positively correlated to inversion strength with a slope of 2-5% K−1. Anecdotes show multi-day low cloud and inversion strength anomalies propagate equatorward from midlatitudes.Previously shown correlations of low clouds to strong inversions and cool SST on monthly and longer time-scales in the stratocumulus regions imply positive cloud-radiative feedbacks with e-folding time scales of 300 days for SST and 14 days for atmospheric boundary layer temperature. On multi-month time scales, removing the effect of SST on low clouds reduces the low cloud amount explained by inversion strength by a factor of 3, but SST has a small effect at other time scales. Contrary to their positive correlation in the stratocumulus cloud decks, low clouds are anticorrelated to inversion strength over most of the tropics on daily and sub-daily time scales.
De, S.; Hazra, Anupam; Chaudhari, Hemantkumar S.De, S., A. Hazra, H. S. Chaudhari, 2016: Does the modification in “critical relative humidity” of NCEP CFSv2 dictate Indian mean summer monsoon forecast? Evaluation through thermodynamical and dynamical aspects. Climate Dynamics, 46(3-4), 1197-1222. doi: 10.1007/s00382-015-2640-z. An accurate seasonal prediction of Indian summer monsoon rainfall (ISMR) is intriguing as well as the most challenging job for monsoon meteorologists. As there is a cause and effect relationship between clouds and precipitation, the modulation of cloud formation in a dynamical model affects profoundly on ISMR. It has already been established that the critical relative humidity (CRH) plays a crucial role on the realistic cloud formation in a general circulation model. Hence, it may be hypothesized that the proper choice of CRH can be instrumental in driving the large scale Indian monsoon by modulating the cloud formation in a global climate model. An endeavor has been made for the first time to test the above hypothesis on the NCEP-CFSv2 model in the perspective of seasonal prediction of ISMR by modifying the CRH profile. The model sensitivity experiments have been carried out for two different CRH profiles along with the existing profile during the normal (2003) and deficient (2009) monsoon years. First profile is the constant CRH following the existing one but with increased magnitude and the second one is the variable CRH at different cloud levels based on the observations and MERRA reanalysis. The ensemble mean of model runs for four initial conditions of each year has revealed that the variable CRH profile in CFSv2 represents seasonal ISMR and its variability best among the three CRH experiments linking with the thermodynamical and dynamical parameters like precipitable water, tropospheric temperature and its gradient, cloud structure and radiation, water vapour flux, systematic error energy with its nonlinear error growth and the length of the rainy seasons during the contrasting years. It has also been shown that the improved depiction of seasonal ISMR has been achieved without disturbing much the forecast biases at other global tropical regions. The indigenous part of this paper is that the CRH modification can play a seminal role in modulating the large scale system like Indian monsoon by representing the realistic variability of cloud formation in CFSv2 and that proves the hypothesis. This work creates an avenue for further development of CFSv2 approaching towards an accurate seasonal forecast of ISMR. Climatology; Oceanography; Geophysics/Geodesy; CFSv2 model; Critical relative humidity; Indian summer monsoon rainfall; Systematic error energy; Water vapour flux
Dodson, J. Brant; Taylor, Patrick C.Dodson, J. B., P. C. Taylor, 2016: Sensitivity of Amazonian TOA Flux Diurnal Cycle Composite Monthly Variability to Choice of Reanalysis. Journal of Geophysical Research: Atmospheres, 121(9), 4404–4428. doi: 10.1002/2015JD024567. Amazonian deep convection experiences a strong diurnal cycle driven by the cycle in surface sensible heat flux, which contributes to a significant diurnal cycle in the top of the atmosphere (TOA) radiative flux. Even when accounting for seasonal variability, the TOA flux diurnal cycle varies significantly on the monthly timescale. Previous work shows evidence supporting a connection between variability in the convective and radiative cycles, likely modulated by variability in monthly atmospheric state (e. g. convective instability). The hypothesized relationships are further investigated with regression analysis of the radiative diurnal cycle and atmospheric state using additional meteorological variables representing convective instability and upper tropospheric humidity. The results are recalculated with three different reanalyses to test the reliability of the results. The radiative diurnal cycle sensitivity to upper tropospheric humidity is about equal in magnitude to that of convective instability. In addition, the results are recalculated with the data subdivided into the wet and dry seasons. Overall, clear-sky radiative effects have a dominant role in radiative diurnal cycle variability during the dry season. Because of this, even in a convectively active region, the clear-sky radiative effects must be accounted for in order to fully explain the monthly variability in diurnal cycle. Finally, while there is general agreement between the different reanalysis-based results when examining the full data time domain (without regard to time of year), there are significant disagreements when the data are divided into wet and dry seasons. The questionable reliability of reanalysis data is a major limitation. CERES; convection; 3305 Climate change and variability; 3374 Tropical meteorology; 3310 Clouds and cloud feedbacks; 3314 Convective processes; reanalysis; 3360 Remote sensing; Amazon; diurnal cycle; TOA flux
Doelling, David R.; Haney, Conor O.; Scarino, Benjamin R.; Gopalan, Arun; Bhatt, RajendraDoelling, D. R., C. O. Haney, B. R. Scarino, A. Gopalan, R. Bhatt, 2016: Improvements to the geostationary visible imager ray-matching calibration algorithm for CERES Edition 4. J. Atmos. Oceanic Technol., 33(12), 2679–2698. doi: 10.1175/JTECH-D-16-0113.1. The Clouds and the Earth’s Radiant Energy System CERES project relies on geostationary- (GEO) imager-derived TOA broadband fluxes and cloud properties to account for the regional diurnal fluctuations between the Terra and Aqua CERES and MODIS measurements. The CERES project employs a ray-matching calibration algorithm in order to transfer the Aqua-MODIS calibration to the GEO imagers, thereby allowing the derivation of consistent fluxes and cloud retrievals across the 16 GEO imagers utilized in the CERES record. The CERES Edition 4 processing scheme grants the opportunity to recalibrate the GEO record using an improved GEO/MODIS all-sky ocean ray-matching algorithm. Using a graduated angle matching method, which is most restrictive for anisotropic clear-sky ocean radiances and least restrictive for isotropic bright cloud radiances, reduces the bidirectional bias while preserving the dynamic range. Furthermore, SCIAMACHY hyperspectral radiances are used to account for both the solar incoming and Earth reflected spectra in order to correct spectral band differences. As a result, the difference between the linear regression offset and the maintained GEO space count was reduced, and the calibration slopes computed from the linear fit and the regression through the space count agreed to within 0.4%. A deep convective cloud (DCC) ray-matching algorithm is also presented. The all-sky ocean and DCC ray-matching timeline gains are within 0.7% of one another. Because DCC are isotropic and the brightest Earth targets with near uniform visible spectra, the temporal standard error of GEO imager gains are reduced by up to 60% from that of all-sky ocean targets.
Doelling, David R.; Sun, Moguo; Nguyen, Le Trang; Nordeen, Michele L.; Haney, Conor O.; Keyes, Dennis F.; Mlynczak, Pamela E.Doelling, D. R., M. Sun, L. T. Nguyen, M. L. Nordeen, C. O. Haney, D. F. Keyes, P. E. Mlynczak, 2016: Advances in Geostationary-Derived Longwave Fluxes for the CERES Synoptic (SYN1deg) Product. J. Atmos. Oceanic Technol., 33(3), 503-521. doi: 10.1175/JTECH-D-15-0147.1. The Clouds and the Earth’s Radiant Energy System (CERES) project has provided the climate community 15 years of globally observed top-of-the-atmosphere fluxes critical for climate and cloud feedback studies. To accurately monitor the earth’s radiation budget, the CERES instrument footprint fluxes must be spatially and temporally averaged properly. The CERES synoptic 1° (SYN1deg) product incorporates derived fluxes from the geostationary satellites (GEOs) to account for the regional diurnal flux variations in between Terra and Aqua CERES measurements. The Edition 4 CERES reprocessing effort has provided the opportunity to reevaluate the derivation of longwave (LW) fluxes from GEO narrowband radiances by examining the improvements from incorporating 1-hourly versus 3-hourly GEO data, additional GEO infrared (IR) channels, and multichannel GEO cloud properties. The resultant GEO LW fluxes need to be consistent across the 16-satellite climate data record. To that end, the addition of the water vapor channel, available on all GEOs, was more effective than using a reanalysis dataset’s column-weighted relative humidity combined with the window channel radiance. The benefit of the CERES LW angular directional model to derive fluxes was limited by the inconsistency of the GEO cloud retrievals. Greater success was found in the direct conversion of window and water vapor channel radiances into fluxes. Incorporating 1-hourly GEO fluxes had the greatest impact on improving the accuracy of high-temporal-resolution fluxes, and normalizing the GEO LW fluxes with CERES greatly reduced the monthly regional LW flux bias.
Dolinar, Erica K.; Dong, Xiquan; Xi, BaikeDolinar, E. K., X. Dong, B. Xi, 2016: Evaluation and intercomparison of clouds, precipitation, and radiation budgets in recent reanalyses using satellite-surface observations. Climate Dynamics, 46(7-8), 2123-2144. doi: 10.1007/s00382-015-2693-z. Atmospheric reanalysis datasets offer a resource for investigating climate processes and extreme events; however, their uncertainties must first be addressed. In this study, we evaluate the five reanalyzed (20CR, CFSR, Era-Interim, JRA-25, and MERRA) cloud fraction (CF), precipitation rates (PR), and top-of-atmosphere (TOA) and surface radiation budgets using satellite observations during the period 03/2000–02/2012. Compared to the annual averaged CF of 56.7 % from CERES MODIS (CM) four of the five reanalyses underpredict CFs by 1.7–4.6 %, while 20CR overpredicts this result by 7.4 %. PR from the Tropical Rainfall Measurement Mission (TRMM) is 3.0 mm/day and the reanalyzed PRs agree with TRMM within 0.1–0.6 mm/day. The shortwave (SW) and longwave (LW) TOA cloud radiative effects (CREtoa) calculated by CERES EBAF (CE) are −48.1 and 27.3 W/m2, respectively, indicating a net cooling effect of −20.8 W/m2. Of the available reanalysis results, the CFSR and MERRA calculated net CREtoa values agree with CE within 1 W/m2, while the JRA-25 result is ~10 W/m2 more negative than the CE result, predominantly due to the underpredicted magnitude of the LW warming in the JRA-25 reanalysis. A regime metric is developed using the vertical motion field at 500 hPa over the oceans. Aptly named the “ascent” and “descent” regimes, these areas are distinguishable in their characteristic synoptic patterns and the predominant cloud-types; convective-type clouds and marine boundary layer (MBL) stratocumulus clouds. In general, clouds are overpredicted (underpredicted) in the ascent (descent) regime and the biases are often larger in the ascent regime than in the descent regime. PRs are overpredicted in both regimes; however the observed and reanalyzed PRs over the ascent regime are an order of magnitude larger than those over the descent regime, indicating different types of clouds exist in these two regimes. Based upon the Atmospheric Radiation Measurement Program ground-based and CM satellite observations, as well as reanalyzed results, the annual CFs are 15 % higher at the Azores site than at the Nauru site (70.2 vs. 55.2 %), less SW radiation (~20 %) is transmitted the surface, and less LW radiation (~60 W/m2) is emitted back to the surface. Also, the seasonal variations in both CF and surface radiation fluxes are much smaller at the Nauru site than at the Azores site. The dichotomy between the atmospheric ascent and descent regimes is a good measure for determining which parameterization scheme requires more improvement (convective vs. MBL clouds) in these five reanalyses. Climatology; Oceanography; Geophysics/Geodesy
Dolinar, Erica K.; Dong, Xiquan; Xi, Baike; Jiang, Jonathan H.; Loeb, Norman G.Dolinar, E. K., X. Dong, B. Xi, J. H. Jiang, N. G. Loeb, 2016: A clear-sky radiation closure study using a one-dimensional radiative transfer model and collocated satellite-surface-reanalysis data sets. Journal of Geophysical Research: Atmospheres, 121(22), 2016JD025823. doi: 10.1002/2016JD025823. Earth's climate is largely determined by the planet's energy budget, i.e., the balance of incoming and outgoing radiation at the surface and top of atmosphere (TOA). Studies have shown that computing clear-sky radiative fluxes are strongly dependent on atmospheric state variables, such as temperature and water vapor profiles, while the all-sky fluxes are greatly influenced by the presence of clouds. NASA-modeled vertical profiles of temperature and water vapor are used to derive the surface radiation budget from Clouds and Earth Radiant Energy System (CERES), which is regarded as one of the primary sources for evaluating climate change in climate models. In this study, we evaluate the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) reanalyzed clear-sky temperature and water vapor profiles with newly generated atmospheric profiles from Department of Energy Atmospheric Radiation Measurement (ARM)-merged soundings and Aura Microwave Limb Sounder retrievals at three ARM sites. The temperature profiles are well replicated in MERRA-2 at all three sites, whereas tropospheric water vapor is slightly dry below ~700 hPa. These profiles are then used to calculate clear-sky surface and TOA radiative fluxes from the Langley-modified Fu-Liou radiative transfer model (RTM). In order to achieve radiative closure at both the surface and TOA, the ARM-measured surface albedos and aerosol optical depths are adjusted to account for surface inhomogeneity. In general, most of the averaged RTM-calculated surface downward and TOA upward shortwave and longwave fluxes agree within ~5 W/m2 of the observations, which is within the uncertainties of the ARM and CERES measurements. Yet still, further efforts are required to reduce the bias in calculated fluxes in coastal regions. 0360 Radiation: transmission and scattering; 1640 Remote sensing; 0394 Instruments and techniques; 3359 Radiative processes; 1990 Uncertainty; CERES SSF; clear-sky flux; MERRA-2; MLS; radiation closure; water vapor profile
Dong, Xiquan; Xi, Baike; Qiu, Shaoyue; Minnis, Patrick; Sun-Mack, Sunny; Rose, FredDong, X., B. Xi, S. Qiu, P. Minnis, S. Sun-Mack, F. Rose, 2016: A Radiation Closure Study of Arctic Stratus Cloud Microphysical Properties using the collocated satellite-surface data and Fu-Liou Radiative Transfer Model. Journal of Geophysical Research: Atmospheres, 121(17), 10,175–10,198. doi: 10.1002/2016JD025255. Retrievals of cloud microphysical properties based on passive satellite imagery are especially difficult over snow-covered surfaces because of the bright and cold surface. To help quantify their uncertainties, single-layered overcast liquid-phase Arctic stratus cloud microphysical properties retrieved using the CERES Ed2 and Ed4 algorithms are compared with ground-based retrievals at the ARM NSA site at Barrow, AK during the period from March 2000 to December 2006. A total of 206 and 140 snow-free cases (Rsfc ≤ 0.3), and 108 and 106 snow cases (Rsfc > 0.3), respectively, were selected from Terra and Aqua satellite passes over the ARM NSA site. The CERES Ed4 and Ed2 optical depth (τ) and LWP retrievals from both Terra and Aqua are almost identical and have excellent agreement with ARM retrievals under snow-free and snow conditions. In order to reach a radiation closure study for both the surface and TOA radiation budgets, the ARM PSP-measured surface albedos were adjusted (63.6% and 80% of the ARM surface albedos for snow-free and snow cases, respectively) to account for the water and land components of the domain of 30-km x 30-km. Most of the RTM calculated SW↓sfc and SW↑TOA fluxes using ARM and CERES cloud retrievals and the domain mean albedos as input agree with the ARM and CERES flux observations within 10 W m-2 for both snow-free and snow conditions. Sensitivity studies show that the ARM LWP and re retrievals are less dependent on solar zenith angle (SZA), but all retrieved optical depths increase with SZA. 0360 Radiation: transmission and scattering; 1640 Remote sensing; satellite remote sensing; 0321 Cloud/radiation interaction; 3359 Radiative processes; 9315 Arctic region; Arctic Stratus Cloud Properties; Radiation Closure Study; Surface Remote Sensing
Feng, Y.; Liu, Q.; Qu, Y.; Liang, S.Feng, Y., Q. Liu, Y. Qu, S. Liang, 2016: Estimation of the Ocean Water Albedo From Remote Sensing and Meteorological Reanalysis Data. IEEE Transactions on Geoscience and Remote Sensing, 54(2), 850-868. doi: 10.1109/TGRS.2015.2468054. Ocean water albedo (OWA) plays an important role in the global climate variation. Compared with the achievements in land surface albedo studies, the global distributions of ocean water and sea ice albedo are seldom addressed. This study designed an operational global OWA algorithm based on the three-component reflectance model of the ocean water: sun glint, whitecaps, and water-leaving reflectance. The related achievements in these three areas are reviewed and integrated into the operational algorithm. After the sensitive analysis, the algorithm is compared with previous studies and validated with ground observations at COVE site located 25 km east of Virginia Beach (36.91° N, 75.71° W), and the results indicate that the proposed algorithm is generally consistent with previous parameterization scheme. As an example, the global OWAs in summer and winter 2011 are generated using the remote sensing reflectance data sets via the Moderate Resolution Imaging Spectroradiometer and Modern-Era Retrospective analysis for Research and Applications meteorological reanalysis data set. The generated product includes instantaneous (e.g., local noon) and daily mean OWAs under both clear-sky and white-sky conditions. Upon the examples, the local noon clear-sky OWA shows a significant latitude variation due to the dominance of the solar angle, whereas the white-sky OWA is sensitive to wind speeds and optical constituents. The global distribution of the daily mean OWA exhibits a similar trend to the local noon OWA. However, the daily mean clear-sky OWA is significantly larger than the local noon OWA; this finding should be noted when using OWA products for energy balance research. Additionally, all forms of OWA products exhibit increase in coastal areas with high input of terrestrial matters. Remote sensing; Data analysis; albedo; Wind speed; sea ice; Sea measurements; Sea surface; Sea ice albedo; AD 2011; Biological system modeling; COVE site; global climate variation; global OWA algorithm; land surface albedo study; Moderate Resolution Imaging Spectroradiometer dataset; Modern-Era Retrospective analysis for Research and Applications meteorological reanalysis dataset; Ocean water albedo (OWA); ocean water albedo estimation; ocean water global distribution; Open wireless architecture; remote sensing reflectance dataset; seawater; solar angle; summer season; sun glint; Virginia beach; water-leaving reflectance; whitecaps; winter season
Foster, M.; Ackerman, S.; Bedka, K.; Frey, R.; Di Girolmao, L.; Heidinger, A.; Sun-Mack, S.; Maddux, B.; Menzel, W.; Minnis, P.; Stengel, M.; Zhao, G.Foster, M., S. Ackerman, K. Bedka, R. Frey, L. Di Girolmao, A. Heidinger, S. Sun-Mack, B. Maddux, W. Menzel, P. Minnis, M. Stengel, G. Zhao, 2016: Cloudiness [in “State of the Climate in 2015"]. Bull. Amer. Meteor. Soc., 96(8), S28-S29. doi: 10.1175/2016BAMSStateoftheClimate.1.
Furtado, K.; Field, P. R.; Boutle, I. A.; Morcrette, C. J.; Wilkinson, J. M.Furtado, K., P. R. Field, I. A. Boutle, C. J. Morcrette, J. M. Wilkinson, 2016: A Physically Based Subgrid Parameterization for the Production and Maintenance of Mixed-Phase Clouds in a General Circulation Model. J. Atmos. Sci., 73(1), 279-291. doi: 10.1175/JAS-D-15-0021.1. A physically based method for parameterizing the role of subgrid-scale turbulence in the production and maintenance of supercooled liquid water and mixed-phase clouds is presented. The approach used is to simplify the dynamics of supersaturation fluctuations to a stochastic differential equation that can be solved analytically, giving increments to the prognostic liquid cloud fraction and liquid water content fields in a general circulation model (GCM). Elsewhere, it has been demonstrated that the approach captures the properties of decameter-resolution large-eddy simulations of a turbulent mixed-phase environment. In this paper, it is shown that it can be implemented in a GCM, and the effects that this has on Southern Ocean biases and on Arctic stratus are investigated. Cloud parameterizations; Cloud water/phase; Condensation; Models and modeling; Physical Meteorology and Climatology; Subgrid-scale processes
Glotfelty, Timothy; Zhang, Yang; Karamchandani, Prakash; Streets, David G.Glotfelty, T., Y. Zhang, P. Karamchandani, D. G. Streets, 2016: Changes in future air quality, deposition, and aerosol-cloud interactions under future climate and emission scenarios. Atmospheric Environment, 139, 176-191. doi: 10.1016/j.atmosenv.2016.05.008. The prospect of global climate change will have wide scale impacts, such as ecological stress and human health hazards. One aspect of concern is future changes in air quality that will result from changes in both meteorological forcing and air pollutant emissions. In this study, the GU-WRF/Chem model is employed to simulate the impact of changing climate and emissions following the IPCC AR4 SRES A1B scenario. An average of 4 future years (2020, 2030, 2040, and 2050) is compared against an average of 2 current years (2001 and 2010). Under this scenario, by the Mid-21st century global air quality is projected to degrade with a global average increase of 2.5 ppb in the maximum 8-hr O3 level and of 0.3 μg m−3 in 24-hr average PM2.5. However, PM2.5 changes are more regional due to regional variations in primary aerosol emissions and emissions of gaseous precursor for secondary PM2.5. Increasing NOx emissions in this scenario combines with a wetter climate elevating levels of OH, HO2, H2O2, and the nitrate radical and increasing the atmosphere’s near surface oxidation state. This differs from findings under the RCP scenarios that experience declines in OH from reduced NOx emissions, stratospheric recovery of O3, and increases in CH4 and VOCs. Increasing NOx and O3 levels enhances the nitrogen and O3 deposition, indicating potentially enhanced crop damage and ecosystem stress under this scenario. The enhanced global aerosol level results in enhancements in aerosol optical depth, cloud droplet number concentration, and cloud optical thickness. This leads to dimming at the Earth’s surface with a global average reduction in shortwave radiation of 1.2 W m−2. This enhanced dimming leads to a more moderate warming trend and different trends in radiation than those found in NCAR’s CCSM simulation, which does not include the advanced chemistry and aerosol treatment of GU-WRF/Chem and cannot simulate the impacts of changing climate and emissions with the same level of detailed treatments. This study indicates that effective climate mitigation and emission control strategies are needed to prevent future health impact and ecosystem stress. Further, studies that are used to develop these strategies should use fully coupled models with sophisticated chemical and aerosol-interaction treatments that can provide a more realistic representation of the atmosphere. aerosol indirect effects; Future air quality; Aerosol direct effect; Online-coupled model; Global climate and emissions change; GU_WRF/Chem
Grise, Kevin M.; Medeiros, BrianGrise, K. M., B. Medeiros, 2016: Understanding the varied influence of mid-latitude jet position on clouds and cloud-radiative effects in observations and global climate models. J. Climate, 29(24), 9005–9025. doi: 10.1175/JCLI-D-16-0295.1. This study examines the dynamical mechanisms responsible for changes in mid-latitude clouds and cloud-radiative effects (CRE) that occur in conjunction with meridional shifts in the jet streams over the North Atlantic, North Pacific, and Southern Oceans. When the mid-latitude jet shifts poleward, extratropical cyclones and their associated upward vertical velocity anomalies closely follow. As a result, a poleward jet shift contributes to a poleward shift in high-topped storm track clouds and their associated longwave CRE. However, when the jet shifts poleward, downward vertical velocity anomalies increase equatorward of the jet, contributing to an enhancement of the boundary layer inversion strength (EIS) and an increase in low cloud amount there. Because shortwave CRE depends on the reflection of solar radiation by clouds in all layers, the shortwave cooling effects of mid-latitude clouds increase with both upward vertical velocity anomalies and positive EIS anomalies. Over mid-latitude oceans where a poleward jet shift contributes to positive EIS anomalies but downward vertical velocity anomalies, the two effects cancel, and net observed changes in shortwave CRE are small.Global climate models generally capture the observed anomalies associated with mid-latitude jet shifts. However, there is large inter-model spread in the shortwave CRE anomalies, with a subset of models showing a large shortwave cloud-radiative warming over mid-latitude oceans with a poleward jet shift. In these models, mid-latitude shortwave CRE is sensitive to vertical velocity perturbations, but the observed sensitivity to EIS perturbations is underestimated. Consequently, these models might incorrectly estimate future mid-latitude cloud feedbacks in regions where appreciable changes in both vertical velocity and EIS are projected.
Gryspeerdt, E.; Quaas, J.; Bellouin, N.Gryspeerdt, E., J. Quaas, N. Bellouin, 2016: Constraining the aerosol influence on cloud fraction. Journal of Geophysical Research: Atmospheres, 121(7), 3566–3583. doi: 10.1002/2015JD023744. Aerosol–cloud interactions have the potential to modify many different cloud properties. There is significant uncertainty in the strength of these aerosol–cloud interactions in analyses of observational data, partly due to the difficulty in separating aerosol effects on clouds from correlations generated by local meteorology. The relationship between aerosol and cloud fraction (CF) is particularly important to determine, due to the strong correlation of CF to other cloud properties and its large impact on radiation. It has also been one of the hardest to quantify from satellites due to the strong meteorological covariations involved. This work presents a new method to analyse the relationship between aerosol optical depth (AOD) and CF. By including information about the cloud droplet number concentration (CDNC), the impact of the meteorological covariations is significantly reduced. This method shows that much of the AOD-CF correlation is explained by relationships other than that mediated by CDNC. By accounting for these, the strength of the global mean AOD-CF relationship is reduced by around 80%. This suggests that the majority of the AOD-CF relationship is due to meteorological covariations, especially in the shallow cumulus regime. Requiring CDNC to mediate the AOD-CF relationship implies an effective anthropogenic radiative forcing from an aerosol influence on liquid CF of -0.48 Wm−2(−0.1 to −0.64 Wm−2), although some uncertainty remains due to possible biases in the CDNC retrievals in broken cloud scenes. clouds; 0320 Cloud physics and chemistry; 0305 Aerosols and particles; aerosols; aerosol-cloud interactions; causality
Gupta, P.; Joiner, J.; Vasilkov, A.; Bhartia, P. K.Gupta, P., J. Joiner, A. Vasilkov, P. K. Bhartia, 2016: Top-of-the-atmosphere shortwave flux estimation from satellite observations: an empirical neural network approach applied with data from the A-train constellation. Atmos. Meas. Tech., 9(7), 2813-2826. doi: 10.5194/amt-9-2813-2016. Estimates of top-of-the-atmosphere (TOA) radiative flux are essential for the understanding of Earth's energy budget and climate system. Clouds, aerosols, water vapor, and ozone (O3) are among the most important atmospheric agents impacting the Earth's shortwave (SW) radiation budget. There are several sensors in orbit that provide independent information related to these parameters. Having coincident information from these sensors is important for understanding their potential contributions. The A-train constellation of satellites provides a unique opportunity to analyze data from several of these sensors. In this paper, retrievals of cloud/aerosol parameters and total column ozone (TCO) from the Aura Ozone Monitoring Instrument (OMI) have been collocated with the Aqua Clouds and Earth's Radiant Energy System (CERES) estimates of total reflected TOA outgoing SW flux (SWF). We use these data to develop a variety of neural networks that estimate TOA SWF globally over ocean and land using only OMI data and other ancillary information as inputs and CERES TOA SWF as the output for training purposes. OMI-estimated TOA SWF from the trained neural networks reproduces independent CERES data with high fidelity. The global mean daily TOA SWF calculated from OMI is consistently within ±1 % of CERES throughout the year 2007. Application of our neural network method to other sensors that provide similar retrieved parameters, both past and future, can produce similar estimates TOA SWF. For example, the well-calibrated Total Ozone Mapping Spectrometer (TOMS) series could provide estimates of TOA SWF dating back to late 1978.
Hakuba, Maria Z.; Folini, Doris; Wild, MartinHakuba, M. Z., D. Folini, M. Wild, 2016: On the Zonal Near-Constancy of Fractional Solar Absorption in the Atmosphere. J. Climate, 29(9), 3423-3440. doi: 10.1175/JCLI-D-15-0277.1. Over Europe, a recent study found the fractional all-sky atmospheric solar absorption to be largely unaffected by variations in latitude, remaining nearly constant at its regional mean of 23% ± 1%, relative to the respective top-of-atmosphere insolation. The satellite-based CERES EBAF dataset (2000–10) confirms the weak latitude dependence within 23% ± 2%, representative of the near-global scale between 60°S and 60°N. Under clear-sky conditions, the fractional absorption follows the spatial imprint of the water vapor path, peaking in the tropics and decreasing toward the poles, accompanied by a slight hemispheric asymmetry. In the northern extratropics, the clear-sky absorption attains zonal near-constancy due to combined water vapor, surface albedo, and aerosol effects that are largely amiss in the Southern Hemisphere. In line with earlier studies, the CERES EBAF suggests an increase in atmospheric solar absorption due to clouds by on average 1.5% (5 W m−2) from 21.5% (78 W m−2) under clear-sky conditions to 23% (83 W m−2) under all-sky conditions (60°S–60°N). The low-level clouds in the extratropics act to enhance the absorption, whereas the high clouds in the tropics exhibit a near-zero effect. Consequently, clouds reduce the latitude dependence of fractional atmospheric solar absorption and yield a near-constant zonal mean pattern under all-sky conditions. In the GEWEX-SRB satellite product and the historical simulations from phase 5 of CMIP (CMIP5; 1996–2005, multimodel mean) the amount of insolation absorbed by the atmosphere is reduced by around −1.3% (5 W m−2) with respect to the CERES EBAF mean. The zonal variability and magnitude of the atmospheric cloud effect are, however, largely in line.
Ham, Seung-Hee; Kato, Seiji; Rose, Fred G.Ham, S., S. Kato, F. G. Rose, 2016: Correction of ocean hemispherical spectral reflectivity for longwave irradiance computations. Journal of Quantitative Spectroscopy and Radiative Transfer, 171, 57-65. doi: 10.1016/j.jqsrt.2015.12.003. This study demonstrates that upward infrared irradiances have negative modeling biases when the ocean hemispherical spectral reflectivity is used. The biases increase with increasing air temperature and with decreasing water vapor amount. Spectral biases in the surface upward longwave irradiance from 4 μm to 80 μm are between −0.4 and 0 W m−2 μm−1, while longwave broadband biases are between −2 and −1 W m−2. The negative biases stem from surface-reflected component because an irradiance radiative transfer model ignores the correlation between the downward radiance and directional reflectivity. Therefore, a positive correction factor to the hemispherical spectral reflectivity for the irradiance radiative transfer model is needed. A simple parameterization using an anisotropic factor for downward radiances is developed to correct reflectivity for various atmospheric conditions. longwave; Irradiance; Directional reflectivity; Hemispherical reflectivity; Reflectivity correction factor
Han, Yang; Weng, Fuzhong; Zou, Xiaolei; Yang, Hu; Scott, DeronHan, Y., F. Weng, X. Zou, H. Yang, D. Scott, 2016: Characterization of Geolocation Accuracy of Suomi NPP Advanced Technology Microwave Sounder Measurements. Journal of Geophysical Research: Atmospheres, 121(9), 4933–4950. doi: 10.1002/2015JD024278. The Advanced Technology Microwave Sounder (ATMS) onboard Suomi National Polar-orbiting Partnership (SNPP) satellite has 22 channels at frequencies ranging from 23 to 183 GHz for probing the atmospheric temperature and moisture under all weather conditions. As part of the ATMS calibration and validation (Cal/Val) activities, the geolocation accuracy of ATMS data must be well characterized and documented. In this study, the coastline crossing method (CCM) and the land-sea fraction method (LFM) are utilized to characterize and quantify the ATMS geolocation accuracy. The CCM is based on the inflection points of the ATMS window channel measurements across the coastlines whereas the LFM collocates the ATMS window channel data with high-resolution land sea mask datasets. Since the ATMS measurements provide five pairs of latitude and longitude data for K, Ka, V, W and G bands, respectively, the window channels 1, 2, 3, 16 and 17 from each of these five bands are chosen for assessing the overall geolocation accuracy. ATMS geolocation errors estimated from both methods are generally consistent from 40 cases in June, 2014. The ATMS along-track (cross-track) errors at nadir are within ±4.2 km (±1.2 km) for K/Ka, ±2.6 km (±2.7 km) for V bands, ±1.2 km (±0.6 km) at W and G band, respectively. At the W band, the geolocation errors derived from both algorithms are probably less reliable due to a reduced contrast of brightness temperatures in coastal areas. These estimated ATMS along-track and cross-track geolocation errors are well within the uncertainty requirements for all bands. 3360 Remote sensing; ATMS geolocation errors assessment; Coastline crossing method (CCM); Land-sea fraction method (LFM)
Hartmann, Dennis L.Hartmann, D. L., 2016: Global Physical Climatology. Global Physical Climatology, Second Edition, provides an introduction to the science of climate and climate change. It begins with a basic introduction to the climate system, and then introduces the physics of the climate system, including the principles and processes that determine the structure and climate of the atmosphere, ocean, and land surface. This basic knowledge is then applied to understanding natural variability of the climate in both the present and past, the sensitivity of climate to external forcing, explanations for the ice ages, and the science of human-induced climate change. The physical principles and computer models necessary for understanding past climate and predicting future climate are introduced.Covers a great range of information on the Earth’s climate system and how it works Includes a basic introduction to the physics of climate suitable for physical science majorsProvides an overview of the central themes of modern research on climate change suitable for beginning researchersIncorporates problem sets to aid learning Offers an authoritative, clearly written, well-illustrated text with up-to-date data and modeling results Science / Earth Sciences / General; Science / Earth Sciences / Meteorology & Climatology
Hay, William W.Hay, W. W., 2016: The Circulation of Earth’s Atmosphere. Experimenting on a Small Planet, 556-577.
Haywood, Jim M.; Jones, Andy; Dunstone, Nick; Milton, Sean; Vellinga, Michael; Bodas-Salcedo, Alejandro; Hawcroft, Matt; Kravitz, Ben; Cole, Jason; Watanabe, Shingo; Stephens, GraemeHaywood, J. M., A. Jones, N. Dunstone, S. Milton, M. Vellinga, A. Bodas-Salcedo, M. Hawcroft, B. Kravitz, J. Cole, S. Watanabe, G. Stephens, 2016: The impact of equilibrating hemispheric albedos on tropical performance in the HadGEM2-ES coupled climate model. Geophysical Research Letters, 43(1), 395-403. doi: 10.1002/2015GL066903. The Earth's hemispheric reflectances are equivalent to within ± 0.2 Wm−2, even though the Northern Hemisphere contains a greater proportion of higher reflectance land areas, because of greater cloud cover in the Southern Hemisphere. This equivalence is unlikely to be by chance, but the reasons are open to debate. Here we show that equilibrating hemispheric albedos in the Hadley Centre Global Environment Model version 2-Earth System coupled climate model significantly improves what have been considered longstanding and apparently intractable model biases. Monsoon precipitation biases over all continental land areas, the penetration of monsoon rainfall across the Sahel, the West African monsoon “jump”, and indicators of hurricane frequency are all significantly improved. Mechanistically, equilibrating hemispheric albedos improves the atmospheric cross-equatorial energy transport and increases the supply of tropical atmospheric moisture to the Hadley cell. We conclude that an accurate representation of the cross-equatorial energy transport appears to be critical if tropical performance is to be improved. 3337 Global climate models; 3374 Tropical meteorology; 3371 Tropical convection; 3372 Tropical cyclones; 3373 Tropical dynamics; couple climate models; HadGEM2-ES; Hemispheric albedo; Hurricane frequency; tropical precipitation
Hill, Peter G.; Allan, Richard P.; Chiu, J. Christine; Stein, Thorwald H. M.Hill, P. G., R. P. Allan, J. C. Chiu, T. H. M. Stein, 2016: A multi-satellite climatology of clouds, radiation and precipitation in southern West Africa and comparison to climate models. Journal of Geophysical Research: Atmospheres, 121(18), 10,857–10,879. doi: 10.1002/2016JD025246. Southern West Africa (SWA) has a large population that relies on highly variable monsoon rainfall, yet climate models show little consensus over projected precipitation in this region. Understanding of the current and future climate of SWA is further complicated by rapidly increasing anthropogenic emissions and a lack of surface observations. Using multiple satellite observations, the ERA-Interim reanalysis, and four climate models, we document the climatology of cloud, precipitation and radiation over SWA in June-July, highlight discrepancies among satellite products, and identify shortcomings in climate models and ERA-Interim. Large differences exist between monthly mean cloud cover estimates from satellites, which range from 68 to 94 %. In contrast, differences among satellite observations in top of atmosphere outgoing radiation and surface precipitation are smaller, with monthly means of about 230 W m–2 of longwave radiation, 145 W m–2 of shortwave radiation and 5.87 mm day–1 of precipitation. Both ERA-Interim and the climate models show less total cloud cover than observations, mainly due to underestimating low cloud cover. Errors in cloud cover, along with uncertainty in surface albedo, lead to a large spread of outgoing shortwave radiation. Both ERA-Interim and the climate models also show signs of convection developing too early in the diurnal cycle, with associated errors in the diurnal cycles of precipitation and outgoing longwave radiation. Clouds, radiation and precipitation are linked in an analysis of the regional energy budget, which shows that inter-annual variability of precipitation and dry static energy divergence are strongly linked clouds; 3309 Climatology; radiation; Precipitation; monsoon; Africa
Hirota, Nagio; Takayabu, Yukari N.; Hamada, AtsushiHirota, N., Y. N. Takayabu, A. Hamada, 2016: Reproducibility of Summer Precipitation over Northern Eurasia in CMIP5 Multiclimate Models. J. Climate, 29(9), 3317-3337. doi: 10.1175/JCLI-D-15-0480.1. Reproducibility of summer precipitation over northern Eurasia in climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) is evaluated in comparison with several observational and reanalysis datasets. All CMIP5 models under- and overestimate precipitation over western and eastern Eurasia, respectively, and the reproducibility measured using the Taylor skill score is largely determined by the severity of these west–east precipitation biases. The following are the two possible causes for the precipitation biases: very little cloud cover and very strong local evaporation–precipitation coupling. The models underestimate cloud cover over Eurasia, allowing too much sunshine and leading to a warm bias at the surface. The associated cyclonic circulation biases in the lower troposphere weaken the modeled moisture transport from the Atlantic to western Eurasia and enhance the northward moisture flux along the eastern coast. Once the dry west and wet east biases appear in the models, they become amplified because of stronger evaporation–precipitation coupling. The CMIP5 models reproduce precipitation events well over a time scale of several days, including the associated low pressure systems and local convection. However, the modeled precipitation events are relatively weaker over western Eurasia and stronger over eastern Eurasia compared to the observations, and these are consistent with the biases found in the seasonal average fields.
Holdaway, Daniel; Yang, YuekuiHoldaway, D., Y. Yang, 2016: Study of the Effect of Temporal Sampling Frequency on DSCOVR Observations Using the GEOS-5 Nature Run Results (Part I): Earth’s Radiation Budget. Remote Sensing, 8(2), 98. doi: 10.3390/rs8020098. Satellites always sample the Earth-atmosphere system in a finite temporal resolution. This study investigates the effect of sampling frequency on the satellite-derived Earth radiation budget, with the Deep Space Climate Observatory (DSCOVR) as an example. The output from NASA’s Goddard Earth Observing System Version 5 (GEOS-5) Nature Run is used as the truth. The Nature Run is a high spatial and temporal resolution atmospheric simulation spanning a two-year period. The effect of temporal resolution on potential DSCOVR observations is assessed by sampling the full Nature Run data with 1-h to 24-h frequencies. The uncertainty associated with a given sampling frequency is measured by computing means over daily, monthly, seasonal and annual intervals and determining the spread across different possible starting points. The skill with which a particular sampling frequency captures the structure of the full time series is measured using correlations and normalized errors. Results show that higher sampling frequency gives more information and less uncertainty in the derived radiation budget. A sampling frequency coarser than every 4 h results in significant error. Correlations between true and sampled time series also decrease more rapidly for a sampling frequency less than 4 h. climate change; radiation budget; Arctic; GEOS-5; DSCOVR; EPIC; Nature Run; satellite sampling frequency; time series
Hong, Yulan; Liu, Guosheng; Li, J.-L. F.Hong, Y., G. Liu, J. F. Li, 2016: Assessing the Radiative Effects of Global Ice Clouds Based on CloudSat and CALIPSO Measurements. J. Climate, 29(21), 7651–7674. doi: 10.1175/JCLI-D-15-0799.1. Although it is well-established that cirrus warms the Earth, the radiative effect of the entire spectrum of ice clouds is not well understood. In this study, the role of all ice clouds in the Earth’s radiation budget is investigated by performing radiative transfer modeling using ice cloud properties retrieved from CloudSat and CALIPSO measurements as inputs. Results show that, for the 2008 period, the warming effect (~21.8 ± 5.4 W m-2) induced by ice clouds due to trapping longwave radiation exceeds their cooling effect (~-16.7 ± 1.7 W m-2) caused by shortwave reflection, resulting in a net warming effect (~5.1 ± 3.8 W m-2) globally on the earth-atmosphere system. The net warming is over 15 W m-2 in the tropical deep convective regions, whereas cooling occurs in the midlatitudes, which is less than 10 W m-2 in magnitude. Seasonal variations of ice cloud radiative effects are evident in the midlatitudes where the net effect changes from warming during winter to cooling during summer, whereas warming occurs all year round in the tropics. Ice cloud optical depth (τ) is shown to be an important factor in determining the sign and magnitude of the net radiative effect. Ice clouds with τ < 4.6 display a warming effect with the largest contributions from those with τ ~ 1.0. In addition, ice clouds cause vertically differential heating and cooling of the atmosphere, particularly with strong heating in the upper troposphere over the tropics. At Earth’s surface, ice clouds produce a cooling effect no matter how small the τ value is.
Huang, Shih-Yu; Deng, Yi; Wang, JingfengHuang, S., Y. Deng, J. Wang, 2016: Revisiting the global surface energy budgets with maximum-entropy-production model of surface heat fluxes. Climate Dynamics, 1-15. doi: 10.1007/s00382-016-3395-x. The maximum-entropy-production (MEP) model of surface heat fluxes, based on contemporary non-equilibrium thermodynamics, information theory, and atmospheric turbulence theory, is used to re-estimate the global surface heat fluxes. The MEP model predicted surface fluxes automatically balance the surface energy budgets at all time and space scales without the explicit use of near-surface temperature and moisture gradient, wind speed and surface roughness data. The new MEP-based global annual mean fluxes over the land surface, using input data of surface radiation, temperature data from National Aeronautics and Space Administration–Clouds and the Earth’s Radiant Energy System (NASA CERES) supplemented by surface specific humidity data from the Modern-Era Retrospective Analysis for Research and Applications (MERRA), agree closely with previous estimates. The new estimate of ocean evaporation, not using the MERRA reanalysis data as model inputs, is lower than previous estimates, while the new estimate of ocean sensible heat flux is higher than previously reported. The MEP model also produces the first global map of ocean surface heat flux that is not available from existing global reanalysis products.
Jia, Aolin; Jiang, Bo; Liang, Shunlin; Zhang, Xiaotong; Ma, HanJia, A., B. Jiang, S. Liang, X. Zhang, H. Ma, 2016: Validation and Spatiotemporal Analysis of CERES Surface Net Radiation Product. Remote Sensing, 8(2), 90. doi: 10.3390/rs8020090. The Clouds and the Earth’s Radiant Energy System (CERES) generates one of the few global satellite radiation products. The CERES ARM Validation Experiment (CAVE) has been providing long-term in situ observations for the validation of the CERES products. However, the number of these sites is low and their distribution is globally sparse, and particularly the surface net radiation product has not been rigorously validated yet. Therefore, additional validation efforts are highly required to determine the accuracy of the CERES radiation products. In this study, global land surface measurements were comprehensively collected for use in the validation of the CERES net radiation (Rn) product on a daily (340 sites) and a monthly (260 sites) basis, respectively. The validation results demonstrated that the CERES Rn product was, overall, highly accurate. The daily validations had a Mean Bias Error (MBE) of 3.43 W·m−2, Root Mean Square Error (RMSE) of 33.56 W·m−2, and R2 of 0.79, and the monthly validations had an MBE of 3.40 W·m−2, RMSE of 25.57 W·m−2, and R2 of 0.84. The accuracy was slightly lower for the high latitudes. Following the validation, the monthly CERES Rn product, from March 2000 to July 2014, was used for a further analysis. The global spatiotemporal variation of the Rn, which occurred during the measurement period, was analyzed. In addition, two hot spot regions, the southern Great Plains and south-central Africa, were then selected for use in determining the driving factors or attribution of the Rn variation. We determined that Rn over the southern Great Plains decreased by −0.33 W·m−2 per year, which was mainly driven by changes in surface green vegetation and precipitation. In south-central Africa, Rn decreased at a rate of −0.63 W·m−2 per year, the major driving factor of which was surface green vegetation. CERES; validation; Net radiation; Attribution; spatiotemporal analysis
Jiang, Bo; Liang, Shunlin; Ma, Han; Zhang, Xiaotong; Xiao, Zhiqiang; Zhao, Xiang; Jia, Kun; Yao, Yunjun; Jia, AolinJiang, B., S. Liang, H. Ma, X. Zhang, Z. Xiao, X. Zhao, K. Jia, Y. Yao, A. Jia, 2016: GLASS Daytime All-Wave Net Radiation Product: Algorithm Development and Preliminary Validation. Remote Sensing, 8(3), 222. doi: 10.3390/rs8030222. Mapping surface all-wave net radiation (Rn) is critically needed for various applications. Several existing Rn products from numerical models and satellite observations have coarse spatial resolutions and their accuracies may not meet the requirements of land applications. In this study, we develop the Global LAnd Surface Satellite (GLASS) daytime Rn product at a 5 km spatial resolution. Its algorithm for converting shortwave radiation to all-wave net radiation using the Multivariate Adaptive Regression Splines (MARS) model is determined after comparison with three other algorithms. The validation of the GLASS Rn product based on high-quality in situ measurements in the United States shows a coefficient of determination value of 0.879, an average root mean square error value of 31.61 Wm−2, and an average bias of −17.59 Wm−2. We also compare our product/algorithm with another satellite product (CERES-SYN) and two reanalysis products (MERRA and JRA55), and find that the accuracy of the much higher spatial resolution GLASS Rn product is satisfactory. The GLASS Rn product from 2000 to the present is operational and freely available to the public. Remote sensing; Satellite; Net radiation; GLASS products
Jin, Zhonghai; Sun, MoguoJin, Z., M. Sun, 2016: An Initial Study on Climate Change Fingerprinting Using the Reflected Solar Spectra. J. Climate, 29(8), 2781-2796. doi: 10.1175/JCLI-D-15-0297.1. Attribution of averaged spectral variation over large spatial and temporal scales to different climate variables is central to climate change fingerprinting. Using 10 years of satellite data for simulation, the authors generate a group of observation-based spectral fingerprints and a time series of monthly mean reflectance spectra over the ocean in five large latitude regions and globally. Next, these fingerprints and the interannual variation spectra are used to retrieve the interannual changes in the relevant climate variables to test the concept of using the spectral fingerprinting approach for climate change attribution. Comparing the fingerprinting retrieval of climate variable change to the actual underlying variable change, the RMS differences between the two are less than twice as large as the monthly variability for all variables in all regions. Instances where larger errors are observed correspond to those variables with large nonlinear radiative response, such as the cloud optical depth and the ice particle size. Using the linear fingerprinting approach and accounting for the nonlinear radiative error in fingerprints results in significantly higher retrieval accuracy; the RMS errors are reduced to less than the monthly variability for nearly all variables, indicating the profound impact of the nonlinear error on fingerprinting retrieval. Another important finding is that if the cloud fraction is known a priori, the retrieval accuracy in cloud optical depth would be improved substantially. Moreover, a better retrieval for the water vapor amount and aerosol optical depth can be achieved from the clear-sky data only. The test results demonstrate that climate change fingerprinting based on reflected solar benchmark spectra is possible.
Jing, Xianwen; Zhang, Hua; Peng, Jie; Li, Jiangnan; Barker, Howard W.Jing, X., H. Zhang, J. Peng, J. Li, H. W. Barker, 2016: Cloud overlapping parameter obtained from CloudSat/CALIPSO dataset and its application in AGCM with McICA scheme. Atmospheric Research, 170, 52-65. doi: 10.1016/j.atmosres.2015.11.007. Vertical decorrelation length (Lcf) as used to determine overlap of cloudy layers in GCMs was obtained from CloudSat/CALIPSO measurements, made between 2007 and 2010, and analyzed in terms of monthly means. Global distributions of Lcf were produced for several cross-sectional lengths. Results show that: Lcf over the tropical convective regions typically exceeds 2 km and shift meridionally with season; the smallest Lcf (< 1 km) tends to occur in regions dominated by marine stratiform clouds; Lcf for mid-to-high latitude continents of the Northern Hemisphere (NH) ranges from 5–6 km during winter to 2–3 km during summer; and there are marked differences between continental and oceanic values of Lcf in the mid-latitudes of the NH. These monthly-gridded, observationally-based values of Lcf data were then used by the Monte Carlo Independent Column Approximation (McICA) radiation routines within the Beijing Climate Center's GCM (BCC_AGCM2.0.1). Additionally, the GCM was run with two other descriptions of Lcf: one varied with latitude only, and the other was simply 2 km everywhere all the time. It is shown that using the observationally-based Lcf in the GCM led to local and seasonal changes in total cloud fraction and shortwave (longwave) cloud radiative effects that serve mostly to reduce model biases. This indicates that usage of Lcf that vary according to location and time has the potential to improve climate simulations. AGCM; Cloud overlap; CloudSat/CALIPSO; Decorrelation length
Johnson, Gregory C.; Lyman, John M.; Loeb, Norman G.Johnson, G. C., J. M. Lyman, N. G. Loeb, 2016: Improving estimates of Earth's energy imbalance. Nature Climate Change, 6(7), 639-640. doi: 10.1038/nclimate3043. climate change; Physical oceanography; Atmospheric science
Jones, Thomas A.; Knopfmeier, Kent; Wheatley, Dustan; Creager, Gerald; Minnis, Patrick; Palikonda, RabindraJones, T. A., K. Knopfmeier, D. Wheatley, G. Creager, P. Minnis, R. Palikonda, 2016: Storm-scale data assimilation and ensemble forecasting with the NSSL Experimental Warn-on-Forecast System. Part II: Combined Radar and Satellite Data Experiments. Wea. Forecasting, 31(1), 297-327. doi: 10.1175/WAF-D-15-0107.1. This research represents the second part of a two part series describing the development of a prototype ensemble data assimilation system for the Warn-on-Forecast (WoF) project known as the NSSL experimental WoF System for ensembles (NEWS-e). Part I describes the NEWS-e design and results from radar reflectivity and radial velocity data assimilation for six severe weather events occurring during 2013 and 2014. Part II describes the impact of assimilating satellite liquid and ice water path (LWP, IWP) retrievals from the GOES Imager along with the radar observations. Assimilating LWP and IWP observations may improve thermodynamic conditions at the surface over the storm-scale domain through better analysis of cloud coverage in the model compared to radar-only experiments. These improvements sometimes corresponded to an improved analysis of supercell storms leading to better forecasts of low-level vorticity. This positive impact was most evident for events where convection is not ongoing at the beginning of the radar and satellite data assimilation period. For more complex cases containing significant amounts of ongoing convection, only assimilating clear-sky satellite retrievals in place of clear-air reflectivity resulted in spurious regions of light precipitation compared to the radar only experiments. The analyzed tornadic storms in these experiments are sometimes too weak and quickly diminished in intensity in the forecasts. The lessons learned as part of these experiments should lead to improved iterations of the NEWS-e system building on the modestly successful results described here.
Jose, Subin; Gharai, Biswadip; Rao, P. V. N.; Dutt, C. B. S.Jose, S., B. Gharai, P. V. N. Rao, C. B. S. Dutt, 2016: Satellite-based shortwave aerosol radiative forcing of dust storm over the Arabian Sea. Atmospheric Science Letters, 17(1), 43-50. doi: 10.1002/asl.597. Dust storm events over the Arabian Sea (AS) have been detected using Moderate Resolution Imaging Spectroradiometer (MODIS) data. Shortwave Aerosol Radiative Forcing (SWARF) due to dust storm is estimated using synchronous observation of Clouds and Earth's Energy System (CERES) and MODIS aerosol optical depth (AOD). Study established a relationship between them as SWARF = −39.12 × AOD − 16.53 (0.4 ≤ AOD ≤ 4.0) with r2 = 0.96. The developed relation can be used for quick, independent estimation of instantaneous SWARF for dust storm over the AS. The relationship can be used to explore the possible effect of dust on climate modulation in this region. AOD; SWARF; SW flux
Kahn, Brian H.; Huang, Xianglei; Stephens, Graeme L.; Collins, William D.; Feldman, Daniel R.; Su, Hui; Wong, Sun; Yue, QingKahn, B. H., X. Huang, G. L. Stephens, W. D. Collins, D. R. Feldman, H. Su, S. Wong, Q. Yue, 2016: ENSO regulation of far- and mid-infrared contributions to clear-sky OLR. Geophysical Research Letters, 43(16), 2016GL070263. doi: 10.1002/2016GL070263. NASA Aqua-derived thermodynamic profiles, calculated spectral clear-sky outgoing longwave radiation (OLR), and vertical velocity fields from meteorological reanalyses are combined to determine the relative proportion of the far-infrared (FIR) and mid-infrared (MIR) spectral contributions to the total clear-sky OLR during different phases of El Niño–Southern Oscillation (ENSO). In the ascending branch of the tropical circulation, the spatial variance of upper tropospheric water vapor is shown to be larger during La Niña than El Niño and is consistent with zonal symmetry changes in the tropical waveguide and associated tropical-extratropical mixing. In the descending branch, upper tropospheric water vapor shows weaker coupling to lower layers that is evidenced by changes in the ratio of FIR to MIR in the clear-sky OLR. Diagnostics from the Geophysical Fluid Dynamics Laboratory AM3 model simulation are generally similar to satellite data, but the ratio of FIR to MIR is 5–10% larger with respect to dynamic regime. tropics; 3359 Radiative processes; 3305 Climate change and variability; water vapor; ENSO; 3360 Remote sensing; 3373 Tropical dynamics; 3379 Turbulence; clear sky; far infrared; upper troposphere
Kato, Seiji; Xu, Kuan-Man; Wong, Takmeng; Loeb, Norman G.; Rose, Fred G.; Trenberth, Kevin E.; Thorsen, Tyler J.Kato, S., K. Xu, T. Wong, N. G. Loeb, F. G. Rose, K. E. Trenberth, T. J. Thorsen, 2016: Investigation of the residual in column integrated atmospheric energy balance using cloud objects. J. Climate, 29(20), 7435–7452. doi: 10.1175/JCLI-D-15-0782.1. Observationally-based atmospheric energy balance is analyzed using Clouds and the Earth’s Radiant Energy System (CERES)-derived TOA and surface irradiance, Global Precipitation Climatology Project (GPCP)-derived precipitation, dry static and kinetic energy tendency and divergence estimated from ERA-Interim, and surface sensible heat flux from SeaFlux. The residual tends to be negative over tropics and positive over mid-latitudes. A negative residual implies that precipitation rate is too small, divergence is too large, or radiative cooling is too large. The residual of atmospheric energy is spatially and temporally correlated with cloud objects to identify cloud types associated with the residual. Spatially, shallow cumulus, cirrostratus, and deep convective cloud object occurrence are positively correlated with the absolute value of the residual. The temporal correlation coefficient between the number of deep convective cloud objects and individual energy components, net atmospheric irradiance, precipitation rate, and the sum of dry static and kinetic energy divergence and their tendency over western Pacific are, respectively, 0.84, 0.95, and 0.93. However, when all energy components are added, the atmospheric energy residual over tropical Pacific is temporally correlated well with the number of shallow cumulus cloud objects over tropical Pacific. Because shallow cumulus alters not enough atmospheric energy compared to the residual, these suggest 1) if retrieval errors associated with deep convective clouds are causing the column integrated atmospheric energy residual, the errors vary among individual deep convective clouds, and 2) it is possible that the residual is associated with processes in which shallow cumulus clouds affect deep convective clouds and hence atmospheric energy budget over tropical western Pacific.
Kay, Jennifer E.; Bourdages, Line; Miller, Nathaniel B.; Morrison, Ariel; Yettella, Vineel; Chepfer, Helene; Eaton, BrianKay, J. E., L. Bourdages, N. B. Miller, A. Morrison, V. Yettella, H. Chepfer, B. Eaton, 2016: Evaluating and improving cloud phase in the Community Atmosphere Model version 5 using spaceborne lidar observations. Journal of Geophysical Research: Atmospheres, 121(8), 4162–417. doi: 10.1002/2015JD024699. Spaceborne lidar observations from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite are used to evaluate cloud amount and cloud phase in the Community Atmosphere Model version 5 (CAM5), the atmospheric component of a widely used state-of-the-art global coupled climate model (Community Earth System Model). By embedding a lidar simulator within CAM5, the idiosyncrasies of spaceborne lidar cloud detection and phase assignment are replicated. As a result, this study makes scale-aware and definition-aware comparisons between model-simulated and observed cloud amount and cloud phase. In the global mean, CAM5 has insufficient liquid cloud and excessive ice cloud when compared to CALIPSO observations. Over the ice-covered Arctic Ocean, CAM5 has insufficient liquid cloud in all seasons. Having important implications for projections of future sea level rise, a liquid cloud deficit contributes to a cold bias of 2–3°C for summer daily maximum near-surface air temperatures at Summit, Greenland. Over the midlatitude storm tracks, CAM5 has excessive ice cloud and insufficient liquid cloud. Storm track cloud phase biases in CAM5 maximize over the Southern Ocean, which also has larger-than-observed seasonal variations in cloud phase. Physical parameter modifications reduce the Southern Ocean cloud phase and shortwave radiation biases in CAM5 and illustrate the power of the CALIPSO observations as an observational constraint. The results also highlight the importance of using a regime-based, as opposed to a geographic-based, model evaluation approach. More generally, the results demonstrate the importance and value of simulator-enabled comparisons of cloud phase in models used for future climate projection. 3311 Clouds and aerosols; 3305 Climate change and variability; 3337 Global climate models; climate model; Cloud Phase; Southern Ocean; Greenland; supercooled liquid clouds
Kay, Jennifer E.; Wall, Casey; Yettella, Vineel; Medeiros, Brian; Hannay, Cecile; Caldwell, Peter; Bitz, CeciliaKay, J. E., C. Wall, V. Yettella, B. Medeiros, C. Hannay, P. Caldwell, C. Bitz, 2016: Global climate impacts of fixing the Southern Ocean shortwave radiation bias in the Community Earth System Model (CESM). J. Climate, 29(12), 4617–4636. doi: 10.1175/JCLI-D-15-0358.1. A large, long-standing, and pervasive climate model bias is excessive absorbed shortwave radiation (ASR) over the mid-latitude oceans, especially the Southern Ocean. This study investigates both the underlying mechanisms for and climate impacts of this bias within the Community Earth System Model with the Community Atmosphere Model version 5 (CESM-CAM5). Excessive Southern Ocean ASR in CESM-CAM5 results in part because low-level clouds contain insufficient amounts of supercooled liquid. In a present-day atmosphere-only run, an observationally motivated modification to the shallow convection detrainment increases supercooled cloud liquid, brightens low-level clouds, and substantially reduces the Southern Ocean ASR bias. Tuning to maintain global energy balance enables reduction of a compensating tropical ASR bias. In the resulting pre-industrial fully coupled run with a brighter Southern Ocean and dimmer Tropics, the Southern Ocean cools and the Tropics warm. As a result of the enhanced meridional temperature gradient, poleward heat transport increases in both hemispheres (especially the Southern Hemisphere) and the Southern Hemisphere atmospheric jet strengthens. Because Northward cross-equatorial heat transport reductions occur primarily in the ocean (80%) not the atmosphere (20%), a proposed atmospheric teleconnection linking Southern Ocean ASR bias reduction and cooling with northward shifts in tropical precipitation has little impact. In summary, observationally motivated supercooled liquid water increases in shallow convective clouds enable large reductions in long-standing climate model shortwave radiation biases. Of relevance to both model bias reduction and climate dynamics, quantifying the influence of Southern Ocean cooling on tropical precipitation requires a model with dynamic ocean heat transport.
Khlopenkov, Konstantin V.; Doelling, David R.Khlopenkov, K. V., D. R. Doelling, 2016: Development of image processing method to detect noise in geostationary imagery. SPIE 10004, Image and Signal Processing for Remote Sensing XXII, 10004, 100041S-100041S-9. doi: 10.1117/12.2241544. The Clouds and the Earth’s Radiant Energy System (CERES) has incorporated imagery from 16 individual geostationary (GEO) satellites across five contiguous domains since March 2000. In order to derive broadband fluxes uniform across satellite platforms it is important to ensure a good quality of the input raw count data. GEO data obtained by older GOES imagers (such as MTSAT-1, Meteosat-5, Meteosat-7, GMS-5, and GOES-9) are known to frequently contain various types of noise caused by transmission errors, sync errors, stray light contamination, and others. This work presents an image processing methodology designed to detect most kinds of noise and corrupt data in all bands of raw imagery from modern and historic GEO satellites. The algorithm is based on a set of different approaches to detect abnormal image patterns, including inter-line and inter-pixel differences within a scanline, correlation between scanlines, analysis of spatial variance, and also a 2D Fourier analysis of the image spatial frequencies. In spite of computational complexity, the described method is highly optimized for performance to facilitate volume processing of multi-year data and runs in fully automated mode. Reliability of this noise detection technique has been assessed by human supervision for each GEO dataset obtained during selected time periods in 2005 and 2006. This assessment has demonstrated the overall detection accuracy of over 99.5% and the false alarm rate of under 0.3%. The described noise detection routine is currently used in volume processing of historical GEO imagery for subsequent production of global gridded data products and for cross-platform calibration.
Kim, Chang Ki; Holmgren, William F.; Stovern, Michael; Betterton, Eric A.Kim, C. K., W. F. Holmgren, M. Stovern, E. A. Betterton, 2016: Toward Improved Solar Irradiance Forecasts: Comparison of Downwelling Surface Shortwave Radiation in Arizona Derived from Satellite with the Gridded Datasets. Pure and Applied Geophysics, 173(8), 2929-2943. doi: 10.1007/s00024-016-1307-y. The downwelling surface shortwave radiation derived from geostationary satellite imagery was compared with the available datasets for the Southwestern United States. The averaged root mean square errors for our instantaneous estimates ranged from 95.0 to 122.7 W m−2, which is lower than those derived from the MODerate resolution Imaging Spectroradiometer (MODIS). The Modern Era Retrospective-analysis for Research and Applications (MERRA) products were used to compare the hourly mean solar insolation. The three hourly mean downwelling surface shortwave radiation was evaluated by comparing the North American Regional Reanalysis (NARR) and the Clouds and the Earth’s Radiant Energy System (CERES) products. Our estimates show the better performance than MERRA, NARR and CERES datasets because of coarse resolution that limits determining the solar dimming due to small clouds.
Kim, Dong-Cheol; Jeong, Myeong-JaeKim, D., M. Jeong, 2016: Derivations of Surface Solar Radiation from Polar Orbiting Satellite Observations. Korean Journal of Remote Sensing, 32(3), 201-220. doi: 10.7780/kjrs.2016.32.3.1. Derivations of Surface Solar Radiation from Polar Orbiting Satellite Observations - Surface Solar Radiation;Satellite Retrievals;MODIS;CERES;
Laliberté, Julien; Bélanger, Simon; Frouin, RobertLaliberté, J., S. Bélanger, R. Frouin, 2016: Evaluation of satellite-based algorithms to estimate photosynthetically available radiation (PAR) reaching the ocean surface at high northern latitudes. Remote Sensing of Environment, 184, 199-211. doi: 10.1016/j.rse.2016.06.014. Two satellite-based methods to estimate daily averaged photosynthetically available radiation (PAR) at the ocean surface are evaluated at high northern latitudes. The first method employs a precomputed Look-Up-Table (LUT) generated from radiative transfer simulations. The LUT associates spectral irradiance reaching the surface to a given set of input parameters, namely solar zenith angle, cloud optical thickness, cloud fraction, ozone concentration, and surface albedo. The second method, as implemented by NASA's Ocean Biology Processing Group (OBPG) in the standard Ocean Color data processing chain, expresses the energy budget of the atmosphere-surface-ocean system via a simple radiative transfer model. The performance of these methods is evaluated using an extensive in situ PAR dataset collected in the Arctic Ocean between 1998 and 2014, with daily values ranging from 0.08 to 61.07 Em− 2 d− 1. A methodology is developed to compare in situ measurements and satellite products of different spatial and temporal resolution. Agreement is generally good between satellite-derived estimates and ship-based data and between methods. Specifically, both methods yield a small positive bias of 6% and 2% and a relative uncertainty larger than that observed at low latitude, with a root mean squared error (RMSE) of 33% and 20% for the LUT and OPBG methods, respectively. This is attributed to the peculiar environmental conditions encountered in the Arctic, namely low solar elevation, changing surface albedo due to sea ice, and persistent cloudiness. The RMSE difference among methods is due to the high temporal resolution (3 h) of the International Satellite Cloud Climatology Project (ISCCP) LUT input not fully compensating for its low spatial resolution (280 km grid cells). The LUT method has the major advantage of providing PAR estimates in all conditions, including ice-covered regions, while the OBPG method is currently limited to open waters and a solar zenith angle lower than 83°. Consequently, the OBPG method may not account for as much as 38% of PAR reaching the Arctic ocean surface annually. Both methods have the potential to provide useful PAR estimates just below the ice, by including information about ice transmittance. Arctic Ocean; Clouds and sea ice; Ocean color; Photochemical processes; Photosynthetically available radiation; Primary production
Larson, Erik J. L.; Portmann, Robert W.Larson, E. J. L., R. W. Portmann, 2016: A Temporal Kernel Method to Compute Effective Radiative Forcing in CMIP5 Transient Simulations. J. Climate, 29(4), 1497-1509. doi: 10.1175/JCLI-D-15-0577.1. Effective radiative forcing (ERF) is calculated as the flux change at the top of the atmosphere after allowing rapid adjustments resulting from a forcing agent, such as greenhouse gases. Rapid adjustments include changes to atmospheric temperature, water vapor, and clouds. Accurate estimates of ERF are necessary in order to understand the drivers of climate change. This work presents a new method of calculating ERF using a kernel derived from the time series of a model variable (e.g., global mean surface temperature) in a model-step change experiment. The top-of-atmosphere (TOA) radiative imbalance has the best noise tolerance for retrieving the ERF of the model variables tested. This temporal kernel method is compared with an energy balance method, which equates ERF to the TOA radiative imbalance plus the scaled surface temperature change. Sensitivities and biases of these methods are quantified using output from phase 5 of the the Coupled Model Intercomparison Project (CMIP5). The temporal kernel method is likely more accurate for models in which a linear fit is a poor approximation for the relationship between temperature change and TOA imbalance. The difference between these methods is most apparent in forcing estimates for the representative concentration pathway 8.5 (RCP8.5) scenario. The CMIP5 multimodel mean ERF calculated for large volcanic eruptions is 80% of the adjusted forcing reported by the IPCC Fifth Assessment Report (AR5). This suggests that about 5% more energy has come into the earth system since 1870 than suggested by the IPCC AR5. radiative forcing; climate models; Models and modeling; Physical Meteorology and Climatology
Lei, Ruibo; Tian-Kunze, Xiangshan; Leppäranta, Matti; Wang, Jia; Kaleschke, Lars; Zhang, ZhanhaiLei, R., X. Tian-Kunze, M. Leppäranta, J. Wang, L. Kaleschke, Z. Zhang, 2016: Changes in summer sea ice, albedo, and portioning of surface solar radiation in the Pacific sector of Arctic Ocean during 1982-2009. Journal of Geophysical Research: Oceans, 121(8), 5470–5486. doi: 10.1002/2016JC011831. SSM/I sea ice concentration and CLARA black-sky composite albedo were used to estimate sea ice albedo in the region 70°–82°N, 130°–180°W. The long-term trends and seasonal evolutions of ice concentration, composite albedo, and ice albedo were then obtained. In July–August 1982–2009, the linear trend of the composite albedo and the ice albedo was −0.069 and −0.046 units per decade, respectively. During 1 June to 19 August, melting of sea ice resulted in an increase of solar heat input to the ice-ocean system by 282 MJ·m−2 from 1982 to 2009. However, because of the counter-balancing effects of the loss of sea ice area and the enhanced ice surface melting, the trend of solar heat input to the ice was insignificant. The summer evolution of ice albedo matched the ice surface melting and ponding well at basin scale. The ice albedo showed a large difference between the multiyear and first-year ice because the latter melted completely by the end of a melt season. At the SHEBA geolocations, a distinct change in the ice albedo has occurred since 2007 because most of the multiyear ice has been replaced by first-year ice. A positive polarity in the Arctic Dipole Anomaly could be partly responsible for the rapid loss of summer ice within the study region in the recent years by bringing warmer air masses from the south and advecting more ice toward the north. Both these effects would enhance ice-albedo feedback. This article is protected by copyright. All rights reserved. albedo; sea ice; Solar radiation; snow; 0758 Remote sensing; 0750 Sea ice; 0736 Snow; Arctic Ocean; 0764 Energy balance; 4908 Albedo; concentration
Li, J.-L. F.; Lee, Wei-Liang; Waliser, Duane; Wang, Yi-Hui; Yu, Jia-Yuh; Jiang, Xianan; L'Ecuyer, Tristan; Chen, Yi-Chun; Kubar, Terry; Fetzer, Eric; Mahakur, M.Li, J. F., W. Lee, D. Waliser, Y. Wang, J. Yu, X. Jiang, T. L'Ecuyer, Y. Chen, T. Kubar, E. Fetzer, M. Mahakur, 2016: Considering the radiative effects of snow on tropical Pacific Ocean radiative heating profiles in contemporary GCMs using A-Train observations. Journal of Geophysical Research: Atmospheres, 121(4), 1621–1636. doi: 10.1002/2015JD023587. This study characterizes biases in water vapor, dynamics, shortwave (SW) and longwave (LW) radiative properties in contemporary global climate models (GCMs) against observations over tropical Pacific Ocean. The observations are based on Atmospheric Infrared Sounder for water vapor, CloudSat 2B-FLXHR-LIDAR for LW and SW radiative heating profiles, and radiative flux from Clouds and the Earth's Radiant Energy System products. The model radiative heating profiles are adopted from the coupled and uncoupled National Center for Atmospheric Research (NCAR) Community Earth System Model version 1 (CESM1) and joint Year of Tropical Convection (YOTC)/Madden Julian Oscillation (MJO) Task Force-Global Energy and Water Cycle Experiment Atmospheric System Studies (GASS) Multi-Model Physical Processes Experiment (YOTC-GASS). The results from the model evaluation for YOTC-GASS and NCAR CESM1 demonstrate a number of systematic radiative biases. These biases include excessive outgoing LW radiation and excessive SW surface radiative fluxes, in conjunction with a radiatively unstable atmosphere with excessive LW cooling in the upper troposphere over convectively active areas, such as the Intertropical Convergence Zone/South Pacific Convergence Zone (ITCZ/SPCZ) and warm pool. Using sensitivity experiments with the NCAR-uncoupled/NCAR-coupled CESM1, we infer that these biases partly result from the interactions between falling snow and radiation that are missing in most contemporary GCMs (e.g., YOTC-GASS, Coupled Model Intercomparison Project 3 (CMIP)3, and Atmospheric Model Intercomparison Project 5 (AMIP5)/CMIP5). A number of biases in the YOTC-GASS model simulations are consistent with model biases in CMIP3, AMIP5/CMIP5, and NCAR-uncoupled/NCAR-coupled model simulation without snow-radiation interactions. These include excessive upper level convection and low level downward motion with outflow from ITCZ/SPCZ. This generates weaker low-level trade winds and excessive precipitation in the Central Pacific Trade wind regions. The excessive LW radiative cooling in NCAR-coupled/NCAR-uncoupled GCM simulations is reduced by 10–20% with snow-radiative effects considered. 3359 Radiative processes; 3337 Global climate models; GCM; 3371 Tropical convection; 3360 Remote sensing; 3373 Tropical dynamics; cloud radiation; Dynamics; heating rate
Li, J.-L. F.; Lee, Wei-Liang; Wang, Yi-Hui; Richardson, Mark; Yu, Jia-Yuh; Suhas, E.; Fetzer, Eric; Lo, Min-Hui; Yue, QingLi, J. F., W. Lee, Y. Wang, M. Richardson, J. Yu, E. Suhas, E. Fetzer, M. Lo, Q. Yue, 2016: Assessing the Radiative Impacts of Precipitating Clouds on Winter Surface Air Temperatures and Land Surface Properties in GCMs Using Observations. Journal of Geophysical Research: Atmospheres, 121(19), 11,536–11,555. doi: 10.1002/2016JD025175. Using CloudSat-CALIPSO ice water, cloud fraction and radiation; CERES radiation and long-term station-measured surface air temperature (SAT), we identified a substantial underestimation of the total ice water path, total cloud fraction, land surface radiative flux, land surface temperature (LST) and SAT during Northern Hemisphere winter in CMIP5 models. We perform sensitivity experiments with the NCAR Community Earth System Model version 1 (CESM1) in fully coupled modes to identify processes driving these biases. We found that biases in land surface properties are associated with the exclusion of downwelling long-wave heating from precipitating ice during Northern Hemisphere winter. The land surface temperature biases introduced by the exclusion of precipitating ice radiative effects in CESM1 and CMIP5 both spatially correlate with winter biases over Eurasia and North America. The underestimated precipitating ice radiative effect leads to colder LST, associated surface energy-budget adjustments and cooler SAT. This bias also shifts regional soil moisture state from liquid to frozen, increases snow cover and depresses evapotranspiration (ET) and total leaf area index (TLAI) in Northern Hemisphere winter. The inclusion of the precipitating ice radiative effects largely reduces the model biases of surface radiative fluxes (more than 15 W m-2), SAT (up to 2-4 K), snow cover and ET (25-30%), compared with those without snow-radiative effects. 0321 Cloud/radiation interaction; 3359 Radiative processes; radiation; 1622 Earth system modeling; 3322 Land/atmosphere interactions; 0550 Model verification and validation; coupled GCM; land model; LST; SAT
Li, J.-L. F.; Lee, Wei-Liang; Yu, Jia-Yuh; Hulley, Glynn; Fetzer, Eric; Chen, Yi-Chun; Wang, Yi-HuiLi, J. F., W. Lee, J. Yu, G. Hulley, E. Fetzer, Y. Chen, Y. Wang, 2016: The impacts of precipitating hydrometeors radiative effects on land surface temperature in contemporary GCMs using satellite observations. Journal of Geophysical Research: Atmospheres, 121(1), 67–79. doi: 10.1002/2015JD023776. An accurate representation of the land surface temperature (LST) climatology of the coupled land-atmosphere system has strong implications for the reliability of projected land surface processes and their variability inferred by the global climate models (GCMs) contributed to the Intergovernmental Panel on Climate Change CMIP5. We have identified a substantial underestimation of the total ice water path and biases of surface radiation budget commonly seen in the CMIP models which are highly correlated to the biases of LST over land. One of the potential causes of the CMIP model biases is the missing representation of large frozen precipitating hydrometeors and their radiative effects (i.e., snow) in all CMIP3 and most CMIP5 models. We examine the impacts of snow on the radiation, all-sky and clear-sky LST, and air-land heat fluxes to explore the implications to the common biases in CMIP models by performing sensitivity experiments with and without snow radiation effects using the National Center for Atmospheric Research Community Earth System Model version 1. It is found that an exclusion of the snow radiative effects the CESM1 generates the LST biases (up to 2–3 K) in the midlatitude and high latitude, in particular, in December, January, and February (DJF). All-sky and clear-sky LST in model simulations are found to be too cold and are mainly due to underestimated downward surface (longwave) LW radiation in DJF, which is consistent with those in CMIP models. The correlation between the changes of the LST and downward surface LW radiation is very high both in summer and winter seasons. cloud; 3359 Radiative processes; radiation; GCM; 3354 Precipitation; 1627 Coupled models of the climate system; 1631 Land/atmosphere interactions; 1626 Global climate models; Land surface temperature
Li, J.-L. F.; Waliser, D. E.; Stephens, G.; Lee, SeungwonLi, J. F., D. E. Waliser, G. Stephens, S. Lee, 2016: Characterizing and Understanding Cloud Ice and Radiation Budget Biases in Global Climate Models and Reanalysis. Meteorological Monographs, 56, 13.1-13.20. doi: 10.1175/AMSMONOGRAPHS-D-15-0007.1. The authors present an observationally based evaluation of the vertically resolved cloud ice water content (CIWC) and vertically integrated cloud ice water path (CIWP) as well as radiative shortwave flux downward at the surface (RSDS), reflected shortwave (RSUT), and radiative longwave flux upward at top of atmosphere (RLUT) of present-day global climate models (GCMs), notably twentieth-century simulations from the fifth phase of the Coupled Model Intercomparison Project (CMIP5), and compare these results to those of the third phase of the Coupled Model Intercomparison Project (CMIP3) and two recent reanalyses. Three different CloudSat and/or Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) combined ice water products and two methods are used to remove the contribution from the convective core ice mass and/or precipitating cloud hydrometeors with variable sizes and falling speeds so that a robust observational estimate can be obtained for model evaluations.The results show that, for annual mean CIWC and CIWP, there are factors of 2–10 (either over- or underestimate) in the differences between observations and models for a majority of the GCMs and for a number of regions. Most of the GCMs in CMIP3 and CMIP5 significantly underestimate the total ice water mass because models only consider suspended cloud mass, ignoring falling and convective core cloud mass. For the annual means of RSDS, RLUT, and RSUT, a majority of the models have significant regional biases ranging from −30 to 30 W m−2. Based on these biases in the annual means, there is virtually no progress in the simulation fidelity of RSDS, RLUT, and RSUT fluxes from CMIP3 to CMIP5, even though there is about a 50% bias reduction improvement of global annual mean CIWP from CMIP3 to CMIP5. It is concluded that at least a part of these persistent biases stem from the common GCM practice of ignoring the effects of precipitating and/or convective core ice and liquid in their radiation calculations.
Li, Ying; Thompson, David W. J.Li, Y., D. W. J. Thompson, 2016: Observed Signatures of the Barotropic and Baroclinic Annular Modes in Cloud Vertical Structure and Cloud Radiative Effects. J. Climate, 29(13), 4723-4740. doi: 10.1175/JCLI-D-15-0692.1. The signatures of large-scale annular variability on the vertical structure of clouds and cloud radiative effects are examined in vertically resolved CloudSat and other satellite and reanalysis data products. The northern and southern “barotropic” annular modes (the NAM and SAM) have a complex vertical structure. Both are associated with a meridional dipole in clouds between subpolar and middle latitudes, but the sign of the anomalies changes between upper, middle, and lower tropospheric levels. In contrast, the northern and southern baroclinic annular modes have a much simpler vertical structure. Both are linked to same-signed anomalies in clouds extending throughout the troposphere at middle to high latitudes. The changes in cloud incidence associated with both the barotropic and baroclinic annular modes are consistent with dynamical forcing by the attendant changes in static stability and/or vertical motion. The results also provide the first observational estimates of the vertically resolved atmospheric cloud radiative effects associated with hemispheric-scale extratropical variability. In general, the anomalies in atmospheric cloud radiative effects associated with the annular modes peak in the middle to upper troposphere, and are consistent with the anomalous trapping of longwave radiation by variations in upper tropospheric clouds. The southern baroclinic annular mode gives rise to periodic behavior in longwave cloud radiative effects at the top of the atmosphere averaged over Southern Hemisphere midlatitudes.
Li, Yuanlong; Han, WeiqingLi, Y., W. Han, 2016: Causes for intraseasonal sea surface salinity variability in the western tropical Pacific Ocean and its seasonality. Journal of Geophysical Research: Oceans, 121(1), 85-103. doi: 10.1002/2015JC011413. Pronounced intraseasonal variability (ISV; 20–90 day) of sea surface salinity (SSS) with a standard deviation of 0.12–0.20 psu is detected in the western tropical Pacific Ocean (PO) from measurements of Aquarius/SAC-D satellite. These variations are not spatially uniform but show distinct regional features. The Hybrid Coordinate Ocean Model (HYCOM) well simulated the observed SSS variations, and a suite of parallel experiments were performed to understand the underlying physical processes. Surface forcing by atmospheric intraseasonal oscillations which are dominated by the Madden-Julian oscillation (MJO) is largely responsible for producing the SSS ISV, while ocean internal variability plays a secondary role. Impact of atmospheric forcing is primarily through precipitation and wind stress-driven oceanic processes. Their relative importance shows spatial variations. They have approximately equal importance in the western equatorial PO west of 155°E and the southwestern tropical PO. Wind stress effect dominates SSS ISV in the equatorial PO east of 155°E, while precipitation effect is larger in the northwestern tropical PO. In comparison, the effect of evaporation induced by wind speed change is smaller. The SSS ISV also shows evident seasonality in some areas, particularly in the far western equatorial basin and southwestern tropical PO. During boreal summer (winter), SSS ISV is enhanced (weakened) in the northwestern PO and weakened (enhanced) in the southwestern PO. Comparing with the strength of atmospheric forcing, seasonal variation of the ocean state, especially the mixed layer depth, is generally more important in causing such seasonality. 4572 Upper ocean and mixed layer processes; Intraseasonal variability; MJO; 4231 Equatorial oceanography; sea surface salinity; 4283 Water masses; western tropical Pacific
Li, Yuanlong; Han, Weiqing; Wang, Wanqiu; Ravichandran, M.Li, Y., W. Han, W. Wang, M. Ravichandran, 2016: Intraseasonal Variability of SST and Precipitation in the Arabian Sea during Indian Summer Monsoon: Impact of Ocean Mixed Layer Depth. J. Climate, 29(21), 7889–7910. doi: 10.1175/JCLI-D-16-0238.1. This study investigates sea surface temperature (SST) and precipitation variations in the eastern Arabian Sea (EAS) induced by the northward-propagating Indian summer monsoon (ISM) intraseasonal oscillations (MISOs), through analyzing satellite observations and the climate forecast system reanalysis (CFSR) and performing ocean general circulation model (OGCM) experiments. MISOs in the EAS achieve the largest intensity in the developing stage (May-June) of the ISM. The MISOs induce intraseasonal SST variability primarily through surface heat flux forcing, contributed by both shortwave radiation and turbulent heat flux, and secondarily through mixed layer entrainment. The shallow MLD (< 40 m) in the developing stage and decaying stage (September-October) of the ISM significantly amplifies the heat flux forcing effect on SST and causes large intraseasonal SST variability. Meanwhile, the high SST (> 29 °C) in the developing stage leads to enhanced response of MISO convection to SST anomaly. It means that the ocean state of the EAS region during the developing stage favors active two-way air-sea interaction and the formation of the strong first-pulse MISO event. These results provide compelling evidence for the vital role played by the ocean in the MISO mechanisms and have implications for understanding and forecasting the ISM onset. Compared to satellite observation, MISOs in CFSR data have weaker SST variability by ~50% and biased SST-precipitation relation. Reducing these biases in CFSR which provides initial conditions of the National Center for Environmental Prediction (NCEP) climate forecast system version 2 (CFSv2) may help improve the ISM rainfall forecast.
Liang, Xinfeng; Yu, LisanLiang, X., L. Yu, 2016: Variations of the Global Net Air-Sea Heat Flux During the “Hiatus” Period (2001–2010). J. Climate, 29(10), 3647–3660. doi: 10.1175/JCLI-D-15-0626.1. An assessment is made of the mean and variability of the net air-sea heat flux, Qnet, from four products (ECCO, OAFlux/CERES, ERA-Interim and NCEP1: acronyms defined in the introduction) over the global ice-free oceans from January 2001 to December 2010. For the 10-year “hiatus” period, all products agree on an overall net heat gain over the global ice-free ocean, but the magnitude varies from 1.7 to 9.5 Wm−2. The differences among products are particularly large in the Southern Ocean, where they cannot even agree on whether the region gains or loses heat on the annual mean basis. Decadal trends of Qnet differ significantly between products. ECCO and OAFlux/CERES show almost no trend, whereas ERA-Interim suggests a downward trend and NCEP1 shows an upward trend. Therefore, numerical simulations utilizing different surface flux forcing products will likely produce diverged trends of the ocean heat content during this period. The downward trend in ERA-Interim started from 2006, driven by a peculiar pattern change in the tropical regions. ECCO, which used ERA-Interim as initial surface forcings and is constrained by ocean dynamics and ocean observations, corrected the pattern. Among the four products, ECCO and OAFlux/CERES show great similarities in the examined spatial and temporal patterns. Given that the two estimates were obtained using different approaches and based on largely independent observations, these similarities are encouraging and instructive. It is more likely that the global net air-sea heat flux does not change much during the “hiatus” period.
Liu, Jianjun; Li, Zhanqing; Cribb, MaureenLiu, J., Z. Li, M. Cribb, 2016: Response of Marine Boundary Layer Cloud Properties to Aerosol Perturbations Associated with Meteorological Conditions from the 19-month AMF-Azores Campaign. J. Atmos. Sci., 73(11), 4253–4268. doi: 10.1175/JAS-D-15-0364.1. This study investigates the response of marine boundary layer (MBL) cloud properties to aerosol loading by accounting for the contributions of large-scale dynamic and thermodynamic conditions, and quantifies the first indirect effect (FIE). It makes use of 19-month measurements of aerosols, clouds, and meteorology acquired during the Atmospheric Radiation Measurement Mobile Facility field campaign over the Azores. Cloud droplet number concentrations (Nc) and cloud optical depth (COD) significantly increased with increasing aerosol number concentration (Na). Cloud droplet effective radius (DER) significantly decreased with increasing Na. The correlations between cloud microphysical properties (Nc, liquid water path (LWP), DER) and Na were stronger under more stable conditions. The correlations between Nc, LWP, DER, and Na were stronger under ascending motion conditions, while the correlation between COD and Na was stronger under descending motion conditions. The magnitude and corresponding uncertainty of the FIE ( at constant LWP) ranged from 0.060±0.022 to 0.101±0.006 depending on the different LWP values. Under more stable conditions, cloud base heights were generally lower than those under less stable conditions. This enabled a more effective interaction with aerosols, resulting in a larger value for the FIE. However, the dependence of the response of cloud properties to aerosol perturbations on stability varied according to whether ground-based or satellite-based DER retrievals were used. The magnitude of the FIE had a larger variation with changing LWP under ascending motion conditions, and tended to be higher under ascending motion conditions for clouds with low LWP and under descending motion conditions for clouds with high LWP. A contrasting dependence of FIE on atmospheric stability estimated from the surface and satellite cloud properties retrievals reported in this study underscores the importance of assessing all-level properties of clouds in aerosol-cloud interaction studies.
Liu, Wei; Xie, Shang-Ping; Lu, JianLiu, W., S. Xie, J. Lu, 2016: Correspondence: Reply to: ‘Correspondence: Variations in ocean heat uptake during the surface warming hiatus’. Nature Communications, 7, 12542. doi: 10.1038/ncomms12542. Nature Communications 7:12542 doi: 10.1038/ncomms12542 ( 2016 ); Published 19 Aug 2016 Energetics arguments are often invoked to explain the early 2000s slowdown of the global mean surface temperature (GMST) increase, a phenomenon often dubbed as the ‘hiatus’.
Loeb, N. G.; Su, W.; Doelling, D. R.; Wong, T.; Minnis, P.; Thomas, S.; Miller, W. F.Loeb, N. G., W. Su, D. R. Doelling, T. Wong, P. Minnis, S. Thomas, W. F. Miller, 2016: Earth's Top-of-Atmosphere Radiation Budget. Reference Module in Earth Systems and Environmental Sciences. The top-of-atmosphere (TOA) Earth radiation budget (ERB) is a key property of the climate system that describes the balance between how much solar energy the Earth absorbs and how much terrestrial thermal infrared radiation it emits. This article provides an overview of the instruments and algorithms used to observe the TOA ERB by the Clouds and the Earth's Radiant Energy System (CERES) project. We summarize the properties of the CERES instruments, their calibration, combined use of CERES and imager measurements for improved cloud-radiation properties, and the approaches used for time interpolation and space averaging of TOA radiative fluxes. calibration; clouds; longwave; shortwave; broadband; CERES; climate; radiation budget; top-of-atmosphere; flux; Time interpolation
Loeb, Norman G.; Manalo-Smith, Natividad; Su, Wenying; Shankar, Mohan; Thomas, SusanLoeb, N. G., N. Manalo-Smith, W. Su, M. Shankar, S. Thomas, 2016: CERES Top-of-Atmosphere Earth Radiation Budget Climate Data Record: Accounting for in-Orbit Changes in Instrument Calibration. Remote Sensing, 8(3), 182. doi: 10.3390/rs8030182. The Clouds and the Earth’s Radiant Energy System (CERES) project provides observations of Earth’s radiation budget using measurements from CERES instruments onboard the Terra, Aqua and Suomi National Polar-orbiting Partnership (S-NPP) satellites. As the objective is to create a long-term climate data record, it is necessary to periodically reprocess the data in order to incorporate the latest calibration changes and algorithm improvements. Here, we focus on the improvements and validation of CERES Terra and Aqua radiances in Edition 4, which are used to generate higher-level climate data products. Onboard sources indicate that the total (TOT) channel response to longwave (LW) radiation has increased relative to the start of the missions by 0.4% to 1%. In the shortwave (SW), the sensor response change ranges from −0.4% to 0.6%. To account for in-orbit changes in SW spectral response function (SRF), direct nadir radiance comparisons between instrument pairs on the same satellite are made and an improved wavelength dependent degradation model is used to adjust the SRF of the instrument operating in a rotating azimuth plane scan mode. After applying SRF corrections independently to CERES Terra and Aqua, monthly variations amongst these instruments are highly correlated and the standard deviation in the difference of monthly anomalies is 0.2 Wm−2 for ocean and 0.3 Wm−2 for land/desert. Additionally, trends in CERES Terra and Aqua monthly anomalies are consistent to 0.21 Wm−2 per decade for ocean and 0.31 Wm−2 per decade for land/desert. In the LW, adjustments to the TOT channel SRF are made to ensure that removal of the contribution from the SW portion of the TOT channel with SW channel radiance measurements during daytime is consistent throughout the mission. Accordingly, anomalies in day–night LW difference in Edition 4 are more consistent compared to Edition 3, particularly for the Aqua land/desert case. calibration; earth radiation budget; Satellite; climate; Radiance
Loew, Alexander; Andersson, Axel; Trentmann, Jӧrg; Schrӧder, MarcLoew, A., A. Andersson, J. Trentmann, M. Schrӧder, 2016: Assessing Surface Solar Radiation Fluxes in the CMIP Ensembles. J. Climate, 29(20), 7231–7246. doi: 10.1175/JCLI-D-14-00503.1. Earth System models are indispensable tools in climate studies. The Coupled Model Intercomparison Project (CMIP) is a coordinated effort of the Earth System Modelling community to inter-compare existing models. An accurate simulation of surface solar radiation fluxes is of major importance for the accuracy of simulations of the near surface climate in Earth System Models. The present study provides a quantitative assessment of the accuracy and multidecadal changes of surface solar radiation fluxes for model results from two phases of CMIP. The entire archive of CMIP5 and its predecessor CMIP3 are analyzed for present day climate conditions. A relative model ranking is provided and its uncertainty is quantified using different global observational records. It is shown that the choice of an observational dataset can have a major influence on relative model ranking between CMIP models. However the multidecadal variability of surface solar radiation fluxes, also known as global “dimming” or “brightening” is largely underestimated by the CMIP models.
Luo, San; Sun, Zhian; Zheng, Xiaogu; Rikus, Lawrie; Franklin, CharmaineLuo, S., Z. Sun, X. Zheng, L. Rikus, C. Franklin, 2016: Evaluation of ACCESS model cloud properties over the Southern Ocean area using multiple-satellite products. Quarterly Journal of the Royal Meteorological Society, 142(694), 160-171. doi: 10.1002/qj.2641. Radiation field and cloud properties over the Southern Ocean area generated by the Australian Community Climate and Earth System Simulator (ACCESS) are evaluated using multiple-satellite products from the Fast Longwave And Shortwave radiative Fluxes (FLASHFlux) project and NASA/GEWEX surface radiation budget (SRB) data. The cloud properties are also evaluated using the observational simulator package COSP, a synthetic brightness temperature model (SBTM) and cloud liquid-water path data (UWisc) from the University of Wisconsin satellite retrievals. All of these evaluations are focused on the Southern Ocean area in an effort to understand the reasons behind the short-wave radiation biases at the surface. It is found that the model overestimates the high-level cloud fraction and frequency of occurrence of small ice-water content and underestimates the middle and low-level cloud fraction and water content. In order to improve the modelled radiation fields over the Southern Ocean area, two main modifications have been made to the physical schemes in the ACCESS model. Firstly the autoconversion rate at which the cloud water is converted into rain and the accretion rate in the warm rain scheme have been modified, which increases the cloud liquid-water content in warm cloud layers. Secondly, the scheme which determines the fraction of supercooled liquid water in mixed-phase clouds in the parametrization of cloud optical properties has been changed to use one derived from CALIPSO data which provides larger liquid cloud fractions and thus higher optical depths than the default scheme. Sensitivity tests of these two schemes in ACCESS climate runs have shown that applying either can lead to a reduction of the solar radiation reaching the surface and reduce the short-wave radiation biases. Satellite simulator; Southern Ocean short-wave radiation biases; supercooled liquid water
Mayer, Michael; Haimberger, Leopold; Pietschnig, Marianne; Storto, AndreaMayer, M., L. Haimberger, M. Pietschnig, A. Storto, 2016: Facets of Arctic energy accumulation based on observations and reanalyses 2000–2015. Geophysical Research Letters, 43(19), 2016GL070557. doi: 10.1002/2016GL070557. Various observation- and reanalysis-based estimates of sea ice mass and ocean heat content trends imply that the energy imbalance of the Arctic climate system was similar [1.0 (0.9,1.2) Wm−2] to the global ocean average during the 2000–2015 period. Most of this extra heat warmed the ocean, and a comparatively small fraction went into sea ice melt. Poleward energy transports and radiation contributed to this energy increase at varying strengths. On a seasonal scale, stronger radiative energy input during summer associated with the ice-albedo feedback enhances seasonal oceanic heat uptake and sea ice melt. In return, lower sea ice extent and higher sea surface temperatures lead to enhanced heat release from the ocean during fall. This weakens meridional temperature gradients, consequently reducing atmospheric energy transports into the polar cap. The seasonal cycle of the Arctic energy budget is thus amplified, whereas the Arctic's long-term energy imbalance is close to the global mean. 1610 Atmosphere; climate change; sea ice; Ocean heat content; energy budget; 0750 Sea ice; 4207 Arctic and Antarctic oceanography; Arctic; 3339 Ocean/atmosphere interactions; 1635 Oceans
McCoy, Daniel T.; Tan, Ivy; Hartmann, Dennis L.; Zelinka, Mark D.; Storelvmo, TrudeMcCoy, D. T., I. Tan, D. L. Hartmann, M. D. Zelinka, T. Storelvmo, 2016: On the relationships among cloud cover, mixed-phase partitioning, and planetary albedo in GCMs. Journal of Advances in Modeling Earth Systems, 8(2), 650–668. doi: 10.1002/2015MS000589. In this study it is shown that CMIP5 global climate models (GCMs) that convert supercooled water to ice at relatively warm temperatures tend to have a greater mean-state cloud fraction and more negative cloud feedback in the middle and high latitude Southern Hemisphere. We investigate possible reasons for these relationships by analyzing the mixed-phase parameterizations in 26 GCMs. The atmospheric temperature where ice and liquid are equally prevalent (T5050) is used to characterize the mixed-phase parameterization in each GCM. Liquid clouds have a higher albedo than ice clouds, so, all else being equal, models with more supercooled liquid water would also have a higher planetary albedo. The lower cloud fraction in these models compensates the higher cloud reflectivity and results in clouds that reflect shortwave radiation (SW) in reasonable agreement with observations, but gives clouds that are too bright and too few. The temperature at which supercooled liquid can remain unfrozen is strongly anti-correlated with cloud fraction in the climate mean state across the model ensemble, but we know of no robust physical mechanism to explain this behavior, especially because this anti-correlation extends through the subtropics. A set of perturbed physics simulations with the Community Atmospheric Model Version 4 (CAM4) shows that, if its temperature-dependent phase partitioning is varied and the critical relative humidity for cloud formation in each model run is also tuned to bring reflected SW into agreement with observations, then cloud fraction increases and liquid water path (LWP) decreases with T5050, as in the CMIP5 ensemble. This article is protected by copyright. All rights reserved. 0320 Cloud physics and chemistry; albedo; 3311 Clouds and aerosols; cloud fraction; 3310 Clouds and cloud feedbacks; Climate sensitivity; cloud feedback; parameterization; 3333 Model calibration; Mixed-phase
McFarlane, Sally A.; Mather, James H.; Mlawer, Eli J.McFarlane, S. A., J. H. Mather, E. J. Mlawer, 2016: ARM’s Progress on Improving Atmospheric Broadband Radiative Fluxes and Heating Rates. Meteorological Monographs, 57, 20.1-20.24. doi: 10.1175/AMSMONOGRAPHS-D-15-0046.1.
McKinnon, Karen A.; Huybers, PeterMcKinnon, K. A., P. Huybers, 2016: Seasonal constraints on inferred planetary heat content. Geophysical Research Letters, 43(20), 10,955–10,964. doi: 10.1002/2016GL071055. Planetary heating can be quantified using top of the atmosphere energy fluxes or through monitoring the heat content of the Earth system. It has been difficult, however, to compare the two methods with each other because of biases in satellite measurements and incomplete spatial coverage of ocean observations. Here we focus on the the seasonal cycle whose amplitude is large relative to satellite biases and observational errors. The seasonal budget can be closed through inferring contributions from high-latitude oceans and marginal seas using the covariance structure of National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM1). In contrast, if these regions are approximated as the average across well-observed regions, the amplitude of the seasonal cycle is overestimated relative to satellite constraints. Analysis of the same CESM1 simulation indicates that complete measurement of the upper ocean would increase the magnitude and precision of interannual trend estimates in ocean heating more than fully measuring the deep ocean. CERES; Ocean heat content; Seasonal cycle; 1635 Oceans; 4262 Ocean observing systems; 4227 Diurnal, seasonal, and annual cycles; Argo
Minnis, Patrick; Hong, Gang; Sun-Mack, Szedung; Smith, William L.; Chen, Yan; Miller, Steven D.Minnis, P., G. Hong, S. Sun-Mack, W. L. Smith, Y. Chen, S. D. Miller, 2016: Estimating Nocturnal Opaque Ice Cloud Optical Depth from MODIS Multispectral Infrared Radiances Using a Neural Network Method. Journal of Geophysical Research: Atmospheres, 121(9), 4907–4932. doi: 10.1002/2015JD024456. Retrieval of ice cloud properties using IR measurements has a distinct advantage over the visible and near-IR techniques by providing consistent monitoring regardless of solar illumination conditions. Historically, the IR bands at 3.7, 6.7, 11.0, and 12.0 µm have been used to infer ice cloud parameters by various methods, but the reliable retrieval of ice cloud optical depth τ is limited to non-opaque cirrus with τ 0320 Cloud physics and chemistry; MODIS; CloudSat; optical depth; ice cloud; 3360 Remote sensing; 0319 Cloud optics; neural network; night
Mlawer, Eli J.; Iacono, Michael J.; Pincus, Robert; Barker, Howard W.; Oreopoulos, Lazaros; Mitchell, David L.Mlawer, E. J., M. J. Iacono, R. Pincus, H. W. Barker, L. Oreopoulos, D. L. Mitchell, 2016: Contributions of the ARM Program to Radiative Transfer Modeling for Climate and Weather Applications. Meteorological Monographs, 57, 15.1-15.19. doi: 10.1175/AMSMONOGRAPHS-D-15-0041.1.
Myers, Timothy A.; Norris, Joel R.Myers, T. A., J. R. Norris, 2016: Reducing the uncertainty in subtropical cloud feedback. Geophysical Research Letters, 43(5), 2144–2148. doi: 10.1002/2015GL067416. Large uncertainty remains on how subtropical clouds will respond to anthropogenic climate change and therefore whether they will act as a positive feedback that amplifies global warming or negative feedback that dampens global warming by altering Earth's energy budget. Here we reduce this uncertainty using an observationally constrained formulation of the response of subtropical clouds to greenhouse forcing. The observed interannual sensitivity of cloud solar reflection to varying meteorological conditions suggests that increasing sea surface temperature and atmospheric stability in the future climate will have largely canceling effects on subtropical cloudiness, overall leading to a weak positive shortwave cloud feedback (0.4 ± 0.9 W m−2 K−1). The uncertainty of this observationally based approximation of the cloud feedback is narrower than the intermodel spread of the feedback produced by climate models. Subtropical cloud changes will therefore complement positive cloud feedbacks identified by previous work, suggesting that future global cloud changes will amplify global warming. clouds; 3305 Climate change and variability; feedbacks; 3310 Clouds and cloud feedbacks; 3307 Boundary layer processes
Norris, Joel R.; Allen, Robert J.; Evan, Amato T.; Zelinka, Mark D.; O’Dell, Christopher W.; Klein, Stephen A.Norris, J. R., R. J. Allen, A. T. Evan, M. D. Zelinka, C. W. O’Dell, S. A. Klein, 2016: Evidence for climate change in the satellite cloud record. Nature, 536(7614), 72-75. doi: 10.1038/nature18273. Clouds substantially affect Earth’s energy budget by reflecting solar radiation back to space and by restricting emission of thermal radiation to space. They are perhaps the largest uncertainty in our understanding of climate change, owing to disagreement among climate models and observational datasets over what cloud changes have occurred during recent decades and will occur in response to global warming. This is because observational systems originally designed for monitoring weather have lacked sufficient stability to detect cloud changes reliably over decades unless they have been corrected to remove artefacts. Here we show that several independent, empirically corrected satellite records exhibit large-scale patterns of cloud change between the 1980s and the 2000s that are similar to those produced by model simulations of climate with recent historical external radiative forcing. Observed and simulated cloud change patterns are consistent with poleward retreat of mid-latitude storm tracks, expansion of subtropical dry zones, and increasing height of the highest cloud tops at all latitudes. The primary drivers of these cloud changes appear to be increasing greenhouse gas concentrations and a recovery from volcanic radiative cooling. These results indicate that the cloud changes most consistently predicted by global climate models are currently occurring in nature.
Norris, Peter M.; da Silva, Arlindo M.Norris, P. M., A. M. da Silva, 2016: Monte Carlo Bayesian inference on a statistical model of sub-gridcolumn moisture variability using high-resolution cloud observations. Part II: Sensitivity tests and results. Quarterly Journal of the Royal Meteorological Society, 142(699), 2528–2540. doi: 10.1002/qj.2844. Part I presented a Monte Carlo Bayesian method for constraining a complex statistical model of GCM sub-gridcolumn moisture variability using high-resolution MODIS cloud data, thereby permitting parameter estimation and cloud data assimilation for large-scale models. This part performs some basic testing of this new approach, verifying that it does indeed significantly reduce mean and standard deviation biases with respect to the assimilated MODIS cloud optical depth, brightness temperature and cloud top pressure, and that it also improves the simulated rotational-Ramman scattering cloud optical centroid pressure (OCP) against independent (non-assimilated) retrievals from the OMI instrument. Of particular interest, the Monte Carlo method does show skill in the especially difficult case where the background state is clear but cloudy observations exist. In traditional linearized data assimilation methods, a subsaturated background cannot produce clouds via any infinitesimal equilibrium perturbation, but the Monte Carlo approach allows non-gradient-based jumps into regions of non-zero cloud probability. In the example provided, the method is able to restore marine stratocumulus near the Californian coast where the background state has a clear swath. This paper also examines a number of algorithmic and physical sensitivities of the new method and provides guidance for its cost-effective implementation. One obvious difficulty for the method, and other cloud data assimilation methods as well, is the lack of information content in passive-radiometer-retrieved cloud observables on cloud vertical structure, beyond cloud top pressure and optical thickness, thus necessitating strong dependence on the background vertical moisture structure. It is found that a simple flow-dependent correlation modification due to [Riishojgaard(1998)] provides some help in this respect, by better honoring inversion structures in the background state. Cloud data assimilation; Correlation models; Monte Carlo Bayesian inference
Oreopoulos, Lazaros; Cho, Nayeong; Lee, Dongmin; Kato, SeijiOreopoulos, L., N. Cho, D. Lee, S. Kato, 2016: Radiative effects of global MODIS cloud regimes. Journal of Geophysical Research: Atmospheres, 121(5), 2299–2317. doi: 10.1002/2015JD024502. We update previously published Moderate Resolution Imaging Spectroradiometer (MODIS) global cloud regimes (CRs) using the latest MODIS cloud retrievals in the Collection 6 data set. We implement a slightly different derivation method, investigate the composition of the regimes, and then proceed to examine several aspects of CR radiative appearance with the aid of various radiative flux data sets. Our results clearly show that the CRs are radiatively distinct in terms of shortwave, longwave, and their combined (total) cloud radiative effect. We show that we can clearly distinguish regimes based on whether they radiatively cool or warm the atmosphere, and thanks to radiative heating profiles, to discern the vertical distribution of cooling and warming. Terra and Aqua comparisons provide information about the degree to which morning and afternoon occurrences of regimes affect the symmetry of CR radiative contribution. We examine how the radiative discrepancies among multiple irradiance data sets suffering from imperfect spatiotemporal matching depend on CR and whether they are therefore related to the complexity of cloud structure, its interpretation by different observational systems, and its subsequent representation in radiative transfer calculations. clouds; 0321 Cloud/radiation interaction; 3359 Radiative processes; 3310 Clouds and cloud feedbacks; MODIS; Cloud radiative effects; 3360 Remote sensing; cloud regimes; a-train; 0319 Cloud optics
Orth, Rene; Dutra, Emanuel; Pappenberger, FlorianOrth, R., E. Dutra, F. Pappenberger, 2016: Improving Weather Predictability by Including Land Surface Model Parameter Uncertainty. Mon. Wea. Rev., 144(4), 1551-1569. doi: 10.1175/MWR-D-15-0283.1. The land surface forms an important component of Earth system models and interacts nonlinearly with other parts such as ocean and atmosphere. To capture the complex and heterogeneous hydrology of the land surface, land surface models include a large number of parameters impacting the coupling to other components of the Earth system model.Focusing on ECMWF’s land surface model Hydrology Tiled ECMWF Scheme of Surface Exchanges over Land (HTESSEL), the authors present in this study a comprehensive parameter sensitivity evaluation using multiple observational datasets in Europe. The authors select six poorly constrained effective parameters (surface runoff effective depth, skin conductivity, minimum stomatal resistance, maximum interception, soil moisture stress function shape, and total soil depth) and explore their sensitivity to model outputs such as soil moisture, evapotranspiration, and runoff using uncoupled simulations and coupled seasonal forecasts. Additionally, the authors investigate the possibility to construct ensembles from the multiple land surface parameters.In the uncoupled runs the authors find that minimum stomatal resistance and total soil depth have the most influence on model performance. Forecast skill scores are moreover sensitive to the same parameters as HTESSEL performance in the uncoupled analysis. The authors demonstrate the robustness of these findings by comparing multiple best-performing parameter sets and multiple randomly chosen parameter sets. The authors find better temperature and precipitation forecast skill with the best-performing parameter perturbations demonstrating representativeness of model performance across uncoupled (and hence less computationally demanding) and coupled settings.Finally, the authors construct ensemble forecasts from ensemble members derived with different best-performing parameterizations of HTESSEL. This incorporation of parameter uncertainty in the ensemble generation yields an increase in forecast skill, even beyond the skill of the default system.
Palle, E.; Goode, P. R.; Montañés-Rodríguez, P. Pilar; Shumko, A.; Gonzalez-Merino, B.; Lombilla, C. Martinez; Jimenez-Ibarra, F.; Shumko, S.; Sanroma, E.; Hulist, A.; Miles-Paez, P.; Murgas, F.; Nowak, G.; Koonin, S. E.Palle, E., P. R. Goode, P. P. Montañés-Rodríguez, A. Shumko, B. Gonzalez-Merino, C. M. Lombilla, F. Jimenez-Ibarra, S. Shumko, E. Sanroma, A. Hulist, P. Miles-Paez, F. Murgas, G. Nowak, S. E. Koonin, 2016: Earth's albedo variations 1998-2014 as measured from ground-based earthshine observations. Geophysical Research Letters, 43(9), 4531–4538. doi: 10.1002/2016GL068025. The Earth's albedo is a fundamental climate parameter for understanding the radiation budget of the atmosphere. It has been traditionally measured from space platforms, but also from the ground for sixteen years from Big Bear Solar Observatory by observing the Moon. The photometric ratio of the dark (earthshine) to the bright (moonshine) sides of the Moon is used to determine nightly anomalies in the terrestrial albedo, with the aim is of quantifying sustained monthly, annual and/or decadal changes. We find two modest decadal scale cycles in the albedo, but with no significant net change over the sixteen years of accumulated data. Within the evolution of the two cycles, we find periods of sustained annual increases, followed by comparable sustained decreases in albedo. The evolution of the earthshine albedo is in remarkable agreement with that from the CERES instruments, although each method measures different slices of the Earth's Bond albedo. clouds; 1610 Atmosphere; 0305 Aerosols and particles; albedo; 0321 Cloud/radiation interaction; aerosol; climate; radiation; 1630 Impacts of global change; earthshine; 0999 General or miscellaneous
Parfitt, R.; Russell, J. E.; Bantges, R.; Clerbaux, N.; Brindley, H.Parfitt, R., J. E. Russell, R. Bantges, N. Clerbaux, H. Brindley, 2016: A study of the time evolution of GERB shortwave calibration by comparison with CERES Edition-3A data. Remote Sensing of Environment, 186, 416-427. doi: 10.1016/j.rse.2016.09.005. This study examines the evolution of the GERB-2 and GERB-1 Edition 1 shortwave radiance calibration between 2004–2007 and 2007–2012 respectively, through comparison with CERES instrument FM1 Edition 3A SSF instantaneous radiances. Two periods when simultaneous observations from both GERB-2 and GERB-1 were available, January 13th to February 11th 2007 and May 1st to May 10th 2007, are also compared. For these two overlap periods respectively, averaged over all CERES ‘unfiltered-to-filtered radiance ratio’ subsets, the GERB-1/CERES unfiltered radiance ratio is on average found to be 1.6% and 1.9% lower than the associated GERB-2/CERES unfiltered radiance ratio. Over the two longer time series the GERB/CERES unfiltered radiance ratio shows a general decrease with time for both GERB-2 and GERB-1. The rate of decrease varies through time but no significant seasonal dependence is seen. Averaged over all subsets the GERB-2/CERES unfiltered radiance ratio showed a decrease of 1.9% between June 2004 and June 2006. Between June 2007 and June 2012, the corresponding decrease in the GERB-1/CERES unfiltered radiance ratio was 6.5%. The evolution of the GERB/CERES unfiltered radiance ratio for both GERB-2 and GERB-1 shows a strong dependence on the CERES unfiltered-to-filtered radiance ratio, indicating that it is spectrally dependent. Further time-series analysis and theoretical work using simulated spectral radiance curves suggests that for GERB-1 the evolution is consistent with a darkening in the GERB shortwave spectral response function which is most pronounced at the shortest wavelengths. For GERB-2, no single spectral cause can be identified, suggesting that the evolution is likely due to a combination of several different effects. earth radiation budget; CERES; GERB; Instrument calibration
Patel, Piyushkumar N.; Kumar, RajPatel, P. N., R. Kumar, 2016: Dust Induced Changes in Ice Cloud and Cloud Radiative Forcing over a High Altitude Site. Aerosol and Air Quality Research, 16(8), 1820-1831. doi: 10.4209/aaqr.2015.05.0325.
Raschke, Ehrhard; Kinne, Stefan; Rossow, William B.; Stackhouse, Paul W.; Wild, MartinRaschke, E., S. Kinne, W. B. Rossow, P. W. Stackhouse, M. Wild, 2016: Comparison of Radiative Energy Flows in Observational Datasets and Climate Modeling. J. Appl. Meteor. Climatol., 55(1), 93-117. doi: 10.1175/JAMC-D-14-0281.1. This study examines radiative flux distributions and local spread of values from three major observational datasets (CERES, ISCCP, and SRB) and compares them with results from climate modeling (CMIP3). Examinations of the spread and differences also differentiate among contributions from cloudy and clear-sky conditions. The spread among observational datasets is in large part caused by noncloud ancillary data. Average differences of at least 10 W m−2 each for clear-sky downward solar, upward solar, and upward infrared fluxes at the surface demonstrate via spatial difference patterns major differences in assumptions for atmospheric aerosol, solar surface albedo and surface temperature, and/or emittance in observational datasets. At the top of the atmosphere (TOA), observational datasets are less influenced by the ancillary data errors than at the surface. Comparisons of spatial radiative flux distributions at the TOA between observations and climate modeling indicate large deficiencies in the strength and distribution of model-simulated cloud radiative effects. Differences are largest for lower-altitude clouds over low-latitude oceans. Global modeling simulates stronger cloud radiative effects (CRE) by +30 W m−2 over trade wind cumulus regions, yet smaller CRE by about −30 W m−2 over (smaller in area) stratocumulus regions. At the surface, climate modeling simulates on average about 15 W m−2 smaller radiative net flux imbalances, as if climate modeling underestimates latent heat release (and precipitation). Relative to observational datasets, simulated surface net fluxes are particularly lower over oceanic trade wind regions (where global modeling tends to overestimate the radiative impact of clouds). Still, with the uncertainty in noncloud ancillary data, observational data do not establish a reliable reference. aerosols; albedo; Radiative fluxes; Radiation budgets; Climatology; Cloud radiative effects
Read, P. L.; Barstow, J.; Charnay, B.; Chelvaniththilan, S.; Irwin, P. G. J.; Knight, S.; Lebonnois, S.; Lewis, S. R.; Mendonça, J.; Montabone, L.Read, P. L., J. Barstow, B. Charnay, S. Chelvaniththilan, P. G. J. Irwin, S. Knight, S. Lebonnois, S. R. Lewis, J. Mendonça, L. Montabone, 2016: Global energy budgets and ‘Trenberth diagrams’ for the climates of terrestrial and gas giant planets. Quarterly Journal of the Royal Meteorological Society, 142(695), 703-720. doi: 10.1002/qj.2704. The climate on Earth is generally determined by the amount and distribution of incoming solar radiation, which must be balanced in equilibrium by the emission of thermal radiation from the surface and atmosphere. The precise routes by which incoming energy is transferred from the surface and within the atmosphere and back out to space, however, are important features that characterize the current climate. This has been analyzed in the past by several groups over the years, based on combinations of numerical model simulations and direct observations of the Earth's climate system. The results are often presented in schematic form to show the main routes for the transfer of energy into, out of and within the climate system. Although relatively simple in concept, such diagrams convey a great deal of information about the climate system in a compact form. Such an approach has not so far been widely adopted in any systematic way for other planets of the Solar System, let alone beyond, although quite detailed climate models of several planets are now available, constrained by many new observations and measurements. Here we present an analysis of the global transfers of energy within the climate systems of a range of planets within the Solar System, including Mars, Titan, Venus and Jupiter, as modelled by relatively comprehensive radiative transfer and (in some cases) numerical circulation models. These results are presented in schematic form for comparison with the classical global energy budget analyses for the Earth, highlighting important similarities and differences. We also take the first steps towards extending this approach to other Solar System and extrasolar planets, including Mars, Venus, Titan, Jupiter and the ‘hot Jupiter’ exoplanet HD 189733b, presenting a synthesis of both previously published and new calculations for all of these planets. energy budget; climate equilibrium; Planetary atmospheres; radiative heat flux; sensible heat flux
Romano, S.; Burlizzi, P.; Perrone, M. R.Romano, S., P. Burlizzi, M. R. Perrone, 2016: Experimental determination of short- and long-wave dust radiative effects in the Central Mediterranean and comparison with model results. Atmospheric Research, 171, 5-20. doi: 10.1016/j.atmosres.2015.11.019. Downward and upward irradiance measurements, in the short-wave (SW) and long-wave (LW) spectral range, have been used in combination with simultaneous aerosol optical depths (AODs) to experimentally determine the instantaneous and clear-sky aerosol Direct Radiative Forcing (DRF) at the surface, during a desert dust outbreak which affected the Central Mediterranean from 9 to 13 July 2012. AODs were retrieved from AERONET (AErosol RObotic NETwork) sun/sky photometer measurements collocated in space and time. The importance of downward and upward radiative flux measurements to properly account for both the surface albedo dependence on the solar zenith angle, and the land surface temperature (TLS) has been highlighted. Measured radiative fluxes were in reasonable agreement with the CERES (Clouds and the Earth's Radiant Energy System) and AERONET corresponding ones collocated in space and time. SW and LW downward fluxes at the surface decreased up to 9% and increased up to 13%, respectively, as a consequence of a factor 5 increase of the AOD at 675 nm (AOD675). This is due to the cooling and warming effect of desert dust in the SW and LW spectral range, respectively. In fact, we have also found that the TLS increased at a rate of about 250 K per unit increase of the AOD675. The aerosol DRF at the surface varied from − 8 to − 74 W m− 2 and from + 1.2 to + 9.6 W m− 2 in the SW and LW spectral domains, respectively. In particular, we have found that the LW-DRF on average offsets 14% of the related SW component. It is shown that a two-stream radiative transfer model can reproduce the experimental findings at the surface by replacing the refractive indices typical of dust particles with the ones obtained for a mixture made of dust and soot particles. The dust contamination by anthropogenic particles during its transport to the monitoring site located several hundred kilometers away from the source region was responsible for this last result. We have also found by model simulations that the LW-DRF increased linearly with TLS both at the surface and at the top of the atmosphere. surface albedo; direct radiative forcing; Land surface temperature; Desert dust aerosol; Irradiance measurements
Sakaeda, Naoko; Roundy, Paul E.Sakaeda, N., P. E. Roundy, 2016: Gross Moist Stability and the Madden-Julian Oscillation in Reanalysis Data. Quarterly Journal of the Royal Meteorological Society, 142(700), 2740–2757. doi: 10.1002/qj.2865. This study uses the ERA-Interm and Climate Forecast System reanalysis datasets to examine the relationship between the convective activity of the Madden-Julian Oscillation (MJO) and the normalized gross moist stability (NGMS) on various timescales. Previous studies based on proposed theories for the MJO and the assessments of general circulation models suggest that MJO convection tends to be more active where the NGMS is smaller or effectively negative. This relationship only appears using reanalysis data on some timescales and limited geographical regions. On seasonal timescales, MJO convective activity shifts with the regions of positive NGMS and net moisture import, indicating positive correlation between MJO convective activity and the NGMS. On interannual to decadal timescales, stronger MJO convective events tend to occur with a background state of smaller NGMS exclusively over the central Pacific basin, indicating negative correlation. When the environment switches between net moisture export to import, MJO convective activity tends follow the region of net moisture import, leading to its positive correlation with NGMS. However, when the environment already has net moisture import and positive NGMS, MJO convective activity is negatively correlated with the NGMS and stronger MJO convective events tend to occur with smaller positive NGMS. Therefore, the background NGMS is not a globally applicable metric for MJO convective activity and it needs to be used with caution over such environments where the NGMS can oscillate around zero. On intraseasonal timescales, as shown by previous modeling and observational studies, the NGMS becomes anomalously negative prior to the onset of MJO enhanced convection and becomes positive as the convection peaks over the Indo-Pacific basin. The results of this study demonstrate that the relationship between MJO convective activity and the NGMS in reanalysis data largely depends on timescales and geographical region. reanalysis; Madden-Julian Oscillation; gross moist stability; intraseasonal tropical convection
Sanchez, Claudio; Williams, Keith D.; Collins, MatthewSanchez, C., K. D. Williams, M. Collins, 2016: Improved stochastic physics schemes for global weather and climate models. Quarterly Journal of the Royal Meteorological Society, 142(694), 147-159. doi: 10.1002/qj.2640. The importance of probabilistic weather predictions and climate projections is growing. One of the key elements of the former is stochastic physics, schemes that perturb some uncertain processes in a general circulation model (GCM), such as physical parametrizations or diffusion. They help to increase the ensemble dispersion of ensemble prediction systems (EPS) and in some cases improve certain atmospheric processes by noise-induced drifts. We have developed a new configuration of stochastic physics schemes for the Met Office Unified Model (MetUM). It consists of an improved Stochastic Kinetic Energy Backscatter v2 (SKEB2), plus the Stochastic Perturbation of Tendencies (SPT). The improvements to SKEB2 remove spurious physical artefacts, e.g. a spurious wave caused by low-wave-number perturbations, and improve the resolution sensitivity of the scheme. The SPT produces a larger ensemble spread in the Tropics than present schemes, but its impact on long-term climate budgets makes the use of conservation constraints for water vapour and energy essential. The new configuration produces a higher impact in the Tropics, increasing the ensemble spread and improving some long-standing climate biases in areas of excessive convection, whilst minimizing the negative impact on tropical processes like tropical convective waves. climate modelling; ensemble prediction; stochastic physics; tropical biases
Sarangi, Chandan; Tripathi, S. N.; Mishra, A. K.; Goel, A.; Welton, E. J.Sarangi, C., S. N. Tripathi, A. K. Mishra, A. Goel, E. J. Welton, 2016: Elevated aerosol layers and their radiative impact over Kanpur during monsoon onset period. Journal of Geophysical Research: Atmospheres, 121(13), 7936–7957. doi: 10.1002/2015JD024711. Accurate information about aerosol vertical distribution is needed to reduce uncertainties in aerosol radiative forcing and its effect on atmospheric dynamics. The present study deals with synergistic analyses of aerosol vertical distribution and aerosol optical depth (AOD) with meteorological variables using multisatellite and ground-based remote sensors over Kanpur in central Indo-Gangetic Plain (IGP). Micro-Pulse Lidar Network-derived aerosol vertical extinction (σ) profiles are analyzed to quantify the interannual and daytime variations during monsoon onset period (May–June) for 2009–2011. The mean aerosol profile is broadly categorized into two layers viz., a surface layer (SL) extending up to 1.5 km (where σ decreased exponentially with height) and an elevated aerosol layer (EAL) extending between 1.5 and 5.5 km. The increase in total columnar aerosol loading is associated with relatively higher increase in contribution from EAL loading than that from SL. The mean contributions of EALs are about 60%, 51%, and 50% to total columnar AOD during 2009, 2010, and 2011, respectively. We observe distinct parabolic EALs during early morning and late evening but uniformly mixed EALs during midday. The interannual and daytime variations of EALs are mainly influenced by long-range transport and convective capacity of the local emissions, respectively. Radiative flux analysis shows that clear-sky incoming solar radiation at surface is reduced with increase in AOD, which indicates significant cooling at surface. Collocated analysis of atmospheric temperature and aerosol loading reveals that increase in AOD not only resulted in surface dimming but also reduced the temperature (∼2–3°C) of lower troposphere (below 3 km altitude). Radiative transfer simulations indicate that the reduction of incoming solar radiation at surface is mainly due to increased absorption by EALs (with increase in total AOD). The observed cooling in lower troposphere in high aerosol loading scenario could be understood as a dynamical feedback of EAL-induced stratification of lower troposphere. Further, the observed radiative effect of EALs increases the stability of the lower troposphere, which could modulate the large-scale atmospheric dynamics during monsoon onset period. These findings encourage follow-up studies on the implication of EALs to the Indian summer monsoon dynamics using numerical models. 0305 Aerosols and particles; 3359 Radiative processes; 3360 Remote sensing; 1803 Anthropogenic effects; atmospheric stability; Daytime variations; Elevated aerosol layer; lower atmospheric cooling; Radiative forcing efficiency
Saud, Trailokya; Dey, Sagnik; Das, Sushant; Dutta, SoumiSaud, T., S. Dey, S. Das, S. Dutta, 2016: A satellite-based 13-year climatology of net cloud radiative forcing over the Indian monsoon region. Atmospheric Research, 182, 76-86. doi: 10.1016/j.atmosres.2016.07.017. We present a satellite-based 13-year (Mar. 2000–Feb. 2013) climatology of net cloud radiative forcing (CRF) over the Indian monsoon region (0–40°N, 60–100°E) using the Clouds and Earth's Radiant Energy System (CERES) radiation data and explained the net CRF variability in terms of cloud properties retrieved by Moderate Resolution Imaging Spectroradiometer (MODIS). Mean (± 1σ) seasonal shortwave (SW) CRF values averaged over the region are − 82.7 ± 24.5, − 32.1 ± 12.1, − 17.2 ± 5.3 and − 30.2 ± 16.2 W m− 2 respectively for the monsoon (JJAS), post-monsoon (ON), winter (DJF) and pre-monsoon (MAM) seasons; while the corresponding longwave (LW) CRF values are 53.7 ± 14.2, 27.9 ± 10.0, 15.8 ± 7.0 and 25.2 ± 9.1 W m− 2. Regional analysis reveals the largest (least) negative net CRF over the northeast (northwest) rainfall homogeneous zone throughout the year due to the dominance of optically thick high clouds (low cloud fraction, fc). Mean JJAS fc is found to increase (by > 0.01 per year) over large parts of the Arabian Sea, Bay of Bengal and the northwest region. Mean annual net CRF values for cumulus, stratocumulus and stratus (low level), altocumulus, altostratus and nimbostratus (mid-level clouds) and cirrus, cirrostratus and deep-convective (high level) clouds over the Indian monsoon region are estimated to be − 0.8, − 4.7, − 6.9, + 3.3, − 6.3, − 23.3, + 5.4, − 23.3 and − 42.1 W m− 2 respectively. Across a wide range of cloud optical depth (COD) and fc < 0.6, near cancellation of SW cooling by LW warming, is observed for low clouds. Net CRF drops below − 15 W m− 2 for clouds evolving above 400 hPa, mainly in the monsoon season. Our results demonstrate that net CRF variability in the Indian monsoon region can be explained by variability in Cloud Top Pressure (CTP), COD and fc. The study highlights the need for resolving a multi-layer cloud field in the future. clouds; Climatology; cloud radiative forcing; satellite observation; Indian region
Scarino, Benjamin R.; Minnis, Patrick; Chee, Thad; Bedka, Kristopher M.; Yost, Christopher R.; Palikonda, RabindraScarino, B. R., P. Minnis, T. Chee, K. M. Bedka, C. R. Yost, R. Palikonda, 2016: Global clear-sky surface skin temperature from multiple satellites using a single-channel algorithm with viewing zenith angle correction. Atmospheric Measurement Techniques Discussions, 1-42. doi: 10.5194/amt-2016-79.
Schneider, David P.; Reusch, David B.Schneider, D. P., D. B. Reusch, 2016: Antarctic and Southern Ocean Surface Temperatures in CMIP5 Models in the Context of the Surface Energy Budget. J. Climate, 29(5), 1689-1716. doi: 10.1175/JCLI-D-15-0429.1. This study examines the biases, intermodel spread, and intermodel range of surface air temperature (SAT) across the Antarctic ice sheet and Southern Ocean in 26 structurally different climate models. Over the ocean (40°–60°S), an ensemble-mean warm bias peaks in late austral summer concurrently with the peak in the intermodel range of SAT. This warm bias lags a spring–summer positive bias in net surface radiation due to weak shortwave cloud forcing and is gradually reduced during autumn and winter. For the ice sheet, inconsistencies among reanalyses and observational datasets give low confidence in the ensemble-mean bias of SAT, but a small summer warm bias is suggested in comparison with nonreanalysis SAT data. The ensemble mean hides a large intermodel range of SAT, which peaks during the summer insolation maximum. In summer on the ice sheet, the SAT intermodel spread is largely associated with the surface albedo. In winter, models universally exhibit a too-strong deficit in net surface radiation related to the downward longwave radiation, implying that the lower atmosphere is too stable. This radiation deficit is balanced by the transfer of sensible heat toward the surface (which largely explains the intermodel spread in SAT) and by a subsurface heat flux. The winter bias in downward longwave radiation is due to the longwave cloud radiative effect, which the ensemble mean underestimates by a factor of 2. The implications of these results for improving climate simulations over Antarctica and the Southern Ocean are discussed.
Sebastian, Dawn Emil; Pathak, Amey; Ghosh, SubimalSebastian, D. E., A. Pathak, S. Ghosh, 2016: Use of Atmospheric Budget to Reduce Uncertainty in Estimated Water Availability over South Asia from Different Reanalyses. Scientific Reports, 6, 29664. doi: 10.1038/srep29664. Disagreements across different reanalyses over South Asia result into uncertainty in assessment of water availability, which is computed as the difference between Precipitation and Evapotranspiration (P–E).
Shields, Christine A.; Kiehl, Jeffrey T.; Meehl, Gerald A.Shields, C. A., J. T. Kiehl, G. A. Meehl, 2016: Future changes in regional precipitation simulated by a half degree coupled climate model: Sensitivity to horizontal resolution. Journal of Advances in Modeling Earth Systems, 8(2), 863–884. doi: 10.1002/2015MS000584. The global fully coupled half degree Community Climate System Model Version 4 (CCSM4) was integrated for a suite of climate change ensemble simulations including five historical runs, five Representative Concentration Pathway 8.5 (RCP8.5) runs, and a long Pre-Industrial control run. This study focuses on precipitation at regional scales and its sensitivity to horizontal resolution. The half degree historical CCSM4 simulations are compared to observations, where relevant, and to the standard one degree CCSM4. Both the half-degree and one-degree resolutions are coupled to a nominal one-degree ocean. North American and South Asian/Indian monsoon regimes are highlighted because these regimes demonstrate improvements due to higher resolution, primarily because of better-resolved topography. Agriculturally sensitive areas are analyzed and include Southwest, Central, and Southeast U.S, Southern Europe, and Australia. Both mean and extreme precipitation is discussed for convective and large-scale precipitation processes. Convective precipitation tends to decrease with increasing resolution and large-scale precipitation tends to increase. Improvements for the half-degree agricultural regions can be found for mean and extreme precipitation in the Southeast U.S., Southern Europe, and Australian regions. Climate change responses differ between the model resolutions for the U.S. Southwest/Central regions and are seasonally dependent in the Southeast and Australian regions. Both resolutions project a clear drying signal across Southern Europe due to increased greenhouse warming. Differences between resolutions tied to the representation of convective and large-scale precipitation play an important role in the character of the climate change and depend on regional influences. This article is protected by copyright. All rights reserved. climate change; 1637 Regional climate change; 3354 Precipitation; 1626 Global climate models; High Resolution GCM Ensembles; Precipitaion
Simmons, Adrian; Fellous, Jean-Louis; Ramaswamy, Venkatachalam; Trenberth, Kevin; Asrar, Ghassem; Balmaseda, Magdalena; Burrows, John P.; Ciais, Philippe; Drinkwater, Mark; Friedlingstein, Pierre; Gobron, Nadine; Guilyardi, Eric; Halpern, David; Heimann, Martin; Johannessen, Johnny; Levelt, Pieternel F.; Lopez-Baeza, Ernesto; Penner, Joyce; Scholes, Robert; Shepherd, TedSimmons, A., J. Fellous, V. Ramaswamy, K. Trenberth, G. Asrar, M. Balmaseda, J. P. Burrows, P. Ciais, M. Drinkwater, P. Friedlingstein, N. Gobron, E. Guilyardi, D. Halpern, M. Heimann, J. Johannessen, P. F. Levelt, E. Lopez-Baeza, J. Penner, R. Scholes, T. Shepherd, 2016: Observation and integrated Earth-system science: A roadmap for 2016–2025. Advances in Space Research, 57(10), 2037–2103. doi: 10.1016/j.asr.2016.03.008. This report is the response to a request by the Committee on Space Research of the International Council for Science to prepare a roadmap on observation and integrated Earth-system science for the coming ten years. Its focus is on the combined use of observations and modelling to address the functioning, predictability and projected evolution of interacting components of the Earth system on timescales out to a century or so. It discusses how observations support integrated Earth-system science and its applications, and identifies planned enhancements to the contributing observing systems and other requirements for observations and their processing. All types of observation are considered, but emphasis is placed on those made from space. The origins and development of the integrated view of the Earth system are outlined, noting the interactions between the main components that lead to requirements for integrated science and modelling, and for the observations that guide and support them. What constitutes an Earth-system model is discussed. Summaries are given of key cycles within the Earth system. The nature of Earth observation and the arrangements for international coordination essential for effective operation of global observing systems are introduced. Instances are given of present types of observation, what is already on the roadmap for 2016–2025 and some of the issues to be faced. Observations that are organised on a systematic basis and observations that are made for process understanding and model development, or other research or demonstration purposes, are covered. Specific accounts are given for many of the variables of the Earth system. The current status and prospects for Earth-system modelling are summarized. The evolution towards applying Earth-system models for environmental monitoring and prediction as well as for climate simulation and projection is outlined. General aspects of the improvement of models, whether through refining the representations of processes that are already incorporated or through adding new processes or components, are discussed. Some important elements of Earth-system models are considered more fully. Data assimilation is discussed not only because it uses observations and models to generate datasets for monitoring the Earth system and for initiating and evaluating predictions, in particular through reanalysis, but also because of the feedback it provides on the quality of both the observations and the models employed. Inverse methods for surface-flux or model-parameter estimation are also covered. Reviews are given of the way observations and the processed datasets based on them are used for evaluating models, and of the combined use of observations and models for monitoring and interpreting the behaviour of the Earth system and for predicting and projecting its future. A set of concluding discussions covers general developmental needs, requirements for continuity of space-based observing systems, further long-term requirements for observations and other data, technological advances and data challenges, and the importance of enhanced international co-operation. observations; Earth system science; Modelling
Slater, Andrew G.Slater, A. G., 2016: Surface Solar Radiation in North America: A Comparison of Observations, Reanalyses, Satellite, and Derived Products. J. Hydrometeor., 17(1), 401-420. doi: 10.1175/JHM-D-15-0087.1. Observations of daily surface solar or shortwave radiation data from over 4000 stations have been gathered, covering much of the continental United States as well as portions of Alberta and British Columbia, Canada. The quantity of data increases almost linearly from 1998, when only several hundred stations had data. A quality-control procedure utilizing threshold values along with computing the clear-sky radiation envelope for individual stations was implemented to both screen bad data and rescue informative data. Over two-thirds of the observations are seen as acceptable. There are 15 different surface solar radiation products assessed relative to observations, including reanalyses [Twentieth-Century Reanalysis (20CR), CFS Reanalysis and Reforecast (CFSRR), ERA-Interim, Japanese 55-year Reanalysis Project (JRA-55), MERRA, NARR, and NCEP–NCAR Reanalysis 1 (NCEP-1)], derived products [observations from the CRU and NCEP-1 (CRU–NCEP); Daily Surface Weather and Climatological Summaries (Daymet); Global Land Data Assimilation System, version 1 (GLDAS-1); Global Soil Wetness Project Phase 3 (GSWP3); Multiscale Synthesis and Terrestrial Model Intercomparison Project (MsTMIP); and phase 2 of the North American Land Data Assimilation System (NLDAS-2)], and two satellite products (CERES and GOES). All except the CERES product have daily or finer temporal resolution. The RMSE of spatial biases is greater than 18 W m−2 for 13 of the 15 products over the summer season (June–August). None of the daily resolution products fulfill all three desirable criteria of low ( satellite observations; Shortwave radiation; Models and modeling; Physical Meteorology and Climatology; North America; Surface observations; bias; Observational techniques and algorithms; Geographic location/entity; Mathematical and statistical techniques; Reanalysis data
Slessarev, E. W.; Lin, Y.; Bingham, N. L.; Johnson, J. E.; Dai, Y.; Schimel, J. P.; Chadwick, O. A.Slessarev, E. W., Y. Lin, N. L. Bingham, J. E. Johnson, Y. Dai, J. P. Schimel, O. A. Chadwick, 2016: Water balance creates a threshold in soil pH at the global scale. Nature, 540(7634), 567-569. doi: 10.1038/nature20139. Soil pH regulates the capacity of soils to store and supply nutrients, and thus contributes substantially to controlling productivity in terrestrial ecosystems. However, soil pH is not an independent regulator of soil fertility—rather, it is ultimately controlled by environmental forcing. In particular, small changes in water balance cause a steep transition from alkaline to acid soils across natural climate gradients. Although the processes governing this threshold in soil pH are well understood, the threshold has not been quantified at the global scale, where the influence of climate may be confounded by the effects of topography and mineralogy. Here we evaluate the global relationship between water balance and soil pH by extracting a spatially random sample (n = 20,000) from an extensive compilation of 60,291 soil pH measurements. We show that there is an abrupt transition from alkaline to acid soil pH that occurs at the point where mean annual precipitation begins to exceed mean annual potential evapotranspiration. We evaluate deviations from this global pattern, showing that they may result from seasonality, climate history, erosion and mineralogy. These results demonstrate that climate creates a nonlinear pattern in soil solution chemistry at the global scale; they also reveal conditions under which soils maintain pH out of equilibrium with modern climate. Element cycles; Geochemistry
Smith, G. L.; Wong, T.Smith, G. L., T. Wong, 2016: Time-Sampling Errors of Earth Radiation From Satellites: Theory for Monthly Mean Albedo. IEEE Transactions on Geoscience and Remote Sensing, 54(6), 3107-3115. doi: 10.1109/TGRS.2015.2503982. The Earth Radiation Budget Experiment wide-field-of-view (WFOV) radiometers aboard the Earth Radiation Budget Satellite (ERBS) provided a 15-year record of high-quality measurements for research into the radiant energy balance of the Earth. Monthly mean maps of RSR and outgoing longwave radiation (OLR) are primary data products from these measurements. The ERBS orbit had an inclination of 57° so as to precess through all local times every 72 days. Because of limited temporal sampling, some regions were not measured sufficiently often by the WFOV radiometers to produce accurate radiation flux values for these maps. The temporal sampling of any one region is very irregular; therefore, it is necessary to consider each region in detail for each month. An analysis of the errors, which result from computing the average value of the albedo of a region over a day or month based on limited sampling, is presented. It is necessary to take into account synoptic variations and their time correlations and differences of the regions' diurnal cycle from that assumed by the time-averaging algorithms. An expression is derived for the variance of the error of the computed daily and monthly mean albedo. Temporal correlation and variability of the albedo field are specified a priori. This analysis has been used for quality assurance to evaluate the temporal sampling errors of monthly mean RSR maps computed from the measurements by the WFOV radiometers aboard the ERBS and to delete those values for which the error variance is excessive. Earth; earth radiation budget; Extraterrestrial measurements; atmospheric techniques; radiometers; Time measurement; Sea measurements; diurnal cycle; Orbits; outgoing longwave radiation; correlation; Error analysis; time-sampling errors; Earth radiation budget experiment wide-field-of-view radiometers; ERBS orbit; high-quality measurements; limited temporal sampling; radiation flux; RSR maps; sampling errors; time-averaging algorithms; WFOV radiometers
Smith, G. Louis; Daniels, Janet; Priestley, Kory; Thomas, Susan; Lee, Robert B.Smith, G. L., J. Daniels, K. Priestley, S. Thomas, R. B. Lee, 2016: Measurement of the Point Response Functions of CERES Scanning Radiometers. IEEE Transactions on Geoscience and Remote Sensing, 54(3), 1260-1266. doi: 10.1109/TGRS.2015.2476759.
Smith, G. Louis; Thomas, Susan; Priestley, Kory J.; Walikainen, DaleSmith, G. L., S. Thomas, K. J. Priestley, D. Walikainen, 2016: Tropical Mean Fluxes: A Tool for Calibration and Validation of CERES Radiometers. IEEE Transactions on Geoscience and Remote Sensing, 54(9), 5135-5142. doi: 10.1109/TGRS.2016.2556581.
Song, Jinjie; Wang, Yuan; Tang, JianpingSong, J., Y. Wang, J. Tang, 2016: A Hiatus of the Greenhouse Effect. Scientific Reports, 6, 33315. doi: 10.1038/srep33315. The rate at which the global average surface temperature is increasing has slowed down since the end of the last century. This study investigates whether this warming hiatus results from a change in the well-known greenhouse effect.
Song, Lei; Wang, YinanSong, L., Y. Wang, 2016: A solely radiance-based spectral angular distribution model and its application in deriving clear-sky spectral fluxes over tropical oceans. Advances in Atmospheric Sciences, 33(2), 259-268. doi: 10.1007/s00376-015-5040-8. The radiation budget at the top of the atmosphere plays a critical role in climate research. Compared to the broadband flux, the spectrally resolved outgoing longwave radiation or flux (OLR), with rich atmospheric information in different bands, has obvious advantages in the evaluation of GCMs. Unlike methods that need auxiliary measurements and information, here we take atmospheric infrared sounder (AIRS) observations as an example to build a self-consistent algorithm by an angular distribution model (ADM), based solely on radiance observations, to estimate clear-sky spectrally resolved fluxes over tropical oceans. As the key step for such an ADM, scene type estimations are obtained from radiance and brightness temperature in selected AIRS channels. Then, broadband OLR as well as synthetic spectral fluxes are derived by the spectral ADM and validated using both synthetic spectra and CERES (Clouds and the Earth’s Radiant Energy System) observations. In most situations, the mean OLR differences between the spectral ADM products and the CERES observations are within ±2 W m-2, which is less than 1% of the typical mean clear-sky OLR over tropical oceans. The whole algorithm described in this study can be easily extended to other similar hyperspectral radiance measurements. Meteorology; Atmospheric Sciences; Geophysics/Geodesy; atmospheric infrared sounder; hyperspectral radiance; scene type; spectral angular distribution model
Stackhouse, P.; Kratz, D. P.; Wong, T.; Sawaengphokhai, P.; Wilber, A. C.; Gupta, SK; Loeb, N. G.Stackhouse, P., D. P. Kratz, T. Wong, P. Sawaengphokhai, A. C. Wilber, S. Gupta, N. G. Loeb, 2016: Earth radiation Budget at Top-of-Atmosphere [in “State of the Climate in 2015"]. Bull. Amer. Meteor. Soc., 97(8), S41-S43. doi: 10.1175/2016BAMSStateoftheClimate.1.
Stenz, Ronald; Dong, Xiquan; Xi, Baike; Feng, Zhe; Kuligowski, Robert J.Stenz, R., X. Dong, B. Xi, Z. Feng, R. J. Kuligowski, 2016: Improving Satellite Quantitative Precipitation Estimation Using GOES-Retrieved Cloud Optical Depth. J. Hydrometeor., 17(2), 557-570. doi: 10.1175/JHM-D-15-0057.1. To address gaps in ground-based radar coverage and rain gauge networks in the United States, geostationary satellite quantitative precipitation estimation (QPE) such as the Self-Calibrating Multivariate Precipitation Retrieval (SCaMPR) can be used to fill in both spatial and temporal gaps of ground-based measurements. Additionally, with the launch of Geostationary Operational Environmental Satellite R series (GOES-R), the temporal resolution of satellite QPEs may be comparable to Weather Surveillance Radar-1988 Doppler (WSR-88D) volume scans as GOES images will be available every 5 min. However, while satellite QPEs have strengths in spatial coverage and temporal resolution, they face limitations, particularly during convective events. Deep convective systems (DCSs) have large cloud shields with similar brightness temperatures (BTs) over nearly the entire system, but widely varying precipitation rates beneath these clouds. Geostationary satellite QPEs relying on the indirect relationship between BTs and precipitation rates often suffer from large errors because anvil regions (little or no precipitation) cannot be distinguished from rain cores (heavy precipitation) using only BTs. However, a combination of BTs and optical depth τ has been found to reduce overestimates of precipitation in anvil regions. A new rain mask algorithm incorporating both τ and BTs has been developed, and its application to the existing SCaMPR algorithm was evaluated. The performance of the modified SCaMPR was evaluated using traditional skill scores and a more detailed analysis of performance in individual DCS components by utilizing the Feng et al. classification algorithm. SCaMPR estimates with the new rain mask benefited from significantly reduced overestimates of precipitation in anvil regions and overall improvements in skill scores. Remote sensing; satellite observations; hydrology; Physical Meteorology and Climatology; Algorithms; Radars/Radar observations; Observational techniques and algorithms; Convective storms
Tang, Shuaiqi; Zhang, Minghua; Xie, ShaochengTang, S., M. Zhang, S. Xie, 2016: An ensemble constrained variational analysis of atmospheric forcing data and its application to evaluate clouds in CAM5. Journal of Geophysical Research: Atmospheres, 121(1), 33–48. doi: 10.1002/2015JD024167. Large-scale atmospheric forcing data can greatly impact the simulations of atmospheric process models (e.g., large eddy simulations, cloud-resolving models, and single column models (SCMs)) that are used to develop physical parameterizations in global climate models. This study introduces an ensemble variationally constrained objective analysis of atmospheric large-scale forcing data and its application to evaluate the cloud biases in the Community Atmospheric Model (CAM5). Sensitivities of the variational objective analysis to background data, error covariance matrix, and constraint variables are presented to quantify the uncertainties in the large-scale forcing data and state variables. Application of the ensemble forcing in the CAM5 SCM during March 2000 intensive operational period at the Southern Great Plains (SGP) of the Atmospheric Radiation Measurement Program shows that the systematic biases in the model simulations (i.e., excessive high clouds and insufficient low clouds) cannot be explained by the uncertainty of large-scale forcing data, which points to the deficiencies of physical parameterizations. These biases are found to also exist in the global simulation of CAM5 when it is compared with satellite data over the surrounding SGP site for annual and seasonal means. 3310 Clouds and cloud feedbacks; ensemble; 3275 Uncertainty quantification; 0520 Data analysis: algorithms and implementation; cloud retrievals; large-scale forcing data; model bias; variational analysis
Tian, Jingjing; Dong, Xiquan; Xi, Baike; Wang, Jingyu; Homeyer, Cameron R.; McFarquhar, Greg M.; Fan, JiwenTian, J., X. Dong, B. Xi, J. Wang, C. R. Homeyer, G. M. McFarquhar, J. Fan, 2016: Retrievals of Ice Cloud Microphysical Properties of Deep Convective Systems using Radar Measurements. Journal of Geophysical Research: Atmospheres, 121(18), 10,820–10,839. doi: 10.1002/2015JD024686. This study presents newly developed algorithms for retrieving ice cloud microphysical properties (ice water content (IWC) and median mass diameter (Dm)) for the stratiform rain and thick anvil regions of Deep Convective Systems (DCSs) using Next-Generation Radar (NEXRAD) reflectivity and empirical relationships from aircraft in situ measurements. A typical DCS case (20 May 2011) during the Midlatitude Continental Convective Clouds Experiment (MC3E) is selected as an example to demonstrate the 4-D retrievals. The vertical distributions of retrieved IWC are compared with previous studies and cloud-resolving model simulations. The statistics from six selected cases during MC3E show that the aircraft in situ derived IWC and Dm are 0.47 ± 0.29 g m-3 and 2.02 ± 1.3 mm, while the mean values of retrievals have a positive bias of 0.19 g m-3 (40%) and negative bias of 0.41 mm (20%), respectively. To evaluate the new retrieval algorithms, IWC and Dm are retrieved for other DCSs observed during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) using NEXRAD reflectivity and compared with aircraft in situ measurements. During BAMEX, a total of 63 1-min collocated aircraft and radar samples are available for comparisons, and the averages of radar retrieved and aircraft in situ measured IWC values are 1.52 g m-3 and 1.25 g m-3 with a correlation of 0.55, and their averaged Dm values are 2.08 and 1.77 mm. In general, the new retrieval algorithms are suitable for continental DCSs during BAMEX, especially within stratiform rain and thick anvil regions. Remote sensing; 0320 Cloud physics and chemistry; 0394 Instruments and techniques; 3314 Convective processes; ice particles; deep convection; 3360 Remote sensing; Radars/Radar observations; Cloud microphysics retrieval; in situ measurement
Trémas, Thierry L.; Aznay, Ouahid; Chomette, OlivierTrémas, T. L., O. Aznay, O. Chomette, 2016: ScaRaB and CERES-Terra: results of the inter-comparison campaigns. doi: 10.1117/12.2237591. ScaRaB (SCAnner for RAdiation Budget) is an Indo-French satellite onboard MEGHA-TROPIQUES launched on October 12th 2011. This radiometer has been designed to fill the gap between the ERBS and CERES missions to study the water cycle and energy exchanges in the tropics. ScaRaB is fit with four parallel and independent channels: channel- 2 and channel-3 being considered as the main ones, channel-1 is dedicated to measure solar radiance while channel-4 is an infrared window. The absolute calibration of ScaRaB is achieved by internal calibration sources (black bodies and a lamp for channel-1). The radiometric properties of deserts sites and more especially their stable spectral response over time made them very good candidates to perform temporal monitoring of ScaRaB channel-1. This paper deals with the corresponding results. High altitude clouds are observed by ScaRaB to survey the balance between channel 2 and channel 3: the earth longwave radiance is isolated by subtracting the short-wave channel to the total channel. Radiometric cross calibration of Earth observation sensors is a crucial need to guarantee or quantify the consistency of measurements from different sensors. CERES and ScaRaB Earth Radiation Budget missions have the same specification: to provide an accuracy of ~1% in the measurement of short-wave and long-wave radiances and an estimation of the short-wave and long-wave fluxes less than 10 W/m2. Taking advantage of the “equatorial” orbit of Megha-Tropiques, NASA proceeded to manoeuvers on CERES-Terra in order to ease an inter-comparison between both instruments over common targets. Actually, The CERES PAPS mode was used to align its swath scan in order to increase the collocated pixels between the two instruments. The experience lasted 3 months from March 22th and May 31st 2015. A previous similar campaign has already been led in 2012. This article presents the results of these inter-comparisons, providing an indication on the temporal stability of the calibration between 2012 and 2015.
Trenberth, Kevin E.; Fasullo, John T.; von Schuckmann, Karina; Cheng, LijingTrenberth, K. E., J. T. Fasullo, K. von Schuckmann, L. Cheng, 2016: Insights into Earth’s energy imbalance from multiple sources. J. Climate, 29(20), 7495–7505. doi: 10.1175/JCLI-D-16-0339.1. The current Earth’s energy imbalance (EEI) can best be estimated from changes in ocean heat content (OHC), complemented by top-of-atmosphere (TOA) radiation measurements and an assessment of the small non-ocean components. Sustained observations from the Argo array of autonomous profiling floats enable near-global estimates of OHC since 2005, which reveal considerable cancellation of variations in the upper 300 m. An analysis of the monthly contributions to EEI from non-ocean (land and ice) using the CESM Large Ensemble reveals standard deviations of 0.3 to 0.4 W m-2 (global); largest values occur in August, but values are below 0.75 W m-2 >95% of the time. Global standard deviations of EEI of 0.64 W m-2 based on top-of-atmosphere observations therefore substantially constrain ocean contributions, given by the tendencies of OHC. Instead, monthly standard deviations of many Argo-based OHC tendencies are 6 to 13 W m-2 and non-physical fluctuations are clearly evident. We show that an ocean reanalysis with multi-variate dynamical data assimilation features much better agreement with TOA radiation, and 44% of the vertically-integrated short-term OHC trend for 2005-14 of 0.8±0.2 W m-2 (globally) occurs below 700 m depth. Largest warming occurs from 20 to 50°S, especially over the Southern Oceans, and near 40°N, in all ocean analyses. The EEI is estimated to be 0.9±0.3 W m-2 for 2005-2014.
Tricht, K. Van; Lhermitte, S.; Lenaerts, J. T. M.; Gorodetskaya, I. V.; L’Ecuyer, T. S.; Noël, B.; Broeke, M. R. van den; Turner, D. D.; Lipzig, N. P. M. vanTricht, K. V., S. Lhermitte, J. T. M. Lenaerts, I. V. Gorodetskaya, T. S. L’Ecuyer, B. Noël, M. R. v. d. Broeke, D. D. Turner, N. P. M. v. Lipzig, 2016: Clouds enhance Greenland ice sheet meltwater runoff. Nature Communications, 7, 10266. doi: 10.1038/ncomms10266. Clouds play a pivotal role in the energy and mass balance of the Greenland ice sheet, thereby affecting its contribution to global sea-level rise. Here, using a combination of observations and model simulations, the authors show that clouds enhance Greenland ice sheet meltwater runoff by more than 30%.
Venugopal, T.; Rahaman, H.; Ravichandran, M.; Ramakrishna, S. S. V. S.Venugopal, T., H. Rahaman, M. Ravichandran, S. S. V. S. Ramakrishna, 2016: Evaluation of MODIS/CERES Downwelling Shortwave and Longwave Radiation over global tropical oceans. Remote Sensing of the Atmosphere, Clouds, and Precipitation Vi, 9876, UNSP 98761F. In the present work, we have evaluated the satellite estimated daily downwelling shortwave (Q(I)) and Longwave (Q(A)) radiation from Moderate Resolution Imaging Spectrometer (MODIS) / Clouds and the Earth's Radiant Energy System (CM) with moored buoy observations of Global Tropical Moored Buoy Array (GTMBA) during 2001-2009. The global observed mean of Q(I) and Q(A) in GTMBA (CM) are 228 (233) W/m(2) and 410 (405) W/m(2) respectively. The mean Q(I) shows a positive bias (similar to 3-7 W/m(2)) whereas Q(A) underestimates with a mean negative bias of similar to 3-6 W/m(2) in the tropical Pacific, Atlantic and Indian Ocean. CM underestimates the buoy observed variability in both Q(I) and Q(A) in all the tropical oceans. The correlation coefficient (CC) values in Q(I) (Qa) are 0.79(0.88) 0.79(0.84) and 0.81(0.94) over the Pacific, Atlantic and Indian ocean respectively. The Root Mean Square Error (RMSE) values in Q(I) ranged between 35-43 W/m(2) with lowest values in the Atlantic Ocean and highest in the Indian Ocean. The RMSE values in Q(A) are less as compared to Q(I) and it is similar to 9 W/m(2) in all the tropical ocean. The spatial distributions of Q(I) and Q(A) shows seasonality with lower and higher values coinciding with the Inter Tropical Convergence Zone(ITCZ) locations in the Q(I) and Q(A). air-sea interaction; budget experiment; CERES; circulation; flux; indian-ocean; Pacific; temperature; validation; Variability
Verma, Manish; Fisher, Joshua B.; Mallick, Kaniska; Ryu, Youngryel; Kobayashi, Hideki; Guillaume, Alexandre; Moore, Gregory; Ramakrishnan, Lavanya; Hendrix, Valerie; Wolf, Sebastian; Sikka, Munish; Kiely, Gerard; Wohlfahrt, Georg; Gielen, Bert; Roupsard, Olivier; Toscano, Piero; Arain, Altaf; Cescatti, AlessandroVerma, M., J. B. Fisher, K. Mallick, Y. Ryu, H. Kobayashi, A. Guillaume, G. Moore, L. Ramakrishnan, V. Hendrix, S. Wolf, M. Sikka, G. Kiely, G. Wohlfahrt, B. Gielen, O. Roupsard, P. Toscano, A. Arain, A. Cescatti, 2016: Global Surface Net-Radiation at 5 km from MODIS Terra. Remote Sensing, 8(9), 739. doi: 10.3390/rs8090739. Reliable and fine resolution estimates of surface net-radiation are required for estimating latent and sensible heat fluxes between the land surface and the atmosphere. However, currently, fine resolution estimates of net-radiation are not available and consequently it is challenging to develop multi-year estimates of evapotranspiration at scales that can capture land surface heterogeneity and are relevant for policy and decision-making. We developed and evaluated a global net-radiation product at 5 km and 8-day resolution by combining mutually consistent atmosphere and land data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board Terra. Comparison with net-radiation measurements from 154 globally distributed sites (414 site-years) from the FLUXNET and Surface Radiation budget network (SURFRAD) showed that the net-radiation product agreed well with measurements across seasons and climate types in the extratropics (Wilmott’s index ranged from 0.74 for boreal to 0.63 for Mediterranean sites). Mean absolute deviation between the MODIS and measured net-radiation ranged from 38.0 ± 1.8 W∙m−2 in boreal to 72.0 ± 4.1 W∙m−2 in the tropical climates. The mean bias was small and constituted only 11%, 0.7%, 8.4%, 4.2%, 13.3%, and 5.4% of the mean absolute error in daytime net-radiation in boreal, Mediterranean, temperate-continental, temperate, semi-arid, and tropical climate, respectively. To assess the accuracy of the broader spatiotemporal patterns, we upscaled error-quantified MODIS net-radiation and compared it with the net-radiation estimates from the coarse spatial (1° × 1°) but high temporal resolution gridded net-radiation product from the Clouds and Earth’s Radiant Energy System (CERES). Our estimates agreed closely with the net-radiation estimates from the CERES. Difference between the two was less than 10 W·m−2 in 94% of the total land area. MODIS net-radiation product will be a valuable resource for the science community studying turbulent fluxes and energy budget at the Earth’s surface. modeling; MODIS; validation; FLUXNET; SURFRAD; surface net-radiation
Voigt, Aiko; Biasutti, Michela; Scheff, Jacob; Bader, Jürgen; Bordoni, Simona; Codron, Francis; Dixon, Ross D.; Jonas, Jeffrey; Kang, Sarah M.; Klingaman, Nicholas P.; Leung, Ruby; Lu, Jian; Mapes, Brian; Maroon, Elizabeth A.; McDermid, Sonali; Park, Jong-yeon; Roehrig, Romain; Rose, Brian E. J.; Russell, Gary L.; Seo, Jeongbin; Toniazzo, Thomas; Wei, Ho-Hsuan; Yoshimori, Masakazu; Vargas Zeppetello, Lucas R.Voigt, A., M. Biasutti, J. Scheff, J. Bader, S. Bordoni, F. Codron, R. D. Dixon, J. Jonas, S. M. Kang, N. P. Klingaman, R. Leung, J. Lu, B. Mapes, E. A. Maroon, S. McDermid, J. Park, R. Roehrig, B. E. J. Rose, G. L. Russell, J. Seo, T. Toniazzo, H. Wei, M. Yoshimori, L. R. Vargas Zeppetello, 2016: The tropical rain belts with an annual cycle and a continent model intercomparison project: TRACMIP. Journal of Advances in Modeling Earth Systems, 8(4), 1868–1891. doi: 10.1002/2016MS000748. This paper introduces the Tropical Rain belts with an Annual cycle and a Continent Model Intercomparison Project (TRACMIP). TRACMIP studies the dynamics of tropical rain belts and their response to past and future radiative forcings through simulations with 13 comprehensive and one simplified atmosphere models coupled to a slab ocean and driven by seasonally varying insolation. Five idealized experiments, two with an aquaplanet setup and three with a setup with an idealized tropical continent, fill the space between prescribed-SST aquaplanet simulations and realistic simulations provided by CMIP5/6. The simulations reproduce key features of present-day climate and expected future climate change, including an annual-mean intertropical convergence zone (ITCZ) that is located north of the equator and Hadley cells and eddy-driven jets that are similar to present-day climate. Quadrupling CO2 leads to a northward ITCZ shift and preferential warming in Northern high latitudes. The simulations show interesting CO2-induced changes in the seasonal excursion of the ITCZ and indicate a possible state dependence of climate sensitivity. The inclusion of an idealized continent modulates both the control climate and the response to increased CO2; for example, it reduces the northward ITCZ shift associated with warming and, in some models, climate sensitivity. In response to eccentricity-driven seasonal insolation changes, seasonal changes in oceanic rainfall are best characterized as a meridional dipole, while seasonal continental rainfall changes tend to be symmetric about the equator. This survey illustrates TRACMIP's potential to engender a deeper understanding of global and regional climate and to address questions on past and future climate change. ITCZ; monsoon; 1626 Global climate models; model hierarchy; 3373 Tropical dynamics; 0429 Climate dynamics; model intercomparison project; rain belts
von Schuckmann, K.; Palmer, M. D.; Trenberth, K. E.; Cazenave, A.; Chambers, D.; Champollion, N.; Hansen, J.; Josey, S. A.; Loeb, N.; Mathieu, P.-P.; Meyssignac, B.; Wild, M.von Schuckmann, K., M. D. Palmer, K. E. Trenberth, A. Cazenave, D. Chambers, N. Champollion, J. Hansen, S. A. Josey, N. Loeb, P. Mathieu, B. Meyssignac, M. Wild, 2016: An imperative to monitor Earth's energy imbalance. Nature Climate Change, 6(2), 138-144. doi: 10.1038/nclimate2876. The current Earth's energy imbalance (EEI) is mostly caused by human activity, and is driving global warming. The absolute value of EEI represents the most fundamental metric defining the status of global climate change, and will be more useful than using global surface temperature. EEI can best be estimated from changes in ocean heat content, complemented by radiation measurements from space. Sustained observations from the Argo array of autonomous profiling floats and further development of the ocean observing system to sample the deep ocean, marginal seas and sea ice regions are crucial to refining future estimates of EEI. Combining multiple measurements in an optimal way holds considerable promise for estimating EEI and thus assessing the status of global climate change, improving climate syntheses and models, and testing the effectiveness of mitigation actions. Progress can be achieved with a concerted international effort. climate change; Research data
Wang, Dongdong; Liang, ShunlinWang, D., S. Liang, 2016: Estimating high-resolution top of atmosphere albedo from Moderate Resolution Imaging Spectroradiometer data. Remote Sensing of Environment, 178, 93-103. doi: 10.1016/j.rse.2016.03.008. High spatial resolution top-of-atmosphere (TOA) albedo data is needed to study the radiative forcing of natural or anthropogenic events at regional scales. However, existing products are typically estimated using broadband sensors with coarse spatial resolutions. This paper presents a hybrid method to retrieve TOA albedo over land from multispectral data collected by Moderate Resolution Imaging Spectroradiometer (MODIS) at its native spatial resolution. The approach is based on extensive atmospheric radiative transfer (RT) simulations using representative surface and atmospheric conditions as inputs. The clear-sky algorithm explicitly takes surface reflectance anisotropy into account using the POLDER3/PARASOL bidirectional reflectance distribution function database as the boundary condition of RT simulations to first generate TOA spectral albedos and then convert them to broadband albedo. In the cloudy-sky method, surfaces are assumed to be Lambertian and surface spectra over the shortwave spectrum are used to directly obtain TOA broadband albedo. The TOA albedo retrieved from MODIS was compared with the Clouds and the Earth's Radiant Energy System (CERES) TOA flux products, using twelve days of global data (one day each month) in 2007. The two data sets are in good agreement, with a root mean square difference (RMSD) of 0.036 (8.6%) for all Terra instantaneous data and 0.039 (9.1%) for all Aqua instantaneous data. Further analysis revealed that larger discrepancies mainly occurred at pixels of large solar or view zenith angles. RMSD between the two data sets was reduced to ~ 0.02 when the solar zenith angles were limited to 60° and the view zenith angles were limited to 30°. CERES; radiative flux; MODIS; radiation budget; planetary albedo; TOA albedo
Wang, Fan; Li, Yuanlong; Wang, JianingWang, F., Y. Li, J. Wang, 2016: Intraseasonal Variability of the Surface Zonal Currents in the Western Tropical Pacific Ocean: Characteristics and Mechanisms. J. Phys. Oceanogr., 46(12), 3639-3660. doi: 10.1175/JPO-D-16-0033.1. The surface circulation of the tropical Pacific Ocean is characterized by alternating zonal currents, such as the North Equatorial Current (NEC), North Equatorial Countercurrent (NECC), South Equatorial Current (SEC), and South Equatorial Countercurrent (SECC). In situ measurements of subsurface moorings and satellite observations reveal pronounced intraseasonal variability (ISV; 20–90 days) of these zonal currents in the western tropical Pacific Ocean (WTPO). The amplitude of ISV is the largest within the equatorial band exceeding 20 cm s−1 and decreases to ~10 cm s−1 in the NECC band and further to 4–8 cm s−1 in the NEC and SECC. The ISV power generally increases from high frequencies to low frequencies and exhibits a peak at 50–60 days in the NECC, SEC, and SECC. These variations are faithfully reproduced by an ocean general circulation model (OGCM) forced by satellite winds, and parallel model experiments are performed to gain insights into the underlying mechanisms. It is found that large-scale ISV (>500 km) is primarily caused by atmospheric intraseasonal oscillations (ISOs), such as the Madden–Julian oscillation (MJO), through wind stress forcing. These signals are confined within 10°S–8°N, mainly as baroclinic ocean wave responses to ISO winds. For scales shorter than 200 km, ISV is dominated by ocean internal variabilities with mesoscale structures. They arise from the baroclinic and barotropic instabilities associated with the vertical and horizontal shears of the upper-ocean circulation. The ISV exhibits evident seasonal variation, with larger (smaller) amplitude in boreal winter (summer) in the SEC and SECC.
Wang, Shuguang; Sobel, Adam H.; Nie, JiWang, S., A. H. Sobel, J. Nie, 2016: Modeling the MJO in a cloud-resolving model with parameterized large-scale dynamics: Vertical structure, radiation, and horizontal advection of dry air. Journal of Advances in Modeling Earth Systems, 8(1), 121–139. doi: 10.1002/2015MS000529. Two Madden-Julian Oscillation (MJO) events, observed during October and November 2011 in the equatorial Indian Ocean during the DYNAMO field campaign, are simulated in a limited-area cloud-resolving model using parameterized large-scale dynamics. Three parameterizations of large-scale dynamics—the conventional weak temperature gradient (WTG) approximation, vertical mode-based spectral WTG (SWTG), and damped gravity wave coupling (DGW)—are employed. A number of changes to the implementation of the large-scale parameterizations, as well as the model itself, are made and lead to improvements in the results. Simulations using all three methods, with imposed time-dependent radiation and horizontal moisture advection, capture the time variations in precipitation associated with the two MJO events well. The three methods produce significant differences in the large-scale vertical motion profile, however. WTG produces the most top-heavy profile, while DGW's is less so, and SWTG produces a profile between the two, and in better agreement with observations. Numerical experiments without horizontal advection of moisture suggest that that process significantly reduces the precipitation and suppresses the top-heaviness of large-scale vertical motion during the MJO active phases. Experiments in which a temporally constant radiative heating profile is used indicate that radiative feedbacks significantly amplify the MJO. Experiments in which interactive radiation is used produce agreement with observations that is much better than that achieved in previous work, though not as good as that with imposed time-varying radiative heating. Our results highlight the importance of both horizontal advection of moisture and radiative feedbacks to the dynamics of the MJO. 3374 Tropical meteorology; 3310 Clouds and cloud feedbacks; 3314 Convective processes; Madden-Julian Oscillation; 3355 Regional modeling; 3373 Tropical dynamics; CINDY/DYNAMO; cloud and radiation; cloud-resolving modeling; horizontal advection of moisture; weak temperature gradient
Wang, W.; Zender, C. S.; van As, D.; Smeets, P. C. J. P.; van den Broeke, M. R.Wang, W., C. S. Zender, D. van As, P. C. J. P. Smeets, M. R. van den Broeke, 2016: A Retrospective, Iterative, Geometry-Based (RIGB) tilt-correction method for radiation observed by automatic weather stations on snow-covered surfaces: application to Greenland. The Cryosphere, 10(2), 727-741. doi: 10.5194/tc-10-727-2016.
Wang, Yong; Zhang, Guang J.Wang, Y., G. J. Zhang, 2016: Global climate impacts of stochastic deep convection parameterization in the NCARCAM5. Journal of Advances in Modeling Earth Systems, 8(4), 1641–1656. doi: 10.1002/2016MS000756. In this study, the stochastic deep convection parameterization of Plant and Craig (PC) is implemented in the Community Atmospheric Model version 5 (CAM5) to incorporate the stochastic processes of convection into the Zhang-McFarlane (ZM) deterministic deep convective scheme. Its impacts on deep convection, shallow convection, large-scale precipitation and associated dynamic and thermodynamic fields are investigated. Results show that with the introduction of the PC stochastic parameterization, deep convection is decreased while shallow convection is enhanced. The decrease in deep convection is mainly caused by the stochastic process and the spatial averaging of input quantities for the PC scheme. More detrained liquid water associated with more shallow convection leads to significant increase in liquid water and ice water paths, which increases large-scale precipitation in tropical regions. Specific humidity, relative humidity, zonal wind in the tropics, and precipitable water are all improved. The simulation of shortwave cloud forcing (SWCF) is also improved. The PC stochastic parameterization decreases the global mean SWCF from −52.25 W/m2 in the standard CAM5 to −48.86 W/m2, close to −47.16 W/m2 in observations. The improvement in SWCF over the tropics is due to decreased low cloud fraction simulated by the stochastic scheme. Sensitivity tests of tuning parameters are also performed to investigate the sensitivity of simulated climatology to uncertain parameters in the stochastic deep convection scheme. convection; 3309 Climatology; 3337 Global climate models; 3314 Convective processes; 3365 Subgrid-scale (SGS) parameterization; CAM5; global climate impacts; stochastic parameterization
Wild, MartinWild, M., 2016: Decadal changes in radiative fluxes at land and ocean surfaces and their relevance for global warming. Wiley Interdisciplinary Reviews: Climate Change, 7(1), 91-107. doi: 10.1002/wcc.372. Anthropogenic interference with climate occurs primarily through modification of radiative fluxes in the climate system. Increasing releases of greenhouse gases into the atmosphere lead to an enhancement of thermal radiation from the atmosphere to the surface by presently about 2 W m−2 per decade, thereby causing global warming. Yet not only thermal radiation undergoes substantial decadal changes at the Earth surface, but also incident solar radiation (SSR), often in line with changes in aerosol emissions. Land-based observations suggest widespread declines in SSR from 1950s to 1980s (‘global dimming’), a partial recovery (‘brightening’) since mid-1980s, and indication for an ‘early’ brightening in 1930s and 1940s. No similar extended observational records are available over oceans. However, modeling studies, conceptual frameworks and available satellite-derived records point to the existence of decadal SSR variations also over oceans. SSR changes overall match with decadal variations in observed warming rates, suggesting that SSR variations may effectively modulate greenhouse gas-induced warming. Specifically, on the Northern Hemisphere, the lack of warming from 1950s to 1980s and its subsequent acceleration in the 1990s fits to the trend reversal from dimming to brightening and associated changes in air pollution levels. From the 1950s to 1980s no warming was also observed over Northern Hemispheric Oceans, in line with conceptual ideas that subtle aerosol changes in pristine ocean areas, effectively amplified by aerosol–cloud interactions, can substantially alter SSR, thereby modulating Sea Surface Temperatures. On the Southern Hemisphere, the absence of significant aerosol levels fits to the observed stable (greenhouse gas-induced) warming rates since the 1950s. WIREs Clim Change 2016, 7:91–107. doi: 10.1002/wcc.372 For further resources related to this article, please visit the WIREs website.
Xiao, Zhixiang; Duan, AnminXiao, Z., A. Duan, 2016: Impacts of Tibetan Plateau snow cover on the interannual variability of the East Asian summer monsoon. J. Climate, 29(23), 8495–8514. doi: 10.1175/JCLI-D-16-0029.1. The relationship between Tibetan Plateau (TP) snow cover and the East Asian summer monsoon (EASM) has long been discussed, but the underlying mechanism remains controversial. In this paper, the snow-albedo and snow-hydrology feedbacks over the TP are investigated based on multiple sources of snow data for the period 1979–2011. The results indicate that winter snow cover plays an important role in cooling local air temperature through the snow-albedo effect; the TP surface net solar radiation in years with above-normal snow cover is approximately 18 W m−2 less than that in below-normal snow cover years. However, data analysis demonstrates that persistent effects of winter snow cover are limited to the period from winter to spring over most parts of the central and eastern TP. Therefore, the preceding snow cover over the central and eastern TP exerts little influence over either the in situ summer atmospheric heat source or the EASM, due to its limited persistence. In contrast, the effects of winter or spring snow cover anomalies over the western TP and the Himalaya can last until summer, and these anomalies further influence the EASM by modulating moisture transport to eastern China and favoring eastward-propagating synoptic disturbances that are generated over the TP. Generally, above-normal snow cover over the western TP and the Himalaya facilitates abundant summer precipitation between the Yangtze and Yellow river basins, which is confirmed by results from a regional Weather Research and Forecasting model simulation.
Xie, Shang-Ping; Kosaka, Yu; Okumura, Yuko M.Xie, S., Y. Kosaka, Y. M. Okumura, 2016: Distinct energy budgets for anthropogenic and natural changes during global warming hiatus. Nature Geoscience, 9(1), 29-33. doi: 10.1038/ngeo2581. The Earth’s energy budget for the past four decades can now be closed, and it supports anthropogenic greenhouse forcing as the cause for climate warming. However, closure depends on invoking an unrealistically large increase in aerosol cooling during the so-called global warming hiatus since the late 1990s (refs 3,4) that was due partly to tropical Pacific Ocean cooling. The difficulty with this closure lies in the assumption that the same climate feedback applies to both anthropogenic warming and natural cooling. Here we analyse climate model simulations with and without anthropogenic increases in greenhouse gas concentrations, and show that top-of-the-atmosphere radiation and global mean surface temperature are much less tightly coupled for natural decadal variability than for the greenhouse-gas-induced response, implying distinct climate feedback between anthropogenic warming and natural variability. In addition, we identify a phase difference between top-of-the-atmosphere radiation and global mean surface temperature such that ocean heat uptake tends to slow down during the surface warming hiatus. This result deviates from existing energy theory but we find that it is broadly consistent with observations. Our study highlights the importance of developing metrics that distinguish anthropogenic change from natural variations to attribute climate variability and to estimate climate sensitivity from observations. climate change; Atmospheric dynamics; Physical oceanography
Xu, Kuan-Man; Cheng, AnningXu, K., A. Cheng, 2016: Understanding the tropical cloud feedback from an analysis of the circulation and stability regimes simulated from an upgraded multiscale modeling framework. Journal of Advances in Modeling Earth Systems, 8(4), 1825–1846. doi: 10.1002/2016MS000767. As revealed from studies using conventional general circulation models (GCMs), the thermodynamic contribution to the tropical cloud feedback dominates the dynamic contribution, but these models have difficulty in simulating the subsidence regimes in the tropics. In this study, we analyze the tropical cloud feedback from a 2 K sea surface temperature (SST) perturbation experiment performed with a multiscale modeling framework (MMF). The MMF explicitly represents cloud processes using 2-D cloud-resolving models with an advanced higher-order turbulence closure in each atmospheric column of the host GCM. We sort the monthly mean cloud properties and cloud radiative effects according to circulation and stability regimes. We find that the regime-sorted dynamic changes dominate the thermodynamic changes in terms of the absolute magnitude. The dynamic changes in the weak subsidence regimes exhibit strong negative cloud feedback due to increases in shallow cumulus and deep clouds while those in strongly convective and moderate-to-strong subsidence regimes have opposite signs, resulting in a small contribution to cloud feedback. On the other hand, the thermodynamic changes are large due to decreases in stratocumulus clouds in the moderate-to-strong subsidence regimes with small opposite changes in the weak subsidence and strongly convective regimes, resulting in a relatively large contribution to positive cloud feedback. The dynamic and thermodynamic changes contribute equally to positive cloud feedback and are relatively insensitive to stability in the moderate-to-strong subsidence regimes. But they are sensitive to stability changes from the SST increase in convective and weak subsidence regimes. These results have implications for interpreting cloud feedback mechanisms. 0321 Cloud/radiation interaction; 3337 Global climate models; 3310 Clouds and cloud feedbacks; cloud feedback; 3307 Boundary layer processes; low clouds; 3365 Subgrid-scale (SGS) parameterization; MMF; dynamical component; thermodynamic component; tropical stability
Xu, Kuan-Man; Wong, Takmeng; Dong, Shengtao; Chen, Feng; Kato, Seiji; Taylor, Patrick C.Xu, K., T. Wong, S. Dong, F. Chen, S. Kato, P. C. Taylor, 2016: Cloud Object Analysis of CERES Aqua Observations of Tropical and Subtropical Cloud Regimes: Four-Year Climatology. J. Climate, 29(5), 1617-1638. doi: 10.1175/JCLI-D-14-00836.1. Four distinct types of cloud objects—tropical deep convection, boundary layer cumulus, stratocumulus, and overcast stratus—were previously identified from CERES Tropical Rainfall Measuring Mission (TRMM) data. Six additional types of cloud objects—cirrus, cirrocumulus, cirrostratus, altocumulus, transitional altocumulus, and solid altocumulus—are identified from CERES Aqua satellite data in this study. The selection criteria for the 10 cloud object types are based on CERES footprint cloud fraction and cloud-top pressure, as well as cloud optical depth for the high-cloud types. The cloud object is a contiguous region of the earth with a single dominant cloud-system type. The data are analyzed according to cloud object types, sizes, regions, and associated environmental conditions. The frequency of occurrence and probability density functions (PDFs) of selected physical properties are produced for the July 2006–June 2010 period. It is found that deep convective and boundary layer types dominate the total population while the six new types other than cirrostratus do not contribute much in the tropics and subtropics. There are pronounced differences in the size spectrum between the types, with the largest ones being of deep convective type and with stratocumulus and overcast types over the ocean basins off west coasts. The summary PDFs of radiative and cloud physical properties differ greatly among the size categories. For boundary layer cloud types, the differences come primarily from the locations of cloud objects: for example, coasts versus open oceans. They can be explained by considerable variations in large-scale environmental conditions with cloud object size, which will be further qualified in future studies.
Xu, Li; Cameron-Smith, Philip; Russell, Lynn M.; Ghan, Steven J.; Liu, Ying; Elliott, Scott; Yang, Yang; Lou, Sijia; Lamjiri, Maryam A.; Manizza, ManfrediXu, L., P. Cameron-Smith, L. M. Russell, S. J. Ghan, Y. Liu, S. Elliott, Y. Yang, S. Lou, M. A. Lamjiri, M. Manizza, 2016: DMS role in the ENSO cycle in the Tropics. Journal of Geophysical Research: Atmospheres, 121(22), 13,537–13,558. doi: 10.1002/2016JD025333. We examined the multi-year mean and variability of dimethyl sulfide (DMS) and its relationship to sulfate aerosols, as well as cloud microphysical and radiative properties. We conducted a 150-year simulation using pre-industrial conditions produced by the Community Earth System Model embedded with a dynamic DMS module. The model simulated the mean spatial distribution of DMS emissions and burden, as well as sulfur budgets associated with DMS, SO2, H2SO4, and sulfate that were generally similar to available observations and inventories for a variety of regions. Changes in simulated sea-to-air DMS emissions and associated atmospheric abundance, along with associated aerosols and cloud and radiative properties, were consistently dominated by the El Niño-Southern Oscillation (ENSO) cycle in the tropical Pacific region. Simulated DMS, aerosols, and clouds showed a weak positive feedback on sea surface temperature. This feedback suggests a link among DMS, aerosols, clouds, and climate on interannual timescales. The variability of DMS emissions associated with ENSO was primarily caused by a higher variation in wind speed during La Niña events. The simulation results also suggest that variations in DMS emissions increase the frequency of La Niña events but do not alter the ENSO variability in terms of the standard deviation of Niño 3 SST anomalies. 0305 Aerosols and particles; cloud; ENSO; 4215 Climate and interannual variability; DMS; sulfate aerosol
Xu, Li; Russell, Lynn M.; Burrows, Susannah M.Xu, L., L. M. Russell, S. M. Burrows, 2016: Potential sea salt aerosol sources from frost flowers in the pan-Arctic region. Journal of Geophysical Research: Atmospheres, 121(18), 10,840–10,856. doi: 10.1002/2015JD024713. In order to better represent observed wintertime aerosol mass and number concentrations in the pan-Arctic (60°N–90°N) region, we implemented an observationally based parameterization for estimating sea salt production from frost flowers in the Community Earth System Model (CESM, version 1.2.1). In this work, we evaluate the potential influence of this sea salt source on the pan-Arctic climate. Results show that frost flower salt emissions increase the modeled surface sea salt aerosol mass concentration by roughly 200% at Barrow and 100% at Alert and accumulation-mode number concentration by about a factor of 2 at Barrow and more than a factor of 10 at Alert in the winter months when new sea ice and frost flowers are present. The magnitude of sea salt aerosol mass and number concentrations at the surface in Barrow during winter simulated by the model configuration that includes this parameterization agrees better with observations by 48% and 12%, respectively, than the standard CESM simulation without a frost flower salt particle source. At Alert, the simulation with this parameterization overestimates observed sea salt aerosol mass concentration by 150% during winter in contrast to the underestimation of 63% in the simulation without this frost flower source, while it produces particle number concentration about 14% closer to observation than the standard CESM simulation. However, because the CESM version used here underestimates transported sulfate in winter, the reference accumulation-mode number concentrations at Alert are also underestimated. Adding these frost flower salt particle emissions increases sea salt aerosol optical depth by 10% in the pan-Arctic region and results in a small cooling at the surface. The increase in salt aerosol mass concentrations of a factor of 8 provides nearly two times the cloud condensation nuclei concentration at supersaturation of 0.1%, as well as 10% increases in cloud droplet number and 40% increases in liquid water content near coastal regions adjacent to continents. These cloud changes reduce longwave cloud forcing at the top of the atmosphere by 3% and cause a small surface warming, increasing the downward longwave flux at the surface by 1.8 W m−2 in the pan-Arctic under the present-day climate. This regional average longwave warming due to the presence of clouds attributed to frost flower sea salts is roughly half of previous observed surface longwave fluxes and cloud-forcing estimates reported in Alaska, implying that the longwave enhancement due to frost flower salts may be comparable to those estimated for anthropogenic aerosol emissions. Since the potential frost flower area is parameterized as the maximum possible region on which frost flowers grow for the modeled atmospheric temperature and sea ice conditions and the model underestimates the number of accumulation-mode particles from midlatitude anthropogenic sources transported in winter, the calculated aerosol indirect effect of frost flower sea salts in this work can be regarded an upper bound. 0305 Aerosols and particles; 0321 Cloud/radiation interaction; Arctic; Longwave cloud radiative forcing; frost flower; sea salt aerosol
Yahya, K.; Wang, K.; Campbell, P.; Glotfelty, T.; He, J.; Zhang, Y.Yahya, K., K. Wang, P. Campbell, T. Glotfelty, J. He, Y. Zhang, 2016: Decadal evaluation of regional climate, air quality, and their interactions over the continental US and their interactions using WRF/Chem version 3.6.1. Geosci. Model Dev., 9(2), 671-695. doi: 10.5194/gmd-9-671-2016. The Weather Research and Forecasting model with Chemistry (WRF/Chem) v3.6.1 with the Carbon Bond 2005 (CB05) gas-phase mechanism is evaluated for its first decadal application during 2001–2010 using the Representative Concentration Pathway 8.5 (RCP 8.5) emissions to assess its capability and appropriateness for long-term climatological simulations. The initial and boundary conditions are downscaled from the modified Community Earth System Model/Community Atmosphere Model (CESM/CAM5) v1.2.2. The meteorological initial and boundary conditions are bias-corrected using the National Center for Environmental Protection's Final (FNL) Operational Global Analysis data. Climatological evaluations are carried out for meteorological, chemical, and aerosol–cloud–radiation variables against data from surface networks and satellite retrievals. The model performs very well for the 2 m temperature (T2) for the 10-year period, with only a small cold bias of −0.3 °C. Biases in other meteorological variables including relative humidity at 2 m, wind speed at 10 m, and precipitation tend to be site- and season-specific; however, with the exception of T2, consistent annual biases exist for most of the years from 2001 to 2010. Ozone mixing ratios are slightly overpredicted at both urban and rural locations with a normalized mean bias (NMB) of 9.7 % but underpredicted at rural locations with an NMB of −8.8 %. PM2.5 concentrations are moderately overpredicted with an NMB of 23.3 % at rural sites but slightly underpredicted with an NMB of −10.8 % at urban/suburban sites. In general, the model performs relatively well for chemical and meteorological variables, and not as well for aerosol–cloud–radiation variables. Cloud-aerosol variables including aerosol optical depth, cloud water path, cloud optical thickness, and cloud droplet number concentration are generally underpredicted on average across the continental US. Overpredictions of several cloud variables over the eastern US result in underpredictions of radiation variables (such as net shortwave radiation – GSW – with a mean bias – MB – of −5.7 W m−2) and overpredictions of shortwave and longwave cloud forcing (MBs of ∼ 7 to 8 W m−2), which are important climate variables. While the current performance is deemed to be acceptable, improvements to the bias-correction method for CESM downscaling and the model parameterizations of cloud dynamics and thermodynamics, as well as aerosol–cloud interactions, can potentially improve model performance for long-term climate simulations.
Yang, Yang; Russell, Lynn M.; Xu, Li; Lou, Sijia; Lamjiri, Maryam A.; Somerville, Richard C. J.; Miller, Arthur J.; Cayan, Daniel R.; DeFlorio, Michael J.; Ghan, Steven J.; Liu, Ying; Singh, Balwinder; Wang, Hailong; Yoon, Jin-Ho; Rasch, Philip J.Yang, Y., L. M. Russell, L. Xu, S. Lou, M. A. Lamjiri, R. C. J. Somerville, A. J. Miller, D. R. Cayan, M. J. DeFlorio, S. J. Ghan, Y. Liu, B. Singh, H. Wang, J. Yoon, P. J. Rasch, 2016: Impacts of ENSO events on cloud radiative effects in preindustrial conditions: Changes in cloud fraction and their dependence on interactive aerosol emissions and concentrations. Journal of Geophysical Research: Atmospheres, 121(11), 6321–6335. doi: 10.1002/2015JD024503. We use three 150 year preindustrial simulations of the Community Earth System Model to quantify the impacts of El Niño–Southern Oscillation (ENSO) events on shortwave and longwave cloud radiative effects (CRESW and CRELW). Compared to recent observations from the Clouds and the Earth's Radiant Energy System data set, the model simulation successfully reproduces larger variations of CRESW and CRELW over the tropics. The ENSO cycle is found to dominate interannual variations of cloud radiative effects. Simulated cooling (warming) effects from CRESW (CRELW) are strongest over the tropical western and central Pacific Ocean during warm ENSO events, with the largest difference between 20 and 60 W m−2, with weaker effects of 10–40 W m−2 over Indonesian regions and the subtropical Pacific Ocean. Sensitivity tests show that variations of cloud radiative effects are mainly driven by ENSO-related changes in cloud fraction. The variations in midlevel and high cloud fractions each account for approximately 20–50% of the interannual variations of CRESW over the tropics and almost all of the variations of CRELW between 60°S and 60°N. The variation of low cloud fraction contributes to most of the variations of CRESW over the midlatitude oceans. Variations in natural aerosol concentrations explained 10–30% of the variations of both CRESW and CRELW over the tropical Pacific, Indonesian regions, and the tropical Indian Ocean. Changes in natural aerosol emissions and concentrations enhance 3–5% and 1–3% of the variations of cloud radiative effects averaged over the tropics. 0305 Aerosols and particles; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; aerosol; 3310 Clouds and cloud feedbacks; 0368 Troposphere: constituent transport and chemistry; Cloud radiative effects; ENSO
Yue, Qing; Kahn, Brian H.; Fetzer, Eric J.; Schreier, Mathias; Wong, Sun; Chen, Xiuhong; Huang, XiangleiYue, Q., B. H. Kahn, E. J. Fetzer, M. Schreier, S. Wong, X. Chen, X. Huang, 2016: Observation-Based Longwave Cloud Radiative Kernels Derived from the A-Train. J. Climate, 29(6), 2023-2040. doi: 10.1175/JCLI-D-15-0257.1. The authors present a new method to derive both the broadband and spectral longwave observation-based cloud radiative kernels (CRKs) using cloud radiative forcing (CRF) and cloud fraction (CF) for different cloud types using multisensor A-Train observations and MERRA data collocated on the pixel scale. Both observation-based CRKs and model-based CRKs derived from the Fu–Liou radiative transfer model are shown. Good agreement between observation- and model-derived CRKs is found for optically thick clouds. For optically thin clouds, the observation-based CRKs show a larger radiative sensitivity at TOA to cloud-cover change than model-derived CRKs. Four types of possible uncertainties in the observed CRKs are investigated: 1) uncertainties in Moderate Resolution Imaging Spectroradiometer cloud properties, 2) the contributions of clear-sky changes to the CRF, 3) the assumptions regarding clear-sky thresholds in the observations, and 4) the assumption of a single-layer cloud. The observation-based CRKs show the TOA radiative sensitivity of cloud types to unit cloud fraction change as observed by the A-Train. Therefore, a combination of observation-based CRKs with cloud changes observed by these instruments over time will provide an estimate of the short-term cloud feedback by maintaining consistency between CRKs and cloud responses to climate variability.
Zhan, Yizhe; Davies, RogerZhan, Y., R. Davies, 2016: Intercalibration of CERES, MODIS, and MISR reflected solar radiation and its application to albedo trends. Journal of Geophysical Research: Atmospheres, 121(11), 6273–6283. doi: 10.1002/2016JD025073. Measurements on the Terra satellite by the Cloud and the Earth's Radiant Energy System (CERES), the Moderate Resolution Imaging Spectroradiometer (MODIS), and the Multiangle Imaging Spectroradiometer (MISR), between 2001 and 2015 over the polar regions, are analyzed in order to investigate the intercalibration differences between these instruments. Direct comparisons of colocated near-nadir radiances from CERES, MODIS, and MISR show relative agreement within 2.4% decade−1. By comparison with the CERES shortwave broadband, MODIS Collection 6 is getting brighter, by 1.0 ± 0.7% decade−1 in the red band and 1.4 ± 0.7% decade−1 in the near infrared. MISR's red and near-infrared bands, however, show darkening trends of −1.0 ± 0.6% decade−1 and −1.1 ± 0.6% decade−1, respectively. The CERES/MODIS or CERES/MISR visible and near IR radiance ratio is shown to have a significant negative correlation with precipitable water content over the Antarctic Plateau. The intercalibration results successfully correct the differential top-of-atmosphere trends in zonal albedos between CERES and MISR. CERES; 3359 Radiative processes; MODIS; 3394 Instruments and techniques; 3360 Remote sensing; intercalibration; MISR; albedo trends
Zhang, Dongxiao; Cronin, Meghan F.; Wen, Caihong; Xue, Yan; Kumar, Arun; McClurg, DaiZhang, D., M. F. Cronin, C. Wen, Y. Xue, A. Kumar, D. McClurg, 2016: Assessing surface heat fluxes in atmospheric reanalyses with a decade of data from the NOAA Kuroshio Extension Observatory. Journal of Geophysical Research: Oceans, 121(9), 6874–6890. doi: 10.1002/2016JC011905. Previous studies have found large biases and uncertainties in the air-sea fluxes from Numerical Weather Prediction model reanalyses, which must be identified and reduced in order to make progress on weather and climate predictions. Here, air-sea heat fluxes from NOAA Kuroshio Extension Observatory (KEO) measurements are used to assess two new reanalyses, NCEP's Climate Forecast System Reanalysis (CFSR) and ECMWF Reanalysis-Interim (ERA-I), suggesting that these two new generation reanalyses have significantly improved. In both reanalyses, all four flux components (sensible and latent heat flux and net longwave and shortwave radiation) are highly correlated with observation, with the correlation of total net surface heat fluxes above 0.96. Although errors of the net surface heat flux have significantly reduced from previous reanalyses, the Root Mean Square Errors (RMSEs) and biases remain high especially for CFSR: the RMSEs of CFSR and ERA-I are reduced by 25-30% to 64 and 61 W/m2 respectively, while biases are reduced by 40-60% to 28 and 20 W/m2. But CFSR overestimates the winter heat release by 90 W/m2. The main cause of biases is the latent heat flux, while RMS errors are primarily due to latent heat flux and shortwave radiation errors. Both reanalyses overestimate the wind speed associated with winter storms and underestimate specific humidity in summer. The ERA-I latent heat flux, and its total net surface heat flux, are however closer to observation. It is the bulk algorithm in CFSR that is found to be mainly responsible for overestimates of winter heat release in CFSR. This article is protected by copyright. All rights reserved. 4504 Air/sea interactions; 3307 Boundary layer processes; 4262 Ocean observing systems; surface heat flux; air-sea interaction; 4260 Ocean data assimilation and reanalysis; 4576 Western boundary currents; atmospheric reanalysis; buoy measurements; NOAA/Ocean Climate Stations
Zhang, Jinting; Kelly, Kathryn A.; Thompson, LuAnneZhang, J., K. A. Kelly, L. Thompson, 2016: The role of heating, winds, and topography on sea level changes in the North Atlantic. Journal of Geophysical Research: Oceans, 121(5), 2887–2900. doi: 10.1002/2015JC011492. Seasonal and interannual-to-decadal variations of large-scale altimetric sea surface height (SSH) owing to surface heating and wind forcing in the presence of topography are investigated using simplified models. The dominant forcing mechanisms are time scale dependent. On the seasonal time scale, locally forced thermosteric height explains most of the SSH variance north of 18°N. First-mode linear long baroclinic Rossby waves forced by changes in the winds and eastern boundary conditions explain most of the variance between 10°N and 15°N and are also important east of Greenland. On interannual-to-decadal time scales, local thermosteric height remains important at several locations in the middle and high latitudes. A topographic Sverdrup response explains interannual-to-decadal SSH between 53°N and 63°N east of Greenland. Farther south, the linear Rossby wave model explains SSH variations on interannual-to-decadal time scales between 30°N and 50°N from mid-basin to the eastern boundary. Propagation of the eastern boundary condition into the interior dominates the interannual-to-decadal SSH signals south of 30°N. The effect from NAO-related heat flux on SSH is small, but forcing the topographic Sverdrup models with NAO-regressed winds gives slightly better agreement with the observed SSH in the subpolar gyre on interannual-to-decadal time scales than using the full winds. 4504 Air/sea interactions; 4556 Sea level: variations and mean; 4532 General circulation; heat flux; 4562 Topographic/bathymetric interactions; Rossby waves; SSH variability; Sverdrup balance; topography
Zhang, X.; Liang, S.; Song, Z.; Niu, H.; Wang, G.; Tang, W.; Chen, Z.; Jiang, B.Zhang, X., S. Liang, Z. Song, H. Niu, G. Wang, W. Tang, Z. Chen, B. Jiang, 2016: Local Adaptive Calibration of the Satellite-Derived Surface Incident Shortwave Radiation Product Using Smoothing Spline. IEEE Transactions on Geoscience and Remote Sensing, 54(2), 1156-1169. doi: 10.1109/TGRS.2015.2475615. Incident solar radiation (Rs) over the Earth's surface plays an important role in determining the Earth's climate and environment. Generally, Rs can be obtained from direct measurements, remotely sensed data, or reanalysis and general circulation model (GCM) data. Each type of product has advantages and limitations: the surface direct measurements provide accurate but sparse spatial coverage, whereas other global products may have large uncertainties. Ground measurements have been normally used for validation and occasionally calibration, but transforming their “true values” spatially to improve the satellite products is still a new and challenging topic. In this paper, an improved thin-plate smoothing spline approach is presented to locally “calibrate” the Global LAnd Surface Satellite (GLASS) Rs product using the reconstructed Rs data from surface meteorological measurements. The influence of surface elevation on Rs estimation was also considered in the proposed method. The point-based surface reconstructed Rs was used as the response variable, and the GLASS Rs product and the surface elevation data at the corresponding locations as explanatory variables to train the thin-plate spline model. We evaluated the performance of the approach using the cross-validation method at both daily and monthly time scales over China. We also validated the estimated Rs based on the thin-plate spline method using independent ground measurements and independent satellite estimates of Rs. These validation results indicated that the thin-plate smoothing spline method can be effectively used for calibrating satellite-derived Rs products using ground measurements to achieve better accuracy. calibration; Land surface; Remote sensing; Satellites; artificial satellites; Incident shortwave radiation; Global irradiance; spatial resolution; GLASS; cross-validation method; Data models; global land surface satellite Rs product; independent ground measurements; independent satellite estimates; local adaptive calibration; satellite-derived surface incident shortwave radiation product; Smoothing methods; splines (mathematics); surface elevation; surface elevation data; thin-plate smoothing spline; thin-plate smoothing spline approach; thin-plate spline model
Zhang, Xiaotong; Liang, Shunlin; Wang, Guoxin; Yao, Yunjun; Jiang, Bo; Cheng, JieZhang, X., S. Liang, G. Wang, Y. Yao, B. Jiang, J. Cheng, 2016: Evaluation of the Reanalysis Surface Incident Shortwave Radiation Products from NCEP, ECMWF, GSFC, and JMA Using Satellite and Surface Observations. Remote Sensing, 8(3), 225. doi: 10.3390/rs8030225. Solar radiation incident at the Earth’s surface (Rs) is an essential component of the total energy exchange between the atmosphere and the surface. Reanalysis data have been widely used, but a comprehensive validation using surface measurements is still highly needed. In this study, we evaluated the Rs estimates from six current representative global reanalyses (NCEP–NCAR, NCEP-DOE; CFSR; ERA-Interim; MERRA; and JRA-55) using surface measurements from different observation networks [GEBA; BSRN; GC-NET; Buoy; and CMA] (674 sites in total) and the Earth’s Radiant Energy System (CERES) EBAF product from 2001 to 2009. The global mean biases between the reanalysis Rs and surface measurements at all sites ranged from 11.25 W/m2 to 49.80 W/m2. Comparing with the CERES-EBAF Rs product, all the reanalyses overestimate Rs, except for ERA-Interim, with the biases ranging from −2.98 W/m2 to 21.97 W/m2 over the globe. It was also found that the biases of cloud fraction (CF) in the reanalyses caused the overestimation of Rs. After removing the averaged bias of CERES-EBAF, weighted by the area of the latitudinal band, a global annual mean Rs values of 184.6 W/m2, 180.0 W/m2, and 182.9 W/m2 were obtained over land, ocean, and the globe, respectively. Remote sensing; reanalysis; Incident shortwave radiation
Zhang, Yang; Hong, Chaopeng; Yahya, Khairunnisa; Li, Qi; Zhang, Qiang; He, KebinZhang, Y., C. Hong, K. Yahya, Q. Li, Q. Zhang, K. He, 2016: Comprehensive evaluation of multi-year real-time air quality forecasting using an online-coupled meteorology-chemistry model over southeastern United States. Atmospheric Environment, 138, 162-182. doi: 10.1016/j.atmosenv.2016.05.006. An online-coupled meteorology-chemistry model, WRF/Chem-MADRID, has been deployed for real time air quality forecast (RT-AQF) in southeastern U.S. since 2009. A comprehensive evaluation of multi-year RT-AQF shows overall good performance for temperature and relative humidity at 2-m (T2, RH2), downward surface shortwave radiation (SWDOWN) and longwave radiation (LWDOWN), and cloud fraction (CF), ozone (O3) and fine particles (PM2.5) at surface, tropospheric ozone residuals (TOR) in O3 seasons (May-September), and column NO2 in winters (December-February). Moderate-to-large biases exist in wind speed at 10-m (WS10), precipitation (Precip), cloud optical depth (COT), ammonium (NH4+), sulfate (SO42−), and nitrate (NO3−) from the IMPROVE and SEARCH networks, organic carbon (OC) at IMPROVE, and elemental carbon (EC) and OC at SEARCH, aerosol optical depth (AOD) and column carbon monoxide (CO), sulfur dioxide (SO2), and formaldehyde (HCHO) in both O3 and winter seasons, column nitrogen dioxide (NO2) in O3 seasons, and TOR in winters. These biases indicate uncertainties in the boundary layer and cloud process treatments (e.g., surface roughness, microphysics cumulus parameterization), emissions (e.g., O3 and PM precursors, biogenic, mobile, and wildfire emissions), upper boundary conditions for all major gases and PM2.5 species, and chemistry and aerosol treatments (e.g., winter photochemistry, aerosol thermodynamics). The model shows overall good skills in reproducing the observed multi-year trends and inter-seasonal variability in meteorological and radiative variables such as T2, WS10, Precip, SWDOWN, and LWDOWN, and relatively well in reproducing the observed trends in surface O3 and PM2.5, but relatively poor in reproducing the observed column abundances of CO, NO2, SO2, HCHO, TOR, and AOD. The sensitivity simulations using satellite-constrained boundary conditions for O3 and CO show substantial improvement for both spatial distribution and domain-mean performance statistics. The model’s forecasting skills for air quality can be further enhanced through improving model inputs (e.g., anthropogenic emissions for urban areas and upper boundary conditions of chemical species), meteorological forecasts (e.g., WS10, Precip) and meteorologically-dependent emissions (e.g., biogenic and wildfire emissions), and model physics and chemical treatments (e.g., gas-phase chemistry in winter conditions, cloud processes and their interactions with radiation and aerosol). satellite data; Categorical evaluation; Discrete evaluation; Multi-year trend analysis; Southeastern U.S.; WRF/Chem-MADRID
Zhang, Yang; Zhang, Xin; Wang, Litao; Zhang, Qiang; Duan, Fengkui; He, KebinZhang, Y., X. Zhang, L. Wang, Q. Zhang, F. Duan, K. He, 2016: Application of WRF/Chem over East Asia: Part I. Model evaluation and intercomparison with MM5/CMAQ. Atmospheric Environment, 124, Part B, 285-300. doi: 10.1016/j.atmosenv.2015.07.022. In this work, the application of the online-coupled Weather Research and Forecasting model with chemistry (WRF/Chem) version 3.3.1 is evaluated over East Asia for January, April, July, and October 2005 and compared with results from a previous application of an offline model system, i.e., the Mesoscale Model and Community Multiple Air Quality modeling system (MM5/CMAQ). The evaluation of WRF/Chem is performed using multiple observational datasets from satellites and surface networks in mainland China, Hong Kong, Taiwan, and Japan. WRF/Chem simulates well specific humidity (Q2) and downward longwave and shortwave radiation (GLW and GSW) with normalized mean biases (NMBs) within 24%, but shows moderate to large biases for temperature at 2-m (T2) (NMBs of −9.8% to 75.6%) and precipitation (NMBs of 11.4–92.7%) for some months, and wind speed at 10-m (WS10) (NMBs of 66.5–101%), for all months, indicating some limitations in the YSU planetary boundary layer scheme, the Purdue Lin cloud microphysics, and the Grell–Devenyi ensemble scheme. WRF/Chem can simulate the column abundances of gases reasonably well with NMBs within 30% for most months but moderately to significantly underpredicts the surface concentrations of major species at all sites in nearly all months with NMBs of −72% to −53.8% for CO, −99.4% to −61.7% for NOx, −84.2% to −44.5% for SO2, −63.9% to −25.2% for PM2.5, and −68.9% to 33.3% for PM10, and aerosol optical depth in all months except for October with NMBs of −38.7% to −16.2%. The model significantly overpredicts surface concentrations of O3 at most sites in nearly all months with NMBs of up to 160.3% and NO 3 - at the Tsinghua site in all months. Possible reasons for large underpredictions include underestimations in the anthropogenic emissions of CO, SO2, and primary aerosol, inappropriate vertical distributions of emissions of SO2 and NO2, uncertainties in upper boundary conditions (e.g., for O3 and CO), missing or inaccurate model representations (e.g., secondary organic aerosol formation, gas/particle partitioning, dust emissions, dry and wet deposition), and inaccurate meteorological fields (e.g., overpredictions in WS10 and precipitation, but underpredictions in T2), as well as the large uncertainties in satellite retrievals (e.g., for column SO2). Comparing to MM5, WRF generally gives worse performance in meteorological predictions, in particular, T2, WS10, GSW, GLW, and cloud fraction in all months, as well as Q2 and precipitation in January and October, due to limitations in the above physics schemes or parameterizations. Comparing to CMAQ, WRF/Chem performs better for surface CO, O3, and PM10 concentrations at most sites in most months, column CO and SO2 abundances, and AOD. It, however, gives poorer performance for surface NOx concentrations at most sites in most months, surface SO2 concentrations at all sites in all months, and column NO2 abundances in January and April. WRF/Chem also gives lower concentrations of most secondary PM and black carbon. Those differences in results are attributed to differences in simulated meteorology, gas-phase chemistry, aerosol thermodynamic and dynamic treatments, dust and sea salt emissions, and wet and dry deposition treatments in both models. model intercomparison; East Asia; WRF/Chem; model evaluation; MM5/CMAQ
Zhao, Ming; Golaz, J.-C.; Held, I. M.; Ramaswamy, V.; Lin, S.-J.; Ming, Y.; Ginoux, P.; Wyman, B.; Donner, L. J.; Paynter, D.; Guo, H.Zhao, M., J. Golaz, I. M. Held, V. Ramaswamy, S. Lin, Y. Ming, P. Ginoux, B. Wyman, L. J. Donner, D. Paynter, H. Guo, 2016: Uncertainty in Model Climate Sensitivity Traced to Representations of Cumulus Precipitation Microphysics. J. Climate, 29(2), 543-560. doi: 10.1175/JCLI-D-15-0191.1. Uncertainty in equilibrium climate sensitivity impedes accurate climate projections. While the intermodel spread is known to arise primarily from differences in cloud feedback, the exact processes responsible for the spread remain unclear. To help identify some key sources of uncertainty, the authors use a developmental version of the next-generation Geophysical Fluid Dynamics Laboratory global climate model (GCM) to construct a tightly controlled set of GCMs where only the formulation of convective precipitation is changed. The different models provide simulation of present-day climatology of comparable quality compared to the model ensemble from phase 5 of CMIP (CMIP5). The authors demonstrate that model estimates of climate sensitivity can be strongly affected by the manner through which cumulus cloud condensate is converted into precipitation in a model’s convection parameterization, processes that are only crudely accounted for in GCMs. In particular, two commonly used methods for converting cumulus condensate into precipitation can lead to drastically different climate sensitivity, as estimated here with an atmosphere–land model by increasing sea surface temperatures uniformly and examining the response in the top-of-atmosphere energy balance. The effect can be quantified through a bulk convective detrainment efficiency, which measures the ability of cumulus convection to generate condensate per unit precipitation. The model differences, dominated by shortwave feedbacks, come from broad regimes ranging from large-scale ascent to subsidence regions. Given current uncertainties in representing convective precipitation microphysics and the current inability to find a clear observational constraint that favors one version of the authors’ model over the others, the implications of this ability to engineer climate sensitivity need to be considered when estimating the uncertainty in climate projections. climate change; Cloud microphysics; climate models; Cloud parameterizations; Climate sensitivity; Models and modeling; Physical Meteorology and Climatology; convective parameterization
Zuidema, Paquita; Chang, Ping; Medeiros, Brian; Kirtman, Ben P.; Mechoso, Roberto; Schneider, Edwin K.; Toniazzo, Thomas; Richter, Ingo; Small, R. Justin; Bellomo, Katinka; Brandt, Peter; de Szoeke, Simon; Farrar, J. Thomas; Jung, Eunsil; Kato, Seiji; Li, Mingkui; Patricola, Christina; Wang, Zaiyu; Wood, Robert; Xu, ZhaoZuidema, P., P. Chang, B. Medeiros, B. P. Kirtman, R. Mechoso, E. K. Schneider, T. Toniazzo, I. Richter, R. J. Small, K. Bellomo, P. Brandt, S. de Szoeke, J. T. Farrar, E. Jung, S. Kato, M. Li, C. Patricola, Z. Wang, R. Wood, Z. Xu, 2016: Challenges and Prospects for Reducing Coupled Climate Model SST Biases in the Eastern Tropical Atlantic and Pacific Oceans: The U.S. CLIVAR Eastern Tropical Oceans Synthesis Working Group. Bull. Amer. Meteor. Soc., 97(12), 2305-2327. doi: 10.1175/BAMS-D-15-00274.1. Well-known problems trouble coupled general circulation models of the eastern Atlantic and Pacific Ocean basins. Model climates are significantly more symmetric about the equator than is observed. Model sea surface temperatures are biased warm south and southeast of the equator, and the atmosphere is too rainy within a band south of the equator. Near-coastal eastern equatorial SSTs are too warm, producing a zonal SST gradient in the Atlantic opposite in sign to that observed. The U.S. Climate Variability and Predictability Program (CLIVAR) Eastern Tropical Ocean Synthesis Working Group (WG) has pursued an updated assessment of coupled model SST biases, focusing on the surface energy balance components, on regional error sources from clouds, deep convection, winds, and ocean eddies; on the sensitivity to model resolution; and on remote impacts. Motivated by the assessment, the WG makes the following recommendations: 1) encourage identification of the specific parameterizations contributing to the biases in individual models, as these can be model dependent; 2) restrict multimodel intercomparisons to specific processes; 3) encourage development of high-resolution coupled models with a concurrent emphasis on parameterization development of finer-scale ocean and atmosphere features, including low clouds; 4) encourage further availability of all surface flux components from buoys, for longer continuous time periods, in persistently cloudy regions; and 5) focus on the eastern basin coastal oceanic upwelling regions, where further opportunities for observational–modeling synergism exist.
Abraham, Carsten; Steiner, Nadja; Monahan, Adam; Michel, ChristineAbraham, C., N. Steiner, A. Monahan, C. Michel, 2015: Effects of subgrid-scale snow thickness variability on radiative transfer in sea ice. Journal of Geophysical Research: Oceans, 120(8), 5597-5614. doi: 10.1002/2015JC010741. Snow is a principal factor in controlling heat and light fluxes through sea ice. With the goal of improving radiative and heat flux estimates through sea ice in regional and global models without the need of detailed snow property descriptions, a new parameterization including subgrid-scale snow thickness variability is presented. One-parameter snow thickness distributions depending only on the gridbox-mean snow thickness are introduced resulting in analytical solutions for the fluxes of heat and light through the snow layer. As the snowpack melts, these snow thickness distributions ensure a smooth seasonal transition of the light field under sea ice. Spatially homogenous melting applied to an inhomogeneous distribution of snow thicknesses allows the appearance of bare sea ice areas and melt ponds before all snow has melted. In comparison to uniform-thickness snow used in previous models, the bias in the under sea-ice light field is halved with this parameterization. Model results from a one-dimensional ocean turbulence model coupled with a thermodynamic sea ice model are compared to observations near Resolute in the Canadian High Arctic. The simulations show substantial improvements not only to the light field at the sea ice base which will affect ice algal growth but also to the sea ice and seasonal snowpack evolution. During melting periods, the snowpack can survive longer while sea ice thickness starts to reduce earlier. 0360 Radiation: transmission and scattering; radiative transfer; 0750 Sea ice; 0736 Snow; 0798 Modeling; Light transfer; sea ice modeling; Snow thickness distribution; Snow variability
Adebiyi, Adeyemi A.; Zuidema, Paquita; Abel, Steven J.Adebiyi, A. A., P. Zuidema, S. J. Abel, 2015: The Convolution of Dynamics and Moisture with the Presence of Shortwave Absorbing Aerosols over the Southeast Atlantic. J. Climate, 28(5), 1997-2024. doi: 10.1175/JCLI-D-14-00352.1. AbstractBiomass burning aerosols seasonally overlie the subtropical southeast Atlantic stratocumulus deck. Previous modeling and observational studies have postulated a semidirect effect whereby shortwave absorption by the aerosol warms and stabilizes the lower troposphere, thickening the low-level clouds. The focus herein is on the dynamical and moisture effects that may be convoluted with the semidirect effect. Almost-daily radiosonde data from remote St. Helena Island (15.9°S, 5.6°W), covering September–October 2000–11, are combined with daily spatial averages (encompassing the island) of the MODIS clear-sky fine-mode aerosol optical depth (). Increases in are associated with increases in 750–500-hPa moisture content. The net maximum longwave cooling by moisture of almost 0.45 K day−1 reduces the aerosol layer warming from shortwave absorption. ERA-Interim spatial composites show that polluted conditions are associated with a strengthening of a deep land-based anticyclone over southern Africa, facilitating the westward offshore transport of both smoke and moisture at 600 hPa. The shallower surface-based South Atlantic anticyclone exhibits a less pronounced shift to the northeast, strengthening the low-level coastal jet exiting into the stratocumulus deck and cooling 1000-hPa potential temperatures. Warm continental outflow further increases the 800-hPa potential temperatures (), reinforcing the lower tropospheric stability () over the stratocumulus deck. Enhanced southerly dry air advection also strengthens the cloud-top humidity inversion. The increased stability helps explain an observed decrease in cloud-top heights despite an anomalous reduction in subsidence. The changes to the horizontal dynamics enhance low-level cloudiness. These are separate but not necessarily distinct from an aerosol semidirect effect, encouraging care in attribution studies. clouds; aerosols; radiative forcing; humidity; Dynamics; Anticyclones
Alexandri, G.; Georgoulias, A. K.; Zanis, P.; Katragkou, E.; Tsikerdekis, A.; Kourtidis, K.; Meleti, C.Alexandri, G., A. K. Georgoulias, P. Zanis, E. Katragkou, A. Tsikerdekis, K. Kourtidis, C. Meleti, 2015: On the ability of RegCM4 regional climate model to simulate surface solar radiation patterns over Europe: an assessment using satellite-based observations. Atmos. Chem. Phys., 15(22), 13195-13216. doi: 10.5194/acp-15-13195-2015. In this work, we assess the ability of RegCM4 regional climate model to simulate surface solar radiation (SSR) patterns over Europe. A decadal RegCM4 run (2000–2009) was implemented and evaluated against satellite-based observations from the Satellite Application Facility on Climate Monitoring (CM SAF), showing that the model simulates adequately the SSR patterns over the region. The SSR bias between RegCM4 and CM SAF is +1.5 % for MFG (Meteosat First Generation) and +3.3 % for MSG (Meteosat Second Generation) observations. The relative contribution of parameters that determine the transmission of solar radiation within the atmosphere to the deviation appearing between RegCM4 and CM SAF SSR is also examined. Cloud macrophysical and microphysical properties such as cloud fractional cover (CFC), cloud optical thickness (COT) and cloud effective radius (Re) from RegCM4 are evaluated against data from CM SAF. Generally, RegCM4 underestimates CFC by 24.3 % and Re for liquid/ice clouds by 36.1 %/28.3 % and overestimates COT by 4.3 %. The same procedure is repeated for aerosol optical properties such as aerosol optical depth (AOD), asymmetry factor (ASY) and single-scattering albedo (SSA), as well as other parameters, including surface broadband albedo (ALB) and water vapor amount (WV), using data from MACv1 aerosol climatology, from CERES satellite sensors and from ERA-Interim reanalysis. It is shown here that the good agreement between RegCM4 and satellite-based SSR observations can be partially attributed to counteracting effects among the above mentioned parameters. The potential contribution of each parameter to the RegCM4–CM SAF SSR deviations is estimated with the combined use of the aforementioned data and a radiative transfer model (SBDART). CFC, COT and AOD are the major determinants of these deviations on a monthly basis; however, the other parameters also play an important role for specific regions and seasons. Overall, for the European domain, CFC, COT and AOD are the most important factors, since their underestimations and overestimations by RegCM4 cause an annual RegCM4–CM SAF SSR absolute deviation of 8.4, 3.8 and 4.5 %, respectively.
Anderson, R. G.; Lo, M.-H.; Swenson, S.; Famiglietti, J. S.; Tang, Q.; Skaggs, T. H.; Lin, Y.-H.; Wu, R.-J.Anderson, R. G., M. Lo, S. Swenson, J. S. Famiglietti, Q. Tang, T. H. Skaggs, Y. Lin, R. Wu, 2015: Using satellite-based estimates of evapotranspiration and groundwater changes to determine anthropogenic water fluxes in land surface models. Geosci. Model Dev. Discuss., 8(4), 3565-3592. doi: 10.5194/gmdd-8-3565-2015. Irrigation is a widely used water management practice that is often poorly parameterized in land surface and climate models. Previous studies have addressed this issue via use of irrigation area, applied water inventory data, or soil moisture content. These approaches have a variety of drawbacks including data latency, accurately prescribing irrigation intensity, and conservation of water volume for soil moisture approach. In this study, we parameterize irrigation fluxes using satellite observations of evapotranspiration (ET) against ET from a suite of land surface models without irrigation. We then apply this water flux into the Community Land Model (CLM) and use an iterative approach to estimate groundwater recharge and partition the water flux between groundwater and surface water. The ET simulated by CLM with irrigation matches the magnitude and seasonality of observed satellite ET well, with a mean difference of 6.3 mm month−1 and a correlation of 0.95. Differences between the new CLM ET values and observed ET values are always less than 30 mm month−1 and the differences show no pattern with respect to seasonality. The results reinforce the importance of accurately parameterizing anthropogenic hydrologic fluxes into land surface and climate models to assess environmental change under current and future climates and land management regimes.
Badgley, Grayson; Fisher, Joshua B.; Jiménez, Carlos; Tu, Kevin P.; Vinukollu, RaghuveerBadgley, G., J. B. Fisher, C. Jiménez, K. P. Tu, R. Vinukollu, 2015: On Uncertainty in Global Terrestrial Evapotranspiration Estimates from Choice of Input Forcing Datasets. J. Hydrometeor., 16(4), 1449-1455. doi: 10.1175/JHM-D-14-0040.1. AbstractEvapotranspiration ET is a critical water, energy, and climate variable, and recent work has been published comparing different global products. These comparisons have been difficult to interpret, however, because in most studies the evapotranspiration products were derived from models forced by different input data. Some studies have analyzed the uncertainty in regional evapotranspiration estimates from choice of forcings. Still others have analyzed how multiple models vary with choice of net radiation forcing data. However, no analysis has been conducted to determine the uncertainty in global evapotranspiration estimates attributable to each class of input forcing datasets. Here, one of these models [Priestly–Taylor JPL (PT-JPL)] is run with 19 different combinations of forcing data. These data include three net radiation products (SRB, CERES, and ISCCP), three meteorological datasets [CRU, Atmospheric Infrared Sounder (AIRS) Aqua, and MERRA], and three vegetation index products [MODIS; Global Inventory Modeling and Mapping Studies (GIMMS); and Fourier-Adjusted, Sensor and Solar Zenith Angle Corrected, Interpolated, Reconstructed (FASIR)]. The choice in forcing data produces an average range in global monthly evapotranspiration of 10.6 W m−2 (~20% of global mean evapotranspiration), with net radiation driving the majority of the difference. Annual average terrestrial ET varied by an average of 8 W m−2, depending on choice of forcings. The analysis shows that the greatest disagreement between input forcings arises from choice of net radiation dataset. In particular, ISCCP data, which are frequently used in global studies, differed widely from the other radiation products examined and resulted in dramatically different estimates of global terrestrial ET. Energy budget/balance; Hydrologic cycle; Trends; Evapotranspiration
Barker, Howard W.; Cole, Jason N. S.; Domenech, Carlos; Shephard, Mark W.; Sioris, Christopher E.; Tornow, Florian; Wehr, TobiasBarker, H. W., J. N. S. Cole, C. Domenech, M. W. Shephard, C. E. Sioris, F. Tornow, T. Wehr, 2015: Assessing the quality of active–passive satellite retrievals using broad-band radiances. Quarterly Journal of the Royal Meteorological Society, 141(689), 1294-1305. doi: 10.1002/qj.2438. Included in the Earth, Clouds, Aerosols, and Radiation Explorer (EarthCARE) satellite's array of instruments is a multi-view broad-band radiometer (BBR). BBR data will facilitate a radiative closure assessment of cloud and aerosol properties inferred from data gathered by EarthCARE's other passive and active sensors. The closure assessment will consist, in part, of comparisons between BBR radiances and radiances computed by three-dimensional (3D) radiative transfer models (RTM) that act on narrow 3D domains that derive from, and include, the retrieved cross-section of cloud and aerosol properties. Assessment domains D will be ∼100 km2. Following a brief outline of the closure experiment, a method is proposed for estimating the likelihood of BBR radiances providing a meaningful closure assessment of cloud and aerosol properties in D. The method capitalizes on the ability of Monte Carlo RTMs to compute contributions to radiances from any constituent in any given D. While this methodology introduces some circularity into the closure test, it might, nevertheless, be tolerable, given that the method's purpose is simply to identify, and thus avoid, assessments that are likely to be fruitless or misleading. A 3000 km long stretch of A-Train satellite data was used in this initial demonstration of the proposed methodology. Only results for solar radiation are shown. All radiative quantities used here were computed by a 3D Monte Carlo RTM. A control simulation provided proxy BBR measurements. Random ‘errors’ were introduced into the A-Train field to produce experimental fields that roughly mimic retrievals. Experimental and control radiances were compared in mock-closure assessments. Arbitrarily assuming that a fruitful assessment requires ∼75% of a BBR radiance to result from cloud and aerosol scattering events inside D, ∼70% of the (11 km)2 domains were flagged as reliably testable for this example. clouds; Satellite; EarthCARE; closure; radiative
Barragan, Ruben; Romano, Salvatore; Sicard, Michaël; Burlizzi, Pasquale; Perrone, Maria-Rita; Comeron, AdolfoBarragan, R., S. Romano, M. Sicard, P. Burlizzi, M. Perrone, A. Comeron, 2015: Estimation of aerosol direct radiative forcing in Lecce during the 2013 ADRIMED campaign. Remote Sensing of Clouds and the Atmosphere XX, 96400J, 9640, 96400J-96400J-12. doi: 10.1117/12.2194095. In the framework of the ChArMEx (Chemistry-Aerosol Mediterranean Experiment, http://charmex.lsce.ipsl.fr/) initiative, a field campaign took place in the western Mediterranean Basin between 10 June and 5 July 2013 within the ADRIMED (Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region) project. The scientific objectives of ADRIMED are the characterization of the typical “Mediterranean aerosol” and its direct radiative forcing (column closure and regional scale). This work is focused on the multi-intrusion Saharan dust transport period of moderate intensity that occurred over the western and central Mediterranean Basin during the period 14 – 27 June. The dust plumes were detected by the EARLINET/ACTRIS (European Aerosol Research Lidar Network / Aerosols, Clouds, and Trace gases Research InfraStructure Network, http://www.actris.net/) lidar stations of Barcelona (16 and 17 June) and Lecce (22 June). First, two well-known and robust radiative transfer models, parametrized by lidar profiles for the aerosol vertical distribution, are validated both in the shortwave and longwave spectral range 1) at the surface with down- and up-ward flux measurements from radiometers and 2) at the top of the atmosphere with upward flux measurements from the CERES (Clouds and the Earth’s Radiant Energy System) radiometers on board the AQUA and TERRA satellites. The differences between models and their limitations are discussed. The instantaneous and clear-sky direct radiative forcing of mineral dust is then estimated using lidar data for parametrizing the particle vertical distribution at Lecce. The difference between the obtained forcings is discussed in regard to the mineralogy and vertical structure of the dust plume.
Bellomo, Katinka; Clement, Amy C.; Mauritsen, Thorsten; Rädel, Gaby; Stevens, BjornBellomo, K., A. C. Clement, T. Mauritsen, G. Rädel, B. Stevens, 2015: The Influence of Cloud Feedbacks on Equatorial Atlantic Variability. J. Climate, 28(7), 2725-2744. doi: 10.1175/JCLI-D-14-00495.1. AbstractObservations show that cloud feedback over the Namibian stratocumulus region is positive because cloud cover is anticorrelated with local sea surface temperature (SST) anomalies. Moreover, regressions of observed atmospheric fields on equatorial Atlantic SST anomalies indicate that cloud feedbacks over the Namibian stratocumulus region covary with Atlantic Niño. However, from observations alone, it is not possible to quantify the influence of regional cloud feedbacks on equatorial climate variability. To address this question, a set of sensitivity experiments are conducted using an atmospheric general circulation model (ECHAM6) coupled to a slab ocean in which the strength of positive cloud feedback is enhanced over several regions in the South Atlantic basin. Enhanced positive cloud feedback over the Namibian stratocumulus region increases local as well as equatorial SST variability, whereas enhanced cloud feedback over other regions in the South Atlantic increases local SST variability but exhibits negligible responses at the equator. The authors’ results indicate that the Namibian region plays a central role in enhancing equatorial SST variability because it is located where the SST anomalies associated with the simulated Atlantic Niño in the slab-ocean model develop. These results highlight the important role of the regional coupling of cloud cover over the Namibian region with local SSTs and its effects on equatorial Atlantic climate variability. clouds; Feedback; Fluxes; cloud forcing; Interannual variability; Multidecadal variability
Boyle, J. S.; Klein, S. A.; Lucas, D. D.; Ma, H.-Y.; Tannahill, J.; Xie, S.Boyle, J. S., S. A. Klein, D. D. Lucas, H. Ma, J. Tannahill, S. Xie, 2015: The parametric sensitivity of CAM5's MJO. Journal of Geophysical Research: Atmospheres, 120(4), 1424–1444. doi: 10.1002/2014JD022507. We systematically explore the ability of the Community Atmospheric Model version 5 (CAM5) to simulate the Madden-Julian Oscillation (MJO), through an analysis of MJO metrics calculated from a 1100-member perturbed parameter ensemble of 5 year simulations with observed sea surface temperatures. Parameters from the deep convection scheme make the greatest contribution to the variance in MJO simulation quality with a much smaller contribution from parameters in the large-scale cloud, shallow convection, and boundary layer turbulence schemes. Improved MJO variability results from a larger lateral entrainment rate and a reduction in the precipitation efficiency of deep convection that was achieved by a smaller autoconversion of cloud to rainwater and a larger evaporation of convective precipitation. Unfortunately, simulations with an improved MJO also have a significant negative impact on the climatological values of low-level cloud and absorbed shortwave radiation, suggesting that structural in addition to parametric modifications to CAM5's parameterization suite are needed in order to simultaneously well simulate the MJO and mean-state climate. 3371 Tropical convection; 1626 Global climate models; 3365 Subgrid-scale (SGS) parameterization; CAM5; MJO
Bras, Rafael L.Bras, R. L., 2015: Complexity and organization in hydrology: A personal view. Water Resources Research, 51(8), 6532-6548. doi: 10.1002/2015WR016958. The hydrologic cycle is an exquisitely coordinated and balanced interaction between the atmosphere, the ocean, and the land that controls, among other things, the planet's temperature by moving large quantities of matter and energy. The system is incredibly complex with a myriad of positive and negative feedbacks acting at a variety of scales. Much of what we experience in our natural and altered environments results from these complex interactions. Surprisingly (or maybe not) this complexity many times results in beautifully organized expressions of the hydrologic state that are commonly amenable to fairly simple explanations. This paper illustrates hydrologic complexity and organization in the context of the author's and collaborator's work during the past decades, a lot published in Water Resources Research. Topics include the impact of soil moisture on the atmosphere and vice versa, the impact of deforestation on the Amazon cloud climate and precipitation, the estimation of surface energy and mass fluxes, the self-organization of landscapes and river basins over very long time periods, and the roles of vegetation on landscape evolution. hydrology; 1843 Land/atmosphere interactions; 1719 Hydrology; 1825 Geomorphology: fluvial; 1847 Modeling; complexity; fluvial geomorphology; land energy fluxes; land-atmosphere interactions; maximum entropy
Brindley, Helen; Bantges, Richard; Russell, Jacqueline; Murray, Jonathan; Dancel, Christopher; Belotti, Claudio; Harries, JohnBrindley, H., R. Bantges, J. Russell, J. Murray, C. Dancel, C. Belotti, J. Harries, 2015: Spectral Signatures of Earth’s Climate Variability over 5 Years from IASI. J. Climate, 28(4), 1649-1660. doi: 10.1175/JCLI-D-14-00431.1. AbstractInterannual variability in spectrally resolved longwave radiances is quantified at a variety of spatial scales using 5 yr of IASI observations. Maximum variability is seen at the smallest scales investigated (10° zonal means) at northern and southern high latitudes across the center of the 15-µm CO2 band. As the spatial scale increases, the overall magnitude of interannual variability is reduced across the spectrum and the spectral shape of the variability changes. In spectral regions sensitive to conditions in the upper troposphere, the effect of increasing spatial scale is relatively small and at the global scale these parts of the spectrum show the greatest year-to-year variability. Conversely, the atmospheric window (8–12 µm), which is sensitive to variations in surface temperature and cloud, shows a marked reduction in interannual variability with increasing spatial scale. Over the 5 yr studied, at global scales the standard deviation in annual mean brightness temperature is less than 0.17 K across the spectrum, dropping to less than 0.05 K across the window. Spectrally integrating the IASI measurements to create pseudobroadband and window channels indicates a variation about the mean that is higher for the broadband channel than for the window channel at the global and quasi-global scales and over the Southern Hemisphere. These findings are in agreement with observations from CERES Terra over the same period and imply that at the largest spatial scales, over the period considered here, fluctuations in mid- to upper-tropospheric temperatures and water vapor, and not cloud or surface temperature, play the dominant role in determining the level of interannual variability in all-sky outgoing longwave radiation. Radiative fluxes; satellite observations; Radiances; Interannual variability
Cao, Yunfeng; Liang, Shunlin; Chen, Xiaona; He, TaoCao, Y., S. Liang, X. Chen, T. He, 2015: Assessment of Sea Ice Albedo Radiative Forcing and Feedback over the Northern Hemisphere from 1982 to 2009 Using Satellite and Reanalysis Data. J. Climate, 28(3), 1248-1259. doi: 10.1175/JCLI-D-14-00389.1. AbstractThe decreasing surface albedo caused by continuously retreating sea ice over Arctic plays a critical role in Arctic warming amplification. However, the quantification of the change in radiative forcing at top of atmosphere (TOA) introduced by the decreasing sea ice albedo and its feedback to the climate remain uncertain. In this study, based on the satellite-retrieved long-term surface albedo product CLARA-A1 (Cloud, Albedo, and Radiation dataset, AVHRR-based, version 1) and the radiative kernel method, an estimated 0.20 ± 0.05 W m−2 sea ice radiative forcing (SIRF) has decreased in the Northern Hemisphere (NH) owing to the loss of sea ice from 1982 to 2009, yielding a sea ice albedo feedback (SIAF) of 0.25 W m−2 K−1 for the NH and 0.19 W m−2 K−1 for the entire globe. These results are lower than the estimate from another method directly using the Clouds and the Earth’s Radiant Energy System (CERES) broadband planetary albedo. Further data analysis indicates that kernel method is likely to underestimate the change in all-sky SIRF because all-sky radiative kernels mask too much of the effect of sea ice albedo on the variation of cloudy albedo. By applying an adjustment with CERES-based estimate, the change in all-sky SIRF over the NH was corrected to 0.33 ± 0.09 W m−2, corresponding to a SIAF of 0.43 W m−2 K−1 for NH and 0.31 W m−2 K−1 for the entire globe. It is also determined that relative to satellite surface albedo product, two popular reanalysis products, ERA-Interim and MERRA, severely underestimate the changes in NH SIRF in melt season (May–August) from 1982 to 2009 and the sea ice albedo feedback to warming climate. Feedback; albedo; sea ice; radiative forcing; Arctic; Trends
Ceppi, Paulo; Hartmann, Dennis L.Ceppi, P., D. L. Hartmann, 2015: Connections Between Clouds, Radiation, and Midlatitude Dynamics: a Review. Current Climate Change Reports, 1(2), 94-102. doi: 10.1007/s40641-015-0010-x. We review the effects of dynamical variability on clouds and radiation in observations and models and discuss their implications for cloud feedbacks. Jet shifts produce robust meridional dipoles in upper-level clouds and longwave cloud-radiative effect (CRE), but low-level clouds, which do not simply shift with the jet, dominate the shortwave CRE. Because the effect of jet variability on CRE is relatively small, future poleward jet shifts with global warming are only a second-order contribution to the total CRE changes around the midlatitudes, suggesting a dominant role for thermodynamic effects. This implies that constraining the dynamical response is unlikely to reduce the uncertainty in extratropical cloud feedback. However, we argue that uncertainty in the cloud-radiative response does affect the atmospheric circulation response to global warming, by modulating patterns of diabatic forcing. How cloud feedbacks can affect the dynamical response to global warming is an important topic of future research. clouds; climate change; Climatology; radiation; Atmospheric dynamics; Atmospheric Sciences; Climate Change Management and Policy; cloud feedbacks; global warming; Interannual variability; Jet streams; Oceanography; Trends
Chen, Gengxin; Han, Weiqing; Li, Yuanlong; Wang, Dongxiao; Shinoda, ToshiakiChen, G., W. Han, Y. Li, D. Wang, T. Shinoda, 2015: Intraseasonal variability of upwelling in the equatorial Eastern Indian Ocean. Journal of Geophysical Research: Oceans, 120(11), 7598-7615. doi: 10.1002/2015JC011223. By analyzing satellite observations and conducting a series of ocean general circulation model experiments, this study examines the physical processes that determine intraseasonal variability (ISV) of the equatorial eastern Indian Ocean (EIO) upwelling for the 2001–2011 period. The ISV of EIO upwelling—as indicated by sea level, thermocline depth, and sea surface temperature (SST)—is predominantly forced by atmospheric intraseasonal oscillations (ISOs), and shows larger amplitudes during winter-spring season (November–April) when atmospheric ISOs are stronger than summer-fall (May–October). The chlorophyll (Chl-a) concentration, another indicator of upwelling, however reveals its largest intraseasonal variability during May–October, when the mean thermocline is shallow and seasonal upwelling occurs. For both winter-spring and summer-fall seasons, the ISV of EIO sea level and thermocline depth is dominated by remote forcing from the equatorial Indian Ocean wind stress, which drives Kelvin waves that propagate along the equator and subsequently along the Sumatra-Java coasts. Local wind forcing within the EIO plays a secondary role. The ISV of SST, however, is dominated by upwelling induced by remote equatorial wind only during summer-fall, with less contribution from surface heat fluxes for this season. During winter-spring, the ISV of SST results primarily from shortwave radiation and turbulent heat flux induced by wind speed associated with the ISOs, and local forcing dominates the SST variability. In this season, the mean thermocline is deep in the warm pool and thus thermocline variability decouples from the ISV of SST. Only in summer-fall when the mean thermocline is shallow, upwelling has important impact on SST. Indian Ocean; Intraseasonal variability; MJO; 4231 Equatorial oceanography; 4279 Upwelling and convergences; 9340 Indian Ocean; equatorial dynamics; remote forcing; upwelling
Chen, Xiaona; Liang, Shunlin; Cao, Yunfeng; He, Tao; Wang, DongdongChen, X., S. Liang, Y. Cao, T. He, D. Wang, 2015: Observed contrast changes in snow cover phenology in northern middle and high latitudes from 2001–2014. Scientific Reports, 5, 16820. doi: 10.1038/srep16820. Quantifying and attributing the phenological changes in snow cover are essential for meteorological, hydrological, ecological, and societal implications.
Cheng, Anning; Xu, Kuan-ManCheng, A., K. Xu, 2015: Improved Low-Cloud Simulation from the Community Atmosphere Model with an Advanced Third-Order Turbulence Closure. J. Climate, 28(14), 5737-5762. doi: 10.1175/JCLI-D-14-00776.1. AbstractIn this study, a simplified intermediately prognostic higher-order turbulence closure (IPHOC) is implemented in the Community Atmosphere Model, version 5 (CAM5), to provide a consistent treatment of subgrid-scale cloud processes, except for deep convection. The planetary boundary layer (PBL) height is prognosticated to better resolve the discontinuity of temperature and moisture above the PBL top. Single-column model tests show that fluxes of liquid water potential temperature and total water, cloud fraction, and liquid water content are improved with this approach. The simplified IPHOC package replaces the boundary layer dry and moist turbulence parameterizations, the shallow convection parameterization, and the liquid-phase part of the cloud macrophysics parameterization in CAM5. CAM5-IPHOC improves the simulation of the low-level clouds off the west coasts of continents and the storm track region in the Southern Hemisphere (SH). The transition from stratocumulus to cumulus clouds is more gradual. There are also improvements on the cloud radiative forcing, especially shortwave, in the subsidence regime. The improvements in the relationships among low cloud amount, surface relative humidity, lower tropospheric stability, and PBL depth are seen in some stratocumulus regions. CAM5-IPHOC, however, produces weaker precipitation at the South Pacific convergence zone than CAM5 because of less energy flux into the SH atmosphere. The more downward surface shortwave radiative cooling and the less top-of-the-atmosphere longwave cloud radiative heating in the SH relative to the Northern Hemisphere explains the anomalous cooling and the lesser energy flux into the SH, which is related to the underestimate of extratropical middle/high clouds in the SH. Model evaluation/performance; Atmospheric circulation; Cloud cover; climate models; Cloud resolving models
Chiacchio, Marc; Solmon, Fabien; Giorgi, Filippo; Stackhouse, Paul; Wild, MartinChiacchio, M., F. Solmon, F. Giorgi, P. Stackhouse, M. Wild, 2015: Evaluation of the radiation budget with a regional climate model over Europe and inspection of dimming and brightening. Journal of Geophysical Research: Atmospheres, 120(5), 1951–1971. doi: 10.1002/2014JD022497. Shortwave (SW) and longwave (LW) components of the radiation budget at the surface and top of atmosphere (TOA) are evaluated in the regional climate model RegCM version 4 driven by European Centre for Medium-Range Weather Forecasts Reanalysis over Europe. The simulated radiative components were evaluated with those from satellite-based products and reanalysis. At the surface the model overestimated the absorbed solar radiation but was compensated by a greater loss of thermal energy while both SW and LW TOA net fluxes were underestimated representing too little solar energy absorbed and too little outgoing thermal energy. Averaged biases in radiative parameters were generally within 25 W m−2, were dependent on differences by as much as 0.2 in cloud fraction, surface, and planetary albedo and less dependent on surface temperature associated with the surface longwave parameters, and are in line with other studies. Clear-sky fluxes showed better results when cloud cover differences had no influence. We also found a clear distinction between land versus water with smaller biases over land at the surface and over water at the TOA due to differences in cloud fraction and albedo. Finally, we inspected dimming and brightening for the period 1979–2010 with an indication for dimming early in the time series (i.e., 1979–1987) and brightening after, which agrees with surface-based observations. After 2000, however, a decrease in the brightening by more than 1 order of magnitude was evident which is in contrast to the continued brightening found in surface records and satellite-derived estimates. 0360 Radiation: transmission and scattering; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; 1637 Regional climate change; radiation budget; dimming and brightening; regional modeling
Corbett, J. G.; Loeb, N. G.Corbett, J. G., N. G. Loeb, 2015: On the relative stability of CERES reflected shortwave and MISR and MODIS visible radiance measurements during the Terra satellite mission. Journal of Geophysical Research: Atmospheres, 120(22), 11,608–11,616. doi: 10.1002/2015JD023484. Fifteen years of visible, near-infrared, and broadband shortwave radiance measurements from Clouds and the Earth's Radiant Energy System (CERES), Multiangle Imaging Spectroradiometer (MISR), and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on board NASA's Terra satellite are analyzed in order to assess their long-term relative stability for climate purposes. A regression-based approach between CERES, MODIS, and MISR (An camera only) reflectances is used to calculate the bias between the different reflectances relative to a reference year. When compared to the CERES shortwave broadband reflectance, relative drift between the MISR narrowbands is within 1% decade−1. Compared to the CERES shortwave reflectance, the MODIS narrowband reflectances show a relative drift of less than −1.33% decade−1. When compared to MISR, the MODIS reflectances show a relative drift of between −0.36% decade−1 and −2.66% decade−1. We show that the CERES Terra SW measurements are stable over the time period relative to CERES Aqua. Using this as evidence that CERES Terra may be absolutely stable, we suggest that the CERES, MISR, and MODIS instruments meet the radiometric stability goals for climate applications set out in Ohring et al. (2005). calibration; 1640 Remote sensing; 1694 Instruments and techniques; CERES; MODIS; 3394 Instruments and techniques; Terra; 3360 Remote sensing; MISR
Corbett, J.; Su, W.Corbett, J., W. Su, 2015: Accounting for the effects of Sastrugi in the CERES Clear-Sky Antarctic shortwave ADMs. Atmos. Meas. Tech. Discuss., 8(1), 375-404. doi: 10.5194/amtd-8-375-2015. The Cloud and Earth's Radiant Energy System (CERES) Instruments on NASA's Terra, Aqua and Soumi-NPP satellites are used to provide a long-term measurement of the Earth's energy budget. To accomplish this, the radiances measured by the instruments must be inverted to fluxes by the use of a scene-type dependent angular distribution model (ADM). For permanent snow scenes over Antarctica, shortwave ADMs are created by compositing radiance measurements over the full viewing zenith and azimuth range. However, the presence of small-scale wind blown roughness features called sastrugi cause the BRDF of the snow to vary significantly based upon the solar azimuth angle and location. This can result in monthly regional biases as large as ±15 Wm−2 in the inverted TOA SW flux. In this paper we created a set of ADMs that account for the sastrugi effect by using measurements from the Multi-Angle Imaging Spectro-Radiometer (MISR) instrument to derive statistical relationships between radiance from different viewing angles. These ADMs reduce the monthly regional biases to ±5 Wm−2 and the monthly-mean biases are reduced by up to 50%. These improved ADMs are used as part of the next edition of the CERES data.
Damiani, A.; Cordero, R. R.; Carrasco, J.; Watanabe, S.; Kawamiya, M.; Lagun, V. E.Damiani, A., R. R. Cordero, J. Carrasco, S. Watanabe, M. Kawamiya, V. E. Lagun, 2015: Changes in the UV Lambertian equivalent reflectivity in the Southern Ocean: Influence of sea ice and cloudiness. Remote Sensing of Environment, 169, 75-92. doi: 10.1016/j.rse.2015.07.030. Existing Lambertian equivalent reflectivity (LER) ultraviolet (UV) data for the west region of the Southern Ocean indicate a decreasing trend. Since the area surrounding Antarctica is largely unpolluted, LER changes can only be due to variations in the cloud cover and/or in the sea ice extension. In order to evaluate their influence on LER and assess the trend of the UV reflectivity under ice-free and various sea ice concentration (SIC) levels, we compared a multi-satellite-based LER dataset with different satellite observations of cloud cover and SIC for October to March from 1979 to 2012. Despite the high cloud fraction for most of this period, sea ice was found to be the main driver of LER variability and had a greater influence on LER variability than cloud cover. The cloud cover was lower in spring than in summer for all datasets, and this difference appears to be primarily associated with the sea ice extent. While an increment of the cloud fraction of 20% has been found to cause an increase in LER of up to 13 reflectivity units (RU) under ice-free conditions, this increase is halved under low SIC. In contrast, no significant changes in LER data were found under high SIC levels. The correlation between LER and SIC is evident when the latter is higher than approximately 30%. The best correlations (r) between LER and SIC were found for the Weddell Sea (r = 0.87), the Ross Sea (r = 0.85), and the Indian Ocean (r = 0.90) for November, and for the Bellingshausen/Amundsen Seas (r = 0.86) and the Pacific Ocean (r = 0.83) for February and October, respectively. In contrast, no correlation was found in the proximity of the coastlines of west Antarctica in October. Overall, an enhancement of SIC from 0% to 100% results in a LER increase of 44 RU. This value is larger than the corresponding sea ice-induced increase computed for the observed and modeled shortwave albedos at the top of the atmosphere (21 and 13 RU, respectively). The LER data distributions for different regions and months show a marked seasonal double peak in reflectivity. The highest relative frequency is driven by the sea ice and peaks at approximately 90 RU, whereas the secondary peak of approximately 50 RU is dominated by cloudiness. Negative trends in the UV reflectivity of the grid cells characterized by a SIC greater than 30% were found for the Bellingshausen/Amundsen Seas (up to − 3.6 ± 1.0 per decade in March). Trends computed over the entire Southern Ocean for mid/high SIC bins are mostly negative, although are often not statistically significant. However, the trend in the reflectivity of the ice-free grid cells was generally positive, probably due to changes in the cloud amount/opacity. albedo; sea ice; Southern Ocean; Lambertian equivalent reflectivity; Total cloud fraction
Daniels, J.L.; Smith, G.L.; Priestley, K.J.; Thomas, S.Daniels, J., G. Smith, K. Priestley, S. Thomas, 2015: Using Lunar Observations to Validate In-Flight Calibrations of Clouds and the Earth's Radiant Energy System Instruments. IEEE Transactions on Geoscience and Remote Sensing, 53(9), 5110-5116. doi: 10.1109/TGRS.2015.2417314. The validation of in-orbit instrument performance requires both stability in calibration source and also calibration corrections to compensate for instrument changes. Unlike internal calibrations, the Moon offers an external source whose signal variance is predictable and nondegrading. This paper describes a method of validation using lunar observations scanning near full moon by the Clouds and the Earth's Radiant Energy System (CERES) Flight Model (FM)-1 and FM-2 aboard the Terra satellite, FM-3 and FM-4 aboard the Aqua satellite, and, as of 2012, FM-5 aboard Suomi National Polar-orbiting Partnership. Given the stability of the source, adjustments within the data set are based entirely on removing orbital effects. Lunar observations were found to require a consistent data set spanning at least two to three years in length to examine instrument stability due to the final step when lunar libration effects are addressed. Initial results show a 20% annual variability in the data set. Using this method, however, results show trends per data channel of 1.0% per decade or less for FM-1 through FM-4. Results for FM-5 are not included in this paper because a sufficient data record has not yet been collected. calibration; clouds; Earth; earth radiation budget; Remote sensing; Satellites; atmospheric radiation; atmospheric techniques; Earth Observing System; Instruments; atmospheric measuring apparatus; radiometry; Detectors; validation; Aqua; Terra; Clouds and the Earth's Radiant Energy System (CERES); Orbits; Moon; Aqua satellite; CERES flight model; CERES instruments; AD 2012; calibration source; Clouds and the Earth Energy System; FM-1 satellite; FM-2 satellite; FM-3 satellite; FM-4 satellite; in-flight calibration; in-orbit instrument performance; in-orbit instrument performance validation; lunar libration; lunar measurements; lunar observations; signal variance; Suomi National Polar-orbiting Partnership; telescope
DeAngelis, Anthony M.; Qu, Xin; Zelinka, Mark D.; Hall, AlexDeAngelis, A. M., X. Qu, M. D. Zelinka, A. Hall, 2015: An observational radiative constraint on hydrologic cycle intensification. Nature, 528(7581), 249-253. doi: 10.1038/nature15770. Intensification of the hydrologic cycle is a key dimension of climate change, with substantial impacts on human and natural systems. A basic measure of hydrologic cycle intensification is the increase in global-mean precipitation per unit surface warming, which varies by a factor of three in current-generation climate models (about 1–3 per cent per kelvin). Part of the uncertainty may originate from atmosphere–radiation interactions. As the climate warms, increases in shortwave absorption from atmospheric moistening will suppress the precipitation increase. This occurs through a reduction of the latent heating increase required to maintain a balanced atmospheric energy budget. Using an ensemble of climate models, here we show that such models tend to underestimate the sensitivity of solar absorption to variations in atmospheric water vapour, leading to an underestimation in the shortwave absorption increase and an overestimation in the precipitation increase. This sensitivity also varies considerably among models due to differences in radiative transfer parameterizations, explaining a substantial portion of model spread in the precipitation response. Consequently, attaining accurate shortwave absorption responses through improvements to the radiative transfer schemes could reduce the spread in the predicted global precipitation increase per degree warming for the end of the twenty-first century by about 35 per cent, and reduce the estimated ensemble-mean increase in this quantity by almost 40 per cent. Climate and Earth system modelling; Projection and prediction
Deng, Min; Mace, Gerald. G.; Wang, Zhien; Berry, ElizabethDeng, M., G. G. Mace, Z. Wang, E. Berry, 2015: CloudSat 2C-ICE product update with a new Ze parameterization in lidar-only region. Journal of Geophysical Research: Atmospheres, 120(23), 12,198–12,208. doi: 10.1002/2015JD023600. The CloudSat 2C-ICE data product is derived from a synergetic ice cloud retrieval algorithm that takes as input a combination of CloudSat radar reflectivity (Ze) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation lidar attenuated backscatter profiles. The algorithm uses a variational method for retrieving profiles of visible extinction coefficient, ice water content, and ice particle effective radius in ice or mixed-phase clouds. Because of the nature of the measurements and to maintain consistency in the algorithm numerics, we choose to parameterize (with appropriately large specification of uncertainty) Ze and lidar attenuated backscatter in the regions of a cirrus layer where only the lidar provides data and where only the radar provides data, respectively. To improve the Ze parameterization in the lidar-only region, the relations among Ze, extinction, and temperature have been more thoroughly investigated using Atmospheric Radiation Measurement long-term millimeter cloud radar and Raman lidar measurements. This Ze parameterization provides a first-order estimation of Ze as a function extinction and temperature in the lidar-only regions of cirrus layers. The effects of this new parameterization have been evaluated for consistency using radiation closure methods where the radiative fluxes derived from retrieved cirrus profiles compare favorably with Clouds and the Earth's Radiant Energy System measurements. Results will be made publicly available for the entire CloudSat record (since 2006) in the most recent product release known as R05. 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; 3359 Radiative processes; CloudSat; 3360 Remote sensing; parameterization; 0319 Cloud optics; 2C-ICE; lidar only
Diaz, J. P.; González, A.; Expósito, F. J.; Pérez, J. C.; Fernández, J.; García-Díez, M.; Taima, D.Diaz, J. P., A. González, F. J. Expósito, J. C. Pérez, J. Fernández, M. García-Díez, D. Taima, 2015: WRF multi-physics simulation of clouds in the African region. Quarterly Journal of the Royal Meteorological Society, 141(692), 2737-2749. doi: 10.1002/qj.2560. The Weather Research and Forecasting (WRF) model has been used to simulate clouds, and their effects on precipitation and radiation, in Africa. The results have been compared with observational databases, mainly based on satellite measurements. The Cloud Feedback Model Intercomparison Project (CFMIP) Observation Simulator Package (COSP) has been used to consistently compare simulated clouds with satellite data, allowing us to evaluate not only the total cloud cover but also the cloud amount of different cloud types, classified according to their optical thickness and cloud-top pressure. Nine WRF simulations, for the 2002–2006 period, were carried out to evaluate the influence on cloud cover of different physical parametrizations and model configurations. In general, model simulations show similar results, underestimating total cloud cover in most of the studied region. In the tropical convective area, high clouds are underestimated, but the net effect on the radiation is partially compensated by the overestimation of cloud optical depth. Major differences appear over subtropical areas dominated by marine boundary-layer clouds, mainly off the coast of Namibia. In this area, simulations show too many thick clouds and too few clouds with lower optical thickness. The net result is an underestimation of low cloud cover. Also, the transition from stratocumulus to shallow cumulus away from the coast is not realistically modelled. MODIS; Cloud cover; ISCCP; Africa; WRF; COSP
Doelling, D.R.; Wu, A.; Xiong, X.; Scarino, B.R.; Bhatt, R.; Haney, C.O.; Morstad, D.; Gopalan, A.Doelling, D., A. Wu, X. Xiong, B. Scarino, R. Bhatt, C. Haney, D. Morstad, A. Gopalan, 2015: The Radiometric Stability and Scaling of Collection 6 Terra- and Aqua-MODIS VIS, NIR, and SWIR Spectral Bands. IEEE Transactions on Geoscience and Remote Sensing, 53(8), 4520-4535. doi: 10.1109/TGRS.2015.2400928. The Moderate Resolution Imaging Spectroradiometer (MODIS) Calibration Team has recently released the Collection 6 (C6) radiances, which offer broad improvements over Collection 5 (C5). The recharacterization of the solar diffuser, lunar measurements, and scan mirror angle corrections removed most of the visible channel calibration drifts. The visible band calibration stability was validated over the Libyan Desert, Dome-C, and deep convective cloud (DCC) invariant Earth targets, for wavelengths less than 1 . The lifetime stability of Terra and Aqua C6 is both within 1%, whereas the Terra C5 degradation exceeded 2% for most visible bands. The MODIS lifetime radiance trends over the invariant targets are mostly within 1%; however, the band-specific target fluctuations are inconsistent, which suggests that the stability limits of the invariant targets have been reached. Based on Terra- and Aqua-MODIS nearly simultaneous nadir overpass (NSNO) radiance comparisons, the Terra and Aqua C6 calibration shows agreement within 1.2%, whereas the C5 calibration exceeds 2%. Because the MODIS instruments are alike, the same NSNOs are used to radiometrically scale the Terra radiances to Aqua. For most visible bands, the Terra-scaled and Aqua C6 radiances are consistent to within 0.5% over Dome-C, DCC, and for geostationary visible imagers having similar spectral response functions, which are used as transfer radiometers. For bands greater than 1 , only minor calibration adjustments were made, and the C6 calibration is stable within 1% based on Libya-4. calibration; Earth; MODIS; Moderate Resolution Imaging Spectroradiometer (MODIS); intercalibration; Degradation; Market research; pseudoinvariant calibration sites (PICS); radiometric scaling; Standards
Doelling, David R.; Khlopenkov, Konstantin V.; Okuyama, Arata; Haney, Conor O.; Gopalan, Arun; Scarino, Benjamin R.; Nordeen, Michele; Bhatt, Rajandra; Avey, LanceDoelling, D. R., K. V. Khlopenkov, A. Okuyama, C. O. Haney, A. Gopalan, B. R. Scarino, M. Nordeen, R. Bhatt, L. Avey, 2015: MTSAT-1R Visible Imager Point Spread Correction Function, Part I: The Need for, Validation of, and Calibration With. IEEE Transactions on Geoscience and Remote Sensing, 53(3), 1513-1526. doi: 10.1109/TGRS.2014.2344678.
Dong, Xiquan; Schwantes, Adam C.; Xi, Baike; Wu, PengDong, X., A. C. Schwantes, B. Xi, P. Wu, 2015: Investigation of the marine boundary layer cloud and CCN properties under coupled and decoupled conditions over the Azores. Journal of Geophysical Research: Atmospheres, 120(12), 6179–6191. doi: 10.1002/2014JD022939. Six coupled and decoupled marine boundary layer (MBL) clouds were chosen from the 19 month Atmospheric Radiation Measurement Mobile Facility data set over the Azores. Thresholds of liquid water potential temperature difference ΔθL 0.5 K) and total water mixing ratio difference Δqt 0.5 g/kg) below the cloud base were used for selecting the coupled (decoupled) cases. A schematic diagram was given to demonstrate the coupled and decoupled MBL vertical structures and how they associate with nondrizzle, virga, and rain drizzle events. Out of a total of 2676 5 min samples, 34.5% were classified as coupled and 65.5% as decoupled, 36.2% as nondrizzle and 63.8% as drizzle (47.7% as virga and 16.1% as rain), and 33.4% as daytime and 66.6% as nighttime. The decoupled cloud layer is deeper (0.406 km) than coupled cloud layer (0.304 km), and its liquid water path and cloud droplet effective radius (re) values (122.1 gm−2 and 13.0 µm) are higher than coupled ones (83.7 gm−2 and 10.4 µm). Conversely, decoupled stratocumuli have lower cloud droplet number concentration (Nd) and surface cloud condensation nucleus (CCN) concentration (NCCN) (74.5 cm−3 and 150.9 cm−3) than coupled stratocumuli (111.7 cm−3 and 216.4 cm−3). The linear regressions between re and Nd with NCCN have demonstrated that coupled re and Nd strongly depend on NCCN and have higher correlations (−0.56 and 0.59) with NCCN than decoupled results (−0.14 and 0.25). The MBL cloud properties under nondrizzle and virga drizzle conditions are similar to each other but significantly different to those of rain drizzle. 0320 Cloud physics and chemistry; 3311 Clouds and aerosols; 3360 Remote sensing; 3354 Precipitation; 3307 Boundary layer processes; Cloud microphysical properties; Marine boundary layer clouds; CCN; coupled and decoupled boundary layers; drizzle and nondrizzle
English, Jason M.; Gettelman, Andrew; Henderson, Gina R.English, J. M., A. Gettelman, G. R. Henderson, 2015: Arctic Radiative Fluxes: Present-Day Biases and Future Projections in CMIP5 Models. J. Climate, 28(15), 6019-6038. doi: 10.1175/JCLI-D-14-00801.1. AbstractRadiative fluxes are critical for understanding the energy budget of the Arctic region, where the climate has been changing rapidly and is projected to continue to change. This work investigates causes of present-day biases and future projections of top-of-atmosphere (TOA) Arctic radiative fluxes in phase 5 of the Coupled Model Intercomparison Project (CMIP5). Compared to Clouds and the Earth’s Radiant Energy System Energy Balanced and Filled (CERES-EBAF), CMIP5 net TOA downward shortwave (SW) flux biases are larger than outgoing longwave radiation (OLR) biases. The primary contributions to modeled TOA SW flux biases are biases in cloud amount and snow cover extent compared to the GCM-Oriented CALIPSO Cloud Product (CALIPSO-GOCCP) and the newly developed Making Earth System Data Records for Use in Research Environments (MEaSUREs) dataset, respectively (with most models predicting insufficient cloud amount and snow cover in the Arctic), and biases with sea ice albedo. Future projections (2081–90) with representative concentration pathway 8.5 (RCP8.5) simulations suggest increasing net TOA downward SW fluxes (+8 W m−2) over the Arctic basin due to a decrease of surface albedo from melting snow and ice, and increasing OLR (+6 W m−2) due to an increase in surface temperatures. The largest contribution to future Arctic net TOA downward SW flux increases is declining sea ice area, followed by declining snow cover area on land, reductions to sea ice albedo, and reductions to snow albedo on land. Cloud amount is not projected to change significantly. These results suggest the importance of accurately representing both the surface area and albedos of sea ice and snow cover as well as cloud amount in order to accurately represent TOA radiative fluxes for the present-day climate and future projections. Radiative fluxes; Model evaluation/performance; Shortwave radiation; Snow cover; climate models; Arctic
Engström, A.; Bender, F. a.-M.; Charlson, R. J.; Wood, R.Engström, A., F. a. Bender, R. J. Charlson, R. Wood, 2015: The nonlinear relationship between albedo and cloud fraction on near-global, monthly mean scale in observations and in the CMIP5 model ensemble. Geophysical Research Letters, 42(21), 9571–9578. doi: 10.1002/2015GL066275. We study the relation between monthly mean albedo and cloud fraction over ocean, 60°S–60°N. Satellite observations indicate that these clouds all fall on the same near-exponential curve, with a monotonic distribution over the ranges of cloud fractions and albedo. Using these observational data as a reference, we examine the degree to which 26 climate models capture this feature of the near-global marine cloud population. Models show a general increase in albedo with increasing cloud fraction, but none of them display a relation that is as well defined as that characterizing the observations. Models typically display larger albedo variability at a given cloud fraction, larger sensitivity in albedo to changes in cloud fraction, and lower cloud fractions. Several models also show branched distributions, contrasting with the smooth observational relation. In the models the present-day cloud scenes are more reflective than the preindustrial, demonstrating the simulated impact of anthropogenic aerosols on planetary albedo. 1610 Atmosphere; albedo; 3311 Clouds and aerosols; cloud fraction; 3337 Global climate models; 3310 Clouds and cloud feedbacks; CMIP5; 1627 Coupled models of the climate system
Engström, Anders; Bender, Frida A.-M.; Charlson, Robert J.; Wood, RobertEngström, A., F. A. Bender, R. J. Charlson, R. Wood, 2015: Geographically coherent patterns of albedo enhancement and suppression associated with aerosol sources and sinks. Tellus B, 67, 26442. doi: 10.3402/tellusb.v67.26442.
Eswaran, K.; Satheesh, S. K.; Srinivasan, J.Eswaran, K., S. K. Satheesh, J. Srinivasan, 2015: Dependence of ‘critical cloud fraction’ on aerosol composition. Atmospheric Science Letters, 16(3), 380-385. doi: 10.1002/asl2.571. Recent studies, over regions influenced by biomass burning aerosol, have shown that it is possible to define a ‘critical cloud fraction’ (CCF) at which the aerosol direct radiative forcing switch from a cooling to a warming effect. Using 4 years of multi-satellite data analysis, we show that CCF varies with aerosol composition and changed from 0.28 to 0.13 from postmonsoon to winter as a result of shift from less absorbing to moderately absorbing aerosol. Our results indicate that we can estimate aerosol absorption from space using independently measured top of the atmosphere (TOA) fluxes [Cloud Aerosol Lidar with Orthogonal Polarization-Moderate resolution Imaging Spectroradiometer-Clouds and the Earth's Radiant Energy System (CALIPSO-MODIS-CERES)] combined algorithms for example. Remote sensing; aerosols
Farmer, G. ThomasFarmer, G. T., 2015: Status of Climate Change Research. Modern Climate Change Science, 43-99. This chapter contains an overview of research in climate change science. Research ongoing and recent publications concerning each topic in Chap. 1. Topics of climate change research, such as temperature change on land and sea, impacts of climate change on glacial ice, the extent of permafrost and its carbon content, research into the carbon cycle, ocean acidification and circulation, and General Circulation Climate Models (GCMs) as well as the biology affected by climate change are discussed with references given. atmosphere; CERES; climate change; NASA; albedo; sea ice; MODIS; Terra; ENSO; GRACE; Tibetan Plateau; CMIP5; Antarctica; Earth Sciences, general; Greenland; Stratosphere; NCDC; Argo; 0.9 °C; 12C; 13C; 14C; Anthropocene; Arrhenius; Atlantic; BEST; Biological; Carbon; Carbon cycle; Chemistry/Food Science, general; Climate, general; Cryosphere; David Archer; Education (general); Eemian; Energy, general; Fast carbon; Fourier; GHCN; GtC; GTNP; Holocene; Homo sapiens; ICOADS; ICOS; Indian; John Cook; La Jolla; La Niña; Larsen B; LGM; Microwave sounding units; Moraine; MSUs; NOAA; NSF; Pacific; PDO; Permafrost; Petagram; PETM; Pleistocene; Pliocene; Sangamonian; Scripps; Slow carbon; Solubility; Solubility pumps; Tyndall; Virkisjökull; Weart; www.skepticalscience.com
Fasullo, J. T.; Sanderson, B. M.; Trenberth, K. E.Fasullo, J. T., B. M. Sanderson, K. E. Trenberth, 2015: Recent Progress in Constraining Climate Sensitivity With Model Ensembles. Current Climate Change Reports, 1(4), 268-275. doi: 10.1007/s40641-015-0021-7. Recently available model ensembles have created an unprecedented opportunity for exploring and narrowing uncertainty in one of climate’s benchmark indices, equilibrium climate sensitivity. A range of novel approaches for constraining the raw sensitivity estimates from these ensembles with observations has also been proposed, applied, and explored in a diversity of contexts. Through subsequent analysis, an increased understanding of the relative merits and limitations of these methods has been gained and their refinement and optimal implementation continue to be actively studied and debated with the hopes of reducing uncertainty in one of climate science’s most persistent and elusive measures. climate change; Climatology; climate models; Climate sensitivity; Atmospheric Sciences; Climate Change Management and Policy; Oceanography; Earth system models; Emergent constraints; Perturbed physics ensembles
Feng, Nan; Christopher, Sundar A.Feng, N., S. A. Christopher, 2015: Measurement-based estimates of direct radiative effects of absorbing aerosols above clouds. Journal of Geophysical Research: Atmospheres, 120(14), 6908–6921. doi: 10.1002/2015JD023252. The elevated layers of absorbing smoke aerosols from western African (e.g., Gabon and Congo) biomass burning activities have been frequently observed above low-level stratocumulus clouds off the African coast, which presents an excellent natural laboratory for studying the effects of aerosols above clouds (AAC) on regional energy balance in tropical and subtropical environments. Using spatially and temporally collocated Moderate Resolution Imaging Spectroradiometer, Ozone Monitoring Instrument (OMI), and Clouds and the Earth's Radiant Energy System data sets, the top-of-atmosphere shortwave aerosol direct shortwave radiative effects (ARE) of absorbing aerosols above low-level water clouds in the southeast Atlantic Ocean was examined in this study. The regional averaged instantaneous ARE has been estimated to be 36.7 ± 20.5 Wm−2 (regional mean ± standard deviation) along with a mean positive OMI Aerosol Index at 1.3 in August 2006 based on multisensors measurements. The highest magnitude of instantaneous ARE can even reach 138.2 Wm−2. We assess that the 660 nm cloud optical depth (COD) values of 8–12 is the critical value above (below) which aerosol absorption (scattering) effect dominates and further produces positive (negative) ARE values. The results further show that ARE values are more sensitive to aerosols above lower COD values than cases for higher COD values. This is among the first studies to provide quantitative estimates of shortwave ARE due to AAC events from an observational perspective. Remote sensing; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; 3359 Radiative processes; 3355 Regional modeling; Absorbing Aerosol above Clouds; radiative effect
García-Díez, Markel; Fernández, Jesús; Vautard, RobertGarcía-Díez, M., J. Fernández, R. Vautard, 2015: An RCM multi-physics ensemble over Europe: multi-variable evaluation to avoid error compensation. Climate Dynamics, 45(11-12), 3141-3156. doi: 10.1007/s00382-015-2529-x. Regional Climate Models are widely used tools to add detail to the coarse resolution of global simulations. However, these are known to be affected by biases. Usually, published model evaluations use a reduced number of variables, frequently precipitation and temperature. Due to the complexity of the models, this may not be enough to assess their physical realism (e.g. to enable a fair comparison when weighting ensemble members). Furthermore, looking at only a few variables makes difficult to trace model errors. Thus, in many previous studies, these biases are described but their underlying causes and mechanisms are often left unknown. In this work the ability of a multi-physics ensemble in reproducing the observed climatologies of many variables over Europe is analysed. These are temperature, precipitation, cloud cover, radiative fluxes and total soil moisture content. It is found that, during winter, the model suffers a significant cold bias over snow covered regions. This is shown to be related with a poor representation of the snow-atmosphere interaction, and is amplified by an albedo feedback. It is shown how two members of the ensemble are able to alleviate this bias, but by generating a too large cloud cover. During summer, a large sensitivity to the cumulus parameterization is found, related to large differences in the cloud cover and short wave radiation flux. Results also show that small errors in one variable are sometimes a result of error compensation, so the high dimensionality of the model evaluation problem cannot be disregarded. CERES; Climatology; radiation; Oceanography; Geophysics/Geodesy; WRF; model evaluation; CORDEX; E-OBS; EURO-CORDEX; GLDAS; Multi-physics; Soil moisture
Geil, Kerrie L.; Zeng, XubinGeil, K. L., X. Zeng, 2015: Quantitative characterization of spurious numerical oscillations in 48 CMIP5 models. Geophysical Research Letters, 42(12), 5066–5073. doi: 10.1002/2015GL063931. Spurious numerical oscillations (SNOs) (e.g., Gibbs oscillations) can appear as unrealistic spatial waves near discontinuities or sharp gradients in global model fields (e.g., orography) and have been a known problem in global models for decades. Multiple methods of oscillation reduction exist; consequently, the oscillations are presumed small in modern climate models and hence are rarely addressed in recent literature. Here we use two metrics to quantify SNOs in 13 variables from 48 Coupled Model Intercomparison Project Phase 5 models along a Pacific ocean transect near the Andes. Results show that 48% of nonspectral models and 95% of spectral models have at least one variable with SNO amplitude as large as, or greater than, atmospheric interannual variability. The impact of SNOs on climate simulations should be thoroughly evaluated and further efforts to substantially reduce SNOs in climate models are urgently needed. 3337 Global climate models; 1622 Earth system modeling; model evaluation; 3336 Numerical approximations and analyses; 3275 Uncertainty quantification; Uncertainty Quantification; Global climate models; numerical approximation
Gettelman, A.; Morrison, H.; Santos, S.; Bogenschutz, P.; Caldwell, P. M.Gettelman, A., H. Morrison, S. Santos, P. Bogenschutz, P. M. Caldwell, 2015: Advanced Two-Moment Bulk Microphysics for Global Models. Part II: Global Model Solutions and Aerosol–Cloud Interactions. J. Climate, 28(3), 1288-1307. doi: 10.1175/JCLI-D-14-00103.1. AbstractA modified microphysics scheme is implemented in the Community Atmosphere Model, version 5 (CAM5). The new scheme features prognostic precipitation. The coupling between the microphysics and the rest of the model is modified to make it more flexible. Single-column tests show the new microphysics can simulate a constrained drizzling stratocumulus case. Substepping the cloud condensation (macrophysics) within a time step improves single-column results. Simulations of mixed-phase cases are strongly sensitive to ice nucleation. The new microphysics alters process rates in both single-column and global simulations, even at low (200 km) horizontal resolution. Thus, prognostic precipitation can be important, even in low-resolution simulations where advection of precipitation is not important. Accretion dominates as liquid water path increases in agreement with cloud-resolving model simulations and estimates from observations. The new microphysics with prognostic precipitation increases the ratio of accretion over autoconversion. The change in process rates appears to significantly reduce aerosol–cloud interactions and indirect radiative effects of anthropogenic aerosols by up to 33% (depending on substepping) to below 1 W m−2 of cooling between simulations with preindustrial (1850) and present-day (2000) aerosol emissions. aerosols; Cloud microphysics; climate models; Cloud parameterizations; Cloud radiative effects
Grise, Kevin M.; Polvani, Lorenzo M.; Fasullo, John T.Grise, K. M., L. M. Polvani, J. T. Fasullo, 2015: Reexamining the Relationship between Climate Sensitivity and the Southern Hemisphere Radiation Budget in CMIP Models. J. Climate, 28(23), 9298-9312. doi: 10.1175/JCLI-D-15-0031.1. Recent efforts to narrow the spread in equilibrium climate sensitivity (ECS) across global climate models have focused on identifying observationally based constraints, which are rooted in empirical correlations between ECS and biases in the models’ present-day climate. This study reexamines one such constraint identified from CMIP3 models: the linkage between ECS and net top-of-the-atmosphere radiation biases in the Southern Hemisphere (SH).As previously documented, the intermodel spread in the ECS of CMIP3 models is linked to present-day cloud and net radiation biases over the midlatitude Southern Ocean, where higher cloud fraction in the present-day climate is associated with larger values of ECS. However, in this study, no physical explanation is found to support this relationship. Furthermore, it is shown here that this relationship disappears in CMIP5 models and is unique to a subset of CMIP models characterized by unrealistically bright present-day clouds in the SH subtropics. In view of this evidence, Southern Ocean cloud and net radiation biases appear inappropriate for providing observationally based constraints on ECS.Instead of the Southern Ocean, this study points to the stratocumulus-to-cumulus transition regions of the SH subtropical oceans as key to explaining the intermodel spread in the ECS of both CMIP3 and CMIP5 models. In these regions, ECS is linked to present-day cloud and net radiation biases with a plausible physical mechanism: models with brighter subtropical clouds in the present-day climate show greater ECS because 1) subtropical clouds dissipate with increasing CO2 concentrations in many models and 2) the dissipation of brighter clouds contributes to greater solar warming of the surface. Radiation budgets; climate models; Climate sensitivity; Models and modeling; Physical Meteorology and Climatology; Southern Ocean; Geographic location/entity; Southern Hemisphere
Guillod, Benoit P.; Orlowsky, Boris; Miralles, Diego G.; Teuling, Adriaan J.; Seneviratne, Sonia I.Guillod, B. P., B. Orlowsky, D. G. Miralles, A. J. Teuling, S. I. Seneviratne, 2015: Reconciling spatial and temporal soil moisture effects on afternoon rainfall. Nature Communications, 6. doi: 10.1038/ncomms7443. Soil moisture impacts on precipitation have been strongly debated. Recent observational evidence of afternoon rain falling preferentially over land parcels that are drier than the surrounding areas (negative spatial effect), contrasts with previous reports of a predominant positive temporal effect. However, whether spatial effects relating to soil moisture heterogeneity translate into similar temporal effects remains unknown. Here we show that afternoon precipitation events tend to occur during wet and heterogeneous soil moisture conditions, while being located over comparatively drier patches. Using remote-sensing data and a common analysis framework, spatial and temporal correlations with opposite signs are shown to coexist within the same region and data set. Positive temporal coupling might enhance precipitation persistence, while negative spatial coupling tends to regionally homogenize land surface conditions. Although the apparent positive temporal coupling does not necessarily imply a causal relationship, these results reconcile the notions of moisture recycling with local, spatially negative feedbacks. Atmospheric science; Climate science; Earth sciences
Guo, H.; Golaz, J.-C.; Donner, L. J.; Wyman, B.; Zhao, M.; Ginoux, P.Guo, H., J. Golaz, L. J. Donner, B. Wyman, M. Zhao, P. Ginoux, 2015: CLUBB as a unified cloud parameterization: Opportunities and challenges. Geophysical Research Letters, 42(11), 4540–4547. doi: 10.1002/2015GL063672. CLUBB (Cloud Layers Unified by Binormals) is a higher-order closure (HOC) method with an assumed joint probability density function (PDF) for the subgrid variations in vertical velocity, temperature, and moisture. CLUBB has been implemented in the atmospheric component (AM3) of the Geophysical Fluid Dynamics Laboratory general circulation model AM3-CLUBB and successfully unifies the treatment of shallow convection, resolved clouds, and planetary boundary layer (PBL). In this study, we further explore the possibility for CLUBB to unify the deep convection in a new configuration referred as AM3-CLUBB+. AM3-CLUBB+ simulations with prescribed sea surface temperature are discussed. Cloud, radiation, and precipitation fields compare favorably with observations and reanalyses. AM3-CLUBB+ successfully captures the transition from stratocumulus to deep convection and the modulated response of liquid water path to aerosols. Simulations of tropical variability and the Madden-Julian oscillation (MJO) are also improved. Deficiencies include excessive tropical water vapor and insufficient ice clouds in the midlatitudes. 3337 Global climate models; 3365 Subgrid-scale (SGS) parameterization; CLUBB; unified parameterization
Guo, Zhun; Wang, Minghuai; Qian, Yun; Larson, Vincent E.; Ghan, Steven; Ovchinnikov, Mikhail; A. Bogenschutz, Peter; Gettelman, Andrew; Zhou, TianjunGuo, Z., M. Wang, Y. Qian, V. E. Larson, S. Ghan, M. Ovchinnikov, P. A. Bogenschutz, A. Gettelman, T. Zhou, 2015: Parametric behaviors of CLUBB in simulations of low clouds in the Community Atmosphere Model (CAM). Journal of Advances in Modeling Earth Systems, 7(3), 1005–1025. doi: 10.1002/2014MS000405. In this study, we investigate the sensitivity of simulated low clouds to 14 selected tunable parameters of Cloud Layers Unified By Binormals (CLUBB), a higher-order closure (HOC) scheme, and four parameters of the Zhang-McFarlane (ZM) deep convection scheme in the Community Atmosphere Model version 5 (CAM5). A Quasi-Monte Carlo (QMC) sampling approach is adopted to effectively explore the high-dimensional parameter space and a generalized linear model is applied to study the responses of simulated cloud fields to tunable parameters. Our results show that the variance in simulated low-cloud properties (cloud fraction and liquid water path) can be explained by the selected tunable parameters in two different ways: macrophysics itself and its interaction with microphysics. First, the parameters related to dynamic and thermodynamic turbulent structure and double Gaussian closure are found to be the most influential parameters for simulating low clouds. The spatial distributions of the parameter contributions show clear cloud-regime dependence. Second, because of the coupling between cloud macrophysics and cloud microphysics, the coefficient of the dissipation term in the total water variance equation is influential. This parameter affects the variance of in-cloud cloud water, which further influences microphysical process rates, such as autoconversion, and eventually low-cloud fraction. This study improves understanding of HOC behavior associated with parameter uncertainties and provides valuable insights for the interaction of macrophysics and microphysics. 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; 3310 Clouds and cloud feedbacks; shallow convection; 3336 Numerical approximations and analyses; stratocumulus; CLUBB; higher-order closure
Ham, Seung-Hee; Kato, Seiji; Barker, Howard W.; Rose, Fred G.; Sun-Mack, SunnyHam, S., S. Kato, H. W. Barker, F. G. Rose, S. Sun-Mack, 2015: Improving the modelling of short-wave radiation through the use of a 3D scene construction algorithm. Quarterly Journal of the Royal Meteorological Society, 141(690), 1870-1883. doi: 10.1002/qj.2491. Active satellite sensors, such as Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and CloudSat, provide cloud properties that are not available from passive sensors, such as MODerate-resolution Imaging Spectroradiometer (MODIS). While active sensors provide vertical profiles of clouds, their spatial coverage is limited to their narrow, nadir ground-track. As a result, estimation of radiation by combining active sensors and broadband instrument has limitations due to their different spatial coverages. This study uses a scene construction algorithm (SCA) and MODIS data to extend two-dimensional (2D) nadir cloud profiles into the cross-track direction, and examines how the resulting constructed 3D cloud fields improve simulation of solar radiative transfer. Clouds and the Earth's Radiant Energy System (CERES) radiances are used as references to assess the improvements. While use of constructed 3D cloud fields only slightly impacts mean-bias errors for instantaneous 20 km CERES footprint-averaged top-of-atmosphere (TOA) radiances, reductions in random errors are about 40%. The largest improvements in TOA radiance simulation are for clouds with small-scale horizontal inhomogeneity such as stratocumulus and cumulus. In contrast, uniform clouds such as nimbostratus, and deep convective clouds (Dc) show little response to the SCA. The impact of using the SCA on instantaneous surface irradiances is significant for stratocumulus and cumulus, but weak for nimbostratus and Dc. Conversely, SCA significantly influences atmospheric absorption and heating rates for nimbostratus and Dc. Differences in TOA radiances simulated by 1D and 3D transfer models are smaller than differences due to use of only the 2D nadir cross-sections and the 3D constructed fields. This is because of smoothing of 3D radiative effects when averaged up to CERES footprints. For surface irradiance and atmospheric absorption, however, differences simulated by 1D and 3D transfer models are more comparable to differences that stem from use of 2D and 3D cloud information. CERES; CloudSat; CALIPSO; independent column approximation (ICA); scene construction algorithm (SCA); three-dimensional (3D) radiative transfer
Harikishan, G.; Padmakumari, B.; Maheskumar, R. S.; Kulkarni, J. R.Harikishan, G., B. Padmakumari, R. S. Maheskumar, J. R. Kulkarni, 2015: Radiative effect of dust aerosols on cloud microphysics and meso-scale dynamics during monsoon breaks over Arabian sea. Atmospheric Environment, 105, 22-31. doi: 10.1016/j.atmosenv.2015.01.037. During monsoon breaks (large scale rainfall below the long term normal), dry air laddened with dust aerosols intrude over central India through Arabian sea (AS) from West Asian desert regions. To understand the effect of these dust aerosols on marine clouds over AS during monsoon breaks, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and Cloud and the Earth's Radiant Energy System (CERES) data have been analyzed for the period 2007 to 2013. The vertical profile of dust backscatter coefficient (DBS) showed an elevated layer between 2 and 5 km and the maximum heating rate observed is 9 K/Day which is higher by 3 K/day as compared to the heating observed in June to September (JJAS) mean. Semi-direct effect due to the interaction of the long range transported dust with pristine cloud environment is observed in both warm and cold clouds. Significant differences in shortwave and longwave fluxes at the top of the atmosphere (TOA), cloud micro and macrophysical parameters are observed between the clouds with and without dust. Also, the percentage differences are more in cold clouds as compared to warm clouds. Dust induced semi-direct effect is found to be more pronounced in cold clouds, while indirect effect in warm clouds. Zonal anomalies of dynamical parameters due to dust induced heating, affect the circulation patterns in the immediate meso-scale environment, which strengthen/extend the monsoon break situation. dust aerosol; radiative heating; cloud micro and macrophysics; monsoon breaks; semi-direct effect
Harrop, Bryce E.; Hartmann, Dennis L.Harrop, B. E., D. L. Hartmann, 2015: The Relationship between Atmospheric Convective Radiative Effect and Net Energy Transport in the Tropical Warm Pool. J. Climate, 28(21), 8620-8633. doi: 10.1175/JCLI-D-15-0151.1. Reanalysis data and radiation budget data are used to calculate the role of the atmospheric cloud radiative effect in determining the magnitude of horizontal export of energy by the tropical atmosphere. Because tropical high clouds result in net radiative heating of the atmosphere, they increase the requirement for the atmosphere to export energy from convective regions. Increases in upper-tropospheric water vapor associated with convection contribute about a fifth of the atmospheric radiative heating anomaly associated with convection. Over the warmest tropical oceans, the radiative effect of convective clouds and associated water vapor is roughly two-thirds the value of the atmospheric energy transport. Cloud radiative heating and atmospheric heat transport increase at the same rate with increasing sea surface temperature, suggesting that the increased energy export is supplied by the radiative heating associated with convective clouds. The net cloud radiative effect at the top of the atmosphere is insensitive to changes in SST over the warm pool. Principal component analysis of satellite-retrieved cloud data reveals that the insensitivity of the net cloud radiative effect to SST is the result of changes in cloud amount offsetting changes in cloud optical thickness and cloud-top height. While increasing upward motion makes the cloud radiative effect more negative, that decrease is offset by reductions in outgoing longwave radiation owing to increases in water vapor. clouds; water vapor; Cloud radiative effects; Physical Meteorology and Climatology; Energy transport; Atm/Ocean Structure/ Phenomena; Heat budgets/fluxes; Circulation/ Dynamics; Warm pool
He, Bian; Wu, Guoxiong; Liu, Yimin; Bao, QingHe, B., G. Wu, Y. Liu, Q. Bao, 2015: Astronomical and Hydrological Perspective of Mountain Impacts on the Asian Summer Monsoon. Scientific Reports, 5, 17586. doi: 10.1038/srep17586. The Asian summer monsoon has great socioeconomic impacts. Understanding how the huge Tibetan and Iranian Plateaus affect the Asian summer monsoon is of great scientific value and has far-reaching significance for sustainable global development.
He, Jian; Zhang, Yang; Glotfelty, Tim; He, Ruoying; Bennartz, Ralf; Rausch, John; Sartelet, KarineHe, J., Y. Zhang, T. Glotfelty, R. He, R. Bennartz, J. Rausch, K. Sartelet, 2015: Decadal simulation and comprehensive evaluation of CESM/CAM5.1 with advanced chemistry, aerosol microphysics, and aerosol-cloud interactions. Journal of Advances in Modeling Earth Systems, 7(1), 110-141. doi: 10.1002/2014MS000360. Earth system models have been used for climate predictions in recent years due to their capabilities to include biogeochemical cycles, human impacts, as well as coupled and interactive representations of Earth system components (e.g., atmosphere, ocean, land, and sea ice). In this work, the Community Earth System Model (CESM) with advanced chemistry and aerosol treatments, referred to as CESM-NCSU, is applied for decadal (2001–2010) global climate predictions. A comprehensive evaluation is performed focusing on the atmospheric component—the Community Atmosphere Model version 5.1 (CAM5.1) by comparing simulation results with observations/reanalysis data and CESM ensemble simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5). The improved model can predict most meteorological and radiative variables relatively well with normalized mean biases (NMBs) of −14.1 to −9.7% and 0.7–10.8%, respectively, although temperature at 2 m (T2) is slightly underpredicted. Cloud variables such as cloud fraction (CF) and precipitating water vapor (PWV) are well predicted, with NMBs of −10.5 to 0.4%, whereas cloud condensation nuclei (CCN), cloud liquid water path (LWP), and cloud optical thickness (COT) are moderately-to-largely underpredicted, with NMBs of −82.2 to −31.2%, and cloud droplet number concentration (CDNC) is overpredictd by 26.7%. These biases indicate the limitations and uncertainties associated with cloud microphysics (e.g., resolved clouds and subgrid-scale cumulus clouds). Chemical concentrations over the continental U.S. (CONUS) (e.g., SO42−, Cl−, OC, and PM2.5) are reasonably well predicted with NMBs of −12.8 to −1.18%. Concentrations of SO2, SO42−, and PM10 are also reasonably well predicted over Europe with NMBs of −20.8 to −5.2%, so are predictions of SO2 concentrations over the East Asia with an NMB of −18.2%, and the tropospheric ozone residual (TOR) over the globe with an NMB of −3.5%. Most meteorological and radiative variables predicted by CESM-NCSU agree well overall with those predicted by CESM-CMIP5. The performance of LWP and AOD predicted by CESM-NCSU is better than that of CESM-CMIP5 in terms of model bias and correlation coefficients. Large biases for some chemical predictions can be attributed to uncertainties in the emissions of precursor gases (e.g., SO2, NH3, and NOx) and primary aerosols (black carbon and primary organic matter) as well as uncertainties in formulations of some model components (e.g., online dust and sea-salt emissions, secondary organic aerosol formation, and cloud microphysics). Comparisons of CESM simulation with baseline emissions and 20% of anthropogenic emissions from the baseline emissions indicate that anthropogenic gas and aerosol species can decrease downwelling shortwave radiation (FSDS) by 4.7 W m−2 (or by 2.9%) and increase SWCF by 3.2 W m−2 (or by 3.1%) in the global mean. 0305 Aerosols and particles; 0365 Troposphere: composition and chemistry; 1622 Earth system modeling; aerosol-cloud interactions; atmospheric chemistry; aerosol microphysics; CESM/CAM5.1; decadal application and evaluation
He, Tao; Liang, Shunlin; Wang, Dongdong; Shi, Qinqing; Goulden, Michael L.He, T., S. Liang, D. Wang, Q. Shi, M. L. Goulden, 2015: Estimation of high-resolution land surface net shortwave radiation from AVIRIS data: Algorithm development and preliminary results. Remote Sensing of Environment, 167, 20-30. doi: 10.1016/j.rse.2015.03.021. Hyperspectral remote sensing provides unique and abundant spectral information for quantification of the land surface shortwave radiation budget, which can be used to calibrate climate models and to estimate surface energy budget for monitoring agriculture and urban environment. However, only single broadband or multispectral data have been used in previous studies. In the present study, two methods are proposed to estimate the instantaneous land surface net shortwave radiation (NSR) with high spatial resolutions using hyperspectral remote sensing observations from the Airborne Visible Infrared Imaging Spectrometer (AVIRIS) data. Method A calculates the NSR based on separate estimation of downward radiation and surface broadband albedo, which requires ancillary information for aerosol optical depth; and Method B directly estimates the NSR from the observed radiance. Results based on radiative transfer simulations showed that the use of hyperspectral data can significantly improve NSR estimation compared with the multispectral data method. Atmospheric water vapor correction was applied to adjust the surface radiation estimation. Validation of AVIRIS NSR estimates against ground measurements from two flux networks for the period of 2006–2014 showed that the two methods were similar and had consistent accuracy in the all-sky instantaneous NSR estimation with root-mean-square-errors (RMSEs) of approximately 28–56 W/m2. The pixel-based water vapor content estimation from AVIRIS data provided slightly different results than those obtained using coarse resolution remote sensing data. A simplified topographic correction algorithm was found to be able to improve the results generated from Method A; however, the degree of improvement provided by Method B was unclear, possibly because of the lack of consideration of horizontal atmospheric scattering effects from adjacent pixels. In general, hyperspectral remote sensing data have been shown to improve the NSR estimation accuracies compared with results obtained in previous studies. Additional efforts are needed to refine the NSR estimation for application to future satellite hyperspectral data. surface albedo; downward shortwave radiation; Direct estimation; HyspIRI; AVIRIS; Hyperspectral; Net shortwave radiation
Hill, P. G.; Morcrette, C. J.; Boutle, I. A.Hill, P. G., C. J. Morcrette, I. A. Boutle, 2015: A regime-dependent parametrization of subgrid-scale cloud water content variability. Quarterly Journal of the Royal Meteorological Society, 141(691), 1975-1986. doi: 10.1002/qj.2506. The subgrid-scale spatial variability in cloud water content can be described by a parameter f called the fractional standard deviation. This is equal to the standard deviation of the cloud water content divided by the mean. This parameter is an input to schemes that calculate the impact of subgrid-scale cloud inhomogeneity on gridbox-mean radiative fluxes and microphysical process rates. A new regime-dependent parametrization of the spatial variability of cloud water content is derived from CloudSat observations of ice clouds. In addition to the dependencies on horizontal and vertical resolution and cloud fraction included in previous parametrizations, the new parametrization includes an explicit dependence on cloud type. The new parametrization is then implemented in the Global Atmosphere 6 (GA6) configuration of the Met Office Unified Model and used to model the effects of subgrid variability of both ice and liquid water content on radiative fluxes and autoconversion and accretion rates in three 20-year atmosphere-only climate simulations. These simulations show the impact of the new regime-dependent parametrization on diagnostic radiation calculations, interactive radiation calculations and both interactive radiation calculations and in a new warm microphysics scheme. The control simulation uses a globally constant f value of 0.75 to model the effect of cloud water content variability on radiative fluxes. The use of the new regime-dependent parametrization in the model results in a global mean which is higher than the control's fixed value and a global distribution of f which is closer to CloudSat observations. When the new regime-dependent parametrization is used in radiative transfer calculations only, the magnitudes of short-wave and long-wave top of atmosphere cloud radiative forcing are reduced, increasing the existing global mean biases in the control. When also applied in a new warm microphysics scheme, the short-wave global mean bias is reduced. radiation; climate model development; cloud heterogeneity
Hinkelman, Laura M.; Lapo, Karl E.; Cristea, Nicoleta C.; Lundquist, Jessica D.Hinkelman, L. M., K. E. Lapo, N. C. Cristea, J. D. Lundquist, 2015: Using CERES SYN Surface Irradiance Data as Forcing for Snowmelt Simulation in Complex Terrain. J. Hydrometeor., 16(5), 2133-2152. doi: 10.1175/JHM-D-14-0179.1. The benefit of using solar and longwave surface irradiance data from NASA’s Clouds and the Earth’s Radiant Energy System (CERES) synoptic (SYN) satellite product in simulations of snowmelt has been examined. The accuracy of the SYN downwelling solar and longwave irradiances was first assessed by comparison to measurements at NOAA’s Surface Radiation Network (SURFRAD) reference stations and to remote mountain observations. Typical shortwave (longwave) biases had magnitudes less than 30 (10) W m−2, with most standard deviations below 140 (30) W m−2. The performance of a range of snow models of varying complexity when using SYN irradiances as forcing data was then evaluated. Simulated snow water equivalent and runoff from cases using SYN data fell in the range of those from simulations forced with irradiances from well-maintained surface observation sites as well as empirical methods that have been shown to perform well in mountainous terrain. The SYN irradiances are therefore judged to be suitable for use in snowmelt modeling. It is also noted that the SYN upwelling shortwave irradiances, and hence albedos derived from them, are frequently not representative of individual monitoring stations because of the high spatial variability of snow cover and other surface properties in mountainous regions. In addition, adjusting the SYN downwelling longwave irradiances to reflect the exact elevation of the point of interest relative to the mean altitude of the satellite grid box is recommended. Radiative fluxes; satellite observations; Snow cover; Hydrologic models; Mountain meteorology
Hogrefe, Christian; Pouliot, George; Wong, David; Torian, Alfreida; Roselle, Shawn; Pleim, Jonathan; Mathur, RohitHogrefe, C., G. Pouliot, D. Wong, A. Torian, S. Roselle, J. Pleim, R. Mathur, 2015: Annual application and evaluation of the online coupled WRF–CMAQ system over North America under AQMEII phase 2. Atmospheric Environment, 115, 683-694. doi: 10.1016/j.atmosenv.2014.12.034. We present an application of the online coupled Weather Research and Forecasting–Community Multiscale Air Quality (WRF–CMAQ) modeling system to two annual simulations over North America performed under Phase 2 of the Air Quality Model Evaluation International Initiative (AQMEII). Operational evaluation shows that model performance is comparable to earlier annual applications of the uncoupled WRF/CMAQ modeling system Results also indicate that factors such as changes in the underlying emissions inventory and chemical boundary conditions likely exert a larger influence on overall model performance than feedback effects. A comparison of the simulated Aerosol Optical Depth (AOD) against observations reveals a tendency toward underprediction in all seasons despite a general overprediction of PM2.5 during wintertime. Summertime sensitivity simulations without feedback effects are used to quantify the average impact of the simulated direct feedback effect on temperature, PBL heights, ozone and PM2.5 concentrations. Model results for 2006 and 2010 are analyzed to compare modeled changes between these years to those seen in observations. The results for summertime average daily maximum 8-h ozone showed that the model tends to underestimate the observed decrease in concentrations. The results for total and speciated PM2.5 vary between seasons, networks and species, but the WRF–CMAQ simulations do capture the substantial decreases in observed PM2.5 concentrations in summer and fall. These 2010–2006 PM2.5 decreases result in simulated increases of summer mean clear-sky shortwave radiation between 5 and 10 W/m2. The WRF–CMAQ configuration without direct feedback effects simulates smaller changes in summertime PM2.5 concentrations, indicating that the direct feedback effect enhances the air quality benefits arising from emission controls and that coupled modeling systems are necessary to quantify such feedback effects. AQMEII; Direct feedbacks; Dynamic evaluation; WRF–CMAQ coupled model
Hong, Gang; Minnis, PatrickHong, G., P. Minnis, 2015: Effects of spherical inclusions on scattering properties of small ice cloud particles. Journal of Geophysical Research: Atmospheres, 120(7), 2951–2969. doi: 10.1002/2014JD022494. The single-scattering properties of small ice crystals containing four types of spherical inclusions, ammonium sulfate (NH4)2SO4, ammonium nitrate NH3NO3, air bubbles, and soot, are investigated at 0.65 and 2.13 µm. Small, randomly oriented hexagonal ice columns with spherical inclusions that are randomly distributed with standard gamma size distributions in the columns are considered in the present study. Ice crystals with inclusions of (NH4)2SO4 and NH3NO3 essentially have the same features due to their similar refractive indices. Nonzero scattering matrix elements are sensitive to inclusion type and amount, and show differences between 0.65 and 2.13 µm. The extinction efficiency Qe of small ice crystals at 0.65 µm is near 2.0 and essentially unaffected by variations in inclusion volume, in contrast to strong influences of inclusion amount on Qe at 2.13 µm. The single-scattering albedo ϖ0 of ice crystals, nearly equal to 1.0, is not affected by inclusions of (NH4)2SO4, NH3NO3, and air bubbles. Soot inclusions strongly affect ϖ0, which decreases to about 0.5 with increasing soot amounts. The asymmetry factor g is substantially affected by (NH4)2SO4, NH3NO3, and soot and the variations in their amounts. Full Stokes parameters of cirrus clouds consisting of uniform hexagonal ice columns with inclusions are computed using a polarized radiative transfer model. Sensitivities of light intensity and polarization of cirrus clouds to types and amounts of inclusions and cirrus cloud optical thicknesses are found to depend on wavelength. The present results suggest that different types of inclusions for small ice crystals should be considered when developing realistic ice crystal optical properties, and that light intensity and polarization of cirrus clouds and their angular distribution features, in the absence of other effects such as cavities and surface roughness, imply the potential for identifying pure ice crystals from those with aerosol inclusions. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 3359 Radiative processes; 3360 Remote sensing; 0319 Cloud optics; Scattering; polarization; small ice cloud particle
Hourdin, Frédéric; Găinusă-Bogdan, Alina; Braconnot, Pascale; Dufresne, Jean-Louis; Traore, Aboul-Khadre; Rio, CatherineHourdin, F., A. Găinusă-Bogdan, P. Braconnot, J. Dufresne, A. Traore, C. Rio, 2015: Air moisture control on ocean surface temperature, hidden key to the warm bias enigma. Geophysical Research Letters, 42(24), 10,885–10,893. doi: 10.1002/2015GL066764. The systematic overestimation by climate models of the surface temperature over the eastern tropical oceans is generally attributed to an insufficient oceanic cooling or to an underestimation of stratocumulus clouds. We show that surface evaporation contributes as much as clouds to the dispersion of the warm bias intensity in a multimodel simulations ensemble. The models with the largest warm biases are those with the highest surface heating by radiation and lowest evaporative cooling in atmospheric simulations with prescribed sea surface temperatures. Surface evaporation also controls the amplitude of the surface temperature response to this overestimated heating, when the atmosphere is coupled to an ocean. Evaporation increases with temperature both because of increasing saturation humidity and of an unexpected drying of the near-surface air. Both the origin of the bias and this temperature adjustment point to the key role of near-surface relative humidity and its control by the atmospheric model. modeling; 3359 Radiative processes; 3337 Global climate models; climate; 3339 Ocean/atmosphere interactions; 3307 Boundary layer processes; coupling; warm bias
Illingworth, A. J.; Barker, H. W.; Beljaars, A.; Ceccaldi, M.; Chepfer, H.; Clerbaux, N.; Cole, J.; Delanoë, J.; Domenech, C.; Donovan, D. P.; Fukuda, S.; Hirakata, M.; Hogan, R. J.; Huenerbein, A.; Kollias, P.; Kubota, T.; Nakajima, T.; Nakajima, T. Y.; Nishizawa, T.; Ohno, Y.; Okamoto, H.; Oki, R.; Sato, K.; Satoh, M.; Shephard, M. W.; Velázquez-Blázquez, A.; Wandinger, U.; Wehr, T.; van Zadelhoff, G.-J.Illingworth, A. J., H. W. Barker, A. Beljaars, M. Ceccaldi, H. Chepfer, N. Clerbaux, J. Cole, J. Delanoë, C. Domenech, D. P. Donovan, S. Fukuda, M. Hirakata, R. J. Hogan, A. Huenerbein, P. Kollias, T. Kubota, T. Nakajima, T. Y. Nakajima, T. Nishizawa, Y. Ohno, H. Okamoto, R. Oki, K. Sato, M. Satoh, M. W. Shephard, A. Velázquez-Blázquez, U. Wandinger, T. Wehr, G. van Zadelhoff, 2015: The EarthCARE Satellite: The Next Step Forward in Global Measurements of Clouds, Aerosols, Precipitation, and Radiation. Bull. Amer. Meteor. Soc., 96(8), 1311-1332. doi: 10.1175/BAMS-D-12-00227.1. The collective representation within global models of aerosol, cloud, precipitation, and their radiative properties remains unsatisfactory. They constitute the largest source of uncertainty in predictions of climatic change and hamper the ability of numerical weather prediction models to forecast high-impact weather events. The joint European Space Agency (ESA)–Japan Aerospace Exploration Agency (JAXA) Earth Clouds, Aerosol and Radiation Explorer (EarthCARE) satellite mission, scheduled for launch in 2018, will help to resolve these weaknesses by providing global profiles of cloud, aerosol, precipitation, and associated radiative properties inferred from a combination of measurements made by its collocated active and passive sensors. EarthCARE will improve our understanding of cloud and aerosol processes by extending the invaluable dataset acquired by the A-Train satellites CloudSat, Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), and Aqua. Specifically, EarthCARE’s cloud profiling radar, with 7 dB more sensitivity than CloudSat, will detect more thin clouds and its Doppler capability will provide novel information on convection, precipitating ice particle, and raindrop fall speeds. EarthCARE’s 355-nm high-spectral-resolution lidar will measure directly and accurately cloud and aerosol extinction and optical depth. Combining this with backscatter and polarization information should lead to an unprecedented ability to identify aerosol type. The multispectral imager will provide a context for, and the ability to construct, the cloud and aerosol distribution in 3D domains around the narrow 2D retrieved cross section. The consistency of the retrievals will be assessed to within a target of ±10 W m–2 on the (10 km)2 scale by comparing the multiview broadband radiometer observations to the top-of-atmosphere fluxes estimated by 3D radiative transfer models acting on retrieved 3D domains.
Inamdar, Anand K.; Guillevic, Pierre C.Inamdar, A. K., P. C. Guillevic, 2015: Net Surface Shortwave Radiation from GOES Imagery—Product Evaluation Using Ground-Based Measurements from SURFRAD. Remote Sensing, 7(8), 10788-10814. doi: 10.3390/rs70810788. The Earth’s surface net radiation controls the energy and water exchanges between the Earth’s surface and the atmosphere, and can be derived from satellite observations. The ability to monitor the net surface radiation over large areas at high spatial and temporal resolution is essential for many applications, such as weather forecasting, short-term climate prediction or water resources management. The objective of this paper is to derive the net surface radiation in the shortwave domain at high temporal (half-hourly) and spatial resolution (~1 km) using visible imagery from Geostationary Operational Environmental Satellite (GOES). The retrieval algorithm represents an adaptation to GOES data of a standard algorithm initially developed for the NASA-operated Clouds and Earth’s Radiant Energy System (CERES) scanner. The methodology relies on: (1) the estimation of top of atmosphere shortwave radiation from GOES spectral measurements; and (2) the calculation of net surface shortwave (SW) radiation accounting for atmospheric effects. Comparison of GOES-retrieved net surface shortwave radiation with ground-measurements at the National Oceanic and Atmospheric Administration’s (NOAA) Surface Radiation (SURFRAD) stations yields very good agreement with average bias lower than 5 W·m−2 and root mean square difference around 70 W·m−2. The algorithm performance is usually higher over areas characterized by low spatial variability in term of land cover type and surface biophysical properties. The technique does not involve retrieval and assessment of cloud properties and can be easily adapted to other meteorological satellites around the globe. clouds and earth’s radiant energy systems (CERES); geostationary operational environmental satellite (GOES); net surface solar radiation retrievals
Jiang, Yiquan; Yang, Xiu-Qun; Liu, XiaohongJiang, Y., X. Yang, X. Liu, 2015: Seasonality in anthropogenic aerosol effects on East Asian climate simulated with CAM5. Journal of Geophysical Research: Atmospheres, 120(20), 10,837–10,861. doi: 10.1002/2015JD023451. This study investigates the seasonality in anthropogenic aerosol optical depth (AOD) distributions and their effects on clouds and precipitation in East Asia with the Community Atmospheric Model version 5. The differences between the model experiments with and without anthropogenic emissions exhibit a northward shift of the maximal AOD change in East Asia from March to July and then a southward withdrawal from September to November, which are induced by East Asian monsoon circulation. Associated with the shift, the direct and semidirect effects of the anthropogenic aerosols are the most pronounced in spring and summer, with a maximum center in North China during summer and a secondary center in South China during spring. The cloud liquid water path and shortwave cloud forcing changes, however, are the weakest in North China during summer. The indirect effect is the strongest in South China during spring, which is related to the large amount of middle-low level clouds in cold seasons in East China. A positive feedback between aerosol induced surface cooling and low-level cloud increase is identified in East China, which acts to enforce the aerosol indirect effect in spring. Accordingly, the climate response to the anthropogenic aerosols is also characterized by a northward shift of reduced precipitation from spring to summer, leading to a spring drought in South China and a summer drought in North China. The spring drought is attributed to both direct and indirect effects of the anthropogenic aerosols, while the summer drought is primarily determined by the aerosols' direct effect. 3311 Clouds and aerosols; 3359 Radiative processes; 3305 Climate change and variability; Cloud and precipitation; 3354 Precipitation; anthropogenic aerosols; climate effect; East Asia; seasonality
Johansson, E.; Devasthale, A.; L'Ecuyer, T.; Ekman, A. M. L.; Tjernström, M.Johansson, E., A. Devasthale, T. L'Ecuyer, A. M. L. Ekman, M. Tjernström, 2015: The vertical structure of cloud radiative heating over the Indian subcontinent during summer monsoon. Atmos. Chem. Phys. Discuss., 15(4), 5423-5459. doi: 10.5194/acpd-15-5423-2015. Every year the monsoonal circulation over the Indian subcontinent gives rise to a variety of cloud types that differ considerably in their ability to heat or cool the atmosphere. These clouds in turn affect monsoon dynamics via their radiative impacts, both at the surface and in the atmosphere. New generation of satellites carrying active radar and lidar sensors are allowing realistic quantification of cloud radiative heating (CRH) by resolving the vertical structure of the atmosphere in an unprecedented detail. Obtaining this information is a first step in closing the knowledge gap in our understanding of the role that different clouds play as regulators of the monsoon and vice versa. Here, we use collocated CloudSat-CALIPSO data sets to understand following aspects of cloud-radiation interactions associated with Indian monsoon circulation. (1) How does the vertical distribution of CRH evolve over the Indian continent throughout monsoon season? (2) What is the absolute contribution of different clouds types to the total CRH? (3) How do active and break periods of monsoon affect the distribution of CRH? And finally, (4) what are the net radiative effects of different cloud types on surface heating? In general, the vertical structure of CRH follows the northward migration and the retreat of monsoon from May to October. It is found that the alto- and nimbostratus clouds intensely warm the middle troposphere and equally strongly cool the upper troposphere. Their warming/cooling consistently exceeds ±0.2 K day−1 (after weighing by vertical cloud fraction) in monthly mean composites throughout the middle and upper troposphere respectively, with largest impact observed in June, July and August. Deep convective towers cause considerable warming in the middle and upper troposphere, but strongly cool the base and inside of the tropical tropopause layer (TTL). Such cooling is stronger during active (−1.23 K day−1) monsoon conditions compared to break periods (−0.36 K day−1). The contrasting warming effect of high clouds inside the TTL is found to be double in magnitude during active conditions compared to break periods. It is further shown that stratiform clouds (combining alto- and nimbostratus clouds) and deep convection significantly cool the surface with net radiative effect in the order of −100 and −400 W m−2, respectively, while warming the atmosphere in the order of 40 and 150 W m−2. While deep convection produces strong cooling at the surface during active periods of monsoon, the importance of stratiform clouds, on the other hand, increases during break periods. The contrasting CREs in the atmosphere and at surface, and during active and break conditions, have direct implications for monsoonal circulation.
Johnson, Richard H.; Ciesielski, Paul E.; Ruppert, James H.; Katsumata, MasakiJohnson, R. H., P. E. Ciesielski, J. H. Ruppert, M. Katsumata, 2015: Sounding-Based Thermodynamic Budgets for DYNAMO. J. Atmos. Sci., 72(2), 598-622. doi: 10.1175/JAS-D-14-0202.1. AbstractThe Dynamics of the Madden–Julian Oscillation (DYNAMO) field campaign, conducted over the Indian Ocean from October 2011 to March 2012, was designed to study the initiation of the Madden–Julian oscillation (MJO). Two prominent MJOs occurred in the experimental domain during the special observing period in October and November. Data from a northern and a southern sounding array (NSA and SSA, respectively) have been used to investigate the apparent heat sources and sinks (Q1 and Q2) and radiative heating rates QR throughout the life cycles of the two MJO events. The MJO signal was far stronger in the NSA than the SSA. Time series of Q1, Q2, and the vertical eddy flux of moist static energy reveal an evolution of cloud systems for both MJOs consistent with prior studies: shallow, nonprecipitating cumulus during the suppressed phase, followed by cumulus congestus, then deep convection during the active phase, and finally stratiform precipitation. However, the duration of these phases was shorter for the November MJO than for the October event. The profiles of Q1 and Q2 for the two arrays indicate a greater stratiform rain fraction for the NSA than the SSA—a finding supported by TRMM measurements. Surface rainfall rates and net tropospheric QR determined as residuals from the budgets show good agreement with satellite-based estimates. The cloud radiative forcing was approximately 20% of the column-integrated convective heating and of the same amplitude as the normalized gross moist stability, leaving open the possibility of radiative–convective instability for the two MJOs. convection; convective clouds; Cloud radiative effects; Madden-Julian Oscillation; Atmosphere-ocean interaction
Kang, Sarah M.; Seager, Richard; Frierson, Dargan M. W.; Liu, XiaojuanKang, S. M., R. Seager, D. M. W. Frierson, X. Liu, 2015: Croll revisited: Why is the northern hemisphere warmer than the southern hemisphere?. Climate Dynamics, 44(5-6), 1457-1472. doi: 10.1007/s00382-014-2147-z. The question of why, in the annual-mean, the northern hemisphere (NH) is warmer than the southern hemisphere (SH) is addressed, revisiting an 1870 paper by James Croll. We first show that ocean is warmer than land in general which, acting alone, would make the SH, with greater ocean fraction, warmer. Croll was aware of this and thought it was caused by greater specific humidity and greenhouse trapping over ocean than over land. However, for any given temperature, it is shown that greenhouse trapping is actually greater over land. Instead, oceans are warmer than land because of the smaller surface albedo. However, hemispheric differences in planetary albedo are negligible because the impact of differences in land-sea fraction are offset by the SH ocean and land reflecting more than their NH counterparts. In the absence of a role for albedo differences it is shown that, in agreement with Croll, northward cross-equatorial ocean heat transport (X-OHT) is critical for the warmer NH. This is examined in a simple box model based on the energy budget of each hemisphere. The hemispheric difference forced by X-OHT is enhanced by the positive water vapor-greenhouse feedback, and is partly compensated by the southward atmospheric energy transport. Due to uncertainties in the ocean data, a range of X-OHT is considered. A X-OHT of larger than 0.5 PW is needed to explain the warmer NH solely by X-OHT. For smaller X-OHT, a larger basic state greenhouse trapping in the NH, conceived as imposed by continental geometry, needs to be imposed. Numerical experiments with a GCM coupled to a slab ocean provide evidence that X-OHT is fundamentally important in determining the hemispheric differences in temperature. Therefore, despite some modifications to his theory, analysis of modern data confirms Croll’s 140-year-old theory that the warmer NH is partly because of northward X-OHT. Climatology; energy budget; Oceanography; Geophysics/Geodesy; Cross-equatorial ocean transport; Greenhouse trapping; Hemispheric temperature difference
Kato, Seiji; Loeb, Norman G.; Rutan, David A.; Rose, Fred G.Kato, S., N. G. Loeb, D. A. Rutan, F. G. Rose, 2015: Clouds and the Earth’s Radiant Energy System (CERES) Data Products for Climate Research. Journal of the Meteorological Society of Japan. Ser. II, 93(6), 597-612. doi: 10.2151/jmsj.2015-048. NASA’s Clouds and the Earth’s Radiant Energy System (CERES) project integrates CERES, Moderate Resolution Imaging Spectroradiometer (MODIS), and geostationary satellite observations to provide top-of-atmosphere (TOA) irradiances derived from broadband radiance observations by CERES instruments. It also uses snow cover and sea ice extent retrieved from microwave instruments as well as thermodynamic variables from reanalysis. In addition, these variables are used for surface and atmospheric irradiance computations. The CERES project provides TOA, surface, and atmospheric irradiances in various spatial and temporal resolutions. These data sets are for climate research and evaluation of climate models. Long-term observations are required to understand how the Earth system responds to radiative forcing. A simple model is used to estimate the time to detect trends in TOA reflected shortwave and emitted longwave irradiances. CERES; radiation budget; climate data
Keellings, David; Engström, Johanna; Waylen, PeterKeellings, D., J. Engström, P. Waylen, 2015: The sunshine state: investigating external drivers of sky conditions. Physical Geography, 36(2), 113-126. doi: 10.1080/02723646.2015.1004995. Following rapid population growth and urbanization in Florida, there is an increased demand for energy. The state currently gets more than 50% of its electricity from burning imported natural gas. As the future of fossil fuels is uncertain and their impact on climate has proven negative, one could expect great potential and interest in further developing the solar industry, which utilizes the most prominent of renewable energy sources in Florida. Solar energy production is dependent on the supply of clear skies and plentiful insolation. This paper seeks to explain variations in the number of clear sunny days by identifying the months with clearest (cloudiest) sky conditions during the years 1950–2009 in relation to some of the most dominant low frequency climate patterns of variability in the Northern Hemisphere. The hypergeometric distribution is used to test for significant association between the phases of El Niño Southern Oscillation (ENSO), North Atlantic Oscillation, Pacific-North American, and Atlantic Multi-decadal Oscillation (AMO) and cloud cover in Florida. We find that ENSO and AMO significantly impact the occurrence of clear/cloudy skies with the warm phase of ENSO associated with cloudier conditions across much of the state and the warm phase of AMO bringing clearer conditions to northern stations.
Khlopenkov, Konstantin V.; Doelling, David R.; Okuyama, ArataKhlopenkov, K. V., D. R. Doelling, A. Okuyama, 2015: MTSAT-1R Visible Imager Point Spread Function Correction, Part II: Theory. IEEE Transactions on Geoscience and Remote Sensing, 53(3), 1504-1512. doi: 10.1109/TGRS.2014.2344627.
Kiran, V. Ravi; Rajeevan, M.; Gadhavi, H.; Rao, S. Vijaya Bhaskara; Jayaraman, A.Kiran, V. R., M. Rajeevan, H. Gadhavi, S. V. B. Rao, A. Jayaraman, 2015: Role of vertical structure of cloud microphysical properties on cloud radiative forcing over the Asian monsoon region. Climate Dynamics, 45(11-12), 3331-3345. doi: 10.1007/s00382-015-2542-0. Five years (2006–2010) of clouds and earth’s radiant energy system (CERES) and CloudSat data have been analyzed to examine the role of vertical structure of cloud microphysical properties on cloud radiative forcing (CRF) parameters at the top-of-the atmosphere over the Asian monsoon region during the summer monsoon season (June–September) and the Pacific warm pool region during April. Vertical profile of cloud properties (optical depth, cloud liquid water content and cloud ice water content) derived from CloudSat data has been used for the present analysis. Shortwave, longwave and net CRF derived from the CERES data have been used. The results suggest an imbalance between shortwave cloud radiative forcing and longwave cloud radiative forcing over the Asian monsoon region consistent with the results reported earlier. The present analysis suggests that over the Bay-of-Bengal (BoB), vertical profile of cloud microphysical properties determine more than 50 % of variance in CRF. However, over the Pacific warm pool region, cloud microphysical property profiles does not contribute significantly to variance in net CRF ( Cloud microphysics; Climatology; cloud vertical structure; cloud radiative forcing; Oceanography; Geophysics/Geodesy; Indian summer monsoon; Radiative budget; Pacific warm pool region
Kottayil, Ajil; Satheesan, K.Kottayil, A., K. Satheesan, 2015: Enhancement in the upper tropospheric humidity associated with aerosol loading over tropical Pacific. Atmospheric Environment, 122, 148-153. doi: 10.1016/j.atmosenv.2015.09.043. Many modeling studies have indicated that aerosol interactions with clouds increase the upper tropospheric humidity (UTH), but observational evidences are sparse. Using satellite datasets of upper tropospheric humidity and aerosols, this study shows that aerosols increase the upper tropospheric humidity over the tropical North West Pacific (NWP) and North East Pacific (NEP). The observations show an increase in the UTH by 2.8%RH over NEP for an increment of 0.12 in aerosol optical depth (AOD) and 2%RH increase in UTH over NWP for an increment of 0.19 in AOD. The study also quantifies the change in longwave cloud radiative forcing (LWCRF) as a consequence of the increase in UTH due to aerosols. The LWCRF increases by 3.38 W m−2 over NEP and by 4.46 W m−2 over NWP. The result that aerosols increase the upper tropospheric humidity is significant since the latter plays a crucial role in regulating the Earth's radiation budget and water vapor feedback. aerosols; Longwave cloud radiative forcing; Upper tropospheric humidity; Water vapor feedback
Kubar, Terence L.; Stephens, Graeme L.; Lebsock, Matthew; Larson, Vincent E.; Bogenschutz, Peter A.Kubar, T. L., G. L. Stephens, M. Lebsock, V. E. Larson, P. A. Bogenschutz, 2015: Regional Assessments of Low Clouds against Large-Scale Stability in CAM5 and CAM-CLUBB Using MODIS and ERA-Interim Reanalysis Data. J. Climate, 28(4), 1685-1706. doi: 10.1175/JCLI-D-14-00184.1. AbstractDaily gridded cloud data from MODIS and ERA-Interim reanalysis have been assessed to examine variations of low cloud fraction (CF) and cloud-top height and their dependence on large-scale dynamics and a measure of stability. To assess the stratocumulus (Sc) to cumulus (Cu) transition (STCT), the observations are used to evaluate two versions of the NCAR Community Atmosphere Model version 5 (CAM5), both the base model and a version that has implemented a new subgrid low cloud parameterization, Cloud Layers Unified by Binormals (CLUBB).The ratio of moist static energy (MSE) at 700–1000 hPa (MSEtotal) is a skillful predictor of median CF of screened low cloud grids. Values of MSEtotal less than 1.00 represent either conditionally or absolutely unstable layers, and probability density functions of CF suggest a preponderance of either trade Cu (median CF < 0.4) or transitional Sc clouds (0.4 < CF < 0.9). With increased stability (MSEtotal > 1.00), an abundance of overcast or nearly overcast low clouds exists. While both MODIS and ERA-Interim indicate a fairly smooth transition between the low cloud regimes, CAM5-Base simulates an abrupt shift from trade Cu to Sc, with trade Cu covering both too much area and occurring over excessively strong stabilities. In contrast, CAM-CLUBB simulates a smoother trade Cu to Sc transition (CTST) as a function of MSEtotal, albeit with too extensive coverage of overcast Sc in the primary northeastern Pacific subsidence region. While the overall CF distribution in CAM-CLUBB is more realistic, too few transitional clouds are simulated for intermediate MSEtotal compared to observations. Stability; Cloud cover; Cloud parameterizations; marine boundary layer; Subsidence; Subtropics
Lettenmaier, Dennis P.; Alsdorf, Doug; Dozier, Jeff; Huffman, George J.; Pan, Ming; Wood, Eric F.Lettenmaier, D. P., D. Alsdorf, J. Dozier, G. J. Huffman, M. Pan, E. F. Wood, 2015: Inroads of remote sensing into hydrologic science during the WRR era. Water Resources Research, 51(9), 7309-7342. doi: 10.1002/2015WR017616. The first issue of WRR appeared eight years after the launch of Sputnik, but by WRR's 25th anniversary, only seven papers that used remote sensing had appeared. Over the journal's second 25 years, that changed remarkably, and remote sensing is now widely used in hydrology and other geophysical sciences. We attribute this evolution to production of data sets that scientists not well versed in remote sensing can use, and to educational initiatives like NASA's Earth System Science Fellowship program that has supported over a thousand scientists, many in hydrology. We review progress in remote sensing in hydrology from a water balance perspective. We argue that progress is primarily attributable to a creative use of existing and past satellite sensors to estimate such variables as evapotranspiration rates or water storage in lakes and reservoirs and to new and planned missions. Recent transforming technologies include the Gravity Recovery and Climate Experiment (GRACE), the European Soil Moisture and Ocean Salinity (SMOS) and U.S. Soil Moisture Active Passive (SMAP) missions, and the Global Precipitation Measurement (GPM) mission. Future missions include Surface Water and Ocean Topography (SWOT) to measure river discharge and lake, reservoir, and wetland storage. Measurement of some important hydrologic variables remains problematic: retrieval of snow water equivalent (SWE) from space remains elusive especially in mountain areas, even though snow cover extent is well observed, and was the topic of 4 of the first 5 remote sensing papers published in WRR. We argue that this area deserves more strategic thinking from the hydrology community. Remote sensing; 1855 Remote sensing; hydrological cycles and budgets; water budgets
Li, Jiangnan; Min, Qilong; Peng, Yiran; Sun, Zhian; Zhao, Jian-QiLi, J., Q. Min, Y. Peng, Z. Sun, J. Zhao, 2015: Accounting for dust aerosol size distribution in radiative transfer. Journal of Geophysical Research: Atmospheres, 120(13), 6537–6550. doi: 10.1002/2015JD023078. The impact of size distribution of mineral dust aerosol on radiative transfer was investigated using the Aerosol Robotic Network-retrieved aerosol size distributions. Three methods for determining the aerosol optical properties using size distributions were discussed. The first is referred to as a bin method in which the aerosol optical properties are determined for each bin of the size distribution. The second is named as an assembly mean method in which the aerosol optical properties are determined with an integration of the aerosol optical parameters over the observed size distribution. The third is a normal parameterization method based on an assumed size distribution. The bin method was used to generate the benchmark results in the radiation calculations against the methods of the assembly mean, and parameterizations based on two size distribution functions, namely, lognormal and gamma were examined. It is seen that the assembly mean method can produce aerosol radiative forcing with accuracy of better than 1%. The accuracies of the parameterizations based on lognormal and gamma size distributions are about 25% and 5%, respectively. Both the lognormal and gamma size distributions can be determined by two parameters, the effective radius and effective variance. The better results from the gamma size distribution can be explained by a third parameter of skewness which is found to be useful for judging how close the assumed distribution is to the observation result. The parameterizations based on the two assumed size distributions are also evaluated in a climate model. The results show that the reflected solar fluxes over the desert areas determined by the scheme based on the gamma size distribution are about 1 W m−2 less than those from the scheme based on the lognormal size distribution, bringing the model results closer to the observations. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 0399 General or miscellaneous; radiative transfer; aerosol size distribution; optical property
Li, Ying; Thompson, David W. J.; Bony, SandrineLi, Y., D. W. J. Thompson, S. Bony, 2015: The Influence of Atmospheric Cloud Radiative Effects on the Large-Scale Atmospheric Circulation. J. Climate, 28(18), 7263-7278. doi: 10.1175/JCLI-D-14-00825.1. The influence of clouds on the large-scale atmospheric circulation is examined in numerical simulations from an atmospheric general circulation model run with and without atmospheric cloud radiative effects (ACRE). In the extratropics of both hemispheres, the primary impacts of ACRE on the circulation include 1) increases in the meridional temperature gradient and decreases in static stability in the midlatitude upper troposphere, 2) strengthening of the midlatitude jet, 3) increases in extratropical eddy kinetic energy by up to 30%, and 4) increases in precipitation at middle latitudes but decreases at subtropical latitudes. In the tropics, the primary impacts of ACRE include 1) eastward wind anomalies in the tropical upper troposphere–lower stratosphere (UTLS) and 2) reductions in tropical precipitation. The impacts of ACRE on the atmospheric circulation are interpreted in the context of a series of dynamical and physical processes. The changes in the extratropical circulation and precipitation are consistent with the influence of ACRE on the baroclinicity and eddy fluxes of momentum in the extratropical upper troposphere, the changes in the zonal wind in the UTLS with the influence of ACRE on the amplitude of the equatorial planetary waves, and the changes in the tropical precipitation with the energetic constraints on the tropical troposphere. The results make clear that ACRE have a pronounced influence on the atmospheric circulation not only at tropical latitudes, but at extratropical latitudes as well. They highlight the critical importance of correctly simulating ACRE in global climate models. clouds; Climatology; Atmospheric circulation; General circulation models; Cloud radiative effects; Dynamics
Li, Yuanlong; Han, Weiqing; Lee, TongLi, Y., W. Han, T. Lee, 2015: Intraseasonal sea surface salinity variability in the equatorial Indo-Pacific Ocean induced by Madden-Julian oscillations. Journal of Geophysical Research: Oceans, 120(3), 2233-2258. doi: 10.1002/2014JC010647. Intraseasonal sea surface salinity (SSS) variability in the equatorial Indo-Pacific Ocean is investigated using the Aquarius/SAC-D satellite measurements and Hybrid Coordinate Ocean Model (HYCOM). Large-scale SSS variations at 20–90 day time scales induced by Madden-Julian oscillations (MJOs) are prominent in the central-to-eastern Indian Ocean (IO) and western Pacific Ocean (PO) with a standard deviation of ∼0.15 psu. The relationship between SSS anomaly and freshwater flux is nearly in phase in the central-to-eastern IO and out of phase in the western PO during a MJO cycle. A series of HYCOM experiments are performed to explore the causes for SSS variability. In most areas of the equatorial Indo-Pacific Ocean, wind stress-forced ocean dynamical processes act as the main driver of intraseasonal SSS, while precipitation plays a secondary role. In some areas of the western PO and western IO, however, precipitation effect is the leading contributor. In comparison, evaporation effect induced by radiation and wind speed changes is generally much smaller. Besides the external forcing by MJOs, ocean internal variability can also cause considerable intraseasonal SSS changes, explaining 10–20% of the total variance in some regions. Composite analysis for MJO events reveals that the effects of wind stress, precipitation, and evaporation vary at different phases of a MJO cycle. The MJO-induced SSS signature is the result of complicated superimposition and interaction of these effects. The effect of wind stress also varies significantly from event to event. It affects SSS variability primarily through horizontal ocean current advection and to a lesser extent through vertical entrainment. 4572 Upper ocean and mixed layer processes; Madden-Julian Oscillation; 4231 Equatorial oceanography; Indo-Pacific Ocean; sea surface salinity
Liu, Chunlei; Allan, Richard P.; Berrisford, Paul; Mayer, Michael; Hyder, Patrick; Loeb, Norman; Smith, Doug; Vidale, Pier-Luigi; Edwards, John M.Liu, C., R. P. Allan, P. Berrisford, M. Mayer, P. Hyder, N. Loeb, D. Smith, P. Vidale, J. M. Edwards, 2015: Combining satellite observations and reanalysis energy transports to estimate global net surface energy fluxes 1985–2012. Journal of Geophysical Research: Atmospheres, 120(18), 9374–9389. doi: 10.1002/2015JD023264. Two methods are developed to estimate net surface energy fluxes based upon satellite-derived reconstructions of radiative fluxes at the top of atmosphere and the atmospheric energy tendencies and transports from the ERA-Interim reanalysis. Method 1 applies the mass-adjusted energy divergence from ERA-Interim, while method 2 estimates energy divergence based upon the net energy difference at the top of atmosphere and the surface from ERA-Interim. To optimize the surface flux and its variability over ocean, the divergences over land are constrained to match the monthly area mean surface net energy flux variability derived from a simple relationship between the surface net energy flux and the surface temperature change. The energy divergences over the oceans are then adjusted to remove an unphysical residual global mean atmospheric energy divergence. The estimated net surface energy fluxes are compared with other data sets from reanalysis and atmospheric model simulations. The spatial correlation coefficients of multiannual means between the estimations made here and other data sets are all around 0.9. There are good agreements in area mean anomaly variability over the global ocean, but discrepancies in the trend over the eastern Pacific are apparent. 1610 Atmosphere; satellite observations; 0325 Evolution of the atmosphere; 1704 Atmospheric sciences; 1630 Impacts of global change; climate models; 1635 Oceans; energy imbalance; surface heat flux
Liu, Jianjun; Li, Zhanqing; Zheng, Youfei; Cribb, MaureenLiu, J., Z. Li, Y. Zheng, M. Cribb, 2015: Cloud-base distribution and cirrus properties based on micropulse lidar measurements at a site in southeastern China. Advances in Atmospheric Sciences, 32(7), 991-1004. doi: 10.1007/s00376-014-4176-2. The cloud fraction (CF) and cloud-base heights (CBHs), and cirrus properties, over a site in southeastern China from June 2008 to May 2009, are examined by a ground-based lidar. Results show that clouds occupied the sky 41% of the time. Significant seasonal variations in CF were found with a maximum/minimum during winter/summer and similar magnitudes of CF in spring and autumn. A distinct diurnal cycle in the overall mean CF was seen. Total, daytime, and nighttime annual mean CBHs were 3.05±2.73 km, 2.46±2.08 km, and 3.51±3.07 km, respectively. The lowest/highest CBH occurred around noon/midnight. Cirrus clouds were present ∼36.2% of the time at night with the percentage increased in summer and decreased in spring. Annual mean values for cirrus geometrical properties were 8.89±1.65 km, 9.80±1.70 km, 10.73±1.86 km and 1.83±0.91 km for the base, mid-cloud, top height, and the thickness, respectively. Seasonal variations in cirrus geometrical properties show a maximum/minimum in summer/winter for all cirrus geometrical parameters. The mean cirrus lidar ratio for all cirrus cases in our study was ∼ 25±17 sr, with a smooth seasonal trend. The cirrus optical depth ranged from 0.001 to 2.475, with a mean of 0.34±0.33. Sub-visual, thin, and dense cirrus were observed in ∼12%, 43%, and 45% of the cases, respectively. More frequent, thicker cirrus clouds occurred in summer than in any other season. The properties of cirrus cloud over the site are compared with other lidar-based retrievals of midlatitude cirrus cloud properties. Meteorology; Lidar; Atmospheric Sciences; Geophysics/Geodesy; cirrus properties; cloud-base distribution; southeastern China
Loeb, N. G.; Wielicki, B. A.Loeb, N. G., B. A. Wielicki, 2015: SATELLITES AND SATELLITE REMOTE SENSING | Earth's Radiation Budget. Encyclopedia of Atmospheric Sciences (Second Edition), 67-76. Synopsis This article discusses the Earth's radiation budget and its role within the climate system. A brief summary of how Earth's radiation budget is determined from satellite observations is provided and the geographical, diurnal, and seasonal variations in its components are shown. The relationship between interannual variations in Earth's radiation budget and their relationship to natural fluctuations in the climate system such as the El Niño-Southern Oscillation are explored, as are the regional patterns of change during the past 12 years. This article also discusses the important role of clouds in modulating Earth's radiation budget at the top-of-atmosphere, surface, and within the atmosphere. clouds; Satellite; Absorption; radiation; energy budget; Diurnal; El Niño-Southern Oscillation; Emission; Greenhouse effect; Interannual
Lukashin, C.; Jin, Z.; Kopp, G.; MacDonnell, D.G.; Thome, K.Lukashin, C., Z. Jin, G. Kopp, D. MacDonnell, K. Thome, 2015: CLARREO Reflected Solar Spectrometer: Restrictions for Instrument Sensitivity to Polarization. IEEE Transactions on Geoscience and Remote Sensing, 53(12), 6703-6709. doi: 10.1109/TGRS.2015.2446197. The foundation for future space mission Climate Absolute Radiance and Refractivity Observatory (CLARREO) is the ability to produce climate change benchmark records and provide on-orbit calibration standard through the highly accurate and Système Internationale-traceable observations. The accuracy of CLARREO measurements is set to 0.3% $(k=2)$ for spectrally resolved reflectance. The instrument sensitivity to polarization and polarization of reflected light at the top of atmosphere are the sources for systematic uncertainty. In this paper, we estimate radiometric errors due to polarization effects for CLARREO benchmark and reference intercalibration observations. Data from the Polarization and Anisotropy of Reflectance for Atmospheric Sciences coupled with Observations from Lidar (PARASOL) instrument, a spaceborne polarimeter, have been used in combination with the orbital modeling of Earth's sampling. For the CLARREO benchmark data, we used simulated annual nadir sampling for the polar orbit with 90° inclination, and for the intercalibration with cross-track sensors on the JPSS, such as CERES and VIIRS, we simulated on-orbit matched data sampling. Selected PARASOL data over one full solar year provided polarization parameters in visible (VIS) spectral range. For estimating polarization in near infrared (NIR) spectral range, we used a radiative transfer model. Our results show that to limit error contribution due to polarization to half of the allowed total, the sensitivity to polarization of CLARREO reflected solar instrument should not exceed 0.5% $(k=2)$ in spectral range from VIS to NIR. calibration; clouds; Instruments; Meteorology; Oceans; sensitivity; Orbits; sensitivity to polarization
L’Ecuyer, Tristan S.; Beaudoing, H. K.; Rodell, M.; Olson, W.; Lin, B.; Kato, S.; Clayson, C. A.; Wood, E.; Sheffield, J.; Adler, R.; Huffman, G.; Bosilovich, M.; Gu, G.; Robertson, F.; Houser, P. R.; Chambers, D.; Famiglietti, J. S.; Fetzer, E.; Liu, W. T.; Gao, X.; Schlosser, C. A.; Clark, E.; Lettenmaier, D. P.; Hilburn, K.L’Ecuyer, T. S., H. K. Beaudoing, M. Rodell, W. Olson, B. Lin, S. Kato, C. A. Clayson, E. Wood, J. Sheffield, R. Adler, G. Huffman, M. Bosilovich, G. Gu, F. Robertson, P. R. Houser, D. Chambers, J. S. Famiglietti, E. Fetzer, W. T. Liu, X. Gao, C. A. Schlosser, E. Clark, D. P. Lettenmaier, K. Hilburn, 2015: The Observed State of the Energy Budget in the Early Twenty-First Century. J. Climate, 28(21), 8319-8346. doi: 10.1175/JCLI-D-14-00556.1. New objectively balanced observation-based reconstructions of global and continental energy budgets and their seasonal variability are presented that span the golden decade of Earth-observing satellites at the start of the twenty-first century. In the absence of balance constraints, various combinations of modern flux datasets reveal that current estimates of net radiation into Earth’s surface exceed corresponding turbulent heat fluxes by 13–24 W m−2. The largest imbalances occur over oceanic regions where the component algorithms operate independent of closure constraints. Recent uncertainty assessments suggest that these imbalances fall within anticipated error bounds for each dataset, but the systematic nature of required adjustments across different regions confirm the existence of biases in the component fluxes. To reintroduce energy and water cycle closure information lost in the development of independent flux datasets, a variational method is introduced that explicitly accounts for the relative accuracies in all component fluxes. Applying the technique to a 10-yr record of satellite observations yields new energy budget estimates that simultaneously satisfy all energy and water cycle balance constraints. Globally, 180 W m−2 of atmospheric longwave cooling is balanced by 74 W m−2 of shortwave absorption and 106 W m−2 of latent and sensible heat release. At the surface, 106 W m−2 of downwelling radiation is balanced by turbulent heat transfer to within a residual heat flux into the oceans of 0.45 W m−2, consistent with recent observations of changes in ocean heat content. Annual mean energy budgets and their seasonal cycles for each of seven continents and nine ocean basins are also presented. Radiative fluxes; Energy budget/balance; satellite observations; Climatology; Surface fluxes; Heat budgets/fluxes
Ma, Po-Lun; Rasch, Philip J.; Wang, Minghuai; Wang, Hailong; Ghan, Steven J.; Easter, Richard C.; Gustafson, William I.; Liu, Xiaohong; Zhang, Yuying; Ma, Hsi-YenMa, P., P. J. Rasch, M. Wang, H. Wang, S. J. Ghan, R. C. Easter, W. I. Gustafson, X. Liu, Y. Zhang, H. Ma, 2015: How does increasing horizontal resolution in a global climate model improve the simulation of aerosol-cloud interactions?. Geophysical Research Letters, 42(12), 5058–5065. doi: 10.1002/2015GL064183. The Community Atmosphere Model Version 5 is run at horizontal grid spacing of 2, 1, 0.5, and 0.25°, with the meteorology nudged toward the Year Of Tropical Convection analysis, and cloud simulators and the collocated A-Train satellite observations are used to explore the resolution dependence of aerosol-cloud interactions. The higher-resolution model produces results that agree better with observations, showing an increase of susceptibility of cloud droplet size, indicating a stronger first aerosol indirect forcing (AIF), and a decrease of susceptibility of precipitation probability, suggesting a weaker second AIF. The resolution sensitivities of AIF are attributed to those of droplet nucleation and precipitation parameterizations. The annual average AIF in the Northern Hemisphere midlatitudes (where most anthropogenic emissions occur) in the 0.25° model is reduced by about 1 W m−2 (−30%) compared to the 2° model, leading to a 0.26 W m−2 reduction (−15%) in the global annual average AIF. 0305 Aerosols and particles; 3311 Clouds and aerosols; 3337 Global climate models; aerosol-cloud interactions; global climate model; aerosol indirect forcing; resolution dependence
Ma, Qian; Wang, Kaicun; Wild, MartinMa, Q., K. Wang, M. Wild, 2015: Impact of geolocations of validation data on the evaluation of surface incident shortwave radiation from Earth System Models. Journal of Geophysical Research: Atmospheres, 120(14), 6825–6844. doi: 10.1002/2014JD022572. Ground-based observations of surface incident solar radiation (Rs) have been used to evaluate simulations of global climate models. Existing studies have shown that biases in simulated clouds have a significant spatial pattern, which may be transferred to the simulated Rs. Therefore, the evaluation results of Rs simulations may depend on the locations of the ground-based observations. In this study, Rs simulations of 48 models participating in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) were first evaluated with ground-based observations from different networks (446 stations in total) from 2000 to 2005. The global mean biases of the CMIP5 Rs simulations were found to vary from 4.8 to 11.9 W m−2 when Rs observations from different networks were used as reference data. To reduce the location impact on the evaluation results, CMIP5 simulated Rs was then evaluated with the latest satellite Rs retrieval at 1° × 1° spatial resolution by the Clouds and the Earth's Radiant Energy System, Energy Balanced and Filled (CERES EBAF). It was found that the CMIP5 simulated multimodel mean Rs has a small bias of 2.6 W m−2 compared with CERES EBAF over the globe, 4.7 W m−2 and 1.7 W m−2 over land and oceans, respectively. CERES EBAF Rs was found to have a positive bias of 1.3 W m−2 compared with ground-based observations. After removing this bias of CERES EBAF Rs, global mean Rs was estimated to be 185 W m−2. clouds; 0321 Cloud/radiation interaction; 1622 Earth system modeling; CMIP5; 1626 Global climate models; Earth system model; Surface incident solar radiation
Maroon, Elizabeth A.; Frierson, Dargan M. W.; Battisti, David S.Maroon, E. A., D. M. W. Frierson, D. S. Battisti, 2015: The Tropical Precipitation Response to Andes Topography and Ocean Heat Fluxes in an Aquaplanet Model. J. Climate, 28(1), 381-398. doi: 10.1175/JCLI-D-14-00188.1. AbstractThis aquaplanet modeling study using the Geophysical Fluid Dynamics Laboratory Atmospheric Model, version 2.1 (GFDL AM2.1), examines how ocean energy transport and topography influence the location of tropical precipitation. Adding realistic Andes topography regionally displaces tropical rainfall from the equator into the Northern Hemisphere, even when the wind–evaporation feedback is disabled. The relative importance of the Andes compared to the asymmetric hemispheric heating of the atmosphere by ocean transport is examined by including idealized and realistic zonally averaged surface heat fluxes (also known as q fluxes) in the slab ocean. A hemispherically asymmetric q flux displaces the tropical rainfall toward the hemisphere receiving the greatest heating by the ocean. The zonal-mean displacement of rainfall is greater in simulations with a realistic q flux than with a realistic Andes topography. Simulations that add both a q flux and topography displace rainfall farther to the north in the region 120° to the west of the Andes than in simulations that only have a q flux. Cloud and clear-sky radiative feedbacks in the tropics and subtropics of this model both act to amplify the energy flux and the precipitation response to a given hemispheric asymmetry in oceanic forcing. Energy budget/balance; General circulation models; Precipitation; Atmosphere-ocean interaction; Intertropical convergence zone
Mason, Shannon; Fletcher, Jennifer K.; Haynes, John M.; Franklin, Charmaine; Protat, Alain; Jakob, ChristianMason, S., J. K. Fletcher, J. M. Haynes, C. Franklin, A. Protat, C. Jakob, 2015: A Hybrid Cloud Regime Methodology Used to Evaluate Southern Ocean Cloud and Shortwave Radiation Errors in ACCESS. J. Climate, 28(15), 6001-6018. doi: 10.1175/JCLI-D-14-00846.1. AbstractA deficit of shortwave cloud forcing over the Southern Ocean is persistent in many global climate models. Cloud regimes have been widely used in model evaluation studies to make a process-oriented diagnosis of cloud parameterization errors, but cloud regimes have some limitations in resolving both observed and simulated cloud behavior. A hybrid methodology is developed for identifying cloud regimes from observed and simulated cloud simultaneously.Through this methodology, 11 hybrid cloud regimes are identified in the ACCESS1.3 model for the high-latitude Southern Ocean. The hybrid cloud regimes resolve the features of observed cloud and characterize cloud errors in the model. The simulated properties of the hybrid cloud regimes, and their occurrence over the Southern Ocean and in the context of extratropical cyclones, are evaluated, and their contributions to the shortwave radiation errors are quantified.Three errors are identified: an overall deficit of cloud fraction, a tendency toward optically thin low and midtopped cloud, and an absence of a shallow frontal-type cloud at high latitudes and in the warm fronts of extratropical cyclones.To demonstrate the utility of the hybrid cloud regimes for the evaluation of changes to the model, the effects of selected changes to the model microphysics are investigated. clouds; Model evaluation/performance; climate models; Southern Ocean; Model errors
Matsui, Toshi; Tao, Wei-Kuo; Munchak, S. Joseph; Grecu, Mircea; Huffman, George J.Matsui, T., W. Tao, S. J. Munchak, M. Grecu, G. J. Huffman, 2015: Satellite view of quasi-equilibrium states in tropical convection and precipitation microphysics. Geophysical Research Letters, 42(6), 1959–1968. doi: 10.1002/2015GL063261. This study shows the time series of statistical composites of precipitation-microphysics signals derived from long-term Tropical Rainfall Measuring Mission (TRMM) satellite observations aggregated over the entire tropical domain (37°N–37°S). The result shows the nearly time-invariant monthly signal statistics throughout this time, confirming convection quasi-equilibrium (CQE) states. Merged precipitation data, with much better temporal and spatial coverage, provide evidence that the equilibrium state occurs on a daily scale. These results further indicate the presence of precipitation microphysics quasi-equilibrium (MQE) within the CQE environment. A simple analytic microphysics framework illustrates the equilibrium precipitation size distribution, as compared with the TRMM radar-based as well as preliminary Global Precipitation Measurement combined retrievals. The MQE readily explains the near-constant tropical precipitation rate, which is roughly balanced with atmospheric radiative cooling rate at the entire tropical scale. Further investigation is required through theoretical, observational, and numerical manners to support the MQE hypothesis. convection; 3359 Radiative processes; microphysics; Precipitation; 3371 Tropical convection; 3360 Remote sensing; 3354 Precipitation; 3373 Tropical dynamics; quasi-equilibrium
Mauritsen, Thorsten; Stevens, BjornMauritsen, T., B. Stevens, 2015: Missing iris effect as a possible cause of muted hydrological change and high climate sensitivity in models. Nature Geoscience, 8(5), 346-351. doi: 10.1038/ngeo2414. Equilibrium climate sensitivity to a doubling of CO2 falls between 2.0 and 4.6 K in current climate models, and they suggest a weak increase in global mean precipitation. Inferences from the observational record, however, place climate sensitivity near the lower end of this range and indicate that models underestimate some of the changes in the hydrological cycle. These discrepancies raise the possibility that important feedbacks are missing from the models. A controversial hypothesis suggests that the dry and clear regions of the tropical atmosphere expand in a warming climate and thereby allow more infrared radiation to escape to space. This so-called iris effect could constitute a negative feedback that is not included in climate models. We find that inclusion of such an effect in a climate model moves the simulated responses of both temperature and the hydrological cycle to rising atmospheric greenhouse gas concentrations closer to observations. Alternative suggestions for shortcomings of models — such as aerosol cooling, volcanic eruptions or insufficient ocean heat uptake — may explain a slow observed transient warming relative to models, but not the observed enhancement of the hydrological cycle. We propose that, if precipitating convective clouds are more likely to cluster into larger clouds as temperatures rise, this process could constitute a plausible physical mechanism for an iris effect.
McCoy, Daniel T.; Burrows, Susannah M.; Wood, Robert; Grosvenor, Daniel P.; Elliott, Scott M.; Ma, Po-Lun; Rasch, Phillip J.; Hartmann, Dennis L.McCoy, D. T., S. M. Burrows, R. Wood, D. P. Grosvenor, S. M. Elliott, P. Ma, P. J. Rasch, D. L. Hartmann, 2015: Natural aerosols explain seasonal and spatial patterns of Southern Ocean cloud albedo. Science Advances, 1(6), e1500157. doi: 10.1126/sciadv.1500157. Atmospheric aerosols, suspended solid and liquid particles, act as nucleation sites for cloud drop formation, affecting clouds and cloud properties—ultimately influencing the cloud dynamics, lifetime, water path, and areal extent that determine the reflectivity (albedo) of clouds. The concentration Nd of droplets in clouds that influences planetary albedo is sensitive to the availability of aerosol particles on which the droplets form. Natural aerosol concentrations affect not only cloud properties themselves but also modulate the sensitivity of clouds to changes in anthropogenic aerosols. It is shown that modeled natural aerosols, principally marine biogenic primary and secondary aerosol sources, explain more than half of the spatiotemporal variability in satellite-observed Nd. Enhanced Nd is spatially correlated with regions of high chlorophyll a, and the spatiotemporal variability in Nd is found to be driven primarily by high concentrations of sulfate aerosol at lower Southern Ocean latitudes (35o to 45oS) and by organic matter in sea spray aerosol at higher latitudes (45o to 55oS). Biogenic sources are estimated to increase the summertime mean reflected solar radiation in excess of 10 W m–2 over parts of the Southern Ocean, which is comparable to the annual mean increases expected from anthropogenic aerosols over heavily polluted regions of the Northern Hemisphere. Sulfate and organic mass in sea spray explain more than half of the variability in Southern Ocean cloud droplet concentration. Sulfate and organic mass in sea spray explain more than half of the variability in Southern Ocean cloud droplet concentration.
McCoy, Daniel T.; Hartmann, Dennis L.McCoy, D. T., D. L. Hartmann, 2015: Observations of a substantial cloud-aerosol indirect effect during the 2014–2015 Bárðarbunga-Veiðivötn fissure eruption in Iceland. Geophysical Research Letters, 42(23), 10,409–10,414. doi: 10.1002/2015GL067070. The Bárðarbunga-Veiðivötn fissure eruption lasted from 31 August 2014 to 28 February 2015, during which its sulfur emissions dwarfed anthropogenic emissions from Europe. This natural experiment offers an excellent opportunity to investigate the aerosol indirect effect and the effect of effusive volcanic eruptions on climate. During the eruption cloud droplet effective radius (re) over the region surrounding Iceland was at the lowest value in the 14 year Moderate Imaging Spectroradiometer data record during September and October 2014. The change in reflected solar radiation due to increased cloud reflectivity during September and October is estimated to exceed 2 W m−2 over the region surrounding Iceland, with increases of 1 W m−2 extending as far south as the Açores. The strength of the aerosol indirect effect diagnosed here reaffirms the ability of volcanic aerosols to affect cloud properties and ultimately the planetary albedo. 0320 Cloud physics and chemistry; 0305 Aerosols and particles; cloud; 0321 Cloud/radiation interaction; aerosol; indirect effect; Climate sensitivity; 0370 Volcanic effects; 0480 Remote sensing; Iceland; Natural Aerosols
Meloni, D.; Junkermann, W.; di Sarra, A.; Cacciani, M.; De Silvestri, L.; Di Iorio, T.; Estellés, V.; Gómez-Amo, J. L.; Pace, G.; Sferlazzo, D. M.Meloni, D., W. Junkermann, A. di Sarra, M. Cacciani, L. De Silvestri, T. Di Iorio, V. Estellés, J. L. Gómez-Amo, G. Pace, D. M. Sferlazzo, 2015: Altitude-resolved shortwave and longwave radiative effects of desert dust in the Mediterranean during the GAMARF campaign: Indications of a net daily cooling in the dust layer. Journal of Geophysical Research: Atmospheres, 120(8), 3386–3407. doi: 10.1002/2014JD022312. Desert dust interacts with shortwave (SW) and longwave (LW) radiation, influencing the Earth radiation budget and the atmospheric vertical structure. Uncertainties on the dust role are large in the LW spectral range, where few measurements are available and the dust optical properties are not well constrained. The first airborne measurements of LW irradiance vertical profiles over the Mediterranean were carried out during the Ground-based and Airborne Measurements of Aerosol Radiative Forcing (GAMARF) campaign, which took place in spring 2008 at the island of Lampedusa. The experiment was aimed at estimating the vertical profiles of the SW and LW aerosol direct radiative forcing (ADRF) and heating rates (AHR), taking advantage of vertically resolved measurements of irradiances, meteorological parameters, and aerosol microphysical and optical properties. Two cases, characterized respectively by the presence of a homogeneous dust layer (3 May, with aerosol optical depth, AOD, at 500 nm of 0.59) and by a low aerosol burden (5 May, with AOD of 0.14), are discussed. A radiative transfer model was initialized with the measured vertical profiles and with different aerosol properties, derived from measurements or from the literature. The simulation of the irradiance vertical profiles, in particular, provides the opportunity to constrain model-derived estimates of the AHR. The measured SW and LW irradiances were reproduced when the model was initialized with the measured aerosol size distributions and refractive indices. For the dust case, the instantaneous (solar zenith angle, SZA, of 55.1°) LW-to-SW ADRF ratio was 23% at the surface and 11% at the top of the atmosphere (TOA), with a more significant LW contribution on a daily basis (52% at the surface and 26% at TOA), indicating a relevant reduction of the SW radiative effects. The AHR profiles followed the aerosol extinction profile, with comparable peaks in the SW (0.72 ± 0.11 K d−1) and in the LW (−0.52 ± 0.12 K d−1) for the considered SZA. On a daily basis, the absolute value of the heating rate was larger in the LW than in the SW, producing a net cooling effect at specific levels. These are quite unexpected results, emphasizing the important role of LW radiation. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 3311 Clouds and aerosols; 3359 Radiative processes; Radiative transfer model; aerosol direct radiative forcing and heating rate; aerosol optical properties; airborne measurements; desert dust; shortwave and longwave radiation
Meyers, Patrick C.; Ferraro, Ralph R.; Wang, Nai-YuMeyers, P. C., R. R. Ferraro, N. Wang, 2015: Updated Screening Procedures for GPROF2010 over Land: Utilization for AMSR-E. J. Atmos. Oceanic Technol., 32(5), 1015-1028. doi: 10.1175/JTECH-D-14-00149.1. AbstractThe Goddard profiling algorithm 2010 (GPROF2010) was revised for the Advanced Microwave Scanning Radiometer for Earth Observing System (EOS; AMSR-E) instrument. The GPROF2010 land algorithm was developed for the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI), which observes slightly different central frequencies than AMSR-E. A linear transfer function was developed to convert AMSR-E brightness temperatures to their corresponding TMI frequency for raining and nonraining instantaneous fields of view (IFOVs) using collocated brightness temperature and TRMM precipitation radar (PR) measurements. Previous versions of the algorithm separated rain from surface ice, snow, and desert using a series of empirical procedures. These occasionally failed to separate raining and nonraining scenes, leading to failed detection and false alarms of rain. The new GPROF2010, version 2 (GPROF2010V2), presented here, prefaced the heritage screening procedures by referencing annual desert and monthly snow climatologies to identify IFOVs where rain retrievals were unreliable. Over a decade of satellite- and ground-based observations from the Interactive Multisensor Snow and Ice Mapping System (IMS) and AMSR-E allowed for the creation of a medium-resolution (0.25° × 0.25°) climatology of monthly snow and ice cover. The scattering signature of rain over ice and snow is not well defined because of complex emissivity signals dependent on snow depth, age, and melting, such that using a static climatology was a more stable approach to defining surface types. GPROF2010V2 was subsequently used for the precipitation environmental data record (EDR) for the AMSR2 sensor aboard the Global Change Observation Mission–Water 1 (GCOM-W1). rainfall; Precipitation; Algorithms; Microwave observations
Michibata, Takuro; Takemura, ToshihikoMichibata, T., T. Takemura, 2015: Evaluation of autoconversion schemes in a single model framework with satellite observations. Journal of Geophysical Research: Atmospheres, 120(18), 9570–9590. doi: 10.1002/2015JD023818. We examined the performance of autoconversion (mass transfer from cloud water to rainwater by the coalescence of cloud droplets) schemes in warm rain, which are commonly used in general circulation models. To exclude biases in the different treatment of the aerosol-cloud-precipitation-radiation interaction other than that of the autoconversion process, sensitivity experiments were conducted within a single model framework using an aerosol-climate model, MIROC-SPRINTARS. The liquid water path (LWP) and cloud optical thickness have a particularly high sensitivity to the autoconversion schemes, and their sensitivity is of the same magnitude as model biases. In addition, the ratio of accretion to autoconversion (Acc/Aut ratio), a key parameter in the examination of the balance of microphysical conversion processes, also has a high sensitivity globally depending on the scheme used. Although the Acc/Aut ratio monotonically increases with increasing LWP, significantly lower ratio is observed in Kessler-type schemes. Compared to satellite observations, a poor representation of cloud macrophysical structure and optically thicker low cloud are found in simulations with any autoconversion scheme. As a result of the cloud-radiation interaction, the difference in the global mean net cloud radiative forcing (NetCRF) among the schemes reaches 10 Wm−2. The discrepancy between the observed and simulated NetCRF is especially large with a high LWP. The potential uncertainty in the parameterization of the autoconversion process is nonnegligible, and no formulation significantly improves the bias in the cloud radiative effect yet. This means that more fundamental errors are still left in other processes of the model. 0321 Cloud/radiation interaction; climate model; 1622 Earth system modeling; 3354 Precipitation; 1626 Global climate models; accretion; autoconversion; cloud physics; cloud-precipitation-radiation interaction
Muhlbauer, A.; Ackerman, T. P.; Lawson, R. P.; Xie, S.; Zhang, Y.Muhlbauer, A., T. P. Ackerman, R. P. Lawson, S. Xie, Y. Zhang, 2015: Evaluation of cloud-resolving model simulations of midlatitude cirrus with ARM and A-train observations. Journal of Geophysical Research: Atmospheres, 120(13), 6597–6618. doi: 10.1002/2014JD022570. Cirrus clouds are ubiquitous in the upper troposphere and still constitute one of the largest uncertainties in climate predictions. This paper evaluates cloud-resolving model (CRM) and cloud system-resolving model (CSRM) simulations of a midlatitude cirrus case with comprehensive observations collected under the auspices of the Atmospheric Radiation Measurements (ARM) program and with spaceborne observations from the National Aeronautics and Space Administration A-train satellites. The CRM simulations are driven with periodic boundary conditions and ARM forcing data, whereas the CSRM simulations are driven by the ERA-Interim product. Vertical profiles of temperature, relative humidity, and wind speeds are reasonably well simulated by the CSRM and CRM, but there are remaining biases in the temperature, wind speeds, and relative humidity, which can be mitigated through nudging the model simulations toward the observed radiosonde profiles. Simulated vertical velocities are underestimated in all simulations except in the CRM simulations with grid spacings of 500 m or finer, which suggests that turbulent vertical air motions in cirrus clouds need to be parameterized in general circulation models and in CSRM simulations with horizontal grid spacings on the order of 1 km. The simulated ice water content and ice number concentrations agree with the observations in the CSRM but are underestimated in the CRM simulations. The underestimation of ice number concentrations is consistent with the overestimation of radar reflectivity in the CRM simulations and suggests that the model produces too many large ice particles especially toward the cloud base. Simulated cloud profiles are rather insensitive to perturbations in the initial conditions or the dimensionality of the model domain, but the treatment of the forcing data has a considerable effect on the outcome of the model simulations. Despite considerable progress in observations and microphysical parameterizations, simulating the microphysical, macrophysical, and radiative properties of cirrus remains challenging. Comparing model simulations with observations from multiple instruments and observational platforms is important for revealing model deficiencies and for providing rigorous benchmarks. However, there still is considerable need for reducing observational uncertainties and providing better observations especially for relative humidity and for the size distribution and chemical composition of aerosols in the upper troposphere. 0320 Cloud physics and chemistry; 1704 Atmospheric sciences; 3355 Regional modeling; cirrus; cloud resolving model simulations
Müller, Richard; Pfeifroth, Uwe; Träger-Chatterjee, Christine; Trentmann, Jörg; Cremer, RoswithaMüller, R., U. Pfeifroth, C. Träger-Chatterjee, J. Trentmann, R. Cremer, 2015: Digging the METEOSAT Treasure—3 Decades of Solar Surface Radiation. Remote Sensing, 7(6), 8067-8101. doi: 10.3390/rs70608067. Solar surface radiation data of high quality is essential for the appropriate monitoring and analysis of the Earth's radiation budget and the climate system. Further, they are crucial for the efficient planning and operation of solar energy systems. However, well maintained surface measurements are rare in many regions of the world and over the oceans. There, satellite derived information is the exclusive observational source. This emphasizes the important role of satellite based surface radiation data. Within this scope, the new satellite based CM-SAF SARAH (Solar surfAce RAdiation Heliosat) data record is discussed as well as the retrieval method used. The SARAH data are retrieved with the sophisticated SPECMAGIC method, which is based on radiative transfer modeling. The resulting climate data of solar surface irradiance, direct irradiance (horizontal and direct normal) and clear sky irradiance are covering 3 decades. The SARAH data set is validated with surface measurements of the Baseline Surface Radiation Network (BSRN) and of the Global Energy and Balance Archive (GEBA). Comparison with BSRN data is performed in order to estimate the accuracy and precision of the monthly and daily means of solar surface irradiance. The SARAH solar surface irradiance shows a bias of 1.3 \(W/m^2\) and a mean absolute bias (MAB) of 5.5 \(W/m^2\) for monthly means. For direct irradiance the bias and MAB is 1 \(W/m^2\) and 8.2 \(W/m^2\) respectively. Thus, the uncertainty of the SARAH data is in the range of the uncertainty of ground based measurements. In order to evaluate the uncertainty of SARAH based trend analysis the time series of SARAH monthly means are compared to GEBA. It has been found that SARAH enables the analysis of trends with an uncertainty of 1 \(W/m^2/dec\); a remarkable good result for a satellite based climate data record. SARAH has been also compared to its legacy version, the satellite based CM-SAF MVIRI climate data record. Overall, SARAH shows a significant higher accuracy and homogeneity than its legacy version. With its high accuracy and temporal and spatial resolution SARAH is well suited for regional climate monitoring and analysis as well as for solar energy applications. Remote sensing; aerosols; interactions with atmosphere (clouds; radiative transfer modeling; solar surface irradiance; water vapor) and land/sea surface
Myers, Timothy A.; Norris, Joel R.Myers, T. A., J. R. Norris, 2015: On the Relationships between Subtropical Clouds and Meteorology in Observations and CMIP3 and CMIP5 Models. J. Climate, 28(8), 2945-2967. doi: 10.1175/JCLI-D-14-00475.1. AbstractClimate models’ simulation of clouds over the eastern subtropical oceans contributes to large uncertainties in projected cloud feedback to global warming. Here, interannual relationships of cloud radiative effect and cloud fraction to meteorological variables are examined in observations and in models participating in phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5, respectively). In observations, cooler sea surface temperature, a stronger estimated temperature inversion, and colder horizontal surface temperature advection are each associated with larger low-level cloud fraction and increased reflected shortwave radiation. A moister free troposphere and weaker subsidence are each associated with larger mid- and high-level cloud fraction and offsetting components of shortwave and longwave cloud radiative effect. It is found that a larger percentage of CMIP5 than CMIP3 models simulate the wrong sign or magnitude of the relationship of shortwave cloud radiative effect to sea surface temperature and estimated inversion strength. Furthermore, most models fail to produce the sign of the relationship between shortwave cloud radiative effect and temperature advection. These deficiencies are mostly, but not exclusively, attributable to errors in the relationship between low-level cloud fraction and meteorology. Poor model performance also arises due to errors in the response of mid- and high-level cloud fraction to variations in meteorology. Models exhibiting relationships closest to observations tend to project less solar reflection by clouds in the late twenty-first century and have higher climate sensitivities than poorer-performing models. Nevertheless, the intermodel spread of climate sensitivity is large even among these realistic models. Model evaluation/performance; climate models; marine boundary layer; Stratiform clouds
Nabat, Pierre; Somot, Samuel; Mallet, Marc; Sevault, Florence; Chiacchio, Marc; Wild, MartinNabat, P., S. Somot, M. Mallet, F. Sevault, M. Chiacchio, M. Wild, 2015: Direct and semi-direct aerosol radiative effect on the Mediterranean climate variability using a coupled regional climate system model. Climate Dynamics, 44(3-4), 1127-1155. doi: 10.1007/s00382-014-2205-6. A fully coupled regional climate system model (CNRM-RCSM4) has been used over the Mediterranean region to investigate the direct and semi-direct effects of aerosols, but also their role in the radiation–atmosphere–ocean interactions through multi-annual ensemble simulations (2003–2009) with and without aerosols and ocean–atmosphere coupling. Aerosols have been taken into account in CNRM-RCSM4 through realistic interannual monthly AOD climatologies. An evaluation of the model has been achieved, against various observations for meteorological parameters, and has shown the ability of CNRM-RCSM4 to reproduce the main patterns of the Mediterranean climate despite some biases in sea surface temperature (SST), radiation and cloud cover. The results concerning the aerosol radiative effects show a negative surface forcing on average because of the absorption and scattering of the incident radiation. The SW surface direct effect is on average −20.9 Wm−2 over the Mediterranean Sea, −14.7 Wm−2 over Europe and −19.7 Wm−2 over northern Africa. The LW surface direct effect is weaker as only dust aerosols contribute (+4.8 Wm−2 over northern Africa). This direct effect is partly counterbalanced by a positive semi-direct radiative effect over the Mediterranean Sea (+5.7 Wm−2 on average) and Europe (+5.0 Wm−2) due to changes in cloud cover and atmospheric circulation. The total aerosol effect is consequently negative at the surface and responsible for a decrease in land (on average −0.4 °C over Europe, and −0.5 °C over northern Africa) and sea surface temperature (on average −0.5 °C for the Mediterranean SST). In addition, the latent heat loss is shown to be weaker (−11.0 Wm−2) in the presence of aerosols, resulting in a decrease in specific humidity in the lower troposphere, and a reduction in cloud cover and precipitation. Simulations also indicate that dust aerosols warm the troposphere by absorbing solar radiation, and prevent radiation from reaching the surface, thus stabilizing the troposphere. The comparison with the model response in atmosphere-only simulations shows that these feedbacks are attenuated if SST cannot be modified by aerosols, highlighting the importance of using coupled regional models over the Mediterranean. Oceanic convection is also strengthened by aerosols, which tends to reinforce the Mediterranean thermohaline circulation. In parallel, two case studies are presented to illustrate positive feedbacks between dust aerosols and regional climate. First, the eastern Mediterranean was subject to high dust aerosol loads in June 2007 which reduce land and sea surface temperature, as well as air–sea humidity fluxes. Because of northern wind over the eastern Mediterranean, drier and cooler air has been consequently advected from the sea to the African continent, reinforcing the direct dust effect over land. On the contrary, during the western European heat wave in June 2006, dust aerosols have contributed to reinforcing an important ridge responsible for dry and warm air advection over western Europe, and thus to increasing lower troposphere (+0.8 °C) and surface temperature (+0.5 °C), namely about 15 % of this heat wave. aerosol; Climatology; radiation; dust; Oceanography; Geophysics/Geodesy; Mediterranean; regional climate
Naud, C. M.; Rangwala, I.; Xu, M.; Miller, J. R.Naud, C. M., I. Rangwala, M. Xu, J. R. Miller, 2015: A Satellite View of the Radiative Impact of Clouds on Surface Downward Fluxes in the Tibetan Plateau. J. Appl. Meteor. Climatol., 54(2), 479-493. doi: 10.1175/JAMC-D-14-0183.1. AbstractUsing 13 yr of satellite observations for the Tibetan Plateau, the sensitivities (or partial derivatives) of daytime surface downward shortwave and longwave fluxes with respect to changes in cloud cover and cloud optical thickness are investigated and quantified. Coincident cloud and surface flux retrievals from the NASA Moderate Resolution Imaging Spectroradiometer and the Clouds and the Earth’s Radiant Energy System, respectively, as well as ground-based observations at 11 stations across the plateau are used to examine the spatial and seasonal variability of this sensitivity over the entire plateau. The downward shortwave flux is found to be modulated primarily by changes in cloud cover, but changes in optical thickness also have an impact, as revealed by a multiple regression fit. The coefficient of determination of the regression increases by more than 15% when optical thickness is added. There is significant seasonal and regional variability in the cloud radiative impact. On average, at all stations, the sensitivity of surface shortwave flux to changes in cloud cover is about −0.5 ± 0.1 W m−2 %−1 in winter according to both ground-based and satellite observations but in summer reaches −1.5 ± 0.3 and −1.8 ± 0.2 W m−2 %−1 according to ground-based and satellite observations, respectively. Cloud cover itself has little impact on the sensitivity when clouds are optically thin, but above an optical thickness of 12, sensitivities increase with both cloud cover and cloud optical thickness. The daytime longwave flux response to changes in cloud properties is also examined. The radiative impact of a decrease in cloud cover on the surface net flux can be offset or even canceled if cloud opacity increases by 5%–10%. satellite observations; Cloud cover; Cloud radiative effects; Complex terrain; Regional effects; Surface fluxes
Nicholls, Stephen D.; Decker, Steven G.Nicholls, S. D., S. G. Decker, 2015: Impact of Coupling an Ocean Model to WRF Nor’easter Simulations. Mon. Wea. Rev., 143(12), 4997-5016. doi: 10.1175/MWR-D-15-0017.1. The impact of ocean–atmosphere coupling and its possible seasonal dependence upon Weather Research and Forecasting (WRF) Model simulations of seven, wintertime cyclone events was investigated. Model simulations were identical aside from the degree of ocean model coupling (static SSTs, 1D mixed layer model, full-physics 3D ocean model). Both 1D and 3D ocean model coupling simulations show that SSTs following the passage of a nor’easter did tend to cool more strongly during the early season (October–December) and were more likely to warm late in the season (February–April). Model simulations produce SST differences of up to 1.14 K, but this change did not lead to significant changes in storm track ( Coupled models; Models and modeling; Model comparison; Atmosphere-ocean interaction; Atm/Ocean Structure/ Phenomena; Geographic location/entity; North Atlantic Ocean
Obregón, M. A.; Pereira, S.; Salgueiro, V.; Costa, M. J.; Silva, A. M.; Serrano, A.; Bortoli, D.Obregón, M. A., S. Pereira, V. Salgueiro, M. J. Costa, A. M. Silva, A. Serrano, D. Bortoli, 2015: Aerosol radiative effects during two desert dust events in August 2012 over the Southwestern Iberian Peninsula. Atmospheric Research, 153, 404-415. doi: 10.1016/j.atmosres.2014.10.007. This study provides an analysis of desert dust aerosol radiative effects in the shortwave solar spectrum. For this purpose, the aerosol radiative forcing (ARF) at the earth's surface was calculated during two desert dust events that occurred during August 2012 over Badajoz (Spain) and Évora (Portugal), both stations are located in southwestern Iberian Peninsula. Aerosol properties from these two AERONET stations have been employed to feed the libRadtran model used to simulate irradiances in the shortwave range at the surface under cloud-free conditions. In addition, simulated irradiances for Évora have been compared with Eppley pyranometer measurements. Simulated irradiance values have been used to calculate ARF values at both sites. The overall mean simulated ARF values for Évora and Badajoz during the first event are − 43.03 and − 43.76 W m− 2, respectively, while, for the second event, the overall mean values are − 19.73 and − 26.07 W m− 2, respectively, indicating that the first event has a greater regional radiative impact than the second one, causing a more pronounced radiate cooling at the surface. The ARF per unit of aerosol optical depth (AOD), called the aerosol radiative forcing efficiency (ARFE), is also evaluated for this shortwave spectral range. The ARFE values obtained for Évora and Badajoz during the first event are − 112.93 ± 6.60 W m− 2 and − 101.63 ± 10.73 W m− 2 per unit of AOD (500 nm), respectively, and, for the second event, − 92.44 ± 9.82 W m− 2 and − 87.85 ± 10.19 W m− 2 per unit of AOD (500 nm), respectively. These values also confirm the previous results, i.e., the first event causes a greater radiate cooling than the second one in both stations, although the second desert dust event is more intense, i.e., with higher aerosol optical depth and PM10 aerosol mass concentration. The presence of absorbing aerosols, together with dust, near the surface during the first event may explain the greater efficiency of this aerosol mixture to reduce the downward shortwave irradiance reaching the surface, inducing a greater radiative cooling than the second event. radiative forcing; Dust aerosols; libRadtran model
Orth, Rene; Seneviratne, Sonia I.Orth, R., S. I. Seneviratne, 2015: Introduction of a simple-model-based land surface dataset for Europe. Environmental Research Letters, 10(4), 044012. doi: 10.1088/1748-9326/10/4/044012. Land surface hydrology can play a crucial role during extreme events such as droughts, floods and even heat waves. We introduce in this study a new hydrological dataset for Europe that consists of soil moisture, runoff and evapotranspiration (ET). It is derived with a simple water balance model (SWBM) forced with precipitation, temperature and net radiation. The SWBM dataset extends over the period 1984–2013 with a daily time step and 0.5° × 0.5° resolution. We employ a novel calibration approach, in which we consider 300 random parameter sets chosen from an observation-based range. Using several independent validation datasets representing soil moisture (or terrestrial water content), ET and streamflow, we identify the best performing parameter set and hence the new dataset. To illustrate its usefulness, the SWBM dataset is compared against several state-of-the-art datasets (ERA-Interim/Land, MERRA-Land, GLDAS-2-Noah, simulations of the Community Land Model Version 4), using all validation datasets as reference. For soil moisture dynamics it outperforms the benchmarks. Therefore the SWBM soil moisture dataset constitutes a reasonable alternative to sparse measurements, little validated model results, or proxy data such as precipitation indices. Also in terms of runoff the SWBM dataset performs well, whereas the evaluation of the SWBM ET dataset is overall satisfactory, but the dynamics are less well captured for this variable. This highlights the limitations of the dataset, as it is based on a simple model that uses uniform parameter values. Hence some processes impacting ET dynamics may not be captured, and quality issues may occur in regions with complex terrain. Even though the SWBM is well calibrated, it cannot replace more sophisticated models; but as their calibration is a complex task the present dataset may serve as a benchmark in future. In addition we investigate the sources of skill of the SWBM dataset and find that the parameter set has a similar impact on the simple model results as the choice of the forcing dataset. The newly derived SWBM dataset is of relevance for a range of applications given the deficit of available land datasets. It is available for download on www.iac.ethz.ch/url/SWBM-Dataset.
Osipov, S.; Stenchikov, G.; Brindley, H.; Banks, J.Osipov, S., G. Stenchikov, H. Brindley, J. Banks, 2015: Diurnal cycle of the dust instantaneous direct radiative forcing over the Arabian Peninsula. Atmos. Chem. Phys. Discuss., 15(8), 12301-12352. doi: 10.5194/acpd-15-12301-2015. In this study we attempted to better quantify radiative effects of dust over the Arabian Peninsula and their dependence on input parameters. For this purpose we have developed a standalone column radiation transport model coupled with the Mie calculations and driven by reanalysis meteorological fields and atmospheric composition. Numerical experiments were carried out for a wide range of aerosol optical depths, including extreme values developed during the dust storm on 18–20 March 2012. Comprehensive ground-based observations and satellite retrievals were used to estimate aerosol optical properties, validate calculations and carry out radiation closure. The broadband surface albedo, fluxes at the bottom and top of the atmosphere as well as instantaneous dust radiative forcing were estimated both from the model and observations. Diurnal cycle of the the shortwave instantaneous dust direct radiative forcing was studied for a range of aerosol and surface characteristics representative for the Arabian Peninsula. Mechanisms and parameters responsible for diurnal variability of the radiative forcing were evaluated. We found that intrinsic variability of the surface albedo and its dependence on atmospheric conditions, along with anisotropic aerosol scattering, are mostly responsible for diurnal effects.
Outten, Stephen; Thorne, Peter; Bethke, Ingo; Seland, ØyvindOutten, S., P. Thorne, I. Bethke, Ø. Seland, 2015: Investigating the recent apparent hiatus in surface temperature increases: 1. Construction of two 30-member Earth System Model ensembles. Journal of Geophysical Research: Atmospheres, 120(17), 8575–8596. doi: 10.1002/2015JD023859. The recent Intergovernmental Panel on Climate Change report, along with numerous studies since, has suggested that the apparent global warming hiatus results from some combination of natural variability and changes to external forcings. Herein the external forcings for greenhouse gases (GHGs), long-lived trace gases, volcanic and tropospheric aerosols, and solar irradiance have been replaced in the Norwegian Earth System Model using recent observational estimates. The potential impact of these alternative forcings, and by residual the internally generated variability, is examined through two 30-member ensembles covering the period 1980 to 2012. The Reference ensemble uses the Coupled Model Intercomparison Project phase 5 historical forcings extended with the Representative Concentration Pathway 8.5 (RCP8.5) scenario, while the Sensitivity ensemble uses the alternative forcings. Over the hiatus period defined herein as 1998–2012, all of the forcings show some change between the Sensitivity and Reference experiments and have a combined net forcing change of −0.03 W m−2. The GHG forcing is 0.012 W m−2 higher in the Sensitivity forcings. The alternative solar forcing differs from the Reference forcing by −0.08 W m−2, the same as the alternative volcanic forcing that was based on the latest estimates from NASA Goddard Institute for Space Studies. Anthropogenic aerosol emissions were replaced using the EU-EclipseV4a data set and produce a mean forcing change of 0.11 W m−2 over the period. Part 1 details the creation of the two 30-member ensembles and their characterization for parameters of particular relevance to the explanation of the hiatus. A detailed investigation of the two resulting ensembles global surface temperature behavior is given in Part 2, along with comparisons to observational data sets. 0399 General or miscellaneous; temperature; 1616 Climate variability; 1626 Global climate models; Forcings; 1872 Time series analysis; ensemble; GCMs; hiatus
Painemal, David; Minnis, Patrick; Nordeen, MichelePainemal, D., P. Minnis, M. Nordeen, 2015: Aerosol variability, synoptic-scale processes, and their link to the cloud microphysics over the northeast Pacific during MAGIC. Journal of Geophysical Research: Atmospheres, 120(10), 5122–5139. doi: 10.1002/2015JD023175. Shipborne aerosol measurements collected from October 2012 to September 2013 along 36 transects between the port of Los Angeles, California (33.7°N, 118.2°), and Honolulu, Hawaii (21.3°N, 157.8°W), during the Marine ARM GPCI (Global Energy and Water Cycle Experiment (GEWEX)-Cloud System Study (GCSS)-Pacific Cross-section Intercomparison) Investigation of Clouds campaign are analyzed to determine the circulation patterns that modulate the synoptic and monthly variability of cloud condensation nuclei (CCN) in the boundary layer. Seasonal changes in CCN are evident, with low magnitudes during autumn/winter, and high CCN during spring/summer accompanied with a characteristic westward decrease. CCN monthly evolution is consistent with satellite-derived cloud droplet number concentration Nd from the Moderate Resolution Imaging Spectroradiometer. One-point correlation (r) analysis between the 1000 hPa zonal wind time series over a region between 125°W and 135°W, 35°N and 45°N, and the Nd field yields a negative r (up to −0.55) over a domain that covers a zonal extent of at least 20° from the California shoreline, indicating that Nd decreases when the zonal wind intensifies. The negative r expands southwestward as the zonal wind precedes Nd by up to 3 days, suggesting a transport mechanism from the coast of North America mediated by the California low-coastal jet, which intensifies in summer when the aerosol concentration and Nd reach a maximum. A first assessment of aerosol-cloud interaction (ACI) is performed by combining CCN and satellite Nd values from the Fifteenth Geostationary Operational Environmental Satellite. The CCN-Nd correlation is 0.66–0.69, and the ACI metric defined as ACI = ∂ln(Nd)/∂ln(CCN) is high at 0.9, similar to other aircraft-based studies and substantially greater than those inferred from satellites and climate models. 0305 Aerosols and particles; 3311 Clouds and aerosols; 3310 Clouds and cloud feedbacks; 3360 Remote sensing; aerosol indirect effect; boundary layer clouds; MAGIC campaign; northeast Pacific; satellite clouds microphysics
Painemal, David; Xu, Kuan-Man; Cheng, Anning; Minnis, Patrick; Palikonda, RabindraPainemal, D., K. Xu, A. Cheng, P. Minnis, R. Palikonda, 2015: Mean Structure and Diurnal Cycle of Southeast Atlantic Boundary Layer Clouds: Insights from Satellite Observations and Multiscale Modeling Framework Simulations. J. Climate, 28(1), 324-341. doi: 10.1175/JCLI-D-14-00368.1. AbstractThe mean structure and diurnal cycle of southeast (SE) Atlantic boundary layer clouds are described with satellite observations and multiscale modeling framework (MMF) simulations during austral spring (September–November). Hourly resolution cloud fraction (CF) and cloud-top height (HT) are retrieved from Meteosat-9 radiances using modified Clouds and the Earth’s Radiant Energy System (CERES) Moderate Resolution Imaging Spectroradiometer (MODIS) algorithms, whereas liquid water path (LWP) is from the University of Wisconsin microwave satellite climatology. The MMF simulations use a 2D cloud-resolving model (CRM) that contains an advanced third-order turbulence closure to explicitly simulate cloud physical processes in every grid column of a general circulation model. The model accurately reproduces the marine stratocumulus spatial extent and cloud cover. The mean cloud cover spatial variability in the model is primarily explained by the boundary layer decoupling strength, whereas a boundary layer shoaling accounts for a coastal decrease in CF. Moreover, the core of the stratocumulus cloud deck is concomitant with the location of the strongest temperature inversion. Although the model reproduces the observed westward boundary layer deepening and the spatial variability of LWP, it overestimates LWP by 50%. Diurnal cycles of HT, CF, and LWP from satellites and the model have the same phase, with maxima during the early morning and minima near 1500 local solar time, which suggests that the diurnal cycle is driven primarily by solar heating. Comparisons with the SE Pacific cloud deck indicate that the observed amplitude of the diurnal cycle is modest over the SE Atlantic, with a shallower boundary layer as well. The model qualitatively reproduces these interregime differences. clouds; Cloud retrieval; satellite observations; Cloud cover; Boundary layer; Diurnal effects
Pan, Xin; Liu, Yuanbo; Fan, XingwangPan, X., Y. Liu, X. Fan, 2015: Comparative Assessment of Satellite-Retrieved Surface Net Radiation: An Examination on CERES and SRB Datasets in China. Remote Sensing, 7(4), 4899-4918. doi: 10.3390/rs70404899. Surface net radiation plays an important role in land–atmosphere interactions. The net radiation can be retrieved from satellite radiative products, yet its accuracy needs comprehensive assessment. This study evaluates monthly surface net radiation generated from the Clouds and the Earth’s Radiant Energy System (CERES) and the Surface Radiation Budget project (SRB) products, respectively, with quality-controlled radiation data from 50 meteorological stations in China for the period from March 2000 to December 2007. Our results show that surface net radiation is generally overestimated for CERES (SRB), with a bias of 26.52 W/m2 (18.57 W/m2) and a root mean square error of 34.58 W/m2 (29.49 W/m2). Spatially, the satellite-retrieved monthly mean of surface net radiation has relatively small errors for both CERES and SRB at inland sites in south China. Substantial errors are found at northeastern sites for two datasets, in addition to coastal sites for CERES. Temporally, multi-year averaged monthly mean errors are large at sites in western China in spring and summer, and in northeastern China in spring and winter. The annual mean error fluctuates for SRB, but decreases for CERES between 2000 and 2007. For CERES, 56% of net radiation errors come from net shortwave (NSW) radiation and 44% from net longwave (NLW) radiation. The errors are attributable to environmental parameters including surface albedo, surface water vapor pressure, land surface temperature, normalized difference vegetation index (NDVI) of land surface proxy, and visibility for CERES. For SRB, 65% of the errors come from NSW and 35% from NLW radiation. The major influencing factors in a descending order are surface water vapor pressure, surface albedo, land surface temperature, NDVI, and visibility. Our findings offer an insight into error patterns in satellite-retrieved surface net radiation and should be valuable to improving retrieval accuracy of surface net radiation. Moreover, our study on radiation data of China provides a case example for worldwide validation. CERES; accuracy assessment; SRB; surface net radiation
Park, Myung-Sook; Ho, Chang-Hoi; Cho, Heeje; Choi, Yong-SangPark, M., C. Ho, H. Cho, Y. Choi, 2015: Retrieval of outgoing longwave radiation from COMS narrowband infrared imagery. Advances in Atmospheric Sciences, 32(3), 375-388. doi: 10.1007/s00376-014-4013-7. Hourly outgoing longwave radiation (OLR) from the geostationary satellite Communication Oceanography Meteorological Satellite (COMS) has been retrieved since June 2010. The COMS OLR retrieval algorithms are based on regression analyses of radiative transfer simulations for spectral functions of COMS infrared channels. This study documents the accuracies of OLRs for future climate applications by making an intercomparison of four OLRs from one single-channel algorithm (OLR12.0 using the 12.0 μm channel) and three multiple-channel algorithms (OLR10.8+12.0 using the 10.8 and 12.0 μm channels; OLR6.7+10.8 using the 6.7 and 10.8 μm channels; and OLRAll using the 6.7, 10.8, and 12.0 μm channels). The COMS OLRs from these algorithms were validated with direct measurements of OLR from a broadband radiometer of the Clouds and Earth’s Radiant Energy System (CERES) over the full COMS field of view [roughly (50°S–50°N, 70°–170°E)] during April 2011. Validation results show that the root-mean-square errors of COMS OLRs are 5–7 W m−2, which indicates good agreement with CERES OLR over the vast domain. OLR6.7+10.8 and OLRAll have much smaller errors (∼6 W m−2) than OLR12.0 and OLR10.8+12.0 (∼8 W m−2). Moreover, the small errors of OLR6.7+10.8 and OLRAll are systematic and can be readily reduced through additional mean bias correction and/or radiance calibration. These results indicate a noteworthy role of the 6.7 μm water vapor absorption channel in improving the accuracy of the OLRs. The dependence of the accuracy of COMS OLRs on various surface, atmospheric, and observational conditions is also discussed. Meteorology; Atmospheric Sciences; Geophysics/Geodesy; outgoing longwave radiation; Cloud and Earth’s Radiant Energy System; Communication Oceanography and Meteorological Satellite
Pyrina, M.; Hatzianastassiou, N.; Matsoukas, C.; Fotiadi, A.; Papadimas, C. D.; Pavlakis, K. G.; Vardavas, I.Pyrina, M., N. Hatzianastassiou, C. Matsoukas, A. Fotiadi, C. D. Papadimas, K. G. Pavlakis, I. Vardavas, 2015: Cloud effects on the solar and thermal radiation budgets of the Mediterranean basin. Atmospheric Research, 152, 14-28. doi: 10.1016/j.atmosres.2013.11.009. The cloud effects on the shortwave (SW), longwave (LW) and net all-wave radiation budgets of the Mediterranean basin were computed using a detailed radiative transfer model together with satellite and reanalysis data for surface and atmospheric properties. The model radiation fluxes at TOA were validated against CERES and ERBE satellite data, while at the Earth's surface they were validated against ground-based GEBA and BSRN station measurements. The cloud radiative effects were obtained for low, middle, high-level clouds, and for total cloud cover. Overall for the basin, the effect on solar radiation is to produce radiative cooling at the top of atmosphere (TOA) and at the surface that more than balances the warming effects on terrestrial radiation. The result is a net radiative cooling at TOA and at the surface, equal to − 18.8 and − 15.9 Wm− 2, respectively. The low-level clouds are most important for the TOA budget through significant SW reflection and little LW emission to space. High clouds play an important role in net surface cooling (− 9.8 Wm− 2) through the combination of SW reflection to space and a much reduced LW warming effect at the surface. The geographical patterns of the effects are mainly characterized by a strong south to north increasing gradient. The seasonal variation of net radiative effects is dominated by solar radiation with maxima in spring and minima in winter. clouds; climate; radiation; Mediterranean
Qiu, Shaoyue; Dong, Xiquan; Xi, Baike; Li, J.-L. F.Qiu, S., X. Dong, B. Xi, J. F. Li, 2015: Characterizing Arctic mixed-phase cloud structure and its relationship with humidity and temperature inversion using ARM NSA observations. Journal of Geophysical Research: Atmospheres, 120(15), 7737–7746. doi: 10.1002/2014JD023022. In this study, the characteristics of the Arctic mixed-phase cloud (AMC) have been investigated using data collected at the Atmospheric Radiation Measurement North Slope Alaska site from October 2006 to September 2009. AMC has an annual occurrence frequency of 42.3%, which includes 18.7% of single-layered AMCs and 23.6% for multiple layers. Two cloud base heights (CBHs) are defined from ceilometer and micropulse lidar (MPL) measurements. For single-layered AMC, the ceilometer-derived CBH represents the base of the liquid-dominant layer near the cloud top, while MPL-derived CBH represents base of the lower ice-dominant layer. The annual mean CBHs from ceilometer and MPL measurements are 1.0 km and 0.6 km, respectively, with the largest difference (~1.0 km) occurring from December to March and the smallest difference in September. The humidity inversion occurrence decreases with increasing humidity inversion intensity (stronger in summer than in winter). During the winter months, AMC occurrences increase from 15% to 35% when the inversion intensity increases from 0.1 to 0.9 g/kg. On the contrary, despite a higher frequency of strong humidity inversion in summer, AMC occurrences are nearly invariant for different inversion intensities. On average, humidity and temperature inversion frequencies of occurrence above an AMC are 5 and 8 times, respectively, as high as those below an AMC. The strong inversion occurrences for both humidity and temperature above an AMC provide the moisture sources from above for the formation and maintenance of AMCs. This result helps to reconcile the persistency of AMCs even when the Arctic surface is covered by snow and ice. 0320 Cloud physics and chemistry; 3394 Instruments and techniques; 3360 Remote sensing; 3307 Boundary layer processes; 3349 Polar meteorology; cloud base height; cloud occurrence; humidity inversion; mixed-phase cloud; temperature inversion
Roca, Rémy; Brogniez, Hélène; Chambon, Philippe; Chomette, Olivier; Cloché, Sophie; Gosset, Marielle Eliane; Mahfouf, Jean-francois; Raberanto, Patrick; Viltard, NicolasRoca, R., H. Brogniez, P. Chambon, O. Chomette, S. Cloché, M. E. Gosset, J. Mahfouf, P. Raberanto, N. Viltard, 2015: The Megha-Tropiques mission: a review after three years in orbit. Atmospheric Science, 3, 17. doi: 10.3389/feart.2015.00017. The Megha-Tropiques mission is operating a suite of payloads dedicated to the documentation of the water and energy cycles in the intertropical region in a low inclination orbit. The satellite was launched in October, 2011 and we here review the scientific activity after the first three years of the mission. The microwave sounder (SAPHIR) and the broad band radiometer (SCARAB) are functioning nominally and exhibit instrumental performances well within the original specifications. The microwave imager, MADRAS, stopped acquisition of scientific data on January 26th, 2013 due to a mechanical failure. During its 16 months of operation, this radiometer experienced electrical issues making its usage difficult and delayed its validation. A suite of geophysical products has been retrieved from the Megha-Tropiques payloads, ranging from TOA radiative flux to water vapor profiles and instantaneous rain rates. Some of these geophysical products have been merged with geostationary data to provide, for instance, daily accumulation of rainfall all over the intertropical region. These products compare favorably with references from ground based or space-borne observation systems. The contribution of the mission unique orbit to its scientific objectives is investigated. Preliminary studies indicate a positive impact on both, humidity Numerical Weather Prediction forecasts thanks to the assimilation of SAPHIR Level 1 data, and on the rainfall estimation derived from the Global Precipitation Mission constellation. After a long commissioning phase, most of the data and the geophysical products suite are validated and readily available for further scientific investigation by the international community. validation; satellite observation; assimilation; Tropical Climate; water and energy cycle
Rodell, M.; Beaudoing, H. K.; L’Ecuyer, T. S.; Olson, W. S.; Famiglietti, J. S.; Houser, P. R.; Adler, R.; Bosilovich, M. G.; Clayson, C. A.; Chambers, D.; Clark, E.; Fetzer, E. J.; Gao, X.; Gu, G.; Hilburn, K.; Huffman, G. J.; Lettenmaier, D. P.; Liu, W. T.; Robertson, F. R.; Schlosser, C. A.; Sheffield, J.; Wood, E. F.Rodell, M., H. K. Beaudoing, T. S. L’Ecuyer, W. S. Olson, J. S. Famiglietti, P. R. Houser, R. Adler, M. G. Bosilovich, C. A. Clayson, D. Chambers, E. Clark, E. J. Fetzer, X. Gao, G. Gu, K. Hilburn, G. J. Huffman, D. P. Lettenmaier, W. T. Liu, F. R. Robertson, C. A. Schlosser, J. Sheffield, E. F. Wood, 2015: The Observed State of the Water Cycle in the Early Twenty-First Century. J. Climate, 28(21), 8289-8318. doi: 10.1175/JCLI-D-14-00555.1. This study quantifies mean annual and monthly fluxes of Earth’s water cycle over continents and ocean basins during the first decade of the millennium. To the extent possible, the flux estimates are based on satellite measurements first and data-integrating models second. A careful accounting of uncertainty in the estimates is included. It is applied within a routine that enforces multiple water and energy budget constraints simultaneously in a variational framework in order to produce objectively determined optimized flux estimates. In the majority of cases, the observed annual surface and atmospheric water budgets over the continents and oceans close with much less than 10% residual. Observed residuals and optimized uncertainty estimates are considerably larger for monthly surface and atmospheric water budget closure, often nearing or exceeding 20% in North America, Eurasia, Australia and neighboring islands, and the Arctic and South Atlantic Oceans. The residuals in South America and Africa tend to be smaller, possibly because cold land processes are negligible. Fluxes were poorly observed over the Arctic Ocean, certain seas, Antarctica, and the Australasian and Indonesian islands, leading to reliance on atmospheric analysis estimates. Many of the satellite systems that contributed data have been or will soon be lost or replaced. Models that integrate ground-based and remote observations will be critical for ameliorating gaps and discontinuities in the data records caused by these transitions. Continued development of such models is essential for maximizing the value of the observations. Next-generation observing systems are the best hope for significantly improving global water budget accounting. Remote sensing; Water budget; Physical Meteorology and Climatology; Observational techniques and algorithms; Mathematical and statistical techniques; Numerical analysis/modeling
Roebeling, Rob; Baum, Bryan; Bennartz, Ralf; Hamann, Ulrich; Heidinger, Andrew; Meirink, Jan Fokke; Stengel, Martin; Thoss, Anke; Walther, Andi; Watts, PhilRoebeling, R., B. Baum, R. Bennartz, U. Hamann, A. Heidinger, J. F. Meirink, M. Stengel, A. Thoss, A. Walther, P. Watts, 2015: Summary of the Fourth Cloud Retrieval Evaluation Workshop. Bull. Amer. Meteor. Soc., 96(4), ES71-ES74. doi: 10.1175/BAMS-D-14-00184.1.
Rondanelli, Roberto; Molina, Alejandra; Falvey, MarkRondanelli, R., A. Molina, M. Falvey, 2015: The Atacama Surface Solar Maximum. Bull. Amer. Meteor. Soc., 96(3), 405-418. doi: 10.1175/BAMS-D-13-00175.1. AbstractSolar radiation reaching Earth’s surface is one of the major drivers of climate dynamics. By setting the surface energy balance, downwelling solar radiation indirectly heats the atmosphere and controls the hydrological cycle. Besides its critical importance as a physical mechanism for driving climate and weather, solar radiation has attracted interest as a potentially major source of energy for human activities.For a given latitude, solar radiation at Earth’s surface depends mostly on the composition along the atmospheric path. Since the early twentieth century, major astronomical observatories have led the search for the best places for observation from Earth, which presents a similar problem to the one of finding the maximum of solar radiation at the surface. In particular, Mount Montezuma in the Atacama Desert, Chile, was identified by the pioneers of solar observation as an ideal place to conduct the search for variations of the solar constant estimated from Earth’s surface.By using available global datasets, a semiempirical model for the surface solar radiation over northern Chile, and a network of surface stations, we confirm Atacama as the place where the highest mean surface solar radiation is found. The most likely location of the maximum downwelling solar radiation over the surface of the planet is on the pre-Andean Domeyko Cordillera (3,500–5,000 m above mean sea level, between 24° and 25°S, along 69°W) with a value of about 310 ± 15 W m–2. We discuss the main regional and local features of this region that conspire to produce the solar maximum.
Rutan, David A.; Kato, Seiji; Doelling, David R.; Rose, Fred G.; Nguyen, Le Trang; Caldwell, Thomas E.; Loeb, Norman G.Rutan, D. A., S. Kato, D. R. Doelling, F. G. Rose, L. T. Nguyen, T. E. Caldwell, N. G. Loeb, 2015: CERES Synoptic Product: Methodology and Validation of Surface Radiant Flux. J. Atmos. Oceanic Technol., 32(6), 1121-1143. doi: 10.1175/JTECH-D-14-00165.1. AbstractThe Clouds and the Earth’s Radiant Energy System Synoptic (SYN1deg), edition 3, product provides climate-quality global 3-hourly 1° × 1°gridded top of atmosphere, in-atmosphere, and surface radiant fluxes. The in-atmosphere surface fluxes are computed hourly using a radiative transfer code based upon inputs from Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS), 3-hourly geostationary (GEO) data, and meteorological assimilation data from the Goddard Earth Observing System. The GEO visible and infrared imager calibration is tied to MODIS to ensure uniform MODIS-like cloud properties across all satellite cloud datasets. Computed surface radiant fluxes are compared to surface observations at 85 globally distributed land (37) and ocean buoy (48) sites as well as several other publicly available global surface radiant flux data products. Computed monthly mean downward fluxes from SYN1deg have a bias (standard deviation) of 3.0 W m−2 (5.7%) for shortwave and −4.0 W m−2 (2.9%) for longwave compared to surface observations. The standard deviation between surface downward shortwave flux calculations and observations at the 3-hourly time scale is reduced when the diurnal cycle of cloud changes is explicitly accounted for. The improvement is smaller for surface downward longwave flux owing to an additional sensitivity to boundary layer temperature/humidity, which has a weaker diurnal cycle compared to clouds. radiative transfer; satellite observations; Climate records; Surface fluxes
Ruzmaikin, Alexander; Aumann, Hartmut H.; Jiang, Jonathan H.Ruzmaikin, A., H. H. Aumann, J. H. Jiang, 2015: Interhemispheric Variability of Earth’s Radiation. J. Atmos. Sci., 72(12), 4615-4628. doi: 10.1175/JAS-D-15-0106.1. The variability of interhemispheric symmetry of Earth’s energy serves as an independent indicator of climate change. The analysis of updated data obtained from satellite measurements at the top of the atmosphere (TOA) shows that in accord with Earth’s orbital requirements the annually averaged incident solar radiation is the same in the Northern and Southern Hemispheres, the annual mean of the reflected shortwave radiation is almost north–south symmetric, and the annual mean of the outgoing longwave radiation is larger in the Northern Hemisphere by 1.4 W m−2. These mean radiations systematically differ from the mean radiations found from the numerical atmospheric models that participated in the Coupled Model Intercomparison Project phase 5 (CMIP5). The hemispheric differences of the TOA radiations vary on the annual and interannual time scales. The multidecadal variability in Earth’s north–south temperature difference reveals a similarity of trends in both hemispheres. The Atlantic meridional transport (in contrast to the Pacific meridional transport) is found to be coherent with the interhemispheric ocean heat content (OHC) difference on decadal and multidecadal time scales, indicating a critical role of the Atlantic in the interhemispheric energy balance change. satellite observations; Oceanic variability; Interannual variability; Climate records; Variability; Atmosphere-ocean interaction; Atm/Ocean Structure/ Phenomena; Climate variability; Observational techniques and algorithms
Sanderson, Benjamin M.; Knutti, Reto; Caldwell, PeterSanderson, B. M., R. Knutti, P. Caldwell, 2015: Addressing Interdependency in a Multimodel Ensemble by Interpolation of Model Properties. J. Climate, 28(13), 5150-5170. doi: 10.1175/JCLI-D-14-00361.1. AbstractThe diverse set of Earth system models used to conduct the CMIP5 ensemble can partly sample the uncertainties in future climate projections. However, combining those projections is complicated by the fact that models developed by different groups share ideas and code and therefore biases. The authors propose a method for combining model results into single or multivariate distributions that are more robust to the inclusion of models with a large degree of interdependency. This study uses a multivariate metric of present-day climatology to assess both model performance and similarity in two recent model intercomparisons, CMIP3 and CMIP5. Model characteristics can be interpolated and then resampled in a space defined by independent climate properties. A form of weighting can be applied by sampling more densely in the region of the space close to the projected observations, thus taking into account both model performance and interdependence. The choice of the sampling distribution’s parameters is a subjective decision that should reflect the researcher’s prior assumptions as to the acceptability of different model errors. Model evaluation/performance; climate models; Climate sensitivity; Ensembles; bias; Statistical techniques
Sanderson, Benjamin M.; Knutti, Reto; Caldwell, PeterSanderson, B. M., R. Knutti, P. Caldwell, 2015: A Representative Democracy to Reduce Interdependency in a Multimodel Ensemble. J. Climate, 28(13), 5171-5194. doi: 10.1175/JCLI-D-14-00362.1. AbstractThe collection of Earth system models available in the archive of phase 5 of CMIP (CMIP5) represents, at least to some degree, a sample of uncertainty of future climate evolution. The presence of duplicated code as well as shared forcing and validation data in the multiple models in the archive raises at least three potential problems: biases in the mean and variance, the overestimation of sample size, and the potential for spurious correlations to emerge in the archive because of model replication. Analytical evidence is presented to demonstrate that the distribution of models in the CMIP5 archive is not consistent with a random sample, and a weighting scheme is proposed to reduce some aspects of model codependency in the ensemble. A method is proposed for selecting diverse and skillful subsets of models in the archive, which could be used for impact studies in cases where physically consistent joint projections of multiple variables (and their temporal and spatial characteristics) are required. climate models; Model errors; Numerical analysis/modeling; Empirical orthogonal functions; Interpolation schemes; Statistical techniques
Sant, V.; Posselt, R.; Lohmann, U.Sant, V., R. Posselt, U. Lohmann, 2015: Prognostic precipitation with three liquid water classes in the ECHAM5-HAM GCM. Atmos. Chem. Phys. Discuss., 15(5), 7783-7836. doi: 10.5194/acpd-15-7783-2015. In order to improve the global representation of rain formation in marine stratiform clouds a new parameterization with three prognostic liquid water classes was implemented into the general circulation model ECHAM5 with the aerosol module HAM. The additionally introduced drizzle class improves the physical representation of the droplet spectrum and more importantly, improves the microphysical processes relevant for precipitation formation compared to the standard parameterization. In order to avoid a mismatch of the liquid and ice phase, the prognostic treatment of snow has been introduced too. This has a significant effect on the amount and altitude of ice clouds, which in turn does not only affect in- and outgoing radiation, but also the parameterized collection rates. With the introduction of a prognostic precipitation scheme a more realistic representation of both liquid and ice phase large-scale precipitation is achieved compared to a diagnostic treatment. An encouraging finding is that the sensitivity of the liquid water path to the anthropogenic aerosol forcing with the prognostic treatment is reduced by about 25%. Although the total net radiative forcing is increased from 1.4±0.4 to 1.6±0.4 W m−2 from the control to the prognostic model version, the difference is within the interannual variability. Altogether the results suggest that the treatment of precipitation in global circulation models has a significant influence on the phase and lifetime of clouds, but also hints towards the uncertainties related to a prognostic precipitation scheme.
Santer, Benjamin D.; Solomon, Susan; Bonfils, Céline; Zelinka, Mark D.; Painter, Jeffrey F.; Beltran, Francisco; Fyfe, John C.; Johannesson, Gardar; Mears, Carl; Ridley, David A.; Vernier, Jean-Paul; Wentz, Frank J.Santer, B. D., S. Solomon, C. Bonfils, M. D. Zelinka, J. F. Painter, F. Beltran, J. C. Fyfe, G. Johannesson, C. Mears, D. A. Ridley, J. Vernier, F. J. Wentz, 2015: Observed multivariable signals of late 20th and early 21st century volcanic activity. Geophysical Research Letters, 42(2), 500–509. doi: 10.1002/2014GL062366. The relatively muted warming of the surface and lower troposphere since 1998 has attracted considerable attention. One contributory factor to this “warming hiatus” is an increase in volcanically induced cooling over the early 21st century. Here we identify the signals of late 20th and early 21st century volcanic activity in multiple observed climate variables. Volcanic signals are statistically discernible in spatial averages of tropical and near-global SST, tropospheric temperature, net clear-sky short-wave radiation, and atmospheric water vapor. Signals of late 20th and early 21st century volcanic eruptions are also detectable in near-global averages of rainfall. In tropical average rainfall, however, only a Pinatubo-caused drying signal is identifiable. Successful volcanic signal detection is critically dependent on removal of variability induced by the El Niño–Southern Oscillation. 1640 Remote sensing; climate change; 1616 Climate variability; 0370 Volcanic effects; 3354 Precipitation; Signal detection; Volcanic forcing
Seiki, Tatsuya; Kodama, Chihiro; Noda, Akira T.; Satoh, MasakiSeiki, T., C. Kodama, A. T. Noda, M. Satoh, 2015: Improvement in Global Cloud-System-Resolving Simulations by Using a Double-Moment Bulk Cloud Microphysics Scheme. J. Climate, 28(6), 2405-2419. doi: 10.1175/JCLI-D-14-00241.1. AbstractThis study examines the impact of an alteration of a cloud microphysics scheme on the representation of longwave cloud radiative forcing (LWCRF) and its impact on the atmosphere in global cloud-system-resolving simulations. A new double-moment bulk cloud microphysics scheme is used, and the simulated results are compared with those of a previous study. It is demonstrated that improvements within the new cloud microphysics scheme have the potential to substantially improve climate simulations. The new cloud microphysics scheme represents a realistic spatial distribution of the cloud fraction and LWCRF, particularly near the tropopause. The improvement in the cirrus cloud-top height by the new cloud microphysics scheme substantially reduces the warm bias in atmospheric temperature from the previous simulation via LWCRF by the cirrus clouds. The conversion rate of cloud ice to snow and gravitational sedimentation of cloud ice are the most important parameters for determining the strength of the radiative heating near the tropopause and its impact on atmospheric temperature. Feedback; Cloud microphysics; Model evaluation/performance; General circulation models; Cloud radiative effects; Nonhydrostatic models
Seiki, Tatsuya; Kodama, Chihiro; Satoh, Masaki; Hashino, Tempei; Hagihara, Yuichiro; Okamoto, HajimeSeiki, T., C. Kodama, M. Satoh, T. Hashino, Y. Hagihara, H. Okamoto, 2015: Vertical grid spacing necessary for simulating tropical cirrus clouds with a high-resolution atmospheric general circulation model. Geophysical Research Letters, 42(10), 4150–4157. doi: 10.1002/2015GL064282. The distribution of simulated cirrus clouds over the tropics is affected by the particular model's vertical grid spacing. To examine this effect, we use a high-resolution atmospheric general circulation model with 28 km and 14 km horizontal meshes. We show that a vertical grid spacing of 400 m or less is necessary to resolve the bulk structure of cirrus clouds. As one reduces the vertical grid spacing below about 1000 m, the visible cirrus cloud fraction decreases, the cloud thins (optically and geometrically), the cloud top height lowers, and consequently, the outgoing longwave radiation increases. These effects are stronger over the tropics. When using a vertical grid spacing of 400 m or less, the vertical profiles of effective radii and ice water content converge toward measurements (CloudSat satellite and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation). 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; Cloud microphysics; cirrus clouds; 1626 Global climate models; general circulation model; vertical resolution
Sena, E. T.; Artaxo, P.Sena, E. T., P. Artaxo, 2015: A novel methodology for large-scale daily assessment of the direct radiative forcing of smoke aerosols. Atmos. Chem. Phys., 15(10), 5471-5483. doi: 10.5194/acp-15-5471-2015. A new methodology was developed for obtaining daily retrievals of the direct radiative forcing of aerosols (24h-DARF) at the top of the atmosphere (TOA) using satellite remote sensing. Simultaneous CERES (Clouds and Earth's Radiant Energy System) shortwave flux at the top of the atmosphere and MODIS (Moderate Resolution Spectroradiometer) aerosol optical depth (AOD) retrievals were used. To analyse the impact of forest smoke on the radiation balance, this methodology was applied over the Amazonia during the peak of the biomass burning season from 2000 to 2009. To assess the spatial distribution of the DARF, background smoke-free scenes were selected. The fluxes at the TOA under clean conditions (Fcl) were estimated as a function of the illumination geometry (θ0) for each 0.5° × 0.5° grid cell. The instantaneous DARF was obtained as the difference between the clean (Fcl (θ0)) and the polluted flux at the TOA measured by CERES in each cell (Fpol (θ0)). The radiative transfer code SBDART (Santa Barbara DISORT Radiative Transfer model) was used to expand instantaneous DARFs to 24 h averages. This new methodology was applied to assess the DARF both at high temporal resolution and over a large area in Amazonia. The spatial distribution shows that the mean 24h-DARF can be as high as −30 W m−2 over some regions. The temporal variability of the 24h-DARF along the biomass burning season was also studied and showed large intraseasonal and interannual variability. We showed that our methodology considerably reduces statistical sources of uncertainties in the estimate of the DARF, when compared to previous approaches. DARF assessments using the new methodology agree well with ground-based measurements and radiative transfer models. This demonstrates the robustness of the new proposed methodology for assessing the radiative forcing for biomass burning aerosols. To our knowledge, this is the first time that satellite remote sensing assessments of the DARF have been compared with ground-based DARF estimates.
Sèze, Geneviève; Pelon, Jacques; Derrien, Marcel; Le Gléau, Hervé; Six, BrunoSèze, G., J. Pelon, M. Derrien, H. Le Gléau, B. Six, 2015: Evaluation against CALIPSO lidar observations of the multi-geostationary cloud cover and type dataset assembled in the framework of the Megha-Tropiques mission. Quarterly Journal of the Royal Meteorological Society, 141(688), 774-797. doi: 10.1002/qj.2392. To support the Megha-Tropiques space mission, cloud mask and cloud type classification are needed at high spatial and time resolutions over the tropical belt for water vapour and precipitation analysis. For this purpose, visible and infrared radiance data from geostationary satellites (GEO) are used with a single algorithm initially developed by SAFNWC (Satellite Application Facility for Nowcasting) for Meteosat Second Generation. This algorithm has been adapted by SAFNWC to the spectral characteristics and field of view of each satellite. Retrieved cloud cover characteristics (cloud mask, classification and top pressure) are evaluated over four months in summer of 2009 against CALIOP lidar observations from the CALIPSO polar-orbiting satellite. To better identify atmospheric and instrumental issues, separate analyses are performed over land and ocean, for 1:30 a.m. and 1:30 p.m. CALIPSO overpasses and for each GEO. Both mean cloud-cover occurrence and instantaneous cloud-cover statistics are compared. We found that each classification has specific features, which depend on observed cloud regimes and instrument capabilities. Most important, a common behaviour of the GEOs against CALIOP depending on cloud type is observed. We found that GEO cloud occurrence is lower by about 10% than for CALIOP, with the largest biases over land during daytime and the smallest over ocean during daytime. Further detailed analysis reveals specific discrepancies in the retrieved cloud types. As expected, high-level clouds are detected more frequently by the lidar. We show that, over ocean when the optical thickness of detected high-level clouds is limited to greater than 0.1 in the comparisons, multi-spectral radiometry performs very similarly. However, the most significant difference is attributed to non-detection of low-level clouds that are often broken, which causes a reduction of up to 20% in low-level cloud fraction and even 30% in some regions. Other significant differences are seen over land, where mid-level clouds are not detected or are misclassified. tropics; satellite observations; Cloud cover; lidar observations
Shankar, Mohan; Priestley, Kory; Smith, Nathaniel; Smith, Nitchie; Thomas, Susan; Walikainen, DaleShankar, M., K. Priestley, N. Smith, N. Smith, S. Thomas, D. Walikainen, 2015: Radiometric calibration and performance trends of the Clouds and Earth’s Radiant Energy System (CERES) instruments onboard the Terra and Aqua spacecraft. Proc. SPIE 9639, Sensors, Systems, and Next-Generation Satellites XIX, 9639, 963915-963915-13. doi: 10.1117/12.2194468. The Clouds and Earth’s Radiant Energy System (CERES) instruments help to study the impact of clouds on the earth's radiation budget. There are currently five instruments- two each on board Aqua and Terra spacecraft and one on the Suomi NPP spacecraft to measure the earth’s reflected shortwave and emitted longwave energy, which represent two components of the earth’s radiation energy budget. Flight Models (FM) 1 and 2 are on Terra, FM 3 and 4 are on Aqua, and FM5 is on Suomi NPP. The measurements are made by three sensors on each instrument: a shortwave sensor that measures the 0.3-5 microns wavelength band, a window sensor that measures the water vapor window between 8-12 microns, and a total sensor that measures all incident energy (0.3- >100 microns). The required accuracy of CERES measurements of 0.5% in the longwave and 1% in the shortwave is achieved through an extensive pre-launch ground calibration campaign as well as on-orbit calibration and validation activities. Onorbit calibration is carried out using the Internal Calibration Module (ICM) that consists of a tungsten lamp, blackbodies, and a solar diffuser known as the Mirror Attenuator Mosaic (MAM). The ICM calibration provides information about the stability of the sensors’ broadband radiometric gains on-orbit. Several validation studies are conducted in order to monitor the behavior of the instruments in various spectral bands. The CERES Edition-4 data products for the FM1-FM4 instruments incorporate the latest calibration methodologies to improve on the Edition-3 data products. In this paper, we discuss the updated calibration methodology and present some validation studies to demonstrate the improvement in the trends using the CERES Edition-4 data products for all four instruments.
Shi, X.; Liu, X.; Zhang, K.Shi, X., X. Liu, K. Zhang, 2015: Effects of pre-existing ice crystals on cirrus clouds and comparison between different ice nucleation parameterizations with the Community Atmosphere Model (CAM5). Atmos. Chem. Phys., 15(3), 1503-1520. doi: 10.5194/acp-15-1503-2015. In order to improve the treatment of ice nucleation in a more realistic manner in the Community Atmosphere Model version 5.3 (CAM5.3), the effects of pre-existing ice crystals on ice nucleation in cirrus clouds are considered. In addition, by considering the in-cloud variability in ice saturation ratio, homogeneous nucleation takes place spatially only in a portion of the cirrus cloud rather than in the whole area of the cirrus cloud. Compared to observations, the ice number concentrations and the probability distributions of ice number concentration are both improved with the updated treatment. The pre-existing ice crystals significantly reduce ice number concentrations in cirrus clouds, especially at mid- to high latitudes in the upper troposphere (by a factor of ~10). Furthermore, the contribution of heterogeneous ice nucleation to cirrus ice crystal number increases considerably. Besides the default ice nucleation parameterization of Liu and Penner (2005, hereafter LP) in CAM5.3, two other ice nucleation parameterizations of Barahona and Nenes (2009, hereafter BN) and Kärcher et al. (2006, hereafter KL) are implemented in CAM5.3 for the comparison. In-cloud ice crystal number concentration, percentage contribution from heterogeneous ice nucleation to total ice crystal number, and pre-existing ice effects simulated by the three ice nucleation parameterizations have similar patterns in the simulations with present-day aerosol emissions. However, the change (present-day minus pre-industrial times) in global annual mean column ice number concentration from the KL parameterization (3.24 × 106 m−2) is less than that from the LP (8.46 × 106 m−2) and BN (5.62 × 106 m−2) parameterizations. As a result, the experiment using the KL parameterization predicts a much smaller anthropogenic aerosol long-wave indirect forcing (0.24 W m−2) than that using the LP (0.46 W m−2) and BN (0.39 W m−2) parameterizations.
Shupe, Matthew D.; Turner, David D.; Zwink, Alexander; Thieman, Mandana M.; Mlawer, Eli J.; Shippert, TimothyShupe, M. D., D. D. Turner, A. Zwink, M. M. Thieman, E. J. Mlawer, T. Shippert, 2015: Deriving Arctic Cloud Microphysics at Barrow, Alaska: Algorithms, Results, and Radiative Closure. J. Appl. Meteor. Climatol., 54(7), 1675-1689. doi: 10.1175/JAMC-D-15-0054.1. AbstractCloud phase and microphysical properties control the radiative effects of clouds in the climate system and are therefore crucial to characterize in a variety of conditions and locations. An Arctic-specific, ground-based, multisensor cloud retrieval system is described here and applied to 2 yr of observations from Barrow, Alaska. Over these 2 yr, clouds occurred 75% of the time, with cloud ice and liquid each occurring nearly 60% of the time. Liquid water occurred at least 25% of the time, even in winter, and existed up to heights of 8 km. The vertically integrated mass of liquid was typically larger than that of ice. While it is generally difficult to evaluate the overall uncertainty of a comprehensive cloud retrieval system of this type, radiative flux closure analyses were performed in which flux calculations using the derived microphysical properties were compared with measurements at the surface and the top of the atmosphere. Radiative closure biases were generally smaller for cloudy scenes relative to clear skies, while the variability of flux closure results was only moderately larger than under clear skies. The best closure at the surface was obtained for liquid-containing clouds. Radiative closure results were compared with those based on a similar, yet simpler, cloud retrieval system. These comparisons demonstrated the importance of accurate cloud-phase and cloud-type classification, and specifically the identification of liquid water, for determining radiative fluxes. Enhanced retrievals of liquid water path for thin clouds were also shown to improve radiative flux calculations. clouds; Cloud microphysics; Cloud retrieval; Cloud radiative effects; Arctic; Cloud water/phase
Sidorenko, D.; Rackow, T.; Jung, T.; Semmler, T.; Barbi, D.; Danilov, S.; Dethloff, K.; Dorn, W.; Fieg, K.; Goessling, H. F.; Handorf, D.; Harig, S.; Hiller, W.; Juricke, S.; Losch, M.; Schröter, J.; Sein, D. V.; Wang, Q.Sidorenko, D., T. Rackow, T. Jung, T. Semmler, D. Barbi, S. Danilov, K. Dethloff, W. Dorn, K. Fieg, H. F. Goessling, D. Handorf, S. Harig, W. Hiller, S. Juricke, M. Losch, J. Schröter, D. V. Sein, Q. Wang, 2015: Towards multi-resolution global climate modeling with ECHAM6–FESOM. Part I: model formulation and mean climate. Climate Dynamics, 44(3-4), 757-780. doi: 10.1007/s00382-014-2290-6. A new climate model has been developed that employs a multi-resolution dynamical core for the sea ice-ocean component. In principle, the multi-resolution approach allows one to use enhanced horizontal resolution in dynamically active regions while keeping a coarse-resolution setup otherwise. The coupled model consists of the atmospheric model ECHAM6 and the finite element sea ice-ocean model (FESOM). In this study only moderate refinement of the unstructured ocean grid is applied and the resolution varies from about 25 km in the northern North Atlantic and in the tropics to about 150 km in parts of the open ocean; the results serve as a benchmark upon which future versions that exploit the potential of variable resolution can be built. Details of the formulation of the model are given and its performance in simulating observed aspects of the mean climate is described. Overall, it is found that ECHAM6–FESOM realistically simulates many aspects of the observed climate. More specifically it is found that ECHAM6–FESOM performs at least as well as some of the most sophisticated climate models participating in the fifth phase of the Coupled Model Intercomparison Project. ECHAM6–FESOM shares substantial shortcomings with other climate models when it comes to simulating the North Atlantic circulation. Climatology; climate model; Oceanography; Geophysics/Geodesy; climate model bias; Finite elements; Multi-resolution model; Unstructured mesh
Smith, Doug M.; Allan, Richard P.; Coward, Andrew C.; Eade, Rosie; Hyder, Patrick; Liu, Chunlei; Loeb, Norman G.; Palmer, Matthew D.; Roberts, Chris D.; Scaife, Adam A.Smith, D. M., R. P. Allan, A. C. Coward, R. Eade, P. Hyder, C. Liu, N. G. Loeb, M. D. Palmer, C. D. Roberts, A. A. Scaife, 2015: Earth's energy imbalance since 1960 in observations and CMIP5 models. Geophysical Research Letters, 42(4), 1205–1213. doi: 10.1002/2014GL062669. Observational analyses of running 5 year ocean heat content trends (Ht) and net downward top of atmosphere radiation (N) are significantly correlated (r ~ 0.6) from 1960 to 1999, but a spike in Ht in the early 2000s is likely spurious since it is inconsistent with estimates of N from both satellite observations and climate model simulations. Variations in N between 1960 and 2000 were dominated by volcanic eruptions and are well simulated by the ensemble mean of coupled models from the Fifth Coupled Model Intercomparison Project (CMIP5). We find an observation-based reduction in N of − 0.31 ± 0.21 W m−2 between 1999 and 2005 that potentially contributed to the recent warming slowdown, but the relative roles of external forcing and internal variability remain unclear. While present-day anomalies of N in the CMIP5 ensemble mean and observations agree, this may be due to a cancelation of errors in outgoing longwave and absorbed solar radiation. 1616 Climate variability; 1626 Global climate models; 1635 Oceans; 4262 Ocean observing systems; 8408 Volcano/climate interactions; Net radiation; ocean uptake
Smith, G.L.; Wong, Takmeng; Bush, K.A.Smith, G., T. Wong, K. Bush, 2015: Time-Sampling Errors of Earth Radiation From Satellites: Theory for Outgoing Longwave Radiation. IEEE Transactions on Geoscience and Remote Sensing, 53(3), 1656-1665. doi: 10.1109/TGRS.2014.2338793. The measurements of radiation budget by satellites in low Earth orbit provide limited sampling of the diurnal cycle. Thus, maps of monthly mean radiation fluxes contain errors due to this limitation. The Earth Radiation Budget Experiment reduced these errors in the data products by using a half-sine fit to account for regional diurnal cycles. An algorithm is presented to compute errors that are created when one computes the average value of outgoing longwave radiative flux (OLR) for a month based on the half-sine fit. Details of the temporal sampling are described by a sampling matrix that gives the number of OLR measurements in each local hour and each day of the month. The error analysis must take into account the correlation in time between irregularly spaced data due to synoptic variations, the weighting of measurements to accommodate the half-sine fit and deviations of the regional diurnal cycle from the half-sine. Using these ingredients, a closed-form expression is presented for the standard deviation of the temporal-sampling errors of the monthly mean OLR as computed from satellite measurements. The method is demonstrated for a well-sampled case and a poorly sampled case. This approach can be used to evaluate data products for existing measurements and for future mission design, or evaluating measurements of other atmospheric parameters. Earth; Extraterrestrial measurements; Remote sensing; atmospheric radiation; atmospheric techniques; Space vehicles; Time measurement; satellite measurements; Sea measurements; Orbits; earth radiation budget experiment; Error analysis; atmospheric parameters; Earth Radiation Budget Experiment (ERBE); half-sine fit; low Earth orbit; mission design; monthly mean radiation fluxes; OLR measurements; outgoing longwave radiative flux; radiation budget measurements; regional diurnal cycles; time-sampling error; time-sampling errors; Weight measurement
Smith, Nathaniel P.; Thomas, Susan; Shankar, Mohan; Hess, Phillip C.; Smith, Natividad M.; Walikainen, Dale R.; Wilson, Robert S.; Priestley, Kory J.Smith, N. P., S. Thomas, M. Shankar, P. C. Hess, N. M. Smith, D. R. Walikainen, R. S. Wilson, K. J. Priestley, 2015: Assessment of the clouds and the Earth’s Radiant Energy System (CERES) instrument performance and stability on the Aqua, Terra, and S-NPP spacecraft. SPIE 9607, Earth Observing Systems XX, 9607, 96070T-96070T-10. doi: 10.1117/12.2190110. The Clouds and the Earth’s Radiant Energy System (CERES) scanning radiometer is designed to measure reflected solar radiation and thermal radiation emitted by the Earth. Five CERES instruments are currently taking active measurements in-orbit with two aboard the Terra spacecraft (FM1 and FM2), two aboard the Aqua spacecraft (FM3 and FM4), and one aboard the S-NPP spacecraft (FM5). The CERES instrument uses three scanning thermistor bolometers to make broadband radiance measurements in the shortwave (0.3 – 5.0 micrometers), total (0.3 - >100 micrometers) and water vapor window (8 – 12 micrometer) regions. An internal calibration module (ICM) used for in-flight calibration is built into the CERES instrument package consisting of an anodized aluminum blackbody source for calibrating the total and window sensors, and a shortwave internal calibration source (SWICS) for the shortwave sensor. The ICM sources, along with a solar diffusor called the Mirror Attenuator Mosaic (MAM), are used to define shifts or drifts in the sensor response over the life of the mission. In addition, validation studies are conducted to understand any spectral changes that may occur with the sensors and assess the pointing accuracy of the instrument, allowing for corrections to be made to the radiance calculations in CERES data products. This paper covers the observed trends in the internal and solar calibration data, discusses the latest techniques used to correct for sensor response, and explains the validation studies used to assess the performance and stability of the instrument.
Soon, Willie; Legates, David R.Soon, W., D. R. Legates, 2015: Response to the comment on: “Soon, W., and Legates, D.R., solar irradiance modulation of equator-to-pole (Arctic) temperature gradients: empirical evidence for climate variation on multi-decadal timescales. Journal of Atmospheric and solar-terrestrial physics, 93, (2013) 45–56” by F. Meunier and A. H. Reis. Journal of Atmospheric and Solar-Terrestrial Physics, 128, 92-93. doi: 10.1016/j.jastp.2015.01.013. We thank Meunier and Reis (hereafter as MR) for their comments on our paper. We, however, do not see the relevance of their alternative interpretation to our original results and believe this reflects their confusion regarding our conclusions rather than a discussion on physical mechanisms. Sun-climate connection
Stanfield, Ryan E.; Dong, Xiquan; Xi, Baike; Del Genio, Anthony D.; Minnis, Patrick; Doelling, David; Loeb, NormanStanfield, R. E., X. Dong, B. Xi, A. D. Del Genio, P. Minnis, D. Doelling, N. Loeb, 2015: Assessment of NASA GISS CMIP5 and Post-CMIP5 Simulated Clouds and TOA Radiation Budgets Using Satellite Observations. Part II: TOA Radiation Budget and CREs. J. Climate, 28(5), 1842-1864. doi: 10.1175/JCLI-D-14-00249.1. AbstractIn Part I of this study, the NASA GISS Coupled Model Intercomparison Project (CMIP5) and post-CMIP5 (herein called C5 and P5, respectively) simulated cloud properties were assessed utilizing multiple satellite observations, with a particular focus on the southern midlatitudes (SMLs). This study applies the knowledge gained from Part I of this series to evaluate the modeled TOA radiation budgets and cloud radiative effects (CREs) globally using CERES EBAF (CE) satellite observations and the impact of regional cloud properties and water vapor on the TOA radiation budgets. Comparisons revealed that the P5- and C5-simulated global means of clear-sky and all-sky outgoing longwave radiation (OLR) match well with CE observations, while biases are observed regionally. Negative biases are found in both P5- and C5-simulated clear-sky OLR. P5-simulated all-sky albedo slightly increased over the SMLs due to the increase in low-level cloud fraction from the new planetary boundary layer (PBL) scheme. Shortwave, longwave, and net CRE are quantitatively analyzed as well. Regions of strong large-scale atmospheric upwelling/downwelling motion are also defined to compare regional differences across multiple cloud and radiative variables. In general, the P5 and C5 simulations agree with the observations better over the downwelling regime than over the upwelling regime. Comparing the results herein with the cloud property comparisons presented in Part I, the modeled TOA radiation budgets and CREs agree well with the CE observations. These results, combined with results in Part I, have quantitatively estimated how much improvement is found in the P5-simulated cloud and radiative properties, particularly over the SMLs and tropics, due to the implementation of the new PBL and convection schemes. Radiation budgets; Model evaluation/performance; climate models; Cloud parameterizations; Cloud radiative effects; Model comparison
Stephens, Graeme L.; L'Ecuyer, TristanStephens, G. L., T. L'Ecuyer, 2015: The Earth's energy balance. Atmospheric Research, 166, 195-203. doi: 10.1016/j.atmosres.2015.06.024. This paper reviews the status of our understanding of the Earth's annual, global mean energy balance, the hemispheric energy balances and the symmetry observed about the equator, and explores the influence of latitudinal changes of energy both on the annual mean and seasonal transports of energy from low latitudes to higher latitudes. Based on the best available information we show that our planet continues to be out of balance with additional heat being added to it at the rate of 0.6 ± 0.4 Wm− 2. This heat appears to be taken up primarily by the oceans of the SH and perhaps mostly equatorward of 37 S. The nature of the adjustments applied to our best estimates of individual, annual mean fluxes of energy to produce a balance are described and the results of applying a more formal constraint for these adjustments are discussed. The energy balances of the Southern and Northern Hemispheres are then shown to be practically identical which in turn suggests the transport of energy across the equator in the net is close to zero. In fact the hemispheres are not identically symmetrical with the SH being slightly out of balance absorbing the additional heat and transporting a small amount of net heat across the equator to the balanced NH. The symmetry in absorbed solar and the near symmetry in OLR are remarkable in their own right and are a result of the effects of clouds both on solar reflection and OLR that act to offset land–ocean interhemispheric differences. We then demonstrate important interhemispheric seasonal influences on the heat transported to the winter pole that conspire to make these seasonal transports lopsided. This asymmetry is a direct result of the eccentricity of the Earth's orbit that induces larger energy losses from the southern winter hemisphere. This in turn produces a latitudinal asymmetry in the location of on the tropical trough zone, a region from which energy is always moved to the winter pole, requiring it be located deeper into the NH.
Stephens, Graeme L.; O'Brien, Denis; Webster, Peter J.; Pilewski, Peter; Kato, Seiji; Li, Jui-linStephens, G. L., D. O'Brien, P. J. Webster, P. Pilewski, S. Kato, J. Li, 2015: The albedo of Earth. Reviews of Geophysics, 53(1), 141–163. doi: 10.1002/2014RG000449. The fraction of the incoming solar energy scattered by Earth back to space is referred to as the planetary albedo. This reflected energy is a fundamental component of the Earth's energy balance, and the processes that govern its magnitude, distribution, and variability shape Earth's climate and climate change. We review our understanding of Earth's albedo as it has progressed to the current time and provide a global perspective of our understanding of the processes that define it. Joint analyses of surface solar flux data that are a complicated mix of measurements and model calculations with top-of-atmosphere (TOA) flux measurements from current orbiting satellites yield a number of surprising results including (i) the Northern and Southern Hemispheres (NH, SH) reflect the same amount of sunlight within ~ 0.2 W m−2. This symmetry is achieved by increased reflection from SH clouds offsetting precisely the greater reflection from the NH land masses. (ii) The albedo of Earth appears to be highly buffered on hemispheric and global scales as highlighted by both the hemispheric symmetry and a remarkably small interannual variability of reflected solar flux (~0.2% of the annual mean flux). We show how clouds provide the necessary degrees of freedom to modulate the Earth's albedo setting the hemispheric symmetry. We also show that current climate models lack this same degree of hemispheric symmetry and regulation by clouds. The relevance of this hemispheric symmetry to the heat transport across the equator is discussed. 0360 Radiation: transmission and scattering; albedo; 0321 Cloud/radiation interaction; 3359 Radiative processes; Solar radiation; Energy balance
Stevens, BjornStevens, B., 2015: Rethinking the Lower Bound on Aerosol Radiative Forcing. J. Climate, 28(12), 4794-4819. doi: 10.1175/JCLI-D-14-00656.1. AbstractBased on research showing that in the case of a strong aerosol forcing, this forcing establishes itself early in the historical record, a simple model is constructed to explore the implications of a strongly negative aerosol forcing on the early (pre-1950) part of the instrumental record. This model, which contains terms representing both aerosol–radiation and aerosol–cloud interactions, well represents the known time history of aerosol radiative forcing as well as the effect of the natural state on the strength of aerosol forcing. Model parameters, randomly drawn to represent uncertainty in understanding, demonstrate that a forcing more negative than −1.0 W m−2 is implausible, as it implies that none of the approximately 0.3-K temperature rise between 1850 and 1950 can be attributed to Northern Hemisphere forcing. The individual terms of the model are interpreted in light of comprehensive modeling, constraints from observations, and physical understanding to provide further support for the less negative (−1.0 W m−2) lower bound. These findings suggest that aerosol radiative forcing is less negative and more certain than is commonly believed. aerosols; climate change; Coupled models; radiative forcing; climate models; Climate sensitivity
Storer, Rachel L.; Zhang, Guang J.; Song, XiaoliangStorer, R. L., G. J. Zhang, X. Song, 2015: Effects of Convective Microphysics Parameterization on Large-Scale Cloud Hydrological Cycle and Radiative Budget in Tropical and Midlatitude Convective Regions. J. Climate, 28(23), 9277-9297. doi: 10.1175/JCLI-D-15-0064.1. A two-moment microphysics scheme for deep convection was previously implemented in the NCAR Community Atmosphere Model version 5 (CAM5) by Song et al. The new scheme improved hydrometeor profiles in deep convective clouds and increased deep convective detrainment, reducing the negative biases in low and midlevel cloud fraction and liquid water path compared to observations. Here, the authors examine in more detail the impacts of this improved microphysical representation on regional-scale water and radiation budgets. As a primary source of cloud water for stratiform clouds is detrainment from deep and shallow convection, the enhanced detrainment leads to larger stratiform cloud fractions, higher cloud water content, and more stratiform precipitation over the ocean, particularly in the subtropics where convective frequency is also increased. This leads to increased net cloud radiative forcing. Over land regions, cloud amounts are reduced as a result of lower relative humidity, leading to weaker cloud forcing and increased OLR. Comparing the water budgets to cloud-resolving model simulations shows improvement in the partitioning between convective and stratiform precipitation, though the deep convection is still too active in the GCM. The addition of convective microphysics leads to an overall improvement in the regional cloud water budgets. Cloud microphysics; climate models; Models and modeling; Physical Meteorology and Climatology; convective parameterization
Su, W.; Corbett, J.; Eitzen, Z.; Liang, L.Su, W., J. Corbett, Z. Eitzen, L. Liang, 2015: Next-generation angular distribution models for top-of-atmosphere radiative flux calculation from CERES instruments: validation. Atmos. Meas. Tech., 8(8), 3297-3313. doi: 10.5194/amt-8-3297-2015. Radiative fluxes at the top of the atmosphere (TOA) from the Clouds and the Earth's Radiant Energy System (CERES) instrument are fundamental variables for understanding the Earth's energy balance and how it changes with time. TOA radiative fluxes are derived from the CERES radiance measurements using empirical angular distribution models (ADMs). This paper evaluates the accuracy of CERES TOA fluxes using direct integration and flux consistency tests. Direct integration tests show that the overall bias in regional monthly mean TOA shortwave (SW) flux is less than 0.2 Wm−2 and the RMSE is less than 1.1 Wm−2. The bias and RMSE are very similar between Terra and Aqua. The bias in regional monthly mean TOA LW fluxes is less than 0.5 Wm−2 and the RMSE is less than 0.8 Wm−2 for both Terra and Aqua. The accuracy of the TOA instantaneous flux is assessed by performing tests using fluxes inverted from nadir- and oblique-viewing angles using CERES along-track observations and temporally and spatially matched MODIS observations, and using fluxes inverted from multi-angle MISR observations. The averaged TOA instantaneous SW flux uncertainties from these two tests are about 2.3 % (1.9 Wm−2) over clear ocean, 1.6 % (4.5 Wm−2) over clear land, and 2.0 % (6.0 Wm−2) over clear snow/ice; and are about 3.3 % (9.0 Wm−2), 2.7 % (8.4 Wm−2), and 3.7 % (9.9 Wm−2) over ocean, land, and snow/ice under all-sky conditions. The TOA SW flux uncertainties are generally larger for thin broken clouds than for moderate and thick overcast clouds. The TOA instantaneous daytime LW flux uncertainties derived from the CERES-MODIS test are 0.5 % (1.5 Wm−2), 0.8 % (2.4 Wm−2), and 0.7 % (1.3 Wm−2) over clear ocean, land, and snow/ice; and are about 1.5 % (3.5 Wm−2), 1.0 % (2.9 Wm−2), and 1.1 % (2.1 Wm−2) over ocean, land, and snow/ice under all-sky conditions. The TOA instantaneous nighttime LW flux uncertainties are about 0.5–1 % (< 2.0 Wm−2) for all surface types. Flux uncertainties caused by errors in scene identification are also assessed by using the collocated CALIPSO, CloudSat, CERES and MODIS data product. Errors in scene identification tend to underestimate TOA SW flux by about 0.6 Wm−2 and overestimate TOA daytime (nighttime) LW flux by 0.4 (0.2) Wm−2 when all CERES viewing angles are considered.
Su, W.; Corbett, J.; Eitzen, Z.; Liang, L.Su, W., J. Corbett, Z. Eitzen, L. Liang, 2015: Next-generation angular distribution models for top-of-atmosphere radiative flux calculation from CERES instruments: methodology. Atmos. Meas. Tech., 8(2), 611-632. doi: 10.5194/amt-8-611-2015. The top-of-atmosphere (TOA) radiative fluxes are critical components to advancing our understanding of the Earth's radiative energy balance, radiative effects of clouds and aerosols, and climate feedback. The Clouds and the Earth's Radiant Energy System (CERES) instruments provide broadband shortwave and longwave radiance measurements. These radiances are converted to fluxes by using scene-type-dependent angular distribution models (ADMs). This paper describes the next-generation ADMs that are developed for Terra and Aqua using all available CERES rotating azimuth plane radiance measurements. Coincident cloud and aerosol retrievals, and radiance measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS), and meteorological parameters from Goddard Earth Observing System (GEOS) data assimilation version 5.4.1 are used to define scene type. CERES radiance measurements are stratified by scene type and by other parameters that are important for determining the anisotropy of the given scene type. Anisotropic factors are then defined either for discrete intervals of relevant parameters or as a continuous functions of combined parameters, depending on the scene type. Significant differences between the ADMs described in this paper and the existing ADMs are over clear-sky scene types and polar scene types. Over clear ocean, we developed a set of shortwave (SW) ADMs that explicitly account for aerosols. Over clear land, the SW ADMs are developed for every 1° latitude × 1° longitude region for every calendar month using a kernel-based bidirectional reflectance model. Over clear Antarctic scenes, SW ADMs are developed by accounting the effects of sastrugi on anisotropy. Over sea ice, a sea-ice brightness index is used to classify the scene type. Under cloudy conditions over all surface types, the longwave (LW) and window (WN) ADMs are developed by combining surface and cloud-top temperature, surface and cloud emissivity, cloud fraction, and precipitable water. Compared to the existing ADMs, the new ADMs change the monthly mean instantaneous fluxes by up to 5 W m−2 on a regional scale of 1° latitude × 1° longitude, but the flux changes are less than 0.5 W m−2 on a global scale.
Sundström, A.-M.; Arola, A.; Kolmonen, P.; Xue, Y.; de Leeuw, G.; Kulmala, M.Sundström, A., A. Arola, P. Kolmonen, Y. Xue, G. de Leeuw, M. Kulmala, 2015: On the use of a satellite remote-sensing-based approach for determining aerosol direct radiative effect over land: a case study over China. Atmos. Chem. Phys., 15(1), 505-518. doi: 10.5194/acp-15-505-2015. A satellite-based approach to derive the aerosol direct shortwave (SW) radiative effect (ADRE) was studied in an environment with highly variable aerosol conditions over eastern China from March to October 2009. The method is based on using coincident SW top-of-the-atmosphere (TOA) fluxes from the Clouds and the Earth's Radiant Energy System (CERES) and aerosol optical depths (AODs) from the MODerate Resolution Imaging Spectroradiometer (MODIS) to derive SW clear-sky ADRE. The estimate for the aerosol-free TOA flux (F0,TOA) is obtained by establishing linear regression between CERES SW TOA fluxes and MODIS AODs. A normalization procedure to a fixed solar zenith angle, Earth–Sun distance and atmospheric water vapor content was applied to the CERES fluxes prior to the linear fit against AOD to reduce the flux variation not related to aerosols. In the majority of the cases, the normalization increased positive correlation between observed SW TOA fluxes and AODs, and it decreased RMSE. The key question in the satellite-based approach is the accuracy of the estimated F0,TOA. Comparison with simulated F0,TOA showed that both the satellite method and the model produced qualitatively similar spatial patterns, but absolute values differed. In 58 % of the cases the satellite-based F0,TOA was within ±10 W m−2 of the modeled value (about 7–8 % difference in flux values). Over bright surfaces, the satellite-based method tend to produce lower F0,TOA than the model. The satellite-based clear-sky estimates for median instantaneous and diurnally averaged ADRE over the study area were −8.8 W m−2 and −5.1 W m−2, respectively. Over heavily industrialized areas, the cooling at TOA was 2 to more than 3 times the median value, and associated with high AODs (> 0.5). Especially during the summer months, positive ADREs were observed locally over dark surfaces. This was most probably a method artifact related to systematic change of aerosol type, sub-visual cloud contamination or both.
Szewczyk, Z. P.; Smith, G. L.; Priestley, Kory J.Szewczyk, Z. P., G. L. Smith, K. J. Priestley, 2015: Comparison of unfiltered CERES radiances measured from the S-NPP and Aqua satellites over matched sites. doi: 10.1117/12.2191506. The focus of this paper is to introduce a novel strategy for comparison of unfiltered radiances in remote sensing devised for CERES scanners. The strategy is referred to as “matched sites targeting”, in which CERES instruments scan at nadir along their respective collocated ground-tracks. This strategy is enabled by similarities in the Suomi-NPP (FM5) and Aqua (FM3) satellite orbits, and a special scan profile available for the CERES scanners. Comparison of collected data in this strategy is done at a footprint level for a more stringent test of the consistency between the two instruments (FM5 and FM3) for specific scene types, as averages of 330 collocated nadir samples are compared. A comparison of comprehensive “all-sky” measurements is also included as a reference. Results of the unfiltered radiance comparison are based on ES8 or ERBE-like data product using Edition-1 for FM5, and Edition-4 for FM3; cloud coverage is verified using MODIS data available in a SSF product.
Taylor, Patrick C.; Kato, Seiji; Xu, Kuan-Man; Cai, MingTaylor, P. C., S. Kato, K. Xu, M. Cai, 2015: Covariance between Arctic sea ice and clouds within atmospheric state regimes at the satellite footprint level. Journal of Geophysical Research: Atmospheres, 120(24), 12656–12678. doi: 10.1002/2015JD023520. Understanding the cloud response to sea ice change is necessary for modeling Arctic climate. Previous work has primarily addressed this problem from the interannual variability perspective. This paper provides a refined perspective of sea ice-cloud relationship in the Arctic using a satellite footprint-level quantification of the covariance between sea ice and Arctic low cloud properties from NASA A-Train active remote sensing data. The covariances between Arctic low cloud properties and sea ice concentration are quantified by first partitioning each footprint into four atmospheric regimes defined using thresholds of lower tropospheric stability and midtropospheric vertical velocity. Significant regional variability in the cloud properties is found within the atmospheric regimes indicating that the regimes do not completely account for the influence of meteorology. Regional anomalies are used to account for the remaining meteorological influence on clouds. After accounting for meteorological regime and regional influences, a statistically significant but weak covariance between cloud properties and sea ice is found in each season for at least one atmospheric regime. Smaller average cloud fraction and liquid water are found within footprints with more sea ice. The largest-magnitude cloud-sea ice covariance occurs between 500 m and 1.2 km when the lower tropospheric stability is between 16 and 24 K. The covariance between low cloud properties and sea ice is found to be largest in fall and is accompanied by significant changes in boundary layer temperature structure where larger average near-surface static stability is found at larger sea ice concentrations. 1610 Atmosphere; sea ice; 3310 Clouds and cloud feedbacks; 0750 Sea ice; 3339 Ocean/atmosphere interactions; 1631 Land/atmosphere interactions; Arctic clouds; sea ice-cloud interaction
Thomas, M. A.; Kahnert, M.; Andersson, C.; Kokkola, H.; Hansson, U.; Jones, C.; Langner, J.; Devasthale, A.Thomas, M. A., M. Kahnert, C. Andersson, H. Kokkola, U. Hansson, C. Jones, J. Langner, A. Devasthale, 2015: Integration of prognostic aerosol–cloud interactions in a chemistry transport model coupled offline to a regional climate model. Geosci. Model Dev., 8(6), 1885-1898. doi: 10.5194/gmd-8-1885-2015. To reduce uncertainties and hence to obtain a better estimate of aerosol (direct and indirect) radiative forcing, next generation climate models aim for a tighter coupling between chemistry transport models and regional climate models and a better representation of aerosol–cloud interactions. In this study, this coupling is done by first forcing the Rossby Center regional climate model (RCA4) with ERA-Interim lateral boundaries and sea surface temperature (SST) using the standard cloud droplet number concentration (CDNC) formulation (hereafter, referred to as the "stand-alone RCA4 version" or "CTRL" simulation). In the stand-alone RCA4 version, CDNCs are constants distinguishing only between land and ocean surface. The meteorology from this simulation is then used to drive the chemistry transport model, Multiple-scale Atmospheric Transport and Chemistry (MATCH), which is coupled online with the aerosol dynamics model, Sectional Aerosol module for Large Scale Applications (SALSA). CDNC fields obtained from MATCH–SALSA are then fed back into a new RCA4 simulation. In this new simulation (referred to as "MOD" simulation), all parameters remain the same as in the first run except for the CDNCs provided by MATCH–SALSA. Simulations are carried out with this model setup for the period 2005–2012 over Europe, and the differences in cloud microphysical properties and radiative fluxes as a result of local CDNC changes and possible model responses are analysed. Our study shows substantial improvements in cloud microphysical properties with the input of the MATCH–SALSA derived 3-D CDNCs compared to the stand-alone RCA4 version. This model setup improves the spatial, seasonal and vertical distribution of CDNCs with a higher concentration observed over central Europe during boreal summer (JJA) and over eastern Europe and Russia during winter (DJF). Realistic cloud droplet radii (CD radii) values have been simulated with the maxima reaching 13 μm, whereas in the stand-alone version the values reached only 5 μm. A substantial improvement in the distribution of the cloud liquid-water paths (CLWP) was observed when compared to the satellite retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) for the boreal summer months. The median and standard deviation values from the "MOD" simulation are closer to observations than those obtained using the stand-alone RCA4 version. These changes resulted in a significant decrease in the total annual mean net fluxes at the top of the atmosphere (TOA) by −5 W m−2 over the domain selected in the study. The TOA net fluxes from the "MOD" simulation show a better agreement with the retrievals from the Clouds and the Earth's Radiant Energy System (CERES) instrument. The aerosol indirect effects are estimated in the "MOD" simulation in comparison to the pre-industrial aerosol emissions (1900). Our simulations estimated the domain averaged annual mean total radiative forcing of −0.64 W m−2 with a larger contribution from the first indirect aerosol effect (−0.57 W m−2) than from the second indirect aerosol effect (−0.14 W m−2).
Thomas, M. A.; Kahnert, M.; Andersson, C.; Kokkola, H.; Hansson, U.; Jones, C.; Langner, J.; Devasthale, A.Thomas, M. A., M. Kahnert, C. Andersson, H. Kokkola, U. Hansson, C. Jones, J. Langner, A. Devasthale, 2015: Development of prognostic aerosol–cloud interactions combining a chemistry transport model and a regional climate model. Geosci. Model Dev. Discuss., 8(2), 897-933. doi: 10.5194/gmdd-8-897-2015. To reduce uncertainties and hence, to obtain a better estimate of aerosol (direct and indirect) radiative forcing, next generation climate models aim for a tighter coupling between chemistry transport models and regional climate models and a better representation of aerosol–cloud interactions. In this study, this coupling is done by first forcing the Rossby Center regional climate model, RCA4 by ERA-Interim lateral boundaries (LBCs) and SST using the standard CDNC (cloud droplet number concentration) formulation (hereafter, referred to as the "stand-alone RCA4 version" or "CTRL" simulation). In this simulation, the CDNCs are assigned fixed numbers based on if the underlying surface is land or oceanic. The meteorology from this simulation is then used to drive the chemistry transport model, MATCH which is coupled online with the aerosol dynamics model, SALSA. CDNC fields obtained from MATCH-SALSA are then fed back into a new RCA4 simulation. In this new simulation (referred to as "MOD" simulation), all parameters remain the same as in the first run except for the CDNCs provided by MATCH-SALSA. Simulations are carried out with this model set up for the period 2005–2012 over Europe and the differences in cloud microphysical properties and radiative fluxes as a result of local CDNC changes and possible model responses are analyzed. Our study shows substantial improvements in the cloud microphysical properties with the input of the MATCH-SALSA derived 3-D CDNCs compared to the stand-alone RCA4 version. This model set up improves the spatial, seasonal and vertical distribution of CDNCs with higher concentration observed over central Europe during summer half of the year and over Eastern Europe and Russia during the winter half of the year. Realistic cloud droplet radii (CD radii) values have been simulated with the maxima reaching 13 μm whereas in the stand-alone version, the values reached only 5 μm. A substantial improvement in the distribution of cloud liquid water path was observed when compared to the satellite retrievals from MODIS for the boreal summer months. The median and SD values from the "MOD" simulation are closer to observations than those obtained using the stand-alone RCA4 version. These changes resulted in a significant decrease in the total annual mean net fluxes at the top of the atmosphere (TOA) by −5 W m−2 over the domain selected in the study. The TOA net fluxes from the "MOD" simulation show a better agreement with the retrievals from CERES instrument. The aerosol indirect effects are evaluated based on 1900 emissions. Our simulations estimated the domain averaged annual mean total radiative forcing of −0.64 W m−2 with larger contribution from the first indirect aerosol effect than from the second indirect aerosol effect.
Tomasi, Claudio; Lanconelli, Christian; Lupi, Angelo; Mazzola, MauroTomasi, C., C. Lanconelli, A. Lupi, M. Mazzola, 2015: Diurnally averaged direct aerosol-induced radiative forcing from cloud-free sky field measurements performed during seven regional experiments. Light Scattering Reviews 9, 297-425. Aerosol particles suspended in the atmosphere may originate from either natural or anthropic sources, or through mixed processes involving their variable combinations. Among the primary natural emissions, the most important are those leading to the formation of (i) mineral dust through wind erosion of natural soil and (ii) sea-salt particles from the ocean surface forced by winds. In addition, significant emission processes include biological particles released by plants and animals, combustion particles forming in forest fires and biomass-burning smokes, and volcanic debris ejections. Remote Sensing/Photogrammetry; Atmospheric Sciences; Earth Sciences, general; Geophysics and Environmental Physics; Physics, general
Tonttila, J.; Järvinen, H.; Räisänen, P.Tonttila, J., H. Järvinen, P. Räisänen, 2015: Explicit representation of subgrid variability in cloud microphysics yields weaker aerosol indirect effect in the ECHAM5-HAM2 climate model. Atmos. Chem. Phys., 15(2), 703-714. doi: 10.5194/acp-15-703-2015. The impacts of representing cloud microphysical processes in a stochastic subcolumn framework are investigated, with emphasis on estimating the aerosol indirect effect. It is shown that subgrid treatment of cloud activation and autoconversion of cloud water to rain reduce the impact of anthropogenic aerosols on cloud properties and thus reduce the global mean aerosol indirect effect by 19%, from −1.59 to −1.28 W m−2. This difference is partly related to differences in the model basic state; in particular, the liquid water path (LWP) is smaller and the shortwave cloud radiative forcing weaker when autoconversion is computed separately for each subcolumn. However, when the model is retuned so that the differences in the basic state LWP and radiation balance are largely eliminated, the global-mean aerosol indirect effect is still 14% smaller (i.e. −1.37 W m−2) than for the model version without subgrid treatment of cloud activation and autoconversion. The results show the importance of considering subgrid variability in the treatment of autoconversion. Representation of several processes in a self-consistent subgrid framework is emphasized. This paper provides evidence that omitting subgrid variability in cloud microphysics contributes to the apparently chronic overestimation of the aerosol indirect effect by climate models, as compared to satellite-based estimates.
Tornow, Florian; Barker, Howard W.; Domenech, CarlosTornow, F., H. W. Barker, C. Domenech, 2015: On the use of simulated photon paths to co-register top-of-atmosphere radiances in EarthCARE radiative closure experiments. Quarterly Journal of the Royal Meteorological Society, 141(693), 3239-3251. doi: 10.1002/qj.2606. The Earth's Cloud, Aerosol and Radiation Explorer (EarthCARE) mission will retrieve vertical profiles of cloud and aerosol properties by combining data from active and passive instruments. The verisimilitude of retrievals will be assessed using data from its broad-band radiometer (BBR), which measures top-of-atmosphere (TOA) short-wave (SW) radiances at three along-track viewing angles. BBR measurements will be compared with their modelled counterparts, simulated by a three-dimensional (3D) Monte Carlo (MC) radiative transfer model acting on retrieved properties, thus defining a radiative closure experiment. Since cloud and aerosol microphysical and hence optical properties within each assessment domain vary horizontally and vertically, one challenge facing the closure process is selection of radiances that will foster the best assessments of retrievals. This study investigates whether co-registration of radiances for closure assessment can be aided by information pertaining to photon paths from the MC model. Unlike methods that provide one effective reflecting layer (ERL), such as cloud-top altitude, simulated photon paths can account for several reflecting layers. For this study, A-Train satellite data provided cloud properties. The MC model was applied to this field to simulate BBR-like measurements. Cloud properties were then perturbed randomly, to represent retrievals in approximate fashion, and the MC model reapplied to them. The resulting sets of radiances mimicked EarthCARE measured and modelled data, thus allowing a test of closure and co-registration methodologies. Through the use of 3D photon path information, the rate of identification of inaccurate cloud retrievals improved over ERL approaches by ∼4% for cirrus clouds and ∼15% for broken clouds. For large-scale deep convective clouds, however, inaccurate photon paths, ostensibly due to poor retrievals, reduced identification performance by 3%. Cloud retrieval; EarthCARE; broad-band radiometer; co-registration; Monte Carlo; photon paths; short-wave broad-band radiance
Tourville, Natalie; Stephens, Graeme; DeMaria, Mark; Vane, DeborahTourville, N., G. Stephens, M. DeMaria, D. Vane, 2015: Remote Sensing of Tropical Cyclones: Observations from CloudSat and A-Train Profilers. Bull. Amer. Meteor. Soc., 96(4), 609-622. doi: 10.1175/BAMS-D-13-00282.1. CloudSat (CS) heralded a new era of profiling the planet’s cloud systems and storms with its launch in 2006. This satellite flies the first 94-GHz spaceborne Cloud Profiling Radar, and the data collected have provided a unique perspective on Earth’s cloudiness and processes that affect clouds. CS flies in formation with the afternoon satellite constellation, a collection of active and passive satellite sensors offering near-simultaneous observations of the same cloud phenomena. While passes of the nadir-pointing Cloud Profiling Radar (CPR) antenna occur infrequently over tropical cyclones, they happen enough to provide a detailed compilation of the inner structure of clouds and precipitation of these complex storm systems. Nearly 8,000 vertical profiles of TCs have been collected during the period June 2006–December 2013 and observations continue as CS flies in daylight-only mode. These observations have been assembled into a one-of-a-kind dataset of three-dimensional features revealing precipitation areas, moats, and multilayered clouds. Each unique overpass profiled by CS has been compiled with corresponding A-Train sensors, model data, and storm-specific best-track information. The multisensor components of the CS and A-Train TC dataset together with these other data are summarized and cataloged as a function of radial distance from storm center. Example imagery is provided along with stratified reflectivity profiles detailing changes in storm structures across varying environmental shear conditions. The data reported on in this paper offer an unprecedented view of these major storm types and their inner structure.
Trémas, Thierry L.; Aznay, Ouahid; Chomette, OlivierTrémas, T. L., O. Aznay, O. Chomette, 2015: ScaRaB: first results of absolute and cross calibration. doi: 10.1117/12.2194866. ScaRaB (SCAnner for RAdiation Budget) is the name of three radiometers whose two first flight models have been launched in 1994 and 1997. The instruments were mounted on-board Russian satellites, METEOR and RESURS. On October 12th 2011, a last model has been launched from the Indian site of Sriharikota. ScaRaB is a passenger of MEGHA-TROPIQUES, an Indo-French joint Satellite Mission for studying the water cycle and energy exchanges in the tropics. ScaRaB is composed of four parallel and independent channels. Channel-2 and channel-3 are considered as the main ones. Channel-1 is dedicated to measure solar radiance (0.5 to 0.7 μm) while channel-4 (10 to 13 μm) is an infrared window. The absolute calibration of ScaRab is assured by internal calibration sources (black bodies and a lamp for channel-1). However, during the commissioning phase, the lamp used for the absolute calibration of channel-1 revealed to be inaccurate. We propose here an alternative calibration method based on terrestrial targets. Due to the spectral range of channel-1, only calibration over desert sites (temporal monitoring) and clouds (cross band) is suitable. Desert sites have been widely used for sensor calibration since they have a stable spectral response over time. Because of their high reflectances, the atmospheric effect on the upward radiance is relatively minimal. In addition, they are spatially uniform. Their temporal instability without atmospheric correction has been determined to be less than 1-2% over a year. Very-high-altitude (10 km) bright clouds are good validation targets in the visible and near-infrared spectra because of their high spectrally consistent reflectance. If the clouds are very high, there is no need to correct aerosol scattering and water vapor absorption as both aerosol and water vapor are distributed near the surface. Only Rayleigh scattering and ozone absorption need to be considered. This method has been found to give a 4% uncertainty. Radiometric cross calibration of Earth observation sensors is a crucial need to guarantee or quantify the consistency of measurements from different sensors. ScaRaB is compatible with CERES mission. Two main spectral bands are measured by the radiometer: A short-wave channel (0.2 to 4 μm) dedicated to solar fluxes and a Total channel (0.2 to 200 μm) for fluxes combining the infrared earth radiance and the albedo. The earth long-wave radiance is isolated by subtracting the short-wave channel to the Total channel. Both Earth Radiation Budget missions (CERES and ScaRaB) have the same specification: to provide an accuracy of ~1% in the measurement of short-wave and long-wave radiances and an estimation of the short-wave and long-wave fluxes less than 10 W/m2. We use the CERES PAPS and Cross-Track SSF datasets for direct radiances and fluxes comparisons during two validation phases. The first one occurred during April 17th to June 8th (51 days) in 2012 and the second one occurred between March 22th and May 31st 2015. The first validation campaign has been held with the CERES team using the Terra FM2 data. The CERES PAPS mode was used to align the swath scan, in order to increase the collocated pixels between the two instruments. This campaign allowed us to validate the ScaRaB radiances and to refine the error budget. The second validation campaign aims to provide a temporal monitoring of ScaRab calibration.
Trenberth, Kevin E.; Zhang, Yongxin; Fasullo, John T.Trenberth, K. E., Y. Zhang, J. T. Fasullo, 2015: Relationships among top-of-atmosphere radiation and atmospheric state variables in observations and CESM. Journal of Geophysical Research: Atmospheres, 120(19), 10,074–10,090. doi: 10.1002/2015JD023381. A detailed examination is made in both observations and the Community Earth System Model (CESM) of relationships among top-of-atmosphere (TOA) radiation, water vapor, temperatures and precipitation for 2000-2014 to assess the origins of radiative perturbations and climate feedbacks empirically. The 30-member large ensemble coupled runs are analyzed along with one run with specified sea surface temperatures for 1994 to 2005 (to avoid volcanic eruptions). The vertical structure of the CESM temperature profile tends to be top-heavy in the model, with too much deep convection and not enough lower stratospheric cooling as part of the response to tropospheric heating. There is too much absorbed solar radiation (ASR) over the southern oceans and not enough in the tropics, and ENSO is too large in amplitude in this version of the model. However, the co-variability of monthly mean anomalies produces remarkably good replication of most of the observed relationships. There is a lot more high frequency variability in radiative fluxes than in temperature, highlighting the role of clouds and transient weather systems in the radiation statistics. Over the Warm Pool in the tropical western Pacific and Indian oceans, where non-local effects from the Walker circulation driven by the ENSO events are important, several related biases emerge: in response to high SST anomalies there is more precipitation, water vapor and cloud, and less ASR and Outgoing Longwave Radiation (OLR) in the model than observed. Different model global mean trends are evident, however, and possibly hinting at too much positive cloud feedback in the model. 1620 Climate dynamics; 3359 Radiative processes; 3305 Climate change and variability; feedbacks; water vapor; radiation; Precipitation; 1627 Coupled models of the climate system; 1626 Global climate models; CESM; temperatures
Trenberth, Kevin E.; Zhang, Yongxin; Fasullo, John T.; Taguchi, ShoichiTrenberth, K. E., Y. Zhang, J. T. Fasullo, S. Taguchi, 2015: Climate variability and relationships between top-of-atmosphere radiation and temperatures on Earth. Journal of Geophysical Research: Atmospheres, 120(9), 3642–3659. doi: 10.1002/2014JD022887. The monthly global and regional variability in Earth's radiation balance is examined using correlations and regressions between atmospheric temperatures and water vapor with top-of-atmosphere outgoing longwave (OLR), absorbed shortwave (ASR), and net radiation (RT = ASR − OLR). Anomalous global mean monthly variability in the net radiation is surprisingly large, often more than ±1 W m−2, and arises mainly from clouds and transient weather systems. Relationships are strongest and positive between OLR and temperatures, especially over land for tropospheric temperatures, except in the deep tropics where high sea surface temperatures are associated with deep convection, high cold cloud tops and thus less OLR but also less ASR. Tropospheric vertically averaged temperatures (surface = 150 hPa) are thus negatively correlated globally with net radiation (−0.57), implying 2.18 ± 0.10 W m−2 extra net radiation to space for 1°C increase in temperature. Water vapor is positively correlated with tropospheric temperatures and thus also negatively correlated with net radiation; however, when the temperature dependency of water vapor is statistically removed, a significant positive feedback between water vapor and net radiation is revealed globally with 0.87 W m−2 less OLR to space per millimeter of total column water vapor. The regression coefficient between global RT and tropospheric temperature becomes −2.98 W m−2 K−1 if water vapor effects are removed, slightly less than expected from blackbody radiation (−3.2 W m−2 K−1), suggesting a positive feedback from clouds and other processes. Robust regional structures provide additional physical insights. The observational record is too short, weather noise too great, and forcing too small to make reliable estimates of climate sensitivity. 1620 Climate dynamics; 3359 Radiative processes; 3305 Climate change and variability; 3310 Clouds and cloud feedbacks; 1616 Climate variability; radiation; climate feedbacks; temperatures; Climate variability
Tsushima, Yoko; Ringer, Mark A.; Koshiro, Tsuyoshi; Kawai, Hideaki; Roehrig, Romain; Cole, Jason; Watanabe, Masahiro; Yokohata, Tokuta; Bodas-Salcedo, Alejandro; Williams, Keith D.; Webb, Mark J.Tsushima, Y., M. A. Ringer, T. Koshiro, H. Kawai, R. Roehrig, J. Cole, M. Watanabe, T. Yokohata, A. Bodas-Salcedo, K. D. Williams, M. J. Webb, 2015: Robustness, uncertainties, and emergent constraints in the radiative responses of stratocumulus cloud regimes to future warming. Climate Dynamics, 1-15. doi: 10.1007/s00382-015-2750-7. Future responses of cloud regimes are analyzed for five CMIP5 models forced with observed SSTs and subject to a patterned SST perturbation. Correlations between cloud properties in the control climate and changes in the warmer climate are investigated for each of a set of cloud regimes defined using a clustering methodology. The only significant (negative) correlation found is in the in-regime net cloud radiative effect for the stratocumulus regime. All models overestimate the in-regime albedo of the stratocumulus regime. Reasons for this bias and its relevance to the future response are investigated. A detailed evaluation of the models’ daily-mean contributions to the albedo from stratocumulus clouds with different cloud cover fractions reveals that all models systematically underestimate the relative occurrence of overcast cases but overestimate those of broken clouds. In the warmer climate the relative occurrence of overcast cases tends to decrease while that of broken clouds increases. This suggests a decrease in the climatological in-regime albedo with increasing temperature (a positive feedback); this is opposite to the feedback suggested by the analysis of the bulk in-regime albedo. Furthermore we find that the inter-model difference in the sign of the in-cloud albedo feedback is consistent with the difference in sign of the in-cloud liquid water path response, and there is a strong positive correlation between the in-regime liquid water path in the control climate and its response to warming. We therefore conclude that further breakdown of the in-regime properties into cloud cover and in-cloud properties is necessary to better understand the behavior of the stratocumulus regime. Since cloud water is a physical property and is independent of a model’s radiative assumptions, it could potentially provide a useful emergent constraint on cloud feedback. Climatology; climate model; cloud radiative effect; cloud feedback; Oceanography; Geophysics/Geodesy; stratocumulus; Liquid water path
Tulich, S. N.Tulich, S. N., 2015: A strategy for representing the effects of convective momentum transport in multiscale models: Evaluation using a new superparameterized version of the Weather Research and Forecast model (SP-WRF). Journal of Advances in Modeling Earth Systems, 7(2), 938-962. doi: 10.1002/2014MS000417. This paper describes a general method for the treatment of convective momentum transport (CMT) in large-scale dynamical solvers that use a cyclic, two-dimensional (2-D) cloud-resolving model (CRM) as a “superparameterization” of convective-system-scale processes. The approach is similar in concept to traditional parameterizations of CMT, but with the distinction that both the scalar transport and diagnostic pressure gradient force are calculated using information provided by the 2-D CRM. No assumptions are therefore made concerning the role of convection-induced pressure gradient forces in producing up or down-gradient CMT. The proposed method is evaluated using a new superparameterized version of the Weather Research and Forecast model (SP-WRF) that is described herein for the first time. Results show that the net effect of the formulation is to modestly reduce the overall strength of the large-scale circulation, via “cumulus friction.” This statement holds true for idealized simulations of two types of mesoscale convective systems, a squall line, and a tropical cyclone, in addition to real-world global simulations of seasonal (1 June to 31 August) climate. In the case of the latter, inclusion of the formulation is found to improve the depiction of key synoptic modes of tropical wave variability, in addition to some aspects of the simulated time-mean climate. The choice of CRM orientation is also found to importantly affect the simulated time-mean climate, apparently due to changes in the explicit representation of wide-spread shallow convective regions. 3337 Global climate models; 3371 Tropical convection; 3373 Tropical dynamics; 3365 Subgrid-scale (SGS) parameterization; Tropical Climate; superparameterization; Convective momentum transport; Convectively coupled tropical waves; Multiscale modeling framework
Turner, E. C.; Lee, H.-T.; Tett, S. F. B.Turner, E. C., H. Lee, S. F. B. Tett, 2015: Using IASI to simulate the total spectrum of outgoing long-wave radiances. Atmos. Chem. Phys., 15(12), 6561-6575. doi: 10.5194/acp-15-6561-2015. A new method of deriving high-resolution top-of-atmosphere spectral radiances in 10 181 bands, over the whole outgoing long-wave spectrum of the Earth, is presented. Correlations between different channels measured by the Infrared Atmospheric Sounding Interfermeter (IASI) on the MetOp-A (Meteorological Operation) satellite and unobserved wavenumbers are used to estimate far infrared (FIR) radiances at 0.5 cm−1 intervals between 25.25 and 644.75 cm−1 (the FIR), and additionally between 2760 and 3000 cm−1 (the NIR – near infrared). Radiances simulated by the line-by-line radiative transfer model (LBLRTM) are used to construct the prediction model. The spectrum is validated by comparing the Integrated Nadir Long-wave Radiance (INLR) product spanning the whole 25.25–3000 cm−1 range with the corresponding broadband measurements from the Clouds and the Earth's Radiant Energy System (CERES) instrument on the Terra and Aqua satellites at points of simultaneous nadir overpass. There is a mean difference of 0.3 W m−2 sr−1 (0.5% relative difference). This is well within the uncertainties associated with the measurements made by either instrument. However, there is a noticeable contrast when the bias is separated into night-time and daytime scenes with the latter being significantly larger, possibly due to errors in the CERES Ed3 Spectral Response Functions (SRF) correction method. In the absence of an operational spaceborne instrument that isolates the FIR, this product provides a useful proxy for such measurements within the limits of the regression model it is based on, which is shown to have very low root mean squared errors. The new high-resolution spectrum is presented for global mean clear and all skies where the FIR is shown to contribute 44 and 47% to the total INLR, respectively. In terms of the spectral cloud effect (Cloud Integrated Nadir Long-wave Radiance – CINLR), the FIR contributes 19% and in some subtropical instances appears to be negative; results that would go unobserved with a traditional broadband analysis.
Valdivieso, Maria; Haines, Keith; Balmaseda, Magdalena; Chang, You-Soon; Drevillon, Marie; Ferry, Nicolas; Fujii, Yosuke; Köhl, Armin; Storto, Andrea; Toyoda, Takahiro; Wang, Xiaochun; Waters, Jennifer; Xue, Yan; Yin, Yonghong; Barnier, Bernard; Hernandez, Fabrice; Kumar, Arun; Lee, Tong; Masina, Simona; Peterson, K. AndrewValdivieso, M., K. Haines, M. Balmaseda, Y. Chang, M. Drevillon, N. Ferry, Y. Fujii, A. Köhl, A. Storto, T. Toyoda, X. Wang, J. Waters, Y. Xue, Y. Yin, B. Barnier, F. Hernandez, A. Kumar, T. Lee, S. Masina, K. A. Peterson, 2015: An assessment of air–sea heat fluxes from ocean and coupled reanalyses. Climate Dynamics, 1-26. doi: 10.1007/s00382-015-2843-3. Sixteen monthly air–sea heat flux products from global ocean/coupled reanalyses are compared over 1993–2009 as part of the Ocean Reanalysis Intercomparison Project (ORA-IP). Objectives include assessing the global heat closure, the consistency of temporal variability, comparison with other flux products, and documenting errors against in situ flux measurements at a number of OceanSITES moorings. The ensemble of 16 ORA-IP flux estimates has a global positive bias over 1993–2009 of 4.2 ± 1.1 W m−2. Residual heat gain (i.e., surface flux + assimilation increments) is reduced to a small positive imbalance (typically, +1–2 W m−2). This compensation between surface fluxes and assimilation increments is concentrated in the upper 100 m. Implied steady meridional heat transports also improve by including assimilation sources, except near the equator. The ensemble spread in surface heat fluxes is dominated by turbulent fluxes (>40 W m−2 over the western boundary currents). The mean seasonal cycle is highly consistent, with variability between products mostly Climatology; Oceanography; Geophysics/Geodesy; Assimilation fluxes; Flux comparisons with in situ buoy flux data; Flux variability; Ocean and coupled reanalyses; Surface heat fluxes
Vázquez-Navarro, M.; Mannstein, H.; Kox, S.Vázquez-Navarro, M., H. Mannstein, S. Kox, 2015: Contrail life cycle and properties from one year of MSG/SEVIRI rapid-scan images. Atmos. Chem. Phys. Discuss., 15(5), 7019-7055. doi: 10.5194/acpd-15-7019-2015. The Automatic Contrail Tracking Algorithm (ACTA) -developed to automatically follow contrails as they age, drift and spread- enables the study of a large number of contrails and the evolution of contrail properties with time. In this paper we present a year's worth of tracked contrails, from August 2008 to July 2009 in order to derive statistically significant mean values. The tracking is performed using the 5 min rapid-scan mode of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on board of the Meteosat Second Generation satellites (MSG). The detection is based on the high spatial resolution of the images provided by the Moderate Resolution Imaging Spectroradiometer on board of the Terra satellite (Terra/MODIS), where a Contrail Detection Algorithm (CDA) is applied. The results show the satellite-derived average lifetimes of contrails and contrail-cirrus along with the probability density function (PDF) of other geometric characteristics such as mean coverage, distribution and width. In combination with specifically developed algorithms (RRUMS and COCS, explained below) it is possible to derive the radiative forcing (RF), energy forcing (EF), optical thickness (τ), and altitude of the tracked contrails. Mean values here retrieved are: duration, 1 h; length, 130 km; width, 8 km; altitude, 11.7 km; optical thickness, 0.34. Radiative forcing and energy forcing are shown for land/water backgrounds in day/night situations.
Viúdez-Mora, A.; Costa-Surós, M.; Calbó, J.; González, J. A.Viúdez-Mora, A., M. Costa-Surós, J. Calbó, J. A. González, 2015: Modeling atmospheric longwave radiation at the surface during overcast skies: The role of cloud base height. Journal of Geophysical Research: Atmospheres, 120(1), 199–214. doi: 10.1002/2014JD022310. The behavior of the atmospheric downward longwave radiation at the surface under overcast conditions is studied. For optically thick clouds, longwave radiation depends greatly on the cloud base height (CBH), besides temperature and water vapor profiles. The CBH determines the cloud emission temperature and the air layers contributing to the longwave radiation that reaches the surface. Overcast situations observed at Girona (NE Iberian Peninsula) were studied by using a radiative transfer model. The data set includes different seasons, and a large range of CBH (0–5000 m). The atmosphere profiles were taken from the European Center for Medium-Range Weather Forecast analysis. The CBH was determined from ceilometer measurements and also estimated by using a suitable method applied to the vertical profile of relative humidity. The agreement between calculations and pyrgeometer measurements is remarkably good (1.6 ± 6.2 W m−2) if the observed CBH is used; poorer results are obtained with the estimated CBH (4.3 ± 7.0 W m−2). These results are better than those obtained from a simple parameterization based upon ground-level data (1.1 ± 11.6 W m−2), which can be corrected by adding a term that takes into account the CBH (−0.1 ± 7.3 W m−2). At this site, the cloud radiative effect (CRE) at the surface lies in the range 50–80 W m−2, has a clear seasonal behavior (higher CRE in winter), and depends upon the CBH. For the cold and the warm seasons, CRE decreases with CBH at a rate of −5 and −4 W m−2/km, respectively. Results obtained for other climates (subarctic and tropical) are also presented. 0321 Cloud/radiation interaction; 3359 Radiative processes; longwave radiation; Radiative transfer model; cloud radiative effect; ceilometer; overcast sky; pyrgeometer
Wall, Casey J.; Hartmann, Dennis L.Wall, C. J., D. L. Hartmann, 2015: On the influence of poleward jet shift on shortwave cloud feedback in global climate models. Journal of Advances in Modeling Earth Systems, 7(4), 2044-2059. doi: 10.1002/2015MS000520. Experiments designed to separate the effect of atmospheric warming from the effect of shifts of the eddy-driven jet on shortwave (SW) cloud feedback are performed with three global climate models (GCMs). In each model a warming simulation produces a robust SW cloud feedback dipole, with a negative (positive) feedback in the high-latitudes (subtropics). The cloud brightening in high-latitudes that characterizes warming simulations is not produced by jet shifts alone in any of the models, but is highly sensitive to perturbations of freezing temperature seen by the cloud microphysics scheme, indicating that thermodynamic mechanisms involving the phase of cloud condensate dominate the SW feedback at high-latitudes. In one of the models a poleward jet shift causes significant cloud dimming throughout the midlatitudes, but in two models it does not. Differences in cloud response to jet shifts in two of the models are attributed to differences in the shallow convection parameterizations. 3310 Clouds and cloud feedbacks; cloud feedbacks
Wang, Dongdong; Liang, Shunlin; He, Tao; Shi, QinqingWang, D., S. Liang, T. He, Q. Shi, 2015: Estimating clear-sky all-wave net radiation from combined visible and shortwave infrared (VSWIR) and thermal infrared (TIR) remote sensing data. Remote Sensing of Environment, 167, 31-39. doi: 10.1016/j.rse.2015.03.022. The surface radiation budget is characterized by the all-wave net radiation. Existing parameterization methods of estimating surface net radiation require the input of many surface and atmospheric parameters and rely heavily on the availability and accuracy of such data. Other methods involve retrieval of the shortwave (0.3–3.0 μm) and longwave (3.0–100.0 μm) components separately from visible and shortwave infrared (VSWIR) and thermal infrared (TIR) data, respectively. The proposed HyspIRI mission will carry a VSWIR spectrometer and a TIR multispectral imager with a nadir spatial resolution of 60 m. The broad range of spectral information will provide a unique opportunity to directly estimate the surface net radiation from the high-resolution HyspIRI data. In this study, we propose a new algorithm to estimate the clear-sky instantaneous all-wave net radiation over the land surface by combining VSWIR and TIR remote sensing data. The new method is based on extensive modeling of atmospheric radiative transfer over the entire solar spectrum. The algorithm is first tested with MODIS data. Validation with 1-year measurements at seven Surface Radiation Budget Network (SURFRAD) sites in 2013 demonstrates that the new method can accurately estimate clear-sky instantaneous all-wave net radiation with a root mean square error (RMSE) of 70.6 W/m2, which is better than the method of separating shortwave and longwave components. MODIS/ASTER Airborne Simulator (MASTER) data from the HyspIRI preparatory airborne campaign are also used as a proxy to demonstrate the suitability of the algorithm for data from the future HyspIRI mission. MODIS; surface radiation budget; Net radiation; Direct estimation; HyspIRI; MASTER; MODTRAN
Wang, Dongdong; Liang, Shunlin; He, Tao; Shi, QinqingWang, D., S. Liang, T. He, Q. Shi, 2015: Estimation of Daily Surface Shortwave Net Radiation From the Combined MODIS Data. IEEE Transactions on Geoscience and Remote Sensing, 53(10), 5519-5529. doi: 10.1109/TGRS.2015.2424716. Surface shortwave net radiation (SSNR) is a key component of the surface radiation budget. In this paper, we refined a direct estimation approach to retrieve daily SSNR estimates from combined Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) data. The retrieved MODIS SSNR estimates were validated against measurements at seven stations of the Surface Radiation Budget Network. We also compared the MODIS retrievals with three existing SSNR products: the Clouds and the Earth's Radiant Energy System (CERES) products, the North American Regional Reanalysis (NARR) data, and the ERA-Interim reanalysis data from the European Centre for Medium-Range Weather Forecasts. MODIS data at 1 km were upscaled to mitigate the mismatch between site measurements and satellite retrievals. Among the four data sets, the aggregated MODIS retrievals agreed best with in situ measurements, with a root-mean-square error (rmse) of 23.1 W/m2 and a negative bias of 6.7 W/m2. The CERES products have a slightly larger rmse of 24.2 W/m2 and a positive bias of 7.6 W/m2. Both reanalysis data (NARR and ERA-Interim) overestimate daily SSNR and have much larger uncertainties. Monthly satellite SSNR data are more accurate than daily values, and the scaling issue in validating monthly MODIS SSNR retrievals is also less prominent. Averaged with a window size of 23 km, the two MODIS sensors can estimate monthly SSNR with an rmse error of 11.6 W/m 2, representing an improvement of 2.4 W/m2 over the CERES products. clouds; Earth; Land surface; Remote sensing; Satellites; atmospheric radiation; aerosols; atmospheric techniques; Moderate Resolution Imaging Spectroradiometer; MODIS; Atmospheric modeling; surface radiation budget; Clouds and the Earth's Radiant Energy System (CERES); Moderate Resolution Imaging Spectroradiometer (MODIS); weather forecasting; ERA-Interim; Aqua MODIS Data; Terra MODIS Data; CERES products; Clouds and the Earth Radiant Energy System; daily SSNR; daily surface shortwave net radiation estimation; ERA-Interim reanalysis data; European Centre for Medium-Range Weather Forecasts; MODIS retrievals; NARR data; North American Regional Reanalysis; North American Regional Reanalysis (NARR); shortwave net radiation; SSNR products; surface radiation budget network
Wang, H.; Shi, G. Y.; Zhang, X. Y.; Gong, S. L.; Tan, S. C.; Chen, B.; Che, H. Z.; Li, T.Wang, H., G. Y. Shi, X. Y. Zhang, S. L. Gong, S. C. Tan, B. Chen, H. Z. Che, T. Li, 2015: Mesoscale modelling study of the interactions between aerosols and PBL meteorology during a haze episode in China Jing–Jin–Ji and its near surrounding region – Part 2: Aerosols' radiative feedback effects. Atmos. Chem. Phys., 15(6), 3277-3287. doi: 10.5194/acp-15-3277-2015. Two model experiments, namely a control (CTL) experiment without aerosol–radiation feedbacks and a experiment with online aerosol–radiation (RAD) interactions, were designed to study the radiative feedback on regional radiation budgets, planetary boundary layer (PBL) meteorology and haze formation due to aerosols during haze episodes over Jing–Jin–Ji, China, and its near surroundings (3JNS region of China: Beijing, Tianjin, Hebei, East Shanxi, West Shandong and North Henan) with a two-way atmospheric chemical transport model. The impact of aerosols on solar radiation reaching Earth's surface, outgoing long-wave emission at the top of the atmosphere, air temperature, PBL turbulence diffusion, PBL height, wind speeds, air pressure pattern and PM2.5 has been studied focusing on a haze episode during the period from 7 to 11 July 2008. The results show that the mean solar radiation flux that reaches the ground decreases by about 15% in 3JNS and 20 to 25%in the region with the highest aerosol optical depth during the haze episode. The fact that aerosol cools the PBL atmosphere but warms the atmosphere above it leads to a more stable atmospheric stratification over the region, which causes a decrease in turbulence diffusion of about 52% and a decrease in the PBL height of about 33%. This consequently forms a positive feedback on the particle concentration within the PBL and the surface as well as the haze formation. Additionally, aerosol direct radiative forcing (DRF) increases PBL wind speed by about 9% and weakens the subtropical high by about 14 hPa, which aids the collapse of haze pollution and results in a negative feedback to the haze episode. The synthetic impacts from the two opposite feedbacks result in about a 14% increase in surface PM2.5. However, the persistence time of both high PM2.5 and haze pollution is not affected by the aerosol DRF. On the contrary over offshore China, aerosols heat the PBL atmosphere and cause unstable atmospheric stratification, but the impact and its feedback on the planetary boundary layer height, turbulence diffusion and wind is weak, with the exception of the evident impacts on the subtropical high.
Wang, Hailan; Su, WenyingWang, H., W. Su, 2015: The ENSO effects on tropical clouds and top-of-atmosphere cloud radiative effects in CMIP5 models. Journal of Geophysical Research: Atmospheres, 120(10), 4443–4465. doi: 10.1002/2014JD022337. The El Niño–Southern Oscillation (ENSO) effects on tropical clouds and top-of-atmosphere (TOA) cloud radiative effects (CREs) in Coupled Model Intercomparison Project Phase 5 (CMIP5) models are evaluated using satellite-based observations and International Satellite Cloud Climatology Project satellite simulator output. Climatologically, most CMIP5 models produce considerably less total cloud amount with higher cloud top and notably larger reflectivity than observations in tropical Indo-Pacific (60°E-200°E; 10°S-10°N). During ENSO, most CMIP5 models strongly underestimate TOA CRE and cloud changes over western tropical Pacific. Over central tropical Pacific, while the multi-model mean resembles observations in TOA CRE and cloud amount anomalies, it notably overestimates cloud top pressure (CTP) decreases; there are also substantial inter-model variations. The relative effects of changes in cloud properties, temperature, and humidity on TOA CRE anomalies during ENSO in the CMIP5 models are assessed using cloud radiative kernels. The CMIP5 models agree with observations in that their TOA shortwave CRE anomalies are primarily contributed by total cloud amount changes, and their TOA longwave CRE anomalies are mostly contributed by changes in both total cloud amount and CTP. The model biases in TOA CRE anomalies particularly the strong underestimations over western tropical Pacific are, however, mainly explained by model biases in CTP and cloud optical thickness (τ) changes. Despite the distinct model climatological cloud biases particularly in τ regime, the TOA CRE anomalies from total cloud amount changes are comparable between the CMIP5 models and observations, because of the strong compensations between model underestimation of TOA CRE anomalies from thin clouds and overestimation from medium and thick clouds. cloud; 0321 Cloud/radiation interaction; 4522 ENSO; cloud radiative effect; Global climate models; El Niño–Southern Oscillation
Wang, Kai; Yahya, Khairunnisa; Zhang, Yang; Pouliot, George; Knote, Christoph; Hodzic, Alma; San Jose, Roberto; Perez, Juan L.; Jiménez-Guerrero, Pedro; Baro, Rocio; Makar, Paul; Bennartz, RalfWang, K., K. Yahya, Y. Zhang, G. Pouliot, C. Knote, A. Hodzic, R. San Jose, J. L. Perez, P. Jiménez-Guerrero, R. Baro, P. Makar, R. Bennartz, 2015: A multi-model assessment for the 2006 and 2010 simulations under the Air Quality Model Evaluation International Initiative (AQMEII) Phase 2 over North America: Part II. Evaluation of column variable predictions using satellite data. Atmospheric Environment, 115, 587-603. doi: 10.1016/j.atmosenv.2014.07.044. Within the context of the Air Quality Model Evaluation International Initiative Phase 2 (AQMEII2) project, this part II paper performs a multi-model assessment of major column abundances of gases, radiation, aerosol, and cloud variables for 2006 and 2010 simulations with three online-coupled air quality models over the North America using available satellite data. It also provides the first comparative assessment of the capabilities of the current generation of online-coupled models in simulating column variables. Despite the use of different model configurations and meteorological initial and boundary conditions, most simulations show comparable model performance for many variables. The evaluation results show an excellent agreement between all simulations and satellite-derived radiation variables including downward surface solar radiation, longwave radiation, and top-of-atmospheric outgoing longwave radiation, as well as precipitable water vapor with domain-average normalized mean biases (NMBs) of typically less than 5% and correlation coefficient (R) typically more than 0.9. Most simulations perform well for column-integrated abundance of CO with domain-average NMBs of −9.4% to −2.2% in 2006 and −12.1% to 4.6% in 2010 and from reasonably well to fair for column NO2, HCHO, and SO2, with domain-average NMBs of −37.7% to 2.1%, −27.3% to 59.2%, and 16.1% to 114.2% in 2006, respectively, and, 12.9% to 102.1%, −25.0% to 87.6%, −65.2% to 7.4% in 2010, respectively. R values are high for CO and NO2 typically between 0.85 and 0.9 (i.e., R2 of 0.7–0.8). Tropospheric ozone residuals are overpredicted by all simulations due to overestimates of ozone profiles from boundary conditions. Model performance for cloud-related variables is mixed and generally worse compared to gases and radiation variables. Cloud fraction (CF) is well reproduced by most simulations. Other aerosol/cloud related variables such as aerosol optical depth (AOD), cloud optical thickness, cloud liquid water path, cloud condensation nuclei, and cloud droplet number concentration (CDNC) are moderately to largely underpredicted by most simulations, due to underpredictions of aerosol loadings and also indicating high uncertainties associated with the current model treatments of aerosol–cloud interactions and the need for further model development. Negative correlations are found for AOD for most simulations due to large negative biases over the western part of the domain. Inter-model discrepancies also exist for a few variables such as column abundances of HCHO and SO2 and CDNC due likely to different chemical mechanisms, biogenic emissions, and treatments of aerosol indirect effects. Most simulations can also capture the inter-annual trend observed by satellites between 2006 and 2010 for several variables such as column abundance of NO2, AOD, CF, and CDNC. Results shown in this work provide the important benchmark for future online-couple air quality model development. satellite data; WRF/Chem; model evaluation; AQMEII; Online-coupled model; GEM–MACH; WRF–CMAQ
Wang, Kai; Zhang, Yang; Yahya, Khairunnisa; Wu, Shiang-Yuh; Grell, GeorgWang, K., Y. Zhang, K. Yahya, S. Wu, G. Grell, 2015: Implementation and initial application of new chemistry-aerosol options in WRF/Chem for simulating secondary organic aerosols and aerosol indirect effects for regional air quality. Atmospheric Environment, 115, 716-732. doi: 10.1016/j.atmosenv.2014.12.007. Atmospheric aerosols play important roles in affecting regional meteorology and air quality through aerosol direct and indirect effects. Two new chemistry-aerosol options have been developed in WRF/Chem v3.4.1 by incorporating the 2005 Carbon Bond (CB05) mechanism and coupling it with the existing aerosol module MADE with SORGAM and VBS modules for simulating secondary organic aerosol (SOA), aqueous-phase chemistry in both large scale and convective clouds, and aerosol feedback processes (hereafter CB05-MADE/SORGAM and CB05-MADE/VBS). As part of the Air Quality Model Evaluation International Initiative (AQMEII) Phase II model intercomparison that focuses on online-coupled meteorology and chemistry models, WRF/Chem with the two new options is applied to an area over North America for July 2006 episode. The simulations with both options can reproduce reasonably well most of the observed meteorological variables, chemical concentrations, and aerosol/cloud properties. Compared to CB05-MADE/SORGAM, CB05-MADE/VBS greatly improves the model performance for organic carbon (OC) and PM2.5, reducing NMBs from −81.2% to −13.1% and from −26.1% to −15.6%, respectively. Sensitivity simulations show that the aerosol indirect effects (including aqueous-phase chemistry) can reduce the net surface solar radiation by up to 53 W m−2 with a domainwide mean of 12 W m−2 through affecting cloud formation and radiation scattering and reflection by increasing cloud cover, which in turn reduce the surface temperature, NO2 photolytic rate, and planetary boundary layer height by up to 0.3 °C, 3.7 min−1, and 64 m, respectively. The changes of those meteorological variables further impact the air quality through the complex chemistry-aerosol-cloud-radiation interactions by reducing O3 mixing ratios by up to 5.0 ppb. The results of this work demonstrate the importance of aerosol indirect effects on the regional climate and air quality. For comparison, the impacts of aerosol direct effects on both regional meteorology and air quality are much lower with the reduction on net surface solar radiation only by up to 17 W m−2 and O3 only by up to 1.4 ppb, which indicates the importance and necessity to accurately represent the aerosol indirect effects in the online-couple regional models. WRF/Chem; AQMEII; Aerosol direct and indirect effects; CB05; VBS SOA
Wang, Kaicun; Ma, Qian; Li, Zhijun; Wang, JiankaiWang, K., Q. Ma, Z. Li, J. Wang, 2015: Decadal variability of surface incident solar radiation over China: Observations, satellite retrievals, and reanalyses. Journal of Geophysical Research: Atmospheres, 120(13), 6500–6514. doi: 10.1002/2015JD023420. Existing studies have shown that observed surface incident solar radiation (Rs) over China may have important inhomogeneity issues. This study provides metadata and reference data to homogenize observed Rs, from which the decadal variability of Rs over China can be accurately derived. From 1958 to 1990, diffuse solar radiation (Rsdif) and direct solar radiation (Rsdir) were measured separately, and Rs was calculated as their sum. The pyranometers used to measure Rsdif had a strong sensitivity drift problem, which introduced a spurious decreasing trend into the observed Rsdif and Rs data, whereas the observed Rsdir did not suffer from this sensitivity drift problem. From 1990 to 1993, instruments and measurement methods were replaced and measuring stations were restructured in China, which introduced an abrupt increase in the observed Rs. Intercomparisons between observation-based and model-based Rs performed in this research show that sunshine duration (SunDu)-derived Rs is of high quality and can be used as reference data to homogenize observed Rs data. The homogenized and adjusted data of observed Rs combines the advantages of observed Rs in quantifying hourly to monthly variability and SunDu-derived Rs in depicting decadal variability and trend. Rs averaged over 105 stations in China decreased at −2.9 W m−2 per decade from 1961 to 1990 and remained stable afterward. This decadal variability is confirmed by the observed Rsdir and diurnal temperature ranges, and can be reproduced by high-quality Earth System Models. However, neither satellite retrievals nor reanalyses can accurately reproduce such decadal variability over China. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 0394 Instruments and techniques; 0321 Cloud/radiation interaction; 1622 Earth system modeling; Surface incident solar radiation
Wang, Leidi; Lü, Daren; He, QingWang, L., D. Lü, Q. He, 2015: The impact of surface properties on downward surface shortwave radiation over the Tibetan Plateau. Advances in Atmospheric Sciences, 32(6), 759-771. doi: 10.1007/s00376-014-4131-2. The complexity of inhomogeneous surface-atmosphere radiation transfer is one of the foremost problems in the field of atmospheric physics and atmospheric radiation. To date, the influence of surface properties on shortwave radiation has not been well studied. The daily downward surface shortwave radiation of the latest FLASHFlux/CERES (Fast Longwave And Shortwave Fluxes_Time Interpolated and Spatially Averaged/Clouds and the Earth’s Radiant Energy System) satellite data was evaluated against in situ data. The comparison indicated that the differences between the two data sets are unstable and large over rugged terrain compared with relatively flat terrain, and the mean absolute error of the satellite products reaches 31.4 W m−2 (12.3%) over rugged terrain. Based on the SSF (single satellite footprint)/CERES product, the influence of surface properties on the distribution of downward surface shortwave radiation (DSSR) was analyzed. The influence of surface properties on DSSR over the Tibetan Plateau is about twice as large as that in two other regions located at the same latitude (eastern China-western Pacific and subtropical North Pacific). A simulation was carried out with the help of the I3RC (International Intercomparision of Three-Dimensional Radiation Code) Monte Carlo 3D radiative transfer community model. The results showed that DSSR increases as surface albedo increases. Moreover, the impact of surface albedo on DSSR is larger if the spatial distribution of clouds is more non-uniform. It is hoped that these results will contribute to the development of 3D radiative transfer models and the improvement of satellite inversion algorithms. surface properties; Meteorology; satellite remote sensing; Shortwave radiation; Tibetan Plateau; Atmospheric Sciences; Geophysics/Geodesy
Wang, Minghuai; Larson, Vincent E.; Ghan, Steven; Ovchinnikov, Mikhail; Schanen, David P.; Xiao, Heng; Liu, Xiaohong; Rasch, Philip; Guo, ZhunWang, M., V. E. Larson, S. Ghan, M. Ovchinnikov, D. P. Schanen, H. Xiao, X. Liu, P. Rasch, Z. Guo, 2015: A multiscale modeling framework model (superparameterized CAM5) with a higher-order turbulence closure: Model description and low-cloud simulations. Journal of Advances in Modeling Earth Systems, 7(2), 484-509. doi: 10.1002/2014MS000375. In this study, a higher-order turbulence closure scheme, called Cloud Layers Unified By Binormals (CLUBB), is implemented into a Multiscale Modeling Framework (MMF) model to improve low-cloud simulations. The performance of CLUBB in MMF simulations with two different microphysics configurations (one-moment cloud microphysics without aerosol treatment and two-moment cloud microphysics coupled with aerosol treatment) is evaluated against observations and further compared with results from the Community Atmosphere Model, Version 5 (CAM5) with conventional cloud parameterizations. CLUBB is found to improve low-cloud simulations in the MMF, and the improvement is particularly evident in the stratocumulus-to-cumulus transition regions. Compared to the single-moment cloud microphysics, CLUBB with two-moment microphysics produces clouds that are closer to the coast and agrees better with observations. In the stratocumulus-to-cumulus transition regions, CLUBB with two-moment cloud microphysics produces short-wave cloud forcing in better agreement with observations, while CLUBB with single-moment cloud microphysics overestimates short-wave cloud forcing. CLUBB is further found to produce quantitatively similar improvements in the MMF and CAM5, with slightly better performance in the MMF simulations (e.g., MMF with CLUBB generally produces low clouds that are closer to the coast than CAM5 with CLUBB). Improved low-cloud simulations in MMF make it an even more attractive tool for studying aerosol-cloud-precipitation interactions. 3311 Clouds and aerosols; 3337 Global climate models; 3307 Boundary layer processes; low clouds; higher-order closure; MMF; SPCAM5
Wang, Shuguang; Sobel, Adam H.; Fridlind, Ann; Feng, Zhe; Comstock, Jennifer M.; Minnis, Patrick; Nordeen, Michele L.Wang, S., A. H. Sobel, A. Fridlind, Z. Feng, J. M. Comstock, P. Minnis, M. L. Nordeen, 2015: Simulations of cloud-radiation interaction using large-scale forcing derived from the CINDY/DYNAMO northern sounding array. Journal of Advances in Modeling Earth Systems, 7(3), 1472–1498. doi: 10.1002/2015MS000461. The recently completed CINDY/DYNAMO field campaign observed two Madden-Julian oscillation (MJO) events in the equatorial Indian Ocean from October to December 2011. Prior work has indicated that the moist static energy anomalies in these events grew and were sustained to a significant extent by radiative feedbacks. We present here a study of radiative fluxes and clouds in a set of cloud-resolving simulations of these MJO events. The simulations are driven by the large scale forcing dataset derived from the DYNAMO northern sounding array observations, and carried out in a doubly-periodic domain using the Weather Research and Forecasting (WRF) model. Simulated cloud properties and radiative fluxes are compared to those derived from the S-Polka radar and satellite observations. To accommodate the uncertainty in simulated cloud microphysics, a number of single moment (1M) and double moment (2M) microphysical schemes in the WRF model are tested. The 1M schemes tend to underestimate radiative flux anomalies in the active phases of the MJO events, while the 2M schemes perform better, but can overestimate radiative flux anomalies. All the tested microphysics schemes exhibit biases in the shapes of the histograms of radiative fluxes and radar reflectivity. Histograms of radiative fluxes and brightness temperature indicate that radiative biases are not evenly distributed; the most significant bias occurs in rainy areas with OLR less than 150 W/m2 in the 2M schemes. Analysis of simulated radar reflectivities indicates that this radiative flux uncertainty is closely related to the simulated stratiform cloud coverage. Single moment schemes underestimate stratiform cloudiness by a factor of two, whereas 2M schemes simulate much more stratiform cloud. This article is protected by copyright. All rights reserved. 0321 Cloud/radiation interaction; 3374 Tropical meteorology; 3310 Clouds and cloud feedbacks; 3314 Convective processes; microphysics; 3371 Tropical convection; MJO; CINDY/DYNAMO; Cloud-radiation interaction; Cloud-resolving simulaitons; Radiative feedback
Wang, Shuguang; Sobel, Adam H.; Zhang, Fuqing; Sun, Y. Qiang; Yue, Ying; Zhou, LeiWang, S., A. H. Sobel, F. Zhang, Y. Q. Sun, Y. Yue, L. Zhou, 2015: Regional Simulation of the October and November MJO Events Observed during the CINDY/DYNAMO Field Campaign at Gray Zone Resolution. J. Climate, 28(6), 2097-2119. doi: 10.1175/JCLI-D-14-00294.1. AbstractThis study investigates the October and November MJO events observed during the Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011 (CINDY)/Dynamics of the MJO (DYNAMO) field campaign through cloud-permitting numerical simulations. The simulations are compared to multiple observational datasets. The control simulation at 9-km horizontal grid spacing captures the slow eastward progression of both the October and November MJO events in surface precipitation, outgoing longwave radiation, zonal wind, humidity, and large-scale vertical motion. The vertical motion shows weak ascent in the leading edge of the MJO envelope, followed by deep ascent during the peak precipitation stage and trailed by a broad second baroclinic mode structure with ascent in the upper troposphere and descent in the lower troposphere. Both the simulation and the observations also show slow northward propagation components and tropical cyclone–like vortices after the passage of the MJO active phase. Comparison with synthesized observations from the northern sounding array shows that the model simulates the passage of the two MJO events over the sounding array region well. Sensitivity experiments to SST indicate that daily SST plays an important role for the November MJO event, but much less so for the October event.Analysis of the moist static energy (MSE) budget shows that both advection and diabatic processes (i.e., surface fluxes and radiation) contribute to the development of the positive MSE anomaly in the active phase, but their contributions differ by how much they lead the precipitation peak. In comparison to the observational datasets used here, the model simulation may have a stronger surface flux feedback and a weaker radiative feedback. The normalized gross moist stability in the simulations shows an increase from near-zero values to ~0.8 during the active phase, similar to what is found in the observational datasets. Intraseasonal variability; deep convection; Madden-Julian Oscillation; Tropical variability
Wang, Wencai; Sheng, Lifang; Jin, Hongchun; Han, YongqingWang, W., L. Sheng, H. Jin, Y. Han, 2015: Dust aerosol effects on cirrus and altocumulus clouds in Northwest China. Journal of Meteorological Research, 29(5), 793-805. doi: 10.1007/s13351-015-4116-9. Dust aerosol effects on the properties of cirrus and altocumulus cloud in Northwest China were studied for the period March–May 2007 by using the satellite data of Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), Aqua, and CloudSat. Dusty clouds were defined as those mixed with dust aerosols or existing in dust aerosol conditions, while pure clouds were those in a dust-free environment. For dusty altocumulus clouds, the mean values of cloud optical depth (OPD), cloud liquid water path (LWP), cloud ice water path (IWP), cloud effective particle radius (Re), and cloud effective particle diameter (D e) were 6.40, 40.23 g m-2, 100.70 g m-2, 8.76 μm, and 40.72 μm, respectively. For pure altocumulus clouds, the corresponding mean values were 9.28, 76.70 g m-2, 128.75 g m-2, 14.03 μm, and 48.92 μm, respectively. These results show a significant decrease of OPD, LWP, IWP, R e, and D e of approximately 31%, 48%, 22%, 38%, and 17% because of the effects of dust aerosols. Moreover, the effects of dust aerosols on liquid-phase altocumulus clouds were greater than on ice-phase altocumulus clouds. Regarding dusty cirrus clouds, the mean values of OPD, IWP, and D e were 5.11, 137.53 g m-2, and 60.44 μm, respectively. In contrast, the mean values were 6.69, 156.17 g m-2, and 66.63 μm, respectively, for pure cirrus clouds, with a 24% decrease in OPD, a 12% decrease in IWP, and a 9% decrease in D e. These results indicate that dust aerosols can significantly change cloud properties, leading to a reduction of OPD, LWP, and effective particle size for both altocumulus and cirrus clouds in Northwest China. Meteorology; Atmospheric Sciences; Atmospheric Protection/Air Quality Control/Air Pollution; aerosol-cloud interaction; altocumulus cloud; cirrus cloud; dusty cloud; Geophysics and Environmental Physics
Wang, Yuan; Jiang, Jonathan H.; Su, HuiWang, Y., J. H. Jiang, H. Su, 2015: Atmospheric responses to the redistribution of anthropogenic aerosols. Journal of Geophysical Research: Atmospheres, 120(18), 9625–9641. doi: 10.1002/2015JD023665. The geographical shift of global anthropogenic aerosols from the developed countries to the Asian continent since the 1980s could potentially perturb the regional and global climate due to aerosol-cloud-radiation interactions. We use an atmospheric general circulation model with different aerosol scenarios to investigate the radiative and microphysical effects of anthropogenic aerosols from different regions on the radiation budget, precipitation, and large-scale circulations. An experiment contrasting anthropogenic aerosol scenarios in 1970 and 2010 shows that the altered cloud reflectivity and solar extinction by aerosols results in regional surface temperature cooling in East and South Asia, and warming in the US and Europe, respectively. These aerosol-induced temperature changes are consistent with the relative temperature trends from 1980 to 2010 over different regions in the reanalysis data. A reduced meridional streamfunction and zonal winds over the tropics as well as a poleward shift of the jet stream suggest weakened and expanded tropical circulations, which are induced by the redistributed aerosols through a relaxing of the meridional temperature gradient. Consequently, precipitation is suppressed in the deep tropics and enhanced in the subtropics. Our assessments of the aerosol effects over the different regions suggest that the increasing Asian pollution accounts for the weakening of the tropics circulation, while the decreasing pollution in Europe and US tends to shift the circulation systems southward. Moreover, the aerosol indirect forcing is predominant over the total aerosol forcing in magnitude, while aerosol radiative and microphysical effects jointly shape the meridional energy distributions and modulate the circulation systems. 3311 Clouds and aerosols; 3337 Global climate models; radiative forcing; anthropogenic aerosols; general circulation model; aerosol-cloud interaction
Weaver, Clark; Herman, Jay; Labow, Gordon; Larko, David; Huang, L.-K.Weaver, C., J. Herman, G. Labow, D. Larko, L. Huang, 2015: Shortwave TOA Cloud Radiative Forcing Derived from a Long-Term (1980–Present) Record of Satellite UV Reflectivity and CERES Measurements. J. Climate, 28(23), 9473-9488. doi: 10.1175/JCLI-D-14-00551.1. A 34-yr record of shortwave top-of-atmosphere (TOA) radiative cloud forcing is derived from UV Lambertian equivalent reflectivity (LER) data constructed using measured upwelling radiances from the Nimbus-7 Solar Backscatter Ultraviolet (SBUV) and from seven NOAA SBUV/2 instruments on polar-orbiting satellites. The approach is to scale the dimensionless UV LER data to match the CERES shortwave cloud radiative forcing when they are concurrent (2000–13). The underlying trends of this new longer-term CERES-like data record are solely based on the UV LER record. The good agreement between trends and anomalies of the CERES-like and CERES shortwave cloud forcing records during the overlapping data period supports using this new dataset for extended climate studies. The estimated linear trend for the shortwave TOA radiative forcing due to clouds from 60°S to 60°N is +1.47 W m−2 with a 0.11 uncertainty at the 95% confidence level over the 34-yr period 1980–2013. cloud forcing; Physical Meteorology and Climatology
Wei, Guangfei; Li, Xiongyao; Wang, ShijieWei, G., X. Li, S. Wang, 2015: Effect of terrestrial radiation on brightness temperature at lunar nearside: Based on theoretical calculation and data analysis. Advances in Space Research, 55(4), 1234-1240. doi: 10.1016/j.asr.2014.11.011. Terrestrial radiation is another possible source of heat in lunar thermal environment at its nearside besides the solar illumination. On the basis of Clouds and the Earth’s Radiant Energy System (CERES) data products, the effect of terrestrial radiation on the brightness temperature ( TB e ) of the lunar nearside has been theoretically calculated. It shows that the mafic lunar mare with high TB e is more sensitive to terrestrial radiation than the feldspathic highland with low TB e value. According to the synchronous rotation of the Moon, we extract TB e on lunar nearside using the microwave radiometer data from the first Chinese lunar probe Chang’E-1 (CE-1). Consistently, the average TB e at Mare Serenitatis is about 1.2 K while the highland around the Geber crater (19.4°S, 13.9°E) is relatively small at ∼0.4 K. Our results indicate that there is no significant effect of terrestrial radiation on TB e at the lunar nearside. However, to extract TB e accurately, effects of heat flow, rock abundance and subsurface rock fragments which are more significant should be considered in the future work. Brightness temperature; Chang’E; Moon; terrestrial radiation
Wild, Martin; Folini, Doris; Hakuba, Maria Z.; Schär, Christoph; Seneviratne, Sonia I.; Kato, Seiji; Rutan, David; Ammann, Christof; Wood, Eric F.; König-Langlo, GertWild, M., D. Folini, M. Z. Hakuba, C. Schär, S. I. Seneviratne, S. Kato, D. Rutan, C. Ammann, E. F. Wood, G. König-Langlo, 2015: The energy balance over land and oceans: an assessment based on direct observations and CMIP5 climate models. Climate Dynamics, 44(11-12), 3393-3429. doi: 10.1007/s00382-014-2430-z. The energy budgets over land and oceans are still afflicted with considerable uncertainties, despite their key importance for terrestrial and maritime climates. We evaluate these budgets as represented in 43 CMIP5 climate models with direct observations from both surface and space and identify substantial biases, particularly in the surface fluxes of downward solar and thermal radiation. These flux biases in the various models are then linearly related to their respective land and ocean means to infer best estimates for present day downward solar and thermal radiation over land and oceans. Over land, where most direct observations are available to constrain the surface fluxes, we obtain 184 and 306 Wm−2 for solar and thermal downward radiation, respectively. Over oceans, with weaker observational constraints, corresponding estimates are around 185 and 356 Wm−2. Considering additionally surface albedo and emissivity, we infer a surface absorbed solar and net thermal radiation of 136 and −66 Wm−2 over land, and 170 and −53 Wm−2 over oceans, respectively. The surface net radiation is thus estimated at 70 Wm−2 over land and 117 Wm−2 over oceans, which may impose additional constraints on the poorly known sensible/latent heat flux magnitudes, estimated here near 32/38 Wm−2 over land, and 16/100 Wm−2 over oceans. Estimated uncertainties are on the order of 10 and 5 Wm−2 for most surface and TOA fluxes, respectively. By combining these surface budgets with satellite-determined TOA budgets we quantify the atmospheric energy budgets as residuals (including ocean to land transports), and revisit the global mean energy balance. Climatology; radiation budget; CMIP5; Oceanography; Geophysics/Geodesy; Global climate models; Global energy balance; Surface and satellite observations
Wong, T; Kratz, D. P.; Stackhouse, P.W.; Sawaengphokhai, P.; Wilber, A. C.; Gupta, S. K.; Loeb, N. G.Wong, T., D. P. Kratz, P. Stackhouse, P. Sawaengphokhai, A. C. Wilber, S. K. Gupta, N. G. Loeb, 2015: Earth radiation Budget at Top-of-Atmosphere [in “State of the Climate in 2014"]. Bull. Amer. Meteor. Soc., 96(7), S37-38. doi: 10.1175/2015BAMSStateoftheClimate.1.
Wu, A.; Xiong, X.; Jin, Z.; Lukashin, C.; Wenny, B.N.; Butler, J.J.Wu, A., X. Xiong, Z. Jin, C. Lukashin, B. Wenny, J. Butler, 2015: Sensitivity of Intercalibration Uncertainty of the CLARREO Reflected Solar Spectrometer Features. IEEE Transactions on Geoscience and Remote Sensing, 53(9), 4741-4751. doi: 10.1109/TGRS.2015.2409030. The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission was recommended by the National Research Council in 2007 to conduct highly accurate and International System of Unit-traceable decadal change observations and provide an on-orbit intercalibration standard with high accuracy for relevant Earth observing sensors. The goal of reference intercalibration is to enable rigorous observations of critical climate change variables, including reflected broadband radiation, cloud properties, and changes in surface albedo, including snow and ice albedo feedback, to be made consistently among different sensors. This requires the CLARREO Reflected Solar Spectrometer (RSS) to provide highly accurate spectral reflectance measurements to establish an on-orbit reference with a radiometric accuracy requirement better than 0.3% for existing sensors. In this paper, MODTRAN-simulated top-of-atmosphere spectral data and spectral measurements from the SCIAMACHY instrument on Envisat are used to determine sensitivity of intercalibration uncertainty on key design parameters of the CLARREO spectrometer: spectral range, sampling and resolution. Their impact on intercalibration uncertainty for MODIS and VIIRS imagers is estimated for various surface types (ocean, vegetation, desert, snow, deep convective clouds, clouds and all-sky). Results indicate that for the visible to near-infrared spectral region (465–856 nm), the RSS instrument under current design concept produces uncertainties of 0.16% for the spectral range and 0.3% for the sampling and resolution. However, for the water vapor absorption bands in the short wavelength infrared region (1242–1629 nm), the same requirement is not met for sampling and resolution due to their high sensitivity to the influence of atmospheric water vapor. calibration; clouds; spectral reflectance; radiometry; MODIS; Sea measurements; Moderate Resolution Imaging Spectroradiometer (MODIS); Sea surface; Climate Absolute Radiance and Refractivity Observatory (CLARREO); intercalibration; Sensors; Visible Infrared Imaging Radiometer Suite (VIIRS)
Wu, Longtao; Li, J.-L. F.; Pi, Chia-Jung; Yu, Jia-Yuh; Chen, Jen-PingWu, L., J. F. Li, C. Pi, J. Yu, J. Chen, 2015: An observationally based evaluation of WRF seasonal simulations over the Central and Eastern Pacific. Journal of Geophysical Research: Atmospheres, 120(20), 10,664–10,680. doi: 10.1002/2015JD023561. This study uses multiple satellite data sets to evaluate seasonal simulations of the Weather Research and Forecasting (WRF) model over Central and Eastern Pacific. Experiments with five different convective parameterizations all show reasonably good performance for precipitation simulations. However, large discrepancies exist in the model-simulated ice clouds compared to CloudSat observations. Underestimations of ice clouds, mainly snow and graupel, are present in the Intertropical Convergence Zone (ITCZ) in all the experiments compared to CloudSat. In the ITCZ, all the experiments show a systematic overestimation of outgoing longwave radiation at the top of the atmosphere and downward shortwave radiation at the surface, along with biased cloud cooling in the middle and upper troposphere and biased cloud warming in the lower troposphere. Vertical motion is enhanced in the ITCZ compared to reanalysis. A weaker low-level circulation over the midlatitude oceans is evidenced in all simulations with an eastward overextension of the South Pacific Convergence Zone and overestimated moisture over the Southern Hemisphere oceans when compared to Special Sensor Microwave/Imager observations. Sensitivity experiment demonstrates that doubling the radiative effect of snow can reduce high biases in vertical motion within the ITCZ and improve the large-scale circulation and moisture over the midlatitude oceans. 3310 Clouds and cloud feedbacks; 3360 Remote sensing; 3355 Regional modeling; WRF; model evaluation; snow radiative effect
Xing, J.; Mathur, R.; Pleim, J.; Hogrefe, C.; Gan, C.-M.; Wong, D. C.; Wei, C.Xing, J., R. Mathur, J. Pleim, C. Hogrefe, C. Gan, D. C. Wong, C. Wei, 2015: Can a coupled meteorology-chemistry model reproduce the historical trend in aerosol direct radiative effects over the Northern Hemisphere?. Atmos. Chem. Phys. Discuss., 15(10), 14027-14073. doi: 10.5194/acpd-15-14027-2015. The ability of a coupled meteorology-chemistry model, i.e., WRF-CMAQ, in reproducing the historical trend in AOD and clear-sky short-wave radiation (SWR) over the Northern Hemisphere has been evaluated through a comparison of 21 year simulated results with observation-derived records from 1990–2010. Six satellite retrieved AOD products including AVHRR, TOMS, SeaWiFS, MISR, MODIS-terra and -aqua as well as long-term historical records from 11 AERONET sites were used for the comparison of AOD trends. Clear-sky SWR products derived by CERES at both TOA and surface as well as surface SWR data derived from seven SURFRAD sites were used for the comparison of trends in SWR. The model successfully captured increasing AOD trends along with the corresponding increased TOA SWR (upwelling) and decreased surface SWR (downwelling) in both eastern China and the northern Pacific. The model also captured declining AOD trends along with the corresponding decreased TOA SWR (upwelling) and increased surface SWR (downwelling) in eastern US, Europe and northern Atlantic for the period of 2000–2010. However, the model underestimated the AOD over regions with substantial natural dust aerosol contributions, such as the Sahara Desert, Arabian Desert, central Atlantic and north Indian Ocean. Estimates of aerosol direct radiative effect (DRE) at TOA are comparable with those derived by measurements. Compared to GCMs, the model exhibits better estimates of surface- aerosol direct radiative efficiency (Eτ). However, surface-DRE tends to be underestimated due to the underestimated AOD in land and dust regions. Further investigation of TOA-Eτ estimations as well as the dust module used for estimates of windblown-dust emissions is needed.
Yahya, Khairunnisa; He, Jian; Zhang, YangYahya, K., J. He, Y. Zhang, 2015: Multiyear applications of WRF/Chem over continental U.S.: Model evaluation, variation trend, and impacts of boundary conditions. Journal of Geophysical Research: Atmospheres, 120(24), 12748–12777. doi: 10.1002/2015JD023819. Multiyear applications of an online-coupled meteorology-chemistry model allow an assessment of the variation trends in simulated meteorology, air quality, and their interactions to changes in emissions and meteorology, as well as the impacts of initial and boundary conditions (ICONs/BCONs) on simulated aerosol-cloud-radiation interactions over a period of time. In this work, the Weather Research and Forecasting model with Chemistry version 3.4.1 (WRF/Chem v. 3.4.1) with the 2005 Carbon Bond mechanism coupled with the Volatility Basis Set module for secondary organic aerosol formation (WRF/Chem-CB05-VBS) is applied for multiple years (2001, 2006, and 2010) over continental U.S. This work also examines the changes in simulated air quality and meteorology due to changes in emissions and meteorology and the model's capability in reproducing the observed variation trends in species concentrations from 2001 to 2010. In addition, the impacts of the chemical ICONs/BCONs on model predictions are analyzed. ICONs/BCONs are downscaled from two global models, the modified Community Earth System Model/Community Atmosphere model version 5.1 (CESM/CAM v5.1) and the Monitoring Atmospheric Composition and Climate model (MACC). The evaluation of WRF/Chem-CB05-VBS simulations with the CESM ICONs/BCONs for 2001, 2006, and 2010 shows that temperature at 2 m (T2) is underpredicted for all three years likely due to inaccuracies in soil moisture and soil temperature, resulting in biases in surface relative humidity, wind speed, and precipitation. With the exception of cloud fraction, other aerosol-cloud variables including aerosol optical depth, cloud droplet number concentration, and cloud optical thickness are underpredicted for all three years, resulting in overpredictions of radiation variables. The model performs well for O3 and particulate matter with diameter less than or equal to 2.5 (PM2.5) for all three years comparable to other studies from literature. The model is able to reproduce observed annual average trends in O3 and PM2.5 concentrations from 2001 to 2006 and from 2006 to 2010 but is less skillful in simulating their observed seasonal trends. The 2006 and 2010 results using CESM and MACC ICONs/BCONs are compared to analyze the impact of ICONs/BCONs on model performance and their feedbacks to aerosol, clouds, and radiation. Comparing to the simulations with MACC ICONs/BCONs, the simulations with the CESM ICONs/BCONs improve the performance of O3 mixing ratios (e.g., the normalized mean bias for maximum 8 h O3 is reduced from −17% to −1% in 2010), PM2.5 in 2010, and sulfate in 2006 (despite a slightly larger normalized mean bias for PM2.5 in 2006). The impacts of different ICONs/BCONs on simulated aerosol-cloud-radiation variables are not negligible, with larger impacts in 2006 compared to 2010. 0305 Aerosols and particles; 0478 Pollution: urban, regional and global; CESM; WRF/Chem; model evaluation; chemistry-climate interactions and feedbacks; impact of boundary conditions; trend analyses
Yahya, Khairunnisa; Wang, Kai; Gudoshava, Masilin; Glotfelty, Timothy; Zhang, YangYahya, K., K. Wang, M. Gudoshava, T. Glotfelty, Y. Zhang, 2015: Application of WRF/Chem over North America under the AQMEII Phase 2: Part I. Comprehensive evaluation of 2006 simulation. Atmospheric Environment, 115, 733-755. doi: 10.1016/j.atmosenv.2014.08.063. The Weather Research and Forecasting model with Chemistry (WRF/Chem) version 3.4.1 has been modified to include the Carbon Bond 2005 (CB05) gas-phase mechanism, the Modal for Aerosol Dynamics for Europe (MADE) and the Volatility Basis Set (VBS) approach for secondary organic aerosol (hereafter WRF/Chem-CB05-MADE/VBS), and aerosol-cloud-radiation feedbacks to improve predictions of secondary organic aerosols (SOA) and to study meteorology-chemistry feedbacks. In this Part I paper, a comprehensive evaluation is performed for WRF/Chem-CB05-MADE/VBS to simulate air quality over a large area in North America for the full year of 2006. Operational, diagnostic, and mechanistic evaluations have been carried out for major meteorological variables, gas and aerosol species, as well as aerosol-cloud-radiation variables against surface measurements, sounding data, and satellite data on a seasonal and annual basis. The model performs well for most meteorological variables with moderate to relatively high correlation and low mean biases (MBs), but with a cold bias of 0.8–0.9 °C in temperature, a moderate overprediction with normalized mean biases (NMBs) of 17–22% in wind speed, and large underpredictions with NMBs of −65% to −62% in cloud optical depths and cloud condensation nuclei over the ocean. Those biases are attributed to uncertainty in physical parameterizations, incomplete treatments of hydrometeors, and inaccurate aerosol predictions. The model shows moderate underpredictions in the mixing ratios of O3 with an annual NMB of −12.8% over rural and national park sites, which may be caused by biases in temperature and wind speed, underestimate in wildfire emissions, and underestimate in biogenic organic emissions (reflected by an NMB of −79.1% in simulated isoprene mixing ratio). The model performs well for PM2.5 concentrations with annual NMBs within ±10%; but with possible bias compensation for PM2.5 species concentrations. The model simulates well the domainwide organic carbon and SOA concentrations at two sites in the southeastern U.S. but it overpredicts SOA concentrations at two sites and underpredicts OC at one site in the same area. Those biases in site-specific SOA and OC predictions are attributed to underestimates in observed SOA, uncertainties in VOC emissions, inaccurate meteorology, and the inadequacies in the VBS treatment. Larger biases exist in predictions of dry and wet deposition fluxes of gas and PM species due mainly to overpredictions in their concentrations and precipitation, uncertainties in model treatments of deposition processes, and uncertainties in the CASTNET dry deposition data. Comparison of WRF and WRF/Chem simulations shows that the inclusion of chemical feedbacks to meteorology, clouds, and radiation results in improved predictions in most meteorological variables. Aerosol optical depth correlates strongly with aerosol concentration and cloud optical depth. The relationships between the aerosol and cloud variables are complex as the cloud variables are not only influenced by aerosol concentrations but by larger-scale dynamical processes. WRF/Chem; AQMEII; Aerosol direct and indirect effects; Annual evaluation; Online-coupled model
Yan, Hongru; Huang, Jianping; Minnis, Patrick; Yi, Yuhong; Sun-Mack, Sunny; Wang, Tianhe; Nakajima, Takashi Y.Yan, H., J. Huang, P. Minnis, Y. Yi, S. Sun-Mack, T. Wang, T. Y. Nakajima, 2015: Comparison of CERES-MODIS cloud microphysical properties with surface observations over Loess Plateau. Journal of Quantitative Spectroscopy and Radiative Transfer, 153, 65-76. doi: 10.1016/j.jqsrt.2014.09.009. To enhance the utility of satellite-derived cloud properties for studying the role of clouds in climate change and the hydrological cycle in semi-arid areas, it is necessary to know their uncertainties. This paper estimates the uncertainties of several cloud properties by comparing those derived over the China Loess Plateau from the MODerate-resolution Imaging Spectroradiometer (MODIS) on Terra and Aqua by the Clouds and Earth׳s Radiant Energy System (CERES) with surface observations at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). The comparisons use data from January 2008 to June 2010 limited to single layer and overcast stratus conditions during daytime. Cloud optical depths (τ) and liquid water paths (LWP) from both Terra and Aqua generally track the variation of the surface counterparts with modest correlation, while cloud effective radius (re) is only weakly correlated with the surface retrievals. The mean differences between Terra and the SACOL retrievals are −4.7±12.9, 2.1±3.2 μm and 30.2±85.3 g m−2 for τ, re and LWP, respectively. The corresponding differences for Aqua are 2.1±8.4, 1.2±2.9 μm and 47.4±79.6 g m−2, respectively. Possible causes for biases of satellite retrievals are discussed through statistical analysis and case studies. Generally, the CERES-MODIS cloud properties have a bit larger biases over the Loess Plateau than those in previous studies over other locations. Satellite; validation; Cloud microphysical properties
Yang, Fan; Han, Yuge; Xuan, YiminYang, F., Y. Han, Y. Xuan, 2015: Large-scale earth surface thermal radiative features in space observation. Optics Communications, 348, 77-84. doi: 10.1016/j.optcom.2015.03.017. It is necessary to complete the earth thermal radiative modeling, since it is the most important background in space infrared observation. A new method was proposed to calculate the earth thermal infrared radiation combined with remote sensing technology. The simplified model also was proposed when the solar radiative impact is neglected properly. The practical split-window algorithm was used to retrieve the global surface temperature from MODIS data products. Integrated with MODTRAN code to calculate the atmospheric radiation and transmittance, the earth thermal infrared features were calculated in typical months. Moreover the radiance dependence on viewing angle was discussed. Through the comparison with CERES measurement results, this model has been proved effective and practicable, and that it would have a further application in space thermal environment analysis or space infrared observation technology. modeling; Earth background; Infrared features; Space observation; Temperature retrieving
Yi, Bingqi; Yang, Ping; Dessler, A.; da Silva, A.M.Yi, B., P. Yang, A. Dessler, A. da Silva, 2015: Response of Aerosol Direct Radiative Effect to the East Asian Summer Monsoon. IEEE Geoscience and Remote Sensing Letters, 12(3), 597-600. doi: 10.1109/LGRS.2014.2352630. Asian summer monsoon and atmospheric aerosol simultaneously influence the climate in the East Asian region. However, substantial uncertainties exist in the current understanding of the interactions between monsoon and aerosol and their combined effects. Previous studies have shown that aerosols influence the strength of monsoon and monsoon-related water cycles; however, monsoon strongly regulates the aerosol spatial distribution. This letter investigates the radiative flux response at the top of the atmosphere to the Asian summer monsoon by using observations made by the Clouds and Earth's Radiant Energy System and the Moderate Resolution Imaging Spectroradiometer. In comparison with the ten-year (2002-2011) mean climatology, the aerosol radiative effect is estimated over two eastern Asia regions for the months of July in 2002 and 2003, corresponding to a weak and a strong summer monsoon event, respectively. The dramatically different influences show the aerosol radiative forcing over land to be strongly responsive to Asian summer monsoon. Furthermore, the reanalysis-based estimate of the aerosol radiative effect is consistent with its observation-only counterpart. clouds; Satellites; aerosols; climate; Climatology; Moderate Resolution Imaging Spectroradiometer; MODIS; Asia; Monsoons; Clouds and Earth's Radiant Energy System; AD 2002; AD 2003; aerosol direct radiative effect response; Aerosol direct radiative forcing; aerosol spatial distribution; atmospheric humidity; Clouds and Earth's Radiant Energy System (CERES) observations; East Asian summer monsoon; MERRAero reanalysis; monsoon-related water cycles; radiative flux response
Yokoi, SatoruYokoi, S., 2015: Multireanalysis Comparison of Variability in Column Water Vapor and Its Analysis Increment Associated with the Madden–Julian Oscillation. J. Climate, 28(2), 793-808. doi: 10.1175/JCLI-D-14-00465.1. AbstractThis study conducts a multireanalysis comparison of variability in column water vapor (CWV) represented in three reanalysis products [Japanese 55-year Reanalysis Project (JRA-55), JRA-25, and ECMWF Interim Re-Analysis (ERA-Interim)] associated with the Madden–Julian oscillation (MJO) in boreal winter, with emphasis on CWV tendency simulated by forecast models and analysis increment calculated by data assimilation systems. Analyses of these variables show that, while the JRA-55 forecast model is able to simulate eastward propagation of the CWV anomaly, this model tends to weaken its amplitude. The multireanalysis comparison of the analysis increment further reveals that this weakening bias is related to excessively weak cloud radiative feedback represented by the model. This bias in the feedback strength makes anomalous moisture supply by the vertical advection term in the CWV budget equation too insensitive to precipitation anomaly, resulting in reduction of the amplitude of CWV anomaly. ERA-Interim has a nearly opposite feature: the forecast model represents excessively strong feedback. These results imply the necessity of accurate representation of the cloud radiative feedback strength for a short-term MJO forecast and may be evidence to support the argument that this feedback is essential for the existence of MJO. Furthermore, this study demonstrates that the multireanalysis comparison of the analysis increment will provide useful information for examining model biases and potentially for estimating parameters that are difficult to estimate from observational data, such as gross moist stability. water vapor; Cloud radiative effects; Budgets; Madden-Julian Oscillation; Reanalysis data
Yoshimura, Hiromasa; Mizuta, Ryo; Murakami, HiroyukiYoshimura, H., R. Mizuta, H. Murakami, 2015: A Spectral Cumulus Parameterization Scheme Interpolating between Two Convective Updrafts with Semi-Lagrangian Calculation of Transport by Compensatory Subsidence. Mon. Wea. Rev., 143(2), 597-621. doi: 10.1175/MWR-D-14-00068.1. AbstractThe authors have developed a new spectral cumulus parameterization scheme that explicitly considers an ensemble of multiple convective updrafts by interpolating in-cloud variables between two convective updrafts with large and small entrainment rates. This cumulus scheme has the advantages that the variables in entraining and detraining convective updrafts are calculated in detail layer by layer as in the Tiedtke scheme, and that a spectrum of convective updrafts with different heights due to the difference in entrainment rates is explicitly represented, as in the Arakawa–Schubert scheme. A conservative and monotonic semi-Lagrangian scheme is used for calculation of transport by convection-induced compensatory subsidence. Use of the semi-Lagrangian scheme relaxes the mass-flux limit due to the Courant–Friedrichs–Lewy (CFL) condition, and moreover ensures nonnegative natural material transport. A global atmospheric model using this cumulus scheme gives an atmospheric simulation that agrees well with the observational climatology. convective parameterization
Yu, Hungjui; Ciesielski, Paul E.; Wang, Junhong; Kuo, Hung-Chi; Vömel, Holger; Dirksen, RuudYu, H., P. E. Ciesielski, J. Wang, H. Kuo, H. Vömel, R. Dirksen, 2015: Evaluation of Humidity Correction Methods for Vaisala RS92 Tropical Sounding Data. J. Atmos. Oceanic Technol., 32(3), 397-411. doi: 10.1175/JTECH-D-14-00166.1. AbstractThis study examines the DigiCORA and Global Climate Observing System Reference Upper-Air Network (GRUAN) humidity corrections of Vaisala RS92 radiosondes at three sites over the tropical Indian Ocean and surrounding areas during the Dynamics of the Madden–Julian Oscillation (DYNAMO) field campaign in 2011. The proprietary DigiCORA correction algorithm is built into the ground station software provided by Vaisala, whereas the GRUAN correction is an open source algorithm. Included in the GRUAN data product are uncertainty estimates for their corrections. This information is used to examine the statistical consistency of the various corrections.In general, the algorithms produce a positive relative humidity (RH) correction that increases with altitude related primarily to a solar radiation dry bias adjustment. For example, in daytime soundings the relative RH correction increases from a few percent for temperatures >0°C to 20%–40% between 100 and 200 hPa. Comparison of corrected RH vertical profiles show only small differences (on the order of a few percent or less at any given level) between the DigiCORA and GRUAN algorithms, such that these corrections are considered to be statistically consistent at most levels.In evaluating corrected humidity data with independent estimates of total precipitable water (TPW), good agreement was found at all sites between corrected sounding and ground-based microwave radiometer (MWR) estimates of TPW with mean differences ≤0.9 mm (or Instrumentation/sensors; Data quality control; Soundings; Radiosonde observations; Global positioning systems (GPS); In situ atmospheric observations
Yu, L.; Jin, X.; Stackhouse, P.; Wilber, A.; Josey, S.; Xue, Y.; Kumar, A.Yu, L., X. Jin, P. Stackhouse, A. Wilber, S. Josey, Y. Xue, A. Kumar, 2015: Ocean surface heat and momentum fluxes [In "State of the Climate in 2014"]. Bull. Amer. Meteor. Soc., 96(7), S68-S71. doi: 10.1175/2015BAMSStateoftheClimate.1.
Yu, Sungduk; Pritchard, Michael S.Yu, S., M. S. Pritchard, 2015: The effect of large-scale model time step and multiscale coupling frequency on cloud climatology, vertical structure, and rainfall extremes in a superparameterized GCM. Journal of Advances in Modeling Earth Systems, 7(4), 1977-1996. doi: 10.1002/2015MS000493. The effect of global climate model (GCM) time step—which also controls how frequently global and embedded cloud resolving scales are coupled—is examined in the Superparameterized Community Atmosphere Model ver 3.0. Systematic bias reductions of time-mean shortwave cloud forcing (∼10 W/m2) and longwave cloud forcing (∼5 W/m2) occur as scale coupling frequency increases, but with systematically increasing rainfall variance and extremes throughout the tropics. An overarching change in the vertical structure of deep tropical convection, favoring more bottom-heavy deep convection as a global model time step is reduced may help orchestrate these responses. The weak temperature gradient approximation is more faithfully satisfied when a high scale coupling frequency (a short global model time step) is used. These findings are distinct from the global model time step sensitivities of conventionally parameterized GCMs and have implications for understanding emergent behaviors of multiscale deep convective organization in superparameterized GCMs. The results may also be useful for helping to tune them. 3309 Climatology; 3337 Global climate models; 3310 Clouds and cloud feedbacks; 3354 Precipitation; cloud forcing; 3373 Tropical dynamics; convective organization; extreme rainfall; scale coupling frequency; superparameterization; time step sensitivity
Zagoni, MiklosZagoni, M., 2015: A new diagram of Earth’s global energy budget. Acta Geodaetica et Geophysica, 1-12. doi: 10.1007/s40328-015-0138-0. cloud radiative effect; Geophysics/Geodesy; Earth’s energy budget; Energy balance equations; Greenhouse effect of clouds
Zhang, Ke; Kimball, John S.; Nemani, Ramakrishna R.; Running, Steven W.; Hong, Yang; Gourley, Jonathan J.; Yu, ZhongboZhang, K., J. S. Kimball, R. R. Nemani, S. W. Running, Y. Hong, J. J. Gourley, Z. Yu, 2015: Vegetation Greening and Climate Change Promote Multidecadal Rises of Global Land Evapotranspiration. Scientific Reports, 5, 15956. doi: 10.1038/srep15956. Recent studies showed that anomalous dry conditions and limited moisture supply roughly between 1998 and 2008, especially in the Southern Hemisphere, led to reduced vegetation productivity and ceased growth in land evapotranspiration (ET).
Zhang, Taiping; Stackhouse Jr., Paul W.; Gupta, Shashi K.; Cox, Stephen J.; Mikovitz, J. ColleenZhang, T., P. W. Stackhouse Jr., S. K. Gupta, S. J. Cox, J. C. Mikovitz, 2015: The validation of the GEWEX SRB surface longwave flux data products using BSRN measurements. Journal of Quantitative Spectroscopy and Radiative Transfer, 150, 134-147. doi: 10.1016/j.jqsrt.2014.07.013. The longwave downward fluxes at the Earth׳s surface are a significant part of the products of the NASA GEWEX SRB (Surface Radiation Budget) project which has produced and archived a 24.5-year continuous record from July 1983 to December 2007 of global shortwave (SW) and longwave (LW) radiation fluxes at TOA and the surface from satellite measurements. The data are generated on a system of grid boxes ranging from 1° latitude by 1° longitude at lower latitudes to 1° latitude by 120° longitude next to the poles. The LW datasets, which are available as 3-hourly, 3-hourly–monthly, daily and monthly means, are produced from two sets of algorithms, the GEWEX LW (GLW) algorithm which is designated as primary and the Langley Parameterized LW (LPLA) algorithm which is designated as quality-check. The inputs of the latest versions, GLW (V3.1) and LPLA (V3.0), include the Geostationary Satellite system (GEOS) Version 4.0.3 meteorological information and cloud properties derived from the International Satellite Cloud Climatology Project (ISCCP) DX data. In this paper, we compare the LW downward fluxes at the Earth׳s surface from both algorithms against over 4000 site-months of the Baseline Surface Radiation Network (BSRN) data from among the 59 BSRN sites. The comparisons are made for the 3-hourly, daily and monthly means each for the entire record, and on a month-by-month basis as well as a site-by-site basis. It is found that the overall daily mean bias/RMS for the GLW (V3.1) and LPLA (V3.0) algorithms are, respectively, 1.1/22.1 and 4.6/22.8 W m−2, their monthly counterparts are, respectively, 0.9/11.1 and 4.5/12.9 W m−2. Anomaly time series for a subset of more continuous BSRN measurement data sets show a standard deviation of 2.3 W m−2 and a correlation of 0.82 indicating the accurate replication of month-to-month variability. Clusters of similar surface types are analyzed showing that the uncertainties are largest over the polar regions. Finally, Kolmogorov–Smirnov (KS) two-sample test and Cramér–von Mises (CvM) two-sample test are used to show that the GLW is able to replicate the cumulative frequency distribution of the measurements at the 0.01 significance level. Satellite; longwave radiation; radiation budget; BSRN; GEWEX SRB
Zhang, Xiaotong; Liang, Shunlin; Wild, Martin; Jiang, BoZhang, X., S. Liang, M. Wild, B. Jiang, 2015: Analysis of surface incident shortwave radiation from four satellite products. Remote Sensing of Environment, 165, 186-202. doi: 10.1016/j.rse.2015.05.015. Incident solar radiation (Rs) over the Earth's surface is important for studying our climate and environment. Global observation networks have been established, but many land surfaces are under-represented. Satellite remote sensing is the only way to estimate Rs at both global and regional scales. Many efforts have been made to evaluate the accuracy of current Rs products generated from satellite observations, but only a limited amount of ground measurements was generally used and the individual satellite products were used for analyzing Rs variability. In this study, four satellite estimates of Rs, including the Global Energy and Water Cycle Experiment — Surface Radiation Budget (GEWEX-SRB V3.0), the International Satellite Cloud Climatology Project — Flux Data (ISCCP-FD), the University of Maryland (UMD)/Shortwave Radiation Budget (SRB) (UMD-SRB V3.3.3) product, and the Earth's Radiant Energy System (CERES) EBAF, were evaluated using comprehensive ground measurements at 1151 sites around the world from the Global Energy Balance Archive (GEBA) and the China Meteorological Administration (CMA). It was found that these satellite estimates of Rs agree better with surface measurements at monthly than at daily time scale and can capture the seasonal variation of Rs very well, but these satellite products overestimated Rs by approximately 10wm−2. The mean bias and the root mean square error (RMSE) of the monthly mean estimates from these four data sets were 10.2wm−2 and 24.8wm−2 respectively. The global annual mean values of Rs were 186.7wm−2, 185.4wm−2, and 188.6wm−2 for CERES-EBAF, ISCCP-FD, and GEWEX-SRB V3.0 respectively. The averaged global annual mean Rs value from ground-measured-calibrated three satellite derived Rs products was 180.6wm−2, which is smaller than that estimated from individual satellite-derived products. The CERES-EBAF product shows the best accuracy among these four data sets, which indicates that including more accurate cloud information from active instruments can improve the accuracy of Rs. These satellite products show different temporal trends. Both GEWEX-SRB V3.0 and ISCCP-FD showed similar trends at the global scale but with different magnitudes. A significant dimming was found between 1984 and 1991, followed by brightening from 1992 to 2000, and then by a significant dimming over 2001–2007. The CERES-EBAF product showed a brightening trend, but not significantly since 2000. The variability from satellite estimates at pixel level was also analyzed. The results are comparable with previous studies based on observed Rs at the surface for specific regions, although some inconsistencies still exist and the magnitudes of the variations should be further quantified. We also found that clouds contribute more to the long-term variations of Rs derived from satellite observations than aerosols. Remote sensing; Satellite; Incident shortwave radiation; Global irradiance
Zhang, Yang; Zhang, Xin; Wang, Kai; He, Jian; Leung, L. Ruby; Fan, Jiwen; Nenes, AthanasiosZhang, Y., X. Zhang, K. Wang, J. He, L. R. Leung, J. Fan, A. Nenes, 2015: Incorporating an advanced aerosol activation parameterization into WRF-CAM5: Model evaluation and parameterization intercomparison. Journal of Geophysical Research: Atmospheres, 120(14), 6952–6979. doi: 10.1002/2014JD023051. Aerosol activation into cloud droplets is an important process that governs aerosol indirect effects. The advanced treatment of aerosol activation by Fountoukis and Nenes (2005) and its recent updates, collectively called the FN series, have been incorporated into a newly developed regional coupled climate-air quality model based on the Weather Research and Forecasting model with the physics package of the Community Atmosphere Model version 5 (WRF-CAM5) to simulate aerosol-cloud interactions in both resolved and convective clouds. The model is applied to East Asia for two full years of 2005 and 2010. A comprehensive model evaluation is performed for model predictions of meteorological, radiative, and cloud variables, chemical concentrations, and column mass abundances against satellite data and surface observations from air quality monitoring sites across East Asia. The model performs overall well for major meteorological variables including near-surface temperature, specific humidity, wind speed, precipitation, cloud fraction, precipitable water, downward shortwave and longwave radiation, and column mass abundances of CO, SO2, NO2, HCHO, and O3 in terms of both magnitudes and spatial distributions. Larger biases exist in the predictions of surface concentrations of CO and NOx at all sites and SO2, O3, PM2.5, and PM10 concentrations at some sites, aerosol optical depth, cloud condensation nuclei over ocean, cloud droplet number concentration (CDNC), cloud liquid and ice water path, and cloud optical thickness. Compared with the default Abdul-Razzack Ghan (2000) parameterization, simulations with the FN series produce ~107–113% higher CDNC, with half of the difference attributable to the higher aerosol activation fraction by the FN series and the remaining half due to feedbacks in subsequent cloud microphysical processes. With the higher CDNC, the FN series are more skillful in simulating cloud water path, cloud optical thickness, downward shortwave radiation, shortwave cloud forcing, and precipitation. The model evaluation identifies several areas of improvements including emissions and their vertical allocation as well as model formulations such as aerosol formation, cloud droplet nucleation, and ice nucleation. 0305 Aerosols and particles; 0365 Troposphere: composition and chemistry; East Asia; aerosol indirect effects; 0478 Pollution: urban, regional and global; CCN activation; model improvement and evaluation; WRF-CAM5
Zhang, Yi; Chen, Haoming; Yu, RucongZhang, Y., H. Chen, R. Yu, 2015: Simulations of Stratus Clouds over Eastern China in CAM5: Sources of Errors. J. Climate, 28(1), 36-55. doi: 10.1175/JCLI-D-14-00350.1. AbstractA previous study by Zhang et al. suggested two biases of the high-resolution configured Community Atmosphere Model, version 5 (CAM5), in simulating stratus clouds over eastern China, including an underestimation of stratus occurrence frequency and a spurious low stratus amount when present (AWP) value center over the Sichuan basin. In this study, the causes for these two problems are further explored.The underestimate of stratus occurrence frequency in the model is attributed to the bias in large-scale ambient environmental fields. This is confirmed by investigating the differences between two climate counterparts. Results suggest that when the environmental fields in the climate ensemble become more realistic, the simulations of stratus cloud radiative forcing and cloud fraction are enhanced, mainly caused by a corresponding increase in the stratus occurrence frequency. The specific sources of the cloud changes between these two ambient climates are then investigated.The presence of a low stratus AWP value center is found to be sensitive to the choice of dynamical core. This is confirmed by comparing the simulations from two dynamical core counterparts: a default finite-volume core and an alternative Eulerian spectral transform core. Experiments with these two cores suggest that the spectral CAM5 is able to alleviate this problem. Correspondingly, the subsiding motions when stratus clouds occur in the default core are largely suppressed in the spectral core. As a result, the spectral CAM5 has more midtopped nimbostratus cloud fraction than the default configuration over the Sichuan basin, especially in the lower levels of the cloud profiles. clouds; General circulation models; Model errors
Zhou, Chen; Zelinka, Mark D.; Dessler, Andrew E.; Klein, Stephen A.Zhou, C., M. D. Zelinka, A. E. Dessler, S. A. Klein, 2015: The relationship between interannual and long-term cloud feedbacks. Geophysical Research Letters, 42(23), 10,463–10,469. doi: 10.1002/2015GL066698. Analyses of Coupled Model Intercomparison Project phase 5 simulations suggest that climate models with more positive cloud feedback in response to interannual climate fluctuations also have more positive cloud feedback in response to long-term global warming. Ensemble mean vertical profiles of cloud change in response to interannual and long-term surface warming are similar, and the ensemble mean cloud feedback is positive on both timescales. However, the average long-term cloud feedback is smaller than the interannual cloud feedback, likely due to differences in surface warming pattern on the two timescales. Low cloud cover (LCC) change in response to interannual and long-term global surface warming is found to be well correlated across models and explains over half of the covariance between interannual and long-term cloud feedback. The intermodel correlation of LCC across timescales likely results from model-specific sensitivities of LCC to sea surface warming. 3305 Climate change and variability; 3310 Clouds and cloud feedbacks; cloud feedback; 3307 Boundary layer processes; climate change and variability; low cloud cover
Zhou, Linjiong; Bao, Qing; Liu, Yimin; Wu, Guoxiong; Wang, Wei-Chyung; Wang, Xiaocong; He, Bian; Yu, Haiyang; Li, JiandongZhou, L., Q. Bao, Y. Liu, G. Wu, W. Wang, X. Wang, B. He, H. Yu, J. Li, 2015: Global energy and water balance: Characteristics from Finite-volume Atmospheric Model of the IAP/LASG (FAMIL1). Journal of Advances in Modeling Earth Systems, 7(1), 1-20. doi: 10.1002/2014MS000349. This paper documents version 1 of the Finite-volume Atmospheric Model of the IAP/LASG (FAMIL1), which has a flexible horizontal resolution up to a quarter of 1°. The model, currently running on the “Tianhe 1A” supercomputer, is the atmospheric component of the third-generation Flexible Global Ocean-Atmosphere-Land climate System model (FGOALS3) which will participate in the Coupled Model Intercomparison Project Phase 6 (CMIP6). In addition to describing the dynamical core and physical parameterizations of FAMIL1, this paper describes the simulated characteristics of energy and water balances and compares them with observational/reanalysis data. The comparisons indicate that the model simulates well the seasonal and geographical distributions of radiative fluxes at the top of the atmosphere and at the surface, as well as the surface latent and sensible heat fluxes. A major weakness in the energy balance is identified in the regions where extensive and persistent marine stratocumulus is present. Analysis of the global water balance also indicates realistic seasonal and geographical distributions with the global annual mean of evaporation minus precipitation being approximately 10−5 mm d−1. We also examine the connections between the global energy and water balance and discuss the possible link between the two within the context of the findings from the reanalysis data. Finally, the model biases as well as possible solutions are discussed. 0325 Evolution of the atmosphere; 3337 Global climate models; 1814 Energy budgets; AGCM; Energy balance; 1876 Water budgets; interactions of energy and water; water balance
Ahlgrimm, Maike; Forbes, RichardAhlgrimm, M., R. Forbes, 2014: Improving the Representation of Low Clouds and Drizzle in the ECMWF Model Based on ARM Observations from the Azores. Mon. Wea. Rev., 142(2), 668-685. doi: 10.1175/MWR-D-13-00153.1.
Allan, Richard P.; Liu, Chunlei; Loeb, Norman G.; Palmer, Matthew D.; Roberts, Malcolm; Smith, Doug; Vidale, Pier-LuigiAllan, R. P., C. Liu, N. G. Loeb, M. D. Palmer, M. Roberts, D. Smith, P. Vidale, 2014: Changes in global net radiative imbalance 1985–2012. Geophysical Research Letters, 41(15), 5588-5597. doi: 10.1002/2014GL060962. Combining satellite data, atmospheric reanalyses, and climate model simulations, variability in the net downward radiative flux imbalance at the top of Earth's atmosphere (N) is reconstructed and linked to recent climate change. Over the 1985–1999 period mean N (0.34 ± 0.67 Wm−2) is lower than for the 2000–2012 period (0.62 ± 0.43 Wm−2, uncertainties at 90% confidence level) despite the slower rate of surface temperature rise since 2000. While the precise magnitude of N remains uncertain, the reconstruction captures interannual variability which is dominated by the eruption of Mount Pinatubo in 1991 and the El Niño Southern Oscillation. Monthly deseasonalized interannual variability in N generated by an ensemble of nine climate model simulations using prescribed sea surface temperature and radiative forcings and from the satellite-based reconstruction is significantly correlated (r∼0.6) over the 1985–2012 period. 1610 Atmosphere; 1640 Remote sensing; radiative flux; temperature; 1616 Climate variability; climate model; satellite data; 1626 Global climate models; 1635 Oceans; Climate variability; Energy balance
Altaratz, O.; Koren, I.; Remer, L. A.; Hirsch, E.Altaratz, O., I. Koren, L. A. Remer, E. Hirsch, 2014: Review: Cloud invigoration by aerosols—Coupling between microphysics and dynamics. Atmospheric Research, 140–141, 38-60. doi: 10.1016/j.atmosres.2014.01.009. The cloud invigoration effect refers here to the link between an increase in aerosol loading and deepening of convective clouds. The effect can be reflected also in a larger cloud fraction and an increase in the condensate mass that is distributed higher in the atmospheric column. Identifying the invigoration effect by aerosols requires attributing certain changes in cloud dynamics to changes in cloud microphysics. More than 10 years of extensive research using data collected in field experiments, analysis of satellite measurements and the employment of state-of-the-art numerical models have been used in an attempt to study this elusive phenomenon. Despite these intensive efforts, the validity of the invigoration effect and the possibility of climate responses to this effect are still considered to be open questions. In this review observational evidence and modeling results for cloud invigoration are discussed. Studies that indicate convective cloud invigoration effects, as well as studies that suggest no or even opposite effects are summarized. A coherent physical mechanism that describes a chain of processes that takes place under the proper conditions in the core of a convective cloud provides explanation for the “ideal” case of invigoration reported by observations and numerical modeling, while the competition between core-based vs. margin-based processes explains the cases that deviate from the “ideal”. Because convective clouds play a key role in the Earth's radiation balance, in the water cycle and atmospheric circulations, invigoration implies possible consequences at scales ranging from a single cloud up to the global. climate; Aerosol and cloud; Cloud and precipitation
Andrews, TimothyAndrews, T., 2014: Using an AGCM to Diagnose Historical Effective Radiative Forcing and Mechanisms of Recent Decadal Climate Change. J. Climate, 27(3), 1193-1209. doi: 10.1175/JCLI-D-13-00336.1.
Ansell, C.; Brindley, Helen E.; Pradhan, Yaswant; Saunders, RogerAnsell, C., H. E. Brindley, Y. Pradhan, R. Saunders, 2014: Mineral dust aerosol net direct radiative effect during GERBILS field campaign period derived from SEVIRI and GERB. Journal of Geophysical Research: Atmospheres, 119(7), 4070-4086. doi: 10.1002/2013JD020681. Colocated Spinning Enhanced Visible and Infrared Imager (SEVIRI) retrieved dust optical depths at 0.55 microns, τ055, and Geostationary Earth Radiation Budget (GERB) fluxes at the top of atmosphere are used to provide, for the first time, an observationally based estimate of the cloud-free net direct radiative effect (DRE) of mineral dust aerosol from geostationary satellite observations, providing new insights into the influence of time of day on the magnitude and sign of the shortwave, longwave, and overall net effect during sunlit hours. Focusing on the Geostationary Earth Radiation Budget Intercomparison of Longwave and Shortwave radiation (GERBILS) campaign over North Africa during June 2007, the presence of mineral dust aerosol reduces the outgoing longwave radiation at all times of day with the peak reduction clearly following the diurnal cycle of surface temperature. The instantaneous shortwave DRE shows strong dependencies on pristine sky albedo and solar zenith angle such that the same dust loading can induce a positive or negative value dependent on time of day. However, the area mean net DRE over the GERBILS period is dominated by the longwave component at all sampled times of day, with mineral dust inducing a reduction in outgoing net flux of the order of 10W m−2. Hence, in the mean sense, Saharan dust is found to warm the Earth-atmosphere system over northern Africa and the Middle East. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; aerosol; direct radiative effect; mineral dust; GERBILS
Bacmeister, Julio T.; Wehner, Michael F.; Neale, Richard B.; Gettelman, Andrew; Hannay, Cecile; Lauritzen, Peter H.; Caron, Julie M.; Truesdale, John E.Bacmeister, J. T., M. F. Wehner, R. B. Neale, A. Gettelman, C. Hannay, P. H. Lauritzen, J. M. Caron, J. E. Truesdale, 2014: Exploratory High-Resolution Climate Simulations using the Community Atmosphere Model (CAM). J. Climate, 27(9), 3073-3099. doi: 10.1175/JCLI-D-13-00387.1. AbstractExtended, high-resolution (0.23° latitude × 0.31° longitude) simulations with Community Atmosphere Model versions 4 and 5 (CAM4 and CAM5) are examined and compared with results from climate simulations conducted at a more typical resolution of 0.9° latitude × 1.25° longitude. Overall, the simulated climate of the high-resolution experiments is not dramatically better than that of their low-resolution counterparts. Improvements appear primarily where topographic effects may be playing a role, including a substantially improved summertime Indian monsoon simulation in CAM4 at high resolution. Significant sensitivity to resolution is found in simulated precipitation over the southeast United States during winter. Some aspects of the simulated seasonal mean precipitation deteriorate notably at high resolution. Prominent among these is an exacerbated Pacific “double ITCZ” bias in both models. Nevertheless, while large-scale seasonal means are not dramatically better at high resolution, realistic tropical cyclone (TC) distributions are obtained. Some skill in reproducing interannual variability in TC statistics also appears. climate models
Banks, Jamie R.; Brindley, Helen E.; Hobby, Matthew; Marsham, John H.Banks, J. R., H. E. Brindley, M. Hobby, J. H. Marsham, 2014: The daytime cycle in dust aerosol direct radiative effects observed in the central Sahara during the Fennec campaign in June 2011. Journal of Geophysical Research: Atmospheres, 119(24), 2014JD022077. doi: 10.1002/2014JD022077. The direct clear-sky radiative effect (DRE) of atmospheric mineral dust is diagnosed over the Bordj Badji Mokhtar (BBM) supersite in the central Sahara during the Fennec campaign in June 2011. During this period, thick dust events were observed, with aerosol optical depth values peaking at 3.5. Satellite observations from Meteosat-9 are combined with ground-based radiative flux measurements to obtain estimates of DRE at the surface, top-of-atmosphere (TOA), and within the atmosphere. At TOA, there is a distinct daytime cycle in net DRE. Both shortwave (SW) and longwave (LW) DRE peak around noon and induce a warming of the Earth-atmosphere system. Toward dusk and dawn, the LW DRE reduces while the SW effect can switch sign triggering net radiative cooling. The net TOA DRE mean values range from −9 Wm−2 in the morning to heating of +59 Wm−2 near midday. At the surface, the SW dust impact is larger than at TOA: SW scattering and absorption by dust results in a mean surface radiative cooling of 145Wm−2. The corresponding mean surface heating caused by increased downward LW emission from the dust layer is a factor of 6 smaller. The dust impact on the magnitude and variability of the atmospheric radiative divergence is dominated by the SW cooling of the surface, modified by the smaller SW and LW effects at TOA. Consequently, dust has a mean daytime net radiative warming effect on the atmosphere of 153Wm−2. 0305 Aerosols and particles; 3359 Radiative processes; 3360 Remote sensing; 9305 Africa; 3399 General or miscellaneous; Bordj Badji Mokhtar; Fennec; geostationary satellite observations; ground observations; radiative effect of dust
Baran, Anthony J.; Hill, Peter; Furtado, Kalli; Field, Paul; Manners, JamesBaran, A. J., P. Hill, K. Furtado, P. Field, J. Manners, 2014: A Coupled Cloud Physics–Radiation Parameterization of the Bulk Optical Properties of Cirrus and Its Impact on the Met Office Unified Model Global Atmosphere 5.0 Configuration. J. Climate, 27(20), 7725-7752. doi: 10.1175/JCLI-D-13-00700.1. AbstractA new coupled cloud physics–radiation parameterization of the bulk optical properties of ice clouds is presented. The parameterization is consistent with assumptions in the cloud physics scheme regarding particle size distributions (PSDs) and mass–dimensional relationships. The parameterization is based on a weighted ice crystal habit mixture model, and its bulk optical properties are parameterized as simple functions of wavelength and ice water content (IWC). This approach directly couples IWC to the bulk optical properties, negating the need for diagnosed variables, such as the ice crystal effective dimension. The parameterization is implemented into the Met Office Unified Model Global Atmosphere 5.0 (GA5) configuration. The GA5 configuration is used to simulate the annual 20-yr shortwave (SW) and longwave (LW) fluxes at the top of the atmosphere (TOA), as well as the temperature structure of the atmosphere, under various microphysical assumptions. The coupled parameterization is directly compared against the current operational radiation parameterization, while maintaining the same cloud physics assumptions. In this experiment, the impacts of the two parameterizations on the SW and LW radiative effects at TOA are also investigated and compared against observations. The 20-yr simulations are compared against the latest observations of the atmospheric temperature and radiative fluxes at TOA. The comparisons demonstrate that the choice of PSD and the assumed ice crystal shape distribution are as important as each other. Moreover, the consistent radiation parameterization removes a long-standing tropical troposphere cold temperature bias but slightly warms the southern midlatitudes by about 0.5 K. Cloud microphysics; cirrus clouds; Optical properties; climate models; Cloud radiative effects; parameterization
Barker, H. W.; Cole, J. N. S.; Shephard, M. W.Barker, H. W., J. N. S. Cole, M. W. Shephard, 2014: Estimation of errors associated with the EarthCARE 3D scene construction algorithm. Quarterly Journal of the Royal Meteorological Society, 140(684), 2260-2271. doi: 10.1002/qj.2294. The EarthCARE satellite mission plans to perform a continuous closure experiment to assess the quality of retrieved cloud and aerosol properties. It will do so by comparing top-of-atmosphere (TOA) broad-band (BB) fluxes with simulated values produced by three-dimensional (3D) radiative transfer models that act on the two-dimensional (2D) retrieved cross-section and a 3D atmosphere around it produced by a scene construction algorithm (SCA). This study proposes and tests a method for estimating errors in simulated TOA BB fluxes due to the SCA. Two methods for estimating SCA-related errors for TOA fluxes are presented. The primary one relies on computation of errors for reconstructed narrow-band imager nadir radiances. A-train satellite data were used to show that for constructed domains measuring (11 km)2, approximately the size of the EarthCARE assessment domains, with total cloud fractions > 0.2, errors for reflected BB short-wave fluxes due to the SCA are smaller than ±4.2 and ±11.5 W m−2 for 66 and 90% of the domains, respectively. Corresponding values for outgoing long-wave fluxes are ±1.2 and ±3.0 W m−2. The largest and smallest errors are associated with fields of broken convective cloud and overcast stratiform cloud, respectively. The SCA was applied to simulated measurements for a (153 km)2 field of deep convective clouds produced by a cloud-system-resolving model. Actual and estimated TOA BB short-wave flux errors due to the SCA agree well and are smaller than ±22 and ±40 W m−2 for 66 and 90% of the (11 km)2 sampled subdomains. Assuming that errors due to the SCA are purely bias errors, they were subtracted from fluxes estimated for the constructed domains. This resulted in TOA BB short-wave flux errors smaller than ±7 and ±25 W m−2 for 66 and 90% of the sampled subdomains. This suggests that estimated errors due to the SCA should be removed directly from simulated TOA BB fluxes before executing a closure assessment. clouds; Remote sensing; aerosols; Satellite; climate; radiation; EarthCARE
Battisti, D. S.; Ding, Qinghua; Roe, G. H.Battisti, D. S., Q. Ding, G. H. Roe, 2014: Coherent pan-Asian climatic and isotopic response to orbital forcing of tropical insolation. Journal of Geophysical Research: Atmospheres, 119(21), 11,997-12,020. doi: 10.1002/2014JD021960. The oxygen-18 isotope composition of calcite in stalagmites across southern and eastern Asia are highly correlated to one another on orbital time scales: large negative excursions are coincident with maxima in summer insolation in the subtropics of the Northern Hemisphere (NH). These isotopic excursions reflect changes in the precipitation-weighted isotopic composition of precipitation, δ18Op. We present results from two core experiments using an isotope-enabled climate model—the“high-insolation” and “low-insolation” experiments—in which the model is forced by extrema in NH summer insolation. Compared to the low-insolation experiment, the high-insolation climate features profound, large-scale changes in the pattern of monsoon precipitation spanning from Africa to Southeast Asia that are due to changes in the relative contributions of temperature and moisture to the near-surface equivalent potential temperature θe. Under high insolation, a more rapid increase in land surface temperature in early summer causes the greatest θe (and hence precipitation) to shift from the oceans in low insolation (such as today) to be over land in high insolation (such as the early Holocene). The model captures the general pattern of isotopic excursions seen in caves spanning from Israel to western China, including large drops in δ18Op over eastern Tibet (−7‰), the Arabian Peninsula, and northeast Africa (−4‰). Although there are large changes in precipitation over Tibet, the change in δ18Op is due to changes in the δ18O of water vapor that is delivered and subsequently precipitated; it does not inform on local precipitation amount or intensity. 3354 Precipitation; 3373 Tropical dynamics; Monsoons; paleoclimate; 3344 Paleoclimatology; 4934 Insolation forcing; 4958 Speleothems; precessional cycle; speleothems
Bellomo, Katinka; Clement, Amy C.; Norris, Joel R.; Soden, Brian J.Bellomo, K., A. C. Clement, J. R. Norris, B. J. Soden, 2014: Observational and Model Estimates of Cloud Amount Feedback over the Indian and Pacific Oceans. J. Climate, 27(2), 925-940. doi: 10.1175/JCLI-D-13-00165.1.
Bellomo, Katinka; Clement, Amy; Mauritsen, Thorsten; Rädel, Gaby; Stevens, BjornBellomo, K., A. Clement, T. Mauritsen, G. Rädel, B. Stevens, 2014: Simulating the Role of Subtropical Stratocumulus Clouds in Driving Pacific Climate Variability. J. Climate, 27(13), 5119-5131. doi: 10.1175/JCLI-D-13-00548.1. AbstractThis study examines the influence of the northeast and southeast Pacific subtropical stratocumulus cloud regions on the modes of Pacific climate variability simulated by an atmospheric general circulation model (ECHAM6) coupled to a slab ocean. The sensitivity of cloud liquid water to underlying SST is changed in the radiation module of the atmospheric model to increase the strength of positive low-cloud feedback in the two regions. Enhanced low-cloud feedback increases the persistence and variance of the leading modes of climate variability at decadal and longer time scales. Additional integrations show that the southeast Pacific influences climate variability in the equatorial ENSO region, whereas the effects of the northeast Pacific remain confined to the North Pacific. The results herein suggest that a positive feedback among SST, cloud cover, and large-scale atmospheric circulation can explain decadal climate variability in the Pacific Ocean. In particular, cloud feedbacks over the subtropical stratocumulus regions set the time scale of climate variability. A proper representation of low-level cloud feedbacks in the subtropical stratocumulus regions could therefore improve the simulation of Pacific climate variability. clouds; Feedback; climate models; Interannual variability; Atmosphere-ocean interaction; Pacific decadal oscillation
Berry, Elizabeth; Mace, Gerald G.Berry, E., G. G. Mace, 2014: Cloud properties and radiative effects of the Asian summer monsoon derived from A-Train data. Journal of Geophysical Research: Atmospheres, 119(15), 2014JD021458. doi: 10.1002/2014JD021458. Using A-Train satellite data, we investigate the distribution of clouds and their microphysical and radiative properties in Southeast Asia during the summer monsoon. We find an approximate balance in the top of the atmosphere (TOA) cloud radiative effect, which is largely due to commonly occurring cirrus layers that warm the atmosphere, and less frequent deep layers, which produce a strong cooling at the surface. The distribution of ice water path (IWP) in these layers, obtained from the 2C-ICE CloudSat data product, is highly skewed with a mean value of 440 g m−2 and a median of 24 g m−2. We evaluate the fraction of the total IWP observed by CloudSat and CALIPSO individually and find that both instruments are necessary for describing the overall IWP statistics and particularly the values that are most important to cirrus radiative impact. In examining how cloud radiative effects at the TOA vary as a function of IWP, we find that cirrus with IWP less than 200 g m−2 produce a net warming in the study region. Weighting the distribution of radiative effect by the frequency of occurrence of IWP values, we determine that cirrus with IWP around 20 g m−2 contribute most to heating at the TOA. We conclude that the mean IWP is a poor diagnostic of radiative impact. We suggest that climate model intercomparisons with data should focus on the median IWP because that statistic is more descriptive of the cirrus that contribute most to the radiative impacts of tropical ice clouds. clouds; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; radiative forcing; 3310 Clouds and cloud feedbacks; 3360 Remote sensing; a-train; ice water path
Bhatt, Rajendra; Doelling, David R.; Wu, Aisheng; Xiong, Xiaoxiong (Jack); Scarino, Benjamin R.; Haney, Conor O.; Gopalan, ArunBhatt, R., D. R. Doelling, A. Wu, X. Xiong, B. R. Scarino, C. O. Haney, A. Gopalan, 2014: Initial Stability Assessment of S-NPP VIIRS Reflective Solar Band Calibration Using Invariant Desert and Deep Convective Cloud Targets. Remote Sensing, 6(4), 2809-2826. doi: 10.3390/rs6042809. The latest CERES FM-5 instrument launched onboard the S-NPP spacecraft will use the VIIRS visible radiances from the NASA Land Product Evaluation and Analysis Tool Elements (PEATE) product for retrieving the cloud properties associated with its TOA flux measurement. In order for CERES to provide climate quality TOA flux datasets, the retrieved cloud properties must be consistent throughout the record, which is dependent on the calibration stability of the VIIRS imager. This paper assesses the NASA calibration stability of the VIIRS reflective solar bands using the Libya-4 desert and deep convective clouds (DCC). The invariant targets are first evaluated for temporal natural variability. It is found for visible (VIS) bands that DCC targets have half of the variability of Libya-4. For the shortwave infrared (SWIR) bands, the desert has less variability. The brief VIIRS record and target variability inhibits high confidence in identifying any trends that are less than ±0.6%/yr for most VIS bands, and ±2.5%/yr for SWIR bands. None of the observed invariant target reflective solar band trends exceeded these trend thresholds. Initial assessment results show that the VIIRS data have been consistently calibrated and that the VIIRS instrument stability is similar to or better than the MODIS instrument. CERES; MODIS; invariant calibration targets; radiometric stability; S-NPP VIIRS; satellite calibration
Blunden, Jessica; Arndt, Derek S.Blunden, J., D. S. Arndt, 2014: State of the Climate in 2013. Bull. Amer. Meteor. Soc., 95(7), S1-S279. doi: 10.1175/2014BAMSStateoftheClimate.1. Editors note: For easy download the posted pdf of the State of the Climate for 2013 is a very low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.
Bodas-Salcedo, A.; Williams, K. D.; Ringer, M. A.; Beau, I.; Cole, J. N. S.; Dufresne, J.-L.; Koshiro, T.; Stevens, B.; Wang, Z.; Yokohata, T.Bodas-Salcedo, A., K. D. Williams, M. A. Ringer, I. Beau, J. N. S. Cole, J. Dufresne, T. Koshiro, B. Stevens, Z. Wang, T. Yokohata, 2014: Origins of the Solar Radiation Biases over the Southern Ocean in CFMIP2 Models*. J. Climate, 27(1), 41-56. doi: 10.1175/JCLI-D-13-00169.1.
Bretherton, Christopher S.; Blossey, Peter N.; Stan, CristianaBretherton, C. S., P. N. Blossey, C. Stan, 2014: Cloud feedbacks on greenhouse warming in the superparameterized climate model SP-CCSM4. Journal of Advances in Modeling Earth Systems, 6(4), 1185–1204. doi: 10.1002/2014MS000355. Cloud feedbacks on greenhouse warming are studied in a superparameterized version of the Community Climate System Model (SP-CCSM4) in an atmospheric component SP-CAM4 that explicitly simulates cumulus convection. A 150 year simulation in an abrupt quadrupling of CO2 is branched from a control run. It develops moderate positive global cloud feedback and an implied climate sensitivity of 2.8 K comparable to the conventionally parameterized CCSM4 and the median of other modern climate models. All of SP-CCSM4's positive shortwave cloud feedback is due to a striking decrease in low cloud over land, which is much more pronounced than in most other climate models, including CCSM4. Four other cloud responses – decreased midlevel cloud, more Arctic water and ice cloud, a slight poleward shift of midlatitude storm track cloud, and an upward shift of high clouds – are also typical of conventional global climate models. SP-CCSM4 does not simulate the large warming-induced decrease in Southern Ocean cloud found in CCSM4. Two companion uncoupled SP-CAM4 simulations, one with a uniform 4 K sea-surface temperature increase and one with quadrupled CO2 but fixed SST, suggest that SP-CCSM4's global-scale cloud changes are primarily mediated by the warming, rather than by rapid adjustments to increased CO2. SP-CAM4 show spatial patterns of cloud response qualitatively similar to the previous-generation superparameterized SP-CAM3, but with systematically more positive low cloud feedbacks over low-latitude land and ocean. cloud-resolving models; 3337 Global climate models; 3310 Clouds and cloud feedbacks; cloud feedbacks; superparameterization; climate modeling; 3323 Large eddy simulation
Burls, N. J.; Fedorov, A. V.Burls, N. J., A. V. Fedorov, 2014: What Controls the Mean East–West Sea Surface Temperature Gradient in the Equatorial Pacific: The Role of Cloud Albedo. J. Climate, 27(7), 2757-2778. doi: 10.1175/JCLI-D-13-00255.1.
Calisto, M.; Folini, D.; Wild, M.; Bengtsson, L.Calisto, M., D. Folini, M. Wild, L. Bengtsson, 2014: Cloud radiative forcing intercomparison between fully coupled CMIP5 models and CERES satellite data. Ann. Geophys., 32(7), 793-807. doi: 10.5194/angeo-32-793-2014. In this paper, radiative fluxes for 10 years from 11 models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) and from CERES satellite observations have been analyzed and compared. Under present-day conditions, the majority of the investigated CMIP5 models show a tendency towards a too-negative global mean net cloud radiative forcing (NetCRF) as compared to CERES. A separate inspection of the long-wave and shortwave contribution (LWCRF and SWCRF) as well as cloud cover points to different shortcomings in different models. Models with a similar NetCRF still differ in their SWCRF and LWCRF and/or cloud cover. Zonal means mostly show excessive SWCRF (too much cooling) in the tropics between 20° S and 20° N and in the midlatitudes between 40 to 60° S. Most of the models show a too-small/too-weak LWCRF (too little warming) in the subtropics (20 to 40° S and N). Difference maps between CERES and the models identify the tropical Pacific Ocean as an area of major discrepancies in both SWCRF and LWCRF. The summer hemisphere is found to pose a bigger challenge for the SWCRF than the winter hemisphere. The results suggest error compensation to occur between LWCRF and SWCRF, but also when taking zonal and/or annual means. Uncertainties in the cloud radiative forcing are thus still present in current models used in CMIP5.
Chang, D. Y.; Tost, H.; Steil, B.; Lelieveld, J.Chang, D. Y., H. Tost, B. Steil, J. Lelieveld, 2014: Aerosol–cloud interactions studied with the chemistry-climate model EMAC. Atmos. Chem. Phys. Discuss., 14(15), 21975-22043. doi: 10.5194/acpd-14-21975-2014. This study uses the EMAC atmospheric chemistry-climate model to simulate cloud properties and estimate cloud radiative effects induced by aerosols. We have tested two prognostic cloud droplet nucleation parameterizations, i.e., the standard STN (osmotic coefficient model) and hybrid (HYB, replacing the osmotic coefficient by the κ hygroscopicity parameter) schemes to calculate aerosol hygroscopicity and critical supersaturation, and consider aerosol–cloud feedbacks with a focus on warm clouds. Both prognostic schemes (STN and HYB) account for aerosol number, size and composition effects on droplet nucleation, and are tested in combination with two different cloud cover parameterizations, i.e., a relative humidity threshold and a statistical cloud cover scheme (RH-CLC and ST-CLC). The use of either STN and HYB leads to very different cloud radiative effects, particularly over the continents. The STN scheme predicts highly effective CCN activation in warm clouds and hazes/fogs near the surface. The enhanced CCN activity increases the cloud albedo effect of aerosols and cools the Earth's surface. The cooler surface enhances the hydrostatic stability of the lower continental troposphere and thereby reduces convection and convective precipitation. In contrast, the HYB simulations calculate lower, more realistic CCN activation and consequent cloud albedo effect, leading to relatively stronger convection and high cloud formation. The enhanced high clouds increase greenhouse warming and moderate the cooling effect of the low clouds. With respect to the cloud radiative effects, the statistical ST-CLC scheme shows much higher sensitivity to aerosol–cloud coupling for all continental regions than the RH-CLC threshold scheme, most pronounced for low clouds but also for high clouds. Simulations of the short wave cloud radiative effect at the top of the atmosphere in ST-CLC are a factor of 2–8 more sensitive to aerosol coupling than the RH-CLC configurations. The long wave cloud radiative effect responds about a factor of 2 more sensitively. Our results show that the coupling with the HYB scheme (κ approach) outperforms the coupling with STN (osmotic coefficient), and also provides a more straightforward approach to account for physicochemical effects on aerosol activation into cloud droplets. Accordingly, the sensitivity of CCN activation to chemical composition is highest in HYB. Overall, the prognostic schemes of cloud cover and cloud droplet formation help improve the agreement between model results and observations, and for the ST-CLC scheme it seems to be a necessity.
Chen, Min; Zhuang, Qianlai; He, YujieChen, M., Q. Zhuang, Y. He, 2014: An Efficient Method of Estimating Downward Solar Radiation Based on the MODIS Observations for the Use of Land Surface Modeling. Remote Sensing, 6(8), 7136-7157. doi: 10.3390/rs6087136. Solar radiation is a critical variable in global change sciences. While most of the current global datasets provide only the total downward solar radiation, we aim to develop a method to estimate the downward global land surface solar radiation and its partitioned direct and diffuse components, which provide the necessary key meteorological inputs for most land surface models. We developed a simple satellite-based computing scheme to enable fast and reliable estimation of these variables. The global Moderate Resolution Imaging Spectroradiometer (MODIS) products at 1° spatial resolution for the period 2003–2011 were used as the forcing data. Evaluations at Baseline Surface Radiation Network (BSRN) sites show good agreement between the estimated radiation and ground-based observations. At all the 48 BSRN sites, the RMSE between the observations and estimations are 34.59, 41.98 and 28.06 W∙m−2 for total, direct and diffuse solar radiation, respectively. Our estimations tend to slightly overestimate the total and diffuse but underestimate the direct solar radiation. The errors may be related to the simple model structure and error of the input data. Our estimation is also comparable to the Clouds and Earth’s Radiant Energy System (CERES) data while shows notable improvement over the widely used National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR) Reanalysis data. Using our MODIS-based datasets of total solar radiation and its partitioned components to drive land surface models should improve simulations of global dynamics of water, carbon and climate. atmosphere; Solar radiation; MODIS; reanalysis; validation; parameterization; performance; data assimilation system; diffuse; direct; global radiation; land surface model; land surface model; NCEP/NCAR reanalysis; Photosynthetically active radiation; shortwave radiation; sky irradiance
Chen, Yi-Chun; Christensen, Matthew W.; Stephens, Graeme L.; Seinfeld, John H.Chen, Y., M. W. Christensen, G. L. Stephens, J. H. Seinfeld, 2014: Satellite-based estimate of global aerosol–cloud radiative forcing by marine warm clouds. Nature Geoscience, 7(9), 643-646. doi: 10.1038/ngeo2214.
Cheng, Jie; Liang, Shunlin; Yao, Yunjun; Ren, Baiyang; Shi, Linpeng; Liu, HaoCheng, J., S. Liang, Y. Yao, B. Ren, L. Shi, H. Liu, 2014: A Comparative Study of Three Land Surface Broadband Emissivity Datasets from Satellite Data. Remote Sensing, 6(1), 111-134. doi: 10.3390/rs6010111. This study compared three broadband emissivity (BBE) datasets from satellite observations. The first is a new global land surface BBE dataset known as the Global Land Surface Satellite (GLASS) BBE. The other two are the North American ASTER Land Surface Emissivity Database (NAALSED) BBE and University of Wisconsin Global Infrared Land Surface Emissivity Database (UWIREMIS) BBE, which were derived from two independent narrowband emissivity products. Firstly, NAALSED BBE was taken as the reference to evaluate the GLASS BBE and UWIREMIS BBE. The GLASS BBE was more close to NAALSED BBE with a bias and root mean square error (RMSE) of −0.001 and 0.007 for the summer season, −0.001 and 0.008 for the winter season, respectively. Then, the spatial distribution and seasonal pattern of global GLASS BBE and UWIREMIS BBE for six dominant land cover types were compared. The BBE difference between vegetated areas and non-vegetated areas can be easily seen from two BBEs. The seasonal variation of GLASS BBE was more reasonable than that of UWIREMIS BBE. Finally, the time series were calculated from GLASS BBE and UWIREMIS BBE using the data from 2003 through 2010. The periodic variations of GLASS BBE were stronger than those of UWIREMIS BBE. The long time series high quality GLASS BBE can be incorporated in land surface models for improving their simulation results. Remote sensing; broadband emissivity; GLASS; NAALSED; UWIREMIS
Chepfer, H.; Noel, V.; Winker, D.; Chiriaco, M.Chepfer, H., V. Noel, D. Winker, M. Chiriaco, 2014: Where and when will we observe cloud changes due to climate warming?. Geophysical Research Letters, 41(23), 2014GL061792. doi: 10.1002/2014GL061792. Climate models predict that the geographic distribution of clouds will change in response to anthropogenic warming, though uncertainties in the existing satellite record are larger than the magnitude of the predicted effects. Here we argue that cloud vertical distribution, observable by active spaceborne sensors, is a more robust signature of climate change. Comparison of Atmospheric Model Intercomparison Project present day and +4 K runs from Coupled Model Intercomparison Project Phase 5 shows that cloud radiative effect and total cloud cover do not represent robust signatures of climate change, as predicted changes fall within the range of variability in the current observational record. However, the predicted forced changes in cloud vertical distribution (directly measurable by spaceborne active sensors) are much larger than the currently observed variability and are expected to first appear at a statistically significant level in the upper troposphere, at all latitudes. clouds; Remote sensing; 1640 Remote sensing; 0321 Cloud/radiation interaction; 0325 Evolution of the atmosphere; climate; 1626 Global climate models; spaceborne lidar
Cheruy, F.; Dufresne, J. L.; Hourdin, F.; Ducharne, A.Cheruy, F., J. L. Dufresne, F. Hourdin, A. Ducharne, 2014: Role of clouds and land-atmosphere coupling in midlatitude continental summer warm biases and climate change amplification in CMIP5 simulations. Geophysical Research Letters, 41(18), 6493-6500. doi: 10.1002/2014GL061145. Over land, most state-of-the-art climate models contributing to Coupled Model Intercomparison Project Phase 5 (CMIP5) share a strong summertime warm bias in midlatitude areas, especially in regions where the coupling between soil moisture and atmosphere is effective. The most biased models overestimate solar incoming radiation, because of cloud deficit and have difficulty to sustain evaporation. These deficiencies are also involved in the spread of the summer temperature projections among models in the midlatitude; the models which simulate a higher-than-average warming overestimate the present climate net shortwave radiation which increases more-than-average in the future, in link with a decrease of cloudiness. They also show a higher-than-average reduction of evaporative fraction in areas with soil moisture-limited evaporation regimes. Over these areas, the most biased models in the present climate simulate a larger warming in response to climate change which is likely to be overestimated. climate change; CMIP5; 3322 Land/atmosphere interactions; 1631 Land/atmosphere interactions; 1626 Global climate models; 1813 Eco-hydrology; 1818 Evapotranspiration; land-atmosphere coupling; model biases
Cho, Mee-Hyun; Boo, Kyung-On; Lee, Johan; Cho, Chunho; Lim, Gyu-HoCho, M., K. Boo, J. Lee, C. Cho, G. Lim, 2014: Regional climate response to land surface changes after harvest in the North China Plain under present and possible future climate conditions. Journal of Geophysical Research: Atmospheres, 119(8), 2013JD020111. doi: 10.1002/2013JD020111. In this study, we investigated the impacts of land use alterations from harvesting practices on the regional surface climate over the North China Plain. The surface climate responses after harvest in June in regions where double-cropping is practiced were evaluated using observations and model simulations with the global climate model HadGEM2-Atmosphere. Responses were modeled under both present and possible future climate conditions. In the model, double-cropping was represented using the monthly varying fraction of vegetation. This contributed to an improvement in the model simulation over East Asia. Modeling results showed that the land surface was warmer and drier after harvest, and these simulation results were consistent with observations. The bare soil surface after harvest in June had biophysical impacts on the surface climate that were mediated by decreasing evapotranspiration and latent heat flux effects, which increased surface air temperatures and decreased surface humidity. An increase in shortwave radiation also contributed to the rise in temperatures. Under two Representative Concentration Pathways (RCP) scenarios for possible future climate conditions, land conversion induced additional warming in addition to greenhouse gases induced global warming. The RCP 8.5 and RCP 2.6 scenarios demonstrated a warming of 1.0°C and 1.4°C due to harvesting practices in June, respectively. The response magnitude was affected by the climate conditions in each RCP. Our results suggest that potential impacts of harvest on the local climate need to be considered in future projections of CO2-induced warming on a regional scale. 0315 Biosphere/atmosphere interactions; regional climate; 0402 Agricultural systems; 0416 Biogeophysics; 0426 Biosphere/atmosphere interactions; 0466 Modeling; bigphysical; future; HadGEM2-A; harvest; North China Plain
Choi, Yong-Sang; Cho, Heeje; Ho, Chang-Hoi; Lindzen, Richard S.; Park, Seon Ki; Yu, XingChoi, Y., H. Cho, C. Ho, R. S. Lindzen, S. K. Park, X. Yu, 2014: Influence of non-feedback variations of radiation on the determination of climate feedback. Theoretical and Applied Climatology, 115(1-2), 355-364. doi: 10.1007/s00704-013-0998-6. Recent studies have estimated the magnitude of climate feedback based on the correlation between time variations in outgoing radiation flux and sea surface temperature (SST). This study investigates the influence of the natural non-feedback variation (noise) of the flux occurring independently of SST on the determination of climate feedback. The observed global monthly radiation flux is used from the Clouds and the Earth's Radiant Energy System (CERES) for the period 2000–2008. In the observations, the time lag correlation of radiation and SST shows a distorted curve with low statistical significance for shortwave radiation while a significant maximum at zero lag for longwave radiation over the tropics. This observational feature is explained by simulations with an idealized energy balance model where we see that the non-feedback variation plays the most significant role in distorting the curve in the lagged correlation graph, thus obscuring the exact value of climate feedback. We also demonstrate that the climate feedback from the tropical longwave radiation in the CERES data is not significantly affected by the noise. We further estimate the standard deviation of radiative forcings (mainly from the noise) relative to that of the non-radiative forcings, i.e., the noise level from the observations and atmosphere–ocean coupled climate model simulations in the framework of the simple model. The estimated noise levels in both CERES (>13 %) and climate models (11–28 %) are found to be far above the critical level (~5 %) that begins to misrepresent climate feedback. Climatology; Atmospheric Sciences; Atmospheric Protection/Air Quality Control/Air Pollution; Waste Water Technology / Water Pollution Control / Water Management / Aquatic Pollution
Choi, Yong-Sang; Kim, Baek-Min; Hur, Sun-Kyong; Kim, Seong-Joong; Kim, Joo-Hong; Ho, Chang-HoiChoi, Y., B. Kim, S. Hur, S. Kim, J. Kim, C. Ho, 2014: Connecting early summer cloud-controlled sunlight and late summer sea ice in the Arctic. Journal of Geophysical Research: Atmospheres, 119(19), 2014JD022013. doi: 10.1002/2014JD022013. This study demonstrates that absorbed solar radiation (ASR) at the top of the atmosphere in early summer (May–July) plays a precursory role in determining the Arctic sea ice concentration (SIC) in late summer (August–October). The monthly ASR anomalies are obtained over the Arctic Ocean (65°N–90°N) from the Clouds and the Earth's Radiant Energy System during 2000–2013. The ASR changes primarily with cloud variation. We found that the ASR anomaly in early summer is significantly correlated with the SIC anomaly in late summer (correlation coefficient, r ≈ −0.8 with a lag of 1 to 4 months). The region exhibiting high (low) ASR anomalies and low (high) SIC anomalies varies yearly. The possible reason is that the solar heat input to ice is most effectively affected by the cloud shielding effect under the maximum TOA solar radiation in June and amplified by the ice-albedo feedback. This intimate delayed ASR-SIC relationship is not represented in most of current climate models. Rather, the models tend to over-emphasize internal sea ice processes in summer. 3359 Radiative processes; Solar radiation; 0750 Sea ice; Arctic sea ice
Coakley, James, A; Yang, PingCoakley, J., P. Yang, 2014: Atmospheric Radiation: A Primer with Illustrative Solutions. A first-look at radiative transfer in planetary atmospheres with a particular focus on the Earth's atmosphere and climate. The textbook covers the basics of the radiative transfer of sunlight, treating absorption and scattering, and the transfer of the thermal infrared appropriate for local thermodynamic equilibrium, absorption and emission. The examples included show how the solutions of the radiative transfer equation are used in remote sensing to probe the thermal structure and composition of planetary atmospheres. This motivates students by leading them to a better understanding of and appreciation for the computer-generated numerical results. Aimed at upper-division undergraduates and beginning graduate students in physics and atmospheric sciences, the book is designed to cover the essence of the material in a 10-week course, while the material in the optional sections will facilitate its use at the more leisurely pace and in-depth focus of a semester course. Science / Earth Sciences / Meteorology & Climatology; Science / Earth Sciences / General
Ćulibrk, Dubravko; Vukobratovic, Dejan; Minic, Vladan; Fernandez, Marta Alonso; Osuna, Javier Alvarez; Crnojevic, VladimirĆulibrk, D., D. Vukobratovic, V. Minic, M. A. Fernandez, J. A. Osuna, V. Crnojevic, 2014: Sources of Remote Sensing Data for Precision Irrigation. Sensing Technologies For Precision Irrigation, 53-67. Satellite observation provides information of a large area with spatial resolution from under a meter up to 50 km and temporal resolution from 5 min up to a few days. Satellites measure radiances over various parts of the spectra of electromagnetic radiation. The data is subsequently processed to derive geophysical parameters for the observed area and delivered in this more informative form as satellite observation products. High resolution products are more suitable for irrigation [1], especially in cases where the land parcels are small. The satellite data of interest for the precision irrigation is mostly data relevant to the water cycle, hydrology and meteorology and provided by missions aimed at gathering such data. Communications Engineering, Networks; Geographical Information Systems/Cartography; Remote Sensing/Photogrammetry
Daniels, Janet; Smith, G. Louis; Priestler, Kory J.; Thomas, SusanDaniels, J., G. L. Smith, K. J. Priestler, S. Thomas, 2014: Using lunar observations to validate pointing accuracy and geolocation, detector sensitivity stability and static point response of the CERES instruments. Remote Sensing of Clouds and the Atmosphere XIX; and Optics in Atmospheric Propagation and Adaptive Systems XVII, 9242, 92420X-92420X-12. doi: 10.1117/12.2065256. Validation of in-orbit instrument performance is a function of stability in both instrument and calibration source. This paper describes a method using lunar observations scanning near full moon by the Clouds and Earth Radiant Energy System (CERES) instruments. The Moon offers an external source whose signal variance is predictable and non-degrading. From 2006 to present, these in-orbit observations have become standardized and compiled for the Flight Models -1 and -2 aboard the Terra satellite, for Flight Models-3 and -4 aboard the Aqua satellite, and beginning 2012, for Flight Model-5 aboard Suomi-NPP. Instrument performance measurements studied are detector sensitivity stability, pointing accuracy and static detector point response function. This validation method also shows trends per CERES data channel of 0.8% per decade or less for Flight Models 1-4. Using instrument gimbal data and computed lunar position, the pointing error of each detector telescope, the accuracy and consistency of the alignment between the detectors can be determined. The maximum pointing error was 0.2o in azimuth and 0.17o in elevation which corresponds to an error in geolocation near nadir of 2.09 km. With the exception of one detector, all instruments were found to have consistent detector alignment from 2006 to present. All alignment error was within 0.1o with most detector telescopes showing a consistent alignment offset of less than 0.02o.
Dee, D. P.; Balmaseda, M.; Balsamo, G.; Engelen, R.; Simmons, A. J.; Thépaut, J.-N.Dee, D. P., M. Balmaseda, G. Balsamo, R. Engelen, A. J. Simmons, J. Thépaut, 2014: Toward a Consistent Reanalysis of the Climate System. Bull. Amer. Meteor. Soc., 95(8), 1235-1248. doi: 10.1175/BAMS-D-13-00043.1. This article reviews past and current reanalysis activities at the European Centre for Medium-Range Weather Forecasts (ECMWF) and describes plans for developing future reanalyses of the coupled climate system. Global reanalyses of the atmosphere, ocean, land surface, and atmospheric composition have played an important role in improving and extending the capabilities of ECMWF's operational forecasting systems. The potential role of reanalysis in support of climate change services in Europe is driving several interesting new developments. These include the production of reanalyses that span a century or more and the implementation of a coupled data assimilation capability suitable for climate reanalysis. Although based largely on ECMWF's achievements, capabilities, and plans, the article serves more generally to provide a review of pertinent issues affecting past and current reanalyses and a discussion of the major challenges in moving to more fully coupled systems.
Dolinar, Erica K.; Dong, Xiquan; Xi, Baike; Jiang, Jonathan H.; Su, HuiDolinar, E. K., X. Dong, B. Xi, J. H. Jiang, H. Su, 2014: Evaluation of CMIP5 simulated clouds and TOA radiation budgets using NASA satellite observations. Climate Dynamics, 44(7-8), 2229-2247. doi: 10.1007/s00382-014-2158-9. A large degree of uncertainty in global climate models (GCMs) can be attributed to the representation of clouds and how they interact with incoming solar and outgoing longwave radiation. In this study, the simulated total cloud fraction (CF), cloud water path (CWP), top of the atmosphere (TOA) radiation budgets and cloud radiative forcings (CRFs) from 28 CMIP5 AMIP models are evaluated and compared with multiple satellite observations from CERES, MODIS, ISCCP, CloudSat, and CALIPSO. The multimodel ensemble mean CF (57.6 %) is, on average, underestimated by nearly 8 % (between 65°N/S) when compared to CERES–MODIS (CM) and ISCCP results while an even larger negative bias (17.1 %) exists compared to the CloudSat/CALIPSO results. CWP bias is similar in comparison to the CF results, with a negative bias of 16.1 gm−2 compared to CM. The model simulated and CERES EBAF observed TOA reflected SW and OLR fluxes on average differ by 1.8 and −0.9 Wm−2, respectively. The averaged SW, LW, and net CRFs from CERES EBAF are −50.1, 27.6, and −22.5 Wm−2, respectively, indicating a net cooling effect of clouds on the TOA radiation budget. The differences in SW and LW CRFs between observations and the multimodel ensemble means are only −1.3 and −1.6 Wm−2, respectively, resulting in a larger net cooling effect of 2.9 Wm−2 in the model simulations. A further investigation of cloud properties and CRFs reveals that the GCM biases in atmospheric upwelling (15°S–15°N) regimes are much less than in their downwelling (15°–45°N/S) counterparts over the oceans. Sensitivity studies have shown that the magnitude of SW cloud radiative cooling increases significantly with increasing CF at similar rates (~−1.25 Wm−2 %−1) in both regimes. The LW cloud radiative warming increases with increasing CF but is regime dependent, suggested by the different slopes over the upwelling and downwelling regimes (0.81 and 0.22 Wm−2 %−1, respectively). Through a comprehensive error analysis, we found that CF is a primary modulator of warming (or cooling) in the atmosphere. The comparisons and statistical results from this study may provide helpful insight for improving GCM simulations of clouds and TOA radiation budgets in future versions of CMIP. cloud fraction; sensitivity; Climatology; CMIP5; Oceanography; Geophysics/Geodesy; CERES–MODIS; Error analysis; TOA radiation budget
Dong, Xiquan; Xi, Baike; Kennedy, Aaron; Minnis, Patrick; Wood, RobertDong, X., B. Xi, A. Kennedy, P. Minnis, R. Wood, 2014: A 19-Month Record of Marine Aerosol–Cloud–Radiation Properties Derived from DOE ARM Mobile Facility Deployment at the Azores. Part I: Cloud Fraction and Single-Layered MBL Cloud Properties. J. Climate, 27(10), 3665-3682. doi: 10.1175/JCLI-D-13-00553.1. AbstractA 19-month record of total and single-layered low (6 km) cloud fractions (CFs) and the single-layered marine boundary layer (MBL) cloud macrophysical and microphysical properties was generated from ground-based measurements at the Atmospheric Radiation Measurement Program (ARM) Azores site between June 2009 and December 2010. This is the most comprehensive dataset of marine cloud fraction and MBL cloud properties. The annual means of total CF and single-layered low, middle, and high CFs derived from ARM radar and lidar observations are 0.702, 0.271, 0.01, and 0.106, respectively. Greater total and single-layered high (>6 km) CFs occurred during the winter, whereas single-layered low ( aerosols; Cloud microphysics; Cloud cover; Boundary layer; Subsidence; Diurnal effects
Dong, Xiquan; Xi, Baike; Wu, PengDong, X., B. Xi, P. Wu, 2014: Investigation of the Diurnal Variation of Marine Boundary Layer Cloud Microphysical Properties at the Azores. J. Climate, 27(23), 8827-8835. doi: 10.1175/JCLI-D-14-00434.1. AbstractA new method has been developed to retrieve the nighttime marine boundary layer (MBL) cloud microphysical properties, which provides a complete 19-month dataset to investigate the diurnal variation of MBL cloud microphysical properties at the Azores. Compared to the corresponding daytime results presented in the authors' previous study over the Azores region, all nighttime monthly means of cloud liquid water path (LWP) exceed their daytime counterparts with an annual-mean LWP of 140 g m−2, which is ~30.9 g m−2 larger than daytime. Because the MBL clouds are primarily driven by convective instabilities caused by cloud-top longwave (LW) radiative cooling, more MBL clouds are well mixed and coupled with the surface during the night; thus, its cloud layer is deeper and its LWP is higher. During the day, the cloud layer is warmed by the absorption of solar radiation and partially offsets the cloud-top LW cooling, which makes the cloud layer thinner with less LWP. The seasonal and diurnal variations of cloud LWC and optical depth basically follow the variation of LWP. There are, however, no significant day–night differences and diurnal variations in cloud-droplet effective radius (re), number concentration (Nd), and corresponding surface measured cloud condensation nuclei (CCN) number concentration (NCCN) (at supersaturation S = 0.2%). Surface NCCN increases from around sunrise (0300–0600 LT) to late afternoon, which strongly correlates with surface wind speed (r = 0.76) from 0300 to 1900 LT. The trend in hourly-mean Nd is consistent with NCCN variation from 0000 to 0900 LT but not for afternoon and evening with an averaged ratio (Nd/NCCN) of 0.35 during the entire study period. Cloud retrieval; Instrumentation/sensors; Radars/Radar observations; Surface observations; Soundings; Microwave observations
Donohoe, Aaron; Marshall, John; Ferreira, David; Armour, Kyle; McGee, DavidDonohoe, A., J. Marshall, D. Ferreira, K. Armour, D. McGee, 2014: The Interannual Variability of Tropical Precipitation and Interhemispheric Energy Transport. J. Climate, 27(9), 3377-3392. doi: 10.1175/JCLI-D-13-00499.1. AbstractThe interannual variability of the location of the intertropical convergence zone (ITCZ) is strongly (R = 0.75) correlated with the atmospheric heat transport across the equator (AHTEQ) over the satellite era (1979–2009). A 1° northward displacement of the ITCZ is associated with 0.34 PW of anomalous AHTEQ from north to south. The AHTEQ and precipitation anomalies are both associated with an intensification of the climatological Hadley cell that is displaced north of the equator. This relationship suggests that the tropical precipitation variability is driven by a hemispheric asymmetry of energy input to the atmosphere at all latitudes by way of the constraint that AHTEQ is balanced by a hemispheric asymmetry in energy input to the atmosphere.A 500-yr coupled model simulation also features strong interannual correlations between the ITCZ location and AHTEQ. The interannual variability of AHTEQ in the model is associated with a hemispheric asymmetry in the top of the atmosphere radiative anomalies in the tropics with the Northern Hemisphere gaining energy when the ITCZ is displaced northward. The surface heat fluxes make a secondary contribution to the interannual variability of AHTEQ despite the fact that the interannual variability of the ocean heat transport across the equator (OHTEQ) is comparable in magnitude to that in AHTEQ. The OHTEQ makes a minimal impact on the atmospheric energy budget because the vast majority of the interannual variability in OHTEQ is stored in the subsurface ocean and, thus, the interannual variability of OHTEQ does not strongly impact the atmospheric circulation. Precipitation; Ocean circulation; Energy transport; Climate variability; Hadley circulation
English, Jason M.; Kay, Jennifer E.; Gettelman, Andrew; Liu, Xiaohong; Wang, Yong; Zhang, Yuying; Chepfer, HeleneEnglish, J. M., J. E. Kay, A. Gettelman, X. Liu, Y. Wang, Y. Zhang, H. Chepfer, 2014: Contributions of Clouds, Surface Albedos, and Mixed-Phase Ice Nucleation Schemes to Arctic Radiation Biases in CAM5. J. Climate, 27(13), 5174-5197. doi: 10.1175/JCLI-D-13-00608.1. AbstractThe Arctic radiation balance is strongly affected by clouds and surface albedo. Prior work has identified Arctic cloud liquid water path (LWP) and surface radiative flux biases in the Community Atmosphere Model, version 5 (CAM5), and reductions to these biases with improved mixed-phase ice nucleation schemes. Here, CAM5 net top-of-atmosphere (TOA) Arctic radiative flux biases are quantified along with the contributions of clouds, surface albedos, and new mixed-phase ice nucleation schemes to these biases. CAM5 net TOA all-sky shortwave (SW) and outgoing longwave radiation (OLR) fluxes are generally within 10 W m−2 of Clouds and the Earth’s Radiant Energy System Energy Balanced and Filled (CERES-EBAF) observations. However, CAM5 has compensating SW errors: Surface albedos over snow are too high while cloud amount and LWP are too low. Use of a new CAM5 Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar simulator that corrects an error in the treatment of snow crystal size confirms insufficient cloud amount in CAM5 year-round. CAM5 OLR is too low because of low surface temperature in winter, excessive atmospheric water vapor in summer, and excessive cloud heights year-round. Simulations with two new mixed-phase ice nucleation schemes—one based on an empirical fit to ice nuclei observations and one based on classical nucleation theory with prognostic ice nuclei—improve surface climate in winter by increasing cloud amount and LWP. However, net TOA and surface radiation biases remain because of increases in midlevel clouds and a persistent deficit in cloud LWP. These findings highlight challenges with evaluating and modeling Arctic cloud, radiation, and climate processes. albedo; Model evaluation/performance; climate models; Cloud radiative effects; Arctic; cloud forcing
Engström, Anders; Bender, Frida A.-M.; Karlsson, JohannesEngström, A., F. A. Bender, J. Karlsson, 2014: Improved Representation of Marine Stratocumulus Cloud Shortwave Radiative Properties in the CMIP5 Climate Models. J. Climate, 27(16), 6175-6188. doi: 10.1175/JCLI-D-13-00755.1. AbstractThe radiative properties of subtropical marine stratocumulus clouds are investigated in an ensemble of current-generation global climate models from phase 5 of the Climate Model Intercomparison Project (CMIP5). Using a previously documented method for determining regional mean cloud albedo, the authors find a closer agreement with observations in the CMIP5 models as compared to the previous generation of models (phase 3 of CMIP). The multimodel average indicates regional mean, monthly mean cloud albedos ranging from 0.32 to 0.5 among 26 models and five regions, to be compared with satellite observations that indicate a range from 0.32 to 0.39 for the same five regions. The intermodel spread in cloud fraction gives rise to a spread in albedo. Within models, there is a tendency for large cloud fraction to be related to low cloud albedo and vice versa, a relationship that dampens the intermodel variability in total albedo. The intramodel variability in albedo, for a given cloud fraction, is found to be up to twice as large in magnitude in models as in satellite observations. The reason for this larger variability in models is not settled, but possible contributing factors may be imperfect representation in the models of cloud type distribution or of sensitivity to meteorological variability or aerosols. Changes in aerosol loading are found to be the likely cause of an increase in cloud albedo over time. The radiative effect of such a scene brightening in marine stratocumulus cloud regions, from preindustrial times to present day, is estimated to be up to −1 W m−2 for the global ocean, but there are no observations to verify this number. clouds; Radiative fluxes; climate models; Cloud parameterizations; Cloud radiative effects
Evans, Katherine J.; Mahajan, Salil; Branstetter, Marcia; McClean, Julie L.; Caron, Julie; Maltrud, Matthew E.; Hack, James J.; Bader, David C.; Neale, Richard; Leifeld, Juliann K.Evans, K. J., S. Mahajan, M. Branstetter, J. L. McClean, J. Caron, M. E. Maltrud, J. J. Hack, D. C. Bader, R. Neale, J. K. Leifeld, 2014: A spectral transform dynamical core option within the Community Atmosphere Model (CAM4). Journal of Advances in Modeling Earth Systems, 6(3), 902-922. doi: 10.1002/2014MS000329. An ensemble of simulations covering the present day observational period using forced sea surface temperatures and prescribed sea-ice extent is configured with an 85 truncation resolution spectral transform dynamical core (T85) within the Community Atmosphere Model (CAM), version 4 and is evaluated relative to observed and model derived data sets and the one degree finite volume (FV) dynamical core. The spectral option provides a well-known base within the climate model community to assess climate behavior and statistics, and its relative computational efficiency for smaller computing platforms allows it to be extended to perform high-resolution climate length simulations. Overall, the quality of the T85 ensemble is similar to FV. Analyzing specific features of the T85 simulations show notable improvements to the representation of wintertime Arctic sea level pressure and summer precipitation over the Western Indian subcontinent. The mean and spatial patterns of the land surface temperature trends over the AMIP period are generally well simulated with the T85 ensemble relative to observations, however the model is not able to capture the extent nor magnitude of changes in temperature extremes over the boreal summer, where the changes are most dramatic. Biases in the wintertime Arctic surface temperature and annual mean surface stress fields persist with T85 as with the CAM3 version of T85, as compared to FV. An experiment to identify the source of differences between dycores has revealed that the longwave cloud forcing is sensitive to the choice of dycore, which has implications for tuning strategies of the physics parameter settings. 1610 Atmosphere; 1620 Climate dynamics; 1626 Global climate models; 3333 Model calibration; climate modeling; Community Atmosphere Model; spectral transform dycore
Fairlie, T. D.; Vernier, J.-P.; Natarajan, M.; Bedka, K. M.Fairlie, T. D., J. Vernier, M. Natarajan, K. M. Bedka, 2014: Dispersion of the Nabro volcanic plume and its relation to the Asian summer monsoon. Atmos. Chem. Phys., 14(13), 7045-7057. doi: 10.5194/acp-14-7045-2014. We use nighttime measurements from the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite, together with a Lagrangian trajectory model, to study the initial dispersion of volcanic aerosol from the eruption of Mt. Nabro (Ethiopia/Eritrea) in June 2011. The Nabro eruption reached the upper troposphere and lower stratosphere (UTLS) directly, and the plume was initially entrained by the flow surrounding the Asian anticyclone, which prevails in the UTLS from the Mediterranean Sea to East Asia during boreal summer. CALIPSO detected aerosol layers, with optical properties consistent with sulfate, in the lower stratosphere above the monsoon convective region in South and Southeast Asia within 10 days of the eruption. We show that quasi-isentropic differential advection in the vertically sheared flow surrounding the Asian anticyclone explains many of these stratospheric aerosol layers. We use Meteosat-7 data to examine the possible role of deep convection in the Asian monsoon in transporting volcanic material to the lower stratosphere during this time, but find no evidence that convection played a direct role, in contrast with claims made in earlier studies. On longer timescales, we use CALIPSO data to illustrate diabatic ascent of the Nabro aerosol in the lower stratosphere at rates of ~ 10 K per month for the first two months after the eruption, falling to ~ 3 K per month after the Asian anticyclone dissipates. Maps of stratospheric aerosol optical depth (AOD) show local peaks of ~ 0.04–0.06 in July in the region of the Asian anticyclone; we find associated estimates of radiative forcing small, ~ 5–10% of those reported for the eruption of Mt. Pinatubo in 1991. Additionally, we find no clear response in outgoing shortwave (SW) flux due to the presence of Nabro aerosol viewed in the context of SW flux variability as measured by CERES (Clouds and Earth Radiant Energy System).
Feng, Nan; Christopher, Sundar A.Feng, N., S. A. Christopher, 2014: Clear sky direct radiative effects of aerosols over Southeast Asia based on satellite observations and radiative transfer calculations. Remote Sensing of Environment, 152, 333-344. doi: 10.1016/j.rse.2014.07.006. Using the Moderate Resolution Imaging Spectroradiometer (MODIS), Clouds and the Earth's Radiant Energy System (CERES) instrument, and a radiative transfer model (RTM), we provide a quantitative assessment of regional cloud-free diurnally averaged shortwave Aerosol Radiative Effects (AREs) at the top of atmosphere (TOA) and at the surface over Southeast Asia (SEAS, 10°S–20 N and 90°E–130°E). The spatial and temporal variations of the annual ARE are calculated based on satellite and ground-based measurements, supplemented by radiative transfer simulations. During 2001–2010, our results indicate that the TOA diurnally averaged ARE is − 5.6 ± 0.8 Wm− 2 over land and − 4.8 ± 0.7 Wm− 2 over ocean, respectively. In contrast, the surface ARE is − 13.8 ± 3.2 Wm− 2 based on radiative transfer calculations. For aerosol layers of 2 km in height with midvisible optical depth of 1.41 and single scattering albedo of 0.91, the shortwave radiative heating can exceed 0.8 K/day. Our results indicate significant inter-annual variability of aerosol radiative properties, which is extremely large over major emission outflow regions like SEAS. This study suggests that an integrated system of satellite data, model calculations coupled with ground-based and meteorological data sets is needed to assess Aerosol Radiative Effects on regional earth-atmosphere energy budgets. CERES; MODIS; Southeast Asia; Radiative transfer model; Aerosol Radiative Effects
Fermepin, Solange; Bony, SandrineFermepin, S., S. Bony, 2014: Influence of low-cloud radiative effects on tropical circulation and precipitation. Journal of Advances in Modeling Earth Systems, 6(3), 513-526. doi: 10.1002/2013MS000288. Low-level clouds, which constitute the most prevalent cloud type over tropical oceans, exert a radiative cooling within the planetary boundary layer. By using an atmospheric general circulation model, we investigate the role that this cloud radiative cooling plays in the present-day climate. Low-cloud radiative effects are found to increase the tropics-wide precipitation, to strengthen the winds at the surface of the tropical oceans, and to amplify the atmospheric overturning circulation. An analysis of the water and energy budgets of the atmosphere reveals that most of these effects arises from the strong coupling of cloud-radiative cooling with turbulent fluxes at the ocean surface. The impact of cloud-radiative effects on atmospheric dynamics and precipitation is shown to occur on very short time scales (a few days). Therefore, short-term atmospheric forecasts constitute a valuable framework for evaluating the interactions between cloud processes and atmospheric dynamics, and for assessing their dependence on model physics. 3359 Radiative processes; 3337 Global climate models; 3310 Clouds and cloud feedbacks; Atmospheric circulation; Precipitation; Cloud radiative effects; 3354 Precipitation; low clouds; 3369 Thermospheric dynamics
Folkins, Ian; Mitovski, T.; Pierce, J. R.Folkins, I., T. Mitovski, J. R. Pierce, 2014: A simple way to improve the diurnal cycle in convective rainfall over land in climate models. Journal of Geophysical Research: Atmospheres, 119(5), 2113-2130. doi: 10.1002/2013JD020149. Within the tropics, and during the summer months in midlatitudes, most of the rainfall reaching the surface is generated by moist convection. Over land, the diurnal cycle in moist convective rainfall usually peaks in the late afternoon. In most climate models, the diurnal peak in convective rainfall occurs several hours too early and is often near local solar noon. We argue that this bias partly originates from the methods used in convective parameterizations to calculate the cloud base mass flux. In most convective parameterizations, the initial convective mass flux is determined from the convective available potential energy (CAPE) of an updraft parcel originating from the model layer closest to the surface. In models, the rapid increase in the CAPE of this near-surface layer following sunrise contributes to a rapid increase in convective precipitation. However, the mass-weighted CAPE of the boundary layer as a whole responds much more slowly to the increase in downward solar radiation at the surface. Using a recently developed convective parameterization in version 4 of the Community Atmosphere Model (CAM4), we show that the overall accuracy in the diurnal simulation of convective precipitation increases as the number of near-surface layers from which convective air parcels are permitted to originate increases from one to four. We also show that the simulation of the diurnal cycle in convective precipitation over land can be improved through the introduction of variables which attempt to represent the persistence of subgrid-scale convective organization within a grid column across model time steps. 0320 Cloud physics and chemistry; 1655 Water cycles; climate models; diurnal cycle; 1631 Land/atmosphere interactions; 1626 Global climate models; convective parameterization; convective rainfall
Forbes, Richard M.; Ahlgrimm, MaikeForbes, R. M., M. Ahlgrimm, 2014: On the Representation of High-Latitude Boundary Layer Mixed-Phase Cloud in the ECMWF Global Model. Mon. Wea. Rev., 142(9), 3425-3445. doi: 10.1175/MWR-D-13-00325.1. AbstractSupercooled liquid water (SLW) layers in boundary layer clouds are abundantly observed in the atmosphere at high latitudes, but remain a challenge to represent in numerical weather prediction (NWP) and climate models. Unresolved processes such as small-scale turbulence and mixed-phase microphysics act to maintain the liquid layer at cloud top, directly affecting cloud radiative properties and prolonging cloud lifetimes. This paper describes the representation of supercooled liquid water in boundary layer clouds in the European Centre for Medium-Range Weather Forecasts (ECMWF) global NWP model and in particular the change from a diagnostic temperature-dependent mixed phase to a prognostic representation with separate cloud liquid and ice variables. Data from the Atmospheric Radiation Measurement site in Alaska and from the CloudSat/Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite missions are used to evaluate the model parameterizations. The prognostic scheme shows a more realistic cloud structure, with an SLW layer at cloud top and ice falling out below. However, because of the limited vertical and horizontal resolution and uncertainties in the parameterization of physical processes near cloud top, the change leads to an overall reduction in SLW water with a detrimental impact on shortwave and longwave radiative fluxes, and increased 2-m temperature errors over land. A reduction in the ice deposition rate at cloud top significantly improves the SLW occurrence and radiative impacts, and highlights the need for improved understanding and parameterization of physical processes for mixed-phase cloud in large-scale models. Cloud microphysics; Arctic; Cloud water/phase; Southern Ocean; parameterization; Numerical weather prediction/forecasting
Gastineau, Guillaume; Soden, Brian J.; Jackson, Darren L.; O’Dell, Chris W.Gastineau, G., B. J. Soden, D. L. Jackson, C. W. O’Dell, 2014: Satellite-Based Reconstruction of the Tropical Oceanic Clear-Sky Outgoing Longwave Radiation and Comparison with Climate Models. J. Climate, 27(2), 941-957. doi: 10.1175/JCLI-D-13-00047.1.
Giglio, Donata; Roemmich, DeanGiglio, D., D. Roemmich, 2014: Climatological monthly heat and freshwater flux estimates on a global scale from Argo. Journal of Geophysical Research: Oceans, 119(10), 6884-6899. doi: 10.1002/2014JC010083. The global pattern of climatological monthly heat and freshwater fluxes at the ocean surface is estimated using Argo temperature and salinity profile data for the period 2004–2013. Temperature or salinity changes are calculated in a volume of water above an isopycnal that is below the mixed layer and not subject to mixed-layer entrainment. Horizontal advection components from geostrophic velocity and from Ekman transport, based on wind stress, are also included. The climatological monthly heat or freshwater flux at the ocean surface is estimated as the sum of advective and time tendency contributions. The air-sea flux estimates from Argo are described in global maps and basin-wide integrals, in comparison to atmospheric reanalysis data and to air-sea flux products based on observations. This ocean-based estimate of surface fluxes is consistent with property variations in the subsurface ocean and indicates greater amplitude for the climatological monthly heat flux values in the subtropics compared to other products. Similarly, the combination of Argo freshwater flux and reanalysis evaporation, suggests greater amplitude for climatological monthly precipitation in the tropics. 4572 Upper ocean and mixed layer processes; 4504 Air/sea interactions; Seasonal cycle; 3339 Ocean/atmosphere interactions; 4262 Ocean observing systems; 4227 Diurnal, seasonal, and annual cycles; air-sea flux; Argo; freshwater flux; heat flux; monthly climatology
Grise, Kevin M.; Polvani, Lorenzo M.Grise, K. M., L. M. Polvani, 2014: Southern Hemisphere Cloud–Dynamics Biases in CMIP5 Models and Their Implications for Climate Projections. J. Climate, 27(15), 6074-6092. doi: 10.1175/JCLI-D-14-00113.1. AbstractThis study quantifies cloud–radiative anomalies associated with interannual variability in the latitude of the Southern Hemisphere (SH) midlatitude eddy-driven jet, in 20 global climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). Two distinct model types are found. In the first class of models (type I models), total cloud fraction is reduced at SH midlatitudes as the jet moves poleward, contributing to enhanced shortwave radiative warming. In the second class of models (type II models), this dynamically induced cloud radiative warming effect is largely absent. Type I and type II models have distinct deficiencies in their representation of observed Southern Ocean clouds, but comparison with two independent satellite datasets indicates that the cloud–dynamics behavior of type II models is more realistic.Because the SH midlatitude jet shifts poleward in response to CO2 forcing, the cloud–dynamics biases uncovered from interannual variability are directly relevant for climate change projections. In CMIP5 model experiments with abruptly quadrupled atmospheric CO2 concentrations, the global-mean surface temperature initially warms more in type I models, even though their equilibrium climate sensitivity is not significantly larger. In type I models, this larger initial warming is linked to the rapid adjustment of the circulation and clouds to CO2 forcing in the SH, where a nearly instantaneous poleward shift of the midlatitude jet is accompanied by a reduction in the reflection of solar radiation by clouds. In type II models, the SH jet also shifts rapidly poleward with CO2 quadrupling, but it is not accompanied by cloud radiative warming anomalies, resulting in a smaller initial global-mean surface temperature warming. Shortwave radiation; climate models; Cloud radiative effects; Southern Hemisphere; Climate prediction; Antarctic Oscillation
Guo, Huan; Golaz, Jean-Christophe; Donner, Leo J.; Ginoux, Paul; Hemler, Richard S.Guo, H., J. Golaz, L. J. Donner, P. Ginoux, R. S. Hemler, 2014: Multivariate Probability Density Functions with Dynamics in the GFDL Atmospheric General Circulation Model: Global Tests. J. Climate, 27(5), 2087-2108. doi: 10.1175/JCLI-D-13-00347.1.
Hakuba, M. Z.; Folini, D.; Sanchez-Lorenzo, A.; Wild, M.Hakuba, M. Z., D. Folini, A. Sanchez-Lorenzo, M. Wild, 2014: Spatial representativeness of ground-based solar radiation measurements—Extension to the full Meteosat disk. Journal of Geophysical Research: Atmospheres, 119(20), 11,760-11,771. doi: 10.1002/2014JD021946. The spatial representativeness of a point measurement of surface solar radiation (SSR) of its larger-scale surrounding, e.g., collocated grid cell, is a potential source of uncertainty in the validation of climate models and satellite products. Here we expand our previous study over Europe to the entire Meteosat disk, covering additional climate zones in Africa, the Middle east, and South America between −70° to 70° East and −70° to 70° North. Using a high-resolution (0.03°) satellite-based SSR data set (2001–2005), we quantify the spatial subgrid variability in grids of 1° and 3° resolution and the spatial representativeness of 887 surface sites with respect to site-centered surroundings of variable size. In the multiannual mean the subgrid variability is the largest in some mountainous and coastal regions but varies seasonally due to changes in the Intertropical Convergence Zone location. The absolute mean representation errors at the surface sites with respect to surroundings of 1° and 3° are on average 1–2% (3 W m−2) and 2–3% (4 W m−2), respectively. The majority of sites are found to be representative within the in situ measurement accuracy. We show that their site-specific representativeness can be reliably approximated by the subgrid variability in a fixed grid (1°). The subgrid variability in turn is only moderately reduced when computed from coarser grid data, typically the only data available in areas not covered by the 0.03° resolved Meteosat disk. Together, this paves the way to a fully global assessment of site-specific spatial representativeness. 0360 Radiation: transmission and scattering; 1610 Atmosphere; 1640 Remote sensing; 0321 Cloud/radiation interaction; Solar radiation; Satellite; spatial variability; point representativeness
Hakuba, M. Z.; Folini, D.; Schaepman-Strub, G.; Wild, M.Hakuba, M. Z., D. Folini, G. Schaepman-Strub, M. Wild, 2014: Solar absorption over Europe from collocated surface and satellite observations. Journal of Geophysical Research: Atmospheres, 119(6), 3420-3437. doi: 10.1002/2013JD021421. Solar radiation is the primary source of energy for the Earth's climate system. Although the incoming and outgoing solar fluxes at the top of atmosphere can be quantified with high accuracy, large uncertainties still exist in the partitioning of solar absorption between surface and atmosphere. To compute best estimates of absorbed solar radiation at the surface and within the atmosphere representative for Europe during 2000–2010, we combine temporally homogeneous and spatially representative ground-based observations of surface downwelling solar radiation with collocated satellite-retrieved surface albedo and top-of-atmosphere net irradiance. We find best estimates of Europe land annual mean surface and atmospheric absorption of 117.3 ± 6 W m−2 (41.6 ± 2% of top-of-atmosphere incident irradiance) and 65.0 ± 3 W m−2 (23.0 ± 1%). The fractional atmospheric absorption of 23% represents a robust estimate largely unaffected by variations in latitude and season, thus, making it a potentially useful quantity for first-order validation of regional climate models. Uncertainties of the individual absorption estimates arise mostly from the measurements themselves. In this context, the surface albedo and the ground-based solar radiation data are the most critical variables. Other sources of uncertainty, like the multiplicative combination of spatially averaged surface solar radiation and surface albedo estimates, and the spatial representativeness of the point observations, are either negligibly small or can be corrected for. 1610 Atmosphere; 1640 Remote sensing; 3359 Radiative processes; 1814 Energy budgets; 7538 Solar irradiance; atmospheric solar absorption; combining surface and spaceborne data
Ham, Seung-Hee; Kato, Seiji; Barker, Howard W.; Rose, Fred G.; Sun-Mack, SunnyHam, S., S. Kato, H. W. Barker, F. G. Rose, S. Sun-Mack, 2014: Effects of 3-D clouds on atmospheric transmission of solar radiation: Cloud type dependencies inferred from A-train satellite data. Journal of Geophysical Research: Atmospheres, 119(2), 943–963. doi: 10.1002/2013JD020683. Three-dimensional (3-D) effects on broadband shortwave top of atmosphere (TOA) nadir radiance, atmospheric absorption, and surface irradiance are examined using 3-D cloud fields obtained from one hour's worth of A-train satellite observations and one-dimensional (1-D) independent column approximation (ICA) and full 3-D radiative transfer simulations. The 3-D minus ICA differences in TOA nadir radiance multiplied by π, atmospheric absorption, and surface downwelling irradiance, denoted as πΔI, ΔA, and ΔT, respectively, are analyzed by cloud type. At the 1 km pixel scale, πΔI, ΔA, and ΔT exhibit poor spatial correlation. Once averaged with a moving window, however, better linear relationships among πΔI, ΔA, and ΔT emerge, especially for moving windows larger than 5 km and large θ0. While cloud properties and solar geometry are shown to influence the relationships amongst πΔI, ΔA, and ΔT, once they are separated by cloud type, their linear relationships become much stronger. This suggests that ICA biases in surface irradiance and atmospheric absorption can be approximated based on ICA biases in nadir radiance as a function of cloud type. CERES; MODIS; CloudSat; CALIPSO; 3D; ICA
Hamann, U.; Walther, A.; Baum, B.; Bennartz, R.; Bugliaro, L.; Derrien, M.; Francis, P. N.; Heidinger, A.; Joro, S.; Kniffka, A.; Le Gléau, H.; Lockhoff, M.; Lutz, H.-J.; Meirink, J. F.; Minnis, P.; Palikonda, R.; Roebeling, R.; Thoss, A.; Platnick, S.; Watts, P.; Wind, G.Hamann, U., A. Walther, B. Baum, R. Bennartz, L. Bugliaro, M. Derrien, P. N. Francis, A. Heidinger, S. Joro, A. Kniffka, H. Le Gléau, M. Lockhoff, H. Lutz, J. F. Meirink, P. Minnis, R. Palikonda, R. Roebeling, A. Thoss, S. Platnick, P. Watts, G. Wind, 2014: Remote sensing of cloud top pressure/height from SEVIRI: analysis of ten current retrieval algorithms. Atmos. Meas. Tech., 7(9), 2839-2867. doi: 10.5194/amt-7-2839-2014. The role of clouds remains the largest uncertainty in climate projections. They influence solar and thermal radiative transfer and the earth's water cycle. Therefore, there is an urgent need for accurate cloud observations to validate climate models and to monitor climate change. Passive satellite imagers measuring radiation at visible to thermal infrared (IR) wavelengths provide a wealth of information on cloud properties. Among others, the cloud top height (CTH) – a crucial parameter to estimate the thermal cloud radiative forcing – can be retrieved. In this paper we investigate the skill of ten current retrieval algorithms to estimate the CTH using observations from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) onboard Meteosat Second Generation (MSG). In the first part we compare ten SEVIRI cloud top pressure (CTP) data sets with each other. The SEVIRI algorithms catch the latitudinal variation of the CTP in a similar way. The agreement is better in the extratropics than in the tropics. In the tropics multi-layer clouds and thin cirrus layers complicate the CTP retrieval, whereas a good agreement among the algorithms is found for trade wind cumulus, marine stratocumulus and the optically thick cores of the deep convective system. In the second part of the paper the SEVIRI retrievals are compared to CTH observations from the Cloud–Aerosol LIdar with Orthogonal Polarization (CALIOP) and Cloud Profiling Radar (CPR) instruments. It is important to note that the different measurement techniques cause differences in the retrieved CTH data. SEVIRI measures a radiatively effective CTH, while the CTH of the active instruments is derived from the return time of the emitted radar or lidar signal. Therefore, some systematic differences are expected. On average the CTHs detected by the SEVIRI algorithms are 1.0 to 2.5 km lower than CALIOP observations, and the correlation coefficients between the SEVIRI and the CALIOP data sets range between 0.77 and 0.90. The average CTHs derived by the SEVIRI algorithms are closer to the CPR measurements than to CALIOP measurements. The biases between SEVIRI and CPR retrievals range from −0.8 km to 0.6 km. The correlation coefficients of CPR and SEVIRI observations vary between 0.82 and 0.89. To discuss the origin of the CTH deviation, we investigate three cloud categories: optically thin and thick single layer as well as multi-layer clouds. For optically thick clouds the correlation coefficients between the SEVIRI and the reference data sets are usually above 0.95. For optically thin single layer clouds the correlation coefficients are still above 0.92. For this cloud category the SEVIRI algorithms yield CTHs that are lower than CALIOP and similar to CPR observations. Most challenging are the multi-layer clouds, where the correlation coefficients are for most algorithms between 0.6 and 0.8. Finally, we evaluate the performance of the SEVIRI retrievals for boundary layer clouds. While the CTH retrieval for this cloud type is relatively accurate, there are still considerable differences between the algorithms. These are related to the uncertainties and limited vertical resolution of the assumed temperature profiles in combination with the presence of temperature inversions, which lead to ambiguities in the CTH retrieval. Alternative approaches for the CTH retrieval of low clouds are discussed.
Hartmann, Dennis L.; Ceppi, PauloHartmann, D. L., P. Ceppi, 2014: Trends in the CERES Dataset, 2000–13: The Effects of Sea Ice and Jet Shifts and Comparison to Climate Models. J. Climate, 27(6), 2444-2456. doi: 10.1175/JCLI-D-13-00411.1.
He, Tao; Liang, Shunlin; Song, Dan-XiaHe, T., S. Liang, D. Song, 2014: Analysis of global land surface albedo climatology and spatial-temporal variation during 1981–2010 from multiple satellite products. Journal of Geophysical Research: Atmospheres, 119(17), 2014JD021667. doi: 10.1002/2014JD021667. For several decades, long-term time series data sets of multiple global land surface albedo products have been generated from satellite observations. These data sets have been used as one of the key variables in climate change studies. This study aims to assess the surface albedo climatology and to analyze long-term albedo changes, from nine satellite-based data sets for the period 1981–2010, on a global basis. Results show that climatological surface albedo data sets derived from satellite observations can be used to validate, calibrate, and further improve surface albedo simulations and parameterizations in current climate models. However, the albedo products derived from the International Satellite Cloud Climatology Project and the Global Energy and Water Exchanges Project have large seasonal biases. At latitudes higher than 50°, the maximal difference in winter zonal albedo ranges from 0.1 to 0.4 among the nine satellite data sets. Satellite-based albedo data sets agree relatively well during the summer at high latitudes, with a standard deviation of 0.04 for the 70°–80° zone in both hemispheres. The fine-resolution (0.05°) data sets agree well with each other for all the land cover types in middle to low latitudes; however, large spread was identified for their albedos at middle to high latitudes over land covers with mixed snow and sparse vegetation. By analyzing the time series of satellite-based albedo products over the past three decades, albedo of the Northern Hemisphere was found to be decreasing in July, likely due to the shrinking snow cover. Meanwhile, albedo in January was found to be increasing, likely because of the expansion of snow cover in northern winter. However, to improve the albedo estimation at high latitudes, and ultimately the climate models used for long-term climate change studies, a still better understanding of differences between satellite-based albedo data sets is required. 1640 Remote sensing; surface albedo; 3309 Climatology; 1616 Climate variability; Climatology; 0416 Biogeophysics; GLASS; trend analysis
Herwehe, Jerold A.; Alapaty, Kiran; Spero, Tanya L.; Nolte, Christopher G.Herwehe, J. A., K. Alapaty, T. L. Spero, C. G. Nolte, 2014: Increasing the credibility of regional climate simulations by introducing subgrid-scale cloud-radiation interactions. Journal of Geophysical Research: Atmospheres, 119(9), 2014JD021504. doi: 10.1002/2014JD021504. The radiation schemes in the Weather Research and Forecasting (WRF) model have previously not accounted for the presence of subgrid-scale cumulus clouds, thereby resulting in unattenuated shortwave radiation, which can lead to overly energetic convection and overpredicted surface precipitation. This deficiency can become problematic when applying WRF as a regional climate model (RCM). Therefore, modifications were made to the WRF model to allow the Kain–Fritsch (KF) convective parameterization to provide subgrid-scale cloud fraction and condensate feedback to the rapid radiative transfer model–global (RRTMG) shortwave and longwave radiation schemes. The effects of these changes are analyzed via 3 year simulations using the standard and modified versions of WRF, comparing the modeled results with the North American Regional Reanalysis (NARR) and Climate Forecast System Reanalysis data, as well as with available data from the Surface Radiation Network and Clouds and Earth's Radiant Energy System. During the summer period, including subgrid cloudiness estimated by KF in the RRTMG reduces the surface shortwave radiation, leading to less buoyant energy, which is reflected in a smaller diabatic convective available potential energy, thereby alleviating the overly energetic convection. Overall, these changes have reduced the overprediction of monthly, regionally averaged precipitation during summer for this RCM application, e.g., by as much as 49 mm for the southeastern U.S., to within 0.7% of the NARR value of 221 mm. These code modifications have been incorporated as an option available in the latest version of WRF (v3.6). 0321 Cloud/radiation interaction; 3310 Clouds and cloud feedbacks; 1637 Regional climate change; cumulus parameterization; radiation budget; cloud feedback; 3355 Regional modeling; WRF; 3365 Subgrid-scale (SGS) parameterization; regional climate model
Huang, Xianglei; Chen, Xiuhong; Potter, Gerald L.; Oreopoulos, Lazaros; Cole, Jason N. S.; Lee, Dongmin; Loeb, Norman G.Huang, X., X. Chen, G. L. Potter, L. Oreopoulos, J. N. S. Cole, D. Lee, N. G. Loeb, 2014: A Global Climatology of Outgoing Longwave Spectral Cloud Radiative Effect and Associated Effective Cloud Properties. J. Climate, 27(19), 7475-7492. doi: 10.1175/JCLI-D-13-00663.1. AbstractLongwave (LW) spectral flux and cloud radiative effect (CRE) are important for understanding the earth’s radiation budget and cloud–radiation interaction. Here, the authors extend their previous algorithms to collocated Atmospheric Infrared Sounder (AIRS) and Cloud and the Earth’s Radiant Energy System (CERES) observations over the entire globe and show that the algorithms yield consistently good performances for measurements over both land and ocean. As a result, the authors are able to derive spectral flux and CRE at 10-cm−1 intervals over the entire LW spectrum from all currently available collocated AIRS and CERES observations. Using this multiyear dataset, they delineate the climatology of spectral CRE, including the far IR, over the entire globe as well as in different climate zones. Furthermore, the authors define two quantities, IR-effective cloud-top height (CTHeff) and cloud amount (CAeff), based on the monthly-mean spectral (or band by band) CRE. Comparisons with cloud fields retrieved by the CERES–Moderate Resolution Imaging Spectroradiometer (MODIS) algorithm indicate that, under many circumstances, the CTHeff and CAeff can be related to the physical retrievals of CTH and CA and thus can enhance understandings of model deficiencies in LW radiation budgets and cloud fields. Using simulations from the GFDL global atmosphere model, version 2 (AM2); NASA’s Goddard Earth Observing System, version 5 (GEOS-5); and Environment Canada’s Canadian Centre for Climate Modelling and Analysis (CCCma) Fourth Generation Canadian Atmospheric General Circulation Model (CanAM4) as case studies, the authors further demonstrate the merits of the CTHeff and CAeff concepts in providing insights on global climate model evaluations that cannot be obtained solely from broadband LW flux and CRE comparisons. satellite observations; longwave radiation; Model evaluation/performance; General circulation models; Cloud radiative effects
Itterly, Kyle F.; Taylor, Patrick C.Itterly, K. F., P. C. Taylor, 2014: Evaluation of the Tropical TOA Flux Diurnal Cycle in MERRA and ERA-Interim Retrospective Analyses. J. Climate, 27(13), 4781-4796. doi: 10.1175/JCLI-D-13-00737.1. AbstractReanalysis model output is extensively used in atmospheric research and must be rigorously and continuously evaluated to understand the strengths and weaknesses. This paper evaluates the tropical top-of-atmosphere (TOA) flux diurnal cycle in NASA’s Modern-Era Retrospective Analysis for Research and Applications (MERRA) and the ECMWF Interim Re-Analysis (ERA-Interim) against Clouds and the Earth’s Radiant Energy System (CERES) synoptic edition 3A (SYN Ed3A) TOA flux data. MERRA and ERA-Interim are able to reproduce large-scale features of the diurnal cycle, including land–ocean contrast. MERRA and ERA-Interim, however, fail to reproduce many regional features of the climatological annual diurnal cycle. The TOA flux diurnal cycle errors in regions dominated by convective diurnal cycles are 5–10 times larger than in nonconvective regions. These errors in the TOA radiative flux diurnal cycle are primarily attributed to errors in the cloud diurnal evolution and specifically the failure to reproduce diurnally forced propagating convection. The largest diurnal cycle errors are found in ocean convective regions (e.g., Indian and equatorial Pacific Oceans); the observed longwave cloud forcing (LWCF) diurnal evolution in several oceanic convective regions shows two peaks: an afternoon and a near midnight peak; however, the reanalysis models produce a single midnight peak. The outgoing longwave radiation (OLR) diurnal cycle over tropical land is 20%–30% too weak in both reanalyses. The small diurnal cycle errors in marine stratocumulus regions are a result of two common misrepresentations in MERRA and ERA-Interim: 1) the dissipation of marine stratocumulus clouds from morning to afternoon is too slow and 2) the cloud diurnal cycle is too weak. Overall, the intermodel differences in the representation of the TOA flux diurnal cycle are smaller than the differences between reanalysis models and observations. tropics; Radiative fluxes; Model evaluation/performance; Climatology; Diurnal effects; Reanalysis data
Jin, Zhonghai; Lukachin, Constantin; Roberts, Yolanda; Wielicki, Bruce; Feldman, Daniel; Collins, WilliamJin, Z., C. Lukachin, Y. Roberts, B. Wielicki, D. Feldman, W. Collins, 2014: Interannual variability of the Earth's spectral solar reflectance from measurements and simulations. Journal of Geophysical Research: Atmospheres, 119(8), 2013JD021056. doi: 10.1002/2013JD021056. The mean solar spectral reflectance averaged over large spatiotemporal scales is an important climate benchmark data product proposed for the Climate Absolute Radiance and Refractivity Observatory mission. The interannual variability of these reflectances over the ocean is examined through satellite-measured hyperspectral data and through satellite instrument emulation based on model simulation. Such large domain-averaged reflectances show small interannual variation, usually under few percent, depending on the latitude region and spatiotemporal scale used for averaging. Although the interannual variation is usually less than the absolute accuracy of model calculation, the model simulated interannual variations are consistent with the measurements because most of the modeling errors in the reflectance averaged in large climate domains are systematic and are canceled out in the interannual difference spectra. The interannual variability is also shown to decrease as the temporal and spatial scales increase. Both the observational data and the model simulations show that the natural variability in the annual mean reflectance is about 50% lower than that in the monthly mean over all spectra. The interannual variability determined from observations in large climate domains also compares favorably with that from the climate Observing System Simulation Experiment based on climate model simulations; both show a standard deviation of less than 1% of the mean reflectance across all spectra for global and annual average over the ocean. 1640 Remote sensing; 3359 Radiative processes; 3305 Climate change and variability; 1616 Climate variability; Interannual variability; climate benchmark; spectral solar reflectance
Johnston, M. S.; Eliasson, S.; Eriksson, P.; Forbes, R. M.; Gettelman, A.; Räisänen, P.; Zelinka, M. D.Johnston, M. S., S. Eliasson, P. Eriksson, R. M. Forbes, A. Gettelman, P. Räisänen, M. D. Zelinka, 2014: Diagnosing the average spatio-temporal impact of convective systems – Part 2: A model intercomparison using satellite data. Atmos. Chem. Phys., 14(16), 8701-8721. doi: 10.5194/acp-14-8701-2014. The representation of the effect of tropical deep convective (DC) systems on upper-tropospheric moist processes and outgoing longwave radiation is evaluated in the EC-Earth3, ECHAM6, and CAM5 (Community Atmosphere Model) climate models using satellite-retrieved data. A composite technique is applied to thousands of deep convective systems that are identified using local rain rate maxima in order to focus on the temporal evolution of the deep convective processes in the model and satellite-retrieved data. The models tend to over-predict the occurrence of rain rates that are less than ≈ 3 mm h−1 compared to Tropical Rainfall Measurement Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA). While the diurnal distribution of oceanic rain rate maxima in the models is similar to the satellite-retrieved data, the land-based maxima are out of phase. Despite having a larger climatological mean upper-tropospheric relative humidity, models closely capture the satellite-derived moistening of the upper troposphere following the peak rain rate in the deep convective systems. Simulated cloud fractions near the tropopause are larger than in the satellite data, but the ice water contents are smaller compared with the satellite-retrieved ice data. The models capture the evolution of ocean-based deep convective systems fairly well, but the land-based systems show significant discrepancies. Over land, the diurnal cycle of rain is too intense, with deep convective systems occurring at the same position on subsequent days, while the satellite-retrieved data vary more in timing and geographical location. Finally, simulated outgoing longwave radiation anomalies associated with deep convection are in reasonable agreement with the satellite data, as well as with each other. Given the fact that there are strong disagreements with, for example, cloud ice water content, and cloud fraction, between the models, this study supports the hypothesis that such agreement with satellite-retrieved data is achieved in the three models due to different representations of deep convection processes and compensating errors.
Kay, J. E.; Medeiros, B.; Hwang, Y.-T.; Gettelman, A.; Perket, J.; Flanner, M. G.Kay, J. E., B. Medeiros, Y. Hwang, A. Gettelman, J. Perket, M. G. Flanner, 2014: Processes controlling Southern Ocean shortwave climate feedbacks in CESM. Geophysical Research Letters, 41(2), 616-622. doi: 10.1002/2013GL058315. A climate model (Community Earth System Model with the Community Atmosphere Model version 5 (CESM-CAM5)) is used to identify processes controlling Southern Ocean (30–70°S) absorbed shortwave radiation (ASR). In response to 21st century Representative Concentration Pathway 8.5 forcing, both sea ice loss (2.6 W m−2) and cloud changes (1.2 W m−2) enhance ASR, but their relative importance depends on location and season. Poleward of ~55°S, surface albedo reductions and increased cloud liquid water content (LWC) have competing effects on ASR changes. Equatorward of ~55°S, decreased LWC enhances ASR. The 21st century cloud LWC changes result from warming and near-surface stability changes but appear unrelated to a small (1°) poleward shift in the eddy-driven jet. In fact, the 21st century ASR changes are 5 times greater than ASR changes resulting from large (5°) naturally occurring jet latitude variability. More broadly, these results suggest that thermodynamics (warming and near-surface stability), not poleward jet shifts, control 21st century Southern Ocean shortwave climate feedbacks. clouds; 1620 Climate dynamics; 1621 Cryospheric change; sea ice; 3310 Clouds and cloud feedbacks; Shortwave radiation; climate feedbacks; Southern Ocean; jet
Khlopenkov, Konstantin V.; Doelling, David R.; Okuyama, ArataKhlopenkov, K. V., D. R. Doelling, A. Okuyama, 2014: Development of 2D deconvolution method to repair blurred MTSAT-1R visible imagery. doi: 10.1117/12.2061121. Spatial cross-talk has been discovered in the visible channel data of the Multi-functional Transport Satellite (MTSAT)-1R. The slight image blurring is attributed to an imperfection in the mirror surface caused either by flawed polishing or a dust contaminant. An image processing methodology is described that employs a two-dimensional deconvolution routine to recover the original undistorted MTSAT-1R data counts. The methodology assumes that the dispersed portion of the signal is small and distributed randomly around the optical axis, which allows the image blurring to be described by a point spread function (PSF) based on the Gaussian profile. The PSF is described by 4 parameters, which are solved using a maximum likelihood estimator using coincident collocated MTSAT-2 images as truth. A subpixel image matching technique is used to align the MTSAT-2 pixels into the MTSAT-1R projection and to correct for navigation errors and cloud displacement due to the time and viewing geometry differences between the two satellite observations. An optimal set of the PSF parameters is derived by an iterative routine based on the 4-dimensional Powell’s conjugate direction method that minimizes the difference between PSF-corrected MTSAT-1R and collocated MTSAT-2 images. This iterative approach is computationally intensive and was optimized analytically as well as by coding in assembly language incorporating parallel processing. The PSF parameters were found to be consistent over the 5-days of available daytime coincident MTSAT-1R and MTSAT-2 images, and can easily be applied to the MTSAT-1R imager pixel level counts to restore the original quality of the entire MTSAT-1R record.
Koren, Ilan; Dagan, Guy; Altaratz, OritKoren, I., G. Dagan, O. Altaratz, 2014: From aerosol-limited to invigoration of warm convective clouds. Science, 344(6188), 1143-1146. doi: 10.1126/science.1252595. Among all cloud-aerosol interactions, the invigoration effect is the most elusive. Most of the studies that do suggest this effect link it to deep convective clouds with a warm base and cold top. Here, we provide evidence from observations and numerical modeling of a dramatic aerosol effect on warm clouds. We propose that convective-cloud invigoration by aerosols can be viewed as an extension of the concept of aerosol-limited clouds, where cloud development is limited by the availability of cloud-condensation nuclei. A transition from pristine to slightly polluted atmosphere yields estimated negative forcing of ~15 watts per square meter (cooling), suggesting that a substantial part of this anthropogenic forcing over the oceans occurred at the beginning of the industrial era, when the marine atmosphere experienced such transformation. Invigorating convection in warm clouds Atmospheric aerosols—tiny airborne particles—affect the way clouds form and how they affect climate. Koren et al. investigated how the formation of warm clouds, such as those that form over the oceans, depends on pollution levels (see the Perspective by Remer). Aerosols affect cloud formation in cleaner air disproportionately more than in more polluted air. Before the widespread air pollution of the industrial era, it seems, warm convective clouds may have covered much less of the oceans than they do today. Science, this issue p. 1143; see also p. 1089
Kratz, D. P.; Stackhouse Jr, PW; Wong, T; Wilber, A. C.; Sawaengphokhai, ParnchaiKratz, D. P., P. Stackhouse Jr, T. Wong, A. C. Wilber, P. Sawaengphokhai, 2014: Earth radiation Budget at Top-of-Atmosphere. Bull. Amer. Meteor. Soc., 95(7), S30-S32. doi: 10.1175/2014BAMSStateoftheClimate.1.
Kratz, David P.; Stackhouse, Paul W.; Gupta, Shashi K.; Wilber, Anne C.; Sawaengphokhai, Parnchai; McGarragh, Greg R.Kratz, D. P., P. W. Stackhouse, S. K. Gupta, A. C. Wilber, P. Sawaengphokhai, G. R. McGarragh, 2014: The Fast Longwave and Shortwave Flux (FLASHFlux) Data Product: Single-Scanner Footprint Fluxes. J. Appl. Meteor. Climatol., 53(4), 1059-1079. doi: 10.1175/JAMC-D-13-061.1. AbstractThe Clouds and the Earth’s Radiant Energy Systems (CERES) project utilizes radiometric measurements taken aboard the Terra and Aqua spacecrafts to derive the world-class data products needed for climate research. Achieving the exceptional fidelity of the CERES data products, however, requires a considerable amount of processing to assure quality and to verify accuracy and precision, which results in the CERES data being released more than 6 months after the satellite observations. For most climate studies such delays are of little consequence; however, there are a significant number of near–real time uses for CERES data products. The Fast Longwave and Shortwave Radiative Flux (FLASHFlux) data product was therefore developed to provide a rapid release version of the CERES results, which could be made available to the research and applications communities within 1 week of the satellite observations by exchanging some accuracy for speed. FLASHFlux has both achieved this 1-week processing objective and demonstrated the ability to provide remarkably good agreement when compared with the CERES data products for both the instantaneous single-scanner footprint (SSF) fluxes and the time- and space-averaged (TISA) fluxes. This paper describes the methods used to expedite the production of the FLASHFlux SSF fluxes by utilizing data from the CERES and Moderate Resolution Imaging Spectroradiometer instruments, as well as other meteorological sources. This paper also reports on the validation of the FLASHFlux SSF results against ground-truth measurements and the intercomparison of FLASHFlux and CERES SSF results. A complementary paper will discuss the production and validation of the FLASHFlux TISA fluxes. satellite observations; longwave radiation; Shortwave radiation; Surface observations; Surface fluxes
Kuebbeler, M.; Lohmann, U.; Hendricks, J.; Kärcher, B.Kuebbeler, M., U. Lohmann, J. Hendricks, B. Kärcher, 2014: Dust ice nuclei effects on cirrus clouds. Atmos. Chem. Phys., 14(6), 3027-3046. doi: 10.5194/acp-14-3027-2014. In order to study aerosol–cloud interactions in cirrus clouds, we apply a new multiple-mode ice microphysical scheme to the general circulation model ECHAM5-HAM. The multiple-mode ice microphysical scheme allows for analysis of the competition between homogeneous freezing of solution droplets, deposition nucleation of pure dust particles, and immersion freezing of coated dust particles and pre-existing ice. We base the freezing efficiencies of coated and pure dust particles on the most recent laboratory data. The effect of pre-existing ice, which has been neglected in previous ice nucleation parameterizations, is to deplete water vapour by depositional growth and thus prevent homogeneous and heterogeneous freezing from occurring. As a first step, we extensively tested the model and validated the results against in situ measurements from various aircraft campaigns. The results compare well with observations; properties such as ice crystal size and number concentration as well as supersaturation are predicted within the observational spread. We find that heterogeneous nucleation on mineral dust particles and the consideration of pre-existing ice in the nucleation process may lead to significant effects: globally, ice crystal number and mass are reduced by 10 and 5%, whereas the ice crystals' size is increased by 3%. The reductions in ice crystal number are most pronounced in the tropics and mid-latitudes in the Northern Hemisphere. While changes in the microphysical and radiative properties of cirrus clouds in the tropics are mostly driven by considering pre-existing ice, changes in the northern hemispheric mid-latitudes mainly result from heterogeneous nucleation. The so-called negative Twomey effect in cirrus clouds is represented in ECHAM5-HAM. The net change in the radiation budget is −0.94 W m−2, implying that both heterogeneous nucleation on dust and pre-existing ice have the potential to modulate cirrus properties in climate simulations and thus should be considered in future studies.
Lacagnina, Carlo; Selten, Frank; Siebesma, A. PierLacagnina, C., F. Selten, A. P. Siebesma, 2014: Impact of changes in the formulation of cloud-related processes on model biases and climate feedbacks. Journal of Advances in Modeling Earth Systems, 6(4), 1224-1243. doi: 10.1002/2014MS000341. To test the impact of modeling uncertainties and biases on the simulation of cloud feedbacks, several configurations of the EC-Earth climate model are built altering physical parameterizations. An overview of the various radiative feedbacks diagnosed from the reference EC-Earth configuration is documented for the first time. The cloud feedback is positive and small. While the total feedback parameter is almost insensitive to model configuration, the cloud feedback, in particular its shortwave (SW) component, can vary considerably depending on the model settings. The lateral mass exchange rate of penetrative convection and the conversion rate from condensed water to precipitation are leading uncertain parameters affecting the radiative feedbacks diagnosed. Consistent with other studies, we find a strong correlation between low-cloud model fidelity and low-cloud response under global warming. It is shown that this relationship holds only for stratocumulus regimes and is contributed by low-cloud cover, rather than low-cloud optical thickness. Model configurations simulating higher stratocumulus cover, which is closer to the observations, exhibit a stronger positive SW cloud feedback. This feedback is likely underestimated in the reference EC-Earth configuration, over the eastern basins of the tropical oceans. In addition, connections between simulated high-cloud top altitude in present-day climate and longwave cloud feedback are discussed. 0321 Cloud/radiation interaction; 3305 Climate change and variability; 3310 Clouds and cloud feedbacks; Cloud radiative effects; cloud feedbacks; 3365 Subgrid-scale (SGS) parameterization; climate model bias; 0550 Model verification and validation; EC-Earth; tuning GCMs
Lee, Jaehwa; Kim, Jhoon; Lee, Yun GonLee, J., J. Kim, Y. G. Lee, 2014: Simultaneous retrieval of aerosol properties and clear-sky direct radiative effect over the global ocean from MODIS. Atmospheric Environment, 92, 309-317. doi: 10.1016/j.atmosenv.2014.04.021. A unified satellite algorithm is presented to simultaneously retrieve aerosol properties (aerosol optical depth; AOD and aerosol type) and clear-sky shortwave direct radiative effect (hereafter, DREA) over ocean. The algorithm is applied to Moderate Resolution Imaging spectroradiometer (MODIS) observations for a period from 2003 to 2010 to assess the DREA over the global ocean. The simultaneous retrieval utilizes lookup table (LUT) containing both spectral reflectances and solar irradiances calculated using a single radiative transfer model with the same aerosol input data. This study finds that aerosols cool the top-of-atmosphere (TOA) and bottom-of-atmosphere (BOA) by 5.2 ± 0.5 W/m2 and 8.3 W/m2, respectively, and correspondingly warm the atmosphere (hereafter, ATM) by 3.1 W/m2. These quantities, solely based on the MODIS observations, are consistent with those of previous studies incorporating chemical transport model simulations and satellite observations. However, the DREAs at BOA and ATM are expected to be less accurate compared to that of TOA due to low sensitivity in retrieving aerosol type information, which is related with the atmospheric heating by aerosols, particularly in low AOD conditions; consequently, the uncertainties could not be quantified. Despite the issue in the aerosol type information, the present method allows us to confine the DREA attributed only to fine-mode dominant aerosols, which are expected to be mostly anthropogenic origin, in the range from −1.1 W/m2 to −1.3 W/m2 at TOA. Improvements in size-resolved AOD and SSA retrievals from current and upcoming satellite instruments are suggested to better assess the DREA, particularly at BOA and ATM, where aerosol absorptivity induces substantial uncertainty. aerosol; radiative forcing; MODIS; direct radiative effect; Ocean
Lee, Myong-In; Kang, Hyun-Suk; Kim, Daehyun; Kim, Dongmin; Kim, Hyerim; Kang, DaehyunLee, M., H. Kang, D. Kim, D. Kim, H. Kim, D. Kang, 2014: Validation of the experimental hindcasts produced by the GloSea4 seasonal prediction system. Asia-Pacific Journal of Atmospheric Sciences, 50(3), 307-326. doi: 10.1007/s13143-014-0019-4. Using 14 year (1996–2009) ensemble hindcast runs produced with the Global Seasonal Forecasting System version 4 (GloSea4), this study evaluates the spatial and temporal structure of the hindcast climatology and the prediction skill of major climate variability. A special focus is on the fidelity of the system to reproduce and to forecast phenomena that are closely related to the East Asian climate. Overall the GloSea4 system exhibits realistic representations of the basic climate even though a few model deficiencies are identified in the sea surface temperature and precipitation. In particular, the capability of GloSea4 to capture the seasonal migration of rain belt associated with Changma implies a good potential for the Asian summer monsoon prediction. It is found that GloSea4 is as skillful as other state-of-the-art seasonal prediction systems in forecasting climate variability including the El-Nino/southern oscillation (ENSO), the East Asian summer monsoon, the Arctic Oscillation (AO), and the Madden-Julian Oscillation (MJO). The results presented in this study will provide benchmark evaluation for next seasonal prediction systems to be developed at the Korea Meteorological Administration. Climatology; ENSO; Atmospheric Sciences; Geophysics/Geodesy; MJO; AO; Asian monsoon; GloSea4; Seasonal prediction
Legates, David R.; Eschenbach, Willis; Soon, WillieLegates, D. R., W. Eschenbach, W. Soon, 2014: Arctic albedo changes are small compared with changes in cloud cover in the tropics. Proceedings of the National Academy of Sciences, 111(21), E2157-E2158. doi: 10.1073/pnas.1404997111.
Li, Gen; Xie, Shang-PingLi, G., S. Xie, 2014: Tropical Biases in CMIP5 Multimodel Ensemble: The Excessive Equatorial Pacific Cold Tongue and Double ITCZ Problems*. J. Climate, 27(4), 1765-1780. doi: 10.1175/JCLI-D-13-00337.1.
Li, J.-L. F.; Forbes, R. M.; Waliser, D. E.; Stephens, G.; Lee, SeungwonLi, J. F., R. M. Forbes, D. E. Waliser, G. Stephens, S. Lee, 2014: Characterizing the radiative impacts of precipitating snow in the ECMWF Integrated Forecast System global model. Journal of Geophysical Research: Atmospheres, 119(16), 2014JD021450. doi: 10.1002/2014JD021450. Global weather and climate models often exclude the effects of precipitating hydrometeors and convective core mass on radiative fluxes. In particular, many models split the ice phase into separate “cloud ice” and “snow” categories representing the smaller and larger ice particles, respectively; a separation that is generally not well defined in observations. A version of the European Centre for Medium-Range Weather Forecasts (ECMWF) global numerical weather prediction model which includes the radiative effects of cloud liquid, cloud ice, and precipitating snow is used to investigate the impact of including and excluding the radiative effects of the precipitating snow category. The results show that exclusion of precipitating snow in the radiation calculations leads to differences in the shortwave and longwave radiative fluxes of 5–15 W m−2 in strongly precipitating and convective areas. These differences are of the same order of magnitude as the systematic errors in the model compared to satellite observations. Corresponding biases in the radiative heating profiles are on the order of 0.15 K d−1. The results imply that precipitating snow should be included in the radiative calculations in all weather and climate models in the context of improving model fidelity and reducing compensating errors. 3359 Radiative processes; 3337 Global climate models; 3371 Tropical convection; 3354 Precipitation; 3373 Tropical dynamics; cloud-radiation; ECMWF IFS; forecast GCM
Li, J.-L. F.; Lee, W.-L.; Waliser, D. E.; David Neelin, J.; Stachnik, Justin P.; Lee, TongLi, J. F., W. Lee, D. E. Waliser, J. David Neelin, J. P. Stachnik, T. Lee, 2014: Cloud-precipitation-radiation-dynamics interaction in global climate models: A snow and radiation interaction sensitivity experiment. Journal of Geophysical Research: Atmospheres, 119(7), 2013JD021038. doi: 10.1002/2013JD021038. Conventional global climate models (GCMs) often consider radiation interactions only with small-particle/suspended cloud mass, ignoring large-particle/falling and convective core cloud mass. We characterize the radiation and atmospheric circulation impacts of frozen precipitating hydrometeors (i.e., snow), using the National Center for Atmospheric Research coupled GCM, by conducting sensitivity experiments that turn off the radiation interaction with snow. The changes associated with the exclusion of precipitating hydrometeors exhibit a number differences consistent with biases in CMIP3 and CMIP5 (Coupled Model Intercomparison Project Phase 3 and Phase 5), including more outgoing longwave flux at the top of atmosphere and downward shortwave flux at the surface in the heavily precipitating regions. Neglecting the radiation interaction of snow increases the net radiative cooling near the cloud top with the resulting increased instability triggering more convection in the heavily precipitating regions of the tropics. In addition, the increased differential vertical heating leads to a weakening of the low-level mean flow and an apparent low-level eastward advection from the warm pool resulting in moisture convergence south of the Intertropical Convergence Zone and north of the South Pacific Convergence Zone (SPCZ). This westerly bias, with effective warm and moist air transport, might be a contributing factor in the model's northeastward overextension of the SPCZ and the concomitant changes in sea surface temperatures, upward motion, and precipitation. Broader dynamical impacts include a stronger local meridional overturning circulation over the middle and east Pacific and commensurate changes in low and upper level winds, large-scale ascending motion, with a notable similarity to the systematic bias in this region in CMIP5 upper level zonal winds. 3359 Radiative processes; 3371 Tropical convection; 3354 Precipitation; Atmospheric dynamics; 3339 Ocean/atmosphere interactions; 3373 Tropical dynamics; cloud radiation; cloud-radiation; coupled GCM; coupled-GCM; SSTs
Li, J.-L. F.; Lee, W.-L.; Waliser, D. E.; Stachnik, Justin P.; Fetzer, Eric; Wong, Sun; Yue, QingLi, J. F., W. Lee, D. E. Waliser, J. P. Stachnik, E. Fetzer, S. Wong, Q. Yue, 2014: Characterizing tropical Pacific water vapor and radiative biases in CMIP5 GCMs: Observation-based analyses and a snow and radiation interaction sensitivity experiment. Journal of Geophysical Research: Atmospheres, 119(19), 2014JD021924. doi: 10.1002/2014JD021924. Significant systematic biases in the moisture fields within the tropical Pacific trade wind regions are found in the Coupled Model Intercomparison Project (CMIP3/CMIP5) against profile and total column water vapor (TotWV) estimates from the Atmospheric Infrared Sounder and TotWV from the Special Sensor Microwave/Imager. Positive moisture biases occur in conjunction with significant biases of eastward low-level moisture convergence north of the South Pacific Convergence Zone and south of the Intertropical Convergence Zone—the V-shaped regions. The excessive moisture there is associated with overestimates of reflected upward shortwave (RSUT), underestimates of outgoing longwave radiation (RLUT) at the top of atmosphere (TOA), and underestimates of downward shortwave flux at the surface (RSDS) compared to Clouds and the Earth's Energy System, Energy Balance and Filled data. We characterize the impacts of falling snow and its radiation interaction, which are not included in most CMIP5 models, on the moisture fields using the National Center for Atmospheric Research-coupled global climate model (GCM). A number of differences in the model simulation without snow-radiation interactions are consistent with biases in the CMIP5 simulations. These include effective low-level eastward/southeastward wind and surface wind stress anomalies, and an increase in TotWV, vertical profile of moisture, and cloud amounts in the V-shaped region. The anomalous water vapor and cloud amount might be associated with the model increase of RSUT and decrease of RLUT at TOA and decreased RSDS in clear and all sky in these regions. These findings hint at the importance of water vapor-radiation interactions in the CMIPS/CMIP5 model simulations that exclude the radiative effect of snow. 3359 Radiative processes; water vapor; radiation; 3371 Tropical convection; 3354 Precipitation; 3339 Ocean/atmosphere interactions; 3373 Tropical dynamics; cloud radiation; cloud-radiation; coupled GCM
Li, Ying; Thompson, David W. J.; Huang, Yi; Zhang, MinghongLi, Y., D. W. J. Thompson, Y. Huang, M. Zhang, 2014: Observed linkages between the northern annular mode/North Atlantic Oscillation, cloud incidence, and cloud radiative forcing. Geophysical Research Letters, 41(5), 1681-1688. doi: 10.1002/2013GL059113. The signature of the northern annular mode/North Atlantic Oscillation (NAM/NAO) in the vertical and horizontal distribution of tropospheric cloudiness is investigated in CloudSat and CALIPSO data from June 2006 to April 2011. During the Northern Hemisphere winter, the positive polarity of the NAM/NAO is marked by increases in zonally averaged cloud incidence north of ~60°N, decreases between ~25 and 50°N, and increases in the subtropics. The tripolar-like anomalies in cloud incidence associated with the NAM/NAO are largest over the North Atlantic Ocean basin/Middle East and are physically consistent with the NAM/NAO-related anomalies in vertical motion. Importantly, the NAM/NAO-related anomalies in tropospheric cloud incidence lead to significant top of atmosphere cloud radiative forcing anomalies that are comparable in amplitude to those associated with the NAM/NAO-related temperature anomalies. The results provide observational evidence that the most prominent pattern of Northern Hemisphere climate variability is significantly linked to variations in cloud radiative forcing. Implications for two-way feedback between extratropical dynamics and cloud radiative forcing are discussed. 1620 Climate dynamics; cloud; 0321 Cloud/radiation interaction; 3310 Clouds and cloud feedbacks; 1616 Climate variability; cloud radiative forcing; CloudSat/CALIPSO; North Atlantic Oscillation; northern annular mode
Li, Yuanlong; Han, Weiqing; Shinoda, Toshiaki; Wang, Chunzai; Ravichandran, M.; Wang, Jih-WangLi, Y., W. Han, T. Shinoda, C. Wang, M. Ravichandran, J. Wang, 2014: Revisiting the Wintertime Intraseasonal SST Variability in the Tropical South Indian Ocean: Impact of the Ocean Interannual Variation. J. Phys. Oceanogr., 44(7), 1886-1907. doi: 10.1175/JPO-D-13-0238.1. AbstractIntraseasonal sea surface temperature (SST) variability over the Seychelles–Chagos thermocline ridge (SCTR; 12°–4°S, 55°–85°E) induced by boreal wintertime Madden–Julian oscillations (MJOs) is investigated with a series of OGCM experiments forced by the best available atmospheric data. The impact of the ocean interannual variation (OIV), for example, the thermocline depth changes in the SCTR, is assessed. The results show that surface shortwave radiation (SWR), wind speed–controlled turbulent heat fluxes, and wind stress–driven ocean processes are all important in causing the MJO-related intraseasonal SST variability. The effect of the OIV is significant in the eastern part of the SCTR (70°–85°E), where the intraseasonal SSTs are strengthened by about 20% during the 2001–11 period. In the western part (55°–70°E), such effect is relatively small and not significant. The relative importance of the three dominant forcing factors is adjusted by the OIV, with increased (decreased) contribution from wind stress (wind speed and SWR). The OIV also tends to intensify the year-to-year variability of the intraseasonal SST amplitude. In general, a stronger (weaker) SCTR favors larger (smaller) SST responses to the MJO forcing. Because of the nonlinearity of the upper-ocean thermal stratification, especially the mixed layer depth (MLD), the OIV imposes an asymmetric impact on the intraseasonal SSTs between the strong and weak SCTR conditions. In the eastern SCTR, both the heat flux forcing and entrainment are greatly amplified under the strong SCTR condition, but only slightly suppressed under the weak SCTR condition, leading to an overall strengthening effect by the OIV. surface temperature; tropics; Oceanic variability; Indian Ocean; Intraseasonal variability; Physical Meteorology and Climatology; Variability; Geographic location/entity; Ocean dynamics; Circulation/ Dynamics
Li, Yuanlong; Han, Weiqing; Wilkin, John L.; Zhang, Weifeng G.; Arango, Hernan; Zavala-Garay, Javier; Levin, Julia; Castruccio, Frederic S.Li, Y., W. Han, J. L. Wilkin, W. G. Zhang, H. Arango, J. Zavala-Garay, J. Levin, F. S. Castruccio, 2014: Interannual variability of the surface summertime eastward jet in the South China Sea. Journal of Geophysical Research: Oceans, 119(10), 7205-7228. doi: 10.1002/2014JC010206. The summertime eastward jet (SEJ) located around 12°N, 110°E–113°E, as the offshore extension of the Vietnam coastal current, is an important feature of the South China Sea (SCS) surface circulation in boreal summer. Analysis of satellite-derived sea level and sea surface wind data during 1992–2012 reveals pronounced interannual variations in its surface strength (SSEJ) and latitudinal position (YSEJ). In most of these years, the JAS (July, August, and September)-mean SSEJ fluctuates between 0.17 and 0.55 m s−1, while YSEJ shifts between 10.7°N and 14.3°N. These variations of the SEJ are predominantly contributed from the geostrophic current component that is linked to a meridional dipole pattern of sea level variations. This sea level dipole pattern is primarily induced by local wind changes within the SCS associated with the El Niño-Southern Oscillation (ENSO). Enhanced (weakened) southwest monsoon at the developing (decaying) stage of an El Niño event causes a stronger (weaker) SEJ located south (north) of its mean position. Remote wind forcing from the tropical Pacific can also affect the sea level in the SCS via energy transmission through the Philippine archipelago, but its effect on the SEJ is small. The impact of the oceanic internal variability, such as eddy-current interaction, is assessed using an ocean general circulation model (OGCM). Such impact can lead to considerable year-to-year changes of sea level and the SEJ, equivalent to ∼20% of the observed variation. This implies the complexity and prediction difficulty of the upper ocean circulation in this region. 4556 Sea level: variations and mean; ENSO; sea level; 3319 General circulation; South China Sea; wind forcing
Liang, Shunlin; Zhang, Xiaotong; Xiao, Zhiqiang; Cheng, Jie; Liu, Qiang; Zhao, XiangLiang, S., X. Zhang, Z. Xiao, J. Cheng, Q. Liu, X. Zhao, 2014: Incident Shortwave Radiation. Global LAnd Surface Satellite (GLASS) Products, 123-142. Incident shortwave radiation (ISR), also known as insolation, is referred to as total solar irradiance incident at the Earth’s surface and is an essential parameter in land surface radiation budget and many land surface process models. This chapter provides a primary introduction to the GLASS ISR product by discussing the algorithm, validation, and analysis. In the first section, a brief introduction will be given. The satellite data used and the implementation of the algorithms are discussed in Sect. 5.2. GLASS ISR product quality control and evaluation using ground measurements are presented in Sect. 5.3. The preliminary analysis and applications are described in Sect. 5.4, followed by a short summary. Remote sensing; MODIS; Shortwave radiation; GOES; Remote Sensing/Photogrammetry; Environmental Science and Engineering; Global irradiance; Insolation; MSG; MTSAT; Physical Geography
Lim, Kyo-Sun Sunny; Fan, Jiwen; Leung, L. Ruby; Ma, Po-Lun; Singh, Balwinder; Zhao, Chun; Zhang, Yang; Zhang, Guang; Song, XiaoliangLim, K. S., J. Fan, L. R. Leung, P. Ma, B. Singh, C. Zhao, Y. Zhang, G. Zhang, X. Song, 2014: Investigation of aerosol indirect effects using a cumulus microphysics parameterization in a regional climate model. Journal of Geophysical Research: Atmospheres, 119(2), 2013JD020958. doi: 10.1002/2013JD020958. A new Zhang and McFarlane (ZM) cumulus scheme includes a two-moment cloud microphysics parameterization for convective clouds. This allows aerosol effects to be investigated more comprehensively by linking aerosols with microphysical processes in both stratiform clouds that are explicitly resolved and convective clouds that are parameterized in climate models. This new scheme is implemented in the Weather Research and Forecasting model, coupled with the physics and aerosol packages from the Community Atmospheric Model version 5. A case of July 2008 during the East Asian summer monsoon is selected to evaluate the performance of the new ZM and to investigate aerosol effects on monsoon precipitation. The precipitation and radiative fluxes simulated by the new ZM show a better agreement with observations compared to simulations with the original ZM that does not include convective cloud microphysics and aerosol-convective cloud interactions. Detailed analysis suggests that an increase in detrained cloud water and ice mass by the new ZM is responsible for this improvement. Aerosol impacts on cloud properties, precipitation, and radiation are examined by reducing the primary aerosols and anthropogenic emissions to 30% of those in the present (polluted) condition. The simulated surface precipitation is reduced by 9.8% from clean to polluted environment, and the reduction is less significant when microphysics processes are excluded from the cumulus clouds. Cloud fraction is reduced by the increased aerosols due to suppressed convection, except during some heavy precipitation periods when cloud fraction, cloud top height, and rain rate are increased due to enhanced convection. 3311 Clouds and aerosols; 3314 Convective processes; convective clouds; aerosol indirect effects; monsoon rainfall; regional climate modeling; WRF model; Zhang and McFarlane cumulus scheme
Lim, Kyo-Sun Sunny; Hong, Song-You; Yoon, Jin-Ho; Han, JongilLim, K. S., S. Hong, J. Yoon, J. Han, 2014: Simulation of the Summer Monsoon Rainfall over East Asia Using the NCEP GFS Cumulus Parameterization at Different Horizontal Resolutions. Wea. Forecasting, 29(5), 1143-1154. doi: 10.1175/WAF-D-13-00143.1. AbstractThe most recent version of the simplified Arakawa–Schubert (SAS) cumulus scheme in the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) (GFS SAS) is implemented in the Weather Research and Forecasting (WRF) Model with a modification of the triggering condition and the convective mass flux in order to make it dependent on the model’s horizontal grid spacing. The East Asian summer monsoon season of 2006 is selected in order to evaluate the performance of the modified GFS SAS scheme. In comparison to the original GFS SAS scheme, the modified GFS SAS scheme shows overall better agreement with the observations in terms of the simulated monsoon rainfall. The simulated precipitation from the original GFS SAS scheme is insensitive to the model’s horizontal grid spacing, which is counterintuitive because the portion of the resolved clouds in a grid box should increase as the model grid spacing decreases. This behavior of the original GFS SAS scheme is alleviated by the modified GFS SAS scheme. In addition, three different cumulus schemes (Grell and Freitas, Kain and Fritsch, and Betts–Miller–Janjić) are chosen to investigate the role of a horizontal resolution on the simulated monsoon rainfall. Although the forecast skill of the surface rainfall does not always improve as the spatial resolution increases, the improvement of the probability density function of the rain rate with the smaller grid spacing is robust regardless of the cumulus parameterization scheme. convective parameterization
Lin, Jia-Lin; Qian, Taotao; Shinoda, ToshiakiLin, J., T. Qian, T. Shinoda, 2014: Stratocumulus Clouds in Southeastern Pacific Simulated by Eight CMIP5–CFMIP Global Climate Models. J. Climate, 27(8), 3000-3022. doi: 10.1175/JCLI-D-13-00376.1. AbstractThis study examines the stratocumulus clouds and associated cloud feedback in the southeast Pacific (SEP) simulated by eight global climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) and Cloud Feedback Model Intercomparison Project (CFMIP) using long-term observations of clouds, radiative fluxes, cloud radiative forcing (CRF), sea surface temperature (SST), and large-scale atmosphere environment. The results show that the state-of-the-art global climate models still have significant difficulty in simulating the SEP stratocumulus clouds and associated cloud feedback. Comparing with observations, the models tend to simulate significantly less cloud cover, higher cloud top, and a variety of unrealistic cloud albedo. The insufficient cloud cover leads to overly weak shortwave CRF and net CRF. Only two of the eight models capture the observed positive cloud feedback at subannual to decadal time scales. The cloud and radiation biases in the models are associated with 1) model biases in large-scale temperature structure including the lack of temperature inversion, insufficient lower troposphere stability (LTS), and insufficient reduction of LTS with local SST warming, and 2) improper model physics, especially insufficient increase of low cloud cover associated with larger LTS. The two models that arguably do best at simulating the stratocumulus clouds and associated cloud feedback are the only ones using cloud-top radiative cooling to drive boundary layer turbulence. climate models; Cloud parameterizations; Cloud radiative effects
Lin, Neng-Huei; Sayer, Andrew M.; Wang, Sheng-Hsiang; Loftus, Adrian M.; Hsiao, Ta-Chih; Sheu, Guey-Rong; Hsu, N. Christina; Tsay, Si-Chee; Chantara, SompornLin, N., A. M. Sayer, S. Wang, A. M. Loftus, T. Hsiao, G. Sheu, N. C. Hsu, S. Tsay, S. Chantara, 2014: Interactions between biomass-burning aerosols and clouds over Southeast Asia: Current status, challenges, and perspectives. Environmental Pollution, 195, 292-307. doi: 10.1016/j.envpol.2014.06.036. The interactions between aerosols, clouds, and precipitation remain among the largest sources of uncertainty in the Earth's energy budget. Biomass-burning aerosols are a key feature of the global aerosol system, with significant annually-repeating fires in several parts of the world, including Southeast Asia (SEA). SEA in particular provides a “natural laboratory” for these studies, as smoke travels from source regions downwind in which it is coupled to persistent stratocumulus decks. However, SEA has been under-exploited for these studies. This review summarizes previous related field campaigns in SEA, with a focus on the ongoing Seven South East Asian Studies (7-SEAS) and results from the most recent BASELInE deployment. Progress from remote sensing and modeling studies, along with the challenges faced for these studies, are also discussed. We suggest that improvements to our knowledge of these aerosol/cloud effects require the synergistic use of field measurements with remote sensing and modeling tools. Remote sensing; Southeast Asia; 7-SEAS; Aerosol chemistry; Aerosol–cloud interaction; Biomass-burning aerosol
Lindsay, R.; Wensnahan, M.; Schweiger, A.; Zhang, J.Lindsay, R., M. Wensnahan, A. Schweiger, J. Zhang, 2014: Evaluation of Seven Different Atmospheric Reanalysis Products in the Arctic*. J. Climate, 27(7), 2588-2606. doi: 10.1175/JCLI-D-13-00014.1.
Liu, C.; Yang, P.; Minnis, P.; Loeb, N.; Kato, S.; Heymsfield, A.; Schmitt, C.Liu, C., P. Yang, P. Minnis, N. Loeb, S. Kato, A. Heymsfield, C. Schmitt, 2014: A two-habit model for the microphysical and optical properties of ice clouds. Atmos. Chem. Phys. Discuss., 14(13), 19545-19586. doi: 10.5194/acpd-14-19545-2014. To provide a better representation of natural ice clouds, a novel ice cloud model containing two particle habits is developed. The microphysical and optical properties of the two-habit model (THM) are compared with both laboratory and in situ measurements, and its performance in downstream satellite remote sensing applications is tested. The THM assumes an ice cloud to be an ensemble of hexagonal columns and twenty-element aggregates, and to have specific habit fractions at each particle size. The ice water contents and median mass diameters calculated based on the THM closely agree with in situ measurements made during 11 field campaigns. In this study, the scattering, absorption, and polarization properties of ice crystals are calculated with a combination of the invariant imbedding T-matrix, pseudo-spectral time domain, and improved geometric-optics methods over an entire range of particle sizes. The phase functions, calculated based on the THM, show excellent agreement with counterparts from laboratory and in situ measurements and from satellite retrievals. For downstream applications in the retrieval of cloud microphysical and optical properties from MODIS observations, the THM presents excellent spectral consistency; specifically, the retrieved cloud optical thicknesses based on the visible/near infrared bands and the thermal infrared bands agree quite well. Furthermore, a comparison between the polarized reflectivities observed by the PARASOL satellite and from theoretical simulations illustrates that the THM can be used to represent ice cloud polarization properties.
Liu, Quanhua; Boukabara, SidLiu, Q., S. Boukabara, 2014: Community Radiative Transfer Model (CRTM) applications in supporting the Suomi National Polar-orbiting Partnership (SNPP) mission validation and verification. Remote Sensing of Environment, 140, 744-754. doi: 10.1016/j.rse.2013.10.011. The Suomi National Polar-orbiting Partnership (SNPP) sensors operationally measure a broad spectrum from microwave to ultraviolet wavelengths for generating 30 satellite products. The wide swath of the SNPP Visible Infrared Imaging Radiometer Suite (VIIRS) observed a historic event: 3 typhoons that all hit China mainland within 5 days. The Community Radiative Transfer Model (CRTM) provides critical supports to the SNPP instrumental validation and verification efforts. For example, the CRTM helped to verify image striping in the Advanced Technology Microwave Sounder (ATMS) upper atmosphere channels. The CRTM has also been used to characterize the ATMS radiometric bias and has led to the development of a complementary cloud screening method. Using the European Centre for Medium-Range Weather Forecasts (ECMWF) 6 h analysis data as inputs to the CRTM, we can statistically quantify the spectral bias for each field of view (FOV) of the Cross-track Infrared Sounder (CrIS). The CRTM is also a very useful tool for cross-sensor verifications. Using the double difference method, it can remove the biases caused by slight differences in the spectral response and geometric angles between two instruments. The CRTM helps our understanding on radiometric and spectral calibrations. It is the CRTM simulations that enable us to determine the root cause of the VIIRS shortwave infrared band image striping during daytime. The CRTM is operationally used at the National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Prediction (NCEP) for weather forecasting and monitoring satellite radiance biases and standard deviation. This study also demonstrated the CRTM capability for Ozone Mapping and Profiler Suite (OMPS) radiance simulations. The first result showed a good agreement between the measurement and simulation. The CRTM for OMPS limb sensing, and Clouds and the Earth's Radiant Energy System (CERES) shortwave radiation and long-wave radiation flux simulation capability need to be extended. CRTM; SNPP instruments; Validation and verification
Loeb, Norman G.; Rutan, David A.; Kato, Seiji; Wang, WeijieLoeb, N. G., D. A. Rutan, S. Kato, W. Wang, 2014: Observing Interannual Variations in Hadley Circulation Atmospheric Diabatic Heating and Circulation Strength. J. Climate, 27(11), 4139-4158. doi: 10.1175/JCLI-D-13-00656.1. AbstractSatellite and reanalysis data are used to observe interannual variations in atmospheric diabatic heating and circulation within the ascending and descending branches of the Hadley circulation (HC) during the past 12 yr. The column-integrated divergence of dry static energy (DSE) and kinetic energy is inferred from satellite-based observations of atmospheric radiation, precipitation latent heating, and reanalysis-based surface sensible heat flux for monthly positions of the HC branches, determined from a mass weighted zonal mean meridional streamfunction analysis. Mean surface radiative fluxes inferred from satellite and surface measurements are consistent to 1 W m−2 ( Energy budget/balance; satellite observations; Atmospheric circulation; Cloud radiative effects; ENSO; Interannual variability
Loginov, S. V.; Ippolitov, I. I.; Kharyutkina, E. V.Loginov, S. V., I. I. Ippolitov, E. V. Kharyutkina, 2014: The relationship of surface air temperature, heat balance at the surface, and radiative balance at the top of atmosphere over the Asian territory of Russia using reanalysis and remote-sensing data. International Journal of Remote Sensing, 35(15), 5878-5898. doi: 10.1080/01431161.2014.945007. In this study over the Asian territory of Russia (ATR) (45° N–80° N, 60° E–180° E) for the period of 1979–2010 the temporal variability of the surface air temperature field was investigated. There are several climatic factors which can influence temperature variability including radiative balance at the top of atmosphere (TOA), heat balance at the surface, total cloud cover, and large-scale atmospheric circulation in the Northern Hemisphere. The contribution of these factors to temperature variability is also investigated. It was found that during the past decade, over the ATR, the process of warming prevails mainly in the warm season, but in the cold season it is either not as marked or there is cooling instead. In the winter season there is a positive relationship between temperature anomalies and anomalies in cloudiness, effective radiation, and the Arctic Oscillation (AO) index. During the same period, a negative relationship between anomalies of temperature and anomalies of net radiation at the TOA, net shortwave radiation at the surface, and the Scandinavian (SCAND) index was observed. In the summer season, the relationship between temperature and cloudiness becomes negative and the relationship between temperature and atmospheric circulation indices decreases. For the period 2001–2010, radiative fluxes obtained from reanalysis data sets Japanese Reanalysis Data (JRA-25) and Modern Era-Retrospective Analysis for Research and Applications (MERRA) were compared to satellite remotely sensed data project Clouds and the Earth’s Radiant Energy System (CERES). It was found that there is a good agreement between estimates of the net radiation at the TOA calculated using reanalysis data and satellite data: the difference is about 1.5 W m−2 and the correlation coefficient is more than 0.7. As for the comparison of radiative fluxes estimates at the surface for clear sky, there is less difference between MERRA and CERES. So, during the period 2001–2010 the relation between atmospheric circulation and surface air temperature variability increased in winter months. Obtained regression models allow us to describe from 27% to 82% of temperature variability in different months if we take into account both circulation and radiative factors.
Luo, Tao; Yuan, Renmin; Wang, ZhienLuo, T., R. Yuan, Z. Wang, 2014: On factors controlling marine boundary layer aerosol optical depth. Journal of Geophysical Research: Atmospheres, 119(6), 2013JD020936. doi: 10.1002/2013JD020936. Sea spray aerosol is one of the largest natural contributors to the global aerosol loading and thus plays an important role in the global radiative budget through both direct and indirect effects. Previous studies have shown either strong or weak relationships between marine boundary layer (MBL) aerosol optical depth (τ) and the near-surface wind speed. However, the marine τ is influenced by a wide range of factors. This study attempts to examine extra contributing factors beyond wind to better characterize MBL τ variations over the global ocean by using 4 year A-train data (2006–2010). The results show that among many factors controlling MBL τ, surface wind speed and MBL depth are the two most important factors. This suggests that not only mechanical production of sea spray particles driven by near-surface wind processes but also vertical redistribution driven by turbulent and shallow convective mixing in the MBL controls MBL τ variations. A new two-parameter parameterization of τ was derived based on satellite measurements. Evaluations with independent data show that the new parameterization improves the prediction of MBL τ. The comparisons between the Fu-Liou radiative transfer model calculations and Aqua Clouds and the Earth's Radiant Energy System observations showed that the new parameterization improves the estimation of aerosol radiative forcing. 0305 Aerosols and particles; 3307 Boundary layer processes; boundary layer height; marine aerosol optical depth; sea salt; surface wind speed
Ma, H.-Y.; Xie, S.; Klein, S. A.; Williams, K. D.; Boyle, J. S.; Bony, S.; Douville, H.; Fermepin, S.; Medeiros, B.; Tyteca, S.; Watanabe, M.; Williamson, D.Ma, H., S. Xie, S. A. Klein, K. D. Williams, J. S. Boyle, S. Bony, H. Douville, S. Fermepin, B. Medeiros, S. Tyteca, M. Watanabe, D. Williamson, 2014: On the Correspondence between Mean Forecast Errors and Climate Errors in CMIP5 Models. J. Climate, 27(4), 1781-1798. doi: 10.1175/JCLI-D-13-00474.1.
Ma, Xiaoyan; Yu, Fangqun; Quaas, JohannesMa, X., F. Yu, J. Quaas, 2014: Reassessment of satellite-based estimate of aerosol climate forcing. Journal of Geophysical Research: Atmospheres, 119(17), 2014JD021670. doi: 10.1002/2014JD021670. Large uncertainties exist in estimations of aerosol direct radiative forcing and indirect radiative forcing, and the values derived from global modeling differ substantially with satellite-based calculations. Following the approach of Quaas et al. (2008; hereafter named Quaas2008), we reassess satellite-based clear- and cloudy-sky radiative forcings and their seasonal variations by employing updated satellite products from 2004 to 2011 in combination with the anthropogenic aerosol optical depth (AOD) fraction obtained from model simulations using the Goddard Earth Observing System-Chemistry-Advanced Particle Microphysics (GEOS-Chem-APM). Our derived annual mean aerosol clear-sky forcing (−0.59 W m−2) is lower, while the cloudy-sky forcing (−0.34 W m−2) is higher than the corresponding results (−0.9 W m−2 and −0.2 W m−2, respectively) reported in Quaas2008. Our study indicates that the derived forcings are sensitive to the anthropogenic AOD fraction and its spatial distribution but insensitive to the temporal resolution used to obtain the regression coefficients, i.e., monthly or seasonal based. The forcing efficiency (i.e., the magnitude per anthropogenic AOD) for the clear-sky forcing based on this study is 19.9 W m−2, which is about 5% smaller than Quaas2008's value of 21.1 W m−2. In contrast, the efficiency for the cloudy-sky forcing of this study (11 W m−2) is more than a factor of 2 larger than Quaas2008's value of 4.7 W m−2. Uncertainties tests indicate that anthropogenic fraction of AOD strongly affects the computed forcings while using aerosol index instead of AOD from satellite data as aerosol proxy does not appear to cause any significant differences in regression slopes and derived forcings. 0305 Aerosols and particles; 0321 Cloud/radiation interaction; aerosol; direct forcing; indirect forcing; satellite-based estimate
Marshall, J.; Donohoe, A.; Ferreira, D.; McGee, D.Marshall, J., A. Donohoe, D. Ferreira, D. McGee, 2014: The ocean’s role in setting the mean position of the Inter-Tropical Convergence Zone. Climate Dynamics, 42(7-8), 1967-1979. doi: 10.1007/s00382-013-1767-z. Through study of observations and coupled climate simulations, it is argued that the mean position of the Inter-Tropical Convergence Zone (ITCZ) north of the equator is a consequence of a northwards heat transport across the equator by ocean circulation. Observations suggest that the hemispheric net radiative forcing of climate at the top of the atmosphere is almost perfectly symmetric about the equator, and so the total (atmosphere plus ocean) heat transport across the equator is small (order 0.2 PW northwards). Due to the Atlantic ocean’s meridional overturning circulation, however, the ocean carries significantly more heat northwards across the equator (order 0.4 PW) than does the coupled system. There are two primary consequences. First, atmospheric heat transport is southwards across the equator to compensate (0.2 PW southwards), resulting in the ITCZ being displaced north of the equator. Second, the atmosphere, and indeed the ocean, is slightly warmer (by perhaps 2 °C) in the northern hemisphere than in the southern hemisphere. This leads to the northern hemisphere emitting slightly more outgoing longwave radiation than the southern hemisphere by virtue of its relative warmth, supporting the small northward heat transport by the coupled system across the equator. To conclude, the coupled nature of the problem is illustrated through study of atmosphere–ocean–ice simulations in the idealized setting of an aquaplanet, resolving the key processes at work. Climatology; ITCZ; Ocean; Oceanography; Geophysics/Geodesy; Energy balance; Heat transport
Mason, Shannon; Jakob, Christian; Protat, Alain; Delanoë, JulienMason, S., C. Jakob, A. Protat, J. Delanoë, 2014: Characterizing Observed Midtopped Cloud Regimes Associated with Southern Ocean Shortwave Radiation Biases. J. Climate, 27(16), 6189-6203. doi: 10.1175/JCLI-D-14-00139.1. AbstractClouds strongly affect the absorption and reflection of shortwave and longwave radiation in the atmosphere. A key bias in climate models is related to excess absorbed shortwave radiation in the high-latitude Southern Ocean. Model evaluation studies attribute these biases in part to midtopped clouds, and observations confirm significant midtopped clouds in the zone of interest. However, it is not yet clear what cloud properties can be attributed to the deficit in modeled clouds. Present approaches using observed cloud regimes do not sufficiently differentiate between potentially distinct types of midtopped clouds and their meteorological contexts.This study presents a refined set of midtopped cloud subregimes for the high-latitude Southern Ocean, which are distinct in their dynamical and thermodynamic background states. Active satellite observations from CloudSat and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) are used to study the macrophysical structure and microphysical properties of the new cloud regimes. The subgrid-scale variability of cloud structure and microphysics is quantified within the cloud regimes by identifying representative physical cloud profiles at high resolution from the radar–lidar (DARDAR) cloud classification mask.The midtopped cloud subregimes distinguish between stratiform clouds under a high inversion and moderate subsidence; an optically thin cold-air advection cloud regime occurring under weak subsidence and including altostratus over low clouds; optically thick clouds with frequent deep structures under weak ascent and warm midlevel anomalies; and a midlevel convective cloud regime associated with strong ascent and warm advection. The new midtopped cloud regimes for the high-latitude Southern Ocean will provide a refined tool for model evaluation and the attribution of shortwave radiation biases to distinct cloud processes and properties. Model evaluation/performance; Cloud radiative effects; Southern Ocean; Radars/Radar observations; Lidars/Lidar observations; Climate classification/regimes
Mateos, D.; Antón, M.; Valenzuela, A.; Cazorla, A.; Olmo, F. J.; Alados-Arboledas, L.Mateos, D., M. Antón, A. Valenzuela, A. Cazorla, F. J. Olmo, L. Alados-Arboledas, 2014: Efficiency of clouds on shortwave radiation using experimental data. Applied Energy, 113, 1216-1219. doi: 10.1016/j.apenergy.2013.08.060. An extended data set of ground-based measurements of shortwave radiation, and cloud optical depth (COD) has been used to evaluate the surface cloud radiative forcing (CRF) in the shortwave range under overcast conditions (confirmed with sky images) at Granada, Spain. CRF varies in linear way with the logarithm of the COT showing a high correlation. The slope of the regression line (b) exhibits a clear dependence on solar zenith angle (SZA). The change in CRF per COD-unit is the cloud forcing efficiency (CFE), which is defined as the CRF derivate with respect to COD. In this case, CFE = b/COD. Experimental CFE varies between −160 W m−2 per COD-unit for SZA = 14° and COD = 1, and −0.3 W m−2 per COD-unit for SZA = 80° and COD = 50. The largest values of CFE are observed at low SZA and low COD. These empirical results are corroborated by radiative transfer simulations carried out by LibRadtran code. clouds; Cloud optical depth; Shortwave radiation; Cloud efficiency; Overcast conditions
Mateos, D.; Sanchez-Lorenzo, A.; Antón, M.; Cachorro, V. E.; Calbó, J.; Costa, M. J.; Torres, B.; Wild, M.Mateos, D., A. Sanchez-Lorenzo, M. Antón, V. E. Cachorro, J. Calbó, M. J. Costa, B. Torres, M. Wild, 2014: Quantifying the respective roles of aerosols and clouds in the strong brightening since the early 2000s over the Iberian Peninsula. Journal of Geophysical Research: Atmospheres, 119(17), 2014JD022076. doi: 10.1002/2014JD022076. The contribution of clouds and aerosols to the decadal variations of downward surface shortwave radiation (SSR) is a current controversial topic. This study proposes a method, which is based on surface-based SSR measurements, aerosol observations, and radiative transfer simulations (in cloud-free and cloud- and aerosol-free scenarios), to evaluate cloud-aerosol (CARE), cloud (CRE), and aerosol (ARE) radiative effects. This method is applied to quantify the role played by, separately, clouds and aerosols on the intense brightening of the SSR observed in the Iberian Peninsula. Clouds and Earth's Radiation Energy Budget System (CERES) and surface-based data exhibit an increase in SSR between 2003 and 2012, exceeding +10 W m−2 over this period for some areas of the peninsula. The calculations are performed for three surface-based sites: Barcelona and Valladolid (Spain), and Évora (Portugal). Ranges in monthly values of CARE, CRE, and ARE are (−80, −20), (−60, −20), and (−30, 0), respectively (in W m−2). The average trends for the analyzed period of CARE, CRE, and ARE are +7, +5, and +2 W m−2 per decade, respectively. Overall, three fourths of the SSR trend is explained by clouds, while the other one fourth is related to aerosol changes. The SSR trends explained by the clouds and aerosol radiative effects are in line with the observed reductions in total cloud cover and aerosol load (both at the surface and in the whole atmospheric column). Furthermore, the CRE values are compared against CERES data showing good agreement between both data series, although some discrepancies are observed in their trends. 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; 3359 Radiative processes; 7538 Solar irradiance; 0764 Energy balance; brightening period; cloud and aerosol radiative effects; downward shortwave radiation trend; total cloud cover and aerosol load
Mayer, Michael; Haimberger, Leopold; Balmaseda, Magdalena A.Mayer, M., L. Haimberger, M. A. Balmaseda, 2014: On the Energy Exchange between Tropical Ocean Basins Related to ENSO. J. Climate, 27(17), 6393-6403. doi: 10.1175/JCLI-D-14-00123.1. AbstractVast amounts of energy are exchanged between the ocean, atmosphere, and space in association with El Niño–Southern Oscillation (ENSO). This study examines energy budgets of all tropical (30°S–30°N) ocean basins and the atmosphere separately using different, largely independent oceanic and atmospheric reanalyses to depict anomalous energy flows associated with ENSO in a consistent framework. It is found that variability of area-averaged ocean heat content (OHC) in the tropical Pacific to a large extent is modulated by energy flow through the ocean surface. While redistribution of OHC within the tropical Pacific is an integral part of ENSO dynamics, variability of ocean heat transport out of the tropical Pacific region is found to be mostly small. Noteworthy contributions arise from the Indonesian Throughflow (ITF), which is anticorrelated with ENSO at a few months lag, and from anomalous oceanic poleward heat export during the La Niña events in 1999 and 2008. Regression analysis reveals that atmospheric energy transport and radiation at the top of the atmosphere (RadTOA) almost perfectly balance the OHC changes and ITF variability associated with ENSO. Only a small fraction of El Niño–related heat lost by the Pacific Ocean through anomalous air–sea fluxes is radiated to space immediately, whereas the major part of the energy is transported away by the atmosphere. Ample changes in tropical atmospheric circulation lead to enhanced surface fluxes and, consequently, to an increase of OHC in the tropical Atlantic and Indian Ocean that almost fully compensates for tropical Pacific OHC loss. This signature of energy redistribution is robust across the employed datasets for all three tropical ocean basins and explains the small ENSO signal in global mean RadTOA. tropics; ENSO; Energy transport; Atmosphere-ocean interaction; Pacific Ocean; Reanalysis data
McCoy, Daniel T.; Hartmann, Dennis L.; Grosvenor, Daniel P.McCoy, D. T., D. L. Hartmann, D. P. Grosvenor, 2014: Observed Southern Ocean Cloud Properties and Shortwave Reflection. Part I: Calculation of SW Flux from Observed Cloud Properties. J. Climate, 27(23), 8836-8857. doi: 10.1175/JCLI-D-14-00287.1. AbstractThe sensitivity of the reflection of shortwave radiation over the Southern Ocean to the cloud properties there is estimated using observations from a suite of passive and active satellite instruments in combination with radiative transfer modeling. A composite cloud property observational data description is constructed that consistently incorporates mean cloud liquid water content, ice water content, liquid and ice particle radius information, vertical structure, vertical overlap, and spatial aggregation of cloud water as measured by optical depth versus cloud-top pressure histograms. The observational datasets used are Moderate Resolution Imaging Spectroradiometer (MODIS) effective radius filtered to mitigate solar zenith angle bias, the Multiangle Imaging Spectroradiometer (MISR) cloud-top height–optical depth (CTH–OD) histogram, the liquid water path from the University of Wisconsin dataset, and ice cloud properties from CloudSat. This cloud database is used to compute reflected shortwave radiation as a function of month and location over the ocean from 40° to 60°S, which compares well with observations of reflected shortwave radiation. This calculation is then used to test the sensitivity of the seasonal variation of shortwave reflection to the observed seasonal variation of cloud properties. Effective radius decreases during the summer season, which results in an increase in reflected solar radiation of 4–8 W m−2 during summer compared to what would be reflected if the effective radius remained constant at its annual-mean value. Summertime increases in low cloud fraction similarly increase the summertime reflection of solar radiation by 9–11 W m−2. In-cloud liquid water path is less in summertime, causing the reflected solar radiation to be 1–4 W m−2 less. Remote sensing; climate change; Cloud radiative effects; Climate sensitivity; cloud forcing; Cloud water/phase
McCoy, Daniel T.; Hartmann, Dennis L.; Grosvenor, Daniel P.McCoy, D. T., D. L. Hartmann, D. P. Grosvenor, 2014: Observed Southern Ocean Cloud Properties and Shortwave Reflection. Part II: Phase Changes and Low Cloud Feedback. J. Climate, 27(23), 8858-8868. doi: 10.1175/JCLI-D-14-00288.1. AbstractClimate models produce an increase in cloud optical depth in midlatitudes associated with climate warming, but the magnitude of this increase and its impact on reflected solar radiation vary from model to model. Transition from ice to liquid in midlatitude clouds is thought to be one mechanism for producing increased cloud optical depth. Here observations of cloud properties are used from a suite of remote sensing instruments to estimate the effect of conversion of ice to liquid associated with warming on reflected solar radiation in the latitude band from 40° to 60°S. The calculated increase in upwelling shortwave radiation (SW↑) is found to be important and of comparable magnitude to the increase in SW↑ associated with warming-induced increases of optical depth in climate models. The region where the authors' estimate increases SW↑ extends farther equatorward than the region where optical depth increases with warming in models. This difference is likely caused by other mechanisms at work in the models but is also sensitive to the amount of ice present in climate models and its susceptibility to warming. Remote sensing; aerosols; Cloud radiative effects; Climate sensitivity; Cloud water/phase; Southern Ocean
Mills, Michael J.; Toon, Owen B.; Lee-Taylor, Julia; Robock, AlanMills, M. J., O. B. Toon, J. Lee-Taylor, A. Robock, 2014: Multidecadal global cooling and unprecedented ozone loss following a regional nuclear conflict. Earth's Future, 2(4), 2013EF000205. doi: 10.1002/2013EF000205. We present the first study of the global impacts of a regional nuclear war with an Earth system model including atmospheric chemistry, ocean dynamics, and interactive sea ice and land components. A limited, regional nuclear war between India and Pakistan in which each side detonates 50 15 kt weapons could produce about 5 Tg of black carbon (BC). This would self-loft to the stratosphere, where it would spread globally, producing a sudden drop in surface temperatures and intense heating of the stratosphere. Using the Community Earth System Model with the Whole Atmosphere Community Climate Model, we calculate an e-folding time of 8.7 years for stratospheric BC compared to 4–6.5 years for previous studies. Our calculations show that global ozone losses of 20%–50% over populated areas, levels unprecedented in human history, would accompany the coldest average surface temperatures in the last 1000 years. We calculate summer enhancements in UV indices of 30%–80% over midlatitudes, suggesting widespread damage to human health, agriculture, and terrestrial and aquatic ecosystems. Killing frosts would reduce growing seasons by 10–40 days per year for 5 years. Surface temperatures would be reduced for more than 25 years due to thermal inertia and albedo effects in the ocean and expanded sea ice. The combined cooling and enhanced UV would put significant pressures on global food supplies and could trigger a global nuclear famine. Knowledge of the impacts of 100 small nuclear weapons should motivate the elimination of more than 17,000 nuclear weapons that exist today. 0305 Aerosols and particles; 0340 Middle atmosphere: composition and chemistry; climate change; 1622 Earth system modeling; black carbon; 1605 Abrupt/rapid climate change; 3334 Middle atmosphere dynamics; atmospheric chemistry; global security; nuclear winter; stratospheric ozone
Muhlbauer, A.; McCoy, I. L.; Wood, R.Muhlbauer, A., I. L. McCoy, R. Wood, 2014: Climatology of stratocumulus cloud morphologies: microphysical properties and radiative effects. Atmos. Chem. Phys., 14(13), 6695-6716. doi: 10.5194/acp-14-6695-2014. An artificial neural network cloud classification scheme is combined with A-train observations to characterize the physical properties and radiative effects of marine low clouds based on their morphology and type of mesoscale cellular convection (MCC) on a global scale. The cloud morphological categories are (i) organized closed MCC, (ii) organized open MCC and (iii) cellular but disorganized MCC. Global distributions of the frequency of occurrence of MCC types show clear regional signatures. Organized closed and open MCCs are most frequently found in subtropical regions and in midlatitude storm tracks of both hemispheres. Cellular but disorganized MCC are the predominant type of marine low clouds in regions with warmer sea surface temperature such as in the tropics and trade wind zones. All MCC types exhibit a pronounced seasonal cycle. The physical properties of MCCs such as cloud fraction, radar reflectivity, drizzle rates and cloud top heights as well as the radiative effects of MCCs are found highly variable and a function of the type of MCC. On a global scale, the cloud fraction is largest for closed MCC with mean cloud fractions of about 90%, whereas cloud fractions of open and cellular but disorganized MCC are only about 51% and 40%, respectively. Probability density functions (PDFs) of cloud fractions are heavily skewed and exhibit modest regional variability. PDFs of column maximum radar reflectivities and inferred cloud base drizzle rates indicate fundamental differences in the cloud and precipitation characteristics of different MCC types. Similarly, the radiative effects of MCCs differ substantially from each other in terms of shortwave reflectance and transmissivity. These differences highlight the importance of low-cloud morphologies and their associated cloudiness on the shortwave cloud forcing.
Muri, H.; Kristjánsson, J. E.; Storelvmo, T.; Pfeffer, M. A.Muri, H., J. E. Kristjánsson, T. Storelvmo, M. A. Pfeffer, 2014: The climatic effects of modifying cirrus clouds in a climate engineering framework. Journal of Geophysical Research: Atmospheres, 119(7), 4174-4191. doi: 10.1002/2013JD021063. The climatic effects of climate engineering—or geoengineering—via cirrus cloud thinning are examined. Thinner cirrus clouds can allow more outgoing longwave radiation to escape to space, potentially cooling the climate. The cloud properties and climatic effects due to perturbing the ice crystal fall speed are investigated in a set of hemispheric scale sensitivity experiments with the Community Earth System Model. It is found that increasing the ice crystal fall speed, as an analog to cirrus cloud seeding, depletes high-level clouds and reduces the longwave cloud forcing. Deliberate depletion of cirrus clouds increases outgoing longwave radiation, reduces the upper tropospheric water vapor, and cools the climate. Global cirrus cloud thinning gave a net cloud forcing change of −1.55 W m−2 and a global annual mean temperature change of −0.94 K. Though there is negligible change in the global annual mean precipitation (−0.001 mm/d), the spatially nonhomogeneous forcing induces circulation changes and hence remote climate changes. Climate engineering the Southern Hemisphere only results in a northward shift of the Intertropical Convergence Zone and possible Sahelian drought alleviation, while targeting the Northern Hemisphere alone causes a greater cooling. It was found that targeting cirrus clouds everywhere outside of the tropics results in changes to the circulation and precipitation even in the nonclimate engineered regions, underscoring the risks of remote side effects and indeed the complexity of the climate system. 1610 Atmosphere; cirrus clouds; 3310 Clouds and cloud feedbacks; 1626 Global climate models; climate effects; Geoengineering
Naud, Catherine M.; Booth, James F.; Del Genio, Anthony D.Naud, C. M., J. F. Booth, A. D. Del Genio, 2014: Evaluation of ERA-Interim and MERRA Cloudiness in the Southern Ocean. J. Climate, 27(5), 2109-2124. doi: 10.1175/JCLI-D-13-00432.1.
Ningombam, Shantikumar S.; Bagare, S. P.; Sinha, N.; Singh, Rajendra B.; Srivastava, A. K.; Larson, E.; Kanawade, V. P.Ningombam, S. S., S. P. Bagare, N. Sinha, R. B. Singh, A. K. Srivastava, E. Larson, V. P. Kanawade, 2014: Characterization of aerosol optical properties over the high-altitude station Hanle, in the trans-Himalayan region. Atmospheric Research, 138, 308-323. doi: 10.1016/j.atmosres.2013.11.025. Optical properties of aerosols over Hanle (4500 m amsl) in the western Himalayas were studied using skyradiometer observations during October 2007 to December 2010. Yearly mean value of aerosol optical depth (AOD) at 500 nm is 0.042 ± 0.002, which demonstrates the pristine environment of the station. Seasonal mean AODs at 500 nm during summer, autumn, winter, and spring are 0.044 ± 0.002, 0.031 ± 0.001, 0.031 ± 0.001, and 0.061 ± 0.002, respectively. The relatively high AOD during spring, associated with an elevated aerosol layer observed from space, supports the hypothesis of middle-upper tropospheric heating during pre-monsoon period. Seasonal mean values of Angstrom exponent (α) estimated from linear regression method varied from minimum 0.65 (spring) to maximum 1.02 (autumn). Dominance of coarse mode aerosols at the site is thus evident during spring. Analysis of AOD profiles obtained from satellite data and airmass back trajectories superimposed with fire-counts data indicated the presence of desert–dust at the altitudes of 5 to 7 km amsl during the episodes of high AOD and low α. These trajectories indicated airmasses mostly coming from different desert regions, e.g in north-west Asia and Iran in the Middle east. Further, arrival of airmasses from the densely populated and industrialized Punjab and Haryana regions from the north-west of India apparently explains the relative contribution of transported anthropogenic aerosols over the station. Aerosol optical depth; Biomass-burning; Desert–dust; Skyradiometer; Trans-Himalayas
Noda, A. T.; Satoh, M.; Yamada, Y.; Kodama, C.; Seiki, T.Noda, A. T., M. Satoh, Y. Yamada, C. Kodama, T. Seiki, 2014: Responses of Tropical and Subtropical High-Cloud Statistics to Global Warming. J. Climate, 27(20), 7753-7768. doi: 10.1175/JCLI-D-14-00179.1. AbstractData from global high-resolution, nonhydrostatic simulations, covering a 1-yr period and with horizontal grid sizes of 7 and 14 km, were analyzed to evaluate the response of high cloud to global warming. The results indicate that, in a warmer atmosphere, high-cloud cover increases robustly and associated longwave (LW) cloud radiative forcing (CRF) increases on average. To develop a better understanding of high-cloud responses to climate change, the geographical distribution of high-cloud size obtained from the model was analyzed and compared with observations. In warmer atmospheres, the contribution per cloud to CRF decreases for both the LW and shortwave (SW) components. However, because of significant increases in the numbers of high clouds in almost all cloud size categories, the magnitude of both LW and SW CRF increases in the simulations. In particular, the contribution from an increase in the number of smaller clouds has more effect on the CRF change. It was also found that the ice and liquid water paths decrease in smaller clouds and that particularly the former contributes to reduced LW CRF per high cloud. clouds; Climatology; Cloud cover; General circulation models; Cloud radiative effects; deep convection
Oreopoulos, Lazaros; Cho, Nayeong; Lee, Dongmin; Kato, Seiji; Huffman, George J.Oreopoulos, L., N. Cho, D. Lee, S. Kato, G. J. Huffman, 2014: An examination of the nature of global MODIS cloud regimes. Journal of Geophysical Research: Atmospheres, 119(13), 2013JD021409. doi: 10.1002/2013JD021409. We introduce global cloud regimes (previously also referred to as “weather states”) derived from cloud retrievals that use measurements by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard the Aqua and Terra satellites. The regimes are obtained by applying clustering analysis on joint histograms of retrieved cloud top pressure and cloud optical thickness. By employing a compositing approach on data sets from satellites and other sources, we examine regime structural and thermodynamical characteristics. We establish that the MODIS cloud regimes tend to form in distinct dynamical and thermodynamical environments and have diverse profiles of cloud fraction and water content. When compositing radiative fluxes from the Clouds and the Earth's Radiant Energy System instrument and surface precipitation from the Global Precipitation Climatology Project, we find that regimes with a radiative warming effect on the atmosphere also produce the largest implied latent heat. Taken as a whole, the results of the study corroborate the usefulness of the cloud regime concept, reaffirm the fundamental nature of the regimes as appropriate building blocks for cloud system classification, clarify their association with standard cloud types, and underscore their distinct radiative and hydrological signatures. Remote sensing; cloud modeling; 3337 Global climate models; 3310 Clouds and cloud feedbacks; MODIS; 3360 Remote sensing; cloud regimes
Painemal, David; Kato, Seiji; Minnis, PatrickPainemal, D., S. Kato, P. Minnis, 2014: Boundary layer regulation in the southeast Atlantic cloud microphysics during the biomass burning season as seen by the A-train satellite constellation. Journal of Geophysical Research: Atmospheres, 119(19), 2014JD022182. doi: 10.1002/2014JD022182. Solar radiation absorption by biomass burning aerosols has a strong warming effect over the southeast Atlantic. Interactions between the overlying smoke aerosols and low-level cloud microphysics and the subsequent albedo perturbation are, however, generally ignored in biomass burning radiative assessments. In this study, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) are combined with Aqua satellite observations from Moderate Resolution Imaging Spectroradiometer (MODIS), Advanced Microwave Scanning Radiometer–EOS (AMSR-E), and Clouds and the Earth's Radiant Energy System (CERES) to assess the effect of variations in the boundary layer height and the separation distance between the cloud and aerosol layers on the cloud microphysics. The merged data analyzed at a daily temporal resolution suggest that overlying smoke aerosols modify cloud properties by decreasing cloud droplet size despite an increase in the cloud liquid water as boundary layer deepens, north of 5°S. These changes are controlled by the proximity of the aerosol layer to the cloud top rather than increases in the column aerosol load. The correlations are unlikely driven by meteorological factors, as three predictors of cloud variability, lower tropospheric stability, surface winds, and mixing ratio suggest that cloud effective radius, cloud top height, and liquid water path should correlate positively. Because cloud effective radius anticorrelates with cloud liquid water over the region with large microphysical changes—north of 5°S—the overall radiative consequence at the top of the atmosphere is a strong albedo susceptibility, equivalent to a 3% albedo increase due to a 10% decrease in cloud effective radius. This albedo enhancement partially offsets the aerosol solar absorption. Our analysis emphasizes the importance of accounting for the indirect effect of smoke aerosols in the cloud microphysics when estimating the radiative impact of the biomass burning at the top of the atmosphere. 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; Cloud microphysics; Biomass burning; Radiative response; marine boundary layer; Southeast Atlantic
Park, SungsuPark, S., 2014: A Unified Convection Scheme (UNICON). Part II: Simulation. J. Atmos. Sci., 71(11), 3931-3973. doi: 10.1175/JAS-D-13-0234.1. AbstractA unified convection scheme (UNICON) is implemented into the Community Atmosphere Model, version 5 (CAM5), and tested in single-column and global simulations forced by observed sea surface temperature. Compared to CAM5, UNICON substantially improves the single-column simulations of stratocumulus-to-cumulus transition and shallow and deep convection cases. The global performance of UNICON is similar to CAM5 with a relative spatiotemporal root-mean-square error (RMSE) of 0.777 (0.755 in CAM5) against the earlier version of the model (CCSM3.5). The notable improvements in the UNICON-simulated climatologies over CAM5 are seasonal precipitation patterns (i.e., monsoon) over the western Pacific and South Asia, reduced biases of cloud radiative forcing in the tropical deep convection regions, aerosol optical depth in the tropical and subtropical regions, and cumulus fraction and in-cumulus condensate. One notable degradation is that UNICON simulates warmer near-surface air temperature over the United States during summer.In addition to the climatology, UNICON significantly improves the simulation of the diurnal cycle of precipitation and the Madden–Julian oscillation (MJO). The surface precipitation simulated by UNICON is a maximum in the late afternoon (early afternoon in CAM5) over the summer continents and in the early morning (predawn in CAM5) over the ocean with a fairly realistic amplitude of the diurnal cycle. Sensitivity simulations indicate that the key for successful MJO simulation in UNICON is a seamless parameterization of the updraft plume dilution rate as convection evolves from shallow to deep convection. The mesoscale perturbation of the vertical velocity and the thermodynamic scalars of convective updrafts is an additional requirement for simulating the observed diurnal cycle of precipitation. climate models; Cloud parameterizations; Madden-Julian Oscillation; convective parameterization; Cumulus clouds; Diurnal effects
Park, Sungsu; Bretherton, Christopher S.; Rasch, Philip J.Park, S., C. S. Bretherton, P. J. Rasch, 2014: Integrating Cloud Processes in the Community Atmosphere Model, Version 5. J. Climate, 27(18), 6821-6856. doi: 10.1175/JCLI-D-14-00087.1. AbstractThis paper provides a description of the integrated representation for the cloud processes in the Community Atmosphere Model, version 5 (CAM5). CAM5 cloud parameterizations add the following unique characteristics to previous versions: 1) a cloud macrophysical structure with horizontally nonoverlapped deep cumulus, shallow cumulus, and stratus in each grid layer, where each of which has its own cloud fraction, and mass and number concentrations for cloud liquid droplets and ice crystals; 2) stratus–radiation–turbulence interactions that allow CAM5 to simulate marine stratocumulus solely from grid-mean relative humidity without relying on a stability-based empirical formula; 3) prognostic treatment of the number concentrations of stratus liquid droplets and ice crystals, with activated aerosols and detrained in-cumulus condensates as the main sources and with evaporation, sedimentation, and precipitation of stratus condensate as the main sinks; and 4) radiatively active cumulus and snow. By imposing consistency between diagnosed stratus fraction and prognosed stratus condensate, unrealistically empty or highly dense stratus is avoided in CAM5. Because of the activation of the prognostic aerosols and the parameterizations of the radiation and stratiform precipitation production as a function of the cloud droplet size, CAM5 simulates various aerosol indirect effects as well as the direct effects: that is, aerosols affect both the radiation budget and the hydrological cycle.Detailed analysis of various simulations indicates that CAM5 improves upon CAM3/CAM4 in global performance as well as in physical formulation. However, several problems are also identified in CAM5, which can be attributed to deficient regional tuning, inconsistency between various physics parameterizations, and incomplete treatment of physics. Efforts are continuing to further improve CAM5. clouds; Cloud cover; climate models; Cloud parameterizations; parameterization
Patadia, Falguni; Christopher, Sundar A.Patadia, F., S. A. Christopher, 2014: Assessment of smoke shortwave radiative forcing using empirical angular distribution models. Remote Sensing of Environment, 140, 233-240. doi: 10.1016/j.rse.2013.08.034. The Clouds and the Earth's Radiant Energy System (CERES) data has been used by several studies to calculate the top of atmosphere (TOA) shortwave aerosol radiative forcing (SWARF) of biomass burning aerosols over land. However, the current CERES angular distribution models that are used to convert measured TOA radiances to fluxes are not characterized by aerosols. Using our newly developed empirical angular models for smoke aerosols we calculate the SWARF over South America for eight years (2000–2008) during the biomass burning season. Our results indicate that when compared to our new angular distribution model-derived values, the instantaneous SWARF is underestimated by the CERES data by nearly 3.3 Wm− 2. Our studies indicate that it is feasible to develop angular models using empirical methods that can then be used to reduce uncertainties in aerosol radiative forcing calculations. More importantly, empirically-based methods for calculating radiative forcing can serve as a benchmark for modeling studies. aerosol; radiative forcing; climate; Biomass burning
Phojanamongkolkij, Nipa; Kato, Seiji; Wielicki, Bruce A.; Taylor, Patrick C.; Mlynczak, Martin G.Phojanamongkolkij, N., S. Kato, B. A. Wielicki, P. C. Taylor, M. G. Mlynczak, 2014: A Comparison of Climate Signal Trend Detection Uncertainty Analysis Methods. J. Climate, 27(9), 3363-3376. doi: 10.1175/JCLI-D-13-00400.1. AbstractTwo climate signal trend analysis methods are the focus of this paper. The uncertainty of trend estimate from these two methods is investigated using Monte Carlo simulation. Several theoretically and randomly generated series of white noise, first-order autoregressive and second-order autoregressive, are explored. The choice of method that is most appropriate for the time series of interest depends upon the autocorrelation structure of the series. If the structure has its autocorrelation coefficients decreased with increasing lags (i.e., an exponential decay pattern), then the method of Weatherhead et al. is adequate. If the structure exhibits a decreasing sinusoid pattern of coefficient with lags (or a damped sinusoid pattern) or a mixture of both exponential decay and damped sinusoid patterns, then the method of Leroy et al. is recommended. The two methods are then applied to the time series of monthly and globally averaged top-of-the-atmosphere (TOA) irradiances for the reflected solar shortwave and emitted longwave regions, using radiance observations made by Clouds and the Earth’s Radiant Energy System (CERES) instruments during March 2000 through June 2011. Examination of the autocorrelation structures indicates that the reflected shortwave region has an exponential decay pattern, while the longwave region has a mixture of exponential decay and damped sinusoid patterns. Therefore, it is recommended that the method of Weatherhead et al. is used for the series of reflected shortwave irradiances and that the method of Leroy et al. is used for the series of emitted longwave irradiances. Model comparison; Climate records; Forecasting techniques; Statistical forecasting
Pistone, Kristina; Eisenman, Ian; Ramanathan, V.Pistone, K., I. Eisenman, V. Ramanathan, 2014: Observational determination of albedo decrease caused by vanishing Arctic sea ice. Proceedings of the National Academy of Sciences, 111(9), 3322-3326. doi: 10.1073/pnas.1318201111. The decline of Arctic sea ice has been documented in over 30 y of satellite passive microwave observations. The resulting darkening of the Arctic and its amplification of global warming was hypothesized almost 50 y ago but has yet to be verified with direct observations. This study uses satellite radiation budget measurements along with satellite microwave sea ice data to document the Arctic-wide decrease in planetary albedo and its amplifying effect on the warming. The analysis reveals a striking relationship between planetary albedo and sea ice cover, quantities inferred from two independent satellite instruments. We find that the Arctic planetary albedo has decreased from 0.52 to 0.48 between 1979 and 2011, corresponding to an additional 6.4 ± 0.9 W/m2 of solar energy input into the Arctic Ocean region since 1979. Averaged over the globe, this albedo decrease corresponds to a forcing that is 25% as large as that due to the change in CO2 during this period, considerably larger than expectations from models and other less direct recent estimates. Changes in cloudiness appear to play a negligible role in observed Arctic darkening, thus reducing the possibility of Arctic cloud albedo feedbacks mitigating future Arctic warming.
Protat, A.; Young, S. A.; McFarlane, S. A.; L’Ecuyer, T.; Mace, G. G.; Comstock, J. M.; Long, C. N.; Berry, E.; Delanoë, J.Protat, A., S. A. Young, S. A. McFarlane, T. L’Ecuyer, G. G. Mace, J. M. Comstock, C. N. Long, E. Berry, J. Delanoë, 2014: Reconciling Ground-Based and Space-Based Estimates of the Frequency of Occurrence and Radiative Effect of Clouds around Darwin, Australia. J. Appl. Meteor. Climatol., 53(2), 456-478. doi: 10.1175/JAMC-D-13-072.1.
Qu, Xin; Hall, AlexQu, X., A. Hall, 2014: On the persistent spread in snow-albedo feedback. Climate Dynamics, 42(1-2), 69-81. doi: 10.1007/s00382-013-1774-0. Snow-albedo feedback (SAF) is examined in 25 climate change simulations participating in the Coupled Model Intercomparison Project version 5 (CMIP5). SAF behavior is compared to the feedback’s behavior in the previous (CMIP3) generation of global models. SAF strength exhibits a fivefold spread across CMIP5 models, ranging from 0.03 to 0.16 W m−2 K−1 (ensemble-mean = 0.08 W m−2 K−1). This accounts for much of the spread in 21st century warming of Northern Hemisphere land masses, and is very similar to the spread found in CMIP3 models. As with the CMIP3 models, there is a high degree of correspondence between the magnitudes of seasonal cycle and climate change versions of the feedback. Here we also show that their geographical footprint is similar. The ensemble-mean SAF strength is close to an observed estimate of the real climate’s seasonal cycle feedback strength. SAF strength is strongly correlated with the climatological surface albedo when the ground is covered by snow. The inter-model variation in this quantity is surprisingly large, ranging from 0.39 to 0.75. Models with large surface albedo when these regions are snow-covered will also have a large surface albedo contrast between snow-covered and snow-free regions, and therefore a correspondingly large SAF. Widely-varying treatments of vegetation masking of snow-covered surfaces are probably responsible for the spread in surface albedo where snow occurs, and the persistent spread in SAF in global climate models. Climatology; Seasonal cycle; Oceanography; Geophysics/Geodesy; Snow-albedo feedback; Spread
Radley, Claire; Fueglistaler, Stephan; Donner, LeoRadley, C., S. Fueglistaler, L. Donner, 2014: Cloud and Radiative Balance Changes in Response to ENSO in Observations and Models. J. Climate, 27(9), 3100-3113. doi: 10.1175/JCLI-D-13-00338.1. AbstractThe authors use observations and four GFDL AGCMs to analyze the relation between variations in spatial patterns and area-averaged quantities in the top-of-the-atmosphere radiative fluxes, cloud amount, and precipitation related to El Niño over the period 1979–2008. El Niño is associated with an increase in tropical average sea surface temperature of order +0.1 K (with a maxima of +0.5 K), large local anomalies of +2 K (maxima +6 K), and tropical tropospheric warming of +0.5 K (maxima +1 K). The authors find that model-to-observation biases in the base state translate into corresponding biases in anomalies in response to El Niño. The pattern and amplitude of model biases in reflected shortwave (SW) and outgoing longwave radiation (OLR) follows expectations based on their biases in cloud amount: models with a positive cloud amount bias, compared to observations, have too strong local responses to El Niño in cloud amount, SW, OLR, and precipitation.Tropical average OLR increases in response to El Niño in observations and models [correlation coefficients (r) with Niño-3.4 index in the range 0.4–0.6]. Weaker correlations are found for SW (r: −0.6 to 0), cloud amount (r: −0.2 to +0.1), and precipitation (r: −0.2 to 0). Compositing El Niño events over the period 2001–07 yields similar results. These results are consistent with El Niño periods being warmer due to a heat pulse from the ocean, and a weak response in clouds and their radiative effect. These weak responses occur despite a large rearrangement in the spatial structure of the tropical circulation, and despite substantial differences in the mean state of observations and models. Radiative fluxes; Cloud cover; climate models; ENSO; Climate variability
Roberts, Y. L.; Pilewskie, P.; Feldman, D. R.; Kindel, B. C.; Collins, W. D.Roberts, Y. L., P. Pilewskie, D. R. Feldman, B. C. Kindel, W. D. Collins, 2014: Temporal variability of observed and simulated hyperspectral reflectance. Journal of Geophysical Research: Atmospheres, 119(17), 10,262-10,280. doi: 10.1002/2014JD021566. Multivariate analysis techniques were used to quantify and compare the spectral and temporal variability of observed and simulated shortwave hyperspectral Earth reflectance. The observed reflectances were measured by the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instrument between 2002 and 2010. The simulated reflectances were calculated using climate Observing System Simulation Experiments (OSSEs), which used two Intergovernmental Panel on Climate Change AR4 scenarios (constant CO2 and A2 emission) to drive Moderate Resolution Atmospheric Transmission simulations. Principal component (PC) spectral shapes and time series exhibited evidence of physical variables including cloud reflectance, vegetation and desert albedo, and water vapor absorption. Comparing the temporal variability of the OSSE-simulated and SCIAMACHY-measured hyperspectral reflectance showed that their Intertropical Convergence Zone-like Southern Hemisphere (SH) tropical PC1 ocean time series had a 90° phase difference. The observed and simulated PC intersection quantified their similarity and directly compared their temporal variability. The intersection showed that despite the similar spectral variability, the temporal variability of the dominant PCs differed as in, for example, the 90° phase difference between the SH tropical intersection PC1s. Principal component analysis of OSSE reflectance demonstrated that the spectral and centennial variability of the two cases differed. The A2 PC time series, unlike the constant CO2 time series, exhibited centennial secular trends. Singular spectrum analysis isolated the A2 secular trends. The A2 OSSE PC1 and PC4 secular trends matched those in aerosol optical depth and total column precipitable water, respectively. This illustrates that time series of hyperspectral reflectance may be used to identify and attribute secular climate trends with a sufficiently long measurement record and high instrument accuracy. 3359 Radiative processes; reflectance; 3307 Boundary layer processes; Variability; hyperspsectral
Roithmayr, C. M.; Lukashin, C.; Speth, P. W.; Young, D. F.; Wielicki, B. A.; Thome, K. J.; Kopp, G.Roithmayr, C. M., C. Lukashin, P. W. Speth, D. F. Young, B. A. Wielicki, K. J. Thome, G. Kopp, 2014: Opportunities to Intercalibrate Radiometric Sensors from International Space Station. J. Atmos. Oceanic Technol., 31(4), 890-902. doi: 10.1175/JTECH-D-13-00163.1. AbstractHighly accurate measurements of Earth’s thermal infrared and reflected solar radiation are required for detecting and predicting long-term climate change. Consideration is given to the concept of using the International Space Station to test instruments and techniques that would eventually be used on a dedicated mission, such as the Climate Absolute Radiance and Refractivity Observatory (CLARREO). In particular, a quantitative investigation is performed to determine whether it is possible to use measurements obtained with a highly accurate (0.3%, with 95% confidence) reflected solar radiation spectrometer to calibrate similar, less accurate instruments in other low Earth orbits. Estimates of numbers of samples useful for intercalibration are made with the aid of yearlong simulations of orbital motion. Results of this study support the conclusion that the International Space Station orbit is ideally suited for the purpose of intercalibration between spaceborne sensors. Remote sensing; satellite observations; Radiances; Shortwave radiation; Sampling; Instrumentation/sensors
Roithmayr, C.M.; Lukashin, C.; Speth, P.W.; Kopp, G.; Thome, K.; Wielicki, B.A.; Young, D.F.Roithmayr, C., C. Lukashin, P. Speth, G. Kopp, K. Thome, B. Wielicki, D. Young, 2014: CLARREO Approach for Reference Intercalibration of Reflected Solar Sensors: On-Orbit Data Matching and Sampling. IEEE Transactions on Geoscience and Remote Sensing, 52(10), 6762-6774. doi: 10.1109/TGRS.2014.2302397. The implementation of the Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission was recommended by the National Research Council in 2007 to provide an on-orbit intercalibration standard with accuracy of 0.3% (k = 2) for relevant Earth observing sensors. The goal of reference intercalibration, as established in the Decadal Survey, is to enable rigorous high-accuracy observations of critical climate change parameters, including reflected broadband radiation [Clouds and Earth's Radiant Energy System (CERES)], cloud properties [Visible Infrared Imaging Radiometer Suite (VIIRS)], and changes in surface albedo, including snow and ice albedo feedback. In this paper, we describe the CLARREO approach for performing intercalibration on orbit in the reflected solar (RS) wavelength domain. It is based on providing highly accurate spectral reflectance and reflected radiance measurements from the CLARREO Reflected Solar Spectrometer (RSS) to establish an on-orbit reference for existing sensors, namely, CERES and VIIRS on Joint Polar Satellite System satellites, Advanced Very High Resolution Radiometer and follow-on imagers on MetOp, Landsat imagers, and imagers on geostationary platforms. One of two fundamental CLARREO mission goals is to provide sufficient sampling of high-accuracy observations that are matched in time, space, and viewing angles with measurements made by existing instruments, to a degree that overcomes the random error sources from imperfect data matching and instrument noise. The data matching is achieved through CLARREO RSS pointing operations on orbit that align its line of sight with the intercalibrated sensor. These operations must be planned in advance; therefore, intercalibration events must be predicted by orbital modeling. If two competing opportunities are identified, one target sensor must be given priority over the other. The intercalibration method is to monitor changes in targeted sensor response function parameters: effective - ffset, gain, nonlinearity, optics spectral response, and sensitivity to polarization. In this paper, we use existing satellite data and orbital simulation methods to determine mission requirements for CLARREO, its instrument pointing ability, methodology, and needed intercalibration sampling and data matching for accurate intercalibration of RS radiation sensors on orbit. We conclude that with the CLARREO RSS in a polar 90° inclination orbit at a 609-km altitude, estimated intercalibration sampling will limit the uncertainty contribution from data matching noise to 0.3% (k = 2) over the climate autocorrelation time period. The developed orbital modeling and intercalibration event prediction will serve as a framework for future mission operations. calibration; clouds; Earth; Extraterrestrial measurements; infrared imaging; Remote sensing; atmospheric radiation; atmospheric techniques; CERES; Instruments; radiometers; Space vehicles; radiometry; albedo; surface albedo; cloud properties; Climatology; atmospheric spectra; Orbits; intercalibration; Sensors; geophysical image processing; Clouds and Earth's Radiant Energy System; Advanced Very High Resolution Radiometer and follow-on imagers; altitude 609 km; CLARREO approach; CLARREO Reflected Solar Spectrometer; Climate Absolute Radiance and Refractivity Observatory; climate autocorrelation time period; critical climate change parameters; Data sampling; Decadal Survey; Earth observing sensors; geostationary platforms; ice albedo feedback; image matching; imperfect data matching; instrument noise; intercalibrated sensor; intercalibration events; Joint Polar Satellite System satellites; Landsat imagers; MetOp; on-orbit data matching; on-orbit intercalibration standard; on-orbit sampli
Rosenfeld, Daniel; Andreae, Meinrat O.; Asmi, Ari; Chin, Mian; de Leeuw, Gerrit; Donovan, David P.; Kahn, Ralph; Kinne, Stefan; Kivekäs, Niku; Kulmala, Markku; Lau, William; Schmidt, K. Sebastian; Suni, Tanja; Wagner, Thomas; Wild, Martin; Quaas, JohannesRosenfeld, D., M. O. Andreae, A. Asmi, M. Chin, G. de Leeuw, D. P. Donovan, R. Kahn, S. Kinne, N. Kivekäs, M. Kulmala, W. Lau, K. S. Schmidt, T. Suni, T. Wagner, M. Wild, J. Quaas, 2014: Global observations of aerosol-cloud-precipitation-climate interactions. Reviews of Geophysics, 52(4), 2013RG000441. doi: 10.1002/2013RG000441. Cloud drop condensation nuclei (CCN) and ice nuclei (IN) particles determine to a large extent cloud microstructure and, consequently, cloud albedo and the dynamic response of clouds to aerosol-induced changes to precipitation. This can modify the reflected solar radiation and the thermal radiation emitted to space. Measurements of tropospheric CCN and IN over large areas have not been possible and can be only roughly approximated from satellite-sensor-based estimates of optical properties of aerosols. Our lack of ability to measure both CCN and cloud updrafts precludes disentangling the effects of meteorology from those of aerosols and represents the largest component in our uncertainty in anthropogenic climate forcing. Ways to improve the retrieval accuracy include multiangle and multipolarimetric passive measurements of the optical signal and multispectral lidar polarimetric measurements. Indirect methods include proxies of trace gases, as retrieved by hyperspectral sensors. Perhaps the most promising emerging direction is retrieving the CCN properties by simultaneously retrieving convective cloud drop number concentrations and updraft speeds, which amounts to using clouds as natural CCN chambers. These satellite observations have to be constrained by in situ observations of aerosol-cloud-precipitation-climate (ACPC) interactions, which in turn constrain a hierarchy of model simulations of ACPC. Since the essence of a general circulation model is an accurate quantification of the energy and mass fluxes in all forms between the surface, atmosphere and outer space, a route to progress is proposed here in the form of a series of box flux closure experiments in the various climate regimes. A roadmap is provided for quantifying the ACPC interactions and thereby reducing the uncertainty in anthropogenic climate forcing. Remote sensing; climate change; 3311 Clouds and aerosols; cloud aerosol interactions
Rosenzweig, Cynthia; Horton, Radley M.; Bader, Daniel A.; Brown, Molly E.; DeYoung, Russell; Dominguez, Olga; Fellows, Merrilee; Friedl, Lawrence; Graham, William; Hall, Carlton; Higuchi, Sam; Iraci, Laura; Jedlovec, Gary; Kaye, Jack; Loewenstein, Max; Mace, Thomas; Milesi, Cristina; Patzert, William; Stackhouse, Paul W.; Toufectis, KimRosenzweig, C., R. M. Horton, D. A. Bader, M. E. Brown, R. DeYoung, O. Dominguez, M. Fellows, L. Friedl, W. Graham, C. Hall, S. Higuchi, L. Iraci, G. Jedlovec, J. Kaye, M. Loewenstein, T. Mace, C. Milesi, W. Patzert, P. W. Stackhouse, K. Toufectis, 2014: Enhancing Climate Resilience at NASA Centers: A Collaboration between Science and Stewardship. Bull. Amer. Meteor. Soc., 95(9), 1351-1363. doi: 10.1175/BAMS-D-12-00169.1. A partnership between Earth scientists and institutional stewards is helping the National Aeronautics and Space Administration (NASA) prepare for a changing climate and growing climate-related vulnerabilities. An important part of this partnership is an agency-wide Climate Adaptation Science Investigator (CASI) Workgroup. CASI has thus far initiated 1) local workshops to introduce and improve planning for climate risks, 2) analysis of climate data and projections for each NASA Center, 3) climate impact and adaptation toolsets, and 4) Center-specific research and engagement. Partnering scientists with managers aligns climate expertise with operations, leveraging research capabilities to improve decision-making and to tailor risk assessment at the local level. NASA has begun to institutionalize this ongoing process for climate risk management across the entire agency, and specific adaptation strategies are already being implemented. A case study from Kennedy Space Center illustrates the CASI and workshop process, highlighting the need to protect launch infrastructure of strategic importance to the United States, as well as critical natural habitat. Unique research capabilities and a culture of risk management at NASA may offer a pathway for other organizations facing climate risks, promoting their resilience as part of community, regional, and national strategies.
Rutan, David A.; Smith, G. Louis; Wong, TakmengRutan, D. A., G. L. Smith, T. Wong, 2014: Diurnal Variations of Albedo Retrieved from Earth Radiation Budget Experiment Measurements. J. Appl. Meteor. Climatol., 53(12), 2747-2760. doi: 10.1175/JAMC-D-13-0119.1. AbstractFive years of measurements from the Earth Radiation Budget Satellite (ERBS) have been analyzed to define the diurnal cycle of albedo from 55°N to 55°S. The ERBS precesses through all local times every 72 days so as to provide data regarding the diurnal cycles for Earth radiation. Albedo together with insolation at the top of the atmosphere is used to compute the heating of the Earth–atmosphere system; thus its diurnal cycle is important in the energetics of the climate system. A principal component (PC) analysis of the diurnal variation of top-of-atmosphere albedo using these data is presented. The analysis is done separately for ocean and land because of the marked differences of cloud behavior over ocean and over land. For ocean, 90%–92% of the variance in the diurnal cycle is described by a single component; for land, the first PC accounts for 83%–89% of the variance. Some of the variation is due to the increase of albedo with increasing solar zenith angle, which is taken into account in the ERBS data processing by a directional model, and some is due to the diurnal cycle of cloudiness. The second PC describes 2%–4% of the variance for ocean and 5% for land, and it is primarily due to variations of cloudiness throughout the day, which are asymmetric about noon. These terms show the response of the atmosphere to the cycle of solar heating. The third PC for ocean is a two-peaked curve, and the associated map shows high values in cloudy regions. Diurnal effects
Santer, Benjamin D.; Bonfils, Céline; Painter, Jeffrey F.; Zelinka, Mark D.; Mears, Carl; Solomon, Susan; Schmidt, Gavin A.; Fyfe, John C.; Cole, Jason N. S.; Nazarenko, Larissa; Taylor, Karl E.; Wentz, Frank J.Santer, B. D., C. Bonfils, J. F. Painter, M. D. Zelinka, C. Mears, S. Solomon, G. A. Schmidt, J. C. Fyfe, J. N. S. Cole, L. Nazarenko, K. E. Taylor, F. J. Wentz, 2014: Volcanic contribution to decadal changes in tropospheric temperature. Nature Geoscience, 7(3), 185-189. doi: 10.1038/ngeo2098. Despite continued growth in atmospheric levels of greenhouse gases, global mean surface and tropospheric temperatures have shown slower warming since 1998 than previously. Possible explanations for the slow-down include internal climate variability, external cooling influences and observational errors. Several recent modelling studies have examined the contribution of early twenty-first-century volcanic eruptions to the muted surface warming. Here we present a detailed analysis of the impact of recent volcanic forcing on tropospheric temperature, based on observations as well as climate model simulations. We identify statistically significant correlations between observations of stratospheric aerosol optical depth and satellite-based estimates of both tropospheric temperature and short-wave fluxes at the top of the atmosphere. We show that climate model simulations without the effects of early twenty-first-century volcanic eruptions overestimate the tropospheric warming observed since 1998. In two simulations with more realistic volcanic influences following the 1991 Pinatubo eruption, differences between simulated and observed tropospheric temperature trends over the period 1998 to 2012 are up to 15% smaller, with large uncertainties in the magnitude of the effect. To reduce these uncertainties, better observations of eruption-specific properties of volcanic aerosols are needed, as well as improved representation of these eruption-specific properties in climate model simulations.
Schmidt, Gavin A.; Kelley, Max; Nazarenko, Larissa; Ruedy, Reto; Russell, Gary L.; Aleinov, Igor; Bauer, Mike; Bauer, Susanne E.; Bhat, Maharaj K.; Bleck, Rainer; Canuto, Vittorio; Chen, Yong-Hua; Cheng, Ye; Clune, Thomas L.; Del Genio, Anthony; de Fainchtein, Rosalinda; Faluvegi, Greg; Hansen, James E.; Healy, Richard J.; Kiang, Nancy Y.; Koch, Dorothy; Lacis, Andy A.; LeGrande, Allegra N.; Lerner, Jean; Lo, Ken K.; Matthews, Elaine E.; Menon, Surabi; Miller, Ron L.; Oinas, Valdar; Oloso, Amidu O.; Perlwitz, Jan P.; Puma, Michael J.; Putman, William M.; Rind, David; Romanou, Anastasia; Sato, Makiko; Shindell, Drew T.; Sun, Shan; Syed, Rahman A.; Tausnev, Nick; Tsigaridis, Kostas; Unger, Nadine; Voulgarakis, Apostolos; Yao, Mao-Sung; Zhang, JinlunSchmidt, G. A., M. Kelley, L. Nazarenko, R. Ruedy, G. L. Russell, I. Aleinov, M. Bauer, S. E. Bauer, M. K. Bhat, R. Bleck, V. Canuto, Y. Chen, Y. Cheng, T. L. Clune, A. Del Genio, R. de Fainchtein, G. Faluvegi, J. E. Hansen, R. J. Healy, N. Y. Kiang, D. Koch, A. A. Lacis, A. N. LeGrande, J. Lerner, K. K. Lo, E. E. Matthews, S. Menon, R. L. Miller, V. Oinas, A. O. Oloso, J. P. Perlwitz, M. J. Puma, W. M. Putman, D. Rind, A. Romanou, M. Sato, D. T. Shindell, S. Sun, R. A. Syed, N. Tausnev, K. Tsigaridis, N. Unger, A. Voulgarakis, M. Yao, J. Zhang, 2014: Configuration and assessment of the GISS ModelE2 contributions to the CMIP5 archive. Journal of Advances in Modeling Earth Systems, 6(1), 141-184. doi: 10.1002/2013MS000265. We present a description of the ModelE2 version of the Goddard Institute for Space Studies (GISS) General Circulation Model (GCM) and the configurations used in the simulations performed for the Coupled Model Intercomparison Project Phase 5 (CMIP5). We use six variations related to the treatment of the atmospheric composition, the calculation of aerosol indirect effects, and ocean model component. Specifically, we test the difference between atmospheric models that have noninteractive composition, where radiatively important aerosols and ozone are prescribed from precomputed decadal averages, and interactive versions where atmospheric chemistry and aerosols are calculated given decadally varying emissions. The impact of the first aerosol indirect effect on clouds is either specified using a simple tuning, or parameterized using a cloud microphysics scheme. We also use two dynamic ocean components: the Russell and HYbrid Coordinate Ocean Model (HYCOM) which differ significantly in their basic formulations and grid. Results are presented for the climatological means over the satellite era (1980–2004) taken from transient simulations starting from the preindustrial (1850) driven by estimates of appropriate forcings over the 20th Century. Differences in base climate and variability related to the choice of ocean model are large, indicating an important structural uncertainty. The impact of interactive atmospheric composition on the climatology is relatively small except in regions such as the lower stratosphere, where ozone plays an important role, and the tropics, where aerosol changes affect the hydrological cycle and cloud cover. While key improvements over previous versions of the model are evident, these are not uniform across all metrics. 3337 Global climate models; Climatology; climate model; 1627 Coupled models of the climate system; 1626 Global climate models; 1635 Oceans; Satellite Era
Schneider, Tapio; Bischoff, Tobias; Haug, Gerald H.Schneider, T., T. Bischoff, G. H. Haug, 2014: Migrations and dynamics of the intertropical convergence zone. Nature, 513(7516), 45-53. doi: 10.1038/nature13636. Rainfall on Earth is most intense in the intertropical convergence zone (ITCZ), a narrow belt of clouds centred on average around six degrees north of the Equator. The mean position of the ITCZ north of the Equator arises primarily because the Atlantic Ocean transports energy northward across the Equator, rendering the Northern Hemisphere warmer than the Southern Hemisphere. On seasonal and longer timescales, the ITCZ migrates, typically towards a warming hemisphere but with exceptions, such as during El Niño events. An emerging framework links the ITCZ to the atmospheric energy balance and may account for ITCZ variations on timescales from years to geological epochs. Atmospheric dynamics; Climate and Earth system modelling; Palaeoclimate
Seidel, Dian J.; Feingold, Graham; Jacobson, Andrew R.; Loeb, NormanSeidel, D. J., G. Feingold, A. R. Jacobson, N. Loeb, 2014: Detection limits of albedo changes induced by climate engineering. Nature Climate Change, 4(2), 93-98. doi: 10.1038/nclimate2076. A key question surrounding proposals for climate engineering by increasing Earth's reflection of sunlight is the feasibility of detecting engineered albedo increases from short-duration experiments or prolonged implementation of solar-radiation management. We show that satellite observations permit detection of large increases, but interannual variability overwhelms the maximum conceivable albedo increases for some schemes. Detection of an abrupt global average albedo increase
Shi, Kaifang; Yu, Bailang; Huang, Yixiu; Hu, Yingjie; Yin, Bing; Chen, Zuoqi; Chen, Liujia; Wu, JianpingShi, K., B. Yu, Y. Huang, Y. Hu, B. Yin, Z. Chen, L. Chen, J. Wu, 2014: Evaluating the Ability of NPP-VIIRS Nighttime Light Data to Estimate the Gross Domestic Product and the Electric Power Consumption of China at Multiple Scales: A Comparison with DMSP-OLS Data. Remote Sensing, 6(2), 1705-1724. doi: 10.3390/rs6021705. The nighttime light data records artificial light on the Earth’s surface and can be used to estimate the spatial distribution of the gross domestic product (GDP) and the electric power consumption (EPC). In early 2013, the first global NPP-VIIRS nighttime light data were released by the Earth Observation Group of National Oceanic and Atmospheric Administration’s National Geophysical Data Center (NOAA/NGDC). As new-generation data, NPP-VIIRS data have a higher spatial resolution and a wider radiometric detection range than the traditional DMSP-OLS nighttime light data. This study aims to investigate the potential of NPP-VIIRS data in modeling GDP and EPC at multiple scales through a case study of China. A series of preprocessing procedures are proposed to reduce the background noise of original data and to generate corrected NPP-VIIRS nighttime light images. Subsequently, linear regression is used to fit the correlation between the total nighttime light (TNL) (which is extracted from corrected NPP-VIIRS data and DMSP-OLS data) and the GDP and EPC (which is from the country’s statistical data) at provincial- and prefectural-level divisions of mainland China. The result of the linear regression shows that R2 values of TNL from NPP-VIIRS with GDP and EPC at multiple scales are all higher than those from DMSP-OLS data. This study reveals that the NPP-VIIRS data can be a powerful tool for modeling socioeconomic indicators; such as GDP and EPC. China; DMSP-OLS; electric power consumption; gross domestic product; linear regression; nighttime light data; NPP-VIIRS
Shrestha, Alok K.; Kato, Seiji; Wong, Takmeng; Rutan, David A.; Miller, Walter F.; Rose, Fred G.; Smith, G. Louis; Bedka, Kristopher M.; Minnis, Patrick; Fernandez, Jose R.Shrestha, A. K., S. Kato, T. Wong, D. A. Rutan, W. F. Miller, F. G. Rose, G. L. Smith, K. M. Bedka, P. Minnis, J. R. Fernandez, 2014: Unfiltering Earth Radiation Budget Experiment (ERBE) Scanner Radiances Using the CERES Algorithm and Its Evaluation with Nonscanner Observations. J. Atmos. Oceanic Technol., 31(4), 843-859. doi: 10.1175/JTECH-D-13-00072.1. AbstractThe NOAA-9 Earth Radiation Budget Experiment (ERBE) scanner measured broadband shortwave, longwave, and total radiances from February 1985 through January 1987. These scanner radiances are reprocessed using the more recent Clouds and the Earth’s Radiant Energy System (CERES) unfiltering algorithm. The scene information, including cloud properties, required for reprocessing is derived using Advanced Very High Resolution Radiometer (AVHRR) data on board NOAA-9, while no imager data were used in the original ERBE unfiltering. The reprocessing increases the NOAA-9 ERBE scanner unfiltered longwave radiances by 1.4%–2.0% during daytime and 0.2%–0.3% during nighttime relative to those derived from the ERBE unfiltering algorithm. Similarly, the scanner unfiltered shortwave radiances increase by ~1% for clear ocean and land and decrease for all-sky ocean, land, and snow/ice by ~1%. The resulting NOAA-9 ERBE scanner unfiltered radiances are then compared with NOAA-9 nonscanner irradiances by integrating the ERBE scanner radiance over the nonscanner field of view. The comparison indicates that the integrated scanner radiances are larger by 0.9% for shortwave and 0.7% smaller for longwave. A sensitivity study shows that the one-standard-deviation uncertainties in the agreement are ±2.5%, ±1.2%, and ±1.8% for the shortwave, nighttime longwave, and daytime longwave irradiances, respectively. The NOAA-9 and ERBS nonscanner irradiances are also compared using 2 years of data. The comparison indicates that the NOAA-9 nonscanner shortwave, nighttime longwave, and daytime longwave irradiances are 0.3% larger, 0.6% smaller, and 0.4% larger, respectively. The longer observational record provided by the ERBS nonscanner plays a critical role in tying the CERES-like NOAA-9 ERBE scanner dataset from the mid-1980s to the present-day CERES scanner data record. Remote sensing; satellite observations; Climate records; Filtering techniques
Sicard, M.; Bertolín, S.; Mallet, M.; Dubuisson, P.; Comerón, A.Sicard, M., S. Bertolín, M. Mallet, P. Dubuisson, A. Comerón, 2014: Estimation of mineral dust long-wave radiative forcing: sensitivity study to particle properties and application to real cases in the region of Barcelona. Atmos. Chem. Phys., 14(17), 9213-9231. doi: 10.5194/acp-14-9213-2014. The aerosol radiative effect in the long-wave (LW) spectral range is sometimes not taken into account in atmospheric aerosol forcing studies at local scale because the LW aerosol effect is assumed to be negligible. At regional and global scale this effect is partially taken into account: aerosol absorption is taken into account but scattering is still neglected. However, aerosols with strong absorbing and scattering properties in the LW region, like mineral dust, can have a non-negligible radiative effect in the LW spectral range (both at surface and top of the atmosphere) which can counteract their cooling effect occurring in the short-wave spectral range. The first objective of this research is to perform a sensitivity study of mineral dust LW radiative forcing (RF) as a function of dust microphysical and optical properties using an accurate radiative transfer model which can compute vertically resolved short-wave and long-wave aerosol RF. Radiative forcing simulations in the LW range have shown an important sensitivity to the following parameters: aerosol load, radius of the coarse mode, refractive index, aerosol vertical distribution, surface temperature and surface albedo. The scattering effect has been estimated to contribute to the LW RF up to 18% at the surface and up to 38% at the top of the atmosphere. The second objective is the estimation of the short-wave and long-wave dust RF for 11 dust outbreaks observed in Barcelona. At the surface, the LW RF varies between +2.8 and +10.2 W m−2, which represents between 11 and 26% (with opposite sign) of the SW component, while at the top of the atmosphere the LW RF varies between +0.6 and +5.8 W m−2, which represents between 6 and 26% (with opposite sign) of the SW component.
Sicard, Michaël; Bertolín, Santi; Muñoz, Constantino; Rodríguez, Alejandro; Rocadenbosch, Francesc; Comerón, AdolfoSicard, M., S. Bertolín, C. Muñoz, A. Rodríguez, F. Rocadenbosch, A. Comerón, 2014: Separation of aerosol fine- and coarse-mode radiative properties: Effect on the mineral dust longwave, direct radiative forcing. Geophysical Research Letters, 41(19), 2014GL060946. doi: 10.1002/2014GL060946. An improvement of the estimation of mineral dust longwave, direct radiative forcing is presented. It is based on recent developments that combine Sun photometer and multiwavelength lidar data to retrieve range-resolved coarse- and fine-mode extinction coefficients. The forcings are calculated separately for each mode, and their sum is compared to the classical approach in which only the total extinction is considered. The results of four cases of mineral dust intrusion in Barcelona, Spain, show that when the coarse mode predominates, the longwave forcings calculated with the classical approach are underestimated up to 20% near the surface. In all cases the strong coarse-mode predominance near the surface has also an effect on the forcing in the upper layers. 0305 Aerosols and particles; 0394 Instruments and techniques; 3359 Radiative processes; radiative forcing; mineral dust; 1630 Impacts of global change; 3360 Remote sensing; coarse-/fine-mode separation; multiwavelength lidar
Smith, G. Louis, G.; Daniels, Janet L.; Priestley, Kory J.; Thomas, SusanSmith, G. L., J. L. Daniels, K. J. Priestley, S. Thomas, 2014: Point response function of the Clouds and Earth Radiant Energy System scanning radiometer. Journal of Applied Remote Sensing, 8(1), 084991-084991. doi: 10.1117/1.JRS.8.084991. Abstract. An overview of work related to the point response function (PRF) of the Clouds and Earth Radiant Energy System (CERES) scanning radiometer is presented. The aspects of the CERES design that affect the PRF are described, and then the design of the PRF is explained. The PRF was designed by shaping the field of view so as to minimize the blur plus alias errors of the radiance field reconstructed from the CERES measurements. The design is conducted in the Fourier domain. The PRF can then be computed by transforming the resulting transfer function to the physical domain. Alternatively, the PRF can be computed in the physical plane. The PRF of each model of the CERES instrument has been tested in the Radiation Calibration Facility by use of a PRF source and compared well with prediction. CERES instruments are aboard the Terra, Aqua, and Suomi-NPP spacecraft. In orbit, lunar observations are used to validate the PRF. These results showed nominal performance except for the longwave window channel of flight model 2, for which a region of anomalously high sensitivity was found.
Smith, G. Louis; Doelling, David R.Smith, G. L., D. R. Doelling, 2014: Computation of Radiation Budget on an Oblate Earth. J. Climate, 27(19), 7203-7206. doi: 10.1175/JCLI-D-14-00058.1. AbstractThe effects of the earth’s oblateness on computation of its radiation budget from satellite measurements are evaluated. For the Clouds and the Earth’s Radiant Energy System (CERES) data processing, geolocations of the measurements are computed in terms of the geodetic coordinate system. Using this system accounts for oblateness in the computed solar zenith angle and length of day. The geodetic and geocentric latitudes are equal at the equator and poles but differ by a maximum of 0.2° at 45° latitude. The area of each region and zone is affected by oblateness as compared to geocentric coordinates, decreasing from zero at the equator to 1.5% at the poles. The global area receiving solar radiation is calculated using the equatorial and polar axes. This area varies with solar declination by 0.0005. For radiation budget computations, the earth oblateness effects are shown to be small compared to error sources of measuring or modeling. Coordinate systems
Smith, G. Louis; Harrison, Edwin F.; Gibson, Gary G.Smith, G. L., E. F. Harrison, G. G. Gibson, 2014: Earth Radiation Budget Research at the NASA Langley Research Center. In the 1970s research studies concentrating on satellite measurements of Earth's radiation budget started at the NASA Langley Research Center. Since that beginning, considerable effort has been devoted to developing measurement techniques, data analysis methods, and time-space sampling strategies to meet the radiation budget science requirements for climate studies. Implementation and success of the Earth Radiation Budget Experiment and the Clouds and the Earth's Radiant Energy System was due to the remarkable teamwork of many engineers, scientists, and data analysts. Data from ERBE have provided a new understanding of the effects of clouds, aerosols, and El Nino/La Nina oscillation on the Earth's radiation. CERES spacecraft instruments have extended the time coverage with high quality climate data records for over a decade. Using ERBE and CERES measurements these teams have created information about radiation at the top of the atmosphere, at the surface, and throughout the atmosphere for a better understanding of our climate. They have also generated surface radiation products for designers of solar power plants and buildings and numerous other applications earth radiation budget; aerosols; CERES; satellite observation; terrestrial radiation; el nino; earth radiation budget experiment; electric power plants; satellite-borne instruments
Smith, G.L.; Priestley, K.J.; Loeb, N.G.Smith, G., K. Priestley, N. Loeb, 2014: Clouds and Earth Radiant Energy System: From Design to Data. IEEE Transactions on Geoscience and Remote Sensing, 52(3), 1729-1738. doi: 10.1109/TGRS.2013.2253782. The Clouds and the Earth's Radiant Energy System (CERES) project has instruments aboard the Terra and Aqua spacecraft that have provided a decade of radiation budget data. In October 2011, the CERES flight model 5 was placed in orbit on the NPOESS Preparatory Project spacecraft. Data from these instruments are being used to investigate the radiation balance of the Earth at various time and space scales and the role of clouds in this balance. The design and calibration, both on the ground and in-orbit, and operation of the instrument are discussed. calibration; clouds; Earth; earth radiation budget; Extraterrestrial measurements; Remote sensing; atmospheric radiation; Earth Observing System; Instruments; Space vehicles; atmospheric measuring apparatus; Aqua; Terra; Clouds and the Earth's Radiant Energy System (CERES); AD 2011 10; Aqua spacecraft; CERES flight model 5; CERES project instrument data; cloud and earth radiant energy system; cloud balance role; data design; Earth radiation balance; ground calibration; ground design; in-orbit calibration; in-orbit design; instrument operation; NPOESS Preparatory Project (NPP); NPOESS preparatory project spacecraft; Orbits; radiation budget data; Temperature measurement; Terra spacecraft; time-space scales
Sobel, Adam; Wang, Shuguang; Kim, DaehyunSobel, A., S. Wang, D. Kim, 2014: Moist Static Energy Budget of the MJO during DYNAMO. J. Atmos. Sci., 71(11), 4276-4291. doi: 10.1175/JAS-D-14-0052.1. AbstractThe authors analyze the column-integrated moist static energy budget over the region of the tropical Indian Ocean covered by the sounding array during the Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011 (CINDY2011)/Dynamics of the Madden–Julian Oscillation (DYNAMO) field experiment in late 2011. The analysis is performed using data from the sounding array complemented by additional observational datasets for surface turbulent fluxes and atmospheric radiative heating. The entire analysis is repeated using the ECMWF Interim Re-Analysis (ERA-Interim). The roles of surface turbulent fluxes, radiative heating, and advection are quantified for the two MJO events that occurred in October and November using the sounding data; a third event in December is also studied in the ERA-Interim data.These results are consistent with the view that the MJO’s moist static energy anomalies grow and are sustained to a significant extent by the radiative feedbacks associated with MJO water vapor and cloud anomalies and that propagation of the MJO is associated with advection of moist static energy. Both horizontal and vertical advection appear to play significant roles in the events studied here. Horizontal advection strongly moistens the atmosphere during the buildup to the active phase of the October event when the low-level winds switch from westerly to easterly. Horizontal advection strongly dries the atmosphere in the wake of the active phases of the November and December events as the westerlies associated with off-equatorial cyclonic gyres bring subtropical dry air into the convective region from the west and north. Vertical advection provides relative moistening ahead of the active phase and drying behind it, associated with an increase of the normalized gross moist stability. deep convection; Madden-Julian Oscillation; Soundings; Conservation equations; Diabatic heating; Radiosonde observations
Spero, Tanya L.; Otte, Martin J.; Bowden, Jared H.; Nolte, Christopher G.Spero, T. L., M. J. Otte, J. H. Bowden, C. G. Nolte, 2014: Improving the representation of clouds, radiation, and precipitation using spectral nudging in the Weather Research and Forecasting model. Journal of Geophysical Research: Atmospheres, 119(20), 2014JD022173. doi: 10.1002/2014JD022173. Spectral nudging—a scale-selective interior constraint technique—is commonly used in regional climate models to maintain consistency with large-scale forcing while permitting mesoscale features to develop in the downscaled simulations. Several studies have demonstrated that spectral nudging improves the representation of regional climate in reanalysis-forced simulations compared with not using nudging in the interior of the domain. However, in the Weather Research and Forecasting (WRF) model, spectral nudging tends to produce degraded precipitation simulations when compared to analysis nudging—an interior constraint technique that is scale indiscriminate but also operates on moisture fields which until now could not be altered directly by spectral nudging. Since analysis nudging is less desirable for regional climate modeling because it dampens fine-scale variability, changes are proposed to the spectral nudging methodology to capitalize on differences between the nudging techniques and aim to improve the representation of clouds, radiation, and precipitation without compromising other fields. These changes include adding spectral nudging toward moisture, limiting nudging to below the tropopause, and increasing the nudging time scale for potential temperature, all of which collectively improve the representation of mean and extreme precipitation, 2 m temperature, clouds, and radiation, as demonstrated using a model-simulated 20 year historical period. Such improvements to WRF may increase the fidelity of regional climate data used to assess the potential impacts of climate change on human health and the environment and aid in climate change mitigation and adaptation studies. 3305 Climate change and variability; 3315 Data assimilation; regional climate modeling; 3355 Regional modeling; WRF; downscaling; 3329 Mesoscale meteorology; spectral nudging
Stan, Cristiana; Xu, LiStan, C., L. Xu, 2014: Climate simulations and projections with a super-parameterized climate model. Environmental Modelling & Software, 60, 134-152. doi: 10.1016/j.envsoft.2014.06.013. The mean climate and its variability are analyzed in a suite of numerical experiments with a fully coupled general circulation model in which subgrid-scale moist convection is explicitly represented through embedded 2D cloud-system resolving models. Control simulations forced by the present day, fixed atmospheric carbon dioxide concentration are conducted using two horizontal resolutions and validated against observations and reanalyses. The mean state simulated by the higher resolution configuration has smaller biases. Climate variability also shows some sensitivity to resolution but not as uniform as in the case of mean state. The interannual and seasonal variability are better represented in the simulation at lower resolution whereas the subseasonal variability is more accurate in the higher resolution simulation. The equilibrium climate sensitivity of the model is estimated from a simulation forced by an abrupt quadrupling of the atmospheric carbon dioxide concentration. The equilibrium climate sensitivity temperature of the model is 2.77 °C, and this value is slightly smaller than the mean value (3.37 °C) of contemporary models using conventional representation of cloud processes. The climate change simulation forced by the representative concentration pathway 8.5 scenario projects an increase in the frequency of severe droughts over most of the North America. climate change; Climate sensitivity; Super-parameterization; Global modeling
Stanfield, Ryan E.; Dong, Xiquan; Xi, Baike; Kennedy, Aaron; Del Genio, Anthony D.; Minnis, Patrick; Jiang, Jonathan H.Stanfield, R. E., X. Dong, B. Xi, A. Kennedy, A. D. Del Genio, P. Minnis, J. H. Jiang, 2014: Assessment of NASA GISS CMIP5 and Post-CMIP5 Simulated Clouds and TOA Radiation Budgets Using Satellite Observations. Part I: Cloud Fraction and Properties. J. Climate, 27(11), 4189-4208. doi: 10.1175/JCLI-D-13-00558.1. AbstractAlthough many improvements have been made in phase 5 of the Coupled Model Intercomparison Project (CMIP5), clouds remain a significant source of uncertainty in general circulation models (GCMs) because their structural and optical properties are strongly dependent upon interactions between aerosol/cloud microphysics and dynamics that are unresolved in such models. Recent changes to the planetary boundary layer (PBL) turbulence and moist convection parameterizations in the NASA GISS Model E2 atmospheric GCM (post-CMIP5, hereafter P5) have improved cloud simulations significantly compared to its CMIP5 (hereafter C5) predecessor. A study has been performed to evaluate these changes between the P5 and C5 versions of the GCM, both of which used prescribed sea surface temperatures. P5 and C5 simulated cloud fraction (CF), liquid water path (LWP), ice water path (IWP), cloud water path (CWP), precipitable water vapor (PWV), and relative humidity (RH) have been compared to multiple satellite observations including the Clouds and the Earth’s Radiant Energy System–Moderate Resolution Imaging Spectroradiometer (CERES-MODIS, hereafter CM), CloudSat–Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO; hereafter CC), Atmospheric Infrared Sounder (AIRS), and Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E). Although some improvements are observed in the P5 simulation on a global scale, large improvements have been found over the southern midlatitudes (SMLs), where correlations increased and both bias and root-mean-square error (RMSE) significantly decreased, in relation to the previous C5 simulation, when compared to observations. Changes to the PBL scheme have resulted in improved total column CFs, particularly over the SMLs where marine boundary layer (MBL) CFs have increased by nearly 20% relative to the previous C5 simulation. Globally, the P5 simulated CWPs are 25 g m−2 lower than the previous C5 results. The P5 version of the GCM simulates PWV and RH higher than its C5 counterpart and agrees well with the AMSR-E and AIRS observations. The moister atmospheric conditions simulated by P5 are consistent with the CF comparison and provide a strong support for the increase in MBL clouds over the SMLs. Over the tropics, the P5 version of the GCM simulated total column CFs and CWPs are slightly lower than the previous C5 results, primarily as a result of the shallower tropical boundary layer in P5 relative to C5 in regions outside the marine stratocumulus decks. clouds; satellite observations; Model evaluation/performance; General circulation models; Model comparison
Storelvmo, T.; Herger, N.Storelvmo, T., N. Herger, 2014: Cirrus cloud susceptibility to the injection of ice nuclei in the upper troposphere. Journal of Geophysical Research: Atmospheres, 119(5), 2375-2389. doi: 10.1002/2013JD020816. Due to their net warming effect, cirrus clouds play a crucial role in the climate system. A recently proposed climate engineering mechanism (CEM) intends to reduce high cloud cover by seeding cirrus clouds with efficient ice nuclei (IN) and therefore cool climate. Here, the susceptibility of cirrus clouds to the injection of ice nuclei in the upper troposphere is investigated in the extended Community Atmospheric Model version 5 (CAM5). Due to large uncertainties associated with the dominant ice nucleation mechanism in cirrus clouds, different control cases were simulated. In addition to pure homogeneous and heterogeneous nucleation, cases with competition between homogeneous and heterogeneous nucleation and different fractions of mineral dust active as IN were considered. Whereas seeding in the pure heterogeneous case leads to a strong warming due to overseeding, an optimal seeding IN concentration of approximately 18 l−1 was found for the other cases. For the optimal seeding concentration, a reduction in the net cloud forcing (NCF) of up to 2 W m−2 was simulated, corresponding to a strong cooling effect. To optimize the cooling and minimize the amount of seeding material, globally nonuniform seeding strategies were tested, with minimal seeding in the summer hemisphere and in the tropics. With seeding applied to less than half the globe, an even stronger reduction in the NCF was achieved. This suggests that the CEM could work for an atmosphere even with considerable heterogeneous ice nucleation and that the desired cooling could be obtained without seeding the entire globe. 0305 Aerosols and particles; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; aerosol; 3310 Clouds and cloud feedbacks; climate; dust; cirrus; Geoengineering; 1605 Abrupt/rapid climate change; susceptibility
Su, W.; Corbett, J.; Eitzen, Z.; Liang, L.Su, W., J. Corbett, Z. Eitzen, L. Liang, 2014: Next-generation angular distribution models for top-of-atmosphere radiative flux calculation from the CERES instruments: methodology. Atmos. Meas. Tech. Discuss., 7(8), 8817-8880. doi: 10.5194/amtd-7-8817-2014. The top-of-atmosphere (TOA) radiative fluxes are critical components to advancing our understanding of the Earth's radiative energy balance, radiative effects of clouds and aerosols, and climate feedback. The Clouds and Earth's Radiant Energy System (CERES) instruments provide broadband shortwave and longwave radiance measurements. These radiances are converted to fluxes by using scene type dependent Angular Distribution Models (ADMs). This paper describes the next-generation ADMs that are developed for Terra and Aqua using all available CERES rotating azimuth plane radiance measurements. Coincident cloud and aerosol retrievals, and radiance measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS), and meteorological parameters from Goddard Earth Observing System (GEOS) data assimilation version 5.4.1 are used to define scene type. CERES radiance measurements are stratified by scene type and by other parameters that are important for determining the anisotropy of the given scene type. Anisotropic factors are then defined either for discrete intervals of relevant parameters or as a continuous functions of combined parameters, depending on the scene type. Compared to the existing ADMs, the new ADMs change the monthly mean instantaneous fluxes by up to 5 W m−2 on a regional scale of 1° latitude × 1° longitude, but the flux changes are less than 0.5 W m−2 on a global scale.
Sun, Wenbo; Lin, Bing; Baize, Rosemary R.; Videen, Gorden; Hu, YongxiangSun, W., B. Lin, R. R. Baize, G. Videen, Y. Hu, 2014: Sensing Hadley cell with space-borne lidar. Journal of Quantitative Spectroscopy and Radiative Transfer, 148, 38-41. doi: 10.1016/j.jqsrt.2014.06.017. Some recent studies reported expansion of the Earth׳s tropical regime in the past few decades. The poleward expansion of the Hadley cell is a strong indication of the warming of the globe. The extent of Hadley cell also has very important implications to the climate of dry subtropical regions because of the prevalence of precipitation in the deep tropical belt. Determination of the Hadley circulation especially its extent has great significance for monitoring global climate change and for the subtropical climate studies. Although many methods have been developed in recent years, reliable measurement of the extent of Hadley cell is still an issue in climate studies. This letter shows that the extent of the Hadley cell could reliably be estimated by measuring the height of the uppermost super-thin clouds in the troposphere with space-borne lidar. Through consecutive multi-year measurements of the height of the uppermost super-thin clouds, a good estimation of the expansion of the Hadley cell could be obtained. climate; Expansion of Hadley cell; Space-borne lidar; Uppermost super-thin clouds
Sun, Zhian; Zeng, Xianning; Liu, Jingmiao; Liang, Hong; Li, J.Sun, Z., X. Zeng, J. Liu, H. Liang, J. Li, 2014: Parametrization of instantaneous global horizontal irradiance: clear-sky component. Quarterly Journal of the Royal Meteorological Society, 140(678), 267-280. doi: 10.1002/qj.2126. Based on an accurate atmospheric radiative transfer scheme, a parametrization of instantaneous global horizontal irradiance (GHI) at the Earth's surface has been developed. The scheme is named SUNFLUX and this article describes the development of the scheme for clear-sky conditions. The work dealing with clouds has been published in a separate article. Unlike traditional methods, this study applies the band model idea used in radiative transfer theory to the development of the surface radiation scheme and, importantly, includes absorption and scattering in the parametrization. Thus the scheme is more accurate compared with those using simple empirical approaches and may be applied to any site without being tuned for local conditions. The parametrization of aerosol transmittance and albedo developed by Kokhanovsky et al. is adopted to account for the effects of aerosols. All variables used in the scheme are available in climate models or from satellite observations. Therefore, the parametrization can be used to determine the GHI at the surface under clear-sky conditions The scheme is evaluated using observations obtained from three US Atmospheric Radiation Measurement (ARM) stations and three stations on the Tibetan Plateau, and the results demonstrate that the scheme is accurate. The relative mean bias difference is less than 4.3% and the relative root-mean-squared difference is less than 0.09%. radiative transfer; global horizontal irradiance; parametrization; transmittance
Sun-Mack, Sunny; Minnis, Patrick; Chen, Yan; Kato, Seiji; Yi, Yuhong; Gibson, Sharon C.; Heck, Patrick W.; Winker, David M.Sun-Mack, S., P. Minnis, Y. Chen, S. Kato, Y. Yi, S. C. Gibson, P. W. Heck, D. M. Winker, 2014: Regional Apparent Boundary Layer Lapse Rates Determined from CALIPSO and MODIS Data for Cloud-Height Determination. J. Appl. Meteor. Climatol., 53(4), 990-1011. doi: 10.1175/JAMC-D-13-081.1. AbstractReliably determining low-cloud heights using a cloud-top temperature from satellite infrared imagery is often challenging because of difficulties in characterizing the local thermal structure of the lower troposphere with the necessary precision and accuracy. To improve low-cloud-top height estimates over water surfaces, various methods have employed lapse rates anchored to the sea surface temperature to replace the boundary layer temperature profiles that relate temperature to altitude. To further improve low-cloud-top height retrievals, collocated Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) data taken from July 2006 to June 2007 and from June 2009 to May 2010 (2 yr) for single-layer low clouds are used here with numerical weather model analyses to develop regional mean boundary apparent lapse rates. These parameters are designated as apparent lapse rates because they are defined using the cloud-top temperatures from satellite retrievals and surface skin temperatures; they do not represent true lapse rates. Separate day and night, seasonal mean lapse rates are determined for 10′-resolution snow-free land, water, and coastal regions, while zonally dependent lapse rates are developed for snow/ice-covered areas for use in the Clouds and the Earth’s Radiant Energy System (CERES) Edition 4 cloud property retrieval system (CCPRS-4). The derived apparent lapse rates over ice-free water range from 5 to 9 K km−1 with mean values of about 6.9 and 7.2 K km−1 during the day and night, respectively. Over land, the regional values vary from 3 to 8 K km−1, with day and night means of 5.5 and 6.2 K km−1, respectively. The zonal-mean apparent lapse rates over snow and ice surfaces generally decrease with increasing latitude, ranging from 4 to 8 K km−1. All of the CCPRS-4 lapse rates were used along with five other lapse rate techniques to retrieve cloud-top heights for 2 months of independent Aqua MODIS data. When compared with coincident CALIPSO data for October 2007, the mean cloud-top height differences between CCPRS-4 and CALIPSO during the daytime (nighttime) are 0.04 ± 0.61 km (0.10 ± 0.62 km) over ice-free water, −0.06 ± 0.85 km (−0.01 ± 0.83 km) over snow-free land, and 0.38 ± 0.95 km (0.03 ± 0.92 km) over snow-covered areas. The CCPRS-4 regional monthly means are generally unbiased and lack spatial error gradients seen in the comparisons for most of the other techniques. Over snow-free land, the regional monthly-mean errors range from −0.28 ± 0.74 km during daytime to 0.04 ± 0.78 km at night. The water regional monthly means are, on average, 0.04 ± 0.44 km less than the CALIPSO values during day and night. Greater errors are realized for snow-covered regions. Overall, the CCPRS-4 lapse rates yield the smallest RMS differences for all times of day over all areas both for individual retrievals and monthly means. These new regional apparent lapse rates, used in processing CERES Edition 4 data, should provide more accurate low-cloud-type heights than previously possible using satellite imager data. clouds; Cloud retrieval; Boundary layer
Taylor, Patrick C.Taylor, P. C., 2014: Variability of Monthly Diurnal Cycle Composites of TOA Radiative Fluxes in the Tropics. J. Atmos. Sci., 71(2), 754-766. doi: 10.1175/JAS-D-13-0112.1. AbstractEarth system variability is generated by a number of different sources and time scales. Understanding sources of atmospheric variability is critical to reducing the uncertainty in climate models and to understanding the impacts of sampling on observational datasets. The diurnal cycle is a fundamental variability evident in many geophysical variables—including top-of-the-atmosphere (TOA) radiative fluxes. This study considers aspects of the TOA flux diurnal cycle not previously analyzed: namely, deseasonalized variations in the monthly diurnal cycle composites, termed monthly diurnal cycle variability. Significant variability in the monthly diurnal cycle composites is found in both outgoing longwave radiation (OLR) and reflected shortwave (RSW). OLR and RSW monthly diurnal cycle variability exhibits a regional structure that follows traditional, climatological diurnal cycle categorization by prevailing cloud and surface types. The results attribute monthly TOA flux diurnal cycle variability to variations in the diurnal cloud evolution, which is sensitive to monthly atmospheric dynamic- and thermodynamic-state anomalies. The results also suggest that monthly diurnal cycle variability can amplify or buffer monthly TOA flux anomalies, depending on the region. Considering the impact of monthly diurnal cycle variability on monthly TOA flux anomalies, the results suggest that monthly TOA flux diurnal cycle variability must be considered when constructing a TOA flux dataset from sun-synchronous orbit. The magnitude of monthly diurnal composite variability in OLR and RSW is regionally dependent—1–7 W m−2 and 10%–80% relative to interannual TOA flux variability. The largest (4–7 W m−2; 40%–80%) and smallest (1–3 W m−2; 10%–30%) TOA flux uncertainties occur in convective and nonconvective regions, respectively, over both land and ocean. tropics; Radiative fluxes; satellite observations; Shortwave radiation; cloud forcing; Diurnal effects
Taylor, Patrick C.Taylor, P. C., 2014: Variability of Regional TOA Flux Diurnal Cycle Composites at the Monthly Time Scale. J. Atmos. Sci., 71(9), 3484-3498. doi: 10.1175/JAS-D-13-0336.1. AbstractDiurnal variability is a fundamental component of Earth’s climate system. Clouds, temperature, and precipitation exhibit robust responses to the daily cycle of solar insolation. Recent work indicates significant variability in the top-of-the-atmosphere (TOA) flux diurnal cycle in the tropics associated with monthly changes in the cloud diurnal cycle evolution. It has been proposed that the observed month-to-month variations in the TOA flux diurnal cycle are caused by anomalies in the atmospheric dynamic and thermodynamic state. This hypothesis is tested using a regression analysis to quantify the relationship between diurnal cycle shape and the atmospheric dynamic and thermodynamic state. TOA radiative fluxes are obtained from Clouds and the Earth’s Radiant Energy System (CERES) Edition 3 data and the atmospheric dynamic and thermodynamic state is taken from the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis. Four regions representing traditional diurnal cycle regimes are used in this analysis: North Africa (land nonconvective), central South America (land convective), Peru marine stratocumulus (ocean nonconvective), and Indian Ocean (ocean convective). The results show a statistically significant diurnal cycle shape change and cloud response related to monthly atmospheric state anomalies. Using the single-variable regression relationships to predict monthly diurnal cycle variability shows improvements of 1%–18% over assuming a climatological diurnal cycle shape; the most significant gains are found in North Africa. The proposed hypothesis, therefore, contributes to diurnal cycle variability explaining at least 10%–20% of the total monthly-mean diurnal cycle variability. convection; tropics; Radiative fluxes; Regional effects; Diurnal effects
Teixeira, Joao; Waliser, Duane; Ferraro, Robert; Gleckler, Peter; Lee, Tsengdar; Potter, GeraldTeixeira, J., D. Waliser, R. Ferraro, P. Gleckler, T. Lee, G. Potter, 2014: Satellite Observations for CMIP5: The Genesis of Obs4MIPs. Bull. Amer. Meteor. Soc., 95(9), 1329-1334. doi: 10.1175/BAMS-D-12-00204.1. The objective of the Observations for Model Intercomparison Projects (Obs4MIPs) is to provide observational data to the climate science community, which is analogous (in terms of variables, temporal and spatial frequency, and periods) to output from the 5th phase of the World Climate Research Programme's (WCRP) Coupled Model Intercomparison Project (CMIP5) climate model simulations. The essential aspect of the Obs4MIPs methodology is that it strictly follows the CMIP5 protocol document when selecting the observational datasets. Obs4MIPs also provides documentation that describes aspects of the observational data (e.g., data origin, instrument overview, uncertainty estimates) that are of particular relevance to scientists involved in climate model evaluation and analysis. In this paper, we focus on the activities related to the initial set of satellite observations, which are being carried out in close coordination with CMIP5 and directly engage NASA's observational (e.g., mission and instrument) science teams. Having launched Obs4MIPs with these datasets, a broader effort is also briefly discussed, striving to engage other agencies and experts who maintain datasets, including reanalysis, which can be directly used to evaluate climate models. Different strategies for using satellite observations to evaluate climate models are also briefly summarized.
Thampi, B. V.; Roca, R.Thampi, B. V., R. Roca, 2014: Investigation of negative cloud radiative forcing over the Indian subcontinent and adjacent oceans during the summer monsoon season. Atmos. Chem. Phys., 14(13), 6739-6758. doi: 10.5194/acp-14-6739-2014. Radiative properties of clouds over the Indian subcontinent and nearby oceanic regions (0–25° N, 60–100° E) during the Asian summer monsoon season (June–September) are investigated using the Clouds and Earth's Radiant Energy System (CERES) top-of-the-atmosphere (TOA) flux data. Using multiyear satellite data, the net cloud radiative forcing (NETCRF) at the TOA over the Indian region during the Asian monsoon season is examined. The seasonal mean NETCRF is found to be negative (with its magnitude exceeding ~30 Wm−2) over (1) the northern Bay of Bengal (close to the Myanmar–Thailand coast), (2) the Western Ghats and (3) the coastal regions of Myanmar. Such strong negative NETCRF values observed over the Indian monsoon region contradict the assumption that near cancellation between LWCRF and SWCRF is a generic property of all tropical convective regions. The seasonal mean cloud amount (high and upper middle) and corresponding cloud optical depth observed over the three regions show relatively large values compared to the rest of the Indian monsoon region. Using satellite-derived cloud data, a statistical cloud vertical model delineating the cloud cover and single-scattering albedo was developed for the three negative NETCRF regions. The shortwave (SW), longwave (LW) and net cloud radiative forcing over the three negative NETCRF regions are calculated using the rapid radiative transfer model (RRTM) with the cloud vertical model as input. The NETCRF estimated from CERES observations show good comparison with that computed using RRTM (within the uncertainty limit of CERES observations). Sensitivity tests are conducted using RRTM to identify the parameters that control the negative NETCRF observed over these regions during the summer monsoon season. Increase in atmospheric water vapor content during the summer monsoon season is found to influence the negative NETCRF values observed over the region.
Trenberth, Kevin E.; Fasullo, John T.; Balmaseda, Magdalena A.Trenberth, K. E., J. T. Fasullo, M. A. Balmaseda, 2014: Earth’s Energy Imbalance. J. Climate, 27(9), 3129-3144. doi: 10.1175/JCLI-D-13-00294.1. AbstractClimate change from increased greenhouse gases arises from a global energy imbalance at the top of the atmosphere (TOA). TOA measurements of radiation from space can track changes over time but lack absolute accuracy. An inventory of energy storage changes shows that over 90% of the imbalance is manifested as a rise in ocean heat content (OHC). Data from the Ocean Reanalysis System, version 4 (ORAS4), and other OHC-estimated rates of change are used to compare with model-based estimates of TOA energy imbalance [from the Community Climate System Model, version 4 (CCSM4)] and with TOA satellite measurements for the year 2000 onward. Most ocean-only OHC analyses extend to only 700-m depth, have large discrepancies among the rates of change of OHC, and do not resolve interannual variability adequately to capture ENSO and volcanic eruption effects, all aspects that are improved with assimilation of multivariate data. ORAS4 rates of change of OHC quantitatively agree with the radiative forcing estimates of impacts of the three major volcanic eruptions since 1960 (Mt. Agung, 1963; El Chichón, 1982; and Mt. Pinatubo, 1991). The natural variability of the energy imbalance is substantial from month to month, associated with cloud and weather variations, and interannually mainly associated with ENSO, while the sun affects 15% of the climate change signal on decadal time scales. All estimates (OHC and TOA) show that over the past decade the energy imbalance ranges between about 0.5 and 1 W m−2. By using the full-depth ocean, there is a better overall accounting for energy, but discrepancies remain at interannual time scales between OHC- and TOA-based estimates, notably in 2008/09. climate change; Radiation budgets; Heating; Volcanoes; ENSO; Climate variability
Tsushima, Yoko; Iga, Shin-ichi; Tomita, Hirofumi; Satoh, Masaki; Noda, Akira T.; Webb, Mark J.Tsushima, Y., S. Iga, H. Tomita, M. Satoh, A. T. Noda, M. J. Webb, 2014: High cloud increase in a perturbed SST experiment with a global nonhydrostatic model including explicit convective processes. Journal of Advances in Modeling Earth Systems, 6(3), 571-585. doi: 10.1002/2013MS000301. Results are presented from a series of sensitivity tests in idealized global warming experiments using the global nonhydrostatic model, NICAM, in which convection at scales of 7–14 km is explicitly resolved. All have a strong positive longwave cloud feedback larger than that seen in conventional GCMs with parameterized convection. Consequently, the global mean net outgoing radiation decreases in response to increased sea surface temperatures. Large increases in high clouds with tops between 180 and 50 hPa are found, and these changes contribute the most to this longwave cloud feedback. Relative humidity and upper tropospheric temperature also increases strongly, again more so than typically seen in conventional GCMs. The magnitude of the response varies considerably between different versions of NICAM. Most of the NICAM control simulations show large overestimates in cloud fraction between 180 and 50 hPa compared to observations. The changes in cloud fraction in the upper troposphere are strongly correlated with their control values. Versions of NICAM with stronger cloud feedbacks have large positive biases in high-top cloud amount and temperature in the free troposphere in their control simulations. The version which has the best agreement with the observations in this regard has the weakest longwave cloud feedback; however, this is still more strongly positive than that typically seen in conventional GCMs. These results demonstrate the potential for stronger high cloud fraction feedbacks in climate warming scenarios than currently predicted by conventional GCMs and highlight the potential relevance of deep convective processes. longwave; 0321 Cloud/radiation interaction; 3337 Global climate models; 3310 Clouds and cloud feedbacks; cloud feedback; global cloud-resolving model; high cloud; NICAM; perturbed SST experiment
Turner, Emma C.; Tett, Simon F. B.Turner, E. C., S. F. B. Tett, 2014: Using longwave HIRS radiances to test climate models. Climate Dynamics, 43(3-4), 1103-1127. doi: 10.1007/s00382-013-1959-6. A ‘model-to-radiance’ comparison of simulated brightness temperatures from the Hadley Centre Global Environmental Model 2 with measurements from the High Resolution Infrared Radiation Sounder/4 (HIRS/4) instrument onboard the MetOp-A satellite is presented. For the all-sky, the model overestimates brightness temperatures in the atmospheric window region with the greatest biases over areas associated with deep convective cloud. In contrast to many global climate models, much smaller clear-sky biases are found indicating that model clouds are the dominating source of error. Simulated values in upper atmospheric CO2 channels approximate observations better as a result of compensating cold biases at the poles and warm biases at lower latitudes, due to a poor representation of the Brewer Dobson circulation in the 38 level ‘low-top’ configuration of the model. Simulated all and clear-sky outgoing longwave radiation (OLR) evaluated against the Clouds and the Earth’s Radiant Energy System (CERES) and HIRS OLR products reveal good agreement, in part due to cancellation of positive and negative biases. Through physical arguments relating to the spectral energy balance within a cloud, it is suggested that broadband agreement could be the result of a balance between positive window biases and unseen negative biases originating from the water vapour rotational band in the far infrared (not sampled by HIRS). clouds; Climatology; radiation; GCM; Oceanography; Geophysics/Geodesy; HadGEM2; HIRS; RTTOV
Voigt, Aiko; Stevens, Bjorn; Bader, Jürgen; Mauritsen, ThorstenVoigt, A., B. Stevens, J. Bader, T. Mauritsen, 2014: Compensation of Hemispheric Albedo Asymmetries by Shifts of the ITCZ and Tropical Clouds. J. Climate, 27(3), 1029-1045. doi: 10.1175/JCLI-D-13-00205.1.
Vuilleumier, L.; Hauser, M.; Félix, C.; Vignola, F.; Blanc, P.; Kazantzidis, A.; Calpini, B.Vuilleumier, L., M. Hauser, C. Félix, F. Vignola, P. Blanc, A. Kazantzidis, B. Calpini, 2014: Accuracy of ground surface broadband shortwave radiation monitoring. Journal of Geophysical Research: Atmospheres, 119(24), 2014JD022335. doi: 10.1002/2014JD022335. The uncertainty of broadband shortwave radiation monitoring is determined for direct, diffuse, and global irradiance for measurements obtained at the Payerne (Switzerland) station of the Baseline Surface Radiation Network (BSRN). The uncertainty estimates include sources that reflect realistic long-term operation conditions. The uncertainties are derived using the methodology specified by the “Guide to the expression of uncertainty in measurement.” The differences between redundant determinations of direct, diffuse, and global irradiance are analyzed and are shown to be compatible with the uncertainties. In addition, the signatures of some uncertainty sources are sought within the error statistics to find out if corrections can be applied and what their magnitude is. The global and diffuse irradiance uncertainties range from 1.8% to 2.4% without correction and are less than 1.8% with corrections. These uncertainties are close to or satisfy the BSRN targets for large signals (global: 1000 W m−2, diffuse: 500 W m−2). For small signals (50 W m−2), the targets are not achieved, mainly as a result of uncertainties associated with the data acquisition electronics (DAQ). The direct irradiance uncertainty is ~1.5%, 3 times larger than the BSRN uncertainty target. An accuracy gain can also be achieved at the DAQ level, but even without considering the DAQ uncertainty, the target is exceeded by a factor of about 2. The direct irradiance uncertainty remains ~1% even using an absolute cavity radiometer as transfer standard for correcting the pyrheliometer sensitivity. Thus, the direct irradiance accuracy target of 0.5% is probably not achievable with the best commercially available technology. shortwave; 3359 Radiative processes; 3394 Instruments and techniques; uncertainty; radiation; accuracy; 0634 Measurement and standards; pyranometer; pyrheliometer
Wang, Aihui; Zeng, XubinWang, A., X. Zeng, 2014: Range of monthly mean hourly land surface air temperature diurnal cycle over high northern latitudes. Journal of Geophysical Research: Atmospheres, 119(10), 2014JD021602. doi: 10.1002/2014JD021602. Daily maximum and minimum temperatures over global land are fundamental climate variables, and their difference represents the diurnal temperature range (DTR). While the differences between the monthly averaged DTR (MDTR) and the range of monthly averaged hourly temperature diurnal cycle (RMDT) are easy to understand qualitatively, their differences have not been quantified over global land areas. Based on our newly developed in situ data (Climatic Research Unit) reanalysis (Modern-Era Retrospective analysis for Research and Applications) merged hourly temperature data from 1979 to 2009, RMDT in January is found to be much smaller than that in July over high northern latitudes, as it is much more affected by the diurnal radiative forcing than by the horizontal advection of temperature. In contrast, MDTR in January is comparable to that in July over high northern latitudes, but it is much larger than January RMDT, as it primarily reflects the movement of lower frequency synoptic weather systems. The area-averaged RMDT trends north of 40°N are near zero in November, December, and January, while the trends of MDTR are negative. These results suggest the need to use both the traditional MDTR and RMDT suggested here in future observational and modeling studies. Furthermore, MDTR and its trend are more sensitive to the starting hour of a 24 h day used in the calculations than those for RMDT, and this factor also needs to be considered in model evaluations using observational data. 3305 Climate change and variability; 1637 Regional climate change; 3322 Land/atmosphere interactions; diurnal temperature range; land surface air temperature
Wang, Fang; Yang, Song; Wu, TongwenWang, F., S. Yang, T. Wu, 2014: Radiation budget biases in AMIP5 models over the East Asian monsoon region. Journal of Geophysical Research: Atmospheres, 119(23), 2014JD022243. doi: 10.1002/2014JD022243. The abilities of 27 Atmospheric Model Intercomparison Projection models to simulate the radiation budget (RB) over the East Asian monsoon region (EAMR) are analyzed based on Clouds and the Earth's Radiant Energy System Energy Balanced and Filled, hereafter CERES, products. The regional mean values of annual top of the atmosphere (TOA) net RB in the simulations are constantly larger than the CERES values in the majority of the models (24 of 27), due mainly to the overestimation of its shortwave (SW) component. The TOA SW RB overestimation in most models (25 of 27) is due mainly to the insufficient SW absorption by the atmosphere and the consequent superfluous downwelling shortwave radiation reaching and being absorbed by the surface. Both the intensity underestimation of SW cloud radiative forcing (CRF) and the inadequate clear-sky atmospheric SW absorption contribute to the overestimation of TOA SW RB in the models. The underestimation of SW CRF intensity is mainly due to the reduced total cloud cover simulated in most of the models compared with the general circulation model-oriented CALIPSO Cloud Product. Black carbon explains the greatest part of the clear-sky atmospheric SW absorption biases in most of the models. The persistent underestimation of TOA SW CRF intensity over the EAMR across all seasons largely explains the seasonally constant overestimation of TOA SW RB. The seasonal variation in clear-sky longwave (LW) RB demonstrates the remarkable seasonal variation in atmospheric and surface LW RB biases. 0321 Cloud/radiation interaction; 3359 Radiative processes; 3337 Global climate models; 3310 Clouds and cloud feedbacks; radiation budget; East Asia; AMIP5
Wang, Minghuai; Liu, Xiaohong; Zhang, Kai; Comstock, Jennifer M.Wang, M., X. Liu, K. Zhang, J. M. Comstock, 2014: Aerosol effects on cirrus through ice nucleation in the Community Atmosphere Model CAM5 with a statistical cirrus scheme. Journal of Advances in Modeling Earth Systems, 6(3), 756-776. doi: 10.1002/2014MS000339. A statistical cirrus scheme that tracks ice saturation ratio in the clear-sky and cloudy portion of a grid box separately has been implemented into the Community Atmosphere Model CAM5 to provide a consistent treatment of ice nucleation and cloud formation. Simulated ice supersaturation and ice crystal number concentrations strongly depend on the number concentrations of heterogeneous ice nuclei (IN), subgrid temperature formulas, and the number concentration of sulfate particles participating in homogeneous freezing, while simulated ice water content is insensitive to these perturbations. Allowing 1–10% of dust particles to serve as heterogeneous IN is found to produce ice supersaturation in better agreement with observations. Introducing a subgrid temperature perturbation based on long-term aircraft observations produces a better hemispheric contrast in ice supersaturation compared to observations. Heterogeneous IN from dust particles alter the net radiative fluxes at the top of atmosphere (TOA) (−0.24 to −1.59 W m−2) with a significant clear-sky longwave component (0.01 to −0.55 W m−2). Different cirrus treatments significantly perturb the net TOA anthropogenic aerosol forcing from −1.21 W m−2 to −1.54 W m−2, with a standard deviation of 0.10 W m−2. Aerosol effects on cirrus exert an even larger impact on the atmospheric component of the radiative fluxes (2 or 3 times the changes in the TOA radiative fluxes) and therefore through the fast atmosphere response on the hydrological cycle. This points to the urgent need to quantify aerosol effects on cirrus through ice nucleation and how these further affect the hydrological cycle. 0320 Cloud physics and chemistry; 3311 Clouds and aerosols; 0798 Modeling; Ice Nucleation; cirrus modeling; cirrus seeding; fast response
Wang, P.; Sneep, M.; Veefkind, J. P.; Stammes, P.; Levelt, P. F.Wang, P., M. Sneep, J. P. Veefkind, P. Stammes, P. F. Levelt, 2014: Evaluation of broadband surface solar irradiance derived from the Ozone Monitoring Instrument. Remote Sensing of Environment, 149, 88-99. doi: 10.1016/j.rse.2014.03.036. Surface solar irradiance (SSI) data are important for planning and estimating the production of solar power plants. Long-term high quality surface solar radiation data are needed for monitoring climate change. This paper presents a new surface solar irradiance dataset, the broadband (0.2–4 μm) surface solar irradiance product derived from the Ozone Monitoring Instrument (OMI). The OMI SSI algorithm is based on the Heliosat method and uses the OMI O2–O2 cloud product as main input. The OMI SSI data are validated against the globally distributed Baseline Surface Radiation Network (BSRN) measurements at 19 stations for the year 2008. Furthermore, the monthly mean OMI SSI data are compared to independent surface solar irradiance products from International Satellite Cloud Climatology Project Flux Data (ISCCP-FD) and Clouds and the Earth's Radiant Energy System (CERES) data for the year 2005. The mean difference between OMI SSI and BSRN global (direct + diffuse) irradiances is − 1.2 W m− 2 (− 0.2%), the root mean square error is 100.1 W m− 2 (18.1%), and the mean absolute error is 67.8 W m− 2 (12.2%). The differences between OMI SSI and BSRN global irradiances are smaller over continental and coastal sites and larger over deserts and islands. OMI SSI has a good agreement with the CERES shortwave (SW) model B surface downward flux (SDF) product. The correlation coefficient and index of agreement between monthly mean 1-degree gridded OMI SSI and CERES SW SDF are > 0.99. OMI SSI is lower than CERES SW SDF which is partly due to the solar zenith angle. On average, OMI SSI is 13.5 W m− 2 (2.5%) lower than the ISCCP-FD SW surface downward flux and the correlation coefficient and index of agreement are > 0.98 for every month. validation; Baseline Surface Radiation Network (BSRN); Broadband surface solar irradiance; CERES shortwave flux; ISCCP radiation product; OMI effective cloud fraction; Ozone Monitoring Instrument (OMI)
Wang, Zhili; Zhang, Hua; Lu, PengWang, Z., H. Zhang, P. Lu, 2014: Improvement of cloud microphysics in the aerosol-climate model BCC_AGCM2.0.1_CUACE/Aero, evaluation against observations, and updated aerosol indirect effect. Journal of Geophysical Research: Atmospheres, 119(13), 2014JD021886. doi: 10.1002/2014JD021886. A two-moment cloud microphysical scheme, to predict both the mass and number concentrations of cloud droplets and ice crystals, is implemented into the aerosol-climate model BCC_AGCM2.0.1_CUACE/Aero. The model results for aerosols, cloud properties, and meteorological fields are evaluated, and the anthropogenic aerosol indirect effect (AIE) is estimated. The new model simulates more realistic aerosol mass concentrations and optical depth compared with the original version using a one-moment bulk cloud microphysical scheme. The global annual mean column cloud droplet number concentration (CDNC) from the new model is 3.3 × 1010 m−2, which is comparable to the 4.0 × 1010 m−2 from satellite retrieval. The global annual mean cloud droplet effective radius at the cloud top from the new model is 8.1 µm, which is smaller than the 10.5 µm from observation. The simulated liquid water path (LWP) in the new model is significantly lower than that in the original model. In particular, the annual mean LWP is lower in the new model by more than 100 g m−2 in some midlatitude regions and hence much more consistent with satellite retrievals. Cloud radiative forcing and precipitation are improved to some extent in the new model. The global annual mean radiation budget at the top of the atmosphere is −0.6 W m−2, which is considerably different from the value of 1.8 W m−2 in the original model. The global annual mean anthropogenic AIE is estimated to be −1.9 W m−2 without imposing a lower bound of CDNC, whereas it is reduced significantly when a higher lower bound of CDNC is prescribed. 0320 Cloud physics and chemistry; 0305 Aerosols and particles; 0321 Cloud/radiation interaction; Cloud microphysics; climate model; aerosol indirect effect; two-moment scheme
Xi, Baike; Dong, Xiquan; Minnis, Patrick; Sun-Mack, SunnyXi, B., X. Dong, P. Minnis, S. Sun-Mack, 2014: Comparison of marine boundary layer cloud properties from CERES-MODIS Edition 4 and DOE ARM AMF measurements at the Azores. Journal of Geophysical Research: Atmospheres, 119(15), 2014JD021813. doi: 10.1002/2014JD021813. Marine boundary layer (MBL) cloud properties derived from the NASA Clouds and the Earth's Radiant Energy System (CERES) project using Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) data are compared with observations taken at the Department of Energy Atmospheric Radiation Measurement (ARM) Mobile Facility at the Azores (AMF-Azores) site from June 2009 through December 2010. Cloud properties derived from ARM ground-based observations were averaged over a 1 h interval centered at the satellite overpass time, while the CERES-MODIS (CM) results were averaged within a 30 km × 30 km grid box centered over the Azores site. A total of 63 daytime and 92 nighttime single-layered overcast MBL cloud cases were selected from 19 months of ARM radar-lidar and satellite observations. The CM cloud top/base heights (Htop/Hbase) were determined from cloud top/base temperatures (Ttop/Tbase) using a regional boundary layer lapse rate method. For daytime comparisons, the CM-derived Htop (Hbase), on average, is 0.063 km (0.068 km) higher (lower) than its ARM radar-lidar-observed counterpart, and the CM-derived Ttop and Tbase are 0.9 K less and 2.5 K greater than the surface values with high correlations (R2 = 0.82 and 0.84, respectively). In general, the cloud top comparisons agree better than the cloud base comparisons, because the CM cloud base temperatures and heights are secondary products determined from cloud top temperatures and heights. No significant day-night difference was found in the analyses. The comparisons of MBL cloud microphysical properties reveal that when averaged over a 30 km × 30 km area, the CM-retrieved cloud droplet effective radius (re) at 3.7 µm is 1.3 µm larger than that from the ARM retrievals (12.8 µm), while the CM-retrieved cloud liquid water path (LWP) is 13.5 gm−2 less than its ARM counterpart (114.2 gm−2) due to its small optical depth (9.6 versus 13.7). The differences are reduced by 50% when the CM averages are computed only using the MODIS pixel nearest the AMF site. Using the effective radius retrieved using 2.1 µm channel to calculate LWP can reduce the difference between the CM and ARM microwave radiometer retrievals from −13.7 to 2.1 gm−2. The 10% differences between the ARM and CERES-MODIS LWP and re retrievals are within the uncertainties of the ARM LWP (~20 gm−2) and re (~10%) retrievals; however, the 30% difference in optical depth is significant. Possible reasons contributing to this discrepancy are increased sensitivities in optical depth from both surface retrievals when τ~10 and topography. The τ differences vary with wind direction and are consistent with the island orography. Much better agreement in τ is obtained when using only those data taken when the wind is from the northeast, where topographical effects on the sampled clouds are minimal. 1640 Remote sensing; 0320 Cloud physics and chemistry; 0394 Instruments and techniques; 0321 Cloud/radiation interaction; validation; 0525 Data management; CERES MODIS; CERES-MODIS; ground-based measurements; macro- and microphysical properties; macrophysical and microphysical properties; Marine boundary layer clouds; microphysica retrieval; microphysical retrieval
Yang, Yuekui; Palm, Stephen P.; Marshak, Alexander; Wu, Dong L.; Yu, Hongbin; Fu, QiangYang, Y., S. P. Palm, A. Marshak, D. L. Wu, H. Yu, Q. Fu, 2014: First satellite-detected perturbations of outgoing longwave radiation associated with blowing snow events over Antarctica. Geophysical Research Letters, 41(2), 2013GL058932. doi: 10.1002/2013GL058932. We present the first satellite-detected perturbations of the outgoing longwave radiation (OLR) associated with blowing snow events over the Antarctic ice sheet using data from Cloud-Aerosol Lidar with Orthogonal Polarization and Clouds and the Earth's Radiant Energy System. Significant cloud-free OLR differences are observed between the clear and blowing snow sky, with the sign and magnitude depending on season and time of the day. During nighttime, OLRs are usually larger when blowing snow is present; the average difference in OLRs between without and with blowing snow over the East Antarctic Ice Sheet is about −5.2 W/m2 for the winter months of 2009. During daytime, in contrast, the OLR perturbation is usually smaller or even has the opposite sign. The observed seasonal variations and day-night differences in the OLR perturbation are consistent with theoretical calculations of the influence of blowing snow on OLR. Detailed atmospheric profiles are needed to quantify the radiative effect of blowing snow from the satellite observations. 0360 Radiation: transmission and scattering; CERES; 3359 Radiative processes; longwave radiation; 3360 Remote sensing; 0736 Snow; Antarctica; CALIPSO; 3349 Polar meteorology; radiative effects; blowing snow
Yin, Dongqin; Roderick, Michael L.; Leech, Guy; Sun, Fubao; Huang, YuefeiYin, D., M. L. Roderick, G. Leech, F. Sun, Y. Huang, 2014: The contribution of reduction in evaporative cooling to higher surface air temperatures during drought. Geophysical Research Letters, 41(22), 2014GL062039. doi: 10.1002/2014GL062039. Higher temperatures are usually reported during meteorological drought and there are two prevailing interpretations for this observation. The first is that the increase in temperature (T) causes an increase in evaporation (E) that dries the environment. The second states that the decline in precipitation (P) during drought reduces the available water thereby decreasing E, and in turn the consequent reduction in evaporative cooling causes higher T. To test which of these interpretations is correct, we use climatic data (T, P) and a recently released database (CERES) that includes incoming and outgoing shortwave and longwave surface radiative fluxes to study meteorological drought at four sites (parts of Australia, US, and Brazil), using the Budyko approximation to calculate E. The results support the second interpretation at arid sites. The analysis also showed that increases in T due to drought have a different radiative signature from increases in T due to elevated CO2. drought; 1812 Drought
Yu, S.; Mathur, R.; Pleim, J.; Wong, D.; Gilliam, R.; Alapaty, K.; Zhao, C.; Liu, X.Yu, S., R. Mathur, J. Pleim, D. Wong, R. Gilliam, K. Alapaty, C. Zhao, X. Liu, 2014: Aerosol indirect effect on the grid-scale clouds in the two-way coupled WRF–CMAQ: model description, development, evaluation and regional analysis. Atmos. Chem. Phys., 14(20), 11247-11285. doi: 10.5194/acp-14-11247-2014. This study implemented first, second and glaciation aerosol indirect effects (AIE) on resolved clouds in the two-way coupled Weather Research and Forecasting Community Multiscale Air Quality (WRF–CMAQ) modeling system by including parameterizations for both cloud drop and ice number concentrations on the basis of CMAQ-predicted aerosol distributions and WRF meteorological conditions. The performance of the newly developed WRF–CMAQ model, with alternate Community Atmospheric Model (CAM) and Rapid Radiative Transfer Model for GCMs (RRTMG) radiation schemes, was evaluated with observations from the Clouds and the See http://ceres.larc.nasa.gov/. Earth's Radiant Energy System (CERES) satellite and surface monitoring networks (AQS, IMPROVE, CASTNET, STN, and PRISM) over the continental US (CONUS) (12 km resolution) and eastern Texas (4 km resolution) during August and September of 2006. The results at the Air Quality System (AQS) surface sites show that in August, the normalized mean bias (NMB) values for PM2.5 over the eastern US (EUS) and the western US (WUS) are 5.3% (−0.1%) and 0.4% (−5.2%) for WRF–CMAQ/CAM (WRF–CMAQ/RRTMG), respectively. The evaluation of PM2.5 chemical composition reveals that in August, WRF–CMAQ/CAM (WRF–CMAQ/RRTMG) consistently underestimated the observed SO42- by −23.0% (−27.7%), −12.5% (−18.9%) and −7.9% (−14.8%) over the EUS at the Clean Air Status Trends Network (CASTNET), Interagency Monitoring of Protected Visual Environments (IMPROVE) and Speciated Trends Network (STN) sites, respectively. Both configurations (WRF–CMAQ/CAM, WRF–CMAQ/RRTMG) overestimated the observed mean organic carbon (OC), elemental carbon (EC) and and total carbon (TC) concentrations over the EUS in August at the IMPROVE sites. Both configurations generally underestimated the cloud field (shortwave cloud forcing, SWCF) over the CONUS in August due to the fact that the AIE on the subgrid convective clouds was not considered when the model simulations were run at the 12 km resolution. This is in agreement with the fact that both configurations captured SWCF and longwave cloud forcing (LWCF) very well for the 4 km simulation over eastern Texas, when all clouds were resolved by the finer resolution domain. The simulations of WRF–CMAQ/CAM and WRF–CMAQ/RRTMG show dramatic improvements for SWCF, LWCF, cloud optical depth (COD), cloud fractions and precipitation over the ocean relative to those of WRF default cases in August. The model performance in September is similar to that in August, except for a greater overestimation of PM2.5 due to the overestimations of SO42-, NH4+, NO3-, and TC over the EUS, less underestimation of clouds (SWCF) over the land areas due to the lower SWCF values, and fewer convective clouds in September. This work shows that inclusion of indirect aerosol effect treatments in WRF–CMAQ represents a significant advancement and milestone in air quality modeling and the development of integrated emissions control strategies for air quality management and climate change mitigation.
Yu, Shaocai; Alapaty, Kiran; Mathur, Rohit; Pleim, Jonathan; Zhang, Yuanhang; Nolte, Chris; Eder, Brian; Foley, Kristen; Nagashima, TatsuyaYu, S., K. Alapaty, R. Mathur, J. Pleim, Y. Zhang, C. Nolte, B. Eder, K. Foley, T. Nagashima, 2014: Attribution of the United States “warming hole”: Aerosol indirect effect and precipitable water vapor. Scientific Reports, 4. doi: 10.1038/srep06929. Aerosols can influence the climate indirectly by acting as cloud condensation nuclei and/or ice nuclei, thereby modifying cloud optical properties. In contrast to the widespread global warming, the central and south central United States display a noteworthy overall cooling trend during the 20th century, with an especially striking cooling trend in summertime daily maximum temperature (Tmax) (termed the U.S. “warming hole”). Here we used observations of temperature, shortwave cloud forcing (SWCF), longwave cloud forcing (LWCF), aerosol optical depth and precipitable water vapor as well as global coupled climate models to explore the attribution of the “warming hole”. We find that the observed cooling trend in summer Tmax can be attributed mainly to SWCF due to aerosols with offset from the greenhouse effect of precipitable water vapor. A global coupled climate model reveals that the observed “warming hole” can be produced only when the aerosol fields are simulated with a reasonable degree of accuracy as this is necessary for accurate simulation of SWCF over the region. These results provide compelling evidence of the role of the aerosol indirect effect in cooling regional climate on the Earth. Our results reaffirm that LWCF can warm both winter Tmax and Tmin. Attribution; Environmental sciences
Zhang, Chengzhu; Wang, Minghuai; Morrison, Hugh; Somerville, Richard C. J.; Zhang, Kai; Liu, Xiaohong; Li, Jui-Lin F.Zhang, C., M. Wang, H. Morrison, R. C. J. Somerville, K. Zhang, X. Liu, J. F. Li, 2014: Investigating ice nucleation in cirrus clouds with an aerosol-enabled Multiscale Modeling Framework. Journal of Advances in Modeling Earth Systems, 6(4), 998-1015. doi: 10.1002/2014MS000343. In this study, an aerosol-dependent ice nucleation scheme has been implemented in an aerosol-enabled Multiscale Modeling Framework (PNNL MMF) to study ice formation in upper troposphere cirrus clouds through both homogeneous and heterogeneous nucleation. The MMF model represents cloud scale processes by embedding a cloud-resolving model (CRM) within each vertical column of a GCM grid. By explicitly linking ice nucleation to aerosol number concentration, CRM-scale temperature, relative humidity and vertical velocity, the new MMF model simulates the persistent high ice supersaturation and low ice number concentration (10–100/L) at cirrus temperatures. The new model simulates the observed shift of the ice supersaturation PDF toward higher values at low temperatures following the homogeneous nucleation threshold. The MMF model predicts a higher frequency of midlatitude supersaturation in the Southern Hemisphere and winter hemisphere, which is consistent with previous satellite and in situ observations. It is shown that compared to a conventional GCM, the MMF is a more powerful model to simulate parameters that evolve over short time scales such as supersaturation. Sensitivity tests suggest that the simulated global distribution of ice clouds is sensitive to the ice nucleation scheme and the distribution of sulfate and dust aerosols. Simulations are also performed to test empirical parameters related to auto-conversion of ice crystals to snow. Results show that with a value of 250 μm for the critical diameter, Dcs, that distinguishes ice crystals from snow, the model can produce good agreement with the satellite-retrieved products in terms of cloud ice water path and ice water content, while the total ice water is not sensitive to the specification of Dcs value. 1610 Atmosphere; 0305 Aerosols and particles; 1863 Snow and ice; 3311 Clouds and aerosols; superparameterization; aerosol cloud interaction; Cirrus Simulation; Ice Nucleation; Super-parameterization
Zhang, Damao; Luo, Tao; Liu, Dong; Wang, ZhienZhang, D., T. Luo, D. Liu, Z. Wang, 2014: Spatial scales of altocumulus clouds observed with collocated CALIPSO and CloudSat measurements. Atmospheric Research, 149, 58-69. doi: 10.1016/j.atmosres.2014.05.023. Altocumulus (Ac) clouds are important, yet climate models have difficulties in simulating and predicting these clouds, due to their small horizontal scales and thin vertical extensions. In this research, 4 years of collocated Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar and CloudSat radar measurements is analyzed to study the along-track horizontal scales and vertical depths of Ac clouds. Methodology to calculate Ac along-track horizontal scale and vertical depth using collocated CALIPSO and CloudSat measurements is introduced firstly. The global mean Ac along-track horizontal scale is 40.2 km, with a standard deviation of 52.3 km. Approximately 93.6% of Ac cannot be resolved by climate models with a grid resolution of 1°. The global mean mixed-phase Ac vertical depth is 1.96 km, with a standard deviation of 1.10 km. Global distributions of the Ac along-track horizontal scales and vertical depths are presented and possible factors contributing to their geographical differences are analyzed. The result from this study can be used to improve Ac parameterizations in climate models and validate the model simulations. Altocumulus clouds; CALIPSO and CloudSat; Horizontal scale and vertical depth
Zhang, Xiaotong; Liang, Shunlin; Zhou, Gongqi; Wu, Haoran; Zhao, XiangZhang, X., S. Liang, G. Zhou, H. Wu, X. Zhao, 2014: Generating Global LAnd Surface Satellite incident shortwave radiation and photosynthetically active radiation products from multiple satellite data. Remote Sensing of Environment, 152, 318-332. doi: 10.1016/j.rse.2014.07.003. Incident shortwave radiation (ISR) at the surface is an essential parameter in the land surface radiation budget and in many land surface process models. Incident photosynthetically active radiation (PAR) is required by nearly all terrestrial ecosystem models. Although several global radiation products from numeric models and satellite observations have been released, their coarse spatial resolutions and low accuracy, especially at high altitude regions, limit their applications in land community. In this study, the Global LAnd Surface Satellite (GLASS) ISR and PAR products are developed based on an improved look-up table method from 2008 to 2010 at a 5 km spatial resolution and a 3 hour temporal resolution, the first global radiation products at such high resolutions, from multiple polar-orbiting and geostationary satellite data, including the Moderate Resolution Imaging Spectroradiometer (MODIS), the Meteosat Second Generation (MSG2) SEVIRI, the Multi-functional Transport Satellite (MTSAT)-1R, and the Geostationary Operational Environmental Satellite (GOES) Imager. The look-up table algorithm primarily considers the influences of surface elevation, atmospheric water vapor because sensitivity experiments indicate that ISR and PAR are more sensitive to surface elevation, and less sensitive to atmospheric profiles and ozone amount. The water vapor absorption has strong impact on ISR but weak on PAR. Moreover, the surface bi-directional reflectance distribution function (BRDF) is taken into account to retrieve spatially and temporally continuous surface reflectances from the geostationary satellite observations, which is an input parameter in the revised look-up table method. Ground-based measurement data from 34 sites are used to validate the improved algorithm and the GLASS products. The validation results of the instantaneous ISR and PAR products at all validation sites are notably good with coefficient of determination values of 0.83 and 0.84, respectively, and root mean square error values of 115.0 Wm− 2 and 49.0 Wm− 2, respectively. We also aggregate the GLASS ISR product for comparing with the corresponding ISCCP and CERES data at 7 SURFRAD sites and demonstrate that the GLASS ISR product is more accurate. The GLASS ISR and PAR products have been made publicly available. Shortwave radiation; Global irradiance; Photosynthetically active radiation
Zhang, Yi; Chen, Haoming; Yu, RucongZhang, Y., H. Chen, R. Yu, 2014: Simulations of Stratus Clouds over Eastern China in CAM5: Sensitivity to Horizontal Resolution. J. Climate, 27(18), 7033-7052. doi: 10.1175/JCLI-D-13-00732.1. AbstractThis paper evaluates the simulations of stratus clouds over eastern China (EC) in the Community Atmosphere Model, version 5 (CAM5), with an emphasis on the impact of changing horizontal resolutions on the performance. CAM5 in all experiments generally satisfactorily simulates the cloud radiative features over EC, including the spatial distributions of the continental shortwave cloud radiative forcing (SWCF) and stratus regimes, the responses of SWCF to the dynamic and thermodynamic ambient environment, and several relations in the environmental fields that are favorable to the stratus formation. Meanwhile, all experiments suffer from similar biases. Models tend to underestimate the stratus amount because of a corresponding underestimate of stratus occurrence frequency, while the stratus amount when present (AWP) is generally higher than that in the observation. Models also simulate similar errors in the environmental fields. The differences between low- and high-resolution experiments are distinct. An increase of resolution enhances the SWCF in southern China, but the skill deteriorates in the Sichuan basin. Correspondingly, the stratus amount increases in southern China from low- to high-resolution experiments, mainly because of more stratus occurrences, which are found to be related to the better represented environmental fields in the high-resolution experiments, especially the dynamic component. Several relations in the ambient environment are also slightly improved in the high-resolution experiments. Meanwhile, the reason for the decrease of stratus AWP within the Sichuan basin, which is mainly responsible for the decreased stratus amounts and weaker SWCF from low- to high-resolution experiments, is also discussed. clouds; Model evaluation/performance; General circulation models
Zhou, C.; Dessler, A. E.; Zelinka, M. D.; Yang, P.; Wang, T.Zhou, C., A. E. Dessler, M. D. Zelinka, P. Yang, T. Wang, 2014: Cirrus feedback on interannual climate fluctuations. Geophysical Research Letters, 2014GL062095. doi: 10.1002/2014GL062095. Cirrus clouds are not only important in determining the current climate but also play an important role in climate change and variability. Analysis of satellite observations shows that the amount and altitude of cirrus clouds (cloud optical depth 1640 Remote sensing; 0321 Cloud/radiation interaction; 1616 Climate variability; cloud feedback; cirrus; 0319 Cloud optics; climate change and variability
Zhou, Liming; Tian, Yuhong; Myneni, Ranga B.; Ciais, Philippe; Saatchi, Sassan; Liu, Yi Y.; Piao, Shilong; Chen, Haishan; Vermote, Eric F.; Song, Conghe; Hwang, TaeheeZhou, L., Y. Tian, R. B. Myneni, P. Ciais, S. Saatchi, Y. Y. Liu, S. Piao, H. Chen, E. F. Vermote, C. Song, T. Hwang, 2014: Widespread decline of Congo rainforest greenness in the past decade. Nature, 509(7498), 86-90. doi: 10.1038/nature13265. Tropical forests are global epicentres of biodiversity and important modulators of climate change, and are mainly constrained by rainfall patterns. The severe short-term droughts that occurred recently in Amazonia have drawn attention to the vulnerability of tropical forests to climatic disturbances. The central African rainforests, the second-largest on Earth, have experienced a long-term drying trend whose impacts on vegetation dynamics remain mostly unknown because in situ observations are very limited. The Congolese forest, with its drier conditions and higher percentage of semi-evergreen trees, may be more tolerant to short-term rainfall reduction than are wetter tropical forests, but for a long-term drought there may be critical thresholds of water availability below which higher-biomass, closed-canopy forests transition to more open, lower-biomass forests. Here we present observational evidence for a widespread decline in forest greenness over the past decade based on analyses of satellite data (optical, thermal, microwave and gravity) from several independent sensors over the Congo basin. This decline in vegetation greenness, particularly in the northern Congolese forest, is generally consistent with decreases in rainfall, terrestrial water storage, water content in aboveground woody and leaf biomass, and the canopy backscatter anomaly caused by changes in structure and moisture in upper forest layers. It is also consistent with increases in photosynthetically active radiation and land surface temperature. These multiple lines of evidence indicate that this large-scale vegetation browning, or loss of photosynthetic capacity, may be partially attributable to the long-term drying trend. Our results suggest that a continued gradual decline of photosynthetic capacity and moisture content driven by the persistent drying trend could alter the composition and structure of the Congolese forest to favour the spread of drought-tolerant species. Climate-change impacts
Alexandri, G.; Meleti, C.; Georgoulias, A. K.; Balis, D.Alexandri, G., C. Meleti, A. K. Georgoulias, D. Balis, 2013: Trends of Shortwave and Longwave Surface Radiation in Europe: Spatiotemporal Analysis and Comparison of Satellite and Ground-Based Observations. Advances in Meteorology, Climatology and Atmospheric Physics, 857-864. A detailed investigation of the shortwave (SW) and longwave (LW) up-welling and down-welling surface radiation trends over Europe is presented here. For the purposes of this work, satellite observations from the International Satellite Cloud Climatology Project (ISCCP) for the period 1984–2009 have been spatiotemporally analyzed at a ~280 × 280 km2 resolution. A Fourier-based harmonic analysis technique has been used for the calculation of the trend also allowing for the assessment of its statistical significance. The results are compared to trends calculated from ground-based observations from several World Radiation Data Center (WRDC) stations. The stations have been categorized taking into account their position and the special characteristics of the surrounding region (rural/urban, high/low elevation, population, etc.). The variability of the SW and LW radiation within selected ISCCP grid cells is investigated with the use of ground-based observations. Observed trends and their significance depends on the area of study. Estimated trend for SW radiation over Europe as derived from ISCCP data for the period 1984–2009 is about −0.6 W/m2 and for LW radiation is about 2.47 W/m2. Meteorology/Climatology; climate change; Atmospheric Protection/Air Quality Control/Air Pollution; Environmental Health; Environmental Monitoring/Analysis; Natural Hazards
Bardeen, C. G.; Gettelman, A.; Jensen, E. J.; Heymsfield, A.; Conley, A. J.; Delanoë, J.; Deng, M.; Toon, O. B.Bardeen, C. G., A. Gettelman, E. J. Jensen, A. Heymsfield, A. J. Conley, J. Delanoë, M. Deng, O. B. Toon, 2013: Improved cirrus simulations in a general circulation model using CARMA sectional microphysics. Journal of Geophysical Research: Atmospheres, 118(20), 11,679–11,697. doi: 10.1002/2013JD020193. We have developed a new cirrus model incorporating sectional ice microphysics from the Community Aerosol and Radiation Model for Atmospheres (CARMA) in the latest version of NCAR's Community Atmosphere Model (CAM5). Comparisons with DARDAR and 2C-ICE show that CAM5/CARMA improves cloud fraction, ice water content, and ice water path compared to the standard CAM5. Prognostic snow in CAM5/CARMA increases overall ice mass and results in a melting layer at 4 km in the tropics that is largely absent in CAM5. Subgrid scale supersaturation following Wilson and Ballard (1999) improves ice mass and relative humidity. Increased middle and upper tropospheric condensate in CAM5/CARMA requires a reduction in low-level cloud for energy balance, resulting in a 3.1 W m−2 improvement in shortwave cloud forcing and a 3.8 W m−2 improvement in downwelling shortwave flux at the surface compared to CAM5 and Clouds and Earth's Radiant Energy Systems (CERES). Total and clear-sky longwave upwelling flux at the top are improved in CAM5/CARMA by 1.0 and 2.6 W m−2, respectively. CAM has a 2–3 K cold bias at the tropical tropopause mostly from the prescribed ozone file. Correction of the prescribed ozone or nudging the CAM5/CARMA model to GEOS5-DAS meteorology yields tropical tropopause temperatures and water vapor that agree with the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) and the Microwave Limb Sounder (MLS). CAM5 relative humidity appears to be too large resulting in a +1.5 ppmv water vapor bias at the tropical tropopause when using GEOS5-DAS meteorology. In CAM5/CARMA, 75% of the cloud ice mass originates from ice particles detrained from convection compared to 25% from in situ nucleation. microphysics; CloudSat; CALIPSO; CARMA; cirrus; tropopause
Benedict, James J.; Maloney, Eric D.; Sobel, Adam H.; Frierson, Dargan M.; Donner, Leo J.Benedict, J. J., E. D. Maloney, A. H. Sobel, D. M. Frierson, L. J. Donner, 2013: Tropical Intraseasonal Variability in Version 3 of the GFDL Atmosphere Model. J. Climate, 26(2), 426-449. doi: 10.1175/JCLI-D-12-00103.1.
Bengtsson, Lennart; Hodges, Kevin I.; Koumoutsaris, Symeon; Zahn, Matthias; Berrisford, PaulBengtsson, L., K. I. Hodges, S. Koumoutsaris, M. Zahn, P. Berrisford, 2013: The Changing Energy Balance of the Polar Regions in a Warmer Climate. J. Climate, 26(10), 3112-3129. doi: 10.1175/JCLI-D-12-00233.1. AbstractEnergy fluxes for polar regions are examined for two 30-yr periods, representing the end of the twentieth and twenty-first centuries, using data from high-resolution simulations with the ECHAM5 climate model. The net radiation to space for the present climate agrees well with data from the Clouds and the Earth’s Radiant Energy System (CERES) over the northern polar region but shows an underestimation in planetary albedo for the southern polar region. This suggests there are systematic errors in the atmospheric circulation or in the net surface energy fluxes in the southern polar region. The simulation of the future climate is based on the Intergovernmental Panel on Climate Change (IPCC) A1B scenario. The total energy transport is broadly the same for the two 30-yr periods, but there is an increase in the moist energy transport on the order of 6 W m−2 and a corresponding reduction in the dry static energy. For the southern polar region the proportion of moist energy transport is larger and the dry static energy correspondingly smaller for both periods.The results suggest a possible mechanism for the warming of the Arctic that is discussed. Changes between the twentieth and twenty-first centuries in the northern polar region show the net ocean surface radiation flux in summer increases ~18 W m−2 (24%). For the southern polar region the response is different as there is a decrease in surface solar radiation. It is suggested that this is caused by changes in cloudiness associated with the poleward migration of the storm tracks. Energy budget/balance; Hydrologic cycle; Atmospheric circulation; Budgets; Heat budgets/fluxes; Anthropogenic effects
Berry, Elizabeth; Mace, Gerald G.Berry, E., G. G. Mace, 2013: Cirrus Cloud Properties and the Large-Scale Meteorological Environment: Relationships Derived from A-Train and NCEP–NCAR Reanalysis Data. J. Appl. Meteor. Climatol., 52(5), 1253-1276. doi: 10.1175/JAMC-D-12-0102.1.
Bizard, A.; Caillault, K.; Lavigne, C.; Roblin, A.; Chervet, P.Bizard, A., K. Caillault, C. Lavigne, A. Roblin, P. Chervet, 2013: Application of Cloud Occurrence Climatology from CALIOP to Evaluate Performances of Airborne and Satellite Electro-Optical Sensors. J. Atmos. Oceanic Technol., 30(10), 2406-2416. doi: 10.1175/JTECH-D-12-00276.1.
Blunden, Jessica; Arndt, Derek S.Blunden, J., D. S. Arndt, 2013: State of the Climate in 2012. Bull. Amer. Meteor. Soc., 94(8), S1-S258. doi: 10.1175/2013BAMSStateoftheClimate.1.
Bogenschutz, Peter A.; Gettelman, Andrew; Morrison, Hugh; Larson, Vincent E.; Craig, Cheryl; Schanen, David P.Bogenschutz, P. A., A. Gettelman, H. Morrison, V. E. Larson, C. Craig, D. P. Schanen, 2013: Higher-Order Turbulence Closure and Its Impact on Climate Simulations in the Community Atmosphere Model. J. Climate, 26(23), 9655-9676. doi: 10.1175/JCLI-D-13-00075.1.
Bourassa, Mark A.; Gille, Sarah T.; Bitz, Cecilia; Carlson, David; Cerovecki, Ivana; Clayson, Carol Anne; Cronin, Meghan F.; Drennan, Will M.; Fairall, Chris W.; Hoffman, Ross N.; Magnusdottir, Gudrun; Pinker, Rachel T.; Renfrew, Ian A.; Serreze, Mark; Speer, Kevin; Talley, Lynne D.; Wick, Gary A.Bourassa, M. A., S. T. Gille, C. Bitz, D. Carlson, I. Cerovecki, C. A. Clayson, M. F. Cronin, W. M. Drennan, C. W. Fairall, R. N. Hoffman, G. Magnusdottir, R. T. Pinker, I. A. Renfrew, M. Serreze, K. Speer, L. D. Talley, G. A. Wick, 2013: High-Latitude Ocean and Sea Ice Surface Fluxes: Challenges for Climate Research. Bull. Amer. Meteor. Soc., 94(3), 403-423. doi: 10.1175/BAMS-D-11-00244.1.
Chambers, Lin; Bethea, KatieChambers, L., K. Bethea, 2013: Energy Budget: Earth's Most Important and Least Appreciated Planetary Attribute. Universe in the Classroom, 1-4. The energy budget involves more than one kind of energy. People can sense this energy in different ways, depending on what type of energy it is. We see visible light using our eyes. We feel infrared energy using our skin . We know some species of animals can see ultraviolet light and portions of the infrared spectrum. NASA satellites use instruments that can "see" different parts of the electromagnetic spectrum to observe various processes in the Earth system, including the energy budget. The Sun is a very hot ball of plasma emitting large amounts of energy. By the time it reaches Earth, this energy amounts to about 340 Watts for every square meter of Earth on average. That's almost 6 60-Watt light bulbs for every square meter of Earth! With all of that energy shining down on the Earth, how does our planet maintain a comfortable balance that allows a complex ecosystem, including humans, to thrive? The key thing to remember is the Sun - hot though it is - is a tiny part of Earth's environment. Earth's energy budget is a critical but little understood aspect of our planetary home. NASA is actively studying this important Earth system feature, and sharing data and knowledge about it with the education community. energy budgets; infrared radiation; ecosystems; electromagnetic spectra; high temperature plasmas; luminaires; sun; ultraviolet radiation
Chen, Siyu; Huang, Jianping; Zhao, Chun; Qian, Yun; Leung, L. Ruby; Yang, BenChen, S., J. Huang, C. Zhao, Y. Qian, L. R. Leung, B. Yang, 2013: Modeling the transport and radiative forcing of Taklimakan dust over the Tibetan Plateau: A case study in the summer of 2006. Journal of Geophysical Research: Atmospheres, 118(2), 797–812. doi: 10.1002/jgrd.50122. The Weather Research and Forecasting model with chemistry (WRF-Chem) is used to investigate an intense dust storm event during 26 to 30 July 2006 that originated over the Taklimakan Desert (TD) and transported to the northern slope of Tibetan Plateau (TP). The dust storm is initiated by the approach of a strong cold frontal system over the TD. In summer, the meridional transport of TD dust to the TP is favored by the thermal effect of the TP and the weakening of the East Asian westerly winds. During this dust storm, the transport of TD dust over the TP is further enhanced by the passage of the cold front. As a result, TD dust breaks through the planetary boundary layer and extends to the upper troposphere over the northern TP. TD dust flux arrived at the TP with a value of 6.6 Gg/day in this 5 day event but decays quickly during the southward migration over the TP due to dry deposition. The simulations show that TD dust cools the atmosphere near the surface and heats the atmosphere above with a maximum heating rate of 0.11 K day−1 at 7 km over the TP. The event-averaged net radiative forcings of TD dust over the TP are −3.97, 1.61, and −5.58 W m−2 at the top of the atmosphere (TOA), in the atmosphere, and at the surface, respectively. The promising performance of WRF-Chem in simulating dust and its radiative forcing provides confidence for use in further investigation of climatic impact of TD dust over the TP. radiative forcing; transport; Tibetan Plateau; Taklimakan dust
Cheng, Anning; Xu, Kuan-ManCheng, A., K. Xu, 2013: Evaluating Low-Cloud Simulation from an Upgraded Multiscale Modeling Framework Model. Part III: Tropical and Subtropical Cloud Transitions over the Northern Pacific. J. Climate, 26(16), 5761-5781. doi: 10.1175/JCLI-D-12-00650.1. AbstractAn analysis of simulated cloud regime transitions along a transect from the subtropical California coast to the tropics for the northern summer season (June–August) is presented in this study. The Community Atmosphere Model, version 5 (CAM5), superparameterized CAM (SPCAM), and an upgraded SPCAM with intermediately prognostic higher-order closure (SPCAM-IPHOC) are used to perform global simulations by imposing climatological sea surface temperature and sea ice distributions. The seasonal-mean properties are compared with recent observations of clouds, radiation, and precipitation and with multimodel intercomparison results. There are qualitative agreements in the characteristics of cloud regimes along the transect among the three models. CAM5 simulates precipitation and shortwave radiative fluxes well but the stratocumulus-to-cumulus transition occurs too close to the coast of California. SPCAM-IPHOC simulates longwave radiative fluxes and precipitable water well, but with systematic biases in shortwave radiative fluxes. The broad, stronger ascending band in SPCAM is related to the large biases in the convective region but the characteristics of the stratocumulus region are still more realistic and the transition occurs slightly farther away from the coast than in CAM5. Even though SPCAM-IPHOC produces the most realistic seasonal-mean transition, it underestimates the mean gradient in low-cloud cover (LCC) across the mean transition location because of an overestimate of LCC in the transition and convective regions that shifts the transition locations farther from the coast. Analysis of two decoupling measures shows consistency in the mean location and the histogram of decoupling locations with those of LCC transition. CAM5, however, lacks such a consistency, suggesting a need for further refinement of its boundary layer cloud parameterization.
Chepfer, H.; Cesana, G.; Winker, D.; Getzewich, B.; Vaughan, M.; Liu, Z.Chepfer, H., G. Cesana, D. Winker, B. Getzewich, M. Vaughan, Z. Liu, 2013: Comparison of Two Different Cloud Climatologies Derived from CALIOP-Attenuated Backscattered Measurements (Level 1): The CALIPSO -ST and the CALIPSO -GOCCP. J. Atmos. Oceanic Technol., 30(4), 725-744. doi: 10.1175/JTECH-D-12-00057.1.
Christensen, Matthew W.; Stephens, Graeme L.; Lebsock, Matthew D.Christensen, M. W., G. L. Stephens, M. D. Lebsock, 2013: Exposing biases in retrieved low cloud properties from CloudSat: A guide for evaluating observations and climate data. Journal of Geophysical Research: Atmospheres, 118(21), 12,120–12,131. doi: 10.1002/2013JD020224. This study provides an assessment of low cloud properties retrieved from CloudSat, MODIS (Moderate Resolution Imaging Spectroradiometer), and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation with the goal of exposing biases that hinder meaningful comparisons with the simulated cloud properties in global climate models (GCMs). Being pertinent to GCM comparisons, CloudSat is the only satellite that can provide the vertical structure of cloud water and ice content from space. Biases in CloudSat low cloud properties are found to be tied to problems involving cloud detection and algorithm retrieval failures related to precipitation and strict cloud screening procedures. We show that MODIS and CloudSat cloud liquid water path (LWP) data agree when carefully screened for lack of precipitation but significantly depart in precipitating clouds due to rain water contamination of LWP in the CloudSat retrieval algorithm. The presence of drizzle and rain (occurring about 20% of the time) is associated with different mean LWP, mean particle sizes, and optical depths of all low clouds and therefore the radiative properties of the oceanic low clouds. Another more significant source of the LWP bias stems from the apparent lack of cloud detection. On average, the Cloud Profiling Radar misses clouds with adequate liquid and ice water retrievals as detected by MODIS in approximately 45% of warm clouds with the bulk of the bias occurring in clouds below 1 km in the so-called “ground clutter zone.” By incorporating additional sensors such as MODIS, the following results suggest that this LWP bias can be greatly reduced. climate; MODIS; LWP; CloudSat; CALIPSO; 2B-CWC-RO
Decoster, I.; Clerbaux, N.; Baudrez, E.; Dewitte, S.; Ipe, A.; Nevens, S.; Velazquez Blazquez, A.; Cornelis, J.Decoster, I., N. Clerbaux, E. Baudrez, S. Dewitte, A. Ipe, S. Nevens, A. Velazquez Blazquez, J. Cornelis, 2013: A Spectral Aging Model for the Meteosat-7 Visible Band. J. Atmos. Oceanic Technol., 30(3), 496-509. doi: 10.1175/JTECH-D-12-00124.1.
Dessler, A. E.Dessler, A. E., 2013: Observations of Climate Feedbacks over 2000–10 and Comparisons to Climate Models*. J. Climate, 26(1), 333-342. doi: 10.1175/JCLI-D-11-00640.1.
Dessler, A. E.; Loeb, N.g.Dessler, A. E., N. Loeb, 2013: Impact of dataset choice on calculations of the short-term cloud feedback. Journal of Geophysical Research: Atmospheres, 118(7), 2821–2826. doi: 10.1002/jgrd.50199. Dessler [2010, hereafter D10] estimated the magnitude of the cloud feedback in response to short-term climate variations and concluded that it was likely positive, with an average magnitude of +0.50 ± 0.75 W/m2/K. This paper investigates the sensitivity of D10's results to the choice of clear-sky top-of-atmosphere flux (ΔRclear-sky), surface temperature (ΔTs), and reanalysis data sets. Most of the alternative ΔRclear-sky data sets produce cloud feedbacks that are close to D10, differing by 0.2–0.3 W/m2/K. An exception is the Terra SSF1deg ΔRclear-sky product, which produces an overall negative cloud feedback. However, a critical examination of those data leads us to conclude that that result is due to problems in the Terra ΔRclear-sky arising from issues with cloud clearing prior to July 2001. Eliminating the problematic early portion yields a cloud feedback in good agreement with D10. We also present an alternative calculation of the cloud feedback that does not require an estimate of ΔRclear-sky, and this calculation also produces a positive cloud feedback in agreement with D10. The various ΔTs data sets produce cloud feedbacks that differ by as much as 0.8 W/m2/K. The choice of reanalysis, used as a source of ΔRclear-sky or as adjustments for the cloud radiative forcing, has a small impact on the inferred cloud feedback. Overall, these results confirm the robustness of D10's estimate of a likely positive feedback. energy budget; cloud feedback
Doelling, David R.; Loeb, Norman G.; Keyes, Dennis F.; Nordeen, Michele L.; Morstad, Daniel; Nguyen, Cathy; Wielicki, Bruce A.; Young, David F.; Sun, MoguoDoelling, D. R., N. G. Loeb, D. F. Keyes, M. L. Nordeen, D. Morstad, C. Nguyen, B. A. Wielicki, D. F. Young, M. Sun, 2013: Geostationary Enhanced Temporal Interpolation for CERES Flux Products. J. Atmos. Oceanic Technol., 30(6), 1072-1090. doi: 10.1175/JTECH-D-12-00136.1.
Donohoe, Aaron; Battisti, David S.Donohoe, A., D. S. Battisti, 2013: The Seasonal Cycle of Atmospheric Heating and Temperature. J. Climate, 26(14), 4962-4980. doi: 10.1175/JCLI-D-12-00713.1.
Donohoe, Aaron; Marshall, John; Ferreira, David; Mcgee, DavidDonohoe, A., J. Marshall, D. Ferreira, D. Mcgee, 2013: The Relationship between ITCZ Location and Cross-Equatorial Atmospheric Heat Transport: From the Seasonal Cycle to the Last Glacial Maximum. J. Climate, 26(11), 3597-3618. doi: 10.1175/JCLI-D-12-00467.1.
Evans, K. J.; Lauritzen, P. H.; Mishra, S. K.; Neale, R. B.; Taylor, M. A.; Tribbia, J. J.Evans, K. J., P. H. Lauritzen, S. K. Mishra, R. B. Neale, M. A. Taylor, J. J. Tribbia, 2013: AMIP Simulation with the CAM4 Spectral Element Dynamical Core. J. Climate, 26(3), 689-709. doi: 10.1175/JCLI-D-11-00448.1.
Feng, Nan; Christopher, Sundar A.Feng, N., S. A. Christopher, 2013: Satellite and surface-based remote sensing of Southeast Asian aerosols and their radiative effects. Atmospheric Research, 122, 544-554. doi: 10.1016/j.atmosres.2012.02.018. Using one year (December 2006–November 2007) of the Moderate Resolution Imaging SpectroRadiometer (MODIS), Multi-Angle Imaging SpectroRadiometer (MISR), and Clouds and the Earth's Radiant Energy System (CERES) data sets from NASA's Terra satellite, we assess the spatial and temporal distributions of aerosol properties (Aerosol Optical Depth, Fine Mode Fraction, and Single Scattering albedo) in the Southeast Asian region (SEA, 10°S–25°N, 90°E–150°E). We also provide a quantitative evaluation of regional cloud-free diurnally averaged shortwave aerosol radiative effects (SWARE) at the top of atmosphere (TOA) over both land and ocean. Our results indicate that the diurnally averaged shortwave radiative effects at the TOA over land and ocean are (− 6.4 ± 1.2 W m− 2) and (− 5.9 ± 1.3 W m− 2) with corresponding 550 nm aerosol optical depths of 0.27 ± 0.24 and 0.12 ± 0.10. Fine aerosol particles (< 0.6 μm) dominate the continental areas during the whole study period, which represents large fractions of biomass burning aerosols and anthropogenic pollutant aerosols. Our results also indicate that the monthly averaged cloud cover fractions over this region are above 60%. Therefore, further sampling of aerosols underneath these cloud layers is needed in future field campaigns. Remote sensing; Southeast Asia; Aerosol Radiative Effects
Feulner, Georg; Rahmstorf, Stefan; Levermann, Anders; Volkwardt, SilviaFeulner, G., S. Rahmstorf, A. Levermann, S. Volkwardt, 2013: On the Origin of the Surface Air Temperature Difference between the Hemispheres in Earth's Present-Day Climate. J. Climate, 26(18), 7136-7150. doi: 10.1175/JCLI-D-12-00636.1.
Franklin, Charmaine N.; Sun, Zhian; Bi, Daohua; Dix, Martin; Yan, Hailin; Bodas-Salcedo, AlejandroFranklin, C. N., Z. Sun, D. Bi, M. Dix, H. Yan, A. Bodas-Salcedo, 2013: Evaluation of clouds in ACCESS using the satellite simulator package COSP: Global, seasonal, and regional cloud properties. Journal of Geophysical Research: Atmospheres, 118(2), 732–748. doi: 10.1029/2012JD018469. Cloud properties from the Australian Community Climate and Earth System Simulator (ACCESS1.3) are evaluated using the Cloud Feedback Model Intercomparison Project (CFMIP) Observational Simulator Package (COSP). CloudSat, CALIPSO, and International Satellite Cloud Climatology Project (ISCCP) observations are used to evaluate the modeled cloud cover, condensate properties, and cloud optical depths for two seasons. The global distribution of cloud in the model is generally well represented with maximum high cloud in the tropics and low cloud over the eastern edges of the ocean basins. The model captures the observed position of the midlatitude storm track clouds and the modeled cloud top heights compare well with the observations in the upper troposphere. However, there is a lack of modeled midlevel cloud in the tropics and midlatitudes. The average high cloud cover in the Tropical Warm Pool region shows good agreement with CALIPSO. However, the modeled radar reflectivities and lidar scattering ratios are biased toward lower values, suggesting that the ice water contents and particles sizes of these clouds in the model are too small. Over the Southern Ocean the modeled cloud cover is underestimated due to a lack of mid- and low-level cloud. The low clouds over the Southern Ocean and the California stratocumulus clouds in the model have too little condensate and optical thickness and too much rain and drizzle. A sensitivity experiment showed that reducing the ice fall speeds improves aspects of the modeled cloud properties by increasing the frequency of occurrence of high clouds with large scattering ratios and optically thick low clouds. ACCESS1.3 has a reasonable representation of cloud. However, the underestimate of ice water content and particles sizes in high clouds and the too frequent occurrence of drizzle may impact the modeled cloud feedbacks and regional precipitation associated with current and perturbed climates. CloudSat; climate model; cloud parameterization; CALIPSO; COSP; ACCESS
Frierson, Dargan M. W.; Hwang, Yen-Ting; Fučkar, Neven S.; Seager, Richard; Kang, Sarah M.; Donohoe, Aaron; Maroon, Elizabeth A.; Liu, Xiaojuan; Battisti, David S.Frierson, D. M. W., Y. Hwang, N. S. Fučkar, R. Seager, S. M. Kang, A. Donohoe, E. A. Maroon, X. Liu, D. S. Battisti, 2013: Contribution of ocean overturning circulation to tropical rainfall peak in the Northern Hemisphere. Nature Geoscience, 6(11), 940-944. doi: 10.1038/ngeo1987. Rainfall in the tropics is largely focused in a narrow zonal band near the Equator, known as the intertropical convergence zone. On average, substantially more rain falls just north of the Equator. This hemispheric asymmetry in tropical rainfall has been attributed to hemispheric asymmetries in ocean temperature induced by tropical landmasses. However, the ocean meridional overturning circulation also redistributes energy, by carrying heat northwards across the Equator. Here, we use satellite observations of the Earth’s energy budget, atmospheric reanalyses and global climate model simulations to study tropical rainfall using a global energetic framework. We show that the meridional overturning circulation contributes significantly to the hemispheric asymmetry in tropical rainfall by transporting heat from the Southern Hemisphere to the Northern Hemisphere, and thereby pushing the tropical rain band north. This northward shift in tropical precipitation is seen in global climate model simulations when ocean heat transport is included, regardless of whether continents are present or not. If the strength of the meridional overturning circulation is reduced in the future as a result of global warming, as has been suggested, precipitation patterns in the tropics could change, with potential societal consequences. Atmospheric dynamics; Physical oceanography
Gautam, Ritesh; Hsu, N. Christina; Eck, Thomas F.; Holben, Brent N.; Janjai, Serm; Jantarach, Treenuch; Tsay, Si-Chee; Lau, William K.Gautam, R., N. C. Hsu, T. F. Eck, B. N. Holben, S. Janjai, T. Jantarach, S. Tsay, W. K. Lau, 2013: Characterization of aerosols over the Indochina peninsula from satellite-surface observations during biomass burning pre-monsoon season. Atmospheric Environment, 78, 51-59. doi: 10.1016/j.atmosenv.2012.05.038. This paper presents characterization of aerosols over the Indochina peninsular regions of Southeast Asia during pre-monsoon season from satellite and ground-based radiometric observations. Our analysis focuses on the seasonal peak period in aerosol loading and biomass burning, prior to the onset of the Asian summer monsoon, as observed in the inter-annual variations of Aerosol Optical Depth (AOD) and fire count data from MODIS. Multi-year (2007–2011) analysis of spaceborne lidar measurements, from CALIOP, indicates presence of aerosols mostly within boundary layer, however extending to elevated altitudes to ∼4 km over northern regions of Indochina, encompassing Myanmar, northern Thailand and southern China. In addition, a strong gradient in aerosol loading and vertical distribution is observed from the relatively clean equatorial conditions to heavy smoke-laden northern regions (greater aerosol extinction and smaller depolarization ratio). Based on column-integrated ground-based measurements from four AERONET locations distributed over Thailand, the regional aerosol loading is found to be significantly absorbing with spectral single scattering albedo (SSA) below 0.91 ± 0.02 in the 440–1020 nm range, with lowest seasonal mean SSA (most absorbing aerosol) over the northern location of Chiang Mai (SSA ∼ 0.85) during pre-monsoon season. The smoke-laden aerosol loading is found to exhibit a significant diurnal pattern with higher AOD departures during early morning observations relative to late afternoon conditions (peak difference of more than 15% amplitude). Finally, satellite-based aerosol radiative impact is assessed using CERES shortwave Top-of-Atmosphere flux, in conjunction with MODIS AOD. Overall, a consistency in the aerosol-induced solar absorption characteristic is found among selected regions from ground-based sunphotometer-derived spectral SSA retrievals and satellite-based radiative forcing analysis. Remote sensing; aerosol; Biomass burning; Southeast Asia
Goldberg, Mitchell D.; Kilcoyne, Heather; Cikanek, Harry; Mehta, AjayGoldberg, M. D., H. Kilcoyne, H. Cikanek, A. Mehta, 2013: Joint Polar Satellite System: The United States next generation civilian polar-orbiting environmental satellite system. Journal of Geophysical Research: Atmospheres, 118(24), 2013JD020389. doi: 10.1002/2013JD020389. NOAA's next generation polar-orbiting environmental satellite system, designated as the Joint Polar Satellite System (JPSS), was proposed in February 2010, as part of the President's Fiscal Year 2011 budget request, to be the Civilian successor to the restructured National Polar-Orbiting Operational Environmental Satellite System (NPOESS). Beginning 1 October 2013, the JPSS baseline consists of a suite of five instruments: advanced microwave and infrared sounders critical for short- and medium-range weather forecasting; an advanced visible and infrared imager needed for environmental assessments such as snow/ice cover, droughts, volcanic ash, forest fires and surface temperature; ozone sensor primarily used for global monitoring of ozone and input to weather and climate models; and an Earth radiation budget sensor for monitoring the Earth's energy budget. NASA will fund the Earth radiation budget sensor and the ozone limb sensor for the second JPSS operational satellite—JPSS-2. JPSS is implemented through a partnership between NOAA and the U.S. National Aeronautics and Space Administration (NASA). NOAA is responsible for overall funding; maintaining the high-level requirements; establishing international and interagency partnerships; developing the science and algorithms, and user engagement; NOAA also provides product data distribution and archiving of JPSS data. NASA's role is to serve as acquisition Center of Excellence, providing acquisition of instruments, spacecraft and the multimission ground system, and early mission implementation through turnover to NOAA for operations. 0480 Remote sensing; ATMS; polar orbiting; satellite system
Guan, Bin; Waliser, Duane E.; Li, Jui-Lin F.; da Silva, ArlindoGuan, B., D. E. Waliser, J. F. Li, A. da Silva, 2013: Evaluating the impact of orbital sampling on satellite–climate model comparisons. Journal of Geophysical Research: Atmospheres, 118(2), 355–369. doi: 10.1029/2012JD018590. The effect of orbital sampling is one of the chief uncertainties in satellite–climate model comparisons. In the context of an ongoing activity to make satellite data more accessible for model evaluation (i.e., obs4MIPs), six variables (temperature, specific humidity, ozone, cloud water, cloud cover, and ocean surface wind) associated with six satellite instruments are evaluated for the orbital sampling effect. Comparisons are made between reanalysis and simulated satellite-sampled data in terms of bias and pattern similarity. It is found that the bias introduced by orbital sampling for long-term annual means, monthly climatologies, and monthly means is largely negligible, which is within 3% of the standard deviation of the three quantities for most fields. The bias for 2-hPa temperature and specific humidity, while relatively large (9–10%), is within the estimated observational uncertainty. In terms of pattern similarity, cloud water and upper level specific humidity are the most sensitive to orbital sampling among the variables considered, with the magnitude of the sampling effect dependent on the spatial resolution—insignificant at 1.25° × 1.25° resolution for both. For all variables considered, orbital sampling effects are not an important consideration for model evaluation at 1.25° × 1.25° resolution. At 0.5° × 0.5°, orbital sampling is potentially important for cloud water and upper level specific humidity when evaluating model long-term annual means and monthly climatologies, and for cloud water when evaluating monthly means, all in terms of pattern similarities. Orbital sampling is not an important factor for evaluating zonal means in call cases considered. Satellite; climate model; bias; orbital sampling; pattern similarity; Taylor diagram
Gustafson, William I.; Ma, Po-Lun; Xiao, Heng; Singh, Balwinder; Rasch, Philip J.; Fast, Jerome D.Gustafson, W. I., P. Ma, H. Xiao, B. Singh, P. J. Rasch, J. D. Fast, 2013: The Separate Physics and Dynamics Experiment (SPADE) framework for determining resolution awareness: A case study of microphysics. Journal of Geophysical Research: Atmospheres, 118(16), 9258–9276. doi: 10.1002/jgrd.50711. Multiresolution dynamical cores for weather and climate modeling are pushing the atmospheric community toward developing scale aware or, more specifically, resolution aware parameterizations that function properly across a range of grid spacings. Determining resolution dependence of specific model parameterizations is difficult due to resolution dependencies in many model components. This study presents the Separate Physics and Dynamics Experiment (SPADE) framework for isolating resolution dependent behavior of specific parameterizations without conflating resolution dependencies from other portions of the model. To demonstrate SPADE, the resolution dependence of the Morrison microphysics, from the Weather Research and Forecasting model, and the Morrison-Gettelman microphysics, from the Community Atmosphere Model, are compared for grid spacings spanning the cloud modeling gray zone. It is shown that the Morrison scheme has stronger resolution dependence than Morrison-Gettelman, and the partial cloud fraction capability of Morrison-Gettelman is not the primary reason for this difference. microphysics; multiresolution; parameterization; resolution aware; scale aware; SPADE
Hagemann, Stefan; Loew, Alexander; Andersson, A.Hagemann, S., A. Loew, A. Andersson, 2013: Combined evaluation of MPI-ESM land surface water and energy fluxes. Journal of Advances in Modeling Earth Systems, 5(2), 259-286. doi: 10.1029/2012MS000173. To assess the robustness of projected changes of the hydrological cycle simulated by an Earth system model (ESM), it is fundamental to validate the ESM and to characterize its major deficits. As the hydrological cycle is closely coupled to the energy cycle, a common large-scale evaluation of these fundamental components of the Earth system is highly beneficial, even though this has been rarely done up to now. Consequently, the purpose of the present study is the combined evaluation of land surface water and energy fluxes from the newest ESM version of the Max Planck Institute for Meteorology (MPI-ESM), which was used to produce an ensemble of Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations. With regard to energy fluxes, we especially make use of recent satellite data sets. Additionally, MPI-ESM results are compared with CMIP3 results from the predecessor of MPI-ESM, ECHAM5/MPIOM, as well as to results from the atmosphere/land part of MPI-ESM (ECHAM6/JSBACH) forced by observed sea surface temperature (SST). Analyses focus on regions where notable differences occur between the two ESM versions as well as between the fully coupled and the uncoupled SST-driven simulations. In general, our results show a considerable improvement of MPI-ESM in simulating surface shortwave radiation fluxes. The precipitation of the fully coupled simulations notably differs from those of the SST-forced simulations over a few river catchments. Over the Amazon catchment, the coupling to the ocean leads to a large negative precipitation bias, while for the Ganges/Brahmaputra, the coupling significantly improves the simulated precipitation. 1620 Climate dynamics; 1655 Water cycles; albedo; 1622 Earth system modeling; model evaluation; 1843 Land/atmosphere interactions; 1804 Catchment; Earth system model; energy fluxes; land surface hydrology; water fluxes
Hakuba, M. Z.; Folini, D.; Sanchez-Lorenzo, A.; Wild, M.Hakuba, M. Z., D. Folini, A. Sanchez-Lorenzo, M. Wild, 2013: Spatial representativeness of ground-based solar radiation measurements. Journal of Geophysical Research: Atmospheres, 118(15), 8585-8597. doi: 10.1002/jgrd.50673. The validation of gridded surface solar radiation (SSR) data often relies on the comparison with ground-based in situ measurements. This poses the question on how representative a point measurement is for a larger-scale surrounding. We use high-resolution (0.03°) SSR data from the Satellite Application Facility on Climate Monitoring (CM SAF) to study the subgrid spatial variability in all-sky SSR over Europe and the spatial representativeness of 143 surface sites with homogeneous records for their site-centered larger surroundings varying in size from 0.25° to 3°, as well as with respect to a given standard grid of 1° resolution. These analyses are done on a climatological annual and monthly mean basis over the period 2001–2005. The spatial variability of the CM SAF data set itself agrees very well with surface measurements in Europe, justifying its use for the present study. The annual mean subgrid variability in the 1° standard grid over European land is on average 1.6% (2.4 W m−2), with maximum of up to 10% in Northern Spain. The annual mean representation error of point values at 143 surface sites with respect to their 1° surrounding is on average 2% (3 W m−2). For larger surroundings of 3°, the representation error increases to 3% (4.8 W m−2). The monthly mean representation error at the surface sites with respect to the 1° standard grid is on average 3.7% (4 W m−2). This error is reduced when site-specific correction factors are applied or when multiple sites are available in the same grid cell, i.e., three more sites reduce the error by 50%. 0360 Radiation: transmission and scattering; 1610 Atmosphere; 1640 Remote sensing; 0321 Cloud/radiation interaction; Solar radiation; Satellite; representativeness; spatial variability
Haynes, John M.; Vonder Haar, Thomas H.; L'Ecuyer, Tristan; Henderson, DavidHaynes, J. M., T. H. Vonder Haar, T. L'Ecuyer, D. Henderson, 2013: Radiative heating characteristics of Earth's cloudy atmosphere from vertically resolved active sensors. Geophysical Research Letters, 40(3), 624–630. doi: 10.1002/grl.50145. High vertical resolution CloudSat radar measurements, supplemented with cloud boundaries and aerosol information from the CALIPSO lidar, are used to examine radiative heating features in the atmosphere that have not previously been characterized by passive sensors. The monthly and annual mean radiative heating/cooling structure for a 4 year period between 2006 and 2010 is derived. The mean atmospheric radiative cooling rate from CloudSat/CALIPSO is 0.98 K d−1 (1.34 K d−1 between 150 and 950 hPa) and is largely a reflection of the Earth's mean water vapor distribution, with sharp vertical gradients introduced by clouds. It is found that there is a minimum in cooling in the tropical lower to middle troposphere, a cooling maximum in the upper-boundary layer of the Southern Hemisphere poleward of −10° latitude, and a minimum in cooling in the lower boundary layer in the middle to high latitudes of both hemispheres. Clouds tops tend to strongly cool the upper-boundary layer all year in the midlatitudes to high latitudes of the Southern Hemisphere (where peak seasonal mean winter cooling is 3.4 K d−1), but this cooling is largely absent in the corresponding parts of the Northern Hemisphere during boreal winter, resulting in a hemispheric asymmetry in cloud radiative cooling. clouds; radar; radiative heating; remove sensing
Henderson, David S.; L’Ecuyer, Tristan; Stephens, Graeme; Partain, Phil; Sekiguchi, MihoHenderson, D. S., T. L’Ecuyer, G. Stephens, P. Partain, M. Sekiguchi, 2013: A Multisensor Perspective on the Radiative Impacts of Clouds and Aerosols. J. Appl. Meteor. Climatol., 52(4), 853-871. doi: 10.1175/JAMC-D-12-025.1. AbstractThe launch of CloudSat and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) in 2006 provided the first opportunity to incorporate information about the vertical distribution of cloud and aerosols directly into global estimates of atmospheric radiative heating. Vertical profiles of radar and lidar backscatter from CloudSat’s Cloud Profiling Radar (CPR) and the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard CALIPSO naturally complement Moderate Resolution Imaging Spectroradiometer (MODIS) radiance measurements, providing a nearly complete depiction of the cloud and aerosol properties that are essential for deriving high-vertical-resolution profiles of longwave (LW) and shortwave (SW) radiative fluxes and heating rates throughout the atmosphere. This study describes a new approach for combining vertical cloud and aerosol information from CloudSat and CALIPSO with MODIS data to assess impacts of clouds and aerosols on top-of-atmosphere (TOA) and surface radiative fluxes. The resulting multisensor cloud–aerosol product is used to document seasonal and annual mean distributions of cloud and aerosol forcing globally from June 2006 through April 2011. Direct comparisons with Clouds and the Earth’s Radiant Energy System (CERES) TOA fluxes exhibit a close correlation, with improved errors relative to CloudSat-only products. Sensitivity studies suggest that remaining uncertainties in SW fluxes are dominated by uncertainties in CloudSat liquid water content estimates and that the largest sources of LW flux uncertainty are prescribed surface temperature and lower-tropospheric humidity. Globally and annually averaged net TOA cloud radiative effect is found to be −18.1 W m−2. The global, annual mean aerosol direct radiative effect is found to be −1.6 ± 0.5 W m−2 (−2.5 ± 0.8 W m−2 if only clear skies over the ocean are considered), which, surprisingly, is more consistent with past modeling studies than with observational estimates that were based on passive sensors. clouds; Remote sensing; aerosols; Radiative fluxes; Radiation budgets; Cloud radiative effects
Herman, J.; DeLand, M. T.; Huang, L.-K.; Labow, G.; Larko, D.; Lloyd, S. A.; Mao, J.; Qin, W.; Weaver, C.Herman, J., M. T. DeLand, L. Huang, G. Labow, D. Larko, S. A. Lloyd, J. Mao, W. Qin, C. Weaver, 2013: A net decrease in the Earth's cloud, aerosol, and surface 340 nm reflectivity during the past 33 yr (1979–2011). Atmos. Chem. Phys., 13(16), 8505-8524. doi: 10.5194/acp-13-8505-2013. Measured upwelling radiances from Nimbus-7 SBUV (Solar Backscatter Ultraviolet) and seven NOAA SBUV/2 instruments have been used to calculate the 340 nm Lambertian equivalent reflectivity (LER) of the Earth from 1979 to 2011 after applying a common calibration. The 340 nm LER is highly correlated with cloud and aerosol cover because of the low surface reflectivity of the land and oceans (typically 2 to 6 RU, reflectivity units, where 1 RU = 0.01 = 1.0%) relative to the much higher reflectivity of clouds plus nonabsorbing aerosols (typically 10 to 90 RU). Because of the nearly constant seasonal and long-term 340 nm surface reflectivity in areas without snow and ice, the 340 nm LER can be used to estimate changes in cloud plus aerosol amount associated with seasonal and interannual variability and decadal climate change. The annual motion of the Intertropical Convergence Zone (ITCZ), episodic El Niño Southern Oscillation (ENSO), and latitude-dependent seasonal cycles are apparent in the LER time series. LER trend estimates from 5° zonal average and from 2° × 5° , latitude × longitude, time series show that there has been a global net decrease in 340 nm cloud plus aerosol reflectivity. The decrease in cos2(latitude) weighted average LER from 60° S to 60° N is 0.79 ± 0.03 RU over 33 yr, corresponding to a 3.6 ± 0.2% decrease in LER. Applying a 3.6% cloud reflectivity perturbation to the shortwave energy balance partitioning given by Trenberth et al. (2009) corresponds to an increase of 2.7 W m−2 of solar energy reaching the Earth's surface and an increase of 1.4% or 2.3 W m−2 absorbed by the surface, which is partially offset by increased longwave cooling to space. Most of the decreases in LER occur over land, with the largest decreases occurring over the US (−0.97 RU decade−1), Brazil (−0.9 RU decade−1), and central Europe (−1.35 RU decade−1). There are reflectivity increases near the west coast of Peru and Chile (0.8 ± 0.1 RU decade−1), over parts of India, China, and Indochina, and almost no change over Australia. The largest Pacific Ocean change is −2 ± 0.1 RU decade−1 over the central equatorial region associated with ENSO. There has been little observed change in LER over central Greenland, but there has been a significant decrease over a portion of the west coast of Greenland. Similar significant decreases in LER are observed over a portion of the coast of Antarctica for longitudes −160° to −60° and 80° to 150°.
Huang, Xianglei; Cole, Jason N. S.; He, Fei; Potter, Gerald L.; Oreopoulos, Lazaros; Lee, Dongmin; Suarez, Max; Loeb, Norman G.Huang, X., J. N. S. Cole, F. He, G. L. Potter, L. Oreopoulos, D. Lee, M. Suarez, N. G. Loeb, 2013: Longwave Band-By-Band Cloud Radiative Effect and Its Application in GCM Evaluation. J. Climate, 26(2), 450-467. doi: 10.1175/JCLI-D-12-00112.1. AbstractThe cloud radiative effect (CRE) of each longwave (LW) absorption band of a GCM’s radiation code is uniquely valuable for GCM evaluation because 1) comparing band-by-band CRE avoids the compensating biases in the broadband CRE comparison and 2) the fractional contribution of each band to the LW broadband CRE (fCRE) is sensitive to cloud-top height but largely insensitive to cloud fraction, thereby presenting a diagnostic metric to separate the two macroscopic properties of clouds. Recent studies led by the first author have established methods to derive such band-by-band quantities from collocated Atmospheric Infrared Sounder (AIRS) and Clouds and the Earth’s Radiant Energy System (CERES) observations. A study is presented here that compares the observed band-by-band CRE over the tropical oceans with those simulated by three different atmospheric GCMs—the GFDL Atmospheric Model version 2 (GFDL AM2), NASA Goddard Earth Observing System version 5 (GEOS-5), and the fourth-generation AGCM of the Canadian Centre for Climate Modelling and Analysis (CCCma CanAM4)—forced by observed SST. The models agree with observation on the annual-mean LW broadband CRE over the tropical oceans within ±1 W m−2. However, the differences among these three GCMs in some bands can be as large as or even larger than ±1 W m−2. Observed seasonal cycles of fCRE in major bands are shown to be consistent with the seasonal cycle of cloud-top pressure for both the amplitude and the phase. However, while the three simulated seasonal cycles of fCRE agree with observations on the phase, the amplitudes are underestimated. Simulated interannual anomalies from GFDL AM2 and CCCma CanAM4 are in phase with observed anomalies. The spatial distribution of fCRE highlights the discrepancies between models and observation over the low-cloud regions and the compensating biases from different bands. tropics; Radiative fluxes; Radiation budgets; Model evaluation/performance; cloud forcing
Huang, YiHuang, Y., 2013: A Simulated Climatology of Spectrally Decomposed Atmospheric Infrared Radiation. J. Climate, 26(5), 1702-1715. doi: 10.1175/JCLI-D-12-00438.1.
Jeong, Ji-Hyun; Kim, Hak-Sung; Kim, Joon-Tae; Park, Yong-Pil; Choi, Hyun-JungJeong, J., H. Kim, J. Kim, Y. Park, H. Choi, 2013: An Analysis of Aerosol Direct Radiative Forcing Using Satellite Data in East Asia During 2001-2010. Journal of the Environmental Sciences international, 22(8), 1053-1062. doi: 10.5322/JESI.2013.22.8.1053.
Jia, Binghao; Xie, Zhenghui; Dai, Aiguo; Shi, Chunxiang; Chen, FengJia, B., Z. Xie, A. Dai, C. Shi, F. Chen, 2013: Evaluation of satellite and reanalysis products of downward surface solar radiation over East Asia: Spatial and seasonal variations. Journal of Geophysical Research: Atmospheres, 118(9), 3431–3446. doi: 10.1002/jgrd.50353. Surface solar radiation plays a crucial role in surface energy and water budgets, and it is also an important forcing for land hydrological models. In this study, the downward surface solar radiation (DSSR) from two satellite products, the Fengyun-2C satellite (FY-2C) and the Fast Longwave and Shortwave Radiative Fluxes project (FLASHFlux), and two reanalysis datasets, NCEP-DOE and ERA-Interim, was evaluated against ground-based observations (OBS) from 94 stations over mainland China during July 2006 to June 2009. It is found that the mean DSSR derived from FY-2C is comparable to OBS, with small positive biases of 3.0 Wm–2 for daily data and 3.5 Wm-2 for monthly data and moderate RMSEs of 49.3 Wm-2 (daily) and 31.9 Wm-2 (monthly). These results are comparable to those for FLASHFlux, which has the lowest RMSEs (43.2 Wm-2 and 30.5 Wm-2 for daily and monthly data, respectively) and the strongest correlations with OBS (r = 0.90 and 0.93 for daily and monthly data, respectively) among the four products. The DSSR from the reanalyses has much larger RMSEs and generally lower correlations with OBS than the satellite products, especially for the NCEP-DOE products. Results also show that daily DSSR values are sensitive to the averaging grid size, while monthly mean DSSR is largely insensitive to the averaging scale. The DSSR from the four datasets over East Asia shows similar spatial patterns with large seasonal variations but differs in magnitude. In summer, high DSSR is observed over western China, while low DSSR is seen primarily over South Asia and the Sichuan Basin associated with extensive cloud cover (CC) and large precipitable water (PW). In winter, the high DSSR center shifts to South Asia due to decreased CC and PW, and the DSSR decreases from the South to the North. Deficiencies in the parameterizations of clouds, aerosols, and water vapor, as well as errors in atmospheric and surface properties for the retrieval algorithms contribute to the lower correlation of the DSSR derived from FY-2C (r = 0.82 and 0.90 for daily and monthly data) with OBS than those from FLASHFlux product. Further improvements to the representation of clouds and aerosols in the FY-2C retrieval algorithm are needed. satellite observations; East Asia; surface solar radiation; ERA-Interim; FY-2C; NCEP-DOE
Jin, Zhonghai; Lukashin, Constantin; Qiao, Yanli; Gopalan, ArunJin, Z., C. Lukashin, Y. Qiao, A. Gopalan, 2013: An efficient and effective method to simulate the earth spectral reflectance over large temporal and spatial scales. Geophysical Research Letters, 40(2), 374-379. doi: 10.1002/grl.50116. Atmospheric and surface properties have been measured from space with various spatial resolutions for decades. It is very challenging to derive the mean solar spectral radiance or reflectance over large temporal and spatial scales by explicit radiative transfer computations from the large volume of instantaneous data, especially at high spectral resolution. We propose a procedurally simple but effective method to compute the solar spectral reflectance in large climate domains, in which the probability distribution function (PDF) of cloud optical depth is used to account for the wide variation of cloud properties in different sensor footprints, and to avoid the repeated computations for footprints with similar conditions. This approach is tested with MODIS/CERES data and evaluated with SCIAMACHY measured spectral reflectance. The mean difference between model and observation is about 3% for the monthly global mean reflectance. This PDF-based approach provides a simple, fast, and effective way to simulate the mean spectral reflectance over large time and space scales with a large volume of high-resolution satellite data. 1640 Remote sensing; spectral reflectance; radiative transfer; 3359 Radiative processes; 3305 Climate change and variability; climate benhmark
Johnston, M. S.; Eliasson, S.; Eriksson, P.; Forbes, R. M.; Wyser, K.; Zelinka, M. D.Johnston, M. S., S. Eliasson, P. Eriksson, R. M. Forbes, K. Wyser, M. D. Zelinka, 2013: Diagnosing the average spatio-temporal impact of convective systems – Part 1: A methodology for evaluating climate models. Atmos. Chem. Phys., 13(23), 12043-12058. doi: 10.5194/acp-13-12043-2013. An earlier method to determine the mean response of upper-tropospheric water to localised deep convective systems (DC systems) is improved and applied to the EC-Earth climate model. Following Zelinka and Hartmann (2009), several fields related to moist processes and radiation from various satellites are composited with respect to the local maxima in rain rate to determine their spatio-temporal evolution with deep convection in the central Pacific Ocean. Major improvements to the earlier study are the isolation of DC systems in time so as to prevent multiple sampling of the same event, and a revised definition of the mean background state that allows for better characterisation of the DC-system-induced anomalies. The observed DC systems in this study propagate westward at ~4 m s−1. Both the upper-tropospheric relative humidity and the outgoing longwave radiation are substantially perturbed over a broad horizontal extent and for periods >30 h. The cloud fraction anomaly is fairly constant with height but small maximum can be seen around 200 hPa. The cloud ice water content anomaly is mostly confined to pressures greater than 150 hPa and reaches its maximum around 450 hPa, a few hours after the peak convection. Consistent with the large increase in upper-tropospheric cloud ice water content, albedo increases dramatically and persists about 30 h after peak convection. Applying the compositing technique to EC-Earth allows an assessment of the model representation of DC systems. The model captures the large-scale responses, most notably for outgoing longwave radiation, but there are a number of important differences. DC systems appear to propagate eastward in the model, suggesting a strong link to Kelvin waves instead of equatorial Rossby waves. The diurnal cycle in the model is more pronounced and appears to trigger new convection further to the west each time. Finally, the modelled ice water content anomaly peaks at pressures greater than 500 hPa and in the upper troposphere between 250 hPa and 500 hPa, there is less ice than the observations and it does not persist as long after peak convection. The modelled upper-tropospheric cloud fraction anomaly, however, is of a comparable magnitude and exhibits a similar longevity as the observations.
Kato, Seiji; Loeb, Norman G.; Rose, Fred G.; Doelling, David R.; Rutan, David A.; Caldwell, Thomas E.; Yu, Lisan; Weller, Robert A.Kato, S., N. G. Loeb, F. G. Rose, D. R. Doelling, D. A. Rutan, T. E. Caldwell, L. Yu, R. A. Weller, 2013: Surface Irradiances Consistent with CERES-Derived Top-of-Atmosphere Shortwave and Longwave Irradiances. J. Climate, 26(9), 2719-2740. doi: 10.1175/JCLI-D-12-00436.1. AbstractThe estimate of surface irradiance on a global scale is possible through radiative transfer calculations using satellite-retrieved surface, cloud, and aerosol properties as input. Computed top-of-atmosphere (TOA) irradiances, however, do not necessarily agree with observation-based values, for example, from the Clouds and the Earth’s Radiant Energy System (CERES). This paper presents a method to determine surface irradiances using observational constraints of TOA irradiance from CERES. A Lagrange multiplier procedure is used to objectively adjust inputs based on their uncertainties such that the computed TOA irradiance is consistent with CERES-derived irradiance to within the uncertainty. These input adjustments are then used to determine surface irradiance adjustments. Observations by the Atmospheric Infrared Sounder (AIRS), Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), CloudSat, and Moderate Resolution Imaging Spectroradiometer (MODIS) that are a part of the NASA A-Train constellation provide the uncertainty estimates. A comparison with surface observations from a number of sites shows that the bias [root-mean-square (RMS) difference] between computed and observed monthly mean irradiances calculated with 10 years of data is 4.7 (13.3) W m−2 for downward shortwave and −2.5 (7.1) W m−2 for downward longwave irradiances over ocean and −1.7 (7.8) W m−2 for downward shortwave and −1.0 (7.6) W m−2 for downward longwave irradiances over land. The bias and RMS error for the downward longwave and shortwave irradiances over ocean are decreased from those without constraint. Similarly, the bias and RMS error for downward longwave over land improves, although the constraint does not improve downward shortwave over land. This study demonstrates how synergetic use of multiple instruments (CERES, MODIS, CALIPSO, CloudSat, AIRS, and geostationary satellites) improves the accuracy of surface irradiance computations. Radiative fluxes; Energy budget/balance; Radiation budgets; radiative transfer
Kay, Jennifer E.; L'Ecuyer, TristanKay, J. E., T. L'Ecuyer, 2013: Observational constraints on Arctic Ocean clouds and radiative fluxes during the early 21st century. Journal of Geophysical Research: Atmospheres, 118(13), 7219-7236. doi: 10.1002/jgrd.50489. Arctic Ocean observations are combined to create a cloud and radiation climatology for the early 21st century (March 2000 to February 2011). Data sources include: active (CloudSat, CALIPSO) and passive (MODIS) satellite cloud observations, observed top-of-atmosphere (TOA) radiative fluxes (CERES-EBAF), observationally constrained radiative flux calculations (2B-FLXHR-LIDAR), and observationally constrained cloud forcing calculations (CERES-EBAF, 2B-FLXHR-LIDAR). Uncertainty in flux calculations is dominated by cloud uncertainty, not surface albedo uncertainty. The climatology exposes large geographic, seasonal, and interannual variability cloud forcing, but on average, Arctic Ocean clouds warm the surface (+10 W m−2, in 2B-FLXHR-LIDAR) and cool the TOA (−12 W m−2, in CERES-EBAF and 2B-FLXHR-LIDAR). Shortwave TOA cloud cooling and longwave TOA cloud warming are stronger in 2B-FLXHR-LIDAR than in CERES-EBAF, but these two differences compensate each other, yielding similar net TOA values. During the early 21st century, summer TOA albedo decreases are consistent with sea ice loss but are unrelated to summer cloud trends that are statistically insignificant. In contrast, both sea ice variability and cloud variability contribute to interannual variability in summer shortwave radiative fluxes. Summer 2007 had the largest persistent cloud, radiation, and sea ice anomalies in the climatology. During that summer, positive net shortwave radiation anomalies exceeded 20 W m−2 over much of the Arctic Ocean. This enhanced shortwave absorption resulted primarily from cloud reductions during early summer and sea ice loss during late summer. In summary, the observations show that while cloud variability influences absorbed shortwave radiation variability, there is no summer cloud trend affecting summer absorbed shortwave radiation. clouds; 0321 Cloud/radiation interaction; 1621 Cryospheric change; 9315 Arctic region; sea ice; radiation; 0750 Sea ice; 4207 Arctic and Antarctic oceanography; Arctic; cloud forcing; cloud radiative effect
Krzysztof So'snica, Carlos Javier Rodr'iguez-SolanoKrzysztof So'snica, C. J. R., 2013: Impact of Earth radiation pressure on LAGEOS orbits and on the global scale.
Lauer, Axel; Hamilton, KevinLauer, A., K. Hamilton, 2013: Simulating Clouds with Global Climate Models: A Comparison of CMIP5 Results with CMIP3 and Satellite Data. J. Climate, 26(11), 3823-3845. doi: 10.1175/JCLI-D-12-00451.1.
Li, J.-L. F.; Waliser, D. E.; Stephens, G.; Lee, Seungwon; L'Ecuyer, T.; Kato, Seiji; Loeb, Norman; Ma, Hsi-YenLi, J. F., D. E. Waliser, G. Stephens, S. Lee, T. L'Ecuyer, S. Kato, N. Loeb, H. Ma, 2013: Characterizing and understanding radiation budget biases in CMIP3/CMIP5 GCMs, contemporary GCM, and reanalysis. Journal of Geophysical Research: Atmospheres, 118(15), 8166-8184. doi: 10.1002/jgrd.50378. We evaluate the annual mean radiative shortwave flux downward at the surface (RSDS) and reflected shortwave (RSUT) and radiative longwave flux upward at top of atmosphere (RLUT) from the twentieth century Coupled Model Intercomparison Project Phase 5 (CMIP5) and Phase 3 (CMIP3) simulations as well as from the NASA GEOS5 model and Modern-Era Retrospective Analysis for Research and Applications analysis. The results show that a majority of the models have significant regional biases in the annual means of RSDS, RLUT, and RSUT, with biases from −30 to 30 W m−2. While the global average CMIP5 ensemble mean biases of RSDS, RLUT, and RSUT are reduced compared to CMIP3 by about 32% (e.g., −6.9 to 2.5 W m−2), 43%, and 56%, respectively. This reduction arises from a more complete cancellation of the pervasive negative biases over ocean and newly larger positive biases over land. In fact, based on these biases in the annual mean, Taylor diagram metrics, and RMSE, there is virtually no progress in the simulation fidelity of RSDS, RLUT, and RSUT fluxes from CMIP3 to CMIP5. A persistent systematic bias in CMIP3 and CMIP5 is the underestimation of RSUT and overestimation of RSDS and RLUT in the convectively active regions of the tropics. The amount of total ice and liquid atmospheric water content in these areas is also underestimated. We hypothesize that at least a part of these persistent biases stem from the common global climate model practice of ignoring the effects of precipitating and/or convective core ice and liquid in their radiation calculations. 3337 Global climate models; radiation; 1855 Remote sensing; CMIP3; CMIP5
Li, Yuanlong; Han, Weiqing; Shinoda, Toshiaki; Wang, Chunzai; Lien, Ren-Chieh; Moum, James N.; Wang, Jih-WangLi, Y., W. Han, T. Shinoda, C. Wang, R. Lien, J. N. Moum, J. Wang, 2013: Effects of the diurnal cycle in solar radiation on the tropical Indian Ocean mixed layer variability during wintertime Madden-Julian Oscillations. Journal of Geophysical Research: Oceans, 118(10), 4945-4964. doi: 10.1002/jgrc.20395. The effects of solar radiation diurnal cycle on intraseasonal mixed layer variability in the tropical Indian Ocean during boreal wintertime Madden-Julian Oscillation (MJO) events are examined using the HYbrid Coordinate Ocean Model. Two parallel experiments, the main run and the experimental run, are performed for the period of 2005–2011 with daily atmospheric forcing except that an idealized hourly shortwave radiation diurnal cycle is included in the main run. The results show that the diurnal cycle of solar radiation generally warms the Indian Ocean sea surface temperature (SST) north of 10°S, particularly during the calm phase of the MJO when sea surface wind is weak, mixed layer is thin, and the SST diurnal cycle amplitude (dSST) is large. The diurnal cycle enhances the MJO-forced intraseasonal SST variability by about 20% in key regions like the Seychelles-Chagos Thermocline Ridge (SCTR; 55°–70°E, 12°–4°S) and the central equatorial Indian Ocean (CEIO; 65°–95°E, 3°S–3°N) primarily through nonlinear rectification. The model also well reproduced the upper-ocean variations monitored by the CINDY/DYNAMO field campaign between September-November 2011. During this period, dSST reaches 0.7°C in the CEIO region, and intraseasonal SST variability is significantly amplified. In the SCTR region where mean easterly winds are strong during this period, diurnal SST variation and its impact on intraseasonal ocean variability are much weaker. In both regions, the diurnal cycle also has a large impact on the upward surface turbulent heat flux QT and induces diurnal variation of QT with a peak-to-peak difference of O(10 W m−2). 4504 Air/sea interactions; sea surface temperature; diurnal cycle; Madden-Julian Oscillation; 4215 Climate and interannual variability; 4227 Diurnal, seasonal, and annual cycles; CINDY/DYNAMO
Lin, Bing; Stackhouse, Jr. , Paul; Sun, Wenbo; Hu, Yongxiang; Liu, Zhaoyan; Fan, Tai-Fang (Alice)Lin, B., J. . Stackhouse, W. Sun, Y. Hu, Z. Liu, T. Fan, 2013: Is Oklahoma getting drier?. Journal of Quantitative Spectroscopy and Radiative Transfer, 122, 208-213. doi: 10.1016/j.jqsrt.2012.07.024. Land surface hydrology is important to regional climate, ecosystem, agriculture, and even human activities. Changes in soil moisture can produce considerable impacts on socioeconomics. Analysis of assimilation model results, especially those from the Community Land Model, shows that soil moisture over Oklahoma region is continuously reduced from 1980 to 2009. The potential drying trend in the Oklahoma region is evaluated by observations taken during last three decades in this study. Satellite data from Global Precipitation Climatology Project exhibit a clear precipitation decrease in the Oklahoma region during the last decade or so compared with those of two or three decades ago. Accompanying with the precipitation variation, land surface net radiation and temperature over the region are found increases by satellite and/or in-situ measurements. These changes in regional climate conditions also likely result in reduction of regional evaporation and enhancement of sensible heat transport from land surface into the atmosphere as indicated in assimilated data. These observed and modeled evidences of the changes in regional water and energy cycles lead us to conclude that the soil moisture over the Oklahoma region was reduced during the last decade. This soil moisture drop could increase a risk in water shortage for agriculture in the Oklahoma state if the dry period continues. Further investigations on the drying in the Oklahoma State or even entire Southern Great Plains are needed to mitigate potential droughts, reductions in vegetation products, and other socioeconomic impacts. surface temperature; satellite remote sensing; Precipitation; Soil moisture; Surface Radiation; In-situ measurement; Surface latent and sensible heat
Masunaga, HirohikoMasunaga, H., 2013: A Satellite Study of Tropical Moist Convection and Environmental Variability: A Moisture and Thermal Budget Analysis. J. Atmos. Sci., 70(8), 2443-2466. doi: 10.1175/JAS-D-12-0273.1.
McCarthy, J.K.; Bitting, H.; Evert, T.A.; Frink, M.E.; Hedman, T.R.; Sakaguchi, P.; Folkman, M.McCarthy, J., H. Bitting, T. Evert, M. Frink, T. Hedman, P. Sakaguchi, M. Folkman, 2013: Performance and Long-Term Stability of the Prelaunch Radiometric Calibration Facility for the Clouds and the Earth's Radiant Energy System Instruments. IEEE Transactions on Geoscience and Remote Sensing, 51(1), 684-694. doi: 10.1109/TGRS.2012.2195726. The Radiometric Calibration Facility (RCF) at Northrop Grumman Aerospace Systems was used between 1995 and 2008 to establish the prelaunch calibration of the first six Clouds and the Earth's Radiant Energy System (CERES) instruments, with the seventh CERES instrument scheduled to be tested in the RCF in 2012. This paper reviews the performance of the RCF radiometric standards, which are the narrow-field blackbody (NFBB) and the short-wave reference source, as well as the RCF transfer active-cavity radiometer, in the context of the CERES prelaunch calibration process. A detailed investigation of the long-term stability of these standards over the 1999-2008 time span of CERES FM5 testing is reported, showing that the RCF calibrations in the long and short waves have remained stable relative to the NFBB absolute reference at levels of 0.06% and 0.5%, respectively, over the eight-year span. calibration; Remote sensing; atmospheric radiation; Clouds and the Earth's Radiant Energy System; Instruments; radiometers; atmospheric measuring apparatus; radiometry; Temperature measurement; global warming; accuracy; AD 1995 to 2008; Cavity resonators; CERES FM5 testing; CERES instruments; CERES prelaunch calibration process; narrow-field blackbody; Northrop Grumman Aerospace Systems; prelaunch radiometric calibration facility; RCF radiometric standards; RCF transfer active-cavity radiometer; short-wave reference source; test facilities; Thermal stability
Myers, Timothy A.; Norris, Joel R.Myers, T. A., J. R. Norris, 2013: Observational Evidence That Enhanced Subsidence Reduces Subtropical Marine Boundary Layer Cloudiness. J. Climate, 26(19), 7507-7524. doi: 10.1175/JCLI-D-12-00736.1.
Myhre, G.; Samset, B. H.; Schulz, M.; Balkanski, Y.; Bauer, S.; Berntsen, T. K.; Bian, H.; Bellouin, N.; Chin, M.; Diehl, T.; Easter, R. C.; Feichter, J.; Ghan, S. J.; Hauglustaine, D.; Iversen, T.; Kinne, S.; Kirkevåg, A.; Lamarque, J.-F.; Lin, G.; Liu, X.; Lund, M. T.; Luo, G.; Ma, X.; van Noije, T.; Penner, J. E.; Rasch, P. J.; Ruiz, A.; Seland, Ø.; Skeie, R. B.; Stier, P.; Takemura, T.; Tsigaridis, K.; Wang, P.; Wang, Z.; Xu, L.; Yu, H.; Yu, F.; Yoon, J.-H.; Zhang, K.; Zhang, H.; Zhou, C.Myhre, G., B. H. Samset, M. Schulz, Y. Balkanski, S. Bauer, T. K. Berntsen, H. Bian, N. Bellouin, M. Chin, T. Diehl, R. C. Easter, J. Feichter, S. J. Ghan, D. Hauglustaine, T. Iversen, S. Kinne, A. Kirkevåg, J. Lamarque, G. Lin, X. Liu, M. T. Lund, G. Luo, X. Ma, T. van Noije, J. E. Penner, P. J. Rasch, A. Ruiz, Ø. Seland, R. B. Skeie, P. Stier, T. Takemura, K. Tsigaridis, P. Wang, Z. Wang, L. Xu, H. Yu, F. Yu, J. Yoon, K. Zhang, H. Zhang, C. Zhou, 2013: Radiative forcing of the direct aerosol effect from AeroCom Phase II simulations. Atmos. Chem. Phys., 13(4), 1853-1877. doi: 10.5194/acp-13-1853-2013. We report on the AeroCom Phase II direct aerosol effect (DAE) experiment where 16 detailed global aerosol models have been used to simulate the changes in the aerosol distribution over the industrial era. All 16 models have estimated the radiative forcing (RF) of the anthropogenic DAE, and have taken into account anthropogenic sulphate, black carbon (BC) and organic aerosols (OA) from fossil fuel, biofuel, and biomass burning emissions. In addition several models have simulated the DAE of anthropogenic nitrate and anthropogenic influenced secondary organic aerosols (SOA). The model simulated all-sky RF of the DAE from total anthropogenic aerosols has a range from −0.58 to −0.02 Wm−2, with a mean of −0.27 Wm−2 for the 16 models. Several models did not include nitrate or SOA and modifying the estimate by accounting for this with information from the other AeroCom models reduces the range and slightly strengthens the mean. Modifying the model estimates for missing aerosol components and for the time period 1750 to 2010 results in a mean RF for the DAE of −0.35 Wm−2. Compared to AeroCom Phase I (Schulz et al., 2006) we find very similar spreads in both total DAE and aerosol component RF. However, the RF of the total DAE is stronger negative and RF from BC from fossil fuel and biofuel emissions are stronger positive in the present study than in the previous AeroCom study. We find a tendency for models having a strong (positive) BC RF to also have strong (negative) sulphate or OA RF. This relationship leads to smaller uncertainty in the total RF of the DAE compared to the RF of the sum of the individual aerosol components. The spread in results for the individual aerosol components is substantial, and can be divided into diversities in burden, mass extinction coefficient (MEC), and normalized RF with respect to AOD. We find that these three factors give similar contributions to the spread in results.
Naeger, Aaron R.; Christopher, Sundar A.; Johnson, Ben T.Naeger, A. R., S. A. Christopher, B. T. Johnson, 2013: Multiplatform analysis of the radiative effects and heating rates for an intense dust storm on 21 June 2007. Journal of Geophysical Research: Atmospheres, 118(16), 9316-9329. doi: 10.1002/jgrd.50713. Dust radiative effects and atmospheric heating rates are investigated for a Saharan dust storm on 21 June 2007 using a combination of multiple satellite data sets and ground and aircraft observations as input into a delta-four stream radiative transfer model (RTM). This combines the strengths of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations and CloudSat satellites and in situ aircraft data to characterize the vertical structure of the dust layers (5 km in height with optical depths between 1.5 and 2.0) and underlying low-level water clouds. These observations were used, along with Aerosol Robotic Network retrievals of aerosol optical properties, as input to the RTM to assess the surface, atmosphere, and top of atmosphere (TOA) shortwave aerosol radiative effects (SWAREs). Our results show that the dust TOA SWARE per unit aerosol optical depth was −56 W m−2 in cloud-free conditions over ocean and +74 W m−2 where the dust overlay low-level clouds, and show heating rates greater than 10 K/d. Additional case studies also confirm the results of the 21 June case. This study shows the importance of identifying clouds beneath dust as they can have a significant impact on the radiative effects of dust, and hence assessments of the role of dust aerosol on the energy budget and climate. 0305 Aerosols and particles; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; dust aerosol; Radiative transfer model; heating rates; multi-satellite; radiative effects
Neale, Richard B.; Richter, Jadwiga; Park, Sungsu; Lauritzen, Peter H.; Vavrus, Stephen J.; Rasch, Philip J.; Zhang, MinghuaNeale, R. B., J. Richter, S. Park, P. H. Lauritzen, S. J. Vavrus, P. J. Rasch, M. Zhang, 2013: The Mean Climate of the Community Atmosphere Model (CAM4) in Forced SST and Fully Coupled Experiments. J. Climate, 26(14), 5150-5168. doi: 10.1175/JCLI-D-12-00236.1. AbstractThe Community Atmosphere Model, version 4 (CAM4), was released as part of the Community Climate System Model, version 4 (CCSM4). The finite volume (FV) dynamical core is now the default because of its superior transport and conservation properties. Deep convection parameterization changes include a dilute plume calculation of convective available potential energy (CAPE) and the introduction of convective momentum transport (CMT). An additional cloud fraction calculation is now performed following macrophysical state updates to provide improved thermodynamic consistency. A freeze-drying modification is further made to the cloud fraction calculation in very dry environments (e.g., the Arctic), where cloud fraction and cloud water values were often inconsistent in CAM3. In CAM4 the FV dynamical core further degrades the excessive trade-wind simulation, but reduces zonal stress errors at higher latitudes. Plume dilution alleviates much of the midtropospheric tropical dry biases and reduces the persistent monsoon precipitation biases over the Arabian Peninsula and the southern Indian Ocean. CMT reduces much of the excessive trade-wind biases in eastern ocean basins. CAM4 shows a global reduction in cloud fraction compared to CAM3, primarily as a result of the freeze-drying and improved cloud fraction equilibrium modifications. Regional climate feature improvements include the propagation of stationary waves from the Pacific into midlatitudes and the seasonal frequency of Northern Hemisphere blocking events. A 1° versus 2° horizontal resolution of the FV dynamical core exhibits superior improvements in regional climate features of precipitation and surface stress. Improvements in the fully coupled mean climate between CAM3 and CAM4 are also more substantial than in forced sea surface temperature (SST) simulations. clouds; tropics; Coupled models; climate models; Dynamics; convective parameterization
Oh, Hye-Ryun; Choi, Yong-Sang; Ho, Chang-Hoi; Jeong, Myeong-JaeOh, H., Y. Choi, C. Ho, M. Jeong, 2013: Estimation of aerosol direct radiative effects for all-sky conditions from CERES and MODIS observations. Journal of Atmospheric and Solar-Terrestrial Physics, 102, 311-320. doi: 10.1016/j.jastp.2013.06.009. Satellite observations have shown the global average of the aerosol direct radiative effect (DRE) at the top of the atmosphere to be approximately −5.0 W m−2. Although there is a general consensus on this quantity, it is essentially biased toward clear-sky conditions. To circumvent this limitation, the present study introduces a new method for retrieving the global DRE of aerosol over the region of 60°S–60°N for all-sky conditions (both clear and cloudy skies). The all-sky DRE was calculated on a monthly basis by combining the measured DRE for a clear sky and the simulated DRE for a cloudy sky in 1°×1° grids. For the measured clear-sky DRE, we employed aerosol, cloud, and radiation fluxes from the Cloud and Earth's Radiant Energy System (CERES) instrument and the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra satellite for May 2000–December 2005. For the simulated cloudy-sky DRE, we performed radiative transfer modeling with the MODIS cloud properties in addition to the aerosol optical properties independently estimated in this study that include asymmetry factor and single scattering albedo. The results show that the global mean±standard deviation of DRE for the all-sky scene is −3.1±1.0 W m−2, which is weaker than that for the clear-sky only. This is in good agreement with the global estimates from previous studies based on different methods. The main advantage of our method is near-real-time estimation of monthly global all-sky DRE that has physical consistency with the CERES data. cloud; satellite observation; All-sky aerosol direct radiative effect
Ollinaho, Pirkka; Laine, Marko; Solonen, Antti; Haario, Heikki; Järvinen, HeikkiOllinaho, P., M. Laine, A. Solonen, H. Haario, H. Järvinen, 2013: NWP model forecast skill optimization via closure parameter variations. Quarterly Journal of the Royal Meteorological Society, 139(675), 1520–1532. doi: 10.1002/qj.2044. We apply a recently developed method, the Ensemble Prediction and Parameter Estimation System (EPPES), to demonstrate how numerical weather prediction (NWP) model closure parameters can be optimized. As proof of concept, we tune the medium-range forecast skill of the ECMWF model HAMburg version (ECHAM5) atmospheric general circulation model using an ensemble prediction system (EPS) emulator. Initial state uncertainty is represented in the EPS emulator by applying the initial state perturbations generated at the European Centre for Medium-range Weather Forecasts (ECMWF). Model uncertainty is represented in the emulator via parameter variations at the initial time. We vary four closure parameters related to parametrizations of subgrid-scale physical processes of clouds and precipitation. With this set-up, we generate ensembles of 10-day global forecasts with the ECHAM5 model at T42L31 resolution twice a day over a period of three months. The cost function in the optimization is formulated in terms of standard forecast skill scores, verified against the ECMWF operational analyses. A summarizing conclusion of the experiments is that the EPPES method is able to find ECHAM5 model closure parameter values that correspond to smaller values of the cost function. The forecast skill score improvements verify positively in dependent and independent samples. The main reason is the reduced temperature bias in the tropical lower troposphere. Moreover, the optimization improved the top-of-atmosphere radiation flux climatology of the ECHAM5 model, as verified against the Clouds and the Earth's Radiant Energy System (CERES) radiation data over a 6-year period, while the simulated tropical cloud cover was reduced, thereby increasing a negative bias as verified against the International Satellite Cloud Climatology Project (ISCCP) data. closure parameter estimation; NWP model tuning; off-line optimization
Painemal, D.; Minnis, P.; Sun-Mack, S.Painemal, D., P. Minnis, S. Sun-Mack, 2013: The impact of horizontal heterogeneities, cloud fraction, and liquid water path on warm cloud effective radii from CERES-like Aqua MODIS retrievals. Atmos. Chem. Phys., 13(19), 9997-10003. doi: 10.5194/acp-13-9997-2013. The impact of horizontal heterogeneities, liquid water path (LWP from AMSR-E), and cloud fraction (CF) on MODIS cloud effective radius (re), retrieved from the 2.1 μm (re2.1) and 3.8 μm (re3.8) channels, is investigated for warm clouds over the southeast Pacific. Values of re retrieved using the CERES algorithms are averaged at the CERES footprint resolution (∼20 km), while heterogeneities (Hσ) are calculated as the ratio between the standard deviation and mean 0.64 μm reflectance. The value of re2.1 strongly depends on CF, with magnitudes up to 5 μm larger than those for overcast scenes, whereas re3.8 remains insensitive to CF. For cloudy scenes, both re2.1 and re3.8 increase with Hσ for any given AMSR-E LWP, but re2.1 changes more than for re3.8. Additionally, re3.8–re2.1 differences are positive ( 45 gm−2, and negative (up to −4 μm) for larger Hσ. While re3.8–re2.1 differences in homogeneous scenes are qualitatively consistent with in situ microphysical observations over the region of study, negative differences – particularly evinced in mean regional maps – are more likely to reflect the dominant bias associated with cloud heterogeneities rather than information about the cloud vertical structure. The consequences for MODIS LWP are also discussed.
Painemal, D.; Zuidema, P.Painemal, D., P. Zuidema, 2013: The first aerosol indirect effect quantified through airborne remote sensing during VOCALS-REx. Atmos. Chem. Phys., 13(2), 917-931. doi: 10.5194/acp-13-917-2013. The first aerosol indirect effect (1AIE) is investigated using a combination of in situ and remotely-sensed aircraft (NCAR C-130) observations acquired during VOCALS-REx over the southeast Pacific stratocumulus cloud regime. Satellite analyses have previously identified a high albedo susceptibitility to changes in cloud microphysics and aerosols over this region. The 1AIE was broken down into the product of two independently-estimated terms: the cloud aerosol interaction metric ACIτ =dlnτ/dlnNa|LWP , and the relative albedo (A) susceptibility SR-τ =dA/3dlnτ|LWP, with τ and Na denoting retrieved cloud optical thickness and in situ aerosol concentration respectively and calculated for fixed intervals of liquid water path (LWP). ACIτ was estimated by combining in situ Na sampled below the cloud, with τ and LWP derived from, respectively, simultaneous upward-looking broadband irradiance and narrow field-of-view millimeter-wave radiometer measurements, collected at 1 Hz during four eight-hour daytime flights by the C-130 aircraft. ACIτ values were typically large, close to the physical upper limit (0.33), with a modest increase with LWP. The high ACIτ values slightly exceed values reported from many previous in situ airborne studies in pristine marine stratocumulus and reflect the imposition of a LWP constraint and simultaneity of aerosol and cloud measurements. SR-τ increased with LWP and τ, reached a maximum SR-τ (0.086) for LWP (τ) of 58 g m−2 (~14), and decreased slightly thereafter. The 1AIE thus increased with LWP and is comparable to a radiative forcing of −3.2– −3.8 W m−2 for a 10% increase in Na, exceeding previously-reported global-range values. The aircraft-derived values are consistent with satellite estimates derived from instantaneous, collocated Clouds and the Earth's Radiant Energy System (CERES) albedo and MOderate resolution Imaging Spectroradiometer (MODIS)-retrieved droplet number concentrations at 50 km resolution. The consistency of the airborne and satellite estimates, despite their independent approaches, differences in observational scales, and retrieval assumptions, is hypothesized to reflect the ideal remote sensing conditions for these homogeneous clouds. We recommend the southeast Pacific for regional model assessments of the first aerosol indirect effect on this basis. This airborne remotely-sensed approach towards quantifying 1AIE should in theory be more robust than in situ calculations because of increased sampling. However, although the technique does not explicitly depend on a remotely-derived cloud droplet number concentration (Nd), the at-times unrealistically-high Nd values suggest more emphasis on accurate airborne radiometric measurements is needed to refine this approach.
Painemal, David; Minnis, Patrick; O'Neill, LarryPainemal, D., P. Minnis, L. O'Neill, 2013: The Diurnal Cycle of Cloud-Top Height and Cloud Cover over the Southeastern Pacific as Observed by GOES-10. J. Atmos. Sci., 70(8), 2393-2408. doi: 10.1175/JAS-D-12-0325.1.
Parkinson, Claire L.Parkinson, C. L., 2013: Summarizing the First Ten Years of NASA's Aqua Mission. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 6(3), 1179-1188. doi: 10.1109/JSTARS.2013.2239608.
Petropoulos, George P.Petropoulos, G. P., 2013: Remote Sensing of Energy Fluxes and Soil Moisture Content. Integrating decades of research conducted by leading scientists in the field, Remote Sensing of Energy Fluxes and Soil Moisture Content provides an overview of state-of-the-art methods and modeling techniques employed for deriving spatio-temporal estimates of energy fluxes and soil surface moisture from remote sensing. It also underscores the range of such techniques available nowadays as well as the operationally distributed networks that provide today in-situ validated relevant observations. The book brings together three types of articles: Comprehensive reviews that examine the developments in concepts, methods, and techniques employed in deriving land surface heat fluxes as well as soil surface moisture on field, regional, and large scales, paying particular emphasis to the techniques exploiting Earth Observation (EO) technology Detailed insights into the principles and operation of the most widely applied approaches for the quantification and analysis of surface fluxes and soil moisture with case studies that directly show the great applicability of remote sensing in this field, or articles discussing specific issues in the retrievals of those parameters from space Focused articles integrating current knowledge and scientific understanding in the remote sensing of energy fluxes and soil moisture, that are highlighting the main issues, challenges, and future prospects of this emerging technology. Designed with different users in mind, the book is organized in four more or less independent units that make specific information easy to find. It presents a discussion on the future trends and prospects, underlying the scientific challenges that need to be addressed adequately in order to derive more accurate estimates of those parameters from space. Science / Earth Sciences / General; Social Science / Human Geography; Technology & Engineering / Agriculture / Agronomy / Soil Science; Technology & Engineering / Agriculture / General; Technology & Engineering / Remote Sensing & Geographic Information Systems
Phakamas, Nittaya; Jintrawet, Attachai; Patanothai, Aran; Sringam, Prakan; Hoogenboom, GerritPhakamas, N., A. Jintrawet, A. Patanothai, P. Sringam, G. Hoogenboom, 2013: Estimation of solar radiation based on air temperature and application with the DSSAT v4.5 peanut and rice simulation models in Thailand. Agricultural and Forest Meteorology, 180, 182-193. doi: 10.1016/j.agrformet.2013.06.015. Estimation of solar radiation (SRAD) from daily air temperature by the modified Bristow–Campbell (B–C) model requires three empirical coefficients that are area specific. Previous estimates of these coefficients for Thailand were based on limited data without any evaluation. Accurate estimation of solar radiation has become more important with the wider application of environmental models. The objective of this study was to calibrate and evaluate the coefficients for Thailand with a broader range of data. Meteorological data from 2008 to 2011 were obtained from eight weather stations, three in the North (Chiang Mai, Chiang Rai and Nakhon Sawan), two in the Northeast (Khon Kaen and Ubon Ratchathani), one in the Central (Lop Buri) and two in the South (Chumporn and Surat Thani). Data for 2010 for all locations except Chiang Rai were used for calibration of the coefficients and the remaining data were used as independent data sets for evaluation. The coefficient of determination (R2), root mean square error (RMSE) and normalized root mean square error (RMSEn) were used as indicators of the agreement between the observed and the calculated SRAD. The results showed that the calibration was acceptable (R2 = 0.56, RMSE = 3.07 MJ m−2 d−1 and RMSEn = 17.5%). The derived values are a = 0.63, b = 1.89 and c = 1.54. These new coefficients performed well during evaluation with the 13 independent data sets from the eight locations for all four regions, with the R2, RMSE and RMSEn values in the range of 0.39–0.70, 2.42–3.79 MJ m−2 d−1 and 14.0–21.7%, respectively. In addition, simulations using estimated SRAD from the derived values provided high R2 values for peanut and rice yield and total dry matter. These new coefficient values can be used to estimate solar radiation from air temperature data for all locations in Thailand and similar environments in Southeast Asia. CSM-CERES-rice model; CSM-CROPGRO-peanut model; Estimation coefficient; Modified Bristow–Campbell model; RMSE; RMSEn
Previdi, Michael; Smith, Karen L.; Polvani, Lorenzo M.Previdi, M., K. L. Smith, L. M. Polvani, 2013: The Antarctic Atmospheric Energy Budget. Part I: Climatology and Intraseasonal-to-Interannual Variability. J. Climate, 26(17), 6406-6418. doi: 10.1175/JCLI-D-12-00640.1. AbstractThe authors present a new, observationally based estimate of the atmospheric energy budget for the Antarctic polar cap (the region poleward of 70°S). This energy budget is constructed using state-of-the-art reanalysis products from ECMWF [the ECMWF Interim Re-Analysis (ERA-Interim)] and Clouds and the Earth's Radiant Energy System (CERES) top-of-atmosphere (TOA) radiative fluxes for the period 2001–10. The climatological mean Antarctic energy budget is characterized by an approximate balance between the TOA net outgoing radiation and the horizontal convergence of atmospheric energy transport, with the net surface energy flux and atmospheric energy storage generally being small in comparison. Variability in the energy budget on intraseasonal-to-interannual time scales bears a strong signature of the southern annular mode (SAM), with El Niño–Southern Oscillation (ENSO) having a smaller impact. The energy budget framework is shown to be a useful alternative to the SAM for interpreting surface climate variability in the Antarctic region. Energy budget/balance; satellite observations; ENSO; Antarctica; Annular mode; Reanalysis data
Radkevich, Alexander; Khlopenkov, Konstantin; Rutan, David; Kato, SeijiRadkevich, A., K. Khlopenkov, D. Rutan, S. Kato, 2013: A Supplementary Clear-Sky Snow and Ice Recognition Technique for CERES Level 2 Products. J. Atmos. Oceanic Technol., 30(3), 557-568. doi: 10.1175/JTECH-D-12-00100.1. AbstractIdentification of clear-sky snow and ice is an important step in the production of cryosphere radiation budget products, which are used in the derivation of long-term data series for climate research. In this paper, a new method of clear-sky snow/ice identification for Moderate Resolution Imaging Spectroradiometer (MODIS) is presented. The algorithm’s goal is to enhance the identification of snow and ice within the Clouds and the Earth’s Radiant Energy System (CERES) data after application of the standard CERES scene identification scheme. The input of the algorithm uses spectral radiances from five MODIS bands and surface skin temperature available in the CERES Single Scanner Footprint (SSF) product. The algorithm produces a cryosphere rating from an aggregated test: a higher rating corresponds to a more certain identification of the clear-sky snow/ice-covered scene. Empirical analysis of regions of interest representing distinctive targets such as snow, ice, ice and water clouds, open waters, and snow-free land selected from a number of MODIS images shows that the cryosphere rating of snow/ice targets falls into 95% confidence intervals lying above the same confidence intervals of all other targets. This enables recognition of clear-sky cryosphere by using a single threshold applied to the rating, which makes this technique different from traditional branching techniques based on multiple thresholds. Limited tests show that the established threshold clearly separates the cryosphere rating values computed for the cryosphere from those computed for noncryosphere scenes, whereas individual tests applied consequently cannot reliably identify the cryosphere for complex scenes. Remote sensing; sea ice; classification; snow; Ice sheets; Spectral analysis/models/distribution
Roehrig, Romain; Bouniol, Dominique; Guichard, Francoise; Hourdin, Frédéric; Redelsperger, Jean-LucRoehrig, R., D. Bouniol, F. Guichard, F. Hourdin, J. Redelsperger, 2013: The Present and Future of the West African Monsoon: A Process-Oriented Assessment of CMIP5 Simulations along the AMMA Transect. J. Climate, 26(17), 6471-6505. doi: 10.1175/JCLI-D-12-00505.1. AbstractThe present assessment of the West African monsoon in the models of the Coupled Model Intercomparison Project (CMIP) phase 5 (CMIP5) indicates little evolution since the third phase of CMIP (CMIP3) in terms of both biases in present-day climate and climate projections.The outlook for precipitation in twenty-first-century coupled simulations exhibits opposite responses between the westernmost and eastern Sahel. The spread in the trend amplitude, however, remains large in both regions. Besides, although all models predict a spring and summer warming of the Sahel that is 10%–50% larger than the global warming, their temperature response ranges from 0 to 7 K.CMIP5 coupled models underestimate the monsoon decadal variability, but SST-imposed simulations succeed in capturing the recent partial recovery of monsoon rainfall. Coupled models still display major SST biases in the equatorial Atlantic, inducing a systematic southward shift of the monsoon. Because of these strong biases, the monsoon is further evaluated in SST-imposed simulations along the 10°W–10°E African Monsoon Multidisciplinary Analysis (AMMA) transect, across a range of time scales ranging from seasonal to intraseasonal and diurnal fluctuations.The comprehensive set of observational data now available allows an in-depth evaluation of the monsoon across those scales, especially through the use of high-frequency outputs provided by some CMIP5 models at selected sites along the AMMA transect. Most models capture many features of the African monsoon with varying degrees of accuracy. In particular, the simulation of the top-of-atmosphere and surface energy balances, in relation with the cloud cover, and the intermittence and diurnal cycle of precipitation demand further work to achieve a reasonable realism.
Rose, Fred G.; Rutan, David A.; Charlock, Thomas; Smith, G. Louis; Kato, SeijiRose, F. G., D. A. Rutan, T. Charlock, G. L. Smith, S. Kato, 2013: An Algorithm for the Constraining of Radiative Transfer Calculations to CERES-Observed Broadband Top-of-Atmosphere Irradiance. J. Atmos. Oceanic Technol., 30(6), 1091-1106. doi: 10.1175/JTECH-D-12-00058.1. AbstractNASA’s Clouds and the Earth’s Radiant Energy System (CERES) project is responsible for operation and data processing of observations from scanning radiometers on board the Tropical Rainfall Measuring Mission (TRMM), Terra, Aqua, and Suomi National Polar-Orbiting Partnership (NPP) satellites. The clouds and radiative swath (CRS) CERES data product contains irradiances computed using a radiative transfer model for nearly all CERES footprints in addition to top-of-atmosphere (TOA) irradiances derived from observed radiances by CERES instruments. This paper describes a method to constrain computed irradiances by CERES-derived TOA irradiances using Lagrangian multipliers. Radiative transfer model inputs include profiles of atmospheric temperature, humidity, aerosols and ozone, surface temperature and albedo, and up to two sets of cloud properties for a CERES footprint. Those inputs are adjusted depending on predefined uncertainties to match computed TOA and CERES-derived TOA irradiance. Because CERES instantaneous irradiances for an individual footprint also include uncertainties, primarily due to the conversion of radiance to irradiance using anisotropic directional models, the degree of the constraint depends on CERES-derived TOA irradiance as well. As a result of adjustment, TOA computed-minus-observed standard deviations are reduced from 8 to 4 W m−2 for longwave irradiance and from 15 to 6 W m−2 for shortwave irradiance. While agreement of computed TOA with CERES-derived irradiances improves, comparisons with surface observations show that model constrainment to the TOA does not reduce computation bias error at the surface. After constrainment, shortwave down at the surface has an increased bias (standard deviation) of 1% (0.5%) and longwave increases by 0.2% (0.1%). Clear-sky changes are negligible.
Sathiyamoorthy, V.; Mahesh, C.; Gopalan, Kaushik; Prakash, Satya; Shukla, Bipasha P.; Mathur, A. K.Sathiyamoorthy, V., C. Mahesh, K. Gopalan, S. Prakash, B. P. Shukla, A. K. Mathur, 2013: Characteristics of low clouds over the Arabian Sea. Journal of Geophysical Research: Atmospheres, 118(24), 13,489–13,503. doi: 10.1002/2013JD020553. This paper studies climatically important low clouds (with cloud top below 680 hPa) over the Arabian Sea using the Kalpana-1 satellite data and International Satellite Cloud Climatology Project cloud data. Characteristics and possible mechanisms behind low-cloud formation in the summer monsoon season are presented. The dominant lower tropospheric circulation over the Arabian Sea during the summer season is the monsoon low-level jet (LLJ). Low clouds are predominantly found on the exit portion of the LLJ with decelerating winds. We postulate that the moisture carried by the LLJ from the entrance region with accelerating winds converge at the exit region with decelerating winds. This low-level convergence (observed 925 hPa level) may be conducive for moisture convergence, parcel uplifting, and low-cloud formation. These clouds are unable to grow vertically due to the presence of lower tropospheric thermal inversion. Change in the spatial extent of low-level convergence is found to influence the spatial coverage of the low clouds. It is found that low cloud cover is inversely related to the Indian summer monsoon activity. It is speculated that the changes in the strength of the lower tropospheric stability and spatial extent of convergence may be possible causes behind the observed inverse relation between low cloud cover and monsoon activity. Based on Clouds and the Earth's Radiant Energy System data, we find that these low clouds exert a peak cooling of about −55 Wm−2. cloud radiative forcing; Arabian Sea; Indian summer monsoon; low clouds
Sathiyamoorthy, V.; Shukla, Bipasha P.; Sikhakolli,R.; Chaurasia, S.; Simon, B.; Gohil, B.S.; Pal, P.K.Sathiyamoorthy, V., B. P. Shukla, . Sikhakolli,R., S. Chaurasia, B. Simon, B. Gohil, P. Pal, 2013: Top of atmosphere flux from the Megha-Tropiques ScaRaB. Current Science, 104(12), 1656-1661.
Scarino, Benjamin; Minnis, Patrick; Palikonda, Rabindra; Reichle, Rolf H.; Morstad, Daniel; Yost, Christopher; Shan, Baojuan; Liu, QingScarino, B., P. Minnis, R. Palikonda, R. H. Reichle, D. Morstad, C. Yost, B. Shan, Q. Liu, 2013: Retrieving Clear-Sky Surface Skin Temperature for Numerical Weather Prediction Applications from Geostationary Satellite Data. Remote Sensing, 5(1), 342-366. doi: 10.3390/rs5010342. Atmospheric models rely on high-accuracy, high-resolution initial radiometric and surface conditions for better short-term meteorological forecasts, as well as improved evaluation of global climate models. Remote sensing of the Earth’s energy budget, particularly with instruments flown on geostationary satellites, allows for near-real-time evaluation of cloud and surface radiation properties. The persistence and coverage of geostationary remote sensing instruments grant the frequent retrieval of near-instantaneous quasi-global skin temperature. Among other cloud and clear-sky retrieval parameters, NASA Langley provides a non-polar, high-resolution land and ocean skin temperature dataset for atmospheric modelers by applying an inverted correlated k-distribution method to clear-pixel values of top-of-atmosphere infrared temperature. The present paper shows that this method yields clear-sky skin temperature values that are, for the most part, within 2 K of measurements from ground-site instruments, like the Southern Great Plains Atmospheric Radiation Measurement (ARM) Infrared Thermometer and the National Climatic Data Center Apogee Precision Infrared Thermocouple Sensor. The level of accuracy relative to the ARM site is comparable to that of the Moderate-resolution Imaging Spectroradiometer (MODIS) with the benefit of an increased number of daily measurements without added bias or increased error. Additionally, matched comparisons of the high-resolution skin temperature product with MODIS land surface temperature reveal a level of accuracy well within 1 K for both day and night. This confidence will help in characterizing the diurnal and seasonal biases and root-mean-square differences between the retrievals and modeled values from the NASA Goddard Earth Observing System Version 5 (GEOS-5) in preparation for assimilation of the retrievals into GEOS-5. Modelers should find the immediate availability and broad coverage of these skin temperature observations valuable, which can lead to improved forecasting and more advanced global climate models. surface temperature; ARM; Infrared; MODIS; GOES; GEOS-5; NCDC; quasi-global; skin temperature
Sena, E. T.; Artaxo, P.; Correia, A. L.Sena, E. T., P. Artaxo, A. L. Correia, 2013: Spatial variability of the direct radiative forcing of biomass burning aerosols and the effects of land use change in Amazonia. Atmos. Chem. Phys., 13(3), 1261-1275. doi: 10.5194/acp-13-1261-2013. This paper addresses the Amazonian shortwave radiative budget over cloud-free conditions after considering three aspects of deforestation: (i) the emission of aerosols from biomass burning due to forest fires; (ii) changes in surface albedo after deforestation; and (iii) modifications in the column water vapour amount over deforested areas. Simultaneous Clouds and the Earth's Radiant Energy System (CERES) shortwave fluxes and aerosol optical depth (AOD) retrievals from the Moderate Resolution Imaging SpectroRadiometer (MODIS) were analysed during the peak of the biomass burning seasons (August and September) from 2000 to 2009. A discrete-ordinate radiative transfer (DISORT) code was used to extend instantaneous remote sensing radiative forcing assessments into 24-h averages. The mean direct radiative forcing of aerosols at the top of the atmosphere (TOA) during the biomass burning season for the 10-yr studied period was −5.6 ± 1.7 W m−2. Furthermore, the spatial distribution of the direct radiative forcing of aerosols over Amazonia was obtained for the biomass burning season of each year. It was observed that for high AOD (larger than 1 at 550 nm) the maximum daily direct aerosol radiative forcing at the TOA may be as high as −20 W m−2 locally. The surface reflectance plays a major role in the aerosol direct radiative effect. The study of the effects of biomass burning aerosols over different surface types shows that the direct radiative forcing is systematically more negative over forest than over savannah-like covered areas. Values of −15.7 ± 2.4 W m−2τ550 nm and −9.3 ± 1.7 W m−2τ550 nm were calculated for the mean daily aerosol forcing efficiencies over forest and savannah-like vegetation respectively. The overall mean annual land use change radiative forcing due to deforestation over the state of Rondônia, Brazil, was determined as −7.3 ± 0.9 W m−2. Biomass burning aerosols impact the radiative budget for approximately two months per year, whereas the surface albedo impact is observed throughout the year. Because of this difference, the estimated impact in the Amazonian annual radiative budget due to surface albedo-change is approximately 6 times higher than the impact due to aerosol emissions. The influence of atmospheric water vapour content in the radiative budget was also studied using AERONET column water vapour. It was observed that column water vapour is on average smaller by about 0.35 cm (around 10% of the total column water vapour) over deforested areas compared to forested areas. Our results indicate that this drying contributes to an increase in the shortwave radiative forcing, which varies from 0.4 W m−2 to 1.2 W m−2 depending on the column water vapour content before deforestation. The large radiative forcing values presented in this study point out that deforestation could have strong implications in convection, cloud development and the ratio of direct to diffuse radiation, which impacts carbon uptake by the forest.
Shi, Qinqing; Liang, ShunlinShi, Q., S. Liang, 2013: Characterizing the surface radiation budget over the Tibetan Plateau with ground-measured, reanalysis, and remote sensing data sets: 1. Methodology. Journal of Geophysical Research: Atmospheres, 118(17), 9642–9657. doi: 10.1002/jgrd.50720. The surface radiation budget (SRB) over the Tibetan Plateau (TP) greatly influences local climate, climate extremes (e.g., drought, flood) in China, and the East Asian monsoon. However, current estimates of SRB from models and satellite data are subject to large errors, and ground-measured data sets within this region are rather limited over the TP. Our objective is to determine the SRB over the TP by integrating information from three sources: (1) four ground-measured data sets from AsiaFlux, ChinaFLUX, GAME/Tibet, and CAMP/Tibet; (2) four reanalysis data sets from Climate Forecast System Reanalysis, Modern-Era Retrospective Analysis for Research and Applications, ERA-Interim, and Japanese 25-year Reanalysis; and (3) two remote sensing data sets, Global Energy and Water Cycle Experiment Surface Radiation Budget and International Satellite Cloud Climatology Project FD. This study, the first of a two-paper series, presents the methodology. Individual radiation components of reanalysis and remote sensing data set were first validated using ground-measured data from 1997 to 2007; then, a linear regression method was applied to generate the fused data from July 1983 to December 2007. The cross-validation results indicate that the monthly mean root-mean-square errors (RMSEs) of fused downward shortwave irradiance and albedo are 15.1 W m−2 and 0.05, respectively; the RMSEs of the downward and upward longwave fluxes are 13.3 and 8.4 W m−2, respectively; and the RMSE of all-wave net radiation is as low as 18.9 W m−2. Compared to nine sites with long-term observation of downward shortwave irradiance, the fused data represent the decadal variations with higher correlation than using individual products, suggesting the potential for application of the fused data sets in climatic and environmental research. surface radiation budget; Tibetan Plateau; data fusion
Smith, Karen L.; Previdi, Michael; Polvani, Lorenzo M.Smith, K. L., M. Previdi, L. M. Polvani, 2013: The Antarctic Atmospheric Energy Budget. Part II: The Effect of Ozone Depletion and its Projected Recovery. J. Climate, 26(24), 9729-9744. doi: 10.1175/JCLI-D-13-00173.1. AbstractIn this study the authors continue their investigation of the atmospheric energy budget of the Antarctic polar cap (the region poleward of 70°S) using integrations of the Whole Atmosphere Community Climate Model from the years 1960 to 2065. In agreement with observational data, it is found that the climatological mean net top-of-atmosphere (TOA) radiative flux is primarily balanced by the horizontal energy flux convergence over the polar cap. On interannual time scales, changes in the net TOA radiative flux are also primarily balanced by changes in the energy flux convergence, with the variability in both terms significantly correlated (positively and negatively, respectively) with the southern annular mode (SAM). On multidecadal time scales, twentieth-century stratospheric ozone depletion produces a negative trend in the net TOA radiative flux due to a decrease in the absorbed solar radiation within the atmosphere–surface column. The negative trend in the net TOA radiative flux is balanced by a positive trend in energy flux convergence, primarily in austral summer. This negative (positive) trend in the net TOA radiation (energy flux convergence) occurs despite a positive trend in the SAM, suggesting that the effects of the SAM on the energy budget are overwhelmed by the direct radiative effects of ozone depletion. In the twenty-first century, ozone recovery is expected to reverse the negative trend in the net TOA radiative flux, which would then, again, be balanced by a decrease in the energy flux convergence. Therefore, over the next several decades, ozone recovery will, in all likelihood, mask the effect of greenhouse gas warming on the Antarctic energy budget. Radiative fluxes; climate models; Antarctica; Energy transport; Multidecadal variability; Ozone
Song, Xiangzhou; Yu, LisanSong, X., L. Yu, 2013: How much net surface heat flux should go into the Western Pacific Warm Pool?. Journal of Geophysical Research: Oceans, 118(7), 3569-3585. doi: 10.1002/jgrc.20246. The western tropical Pacific warm pool, with the surface area bounded by the 28°C isotherm, receives heat from the atmosphere through the year. However, the exact amount of net surface heat flux into this area remains to be determined. A survey of nine heat flux climatologies (including three latest atmospheric reanalyses, three early reanalyses, and three analyzed products) shows that the estimates are clustered into two groups, with a mean of 18 Wm−2 for the five-member low net heat flux group (ERA-Interim, CORE.2, NCEP 1 and 2, and ERA-40) and of 49 Wm−2 for the four-member high net heat flux group (CFSR, OAFlux+ISCCP, NOCSv2.0, and MERRA). This study used a pool-area based heat budget analysis together with in situ air-sea and subsurface measurements to examine the physical consistency of the nine flux climatologies and to ascribe the statistical uncertainty of each product. The heat budget analysis indicates that the annual mean net surface heat flux should be 28 ± 10 Wm−2. The observed eddy coefficient along the 28°C isotherm is 1.5 cm2s−1 based on the TAO/TRION buoys and the historical records. The ocean cannot dissipate the excessive high heat fluxes, while the low fluxes cannot balance the estimated diffusive heat flux across the isotherm. Both the one-point direct comparison and pool integrated eddy diffusive heat flux analysis demonstrate that, the high net heat flux climatologies have high bias; on the other hand, the low fluxes have low bias. These biases and uncertainties are given and documented in this paper. 4504 Air/sea interactions; heat budget analysis; net air-sea heat flux; western Pacific warm pool
Stackhouse, P.W.; Wong, T; Kratz, D. P.; Sawaengphokhai, P.; Wilber, A. C.; Gupta, S. K.; Loeb, N. G.Stackhouse, P., T. Wong, D. P. Kratz, P. Sawaengphokhai, A. C. Wilber, S. K. Gupta, N. G. Loeb, 2013: Earth radiation Budget at Top-of-Atmosphere [in “State of the Climate in 2012"]. Bull. Amer. Meteor. Soc., 94(8), S41-S43. doi: 10.1175/2013BAMSStateoftheClimate.1.
Stevens, Bjorn; Giorgetta, Marco; Esch, Monika; Mauritsen, Thorsten; Crueger, Traute; Rast, Sebastian; Salzmann, Marc; Schmidt, Hauke; Bader, Jürgen; Block, Karoline; Brokopf, Renate; Fast, Irina; Kinne, Stefan; Kornblueh, Luis; Lohmann, Ulrike; Pincus, Robert; Reichler, Thomas; Roeckner, ErichStevens, B., M. Giorgetta, M. Esch, T. Mauritsen, T. Crueger, S. Rast, M. Salzmann, H. Schmidt, J. Bader, K. Block, R. Brokopf, I. Fast, S. Kinne, L. Kornblueh, U. Lohmann, R. Pincus, T. Reichler, E. Roeckner, 2013: Atmospheric component of the MPI-M Earth System Model: ECHAM6. Journal of Advances in Modeling Earth Systems, 5(2), 146–172. doi: 10.1002/jame.20015. ECHAM6, the sixth generation of the atmospheric general circulation model ECHAM, is described. Major changes with respect to its predecessor affect the representation of shortwave radiative transfer, the height of the model top. Minor changes have been made to model tuning and convective triggering. Several model configurations, differing in horizontal and vertical resolution, are compared. As horizontal resolution is increased beyond T63, the simulated climate improves but changes are incremental; major biases appear to be limited by the parameterization of small-scale physical processes, such as clouds and convection. Higher vertical resolution in the middle atmosphere leads to a systematic reduction in temperature biases in the upper troposphere, and a better representation of the middle atmosphere and its modes of variability. ECHAM6 represents the present climate as well as, or better than, its predecessor. The most marked improvements are evident in the circulation of the extratropics. ECHAM6 continues to have a good representation of tropical variability. A number of biases, however, remain. These include a poor representation of low-level clouds, systematic shifts in major precipitation features, biases in the partitioning of precipitation between land and sea (particularly in the tropics), and midlatitude jets that appear to be insufficiently poleward. The response of ECHAM6 to increasing concentrations of greenhouse gases is similar to that of ECHAM5. The equilibrium climate sensitivity of the mixed-resolution (T63L95) configuration is between 2.9 and 3.4 K and is somewhat larger for the 47 level model. Cloud feedbacks and adjustments contribute positively to warming from increasing greenhouse gases. climate change; climate; cloud feedback; general circulation model; resolution
Stubenrauch, C. J.; Rossow, W. B.; Kinne, S.; Ackerman, S.; Cesana, G.; Chepfer, H.; Di Girolamo, L.; Getzewich, B.; Guignard, A.; Heidinger, A.; Maddux, B. C.; Menzel, W. P.; Minnis, P.; Pearl, C.; Platnick, S.; Poulsen, C.; Riedi, J.; Sun-Mack, S.; Walther, A.; Winker, D.; Zeng, S.; Zhao, G.Stubenrauch, C. J., W. B. Rossow, S. Kinne, S. Ackerman, G. Cesana, H. Chepfer, L. Di Girolamo, B. Getzewich, A. Guignard, A. Heidinger, B. C. Maddux, W. P. Menzel, P. Minnis, C. Pearl, S. Platnick, C. Poulsen, J. Riedi, S. Sun-Mack, A. Walther, D. Winker, S. Zeng, G. Zhao, 2013: Assessment of Global Cloud Datasets from Satellites: Project and Database Initiated by the GEWEX Radiation Panel. Bull. Amer. Meteor. Soc., 94(7), 1031-1049. doi: 10.1175/BAMS-D-12-00117.1. MODIS; a-train; cirrus; water path; imagers isccp; level clouds; microphysical properties; part i; sounders 3i; statistical-analysis
Su, Hui; Jiang, Jonathan H.Su, H., J. H. Jiang, 2013: Tropical Clouds and Circulation Changes during the 2006/07 and 2009/10 El Niños. J. Climate, 26(2), 399-413. doi: 10.1175/JCLI-D-12-00152.1.
Su, Wenying; Loeb, Norman G.; Schuster, Gregory L.; Chin, Mian; Rose, Fred G.Su, W., N. G. Loeb, G. L. Schuster, M. Chin, F. G. Rose, 2013: Global all-sky shortwave direct radiative forcing of anthropogenic aerosols from combined satellite observations and GOCART simulations. Journal of Geophysical Research: Atmospheres, 118(2), 655–669. doi: 10.1029/2012JD018294. Estimation of aerosol direct radiative forcing (DRF) from satellite measurements is challenging because current satellite sensors do not have the capability of discriminating between anthropogenic and natural aerosols. We combine 3-hourly cloud properties from satellite retrievals with two aerosol data sets to calculate the all-sky aerosol direct radiative effect (DRE), which is the mean radiative perturbation due to the presence of both natural and anthropogenic aerosols. The first aerosol data set is based upon Moderate Resolution Imaging Spectroradiometer (MODIS) and Model for Atmospheric Transport and Chemistry (MATCH) assimilation model and is largely constrained by MODIS aerosol optical depth, but it does not distinguish between anthropogenic and natural aerosols. The other aerosol data set is based upon the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model, which does not assimilate aerosol observations but predicts the anthropogenic and natural components of aerosols. Thus, we can calculate the aerosol DRF using GOCART classifications of anthropogenic and natural aerosols and the ratio of DRF to DRE. We then apply this ratio to DRE calculated using MODIS/MATCH aerosols to partition it into DRF (MODIS/MATCH DRF) by assuming that the anthropogenic fractions from GOCART are representative. The global (60°N 60°S) mean all-sky MODIS/MATCH DRF is −0.51 Wm−2 at the top of the atmosphere (TOA), 2.51 Wm−2 within the atmosphere, and −3.02 Wm−2 at the surface. The GOCART all-sky DRF is −0.17 Wm−2 at the TOA, 2.02 Wm−2 within the atmosphere, and −2.19 Wm−2 at the surface. The differences between MODIS/MATCH DRF and GOCART DRF are solely due to the differences in aerosol properties, since both computations use the same cloud properties and surface albedo and the same proportion of anthropogenic contributions to aerosol DRE. Aerosol optical depths simulated by the GOCART model are smaller than those in MODIS/MATCH, and aerosols in the GOCART model are more absorbing than those in MODIS/MATCH. Large difference in all-sky TOA DRF from these two aerosol data sets highlights the complexity in determining the all-sky DRF, since the presence of clouds amplifies the sensitivities of DRF to aerosol single-scattering albedo and aerosol vertical distribution. clouds; aerosol; direct radiative effect; direct radiative forcing
Tang, Qiuhong; Leng, GuoyongTang, Q., G. Leng, 2013: Changes in Cloud Cover, Precipitation, and Summer Temperature in North America from 1982 to 2009. J. Climate, 26(5), 1733-1744. doi: 10.1175/JCLI-D-12-00225.1. In North America (NA), trends in summer surface air temperatures vary on decadal time scales, and some regions have temperature trends that exhibit a lack of warming in 1982–2009. From a surface energy balance perspective, the summer mean daily maximum temperature change can be affected by changes in solar heating that are associated with cloud cover change and changes in surface evaporative cooling caused by different precipitation and land surface wetness, but little is known about regional cloud cover and precipitation feedbacks to decadal temperature trends. Changes in cloudiness and precipitation and their connections with summer mean daily maximum temperature variations in NA were investigated using observation-based products of temperature and precipitation and satellite-derived cloud cover and radiation products. Results show that summer mean daily maximum temperature variance is largely explained by changes in cloud cover and precipitation. Cloud cover effect dominates at the high and middle latitudes of NA, and precipitation is a more dominant factor in the southern United States. The results indicate that cloud cover is either the major indicator of the summer mean daily maximum temperature changes (the effect) or the important local factor influencing the changes (the cause). Cloud cover is negatively correlated with mean daily maximum temperature variation in spring and autumn at the middle latitudes of NA but not at the high latitudes. Cloud cover; hydrology
Tett, Simon F. B.; Mineter, Michael J.; Cartis, Coralia; Rowlands, Daniel J.; Liu, PingTett, S. F. B., M. J. Mineter, C. Cartis, D. J. Rowlands, P. Liu, 2013: Can Top-of-Atmosphere Radiation Measurements Constrain Climate Predictions? Part I: Tuning. J. Climate, 26(23), 9348-9366. doi: 10.1175/JCLI-D-12-00595.1.
Tett, Simon F. B.; Rowlands, Daniel J.; Mineter, Michael J.; Cartis, CoraliaTett, S. F. B., D. J. Rowlands, M. J. Mineter, C. Cartis, 2013: Can Top-of-Atmosphere Radiation Measurements Constrain Climate Predictions? Part II: Climate Sensitivity. J. Climate, 26(23), 9367-9383. doi: 10.1175/JCLI-D-12-00596.1. AbstractA large number of perturbed-physics simulations of version 3 of the Hadley Centre Atmosphere Model (HadAM3) were compared with the Clouds and the Earth's Radiant Energy System (CERES) estimates of outgoing longwave radiation (OLR) and reflected shortwave radiation (RSR) as well as OLR and RSR from the earlier Earth Radiation Budget Experiment (ERBE) estimates. The model configurations were produced from several independent optimization experiments in which four parameters were adjusted. Model–observation uncertainty was estimated by combining uncertainty arising from satellite measurements, observational radiation imbalance, total solar irradiance, radiative forcing, natural aerosol, internal climate variability, and sea surface temperature and that arising from parameters that were not varied. Using an emulator built from 14 001 “slab” model evaluations carried out using the climateprediction.net ensemble, the climate sensitivity for each configuration was estimated. Combining different prior probabilities for model configurations with the likelihood for each configuration and taking account of uncertainty in the emulated climate sensitivity gives, for the HadAM3 model, a 2.5%–97.5% range for climate sensitivity of 2.7–4.2 K if the CERES observations are correct. If the ERBE observations are correct, then they suggest a larger range, for HadAM3, of 2.8–5.6 K. Amplifying the CERES observational covariance estimate by a factor of 20 brings CERES and ERBE estimates into agreement. In this case the climate sensitivity range is 2.7–5.4 K. The results rule out, at the 2.5% level for HadAM3 and several different prior assumptions, climate sensitivities greater than 5.6 K. climate models; Bayesian methods; Climate sensitivity
Thorsen, Tyler J.; Fu, Qiang; Comstock, Jennifer M.Thorsen, T. J., Q. Fu, J. M. Comstock, 2013: Cloud effects on radiative heating rate profiles over Darwin using ARM and A-train radar/lidar observations. Journal of Geophysical Research: Atmospheres, 118(11), 5637–5654. doi: 10.1002/jgrd.50476. Observations of clouds from the ground-based U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program and satellite-based A-train are used to compute cloud radiative forcing profiles over the ARM Darwin, Australia site. Cloud properties are obtained from both radar (the ARM Millimeter Cloud Radar (MMCR) and the CloudSat satellite in the A-train) and lidar (the ARM Micropulse lidar (MPL) and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite in the A-train) observations. Cloud microphysical properties are taken from combined radar and lidar retrievals for ice clouds and radar-only or lidar-only retrievals for liquid clouds. Large, statistically significant differences of up to 1.43 K/d exist between the mean ARM and A-train net cloud radiative forcing profiles. The majority of the difference in cloud radiative forcing profiles is shown to be due to a large difference in the cloud fraction above 12 km. Above this altitude, the A-train cloud fraction is significantly larger because many more clouds are detected by CALIPSO than by the ground-based MPL. It is shown that the MPL is unable to observe as many high clouds as CALIPSO due to being more frequently attenuated and a poorer sensitivity. We also isolate the difference in cloud radiative forcing due to sampling and retrieval differences which are of comparable importance but are of smaller impact than cloud fraction differences. This study demonstrates that A-train observations are better suited for the calculation of cloud radiative forcing profiles at Darwin. In addition, we find that it is necessary to supplement CloudSat with CALIPSO observations to obtain accurate cloud radiative forcing profiles. ARM; cloud forcing; a-train; radiative heating
Trenberth, Kevin E.; Fasullo, John T.Trenberth, K. E., J. T. Fasullo, 2013: Regional Energy and Water Cycles: Transports from Ocean to Land. J. Climate, 26(20), 7837-7851. doi: 10.1175/JCLI-D-13-00008.1.
Tsushima, Yoko; Manabe, SyukuroTsushima, Y., S. Manabe, 2013: Assessment of radiative feedback in climate models using satellite observations of annual flux variation. Proceedings of the National Academy of Sciences, 110(19), 7568-7573. doi: 10.1073/pnas.1216174110. In the climate system, two types of radiative feedback are in operation. The feedback of the first kind involves the radiative damping of the vertically uniform temperature perturbation of the troposphere and Earth’s surface that approximately follows the Stefan–Boltzmann law of blackbody radiation. The second kind involves the change in the vertical lapse rate of temperature, water vapor, and clouds in the troposphere and albedo of the Earth’s surface. Using satellite observations of the annual variation of the outgoing flux of longwave radiation and that of reflected solar radiation at the top of the atmosphere, this study estimates the so-called “gain factor,” which characterizes the strength of radiative feedback of the second kind that operates on the annually varying, global-scale perturbation of temperature at the Earth’s surface. The gain factor is computed not only for all sky but also for clear sky. The gain factor of so-called “cloud radiative forcing” is then computed as the difference between the two. The gain factors thus obtained are compared with those obtained from 35 models that were used for the fourth and fifth Intergovernmental Panel on Climate Change assessment. Here, we show that the gain factors obtained from satellite observations of cloud radiative forcing are effective for identifying systematic biases of the feedback processes that control the sensitivity of simulated climate, providing useful information for validating and improving a climate model. ERBE; CERES; cloud feedback; CMIP; metric of radiative feedback
Vázquez-Navarro, M.; Mayer, B.; Mannstein, H.Vázquez-Navarro, M., B. Mayer, H. Mannstein, 2013: A fast method for the retrieval of integrated longwave and shortwave top-of-atmosphere upwelling irradiances from MSG/SEVIRI (RRUMS). Atmos. Meas. Tech., 6(10), 2627-2640. doi: 10.5194/amt-6-2627-2013. A new Rapid Retrieval of Upwelling irradiances from MSG/SEVIRI (RRUMS) is presented. It has been developed to observe the top-of-atmosphere irradiances of small scale and rapidly changing features that are not sufficiently resolved by specific Earth radiation budget sensors. Our retrieval takes advantage of the spatial and temporal resolution of MSG/SEVIRI and provides outgoing longwave and reflected shortwave radiation only by means of a combination of SEVIRI channels. The longwave retrieval is based on a simple linear combination of brightness temperatures from the SEVIRI infrared channels. The shortwave retrieval is based on a neural network that requires as input the visible and near-infrared SEVIRI channels. Both LW and SW algorithms have been validated by comparing their results with CERES and GERB irradiance observations. While being less accurate than their dedicated counterparts, the SEVIRI-based methods have two major advantages compared to CERES and GERB: their higher spatial resolution and the better temporal resolution. With our retrievals it is possible to observe the radiative effect of small-scale features such as cumulus clouds, cirrus clouds, or aircraft contrails. The spatial resolution of SEVIRI is 3 km × 3 km in the sub-satellite point, remarkably better than that of CERES (20 km) or GERB (45 km). The temporal resolution is 15 min (5 min in the Rapid-Scan mode), the same as GERB, but significantly better than that of CERES which, being on board of a polar orbiting satellite, has a temporal resolution as low as 2 overpasses per day.
Virts, Katrina S.; Wallace, John M.; Hutchins, Michael L.; Holzworth, Robert H.Virts, K. S., J. M. Wallace, M. L. Hutchins, R. H. Holzworth, 2013: Diurnal Lightning Variability over the Maritime Continent: Impact of Low-Level Winds, Cloudiness, and the MJO. J. Atmos. Sci., 70(10), 3128-3146. doi: 10.1175/JAS-D-13-021.1.
Voigt, Aiko; Stevens, Bjorn; Bader, Juergen; Mauritsen, ThorstenVoigt, A., B. Stevens, J. Bader, T. Mauritsen, 2013: The Observed Hemispheric Symmetry in Reflected Shortwave Irradiance. J. Climate, 26(2), 468-477. doi: 10.1175/JCLI-D-12-00132.1. While the concentration of landmasses and atmospheric aerosols on the Northern Hemisphere suggests that the Northern Hemisphere is brighter than the Southern Hemisphere, satellite measurements of top-of-atmosphere irradiances found that both hemispheres reflect nearly the same amount of shortwave irradiance. Here, the authors document that the most precise and accurate observation, the energy balanced and filled dataset of the Clouds and the Earth's Radiant Energy System covering the period 2000-10, measures an absolute hemispheric difference in reflected shortwave irradiance of 0.1 W m(-2). In contrast, the longwave irradiance of the two hemispheres differs by more than 1 W m(-2), indicating that the observed climate system exhibits hemispheric symmetry in reflected shortwave irradiance but not in longwave irradiance. The authors devise a variety of methods to estimate the spatial degrees of freedom of the time-mean reflected shortwave irradiance. These are used to show that the hemispheric symmetry in reflected shortwave irradiance is a nontrivial property of the Earth system in the sense that most partitionings of Earth into two random halves do not exhibit hemispheric symmetry in reflected shortwave irradiance. Climate models generally do not reproduce the observed hemispheric symmetry, which the authors interpret as further evidence that the symmetry is nontrivial. While the authors cannot rule out that the observed hemispheric symmetry in reflected shortwave irradiance is accidental, their results motivate a search for mechanisms that minimize hemispheric differences in reflected shortwave irradiance and planetary albedo. atmosphere; earth radiation budget; climate; top
von Salzen, Knut; Scinocca, John F.; McFarlane, Norman A.; Li, Jiangnan; Cole, Jason N. S.; Plummer, David; Verseghy, Diana; Reader, M. Cathy; Ma, Xiaoyan; Lazare, Michael; Solheim, Larryvon Salzen, K., J. F. Scinocca, N. A. McFarlane, J. Li, J. N. S. Cole, D. Plummer, D. Verseghy, M. C. Reader, X. Ma, M. Lazare, L. Solheim, 2013: The Canadian Fourth Generation Atmospheric Global Climate Model (CanAM4). Part I: Representation of Physical Processes. Atmosphere-Ocean, 51(1), 104-125. doi: 10.1080/07055900.2012.755610. The Canadian Centre for Climate Modelling and Analysis (CCCma) has developed the fourth generation of the Canadian Atmospheric Global Climate Model (CanAM4). The new model includes substantially modified physical parameterizations compared to its predecessor. In particular, the treatment of clouds, cloud radiative effects, and precipitation has been modified. Aerosol direct and indirect effects are calculated based on a bulk aerosol scheme. Simulation results for present-day global climate are analyzed, with a focus on cloud radiative effects and precipitation. Good overall agreement is found between climatological mean short- and longwave cloud radiative effects and observations from the Clouds and Earth's Radiant Energy System (CERES) experiment. An analysis of the responses of cloud radiative effects to variations in climate will be presented in a companion paper. [Traduit par la rédaction] Le Centre canadien de la modélisation et de l'analyse climatique (CCmaC) a mis au point la quatrième génération du modèle canadien de circulation générale de l'atmosphère (CanAM4). Le nouveau modèle comprend des paramétrisations physiques passablement modifiées comparativement à son prédécesseur. En particulier, le traitement des nuages, des effets radiatifs des nuages et des précipitations a été modifié. Les effets directs et indirects des aérosols sont calculés à l'aide d'un schéma d'aérosols en bloc. Nous analysons des résultats de simulation pour le climat général du jour présent en mettant l'accent sur les effets radiatifs des nuages et les précipitations. Nous trouvons un bon accord général entre la moyenne climatologique des effets radiatifs des nuages pour les courtes et les grandes longueurs d'onde et les observations de l'expérience CERES (Clouds and Earth's Radiant Energy System). Une analyse de la réponse des effets radiatifs des nuages aux variations du climat sera présentée dans un article connexe.
Wang, Hailan; Su, WenyingWang, H., W. Su, 2013: Evaluating and understanding top of the atmosphere cloud radiative effects in Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) Coupled Model Intercomparison Project Phase 5 (CMIP5) models using satellite observations. Journal of Geophysical Research-Atmospheres, 118(2), 683-699. doi: 10.1029/2012JD018619. In this study, the annual mean climatology of top of the atmosphere (TOA) shortwave and longwave cloud radiative effects in 12 Atmospheric Model Intercomparison Project (AMIP)-type simulations participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) is evaluated and investigated using satellite-based observations, with a focus on the tropics. Results show that the CMIP5 AMIPs simulate large-scale regional mean TOA radiative fluxes and cloud radiative forcings (CRFs) well but produce considerably less cloud amount, particularly in the middle and lower troposphere. The good model simulations in tropical means, with multimodel mean biases of -3.6 W/m(2) for shortwave CRF and -1.0 W/m(2) for longwave CRF, are, however, a result of compensating errors over different dynamical regimes. Over the Maritime Continent, most of the models simulate moderately less high-cloud fraction, leading to weaker shortwave cooling and longwave warming and a larger net cooling. Over subtropical strong subsidence regimes, most of the CMIP5 models strongly underestimate stratocumulus cloud amount and show considerably weaker local shortwave CRF. Over the transitional trade cumulus regimes, a notable feature is that while at varying amplitudes, most of the CMIP5 models consistently simulate a deeper and drier boundary layer, more moist free troposphere, and more high clouds and, consequently, overestimate shortwave cooling and longwave warming effects there. While most of the CMIP5 models show the same sign as the multimodel mean, there are substantial model spreads, particularly over the tropical deep convective and subtropical strong subsidence regimes. Representing clouds and their TOA radiative effects remains a challenge in the CMIP5 models. radiative flux; cloud fraction; cloud radiative effect; global climate model; budget experiment; general-circulation models; impact; performance; relative humidity; surface; system
Wang, Kaicun; Dickinson, Robert E.Wang, K., R. E. Dickinson, 2013: Global atmospheric downward longwave radiation at the surface from ground-based observations, satellite retrievals, and reanalyses. Reviews of Geophysics, 51(2), 150-185. doi: 10.1002/rog.20009. Atmospheric downward longwave radiation at the surface (Ld) varies with increasing CO2 and other greenhouse gases. This study quantifies the uncertainties of current estimates of global Ld at monthly to decadal timescales and its global climatology and trends during the past decades by a synthesis of the existing observations, reanalyses, and satellite products. We find that current Ld observations have a standard deviation error of ~3.5 W m−2 on a monthly scale. Observations of Ld by different pyrgeometers may differ substantially for lack of a standard reference. The calibration of a pyrgeometer significantly affects its quantification of annual variability. Compared with observations collected at 169 global land sites from 1992 to 2010, the Ld derived from state-of-the-art satellite cloud observations and reanalysis temperature and humidity profiles at a grid scale of ~1° has a bias of ±9 W m−2 and a standard deviation of 7 W m−2, with a nearly zero overall bias. The standard deviations are reduced to 4 W m−2 over tropical oceans when compared to Ld observations collected by 24 buoy sites from 2002 to 2011. The −4 W m−2 bias of satellite Ld retrievals over tropical oceans is likely because of the overestimation of Ld observations resulting from solar heating of the pyrgeometer. Our best estimate of global means Ld from 2003 to 2010 are 342 ± 3 W m−2 (global), 307 ± 3 W m−2 (land), and 356 ± 3 W m−2 (ocean). Estimates of Ld trends are seriously compromised by the changes in satellite sensors giving changes of water vapor profiles. 0360 Radiation: transmission and scattering; 0321 Cloud/radiation interaction; 1616 Climate variability; uncertainty; downward longwave radiation; 1622 Earth system modeling; greenhouse gases; 1631 Land/atmosphere interactions
Wang, Wencai; Huang, Jianping; Zhou, Tian; Bi, Jianrong; Lin, Lei; Chen, Yonghang; Huang, Zhongwei; Su, JingWang, W., J. Huang, T. Zhou, J. Bi, L. Lin, Y. Chen, Z. Huang, J. Su, 2013: Estimation of radiative effect of a heavy dust storm over northwest China using Fu–Liou model and ground measurements. Journal of Quantitative Spectroscopy and Radiative Transfer, 122, 114-126. doi: 10.1016/j.jqsrt.2012.10.018. A heavy dust storm that occurred in Northwestern China during April 24–30 2010 was studied using observational data along with the Fu–Liou radiative transfer model. The dust storm was originated from Mongolia and affected more than 10 provinces of China. Our results showed that dust aerosols have a significant impact on the radiative energy budget. At Minqin (102.959°E, 38.607°N) and Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL, 104.13°E, 35.95°N) sites, the net radiative forcing (RF) ranged from 5.93 to 35.7 W m−2 at the top of the atmosphere (TOA), −6.3 to −30.94 W m−2 at surface, and 16.77 to 56.32 W m−2 in the atmosphere. The maximum net radiative heating rate reached 5.89 K at 1.5 km on 24 April at the Minqin station and 4.46 K at 2.2 km on 29 April at the SACOL station. Our results also indicated that the radiative effect of dust aerosols is affected by aerosol optical depth (AOD), single-scattering albedo (SSA) and surface albedo. Modifications of the radiative energy budget by dust aerosols may have important implications for atmospheric circulation and regional climate. radiative forcing; dust aerosol; Fu–Liou model
Watanabe, Masahiro; Kamae, Youichi; Yoshimori, Masakazu; Oka, Akira; Sato, Makiko; Ishii, Masayoshi; Mochizuki, Takashi; Kimoto, MasahideWatanabe, M., Y. Kamae, M. Yoshimori, A. Oka, M. Sato, M. Ishii, T. Mochizuki, M. Kimoto, 2013: Strengthening of ocean heat uptake efficiency associated with the recent climate hiatus. Geophysical Research Letters, 40(12), 3175-3179. doi: 10.1002/grl.50541. The rate of increase of global-mean surface air temperature (SAT(g)) has apparently slowed during the last decade. We investigated the extent to which state-of-the-art general circulation models (GCMs) can capture this hiatus period by using multimodel ensembles of historical climate simulations. While the SAT(g) linear trend for the last decade is not captured by their ensemble means regardless of differences in model generation and external forcing, it is barely represented by an 11-member ensemble of a GCM, suggesting an internal origin of the hiatus associated with active heat uptake by the oceans. Besides, we found opposite changes in ocean heat uptake efficiency (), weakening in models and strengthening in nature, which explain why the models tend to overestimate the SAT(g) trend. The weakening of commonly found in GCMs seems to be an inevitable response of the climate system to global warming, suggesting the recovery from hiatus in coming decades. surface temperature; sensitivity; energy budget; GCM; aogcm; climate hiatus; earths energy; energy budget; ocean heat uptake
Wen, Guoyong; Marshak, Alexander; Levy, Robert C.; Remer, Lorraine A.; Loeb, Norman G.; Várnai, Tamás; Cahalan, Robert F.Wen, G., A. Marshak, R. C. Levy, L. A. Remer, N. G. Loeb, T. Várnai, R. F. Cahalan, 2013: Improvement of MODIS aerosol retrievals near clouds. Journal of Geophysical Research: Atmospheres, 118(16), 9168–9181. doi: 10.1002/jgrd.50617. The retrieval of aerosol properties near clouds from reflected sunlight is challenging. Sunlight reflected from clouds can effectively enhance the reflectance in nearby clear regions. Ignoring cloud 3-D radiative effects can lead to large biases in aerosol retrievals, risking an incorrect interpretation of satellite observations on aerosol-cloud interaction. Earlier, we developed a simple model to compute the cloud-induced clear-sky radiance enhancement that is due to radiative interaction between boundary layer clouds and the molecular layer above. This paper focuses on the application and implementation of the correction algorithm. This is the first time that this method is being applied to a full Moderate Resolution Imaging Spectroradiometer (MODIS) granule. The process of the correction includes converting Clouds and the Earth's Radiant Energy System broadband flux to visible narrowband flux, computing the clear-sky radiance enhancement, and retrieving aerosol properties. We find that the correction leads to smaller values in aerosol optical depth (AOD), Ångström exponent, and the small mode aerosol fraction of the total AOD. It also makes the average aerosol particle size larger near clouds than far away from clouds, which is more realistic than the opposite behavior observed in operational retrievals. We discuss issues in the current correction method as well as our plans to validate the algorithm. clouds; aerosol; MODIS; 3-D
Wielicki, Bruce A.; Young, D. F.; Mlynczak, M. G.; Thome, K. J.; Leroy, S.; Corliss, J.; Anderson, J. G.; Ao, C.O.; Bantges, R.; Best, F.; Bowman, K.; Brindley, H.; Butler, J. J.; Collins, W.; Dykema, J. A.; Doelling, D. R.; Feldman, D. R.; Fox, N.; Huang, X.; Holz, R.; Huang, Y.; Jin, Z.; Jennings, D.; Johnson, D. G.; Jucks, K.; Kato, S.; Kirk-Davidoff, D. B.; Knuteson, R.; Kopp, G.; Kratz, D. P.; Liu, X.; Lukashin, C.; Mannucci, A. J.; Phojanamongkolkij, N.; Pilewskie, P.; Ramaswamy, V.; Revercomb, H.; Rice, J.; Roberts, Y.; Roithmayr, C. M.; Rose, F.; Sandford, S.; Shirley, E. L.; Smith, W.L.; Soden, B.; Speth, P. W.; Sun, W.; Taylor, P.C.; Tobin, D.; Xiong, X.Wielicki, B. A., D. F. Young, M. G. Mlynczak, K. J. Thome, S. Leroy, J. Corliss, J. G. Anderson, C. Ao, R. Bantges, F. Best, K. Bowman, H. Brindley, J. J. Butler, W. Collins, J. A. Dykema, D. R. Doelling, D. R. Feldman, N. Fox, X. Huang, R. Holz, Y. Huang, Z. Jin, D. Jennings, D. G. Johnson, K. Jucks, S. Kato, D. B. Kirk-Davidoff, R. Knuteson, G. Kopp, D. P. Kratz, X. Liu, C. Lukashin, A. J. Mannucci, N. Phojanamongkolkij, P. Pilewskie, V. Ramaswamy, H. Revercomb, J. Rice, Y. Roberts, C. M. Roithmayr, F. Rose, S. Sandford, E. L. Shirley, W. Smith, B. Soden, P. W. Speth, W. Sun, P. Taylor, D. Tobin, X. Xiong, 2013: Achieving Climate Change Absolute Accuracy in Orbit. Bull. Amer. Meteor. Soc., 130308154356007. doi: 10.1175/BAMS-D-12-00149.1.
Williams, K. D.; Bodas-Salcedo, A.; Déqué, M.; Fermepin, S.; Medeiros, B.; Watanabe, M.; Jakob, C.; Klein, S. A.; Senior, C. A.; Williamson, D. L.Williams, K. D., A. Bodas-Salcedo, M. Déqué, S. Fermepin, B. Medeiros, M. Watanabe, C. Jakob, S. A. Klein, C. A. Senior, D. L. Williamson, 2013: The Transpose-AMIP II Experiment and Its Application to the Understanding of Southern Ocean Cloud Biases in Climate Models. J. Climate, 26(10), 3258-3274. doi: 10.1175/JCLI-D-12-00429.1.
Xie, Shaocheng; Liu, Xiaohong; Zhao, Chuanfeng; Zhang, YuyingXie, S., X. Liu, C. Zhao, Y. Zhang, 2013: Sensitivity of CAM5-Simulated Arctic Clouds and Radiation to Ice Nucleation Parameterization. J. Climate, 26(16), 5981-5999. doi: 10.1175/JCLI-D-12-00517.1.
Xu, Kuan-Man; Cheng, AnningXu, K., A. Cheng, 2013: Evaluating Low Cloud Simulation from an Upgraded Multiscale Modeling Framework Model. Part II: Seasonal Variations over the Eastern Pacific. J. Climate, 130130122615008. doi: 10.1175/JCLI-D-12-00276.1.
Xu, Yangyang; Bahadur, Ranjit; Zhao, Chun; Ruby Leung, L.Xu, Y., R. Bahadur, C. Zhao, L. Ruby Leung, 2013: Estimating the radiative forcing of carbonaceous aerosols over California based on satellite and ground observations. Journal of Geophysical Research: Atmospheres, 118(19), 11,148–11,160. doi: 10.1002/jgrd.50835. Carbonaceous aerosols have the potential to impact climate directly through absorption of incoming solar radiation and indirectly by affecting cloud and precipitation. Recent modeling studies have made great efforts to simulate both the spatial and temporal distributions of carbonaceous aerosol's optical properties and radiative forcing. This study makes the first observationally constrained assessment of the direct radiative forcing of carbonaceous aerosols over California. By exploiting multiple observations (including ground sites and satellites), we constructed the distribution of aerosol optical depths and aerosol absorption optical depths (AAOD) over California for a 10 year period (2000–2010). We partitioned the total solar absorption into individual contributions from elemental carbon (EC), organic carbon (OC), and dust aerosols, using a newly developed scheme. Our results show that AAOD due to carbonaceous aerosols (EC and OC) at 440 nm was 50%–200% larger than natural dust, with EC contributing the bulk (70%–90%). Observationally constrained EC absorption agrees reasonably well with estimates from global and regional chemical transport models, but the models underestimate the OC AAOD by at least 50%. We estimated that the top of the atmosphere (TOA) forcing from carbonaceous aerosols was 0.7 W/m2 and the TOA forcing due to OC was close to zero. The atmospheric heating of carbonaceous aerosol was 2.2–2.9 W/m2, of which EC contributed about 80–90%. We estimated the atmospheric heating of OC at 0.1–0.4 W/m2, larger than model simulations. EC reduction over the last two decades may have caused a surface brightening of 1.5–3.5 W/m2. climate; radiation; AERONET; black carbon; brown carbon; organic carbon
Yang, Ben; Qian, Yun; Lin, Guang; Leung, L. Ruby; Rasch, Philip J.; Zhang, Guang J.; McFarlane, Sally A.; Zhao, Chun; Zhang, Yaocun; Wang, Hailong; Wang, Minghuai; Liu, XiaohongYang, B., Y. Qian, G. Lin, L. R. Leung, P. J. Rasch, G. J. Zhang, S. A. McFarlane, C. Zhao, Y. Zhang, H. Wang, M. Wang, X. Liu, 2013: Uncertainty quantification and parameter tuning in the CAM5 Zhang-McFarlane convection scheme and impact of improved convection on the global circulation and climate. Journal of Geophysical Research: Atmospheres, 118(2), 395-415. doi: 10.1029/2012JD018213. In this study, we applied an uncertainty quantification (UQ) technique to improve convective precipitation in the global climate model, the Community Atmosphere Model version 5 (CAM5), in which the convective and stratiform precipitation partitioning is very different from observational estimates. We examined the sensitivity of precipitation and circulation to several key parameters in the Zhang-McFarlane deep convection scheme in CAM5, using a stochastic importance-sampling algorithm that can progressively converge to optimal parameter values. The impact of improved deep convection on the global circulation and climate was subsequently evaluated. Our results show that the simulated convective precipitation is most sensitive to the parameters of the convective available potential energy consumption time scale, parcel fractional mass entrainment rate, and maximum downdraft mass flux fraction. Using the optimal parameters constrained by the observed Tropical Rainfall Measuring Mission, convective precipitation improves the simulation of convective to stratiform precipitation ratio and rain-rate spectrum remarkably. When convection is suppressed, precipitation tends to be more confined to the regions with strong atmospheric convergence. As the optimal parameters are used, positive impacts on some aspects of the atmospheric circulation and climate, including reduction of the double Intertropical Convergence Zone, improved East Asian monsoon precipitation, and improved annual cycles of the cross-equatorial jets, are found as a result of the vertical and horizontal redistribution of latent heat release from the revised parameterization. Positive impacts of the optimal parameters derived from the 2° simulations are found to transfer to the 1° simulations to some extent. 0320 Cloud physics and chemistry; 1620 Climate dynamics; 1616 Climate variability; 1626 Global climate models; convection scheme; CAM5; convective precipitation; parameter tuning; Uncertainty Quantification
Zhang, Feng; Liang, Xin-Zhong; 曾庆存, Qingcun Zeng; Gu, Yu; Su, ShenjianZhang, F., X. Liang, Q. Z. 曾庆存, Y. Gu, S. Su, 2013: Cloud-Aerosol-Radiation (CAR) ensemble modeling system: Overall accuracy and efficiency. Advances in Atmospheric Sciences, 30(4), 955-973. doi: 10.1007/s00376-012-2171-z. The Cloud-Aerosol-Radiation (CAR) ensemble modeling system has recently been built to better understand cloud/aerosol/radiation processes and determine the uncertainties caused by different treatments of cloud/aerosol/radiation in climate models. The CAR system comprises a large scheme collection of cloud, aerosol, and radiation processes available in the literature, including those commonly used by the world’s leading GCMs. In this study, detailed analyses of the overall accuracy and efficiency of the CAR system were performed. Despite the different observations used, the overall accuracies of the CAR ensemble means were found to be very good for both shortwave (SW) and longwave (LW) radiation calculations. Taking the percentage errors for July 2004 compared to ISCCP (International Satellite Cloud Climatology Project) data over (60°N, 60°S) as an example, even among the 448 CAR members selected here, those errors of the CAR ensemble means were only about −0.67% (−0.6 W m−2) and −0.82% (−2.0 W m−2) for SW and LW upward fluxes at the top of atmosphere, and 0.06% (0.1 W m−2) and −2.12% (−7.8 W m−2) for SW and LW downward fluxes at the surface, respectively. Furthermore, model SW frequency distributions in July 2004 covered the observational ranges entirely, with ensemble means located in the middle of the ranges. Moreover, it was found that the accuracy of radiative transfer calculations can be significantly enhanced by using certain combinations of cloud schemes for the cloud cover fraction, particle effective size, water path, and optical properties, along with better explicit treatments for unresolved cloud structures. Meteorology; radiation; cloud radiative forcing; Atmospheric Sciences; Geophysics/Geodesy; ensemble; CAR
Zhang, Taiping; Stackhouse Jr., Paul W.; Gupta, Shashi K.; Cox, Stephen J.; Colleen Mikovitz, J.; Hinkelman, Laura M.Zhang, T., P. W. Stackhouse Jr., S. K. Gupta, S. J. Cox, J. Colleen Mikovitz, L. M. Hinkelman, 2013: The validation of the GEWEX SRB surface shortwave flux data products using BSRN measurements: A systematic quality control, production and application approach. Journal of Quantitative Spectroscopy and Radiative Transfer, 122, 127-140. doi: 10.1016/j.jqsrt.2012.10.004. The NASA/GEWEX Surface Radiation Budget (SRB) project has produced a 24.5-year continuous record of global shortwave and longwave radiation fluxes at TOA and the Earth's surface from satellite measurements. The time span of the data is from July 1983 to December 2007, and the spatial resolution is 1° latitude×1° longitude. The inputs of the latest version (Release 3.0) include the GEOS Version 4.0.3 meteorological information and cloud properties derived from ISCCP DX data. The SRB products are available on 3-hourly, 3-hourly-monthly, daily and monthly time scales. To assess the quality of the product, we extensively validated the SRB data against 5969 site-months of ground-based measurements from 52 Baseline Surface Radiation Network (BSRN) stations. This paper describes first the characteristics of the BSRN data and the GEWEX SRB data, the methodology for quality control and processing of the shortwave BSRN data, and then the systematic SRB-BSRN comparisons. It is found that, except for occasional extreme outliers as seen in scatter plots, the satellite-based surface radiation data generally agree very well with BSRN measurements. Specifically, the bias/RMS for the daily and monthly mean shortwave fluxes are, respectively, -3.6/35.5 and -5.2/23.3 W° m−2 under all-sky conditions. Solar radiation; Satellite; BSRN; validation; GEWEX SRB
Zhang, Yi; Yu, Rucong; Li, Jian; Yuan, Weihua; Zhang, MinghuaZhang, Y., R. Yu, J. Li, W. Yuan, M. Zhang, 2013: Dynamic and Thermodynamic Relations of Distinctive Stratus Clouds on the Lee Side of the Tibetan Plateau in the Cold Season. J. Climate, 26(21), 8378-8391. doi: 10.1175/JCLI-D-13-00009.1.
Zhou, Chen; Zelinka, Mark D.; Dessler, Andrew E.; Yang, PingZhou, C., M. D. Zelinka, A. E. Dessler, P. Yang, 2013: An Analysis of the Short-Term Cloud Feedback Using MODIS Data. J. Climate, 26(13), 4803-4815. doi: 10.1175/JCLI-D-12-00547.1.
Zhou, Tian; Huang, Jianping; Huang, Zhongwei; Liu, Jingjing; Wang, Wencai; Lin, LeiZhou, T., J. Huang, Z. Huang, J. Liu, W. Wang, L. Lin, 2013: The depolarization–attenuated backscatter relationship for dust plumes. Optics Express, 21(13), 15195-15204. doi: 10.1364/OE.21.015195. This study identified the relationship between the layer-integrated attenuated backscatter coefficient and layer-integrated depolarization ratio of dust plumes and compared it with that of cloud, using CALIPSO LIDAR measurements. The histogram distribution of the integrated color ratio for dust and cloud was also examined. On the basis of the layer-integrated attenuated backscatter coefficient and layer-integrated depolarization ratio relation, a simple method of detecting dust plumes was developed. A case study of dust identification over the Taklimakan Desert was conducted and compared with the current CALIPSO products. The result shows that the proposed method can significantly improve the classification of cloud and dust plumes and can supplement the current space-borne LIDAR discrimination approach, especially over dust source regions. In addition, The zonal and meridional mean occurrence derived by the proposed method and the CALIPSO’s method were compared for Asian dust over East Asia region (30°N −45°N, 80°E −180°E) using the night measurements of CALIPSO from March to May, 2007. The comparison showed that the dust occurrence obtained from the proposed method is larger than that of CALIPSO’s method. The dust could be found up to around 6-8 km (Above Sea Level, ASL) near the Taklimakan desert region, and maximum occurrence is over 80%. The transport altitude remained at 3km-7km (ASL) as the dust was transported across the Pacific Ocean. Lidar; Aerosol detection; Remote sensing and sensors; Backscattering
Aumann, Hartmut H.; Ruzmaikin, Alexander; Behrangi, AliAumann, H. H., A. Ruzmaikin, A. Behrangi, 2012: On the Surface Temperature Sensitivity of the Reflected Shortwave, Outgoing Longwave, and Net Incident Radiation. J. Climate, 25(19), 6585-6593. doi: 10.1175/JCLI-D-11-00607.1. AbstractThe global-mean top-of-atmosphere incident solar radiation (ISR) minus the outgoing longwave radiation (OLR) and the reflected shortwave radiation (RSW) is the net incident radiation (NET). This study analyzes the global-mean NET sensitivity to a change in the global-mean surface temperature by applying the interannual anomaly correlation technique to 9 yr of Atmospheric Infrared Sounder (AIRS) global measurements of RSW and OLR under cloudy and clear conditions. The study finds the observed sensitivity of NET that includes the effects of clouds to be −1.5 ± 0.25 (1σ) W m−2 K−1 and the clear NET sensitivity to be −2.0 ± 0.2 (1σ) W m−2 K−1, consistent with previous work using Earth Radiation Budget Experiment and Clouds and the Earth’s Radiant Energy System data. The cloud effect, +0.5 ± 0.2 (1σ) W m−2 K−1, is a positive component of the NET sensitivity. The similarity of the NET sensitivities derived from forced and unforced models invites a comparison between the observed sensitivities and the effective sensitivities calculated for the Fourth Assessment Report models, although this requires some caution: The effective model sensitivities with clouds range from −0.88 to −1.64 W m−2 K−1, the clear NET sensitivity in the models ranges from −2.32 to −1.73 W m−2 K−1, and the cloud forcing sensitivities range from +0.14 to +1.18 W m−2 K−1. The effective NET and clear NET sensitivities derived from the models are statistically consistent with those derived from the AIRS data, considering the observational and model derivation uncertainties. satellite observations; Climate sensitivity
Barker, H. W.; Kato, S.; Wehr, T.Barker, H. W., S. Kato, T. Wehr, 2012: Computation of Solar Radiative Fluxes by 1D and 3D Methods Using Cloudy Atmospheres Inferred from A-train Satellite Data. Surveys in Geophysics, 33(3-4), 657-676. doi: 10.1007/s10712-011-9164-9. This study used realistic representations of cloudy atmospheres to assess errors in solar flux estimates associated with 1D radiative transfer models. A scene construction algorithm, developed for the EarthCARE mission, was applied to CloudSat, CALIPSO and MODIS satellite data thus producing 3D cloudy atmospheres measuring 61 km wide by 14,000 km long at 1 km grid-spacing. Broadband solar fluxes and radiances were then computed by a Monte Carlo photon transfer model run in both full 3D and 1D independent column approximation modes. Results were averaged into 1,303 (50 km)2 domains. For domains with total cloud fractions A c < 0.7 top-of-atmosphere (TOA) albedos tend to be largest for 3D transfer with differences increasing with solar zenith angle. Differences are largest for A c > 0.7 and characterized by small bias yet large random errors. Regardless of A c , differences between 3D and 1D transfer rarely exceed ±30 W m−2 for net TOA and surface fluxes and ±10 W m−2 for atmospheric absorption. Horizontal fluxes through domain sides depend on A c with ∼20% of cases exceeding ±30 W m−2; the largest values occur for A c > 0.7. Conversely, heating rate differences rarely exceed ±20%. As a cursory test of TOA radiative closure, fluxes produced by the 3D model were averaged up to (20 km)2 and compared to values measured by CERES. While relatively little attention was paid to optical properties of ice crystals and surfaces, and aerosols were neglected entirely, ∼30% of the differences between 3D model estimates and measurements fall within ±10 W m−2; this is the target agreement set for EarthCARE. This, coupled with the aforementioned comparison between 3D and 1D transfer, leads to the recommendation that EarthCARE employ a 3D transport model when attempting TOA radiative closure. cloud; Satellite; climate; CloudSat; radiation; EarthCARE; Geophysics/Geodesy; Astronomy, Observations and Techniques; Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations; Clouds and Earth’s Radiant Energy System; Earth Sciences, general; The Moderate Resolution Imaging Spectroradiometer
Behrangi, Ali; Kubar, Terry; Lambrigtsen, BjornBehrangi, A., T. Kubar, B. Lambrigtsen, 2012: Phenomenological Description of Tropical Clouds Using CloudSat Cloud Classification. Mon. Wea. Rev., 140(10), 3235-3249. doi: 10.1175/MWR-D-11-00247.1. AbstractTwo years of tropical oceanic cloud observations are analyzed using the operational CloudSat cloud classification product and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar. Relationships are examined between cloud types, sea surface temperature (SST), and location during the CloudSat early morning and afternoon overpasses. Based on CloudSat and combined lidar–radar products, the maximum and minimum cloud fractions occur at SSTs near 303 and 299 K, respectively, corresponding to deep convective/detrained cloud populations and the transition from shallow to deep convection. For SSTs below approximately 301 K, low clouds (stratiform and stratocumulus) are dominant (cloud fraction between 0.15 and 0.37) whereas high clouds are dominant for SSTs greater than about 301 K (cloud fraction between 0.18 and 0.28). Consistent with previous studies, most tropical low clouds are associated with lower SSTs, with a strong inverse linear relationship between low cloud frequency and SST. For all cloud types except nimbostratus, stratus, and stratocumulus, a sharp increase in frequency of occurrence is observed for SSTs between 299 and 300.5 K, deduced as the onset of deeper convection. Peak fractions of high, deep convective, altostratus, and altocumulus clouds occur at SSTs close to 303 K, while cumulus clouds, which have lower tops, show a smooth cloud fractional peak about 2° cooler. Deep convective and other high cloud types decrease sharply above SSTs of 303 K, in accordance with previous work suggesting a narrow window of tropical deep convection. Finally, significant cloud frequency differences exist between CloudSat early morning and afternoon overpasses, suggesting a diurnal cycle of some cloud types, particularly stratocumulus, high, and deep convective clouds. clouds; Remote sensing; tropics; satellite observations; classification; convective clouds; Cloud cover; Radars/Radar observations
Bender, Frida A.-M.; Ramanathan, V.; Tselioudis, GeorgeBender, F. A., V. Ramanathan, G. Tselioudis, 2012: Changes in extratropical storm track cloudiness 1983–2008: observational support for a poleward shift. Climate Dynamics, 38(9-10), 2037-2053. doi: 10.1007/s00382-011-1065-6. Climate model simulations suggest that the extratropical storm tracks will shift poleward as a consequence of global warming. In this study the northern and southern hemisphere storm tracks over the Pacific and Atlantic ocean basins are studied using observational data, primarily from the International Satellite Cloud Climatology Project, ISCCP. Potential shifts in the storm tracks are examined using the observed cloud structures as proxies for cyclone activity. Different data analysis methods are employed, with the objective to address difficulties and uncertainties in using ISCCP data for regional trend analysis. In particular, three data filtering techniques are explored; excluding specific problematic regions from the analysis, regressing out a spurious viewing geometry effect, and excluding specific cloud types from the analysis. These adjustments all, to varying degree, moderate the cloud trends in the original data but leave the qualitative aspects of those trends largely unaffected. Therefore, our analysis suggests that ISCCP data can be used to interpret regional trends in cloudiness, provided that data and instrumental artefacts are recognized and accounted for. The variation in magnitude between trends emerging from application of different data correction methods, allows us to estimate possible ranges for the observational changes. It is found that the storm tracks, here represented by the extent of the midlatitude-centered band of maximum cloud cover over the studied ocean basins, experience a poleward shift as well as a narrowing over the 25 year period covered by ISCCP. The observed magnitudes of these effects are larger than in current generation climate models (CMIP3). The magnitude of the shift is particularly large in the northern hemisphere Atlantic. This is also the one of the four regions in which imperfect data primarily prevents us from drawing firm conclusions. The shifted path and reduced extent of the storm track cloudiness is accompanied by a regional reduction in total cloud cover. This decrease in cloudiness can primarily be ascribed to low level clouds, whereas the upper level cloud fraction actually increases, according to ISCCP. Independent satellite observations of radiative fluxes at the top of the atmosphere are consistent with the changes in total cloud cover. The shift in cloudiness is also supported by a shift in central position of the mid-troposphere meridional temperature gradient. We do not find support for aerosols playing a significant role in the satellite observed changes in cloudiness. The observed changes in storm track cloudiness can be related to local cloud-induced changes in radiative forcing, using ERBE and CERES radiative fluxes. The shortwave and the longwave components are found to act together, leading to a positive (warming) net radiative effect in response to the cloud changes in the storm track regions, indicative of positive cloud feedback. Among the CMIP3 models that simulate poleward shifts in all four storm track areas, all but one show decreasing cloud amount on a global mean scale in response to increased CO2 forcing, further consistent with positive cloud feedback. Models with low equilibrium climate sensitivity to a lesser extent than higher-sensitivity models simulate a poleward shift of the storm tracks. Meteorology/Climatology; Oceanography; Geophysics/Geodesy
Bodas-Salcedo, A.; Williams, K. D.; Field, P. R.; Lock, A. P.Bodas-Salcedo, A., K. D. Williams, P. R. Field, A. P. Lock, 2012: The Surface Downwelling Solar Radiation Surplus over the Southern Ocean in the Met Office Model: The Role of Midlatitude Cyclone Clouds. J. Climate, 25(21), 7467-7486. doi: 10.1175/JCLI-D-11-00702.1. AbstractThe authors study the role of clouds in the persistent bias of surface downwelling shortwave radiation (SDSR) in the Southern Ocean in the atmosphere-only version of the Met Office model. The reduction of this bias in the atmosphere-only version is important to minimize sea surface temperature biases when the atmosphere model is coupled to a dynamic ocean. The authors use cloud properties and radiative fluxes estimates from the International Satellite Cloud Climatology Project (ISCCP) and apply a clustering technique to classify clouds into different regimes over the Southern Ocean. Then, they composite the cloud regimes around cyclone centers, which allows them to study the role of each cloud regime in a mean composite cyclone. Low- and midlevel clouds in the cold-air sector of the cyclones are responsible for most of the bias. Based on this analysis, the authors develop and test a new diagnosis of shear-dominated boundary layers. This change improves the simulation of the SDSR through a better simulation of the frequency of occurrence of the cloud regimes in the cyclone composite. Substantial biases in the radiative properties of the midtop and stratocumulus regimes are still present, which suggests the need to increase the optical depth of the low-level cloud with moderate optical depth and cloud with tops at midlevels. Radiation budgets; Shortwave radiation; Cloud radiative effects; Extratropical cyclones; Southern Ocean
Boening, Carmen; Willis, Josh K.; Landerer, Felix W.; Nerem, R. Steven; Fasullo, JohnBoening, C., J. K. Willis, F. W. Landerer, R. S. Nerem, J. Fasullo, 2012: The 2011 La Niña: So strong, the oceans fell. Geophysical Research Letters, 39(19), L19602. doi: 10.1029/2012GL053055. Global mean sea level (GMSL) dropped by 5 mm between the beginning of 2010 and mid 2011. This drop occurred despite the background rate of rise, 3 mm per year, which dominates most of the 18-year record observed by satellite altimeters. Using a combination of satellite andin situdata, we show that the decline in ocean mass, which explains the sea level drop, coincides with an equivalent increase in terrestrial water storage, primarily over Australia, northern South America, and Southeast Asia. This temporary shift of water from the ocean to land is closely related to the transition from El Niño conditions in 2009/10 to a strong 2010/11 La Niña, which affected precipitation patterns world-wide. 1640 Remote sensing; 1655 Water cycles; 1641 Sea level change; 4522 ENSO; 4556 Sea level: variations and mean; altimetry; ENSO; GRACE; la nina; sea level
Brient, F.; Bony, S.Brient, F., S. Bony, 2012: How may low-cloud radiative properties simulated in the current climate influence low-cloud feedbacks under global warming?. Geophysical Research Letters, 39(20), L20807. doi: 10.1029/2012GL053265. The influence of cloud modelling uncertainties on the projection of the tropical low-cloud response to global warming is explored by perturbing model parameters of the IPSL-CM5A climate model in a range of configurations (realistic general circulation model, aqua-planet, single-column model). While the positive sign and the mechanism of the low-cloud response to climate warming predicted by the model are robust, the amplitude of the response can vary considerably depending on the model tuning parameters. Moreover, the strength of the low-cloud response to climate change exhibits a strong correlation with the strength of the low-cloud radiative effects simulated in the current climate. We show that this correlation primarily results from a local positive feedback (referred to as the “beta feedback”) between boundary-layer cloud radiative cooling, relative humidity and low-cloud cover. Based on this correlation and observational constraints, it is suggested that the strength of the tropical low-cloud feedback predicted by the IPSL-CM5A model in climate projections might be overestimated by about fifty percent. 1610 Atmosphere; 0321 Cloud/radiation interaction; 3310 Clouds and cloud feedbacks; Climate sensitivity; low-cloud feedback; 1626 Global climate models; model hierarchy; model tuning; MSE budget; observational constraints
Cesana, G.; Chepfer, H.Cesana, G., H. Chepfer, 2012: How well do climate models simulate cloud vertical structure? A comparison between CALIPSO-GOCCP satellite observations and CMIP5 models. Geophysical Research Letters, 39(20), L20803. doi: 10.1029/2012GL053153. The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite provides robust and global direct measurements of the cloud vertical structure. The GCM-Oriented CALIPSO Cloud Product is used to evaluate the simulated clouds in five climate models using a lidar simulator. The total cloud cover is underestimated in all models (51% to 62% vs. 64% in observations) except in the Arctic. Continental cloud covers (at low, mid, high altitudes) are highly variable depending on the model. In the tropics, the top of deep convective clouds varies between 14 and 18 km in the models versus 16 km in the observations, and all models underestimate the low cloud amount (16% to 25%) compared to observations (29%). In the Arctic, the modeled low cloud amounts (37% to 57%) are slightly biased compared to observations (44%), and the models do not reproduce the observed seasonal variation. cloud; 3311 Clouds and aerosols; 3309 Climatology; 3337 Global climate models; CMIP5; CALIPSO-GOCCP; COSP; evaluation; model
Chen, Ling; Yan, Guangjian; Wang, Tianxing; Ren, Huazhong; Calbó, Josep; Zhao, Jing; McKenzie, RichardChen, L., G. Yan, T. Wang, H. Ren, J. Calbó, J. Zhao, R. McKenzie, 2012: Estimation of surface shortwave radiation components under all sky conditions: Modeling and sensitivity analysis. Remote Sensing of Environment, 123, 457-469. doi: 10.1016/j.rse.2012.04.006. Clouds are the most important modulator of the amount of solar energy absorbed by the earth–atmosphere system. Traditional one-dimensional (1D) plane-parallel atmospheric radiative transfer models which use the independent pixel approximation (IPA) can only consider two extreme conditions, i.e., either cloud-free or overcast cases. In this paper, two cloud fraction related factors (hemispherical effective cloud fraction and regional cloud fraction) are calculated and incorporated into MODTRAN 4 (one of the most popular radiative transfer packages) to simulate the surface shortwave radiation components and the top-of-atmosphere (TOA) radiance for all possible solar-cloud-viewing geometries. The accuracy of this modified solar radiative transfer model (named as MODTRAN-CF) is consistent with its prototype (MODTRAN 4) which has been widely used and validated in radiative transfer modeling. Some field measurements are used to validate the superiority of MODTRAN-CF. For further understanding and simplifying of this physical model, a global sensitivity analysis (GSA) method is employed to analyze the effect of model parameters on each surface shortwave radiation component. Five parameters including solar zenith angle, surface albedo, hemispherical effective cloud fraction, ground altitude and atmospheric visibility show non-negligible impacts on almost all surface shortwave fluxes, which indicates that these five parameters should be carefully considered in the future modeling of the surface shortwave radiation fluxes. Two cloud optical thickness related parameters (cloud extinction coefficient and cloud thickness) exhibit obvious importance only under cloudy illumination condition especially with optically thin clouds. These findings on the improved model will enhance our knowledge on how to accurately model the surface shortwave radiation fluxes under all sky conditions. Global sensitivity analysis; Hemispherical effective cloud fraction; MODTRAN-CF
Christopher, Sundar A.; Feng, Nan; Naeger, Aaron; Johnson, Ben; Marenco, FrancoChristopher, S. A., N. Feng, A. Naeger, B. Johnson, F. Marenco, 2012: Satellite remote sensing analysis of the 2010 Eyjafjallajökull volcanic ash cloud over the North Sea during 4–18 May 2010. Journal of Geophysical Research: Atmospheres, 117(D20), D00U20. doi: 10.1029/2011JD016850. Using the Moderate Resolution Imaging Spectroradiometer (MODIS), Spinning Enhanced Visible and Infrared Imager (SEVIRI), Clouds and the Earth's Radiant Energy System (CERES) instrument, and BaE146 aircraft data sets, we provide an overview of volcanic ash spatial distribution for six days (4–18 May 2010) and assess their properties and radiative impacts for 17 May primarily over the North Sea. We describe spectral signatures of volcanic ash, compare the MODIS-retrieved 550 nm aerosol optical thickness (AOT) and effective radii with the aircraft data, and then assess the change in radiative fluxes at the top of atmosphere using CERES. Our results indicate that the MODIS and SEVIRI thermal channels are adept at identifying volcanic ash near the source. However, the volcanic ash far from the volcanic source, especially over land, is contaminated by surface/atmospheric features. We assess the 17 May case in detail and show that MODIS AOTs (0.23–0.86) are higher than the aircraft values (0.07–0.54), probably due to different aerosol models used in the retrieval process. The MODIS effective radii values are between 0.4 and 0.9 μm with fine mode fraction values between 0.4 and 0.7. The aircraft-derived effective radii values are between 0.82 and 1.2 μm. The TOA shortwave radiative forcing for unit AOT of volcanic ash aerosols at the time of the satellite overpass is −77 ± 4.0 W m−2 and is larger than the longwave forcing per unit optical depth (11 ± 1.2 W m−2) by seven times indicating that ash could significantly impact radiative energy fluxes. aerosols; satellite remote sensing; 8485 Remote sensing of volcanoes; volcanic ash
Corbett, J. G.; Su, W.; Loeb, N. G.Corbett, J. G., W. Su, N. G. Loeb, 2012: Observed effects of sastrugi on CERES top-of-atmosphere clear-sky reflected shortwave flux over Antarctica. Journal of Geophysical Research: Atmospheres, 117(D18), D18104. doi: 10.1029/2012JD017529. Determining the clear-sky top-of-atmosphere (TOA) albedo over snow from space requires knowledge of the bi-directional reflectance distribution function (BRDF), which itself is strongly influenced by the surface roughness of the snow. Sastrugi, a common element of surface roughness on Antarctica, tend to have a preferred azimuth direction, meaning the BRDF depends on the location and time of sampling. In this study we demonstrate that a sastrugi signal is present in the Clouds and the Earth's Radiant Energy System (CERES) reflectance measurements and TOA albedo estimates, leading to a spurious variation in instantaneous albedo as a function of solar azimuth of up to 0.08. By using the difference in flux between oblique and nadir views, we estimate the biases in monthly- and annual-mean 24-hour energy weighted clear-sky reflected TOA fluxes caused by sastrugi over Antarctica. At the grid box level, statistically significant monthly-mean biases of between ±15 Wm−2are found. For the entire Antarctic continent, monthly-mean biases are between 0.2 ± 0.9 Wm−2 to −1.7 ± 1.1 Wm−2 where a negative bias indicates the reflected flux is being underestimated. On an annual basis, the Antarctic bias is between −0.9 ± 1.1 Wm−2 and −1.0 ± 1.1 Wm−2. For the global annual mean clear-sky TOA flux, the bias caused by the presence of sastrugi is insignificant, −0.01 ± 0.02 Wm−2. By examining the anisotropy and the wind direction we infer that the negative TOA flux biases are likely to caused by sastrugi perpendicular to the solar azimuth whereas the positive TOA flux biases are likely to be caused by sastrugi parallel to the solar azimuth. CERES; albedo; 3359 Radiative processes; 0758 Remote sensing; 0736 Snow; Antarctica; sastrugi
Cullather, Richard I.; Bosilovich, Michael G.Cullather, R. I., M. G. Bosilovich, 2012: The Energy Budget of the Polar Atmosphere in MERRA. J. Climate, 25(1), 5-24. doi: 10.1175/2011JCLI4138.1. AbstractComponents of the atmospheric energy budget from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) are evaluated in polar regions for the period 1979–2005 and compared with previous estimates, in situ observations, and contemporary reanalyses. Closure of the budget is reflected by the analysis increments term, which indicates an energy surplus of 11 W m−2 over the North Polar cap (70°–90°N) and 22 W m−2 over the South Polar cap (70°–90°S). Total atmospheric energy convergence from MERRA compares favorably with previous studies for northern high latitudes but exceeds the available previous estimate for the South Polar cap by 46%. Discrepancies with the Southern Hemisphere energy transport are largest in autumn and may be related to differences in topography with earlier reanalyses. For the Arctic, differences between MERRA and other sources in top of atmosphere (TOA) and surface radiative fluxes are largest in May. These differences are concurrent with the largest discrepancies between MERRA parameterized and observed surface albedo. For May, in situ observations of the upwelling shortwave flux in the Arctic are 80 W m−2 larger than MERRA, while the MERRA downwelling longwave flux is underestimated by 12 W m−2 throughout the year. Over grounded ice sheets, the annual mean net surface energy flux in MERRA is erroneously nonzero. Contemporary reanalyses from the Climate Forecast Center (CFSR) and the Interim Re-Analyses of the European Centre for Medium-Range Weather Forecasts (ERA-I) are found to have better surface parameterizations; however, these reanalyses also disagree with observed surface and TOA energy fluxes. Discrepancies among available reanalyses underscore the challenge of reproducing credible estimates of the atmospheric energy budget in polar regions. albedo; Radiative fluxes; Energy budget/balance; longwave radiation; Arctic; Ice sheets
de Boer, Gijs; Chapman, William; Kay, Jennifer E.; Medeiros, Brian; Shupe, Matthew D.; Vavrus, Steve; Walsh, Johnde Boer, G., W. Chapman, J. E. Kay, B. Medeiros, M. D. Shupe, S. Vavrus, J. Walsh, 2012: A Characterization of the Present-Day Arctic Atmosphere in CCSM4. J. Climate, 25(8), 2676-2695. doi: 10.1175/JCLI-D-11-00228.1. AbstractSimulation of key features of the Arctic atmosphere in the Community Climate System Model, version 4 (CCSM4) is evaluated against observational and reanalysis datasets for the present-day (1981–2005). Surface air temperature, sea level pressure, cloud cover and phase, precipitation and evaporation, the atmospheric energy budget, and lower-tropospheric stability are evaluated. Simulated surface air temperatures are found to be slightly too cold when compared with the 40-yr ECMWF Re-Analysis (ERA-40). Spatial patterns and temporal variability are well simulated. Evaluation of the sea level pressure demonstrates some large biases, most noticeably an under simulation of the Beaufort High during spring and autumn. Monthly Arctic-wide biases of up to 13 mb are reported. Cloud cover is underpredicted for all but summer months, and cloud phase is demonstrated to be different from observations. Despite low cloud cover, simulated all-sky liquid water paths are too high, while ice water path was generally too low. Precipitation is found to be excessive over much of the Arctic compared to ERA-40 and the Global Precipitation Climatology Project (GPCP) estimates. With some exceptions, evaporation is well captured by CCSM4, resulting in P − E estimates that are too high. CCSM4 energy budget terms show promising agreement with estimates from several sources. The most noticeable exception to this is the top of the atmosphere (TOA) fluxes that are found to be too low while surface fluxes are found to be too high during summer months. Finally, the lower troposphere is found to be too stable when compared to ERA-40 during all times of year but particularly during spring and summer months. clouds; Coupled models; Model evaluation/performance; climate models; Arctic; Seasonal variability
Domenech, Carlos; Lopez-Baeza, ErnestoDomenech, C., E. Lopez-Baeza, 2012: Analysis of broadband surface BRDFs derived from TOA SW CERES measurements for surfaces classified by the IGBP land cover. International Journal of Remote Sensing, 33(14), 4374-4392. doi: 10.1080/01431161.2011.648282. Most studies on the reflectance properties of the Earth's surface are addressed estimating the bidirectional reflectance distribution function (BRDF) of high spatial resolution and high spectral resolution satellite measurements. This article assesses the development of broadband (BB) BRDFs from radiances corresponding to large footprints classified according to the International Geosphere-Biosphere Programme (IGBP) land-cover classification. Top-of-atmosphere (TOA) shortwave (SW) CERES (Clouds and the Earth's Radiant Energy System) measurements are employed to invert the bidirectional reflectance factor (BRF) Rahman–Pinty–Verstraete (RPV) model for regions identified with the same IGBP type. The inversion of this non-linear parametric model is optimized to improve the computation efficiency and merged into a radiative transfer model to correct the surface radiances for the atmospheric effect. Analysis of the nature of the reflectance field simulated for several regions selected for every IGBP type determines whether the creation of general BRF models for surfaces defined by the same IGBP land cover is feasible. According to the results gathered in this study, the BB BRDFs for regions classified by the IGBP classification show values for the coefficient of variation (CV) between 3.5% and 44.1%. Consequently, the high differences achieved in the reflectance fields discourage the creation of BRDFs based on the IGBP land types.
Domenech, Carlos; Lopez-Baeza, Ernesto; Donovan, David P.; Wehr, TobiasDomenech, C., E. Lopez-Baeza, D. P. Donovan, T. Wehr, 2012: Radiative Flux Estimation from a Broadband Radiometer Using Synthetic Angular Models in the EarthCARE Mission Framework. Part II: Evaluation. J. Appl. Meteor. Climatol., 51(9), 1714-1731. doi: 10.1175/JAMC-D-11-0268.1. AbstractThe instantaneous top-of-atmosphere (TOA) radiance-to-flux conversion for the broadband radiometer (BBR) on board the Earth Clouds, Aerosols, and Radiation Explorer (EarthCARE) was assessed in Part I of this paper, by developing theoretical angular distribution models (ADMs) specifically designed for the instrument viewing configuration. This paper validates the BBR ADMs by comparing derived flux estimates with flux retrievals obtained from the Clouds and the Earth’s Radiant Energy System (CERES) Terra models. A CERES BBR-like database is employed in the assessment, which is an optimum dataset to validate the BBR algorithms and to determine the benefits of the multiangular conversion procedures in the BBR instrument. The validation of theoretical results with empirical data is essential to prepare the conversion algorithms prior to the launch of EarthCARE. This paper demonstrates that the application of a linear combination method is not recommended when outgoing radiances do not follow the response modeled in the radiative transfer calculations. An effective radiance averaged model outperforms all other developed models, in terms of the coefficient of variation of the root-mean-square error, in the validation study of the shortwave (SW) regime (clear sky 1.9%; cloudy 7.1%) while an effective radiance along-track model obtains the best comparisons for the longwave (LW) regime (clear sky 1.4%; cloudy 1.5%). The evaluation of the multiangular models with scenes with high anisotropy shows that multiview flux conversion algorithms can statistically improve CERES ADM results when CERES flux discrepancies of a target are higher than 4 W m−2 in the LW domain and SW clear-sky scenes and higher than 20 W m−2 in scenes with cloudy conditions. Radiative fluxes; radiative transfer; longwave radiation; Model evaluation/performance; Climatology; Shortwave radiation
Donohoe, Aaron; Battisti, David S.Donohoe, A., D. S. Battisti, 2012: What Determines Meridional Heat Transport in Climate Models?. J. Climate, 25(11), 3832-3850. doi: 10.1175/JCLI-D-11-00257.1. AbstractThe annual mean maximum meridional heat transport (MHTMAX) differs by approximately 20% among coupled climate models. The value of MHTMAX can be expressed as the difference between the equator-to-pole contrast in absorbed solar radiation (ASR*) and outgoing longwave radiation (OLR*). As an example, in the Northern Hemisphere observations, the extratropics (defined as the region with a net radiative deficit) receive an 8.2-PW deficit of net solar radiation (ASR*) relative to the global average that is balanced by a 2.4-PW deficit of outgoing longwave radiation (OLR*) and 5.8 PW of energy import via the atmospheric and oceanic circulation (MHTMAX). The intermodel spread of MHTMAX in the Coupled Model Intercomparison Project Phase 3 (CMIP3) simulations of the preindustrial climate is primarily (R2 = 0.72) due to differences in ASR* while model differences in OLR* are uncorrelated with the MHTMAX spread. The net solar radiation (ASR*) is partitioned into contributions from (i) the equator-to-pole contrast in incident radiation acting on the global average albedo and (ii) the equator-to-pole contrast of planetary albedo, which is further subdivided into components due to atmospheric and surface reflection. In the observations, 62% of ASR* is due to the meridional distribution of incident radiation, 33% is due to atmospheric reflection, and 5% is due to surface reflection. The intermodel spread in ASR* is due to model differences in the equator-to-pole gradient in planetary albedo, which are primarily a consequence of atmospheric reflection differences (92% of the spread), and is uncorrelated with differences in surface reflection. As a consequence, the spread in MHTMAX in climate models is primarily due to the spread in cloud reflection properties. albedo; Energy budget/balance; climate models; Cloud radiative effects; Energy transport; Ensembles
Douglass, D. H.; Knox, R. S.Douglass, D. H., R. S. Knox, 2012: Ocean heat content and Earthʼs radiation imbalance. II. Relation to climate shifts. Physics Letters A, 376(14), 1226-1229. doi: 10.1016/j.physleta.2012.02.027. In an earlier study of ocean heat content (OHC) we showed that Earthʼs empirically implied radiation imbalance has undergone abrupt changes. Other studies have identified additional such climate shifts since 1950. The shifts can be correlated with features in recently updated OHC data. The implied radiation imbalance may possibly alternate in sign at dates close to the climate shifts. The most recent shifts occurred during 2001–2002 and 2008–2009. The implied radiation imbalance between these dates, in the direction of ocean heat loss, was − 0.03 ± 0.06 W / m 2 , with a possible systematic error of [ − 0.00 , + 0.09 ] W / m 2 . Ocean heat content; Climate shifts; Radiation imbalance
Eckman, Richard S.; Stackhouse Jr., Paul W.Eckman, R. S., P. W. Stackhouse Jr., 2012: CEOS contributions to informing energy management and policy decision making using space-based Earth observations. Applied Energy, 90(1), 206-210. doi: 10.1016/j.apenergy.2011.03.001. Earth observations are playing an increasingly significant role in informing decision making in the energy sector. In renewable energy applications, space-based observations now routinely augment sparse ground-based observations used as input for renewable energy resource assessment applications. As one of the nine Group on Earth Observations (GEO) societal benefit areas, the enhancement of management and policy decision making in the energy sector is receiving attention in activities conducted by the Committee on Earth Observation Satellites (CEOS). CEOS has become the “space arm” for the implementation of the Global Earth Observation System of Systems (GEOSS) vision. It is directly supporting the space-based, near-term tasks articulated in the GEO three-year work plan. This paper describes a coordinated program of demonstration projects conducted by CEOS member agencies and partners to utilize Earth observations to enhance energy management end-user decision support systems. We discuss the importance of engagement with stakeholders and understanding their decision support needs in successfully increasing the uptake of Earth observation products for societal benefit. Several case studies are presented, demonstrating the importance of providing data sets in formats and units familiar and immediately usable by decision makers. These projects show the utility of Earth observations to enhance renewable energy resource assessment in the developing world, forecast space weather impacts on the power grid, and improve energy efficiency in the built environment. Energy management; Committee on Earth Observation Satellites; Decision support; Energy efficiency; Group on Earth Observations; Renewable energy resource assessment
Evans, S. M.; Marchand, R. T.; Ackerman, T. P.; Beagley, N.Evans, S. M., R. T. Marchand, T. P. Ackerman, N. Beagley, 2012: Identification and analysis of atmospheric states and associated cloud properties for Darwin, Australia. Journal of Geophysical Research: Atmospheres, 117(D6), D06204. doi: 10.1029/2011JD017010. An iterative automated classification technique that combines European Centre for Medium-Range Weather Forecasts analysis data and vertically pointing millimeter wavelength cloud radar observations is used to identify commonly occurring atmospheric patterns or states around Darwin, Australia. The technique defines the atmospheric states by large-scale, synoptic variables such that, once defined, these states will be suitable to composite climate model output. Radar observations of clouds are used to test the statistical significance of each state and prompt the automated refinement of the states until each state produces a statistically stable and unique hydrometeor occurrence profile. The technique identifies eight atmospheric states: two monsoon states, two transition season states, and four dry season states. The two monsoon states can be identified as the active monsoon and the break monsoon. Among the dry season states, periods of isolated and suppressed convection can be identified. We use these states as the basis for compositing hydrometeor occurrence, precipitation rate, outgoing longwave radiation, and Madden-Julian Oscillation phase to further understand the meteorology of each state. 3374 Tropical meteorology; 3310 Clouds and cloud feedbacks; atmospheric state; Australia; classification; cloud properties; clustering; Darwin; tropical meteorology
Fasullo, John T.; Trenberth, Kevin E.Fasullo, J. T., K. E. Trenberth, 2012: A Less Cloudy Future: The Role of Subtropical Subsidence in Climate Sensitivity. Science, 338(6108), 792-794. doi: 10.1126/science.1227465. An observable constraint on climate sensitivity, based on variations in mid-tropospheric relative humidity (RH) and their impact on clouds, is proposed. We show that the tropics and subtropics are linked by teleconnections that induce seasonal RH variations that relate strongly to albedo (via clouds), and that this covariability is mimicked in a warming climate. A present-day analog for future trends is thus identified whereby the intensity of subtropical dry zones in models associated with the boreal monsoon is strongly linked to projected cloud trends, reflected solar radiation, and model sensitivity. Many models, particularly those with low climate sensitivity, fail to adequately resolve these teleconnections and hence are identifiably biased. Improving model fidelity in matching observed variations provides a viable path forward for better predicting future climate.
Feng, Zhe; Dong, Xiquan; Xi, Baike; McFarlane, Sally A.; Kennedy, Aaron; Lin, Bing; Minnis, PatrickFeng, Z., X. Dong, B. Xi, S. A. McFarlane, A. Kennedy, B. Lin, P. Minnis, 2012: Life cycle of midlatitude deep convective systems in a Lagrangian framework. Journal of Geophysical Research: Atmospheres, 117(D23), D23201. doi: 10.1029/2012JD018362. Deep convective systems (DCSs) consist of intense convective cores (CC), large stratiform rain (SR) regions, and extensive nonprecipitating anvil clouds (AC). This study focuses on the evolution of these three components and the factors that affect system lifetime and AC production. An automated satellite tracking method is used in conjunction with a recently developed multisensor hybrid classification to analyze the evolution of DCS structure in a Lagrangian framework over the central United States. Composite analysis from 4221 tracked DCSs during two warm seasons (May–August, 2010–2011) shows that maximum system size correlates with lifetime, and longer-lived DCSs have more extensive SR and AC. For short to medium systems (lifetimes 120 km) they are 24% and 20% higher, respectively, than those with small AC (radius = 20 km). cloud; convection; 3310 Clouds and cloud feedbacks; 3314 Convective processes; anvil; Lagrangian; life cycle; tracking
Ferguson, Craig R.; Wood, Eric F.; Vinukollu, Raghuveer K.Ferguson, C. R., E. F. Wood, R. K. Vinukollu, 2012: A Global Intercomparison of Modeled and Observed Land–Atmosphere Coupling*. J. Hydrometeor., 13(3), 749-784. doi: 10.1175/JHM-D-11-0119.1.
Fridlind, A. M.; Ackerman, A. S.; Chaboureau, J.-P.; Fan, J.; Grabowski, W. W.; Hill, A. A.; Jones, T. R.; Khaiyer, M. M.; Liu, G.; Minnis, P.; Morrison, H.; Nguyen, L.; Park, S.; Petch, J. C.; Pinty, J.-P.; Schumacher, C.; Shipway, B. J.; Varble, A. C.; Wu, X.; Xie, S.; Zhang, M.Fridlind, A. M., A. S. Ackerman, J. Chaboureau, J. Fan, W. W. Grabowski, A. A. Hill, T. R. Jones, M. M. Khaiyer, G. Liu, P. Minnis, H. Morrison, L. Nguyen, S. Park, J. C. Petch, J. Pinty, C. Schumacher, B. J. Shipway, A. C. Varble, X. Wu, S. Xie, M. Zhang, 2012: A comparison of TWP-ICE observational data with cloud-resolving model results. Journal of Geophysical Research: Atmospheres, 117(D5). doi: 10.1029/2011JD016595. Observations made during the TWP-ICE campaign are used to drive and evaluate thirteen cloud-resolving model simulations with periodic lateral boundary conditions. The simulations employ 2D and 3D dynamics, one- and two-moment microphysics, several variations on large-scale forcing, and the use of observationally derived aerosol properties to prognose droplet numbers. When domain means are averaged over a 6-day active monsoon period, all simulations reproduce observed surface precipitation rate but not its structural distribution. Simulated fractional areas covered by convective and stratiform rain are uncorrelated with one another, and are both variably overpredicted by up to a factor of ∼2. Stratiform area fractions are strongly anticorrelated with outgoing longwave radiation (OLR) but are negligibly correlated with ice water path (IWP), indicating that ice spatial distribution controls OLR more than mean IWP. Overpredictions of OLR tend to be accompanied by underpredictions of reflected shortwave radiation (RSR). When there are two simulations differing only in microphysics scheme or large-scale forcing, the one with smaller stratiform area tends to exhibit greater OLR and lesser RSR by similar amounts. After ∼10 days, simulations reach a suppressed monsoon period with a wide range of mean precipitable water vapor, attributable in part to varying overprediction of cloud-modulated radiative flux divergence compared with observationally derived values. Differences across the simulation ensemble arise from multiple sources, including dynamics, microphysics, and radiation treatments. Close agreement of spatial and temporal averages with observations may not be expected, but the wide spreads of predicted stratiform fraction and anticorrelated OLR indicate a need for more rigorous observation-based evaluation of the underlying micro- and macrophysical properties of convective and stratiform structures. convection; modeling; tropics
Fu, Peijian; Zhong, Shiyuan; Huang, Jianping; Song, GuangningFu, P., S. Zhong, J. Huang, G. Song, 2012: An observational study of aerosol and turbulence properties during dust storms in northwest China. Journal of Geophysical Research: Atmospheres, 117(D9), D09202. doi: 10.1029/2011JD016696. Since late 2003, measurements of aerosol properties and meteorology have been made at three sites, Minqin, Jiuquan and Dunhuang, in the border areas of the Gobi and Taklimakan Deserts in the northwest of China as part of an observational program for Asian Dust Storms (ADS). The aerosol observations include mass concentration and optical depth, and the meteorological observations include both mean and turbulent quantities. The data from a three-year period (2004–2007) have been analyzed to characterize aerosol and meteorological conditions during dust storms. The results show that during ADS the aerosol mass concentration (PM10) can reach above 7∼8 mg m−3, 10∼100 times of that on clear days, and the scatter coefficient of fine particles (PM2.5) is 2000∼2500 10−6 m−1, 20∼25 times of the clear day values. There is a dramatic reduction in the visibility during dust storms with average visibility about 2 km, which is only 1/20∼1/30 of that on clear days. The aerodynamic roughness is 0.018 and 0.046 m for the Taklimakan and Gobi Deserts respectively, and the friction velocity is about 0.71 and 0.56 m s−1 during ADS periods, doubling the value found on quiescent days. Turbulence in the lower atmosphere is more intense during ADS period due mainly to increased vertical wind shear associated with strong winds. The large-scale circulation patterns show that during the ADS conditions the Gobi Desert is typically in the path of cold air from high latitudes moving toward the south or southeast and the data suggest that there is a declining trend for dust storms during the past 5 decades. 1610 Atmosphere; 0305 Aerosols and particles; dust aerosol; 1630 Impacts of global change; air quality; dust storms; turbulent characteristics; wind blowing index
Garnier, Anne; Pelon, Jacques; Dubuisson, Philippe; Faivre, Michaël; Chomette, Olivier; Pascal, Nicolas; Kratz, David P.Garnier, A., J. Pelon, P. Dubuisson, M. Faivre, O. Chomette, N. Pascal, D. P. Kratz, 2012: Retrieval of Cloud Properties Using CALIPSO Imaging Infrared Radiometer. Part I: Effective Emissivity and Optical Depth. J. Appl. Meteor. Climatol., 51(7), 1407-1425. doi: 10.1175/JAMC-D-11-0220.1. AbstractThe paper describes the operational analysis of the Imaging Infrared Radiometer (IIR) data, which have been collected in the framework of the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission for the purpose of retrieving high-altitude (above 7 km) cloud effective emissivity and optical depth that can be used in synergy with the vertically resolved Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) collocated observations. After an IIR scene classification is built under the CALIOP track, the analysis is applied to features detected by CALIOP when found alone in the atmospheric column or when CALIOP identifies an opaque layer underneath. The fast-calculation radiative transfer (FASRAD) model fed by ancillary meteorological and surface data is used to compute the different components involved in the effective emissivity retrievals under the CALIOP track. The track analysis is extended to the IIR swath using homogeneity criteria that are based on radiative equivalence. The effective optical depth at 12.05 μm is shown to be a good proxy for about one-half of the cloud optical depth, allowing direct comparisons with other databases in the visible spectrum. A step-by-step quantitative sensitivity and performance analysis is provided. The method is validated through comparisons of collocated IIR and CALIOP optical depths for elevated single-layered semitransparent cirrus clouds, showing excellent agreement (within 20%) for values ranging from 1 down to 0.05. Uncertainties have been determined from the identified error sources. The optical depth distribution of semitransparent clouds is found to have a nearly exponential shape with a mean value of about 0.5–0.6. infrared radiation; cirrus clouds; satellite observations; Optical properties; Algorithms; Lidars/Lidar observations
Gettelman, A.; Liu, X.; Barahona, D.; Lohmann, U.; Chen, C.Gettelman, A., X. Liu, D. Barahona, U. Lohmann, C. Chen, 2012: Climate impacts of ice nucleation. Journal of Geophysical Research: Atmospheres, 117(D20), D20201. doi: 10.1029/2012JD017950. Several different ice nucleation parameterizations in two different General Circulation Models (GCMs) are used to understand the effects of ice nucleation on the mean climate state, and the Aerosol Indirect Effects (AIE) of cirrus clouds on climate. Simulations have a range of ice microphysical states that are consistent with the spread of observations, but many simulations have higher present-day ice crystal number concentrations than in-situ observations. These different states result from different parameterizations of ice cloud nucleation processes, and feature different balances of homogeneous and heterogeneous nucleation. Black carbon aerosols have a small (−0.06 Wm−2) and not statistically significant AIE when included as ice nuclei, for nucleation efficiencies within the range of laboratory measurements. Indirect effects of anthropogenic aerosols on cirrus clouds occur as a consequence of increasing anthropogenic sulfur emissions with different mechanisms important in different models. In one model this is due to increases in homogeneous nucleation fraction, and in the other due to increases in heterogeneous nucleation with coated dust. The magnitude of the effect is the same however. The resulting ice AIE does not seem strongly dependent on the balance between homogeneous and heterogeneous ice nucleation. Regional effects can reach several Wm−2. Indirect effects are slightly larger for those states with less homogeneous nucleation and lower ice number concentration in the base state. The total ice AIE is estimated at 0.27 ± 0.10 Wm−2 (1σ uncertainty). This represents a 20% offset of the simulated total shortwave AIE for ice and liquid clouds of −1.6 Wm−2. 3311 Clouds and aerosols; 3305 Climate change and variability; 3337 Global climate models; climate; cirrus; nucleation
Harrop, Bryce E.; Hartmann, Dennis L.Harrop, B. E., D. L. Hartmann, 2012: Testing the Role of Radiation in Determining Tropical Cloud-Top Temperature. J. Climate, 25(17), 5731-5747. doi: 10.1175/JCLI-D-11-00445.1. AbstractA cloud-resolving model is used to test the hypothesis that radiative cooling by water vapor emission is the primary control on the temperature of tropical anvil clouds. The temperature of ice clouds in the simulation can be increased or decreased by changing only the emissivity of water vapor in the upper troposphere. The effect of the model’s fixed ozone profile on stability creates a pressure-dependent inhibition of convection, leading to a small warming in cloud-top temperature as SST is increased. Increasing stratospheric water vapor also warms the cloud-top temperature slightly. Changing the latent heat of fusion reduces the cloud fraction at high altitudes, but does not significantly change temperature at which cloud fraction peaks in the upper troposphere. The relationship between radiatively driven horizontal mass convergence and cloud fraction that causes cloud temperature to be insensitive to surface temperature is preserved when a large model domain is used so that convection aggregates in a small part of the model domain. clouds; convective clouds; water vapor; cloud forcing
Hong, Gang; Minnis, Patrick; Doelling, David; Ayers, J. Kirk; Sun-Mack, SzedungHong, G., P. Minnis, D. Doelling, J. K. Ayers, S. Sun-Mack, 2012: Estimating effective particle size of tropical deep convective clouds with a look-up table method using satellite measurements of brightness temperature differences. Journal of Geophysical Research: Atmospheres, 117(D6), D06207. doi: 10.1029/2011JD016652. A method for estimating effective ice particle radius Re at the tops of tropical deep convective clouds (DCC) is developed on the basis of precomputed look-up tables (LUTs) of brightness temperature differences (BTDs) between the 3.7 and 11.0 μm bands. A combination of discrete ordinates radiative transfer and correlated k distribution programs, which account for the multiple scattering and monochromatic molecular absorption in the atmosphere, is utilized to compute the LUTs as functions of solar zenith angle, satellite zenith angle, relative azimuth angle, Re, cloud top temperature (CTT), and cloud visible optical thickness τ. The LUT-estimated DCC Re agrees well with the cloud retrievals of the Moderate Resolution Imaging Spectroradiometer (MODIS) for the NASA Clouds and Earth's Radiant Energy System with a correlation coefficient of 0.988 and differences of less than 10%. The LUTs are applied to 1 year of measurements taken from MODIS aboard Aqua in 2007 to estimate DCC Re and are compared to a similar quantity from CloudSat over the region bounded by 140°E, 180°E, 0°N, and 20°N in the Western Pacific Warm Pool. The estimated DCC Re values are mainly concentrated in the range of 25–45 μm and decrease with CTT. Matching the LUT-estimated Re with ice cloud Re retrieved by CloudSat, it is found that the ice cloud τ values from DCC top to the vertical location where LUT-estimated Re is located at the CloudSat-retrieved Re profile are mostly less than 2.5 with a mean value of about 1.3. Changes in the DCC τ can result in differences of less than 10% for Re estimated from LUTs. The LUTs of 0.65 μm bidirectional reflectance distribution function (BRDF) are built as functions of viewing geometry and column amount of ozone above upper troposphere. The 0.65 μm BRDF can eliminate some noncore portions of the DCCs detected using only 11 μm brightness temperature thresholds, which result in a mean difference of only 0.6 μm for DCC Re estimated from BTD LUTs. 0320 Cloud physics and chemistry; 3371 Tropical convection; brightness temperature difference; deep convection; effective particle size; look-up table
Huang, Xianglei; Loeb, Norman G.; Chuang, HuiwenHuang, X., N. G. Loeb, H. Chuang, 2012: Assessing Stability of CERES-FM3 Daytime Longwave Unfiltered Radiance with AIRS Radiances. J. Atmos. Oceanic Technol., 29(3), 375-381. doi: 10.1175/JTECH-D-11-00066.1.
Ichikawa, Hiroki; Masunaga, Hirohiko; Tsushima, Yoko; Kanzawa, HiroshiIchikawa, H., H. Masunaga, Y. Tsushima, H. Kanzawa, 2012: Reproducibility by Climate Models of Cloud Radiative Forcing Associated with Tropical Convection. J. Climate, 25(4), 1247-1262. doi: 10.1175/JCLI-D-11-00114.1. AbstractIn this study, cloud radiative forcing (CRF) associated with convective activity over tropical oceans is analyzed for monthly mean data from twentieth-century simulations of 18 climate models participating in phase 3 of the Coupled Model Intercomparison Project (CMIP3) in comparison with observational and reanalysis data. The analysis is focused on the warm oceanic regions with sea surface temperatures (SSTs) above 27°C to exclude the regions with cold SSTs typically covered by low stratus clouds. CRF is evaluated for different regimes sorted by pressure-coordinated vertical motion at 500 hPa (ω500) as an index of large-scale circulation. The warm oceanic regions cover the regime of vertical motion ranging from strong ascent to weak descent. The most notable feature found in this study is a systematic underestimation by most models of the ratio of longwave cloud radiative forcing (LWCRF) to shortwave cloud radiative forcing (SWCRF) over the weak vertical motion regime defined as −10 < ω500 < 20 hPa day−1. The underestimation of the ratio corresponds to the underestimation of LWCRF and the overestimation of SWCRF. Clouds in models seem to be lower in the amount of high clouds but more reflective than those in the observations in this regime.In the weak vertical motion regime, the lower free troposphere is dry. In the large-scale environment condition, the reproducibility of LWCRF is high in models adopting the scheme where the relative humidity–based suppression for deep convection occurrence is implemented. Models adopting the Zhang and McFarlane scheme show good performance without such a suppression mechanism. clouds; convection; tropics; climate models; cloud forcing; Model comparison
Imaoka, Keiji; Nakamura, KenjiImaoka, K., K. Nakamura, 2012: Statistical Analysis of the Life Cycle of Isolated Tropical Cold Cloud Systems Using MTSAT-1R and TRMM Data. Mon. Wea. Rev., 140(11), 3552-3572. doi: 10.1175/MWR-D-11-00364.1. AbstractObservations from the Multifunctional Transport Satellite-1R (MTSAT-1R) and the Tropical Rainfall Measuring Mission (TRMM) satellites are analyzed to show the universal view of the cloud life cycle, including the changes of vertical structure of rainfall, over the Maritime Continent and a part of the tropical western Pacific, with a focus on the isolated cold cloud systems. Temporally connected cold cloud systems are identified by a cloud tracking procedure and compared with the collocated observations from TRMM. Clear life cycle changes of the average reflectivity profile from the Precipitation Radar (PR), such as those of radar echo height and the brightband feature, are statistically confirmed over the ocean area. Systems with a lifetime of 5 h show a behavior similar to those of typical mesoscale convective systems, with an extension of anvil clouds up to an area of about 6000 km2 as a delayed response to the earlier intense convection, indicated by the peaks of rain rates and radar echo height at the early stages. In contrast, the 2-h lifetime systems decay rapidly and do not produce an extension of cloud and precipitation. The results also show that the difference between rainfall estimates of the TRMM Microwave Imager (TMI) and PR depends on the phase in the lifetime. TMI tends to provide higher conditional average rain rates at the mature phase than that of PR. clouds; satellite observations; Precipitation; Cloud tracking/cloud motion winds
Jiménez-Muñoz, Juan C.; Sobrino, José A.; Mattar, CristianJiménez-Muñoz, J. C., J. Sobrino, . A., C. Mattar, 2012: Recent trends in solar exergy and net radiation at global scale. Ecological Modelling, 228, 59-65. doi: 10.1016/j.ecolmodel.2011.12.027. The availability during the last decades of remotely sensed images and global climatic data allow us to analyse the “Earth system” as a whole in order to develop concepts for global environmental management. This system can be considered a complex, dissipative, dynamic entity, far from thermodynamic equilibrium (Schellnhuber, 1999). Energy balance has been considered for many decades to understand the functioning of ecosystems, the biosphere or the Earth planet as a whole, but it is also possible to study our planet from a thermodynamic point of view. In this letter we analyse recent trends in solar exergy and net radiation at global scale during the period 1980–2010, distinguishing between land and ocean and between different land cover classes. Variations on the solar constant were also analysed. Results show a significant global decrease in solar exergy, in accordance also with a decrease in the solar constant. Net radiation also shows a global decrease during the study period, although in this case the results were not statistically significant. reanalysis; Thermodynamics; Net radiation; Solar constant; Solar exergy
Jin, Zhonghai; Lukachin, Constantin; Gopalan, Arun; Sun, WenboJin, Z., C. Lukachin, A. Gopalan, W. Sun, 2012: Correlation between SCIAMACHY, MODIS, and CERES reflectance measurements: Implications for CLARREO. Journal of Geophysical Research: Atmospheres, 117(D5), D05114. doi: 10.1029/2011JD017051. We have analyzed the correlation between measurements by three different satellite sensors (SCIAMACHY, MODIS, and CERES) on two independent space platforms (Envisat and Terra). Though the instantaneous measurements from the two satellites are not collocated due to orbit offset, the monthly mean broadband and narrowband reflectances and their anomalies from the three instruments are highly correlated when averaged over large latitude regions. The mean reflectance from MODIS in each of those large domains is nearly the same as that derived from SCIAMACHY spectrum convolved with the filter function of the corresponding MODIS channel, with all correlation coefficients higher than 0.93. The interannual variability of monthly mean reflectance is also correlated with the variations of mean cloud and surface properties in large climate zones. The reflectance variation is correlated with the cloud fraction in low and middle latitude regions with correlation coefficients higher than 0.76 and with the snow and sea ice changes in the polar regions with correlation coefficients higher than 0.6. These correlations indicate that the nadir sampling strategy as proposed for CLARREO is sufficient for climate benchmarking of the reflected solar spectrum and provide the physical foundation for climate fingerprinting. However, the results also show the relatively large differences in trends in reflectance due to different instrument degradations and inconsistent calibrations which will affect the attribution of radiative signals of long-term climate change. 1640 Remote sensing; atmospheric radiation; spectral reflectance; 3359 Radiative processes; 3305 Climate change and variability; 1616 Climate variability; Interannual variability; correlation; climate benchmark; climate fingerprinting
Johnston, M. S.; Eriksson, P.; Eliasson, S.; Jones, C. G.; Forbes, R. M.; Murtagh, D. P.Johnston, M. S., P. Eriksson, S. Eliasson, C. G. Jones, R. M. Forbes, D. P. Murtagh, 2012: The representation of tropical upper tropospheric water in EC Earth V2. Climate Dynamics, 39(11), 2713-2731. doi: 10.1007/s00382-012-1511-0. Tropical upper tropospheric humidity, clouds, and ice water content, as well as outgoing longwave radiation (OLR), are evaluated in the climate model EC Earth with the aid of satellite retrievals. The Atmospheric Infrared Sounder and Microwave Limb Sounder together provide good coverage of relative humidity. EC Earth’s relative humidity is in fair agreement with these observations. CloudSat and CALIPSO data are combined to provide cloud fractions estimates throughout the altitude region considered (500–100 hPa). EC Earth is found to overestimate the degree of cloud cover above 200 hPa and underestimate it below. Precipitating and non-precipitating EC Earth ice definitions are combined to form a complete ice water content. EC Earth’s ice water content is below the uncertainty range of CloudSat above 250 hPa, but can be twice as high as CloudSat’s estimate in the melting layer. CERES data show that the model underestimates the impact of clouds on OLR, on average with about 9 W m−2. Regionally, EC Earth’s outgoing longwave radiation can be ∼20 W m−2 higher than the observation. A comparison to ERA-Interim provides further perspectives on the model’s performance. Limitations of the satellite observations are emphasised and their uncertainties are, throughout, considered in the analysis. Evaluating multiple model variables in parallel is a more ambitious approach than is customary. clouds; Meteorology/Climatology; tropics; Satellite; climate; humidity; Oceanography; Geophysics/Geodesy; IWC
Kandel, RobertKandel, R., 2012: Understanding and Measuring Earth’s Energy Budget: From Fourier, Humboldt, and Tyndall to CERES and Beyond. Surveys in Geophysics, 33(3-4), 337-350. doi: 10.1007/s10712-011-9162-y. This historical perspective on the determination of Earth’s energy fluxes, beginning with the classical description of climate, outlines the establishment of the basic physics of the Earth climate system in the nineteenth century. After recalling the early twentieth century ground-based attempts to determine the Earth’s energy budget, I review the growing contributions of observations from space to quantifying these exchanges. In particular, space observations have shown that variations of solar luminosity have been extremely small (of order 0.1%) over past decades and probably past centuries and that they play practically no role in present-day climate variations or variations that may be expected in coming decades. Overall geographical structure, diurnal and seasonal cycles, and some of the interannual and interdecadal variations of Earth’s energy exchanges with the Sun and space are now quite well determined, but much remains to be done regarding, on the one hand, fluxes at the surface and, on the other hand, variations of clouds. Improvements are essential if scientific assessment of anthropogenic climate change risk is to keep up with the changes themselves. satellite observations; Geophysics/Geodesy; Astronomy, Observations and Techniques; Earth Sciences, general; Earth’s energy flows; Historical background
Kato, Seiji; Loeb, Norman G.; Rutan, David A.; Rose, Fred G.; Sun-Mack, Sunny; Miller, Walter F.; Chen, YanKato, S., N. G. Loeb, D. A. Rutan, F. G. Rose, S. Sun-Mack, W. F. Miller, Y. Chen, 2012: Uncertainty Estimate of Surface Irradiances Computed with MODIS-, CALIPSO-, and CloudSat-Derived Cloud and Aerosol Properties. Surveys in Geophysics, 33(3-4), 395-412. doi: 10.1007/s10712-012-9179-x. Differences of modeled surface upward and downward longwave and shortwave irradiances are calculated using modeled irradiance computed with active sensor-derived and passive sensor-derived cloud and aerosol properties. The irradiance differences are calculated for various temporal and spatial scales, monthly gridded, monthly zonal, monthly global, and annual global. Using the irradiance differences, the uncertainty of surface irradiances is estimated. The uncertainty (1σ) of the annual global surface downward longwave and shortwave is, respectively, 7 W m−2 (out of 345 W m−2) and 4 W m−2 (out of 192 W m−2), after known bias errors are removed. Similarly, the uncertainty of the annual global surface upward longwave and shortwave is, respectively, 3 W m−2 (out of 398 W m−2) and 3 W m−2 (out of 23 W m−2). The uncertainty is for modeled irradiances computed using cloud properties derived from imagers on a sun-synchronous orbit that covers the globe every day (e.g., moderate-resolution imaging spectrometer) or modeled irradiances computed for nadir view only active sensors on a sun-synchronous orbit such as Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation and CloudSat. If we assume that longwave and shortwave uncertainties are independent of each other, but up- and downward components are correlated with each other, the uncertainty in global annual mean net surface irradiance is 12 W m−2. One-sigma uncertainty bounds of the satellite-based net surface irradiance are 106 W m−2 and 130 W m−2. Geophysics/Geodesy; Astronomy, Observations and Techniques; Earth Sciences, general; Surface net irradiance; Surface radiative energy budget
Kay, J. E.; Hillman, B. R.; Klein, S. A.; Zhang, Y.; Medeiros, B.; Pincus, R.; Gettelman, A.; Eaton, B.; Boyle, J.; Marchand, R.; Ackerman, T. P.Kay, J. E., B. R. Hillman, S. A. Klein, Y. Zhang, B. Medeiros, R. Pincus, A. Gettelman, B. Eaton, J. Boyle, R. Marchand, T. P. Ackerman, 2012: Exposing Global Cloud Biases in the Community Atmosphere Model (CAM) Using Satellite Observations and Their Corresponding Instrument Simulators. J. Climate, 25(15), 5190-5207. doi: 10.1175/JCLI-D-11-00469.1. AbstractSatellite observations and their corresponding instrument simulators are used to document global cloud biases in the Community Atmosphere Model (CAM) versions 4 and 5. The model–observation comparisons show that, despite having nearly identical cloud radiative forcing, CAM5 has a much more realistic representation of cloud properties than CAM4. In particular, CAM5 exhibits substantial improvement in three long-standing climate model cloud biases: 1) the underestimation of total cloud, 2) the overestimation of optically thick cloud, and 3) the underestimation of midlevel cloud. While the increased total cloud and decreased optically thick cloud in CAM5 result from improved physical process representation, the increased midlevel cloud in CAM5 results from the addition of radiatively active snow. Despite these improvements, both CAM versions have cloud deficiencies. Of particular concern, both models exhibit large but differing biases in the subtropical marine boundary layer cloud regimes that are known to explain intermodel differences in cloud feedbacks and climate sensitivity. More generally, this study demonstrates that simulator-facilitated evaluation of cloud properties, such as amount by vertical level and optical depth, can robustly expose large and at times radiatively compensating climate model cloud biases. clouds; Model evaluation/performance; climate models; Cloud radiative effects
Kay, Jennifer E.; Holland, Marika M.; Bitz, Cecilia M.; Blanchard-Wrigglesworth, Edward; Gettelman, Andrew; Conley, Andrew; Bailey, DavidKay, J. E., M. M. Holland, C. M. Bitz, E. Blanchard-Wrigglesworth, A. Gettelman, A. Conley, D. Bailey, 2012: The Influence of Local Feedbacks and Northward Heat Transport on the Equilibrium Arctic Climate Response to Increased Greenhouse Gas Forcing. J. Climate, 25(16), 5433-5450. doi: 10.1175/JCLI-D-11-00622.1. AbstractThis study uses coupled climate model experiments to identify the influence of atmospheric physics [Community Atmosphere Model, versions 4 and 5 (CAM4; CAM5)] and ocean model complexity (slab ocean, full-depth ocean) on the equilibrium Arctic climate response to an instantaneous CO2 doubling. In slab ocean model (SOM) experiments using CAM4 and CAM5, local radiative feedbacks, not atmospheric heat flux convergence, are the dominant control on the Arctic surface response to increased greenhouse gas forcing. Equilibrium Arctic surface air temperature warming and amplification are greater in the CAM5 SOM experiment than in the equivalent CAM4 SOM experiment. Larger 2 × CO2 radiative forcing, more positive Arctic surface albedo feedbacks, and less negative Arctic shortwave cloud feedbacks all contribute to greater Arctic surface warming and sea ice loss in CAM5 as compared to CAM4. When CAM4 is coupled to an active full-depth ocean model, Arctic Ocean horizontal heat flux convergence increases in response to the instantaneous CO2 doubling. Though this increased ocean northward heat transport slightly enhances Arctic sea ice extent loss, the representation of atmospheric processes (CAM4 versus CAM5) has a larger influence on the equilibrium Arctic surface climate response than the degree of ocean coupling (slab ocean versus full-depth ocean). These findings underscore that local feedbacks can be more important than northward heat transport for explaining the equilibrium Arctic surface climate response and response differences in coupled climate models. That said, the processes explaining the equilibrium climate response differences here may be different than the processes explaining intermodel spread in transient climate projections. clouds; climate models; greenhouse gases; Arctic
Kim, Dohyeong; Ramanathan, V.Kim, D., V. Ramanathan, 2012: Improved estimates and understanding of global albedo and atmospheric solar absorption. Geophysical Research Letters, 39(24), L24704. doi: 10.1029/2012GL053757. This study integrates available surface-based and satellite observations of solar radiation at the surface and the top of the atmosphere (TOA) with a comprehensive set of satellite observations of atmospheric and surface optical properties and a Monte Carlo Aerosol-Cloud-Radiation (MACR) model to estimate the three fundamental components of the planetary solar radiation budget: Albedo at the TOA; atmospheric solar absorption; and surface solar absorption. The MACR incorporates most if not all of our current understanding of the theory of solar radiation physics including modern spectroscopic water vapor data, minor trace gases, absorbing aerosols including its effects inside cloud drops, 3-D cloud scattering effects. The model is subject to a severe test by comparing the simulated solar radiation budget with data from 34 globally distributed state-of-the art BSRN (Baseline Surface Radiation Network) land stations which began data collection in the mid 1990s. The TOA over these sites were obtained from the CERES (Cloud and Earth's Radiant Energy System) satellites. The simulated radiation budget was within 2 Wm−2for all three components over the BSRN sites. On the other hand, over these same sites, the IPCC-2007 simulation of atmospheric absorption is smaller by 7–8 Wm−2. MACR was then used with a comprehensive set of model input from satellites to simulate global solar radiation budget. The simulated planetary albedo of 29.0% confirms the value (28.6%) observed by CERES. We estimate the atmospheric absorption to be 82 ± 8 Wm−2 to be compared with the 67 Wm−2 by IPCC models as of 2001 and updated to 76 Wm−2by IPCC-2007. The primary reasons for the 6 Wm−2 larger solar absorption in our estimates are: updated water vapor spectroscopic database (∼1 Wm−2), inclusion of minor gases (∼0.5 Wm−2), black and brown carbon aerosols (∼4 Wm−2), the inclusion of black carbon in clouds (∼1 Wm−2) and 3-D effect of clouds (∼1 Wm−2). The fundamental deduction from our study is the remarkable consistency between satellite measurements of the radiation budget and the parameters (aerosols, clouds and surface reflectivity) which determine the radiation budget. Because of this consistency we can account for and explain the global solar radiation budget of the planet within few Wm−2. 0320 Cloud physics and chemistry; 1620 Climate dynamics; 0321 Cloud/radiation interaction; 1814 Energy budgets; BSRN; solar radiation budget; 1626 Global climate models; atmospheric solar absorption; GEBA; global albedo; MACR
Konsta, Dimitra; Chepfer, Helene; Dufresne, Jean-LouisKonsta, D., H. Chepfer, J. Dufresne, 2012: A process oriented characterization of tropical oceanic clouds for climate model evaluation, based on a statistical analysis of daytime A-train observations. Climate Dynamics, 39(9-10), 2091-2108. doi: 10.1007/s00382-012-1533-7. This paper aims at characterizing how different key cloud properties (cloud fraction, cloud vertical distribution, cloud reflectance, a surrogate of the cloud optical depth) vary as a function of the others over the tropical oceans. The correlations between the different cloud properties are built from 2 years of collocated A-train observations (CALIPSO-GOCCP and MODIS) at a scale close to cloud processes; it results in a characterization of the physical processes in tropical clouds, that can be used to better understand cloud behaviors, and constitute a powerful tool to develop and evaluate cloud parameterizations in climate models. First, we examine a case study of shallow cumulus cloud observed simultaneously by the two sensors (CALIPSO, MODIS), and develop a methodology that allows to build global scale statistics by keeping the separation between clear and cloudy areas at the pixel level (250, 330 m). Then we build statistical instantaneous relationships between the cloud cover, the cloud vertical distribution and the cloud reflectance. The vertical cloud distribution indicates that the optically thin clouds (optical thickness 3.4) are composed of high and mid-level clouds associated with deep convection along the ITCZ and SPCZ and over the warm pool, and by stratocumulus low level clouds located along the East coast of tropical oceans. The cloud properties are analyzed as a function of the large scale circulation regime. Optically thick high clouds are dominant in convective regions (CF > 80 %), while low level clouds with low optical thickness ( Meteorology/Climatology; Oceanography; Geophysics/Geodesy
Kubar, Terence L.; Waliser, Duane E.; Li, J.-L.; Jiang, XiananKubar, T. L., D. E. Waliser, J. Li, X. Jiang, 2012: On the Annual Cycle, Variability, and Correlations of Oceanic Low-Topped Clouds with Large-Scale Circulation Using Aqua MODIS and ERA-Interim. J. Climate, 25(18), 6152-6174. doi: 10.1175/JCLI-D-11-00478.1. AbstractEight years of Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) level-3 cloud data in conjunction with collocated Interim ECMWF Re-Analysis are used to investigate relationships between isolated low-topped cloud fraction (LCF) and dynamics/thermodynamics versus averaging time scale. Correlation coefficients between LCF and −SST exceed 0.70 over 56% of ocean regions from 25°S to 25°N for 90-day running means and exceed 0.70 between LCF and 500-hPa omega (ω500) for over one-third of oceans from 50°S to 50°N. Correlations increase most dramatically by increasing the averaging time scale from 1 day to about 15, owing to the large LCF synoptic variability and random effects that are suppressed by averaging. In five regions selected with monthly mean SSTs between 291 and 303 K, SST decreases by −0.13 K %-1 low-cloud cover increase. Monthly LCF is also correlated with estimated inversion strength (EIS), which is SST dominated in low latitudes and free tropospheric temperature dominated in the northeast Atlantic, Pacific, and midlatitudes, though SST and stability are poor predictors of LCF over the southern oceans.Where the fraction of variance explained by the annual LCF harmonic is high, maximum LCF tends to lead minimum SST by ~15–30 days such that clouds can amplify the SST annual cycle, especially when LCF maxima coexist with insolation minima. Monthly mean LCF tends to scale with ω500 exponentially over the convective margins and offshore of the Pacific Northwest, but daily climatology relationships indicate that LCF levels off and even diminishes for ω500 > 0.05 Pa s−1, suggesting a limit through, perhaps, a too strong suppression of boundary layer heights. This suggests the need for dynamic-regime analysis in diagnosing low cloud/circulation feedbacks. sea surface temperature; satellite observations; Atmospheric circulation; Seasonal cycle; Cloud cover; marine boundary layer
Lauer, Axel; Bennartz, Ralf; Hamilton, Kevin; Wang, YuqingLauer, A., R. Bennartz, K. Hamilton, Y. Wang, 2012: Modeling the Response of Marine Boundary Layer Clouds to Global Warming: The Impact of Subgrid-Scale Precipitation Formation. J. Climate, 25(19), 6610-6626. doi: 10.1175/JCLI-D-11-00623.1. AbstractAn important parameter often adjusted to achieve agreement between simulated and observed radiative fluxes in climate models is the rain formation efficiency. This adjustment has been justified as accounting for the effects of subgrid-scale variability in cloud properties, but this tuning approach is rather arbitrary. This study examines results from a regional climate model with precipitation formation schemes that have been conventionally tuned, and it compares them with simulations employing a recently developed scheme that uses satellite observations to explicitly account for the subgrid-scale variability of clouds (“integral constraint method”). Simulations with the International Pacific Research Center’s Regional Atmospheric Model (iRAM) show that the integral constraint method is capable of simulating cloud fields over the eastern Pacific that are in good agreement with observations, without requiring model tuning. A series of global warming simulations for late twenty-first-century conditions is performed to investigate the impact of the treatment of the precipitation formation efficiency on modeled cloud–climate feedbacks. The results with the integral constraint method show that the simulated cloud feedbacks have similar patterns at all the model resolutions considered (grid spacings of 50, 100, and 200 km), but there are some quantitative differences (with smaller feedbacks at finer resolution). The cloud responses to global warming in simulations with a conventionally tuned autoconversion scheme and with the integral constraint method were found to be quite consistent, although differences in individual regions of ~10%–30% are evident. No conclusions can be drawn from this study on the validity of model tuning for thick clouds and mixed phase or ice clouds, however. climate change; Cloud parameterizations; Regional models
Leahy, L. V.; Wood, R.; Charlson, R. J.; Hostetler, C. A.; Rogers, R. R.; Vaughan, M. A.; Winker, D. M.Leahy, L. V., R. Wood, R. J. Charlson, C. A. Hostetler, R. R. Rogers, M. A. Vaughan, D. M. Winker, 2012: On the nature and extent of optically thin marine low clouds. Journal of Geophysical Research: Atmospheres, 117(D22), D22201. doi: 10.1029/2012JD017929. Macrophysical properties of optically thin marine low clouds over the nonpolar oceans (60°S–60°N) are measured using 2 years of full-resolution nighttime data from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). Optically thin clouds, defined as the subset of marine low clouds that do not fully attenuate the lidar signal, comprise almost half of the low clouds over the marine domain. Regionally, the fraction of low clouds that are optically thin (fthin,cld) exhibits a strong inverse relationship with the low-cloud cover, with maxima in the tropical trades (fthin,cld > 0.8) and minima in regions of persistent marine stratocumulus and in midlatitudes (fthin,cld< 0.3). Domain-wide, a power law fit describes the cloud length distribution, with exponentβ = 2.03 ± 0.06 (±95% confidence interval). On average, the fraction of a cloud that is optically thin decreases from ∼1 for clouds smaller than 2 km to 3311 Clouds and aerosols; 0480 Remote sensing; marine low clouds; CALIOP; cloud size; optically thin clouds
Li, J.-L. F.; Waliser, D. E.; Chen, W.-T.; Guan, B.; Kubar, T.; Stephens, G.; Ma, H.-Y.; Deng, M.; Donner, L.; Seman, C.; Horowitz, L.Li, J. F., D. E. Waliser, W. Chen, B. Guan, T. Kubar, G. Stephens, H. Ma, M. Deng, L. Donner, C. Seman, L. Horowitz, 2012: An observationally based evaluation of cloud ice water in CMIP3 and CMIP5 GCMs and contemporary reanalyses using contemporary satellite data. Journal of Geophysical Research: Atmospheres, 117(D16), D16105. doi: 10.1029/2012JD017640. We perform an observationally based evaluation of the cloud ice water content (CIWC) and path (CIWP) of present-day GCMs, notably 20th century CMIP5 simulations, and compare these results to CMIP3 and two recent reanalyses. We use three different CloudSat + CALIPSO ice water products and two methods to remove the contribution from the convective core ice mass and/or precipitating cloud hydrometeors with variable sizes and falling speeds so that a robust observational estimate can be obtained for model evaluations. The results show that for annual mean CIWP, there are factors of 2–10 in the differences between observations and models for a majority of the GCMs and for a number of regions. However, there are a number of CMIP5 models, including CNRM-CM5, MRI, CCSM4 and CanESM2, as well as the UCLA CGCM, that perform well compared to our past evaluations. Systematic biases in CIWC vertical structure occur below the mid-troposphere where the models overestimate CIWC, with this bias arising mostly from the extratropics. The tropics are marked by model differences in the level of maximum CIWC (∼250–550 hPa). Based on a number of metrics, the ensemble behavior of CMIP5 has improved considerably relative to CMIP3, although neither the CMIP5 ensemble mean nor any individual model performs particularly well, and there are still a number of models that exhibit very large biases despite the availability of relevant observations. The implications of these results on model representations of the Earth radiation balance are discussed, along with caveats and uncertainties associated with the observational estimates, model and observation representations of the precipitating and cloudy ice components, relevant physical processes and parameterizations. 3337 Global climate models; CloudSat; 1855 Remote sensing; CMIP5; IWC
Liu, Yang; Liu, RonggaoLiu, Y., R. Liu, 2012: Evaluation of the Spatial and Temporal Uncertainties Distribution of Daily-Integrated Shortwave Downward Radiation Estimated from Polar-Orbiting Satellite Observation. J. Atmos. Oceanic Technol., 29(10), 1481-1491. doi: 10.1175/JTECH-D-11-00142.1. AbstractThe polar-orbiting satellite sensor, which can observe the entire Earth’s surface with good spatial and spectral resolution, is a potential tool for estimation of global downward shortwave radiation (DSR). However, it can only provide a couple of snapshots in one day, which should be extended to daily-integrated DSR in order to drive the ecosystem models. In this paper, the temporal and spatial uncertainties for estimating of daily-integrated DSR from instantaneous measurements of polar-orbiting satellites are evaluated using geostationary Geosynchronous Meteorological Satellite-5 (GMS-5) observations over East Asia. Those overpass times—including 1030, 1200, and 1330 local time (LT), which correspond to Terra/Moderate Resolution Imaging Spectroradiometer (MODIS), Sea-Viewing Wide Field-of-View Sensor (SeaWiFS), and Aqua/MODIS—are evaluated. The combinations of multiobservations are also assessed.The results show that the daily-integrated DSR from polar-orbiting satellite observations of 1030, 1200, and 1330 underestimate solar radiation by 2.16% (0.46 MJ m−2), 5.44% (1.16 MJ m−2), and 5.54% (1.09 MJ m−2), with an RMSE of 2.05 MJ m−2 (12.92%), 2.50 MJ m−2 (13.33%), and 2.34 MJ m−2 (13.95%) in East Asia with large spatial and seasonal variations. In general, the bias is higher in the southern than in the northern part of East Asia. It is low in January, February, and March, then increases from April and reaches the maximum in June and July, and decreases rapidly to lower than 1.0 MJ m−2 in October. The uncertainties of daily-integrated DSR could be reduced by averaging multiday observations or combining of multitime observations. These uncertainties’ distributions are important for evaluation the usability of daily-integrated DSR from polar-orbiting satellite data and probably can be used for its calibration. Remote sensing
Loeb, Norman G.; Kato, Seiji; Su, Wenying; Wong, Takmeng; Rose, Fred G.; Doelling, David R.; Norris, Joel R.; Huang, XiangleiLoeb, N. G., S. Kato, W. Su, T. Wong, F. G. Rose, D. R. Doelling, J. R. Norris, X. Huang, 2012: Advances in Understanding Top-of-Atmosphere Radiation Variability from Satellite Observations. Surveys in Geophysics, 33(3-4), 359-385. doi: 10.1007/s10712-012-9175-1. This paper highlights how the emerging record of satellite observations from the Earth Observation System (EOS) and A-Train constellation are advancing our ability to more completely document and understand the underlying processes associated with variations in the Earth’s top-of-atmosphere (TOA) radiation budget. Large-scale TOA radiation changes during the past decade are observed to be within 0.5 Wm−2 per decade based upon comparisons between Clouds and the Earth’s Radiant Energy System (CERES) instruments aboard Terra and Aqua and other instruments. Tropical variations in emitted outgoing longwave (LW) radiation are found to closely track changes in the El Niño-Southern Oscillation (ENSO). During positive ENSO phase (El Niño), outgoing LW radiation increases, and decreases during the negative ENSO phase (La Niña). The coldest year during the last decade occurred in 2008, during which strong La Nina conditions persisted throughout most of the year. Atmospheric Infrared Sounder (AIRS) observations show that the lower temperatures extended throughout much of the troposphere for several months, resulting in a reduction in outgoing LW radiation and an increase in net incoming radiation. At the global scale, outgoing LW flux anomalies are partially compensated for by decreases in midlatitude cloud fraction and cloud height, as observed by Moderate Resolution Imaging Spectrometer and Multi-angle Imaging SpectroRadiometer, respectively. CERES data show that clouds have a net radiative warming influence during La Niña conditions and a net cooling influence during El Niño, but the magnitude of the anomalies varies greatly from one ENSO event to another. Regional cloud-radiation variations among several Terra and A-Train instruments show consistent patterns and exhibit marked fluctuations at monthly timescales in response to tropical atmosphere-ocean dynamical processes associated with ENSO and Madden–Julian Oscillation. clouds; radiation budget; Geophysics/Geodesy; Astronomy, Observations and Techniques; Earth Sciences, general; Climate variability
Loeb, Norman G.; Lyman, John M.; Johnson, Gregory C.; Allan, Richard P.; Doelling, David R.; Wong, Takmeng; Soden, Brian J.; Stephens, Graeme L.Loeb, N. G., J. M. Lyman, G. C. Johnson, R. P. Allan, D. R. Doelling, T. Wong, B. J. Soden, G. L. Stephens, 2012: Observed changes in top-of-the-atmosphere radiation and upper-ocean heating consistent within uncertainty. Nature Geoscience, 5(2), 110-113. doi: 10.1038/ngeo1375. Global climate change results from a small yet persistent imbalance between the amount of sunlight absorbed by Earth and the thermal radiation emitted back to space. An apparent inconsistency has been diagnosed between interannual variations in the net radiation imbalance inferred from satellite measurements and upper-ocean heating rate from in situ measurements, and this inconsistency has been interpreted as ‘missing energy’ in the system. Here we present a revised analysis of net radiation at the top of the atmosphere from satellite data, and we estimate ocean heat content, based on three independent sources. We find that the difference between the heat balance at the top of the atmosphere and upper-ocean heat content change is not statistically significant when accounting for observational uncertainties in ocean measurements, given transitions in instrumentation and sampling. Furthermore, variability in Earth’s energy imbalance relating to El Niño-Southern Oscillation is found to be consistent within observational uncertainties among the satellite measurements, a reanalysis model simulation and one of the ocean heat content records. We combine satellite data with ocean measurements to depths of 1,800 m, and show that between January 2001 and December 2010, Earth has been steadily accumulating energy at a rate of 0.50±0.43 Wm−2 (uncertainties at the 90% confidence level). We conclude that energy storage is continuing to increase in the sub-surface ocean. Oceanography; Atmospheric science; Climate science
Lu, Yaqiong; Kueppers, Lara M.Lu, Y., L. M. Kueppers, 2012: Surface energy partitioning over four dominant vegetation types across the United States in a coupled regional climate model (Weather Research and Forecasting Model 3–Community Land Model 3.5). Journal of Geophysical Research: Atmospheres, 117(D6), D06111. doi: 10.1029/2011JD016991. Accurate representation of surface energy partitioning is crucial for studying land surface processes and the climatic influence of land cover and land use change using coupled climate-land surface models. A critical question for these models, especially for newly coupled ones, is whether they can adequately distinguish differences in surface energy partitioning among different vegetation types. We evaluated 3 years (2004–2006) of surface energy partitioning and surface climate over four dominant vegetation types (cropland, grassland, needleleaf evergreen forest, and broadleaf deciduous forest) across the United States in a recently coupled regional climate model, Weather Research and Forecasting Model 3–Community Land Model 3.5 (WRF3-CLM3.5), by comparing model output to observations (AmeriFlux, Clouds and the Earth's Radiant Energy System (CERES), and Parameter-elevation Regressions on Independent Slopes Model (PRISM) data) and to standard WRF model output. We found that WRF3-CLM3.5 can capture the seasonal pattern in energy partitioning for needleleaf evergreen forest but needs improvements in cropland, grassland, and broadleaf deciduous forest. Correcting the leaf area index representation for cropland and grassland could immediately improve the simulation of latent heat flux and hence the energy partitioning. Adding an irrigation scheme is especially important for cropland in the Midwest, where the strongly coupled soil moisture and precipitation can form a positive feedback that reduces latent heat flux and increases the warm bias. For deciduous forest, the simulated excess latent heat flux before leaf emergence is mainly from soil evaporation, requiring further improvement in the soil evaporation scheme. Finally, the domain-wide overestimated net radiation contributes to positive biases in sensible, latent, and ground heat flux, as well as surface temperature. The standard WRF simulation has a similar warm bias, implicating errors in modules other than the land surface code. A sensitivity test suggests that improved simulation of downward solar radiation could reduce the energy flux and temperature biases. After adding irrigation process and correcting the leaf area index, WRF3-CLM3.5 appears reliable for studying conversions between natural grassland and irrigated cropland and between needleleaf evergreen forest and grassland. 1620 Climate dynamics; validation; 1622 Earth system modeling; 1627 Coupled models of the climate system; 1631 Land/atmosphere interactions; 3333 Model calibration; AmeriFlux; surface energy flux partitioning; WRF3-CLM3.5
Ma, Y.; Pinker, R. T.Ma, Y., R. T. Pinker, 2012: Modeling shortwave radiative fluxes from satellites. Journal of Geophysical Research: Atmospheres, 117(D23), D23202. doi: 10.1029/2012JD018332. During the last two decades, significant progress has been made in assessing the Earth Radiation Balance from satellite observations. Yet, satellite based estimates differ from each other and from those provided by numerical models. Major issues are related to quality of satellite observations, such as the frequent changes in satellite observing systems, degradation of sensors, restricted spectral intervals and viewing geometry of sensors, and changes in the quality of atmospheric inputs that drive the inference schemes. To reduce differences among the satellite based estimates requires, among others, updates to inference schemes so that most recent auxiliary information can be fully utilized. This paper reports on improvements introduced to a methodology developed at the University of Maryland to estimate shortwave (SW) radiative fluxes within the atmosphere system from satellite observations, the implementation of the approach with newly available auxiliary information, evaluation of the downwelling SW flux against ground observations, and comparison with independent satellite methods and numerical models. Specifically, introduced are: new Narrow to Broadband (N/B) transformations and new Angular Distribution Models (ADM) for clear and cloudy sky that incorporate most recent land use classifications; improved aerosol treatment; separation of clouds by phase; improved sun-earth geometry; and implementation at 0.5° spatial resolution at 3-hourly intervals integrated to daily and monthly time scales. When compared to an earlier version of the model as implemented at 2.5° at global scale and against observations from the globally distributed Baseline Surface Radiation Network (BSRN) stations for a period of six years (at monthly time scale), the bias was reduced from 8.6 (4.6%) to −0.5 (0.3%) W/m2, the standard deviation from 16.6 (8.9%) to 14.5 (7.8%) W/m2while the correlation remained high at 0.98 in both cases. Evaluation was also done over oceanic sites as available from the Pilot Research Moored Array in the Tropical Atlantic (PIRATA) moorings and from the Tropical Atmosphere Ocean/Triangle Trans-Ocean Buoy Network (TAO/TRITON) moorings in the tropical Pacific Ocean. Overall, results over oceans were not as good as over land for all the satellite retrievals compared in this study. 0764 Energy balance; global scale shortwave radiative fluxes; satellite shortwave radiative fluxes; surface radiative fluxes
Ma, Yingying; Gong, WeiMa, Y., W. Gong, 2012: Evaluating the Performance of SVM in Dust Aerosol Discrimination and Testing its Ability in an Extended Area. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 5(6), 1849-1858. doi: 10.1109/JSTARS.2012.2206572. The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) has been run more than five years, and one of its payloads-the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP)-can offer global atmospheric vertical profiles, resulting in it being widely used in aerosol research. Because the Lidar ratio is an important parameter for aerosol parameter retrieval and the choice of the Lidar ratio needs confirm the type of layers (aerosol or cloud), the data process cannot do without accurate and efficient aerosol and cloud classification. Initially, we found the classification errors existed in PDF version 1 data, so we introduce the SVM classifier to improve the accurate of thick dust and cloud classification. Despite NASA issued the PDF version 2 and improve the correct rate greatly, but we cannot ignore SVM advantages. Therefore in this paper, to continue the former study, we will not only validate the feasibility of this method (especially in dust source areas), but also make a thorough study of classification result effected by different feature vectors and samples. Through the accuracy testing we found, with the increase of the number of samples, SVM have the better result, and the feature space which include depolarization ratio have the more stable result. Though we validated the advantage of SVM, but if we want to use this algorithm in global scale or the whole process of dust deposition, there are still some improvements we need to do. To obtain the thinking of algorithm revision, we using MODIS, HYSPLIT, and CALIPSO products in a dust storm and observe its transmission, then the deficiencies of SVM can be found when compare with PDF version 2. Indeed PDF considered the regional variation, with this transmission of dust storm we need adjustment training samples and hyperplane of classifier. The diversity between SVM and PDF will be applied in the future research as the reference to make the new algorithm more robust and accurate. clouds; aerosols; atmospheric techniques; MODIS; dust aerosol; dust; CALIPSO; Laser radar; aerosol classification; aerosol research; Backscatter; CALIOP; CALIPSO product; classification errors; cloud classification; Cloud-Aerosol Lidar; depolarization ratio; discrimination algorithm; dust aerosol discrimination; dust deposition process; dust storm; geophysical image processing; global atmospheric vertical profiles; HYSPLIT product; image classification; Infrared Pathfinder Satellite Observation; Lidar ratio; MODIS product; Orthogonal Polarization; PDF data; Support Vector Machine (SVM); Support vector machines; SVM classifier; SVM performance
Masters, T.Masters, T., 2012: On the determination of the global cloud feedback from satellite measurements. Earth System Dynamics, 3(2), 97-107. doi: 10.5194/esd-3-97-2012.
Mayer, Michael; Haimberger, LeopoldMayer, M., L. Haimberger, 2012: Poleward Atmospheric Energy Transports and Their Variability as Evaluated from ECMWF Reanalysis Data. J. Climate, 25(2), 734-752. doi: 10.1175/JCLI-D-11-00202.1. AbstractThe vertically integrated global energy budget is evaluated with a direct and an indirect method (both corrected for mass inconsistencies of the forecast model), mainly using the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis Interim (ERA-Interim) data. A new estimate for the net poleward total energy transport is given. Comparison to satellite-derived radiation data proves that ERA-Interim is better suited for investigation of interannual variations of the global energy budget than available satellite data since these either cover a relatively short period of time or are too inhomogeneous in time. While much improved compared to the 40-yr ECMWF Re-Analysis (ERA-40), regionally averaged energy budgets of ERA-Interim show that strong anomalies of forecasted vertical fluxes tend to be partly compensated by unrealistically large forecasted energy storage rates. Discrepancies between observed and forecasted monthly mean tendencies can be taken as rough measure for the uncertainties involved in the ERA-Interim energy budget. El Niño–Southern Oscillation (ENSO) is shown to have large impact on regional energy budgets, but strong compensation occurs between the western and eastern Pacific, leading to only small net variations of the total poleward energy transports (similar magnitude as the uncertainty of the computations). However, Hovmöller longitude–time plots of tropical energy exports show relatively strong slowly eastward-moving poleward transport anomalies in connection with ENSO. Verification of these findings using independent estimates still needs to be done. Energy budget/balance; ENSO; Interannual variability; Energy transport
Merrelli, Aronne; Turner, David D.Merrelli, A., D. D. Turner, 2012: Comparing Information Content of Upwelling Far-Infrared and Midinfrared Radiance Spectra for Clear Atmosphere Profiling. J. Atmos. Oceanic Technol., 29(4), 510-526. doi: 10.1175/JTECH-D-11-00113.1. AbstractThe information content of high-spectral-resolution midinfrared (MIR; 650–2300 cm−1) and far-infrared (FIR; 200–685 cm−1) upwelling radiance spectra is calculated for clear-sky temperature and water vapor profiles. The wavenumber ranges of the two spectral bands overlap at the central absorption line in the CO2 ν2 absorption band, and each contains one side of the full absorption band. Each spectral band also includes a water vapor absorption band; the MIR contains the first vibrational–rotational absorption band, while the FIR contains the rotational absorption band. The upwelling spectral radiances are simulated with the line-by-line radiative transfer model (LBLRTM), and the retrievals and information content analysis are computed using standard optimal estimation techniques. Perturbations in the surface temperature and in the trace gases methane, ozone, and nitrous oxide (CH4, O3, and N2O) are introduced to represent forward-model errors. Each spectrum is observed by a simulated infrared spectrometer, with a spectral resolution of 0.5 cm−1, with realistic spectrally varying sensor noise levels. The modeling and analysis framework is applied identically to each spectral range, allowing a quantitative comparison. The results show that for similar sensor noise levels, the FIR shows an advantage in water vapor profile information content and less sensitivity to forward-model errors. With a higher noise level in the FIR, which is a closer match to current FIR detector technology, the FIR information content drops and shows a disadvantage relative to the MIR. Remote sensing; infrared radiation; Sensitivity studies; Soundings
Nam, C.; Bony, S.; Dufresne, J.-L.; Chepfer, H.Nam, C., S. Bony, J. Dufresne, H. Chepfer, 2012: The ‘too few, too bright’ tropical low-cloud problem in CMIP5 models. Geophysical Research Letters, 39(21), L21801. doi: 10.1029/2012GL053421. Previous generations of climate models have been shown to under-estimate the occurrence of tropical low-level clouds and to over-estimate their radiative effects. This study analyzes outputs from multiple climate models participating in the Fifth phase of the Coupled Model Intercomparison Project (CMIP5) using the Cloud Feedback Model Intercomparison Project Observations Simulator Package (COSP), and compares them with different satellite data sets. Those include CALIPSO lidar observations, PARASOL mono-directional reflectances and CERES radiative fluxes at the top of the atmosphere. We show that current state-of-the-art climate models predict overly bright low-clouds, even for a correct low-cloud cover. The impact of these biases on the Earth' radiation budget, however, is reduced by compensating errors. Those include the tendency of models to under-estimate the low-cloud cover and to over-estimate the occurrence of mid- and high-clouds above low-clouds. Finally, we show that models poorly represent the dependence of the vertical structure of low-clouds on large-scale environmental conditions. The implications of this ‘too few, too bright low-cloud problem’ for climate sensitivity and model development are discussed. 0360 Radiation: transmission and scattering; 1610 Atmosphere; 0321 Cloud/radiation interaction; parasol; 1622 Earth system modeling; CMIP5; CALIPSO; 1626 Global climate models; COSP; Cloud-radiative effects; low-level clouds
Nam, Christine C. W.; Quaas, JohannesNam, C. C. W., J. Quaas, 2012: Evaluation of Clouds and Precipitation in the ECHAM5 General Circulation Model Using CALIPSO and CloudSat Satellite Data. J. Climate, 25(14), 4975-4992. doi: 10.1175/JCLI-D-11-00347.1. AbstractObservations from Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and CloudSat satellites are used to evaluate clouds and precipitation in the ECHAM5 general circulation model. Active lidar and radar instruments on board CALIPSO and CloudSat allow the vertical distribution of clouds and their optical properties to be studied on a global scale. To evaluate the clouds modeled by ECHAM5 with CALIPSO and CloudSat, the lidar and radar satellite simulators of the Cloud Feedback Model Intercomparison Project’s Observation Simulator Package are used. Comparison of ECHAM5 with CALIPSO and CloudSat found large-scale features resolved by the model, such as the Hadley circulation, are captured well. The lidar simulator demonstrated ECHAM5 overestimates the amount of high-level clouds, particularly optically thin clouds. High-altitude clouds in ECHAM5 consistently produced greater lidar scattering ratios compared with CALIPSO. Consequently, the lidar signal in ECHAM5 frequently attenuated high in the atmosphere. The large scattering ratios were due to an underestimation of effective ice crystal radii in ECHAM5. Doubling the effective ice crystal radii improved the scattering ratios and frequency of attenuation. Additionally, doubling the effective ice crystal radii improved the detection of ECHAM5’s highest-level clouds by the radar simulator, in better agreement with CloudSat. ECHAM5 was also shown to significantly underestimate midlevel clouds and (sub)tropical low-level clouds. The low-level clouds produced were consistently perceived by the lidar simulator as too optically thick. The radar simulator demonstrated ECHAM5 overestimates the frequency of precipitation, yet underestimates its intensity compared with CloudSat observations. These findings imply compensating mechanisms in ECHAM5 balance out the radiative imbalance caused by incorrect optical properties of clouds and consistently large hydrometeors in the atmosphere. satellite observations; Model evaluation/performance; climate models; Radars/Radar observations; Lidars/Lidar observations
Naud, Catherine M.; Miller, James R.; Landry, ChrisNaud, C. M., J. R. Miller, C. Landry, 2012: Using satellites to investigate the sensitivity of longwave downward radiation to water vapor at high elevations. Journal of Geophysical Research: Atmospheres, 117(D5), D05101. doi: 10.1029/2011JD016917. Many studies suggest that high-elevation regions may be among the most sensitive to future climate change. However, in situ observations in these often remote locations are too sparse to determine the feedbacks responsible for enhanced warming rates. One of these feedbacks is associated with the sensitivity of longwave downward radiation (LDR) to changes in water vapor, with the sensitivity being particularly large in many high-elevation regions where the average water vapor is often low. We show that satellite retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Clouds and the Earth’s Radiant Energy System (CERES) can be used to expand the current ground-based observational database and that the monthly averaged clear-sky satellite estimates of humidity and LDR are in good agreement with the well-instrumented Center for Snow and Avalanche Studies ground-based site in the southwestern Colorado Rocky Mountains. The relationship between MODIS-retrieved precipitable water vapor and surface specific humidity across the contiguous United States was found to be similar to that previously found for the Alps. More important, we show that satellites capture the nonlinear relationship between LDR and water vapor and confirm that LDR is especially sensitive to changes in water vapor at high elevations in several midlatitude mountain ranges. Because the global population depends on adequate fresh water, much of which has its source in high mountains, it is critically important to understand how climate will change there. We demonstrate that satellites can be used to investigate these feedbacks in high-elevation regions where the coverage of surface-based observations is insufficient to do so. 1640 Remote sensing; satellite observations; 1637 Regional climate change; high elevation; longwave downward flux; precipitable water vapor; specific humidity
Niu, Xiaolei; Pinker, Rachel T.Niu, X., R. T. Pinker, 2012: Revisiting satellite radiative flux computations at the top of the atmosphere. International Journal of Remote Sensing, 33(5), 1383-1399. doi: 10.1080/01431161.2011.571298. Most satellite observations of radiative fluxes at the top of the atmosphere (TOA) are at narrow spectral intervals and at particular viewing angles. Critical elements in the formulation of TOA shortwave (SW) radiative fluxes are (1) the transformation from narrowband to broadband values (n/b) and (2) the application of angular distribution models (ADMs) to correct for anisotropy. In this article, the n/b transformations are based on theoretical simulations with a radiative transfer model Moderate Resolution Atmospheric Transmission (MODTRAN) 3.7 using land classification types based on the International Geosphere-Biosphere Programme (IGBP) scheme and a range of realistic atmospheric conditions. The newly developed ADMs are a combination of MODTRAN-3.7 simulations and the Clouds and the Earth's Radiant Energy System (CERES)-observed ADMs. To evaluate the impact of the proposed corrections, they are implemented with observations from the Spinning Enhanced Visible Infrared Imager (SEVIRI) on the Meteorological Satellite (METEOSAT) 8 to derive TOA fluxes and compared to similar quantities from CERES. It is shown that the estimated TOA radiative fluxes have –3% bias and 7% root mean square error (RMSE) when compared with CERES observations at a monthly timescale.
Oreopoulos, Lazaros; Mlawer, Eli; Delamere, Jennifer; Shippert, Timothy; Cole, Jason; Fomin, Boris; Iacono, Michael; Jin, Zhonghai; Li, Jiangnan; Manners, James; Räisänen, Petri; Rose, Fred; Zhang, Yuanchong; Wilson, Michael J.; Rossow, William B.Oreopoulos, L., E. Mlawer, J. Delamere, T. Shippert, J. Cole, B. Fomin, M. Iacono, Z. Jin, J. Li, J. Manners, P. Räisänen, F. Rose, Y. Zhang, M. J. Wilson, W. B. Rossow, 2012: The Continual Intercomparison of Radiation Codes: Results from Phase I. Journal of Geophysical Research: Atmospheres, 117(D6), D06118. doi: 10.1029/2011JD016821. We present results from Phase I of the Continual Intercomparison of Radiation Codes (CIRC), intended as an evolving and regularly updated reference source for evaluation of radiative transfer (RT) codes used in global climate models and other atmospheric applications. CIRC differs from previous intercomparisons in that it relies on an observationally validated catalog of cases. The seven CIRC Phase I baseline cases, five cloud free and two with overcast liquid clouds, are built around observations by the Atmospheric Radiation Measurements program that satisfy the goals of Phase I, namely, to examine RT model performance in realistic, yet not overly complex, atmospheric conditions. Besides the seven baseline cases, additional idealized “subcases” are also employed to facilitate interpretation of model errors. In addition to quantifying individual model performance with respect to reference line-by-line calculations, we also highlight RT code behavior for conditions of doubled CO2, issues arising from spectral specification of surface albedo, and the impact of cloud scattering in the thermal infrared. Our analysis suggests that improvements in the calculation of diffuse shortwave flux, shortwave absorption, and shortwave CO2 forcing as well as in the treatment of spectral surface albedo should be considered for many RT codes. On the other hand, longwave calculations are generally in agreement with the reference results. By expanding the range of conditions under which participating codes are tested, future CIRC phases will hopefully allow even more rigorous examination of RT codes. 0360 Radiation: transmission and scattering; 0321 Cloud/radiation interaction; radiative transfer; 3359 Radiative processes; 3337 Global climate models; radiative forcing; climate models; intercomparison
Painemal, David; Minnis, PatrickPainemal, D., P. Minnis, 2012: On the dependence of albedo on cloud microphysics over marine stratocumulus clouds regimes determined from Clouds and the Earth's Radiant Energy System (CERES) data. Journal of Geophysical Research: Atmospheres, 117(D6), D06203. doi: 10.1029/2011JD017120. The dependence of the top-of-the-atmosphere (TOA) albedo A on cloud microphysical properties was investigated for the three largest maritime stratocumulus clouds regimes: off California, Southeast Pacific (Chile-Peru), and southwest Africa (Namibia-Angola). Absolute S and relative SR albedo susceptibilities to perturbations in cloud droplet number concentrations Nd, defined as dA/dNd and dA/dln(Nd) respectively, were calculated for the season having maximum cloud cover during the period 2006–2010. Satellite-based susceptibilities were computed by combining an adiabatically based Nd estimate and liquid water path (LWP) derived from Terra Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals matched with TOA A from the Clouds and the Earth's Radiant Energy System. Empirical susceptibility maps were calculated for three constant LWP intervals at 25, 50, and 90 g−2. It was found that S increases with LWP, with small and spatially homogeneous values for low LWP, and a contrasting increase far offshore for larger LWP values. An overall increase of SR with LWP was also observed, with larger values near the coast for LWP = 25 and 50 g−2. A relatively homogeneous spatial pattern of maximum SR values covered most of each regime's domain for a LWP of 90 g−2. These results highlight the importance of LWP in modulating the albedo susceptibility. The dependencies of S and SR on LWP are mostly explained by variations in the mean Nd and cloud optical thickness (τ), with an increase of S with LWP linked to a decrease in Nd, whereas SR increased with τ and A, until reaching a maximum for A and τ near 0.36–0.4 and 12–14 respectively, and decreasing thereafter, consistent with expectations based on two-stream estimates. Larger SR values in the Southeast Pacific are thought to be the consequence of a drier and more pristine atmosphere. Radiative transfer simulations with realistic values of above-cloud water vapor path and aerosol optical thickness showed that differing atmospheric compositions could explain why the Chile-Peru regime was the marine stratocumulus cloud deck most susceptible to change its TOA albedo due to fractional changes in Nd. Clouds and the Earth's Radiant Energy System; albedo; 0321 Cloud/radiation interaction; 3310 Clouds and cloud feedbacks; microphysics; 3307 Boundary layer processes; stratocumulus
Painemal, David; Minnis, PatrickPainemal, D., P. Minnis, 2012: Correction to “On the dependence of albedo on cloud microphysics over marine stratocumulus clouds regimes determined from Clouds and the Earth's Radiant Energy System (CERES) data”. Journal of Geophysical Research: Atmospheres, 117(D9), D09299. doi: 10.1029/2012JD017902. Clouds and the Earth's Radiant Energy System; albedo; 0321 Cloud/radiation interaction; 3310 Clouds and cloud feedbacks; microphysics; 3307 Boundary layer processes; stratocumulus; 9900 Corrections
Palmer, Matthew D.Palmer, M. D., 2012: Climate and Earth’s Energy Flows. Surveys in Geophysics, 33(3-4), 351-357. doi: 10.1007/s10712-011-9165-8. Under equilibrium conditions, climate can be viewed in simple terms as the average energy pathways that incoming solar radiation takes before exiting the system in order to maintain overall energy balance. Similarly, future climate change will ultimately be determined by how the Earth’s energy balance and average energy pathways change in response to external radiative forcings, such as anthropogenic greenhouse gases, and internal redistributions. Here, we give an overview of climate research in the context of Earth’s energy flows and make the case for improved observations of total energy as a more physically robust metric of climate change than the commonly used surface temperature record. Oceans; climate; Ocean heat content; radiation; energy; Geophysics/Geodesy; Astronomy, Observations and Techniques; Earth Sciences, general
Penner, Joyce E.; Zhou, Cheng; Xu, LiPenner, J. E., C. Zhou, L. Xu, 2012: Consistent estimates from satellites and models for the first aerosol indirect forcing. Geophysical Research Letters, 39(13), L13810. doi: 10.1029/2012GL051870. Satellite-based estimates for the aerosol indirect forcing are consistently smaller than those from models due, in part, to the use of present-day results that do not capture the temporal changes between present day and pre-industrial conditions. Here, we use results from a coupled aerosol-climate model to pick regions and seasons that are sufficiently pristine to represent pre-industrial conditions. Then we use results from MODIS and CERES to estimate the forcing between present and pre-industrial conditions. The estimated forcing in the North Pacific Ocean region ranges from −1.8 to −2.2 Wm−2 from observations. This range is similar to our modeled forcing for this region, −2.65 Wm−2, but is smaller than the modeled forcing using the same methodology as that used with the satellite observations, −3.6 W/m2. Nevertheless, a previous estimate based on satellite observations was a factor of 10 smaller, −0.2 to −0.5 Wm−2. Results demonstrate that while the estimated forcing from models may be somewhat larger than estimates based on satellite data, a judicious choice of analysis methods, yields results that are much closer than previous satellite and model-based comparisons. 1610 Atmosphere; 0305 Aerosols and particles; 3311 Clouds and aerosols; aerosol/cloud interactions; climate forcing
Pincus, Robert; Platnick, Steven; Ackerman, Steven A.; Hemler, Richard S.; Patrick Hofmann, Robert J.Pincus, R., S. Platnick, S. A. Ackerman, R. S. Hemler, R. J. Patrick Hofmann, 2012: Reconciling Simulated and Observed Views of Clouds: MODIS, ISCCP, and the Limits of Instrument Simulators. J. Climate, 25(13), 4699-4720. doi: 10.1175/JCLI-D-11-00267.1. AbstractThe properties of clouds that may be observed by satellite instruments, such as optical thickness and cloud-top pressure, are only loosely related to the way clouds are represented in models of the atmosphere. One way to bridge this gap is through “instrument simulators,” diagnostic tools that map the model representation to synthetic observations so that differences can be interpreted as model error. But simulators may themselves be restricted by limited information or by internal assumptions. This paper considers the extent to which instrument simulators are able to capture essential differences between the Moderate Resolution Imaging Spectroradiometer (MODIS) and the International Satellite Cloud Climatology Project (ISCCP), two similar but independent estimates of cloud properties. The authors review the measurements and algorithms underlying these two cloud climatologies, introduce a MODIS simulator, and detail datasets developed for comparison with global models using ISCCP and MODIS simulators. In nature MODIS observes less midlevel cloudiness than ISCCP, consistent with the different methods used to determine cloud-top pressure; aspects of this difference are reproduced by the simulators. Differences in observed distributions of optical thickness, however, are not captured. The largest differences can be traced to different approaches to partly cloudy pixels, which MODIS excludes and ISCCP treats as homogeneous. These cover roughly 15% of the planet and account for most of the optically thinnest clouds. Instrument simulators cannot reproduce these differences because there is no way to synthesize partly cloudy pixels. Nonetheless, MODIS and ISCCP observations are consistent for all but the optically thinnest clouds, and models can be robustly evaluated using instrument simulators by integrating over the robust subset of observations. clouds; Remote sensing; satellite observations; Model evaluation/performance; climate models
Posselt, Derek J.; Jongeward, Andrew R.; Hsu, Chuan-Yuan; Potter, Gerald L.Posselt, D. J., A. R. Jongeward, C. Hsu, G. L. Potter, 2012: Object-Based Evaluation of MERRA Cloud Physical Properties and Radiative Fluxes during the 1998 El Niño–La Niña Transition. J. Climate, 25(21), 7313-7327. doi: 10.1175/JCLI-D-11-00724.1. AbstractThe Modern-Era Retrospective Analysis for Research and Application (MERRA) is a reanalysis designed to produce an improved representation of the Earth’s hydrologic cycle. This study examines the representation of deep convective clouds in MERRA, comparing analyzed liquid and ice clouds with deep convective cloud objects observed by instruments on the Tropical Rainfall Measuring Mission satellite. Results show that MERRA contains deep convective cloud in 98.1% of the observed cases. MERRA-derived probability density functions (PDFs) of cloud properties have a similar form as the observed PDFs and exhibit a similar trend with changes in object size. Total water path, optical depth, and outgoing shortwave radiation (OSR) in MERRA are found to match the cloud object observations quite well; however, there appears to be a bias toward higher-than-observed cloud tops in the MERRA. The reanalysis fits the observations most closely for the largest class of convective systems, with performance generally decreasing with a transition to smaller convective systems. Comparisons of simulated total water path, optical depth, and OSR are found to be highly sensitive to the assumed subgrid distribution of condensate and indicate the need for caution when interpreting model-data comparisons that require disaggregation of grid-scale cloud to satellite pixel scales. tropics; satellite observations; Model evaluation/performance; convective clouds; ENSO
Prasad, Abhnil Amtesh; Davies, RogerPrasad, A. A., R. Davies, 2012: Detecting tropical thin cirrus using Multiangle Imaging SpectroRadiometer's oblique cameras and modeled outgoing longwave radiation. Journal of Geophysical Research: Atmospheres, 117(D6), D06208. doi: 10.1029/2011JD016798. We report the improved detection of thin cirrus clouds over the Tropics using oblique camera stereo retrieval of cloud top heights from the Multiangle Imaging SpectroRadiometer (MISR) instrument on the Terra satellite. The MISR oblique stereo captures 10% of thin cirrus with mean height of 13 km over all scenes that the standard stereo misses completely, especially when they are over lower-level clouds that provide more contrast. To determine thin cirrus properties missed by MISR, differences between modeled and measured outgoing longwave radiation (OLR) were used to compute its fractional cover and optical depth. The oblique MISR measurements were used as inputs to the model and a merged data set from CERES, MODIS and MISR instruments on the Terra satellite provided the measured fluxes and the cloud properties. For the cases investigated including all clear and cloudy scenes in the Tropics, the difference between modeled and measured OLR (Cirrus Forcing) averaged ≈ 19 W m−2. This can be accounted for by the addition of thin cirrus of coverage 77%. However, oblique analysis only detects 10% of thin cirrus (0.1 < τ < 0.3) and misses 67% of cirrus with τ < 0.3. The missed cirrus coverage includes 32% of homogeneous cirrus (0.1 < τ < 0.3) and 35% of subvisual cirrus (τ < 0.1). To improve the detection of homogeneous cirrus with MISR, the current contrast threshold should be decreased. This will increase the number of pixels to be matched stereoscopically that were screened as noise initially. 0321 Cloud/radiation interaction; 3310 Clouds and cloud feedbacks; Multiangle Imaging SpectroRadiometer; stereo; thin cirrus
Qiu, Hong; Hu, Liqin; Zhang, Yan; Lu, Duanjun; Qi, JinQiu, H., L. Hu, Y. Zhang, D. Lu, J. Qi, 2012: Absolute Radiometric Calibration of Earth Radiation Measurement on FY-3B and Its Comparison With CERES/Aqua Data. IEEE Transactions on Geoscience and Remote Sensing, 50(12), 4965-4974. doi: 10.1109/TGRS.2012.2202668. The Earth Radiation Measurement (ERM) instrument onboard FengYun (FY)-3B satellite observes the Earth's atmosphere through a narrow scanning field of view (NFOV) and a wide nonscanning FOV. For each field of view, the measurements are made from two broadband channels: a total waveband channel covering 0.2-50 μm and a shortwave (SW) band covering 0.2-4.3 μm. The validation to the ERM calibration was carried out by comparing the unfiltered longwave (LW) and SW radiances from ERM with those from Clouds and Earth's Radiation Energy System (CERES) flight model 3 onboard Earth Observing System Aqua satellite. While the ERM LW and SW radiances have a good correlation with CERES data, there is a systemic bias between the two data sets. A spectral correction is made for the ERM data using the CERES data. After the correction, the error of the ERM LW radiance is reduced from -3.00 to -0.60 W/sr · m2. For the SW radiance, the bias is reduced from 6.00 to 4.00 W/sr · m2. Based on the ERM in-orbit calibration data, the stability of the ERM LW radiometric response is analyzed, and it is shown that the gains are stable with a variation of less than 1.5% during its first 9 months in orbit. However, the gains at the SW channels have larger changes and exceed 3%. These drifts might be caused by the detector degradation. Also, the NFOV scanner at the SW channel is no longer working after its 8 months in orbit. calibration; Extraterrestrial measurements; Remote sensing; Satellites; atmospheric radiation; atmospheric techniques; Earth Observing System; radiometry; CERES data; Earth radiation budget (ERB); Absolute calibration; absolute radiometric calibration; Broadband communication; CERES flight model; CERES-Aqua data comparison; Clouds and Earth Radiation Energy System; Earth atmosphere observations; Earth Radiation Measurement; Earth Radiation Measurement (ERM); EOS Aqua satellite; ERM calibration validation; ERM data spectral correction; ERM instrument; ERM longwave radiometric response; FengYun-3B satellite; FY-3B satellite; narrow scanning field of view; shortwave band; spectral correction; total waveband channel; unfiltered longwave radiances; unfiltered shortwave radiances; wavelength 0.2 mum to 50 mum; wide nonscanning field of view
Riihimaki, Laura D.; McFarlane, Sally A.; Liang, Calvin; Massie, Steven T.; Beagley, Nathaniel; Toth, Travis D.Riihimaki, L. D., S. A. McFarlane, C. Liang, S. T. Massie, N. Beagley, T. D. Toth, 2012: Comparison of methods to determine Tropical Tropopause Layer cirrus formation mechanisms. Journal of Geophysical Research: Atmospheres, 117(D6), D06218. doi: 10.1029/2011JD016832. A new method of estimating Tropical Tropopause Layer Cirrus (TTLC) formation mechanism (object method) is compared to interpretations of formation from previous studies using back trajectory calculations matched to convection identified from satellites and statistical relationships of TTLC with temperature and water vapor. The object method groups neighboring Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) TTLC cloud profiles into cloud objects and classifies them as convective (35% of TTLC) if they are directly attached to a convective cloud along the CALIPSO track. The percentage of back trajectory calculations that intersect convection (39–95% of TTLC within 5 days) depends strongly on the spatial and temporal resolution of the convection data set, and the manner in which deep convection is identified. Using minimum brightness temperature in 3 hourly, 1° resolution grid boxes to define convection, 46% of non-convective TTLC (37% of all TTLC) did not trace back to convection within 24 h. Back trajectory calculations of thin cirrus identified by the High Resolution Dynamics Limb Sounder (HIRDLS) gave similar results. Temperature is not a good proxy for formation mechanism as convective and non-convective TTLC frequencies both increase monotonically with decreasing temperature at approximately the same rate. Non-convective TTLC frequencies have a stronger relationship with relative humidity than convective TTLC frequencies, though are not sufficiently different to distinguish object method categories. A decrease in TTL cirrus frequency found at low temperatures in previous studies is caused by insufficient variability in reanalysis temperature data and is not indicative of TTLC formation mechanism. 0320 Cloud physics and chemistry; 3310 Clouds and cloud feedbacks; 3362 Stratosphere/troposphere interactions; 3371 Tropical convection; CALIPSO; 3375 Tropopause dynamics; trajectories; Tropical Tropopause Layer Cirrus; TTL
Rodriguez-Solano, C. J.; Hugentobler, U.; Steigenberger, P.Rodriguez-Solano, C. J., U. Hugentobler, P. Steigenberger, 2012: Impact of Albedo Radiation on GPS Satellites. Geodesy for Planet Earth, 113-119. GPS satellite orbits available from the International GNSS Service (IGS) show a peculiar pattern in the SLR residuals at the few centimeter level that is related to radiation pressure mismodeling. Part of the mismodeling may be attributed to neglecting the solar radiation reflected and reemitted from the Earth, the albedo radiation, as most IGS analysis centers do not yet take into account this radiation pressure component. In this study the relative importance of different albedo model constituents is analyzed. The impact of nine albedo models with increasing complexity is investigated using 1 year of global GPS data from the IGS tracking network. The most important model components are the solar panels of the satellites while different Earth radiation models have a minor impact on orbits at GPS altitudes. Albedo radiation has the potential to remove part of the anomalous SLR residual pattern observed by Urschl et al. (Calibrating GNSS orbits with SLR tracking data. Proceedings of the 15th International Workshop on Laser Ranging, 2008) in a Sun-fixed reference frame. Geophysics/Geodesy; Geophysics and Environmental Physics; Geoengineering, Foundations, Hydraulics
Smith, G. Louis; Mlynczak, Pamela E.; Potter, Gerald L.Smith, G. L., P. E. Mlynczak, G. L. Potter, 2012: A technique using principal component analysis to compare seasonal cycles of Earth radiation from CERES and model computations. Journal of Geophysical Research: Atmospheres, 117(D9), D09116. doi: 10.1029/2011JD017343. A method for quantitatively comparing the seasonal cycles of two global data sets is presented. The seasonal cycles of absorbed solar radiation (ASR) and outgoing longwave radiation (OLR) have been computed from an eight-year data set from the Clouds and Earth's Radiant Energy System (CERES) scanning radiometers and from a model data set produced by the NASA Goddard Space Flight Center Global Modeling and Assimilation Office. To compare the seasonal cycles from these two data sets, principal component (PC) analysis is used, where the PCs express the time variations and the corresponding empirical orthogonal functions (EOFs) describe the geographic variations. Ocean has a long thermal response time compared to land, so land and ocean are separated for the analysis. The root-mean square values for the seasonal cycles of ASR and OLR are extremely close for the two data sets. The first three PCs are quite close, showing that the time responses and magnitudes over the globe are very similar. The agreement between the two sets of PCs is quantified by computing the matrix of inner products of the two sets. For ASR over land, the first PCs of CERES and the model agree to better than 99.9%. The EOF maps are similar for most of the globe, but differ in a few places, and the agreement of the EOF maps is likewise quantified. Maps of differences between the annual cycles show regions of agreement and disagreement. 3359 Radiative processes; 0550 Model verification and validation; model validation
Smith, William L.; Minnis, Patrick; Fleeger, Cecilia; Spangenberg, Douglas; Palikonda, Rabindra; Nguyen, LouisSmith, W. L., P. Minnis, C. Fleeger, D. Spangenberg, R. Palikonda, L. Nguyen, 2012: Determining the Flight Icing Threat to Aircraft with Single-Layer Cloud Parameters Derived from Operational Satellite Data. J. Appl. Meteor. Climatol., 51(10), 1794-1810. doi: 10.1175/JAMC-D-12-057.1. AbstractAn algorithm is developed to determine the flight icing threat to aircraft utilizing quantitative information on clouds derived from meteorological satellite data as input. Algorithm inputs include the satellite-derived cloud-top temperature, thermodynamic phase, water path, and effective droplet size. The icing-top and -base altitude boundaries are estimated from the satellite-derived cloud-top and -base altitudes using the freezing level obtained from numerical weather analyses or a lapse-rate approach. The product is available at the nominal resolution of the satellite pixel. Aircraft pilot reports (PIREPs) over the United States and southern Canada provide direct observations of icing and are used extensively in the algorithm development and validation on the basis of correlations with Geostationary Operational Environmental Satellite imager data. Verification studies using PIREPs, Tropospheric Airborne Meteorological Data Reporting, and NASA Icing Remote Sensing System data indicate that the satellite algorithm performs reasonably well, particularly during the daytime. The algorithm is currently being run routinely using data taken from a variety of satellites across the globe and is providing useful information on icing conditions at high spatial and temporal resolutions that are unavailable from any other source. Cloud retrieval; satellite observations; Algorithms; Icing; Nowcasting
Stephens, Graeme L.; Li, Juilin; Wild, Martin; Clayson, Carol Anne; Loeb, Norman; Kato, Seiji; L'Ecuyer, Tristan; Jr, Paul W. Stackhouse; Lebsock, Matthew; Andrews, TimothyStephens, G. L., J. Li, M. Wild, C. A. Clayson, N. Loeb, S. Kato, T. L'Ecuyer, P. W. S. Jr, M. Lebsock, T. Andrews, 2012: An update on Earth's energy balance in light of the latest global observations. Nature Geoscience, 5(10), 691-696. doi: 10.1038/ngeo1580. Climate change is governed by changes to the global energy balance. At the top of the atmosphere, this balance is monitored globally by satellite sensors that provide measurements of energy flowing to and from Earth. By contrast, observations at the surface are limited mostly to land areas. As a result, the global balance of energy fluxes within the atmosphere or at Earth's surface cannot be derived directly from measured fluxes, and is therefore uncertain. This lack of precise knowledge of surface energy fluxes profoundly affects our ability to understand how Earth's climate responds to increasing concentrations of greenhouse gases. In light of compilations of up-to-date surface and satellite data, the surface energy balance needs to be revised. Specifically, the longwave radiation received at the surface is estimated to be significantly larger, by between 10 and 17 Wm−2, than earlier model-based estimates. Moreover, the latest satellite observations of global precipitation indicate that more precipitation is generated than previously thought. This additional precipitation is sustained by more energy leaving the surface by evaporation — that is, in the form of latent heat flux — and thereby offsets much of the increase in longwave flux to the surface. View full text hydrology; Atmospheric science; Climate science; hydrogeology and limnology
Stephens, Graeme L.; Wild, Martin; Stackhouse, Paul W.; L’Ecuyer, Tristan; Kato, Seiji; Henderson, David S.Stephens, G. L., M. Wild, P. W. Stackhouse, T. L’Ecuyer, S. Kato, D. S. Henderson, 2012: The Global Character of the Flux of Downward Longwave Radiation. J. Climate, 25(7), 2329-2340. doi: 10.1175/JCLI-D-11-00262.1. AbstractFour different types of estimates of the surface downwelling longwave radiative flux (DLR) are reviewed. One group of estimates synthesizes global cloud, aerosol, and other information in a radiation model that is used to calculate fluxes. Because these synthesis fluxes have been assessed against observations, the global-mean values of these fluxes are deemed to be the most credible of the four different categories reviewed. The global, annual mean DLR lies between approximately 344 and 350 W m−2 with an error of approximately ±10 W m−2 that arises mostly from the uncertainty in atmospheric state that governs the estimation of the clear-sky emission. The authors conclude that the DLR derived from global climate models are biased low by approximately 10 W m−2 and even larger differences are found with respect to reanalysis climate data. The DLR inferred from a surface energy balance closure is also substantially smaller that the range found from synthesis products suggesting that current depictions of surface energy balance also require revision. The effect of clouds on the DLR, largely facilitated by the new cloud base information from the CloudSat radar, is estimated to lie in the range from 24 to 34 W m−2 for the global cloud radiative effect (all-sky minus clear-sky DLR). This effect is strongly modulated by the underlying water vapor that gives rise to a maximum sensitivity of the DLR to cloud occurring in the colder drier regions of the planet. The bottom of atmosphere (BOA) cloud effect directly contrast the effect of clouds on the top of atmosphere (TOA) fluxes that is maximum in regions of deepest and coldest clouds in the moist tropics. Energy budget/balance; Hydrologic cycle; Climatology; Energy transport; Planetary atmospheres
Sun, Moguo; Cess, Robert D.; Doelling, Dave R.Sun, M., R. D. Cess, D. R. Doelling, 2012: Interpretation of cloud structure anomalies over the tropical Pacific during the 1997/98 El Niño. Journal of Geophysical Research: Atmospheres, 117(D16), D16114. doi: 10.1029/2011JD015861. Cloud structure changes and their associated radiative property changes over the tropical Pacific Ocean during the strong 1997/98 El Niño are studied using a merged satellite data set from the Clouds and the Earth's Radiant Energy System (CERES) project. This one-degree by one-degree gridded data set provides monthly mean values of radiative fluxes at the top of the atmosphere in addition to cloud fraction, cloud top altitude and cloud optical depth for the first eight months of 1998. This time period includes much of the 1997/98 El Niño, which reached peak intensity in March 1998 and essentially subsided by August 1998. The west-to-east shift of the center of convection that occurred during the El Niño resulted in cloud fraction, cloud top altitude and cloud optical depth increasing in the eastern equatorial Pacific while decreasing in the western tropical Pacific. For both regions all three cloud parameters are strongly correlated with each other and contribute to the strong linear relationship between longwave (LW) and shortwave (SW) cloud-radiative forcings (CRFs). This strong El Niño serves as a suitable test case for climate models. Results using the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM) 4.0 show many of the observed changes in 500 hPa vertical velocity, cloud-radiative forcing, cloud top altitude and cloud fraction within the tropical Pacific during the El Niño event, but fail to capture the observed relationship between radiation anomalies and cloud optical depth anomalies. CERES; cloud; 3337 Global climate models; 3374 Tropical meteorology; 3310 Clouds and cloud feedbacks; climate model; El Niño; cloud radiative forcing; 1626 Global climate models; 4928 Global climate models
Susskind, Joel; Molnar, Gyula; Iredell, Lena; Loeb, Norman G.Susskind, J., G. Molnar, L. Iredell, N. G. Loeb, 2012: Interannual variability of outgoing longwave radiation as observed by AIRS and CERES. Journal of Geophysical Research: Atmospheres, 117(D23), D23107. doi: 10.1029/2012JD017997. The paper examines spatial anomaly time series of outgoing longwave radiation (OLR) and Clear Sky OLR (OLRCLR) as determined using observations from CERES Terra and AIRS over the time period September 2002 through June 2011. We find excellent agreement of the two OLR data sets in almost every detail down to the 1° × 1° spatial grid point level. The extremely close agreement of OLR anomaly time series derived from observations by two different instruments implies high stability of both sets of results. Anomalies of global mean, and especially tropical mean, OLR are shown to be strongly correlated with an El Niño Index. These correlations explain that the recent global and tropical mean decreases in OLR over the time period studied are primarily the result of a transition from an El Niño condition at the beginning of the data record to La Niña conditions toward the end of the data period. We show that the close correlation of mean OLR anomalies with the El Niño Index can be well accounted for by temporal changes of OLR within two spatial regions, one to the east of, and one to the west of, the NOAA Niño-4 region. Anomalies of OLR in these two spatial regions are both strongly correlated with the El Niño Index as a result of the strong anticorrelation of anomalies of cloud cover and midtropospheric water vapor in these two regions with the El Niño Index. 1640 Remote sensing; CERES; 1616 Climate variability; AIRS; OLR; el nino
Taylor, Patrick C.Taylor, P. C., 2012: The Role of Clouds: An Introduction and Rapporteur Report. Surveys in Geophysics, 33(3-4), 609-617. doi: 10.1007/s10712-012-9182-2. This paper presents an overview of discussions during the Cloud’s Role session at the Observing and Modelling Earth’s Energy Flows Workshop. N. Loeb and B. Soden convened this session including 10 presentations by B. Stevens, B. Wielicki, G. Stephens, A. Clement, K. Sassen, D. Hartmann, T. Andrews, A. Del Genio, H. Barker, and M. Sugi addressing critical aspects of the role of clouds in modulating Earth energy flows. Presentation topics covered a diverse range of areas from cloud microphysics and dynamics, cloud radiative transfer, and the role of clouds in large-scale atmospheric circulations patterns in both observations and atmospheric models. The presentations and discussions, summarized below, are organized around several key questions raised during the session. (1) What is the best way to evaluate clouds in climate models? (2) How well do models need to represent clouds to be acceptable for making climate predictions? (3) What are the largest uncertainties in clouds? (4) How can these uncertainties be reduced? (5) What new observations are needed to address these problems? Answers to these critical questions are the topics of ongoing research and will guide the future direction of this area of research. clouds; cloud feedback; cloud radiative forcing; Geophysics/Geodesy; Astronomy, Observations and Techniques; Earth Sciences, general; Cloud uncertainties; Model cloud evaluation
Taylor, Patrick C.Taylor, P. C., 2012: Tropical Outgoing Longwave Radiation and Longwave Cloud Forcing Diurnal Cycles from CERES. J. Atmos. Sci., 69(12), 3652-3669. doi: 10.1175/JAS-D-12-088.1. AbstractThe diurnal cycle is a fundamental earth system variability driven by daily variations in solar insolation. Understanding diurnal variability is important for characterizing top-of-atmosphere and surface energy budgets. Climatological and seasonal first diurnal cycle harmonics of outgoing longwave radiation (OLR) and longwave cloud forcing (LWCF) are investigated using the Clouds and the Earth’s Radiant Energy System (CERES) synoptic 3-hourly data. A comparison with previous studies indicates generally similar results. However, the results indicate that the CERES OLR diurnal cycle amplitudes are 10%–20% larger in desert regions than previous analyses. This difference results from the temporal interpolation technique overestimating the daily maximum OLR. OLR diurnal cycle amplitudes in other tropical regions agree with previous work. Results show that the diurnal maximum and minimum OLR variability contributes equally to the total OLR variance over ocean; however, over land the diurnal maximum OLR variance contributes at least 50% more to the total OLR variability than the minimum OLR. The differences in maximum and minimum daily OLR variability are largely due to differences in surface temperature standard deviations at these times, about 5–6 and 3–4 K, respectively. The OLR variance at diurnal maximum and minimum is also influenced by negative and positive correlations, respectively, between LWCF and clear-sky OLR. The anticorrelation between LWCF and clear-sky OLR at diurnal OLR maximum indicates smaller cloud fractions at warmer surface temperatures. The relationship between LWCF and clear-sky OLR at diurnal minimum OLR appears to result from a preference for deep convection, more high clouds, and larger LWCF values to occur with warmer surface temperatures driving a narrower diurnal minimum OLR distribution. longwave radiation; Cloud radiative effects; Diurnal effects
Tobin, Isabelle; Bony, Sandrine; Roca, RemyTobin, I., S. Bony, R. Roca, 2012: Observational Evidence for Relationships between the Degree of Aggregation of Deep Convection, Water Vapor, Surface Fluxes, and Radiation. J. Climate, 25(20), 6885-6904. doi: 10.1175/JCLI-D-11-00258.1. AbstractTropical deep convection exhibits complex organization over a wide range of scales. This study investigates the relationships between the spatial organization of deep convection and the large-scale atmospheric state. By using several satellite datasets and reanalyses, and by defining a simple diagnostic of convective aggregation, relationships between the degree of convective aggregation and the amount of water vapor, turbulent surface fluxes, and radiation are highlighted above tropical oceans. When deep convection is more aggregated, the middle and upper troposphere are drier in the convection-free environment, turbulent surface fluxes are enhanced, and the low-level and midlevel cloudiness is reduced in the environment. Humidity and cloudiness changes lead to a large increase in outgoing longwave radiation. Cloud changes also result in reduced reflected shortwave radiation. Owing to these opposing effects, the sensitivity of the radiative budget at the top of the atmosphere to convective aggregation turns out to be weak, but the distribution of radiative heating throughout the troposphere is affected. These results suggest that feedbacks between convective aggregation and the large-scale atmospheric state might influence large-scale dynamics and the transports of water and energy and, thus, play a role in the climate variability and change. These observational findings are qualitatively consistent with previous cloud-resolving model results, except for the effects on cloudiness and reflected shortwave radiation. The proposed methodology may be useful for assessing the representation of convective aggregation and its interaction with the large-scale atmospheric state in various numerical models. deep convection
Trenberth, Kevin E.; Fasullo, John T.Trenberth, K. E., J. T. Fasullo, 2012: Tracking Earth’s Energy: From El Niño to Global Warming. Surveys in Geophysics, 33(3-4), 413-426. doi: 10.1007/s10712-011-9150-2. The state of knowledge and outstanding issues with respect to the global mean energy budget of planet Earth are described, along with the ability to track changes over time. Best estimates of the main energy components involved in radiative transfer and energy flows through the climate system do not satisfy physical constraints for conservation of energy without adjustments. The main issues relate to the downwelling longwave (LW) radiation and the hydrological cycle, and thus the surface evaporative cooling. It is argued that the discrepancy is 18% of the surface latent energy flux, but only 4% of the downwelling LW flux and, for various reasons, it is most likely that the latter is astray in some calculations, including many models, although there is also scope for precipitation estimates to be revised. Beginning in 2000, the top-of-atmosphere radiation measurements provide stable estimates of the net global radiative imbalance changes over a decade, but after 2004 there is “missing energy” as the observing system of the changes in ocean heat content, melting of land ice, and so on is unable to account for where it has gone. Based upon a number of climate model experiments for the twenty-first century where there are stases in global surface temperature and upper ocean heat content in spite of an identifiable global energy imbalance, we infer that the main sink of the missing energy is likely the deep ocean below 275 m depth. climate change; Ocean heat content; El Niño; global warming; Geophysics/Geodesy; Astronomy, Observations and Techniques; Earth Sciences, general; Atmospheric radiation budget; Earth’s energy
Weng, FuZhong; Liu, QuanHua; Zou, XiaoLeiWeng, F., Q. Liu, X. Zou, 2012: On the environmental information for solar and wind energy facilities. Science China Earth Sciences, 55(5), 796-801. doi: 10.1007/s11430-012-4365-8. Wind and solar energy are projected to be major sources of the world’s power in the coming decades. In this study, we first introduce satellite observations for surface solar irradiance and wind, and then discuss using the data for prediction and assessment of energy distribution. Using the current NCEP global forecast model (GFS), the global mean and standard deviation of solar power at the surface for the 5-d forecast are about 212 and 124 W/m2, respectively. For a 24-h forecast of a 3-h mean, the relative error is about 30%, and for a prediction of the daily mean, it is about 15%. The relative error of wind power forecasts for a 24-h forecast of a 3-h mean and a daily mean is 70% and 35%, respectively. The reanalysis results based on satellite observations and numerical weather prediction model are also used to study the distribution of solar and wind energy and the variation of the distribution related to climate change. No significant trend in downward solar radiation is found at the surface in the reanalysis data sets. Surface wind power however exhibits a significant positive trend as the global temperature is warming up. A comparison of a decadal mean wind energy between two decades (from 1949 to 1958 vs. from 1999 to 2008) shows that most of Asia had experienced a decrease in surface wind energy. Therefore, decisions about renewable energy developments need to consider such climate change scenarios. solar energy; wind energy; Earth Sciences, general; assessment; predictability
Wong, T. M.; Stackhouse Jr, PW; Kratz, D. P.; Wilber, A. C.; Loeb, N. GWong, T. M., P. Stackhouse Jr, D. P. Kratz, A. C. Wilber, N. G. Loeb, 2012: Earth Radiation Budget at Top-of-atmosphere [in "State of the Climate in 2011"]. Bull. Amer. Meteor. Soc., 93(7), S38-S40. doi: 10.1175/2012BAMSStateoftheClimate.1.
Wong, T. M.; Stackhouse Jr, PW; Kratz, D. P.; Wilber, A. C.; Loeb, N. GWong, T. M., P. Stackhouse Jr, D. P. Kratz, A. C. Wilber, N. G. Loeb, 2012: Earth Radiation Budget at Top-of-atmosphere [in "State of the Climate in 2011"]. Bull. Amer. Meteor. Soc., 93(7), S38-S40. doi: 10.1175/2012BAMSStateoftheClimate.1.
Wu, L.; Su, H.; Jiang, J. H.; Read, W. G.Wu, L., H. Su, J. H. Jiang, W. G. Read, 2012: Hydration or dehydration: competing effects of upper tropospheric cloud radiation on the TTL water vapor. Atmos. Chem. Phys., 12(16), 7727-7735. doi: 10.5194/acp-12-7727-2012. A tropical channel version of the Weather Research and Forecasting (WRF) model is used to investigate the radiative impacts of upper tropospheric clouds on water vapor in the tropical tropopause layer (TTL). The WRF simulations of cloud radiative effects and water vapor in the upper troposphere and lower stratosphere show reasonable agreement with observations, including approximate reproduction of the water vapor "tape recorder" signal. By turning on and off the upper tropospheric cloud radiative effect (UTCRE) above 200 hPa, we find that UTCRE induces a warming of 0.76 K and a moistening of 9% in the upper troposphere at 215 hPa. However, UTCRE cools and dehydrates the TTL, with a cooling of 0.82 K and a dehydration of 16% at 100 hPa. The enhanced vertical ascent due to UTCRE contributes substantially to mass transport and the dehydration in the TTL. The hydration due to the enhanced vertical transport is counteracted by the dehydration from adiabatic cooling associated with the enhanced vertical motion. UTCRE also substantially changes the horizontal winds in the TTL, resulting in shifts of the strongest dehydration away from the lowest temperature anomalies in the TTL. UTCRE increases in-situ cloud formation in the TTL. A seasonal variation is shown in the simulated UTCRE, with stronger impact in the moist phase from June to November than in the dry phase from December to May.
Xie, H.; Longuevergne, L.; Ringler, C.; Scanlon, B. R.Xie, H., L. Longuevergne, C. Ringler, B. R. Scanlon, 2012: Calibration and evaluation of a semi-distributed watershed model of Sub-Saharan Africa using GRACE data. Hydrol. Earth Syst. Sci., 16(9), 3083-3099. doi: 10.5194/hess-16-3083-2012. Irrigation development is rapidly expanding in mostly rainfed Sub-Saharan Africa. This expansion underscores the need for a more comprehensive understanding of water resources beyond surface water. Gravity Recovery and Climate Experiment (GRACE) satellites provide valuable information on spatio-temporal variability in water storage. The objective of this study was to calibrate and evaluate a semi-distributed regional-scale hydrologic model based on the Soil and Water Assessment Tool (SWAT) code for basins in Sub-Saharan Africa using seven-year (July 2002–April 2009) 10-day GRACE data and multi-site river discharge data. The analysis was conducted in a multi-criteria framework. In spite of the uncertainty arising from the tradeoff in optimising model parameters with respect to two non-commensurable criteria defined for two fluxes, SWAT was found to perform well in simulating total water storage variability in most areas of Sub-Saharan Africa, which have semi-arid and sub-humid climates, and that among various water storages represented in SWAT, water storage variations in soil, vadose zone and groundwater are dominant. The study also showed that the simulated total water storage variations tend to have less agreement with GRACE data in arid and equatorial humid regions, and model-based partitioning of total water storage variations into different water storage compartments may be highly uncertain. Thus, future work will be needed for model enhancement in these areas with inferior model fit and for uncertainty reduction in component-wise estimation of water storage variations.
Xie, Shaocheng; Ma, Hsi-Yen; Boyle, James S.; Klein, Stephen A.; Zhang, YuyingXie, S., H. Ma, J. S. Boyle, S. A. Klein, Y. Zhang, 2012: On the Correspondence between Short- and Long-Time-Scale Systematic Errors in CAM4/CAM5 for the Year of Tropical Convection. J. Climate, 25(22), 7937-7955. doi: 10.1175/JCLI-D-12-00134.1.
Yang, Weidong; Marshak, Alexander; Várnai, Tamás; Liu, ZhaoyanYang, W., A. Marshak, T. Várnai, Z. Liu, 2012: Effect of CALIPSO cloud–aerosol discrimination (CAD) confidence levels on observations of aerosol properties near clouds. Atmospheric Research, 116, 134-141. doi: 10.1016/j.atmosres.2012.03.013. CALIPSO aerosol backscatter enhancement in the transition zone between clouds and clear sky areas is revisited with particular attention to effects of data selection based on the confidence level of cloud–aerosol discrimination (CAD). The results show that backscatter behavior in the transition zone strongly depends on the CAD confidence level. Higher confidence level data has a flatter backscatter far away from clouds and a much sharper increase near clouds (within 4 km), thus a smaller transition zone. For high confidence level data it is shown that the overall backscatter enhancement is more pronounced for small clear-air segments and horizontally larger clouds. The results suggest that data selection based on CAD reduces the possible effects of cloud contamination when studying aerosol properties in the vicinity of clouds. Remote sensing; aerosol; CALIPSO; Backscatter enhancement; Transition zone; Twilight zone
Yao, Mao-Sung; Cheng, YeYao, M., Y. Cheng, 2012: Cloud Simulations in Response to Turbulence Parameterizations in the GISS Model E GCM. J. Climate, 25(14), 4963-4974. doi: 10.1175/JCLI-D-11-00399.1. AbstractThe response of cloud simulations to turbulence parameterizations is studied systematically using the GISS general circulation model (GCM) E2 employed in the Intergovernmental Panel on Climate Change’s (IPCC) Fifth Assessment Report (AR5). Without the turbulence parameterization, the relative humidity (RH) and the low cloud cover peak unrealistically close to the surface; with the dry convection or with only the local turbulence parameterization, these two quantities improve their vertical structures, but the vertical transport of water vapor is still weak in the planetary boundary layers (PBLs); with both local and nonlocal turbulence parameterizations, the RH and low cloud cover have better vertical structures in all latitudes due to more significant vertical transport of water vapor in the PBL. The study also compares the cloud and radiation climatologies obtained from an experiment using a newer version of turbulence parameterization being developed at GISS with those obtained from the AR5 version. This newer scheme differs from the AR5 version in computing nonlocal transports, turbulent length scale, and PBL height and shows significant improvements in cloud and radiation simulations, especially over the subtropical eastern oceans and the southern oceans. The diagnosed PBL heights appear to correlate well with the low cloud distribution over oceans. This suggests that a cloud-producing scheme needs to be constructed in a framework that also takes the turbulence into consideration. climate models
Yu, Shaocai; Mathur, Rohit; Pleim, Jonathan; Wong, David; Carlton, Annmarie G.; Roselle, Shawn; Rao, S. T.; Shao, YangYu, S., R. Mathur, J. Pleim, D. Wong, A. G. Carlton, S. Roselle, S. T. Rao, Y. Shao, 2012: Simulation of the Indirect Radiative Forcing of Climate Due to Aerosols by the Two-Way Coupled WRF-CMAQ over the Eastern United States. Air Pollution Modeling and its Application XXI, 579-583. In this study, the shortwave cloud forcing (SWCF) and longwave cloud forcing (LWCF) are estimated with the newly developed two-way coupled WRF-CMAQ over the eastern United States. Preliminary indirect aerosol forcing has been successfully implemented in WRF-CMAQ. The comparisons with the observed PM2.5 at the AIRNow sites indicates that the models captured a majority of observed daily PM2.5 within a factor of 2, but generally underestimated the observations in the high PM2.5 concentration range. The domain means of CERES satellite observations, WRF-CMAQ/CAM and WRF-CMAQ/RRTMg for SWCF (LWCF) are −48.1 (31.9), −31.9 (22.6), −19.8 (15.5) watts m−2, respectively. This means that the WRF-CMAQ model generally underestimated the cloud field for the 12-km resolution simulations. Atmospheric Protection/Air Quality Control/Air Pollution; Environmental Monitoring/Analysis; Indirect aerosol forcing; Two-way; WRF-CMAQ
Zib, Behnjamin J.; Dong, Xiquan; Xi, Baike; Kennedy, AaronZib, B. J., X. Dong, B. Xi, A. Kennedy, 2012: Evaluation and Intercomparison of Cloud Fraction and Radiative Fluxes in Recent Reanalyses over the Arctic Using BSRN Surface Observations. J. Climate, 25(7), 2291-2305. doi: 10.1175/JCLI-D-11-00147.1. AbstractWith continual advancements in data assimilation systems, new observing systems, and improvements in model parameterizations, several new atmospheric reanalysis datasets have recently become available. Before using these new reanalyses it is important to assess the strengths and underlying biases contained in each dataset. A study has been performed to evaluate and compare cloud fractions (CFs) and surface radiative fluxes in several of these latest reanalyses over the Arctic using 15 years (1994–2008) of high-quality Baseline Surface Radiation Network (BSRN) observations from Barrow (BAR) and Ny-Alesund (NYA) surface stations. The five reanalyses being evaluated in this study are (i) NASA's Modern-Era Retrospective analysis for Research and Applications (MERRA), (ii) NCEP's Climate Forecast System Reanalysis (CFSR), (iii) NOAA's Twentieth Century Reanalysis Project (20CR), (iv) ECMWF's Interim Reanalysis (ERA-I), and (v) NCEP–Department of Energy (DOE)'s Reanalysis II (R2). All of the reanalyses show considerable bias in reanalyzed CF during the year, especially in winter. The large CF biases have been reflected in the surface radiation fields, as monthly biases in shortwave (SW) and longwave (LW) fluxes are more than 90 (June) and 60 W m−2 (March), respectively, in some reanalyses. ERA-I and CFSR performed the best in reanalyzing surface downwelling fluxes with annual mean biases less than 4.7 (SW) and 3.4 W m−2 (LW) over both Arctic sites. Even when producing the observed CF, radiation flux errors were found to exist in the reanalyses suggesting that they may not always be dependent on CF errors but rather on variations of more complex cloud properties, water vapor content, or aerosol loading within the reanalyses. Radiative fluxes; Model evaluation/performance; Cloud cover; Arctic
Allan, Richard P.Allan, R. P., 2011: Combining satellite data and models to estimate cloud radiative effect at the surface and in the atmosphere. Meteorological Applications, 18(3), 324-333. doi: 10.1002/met.285. Satellite measurements and numerical forecast model reanalysis data are used to compute an updated estimate of the cloud radiative effect on the global multi-annual mean radiative energy budget of the atmosphere and surface. The cloud radiative cooling effect through reflection of short wave radiation dominates over the long wave heating effect, resulting in a net cooling of the climate system of − 21 Wm−2. The short wave radiative effect of cloud is primarily manifest as a reduction in the solar radiation absorbed at the surface of − 53 Wm−2. Clouds impact long wave radiation by heating the moist tropical atmosphere (up to around 40 Wm−2 for global annual means) while enhancing the radiative cooling of the atmosphere over other regions, in particular higher latitudes and sub-tropical marine stratocumulus regimes. While clouds act to cool the climate system during the daytime, the cloud greenhouse effect heats the climate system at night. The influence of cloud radiative effect on determining cloud feedbacks and changes in the water cycle are discussed. Copyright © 2011 Royal Meteorological Society clouds; radiative flux; climate; General circulation models
Allan, Richard P.; Woodage, Margaret J.; Milton, Sean F.; Brooks, Malcolm E.; Haywood, James M.Allan, R. P., M. J. Woodage, S. F. Milton, M. E. Brooks, J. M. Haywood, 2011: Examination of long-wave radiative bias in general circulation models over North Africa during May–July. Quarterly Journal of the Royal Meteorological Society, 137(658), 1179-1192. doi: 10.1002/qj.717. Satellite data are used to quantify and examine the bias in the outgoing long-wave (LW) radiation over North Africa during May–July simulated by a range of climate models and the Met Office global numerical weather prediction (NWP) model. Simulations from an ensemble-mean of multiple climate models overestimate outgoing clear-sky long-wave radiation (LWc) by more than 20 W m−2 relative to observations from Clouds and the Earth's Radiant Energy System (CERES) for May–July 2000 over parts of the west Sahara, and by 9 W m−2 for the North Africa region (20°W–30°E, 10–40°N). Experiments with the atmosphere-only version of the High-resolution Hadley Centre Global Environment Model (HiGEM), suggest that including mineral dust radiative effects removes this bias. Furthermore, only by reducing surface temperature and emissivity by unrealistic amounts is it possible to explain the magnitude of the bias. Comparing simulations from the Met Office NWP model with satellite observations from Geostationary Earth Radiation Budget (GERB) instruments suggests that the model overestimates the LW by 20–40 W m−2 during North African summer. The bias declines over the period 2003–2008, although this is likely to relate to improvements in the model and inhomogeneity in the satellite time series. The bias in LWc coincides with high aerosol dust loading estimated from the Ozone Monitoring Instrument (OMI), including during the GERBILS field campaign (18–28 June 2007) where model overestimates in LWc greater than 20 W m−2 and OMI-estimated aerosol optical depth (AOD) greater than 0.8 are concurrent around 20°N, 0–20°W. A model-minus-GERB LW bias of around 30 W m−2 coincides with high AOD during the period 18–21 June 2007, although differences in cloud cover also impact the model–GERB differences. Copyright © Royal Meteorological Society and Crown Copyright, 2010 satellite data; radiative processes; climate models; mineral dust aerosol
Barker, H. W.; Jerg, M. P.; Wehr, T.; Kato, S.; Donovan, D. P.; Hogan, R. J.Barker, H. W., M. P. Jerg, T. Wehr, S. Kato, D. P. Donovan, R. J. Hogan, 2011: A 3D cloud-construction algorithm for the EarthCARE satellite mission. Quarterly Journal of the Royal Meteorological Society, 137(657), 1042-1058. doi: 10.1002/qj.824. This article presents and assesses an algorithm that constructs 3D distributions of cloud from passive satellite imagery and collocated 2D nadir profiles of cloud properties inferred synergistically from lidar, cloud radar and imager data. It effectively widens the active–passive retrieved cross-section (RXS) of cloud properties, thereby enabling computation of radiative fluxes and radiances that can be compared with measured values in an attempt to perform radiative closure experiments that aim to assess the RXS. For this introductory study, A-train data were used to verify the scene-construction algorithm and only 1D radiative transfer calculations were performed. The construction algorithm fills off-RXS recipient pixels by computing sums of squared differences (a cost function F) between their spectral radiances and those of potential donor pixels/columns on the RXS. Of the RXS pixels with F lower than a certain value, the one with the smallest Euclidean distance to the recipient pixel is designated as the donor, and its retrieved cloud properties and other attributes such as 1D radiative heating rates are consigned to the recipient. It is shown that both the RXS itself and Moderate Resolution Imaging Spectroradiometer (MODIS) imagery can be reconstructed extremely well using just visible and thermal infrared channels. Suitable donors usually lie within 10 km of the recipient. RXSs and their associated radiative heating profiles are reconstructed best for extensive planar clouds and less reliably for broken convective clouds. Domain-average 1D broadband radiative fluxes at the top of the atmosphere (TOA) for (21 km)2 domains constructed from MODIS, CloudSat and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) data agree well with coincidental values derived from Clouds and the Earth's Radiant Energy System (CERES) radiances: differences between modelled and measured reflected shortwave fluxes are within ±10 W m−2 for ∼35% of the several hundred domains constructed for eight orbits. Correspondingly, for outgoing longwave radiation ∼65% are within ±10 W m−2. Copyright © 2011 Royal Meteorological Society and Crown in the right of Canada cloud; radiative transfer; Satellite; EarthCARE
Bender, Frida A.-M.; Charlson, Robert J.; Ekman, Annica M. L.; Leahy, Louise V.Bender, F. A., R. J. Charlson, A. M. L. Ekman, L. V. Leahy, 2011: Quantification of Monthly Mean Regional-Scale Albedo of Marine Stratiform Clouds in Satellite Observations and GCMs. J. Appl. Meteor. Climatol., 50(10), 2139-2148. doi: 10.1175/JAMC-D-11-049.1. AbstractPlanetary albedo—the reflectivity for solar radiation—is of singular importance in determining the amount of solar energy taken in by the Earth–atmosphere system. Modeling albedo, and specifically cloud albedo, correctly is crucial for realistic climate simulations. A method is presented herein by which regional cloud albedo can be quantified from the relation between total albedo and cloud fraction, which in observations is found to be approximately linear on a monthly mean scale. This analysis is based primarily on the combination of cloud fraction data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and albedo data from the Clouds and the Earth’s Radiant Energy System (CERES), but the results presented are also supported by the combination of cloud fraction and proxy albedo data from satelliteborne lidar [Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO)]. These data are measured and derived completely independently from the CERES–MODIS data. Applied to low-level marine stratiform clouds in three regions (off the coasts of South America, Africa, and North America), the analysis reveals regionally uniform monthly mean cloud albedos, indicating that the variation in cloud shortwave radiative properties is small on this scale. A coherent picture of low “effective” cloud albedo emerges, in the range from 0.35 to 0.42, on the basis of data from CERES and MODIS. In its simplicity, the method presented appears to be useful as a diagnostic tool and as a constraint on climate models. To demonstrate this, the same method is applied to cloud fraction and albedo output from several current-generation climate models [from the Coupled Model Intercomparison Project, phase 3 (CMIP3), archive]. Although the multimodel mean cloud albedo estimates agree to within 20% with the satellite-based estimates for the three focus regions, model-based estimates of cloud albedo are found to display much larger variability than do the observations, within individual models as well as between models. albedo; satellite observations; Model evaluation/performance; Cloud cover; Cloud radiative effects
Berrisford, P.; Kållberg, P.; Kobayashi, S.; Dee, D.; Uppala, S.; Simmons, A. J.; Poli, P.; Sato, H.Berrisford, P., P. Kållberg, S. Kobayashi, D. Dee, S. Uppala, A. J. Simmons, P. Poli, H. Sato, 2011: Atmospheric conservation properties in ERA-Interim. Quarterly Journal of the Royal Meteorological Society, 137(659), 1381-1399. doi: 10.1002/qj.864. We study the global atmospheric budgets of mass, moisture, energy and angular momentum in the latest reanalysis from the European Centre for Medium-Range Weather Forecasts (ECMWF), ERA-Interim, for the period 1989–2008 and compare with ERA-40. Most of the measures we use indicate that the ERA-Interim reanalysis is superior in quality to ERA-40. In ERA-Interim the standard deviation of the monthly mean global dry mass of 0.7 kg m−2 (0.007%) is slightly worse than in ERA-40, and long time-scale variations in dry mass originate predominately in the surface pressure field. The divergent winds are improved in ERA-Interim: the global standard deviation of the time-averaged dry mass budget residual is 10 kg m−2 day−1 and the quality of the cross-equatorial mass fluxes is improved. The temporal variations in the global evaporation minus precipitation (E − P) are too large but the global moisture budget residual is 0.003 kg m−2 day−1 with a spatial standard deviation of 0.3 kg m−2 day−1. Both the E − P over ocean and P − E over land are about 15% larger than the 1.1 Tg s−1 transport of water from ocean to land. The top of atmosphere (TOA) net energy losses are improved, with a value of 1 W m−2, but the meridional gradient of the TOA net energy flux is smaller than that from the Clouds and the Earth's Radiant Energy System (CERES) data. At the surface the global energy losses are worse, with a value of 7 W m−2. Over land however, the energy loss is only 0.5 W m−2. The downwelling thermal radiation at the surface in ERA-Interim of 341 W m−2 is towards the higher end of previous estimates. The global mass-adjusted energy budget residual is 8 W m−2 with a spatial standard deviation of 11 W m−2, and the mass-adjusted atmospheric energy transport from low to high latitudes (the sum for the two hemispheres) is 9.5 PW. Copyright © 2011 Royal Meteorological Society Moisture; angular momentum; Budgets; energy; ERA; mass
Bosilovich, Michael G.; Robertson, Franklin R.; Chen, JunyeBosilovich, M. G., F. R. Robertson, J. Chen, 2011: Global Energy and Water Budgets in MERRA. J. Climate, 24(22), 5721-5739. doi: 10.1175/2011JCLI4175.1. AbstractReanalyses, retrospectively analyzing observations over climatological time scales, represent a merger between satellite observations and models to provide globally continuous data and have improved over several generations. Balancing the earth’s global water and energy budgets has been a focus of research for more than two decades. Models tend to their own climate while remotely sensed observations have had varying degrees of uncertainty. This study evaluates the latest NASA reanalysis, the Modern Era Retrospective-Analysis for Research and Applications (MERRA), from a global water and energy cycles perspective, to place it in context of previous work and demonstrate the strengths and weaknesses.MERRA was configured to provide complete budgets in its output diagnostics, including the incremental analysis update (IAU), the term that represents the observations influence on the analyzed states, alongside the physical flux terms. Precipitation in reanalyses is typically sensitive to the observational analysis. For MERRA, the global mean precipitation bias and spatial variability are more comparable to merged satellite observations [the Global Precipitation and Climatology Project (GPCP) and Climate Prediction Center Merged Analysis of Precipitation (CMAP)] than previous generations of reanalyses. MERRA ocean evaporation also has a much lower value, which is comparable to independently derived estimate datasets. The global energy budget shows that MERRA cloud effects may be generally weak, leading to excess shortwave radiation reaching the ocean surface.Evaluating the MERRA time series of budget terms, a significant change occurs that does not appear to be represented in observations. In 1999, the global analysis increments of water vapor changes sign from negative to positive and primarily lead to more oceanic precipitation. This change is coincident with the beginning of Advanced Microwave Sounding Unit (AMSU) radiance assimilation. Previous and current reanalyses all exhibit some sensitivity to perturbations in the observation record, and this remains a significant research topic for reanalysis development. The effect of the changing observing system is evaluated for MERRA water and energy budget terms. Energy budget/balance; satellite observations; Precipitation; Evaporation; Water budget
Chen, Lin; , Guangyu Shi; , Shiguang Qin; , Su Yang; , Peng ZhangChen, L., G. S. , S. Q. , S. Y. , P. Z. , 2011: Direct radiative forcing of anthropogenic aerosols over oceans from satellite observations. Advances in Atmospheric Sciences, 28(4), 973-984. doi: 10.1007/s00376-010-9210-4. Anthropogenic aerosols play an important role in the atmospheric energy balance. Anthropogenic aerosol optical depth (AOD) and its accompanying shortwave radiative forcing (RF) are usually simulated by numerical models. Recently, with the development of space-borne instruments and sophisticated retrieval algorithms, it has become possible to estimate aerosol radiative forcing based on satellite observations. In this study, we have estimated shortwave direct radiative forcing due to anthropogenic aerosols over oceans in all-sky conditions by combining clouds and the Single Scanner Footprint data of the Clouds and Earth’s Radiant Energy System (CERES/SSF) experiment, which provide measurements of upward shortwave fluxes at the top of atmosphere, with Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol and cloud products. We found that globally averaged aerosol radiative forcing over oceans in the clear-sky conditions and all-sky conditions were −1.03±0.48 W m−2 and −0.34 ±0.16 W m−2, respectively. Direct radiative forcing by anthropogenic aerosols shows large regional and seasonal variations. In some regions and in particular seasons, the magnitude of direct forcing by anthropogenic aerosols can be comparable to the forcing of greenhouse gases. However, it shows that aerosols caused the cooling effect, rather than warming effect from global scale, which is different from greenhouse gases. Meteorology/Climatology; satellite measurements; Geophysics/Geodesy; anthropogenic aerosols optical depth; shortwave radiative forcing
Chou, Ming-Dah; Wu, Chi-Hua; Kau, Wen-ShungChou, M., C. Wu, W. Kau, 2011: Large-Scale Control of Summer Precipitation in Taiwan. J. Climate, 24(19), 5081-5093. doi: 10.1175/2011JCLI4057.1. AbstractTaiwan is located at the western stretch of the North Pacific high pressure (NP high) ridge in boreal summer, and its climate is highly sensitive to the NP high. By grouping years of anomalously high and low summer precipitation in Taiwan, this study investigated the large-scale atmospheric circulation and the land–sea temperature contrast during these two groups of years and identified the control of summer precipitation in Taiwan. It is found that in years when summer precipitation in Taiwan is anomalously high, the western stretch of the NP high weakens. Weakening of the western stretch of the NP high induces strengthened southerly wind and enhanced vertical motion in East Asia and the western NP (EA–WNP) region, which is essentially an invigorated summer monsoon circulation. Corresponding to the invigorated circulation, precipitation increases in the southern section of the EA–WNP but decreases in the midlatitude section of the EA–WNP. It is further found that in those wet years, the land–sea temperature contrast between Asia and the surrounding seas is anomalously large and that the westerly wind in the tropical Indian Ocean and the southerly wind in the South China Sea and the subtropical East Asia are strengthened, which is an accelerated cyclonic circulation surrounding South and Southeast Asia. Coincident with the invigorated monsoon circulation in the EA–WNP region is a weakened Asian high pressure (Asian high). This is in variance with the expectation that the invigorated monsoon circulation in the EA–WNP region is related to a strengthened Asian high. The weakened Asian high is related to the weakened monsoon circulation in South and Southeast Asia. It is suggested that these unexpected results might be due to the interannual time scale of this study as opposed to either climatological or decadal scales of previous studies. Precipitation; Asia; Large-scale motions; Monsoons; Summer/warm season
Christopher, Sundar A.Christopher, S. A., 2011: Satellite remote sensing methods for estimating clear Sky shortwave Top of atmosphere fluxes used for aerosol studies over the global oceans. Remote Sensing of Environment, 115(12), 3002-3006. doi: 10.1016/j.rse.2011.06.003. The difference between the top of atmosphere shortwave clear sky (cloud and aerosol free, SWCLR) and aerosol sky radiative fluxes is known as direct radiative effect (DRE) for all aerosols or Direct Climate Forcing (DCF) for anthropogenic aerosols. There are several methods for calculating SWCLR including satellite-based methods and radiative transfer approaches. Since uncertainties in SWCLR can propagate into errors in DRE or DCF, we assess the SWCLR estimates over the global oceans using three approaches and quantify the differences among these methods both as a function of space and season. Our results indicate that the more commonly used intercept (73.4 ± 3.6) and radiative transfer methods (74.7 ± 4.0 Wm− 2) are in close agreement to within ± 1.3 Wm− 2. Values of SWCLR are provided as a function of space and season that can be used by other studies that require such values or as a source of validation. We further recommend that research studies report the methods and assumptions used to estimate SWCLR to facilitate easier intercomparisons among methods. CERES; aerosol; Solar radiation; MODIS; climate forcing
Cole, Jason; Barker, Howard W.; Loeb, Norman G.; von Salzen, KnutCole, J., H. W. Barker, N. G. Loeb, K. von Salzen, 2011: Assessing Simulated Clouds and Radiative Fluxes Using Properties of Clouds Whose Tops are Exposed to Space. J. Climate, 24(11), 2715-2727. doi: 10.1175/2011JCLI3652.1. AbstractCoincident top-of-atmosphere (TOA) radiative fluxes and cloud optical properties for portions of clouds whose tops are exposed to space within several pressure ranges are used to evaluate how a GCM realizes its all-sky radiative fluxes and vertical structure. In particular, observations of cloud properties and radiative fluxes from the Clouds and the Earth’s Radiant Energy System (CERES) Science Team are used to assess the Canadian Centre for Climate Modeling and Analysis atmospheric global climate model (CanAM4). Through comparison of CanAM4 with CERES observations it was found that, while the July-mean all-sky TOA shortwave and longwave fluxes simulated by CanAM4 agree well with those observed, this agreement rests on compensating biases in simulated cloud properties and radiative fluxes for low, middle, and high clouds. Namely, low and middle cloud albedos simulated by CanAM4 are larger than those observed by CERES attributable to CanAM4 simulating cloud optical depths via large liquid water paths that are too large but are partly compensated by too small cloud fractions. It was also found that CanAM4 produces 2D histograms of cloud fraction and cloud albedo for low, middle, and high clouds that are significantly different than generated using the CERES observations. clouds; Remote sensing; albedo; Radiative fluxes; Optical properties; climate models
Domenech, C.; Wehr, T.Domenech, C., T. Wehr, 2011: Use of Artificial Neural Networks to Retrieve TOA SW Radiative Fluxes for the EarthCARE Mission. IEEE Transactions on Geoscience and Remote Sensing, 49(6), 1839-1849. doi: 10.1109/TGRS.2010.2102768. The Earth Clouds, Aerosols, and Radiation Explorer (EarthCARE) mission responds to the need to improve the understanding of the interactions between cloud, aerosol, and radiation processes. The fundamental mission objective is to constrain retrievals of cloud and aerosol properties such that their impact on top-of-atmosphere (TOA) radiative fluxes can be determined with an accuracy of 10 W · m-2. However, TOA fluxes cannot be measured instantaneously from a satellite. For the EarthCARE mission, fluxes will be estimated from the observed solar and thermal radiances measured by the Broadband Radiometer (BBR). This paper describes an approach to obtain shortwave (SW) fluxes from BBR radiance measurements. The retrieval algorithms are developed relying on the angular distribution models (ADMs) employed by Clouds and the Earth's Radiant Energy System (CERES) instrument. The solar radiance-to-flux conversion for the BBR is performed by simulating the Terra CERES ADMs us ing a backpropagation artificial neural network (ANN) technique. The ANN performance is optimized by testing different architectures, namely, feedforward, cascade forward, and a customized forward network. A large data set of CERES measurements used to resemble the forthcoming BBR acquisitions has been collected. The CERES BBR-like database is sorted by their surface type, sky conditions, and scene type and then stratified by four input variables (solar zenith angle and BBR SW radiances) to construct three different training data sets. Then, the neural networks are analyzed, and the adequate ADM classification scheme is selected. The results of the BBR ANN-based ADMs show SW flux retrievals compliant with the CERES flux estimates. clouds; Remote sensing; atmospheric radiation; aerosols; cloud; Clouds and the Earth's Radiant Energy System; atmospheric measuring apparatus; radiometry; atmospheric optics; radiative transfer; aerosol; ADM classification scheme; angular distribution models; Angular distribution models (ADMs); anisotropic correction; artificial neural network (ANN); Artificial neural networks; atmospheric radiation process; backpropagation; backpropagation artificial neural network; broadband radiometer; CERES instrument; Earth Clouds, Aerosols, and Radiation Explorer; Earth Clouds, Aerosols, and Radiation Explorer (EarthCARE); EarthCARE mission; Feedforward neural networks; geophysics computing; information retrieval; Input variables; neural nets; Neurons; shortwave flux; solar radiance; solar radiative flux; thermal radiance; TOA SW radiative flux retrieval; top-of-atmosphere radiative flux; Training; Transfer functions
Domenech, C.; Wehr, T.; Fischer, J.Domenech, C., T. Wehr, J. Fischer, 2011: Toward an Earth Clouds, Aerosols and Radiation Explore (EarthCARE) thermal flux determination: Evaluation using Clouds and the Earth's Radiant Energy System (CERES) true along-track data. Journal of Geophysical Research: Atmospheres, 116(D6), D06115. doi: 10.1029/2010JD015212. The Earth Clouds, Aerosols and Radiation Explorer (EarthCARE) mission developed by the European Space Agency and the Japan Aerospace Exploration Agency addresses the need to improve the understanding of the interactions between cloud, aerosol, and radiation processes. The broadband radiometer (BBR) instrument on board the EarthCARE spacecraft provides measurements of broadband reflected solar and emitted thermal radiances at the top of atmosphere (TOA) over the along-track satellite path at three fixed viewing zenith angles. The multiangular information provided by the BBR, combined with the spectral information from the EarthCARE's multispectral imager (MSI) can be exploited to construct accurate thermal radiance-to-flux conversion algorithms on the basis of radiative transfer modeling. In this study, the methodology to derive longwave (LW) fluxes from BBR and MSI data is described, and the performance of the LW BBR angular models is compared with the Clouds and the Earth's Radiant Energy System (CERES) Terra flux retrievals in order to evaluate the reliability of the BBR synthetic models when applied to satellite-based radiances. For this purpose, the BBR methodology proposed in this work is adapted to the CERES and the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument specifications, and new LW angular models for CERES are developed. According to plane-parallel simulations, the BBR LW flux uncertainty caused by flux inversion could be reduced up to 0.4 W m−2. The intercomparison between CERES BBR-like adapted and CERES original angular models is performed over a BBR-like database of CERES true along track, and the averaged instantaneous retrievals agree to within 2 W m−2. 1610 Atmosphere; 1640 Remote sensing; radiative transfer; 3309 Climatology; 3359 Radiative processes; angular distribution models; broadband radiometer; EarthCARE; Clouds and the Earth's Radiant Energy System (CERES); thermal fluxes
Domenech, Carlos; Lopez-Baeza, Ernesto; Donovan, David P.; Wehr, TobiasDomenech, C., E. Lopez-Baeza, D. P. Donovan, T. Wehr, 2011: Radiative Flux Estimation from a Broadband Radiometer Using Synthetic Angular Models in the EarthCARE Mission Framework. Part I: Methodology. J. Appl. Meteor. Climatol., 50(5), 974-993. doi: 10.1175/2010JAMC2526.1. AbstractThe forthcoming broadband radiometer (BBR) on board the Earth Clouds, Aerosols, and Radiation Explorer (EarthCARE) will provide quasi-instantaneous top-of-atmosphere radiance measurements for three different viewing angles. The role of BBR data will be to constrain the vertical radiative flux divergence profiles derived from EarthCARE measurements. Thus, the development of an instantaneous radiance-to-flux conversion procedure is of paramount importance. This paper studies the scientific basis for determining fluxes from radiances measured by the BBR instrument. This is an attempt to evaluate a possible solution and assess its potential advantages and drawbacks. The approach considered has been to construct theoretical angular distribution models (ADMs) based on the multiangular pointing feature of this instrument. This configuration provides extra information on the anisotropy of the observed radiance field, which can be employed to construct accurate inversion schemes. The proposal relies on radiative transfer calculations performed with a Monte Carlo algorithm. Considering the intrinsic difficulty associated with addressing the range of atmospheric conditions needed to determine reliable ADMs, a synthetic database has been thoroughly constructed that considers a diverse range of surface, atmospheric, and cloud conditions that are conditioned to the EarthCARE orbit and physical constraints. Three inversion methodologies have been specifically designed for the BBR flux retrieval algorithm. In particular, an optimized classical inversion procedure in which the definition of an effective radiance leads to derive fluxes with averaged errors up to 1.2 and 5.2 W m−2 for shortwave clear and cloudy sky and 1.5 W m−2 for longwave radiation scenes and a linear combination of the three instantaneous radiances from which averaged errors up to 0.4 and 2.7 W m−2 for shortwave clear and cloudy sky and 0.5 W m−2 for longwave scenes can be obtained. satellite observations; Fluxes; radiation
Dong, Xiquan; Xi, Baike; Kennedy, Aaron; Feng, Zhe; Entin, Jared K.; Houser, Paul R.; Schiffer, Robert A.; L'Ecuyer, Tristan; Olson, William S.; Hsu, Kuo-lin; Liu, W. Timothy; Lin, Bing; Deng, Yi; Jiang, TianyuDong, X., B. Xi, A. Kennedy, Z. Feng, J. K. Entin, P. R. Houser, R. A. Schiffer, T. L'Ecuyer, W. S. Olson, K. Hsu, W. T. Liu, B. Lin, Y. Deng, T. Jiang, 2011: Investigation of the 2006 drought and 2007 flood extremes at the Southern Great Plains through an integrative analysis of observations. Journal of Geophysical Research: Atmospheres, 116(D3), D03204. doi: 10.1029/2010JD014776. Hydrological years 2006 (HY06; October 2005 to September 2006) and 2007 (HY07; October 2006 to September 2007) provide a unique opportunity to examine hydrological extremes in the central United States because there are no other examples of two such highly contrasting precipitation extremes occurring in consecutive years at the Southern Great Plains (SGP) in recorded history. The HY06 annual precipitation in the state of Oklahoma, as observed by the Oklahoma Mesonet, is around 61% of the normal (92.84 cm, based on the 1921–2008 climatology), which results in HY06 as the second-driest year in the record. In particular, the total precipitation during the winter of 2005–2006 is only 27% of the normal, and this winter ranks as the driest season. On the other hand, the HY07 annual precipitation amount is 121% of the normal, and HY07 ranks as the seventh-wettest year for the entire state and the wettest year for the central region of the state. Summer 2007 is the second-wettest season for the state. Large-scale dynamics play a key role in these extreme events. During the extreme dry period (11/2005–02/2006), a dipole pattern in the 500 hPa geopotential height anomaly existed where an anomalous high was over the southwestern U.S. region and an anomalous low was over the Great Lakes. This pattern is associated with inhibited moisture transport from the Gulf of Mexico and strong sinking motion over the SGP, both contributing to the extreme dryness. The precipitation deficit over the SGP during the extreme dry period is clearly linked to significantly suppressed cyclonic activity over the southwestern United States, which shows a robust relationship with the western Pacific teleconnection pattern. The precipitation events during the extreme wet period (May–July 2007) were initially generated by active synoptic weather patterns, linked with moisture transport from the Gulf of Mexico by the northward low-level jet, and enhanced the frequency of thunderstorms and their associated latent heat release. Although the drought and pluvial conditions are dominated by large-scale dynamic patterns, we have found two possible positive feedback processes during the extreme dry and wet periods in this study that play key certain roles to maintain and reinforce the length and severity of existing drought and flood events. For example, during the extreme dry period, with less clouds, liquid water path, precipitable water vapor, precipitation, and thinner Cu cloud thickness, more net radiation was absorbed and used to evaporate water from the ground. The evaporated moisture, however, was removed by low-level divergence. Thus, with less precipitation and removed atmospheric moisture, more absorbed incoming solar radiation was used to increase surface temperature and to make the ground drier. cloud; 0321 Cloud/radiation interaction; radiation; Precipitation; drought; 1812 Drought; 1817 Extreme events; 1821 Floods; extreme; flood
Donner, Leo J.; Wyman, Bruce L.; Hemler, Richard S.; Horowitz, Larry W.; Ming, Yi; Zhao, Ming; Golaz, Jean-Christophe; Ginoux, Paul; Lin, S.-J.; Schwarzkopf, M. Daniel; Austin, John; Alaka, Ghassan; Cooke, William F.; Delworth, Thomas L.; Freidenreich, Stuart M.; Gordon, C. T.; Griffies, Stephen M.; Held, Isaac M.; Hurlin, William J.; Klein, Stephen A.; Knutson, Thomas R.; Langenhorst, Amy R.; Lee, Hyun-Chul; Lin, Yanluan; Magi, Brian I.; Malyshev, Sergey L.; Milly, P. C. D.; Naik, Vaishali; Nath, Mary J.; Pincus, Robert; Ploshay, Jeffrey J.; Ramaswamy, V.; Seman, Charles J.; Shevliakova, Elena; Sirutis, Joseph J.; Stern, William F.; Stouffer, Ronald J.; Wilson, R. John; Winton, Michael; Wittenberg, Andrew T.; Zeng, FanrongDonner, L. J., B. L. Wyman, R. S. Hemler, L. W. Horowitz, Y. Ming, M. Zhao, J. Golaz, P. Ginoux, S. Lin, M. D. Schwarzkopf, J. Austin, G. Alaka, W. F. Cooke, T. L. Delworth, S. M. Freidenreich, C. T. Gordon, S. M. Griffies, I. M. Held, W. J. Hurlin, S. A. Klein, T. R. Knutson, A. R. Langenhorst, H. Lee, Y. Lin, B. I. Magi, S. L. Malyshev, P. C. D. Milly, V. Naik, M. J. Nath, R. Pincus, J. J. Ploshay, V. Ramaswamy, C. J. Seman, E. Shevliakova, J. J. Sirutis, W. F. Stern, R. J. Stouffer, R. J. Wilson, M. Winton, A. T. Wittenberg, F. Zeng, 2011: The Dynamical Core, Physical Parameterizations, and Basic Simulation Characteristics of the Atmospheric Component AM3 of the GFDL Global Coupled Model CM3. J. Climate, 24(13), 3484-3519. doi: 10.1175/2011JCLI3955.1. AbstractThe Geophysical Fluid Dynamics Laboratory (GFDL) has developed a coupled general circulation model (CM3) for the atmosphere, oceans, land, and sea ice. The goal of CM3 is to address emerging issues in climate change, including aerosol–cloud interactions, chemistry–climate interactions, and coupling between the troposphere and stratosphere. The model is also designed to serve as the physical system component of earth system models and models for decadal prediction in the near-term future—for example, through improved simulations in tropical land precipitation relative to earlier-generation GFDL models. This paper describes the dynamical core, physical parameterizations, and basic simulation characteristics of the atmospheric component (AM3) of this model. Relative to GFDL AM2, AM3 includes new treatments of deep and shallow cumulus convection, cloud droplet activation by aerosols, subgrid variability of stratiform vertical velocities for droplet activation, and atmospheric chemistry driven by emissions with advective, convective, and turbulent transport. AM3 employs a cubed-sphere implementation of a finite-volume dynamical core and is coupled to LM3, a new land model with ecosystem dynamics and hydrology. Its horizontal resolution is approximately 200 km, and its vertical resolution ranges approximately from 70 m near the earth’s surface to 1 to 1.5 km near the tropopause and 3 to 4 km in much of the stratosphere. Most basic circulation features in AM3 are simulated as realistically, or more so, as in AM2. In particular, dry biases have been reduced over South America. In coupled mode, the simulation of Arctic sea ice concentration has improved. AM3 aerosol optical depths, scattering properties, and surface clear-sky downward shortwave radiation are more realistic than in AM2. The simulation of marine stratocumulus decks remains problematic, as in AM2. The most intense 0.2% of precipitation rates occur less frequently in AM3 than observed. The last two decades of the twentieth century warm in CM3 by 0.32°C relative to 1881–1920. The Climate Research Unit (CRU) and Goddard Institute for Space Studies analyses of observations show warming of 0.56° and 0.52°C, respectively, over this period. CM3 includes anthropogenic cooling by aerosol–cloud interactions, and its warming by the late twentieth century is somewhat less realistic than in CM2.1, which warmed 0.66°C but did not include aerosol–cloud interactions. The improved simulation of the direct aerosol effect (apparent in surface clear-sky downward radiation) in CM3 evidently acts in concert with its simulation of cloud–aerosol interactions to limit greenhouse gas warming. clouds; aerosols; Coupled models; sea ice; Model evaluation/performance; General circulation models; parameterization
Donohoe, Aaron; Battisti, David S.Donohoe, A., D. S. Battisti, 2011: Atmospheric and Surface Contributions to Planetary Albedo. J. Climate, 24(16), 4402-4418. doi: 10.1175/2011JCLI3946.1. AbstractThe planetary albedo is partitioned into a component due to atmospheric reflection and a component due to surface reflection by using shortwave fluxes at the surface and top of the atmosphere in conjunction with a simple radiation model. The vast majority of the observed global average planetary albedo (88%) is due to atmospheric reflection. Surface reflection makes a relatively small contribution to planetary albedo because the atmosphere attenuates the surface contribution to planetary albedo by a factor of approximately 3. The global average planetary albedo in the ensemble average of phase 3 of the Coupled Model Intercomparison Project (CMIP3) preindustrial simulations is also primarily (87%) due to atmospheric albedo. The intermodel spread in planetary albedo is relatively large and is found to be predominantly a consequence of intermodel differences in atmospheric albedo, with surface processes playing a much smaller role despite significant intermodel differences in surface albedo. The CMIP3 models show a decrease in planetary albedo under a doubling of carbon dioxide—also primarily due to changes in atmospheric reflection (which explains more than 90% of the intermodel spread). All models show a decrease in planetary albedo due to the lowered surface albedo associated with a contraction of the cryosphere in a warmer world, but this effect is small compared to the spread in planetary albedo due to model differences in the change in clouds. albedo; Radiation budgets; Shortwave radiation; Model comparison
Eitzen, Zachary A.; Xu, Kuan-Man; Wong, TakmengEitzen, Z. A., K. Xu, T. Wong, 2011: An Estimate of Low-Cloud Feedbacks from Variations of Cloud Radiative and Physical Properties with Sea Surface Temperature on Interannual Time Scales. J. Climate, 24(4), 1106-1121. doi: 10.1175/2010JCLI3670.1. Abstract Simulations of climate change have yet to reach a consensus on the sign and magnitude of the changes in physical properties of marine boundary layer clouds. In this study, the authors analyze how cloud and radiative properties vary with SST anomaly in low-cloud regions, based on five years (March 2000–February 2005) of Clouds and the Earth’s Radiant Energy System (CERES)–Terra monthly gridded data and matched European Centre for Medium-Range Weather Forecasts (ECMWF) meteorological reanalaysis data. In particular, this study focuses on the changes in cloud radiative effect, cloud fraction, and cloud optical depth with SST anomaly. The major findings are as follows. First, the low-cloud amount (−1.9% to −3.4% K−1) and the logarithm of low-cloud optical depth (−0.085 to −0.100 K−1) tend to decrease while the net cloud radiative effect (3.86 W m−2 K−1) becomes less negative as SST anomalies increase. These results are broadly consistent with previous observational studies. Second, after the changes in cloud and radiative properties with SST anomaly are separated into dynamic, thermodynamic, and residual components, changes in the dynamic component (taken as the vertical velocity at 700 hPa) have relatively little effect on cloud and radiative properties. However, the estimated inversion strength decreases with increasing SST, accounting for a large portion of the measured decreases in cloud fraction and cloud optical depth. The residual positive change in net cloud radiative effect (1.48 W m−2 K−1) and small changes in low-cloud amount (−0.81% to 0.22% K−1) and decrease in the logarithm of optical depth (–0.035 to –0.046 K−1) with SST are interpreted as a positive cloud feedback, with cloud optical depth feedback being the dominant contributor. Last, the magnitudes of the residual changes differ greatly among the six low-cloud regions examined in this study, with the largest positive feedbacks (∼4 W m−2 K−1) in the southeast and northeast Atlantic regions and a slightly negative feedback (−0.2 W m−2 K−1) in the south-central Pacific region. Because the retrievals of cloud optical depth and/or cloud fraction are difficult in the presence of aerosols, the transport of heavy African continental aerosols may contribute to the large magnitudes of estimated cloud feedback in the two Atlantic regions. Feedback; sea surface temperature; Optical properties; Cloud radiative effects; Interannual variability
Feldman, Daniel R.; Algieri, Chris A.; Collins, William D.; Roberts, Yolanda L.; Pilewskie, Peter A.Feldman, D. R., C. A. Algieri, W. D. Collins, Y. L. Roberts, P. A. Pilewskie, 2011: Simulation studies for the detection of changes in broadband albedo and shortwave nadir reflectance spectra under a climate change scenario. Journal of Geophysical Research: Atmospheres, 116(D24), D24103. doi: 10.1029/2011JD016407. Climate forcing by greenhouse gases and aerosols and climate feedbacks from snow, sea-ice, and clouds all significantly impact the future evolution of the climate system's shortwave energy budget. We examine prospects for tracking changes in these forcings and feedbacks using top-of-atmosphere measurements of shortwave reflected radiation. We quantify the extent to which spectral measurements may reduce the time required to detect changes in the climate the climate system with high statistical confidence relative to conventional broadband measurements. We have developed an Observing System Simulation Experiment (OSSE) based on the Community Climate System Model 3.0 for the NASA CLARREO mission and have analyzed forced and unforced simulations of the 21st Century from the Intergovernmental Panel on Climate Change assessments. We find that changes in the simulated nadir spectral reflectance measurements in the visible window and between near-infrared water-vapor overtone channels under clear-sky conditions are detectible faster than the corresponding changes in broadband albedo, with many trends detectible within a five-year satellite mission lifetime. Under all-sky conditions, the superposition of unforced cloud variability on the secular climate trends lengthens the times required for climate-change detection in both the spectral and broadband data. However, migration of the ITCZ and stratus regions can be detected after 16–18 years of observation while broadband albedo measurements require 33–61 years of observation. We find that measurement uncertainty and instrument drift significantly lengthen detection times for broadband albedo and spectral reflectances in window channels but do not have the same effect for spectral measurements in water vapor bands. 1640 Remote sensing; 1694 Instruments and techniques; albedo; 1616 Climate variability; 1626 Global climate models; change detection; hyperspectral reflectance
Ferguson, Craig R.; Wood, Eric F.Ferguson, C. R., E. F. Wood, 2011: Observed Land–Atmosphere Coupling from Satellite Remote Sensing and Reanalysis. J. Hydrometeor., 12(6), 1221-1254. doi: 10.1175/2011JHM1380.1. AbstractThe lack of observational data for use in evaluating the realism of model-based land–atmosphere feedback signal and strength has been deemed a major obstacle to future improvements to seasonal weather prediction by the Global Land–Atmosphere Coupling Experiment (GLACE). To address this need, a 7-yr (2002–09) satellite remote sensing data record is exploited to produce for the first time global maps of predominant coupling signals. Specifically, a previously implemented convective triggering potential (CTP)–humidity index (HI) framework for describing atmospheric controls on soil moisture–rainfall feedbacks is revisited and generalized for global application using CTP and HI from the Atmospheric Infrared Sounder (AIRS), soil moisture from the Advanced Microwave Scanning Radiometer for Earth Observing System (EOS) (AMSR-E), and the U.S. Climate Prediction Center (CPC) merged satellite rainfall product (CMORPH). Based on observations taken during an AMSR-E-derived convective rainfall season, the global land area is categorized into four convective regimes: 1) those with atmospheric conditions favoring deep convection over wet soils, 2) those with atmospheric conditions favoring deep convection over dry soils, 3) those with atmospheric conditions that suppress convection over any land surface, and 4) those with atmospheric conditions that support convection over any land surface. Classification maps are produced using both the original and modified frameworks, and later contrasted with similarly derived maps using inputs from the National Aeronautics and Space Administration (NASA) Modern Era Retrospective Analysis for Research and Applications (MERRA). Both AIRS and MERRA datasets of CTP and HI are validated using radiosonde observations. The combinations of methods and data sources employed in this study enable evaluation of not only the sensitivity of the classification schemes themselves to their inputs, but also the uncertainty in the resultant classification maps. The findings are summarized for 20 climatic regions and three GLACE coupling hot spots, as well as zonally and globally. Globally, of the four-class scheme, regions for which convection is favored over wet and dry soils accounted for the greatest and least extent, respectively. Despite vast differences among the maps, many geographically large regions of concurrence exist. Through its ability to compensate for the latitudinally varying CTP–HI–rainfall tendency characteristics observed in this study, the revised classification framework overcomes limitations of the original framework. By identifying regions where coupling persists using satellite remote sensing this study provides the first observationally based guidance for future spatially and temporally focused studies of land–atmosphere interactions. Joint distributions of CTP and HI and soil moisture, rainfall occurrence, and depth demonstrate the relevance of CTP and HI in coupling studies and their potential value in future model evaluation, rainfall forecast, and/or hydrologic consistency applications. Remote sensing; Feedback; satellite data; Atmosphere–land interaction
Golaz, Jean-Christophe; Salzmann, Marc; Donner, Leo J.; Horowitz, Larry W.; Ming, Yi; Zhao, MingGolaz, J., M. Salzmann, L. J. Donner, L. W. Horowitz, Y. Ming, M. Zhao, 2011: Sensitivity of the Aerosol Indirect Effect to Subgrid Variability in the Cloud Parameterization of the GFDL Atmosphere General Circulation Model AM3. J. Climate, 24(13), 3145-3160. doi: 10.1175/2010JCLI3945.1. AbstractThe recently developed GFDL Atmospheric Model version 3 (AM3), an atmospheric general circulation model (GCM), incorporates a prognostic treatment of cloud drop number to simulate the aerosol indirect effect. Since cloud drop activation depends on cloud-scale vertical velocities, which are not reproduced in present-day GCMs, additional assumptions on the subgrid variability are required to implement a local activation parameterization into a GCM.This paper describes the subgrid activation assumptions in AM3 and explores sensitivities by constructing alternate configurations. These alternate model configurations exhibit only small differences in their present-day climatology. However, the total anthropogenic radiative flux perturbation (RFP) between present-day and preindustrial conditions varies by ±50% from the reference, because of a large difference in the magnitude of the aerosol indirect effect. The spread in RFP does not originate directly from the subgrid assumptions but indirectly through the cloud retuning necessary to maintain a realistic radiation balance. In particular, the paper shows a linear correlation between the choice of autoconversion threshold radius and the RFP.Climate sensitivity changes only minimally between the reference and alternate configurations. If implemented in a fully coupled model, these alternate configurations would therefore likely produce substantially different warming from preindustrial to present day. General circulation models; Cloud parameterizations; Condensation; Aerosols/particulates; Cloud droplets
Goldberg, M.; Ohring, G.; Butler, J.; Cao, C.; Datla, R.; Doelling, D.; Gärtner, V.; Hewison, T.; Iacovazzi, B.; Kim, D.; Kurino, T.; Lafeuille, J.; Minnis, P.; Renaut, D.; Schmetz, J.; Tobin, D.; Wang, L.; Weng, F.; Wu, X.; Yu, F.; Zhang, P.; Zhu, T.Goldberg, M., G. Ohring, J. Butler, C. Cao, R. Datla, D. Doelling, V. Gärtner, T. Hewison, B. Iacovazzi, D. Kim, T. Kurino, J. Lafeuille, P. Minnis, D. Renaut, J. Schmetz, D. Tobin, L. Wang, F. Weng, X. Wu, F. Yu, P. Zhang, T. Zhu, 2011: The Global Space-Based Inter-Calibration System. Bull. Amer. Meteor. Soc., 92(4), 467-475. doi: 10.1175/2010BAMS2967.1. The Global Space-based Inter-Calibration System (GSICS) is a new international program to assure the comparability of satellite measurements taken at different times and locations by different instruments operated by different satellite agencies. Sponsored by the World Meteorological Organization and the Coordination Group for Meteorological Satellites, GSICS will intercalibrate the instruments of the international constellation of operational low-earth-orbiting (LEO) and geostationary earth-orbiting (GEO) environmental satellites and tie these to common reference standards. The intercomparability of the observations will result in more accurate measurements for assimilation in numerical weather prediction models, construction of more reliable climate data records, and progress toward achieving the societal goals of the Global Earth Observation System of Systems. GSICS includes globally coordinated activities for prelaunch instrument characterization, onboard routine calibration, sensor intercomparison of near-simultaneous observations of individual scenes or overlapping time series, vicarious calibration using Earth-based or celestial references, and field campaigns. An initial strategy uses high-accuracy satellite instruments, such as the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) and Atmospheric Infrared Sounder (AIRS) and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT)'s Centre National d'Études Spatiales (CNES) Infrared Atmospheric Sounding Interferometer (IASI), as space-based reference standards for intercalibrating the operational satellite sensors. Examples of initial intercalibration results and future plans are presented. Agencies participating in the program include the Centre National d'Études Spatiales, China Meteorological Administration, EUMETSAT, Japan Meteorological Agency, Korea Meteorological Administration, NASA, National Institute of Standards and Technology, and NOAA.
Greuell, Wouter; van Meijgaard, Erik; Clerbaux, Nicolas; Meirink, Jan FokkeGreuell, W., E. van Meijgaard, N. Clerbaux, J. F. Meirink, 2011: Evaluation of Model-Predicted Top-of-Atmosphere Radiation and Cloud Parameters over Africa with Observations from GERB and SEVIRI. J. Climate, 24(15), 4015-4036. doi: 10.1175/2011JCLI3856.1. AbstractThis study compared the Regional Atmospheric Climate Model version 2 (RACMO) with satellite data by simultaneously looking at cloud properties and top-of-atmosphere (TOA) fluxes. This study used cloud properties retrieved from Spinning Enhanced Visible and Infrared Imager (SEVIRI) data and TOA shortwave and longwave outgoing radiative fluxes measured by one of the Geostationary Earth Radiation Budget (GERB) sensors. Both SEVIRI and GERB resolve the diurnal cycle extremely well with 96 images per day. To test the physical parameterizations of the model, RACMO was run for a domain-enclosing Africa and part of the surrounding oceans. Simulations for July 2006, forced at the lateral boundaries by ERA-Interim reanalyses, show generally accurate positioning of the various cloud regimes but also some important model–observation differences, which the authors tried to reduce by altering model parameterizations. These differences are as follows: 1) TOA albedo differences in clear-sky regions like the Sahara and southern Africa. These differences were considerably reduced by prescribing the surface albedo from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data. 2) A considerable overestimation of outgoing longwave radiation within the continental ITCZ caused by the fact that modeled cirrus clouds are far too thin. 3) Underestimation by the model of cloud cover, condensed water path and albedo of the stratocumulus fields off the coast of Angola. The authors reduced these underestimations by suppressing the amount of turbulent mixing above the boundary layer, by prescribing droplet radii derived from SEVIRI data, and by assuming in-cloud horizontal homogeneity for the radiation calculations. 4) Overestimation by the model of the albedo of the trade wind cumulus fields over the Atlantic Ocean. This study argues that this overestimation is likely caused by a model overestimation of condensed water path. In general, the analyses demonstrate the power of the simultaneous evaluation of the TOA fluxes and cloud properties. clouds; Radiative fluxes; satellite observations; Model evaluation/performance; Africa; Regional models
Griffies, Stephen M.; Winton, Michael; Donner, Leo J.; Horowitz, Larry W.; Downes, Stephanie M.; Farneti, Riccardo; Gnanadesikan, Anand; Hurlin, William J.; Lee, Hyun-Chul; Liang, Zhi; Palter, Jaime B.; Samuels, Bonita L.; Wittenberg, Andrew T.; Wyman, Bruce L.; Yin, Jianjun; Zadeh, NikiGriffies, S. M., M. Winton, L. J. Donner, L. W. Horowitz, S. M. Downes, R. Farneti, A. Gnanadesikan, W. J. Hurlin, H. Lee, Z. Liang, J. B. Palter, B. L. Samuels, A. T. Wittenberg, B. L. Wyman, J. Yin, N. Zadeh, 2011: The GFDL CM3 Coupled Climate Model: Characteristics of the Ocean and Sea Ice Simulations. J. Climate, 24(13), 3520-3544. doi: 10.1175/2011JCLI3964.1. AbstractThis paper documents time mean simulation characteristics from the ocean and sea ice components in a new coupled climate model developed at the NOAA Geophysical Fluid Dynamics Laboratory (GFDL). The GFDL Climate Model version 3 (CM3) is formulated with effectively the same ocean and sea ice components as the earlier CM2.1 yet with extensive developments made to the atmosphere and land model components. Both CM2.1 and CM3 show stable mean climate indices, such as large-scale circulation and sea surface temperatures (SSTs). There are notable improvements in the CM3 climate simulation relative to CM2.1, including a modified SST bias pattern and reduced biases in the Arctic sea ice cover. The authors anticipate SST differences between CM2.1 and CM3 in lower latitudes through analysis of the atmospheric fluxes at the ocean surface in corresponding Atmospheric Model Intercomparison Project (AMIP) simulations. In contrast, SST changes in the high latitudes are dominated by ocean and sea ice effects absent in AMIP simulations. The ocean interior simulation in CM3 is generally warmer than in CM2.1, which adversely impacts the interior biases. sea surface temperature; Coupled models; sea ice; Model evaluation/performance; climate models; Atmosphere–ocean interaction; Ocean circulation
Huber, Markus; Mahlstein, Irina; Wild, Martin; Fasullo, John; Knutti, RetoHuber, M., I. Mahlstein, M. Wild, J. Fasullo, R. Knutti, 2011: Constraints on Climate Sensitivity from Radiation Patterns in Climate Models. J. Climate, 24(4), 1034-1052. doi: 10.1175/2010JCLI3403.1. Abstract The estimated range of climate sensitivity, the equilibrium warming resulting from a doubling of the atmospheric carbon dioxide concentration, has not decreased substantially in past decades. New statistical methods for estimating the climate sensitivity have been proposed and provide a better quantification of relative probabilities of climate sensitivity within the almost canonical range of 2–4.5 K; however, large uncertainties remain, in particular for the upper bound. Simple indices of spatial radiation patterns are used here to establish a relationship between an observable radiative quantity and the equilibrium climate sensitivity. The indices are computed for the Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel dataset and offer a possibility to constrain climate sensitivity by considering radiation patterns in the climate system. High correlations between the indices and climate sensitivity are found, for example, in the cloud radiative forcing of the incoming longwave surface radiation and in the clear-sky component of the incoming surface shortwave flux, the net shortwave surface budget, and the atmospheric shortwave attenuation variable β. The climate sensitivity was estimated from the mean of the indices during the years 1990–99 for the CMIP3 models. The surface radiative flux dataset from the Clouds and the Earth’s Radiant Energy System (CERES) together with its top-of-atmosphere Energy Balanced and Filled equivalent (CERES EBAF) are used as a reference observational dataset, resulting in a best estimate for climate sensitivity of 3.3 K with a likely range of 2.7–4.0 K. A comparison with other satellite and reanalysis datasets show similar likely ranges and best estimates of 1.7–3.8 (3.3 K) [Earth Radiation Budget Experiment (ERBE)], 2.9–3.7 (3.3 K) [International Satellite Cloud Climatology Project radiative surface flux data (ISCCP-FD)], 2.8–4.1 (3.5 K) [NASA’s Modern Era Retrospective-Analysis for Research and Application (MERRA)], 3.0–4.2 (3.6 K) [Japanese 25-yr Reanalysis (JRA-25)], 2.7–3.9 (3.4 K) [European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-Interim)], 3.0–4.0 (3.5 K) [ERA-40], and 3.1–4.7 (3.6 K) for the NCEP reanalysis. For each individual reference dataset, the results suggest that values for the sensitivity below 1.7 K are not likely to be consistent with observed radiation patterns given the structure of current climate models. For the aggregation of the reference datasets, the climate sensitivity is not likely to be below 2.9 K within the framework of this study, whereas values exceeding 4.5 K cannot be excluded from this analysis. While these ranges cannot be interpreted properly in terms of probability, they are consistent with other estimates of climate sensitivity and reaffirm that the current climatology provides a strong constraint on the lower bound of climate sensitivity even in a set of structurally different models. radiative forcing; climate models; Climate sensitivity
Hudson, Stephen R.Hudson, S. R., 2011: Estimating the global radiative impact of the sea ice–albedo feedback in the Arctic. Journal of Geophysical Research: Atmospheres, 116(D16), D16102. doi: 10.1029/2011JD015804. A simple method for estimating the global radiative forcing caused by the sea ice–albedo feedback in the Arctic is presented. It is based on observations of cloud cover, sea ice concentration, and top-of-atmosphere broadband albedo. The method does not rely on any sort of climate model, making the assumptions and approximations clearly visible and understandable and allowing them to be easily changed. Results show that the globally and annually averaged radiative forcing caused by the observed loss of sea ice in the Arctic between 1979 and 2007 is approximately 0.1 W m−2; a complete removal of Arctic sea ice results in a forcing of about 0.7 W m−2, while a more realistic ice-free summer scenario (no ice for 1 month and decreased ice at all other times of the year) results in a forcing of about 0.3 W m−2, similar to present-day anthropogenic forcing caused by halocarbons. The potential for changes in cloud cover as a result of the changes in sea ice makes the evaluation of the actual forcing that may be realized quite uncertain since such changes could overwhelm the forcing caused by the sea ice loss itself, if the cloudiness increases in the summertime. albedo; 0321 Cloud/radiation interaction; 3359 Radiative processes; 0748 Ponds; 1621 Cryospheric change; 9315 Arctic region; Climate feedback; sea ice; Solar radiation
Jin, Zhonghai; Wielicki, Bruce A.; Loukachine, Constantin; Charlock, Thomas P.; Young, David; Noël, StefanJin, Z., B. A. Wielicki, C. Loukachine, T. P. Charlock, D. Young, S. Noël, 2011: Spectral kernel approach to study radiative response of climate variables and interannual variability of reflected solar spectrum. Journal of Geophysical Research: Atmospheres, 116(D10), D10113. doi: 10.1029/2010JD015228. The radiative kernel approach provides a simple way to separate the radiative response to different climate parameters and to decompose the feedback into radiative and climate response components. Using CERES/MODIS/Geostationary data, we calculated and analyzed the solar spectral reflectance kernels for various climate parameters on zonal, regional, and global spatial scales. The kernel linearity is tested. Errors in the kernel due to nonlinearity can vary strongly depending on climate parameter, wavelength, surface, and solar elevation; they are large in some absorption bands for some parameters but are negligible in most conditions. The spectral kernels are used to calculate the radiative responses to different climate parameter changes in different latitudes. The results show that the radiative response in high latitudes is sensitive to the coverage of snow and sea ice. The radiative response in low latitudes is contributed mainly by cloud property changes, especially cloud fraction and optical depth. The large cloud height effect is confined to absorption bands, while the cloud particle size effect is found mainly in the near infrared. The kernel approach, which is based on calculations using CERES retrievals, is then tested by direct comparison with spectral measurements from Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) (a different instrument on a different spacecraft). The monthly mean interannual variability of spectral reflectance based on the kernel technique is consistent with satellite observations over the ocean, but not over land, where both model and data have large uncertainty. RMS errors in kernel-derived monthly global mean reflectance over the ocean compared to observations are about 0.001, and the sampling error is likely a major component. 1640 Remote sensing; 3359 Radiative processes; 3305 Climate change and variability; 1616 Climate variability; Interannual variability; 3225 Numerical approximations and analysis; climate attribution; Radiative response; reflectance; spectral radiative kernel
Jones, T. A.; Christopher, S. A.Jones, T. A., S. A. Christopher, 2011: A reanalysis of MODIS fine mode fraction over ocean using OMI and daily GOCART simulations. Atmos. Chem. Phys., 11(12), 5805-5817. doi: 10.5194/acp-11-5805-2011. Using daily Goddard Chemistry Aerosol Radiation and Transport (GOCART) model simulations and columnar retrievals of 0.55 μm aerosol optical thickness (AOT) and fine mode fraction (FMF) from the Moderate Resolution Imaging Spectroradiometer (MODIS), we estimate the satellite-derived aerosol properties over the global oceans between June 2006 and May 2007 due to black carbon (BC), organic carbon (OC), dust (DU), sea-salt (SS), and sulfate (SU) components. Using Aqua-MODIS aerosol properties embedded in the CERES-SSF product, we find that the mean MODIS FMF values for each aerosol type are SS: 0.31 ± 0.09, DU: 0.49 ± 0.13, SU: 0.77 ± 0.16, and (BC + OC): 0.80 ± 0.16. We further combine information from the ultraviolet spectrum using the Ozone Monitoring Instrument (OMI) onboard the Aura satellite to improve the classification process, since dust and carbonate aerosols have positive Aerosol Index (AI) values >0.5 while other aerosol types have near zero values. By combining MODIS and OMI datasets, we were able to identify and remove data in the SU, OC, and BC regions that were not associated with those aerosol types. The same methods used to estimate aerosol size characteristics from MODIS data within the CERES-SSF product were applied to Level 2 (L2) MODIS aerosol data from both Terra and Aqua satellites for the same time period. As expected, FMF estimates from L2 Aqua data agreed well with the CERES-SSF dataset from Aqua. However, the FMF estimate for DU from Terra data was significantly lower (0.37 vs. 0.49) indicating that sensor calibration, sampling differences, and/or diurnal changes in DU aerosol size characteristics were occurring. Differences for other aerosol types were generally smaller. Sensitivity studies show that a difference of 0.1 in the estimate of the anthropogenic component of FMF produces a corresponding change of 0.2 in the anthropogenic component of AOT (assuming a unit value of AOT). This uncertainty would then be passed along to any satellite-derived estimates of anthropogenic aerosol radiative effects.
Kato, Seiji; Rose, Fred G.; Sun-Mack, Sunny; Miller, Walter F.; Chen, Yan; Rutan, David A.; Stephens, Graeme L.; Loeb, Norman G.; Minnis, Patrick; Wielicki, Bruce A.; Winker, David M.; Charlock, Thomas P.; Stackhouse, Paul W.; Xu, Kuan-Man; Collins, William D.Kato, S., F. G. Rose, S. Sun-Mack, W. F. Miller, Y. Chen, D. A. Rutan, G. L. Stephens, N. G. Loeb, P. Minnis, B. A. Wielicki, D. M. Winker, T. P. Charlock, P. W. Stackhouse, K. Xu, W. D. Collins, 2011: Improvements of top-of-atmosphere and surface irradiance computations with CALIPSO-, CloudSat-, and MODIS-derived cloud and aerosol properties. Journal of Geophysical Research: Atmospheres, 116(D19), D19209. doi: 10.1029/2011JD016050. One year of instantaneous top-of-atmosphere (TOA) and surface shortwave and longwave irradiances are computed using cloud and aerosol properties derived from instruments on the A-Train Constellation: the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite, the CloudSat Cloud Profiling Radar (CPR), and the Aqua Moderate Resolution Imaging Spectrometer (MODIS). When modeled irradiances are compared with those computed with cloud properties derived from MODIS radiances by a Clouds and the Earth's Radiant Energy System (CERES) cloud algorithm, the global and annual mean of modeled instantaneous TOA irradiances decreases by 12.5 W m−2 (5.0%) for reflected shortwave and 2.5 W m−2 (1.1%) for longwave irradiances. As a result, the global annual mean of instantaneous TOA irradiances agrees better with CERES-derived irradiances to within 0.5W m−2 (out of 237.8 W m−2) for reflected shortwave and 2.6W m−2 (out of 240.1 W m−2) for longwave irradiances. In addition, the global annual mean of instantaneous surface downward longwave irradiances increases by 3.6 W m−2 (1.0%) when CALIOP- and CPR-derived cloud properties are used. The global annual mean of instantaneous surface downward shortwave irradiances also increases by 8.6 W m−2 (1.6%), indicating that the net surface irradiance increases when CALIOP- and CPR-derived cloud properties are used. Increasing the surface downward longwave irradiance is caused by larger cloud fractions (the global annual mean by 0.11, 0.04 excluding clouds with optical thickness less than 0.3) and lower cloud base heights (the global annual mean by 1.6 km). The increase of the surface downward longwave irradiance in the Arctic exceeds 10 W m−2 (∼4%) in winter because CALIOP and CPR detect more clouds in comparison with the cloud detection by the CERES cloud algorithm during polar night. The global annual mean surface downward longwave irradiance of 345.4 W m−2 is estimated by combining the modeled instantaneous surface longwave irradiance computed with CALIOP and CPR cloud profiles with the global annual mean longwave irradiance from the CERES product (AVG), which includes the diurnal variation of the irradiance. The estimated bias error is −1.5 W m−2 and the uncertainty is 6.9 W m−2. The uncertainty is predominately caused by the near-surface temperature and column water vapor amount uncertainties. clouds; 0360 Radiation: transmission and scattering; 1610 Atmosphere; 1640 Remote sensing; aerosols; radiation; surface energy budget
Kay, J. E.; Raeder, K.; Gettelman, A.; Anderson, J.Kay, J. E., K. Raeder, A. Gettelman, J. Anderson, 2011: The Boundary Layer Response to Recent Arctic Sea Ice Loss and Implications for High-Latitude Climate Feedbacks. J. Climate, 24(2), 428-447. doi: 10.1175/2010JCLI3651.1. Abstract This study documents and evaluates the boundary layer and energy budget response to record low 2007 sea ice extents in the Community Atmosphere Model version 4 (CAM4) using 1-day observationally constrained forecasts and 10-yr runs with a freely evolving atmosphere. While near-surface temperature and humidity are minimally affected by sea ice loss in July 2007 forecasts, near-surface stability decreases and atmospheric humidity increases aloft over newly open water in September 2007 forecasts. Ubiquitous low cloud increases over the newly ice-free Arctic Ocean are found in both the July 2007 and the September 2007 forecasts. In response to the 2007 sea ice loss, net surface [top of the atmosphere (TOA)] energy budgets change by +19.4 W m−2 (+21.0 W m−2) and −17.9 W m−2 (+1.4 W m−2) in the July 2007 and September 2007 forecasts, respectively. While many aspects of the forecasted response to sea ice loss are consistent with physical expectations and available observations, CAM4’s ubiquitous July 2007 cloud increases over newly open water are not. The unrealistic cloud response results from the global application of parameterization designed to diagnose stratus clouds based on lower-tropospheric stability (CLDST). In the Arctic, the well-mixed boundary layer assumption implicit in CLDST is violated. Requiring a well-mixed boundary layer to diagnose stratus clouds improves the CAM4 cloud response to sea ice loss and increases July 2007 surface (TOA) energy budgets over newly open water by +11 W m−2 (+14.9 W m−2). Of importance to high-latitude climate feedbacks, unrealistic stratus cloud compensation for sea ice loss occurs only when stable and dry atmospheric conditions exist. Therefore, coupled climate projections that use CAM4 will underpredict Arctic sea ice loss only when dry and stable summer conditions occur. Feedback; sea ice; climate; Arctic Ocean; Boundary layer
Kelektsoglou, Kyriaki; Kourtidis, Konstantinos; Balis, Dimitris S.; Rapsomanikis, SpyridonKelektsoglou, K., K. Kourtidis, D. S. Balis, S. Rapsomanikis, 2011: A 1-year remote sensing study of radiative effects of aerosol and clouds over the NE Mediterranean. International Journal of Remote Sensing, 32(23), 8747-8762. doi: 10.1080/01431161.2010.549524. Direct aerosol radiative forcing (ARF) and cloud radiative forcing (CRF) over the Aegean Sea are investigated using 1 year of almost continuous observations of aerosol optical properties, cloud data and Clouds and the Earth's Radiant Energy System (CERES) satellite short-wave (SW) and long-wave (LW) fluxes during 2005–2006. Aerosol optical depth (AOD) values from moderate resolution imaging spectroradiometer (MODIS) over the Aegean Sea are found to be high during summer and spring months. This period of the year, the air masses come predominantly from the eastern and northeastern part of Europe. The monthly mean ARF at the top of the atmosphere (TOA) over the Aegean Sea resulted in net cooling and ranged from −6.0 to −15.8 W m−2, within the range of results from previous studies. The presence of fine particles greatly influenced the ARF. The CRF was also characterized by net cooling and ranged from −23 to −84 W m−2 and appeared to be driven primarily by changes in cloud fraction. An apparent aerosol weekly cycle with lower values during the weekend as well as a cloud fraction weekly cycle with lower values during the weekend is observed over the Aegean Sea, which, if confirmed, could result in net TOA forcing of around −20 W m−2.
Kennedy, Aaron D.; Dong, Xiquan; Xi, Baike; Xie, Shaocheng; Zhang, Yunyan; Chen, JunyeKennedy, A. D., X. Dong, B. Xi, S. Xie, Y. Zhang, J. Chen, 2011: A Comparison of MERRA and NARR Reanalyses with the DOE ARM SGP Data. J. Climate, 24(17), 4541-4557. doi: 10.1175/2011JCLI3978.1. AbstractAtmospheric states from the Modern-Era Retrospective analysis for Research and Applications (MERRA) and the North American Regional Reanalysis (NARR) are compared with data from the Atmospheric Radiation Measurement Program (ARM) Southern Great Plains (SGP) site, including the ARM continuous forcing product and Cloud Modeling Best Estimate (CMBE) soundings, during the period 1999–2001 to understand their validity for single-column model (SCM) and cloud-resolving model (CRM) forcing datasets. Cloud fraction, precipitation, and radiation information are also compared to determine what errors exist within these reanalyses. For the atmospheric state, ARM continuous forcing and the reanalyses have good agreement with the CMBE sounding information, with biases generally within 0.5 K for temperature, 0.5 m s−1 for wind, and 5% for relative humidity. Larger disagreements occur in the upper troposphere (p < 300 hPa) for temperature, humidity, and zonal wind, and in the boundary layer (p > 800 hPa) for meridional wind and humidity. In these regions, larger errors may exist in derived forcing products. Significant differences exist for vertical pressure velocity, with the largest biases occurring during the spring upwelling and summer downwelling periods. Although NARR and MERRA share many resemblances to each other, ARM outperforms these reanalyses in terms of correlation with cloud fraction. Because the ARM forcing is constrained by observed precipitation that gives the adequate mass, heat, and moisture budgets, much of the precipitation (specifically during the late spring/early summer) is caused by smaller-scale forcing that is not captured by the reanalyses. While reanalysis-based forcing appears to be feasible for the majority of the year at this location, it may have limited usage during the late spring and early summer, when convection is common at the ARM SGP site. Both NARR and MERRA capture the seasonal variation of cloud fractions (CFs) observed by ARM radar–lidar and Geostationary Operational Environmental Satellite (GOES) with high correlations (0.92–0.78) but with negative biases of 14% and 3%, respectively. Compared to the ARM observations, MERRA shows better agreement for both shortwave (SW) and longwave (LW) fluxes except for LW-down (due to a negative bias in water vapor): NARR has significant positive bias for SW-down and negative bias for LW-down under clear-sky and all-sky conditions. The NARR biases result from a combination of too few clouds and a lack of sufficient extinction by aerosols and water vapor in the atmospheric column. The results presented here represent only one location for a limited period, and more comparisons at different locations and longer periods are needed. Radiative fluxes; Fluxes; Precipitation; Cloud resolving models; Forcings
Klocke, Daniel; Pincus, Robert; Quaas, JohannesKlocke, D., R. Pincus, J. Quaas, 2011: On Constraining Estimates of Climate Sensitivity with Present-Day Observations through Model Weighting. J. Climate, 24(23), 6092-6099. doi: 10.1175/2011JCLI4193.1. AbstractThe distribution of model-based estimates of equilibrium climate sensitivity has not changed substantially in more than 30 years. Efforts to narrow this distribution by weighting projections according to measures of model fidelity have so far failed, largely because climate sensitivity is independent of current measures of skill in current ensembles of models. This work presents a cautionary example showing that measures of model fidelity that are effective at narrowing the distribution of future projections (because they are systematically related to climate sensitivity in an ensemble of models) may be poor measures of the likelihood that a model will provide an accurate estimate of climate sensitivity (and thus degrade distributions of projections if they are used as weights). Furthermore, it appears unlikely that statistical tests alone can identify robust measures of likelihood. The conclusions are drawn from two ensembles: one obtained by perturbing parameters in a single climate model and a second containing the majority of the world’s climate models. The simple ensemble reproduces many aspects of the multimodel ensemble, including the distributions of skill in reproducing the present-day climatology of clouds and radiation, the distribution of climate sensitivity, and the dependence of climate sensitivity on certain cloud regimes. Weighting by error measures targeted on those regimes permits the development of tighter relationships between climate sensitivity and model error and, hence, narrower distributions of climate sensitivity in the simple ensemble. These relationships, however, do not carry into the multimodel ensemble. This suggests that model weighting based on statistical relationships alone is unfounded and perhaps that climate model errors are still large enough that model weighting is not sensible. clouds; statistics; Climate sensitivity; Ensembles; Model errors
Kratz, D. P.; Stackhouse, P.W.; Wong, T; Sawaengphokhai, P.; Wilber, A. C.; Loeb, N. G.Kratz, D. P., P. Stackhouse, T. Wong, P. Sawaengphokhai, A. C. Wilber, N. G. Loeb, 2011: Earth Radiation Budget at top-of-atmosphere in 'State of the Climate 2010'. Bulletin of the American Meterological Society, 92(6). doi: 10.1175/1520-0477-92.6.S1.
Krüger, Olaf; Graßl, HartmutKrüger, O., H. Graßl, 2011: Southern Ocean phytoplankton increases cloud albedo and reduces precipitation. Geophysical Research Letters, 38(8), L08809. doi: 10.1029/2011GL047116. Effects of natural and anthropogenic aerosol particles on the radiation budget in cloudy atmospheres are still a major research topic. For example, can an increase or decrease in aerosol particle number, originating from changed dimethylsulfide (DMS) and isoprene emissions by marine phytoplankton, impact the earth radiation budget via increasing or decreasing planetary albedo and lifetime of clouds? And if so, is a shifted cloud droplet spectrum accompanied by a regional change in precipitation? Here, we show by a synergistic analysis of satellite observations (MODIS, SeaWiFS, AIRS, SSM/I and CERES) that the phytoplankton related emission of the mentioned gases into the atmosphere strongly influences cloud properties within a broad latitude belt in the Southern Hemisphere during the austral summer. For this season we detected indirect aerosol effects over the Southern Ocean from 45°S to 65°S, especially in regions with plankton blooms, indicated by high chlorophyll-a concentration in seawater. The strong increase in cloud condensation nuclei column content from 2.0 × 108 to more than 5.0 × 108 CCN/cm2 for a chlorophyll increase from 0.3 to about 0.5 mg/m3 in these regions decreases cloud droplet effective radius and increases cloud optical thickness for water clouds. Consequently, the upward short-wave radiative flux at the top of the atmosphere increases. Our analysis also reveals reduced precipitation over the Antarctic Polar Frontal Zone during strong plankton blooms. We suggest that due to fine particles formed in the atmosphere originating from gaseous DMS and possibly isoprene emissions the reduction of precipitation is caused by delayed homogeneous freezing in water clouds. clouds; 0312 Air/sea constituent fluxes; 0320 Cloud physics and chemistry; 0305 Aerosols and particles; aerosols; phytoplankton
Li, Jiming; Yi, Yuhong; Minnis, Patrick; Huang, Jianping; Yan, Hongru; Ma, Yuejie; Wang, Wencai; Kirk Ayers, J.Li, J., Y. Yi, P. Minnis, J. Huang, H. Yan, Y. Ma, W. Wang, J. Kirk Ayers, 2011: Radiative effect differences between multi-layered and single-layer clouds derived from CERES, CALIPSO, and CloudSat data. Journal of Quantitative Spectroscopy and Radiative Transfer, 112(2), 361-375. doi: 10.1016/j.jqsrt.2010.10.006. Clouds alter general circulation through modification of the radiative heating profile within the atmosphere. Their effects are complex and depend on height, vertical structure, and phase. The instantaneous cloud radiative effect (CRE) induced by multi-layered (ML) and single-layer (SL) clouds is estimated by analyzing data collected by the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), CloudSat, and Clouds and Earth’s Radiation Energy Budget System (CERES) missions from March 2007 through February 2008. The CRE differences between ML and SL clouds at the top of the atmosphere (TOA) and at the surface were also examined. The zonal mean shortwave (SW) CRE differences between the ML and SL clouds at the TOA and surface were positive at most latitudes, peaking at 120 W m−2 in the tropics and dropping to −30 W m−2 at higher latitudes. This indicated that the ML clouds usually reflected less sunlight at the TOA and transmitted more to the surface than the SL clouds, due to their higher cloud top heights. The zonal mean longwave (LW) CRE differences between ML and SL clouds at the TOA and surface were relatively small, ranging from −30 to 30 W m−2. This showed that the ML clouds only increased the amount of thermal radiation at the TOA relative to the SL clouds in the tropics, decreasing it elsewhere. In other words, ML clouds tended to cool the atmosphere in the tropics and warm it elsewhere when compared to SL clouds. The zonal mean net CRE differences were positive at most latitudes and dominated by the SW CRE differences. cloud radiative effect; Layer thickness; Layer top (base) height; Multi-layered cloud; Single-layer cloud
Lin, Bing; Min, Qilong; Sun, Wenbo; Hu, Yongxiang; Fan, Tai-FangLin, B., Q. Min, W. Sun, Y. Hu, T. Fan, 2011: Can climate sensitivity be estimated from short-term relationships of top-of-atmosphere net radiation and surface temperature?. Journal of Quantitative Spectroscopy and Radiative Transfer, 112(2), 177-181. doi: 10.1016/j.jqsrt.2010.03.012. Increasing the knowledge in climate radiative feedbacks is critical for current climate studies. This work focuses on short-term relationships between global mean surface temperature and top-of-atmosphere (TOA) net radiation. The relationships may be used to characterize the climate feedback as suggested by some recent studies. As those recent studies, an energy balance model with ocean mixed layer and both radiative and non-radiative heat sources is used here. The significant improvement of current model is that climate system memories are considered. Based on model simulations, short-term relationship between global mean surface temperature and TOA net radiation (or the linear striation feature as suggested by previous studies) might represent climate feedbacks when the system had no memories. However, climate systems with the same short-term feedbacks but different memories would have a similar linear striation feature. This linear striation feature reflects only fast components of climate feedbacks and may not represent the total climate feedback even when the memory length of climate systems is minimal. The potential errors in the use of short-term relationships in estimations of climate sensitivity could be big. In short time scales, fast climate processes may overwhelm long-term climate feedbacks. Thus, the climate radiative feedback parameter obtained from short-term data may not provide a reliable estimate of climate sensitivity. This result also suggests that long-term observations of global surface temperature and TOA radiation are critical in the understanding of climate feedbacks and sensitivities.
Lin, Yanluan; Donner, Leo J.; Colle, Brian A.Lin, Y., L. J. Donner, B. A. Colle, 2011: Parameterization of Riming Intensity and Its Impact on Ice Fall Speed Using ARM Data. Mon. Wea. Rev., 139(3), 1036-1047. doi: 10.1175/2010MWR3299.1. Abstract Riming within mixed-phase clouds can have a large impact on the prediction of clouds and precipitation within weather and climate models. The increase of ice particle fall speed due to riming has not been considered in most general circulation models (GCMs), and many weather models only consider ice particles that are either unrimed or heavily rimed (not a continuum of riming amount). Using the Atmospheric Radiation Measurement (ARM) Program dataset at the Southern Great Plains (SGP) site of the United States, a new parameterization for riming is derived, which includes a diagnosed rimed mass fraction and its impact on the ice particle fall speed. When evaluated against a vertical-pointing Doppler radar for stratiform mixed-phase clouds, the new parameterization produces better ice fall speeds than a conventional parameterization. The new parameterization is tested in the recently developed Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric model (AM3) using prescribed sea surface temperature (SST) simulations. Compared with the standard (CTL) simulation, the new parameterization increases ice amount aloft by ∼20%–30% globally, which reduces the global mean outgoing longwave radiation (OLR) by ∼2.8 W m−2 and the top-of-atmosphere (TOA) shortwave absorption by ∼1.5 W m−2. Global mean precipitation is also slightly reduced, especially over the tropics. Overall, the new parameterization produces a comparable climatology with the CTL simulation and it improves the physical basis for using a fall velocity larger than a conventional parameterization in the current AM3.
Lindzen, Richard S.; Choi, Yong-SangLindzen, R. S., Y. Choi, 2011: On the observational determination of climate sensitivity and its implications. Asia-Pacific Journal of Atmospheric Sciences, 47(4), 377-390. doi: 10.1007/s13143-011-0023-x. We estimate climate sensitivity from observations, using the deseasonalized fluctuations in sea surface temperatures (SSTs) and the concurrent fluctuations in the top-of-atmosphere (TOA) outgoing radiation from the ERBE (1985–1999) and CERES (2000–2008) satellite instruments. Distinct periods of warming and cooling in the SSTs were used to evaluate feedbacks. An earlier study (Lindzen and Choi, 2009) was subject to significant criticisms. The present paper is an expansion of the earlier paper where the various criticisms are taken into account. The present analysis accounts for the 72 day precession period for the ERBE satellite in a more appropriate manner than in the earlier paper. We develop a method to distinguish noise in the outgoing radiation as well as radiation changes that are forcing SST changes from those radiation changes that constitute feedbacks to changes in SST. We demonstrate that our new method does moderately well in distinguishing positive from negative feedbacks and in quantifying negative feedbacks. In contrast, we show that simple regression methods used by several existing papers generally exaggerate positive feedbacks and even show positive feedbacks when actual feedbacks are negative. We argue that feedbacks are largely concentrated in the tropics, and the tropical feedbacks can be adjusted to account for their impact on the globe as a whole. Indeed, we show that including all CERES data (not just from the tropics) leads to results similar to what are obtained for the tropics alone — though with more noise. We again find that the outgoing radiation resulting from SST fluctuations exceeds the zerofeedback response thus implying negative feedback. In contrast to this, the calculated TOA outgoing radiation fluxes from 11 atmospheric models forced by the observed SST are less than the zerofeedback response, consistent with the positive feedbacks that characterize these models. The results imply that the models are exaggerating climate sensitivity. Meteorology/Climatology; cloud; Climate feedback; Satellite; radiation; Climate sensitivity; Geophysics/Geodesy
Lu, Peng; Zhang, Hua; Li, JiangnanLu, P., H. Zhang, J. Li, 2011: Correlated k-Distribution Treatment of Cloud Optical Properties and Related Radiative Impact. J. Atmos. Sci., 68(11), 2671-2688. doi: 10.1175/JAS-D-10-05001.1. AbstractA new scheme of water cloud optical properties is proposed for correlated k-distribution (CKD) models, in which the correlation in spectral distributions between the gaseous absorption coefficient and cloud optical properties is maintained. This is an extension of the CKD method from gas to cloud by dealing with the gas absorption coefficient and cloud optical properties in the same way.Compared to the results of line-by-line benchmark calculations, the band-mean cloud optical property scheme can overestimate cloud solar heating rate, with a relative error over 30% in general. Also, the error in the flux at the top of the atmosphere can be up to 20 W m−2 at a solar zenith angle of 0°. However, the error is considerably reduced by applying the new proposed CKD cloud scheme. The physical explanation of the large error for the band-mean cloud scheme is the absence of a spectral correlation between the gaseous absorption coefficient and the cloud optical properties. The overestimation of the solar heating rate at the cloud-top layer could affect the moisture circulation and limit the growth of cloud. It is found that the error in the longwave cooling rate caused by the band-mean cloud scheme is very small. In the infrared, the local thermal emission strongly affects the spectral distribution of the radiative flux, which makes the correlation between the gaseous absorption coefficient and cloud optical properties very weak. Therefore, there is no obvious advantage in emphasizing the spectral correlation between gas and cloud. Cloud parameterizations; Single column models; parameterization
Minnis, P.; Sun-Mack, Szedung; Chen, Yan; Khaiyer, M.M.; Yi, Yuhong; Ayers, J.K.; Brown, R.R.; Dong, Xiquan; Gibson, S.C.; Heck, P.W.; Lin, Bing; Nordeen, M.L.; Nguyen, L.; Palikonda, R.; Smith, W.L.; Spangenberg, D.A.; Trepte, Q.Z.; Xi, BaikeMinnis, P., S. Sun-Mack, Y. Chen, M. Khaiyer, Y. Yi, J. Ayers, R. Brown, X. Dong, S. Gibson, P. Heck, B. Lin, M. Nordeen, L. Nguyen, R. Palikonda, W. Smith, D. Spangenberg, Q. Trepte, B. Xi, 2011: CERES Edition-2 Cloud Property Retrievals Using TRMM VIRS and Terra and Aqua MODIS Data #x2014;Part II: Examples of Average Results and Comparisons With Other Data. IEEE Transactions on Geoscience and Remote Sensing, 49(11), 4401-4430. doi: 10.1109/TGRS.2011.2144602. Cloud properties were retrieved by applying the Clouds and Earth's Radiant Energy System (CERES) project Edition-2 algorithms to 3.5 years of Tropical Rainfall Measuring Mission Visible and Infrared Scanner data and 5.5 and 8 years of MODerate Resolution Imaging Spectroradiometer (MODIS) data from Aqua and Terra, respectively. The cloud products are consistent quantitatively from all three imagers; the greatest discrepancies occur over ice-covered surfaces. The retrieved cloud cover ( 59%) is divided equally between liquid and ice clouds. Global mean cloud effective heights, optical depth, effective particle sizes, and water paths are 2.5 km, 9.9, 12.9 μm , and 80 g·m-2, respectively, for liquid clouds and 8.3 km, 12.7, 52.2 μm, and 230 g·m-2 for ice clouds. Cloud droplet effective radius is greater over ocean than land and has a pronounced seasonal cycle over southern oceans. Comparisons with independent measurements from surface sites, the Ice Cloud and Land Elevation Satellite, and the Aqua Advanced Microwave Scanning Radiometer-Earth Observing System are used to evaluate the results. The mean CERES and MODIS Atmosphere Science Team cloud properties have many similarities but exhibit large discrepancies in certain parameters due to differences in the algorithms and the number of unretrieved cloud pixels. Problem areas in the CERES algorithms are identified and discussed. clouds; infrared imaging; Remote sensing; Satellites; atmospheric techniques; cloud; radiometry; Atmospheric measurements; Cloud optical depth; climate; ice clouds; data acquisition; Moderate Resolution Imaging Spectroradiometer; MODIS; Cloud cover; Clouds and the Earth's Radiant Energy System (CERES); Moderate Resolution Imaging Spectroradiometer (MODIS); effective particle size; cloud remote sensing; ice; Integrated optics; water path; Aqua MODIS Data; ice-covered surface; Pixel; Terra MODIS Data; TRMM VIRS; Visible and Infrared Scanner (VIRS); Aqua Advanced Microwave Scanning Radiometer-Earth Observing System; atmospheric precipitation; CERES Edition-2; CERES project; cloud droplet effective radius; cloud effective height; cloud product; cloud property retrieval; Clouds and Earth's Radiant Energy System; Ice Cloud and Land Elevation Satellite; liquid clouds; MODIS Atmosphere Science Team; southern oceans; time 3.5 yr; time 5.5 yr; time 8 yr; Tropical Rainfall Measuring Mission Visib
Minnis, P.; Sun-Mack, Szedung; Young, D.F.; Heck, P.W.; Garber, D.P.; Chen, Yan; Spangenberg, D.A.; Arduini, R.F.; Trepte, Q.Z.; Smith, W.L.; Ayers, J.K.; Gibson, S.C.; Miller, W.F.; Hong, G.; Chakrapani, V.; Takano, Y.; Liou, Kuo-Nan; Xie, Yu; Yang, PingMinnis, P., S. Sun-Mack, D. Young, P. Heck, D. Garber, Y. Chen, D. Spangenberg, R. Arduini, Q. Trepte, W. Smith, J. Ayers, S. Gibson, W. Miller, G. Hong, V. Chakrapani, Y. Takano, K. Liou, Y. Xie, P. Yang, 2011: CERES Edition-2 Cloud Property Retrievals Using TRMM VIRS and Terra and Aqua MODIS Data #x2014;Part I: Algorithms. IEEE Transactions on Geoscience and Remote Sensing, 49(11), 4374-4400. doi: 10.1109/TGRS.2011.2144601. The National Aeronautics and Space Administration's Clouds and the Earth's Radiant Energy System (CERES) Project was designed to improve our understanding of the relationship between clouds and solar and longwave radiation. This is achieved using satellite broad-band instruments to map the top-of-atmosphere radiation fields with coincident data from satellite narrow-band imagers employed to retrieve the properties of clouds associated with those fields. This paper documents the CERES Edition-2 cloud property retrieval system used to analyze data from the Tropical Rainfall Measuring Mission Visible and Infrared Scanner and by the MODerate-resolution Imaging Spectrometer instruments on board the Terra and Aqua satellites covering the period 1998 through 2007. Two daytime retrieval methods are explained: the Visible Infrared Shortwave-infrared Split-window Technique for snow-free surfaces and the Shortwave-infrared Infrared Near-infrared Technique for snow or ice-covered surfaces. The Shortwave-infrared Infrared Split-window Technique is used for all surfaces at night. These methods, along with the ancillary data and empirical parameterizations of cloud thickness, are used to derive cloud boundaries, phase, optical depth, effective particle size, and condensed/frozen water path at both pixel and CERES footprint levels. Additional information is presented, detailing the potential effects of satellite calibration differences, highlighting methods to compensate for spectral differences and correct for atmospheric absorption and emissivity, and discussing known errors in the code. Because a consistent set of algorithms, auxiliary input, and calibrations across platforms are used, instrument and algorithm-induced changes in the data record are minimized. This facilitates the use of the CERES data products for studying climate-scale trends. calibration; clouds; Land surface; Satellites; atmospheric radiation; atmospheric techniques; cloud; Data analysis; rain; Tropical Rainfall Measuring Mission; Solar radiation; climate; longwave radiation; snow; MODIS; Clouds and the Earth's Radiant Energy System (CERES); Terra satellite; Sea surface; Ocean temperature; National Aeronautics and Space Administration; cloud remote sensing; AD 1998 to 2007; algorithm-induced change analysis; Aqua MODIS Data; Aqua satellite; atmospheric absorption; CERES data analysis; CERES Edition-2 cloud property retrieval system; Clouds Earth's Radiant Energy System; condensed water path; frozen water path; ice-covered surface; MODerate-resolution Imaging Spectrometer (MODIS); Moderate-Resolution Imaging Spectrometer instrument; particle size; Pixel; satellite broad-band instrument; satellite calibration effect; satellite narrow-band image; shortwave-infrared infrared near-infrared technique; snow surface; Terra MODIS Data; top-of-atmosphere radiation f
Mlynczak, Pamela E.; Smith, G. Louis; Doelling, David R.Mlynczak, P. E., G. L. Smith, D. R. Doelling, 2011: The Annual Cycle of Earth Radiation Budget from Clouds and the Earth’s Radiant Energy System (CERES) Data. J. Appl. Meteor. Climatol., 50(12), 2490-2503. doi: 10.1175/JAMC-D-11-050.1. AbstractThe seasonal cycle of the Earth radiation budget is investigated by use of data from the Clouds and the Earth’s Radiant Energy System (CERES). Monthly mean maps of reflected solar flux and Earth-emitted flux on a 1° equal-angle grid are used for the study. The seasonal cycles of absorbed solar radiation (ASR), outgoing longwave radiation (OLR), and net radiation are described by use of principal components for the time variations, for which the corresponding geographic variations are the empirical orthogonal functions. Earth’s surface is partitioned into land and ocean for the analysis. The first principal component describes more than 95% of the variance in the seasonal cycle of ASR and the net radiation fluxes and nearly 90% of the variance of OLR over land. Because one term can express so much of the variance, principal component analysis is very useful to describe these seasonal cycles. The annual cycles of ASR are about 100 W m−2 over land and ocean, but the amplitudes of OLR are about 27 W m−2 over land and 15 W m−2 over ocean. The magnitude of OLR and its time lag relative to that of ASR are important descriptors of the climate system and are computed for the first principal components. OLR lags ASR by about 26 days over land and 42 days over ocean. The principal components are useful for comparing the observed radiation budget with that computed by a model. Energy budget/balance
Mlynczak, Pamela E.; Smith, G. Louis; Wilber, Anne C.; Stackhouse, Paul W.Mlynczak, P. E., G. L. Smith, A. C. Wilber, P. W. Stackhouse, 2011: Annual Cycle of Surface Longwave Radiation. J. Appl. Meteor. Climatol., 50(6), 1212-1224. doi: 10.1175/2011JAMC2663.1. AbstractThe annual cycles of upward and downward longwave fluxes at the earth’s surface are investigated by use of the NASA Global Energy and Water Cycle Experiment (GEWEX) Surface Radiation Budget Dataset. Principal component analysis is used to quantify the annual cycles. Because of the immense difference between the heat capacity of land and ocean, the surface of the earth is partitioned into these two categories. Over land, the first principal component describes over 95% of the variance of the annual cycle of the upward and downward longwave fluxes. Over ocean the first term describes more than 87% of these annual cycles. Empirical orthogonal functions show the corresponding geographical distributions of these cycles. Phase-plane diagrams of the annual cycles of upward longwave fluxes as a function of net shortwave flux show the thermal inertia of land and ocean. Radiative fluxes; longwave radiation; Surface fluxes; Annual variations; Principal components analysis
Mo, Kingtse C.; Long, Lindsey N.; Xia, Youlong; Yang, S. K.; Schemm, Jae E.; Ek, MichaelMo, K. C., L. N. Long, Y. Xia, S. K. Yang, J. E. Schemm, M. Ek, 2011: Drought Indices Based on the Climate Forecast System Reanalysis and Ensemble NLDAS. J. Hydrometeor., 12(2), 181-205. doi: 10.1175/2010JHM1310.1. Abstract Drought indices derived from the Climate Forecast System Reanalysis (CFSR) are compared with indices derived from the ensemble North American Land Data Assimilation System (NLDAS) and the North American Regional Reanalysis (NARR) over the United States. Uncertainties in soil moisture, runoff, and evapotranspiration (E) from three systems are assessed by comparing them with limited observations, including E from the AmeriFlux data, soil moisture from the Oklahoma Mesonet and the Illinois State Water Survey, and streamflow data from the U.S. Geological Survey (USGS). The CFSR has positive precipitation (P) biases over the western mountains, the Pacific Northwest, and the Ohio River valley in winter and spring. In summer, it has positive biases over the Southeast and large negative biases over the Great Plains. These errors limit the ability to use the standardized precipitation indices (SPIs) derived from the CFSR to measure the severity of meteorological droughts. To compare with the P analyses, the Heidke score for the 6-month SPI derived from the CFSR is on average about 0.5 for the three-category classification of drought, floods, and neutral months. The CFSR has positive E biases in spring because of positive biases in downward solar radiation and high potential evaporation. The negative E biases over the Great Plains in summer are due to less P and soil moisture in the root zone. The correlations of soil moisture percentile between the CFSR and the ensemble NLDAS are regionally dependent. The correlations are higher over the area east of 100°W and the West Coast. There is less agreement between them over the western interior region. drought; North America; Climate prediction
Parding, Kajsa; Hinkelman, Laura M.; Ackerman, Thomas P.; McFarlane, Sally A.Parding, K., L. M. Hinkelman, T. P. Ackerman, S. A. McFarlane, 2011: Shortwave absorptance in a tropical cloudy atmosphere: Reconciling calculations and observations. Journal of Geophysical Research: Atmospheres, 116(D19), D19202. doi: 10.1029/2011JD015639. The absorption of shortwave (SW) radiation by clouds is a topic surrounded by contradictory reports and controversy. Some studies have shown large discrepancies between observed SW absorption and absorption predicted by models, while others have found no significant difference. In this study, values of column SW absorptance obtained by combining collocated top-of-atmosphere (TOA) and surface observations at an island site in the tropical western Pacific are compared to radiative transfer model (RTM) output. To compensate for the field of view difference between satellite and surface instruments, the surface data are averaged over time. Scatterplots and statistical measures show that there is a significant discrepancy between models and observations with the RTMs apparently underestimating SW absorptance. The large variability of the absorptance computed from the observations, including negative values, suggests that the field of view mismatch between satellite and surface observations remains even after averaging of the surface data. This mismatch may contribute to the observation-model bias. In previous observational studies showing highly enhanced absorption compared to models, the slope of a linear fit to dαTOA/dT (the derivative of TOA albedo with respect to transmittance) was used to quantify cloud SW absorption, while nonlinearity of dα TOA/dT was interpreted as a sign of sampling issues. Here the models produce a steeper slope (about −0.9) than observations (−0.6 to −0.8), indicating that models predict too little cloud SW absorption. However, when the surface observations are averaged over a longer period, their slope grows steeper, and the root-mean-square difference between linear and quadratic fits to dα TOA/dT is reduced. This implies that insufficient averaging of surface data contributes to the observed SW absorption discrepancy. Reexamination of the observational data using the difference between cloud fraction estimated from satellite and surface measurements as an estimate of field of view mismatch supports this hypothesis. High measured absorptance values are shown to correspond to occasions of large field of view mismatch. When such data are excluded, the difference between the linear and quadratic fits is reduced, and the slope of the best fit line becomes steeper. We conclude that averaging surface data over 3 h or less is not always sufficient to eliminate sampling issues. However, the possibility that shortcomings of the RTMs contribute to the discrepancy in SW absorption values cannot be excluded. 0360 Radiation: transmission and scattering; 0321 Cloud/radiation interaction; 3359 Radiative processes; Shortwave radiation; anomalous cloud absorption
Patadia, Falguni; Christopher, Sundar A.; Zhang, JianglongPatadia, F., S. A. Christopher, J. Zhang, 2011: Development of empirical angular distribution models for smoke aerosols: Methods. Journal of Geophysical Research: Atmospheres, 116(D14), D14203. doi: 10.1029/2010JD015033. Using broadband shortwave radiance measurements from the Clouds and Earth Radiant Energy System (CERES) sensors onboard the Terra and Aqua satellites, empirical angular distribution models (EADM) are constructed for smoke aerosols. These EADMs are constructed for smoke aerosols emitted during the biomass burning season (August-October), in South America. All available years (2000–2008) of both rotating azimuth plane and cross-track radiance data from CERES have been utilized. Aerosol scenes are identified using coincident aerosol optical thickness retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS). The new EADMs are used to estimate top-of-atmosphere (TOA) shortwave flux for cloud free scenes. The CERES clearly shows the angular dependence of shortwave radiance on smoke aerosol optical thickness. A comparison of TOA shortwave fluxes estimated from the new smoke EADM with the existing CERES TOA shortwave fluxes shows that the CERES fluxes are higher (lower) for aerosol optical thickness less (greater) than 0.3, largely due to the use of aerosol optical thickness in characterizing the new EADMs developed in this study. Empirical ADMs for smoke aerosols over land are developed for the first time in this study, and our results demonstrate that large amounts of aerosols emitted during biomass burning activities contribute to the anisotropy of the radiance distribution at the TOA. Therefore, it is imperative to include aerosol information in the angular distribution models, especially now that more than a 10 year record of Terra data is available. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; aerosol; Biomass burning; empirical angular distribution models
Porter, David F.; Cassano, John J.; Serreze, Mark C.Porter, D. F., J. J. Cassano, M. C. Serreze, 2011: Analysis of the Arctic atmospheric energy budget in WRF: A comparison with reanalyses and satellite observations. Journal of Geophysical Research: Atmospheres, 116(D22), D22108. doi: 10.1029/2011JD016622. The Weather Research and Forecasting (WRF) model is used to dynamically downscale the regional climate of the Arctic, an area undergoing rapid climate changes. Because the WRF model is increasingly being run over larger spatial and temporal scales, an assessment of its ability to reconstruct basic properties of regional climates, such as terms in the energy budget, is crucial. Estimates of the Arctic energy budget from WRF are compared with estimates from reanalyses and satellite observations. The WRF model was run on a large pan-Arctic domain continuously from 2000 to 2008. Apart from a few systematic shortcomings, WRF sufficiently captures the Arctic energy budget. The major deficiency, with differences from reanalyses and satellite observations as large as 40 W m−2 in summer months, is in the shortwave radiative fluxes at both the surface and top of atmosphere (TOA). WRF's positive bias in upwelling shortwave radiation is due to a specified constant sea ice albedo of 0.8, which is too high during the summer. When sea ice albedo in WRF is allowed to vary in a more realistic manner in a test simulation, both surface and TOA energy budget components improve, while showing little impact on the atmospheric energy convergence and storage. A second, similar WRF simulation was performed but with gridded nudging enabled. When the large-scale circulation is constrained to the forcing data, the two energy budget terms that are most dependent on weather patterns, the convergence of atmospheric energy transport and the tendency of column-integrated energy, closely resemble their reanalysis counterparts. 1863 Snow and ice; energy budget; Arctic; WRF; 3349 Polar meteorology; 0764 Energy balance; 0798 Modeling; downscale
Priestley, Kory J.; Smith, G. Louis; Thomas, Susan; Cooper, Denise; Lee, Robert B.; Walikainen, Dale; Hess, Phillip; Szewczyk, Z. Peter; Wilson, RobertPriestley, K. J., G. L. Smith, S. Thomas, D. Cooper, R. B. Lee, D. Walikainen, P. Hess, Z. P. Szewczyk, R. Wilson, 2011: Radiometric Performance of the CERES Earth Radiation Budget Climate Record Sensors on the EOS Aqua and Terra Spacecraft through April 2007. J. Atmos. Oceanic Technol., 28(1), 3-21. doi: 10.1175/2010JTECHA1521.1. Abstract The Clouds and the Earth’s Radiant Energy System (CERES) flight models 1 through 4 instruments were launched aboard NASA’s Earth Observing System (EOS) Terra and Aqua spacecraft into 705-km sun-synchronous orbits with 10:30 p.m. and 1:30 a.m. local time equatorial crossing times. With these instruments CERES provides state-of-the-art observations and products related to the earth’s radiation budget at the top of the atmosphere (TOA). The archived CERES science data products consist of geolocated and calibrated instantaneous filtered and unfiltered radiances through temporally and spatially averaged TOA, surface, and atmospheric fluxes. CERES-filtered radiance measurements cover three spectral bands: shortwave (0.3–5 μm), total (0.3>100 μm), and an atmospheric window channel (8–12 μm). CERES climate data products realize a factor of 2–4 improvement in calibration accuracy and stability over the previotus Earth Radiation Budget Experiment (ERBE) products. To achieve this improvement there are three editions of data products. Edition 1 generates data products using gain coefficients derived from ground calibrations. After a minimum of four months, the calibration data are examined to remove drifts in the calibration. The data are then reprocessed to produce the edition 2 data products. These products are available for science investigations for which an accuracy of 2% is sufficient. Also, a validation protocol is applied to these products to find problems and develop solutions, after which edition 3 data products will be computed, for which the objectives are calibration stability of better than 0.2% and calibration traceability from ground to flight of 0.25%. This paper reports the status of the radiometric accuracy and stability of the CERES edition 2 instrument data products through April 2007. Radiation budgets; satellite observations; Instrumentation/sensors; Climate records
Ritz, Stefan P.; Stocker, Thomas F.; Joos, FortunatRitz, S. P., T. F. Stocker, F. Joos, 2011: A Coupled Dynamical Ocean–Energy Balance Atmosphere Model for Paleoclimate Studies. J. Climate, 24(2), 349-375. doi: 10.1175/2010JCLI3351.1. Abstract The Bern3D coupled three-dimensional dynamical ocean–energy balance atmosphere model is introduced and the atmospheric component is discussed in detail. The model is of reduced complexity, developed to perform extensive sensitivity studies and ensemble simulations extending over several glacial–interglacial cycles. On large space scales, the modern steady state of the model compares well with observations. In a first application, several 800 000-yr simulations with prescribed orbital, greenhouse gas, and ice sheet forcings are performed. The model shows an increase of Atlantic meridional overturning circulation strength at glacial inceptions followed by a decrease throughout the glaciation and ending in a circulation at glacial maxima that is weaker than at present. The sensitivity of ocean temperature to atmospheric temperature, Atlantic meridional overturning circulation (AMOC), and Antarctic bottom water (AABW) strength is analyzed at 23 locations. In a second application the climate sensitivities of the modern and of the Last Glacial Maximum (LGM) state are compared. The temperature rise for a doubling of the CO2 concentration from LGM conditions is 4.3°C and thus notably larger than in the modern case (3°C). The relaxation time scale is strongly dependent on the response of AABW to the CO2 change, since it determines the ventilation of the deep Pacific and Indian Ocean. Energy budget/balance; Coupled models; forcing; Atmosphere-ocean interaction; paleoclimate
Roberts, Yolanda L.; Pilewskie, Peter; Kindel, Bruce C.Roberts, Y. L., P. Pilewskie, B. C. Kindel, 2011: Evaluating the observed variability in hyperspectral Earth-reflected solar radiance. Journal of Geophysical Research: Atmospheres, 116(D24), D24119. doi: 10.1029/2011JD016448. We explore the potential for directly measured hyperspectral Earth-reflected solar radiances to provide sufficient information to study changes in Earth's climate based on the quantified variability of the data using principal component analysis (PCA) and singular spectrum analysis. To do this we used these two multivariate analysis techniques on Earth-reflected radiances between 300 and 1750 nm measured from space by the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) instrument. The spatial and temporal variability of hyperspectral reflected radiances over global, hemispherical, and regional scales was quantified. As few as six components were needed to explain over 99.5% of the variance in all cases studied, with the exception of an Arctic Ocean case in which only four components were needed. Both of these values represent large reductions in dimensionality of the input radiances from 291 spectral bands. PCA facilitated attribution of the dominant spectral patterns extracted to atmospheric and surface variables, including water vapor, clouds, surface albedo, and sea ice. The second most dominant spectral variable, that is, the second principal component, in the Arctic closely resembled sea ice reflectance and followed the temporal behavior of sea ice extent determined from AMSR-E observations. The extraction of the spectral, spatial, and temporal variability in reflected shortwave hyperspectral radiance using multivariate analysis provides an alternate and complementary approach to inverse methods for applying space-based observations to climate studies. 3359 Radiative processes; 3305 Climate change and variability; solar radiance; principal component analysis; 3255 Spectral analysis; singular spectrum analysis
Sanderson, Benjamin M.Sanderson, B. M., 2011: A Multimodel Study of Parametric Uncertainty in Predictions of Climate Response to Rising Greenhouse Gas Concentrations. J. Climate, 24(5), 1362-1377. doi: 10.1175/2010JCLI3498.1. Abstract One tool for studying uncertainties in simulations of future climate is to consider ensembles of general circulation models where parameterizations have been sampled within their physical range of plausibility. This study is about simulations from two such ensembles: a subset of the climateprediction.net ensemble using the Met Office Hadley Centre Atmosphere Model, version 3.0 and the new “CAMcube” ensemble using the Community Atmosphere Model, version 3.5. The study determines that the distribution of climate sensitivity in the two ensembles is very different: the climateprediction.net ensemble subset range is 1.7–9.9 K, while the CAMcube ensemble range is 2.2–3.2 K. On a regional level, however, both ensembles show a similarly diverse range in their mean climatology. Model radiative flux changes suggest that the major difference between the ranges of climate sensitivity in the two ensembles lies in their clear-sky longwave responses. Large clear-sky feedbacks present only in the climateprediction.net ensemble are found to be proportional to significant biases in upper-tropospheric water vapor concentrations, which are not observed in the CAMcube ensemble. Both ensembles have a similar range of shortwave cloud feedback, making it unlikely that they are causing the larger climate sensitivities in climateprediction.net. In both cases, increased negative shortwave cloud feedbacks at high latitudes are generally compensated by increased positive feedbacks at lower latitudes. climate change; General circulation models; greenhouse gases; Ensembles; Climate prediction
Smith, G. L.; Priestley, K. J.; Loeb, N. G.; Wielicki, B. A.; Charlock, T. P.; Minnis, P.; Doelling, D. R.; Rutan, D. A.Smith, G. L., K. J. Priestley, N. G. Loeb, B. A. Wielicki, T. P. Charlock, P. Minnis, D. R. Doelling, D. A. Rutan, 2011: Clouds and Earth Radiant Energy System (CERES), a review: Past, present and future. Advances in Space Research, 48(2), 254-263. doi: 10.1016/j.asr.2011.03.009. The Clouds and Earth Radiant Energy System (CERES) project’s objectives are to measure the reflected solar radiance (shortwave) and Earth-emitted (longwave) radiances and from these measurements to compute the shortwave and longwave radiation fluxes at the top of the atmosphere (TOA) and the surface and radiation divergence within the atmosphere. The fluxes at TOA are to be retrieved to an accuracy of 2%. Improved bidirectional reflectance distribution functions (BRDFs) have been developed to compute the fluxes at TOA from the measured radiances with errors reduced from ERBE by a factor of two or more. Instruments aboard the Terra and Aqua spacecraft provide sampling at four local times. In order to further reduce temporal sampling errors, data are used from the geostationary meteorological satellites to account for changes of scenes between observations by the CERES radiometers. A validation protocol including in-flight calibrations and comparisons of measurements has reduced the instrument errors to less than 1%. The data are processed through three editions. The first edition provides a timely flow of data to investigators and the third edition provides data products as accurate as possible with resources available. A suite of cloud properties retrieved from the MODerate-resolution Imaging Spectroradiometer (MODIS) by the CERES team is used to identify the cloud properties for each pixel in order to select the BRDF for each pixel so as to compute radiation fluxes from radiances. Also, the cloud information is used to compute radiation at the surface and through the atmosphere and to facilitate study of the relationship between clouds and the radiation budget. The data products from CERES include, in addition to the reflected solar radiation and Earth emitted radiation fluxes at TOA, the upward and downward shortwave and longwave radiation fluxes at the surface and at various levels in the atmosphere. Also at the surface the photosynthetically active radiation and ultraviolet radiation (total, UVA and UVB) are computed. The CERES instruments aboard the Terra and Aqua spacecraft have served well past their design life times. A CERES instrument has been integrated onto the NPP platform and is ready for launch in 2011. Another CERES instrument is being built for launch in 2014, and plans are being made for a series of follow-on missions. earth radiation budget; radiometry
Spencer, Roy W.; Braswell, William D.Spencer, R. W., W. D. Braswell, 2011: On the Misdiagnosis of Surface Temperature Feedbacks from Variations in Earth’s Radiant Energy Balance. Remote Sensing, 3(8), 1603-1613. doi: 10.3390/rs3081603. The sensitivity of the climate system to an imposed radiative imbalance remains the largest source of uncertainty in projections of future anthropogenic climate change. Here we present further evidence that this uncertainty from an observational perspective is largely due to the masking of the radiative feedback signal by internal radiative forcing, probably due to natural cloud variations. That these internal radiative forcings exist and likely corrupt feedback diagnosis is demonstrated with lag regression analysis of satellite and coupled climate model data, interpreted with a simple forcing-feedback model. While the satellite-based metrics for the period 2000–2010 depart substantially in the direction of lower climate sensitivity from those similarly computed from coupled climate models, we find that, with traditional methods, it is not possible to accurately quantify this discrepancy in terms of the feedbacks which determine climate sensitivity. It is concluded that atmospheric feedback diagnosis of the climate system remains an unsolved problem, due primarily to the inability to distinguish between radiative forcing and radiative feedback in satellite radiative budget observations. clouds; CERES; Feedback; climate; Models; sensitivity; temperature; warming
Stackhouse Jr, PW; Gupta, SK; Cox, SJ; Zhang, T; Mikovitz, J Colleen; Hinkelman, LMStackhouse Jr, P., S. Gupta, S. Cox, T. Zhang, J. C. Mikovitz, L. Hinkelman, 2011: The NASA/GEWEX surface radiation budget release 3.0: 24.5-year dataset. GEWEX News, 21(1), 10–12.
Sun, Wenbo; Lin, Bing; Hu, Yongxiang; Lukashin, Constantine; Kato, Seiji; Liu, ZhaoyanSun, W., B. Lin, Y. Hu, C. Lukashin, S. Kato, Z. Liu, 2011: On the consistency of CERES longwave flux and AIRS temperature and humidity profiles. Journal of Geophysical Research: Atmospheres, 116(D17), D17101. doi: 10.1029/2011JD016153. In this paper, the temperature and humidity profiles from the Atmospheric Infrared Sounder (AIRS) are evaluated with outgoing longwave radiation (OLR) from the Clouds and the Earth's Radiant Energy System (CERES) measurements. Using collocated CERES and AIRS measurements from A-train observations, the temperature and humidity profiles from the AIRS are evaluated by using them in a radiative transfer model and comparing the modeled OLR with that from the CERES. Both the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) measurements are used to ensure a strict clear-sky condition over the CERES fields-of-view (FOVs) in the evaluation. The paper shows that model-computed OLRs using the AIRS temperature and humidity profiles and surface skin temperature agree well with CERES data for daytime oceans, indicating good accuracies of both the AIRS and the CERES products. However, it is found that a certain discrepancy exists between OLR from the modeling with the AIRS atmospheric profiles and that from the CERES measurements. For nighttime oceans, the AIRS temperature and humidity profiles and surface skin temperature likely have significant bias errors in tropical and subtropical areas that are due to undetected thin cirrus clouds. The inconsistency of the CERES and the AIRS product in OLR needs to be understood for reliable earth radiation studies. 0360 Radiation: transmission and scattering; 1640 Remote sensing; 0305 Aerosols and particles; CERES; AIRS; outgoing longwave radiation; 0350 Pressure, density, and temperature; temperature and humidity profiles
Sun, Wenbo; Videen, Gorden; Kato, Seiji; Lin, Bing; Lukashin, Constantine; Hu, YongxiangSun, W., G. Videen, S. Kato, B. Lin, C. Lukashin, Y. Hu, 2011: A study of subvisual clouds and their radiation effect with a synergy of CERES, MODIS, CALIPSO, and AIRS data. Journal of Geophysical Research: Atmospheres, 116(D22), D22207. doi: 10.1029/2011JD016422. Subvisual cirrus clouds that are defined as those whose optical thickness is less than ∼0.3 are found in ∼50% of global observations. Passive remote-sensing instruments, such as the Moderate Resolution Imaging Spectroradiometer (MODIS), generally fail to detect these optically thin clouds. The launch of NASA's Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite provides an unprecedented ability to detect thin cloud layers globally. Also, the Clouds and the Earth's Radiant Energy System (CERES) provides accurate measurements of top-of-atmosphere radiation. By using CERES, MODIS, and CALIPSO measurements in a synergistic manner, a quantitative assessment of the influence of subvisual clouds on the Earth's shortwave (SW) radiation is accomplished. The difference between clear-sky radiation flux and the flux obtained with the presence of subvisual clouds clearly shows the cooling effect of subvisual clouds in the SW. The subvisual clouds increase the diurnal mean reflected SW flux by ∼2.5 W m−2. The subvisual clouds' effect on outgoing longwave radiation is also studied using a radiative-transfer model. The model results show that a layer of subvisual clouds having optical thickness of 0.1 can have a warming effect of ∼15 W m−2. These clouds can also affect the polarization of the reflected SW radiation and the accuracy of aerosol retrieval with satellite measurements. This work demonstrates that the study of subvisual clouds is necessary for an accurate and detailed understanding of Earth-atmosphere radiation. 0305 Aerosols and particles; CERES; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; 3359 Radiative processes; MODIS; CALIPSO; radiation effect; subvisual clouds
Szewczyk, Z. Peter; Priestley, Kory J.; Walikainen, Dale R.; Loeb, Norman G.; Smith, G. LouisSzewczyk, Z. P., K. J. Priestley, D. R. Walikainen, N. G. Loeb, G. L. Smith, 2011: Putting all CERES instruments (Terra/Aqua) on the same radiometric scale. Proc. SPIE, 8177, 817704-817704-11. doi: 10.1117/12.896897. Clouds and the Earth's Radiant Energy System (CERES) instruments are scanning radiometers on board the Terra and Aqua satellites since March of 2000 and June of 2002, respectively; hence, their continuous Earth's radiation budget dataset is more than a decade long. Since there are four CERES scanners in operation, it is important that their measurements are consistent. A focus of this paper is on placing two Aqua CERES sensors on the same radiometric scale as FM1 on Terra. The paper contains a description of radiation budget experiments that are used in this task, and a complete set of results. It is shown that one-time adjustments to gains and spectral response functions are sufficient in putting FM3 and FM4 on the same radiometric scale as FM1 at the beginning of their mission. The Edition 3 of ERBE-like data products use derived corrections for Aqua CERES sensors.
Taylor, Patrick C.; Ellingson, Robert G.; Cai, MingTaylor, P. C., R. G. Ellingson, M. Cai, 2011: Seasonal Variations of Climate Feedbacks in the NCAR CCSM3. J. Climate, 24(13), 3433-3444. doi: 10.1175/2011JCLI3862.1. AbstractThis study investigates the annual cycle of radiative contributions to global climate feedbacks. A partial radiative perturbation (PRP) technique is used to diagnose monthly radiative perturbations at the top of atmosphere (TOA) due to CO2 forcing; surface temperature response; and water vapor, cloud, lapse rate, and surface albedo feedbacks using NCAR Community Climate System Model, version 3 (CCSM3) output from a Special Report on Emissions Scenarios (SRES) A1B emissions-scenario-forced climate simulation. The seasonal global mean longwave TOA radiative feedback was found to be minimal. However, the global mean shortwave (SW) TOA cloud and surface albedo radiative perturbations exhibit large seasonality. The largest contributions to the negative SW cloud feedback occur during summer in each hemisphere, marking the largest differences with previous results. Results suggest that intermodel spread in climate sensitivity may occur, partially from cloud and surface albedo feedback seasonality differences. Further, links between the climate feedback and surface temperature response seasonality are investigated, showing a strong relationship between the seasonal climate feedback distribution and the seasonal surface temperature response. Feedback; forcing; general circulation model; Seasonal variability
Teixeira, J.; Cardoso, S.; Bonazzola, M.; Cole, J.; DelGenio, A.; DeMott, C.; Franklin, C.; Hannay, C.; Jakob, C.; Jiao, Y.; Karlsson, J.; Kitagawa, H.; Köhler, M.; Kuwano-Yoshida, A.; LeDrian, C.; Li, J.; Lock, A.; Miller, M. J.; Marquet, P.; Martins, J.; Mechoso, C. R.; Meijgaard, E. v.; Meinke, I.; Miranda, P. M. A.; Mironov, D.; Neggers, R.; Pan, H. L.; Randall, D. A.; Rasch, P. J.; Rockel, B.; Rossow, W. B.; Ritter, B.; Siebesma, A. P.; Soares, P. M. M.; Turk, F. J.; Vaillancourt, P. A.; Von Engeln, A.; Zhao, M.Teixeira, J., S. Cardoso, M. Bonazzola, J. Cole, A. DelGenio, C. DeMott, C. Franklin, C. Hannay, C. Jakob, Y. Jiao, J. Karlsson, H. Kitagawa, M. Köhler, A. Kuwano-Yoshida, C. LeDrian, J. Li, A. Lock, M. J. Miller, P. Marquet, J. Martins, C. R. Mechoso, E. v. Meijgaard, I. Meinke, P. M. A. Miranda, D. Mironov, R. Neggers, H. L. Pan, D. A. Randall, P. J. Rasch, B. Rockel, W. B. Rossow, B. Ritter, A. P. Siebesma, P. M. M. Soares, F. J. Turk, P. A. Vaillancourt, A. Von Engeln, M. Zhao, 2011: Tropical and Subtropical Cloud Transitions in Weather and Climate Prediction Models: The GCSS/WGNE Pacific Cross-Section Intercomparison (GPCI). J. Climate, 24(20), 5223-5256. doi: 10.1175/2011JCLI3672.1. AbstractA model evaluation approach is proposed in which weather and climate prediction models are analyzed along a Pacific Ocean cross section, from the stratocumulus regions off the coast of California, across the shallow convection dominated trade winds, to the deep convection regions of the ITCZ—the Global Energy and Water Cycle Experiment Cloud System Study/Working Group on Numerical Experimentation (GCSS/WGNE) Pacific Cross-Section Intercomparison (GPCI). The main goal of GPCI is to evaluate and help understand and improve the representation of tropical and subtropical cloud processes in weather and climate prediction models. In this paper, a detailed analysis of cloud regime transitions along the cross section from the subtropics to the tropics for the season June–July–August of 1998 is presented. This GPCI study confirms many of the typical weather and climate prediction model problems in the representation of clouds: underestimation of clouds in the stratocumulus regime by most models with the corresponding consequences in terms of shortwave radiation biases; overestimation of clouds by the 40-yr ECMWF Re-Analysis (ERA-40) in the deep tropics (in particular) with the corresponding impact in the outgoing longwave radiation; large spread between the different models in terms of cloud cover, liquid water path and shortwave radiation; significant differences between the models in terms of vertical cross sections of cloud properties (in particular), vertical velocity, and relative humidity. An alternative analysis of cloud cover mean statistics is proposed where sharp gradients in cloud cover along the GPCI transect are taken into account. This analysis shows that the negative cloud bias of some models and ERA-40 in the stratocumulus regions [as compared to the first International Satellite Cloud Climatology Project (ISCCP)] is associated not only with lower values of cloud cover in these regimes, but also with a stratocumulus-to-cumulus transition that occurs too early along the trade wind Lagrangian trajectory. Histograms of cloud cover along the cross section differ significantly between models. Some models exhibit a quasi-bimodal structure with cloud cover being either very large (close to 100%) or very small, while other models show a more continuous transition. The ISCCP observations suggest that reality is in-between these two extreme examples. These different patterns reflect the diverse nature of the cloud, boundary layer, and convection parameterizations in the participating weather and climate prediction models. clouds; tropics; Trends; Model comparison; Climate prediction; Pacific Ocean
Trenberth, Kevin E.; Fasullo, John T.; Mackaro, JessicaTrenberth, K. E., J. T. Fasullo, J. Mackaro, 2011: Atmospheric Moisture Transports from Ocean to Land and Global Energy Flows in Reanalyses. J. Climate, 24(18), 4907-4924. doi: 10.1175/2011JCLI4171.1. AbstractAn assessment is made of the global energy and hydrological cycles from eight current atmospheric reanalyses and their depiction of changes over time. A brief evaluation of the water and energy cycles in the latest version of the NCAR climate model referred to as CCSM4 is also given. The focus is on the mean ocean, land, and global precipitation P; the corresponding evaporation E; their difference corresponding to the surface freshwater flux E–P; and the vertically integrated atmospheric moisture transports. Using the model-based P and E, the time- and area-average E–P for the oceans, P–E for land, and the moisture transport from ocean to land should all be identical but are not close in most reanalyses, and often differ significantly from observational estimates of the surface return flow based on net river discharge into the oceans. Their differences reveal outstanding issues with atmospheric models and their biases, which are manifested as analysis increments in the reanalyses. The NCAR CCSM4, along with most reanalysis models, the exception being MERRA, has too-intense water cycling (P and E) over the ocean although ocean-to-land transports are very close to observed. Precipitation from reanalyses that assimilate moisture from satellite observations exhibits large changes identified with the changes in the observing system, as new and improved temperature and water vapor channels are assimilated and, while P improves after about 2002, E–P does not. Discrepancies among hydrological cycle components arise from analysis increments that can add or subtract moisture. The large-scale moisture budget divergences are more stable in time and similar across reanalyses than model-based estimates of E–P. Results are consistent with the view that recycling of moisture is too large in most models and the lifetime of moisture is too short. For the energy cycle, most reanalyses have spurious imbalances of ~10 W m−2 within the atmosphere, and ~5–10 W m−2 in net fluxes into the surface and to space. Major improvements are needed in model treatment and assimilation of moisture, and surface fluxes from reanalyses should only be used with great caution. Moisture; Hydrologic cycle; Model evaluation/performance; transport; Precipitation; Evaporation
Wang, Lei; Wang, Yuqing; Lauer, Axel; Xie, Shang-PingWang, L., Y. Wang, A. Lauer, S. Xie, 2011: Simulation of Seasonal Variation of Marine Boundary Layer Clouds over the Eastern Pacific with a Regional Climate Model*. J. Climate, 24(13), 3190-3210. doi: 10.1175/2010JCLI3935.1. AbstractThe seasonal cycle of marine boundary layer (MBL) clouds over the eastern Pacific Ocean is studied with the International Pacific Research Center (IPRC) Regional Atmospheric Model (iRAM). The results show that the model is capable of simulating not only the overall seasonal cycle but also the spatial distribution, cloud regime transition, and vertical structure of MBL clouds over the eastern Pacific. Although the modeled MBL cloud layer is generally too high in altitude over the open ocean when compared with available satellite observations, the model simulated well the westward deepening and decoupling of the MBL, the rise in cloud base and cloud top of the low cloud decks off the Peru and California coasts, and the cloud regime transition from stratocumulus near the coast to trade cumulus farther to the west in both the southeast and northeast Pacific. In particular, the model reproduced major features of the seasonal variations in stratocumulus decks off the Peru and California coasts, including cloud amount, surface latent heat flux, subcloud-layer mixing, and the degree of MBL decoupling. In both observations and the model simulation, in the season with small low-level cloudiness, surface latent heat flux is large and the cloud base is high. This coincides with weak subcloud-layer mixing and strong entrainment at cloud top, characterized by a high degree of MBL decoupling, while the opposite is true for the season with large low-level cloudiness. This seasonal cycle in low-cloud properties resembles the downstream stratocumulus-to-cumulus transition of marine low clouds and can be explained by the “deepening–decoupling” mechanism proposed in previous studies. It is found that the seasonal variations of low-level clouds off the Peru coast are mainly caused by a large seasonal variability in sea surface temperature, whereas those off the California coast are largely attributed to the seasonal cycle in lower-tropospheric temperature.
White, Jeffrey W.; Hoogenboom, Gerrit; Wilkens, Paul W.; Stackhouse, Paul W.; Hoel, James M.White, J. W., G. Hoogenboom, P. W. Wilkens, P. W. Stackhouse, J. M. Hoel, 2011: Evaluation of Satellite-Based, Modeled-Derived Daily Solar Radiation Data for the Continental United States. Agronomy Journal, 103(4), 1242. doi: 10.2134/agronj2011.0038.
Yan, Hongru; Huang, Jianping; Minnis, Patrick; Wang, Tianhe; Bi, JianrongYan, H., J. Huang, P. Minnis, T. Wang, J. Bi, 2011: Comparison of CERES surface radiation fluxes with surface observations over Loess Plateau. Remote Sensing of Environment, 115(6), 1489-1500. doi: 10.1016/j.rse.2011.02.008. Surface energy budget is an important factor in weather and climate processes. To estimate the errors in satellite-retrieved surface radiation budget over the interior of China, instantaneous-footprint surface radiation fluxes from the Terra/Aqua FLASHFlux SSF product are compared with the measurements taken at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) from July 2008 to March 2010. Validation is performed separately for different conditions: clear-sky and cloudy-sky, daytime and nighttime for four seasons. Differences between the FLASHFlux CERES shortwave radiation flux and surface measurements have larger standard deviations in cloudy-sky conditions than in clear-sky conditions, indicating that cloud contamination increases uncertainty in the retrieval algorithm. Upward shortwave radiation flux (USW) is overestimated in cloudy conditions suggesting that the cloud parameters and surface scene type in the retrieval process are not optimal for northwestern China. The CERES downward longwave radiation fluxes (DLW) accurately follow the variation of surface measurements during daytime, but are slightly underestimated during nighttime due to the coarse sounding profile and undetected low clouds at nighttime. The CERES upwelling longwave radiation fluxes (ULW) are strongly underestimated during daytime but are slightly underestimated during nighttime regardless of cloud coverage. This large bias could be caused by an underestimate of surface skin temperature and/or surface emissivity, or spatial inhomogeneity around the site. Generally, except for diurnal ULW, other components of the surface radiative fluxes obtained from CERES SSF datasets are close to meeting the accuracy requirements for climate research.
Yang, Q.; W. I. Gustafson Jr.; Fast, J. D.; Wang, H.; Easter, R. C.; Morrison, H.; Lee, Y.-N.; Chapman, E. G.; Spak, S. N.; Mena-Carrasco, M. A.Yang, Q., . W. I. Gustafson Jr., J. D. Fast, H. Wang, R. C. Easter, H. Morrison, Y. Lee, E. G. Chapman, S. N. Spak, M. A. Mena-Carrasco, 2011: Assessing regional scale predictions of aerosols, marine stratocumulus, and their interactions during VOCALS-REx using WRF-Chem. Atmos. Chem. Phys., 11(23), 11951-11975. doi: 10.5194/acp-11-11951-2011. This study assesses the ability of the recent chemistry version (v3.3) of the Weather Research and Forecasting (WRF-Chem) model to simulate boundary layer structure, aerosols, stratocumulus clouds, and energy fluxes over the Southeast Pacific Ocean. Measurements from the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) and satellite retrievals (i.e., products from the MODerate resolution Imaging Spectroradiometer (MODIS), Clouds and Earth's Radiant Energy System (CERES), and GOES-10) are used for this assessment. The Morrison double-moment microphysics scheme is newly coupled with interactive aerosols in the model. The 31-day (15 October–16 November 2008) WRF-Chem simulation with aerosol-cloud interactions (AERO hereafter) is also compared to a simulation (MET hereafter) with fixed cloud droplet number concentrations in the microphysics scheme and simplified cloud and aerosol treatments in the radiation scheme. The well-simulated aerosol quantities (aerosol number, mass composition and optical properties), and the inclusion of full aerosol-cloud couplings lead to significant improvements in many features of the simulated stratocumulus clouds: cloud optical properties and microphysical properties such as cloud top effective radius, cloud water path, and cloud optical thickness. In addition to accounting for the aerosol direct and semi-direct effects, these improvements feed back to the simulation of boundary-layer characteristics and energy budgets. Particularly, inclusion of interactive aerosols in AERO strengthens the temperature and humidity gradients within the capping inversion layer and lowers the marine boundary layer (MBL) depth by 130 m from that of the MET simulation. These differences are associated with weaker entrainment and stronger mean subsidence at the top of the MBL in AERO. Mean top-of-atmosphere outgoing shortwave fluxes, surface latent heat, and surface downwelling longwave fluxes are in better agreement with observations in AERO, compared to the MET simulation. Nevertheless, biases in some of the simulated meteorological quantities (e.g., MBL temperature and humidity) and aerosol quantities (e.g., underestimations of accumulation mode aerosol number) might affect simulated stratocumulus and energy fluxes over the Southeastern Pacific, and require further investigation. The well-simulated timing and outflow patterns of polluted and clean episodes demonstrate the model's ability to capture daily/synoptic scale variations of aerosol and cloud properties, and suggest that the model is suitable for studying atmospheric processes associated with pollution outflow over the ocean. The overall performance of the regional model in simulating mesoscale clouds and boundary layer properties is encouraging and suggests that reproducing gradients of aerosol and cloud droplet concentrations and coupling cloud-aerosol-radiation processes are important when simulating marine stratocumulus over the Southeast Pacific.
Zhao, Tom X.-P.; Loeb, Norman G.; Laszlo, Istvan; Zhou, MiZhao, T. X., N. G. Loeb, I. Laszlo, M. Zhou, 2011: Global component aerosol direct radiative effect at the top of atmosphere. International Journal of Remote Sensing, 32(3), 633-655. doi: 10.1080/01431161.2010.517790. The two-step approach of combining Clouds and the Earth's Radiant Energy System (CERES)/Moderate Resolution Imaging Spectroradiometer (MODIS) shortwave (SW) flux and aerosol optical thickness (AOT) at 0.55 μm with the component AOT fractions from the Goddard Space Flight Centre (GSFC)/Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model to derive top of atmosphere (TOA) component aerosol direct radiative effect (ADRE) over the global cloud-free oceans proposed by the first author in a previous publication has been extended to cloud-free land areas for nearly global coverage. Validation has also been performed by comparing the ADRE computation with calculations from the Fu–Liou radiative transfer model at globally distributed AErosol RObotic NETwork (AERONET) sites by using the aerosol optical properties observed from AERONET and surface reflectance obtained from MODIS observations as the model inputs. The promising validation results provide support for extending the two-step approach from global clear-sky oceans to global clear-sky land areas. The global annual mean values of ADRE for clear-sky condition are +0.3 ± 0.2 W m−2 for black carbon, −1.0 ± 0.6 W m−2 for organic carbon; −2.3 ± 0.7 W m−2 for sulphate; −1.6 ± 0.5 W m−2 for dust; −2.2 ± 0.6 W m−2 for sea salt; −2.4 ± 0.8 W m−2 for anthropogenic aerosol; −4.5 ± 1.2 W m−2 for natural aerosol; and −6.8 ± 1.7 W m−2 for total aerosols. For global average cloudy skies, the all-sky values of component ADRE are about 42% of their clear-sky counterparts. The major sources of uncertainty in the estimates are also discussed.
Anantharaj, Valentine G.; Nair, Udaysankar S.; Lawrence, Peter; Chase, Thomas N.; Christopher, Sundar; Jones, ThomasAnantharaj, V. G., U. S. Nair, P. Lawrence, T. N. Chase, S. Christopher, T. Jones, 2010: Comparison of satellite-derived TOA shortwave clear-sky fluxes to estimates from GCM simulations constrained by satellite observations of land surface characteristics. International Journal of Climatology, 30(13), 2088-2104. doi: 10.1002/joc.2107. Clear-sky, upwelling shortwave flux at the top of the atmosphere $\left(S_{\rm {TOA}}^{\uparrow}\right)$, simulated using the atmospheric and land model components of the Community Climate System Model 3 (CCSM3), is compared to corresponding observational estimates from the Clouds and Earth's Radiant Energy System (CERES) sensor. Improvements resulting from the use of land surface albedo derived from Moderate Resolution Imaging Spectroradiometer (MODIS) to constrain the simulations are also examined. Compared to CERES observations, CCSM3 overestimates global, annual averaged $S_{\rm {TOA}}^{\uparrow}$ over both land and oceans. However, regionally, CCSM3 overestimates $S_{\rm {TOA}}^{\uparrow}$ over some land and ocean areas while underestimating it over other sites. CCSM3 underestimates $S_{\rm {TOA}}^{\uparrow}$ over the Saharan and Arabian Deserts and substantial differences exist between CERES observations and CCSM3 over agricultural areas. Over selected sites, after using ground-based observations to remove systematic biases that exist in CCSM computation of $S_{\rm {TOA}}^{\uparrow}$, it is found that use of MODIS albedo improves the simulation of $S_{\rm {TOA}}^{\uparrow}$. Inability of coarse resolution CCSM3 simulation to resolve spatial heterogeneity of snowfall over high altitude sites such as the Tibetan Plateau causes overestimation of $S_{\rm {TOA}}^{\uparrow}$ in these areas. Discrepancies also exist in the simulation of $S_{\rm {TOA}}^{\uparrow}$ over ocean areas as CCSM3 does not account for the effect of wind speed on ocean surface albedo. This study shows that the radiative energy budget at the TOA is improved through the use of MODIS albedo in Global Climate Models. Copyright © 2010 Royal Meteorological Society CERES; global circulation model; MODIS land surface albedo; ocean albedo; radiation energy budget; shortwave fluxes; vegetation albedo
Bedka, Kristopher M.; Minnis, PatrickBedka, K. M., P. Minnis, 2010: GOES 12 observations of convective storm variability and evolution during the Tropical Composition, Clouds and Climate Coupling Experiment field program. Journal of Geophysical Research: Atmospheres, 115(D10), D00J13. doi: 10.1029/2009JD013227. This study characterizes convective clouds that occurred during the Tropical Composition, Clouds and Climate Coupling Experiment as observed within GOES imagery. Overshooting deep convective cloud tops (OT) that penetrate through the tropical tropopause layer and into the stratosphere are of particular interest in this study. The results show that there were clear differences in the areal coverage of anvil cloud, deep convection, and OT activity over land and water and also throughout the diurnal cycle. The offshore waters of Panama, northwest Colombia, and El Salvador were the most active regions for OT-producing convection. A cloud object tracking system is used to monitor the duration and areal coverage of convective cloud complexes as well as the time evolution of their cloud-top microphysical properties. The mean lifetime for these complexes is 5 hours, with some existing for longer than 16 hours. Deep convection is found within the anvil cloud during 60% of the storm lifetime and covered 24% of the anvil cloud. The cloud-top height and optical depth at the storm core followed a reasonable pattern, with maximum values occurring 20% into the storm lifetime. The values in the surrounding anvil cloud peaked at a relative age of 20%–50% before decreasing as the convective cloud complex decayed. Ice particle diameter decreased with distance from the core but generally increased with storm age. These results, which characterize the average convective system during the experiment, should be valuable for formulating and validating convective cloud process models. 3311 Clouds and aerosols; convection; 3374 Tropical meteorology; 3314 Convective processes; 3362 Stratosphere/troposphere interactions; microphysics; Satellite
Bryan, Frank O.; Tomas, Robert; Dennis, John M.; Chelton, Dudley B.; Loeb, Norman G.; McClean, Julie L.Bryan, F. O., R. Tomas, J. M. Dennis, D. B. Chelton, N. G. Loeb, J. L. McClean, 2010: Frontal Scale Air–Sea Interaction in High-Resolution Coupled Climate Models. J. Climate, 23(23), 6277-6291. doi: 10.1175/2010JCLI3665.1. Abstract The emerging picture of frontal scale air–sea interaction derived from high-resolution satellite observations of surface winds and sea surface temperature (SST) provides a unique opportunity to test the fidelity of high-resolution coupled climate simulations. Initial analysis of the output of a suite of Community Climate System Model (CCSM) experiments indicates that characteristics of frontal scale ocean–atmosphere interaction, such as the positive correlation between SST and surface wind stress, are realistically captured only when the ocean component is eddy resolving. The strength of the coupling between SST and surface stress is weaker than observed, however, as has been found previously for numerical weather prediction models and other coupled climate models. The results are similar when the atmospheric component model grid resolution is doubled from 0.5° to 0.25°, an indication that shortcomings in the representation of subgrid scale atmospheric planetary boundary layer processes, rather than resolved scale processes, are responsible for the weakness of the coupling. In the coupled model solutions the response to mesoscale SST features is strongest in the atmospheric boundary layer, but there is a deeper reaching response of the atmospheric circulation apparent in free tropospheric clouds. This simulated response is shown to be consistent with satellite estimates of the relationship between mesoscale SST and all-sky albedo. albedo; sea surface temperature; Airndashsea interaction; Coupled models; Mesoscale systems; Wind stress
Chang, Fu-Lung; Minnis, Patrick; Ayers, J. Kirk; McGill, Matthew J.; Palikonda, Rabindra; Spangenberg, Douglas A.; Smith, William L.; Yost, Christopher R.Chang, F., P. Minnis, J. K. Ayers, M. J. McGill, R. Palikonda, D. A. Spangenberg, W. L. Smith, C. R. Yost, 2010: Evaluation of satellite-based upper troposphere cloud top height retrievals in multilayer cloud conditions during TC4. Journal of Geophysical Research: Atmospheres, 115(D10), D00J05. doi: 10.1029/2009JD013305. Upper troposphere cloud top heights (CTHs), restricted to cloud top pressures (CTPs) < 500 hPa, inferred using four satellite retrieval methods applied to Twelfth Geostationary Operational Environmental Satellite (GOES-12) data are evaluated using measurements during the July–August 2007 Tropical Composition, Cloud and Climate Coupling Experiment (TC4). The four methods are the single-layer CO2-absorption technique (SCO2AT), a modified CO2-absorption technique (MCO2AT) developed for improving both single-layered and multilayered cloud retrievals, a standard version of the Visible Infrared Solar-infrared Split-window Technique (old VISST), and a new version of VISST (new VISST) recently developed to improve cloud property retrievals. They are evaluated by comparing with ER-2 aircraft-based Cloud Physics Lidar (CPL) data taken during 9 days having extensive upper troposphere cirrus, anvil, and convective clouds. Compared to the 89% coverage by upper tropospheric clouds detected by the CPL, the SCO2AT, MCO2AT, old VISST, and new VISST retrieved CTPs < 500 hPa in 76, 76, 69, and 74% of the matched pixels, respectively. Most of the differences are due to subvisible and optically thin cirrus clouds occurring near the tropopause that were detected only by the CPL. The mean upper tropospheric CTHs for the 9 days are 14.2 (±2.1) km from the CPL and 10.7 (±2.1), 12.1 (±1.6), 9.7 (±2.9), and 11.4 (±2.8) km from the SCO2AT, MCO2AT, old VISST, and new VISST, respectively. Compared to the CPL, the MCO2AT CTHs had the smallest mean biases for semitransparent high clouds in both single-layered and multilayered situations whereas the new VISST CTHs had the smallest mean biases when upper clouds were opaque and optically thick. The biases for all techniques increased with increasing numbers of cloud layers. The transparency of the upper layer clouds tends to increase with the numbers of cloud layers. 3311 Clouds and aerosols; 3359 Radiative processes; 3394 Instruments and techniques; cloud top height; multilayer cloud; satellite cloud retrieval
Chang, Fu-Lung; Minnis, Patrick; Lin, Bing; Khaiyer, Mandana M.; Palikonda, Rabindra; Spangenberg, Douglas A.Chang, F., P. Minnis, B. Lin, M. M. Khaiyer, R. Palikonda, D. A. Spangenberg, 2010: A modified method for inferring upper troposphere cloud top height using the GOES 12 imager 10.7 and 13.3 μm data. Journal of Geophysical Research: Atmospheres, 115(D6), D06208. doi: 10.1029/2009JD012304. Passive satellite retrievals using conventional CO2 absorption techniques tend to systematically underestimate the upper transmissive cloud top heights (CTHs). These techniques are based on single-layer assumptions that the upper cloud occupies a geometrically thin layer above a cloud-free surface. This study presents a new modified CO2 absorption technique (MCO2AT) to improve the inference of transmissive CTHs in the upper troposphere above 600 hPa. The MCO2AT employs an iterative algorithm that starts with a single-layer CO2 absorption technique (SCO2AT) followed by an iterative procedure to retrieve an enhanced upper CTH based on inferred effective background radiances. Both techniques are applied to the 10.7 and 13.3 μm channel data of the Twelfth Geostationary Operational Environmental Satellite (GOES 12) imager and their retrievals of upper tropospheric CTHs are compared with two active sensing products: the ground-based Active Remotely Sensed Cloud Location (ARSCL) products from the Atmospheric Radiation Measurement Program (ARM) Southern Great Plains (SGP) site and the satellite-based Cloud Aerosol Lidar With Orthogonal Polarization (CALIOP) products. On average, the CTHs from MCO2AT and SCO2AT are lower than those from both of the active sensors by ∼1 and 2.4 km, respectively, possibly due to the different sensitivities and spatial resolutions between passive and active sensors. Preliminary validation of the new modified method is encouraging, especially the improvements for upper transmissive clouds in geometrically thick and/or multilayered cloud situations. The development of the modified method is particularly useful for sensors like the GOES 12, Meteosat-9, and others, which carry only one CO2 absorption channel at ∼13.3 μm. 3359 Radiative processes; 3394 Instruments and techniques; cloud top height; CO2 absorption technique; multilayer cloud
Chen, B.; Huang, J.; Minnis, P.; Hu, Y.; Yi, Y.; Liu, Z.; Zhang, D.; Wang, X.Chen, B., J. Huang, P. Minnis, Y. Hu, Y. Yi, Z. Liu, D. Zhang, X. Wang, 2010: Detection of dust aerosol by combining CALIPSO active lidar and passive IIR measurements. Atmos. Chem. Phys., 10(9), 4241-4251. doi: 10.5194/acp-10-4241-2010. The version 2 Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) dust layer detection method, which is based only on lidar measurements, misclassified about 43% dust layers (mainly dense dust layers) as cloud layers over the Taklamakan Desert. To address this problem, a new method was developed by combining the CALIPSO Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and passive Infrared Imaging Radiometer (IIR) measurements. This combined lidar and IR measurement (hereafter, CLIM) method uses the IIR tri-spectral IR brightness temperatures to discriminate between ice cloud and dense dust layers, and lidar measurements alone to detect thin dust and water cloud layers. The brightness temperature difference between 10.60 and 12.05 μm (BTD11−12) is typically negative for dense dust and generally positive for ice cloud, but it varies from negative to positive for thin dust layers, which the CALIPSO lidar correctly identifies. Results show that the CLIM method could significantly reduce misclassification rates to as low as ~7% for the active dust season of spring 2008 over the Taklamakan Desert. The CLIM method also revealed 18% more dust layers having greatly intensified backscatter between 1.8 and 4 km altitude over the source region compared to the CALIPSO version 2 data. These results allow a more accurate assessment of the effect of dust on climate.
Chen, Yonghang; Peng, Kuanjun; Huang, Jianping; Kang, Yanming; Zhang, Hua; Jiang, XiaobinChen, Y., K. Peng, J. Huang, Y. Kang, H. Zhang, X. Jiang, 2010: Seasonal and regional variability of cloud liquid water path in northwestern China derived from MODIS/CERES observations. International Journal of Remote Sensing, 31(4), 1037-1042. doi: 10.1080/01431160903154309. This article describes the seasonal and regional variability of cloud liquid water path (LWP) in northwestern China. The regions of interest are: the area influenced by the Asian monsoon, the Tianshan Mountains, the Qilian Mountains and the Taklimakan Desert. The results presented here were derived from the instantaneous observations of cloud LWP from National Aeronautics and Space Administration (NASA) Clouds and the Earth's Radiant Energy System (CERES) Single Scanner Footprint (SSF) Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) Edition 1B data from July 2002 to June 2004, and reflect more detailed subregional features than previous results from International Satellite Cloud Climatology Project (ISCCP) D2 monthly mean data. The seasonal and annual variation in cloud LWP is found to be significant in northwestern China, even within the same climate region.
Christopher, Sundar A.; Jones, Thomas A.Christopher, S. A., T. A. Jones, 2010: Satellite and surface-based remote sensing of Saharan dust aerosols. Remote Sensing of Environment, 114(5), 1002-1007. doi: 10.1016/j.rse.2009.12.007. The spatial and temporal characteristics of dust aerosols and their properties are assessed from satellite and ground-based sensors. The spatial distribution of total column aerosol optical depth at 550 nm (AOD) from the Moderate Resolution Imaging SpectroRadiometer (MODIS) coupled with top of atmosphere Clouds and the Earth's Radiant Energy System (CERES) shortwave fluxes are examined from the Terra satellite over the Atlantic Ocean. These data are then compared with AOD from two Aerosol Robotic Network (AERONET) ground-based sun photometer measurement sites for nearly six years (2000–2005). These two sites include Capo Verde (CV) (16°N, 24°W) near the Saharan dust source region and La Paguera (LP) (18°N, 67°W) that is downwind of the dust source regions. The AOD is two to three times higher during spring and summer months over CV when compared to LP and the surrounding regions. For a unit AOD value, the instantaneous TOA shortwave direct radiative effect (DRE) defined as the change in shortwave flux between clear and aerosol skies for CV and LP are − 53 and − 68 Wm− 2 respectively. DRE for LP is likely more negative due to fall out of larger particles during transport from CV to LP. However, separating the CERES-derived DRE by MODIS aerosol effective radii was difficult. Satellite and ground-based dust aerosol data sets continue to be useful to understand dust processes related to the surface and the atmosphere. Remote sensing; aerosols; CERES; MODIS; forcing; dust; AERONET
Chung, Eui-Seok; Soden, Brian J.; Sohn, Byung-JuChung, E., B. J. Soden, B. Sohn, 2010: Revisiting the determination of climate sensitivity from relationships between surface temperature and radiative fluxes. Geophysical Research Letters, 37(10), L10703. doi: 10.1029/2010GL043051. We analyze the radiative damping of climatological variations in surface temperature based on relationships between surface temperature and top-of-atmosphere radiative fluxes for both satellite observations and climate model simulations. The observed damping rates are generally consistent with positive radiative feedbacks over the tropical oceans, in agreement with climate model simulations. The model-simulated radiative damping rates are shown to be much more robust when analyzed at global scales, rather than tropical-means. Moreover, the model-simulated values of global-mean radiative damping rates deduced from interannual variability are shown to be modestly correlated to the climate sensitivity of the model in response to increasing CO2. 3309 Climatology; 3359 Radiative processes; 3305 Climate change and variability; 3337 Global climate models; 3310 Clouds and cloud feedbacks; Climate sensitivity; feedback parameter; relationships between surface temperature and radiative fluxes
Chung, Eui-Seok; Yeomans, David; Soden, Brian J.Chung, E., D. Yeomans, B. J. Soden, 2010: An assessment of climate feedback processes using satellite observations of clear-sky OLR. Geophysical Research Letters, 37(2), L02702. doi: 10.1029/2009GL041889. Clear-sky longwave radiative feedback processes depicted in climate models prepared for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) are investigated using satellite observations of the clear-sky outgoing longwave radiation (OLR). Estimates of clear-sky longwave radiative damping are derived from regional, seasonal, and interannual sources of variability. In spite of well-known biases of tropospheric temperature and humidity in climate models, comparisons indicate that the intermodel range in the rate of clear-sky radiative damping are small despite large intermodel variability in the mean clear-sky OLR. Moreover, the model-simulated rates of radiative damping are consistent with those obtained from satellite observations and are indicative of a strong positive correlation between temperature and water vapor variations over a broad range of spatiotemporal scales. 3309 Climatology; 3359 Radiative processes; 3305 Climate change and variability; 3337 Global climate models; clear-sky OLR; climate feedback processes
Dessler, A. E.Dessler, A. E., 2010: A Determination of the Cloud Feedback from Climate Variations over the Past Decade. Science, 330(6010), 1523-1527. doi: 10.1126/science.1192546. Estimates of Earth's climate sensitivity are uncertain, largely because of uncertainty in the long-term cloud feedback. I estimated the magnitude of the cloud feedback in response to short-term climate variations by analyzing the top-of-atmosphere radiation budget from March 2000 to February 2010. Over this period, the short-term cloud feedback had a magnitude of 0.54 ± 0.74 (2σ) watts per square meter per kelvin, meaning that it is likely positive. A small negative feedback is possible, but one large enough to cancel the climate’s positive feedbacks is not supported by these observations. Both long- and short-wave components of short-term cloud feedback are also likely positive. Calculations of short-term cloud feedback in climate models yield a similar feedback. I find no correlation in the models between the short- and long-term cloud feedbacks.
Di Biagio, Claudia; di Sarra, Alcide; Meloni, DanielaDi Biagio, C., A. di Sarra, D. Meloni, 2010: Large atmospheric shortwave radiative forcing by Mediterranean aerosols derived from simultaneous ground-based and spaceborne observations and dependence on the aerosol type and single scattering albedo. Journal of Geophysical Research: Atmospheres, 115(D10), D10209. doi: 10.1029/2009JD012697. Aerosol optical properties and shortwave irradiance measurements at the island of Lampedusa (central Mediterranean) during 2004–2007 are combined with Clouds and the Earth's Radiant Energy System observations of the outgoing shortwave flux at the top of the atmosphere (TOA). The measurements are used to estimate the surface (FES), the top of the atmosphere (FETOA), and the atmospheric (FEATM) shortwave aerosol forcing efficiencies for solar zenith angle (θ) between 15° and 55° for desert dust (DD), urban/industrial-biomass burning aerosols (UI-BB), and mixed aerosols (MA). The forcing efficiency at the different atmospheric levels is derived by applying the direct method, that is, as the derivative of the shortwave net flux versus the aerosol optical depth at fixed θ. The diurnal average forcing efficiency at the surface/TOA at the equinox is (−68.9 ± 4.0)/(−45.5 ± 5.4) W m−2 for DD, (−59.0 ± 4.3)/(−19.2 ± 3.3) W m−2 for UI-BB, and (−94.9 ± 5.1)/(−36.2 ± 1.7) W m−2 for MA. The diurnal average atmospheric radiative forcing at the equinox is (+7.3 ± 2.5) W m−2 for DD, (+8.4 ± 1.9) W m−2 for UI-BB, and (+8.2 ± 1.9) W m−2 for MA, suggesting that the mean atmospheric forcing is almost independent of the aerosol type. The largest values of the atmospheric forcing may reach +35 W m−2 for DD, +23 W m−2 for UI-BB, and +34 W m−2 for MA. FETOA is calculated for MA and 25° ≤ θ ≤ 35° for three classes of single scattering albedo (0.7 ≤ ω < 0.8, 0.8 ≤ ω < 0.9, and 0.9 ≤ ω ≤ 1) at 415.6 and 868.7 nm: FETOA increases, in absolute value, for increasing ω. A 0.1 increment in ω determines an increase in FETOA by 10–20 W m−2. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 3359 Radiative processes; Aerosol optical depth; aerosol single scattering albedo; atmospheric aerosols; atmospheric forcing; direct radiative forcing
Dong, Xiquan; Xi, Baike; Crosby, Kathryn; Long, Charles N.; Stone, Robert S.; Shupe, Matthew D.Dong, X., B. Xi, K. Crosby, C. N. Long, R. S. Stone, M. D. Shupe, 2010: A 10 year climatology of Arctic cloud fraction and radiative forcing at Barrow, Alaska. Journal of Geophysical Research: Atmospheres, 115(D17), D17212. doi: 10.1029/2009JD013489. A 10 year record of Arctic cloud fraction and radiative forcing has been generated using data collected at the Atmospheric Radiation Measurement (ARM) North Slope of Alaska site and the nearby NOAA Barrow Observatory (BRW) from June 1998 to May 2008. The cloud fractions (CFs) derived from ARM radar-lidar and ceilometer measurements increase significantly from March to May (0.57→0.84), remain relatively high (∼0.80–0.9) from May to October, and then decrease from November to the following March (0.8→0.57), having an annual average of 0.76. These CFs are comparable to those derived from ground-based radar-lidar observations during the Surface Heat Budget of the Arctic Ocean experiment and from satellite observations over the western Arctic regions. The monthly means of estimated clear-sky and measured all-sky shortwave (SW)-down and longwave (LW)-down fluxes at the two facilities are almost identical with the annual mean differences less than 1.6 Wm−2. Values of LW cloud radiative forcing (CRF) are minimum (6 Wm−2) in March, then increase monotonically to reach maximum (63 Wm−2) in August, then decrease continuously to the following March. The cycle of SW CRF mirrors its LW counterpart with the greatest negative impact occurring during the snow-free months of July and August. On annual average, the negative SW CRFs and positive LW CRFs nearly cancel, resulting in annual average NET CRF of about 3.5 Wm−2 on the basis of the combined ARM and BRW analysis. Compared with other studies, we find that LW CRF does not change over the Arctic regions significantly, but NET CRFs change from negative to positive from Alaska to the Beaufort Sea, indicating that Barrow is at a critical latitude for neutral NET CRF. The sensitivity study has shown that LW CRFs increase with increasing cloud fraction, liquid water path, and radiating temperature with high positive correlations (0.8–0.9). Negative correlations are found for SW CRFs, but a strong positive correlation between SW CRF and surface albedo exists. 1610 Atmosphere; 0321 Cloud/radiation interaction; radiative forcing; 1637 Regional climate change; 0480 Remote sensing; Arctic cloud fraction
Gautam, Ritesh; Hsu, N. Christina; Lau, K.-M.Gautam, R., N. C. Hsu, K. Lau, 2010: Premonsoon aerosol characterization and radiative effects over the Indo-Gangetic Plains: Implications for regional climate warming. Journal of Geophysical Research: Atmospheres, 115(D17), D17208. doi: 10.1029/2010JD013819. The Himalayas have a profound effect on the South Asian climate and the regional hydrological cycle, as it forms a barrier for the strong monsoon winds and serves as an elevated heat source, thus controlling the onset and distribution of precipitation during the Indian summer monsoon. Recent studies have suggested that radiative heating by absorbing aerosols, such as dust and black carbon over the Indo-Gangetic Plains (IGP) and slopes of the Himalayas, may significantly accelerate the seasonal warming of the Hindu Kush–Himalayas–Tibetan Plateau (HKHT) and influence the subsequent evolution of the summer monsoon. This paper presents a detailed characterization of aerosols over the IGP and their radiative effects during the premonsoon season (April-May-June) when dust transport constitutes the bulk of the regional aerosol loading, using ground radiometric and spaceborne observations. During the dust-laden period, there is a strong response of surface shortwave flux to aerosol absorption indicated by the diurnally averaged forcing efficiency of −70 Wm−2 per unit optical depth. The simulated aerosol single-scattering albedo, constrained by surface flux and aerosol measurements, is estimated to be 0.89 ± 0.01 (at ∼550 nm) with diurnal mean surface and top-of-atmosphere forcing values ranging from −11 to −79.8 Wm−2 and +1.4 to +12 Wm−2, respectively, for the premonsoon period. The model-simulated solar heating rate profile peaks in the lower troposphere with enhanced heating penetrating into the middle troposphere (5–6 km), caused by vertically extended aerosols over the IGP with peak altitude of ∼5 km as indicated by spaceborne Cloud-Aerosol Lidar with Orthogonal Polarization observations. On a long-term climate scale, our analysis, on the basis of microwave satellite measurements of tropospheric temperatures from 1979 to 2007, indicates accelerated annual mean warming rates found over the Himalayan–Hindu Kush region (0.21°C/decade ± 0.08°C/decade) and underscores the potential role of enhanced aerosol solar absorption in the maximum warming localized over the western Himalayas (0.26°C/decade ± 0.09°C/decade) that significantly exceed the entire HKHT and global warming rates. We believe the accelerated warming rates reported here are critical to both the South Asian summer monsoon and hydro-glaciological resource variability in the Himalayan–Hindu Kush snowpack and therefore to the densely populated downstream regions. 0360 Radiation: transmission and scattering; 1640 Remote sensing; 0305 Aerosols and particles; 0345 Pollution: urban and regional; aerosols; 3311 Clouds and aerosols; warming; Himalayas
Ge, J. M.; Su, J.; Ackerman, T. P.; Fu, Q.; Huang, J. P.; Shi, J. S.Ge, J. M., J. Su, T. P. Ackerman, Q. Fu, J. P. Huang, J. S. Shi, 2010: Dust aerosol optical properties retrieval and radiative forcing over northwestern China during the 2008 China-U.S. joint field experiment. Journal of Geophysical Research: Atmospheres, 115(D7), D00K12. doi: 10.1029/2009JD013263. The Atmosphere Radiation Measurements Program's Ancillary Facility (AAF/SMART-COMMIT) was deployed to Zhangye (39.082°N, 100.276°E), which is located in a semidesert area of northwest China, during the period of late April to mid June in 2008. We selected 11 cases to retrieve dust aerosol optical depth (AOD), Angstrom exponent, size distribution, single-scattering albedo (SSA) and asymmetry parameter (ASY) from multifilter rotating shadowband radiometer (MFRSR) measurements. These cases are dominated by large particles with Angstrom exponent values ranging from 0.34 to 0.93. The values of AOD at 0.67 μm range from 0.07 to 0.25. The mean SSA value increases with wavelength from 0.76 ± 0.02 at 0.415 μm to 0.86 ± 0.01 at 0.870 μm, while the mean ASY value decreases from 0.74 ± 0.04 to 0.70 ± 0.02. Before estimating dust aerosol direct radiative forcing, a radiative closure experiment was performed to verify that the retrieved aerosol optical properties and other input parameters to the radiative transfer model appropriately represent atmospheric conditions. The daytime-averaged differences between model simulations and ground observations are −8.5, −2.9, and −2.1 W m−2 for the total, diffuse, and direct normal fluxes, respectively. The mean difference in the instantaneous reflected solar fluxes at the top of atmosphere (TOA) between the model and CERES observations is 8.0 W m−2. The solar aerosol direct radiative forcing (ARF), averaged over a 24 h period, at the surface is −22.4 ± 8.9 W m−2, while the TOA ARF is small and has an average value of only 0.52 ± 1.69 W m−2. The daily averaged surface aerosol radiative forcing efficiency at 0.5 μm is −95.1 ± 10.3 W m−2τ−1. Our results illustrate that the primary role of dust aerosol is to alter the distribution of solar radiation within the climate system rather than to reflect solar energy to space. We assess the satellite aerosol optical depth products from Mutiangle Imaging Spectroradiometer (MISR) and Moderate Resolution Imaging Spectroradiometer (MODIS) observations by comparing them with our ground-based retrievals. Reasonable agreements with the ground-based observations are found for the MISR product and MODIS Deep Blue product. 0305 Aerosols and particles; 3311 Clouds and aerosols; 3359 Radiative processes; radiative forcing; Optical properties; Asian dust
Gui, Sheng; Liang, Shunlin; Li, LinGui, S., S. Liang, L. Li, 2010: Evaluation of satellite-estimated surface longwave radiation using ground-based observations. Journal of Geophysical Research: Atmospheres, 115(D18), D18214. doi: 10.1029/2009JD013635. This study evaluates four satellite-estimated data sets of surface longwave radiation (LW), the Global Energy and Water Cycle Experiment-Surface Radiation Budget (GEWEX-SRB), the International Satellite Cloud Climatology Project-Flux Data (ISCCP-FD), the Clouds and Earth Radiant Energy System-Gridded Radiative Fluxes and Clouds (CERES-FSW), and a newly developed data set from the Moderate Resolution Imaging Spectroradiometer (MODIS), with ground measurements at 15 sites of 2003. GEWEX-SRB (1°*1°) and ISCCP-FD (280 km*280 km) irradiance are available at 3-hourly intervals, CERES-FSW (1°*1°) and MODIS (1 km*1 km) irradiance are available at satellite overpass time. Evaluation is carried out separately for clear-sky, cloudy sky and all-sky conditions. Results show that, under all-sky conditions, downwelling LW (LWDN) in ISCCP-FD is overestimated while in CERES-FSW it is underestimated; but for LWDN in GEWEX-SRB and upwelling LW (LWUP) in all data sets, estimation errors are region-dependent: no uniform trend can be found. Under clear-sky conditions, LWDN in most data sets is underestimated, with some exceptions; LWUP in GEWEX-SRB and ISCCP-FD is overestimated while in CERES-FSW and MODIS it is underestimated with some exceptions. Under cloudy sky conditions, LWDN is overestimated in GEWEX-SRB and ISCCP-FD while it is underestimated in CERES-FSW; LWUP in most data sets is underestimated, with some exceptions. All data sets perform better when estimating LWUP than LWDN, during the nighttime than during the daytime, and under clear-sky conditions than under cloudy sky conditions. However, there are substantial errors in some regions, such as LWDN overestimation by ISCCP-FD on the Qinghai-Tibetan Plateau. Such errors are related to the errors of input precipitable water vapor, temperature, and elevation differences. 0360 Radiation: transmission and scattering; longwave radiation; water vapor; 1873 Uncertainty assessment; 3322 Land/atmosphere interactions; evaluation; 3275 Uncertainty quantification; surface air temperature; surface skin temperature
Gui, Sheng; Liang, Shunlin; Wang, Kaicun; Li, Lin; Zhang, XiaotongGui, S., S. Liang, K. Wang, L. Li, X. Zhang, 2010: Assessment of Three Satellite-Estimated Land Surface Downwelling Shortwave Irradiance Data Sets. IEEE Geoscience and Remote Sensing Letters, 7(4), 776-780. doi: 10.1109/LGRS.2010.2048196. This letter assesses three satellite-estimated surface downwelling shortwave irradiance data sets: 1) GEWEX-SRB; 2) ISCCP-FD; and 3) CERES-FSW, using ground measurements collected at 36 globally distributed sites from 2000-2002. SRB and FD solar irradiance are available at three hourly intervals during daytime and FSW hourly solar irradiance is available at late morning. The data are compared to ground measurements at the temporal resolutions of the satellite measurements. Results indicate that the downwelling solar irradiances of the three products show good overall agreement with ground measurements. FSW has an overall coefficient of determination of R2 = 0.69, a bias of 29.7 Wm-2 (6.0% in relative value), and a standard deviation (STD) of 123.2 Wm-2 (25.1% in relative value). The values are 0.83, -5.5 Wm-2 (-1.9%), 101.3 Wm-2 (35.0%) for SRB, and 0.83, 2.8 Wm-2 (0.3%), 101.7 W m 2 (35.0%) for FD. However, there are substantial uncertainties in these products in some regions. For example, large biases ranging from -90.2 Wm-2 to 45.8 Wm-2 are found in SRB in Southeast Asia. FD has large biases in Southeast Asia (58.9 Wm-2) and Greenland (-33.2 Wm-2). FSW has substantial biases in Southeast Asia (72.6 Wm-2) and Japan (66.5 Wm-2); while R2 is 0.35 in Tibetan Plateau and 0.47 in Southeast Asia. clouds; Land surface; Remote sensing; Satellites; ground truth; atmospheric techniques; Solar radiation; solar irradiance; artificial satellites; uncertainty; Atmospheric modeling; Southeast Asia; Decision support systems; CERES-FSW; Geography; Tibetan Plateau; Asia; AD 2000 to 2002; Data sets; downwelling shortwave irradiance; GEWEX-SRB; Greenland; ISCCP-FD; Japan; Performance evaluation; satellite estimated land surface downwelling shortwave irradiance; satellite-estimated; sunlight; technology assessment
Gupta, Shashi K.; Kratz, David P.; Stackhouse, Paul W.; Wilber, Anne C.; Zhang, Taiping; Sothcott, Victor E.Gupta, S. K., D. P. Kratz, P. W. Stackhouse, A. C. Wilber, T. Zhang, V. E. Sothcott, 2010: Improvement of Surface Longwave Flux Algorithms Used in CERES Processing. J. Appl. Meteor. Climatol., 49(7), 1579-1589. doi: 10.1175/2010JAMC2463.1. Abstract An improvement was developed and tested for surface longwave flux algorithms used in the Clouds and the Earth’s Radiant Energy System processing based on lessons learned during the validation of global results of those algorithms. The algorithms involved showed significant overestimation of downward longwave flux for certain regions, especially dry–arid regions during hot times of the day. The primary cause of this overestimation was identified and the algorithms were modified to (i) detect meteorological conditions that would produce an overestimation, and (ii) apply a correction when the overestimation occurred. The application of this correction largely eliminated the positive bias that was observed in earlier validation studies. Comparisons of validation results before and after the application of correction are presented. Fluxes; longwave radiation; Algorithms
Harries, John E.; Belotti, ClaudioHarries, J. E., C. Belotti, 2010: On the Variability of the Global Net Radiative Energy Balance of the Nonequilibrium Earth. J. Climate, 23(6), 1277-1290. doi: 10.1175/2009JCLI2797.1. Abstract Recent observations and model studies of the earth’s radiative energy balance have focused attention on the earth’s top of atmosphere (TOA) energy balance. This is the balance between the shortwave energy absorbed by the earth, which is represented by a spatially and temporally averaged absorbed flux , and the emitted longwave energy, which is represented by the corresponding averaged emitted flux . The TOA average net flux FN is defined as the difference between the two over the averaged area and time, which may be a local, regional, or global average. A global nonzero net flux represents a measure of imbalance between the energy being absorbed and emitted by the earth for the time interval in question. It is of interest to ask what the natural variability of the net flux might be and whether, during times of climate change, signals of important climate change processes might be detected against this natural background variation; examples of these signals include evidence of ocean heat storage, the effects of El Niño, and the radiative effects of volcanic eruptions. In this paper, the authors review the significance of the net flux, survey the observational evidence from a range of satellite instruments over several decades, and analyze some of the most recent observations from the Clouds and the Earth’s Radiant Energy System (CERES) program to determine what signals and what natural variability might be expected in the TOA net flux. Based on this analysis, the use of broadband radiation measurements for global climate change studies can be assessed. Radiative fluxes; Energy budget/balance; Radiation budgets; Climate predictions
Huang, J.; Minnis, P.; Yan, H.; Yi, Y.; Chen, B.; Zhang, L.; Ayers, J. K.Huang, J., P. Minnis, H. Yan, Y. Yi, B. Chen, L. Zhang, J. K. Ayers, 2010: Dust aerosol effect on semi-arid climate over Northwest China detected from A-Train satellite measurements. Atmos. Chem. Phys., 10(14), 6863-6872. doi: 10.5194/acp-10-6863-2010. The impact of dust aerosols on the semi-arid climate of Northwest China is analyzed by comparing aerosol and cloud properties derived over the China semi-arid region (hereafter, CSR) and the United States semi-arid region (hereafter, USR) using several years of surface and A-Train satellite observations during active dust event seasons. These regions have similar climatic conditions, but aerosol concentrations are greater over the CSR. Because the CSR is close to two major dust source regions (Taklamakan and Gobi deserts), the aerosols over the CSR not only contain local anthropogenic aerosols (agricultural dust, black carbon and other anthropogenic aerosols), but also include natural dust transported from the source regions. The aerosol optical depth, averaged over a 3-month period, derived from MODIS for the CSR is 0.27, which is 47% higher than that over the USR (0.19). Although transported natural dust only accounts for 53% of this difference, it is a major contributor to the average absorbing aerosol index, which is 27% higher in the CSR (1.07) than in the USR (0.84). During dust event periods, liquid water cloud particle size, optical depth and liquid water path are smaller by 9%, 30% and 33% compared to dust-free conditions, respectively.
Huang, Xianglei; Loeb, Norman G.; Yang, WenzeHuang, X., N. G. Loeb, W. Yang, 2010: Spectrally resolved fluxes derived from collocated AIRS and CERES measurements and their application in model evaluation: 2. Cloudy sky and band-by-band cloud radiative forcing over the tropical oceans. Journal of Geophysical Research: Atmospheres, 115(D21), D21101. doi: 10.1029/2010JD013932. We first present an algorithm for deriving cloudy sky outgoing spectral flux through the entire longwave spectrum from the collocated Atmospheric Infrared Sounder (AIRS) and Cloud and the Earth's Radiant Energy System (CERES) measurements over the tropical oceans. The algorithm is similar to the one described in part 1 of this series of studies: spectral angular dependent models are developed to estimate the spectral flux of each AIRS channel, and then a multivariate linear prediction scheme is used to estimate spectral fluxes at frequencies not covered by the AIRS instrument. The entire algorithm is validated against synthetic spectra as well as the CERES outgoing longwave radiation (OLR) measurements. Mean difference between the OLR estimated in this way and the collocated CERES OLR is 2.15 W m−2 with a standard deviation of 5.51 W m−2. The algorithm behaves consistently well for different combinations of cloud fractions and cloud-surface temperature difference, indicating the robustness of the algorithm for various cloudy scenes. Then, using the Geophysical Fluid Dynamics Laboratory AM2 model as a case study, we illustrate the merit of band-by-band cloud radiative forcings (CRFs) derived from this algorithm in model evaluation. The AM2 tropical annual mean band-by-band CRFs generally agree with the observed counterparts, but some systematic biases in the window bands and over the marine-stratus regions can be clearly identified. An idealized model is used to interpret the results and to explain why the fractional contribution of each band to the broadband CRF is worthy for studying: it is sensitive to cloud height but largely insensitive to the cloud fraction. 3359 Radiative processes; 3310 Clouds and cloud feedbacks; 1626 Global climate models; band-by-band cloud radiative forcing; GCM evaluation; spectral fluxes
Hudson, Stephen R.; Kato, Seiji; Warren, Stephen G.Hudson, S. R., S. Kato, S. G. Warren, 2010: Evaluating CERES angular distribution models for snow using surface reflectance observations from the East Antarctic Plateau. Journal of Geophysical Research: Atmospheres, 115(D3), D03101. doi: 10.1029/2009JD012624. Clouds and the Earth's radiant energy system (CERES) is a satellite-based remote sensing system designed to monitor the Earth's radiation budget. In this paper we examine uncertainties in the angular distribution models (ADMs) used by CERES over permanently snow covered surfaces with clear skies. These ADMs are a key part of the CERES data processing algorithms, used to convert the observed upwelling radiance to an estimate of the upwelling hemispheric flux. We model top-of-atmosphere anisotropic reflectance factors using an atmospheric radiative transfer model with a lower boundary condition based on extensive reflectance observations made at Dome C, Antarctica. The model results and subsequent analysis show that the CERES operational clear-sky permanent-snow ADMs are appropriate for use over Dome C, with differences of less than 5% between the model results and the ADMs at most geometries used by CERES operationally. We show that the uncertainty introduced into the flux estimates through the use of the modeled radiances used in the ADM development is small when the fluxes are averaged over time and space. Finally, we show that variations in the angular distribution of radiance at the top of the atmosphere due to atmospheric variability over permanently snow covered regions are in most cases unlikely to mask the real variations in flux caused by these atmospheric variations. Remote sensing; 0360 Radiation: transmission and scattering; 3359 Radiative processes; Solar radiation; snow; 0758 Remote sensing; 0736 Snow; 9310 Antarctica
Hudson, Stephen R.; Warren, Stephen G.; Kato, SeijiHudson, S. R., S. G. Warren, S. Kato, 2010: A comparison of shortwave reflectance over the East Antarctic Plateau observed by CERES to that estimated from surface reflectance observations. Journal of Geophysical Research: Atmospheres, 115(D20), D20110. doi: 10.1029/2010JD013912. Spectral albedo and bidirectional reflectance of snow were measured at Dome C on the East Antarctic Plateau for wavelengths of 350–2400 nm and solar zenith angles of 52°–87°. A parameterization of bidirectional reflectance, based on those measurements, is used as the lower boundary condition in the atmospheric radiation model SBDART to calculate radiance and flux at the top of the atmosphere (TOA). The model's atmospheric profile is based on radiosoundings at Dome C and ozonesoundings at the South Pole. Computed TOA radiances are integrated over wavelength for comparison with the Clouds and the Earth's Radiant Energy System (CERES) shortwave channel. CERES radiance observations and flux estimates from four clear days in January 2004 and January 2005 from within 200 km of Dome C are compared with the TOA radiances and fluxes computed for the same solar zenith angle and viewing geometry, providing 11,000 comparisons. The measured radiance and flux are lower than the computed values. The median difference is about 7% for CERES on Terra, and 9% on Aqua. Sources of uncertainty in the model and observations are examined in detail and suggest that the measured values should be less than the computed values, but only by 1.7% ± 4%. The source of the discrepancy of about 6% cannot be identified here; however, the modeled values do agree with observations from another satellite instrument (Multiangle Imaging Spectroradiometer), suggesting that the CERES calibration must be considered a possible source of the discrepancy. Remote sensing; 0360 Radiation: transmission and scattering; 3359 Radiative processes; Solar radiation; 0758 Remote sensing; 0736 Snow; Antarctica; 9310 Antarctica
Kandel, Robert; Viollier, MichelKandel, R., M. Viollier, 2010: Observation of the Earth's radiation budget from space. Comptes Rendus Geoscience, 342(4–5), 286-300. doi: 10.1016/j.crte.2010.01.005. The planet's radiation budget includes practically all energy exchange between the Sun, the Earth, and space, and so is a fundamental factor of climate. The terms of this budget, observable only from space, are determined from sampled direct measurements of the solar and terrestrial radiation fields. On the contrary, however, it should be remembered that energy exchange between the Earth's surface and its atmosphere involves not only radiative but also non-radiative energy fluxes. Nevertheless, only observations from space can provide satisfactory global coverage of the different energy fluxes that determine climate at the Earth's surface, by way of indirect retrievals of radiative fluxes at the surface and at different heights in the atmosphere. We describe the methods, applied to measurements made with a variety of instruments on board different artificial satellites, that have led to our present knowledge of the Earth's radiation budget (ERB) at the “top of the atmosphere”: global annual mean values of the ERB terms, its annual cycle, its geographical structure, and its variations. We know that solar irradiance, averaged over the globe and the year, varies by only 0.1% with the solar activity cycle; we also know that planetary (Bond) albedo is close to 0.3, that the global annual mean emission of thermal infrared radiation to space is close to 240 Wm−2, and that these terms exhibit a weak but well determined annual cycle. We also know that cloud cover plays a major role in the radiation budget, both in the “shortwave” domain (global SW “cloud radiative forcing” –50 Wm−2) and in the “longwave” domain (+20 Wm−2), thus a net forcing of –30 Wm−2. Successive satellite missions give consistent results for the shape, the phase, and the amplitude of the annual cycle of the planetary radiation balance. However, the different estimates of its annual mean absolute value remain uncertain, not differing significantly from zero, although generally excessively positive. We also rapidly review the methods used to determine the surface radiation budget as well as that of the atmosphere. For the planetary (TOA) radiation budget, we examine to what extent interannual variations and interdecadal trends have been or could be detected. We conclude with a review of projects under way. We also discuss priorities for future efforts, considering in particular, on the one hand (Ringer, 1997), the need to better quantify the factors that govern climate sensitivity to modifications of the atmosphere's radiative properties, on the other hand, the importance of monitoring the evolution of the present disequilibrium situation. albedo; solar irradiance; Bilan radiatif de la Terre (BRT), Forçage radiatif de la nébulosité, Irradiance solaire, Albédo, Rétroactions climatiques, Observation satellitale de la Terre; climate feedbacks; Cloud radiative forcing (CRF); Earth radiation budget (ERB); Satellite observation of the Earth
Kato, Seiji; Sun-Mack, Sunny; Miller, Walter F.; Rose, Fred G.; Chen, Yan; Minnis, Patrick; Wielicki, Bruce A.Kato, S., S. Sun-Mack, W. F. Miller, F. G. Rose, Y. Chen, P. Minnis, B. A. Wielicki, 2010: Relationships among cloud occurrence frequency, overlap, and effective thickness derived from CALIPSO and CloudSat merged cloud vertical profiles. Journal of Geophysical Research: Atmospheres, 115(D4), D00H28. doi: 10.1029/2009JD012277. A cloud frequency of occurrence matrix is generated using merged cloud vertical profiles derived from the satellite-borne Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and cloud profiling radar. The matrix contains vertical profiles of cloud occurrence frequency as a function of the uppermost cloud top. It is shown that the cloud fraction and uppermost cloud top vertical profiles can be related by a cloud overlap matrix when the correlation length of cloud occurrence, which is interpreted as an effective cloud thickness, is introduced. The underlying assumption in establishing the above relation is that cloud overlap approaches random overlap with increasing distance separating cloud layers and that the probability of deviating from random overlap decreases exponentially with distance. One month of Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and CloudSat data (July 2006) support these assumptions, although the correlation length sometimes increases with separation distance when the cloud top height is large. The data also show that the correlation length depends on cloud top hight and the maximum occurs when the cloud top height is 8 to 10 km. The cloud correlation length is equivalent to the decorrelation distance introduced by Hogan and Illingworth (2000) when cloud fractions of both layers in a two-cloud layer system are the same. The simple relationships derived in this study can be used to estimate the top-of-atmosphere irradiance difference caused by cloud fraction, uppermost cloud top, and cloud thickness vertical profile differences. clouds; 0360 Radiation: transmission and scattering; 1610 Atmosphere; 0321 Cloud/radiation interaction; overlap; vertical profile
Kennedy, Aaron D.; Dong, Xiquan; Xi, Baike; Minnis, Patrick; Del Genio, Anthony D.; Wolf, Audrey B.; Khaiyer, Mandana M.Kennedy, A. D., X. Dong, B. Xi, P. Minnis, A. D. Del Genio, A. B. Wolf, M. M. Khaiyer, 2010: Evaluation of the NASA GISS Single-Column Model Simulated Clouds Using Combined Surface and Satellite Observations. J. Climate, 23(19), 5175-5192. doi: 10.1175/2010JCLI3353.1. Abstract Three years of surface and Geostationary Operational Environmental Satellite (GOES) data from the Department of Energy Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site are used to evaluate the NASA GISS Single Column Model (SCM) simulated clouds from January 1999 to December 2001. The GOES-derived total cloud fractions for both 0.5° and 2.5° grid boxes are in excellent agreement with surface observations, suggesting that ARM point observations can represent large areal observations. Low (6 km) levels of cloud fractions, however, have negative biases as compared to the ARM results due to multilayer cloud scenes that can either mask lower cloud layers or cause misidentifications of cloud tops. Compared to the ARM observations, the SCM simulated most midlevel clouds, overestimated low clouds (4%), and underestimated total and high clouds by 7% and 15%, respectively. To examine the dependence of the modeled high and low clouds on the large-scale synoptic patterns, variables such as relative humidity (RH) and vertical pressure velocity (omega) from North American Regional Reanalysis (NARR) data are included. The successfully modeled and missed high clouds are primarily associated with a trough and ridge upstream of the ARM SGP, respectively. The PDFs of observed high and low occurrence as a function of RH reveal that high clouds have a Gaussian-like distribution with mode RH values of ∼40%–50%, whereas low clouds have a gammalike distribution with the highest cloud probability occurring at RH ∼75%–85%. The PDFs of modeled low clouds are similar to those observed; however, for high clouds the PDFs are shifted toward higher values of RH. This results in a negative bias for the modeled high clouds because many of the observed clouds occur at RH values below the SCM-specified stratiform parameterization threshold RH of 60%. Despite many similarities between PDFs derived from the NARR and ARM forcing datasets for RH and omega, differences do exist. This warrants further investigation of the forcing and reanalysis datasets. satellite observations; Cloud cover; humidity; forcing; Cloud resolving models; Single column models
Kratz, David P.; Gupta, Shashi K.; Wilber, Anne C.; Sothcott, Victor E.Kratz, D. P., S. K. Gupta, A. C. Wilber, V. E. Sothcott, 2010: Validation of the CERES Edition 2B Surface-Only Flux Algorithms. J. Appl. Meteor. Climatol., 49(1), 164-180. doi: 10.1175/2009JAMC2246.1. Abstract The Clouds and the Earth’s Radiant Energy System (CERES) project uses two shortwave (SW) and two longwave (LW) algorithms to derive surface radiative fluxes on an instantaneous footprint basis from a combination of top-of-atmosphere fluxes, ancillary meteorological data, and retrieved cloud properties. Since the CERES project examines the radiative forcings and feedbacks for Earth’s entire climate system, validation of these models for a wide variety of surface conditions is paramount. The present validation effort focuses upon the ability of these surface-only flux algorithms to produce accurate CERES Edition 2B single scanner footprint data from the Terra and Aqua spacecraft measurements. To facilitate the validation process, high-quality radiometric surface observations have been acquired that were coincident with the CERES-derived surface fluxes. For both SW models, systematic errors range from −20 to −12 W m−2 (from −2.8% to −1.6%) for global clear-sky cases, while for the all-sky SW model, the systematic errors range from 14 to 21 W m−2 (3.2%–4.8%) for global cloudy-sky cases. Larger systematic errors were seen for the individual surface types, and significant random errors where observed, especially for cloudy-sky cases. While the SW models nearly achieved the 20 W m−2 accuracy requirements established for climate research, further improvements are warranted. For the clear-sky LW model, systematic errors were observed to fall within ±5.4 W m−2 (±1.9%) except for the polar case in which systematic errors on the order from −15 to −11 W m−2 (from −13% to −7.2%) occurred. For the all-sky LW model, systematic errors were less than ±9.2 W m−2 (±7.6%) for both the clear-sky and cloudy-sky cases. The random errors were less than 17 W m−2 (6.2%) for clear-sky cases and 28 W m−2 (13%) for cloudy-sky cases, except for the desert cases in which very high surface skin temperatures caused an overestimation in the model-calculated surface fluxes. Overall, however, the LW models met the accuracy requirements for climate research. satellite observations; longwave radiation; Shortwave radiation; Surface fluxes
Lebsock, Matthew D.; Kummerow, Christian; Stephens, Graeme L.Lebsock, M. D., C. Kummerow, G. L. Stephens, 2010: An Observed Tropical Oceanic Radiative–Convective Cloud Feedback. J. Climate, 23(8), 2065-2078. doi: 10.1175/2009JCLI3091.1. Abstract Anomalies of precipitation, cloud, thermodynamic, and radiation variables are analyzed on the large spatial scale defined by the tropical oceans. In particular, relationships between the mean tropical oceanic precipitation anomaly and radiative anomalies are examined. It is found that tropical mean precipitation is well correlated with cloud properties and radiative fields. In particular, the tropical mean precipitation anomaly is positively correlated with the top of the atmosphere reflected shortwave anomaly and negatively correlated with the emitted longwave anomaly. The tropical mean relationships are found to primarily result from a coherent oscillation of precipitation and the area of high-level cloudiness. The correlations manifest themselves radiatively as a modest decrease in net downwelling radiation at the top of the atmosphere, and a redistribution of energy from the surface to the atmosphere through reduced solar radiation to the surface and decreased longwave emission to space. Integrated over the tropical oceanic domain, the anomalous atmospheric column radiative heating is found to be about 10% of the magnitude of the anomalous latent heating. The temporal signature of the radiative heating is observed in the column mean temperature that indicates a coherent phase-lagged oscillation between atmospheric stability and convection. These relationships are identified as a radiative–convective cloud feedback that is observed on intraseasonal time scales in the tropical atmosphere. Feedback; convective clouds; radiation budget; Intraseasonal variability; Precipitation
Li, R.; Min, Q-L.; Harrison, L. C.Li, R., Q. Min, L. C. Harrison, 2010: A Case Study: The Indirect Aerosol Effects of Mineral Dust on Warm Clouds. J. Atmos. Sci., 67(3), 805-816. doi: 10.1175/2009JAS3235.1. Abstract The indirect aerosol effect (Twomey effect) is studied during a Saharan dust-transport event that presented an unusually favorable combination of a dust-loading gradient across clouds with warm cloud-top temperatures. Standard retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS), the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E), and the Clouds and the Earth’s Radiant Energy System (CERES) provide cloud-top temperature (a surrogate for height), liquid water path (LWP), classification of precipitation regime, and radiation flux. The authors correlate a retrieved mean effective droplet radius (re) versus the number concentration of cloud condensation nuclei (NCCN), using the regressed slope d lnre/d lnNCCN as the estimator of the aerosol indirect effect (AIE). Results demonstrate statistically significant AIE for only some of the segregated cloud classes. For nonprecipitating clouds (the most direct test of Twomey effect), the estimated AIE is effectively −0.07 over all wider temperature bands and is statistically significant from 1.1 to 1.9 σ. Further classification by LWP strengthens both the AIE (for all LWP > 150 g m−2) to approximately −0.16, and substantially increases the statistical significance, to better than 5σ. Shortwave radiation forcing of dust aerosols is also estimated directly from satellite measurements. The direct shortwave (SW) radiation effect of Saharan dusts at solar zenith angle 21.6° is 53.48 ± 8.56 W m−2 per unit aerosol optical depth, with a correlation coefficient of 0.92. The indirect SW forcing of Saharan dust is 29.88 ± 2.42 W m−2 per unit AOD for clouds with LWP of 100 g m−2. clouds; aerosols; transport; Shortwave radiation; Precipitation; dust
Lin, B.; Chambers, L.; P. Stackhouse Jr.; Wielicki, B.; Hu, Y.; Minnis, P.; Loeb, N.; Sun, W.; Potter, G.; Min, Q.; Schuster, G.; Fan, T.-F.Lin, B., L. Chambers, . P. Stackhouse Jr., B. Wielicki, Y. Hu, P. Minnis, N. Loeb, W. Sun, G. Potter, Q. Min, G. Schuster, T. Fan, 2010: Estimations of climate sensitivity based on top-of-atmosphere radiation imbalance. Atmos. Chem. Phys., 10(4), 1923-1930. doi: 10.5194/acp-10-1923-2010. Large climate feedback uncertainties limit the accuracy in predicting the response of the Earth's climate to the increase of CO2 concentration within the atmosphere. This study explores a potential to reduce uncertainties in climate sensitivity estimations using energy balance analysis, especially top-of-atmosphere (TOA) radiation imbalance. The time-scales studied generally cover from decade to century, that is, middle-range climate sensitivity is considered, which is directly related to the climate issue caused by atmospheric CO2 change. The significant difference between current analysis and previous energy balance models is that the current study targets at the boundary condition problem instead of solving the initial condition problem. Additionally, climate system memory and deep ocean heat transport are considered. The climate feedbacks are obtained based on the constraints of the TOA radiation imbalance and surface temperature measurements of the present climate. In this study, the TOA imbalance value of 0.85 W/m2 is used. Note that this imbalance value has large uncertainties. Based on this value, a positive climate feedback with a feedback coefficient ranging from −1.3 to −1.0 W/m2/K is found. The range of feedback coefficient is determined by climate system memory. The longer the memory, the stronger the positive feedback. The estimated time constant of the climate is large (70~120 years) mainly owing to the deep ocean heat transport, implying that the system may be not in an equilibrium state under the external forcing during the industrial era. For the doubled-CO2 climate (or 3.7 W/m2 forcing), the estimated global warming would be 3.1 K if the current estimate of 0.85 W/m2 TOA net radiative heating could be confirmed. With accurate long-term measurements of TOA radiation, the analysis method suggested by this study provides a great potential in the estimations of middle-range climate sensitivity.
Lin, Bing; Minnis, Patrick; Fan, Tai-Fang; Hu, Yongxiang; Sun, WenboLin, B., P. Minnis, T. Fan, Y. Hu, W. Sun, 2010: Radiation characteristics of low and high clouds in different oceanic regions observed by CERES and MODIS. International Journal of Remote Sensing, 31(24), 6473-6492. doi: 10.1080/01431160903548005. Radiative properties measured by the Clouds and the Earth's Radiant Energy System (CERES) and the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Aqua spacecraft are evaluated for the same types of clouds in selected areas. Individual measurements are analysed statistically to take advantage of both gridded and individual cloud characteristics. The seasonal variations of radiative fluxes for the same types of clouds from different areas are remarkably similar. Although cloud liquid water paths (LWPs) or ice water paths (IWPs) vary considerably for the same types of clouds, their statistical distributions are very stable for different periods and areas, suggesting that the regional differences in dynamics and thermodynamics primarily cause changes in the cloud frequency or coverage and only secondarily in the cloud macrophysical characteristics such as IWPs or LWPs. These results establish a systematic approach of observations for testing modelled cloud statistics and for improving cloud model parameterizations.
Lin, Wuyin; Zhang, Minghua; Loeb, Norman G.Lin, W., M. Zhang, N. G. Loeb, 2010: Reply to Comments on “Seasonal Variation of the Physical Properties of Marine Boundary Layer Clouds off the California Coast”. J. Climate, 23(12), 3421-3423. doi: 10.1175/2010JCLI3483.1. clouds; satellite observations; North America; marine boundary layer; Seasonal variability
Liu, YangangLiu, Y., 2010: Comments on “Seasonal Variation of the Physical Properties of Marine Boundary Layer Clouds off the California Coast”. J. Climate, 23(12), 3416-3420. doi: 10.1175/2010JCLI3407.1. clouds; satellite observations; North America; marine boundary layer; Seasonal variability
Loeb, Norman G.; Su, WenyingLoeb, N. G., W. Su, 2010: Direct Aerosol Radiative Forcing Uncertainty Based on a Radiative Perturbation Analysis. J. Climate, 23(19), 5288-5293. doi: 10.1175/2010JCLI3543.1. Abstract To provide a lower bound for the uncertainty in measurement-based clear- and all-sky direct aerosol radiative forcing (DARF), a radiative perturbation analysis is performed for the ideal case in which the perturbations in global mean aerosol properties are given by published values of systematic uncertainty in Aerosol Robotic Network (AERONET) aerosol measurements. DARF calculations for base-state climatological cloud and aerosol properties over ocean and land are performed, and then repeated after perturbing individual aerosol optical properties (aerosol optical depth, single-scattering albedo, asymmetry parameter, scale height, and anthropogenic fraction) from their base values, keeping all other parameters fixed. The total DARF uncertainty from all aerosol parameters combined is 0.5–1.0 W m−2, a factor of 2–4 greater than the value cited in the Intergovernmental Panel on Climate Change’s (IPCC’s) Fourth Assessment Report. Most of the total DARF uncertainty in this analysis is associated with single-scattering albedo uncertainty. Owing to the greater sensitivity to single-scattering albedo in cloudy columns, DARF uncertainty in all-sky conditions is greater than in clear-sky conditions, even though the global mean clear-sky DARF is more than twice as large as the all-sky DARF. aerosols; Radiation budgets; radiative forcing; Surface observations
Logan, Timothy; Xi, Baike; Dong, Xiquan; Obrecht, Rebecca; Li, Zhanqing; Cribb, MaureenLogan, T., B. Xi, X. Dong, R. Obrecht, Z. Li, M. Cribb, 2010: A study of Asian dust plumes using satellite, surface, and aircraft measurements during the INTEX-B field experiment. Journal of Geophysical Research: Atmospheres, 115(D7), D00K25. doi: 10.1029/2010JD014134. Asian dust events occur frequently during the boreal spring season. Their optical properties have been analyzed by using a combination of source region (ground-based and satellite) and remote Pacific Ocean (aircraft) measurements during the Intercontinental Chemical Transport Experiment-Phase B (INTEX-B) field campaign which lasted from 7 April to 15 May 2006. A strong dust event originating from the Gobi Desert and passing over the Xianghe surface site on 17 April 2006 has been extensively analyzed. The surface averaged aerosol optical depth (AOD) values increased from 0.17 (clear sky) to 4.0 (strong dust), and the Angström exponent (α) dropped from 1.26 (clear sky) to below 0.1. Its total downwelling SW flux over the Xianghe site (thousands of kilometers away from the dust source region) is only 46% of the clear-sky value with almost no direct transmission and nearly double the diffuse SW clear-sky value. This event was also captured 6 days later by satellite observations as well as the UND/NASA DC-8 aircraft over the eastern Pacific Ocean. The DC-8 measurements in the remote Pacific region further classified the plumes into dust dominant, pollution dominant, and a mixture of dust and pollution events. HYSPLIT backward trajectories not only verified the origins of each case we selected but also showed (1) two possible origins for the dust: the Gobi and Taklimakan deserts; and (2) pollution: urban areas in eastern China, Japan, and other industrialized cities east of the two deserts. Based on the averaged satellite retrieved AOD data (0.5° × 0.5° grid box), declining AOD values with respect to longitude demonstrated the evolution of the transpacific transport pathway of Asian dust and pollution over the period of the field campaign. 0305 Aerosols and particles; 0340 Middle atmosphere: composition and chemistry; 0368 Troposphere: constituent transport and chemistry; dust; 0341 Middle atmosphere: constituent transport and chemistry; 0322 Constituent sources and sinks; aerosol physics; transpacific transport
L’Ecuyer, Tristan S.; McGarragh, GregL’Ecuyer, T. S., G. McGarragh, 2010: A 10-Year Climatology of Tropical Radiative Heating and Its Vertical Structure from TRMM Observations. J. Climate, 23(3), 519-541. doi: 10.1175/2009JCLI3018.1. Abstract This paper outlines recent advances in estimating atmospheric radiative heating rate profiles from the sensors aboard the Tropical Rainfall Measuring Mission (TRMM). The approach employs a deterministic framework in which four distinct retrievals of clouds, precipitation, and other atmospheric and surface properties are combined to form input to a broadband radiative transfer model that simulates profiles of upwelling and downwelling longwave and shortwave radiative fluxes in the atmosphere. Monthly, 5° top of the atmosphere outgoing longwave and shortwave flux estimates agree with corresponding observations from the Clouds and the Earth’s Radiant Energy System (CERES) to within 7 W m−2 and 3%, respectively, suggesting that the resulting products can be thought of as extending the eight-month CERES dataset to cover the full lifetime of TRMM. The analysis of a decade of TRMM data provides a baseline climatology of the vertical structure of atmospheric radiative heating in today’s climate and an estimate of the magnitude of its response to environmental forcings on weekly to interannual time scales. In addition to illustrating the scope and properties of the dataset, the results highlight the strong influence of clouds, water vapor, and large-scale dynamics on regional radiation budgets and the vertical structure of radiative heating in the tropical and subtropical atmospheres. The combination of the radiative heating rate product described here, with profiles of latent heating that are now also being generated from TRMM sensors, provides a unique opportunity to develop large-scale estimates of vertically resolved atmospheric diabatic heating using satellite observations. tropics; Radiative fluxes; satellite observations; Climatology; Heating
Ma, X.; von Salzen, K.; Cole, J.Ma, X., K. von Salzen, J. Cole, 2010: Constraints on interactions between aerosols and clouds on a global scale from a combination of MODIS-CERES satellite data and climate simulations. Atmos. Chem. Phys., 10(20), 9851-9861. doi: 10.5194/acp-10-9851-2010. Satellite-based cloud top effective radius retrieved by the CERES Science Team were combined with simulated aerosol concentrations from CCCma CanAM4 to examine relationships between aerosol and cloud that underlie the first aerosol indirect (cloud albedo) effect. Evidence of a strong negative relationship between sulphate, and organic aerosols, with cloud top effective radius was found for low clouds, indicating both aerosol types are contributing to the first indirect effect on a global scale. Furthermore, effects of aerosol on the cloud droplet effective radius are more pronounced for larger cloud liquid water paths. While CanAM4 broadly reproduces the observed relationship between sulphate aerosols and cloud droplets, it does not reproduce the dependency of cloud top droplet size on organic aerosol concentrations nor the dependency on cloud liquid water path. Simulations with a modified version of the model yield a more realistic dependency of cloud droplets on organic carbon. The robustness of the methods used in the study are investigated by repeating the analysis using aerosol simulated by the GOCART model and cloud top effective radii derived from the MODIS Science Team.
Mauger, Guillaume S.; Norris, Joel R.Mauger, G. S., J. R. Norris, 2010: Assessing the Impact of Meteorological History on Subtropical Cloud Fraction. J. Climate, 23(11), 2926-2940. doi: 10.1175/2010JCLI3272.1. Abstract This study presents findings from the application of a new Lagrangian method used to evaluate the meteorological sensitivities of subtropical clouds in the northeast Atlantic. Parcel back trajectories are used to account for the influence of previous meteorological conditions on cloud properties, whereas forward trajectories highlight the continued evolution of cloud state. Satellite retrievals from Moderate Resolution Imaging Spectroradiometer (MODIS), Clouds and the Earth’s Radiant Energy System (CERES), Quick Scatterometer (QuikSCAT), and Special Sensor Microwave Imager (SSM/I) provide measurements of cloud properties as well as atmospheric state. These are complemented by meteorological fields from the ECMWF operational analysis model. Observations are composited by cloud fraction, and mean trajectories are used to evaluate differences between each composite. Systematic differences in meteorological conditions are found to extend through the full 144-h trajectories, confirming the need to account for cloud history in assessing impacts on cloud properties. Most striking among these is the observation that strong synoptic-scale divergence is associated with reduced cloud fraction 0–12 h later. Consistent with prior work, the authors find that cloud cover variations correlate best with variations in lower-tropospheric stability (LTS) and SST that are 36 h upwind. In addition, the authors find that free-tropospheric humidity, along-trajectory SST gradient, and surface fluxes all correlate best at lags ranging from 0 to 12 h. Overall, cloud cover appears to be most strongly impacted by variations in surface divergence over short time scales ( clouds; satellite observations; History
Medvigy, David; Walko, Robert L.; Otte, Martin J.; Avissar, RoniMedvigy, D., R. L. Walko, M. J. Otte, R. Avissar, 2010: The Ocean–Land–Atmosphere Model: Optimization and Evaluation of Simulated Radiative Fluxes and Precipitation. Mon. Wea. Rev., 138(5), 1923-1939. doi: 10.1175/2009MWR3131.1. Abstract This work continues the presentation and evaluation of the Ocean–Land–Atmosphere Model (OLAM), focusing on the model’s ability to represent radiation and precipitation. OLAM is a new, state-of-the-art earth system model, capable of user-specified grid resolution and local mesh refinement. An objective optimization of the microphysics parameterization is carried out. Data products from the Clouds and the Earth’s Radiant Energy System (CERES) and the Global Precipitation Climatology Project (GPCP) are used to construct a maximum likelihood function, and thousands of simulations using different values for key parameters are carried out. Shortwave fluxes are found to be highly sensitive to both the density of cloud droplets and the assumed shape of the cloud droplet diameter distribution function. Because there is considerable uncertainty in which values for these parameters to use in climate models, they are targeted as the tunable parameters of the objective optimization procedure, which identified high-likelihood volumes of parameter space as well as parameter uncertainties and covariances. Once optimized, the model closely matches observed large-scale radiative fluxes and precipitation. The impact of model resolution is also tested. At finer characteristic length scales (CLS), smaller-scale features such as the ITCZ are better resolved. It is also found that the Amazon was much better simulated at 100- than 200-km CLS. Furthermore, a simulation using OLAM’s variable resolution functionality to cover South America with 100-km CLS and the rest of the world with 200-km CLS generates a precipitation pattern in the Amazon similar to the global 100-km CLS run. Radiative fluxes; Coupled models; Precipitation; Atmosphere-land interaction; Ocean models
Moy, L. A.; Knuteson, R. O.; Tobin, D. C.; Revercomb, H. E.; Borg, L. A.; Susskind, J.Moy, L. A., R. O. Knuteson, D. C. Tobin, H. E. Revercomb, L. A. Borg, J. Susskind, 2010: Comparison of measured and modeled outgoing longwave radiation for clear-sky ocean and land scenes using coincident CERES and AIRS observations. Journal of Geophysical Research: Atmospheres, 115(D15), D15110. doi: 10.1029/2009JD012758. Clear-sky outgoing longwave radiation (OLR) is computed using the Atmospheric and Environmental Research (AER), Inc., Rapid Radiative Transfer Model (RRTM) for comparison with the observations of the Clouds and the Earth's Radiant Energy System (CERES) for both ocean and land scenes. CERES clear-sky OLR is in agreement with RRTM model calculations to 0.2% accuracy using best estimate radiosondes (BE) launched coincident with NASA Aqua overpasses at the Atmospheric Radiation Measurement Southern Great Plains (SGP) site and 0.8% using retrieved profiles of temperature, water vapor, ozone, and surface parameters from the Atmospheric Infrared Sounder (AIRS) on the Aqua platform. A partial flux analysis using AIRS radiances implies an accuracy for the RRTM model in the far infrared of 0.4% (about 0.5 W/m2) for wave numbers less than 650 cm−1 (wavelengths greater than 15.4 μm). CERES minus model biases over clear-sky ocean are similar to previously published results. Ordering the results according to the magnitude of the measured minus model mean bias for nighttime, tropical, ocean gives: +0.57 ± 1.9 W/m2 (Dessler/Fu-Liou), +0.83 ± 1.5 W/m2 (Huang/MODTRAN5), +1.6 ± 1.6 W/m2 (Moy/RRTM), +3.7 ± 2.1 W/m2 (Dessler/Chou). Comparison of observed minus modeled OLR over land are included in this study. Excluding nonfrozen ocean, a mean difference over land of +2.0 W/m2 for nighttime cases and +1.0 W/m2 for daytime cases is found where the land classes are weighted inversely by their standard error. The nighttime bias is quite consistent across all the land classes. The daytime bias shows less consistency with a tendency toward larger CERES minus AIRS RRTM OLR bias for the land classes with smaller vegetation fraction. Comparison of clear-sky CERES and AIRS RRTM OLR over cold snow-/ice-covered surfaces (mainly in the polar regions) is complicated by the use of the MODIS cloud mask in the identification of the clear CERES footprints used in the comparison. Clear scenes over cold surfaces can be identified more reliably in the daytime, for which the comparison between CERES and AIRS RRTM is better than 1.2 W/m2 indicating good agreement. 1610 Atmosphere; 1640 Remote sensing; 3359 Radiative processes; clear-sky OLR
Murphy, D. M.; Forster, P. M.Murphy, D. M., P. M. Forster, 2010: On the Accuracy of Deriving Climate Feedback Parameters from Correlations between Surface Temperature and Outgoing Radiation. J. Climate, 23(18), 4983-4988. doi: 10.1175/2010JCLI3657.1. Abstract Changes in outgoing radiation are both a consequence and a cause of changes in the earth’s temperature. Spencer and Braswell recently showed that in a simple box model for the earth the regression of outgoing radiation against surface temperature gave a slope that differed from the model’s true feedback parameter. They went on to select input parameters for the box model based on observations, computed the difference for those conditions, and asserted that there is a significant bias for climate studies. This paper shows that Spencer and Braswell overestimated the difference. Differences between the regression slope and the true feedback parameter are significantly reduced when 1) a more realistic value for the ocean mixed layer depth is used, 2) a corrected standard deviation of outgoing radiation is used, and 3) the model temperature variability is computed over the same time interval as the observations. When all three changes are made, the difference between the slope and feedback parameter is less than one-tenth of that estimated by Spencer and Braswell. Absolute values of the difference for realistic cases are less than 0.05 W m−2 K−1, which is not significant for climate studies that employ regressions of outgoing radiation against temperature. Previously published results show that the difference is negligible in the Hadley Centre Slab Climate Model, version 3 (HadSM3). Feedback; Energy budget/balance; radiative forcing; temperature; Climate sensitivity
Murphy, Daniel M.Murphy, D. M., 2010: Constraining climate sensitivity with linear fits to outgoing radiation. Geophysical Research Letters, 37(9), L09704. doi: 10.1029/2010GL042911. Several papers have used correlations between outgoing radiation and surface temperature to estimate climate sensitivity via a linearized energy balance equation. A crucial assumption in such studies is the use of global averages to relate radiation and temperature data that are actually functions of space and time. Here it is shown that this assumption is important to understanding why transient and equilibrium climate feedbacks may differ. There are important limitations to derivations of climate sensitivity from correlations between radiation and temperature data. In particular, because of heat transport between regions, obtaining the equilibrium temperature change by multiplying the forcing by a climate sensitivity is valid only for a global domain. The analysis of Lindzen and Choi (2009) erroneously applies global concepts to a limited region. I also show that a simple, point-by-point regression of outgoing radiation against surface temperature gives better slope estimates than the interval method used by Lindzen and Choi (2009). 0360 Radiation: transmission and scattering; 1620 Climate dynamics; 3305 Climate change and variability; Climate sensitivity; correlation
Nezlin, Nikolay P.; Polikarpov, Igor G.; Al-Yamani, Faiza Y.; Subba Rao, D. V.; Ignatov, Alexander M.Nezlin, N. P., I. G. Polikarpov, F. Y. Al-Yamani, D. V. Subba Rao, A. M. Ignatov, 2010: Satellite monitoring of climatic factors regulating phytoplankton variability in the Arabian (Persian) Gulf. Journal of Marine Systems, 82(1–2), 47-60. doi: 10.1016/j.jmarsys.2010.03.003. Possible factors regulating phytoplankton variability in the Arabian (Persian) Gulf were analyzed on the basis of satellite observations and meteorological data (1997–2009), including remotely-sensed chlorophyll a concentration (CHL), sea surface temperature, wind, solar radiation, precipitation, and aerosols. Shallow waters of northwestern Gulf influenced by Shatt Al-Arab River discharge were more productive than open Gulf waters, although seasonal CHL patterns in this and other shallow regions looked unrealistic likely because the CHL signal was obscured by bottom reflection. Therefore our further analyses focused on the open Gulf waters, which show a subtropical seasonal CHL cycle with maximum in winter and minimum in spring–summer. This cycle, however, was decoupled from the seasonal extremes of wind mixing. Interannual variations of CHL in the open Gulf regions were correlated with precipitation and aerosol data rather than with wind and sea surface temperature, consistent with the hypothesis of atmospheric deposition as a factor regulating phytoplankton growth. The effect of dust fertilization was likely observed in 2000 and 2008, when low precipitation and aerosol properties indicating elevated level of aeolian dust transport were followed by phytoplankton blooms. Remote sensing; aerosols; Oceanography; 23°–31°N; 47°–56°E; Aeolian dust; Arabian (Persian) Gulf; Chlorophyll; Seasonal variations
Porter, David F.; Cassano, John J.; Serreze, Mark C.; Kindig, David N.Porter, D. F., J. J. Cassano, M. C. Serreze, D. N. Kindig, 2010: New estimates of the large-scale Arctic atmospheric energy budget. Journal of Geophysical Research: Atmospheres, 115(D8), D08108. doi: 10.1029/2009JD012653. New estimates of the current energy budget of the north polar cap (the region north of 70°N) are synthesized by combining data from new atmospheric reanalyses and satellite retrievals. For the period 2000–2005, monthly means from the Clouds and the Earth's Radiant Energy System (CERES) satellite data set are considered to provide the most reliable top-of-atmosphere (TOA) radiation budget. The remaining components of the energy budget, comprising of the energy storage, horizontal convergence of energy, and the net surface flux between the atmospheric and subsurface columns, are compiled using data from the Japanese 25 Year Reanalysis Project (JRA) and the National Centers for Environmental Prediction (NCEP) /National Center for Atmospheric Research (NCAR) Reanalysis (NRA). The annual cycles of energy budget components for the polar cap are fairly consistent between the JRA and NRA, but with some systematic differences. JRA depicts an annual mean surface flux of 14 W m−2 (upward), compared to only 5 W m−2 in NRA. Most of this disparity appears to be due to differences in sea ice and albedo. Horizontal atmospheric energy flux divergence calculated using mass-corrected flux values contains artifacts leading to unphysical results. We argue that backing out the energy flux convergence as a residual from the net surface heat flux and time change in energy storage from each reanalysis, and the TOA radiation budget from CERES, provides for more physically realistic results in the Arctic. Monthly mean anomalies of budget terms, used to examine conditions leading to the extreme seasonal sea ice extent minimum of September 2005, point to the importance of albedo feedback. 3309 Climatology; 9315 Arctic region; 1814 Energy budgets; energy; Arctic; 3349 Polar meteorology; 0764 Energy balance; budget
Priestley, Kory J.; Thomas, Susan; Smith, G. LouisPriestley, K. J., S. Thomas, G. L. Smith, 2010: Validation of Point Spread Functions of CERES Radiometers by the Use of Lunar Observations. J. Atmos. Oceanic Technol., 27(6), 1005-1011. doi: 10.1175/2010JTECHA1322.1. Abstract The Clouds and the Earth’s Radiant Energy System (CERES) scanning radiometers have been operating to make raster scans of the moon on a quarterly basis to validate the point response function for the three channels of flight models 1–4 aboard the Terra and Aqua spacecraft. Instrument pointing accuracy was verified by this method to 0.2° for the total channel of FM-3. The point response functions were computed from the lunar observations and were found to be nominal with the exception of the FM-2 window channel, which was found to have a region of high sensitivity. This anomaly is attributed to a delamination of the detector flake from the heat sink in that region. The influence of this anomaly is accounted for by the in-flight calibration and has no adverse effect on the application of the data. satellite observations; Radiances
Spencer, Roy W.; Braswell, William D.Spencer, R. W., W. D. Braswell, 2010: On the diagnosis of radiative feedback in the presence of unknown radiative forcing. Journal of Geophysical Research: Atmospheres, 115(D16), D16109. doi: 10.1029/2009JD013371. The impact of time-varying radiative forcing on the diagnosis of radiative feedback from satellite observations of the Earth is explored. Phase space plots of variations in global average temperature versus radiative flux reveal linear striations and spiral patterns in both satellite measurements and in output from coupled climate models. A simple forcing-feedback model is used to demonstrate that the linear striations represent radiative feedback upon nonradiatively forced temperature variations, while the spiral patterns are the result of time-varying radiative forcing generated internal to the climate system. Only in the idealized special case of instantaneous and then constant radiative forcing, a situation that probably never occurs either naturally or anthropogenically, can feedback be observed in the presence of unknown radiative forcing. This is true whether the unknown radiative forcing is generated internal or external to the climate system. In the general case, a mixture of both unknown radiative and nonradiative forcings can be expected, and the challenge for feedback diagnosis is to extract the signal of feedback upon nonradiatively forced temperature change in the presence of the noise generated by unknown time-varying radiative forcing. These results underscore the need for more accurate methods of diagnosing feedback from satellite data and for quantitatively relating those feedbacks to long-term climate sensitivity. 1640 Remote sensing; 1620 Climate dynamics; Feedback; climate; 1616 Climate variability; forcing; 1626 Global climate models; 1635 Oceans
Stackhouse Jr, PW; Wong, T.; Loeb, N. G; Kratz, D. P.; Wilber, A. C.; Doelling, D. R.; Nguyen, L. CathyStackhouse Jr, P., T. Wong, N. G. Loeb, D. P. Kratz, A. C. Wilber, D. R. Doelling, L. C. Nguyen, 2010: Earth Radiation Budget at top-of-atmosphere [in "State of the Climate in 2009”]. Bull. Amer. Meteor. Soc., 91(7), S41. doi: 10.1175/BAMS-91-7-StateoftheClimate.
Su, Wenying; Bodas-Salcedo, Alejandro; Xu, Kuan-Man; Charlock, Thomas P.Su, W., A. Bodas-Salcedo, K. Xu, T. P. Charlock, 2010: Comparison of the tropical radiative flux and cloud radiative effect profiles in a climate model with Clouds and the Earth's Radiant Energy System (CERES) data. Journal of Geophysical Research: Atmospheres, 115(D1), D01105. doi: 10.1029/2009JD012490. An insightful link of model performance to the physical assumptions in general circulation models (GCMs) can be explored if assessment of radiative fluxes and cloud radiative effects go beyond those at the top of the atmosphere (TOA). In this study, we compare the radiative flux profiles (at surface, 500 hPa, 200 hPa, 70 hPa, and TOA) and cloud effect profiles (500 hPa, 200 hPa, and TOA) from HadGAM1, using Surface and Atmospheric Radiation Budget (SARB) data from Clouds and the Earth's Radiant Energy System (CERES) on the TRMM satellite over the tropics (30°S–30°N). Comparison at TOA reveals that HadGAM1 agrees well with CERES for mean cloud height but lacks in cloudiness. Comparing to its predecessor, HadAM3, HadGAM1 agrees better with observations in TOA LW cloud effects, net cloud effects, and the ratio of SW to LW cloud effects. Extending the comparison to multiple levels, we gain additional insight into the vertical differences in clouds: for clouds at heights below 500 hPa, HadGAM1 and CERES are in good agreement in terms of cloudiness, but HadGAM1 underestimates the average cloud height; for clouds between 500 and 200 hPa, HadGAM1 underestimates the cloudiness but overestimates the average cloud height; for clouds at heights above 200 hPa, HadGAM1 produces more clouds than in CERES. Stratifying the cloud effects by dynamic regimes, we find that HadGAM1 underestimates cloudiness and overestimates averaged cloud height in the convective regimes, but the opposite is true in the strong subsidence regimes. radiative flux; 0321 Cloud/radiation interaction; 1616 Climate variability; cloud radiative effect; 1626 Global climate models; global climate model
Su, Wenying; Loeb, Norman G.; Xu, Kuan-Man; Schuster, Gregory L.; Eitzen, Zachary A.Su, W., N. G. Loeb, K. Xu, G. L. Schuster, Z. A. Eitzen, 2010: An estimate of aerosol indirect effect from satellite measurements with concurrent meteorological analysis. Journal of Geophysical Research: Atmospheres, 115(D18), D18219. doi: 10.1029/2010JD013948. Many studies have used satellite retrievals to investigate the effect of aerosols on cloud properties, but these retrievals are subject to artifacts that can confound interpretation. Additionally, large-scale meteorological differences over a study region dominate cloud dynamics and must be accounted for when studying aerosol and cloud interactions. We have developed an analysis method which minimizes the effect of retrieval artifacts and large-scale meteorology on the assessment of the aerosol indirect effect. The method divides an oceanic study region into 1° × 1° grid boxes and separates the grid boxes into two populations according to back trajectory analysis: one population contains aerosols of oceanic origin, and the other population contains aerosols of continental origin. We account for variability in the large-scale dynamical and thermodynamical conditions by stratifying these two populations according to vertical velocity (at 700 hPa) and estimated inversion strength and analyze differences in the aerosol optical depths, cloud properties, and top of atmosphere (TOA) albedos. We also stratify the differences by cloud liquid water path (LWP) in order to quantify the first aerosol indirect effect. We apply our method to a study region off the west coast of Africa and only consider single-layer low-level clouds. We find that grid boxes associated with aerosols of continental origin have higher cloud fraction than those associated with oceanic origin. Additionally, we limit our analysis to those grid boxes with cloud fractions larger than 80% to ensure that the two populations have similar retrieval biases. This is important for eliminating the retrieval biases in our difference analysis. We find a significant reduction in cloud droplet effective radius associated with continental aerosols relative to that associated with oceanic aerosols under all LWP ranges; the overall reduction is about 1.0 μm, when cloud fraction is not constrained, and is about 0.5 μm, when cloud fraction is constrained to be larger than 80%. We also find significant increases in cloud optical depth and TOA albedo associated with continental aerosols relative to those associated with oceanic aerosols under all LWP ranges. The overall increase in cloud optical depth is about 0.6, and the overall increase in TOA albedo is about 0.021, when we do not constrained cloud fraction. The overall increases in cloud optical depth and TOA albedo are 0.4 and 0.008, when we only use grid boxes with cloud fraction larger than 80%. clouds; 0320 Cloud physics and chemistry; 0305 Aerosols and particles; aerosols; 3311 Clouds and aerosols
Sun, Fengying; Goldberg, Mitchell D.; Liu, Xingpin; Bates, John J.Sun, F., M. D. Goldberg, X. Liu, J. J. Bates, 2010: Estimation of outgoing longwave radiation from Atmospheric Infrared Sounder radiance measurements. Journal of Geophysical Research: Atmospheres, 115(D9), D09103. doi: 10.1029/2009JD012799. This study demonstrates the ability to use Atmospheric Infrared Sounder (AIRS) hyperspectral radiance measurements and collocated Clouds and the Earth's Radiant Energy System outgoing longwave fluxes to estimate top-of-atmosphere outgoing longwave radiation (OLR) from AIRS radiance measurements. The first 35 principal component scores of AIRS radiances from its 1707 pristine channels are used as predictors, and the regression coefficients are generated in eight regimes of AIRS view angle to account for angular dependence of the AIRS radiance observations. Tests on an independence test ensemble show that the accuracy of the AIRS OLR is near zero and the precision is less than 3 Wm−2 for all scenes and 2 Wm−2 for uniform scenes. The AIRS OLR precision for uniform scenes is much higher than the High-Resolution Infrared Sounder OLR of 5 Wm−2 for similar comparisons with the Earth Radiation Budget Experiment OLR. The same technique of empirical regression OLR can be applied to other hyperspectral sounders such as the Cross-track Infrared Sounder that will be on board the National Polar-Orbiting Operational Environmental Satellite System and the Infrared Atmospheric Sounding Interferometer on the European Meteorological Polar-orbiting satellites. 1610 Atmosphere; 1640 Remote sensing; 3359 Radiative processes; 1616 Climate variability; 1814 Energy budgets; AIRS; OLR; hyperspectral sounder
Trenberth, Kevin E.; Fasullo, John T.Trenberth, K. E., J. T. Fasullo, 2010: Tracking Earth's Energy. Science, 328(5976), 316-317. doi: 10.1126/science.1187272. By measuring the net radiative incoming and outgoing energy at the top of Earth's atmosphere, it is possible to determine how much energy remains in the Earth system. But where exactly does the energy go? The main energy reservoir is the ocean, which sequesters energy as heat. Because energy is exchanged between the atmosphere and the ocean, this heat can resurface at a later time to affect weather and climate on a global scale. A change in the overall energy balance will thus sooner or later have consequences for the climate. Existing observing systems can measure all the required quantities, but it nevertheless remains a challenge to obtain closure of the energy budget. This inability to properly track energy—due to either inadequate measurement accuracy or inadequate data processing—has implications for understanding and predicting future climate.
Trenberth, Kevin E.; Fasullo, John T.Trenberth, K. E., J. T. Fasullo, 2010: Simulation of Present-Day and Twenty-First-Century Energy Budgets of the Southern Oceans. J. Climate, 23(2), 440-454. doi: 10.1175/2009JCLI3152.1. Abstract The energy budget of the modern-day Southern Hemisphere is poorly simulated in both state-of-the-art reanalyses and coupled global climate models. The ocean-dominated Southern Hemisphere has low surface reflectivity and therefore its albedo is particularly sensitive to cloud cover. In modern-day climates, mainly because of systematic deficiencies in cloud and albedo at mid- and high latitudes, too much solar radiation enters the ocean. Along with too little radiation absorbed at lower latitudes because of clouds that are too bright, unrealistically weak poleward transports of energy by both the ocean and atmosphere are generally simulated in the Southern Hemisphere. This implies too little baroclinic eddy development and deficient activity in storm tracks. However, projections into the future by coupled climate models indicate that the Southern Ocean features a robust and unique increase in albedo, related to clouds, in association with an intensification and poleward shift in storm tracks that is not observed at any other latitude. Such an increase in cloud may be untenable in nature, as it is likely precluded by the present-day ubiquitous cloud cover that models fail to capture. There is also a remarkably strong relationship between the projected changes in clouds and the simulated current-day cloud errors. The model equilibrium climate sensitivity is also significantly negatively correlated with the Southern Hemisphere energy errors, and only the more sensitive models are in the range of observations. As a result, questions loom large about how the Southern Hemisphere will actually change as global warming progresses, and a better simulation of the modern-day climate is an essential first step. Energy budget/balance; forcing; Annular mode; Anthropogenic effects; Ozone
Trenberth, Kevin E.; Fasullo, John T.; O'Dell, Chris; Wong, TakmengTrenberth, K. E., J. T. Fasullo, C. O'Dell, T. Wong, 2010: Relationships between tropical sea surface temperature and top-of-atmosphere radiation. Geophysical Research Letters, 37(3), L03702. doi: 10.1029/2009GL042314. To assess climate sensitivity from Earth radiation observations of limited duration and observed sea surface temperatures (SSTs) requires a closed and therefore global domain, equilibrium between the fields, and robust methods of dealing with noise. Noise arises from natural variability in the atmosphere and observational noise in precessing satellite observations. This paper explores the meaning of results that use only the tropical region. We compute correlations and regressions between tropical SSTs and top-of-atmosphere (TOA) longwave, shortwave and net radiation using a variety of methods to test robustness of results. The main changes in SSTs throughout the tropics are associated with El Niño Southern Oscillation (ENSO) events in which the dominant changes in energy into an atmospheric column come from ocean heat exchange through evaporation, latent heat release in precipitation, and redistribution of that heat through atmospheric winds. These changes can be an order of magnitude larger than the net TOA radiation changes, and their effects are teleconnected globally, and especially into the subtropics. Atmospheric model results are explored and found to be consistent with observations. From 1985 to 1999 the largest perturbation in TOA radiative fluxes was from the eruption of Mount Pinatubo and clearly models which do not include that forcing will not simulate the effects. Consequently, regressions of radiation with SSTs in the tropics may have nothing to say about climate sensitivity. 1610 Atmosphere; 1620 Climate dynamics; 0321 Cloud/radiation interaction; climate; radiation; 1626 Global climate models; temperatures
Trigo, Isabel F.; Barroso, Carla; Viterbo, Pedro; Freitas, Sandra C.; Monteiro, Isabel T.Trigo, I. F., C. Barroso, P. Viterbo, S. C. Freitas, I. T. Monteiro, 2010: Estimation of downward long-wave radiation at the surface combining remotely sensed data and NWP data. Journal of Geophysical Research: Atmospheres, 115(D24), D24118. doi: 10.1029/2010JD013888. Here we assess established algorithms and a newly developed scheme for the estimation of downward long-wave radiation flux at the surface (DLR), i.e., the irradiance reaching the surface within 4 and 100 μm. These different methods correspond to bulk parameterization schemes, which merge the signature of clouds on Meteosat second-generation (MSG) data with information on atmosphere water content and near-surface air temperature available from numerical weather prediction (NWP) fields. The new formulation consists of a generalization of a method first developed for clear sky cases and now fine-tuned for a wider range of atmospheric conditions. The performance of this and three other parameterization schemes is compared with independent ground observations. Such a validation exercise is extended also to European Centre for Medium-Range Weather Forecast (ECMWF) flux forecasts, since the ECMWF model is the main source of information on air temperature and water vapor content, and to surface fluxes obtained from the Clouds and the Earth's Radiant Energy System (CERES). It is shown that the new parameterization scheme performs well when compared to other methods, with root mean square errors within 20 Wm−2. The overall good matching between parameterized values and in situ data suggests a good performance of a relatively simple bulk scheme and also of the use of MSG-based cloud identification. 0321 Cloud/radiation interaction; 3359 Radiative processes; SEVIRI; 1855 Remote sensing; long-wave flux
Viollier, Michel; Raberanto, PatrickViollier, M., P. Raberanto, 2010: Radiometric and Spectral Characteristics of the ScaRaB-3 Instrument on Megha-Tropiques: Comparisons with ERBE, CERES, and GERB. J. Atmos. Oceanic Technol., 27(3), 428-442. doi: 10.1175/2009JTECHA1307.1. Abstract The Indian–French Megha-Tropiques mission, scheduled to be launched in 2010, will carry radiation and microwave sensors to study the energy and water cycle in the tropics. The radiation sensor, the third model of the Scanner for Radiation Budget (ScaRaB-3), is dedicated to the earth’s radiation budget, the difference between the solar absorbed flux and the terrestrial emitted flux. These fluxes are calculated from satellite measurements of outgoing shortwave (SW) and longwave (LW) radiances using angular distribution models (ADMs). For practical reasons, the LW radiation is calculated from the difference between a total (T) channel (0.2–100 μm) and an SW channel (0.2–4 μm). With the ADM application, the radiance calibration remains the most critical issue in the radiation budget estimation. The 1% accuracy goal is difficult to achieve, specifically in the SW domain. The authors explain their efforts to improve the radiometric calibration of ScaRaB-3. The internal calibration module is improved: the sensor is switched between SW and T channels by rotating the filter wheel on which the SW filter is now installed. Because the pyroelectric detector is sensitive to the thermal effect of the electromagnetic radiation independently of its spectral range, this plan allows calibrating the SW channel as a T channel by viewing a blackbody. Indeed, the transfer of the T calibration to the SW domain requires perfect knowledge of the total spectral response and of the transmittance of the SW filter, which is discussed in the article. Spectral errors are calculated with updated data. In the SW domain, they are found to be the smallest compared to those of the Earth Radiation Budget Experiment (ERBE), the Clouds and the Earth’s Radiant Energy System (CERES), and the Geostationary Earth Radiation Budget (GERB). Remote sensing; satellite observations; radiation budget; Instrumentation/sensors; Spectral analysis/models/distribution
Wang, Wencai; Huang, Jianping; Minnis, Patrick; Hu, Yongxiang; Li, Jiming; Huang, Zhongwei; Ayers, J. Kirk; Wang, TianheWang, W., J. Huang, P. Minnis, Y. Hu, J. Li, Z. Huang, J. K. Ayers, T. Wang, 2010: Dusty cloud properties and radiative forcing over dust source and downwind regions derived from A-Train data during the Pacific Dust Experiment. Journal of Geophysical Research: Atmospheres, 115(D4), D00H35. doi: 10.1029/2010JD014109. Dusty cloud properties and radiative forcing over northwestern China (source region) are compared to the same quantities over the northwestern Pacific (downwind region) during the Pacific Dust Experiment (PACDEX; April 2007 to May 2007) using collocated data from three satellites in the A-Train constellation: CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations), the Clouds and Earth Radiant Energy System on Aqua, and CloudSat. Dusty clouds are defined as clouds extant in a dust plume environment (i.e., dust aerosols observed within 50 m of the cloud), while pure clouds are those in dust-free conditions. CALIPSO lidar and CloudSat radar measurements are used to discriminate between dusty and pure clouds in both study regions. It was found that dust aerosols change the microphysical characteristics of clouds, reducing the cloud optical depth, liquid and ice water path, and effective droplet size. The decreased cloud optical depths and water paths diminish the cloud cooling effect, leading to a greater warming effect. The dust aerosols cause an instantaneous net cloud cooling effect of 43.4% and 16.7% in the source and downwind regions, respectively. The dust aerosol effects appear to be greater for ice clouds than for liquid water clouds in the downwind region. These results are consistent with PACDEX aircraft observations. 1640 Remote sensing; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; 3305 Climate change and variability; cloud radiative forcing; dusty cloud; CALIPSO/CERES
Wang, Xianwei; Zender, Charles S.Wang, X., C. S. Zender, 2010: Constraining MODIS snow albedo at large solar zenith angles: Implications for the surface energy budget in Greenland. Journal of Geophysical Research: Earth Surface, 115(F4), F04015. doi: 10.1029/2009JF001436. An understanding of the surface albedo of high latitudes is crucial for climate change studies. MODIS albedo retrievals flagged as high-quality compare well with in situ Greenland Climate Network (GC-Net) measurements but cover too small an area to fully characterize Greenland's albedo in nonsummer months. In contrast, poor quality MODIS retrievals provide adequate spatiotemporal coverage, but are not recommended for use at large solar zenith angles (SZAs) where they have a systematic low bias. We introduce an empirical adjustment to the poor quality data based on high-quality reference albedos and constrained by GC-Net data and theory, and use the adjusted data to improve estimates and fill in gaps of the year-round, Greenland-wide, albedo and surface energy budget. For observations made with SZAs between 55° and 75°, the mean differences (MODIS minus GC-Net) between our adjusted MODIS albedo and GC-Net measurements are −0.02 and −0.03 at Saddle and Summit, respectively, compared to −0.05 and −0.08 between the unadjusted MODIS albedo and GC-Net measurements. The adjusted MODIS snow albedos are usually between 0.75 and 0.87 over dry snow when SZA is larger than 55°, and they reduce unrealistic seasonal and meridional trends associated with MODIS retrievals at large SZA, defined as SZA > 55° and 70°, respectively, for low- and high-quality retrievals. The impact of the adjusted albedo on the surface energy budget, relative to the unadjusted albedo from all MODIS data, is smallest (−0.7 ± 0.1W/m2) in June, and largest (−6.2 ± 0.9 W/m2) in September for the black-sky albedo (BSA). The mean annual absorbed solar radiation (ASR) reduction by the adjusted MODIS albedo in Greenland from 2003 to 2005 is 3.1 ± 0.2 and 4.3 ± 0.2 W/m2 for BSA and white-sky albedo (WSA), respectively, about 8.0 ± 0.5% and 10.8 ± 0.4% of ASR based on the raw BSA and WSA. The ASR reduction by the adjusted blue-sky (actual) albedo is between 2.9 and 4.5 W/m2, enough to annually melt 27.1 to 41.7 cm snow water equivalent (SWE), or to sublimate 3.2 to 4.9 cm SWE. The ASR difference between the adjusted MODIS BSA and CERES albedo in March from 2003 to 2005 is only −0.1 ± 0.9 W/m2, much less than the difference (4.9 ± 1.4 W/m2) between the unadjusted MODIS BSA and CERES. The albedo adjustments exceed the likely direct anthropogenic radiative forcing experienced by Greenland due to greenhouse gases or aerosols. The proposed adjustment preserves most of the zonal and meridional structure of raw MODIS albedo, and extends its usefulness as a cryospheric climate record in times and regions of Greenland with large SZA. MODIS; 0758 Remote sensing; 0736 Snow; surface energy budget; Greenland; 0720 Glaciers; 0726 Ice sheets; 0764 Energy balance; snow albedo; solar zenith angle
Watanabe, Masahiro; Suzuki, Tatsuo; O’ishi, Ryouta; Komuro, Yoshiki; Watanabe, Shingo; Emori, Seita; Takemura, Toshihiko; Chikira, Minoru; Ogura, Tomoo; Sekiguchi, Miho; Takata, Kumiko; Yamazaki, Dai; Yokohata, Tokuta; Nozawa, Toru; Hasumi, Hiroyasu; Tatebe, Hiroaki; Kimoto, MasahideWatanabe, M., T. Suzuki, R. O’ishi, Y. Komuro, S. Watanabe, S. Emori, T. Takemura, M. Chikira, T. Ogura, M. Sekiguchi, K. Takata, D. Yamazaki, T. Yokohata, T. Nozawa, H. Hasumi, H. Tatebe, M. Kimoto, 2010: Improved Climate Simulation by MIROC5: Mean States, Variability, and Climate Sensitivity. J. Climate, 23(23), 6312-6335. doi: 10.1175/2010JCLI3679.1. Abstract A new version of the atmosphere–ocean general circulation model cooperatively produced by the Japanese research community, known as the Model for Interdisciplinary Research on Climate (MIROC), has recently been developed. A century-long control experiment was performed using the new version (MIROC5) with the standard resolution of the T85 atmosphere and 1° ocean models. The climatological mean state and variability are then compared with observations and those in a previous version (MIROC3.2) with two different resolutions (medres, hires), coarser and finer than the resolution of MIROC5. A few aspects of the mean fields in MIROC5 are similar to or slightly worse than MIROC3.2, but otherwise the climatological features are considerably better. In particular, improvements are found in precipitation, zonal mean atmospheric fields, equatorial ocean subsurface fields, and the simulation of El Niño–Southern Oscillation. The difference between MIROC5 and the previous model is larger than that between the two MIROC3.2 versions, indicating a greater effect of updating parameterization schemes on the model climate than increasing the model resolution. The mean cloud property obtained from the sophisticated prognostic schemes in MIROC5 shows good agreement with satellite measurements. MIROC5 reveals an equilibrium climate sensitivity of 2.6 K, which is lower than that in MIROC3.2 by 1 K. This is probably due to the negative feedback of low clouds to the increasing concentration of CO2, which is opposite to that in MIROC3.2. Feedback; sea surface temperature; climate models; Climate sensitivity; Carbon dioxide
Winker, D. M.; Pelon, J.; Coakley, J. A.; Ackerman, S. A.; Charlson, R. J.; Colarco, P. R.; Flamant, P.; Fu, Q.; Hoff, R. M.; Kittaka, C.; Kubar, T. L.; Le Treut, H.; McCormick, M. P.; Mégie, G.; Poole, L.; Powell, K.; Trepte, C.; Vaughan, M. A.; Wielicki, B. A.Winker, D. M., J. Pelon, J. A. Coakley, S. A. Ackerman, R. J. Charlson, P. R. Colarco, P. Flamant, Q. Fu, R. M. Hoff, C. Kittaka, T. L. Kubar, H. Le Treut, M. P. McCormick, G. Mégie, L. Poole, K. Powell, C. Trepte, M. A. Vaughan, B. A. Wielicki, 2010: The CALIPSO Mission: A Global 3D View of Aerosols and Clouds. Bull. Amer. Meteor. Soc., 91(9), 1211-1229. doi: 10.1175/2010BAMS3009.1. Abstract Aerosols and clouds have important effects on Earth's climate through their effects on the radiation budget and the cycling of water between the atmosphere and Earth's surface. Limitations in our understanding of the global distribution and properties of aerosols and clouds are partly responsible for the current uncertainties in modeling the global climate system and predicting climate change. The CALIPSO satellite was developed as a joint project between NASA and the French space agency CNES to provide needed capabilities to observe aerosols and clouds from space. CALIPSO carries CALIOP, a two-wavelength, polarization-sensitive lidar, along with two passive sensors operating in the visible and thermal infrared spectral regions. CALIOP is the first lidar to provide long-term atmospheric measurements from Earth's orbit. Its profiling and polarization capabilities offer unique measurement capabilities. Launched together with the CloudSat satellite in April 2006 and now flying in formation with the A-train satellite constellation, CALIPSO is now providing information on the distribution and properties of aerosols and clouds, which is fundamental to advancing our understanding and prediction of climate. This paper provides an overview of the CALIPSO mission and instruments, the data produced, and early results.
Xi, Baike; Dong, Xiquan; Minnis, Patrick; Khaiyer, Mandana M.Xi, B., X. Dong, P. Minnis, M. M. Khaiyer, 2010: A 10 year climatology of cloud fraction and vertical distribution derived from both surface and GOES observations over the DOE ARM SPG site. Journal of Geophysical Research: Atmospheres, 115(D12), D12124. doi: 10.1029/2009JD012800. Analysis of one decade of radar-lidar and Geostationary Operational Environmental Satellite (GOES) observations at the Department of Energy (DOE) Atmospheric Radiation Measurement Program (ARM) Southern Great Plains (SGP) site reveals that there is excellent agreement in the long-term mean cloud fractions (CFs) derived from the surface and GOES data, and the CF is independent of temporal resolution and spatial scales for grid boxes of size 0.5° to 2.5°. When computed over a a 0.5 h (4 h) period, cloud frequency of occurrence (FREQ) and amount when present (AWP) derived from the point surface data agree very well with the same quantities determined from GOES for a 0.5° (2.5°) region centered on the DOE ARM SGP site. The values of FREQ (AWP) derived from the radar-lidar observations at a given altitude increase (decrease) as the averaging period increases from 5 min to 6 h. Similarly, CF at a given altitude increases as the vertical resolution increases from 90 to 1000 m. The profiles of CF have distinct bimodal vertical distributions, with a lower peak between 1 and 2 km and a higher one between 8 and 11 km. The 10 year mean total CF, 46.9%, varies seasonally from a summer minimum of 39.8% to a maximum of 54.6% during the winter. The annual mean CF is 1%–2% less than that from previous studies, ∼48%–49%, because fewer clouds occurred during 2005 and 2006, especially during winter. The differences in single- and multilayered CFs between this study and an earlier analysis can be explained by the different temporal resolutions used in the two studies, where single-layered CFs decrease but multilayered CFs increase from a 5 min resolution to a 1 h resolution. The vertical distribution of nighttime GOES high cloud tops agrees well with surface observations, but during the daytime, fewer high clouds are retrieved by the GOES analysis than seen from the surface observations. The FREQs for both daytime and nighttime GOES low cloud tops are significantly higher than surface observations, but the CFs are in good agreement. 0320 Cloud physics and chemistry; 0321 Cloud/radiation interaction; 3310 Clouds and cloud feedbacks; spatial; temporal; vertical
Xu, Kuan-Man; Cheng, Anning; Zhang, MinghuaXu, K., A. Cheng, M. Zhang, 2010: Cloud-Resolving Simulation of Low-Cloud Feedback to an Increase in Sea Surface Temperature. J. Atmos. Sci., 67(3), 730-748. doi: 10.1175/2009JAS3239.1. Abstract This study investigates the physical mechanisms of the low cloud feedback through cloud-resolving simulations of cloud-radiative equilibrium response to an increase in sea surface temperature (SST). Six pairs of perturbed and control simulations are performed to represent different regimes of low clouds in the subtropical region by specifying SST differences (ΔSST) in the range of 4 and 14 K between the warm tropical and cool subtropical regions. The SST is uniformly increased by 2 K in the perturbed set of simulations. Equilibrium states are characterized by cumulus and stratocumulus cloud regimes with variable thicknesses and vertical extents for the range of specified ΔSSTs, with the perturbed set of simulations having higher cloud bases and tops and larger geometric thicknesses. The cloud feedback effect is negative for this ΔSST range (−0.68 to −5.22 W m−2 K−1) while the clear-sky feedback effect is mostly negative (−1.45 to 0.35 W m−2 K−1). The clear-sky feedback effect contributes greatly to the climate sensitivity parameter for the cumulus cloud regime whereas the cloud feedback effect dominates for the stratocumulus regime. The increase of liquid water path (LWP) and cloud optical depth is related to the increase of cloud thickness and liquid water content with SST. The rates of change in surface latent heat flux are much higher than those of saturation water vapor pressure in the cumulus simulations. The increase in surface latent heat flux is the primary mechanism for the large change of cloud physical properties with +2 K SST, which leads to the negative cloud feedback effects. The changes in cloud fraction also contribute to the negative cloud feedback effects in the cumulus regime. Comparison of these results with prior modeling studies is also discussed. cloud-resolving models; Feedback; sea surface temperature; Stratiform clouds; Cloud-radiative effects; Cumulus clouds
Yost, Christopher R.; Minnis, Patrick; Ayers, J. Kirk; Spangenberg, Douglas A.; Heymsfield, Andrew J.; Bansemer, Aaron; McGill, Matthew J.; Hlavka, Dennis L.Yost, C. R., P. Minnis, J. K. Ayers, D. A. Spangenberg, A. J. Heymsfield, A. Bansemer, M. J. McGill, D. L. Hlavka, 2010: Comparison of GOES-retrieved and in situ measurements of deep convective anvil cloud microphysical properties during the Tropical Composition, Cloud and Climate Coupling Experiment (TC4). Journal of Geophysical Research: Atmospheres, 115(D10), D00J06. doi: 10.1029/2009JD013313. One of the main goals of the Tropical Composition, Cloud and Climate Coupling Experiment (TC4) during July and August 2007 was to gain a better understanding of the formation and life cycle of cirrus clouds in the upper troposphere and lower stratosphere and how their presence affects the exchange of water vapor between these layers. Additionally, it is important to compare in situ measurements taken by aircraft instruments with products derived from satellite observations and find a meaningful way to interpret the results. In this study, cloud properties derived using radiance measurements from the Geostationary Operational Environmental Satellite (GOES) imagers are compared to similar quantities from aircraft in situ observations and are examined for meaningful relationships. A new method using dual-angle satellite measurements is used to derive the ice water content (IWC) for the top portion of deep convective clouds and anvils. The results show the in situ and remotely sensed mean microphysical properties agree to within ∼10 μm in the top few kilometers of thick anvils despite the vastly different temporal and spatial resolutions of the aircraft and satellite instruments. Mean particle size and IWC are shown to increase with decreasing altitude in the top few kilometers of the cloud. Given these relationships, it may be possible to derive parameterizations for effective particle size and IWC as a function of altitude from satellite observations. 1610 Atmosphere; 1640 Remote sensing; cloud; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; validation; cirrus
Zelinka, Mark D.; Hartmann, Dennis L.Zelinka, M. D., D. L. Hartmann, 2010: Why is longwave cloud feedback positive?. Journal of Geophysical Research: Atmospheres, 115(D16), D16117. doi: 10.1029/2010JD013817. Longwave cloud feedback is systematically positive and nearly the same magnitude across all global climate models used in the Intergovernmental Panel on Climate Change Fourth Assessment Report (AR4). Here it is shown that this robust positive longwave cloud feedback is caused in large part by the tendency for tropical high clouds to rise in such a way as to remain at nearly the same temperature as the climate warms. Furthermore, it is shown that such a cloud response to a warming climate is consistent with well-known physics, specifically the requirement that, in equilibrium, tropospheric heating by convection can only be large in the altitude range where radiative cooling is efficient, following the fixed anvil temperature hypothesis of Hartmann and Larson (2002). Longwave cloud feedback computed assuming that high-cloud temperature follows upper tropospheric convergence-weighted temperature, which we refer to as proportionately higher anvil temperature, gives an excellent prediction of the longwave cloud feedback in the AR4 models. The ensemble-mean feedback of 0.5 W m−2 K−1 is much larger than that calculated assuming clouds remain at fixed pressure, highlighting the large contribution from rising cloud tops to the robustly positive feedback. An important result of this study is that the convergence profile computed from clear-sky energy and mass balance warms slightly as the climate warms, in proportion to the increase in stability, which results in a longwave cloud feedback that is slightly smaller than that calculated assuming clouds remain at fixed temperature. 1610 Atmosphere; 1620 Climate dynamics; 0321 Cloud/radiation interaction; cloud feedback; 1626 Global climate models
Zhang, Xiaoli; Forbes, Jeffrey M.; Hagan, Maura E.Zhang, X., J. M. Forbes, M. E. Hagan, 2010: Longitudinal variation of tides in the MLT region: 1. Tides driven by tropospheric net radiative heating. Journal of Geophysical Research: Space Physics, 115(A6), A06316. doi: 10.1029/2009JA014897. This study demonstrates that the diurnal cycle of net radiative heating in the troposphere accounts for considerable longitudinal variability of diurnal and semidiurnal tidal fields in the mesosphere and lower thermosphere (MLT) (∼80–120 km), whereas previously it was thought that latent heating associated with deep tropical convection is the predominant driver of this variability. The heating rates used for this study are derived from radiative flux products by NASA Goddard Institute for Space Studies (GISS), and the model employed to estimate the corresponding MLT tides is the Global-Scale Wave Model (GSWM). The radiative flux products by NASA GISS utilize improved International Satellite Cloud Climatology Project (ISCCP) cloud climatology and ancillary data sets and were validated by Earth radiation Budget Experiment (ERBE) and Clouds and the Earth's Radiant Energy System (CERES) radiative flux (0.2–200.0 microns) measurements at the top of the atmosphere and the Earth surface. Typical magnitudes of tidal temperature longitude variations at, e.g., 95 km or 110 km are 20 ± 5 K for the diurnal tide and 6 ± 2 K for the semidiurnal tide. The computed tides and their longitude variability are of comparable amplitude to those derived from TIMED SABER temperature measurements. Part 2 of this study provides new estimates of tidal forcing by latent heating and assesses the total MLT tidal response to these combined heat sources in comparison to tidal climatologies derived from TIMED SABER measurements. 0342 Middle atmosphere: energy deposition; 0520 Data analysis: algorithms and implementation; 0550 Model verification and validation; 3389 Tides and planetary waves; 5770 Tidal forces; GSWM MLT tides; ISCCP troposphere radiative heating; SABER
Allan, Richard P.Allan, R. P., 2009: Examination of Relationships between Clear-Sky Longwave Radiation and Aspects of the Atmospheric Hydrological Cycle in Climate Models, Reanalyses, and Observations. J. Climate, 22(11), 3127-3145. doi: 10.1175/2008JCLI2616.1. Abstract Relationships between clear-sky longwave radiation and aspects of the atmospheric hydrological cycle are quantified in models, reanalyses, and observations over the period 1980–2000. The robust sensitivity of clear-sky surface net longwave radiation (SNLc) to column-integrated water vapor (CWV) of 1–1.5 W m−2 mm−1 combined with the positive relationship between CWV and surface temperature (Ts) explains substantial increases in clear-sky longwave radiative cooling of the atmosphere (QLWc) to the surface over the period. Clear-sky outgoing longwave radiation (OLRc) is highly sensitive to changes in aerosol and greenhouse gas concentrations in addition to temperature and humidity. Over tropical ocean regions of mean descent, QLWc increases with Ts at ∼3.5–5.5 W m−2 K−1 for reanalyses, estimates derived from satellite data, and models without volcanic forcing included. Increased QLWc with warming across the tropical oceans helps to explain model ensemble mean increases in precipitation of 0.1–0.15 mm day−1 K−1, which are primarily determined by ascent regions where precipitation increases at the rate expected from the Clausius–Clapeyron equation. The implications for future projections in the atmospheric hydrological cycle are discussed. Hydrologic cycle; in situ observations; longwave radiation; Model evaluation/performance
Andronova, Natalia; Penner, Joyce E.; Wong, TakmengAndronova, N., J. E. Penner, T. Wong, 2009: Observed and modeled evolution of the tropical mean radiation budget at the top of the atmosphere since 1985. Journal of Geophysical Research: Atmospheres, 114(D14), D14106. doi: 10.1029/2008JD011560. We have used satellite-based broadband radiation observations to construct a long-term continuous 1985–2005 record of the radiative budget components at the top of the atmosphere for the tropical region (20°S–20°N). On the basis of the constructed record we have derived the most conservative estimate of their trends. We compared the interannual variability of the net radiative fluxes at the top of the tropical atmosphere with model simulations from the Intergovernmental Panel on Climate Change fourth assessment report (AR4) archive available up to 2000 and showed that most of the models capture the 1991 Mount Pinatubo eruption signal in both its timing and amplitude; however, none of them simulate the observed trends. Further comparison showed that among the “best skilled” models, which are those that showed the highest value of the correlation in simulating one or all of the observed net, shortwave, and longwave radiative fluxes at the top of the atmosphere, the model with an equilibrium climate sensitivity ∼3.4°C for the doubling CO2 represents the observed amplifying total feedback effect in the tropical atmosphere better than the models with a climate sensitivity ∼2.7°C or 4.3°C. This total feedback effect was calculated on the basis of an assumed simplified system of interactions between the near-surface temperature and the net radiation at the top of the atmosphere. 3359 Radiative processes; 0325 Evolution of the atmosphere; 3305 Climate change and variability; 3337 Global climate models; 3374 Tropical meteorology; feedbacks; radiative forcing; tropical atmosphere
Chen, Y; Li, QB; Kahn, RA; Randerson, JT; Diner, DJChen, Y., Q. Li, R. Kahn, J. Randerson, D. Diner, 2009: Quantifying aerosol direct radiative effect with Multiangle Imaging Spectroradiometer observations: Top-of-atmosphere albedo change by aerosols based on land surface types. JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 114. doi: 10.1029/2008JD010754. Using internally consistent albedo, aerosol, cloud, and surface data from the Multiangle Imaging Spectroradiometer (MISR) instrument onboard the Terra satellite, top-of-atmosphere (TOA) spectral albedo change (d alpha) in the presence of aerosols over land is estimated and its dependence on aerosol and surface properties is analyzed. Linear regressions between spectral TOA albedo and aerosol optical depth (AOD) for different surface types are examined to derive the aerosol-free TOA albedo. MISR surface BiHemispherical Reflectance (BHR) values are used to differentiate surface types. We find relatively high correlations between spectral TOA albedo and AOD for BHR-stratified data in 2 degrees x 2 degrees grid cells. The global mean values of cloud-free d alpha over land for June - September 2007 are estimated to be 0.018 +/- 0.003 (blue), 0.010 +/- 0.003 (green), 0.007 +/- 0.003 (red), and 0.008 +/- 0.006 (near-infrared). Individual regions show large variations from these values. Global patterns of d alpha are determined mainly by AOD and aerosol radiative efficiency. Large positive values of d alpha are observed over regions with high aerosol loading and large single-scattering albedo, where the aerosol scattering effect is dominant. The presence of light-absorbing aerosols reduces aerosol radiative efficiency and d alpha. Surface reflectance influences both aerosol scattering and absorbing effects. Generally, the aerosol radiative efficiency decreases with increasing BHR. We also examined d alpha-AOD correlations over different vegetation types. We find the smallest d alpha values are over needleleaf forests and shrublands, whereas the largest values are over cropland and barren regions. The aerosol radiative efficiencies are lowest over needleleaf forests and barren regions and highest over grasslands and croplands.
Choi, Yong-Sang; Ho, Chang-Hoi; Oh, Hye-Ryun; Park, Rokjin J.; Song, Chang-GeunChoi, Y., C. Ho, H. Oh, R. J. Park, C. Song, 2009: Estimating bulk optical properties of aerosols over the western North Pacific by using MODIS and CERES measurements. Atmospheric Environment, 43(35), 5654-5660. doi: 10.1016/j.atmosenv.2009.07.036. Over the western North Pacific, a large amount of land aerosols from Asian-Pacific countries is transported by the prevailing westerlies. This transport makes the radiative characteristics of these aerosols diverse, particularly when one compares those characteristics over the coastal sea with those over the open sea. In this paper we discuss a method that uses satellite data to obtain the single-scattering albedo (ω) and asymmetry factor (g) of atmospheric aerosols for two large-scale subdivisions—the coastal sea (within 250 km from the coast) and the open sea (the remaining area)—over the western North Pacific (110°E–180°, 20°N–50°N). Our estimation method uses satellite measurements, obtained over a six-year period (2000–2005), of aerosol optical depth (AOD) and shortwave fluxes at both the surface and the top of the atmosphere (TOA); the measurements are obtained using the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Clouds and the Earth's Radiant Energy System (CERES). For the two subdivisions, the estimated annual means of (ω, g) at 630 nm are significantly different: (0.94, 0.65) over the coastal sea and (0.97, 0.70) over the open sea. From a quantitative viewpoint, this result indicates that in comparison with aerosols over the open sea, those over the coastal sea show greater absorption and lesser forward scattering of solar radiation. The estimated optical properties are responsible for the aerosol surface cooling observed by MODIS and CERES, which is approximately 138 and 108 W m−2 per AOD over the coastal sea and open sea, respectively. CERES; aerosol; radiative forcing; MODIS; WNP
Clerbaux, N.; Russell, J. E.; Dewitte, S.; Bertrand, C.; Caprion, D.; De Paepe, B.; Sotelino, L. G.; Ipe, A.; Bantges, R.; Brindley, H. E.Clerbaux, N., J. E. Russell, S. Dewitte, C. Bertrand, D. Caprion, B. De Paepe, L. G. Sotelino, A. Ipe, R. Bantges, H. E. Brindley, 2009: Comparison of GERB instantaneous radiance and flux products with CERES Edition-2 data. Remote Sensing of Environment, 113(1), 102-114. doi: 10.1016/j.rse.2008.08.016. Whenever possible, intercomparisons of Earth radiation budget data from different spaceborne instruments should be made as they are important steps in the overall validation process. Intercomparisons are also key elements to compile long-term climate datasets by merging data from several instruments. In this study the GERB Edition-1 and CERES Edition-2 data are compared for June and December 2004. The comparisons concern shortwave and longwave radiance and flux at the top-of-atmosphere. Three different GERB level-2 data products with differing space-time characteristics are compared with data from the 4 CERES instruments. In general, the GERB unfiltered radiances and fluxes are found to be 5.9% and 7.5% higher than CERES for the shortwave. The GERB longwave radiance and flux are 1.3% lower than CERES. Analysis separated by scene type reveals differences between the GERB products. These differences should be taken into account by the user of the GERB data. The LW flux intercomparison shows angular dependency problem affecting the GERB dataset in cloudy and aerosol regions. (C) 2008 Elsevier Inc. All rights reserved.
Douglass, David H.; Knox, Robert S.Douglass, D. H., R. S. Knox, 2009: Ocean heat content and Earth's radiation imbalance. Physics Letters A, 373(36), 3296-3300. doi: 10.1016/j.physleta.2009.07.023. Earth's radiation imbalance is determined from ocean heat content data and compared with results of direct measurements. Distinct time intervals of alternating positive and negative values are found: 1960–mid-1970s (−0.15), mid-1970s–2000 (+0.15), 2001–present (−0.2 W/m2), and are consistent with prior reports. These climate shifts limit climate predictability. climate; Ocean heat content; Radiative imbalance
Eitzen, Zachary A.; Xu, Kuan-Man; Wong, TakmengEitzen, Z. A., K. Xu, T. Wong, 2009: Cloud and Radiative Characteristics of Tropical Deep Convective Systems in Extended Cloud Objects from CERES Observations. J. Climate, 22(22), 5983-6000. doi: 10.1175/2009JCLI3038.1. Abstract The physical and radiative properties of tropical deep convective systems for the period from January to August 1998 are examined with the use of Clouds and the Earth’s Radiant Energy System Single-Scanner Footprint (SSF) data from the Tropical Rainfall Measuring Mission satellite. Deep convective (DC) cloud objects are contiguous regions of satellite footprints that fulfill the DC criteria (i.e., overcast footprints with cloud optical depths >10 and cloud-top heights >10 km). Extended cloud objects (ECOs) start with the original cloud object but include all other cloudy footprints within a rectangular box that completely covers the original cloud object. Most of the non-DC footprints are overcast but have optical depths and/or cloud-top heights that are too low to fit the DC criteria. The histograms of cloud physical and radiative properties are analyzed according to the size of the ECO and the SST of the underlying ocean. Larger ECOs are associated with greater magnitudes of large-scale upward motion, which supports stronger convection for larger sizes of ECOs. This leads to shifts toward higher values in the DC distributions of cloud-top height, albedo, condensate water path, and cloud optical depth. However, non-DC footprints become less reflective with increasing ECO size, as the longer-lived large convective systems have more time to develop thin cirrus anvils. The proportion of DC footprints remains fairly constant with size. The proportion of DC footprints also remains nearly constant with SST within a given size class, although the number of footprints per object increases with SST for large objects. As SSTs increase, there is a decrease in the proportion of updraft water that goes into detrainment, causing the non-DC distributions of albedo, condensate water path, and cloud optical depth to shift toward lower values. The all-cloud distributions of cloud-top temperature and outgoing longwave radiation (OLR) shift toward lower values as SST increases owing to the increase in convective instability with SST. Both the DC and non-DC distributions of cloud-top temperature do not change much with satellite precession cycle, supporting the fixed anvil temperature hypothesis of Hartmann and Larson. When a joint histogram is formed from the cloud-top pressures and cloud optical depths of the ECOs, it is very similar to the corresponding histogram of the deep convective weather state obtained by cluster analysis of International Satellite Cloud Climatology Project data. convection; Cloud microphysics; Radiative fluxes; sea surface temperature; Updrafts
Feng, Zhe; Dong, Xiquan; Xi, BaikeFeng, Z., X. Dong, B. Xi, 2009: A Method to Merge WSR-88D Data with ARM SGP Millimeter Cloud Radar Data by Studying Deep Convective Systems. J. Atmos. Oceanic Technol., 26(5), 958-971. doi: 10.1175/2008JTECHA1190.1. Abstract A decade of collocated Atmospheric Radiation Measurement Program (ARM) 35-GHz Millimeter Cloud Radar (MMCR) and Weather Surveillance Radar-1988 Doppler (WSR-88D) data over the ARM Southern Great Plains (SGP) site have been collected during the period of 1997–2006. A total of 28 winter and 45 summer deep convective system (DCS) cases over the ARM SGP site have been selected for this study during the 10-yr period. For the winter cases, the MMCR reflectivity, on average, is only 0.2 dB lower than that of the WSR-88D, with a correlation coefficient of 0.85. This result indicates that the MMCR signals have not been attenuated for ice-phase convective clouds, and the MMCR reflectivity measurements agree well with the WSR-88D, regardless of their vastly different characteristics. For the summer nonprecipitating convective clouds, however, the MMCR reflectivity, on average, is 10.6 dB lower than the WSR-88D measurement, and the average differences between the two radar reflectivities are nearly constant with height above cloud base. Three lookup tables with Mie calculations have been generated for correcting the MMCR signal attenuation. After applying attenuation correction for the MMCR reflectivity measurements, the averaged difference between the two radars has been reduced to 9.1 dB. Within the common sensitivity range (−10 to 20 dBZ), the mean differences for the uncorrected and corrected MMCR reflectivities have been reduced to 6.2 and 5.3 dB, respectively. The corrected MMCR reflectivities were then merged with the WSR-88D data to fill in the gaps during the heavy precipitation periods. This merged dataset provides a more complete radar reflectivity profile for studying convective systems associated with heavier precipitation than the original MMCR dataset. It also provides the intensity, duration, and frequency of the convective systems as they propagate over the ARM SGP for climate modelers. Eventually, it will be possible to improve understanding of the cloud-precipitation processes, and evaluate GCM predictions using the long-term merged dataset, which could not have been done with either the MMCR or the WSR-88D dataset alone. clouds; Precipitation; deep convection; Radars
Forman, B. A.; Margulis, S. A.Forman, B. A., S. A. Margulis, 2009: High-resolution satellite-based cloud-coupled estimates of total downwelling surface radiation for hydrologic modelling applications. Hydrol. Earth Syst. Sci., 13(7), 969-986. doi: 10.5194/hess-13-969-2009. A relatively simple satellite-based radiation model yielding high-resolution (in space and time) downwelling longwave and shortwave radiative fluxes at the Earth's surface is presented. The primary aim of the approach is to provide a basis for deriving physically consistent forcing fields for distributed hydrologic models using satellite-based remote sensing data. The physically-based downwelling radiation model utilises satellite inputs from both geostationary and polar-orbiting platforms and requires only satellite-based inputs except that of a climatological lookup table derived from a regional climate model. Comparison against ground-based measurements over a 14-month simulation period in the Southern Great Plains of the United States demonstrates the ability to reproduce radiative fluxes at a spatial resolution of 4 km and a temporal resolution of 1 h with good accuracy during all-sky conditions. For hourly fluxes, a mean difference of −2 W m−2 with a root mean square difference of 21 W m−2 was found for the longwave fluxes whereas a mean difference of −7 W m−2 with a root mean square difference of 29 W m−2 was found for the shortwave fluxes. Additionally, comparison against advanced downwelling longwave and solar insolation products during all-sky conditions showed comparable uncertainty in the longwave estimates and reduced uncertainty in the shortwave estimates. The relatively simple form of the model enables future usage in ensemble-based applications including data assimilation frameworks in order to explicitly account for input uncertainties while providing the potential for conditioning estimates from other readily available products derived from more sophisticated retrieval algorithms.
Gueymard, Christian A.; Thevenard, DidierGueymard, C. A., D. Thevenard, 2009: Monthly average clear-sky broadband irradiance database for worldwide solar heat gain and building cooling load calculations. Solar Energy, 83(11), 1998-2018. doi: 10.1016/j.solener.2009.07.011. This paper establishes the formulation of a new clear-sky solar radiation model appropriate for algorithms calculating cooling loads in buildings. The aim is to replace the ASHRAE clear-sky model of 1967, whose limitations are well known and are reviewed. The new model is derived in two steps. The first step consists of obtaining a reference irradiance dataset from the REST2 model, which uses a high-performance, validated, two-band clear-sky algorithm. REST2 requires detailed inputs about atmospheric conditions such as aerosols, water vapor, ozone, and ground albedo. The development of global atmospheric datasets used as inputs to REST2 is reviewed. For the most part, these datasets are derived from space observations to guarantee universality and accuracy. In the case of aerosols, point-source terrestrial measurements were also used as ground truthing of the satellite data. The second step of the model consists of fits derived from a REST2-based reference irradiance dataset. These fits enable the derivation of compact, but relatively accurate expressions, for beam and diffuse clear-sky irradiance. The fitted expressions require the tabulation of only two pseudo-optical depths for each month of the year. The resulting model, and its tabulated data, are expected to be incorporated in the 2009 edition of the ASHRAE Handbook of Fundamentals. Aerosol optical depth; ASHRAE; Cooling loads; Direct and diffuse radiation; Solar heat gains; solar irradiance
Gui, Sheng; Liang, Shunlin; Li, LinGui, S., S. Liang, L. Li, 2009: Validation of surface radiation data provided by the CERES over the Tibetan Plateau. 2009 17th International Conference on Geoinformatics, 1-6. doi: 10.1109/GEOINFORMATICS.2009.5292880. As one of the major satellite-estimated surface radiation budget (SRB) dataset, the clouds and the Earth's radiant energy system-monthly gridded radiative fluxes and clouds (CERES-FSW) data have been widely used in various applications. Although CERES/ARM validation experiment (CAVE) has performed the validation work of the input data of CERES-FSW, accuracy of the CERES-FSW data itself is still unknown. So there is a need for a validation of this radiation dataset, especially at some regions with special climate or terrain conditions. The Tibetan Plateau, due to its protruding nature, has an impact on energy and water cycles on both regional and global scales, and it is a perfect research area for comprehensive awareness of data quality and applicability of estimation algorithms. Accordingly, the Plateau has been the subject of climate research for several decades. In this paper, we validates the four major components SRB of the CERES-FSW dataset with ground measurement at the Tibetan Plateau. The four components include: downward shortwave radiation (SWDN), upward shortwave radiation (SWUP), downward longwave radiation (LWDN) and upward longwave radiation (LWUP). It is found that CERES-FSW data have comparatively high accuracy in LWDN and LWUP, while there is slight underestimation at most sites in these two components. The mean bias is -27.3 W/m2 in LWDN and -7.0 W/m2 in LWUP, the mean root mean square errors (RMSE) is 40.0 W/m2 in LWDN and 40.4 W/m2 in LWUP. Mean coefficient of determination (R2) of the two components are both over 0.80. But the accuracy of SW is not as good as that of LW. SWDN of CERES-FSW data are overestimated at most sites with lower R2, large bias and RMSE. SWDN has a mean bias of 41.7 W/m2, mean RMSE of 174.0 W/m2 and mean R2 of 0.39. And for SWUP, CERES-FSW data have low accuracy with very small R2 and large RMSE. SWUP has a mean - bias of 9.7 W/m2 and mean RMSE of 95.2 W/m2, but the mean R2 is only 0.08. Therefore, special attention should be given when using CERES-FSW data at Tibetan Plateau. clouds; Earth; Land surface; longwave; Remote sensing; Satellites; shortwave; validation; Sea measurements; surface radiation budget; CERES-ARM validation experiment; CERES-FSW; Cities and towns; cloud data; data quality; downward longwave radiation; downward shortwave radiation; Earth radiant energy system; Educational institutions; energy cycles; estimation algorithm; Geography; ground measurement; Hydrologic measurements; mean root mean square errors; monthly gridded radiative fluxes; satellite-estimated surface radiation budget dataset; Sea surface; surface electromagnetic waves; surface radiation data validation; Tibetan Plateau; upward longwave radiation; upward shortwave radiation; water cycles
Ham, Seung-Hee; Sohn, Byung-Ju; Yang, Ping; Baum, Bryan A.Ham, S., B. Sohn, P. Yang, B. A. Baum, 2009: Assessment of the Quality of MODIS Cloud Products from Radiance Simulations. J. Appl. Meteor. Climatol., 48(8), 1591-1612. doi: 10.1175/2009JAMC2121.1. Abstract Observations made by the Moderate Resolution Imaging Spectroradiometer (MODIS), the Atmospheric Infrared Sounder (AIRS), the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), and CloudSat are synergistically used to evaluate the accuracy of theoretical simulations of the radiances at the top of the atmosphere (TOA). Specifically, TOA radiances of 15 MODIS bands are simulated for overcast, optically thick, and single-phase clouds only over the ocean from 60°N to 60°S, corresponding to about 12% of all the MODIS cloud observations. Plane parallel atmosphere is assumed in the simulation by restricting viewing/solar zenith angle to be less than 40°. Input data for the radiative transfer model (RTM) are obtained from the operational MODIS-retrieved cloud optical thickness, effective radius, and cloud-top pressure (converted to height) collocated with the AIRS-retrieved temperature and humidity profiles. In the RTM, ice cloud bulk scattering properties, based on theoretical scattering computations and in situ microphysical data, are used for the radiative transfer simulations. The results show that radiances for shortwave bands between 0.466 and 0.857 μm appear to be very accurate with errors on the order of 5%, implying that MODIS cloud parameters provide sufficient information for the radiance simulations. However, simulated radiances for the 1.24-, 1.63-, and 3.78-μm bands do not agree as well with the observed radiances as a result of the use of a single effective radius for a cloud layer that may be vertically inhomogeneous in reality. Furthermore, simulated radiances for the water vapor absorption bands located near 0.93 and 1.38 μm show positive biases, whereas the window bands from 8.5 to 12 μm show negative biases compared to observations, likely due to the less accurate estimate of cloud-top and cloud-base heights. It is further shown that the accuracies of the simulations for water vapor and window bands can be substantially improved by accounting for the vertical cloud distribution provided by the CALIPSO and CloudSat measurements. clouds; satellite observations; Data assimilation; Instrumentation/sensors; Quality assurance/control
Hinkelman, Laura M.; Stackhouse, Paul W.; Wielicki, Bruce A.; Zhang, Taiping; Wilson, Sara R.Hinkelman, L. M., P. W. Stackhouse, B. A. Wielicki, T. Zhang, S. R. Wilson, 2009: Surface insolation trends from satellite and ground measurements: Comparisons and challenges. Journal of Geophysical Research: Atmospheres, 114(D10), D00D20. doi: 10.1029/2008JD011004. Global “dimming” and “brightening,” the decrease and subsequent increase in solar downwelling flux reaching the surface observed in many locations over the past several decades, and related issues are examined using satellite data from the NASA/Global Energy and Water Cycle Experiment (GEWEX) Surface Radiation Budget (SRB) product, version 2.8. A 2.51 W m−2 decade−1 dimming is found between 1983 and 1991, followed by 3.17 W m−2 decade−1 brightening from 1991 to 1999, returning to 5.26 W m−2 decade−1 dimming over 1999–2004 in the SRB global mean. This results in an insignificant overall trend for the entire satellite period. However, patterns of variability for smaller regions (continents, land, and ocean) are found to differ significantly from the global signal. The significance of the computed linear trends is assessed using a statistical technique that accommodates the autocorrelation typically found in surface insolation time series. Satellite fluxes are compared to measurements from surface radiation stations on both a site-by-site and ensemble basis. Comparison of an ensemble of the most continuous Global Energy Balance Archive (GEBA) sites to SRB data yields a root-mean-square difference and correlation of 2.6 W m−2 and 0.822, respectively. However, the GEBA time series does not correspond well to the SRB global mean owing to its extremely limited distribution of sites. Simulations of the Baseline Surface Radiometer Network using SRB data suggest that the network is becoming more representative of the globe as it expands, but that the Southern Hemisphere and oceans remain seriously underrepresented in the surface networks. This study indicates that it is inappropriate to describe the variability of global surface insolation in the current satellite record using a single linear fit because major changes in slope have been observed over the last 20 years. Further efforts to improve the quality of satellite flux records and the spatial distribution of surface measurement sites are recommended, along with more rigorous analysis of the origins of observed insolation variations, in order to improve our understanding of both long- and short-term variability in the downwelling solar flux at the Earth's surface. 1640 Remote sensing; 3359 Radiative processes; 3305 Climate change and variability; Satellite; Shortwave radiation; 1814 Energy budgets; trend
Huang, J.; Fu, Q.; Su, J.; Tang, Q.; Minnis, P.; Hu, Y.; Yi, Y.; Zhao, Q.Huang, J., Q. Fu, J. Su, Q. Tang, P. Minnis, Y. Hu, Y. Yi, Q. Zhao, 2009: Taklimakan dust aerosol radiative heating derived from CALIPSO observations using the Fu-Liou radiation model with CERES constraints. Atmos. Chem. Phys., 9(12), 4011-4021. doi: 10.5194/acp-9-4011-2009. The dust aerosol radiative forcing and heating rate over the Taklimakan Desert in Northwestern China in July 2006 are estimated using the Fu-Liou radiative transfer model along with satellite observations. The vertical distributions of the dust aerosol extinction coefficient are derived from the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) lidar measurements. The CERES (Cloud and the Earth's Energy Budget Scanner) measurements of reflected solar radiation are used to constrain the dust aerosol type in the radiative transfer model, which determines the dust aerosol single-scattering albedo and asymmetry factor as well as the aerosol optical properties' spectral dependencies. We find that the dust aerosols have a significant impact on the radiative energy budget over the Taklimakan desert. In the atmospheres containing light, moderate and heavy dust layers, the dust aerosols heat the atmosphere (daily mean) by up to 1, 2, and 3 K day−1, respectively. The maximum daily mean radiative heating rate reaches 5.5 K day−1 at 5 km on 29 July. The averaged daily mean net radiative effect of the dust are 44.4, −41.9, and 86.3 W m−2, respectively, at the top of the atmosphere (TOA), surface, and in the atmosphere. Among these effects about two thirds of the warming effect at the TOA is related to the longwave radiation, while about 90% of the atmospheric warming is contributed by the solar radiation. At the surface, about one third of the dust solar radiative cooling effect is compensated by its longwave warming effect. The large modifications of radiative energy budget by the dust aerosols over Taklimakan Desert should have important implications for the atmospheric circulation and regional climate, topics for future investigations.
Imhoff, Marc L.; Wolfe, Robert; Diner, David J.; Chopping, Mark; Kahn, Ralph; Salomonson, Vincent; Gille, John; Drummond, James; Edwards, David; Loeb, Norm; Wielicki, Bruce; Abrams, Michael; Eng, Bjorn; Tsay, Si-Chee; Ranson, K. JonImhoff, M. L., R. Wolfe, D. J. Diner, M. Chopping, R. Kahn, V. Salomonson, J. Gille, J. Drummond, D. Edwards, N. Loeb, B. Wielicki, M. Abrams, B. Eng, S. Tsay, K. J. Ranson, 2009: An Overview of Terra Mission Results Related to the Carbon Cycle. Geography Compass, 3(2), 536-559. doi: 10.1111/j.1749-8198.2008.00183.x. Launched in December 1999 as the Earth Observing System's flagship observatory, the Terra Mission (formerly EOS AM-1) carries a suite of five instruments that collect comprehensive global measurements of earth's atmosphere, cryosphere, lands, and oceans. One of the mission's science goals is the collection of data that will enable a better quantitative understanding of earth's carbon cycle through direct observation of atmospheric constituents and the provision of spatially explicit information about biophysical surface properties useful for modeling. In this article, highlights of the mission's use of five main instruments (ASTER, CERES, MISR, MODIS, and MOPITT) to address various aspects of the carbon cycle are reviewed, using examples of earth's photosynthetic production on land, vegetation structure and ecosystem response, and the extent and frequency of fires and their contribution of aerosols and carbon emissions to the atmosphere.
Jones, T. A.; Christopher, S. A.; Quaas, J.Jones, T. A., S. A. Christopher, J. Quaas, 2009: A six year satellite-based assessment of the regional variations in aerosol indirect effects. Atmos. Chem. Phys., 9(12), 4091-4114. doi: 10.5194/acp-9-4091-2009. Aerosols act as cloud condensation nuclei (CCN) for cloud water droplets, and changes in aerosol concentrations have significant microphysical impacts on the corresponding cloud properties. Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol and cloud properties are combined with NCEP Reanalysis data for six different regions around the globe between March 2000 and December 2005 to study the effects of different aerosol, cloud, and atmospheric conditions on the aerosol indirect effect (AIE). Emphasis is placed in examining the relative importance of aerosol concentration, type, and atmospheric conditions (mainly vertical motion) to AIE from region to region. Results show that in most regions, AIE has a distinct seasonal cycle, though the cycle varies in significance and period from region to region. In the Arabian Sea (AS), the six-year mean anthropogenic + dust AIE is −0.27 Wm−2 and is greatest during the summer months (
Kato, SeijiKato, S., 2009: Interannual Variability of the Global Radiation Budget. J. Climate, 22(18), 4893-4907. doi: 10.1175/2009JCLI2795.1. Abstract Interannual variability of the global radiation budget, regions that contribute to its variability, and what limits albedo variability are investigated using Clouds and the Earth’s Radiant Energy System (CERES) data taken from March 2000 through February 2004. Area-weighted mean top-of-atmosphere (TOA) reflected shortwave, longwave, and net irradiance standard deviations computed from monthly anomalies over a 1° × 1° region are 9.6, 7.6, and 7.6 W m−2, respectively. When standard deviations are computed from global monthly anomalies, they drop to 0.5, 0.4, and 0.4 W m−2, respectively. Clouds are mostly responsible for the variation. Regions with a large standard deviation of TOA shortwave and longwave irradiance at TOA are the tropical western and central Pacific, which is caused by shifting from La Niña to El Niño during this period. However, a larger standard deviation of 300–1000-hPa thickness anomalies occurs in the polar region instead of the tropics. The correlation coefficient between atmospheric net irradiance anomalies and 300–1000-hPa thickness anomalies is negative. These indicate that temperature anomalies in the atmosphere are mostly a result of anomalies in longwave and dynamical processes that transport energy poleward, instead of albedo anomalies by clouds directly affecting temperature anomalies in the atmosphere. With simple zonal-mean thermodynamic energy equations it is demonstrated that temperature anomalies decay exponentially with time by longwave emission and by dynamical processes. As a result, the mean meridional temperature gradient is maintained. Therefore, mean meridional circulations are not greatly altered by albedo anomalies on an annual time scale, which in turn provides small interannual variability of the global mean albedo. albedo; Radiation budgets; Climatology; Interannual variability; Energy transport
Kato, Seiji; Marshak, AlexanderKato, S., A. Marshak, 2009: Solar zenith and viewing geometry-dependent errors in satellite retrieved cloud optical thickness: Marine stratocumulus case. Journal of Geophysical Research: Atmospheres, 114(D1), D01202. doi: 10.1029/2008JD010579. The error in the domain-averaged cloud optical thickness retrieved from satellite-based imagers is investigated using a cloud field generated by a cloud model and a 3D radiative transfer model. The objective of this study is to identify the optimal geometry for the optical thickness retrieval and quantify the error. The cloud field used in the simulation is a relatively uniform (retrieved shape parameter of a gamma distribution averaged over all simulated viewing and solar zenith angles is 18) and nearly isotropic stratocumulus field. The retrieved cloud cover with a 1-km pixel resolution is 100%. The domain-averaged optical thickness error is separated into two terms, the error caused by an assumption of a horizontally uniform cloud over a 1-km pixel (internal variability) and error caused by neglecting the horizontal flux through the boundary of subpixels (external variability). For the cloud field used in this study, the external variability term increases with solar zenith angle and the sign changes from negative to positive while the internal variability term is generally negative and becomes more negative as the solar zenith angle increases. At a small solar zenith angle, therefore, both terms are negative, but the error partially cancels at a large solar zenith angle. When the solar zenith angle is less than 30°, both terms are small; the error in the viewing zenith angle and domain-averaged cloud optical thickness derived from the relative azimuth angle smaller than 150 is less than 10%. However, if the optical thickness is derived from nadir view only for overhead sun, the domain-averaged optical thickness is underestimated by more than 10%. When the solar zenith angle increases to 60°, the internal variability term exceeds 10%, especially viewed from the forward direction, but the domain and viewing zenith angle averaged optical thickness error can be less than 10% in the backward direction. When the solar zenith angle is 70°, both terms are greater than 10%. The shape parameter of a gamma distribution derived from retrieved optical thicknesses increases with the viewing zenith angle but decreases with solar zenith angle. On the basis of this simulation and Terra Moderate Resolution Imaging Spectroradiometer (MODIS) viewing geometry and solar zenith angle at the sampling time over the northeastern Pacific, the error in the domain-averaged retrieved optical thickness of uniform stratocumulus over northeastern Pacific is less than 10% in March and September. atmosphere; clouds; Remote sensing; 0360 Radiation: transmission and scattering; 1640 Remote sensing; 0321 Cloud/radiation interaction
Lin, Wuyin; Zhang, Minghua; Loeb, Norman G.Lin, W., M. Zhang, N. G. Loeb, 2009: Seasonal Variation of the Physical Properties of Marine Boundary Layer Clouds off the California Coast. J. Climate, 22(10), 2624-2638. doi: 10.1175/2008JCLI2478.1. Abstract Marine boundary layer (MBL) clouds can significantly regulate the sensitivity of climate models, yet they are currently poorly simulated. This study aims to characterize the seasonal variations of physical properties of these clouds and their associated processes by using multisatellite data. Measurements from several independent satellite datasets [International Satellite Cloud Climatology Project (ISCCP), Clouds and the Earth’s Radiant Energy System–Moderate Resolution Imaging Spectroradiometer (CERES–MODIS), Geoscience Laser Altimeter System (GLAS), and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO)], in conjunction with balloon soundings from the mobile facility of the Atmospheric Radiation Measurement (ARM) program at Point Reyes and reanalysis products, are used to characterize the seasonal variations of MBL cloud-top and cloud-base heights, cloud thickness, the degree of decoupling between clouds and MBL, and inversion strength off the California coast. The main results from this study are as follows: (i) MBL clouds over the northeast subtropical Pacific in the summer are more prevalent and associated with a larger in-cloud water path than in winter. The cloud-top and cloud-base heights are lower in the summer than in the winter. (ii) Although the lower-tropospheric stability of the atmosphere is higher in the summer, the MBL inversion strength is only weakly stronger in the summer because of a negative feedback from the cloud-top altitude. Summertime MBL clouds are more homogeneous and are associated with lower surface latent heat flux than those in the winter. (iii) Seasonal variations of low-cloud properties from summer to winter resemble the downstream stratocumulus-to-cumulus transition of MBL clouds in terms of MBL depth, cloud-top and cloud-base heights, inversion strength, and spatial homogeneity. The “deepening–warming” mechanism of Bretherton and Wyant for the stratocumulus-to-trade-cumulus transition downstream of the cold eastern ocean can also explain the seasonal variation of low clouds from the summer to the winter, except that warming of the sea surface temperature needs to be taken as relative to the free-tropospheric air temperature, which occurs in the winter. The observed variation of low clouds from summer to winter is attributed to the much larger seasonal cooling of the free-tropospheric air temperature than that of the sea surface temperature. clouds; satellite observations; North America; marine boundary layer; Seasonal variability
Loeb, Norman G.; Wielicki, Bruce A.; Doelling, David R.; Smith, G. Louis; Keyes, Dennis F.; Kato, Seiji; Manalo-Smith, Natividad; Wong, TakmengLoeb, N. G., B. A. Wielicki, D. R. Doelling, G. L. Smith, D. F. Keyes, S. Kato, N. Manalo-Smith, T. Wong, 2009: Toward Optimal Closure of the Earth's Top-of-Atmosphere Radiation Budget. J. Climate, 22(3), 748-766. doi: 10.1175/2008JCLI2637.1. Abstract Despite recent improvements in satellite instrument calibration and the algorithms used to determine reflected solar (SW) and emitted thermal (LW) top-of-atmosphere (TOA) radiative fluxes, a sizeable imbalance persists in the average global net radiation at the TOA from satellite observations. This imbalance is problematic in applications that use earth radiation budget (ERB) data for climate model evaluation, estimate the earth’s annual global mean energy budget, and in studies that infer meridional heat transports. This study provides a detailed error analysis of TOA fluxes based on the latest generation of Clouds and the Earth’s Radiant Energy System (CERES) gridded monthly mean data products [the monthly TOA/surface averages geostationary (SRBAVG-GEO)] and uses an objective constrainment algorithm to adjust SW and LW TOA fluxes within their range of uncertainty to remove the inconsistency between average global net TOA flux and heat storage in the earth–atmosphere system. The 5-yr global mean CERES net flux from the standard CERES product is 6.5 W m−2, much larger than the best estimate of 0.85 W m−2 based on observed ocean heat content data and model simulations. The major sources of uncertainty in the CERES estimate are from instrument calibration (4.2 W m−2) and the assumed value for total solar irradiance (1 W m−2). After adjustment, the global mean CERES SW TOA flux is 99.5 W m−2, corresponding to an albedo of 0.293, and the global mean LW TOA flux is 239.6 W m−2. These values differ markedly from previously published adjusted global means based on the ERB Experiment in which the global mean SW TOA flux is 107 W m−2 and the LW TOA flux is 234 W m−2. Radiation budgets; satellite observations; Fluxes
Loeb, Norman G.; Wielicki, Bruce A.; Wong, Takmeng; Parker, Peter A.Loeb, N. G., B. A. Wielicki, T. Wong, P. A. Parker, 2009: Impact of data gaps on satellite broadband radiation records. Journal of Geophysical Research: Atmospheres, 114(D11), D11109. doi: 10.1029/2008JD011183. A simulated 30-year climate data record of net cloud radiative effect (defined as the difference between clear- and all-sky net top-of-atmosphere radiative flux) based on the first 5 years of Clouds and the Earth's Radiant Energy System (CERES) Terra measurements is created in order to investigate how gaps in the record affect our ability to constrain cloud radiative feedback. To ensure a trend estimate with an uncertainty small enough to constrain cloud radiative feedback to 25% of anthropogenic forcing in the next few decades, the absolute calibration change across the gap must be 0321 Cloud/radiation interaction; 3305 Climate change and variability; 1616 Climate variability; radiation; overlap; gaps
Lu, Duan-Jun; Wang, Mo-Chang; YU, Yun-Jian; Hong, Xiao-JuLu, D., M. Wang, Y. YU, X. Hong, 2009: RADIATION CALIBRATION METHOD OF EARTH RADIATION MEASUREMENT NONSCANNER. Journal of Infrared and Millimeter Waves, 1, 010.
Marshak, A.; Knyazikhin, Y.; Chiu, J. C.; Wiscombe, W. J.Marshak, A., Y. Knyazikhin, J. C. Chiu, W. J. Wiscombe, 2009: Spectral invariant behavior of zenith radiance around cloud edges observed by ARM SWS. Geophysical Research Letters, 36(16), L16802. doi: 10.1029/2009GL039366. The ARM Shortwave Spectrometer (SWS) measures zenith radiance at 418 wavelengths between 350 and 2170 nm. Because of its 1-sec sampling resolution, the SWS provides a unique capability to study the transition zone between cloudy and clear sky areas. A spectral invariant behavior is found between ratios of zenith radiance spectra during the transition from cloudy to cloud-free. This behavior suggests that the spectral signature of the transition zone is a linear mixture between the two extremes (definitely cloudy and definitely clear). The weighting function of the linear mixture is a wavelength-independent characteristic of the transition zone. It is shown that the transition zone spectrum is fully determined by this function and zenith radiance spectra of clear and cloudy regions. An important result of these discoveries is that high temporal resolution radiance measurements in the clear-to-cloud transition zone can be well approximated by lower temporal resolution measurements plus linear interpolation. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 0321 Cloud/radiation interaction; 0317 Chemical kinetic and photochemical properties; shortwave spectrometer; wavelength-independent; zenith radiance
Matthews, GrantMatthews, G., 2009: In-Flight Spectral Characterization and Calibration Stability Estimates for the Clouds and the Earth’s Radiant Energy System (CERES). J. Atmos. Oceanic Technol., 26(9), 1685-1716. doi: 10.1175/2009JTECHA1243.1. Abstract It is essential to maintain global measurements of the earth radiation budget (ERB) from space, the scattered solar and emitted thermal radiative fluxes leaving the planet. These are required for the purpose of validating current climate model predictions of the planet’s future response to anthropogenic greenhouse gas forcing. The measurement accuracy and calibration stability required to resolve the magnitude of model-suggested cloud–climate feedbacks on the ERB have recently been estimated. The suggestion is for ERB data to strive for a calibration stability of ±0.3% decade−1 for scattered solar, ±0.5% decade−1 for emitted thermal, and an overall absolute accuracy of 1 W m−2. The Clouds and the Earth’s Radiant Energy System (CERES) is currently the only satellite program to make global ERB measurements, beginning in January 1998. However, the new climate calibration standards are beyond those originally specified by the NASA CERES program for its edition 2 data release. Furthermore, the CERES instrument optics have been discovered to undergo substantial in-flight degradation because of contaminant issues. This is not directly detectable by using established calibration methods. Hence, user-applied revisions for edition 2 shortwave (SW) data were derived to compensate for this effect, which is described as “spectral darkening.” Also, an entirely new in-flight calibration protocol has been developed for CERES that uses deep convective cloud albedo as a primary solar wavelength stability metric. This is then combined with a sophisticated contamination mobilization/polymerization model. The intention is to assign spectral coloration to any optical degradation occurring to the different CERES Earth observing telescopes. This paper quantifies the stability of revised edition 2 data. It also calculates stability, which the new protocols could give CERES measurements if used. The conclusion is that the edition 2 revisions restore the originally specified stability of CERES SW data. It is also determined that the climate calibration stability goals are reachable by using the new in-flight methodologies presented in this paper. However, this will require datasets of longer than approximately 10 yr. It will also require obtaining regular raster scans of the Moon by all operational CERES instruments. clouds; Radiation budgets; satellite observations; climate models
Murphy, D. M.; Solomon, S.; Portmann, R. W.; Rosenlof, K. H.; Forster, P. M.; Wong, T.Murphy, D. M., S. Solomon, R. W. Portmann, K. H. Rosenlof, P. M. Forster, T. Wong, 2009: An observationally based energy balance for the Earth since 1950. Journal of Geophysical Research: Atmospheres, 114(D17), D17107. doi: 10.1029/2009JD012105. We examine the Earth's energy balance since 1950, identifying results that can be obtained without using global climate models. Important terms that can be constrained using only measurements and radiative transfer models are ocean heat content, radiative forcing by long-lived trace gases, and radiative forcing from volcanic eruptions. We explicitly consider the emission of energy by a warming Earth by using correlations between surface temperature and satellite radiant flux data and show that this term is already quite significant. About 20% of the integrated positive forcing by greenhouse gases and solar radiation since 1950 has been radiated to space. Only about 10% of the positive forcing (about 1/3 of the net forcing) has gone into heating the Earth, almost all into the oceans. About 20% of the positive forcing has been balanced by volcanic aerosols, and the remaining 50% is mainly attributable to tropospheric aerosols. After accounting for the measured terms, the residual forcing between 1970 and 2000 due to direct and indirect forcing by aerosols as well as semidirect forcing from greenhouse gases and any unknown mechanism can be estimated as −1.1 ± 0.4 W m−2 (1σ). This is consistent with the Intergovernmental Panel on Climate Change's best estimates but rules out very large negative forcings from aerosol indirect effects. Further, the data imply an increase from the 1950s to the 1980s followed by constant or slightly declining aerosol forcing into the 1990s, consistent with estimates of trends in global sulfate emissions. An apparent increase in residual forcing in the late 1990s is discussed. 0305 Aerosols and particles; climate change; radiative forcing; 1616 Climate variability; 1626 Global climate models; 1635 Oceans
Myhre, G.; Berglen, T. F.; Hoyle, C. R.; Christopher, S.a.; Coe, H.; Crosier, J.; Formenti, P.; Haywood, J.m.; Johnsrud, M.; Jones, T.a.; Loeb, N.; Osborne, S.; Remer, L.a.Myhre, G., T. F. Berglen, C. R. Hoyle, S. Christopher, H. Coe, J. Crosier, P. Formenti, J. Haywood, M. Johnsrud, T. Jones, N. Loeb, S. Osborne, L. Remer, 2009: Modelling of chemical and physical aerosol properties during the ADRIEX aerosol campaign. Quarterly Journal of the Royal Meteorological Society, 135(638), 53-66. doi: 10.1002/qj.350. A global aerosol model with relatively high resolution is used to simulate the distribution and radiative effect of aerosols during the Aerosol Direct Radiative Impact Experiment (ADRIEX) campaign in August and September 2004. The global chemical transport model Oslo CTM2 includes detailed chemistry, which is coupled to aerosol partitioning of sulphate, nitrate and secondary organic aerosols. In accordance with aircraft observations the aerosol model simulates a dominance of secondary aerosols compared to primary aerosols in the ADRIEX study region. The model underestimates the aerosol optical depth (AOD) at 550 nm in the main region of the campaign around Venice. This underestimation mainly occurs during a 3–4 day period of highest AODs. At two AERONET (Aerosol Robotic Network) stations related to the ADRIEX campaign outside the Po valley area, the model compares very well with the observed AOD. Comparisons with observed chemical composition show that the model mainly underestimates organic carbon, with better agreement for other aerosol species. The model simulations indicate that the emission of aerosols and their precursors may be underestimated in the Po valley. Recent results show a large spread in radiative forcing due to the direct aerosol effect in global aerosol models, which is likely linked to large differences in the vertical profile of aerosols and aerosol absorption. The modelled vertical profile of aerosol compares reasonably well to the aircraft measurements as was the case in two earlier campaigns involving biomass burning and dust aerosols. The radiative effect of aerosols over the northern part of the Adriatic Sea agrees well with the mean of three satellite-derived estimates despite large differences between the satellite-derived data. The difference between the model and the mean of the satellite data is within 10% for the radiative effect. The radiative forcing due to anthropogenic aerosols is simulated to be negative in the ADRIEX region with values between − 5 and − 2 W m−2. Copyright © 2008 Royal Meteorological Society radiative forcing; aircraft measurements; secondary organic aerosols
Myhre, G.; Berglen, T. F.; Johnsrud, M.; Hoyle, C. R.; Berntsen, T. K.; Christopher, S. A.; Fahey, D. W.; Isaksen, I. S. A.; Jones, T. A.; Kahn, R. A.; Loeb, N.; Quinn, P.; Remer, L.; Schwarz, J. P.; Yttri, K. E.Myhre, G., T. F. Berglen, M. Johnsrud, C. R. Hoyle, T. K. Berntsen, S. A. Christopher, D. W. Fahey, I. S. A. Isaksen, T. A. Jones, R. A. Kahn, N. Loeb, P. Quinn, L. Remer, J. P. Schwarz, K. E. Yttri, 2009: Modelled radiative forcing of the direct aerosol effect with multi-observation evaluation. Atmos. Chem. Phys., 9(4), 1365-1392. doi: 10.5194/acp-9-1365-2009. A high-resolution global aerosol model (Oslo CTM2) driven by meteorological data and allowing a comparison with a variety of aerosol observations is used to simulate radiative forcing (RF) of the direct aerosol effect. The model simulates all main aerosol components, including several secondary components such as nitrate and secondary organic carbon. The model reproduces the main chemical composition and size features observed during large aerosol campaigns. Although the chemical composition compares best with ground-based measurement over land for modelled sulphate, no systematic differences are found for other compounds. The modelled aerosol optical depth (AOD) is compared to remote sensed data from AERONET ground and MODIS and MISR satellite retrievals. To gain confidence in the aerosol modelling, we have tested its ability to reproduce daily variability in the aerosol content, and this is performing well in many regions; however, we also identified some locations where model improvements are needed. The annual mean regional pattern of AOD from the aerosol model is broadly similar to the AERONET and the satellite retrievals (mostly within 10–20%). We notice a significant improvement from MODIS Collection 4 to Collection 5 compared to AERONET data. Satellite derived estimates of aerosol radiative effect over ocean for clear sky conditions differs significantly on regional scales (almost up to a factor two), but also in the global mean. The Oslo CTM2 has an aerosol radiative effect close to the mean of the satellite derived estimates. We derive a radiative forcing (RF) of the direct aerosol effect of −0.35 Wm−2 in our base case. Implementation of a simple approach to consider internal black carbon (BC) mixture results in a total RF of −0.28 Wm−2. Our results highlight the importance of carbonaceous particles, producing stronger individual RF than considered in the recent IPCC estimate; however, net RF is less different. A significant RF from secondary organic aerosols (SOA) is estimated (close to −0.1 Wm−2). The SOA also contributes to a strong domination of secondary aerosol species for the aerosol composition over land. A combination of sensitivity simulations and model evaluation show that the RF is rather robust and unlikely to be much stronger than in our best estimate.
Pallé, E.; Goode, P. R.; Montañés-Rodríguez, P.Pallé, E., P. R. Goode, P. Montañés-Rodríguez, 2009: Interannual variations in Earth's reflectance 1999–2007. Journal of Geophysical Research: Atmospheres, 114(D10), D00D03. doi: 10.1029/2008JD010734. The overall reflectance of sunlight from Earth is a fundamental parameter for climate studies. Recently, measurements of earthshine were used to find large decadal variability in Earth's reflectance of sunlight. However, the results did not seem consistent with contemporaneous independent albedo measurements from the low Earth orbit satellite, Clouds and the Earth's Radiant Energy System (CERES), which showed a weak, opposing trend. Now more data for both are available, all sets have been either reanalyzed (earthshine) or recalibrated (CERES), and they present consistent results. Albedo data are also available from the recently released International Satellite Cloud Climatology Project flux data (FD) product. Earthshine and FD analyses show contemporaneous and climatologically significant increases in the Earth's reflectance from the outset of our earthshine measurements beginning in late 1998 roughly until mid-2000. After that and to date, all three show a roughly constant terrestrial albedo, except for the FD data in the most recent years. Using satellite cloud data and Earth reflectance models, we also show that the decadal-scale changes in Earth's reflectance measured by earthshine are reliable and are caused by changes in the properties of clouds rather than any spurious signal, such as changes in the Sun-Earth-Moon geometry. 1610 Atmosphere; 0305 Aerosols and particles; albedo; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; 3310 Clouds and cloud feedbacks; dimming; earthshine
Pinker, Rachel T.; Wang, Hengmao; Grodsky, Semyon A.Pinker, R. T., H. Wang, S. A. Grodsky, 2009: How good are ocean buoy observations of radiative fluxes?. Geophysical Research Letters, 36(10), L10811. doi: 10.1029/2009GL037840. Satellite-derived surface shortwave radiation (SWR) has been extensively evaluated against ground observations over land but to a lesser extent over oceans that cover larger portion of the Earth surface. In this study new surface radiative flux estimates from the Moderate Resolution Imaging Spectro-radiometer (MODIS) are evaluated against buoy measurements of downwelling SWR in the tropical oceans. As a benchmark for achievable accuracies from satellites, similar evaluation is performed over land against the Baseline Surface Radiation Network (BSRN) observations, believed to be of highest available quality. Comparable accuracy of the new satellite SWR data is found over land and over oceans. 0360 Radiation: transmission and scattering; 0399 General or miscellaneous; Radiative fluxes; 0434 Data sets; MODIS estimates of radiative fluxes; radiative fluxes over oceans
Rutan, David; Rose, Fred; Roman, Miguel; Manalo-Smith, Natividad; Schaaf, Crystal; Charlock, TomRutan, D., F. Rose, M. Roman, N. Manalo-Smith, C. Schaaf, T. Charlock, 2009: Development and assessment of broadband surface albedo from Clouds and the Earth's Radiant Energy System Clouds and Radiation Swath data product. Journal of Geophysical Research: Atmospheres, 114(D8), D08125. doi: 10.1029/2008JD010669. We describe a method to determine broadband albedo globally over land viewed by the Clouds and the Earth's Radiant Energy System (CERES) scanning radiometers on board the TRMM, Terra, and Aqua satellites. This albedo is used as a surface boundary condition for a fast radiation transfer code in the Surface and Atmospheric Radiation Budget (SARB) subsystem of the CERES processing scheme. Cloudy sky surface albedo is estimated from derived clear sky values. Clear sky surface albedo is assessed by comparing the CERES/SARB-based surface albedo with the bidirectional reflectance distribution function (BRDF)–based surface albedo supplied by the MODIS land surfaces group. The SARB method employs broadband observations at the top of atmosphere (TOA) and assumes relative spectral shape of surface albedo. The MODIS group uses higher spatial resolution observations in several shortwave window channels to retrieve spectral surface albedos and then scales up to broadband surface albedo. Comparisons over snow-free land show good agreement between the two independent products on the scale of the CERES footprint. Biases run approximately 0.005 absolute or 0.02 relative with SARB albedo, generally lower than MODIS. We find little dependence on view geometry and slight functional dependence on aerosol optical depth. The value selected for a priori surface spectral albedo is important, but not critical, when retrieving broadband surface albedo with broadband TOA data. However, based on calculations, aerosol forcing to TOA flux changes in spectral albedo shape can affect aerosol forcing for as much as would a 15% absolute change in the original broadband surface albedo. 0360 Radiation: transmission and scattering; 1640 Remote sensing; 1694 Instruments and techniques; CERES; albedo; modeling; 1631 Land/atmosphere interactions
Saunders, Will; Lawrence, Jon S.; Storey, John W. V.; Ashley, Michael C. B.; Kato, Seiji; Minnis, Patrick; Winker, David M.; Liu, Guiping; Kulesa, CraigSaunders, W., J. S. Lawrence, J. W. V. Storey, M. C. B. Ashley, S. Kato, P. Minnis, D. M. Winker, G. Liu, C. Kulesa, 2009: Where Is the Best Site on Earth? Domes A, B, C, and F, and Ridges A and B. Publications of the Astronomical Society of the Pacific, 121(883), 976-992. doi: 10.1086/605780. ABSTRACT. The Antarctic plateau contains the best sites on earth for many forms of astronomy, but none of the existing bases was selected with astronomy as the primary motivation. In this article, we try to systematically compare the merits of potential observatory sites. We include South Pole, Domes A, C, and F, and also Ridge B (running northeast from Dome A), and what we call “Ridge A” (running southwest from Dome A). Our analysis combines satellite data, published results, and atmospheric models, to compare the boundary layer, weather, aurorae, airglow, precipitable water vapor, thermal sky emission, surface temperature, and the free atmosphere, at each site. We find that all Antarctic sites are likely to be compromised for optical work by airglow and aurorae. Of the sites with existing bases, Dome A is easily the best overall; but we find that Ridge A offers an even better site. We also find that Dome F is a remarkably good site. Dome C is less good as a thermal infrared or terahertz site, but would be able to take advantage of a predicted “OH hole” over Antarctica during spring.
Slingo, A.; White, H. E.; Bharmal, N. A.; Robinson, G. J.Slingo, A., H. E. White, N. A. Bharmal, G. J. Robinson, 2009: Overview of observations from the RADAGAST experiment in Niamey, Niger: 2. Radiative fluxes and divergences. Journal of Geophysical Research: Atmospheres, 114(D13), D00E04. doi: 10.1029/2008JD010497. Broadband shortwave and longwave radiative fluxes observed both at the surface and from space during the Radiative Atmospheric Divergence using ARM Mobile Facility, GERB data and AMMA Stations (RADAGAST) experiment in Niamey, Niger, in 2006 are presented. The surface fluxes were measured by the Atmospheric Radiation Measurement (ARM) Program Mobile Facility (AMF) at Niamey airport, while the fluxes at the top of the atmosphere (TOA) are from the Geostationary Earth Radiation Budget (GERB) instrument on the Meteosat-8 satellite. The data are analyzed as daily averages, in order to minimize sampling differences between the surface and top of atmosphere instruments, while retaining the synoptic and seasonal changes that are the main focus of this study. A cloud mask is used to identify days with cloud versus those with predominantly clear skies. The influence of temperature, water vapor, aerosols, and clouds is investigated. Aerosols are ubiquitous throughout the year and have a significant impact on both the shortwave and longwave fluxes. The large and systematic seasonal changes in temperature and column integrated water vapor (CWV) through the dry and wet seasons are found to exert strong influences on the longwave fluxes. These influences are often in opposition to each other, because the highest temperatures occur at the end of the dry season when the CWV is lowest, while in the wet season the lowest temperatures are associated with the highest values of CWV. Apart from aerosols, the shortwave fluxes are also affected by clouds and by the seasonal changes in CWV. The fluxes are combined to provide estimates of the divergence of radiation across the atmosphere throughout 2006. The longwave divergence shows a relatively small variation through the year, because of a partial compensation between the seasonal variations in the outgoing longwave radiation (OLR) and surface net longwave radiation. A simple model of the greenhouse effect is used to interpret this result in terms of the dependence of the normalized greenhouse effect at the TOA and of the effective emissivity of the atmosphere at the surface on the CWV. It is shown that, as the CWV increases, the atmosphere loses longwave energy to the surface with about the same increasing efficiency with which it traps the OLR. When combined with the changes in temperature, this maintains the atmospheric longwave divergence within the narrow range that is observed. The shortwave divergence is mainly determined by the CWV and aerosol loadings and the effect of clouds is much smaller than on the component fluxes. 0360 Radiation: transmission and scattering; atmospheric radiation; 3311 Clouds and aerosols; 3374 Tropical meteorology; 9305 Africa; AMMA; RADAGAST
Smith, G. Louis; Priestley, Kory J.; Hess, Phillip C.; Currey, Chris; Spence, PeterSmith, G. L., K. J. Priestley, P. C. Hess, C. Currey, P. Spence, 2009: Validation of Geolocation of Measurements of the Clouds and the Earth’s Radiant Energy System (CERES) Scanning Radiometers aboard Three Spacecraft. J. Atmos. Oceanic Technol., 26(11), 2379-2391. doi: 10.1175/2009JTECHA1207.1. Abstract The Clouds and the Earth’s Radiant Energy System (CERES) instrument is a scanning radiometer for measuring Earth-emitted and -reflected solar radiation to understand Earth’s energy balance. One CERES instrument was placed into orbit aboard the Tropical Rainfall Measuring Mission (TRMM) in 1997; two were aboard the Terra spacecraft, launched in 1999; and two were aboard the Aqua spacecraft, launched in 2002. These measurements are used together with data from higher-resolution instruments to generate a number of data products. The nominal footprint size of the pixel at Earth’s surface is 16 km in the cross-scan direction and 23 km in the scan direction for the TRMM platform and 36 km in the cross-scan direction and 46 km in the scan direction for the Terra and Aqua platforms. It is required that the location on Earth of each pixel be known to 1–2 km to use the CERES data with the higher-resolution instruments on a pixel basis. A technique has been developed to validate the computed geolocation of the measurements by use of coastlines. Scenes are chosen in which the reflected solar radiation changes abruptly from the land surface to the darker ocean surface and the Earth-emitted radiation changes from the warm land to the cool ocean, or vice versa, so that scenes can be detected both day and night. The computed coastline location is then compared with the World Bank II map. The method has been applied to data from the three spacecraft and shows that the pixel geolocations are accurate to within 10% of the pixel size and that the geolocation is adequate for current scientific investigations. Remote sensing; Energy budget/balance; satellite observations; Radiances; radiation budget
Sorensen, Ira J.; Mahan, James R.Sorensen, I. J., J. R. Mahan, 2009: Enhancing the simulation of radiometric instrument models using genetic algorithms. Journal of Applied Remote Sensing, 3(1), 033509-033509-20. doi: 10.1117/1.3096955. A primary objective of the effort described here is to optimize the performance of a modeling environment for radiometric instruments capable of predicting their complete end-to-end behavior, integrating the optical, electrothermal, and electronic systems. The numerical environment consists of a Monte Carlo ray-trace (MCRT) model of the optical system coupled to a transient three-dimensional finite-difference electrothermal model of the detector assembly with an analytical model of the signal-conditioning circuitry. The resulting model provides a complete simulation of the dynamic optical and electrothermal behavior of the instrument. The modeling environment has been used to create an end-to-end model of the CERES scanning radiometer, and its performance compared to the calibration performance of an operational CERES total channel as a benchmark. To optimize the accuracy of the electrothermal model, the nominal properties of certain key parameters in that model are modified using an evolutionary search algorithm such that the model's simulated output exactly matches the actual instrument ground calibration data. Results indicate that varying the layer thickness, effective thermal conductivity, and effective thermal capacitance of the thermistor, kapton, and epoxy layers in the thermistor bolometer within reasonable uncertainty bounds provides an excellent match with the recorded instrument data.
Trenberth, Kevin E.; Fasullo, John T.Trenberth, K. E., J. T. Fasullo, 2009: Changes in the flow of energy through the Earth's climate system. Meteorologische Zeitschrift, 18(4), 369-377. doi: 10.1127/0941-2948/2009/0388. A review is given of the trends, variability, mean and annual cycle of energy flowing through the climate system, and its storage, release, and transport in the atmosphere, ocean, and land surface as estimated with recent observations, with some new updates using the latest datasets. The current imbalance in radiation at the top-of-atmosphere owing to human-induced increases in greenhouse gases means that the atmosphere, land and ocean are warming up, and ice is melting, leading to a rise in sea level. A discussion is given of our ability to track these changes with current observations and analyses. Current global analyses of the atmosphere and the ocean contain spurious variability on decadal time scales that arises from inadequacies and changes in the observing system. A holistic integrated approach that brings all information to bear can provide constraints on what is happening and where the main weaknesses are in the observing system. Results for ocean heat content are discussed in the light of recent corrections to ocean soundings and new ocean observations, and in the context of the thermosteric contributions to sea level rise. German Diese Studie gibt, basierend auf den neuesten, verfügbaren Beobachtungsdaten, einen Überblick über Trends, Variabilitäat, Mittelwert und Jahresgang des Energieflusses durch das Klimasystem sowie über seine Speicherung, Freisetzung und seinen Transport in der Atmosphäre, im Ozean und auf Landoberfächen. Das momentane, durch den anthropogenen Treibhausgasanstieg verursachte Strahlungsungleichgewicht bewirkt, dass die Atmosphäre, die Landoberflächen und der Ozean sich erwärmen und das Schmelzen des Eises zu einem Anstieg des Meeresspiegels führt. Unsere augenblickliche Fähigkeit, diese Veränderungen mit Beobachtungen und Analysen zu verfolgen, wird diskutiert. Aktuelle, globale Analysen der Atmosphäre und des Ozeans enthalten teilweise eine unechte Variabilität auf der dekadalen Zeitskala, die von Unzulänglichkeiten und Veränderungen im Beobachtungssystem herrührt. Ein ganzheitlicher, integrierter Ansatz, der alle verfügbaren Informationen berücksichtigt, kann Randbedingungen liefern, die zeigen, wo die Schwächen des Beobachtungssystems liegen. Ergebnisse für den Wärmeinhalt des Ozeans werden im Lichte kürzlich publizierter Korrekturen von früheren Ozeansondierungen und neuer ozeanischer Messungen sowie vor dem Hintergrund des thermosterischen Beitrags zum Anstieg des Meeresspiegels diskutiert.
Trenberth, Kevin E.; Fasullo, John T.Trenberth, K. E., J. T. Fasullo, 2009: Global warming due to increasing absorbed solar radiation. Geophysical Research Letters, 36(7), L07706. doi: 10.1029/2009GL037527. Global climate models used in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) are examined for the top-of-atmosphere radiation changes as carbon dioxide and other greenhouse gases build up from 1950 to 2100. There is an increase in net radiation absorbed, but not in ways commonly assumed. While there is a large increase in the greenhouse effect from increasing greenhouse gases and water vapor (as a feedback), this is offset to a large degree by a decreasing greenhouse effect from reducing cloud cover and increasing radiative emissions from higher temperatures. Instead the main warming from an energy budget standpoint comes from increases in absorbed solar radiation that stem directly from the decreasing cloud amounts. These findings underscore the need to ascertain the credibility of the model changes, especially insofar as changes in clouds are concerned. 1610 Atmosphere; climate change; 3359 Radiative processes; 3310 Clouds and cloud feedbacks; climate models; global warming; 1626 Global climate models
Trenberth, Kevin E.; Fasullo, John T.; Kiehl, JeffreyTrenberth, K. E., J. T. Fasullo, J. Kiehl, 2009: Earth's Global Energy Budget. Bull. Amer. Meteor. Soc., 90(3), 311-323. doi: 10.1175/2008BAMS2634.1. Abstract An update is provided on the Earth's global annual mean energy budget in the light of new observations and analyses. In 1997, Kiehl and Trenberth provided a review of past estimates and performed a number of radiative computations to better establish the role of clouds and various greenhouse gases in the overall radiative energy flows, with top-of-atmosphere (TOA) values constrained by Earth Radiation Budget Experiment values from 1985 to 1989, when the TOA values were approximately in balance. The Clouds and the Earth's Radiant Energy System (CERES) measurements from March 2000 to May 2004 are used at TOA but adjusted to an estimated imbalance from the enhanced greenhouse effect of 0.9 W m−2. Revised estimates of surface turbulent fluxes are made based on various sources. The partitioning of solar radiation in the atmosphere is based in part on the International Satellite Cloud Climatology Project (ISCCP) FD computations that utilize the global ISCCP cloud data every 3 h, and also accounts for increased atmospheric absorption by water vapor and aerosols. Surface upward longwave radiation is adjusted to account for spatial and temporal variability. A lack of closure in the energy balance at the surface is accommodated by making modest changes to surface fluxes, with the downward longwave radiation as the main residual to ensure a balance. Values are also presented for the land and ocean domains that include a net transport of energy from ocean to land of 2.2 petawatts (PW) of which 3.2 PW is from moisture (latent energy) transport, while net dry static energy transport is from land to ocean. Evaluations of atmospheric re-analyses reveal substantial biases.
Várnai, Tamás; Marshak, AlexanderVárnai, T., A. Marshak, 2009: MODIS observations of enhanced clear sky reflectance near clouds. Geophysical Research Letters, 36(6), L06807. doi: 10.1029/2008GL037089. Several recent studies have found that the brightness of clear sky systematically increases near clouds. Understanding this increase is important both for a correct interpretation of observations and for improving our knowledge of aerosol-cloud interactions. However, while the studies suggested several processes to explain the increase, the significance of each process is yet to be determined. This study examines one of the suggested processes—three-dimensional (3-D) radiative interactions between clouds and their surroundings—by analyzing a large dataset of MODIS (Moderate Resolution Imaging Spectroradiometer) observations over the Northeast Atlantic Ocean. The results indicate that 3-D effects are responsible for a large portion of the observed increase, which extends to about 15 km away from clouds and is stronger (i) at shorter wavelengths (ii) near optically thicker clouds and (iii) near illuminated cloud sides. This implies that it is important to account for 3-D radiative effects in the interpretation of solar reflectance measurements over clear regions in the vicinity of clouds. cloud; 3311 Clouds and aerosols; 3359 Radiative processes; Satellite; three-dimensional
Viollier, Michel; Standfuss, Carsten; Chomette, Olivier; Quesney, ArnaudViollier, M., C. Standfuss, O. Chomette, A. Quesney, 2009: Top-of-Atmosphere Radiance-to-Flux Conversion in the SW Domain for the ScaRaB-3 Instrument on Megha-Tropiques. J. Atmos. Oceanic Technol., 26(10), 2161-2171. doi: 10.1175/2009JTECHA1264.1. Abstract The earth radiation budget (ERB) is the difference between the solar absorbed flux and the terrestrial emitted flux. These fluxes are calculated from satellite measurements of outgoing shortwave (SW) and longwave (LW) radiances using empirical or theoretical models of the radiation anisotropy, which are called angular distribution models (ADMs). Owing to multidirectional measurement analyses and synergy with multispectral information at subpixel scale, the ADM developed for the NASA Clouds and the Earth’s Radiant Energy System (CERES) mission is presently the best knowledge and has to be taken into account for future ERB missions, such as the Indian–French Megha-Tropiques mission to be launched in 2010. This mission will carry an ERB instrument called the Scanner for Radiation Budget (ScaRaB). To prepare the algorithms for the ScaRaB ADM retrievals, the artificial neural network (ANN) method described by the CERES team has been adopted and improved by replacing the broadband (BB) radiances by narrowband (NB) radiances from the auxiliary channels of ScaRaB as input variables of the ANN. This article is restricted to the SW domain, the most critical case, and shows that the flux error is reduced by 60% compared to the former ERB Experiment–like model. The rms differences with the CERES fluxes are around 8.4 W m−2. ScaRaB/Megha-Tropiques measurements have a 4 times lower spatial resolution than those of the CERES/Tropical Rainfall Measuring Mission (TRMM). The impact of this spatial degradation has also been explored. There is a small systematic bias of about 1.5 W m−2 (or an absolute albedo error of 0.0015) and the rms differences are less than 3 W m−2; this is not significant compared to the overall error budget. For the radiance-to-flux conversion in the SW domain, the BB and NB ANN methods will be implemented in the ScaRaB/Megha-Tropiques data processing in order to provide SW flux estimates with an accuracy that is as consistent as possible with CERES results. Remote sensing; infrared radiation; Radiation budgets; Fluxes; longwave radiation; Shortwave radiation; Neural networks
Waliser, Duane E.; Li, Jui-Lin F.; Woods, Christopher P.; Austin, Richard T.; Bacmeister, Julio; Chern, Jiundar; Del Genio, Anthony; Jiang, Jonathan H.; Kuang, Zhiming; Meng, Huan; Minnis, Patrick; Platnick, Steve; Rossow, William B.; Stephens, Graeme L.; Sun-Mack, Szedung; Tao, Wei-Kuo; Tompkins, Adrian M.; Vane, Deborah G.; Walker, Christopher; Wu, DongWaliser, D. E., J. F. Li, C. P. Woods, R. T. Austin, J. Bacmeister, J. Chern, A. Del Genio, J. H. Jiang, Z. Kuang, H. Meng, P. Minnis, S. Platnick, W. B. Rossow, G. L. Stephens, S. Sun-Mack, W. Tao, A. M. Tompkins, D. G. Vane, C. Walker, D. Wu, 2009: Cloud ice: A climate model challenge with signs and expectations of progress. Journal of Geophysical Research: Atmospheres, 114(D8), D00A21. doi: 10.1029/2008JD010015. Present-day shortcomings in the representation of upper tropospheric ice clouds in general circulation models (GCMs) lead to errors in weather and climate forecasts as well as account for a source of uncertainty in climate change projections. An ongoing challenge in rectifying these shortcomings has been the availability of adequate, high-quality, global observations targeting ice clouds and related precipitating hydrometeors. In addition, the inadequacy of the modeled physics and the often disjointed nature between model representation and the characteristics of the retrieved/observed values have hampered GCM development and validation efforts from making effective use of the measurements that have been available. Thus, even though parameterizations in GCMs accounting for cloud ice processes have, in some cases, become more sophisticated in recent years, this development has largely occurred independently of the global-scale measurements. With the relatively recent addition of satellite-derived products from Aura/Microwave Limb Sounder (MLS) and CloudSat, there are now considerably more resources with new and unique capabilities to evaluate GCMs. In this article, we illustrate the shortcomings evident in model representations of cloud ice through a comparison of the simulations assessed in the Intergovernmental Panel on Climate Change Fourth Assessment Report, briefly discuss the range of global observational resources that are available, and describe the essential components of the model parameterizations that characterize their “cloud” ice and related fields. Using this information as background, we (1) discuss some of the main considerations and cautions that must be taken into account in making model-data comparisons related to cloud ice, (2) illustrate present progress and uncertainties in applying satellite cloud ice (namely from MLS and CloudSat) to model diagnosis, (3) show some indications of model improvements, and finally (4) discuss a number of remaining questions and suggestions for pathways forward. 1640 Remote sensing; 3310 Clouds and cloud feedbacks; CloudSat; 1626 Global climate models; 0550 Model verification and validation
Wang, H.; Pinker, R. T.Wang, H., R. T. Pinker, 2009: Shortwave radiative fluxes from MODIS: Model development and implementation. Journal of Geophysical Research: Atmospheres, 114(D20), D20201. doi: 10.1029/2008JD010442. A forward inference scheme driven with satellite-based information is developed to derive top of the atmosphere, surface, and atmospheric spectral shortwave radiative fluxes at global scale. The model takes into account all major atmospheric constituents, the characteristics of water and ice clouds, and the variation of cloud particle effective radius. The multilayered structure accounts for surface elevation effects and for the vertical distribution of the radiative fluxes. Spectral fluxes such as photosynthetically active radiation and near-infrared radiation can also be estimated. The model is implemented with products from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor both on Terra and Aqua at 1° spatial resolution for a 3-year period (2003–2005) and at global scale. The derived surface fluxes are evaluated against the globally distributed Baseline Surface Radiation Network (BSRN) measurements and compared with products from independent sources. It is demonstrated that the twice a day MODIS-based estimates of daily radiative fluxes adjusted for the diurnal cycle and the ground observations have a correlation coefficient greater than 0.96, a relative root-mean-square error less than 18%, and a relative bias between 0 and 6% for BSRN sites located in the Antarctic, the Atlantic (islands), North America, Europe, and other continental sites. 0360 Radiation: transmission and scattering; 0321 Cloud/radiation interaction; MODIS; radiation; 0480 Remote sensing
Wang, Wenhui; Liang, Shunlin; Augustine, J.A.Wang, W., S. Liang, J. Augustine, 2009: Estimating High Spatial Resolution Clear-Sky Land Surface Upwelling Longwave Radiation From MODIS Data. IEEE Transactions on Geoscience and Remote Sensing, 47(5), 1559-1570. doi: 10.1109/TGRS.2008.2005206. Surface upwelling longwave radiation (LWUP) is an important component in the surface radiation budget. Existing satellite-derived LWUP data sets are too coarse to support high-resolution numerical models, and their accuracy needs to be improved. In this paper, we evaluate three methods for estimating clear-sky land LWUP from the Moderate Resolution Imaging Spectroradiometer (MODIS) data at 1-km spatial resolution. The three methods are as follows: (1) the temperature-emissivity method; (2) the linear model method; and (3) the artificial neural network (ANN) model method. Methods 2 and 3 are new methods based on extensive radiative transfer simulations and statistical analysis. We explicitly considered surface emissivity effects by incorporating the University of California Santa Barbara emissivity library in the radiative transfer simulation. The three methods were evaluated using ground-measured LWUP from six SURFRAD sites. Although methods 2 and 3 were developed using MODIS Terra atmospheric profiles, they were applied to both Terra and Aqua data because the designs of the two sensors are similar. The root mean squared errors (rmses) of the ANN model method are smaller than that of the other two methods at all sites. The averaged rmses of the ANN model method are 15.89 W/m2 (Terra) and 14.57 W/m>2 (Aqua); the averaged biases are -8.67 W/m2 (Terra) and -7.21 W/m2 (Aqua). The biases and rmses for Aqua are 1.3 W/m2 smaller than that of Terra. The biases and rmses of the ANN model method are 5 W/m2 smaller than that of the temperature-emissivity method and 2.5 W/m2 smaller than that of the linear model method. geophysical techniques; Remote sensing; atmospheric radiation; radiative transfer; geophysics computing; neural nets; Moderate Resolution Imaging Spectroradiometer; statistical analysis; surface radiation budget (SRB); Artificial neural network; surface radiation budget; Moderate Resolution Imaging Spectroradiometer (MODIS); satellite applications; Neural networks; sunlight; mean square error methods; ANN model method; Aqua data; atmospheric profile; clear sky observation; high-resolution numerical model; land surface upwelling longwave radiation; linear model method; LWUP; MODIS data; radiative transfer simulation; rmses; root mean squared error; Santa Barbara emissivity library; Surface Radiation; surface upwelling longwave radiation (LWUP); SURFRAD; temperature-emissivity method; Terra data; University of California
Wild, MartinWild, M., 2009: Global dimming and brightening: A review. Journal of Geophysical Research: Atmospheres, 114(D10), D00D16. doi: 10.1029/2008JD011470. There is increasing evidence that the amount of solar radiation incident at the Earth's surface is not stable over the years but undergoes significant decadal variations. Here I review the evidence for these changes, their magnitude, their possible causes, their representation in climate models, and their potential implications for climate change. The various studies analyzing long-term records of surface radiation measurements suggest a widespread decrease in surface solar radiation between the 1950s and 1980s (“global dimming”), with a partial recovery more recently at many locations (“brightening”). There are also some indications for an “early brightening” in the first part of the 20th century. These variations are in line with independent long-term observations of sunshine duration, diurnal temperature range, pan evaporation, and, more recently, satellite-derived estimates, which add credibility to the existence of these changes and their larger-scale significance. Current climate models, in general, tend to simulate these decadal variations to a much lesser degree. The origins of these variations are internal to the Earth's atmosphere and not externally forced by the Sun. Variations are not only found under cloudy but also under cloud-free atmospheres, indicative of an anthropogenic contribution through changes in aerosol emissions governed by economic developments and air pollution regulations. The relative importance of aerosols, clouds, and aerosol-cloud interactions may differ depending on region and pollution level. Highlighted are further potential implications of dimming and brightening for climate change, which may affect global warming, the components and intensity of the hydrological cycle, the carbon cycle, and the cryosphere among other climate elements. 0360 Radiation: transmission and scattering; 1610 Atmosphere; 0321 Cloud/radiation interaction; 1616 Climate variability; 1630 Impacts of global change; surface solar radiation; global dimming/brightening; review
Wong, T.; Stackhouse Jr, PW; Kratz, D. P.; Wilber, A. C.Wong, T., P. Stackhouse Jr, D. P. Kratz, A. C. Wilber, 2009: Earth Radiation Budget at top-of-atmosphere [in "State of the Climate in 2008"]. Bull. Amer. Meteor. Soc.. doi: 10.1175/BAMS-90-8-StateoftheClimate.
Xia, Xiangao; Zong, XuemeiXia, X., X. Zong, 2009: Shortwave versus longwave direct radiative forcing by Taklimakan dust aerosols. Geophysical Research Letters, 36(7), L07803. doi: 10.1029/2009GL037237. Six Mays from 2001 to 2006 of aerosol optical depth from the Multiangle Imaging SpectroRadiometer and short- and longwave flux from the Clouds and Earth's Radiant Energy Budget Scanner are combined to estimate radiative forcing of dust aerosols in the Taklimakan Desert (75°E–95°E, 36°N–42°N, elevation < 1600 m). The cloud-free dust shortwave versus longwave forcing per aerosol optical depth at about 05:00 UTC are −48.1 and 28.4 W m−2, respectively. Dust longwave warming offsets 58% of dust shortwave cooling and the overall dust radiative effect is to cool the Earth system. Annual shortwave and longwave forcing efficiencies vary from 26.7 to 63.8 and 18.3 to 39.3 W m−2, respectively, due to changes in surface properties. Radiative transfer model simulations also suggest Earth's system is cooled in the shortwave but warmed in the longwave by Taklimakan dust aerosols. 0305 Aerosols and particles; 0345 Pollution: urban and regional; aerosol; 4801 Aerosols
Xu, K. M.; Su, W. Y.; Eitzen, Z.Xu, K. M., W. Y. Su, Z. Eitzen, 2009: Use of CERES cloud and radiation data for model evaluation and cloud feedback studies. Proceedings of the 5th Wseas International Conference on Remote, 55-61.
Xu, Kuan-ManXu, K., 2009: Evaluation of Cloud Physical Properties of ECMWF Analysis and Re-Analysis (ERA) against CERES Tropical Deep Convective Cloud Object Observations. Mon. Wea. Rev., 137(1), 207-223. doi: 10.1175/2008MWR2633.1. Abstract This study presents an approach that converts the vertical profiles of grid-averaged cloud properties from large-scale models to probability density functions (pdfs) of subgrid-cell cloud physical properties measured at satellite footprints. Cloud physical and radiative properties, rather than just cloud and precipitation occurrences, of assimilated cloud systems by the European Centre for Medium-Range Weather Forecasts (ECMWF) operational analysis (EOA) and 40-yr ECMWF Re-Analysis (ERA-40) are validated against those obtained from Earth Observing System satellite cloud object data for the January–August 1998 and March 2000 periods. These properties include the ice water path (IWP), cloud-top height and temperature, cloud optical depth, and solar and infrared radiative fluxes. Each cloud object, a contiguous region with similar cloud physical properties, is temporally and spatially matched with EOA and ERA-40 data. Results indicate that most pdfs of EOA and ERA-40 cloud physical and radiative properties agree with those of satellite observations of the tropical deep convective cloud object type for the January–August 1998 period. There are, however, significant discrepancies in selected ranges of the cloud property pdfs such as the upper range of EOA cloud-top height. A major discrepancy is that the dependence of the pdfs on the cloud object size for both EOA and ERA-40 is not as strong as in the observations. Modifications to the cloud parameterization in ECMWF that occurred in October 1999 eliminate the clouds near the tropopause but shift power of the pdf to lower cloud-top heights and greatly reduce the ranges of IWP and cloud optical depth pdfs. These features persist in ERA-40 due to the use of the same cloud parameterizations. The less sophisticated data assimilation technique and the lack of snow water content information in ERA-40, not the larger horizontal grid spacing, are also responsible for the disagreements with observed pdfs of cloud physical properties, although the detection rates of cloud object occurrence are improved for small-size categories. A possible improvement to the convective parameterization is to introduce a stronger dependence of updraft penetration heights on grid-cell dynamics. clouds; satellite observations; convective clouds; Precipitation; Optical properties; Data assimilation
Yang, Eun-Su; Gupta, Pawan; Christopher, Sundar A.Yang, E., P. Gupta, S. A. Christopher, 2009: Net radiative effect of dust aerosols from satellite measurements over Sahara. Geophysical Research Letters, 36(18), L18812. doi: 10.1029/2009GL039801. The clear-sky aerosol top of atmosphere shortwave (SW) and longwave (LW) radiative effects over the Saharan desert (15–30°N, 10°W–30°E) are investigated based entirely on the satellite observations of aerosol optical thickness (AOT), surface albedo, surface temperature, surface emissivity, atmospheric water vapor content, and SW/LW fluxes. The Ozone Monitoring Instrument (OMI) on Aura and the Multi-angle SpectroRadiometer (MISR) on Terra satellite are used to estimate AOT at 558 nm (EAOT) for June to September, 2005–2006 when the predominant aerosol type is dust. We then use these EAOT values in conjunction with broadband measurements from the Clouds and the Earth's Radiant Energy System (CERES) to calculate the top-of-atmosphere SW and LW flux radiative effect due to these aerosols. The difference in SW flux between desert surface and dust aerosols is found to be negligible due to the high surface reflectance over the Sahara desert. The instantaneous area-averaged LW radiative effect is calculated as +11.4 Wm−2 with radiative efficiencies ranging from +11 to +26 Wm−2/AOT. The results indicate that net radiative effect of dust over the Sahara desert is dominated by the longwave effect in contrast to oceans where the shortwave effect dominates. Remote sensing; 0305 Aerosols and particles; aerosols; 3359 Radiative processes; 4801 Aerosols; radiative processes
Yang, Shi-King; Long, C. S.; Miller, A. J.; He, Xuming; Yang, Yunwen; Wuebbles, D. J.; Tiao, GeorgeYang, S., C. S. Long, A. J. Miller, X. He, Y. Yang, D. J. Wuebbles, G. Tiao, 2009: Modulation of natural variability on a trend analysis of the updated cohesive SBUV(/2) total ozone. International Journal of Remote Sensing, 30(15-16), 3975-3986. doi: 10.1080/01431160902821924. Utilizing the series of Solar Backscattered Ultraviolet (SBUV) instruments, total ozone measurements from the NASA/Nimbus-7 and the operational NOAA polar orbiting satellites, the NOAA/Climate Prediction Center has compiled a long term ‘cohesive’ SBUV(/2) total ozone dataset. The compilations are aimed at achieving a level of quality suitable for trend analysis. The zonal dataset starts in 1979, and extends to 2007. This paper provides an update of the statistical analysis of the above dataset to examine the impact of the Montreal Protocol and its later revisions. The traditional statistical time series trend, or hockey-stick algorithm, is applied to this cohesive total ozone dataset. The algorithm allows for a change in trend in January 1996. Specifically, we examine the net slope post 1996 to see if it is both positive and statistically significant at the 95% confidence level. Our results indicate the following: (1) For 45°N the net slope after 1996, while positive, is not statistically significant at the 95% level of confidence. Thus, we cannot state that the ozone is actually increasing in this area. (2) For 45°S the net slope remains negative, but not statistically significant at the 95% level of confidence. For this region it appears that the best we can state is that the ozone may be levelling off. Our results do indicate, however, that the ozone variability in the southern hemisphere is impacted by the Antarctic oscillation much like the northern hemisphere is impacted by the Arctic oscillation, suggesting a real linkage of these terms. (3) For the integrated domain of 50°N–50°S, the averaging process diminishes greatly the standard errors of the terms. The result is that the net slope for the integrated domain is +1.24% per decade and is statistically significant at the 95% confidence level. Also, the solar coefficient is statistically significant indicating a tropical dominance of this effect.
Yorks, John E.; McGill, Matt; Rodier, Sharon; Vaughan, Mark; Hu, Yongxiang; Hlavka, DennisYorks, J. E., M. McGill, S. Rodier, M. Vaughan, Y. Hu, D. Hlavka, 2009: Radiative effects of African dust and smoke observed from Clouds and the Earth's Radiant Energy System (CERES) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) data. Journal of Geophysical Research: Atmospheres, 114(D4), D00H04. doi: 10.1029/2009JD012000. Cloud and aerosol effects have a significant impact on the atmospheric radiation budget in the tropical Atlantic because of the spatial and temporal extent of desert dust and smoke from biomass burning in the atmosphere. The influences of African dust and smoke aerosols on cloud radiative properties over the tropical Atlantic Ocean were analyzed for the month of July for 3 years (2006–2008) using colocated data collected by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Clouds and the Earth's Radiant Energy System (CERES) instruments on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and Aqua satellites. Aerosol layer height and type can be accurately determined using CALIOP data through directly measured parameters such as optical depth, volume depolarization ratio, attenuated backscatter, and color ratio. On average, clouds below 5 km had a daytime instantaneous shortwave (SW) radiative flux of 270.2 ± 16.9 W/m2 and thin cirrus clouds had a SW radiative flux of 208.0 ± 12.7 W/m2. When dust aerosols interacted with clouds below 5 km, as determined from CALIPSO, the SW radiative flux decreased to 205.4 ± 13.0 W/m2. Similarly, smoke aerosols decreased the SW radiative flux of low clouds to a value of 240.0 ± 16.6 W/m2. These decreases in SW radiative flux were likely attributed to the aerosol layer height and changes in cloud microphysics. CALIOP lidar observations, which more accurately identify aerosol layer height than passive instruments, appear essential for better understanding of cloud-aerosol interactions, a major uncertainty in predicting the climate system. 0305 Aerosols and particles; aerosols; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; 3310 Clouds and cloud feedbacks; radiation; Lidar
Bender, F. a.-M.Bender, F. a., 2008: A note on the effect of GCM tuning on climate sensitivity. Environmental Research Letters, 3(1), 014001. doi: 10.1088/1748-9326/3/1/014001. A tuning experiment is carried out with the Community Atmosphere Model version 3, where the top-of-the-atmosphere radiative balance is tuned to agree with global satellite estimates from ERBE and CERES, respectively, to investigate if the climate sensitivity of the model is dependent upon which of the datasets is used. The tuning is done through alterations of cloud parameters that affect, for instance, the model cloud water content, but the difference in cloud water content between the two model configurations is found to be negligible compared to the wide spread of the same quantity in a number of state-of-the-art GCMs. The equilibrium climate sensitivities of the two model configurations differ by ca. 0.24 K, and both lie well within the range of present estimates of climate sensitivity in different GCMs. This indicates that it is possible to tune the model to either of the two satellite datasets without drastically changing the climate sensitivity. However, the study illustrates that the climate sensitivity is a product of choices of parameter values that are not well restricted by observations, which allows for a certain degree of arbitrariness in the estimates of climate sensitivity.
Bertrand, C.; Gonzalez, L.; Ipe, A.; Clerbaux, N.; Dewitte, S.Bertrand, C., L. Gonzalez, A. Ipe, N. Clerbaux, S. Dewitte, 2008: Improvement in the GERB short wave flux estimations over snow covered surfaces. Advances in Space Research, 41(11), 1894-1905. doi: 10.1016/j.asr.2006.12.016. Because space-borne radiometers do not measure the Earth’s outgoing fluxes directly, angular distribution models (ADMs) are required to relate actual radiance measurement to flux at given solar angle, satellite-viewing geometries, surface, and atmospheric conditions. The conversion of one footprint broad-band radiance into the corresponding flux requires therefore one to first characterize each footprint in terms of surface type and cloud cover properties to properly select the adequate ADM. A snow (and sea-ice) retrieval technique based on spectral measurements from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on board Meteosat 8 is presented. It has been developed to improve the scene identification and thus the ADM selection in the near-real time processing of the Geostationary Earth Radiation Budget (GERB) data at the Royal Meteorological Institute of Belgium. The improvement in the GERB short wave flux estimations over snow covered scene types resulting from angular conversion using dedicated snow ADMs (e.g., empirical snow ADMs and/or pre-computed theoretical snow ADM) instead of empirical snow-free ADMs is discussed. Remote sensing; angular distribution model; Radiance-to-flux conversion; Short wave flux; Snow cover
Brindley, Helen E.; Russell, Jacqueline E.Brindley, H. E., J. E. Russell, 2008: Assessing the Errors in Shortwave Radiative Fluxes Inferred from the Geostationary Earth Radiation Budget (GERB) Instrument in the Presence of Dust Aerosol. J. Appl. Meteor. Climatol., 47(6), 1659-1680. doi: 10.1175/2007JAMC1723.1. Abstract The Geostationary Earth Radiation Budget (GERB) instruments flying on the Meteosat Second Generation series of satellites provide a unique tool with which to monitor the diurnal evolution of top-of-atmosphere broadband radiation fields. GERB products, which have recently been released to the scientific community, include aerosol information in addition to the observed radiances and inferred fluxes. However, no account of the anisotropic characteristics of aerosol has been incorporated in the radiance-to-flux conversion, which uses angular distribution models developed for clear or cloudy conditions. Here an attempt is made to quantify the impact of this omission in the shortwave (SW), focusing on dust-contaminated scenes. An observationally based representation of dust is used to develop a theoretical angular distribution model, which is tested through comparison with observed GERB radiances. For dusty scenes that have been processed as clear ocean, applying the dust model to convert GERB radiances to fluxes reduces the SW reflected flux by an average of approximately 12 W m−2 relative to the original GERB fluxes. This value ranges from −4 to +55 W m−2, depending on observation geometry and dust loading. For dusty scenes that the GERB processing has treated as cloudy, GERB fluxes are generally smaller than values obtained using the dust-specific model. On average, over the time period studied here, the two effects partially cancel, and the overall mean difference is 2.5 W m−2. However, it is shown that this cancellation is highly sensitive to the location and time period under consideration. Remote sensing; aerosols; Radiative fluxes; satellite observations; Dust or dust storms; Shortwave radiation
Chen, Yonghang; Bai, Hongtao; Huang, Jianping; Zhang, Hua; Ge, Jinming; Guan, Xiaodan; Mao, XiaoqinChen, Y., H. Bai, J. Huang, H. Zhang, J. Ge, X. Guan, X. Mao, 2008: Seasonal variability of cloud optical depth over northwestern China derived from CERES/MODIS satellite measurements. Chinese Optics Letters, 6(6), 454-457. The seasonal variability of cloud optical depth over northwestern China derived from Clouds and the Earth's Radiant Energy System (CERES) Single Scanner Footprint (SSF) Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) Edition 1B data from July 2002 to June 2004 is presented. The regions of interest are those with Asia monsoon influence, the Tianshan and Qilian Mountains, and the Taklimakan Desert. The results show that the instantaneous measurements presented here are much higher than the previous results derived from International Satellite Cloud Climatology Project (ISCCP) D2 monthly mean data. Generally the measurements of cloud optical depth are the highest in summer and the lowest in winter, however, Taklimakan Desert has the lowest measurements in autumn. The regional variation is quite significant over northwestern China. Meteorology; Atmospheric scattering; Remote sensing and sensors; Instrumentation, measurement, and metrology; Atmospheric and oceanic optics
Christopher, S.A.; Jones, T.A.Christopher, S., T. Jones, 2008: Dust Radiative Effects Over Global Oceans. IEEE Geoscience and Remote Sensing Letters, 5(1), 74-77. doi: 10.1109/LGRS.2007.909938. Using one year of moderate resolution imaging spectroradiometer (MODIS) and clouds and the Earth's radiant energy system (CERES) data, we provide a satellite-based assessment of top-of-atmosphere (TOA) cloud-free shortwave and longwave dust radiative effects over global oceans from the Terra satellite. Over global cloud-free oceans, the dust net radiative effect is -0.7 plusmn0.2 W middotm-2, and the TOA dust shortwave radiative effect (SWRE) dominates the longwave radiative effect (LWRE). Globally, the annual mean dust contribution to the total MODIS level 2 aerosol optical thickness (AOT, at 550 nm) is about 30% with a dust SWRE of -0.7 plusmn0.2 W middotm-2 and LWRE of 0.03 plusmn0.02 W middotm-2. Averaged over all seasons, the cloud-free diurnal mean dust radiative efficiency is -33 plusmn5 W middotm-2 middottau-1, and there is a remarkable linear relationship between the CERES SWRE and the MODIS AOT. This is the first satellite-based assessment of dust net radiative effect over the global oceans and will serve as a useful constraint for numerical modeling analysis. clouds; Remote sensing; Satellites; atmospheric radiation; aerosols; Oceans; aerosol; Solar radiation; MODIS; uncertainty; Terra; aerosol optical thickness; Carbon dioxide; CERES data; Clouds and the Earth's Radiant Energy System (CERES); direct radiative effect (DRE); dust; dust radiative effects; global oceans; Moderate Resolution Imaging Spectroradiometer (MODIS); moderate resolution imaging spectroradiometer MODIS data; Numerical models; Production; Terra satellite
Christopher, S.A.; Jones, T.A.Christopher, S., T. Jones, 2008: Sample Bias Estimation for Cloud-Free Aerosol Effects Over Global Oceans. IEEE Transactions on Geoscience and Remote Sensing, 46(6), 1728-1732. doi: 10.1109/TGRS.2008.916218. Satellite-based methods for estimating the top-of-atmosphere shortwave direct radiative effect (SWRE) either use the spatial distribution of aerosol optical thickness (AOT) coupled with radiative transfer calculations or combine the AOT with broadband radiative energy data sets such as the Clouds and the Earth's Radiant Energy System (CERES). The first approach typically utilizes the AOT at a spatial resolution of from the Moderate Resolution Imaging Spectroradiometer (MODIS), and the second method relies on the same AOT, but it is convolved within the CERES footprint and has spatial resolutions that are greater than . Therefore, the SWRE may vary as a result of this difference in spatial resolution that we call sample bias. We correct for this sample bias using the AOT reported at the MODIS and the CERES product levels coupled with the radiative efficiency (SWRE per-unit optical depth) for 13 regions over the ocean as a function of season between December 2003 and November 2004 and demonstrate that the sample biases are seasonally and spatially dependent. Overall, nearly 75% of the pixels over the global oceans require a sample bias adjustment of some form. However, the adjustment is large , which is less than 7% of the time, primarily during the spring and summer months, in association with large dust aerosol concentrations with large optical depth gradients. If sample biases are not accounted for, they will globally reduce the SWRE by an average of 30% (4.1 versus ), although regionally, the adjustment could be larger (). We argue that these bias corrections are robust and simpler to use when compared with methods that employ narrow- to broadband relationships. atmospheric radiation; aerosols; atmospheric techniques; radiative transfer; aerosol optical thickness; global oceans; AD 2003 12 to 2004 11; broadband radiative energy data sets; cloud-free aerosol effects; Clouds and the Earth's Radiant Energy System CERES; radiative transfer calculations; sample bias estimation; top-of-atmosphere shortwave direct radiative effect
Christopher, Sundar A.; Jones, Thomas A.Christopher, S. A., T. A. Jones, 2008: Short-wave aerosol radiative efficiency over the global oceans derived from satellite data. Tellus B, 60(4), 636-640. doi: 10.1111/j.1600-0889.2008.00353.x. Using 5 yr (December 2000–November 2005) of satellite data from the clouds and the earths radiant energy system (CERES) and moderate resolution imaging spectroradiometer (MODIS), we examine the instantaneous short-wave radiative efficiency (Eτ) of aerosols during the morning Terra satellite overpass time over the global oceans (60°N–60°S). We calculate Eτ using two commonly used methods. The first method uses the MODIS aerosol optical thickness (AOT) at 0.55 μm with radiative transfer calculations, whereas the second method utilizes the same AOT values along with a new generation of aerosol angular distribution models to convert the CERES-measured broad-band radiances to fluxes. Over the 5 yr, the global mean instantaneous Eτ between the methods is remarkably consistent and within 5 W m−2τ−1 with a mean value of –70 W m−2τ−1. The largest differences between the methods occur in high-latitude regions, primarily in the Southern Hemisphere, where AOT is low. In dust dominated regions, there is an excellent agreement between the methods with differences of
Clerbaux, N.; Dewitte, S.; Bertrand, C.; Caprion, D.; De Paepe, B.; Gonzalez, L.; Ipe, A.; Russell, J. E.Clerbaux, N., S. Dewitte, C. Bertrand, D. Caprion, B. De Paepe, L. Gonzalez, A. Ipe, J. E. Russell, 2008: Unfiltering of the Geostationary Earth Radiation Budget (GERB) data. Part II: Longwave radiation. J. Atmos. Oceanic Technol., 25(7), 1106-1117. doi: 10.1175/2008jtecha1002.1. The method used to estimate the unfiltered longwave broadband radiance from the filtered radiances measured by the Geostationary Earth Radiation Budget (GERB) instrument is presented. This unfiltering method is used to generate the first released edition of the GERB-2 dataset. This method involves a set of regressions between the unfiltering factor (i.e., the ratio of the unfiltered and filtered broadband radiances) and the narrowband observations of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) instrument. The regressions are theoretically derived from a large database of simulated spectral radiance curves obtained by radiative transfer computations. The generation of this database is fully described. Different sources of error that may affect the GERB unfiltering have been identified and the associated error magnitudes are assessed on the database. For most of the earth-atmosphere conditions, the error introduced during the unfiltering processes is well under 0.5% (RMS error of about 0.1%). For more confidence, the unfiltered radiances of GERB-2 are validated by cross comparison with collocated and coangular Clouds and the Earth's Radiant Energy System (CERES) observations. The agreement between the unfiltered radiances is within the science goals (1% accuracy for GERB and 0.5% for CERES) for the Flight Model 2 (FM2). For the CERES Flight Model 3 (FM3) instrument, an overall difference of 1.8% is observed. The intercomparisons indicate some scene-type dependency, which is due to the unfiltering for the cloudy scenes. This should be corrected for subsequent editions of the database.
Clerbaux, N.; Dewitte, S.; Bertrand, C.; Caprion, D.; De Paepe, B.; Gonzalez, L.; Ipe, A.; Russell, J. E.; Brindley, H.Clerbaux, N., S. Dewitte, C. Bertrand, D. Caprion, B. De Paepe, L. Gonzalez, A. Ipe, J. E. Russell, H. Brindley, 2008: Unfiltering of the Geostationary Earth Radiation Budget (GERB) Data. Part I: Shortwave Radiation. J. Atmos. Oceanic Technol., 25(7), 1087-1105. doi: 10.1175/2007JTECHA1001.1. Abstract The method used to estimate the unfiltered shortwave broadband radiance from the filtered radiances measured by the Geostationary Earth Radiation Budget (GERB) instrument is presented. This unfiltering method is used to generate the first released edition of the GERB-2 dataset. The method involves a set of regressions between the unfiltering factor (i.e., the ratio of the unfiltered and filtered broadband radiances) and the narrowband observations of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) instrument. The regressions are theoretically derived from a large database of simulated spectral radiance curves obtained by radiative transfer computations. The generation of the database is fully described. Different sources of error that may affect the GERB unfiltering have been identified and the associated error magnitudes are assessed on this database. For most of the earth–atmosphere conditions, the error introduced during the unfiltering process is below 1%. In some conditions (e.g., low sun elevation above the horizon) the error can present a higher relative value, but the absolute error value remains well under the accuracy goal of 1% of the full instrument scale (2.4 W m−2 sr−1). To increase the confidence level, the edition 1 unfiltered radiances of GERB-2 are validated by cross comparison with collocated and coangular Clouds and the Earth’s Radiant Energy System (CERES) observations for different scene types. In addition to an overall offset between the two instruments, the intercomparisons indicate a scene-type dependency up to 4% in unfiltered radiance. Further studies are required to confirm the cause, but an insufficiently accurate characterization of the shortwave spectral response of the GERB instrument in the visible part of the spectrum is one area under further investigation. Radiation budgets; satellite observations; Radiances; instrumentation
De Paepe, Bart; Ignatov, Alexander; Dewitte, Steven; Ipe, AlessandroDe Paepe, B., A. Ignatov, S. Dewitte, A. Ipe, 2008: Aerosol retrieval over ocean from SEVIRI for the use in GERB Earth's radiation budget analyses. Remote Sensing of Environment, 112(5), 2455-2468. doi: 10.1016/j.rse.2007.11.005. To study the effect of aerosols on the Earth's radiation budget (ERB), the Royal Meteorological Institute of Belgium (RMIB) has integrated spectral aerosol optical depth (AOD) measurements over the ocean from the Spinning Enhanced Visible and Infra-Red Scanner (SEVIRI) into its Geostationary Earth's Radiation Budget, or GERB, processing system referred to as the RGP. Aerosols affect the ERB both directly (when radiation interacts with an aerosol particle) and indirectly (when aerosols act as cloud condensation nuclei). Quantifying the indirect effect is challenging as it requires accurate aerosol retrievals in the close proximity to clouds, where aerosol retrievals may be biased due to leakages from the cloud mask (CM). The initial focus of the RGP project was on the direct effect using confidently clear scenes. A single channel CM exploiting the SEVIRI temporal sampling was developed at the RMIB for the use in the RGP project. In this study, that single channel mask was evaluated against two multi-channel CMs, one from the Meteorological Products Extraction Facility (MPEF) at the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT), and the other from the Satellite Application Facility for Supporting NoWCasting and Very Short Range Forecasting (SAFNWC), respectively. The NOAA/NESDIS Advanced Very High Resolution Radiometer (AVHRR) single channel aerosol algorithm was adjusted to SEVIRI spectral bands and consistently applied to the pixels identified as cloud-free. The aerosol products corresponding to the three CMs were compared, and the RMIB CM was found to be sufficiently accurate and conservative, for RGP applications. Comparisons with independent AODs derived from the MODerate resolution Imaging Spectroradiometer (MODIS) onboard Terra and Aqua satellites show that the RMIB CM-based SEVIRI aerosol product compares well with its MODIS counterpart. However, a small fraction of cloud-contaminated pixels may still remain in the SEVIRI AOD imagery, chiefly within one to two SEVIRI pixels of the cloud boundary, thus limiting its use for indirect forcing studies. Also, the RMIB CM may screen high AOD non-dust aerosol events (e.g., smoke from biomass burning) as cloud. The potential of the new SEVIRI aerosol product is illustrated by generating 9 km-resolution seasonal maps of AODs and ´ÅǺngström Exponents, and by using the GERB radiative flux measurements for a preliminary quick assessment of the direct aerosol forcing. Aerosol optical depth; Cloud screening; direct radiative effect; SEVIRI
Dessler, A. E.; Yang, P.; Lee, J.; Solbrig, J.; Zhang, Z.; Minschwaner, K.Dessler, A. E., P. Yang, J. Lee, J. Solbrig, Z. Zhang, K. Minschwaner, 2008: An analysis of the dependence of clear-sky top-of-atmosphere outgoing longwave radiation on atmospheric temperature and water vapor. Journal of Geophysical Research: Atmospheres, 113(D17), D17102. doi: 10.1029/2008JD010137. We have analyzed observations of clear-sky top-of-atmosphere outgoing longwave radiation (OLR) measured by the Clouds and the Earth's Radiant Energy System (CERES). These measurements were obtained during March 2005 at night and over the ocean and cover latitudes from 70°N to 70°S. First, we compare the OLR measurements to OLR calculated from two radiative transfer models. The models use as input simultaneous and collocated measurements of atmospheric temperature and atmospheric water vapor made by the Atmospheric Infrared Sounder (AIRS). We find excellent agreement between the models' predictions of OLR and observations, well within the uncertainty of the measurements. We also analyze the sensitivity of OLR to changing surface temperature Ts, atmospheric temperature Ta, and atmospheric water vapor q. We find that OLR is most sensitive to unit changes in Ta when that change occurs in the lower troposphere. For q, the altitude distribution of sensitivity varies between the midlatitudes, subtropics, and the convective region. We also partition the observed variations in OLR into contributions from changing Ts, Ta, and q. In the midlatitudes, changes in Ts and Ta contribute approximately equally, and are partially offset by changes in q. In the subtropics, changes in Ta dominate, with a smaller contribution from changes in Ts and a relatively small offsetting contribution from q. In the tropical convective region, a rapid increase in q in the midtroposphere leads to a dramatic reduction in OLR with increasing Ts, which has been termed the “super greenhouse effect”. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 0394 Instruments and techniques; CERES; AIRS; outgoing longwave radiation
Dewitte, S.; Gonzalez, L.; Clerbaux, N.; Ipe, A.; Bertrand, C.; De Paepe, B.Dewitte, S., L. Gonzalez, N. Clerbaux, A. Ipe, C. Bertrand, B. De Paepe, 2008: The Geostationary Earth Radiation Budget Edition 1 data processing algorithms. Advances in Space Research, 41(11), 1906-1913. doi: 10.1016/j.asr.2007.07.042. The Geostationary Earth Radiation Budget (GERB) instrument is the first to measure the earth radiation budget from a geostationary orbit. This allows a full sampling of the diurnal cycle of radiation and clouds – which is important for climate studies, as well as detailed process studies, e.g. the lifecycle of clouds or particular aerosol events such as desert storms. GERB data is now for the first time released as Edition 1 data for public scientific use. In this paper we summarise the algorithms used for the Edition 1 GERB data processing and the main validation results. Based on the comparison with the independent CERES instrument, the Edition 1 GERB accuracy is 5% for the reflected solar radiances and 2% for the emitted thermal radiances. earth radiation budget; Geostationary
Dong, Xiquan; Minnis, Patrick; Xi, Baike; Sun-Mack, Sunny; Chen, YanDong, X., P. Minnis, B. Xi, S. Sun-Mack, Y. Chen, 2008: Comparison of CERES-MODIS stratus cloud properties with ground-based measurements at the DOE ARM Southern Great Plains site. Journal of Geophysical Research: Atmospheres, 113(D3), D03204. doi: 10.1029/2007JD008438. Overcast stratus cloud properties derived for the Clouds and the Earth's Radiant Energy System (CERES) project using Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) data are compared with observations taken at the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Southern Great Plains site from March 2000 through December 2004. Retrievals from ARM surface-based data were averaged over a 1-h interval centered at the time of each satellite overpass, and the CERES-MODIS cloud properties were averaged within a 30 km × 30 km box centered on the ARM SGP site. Two data sets were analyzed: all of the data (ALL), which include multilayered, single-layered, and slightly broken stratus decks and a subset, single-layered unbroken decks (SL). The CERES-MODIS effective cloud heights were determined from effective cloud temperature using a lapse rate method with the surface temperature specified as the 24-h mean surface air temperature. For SL stratus, they are, on average, within the ARM radar-lidar estimated cloud boundaries and are 0.534 ± 0.542 km and 0.108 ± 0.480 km lower than the cloud physical tops and centers, respectively, and are comparable for day and night observations. The mean differences and standard deviations are slightly larger for ALL data, but not statistically different to those of SL data. The MODIS-derived effective cloud temperatures are 2.7 ± 2.4 K less than the surface-observed SL cloud center temperatures with very high correlations (0.86–0.97). Variations in the height differences are mainly caused by uncertainties in the surface air temperatures, lapse rates, and cloud top height variability. The biases are mainly the result of the differences between effective and physical cloud top, which are governed by cloud liquid water content and viewing zenith angle, and the selected lapse rate, −7.1 K km−1. On the basis of a total of 43 samples, the means and standard deviations of the differences between the daytime Terra and surface retrievals of effective radius re, optical depth, and liquid water path for SL stratus are 0.1 ± 1.9 μm (1.2 ± 23.5%), −1.3 ± 9.5 (−3.6 ± 26.2%), and 0.6 ± 49.9 gm−2 (0.3 ± 27%), respectively, while the corresponding correlation coefficients are 0.44, 0.87, and 0.89. For Aqua, they are 0.2 ± 1.9 μm (2.5 ± 23.4%), 2.5 ± 7.8 (7.8 ± 24.3%), and 28.1 ± 52.7 gm−2 (17.2 ± 32.2%), as well as 0.35, 0.96, and 0.93 from a total of 21 cases. The results for ALL cases are comparable. Although a bias in re was expected because the satellite retrieval of effective radius only represents the top of the cloud, the surface-based radar retrievals revealed that the vertical profile of re is highly variable with smaller droplets occurring at cloud top in some cases. The larger bias in optical depth and liquid water path for Aqua is due, at least partially, to differences in the Terra and Aqua MODIS visible channel calibrations. Methods for improving the cloud top height and microphysical property retrievals are suggested. 0320 Cloud physics and chemistry; 3311 Clouds and aerosols; 3310 Clouds and cloud feedbacks; macrophysics and microphysics; stratus clouds; surface and satellite remote sensing
Dong, Xiquan; Wielicki, Bruce A.; Xi, Baike; Hu, Yongxiang; Mace, Gerald G.; Benson, Sally; Rose, Fred; Kato, Seiji; Charlock, Thomas; Minnis, PatrickDong, X., B. A. Wielicki, B. Xi, Y. Hu, G. G. Mace, S. Benson, F. Rose, S. Kato, T. Charlock, P. Minnis, 2008: Using observations of deep convective systems to constrain atmospheric column absorption of solar radiation in the optically thick limit. Journal of Geophysical Research: Atmospheres, 113(D10), D10206. doi: 10.1029/2007JD009769. Atmospheric column absorption of solar radiation (Acol) is a fundamental part of the Earth's energy cycle but is an extremely difficult quantity to measure directly. To investigate Acol, we have collocated satellite-surface observations for the optically thick Deep Convective Systems (DCS) at the Department of Energy Atmosphere Radiation Measurement (ARM) Tropical Western Pacific (TWP) and Southern Great Plains (SGP) sites during the period of March 2000–December 2004. The surface data were averaged over a 2-h interval centered at the time of the satellite overpass, and the satellite data were averaged within a 1° × 1° area centered on the ARM sites. In the DCS, cloud particle size is important for top-of-atmosphere (TOA) albedo and Acol although the surface absorption is independent of cloud particle size. In this study, we find that the Acol in the tropics is ∼0.011 more than that in the middle latitudes. This difference, however, disappears, i.e., the Acol values at both regions converge to the same value (∼0.27 of the total incoming solar radiation) in the optically thick limit (τ > 80). Comparing the observations with the NASA Langley modified Fu_Liou 2-stream radiative transfer model for optically thick cases, the difference between observed and model-calculated surface absorption, on average, is less than 0.01, but the model-calculated TOA albedo and Acol differ by 0.01 to 0.04, depending primarily on the cloud particle size observation used. The model versus observation discrepancies found are smaller than many previous studies and are just within the estimated error bounds. We did not find evidence for a large cloud absorption anomaly for the optically thick limit of extensive ice cloud layers. A more modest cloud absorption difference of 0.01 to 0.04 cannot yet be ruled out. The remaining uncertainty could be reduced with additional cases, and by reducing the current uncertainty in cloud particle size. 0321 Cloud/radiation interaction; 3359 Radiative processes; 3310 Clouds and cloud feedbacks; 3314 Convective processes; radiation budget; DCS; SW radiation
Eitzen, ZA; Xu, KM; Wong, TEitzen, Z., K. Xu, T. Wong, 2008: Statistical Analyses of Satellite Cloud Object Data from CERES. Part V: Relationships between Physical Properties of Marine Boundary Layer Clouds. JOURNAL OF CLIMATE, 21(24), 6668-6688. doi: 10.1175/2008JCLI2307.1. Relationships between physical properties are studied for three types of marine boundary layer cloud objects identified with the Clouds and the Earth's Radiant Energy System (CERES) footprint data from the Tropical Rainfall Measuring Mission satellite between 30 degrees S and 30 degrees N. Each cloud object is a contiguous region of CERES footprints that have cloud-top heights below 3 km, and cloud fractions of 99%-100% (overcast type), 40%-99% (stratocumulus type), or 10%-40% (shallow cumulus type). These cloud fractions represent the fraction of similar to 2 km x 2 km Visible/Infrared Scanner pixels that are cloudy within each similar to 10 km x 10 km footprint. The cloud objects have effective diameters that are greater than 300 km for the overcast and stratocumulus types, and greater than 150 km for the shallow cumulus type. The Spearman rank correlation coefficient is calculated between many microphysical/optical [effective radius (r(e)), cloud optical depth (tau), albedo, liquid water path, and shortwave cloud radiative forcing (SW CRF)] and macrophysical [outgoing longwave radiation (OLR), cloud fraction, cloud-top temperature, longwave cloud radiative forcing (LW CRF), and sea surface temperature (SST)] properties for each of the three cloud object types. When both physical properties are of the same category (microphysical/optical or macrophysical), the magnitude of the correlation tends to be higher than when they are from different categories. The magnitudes of the correlations also change with cloud object type, with the correlations for overcast and stratocumulus cloud objects tending to be higher than those for shallow cumulus cloud objects. Three pairs of physical properties are studied in detail, using a k-means cluster analysis: r(e) and tau, OLR and SST, and LW CRF and SW CRF. The cluster analysis of r(e) and tau reveals that for each of the cloud types, there is a cluster of cloud objects with negative slopes, a cluster with slopes near zero, and two clusters with positive slopes. The joint OLR and SST probability plots show that the OLR tends to decrease with SST in regions with boundary layer clouds for SSTs above approximately 298 K. When the cloud objects are split into "dry" and "moist" clusters based on the amount of precipitable water above 700 hPa, the associated OLRs increase with SST throughout the SST range for the dry clusters, but the OLRs are roughly constant with SST for the moist cluster. An analysis of the joint PDFs of LW CRF and SW CRF reveals that while the magnitudes of both LW and SW CRFs generally increase with cloud fraction, there is a cluster of overcast cloud objects that has low values of LW and SW CRF. These objects are generally located near the Sahara Desert, and may be contaminated with dust. Many of these overcast objects also appear in the re and tau cluster with negative slopes.
Eitzen, Zachary A.; Xu, Kuan-ManEitzen, Z. A., K. Xu, 2008: Sensitivity of a Large Ensemble of Tropical Convective Systems to Changes in the Thermodynamic and Dynamic Forcings. J. Atmos. Sci., 65(6), 1773-1794. doi: 10.1175/2007JAS2446.1. Abstract A two-dimensional cloud-resolving model (CRM) is used to perform five sets of simulations of 68 deep convective cloud objects identified with Clouds and the Earth’s Radiant Energy System (CERES) data to examine their sensitivity to changes in thermodynamic and dynamic forcings. The control set of simulations uses observed sea surface temperatures (SSTs) and is forced by advective cooling and moistening tendencies derived from a large-scale model analysis matched to the time and location of each cloud object. Cloud properties, such as albedo, effective cloud height, cloud ice and snow path, and cloud radiative forcing (CRF), are analyzed in terms of their frequency distributions rather than their mean values. Two sets of simulations, F+50% and F−50%, use advective tendencies that are 50% greater and 50% smaller than the control tendencies, respectively. The increased cooling and moistening tendencies cause more widespread convection in the F+50% set of simulations, resulting in clouds that are optically thicker and higher than those produced by the control and F−50% sets of simulations. The magnitudes of both longwave and shortwave CRF are skewed toward higher values with the increase in advective forcing. These significant changes in overall cloud properties are associated with a substantial increase in deep convective cloud fraction (from 0.13 for the F−50% simulations to 0.34 for the F+50% simulations) and changes in the properties of non–deep convective clouds, rather than with changes in the properties of deep convective clouds. Two other sets of simulations, SST+2K and SST−2K, use SSTs that are 2 K higher and 2 K lower than those observed, respectively. The updrafts in the SST+2K simulations tend to be slightly stronger than those of the control and SST−2K simulations, which may cause the SST+2K cloud tops to be higher. The changes in cloud properties, though smaller than those due to changes in the dynamic forcings, occur in both deep convective and non–deep convective cloud categories. The overall changes in some cloud properties are moderately significant when the SST is changed by 4 K. The changes in the domain-averaged shortwave and longwave CRFs are larger in the dynamic forcing sensitivity sets than in the SST sensitivity sets. The cloud feedback effects estimated from the SST−2K and SST+2K sets are comparable to prior studies. convection; tropics; Cloud resolving models; Dynamics; Thermodynamics
Fasullo, John T.; Trenberth, Kevin E.Fasullo, J. T., K. E. Trenberth, 2008: The Annual Cycle of the Energy Budget. Part I: Global Mean and Land–Ocean Exchanges. J. Climate, 21(10), 2297-2312. doi: 10.1175/2007JCLI1935.1. Abstract The mean and annual cycle of energy flowing into the climate system and its storage, release, and transport in the atmosphere, ocean, and land surface are estimated with recent observations. An emphasis is placed on establishing internally consistent quantitative estimates with discussion and assessment of uncertainty. At the top of the atmosphere (TOA), adjusted radiances from the Earth Radiation Budget Experiment (ERBE) and Clouds and the Earth’s Radiant Energy System (CERES) are used, while in the atmosphere the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis and 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) estimates are used. The net upward surface flux (FS) over ocean is derived as the residual of the TOA and atmospheric energy budgets, and is compared with direct calculations of ocean heat content (OE) and its tendency (δOE/δt) from several ocean temperature datasets. Over land, FS from a stand-alone simulation of the Community Land Model forced by observed fields is used. A depiction of the full energy budget based on ERBE fluxes from 1985 to 1989 and CERES fluxes from 2000 to 2004 is constructed that matches estimates of the global, global ocean, and global land imbalances. In addition, the annual cycle of the energy budget during both periods is examined and compared with ocean heat content changes. The near balance between the net TOA radiation (RT) and FS over ocean and thus with OE, and between RT and atmospheric total energy divergence over land, are documented both in the mean and for the annual cycle. However, there is an annual mean transport of energy by the atmosphere from ocean to land regions of 2.2 ± 0.1 PW (1 PW = 1015 W) primarily in the northern winter when the transport exceeds 5 PW. The global albedo is dominated by a semiannual cycle over the oceans, but combines with the large annual cycle in solar insolation to produce a peak in absorbed solar and net radiation in February, somewhat after the perihelion, and with the net radiation 4.3 PW higher than the annual mean, as it is enhanced by the annual cycle of outgoing longwave radiation that is dominated by land regions. In situ estimates of the annual variation of OE are found to be unrealistically large. Challenges in diagnosing the interannual variability in the energy budget and its relationship to climate change are identified in the context of the episodic and inconsistent nature of the observations. satellite observations; energy budget; Energy transport
Fasullo, John T.; Trenberth, Kevin E.Fasullo, J. T., K. E. Trenberth, 2008: The Annual Cycle of the Energy Budget. Part II: Meridional Structures and Poleward Transports. J. Climate, 21(10), 2313-2325. doi: 10.1175/2007JCLI1936.1. Abstract Meridional structure and transports of energy in the atmosphere, ocean, and land are evaluated holistically for the mean and annual cycle zonal averages over the ocean, land, and global domains, with discussion and assessment of uncertainty. At the top of the atmosphere (TOA), adjusted radiances from the Earth Radiation Budget Experiment (ERBE) and Clouds and Earth’s Radiant Energy System (CERES) are used along with estimates of energy storage and transport from two global reanalysis datasets for the atmosphere. Three ocean temperature datasets are used to assess changes in the ocean heat content (OE) and their relationship to the net upward surface energy flux over ocean (FoS), which is derived from the residual of the TOA and atmospheric energy budgets. The surface flux over land is from a stand-alone simulation of the Community Land Model forced by observed fields. In the extratropics, absorbed solar radiation (ASR) achieves a maximum in summer with peak values near the solstices. Outgoing longwave radiation (OLR) maxima also occur in summer but lag ASR by 1–2 months, consistent with temperature maxima over land. In the tropics, however, OLR relates to high cloud variations and peaks late in the dry monsoon season, while the OLR minima in summer coincide with deep convection in the monsoon trough at the height of the rainy season. Most of the difference between the TOA radiation and atmospheric energy storage tendency is made up by a large heat flux into the ocean in summer and out of the ocean in winter. In the Northern Hemisphere, the transport of energy from ocean to land regions is substantial in winter, and modest in summer. In the Southern Hemisphere extratropics, land − ocean differences play only a small role and the main energy transport by the atmosphere and ocean is poleward. There is reasonably good agreement between FoS and observed changes in OE, except for south of 40°S, where differences among several ocean datasets point to that region as the main source of errors in achieving an overall energy balance. The winter hemisphere atmospheric circulation is the dominant contributor to poleward energy transports outside of the tropics [6–7 PW (1 petawatt = 1015 W)], with summer transports being relatively weak (∼3 PW)—slightly more in the Southern Hemisphere and slightly less in the Northern Hemisphere. Ocean transports outside of the tropics are found to be small ( satellite observations; energy budget; Energy transport
Guo, G.; Coakley, J. A.Guo, G., J. A. Coakley, 2008: Satellite Estimates and Shipboard Observations of Downward Radiative Fluxes at the Ocean Surface. J. Atmos. Oceanic Technol., 25(3), 429-441. doi: 10.1175/2007JTECHA990.1. Abstract Clouds and the Earth’s Radiant Energy System (CERES) uses a suite of instruments on the Terra and Aqua satellites combined with analyzed weather data and information on surface conditions to estimate surface radiative fluxes. CERES estimates for the Terra satellite were compared with measurements of the surface radiative fluxes collected with the research vessels (RVs) Wecoma and Thomas G. Thompson radiometers for cruises off the Oregon coast undertaken during 2000–03. To assess the shipboard measurements, the radiometer observations were analyzed to identify cloud-free conditions characterized by ∼1–2 h of relatively stable radiative fluxes. Fluxes for the cloud-free conditions were compared with those calculated using profiles of temperature and humidity from analyzed meteorological fields for the times and locations of the measurements and broadband radiative transfer models. For summertime conditions along the Oregon coast, and assuming a marine aerosol having 0.55-μm optical depth of 0.05, modeled and observed values of the shortwave flux agreed to within 1%–2%. Similar comparisons for the downward cloud-free longwave flux were within 1%–3%. This agreement also held for the CERES surface radiative flux estimates with CERES cloud-free fields of view for ocean scenes within 50 km of the ship being compared with 30-min averages of the shipboard measurements centered on the times of the Terra overpass. Using the CERES observations to identify cloud-free conditions for the Wecoma revealed that in some cases the shipboard measurements of the shortwave flux varied erratically. Criteria were adopted to avoid such behavior, yielding periods in which the surface radiative fluxes were reasonably stable for a range of cloud-free and cloudy conditions. With the criteria applied, the absolute magnitude of the mean differences between the shipboard measurements and the CERES estimates for the downward shortwave flux were within 2%, with RMS differences less than 6% within each month of CERES–shipboard matchups. The absolute magnitude of the mean differences for the downward longwave flux was less than 2%, with RMS differences less than 5%. satellite observations; Fluxes; Ship observations
Guo, Song; Leighton, HenryGuo, S., H. Leighton, 2008: Satellite‐derived aerosol radiative forcing from the 2004 British Columbia wildfires. Atmosphere-Ocean, 46(2), 203-212. doi: 10.3137/ao.460201. The British Columbia wildfires of 2004 was one of the largest wildfire events in the last ten years in Canada. Both the shortwave and longwave smoke aerosol radiative forcing at the top‐of‐atmosphere (TOA) are investigated using data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Clouds and the Earth's Radiant Energy System (CERES) instruments. Relationships between the radiative forcing fluxes (?F) and wildfire aerosol optical thickness (AOT) at 0.55 μm (τ0.55) are deduced for both noontime instantaneous forcing and diurnally averaged forcing. The noontime averaged instantaneous shortwave and longwave smoke aerosol radiative forcing at the TOA are 45.8±27.5 W m−2 and ‐12.6±6.9 W m−2, respectively for a selected study area between 62°N and 68°N in latitude and 125°W and 145°W in longitude over three mainly clear‐sky days (23–25 June). The derived diurnally averaged smoke aerosol shortwave radiative forcing is 19.9±12.1 W m−2 for a mean τ0.55 of 1.88±0.71 over the same time period. The derived ?F‐τ relationship can be implemented in the radiation scheme used in regional climate models to assess the effect of wildfire aerosols.
Gupta, P.; Patadia, F.; Christopher, S.A.Gupta, P., F. Patadia, S. Christopher, 2008: Multisensor Data Product Fusion for Aerosol Research. IEEE Transactions on Geoscience and Remote Sensing, 46(5), 1407-1415. doi: 10.1109/TGRS.2008.916087. Combining data sets from multiple satellite sensors is a powerful method for studying Earth-atmosphere problems. By fusing data, we can utilize the strengths of the individual sensors that may not be otherwise possible. In this paper, we provide the framework for combining level 2 data products, using data from three sensors aboard the National Aeronautics and Space Administration (NASA)'s Terra satellite. These data include top-of-the-atmosphere (TOA) radiative energy fluxes obtained from the Clouds and the Earth's Radiant Energy System (CERES), aerosol optical thickness from the multispectral Moderate Resolution Imaging Spectroradiometer (MODIS), and aerosol properties from the Multi-angle Imaging SpectroRadiometer (MISR). The CERES Single Scanner Footprint (SSF) contains the pixel level CERES TOA fluxes and the level 2 MODIS aerosol data. We specifically focus upon fusing the CERES SSF with the MISR aerosol products. Although this project was undertaken specifically to address aerosol research, the methods employed for fusing data products can be used for other problems requiring synergistic data sets. We present selected case studies over different aerosol regimes and indicate that multisensor information provides value-added information for aerosol research that is not available from a single sensor. clouds; atmospheric radiation; aerosols; Clouds and the Earth's Radiant Energy System; Earth Observing System; climate; MODIS; Aerosol forcing; aerosol optical thickness; Carbon dioxide; Clouds and the Earth's Radiant Energy System (CERES); Moderate Resolution Imaging Spectroradiometer (MODIS); atmospheric composition; data fusion; aerosol properties; CERES Single Scanner Footprint; Earth-atmosphere problems; Laser radar; level 2 MODIS aerosol data; MISR; Multi-angle Imaging SpectroRadiometer (MISR); Multiangle Imaging SpectroRadiometer; multisensor data product fusion; multispectral Moderate Resolution Imaging Spectroradiometer; NASA Terra satellite; National Aeronautics and Space Administration; Optical imaging; Satellite broadcasting; sensor fusion; Spectroradiometers; SSF; Thermal pollution; top-of-the-atmosphere radiative energy fluxes
Huang, Xianglei; Yang, Wenze; Loeb, Norman G.; Ramaswamy, V.Huang, X., W. Yang, N. G. Loeb, V. Ramaswamy, 2008: Spectrally resolved fluxes derived from collocated AIRS and CERES measurements and their application in model evaluation: Clear sky over the tropical oceans. Journal of Geophysical Research: Atmospheres, 113(D9), D09110. doi: 10.1029/2007JD009219. Spectrally resolved outgoing thermal-IR flux, the integrand of the outgoing longwave radiation (OLR), has a unique value in evaluating model simulations. Here we describe an algorithm for deriving such clear-sky outgoing spectral flux through the entire thermal-IR spectrum from the collocated Atmospheric Infrared Sounder (AIRS) and the Clouds and the Earth's Radiant Energy System (CERES) measurements over the tropical oceans. On the basis of the predefined scene types in the CERES Single Satellite Footprint (SSF) data set, spectrally dependent ADMs are developed and used to estimate the spectral flux each AIRS channel. A multivariate linear prediction scheme is then used to estimate spectral fluxes at frequencies not covered by the AIRS instrument. The whole algorithm is validated using synthetic spectra as well as the CERES OLR measurements. Using the GFDL AM2 model simulation as a case study, applications of the derived clear-sky outgoing spectral fluxes in model evaluation are illustrated. By comparing the observed spectral fluxes and simulated ones for the year of 2004, compensating errors in the simulated OLR from different absorption bands are revealed, along with the errors from frequencies within a given absorption band. Discrepancies between the simulated and observed spatial distributions and seasonal evolutions of the spectral fluxes are further discussed. The methodology described in this study can be applied to other surface types as well as cloudy-sky observations and also to corresponding model evaluations. 3359 Radiative processes; 3310 Clouds and cloud feedbacks; 1626 Global climate models; clear-sky spectral flux; model evaluation
Huang, Yi; Ramaswamy, V.Huang, Y., V. Ramaswamy, 2008: Observed and simulated seasonal co-variations of outgoing longwave radiation spectrum and surface temperature. Geophysical Research Letters, 35(17), L17803. doi: 10.1029/2008GL034859. We analyze the seasonal variations of Outgoing Longwave Radiation (OLR) accompanying the variations in sea surface temperature (SST) from satellite observations and model simulations, focusing on the tropical oceans where the two quantities are strikingly anti-correlated. A spectral perspective of this “super-greenhouse effect” is provided, which demonstrates the roles of water vapor line and continuum absorptions at different altitudes and the influences due to clouds. A model-satellite comparison indicates that the GFDL General Circulation Model can fairly well represent the total-sky radiative response to SST in the water vapor infrared absorption band despite the significant bias in the mean state, but this comprises compensating water vapor- and cloud-related errors. The analysis also reveals that the GCM significantly underestimates the cloud induced radiative responses in the window region which arises from the model bias in the mean cloud forcing in convectively active regions. Thus, spectral decomposition proves essential to understand and assess the OLR-SST relationship and the impacts of water vapor and cloud upon this linkage. 0321 Cloud/radiation interaction; 3359 Radiative processes; 3305 Climate change and variability; 1616 Climate variability; 1626 Global climate models; OLR spectrum; SST; super-greenhouse effect
Jin, Zhonghai; Charlock, Thomas P.; Yang, Ping; Xie, Yu; Miller, WalterJin, Z., T. P. Charlock, P. Yang, Y. Xie, W. Miller, 2008: Snow optical properties for different particle shapes with application to snow grain size retrieval and MODIS/CERES radiance comparison over Antarctica. Remote Sensing of Environment, 112(9), 3563-3581. doi: 10.1016/j.rse.2008.04.011. We investigated the single scattering optical properties of snow for different ice particle shapes and degrees of microscopic scale roughness. These optical properties were implemented and tested in a coupled atmosphere-snow radiative transfer model. The modeled surface spectral albedo and radiance distribution were compared with surface measurements. The results show that the reflected radiance and irradiance over snow are sensitive to the snow grain size and its vertical profile. When inhomogeneity of the particle size distribution in the vertical is taken into account, the measured spectral albedo can be matched, regardless of the particle shapes. But this is not true for the modeled radiance distribution, which depends a lot on the particle shape. The usual “equivalent spheres” assumption significantly overestimates forward reflected radiances, and underestimates backscattering radiances, around the principal plane. On average, the aggregate shape assumption has the best agreement with the measured radiances to a mean bias within 2%. The snow optical properties with the aggregate assumption were applied to the retrieval of snow grain size over the Antarctic plateau. The retrieved grain sizes of the top layer showed similar and large seasonal variation in all years, but only small year to year variation. Using the retrieved snow grain sizes, the modeled spectral and broadband radiances showed good agreements with MODIS and CERES measurements over the Antarctic plateau. Except for the MODIS 2.13 μm channel, the mean relative model-observation differences are within few percent. The modeled MODIS radiances using measured surface reflectance at Dome C also showed good agreement in visible channels, where radiation is not sensitive to snow grain size and the measured surface bidirectional reflectance is applicable over the Antarctic plateau. But modeled radiances using local, surface-measured reflectance in the near infrared yielded large errors because of the high sensitivity to the snow grain size, which varies spatially and temporally. The CERES broadband shortwave radiance is moderately sensitive to the snow grain size, comparable to the MODIS 0.86 μm channel. The variation of broadband snow reflectance due to the seasonal variation in snow grain size is about 5% in a year over the Antarctic plateau. CERES broadband radiances simulated with grain sizes retrieved using MODIS are about 2% larger than those observed. radiative transfer; Radiance; snow; Snow grain size retrieval
Jones, T.A.; Christopher, S.A.Jones, T., S. Christopher, 2008: Multispectral Analysis of Aerosols Over Oceans Using Principal Components. IEEE Transactions on Geoscience and Remote Sensing, 46(9), 2659-2665. doi: 10.1109/TGRS.2008.920019. Applying principal component analysis (PCA) to one month of Moderate Resolution Imaging Spectroradiometer (MODIS) narrow-band short-wave radiance data and comparing with the Goddard Global Ozone Chemistry Aerosol Radiation Transport (GOCART) model simulations, we show that aerosol size and speciation information can be inferred from multispectral radiance information without having to use other parameters, such as a fine mode fraction (FMF), that are difficult to validate. PCA was applied to seven highly correlated MODIS solar channels (0.47, 0.55, 0.66, 0.86, 1.24, 1.64, and 2.12 mum) to extract noncorrelated pseudochannels, each with a unique interpretation. The first pseudochannel (PCI) can be interpreted as the mean radiance across the seven channels, which is directly proportional to the aerosol concentration. The second pseudochannel (PC2) is sensitive to the aerosol size since different aerosol types scatter and absorb differently across the seven MODIS short-wave channels. PC3 is inversely related to the aerosol optical thickness (AOT) and the FMF and appears most sensitive to changes in sulfate and maritime sea-salt concentrations. Results indicate that high values of PCI are indicative of high dust aerosol concentrations comprising more than 40% of the total AOT, whereas high values of PC2 indicate anthropogenic aerosol concentrations (deduced from GOCART) in excess of 60%. Compared to simple 0.55-mum FMF thresholds, the PC channels are much more sensitive to dust aerosol concentrations and certain aspects of anthropogenic aerosols, with very low FMF values alone (< 0.2) being the best indicator of predominately sea-salt aerosol concentrations. Our results indicate that PCA could be used as an alternate method for inferring aerosol speciation information in future research over ocean and more complex land surfaces. Remote sensing; aerosols; Moderate Resolution Imaging Spectroradiometer; statistics; aerosol optical thickness; dust; aerosol size; aerosol types scatter; anthropogenic aerosol concentrations; atmospheric composition; dust aerosol concentrations; fine mode fraction; GOCART model simulations; Goddard Global Ozone Chemistry Aerosol Radiation Transport; maritime sea-salt concentration; MODIS radiance data; principal component analysis; pseudochannel; sulfate concentration
Jones, Thomas A.; Christopher, Sundar A.Jones, T. A., S. A. Christopher, 2008: Seasonal variation in satellite-derived effects of aerosols on clouds in the Arabian Sea. Journal of Geophysical Research: Atmospheres, 113(D9), D09207. doi: 10.1029/2007JD009118. Aerosols act as cloud condensation nuclei for cloud water droplets, with changes in aerosol concentrations having significant impacts on the corresponding cloud properties. An increase in aerosol concentration may lead to an increase in CCN, with an associated decrease in cloud droplet size for a given cloud liquid water content. Smaller droplet sizes may then lead to a reduction in precipitation efficiency and an increase in cloud lifetimes. However, these effects are highly dependent on the aerosol concentration, aerosol species, and the meteorological conditions. In the Arabian Sea (10–20°N, 62–72°E), prevailing aerosol type transitions from mostly small-mode anthropogenic aerosols during the winter months to mostly coarse-mode mineral dust and sea salt during the summer due to a change in prevailing wind speed and direction, is likely to impart substantial variability on any associated indirect effects. To examine this variability, we use one year (2004) of MODIS derived aerosol optical thickness (AOT) and cloud products over the Arabian Sea to quantify aerosol indirect effects. Results show that indirect effects in the Arabian Sea are a strong function of season, which is a result of the changing aerosol and moisture (humidity) concentrations during the course of the year. During the winter months (DJF), cloud-droplet size and AOT were found to have a weak positive correlation (r = 0.12), opposite of the expected effect. The low atmospheric humidity coupled with wide-spread subsidence and other dynamical factors may prevent these aerosols from being activated. During the summer months (JJA), AOT increases with the addition of mineral dust and sea salt aerosols and the correlation between AOT and cloud droplet size becomes negative (r = −0.22). The magnitude of the first indirect effect corresponds to an increase in low level wind speeds, increasing the concentration of hygroscopic sea salt into the atmosphere. For both periods, a positive correlation (r = 0.16, 0.32) was found between AOT and LWP indicating a reduction in precipitation efficiency. clouds; 0305 Aerosols and particles; 0345 Pollution: urban and regional; aerosols; 0321 Cloud/radiation interaction; MODIS; 0478 Pollution: urban, regional and global; indirect effects
Kato, Seiji; Rose, Fred G.; Rutan, David A.; Charlock, Thomas P.Kato, S., F. G. Rose, D. A. Rutan, T. P. Charlock, 2008: Cloud Effects on the Meridional Atmospheric Energy Budget Estimated from Clouds and the Earth’s Radiant Energy System (CERES) Data. J. Climate, 21(17), 4223-4241. doi: 10.1175/2008JCLI1982.1. Abstract The zonal mean atmospheric cloud radiative effect, defined as the difference between the top-of-the-atmosphere (TOA) and surface cloud radiative effects, is estimated from 3 yr of Clouds and the Earth’s Radiant Energy System (CERES) data. The zonal mean shortwave effect is small, though it tends to be positive (warming). This indicates that clouds increase shortwave absorption in the atmosphere, especially in midlatitudes. The zonal mean atmospheric cloud radiative effect is, however, dominated by the longwave effect. The zonal mean longwave effect is positive in the tropics and decreases with latitude to negative values (cooling) in polar regions. The meridional gradient of the cloud effect between midlatitude and polar regions exists even when uncertainties in the cloud effect on the surface enthalpy flux and in the modeled irradiances are taken into account. This indicates that clouds increase the rate of generation of the mean zonal available potential energy. Because the atmospheric cooling effect in polar regions is predominately caused by low-level clouds, which tend to be stationary, it is postulated here that the meridional and vertical gradients of the cloud effect increase the rate of meridional energy transport by the dynamics of the atmosphere from the midlatitudes to the polar region, especially in fall and winter. Clouds then warm the surface in the polar regions except in the Arctic in summer. Clouds, therefore, contribute toward increasing the rate of meridional energy transport from the midlatitudes to the polar regions through the atmosphere. energy budget; Cloud radiative effects; Irradiance
Kim, Dohyeong; Ramanathan, V.Kim, D., V. Ramanathan, 2008: Solar radiation budget and radiative forcing due to aerosols and clouds. Journal of Geophysical Research: Atmospheres, 113(D2), D02203. doi: 10.1029/2007JD008434. This study integrates global data sets for aerosols, cloud physical properties, and shortwave radiation fluxes with a Monte Carlo Aerosol-Cloud-Radiation (MACR) model to estimate both the surface and the top-of-atmosphere (TOA) solar radiation budget as well as atmospheric column solar absorption. The study also quantifies the radiative forcing of aerosols and that of clouds. The observational input to MACR includes data from the Multiangle Imaging Spectroradiometer (MISR) for aerosol optical depths, single scattering albedos, and asymmetry factors; satellite retrieved column water vapor amount; the Total Ozone Mapping Spectrometer (TOMS) total ozone amount; and cloud fraction and cloud optical depth from the Cloud and Earth's Radiant Energy System (CERES) cloud data. The present radiation budget estimates account for the diurnal variation in cloud properties. The model was validated against instantaneous, daily and monthly solar fluxes from the ground-based Baseline Surface Radiation Network (BSRN) network, the Global Energy Balance Archive (GEBA) surface solar flux data, and CERES TOA measurements. The agreement between simulated and observed values are within experimental errors, for all of the cases considered here: instantaneous fluxes and monthly mean fluxes at stations around the world and TOA fluxes and cloud forcing for global annual mean and zonal mean fluxes; in addition the estimated aerosol forcing at TOA also agrees with other observationally derived estimates. Overall, such agreements suggest that global data sets of aerosols and cloud parameters released by recent satellite experiments (MISR, MODIS and CERES) meet the required accuracy to use them as input to simulate the radiative fluxes within instrumental errors. Last, the atmospheric solar absorption derived in this study should be treated as an improved estimate when compared with earlier published studies. The main source of improvement in the present estimate is the use of global distribution of observed parameters for model input such as aerosols and clouds. The agreement between simulated and observed solar fluxes at the surface supports our conclusion that the present estimate is an improvement over previous studies. MACR with the global input data was used to simulate the global and regional solar radiation budget, aerosol radiative forcing and cloud radiative forcing for a 3-year period from 2000 to 2002. We estimate the planetary albedo for a 3-year average to be 28.9 ± 1.2% to be compared with CERES estimate of 28.6% and ERBE's estimate of 29.6%. Without clouds (including aerosols) the planetary albedo is only 15.0 ± 0.6%. The global mean TOA shortwave cloud forcing is −47.5 ± 4 W m−2, comparing well with the CERES and ERBE estimates of −46.5 and −48 W m−2, respectively. The clear-sky atmospheric absorption is 72 ± 3 W m−2, and the surface absorption is 218 ± 4 W m−2. Clouds in all-sky conditions enhance atmospheric absorption from 72 ± 3 W m−2 to 79 ± 5 W m−2 and decrease surface solar absorption from 218 ± 4 W m−2 to 164 ± 6 W m−2. The present estimate of 79 W m−2 for all-sky solar absorption is much larger than the Intergovernmental Panel on Climate Change (2001) values of about 67 W m−2. Most of the increased atmospheric solar absorption is due to improved treatment of aerosol absorption (backed by surface based aerosol network and chemical transport models) and water vapor spectroscopic data. The global mean clear-sky aerosol (both natural and anthropogenic) radiative forcing at the TOA and the surface are −6.0 ± 1 W m−2 and −11.0 ± 2 W m−2, respectively. In the presence of clouds the aerosol radiative forcing is −3.0 ± 1 W m−2 (at TOA) and −7.0 ± 2 W m−2 (at the surface). The study also documents the significant regional variations in the solar radiation budget and radiative forcing of aerosols and clouds. 3311 Clouds and aerosols; 3359 Radiative processes; 3305 Climate change and variability; 3337 Global climate models; aerosol radiative forcing; 3315 Data assimilation; cloud radiative forcing; solar radiation budget
Kratz, David P.Kratz, D. P., 2008: The sensitivity of radiative transfer calculations to the changes in the HITRAN database from 1982 to 2004. Journal of Quantitative Spectroscopy and Radiative Transfer, 109(6), 1060-1080. doi: 10.1016/j.jqsrt.2007.10.010. Over the last quarter century, improvements in the determination of the spectroscopic characteristics of the infrared-active trace species have enhanced our ability to retrieve quantitative distributions of temperatures, clouds, and abundances for various trace species within the Earth's atmosphere. These improvements have also allowed for refinements in the estimates of climatic effects attributed to changes in the Earth's atmospheric composition. Modeling efforts, however, have frequently experienced significant delays in assimilating improved spectroscopic information. Such is the case for highly parameterized models, where considerable effort is typically required to incorporate any revisions. Thus, a line-by-line radiative transfer model has been used to investigate the magnitude of the effects resulting from modifications to the spectroscopic information. Calculations from this line-by-line model have demonstrated that recent modifications to the HITRAN (High Resolution Transmission) line parameters, the continuum formulation, and the CO2 line-mixing formulation can significantly affect the interpretation of the high spectral resolution radiance and brightness temperature retrievals. For certain moderate-resolution satellite remote sensing channels, modifications to these spectroscopic parameters and formulations have shown the capacity to induce changes in the calculated radiances equivalent to brightness temperature differences of 1–2 K. Model calculations have further shown that modifications of the spectroscopic characteristics tend to have a modest effect on the determination of spectrally integrated radiances, fluxes, and radiative forcing estimates, with the largest differences being of order 1 W m−2 for the total thermal infrared fluxes, and of order 2–3% of the calculated radiative forcing at the tropopause attributed to the combined doubling of CO2, N2O, and CH4. The results from this investigation are intended to function as a guide to differentiate between cases where older parameterizations provide acceptable results, within specified accuracy bounds, and cases where upgrades to the latest spectroscopic database are necessary. Correlated k-distribution; Fluxes; HITRAN database; Infrared; Line parameters; Line-by-line calculation; Radiances; Radiative forcings
L'Ecuyer, Tristan S.; Wood, Norman B.; Haladay, Taryn; Stephens, Graeme L.; Stackhouse, Paul W.L'Ecuyer, T. S., N. B. Wood, T. Haladay, G. L. Stephens, P. W. Stackhouse, 2008: Impact of clouds on atmospheric heating based on the R04 CloudSat fluxes and heating rates data set. Journal of Geophysical Research: Atmospheres, 113(D8), D00A15. doi: 10.1029/2008JD009951. Among the largest uncertainties in quantifying the radiative impacts of clouds are those that arise from the inherent difficulty in precisely specifying the vertical distribution of cloud optical properties using passive satellite measurements. Motivated by the need to address this problem, CloudSat was launched in April 2006 carrying into orbit the first millimeter wavelength cloud radar to be flown in space. Retrieved profiles of liquid and ice cloud microphysical properties from this Cloud Profiling Radar form the basis of the CloudSat's fluxes and heating rates algorithm, 2B-FLXHR, a standard product that provides high vertical resolution profiles of radiative fluxes and atmospheric heating rates on the global scale. This paper describes the physical basis of the 2B-FLXHR algorithm and documents the first year of 2B-FLXHR data in the context of assessing the radiative impact of clouds on global and regional scales. The analysis confirms that cloud contributions to atmospheric radiative heating are small on the global scale because of a cancelation of the much larger regional heating from high clouds in the tropics and cooling from low clouds at higher latitudes. Preliminary efforts to assess the accuracy of the 2B-FLXHR product using coincident CERES data demonstrate that outgoing longwave fluxes are better represented than those in the shortwave but both exhibit good agreement with CERES on scales longer than 5 days and larger than 5°. Colocated CALIPSO observations of clouds that are undetected by CloudSat further indicate that while thin cirrus can introduce modest uncertainty in the products, low clouds that are obscured by ground clutter represent a far more important source of error in the current 2B-FLXHR product that must be addressed in subsequent versions of the algorithm. clouds; 0321 Cloud/radiation interaction; 3359 Radiative processes; 3310 Clouds and cloud feedbacks; CloudSat; radiation; 0341 Middle atmosphere: constituent transport and chemistry
Laszlo, Istvan; Ciren, Pubu; Liu, Hongqing; Kondragunta, Shobha; Tarpley, J. Dan; Goldberg, Mitchell D.Laszlo, I., P. Ciren, H. Liu, S. Kondragunta, J. D. Tarpley, M. D. Goldberg, 2008: Remote sensing of aerosol and radiation from geostationary satellites. Advances in Space Research, 41(11), 1882-1893. doi: 10.1016/j.asr.2007.06.047. The paper presents a high-level overview of current and future remote sensing of aerosol and shortwave radiation budget carried out at the US National Oceanic and Atmospheric Administration (NOAA) from the US Geostationary Operational Environmental Satellite (GOES) series. The retrievals from the current GOES imagers are based on physical principles. Aerosol and radiation are estimated in separate processing from the comparison of satellite-observed reflectances derived from a single visible channel with those calculated from detailed radiative transfer. The radiative transfer calculation accounts for multiple scattering by molecules, aerosol and cloud and absorption by the major atmospheric gases. The retrievals are performed operationally every 30 min for aerosol and every hour for radiation for pixel sizes of 4-km (aerosol) and 15- to 50-km (radiation). Both retrievals estimate the surface reflectance as a byproduct from the time composite of clear visible reflectances assuming fixed values of the aerosol optical depth. With the launch of GOES-R NOAA will begin a new era of geostationary remote sensing. The Advanced Baseline Imager (ABI) onboard GOES-R will offer capabilities for aerosol remote sensing similar to those currently provided by the Moderate Resolution Imaging Spectroradiometer (MODIS) flown on the NASA Earth Observing System (EOS) satellites. The ABI aerosol algorithm currently under development uses a multi-channel approach to estimate the aerosol optical depth and aerosol model simultaneously, both over water and land. Its design is strongly inspired by the MODIS aerosol algorithm. The ABI shortwave radiation budget algorithm is based on the successful GOES Surface and Insolation Product system of NOAA and the NASA Clouds and the Earth’s Radiant Energy System (CERES), Surface and Atmospheric Radiation Budget (SARB) algorithm. In all phases of the development, the algorithms are tested with proxy data generated from existing satellite observations and forward simulations. Final assessment of the performance will be made after the launch of GOES-R scheduled in 2012. aerosol; Geostationary satellite; Shortwave radiation budget
Laszlo, Istvan; Liu, Hongqing; Ignatov, AlexanderLaszlo, I., H. Liu, A. Ignatov, 2008: Comparison of single-channel and multichannel aerosol optical depths derived from MAPSS data. Journal of Geophysical Research: Atmospheres, 113(D19), D19S90. doi: 10.1029/2007JD009664. Previous comparisons of the single-channel and multichannel aerosol products reported in the Clouds and the Earth's Radiant Energy System (CERES) Single Scanner Footprint (SSF) data sets showed systematic differences that were partly attributed to differences in sampling and cloud screening. This study concentrates on quantifying the aerosol optical depth (AOD) differences when the above differences are absent and exactly the same clear radiances are inputted to the aerosol algorithms used to generate the two products. This is accomplished by retrieving AOD with the single-channel algorithm at 22 oceanic locations from the reflectance data in the Moderate Resolution Imaging Spectroradiometer (MODIS) Atmosphere Parameters Subset Statistics (MAPSS) data set for the period of 2000–2007 and then by comparing them to the corresponding MODIS AOD data reported in MAPSS. Comparisons of AODs are performed for two MODIS instruments flown onboard the Terra and Aqua platforms at two wavelengths. On average, the mean differences are wavelength and platform dependent. The single-channel 644-nm AODs are larger by 0.004–0.015 (∼2–9%) than those from the multichannel algorithm. The mean AOD at 1632 nm from both algorithms are very similar from Terra, but the single-channel AOD from Aqua at 2119 nm is lower by 0.02 (∼24%). The mean absolute differences are 0.022–0.025 and do not change much with wavelength or platform. Slight dependence of the mean differences on the scattering angle is observed, which is partially explained by the differences between the retrieved aerosol model in the multichannel retrieval and the fixed aerosol model used in the single-channel algorithm. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; Oceans; 3311 Clouds and aerosols; Satellite; aerosol retrieval; optical depth; 0343 Planetary atmospheres
Li, Gang; Zhang, Guang JunLi, G., G. J. Zhang, 2008: Understanding biases in shortwave cloud radiative forcing in the National Center for Atmospheric Research Community Atmosphere Model (CAM3) during El Niño. Journal of Geophysical Research: Atmospheres, 113(D2), D02103. doi: 10.1029/2007JD008963. This study aims to understand the weak response of shortwave cloud radiative forcing (SWCF) to El Niño in the NCAR CAM3. Observations from ERBE and CERES show strong negative SWCF in the central and eastern equatorial Pacific during El Niño. The standard CAM3 simulation at T42 resolution severely underestimates this response, with even wrong sign in the eastern Pacific. However, an experimental simulation at the same resolution, but with a modified convection parameterization scheme, simulates the cloud shortwave response to El Niño well, although the improvement in the eastern Pacific is not as significant as in the western and central Pacific. To unravel the mechanistic differences in SWCF response to El Niño between the two simulations, the authors analyze the cloud amount, cloud liquid water path (LWP), cloud ice water path (IWP), and convective and large-scale precipitation. It is shown that positive LWP anomalies are mainly responsible for the improved SWCF response to El Niño in the experimental simulation. Interaction among deep convection, shallow convection and low-level clouds is explored to explain this result. Negative LWP anomalies, largely due to reduced cloud water content and amount of low clouds during El Niño in the standard CAM3, weaken the SWCF response. Comparison with a higher-resolution simulation of CAM3 at T85 shows that the T85 simulation produces realistic SWCF response through greatly increased cloud water and ice content in the middle and upper troposphere, while reduced low-level cloud water content remains a problem. 3359 Radiative processes; 3337 Global climate models; 3374 Tropical meteorology; 3310 Clouds and cloud feedbacks; 3314 Convective processes; El Niño response; NCAR CAM3; shortwave cloud forcing
Lin, Bing; Stackhouse, Paul W.; Minnis, Patrick; Wielicki, Bruce A.; Hu, Yongxiang; Sun, Wenbo; Fan, Tai-Fang; Hinkelman, Laura M.Lin, B., P. W. Stackhouse, P. Minnis, B. A. Wielicki, Y. Hu, W. Sun, T. Fan, L. M. Hinkelman, 2008: Assessment of global annual atmospheric energy balance from satellite observations. Journal of Geophysical Research: Atmospheres, 113(D16), D16114. doi: 10.1029/2008JD009869. Global atmospheric energy balance is one of the fundamental processes for the earth's climate system. This study uses currently available satellite data sets of radiative energy at the top of atmosphere (TOA) and surface as well as latent and sensible heat over the oceans for the year 2000 to assess the global annual energy budget. Over land, surface radiation data are used to constrain assimilated results and to force the radiation, turbulent heat, and heat storage into balance due to a lack of observation-based turbulent heat flux estimates. Global annual means of the TOA net radiation obtained from both satellite direct measurements and calculations are close to zero. The net radiative energy fluxes into the surface and the surface latent heat transported into the atmosphere are about 113 and 86 W/m2, respectively. The estimated atmospheric and surface heat imbalances are about −8 and 9 W/m2, respectively, values that are within the uncertainties of surface radiation and sea surface turbulent flux estimates and the likely systematic biases in the analyzed observations. The potential significant additional absorption of solar radiation within the atmosphere suggested by previous studies does not appear to be required to balance the energy budget: the spurious heat imbalances in the current data are much smaller (about half) than those obtained previously and debated about a decade ago. Progress in surface radiation and oceanic turbulent heat flux estimations from satellite measurements has significantly reduced the bias errors in the observed global energy budgets of the climate system. 3309 Climatology; radiation; 1814 Energy budgets; energy budget; latent and sensible heat
Lin, Bing; Sun, Wenbo; Min, Qilong; Hu, YongxiangLin, B., W. Sun, Q. Min, Y. Hu, 2008: Numerical Studies of Scattering Properties of Leaves and Leaf Moisture Influences on the Scattering at Microwave Wavelengths. IEEE Transactions on Geoscience and Remote Sensing, 46(2), 353-360. doi: 10.1109/TGRS.2007.912434. This paper uses a 3-D finite-difference time-domain method to accurately calculate the single-scattering properties of randomly oriented leaves and evaluate the influence of vegetation water content (VWC) on these properties at frequencies of 19.35 and 37.0 GHz. The studied leaves are assumed to be thin elliptical disks with two different sizes and have various VWC values. Although leaf moisture causes considerable absorption in the scattering process, the effective efficiencies of extinction and scattering of leaves essentially linearly increase with VWC, which is critical for forest remote sensing. Calculated asymmetry factors and phase functions also indicate that there is a significant amount of scattered energy at large scattering angles at microwave wavelengths. This paper can improve the modeling of the radiative transfer by vegetation canopies at the higher frequencies of the microwave spectrum, which is important for passive microwave remote sensing. Remote sensing; Moisture; radiative transfer; Water; Vegetation water content; 3D finite difference time domain method; asymmetry factors; atmospheric boundary layer; Electromagnetic wave absorption; Finite difference methods; finite difference time-domain analysis; Frequency; leaf moisture; leaves; Microwave propagation; passive microwave remote sensing; phase functions; Scattering; scattering properties; Time domain analysis; vegetation; vegetation canopies
Loeb, Norman G.; Schuster, Gregory L.Loeb, N. G., G. L. Schuster, 2008: An observational study of the relationship between cloud, aerosol and meteorology in broken low-level cloud conditions. Journal of Geophysical Research: Atmospheres, 113(D14), D14214. doi: 10.1029/2007JD009763. Global satellite analyses showing strong correlations between aerosol optical depth and cloud cover have stirred much debate recently. While it is tempting to interpret the results as evidence of aerosol enhancement of cloud cover, other factors such as the influence of meteorology on both the aerosol and cloud distributions can also play a role, as both aerosols and clouds depend upon local meteorology. This study uses satellite observations to examine aerosol-cloud relationships for broken low-level cloud regions off the coast of Africa. The analysis approach minimizes the influence of large-scale meteorology by restricting the spatial and temporal domains in which the aerosol and cloud properties are compared. While distributions of several meteorological variables within 5° × 5° latitude-longitude regions are nearly identical under low and high aerosol optical depth, the corresponding distributions of single-layer low cloud properties and top-of-atmosphere radiative fluxes differ markedly, consistent with earlier studies showing increased cloud cover with aerosol optical depth. Furthermore, fine-mode fraction and Angstrom Exponent are also larger in conditions of higher aerosol optical depth, even though no evidence of systematic latitudinal or longitudinal gradients between the low and high aerosol optical depth populations are observed. When the analysis is repeated for all 5° × 5° latitude-longitude regions over the global oceans (after removing cases in which significant meteorological differences are found between the low and high aerosol populations), results are qualitatively similar to those off the coast of Africa. clouds; aerosols; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; 3359 Radiative processes; radiation
Marshak, Alexander; Wen, Guoyong; Coakley, James A.; Remer, Lorraine A.; Loeb, Norman G.; Cahalan, Robert F.Marshak, A., G. Wen, J. A. Coakley, L. A. Remer, N. G. Loeb, R. F. Cahalan, 2008: A simple model for the cloud adjacency effect and the apparent bluing of aerosols near clouds. Journal of Geophysical Research: Atmospheres, 113(D14), D14S17. doi: 10.1029/2007JD009196. In determining aerosol-cloud interactions, the properties of aerosols must be characterized in the vicinity of clouds. Numerous studies based on satellite observations have reported that aerosol optical depths increase with increasing cloud cover. Part of the increase comes from the humidification and consequent growth of aerosol particles in the moist cloud environment, but part comes from 3-D cloud-radiative transfer effects on the retrieved aerosol properties. Often, discerning whether the observed increases in aerosol optical depths are artifacts or real proves difficult. The paper only addresses the cloud-clear sky radiative transfer interaction part. It provides a simple model that quantifies the enhanced illumination of cloud-free columns in the vicinity of clouds that are used in the aerosol retrievals. This model is based on the assumption that the enhancement in the cloud-free column radiance comes from enhanced Rayleigh scattering that results from the presence of the nearby clouds. This assumption leads to a larger increase of AOT for shorter wavelengths, or to a “bluing” of aerosols near clouds. The assumption that contribution from molecular scattering dominates over aerosol scattering and surface reflection is justified for the case of shorter wavelengths, dark surfaces, and an aerosol layer below the cloud tops. The enhancement in Rayleigh scattering is estimated using a stochastic cloud model to obtain the radiative flux reflected by broken clouds and comparing this flux with that obtained with the molecules in the atmosphere causing extinction, but no scattering. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; aerosols; 0321 Cloud/radiation interaction; radiation; cloud adjacency
Matthews, GrantMatthews, G., 2008: Celestial body irradiance determination from an underfilled satellite radiometer: application to albedo and thermal emission measurements of the Moon using CERES. Applied Optics, 47(27), 4981. doi: 10.1364/AO.47.004981.
Menon, Surabi; Del Genio, Anthony D.; Kaufman, Yoram; Bennartz, Ralf; Koch, Dorothy; Loeb, Norman; Orlikowski, DanielMenon, S., A. D. Del Genio, Y. Kaufman, R. Bennartz, D. Koch, N. Loeb, D. Orlikowski, 2008: Analyzing signatures of aerosol-cloud interactions from satellite retrievals and the GISS GCM to constrain the aerosol indirect effect. Journal of Geophysical Research: Atmospheres, 113(D14), D14S22. doi: 10.1029/2007JD009442. Evidence of aerosol-cloud interactions is evaluated using satellite data from MODIS, CERES, and AMSR-E; reanalysis data from NCEP; and data from the NASA Goddard Institute for Space Studies climate model. We evaluate a series of model simulations: (1) Exp N, aerosol direct radiative effects; (2) Exp C, like Exp N but with aerosol effects on liquid-phase cumulus and stratus clouds; and (3) Exp CN, like Exp C but with model wind fields nudged to reanalysis data. Comparison between satellite-retrieved data and model simulations for June to August 2002 over the Atlantic Ocean indicate the following: a negative correlation between aerosol optical thickness (AOT) and cloud droplet effective radius (Reff) for all cases and satellite data, except for Exp N, a weak but negative correlation between liquid water path (LWP) and AOT for MODIS and CERES, and a robust increase in cloud cover with AOT for both MODIS and CERES. In all simulations, there is a positive correlation between AOT and both cloud cover and LWP (except in the case of LWP-AOT for Exp CN). The largest slopes are obtained for Exp N, implying that meteorological variability may be an important factor. On the basis of NCEP data, warmer temperatures and increased subsidence were found for less clean cases (AOT > 0.06) that were not well captured by the model. Simulated cloud fields compared with an enhanced data product from MODIS and AMSR-E indicate that model cloud thickness is overpredicted and cloud droplet number is within retrieval uncertainties. Since LWP fields are comparable, this implies an underprediction of Reff and thus an overprediction of the indirect effect. 0320 Cloud physics and chemistry; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; Cloud microphysics; 3337 Global climate models; aerosol optical thickness; aerosol indirect effect
Milton, S. F.; Greed, G.; Brooks, M. E.; Haywood, J.; Johnson, B.; Allan, R. P.; Slingo, A.; Grey, W. M. F.Milton, S. F., G. Greed, M. E. Brooks, J. Haywood, B. Johnson, R. P. Allan, A. Slingo, W. M. F. Grey, 2008: Modeled and observed atmospheric radiation balance during the West African dry season: Role of mineral dust, biomass burning aerosol, and surface albedo. Journal of Geophysical Research: Atmospheres, 113(D23), D00C02. doi: 10.1029/2007JD009741. The global radiation balance of the atmosphere is still poorly observed, particularly at the surface. We investigate the observed radiation balance at (1) the surface using the ARM Mobile Facility in Niamey, Niger, and (2) the top of the atmosphere (TOA) over West Africa using data from the Geostationary Earth Radiation Budget (GERB) instrument on board Meteosat-8. Observed radiative fluxes are compared with predictions from the global numerical weather prediction (NWP) version of the Met Office Unified Model (MetUM). The evaluation points to major shortcomings in the NWP model's radiative fluxes during the dry season (December 2005 to April 2006) arising from (1) a lack of absorbing aerosol in the model (mineral dust and biomass burning aerosol) and (2) a poor specification of the surface albedo. A case study of the major Saharan dust outbreak of 6–12 March 2006 is used to evaluate a parameterization of mineral dust for use in the NWP models. The model shows good predictability of the large-scale flow out to 4–5 days with the dust parameterization providing reasonable dust uplift, spatial distribution, and temporal evolution for this strongly forced dust event. The direct radiative impact of the dust reduces net downward shortwave (SW) flux at the surface (TOA) by a maximum of 200 W m−2 (150 W m−2), with a SW heating of the atmospheric column. The impacts of dust on terrestrial radiation are smaller. Comparisons of TOA (surface) radiation balance with GERB (ARM) show the “dusty” forecasts reduce biases in the radiative fluxes and improve surface temperatures and vertical thermodynamic structure. 0305 Aerosols and particles; aerosols; 3359 Radiative processes; 0325 Evolution of the atmosphere; 1631 Land/atmosphere interactions; 0550 Model verification and validation; dust modelling; Surface energy balance
Minnis, P.; Trepte, Q. Z.; Sun-Mack, S.; Chen, Y.; Doelling, D. R.; Young, D. F.; Spangenberg, D. A.; Miller, W. F.; Wielicki, B. A.; Brown, R. R.; Gibson, S. C.; Geier, E. B.Minnis, P., Q. Z. Trepte, S. Sun-Mack, Y. Chen, D. R. Doelling, D. F. Young, D. A. Spangenberg, W. F. Miller, B. A. Wielicki, R. R. Brown, S. C. Gibson, E. B. Geier, 2008: Cloud Detection in Nonpolar Regions for CERES Using TRMM VIRS and Terra and Aqua MODIS Data. Ieee Transactions on Geoscience and Remote Sensing, 46(11), 3857-3884. doi: 10.1109/tgrs.2008.2001351. Objective techniques have been developed to consistently identify cloudy pixels over nonpolar regions in multispectral imager data coincident with measurements taken by the Clouds and Earth's Radiant Energy System (CERES) on the Tropical Rainfall Measuring Mission (TRMM), Terra, and Aqua satellites. The daytime method uses the 0.65-, 3.8-, 10.8-, and 12.0-mu m channels on the TRMM Visible and Infrared Scanner (VIRS) and the Terra and Aqua MODIS. The VIRS and Terra 1.6-mu m channel and the Aqua 1.38- and 2.1-mu m channels are used secondarily. The primary nighttime radiances are from the 3.8-, 10.8-, and 12.0-mu m channels. Significant differences were found between the VIRS and Terra 1.6-mu m and the Terra and Aqua 3.8-mu m channels' calibrations. Cascading threshold tests provide clear or cloudy classifications that are qualified according to confidence levels or other conditions, such as sunglint, that affect the classification. The initial infrared threshold test classifies similar to 43% of the pixels as clouds. The next level seeks consistency in three (two) different channels during daytime (nighttime) and accounts for roughly 40% (25%) of the pixels. The third tier uses refined thresholds to classify remaining pixels. For cloudy pixels, similar to 4% yield no retrieval when analyzed with a cloud retrieval algorithm. The techniques were applied to data between 1998 and 2006 to yield average nonpolar cloud amounts of similar to 0.60. Averages among the platforms differ by < 0.01 and are comparable to surface climatological values, but roughly 0.07 less than means from two other satellite analyses, primarily as a result of missing small subpixel and thin clouds.
Minnis, Patrick; Doelling, David R.; Nguyen, Louis; Miller, Walter F.; Chakrapani, VenkatesanMinnis, P., D. R. Doelling, L. Nguyen, W. F. Miller, V. Chakrapani, 2008: Assessment of the Visible Channel Calibrations of the VIRS on TRMM and MODIS on Aqua and Terra. J. Atmos. Oceanic Technol., 25(3), 385-400. doi: 10.1175/2007JTECHA1021.1. Abstract Several recent research satellites carry self-calibrating multispectral imagers that can be used for calibrating operational imagers lacking complete self-calibrating capabilities. In particular, the visible (VIS, 0.65 μm) channels on operational meteorological satellites are generally calibrated before launch, but require vicarious calibration techniques to monitor the gains and offsets once they are in orbit. To ensure that the self-calibrating instruments are performing as expected, this paper examines the consistencies between the VIS channel (channel 1) reflectances of the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on the Terra and Aqua satellites and the version 5a and 6 reflectances of the Visible Infrared Scanner (VIRS) on the Tropical Rainfall Measuring Mission using a variety of techniques. These include comparisons of Terra and Aqua VIS radiances with coincident broadband shortwave radiances from the well-calibrated Clouds and the Earth’s Radiant Energy System (CERES), time series of deep convective cloud (DCC) albedos, and ray-matching intercalibrations between each of the three satellites. Time series of matched Terra and VIRS data, Aqua and VIRS data, and DCC reflected fluxes reveal that an older version (version 5a, ending in early 2004) of the VIRS calibration produced a highly stable record, while the latest version (version 6) appears to overestimate the sensor gain change by ∼1% yr−1 as the result of a manually induced gain adjustment. Comparisons with the CERES shortwave radiances unearthed a sudden change in the Terra MODIS calibration that caused a 1.17% decrease in the gain on 19 November 2003 that can be easily reversed. After correction for these manual adjustments, the trends in the VIRS and Terra channels are no greater than 0.1% yr−1. Although the results were more ambiguous, no statistically significant trends were found in the Aqua MODIS channel 1 gain. The Aqua radiances are 1% greater, on average, than their Terra counterparts, and after normalization are 4.6% greater than VIRS radiances, in agreement with theoretical calculations. The discrepancy between the two MODIS instruments should be taken into account to ensure consistency between parameters derived from them. With the adjustments, any of the three instruments can serve as references for calibrating other satellites. Monitoring of the calibrations continues in near–real time and the results are available via the World Wide Web. rainfall; satellite observations; Instrumentation/sensors; Sensitivity studies
Patadia, Falguni; Gupta, Pawan; Christopher, Sundar A.Patadia, F., P. Gupta, S. A. Christopher, 2008: First observational estimates of global clear sky shortwave aerosol direct radiative effect over land. Geophysical Research Letters, 35(4), L04810. doi: 10.1029/2007GL032314. Using one year (2000–2001) of merged Multiangle Imaging SpectroRadiometer (MISR), Moderate Resolution Imaging SpectroRadiometer (MODIS) and Clouds and the Earth's Radiant Energy System (CERES) data sets from NASA's Terra satellite, we estimate the top of atmosphere cloud-free direct radiative effect (DRE) of aerosols over global land areas. The global mean shortwave DRE is −5.1 ± 1.1 Wm−2 although substantial regional variability in DRE over land exists due to differences in aerosol properties and land cover types. This value is consistent with those reported in the literature although this is the first observational estimate of the global DRE over land using satellite data alone. Future studies need to separate the anthropogenic component of aerosols from satellite data to examine aerosol climate forcing over global scales. 0305 Aerosols and particles; aerosols; CERES; 3359 Radiative processes; Satellite; climate; MODIS; 4801 Aerosols; MISR; global direct radiative effects
Patadia, Falguni; Gupta, Pawan; Christopher, Sundar A.; Reid, Jeffrey S.Patadia, F., P. Gupta, S. A. Christopher, J. S. Reid, 2008: A Multisensor satellite-based assessment of biomass burning aerosol radiative impact over Amazonia. Journal of Geophysical Research: Atmospheres, 113(D12), D12214. doi: 10.1029/2007JD009486. Using spatially and temporally collocated multispectral, multiangle and broadband data sets from the Terra satellite, the role of biomass burning (BB) smoke particles on cloud-free top of atmosphere (TOA) direct shortwave aerosol radiative forcing (SWARF) is examined. A 5-year analysis during the peak biomass burning months of August and September is presented over South America (0°–20°S and 45°W–65°W). Our results indicate that over 5 years, the TOA diurnally averaged SWARF (DSWARF) from the Clouds and the Earth's Radiant Energy System (CERES) scanner ranges between −5.2 Wm−2 and −9.4 Wm−2 with a mean value of −7.6 Wm−2 and an estimated uncertainty of ±1.4 Wm−2. The corresponding Multi Angle Spectroradiometer (MISR) aerosol optical thickness (AOT at 0.558 μm) ranged from 0.15 to 0.36 with a mean value of 0.24. The estimated mean TOA aerosol radiative forcing efficiency (Eτ) is −44.2 Wm−2τ−1 and is in good agreement with previous studies. We also examined the beta versions of the MISR data products such as the angstrom exponent (AE) and fraction of AOT in different size bins to assess the role of BB aerosol particle properties on SWARF. Our analysis indicates that the MISR retrieved 5 year mean AE is 1.54. Contribution to total AOT from small, medium and large particles is 66%, 16% and 18% respectively. This is the first multiyear assessment of SWARF for biomass burning aerosol particles using satellite observations alone and should serve as a useful constraint for numerical modeling simulations that estimate SWARF. 0305 Aerosols and particles; aerosols; CERES; satellite remote sensing; 3359 Radiative processes; radiative forcing; MODIS; 4801 Aerosols; Biomass burning; AERONET; MISR
Pfister, G. G.; Hess, P. G.; Emmons, L. K.; Rasch, P. J.; Vitt, F. M.Pfister, G. G., P. G. Hess, L. K. Emmons, P. J. Rasch, F. M. Vitt, 2008: Impact of the summer 2004 Alaska fires on top of the atmosphere clear-sky radiation fluxes. Journal of Geophysical Research: Atmospheres, 113(D2), D02204. doi: 10.1029/2007JD008797. In this study we estimate the radiative impact of wildfires in Alaska during the record wildfire season of 2004 by integrating model simulations and satellite observations of the top of the atmosphere (TOA) radiative fluxes and aerosol optical depth. We compare results for the summer of 2004 to results for the summer of 2000 when fire activity in the boreal zone was low. Both observations and model show a decrease in TOA clear-sky fluxes over the Alaska fire region during summer 2004 of −7 ± 6 W m−2 and −10 ± 4 W m−2, respectively. About two thirds of the change occurs in the longwave, and one third in the shortwave, spectral range. On the bases of detailed model analysis we estimate that the changes in the longwave flux are predominantly explained by a higher surface temperature in summer 2004 compared to 2000. The change in the shortwave flux is largely caused by scattering of solar radiation on organic carbon aerosols emitted from the 2004 fires. This cooling is somewhat mitigated by the warming effect due to absorbing black carbon aerosols emitted from the fires and to a lesser extent by ozone and other greenhouse gases produced and released from the fires. Sensitivity studies with varying aerosol emission scenarios indicate that the ratio of black to organic carbon aerosol emissions of the boreal fires used in this study needs to be increased considerably to match both observations of aerosol optical depth and TOA radiation fluxes, or the biomass burning aerosols must be considerably more absorbing than parameterized in the model. While this study cannot resolve the cause of this discrepancy, it presents a powerful methodology to constrain aerosol emissions. This methodology will benefit from future improvements in measurements and modeling techniques. 0305 Aerosols and particles; 3359 Radiative processes; radiative forcing; 1637 Regional climate change; 0322 Constituent sources and sinks; boreal fires; carbonaceous aerosols
Pincus, Robert; Batstone, Crispian P.; Hofmann, Robert J. Patrick; Taylor, Karl E.; Glecker, Peter J.Pincus, R., C. P. Batstone, R. J. P. Hofmann, K. E. Taylor, P. J. Glecker, 2008: Evaluating the present-day simulation of clouds, precipitation, and radiation in climate models. Journal of Geophysical Research: Atmospheres, 113(D14), D14209. doi: 10.1029/2007JD009334. This paper describes a set of metrics for evaluating the simulation of clouds, radiation, and precipitation in the present-day climate. As with the skill scores used to measure the accuracy of short-term weather forecasts, these metrics are low-order statistical measures of agreement with relevant, well-observed physical quantities. The metrics encompass five statistical summaries computed for five physical quantities (longwave, shortwave, and net cloud radiative effect, projected cloud fraction, and surface precipitation rate) over the global climatological annual cycle. Agreement is measured against two independent observational data sets. The metrics are computed for the models that participated in the Coupled Model Intercomparison Project phase 3, which formed the basis for the Fourth Assessment of the IPCC. Model skill does not depend strongly on the data set used for verification, indicating that observational uncertainty does not limit the ability to assess model simulations of these fields. No individual model excels in all scores though the “IPCC mean model,” constructed by averaging the fields produced by all the CMIP models, performs particularly well across the board. This skill is due primarily to the individual model errors being distributed on both sides of the observations, and to a lesser degree to the models having greater skill at simulating large-scale features than those near the grid scale. No measure of model skill considered here is a good predictor of the strength of cloud feedbacks under climate change. The model climatologies, observational data sets, and metric scores are available on-line. 3311 Clouds and aerosols; climate model; 1626 Global climate models; 0550 Model verification and validation; Metrics
Quaas, Johannes; Boucher, Olivier; Bellouin, Nicolas; Kinne, StefanQuaas, J., O. Boucher, N. Bellouin, S. Kinne, 2008: Satellite-based estimate of the direct and indirect aerosol climate forcing. Journal of Geophysical Research: Atmospheres, 113(D5), D05204. doi: 10.1029/2007JD008962. The main uncertainty in anthropogenic forcing of the Earth's climate stems from pollution aerosols, particularly their “indirect effect” whereby aerosols modify cloud properties. We develop a new methodology to derive a measurement-based estimate using almost exclusively information from an Earth radiation budget instrument (CERES) and a radiometer (MODIS). We derive a statistical relationship between planetary albedo and cloud properties, and, further, between the cloud properties and column aerosol concentration. Combining these relationships with a data set of satellite-derived anthropogenic aerosol fraction, we estimate an anthropogenic radiative forcing of −0.9 ± 0.4 Wm−2 for the aerosol direct effect and of −0.2 ± 0.1 Wm−2 for the cloud albedo effect. Because of uncertainties in both satellite data and the method, the uncertainty of this result is likely larger than the values given here which correspond only to the quantifiable error estimates. The results nevertheless indicate that current global climate models may overestimate the cloud albedo effect. 1640 Remote sensing; 0305 Aerosols and particles; climate change; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; 3305 Climate change and variability; radiative forcing; aerosol indirect effects
Rondanelli, Roberto; Lindzen, Richard S.Rondanelli, R., R. S. Lindzen, 2008: Observed variations in convective precipitation fraction and stratiform area with sea surface temperature. Journal of Geophysical Research: Atmospheres, 113(D16), D16119. doi: 10.1029/2008JD010064. This paper focuses on the relation between local sea surface temperature (SST) and convective precipitation fraction and stratiform rainfall area from radar observations of precipitation, using data from the Kwajalein atoll ground-based radar as well as the precipitation radar on board the TRMM satellite. We find that the fraction of convective precipitation increases with SST at a rate of about 6 to 12%/K and the area of stratiform rainfall normalized by total precipitation decreases with SST at rates between −5 and −28%/K. These relations are observed to hold for different regions over the tropical oceans and also for different periods of time. Correlations are robust to outliers and to undersampled precipitation regions. Kwajalein results are relatively insensitive to the parameters in the stratiform-convective classification algorithm. Quantitative differences between the results obtained using the two different radars could be explained by the smoothing in the reflectivity of convective regions due to the relatively large pixel size of the TRMM precipitation radar compared to the size of the convective clouds. Although a dependence on temperature such as the one documented is consistent with an increase in the efficiency of convective precipitation (and therefore consistent with one of the mechanisms invoked to explain the original Iris effect observations) this is but one step in studying the possibility of a climate feedback. Further work is required to clarify the particular mechanism involved. 3374 Tropical meteorology; 3310 Clouds and cloud feedbacks; tropical precipitation; 1853 Precipitation-radar
Stone, R. S.; Anderson, G. P.; Shettle, E. P.; Andrews, E.; Loukachine, K.; Dutton, E. G.; Schaaf, C.; Roman, M. O.Stone, R. S., G. P. Anderson, E. P. Shettle, E. Andrews, K. Loukachine, E. G. Dutton, C. Schaaf, M. O. Roman, 2008: Radiative impact of boreal smoke in the Arctic: Observed and modeled. Journal of Geophysical Research: Atmospheres, 113(D14), D14S16. doi: 10.1029/2007JD009657. The Arctic climate is modulated, in part, by the presence of aerosols that affect the horizontal and vertical distribution of radiant energy passing through the atmosphere. Aerosols affect the surface-atmosphere radiation balance directly through interactions with solar and terrestrial radiation and indirectly through interactions with cloud particles. During summer 2004 forest fires destroyed vast areas of boreal forest in Alaska and western Canada, releasing smoke into the atmosphere. Smoke aerosol passing over instrumented field sites near Barrow, Alaska, was monitored to determine its physical and optical properties and its impact on the surface radiation budget. Empirical determinations of the direct aerosol radiative forcing (DARF) by the smoke were used to corroborate simulations made using the Moderate Resolution Transmittance radiative transfer model, MODTRAN™5. DARF is defined as the change in net shortwave irradiance per unit of aerosol optical depth (AOD). DARF, varying with solar angle and surface type, was evaluated at the surface, at the top of the atmosphere (TOA), and within the intervening layers of the atmosphere. The TOA results are compared with fluxes derived from coincident satellite retrievals made using the Clouds and the Earth's Radiant Energy System (CERES) radiance data. Smoke tends to reduce the net shortwave irradiance at the surface while increasing it within layers in which it resides. Over the Arctic tundra during summer, a layer of smoke having AOD = 0.5 at 500 nm produces a diurnally averaged DARF of about −40 W m−2 at the surface and −20 W m−2 at TOA, while the layer itself tends to warm at a rate of ≈1 K d−1. The tendency of smoke to cool the surface while heating the layer above may lead to increased atmospheric stability and suppress cloud formation. Radiative forcing at the top of the atmosphere is especially sensitive to small changes in surface albedo, evidenced in both the model results and satellite retrievals. TOA net shortwave flux decreases when smoke is present over dark surfaces and tends to increase if the underlying surface is bright. For example, at solar noon during midsummer at Barrow, a layer of smoke having AOD(500) = 0.5 will reduce the net shortwave flux at TOA by ≈30 W m−2 over the ocean while at the same time increasing it by 20 W m−2 over an adjacent area of melting sea ice. For smoke aerosol, the sensitivity of DARF to changing surface albedo (assuming a solar zenith angle of 50°) is about +15 W m−2 AOD−1 for every increase in surface albedo of 0.10. Throughout the Arctic summer, surface and TOA cooling and a tendency toward warming in the intervening atmospheric layers are the dominant radiative impacts of boreal smoke over the ocean and tundra areas, but the radiative forcing at TOA is positive over regions covered by ice or snow. Enhanced differential cooling/heating of ocean, ice, and snow due to the presence of smoke in the atmosphere may affect regional circulation patterns by perturbing diabatic processes. Should the frequency and intensity of boreal fires increase in the future because of global warming, the more persistent presence of smoke in the atmosphere may be manifest as a negative feedback at the surface. In addition, there will likely be indirect radiative impacts of the smoke as it influences cloudiness, which in turn further modulates the Arctic radiation budget. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; radiative forcing; 1637 Regional climate change; Aerosol optical depth; 0758 Remote sensing; Arctic climate change; boreal smoke; MODTRAN™
Su, J.; Jianping Huang; Qiang Fu; Minnis, P.; Jinming Ge; Jianrong BiSu, J., . Jianping Huang, . Qiang Fu, P. Minnis, . Jinming Ge, . Jianrong Bi, 2008: Estimation of Asian dust aerosol effect on cloud radiation forcing using Fu-Liou radiative model and CERES measurements. Atmos. Chem. Phys., 8(10), 2763-2771. doi: 10.5194/acp-8-2763-2008. The impact of Asian dust on cloud radiative forcing during 2003–2006 is studied by using the Clouds and Earth's Radiant Energy Budget Scanner (CERES) data and the Fu-Liou radiative transfer model. Analysis of satellite data shows that the dust aerosol significantly reduced the cloud cooling effect at TOA. In dust contaminated cloudy regions, the 4-year mean values of the instantaneous shortwave, longwave and net cloud radiative forcing are −138.9, 69.1, and −69.7 Wm−2, which are 57.0, 74.2, and 46.3%, respectively, of the corresponding values in pristine cloudy regions. The satellite-retrieved cloud properties are significantly different in the dusty regions and can influence the radiative forcing indirectly. The contributions to the cloud radiation forcing by the dust direct, indirect and semi-direct effects are estimated using combined satellite observations and Fu-Liou model simulation. The 4-year mean value of combination of dust indirect and semi-direct shortwave radiative forcing (SWRF) is 82.2 Wm−2, which is 78.4% of the total dust effect. The dust direct effect is only 22.7 Wm−2, which is 21.6% of the total effect. Because both first and second indirect effects enhance cloud cooling, the aerosol-induced cloud warming is mainly the result of the semi-direct effect of dust.
Su, Wenying; Dutton, Ellsworth; Charlock, Thomas P.; Wiscombe, WarrenSu, W., E. Dutton, T. P. Charlock, W. Wiscombe, 2008: Performance of Commercial Radiometers in Very Low Temperature and Pressure Environments Typical of Polar Regions and of the Stratosphere: A Laboratory Study. J. Atmos. Oceanic Technol., 25(4), 558-569. doi: 10.1175/2007JTECHA1005.1. Abstract Characterizing the performance of ground-based commercial radiometers in cold and/or low-pressure environments is critical for developing accurate flux measurements in the polar regions and in the upper troposphere and stratosphere. Commercially available broadband radiometers have a stated operational temperature range of, typically, −20° to +50°C. Within this range, their temperature dependencies of sensitivities change less than 1%. But for deployments on high-altitude platforms or in polar regions, which can be much colder than −20°C, information on temperature dependency of sensitivity is not always available. In this paper, the temperature dependencies of sensitivities of popular pyranometers and pyrgeometers manufactured by Kipp and Zonen were tested in a thermal-vacuum chamber. When their body temperature is lowered to −60°C, pyranometer sensitivity drops by 4%–6% from the factory-default specification. Pyrgeometer sensitivity increases by 13% from the factory-default specification during a similar temperature change. When the chamber pressure is lowered from 830 to 6 hPa, the sensitivity decreases by about 2% for the pyranometer, and increases by about 2% for the pyrgeometer. Note that these temperature and pressure dependencies of sensitivities are specific for the instruments that were tested and should not be applied to others. These findings show that for measurements suitable for climate studies, it is crucial to characterize temperature and/or pressure effects on radiometer sensitivity for deployments on high-altitude platforms and in polar regions. temperature; instrumentation; Arctic; Pressure; Stratosphere
Su, Wenying; Schuster, Gregory L.; Loeb, Norman G.; Rogers, Raymond R.; Ferrare, Richard A.; Hostetler, Chris A.; Hair, Johnathan W.; Obland, Michael D.Su, W., G. L. Schuster, N. G. Loeb, R. R. Rogers, R. A. Ferrare, C. A. Hostetler, J. W. Hair, M. D. Obland, 2008: Aerosol and cloud interaction observed from high spectral resolution lidar data. Journal of Geophysical Research: Atmospheres, 113(D24), D24202. doi: 10.1029/2008JD010588. Recent studies utilizing satellite retrievals have shown a strong correlation between aerosol optical depth (AOD) and cloud cover. However, these retrievals from passive sensors are subject to many limitations, including cloud adjacency (or three-dimensional) effects, possible cloud contamination, uncertainty in the AOD retrieval. Some of these limitations do not exist in High Spectral Resolution Lidar (HSRL) observations; for instance, HSRL observations are not affected by cloud adjacency effects, are less prone to cloud contamination, and offer accurate aerosol property measurements (backscatter coefficient, extinction coefficient, lidar ratio, backscatter Angstrom exponent, and aerosol optical depth) at a fine spatial resolution ( 0305 Aerosols and particles; cloud; 3311 Clouds and aerosols; 3359 Radiative processes; aerosol
Sun, Wenbo; Hu, Yongxiang; Loeb, N.G.; Lin, Bing; Mlynczak, M.G.Sun, W., Y. Hu, N. Loeb, B. Lin, M. Mlynczak, 2008: Using CERES Data to Evaluate the Infrared Flux Derived From Diffusivity Approximation. IEEE Geoscience and Remote Sensing Letters, 5(1), 17-20. doi: 10.1109/LGRS.2007.905198. Based on the diffusivity approximation theory, the infrared flux at the top of atmosphere (TOA) can be obtained by multiplying a factor of pi on the infrared radiance that was measured at a viewing zenith angle (VZA) of 53deg. This letter applies the diffusivity approximation on radiance measurements of the Clouds and the Earth's Radiant Energy System (CERES) to derive TOA infrared fluxes and compares these fluxes with the state-of-the-art CERES outgoing radiative fluxes. We find that the mean difference between the two kinds of instantaneous flux that were estimated at the window channel is 1 Wmiddotm-2, with a root-mean-square error of 1.7 Wmiddotm-2. This result shows that radiance measurement at a fixed VZA of 53 deg is a simple and effective method in the remote sensing of the infrared flux for satellite missions that monitor some specific climate processes and require longwave/window TOA fluxes, such as the Broad Band Radiometer instrument on EarthCARE; however, this approach may involve errors from an inhomogeneous scene or non-Lambertian emission of the surface. A careful design of the VZA and scan mode, such as a conical scan at 53deg, would produce much more convenient infrared flux measurements for the Earth-atmosphere system than other designs. Remote sensing; atmospheric radiation; Clouds and the Earth's Radiant Energy System; EarthCARE; CERES data; Clouds and the Earth's Radiant Energy System (CERES); Broad Band Radiometer instrument; climate processes; diffusivity approximation; diffusivity approximation theory; Earth-atmosphere system; infrared flux; infrared radiance; nonLambertian emission; outgoing radiative fluxes; root-mean-square error; satellite missions; top-of-atmosphere infrared fluxes; viewing zenith angle
Trenberth, Kevin E.; Fasullo, John T.Trenberth, K. E., J. T. Fasullo, 2008: An Observational Estimate of Inferred Ocean Energy Divergence. J. Phys. Oceanogr., 38(5), 984-999. doi: 10.1175/2007JPO3833.1. Abstract Monthly net surface energy fluxes (FS) over the oceans are computed as residuals of the atmospheric energy budget using top-of-atmosphere (TOA) net radiation (RT) and the complete atmospheric energy (AE) budget tendency (δAE/δt) and divergence (∇ · FA). The focus is on TOA radiation from the Earth Radiation Budget Experiment (ERBE) (February 1985–April 1989) and the Clouds and Earth’s Radiant Energy System (CERES) (March 2000–May 2004) satellite observations combined with results from two atmospheric reanalyses and three ocean datasets that enable a comprehensive estimate of uncertainties. Surface energy flux departures from the annual mean and the implied annual cycle in “equivalent ocean energy content” are compared with the directly observed ocean energy content (OE) and tendency (δOE/δt) to reveal the inferred annual cycle of divergence (∇ · FO). In the extratropics, the surface flux dominates the ocean energy tendency, although it is supplemented by ocean Ekman transports that enhance the annual cycle in ocean heat content. In contrast, in the tropics, ocean dynamics dominate OE variations throughout the year in association with the annual cycle in surface wind stress and the North Equatorial Current. An analysis of the regional characteristics of the first joint empirical orthogonal function (EOF) of FS, δOE/δt, and ∇ · FO is presented, and the largest sources of uncertainty are attributed to variations in OE. The mean and annual cycle of zonal mean global ocean meridional heat transports are estimated. The annual cycle reveals the strongest poleward heat transports in each hemisphere in the cold season, from November to April in the north and from May to October in the south, with a substantial across-equatorial transport, exceeding 4 PW in some months. Annual mean results do not differ greatly from some earlier estimates, but the sources of uncertainty are exposed. Comparison of annual means with direct ocean observations gives reasonable agreement, except in the North Atlantic, where transports from the ocean transects are slightly greater than the estimates presented here. Radiation budgets; Energy transport; Ocean dynamics
Trenberth, Kevin E.; Smith, LesleyTrenberth, K. E., L. Smith, 2008: Atmospheric Energy Budgets in the Japanese Reanalysis : Evaluation and Variability. Journal of the Meteorological Society of Japan. Ser. II, 86(5), 579-592. The vertically-integrated atmospheric energy and moisture budgets have been computed for all available months for the Japanese reanalysis (1979 to 2004), and results are described in detail for the month of January 1989 and compared with those of other reanalyses. Time series are also presented. The moistening, diabatic heating and total energy forcing of the atmosphere are computed as a residual from the analyses using the moisture, dry energy (dry static energy plus kinetic energy) and total atmospheric (moist static plus kinetic) energy budget equations. These fields are also computed from the model output based on the assimilating model parameterizations. Moreover, some component fields can also be computed from observations to evaluate the results. In particular, when the vertically-integrated forcings computed from the model parameterizations are compared with available observations and the budget-derived values, significant JRA model biases are revealed in radiation and precipitation. The energy and moisture budget-derived quantities are more realistic than the model output and better depict the real atmosphere. However, low frequency decadal variability is spurious and is mainly associated with changes in the observing system. Results also depend on the quality of the analyses which are not constructed to conserve mass, moisture or energy, owing to analysis increments. Although there has been considerable progress in depicting the diabatic components of the atmosphere, some problems remain, and suggestions are made on where research can make further improvements.
White, Jeffrey W.; Hoogenboom, Gerrit; Stackhouse Jr., Paul W.; Hoell, James M.White, J. W., G. Hoogenboom, P. W. Stackhouse Jr., J. M. Hoell, 2008: Evaluation of NASA satellite- and assimilation model-derived long-term daily temperature data over the continental US. Agricultural and Forest Meteorology, 148(10), 1574-1584. doi: 10.1016/j.agrformet.2008.05.017. Agricultural research increasingly is expected to provide precise, quantitative information with an explicit geographic coverage. Limited availability of daily meteorological records often constrains efforts to provide such information through use of simulation models, spatial analysis, and related decision support tools. The Prediction Of Worldwide Energy Resources (NASA/POWER) project at the NASA Langley Research Center provides daily data globally for maximum and minimum temperatures and other weather variables on a 1° latitude–longitude grid. The data are assembled from a range of products derived from satellite imagery, ground observations, windsondes, modeling and data assimilation. Daily temperature data from NASA/POWER for 1983 to 2004 for the continental US were compared with data of 855 individual ground stations from the National Weather Service Cooperative Observer Program (COOP). Additionally, a wheat (Triticum aestivum L.) simulation model was used to compare predicted time to anthesis using the two data sources. Comparisons of daily maximum temperatures (Tmax) gave an r2-value of 0.88 (P < 0.001) and root-mean-squared error (RMSE) of 4.1 °C. For minimum temperature (Tmin), the r2-value was 0.88 (P < 0.001) and RMSE, 3.7 °C. Mean values of Tmax, and Tmin from NASA/POWER were, respectively, 2.4 °C cooler and 1.1 °C warmer than the COOP data. Differences in temperature were least during summer months. When data were aggregated over periods of 8 days or more, the RMSE values declined to below 2.7 °C for Tmax and Tmin. Simulations of time to anthesis with the two data sources were also strongly correlated (r2 = 0.92, P < 0.001, RMSE = 14.5 d). Anthesis dates of winter wheat regions showed better agreement than southern, winter-grown spring wheat regions. The differences between the data sources were associated with differences in elevation, which in large part resulted from NASA/POWER data being based on mean elevations over a 1° grid cells vs. COOP data corresponding to the elevation of specific stations. Additional sources of variation might include proximity to coastlines and differences in observation time, although these factors were not quantified. Overall, if mountainous and coastal regions are excluded, the NASA/POWER data appeared promising as a source of continuous daily temperature data for the USA for research and management applications concerned with scales appropriate to the 1° coordinate grid. It further appeared that the POWER data could be improved by adjusting for elevation (lapse rate) effects, reducing seasonal bias, and refining estimation of actual maximum and minimum temperatures in diurnal cycles. Decision support systems; Phenology; Triticum aestivum
Xu, K. M.; Wong, T.; Wielicki, B. A.; Parker, L.Xu, K. M., T. Wong, B. A. Wielicki, L. Parker, 2008: Statistical analyses of satellite cloud object data from CERES. Part IV: Boundary layer cloud objects during 1998 El Nino. J. Climate, 21(7), 1500-1521. doi: 10.1175/2007jcli1710.1. Three boundary layer cloud object types-overcast, stratocumulus, and cumulus-that occurred over the Pacific Ocean during January-August 1998 are identified from the Clouds and the Earth's Radiant Energy System (CERES) single scanner footprint data. Characteristics of each cloud object type matched with atmospheric states are examined for large regions in the tropics and subtropics and for different size categories. Stratocumulus cloud objects dominate the entire boundary layer cloud population in all regions and size categories. Overcast cloud objects, which have the largest average size, are more prevalent in the subtropics and near the coastal regions, while cumulus cloud objects are prevalent over the open oceans and the equatorial regions, particularly within the small-size categories. Cloud objects with equivalent diameters less than 75 km are excluded in the analysis. The differences between the tropical and subtropical statistical distributions of cloud properties are small for liquid water path (LWP), cloud optical depth, and top-of-the-atmosphere (TOA) albedo, but large for cloud-top temperature and outgoing longwave radiation (OLR), for each of the three cloud object types. The larger cloud objects have higher LWPs, cloud optical depths, TOA albedos, and OLRs, but lower SSTs and cloud-top heights for the stratocumulus and overcast types. Lower-tropospheric stability seems to be the primary factor for the differences in the distributions of cloud physical properties between the regions or between the size categories. Atmospheric dynamics also play a role in determining the differences in the distributions of cloud physical properties between the size categories, but not a significant role for those between the types or between the regions. The latter may be due to uncertainties in the matched vertical velocity data. When the three cloud object types are combined in small regions, lower-tropospheric stability determines the transition of boundary layer cloud types along a Pacific transect. The proportion of each type is the most important factor for diagnosing the combined cloud properties along this transect, such as LWP, cloud optical depth, and TOA albedo. Atmospheric dynamics also play complicated roles in determining the combined cloud properties along this transect.
Yang, Kun; Pinker, Rachel T.; Ma, Yaoming; Koike, Toshio; Wonsick, Margaret M.; Cox, Stephen J.; Zhang, Yuanchong; Stackhouse, PaulYang, K., R. T. Pinker, Y. Ma, T. Koike, M. M. Wonsick, S. J. Cox, Y. Zhang, P. Stackhouse, 2008: Evaluation of satellite estimates of downward shortwave radiation over the Tibetan Plateau. Journal of Geophysical Research: Atmospheres, 113(D17), D17204. doi: 10.1029/2007JD009736. The state-of-the-art satellite products of downward shortwave radiation over the Tibetan Plateau against ground observations are evaluated in this study. The satellite products include the International Satellite Cloud Climatology Project-Flux Data (ISCCP-FD) as produced at the NASA Goddard Institute for Space Studies (GISS) from the ISCCP D1 data, the Global Energy and Water Cycle Experiment-Surface Radiation Budget (GEWEX-SRB) results as derived at the NASA Langley Research Center (LaRC) from the ISCCP DX data, and a University of Maryland product derived with a modified version of the University of Maryland Surface Radiation Budget (UMD-SRB) model as implemented with METEOSAT-5 observations. These products are at different spatial and temporal resolutions, and the evaluation is performed at their native resolutions. Comparisons indicate that, in this region of great variation in elevation, using hourly, spatially homogeneous, and high resolution satellite data (UMD-SRB) compares more favorably with surface measurements than products that use three hourly, sparse subsamples at coarse resolutions (ISCCP-FD and GEWEX-SRB). Discrepancies among the satellite products are usually larger in highly variable terrain (such as in the Himalayas region) and smaller for nonvariable terrain (such as in the central Plateau). This suggests that errors of satellite products are spatially dependent over the Tibet. Therefore caution needs to be exercised when extending comparison results based on limited in situ data from accessible sites to the entire Plateau. Attention should be also given to the quality of input parameters besides cloud properties, as there are large discrepancies among the satellite products for clear-sky radiation. satellite remote sensing; 3311 Clouds and aerosols; 3359 Radiative processes; Shortwave radiation; Tibetan Plateau; 3322 Land/atmosphere interactions; 3333 Model calibration
Yuan, Jian; Hartmann, Dennis L.Yuan, J., D. L. Hartmann, 2008: Spatial and temporal dependence of clouds and their radiative impacts on the large-scale vertical velocity profile. Journal of Geophysical Research: Atmospheres, 113(D19), D19201. doi: 10.1029/2007JD009722. The structure of tropical large-scale vertical velocity from the European Centre for Medium-Range Weather Forecasts Re-Analysis is compared with simultaneous satellite measurements of precipitation, top of atmosphere radiation, and clouds from the Tropical Rainfall Measuring Mission (TRMM) on timescales ranging from hours to months. The first two empirical orthogonal functions of the vertical velocity profile represent the traditional deep circulation (PC1) and a shallower circulation (PC2) associated with middle-level divergence. Together they explain 90% of total variance and can distinguish two types of upward and downward motion: “top heavy” and “bottom heavy.” Cloud and radiation budget quantities measured on TRMM have coherent relationships to PC1 and PC2 on all timescales from simultaneous to long-term means. The relative importance of PC2 is greater on short temporal and small spatial scales. “Top heavy” ascent is associated with deep cloud systems, more intense precipitation, lower outgoing long-wave radiation, stronger cloud long-wave forcing, and extensive anvils. Cloud short-wave forcing depends primarily on PC1, while the net cloud forcing depends more on PC2. High-thin clouds are less correlated with short-term variations of the vertical velocity. Shallow precipitation measured by TRMM precipitation radar is associated with “bottom heavy” upward motion. Temporal compositing with respect to intense precipitating events shows that strong upward motions tend to develop in the lower atmosphere first and then change to the more “top heavy” type of upward motion. The associated cloud systems show consistent temporal changes in which high-thick clouds develop first and extensive anvil clouds develop later. These results suggest that the elevated latent heating from stratiform precipitation and the development of “top heavy” upward motion profiles in the tropics are related to each other. The coherent relationships shown here between large-scale vertical velocity and independently measured cloud and precipitation data can be used to test the performance of climate models. clouds; 1620 Climate dynamics; 3310 Clouds and cloud feedbacks; 3314 Convective processes; 3329 Mesoscale meteorology; cloud radiative impact; large-scale vertical velocity profiles
Yuan, Jian; Hartmann, Dennis L.; Wood, RobertYuan, J., D. L. Hartmann, R. Wood, 2008: Dynamic Effects on the Tropical Cloud Radiative Forcing and Radiation Budget. J. Climate, 21(11), 2337-2351. doi: 10.1175/2007JCLI1857.1. Abstract Vertical velocity is used to isolate the effect of large-scale dynamics on the observed radiation budget and cloud properties in the tropics, using the methodology suggested by Bony et al. Cloud and radiation budget quantities in the tropics show well-defined responses to the large-scale vertical motion at 500 hPa. For the tropics as a whole, the ratio of shortwave to longwave cloud forcing (hereafter N) is about 1.2 in regions of upward motion, and increases to about 1.9 in regions of strong subsidence. If the analysis is restricted to oceanic regions with SST > 28°C, N does not increase as much for subsiding motions, because the stratocumulus regions are eliminated, and the net cloud forcing decreases linearly from about near zero for zero vertical velocity to about −15 W m−2 for strongly subsiding motion. Increasingly negative cloud forcing with increasing upward motion is mostly related to an increasing abundance of high, thick clouds. Although a consistent dynamical effect on the annual cycle of about 1 W m−2 can be identified, the effect of the probability density function (PDF) of the large-scale vertical velocity on long-term trends in the tropical mean radiation budget is very small compared to the observed variations. Observed tropical mean changes can be as large as ±3 W m−2, while the dynamical components are generally smaller than ±0.5 W m−2. For relatively small regions in the east and west Pacific, changes in the relative magnitude of longwave and shortwave cloud forcing can be related to the PDF of vertical velocity. The east Pacific in 1987 and 1998 showed large reductions of N in association with an increase in the fraction of the area in the domain with upward motion, and concomitant increases in high cloud. For the west Pacific in 1998, a large increase in N was caused not so much by a change in the mean vertical motion, but rather by a shift from top- to bottom-heavy upward motion. tropics; Radiation budgets; Cloud radiative effects; cloud forcing; Dynamics
Zell, E.; Engel-Cox, J.; Eckman, R.; Stackhouse, P.Zell, E., J. Engel-Cox, R. Eckman, P. Stackhouse, 2008: Application of Satellite Sensor Data and Models for Energy Management. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 1(1), 5-17. doi: 10.1109/JSTARS.2008.2001142. Effective, environmentally sound development, production, and delivery of energy depend on Earth monitoring information. Satellite remote sensing data and products provide unique, objective information that has the additional advantage of yielding global, homogeneous, and repetitive coverage. Satellite remote sensing data and products have been used extensively in parts of the energy sector for applications ranging from climatology to identification of solar and wind energy sources, yet there is significant potential to expand energy applications. This paper discusses the key energy sector organizations and decision-support tools with the greatest potential to benefit from new applications of satellite remote sensing data, identifies relevant remote sensing data and products with a focus on NASA Earth science resources, and provides examples that show the added value of the Earth observations. These examples come from the application of NASA data to solar energy information needs. Although continued work for support of solar energy is warranted, this paper focuses on areas identified with the greatest demonstrated potential for new or expanded applications: renewable energy (specifically wind, biomass, and hydroelectric resources), load forecasting, and long-term energy modeling. This study also addresses the evolving context of the Global Earth Observation System of Systems (GEOSS), and the broader framework of integrating satellite remote sensing into energy sector decision-support tools. Remote sensing; Satellites; NASA; artificial satellites; solar energy; Acoustic sensors; biofuel; biomass resource; decision support tools; Earth monitoring information; ecology; energy delivery; energy development; Energy management; energy production; energy sector organizations; Geoscience; GEOSS; Global Earth Observation System of Systems; hydroelectric power; hydroelectric resource; load forecasting; long term energy modeling; NASA Earth science resources; Remote monitoring; renewable energy; satellite remote sensing data; satellite remote sensing products; satellite sensor data; solar power; sustainable development; wind energy; wind power; wind resource
Zhao, T. X. P.; Yu, H. B.; Laszlo, I.; Chin, M.; Conant, W. C.Zhao, T. X. P., H. B. Yu, I. Laszlo, M. Chin, W. C. Conant, 2008: Derivation of component aerosol direct radiative forcing at the top of atmosphere for clear-sky oceans. Journal of Quantitative Spectroscopy & Radiative Transfer, 109(7), 1162-1186. doi: 10.1016/j.jqsrt.2007.10.006. A two-step approach is proposed to derive component aerosol direct radiative forcing (ADRF) at the top of atmosphere (TOA) over global oceans from 60 degrees S to 60 degrees N for clear-sky condition by combining Terra CERES/MODIS-SSF shortwave (SW) flux and aerosol optical thickness (AOT) observations with the fractions of component AOTs from the GSFC/GOCART model. The derived global annual mean component ADRF is +0.08 +/- 0.17 W/m(2) for black carbon, -0.52 +/- 0.24 W/m(2) for organic carbon, -1.10 +/- 0.42 W/m(2) for sulfate, -0.99 +/- 0.37 W/m(2) for dust, -2.44 +/- 0.84 W/m(2) for sea salt, and -4.98 +/- 1.67 W/m(2) for total aerosols. The total ADRF has also been partitioned into anthropogenic and natural components with a value of -1.25 +/- 0.43 and -3.73 +/- 1.27 W/m(2), respectively. The major sources of error in the estimates have also been discussed. The analysis adds an alternative technique to narrow the large difference between current model-based and observation-based global estimates of component ADRF by combining the satellite measurement with the model simulation. (c) 2007 Elsevier Ltd. All rights reserved.
Zhao, Tom X.-P.; Laszlo, Istvan; Guo, Wei; Heidinger, Andrew; Cao, Changyong; Jelenak, Aleksandar; Tarpley, Dan; Sullivan, JerryZhao, T. X., I. Laszlo, W. Guo, A. Heidinger, C. Cao, A. Jelenak, D. Tarpley, J. Sullivan, 2008: Study of long-term trend in aerosol optical thickness observed from operational AVHRR satellite instrument. Journal of Geophysical Research: Atmospheres, 113(D7), D07201. doi: 10.1029/2007JD009061. The long-term trend of aerosol optical thickness (AOT) over the global oceans has been studied by using a nearly 25-year aerosol record from the Advanced Very High Resolution Radiometer (AVHRR) Pathfinder Atmosphere extended (PATMOS-x) data set. Both global and regional analyses have been performed to derive the AOT tendencies for monthly, seasonal, and annual mean AOT values at AVHRR 0.63 μm channel (or Channel-1). A linear decadal change of −0.01 is obtained for globally and monthly averaged aerosol optical thickness, τ1, of AVHRR Channel-1. This negative tendency is even more evident for globally and annually averaged τ1 and the magnitude can be up to −0.03/decade. Seasonal patterns in the AOT regional long-term trend are evident. In general, negative tendencies are observed for seasonally averaged τ1 in regions influenced by emissions from industrialized countries and the magnitude can be up to −0.10/decade. Positive tendencies are observed in regions influenced by emissions from fast developing countries and the magnitude can be up to +0.04/decade. For regions heavily influenced by Saharan desert particles, a negative trend with a maximum magnitude of −0.03/decade is detected. However, over regions influenced by smoke from biomass burning, positive tendencies with a maximum magnitude of +0.04/decade are observed. Sensitivity analyses have also been performed to study the effects of radiance calibration, aerosol retrieval algorithm, and spatial resolution of input retrieval radiances on the global aerosol long-term tendencies. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 0345 Pollution: urban and regional; 4801 Aerosols; 0365 Troposphere: composition and chemistry; aerosol optical thickness; AVHRR; Long term trend
Allan, Richard P.Allan, R. P., 2007: Improved simulation of water vapour and clear-sky radiation using 24-hour forecasts from ERA40. Tellus A, 59(3), 336-343. doi: 10.1111/j.1600-0870.2007.00229.x. Monthly mean water vapour and clear-sky radiation extracted from the European Centre for Medium Range Weather Forecasts 40-year reanalysis (ERA40) forecasts are assessed using satellite observations and additional reanalysis data. There is a marked improvement in the interannual variability of column-integrated water vapour (CWV) over the oceans when using the 24-hour forecasts compared with the standard 6-hour forecasts products. The spatial distribution of CWV are well simulated by the 6-hour forecasts; using the 24-hour forecasts does not degrade this simulation substantially and in many cases improves on the quality. There is also an improved simulation of clear-sky radiation from the 24-hour forecasts compared with the 6-hour forecasts based on comparison with satellite observations and empirical estimates. Further work is required to assess the quality of water vapour simulation by reanalyses over land regions. Over the oceans, it is recommended that 24-hour forecasts of CWV and clear-sky radiation are used in preference to the standard 6-hour forecast products from ERA40.
Allan, Richard PhilipAllan, R. P., 2007: Monitoring present day changes in water vapour and the radiative energy balance using satellite data, reanalyses and models. Joint 2007 EUMETSAT Meteorological Satellite Conference and the 15th Satellite Meteorology & Oceanography Conference of the American Meteorological Society, P.50. A combination of satellite data, reanalysis products and climate models are combined to monitor changes in water vapour, clear-sky radiative cooling of the atmosphere and precipitation over the period 1979-2006. Climate models are able to simulate observed increases in column integrated water vapour (CWV) with surface temperature (Ts) over the ocean. Changes in the observing system lead to spurious variability in water vapour and clear-sky longwave radiation in reanalysis products. Nevertheless all products considered exhibit a robust increase in clear-sky longwave radiative cooling from the atmosphere to the surface; clear-sky longwave radiative cooling of the atmosphere is found to increase with Ts at the rate of ~4 Wm-2 K-1 over tropical ocean regions of mean descending vertical motion. Precipitation (P) is tightly coupled to atmospheric radiative cooling rates and this implies an increase in P with warming at a slower rate than the observed increases in CWV. Since convective precipitation depends on moisture convergence, the above implies enhanced precipitation over convective regions and reduced precipitation over convectively suppressed regimes. To quantify this response, observed and simulated changes in precipitation rate are analysed separately over regions of mean ascending and descending vertical motion over the tropics. The observed response is found to be substantially larger than the model simulations and climate change projections. It is currently not clear whether this is due to deficiencies in model parametrizations or errors in satellite retrievals.
Ben Rehouma, A.; Viollier, M.; Desbois, M.Ben Rehouma, A., M. Viollier, M. Desbois, 2007: Radiation budget estimates over Africa and surrounding oceans: inter-annual comparisons. Atmos. Chem. Phys., 7(10), 2617-2629. doi: 10.5194/acp-7-2617-2007. Three independent datasets of Radiation Budget at the top of the atmosphere (TOA) spanning two decades are compared: the Scanner Narrow Field of View data (from ERBE, ScaRaB, and CERES instruments, 1985–2005), the ERBS Nonscanner Wide Field of View data (1985–1998) and the simulated broadband fluxes from the International Satellite Cloud Climatology Project (ISCCP-FD, 1983–2004). The analysis concerns the shortwave (SW) reflected flux, the longwave (LW) emitted flux and the net flux at the Top Of the Atmosphere (TOA) over Africa and the surrounding oceans (45° S–45° N/60° W–60° E), a region particularly impacted by climate variability. For each month, local anomalies are computed with reference to the average over this large region, and their differences between the 2002–2005 and 1985–1989 periods are analysed. These anomalies are, for a large part, independent on the general observed trends (about 2.5 W m−2 per decade), which may be affected by possible calibration drifts. Although the regional flux anomalies can be related to calibration through the scene identification and the choice of the anisotropy correction, this effect is limited if the calibration drifts remains reasonable. Large inter-annual variations are observed locally. Over a part of the South East Atlantic (35°–10° S/10° W–10° E), including the marine low cloud area off Angola, there is a decrease of the yearly means of net flux estimated to 2.2, 3 and 6 W m−2 respectively for the Scanner, Nonscanner and ISCPP-FD data. Over a narrow strip of the Sahel Zone, the net flux increases by about 5 W m−2. We believe that these observations are real. They could be due to the impact of calibration drift but only if the drifts were significant (>4%) and correlated between the datasets, which is highly improbable.
Buriez, Jean-Claude; Parol, Frédéric; Poussi, Zegbeu; Viollier, MichelBuriez, J., F. Parol, Z. Poussi, M. Viollier, 2007: An improved derivation of the top-of-atmosphere albedo from POLDER/ADEOS-2: 2. Broadband albedo. Journal of Geophysical Research: Atmospheres, 112(D19), D19201. doi: 10.1029/2006JD008257. The narrowband albedos derived from Polarization and Directionality of Earth Reflectances (POLDER) measurements have been described in a companion paper (Buriez et al., 2005). Here, they are used to estimate the broadband shortwave albedo. Except for the gaseous absorption, the albedos at 443 and 670 nm are considered as representative of the UV-visible range, and the albedo at 865 nm is considered as representative of the near infrared. The gaseous absorption is estimated from TOMS data and from the POLDER 910- to 865-nm reflectance ratio. In a previous approach, the respective weights of the three narrowband albedos were based on radiative transfer simulations. Now, we take advantage of spatiotemporal coincidences between the second Advanced Earth Observing Satellite (ADEOS-2) and Terra to adjust these weights from the comparison between POLDER narrowband and CERES broadband reflectances. With no adjustment, the POLDER albedos are underestimated by 2% (in relative value) whereas the associated reflectances are underestimated by 4%. With an adjustment to the CERES reflectances, the POLDER shortwave albedos are overestimated by 2%. With or without adjustment the RMS difference between the POLDER and the CERES 1°-regional instantaneous shortwave albedos is 6%; this is quite satisfactory since it is comparable to the CERES SW albedo consistency between nadir and oblique viewing zenith angles. When considering only homogeneous areas, the agreement between POLDER and CERES estimates was rather less good in the previous approach; it is now more than twice better. The difference between POLDER and CERES shortwave albedo estimates appears, for a large part, due to our plane-parallel assumption that is crucial for the heterogeneous liquid water clouds. It results in a bias in monthly mean shortwave flux around 2 W m−2 that is found to present only small variations in latitude. 1610 Atmosphere; 1640 Remote sensing; CERES; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; POLDER; TOA SW albedo
Chepfer, H.; Minnis, P.; Dubuisson, P.; Chiriaco, M.; Sun-Mack, S.; Rivière, E. D.Chepfer, H., P. Minnis, P. Dubuisson, M. Chiriaco, S. Sun-Mack, E. D. Rivière, 2007: Nitric acid particles in cold thick ice clouds observed at global scale: Link with lightning, temperature, and upper tropospheric water vapor. Journal of Geophysical Research: Atmospheres, 112(D5), D05212. doi: 10.1029/2005JD006602. Signatures of nitric acid particles (NAP) in cold thick ice clouds have been derived from satellite observations. Most NAP are detected in the tropics (9 to 20% of clouds with T < 202.5 K). Higher occurrences were found in the rare midlatitudes very cold clouds. NAP occurrence increases as cloud temperature decreases, and NAP are more numerous in January than July. Comparisons of NAP and lightning distributions show that lightning seems to be the main source of the NOx, which forms NAP in cold clouds over continents. Qualitative comparisons of NAP with upper tropospheric humidity distributions suggest that NAP may play a role in the dehydration of the upper troposphere when the tropopause is colder than 195 K. 1640 Remote sensing; 0320 Cloud physics and chemistry; 0321 Cloud/radiation interaction; 3324 Lightning; global scale; ice clouds; nitric acid
Chiriaco, M.; Chepfer, H.; Minnis, P.; Haeffelin, M.; Platnick, S.; Baumgardner, D.; Dubuisson, P.; McGill, M.; Noël, V.; Pelon, J.; Spangenberg, D.; Sun-Mack, S.; Wind, G.Chiriaco, M., H. Chepfer, P. Minnis, M. Haeffelin, S. Platnick, D. Baumgardner, P. Dubuisson, M. McGill, V. Noël, J. Pelon, D. Spangenberg, S. Sun-Mack, G. Wind, 2007: Comparison of CALIPSO-Like, LaRC, and MODIS Retrievals of Ice-Cloud Properties over SIRTA in France and Florida during CRYSTAL-FACE. J. Appl. Meteor. Climatol., 46(3), 249-272. doi: 10.1175/JAM2435.1. Abstract This study compares cirrus-cloud properties and, in particular, particle effective radius retrieved by a Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO)-like method with two similar methods using Moderate-Resolution Imaging Spectroradiometer (MODIS), MODIS Airborne Simulator (MAS), and Geostationary Operational Environmental Satellite imagery. The CALIPSO-like method uses lidar measurements coupled with the split-window technique that uses the infrared spectral information contained at the 8.65-, 11.15-, and 12.05-μm bands to infer the microphysical properties of cirrus clouds. The two other methods, using passive remote sensing at visible and infrared wavelengths, are the operational MODIS cloud products (using 20 spectral bands from visible to infrared, referred to by its archival product identifier MOD06 for MODIS Terra) and MODIS retrievals performed by the Clouds and the Earth’s Radiant Energy System (CERES) team at Langley Research Center (LaRC) in support of CERES algorithms (using 0.65-, 3.75-, 10.8-, and 12.05-μm bands); the two algorithms will be referred to as the MOD06 and LaRC methods, respectively. The three techniques are compared at two different latitudes. The midlatitude ice-clouds study uses 16 days of observations at the Palaiseau ground-based site in France [Site Instrumental de Recherche par Télédétection Atmosphérique (SIRTA)], including a ground-based 532-nm lidar and the MODIS overpasses on the Terra platform. The tropical ice-clouds study uses 14 different flight legs of observations collected in Florida during the intensive field experiment known as the Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment (CRYSTAL-FACE), including the airborne cloud-physics lidar and the MAS. The comparison of the three methods gives consistent results for the particle effective radius and the optical thickness but discrepancies in cloud detection and altitudes. The study confirms the value of an active remote sensing method (CALIPSO like) for the study of subvisible ice clouds, in both the midlatitudes and Tropics. Nevertheless, this method is not reliable in optically very thick tropical ice clouds, because of their particular microphysical properties. Remote sensing; Cloud microphysics; cirrus clouds; Cloud retrieval; satellite observations
Christopher, Sundar A.; Jones, ThomasChristopher, S. A., T. Jones, 2007: Satellite-based assessment of cloud-free net radiative effect of dust aerosols over the Atlantic Ocean. Geophysical Research Letters, 34(2), L02810. doi: 10.1029/2006GL027783. Using eighteen months (June–August, 2000–2005) of spatially and temporally collocated Moderate Resolution Imaging Spectroradiometer (MODIS) and the Clouds and the Earth's Radiant Energy System (CERES) data from the Terra satellite over the Atlantic Ocean [10W–60W, 0–30N], we first separate the dust aerosol optical thickness at 0.55 μm (AOT) from the total column MODIS AOT. We then calculate the cloud-free TOA net radiative effect (NRE) of dust aerosols by accounting for diurnal effects and sample biases. The cloud-free NRE is −6.31 ± 1.16 Wm−2 and nearly twenty percent of the shortwave radiative effect (−7.75 ± 0.86 Wm−2) is cancelled by the longwave radiative effect (+1.44 ± 0.57 Wm−2) indicating the importance of the dust aerosols in the thermal portion of the electromagnetic spectrum. This is the first multi-year satellite-based assessment of the NRE of dust aerosols indicating the importance of both the shortwave and longwave radiative effects of dust aerosols over the oceans unlike anthropogenic aerosols that have negligible TOA longwave radiative forcing effects. 0305 Aerosols and particles; 3359 Radiative processes; Satellite; 4801 Aerosols; dust; CERES/MODIS
Fitzpatrick, Melanie F.; Warren, Stephen G.Fitzpatrick, M. F., S. G. Warren, 2007: The Relative Importance of Clouds and Sea Ice for the Solar Energy Budget of the Southern Ocean. J. Climate, 20(6), 941-954. doi: 10.1175/JCLI4040.1. Abstract The effects of clouds and sea ice on the solar radiation budget are determined for the Southern Ocean around Antarctica between latitudes 50° and 80°S. Distributions of cloud optical depth are used, together with distributions of surface albedo, to estimate the geographical and seasonal variations of shortwave irradiance and cloud radiative forcing at the surface, both for the present climate and for altered surface and cloud conditions. Poleward of 68°S in spring, ice causes a greater reduction of solar energy input to the surface than does cloud. However, in summer the clouds are more important than ice at all latitudes in the Southern Ocean. In the present climate the clouds are optically thicker over open water than over sea ice, suggesting a possible negative feedback if the sea ice area shrinks with climatic warming. Compared to the present climate in spring, removing sea ice results in an increase in irradiance reaching the ocean surface, regardless of the type of cloud remaining. However, in summer the removal of ice results in higher irradiance at the surface only if clouds remain unchanged. If clouds become as thick as those presently over the ocean at 55°–60°S, irradiance reaching the ocean surface in summer decreases poleward of 65°S. clouds; albedo; optical depth; Sea ice albedo; Solar energy budget
Huang, Yi; Ramaswamy, V.; Huang, Xianglei; Fu, Qiang; Bardeen, CharlesHuang, Y., V. Ramaswamy, X. Huang, Q. Fu, C. Bardeen, 2007: A strict test in climate modeling with spectrally resolved radiances: GCM simulation versus AIRS observations. Geophysical Research Letters, 34(24), L24707. doi: 10.1029/2007GL031409. The spectrally resolved infrared radiances observed by AIRS provide a strict and insightful test for general circulation models (GCMs). We compare the clear- and total- sky spectra simulated from the Geophysical Fluid Dynamics Laboratory GCM using a high resolution radiation code with the AIRS observations. After ensuring consistency in the sampling of the observed and simulated spectra and a proper representation of clouds in the radiance simulation, the observed and simulated global-mean radiances are shown to agree to within 2 K in the window region. Radiance discrepancies in the water vapor v2 (1300–1650 cm−1) and carbon dioxide v2 (650–720 cm−1) bands are consistent with the model biases in atmospheric temperature and water vapor. The existence of radiance biases of opposite signs in different spectral regions suggests that a seemingly good agreement of the model's broadband longwave flux with observations may be due to a fortuitous cancellation of spectral errors. Moreover, an examination of the diurnal difference spectrum indicates pronounced biases in the model-simulated diurnal hydrologic cycle over the tropical oceans, a feature seen to occur in other GCMs as well. 0321 Cloud/radiation interaction; 3359 Radiative processes; 3337 Global climate models; GCM; AIRS
Jones, T. A.; Christopher, S. A.Jones, T. A., S. A. Christopher, 2007: Statistical variability of top of atmosphere cloud-free shortwave aerosol radiative effect. Atmos. Chem. Phys., 7(11), 2937-2948. doi: 10.5194/acp-7-2937-2007. The statistical variability of globally averaged MODIS aerosol optical thickness at 0.55 μm (AOT) and top of atmosphere CERES cloud-free shortwave radiative effect (SWRE) is presented. Statistical variability is defined as the robustness of globally averaged statistics relative to data distribution. At the CERES footprint level, which we label "raw data", both the AOT and SWRE data derived from clear-sky CERES-SSF products show significant deviations from a normal distribution as evidenced by high skewness values. The spatial and temporal distribution of the data is also not uniform, with a greater concentration of data occurring in aerosol heavy-regions. As a result, globally averaged AOT and SWRE are overestimated when derived from raw data alone. To compensate, raw data are gridded into 2×2 degree grid-cells (called "gridded" data) to reduce the effect of spatial non-uniformity. However, the underlying non-normal distribution remains and manifests itself by increasing the uncertainty of grid-cell values. Globally averaged AOT and SWRE derived from a gridded dataset are substantially lower than those derived from raw data alone. The range of globally averaged AOT and SWRE values suggests that up to a 50% statistical variability exists, much of which is directly tied to how the data are manipulated prior to averaging. This variability increases when analyzing aerosol components (e.g. anthropogenic) since component AOT (and SWRE) may not exist at all locations were AOT is present. As a result, regions where a particular component AOT does not exist must either not be included in the global average or have data within these regions set to null values. However, each method produces significantly different results. The results of this work indicate simple mean and standard deviation statistics do not adequately describe global aerosol climate forcing data sets like the one used here. We demonstrate that placing raw observations on to a uniform grid is a necessary step before calculating global statistics. However, this by no means eliminates uncertainty in globally averaged AOT and SWRE values, while adding its own set of assumptions. When reporting any globally averaged statistic, it is important to report corresponding distribution and coverage information, in the form of skewness values, probability density functions, and spatial distribution plots, to help quantify its usefulness and robustness.
Jones, Thomas A.; Christopher, Sundar A.Jones, T. A., S. A. Christopher, 2007: Is the top of atmosphere dust net radiative effect different between Terra and Aqua?. Geophysical Research Letters, 34(2), L02812. doi: 10.1029/2006GL028262. We assess the difference in Top of Atmosphere (TOA) cloud-free Net Radiative Effect (NRE) of dust aerosols between the Terra and Aqua satellites using three years of collocated Moderate Resolution Imaging SpectroRadiometer (MODIS) and the Clouds and the Earth's Radiant Energy System (CERES) data over the Atlantic Ocean [0–30°N, 10–60°W]. The dust aerosol optical thickness at 0.55 μm (τdust) was first separated from the total aerosol column aerosol optical thickness (τ) and our results indicate that the Terra minus Aqua difference for both τ and τdust is approximately 10%, with Terra values generally being slightly higher. The resulting difference in TOA NRE from dust aerosols is less than 1 Wm−2. The difference between Terra and Aqua NRE lies well within previously reported uncertainties indicating that data from either satellite can be used interchangeably if independent adjustments for diurnal effects and clear-sky sample biases are made. 0305 Aerosols and particles; 3359 Radiative processes; 4801 Aerosols; dust radiative effects; MODS-CERES; terra-aqua
Lee, Hai-Tien; Gruber, Arnold; Ellingson, Robert G.; Laszlo, IstvanLee, H., A. Gruber, R. G. Ellingson, I. Laszlo, 2007: Development of the HIRS Outgoing Longwave Radiation Climate Dataset. J. Atmos. Oceanic Technol., 24(12), 2029-2047. doi: 10.1175/2007JTECHA989.1. Abstract The Advanced Very High Resolution Radiometer (AVHRR) outgoing longwave radiation (OLR) product, which NOAA has been operationally generating since 1979, is a very long data record that has been used in many applications, yet past studies have shown its limitations and several algorithm-related deficiencies. Ellingson et al. have developed the multispectral algorithm that largely improved the accuracy of the narrowband-estimated OLR as well as eliminated the problems in AVHRR. NOAA has been generating High Resolution Infrared Radiation Sounder (HIRS) OLR operationally since September 1998. In recognition of the need for a continuous and long OLR data record that would be consistent with the earth radiation budget broadband measurements in the National Polar-orbiting Operational Environmental Satellite System (NPOESS) era, and to provide a climate data record for global change studies, a vigorous reprocessing of the HIRS radiance for OLR derivation is necessary. This paper describes the development of the new HIRS OLR climate dataset. The HIRS level 1b data from the entire Television and Infrared Observation Satellite N-series (TIROS-N) satellites have been assembled. A new radiance calibration procedure was applied to obtain more accurate and consistent HIRS radiance measurements. The regression coefficients of the HIRS OLR algorithm for all satellites were rederived from calculations using an improved radiative transfer model. Intersatellite calibrations were performed to remove possible discontinuity in the HIRS OLR product from different satellites. A set of global monthly diurnal models was constructed consistent with the HIRS OLR retrievals to reduce the temporal sampling errors and to alleviate an orbital-drift-induced artificial trend. These steps significantly improved the accuracy, continuity, and uniformity of the HIRS monthly mean OLR time series. As a result, the HIRS OLR shows a comparable stability as in the Earth Radiation Budget Satellite (ERBS) nonscanner OLR measurements. HIRS OLR has superb agreement with the broadband observations from Earth Radiation Budget Experiment (ERBE) and Clouds and the Earth’s Radiant Energy System (CERES) in the ENSO-monitoring regions. It shows compatible ENSO-monitoring capability with the AVHRR OLR. Globally, HIRS OLR agrees with CERES with an accuracy to within 2 W m−2 and a precision of about 4 W m−2. The correlation coefficient between HIRS and CERES global monthly mean is 0.997. Regionally, HIRS OLR agrees with CERES to within 3 W m−2 with precisions better than 3 W m−2 in most places. HIRS OLR could be used for constructing climatology for applications that plan to use NPOESS ERBS and previously used AVHRR OLR observations. The HIRS monthly mean OLR data have high accuracy and precision with respect to the broadband observations of ERBE and CERES. It can be used as an independent validation data source. The uniformity and continuity of HIRS OLR time series suggest that it could be used as a reliable transfer reference for the discontinuous broadband measurements from ERBE, CERES, and ERBS. satellite observations; longwave radiation; Databases
Lin, Bing; Xu, Kuan-Man; Minnis, Patrick; Wielicki, Bruce A.; Hu, Yongxiang; Chambers, Lin; Fan, Tai-Fang; Sun, WenboLin, B., K. Xu, P. Minnis, B. A. Wielicki, Y. Hu, L. Chambers, T. Fan, W. Sun, 2007: Coincident occurrences of tropical individual cirrus clouds and deep convective systems derived from TRMM observations. Geophysical Research Letters, 34(14), L14804. doi: 10.1029/2007GL029768. Satellite measurements of cloud properties and atmospheric radiation were used to investigate the effect of spatial and temporal scales on the coincident occurrences of tropical individual cirrus clouds (ICCs) and deep convective systems (DCSs). There is little or even negative correlation between instantaneous occurrences of ICC and DCS in small areas. When spatial and temporal domains are increased, ICCs become more dependent on DCSs due to the origination of many ICCs from DCSs and moisture supply from the DCS in the upper troposphere for the ICCs to grow, resulting in significant positive correlation between the two types of clouds. The estimated radiative feedback due to the change in tropical high cloud area coverage with sea surface temperature appears small and about −0.14 Wm−2K−1, which would not cancel out the estimated anthropogenic forcing of doubled atmospheric CO2. Feedback; 3359 Radiative processes; 3310 Clouds and cloud feedbacks; 3314 Convective processes; 1616 Climate variability; radiation; tropical high clouds
Lin, Xin; Zhang, Sara Q.; Hou, Arthur Y.Lin, X., S. Q. Zhang, A. Y. Hou, 2007: Variational Assimilation of Global Microwave Rainfall Retrievals: Physical and Dynamical Impact on GEOS Analyses. Mon. Wea. Rev., 135(8), 2931-2957. doi: 10.1175/MWR3434.1. Abstract Global microwave rainfall retrievals from a five-satellite constellation, including the Tropical Rainfall Measuring Mission Microwave Imager, Special Sensor Microwave Imager from the Defense Meteorological Satellite Program F13, F14, and F15, and the Advanced Microwave Scanning Radiometer from the Earth Observing System Aqua, are assimilated into the NASA Goddard Earth Observing System (GEOS) Data Assimilation System using a 1D variational continuous assimilation (VCA) algorithm. The physical and dynamical impact of rainfall assimilation on GEOS analyses is examined at various temporal and spatial scales. This study demonstrates that the 1D VCA algorithm, which was originally developed and evaluated for rainfall assimilations over tropical oceans, can effectively assimilate satellite microwave rainfall retrievals and improve GEOS analyses over both the Tropics and the extratropics where the atmospheric processes are dominated by different large-scale dynamics and moist physics, and also over land, where rainfall estimates from passive microwave radiometers are believed to be less accurate. Results show that rainfall assimilation renders the GEOS analysis physically and dynamically more consistent with the observed precipitation at the monthly mean and 6-h time scales. Over regions where the model precipitation tends to misbehave in distinctly different rainy regimes, the 1D VCA algorithm, by compensating for errors in the model’s moist time tendency in a 6-h analysis window, is able to bring the rainfall analysis closer to the observed. The radiation and cloud fields also tend to be in better agreement with independent satellite observations in the rainfall–assimilation run especially over regions where rainfall analyses indicate large improvements. Assimilation experiments with and without rainfall data for a midlatitude frontal system clearly indicate that the GEOS analysis is improved through changes in the thermodynamic and dynamic fields that respond to the rainfall assimilation. The synoptic structures of temperature, moisture, winds, divergence, and vertical motion, as well as vorticity, are more realistically captured across the front. Remote sensing; satellite observations; Algorithms
Loeb, N. G.; Kato, S.; Loukachine, K.; Manalo-Smith, N.; Doelling, D. R.Loeb, N. G., S. Kato, K. Loukachine, N. Manalo-Smith, D. R. Doelling, 2007: Angular distribution models for top-of-atmosphere radiative flux estimation from the Clouds and the Earth's Radiant Energy System instrument on the Terra satellite. Part II: Validation. J. Atmos. Oceanic Technol., 24(4), 564-584. doi: 10.1175/jtech1983.1. Errors in top- of- atmosphere ( TOA) radiative fluxes from the Clouds and the Earth's Radiant Energy System ( CERES) instrument due to uncertainties in radiance- to- flux conversion from CERES Terra angular distribution models ( ADMs) are evaluated through a series of consistency tests. These tests show that the overall bias in regional monthly mean shortwave ( SW) TOA flux is less than 0.2Wm(-2) and the regional RMS error ranges from 0.70 to 1.4 W m(-2). In contrast, SW TOA fluxes inferred using theoretical ADMs that assume clouds are plane parallel are overestimated by 3 - 4 W m(-2) and exhibit a strong latitudinal dependence. In the longwave ( LW), the bias error ranges from 0.2 to 0.4 W m(-2) and regional RMS errors remain smaller than 0.7 W m(-2). Global mean albedos derived from ADMs developed during the Earth Radiation Budget Experiment ( ERBE) and applied to CERES measurements show a systematic increase with viewing zenith angle of 4% - 8%, while albedos from the CERES Terra ADMs show a smaller increase of 1% - 2%. The LW fluxes from the ERBE ADMs show a systematic decrease with viewing zenith angle of 2% - 2.4%, whereas fluxes from the CERES Terra ADMs remain within 0.7% - 0.8% at all angles. Based on several months of multiangle CERES along- track data, the SW TOA flux consistency between nadir-and oblique- viewing zenith angles is generally 5% ( < 17 W m(-2)) over land and ocean and 9% ( 26 W m(-2)) in polar regions, and LW TOA flux consistency is approximate 3% ( 7 W m(-2)) over all surfaces. Based on these results and a theoretically derived conversion between TOA flux consistency and TOA flux error, the best estimate of the error in CERES TOA flux due to the radiance- to- flux conversion is 3% ( 10 W m(-2)) in the SW and 1.8% ( 3 - 5 W m(-2)) in the LW. Monthly mean TOA fluxes based on ERBE ADMs are larger than monthly mean TOA fluxes based on CERES Terra ADMs by 1.8 and 1.3 W m(-2) in the SW and LW, respectively.
Loeb, Norman G.; Wielicki, Bruce A.; Rose, Fred G.; Doelling, David R.Loeb, N. G., B. A. Wielicki, F. G. Rose, D. R. Doelling, 2007: Variability in global top-of-atmosphere shortwave radiation between 2000 and 2005. Geophysical Research Letters, 34(3), L03704. doi: 10.1029/2006GL028196. Measurements from various instruments and analysis techniques are used to directly compare changes in Earth-atmosphere shortwave (SW) top-of-atmosphere (TOA) radiation between 2000 and 2005. Included in the comparison are estimates of TOA reflectance variability from published ground-based Earthshine observations and from new satellite-based CERES, MODIS and ISCCP results. The ground-based Earthshine data show an order-of-magnitude more variability in annual mean SW TOA flux than either CERES or ISCCP, while ISCCP and CERES SW TOA flux variability is consistent to 40%. Most of the variability in CERES TOA flux is shown to be dominated by variations global cloud fraction, as observed using coincident CERES and MODIS data. Idealized Earthshine simulations of TOA SW radiation variability for a lunar-based observer show far less variability than the ground-based Earthshine observations, but are still a factor of 4–5 times more variable than global CERES SW TOA flux results. Furthermore, while CERES global albedos exhibit a well-defined seasonal cycle each year, the seasonal cycle in the lunar Earthshine reflectance simulations is highly variable and out-of-phase from one year to the next. Radiative transfer model (RTM) approaches that use imager cloud and aerosol retrievals reproduce most of the change in SW TOA radiation observed in broadband CERES data. However, assumptions used to represent the spectral properties of the atmosphere, clouds, aerosols and surface in the RTM calculations can introduce significant uncertainties in annual mean changes in regional and global SW TOA flux. 1610 Atmosphere; 1640 Remote sensing; radiative flux; albedo; 1616 Climate variability; Variability
Loeb, Norman G.; Wielicki, Bruce A.; Su, Wenying; Loukachine, Konstantin; Sun, Wenbo; Wong, Takmeng; Priestley, Kory J.; Matthews, Grant; Miller, Walter F.; Davies, R.Loeb, N. G., B. A. Wielicki, W. Su, K. Loukachine, W. Sun, T. Wong, K. J. Priestley, G. Matthews, W. F. Miller, R. Davies, 2007: Multi-Instrument Comparison of Top-of-Atmosphere Reflected Solar Radiation. J. Climate, 20(3), 575-591. doi: 10.1175/JCLI4018.1. Abstract Observations from the Clouds and the Earth’s Radiant Energy System (CERES), Moderate Resolution Imaging Spectroradiometer (MODIS), Multiangle Imaging Spectroradiometer (MISR), and Sea-Viewing Wide-Field-of-View Sensor (SeaWiFS) between 2000 and 2005 are analyzed in order to determine if these data are meeting climate accuracy goals recently established by the climate community. The focus is primarily on top-of-atmosphere (TOA) reflected solar radiances and radiative fluxes. Direct comparisons of nadir radiances from CERES, MODIS, and MISR aboard the Terra satellite reveal that the measurements from these instruments exhibit a year-to-year relative stability of better than 1%, with no systematic change with time. By comparison, the climate requirement for the stability of visible radiometer measurements is 1% decade−1. When tropical ocean monthly anomalies in shortwave (SW) TOA radiative fluxes from CERES on Terra are compared with anomalies in Photosynthetically Active Radiation (PAR) from SeaWiFS—an instrument whose radiance stability is better than 0.07% during its first six years in orbit—the two are strongly anticorrelated. After scaling the SeaWiFS anomalies by a constant factor given by the slope of the regression line fit between CERES and SeaWiFS anomalies, the standard deviation in the difference between monthly anomalies from the two records is only 0.2 W m−2, and the difference in their trend lines is only 0.02 ± 0.3 W m−2 decade−1, approximately within the 0.3 W m−2 decade−1 stability requirement for climate accuracy. For both the Tropics and globe, CERES Terra SW TOA fluxes show no trend between March 2000 and June 2005. Significant differences are found between SW TOA flux trends from CERES Terra and CERES Aqua between August 2002 and March 2005. This discrepancy is due to uncertainties in the adjustment factors used to account for degradation of the CERES Aqua optics during hemispheric scan mode operations. Comparisons of SW TOA flux between CERES Terra and the International Satellite Cloud Climatology Project (ISCCP) radiative flux profile dataset (FD) RadFlux product show good agreement in monthly anomalies between January 2002 and December 2004, and poor agreement prior to this period. Commonly used statistical tools applied to the CERES Terra data reveal that in order to detect a statistically significant trend of magnitude 0.3 W m−2 decade−1 in global SW TOA flux, approximately 10 to 15 yr of data are needed. This assumes that CERES Terra instrument calibration remains highly stable, long-term climate variability remains constant, and the Terra spacecraft has enough fuel to last 15 yr. satellite observations; radiative forcing; Shortwave radiation
Luo, Yali; Xu, Kuan-Man; Wielicki, Bruce A.; Wong, Takmeng; Eitzen, Zachary A.Luo, Y., K. Xu, B. A. Wielicki, T. Wong, Z. A. Eitzen, 2007: Statistical Analyses of Satellite Cloud Object Data from CERES. Part III: Comparison with Cloud-Resolving Model Simulations of Tropical Convective Clouds. J. Atmos. Sci., 64(3), 762-785. doi: 10.1175/JAS3871.1. Abstract The present study evaluates the ability of a cloud-resolving model (CRM) to simulate the physical properties of tropical deep convective cloud objects identified from a Clouds and the Earth’s Radiant Energy System (CERES) data product. The emphasis of this study is the comparisons among the small-, medium-, and large-size categories of cloud objects observed during March 1998 and between the large-size categories of cloud objects observed during March 1998 (strong El Niño) and March 2000 (weak La Niña). Results from the CRM simulations are analyzed in a way that is consistent with the CERES retrieval algorithm and they are averaged to match the scale of the CERES satellite footprints. Cloud physical properties are analyzed in terms of their summary histograms for each category. It is found that there is a general agreement in the overall shapes of all cloud physical properties between the simulated and observed distributions. Each cloud physical property produced by the CRM also exhibits different degrees of disagreement with observations over different ranges of the property. The simulated cloud tops are generally too high and cloud-top temperatures are too low except for the large-size category of March 1998. The probability densities of the simulated top-of-the-atmosphere (TOA) albedos for all four categories are underestimated for high albedos, while those of cloud optical depth are overestimated at its lowest bin. These disagreements are mainly related to uncertainties in the cloud microphysics parameterization and inputs such as cloud ice effective size to the radiation calculation. Summary histograms of cloud optical depth and TOA albedo from the CRM simulations of the large-size category of cloud objects do not differ significantly between the March 1998 and 2000 periods, consistent with the CERES observations. However, the CRM is unable to reproduce the significant differences in the observed cloud-top height while it overestimates the differences in the observed outgoing longwave radiation and cloud-top temperature between the two periods. Comparisons between the CRM results and the observations for most parameters in March 1998 consistently show that both the simulations and observations have larger differences between the large- and small-size categories than between the large- and medium-size, or between the medium- and small-size categories. However, the simulated cloud properties do not change as much with size as observed. These disagreements are likely related to the spatial averaging of the forcing data and the mismatch in time and space between the numerical weather prediction model from which the forcing data are produced and the CERES observed cloud systems. cloud-resolving models; Cloud microphysics; satellite observations; convective clouds; statistics
Lyapustin, A; Wang, Y; Kahn, R; Xiong, J; Ignatov, A; Wolfe, R; Wu, A; Holben, B; Bruegge, CLyapustin, A., Y. Wang, R. Kahn, J. Xiong, A. Ignatov, R. Wolfe, A. Wu, B. Holben, C. Bruegge, 2007: Analysis of MODIS-MISR calibration differences using surface albedo around AERONET sites and cloud reflectance. REMOTE SENSING OF ENVIRONMENT, 107(1-2), 12-21. doi: 10.1016/j.rse.2006.09.028. MODIS and MISR are two Earth Observing System instruments flown onboard the TerTa satellite. Their synergistic use could greatly benefit the broad user community by ensuring a global view of the Earth with high-quality products. A necessary condition for data fusion is radiometric calibration agreement between the two instruments. Earlier studies showed about 3% absolute radiometric difference between MISR and respective MODIS land bands in the visible and near-IR spectrum, which are also used in aerosol and cloud research. This study compared two surface albedo products derived from MODIS and MISR LIB data using the AERONET-based Surface Reflectance Validation Network (ASRVN). The ASRVN shows a positive MISR-MODIS albedo bias of + (0.01-0.03). Cross-sensor calibration inconsistencies were identified as a primary cause of the albedo biases. To establish an independent MODIS-MISR calibration link, top-of-atmosphere MODIS and MISR reflectances were regressed against each other over liquid water clouds. The empirical regression results have been adjusted for the differences in the respective MISR and MODIS spectral responses using radiative transfer simulations. The MISR-MODIS band gain differences for the top-of-atmosphere reflectance estimated with this technique are +6.0% in the Blue, +3.3% in the Green, +2.7% in the Red, and +0.8% in the NIR band. Applying the derived values to rescale the MODIS or MISR LIB data is shown to significantly reduce the cross-sensor ASRVN surface albedo biases. An absolute calibration scale for both sensors could be established based on independent ground-based measurements of the surface albedo at selected AERONET sites. (c) 2006 Elsevier Inc. All rights reserved.
Matthews, Grant; Priestley, Kory; Thomas, SusanMatthews, G., K. Priestley, S. Thomas, 2007: Transfer of radiometric standards between multiple low earth orbit climate observing broadband radiometers: application to CERES. Optical Engineering+ Applications, 6677, 66770I-66770I-10. doi: 10.1117/12.734478. The Clouds and the Earth's Radiant Energy System (CERES) is the only project currently measuring the global Earth Radiation Budget (ERB) from space. Two CERES instruments are located on the EOS Terra platform and two more are placed on the EOS Aqua satellite. One more CERES unit provided 8 months of ERB data in 1998 from the TRMM platform. Each of the CERES devices uses three broadband radiometric scanning telescopes: the shortwave (SW 0.3 → 5μm), Total (0.3 → 100μm), and window (8 → 12μm) channels. Rigorous pre-launch ground calibration is performed on each CERES unit to achieve an accuracy goal of 1% for Short Wave (SW) and 0.5% for outgoing Long Wave (LW) radiance. Any ground to flight or in-flight changes in radiometer response is monitored using onboard calibration sources. For the total and window channels these take the form of concentric groove blackbodies, while the SW channels use stable tungsten lamps. Recent studies have shown that the SW response of space based broadband radiometers can change dramatically due to optical contamination. With these changes having most impact on optical response to blue-UV radiance, where tungsten lamps are largely devoid of output, such changes are hard to monitor accurately using existing on-board sources. This study details an attempt to use the vicarious stability metric of deep convective clouds (DCC), nighttime LW scenes and a newly developed SW optical darkening model to place all CERES instrument measurements on the same radiometric scale. The results show that scene dependant dispersion in nadir comparisons between instruments on the same satellite are significantly reduced. Also the suggestion is that the pre-flight contamination of the CERES instruments may require an increase in Terra and Aqua measured SW flux. A larger necessary increase in Aqua SW flux is believed to be due to greater pre-flight contamination of the CERES Aqua optics.
Matthews, Grant; Priestley, Kory; Thomas, SusanMatthews, G., K. Priestley, S. Thomas, 2007: Spectral balancing of a broadband Earth observing radiometer with co-aligned Short Wave channel to ensure accuracy and stability of broadband daytime Outgoing Long-Wave Radiance measurements: Application to CERES. Optical Engineering+ Applications, 6678, 66781H-66781H-10. doi: 10.1117/12.734492. In order to best detect real changes in the Earth's climate system, it is estimated that in space based instrumentation measuring the Earth Radiation Budget (ERB) must remain calibrated with a stability of 0.3Wm −2 per decade and reach an absolute accuracy of 1Wm −2. Such stability is beyond that specified by existing ERB programs such as the Clouds and the Earth's Radiant Energy System (CERES, using three broadband radiometric scanning channels: the shortwave (SW 0.3−5um), Total (0.3− > 100um), and window (8−12um)). The CERES measurement of daytime outgoing longwave radiance (OLR) is obtained using subtraction of the SW channel signal from that of the co-aligned Total channel telescope. This requires precise balancing of the estimated response of the Total channel optics with those of the SW only channel when viewing daytime Earth scenes. Any post ground calibration contamination of Total channel optics that reduces its response to SW radiance can therefore upset this balancing process, introducing biases and trends in measurements of daytime LW radiance. This paper presents a new methodology used for balancing Total and SW channel spectral responses for all daytime Earth scenes using a model of contaminant spectral darkening. The results of the technique when applied to both CERES units on Terra are shown to remove significant trends and biases in measurements of daytime LW radiance.
Mazzola, M.; Lanconelli, C.; Lupi, A.; Vitale, V.; Tomasi, C.Mazzola, M., C. Lanconelli, A. Lupi, V. Vitale, C. Tomasi, 2007: Short-wave direct aerosol forcing over the Mediterranean Sea region using MISR data. Il Nuovo Cimento B, 719-728. doi: 10.1393/ncb/i2007-10407-6. The MISR data-set collected in 2003 over the Mediterranean Sea area and its products relative to the four MISR narrow-band channels were examined to obtain evaluations of the upwelling radiation flux at the Top Of the Atmosphere (TOA), using a computational procedure based on the 6S Radiative Transfer Code (RTC). The spectral series of the narrow-band radiation fluxes were then converted into the corresponding broad-band evaluations of upwelling TOA flux F. Compared with the CERES estimates, the values of F were found to agree closely over land areas, and to be underestimated over sea, mainly by 12-21%. These broad-band values of F were used to determine the instantaneous cloud-free short-wave radiative forcing Delta F induced by aerosols at TOA, relative to each satellite overpassing, from which the values of corresponding diurnally averaged radiative forcing Delta F-d were evaluated by adopting an appropriate scaling factor relative to the 24-hour period. Monthly maps of Delta F-d were finally produced, presenting average values varying between null and -4.7W m(-2) over land, and between -8.6 and -2.3 W m(-2) over sea, with mean values and corresponding standard deviations of -2.2 +/- 4.4 W m(-2) and -5.1 +/- 3.1 W m(-2), respectively. Particularly high positive values of Delta F-d were obtained in the Sahara and Middle East regions throughout the year, giving evidence of the marked warming effects induced by desert dust particles.
Minnis, Patrick; Huang, Jianping; Lin, Bing; Yi, Yuhong; Arduini, Robert F.; Fan, Tai-Fang; Ayers, J. Kirk; Mace, Gerald G.Minnis, P., J. Huang, B. Lin, Y. Yi, R. F. Arduini, T. Fan, J. K. Ayers, G. G. Mace, 2007: Ice cloud properties in ice-over-water cloud systems using Tropical Rainfall Measuring Mission (TRMM) visible and infrared scanner and TRMM Microwave Imager data. Journal of Geophysical Research: Atmospheres, 112(D6), D06206. doi: 10.1029/2006JD007626. A multilayered cloud retrieval system (MCRS) is updated and used to estimate ice water path in maritime ice-over-water clouds using Visible and Infrared Scanner (VIRS) and Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) measurements acquired over the Tropics between January and August 1998. Lookup tables of top-of-atmosphere 0.65-μm reflectance are developed for ice-over-water cloud systems using radiative transfer calculations for various combinations of ice-over-water cloud layers. The liquid and ice water paths, LWP and IWP, respectively, are determined with the MCRS using these lookup tables with a combination of microwave (MW), visible (VIS), and infrared (IR) data. LWP, determined directly from the TMI MW data, is used to define the lower-level cloud properties to select the proper lookup table. The properties of the upper-level ice clouds, such as optical depth and effective size, are then derived using the Visible–Infrared Solar-infrared Split-Window technique (VISST), which matches the VIRS IR, 3.9 μm, and VIS data to the multilayer cloud lookup table reflectances and a set of emittance parameterizations. Initial comparisons with surface-based radar retrievals suggest that this enhanced MCRS can significantly improve the accuracy and decrease the IWP in overlapped clouds by 42 and 13% compared to using the single-layer VISST and an earlier simplified MW–VIS–IR (MVI) differencing method, respectively, for ice-over-water cloud systems. The tropical distribution of ice-over-water clouds is the same as derived earlier from combined TMI and VIRS data, but the new values of IWP and optical depth are slightly larger than the older MVI values and exceed those of single-layered clouds by 7 and 11%, respectively. The mean IWP from the MCRS is 8–14% greater than that retrieved from radar retrievals of overlapped clouds over two surface sites, and the standard deviations of the differences are similar to those for single-layered clouds. Examples of a method for applying the MCRS over land without MW data yield similar differences with the surface retrievals. By combining the MCRS with other techniques that focus primarily on optically thin cirrus over low water clouds, it will be possible to more fully assess the IWP in all conditions over ocean except for precipitating systems. 0360 Radiation: transmission and scattering; TRMM; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; 0365 Troposphere: composition and chemistry; Cloud overlap; ice water path
Nair, Udaysankar S.; Ray, Deepak K.; Wang, Jun; Christopher, Sundar A.; Lyons, Tom J.; Welch, Ronald M.; Pielke, R. A.Nair, U. S., D. K. Ray, J. Wang, S. A. Christopher, T. J. Lyons, R. M. Welch, R. A. Pielke, 2007: Observational estimates of radiative forcing due to land use change in southwest Australia. Journal of Geophysical Research: Atmospheres, 112(D9), D09117. doi: 10.1029/2006JD007505. Radiative forcing associated with land use change is largely derived from global circulation models (GCM), and the accuracy of these estimates depends on the robustness of the vegetation characterization used in the GCMs. In this study, we use observations from the Clouds and Earth's Radiant Energy System (CERES) instrument on board the Terra satellite to report top-of-the-atmosphere (TOA) radiative forcing values associated with clearing of native vegetation for agricultural purposes in southwest Australia. Over agricultural areas, observations show consistently higher shortwave fluxes at the TOA compared to native vegetation, especially during the time period between harvest and planting. Estimates using CERES observations show that over a specific area originally covered by native vegetation, replacement of half the area by croplands results in a diurnally averaged shortwave radiative forcing of approximately −7 W m−2. GCM-derived estimates for areas with 30% or more croplands range from −1 to −2 W m−2 compared to observational estimate of −4.2 W m−2, thus significantly underestimating radiative forcing due to land use change by a factor of 2 or more. Two potential reasons for this underestimation are incorrect specification of the multiyear land use change scenario and the inaccurate prescription of seasonal cycles of crops in GCMs. 3359 Radiative processes; radiative forcing; Australia; 1631 Land/atmosphere interactions; 1843 Land/atmosphere interactions; 0315 Biosphere/atmosphere interactions; 1632 Land cover change; land use change
Priestley, Kory J.; Smith, G. Louis; Thomas, Susan; Matthews, GrantPriestley, K. J., G. L. Smith, S. Thomas, G. Matthews, 2007: Validation protocol for climate quality CERES measurements. Optical Engineering+ Applications, 6678, 66781I-66781I-12. doi: 10.1117/12.735312. The CERES Flight Model-1 and -2 instruments flew aboard the Terra into orbit in December 1999 and the FM-3 and -4 instruments flew on the Aqua spacecraft in May 2002. To date these instruments have provided seven years of measurements on Terra and five years on Aqua. The accuracy requirement for CERES is 0.5% for longwave radiances and 1.0% for shortwave. Achieving this objective is possible by using experience from the ERBE instrument to evolve the CERES design and the methods for analyzing the data. In order to achieve and maintain this accuracy, an internal calibration system and an attenuated view of the Sun are used. Subsequently, to validate that this accuracy has been achieved, a number of techniques have been developed which cover a range of temporal and spatial scales. This ensemble of methods provides a protocol which assures that the CERES measurements are of climate quality. In addition to retrieving fluxes at the top of the atmosphere, the CERES program uses data from other instruments aboard the spacecraft to compute the radiation balance at the surface and at levels through the atmosphere. Finally, the CERES data products are upgraded as higher-level data products show the need for revisions. The calibration stability is better than 0.2% and traceability from ground to in-flight calibration is 0.25%
Priestley, Kory J; Smith, G Louis; Thomas, Susan; Cooper, Denise; Lee III, Robert B; Walikainen, Dale; Hess, Phil; Szewczyk, Z Peter; Wilson, RobertPriestley, K. J., G. L. Smith, S. Thomas, D. Cooper, R. B. Lee III, D. Walikainen, P. Hess, Z. P. Szewczyk, R. Wilson, 2007: Radiometric performance of the CERES Earth Radiation Budget climate record sensors on the EOS Aqua and Terra Spacecraft. Optical Engineering+ Applications, 66770H–66770H. doi: http://dx.doi.org/10.1117/12.735294. The CERES Flight Models 1 through 4 instruments were launched aboard NASA's Earth Observing System (EOS) Terra and Aqua Spacecraft into 705 Km sun-synchronous orbits with 10:30 a.m. and 1:30 p.m. equatorial crossing times. These instruments supplement measurements made by the CERES Proto Flight Model (PFM) instrument launched aboard NASA's Tropical Rainfall Measuring Mission (TRMM) spacecraft on November 27, 1997 into a 350 Km, 38-degree mid-inclined orbit. The archived CERES Science data products consist of geolocated and calibrated instantaneous filtered and unfiltered radiances through temporally and spatially averaged TOA, Surface, and Atmospheric fluxes. CERES filtered radiance measurements cover three spectral bands including shortwave (0.3 to 5 micron), total (0.3 to
Spencer, Roy W.; Braswell, William D.; Christy, John R.; Hnilo, JustinSpencer, R. W., W. D. Braswell, J. R. Christy, J. Hnilo, 2007: Cloud and radiation budget changes associated with tropical intraseasonal oscillations. Geophysical Research Letters, 34(15), L15707. doi: 10.1029/2007GL029698. We explore the daily evolution of tropical intraseasonal oscillations in satellite-observed tropospheric temperature, precipitation, radiative fluxes, and cloud properties. The warm/rainy phase of a composited average of fifteen oscillations is accompanied by a net reduction in radiative input into the ocean-atmosphere system, with longwave heating anomalies transitioning to longwave cooling during the rainy phase. The increase in longwave cooling is traced to decreasing coverage by ice clouds, potentially supporting Lindzen's “infrared iris” hypothesis of climate stabilization. These observations should be considered in the testing of cloud parameterizations in climate models, which remain sources of substantial uncertainty in global warming prediction. 3359 Radiative processes; 3305 Climate change and variability; 3374 Tropical meteorology; feedbacks; 3310 Clouds and cloud feedbacks; climate; tropical
Su, Wenying; Charlock, Thomas P.; Rose, Fred G.; Rutan, DavidSu, W., T. P. Charlock, F. G. Rose, D. Rutan, 2007: Photosynthetically active radiation from Clouds and the Earth's Radiant Energy System (CERES) products. Journal of Geophysical Research: Biogeosciences, 112(G2), G02022. doi: 10.1029/2006JG000290. We describe a method that retrieves surface photosynthetically active radiation (PAR) and its direct and diffuse components from the Surface and Atmospheric Radiation Budget (SARB) product of Clouds and the Earth's Radiant Energy System (CERES). The shortwave spectrum in the SARB Edition 2 is calculated in 15 bands, 4 of which are used to develop the PAR, in conjunction with the look-up tables described in this paper. We apply these look-up tables to existing CERES Terra Edition 2 products. The new retrieved surface PAR is validated with LI-COR PAR measurements at seven Surface Radiation Budget Network (SURFRAD) sites using data from March 2000 to June 2005. The relative bias of retrieved all-sky PAR at the SURFRAD sites is 4.6% (positive sign indicating retrieval exceeds measurement), and 54% of the all-sky samples are within the ±10% uncertainty of the LI-COR PAR measurements. The satellite field-of-view (FOV) is more representative of the ground instrument FOV under clear conditions, so 89% of clear-sky retrievals are within the uncertainty of the LI-COR PAR measurements at SURFRAD sites with positive biases at most sites. The retrieved PAR is also validated at the Atmospheric Radiation Measurement (ARM) Southern Great Plains Central Facility (CF) site using data from October 2003 to June 2004 for those FOVs having both LI-COR and Rotating Shadowband Spectroradiometer (RSS) ground measurements; for this small domain, all-sky relative biases are again positive (1.9%) for LI-COR but negative (−4.2%) for RSS. The direct-to-diffuse ratio derived from CERES is smaller than that from RSS for both clear and cloudy conditions. CERES also retrieves the broadband shortwave insolation, and the relative biases for the broadband retrievals are much less than those for PAR at the above sites. It appears that some of the ground-based measurements of PAR do not have the fidelity of those for broadband shortwave insolation. 0360 Radiation: transmission and scattering; 3311 Clouds and aerosols; radiative transfer; PAR; 0428 Carbon cycling; carbon sequestration
Sun, Wenbo; Videen, Gorden; Lin, Bing; Hu, YongxiangSun, W., G. Videen, B. Lin, Y. Hu, 2007: Modeling light scattered from and transmitted through dielectric periodic structures on a substrate. Applied Optics, 46(7), 1150-1156. doi: 10.1364/AO.46.001150. Light scattering and transmission by rough surfaces are of considerable interest in a variety of applications including remote sensing and characterization of surfaces. In this work, the finite-difference time-domain technique is applied to calculate the scattered and transmitted electromagnetic fields of an infinite periodic rough surface. The elements of the Mueller matrix for scattered light are calculated by an integral of the near fields over a significant number of periods of the surface. The normalized Mueller matrix elements of the scattered light and the spatial distribution of the transmitted flux for a monolayer of micrometer-sized dielectric spheres on a silicon substrate are presented. The numerical results show that the nonzero Mueller matrix elements for scattering from a surface consisting of a monolayer of dielectric spheres on a silicon substrate have specific maxima at some scattering angles. These maxima may be used in the characterization of features of the surface. For light transmitted through the monolayer of spheres, our results show that the transmitted energy focuses around the ray passing through centers of the spheres. At other locations, the transmitted flux is very small. Therefore, micrometer-sized dielectric spheres might be placed on a semiconductor surface to burn nanometer-sized holes in a layer using laser pulses. The method may also be useful in the assembly of periodic microstructures on surfaces. Microstructure fabrication; Roughness; Scattering, rough surfaces
Thomas, Susan; Priestley, K. J.; Matthews, G. M.Thomas, S., K. J. Priestley, G. M. Matthews, 2007: Analysis of clouds and the Earth's radiant energy system (CERES) lunar measurements. doi: 10.1117/12.735839. Clouds and the Earth's Radiant Energy System (CERES) instruments were designed to measure the reflected shortwave and emitted longwave radiances of the Earth's radiation budget and to investigate the cloud interactions with global radiances for the long-term monitoring of Earth's climate. The CERES instrument with the three scanning thermistor bolometers measure broadband radiances in the shortwave (0.3 to 5.0 micrometer), total (0.3 to >100 micrometer) and 8 - 12 micrometer water vapor window regions. The four CERES instruments (Flight Models 1 through 4) aboard Earth Observing System (EOS) Terra and Aqua platforms were instrumental in conducting lunar radiance measurement on a regular basis. Moon-reflected solar radiances were measured with the shortwave sensor while both moon-reflected solar and moon-emitted longwave radiances were measured using the total sensor. The CERES sensors performed lunar measurements at various phase angles ranging from four to ten degrees before and after each full moon phase. Additional measurements were also conducted during the lunar eclipse events. The resulting filtered radiances were normalized to the mean sun-moon distance and the mean earth-moon distance. The lunar radiances measured by the sensors from all CERES instruments for a period of January 2001 to June 2007 were analyzed and compared. The CERES total sensor results showed a variation of about +/- 0.5 percent, while a +/- 2.0 percent variation was seen in shortwave sensor results.
Turner, D. D.; Vogelmann, A. M.; Johnson, K.; Miller, M.; Austin, R. T.; Barnard, J. C.; Flynn, C.; Long, C.; McFarlane, S. A.; Cady-Pereira, K.; Clough, S. A.; Chiu, J. C.; Khaiyer, M. M.; Liljegren, J.; Lin, B.; Minnis, P.; Marshak, A.; Matrosov, S. Y.; Min, Q.; O'Hirok, W.; Wang, Z.; Wiscombe, W.Turner, D. D., A. M. Vogelmann, K. Johnson, M. Miller, R. T. Austin, J. C. Barnard, C. Flynn, C. Long, S. A. McFarlane, K. Cady-Pereira, S. A. Clough, J. C. Chiu, M. M. Khaiyer, J. Liljegren, B. Lin, P. Minnis, A. Marshak, S. Y. Matrosov, Q. Min, W. O'Hirok, Z. Wang, W. Wiscombe, 2007: Thin Liquid Water Clouds: Their Importance and Our Challenge. Bull. Amer. Meteor. Soc., 88(2), 177-190. doi: 10.1175/BAMS-88-2-177. Abstract Many of the clouds important to the Earth's energy balance, from the Tropics to the Arctic, contain small amounts of liquid water. Longwave and shortwave radiative fluxes are very sensitive to small perturbations of the cloud liquid water path (LWP), when the LWP is small (i.e., < 100 g m−2; clouds with LWP less than this threshold will be referred to as “thin”). Thus, the radiative properties of these thin liquid water clouds must be well understood to capture them correctly in climate models. We review the importance of these thin clouds to the Earth's energy balance, and explain the difficulties in observing them. In particular, because these clouds are thin, potentially mixed phase, and often broken (i.e., have large 3D variability), it is challenging to retrieve their microphysical properties accurately. We describe a retrieval algorithm intercomparison that was conducted to evaluate the issues involved. The intercomparison used data collected at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site and included 18 different algorithms to evaluate their retrieved LWP, optical depth, and effective radii. Surprisingly, evaluation of the simplest case, a single-layer overcast stratocumulus, revealed that huge discrepancies exist among the various techniques, even among different algorithms that are in the same general classification. This suggests that, despite considerable advances that have occurred in the field, much more work must be done, and we discuss potential avenues for future research.)
Verlinde, J.; Harrington, J. Y.; Yannuzzi, V. T.; Avramov, A.; Greenberg, S.; Richardson, S. J.; Bahrmann, C. P.; McFarquhar, G. M.; Zhang, G.; Johnson, N.; Poellot, M. R.; Mather, J. H.; Turner, D. D.; Eloranta, E. W.; Tobin, D. C.; Holz, R.; Zak, B. D.; Ivey, M. D.; Prenni, A. J.; DeMott, P. J.; Daniel, J. S.; Kok, G. L.; Sassen, K.; Spangenberg, D.; Minnis, P.; Tooman, T. P.; Shupe, M.; Heymsfield, A. J.; Schofield, R.Verlinde, J., J. Y. Harrington, V. T. Yannuzzi, A. Avramov, S. Greenberg, S. J. Richardson, C. P. Bahrmann, G. M. McFarquhar, G. Zhang, N. Johnson, M. R. Poellot, J. H. Mather, D. D. Turner, E. W. Eloranta, D. C. Tobin, R. Holz, B. D. Zak, M. D. Ivey, A. J. Prenni, P. J. DeMott, J. S. Daniel, G. L. Kok, K. Sassen, D. Spangenberg, P. Minnis, T. P. Tooman, M. Shupe, A. J. Heymsfield, R. Schofield, 2007: The Mixed-Phase Arctic Cloud Experiment. Bull. Amer. Meteor. Soc., 88(2), 205-221. doi: 10.1175/BAMS-88-2-205. Abstract The Mixed-Phase Arctic Cloud Experiment (M-PACE) was conducted from 27 September through 22 October 2004 over the Department of Energy's Atmospheric Radiation Measurement (ARM) Climate Research Facility (ACRF) on the North Slope of Alaska. The primary objectives were to collect a dataset suitable to study interactions between microphysics, dynamics, and radiative transfer in mixed-phase Arctic clouds, and to develop/evaluate cloud property retrievals from surface- and satellite-based remote sensing instruments. Observations taken during the 1977/98 Surface Heat and Energy Budget of the Arctic (SHEBA) experiment revealed that Arctic clouds frequently consist of one (or more) liquid layers precipitating ice. M-PACE sought to investigate the physical processes of these clouds by utilizing two aircraft (an in situ aircraft to characterize the microphysical properties of the clouds and a remote sensing aircraft to constraint the upwelling radiation) over the ACRF site on the North Slope of Alaska. The measurements successfully documented the microphysical structure of Arctic mixed-phase clouds, with multiple in situ profiles collected in both single- and multilayer clouds over two ground-based remote sensing sites. Liquid was found in clouds with cloud-top temperatures as cold as −30°C, with the coldest cloud-top temperature warmer than −40°C sampled by the aircraft. Remote sensing instruments suggest that ice was present in low concentrations, mostly concentrated in precipitation shafts, although there are indications of light ice precipitation present below the optically thick single-layer clouds. The prevalence of liquid down to these low temperatures potentially could be explained by the relatively low measured ice nuclei concentrations.
Wang, D.; Minnis, P.; Charlock, T. P.; Zhou, D. K.; Rose, F. G.; Smith, W. L.; Jr, W. L. Smith; Nguyen, L.Wang, D., P. Minnis, T. P. Charlock, D. K. Zhou, F. G. Rose, W. L. Smith, W. L. S. Jr, L. Nguyen, 2007: Real-time mesoscale forecast support during the CLAMS field campaign. Advances in Atmospheric Sciences, 24(4), 599-605. doi: 10.1007/s00376-007-0599-3. This paper reports the use of a specialized, mesoscale, numerical weather prediction (NWP) system and a satellite imaging and prediction system that were set up to support the CLAMS (Chesapeake Lighthouse and Aircraft Measurements for Satellites) field campaign during the summer of 2001. The primary objective of CLAMS was to validate satellite-based retrievals of aerosol properties and vertical profiles of the radiative flux, temperature and water vapor. Six research aircraft were deployed to make detailed coincident measurements of the atmosphere and ocean surface with the research satellites that orbited overhead. The mesoscale weather modeling system runs in real-time to provide high spatial and temporal resolution for forecasts that are delivered via the World Wide Web along with a variety of satellite imagery and satellite location predictions. This system is a multi-purpose modeling system capable of both data analysis/assimilation and multi-scale NWP ranging from cloud-scale to larger than regional scale. This is a three-dimensional, nonhydrostatic compressible model in a terrain-following coordinate. The model employs advanced numerical techniques and contains detailed interactive physical processes. The utility of the forecasting system is illustrated throughout the discussion on the impact of the surface-wind forecast on BRDF (Bidirectional Reflectance Distribution Function) and the description of the cloud/moisture forecast versus the aircraft measurement. Meteorology/Climatology; CLAMS field campaign; forecast support; Geophysics/Geodesy; mesoscale numerical weather prediction
Wang, Zhuo; Zeng, Xubin; Barlage, MichaelWang, Z., X. Zeng, M. Barlage, 2007: Moderate Resolution Imaging Spectroradiometer bidirectional reflectance distribution function–based albedo parameterization for weather and climate models. Journal of Geophysical Research: Atmospheres, 112(D2), D02103. doi: 10.1029/2005JD006736. The albedo of land surfaces is an important parameter for surface energy balance and is dependent on the solar zenith angle and the three-dimensional structure of the canopies. The Moderate Resolution Imaging Spectroradiometer (MODIS) bidirectional reflectance distribution function (BRDF) algorithm is reformulated to derive a new two-parameter scheme for the computation of land surface albedo and its solar zenith angle (SZA) dependence for use in weather and climate models as well as in the remote sensing retrieval of surface solar fluxes. In this formulation the season- and pixel-dependent black-sky albedo at 60° SZA can be directly prescribed using the MODIS BRDF data while the two parameters are taken as a function of vegetation type only. Comparison of this formulation with those used in weather, climate, and data assimilation models (at NCAR, NCEP, and NASA) reveals the deficiencies in the treatment of SZA dependence and white-sky albedo in these models. Similarly, comparison of this formulation with those computed using the remotely sensed solar flux data from three groups (International Satellite Cloud Climatology Project (ISCCP)-FD, NASA's Clouds and the Earth's Radiant Energy System Tropical Rainfall Measuring Mission (CERES/TRMM), and University of Maryland) shows that surface albedos from these data sets are at times unrealistic, and suggestions are made regarding how to better treat the surface albedo and its SZA dependence in the retrieval of surface and atmospheric solar fluxes. Remote sensing; 3359 Radiative processes; radiative processes; 3322 Land/atmosphere interactions; land/atmosphere interactions
Xia, Xiangao; Li, Zhanqing; Holben, Brent; Wang, Pucai; Eck, Tom; Chen, Hongbin; Cribb, Maureen; Zhao, YanxiaXia, X., Z. Li, B. Holben, P. Wang, T. Eck, H. Chen, M. Cribb, Y. Zhao, 2007: Aerosol optical properties and radiative effects in the Yangtze Delta region of China. Journal of Geophysical Research: Atmospheres, 112(D22), D22S12. doi: 10.1029/2007JD008859. One year's worth of aerosol and surface irradiance data from September 2005 to August 2006 were obtained at Taihu, the second supersite for the East Asian Study of Tropospheric Aerosols: An International Regional Experiment (EAST-AIRE). Aerosol optical properties derived from measurements by a Sun photometer were analyzed. The aerosol data were used together with surface irradiance data to quantitatively estimate aerosol effects on surface shortwave radiation (SWR) and photosynthetically active radiation (PAR). The annual mean aerosol optical depth at 500 nm is 0.77, and mean Ångstrom wavelength exponent is 1.17. The annual mean aerosol single scattering albedo and mean aerosol asymmetry factor at 440 nm are 0.90 and 0.72, respectively. Both parameters show a weak seasonal variation, with small values occurring during the winter and larger values during the summer. Clear positive relationships between relative humidity and aerosol properties suggest aerosol hygroscopic growth greatly modifies aerosol properties. The annual mean aerosol direct radiative forcing at the surface (ADRF) is −38.4 W m−2 and −17.8 W m−2 for SWR and PAR, respectively. Because of moderate absorption, the instantaneous ADRF at the top of the atmosphere derived from CERES SSF data is close to zero. Heavy aerosol loading in this region leads to −112.6 W m−2 and −45.5 W m−2 reduction in direct and global SWR, but 67.1 W m−2 more diffuse SWR reaching the surface. With regard to PAR, the annual mean differences in global, direct and diffuse irradiance are −23.1 W m−2, −65.2 W m−2 and 42.1 W m−2 with and without the presence of aerosol, respectively. 0305 Aerosols and particles; 0345 Pollution: urban and regional; CERES; aerosol; radiative forcing; climate; 0478 Pollution: urban, regional and global; EAST-AIRE; Yangtze delta
Xu, K. M.; Wong, T.; Wielicki, B. A.; Parker, L.; Lin, B.; Eitzen, Z. A.; Branson, M.Xu, K. M., T. Wong, B. A. Wielicki, L. Parker, B. Lin, Z. A. Eitzen, M. Branson, 2007: Statistical analyses of satellite cloud object data from CERES. Part II: Tropical convective cloud objects during 1998 El Nino and evidence for supporting the fixed anvil temperature hypothesis. J. Climate, 20(5), 819-842. doi: 10.1175/jcli4069.1. Characteristics of tropical deep convective cloud objects observed over the tropical Pacific during January-August 1998 are examined using the Tropical Rainfall Measuring Mission/Clouds and the Earth's Radiant Energy System Single Scanner Footprint (SSF) data. These characteristics include the frequencies of occurrence and statistical distributions of cloud physical properties. Their variations with cloud object size, sea surface temperature (SST), and satellite precession cycle are analyzed in detail. A cloud object is defined as a contiguous patch of the earth composed of satellite footprints within a single dominant cloud-system type. It is found that statistical distributions of cloud physical properties are significantly different among three size categories of cloud objects with equivalent diameters of 100-150 (small), 150-300 (medium), and > 300 km (large), except for the distributions of ice particle size. The distributions for the larger-size category of cloud objects are more skewed toward high SSTs, high cloud tops, low cloud-top temperature, large ice water path, high cloud optical depth, low outgoing longwave (LW) radiation, and high albedo than the smaller-size category. As SST varied from one satellite precession cycle to another, the changes in macrophysical properties of cloud objects over the entire tropical Pacific were small for the large-size category of cloud objects, relative to those of the small- and medium-size categories. This evidence supports the fixed anvil temperature hypothesis of Hartmann and Larson for the large-size category. Combined with the result that a higher percentage of the large-size category of cloud objects occurs during higher SST subperiods, this implies that macro-physical properties of cloud objects would be less sensitive to further warming of the climate. On the other hand, when cloud objects are classified according to SST ranges, statistical characteristics of cloud microphysical properties, optical depth, and albedo are not sensitive to the SST, but those of cloud macrophysical properties are dependent upon the SST. This result is related to larger differences in large-scale dynamics among the SST ranges than among the satellite precession cycles. Frequency distributions of vertical velocity from the European Centre for Medium-Range Weather Forecasts model that is matched to each cloud object are used to further understand some of the findings in this study.
Zhou, Yaping; Kratz, David P.; Wilber, Anne C.; Gupta, Shashi K.; Cess, Robert D.Zhou, Y., D. P. Kratz, A. C. Wilber, S. K. Gupta, R. D. Cess, 2007: An improved algorithm for retrieving surface downwelling longwave radiation from satellite measurements. Journal of Geophysical Research: Atmospheres, 112(D15), D15102. doi: 10.1029/2006JD008159. Zhou and Cess (2001) developed an algorithm for retrieving surface downwelling longwave radiation (SDLW) based upon detailed studies using radiative transfer model calculations and surface radiometric measurements. The algorithm links clear sky SDLW with surface upwelling longwave (LW) flux and column precipitable water vapor. For cloudy sky cases, the cloud liquid water path is used as an additional parameter to account for the effects of clouds. Despite the simplicity of the algorithm, it performs very well for most geographical regions except for those regions where the atmospheric conditions near the surface tend to be extremely cold and dry. Systematic errors are also found for scenes that are covered with ice clouds. An improved version of the algorithm prevents the large errors in the SDLW at low water vapor amounts by taking into account that, under such conditions, the SDLW and water vapor amount are nearly linear in their relationship. The new algorithm also utilizes cloud fraction and cloud liquid and ice water paths available from the Cloud and the Earth's Radiant Energy System (CERES) single-scanner footprint (SSF) product to separately compute the clear and cloudy portions of the fluxes. The new algorithm has been validated against surface measurements at 29 stations around the globe for Terra and Aqua satellites. The results show significant improvement over the original version. Preliminary tests also suggest that the new algorithm works quite well for high elevation locations such as Tibet site where current satellite products exhibit large biases. The revised Zhou-Cess algorithm is also slightly better or comparable to more sophisticated algorithms currently implemented in the CERES processing and will be incorporated as one of the CERES empirical surface radiation algorithms. 0360 Radiation: transmission and scattering; 1640 Remote sensing; CERES; 3359 Radiative processes; 3337 Global climate models; 1622 Earth system modeling; empirical surface radiation algorithm; Radiative transfer in atmosphere
Allan, Richard P.Allan, R. P., 2006: Variability in clear-sky longwave radiative cooling of the atmosphere. Journal of Geophysical Research: Atmospheres, 111(D22), D22105. doi: 10.1029/2006JD007304. The longwave radiative cooling of the clear-sky atmosphere (QLWc) is a crucial component of the global hydrological cycle and is composed of the clear-sky outgoing longwave radiation to space (OLRc) and the net downward minus upward clear-sky longwave radiation to the surface (SNLc). Estimates of QLWc from reanalyses and observations are presented for the period 1979–2004. Compared to other reanalyses data sets, the European Centre for Medium-range Weather Forecasts 40-year reanalysis (ERA40) produces the largest QLWc over the tropical oceans (217 W m−2), explained by the least negative SNLc. On the basis of comparisons with data derived from satellite measurements, ERA40 provides the most realistic QLWc climatology over the tropical oceans but exhibits a spurious interannual variability for column integrated water vapor (CWV) and SNLc. Interannual monthly anomalies of QLWc are broadly consistent between data sets with large increases during the warm El Niño events. Since relative humidity (RH) errors applying throughout the troposphere result in compensating effects on the cooling to space and to the surface, they exert only a marginal effect on QLWc. An observed increase in CWV with surface temperature of 3 kg m−2 K−1 over the tropical oceans is important in explaining a positive relationship between QLWc and surface temperature, in particular over ascending regimes; over tropical ocean descending regions this relationship ranges from 3.6 to 4.6 ± 0.4 W m−2 K−1 for the data sets considered, consistent with idealized sensitivity tests in which tropospheric warming is applied and RH is held constant and implying an increase in precipitation with warming. 1655 Water cycles; 3359 Radiative processes; 3305 Climate change and variability; 1616 Climate variability; water vapor; hydrological cycle; radiation balance
Bender, Frida a-M.; Rodhe, Henning; Charlson, Robert J.; Ekman, Annica M. L.; Loeb, NormanBender, F. a., H. Rodhe, R. J. Charlson, A. M. L. Ekman, N. Loeb, 2006: 22 views of the global albedo—comparison between 20 GCMs and two satellites. Tellus A, 58(3), 320-330. doi: 10.1111/j.1600-0870.2006.00181.x. A comprehensive comparison of characteristics of the planetary albedo (α) in data from two satellite measurement campaigns (ERBE and CERES) and output from 20 GCMs, simulating the 20th-century climate, is performed. Discrepancies between different data sets and models exist; thus, it is clear that conclusions about absolute magnitude and accuracy of albedo should be drawn with caution. Yet, given the present calibrations, a bias is found between different estimates of α, with modelled global albedos being systematically higher than the observed. The difference between models and observations is larger for the more recent CERES measurements than the older ERBE measurements. Through the study of seasonal anomalies and space and time distribution of correaltions between models and observations, specific regions with large discrepancies can be identified. It is hereby found that models appear to over-estimate the albedo during boreal summer and under-estimate it during austral summer. Furthermore, the seasonal variations of albedo in subtropical areas dominated by low stratiform clouds, as well as in dry desert regions in the subtropics, seem to be poorly simulated by the models.
Bertrand, C.; Futyan, J.; Ipe, A.; Gonzalez, L.; Clerbaux, N.Bertrand, C., J. Futyan, A. Ipe, L. Gonzalez, N. Clerbaux, 2006: Diurnal Asymmetry in the GERB SW Fluxes. IEEE Transactions on Geoscience and Remote Sensing, 44(12), 3585-3600. doi: 10.1109/TGRS.2006.881119. The launch of the Geostationary Earth Radiation Budget (GERB) instrument onboard the Meteostat 8 allows a diurnal sampling of the Earth's Radiation Budget for the first time, providing a unique and important addition to polar-orbiting measurements. However, preliminary data from the GERB instrument exhibit systematic asymmetry in the short-wave (SW) flux diurnal variation. Such asymmetries are not found in the Clouds and the Earth's Radiant Energy System angular distribution models used to convert the directional broad-band GERB SW radiances to fluxes. Comparison between angularly matched estimations of reflected SW flux at the top of the atmosphere from the Spinning Enhanced Visible and Infra Red Imager (SEVIRI) and GERB data indicates that the SEVIRI spectral modeling could be a major issue. In addition, the results indicate that other factors such as the GERB SW geolocation, the GERB detector spectral response functions, the GERB nominal footprint resolution, and cloud cover could also potentially have an influence on the diurnal evolution of the GERB SW fluxes, as they can erroneously impact on the GERB SW correction factor atmosphere; clouds; Earth; earth radiation budget; Remote sensing; Sampling methods; Satellites; atmospheric radiation; atmospheric techniques; Instruments; Solar radiation; Atmospheric modeling; Cloud cover; detector spectral response functions; Detectors; Earth radiant energy system angular distribution models; geolocation; Geostationary Earth Radiation Budget instrument; Image converters; Meteostat 8; polar-orbiting measurements; short-wave flux diurnal variation; sky brightness; solar energy; spectral modeling; Spinning; Spinning Enhanced Visible and Infra Red Imager; Time measurement
Bertrand, Cédric; Clerbaux, Nicolas; Ipe, Alessandro; Dewitte, Steven; Gonzalez, LuisBertrand, C., N. Clerbaux, A. Ipe, S. Dewitte, L. Gonzalez, 2006: Angular distribution models anisotropic correction factors and sun glint: a sensitivity study. International Journal of Remote Sensing, 27(9), 1741-1757. doi: 10.1080/01431160500107015. Because radiometers do not measure the Earth's outgoing fluxes directly, angular distribution models (ADMs) are used to invert measured radiances at the top of atmosphere (TOA) to fluxes. In this study, we have investigated if the use of the newly developed clear ocean Clouds and the Earth's Radiant Energy System (CERES) broadband short wave (SW) ADMs from the Tropical Rainfall Measuring Mission (TRMM) satellite will allow reliable estimation of the instantaneous reflected SW fluxes at the TOA when the measured radiances are contaminated by sun glint. Using SW fluxes estimations computed from Meteosat‐7 visible radiances as a surrogate of the forthcoming Geostationary Earth Radiation Budget SW fluxes, our results indicate that while CERES‐TRMM ADMs angular resolution presents an advance over the previously built Earth Radiation Budget Experiment (ERBE) ADMs, the angular resolution is still too coarse to suitably define anisotropic correction factors in the sunlight region. SW fluxes are overestimated in the strong sun glint region and underestimated in the surrounding regions. Nevertheless, we show that by combining the high temporal sampling of the sun glint regions afforded by the geostationary orbit of the instrument with information contained in the clear ocean wind‐speed‐dependent CERES‐TRMM ADMs, an improved estimation of the reflected SW flux at the TOA is possible by comparison to a simple ADM flux interpolation.
Capderou, Michel; Viollier, MichelCapderou, M., M. Viollier, 2006: True Along-Track Scan to Improve Radiation Budget Estimations. J. Atmos. Oceanic Technol., 23(8), 1093-1103. doi: 10.1175/JTECH1907.1. Abstract Multiangle approaches for radiance-to-flux conversion require accurate coregistration between the observations from nadir- and oblique-viewing directions. The along-track mode of Earth Radiation Budget (ERB) scanning instruments, such as the Clouds and the Earth’s Radiant Energy System (CERES), provides some multiangular observations with almost the same target observed from nadir, aft, and fore directions. To improve the overlaps of multiangle observations, this study explains how to introduce a yaw steering angle in the along-track scan mode so as to reduce the residual collocations errors. The implementation of this correction to the CERES/Terra along-track mode shows that the distances between the nadir and the oblique (55°) observations are reduced from about 40 to 2 km. Both oblique radiances are shown to be equal with small rms differences: 3.9% (all scenes) and 1.8% (homogeneous scenes), compared, respectively, to 7.0% and 3.5% before the scan adjustment.
Choi, Yong-Sang; Ho, Chang-HoiChoi, Y., C. Ho, 2006: Radiative effect of cirrus with different optical properties over the tropics in MODIS and CERES observations. Geophysical Research Letters, 33(21), L21811. doi: 10.1029/2006GL027403. The radiative effects of cirrus clouds are evaluated based on observations extending over a period of six years (2000–2005) from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Clouds and the Earth's Radiant Energy System (CERES) over the Tropics (25°S–25°N). The cloud radiative effect (CRE) shows a positive sign for optically thin cirrus (total-column cloud optical depth: τ < 10) and a negative sign for thicker clouds (τ ≥ 10), regardless of the region and season. Since a considerable portion of tropical ice clouds consists in thin cirrus clouds (>60%), their net effective CRE (net CRE × cloud amount) is roughly twice as strong as that of thicker clouds; the modulation of the net radiative flux by variations in thin cirrus (particularly with 1 ≤ τ < 9) dominates—up to 15 W m−2—that by thicker clouds. These results suggest that thin cirrus has a significant effect on the tropical energy balance. 0321 Cloud/radiation interaction; 3359 Radiative processes; 3374 Tropical meteorology; 3310 Clouds and cloud feedbacks
Christopher, Sundar A.; Zhang, Jianglong; Kaufman, Yoram J.; Remer, Lorraine A.Christopher, S. A., J. Zhang, Y. J. Kaufman, L. A. Remer, 2006: Satellite-based assessment of top of atmosphere anthropogenic aerosol radiative forcing over cloud-free oceans. Geophysical Research Letters, 33(15), L15816. doi: 10.1029/2005GL025535. Most assessments of the direct climate forcing (DCF) of anthropogenic aerosols are from numerical simulations. However, recent advances in remote sensing techniques allow the separation of fine mode aerosols (anthropogenic aerosol is mostly fine aerosol) from coarse mode aerosols (largely marine and dust, which are mostly natural) from satellite data such as the Moderate Resolution Imaging SpectroRadiometer (MODIS). Here, by combining MODIS narrowband measurements with broadband radiative flux data sets from the Clouds and the Earth's Radiant Energy System (CERES), we provide a measurement-based assessment of the global direct climate forcing (DCF) of anthropogenic aerosols at the top of atmosphere (TOA) only for cloud free oceans. The mean TOA DCF of anthropogenic aerosols over cloud-freeoceans [60N–60S] is −1.4 ± 0.9 Wm−2, which is in excellent agreement (mean value of −1.4 Wm−2) with a recent observational study by Kaufman et al. [2005]. 0305 Aerosols and particles; 3359 Radiative processes; 4801 Aerosols
Clement, Amy C.Clement, A. C., 2006: The Role of the Ocean in the Seasonal Cycle of the Hadley Circulation. J. Atmos. Sci., 63(12), 3351-3365. doi: 10.1175/JAS3811.1. Abstract The influence of ocean heat transport on the seasonal cycle of the Hadley circulation is investigated using idealized experiments with a climate model. It is found that ocean heat transport plays a fundamental role in setting the structure and intensity of the seasonal Hadley cells. The ocean’s influence can be understood primarily via annual mean considerations. By cooling the equatorial regions and warming the subtropics in a year-round sense, the ocean heat transport allows for regions of SST maxima to occur off the equator in the summer hemisphere. This leads to large meridional excursions of convection over the ocean and a seasonal Hadley circulation that is strongly asymmetric about the equator. The broadening of the latitudinal extent of the SST maximum and the convecting regions by the ocean heat transport also weakens the annual mean Hadley circulation in a manner that is consistent with simpler models. The results are discussed in the context of prior studies of the controls on the strength and structure of the Hadley circulation. It is suggested that a complete understanding of the seasonal Hadley circulation must include both oceanic and atmospheric processes and their interactions. Atmospheric circulation; Heating; Oceanic variability; Seasonal cycle; transport
Dong, Xiquan; Xi, Baike; Minnis, PatrickDong, X., B. Xi, P. Minnis, 2006: A Climatology of Midlatitude Continental Clouds from the ARM SGP Central Facility. Part II: Cloud Fraction and Surface Radiative Forcing. J. Climate, 19(9), 1765-1783. doi: 10.1175/JCLI3710.1. Abstract Data collected at the Department of Energy Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) Central Facility (SCF) are analyzed to determine the monthly and hourly variations of cloud fraction and radiative forcing between January 1997 and December 2002. Cloud fractions are estimated for total cloud cover and for single-layered low (0–3 km), middle (3–6 km), and high clouds (>6 km) using ARM SCF ground-based paired lidar–radar measurements. Shortwave (SW) and longwave (LW) fluxes are derived from up- and down-looking standard precision spectral pyranometers and precision infrared radiometer measurements with uncertainties of ∼10 W m−2. The annual averages of total and single-layered low-, middle-, and high-cloud fractions are 0.49, 0.11, 0.03, and 0.17, respectively. Both total- and low-cloud amounts peak during January and February and reach a minimum during July and August; high clouds occur more frequently than other types of clouds with a peak in summer. The average annual downwelling surface SW fluxes for total and low clouds (151 and 138 W m−2, respectively) are less than those under middle and high clouds (188 and 201 W m−2, respectively), but the downwelling LW fluxes (349 and 356 W m−2) underneath total and low clouds are greater than those from middle and high clouds (337 and 333 W m−2). Low clouds produce the largest LW warming (55 W m−2) and SW cooling (−91 W m−2) effects with maximum and minimum absolute values in spring and summer, respectively. High clouds have the smallest LW warming (17 W m−2) and SW cooling (−37 W m−2) effects at the surface. All-sky SW cloud radiative forcing (CRF) decreases and LW CRF increases with increasing cloud fraction with mean slopes of −0.984 and 0.616 W m−2 %−1, respectively. Over the entire diurnal cycle, clouds deplete the amount of surface insolation more than they add to the downwelling LW flux. The calculated CRFs do not appear to be significantly affected by uncertainties in data sampling and clear-sky screening. Traditionally, cloud radiative forcing includes not only the radiative impact of the hydrometeors, but also the changes in the environment. Taken together over the ARM SCF, changes in humidity and surface albedo between clear and cloudy conditions offset ∼20% of the NET radiative forcing caused by the cloud hydrometeors alone. Variations in water vapor, on average, account for 10% and 83% of the SW and LW CRFs, respectively, in total cloud cover conditions. The error analysis further reveals that the cloud hydrometeors dominate the SW CRF, while water vapor changes are most important for LW flux changes in cloudy skies. Similar studies over other locales are encouraged where water and surface albedo changes from clear to cloudy conditions may be much different than observed over the ARM SCF.
Dong, Xiquan; Xi, Baike; Minnis, PatrickDong, X., B. Xi, P. Minnis, 2006: Observational evidence of changes in water vapor, clouds, and radiation at the ARM SGP site. Geophysical Research Letters, 33(19), L19818. doi: 10.1029/2006GL027132. Characterizing water vapor and cloud effects on the surface radiation budget is critical for understanding the current climate because water vapor is the most important greenhouse gas in the atmosphere and clouds are one of the largest sources of uncertainty in predicting potential future climate change. Several studies have shown that insolation over land declined until 1990 then increased until the present. Using 8 years of data collected at the ARM Southern Great Plains (SGP) surface site, we found that the insolation increased from 1997 to 2000, but significantly decreased from 2001 to 2004, changes that exactly mirror the variation in the second-order fit of cloud fraction. Under clear-sky conditions, the rates of change of water vapor, insolation and downwelling longwave (LW) flux are −0.0166 cm/yr, 0.48 Wm−2/yr, and −1.16 Wm−2/yr, respectively, indicating that water vapor changes are more important for LW flux than for insolation. 1640 Remote sensing; 0321 Cloud/radiation interaction; 1616 Climate variability; 1637 Regional climate change
Huang, J.P.; Yujie, Wang; Tianhe, Wang; Yuhong, YiHuang, J., W. Yujie, W. Tianhe, Y. Yuhong, 2006: Dusty cloud radiative forcing derived from satellite data for middle latitude regions of East Asia. Progress in Natural Science, 16(10), 1084-1089. doi: 10.1080/10020070612330114. The dusty cloud radiative forcing over the middle latitude regions of East Asia was estimated by using the 2-year (July 2002-June 2004) data of collocated clouds and the Earth's radiant energy system (CERES) scanner and moderate resolution imaging spectroradiometer (MODIS) from Aqua Edition 1B SSF (single scanner footprint). The dusty cloud is defined as the cloud in dust storm environment or dust contaminated clouds. For clouds growing in the presence of dust, the instantaneous short-wave (SW) forcing at the top of the atmosphere (TOA) is about -275.7 W/m2 for cloud over dust (COD) region. The clouds developing in no-dust cloud (CLD) regions yield the most negative short-wave (SW) forcint (-311.0 W/m2), which is about 12.8% stronger than those in COD regions. For long-wave (LW) radiative forcing, the no-dust cloud (CLD) is around 102.8 W/m2, which is 20% less than the LW forcing from COD regions. The instantaneous TOA net radiative forcing for the CLD region is about -208.2W/m2, which is 42.1% larger than the values of COD regions. The existence of dust aerosols under clouds significantly reduces the cooling effect of clouds. * Supported by the Major State Basic Research Development Program of China (Grant No. 2006CB400501) and National Natural Science Foundation of China (Grant No. 40575036)
Huang, Jianping; Lin, Bing; Minnis, Patrick; Wang, Tianhe; Wang, Xin; Hu, Yongxiang; Yi, Yuhong; Ayers, J. KirkHuang, J., B. Lin, P. Minnis, T. Wang, X. Wang, Y. Hu, Y. Yi, J. K. Ayers, 2006: Satellite-based assessment of possible dust aerosols semi-direct effect on cloud water path over East Asia. Geophysical Research Letters, 33(19), L19802. doi: 10.1029/2006GL026561. The semi-direct effects of dust aerosols are analyzed over eastern Asia using 2 years (June 2002 to June 2004) of data from the Clouds and the Earth's Radiant Energy System (CERES) scanning radiometer and MODerate Resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite, and 18 years (1984 to 2001) of International Satellite Cloud Climatology Project (ISCCP) data. The results show that the water path of dust-contaminated clouds is considerably smaller than that of dust-free clouds. The mean ice water path (IWP) and liquid water path (LWP) of dusty clouds are less than their dust-free counterparts by 23.7% and 49.8%, respectively. The long-term statistical relationship derived from ISCCP also confirms that there is significant negative correlation between dust storm index and ISCCP cloud water path (CWP). These results suggest that dust aerosols warm clouds, increase the evaporation of cloud droplets and further reduce the CWP, the so-called semi-direct effect. The semi-direct effect may play a role in cloud development over arid and semi-arid areas of East Asia and contribute to the reduction of precipitation. 0320 Cloud physics and chemistry; 1620 Climate dynamics; 3309 Climatology; 3359 Radiative processes
Huang, Jianping; Minnis, Patrick; Lin, Bing; Wang, Tianhe; Yi, Yuhong; Hu, Yongxiang; Sun-Mack, Sunny; Ayers, KirkHuang, J., P. Minnis, B. Lin, T. Wang, Y. Yi, Y. Hu, S. Sun-Mack, K. Ayers, 2006: Possible influences of Asian dust aerosols on cloud properties and radiative forcing observed from MODIS and CERES. Geophysical Research Letters, 33(6), L06824. doi: 10.1029/2005GL024724. The effects of dust storms on cloud properties and Radiative Forcing (RF) are analyzed over Northwestern China from April 2001 to June 2004 using data collected by the MODerate Resolution Imaging Spectroradiometer (MODIS) and Clouds and the Earth's Radiant Energy System (CERES) instruments on the Aqua and Terra satellites. On average, ice cloud effective particle diameter, optical depth and ice water path of cirrus clouds under dust polluted conditions are 11%, 32.8%, and 42% less, respectively, than those derived from ice clouds in dust-free atmospheric environments. Due to changes in cloud microphysics, the instantaneous net RF is increased from −161.6 W/m2 for dust-free clouds to −118.6 W/m2 for dust-contaminated clouds. 0320 Cloud physics and chemistry; 0305 Aerosols and particles; 3359 Radiative processes
Huang, Jianping; Minnis, Patrick; Lin, Bing; Yi, Yuhong; Fan, T.-F.; Sun-Mack, Sunny; Ayers, J. K.Huang, J., P. Minnis, B. Lin, Y. Yi, T. Fan, S. Sun-Mack, J. K. Ayers, 2006: Determination of ice water path in ice-over-water cloud systems using combined MODIS and AMSR-E measurements. Geophysical Research Letters, 33(21), L21801. doi: 10.1029/2006GL027038. To provide more accurate ice cloud microphysical properties, the multi-layered cloud retrieval system (MCRS) is used to retrieve ice water path (IWP) in ice-over-water cloud systems globally over oceans using combined instrument data from Aqua. The liquid water path (LWP) of lower-layer water clouds is estimated from the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) measurements. The properties of the upper-level ice clouds are then derived from Moderate Resolution Imaging Spectroradiometer (MODIS) measurements by matching simulated radiances from a two-cloud-layer radiative transfer model. The results show that the MCRS can significantly improve the accuracy and reduce the over-estimation of optical depth and IWP retrievals for ice-over-water cloud systems. The mean daytime ice cloud optical depth and IWP for overlapped ice-over-water clouds over oceans from Aqua are 7.6 and 146.4 gm−2, respectively, down from the initial single-layer retrievals of 17.3 and 322.3 gm−2. The mean IWP for actual single-layer clouds is 128.2 gm−2. 0320 Cloud physics and chemistry; 1620 Climate dynamics; 3359 Radiative processes
Ignatov, Alexander; Minnis, Patrick; Miller, Walter F.; Wielicki, Bruce A.; Remer, LorraineIgnatov, A., P. Minnis, W. F. Miller, B. A. Wielicki, L. Remer, 2006: Consistency of global MODIS aerosol optical depths over ocean on Terra and Aqua CERES SSF data sets. Journal of Geophysical Research: Atmospheres, 111(D14), D14202. doi: 10.1029/2005JD006645. Aerosol retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Terra and Aqua platforms are available from the Clouds and the Earth's Radiant Energy System (CERES) Single Scanner Footprint (SSF) data sets. Over ocean, two aerosol products are reported side by side. The primary M product is generated by subsetting and remapping the multispectral (from 0.47 to 2.1 μm) MOD04/MYD04 oceanic aerosol data onto CERES footprints. M*D04 processing uses cloud screening and aerosol algorithms developed by the MODIS science team. The secondary AVHRR-like A product is generated in only two MODIS bands. The A processing uses the CERES cloud-screening algorithm and NOAA/NESDIS glint identification and single-channel aerosol retrieval algorithms. The M and A products have been documented elsewhere and preliminarily compared using 2 weeks of global Terra CERES SSF edition 1A data, in which the M product was based on MOD04 collection 3. In this study, the comparisons between the M and A aerosol optical depths (AOD) in MODIS band 1 (0.64 μm), τ1M and τ1A, are reexamined using 9 days of global CERES SSF Terra edition 2A and Aqua edition 1B data from 13 to 21 October 2002 and extended to include cross-platform comparisons. The M and A products on the new CERES SSF release are generated using the same aerosol algorithms as before but with different preprocessing and sampling procedures, thus lending themselves to a simple sensitivity check to nonaerosol factors. Both τ1M and τ1A generally compare well across platforms. However, the M product shows larger differences, which increase with ambient cloud amount and toward the solar side of the orbit. The cross-platform, cross-product, and cross-release comparisons conducted in this study confirm an earlier observation that the major area for improvement in the current aerosol processing lies in a more formalized and standardized sampling (most importantly, cloud screening), whereas optimization of the aerosol algorithm is deemed to be an important yet less critical element. 1640 Remote sensing; 0305 Aerosols and particles; aerosol; MODIS; 0758 Remote sensing; consistency
Jin, Zhonghai; Charlock, Thomas P.; Rutledge, Ken; Stamnes, Knut; Wang, YingjianJin, Z., T. P. Charlock, K. Rutledge, K. Stamnes, Y. Wang, 2006: Analytical solution of radiative transfer in the coupled atmosphere-ocean system with a rough surface. Applied Optics, 45(28), 7443. doi: 10.1364/AO.45.007443.
Kato, Seiji; Hinkelman, Laura M.; Cheng, AnningKato, S., L. M. Hinkelman, A. Cheng, 2006: Estimate of satellite-derived cloud optical thickness and effective radius errors and their effect on computed domain-averaged irradiances. Journal of Geophysical Research: Atmospheres, 111(D17), D17201. doi: 10.1029/2005JD006668. The process of retrieving cloud optical thickness and effective radius from radiances measured by satellite instruments is simulated to determine the error in both the retrieved properties and in the irradiances computed with them. The radiances at 0.64 μm and 3.7 μm are computed for three cloud fields (stratus, stratocumulus, and cumulus) generated by large eddy simulation models. When overcast pixels are assumed and the horizontal flux is neglected in the retrieval process, the error in the domain-averaged retrieved optical thickness from nadir is 1% to −32% (1% to −27%) and the error in the retrieved effective radius is 0% to 67% (0% to 63%) for the solar zenith angle of 30° (50°). Using the radiance averaged over a 1 km size pixel also introduces error in the optical thickness because of the nonlinear relation between the reflected radiance and optical thickness. Both optical thickness and effective radius errors increase with increasing horizontal inhomogeneity. When the 0.64 μm albedo is computed with the independent column approximation using retrieved properties from nadir (oblique) view for a solar zenith angle of 50°, the error is −0.3% to 14% (−5% to −30%) relative to the albedo from 3-D radiative transfer computations with the true cloud properties. The albedo error occurs even though the radiance at one angle is forced to agree because a plane parallel cloud with a single value of optical thickness and effective radius cannot consistently match the radiance angular distribution. In addition, the error in the retrieved cloud properties contributes to the albedo error. When albedos computed with cloud properties derived from nadir and oblique views are averaged, the albedo error can partially cancel. The absolute error in the narrowband 0.64 μm (3.7 μm) albedo averaged over a 1° × 1° domain is less than 1.5% (0.6%), 5.0% (4.1%), and 7.1% (11%) in order of increasing inhomogeneity, when albedos computed with cloud properties derived from viewing zenith angles between 0° and 60° are averaged and when the solar zenith angle is between 10° and 50°. When the solar zenith angle is 70°, the error increases to up to +24% (+37%) for all three scenes. 0360 Radiation: transmission and scattering; 0321 Cloud/radiation interaction; 3359 Radiative processes; radiation budget; remote sensing of clouds
Kato, Seiji; Loeb, Norman G.; Minnis, Patrick; Francis, Jennifer A.; Charlock, Thomas P.; Rutan, David A.; Clothiaux, Eugene E.; Sun-Mack, SzedungKato, S., N. G. Loeb, P. Minnis, J. A. Francis, T. P. Charlock, D. A. Rutan, E. E. Clothiaux, S. Sun-Mack, 2006: Seasonal and interannual variations of top-of-atmosphere irradiance and cloud cover over polar regions derived from the CERES data set. Geophysical Research Letters, 33(19), L19804. doi: 10.1029/2006GL026685. The daytime cloud fraction derived by the Clouds and the Earth's Radiant Energy System (CERES) cloud algorithm using Moderate Resolution Imaging Spectroradiometer (MODIS) radiances over the Arctic from March 2000 through February 2004 increases at a rate of 0.047 per decade. The trend is significant at an 80% confidence level. The corresponding top-of-atmosphere (TOA) shortwave irradiances derived from CERES radiance measurements show less significant trend during this period. These results suggest that the influence of reduced Arctic sea ice cover on TOA reflected shortwave radiation is reduced by the presence of clouds and possibly compensated by the increase in cloud cover. The cloud fraction and TOA reflected shortwave irradiance over the Antarctic show no significant trend during the same period. 3311 Clouds and aerosols; 3359 Radiative processes; 1616 Climate variability; 3339 Ocean/atmosphere interactions
Kiehl, J. T.; Ramanathan, V.Kiehl, J. T., V. Ramanathan, 2006: Frontiers of Climate Modeling. The physics and dynamics of the atmosphere and atmosphere-ocean interactions provide the foundation of modern climate models, upon which our understanding of the chemistry and biology of ocean and land surface processes are built. Originally published in 2006, Frontiers of Climate Modeling captures developments in modeling the atmosphere, and their implications for our understanding of climate change, whether due to natural or anthropogenic causes. Emphasis is on elucidating how greenhouse gases and aerosols are altering the radiative forcing of the climate system and the sensitivity of the system to such perturbations. An expert team of authors address key aspects of the atmospheric greenhouse effect, clouds, aerosols, atmospheric radiative transfer, deep convection dynamics, large scale ocean dynamics, stratosphere-troposphere interactions, and coupled ocean-atmosphere model development. The book is an important reference for researchers and advanced students interested in the forces driving the climate system and how they are modeled by climate scientists. Computers / Desktop Applications / Design & Graphics; Science / Earth Sciences / Meteorology & Climatology
Lee, Yong-Keun; Yang, Ping; Hu, Yongxiang; Baum, Bryan A.; Loeb, Norman G.; Gao, Bo-CaiLee, Y., P. Yang, Y. Hu, B. A. Baum, N. G. Loeb, B. Gao, 2006: Potential nighttime contamination of CERES clear-sky fields of view by optically thin cirrus during the CRYSTAL-FACE campaign. Journal of Geophysical Research: Atmospheres, 111(D9), D09203. doi: 10.1029/2005JD006372. We investigate the outgoing broadband longwave (LW, 5∼200 μm) and window (WIN, 8∼12 μm) channel radiances at the top of atmosphere (TOA) under clear-sky conditions, using data acquired by the Cloud and the Earth's Radiant Energy System (CERES) and Moderate-Resolution Imaging Spectroradiometer (MODIS) instruments on board the NASA Terra satellite platform. In this study, detailed analyses are performed on the CERES Single Scanner Footprint TOA/Surface Fluxes and Clouds product to understand the radiative effect of thin cirrus. The data are acquired over the Florida area during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers – Florida Area Cirrus Experiment (CRYSTAL-FACE) field program. Of particular interest is the anisotropy associated with the radiation field. Measured CERES broadband radiances are compared to those obtained from rigorous radiative transfer simulations. Analysis of results from this comparison indicates that the simulated radiances tend to be larger than their measured counterparts, with differences ranging from 2.1% to 8.3% for the LW band and from 1.7% to 10.6% for the WIN band. The averaged difference in radiance is approximately 4% for both the LW and WIN channels. A potential cause for the differences could be the presence of thin cirrus (i.e., optically thin ice clouds with visible optical thicknesses smaller than approximately 0.3). The detection and quantitative analysis of these thin cirrus clouds are challenging even with sophisticated multispectral instruments. While large differences in radiance between the CERES observations and the theoretical calculations are found, the corresponding difference in the anisotropic factors is very small (0.2%). Furthermore, sensitivity studies show that the influence due to a ±1 K bias of the surface temperature on the errors of the LW and WIN channel radiances is of the same order as that associated with a ±2% bias of the surface emissivity. The LW and WIN errors associated with a ±5% bias of water vapor amount in the lower atmosphere in conjunction with a ±50% bias of water vapor amount in the upper atmosphere is similar to that of a ±1 K bias of the vertical temperature profile. Even with the uncertainties considered for these various factors, the simulated LW and WIN radiances are still larger than the observed radiances if thin cirrus clouds are excluded. 0360 Radiation: transmission and scattering; CERES; 0321 Cloud/radiation interaction; cirrus clouds
Li, J.; Scinocca, J.; Lazare, M.; McFarlane, N.; von Salzen, K.; Solheim, L.Li, J., J. Scinocca, M. Lazare, N. McFarlane, K. von Salzen, L. Solheim, 2006: Ocean Surface Albedo and Its Impact on Radiation Balance in Climate Models. J. Climate, 19(24), 6314-6333. doi: 10.1175/JCLI3973.1. Abstract An analysis of several ocean surface albedo (OSA) schemes is undertaken through offline comparisons and through application in the Canadian Centre for Climate Modelling and Analysis (CCCma) fourth-generation atmospheric general circulation model (AGCM4). In general, each scheme requires different input quantities to determine the OSA. Common to all schemes is a dependence on the solar zenith angle (SZA). A direct comparison of the SZA dependence of the schemes reveals significant differences in the predicted albedos. Other input quantities include wind speed and aerosol/cloud optical depth, which are also analyzed. An offline one-dimensional radiative transfer model is used to quantitatively study the impact of ocean surface albedo on the radiative transfer process. It is found that, as a function of SZA and wind speed, the difference in reflected solar flux at the top of the atmosphere is in general agreement between OSA schemes that depend on these quantities, with a difference albedo; Radiation budgets; climate models
Lin, Bing; Wielicki, Bruce A.; Minnis, Patrick; Chambers, Lin; Xu, Kuan-Man; Hu, Yongxiang; Fan, AliceLin, B., B. A. Wielicki, P. Minnis, L. Chambers, K. Xu, Y. Hu, A. Fan, 2006: The Effect of Environmental Conditions on Tropical Deep Convective Systems Observed from the TRMM Satellite. J. Climate, 19(22), 5745-5761. doi: 10.1175/JCLI3940.1. Abstract This study uses measurements of radiation and cloud properties taken between January and August 1998 by three Tropical Rainfall Measuring Mission (TRMM) instruments, the Clouds and the Earth’s Radiant Energy System (CERES) scanner, the TRMM Microwave Imager (TMI), and the Visible and Infrared Scanner (VIRS), to evaluate the variations of tropical deep convective systems (DCSs) with sea surface temperature and precipitation. The authors find that DCS precipitation efficiency increases with SST at a rate of ∼2% K−1. Despite increasing rainfall efficiency, the cloud areal coverage rises with SST at a rate of about 7% K−1 in the warm tropical seas. There, the boundary layer moisture supply for deep convection and the moisture transported to the upper troposphere for cirrus anvil cloud formation increase by ∼6.3% and ∼4.0% K−1, respectively. The changes in cloud formation efficiency, along with the increased transport of moisture available for cloud formation, likely contribute to the large rate of increasing DCS areal coverage. Although no direct observations are available, the increase of cloud formation efficiency with rising SST is deduced indirectly from measurements of changes in the ratio of DCS ice water path and boundary layer water vapor amount with SST. Besides the cloud areal coverage, DCS cluster effective sizes also increase with precipitation. Furthermore, other cloud properties, such as cloud total water and ice water paths, increase with SST. These changes in DCS properties will produce a negative radiative feedback for the earth’s climate system due to strong reflection of shortwave radiation by the DCS. These results significantly differ from some previously hypothesized dehydration scenarios for warmer climates, partially support the thermostat hypothesis but indicate a smaller magnitude of the negative feedback, and have great potential in testing current cloud-system-resolving models and convective parameterizations of general circulation models. cloud properties; radiation; Cirrus anvils; Convective systems; SST–moist convection feedback
Loeb, Norman G.; Sun, Wenbo; Miller, Walter F.; Loukachine, Konstantin; Davies, RogerLoeb, N. G., W. Sun, W. F. Miller, K. Loukachine, R. Davies, 2006: Fusion of CERES, MISR, and MODIS measurements for top-of-atmosphere radiative flux validation. Journal of Geophysical Research: Atmospheres, 111(D18), D18209. doi: 10.1029/2006JD007146. The Clouds and the Earth's Radiant Energy System (CERES), Multiangle Imaging Spectroradiometer (MISR), and Moderate-resolution Imaging Spectroradiometer (MODIS) instruments aboard the Terra satellite make critical measurements of cloud and aerosol properties and their effects on the Earth's radiation budget. In this study, a new multiangle, multichannel data set that combines measurements from all three instruments is created to assess uncertainties in instantaneous shortwave (SW) top-of-atmosphere (TOA) radiative fluxes inferred from CERES Angular Distribution Models (ADMs). MISR Level 1B2 ellipsoid-projected radiances from nine viewing directions in four spectral bands are merged with CERES by convolving the MISR radiances with the CERES Point Spread Function. The merged CERES-MISR data are then combined with the CERES Single Scanner Footprint TOA/Surface Fluxes and Clouds (SSF) product to produce the first merged CERES-MISR-MODIS data set. CERES and MISR data are used to generate narrow-to-broadband regression coefficients to convert narrowband MISR radiances to broadband SW radiances as a function of MODIS-based scene type. The regression uncertainty for all-sky conditions over ocean is approximately 4%. Up to nine SW TOA fluxes for every CERES footprint are estimated by applying the CERES Terra ADMs to each MISR angle. Assuming that differences along the line-of-sight from the different MISR angles are small, the consistency of the TOA fluxes provides an indication of the instantaneous TOA flux uncertainty. The overall relative consistency of all-sky ocean TOA fluxes is 6% (17 W m−2). When stratified by cloud type, TOA fluxes are consistent to 2–3% ( 1610 Atmosphere; 1640 Remote sensing; radiative flux; 3311 Clouds and aerosols; data fusion; top-of-atmosphere
Mace, Gerald G.; Benson, Sally; Kato, SeijiMace, G. G., S. Benson, S. Kato, 2006: Cloud radiative forcing at the Atmospheric Radiation Measurement Program Climate Research Facility: 2. Vertical redistribution of radiant energy by clouds. Journal of Geophysical Research: Atmospheres, 111(D11), D11S91. doi: 10.1029/2005JD005922. Documentation of the effects of clouds on the radiant energy balance of the surface and atmosphere represents a shortcoming in the set of observations that are needed to ascertain the validity of climate model simulations. While clouds are known to cool the climate system from top of atmosphere (TOA) radiation budget studies, the redistribution of energy between the surface and atmosphere and within the atmosphere by clouds has not been examined in detail with observations. Using data collected at the Atmospheric Radiation Measurement Program (ARM) Southern Great Plains (SGP) site, we use measurements of cloud occurrence and structure together with a scheme to characterize the cloud microphysical and radiative properties to estimate the uncertainty in our ability to calculate the radiative forcing and effect of clouds at the top of atmosphere, the surface and within the atmosphere. We find that overcast clouds during 2000 tended to have a small net influence on the atmosphere (6 W m−2 ± 3 W m−2 of heating) with net TOA and surface cooling (25 W m−2 ± 3 W m−2 and 32 ± 3 W m−2, respectively). These statistics mask a significant redistribution of radiant energy within the atmosphere by clouds where low overcast clouds resulted in strong atmospheric cooling (37 W m−2 ± 9 W m−2), and thin high clouds resulted in warming (21 W m−2 ± 6 W m−2) suggesting that accurate prediction of the phasing of these cloud types within meteorological features is important for capturing the essential feedbacks by clouds to the general circulation. clouds; 3359 Radiative processes; 3310 Clouds and cloud feedbacks; climate; radiation; 3364 Synoptic-scale meteorology
Mace, Gerald G.; Benson, Sally; Sonntag, Karen L.; Kato, Seiji; Min, Qilong; Minnis, Patrick; Twohy, Cynthia H.; Poellot, Michael; Dong, Xiquan; Long, Charles; Zhang, Qiuqing; Doelling, David R.Mace, G. G., S. Benson, K. L. Sonntag, S. Kato, Q. Min, P. Minnis, C. H. Twohy, M. Poellot, X. Dong, C. Long, Q. Zhang, D. R. Doelling, 2006: Cloud radiative forcing at the Atmospheric Radiation Measurement Program Climate Research Facility: 1. Technique, validation, and comparison to satellite-derived diagnostic quantities. Journal of Geophysical Research: Atmospheres, 111(D11), D11S90. doi: 10.1029/2005JD005921. It has been hypothesized that continuous ground-based remote sensing measurements from collocated active and passive remote sensors combined with regular soundings of the atmospheric thermodynamic structure can be combined to describe the effects of clouds on the clear sky radiation fluxes. We critically test that hypothesis in this paper and a companion paper (part 2). Using data collected at the Southern Great Plains (SGP) Atmospheric Radiation Measurement (ARM) site sponsored by the U.S. Department of Energy, we explore an analysis methodology that results in the characterization of the physical state of the atmospheric profile at time resolutions of 5 min and vertical resolutions of 90 m. The description includes thermodynamics and water vapor profile information derived by merging radiosonde soundings with ground-based data and continues through specification of the cloud layer occurrence and microphysical and radiative properties derived from retrieval algorithms and parameterizations. The description of the atmospheric physical state includes a calculation of the clear and cloudy sky solar and infrared flux profiles. Validation of the methodology is provided by comparing the calculated fluxes with top of atmosphere (TOA) and surface flux measurements and by comparing the total column optical depths to independently derived estimates. We find over a 1-year period of comparison in overcast uniform skies that the calculations are strongly correlated to measurements with biases in the flux quantities at the surface and TOA of less than 6% and median fractional errors ranging from 12% to as low as 2%. In the optical depth comparison for uniform overcast skies during the year 2000 where the optical depth varies over more than 3 orders of magnitude we find a mean positive bias of less than 1% and a 0.6 correlation coefficient. In addition to a case study where we examine the cloud radiative effects at the TOA, surface and atmosphere by a middle latitude cyclone, we examine the cloud top pressure and optical depth retrievals of ISCCP and LBTM over a period of 1 year. Using overcast periods from the year 2000, we find that the satellite algorithms tend to compare well with data overall but there is a tendency to bias cloud tops into the middle troposphere and underestimate optical depth in high optical depth events. clouds; Remote sensing; 3311 Clouds and aerosols; 3359 Radiative processes; 3310 Clouds and cloud feedbacks; 3394 Instruments and techniques; radiation
Michalsky, J. J.; Anderson, G. P.; Barnard, J.; Delamere, J.; Gueymard, C.; Kato, S.; Kiedron, P.; McComiskey, A.; Ricchiazzi, P.Michalsky, J. J., G. P. Anderson, J. Barnard, J. Delamere, C. Gueymard, S. Kato, P. Kiedron, A. McComiskey, P. Ricchiazzi, 2006: Shortwave radiative closure studies for clear skies during the Atmospheric Radiation Measurement 2003 Aerosol Intensive Observation Period. Journal of Geophysical Research: Atmospheres, 111(D14), D14S90. doi: 10.1029/2005JD006341. The Department of Energy's Atmospheric Radiation Measurement (ARM) program sponsored a large aerosol intensive observation period (AIOP) to study aerosol during the month of May 2003 around the Southern Great Plains (SGP) Climate Research Facility (CRF) in north central Oklahoma. Redundant measurements of aerosol optical properties were made using different techniques at the surface as well as in vertical profile with sensors aboard two aircraft. One of the principal motivations for this experiment was to resolve the disagreement between models and measurements of diffuse horizontal broadband shortwave irradiance at the surface, especially for modest aerosol loading. This paper focuses on using the redundant aerosol and radiation measurements during this AIOP to compare direct beam and diffuse horizontal broadband shortwave irradiance measurements and models at the surface for a wide range of aerosol cases that occurred during 30 clear-sky periods on 13 days of May 2003. Models and measurements are compared over a large range of solar-zenith angles. Six different models are used to assess the relative agreement among them and the measurements. Better agreement than previously achieved appears to be the result of better specification of input parameters and better measurements of irradiances than in prior studies. Biases between modeled and measured direct irradiances are in the worst case 1%, and biases between modeled and measured diffuse irradiances are less than 1.9%. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 0394 Instruments and techniques; 3359 Radiative processes; diffuse shortwave irradiance; direct shortwave irradiance; radiative transfer models
Min, Qilong; Lin, BingMin, Q., B. Lin, 2006: Remote sensing of evapotranspiration and carbon uptake at Harvard Forest. Remote Sensing of Environment, 100(3), 379-387. doi: 10.1016/j.rse.2005.10.020. A land surface vegetation index, defined as the difference of microwave land surface emissivity at 19 and 37 GHz, was calculated for a heavily forested area in north central Massachusetts. The microwave emissivity difference vegetation index (EDVI) was estimated from satellite SSM/I measurements at the defined wavelengths and used to estimate land surface turbulent fluxes. Narrowband visible and infrared measurements and broadband solar radiation observations were used in the EDVI retrievals and turbulent flux estimations. The EDVI values represent physical properties of crown vegetation such as vegetation water content of crown canopies. The collocated land surface turbulent and radiative fluxes were empirically linked together by the EDVI values. The EDVI values are statistically sensitive to evapotranspiration fractions (EF) with a correlation coefficient (R) greater than 0.79 under all-sky conditions. For clear skies, EDVI estimates exhibit a stronger relationship with EF than normalized difference vegetation index (NDVI). Furthermore, the products of EDVI and input energy (solar and photosynthetically active radiation) are statistically significantly correlated to evapotranspiration (R = 0.95) and CO2 uptake flux (R = 0.74), respectively. Carbon uptake; Evapotranspiration; Microwave emissivity; Vegetation water content
Min, Qilong; Lin, BingMin, Q., B. Lin, 2006: Determination of spring onset and growing season leaf development using satellite measurements. Remote Sensing of Environment, 104(1), 96-102. doi: 10.1016/j.rse.2006.05.006. An integrated approach to retrieve microwave emissivity difference vegetation index (EDVI) over land regions has been developed from combined multi-platform/multi-sensor satellite measurements, including SSM/I measurements. A possible relationship of the remotely sensed EDVI and the leaf physiology of canopy is explored at the Harvard Forest site for two growing seasons. This study finds that the EDVI is sensitive to leaf development through vegetation water content of the crown layer of the forest canopy, and has demonstrated that the spring onset and growing season duration can be determined accurately from the time series of satellite estimated EDVI within uncertainties of approximately 3 and 7 days for spring onset and growing season duration, respectively, compared to in situ observations. The leaf growing stage can also be monitored by a normalized EDVI. EDVI retrievals from satellite generally are possible during both daytime and nighttime when it is not raining. The EDVI technique studied here may provide higher temporal resolution observations for monitoring the onset of spring, the duration of growing season, and leaf development stage compared to current operational satellite methods. Emissivity difference vegetation index (EDVI); Growing season duration; Leaf development; Microwave remote sensing; Spring onset detection
Mitas, Christos M.; Clement, AmyMitas, C. M., A. Clement, 2006: Recent behavior of the Hadley cell and tropical thermodynamics in climate models and reanalyses. Geophysical Research Letters, 33(1), L01810. doi: 10.1029/2005GL024406. The behavior of the Hadley cell and the thermodynamic structure of the tropical atmosphere is analyzed over the period 1979–2000 in climate models and reanalyses. Significant trends in the strength of the Hadley cell are present in reanalyses that are not reproduced by models. Analysis of the thermodynamic structure also shows significant discrepancies between models and reanalyses, the former show warming aloft and increased static stability while the latter show a cooling trend and decreased static stability in the tropical mid-troposphere. Additional energy balance analysis reveals that models and reanalyses have a fundamentally different balance between diabatic heating, circulation and thermodynamic structure over the period 1979–2000. Uncertainties in the observations of tropospheric temperatures as well as potential biases and errors in the climate models raise questions about the true long-term behavior of the thermodynamic structure of the tropical troposphere and the Hadley cell. 3305 Climate change and variability; 3374 Tropical meteorology; 3319 General circulation
Randall, D. A.; Schlesinger, M. E.; Galin, V.Randall, D. A., M. E. Schlesinger, V. Galin, 2006: Cloud Feedbacks. Frontiers in the Science of Climate Modeling, 217-250.
Remer, L. A.; Kaufman, Y. J.Remer, L. A., Y. J. Kaufman, 2006: Aerosol direct radiative effect at the top of the atmosphere over cloud free ocean derived from four years of MODIS data. Atmos. Chem. Phys., 6(1), 237-253. doi: 10.5194/acp-6-237-2006. A four year record of MODIS spaceborne data provides a new measurement tool to assess the aerosol direct radiative effect at the top of the atmosphere. MODIS derives the aerosol optical thickness and microphysical properties from the scattered sunlight at 0.55–2.1 μm. The monthly MODIS data used here are accumulated measurements across a wide range of view and scattering angles and represent the aerosol's spectrally resolved angular properties. We use these data consistently to compute with estimated accuracy of ±0.6 Wm−2 the reflected sunlight by the aerosol over global oceans in cloud free conditions. The MODIS high spatial resolution (0.5 km) allows observation of the aerosol impact between clouds that can be missed by other sensors with larger footprints. We found that over the clear-sky global ocean the aerosol reflected 5.3±0.6 Wm−2 with an average radiative efficiency of −49±2 Wm−2 per unit optical thickness. The seasonal and regional distribution of the aerosol radiative effects are discussed. The analysis adds a new measurement perspective to a climate change problem dominated so far by models.
Rutledge, Charles K.; Schuster, Gregory L.; Charlock, Thomas P.; Denn, Frederick M.; Smith, William L.; Fabbri, Bryan E.; Madigan, James J.; Knapp, Robert J.Rutledge, C. K., G. L. Schuster, T. P. Charlock, F. M. Denn, W. L. Smith, B. E. Fabbri, J. J. Madigan, R. J. Knapp, 2006: Offshore Radiation Observations for Climate Research at the CERES Ocean Validation Experiment: A New “Laboratory” for Retrieval Algorithm Testing. Bull. Amer. Meteor. Soc., 87(9), 1211-1222. doi: 10.1175/BAMS-87-9-1211. Abstract When radiometers on satellites point toward Earth with the goal of sensing an important variable quantitatively, rather than just creating a pleasing image, the task at hand is often not simple. The electromagnetic energy detected by the radiometers is a puzzle of various signals; it must be solved to quantify the specific physical variable. This task, called the retrieval or remote-sensing process, is important to most satellite-based observation programs. It would be ideal to test the algorithms for retrieval processes in a sealed laboratory, where all the relevant parameters could be easily measured. The size and complexity of the Earth make this impractical. NASA's Clouds and the Earth's Radiant Energy System (CERES) project has done the next-best thing by developing a long-term radiation observation site over the ocean. The relatively low and homogeneous surface albedo of the ocean make this type of site a simpler environment for observing and validating radiation parameters from satellite-based instruments. To characterize components of the planet's energy budget, CERES uses a variety of retrievals associated with several satellite-based instruments onboard NASA's Earth Observing System (EOS). A new surface observation project called the CERES Ocean Validation Experiment (COVE), operating on a rigid ocean platform, is supplying data to validate some of these instruments and retrieval products. This article describes the ocean platform and the types of observations being performed there, and highlights of some scientific problems being addressed.
Schuster, Gregory L.; Dubovik, Oleg; Holben, Brent N.Schuster, G. L., O. Dubovik, B. N. Holben, 2006: Angstrom exponent and bimodal aerosol size distributions. Journal of Geophysical Research: Atmospheres, 111(D7), D07207. doi: 10.1029/2005JD006328. Power laws have long been used to describe the spectral dependence of aerosol extinction, and the wavelength exponent of the aerosol extinction law is commonly referred to as the Angstrom exponent. The Angstrom exponent is often used as a qualitative indicator of aerosol particle size, with values greater than 2 indicating small particles associated with combustion byproducts, and values less than 1 indicating large particles like sea salt and dust. In this study, we investigate the relationship between the Angstrom exponent and the mode parameters of bimodal aerosol size distributions using Mie theory calculations and Aerosol Robotic Network (AERONET) retrievals. We find that Angstrom exponents based upon seven wavelengths (0.34, 0.38, 0.44, 0.5, 0.67, 0.87, and 1.02 μm) are sensitive to the volume fraction of aerosols with radii less then 0.6 μm but not to the fine mode effective radius. The Angstrom exponent is also known to vary with wavelength, which is commonly referred to as curvature; we show how the spectral curvature can provide additional information about aerosol size distributions for intermediate values of the Angstrom exponent. Curvature also has a significant effect on the conclusions that can be drawn about two-wavelength Angstrom exponents; long wavelengths (0.67, 0.87 μm) are sensitive to fine mode volume fraction of aerosols but not fine mode effective radius, while short wavelengths (0.38, 0.44 μm) are sensitive to the fine mode effective radius but not the fine mode volume fraction. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 0394 Instruments and techniques; aerosols; angstrom exponent; sunphotometry
Sharon, Tarah M.; Albrecht, Bruce A.; Jonsson, Haflidi H.; Minnis, Patrick; Khaiyer, Mandana M.; van Reken, Timothy M.; Seinfeld, John; Flagan, RickSharon, T. M., B. A. Albrecht, H. H. Jonsson, P. Minnis, M. M. Khaiyer, T. M. van Reken, J. Seinfeld, R. Flagan, 2006: Aerosol and Cloud Microphysical Characteristics of Rifts and Gradients in Maritime Stratocumulus Clouds. J. Atmos. Sci., 63(3), 983-997. doi: 10.1175/JAS3667.1. Abstract A cloud rift is characterized as a large-scale, persistent area of broken, low-reflectivity stratocumulus clouds usually surrounded by a solid deck of stratocumulus. A rift observed off the coast of California was investigated using an instrumented aircraft to compare the aerosol, cloud microphysical, and thermodynamic properties in the rift with those of the surrounding solid stratocumulus deck. The microphysical characteristics in the solid stratocumulus deck differ substantially from those of a broken, cellular rift where cloud droplet concentrations are a factor of 2 lower than those in the solid cloud. Furthermore, cloud condensation nuclei (CCN) concentrations were found to be about 3 times greater in the solid-cloud area compared with those in the rift. Although drizzle was observed near cloud top in parts of the solid stratocumulus cloud, the largest drizzle rates were associated with the broken clouds within the rift area and with extremely large effective droplet sizes retrieved from satellite data. Minimal thermodynamic differences between the rift and solid cloud deck were observed. In addition to marked differences in particle concentrations, evidence of a mesoscale circulation near the solid cloud–rift boundary is presented. This mesoscale circulation may provide a mechanism for maintaining a rift, but further study is required to understand the initiation of a rift and the conditions that may cause it to fill. A review of results from previous studies indicates similar microphysical characteristics in rift features sampled serendipitously. These observations indicate that cloud rifts are depleted of aerosols through the cleansing associated with drizzle and are a manifestation of natural processes occurring in marine stratocumulus.
Slingo, A.; Ackerman, T. P.; Allan, R. P.; Kassianov, E. I.; McFarlane, S. A.; Robinson, G. J.; Barnard, J. C.; Miller, M. A.; Harries, J. E.; Russell, J. E.; Dewitte, S.Slingo, A., T. P. Ackerman, R. P. Allan, E. I. Kassianov, S. A. McFarlane, G. J. Robinson, J. C. Barnard, M. A. Miller, J. E. Harries, J. E. Russell, S. Dewitte, 2006: Observations of the impact of a major Saharan dust storm on the atmospheric radiation balance. Geophysical Research Letters, 33(24), L24817. doi: 10.1029/2006GL027869. Saharan dust storms have often been observed from space, but the full impact on the Earth's radiation balance has been difficult to assess, due to limited observations from the surface. We present the first simultaneous observations from space and from a comprehensive new mobile facility in Niamey, Niger, of a major dust storm in March 2006. The results indicate major perturbations to the radiation balance both at the top of the atmosphere and at the surface. Combining the satellite and surface data, we also estimate the impact on the radiation balance of the atmosphere itself. Using independent data from the mobile facility, we derive the optical properties of the dust and input these and other information into two radiation models to simulate the radiative fluxes. We show that the radiation models underestimate the observed absorption of solar radiation in the dusty atmosphere. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 3359 Radiative processes; radiation; aerosols and particles; radiative processes; transmission and scattering
Smirnov, A.; Holben, B. N.; Sakerin, S. M.; Kabanov, D. M.; Slutsker, I.; Chin, M.; Diehl, T. L.; Remer, L. A.; Kahn, R.; Ignatov, A.; Liu, L.; Mishchenko, M.; Eck, T. F.; Kucsera, T. L.; Giles, D.; Kopelevich, O. V.Smirnov, A., B. N. Holben, S. M. Sakerin, D. M. Kabanov, I. Slutsker, M. Chin, T. L. Diehl, L. A. Remer, R. Kahn, A. Ignatov, L. Liu, M. Mishchenko, T. F. Eck, T. L. Kucsera, D. Giles, O. V. Kopelevich, 2006: Ship-based aerosol optical depth measurements in the Atlantic Ocean: Comparison with satellite retrievals and GOCART model. Geophysical Research Letters, 33(14), L14817. doi: 10.1029/2006GL026051. Aerosol optical depth measurements were made in October–December 2004 onboard the R/V Akademik Sergey Vavilov. The cruise area included an Atlantic transect from North Sea to Cape Town and then a crossing in the South Atlantic to Argentina. In the open oceanic areas not influenced by continental sources aerosol optical depth values were close to background oceanic conditions (τa ∼ 0.06–0.08). Spectral dependence, especially in the high latitude Southern Atlantic, can be considered as quasi-neutral (Angstrom parameter α was less than 0.4). Back-trajectory analysis allowed statistical division of the aerosol optical parameters and showed similar properties for the North Atlantic polar marine, South Atlantic subtropical marine and South Atlantic polar marine air. Ship-borne aerosol optical depth comparisons to GOCART model and satellite retrievals revealed systematic biases. Satellite retrieved optical depths are generally higher by 0.02–0.07 (depending on the sensor), especially in low τa conditions. GOCART model simulated optical depths correlate well with the ship measurements and, despite overall bias and a notable disparity with the observations in a number of cases, about 30% agree within ±0.01. 0360 Radiation: transmission and scattering; 1640 Remote sensing; 0305 Aerosols and particles; 0345 Pollution: urban and regional; 4548 Ocean fog
Smith, G. Louis; Szewczyk, Z. Peter; Rutan, David A.; Lee, Robert B.Smith, G. L., Z. P. Szewczyk, D. A. Rutan, R. B. Lee, 2006: Comparison of measurements from satellite radiation budget instruments. Journal of Geophysical Research: Atmospheres, 111(D4), D04101. doi: 10.1029/2005JD006307. Successive radiometers have been flown on spacecraft for measurement of the radiation budget of the Earth and to date have provided data sets which overlap in time over a 25-year period. Together these data sets cover two cycles of any decadal oscillation and are useful for climate research. However, before multiple data sets can be used, it is necessary first to establish precisions and relative biases of the data sets. Although these instruments were all calibrated with great care, inevitably there are differences between the instruments. Also, instruments change while in orbit due to degradation of optical elements and changes of the detectors. A number of studies have compared measurements between pairs of radiometers in order to establish these differences. In this paper we compile these results and by use of a bar chart demonstrate the traceability of calibration of satellite radiation budget instruments over these two decades. Using this compilation the differences are computed for any two instruments listed. The instruments considered here include the ERBE scanning and nonscanning radiometers, ScaRaB I and II, and the CERES instruments aboard the TRMM, Terra, and Aqua spacecraft. These results are a prerequisite to use of multiple data sets for long-term studies of climate process. The largest biases are between the ERBS scanning and non-scanning radiometers, which at the “top of the atmosphere” differ by 5.4 W m−2 for shortwave fluxes and by 5.8 W m−2 for daytime longwave fluxes. The standard deviations of the biases, which define how well the data sets can be connected, are less than 1 W m−2 for longwave and between 1 and 2 W m−2 for shortwave fluxes. earth radiation budget; 1640 Remote sensing; 1694 Instruments and techniques; radiometry; satellite climatology
Soden, Brian J.; Held, Isaac M.Soden, B. J., I. M. Held, 2006: An Assessment of Climate Feedbacks in Coupled Ocean–Atmosphere Models. J. Climate, 19(14), 3354-3360. doi: 10.1175/JCLI3799.1. Abstract The climate feedbacks in coupled ocean–atmosphere models are compared using a coordinated set of twenty-first-century climate change experiments. Water vapor is found to provide the largest positive feedback in all models and its strength is consistent with that expected from constant relative humidity changes in the water vapor mixing ratio. The feedbacks from clouds and surface albedo are also found to be positive in all models, while the only stabilizing (negative) feedback comes from the temperature response. Large intermodel differences in the lapse rate feedback are observed and shown to be associated with differing regional patterns of surface warming. Consistent with previous studies, it is found that the vertical changes in temperature and water vapor are tightly coupled in all models and, importantly, demonstrate that intermodel differences in the sum of lapse rate and water vapor feedbacks are small. In contrast, intermodel differences in cloud feedback are found to provide the largest source of uncertainty in current predictions of climate sensitivity.
Sun, Wenbo; Lin, BingSun, W., B. Lin, 2006: Optical characterization of metallic aerosols. Journal of Quantitative Spectroscopy and Radiative Transfer, 100(1–3), 359-372. doi: 10.1016/j.jqsrt.2005.11.075. Airborne metallic particulates from industry and urban sources are highly conducting aerosols. The characterization of these pollutant particles is important for environment monitoring and protection. Because these metallic particulates are highly reflective, their effect on local weather or regional radiation budget may also need to be studied. In this work, light scattering characteristics of these metallic aerosols are studied using exact solutions on perfectly conducting spherical and cylindrical particles. It is found that for perfectly conducting spheres and cylinders, when scattering angle is larger than ∼90° the linear polarization degree of the scattered light is very close to zero. This light scattering characteristics of perfectly conducting particles is significantly different from that of other aerosols. When these perfectly conducting particles are immersed in an absorbing medium, this light scattering characteristics does not show significant change. Therefore, measuring the linear polarization of scattered lights at backward scattering angles can detect and distinguish metallic particulates from other aerosols. This result provides a great potential of metallic aerosol detection and monitoring for environmental protection. Light scattering; Environmental protection; Metallic aerosol
Sun, Wenbo; Loeb, Norman G.; Davies, Roger; Loukachine, Konstantin; Miller, Walter F.Sun, W., N. G. Loeb, R. Davies, K. Loukachine, W. F. Miller, 2006: Comparison of MISR and CERES top-of-atmosphere albedo. Geophysical Research Letters, 33(23), L23810. doi: 10.1029/2006GL027958. The Clouds and the Earth's Radiant Energy System (CERES) and the Multi-angle Imaging SpectroRadiometer (MISR) on Terra satellite measure the Earth's top-of-atmosphere (TOA) albedo in broadband and narrowband, respectively. This study presents the first direct comparison of the CERES and MISR albedos. An algorithm for converting the MISR spectral albedos to broadband is derived. The MISR and CERES albedos for overcast ocean scenes are compared between 75°S–75°N for solar zenith angles ≤75°. For overcast 1° × 1° ocean regions, the relative differences and the relative root-mean-square (RMS) differences between the MISR and CERES albedos are ∼0.8% and ∼4.3%, respectively. Accounting for a ∼2.0% error in the MISR albedos due to narrow-to-broadband albedo conversion errors, the RMS difference between the MISR and CERES albedos due to angular distribution model (ADM) differences is estimated to be ∼3.8%. The remarkable consistency between the CERES and MISR albedos for overcast oceans suggests that both instrument teams have derived accurate corrections for the radiance anisotropy of cloud scenes. This consistency will strongly enhance the confidence in the temporal trends of cloud albedo measured by the CERES and have significant impact on climate studies. 0360 Radiation: transmission and scattering; 1640 Remote sensing; broadband; 1694 Instruments and techniques; CERES; albedo; MISR; spectral
Tang, Bohui; Li, Zhao-Liang; Zhang, RenhuaTang, B., Z. Li, R. Zhang, 2006: A direct method for estimating net surface shortwave radiation from MODIS data. Remote Sensing of Environment, 103(1), 115-126. doi: 10.1016/j.rse.2006.04.008. The Net Surface Shortwave Radiation (NSSR) is of primary interest in climate research because it controls the total energy exchange between the atmosphere and the land/ocean surface. The conventional methods for estimating NSSR rely on broadband satellite data such as Earth Radiation Budget Experiment (ERBE) wide-field-of-view planetary albedo. The spatial resolution of the current ERBE satellite data having nadir footprints larger than 30 km is too coarse. The primary objective of this study is to estimate NSSR using multispectral narrowband data such as Moderate Resolution Imaging Spectroradiometer (MODIS) data. A direct method was developed for narrowband-to-broadband albedo conversion, which links the narrowband apparent reflectance at the Top Of Atmosphere (TOA) to shortwave broadband albedo for clear and cloudy skies without performing any surface angular modeling. The conversion coefficients were derived as functions of the secant Viewing Zenith Angle (VZA) for a given Solar Zenith Angle (SZA) and a given interval of Relative Azimuth angle (RAA). The result of comparing the values of estimated MODIS TOA shortwave broadband albedos with those of the Clouds and the Earth's Radiant Energy System (CERES) data indicated that this direct method could predict TOA shortwave broadband albedo accurately with Root Mean Square (RMS) error between CERES observations and the estimated instantaneous MODIS TOA albedos less than 0.02. Based on more accurate radiative transfer model MODTRAN 4, the parameterization coefficients of Masuda et al. for the estimation of the NSSR from TOA broadband albedo were recalculated. The result showed that the coefficients should be categorized by land surfaces, ocean surface and snow/ice surface, respectively. Finally, the NSSR estimated from MODIS data was compared with the measurements of meteorological data for an extended period of time covering all seasons in a year 2003. The RMS error is less than 20 W/m2 for clear skies and 35 W/m2 for cloudy skies. CERES; albedo; MODIS; Narrowband-to-broadband conversion; Net surface shortwave radiation
Wong, Takmeng; Wielicki, Bruce A.; Lee, Robert B.; Smith, G. Louis; Bush, Kathryn A.; Willis, Joshua K.Wong, T., B. A. Wielicki, R. B. Lee, G. L. Smith, K. A. Bush, J. K. Willis, 2006: Reexamination of the Observed Decadal Variability of the Earth Radiation Budget Using Altitude-Corrected ERBE/ERBS Nonscanner WFOV Data. J. Climate, 19(16), 4028-4040. doi: 10.1175/JCLI3838.1. Abstract This paper gives an update on the observed decadal variability of the earth radiation budget (ERB) using the latest altitude-corrected Earth Radiation Budget Experiment (ERBE)/Earth Radiation Budget Satellite (ERBS) Nonscanner Wide Field of View (WFOV) instrument Edition3 dataset. The effects of the altitude correction are to modify the original reported decadal changes in tropical mean (20°N to 20°S) longwave (LW), shortwave (SW), and net radiation between the 1980s and the 1990s from 3.1, −2.4, and −0.7 to 1.6, −3.0, and 1.4 W m−2, respectively. In addition, a small SW instrument drift over the 15-yr period was discovered during the validation of the WFOV Edition3 dataset. A correction was developed and applied to the Edition3 dataset at the data user level to produce the WFOV Edition3_Rev1 dataset. With this final correction, the ERBS Nonscanner-observed decadal changes in tropical mean LW, SW, and net radiation between the 1980s and the 1990s now stand at 0.7, −2.1, and 1.4 W m−2, respectively, which are similar to the observed decadal changes in the High-Resolution Infrared Radiometer Sounder (HIRS) Pathfinder OLR and the International Satellite Cloud Climatology Project (ISCCP) version FD record but disagree with the Advanced Very High Resolution Radiometer (AVHRR) Pathfinder ERB record. Furthermore, the observed interannual variability of near-global ERBS WFOV Edition3_Rev1 net radiation is found to be remarkably consistent with the latest ocean heat storage record for the overlapping time period of 1993 to 1999. Both datasets show variations of roughly 1.5 W m−2 in planetary net heat balance during the 1990s.
Yu, H.; Kaufman, Y. J.; Chin, M.; Feingold, G.; Remer, L. A.; Anderson, T. L.; Balkanski, Y.; Bellouin, N.; Boucher, O.; Christopher, S.; DeCola, P.; Kahn, R.; Koch, D.; Loeb, N.; Reddy, M. S.; Schulz, M.; Takemura, T.; Zhou, M.Yu, H., Y. J. Kaufman, M. Chin, G. Feingold, L. A. Remer, T. L. Anderson, Y. Balkanski, N. Bellouin, O. Boucher, S. Christopher, P. DeCola, R. Kahn, D. Koch, N. Loeb, M. S. Reddy, M. Schulz, T. Takemura, M. Zhou, 2006: A review of measurement-based assessments of the aerosol direct radiative effect and forcing. Atmos. Chem. Phys., 6(3), 613-666. doi: 10.5194/acp-6-613-2006. Aerosols affect the Earth's energy budget directly by scattering and absorbing radiation and indirectly by acting as cloud condensation nuclei and, thereby, affecting cloud properties. However, large uncertainties exist in current estimates of aerosol forcing because of incomplete knowledge concerning the distribution and the physical and chemical properties of aerosols as well as aerosol-cloud interactions. In recent years, a great deal of effort has gone into improving measurements and datasets. It is thus feasible to shift the estimates of aerosol forcing from largely model-based to increasingly measurement-based. Our goal is to assess current observational capabilities and identify uncertainties in the aerosol direct forcing through comparisons of different methods with independent sources of uncertainties. Here we assess the aerosol optical depth (τ), direct radiative effect (DRE) by natural and anthropogenic aerosols, and direct climate forcing (DCF) by anthropogenic aerosols, focusing on satellite and ground-based measurements supplemented by global chemical transport model (CTM) simulations. The multi-spectral MODIS measures global distributions of aerosol optical depth (τ) on a daily scale, with a high accuracy of ±0.03±0.05τ over ocean. The annual average τ is about 0.14 over global ocean, of which about 21%±7% is contributed by human activities, as estimated by MODIS fine-mode fraction. The multi-angle MISR derives an annual average AOD of 0.23 over global land with an uncertainty of ~20% or ±0.05. These high-accuracy aerosol products and broadband flux measurements from CERES make it feasible to obtain observational constraints for the aerosol direct effect, especially over global the ocean. A number of measurement-based approaches estimate the clear-sky DRE (on solar radiation) at the top-of-atmosphere (TOA) to be about -5.5±0.2 Wm-2 (median ± standard error from various methods) over the global ocean. Accounting for thin cirrus contamination of the satellite derived aerosol field will reduce the TOA DRE to -5.0 Wm-2. Because of a lack of measurements of aerosol absorption and difficulty in characterizing land surface reflection, estimates of DRE over land and at the ocean surface are currently realized through a combination of satellite retrievals, surface measurements, and model simulations, and are less constrained. Over the oceans the surface DRE is estimated to be -8.8±0.7 Wm-2. Over land, an integration of satellite retrievals and model simulations derives a DRE of -4.9±0.7 Wm-2 and -11.8±1.9 Wm-2 at the TOA and surface, respectively. CTM simulations derive a wide range of DRE estimates that on average are smaller than the measurement-based DRE by about 30-40%, even after accounting for thin cirrus and cloud contamination. A number of issues remain. Current estimates of the aerosol direct effect over land are poorly constrained. Uncertainties of DRE estimates are also larger on regional scales than on a global scale and large discrepancies exist between different approaches. The characterization of aerosol absorption and vertical distribution remains challenging. The aerosol direct effect in the thermal infrared range and in cloudy conditions remains relatively unexplored and quite uncertain, because of a lack of global systematic aerosol vertical profile measurements. A coordinated research strategy needs to be developed for integration and assimilation of satellite measurements into models to constrain model simulations. Enhanced measurement capabilities in the next few years and high-level scientific cooperation will further advance our knowledge.Citation: Yu, H., Kaufman, Y. J., Chin, M., Feingold, G., Remer, L. A., Anderson, T. L., Balkanski, Y., Bellouin, N., Boucher, O., Christopher, S., DeCola, P., Kahn, R., Koch, D., Loeb, N., Reddy, M. S., Schulz, M., Takemura, T., and Zhou, M.: A review of measurement-based assessments of the aerosol direct radiative effect and forcing, Atmos. Chem. Phys., 6, 613-666, doi:10.5194/acp-6-613-2006, 2006.
Allan, Richard P.; Slingo, Anthony; Milton, Sean F.; Culverwell, IanAllan, R. P., A. Slingo, S. F. Milton, I. Culverwell, 2005: Exploitation of Geostationary Earth Radiation Budget data using simulations from a numerical weather prediction model: Methodology and data validation. Journal of Geophysical Research: Atmospheres, 110(D14), D14111. doi: 10.1029/2004JD005698. We describe a new methodology for comparing satellite radiation budget data with a numerical weather prediction (NWP) model. This is applied to data from the Geostationary Earth Radiation Budget (GERB) instrument on Meteosat-8. The methodology brings together, in near-real time, GERB broadband shortwave and longwave fluxes with simulations based on analyses produced by the Met Office global NWP model. Results for the period May 2003 to February 2005 illustrate the progressive improvements in the data products as various initial problems were resolved. In most areas the comparisons reveal systematic errors in the model's representation of surface properties and clouds, which are discussed elsewhere. However, for clear-sky regions over the oceans the model simulations are believed to be sufficiently accurate to allow the quality of the GERB fluxes themselves to be assessed and any changes in time of the performance of the instrument to be identified. Using model and radiosonde profiles of temperature and humidity as input to a single-column version of the model's radiation code, we conduct sensitivity experiments which provide estimates of the expected model errors over the ocean of about ±5–10 W m−2 in clear-sky outgoing longwave radiation (OLR) and ±0.01 in clear-sky albedo. For the more recent data the differences between the observed and modeled OLR and albedo are well within these error estimates. The close agreement between the observed and modeled values, particularly for the most recent period, illustrates the value of the methodology. It also contributes to the validation of the GERB products and increases confidence in the quality of the data, prior to their release. 3359 Radiative processes; 3337 Global climate models; radiation budget; 1814 Energy budgets; 3364 Synoptic-scale meteorology; General circulation models; satellite data
Anderson, Theodore L.; Charlson, Robert J.; Bellouin, Nicolas; Boucher, Olivier; Chin, Mian; Christopher, Sundar A.; Haywood, Jim; Kaufman, Yoram J.; Kinne, Stefan; Ogren, John A.; Remer, Lorraine A.; Takemura, Toshihiko; Tanré, Didier; Torres, Omar; Trepte, Charles R.; Wielicki, Bruce A.; Winker, David M.; Yu, HongbinAnderson, T. L., R. J. Charlson, N. Bellouin, O. Boucher, M. Chin, S. A. Christopher, J. Haywood, Y. J. Kaufman, S. Kinne, J. A. Ogren, L. A. Remer, T. Takemura, D. Tanré, O. Torres, C. R. Trepte, B. A. Wielicki, D. M. Winker, H. Yu, 2005: An “A-Train” Strategy for Quantifying Direct Climate Forcing by Anthropogenic Aerosols. Bull. Amer. Meteor. Soc., 86(12), 1795-1809. doi: 10.1175/BAMS-86-12-1795. Abstract This document outlines a practical strategy for achieving an observationally based quantification of direct climate forcing by anthropogenic aerosols. The strategy involves a four-step program for shifting the current assumption-laden estimates to an increasingly empirical basis using satellite observations coordinated with suborbital remote and in situ measurements and with chemical transport models. Conceptually, the problem is framed as a need for complete global mapping of four parameters: clear-sky aerosol optical depth δ, radiative efficiency per unit optical depth E, fine-mode fraction of optical depth ff, and the anthropogenic fraction of the fine mode faf. The first three parameters can be retrieved from satellites, but correlative, suborbital measurements are required for quantifying the aerosol properties that control E, for validating the retrieval of ff, and for partitioning fine-mode δ between natural and anthropogenic components. The satellite focus is on the “A-Train,” a constellation of six spacecraft that will fly in formation from about 2005 to 2008. Key satellite instruments for this report are the Moderate Resolution Imaging Spectroradiometer (MODIS) and Clouds and the Earth's Radiant Energy System (CERES) radiometers on Aqua, the Ozone Monitoring Instrument (OMI) radiometer on Aura, the Polarization and Directionality of Earth's Reflectances (POLDER) polarimeter on the Polarization and Anistropy of Reflectances for Atmospheric Sciences Coupled with Observations from a Lidar (PARASOL), and the Cloud and Aerosol Lider with Orthogonal Polarization (CALIOP) lidar on the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). This strategy is offered as an initial framework—subject to improvement over time—for scientists around the world to participate in the A-Train opportunity. It is a specific implementation of the Progressive Aerosol Retrieval and Assimilation Global Observing Network (PARAGON) program, presented earlier in this journal, which identified the integration of diverse data as the central challenge to progress in quantifying global-scale aerosol effects. By designing a strategy around this need for integration, we develop recommendations for both satellite data interpretation and correlative suborbital activities that represent, in many respects, departures from current practice.
Bertrand, C.; Clerbaux, N.; Ipe, A.; Dewitte, S.; Gonzalez, L.Bertrand, C., N. Clerbaux, A. Ipe, S. Dewitte, L. Gonzalez, 2005: Angular distribution models, anisotropic correction factors, and mixed clear-scene types: A sensitivity study. Ieee Transactions on Geoscience and Remote Sensing, 43(1), 92-102. doi: 10.1109/tgrs.2004.838361. Because radiometers do not measure the earth's outgoing flux directly, angular distribution models (ADMs) are used to invert measured radiances at the top of atmosphere (TOA) to flux. However, data used to build ADMs are generally not sorted for mixed scene types, and anisotropic correction factors for such scenes are not usually available. In the present study, we have analyzed shortwave (SW) flux values retrieved over nine areas representative of a junction between two different ADM scene types in the Meteosat-7 field of view. The Clouds and the Earth's Radiant Energy System (CERES) broadband SW ADMs were used to perform the radiance-to-flux conversion. Because of the large anisotropy difference that can exist between ADMs, use of the ADM that corresponds to the scene type with the highest percent coverage over footprints containing a mixture of scene types generates instantaneous as well as systematic errors in the retrieved SW flux values. Nevertheless, in the absence of available mixed scene type ADMs, we show that the CERES on the Tropical Rainfall Measuring Mission satellite SW ADMs can be combined together to provide reliable mixed scene types anisotropic correction factors. The use of such anisotropic factors appears to be especially well suited along the coastline of continents.
Cess, Robert D.Cess, R. D., 2005: Water Vapor Feedback in Climate Models. Science, 310(5749), 795-796. doi: 10.1126/science.1119258.
Chepfer, H.; Noel, V.; Minnis, P.; Baumgardner, D.; Nguyen, L.; Raga, G.; McGill, M. J.; Yang, P.Chepfer, H., V. Noel, P. Minnis, D. Baumgardner, L. Nguyen, G. Raga, M. J. McGill, P. Yang, 2005: Particle habit in tropical ice clouds during CRYSTAL-FACE: Comparison of two remote sensing techniques with in situ observations. Journal of Geophysical Research: Atmospheres, 110(D16), D16204. doi: 10.1029/2004JD005455. Ice crystal shapes in tropical ice clouds are estimated with two different remote sensing methods and compared with measurements from an in situ cloud aerosol spectrometer (CAS) during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment (CRYSTAL-FACE) campaign conducted in Florida during July 2002. The remote sensing techniques use dual-satellite reflectances and lidar linear depolarization rates. The ice crystal shape is derived from CAS measurements of forward and backscattered light from individual particles in the size range from 1 to 45 μm. The remote sensing and in situ retrievals are based on ice crystal optical models, which incorporate the scattering phase functions integrated over the collection angles used by the CAS, the view angles from dual-satellites retrievals, and the complete scattering matrix for lidar. Owing to the space and time collocation constraint between in situ and remote sensing techniques, data from only 1 day are used to evaluate the dual-satellite technique (11 July) and from 3 days for the lidar (23, 26, and 29 July). Data from 23 and 29 July are also used to compare the two remote sensing techniques. In total, 40 shape retrievals were obtained for 20 different cloud areas, allowing paired comparisons of the methods. The results show consistent particle shapes for half of the cloud areas studied. The discrepancies for the other cases can be explained by insufficient spatial-temporal collocations of the data or limitations of the CAS that constrain its range to particles Remote sensing; 0320 Cloud physics and chemistry; in situ observations; 0649 Optics; crystal habit
Chou, Ming-Dah; Lindzen, Richard S.Chou, M., R. S. Lindzen, 2005: Comments on “Examination of the Decadal Tropical Mean ERBS Nonscanner Radiation Data for the Iris Hypothesis”. J. Climate, 18(12), 2123-2127. doi: 10.1175/JCLI3406.1.
Clement, Amy C.; Seager, Richard; Murtugudde, RaghuClement, A. C., R. Seager, R. Murtugudde, 2005: Why Are There Tropical Warm Pools?. J. Climate, 18(24), 5294-5311. doi: 10.1175/JCLI3582.1. Abstract Tropical warm pools appear as the primary mode in the distribution of tropical sea surface temperature (SST). Most previous studies have focused on the role of atmospheric processes in homogenizing temperatures in the warm pool and establishing the observed statistical SST distribution. In this paper, a hierarchy of models is used to illustrate both oceanic and atmospheric mechanisms that contribute to the establishment of tropical warm pools. It is found that individual atmospheric processes have competing effects on the SST distribution: atmospheric heat transport tends to homogenize SST, while the spatial structure of atmospheric humidity and surface wind speeds tends to remove homogeneity. The latter effects dominate, and under atmosphere-only processes there is no warm pool. Ocean dynamics counter this effect by homogenizing SST, and it is argued that ocean dynamics is fundamental to the existence of the warm pool. Under easterly wind stress, the thermocline is deep in the west and shallow in the east. Because of this, poleward Ekman transport of water at the surface, compensated by equatorward geostrophic flow below and linked by equatorial upwelling, creates a cold tongue in the east but homogenizes SST in the west, creating a warm pool. High clouds may also homogenize the SST by reducing the surface solar radiation over the warmest water, but the strength of this feedback is quite uncertain. Implications for the role of these processes in climate change are discussed.
Clement, Amy C.; Soden, BrianClement, A. C., B. Soden, 2005: The Sensitivity of the Tropical-Mean Radiation Budget. J. Climate, 18(16), 3189-3203. doi: 10.1175/JCLI3456.1. Abstract A key disagreement exists between global climate model (GCM) simulations and satellite observations of the decadal variability in the tropical-mean radiation budget. Measurements from the Earth Radiation Budget Experiment (ERBE) over the period 1984–2001 indicate a trend of increasing longwave emission and decreasing shortwave reflection that no GCM can currently reproduce. Motivated by these results, a series of model sensitivity experiments is performed to investigate hypotheses that have been advanced to explain this discrepancy. Specifically, the extent to which a strengthening of the Hadley circulation or a change in convective precipitation efficiency can alter the tropical-mean radiation budget is assessed. Results from both model sensitivity experiments and an empirical analysis of ERBE observations suggest that the tropical-mean radiation budget is remarkably insensitive to changes in the tropical circulation. The empirical estimate suggests that it would require at least a doubling in strength of the Hadley circulation in order to generate the observed decadal radiative flux changes. In contrast, rather small changes in a model’s convective precipitation efficiency can generate changes comparable to those observed, provided that the precipitation efficiency lies near the upper end of its possible range. If, however, the precipitation efficiency of tropical convective systems is more moderate, the model experiments suggest that the climate would be rather insensitive to changes in its value. Further observations are necessary to constrain the potential effects of microphysics on the top-of-atmosphere radiation budget.
Coakley, James A.; Friedman, Michael A.; Tahnk, William R.Coakley, J. A., M. A. Friedman, W. R. Tahnk, 2005: Retrieval of Cloud Properties for Partly Cloudy Imager Pixels. J. Atmos. Oceanic Technol., 22(1), 3-17. doi: 10.1175/JTECH-1681.1. Abstract Retrievals of cloud properties from satellite imagery often invoke the assumption that the fields of view are overcast when cloud-contaminated, even though a significant fraction are only partially cloud-covered. The overcast assumption leads to biases in the retrieved cloud properties: cloud amounts and droplet effective radii are typically overestimated, while visible optical depths, cloud altitudes, cloud liquid water amounts, and column droplet number concentrations are typically underestimated. In order to estimate these biases, a retrieval scheme was developed to obtain the properties of clouds for partially covered imager fields of view. The partly cloudy pixel retrieval scheme is applicable to single-layered cloud systems and invokes the assumption that clouds that only partially cover a field of view are at the same altitude as nearby clouds from the same layer that completely cover imager pixels. The properties of the retrieval are illustrated through its application to 2-km Visible and Infrared Scanner (VIRS) data from the Tropical Rainfall Measuring Mission (TRMM) for a marine stratocumulus scene. The scene was chosen because the cloud properties are typical of such systems based on an analysis of VIRS data for February and March 1998. Comparisons of properties for clouds in partly cloudy pixels and those for clouds in nearby overcast pixels reveal that the optical depths and droplet effective radii are generally smaller for the clouds in the partly cloudy pixels. In addition, for pixel-scale cloud fractions between 0.2 and 0.8, optical depth, droplet effective radius, and column droplet number concentration decrease slowly with decreasing cloud cover fraction. The changes are only about 20%–30%, while cloud cover fraction changes by 80%. For comparison, changes in optical depth and column number concentration retrieved using a threshold method decrease by 80%–90%. As long as the cloud cover in partly cloudy pixels is greater than about 0.1, uncertainties in the estimates of the cloud altitudes and of the radiances for the cloud-free portions of the fields of view give rise to uncertainties in the retrieved cloud properties that are comparable to the uncertainties in the properties retrieved for overcast pixels.
Diner, D. J.; Braswell, B. H.; Davies, R.; Gobron, N.; Hu, J. N.; Jin, Y. F.; Kahn, R. A.; Knyazikhin, Y.; Loeb, N.; Muller, J. P.; Nolin, A. W.; Pinty, B.; Schaaf, C. B.; Seiz, G.; Stroeve, J.Diner, D. J., B. H. Braswell, R. Davies, N. Gobron, J. N. Hu, Y. F. Jin, R. A. Kahn, Y. Knyazikhin, N. Loeb, J. P. Muller, A. W. Nolin, B. Pinty, C. B. Schaaf, G. Seiz, J. Stroeve, 2005: The value of multiangle measurements for retrieving structurally and radiatively consistent properties of clouds, aerosols, and surfaces. Remote Sensing of Environment, 97(4), 495-518. doi: 10.1016/j.rse.2005.06.006. Passive optical multiangle observations make possible the retrieval of scene structural characteristics that cannot be obtained with, or require fewer underlying assumptions than, single-angle sensors. Retrievable quantities include aerosol amount over a wide variety of surfaces (including bright targets); aerosol microphysical properties such as particle shape; geometrically-derived cloud-top heights and 3-D cloud morphologies; distinctions between polar clouds and ice; and textural measures of sea ice, ice sheets, and vegetation. At the same time, multiangle data are necessary for accurate retrievals of radiative quantities such as surface and top-of-atmosphere albedos, whose magnitudes are governed by structural characteristics of the reflecting media and which involve angular integration over intrinsically anisotropic intensity fields. Measurements of directional radiation streams also provide independent checks on model assumptions conventionally used in satellite retrievals, such as the application of 1-D radiative transfer theory, and provide data required to constrain more sophisticated, 3-D approaches. In this paper, the value of multiangle remote sensing in establishing physical correspondence and self-consistency between scene structural and radiative characteristics is demonstrated using simultaneous observations from instruments aboard NASA's Terra satellite (MISR, CERES, ASTER, and MODIS). Illustrations pertaining to the remote sensing of clouds, aerosols, ice, and vegetation properties are presented. (C) 2005 Elsevier Inc. All rights reserved.
Dong, XiquanDong, X., 2005: The impact of surface albedo on the retrievals of low-level stratus cloud properties: An updated parameterization. Geophysical Research Letters, 32(10), L10802. doi: 10.1029/2005GL022548. An updated version of Dong et al. (1998, hereinafter referred to as D98) parameterization is developed from a total of 40 hours of data with a broad range of surface albedos (0.1–0.8) during the 2000–2002 winter seasons at the DOE ARM SGP site. The updated parameterization includes the impact of surface albedo on the retrievals of stratus cloud microphysical and radiative properties, and has a significant improvement over D98 when surface albedo is high. Comparing the retrievals, the cloud-droplet effective radii (re) calculated from the updated parameterization have a higher correlation coefficient (0.733) and lower Root-Mean-Square (RMS) error (1.74 μm or 17.4%) than those (0.602, 4.0 μm or 40%) from the D98. The cloud albedos also have a much higher correlation coefficient (0.983) and lower RMS (3%) than those (0.465, 26%) from the D98. The upper limit of surface albedo is 0.3 in applying the D98. 0360 Radiation: transmission and scattering; 0321 Cloud/radiation interaction; 3359 Radiative processes; 3314 Convective processes
Dong, Xiquan; Minnis, Patrick; Xi, BaikeDong, X., P. Minnis, B. Xi, 2005: A Climatology of Midlatitude Continental Clouds from the ARM SGP Central Facility: Part I: Low-Level Cloud Macrophysical, Microphysical, and Radiative Properties. J. Climate, 18(9), 1391-1410. doi: 10.1175/JCLI3342.1. Abstract A record of single-layer and overcast low cloud (stratus) properties has been generated using approximately 4000 h of data collected from January 1997 to December 2002 at the Atmospheric Radiation Measurement (ARM) Southern Great Plains Central Facility (SCF). The cloud properties include liquid-phase and liquid-dominant mixed-phase low cloud macrophysical, microphysical, and radiative properties including cloud-base and -top heights and temperatures, and cloud physical thickness derived from a ground-based radar and lidar pair, and rawinsonde sounding; cloud liquid water path (LWP) and content (LWC), and cloud-droplet effective radius (re) and number concentration (N) derived from the macrophysical properties and radiometer data; and cloud optical depth (τ), effective solar transmission (γ), and cloud/top-of-atmosphere albedos (Rcldy/RTOA) derived from Eppley precision spectral pyranometer measurements. The cloud properties were analyzed in terms of their seasonal, monthly, and hourly variations. In general, more stratus clouds occur during winter and spring than in summer. Cloud-layer altitudes and physical thicknesses were higher and greater in summer than in winter with averaged physical thicknesses of 0.85 and 0.73 km for day and night, respectively. The seasonal variations of LWP, LWC, N, τ, Rcldy, and RTOA basically follow the same pattern with maxima and minima during winter and summer, respectively. There is no significant variation in mean re, however, despite a summertime peak in aerosol loading. Although a considerable degree of variability exists, the 6-yr average values of LWP, LWC, re, N, τ, γ, Rcldy, and RTOA are 151 gm−2 (138), 0.245 gm−3 (0.268), 8.7 μm (8.5), 213 cm−3 (238), 26.8 (24.8), 0.331, 0.672, and 0.563 for daytime (nighttime). A new conceptual model of midlatitude continental low clouds at the ARM SGP site has been developed from this study. The low stratus cloud amount monotonically increases from midnight to early morning (0930 LT), and remains large until around local noon, then declines until 1930 LT when it levels off for the remainder of the night. In the morning, the stratus cloud layer is low, warm, and thick with less LWC, while in the afternoon it is high, cold, and thin with more LWC. Future parts of this series will consider other cloud types and cloud radiative forcing at the ARM SCF.
Eitzen, Zachary A.; Xu, Kuan-ManEitzen, Z. A., K. Xu, 2005: A statistical comparison of deep convective cloud objects observed by an Earth Observing System satellite and simulated by a cloud-resolving model. Journal of Geophysical Research: Atmospheres, 110(D15), D15S14. doi: 10.1029/2004JD005086. The single scanner footprint (SSF) data product produced by the Clouds and the Earth's Radiant Energy System (CERES) instrument on board the Tropical Rainfall Measuring Mission (TRMM) satellite is used to diagnose 68 deep convective cloud objects observed in March 1998. The probability density functions (PDFs) of several observed and retrieved fields from the CERES SSF data product are used to evaluate two sets of simulations produced by a cloud-resolving model. The simulations that use an improved microphysics scheme are found to produce more realistic distributions of albedo, outgoing longwave radiation, cloud top temperature, and cloud height than the control simulations, using an objective measure of the differences between the simulated and observed PDFs. The distribution of cloud optical depth produced by the new simulations is further from that observed than the control simulations. Using a bootstrapping technique, these differences are found to be statistically significant. The reflectivities and precipitation rates associated with the cloud objects observed with the TRMM precipitation radar and TRMM microwave imager are also used to evaluate the two sets of simulations. Both sets are found to produce similar distributions of the precipitation rate. The simulated radar reflectivities produced by the new simulations are somewhat more realistic than those of the control simulations, although both sets produce reflectivities that are too high at altitudes above the freezing level. CERES; 0321 Cloud/radiation interaction; convection; 3314 Convective processes; bootstrap technique; microphysics parameterization
Futyan, J. M.; Russell, J. E.Futyan, J. M., J. E. Russell, 2005: Developing Clear-Sky Flux Products for the Geostationary Earth Radiation Budget Experiment. Journal of Applied Meteorology, 44(9), 1361-1374. doi: 10.1175/JAM2291.1. Abstract This paper describes the planned processing of monthly mean and monthly mean diurnal cycle flux products for the Geostationary Earth Radiation Budget (GERB) experiment. The use of higher-spatial-resolution flux estimates based on multichannel narrowband imager data to improve clear-sky sampling is investigated. Significant improvements in temporal sampling are found, leading to reduced temporal sampling errors and less dependence on diurnal models for the monthly mean products. The reduction in temporal sampling errors is found to outweigh any spatial sampling errors that are introduced. The resulting flux estimates are used to develop an improved version of the half-sine model that is used for the diurnal interpolation of clear-sky longwave fluxes over land in the Earth Radiation Budget Experiment (ERBE) and Clouds and the Earth’s Radiant Energy System (CERES) missions. Maximum outgoing longwave radiation occurs from 45 min to 1.5 h after local noon for most of the GERB field of view. Use of the ERBE half-sine model for interpolation therefore results in significant distortion of the diurnal cycle shape. The model that is proposed here provides a well-constrained fit to the true diurnal shape, even for limited clear-sky sampling, making it suitable for use in the processing of both GERB and CERES second-generation monthly mean clear-sky data products.
Halthore, Rangasayi N.; Crisp, David; Schwartz, Stephen E.; Anderson, G. P.; Berk, A.; Bonnel, B.; Boucher, O.; Chang, Fu-Lung; Chou, Ming-Dah; Clothiaux, Eugene E.; Dubuisson, P.; Fomin, Boris; Fouquart, Y.; Freidenreich, S.; Gautier, Catherine; Kato, Seiji; Laszlo, Istvan; Li, Z.; Mather, J. H.; Plana-Fattori, Artemio; Ramaswamy, V.; Ricchiazzi, P.; Shiren, Y.; Trishchenko, A.; Wiscombe, W.Halthore, R. N., D. Crisp, S. E. Schwartz, G. P. Anderson, A. Berk, B. Bonnel, O. Boucher, F. Chang, M. Chou, E. E. Clothiaux, P. Dubuisson, B. Fomin, Y. Fouquart, S. Freidenreich, C. Gautier, S. Kato, I. Laszlo, Z. Li, J. H. Mather, A. Plana-Fattori, V. Ramaswamy, P. Ricchiazzi, Y. Shiren, A. Trishchenko, W. Wiscombe, 2005: Intercomparison of shortwave radiative transfer codes and measurements. Journal of Geophysical Research: Atmospheres, 110(D11), D11206. doi: 10.1029/2004JD005293. Computation of components of shortwave (SW) or solar irradiance in the surface-atmospheric system forms the basis of intercomparison between 16 radiative transfer models of varying spectral resolution ranging from line-by-line models to broadband and general circulation models. In order of increasing complexity the components are: direct solar irradiance at the surface, diffuse irradiance at the surface, diffuse upward flux at the surface, and diffuse upward flux at the top of the atmosphere. These components allow computation of the atmospheric absorptance. Four cases are considered from pure molecular atmospheres to atmospheres with aerosols and atmosphere with a simple uniform cloud. The molecular and aerosol cases allow comparison of aerosol forcing calculation among models. A cloud-free case with measured atmospheric and aerosol properties and measured shortwave radiation components provides an absolute basis for evaluating the models. For the aerosol-free and cloud-free dry atmospheres, models agree to within 1% (root mean square deviation as a percentage of mean) in broadband direct solar irradiance at surface; the agreement is relatively poor at 5% for a humid atmosphere. A comparison of atmospheric absorptance, computed from components of SW radiation, shows that agreement among models is understandably much worse at 3% and 10% for dry and humid atmospheres, respectively. Inclusion of aerosols generally makes the agreement among models worse than when no aerosols are present, with some exceptions. Modeled diffuse surface irradiance is higher than measurements for all models for the same model inputs. Inclusion of an optically thick low-cloud in a tropical atmosphere, a stringent test for multiple scattering calculations, produces, in general, better agreement among models for a low solar zenith angle (SZA = 30°) than for a high SZA (75°). All models show about a 30% increase in broadband absorptance for 30° SZA relative to the clear-sky case and almost no enhancement in absorptance for a higher SZA of 75°, possibly due to water vapor line saturation in the atmosphere above the cloud. shortwave; 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; model intercomparison; RT models
Han, Qingyuan; Zeng, Jian; Kuo, Kwo-Sen; Chen, Hui; Smith, ErikHan, Q., J. Zeng, K. Kuo, H. Chen, E. Smith, 2005: Effect of particle size distributions on the retrieval of ice cloud properties. Geophysical Research Letters, 32(13), L13818. doi: 10.1029/2005GL022659. Various measured size distributions obtained from aircraft measurements at different regions and seasons are used in the retrieval algorithms for ice cloud properties by several major satellite instruments such as MODIS, CERES and VIIRS. These measured size distributions are characterized by one parameter: effective size (diameter or radius). This study shows that the adoption of such measured size distributions leads to inconsistent results in retrieved cloud properties because neglecting the effect of effective variances causes non-monotonic relations between crystal size and single scattering properties. We also show that single scattering properties of most observed size distributions of hexagonal columns can be adequately characterized by effective radius and effective variance. Therefore, in remote sensing of ice cloud properties, theoretical size distributions with explicitly assumed effective variances should be used, similar to the practice adopted for water clouds. 0360 Radiation: transmission and scattering; 1640 Remote sensing; 1655 Water cycles; 0321 Cloud/radiation interaction; 0319 Cloud optics
Hansen, J.; Sato, M.; Ruedy, R.; Nazarenko, L.; Lacis, A.; Schmidt, G. A.; Russell, G.; Aleinov, I.; Bauer, M.; Bauer, S.; Bell, N.; Cairns, B.; Canuto, V.; Chandler, M.; Cheng, Y.; Del Genio, A.; Faluvegi, G.; Fleming, E.; Friend, A.; Hall, T.; Jackman, C.; Kelley, M.; Kiang, N.; Koch, D.; Lean, J.; Lerner, J.; Lo, K.; Menon, S.; Miller, R.; Minnis, P.; Novakov, T.; Oinas, V.; Perlwitz, Ja.; Perlwitz, Ju.; Rind, D.; Romanou, A.; Shindell, D.; Stone, P.; Sun, S.; Tausnev, N.; Thresher, D.; Wielicki, B.; Wong, T.; Yao, M.; Zhang, S.Hansen, J., M. Sato, R. Ruedy, L. Nazarenko, A. Lacis, G. A. Schmidt, G. Russell, I. Aleinov, M. Bauer, S. Bauer, N. Bell, B. Cairns, V. Canuto, M. Chandler, Y. Cheng, A. Del Genio, G. Faluvegi, E. Fleming, A. Friend, T. Hall, C. Jackman, M. Kelley, N. Kiang, D. Koch, J. Lean, J. Lerner, K. Lo, S. Menon, R. Miller, P. Minnis, T. Novakov, V. Oinas, J. Perlwitz, J. Perlwitz, D. Rind, A. Romanou, D. Shindell, P. Stone, S. Sun, N. Tausnev, D. Thresher, B. Wielicki, T. Wong, M. Yao, S. Zhang, 2005: Efficacy of climate forcings. Journal of Geophysical Research: Atmospheres, 110(D18), D18104. doi: 10.1029/2005JD005776. We use a global climate model to compare the effectiveness of many climate forcing agents for producing climate change. We find a substantial range in the “efficacy” of different forcings, where the efficacy is the global temperature response per unit forcing relative to the response to CO2 forcing. Anthropogenic CH4 has efficacy ∼110%, which increases to ∼145% when its indirect effects on stratospheric H2O and tropospheric O3 are included, yielding an effective climate forcing of ∼0.8 W/m2 for the period 1750–2000 and making CH4 the largest anthropogenic climate forcing other than CO2. Black carbon (BC) aerosols from biomass burning have a calculated efficacy ∼58%, while fossil fuel BC has an efficacy ∼78%. Accounting for forcing efficacies and for indirect effects via snow albedo and cloud changes, we find that fossil fuel soot, defined as BC + OC (organic carbon), has a net positive forcing while biomass burning BC + OC has a negative forcing. We show that replacement of the traditional instantaneous and adjusted forcings, Fi and Fa, with an easily computed alternative, Fs, yields a better predictor of climate change, i.e., its efficacies are closer to unity. Fs is inferred from flux and temperature changes in a fixed-ocean model run. There is remarkable congruence in the spatial distribution of climate change, normalized to the same forcing Fs, for most climate forcing agents, suggesting that the global forcing has more relevance to regional climate change than may have been anticipated. Increasing greenhouse gases intensify the Hadley circulation in our model, increasing rainfall in the Intertropical Convergence Zone (ITCZ), Eastern United States, and East Asia, while intensifying dry conditions in the subtropics including the Southwest United States, the Mediterranean region, the Middle East, and an expanding Sahel. These features survive in model simulations that use all estimated forcings for the period 1880–2000. Responses to localized forcings, such as land use change and heavy regional concentrations of BC aerosols, include more specific regional characteristics. We suggest that anthropogenic tropospheric O3 and the BC snow albedo effect contribute substantially to rapid warming and sea ice loss in the Arctic. As a complement to a priori forcings, such as Fi, Fa, and Fs, we tabulate the a posteriori effective forcing, Fe, which is the product of the forcing and its efficacy. Fe requires calculation of the climate response and introduces greater model dependence, but once it is calculated for a given amount of a forcing agent it provides a good prediction of the response to other forcing amounts. 1620 Climate dynamics; 1616 Climate variability; 1637 Regional climate change; climate models; 1622 Earth system modeling; climate forcings; greenhouse gases
Harries, J. E.; Russell, J. E.; Hanafin, J. A.; Brindley, H.; Futyan, J.; Rufus, J.; Kellock, S.; Matthews, G.; Wrigley, R.; Last, A.; Mueller, J.; Mossavati, R.; Ashmall, J.; Sawyer, E.; Parker, D.; Caldwell, M.; Allan, P. M.; Smith, A.; Bates, M. J.; Coan, B.; Stewart, B. C.; Lepine, D. R.; Cornwall, L. A.; Corney, D. R.; Ricketts, M. J.; Drummond, D.; Smart, D.; Cutler, R.; Dewitte, S.; Clerbaux, N.; Gonzalez, L.; Ipe, A.; Bertrand, C.; Joukoff, A.; Crommelynck, D.; Nelms, N.; Llewellyn-Jones, D. T.; Butcher, G.; Smith, G. L.; Szewczyk, Z. P.; Mlynczak, P. E.; Slingo, A.; Allan, R. P.; Ringer, M. A.Harries, J. E., J. E. Russell, J. A. Hanafin, H. Brindley, J. Futyan, J. Rufus, S. Kellock, G. Matthews, R. Wrigley, A. Last, J. Mueller, R. Mossavati, J. Ashmall, E. Sawyer, D. Parker, M. Caldwell, P. M. Allan, A. Smith, M. J. Bates, B. Coan, B. C. Stewart, D. R. Lepine, L. A. Cornwall, D. R. Corney, M. J. Ricketts, D. Drummond, D. Smart, R. Cutler, S. Dewitte, N. Clerbaux, L. Gonzalez, A. Ipe, C. Bertrand, A. Joukoff, D. Crommelynck, N. Nelms, D. T. Llewellyn-Jones, G. Butcher, G. L. Smith, Z. P. Szewczyk, P. E. Mlynczak, A. Slingo, R. P. Allan, M. A. Ringer, 2005: The Geostationary Earth Radiation Budget Project. Bull. Amer. Meteor. Soc., 86(7), 945-960. doi: 10.1175/BAMS-86-7-945. Abstract This paper reports on a new satellite sensor, the Geostationary Earth Radiation Budget (GERB) experiment. GERB is designed to make the first measurements of the Earth's radiation budget from geostationary orbit. Measurements at high absolute accuracy of the reflected sunlight from the Earth, and the thermal radiation emitted by the Earth are made every 15 min, with a spatial resolution at the subsatellite point of 44.6 km (north–south) by 39.3 km (east–west). With knowledge of the incoming solar constant, this gives the primary forcing and response components of the top-of-atmosphere radiation. The first GERB instrument is an instrument of opportunity on Meteosat-8, a new spin-stabilized spacecraft platform also carrying the Spinning Enhanced Visible and Infrared (SEVIRI) sensor, which is currently positioned over the equator at 3.5°W. This overview of the project includes a description of the instrument design and its preflight and in-flight calibration. An evaluation of the instrument performance after its first year in orbit, including comparisons with data from the Clouds and the Earth's Radiant Energy System (CERES) satellite sensors and with output from numerical models, are also presented. After a brief summary of the data processing system and data products, some of the scientific studies that are being undertaken using these early data are described. This marks the beginning of a decade or more of observations from GERB, as subsequent models will fly on each of the four Meteosat Second Generation satellites.
Huang, Jianping; Minnis, Patrick; Lin, Bing; Yi, Yuhong; Khaiyer, Mandana M.; Arduini, Robert F.; Fan, Alice; Mace, Gerald G.Huang, J., P. Minnis, B. Lin, Y. Yi, M. M. Khaiyer, R. F. Arduini, A. Fan, G. G. Mace, 2005: Advanced retrievals of multilayered cloud properties using multispectral measurements. Journal of Geophysical Research: Atmospheres, 110(D15), D15S18. doi: 10.1029/2004JD005101. Current satellite cloud retrievals are usually based on the assumption that all clouds consist of a homogenous single layer despite the frequent occurrence of cloud overlap. As such, cloud overlap will cause large errors in the retrievals of many cloud properties. To address this problem, a multilayered cloud retrieval system (MCRS) is developed by combining satellite visible and infrared radiances and surface microwave radiometer measurements. A two-layer cloud model was used to simulate ice-over-water cloud radiative characteristics. The radiances emanating from the combined low cloud and surface are estimated using the microwave liquid water with an assumption of effective droplet size. These radiances replace the background radiances traditionally used in single-layer cloud retrievals. The MCRS is applied to data from March through October 2000 over four Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) sites. The results are compared to the available retrievals of ice water path (IWP) from radar data and show that the MCRS clearly produces a more accurate retrieval of ice-over-water cloud properties. MCRS yields values of IWP that are closest to those from the radar retrieval. For ice-over-water cloud systems, on average, the optical depth and IWP are reduced, from original overestimates, by approximately 30%. The March–October mean cloud effective temperatures from the MCRS are decreased by 10 ± 12 K, which translates to an average height difference of ∼1.4 km. These results indicate that ice-cloud height derived from traditional single-layer retrieval is underestimated, and the midlevel ice cloud coverage is over classified. Effective ice crystal particle sizes are increased by only a few percent with the new method. This new physically based technique should be robust and directly applicable when data are available simultaneously from a satellite imager and the appropriate satellite or surface microwave sensor. 3311 Clouds and aerosols; 3359 Radiative processes; Cloud retrieval; 3310 Clouds and cloud feedbacks; 3394 Instruments and techniques; ice cloud; ice cloud path; microwave multiplayer; overlap
Ignatov, Alexander; Minnis, Patrick; Loeb, Norman; Wielicki, Bruce; Miller, Walter; Sun-Mack, Sunny; Tanré, Didier; Remer, Lorraine; Laszlo, Istvan; Geier, ErikaIgnatov, A., P. Minnis, N. Loeb, B. Wielicki, W. Miller, S. Sun-Mack, D. Tanré, L. Remer, I. Laszlo, E. Geier, 2005: Two MODIS Aerosol Products over Ocean on the Terra and Aqua CERES SSF Datasets. J. Atmos. Sci., 62(4), 1008-1031. doi: 10.1175/JAS3383.1. Abstract Understanding the impact of aerosols on the earth’s radiation budget and the long-term climate record requires consistent measurements of aerosol properties and radiative fluxes. The Clouds and the Earth’s Radiant Energy System (CERES) Science Team combines satellite-based retrievals of aerosols, clouds, and radiative fluxes into Single Scanner Footprint (SSF) datasets from the Terra and Aqua satellites. Over ocean, two aerosol products are derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) using different sampling and aerosol algorithms. The primary, or M, product is taken from the standard multispectral aerosol product developed by the MODIS aerosol group while a simpler, secondary [Advanced Very High Resolution Radiometer (AVHRR) like], or A, product is derived by the CERES Science Team using a different cloud clearing method and a single-channel aerosol algorithm. Two aerosol optical depths (AOD), τA1 and τA2, are derived from MODIS bands 1 (0.644 μm) and 6 (1.632 μm) resembling the AVHRR/3 channels 1 and 3A, respectively. On Aqua the retrievals are made in band 7 (2.119 μm) because of poor quality data from band 6. The respective Ångström exponents can be derived from the values of τ. The A product serves as a backup for the M product. More importantly, the overlap of these aerosol products is essential for placing the 20+ year heritage AVHRR aerosol record in the context of more advanced aerosol sensors and algorithms such as that used for the M product. This study documents the M and A products, highlighting their CERES SSF specifics. Based on 2 weeks of global Terra data, coincident M and A AODs are found to be strongly correlated in both bands. However, both domains in which the M and A aerosols are available, and the respective τ/α statistics significantly differ because of discrepancies in sampling due to differences in cloud and sun-glint screening. In both aerosol products, correlation is observed between the retrieved aerosol parameters (τ/α) and ambient cloud amount, with the dependence in the M product being more pronounced than in the A product.
Jin, Zhonghai; Charlock, Thomas P.; Rutledge, Ken; Cota, Glenn; Kahn, Ralph; Redemann, Jens; Zhang, Taiping; Rutan, David A.; Rose, FredJin, Z., T. P. Charlock, K. Rutledge, G. Cota, R. Kahn, J. Redemann, T. Zhang, D. A. Rutan, F. Rose, 2005: Radiative Transfer Modeling for the CLAMS Experiment. J. Atmos. Sci., 62(4), 1053-1071. doi: 10.1175/JAS3351.1. Abstract Spectral and broadband radiances and irradiances (fluxes) were measured from surface, airborne, and spaceborne platforms in the Chesapeake Lighthouse and Aircraft Measurements for Satellites (CLAMS) campaign. The radiation data obtained on the 4 clear days over ocean during CLAMS are analyzed here with the Coupled Ocean–Atmosphere Radiative Transfer (COART) model. The model is successively compared with observations of broadband fluxes and albedos near the ocean surface from the Clouds and the Earth's Radiant Energy System (CERES) Ocean Validation Experiment (COVE) sea platform and a low-level OV-10 aircraft, of near-surface spectral albedos from COVE and OV-10, of broadband radiances at multiple angles and inferred top-of-atmosphere (TOA) fluxes from CERES, and of spectral radiances at multiple angles from Airborne Multiangle Imaging Spectroradiometer (MISR), or “AirMISR,” at 20-km altidude. The radiation measurements from different platforms are shown to be consistent with each other and with model results. The discrepancies between the model and observations at the surface are less than 10 W m−2 for downwelling and 2 W m−2 for upwelling fluxes. The model–observation discrepancies for shortwave ocean albedo are less than 8%; some discrepancies in spectral albedo are larger but less than 20%. The discrepancies between low-altitude aircraft and surface measurements are somewhat larger than those between the model and the surface measurements; the former are due to the effects of differences in height, aircraft pitch and roll, and the noise of spatial and temporal variations of atmospheric and oceanic properties. The discrepancy between the model and the CERES observations for the upwelling radiance is 5.9% for all angles; this is reduced to 4.9% if observations within 15° of the sun-glint angle are excluded. The measurements and model agree on the principal impacts that ocean optical properties have on upwelling radiation at low levels in the atmosphere. Wind-driven surface roughness significantly affects the upwelling radiances measured by aircraft and satellites at small sun-glint angles, especially in the near-infrared channel of MISR. Intercomparisons of various measurements and the model show that most of the radiation observations in CLAMS are robust, and that the coupled radiative transfer model used here accurately treats scattering and absorption processes in both the air and the water.
Kandel, R.; Viollier, M.Kandel, R., M. Viollier, 2005: Planetary radiation budgets. Space Science Reviews, 120(1-2), 1-26. doi: 10.1007/s11214-005-6482-6. The energy state of a planet depends fundamentally on its radiation budget. Measurements made from space over past decades have led to significant revisions of ground-based estimates, both of the reflected fraction (the Bond albedo) of solar radiative flux and of the emitted thermal infrared radiation flux, for the Earth as well as for the other planets. After a brief survey of methods and difficulties in accurately determining planetary radiation budgets, we note contradictions in existing tabulations of global parameters, in particular Bond albedo. For the Earth, such contradictions are unjustified, considering that global and annual means as well as the seasonal cycle of Earth Radiation Budget components have now been determined with high accuracy. The Earth's Bond albedo is close to 0.3. Net storage of energy in the Earth-ocean system is close to zero, with a well-established annual cycle of amplitude close to +/- 12 Wm(-2). Some contradictions remain for the other terrestrial planets. For the giant planets, modem reduced values of the Bond albedo imply reduced but still significant internal energy generation.
Kato, Seiji; Loeb, Norman G.Kato, S., N. G. Loeb, 2005: Top-of-atmosphere shortwave broadband observed radiance and estimated irradiance over polar regions from Clouds and the Earth's Radiant Energy System (CERES) instruments on Terra. Journal of Geophysical Research: Atmospheres, 110(D7), D07202. doi: 10.1029/2004JD005308. Empirical angular distribution models for estimating top-of-atmosphere shortwave irradiances from radiance measurements over permanent snow, fresh snow, and sea ice are developed using CERES measurements on Terra. Permanent snow angular distribution models depend on cloud fraction, cloud optical thickness, and snow brightness. Fresh snow and sea ice angular distribution models depend on snow and sea ice fraction, cloud fraction, cloud optical thickness, and snow and ice brightness. These classifications lead to 10 scene types for permanent snow and 25 scene types for fresh snow and sea ice. The average radiance over clear-sky permanent snow is more isotropic with satellite viewing geometry than that over overcast permanent snow. On average, the albedo of clear-sky permanent snow varies from 0.65 to 0.68 for solar zenith angles between 60° and 80°, while the corresponding albedo of overcast scenes varies from 0.70 to 0.73. Clear-sky permanent snow albedos over Antarctica estimated from two independent angular distribution models are consistent to within 0.6%, on average. Despite significant variability in sea ice optical properties with season, the estimated mean relative albedo error is −1.0% for very dark sea ice and 0.1% for very bright sea ice when albedos derived from different viewing angles are averaged. The estimated regional root-mean-square (RMS) relative albedo error is 5.6% and 2.6% when the sea ice angular distribution models are applied to a region that contains very dark and very bright sea ice, respectively. Similarly, the estimated relative albedo bias error for fresh snow is −0.1% for very dark snow scenes and 0.1% for very bright snow scenes. The estimated regional RMS relative albedo error is 3.5% and 5.0% when angular distribution models are applied to a region that contains very dark and very bright fresh snow, respectively. These error estimates are only due to angular distribution model error and do not include the error caused by scene identification. 1610 Atmosphere; 1640 Remote sensing; Shortwave radiation; 1635 Oceans; irradiance estimate; polar regions
Kato, Seiji; Rose, Fred G.; Charlock, Thomas P.Kato, S., F. G. Rose, T. P. Charlock, 2005: Computation of Domain-Averaged Irradiance Using Satellite-Derived Cloud Properties. J. Atmos. Oceanic Technol., 22(2), 146-164. doi: 10.1175/JTECH-1694.1. Abstract The respective errors caused by the gamma-weighted two-stream approximation and the effective thickness approximation for computing the domain-averaged broadband shortwave irradiance are evaluated using cloud optical thicknesses derived from 1 h of radiance measurements by the Moderate Resolution Imaging Spectrometer (MODIS) over footprints of Clouds and the Earth’s Radiant Energy System (CERES) instruments. Domains are CERES footprints of which dimension varies approximately from 20 to 70 km, depending on the viewing zenith angle of the instruments. The average error in the top-of-atmosphere irradiance at a 30° solar zenith angle caused by the gamma-weighted two-stream approximation is 6.1 W m−2 (0.005 albedo bias) with a one-layer overcast cloud where a positive value indicates an overestimate by the approximation compared with the irradiance computed using the independent column approximation. Approximately one-half of the error is due to deviations of optical thickness distributions from a gamma distribution and the other half of the error is due to other approximations in the model. The error increases to 14.7 W m−2 (0.012 albedo bias) when the computational layer dividing the cloud layer is increased to four. The increase is because of difficulties in treating the correlation of cloud properties in the vertical direction. Because the optical thickness under partly cloudy conditions, which contribute two-thirds of cloudy footprints, is smaller, the error is smaller than under overcast conditions; the average error for partly cloudy condition is −2.4 W m−2 (−0.002 albedo bias) at a 30° solar zenith angle. The corresponding average error caused by the effective thickness approximation is 0.5 W m−2 for overcast conditions and −21.5 W m−2 (−0.018 albedo bias) for partly cloudy conditions. Although the error caused by the effective thickness approximation depends strongly on the optical thickness, its average error under overcast conditions is smaller than the error caused by the gamma-weighted two-stream approximation because the errors at small and large optical thicknesses cancel each other. Based on these error analyses, the daily average error caused by the gamma-weighted two-stream and effective thickness approximations is less than 2 W m−2.
Kratz, D. P.; Mlynczak, M. G.; Mertens, C. J.; Brindley, H.; Gordley, L. L.; Martin-Torres, J.; Miskolczi, F. M.; Turner, D. D.Kratz, D. P., M. G. Mlynczak, C. J. Mertens, H. Brindley, L. L. Gordley, J. Martin-Torres, F. M. Miskolczi, D. D. Turner, 2005: An inter-comparison of far-infrared line-by-line radiative transfer models. Journal of Quantitative Spectroscopy & Radiative Transfer, 90(3-4), 323-341. doi: 10.1016/j.jqsrt.2004.04.006. A considerable fraction (>40%) of the outgoing longwave radiation escapes from the Earth's atmosphere-surface system within a region of the spectrum known as the far-infrared (wave-numbers less than 650 cm(-1)). Dominated by the line and continuum spectral features of the pure rotation band of water vapor, the far-infrared has a strong influence upon the radiative balance of the troposphere, and hence upon the climate of the Earth. Despite the importance of the far-infrared contribution, however, very few spectrally resolved observations have been made of the atmosphere for wave-numbers less than 650 cm(-1). The National Aeronautics and Space Administration (NASA), under its Instrument Incubator Program (IIP), is currently developing technology that will enable routine, space-based spectral measurements of the far-infrared. As part of NASA's IIP, the Far-Infrared Spectroscopy of the Troposphere (FIRST) project is developing an instrument that will have the capability of measuring the spectrum over the range from 100 to 1000 cm(-1) at a resolution of 0.6 cm(-1). To properly analyze the data from the FIRST instrument, accurate radiative transfer models will be required. Unlike the mid-infrared, however, no inter-comparison of codes has been performed for the far-infrared. Thus, in parallel with the development of the FIRST instrument, an investigation has been under-taken to inter-compare radiative transfer models for potential use in the analysis of far-infrared measurements. The initial phase of this investigation has focused upon the inter-comparison of six distinct line-by-line models. The results from this study have demonstrated remarkably good agreement among the models, with differences being of order 0.5%, thereby providing a high measure of confidence in our ability to accurately compute spectral radiances in the far-infrared. (C) 2004 Elsevier Ltd. All rights reserved.
Latifovic, Rasim; Trishchenko, Alexander P.; Chen, Ji; Park, William B.; Khlopenkov, Konstantin V.; Fernandes, Richard; Pouliot, Darren; Ungureanu, Calin; Luo, Yi; Wang, Shusen; Davidson, Andrew; Cihlar, JosefLatifovic, R., A. P. Trishchenko, J. Chen, W. B. Park, K. V. Khlopenkov, R. Fernandes, D. Pouliot, C. Ungureanu, Y. Luo, S. Wang, A. Davidson, J. Cihlar, 2005: Generating historical AVHRR 1 km baseline satellite data records over Canada suitable for climate change studies. Canadian Journal of Remote Sensing, 31(5), 324-346. doi: 10.5589/m05-024. Generating historical AVHRR 1 km baseline satellite data records over Canada suitable for climate change studies Rasim Latifovic, Alexander P. Trishchenko, Ji Chen, William B. Park, Konstantin V. Khlopenkov, Richard Fernandes, Darren Pouliot, Calin Ungureanu, Yi Luo, Shusen Wang, Andrew Davidson, and Josef Cihlar Pages 324-346 Abstract. Satellite data are an important component of the global climate observing system (GCOS). To serve the purpose of climate change monitoring, these data should satisfy certain criteria in terms of the length of observations and the continuity and consistency between different missions and instruments. Despite the great potential and obvious advantages of satellite observations, such as frequent repeat cycles and global coverage, their use in climate studies is hindered by substantial difficulties arising from large data volumes, complicated processing, and significant computer resources required for archiving and analysis. Successful examples of satellite earth observation (EO) data in climate studies include, among others, analyses of the earth's radiation budget (Earth Radiation Budget Experiment (ERBE), Scanner for Radiation Budget (ScaRaB), and Cloud and the Earth's Radiant Energy System (CERES)), cloudiness (International Satellite Cloud Climatology Project (ISCCP)), vegetation research (Global Inventory Modeling and Mapping Studies (GIMMS)), and the National Oceanic and Atmospheric Administration – National Aeronautics and Space Administration (NOAA–NASA) Pathfinder Program. Despite several attempts, the great potential of the advanced very high resolution radiometer (AVHRR) 1 km satellite data for climate research remains substantially underutilized. To address this issue, the generation of a comprehensive satellite data archive of AVHRR data and products at 1 km spatial resolution over Canada for 1981–2004 (24 years) has been initiated, and a new system for processing at level 1B has been developed. This processing system was employed to generate baseline 1 day and 10 day year-round clear-sky composites for a 5700 km × 4800 km area of North America. This region is centred over Canada but also includes the northern United States, Alaska, Greenland, and surrounding ocean regions. The baseline products include top-of-atmosphere (TOA) visible and near-infrared reflectance, TOA band 4 and band 5 brightness temperature, a cloud – clear – shadow – snow and ice mask, and viewing geometry. Details of the data processing system are presented in the paper. An evaluation of the system characteristics and comparison with previous results demonstrate important improvements in the quality and efficiency of the data processing. The system can process data in a highly automated manner, both for snow-covered and snow-free scenes, and for daytime and nighttime orbits, with high georeferencing accuracy and good radiometric consistency for all sensors from AVHRR NOAA-6 to AVHRR NOAA-17. Other processing improvements include the implementation of advanced algorithms for clear sky – cloud – shadow – snow and ice scene identification, as well as atmospheric correction and compositing. At the time of writing, the assembled dataset is the most comprehensive AVHRR archive at 1 km spatial resolution over Canada that includes all available observations from AVHRR between 1981 and 2004. The archive and the processing system are valuable assets for studying different aspects of land, oceans, and atmosphere related to climate variability and climate change.
Levy, R. C.; Remer, L. A.; Martins, J. V.; Kaufman, Y. J.; Plana-Fattori, A.; Redemann, J.; Wenny, B.Levy, R. C., L. A. Remer, J. V. Martins, Y. J. Kaufman, A. Plana-Fattori, J. Redemann, B. Wenny, 2005: Evaluation of the MODIS Aerosol Retrievals over Ocean and Land during CLAMS. J. Atmos. Sci., 62(4), 974-992. doi: 10.1175/JAS3391.1. Abstract The Chesapeake Lighthouse Aircraft Measurements for Satellites (CLAMS) experiment took place from 10 July to 2 August 2001 in a combined ocean–land region that included the Chesapeake Lighthouse [Clouds and the Earth’s Radiant Energy System (CERES) Ocean Validation Experiment (COVE)] and the Wallops Flight Facility (WFF), both along coastal Virginia. This experiment was designed mainly for validating instruments and algorithms aboard the Terra satellite platform, including the Moderate Resolution Imaging Spectroradiometer (MODIS). Over the ocean, MODIS retrieved aerosol optical depths (AODs) at seven wavelengths and an estimate of the aerosol size distribution. Over the land, MODIS retrieved AOD at three wavelengths plus qualitative estimates of the aerosol size. Temporally coincident measurements of aerosol properties were made with a variety of sun photometers from ground sites and airborne sites just above the surface. The set of sun photometers provided unprecedented spectral coverage from visible (VIS) to the solar near-infrared (NIR) and infrared (IR) wavelengths. In this study, AOD and aerosol size retrieved from MODIS is compared with similar measurements from the sun photometers. Over the nearby ocean, the MODIS AOD in the VIS and NIR correlated well with sun-photometer measurements, nearly fitting a one-to-one line on a scatterplot. As one moves from ocean to land, there is a pronounced discontinuity of the MODIS AOD, where MODIS compares poorly to the sun-photometer measurements. Especially in the blue wavelength, MODIS AOD is too high in clean aerosol conditions and too low under larger aerosol loadings. Using the Second Simulation of the Satellite Signal in the Solar Spectrum (6S) radiative code to perform atmospheric correction, the authors find inconsistency in the surface albedo assumptions used by the MODIS lookup tables. It is demonstrated how the high bias at low aerosol loadings can be corrected. By using updated urban/industrial aerosol climatology for the MODIS lookup table over land, it is shown that the low bias for larger aerosol loadings can also be corrected. Understanding and improving MODIS retrievals over the East Coast may point to strategies for correction in other locations, thus improving the global quality of MODIS. Improvements in regional aerosol detection could also lead to the use of MODIS for monitoring air pollution.
Lin, Bing; Wong, Takmeng; Wielicki, Bruce A.; Hu, YongxiangLin, B., T. Wong, B. A. Wielicki, Y. Hu, 2005: Comments on "Examination of the decadal tropical mean ERBS nonscanner radiation data for the iris hypothesis" - Reply. J. Climate, 18(12), 2128-2131. doi: 10.1175/JCLI3393.1.
Loeb, Norman G.; Kato, Seiji; Loukachine, Konstantin; Manalo-Smith, NatividadLoeb, N. G., S. Kato, K. Loukachine, N. Manalo-Smith, 2005: Angular Distribution Models for Top-of-Atmosphere Radiative Flux Estimation from the Clouds and the Earth’s Radiant Energy System Instrument on the Terra Satellite. Part I: Methodology. J. Atmos. Oceanic Technol., 22(4), 338-351. doi: 10.1175/JTECH1712.1. Abstract The Clouds and Earth’s Radiant Energy System (CERES) provides coincident global cloud and aerosol properties together with reflected solar, emitted terrestrial longwave, and infrared window radiative fluxes. These data are needed to improve the understanding and modeling of the interaction between clouds, aerosols, and radiation at the top of the atmosphere, surface, and within the atmosphere. This paper describes the approach used to estimate top-of-atmosphere (TOA) radiative fluxes from instantaneous CERES radiance measurements on the Terra satellite. A key component involves the development of empirical angular distribution models (ADMs) that account for the angular dependence of the earth’s radiation field at the TOA. The CERES Terra ADMs are developed using 24 months of CERES radiances, coincident cloud and aerosol retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS), and meteorological parameters from the Global Modeling and Assimilation Office (GMAO)’s Goddard Earth Observing System (GEOS) Data Assimilation System (DAS) V4.0.3 product. Scene information for the ADMs is from MODIS retrievals and GEOS DAS V4.0.3 properties over the ocean, land, desert, and snow for both clear and cloudy conditions. Because the CERES Terra ADMs are global, and far more CERES data are available on Terra than were available from CERES on the Tropical Rainfall Measuring Mission (TRMM), the methodology used to define CERES Terra ADMs is different in many respects from that used to develop CERES TRMM ADMs, particularly over snow/sea ice, under cloudy conditions, and for clear scenes over land and desert.
Loeb, Norman G.; Manalo-Smith, NatividadLoeb, N. G., N. Manalo-Smith, 2005: Top-of-Atmosphere Direct Radiative Effect of Aerosols over Global Oceans from Merged CERES and MODIS Observations. J. Climate, 18(17), 3506-3526. doi: 10.1175/JCLI3504.1. Abstract The direct radiative effect of aerosols (DREA) is defined as the difference between radiative fluxes in the absence and presence of aerosols. In this study, the direct radiative effect of aerosols is estimated for 46 months (March 2000–December 2003) of merged Clouds and the Earth’s Radiant Energy System (CERES) and Moderate Resolution Imaging Spectroradiometer (MODIS) Terra global measurements over ocean. This analysis includes the contribution from clear regions in both clear and partly cloudy CERES footprints. MODIS–CERES narrow-to-broadband regressions are developed to convert clear-sky MODIS narrowband radiances to broadband shortwave (SW) radiances, and CERES clear-sky angular distribution models (ADMs) are used to estimate the corresponding top-of-atmosphere (TOA) radiative fluxes that are needed to determine the DREA. Clear-sky MODIS pixels are identified using two independent cloud masks: (i) the NOAA/National Environmental Satellite, Data, and Information Service (NESDIS) algorithm that is used for inferring aerosol properties from MODIS on the CERES Single Scanner Footprint TOA/Surface Fluxes and Clouds (SSF) product (NOAA SSF); and (ii) the standard algorithm that is used by the MODIS aerosol group to produce the MODIS aerosol product (MOD04). Over global oceans, direct radiative cooling by aerosols for clear scenes that are identified from MOD04 is estimated to be 40% larger than for clear scenes from NOAA SSF (5.5 compared to 3.8 W m−2). Regionally, differences are largest in areas that are affected by dust aerosol, such as oceanic regions that are adjacent to the Sahara and Saudi Arabian deserts, and in northern Pacific Ocean regions that are influenced by dust transported from Asia. The net total-sky (clear and cloudy) DREA is negative (cooling) and is estimated to be −2.0 W m−2 from MOD04, and −1.6 W m−2 from NOAA SSF. The DREA is shown to have pronounced seasonal cycles in the Northern Hemisphere and large year-to-year fluctuations near deserts. However, no systematic trend in deseasonalized anomalies of the DREA is observed over the 46-month time series that is considered.
Luderer, Gunnar; Coakley, James A.; Tahnk, William R.Luderer, G., J. A. Coakley, W. R. Tahnk, 2005: Using Sun Glint to Check the Relative Calibration of Reflected Spectral Radiances. J. Atmos. Oceanic Technol., 22(10), 1480-1493. doi: 10.1175/JTECH1774.1. Abstract Observations of sunlight reflected from regions of sun glint are used to check the relative calibration of spectral radiances obtained with imaging radiometers. Reflectances at different wavelengths for sun-glint regions are linearly related. Provided that the atmosphere is reasonably transparent at the wavelengths, the aerosol burden is reasonably light, 0.64-μm optical depth less than 0.2; the particles constituting the aerosol are reasonably large, as is the case for marine aerosols; and the solar zenith angle is less than about 35°, the linear relationships between reflectances at different wavelengths are rather insensitive to the factors that govern the reflectances themselves. The relationships are remarkably insensitive to atmospheric composition, surface wind speed and direction, illumination, and viewing geometry. The slopes and offsets of the linear relationships are used to assess the relative accuracies of the calibrations of the different channels. Such assessments would appear to be attractive for checks on the in-flight performance of aircraft-borne imaging radiometers. Here, observations of reflectances at 0.64, 0.84, 1.6, and 2.1 μm for regions of sun glint obtained with the Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) instruments are shown to be consistent with each other. Observations of the 0.64- and 1.6-μm reflectances for the Tropical Rainfall Measuring Mission (TRMM) Visible and Infrared Scanner (VIRS) instrument are shown to be inconsistent with the MODIS observations, the VIRS 1.6-μm gain appearing to be too low by 9%. The 0.64-, 0.84-, and 1.6-μm reflectances obtained with the NOAA-16 and NOAA-17 Advanced Very High Resolution Radiometers (AVHRRs) for December 2002 are shown to be inconsistent with each other and inconsistent with the MODIS observations. Based on observations of the extensive ice sheets of Antarctica, the NOAA-16 0.64-μm gain is found to be too low by 5% and that for the 0.84-μm reflectance is too low by 12%; the NOAA-17 0.64-μm gain is found to be accurate (within 2%), but the 0.84-μm gain is too low by 15%. With the gains adjusted, the 0.64- and 0.84-μm reflectances obtained for regions of sun glint with the AVHRRs are consistent with each other and consistent with the Terra and Aqua MODIS observations. These results suggest that the gain for the NOAA-16 AVHRR 1.6-μm reflectance is accurate (within 1%) and that for the NOAA-17 AVHRR is too low by 5%. All of the observations were made with the AVHRR in the low-reflectance (high gain) mode. The accuracy of these assessments is expected to be about 5%.
Mace, Gerald G.; Zhang, Yuying; Platnick, Steven; King, Michael D.; Minnis, Patrick; Yang, PingMace, G. G., Y. Zhang, S. Platnick, M. D. King, P. Minnis, P. Yang, 2005: Evaluation of Cirrus Cloud Properties Derived from MODIS Data Using Cloud Properties Derived from Ground-Based Observations Collected at the ARM SGP Site. Journal of Applied Meteorology, 44(2), 221-240. doi: 10.1175/JAM2193.1. Abstract The Moderate Resolution Imaging Spectroradiometer (MODIS) on board the NASA Terra satellite has been collecting global data since March 2000 and the one on the Aqua satellite since June 2002. In this paper, cirrus cloud properties derived from ground-based remote sensing data are compared with similar cloud properties derived from MODIS data on Terra. To improve the space–time correlation between the satellite and ground-based observations, data from a wind profiler are used to define the cloud advective streamline along which the comparisons are made. In this paper, approximately two dozen cases of cirrus are examined and a statistical approach to the comparison that relaxes the requirement that clouds occur over the ground-based instruments during the overpass instant is explored. The statistical comparison includes 168 cloudy MODIS overpasses of the Southern Great Plains (SGP) region and approximately 300 h of ground-based cirrus observations. The physical and radiative properties of cloud layers are derived from MODIS data separately by the MODIS Atmospheres Team and the Clouds and the Earth’s Radiant Energy System (CERES) Science Team using multiwavelength reflected solar and emitted thermal radiation measurements. Using two ground-based cloud property retrieval algorithms and the two MODIS algorithms, a positive correlation in the effective particle size, the optical thickness, the ice water path, and the cloud-top pressure between the various methods is shown, although sometimes there are significant biases. Classifying the clouds by optical thickness, it is demonstrated that the regionally averaged cloud properties derived from MODIS are similar to those diagnosed from the ground. Because of a conservative approach toward identifying thin cirrus pixels over this region, the area-averaged cloud properties derived from the MODIS Atmospheres MOD06 product tend to be biased slightly toward the optically thicker pixels. This bias tendency has implications for model validation and parameterization development applied to thin cirrus retrieved over SGP-like land surfaces. A persistent bias is also found in the derived cloud tops of thin cirrus with both satellite algorithms reporting cloud top several hundred meters less than that reported by the cloud radar. Overall, however, it is concluded that the MODIS retrieval algorithms characterize with reasonable accuracy the properties of thin cirrus over this region.
Mitas, Christos M.; Clement, AmyMitas, C. M., A. Clement, 2005: Has the Hadley cell been strengthening in recent decades?. Geophysical Research Letters, 32(3), L03809. doi: 10.1029/2004GL021765. The intensity and structure of the Northern Hemisphere DJF Hadley cell as depicted in various commonly used data sets are examined. We find that the NCEP/NCAR and ECMWF reanalyses show a statistically significant intensification of their Hadley circulation throughout their periods. In marked contrast the NCEP-DOE reanalysis does not show any discernible trend over its period. Furthermore, the Hadley cell structure differs substantially from the other two reanalyses. We also examine a data set of global rawinsonde observations in which the Hadley cell shows no intensification. Finally, we investigate the Hadley cell simulated by an atmospheric GCM. The ensemble mean shows a statistically significant intensification, though it is smaller in magnitude than the reanalyses. We conclude that the two major reanalyses appear to be in agreement on the strengthening of the Hadley cell in recent decades. However, discrepancies among data sets do raise questions about the robustness of this strengthening. 3309 Climatology; 3374 Tropical meteorology; 3319 General circulation
Myhre, G.; Stordal, F.; Johnsrud, M.; Diner, D. J.; Geogdzhayev, I. V.; Haywood, J. M.; Holben, B. N.; Holzer-Popp, T.; Ignatov, A.; Kahn, R. A.; Kaufman, Y. J.; Loeb, N.; Martonchik, J. V.; Mishchenko, M. I.; Nalli, N. R.; Remer, L. A.; Schroedter-Homscheidt, M.; Tanré, D.; Torres, O.; Wang, M.Myhre, G., F. Stordal, M. Johnsrud, D. J. Diner, I. V. Geogdzhayev, J. M. Haywood, B. N. Holben, T. Holzer-Popp, A. Ignatov, R. A. Kahn, Y. J. Kaufman, N. Loeb, J. V. Martonchik, M. I. Mishchenko, N. R. Nalli, L. A. Remer, M. Schroedter-Homscheidt, D. Tanré, O. Torres, M. Wang, 2005: Intercomparison of satellite retrieved aerosol optical depth over ocean during the period September 1997 to December 2000. Atmos. Chem. Phys., 5(6), 1697-1719. doi: 10.5194/acp-5-1697-2005. Monthly mean aerosol optical depth (AOD) over ocean is compared from a total of 9 aerosol retrievals during a 40 months period. Comparisons of AOD have been made both for the entire period and sub periods. We identify regions where there is large disagreement and good agreement between the aerosol satellite retrievals. Significant differences in AOD have been identified in most of the oceanic regions. Several analyses are performed including spatial correlation between the retrievals as well as comparison with AERONET data. During the 40 months period studied there have been several major aerosol field campaigns as well as events of high aerosol content. It is studied how the aerosol retrievals compare during such circumstances. The differences found in this study are larger than found in a previous study where 5 aerosol retrievals over an 8 months period were compared. Part of the differences can be explained by limitations and deficiencies in some of the aerosol retrievals. In particular, results in coastal regions are promising especially for aerosol retrievals from satellite instruments particularly suited for aerosol research. In depth analyses explaining the differences between AOD obtained in different retrievals are clearly needed. We limit this study to identifying differences and similarities and indicating possible sources that affect the quality of the retrievals. This is a necessary first step towards understanding the differences and improving the retrievals.
Palikonda, Rabindra; Minnis, Patrick; Duda, David P.; Mannstein, HermannPalikonda, R., P. Minnis, D. P. Duda, H. Mannstein, 2005: Contrail coverage derived from 2001 AVHRR data over the continental United States of America and surrounding areas. Meteorologische Zeitschrift, 14(4), 525-536. doi: 10.1127/0941-2948/2005/0051. Linear contrail coverage, optical depth, and longwave radiative forcing are derived from NOAA-15 and NOAA-16 Advanced Very High Resolution Radiometer data taken during daytime over the continental United States of America (USA), southern Canada, northern Mexico, and the adjacent oceans. Analyses were performed for all available overpasses during 2001, but for NOAA-15 were primarily limited to the eastern half and the northwestern corner of the domain. Contrail coverage averaged 1.17 % and 0.65 % from the early morning NOAA-15 and midafternoon NOAA-16, respectively, for the areas and month common to both satellites. The NOAA-16 contrail coverage and radiative properties for the limited NOAA-15 domain are, on average, nearly identical to those for the entire domain. The estimated combined maximum coverage for the entire domain was ∼1.05 % during February, while the minimum of 0.57 % occurred during August. Mean optical depths varied by ∼20 % with winter minima and summer maxima. The annual mean optical depth of 0.27 translated to a normalized contrail longwave radiative forcing of 15.5 Wm. The overall daytime longwave radiative forcing for the domain is 0.11 Wm. The normalized radiative forcing peaked during summer while the overall forcing was at a maximum during winter because of the greater contrail coverage. A detailed error analysis showed that the linear contrail coverage was overestimated by ∼40 % for both satellites the true coverage is closer to 0.70 and 0.40 % for NOAA-15 and 16, respectively. Errors in the mean NOAA-15 optical depths and radiative forcing were negligible while their NOAA-16 counterparts were overestimated by approximately 13 %. Contrail coverage was dramatically lower than expected from previous studies, but is most likely due to the significant decrease in upper tropospheric humidity observed in numerical weather analysis data. Contrail optical depths are much greater than both theoretical estimates for this part of North America and empirical retrievals over Europe. The cause of the morning-afternoon difference in contrail coverage is not yet known. Further modelling studies and additional satellite analyses are needed to understand this diurnal cycle and to explain the differences between the present and previous results. German Der Bedeckungsgrad an linearen Kondensstreifen, deren optische Dicke und der daraus resultierende Strahlungsantrieb werden aus NOAA-15 und NOAA-16 Advanced Very High Resolution Radiometer Daten über den Vereinigten Staaten von Nordamerika (USA), dem südlichen Kanada, nördlichem Mexiko und den angrenzenden Meeresgebieten abgeleitet. Die Analysen wurden für alle vorhandenen Tagpassagen im Jahr 2001 durchgeführt, wobei aber NOAA-15 auf die Osthälfte und den nordwestlichen Teil des Gebietes beschränkt war. Als Bedeckungsgrad wurde für die morgendlichen NOAA-15 Daten 1,17 % und nachmittags für NOAA-16 0,65 % für die übereinstimmenden Gebiete und Zeiten gefunden. Der Bedeckungsgrad und die optischen Eigenschaften für das Gesamtgebiet stimmen bei NOAA-16 mit denen des begrenzten NOAA-15 Gebietes überein. Der höochste Bedeckungsgrad war ∼1.05 % im Februar, das Minimum im August mit 0,57 %. Die optische Dicke variierte um 20 % zwischen dem Winterminimum und dem Sommermaximum. Der jährliche Mittelwert von 0,27 führt zu einem langwelligen Strahlungsantrieb von 15,5 Wm−2. Im Mittel über das Gesamtgebiet beträgt der langwellige Strahlungsantrieb 0,11 Wm−2. Der normalisierte Strahlungsantrieb hat sein Maximum im Sommer, während der Gesamtstrahlungsantrieb wegen des höheren Bedeckungsgrades ein winterliches Maximum hat. Eine ausführliche Fehleranalyse zeigte, dass der Kondensstreifenbedeckungsgrad bei beiden Satelliten um ∼40 % für beide überschätzt wurde, so dass der wahre Bedeckungsgrad eher bei 0,70 % für NOAA-15 und 0,40 % für NOAA-16 liegt. Fehler in der optischen Dicke und im Strahlungsantrieb sind bei NOAA-15 unerheblich, während sie bei NOAA-16 um etwa 13 % überschätzt wurden. Der Kondensstreifenbedeckungsgrad war drastisch niedriger als aus früheren Untersuchungen erwartet. Mit hoher Wahrscheinlichkeit ist dies jedoch eine Folge der deutlich verringerten Feuchtigkeit der oberen Troposphäre. Die hier bestimmte optische Dicke ist höher als theoretische Schätzungen für die USA erwarten lassen und auch höher als die über Europa bestimmten Werte. Die Ursachen für den Unterschied zwischen Vor- und Nachmittag sind noch unbekannt. Weitere Modellstudien und zusätzliche Satellitenanalysen sind erforderlich, um den Tagesgang und die Unterschiede zwischen den gegenwärtigen Ergebnissen und früheren Studien zu erklären.
Pallé, E.; Montañés‐Rodriguez, P.; Goode, P. R.; Koonin, S. E.; Wild, M.; Casadio, S.Pallé, E., P. Montañés‐Rodriguez, P. R. Goode, S. E. Koonin, M. Wild, S. Casadio, 2005: A multi-data comparison of shortwave climate forcing changes. Geophysical Research Letters, 32(21). doi: 10.1029/2005GL023847. Traditionally the Earth's reflectance has been assumed to be roughly constant, but large decadal variability, not reproduced by current climate models, has been reported lately from a variety of sources. We compare here the available data sets related to Earth's reflectance, in order to assess the observational constraints on the models. We find a consistent picture among all data sets of an albedo decreased during 1985–2000 between 2–3 and 6–7 W/m2, which is highly climatically significant. The largest discrepancy among the data sets occurs during 2000–2004, when some present an increasing reflectance trend, while CERES observations show a steady decrease of about 2 W/m2.
Ramachandran, Rahul; Christopher, Sundar A.; Movva, Sunil; Li, Xiang; Conover, Helen T.; Keiser, Ken R.; Graves, Sara J.; McNider, Richard T.Ramachandran, R., S. A. Christopher, S. Movva, X. Li, H. T. Conover, K. R. Keiser, S. J. Graves, R. T. McNider, 2005: Earth Science Markup Language: A Solution to Address Data Format Heterogeneity Problems in Atmospheric Sciences. Bull. Amer. Meteor. Soc., 86(6), 791-794. doi: 10.1175/BAMS-86-6-791. Abstract No Abstract Available.
Redemann, J.; Schmid, B.; Eilers, J. A.; Kahn, R.; Levy, R. C.; Russell, P. B.; Livingston, J. M.; Hobbs, P. V.; Smith, W. L.; Holben, B. N.Redemann, J., B. Schmid, J. A. Eilers, R. Kahn, R. C. Levy, P. B. Russell, J. M. Livingston, P. V. Hobbs, W. L. Smith, B. N. Holben, 2005: Suborbital Measurements of Spectral Aerosol Optical Depth and Its Variability at Subsatellite Grid Scales in Support of CLAMS 2001. J. Atmos. Sci., 62(4), 993-1007. doi: 10.1175/JAS3387.1. Abstract As part of the Chesapeake Lighthouse and Aircraft Measurements for Satellites (CLAMS) experiment, 10 July–2 August 2001, off the central East Coast of the United States, the 14-channel NASA Ames Airborne Tracking Sunphotometer (AATS-14) was operated aboard the University of Washington’s Convair 580 (CV-580) research aircraft during 10 flights (∼45 flight hours). One of the main research goals in CLAMS was the validation of satellite-based retrievals of aerosol properties. The goal of this study in particular was to perform true over-ocean validations (rather than over-ocean validation with ground-based, coastal sites) at finer spatial scales and extending to longer wavelengths than those considered in previous studies. Comparisons of aerosol optical depth (AOD) between the Aerosol Robotic Network (AERONET) Cimel instrument at the Chesapeake Lighthouse and airborne measurements by AATS-14 in its vicinity showed good agreement with the largest r-square correlation coefficients at wavelengths of 0.38 and 0.5 μm (>0.99). Coordinated low-level flight tracks of the CV-580 during Terra overpass times permitted validation of over-ocean Moderate Resolution Imaging Spectroradiometer (MODIS) level 2 (MOD04_L2) multiwavelength AOD data (10 km × 10 km, nadir) in 16 cases on three separate days. While the correlation between AATS-14- and MODIS-derived AOD was weak with an r square of 0.55, almost 75% of all MODIS AOD measurements fell within the prelaunch estimated uncertainty range Δτ = ±0.03 ± 0.05τ. This weak correlation may be due to the small AODs (generally less than 0.1 at 0.5 μm) encountered in these comparison cases. An analogous coordination exercise resulted in seven coincident over-ocean matchups between AATS-14 and Multiangle Imaging Spectroradiometer (MISR) measurements. The comparison between AATS-14 and the MISR standard algorithm regional mean AODs showed a stronger correlation with an r square of 0.94. However, MISR AODs were systematically larger than the corresponding AATS values, with an rms difference of ∼0.06. AATS data collected during nine extended low-level CV-580 flight tracks were used to assess the spatial variability in AOD at horizontal scales up to 100 km. At UV and midvisible wavelengths, the largest absolute gradients in AOD were 0.1–0.2 per 50-km horizontal distance. In the near-IR, analogous gradients rarely reached 0.05. On any given day, the relative gradients in AOD were remarkably similar for all wavelengths, with maximum values of 70% (50 km)−1 and more typical values of 25% (50 km)−1. The implications of these unique measurements of AOD spatial variability for common validation practices of satellite data products and for comparisons to large-scale aerosol models are discussed.
Schuster, Gregory L.; Dubovik, Oleg; Holben, Brent N.; Clothiaux, Eugene E.Schuster, G. L., O. Dubovik, B. N. Holben, E. E. Clothiaux, 2005: Inferring black carbon content and specific absorption from Aerosol Robotic Network (AERONET) aerosol retrievals. Journal of Geophysical Research: Atmospheres, 110(D10), D10S17. doi: 10.1029/2004JD004548. Black carbon is ubiquitous in the atmosphere and is the main anthropogenic absorbing particulate. Absorption by black carbon is thought to be comparable to the cooling associated with sulfate aerosols, although present-day satellites are incapable of obtaining this measurement, and model estimates are highly uncertain. More measurements of black carbon concentration are necessary for improving and validating transport and general circulation models. The Aerosol Robotics Network (AERONET) of 180 worldwide radiometers offers an opportunity to obtain these measurements. We use the Maxwell Garnett effective medium approximation to infer the column-averaged black carbon concentration and specific absorption of AERONET retrievals at 46 locations. The yearly averaged black carbon column concentrations exhibit the expected regional dependence, with remote island locations having values about an order of magnitude lower than the continental biomass burning locations. The yearly averaged black carbon specific absorption cross section is consistent with other measured values, 9.9 m2 g−1 for 19,591 retrievals, but varies from 7.7 to 12.5 m2 g−1. We attribute this variability to the details of the size distributions and the fraction of black carbon contained in the aerosol mixture. We also used the Maxwell Garnett equations to parameterize the imaginary refractive index with respect to the black carbon volume fraction, enabling simple but accurate absorption estimates for aerosol mixtures when the black carbon fraction and size distribution is known. The black carbon concentrations that we derive from AERONET measurements correctly describe the radiance field and represent an alternative to absorption optical thickness in the link between models and AERONET measurements. 1640 Remote sensing; 0305 Aerosols and particles; 0394 Instruments and techniques; 0345 Pollution: urban and regional; 1694 Instruments and techniques; absorption cross section; absorption efficiency; elemental carbon; emissions inventory; particulate carbon; soot
Smith, W. L.; Charlock, T. P.; Kahn, R.; Martins, J. V.; Remer, L. A.; Hobbs, P. V.; Redemann, J.; Rutledge, C. K.Smith, W. L., T. P. Charlock, R. Kahn, J. V. Martins, L. A. Remer, P. V. Hobbs, J. Redemann, C. K. Rutledge, 2005: EOS Terra Aerosol and Radiative Flux Validation: An Overview of the Chesapeake Lighthouse and Aircraft Measurements for Satellites (CLAMS) Experiment. J. Atmos. Sci., 62(4), 903-918. doi: 10.1175/JAS3398.1. Abstract NASA developed an Earth Observing System (EOS) to study global change and reduce uncertainties associated with aerosols and other key parameters controlling climate. The first EOS satellite, Terra, was launched in December 1999. The Chesapeake Lighthouse and Aircraft Measurements for Satellites (CLAMS) field campaign was conducted from 10 July to 2 August 2001 to validate several Terra data products, including aerosol properties and radiative flux profiles derived from three complementary Terra instruments: the Clouds and the Earth’s Radiant Energy System (CERES), the Multiangle Imaging Spectroradiometer (MISR), and the Moderate Resolution Imaging Spectroradiometer (MODIS). CERES, MISR, and MODIS are being used to investigate the critical role aerosols play in modulating the radiative heat budget of the earth–atmosphere system. CLAMS’ primary objectives are to improve understanding of atmospheric aerosols, to validate and improve the satellite data products, and to test new instruments and measurement concepts. A variety of in situ sampling devices and passive remote sensing instruments were flown on six aircraft to characterize the state of the atmosphere, the composition of atmospheric aerosols, and the associated surface and atmospheric radiation parameters over the U.S. eastern seaboard. Aerosol particulate matter was measured at two ground stations established at Wallops Island, Virginia, and the Chesapeake Lighthouse, the site of an ongoing CERES Ocean Validation Experiment (COVE) where well-calibrated radiative fluxes and Aerosol Robotic Network (AERONET) aerosol properties have been measured since 1999. Nine coordinated aircraft missions and numerous additional sorties were flown under a variety of atmospheric conditions and aerosol loadings. On one “golden day” (17 July 2001), under moderately polluted conditions with midvisible optical depths near 0.5, all six aircraft flew coordinated patterns vertically stacked between 100 and 65 000 ft over the COVE site as Terra flew overhead. This overview presents a description of CLAMS objectives, measurements, and sampling strategies. Key results, reported in greater detail in the collection of papers found in this special issue, are also summarized.
Su, Wenying; Charlock, Thomas P.; Rose, Fred G.Su, W., T. P. Charlock, F. G. Rose, 2005: Deriving surface ultraviolet radiation from CERES surface and atmospheric radiation budget: Methodology. Journal of Geophysical Research: Atmospheres, 110(D14), D14209. doi: 10.1029/2005JD005794. We describe an algorithm that retrieves the surface UVB (280–315 nm) and UVA (315–400 nm) irradiances from the Surface and Atmosphere Radiation Budget (SARB) product of Clouds and the Earth's Radiant Energy System (CERES). The SARB product we use here routinely calculates the vertical profiles of shortwave, longwave, and window channel irradiances with inputs of retrievals from imagers collocated with CERES. The top of the atmosphere broadband irradiance from SARB is constrained by CERES broadband irradiance. The shortwave spectrum in the SARB calculation is divided into 15 bands, and the two ultraviolet spectral bands, band 5 (298.5–322.5 nm) and band 6 (322.5–357.5 nm), are used to generate surface UVB and UVA irradiances. In this study, we develop a set of ratio lookup tables to derive surface UVB and UVA irradiances from SARB band 5 and band 6 outputs. We show that the ratio of band 5 to UVB irradiance is sensitive to total column ozone, solar zenith angle, surface albedo, and the atmospheric profile in cloud-free conditions; in cloudy conditions, the ratio of band 5 to UVB irradiance is also sensitive to cloud optical depth and height. Additionally, we show that the ratio of band 6 to UVA irradiance is sensitive to solar zenith angle, surface albedo, and cloud optical depth. We also derive a UV index from the UVB irradiance. Our algorithm may be applied at any surface elevation or surface type, including snow and ice. Surface UV irradiances derived from the lookup table that we created agree well with those computed by the high-resolution, multistream radiative transfer code, with differences ranging from −10% to +4% for UVB and UVA irradiances. The relative differences for the UV index are higher, ranging from −26% to +16%. 3311 Clouds and aerosols; radiative transfer; 3359 Radiative processes; surface UV radiation; UV index
Sun, Moguo; Cess, Robert D.Sun, M., R. D. Cess, 2005: Improvements in cloud identification over snow/ice surfaces from ERBE to CERES. Geophysical Research Letters, 32(5), L05801. doi: 10.1029/2004GL022009. The procedure used in the Earth Radiation Budget Experiment for identifying the presence of clouds over snow/ice surfaces is known to have shortcomings, and this is corroborated through use of surface insolation measurements at the South Pole as an independent means of identifying clouds. These surface insolation measurements are then used to validate the more detailed cloud identification scheme used in the follow-up Clouds and the Earth's Radiant Energy System (CERES), and this validation is extended to the polar night through use of CERES measurements of the outgoing longwave radiation. 1640 Remote sensing; 0321 Cloud/radiation interaction; 3309 Climatology
Sun, Wenbo; Loeb, Norman G.; Lin, BingSun, W., N. G. Loeb, B. Lin, 2005: Light Scattering by an Infinite Circular Cylinder Immersed in an Absorbing Medium. Applied Optics, 44(12), 2338-2342. doi: 10.1364/AO.44.002338. Analytic solutions are developed for the single-scattering properties of an infinite dielectric cylinder embedded in an absorbing medium with normal incidence, which include extinction, scattering and absorption efficiencies, the scattering phase function, and the asymmetry factor. The extinction and scattering efficiencies are derived by the near-field solutions at the surface of the particle. The normalized scattering phase function is obtained by use of the far-field approximation. Computational results show that, although the absorbing medium significantly reduces the scattering efficiency, it has little effect on absorption efficiency. The absorbing medium can significantly change the conventional phase function. The absorbing medium also strongly affects the polarization of the scattered light. However, for large absorbing particles the degrees of polarization change little with the medium’s absorption. This implies that, if the transmitting lights are strongly weakened inside the particle, the scattered polarized lights can be used to identify objects even when the absorption property of the host medium is unknown, which is important for both active and passive remote sensing. Atmospheric scattering; Oceanic optics; Scattering, stimulated
Szewczyk, Z. Peter; Smith, G. Louis; Priestley, Kory J.Szewczyk, Z. P., G. L. Smith, K. J. Priestley, 2005: Validation of Clouds and Earth Radiant Energy System instruments aboard the Terra and Aqua satellites. Journal of Geophysical Research: Atmospheres, 110(D2), D02103. doi: 10.1029/2004JD004776. A comparison of unfiltered radiances measured by Clouds and Earth Radiant Energy System (CERES) instruments (FM1 and FM4) operating on two different platforms, Terra and Aqua satellites, is presented. Data for the comparison were collected at orbital crossings in July and August 2002 and June 2003. Using a special scanning mode, viewing geometries of the instruments were matched to provide a large data set for comparing all three channels. In addition, the data collected over Greenland were used for a more stringent test of the consistency of the shortwave radiances. Statistics are computed for different scene types, and a confidence test is applied to compiled averages to show the consistency of 1% between measurements taken from the two different platforms. Results of the unfiltered radiance comparison are based on Edition2 of the FM1 and FM4 ES8 (Earth Radiation Budget Experiment–like) data product. 1640 Remote sensing; 1694 Instruments and techniques; 3359 Radiative processes; Aqua; Terra; CERES validation
Vant-Hull, Brian; Li, Zhanqing; Taubman, Brett F.; Levy, Robert; Marufu, Lackson; Chang, Fu-Lung; Doddridge, Bruce G.; Dickerson, Russell R.Vant-Hull, B., Z. Li, B. F. Taubman, R. Levy, L. Marufu, F. Chang, B. G. Doddridge, R. R. Dickerson, 2005: Smoke over haze: Comparative analysis of satellite, surface radiometer, and airborne in situ measurements of aerosol optical properties and radiative forcing over the eastern United States. Journal of Geophysical Research: Atmospheres, 110(D10), D10S21. doi: 10.1029/2004JD004518. In July 2002 Canadian forest fires produced a major smoke episode that blanketed the east coast of the United States. Properties of the smoke aerosol were measured in situ from aircraft, complementing operational Aerosol Robotic Network (AERONET), and Moderate Resolution Imaging Spectroradiometer (MODIS) remotely sensed aerosol retrievals. This study compares single scattering albedo and phase function derived from the in situ measurements and AERONET retrievals in order to evaluate their consistency for application to satellite retrievals of optical depth and radiative forcing. These optical properties were combined with MODIS reflectance observations to calculate optical depth. The use of AERONET optical properties yielded optical depths 2–16% lower than those directly measured by AERONET. The use of in situ–derived optical properties resulted in optical depths 22–43% higher than AERONET measurements. These higher optical depths are attributed primarily to the higher absorption measured in situ, which is roughly twice that retrieved by AERONET. The resulting satellite retrieved optical depths were in turn used to calculate integrated radiative forcing at both the surface and top of atmosphere. Comparisons to surface (Surface Radiation Budget Network (SURFRAD) and ISIS) and to satellite (Clouds and Earth Radiant Energy System CERES) broadband radiometer measurements demonstrate that the use of optical properties derived from the aircraft measurements provided a better broadband forcing estimate (21% error) than those derived from AERONET (33% error). Thus AERONET-derived optical properties produced better fits to optical depth measurements, while in situ properties resulted in better fits to forcing measurements. These apparent inconsistencies underline the significant challenges facing the aerosol community in achieving column closure between narrow and broadband measurements and calculations. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 0394 Instruments and techniques; 0345 Pollution: urban and regional; 3359 Radiative processes; aerosol; radiative forcing; smoke
Wielicki, Bruce A.; Wong, Takmeng; Loeb, Norman; Minnis, Patrick; Priestley, Kory; Kandel, RobertWielicki, B. A., T. Wong, N. Loeb, P. Minnis, K. Priestley, R. Kandel, 2005: Changes in Earth's Albedo Measured by Satellite. Science, 308(5723), 825-825. doi: 10.1126/science.1106484. NASA global satellite data provide observations of Earth's albedo, i.e., the fraction of incident solar radiation that is reflected back to space. The satellite data show that the last four years are within natural variability and fail to confirm the 6% relative increase in albedo inferred from observations of earthshine from the moon. Longer global satellite records will be required to discern climate trends in Earth's albedo.
Xu, Kuan-Man; Wong, Takmeng; Wielicki, Bruce A.; Parker, Lindsay; Eitzen, Zachary A.Xu, K., T. Wong, B. A. Wielicki, L. Parker, Z. A. Eitzen, 2005: Statistical Analyses of Satellite Cloud Object Data from CERES. Part I: Methodology and Preliminary Results of the 1998 El Niño/2000 La Niña. J. Climate, 18(13), 2497-2514. doi: 10.1175/JCLI3418.1. Abstract This study presents an objective classification methodology that uses Earth Observing System (EOS) satellite data to classify distinct “cloud objects” defined by cloud-system types, sizes, geographic locations, and matched large-scale environments. This analysis method identifies a cloud object as a contiguous region of the earth with a single dominant cloud-system type. It determines the shape and size of the cloud object from the satellite data and the cloud-system selection criteria. The statistical properties of the identified cloud objects are analyzed in terms of probability density functions (PDFs) based upon the Clouds and the Earth’s Radiant Energy System (CERES) Single Satellite Footprint (SSF) data. Four distinct types of oceanic cloud objects—tropical deep convection, boundary layer cumulus, transition stratocumulus, and solid stratus—are initially identified from the CERES data collected from the Tropical Rainfall Measuring Mission (TRMM) satellite for this study. Preliminary results are presented from the analysis of the grand-mean PDFs of these four distinct types of cloud objects associated with the strong 1997/98 El Niño in March 1998 and the very weak 2000 La Niña in March 2000. A majority of the CERES footprint statistical characteristics of observed tropical deep convection are similar between the two periods in spite of the climatological contrast. There are, however, statistically significant differences in some cloud macrophysical properties such as the cloud-top height and cloud-top pressure and moderately significant differences in outgoing longwave radiation (OLR), cloud-top temperature, and ice diameter. The footprint statistical characteristics of the three observed boundary layer cloud-system types are distinctly different from one another in all cloud microphysical, macrophysical, optical properties, and radiative fluxes. The differences between the two periods are not significant for most cloud microphysical and optical properties and the top-of-the-atmosphere albedo, but are statistically significant for some cloud macrophysical properties and OLR. These characteristics of the grand-mean PDFs of cloud microphysical, macrophysical, and optical properties and radiative fluxes can be usefully compared with cloud model simulations. Furthermore, the proportion of different boundary layer cloud types is changed between the two periods in spite of small differences in their grand-mean statistical properties. An increase of the stratus population and a decrease of the cumulus population are evident in the El Niño period compared to the very weak La Niña period. The number of the largest tropical convective cloud objects is larger during the El Niño period, but the total number of tropical convective cloud objects is approximately the same in the two periods.
Yoon, Soon-Chang; Won, Jae-Gwang; Omar, Ali H.; Kim, Sang-Woo; Sohn, Byung-JuYoon, S., J. Won, A. H. Omar, S. Kim, B. Sohn, 2005: Estimation of the radiative forcing by key aerosol types in worldwide locations using a column model and AERONET data. Atmospheric Environment, 39(35), 6620-6630. doi: 10.1016/j.atmosenv.2005.07.058. The aerosol direct radiative forcing (ADRF) is calculated using aerosol robotic network (AERONET) data, and based on aerosol categorization results, the global ADRF is estimated. The CRM-2.1.2, a stand-alone version of the radiative transfer model implemented in NCAR's community climate model, CCM-3.6, is used for the evaluation. A method of determining the aerosol optical parameters is proposed for the ADRF calculation using AERONET data. Linear regression in the log–log plane makes it possible to represent the wavelength-dependent optical properties in the model using AERONET measurements. The local ADRF is estimated at Gosan, Jeju in Korea in Spring from 2001 to 2003, and the ground-based radiation measurements during the ACE-Asia IOP are used to validate the calculation. Using 3 years of AERONET data, the mean forcing efficiency at 500nm at Gosan in Spring season is evaluated as −80.5±13.2Wm−2 at the surface and −29.9±4.9Wm−2 at the top of atmosphere (TOA). The seasonal variations of the ADRF at eight AERONET sites are calculated from AERONET climatology data. The ADRF calculation at the TOA is compared with the CERES/Terra measurement, and the comparison verifies that the methodology used in this study is suitable for the global ADRF evaluation. Finally, the ADRF values in 14 regions are evaluated. Large ADRF values in Asia and Sahara regions suggest the relative importance of the aerosols on the energy budget in these regions. ACE-Asia; AERONET; Aerosol direct radiative forcing (ADRF); CRM-2.1.2; Wavelength-dependent optical properties
Zhang, Jianglong; Christopher, Sundar A.; Remer, Lorraine A.; Kaufman, Yoram J.Zhang, J., S. A. Christopher, L. A. Remer, Y. J. Kaufman, 2005: Shortwave aerosol radiative forcing over cloud-free oceans from Terra: 2. Seasonal and global distributions. Journal of Geophysical Research: Atmospheres, 110(D10), D10S24. doi: 10.1029/2004JD005009. Using 10 months of collocated Clouds and the Earth's Radiant Energy System (CERES) scanner and Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol and cloud data from Terra, we provide estimates of the shortwave aerosol direct radiative forcing (SWARF) and its uncertainties over the cloud-free global oceans. Newly developed aerosol angular distribution models (ADMs) (Zhang et al., 2005), specifically for different sea surface conditions and aerosol types, are used for inverting the CERES observed radiances to shortwave fluxes while accounting for the effect of aerosol optical properties on the anisotropy of the top of atmosphere (TOA) shortwave radiation fields. The spatial and seasonal distributions of SWARF are presented, and the MODIS retrieved aerosol optical depth (τ0.55) and the independently derived SWARF show a high degree of correlation and can be estimated using the equation SWARF = 0.05 − 74.6 τ0.55 + 18.2 τ0.552 W m−2 (τ0.55 < 0.8). The instantaneous TOA SWARF from Terra overpass time is −6.4 ± 2.6 W m−2 for cloud-free oceans. Accounting for sample biases and diurnal averaging, we estimate the SWARF over cloud-free oceans to be −5.3 ± 1.7 W m−2, consistent with previous studies. Our study is an independent measurement-based assessment of cloud-free aerosol radiative forcing that could be used as a validation tool for numerical modeling studies. Remote sensing; 1610 Atmosphere; 0305 Aerosols and particles; aerosol; radiative forcing
Zhang, Jianglong; Christopher, Sundar A.; Remer, Lorraine A.; Kaufman, Yoram J.Zhang, J., S. A. Christopher, L. A. Remer, Y. J. Kaufman, 2005: Shortwave aerosol radiative forcing over cloud-free oceans from Terra: 1. Angular models for aerosols. Journal of Geophysical Research: Atmospheres, 110(D10), D10S23. doi: 10.1029/2004JD005008. Using multiple satellite instruments, we demonstrate a new empirical method for obtaining shortwave (SW) aerosol angular distribution models (ADMs) over cloud-free oceans. We use nearly a year's worth of multispectral Moderate Resolution Imaging Spectroradiometer (MODIS) data to obtain aerosol properties within a Clouds and Earth Radiant Energy System (CERES) footprint and Special Sensor Microwave Imager (SSM/I) data to obtain near surface wind speed. The new aerosol ADMs are built as functions of near-surface ocean wind speed and MODIS aerosol optical depth at 0.55 μm (τ0.55). Among the new features are ADMs as a function of the ratio of fine mode to total aerosol optical depth (η), which contains information on aerosol type, and the combination of the CERES rotation azimuth plane scan mode CERES data and MODIS aerosol products to characterize aerosol properties over glint regions. The instantaneous aerosol forcing efficiencies (SW flux per unit optical depth at τ0.55) are 80.5, 63.1, and 73.0 Wm−2, derived using the Earth Radiation Budget Experiment (ERBE), Tropical Rainfall Measuring Mission (TRMM), and the current Terra ADMs, respectively. This study highlights the necessity for building empirical aerosol ADMs as a function of wind speed, τ0.55 and η, and gives examples of newly constructed aerosol ADMs over cloud-free oceans. We conclude that an overall uncertainty of 10% will be introduced in the derived SW aerosol direct forcing over cloud-free oceans if the ADMs are constructed without considering aerosol darkening effect over glint regions and aerosol brightening over nonglint regions (like ERBE ADMs) or the variations in aerosol properties (like TRMM ADMs). In a companion paper (Zhang et al., 2005), these new ADMs are used to calculate the shortwave aerosol radiative forcing over the global oceans. Remote sensing; 1610 Atmosphere; 0305 Aerosols and particles; aerosol; angular model
Zhang, M. H.; Lin, W. Y.; Klein, S. A.; Bacmeister, J. T.; Bony, S.; Cederwall, R. T.; Del Genio, A. D.; Hack, J. J.; Loeb, N. G.; Lohmann, U.; Minnis, P.; Musat, I.; Pincus, R.; Stier, P.; Suarez, M. J.; Webb, M. J.; Wu, J. B.; Xie, S. C.; Yao, M.-S.; Zhang, J. H.Zhang, M. H., W. Y. Lin, S. A. Klein, J. T. Bacmeister, S. Bony, R. T. Cederwall, A. D. Del Genio, J. J. Hack, N. G. Loeb, U. Lohmann, P. Minnis, I. Musat, R. Pincus, P. Stier, M. J. Suarez, M. J. Webb, J. B. Wu, S. C. Xie, M. Yao, J. H. Zhang, 2005: Comparing clouds and their seasonal variations in 10 atmospheric general circulation models with satellite measurements. Journal of Geophysical Research: Atmospheres, 110(D15), D15S02. doi: 10.1029/2004JD005021. To assess the current status of climate models in simulating clouds, basic cloud climatologies from ten atmospheric general circulation models are compared with satellite measurements from the International Satellite Cloud Climatology Project (ISCCP) and the Clouds and Earth's Radiant Energy System (CERES) program. An ISCCP simulator is employed in all models to facilitate the comparison. Models simulated a four-fold difference in high-top clouds. There are also, however, large uncertainties in satellite high thin clouds to effectively constrain the models. The majority of models only simulated 30–40% of middle-top clouds in the ISCCP and CERES data sets. Half of the models underestimated low clouds, while none overestimated them at a statistically significant level. When stratified in the optical thickness ranges, the majority of the models simulated optically thick clouds more than twice the satellite observations. Most models, however, underestimated optically intermediate and thin clouds. Compensations of these clouds biases are used to explain the simulated longwave and shortwave cloud radiative forcing at the top of the atmosphere. Seasonal sensitivities of clouds are also analyzed to compare with observations. Models are shown to simulate seasonal variations better for high clouds than for low clouds. Latitudinal distribution of the seasonal variations correlate with satellite measurements at >0.9, 0.6–0.9, and −0.2–0.7 levels for high, middle, and low clouds, respectively. The seasonal sensitivities of cloud types are found to strongly depend on the basic cloud climatology in the models. Models that systematically underestimate middle clouds also underestimate seasonal variations, while those that overestimate optically thick clouds also overestimate their seasonal sensitivities. Possible causes of the systematic cloud biases in the models are discussed. 1620 Climate dynamics; cloud modeling; 3337 Global climate models; 3310 Clouds and cloud feedbacks; climate models; 1626 Global climate models; seasonal variation of clouds
Zhao, Tom X.-P.; Laszlo, Istvan; Minnis, Patrick; Remer, LorraineZhao, T. X., I. Laszlo, P. Minnis, L. Remer, 2005: Comparison and analysis of two aerosol retrievals over the ocean in the Terra/Clouds and the Earth's Radiant Energy System–Moderate Resolution Imaging Spectroradiometer single scanner footprint data: 1. Global evaluation. Journal of Geophysical Research: Atmospheres, 110(D21), D21208. doi: 10.1029/2005JD005851. Satellite aerosol remote sensing entered a new era with the deployment of advanced satellite imaging instruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS) on the NASA Terra and Aqua satellites. These new instruments provide the opportunity to learn more about aerosol properties than was possible using the simpler NOAA Advanced Very High Resolution Radiometer (AVHRR), which has been used to retrieve aerosol optical thickness for more than 20 years. Combining historical AVHRR and the more advanced MODIS aerosol retrievals to form a long-term aerosol data record is critical for studying aerosol climate forcing. To achieve this objective, it is necessary to build a connection and establish consistency between the two retrievals through a careful evaluation of the two retrieval methods applied to the same data. As a first step in this effort, this paper exploits the potential of the Clouds and the Earth's Radiant Energy System (CERES) Single-Scanner Footprint (SSF) data set that includes aerosol products derived from Terra MODIS data at the same locations using both the multichannel MODIS and the two-channel AVHRR aerosol retrieval algorithms. The analysis examines the differences in the results seen over oceans on a global scale. It was found in a global mean sense that advancement in the aerosol retrieval over ocean from the MODIS algorithm relative to the AVHRR method is realized mostly in the improvement of the aerosol size parameter (ASP) rather than in the aerosol optical thickness (AOT). However, regional differences were observed in both AOT and ASP retrieved from the MODIS and AVHRR algorithms. These are examined further in the second part of this two-part paper. Cloud contamination and surface roughness appear to affect both aerosol retrievals, effects that need further investigation. Remote sensing; 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 0345 Pollution: urban and regional; 4801 Aerosols; 0365 Troposphere: composition and chemistry; validation; aerosol retrieval
Zhao, Tom X.-P.; Laszlo, Istvan; Minnis, Patrick; Remer, LorraineZhao, T. X., I. Laszlo, P. Minnis, L. Remer, 2005: Comparison and analysis of two aerosol retrievals over the ocean in the Terra/Clouds and the Earth's Radiant Energy System–Moderate Resolution Imaging Spectroradiometer single scanner footprint data: 2. Regional evaluation. Journal of Geophysical Research: Atmospheres, 110(D21), D21209. doi: 10.1029/2005JD005852. The advanced multichannel Moderate Resolution Imaging Spectroradiometer (MODIS) and simple independent two-channel Advanced Very High Resolution Radiometer (AVHRR) aerosol retrieval algorithms were compared regionally using the Terra/CERES-MODIS Single Scanner Footprint (SSF) data. On average, it was found that the two methods tend to overestimate 0.66-μm aerosol optical thickness (AOT) compared to AERONET surface observations in the original SSF data. If the most cloud-free data are used, the mean satellite retrievals agree to within ±10% of the AERONET data. The MODIS near-infrared (1.60-μm) AOTs are in better agreement with the surface data than the AVHRR-type retrievals. The satellite-derived aerosol size parameters are 20–30% smaller than the surface-based values with the MODIS values closer to the AERONET values than that of AVHRR-type. The effects of aerosol model assumptions, cloud contamination, and surface roughness on the two aerosol retrievals were analyzed in detail with the careful classification of clear-sky and surface roughness conditions. For most of the regions examined, the annual mean AOTs from the MODIS retrieval are 0.03 and 0.02 less than their AVHRR-type counterparts at 0.66 and 1.60 μm, respectively. However, the MODIS values may exceed the AVHRR-type values in regions where the prevailing aerosol type varies with season or is under an apparent influence of cloud or surface disturbance. Examination of the surface treatments used by the two retrieval methods indicates the need for improvement over very rough ocean surfaces, especially for the AVHRR method. The results indicate that aerosol model assumptions become important for regional retrievals and the dynamic aerosol models used in the MODIS retrieval are better suited for simultaneously measuring the regional variations in aerosol optical properties and their global mean values. Remote sensing; 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 0345 Pollution: urban and regional; 4801 Aerosols; 0365 Troposphere: composition and chemistry; validation; aerosol retrieval
Allan, Richard P.; Ringer, Mark A.; Pamment, J. Alison; Slingo, AnthonyAllan, R. P., M. A. Ringer, J. A. Pamment, A. Slingo, 2004: Simulation of the Earth's radiation budget by the European Centre for Medium-Range Weather Forecasts 40-year reanalysis (ERA40). Journal of Geophysical Research: Atmospheres, 109(D18). doi: https://doi.org/10.1029/2004JD004816. The radiation budget simulated by the European Centre for Medium-Range Weather Forecasts (ECMWF) 40-year reanalysis (ERA40) is evaluated for the period 1979–2001 using independent satellite data and additional model data. This provides information on the quality of the radiation products and indirect evaluation of other aspects of the climate produced by ERA40. The climatology of clear-sky outgoing longwave radiation (OLR) is well captured by ERA40. Underestimations of about 10 W m−2 in clear-sky OLR over tropical convective regions by ERA40 compared to satellite data are substantially reduced when the satellite sampling is taken into account. The climatology of column-integrated water vapor is well simulated by ERA40 compared to satellite data over the ocean, indicating that the simulation of downward clear-sky longwave fluxes at the surface is likely to be good. Clear-sky absorbed solar radiation (ASR) and clear-sky OLR are overestimated by ERA40 over north Africa and high-latitude land regions. The observed interannual changes in low-latitude means are not well reproduced. Using ERA40 to analyze trends and climate feedbacks globally is therefore not recommended. The all-sky radiation budget is poorly simulated by ERA40. OLR is overestimated by around 10 W m−2 over much of the globe. ASR is underestimated by around 30 W m−2 over tropical ocean regions. Away from marine stratocumulus regions, where cloud fraction is underestimated by ERA40, the poor radiation simulation by ERA40 appears to be related to inaccurate radiative properties of cloud rather than inaccurate cloud distributions. radiation budget; reanalysis; water vapor
Anderson, J.L.; Balaji, V.; Broccoli, A.J.; Cooke, W.F.; Delworth, T.L.; Dixon, K.W.; Donner, L.J.; Dunne, K.A.; Freidenreich, S.M.; Garner, S.T.; Gudgel, R.G.; Gordon, C.T.; Held, I.M.; Hemler, R.S.; Horowitz, L.W.; Klein, S.A.; Knutson, T.R.; Kushner, P.J.; Langenhost, A.R.; Lau, N.-C.; Liang, Z.; Malyshev, S.L.; Milly, P.C.D.; Nath, M.J.; Ploshay, J.J.; Ramaswamy, V.; Schwarzkopf, M.D.; Shevliakova, E.; Sirutis, J.J.; Soden, B.J.; Stern, W.F.; Thompson, L.A.; Wilson, R.J.; Wittenberg, A.T.; Wyman, B.L.Anderson, J., V. Balaji, A. Broccoli, W. Cooke, T. Delworth, K. Dixon, L. Donner, K. Dunne, S. Freidenreich, S. Garner, R. Gudgel, C. Gordon, I. Held, R. Hemler, L. Horowitz, S. Klein, T. Knutson, P. Kushner, A. Langenhost, N. Lau, Z. Liang, S. Malyshev, P. Milly, M. Nath, J. Ploshay, V. Ramaswamy, M. Schwarzkopf, E. Shevliakova, J. Sirutis, B. Soden, W. Stern, L. Thompson, R. Wilson, A. Wittenberg, B. Wyman, 2004: The New GFDL Global Atmosphere and Land Model AM2–LM2: Evaluation with Prescribed SST Simulations. J. Climate, 17(24), 4641-4673. doi: 10.1175/JCLI-3223.1. The configuration and performance of a new global atmosphere and land model for climate research developed at the Geophysical Fluid Dynamics Laboratory (GFDL) are presented. The atmosphere model, known as AM2, includes a new gridpoint dynamical core, a prognostic cloud scheme, and a multispecies aerosol climatology, as well as components from previous models used at GFDL. The land model, known as LM2, includes soil sensible and latent heat storage, groundwater storage, and stomatal resistance. The performance of the coupled model AM2-LM2 is evaluated with a series of prescribed sea surface temperature (SST) simulations. Particular focus is given to the model's climatology and the characteristics of interannual variability related to El Nin??o-Southern Oscillation (ENSO). One AM2-LM2 integration was perfor med according to the prescriptions of the second Atmospheric Model Intercomparison Project (AMIP II) and data were submitted to the Program for Climate Model Diagnosis and Intercomparison (PCMDI). Particular strengths of AM2-LM2, as judged by comparison to other models participating in AMIP II, include its circulation and distributions of precipitation. Prominent problems of AM2-LM2 include a cold bias to surface and tropospheric temperatures, weak tropical cyclone activity, and weak tropical intraseasonal activity associated with the Madden-Julian oscillation. An ensemble of 10 AM2-LM 2 integrations with observed SSTs for the second half of the twentieth century permits a statistically reliable assessment of the model's response to ENSO. In general, AM2-LM2 produces a realistic simulation of the anomalies in tropical precipitation and extratropical circulation that are associated with ENSO. ?? 2004 American Meteorological Society.
Ba, Mamoudou B.; Ellingson, Robert G.; Gruber, ArnoldBa, M. B., R. G. Ellingson, A. Gruber, 2004: Enhancement of ERBS data by using data from sounders onboard NPP/NPOESS and METOP satellites. Advances in Space Research, 33(7), 1132-1135. doi: 10.1016/S0273-1177(03)00751-8. The operational climate monitoring and diagnostic community will continue to favor in using outgoing longwave radiation (OLR) estimates that have long and continuous time series such as those estimated from the High Resolution Infrared Sounder (HIRS). OLR from HIRS data could be generated since these data exist since 1979 and will continue during NPOESS era with Cross-Track Infrared Sounder (CrIS) and HIRS/4 on NPOESS and METOP satellites, respectively. OLR estimated from Earth Radiation Budget Suite (ERBS)/Clouds and the Earth’s Radiant Energy System (CERES) can be used to calibrate the HIRS technique that will be used to generate continuous time series of OLR. This will ensure to have a consistent climate data involving different data sources. OLR generated from CrIS on the afternoon orbit could provide a backup in the event of ERBS’s failure. There will be three evenly spaced sounders (two CrIS and one HIRS/4) that could be used to retrieve OLR allowing therefore a better definition of the diurnal variability of OLR. This paper will present results from GOES sounder data to estimate OLR using an approach similar to that used for HIRS. The instantaneous OLR estimates are compared with collocated OLR products from the CERES instruments onboard TRMM and Terra spacecraft to establish the instantaneous accuracy of the multi-spectral estimation techniques for homogeneous scenes. The hourly GOES sounder OLR estimates are used to study the diurnal cycle of OLR. The time-averaged data are used to estimate the accuracy of the ERBE/CERES and HIRS diurnal cycle models as applied to daily- and monthly-averaged products at different spatial resolutions. The study suggests that the technique can be implemented for NPOESS using the CrIS and HIRS/4 for both augmenting the temporal sampling of OLR estimates and reducing the risk of OLR EDR generation.
Borgne, Pierre Le; Legendre, Gérard; Marsouin, AnneBorgne, P. L., G. Legendre, A. Marsouin, 2004: Meteosat and GOES-East Imager Visible Channel Calibration. J. Atmos. Oceanic Technol., 21(11), 1701-1709. doi: 10.1175/JTECHJTECH-1675.1. AbstractAs a preliminary step to solar irradiance calculations, the Centre de Météorologie Spatiale (CMS) has developed a pragmatic approach to calibrate the visible channels of Meteosat and GOES-East imagers. The responsivity of the Meteosat visible channel has been monitored with three desert targets from 1989 to 2002. The annual degradation rate has been estimated to 1.8% for Meteosat-4, 1.4% for Meteosat-5, and 1.9% for Meteosat-7. A reference calibration coefficient for Meteosat-7 has been derived from a comparison with Clouds and Earth's Radiant Energy System (CERES) data in summer 1998. Meteosat and GOES-East data corresponding to homogenous pixels along longitude 37.5°W and around 1200 LST have been compared on a monthly basis, leading to a calibration of GOES-East visible channel. GOES-8 data have been processed from June 1998 to December 2002 and the annual degradation rate obtained during this period is 4.0%. GOES-12 data have been processed from April to August 2003. During this short period, no degradation rate can be estimated but only a mean value of the calibration coefficient, which corresponds to a 7% increase of the prelaunch coefficient.
Chandler, William S.; Whitlock, Charles H.; Stackhouse, , Paul W. , Jr.Chandler, W. S., C. H. Whitlock, . Stackhouse, 2004: NASA Climatological Data for Renewable Energy Assessment. Journal of Solar Energy Engineering, 126(3), 945-949. doi: 10.1115/1.1748466. This article presents the latest parameters and delivery methods that provide global solar energy and meteorological resources on the Internet. Over the past several years the number of parameters in the Surface meteorology and Solar Energy Data Set has tripled. The newest parameters include solar geometry, a suite of wind speed and wind direction data, diffuse, direct normal and tilted surface solar irradiance. Requests by users and recommendations by the renewable energy industry have prompted the growth.
Christopher, Sundar A.; Zhang, JianglongChristopher, S. A., J. Zhang, 2004: Cloud-free shortwave aerosol radiative effect over oceans: Strategies for identifying anthropogenic forcing from Terra satellite measurements. Geophysical Research Letters, 31(18). doi: https://doi.org/10.1029/2004GL020510. Using the Single Scanner Footprint (SSF) data that combines the multi-spectral Moderate Resolution Imaging Spectroradiometer (MODIS) cloud and aerosol products with the Clouds and the Earth's Radiant Energy System (CERES) top of atmosphere broadband radiative fluxes, we first provide observational estimates of the instantaneous cloud-free shortwave aerosol radiative forcing (SWARF) over the global oceans. Different from our previous research, we corrected for both the sample biases and the diurnal cycle of SWARF and the cloud-free diurnally averaged SWARF is −5.3 ± 1.7 Wm−2, a value that is consistent with previous studies. Furthermore, we partition the CERES shortwave flux as a function of MODIS aerosol optical thickness and the fraction of fine mode aerosol to the total aerosol optical depth (η). Since η is related to particle size and is a good surrogate for aerosol type, we present strategies for estimating the radiative forcing of anthropogenic aerosols from MODIS and CERES measurements that is important for quantifying the climate forcing of aerosols.
Costa, Maria João; Levizzani, Vincenzo; Silva, Ana MariaCosta, M. J., V. Levizzani, A. M. Silva, 2004: Aerosol Characterization and Direct Radiative Forcing Assessment over the Ocean. Part II: Application to Test Cases and Validation. J. Appl. Meteor. Climatol., 43(12), 1818-1833. doi: 10.1175/JAM2157.1. AbstractA method based on the synergistic use of low earth orbit and geostationary earth orbit satellite data for aerosol-type characterization and aerosol optical thickness (AOT: τa) retrieval and monitoring over the ocean is presented in Part I of this paper. The method is now applied to a strong dust outbreak over the Atlantic Ocean in June 1997 and to two other relevant transport events of biomass burning and desert dust aerosol that occurred in 2000 over the Atlantic and Indian Oceans, respectively. The retrievals of the aerosol optical properties are checked against retrievals from sun and sky radiance measurements from the ground-based Aerosol Robotic Network (AERONET). The single-scattering albedo values obtained from AERONET are always within the error bars presented for Global Ozone Monitoring Experiment (GOME) retrievals, resulting in differences lower than 0.041. The retrieved AOT values are compared with the independent space–time-collocated measurements from the AERONET, as well as to the satellite aerosol official products of the Polarization and Directionality of the Earth Reflectances (POLDER) and the Moderate Resolution Imaging Spectroradiometer (MODIS). A first estimate of the AOT accuracy derived from comparisons with AERONET data leads to ±0.02 ± 0.22τa when all AOT values are retained or to ±0.02 ± 0.16τa for aerosol transport events (AOT > 0.4). The upwelling flux at the top of the atmosphere (TOA) was computed with radiative transfer calculations and used to estimate the TOA direct shortwave aerosol radiative forcing; a comparison with space–time-collocated measurements from the Clouds and the Earth's Radiant Energy System (CERES) TOA flux product was also done. It was found that more than 90% of the values differ from CERES fluxes by less than ±15%.
Futyan, J. M.; Russell, J. E.; Harries, J. E.Futyan, J. M., J. E. Russell, J. E. Harries, 2004: Cloud Radiative Forcing in Pacific, African, and Atlantic Tropical Convective Regions. J. Climate, 17(16), 3192-3202. doi: 10.1175/1520-0442(2004)017<3192:CRFIPA>2.0.CO;2. AbstractThe high degree of cancellation between longwave (LW) and shortwave (SW) cloud radiative forcing (CRF) observed in the Pacific warm pool region has generally been assumed to be a property of all convective regions in the Tropics. Analysis of the (Earth Radiation Budget Experiment) ERBE-like data from the Clouds and the Earth's Radiant Energy System (CERES) instrument on the Terra satellite reveals that a similar degree of cancellation occurs over the African convective region at monthly and longer time scales, but only in the area average. In the Atlantic intertropical convergence zone (ITCZ), the degree of cancellation is lower, particularly during the summer months, where the area-average SW forcing typically exceeds the LW forcing by more than 20 W m−2. This behavior is similar to that found previously for the eastern Pacific ITCZ region, which is consistent with the similarity in dynamics between these two regions.Over Africa, substantial seasonal and spatial variations in net CRF occur, with significant departures from cancellation within the convective region. These are explained here by a combination of surface albedo and cloud effects. In particular the large negative values of net CRF found in the summer months result from the inclusion of the radiative effects of low cloud present during the course of the month in the monthly mean cloud forcings. This work highlights the limitations of monthly mean radiation budget data for studies of rapidly evolving processes such as convection, indicating the need for studies at a higher time resolution.
Govaerts, Y. M.; Clerici, M.; Clerbaux, N.Govaerts, Y. M., M. Clerici, N. Clerbaux, 2004: Operational calibration of the Meteosat radiometer VIS band. IEEE Transactions on Geoscience and Remote Sensing, 42(9), 1900-1914. doi: 10.1109/TGRS.2004.831882. An advanced operational algorithm has been developed for the routine calibration of the Meteosat radiometer solar channel. The calibration method relies on calculated radiances over bright desert sites whereas ocean targets are used for consistency checks. Calibration errors are estimated accounting for the uncertainties of both the sensor spectral response characterization and target property description. This algorithm has been used to systematically calibrate Meteosat-5 and -7 observations. Results show that it is possible to calibrate the visible band with an estimated accuracy of about 6% when the sensor response characterization is reliable and to monitor the sensor long-term drift. These results are confirmed by Clouds and the Earth's Radiant Energy System observations. calibration; atmospheric radiation; Clouds and the Earth's Radiant Energy System; Instruments; Meteorology; radiometry; Monitoring; Oceans; atmospheric spectra; remote sensing; Clouds; Radiometry; Calibration; Uncertainty; bright desert sites; calculated radiances; calibration error estimation; calibration method; CERES observations; consistency checks; measurement errors; measurement uncertainties; measurement uncertainty; Meteosat radiometer solar channel; Meteosat radiometer VIS band; Meteosat-5 observations; Meteosat-7 observations; microwave measurement; ocean targets; operational algorithm; operational calibration; routine calibration; sensor long-term drift monitoring; Sensor phenomena and characterization; sensor spectral response characterization; target property description; visible band calibration
Gupta, Shashi K.; Kratz, David P.; Wilber, Anne C.; Nguyen, L. CathyGupta, S. K., D. P. Kratz, A. C. Wilber, L. C. Nguyen, 2004: Validation of Parameterized Algorithms Used to Derive TRMM–CERES Surface Radiative Fluxes. J. Atmos. Oceanic Technol., 21(5), 742-752. doi: 10.1175/1520-0426(2004)021<0742:VOPAUT>2.0.CO;2. AbstractParameterized shortwave and longwave algorithms developed at the Langley Research Center have been used to derive surface radiative fluxes in the processing of the Clouds and the Earth's Radiant Energy System (CERES) data obtained from flight aboard the Tropical Rainfall Measuring Mission (TRMM) satellite. Retrieved fluxes were validated on an instantaneous–footprint basis using coincident surface measurements obtained from the Atmospheric Radiation Measurement (ARM) program's Southern Great Plains (SGP) central facility, the ARM/SGP network of extended facilities, and a number of surface sites of the Baseline Surface Radiation Network (BSRN) and the Climate Monitoring and Diagnostics Laboratory (CMDL). Validation was carried out separately for clear-sky and all-sky conditions. For the shortwave, systematic errors varied from −12 to 10 W m−2 for clear skies and from −5 to 35 W m−2 for all-sky conditions. Random errors varied from 20 to 40 W m−2 for clear skies but were much larger (45–85 W m−2) for all-sky conditions. For the longwave, systematic errors were comparatively small for both clear-sky and all-sky conditions (0 to −10 W m−2) and random errors were within about 20 W m−2. In general, comparisons with surface data from the ARM/SGP site (especially the central facility) showed the best agreement. Large systematic errors in shortwave comparisons for some sites were related to flaws in the surface measurements. Larger errors in longwave fluxes for some footprints were found to be related to the errors in cloud mask retrievals, mostly during the nighttime. Smaller longwave errors related to potential errors in the operational analysis products used in satellite retrievals were also found. Still, longwave fluxes obtained with the present algorithm nearly meet the accuracy requirements for climate research.
Ignatov, A.; Laszlo, I.; Harrod, E. D.; Kidwell, K. B.; Goodrum, G. P.Ignatov, A., I. Laszlo, E. D. Harrod, K. B. Kidwell, G. P. Goodrum, 2004: Equator crossing times for NOAA, ERS and EOS sun-synchronous satellites. International Journal of Remote Sensing, 25(23), 5255-5266. doi: 10.1080/01431160410001712981. The local Equator Crossing Times (EXT) of the 13 National Oceanic and Atmospheric Administration (NOAA) platforms (TIROS-N and NOAA-6 through -17) flown from 1978 until the present have been summarized as a function of time and approximated analytically. The fit equations accurately reconstruct all past EXTs to within ±2 min and also allow extrapolation in time, thus providing a useful insight into the phenomenology of its evolution. The EXTs of the three European Research Satellites (ERS: ERS1, ERS2 and Envisat) and two Earth Observing System satellites (EOS: Terra and Aqua) are also presented. In contrast to the NOAA platforms, the ERS/EOS orbits are adjusted in-flight. This makes an analytical fit to the resulting man-made EXTs impractical, and less needed as the EXTs are more stable.
Ignatov, Alexander; Sapper, John; Cox, Stephen; Laszlo, Istvan; Nalli, Nicholas R.; Kidwell, Katherine B.Ignatov, A., J. Sapper, S. Cox, I. Laszlo, N. R. Nalli, K. B. Kidwell, 2004: Operational Aerosol Observations (AEROBS) from AVHRR/3 On Board NOAA-KLM Satellites. J. Atmos. Oceanic Technol., 21(1), 3-26. doi: 10.1175/1520-0426(2004)021<0003:OAOAFO>2.0.CO;2. AbstractSince 1988, the National Oceanic and Atmospheric Administration (NOAA) has provided operational aerosol observations (AEROBS) from the Advanced Very High Resolution Radiometer (AVHRR/2) on board the afternoon NOAA satellites [nominal equator crossing time, (EXT) ∼1330]. Aerosol optical depth (AOD) has been retrieved over oceans from channel 1 of AVHRR/2 on board NOAA-11 (1988–94) and -14 (1995–2000) using the first- and second-generation algorithms, respectively. With the launch of the NOAA-KLM series of satellites, in particular NOAA-16 (L) in September 2000 (EXT ∼1400), and NOAA-17 (M) in June 2002 (EXT ∼1000), an extended and improved third-generation algorithm was enabled. Like its predecessors, this algorithm continues to employ a single-channel methodology, by which all parameters in the retrieval algorithm (excluding AOD) are set globally as nonvariables. But now, in addition to AOD from channel 1, τ1 (λ1 = 0.63 μm), the algorithm also retrieves τ2 and τ3 in AVHRR/3 channels 2 (λ2 = 0.83 μm) and 3A (λ3 = 1.61 μm). The retrievals are made with more accurate and flexible, satellite- and channel-specific lookup tables generated with the Second Simulation of the Satellite Signal in the Solar Spectrum (6S) radiative transfer code. From pairs of τi and τj, the Ångstrom exponent (AE) parameters can then be determined as αij = −ln(τi/τj)/ln(λi/λj).This paper describes the AEROBS processing and gives examples of aerosol products, along with a preliminary diagnostics of their quality using some of the previously developed self-consistency checks. Interconsistency between the NOAA-16 and -17 aerosol retrievals is also checked. The AODs are largely coherent but distorted by the AVHRR calibration uncertainties, and subject to noise and outliers. These τ errors, unavoidable in real-time AVHRR processing, severely impact the derived AE, demonstrating a fundamental instability in estimating the aerosol model under typical maritime conditions from AVHRR. Consequently, it is concluded that the robust single-channel retrievals should be continued in the AEROBS operations in the KLM era. The more sophisticated multichannel techniques may be tested while reprocessing historical AVHRR data, only after the data quality issues have been resolved (viz., calibration uncertainties constrained, outliers removed, and noise suppressed by spatial averaging).
Inamdar, Anand K.; Ramanathan, V.; Loeb, Norman G.Inamdar, A. K., V. Ramanathan, N. G. Loeb, 2004: Satellite observations of the water vapor greenhouse effect and column longwave cooling rates: Relative roles of the continuum and vibration-rotation to pure rotation bands. Journal of Geophysical Research: Atmospheres, 109(D6). doi: https://doi.org/10.1029/2003JD003980. The Clouds and the Earth's Radiant Energy System (CERES) instrument on board the Tropical Rainfall Measuring Mission (TRMM) satellite provides, for the first time, a large-scale (40 S to 40 N) data set for the atmospheric greenhouse effect and the column-averaged longwave (LW) radiative cooling rates in the broadband (5–100 microns) and the window (8–12 microns) regions. We demonstrate here that the separation into the window and the nonwindow (5–8 microns and 12–100 microns) fluxes provides the first global-scale data set to exhibit the sensitivity of the atmospheric greenhouse effect to vertical water vapor distribution. The nonwindow greenhouse effect varies linearly with the logarithm of column water vapor amount weighted with the atmospheric pressure, while the window component varies quadratically with the water vapor partial pressure. The column cooling rates range from about −170 to −210 W m−2 for the nonwindow region. The window cooling rates are only about 10% to 20% of the above range and approach rapidly to near-zero values for surface temperatures less than 288 K. The nonwindow component of the greenhouse effect and cooling rates are shown to be more sensitive to upper troposphere water vapor, while the window greenhouse effect and cooling rates are shown to be more sensitive to the lower troposphere water vapor amount. In addition, the data reveal that in tropical regions, with warm sea surface temperatures (greater than 297 K) and elevated upper tropospheric water vapor amounts, the continuum emission in the window region leads to enhanced cooling of the column, while the rotational bands in the nonwindow region lead to a net decrease in the longwave cooling of the atmospheric column. radiative processes; remote sensing; instruments and techniques
Ipe, A.; Bertrand, C.; Clerbaux, N.; Dewitte, S.; Gonzalez, L.Ipe, A., C. Bertrand, N. Clerbaux, S. Dewitte, L. Gonzalez, 2004: Validation and homogenization of cloud optical depth and cloud fraction retrievals for GERB/SEVIRI scene identification using Meteosat-7 data. Atmospheric Research, 72(1), 17-37. doi: 10.1016/j.atmosres.2004.03.010. The Geostationary Earth Radiation Budget (GERB) instrument was launched during the 2002 summer together with the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) on board of the Meteosat Second Generation (MSG) satellite. This broadband radiometer will aim to deliver near real-time estimates of the top of the atmosphere (TOA) radiative fluxes at high temporal resolution thanks to the geostationary orbit. To infer these fluxes, a radiance-to-flux conversion needs to be performed on measured radiances. Since we plan to carry out such a conversion by using the angular dependency models (ADMs) developed from the Clouds and the Earth's Radiant Energy System (CERES) experiment, the GERB ground segment will have to rely on some scene identification on SEVIRI data which mimic as close as possible the one from CERES in order to select the proper ADM. In this paper, we briefly present the method we used to retrieve cloud optical depth and cloud fraction on footprints made of several imager pixels. We then compare the retrieval of both features on the same targets using nearly time-simultaneous Meteosat-7 imager and CERES Single Satellite Footprint data. The targets are defined as CERES radiometer footprints. We investigate the possible discrepancies between the two datasets according to surface type and cloud phase and, if they exist, suggest some strategies to homogenize GERB retrievals based on CERES ones. Cloud optical depth; Cloud fraction; Scene identification; Visible imager
Jin, Zhonghai; Charlock, Thomas P.; Smith, William L.; Rutledge, KenJin, Z., T. P. Charlock, W. L. Smith, K. Rutledge, 2004: A parameterization of ocean surface albedo. Geophysical Research Letters, 31(22). doi: https://doi.org/10.1029/2004GL021180. Measurements at a sea platform show that the ocean surface albedo is highly variable and is sensitive to four physical parameters: solar zenith angle, wind speed, transmission by atmospheric cloud/aerosol, and ocean chlorophyll concentration. Using a validated coupled ocean-atmosphere radiative transfer model, an ocean albedo look up table is created in terms of these four important parameters. A code to read the table is also provided; it gives spectral albedos for a range of oceanic and atmospheric conditions specified by the user. The result is a fast and accurate parameterization of ocean surface albedo for radiative transfer and climate modeling.
Li, F.; Vogelmann, A. M.; Ramanathan, V.Li, F., A. M. Vogelmann, V. Ramanathan, 2004: Saharan Dust Aerosol Radiative Forcing Measured from Space. J. Climate, 17(13), 2558-2571. doi: 10.1175/1520-0442(2004)017<2558:SDARFM>2.0.CO;2. AbstractThis study uses data collected from the Clouds and the Earth's Radiant Energy System (CERES) and the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments to determine Saharan dust broadband shortwave aerosol radiative forcing over the Atlantic Ocean near the African coast (15°–25°N, 45°–15°W). The clear-sky aerosol forcing is derived directly from these data, without requiring detailed information about the aerosol properties that are not routinely observed such as chemical composition, microphysical properties, and their height variations. To determine the diurnally averaged Saharan dust radiative forcing efficiency (i.e., broadband shortwave forcing per unit optical depth at 550 nm, W m−2 τ−1a), two extreme seasons are juxtaposed: the high-dust months [June–August (JJA)] and the low-dust months [November–January (NDJ)]. It is found that the top-of-atmosphere (TOA) diurnal mean forcing efficiency is −35 ± 3 W m−2 τ−1a for JJA, and −26 ± 3 W m−2 τ−1a for NDJ. These efficiencies can be fit by reducing the spectrally varying aerosol single-scattering albedo such that its value at 550 nm is reduced from 0.95 ± 0.04 for JJA to about 0.86 ± 0.04 for NDJ. The lower value for the low-dust months might be influenced by biomass-burning aerosols that were transported into the study region from equatorial Africa. Although the high-dust season has a greater (absolute value of the) TOA forcing efficiency, the low-dust season may have a greater surface forcing efficiency. Extrapolations based on model calculations suggest the surface forcing efficiencies to be about −65 W m−2 τ−1a for the high-dust season versus −81 W m−2 τ−1a for the low-dust season. These observations indicate that the aerosol character within a region can be readily modified, even immediately adjacent to a powerful source region such as the Sahara. This study provides important observational constraints for models of dust radiative forcing.
Lin, Bing; Wong, Takmeng; Wielicki, Bruce A.; Hu, YongxiangLin, B., T. Wong, B. A. Wielicki, Y. Hu, 2004: Examination of the Decadal Tropical Mean ERBS Nonscanner Radiation Data for the Iris Hypothesis. J. Climate, 17(6), 1239-1246. doi: 10.1175/1520-0442(2004)017<1239:EOTDTM>2.0.CO;2. AbstractRecent studies of the Earth Radiation Budget Satellite (ERBS) nonscanner radiation data indicate decadal changes in tropical cloudiness and unexpected radiative anomalies between the 1980s and 1990s. In this study, the ERBS decadal observations are compared with the predictions of the Iris hypothesis using 3.5-box model. To further understand the predictions, the tropical radiative properties observed from recent Clouds and the Earth's Radiant Energy System (CERES) radiation budget experiment [the NASA Langley Research Center (LaRC) parameters] are used to replace the modeled values in the Iris hypothesis. The predicted variations of the radiation fields strongly depend on the relationship (−22% K−1) of tropical high cloud and sea surface temperature (SST) assumed by the Iris hypothesis.On the decadal time scale, the predicted tropical mean radiative flux anomalies are generally significantly different from those of the ERBS measurements, suggesting that the decadal ERBS nonscanner radiative energy budget measurements do not support the strong negative feedback of the Iris effect. Poor agreements between the satellite data and model predictions even when the tropical radiative properties from CERES observations (LaRC parameters) are used imply that besides the Iris-modeled tropical radiative properties, the unrealistic variations of tropical high cloud generated from the detrainment of deep convection with SST assumed by the Iris hypothesis are likely to be another major factor for causing the deviation between the predictions and observations.
Lin, Jia-Lin; Mapes, Brian E.Lin, J., B. E. Mapes, 2004: Radiation Budget of the Tropical Intraseasonal Oscillation. J. Atmos. Sci., 61(16), 2050-2062. doi: 10.1175/1520-0469(2004)061<2050:RBOTTI>2.0.CO;2. AbstractThis study examines the relationship between precipitation and radiative heating on intraseasonal time scales in the Tropics using collocated top-of-atmosphere (TOA) and surface radiative flux measurements from special field program data [Atmospheric Radiation Measurement (ARM) Program and Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) experiments] as well as long-term TOA flux data [from Earth Radiation Budget Experiment (ERBE) and Advanced Very High Resolution Radiometer (AVHRR) satellite data]. All the different datasets consistently show that the atmosphere-integrated radiative heating is nearly in phase with the precipitation and enhances the net condensation heating by about 10%–15%. The dominant contribution to this radiative warming during wet periods is the reduction of TOA outgoing longwave radiation (OLR), primarily by clouds but with a small contribution by water vapor. This radiative heating is reduced slightly by enhanced surface downwelling longwave radiation, attributable to low cloud bases and reduced atmospheric shortwave absorption attributable to shadowing by high cloud tops.The intraseasonal budget of TOA radiation, reflecting heating of the whole ocean plus atmosphere column, is characterized by shortwave cloud forcing anomalies that are substantially larger than the longwave cloud forcing anomaly. This imbalance is in contrast with the near cancellation between these two terms at the seasonal time scale.
Loukachine, Konstantin; Loeb, Norman G.Loukachine, K., N. G. Loeb, 2004: Top-of-atmosphere flux retrievals from CERES using artificial neural networks. Remote Sensing of Environment, 93(3), 381-390. doi: 10.1016/j.rse.2004.08.005. The Clouds and the Earth's Radiant Energy System (CERES) instruments on the Terra spacecraft provide accurate shortwave (SW), longwave (LW) and window (WN) region top-of-atmosphere (TOA) radiance measurements from which TOA radiative flux values are obtained by applying Angular Distribution Models (ADMs). These models are developed empirically as functions of the surface and cloud properties provided by coincident high-resolution imager measurements over CERES field-of-view. However, approximately 5.6% of the CERES/Terra footprints lack sufficient imager information for a reliable scene identification. To avoid any systematic biases in regional mean radiative fluxes, it is important to provide TOA fluxes for these footprints. For this purpose, we apply a feedforward error-backpropagation Artificial Neural Network (ANN) technique to reproduce CERES/Terra ADMs relying only on CERES measurements. All-sky ANN-based angular distribution models are developed for 10 surface types separately for shortwave, longwave and window TOA flux retrievals. To optimize the ANN performance, we use a partially connected first hidden neuron layer and compact training sets with reduced data noise. We demonstrate the performance of the ANN-based ADMs by comparing TOA fluxes inferred from ANN and CERES anisotropic factors. The global annual average bias in ANN-derived fluxes relative to CERES is less than 0.5% for all ANN scene types. The maximum bias occurs over sea ice and permanent snow surfaces. For all surface types, instantaneous ANN-derived TOA fluxes are self-consistent in viewing zenith angle to within 9% for shortwave, 3.5% and 3% longwave daytime and nighttime, respectively. Artificial neural network; Radiation budget; Top-of-atmosphere flux
Lu, Riyu; Dong, Buwen; Cess, Robert D.; Potter, Gerald L.Lu, R., B. Dong, R. D. Cess, G. L. Potter, 2004: The 1997/98 El Niño: A test for climate models. Geophysical Research Letters, 31(12). doi: https://doi.org/10.1029/2004GL019956. Version 3 of the Hadley Centre Atmospheric Model (HadAM3) has been used to demonstrate one means of comparing a general circulation model with observations for a specific climate perturbation, namely the strong 1997/98 El Niño. This event was characterized by the collapse of the tropical Pacific's Walker circulation, caused by the lack of a zonal sea surface temperature gradient during the El Niño. Relative to normal years, cloud altitudes were lower in the western portion of the Pacific and higher in the eastern portion. HadAM3 likewise produced the observed collapse of the Walker circulation, and it did a reasonable job of reproducing the west/east cloud structure changes. This illustrates that the 1997/98 El Niño serves as a useful means of testing cloud-climate interactions in climate models.
Marsden, David; Valero, Francisco P. J.Marsden, D., F. P. J. Valero, 2004: Observation of Water Vapor Greenhouse Absorption over the Gulf of Mexico Using Aircraft and Satellite Data. J. Atmos. Sci., 61(6), 745-753. doi: 10.1175/1520-0469(2004)061<0745:OOWVGA>2.0.CO;2. AbstractThrough its interaction with radiation, water vapor provides an important link between the ocean and atmosphere. One way this occurs is through the greenhouse effect; observations of water vapor greenhouse absorption in the Gulf of Mexico during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers—Florida Area Cirrus Experiment during July 2002 are reported here. The quantity dGa/dTs is the change in the amount of upwelling infrared flux absorbed by water vapor as the sea surface temperature increases, and therefore parameterizes the strength of the evaporative feedback between the ocean and atmosphere. Using hemispherical infrared broadband (IRBR) and narrow field of view (NFOV) radiometers aboard a NASA ER-2 aircraft, dGa/dTs was measured during flights on 9 and 26 July marked by large-scale convective and quiescent conditions, respectively. Using the NFOV over the wavelength range 4–40 μm, dGa/dTs = 13.4 ± 1.0 W m−2 K−1 on 9 July, while on 26 July dGa/dTs = 9.7 ± 0.3 W m−2 K−1. The NFOV measurement of dGa/dTs in the 8–12-μm wavelength range yielded values of ∼2.5 W m−2 K−1 for both days, indicating that most of the change in greenhouse absorption with increasing ocean temperature occurs in the rotational and vibrational spectral regions of water vapor. The IRBR measurements yielded higher values of dGa/dTs on both days, but were likely affected by cold clouds in the hemispherical radiometer field of view. These results support the link between greenhouse efficiency, mid- to upper-tropospheric water vapor concentration, and convection.
Matthews, GrantMatthews, G., 2004: Calculation of the static in-flight telescope-detector response by deconvolution applied to point-spread function for the Geostationary Earth Radiation Budget experiment. Applied Optics, 43(34), 6313-6322. doi: 10.1364/AO.43.006313. The Geostationary Earth Radiation Budget (GERB) experiment is a broadband satellite radiometer instrument program intended to resolve remaining uncertainties surrounding the effect of cloud radiative feedback on future climate change. By use of a custom-designed diffraction-aberration telescope model, the GERB detector spatial response is recovered by deconvolution applied to the ground calibration point-spread function (PSF) measurements. An ensemble of randomly generated white-noise test scenes, combined with the measured telescope transfer function results in the effect of noise on the deconvolution being significantly reduced. With the recovered detector response as a base, the same model is applied in construction of the predicted in-flight field-of-view response of each GERB pixel to both short- and long-wave Earth radiance. The results of this study can now be used to simulate and investigate the instantaneous sampling errors incurred by GERB. Also, the developed deconvolution method may be highly applicable in enhancing images or PSF data for any telescope system for which a wave-front error measurement is available. Cloud effects; Detector arrays; Discrete Fourier transforms; Image enhancement; Space instrumentation; Temporal resolution
Min, Qilong; Minnis, Patrick; Khaiyer, Mandana M.Min, Q., P. Minnis, M. M. Khaiyer, 2004: Comparison of cirrus optical depths derived from GOES 8 and surface measurements. Journal of Geophysical Research: Atmospheres, 109(D15). doi: https://doi.org/10.1029/2003JD004390. Ground-based passive radiometer measurements are used to validate satellite-derived cirrus optical depths over the Atmospheric Radiation Measurement Program Southern Great Plains site during March 2000. Optical depths derived from direct beam measurements by a multifilter rotating shadow band radiometer were well correlated with those determined from the Geostationary Operational Environmental Satellite, especially in relatively homogenous cloud fields. Compared to the multifilter rotating shadow band radiometer (MFRSR) results, on average, the satellite retrieval overestimated optical depth by ∼0.67 (29%), even though 75% of the GOES values were within ±1.0 of the MFRSR results. Some of the bias is attributable to cloud inhomogeneities, mismatches in observed clouds, errors in the surface albedo, and possible errors in the ice crystal scattering phase function. The results demonstrate the potential for using MFRSR data, available over many parts of the globe, for validating satellite cloud retrievals in many different surface and atmospheric conditions. GOES; cloud optical depth; MFRSR
Minnis, Patrick; Gambheer, Arvind V.; Doelling, David R.Minnis, P., A. V. Gambheer, D. R. Doelling, 2004: Azimuthal anisotropy of longwave and infrared window radiances from the Clouds and the Earth's Radiant Energy System on the Tropical Rainfall Measuring Mission and Terra satellites. Journal of Geophysical Research: Atmospheres, 109(D8). doi: https://doi.org/10.1029/2003JD004471. Shadowing by vegetation, landforms, or clouds can reduce the surface temperature relative to unshadowed portions of the same land area. This shading effect can cause azimuthal variation of the outgoing infrared radiance that is currently not taken into account in remote sensing and Earth radiation budget analyses. In this paper, multiangle longwave (LW) (5–200 μm) and window (WN) (8–12 μm) radiances taken by the Clouds and the Earth's Radiant Energy System (CERES) rotating azimuth plane scanner on the Tropical Rainfall Measuring Mission (TRMM) and Terra satellites are used to determine the azimuthal anisotropy of LW and WN fields over all solar zenith angles and surface types in clear and cloudy conditions. The azimuthal component of the anisotropy is isolated by constructing limb-darkening models for each category of surface type and topography in each solar zenith angle (SZA) bin. The viewing zenith angle dependence of WN and LW radiances in clear scenes depends on the SZA, possibly because of changes in the boundary layer temperature structure during the day. The observed mean radiances, in general, are greater when viewing the sunlit hemisphere (backscattering) than when viewing the shaded (forward scattering) hemisphere. This forward-back contrast increases with increasing terrain roughness and is stronger for surfaces with open vegetation such as shrubs and grass than for contiguous vegetation like forests. The anisotropy is less well defined for barren deserts. Maximum anisotropy occurs for SZAs between 48° and 70°. This paper provides the first evidence that clouds also induce longwave azimuthal anisotropy. Strong forward-back radiance contrast is evident for partly, mostly, and overcast scenes for SZA < 48°. The contrast disappears for overcast scenes and decreases for partly and mostly cloudy scenes at higher SZAs. The TRMM sampling is limited and causes some biases at particular angle sets but overall provides a reasonable depiction of the anisotropy at all SZAs. Terra yields a more accurate anisotropy characterization but only for SZAs between 48° and 70°. A simple model constructed from the TRMM results for clear scenes reduces clear-sky temperature prediction RMS errors by 38% or more while minimizing the biases associated with azimuthal anisotropy. The model should yield similar or better reductions in the errors associated with retrievals of skin temperature or LW fluxes, especially those from geostationary satellites. In addition, future analyses of combined TRMM, Terra, and Aqua CERES data will likely provide more accurate correction models that could further reduce errors in surface skin temperature and radiative flux for both clear and cloudy scenes. surface temperature; infrared radiation; remote sensing
Myhre, Gunnar; Stordal, Frode; Johnsrud, Mona; Ignatov, Alexander; Mishchenko, Michael I.; Geogdzhayev, Igor V.; Tanré, Didier; Deuzé, Jean-Luc; Goloub, Philippe; Nakajima, Teruyuki; Higurashi, Akiko; Torres, Omar; Holben, BrentMyhre, G., F. Stordal, M. Johnsrud, A. Ignatov, M. I. Mishchenko, I. V. Geogdzhayev, D. Tanré, J. Deuzé, P. Goloub, T. Nakajima, A. Higurashi, O. Torres, B. Holben, 2004: Intercomparison of Satellite Retrieved Aerosol Optical Depth over the Ocean. J. Atmos. Sci., 61(5), 499-513. doi: 10.1175/1520-0469(2004)061<0499:IOSRAO>2.0.CO;2. AbstractFor an 8-month period aerosol optical depth (AOD) is compared, derived over global oceans with five different retrieval algorithms applied to four satellite instruments flown on board three satellite platforms. The Advanced Very High Resolution Radiometer (AVHRR) was flown on board NOAA-14, the Ocean Color and Temperature Scanner (OCTS) and the Polarization and Directionality of the Earth's Reflectances (POLDER) on board the Advanced Earth Observing Satellite (ADEOS), and the Total Ozone Mapping Spectrometer (TOMS) on board the Earth Probe satellites. The aerosol data are presented on the same format and converted to the same wavelength in the comparison and can therefore be a useful tool in validation of global aerosol models, in particular models that can be driven with meteorological data for the November 1996 to June 1997 period studied here. Large uncertainties in the global mean AOD are found. There is at least a factor of 2 difference between the AOD from the retrievals. The largest uncertainties are found in the Southern Hemisphere, and the smallest differences mostly near the continents in the Northern Hemisphere. The largest relative differences are probably caused by differences in cloud screening.
Parol, F.; Buriez, J. C.; Vanbauce, C.; Riedi, J.; C.-Labonnote, L.; Doutriaux-Boucher, M.; Vesperini, M.; Sèze, G.; Couvert, P.; Viollier, M.; Bréon, F. M.Parol, F., J. C. Buriez, C. Vanbauce, J. Riedi, L. C.-Labonnote, M. Doutriaux-Boucher, M. Vesperini, G. Sèze, P. Couvert, M. Viollier, F. M. Bréon, 2004: Review of capabilities of multi-angle and polarization cloud measurements from POLDER. Advances in Space Research, 33(7), 1080-1088. doi: 10.1016/S0273-1177(03)00734-8. Polarization and directionality of the Earth’s reflectances (POLDER) is a multispectral imaging radiometer–polarimeter with a wide field-of-view, a moderate spatial resolution, and a multi-angle viewing capability. It functioned nominally aboard ADEOS1 from November 1996 to June 1997. When the satellite passes over a target, POLDER allows to observe it under up to 14 different viewing directions and in several narrow spectral bands of the visible and near-infrared spectrum (443–910 nm). This new type of multi-angle instruments offers new opportunity for deriving cloud parameters at global scale. The aim of this short overview paper is to point out the main contributions of such an instrument for cloud study through its original instrumental capabilities (multidirectionality, multipolarization, and multispectrality). This is mainly illustrated by using ADEOS 1-POLDER derived cloud parameters which are operationally processed by CNES and are available since the beginning of 1999.
Penner, Joyce E.; Dong, Xiquan; Chen, YangPenner, J. E., X. Dong, Y. Chen, 2004: Observational evidence of a change in radiative forcing due to the indirect aerosol effect. Nature, 427(6971), 231-234. doi: 10.1038/nature02234. Anthropogenic aerosols enhance cloud reflectivity by increasing the number concentration of cloud droplets, leading to a cooling effect on climate known as the indirect aerosol effect. Observational support for this effect is based mainly on evidence that aerosol number concentrations are connected with droplet concentrations, but it has been difficult to determine the impact of these indirect effects on radiative forcing1,2,3. Here we provide observational evidence for a substantial alteration of radiative fluxes due to the indirect aerosol effect. We examine the effect of aerosols on cloud optical properties using measurements of aerosol and cloud properties at two North American sites that span polluted and clean conditions—a continental site in Oklahoma with high aerosol concentrations, and an Arctic site in Alaska with low aerosol concentrations. We determine the cloud optical depth required to fit the observed shortwave downward surface radiation. We then use a cloud parcel model to simulate the cloud optical depth from observed aerosol properties due to the indirect aerosol effect. From the good agreement between the simulated indirect aerosol effect and observed surface radiation, we conclude that the indirect aerosol effect has a significant influence on radiative fluxes.
Potter, Gerald L.; Cess, Robert D.Potter, G. L., R. D. Cess, 2004: Testing the impact of clouds on the radiation budgets of 19 atmospheric general circulation models. Journal of Geophysical Research: Atmospheres, 109(D2). doi: https://doi.org/10.1029/2003JD004018. We compare cloud-radiative forcing (CRF) at the top-of-the atmosphere from 19 atmospheric general circulation models, employing simulations with prescribed sea-surface temperatures, to observations from the Earth Radiation Budget Experiment (ERBE). With respect to 60°N to 60°S means, a surprising result is that many of the 19 models produce unusually large biases in Net CRF that are all of the same sign (negative), meaning that many of the models significantly overestimate cloud radiative cooling. The primary focus of this study, however, is to demonstrate a diagnostic procedure, using ERBE data, to test if a model might produce, for a given region, reasonable CRF as a consequence of compensating errors caused either by unrealistic cloud vertical structure, cloud optical depth or cloud fraction. For this purpose we have chosen two regions, one in the western tropical Pacific characterized by high clouds spanning the range from thin cirrus to deep convective clouds, and the other in the southeastern Pacific characterized by trade cumulus. For a subset of eight models, it is found that most typically produce more realistic regionally-averaged CRF (and its longwave and shortwave components) for the southeastern region as opposed to the western region. However, when the diagnostic procedure for investigating cloud vertical structure and cloud optical depth is imposed, this somewhat better agreement in the southeastern region is found to be the result of compensating errors in either cloud vertical structure, cloud optical depth or cloud fraction. The comparison with ERBE data also shows large errors in clear-sky fluxes for many of the models. clouds; climate; radiation
Sherwood, Steven C.; Chae, Jung-Hyo; Minnis, Patrick; McGill, MatthewSherwood, S. C., J. Chae, P. Minnis, M. McGill, 2004: Underestimation of deep convective cloud tops by thermal imagery. Geophysical Research Letters, 31(11). doi: https://doi.org/10.1029/2004GL019699. The most common method of ascertaining cloud heights from space is from thermal brightness temperatures. Deep convective clouds of high water content are expected to radiate as black bodies. Here, thermal cloud top estimates from GOES-8 are compared with direct estimates of where the top should be sensed, based on colocated Goddard Cloud Physics Lidar (CPL) observations collected during the Cirrus Regional Study of Tropical Anvils and Florida Area Cirrus Experiment (CRYSTAL-FACE). GOES-8 cloud top heights are consistently ∼1 km lower than the “visible” cloud top estimates from the lidar, even though the latter take into account the finite visible opacity of the clouds and any overlying thin cirrus layers, and are often far below the position of highest detected cloud. The low bias in thermal estimates appears to get worse for the tallest clouds, perhaps by an additional kilometer, and depends little on cloud albedo. The consistency of the bias over multiple satellites suggests that cloud retrievals are affected by an unexpected radiative transfer issue.
Smith, G. Louis; Wielicki, Bruce A.; Barkstrom, Bruce R.; Lee, Robert B.; Priestley, Kory J.; Charlock, Thomas P.; Minnis, Patrick; Kratz, David P.; Loeb, Norman; Young, David F.Smith, G. L., B. A. Wielicki, B. R. Barkstrom, R. B. Lee, K. J. Priestley, T. P. Charlock, P. Minnis, D. P. Kratz, N. Loeb, D. F. Young, 2004: Clouds and Earth radiant energy system: an overview. Advances in Space Research, 33(7), 1125-1131. doi: 10.1016/S0273-1177(03)00739-7. The Clouds and Earth radiant energy system (CERES) instrument was first flown aboard the TRMM spacecraft whose 35° inclination orbit allowed for the collection of radiation budget data over all local times, i.e. all solar zenith angles for the latitude range. Moreover, this instrument has gathered the only bidirectional radiance data covering all local times. An additional quartet of CERES instruments are now operating in pairs on both the TERRA and AQUA spacecrafts. Thus far, these instruments have collected several years of Earth radiation budget observations and continue to operate. For each of the TERRA and AQUA spacecrafts, one CERES instrument operates in a cross-track scan mode for the purpose of mapping the Earth’s outgoing longwave radiation and reflected solar radiation. The other operates in an azimuthal rotation while scanning also in zenith angle for the purpose of gathering measurements for the angular distribution of radiance from various scene types, to improve the computation of fluxes from radiance measurements. The CERES instruments carry in-flight calibration systems to maintain the measurement accuracy of 1% for measured radiances. In addition to retrieving fluxes at the top of the atmosphere, the CERES program uses data from other instruments aboard the spacecraft to compute the radiation balance at the surface and at levels through the atmosphere. CERES; radiation budget; Aqua; Earth observation system; Terra
Stephens, Graeme L.; Webster, Peter J.; Johnson, Richard H.; Engelen, Richard; L'Ecuyer, TristanStephens, G. L., P. J. Webster, R. H. Johnson, R. Engelen, T. L'Ecuyer, 2004: Observational Evidence for the Mutual Regulation of the Tropical Hydrological Cycle and Tropical Sea Surface Temperatures. J. Climate, 17(11), 2213-2224. doi: 10.1175/1520-0442(2004)017<2213:OEFTMR>2.0.CO;2. AbstractFrom the analysis of surface, upper-air, and satellite observations it is suggested that the hydrological cycle associated with the Madden–Julian oscillation acts in the mode of a self-regulating oscillator. The regulation occurs as a feedback between hydrological processes in the atmosphere; radiation processes; and the dynamical movement of air over the tropical oceans controling variations of rainfall, cloudiness, and sea surface temperature (SST) on time scales varying between 30 and 60 days. The conjectured feedback occurs in three main phases: (i) the destablization phase: the atmosphere becomes increasingly unstable by the combination of radiative cooling of the upper troposphere, the gradual build up of shallow convection, and the warming of the SSTs under near-clear-sky and calm conditions; (ii) the convective stage: large-scale convection develops over the region resulting in widespread heavy precipitation, deepening of the oceanic mixed layer, cooling of the SST, and moistening of the upper troposphere; and (iii) the restoring phase: the combination of continued cooling of the SSTs maintained by the strong low-level winds and reduced solar heating, with the radiative heating of the upper atmosphere by high clouds sustained by high humidity, are major factors in stabilizing the atmosphere, suppressing convection, bringing an end to the cooling of the SSTs, and eventually leading to a calming of the winds, dissipation of the thick upper-level clouds, and a restoration of the cycle to its warming phase.
Sun, Moguo; Cess, Robert D.Sun, M., R. D. Cess, 2004: A procedure for evaluating feedback mechanisms in coupled atmosphere/ocean climate models. Geophysical Research Letters, 31(12). doi: https://doi.org/10.1029/2004GL019876. To understand inter-model differences in long-term simulations of climate change, as exist between coupled atmosphere/ocean general circulation models, it is necessary to first understand climate feedback mechanisms that operate within each of the various models. With this goal in mind, we have employed an 1870 to 1989 simulation, with prescribed increases in greenhouse gases, that was performed using the National Center for Atmospheric Research Community Climate System Model Version 1, as a vehicle for determining two feedback processes operating within that model. These are cloud feedback and snow/ice albedo feedback. A prerequisite to evaluating feedback mechanisms is to first evaluate the direct radiative forcing, caused by the increasing greenhouse gases, which produces global warming by the model, and a procedure for doing this is presented. Cloud feedback is then evaluated by referencing the model's change in global-mean cloud-radiative forcing to the direct greenhouse-gas induced radiative forcing, and a comparable procedure is employed to determine snow/ice albedo feedback. This model produces a moderately strong negative cloud feedback and a modest positive snow/ice albedo feedback. But the main purpose of this study is to provide a reasonably simple procedure for determining both cloud feedback and snow/ice albedo feedback within coupled atmosphere/ocean GCMs.
Sun, Wenbo; G Loeb, Norman; Fu, QiangSun, W., N. G Loeb, Q. Fu, 2004: Light scattering by coated sphere immersed in absorbing medium: a comparison between the FDTD and analytic solutions. Journal of Quantitative Spectroscopy and Radiative Transfer, 83(3), 483-492. doi: 10.1016/S0022-4073(03)00101-8. A recently developed finite-difference time domain scheme is examined using the exact analytic solutions for light scattering by a coated sphere immersed in an absorbing medium. The relative differences are less than 1% in the extinction, scattering, and absorption efficiencies and less than 5% in the scattering phase functions. The definition of apparent single-scattering properties is also discussed. Light scattering; Absorbing medium; Coated sphere
Sun, Wenbo; Loeb, Norman G.; Kato, SeijiSun, W., N. G. Loeb, S. Kato, 2004: Estimation of instantaneous TOA albedo at 670 nm over ice clouds from POLDER multidirectional measurements. Journal of Geophysical Research: Atmospheres, 109(D2). doi: https://doi.org/10.1029/2003JD003801. An algorithm that determines the 670-nm top-of-atmosphere (TOA) albedo of ice clouds over ocean using Polarization and Directionality of the Earth's Reflectance (POLDER) multidirectional measurements is developed. A plane-parallel layer of ice cloud with various optical thicknesses and light scattering phase functions is assumed. For simplicity, we use a double Henyey-Greenstein phase function to approximate the volume-averaged phase function of the ice clouds. A multidirectional reflectance best-fit match between theoretical and POLDER reflectances is used to infer effective cloud optical thickness, phase function and TOA albedo. Sensitivity tests show that while the method does not provide accurate independent retrievals of effective cloud optical depth and phase function, TOA albedo retrievals are accurate to within ∼3% for both a single layer of ice clouds or a multilayer system of ice clouds and water clouds. When the method is applied to POLDER measurements and retrieved albedos are compared with albedos based on empirical angular distribution models (ADMs), zonal albedo differences are generally smaller than ∼3%. When albedos are compared with those on the POLDER-I ERB and Cloud product, the differences can reach ∼15% at small solar zenith angles. albedo; ice clouds; angular distribution model; POLDER multidirectional measurement
Sutter, Marcel; Dürr, Bruno; Philipona, RolfSutter, M., B. Dürr, R. Philipona, 2004: Comparison of two radiation algorithms for surface-based cloud-free sky detection. Journal of Geophysical Research: Atmospheres, 109(D17), D17202. doi: 10.1029/2004JD004582. Two methods to automatically detect cloud-free skies from the Earth's surface, which are based on algorithms using surface radiation measurements, are compared with Weather Service ground observations and each other. One algorithm uses total and diffuse shortwave downward radiation (referred to as the shortwave radiation algorithm (SWRA)), and the other uses longwave downward radiation in combination with surface temperature and humidity (referred to as the longwave radiation algorithm (LWRA)). The data used for the comparison originate from five Baseline Surface Radiation Network (BSRN) stations, two in polar regions, one in central Europe, and two at low latitudes, covering time periods of 2–6 years. After determination of the parameterization both algorithms can be applied without further effort, offering a straightforward technique to identify cloud-free skies over long time periods. With Weather Service ground observations as reference, LWRA detects cloud-free skies around 80% of the time. Significant overestimation of cloud cover happens during strong inversions. Thin high clouds on the one hand and dry haze (in an otherwise cloud-free sky) on the other hand can cause LWRA to wrongly calculate a clear sky. The percentage of detected and missed cloud-free skies by SWRA depends on the parameterization (i.e., the definition of cloud-free sky). Compared to Weather Service ground observations, we noticed lower rates of detected cloud-free skies at stations with frequent events with increased turbidity and underestimation of cloud cover occasionally during periods with only thin high clouds, especially if they are accompanied by increased turbidity. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1640 Remote sensing; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3394 Meteorology and Atmospheric Dynamics: Instruments and techniques; 1694 Instruments and techniques; radiation; automatic cloud detection
Valero, Francisco P. J.; Cess, Robert D.; Pope, Shelly K.Valero, F. P. J., R. D. Cess, S. K. Pope, 2004: Disagreements Over Cloud Absorption. Science, 305(5688), 1239-1240. doi: 10.1126/science.305.5688.1239. In their Letter “Have clouds darkened since 1995?” (14 Nov. 2003, p. [1151][1]), Z. Li and colleagues discuss points raised in an earlier news article on climate models and clouds (“Making clouds darker sharpens cloudy climate models,” R. A. Kerr, News of the Week, 20 June 2003, p. [1859][2]). Li et al. state that “Agreements [between model calculations and observations] within the range of uncertainties were found by all teams… except for one…,” where a paper of ours is cited ([1][3]) as the exception and no references are given for “all teams.” This statement is misleading and inaccurate. Cloud absorptances were calculated in ([1][3]) with a suite of five different radiative transfer models, and, contrary to Li et al. 's Letter, agreement within the uncertainties was indeed found for most models. Figures 11 and 14 and Table 3 in ([1][3]) show observed and modeled absorptances and the overlap of error bars. For example, in the 29 March case [the most favorable case for measurements and analysis ([2][4])], the differences are 20 to 23 W m−2 for three models and 61 W m−2 for the two other models ([1][3]). Other ARESE II studies find measurement-calculation differences of 18 to 35 W m−2 ([3][5]) and 15 to 28 W m−2 ([4][6]). Hence, the results in ([1][3]), ([3][5]), and ([4][6]) are in general agreement (given model and measurement errors and variations in model implementation between the various studies) for the higher performance models. Very importantly, however, all the studies find systematic model-observation discrepancies. In our view, the true disagreement in the few cases studied is on the interpretation of the model-measurement differences. Li et al. and Ackerman et al. ([4][6]) appear to conclude that cloud absorptance can be calculated adequately, whereas Valero et al. ([1][3]) and O'Hirok and Gautier ([3][5]) conclude that model-measurement differences, even if within error bars, are important because of their systematic character; models consistently underpredict and never overpredict the value. The source (experimental or modeling) of such a bias is of major concern because these results are fundamental for both climate and remote sensing applications. 1. 1.[↵][7] 1. F. P. J. Valero 2. et al. , J. Geophys. Res. 108, 10 (2003) 1029/2001JD001384. [OpenUrl][8] 2. 2.[↵][9] 1. L. Oreopoulos 2. et al. , J. Geophys. Res. 108, 10 (2003) 1029/2002JD002243. [OpenUrl][8] 3. 3.[↵][10] 1. W. O'Hirok, 2. C. Gautier , J. Geophys. Res. 108, 10 (2003) 1029/2002JD002818. [OpenUrl][8] 4. 4.[↵][11] 1. T. Ackerman 2. et al. , J. Geophys. Res. 108, 10 (2003) 1029/2002JD002674. [OpenUrl][8] # Response {#article-title-2} The purpose of our letter was to refute a misimpression left by a news article by Richard A. Kerr: that atmospheric radiation models have become a lot more absorbing as a result of the claim of enhanced cloud absorption in 1995. In fact, the best models are not much more absorbing now than in 1995, and their extra absorption is due to gases and aerosols and a better treatment of surface albedo, not clouds. What is true about models is that many climate-model radiation packages were too transparent ([1][12]); this was brought to the community's attention by a few studies comparing modeled and observed solar energy disposition ([2][13]–[4][14]) that were published in 1995, independently of the enhanced cloud absorption controversy. Our discussion of Valero's work was a side issue not directly related to this main point about whether models have really changed radically or not and the main factors driving the changes. The conclusion of his study seems to be rather mixed. If we misinterpreted his results, we apologize. We are not denying that there may still be a bias between models and measurements, nor are we denying the reality of disagreements that existed in 1990 as summarized by ([5][15]). We are merely saying that the general increases in atmospheric absorption in Global Climate Models since 1995 have been attributed much more to the treatment of clear-sky solar radiative transfer processes than to the cloud absorption. In spite of the substantial progress in observational technology since 1995, spurred by the controversy, we are still not at the point where the bias can be unambiguously separated from possible measurement error. More field campaigns with even better technology are necessary to nail down the remaining much smaller bias. 1. 1.[↵][16] 1. Z. Li 2. et al. , Bull. Am. Meteorol. Soc. 78, 53 (1997). [OpenUrl][17] 2. 2.[↵][18] 1. M. Wild 2. et al. , J. Clim. 8, 1309 (1995). [OpenUrl][19] 3. 3. 1. H. W. Barker, 2. Z. Li , J. Clim. 8, 2213 (1995). [OpenUrl][20] 4. 4.[↵][21] 1. D. M. Ward , J. Clim. 8, 2824 (1995). [OpenUrl][22] 5. 5.[↵][2
Viollier, M.; Kandel, R.; Raberanto, P.Viollier, M., R. Kandel, P. Raberanto, 2004: Combination of ScaRaB-2 and CERES with Meteosat-5 to remove time sampling bias and improve radiation budget estimations in the INDOEX region. Journal of Geophysical Research: Atmospheres, 109(D5). doi: https://doi.org/10.1029/2003JD003947. Using data available over the INDOEX area, Meteosat-5 visible and infrared data have been combined with ScaRaB/Resurs and CERES/TRMM broadband data for March 1999, and with CERES/TRMM and CERES/Terra data for March 2000. The study proceeds by collocation of the data sets, comparison of narrowband Meteosat radiances to broadband ScaRaB radiances, and conversion of radiances to fluxes. In the longwave (LW) domain, a multiple regression is found between ScaRaB and CERES fluxes, the two Meteosat infrared channels (infrared window and water vapor) and the viewing zenith angle. In the shortwave (SW) domain, narrowband-to-broadband (NB-BB) and ERBE-like radiance-to-flux conversions are applied. The RMS differences between the ScaRaB/CERES and Meteosat instantaneous flux retrievals are about 10 Wm−2 and 40 Wm−2 respectively in the LW and SW domains. A large part of these differences comes from the residual coregistration and narrow-band-to-broadband conversion errors. On the contrary, the mean difference or bias between all data sets is very small, consistent at the 1% (LW) and 4% (SW) level. The LW and SW conversion equations have been used to convert Meteosat observations at each half hour into instantaneous broadband flux estimates consistent with the instantaneous CERES flux estimates for the same day. New monthly means are computed in this way: the changes are small in the LW but significant in the SW domain (regional means: ∼20 Wm−2, 20°S–20°N means: ∼4 Wm−2), especially for studies of long-term changes. climate; Meteosat; Earth radiation budget
Yongxiang Hu; Wielicki, B. A.; Ping Yang; Stackhouse, P. W.; Lin, B.; Young, D. F.Yongxiang Hu, ., B. A. Wielicki, . Ping Yang, P. W. Stackhouse, B. Lin, D. F. Young, 2004: Application of deep convective cloud albedo observation to satellite-based study of the terrestrial atmosphere: monitoring the stability of spaceborne measurements and assessing absorption anomaly. IEEE Transactions on Geoscience and Remote Sensing, 42(11), 2594-2599. doi: 10.1109/TGRS.2004.834765. An objective method is developed to monitor the stability of spaceborne instruments, aimed at distinguishing climate trend from instrument drift in satellite-based climate observation records. This method is based on four-years of Clouds and the Earth's Radiant Energy System (CERES) broadband observations of deep convective cloud systems with cloud-top temperature lower than 205 K and with large optical depths. The implementation of this method to the CERES instrument stability analysis reveals that the monthly albedo distributions are practically the same for deep convective clouds with CERES measurements acquired from both the Tropical Rainfall Measuring Mission and Terra satellite platforms, indicating that CERES instruments are well calibrated and stable during both missions. Furthermore, with a nonlinear regression neural network narrowband-broadband conversion, this instrument-stability monitoring method can also be applied to narrowband instruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Visible Infrared Scanner (VIRS). The results show that the drifts associated with both VIRS and MODIS instruments are less than 1% during a four-year period. Since the CERES albedo measurements are highly accurate, the absorptance of these opaque clouds can be reliably estimated. The absorptions of these clouds from observations are around 25%, whereas the absorptions from theory can be as low as 18%, depending on ice cloud microphysics. calibration; clouds; Earth; atmospheric techniques; Clouds and the Earth's Radiant Energy System; Instruments; Terrestrial atmosphere; atmospheric measuring apparatus; Tropical Rainfall Measuring Mission; Monitoring; albedo; Atmospheric measurements; radiative transfer; Absorption; artificial satellites; data acquisition; deep convective cloud; instrumentation; Moderate Resolution Imaging Spectroradiometer; MODIS; Stability; VIRS; climatology; remote sensing; Clouds; 4 yr; absorptance estimation; Absorption anomaly; absorption anomaly assessment; albedo distributions; CERES broadband observations; climate trend; cloud optical depths; cloud-top temperature; deep convective cloud albedo observation; deep convective cloud systems; ice cloud microphysics; instrument drift; instrument stability; narrowband instruments; nonlinear regression neural network narrowband-broadband conversion; objective method; opaque cloud absorptions; satellite-based climate observation; satellite-based study; s
Zhang, Yuanchong; Rossow, William B.; Lacis, Andrew A.; Oinas, Valdar; Mishchenko, Michael I.Zhang, Y., W. B. Rossow, A. A. Lacis, V. Oinas, M. I. Mishchenko, 2004: Calculation of radiative fluxes from the surface to top of atmosphere based on ISCCP and other global data sets: Refinements of the radiative transfer model and the input data. Journal of Geophysical Research: Atmospheres, 109(D19). doi: https://doi.org/10.1029/2003JD004457. We continue reconstructing Earth's radiation budget from global observations in as much detail as possible to allow diagnosis of the effects of cloud (and surface and other atmospheric constituents) variations on it. This new study was undertaken to reduce the most noticeable systematic errors in our previous results (flux data set calculated mainly using International Satellite Cloud Climatology Project–C1 input data (ISCCP-FC)) by exploiting the availability of a more advanced NASA Goddard Institute for Space Studies (GISS) radiative transfer model and improved ISCCP cloud climatology and ancillary data sets. The most important changes are the introduction of a better treatment of ice clouds, revision of the aerosol climatology, accounting for diurnal variations of surface skin/air temperatures and the cloud-radiative effects on them, revision of the water vapor profiles used, and refinement of the land surface albedos and emissivities. We also extend our previous flux results, limited to the top of atmosphere (TOA) and surface (SRF), to also include three levels within the atmosphere, forming one integrated vertical atmospheric flux profile from SRF to TOA, inclusive, by combining a new climatology of cloud vertical structure with the ISCCP cloud product. Using the new radiative transfer model and new input data sets, we have produced an 18-year at 3-hour time steps, global at 280-km intervals, radiative flux profile data set (called ISCCP-FD) that provides full- and clear-sky, shortwave and longwave, upwelling and downwelling fluxes at five levels (SRF, 680 mbar, 440 mbar, 100 mbar, and TOA). Evaluation is still only possible for TOA and SRF fluxes: Comparisons of monthly, regional mean values from FD with Earth Radiation Budget Experiment, Clouds and the Earth's Radiant Energy System and Baseline Surface Radiation Network values suggest that we have been able to reduce the overall uncertainties from 10–15 to 5–10 W/m2 at TOA and from 20–25 to 10–15 W/m2 at SRF. Annual mean pressure-latitude cross sections of the cloud effects on atmospheric net radiative fluxes show that clouds shift the longwave cooling downward in the Intertropical Convergence Zone, acting to stabilize the tropical atmosphere while increasing the horizontal heating gradient forcing the Hadley circulation, and shift the longwave cooling upward in the midlatitude storm zones, acting to destabilize the baroclinic zones while decreasing the horizontal heating gradient there. ERBE; CERES; BSRN; cloud vertical structure; surface radiation budget (SRB); Earth radiation budget
Allan, Richard P.; Ringer, M. A.; Slingo, A.Allan, R. P., M. A. Ringer, A. Slingo, 2003: Evaluation of moisture in the Hadley Centre climate model using simulations of HIRS water-vapour channel radiances. Quarterly Journal of the Royal Meteorological Society, 129(595), 3371-3389. doi: 10.1256/qj.02.217. It is important to establish that climate models can accurately simulate the observed present-day fluctuations of water vapour. In particular, water-vapour and cloud-radiative feedbacks are intrinsically linked to processes governing relative-humidity distribution and variability. To explore these issues, clear-sky radiances, sensitive to upper-tropospheric relative humidity, are simulated within the Hadley Centre atmospheric climate model, version HadAM3, allowing direct comparison with High Resolution Infrared Sounder (HIRS) observations. The model is forced by observed sea surface temperatures and sea-ice fields over the period 1979–98. Evaluation of the simulated distribution and variability of water vapour is undertaken utilizing the HIRS 6.7 μm brightness temperature (T6.7) and satellite measurements of column-integrated water vapour and clear-sky outgoing long-wave radiation (OLR). Modifications are made to the clear-sky OLR and T6.7 HadAM3 diagnostics to reduce sampling inconsistencies with the observed products. Simulated T6.7 over subtropical dry zones are higher than T6.7 from observations, particularly in the southern hemisphere, and is symptomatic of an overactive circulation. The observed spatial signature of the T6.7 interannual variability is dominated by El Niño and is captured well by HadAM3. Interannual variability of the tropical ocean mean T6.7 is consistent between HadAM3 and the HIRS observations, suggesting that the small simulated decadal changes in relative humidity are realistic. © Crown copyright, 2003. Royal Meteorological Society Clear-sky sampling Long-wave radiation Relative humidity
Allan, Richard P.; Ringer, Mark A.Allan, R. P., M. A. Ringer, 2003: Inconsistencies between satellite estimates of longwave cloud forcing and dynamical fields from reanalyses. Geophysical Research Letters, 30(9), 1491. doi: 10.1029/2003GL017019. The greenhouse effect of cloud may be quantified as the difference between outgoing longwave radiation (OLR) and its clear-sky component (OLRc). Clear-sky measurements from satellite preferentially sample drier, more stable conditions relative to the monthly-mean state. The resulting observational bias is evident when OLRc is stratified by vertical motion; differences to climate model OLRc of 15 Wm−2 occur over warm regions of strong ascent. Using data from the ECMWF 40-year reanalysis, an estimate of cloud longwave radiative effect is made which is directly comparable with standard climate model diagnostics. The impact of this methodology on the cancellation of cloud longwave and shortwave radiative forcing in the tropics is estimated. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1640 Remote sensing; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 1620 Climate dynamics; 1694 Instruments and techniques
Ba, Mamoudou B.; Ellingson, Robert G.; Gruber, A.Ba, M. B., R. G. Ellingson, A. Gruber, 2003: Validation of a Technique for Estimating OLR with the GOES Sounder. J. Atmos. Oceanic Technol., 20(1), 79-89. doi: 10.1175/1520-0426(2003)020<0079:VOATFE>2.0.CO;2. Abstract In order to eventually use the capability of the Geostationary Operational Environmental Satellite (GOES) Sounder to capture the diurnal signal of outgoing longwave radiation (OLR), it is necessary to establish its instantaneous accuracy. Error characteristics of OLR derived from the GOES Sounder are analyzed using Clouds and Earth's Radiant Energy System (CERES) observations. The comparisons are based on over 28 000 data collected in July 1998 and April 2000 over the continental United States. The July data correspond to observations from GOES-8 and -9 and the CERES instrument on board the Tropical Rainfall Measurement Mission (TRMM) satellite. The April data correspond to GOES-8 and -10, and two CERES instruments on board the Terra satellite. The comparisons are for instantaneous, homogeneous scenes of 1° × 1° boxes. Comparisons of GOES Sounder with collocated TRMM and Terra CERES OLR show instantaneous rms agreement to within about 7 W m−2 for day and/or night homogeneous scenes. The GOES technique explained over 91% and 96% of the variance of CERES observations for both night and day, and for both land and ocean scenes for July 1998 and April 2000, respectively.
Bertrand, C.; Clerbaux, N.; Ipe, A.; Gonzalez, L.Bertrand, C., N. Clerbaux, A. Ipe, L. Gonzalez, 2003: Estimation of the 2002 Mount Etna eruption cloud radiative forcing from Meteosat-7 data. Remote Sensing of Environment, 87(2–3), 257-272. doi: 10.1016/S0034-4257(03)00183-4. On 27th October 2002, after 15 months of small activity, the Mount Etna located on the island of Sicily, Italy (37.73°N, 15.00°E) erupted undergoing one of its most vigorous eruptions in years. During a few days, Europe's highest and most active volcano hurled lava and spewed significant amounts of ash and trace gases into the atmosphere. The smoke and ash plume originating from the volcano stretched from the Sicily to the north African coast. The plume from the volcano has been identified and tracked using half-hourly Meteosat-7 visible, infrared, and water vapor imagery in order to estimate the radiative forcing produced by the introduction of the volcanic cloud in a previously clear sky. Our results indicate that, while the volcanic cloud has introduced a well-discernable radiative perturbation, the magnitude of the shortwave volcanic forcing appears in the range of the one introduced by large clouds above the Mediterranean Sea. By contrast, the perturbation generated in the longwave spectrum at the top of the atmosphere is larger than the one introduced by large meteorological clouds. atmosphere; Remote sensing; Eruptions; satellite measurements; Volcanoes
Bodas-Salcedo, A.; Gimeno-Ferrer, J. F.; López-Baeza, E.Bodas-Salcedo, A., J. F. Gimeno-Ferrer, E. López-Baeza, 2003: Flux retrieval optimization with a nonscanner along-track broadband radiometer. Journal of Geophysical Research: Atmospheres, 108(D2), 4061. doi: 10.1029/2002JD002162. The theoretical behavior of broadband flux retrieval is analyzed with the aid of a radiance field database. Several angular inversion models are developed for different viewing configurations, with special emphasis in a nonscanner along-track design concept. Results show that the performance of these angular models depends on the viewing zenith angle (VZA). When cloud cover is predominant within the observed scene, VZAs around 55° (shortwave) and 50° (longwave) minimize the error when deriving fluxes. These results might help in the design of future missions where the main idea is to obtain accurate instantaneous measurements of top of atmosphere reflected and emitted fluxes. Such measurements can be used as a constraint to derive atmospheric profiles from active instruments (lidar and cloud profiling radar), onboard the same platform. For this purpose, along-track configurations are very good candidates because the flux retrieval can be optimized by using different views of the same pixel almost simultaneously from the same platform. earth radiation budget; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1610 Atmosphere; 1640 Remote sensing; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; angular distribution model; flux retrieval
Cess, Robert D.; Udelhofen, Petra M.Cess, R. D., P. M. Udelhofen, 2003: Climate change during 1985–1999: Cloud interactions determined from satellite measurements. Geophysical Research Letters, 30(1), 1019. doi: 10.1029/2002GL016128. We have extended two recent studies that present evidence for significant decadal variability in the top-of-atmosphere (TOA) tropical radiative energy budget by combining satellite measurements of the TOA energy budget and cloud cover with measurements of the Earth's surface temperature. The domain studied is from 40°S to 40°N. As in the prior studies, which were restricted to lower latitudes, there is a significant increase in the TOA outgoing longwave radiation during the period 1985 to 1999 together with an increase in solar (shortwave) radiation absorbed by the climate system. It is suggested that these changes are related to an observed reduction in cloud cover. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1610 Atmosphere; 3309 Meteorology and Atmospheric Dynamics: Climatology
Chambers, Lin H.; Young, David F.; Costulis, P. Kay; Detweiler, Pauline T.; Fischer, Joyce D.; Sepulveda, Roberto; Stoddard, Douglas B.; Falcone, AmandaChambers, L. H., D. F. Young, P. K. Costulis, P. T. Detweiler, J. D. Fischer, R. Sepulveda, D. B. Stoddard, A. Falcone, 2003: The CERES S'COOL Project. Bull. Amer. Meteor. Soc., 84(6), 759-765. doi: 10.1175/BAMS-84-6-759. Abstract In recent years, an education plan has been a required part of most proposals for new scientific research funding from NASA. Likewise, the National Science Foundation considers “integration of research and education” as one of its principal strategies. As a result, many scientists are seeking effective ways to incorporate education into their work. This article shares important lessons learned by one group of scientists embarking on outreach efforts. Experience with the Students' Cloud Observations On-line (S'COOL) Project, the educational outreach portion of the Clouds and the Earth's Radiant Energy System (CERES) investigation, yields lessons that may help other scientists to develop useful outreach efforts. CERES scientists developed S'COOL over a 15-month period, with direct involvement and feedback from teachers. S'COOL has continued to evolve, thanks to ongoing feedback from participants. As a result, the project has been quite successful, currently involving over 1400 registered participants in 61 countries around the world. Student reports of cloud conditions help scientists verify their cloud property retrieval algorithms and allow students to obtain and analyze real scientific data. A number of educational materials, including an extensive multilingual Web site, have been developed to help teachers and students understand the research questions and the challenges of working with global remote-sensing datasets.
Chambers, Lin, LChambers, L., 2003: NASA: Practical Uses of Math And Science (PUMAS). NASA's Practical Uses of Math And Science (PUMAS). A collection of one-page examples of how math and science topics taught in K-12 classes can be used in interesting settings, including every day life., Logarithms are very handy when dealing with numbers at lots of different scales (see related PUMAS example: Just What is a Logarithm, Anyway?). But they also have another useful feature: they help us average measurements of physical phenomena that have nonlinear behavior. A common example in my field of study relates cloud “albedo” to cloud optical depth (Fig. 1); but similar examples may be found when examining many natural phenomena.
Christopher, Sundar A.; Wang, Jun; Ji, Qiang; Tsay, Si-CheeChristopher, S. A., J. Wang, Q. Ji, S. Tsay, 2003: Estimation of diurnal shortwave dust aerosol radiative forcing during PRIDE. Journal of Geophysical Research: Atmospheres, 108(D19), 8596. doi: 10.1029/2002JD002787. Using measured and derived aerosol properties from the Puerto Rico Dust Experiment (PRIDE), a four-stream broadband radiative transfer model is used to calculate the downward shortwave irradiance (DSWI) at the surface and the shortwave irradiance at the top of atmosphere (TOA). The results of the calculated DSWI are compared against pyranometer measurements from the Surface Measurements For Atmospheric Radiative Transfer (SMART) instrument suite at Roosevelt Road (18.20°N, 65.60°W). Using aerosol optical thickness retrievals from half-hourly geostationary satellite data (GOES 8 imager), the diurnal short wave aerosol forcing (SWARF) of dust aerosols both at the surface and TOA are calculated for the entire study area (14°N ∼ 26°N, 61°W ∼ 73°W). For selected days, the Clouds and the Earth Radiant Energy System (CERES) TOA shortwave irradiance values from Terra are compared with radiative transfer calculations. Wang et al. [2003] show that the satellite derived aerosol optical thickness is in excellent agreement with Aerosol Robotic Network (AERONET) values. Results of this study show that the calculated direct, diffuse and total DSWI are in excellent agreement with the corresponding SMART values with biases of 1.8%, −3.3% and 0.5% respectively, indicating that dust aerosols are well characterized in the radiative transfer model. This is well within the measured uncertainties (1.3%) and the model uncertainties (5%). The monthly mean value and standard deviation of aerosol optical thickness at 670 nm (AOT670) during PRIDE are 0.26 ± 0.13, and the corresponding monthly mean daytime SWARF values are −12.34 ± 9.62 W m−2 at TOA and −18.13 ± 15.81 W m−2 at the surface, respectively. Our results also show that if diurnal changes in aerosol optical thickness are not considered, it leads to uncertainties in SWARF of 4 W m−2 at the surface and 2 W m−2 at the TOA. The CERES TOA short wave irradiance underestimates calculated values by about 10 W m−2 mainly due problems in misclassification of aerosols and lack of aerosol angular dependence models (ADMs) in the current CERES algorithms. This study is among the first to demonstrate the potential of the GOES 8 imagers in retrieving aerosol optical thickness and estimating the daytime diurnal SWARF of dust, both at the TOA and surface, in low to moderate dust loading regions over the oceans. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0305 Aerosols and particles; diurnal forcing; Dust aerosols; dust optical properties; flux calculation and comparison; forcing uncertainties
Clerbaux, N.; Dewitte, S.; Gonzalez, L.; Bertrand, C.; Nicula, B.; Ipe, A.Clerbaux, N., S. Dewitte, L. Gonzalez, C. Bertrand, B. Nicula, A. Ipe, 2003: Outgoing longwave flux estimation: improvement of angular modelling using spectral information. Remote Sensing of Environment, 85(3), 389-395. doi: 10.1016/s0034-4257(03)00015-4. A radiance-to-flux conversion is needed to estimate radiative fluxes at the top of the atmosphere from directional measurements made by broadband (BB) radiometers on satellites. Such a conversion is known to be one of the major sources of error in the resulting instantaneous shortwave and longwave fluxes. This paper analyzes the possibility to improve the radiance-to-flux conversion for the longwave radiation when spectral information about the radiation is available through a set of narrow-band (NB) measurements. The study is based on a database of spectral radiance fields at the top of the atmosphere built using radiative transfer computation. The analysis of this database shows that there exists a certain degree of correlation between the angular and the spectral behaviors of the radiation field. According to the type and the accuracy of the spectral information, this correlation allows a 25-55% reduction of the error introduced by the radiance-to-flux conversion with respect to a simple model that uses only broadband information. The method discussed in this paper might be used when broadband radiometer and spectral imager data are available together like the combination of Geostationary Earth Radiation Budget (GERB) and Spinning Enhanced Visible and Infrared Radiometer Imager (SEVIRI) or the combination of CERES and MODIS. (C) 2003 Elsevier Science Inc. All rights reserved.
Cooper, Steven J.; L'Ecuyer, Tristan S.; Stephens, Graeme L.Cooper, S. J., T. S. L'Ecuyer, G. L. Stephens, 2003: The impact of explicit cloud boundary information on ice cloud microphysical property retrievals from infrared radiances. Journal of Geophysical Research: Atmospheres, 108(D3), 4107. doi: 10.1029/2002JD002611. Cirrus clouds have a profound impact on the radiation balance of the Earth–atmosphere system. Accurate representation of their radiative properties is critical to understanding climate and predicting climate change. This paper casts the split-window cirrus cloud retrieval technique in an optimal estimation framework facilitating direct inclusion of explicit cloud boundary information from complementary sensors as well as providing a suite of diagnostic tools for evaluating the dominant sources of uncertainty in all retrieved quantities. Errors in retrieved microphysical properties are used to determine the resulting errors in the calculation of global-scale radiative budgets. Uncertainties in optical depth and effective radius are found to diminish from ∼45% and ∼80%, respectively, in the absence of explicit cloud boundary information to ∼15% and ∼60% when accurate radar-based or lidar-based estimates are included. It is demonstrated that the improvements to cirrus cloud optical properties afforded by accurate cloud boundary information may lead to as much as a factor of 3 increase in the accuracy to which their impact on the Earth's radiative balance can be modeled. Colocated infrared radiances from the Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument aboard the Earth Observing System (EOS) Aqua satellite and cloud radar observations from the CloudSat satellite will soon allow the retrieval presented here to be integrated into an operational retrieval of the vertical distribution of cloud properties on a global scale. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0320 Cloud physics and chemistry; 3394 Meteorology and Atmospheric Dynamics: Instruments and techniques; Radiative fluxes; cirrus clouds; 3374 Meteorology and Atmospheric Dynamics: Tropical meteorology; CloudSat; split-window
Dong, Xiquan; Mace, Gerald G.Dong, X., G. G. Mace, 2003: Profiles of Low-Level Stratus Cloud Microphysics Deduced from Ground-Based Measurements. J. Atmos. Oceanic Technol., 20(1), 42-53. doi: 10.1175/1520-0426(2003)020<0042:POLLSC>2.0.CO;2. Abstract The microwave radiometer–derived cloud liquid water path (LWP) and a profile of radar reflectivity are used to derive a profile of cloud liquid water content (LWC). Two methods (M1 and M2) have been developed for inferring the profile of cloud-droplet effective radius (re) in liquid phase or liquid dominant mixed phase stratocumulus clouds. The M1-inferred re profile is proportional to a previously derived layer-mean re and to the ratio of the radar reflectivity to the integrated radar reflectivity. This algorithm is independent of the radar calibration and is applicable to overcast low-level stratus clouds that occur during the day because it is dependent on solar transmission observations. In order to extend the retrieval algorithm to a wider range of conditions, a second method is described that uses an empirical relationship between effective radius and radar reflectivity based on theory and the results of M1. Sensitivity studies show that the surface-retrieved re is more sensitive to the variation of radar reflectivity when the radar reflectivity is large, and the uncertainties of retrieved re related to the assumed vertically constant cloud-droplet number concentration and shape of the size distribution are about 9% and 2%, respectively. For validation, a total of 10 h of aircraft data and 36 h of surface data were collected over the Atmospheric Radiation Measurement (ARM) program's Southern Great Plains (SGP) site during the March 2000 cloud intensive observational period (IOP). More detailed comparisons in two cases quantify the agreement between the aircraft data and the surface retrievals. When the temporal averages of the two datasets increase from 1 min to 30 min, the means and standard deviations of differences between the two datasets decrease from −2.5% ± 84% to 1.3% ± 42.6% and their corresponding correlation coefficients increase from 0.47 to 0.8 for LWC; and decrease from −4.8% ± 36.4% to −3.3% ± 22.5% with increased coefficients from 0.64 to 0.94 for re (both M1 and M2). The agreement between the aircraft and surface data in the 30-min averages suggests that the two platforms are capable of characterizing the cloud microphysics over this temporal scale. On average, the surface retrievals are unbiased relative to the aircraft in situ measurements. However, when only the 1-min averaged aircraft data within 3 km of the surface site were selected, the means and standard deviations of differences between the two datasets are larger (23.4% ± 113% for LWC and 28.3% ± 60.7% for re) and their correlation coefficients are smaller (0.32 for LWC and 0.3 for re) than those from all 1-min samples. This result suggests that restricting the comparison to the samples better matched in space and time between the surface and aircraft data does not result in a better comparison.
Dong, Xiquan; Mace, Gerald G.Dong, X., G. G. Mace, 2003: Arctic Stratus Cloud Properties and Radiative Forcing Derived from Ground-Based Data Collected at Barrow, Alaska. J. Climate, 16(3), 445-461. doi: 10.1175/1520-0442(2003)016<0445:ASCPAR>2.0.CO;2. Abstract A record of single-layer and overcast low-level Arctic stratus cloud properties has been generated using data collected from May to September 2000 at the Atmospheric Radiation Measurement (ARM) North Slope of Alaska (NSA) (71.3°N, 156.6°W) site near Barrow, Alaska. The record includes liquid-phase and liquid dominant mixed-phase Arctic stratus macrophysical, microphysical, and radiative properties, as well as surface radiation budget and cloud radiative forcing. The macrophysical properties consist of cloud fractions, cloud-base/top heights and temperatures, and cloud thickness derived from a ground-based radar and lidar pair, and rawinsonde sounding. The microphysical properties include cloud liquid water path and content, and cloud-droplet effective radius and number concentration obtained from microwave radiometer brightness temperature measurements, and the new cloud parameterization. The radiative properties contain cloud optical depth, effective solar transmission, and surface/cloud/top-of-atmosphere albedos derived from the new cloud parameterization and standard Epply precision spectral pyranometers. The shortwave, longwave, and net cloud radiative forcings at the surface are inferred from measurements by standard Epply precision spectral pyranometers and pyrgeometers. There are approximately 300 h and more than 3600 samples (5-min resolution) of single-layer and overcast low-level stratus during the study period. The 10-day averaged total and low-level cloud (Ztop < 3 km) fractions are 0.87 and 0.55, and low-level cloud-base and -top heights are around 0.4 and 0.8 km. The cloud-droplet effective radii and number concentrations in the spring are similar to midlatitude continental stratus cloud microphysical properties, and in the summer they are similar to midlatitude marine stratus clouds. The total cloud fractions in this study show good agreement with the satellite and surface results compiled from data collected during the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE) Arctic Cloud Experiment (ACE) and the Surface Heat Budget of the Arctic Ocean (SHEBA) (∼77°N, 165°W) field experiments in 1998. The cloud microphysics derived from this study are similar, in general, to those collected in past field programs, although these comparisons are based on data collected at different locations and years. At the ARM NSA site, the summer cooling period is much longer (2–3 months vs 1–2 weeks), and the summer cooling magnitude is much larger (−100 W m−2 vs −5 W m−2) than at the SHEBA ship under the conditions of all skies at the SHEBA and overcast low-level stratus clouds at the NSA site.
Donner, L.Donner, L., 2003: Multiple scales in cumulus convection and their implications for cumulus parameterizations in large-scale models. EGS - AGU - EUG Joint Assembly, -1, 2917.
Donner, Leo J.; Phillips, Vaughan T.Donner, L. J., V. T. Phillips, 2003: Boundary layer control on convective available potential energy: Implications for cumulus parameterization. Journal of Geophysical Research: Atmospheres, 108(D22), 4701. doi: 10.1029/2003JD003773. Convective available potential energy (CAPE), frequently regarded as an indicator of the potential intensity of deep convection, is strongly controlled by the properties of the planetary boundary layer (BL). Variations in CAPE observed during field experiments in midcontinent North America, the tropical east Atlantic, and the tropical west Pacific, can be accounted for mostly by changes in the temperature and humidity in the BL. The coupling between CAPE and the BL holds for both convective and nonconvective conditions. The coupling under conditions of deep convection implies a constraint on the intensity of deep convection which can be used as a closure for cumulus parameterization. This constraint requires equilibrium in the environment of the parcel used as a basis for calculating CAPE. Over many cases, parcel-environment equilibrium is observed to hold more robustly than equilibrium of CAPE itself. When observational uncertainties are considered, it is uncertain whether quasi-equilibrium, in which the rate of change of CAPE is substantially less than the rate at which mean advection and BL fluxes change CAPE, holds at subdiurnal timescales in the eastern Atlantic and the western Pacific. Quasi-equilibrium is a poor approximation at subdiurnal timescales in midcontinent North America. At timescales approaching diurnal, quasi-equilibrium holds in all cases. Cumulus parameterizations based on quasi-equilibrium may be limited in their ability to model diurnal cycles as a result. CAPE fluctuations related to large, subdiurnal variations in surface fluxes are much sharper than CAPE fluctuations related to changes in mean advection above the BL, especially over land. The strong BL control on CAPE indicates that deep convection does not equilibrate rapid, high-amplitude variations in CAPE originating there. 3337 Meteorology and Atmospheric Dynamics: Numerical modeling and data assimilation; 3319 Meteorology and Atmospheric Dynamics: General circulation; 3307 Meteorology and Atmospheric Dynamics: Boundary layer processes; 3314 Meteorology and Atmospheric Dynamics: Convective processes; convective available potential energy; cumulus parameterization; planetary boundary layer
Ellingson, Robert G.; Ba, Mamoudou B.Ellingson, R. G., M. B. Ba, 2003: A Study of Diurnal Variation of OLR from the GOES Sounder. J. Atmos. Oceanic Technol., 20(1), 90-98. doi: 10.1175/1520-0426(2003)020<0090:ASODVO>2.0.CO;2. Abstract A multispectral outgoing longwave radiation (OLR) estimation technique is applied to GOES Sounder data to study the diurnal cycle of OLR. OLR data collected from several regional areas over the continental United States and adjacent oceans during July 1998 are analyzed to determine diurnal variations for clear-sky and all-sky conditions. It is found that the desert regions exhibit a diurnal range that can reach up to about 70 W m−2 while the vegetated areas and ocean regions exhibit much lower diurnal range. The results for this one month show that the form of the monthly diurnal variation of the different regions can be approximated with a sine-like function, with the desert sites exhibiting a more nearly perfect sine curve. It is also found that the rms errors associated with sparse data such as those of polar orbiting satellites depend on sampling time and interval. The high temporal and spatial characteristics of OLR data from geostationary satellites offer a unique opportunity to obtain increased understanding of the diurnal cycles of atmospheric processes.
Haywood, Jim; Francis, Pete; Osborne, Simon; Glew, Martin; Loeb, Norman; Highwood, Eleanor; Tanré, Didier; Myhre, Gunnar; Formenti, Paola; Hirst, EdwinHaywood, J., P. Francis, S. Osborne, M. Glew, N. Loeb, E. Highwood, D. Tanré, G. Myhre, P. Formenti, E. Hirst, 2003: Radiative properties and direct radiative effect of Saharan dust measured by the C-130 aircraft during SHADE: 1. Solar spectrum. Journal of Geophysical Research: Atmospheres, 108(D18), 8577. doi: 10.1029/2002JD002687. The physical and optical properties of Saharan dust aerosol measured by the Met Office C-130 during the Saharan Dust Experiment (SHADE) are presented. Additional radiation measurements enable the determination of the aerosol optical depth, τaerλ, and the direct radiative effect (DRE) of the mineral dust. The results suggest that the absorption by Saharan dust is significantly overestimated in the solar spectrum if standard refractive indices are used. Our measurements suggest an imaginary part of the refractive index of 0.0015i is appropriate at a wavelength λ of 0.55 μm. Different methods for determining τaerλ=0.55 are presented, and the accuracy of each retrieval method is assessed. The value τaerλ=0.55 is estimated as 1.48 ± 0.05 during the period of heaviest dust loading, which is derived from an instantaneous DRE of approximately −129 ± 5 Wm−2 or an enhancement of the local planetary albedo over ocean of a factor of 2.7 ± 0.1. A comparison of the DRE derived from the C-130 instrumentation and from the Clouds and the Earth's Radiant Energy System (CERES) instrument on the Tropical Rainfall Measuring Mission (TRMM) satellite is presented; the results generally showing agreement to within a factor of 1.2. The results suggest that Saharan dust aerosol exerts the largest local and global DRE of all aerosol species and should be considered explicitly in global radiation budget studies. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 0360 Radiation: transmission and scattering; 1640 Remote sensing; 0305 Aerosols and particles; aerosols; radiative forcing; radiation balance; aircraft measurements; mineral dust; Saharan dust
Ho, Shu-peng; Lin, Bing; Minnis, Patrick; Fan, Tai-FangHo, S., B. Lin, P. Minnis, T. Fan, 2003: Estimates of cloud vertical structure and water amount over tropical oceans using VIRS and TMI data. Journal of Geophysical Research: Atmospheres, 108(D14), 4419. doi: 10.1029/2002JD003298. A microwave, visible and infrared (MVI) method was applied to coincident, collocated Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and VIRS (Visible and Infrared Scanner) data collected from January to August 1998 to estimate the cloud vertical structure and water path over tropical oceans. The derived quantities include the liquid water path (LWP), ice water path (IWP), total water path (WP), the frequencies of single-layer and overlapping nonprecipitating clouds, and the cloud top-height, base-height and thickness for single-layered water clouds. LWP data retrieved from TMI measurements were compared with global and regional LWP retrieved from VIRS for warm nonprecipitating clouds for different seasons. The global mean difference between TMI LWP and VIRS LWP is less than 0.01 mm and varies with season. For cold clouds, the TMI LWP is only 25–30% of the VIRS WP. In these cases, the ice clouds observed by VIRS overlap liquid water clouds. This result is similar to that from an earlier study, however, the well-matched TMI and VIRS data provide more accurate instantaneous estimates than were previously possible. The assumption, that the cloud is entirely ice, used to compute IWP introduces some errors in the WP because of cloud overlapping. However, the difference between IWP estimated for all TMI FOVs containing only ice-phase VIRS pixels and the IWP estimated from the difference between the VIRS WP and TMI LWP is less than 10%. This result suggests that IWP is independent of the lower-level clouds for nonprecipitating systems. For warm single-layered clouds, the estimated low-cloud-base altitudes (∼800m) and thicknesses (between 800 m to 1000 m) are, on average, very close to low-cloud results derived from combined surface and upper-air observations. The frequency of overlapped nonprecipitating clouds over ocean was about 4%, 16% and 38% for low, middle, and high clouds, respectively. The results clearly demonstrate the potential for enhanced monitoring of maritime clouds using infrared, solar, and microwave imagers on the same platform. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; cloud; 3399 Meteorology and Atmospheric Dynamics: General or miscellaneous; 1655 Water cycles; VIRS; LWP; overlapped cloud; TMI
Hsu, N. Christina; Herman, Jay R.; Tsay, Si-CheeHsu, N. C., J. R. Herman, S. Tsay, 2003: Radiative impacts from biomass burning in the presence of clouds during boreal spring in southeast Asia. Geophysical Research Letters, 30(5), 1224. doi: 10.1029/2002GL016485. The impact of smoke aerosols generated from biomass burning activities in Southeast Asia on the total (i.e., direct and indirect effects) reflected solar and emitted thermal radiation from clouds was investigated using satellite data. We combine narrowband radiance measurements, from ultraviolet to near-infrared wavelengths (e.g., SeaWiFS and TOMS), with broadband irradiance measurements (e.g., CERES) to quantify how smoke aerosols modulate the cloud radiative forcing. In Southeast Asia, our results reveal that smoke is frequently present over large areas of cloud-covered regions during boreal spring. The reflected solar (emitted thermal) radiation from clouds due to smoke aerosols can be reduced (enhanced) by as much as 100 (20) W m−2 over the month of March 2000. We also found that the reduction in cloud spectral reflectance at 670 nm is large enough to lead to significant errors in retrieving cloud properties (e.g., optical thickness and effective radius) from current satellite measurements, such as AVHRR and MODIS. clouds; 0360 Radiation: transmission and scattering; 1610 Atmosphere; 0320 Cloud physics and chemistry; 0305 Aerosols and particles; 0345 Pollution: urban and regional; aerosols; radiative forcing; Biomass burning; monsoon; Southeast Asia
Ignatov, AlexanderIgnatov, A., 2003: Spurious Signals in TRMM/VIRS Reflectance Channels and Their Effect on Aerosol Retrievals. J. Atmos. Oceanic Technol., 20(8), 1120-1137. doi: 10.1175/1520-0426(2003)020<1120:SSIVRC>2.0.CO;2. Abstract Aerosol optical depths, τ1 and τ2, and the Ångström exponent α = –ln(τ1/τ2)/ln(λ1/λ2), are retrieved from daytime measurements (sun zenith angle θo < 60°) over ocean in reflectance bands 1 (λ1 = 0.63 µm) and 2 (λ2 = 1.61 µm) of the five-channel visible and infrared scanner (VIRS) on board the Tropical Rainfall Measuring Mission (TRMM) satellite. In band 2, a thermal leak originating from the secondary spectral response peak at ∼5.2 µm contributes radiance comparable to the signal scattered by aerosols. In the past two corrections, the thermal signal was parameterized empirically as a linear function of radiances in bands 4 and 5 (centered at 10.8 and 11.9 µm, respectively), R4 and R5, and a quadratic function of view angle θ through multiple regression analyses. The regression coefficients were estimated from a limited amount of all-sky nighttime (100° < θo < 170°) data over land and ocean, and were used to predict and remove the false signal from daytime data. As a result, retrievals of τ2 and α have been improved, but they still remain seriously flawed. This study reexamines the nighttime signal in VIRS channel 2 using two representative 9-day segments of the TRMM single scanner footprint (SSF) data collected from 4–12 February and 2–10 April 1998. The past parameterizations did not always perform accurately. Their residuals are biased and skewed, and reveal artificial trends with time, latitude, θ, R4, and R5. A new parameterization of the nighttime signal is proposed that makes use of 1) clear-sky ocean data only (rather than previously used all sky, full set); 2) more accurate principal component analyses (PCA) to approximate the θ, R4, and R5 dependencies of the false signal (in place of the formerly used liner/quadratic regressions); and 3) explicit accounting for temporal instability of the spurious signal (rather than assuming it to be stable as was done in the past). The new parameterization substantially relieves the problems found in the previous two parameterizations. A much smaller false signal of unknown origin, found in channel 1, is also analyzed and parameterized in this study, consistently with channel 2. The effects of false signals and residuals of different corrections on retrieved τ and α are preliminarily estimated using an approximate formulation based on a simplified treatment of the radiative transfer equation.
Ipe, A.; Clerbaux, N.; Bertrand, C.; Dewitte, S.; Gonzalez, L.Ipe, A., N. Clerbaux, C. Bertrand, S. Dewitte, L. Gonzalez, 2003: Pixel-scale composite top-of-the-atmosphere clear-sky reflectances for Meteosat-7 visible data. Journal of Geophysical Research: Atmospheres, 108(D19), 4612. doi: 10.1029/2002JD002771. A new method to estimate composite top of the atmosphere (TOA) visible clear-sky reflectances for wide narrow band geostationary satellites such as the Meteosat constellation is presented. This method relies on some a priori knowledge of angular variations of TOA broadband reflectances associated with clear-sky conditions above mean surface types through the use of the clear-sky Cloud and the Earth's Radiant Energy System (CERES) shortwave broadband angular dependency models (ADMs). Each pixel (or Earth location) viewed from such geostationary imager at a given daytime is associated with a reflectance time series made up of its chronological daily measurements. This time series can be seen as a clear-sky visible narrow band reflectance curve of the associated pixel surface plus an additive random noise modeling cloudy conditions above it. On the basis of this assumption, TOA clear-sky broadband reflectances extracted from the CERES ADMs are used to compute curve-driven fifth percentiles on these time series in order to estimate the TOA clear-sky visible narrow band reflectance curves for all pixels, while the percentile approach exhibits only a reduced sensitivity to cloud shadows. Benefits of our method are discussed with respect to its application to 7 months of Meteosat-7 daytime visible narrow band measurements. Finally, the performance of our algorithm is assessed through comparisons with its predicted and associated International Cloud Climatology Project DX clear-sky values with respect to a visually generated clear-sky pixels database. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3394 Meteorology and Atmospheric Dynamics: Instruments and techniques; clear-sky; Meteosat-7 imager; pixel-scale; TOA composite
Jensen, Michael P.; Del Genio, Anthony D.Jensen, M. P., A. D. Del Genio, 2003: Radiative and Microphysical Characteristics of Deep Convective Systems in the Tropical Western Pacific. Journal of Applied Meteorology, 42(9), 1234-1254. doi: 10.1175/1520-0450(2003)042<1234:RAMCOD>2.0.CO;2. Abstract The radiative and microphysical characteristics of 17 precipitating systems observed by the Tropical Rainfall Measuring Mission (TRMM) satellite over Manus, Papua New Guinea, and Nauru Island are modeled. These cases represent both deep and midlevel convection. Reflectivity data from the TRMM precipitation radar and Geostationary Meteorological Satellite infrared radiometer measurements are used to parameterize the three-dimensional cloud microphysics of each precipitating cloud system. These parameterized cloud properties are used as input for a two-stream radiative transfer model. Comparisons with measurements of broadband radiative fluxes at the top of atmosphere and the surface show agreement to within 20%. In cases in which the convective available potential energy (CAPE) is large, deep convective clouds with extended anvil decks form, containing layers of ice crystals that are too small to be detected by the TRMM radar but have a large optical thickness. This results in maximum shortwave heating and longwave cooling near cloud top at heights of 12–14 km. When CAPE is small, convective clouds extend only to midlevels (4–7 km), and there are no cloud layers below the detectability limit of the TRMM radar. Radiative heating and cooling in these cases are maximum near the freezing level. A sensitivity analysis suggests that the small ice crystals near the cloud top and larger precipitation-sized particles play equally significant roles in producing the high albedos of tropical anvil clouds. A comparison of the radiative heating profiles calculated in this study with latent heating profiles from previous studies shows that for cases of mature deep convection near local solar noon, the maximum radiative heating is 10%–30% of the magnitude of the maximum latent heating.
Jin, Yufang; Schaaf, Crystal B.; Woodcock, Curtis E.; Gao, Feng; Li, Xiaowen; Strahler, Alan H.; Lucht, Wolfgang; Liang, ShunlinJin, Y., C. B. Schaaf, C. E. Woodcock, F. Gao, X. Li, A. H. Strahler, W. Lucht, S. Liang, 2003: Consistency of MODIS surface bidirectional reflectance distribution function and albedo retrievals: 2. Validation. Journal of Geophysical Research: Atmospheres, 108(D5), 4159. doi: 10.1029/2002JD002804. The evaluation of the first available satellite-based global albedo product at 1-km resolution is essential for its application in climate studies. We evaluate the accuracy of the Moderate-Resolution Imaging Spectroradiometer (MODIS) albedo product using available field measurements at Surface Radiation Budget Network (SURFRAD) and Cloud and Radiation Testbed–Southern Great Plains (CART/SGP) stations and examine the consistency between the MODIS surface albedos and the Clouds and Earth's Radiant Energy System (CERES) top-of-the-atmosphere albedos as well as historical global albedos from advanced very high resolution radiometer (AVHRR) and Earth Radiation Budget Experiment (ERBE) observations. A comparison with the field measurements shows that the MODIS surface albedo generally meets an absolute accuracy requirement of 0.02 for our study sites during April–September 2001, with the root mean square errors less than 0.018. Larger differences appear in the winter season probably due to the increased heterogeneity of surface reflectivity in the presence of snow. To examine the effect of spatial heterogeneity on the validation of the MODIS albedos using fine resolution field measurements, we derive an intermediate albedo product from four Landsat Enhanced Thematic Mapper Plus (ETM+) images at 30-m spatial resolution as a surrogate for the distributed field measurements. The surface albedo is relatively homogeneous over the study stations in growing seasons, and therefore the validation during April–September is supported. A case study over three SURFRAD stations reveals that the MODIS bidirectional reflectance distribution function model is able to capture the solar zenith angle dependence of surface albedo as shown by the field measurements. We also find that the MODIS surface shortwave albedo is consistent with the contemporary and collocated CERES top-of atmosphere albedos derived directly from broadband observations. The MODIS albedo is also well correlated with historical surface albedos derived from AVHRR and ERBE observations, and a high bias of 0.016 and a low bias of 0.034 compared to those of the latter albedos are reasonable considering the differences in instruments and retrieval algorithms as well as environmental changes. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; surface albedo; MODIS; 3322 Meteorology and Atmospheric Dynamics: Land/atmosphere interactions; validation
Kato, SeijiKato, S., 2003: Computation of Domain-Averaged Shortwave Irradiance by a One-Dimensional Algorithm Incorporating Correlations between Optical Thickness and Direct Incident Radiation. J. Atmos. Sci., 60(1), 182-193. doi: 10.1175/1520-0469(2003)060<0182:CODASI>2.0.CO;2. Abstract A one-dimensional radiative transfer algorithm that accounts for correlations between the optical thickness and the incident direct solar radiation is developed to compute the domain-averaged shortwave irradiance profile. It divides the direct irradiance into four components and treats the direct irradiance in two separate, clear and cloudy columns to account for the fact that clouds attenuate the direct irradiance more than clear sky. The horizontal inhomogeneity of clouds in the cloudy column is treated by the gamma-weighted two-stream approximation, which assumes that the optical thickness of clouds follows a gamma distribution. The algorithm inputs the cloud fraction, cumulative cloud fraction as a function of height, and a parameter expressing the shape of the probability density function of the cloud optical thickness distribution in addition to inputs required for a two-stream radiative transfer model. These cloud property inputs can be obtained using ground- and satellite-based instruments. Therefore, the algorithm can treat realistic cloud overlap features and horizontal inhomogeneity of clouds in a framework of one-dimensional radiative transfer. Heating rates computed by the algorithm using cloud fields generated by cloud resolving models agree with those computed with a Monte Carlo model.
Kato, Seiji; Loeb, Norman G.Kato, S., N. G. Loeb, 2003: Twilight Irradiance Reflected by the Earth Estimated from Clouds and the Earth's Radiant Energy System (CERES) Measurements. J. Climate, 16(15), 2646-2650. doi: 10.1175/1520-0442(2003)016<2646:TIRBTE>2.0.CO;2. Abstract The upward shortwave irradiance at the top of the atmosphere when the solar zenith angle is greater than 90° (twilight irradiance) is estimated from radiance measurements by the Clouds and the Earth's Radiant Energy System (CERES) instrument on the Tropical Rainfall Measuring Mission (TRMM) satellite. The irradiance decreases with solar zenith angle from 7.5 W m−2 at 90.5° to 0.6 W m−2 at 95.5°. The global and daily average twilight irradiance is 0.2 W m−2, which is three orders of magnitude smaller than the daily and global average reflected irradiance at the top of the atmosphere. Therefore, the twilight irradiance can be neglected in global radiation budget estimate. The daily average twilight irradiance, however, can be more than 1 W m−2 at polar regions during seasons when the sun stays just below the horizon for a long period of time.
L'Ecuyer, Tristan S.; Stephens, Graeme L.L'Ecuyer, T. S., G. L. Stephens, 2003: The Tropical Oceanic Energy Budget from the TRMM Perspective. Part I: Algorithm and Uncertainties. J. Climate, 16(12), 1967-1985. doi: 10.1175/1520-0442(2003)016<1967:TTOEBF>2.0.CO;2. Abstract The earth's weather and climate is driven by the meridional transport of energy required to establish a global balance between incoming energy from the sun and outgoing thermal energy emitted by the atmosphere and surface. Clouds and precipitation play an integral role in the exchange of these sources of energy between the surface, atmosphere, and space—enhancing reflection of solar radiation to space, trapping thermal emission from the surface, and providing a mechanism for the direct transfer of energy to the atmosphere through the release of latent heat in precipitation. This paper introduces a new multisensor algorithm for extracting longwave, shortwave, and latent heat fluxes over oceans from the sensors aboard the Tropical Rainfall Measuring Mission (TRMM) satellite. The technique synthesizes complementary information from distinct retrievals of high and low clouds and precipitation from the TRMM Microwave Imager (TMI) and Visible and Infrared Scanner (VIRS) instruments to initialize broadband radiative transfer calculations for deriving the structure of radiative heating in oceanic regions from 40°S to 40°N and its evolution on daily and monthly timescales. Sensitivity studies using rigorous estimates of the uncertainties in all input parameters and detailed comparisons with flux observations from the Clouds and Earth's Radiant Energy System (CERES) are used to study the dominant influences on the algorithm's performance and to assess the accuracy of its products. The results demonstrate that the technique provides monthly mean estimates of oceanic longwave fluxes at 1° resolution to an accuracy of ∼10 W m−2. Uncertainties in these estimates are found to arise primarily from a lack of explicit vertical cloud boundary information and errors in prescribed temperature and humidity profiles. Corresponding shortwave flux estimates are shown to be accurate to ∼25 W m−2, with uncertainties due to errors in cloud detection, poorly constrained cloud particle sizes, and uncertainties in the prescribed surface albedo. When viewed as a whole, the components of the method provide a tool to diagnose relationships between the climate, hydrologic cycle, and the earth's energy budget.
Lin, Bing; Minnis, Patrick; Fan, AliceLin, B., P. Minnis, A. Fan, 2003: Cloud liquid water path variations with temperature observed during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment. Journal of Geophysical Research: Atmospheres, 108(D14), 4427. doi: 10.1029/2002JD002851. Because clouds play such a significant role in climate, understanding their responses to climatic temperature changes is essential to determining the overall impact of a given climate forcing. Cloud liquid water path (LWP) over tropical and midlatitude oceans has been observed to decrease with increasing cloud temperature. The presence of an ice sheet over the Arctic Ocean alters the energy and moisture exchange between the ocean and the atmospheric boundary layer and thus may affect the relationship between LWP and temperature. The variations of LWP with cloud and surface temperatures are examined in this paper using a combination of surface and satellite data taken during the 1998 Surface Heat Budget of the Arctic Ocean and the FIRE Arctic Clouds Experiments. The results show that LWP increases with temperature primarily because of an increase in cloud thickness that is enabled by the rise in surface moisture during the melt season. Cloud base heights and lifting condensation levels decrease as a result of the greater surface relative humidity and temperature. The average change rate of LWP with cloud temperature is 3.3% K−1, a value slightly smaller than earlier observations taken over cold midlatitude land areas. This cloud LWP feedback with temperature differs significantly from that estimated over other marine environments and should be taken into account in all climate models with explicit cloud feedbacks. 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0320 Cloud physics and chemistry; 6969 Remote sensing; 3349 Meteorology and Atmospheric Dynamics: Polar meteorology
Liu, X.; Wang, J.; Christopher, S.Liu, X., J. Wang, S. Christopher, 2003: Shortwave direct radiative forcing of Saharan dust aerosols over the Atlantic Ocean. International Journal of Remote Sensing, 24(24), 5147-5160. doi: 10.1080/0143116031000114824. Using collocated Visible and Infrared Scanner (VIRS) and Clouds and the Earth's Radiant Energy Budget Scanner (CERES) data on board the Tropical Rainfall Measuring Mission (TRMM) satellite, the instantaneous Shortwave Aerosol Radiative Forcing (SWARF) and daytime diurnally averaged SWARF at the top-of-atmosphere (TOA) are estimated for Saharan dust over the Atlantic Ocean (10degrees N-25degrees N, 30degrees W-15degrees W) for July 1998. A combination of reflectance thresholds, along with infrared spatial coherence techniques, are used to separate dust aerosols from clouds. Using Mie and Discrete Ordinate Radiative Transfer (DISORT) calculations and the VIRS channel 1 reflectance, dust optical thickness ( tau ) is retrieved. The average instantaneous direct SWARF of dust aerosols per unit tau is -50 W m -2 . The daytime diurnally averaged SWARF of dust aerosols is -15.2+/-10.9 W m -2 for a mean tau of 0.79+/-0.39. This study demonstrates that the synergistic use of instruments from different parts of the electromagnetic spectrum can be used to study the radiative effects of dust aerosols. This study is also among the first to estimate the diurnal SWARF of dust aerosols using satellite sensor data.
Loeb, Norman G.; Loukachine, Konstantin; Manalo-Smith, Natividad; Wielicki, Bruce A.; Young, David F.Loeb, N. G., K. Loukachine, N. Manalo-Smith, B. A. Wielicki, D. F. Young, 2003: Angular Distribution Models for Top-of-Atmosphere Radiative Flux Estimation from the Clouds and the Earth's Radiant Energy System Instrument on the Tropical Rainfall Measuring Mission Satellite. Part II: Validation. Journal of Applied Meteorology, 42(12), 1748-1769. doi: 10.1175/1520-0450(2003)042<1748:ADMFTR>2.0.CO;2. Abstract Top-of-atmosphere (TOA) radiative fluxes from the Clouds and the Earth's Radiant Energy System (CERES) are estimated from empirical angular distribution models (ADMs) that convert instantaneous radiance measurements to TOA fluxes. This paper evaluates the accuracy of CERES TOA fluxes obtained from a new set of ADMs developed for the CERES instrument onboard the Tropical Rainfall Measuring Mission (TRMM). The uncertainty in regional monthly mean reflected shortwave (SW) and emitted longwave (LW) TOA fluxes is less than 0.5 W m−2, based on comparisons with TOA fluxes evaluated by direct integration of the measured radiances. When stratified by viewing geometry, TOA fluxes from different angles are consistent to within 2% in the SW and 0.7% (or 2 W m−2) in the LW. In contrast, TOA fluxes based on ADMs from the Earth Radiation Budget Experiment (ERBE) applied to the same CERES radiance measurements show a 10% relative increase with viewing zenith angle in the SW and a 3.5% (9 W m−2) decrease with viewing zenith angle in the LW. Based on multiangle CERES radiance measurements, 1° regional instantaneous TOA flux errors from the new CERES ADMs are estimated to be
Loeb, Norman G.; Manalo-Smith, Natividad; Kato, Seiji; Miller, Walter F.; Gupta, Shashi K.; Minnis, Patrick; Wielicki, Bruce A.Loeb, N. G., N. Manalo-Smith, S. Kato, W. F. Miller, S. K. Gupta, P. Minnis, B. A. Wielicki, 2003: Angular Distribution Models for Top-of-Atmosphere Radiative Flux Estimation from the Clouds and the Earth’s Radiant Energy System Instrument on the Tropical Rainfall Measuring Mission Satellite. Part I: Methodology. Journal of Applied Meteorology, 42(2), 240-265. doi: 10.1175/1520-0450(2003)042<0240:ADMFTO>2.0.CO;2. Abstract Clouds and the Earth's Radiant Energy System (CERES) investigates the critical role that clouds and aerosols play in modulating the radiative energy flow within the Earth–atmosphere system. CERES builds upon the foundation laid by previous missions, such as the Earth Radiation Budget Experiment, to provide highly accurate top-of-atmosphere (TOA) radiative fluxes together with coincident cloud and aerosol properties inferred from high-resolution imager measurements. This paper describes the method used to construct empirical angular distribution models (ADMs) for estimating shortwave, longwave, and window TOA radiative fluxes from CERES radiance measurements on board the Tropical Rainfall Measuring Mission satellite. To construct the ADMs, multiangle CERES measurements are combined with coincident high-resolution Visible Infrared Scanner measurements and meteorological parameters from the European Centre for Medium-Range Weather Forecasts data assimilation product. The ADMs are stratified by scene types defined by parameters that have a strong influence on the angular dependence of Earth's radiation field at the TOA. Examples of how the new CERES ADMs depend upon the imager-based parameters are provided together with comparisons with existing models.
Loukachine, Konstantin; Loeb, Norman G.Loukachine, K., N. G. Loeb, 2003: Application of an Artificial Neural Network Simulation for Top-of-Atmosphere Radiative Flux Estimation from CERES. J. Atmos. Oceanic Technol., 20(12), 1749-1757. doi: 10.1175/1520-0426(2003)020<1749:AOAANN>2.0.CO;2. Abstract The Clouds and the Earth's Radiant Energy System (CERES) provides top-of-atmosphere (TOA) radiative flux estimates from shortwave (SW) and longwave (LW) radiance measurements by applying empirical angular distribution models (ADMs) for scene types defined by coincident high-resolution imager-based cloud retrievals. In this study, CERES ADMs are simulated using a feed-forward error back-propagation (FFEB) artificial neural network (ANN) simulation to provide a means of estimating TOA SW and LW radiative fluxes for different scene types in the absence of imager radiance measurements. In all cases, the ANN-derived TOA fluxes deviate from CERES TOA fluxes by less than 0.3 W m−2, on average, and show a smaller dependence on viewing geometry than TOA fluxes derived using ADMs from the Earth Radiation Budget Experiment (ERBE). The ANN-derived TOA SW and LW fluxes show a significant improvement in accuracy over the CERES ERBE-like fluxes when compared regionally.
Markowicz, Krzysztof M.; Flatau, Piotr J.; Quinn, P. K.; Carrico, Christian M.; Flatau, M. K.; Vogelmann, A. M.; Bates, David; Liu, M.; Rood, Mark J.Markowicz, K. M., P. J. Flatau, P. K. Quinn, C. M. Carrico, M. K. Flatau, A. M. Vogelmann, D. Bates, M. Liu, M. J. Rood, 2003: Influence of relative humidity on aerosol radiative forcing: An ACE-Asia experiment perspective. Journal of Geophysical Research: Atmospheres, 108(D23), 8662. doi: 10.1029/2002JD003066. We present direct radiometric observations of aerosol radiative forcing during the ACE-Asia experiment (March and April of 2001). The observational analysis is based on radiometer data obtained from the NOAA ship Ronald H. Brown, and shipboard measurements of the aerosol chemical and scattering properties are used to construct a model of the aerosol optical properties for use in radiative transfer calculations. The model is validated against the radiometric observations and is used to diagnose the aerosol and environmental factors that contribute to the observed forcings. The mean value of aerosol optical thickness observed during the ACE-Asia cruise over the Sea of Japan was 0.43 (±0.25) at 500 nm, while the single-scattering albedo was 0.95 (±0.03) at ambient relative humidity. We find a large correlation (r2 = 0.69) between single-scattering albedo and relative humidity. Aerosols caused a mean decrease in the diurnally averaged solar radiation of 26.1 W m−2 at the surface, while increasing the atmospheric solar absorption and top of atmosphere reflected solar radiation by 13.4 W m−2 and 12.7 W m−2, respectively. The mean surface aerosol forcing efficiency (forcing per unit optical depth) over the Sea of Japan was −60 W m−2 and is influenced by high values of relative humidity. We show that decreasing the relative humidity to 55% enhances the aerosol forcing efficiency by as much as 6–10 W m−2. This dependency on relative humidity has implications for comparisons of aerosol forcing efficiencies between different geographical locations. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1640 Remote sensing; 0305 Aerosols and particles; 3307 Meteorology and Atmospheric Dynamics: Boundary layer processes; 0345 Pollution: urban and regional; aerosol; humidity; forcing; ACE-Asia; optical depth
Markowicz, Krzysztof M.; Flatau, Piotr J.; Vogelmann, Andrew M.; Quinn, Patricia K.; Welton, Ellsworth J.Markowicz, K. M., P. J. Flatau, A. M. Vogelmann, P. K. Quinn, E. J. Welton, 2003: Clear-sky infrared aerosol radiative forcing at the surface and the top of the atmosphere. Quarterly Journal of the Royal Meteorological Society, 129(594), 2927-2947. doi: 10.1256/qj.02.224. We study the aerosol radiative forcing at infrared (IR) wavelengths using data from the Aerosol Characterization Experiment, ACE-Asia, cruise of the National Oceanic and Atmospheric Administration research vessel Ronald H. Brown. The analyses apply to the daytime periods of clear-sky conditions for the area within the immediate vicinity of the ship. An optical model is derived from chemical measurements, lidar profiles, and visible-extinction measurements, which are used to estimate the IR aerosol optical thickness and the single-scattering albedo. The IR model results are compared to detailed Fourier transform interferometer-based IR aerosol forcing estimates, pyrgeometer-based IR downward fluxes, and to observations of the direct aerosol solar forcing. This combined approach attests to the self-consistency of the optical model, and allows us to derive quantities such as the IR forcing at the top of the atmosphere (TOA) and the IR optical thickness. The mean IR aerosol optical thickness at 10 µm is 0.08 and the single-scattering albedo is 0.55. The modelled IR aerosol surface forcing reaches 10 W m−2 during the cruise, which is a significant contribution compared to the total direct aerosol forcing. The surface IR aerosol radiative forcing is between 10 and 25% of the short-wave aerosol forcing. The IR aerosol forcing at the TOA can be up to 19% of the solar aerosol forcing. We show good agreement between TOA aerosol IR forcing derived from the model and from the CERES (Clouds and the Earth's Radiant Energy System) satellite data. Over the Sea of Japan, the average IR aerosol radiative forcing is 4.6 W m−2 at the surface, and 1.5 W m−2 at the TOA. The IR forcing efficiency at the TOA is a strong function of aerosol temperature (which is coupled to vertical structure) and changes between 10 and 18 W m−2 (per IR optical depth unit), while the surface IR forcing efficiency varies between 37 and 55 W m−2 (per IR optical depth unit). Copyright © 2003 Royal Meteorological Society climate change; Aerosol forcing; Aerosol infrared forcing
Matrosov, Sergey Y.; Shupe, Matthew D.; Heymsfield, Andrew J.; Zuidema, PaquitaMatrosov, S. Y., M. D. Shupe, A. J. Heymsfield, P. Zuidema, 2003: Ice Cloud Optical Thickness and Extinction Estimates from Radar Measurements. Journal of Applied Meteorology, 42(11), 1584-1597. doi: 10.1175/1520-0450(2003)042<1584:ICOTAE>2.0.CO;2. Abstract A remote sensing method is proposed to derive vertical profiles of the visible extinction coefficients in ice clouds from measurements of the radar reflectivity and Doppler velocity taken by a vertically pointing 35-GHz cloud radar. The extinction coefficient and its vertical integral, optical thickness τ, are among the fundamental cloud optical parameters that, to a large extent, determine the radiative impact of clouds. The results obtained with this method could be used as input for different climate and radiation models and for comparisons with parameterizations that relate cloud microphysical parameters and optical properties. An important advantage of the proposed method is its potential applicability to multicloud situations and mixed-phase conditions. In the latter case, it might be able to provide the information on the ice component of mixed-phase clouds if the radar moments are dominated by this component. The uncertainties of radar-based retrievals of cloud visible optical thickness are estimated by comparing retrieval results with optical thicknesses obtained independently from radiometric measurements during the yearlong Surface Heat Budget of the Arctic Ocean (SHEBA) field experiment. The radiometric measurements provide a robust way to estimate τ but are applicable only to optically thin ice clouds without intervening liquid layers. The comparisons of cloud optical thicknesses retrieved from radar and from radiometer measurements indicate an uncertainty of about 77% and a bias of about −14% in the radar estimates of τ relative to radiometric retrievals. One possible explanation of the negative bias is an inherently low sensitivity of radar measurements to smaller cloud particles that still contribute noticeably to the cloud extinction. This estimate of the uncertainty is in line with simple theoretical considerations, and the associated retrieval accuracy should be considered good for a nonoptical instrument, such as radar. This paper also presents relations between radar-derived characteristic cloud particle sizes and effective sizes used in models. An average relation among τ, cloud ice water path, and the layer mean value of cloud particle characteristic size is also given. This relation is found to be in good agreement with in situ measurements. Despite a high uncertainty of radar estimates of extinction, this method is useful for many clouds where optical measurements are not available because of cloud multilayering or opaqueness.
Miller, A. J.; Zhou, S.; Yang, S-K.Miller, A. J., S. Zhou, S. Yang, 2003: Relationship of the Arctic and Antarctic Oscillations to the Outgoing Longwave Radiation. J. Climate, 16(10), 1583-1592. doi: 10.1175/1520-0442(2003)016<1583:ROTAAA>2.0.CO;2. Abstract While several mechanisms have been suggested to account for the association of the Arctic and Antarctic Oscillations (AO/AAO) with atmospheric parameters, this paper focuses on the relationship with the atmospheric outgoing longwave radiation (OLR). The main objective of this paper is to demonstrate through AO/AAO composite analysis that the NCEP–NCAR reanalysis OLR agrees with the independent observations of the NASA Earth Radiation Budget Experiment (ERBE) broadband satellite instruments both in zonal averages and in geographically mapped space, and to verify AO/AAO characterized general circulations derived from models and analyses. The results indicate several pronounced areas of storminess that are AO/AAO dependent. One is the well-known variation over the North Atlantic Ocean toward Europe. Also, several major areas are indicated in the tropical region—one in the Indian Ocean and the others in the west and central Pacific Ocean. In addition to demonstrating that the signals are statistically significant, also tested is the relationship of the features to other well-known tropical forcing mechanisms: the Madden–Julian oscillation (MJO) and the El Niño–La Niña sea surface temperature variations. It is shown that the tropical features do, in fact, have a strong relationship to the MJO, which indicates an additional tropical–extratropical interaction. With regard to the sea surface temperature, no correlation associated with the AO/AAO variability is seen. These associations with the cloudiness and atmospheric radiation budget suggest that if there is to be improvement of numerical model forecasts to an extended time period that numerical model radiation physics will have to be taken into consideration and improved.
Parkinson, C.L.Parkinson, C., 2003: Aqua: an Earth-Observing Satellite mission to examine water and other climate variables. IEEE Transactions on Geoscience and Remote Sensing, 41(2), 173-183. doi: 10.1109/TGRS.2002.808319. Aqua is a major satellite mission of the Earth Observing System (EOS), an international program centered at the U.S. National Aeronautics and Space Administration (NASA). The Aqua satellite carries six distinct Earth-observing instruments to measure numerous aspects of Earth's atmosphere, land, oceans, biosphere, and cryosphere, with a concentration on water in the Earth system. Launched on May 4, 2002, the satellite is in a Sun-synchronous orbit at an altitude of 705 km, with a track that takes it north across the equator at 1:30 p.m. and south across the equator at 1:30 a.m. All of its Earth-observing instruments are operating, and all have the ability to obtain global measurements within two days. The Aqua data will be archived and available to the research community through four Distributed Active Archive Centers (DAACs). atmosphere; Extraterrestrial measurements; geophysical measurement technique; geophysical techniques; Land surface; Remote sensing; Satellites; Biosphere; atmospheric techniques; CERES; Earth Observing System; EOS; Instruments; Meteorology; satellite remote sensing; Terrestrial atmosphere; atmospheric measuring apparatus; IR radiometry; NASA; Oceans; Atmospheric measurements; MODIS; water vapor; humidity; Aqua; AIRS; AMSR; AMSR-E; AMSU; Earth Observing Satellite; geophysical equipment; HSB; hydrological equipment; hydrological techniques; hydrology; infrared method; instrument; microwave radiometry; Ocean; oceanographic equipment; oceanographic techniques; Sea measurements; sun-synchronous orbit; terrain mapping; visible; water vapour
Pilewskie, P.; Pommier, J.; Bergstrom, R.; Gore, W.; Howard, S.; Rabbette, M.; Schmid, B.; Hobbs, P. V.; Tsay, S. C.Pilewskie, P., J. Pommier, R. Bergstrom, W. Gore, S. Howard, M. Rabbette, B. Schmid, P. V. Hobbs, S. C. Tsay, 2003: Solar spectral radiative forcing during the Southern African Regional Science Initiative. Journal of Geophysical Research: Atmospheres, 108(D13), 8486. doi: 10.1029/2002JD002411. During the dry season component of the Southern African Regional Science Initiative (SAFARI) in late winter 2000, the net solar spectral irradiance was measured at flight levels throughout biomass burning haze layers. From these measurements, the flux divergence, fractional absorption, instantaneous heating rate, and absorption efficiency were derived. Two cases are examined: on 24 August 2000 off the coast of Mozambique in the vicinity of Inhaca Island and on 6 September 2000 in a very thick continental haze layer over Mongu, Zambia. The measured absolute absorption was substantially higher for the case over Mongu where the measured midvisible optical depth exceeded unity. Instantaneous heating from aerosol absorption was 4 K d−1 over Mongu, Zambia and 1.5 K d−1 near Inhaca Island, Mozambique. However, the spectral absorption efficiency was nearly identical for both cases. Although the observations over Inhaca Island preceded the “river of smoke” from the southern African continent by nearly 2 weeks, the evidence here suggests a continental influence in the lower tropospheric aerosol far from source regions of burning. 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 0394 Instruments and techniques; 0345 Pollution: urban and regional; aerosols; Solar radiation; climate; 0342 Atmospheric Composition and Structure: Middle atmosphere—energy deposition; radiometric measurements
Ruddiman, William F.Ruddiman, W. F., 2003: The Anthropogenic Greenhouse Era Began Thousands of Years Ago. Climatic Change, 61(3), 261-293. doi: 10.1023/B:CLIM.0000004577.17928.fa. The anthropogenic era is generally thought to have begun 150 to 200 years ago, when the industrial revolution began producing CO2 andCH4 at rates sufficient to alter their compositions in the atmosphere. A different hypothesis is posed here: anthropogenic emissions of these gases first altered atmospheric concentrations thousands of years ago. This hypothesis is based on three arguments. (1) Cyclic variations in CO2 andCH4 driven by Earth-orbital changes during the last 350,000 years predict decreases throughout the Holocene, but the CO2 trend began ananomalous increase 8000 years ago, and the CH4 trend did so 5000 years ago.(2) Published explanations for these mid- to late-Holocene gas increases basedon natural forcing can be rejected based on paleoclimatic evidence. (3) A wide array of archeological, cultural, historical and geologic evidence points to viable explanations tied to anthropogenic changes resulting from early agriculture in Eurasia, including the start of forest clearance by 8000 years ago and of rice irrigation by 5000 years ago. In recent millennia, the estimated warming caused by these early gas emissions reached a global-mean value of ∼ 0.8 °C and roughly 2 °C at high latitudes, large enough to have stopped a glaciation of northeastern Canada predicted by two kinds of climatic models. CO2 oscillations of ∼ 10 ppm in the last 1000 years are toolarge to be explained by external (solar-volcanic) forcing, but they can be explained by outbreaks of bubonic plague that caused historically documented farm abandonment in western Eurasia. Forest regrowth on abandoned farms sequestered enough carbon to account for the observed CO2decreases. Plague-driven CO2 changes were also a significant causal factor in temperature changes during the Little Ice Age (1300–1900 AD). Meteorology/Climatology
Smith, G. Louis; Rutan, David A.Smith, G. L., D. A. Rutan, 2003: The Diurnal Cycle of Outgoing Longwave Radiation from Earth Radiation Budget Experiment Measurements. J. Atmos. Sci., 60(13), 1529-1542. doi: 10.1175/2997.1. Abstract The diurnal cycle of outgoing longwave radiation (OLR) from the earth is analyzed by decomposing satellite observations into a set of empirical orthogonal functions (EOFs). The observations are from the Earth Radiation Budget Experiment (ERBE) scanning radiometer aboard the Earth Radiation Budget Satellite, which had a precessing orbit with 57° inclination. The diurnal cycles of land and ocean differ considerably. The first EOF for land accounts for 73% to 85% of the variance, whereas the first EOF for ocean accounts for only 16% to 20% of the variance, depending on season. The diurnal cycle for land is surprisingly symmetric about local noon for the first EOF, which is approximately a half-sine during day and flat at night. The second EOF describes lead–lag effects due to surface heating and cloud formation. For the ocean, the first EOF and second EOF are similar to that of land, except for spring, when the first ocean EOF is a semidiurnal cycle and the second ocean EOF is the half-sine. The first EOF for land has a daytime peak of about 50 W m−2, whereas the first ocean EOF peaks at about 25 W m−2. The geographical and seasonal patterns of OLR diurnal cycle provide insights into the interaction of radiation with the atmosphere and surface and are useful for validating and upgrading circulation models.
Tanré, D.; Haywood, J.; Pelon, J.; Léon, J. F.; Chatenet, B.; Formenti, P.; Francis, P.; Goloub, P.; Highwood, E. J.; Myhre, G.Tanré, D., J. Haywood, J. Pelon, J. F. Léon, B. Chatenet, P. Formenti, P. Francis, P. Goloub, E. J. Highwood, G. Myhre, 2003: Measurement and modeling of the Saharan dust radiative impact: Overview of the Saharan Dust Experiment (SHADE). Journal of Geophysical Research: Atmospheres, 108(D18), 8574. doi: 10.1029/2002JD003273. Aerosols are known to be important in determining Earth's radiative balance. Dust aerosols are of particular interest since, in addition to their scattering and absorbing properties that affect the solar radiation, they also perturb the terrestrial radiation. Recent studies have shown that a significant proportion of mineral dust in the atmosphere may be of anthropogenic origin, and therefore they may have an important role in climate change by exerting a significant radiative forcing. However, the optical and radiative properties of dust are not yet very well-determined, and even the sign of the resulting forcing is still questionable. The Saharan Dust Experiment (SHADE) was designed to better determine the parameters that are relevant for computing the direct radiative effect. Two aircraft combining in situ and remote sensing instruments were coordinated with satellite overpasses and ground-based observations during the experiment, which was based in the Cape Verde area during the period 19–29 September 2000. These in situ and remotely sensed data provide new valuable information on the microphysical, optical properties, and radiative effects of a large mineral dust outbreak. In addition, a global chemical transport model was used for assessing the radiative impact of these events, which are shown to be important on regional and global scales. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0305 Aerosols and particles; Saharan dust; dust direct radiative forcing; physical and optical properties
Tian, Baijun; Ramanathan, V.Tian, B., V. Ramanathan, 2003: A Simple Moist Tropical Atmosphere Model: The Role of Cloud Radiative Forcing. J. Climate, 16(12), 2086-2092. doi: 10.1175/1520-0442(2003)016<2086:ASMTAM>2.0.CO;2. Abstract A simple moist model for the large-scale tropical atmospheric circulation is constructed by combining the simple models of Gill and Neelin and Held. The model describes the first baroclinic mode of the moist troposphere with variable “gross moist stability” in response to given thermodynamic forcing from surface evaporation and atmospheric cloud radiative forcing (CRF), which is a measure of the radiative effects of clouds in the atmospheric radiative heating. When the present model is forced solely by the observed atmospheric CRF, quantitatively reasonable Hadley and Walker circulations are obtained, such as the trades, the ascending branches in the intertropical convergence zone (ITCZ) and the South Pacific Convergence Zone (SPCZ), as well as the descending branches in the cold tongue and subtropics. However, when the model is forced only by the observed surface evaporation, the Walker circulation totally disappears, and the Hadley circulation reverses. These results indicate that, in the context of a moist dynamic model, the spatial variations of atmospheric CRF are more important in terms of driving and maintaining the Hadley and Walker circulations than the spatial variation of surface evaporation.
Valero, Francisco P. J.; Pope, Shelly K.; Bush, Brett C.; Nguyen, Quyen; Marsden, David; Cess, Robert D.; Simpson-Leitner, A. Sabrina; Bucholtz, Anthony; Udelhofen, Petra M.Valero, F. P. J., S. K. Pope, B. C. Bush, Q. Nguyen, D. Marsden, R. D. Cess, A. S. Simpson-Leitner, A. Bucholtz, P. M. Udelhofen, 2003: Absorption of solar radiation by the clear and cloudy atmosphere during the Atmospheric Radiation Measurement Enhanced Shortwave Experiments (ARESE) I and II: Observations and models. Journal of Geophysical Research: Atmospheres, 108(D1), 4016. doi: 10.1029/2001JD001384. As a follow-on to the Atmospheric Radiation Measurement (ARM) Enhanced Shortwave Experiment (ARESE) I, which provided atmospheric shortwave measurements from collocated aircraft, ARESE II performed similar measurements with a single aircraft flying at an altitude of 7 km over an instrumented surface site. ARESE I and ARESE II absorptance measurements are found to agree with each other and, when converted to top of the atmosphere (TOA) instantaneous column absorption, are also consistent with GOES 8 and Scanner for Radiation Budget (ScaRaB) satellite observations. Measurements are compared to calculations performed with five different radiative transfer models. It is found that the calculated absorption differs systematically from the observations in cloudy conditions, with models underpredicting the absorption. In particular, all the models tested here underpredict the measured instantaneous cloudy column absorption by amounts ranging from 17 to 61 W m−2, depending on the models and cases studied. The various models, using identical input, differ among themselves; for example, for the same cloudy case, absorptance estimates range from 0.22 to 0.27 for the atmospheric column from the surface to the TOA. It is also found that model-calculated absorptances appear not as well correlated to cloud optical depth variations as the measured absorptances appear to be. Measured and calculated clear-sky absorptances agree well within the uncertainties. Cloudy-sky absorptances in the visible spectral region (300 to 700 nm) reach values of as much as 0.02 during ARESE II while the equivalent measurements for ARESE I range around 0.06. This visible absorptance may be related to aerosols and their day-to-day and seasonal variability. clouds; 0360 Radiation: transmission and scattering; 1610 Atmosphere; 0320 Cloud physics and chemistry; 0394 Instruments and techniques; Solar radiation; Models; Absorption; aircraft; Measurements
Vogelmann, Andrew M.; Flatau, Piotr J.; Szczodrak, Malgorzata; Markowicz, Krzysztof M.; Minnett, Peter J.Vogelmann, A. M., P. J. Flatau, M. Szczodrak, K. M. Markowicz, P. J. Minnett, 2003: Observations of large aerosol infrared forcing at the surface. Geophysical Research Letters, 30(12), 1655. doi: 10.1029/2002GL016829. Studies of aerosol effects on the Earth’s energy budget usually consider only the cooling effects at short (solar) wavelengths, but we demonstrate that they also have important warming effects at thermal infrared (IR) wavelengths that have rarely been observed and are commonly ignored in climate models. We use high-resolution spectra to obtain the IR radiative forcing at the surface for aerosols encountered in the outflow from northeastern Asia. The spectra were measured by the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI) from the NOAA Ship Ronald H. Brown during the Aerosol Characterization Experiment-Asia (ACE-Asia). We show that the daytime surface IR forcing are often a few Wm−2 and can reach almost 10 Wm−2 for large aerosol loadings. Thus, even the smaller aerosol IR forcing observed here are comparable to or greater than the 1 to 2 Wm−2 IR surface enhancement from increases in greenhouse gases. These results highlight the importance of aerosol IR forcing which should be included in climate model simulations. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0305 Aerosols and particles; 0394 Instruments and techniques; 1630 Impacts of global change
Wang, Jun; Christopher, Sundar A.; Reid, Jeffrey S.; Maring, Hal; Savoie, Dennis; Holben, Brent N.; Livingston, John M.; Russell, Philip B.; Yang, Shi-KengWang, J., S. A. Christopher, J. S. Reid, H. Maring, D. Savoie, B. N. Holben, J. M. Livingston, P. B. Russell, S. Yang, 2003: GOES 8 retrieval of dust aerosol optical thickness over the Atlantic Ocean during PRIDE. Journal of Geophysical Research: Atmospheres, 108(D19), 8595. doi: 10.1029/2002JD002494. Using 30 days of half-hourly, high temporal resolution GOES 8 imager data and radiative transfer calculations, dust aerosol optical thickness (AOT) was retrieved over the Atlantic Ocean (14°N ∼ 26°N, 73°W–63°W) during the Puerto Rico Dust Experiment (PRIDE). Dust aerosol size distributions and complex index of refraction inferred from ground-based measurements (1.53–0.0015i at 0.55 μm), which were used in Mie calculations and a plane-parallel discrete ordinate radiative transfer model (DISORT) to compute look up tables for AOT retrievals. Using a combination of spectral, spatial, and temporal tests, a dust detection algorithm was developed from the GOES 8 imager data. The degradation of the signal response relative to the prelaunched calibration of the GOES 8 visible channel was 39% in July 2000 and the GOES 8 AOT detection limit was estimated to be 0.04 in AOT (0.67 μm). The satellite-retrieved AOT were then compared with AOT values derived from ground-based Sun photometer (SP) sites. The comparison showed that GOES 8 retrieved AOT are in good agreement with the SP derived values, with linear correlation coefficient of 0.91 and 0.80 for the two sites. The GOES 8 monthly mean 0.67 μm AOT (0.19 ± 0.13, 0.22 ± 0.12) over the two SP sites matched the monthly mean SP AOT values (0.23 ± 0.13, 0.22 ± 0.10). The linear correlation between the GOES 8 retrieved AOT and the aircraft derived values from particle probe data and airborne Sun photometer AATS-6 measurements were 0.88 and 0.83, respectively. Besides the uncertainties from the nonspherical effect of dust aerosols, sensitivity studies showed that the uncertainties (Δτ) of the GOES 8 retrieved AOT values were mainly from the uncertainties due to the imaginary part of refractive index (Δτ = ±0.05) and surface reflectance [Δτ = ±(0.02 ∼ 0.04)]. This paper demonstrates the application of geostationary satellites to detect and retrieve dust AOT even at low to moderate AOTs. The GOES 8 imager with high temporal resolutions also captures aerosol diurnal variation in this study that can further reduce the uncertainties in the current aerosol forcing estimations caused by the high temporal variations of AOT, thereby playing a complementary role with global AOT retrievals from polar orbiting satellites. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0305 Aerosols and particles; radiative forcing; diurnal optical depth; dust aerosol; GOES 8
Wang, Pi-Huan; Minnis, Patrick; Wielicki, Bruce A.; Wong, Takmeng; Cess, Robert D.; Zhang, Minghua; Vann, Lelia B.; Kent, Geoffrey S.Wang, P., P. Minnis, B. A. Wielicki, T. Wong, R. D. Cess, M. Zhang, L. B. Vann, G. S. Kent, 2003: Characteristics of the 1997/1998 El Niño cloud distributions from SAGE II observations. Journal of Geophysical Research: Atmospheres, 108(D1), 4009. doi: 10.1029/2002JD002501. The present study examines the characteristics of cloud distributions with emphasis on cloud longwave radiative forcing (CLRF) during the peak of the 1997/1998 El Niño in relation to climatological conditions, based on measurements from the Stratospheric Aerosol and Gas Experiment (SAGE) II. The observed distinct cloud occurrence and CLRF during this unusual 1997/1998 El Niño constitutes a unique data set for validating and improving cloud-radiation-climate interactions in general circulation and climate models. Using the solar occultation technique, the SAGE II satellite instrument is capable of providing measurements with a 1-km vertical resolution facilitating the analysis with sufficient vertical as well as near global scale (70°S–70°N) details. The present study indicates (1) above normal high-altitude opaque cloud occurrence over the eastern tropical Pacific and an opposite situation over the Pacific warm pool, leading to a distribution of the cumulative opaque cloud anomalies above 3 km generally consistent with the pattern of observed tropical sea surface temperature and precipitation anomalies; (2) a similar behavior in the subvisual cloud distributions near the tropical tropopause; (3) a zonally averaged cloud distribution that is characterized by reduced opaque clouds at low latitudes, except in the southern tropics below 10 km, and by enhanced opaque clouds at high latitudes, along with increased subvisual clouds in the southern tropics and decreased subvisual clouds in the northern subtropics in the upper troposphere; and (4) a geographic distribution of model-calculated CLRF anomalies that resembles closely that inferred from the Earth Radiation Budget Experiment and the Clouds and the Earth's Radiant Energy System. A discussion on the influence of the El Niño on large-scale mean tropospheric circulations is also provided. clouds; Remote sensing; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 0320 Cloud physics and chemistry; 3319 Meteorology and Atmospheric Dynamics: General circulation; 3309 Meteorology and Atmospheric Dynamics: Climatology; climate; 1630 Impacts of global change; El Niño
Wilcox, Eric M.Wilcox, E. M., 2003: Spatial and Temporal Scales of Precipitating Tropical Cloud Systems in Satellite Imagery and the NCAR CCM3*. J. Climate, 16(22), 3545-3559. doi: 10.1175/1520-0442(2003)016<3545:SATSOP>2.0.CO;2. Abstract Testing general circulation model parameterizations against observations is traditionally done by comparing simulated and observed, time-averaged quantities, such as monthly mean cloud cover, evaluated on a stationary grid. This approach ignores the dynamical aspects of clouds, such as their life cycle characteristics, spatial coverage, temporal duration, and internal variability. In this study, a complementary Lagrangian approach to the validation of modeled tropical cloudiness is explored. An automated cloud detection and tracking algorithm is used to observe and track overcast decks of cloud in a consecutive set of hourly Meteosat-5 images and the National Center for Atmospheric Research Community Climate Model version 3 (NCAR CCM3). The algorithm is applied to the deep convective cloud systems of the tropical Indian Ocean region during a 49-day period of the 1999 winter monsoon season. Observations of precipitation are taken from the Tropical Rainfall Measuring Mission (TRMM) satellite in addition to a Meteosat-5 infrared rainfall technique that is calibrated using the TRMM data. Clouds, defined as overcast decks, are observed spanning spatial scales from 25 km2 to greater than 107 km2, as well as temporal scales from 1 h to greater than 100 h. Semipermanent decks of anvil and cirrus cloud, with numerous regions of deep convection embedded within, dominate total cloud cover. Bridging between convective centers within the deck by cirrus clouds, particularly during the suppressed portion of the diurnal cycle of convection, may help to maintain the integrity of semipermanent overcast decks over long timescales. At scales greater than 106 km2 the size distribution of simulated clouds is biased such that the dominant scale of clouds is several million square kilometers larger than the dominant scale of observed clouds. Virtually all of the simulated precipitation occurs at rain rates lower than 2 mm h−1, while as much as 25% of observed precipitation occurs at rain rates higher than 2 mm h−1. Precipitation associated with deep convection in observed semipermanent cloud systems is organized into more localized mesoscale structures of adjacent convective cells attached to stratiform precipitation regions. A separate analysis of TRMM data by Wilcox and Ramanathan determined that such structures can exceed the size of grid cells in coarse-grid global models and have area-averaged rain rates up to and exceeding 2 mm h−1. These mesoscale convective systems are responsible for the extreme, episodic precipitation events that are not parameterized in the model. The simulated cloud systems gently precipitate throughout their duration and everywhere within their boundaries. The model lacks a process that acts to organize the convective cells within fewer grid cells, in addition to a representation of the observed stratiform precipitation structures. A modification to CCM3 is tested that is intended to account for the evaporation of upper-level precipitation in midlevel mesoscale downdrafts. The modification results in only a slight change in domain-averaged precipitation. However, it causes a significant shift in the distribution of precipitation toward higher rain rates that is more consistent with the distribution of TRMM observed rain rates. The modification demonstrates the sensitivity of the model to one important component of mesoscale organized convection.
Yano, J. I.; Donner, L. J.; Yin, Y.; Lawrence, M. J.; Mari, C.; Stohl, A.Yano, J. I., L. J. Donner, Y. Yin, M. J. Lawrence, C. Mari, A. Stohl, 2003: Multidisciplinary discussions of convective chemical transport. Eos, Transactions American Geophysical Union, 84(34), 327-330. doi: 10.1029/2003EO340005. The importance of atmospheric chemical transport processes by moist convection has been increasingly recognized in the atmospheric chemistry community in recent years. In turn, the moist convection community has begun to recognize the value of trace gas measurements as a diagnostic tool for studying the detailed physics of convective clouds. This has led to a wide array of theoretical and experimental scientific investigations, and has been emphasized in various field experiments such as PEM (Pacific Exploratory Missions) Tropics A and B, TRACE-P (TRAnsport and Chemical Evolution over the Pacific), EULINOX (European Lightning Nitrogen Oxides Project), INDOEX (INDian Ocean Experiment), and CONTRACE (CONvective transport of TRACe gases into the middle and upper troposphere over Europe). Moist convection can efficiently transport the chemical species vertically via strong convective updrafts. But at the same time, the scavenging associated with convective precipitation can efficiently remove the soluble species. Contributions of microphysics to chemistry are also critical. Yet, the parameterization of these convective processes, even at the basic thermodynamic level, still remains an overall unresolved problem in global modeling. 0320 Cloud physics and chemistry; 3314 Meteorology and Atmospheric Dynamics: Convective processes; 9950 Meetings
Zhang, Jianglong; Christopher, Sundar A.Zhang, J., S. A. Christopher, 2003: Longwave radiative forcing of Saharan dust aerosols estimated from MODIS, MISR, and CERES observations on Terra. Geophysical Research Letters, 30(23), 2188. doi: 10.1029/2003GL018479. Using observations from the Multi-angle Imaging Spectroradiometer (MISR), the Moderate Resolution Imaging Spectroradiometer (MODIS), and the Clouds and the Earth's Radiant Energy System (CERES) instruments onboard the Terra satellite; we present a new technique for studying longwave (LW) radiative forcing of dust aerosols over the Saharan desert for cloud-free conditions. The monthly-mean LW forcing for September 2000 is 7 Wm−2 and the LW forcing efficiency (LWeff) is 15 Wm−2 per unit aerosol optical depth. Using radiative transfer calculations, we show that simultaneous measurements of the vertical distribution of aerosols, surface temperature and water vapor are critical to the understanding of dust LW aerosol forcing, and must come from other sources. Using well calibrated, spatially and temporally collocated data sets, we have combined the strengths of three sensors from the same satellite to quantify the LW forcing, and show that dust aerosols have a “warming” effect over the Saharan desert that will counteract the shortwave “cooling effect” of other aerosols. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0305 Aerosols and particles
Zhao, Tom X.-P.; Laszlo, Istvan; Dubovik, Oleg; Holben, Brent N.; Sapper, John; Tanré, Didier; Pietras, ChristopheZhao, T. X., I. Laszlo, O. Dubovik, B. N. Holben, J. Sapper, D. Tanré, C. Pietras, 2003: A study of the effect of non-spherical dust particles on the AVHRR aerosol optical thickness retrievals. Geophysical Research Letters, 30(6), 1317. doi: 10.1029/2002GL016379. Non-spherical assumption of particle shape has been used to replace the spherical assumption in the AVHRR aerosol optical thickness (τ) retrievals for dust particles. Retrieved τ with both spherical and non-spherical assumptions have been compared to the surface AERONET observations at two desert dust sites to evaluate and quantify the effect of non-spherical dust particles on the satellite aerosol retrievals. The errors (especially the random error) in the satellite retrieved τ have been reduced as a result of adopting the non-spherical assumption in the NOAA/NESDIS AVHRR aerosol retrieval algorithm. This result suggests the importance of taking into account the effects of non-sphericity in the retrieval of dust particles from AVHRR measurements. 0305 Aerosols and particles; 4801 Aerosols; 0933 Remote sensing; 4548 Ocean fog
Zhao, Tom X.-P.; Laszlo, Istvan; Holben, Brent N.; Pietras, Christophe; Voss, Kenneth J.Zhao, T. X., I. Laszlo, B. N. Holben, C. Pietras, K. J. Voss, 2003: Validation of two-channel VIRS retrievals of aerosol optical thickness over ocean and quantitative evaluation of the impact from potential subpixel cloud contamination and surface wind effect. Journal of Geophysical Research: Atmospheres, 108(D3), 4106. doi: 10.1029/2002JD002346. TRMM/CERES-VIRS Single Satellite Footprint (SSF) data and AERONET Sun/sky radiometer observations from 1998 have been combined to validate SSF aerosol optical thickness (τ) retrievals over ocean along with a quantitative evaluation of the effects of potential subpixel cloud contamination and surface wind on the satellite τ retrievals. Potential subpixel cloud contamination is verified in Visible/Infrared Scanner (VIRS) SSF aerosol retrievals and constitutes a major source of systematic and random errors of the retrieval algorithm as determined from comparisons with AERONET observations. A positive correlation between the surface wind speed (which determines the roughness of the ocean surface) and the SSF τ has been observed for large surface wind speed. The validation results imply this correlation represents the real relationship between the surface wind and the wind-driven aerosols rather than the disturbing effect of the surface reflectance associated with the rough ocean surface. After the potential subpixel cloud contamination is minimized and the effects of large surface wind are removed in the τ match-ups, the positive biases in the SSF τ (compared to AERONET τ) for mean conditions have been reduced from 0.05 to 0.02 in VIRS channel 1 (0.63 μm) and 0.05 to 0.03 in channel 2 (1.61 μm). Random errors have also been reduced from 0.09 to 0.06 at 0.63 μm, and from 0.06 to 0.05 at 1.61 μm. The validation results support the application of the SSF aerosol data in radiation and climate studies as well as supply useful guidance for the adjustment and improvement of the aerosol retrieval algorithm. Remote sensing; 0360 Radiation: transmission and scattering; 0305 Aerosols and particles; 0345 Pollution: urban and regional; 0365 Troposphere: composition and chemistry; validation; aerosol retrieval; cloud contamination
Allan, Richard P.; Ramaswamy, V.; Slingo, A.Allan, R. P., V. Ramaswamy, A. Slingo, 2002: Diagnostic analysis of atmospheric moisture and clear-sky radiative feedback in the Hadley Centre and Geophysical Fluid Dynamics Laboratory (GFDL) climate models. Journal of Geophysical Research: Atmospheres, 107(D17), 4329. doi: 10.1029/2001JD001131. The interannual variability of the hydrological cycle is diagnosed from the Hadley Centre and Geophysical Fluid Dynamics Laboratory (GFDL) climate models, both of which are forced by observed sea surface temperatures. The models produce a similar sensitivity of clear-sky outgoing longwave radiation to surface temperature of ∼2 W m−2 K−1, indicating a consistent and positive clear-sky radiative feedback. However, differences between changes in the temperature lapse-rate and the height dependence of moisture fluctuations suggest that contrasting mechanisms bring about this result. The GFDL model appears to give a weaker water vapor feedback (i.e., changes in specific humidity). This is counteracted by a smaller upper tropospheric temperature response to surface warming, which implies a compensating positive lapse-rate feedback. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1610 Atmosphere; Feedback; water vapor; 1878 Water/energy interactions; climate model; temperature lapse-rate
Allan, Richard P.; Slingo, A.Allan, R. P., A. Slingo, 2002: Can current climate model forcings explain the spatial and temporal signatures of decadal OLR variations?. Geophysical Research Letters, 29(7), 45-1. doi: 10.1029/2001GL014620. Top of atmosphere broadband radiative fluxes derived from satellite measurements exhibit surprisingly large decadal variability in the tropics which appears to be related to changes in cloudiness. Climate models fail to reproduce these changes, even when all of the currently known climate forcing agents are prescribed. The interannual variability and spatial signal of the observed changes are analysed and compared to various configurations of the Hadley Centre climate model. Applying EOF analysis to the spatial patterns of the variability shows that these are dominated by El Niño in both the satellite data and the model. However, the second EOF reveals the pattern due to the observed decadal-scale variation in outgoing longwave radiation (OLR), but this is not captured by the climate model. This suggests that either the model lacks some internal physical process or some additional external forcing that is responsible for the observed changes in OLR. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1610 Atmosphere; 3360 Meteorology and Atmospheric Dynamics: Remote sensing
Allan, Richard P.; Slingo, A.; Ringer, M. A.Allan, R. P., A. Slingo, M. A. Ringer, 2002: Influence of Dynamics on the Changes in Tropical Cloud Radiative Forcing during the 1998 El Niño. J. Climate, 15(14), 1979-1986. doi: 10.1175/1520-0442(2002)015<1979:IODOTC>2.0.CO;2. Abstract Satellite measurements of the radiation budget and data from the U.S. National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis are used to investigate the links between anomalous cloud radiative forcing over the tropical west Pacific warm pool and the tropical dynamics and sea surface temperature (SST) distribution during 1998. The ratio, N, of the shortwave cloud forcing (SWCF) to longwave cloud forcing (LWCF) (N = −SWCF/LWCF) is used to infer information on cloud altitude. A higher than average N during 1998 appears to be related to two separate phenomena. First, dynamic regime-dependent changes explain high values of N (associated with low cloud altitude) for small magnitudes of SWCF and LWCF (low cloud fraction), which reflect the unusual occurrence of mean subsiding motion over the tropical west Pacific during 1998, associated with the anomalous SST distribution. Second, Tropics-wide long-term changes in the spatial-mean cloud forcing, independent of dynamic regime, explain the higher values of N during both 1998 and in 1994/95. The changes in dynamic regime and their anomalous structure in 1998 are well simulated by version HadAM3 of the Hadley Centre climate model, forced by the observed SSTs. However, the LWCF and SWCF are poorly simulated, as are the interannual changes in N. It is argued that improved representation of LWCF and SWCF and their dependence on dynamical forcing are required before the cloud feedbacks simulated by climate models can be trusted.
Almasri, M.; Celik-Butler, Z.; Butler, D. P.; Yaradanakul, A.; Yildiz, A.Almasri, M., Z. Celik-Butler, D. P. Butler, A. Yaradanakul, A. Yildiz, 2002: Uncooled multimirror broad-band infrared microbolometers. Journal of Microelectromechanical Systems, 11(5), 528-535. doi: 10.1109/jmems.2002.803413. A new generation of microbolometers were designed, fabricated and tested for the NASA CERES (Clouds and the Earth's Radiant Energy System) instrument to measure the radiation flux at the Earth's surface and the radiant energy flow within the atmosphere. These detectors are designed to measure the earth radiances in three spectral channels consisting of a short wave channel of 0.3 to 5 mum, a wide-band channel of 0.3 to 100 mum and a window channel from 8 to 12 pm each housing a 1.5 mm x 1.5 mm microbolometers or alternatively 400 pm x 400 pm microbolometers in a 1 x 4 array of detectors in each of the three wavelength bands, thus yielding a total of 12 channels. The microbolometers were fabricated by radio frequency (RF) magnetron sputtering at ambient temperature, using polyimide sacrificial layers and standard micromachining techniques. A semiconducting YBaCuO thermometer was employed. A double micromirror structure with multiple resonance cavities was designed to achieve a relatively uniform absorption from 0.3 to 100 pin wavelength. Surface micromachining techniques in conjunction with a polyimide sacrificial layer were utilized to create a gap underneath the detector and the Si3N4 bridge layer. The temperature coefficient of resistance was measured to be -2.8%/K. The voltage responsivities were over 10degrees V/W, detectivities above 10(8) cm Hz(1/2)/W, noise equivalent power less than 4 x 10(-10)W/Hz(1/2) and thermal time constant less than 15 ms.
Andronache, C.; Donner, , L. J.; Seman, , C. J.; Hemler, R. S.Andronache, C., . Donner, . Seman, R. S. Hemler, 2002: A study of the impact of the Intertropical Convergence Zone on aerosols during INDOEX. Journal of Geophysical Research: Atmospheres, 107(D19), 8027. doi: 10.1029/2001JD900248. We report model simulations of the effect of deep convection on aerosol under typical Intertropical Convergence Zone (ITCZ) conditions in the tropical Indian Ocean as encountered during the Indian Ocean Experiment (INDOEX). Measurements taken during various phases of INDOEX showed significant aerosol mass concentrations of nss-sulfate, carbonaceous, and mineral dust over the northern Indian Ocean. During the winter dry season these aerosol species accumulate and are transported long distances to the tropical regions. In contrast, aerosol measurements south of the ITCZ exhibit significantly lower aerosol concentrations, and the convective activity, mixing, and wet removal in the ITCZ are responsible for their depletion. Our results, based on a cloud-resolving model, driven by National Centers for Environmental Prediction analysis, show that convection and precipitation can remove significant amounts of aerosol, as observed in the Indian Ocean ITCZ. The aerosol lifetime in the boundary layer (BL) is of the order of hours in intense convection with precipitation, but on average is in the range of 1–3 days for the case studied here. Since the convective events occur in a small fraction of the ITCZ area, the aerosol lifetime can vary significantly due to variability of precipitation. Our results show that the decay in concentration of various species of aerosols is comparable with in situ measurements and that the ITCZ can act to reduce the transport of polluted air masses into the Southern Hemisphere especially in cases with significant precipitation. Another finding is that aerosol loading typical to north of ITCZ tends to induce changes in cloud microphysical properties. We found that a difference between clean air masses as those encountered south of the ITCZ to aerosol polluted air masses as encountered north of the ITCZ is associated with a slight decrease of the cloud droplet effective radius (average changes of about 2 μm) and an increase in cloud droplet number concentration (average changes by about 40 to 100 cm−3) consistent with several in situ measurements. Thus polluted air masses from the northern Indian Ocean are associated with altered microphysics, and the extent of these effects is dependent on the efficiency of aerosol removal by ITCZ precipitation and dilution by mixing with pristine air masses from the Southern Hemisphere. INDOEX; 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution--urban and regional (0305); 0365 Troposphere: composition and chemistry; 0368 Troposphere: constituent transport and chemistry; aerosol removal; aerosols and clouds; indirect effect; ITCZ; tropospheric aerosols
Chambers, Lin H.; Lin, Bing; Young, David F.Chambers, L. H., B. Lin, D. F. Young, 2002: Examination of New CERES Data for Evidence of Tropical Iris Feedback. J. Climate, 15(24), 3719-3726. doi: 10.1175/1520-0442(2002)015<3719:EONCDF>2.0.CO;2. Abstract New data products from the Clouds and the Earth's Radiant Energy System (CERES) instrument on the Tropical Rainfall Measuring Mission Satellite have been examined in the context of the recently proposed adaptive tropical infrared Iris hypothesis. The CERES Single Scanner Footprint data products combine radiative fluxes with cloud properties obtained from a co-orbiting imaging instrument. This enables the use of cloud property–based definitions of the various regions in the simple Iris climate model. Regardless of definition, the radiative properties are found to be different from those assigned in the original Iris hypothesis. As a result, the strength of the feedback effect is reduced by a factor of 10 or more. Contrary to the initial Iris hypothesis, most of the definitions tested in this paper result in a small positive feedback. Thus, the existence of an effective infrared iris to counter greenhouse warming is not supported by the CERES data.
Chambers, Lin; Lin, Bing; Wielicki, Bruce; Hu, Yongxiang; Xu, Kuan-ManChambers, L., B. Lin, B. Wielicki, Y. Hu, K. Xu, 2002: Comments on "The iris hypothesis: A negative or positive cloud feedback?" - Reply. J. Climate, 15(18), 2716-2717. doi: 10.1175/1520-0442(2002)015<2716:R>2.0.CO;2.
Chen, Junye; Carlson, Barbara E.; Genio, Anthony D. DelChen, J., B. E. Carlson, A. D. D. Genio, 2002: Evidence for Strengthening of the Tropical General Circulation in the 1990s. Science, 295(5556), 838-841. doi: 10.1126/science.1065835. Satellite observations suggest that the thermal radiation emitted by Earth to space increased by more than 5 watts per square meter, while reflected sunlight decreased by less than 2 watts per square meter, in the tropics over the period 1985–2000, with most of the increase occurring after 1990. By analyzing temporal changes in the frequency of occurrence of emitted thermal and reflected solar fluxes, the effects of El Niño–Southern Oscillation are minimized, and an independent longer-time-scale variation of the radiation budget is identified. Similar analyses of upper tropospheric humidity, cloud amount, surface air temperature, and vertical velocity confirm that these flux changes are associated with a decadal-time-scale strengthening of the tropical Hadley and Walker circulations. Equatorial convective regions have intensified in upward motion and moistened, while both the equatorial and subtropical subsidence regions have become drier and less cloudy.
Chen, Ting; Rossow, William B.Chen, T., W. B. Rossow, 2002: Determination of top-of-atmosphere longwave radiative fluxes: A comparison between two approaches using ScaRaB data. Journal of Geophysical Research: Atmospheres, 107(D8), ACL 6-1. doi: 10.1029/2001JD000914. Two conceptually different approaches (broadband-based ERBE (Earth Radiation Budget Experiment) and narrowband-based ISCCP (International Satellite Cloud Climatology Project) approaches), used to derive the TOA (top of atmosphere) longwave radiative fluxes, are compared using the ScaRaB simultaneous narrowband and broadband measurements. Except for very thin cirrus clouds, differences between the ERBE and the ISCCP approaches are in general ERBE; longwave; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3399 Meteorology and Atmospheric Dynamics: General or miscellaneous; ADM; ISCCP; radiation; ScaRaB
Chepfer, Helene; Minnis, Patrick; Young, David; Nguyen, Louis; Arduini, Robert F.Chepfer, H., P. Minnis, D. Young, L. Nguyen, R. F. Arduini, 2002: Estimation of cirrus cloud effective ice crystal shapes using visible reflectances from dual-satellite measurements. Journal of Geophysical Research: Atmospheres, 107(D23), 4730. doi: 10.1029/2000JD000240. This study develops and examines a multiangle, multisatellite method for determining effective cloud particle shapes from reflectances observed at visible wavelengths. The technique exploits the significant differences in the various cloud particle shape phase functions near the backscatter direction to infer particle shape from a combination of views from a near-backscatter angle and a side scattering angle. Adding-doubling calculations confirm that the optimal viewing combinations include one near-backscatter angle and another between 60° and 150°. Sensitivity to shape increases with solar zenith angle. A total of 28 collocated, visible images from pairs of currently operating meteorological satellites with the desired viewing combinations were analyzed for particle shape. Matching reflectances from images with optimal viewing angles clearly separates water droplet from ice crystal clouds. Reflectance pairs from matched pixels containing ice crystals can be explained by the range of selected microphysical models. The most common retrieved shapes correspond to combinations of hexagonal compacts (aspect ratio of unity), hexagonal columns, and bullet rosettes. Although no single microphysical model can account for the observed variability, taken together, the models used for retrieving cloud particle size by the Clouds and the Earth's Radiant Energy System and the Moderate Resolution Imaging Spectroradiometer Projects can account for most of the reflectance variability observed in this limited data set. Additional studies are needed to assess the uncertainties in retrieved shapes due to temporal and spatial mismatches, anisotropic and bright background reflectances, and calibration errors and to validate the retrieved shapes. While applicable to a limited number of dual-satellite viewing combinations for current research and operational meteorological satellites, this approach could be used most extensively to derive effective particle size, shape, and optical depth from a combination of an imaging satellite in an L1 orbit, like Triana, and any other lower Earth orbiting satellites. 1610 Atmosphere; 1640 Remote sensing; 0320 Cloud physics and chemistry; 0394 Instruments and techniques; ice clouds; crystal shape; geostationary satellites
Chiacchio, Marc; Francis, Jennifer; Stackhouse, PaulChiacchio, M., J. Francis, P. Stackhouse, 2002: Evaluation of Methods to Estimate the Surface Downwelling Longwave Flux during Arctic Winter. Journal of Applied Meteorology, 41(3), 306-318. doi: 10.1175/1520-0450(2002)041<0306:EOMTET>2.0.CO;2. Abstract Surface longwave radiation fluxes dominate the energy budget of nighttime polar regions, yet little is known about the relative accuracy of existing satellite-based techniques to estimate this parameter. We compare eight methods to estimate the downwelling longwave radiation flux and to validate their performance with measurements from two field programs in the Arctic: the Coordinated Eastern Arctic Experiment (CEAREX) conducted in the Barents Sea during the autumn and winter of 1988, and the Lead Experiment performed in the Beaufort Sea in the spring of 1992. Five of the eight methods were developed for satellite-derived quantities, and three are simple parameterizations based on surface observations. All of the algorithms require information about cloud fraction, which is provided from the NASA–NOAA Television and Infrared Observation Satellite (TIROS) Operational Vertical Sounder (TOVS) polar pathfinder dataset (Path-P); some techniques ingest temperature and moisture profiles (also from Path-P); one-half of the methods assume that clouds are opaque and have a constant geometric thickness of 50 hPa, and three include no thickness information whatsoever. With a somewhat limited validation dataset, the following primary conclusions result: 1) all methods exhibit approximately the same correlations with measurements and rms differences, but the biases range from −34 W m−2 (16% of the mean) to nearly 0; 2) the error analysis described here indicates that the assumption of a 50-hPa cloud thickness is too thin by a factor of 2 on average in polar nighttime conditions; 3) cloud-overlap techniques, which effectively increase mean cloud thickness, significantly improve the results; 4) simple Arctic-specific parameterizations performed poorly, probably because they were developed with surface-observed cloud fractions whereas the tests discussed here used satellite-derived effective cloud fractions; and 5) the single algorithm that includes an estimate of cloud thickness exhibits the smallest differences from observations.
Chou, Ming-Dah; Chan, Pui-King; Wang, MenghuaChou, M., P. Chan, M. Wang, 2002: Aerosol Radiative Forcing Derived from SeaWiFS-Retrieved Aerosol Optical Properties. J. Atmos. Sci., 59(3), 748-757. doi: 10.1175/1520-0469(2002)059<0748:ARFDFS>2.0.CO;2. Abstract To understand climatic implications of aerosols over global oceans, the aerosol optical properties retrieved from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) are analyzed, and the effects of the aerosols on the earth's radiation budgets [aerosol radiative forcing (ARF)] are computed using a radiative transfer model. It is found that the distribution of the SeaWiFS-retrieved aerosol optical thickness is distinctively zonal. The maximum in the equatorial region coincides with the intertropical convergence zone, and the maximum in the Southern Hemispheric high latitudes coincides with the region of prevailing westerlies. The minimum aerosol optical thickness is found in the subtropical high pressure regions, especially in the Southern Hemisphere. These zonal patterns clearly demonstrate the influence of atmospheric circulation on the oceanic aerosol distribution. Over global oceans, aerosols reduce the annual-mean net downward solar flux by 5.4 W m−2 at the top of the atmosphere, and by 5.9 W m−2 at the surface. The largest ARF is found in the tropical Atlantic, Arabian Sea, Bay of Bengal, the coastal regions of Southeast and East Asia, and the Southern Hemispheric high latitudes. During the period of the big Indonesian fires (September–December 1997), the cooling due to aerosols is more than 10 W m−2 at the top of the atmosphere, and more than 25 W m−2 at the surface in the vicinity of Indonesia. The atmosphere receives extra solar radiation by more than 15 W m−2 over a large area. These large changes in radiative fluxes are expected to have enhanced the atmospheric stability, weakened the atmospheric circulation, and augmented the drought condition during that period. It would be very instructive to simulate the regional climatic impact of the big Indonesian fires during the 1987–88 El Niño event using a general circulation model.
Chou, Ming-Dah; Lindzen, Richard S.Chou, M., R. S. Lindzen, 2002: Comments on “Tropical Convection and the Energy Balance at the Top of the Atmosphere”. J. Climate, 15(17), 2566-2570. doi: 10.1175/1520-0442(2002)015<2566:COTCAT>2.0.CO;2.
Chou, Ming-Dah; Lindzen, Richard S.; Hou, Arthur Y.Chou, M., R. S. Lindzen, A. Y. Hou, 2002: Comments on “The Iris Hypothesis: A Negative or Positive Cloud Feedback?”. J. Climate, 15(18), 2713-2715. doi: 10.1175/1520-0442(2002)015<2713:COTIHA>2.0.CO;2.
Christopher, S. A.; Zhang, J.; Holben, B. N.; Yang, S.-K.Christopher, S. A., J. Zhang, B. N. Holben, S. Yang, 2002: GOES-8 and NOAA-14 AVHRR retrieval of smoke aerosol optical thickness during SCAR-B. International Journal of Remote Sensing, 23(22), 4931-4944. doi: 10.1080/01431160110111045. Using the NOAA-14 1-km Advanced Very High Resolution Radiometer (AVHRR) and the Geostationary Operational Environmental Satellite (GOES-8) imager data, smoke aerosol optical thickness ( ‰ ) is retrieved over land during the Smoke, Clouds and Radiation-Brazil (SCAR-B) experiment in Brazil during August-September 1995. The satellite-retrieved ‰ values are then compared against ground-based sunphotometer derived ‰ values from the Aerosol Robotic Network (AERONET) program. Both the AVHRR and GOES-8 retrieved ‰ values are in excellent agreement with the AERONET derived ‰ values with linear correlation coefficients of 0.93. A single scattering albedo of 0.90 (at 0.67 w m) provides the best fit between the GOES-8 and AERONET ‰ values. The sensitivity of the retrieved ‰ to assumed surface albedo and aerosol single scattering albedo are also examined. A simple multi-spectral thresholding algorithm is used to separate smoke from other features from GOES-8 satellite imagery and regional maps of ‰ are provided. Our results show that the aerosol properties used in this paper are adequate to characterize biomass burning aerosols and can be used in studies that model the role of biomass burning on regional climate.
Christopher, Sundar A.; Zhang, JianglongChristopher, S. A., J. Zhang, 2002: Shortwave Aerosol Radiative Forcing from MODIS and CERES observations over the oceans. Geophysical Research Letters, 29(18), 1859. doi: 10.1029/2002GL014803. Using spatially and temporally collocated data sets from the Clouds and Earth's Radiant Energy System (CERES) and Moderate-Resolution Imaging Spectroradiometer (MODIS) instruments on the Terra satellite, a new strategy is presented for studying the Shortwave Aerosol Radiative Forcing (SWARF) over the global oceans. Using collocated data, for September 2000, the global averaged optical thickness (τ0.55) for cloud-free CERES pixels is 0.07 with a SWARF of −6 Wm−2. The τ0.55 and SWARF values derived from two independent instruments are in excellent agreement with the following relationship: SWARF = 0.35 −105.34τ0.55 +61.47τ0.552 (0 ≤ τ0.55 ≤ 0.7) Wm−2. The synergistic use of the MODIS and CERES data sets can be used to provide independent estimates of SWARF, and can be used as a validation tool for studies that attempt to model the role of aerosols on climate. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0305 Aerosols and particles
Christopher, Sundar A.; Zhang, JianglongChristopher, S. A., J. Zhang, 2002: Daytime Variation of Shortwave Direct Radiative Forcing of Biomass Burning Aerosols from GOES-8 Imager. J. Atmos. Sci., 59(3), 681-691. doi: 10.1175/1520-0469(2002)059<0681:DVOSDR>2.0.CO;2. Abstract Hourly Geostationary Operational Environmental Satellite-8 (GOES-8) imager data (1344–1944 UTC) from 20 July–31 August 1998 were used to study the daytime variation of shortwave direct radiative forcing (SWARF) of smoke aerosols over biomass burning regions in South America (4°–16°S, 51°–65°W). Vicarious calibration procedures were used to adjust the GOES visible channel reflectance values for the degradation in signal response. Using Mie theory and discrete ordinate radiative transfer (DISORT) calculations, smoke aerosol optical thickness (AOT) was estimated at 0.67 μm. The GOES-retrieved AOT was then compared against ground-based AOT retrieved values. Using the retrieved GOES-8 AOT, a four-stream broadband radiative transfer model was used to compute shortwave fluxes for smoke aerosols at the top of the atmosphere (TOA). The daytime variation of smoke AOT and SWARF was examined for the study area. For selected days, the Clouds and the Earth's Radiant Energy System (CERES) TOA shortwave (SW) fluxes are compared against the model-derived SW fluxes. Results of this study show that the GOES-derived AOT is in excellent agreement with Aerosol Robotic Network (AERONET)-derived AOT values with linear correlation coefficient of 0.97. The TOA CERES-estimated SW fluxes compare well with the model-calculated SW fluxes with linear correlation coefficient of 0.94. For August 1998 the daytime diurnally averaged AOT and SWARF for the study area is 0.63 ± 0.39 and −45.8 ± 18.8 W m−2, respectively. This is among the first studies to estimate the daytime diurnal variation of SWARF of smoke aerosols using satellite data.
Coakley, James A.; Tahnk, William R.; Jayaraman, A.; Quinn, Patricia K.; Devaux, Claude; Tanré, DidierCoakley, J. A., W. R. Tahnk, A. Jayaraman, P. K. Quinn, C. Devaux, D. Tanré, 2002: Aerosol optical depths and direct radiative forcing for INDOEX derived from AVHRR: Theory. Journal of Geophysical Research: Atmospheres, 107(D19), INX2 8-1. doi: 10.1029/2000JD000182. A scheme is presented for retrieving aerosol properties for ocean regions from reflected sunlight at both the visible and near infrared wavelengths measured by the NOAA advanced very high resolution radiometer (AVHRR). For the Indian Ocean Experiment (INDOEX), aerosols were presumed to be a mixture of a continental haze that had small particles, contained soot, and absorbed sunlight, and a marine haze that had large particles and absorbed practically no sunlight. Because of the difference in particle sizes, the two aerosols reflect sunlight differently at visible and near infrared wavelengths. Reflectances at visible and near infrared wavelengths were thus used to determine mixing fractions for the continental and marine aerosols and the optical depth of the aerosol mixture. The fractions and optical depths along with the optical properties of the aerosols were then used in radiative transfer calculations to estimate the diurnally averaged top of the atmosphere and surface aerosol direct radiative forcing for ocean regions. Comparison of retrieved optical depths at visible and near infrared wavelengths with surface measurements revealed that several different retrieval schemes employing a variety of aerosol types provided comparable levels of agreement, but none of the aerosol models or retrieval schemes produced ratios of the near infrared to visible optical depths that agreed with the ratios obtained with the surface measurements. In estimating the top of the atmosphere radiative forcing, errors in the retrieved optical depths were in some cases found to be partially compensated by the effect of the aerosol on the radiative flux. For example, different aerosol models led to retrieved optical depths that differed by as much as 60%, but the top of the atmosphere forcing obtained with the models differed by less than 35% for cloud-free conditions. When aerosols absorb sunlight, there is no comparable compensation for the surface forcing. Cloud conditions contribute sizable uncertainties to estimates of the aerosol direct radiative forcing. For INDOEX, estimates of the aerosol direct radiative forcing for average cloud conditions were obtained by (1) setting the forcing to zero for all 1° × 1° latitude-longitude boxes that contained any amount of upper-level cloud; (2) ascribing to regions with upper-level clouds the radiative forcing obtained for regions having only low-level clouds and, (3) setting the forcing to zero for all regions containing upper-level clouds and all portions of regions overcast by low-level clouds. Relative differences in the extreme values for the top of the atmosphere aerosol direct radiative forcing were less than 50%, but for the surface, the relative differences of the extreme values reached 70%. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1640 Remote sensing; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0305 Aerosols and particles; aerosols; Aerosol optical depth; INDOEX; radiative forcing of climate; remote sensing of aerosols
Del Genio, Anthony D.; Kovari, WilliamDel Genio, A. D., W. Kovari, 2002: Climatic Properties of Tropical Precipitating Convection under Varying Environmental Conditions. J. Climate, 15(18), 2597-2615. doi: 10.1175/1520-0442(2002)015<2597:CPOTPC>2.0.CO;2. Abstract A clustering algorithm is used to define the radiative, hydrological, and microphysical properties of precipitating convective events in the equatorial region observed by the Tropical Rainfall Measuring Mission (TRMM) satellite. Storms are separated by surface type, size, and updraft strength, the latter defined by the presence or absence of lightning. SST data and global reanalysis products are used to explore sensitivity to changes in environmental conditions. Small storms are much more numerous than mesoscale convective systems, and account for fairly little of the total rainfall but contribute significantly to reflection of sunlight. Lightning storms rain more heavily, have greater cloud area, extend to higher altitude, and have higher albedos than storms without lightning. Lightning is favored by a steep lower-troposphere lapse rate and moist midlevel humidity. Storms occur more often at SST ≥ 28°C and with strong upward 500-mb mean vertical velocity. In general, storms over warmer ocean waters rain more heavily, are larger, and have higher cloud tops, but they do not have noticeably higher albedos than storms over cooler ocean waters. Mesoscale convective system properties are more sensitive to SST. Rain rates and cloud-top heights increase statistically significantly with mean upward motion. Rain rates increase with albedo and cloud-top height over ocean, but over land there are also storms with cloud-top temperatures >−35°C whose rain rates decrease with increasing albedo. Both the fraction of available moisture that rains out and the fraction that detrains as ice increase with SST, the former faster than the latter. TRMM ice water paths derived from cloud-resolving models but constrained by observed microwave radiances are only weakly correlated with observed albedo. The results are inconsistent with the “adaptive iris” hypothesis and suggest feedbacks due primarily to increasing convective cloud cover with warming, but more weakly than predicted by the “thermostat” hypothesis.
Dong, Xiquan; Mace, Gerald G.; Minnis, Patrick; Smith, William L.; Poellot, Michael; Marchand, Roger T.; Rapp, Anita D.Dong, X., G. G. Mace, P. Minnis, W. L. Smith, M. Poellot, R. T. Marchand, A. D. Rapp, 2002: Comparison of Stratus Cloud Properties Deduced from Surface, GOES, and Aircraft Data during the March 2000 ARM Cloud IOP. J. Atmos. Sci., 59(23), 3265-3284. doi: 10.1175/1520-0469(2002)059<3265:COSCPD>2.0.CO;2. Abstract Low-level stratus cloud microphysical properties derived from surface and Geostationary Operational Environmental Satellite (GOES) data during the March 2000 cloud intensive observational period (IOP) at the Atmospheric Radiation Measurement (ARM) program Southern Great Plains (SGP) site are compared with aircraft in situ measurements. For the surface retrievals, the cloud droplet effective radius and optical depth are retrieved from a δ2-stream radiative transfer model with the input of ground-based measurements, and the cloud liquid water path (LWP) is retrieved from ground-based microwave-radiometer-measured brightness temperature. The satellite results, retrieved from GOES visible, solar-infrared, and infrared radiances, are averaged in a 0.5° × 0.5° box centered on the ARM SGP site. The forward scattering spectrometer probe (FSSP) on the University of North Dakota Citation aircraft provided in situ measurements of the cloud microphysical properties. During the IOP, four low-level stratus cases were intensively observed by the ground- and satellite-based remote sensors and aircraft in situ instruments resulting in a total of 10 h of simultaneous data from the three platforms. In spite of the large differences in temporal and spatial resolution between surface, GOES, and aircraft, the surface retrievals have excellent agreement with the aircraft data overall for the entire 10-h period, and the GOES results agree reasonably well with the surface and aircraft data and have similar trends and magnitudes except for the GOES-derived effective radii, which are typically larger than the surface- and aircraft-derived values. The means and standard deviations of the differences between the surface and aircraft effective radius, LWP, and optical depth are −4% ± 20.1%, −1% ± 31.2%, and 8% ± 29.3%, respectively; while their correlation coefficients are 0.78, 0.92, and 0.89, respectively, during the 10-h period. The differences and correlations between the GOES-8 and aircraft results are of a similar magnitude, except for the droplet sizes. The averaged GOES-derived effective radius is 23% or 1.8 μm greater than the corresponding aircraft values, resulting in a much smaller correlation coefficient of 0.18. Additional surface–satellite datasets were analyzed for time periods when the aircraft was unavailable. When these additional results are combined with the retrievals from the four in situ cases, the means and standard deviations of the differences between the satellite-derived cloud droplet effective radius, LWP, and optical depth and their surface-based counterparts are 16% ± 31.2%, 4% ± 31.6%, and −6% ± 39.9%, respectively. The corresponding correlation coefficients are 0.24, 0.88, and 0.73. The frequency distributions of the two datasets are very similar indicating that the satellite retrieval method should be able to produce reliable statistics of boundary layer cloud properties for use in climate and cloud process models.
Duda, David P.; Minnis, PatrickDuda, D. P., P. Minnis, 2002: Observations of Aircraft Dissipation Trails from GOES. Mon. Wea. Rev., 130(2), 398-406. doi: 10.1175/1520-0493(2002)130<0398:OOADTF>2.0.CO;2. Abstract Two cases of aircraft dissipation trails (distrails) with associated fall streak clouds were analyzed with multispectral geostationary satellite data. One dissipation trail was observed in a single cloud layer on 23 July 2000 over southeastern Virginia and the Chesapeake Bay. Another set of trails developed at the top of multilayer cloudiness off the coasts of Georgia and South Carolina on 6 January 2000. The distrails on both days formed in optically thin, midlevel stratified clouds with cloud-top heights between 7.6 and 9.1 km. The distrail features remained intact and easily visible from satellite images over a period of 1–2 h despite winds near 50 kt at cloud level. The width of the distrails became as large as 20 km within a period of 90 min or less. Differences between the optical properties of the fall streak particles inside the distrails and those of the clouds surrounding the trails allowed for the easy identification of the fall streak clouds in either the 3.9-μm brightness temperature imagery, or the 10.7-μm minus 12.0-μm brightness temperature difference imagery. Two independent remote sensing retrievals of both distrail cases showed that the fall streaks had larger particle sizes than the clouds outside of the trails, although the three-channel infrared retrieval was better at retrieving cloud properties in the multilayer cloud case.
Fowler, Laura D.; Randall, David A.Fowler, L. D., D. A. Randall, 2002: Interactions between Cloud Microphysics and Cumulus Convection in a General Circulation Model. J. Atmos. Sci., 59(21), 3074-3098. doi: 10.1175/1520-0469(2002)059<3074:IBCMAC>2.0.CO;2. Abstract In the Colorado State University general circulation model, cumulus detrainment of cloud water and cloud ice has been, up to now, the only direct coupling between convective and large-scale condensation processes. This one-way interaction from the convective to the large-scale environment parameterizes, in a highly simplified manner, the growth of anvils spreading horizontally at the tops of narrow cumulus updrafts. The reverse interaction from the large-scale to the convective updrafts, through which large-scale cloud water and cloud ice can affect microphysical processes occurring in individual convective updrafts, is missing. In addition, the effects of compensating subsidence on cloud water and cloud ice are not taken into account. A new parameterization of convection, called “EAUCUP,” has been developed, in which large-scale water vapor, cloud water, and cloud ice are allowed to enter the sides of the convective updrafts and can be lifted to the tops of the clouds. As the various water species are lifted, cloud microphysical processes take place, removing excess cloud water and cloud ice in the form of rain and snow. The partitioning of condensed vapor between cloud water and cloud ice, and between rain and snow, is based on temperature. The effects of compensating subsidence on the large-scale water vapor, cloud water, and cloud ice are computed separately. Convective rain is assumed to fall instantaneously to the surface. Three treatments of the convective snow are tested: 1) assuming that all snow is detrained at the tops of convective updrafts, 2) assuming that all snow falls outside of the updrafts and may evaporate, and 3) assuming that snow falls entirely inside the updrafts and melts to form rain. Including entrainment of large-scale cloud water and cloud ice inside the updrafts, large-scale compensating subsidence unifies the parameterizations of large-scale cloud microphysics and convection, but have a lesser impact than the treatment of convective snow on the simulated climate. Differences between the three alternate treatments of convective snow are discussed. Emphasis is on the change in the convective, large-scale, and radiative tendencies of temperature, and change in the convective and large-scale tendencies of water vapor, cloud water, cloud ice, and snow. Below the stratiform anvils, the change in latent heating due to the change in both convective and large-scale heatings contributes a major part to the differences in diabatic heating among the three simulations. Above the stratiform anvils, differences in the diabatic heating between the three simulations result primarily because of differences in the longwave radiative cooling. In particular, detraining convective snow at the tops of convective updrafts yields a strong increase in the longwave radiative cooling associated with increased upper-tropospheric cloudiness. The simulated climate is wetter and colder when convective snow is detrained at the tops of the updrafts than when it is detrained on the sides of the updrafts or when it falls entirely inside the updrafts. This result highlights the importance of the treatment of the ice phase and associated precipitation in the convective cloud models used in cumulus parameterizations.
Han, Qingyuan; Rossow, William B.; Zeng, Jian; Welch, RonaldHan, Q., W. B. Rossow, J. Zeng, R. Welch, 2002: Three Different Behaviors of Liquid Water Path of Water Clouds in Aerosol–Cloud Interactions. J. Atmos. Sci., 59(3), 726-735. doi: 10.1175/1520-0469(2002)059<0726:TDBOLW>2.0.CO;2. Abstract Estimates of the indirect aerosol effect in GCMs assume that either cloud liquid water path is constant (Twomey effect) or increases with increased droplet number concentration (drizzle-suppression or Albrecht effect). On the other hand, if cloud thermodynamics and dynamics are considered, cloud liquid water path may also decrease with increasing droplet number concentration, which has been predicted by model calculations and observed in ship track and urban influence studies. This study examines the different changes of cloud liquid water path associated with changes of cloud droplet number concentration. Satellite data (January, April, July, and October 1987) are used to determine the cloud liquid water sensitivity, defined as the ratio of changes of liquid water path and changes of column droplet number concentration. The results of a global survey for water clouds (cloud-top temperature >273 K, optical thickness 1 ≤ τ < 15) reveal all three behaviors of cloud liquid water path with aerosol changes: increasing, approximately constant, or decreasing as cloud column number concentration increases. The authors find that 1) in about one-third of the cases, predominantly in warmer locations or seasons, the cloud liquid water sensitivity is negative, and the regional and seasonal variations of the negative liquid water sensitivity are consistent with other observations; 2) in about one-third of the cases, a minus one-third (−1/3) power-law relation between effective droplet radius and column number concentration is found, consistent with a nearly constant cloud water path; and 3) in the remaining one-third of the cases, the cloud liquid water sensitivity is positive. These results support the suggestion that it is possible for an increase of cloud droplet number concentration to both reduce cloud droplet size and enhance evaporation just below cloud base, which decouples the cloud from the boundary layer in warmer locations, decreasing water supply from surface and reducing cloud liquid water. Results of this study also suggest that the current evaluations of the negative aerosol indirect forcing by GCMs, which are based on either the Twomey or Albrecht effects, may be overestimated in magnitude.
Ignatov, AlexanderIgnatov, A., 2002: Sensitivity and information content of aerosol retrievals from the Advanced Very High Resolution Radiometer: radiometric factors. Applied Optics, 41(6), 991-1011. doi: 10.1364/AO.41.000991. The sensitivity of aerosol optical depths τ1 and τ2 derived from the Advanced Very High Resolution Radiometer (AVHRR) channels 1 and 2, centered at λ1 = 0.63 and λ2 = 0.83 µm, respectively, and of an effective Ångstrom exponent α, derived therefrom as α = -ln(τ1/τ2)/ln(λ1/λ2), to calibration uncertainties, radiometric noise, and digitization is estimated. Analyses are made both empirically (by introduction of perturbations into the measured radiances and estimation of the respective partial derivatives) and theoretically (by use of a decoupled form of the single-scattering approximation of the radiative transfer equation). The two results are in close agreement. The errors, Δτi and Δαi, are parameterized empirically as functions of τi, radiometric errors, and Sun and view geometry. In particular, the α errors change in approximately inverse proportion to τ and are comparable with, or even exceed, typical α signals over oceans when τ < 0.25. Their detrimental effect on the information content of the AVHRR-derived size parameter gradually weakens as τ increases. aerosols; radiometry; Atmospheric scattering; Aerosol detection; Remote sensing and sensors
Ignatov, Alexander; Nalli, Nicholas R.Ignatov, A., N. R. Nalli, 2002: Aerosol Retrievals from the Multiyear Multisatellite AVHRR Pathfinder Atmosphere (PATMOS) Dataset for Correcting Remotely Sensed Sea Surface Temperatures. J. Atmos. Oceanic Technol., 19(12), 1986-2008. doi: 10.1175/1520-0426(2002)019<1986:ARFTMM>2.0.CO;2. Abstract Eight-year (1990–98), two-satellite (NOAA-11 and -14), global daily ∼(110 km)2 gridded observations from the Advanced Very High Resolution Radiometer (AVHRR) Pathfinder Atmosphere (PATMOS) dataset have been previously merged with the Pathfinder Matchup Database (PFMDB) and used to develop the Phase I aerosol correction for sea surface temperatures (SSTs) from AVHRR. In this study, this unique PATMOS–BUOY matchup dataset (N = 105 831) is used to derive and quality control an advanced set of aerosol parameters to be used in the Phase II algorithm: aerosol optical depths in channels 1 (λ1 = 0.63 μm) and 2 (λ2 = 0.83 μm), τ1 and τ2, and Ångström exponent α = −ln(τ1/τ2)/ln(λ1/λ2). Inaccurate retrievals at low sun and outliers are removed from the data. PATMOS global, multiyear, multisatellite aerosol properties, derived from cloud-free portions of the (110 km)2 grid, resemble many features previously observed in the space–time-restricted, (8 km)2 resolution Aerosol Observation (AEROBS) operational retrievals, in spite of a different spatial resolution, cloud screening, and sampling. Histograms of τ and α are accurately fit by lognormal and normal probability density functions, respectively. Retrievals of τ2 are consistent with τ1 at low τ, but reveal high multiplicative bias, resulting in a low additive bias in α. Random errors in α are inversely proportional to τ, with signal-to-noise ratio well approximated as η = τ1/τ1o. Parameter τ1o (τ threshold at which signal in α compares to its noise, i.e., η = 1) in PATMOS data (τ1o ∼ 0.11 ± 0.01) is less than in AEROBS (τ1o ∼ 0.18 ± 0.02), since noise is suppressed by the additional spatial averaging in PATMOS. The effect of cloud screening and sampling is also quantified. PATMOS τ1, τ2, and α reveal a strong trend against cloud amount, which is not fully understood, and some residual artificial time/angle trends, due to undercorrected calibration errors and remaining algorithm problems. But overall, they show a high degree of self- and interconsistency, thus providing a superior set of aerosol predictors to be used in the Phase II SST aerosol correction algorithm.
Ignatov, Alexander; Stowe, LarryIgnatov, A., L. Stowe, 2002: Aerosol Retrievals from Individual AVHRR Channels. Part I: Retrieval Algorithm and Transition from Dave to 6S Radiative Transfer Model. J. Atmos. Sci., 59(3), 313-334. doi: 10.1175/1520-0469(2002)059<0313:ARFIAC>2.0.CO;2. Abstract The present second-generation aerosol retrieval algorithm over oceans used at NOAA/National Environmental Satellite, Data, and Information Service (NESDIS) separately retrieves two values of aerosol optical depth, τ1 and τ2, from Advanced Very High Resolution Radiometer (AVHRR) channels 1 and 2 centered at λ1 = 0.63 (operational) and λ2 = 0.83 μm (experimental), respectively. From these, an effective Ångström exponent α, related to particle size, can be derived as α = −ln(τ1/τ2)/ln(λ1/λ2). The single-channel lookup tables, relating reflectance to optical depth in the retrievals, have been precalculated with the Dave (1973) scalar radiative transfer (RT) model. This first part of a two-part paper describes the retrieval algorithm, with emphasis on its RT modeling related elements, and documents the transition to the Second Simulation of the Satellite Signal in the Solar Spectrum (6S; 1997) RT model. The new 6S RT model has the capability to account for reflection from wind-roughened sea surface, offers a wide choice of flexible aerosol and gaseous absorption models, and allows easy convolution with the sensor's spectral response. The value of these new features for aerosol remote sensing from AVHRR is discussed in detail. The transition effect is quantified by directly applying the Dave- and 6S-based algorithms to four large datasets of NOAA-14 AVHRR measurements, collected between February 1998 and May 1999 over the latitudinal belt of 5°–25°S. Statistics of the differences (δτ = τDave − τ6S and δα = αDave − α6S) are as follows: averages − 〈δτ1〉 < 1 × 10−3, 〈δτ2〉 ≈ −4 × 10−3, and 〈δα〉 ≈ +8 × 10−2; and standard deviations are στ1 ∼ 6 × 10−3, στ2 ∼ 4 × 10−3, and σα ≈ 9 × 10−2. These are found to be well within a few percent of typical values of τ and α and their respective ranges of variability, thus ensuring a smooth transition and continuity in the operational aerosol retrieval. On the other hand, the 6S model provides a much more flexible RT modeling tool compared to the previously used Dave code.
Ignatov, Alexander; Stowe, LarryIgnatov, A., L. Stowe, 2002: Aerosol Retrievals from Individual AVHRR Channels. Part II: Quality Control, Probability Distribution Functions, Information Content, and Consistency Checks of Retrievals. J. Atmos. Sci., 59(3), 335-362. doi: 10.1175/1520-0469(2002)059<0335:ARFIAC>2.0.CO;2. Abstract This second part of a two-part study evaluates retrievals of aerosol optical depths, τ1 and τ2, in Advanced Very High Resolution Radiometer (AVHRR) channels 1 and 2 centered at λ1 = 0.63 and λ2 = 0.83 μm, and an effective Ångström exponent, α, derived therefrom as α = −ln(τ1/τ2)/ln(λ1/λ2). The retrievals are made with the Second Simulation of the Satellite Signal in the Solar Spectrum (6S) radiative transfer model from four NOAA-14 AVHRR datasets, collected between February 1998 and May 1999 in the latitudinal belt of 5°–25°S. A series of quality control (QC) checks applied to the retrievals to identify outliers are described. These remove a total of ∼1% of points, which presumably originate from channel misregistration, residual cloud in AVHRR cloud-screened pixels, and substantial deviations from the assumptions used in the retrieval model (e.g., bright coastal and high altitude inland waters). First, from examining histograms of the derived parameters it is found that τ and α are accurately fit by lognormal and normal probability distribution functions (PDFs), respectively. Second, the scattergrams τ1 versus τ2 are analyzed to see if they form a coherent pattern. They do indeed converge at the origin, as expected, but frequently are outside of the expected domain in τ1–τ2 space, defined by two straight lines corresponding to α = 0 and α = 2. This results in a low bias in α, which tends to fill in an interval of α ∈ [−1, 1] rather than α ∈ [0, 2]. Third, scattergrams of α versus τ are used to empirically confirm a previously drawn theoretical conclusion that errors in α are inversely proportional to τ. More in-depth quantitative analyses suggest that the AVHRR-derived Ångström exponent becomes progressively more meaningful when τ > 0.2. Geographical trends are studied to demonstrate that the selected ocean area is reasonably uniform to justify application of consistency checks to reveal angular trends in the retrievals. These checks show that in most cases, the artifacts in the retrieved τ and α are statistically insignificant. On average, the analyses suggest that the retrieved τ1, τ2, and α show a high degree of self- and interconsistency, with the exception of a troublesome May 1999 dataset. The most prominent problem noticed so far is the inconsistency between τ1 and τ2, persistent from one dataset to another, which calls for fine-tuning some (not aerosol-model related) elements of the retrieval algorithm. These adjustments will be discussed elsewhere.
Inoue, Toshiro; Ackerman, Steven A.Inoue, T., S. A. Ackerman, 2002: Radiative Effects of Various Cloud Types as Classified by the Split Window Technique over the Eastern Sub-tropical Pacific Derived from Collocated ERBE and AVHRR Data. Journal of the Meteorological Society of Japan. Ser. II, 80(6), 1383-1394. doi: 10.2151/jmsj.80.1383. The radiative effects of several cloud types as classified by the split window (11 and 12 μm) technique were studied using coincident and collocated Earth Radiation Budget Experiment (ERBE) S-8 data and Advanced Very High Resolution Radiometer (AVHRR) data from NOAA-9. The parameter investigated was cloud radiative forcing (CRF), the difference between clear and cloudy shortwave flux (SW) and longwave flux (OLR) at the top of the atmosphere. In computing the CRF, the accuracy of clear SW and OLR is essential. Clear scene IDs in the ERBE dataset were evaluated using coincident and collocated AVHRR image data. The mean visible reflectance and SW for clear footprints defined by the ERBE are reasonably small and are 3.2% and 89.0 Wm-2, respectively. However, the values computed using our technique are smaller, 2.7% and 83.9 Wm-2, respectively. The use of collocated AVHRR image data improves clear footprint definition and implies that care should be taken when computing CRF from ERBE data alone. The CRF from several cloud types classified by the split window were compared. Cumulonimbus clouds show the largest impact on top of the atmosphere radiation for both SW and OLR. Cirrus and lowlevel cumulus clouds have similar effects on OLR, but large differences between them are seen for SW. The impact of low-level cumulus clouds on SW is much larger than that of cirrus clouds. Some optically thin cirrus clouds show positive cloud radiative forcing (warming effect). The relationships between OLR and cloud types (including cloud-free) as classified by the split window technique were investigated. By using brightness temperature differences between the split window channels, OLR estimation is improved for cloud-free and low-level cumulus clouds when compared with OLR estimated by the National Oceanic and Atmospheric Administration (NOAA) operational algorithm.
Intrieri, J. M.; Fairall, C. W.; Shupe, M. D.; Persson, P. O. G.; Andreas, E. L.; Guest, P. S.; Moritz, R. E.Intrieri, J. M., C. W. Fairall, M. D. Shupe, P. O. G. Persson, E. L. Andreas, P. S. Guest, R. E. Moritz, 2002: An annual cycle of Arctic surface cloud forcing at SHEBA. Journal of Geophysical Research: Oceans, 107(C10), 8039. doi: 10.1029/2000JC000439. We present an analysis of surface fluxes and cloud forcing from data obtained during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment, conducted in the Beaufort and Chuchki Seas and the Arctic Ocean from November 1997 to October 1998. The measurements used as part of this study include fluxes from optical radiometer sets, turbulent fluxes from an instrumented tower, cloud fraction from a depolarization lidar and ceilometer, and atmospheric temperature and humidity profiles from radiosondes. Clear-sky radiative fluxes were modeled in order to estimate the cloud radiative forcing since direct observation of fluxes in cloud-free conditions created large statistical sampling errors. This was particularly true during summer when cloud fractions were typically very high. A yearlong data set of measurements, obtained on a multiyear ice floe at the SHEBA camp, was processed in 20-day blocks to produce the annual evolution of the surface cloud forcing components: upward, downward, and net longwave and shortwave radiative fluxes and turbulent (sensible and latent heat) fluxes. We found that clouds act to warm the Arctic surface for most of the annual cycle with a brief period of cooling in the middle of summer. Our best estimates for the annual average surface cloud forcings are −10 W m−2 for shortwave, 38 W m−2 for longwave, and −6 W m−2 for turbulent fluxes. Total cloud forcing (the sum of all components) is about 30 W m−2 for the fall, winter, and spring, dipping to a minimum of −4 W m−2 in early July. We compare the results of this study with satellite, model, and drifting station data. clouds; Remote sensing; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3394 Meteorology and Atmospheric Dynamics: Instruments and techniques; atmospheric radiation; 3349 Meteorology and Atmospheric Dynamics: Polar meteorology; polar meteorology; forcing
Intrieri, J. M.; Shupe, M. D.; Uttal, T.; McCarty, B. J.Intrieri, J. M., M. D. Shupe, T. Uttal, B. J. McCarty, 2002: An annual cycle of Arctic cloud characteristics observed by radar and lidar at SHEBA. Journal of Geophysical Research: Oceans, 107(C10), SHE 5-1. doi: 10.1029/2000JC000423. The temporal distributions of cloudiness, vertical distribution of cloud boundary heights, and occurrence of liquid phase in clouds are determined from radar and lidar data sets collected from October 1997 to October 1998 during the Surface Heat Budget of the Arctic Ocean (SHEBA) project. The radar/lidar combination was necessary for comprehensive cloud detection over a variety of physical conditions and is significantly more detailed (5–9 s temporal resolution, 30–40 m vertical resolution) than measurements made by surface observers or satellites. The combined measurements revealed that clouds were almost continuously present, with an annual average occurrence of 85%, and displayed an overall annual trend of a cloudier summer and clearer winter. A monthly averaged cloud occurrence maximum of 97% was observed in September and a minimum of 63% was observed in February. Monthly averaged lowest cloud base heights were between 0.25 and 1.0 km above ground level (agl) and monthly averaged highest cloud top heights were between 2.5 and 5.5 km agl, and displayed no significant seasonal variation. The number of cloud layers was typically 1 or 2, with the summer months tending to be multilayered. The lidar utilized depolarization ratios to detect liquid water; the percentage of lidar-observed clouds containing liquid was 73% for the year. The least amount of liquid water phase was observed during December in 25% of the lidar-detected clouds and the maximum was observed during July in 95% of the lidar-detected clouds. Liquid was distributed in a combination of all-liquid and mixed phase clouds, and was detected at altitudes as high as 6.5 km agl and at temperatures as low as −34°C. clouds; Remote sensing; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3309 Meteorology and Atmospheric Dynamics: Climatology; 1694 Instruments and techniques; Climatology; 3349 Meteorology and Atmospheric Dynamics: Polar meteorology; Lidar; polar meteorology; radar
Jin, Zhonghai; Charlock, Thomas P.; Rutledge, KenJin, Z., T. P. Charlock, K. Rutledge, 2002: Analysis of Broadband Solar Radiation and Albedo over the Ocean Surface at COVE. J. Atmos. Oceanic Technol., 19(10), 1585-1601. doi: 10.1175/1520-0426(2002)019<1585:AOBSRA>2.0.CO;2. Abstract A coupled atmosphere–ocean radiative transfer model has been applied to analyze a full year of broadband solar irradiances (up and down) measured over an ocean site 25 km east of the coast of Virginia in the Atlantic. The coupled model treats absorption and scattering by layers for both the atmosphere and the ocean explicitly and consistently. Key input parameters for the model (aerosol optical depth, wind speed, and total precipitable water) are also from in situ measurements. Having more observations to specify properties of the atmosphere than of the ocean, better model–observation agreement is obtained for the downwelling irradiance, which depends primarily on the atmospheric optical properties, than for the upwelling irradiance, which depends heavily on the ocean optical properties. The mean model–observation differences for the ocean surface albedo are generally less than 0.01. However, the modeled upwelling irradiances and albedo over the ocean surface are mostly less than the observations for all seasons, implying that more scattering in the ocean needs to be included in the model calculations. Sensitivity tests indicate that the uncertainties in aerosol optical properties, chlorophyll concentration, wind speed, or foams are not the primary factors for the model–observation differences in the ocean surface albedo, whereas the scattering by air bubbles and/or by suspended materials have the potential to significantly reduce or eliminate the model–observation differences in the ocean surface reflection.
Kanamitsu, Masao; Ebisuzaki, Wesley; Woollen, Jack; Yang, Shi-Keng; Hnilo, J. J.; Fiorino, M.; Potter, G. L.Kanamitsu, M., W. Ebisuzaki, J. Woollen, S. Yang, J. J. Hnilo, M. Fiorino, G. L. Potter, 2002: NCEP–DOE AMIP-II Reanalysis (R-2). Bull. Amer. Meteor. Soc., 83(11), 1631-1643. doi: 10.1175/BAMS-83-11-1631. Abstract The NCEP–DOE Atmospheric Model Intercomparison Project (AMIP-II) reanalysis is a follow-on project to the “50-year” (1948-present) NCEP-NCAR Reanalysis Project. NCEP–DOE AMIP-II reanalysis covers the “20-year” satellite period of 1979 to the present and uses an updated forecast model, updated data assimilation system, improved diagnostic outputs, and fixes for the known processing problems of the NCEP-NCAR reanalysis. Only minor differences are found in the primary analysis variables such as free atmospheric geopotential height and winds in the Northern Hemisphere extratropics, while significant improvements upon NCEP-NCAR reanalysis are made in land surface parameters and land-ocean fluxes. This analysis can be used as a supplement to the NCEP-NCAR reanalysis especially where the original analysis has problems. The differences between the two analyses also provide a measure of uncertainty in current analyses.
Kato, Seiji; Loeb, Norman G.; Rutledge, C. KenKato, S., N. G. Loeb, C. K. Rutledge, 2002: Estimate of top-of-atmosphere albedo for a molecular atmosphere over ocean using Clouds and the Earth's Radiant Energy System measurements. Journal of Geophysical Research: Atmospheres, 107(D19), 4396. doi: 10.1029/2001JD001309. The shortwave broadband albedo at the top of a molecular atmosphere over ocean between 40°N and 40°S is estimated using radiance measurements from the Clouds and the Earth's Radiant Energy System (CERES) instrument and the Visible Infrared Scanner (VIRS) aboard the Tropical Rainfall Measuring Mission satellite. The albedo monotonically increases from 0.059 at a solar zenith angle of 10° to 0.107 at a solar zenith angle of 60°. The estimated uncertainty in the albedo is 3.5 × 10−3 caused by the uncertainty in CERES-derived irradiances, uncertainty in VIRS-derived aerosol optical thicknesses, variations in surface wind speed and variations in ozone and water vapor. The estimated uncertainty is similar in magnitude to the standard deviation of 0.003 that is derived from 72 areas which are divided by 20° latitude by 20° longitude grid boxes. The empirically estimated albedo is compared with the modeled albedo using a radiative transfer model combined with an ocean surface bidirectional reflectivity model. The modeled albedo with standard tropical atmosphere is 0.061 and 0.111 at the solar zenith angles of 10° and 60°, respectively. The empirically estimated albedo can be used to estimate the direct radiative effect of aerosols at the top of the atmosphere over oceans. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1640 Remote sensing; 0305 Aerosols and particles; 4264 Ocean optics; aerosol radiative forcing; molecular atmosphere; ocean surface reflectance; planetary albedo
Kaufman, Yoram J.; Tanré, Didier; Boucher, OlivierKaufman, Y. J., D. Tanré, O. Boucher, 2002: A satellite view of aerosols in the climate system. Nature, 419(6903), 215-223. doi: 10.1038/nature01091. Anthropogenic aerosols are intricately linked to the climate system and to the hydrologic cycle. The net effect of aerosols is to cool the climate system by reflecting sunlight. Depending on their composition, aerosols can also absorb sunlight in the atmosphere, further cooling the surface but warming the atmosphere in the process. These effects of aerosols on the temperature profile, along with the role of aerosols as cloud condensation nuclei, impact the hydrologic cycle, through changes in cloud cover, cloud properties and precipitation. Unravelling these feedbacks is particularly difficult because aerosols take a multitude of shapes and forms, ranging from desert dust to urban pollution, and because aerosol concentrations vary strongly over time and space. To accurately study aerosol distribution and composition therefore requires continuous observations from satellites, networks of ground-based instruments and dedicated field experiments. Increases in aerosol concentration and changes in their composition, driven by industrialization and an expanding population, may adversely affect the Earth's climate and water supply.
Key, Jeffrey R.; Yang, Ping; Baum, Bryan A.; Nasiri, Shaima L.Key, J. R., P. Yang, B. A. Baum, S. L. Nasiri, 2002: Parameterization of shortwave ice cloud optical properties for various particle habits. Journal of Geophysical Research: Atmospheres, 107(D13), AAC 7-1. doi: 10.1029/2001JD000742. The relative importance of ice clouds in the climate system is highly uncertain. Measurements of their microphysical properties are sparse, especially given their complex structure and large variability in particle size, shape, and density. To better understand the role of ice clouds in the climate system, parameterizations of their radiative properties are needed. The shortwave bulk optical properties of seven ice particle shapes, or “habits,” are parameterized as a function of the effective “radius” and ice water content by integrating the scattering properties over 30 in situ size distributions. The particle habits are solid and hollow hexagonal columns, hexagonal plates, two- and three-dimensional bullet rosettes, aggregates of columns, and dendrites. Parameterizations of the volume extinction coefficient, single-scattering albedo, and the asymmetry parameter are presented for 6, 24, and 56 band shortwave schemes from 0.2 to 5.0 μm. Applications to downwelling flux and upwelling radiance calculations indicate that differences in fluxes for various habits can be more than 15%, and differences in retrievals of cloud optical depth from satellite visible reflectances can be more than 50%. clouds; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 0360 Radiation: transmission and scattering; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; radiative transfer; ice particles; Optical properties
Kratz, David P.; Priestley, Kory J.; Green, Richard N.Kratz, D. P., K. J. Priestley, R. N. Green, 2002: Establishing the relationship between the CERES window and total channel measured radiances for conditions involving deep convective clouds at night. Journal of Geophysical Research: Atmospheres, 107(D15), ACL 5-1. doi: 10.1029/2001JD001170. Characterizing the stability of the Clouds and the Earth's Radiant Energy System (CERES) instrument is critical to obtaining accurate measurements of the radiative energy budget of the Earth's atmosphere-surface system. Composed of three broadband radiometers, the CERES instrument measures radiances in the shortwave (>2000 cm−1), infrared window (835–1250 cm−1), and total regions of the spectrum. Such a choice of radiometers does not allow for a straightforward three channel intercomparison of the CERES measurements. We observed, however, the outgoing infrared spectra of high, cold, optically thick clouds were fairly representative of blackbody emission. This observation suggested a potential relationship between the infrared window radiometer and longwave portion of the total radiometer. Using nighttime measurements made by the CERES instrument aboard the Tropical Rainfall Measuring Mission (TRMM) spacecraft during the first eight months of 1998, we were able to determine a highly correlated relationship between the infrared window and total channel radiances for conditions corresponding to high, cold, optically thick clouds. Comparisons were then made between the measurements and reference line-by-line calculations. From these comparisons, a quantified relationship was derived between the total and window channel radiances which could accurately reproduce one set of results from the other. Such a relationship has allowed for the establishment of a three channel intercomparison for the CERES instrument with an accuracy of ∼1% for the case of high, cold, optically thick clouds. An independent relationship based upon the tropical mean is shown to produce results which support the three channel analysis for the deep convective cloud systems. 0360 Radiation: transmission and scattering; 1640 Remote sensing; 0394 Instruments and techniques; 1694 Instruments and techniques; CERES; TRMM; 0325 Evolution of the atmosphere; deep-convective-clouds; infrared-window; radiometer; three-channel-intercomparison
Li, F.; Ramanathan, V.Li, F., V. Ramanathan, 2002: Winter to summer monsoon variation of aerosol optical depth over the tropical Indian Ocean. Journal of Geophysical Research: Atmospheres, 107(D16), AAC 2-1. doi: 10.1029/2001JD000949. The northern Indian Ocean undergoes a major transition from anthropogenic aerosols during the northeasterly winter monsoon season to mineral dust and sea salt during the southwest summer monsoon. The former is dominated by low-level transport from south and southeast Asia, while the latter results from low to mid tropospheric transport from the African continent and the Arabian Peninsula. During the winter monsoon, low-level transport from the Indian subcontinent and neighboring nations is particularly important. This paper uses 5 years of satellite-derived aerosol optical depths (AODs) to document the large seasonal variations in AODs modulated by the monsoons. In situ data are used to develop and validate the procedure we employ to derive visible AODs from the radiances observed by the advanced very high resolution radiometer (AVHRR) onboard polar-orbiting satellites. Monthly mean AOD over the Arabian Sea displays a clear annual cycle with a maximum (0.60 ± 0.10) in July and a minimum (0.20 ± 0.05) in January. The summer monsoon maximum is due both to the southwest winds bringing dust from the Horn of Africa over the Arabian Sea and mid tropospheric transport of dust from the Arabian Peninsula. Such long-range transports also lead to aerosol loading south of the equator. We also show that the Indonesia forest fires during the 1997 El Niño led to a large increase in AOD over most of the equatorial Indian Ocean. Remote sensing; 0360 Radiation: transmission and scattering; 1640 Remote sensing; 0305 Aerosols and particles; aerosols and particles; transmission and scattering of radiation
Lin, Bing; Wielicki, Bruce A.; Chambers, Lin H.; Hu, Yongxiang; Xu, Kuan-ManLin, B., B. A. Wielicki, L. H. Chambers, Y. Hu, K. Xu, 2002: The Iris Hypothesis: A Negative or Positive Cloud Feedback?. J. Climate, 15(1), 3-7. doi: 10.1175/1520-0442(2002)015<0003:TIHANO>2.0.CO;2. Abstract Using the Tropical Rainfall Measuring Mission (TRMM) satellite measurements over tropical oceans, this study evaluates the iris hypothesis recently proposed by Lindzen et al. that tropical upper-tropospheric anvils act as a strong negative feedback in the global climate system. The modeled radiative fluxes of Lindzen et al. are replaced by the Clouds and the Earth's Radiant Energy System (CERES) directly observed broadband radiation fields. The observations show that the clouds have much higher albedos and moderately larger longwave fluxes than those assumed by Lindzen et al. As a result, decreases in these clouds would cause a significant but weak positive feedback to the climate system, instead of providing a strong negative feedback.
Lin, Xin; Fowler, Laura D.; Randall, David A.Lin, X., L. D. Fowler, D. A. Randall, 2002: Flying the TRMM Satellite in a general circulation model. Journal of Geophysical Research: Atmospheres, 107(D16), ACH 4-1. doi: 10.1029/2001JD000619. By incorporating the Tropical Rainfall Measurement Mission (TRMM) satellite orbital information into the Colorado State University General Circulation Model (CSU GCM), we are able to “fly” a satellite in the GCM and sample the simulated atmosphere in the same way as the TRMM sensors sample the real atmosphere. The TRMM-sampled statistics for precipitation and radiative fluxes at annual, intraseasonal, monthly mean, and seasonal-mean diurnal timescales are evaluated by comparing the satellite-sampled against fully sampled simulated atmospheres. The sampling rates of the TRMM sensors are significantly affected by the sensors' swath widths. The TRMM Microwave Imager (TMI) and the Visible Infrared Scanner (VIRS) sample each 2.25° × 2.25° grid box in the tropics and subtropics about once per day, but at a different local time every day, while the precipitation radar (PR) and the Clouds and the Earth's Radiant Energy System (CERES) sensor visit each grid box about once every 3 days and twice per day, respectively. Besides inadequate samplings resulting from sensors' swath widths, there is a large, systematic diurnal undersampling associated with TRMM's orbital geometry for grid boxes away from the equator. When only 1 month of TRMM data are used, this diurnal undersampling can lead to more daytime samples relative to nighttime samples in one hemisphere and more nighttime samples relative to daytime samples in the other hemisphere. The resulting sampling biases (3–6 W m−2) are very pronounced in outgoing longwave radiation (OLR) over the subtropical landmasses. The sampling errors in OLR monthly and seasonal means are less than 8 W m−2 (5%) for each 2.25° × 2.25° grid box. The OLR monthly and seasonal means are not sensitive to diurnal undersamplings associated with the TRMM orbits and sensors' swath widths. However, this is not the case for total precipitation. Diurnal undersampling could produce errors as large as 20% in the tropics and 40% in the subtropics, for the zonally averaged monthly mean rain rates. The TRMM orbits sample each 2.25° × 2.25° grid box in the tropics and subtropics 1–6 times for each hour of the day within a single season. The seasonal-mean diurnal cycles of precipitation and OLR are not well sampled for any one grid box. By either accumulating the satellite data for a long enough period, or averaging the data over a large area with a relatively uniform diurnal signal, the diurnal cycles of precipitation and OLR can be satisfactorily sampled. The effects of TRMM sampling errors on the inferred tropical-mean hydrologic cycle and radiative fluxes are also evaluated. There are strong spurious oscillations associated with TRMM's orbital geometry, with periods of 23 days and 3–4 months, in tropical-mean daily and monthly precipitation. While the relative fluctuations of the sampled OLR are negligible, the relative fluctuations of the sampled precipitation have magnitudes similar to those of the observed climate variability. Caution must therefore be used when applying TRMM observations of tropical-mean precipitation to interpret climate variations at intraseasonal and interannual scales. 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3319 Meteorology and Atmospheric Dynamics: General circulation; TRMM; 3354 Meteorology and Atmospheric Dynamics: Precipitation; 3374 Meteorology and Atmospheric Dynamics: Tropical meteorology; GCM; orbit; Precipitation; Sampling
Loeb, Norman G.; Kato, SeijiLoeb, N. G., S. Kato, 2002: Top-of-Atmosphere Direct Radiative Effect of Aerosols over the Tropical Oceans from the Clouds and the Earth's Radiant Energy System (CERES) Satellite Instrument. J. Climate, 15(12), 1474-1484. doi: 10.1175/1520-0442(2002)015<1474:TOADRE>2.0.CO;2. Abstract Nine months of the Clouds and the Earth's Radiant Energy System (CERES)/Tropical Rainfall Measuring Mission (TRMM) broadband fluxes combined with the TRMM visible infrared scanner (VIRS) high-resolution imager measurements are used to estimate the daily average direct radiative effect of aerosols for clear-sky conditions over the tropical oceans. On average, aerosols have a cooling effect over the Tropics of 4.6 ± 1 W m–2. The magnitude is ≈2 W m–2 smaller over the southern tropical oceans than it is over northern tropical oceans. The direct effect derived from CERES is highly correlated with coincident aerosol optical depth (τ) retrievals inferred from 0.63-μm VIRS radiances (correlation coefficient of 0.96). The slope of the regression line is ≈−32 W m–2 τ–1 over the equatorial Pacific Ocean, but changes both regionally and seasonally, depending on the aerosol characteristics. Near sources of biomass burning and desert dust, the aerosol direct effect reaches −25 to −30 W m–2. The direct effect from CERES also shows a dependence on wind speed. The reason for this dependence is unclear—it may be due to increased aerosol (e.g., sea-salt or aerosol transport) or increased surface reflection (e.g., due to whitecaps). The uncertainty in the tropical average direct effect from CERES is ≈1 W m–2 (≈20%) due mainly to cloud contamination, the radiance-to-flux conversion, and instrument calibration. By comparison, uncertainties in the direct effect from the Earth Radiation Budget Experiment (ERBE) and CERES “ERBE-like” products are a factor of 3–5 times larger.
Loeb, Norman G.; Kato, Seiji; Wielicki, Bruce A.Loeb, N. G., S. Kato, B. A. Wielicki, 2002: Defining Top-of-the-Atmosphere Flux Reference Level for Earth Radiation Budget Studies. J. Climate, 15(22), 3301-3309. doi: 10.1175/1520-0442(2002)015<3301:DTOTAF>2.0.CO;2. Abstract To estimate the earth's radiation budget at the top of the atmosphere (TOA) from satellite-measured radiances, it is necessary to account for the finite geometry of the earth and recognize that the earth is a solid body surrounded by a translucent atmosphere of finite thickness that attenuates solar radiation differently at different heights. As a result, in order to account for all of the reflected solar and emitted thermal radiation from the planet by direct integration of satellite-measured radiances, the measurement viewing geometry must be defined at a reference level well above the earth's surface (e.g., 100 km). This ensures that all radiation contributions, including radiation escaping the planet along slant paths above the earth's tangent point, are accounted for. By using a field-of-view (FOV) reference level that is too low (such as the surface reference level), TOA fluxes for most scene types are systematically underestimated by 1–2 W m−2. In addition, since TOA flux represents a flow of radiant energy per unit area, and varies with distance from the earth according to the inverse-square law, a reference level is also needed to define satellite-based TOA fluxes. From theoretical radiative transfer calculations using a model that accounts for spherical geometry, the optimal reference level for defining TOA fluxes in radiation budget studies for the earth is estimated to be approximately 20 km. At this reference level, there is no need to explicitly account for horizontal transmission of solar radiation through the atmosphere in the earth radiation budget calculation. In this context, therefore, the 20-km reference level corresponds to the effective radiative “top of atmosphere” for the planet. Although the optimal flux reference level depends slightly on scene type due to differences in effective transmission of solar radiation with cloud height, the difference in flux caused by neglecting the scene-type dependence is less than 0.1%. If an inappropriate TOA flux reference level is used to define satellite TOA fluxes, and horizontal transmission of solar radiation through the planet is not accounted for in the radiation budget equation, systematic errors in net flux of up to 8 W m−2 can result. Since climate models generally use a plane-parallel model approximation to estimate TOA fluxes and the earth radiation budget, they implicitly assume zero horizontal transmission of solar radiation in the radiation budget equation, and do not need to specify a flux reference level. By defining satellite-based TOA flux estimates at a 20-km flux reference level, comparisons with plane-parallel climate model calculations are simplified since there is no need to explicitly correct plane-parallel climate model fluxes for horizontal transmission of solar radiation through a finite earth.
Lynch, D. K.; Sassen, K; Del Genio; Heymsfield, A; Minnis, P; Platt, M; Quante, M.; Schumann, U.; Sundqvist, HLynch, D. K., K. Sassen, . Del Genio, A. Heymsfield, P. Minnis, M. Platt, M. Quante, U. Schumann, H. Sundqvist, 2002: Cirrus: The Future, Chapter 21. Cirrus, 449-455.
Marécal, Virginie; Mahfouf, Jean-FrançoisMarécal, V., J. Mahfouf, 2002: Four-Dimensional Variational Assimilation of Total Column Water Vapor in Rainy Areas. Mon. Wea. Rev., 130(1), 43-58. doi: 10.1175/1520-0493(2002)130<0043:FDVAOT>2.0.CO;2. Abstract This paper studies the impact of assimilating rain-derived information in the European Centre for Medium-Range Weather Forecasts (ECMWF) four-dimensional variational (4DVAR) system. The approach is based on a one-dimensional variational (1DVAR) method. First, model temperature and humidity profiles are adjusted by assimilating observed surface rain rates in 1DVAR. Second, 1DVAR total column water vapor (TCWV) estimates are assimilated in 4DVAR. Observations used are Tropical Rainfall Measuring Mission (TRMM) surface rain-rate estimates from the TRMM Microwave Imager. Two assimilation experiments making use of 1DVAR TCWV were run for a 15-day period. The “Rain-1” experiment only assimilates 1DVAR retrievals where the observed rain rate is nonzero while the “Rain-2” experiment assimilates all 1DVAR TCWV estimates. The period selected includes Hurricane Bonnie, which was well sampled by TRMM (late August 1998). Results show a positive impact on the humidity analysis of assimilating 1DVAR TCWV in 4DVAR. The model rain rates at the analysis time are closer to the TRMM observations showing a posteriori the consistency of the two-step approach chosen to assimilate rain-rate information in 4DVAR. The modification of the humidity analysis induces changes in the wind and pressure analysis. In particular the analysis of the track of Hurricane Bonnie is noticeably improved for the early stage of the storm development for both the Rain-1 and Rain-2 experiments. When Bonnie is in a mature stage the influence of the 1DVAR TCWV assimilation is to intensify the hurricane. Comparison with Clouds and the Earth's Radiant Energy System (CERES) measurements also show a neutral impact on the radiative fluxes at the top-of-the atmosphere when using 1DVAR TCWV estimates. The impact on the forecasts is a slight reduction of the model precipitation spindown over tropical oceans. Objective scores for the Tropics are improved, particularly for wind and for upper-tropospheric temperature. Analysis and forecast results are generally better for the Rain-2 experiment compared to Rain-1, implying that the 1DVAR TCWV estimates retrieved where no rain is observed provide useful information to 4DVAR.
Matrosov, Sergey Y.; Korolev, Alexei V.; Heymsfield, Andrew J.Matrosov, S. Y., A. V. Korolev, A. J. Heymsfield, 2002: Profiling Cloud Ice Mass and Particle Characteristic Size from Doppler Radar Measurements. J. Atmos. Oceanic Technol., 19(7), 1003-1018. doi: 10.1175/1520-0426(2002)019<1003:PCIMAP>2.0.CO;2. Abstract A remote sensing method is proposed for the retrievals of vertical profiles of ice cloud microphysical parameters from ground-based measurements of radar reflectivity and Doppler velocity with a vertically pointed cloud radar. This method relates time-averaged Doppler velocities (which are used as a proxy for the reflectivity-weighted particle fall velocities) to particle characteristic sizes such as median or mean. With estimated profiles of particle characteristic size, profiles of cloud ice water content (IWC) are then calculated using reflectivity measurements. The method accounts for the intrinsic correlation between particle sizes and parameters of the fall velocity–size relations. It also accounts for changes of particle bulk density with size. The range of applicability of this method encompasses ice-phase clouds and also mixed-phase clouds that contain liquid drops, which are small compared to ice particles, so the radar signals are dominated by these larger particles. It is, however, limited to the observational situations without strong up- and downdrafts, so the residual of mean vertical air motions is small enough compared to the reflectivity-weighted cloud particle fall velocities. The Doppler-velocity reflectivity method was applied to the data obtained with an 8.6-mm wavelength radar when observing Arctic clouds. Typical retrieval uncertainties are about 35%–40% for particle characteristic size and 60%–70% for IWC, though in some cases IWC uncertainties can be as high as factor of 2 (i.e., −50%, +100%). Comparisons with in situ data for one observational case yielded 25% and 55% differences in retrieved and in situ estimates of characteristic size and IWC, respectively. The results of the microphysical retrievals obtained from the remote sensing method developed here were compared with data obtained from the multisensor technique that utilizes combined radar–IR radiometer measurements. For pure ice-phase layers unobstructed by liquid clouds (i.e., conditions where the multisensor approach is applicable), the relative standard deviations between the results of both remote sensing approaches were about 27% for mean particle size and 38% for IWC, with relative biases of only 5% and 20%, respectively.
Minnis, Patrick; Nguyen, Louis; Doelling, David R.; Young, David F.; Miller, Walter F.; Kratz, David P.Minnis, P., L. Nguyen, D. R. Doelling, D. F. Young, W. F. Miller, D. P. Kratz, 2002: Rapid Calibration of Operational and Research Meteorological Satellite Imagers. Part II: Comparison of Infrared Channels. J. Atmos. Oceanic Technol., 19(9), 1250-1266. doi: 10.1175/1520-0426(2002)019<1250:RCOOAR>2.0.CO;2. Abstract To establish a more reliable reference instrument for calibration normalization, this paper examines the differences between the various thermal infrared imager channels on a set of research and operational satellites. Mean brightness temperatures from the Visible Infrared Scanner (VIRS) on the Tropical Rainfall Measuring Mission (TRMM) satellite and the second Along-Track Scanning Radiometer (ATSR-2) on the second European Remote Sensing Satellite (ERS-2) are correlated with matched data from the eighth Geostationary Operational Environmental Satellite (GOES-8), the fifth Geostationary Meteorological Satellite (GMS-5), and with each other. VIRS data are also correlated with the Terra satellite's Moderate Resolution Imaging Spectroradiometer (MODIS) provisional data as a preliminary assessment of their relative calibrations. As an additional check on their long-term stability, the VIRS data are compared to the broadband longwave radiances of the Clouds and the Earth's Radiant Energy System (CERES) scanners on TRMM. No statistically significant trend in the calibration of any of the three (3.7, 10.8, and 12.0 μm) VIRS thermal channels could be detected from the comparisons with CERES data taken during 1998 and 2000 indicating that the VIRS channels can serve as a reliable reference for intercalibrating satellite imagers. However, a small day–night difference in the VIRS thermal channels detected at very low temperatures should be taken into account. In general, most of the channels agreed to within less than ±0.7 K over a temperature range between 200 and 300 K. Some of the smaller differences can be explained by spectral differences in the channel response functions. A few larger differences were found at 200 K for some of the channels suggesting some basic calibration differences for lower temperatures. A nearly 3-K bias in the ATSR-2 11-μm channel relative to VIRS and GOES-8 was found at the cold end of the temperature range. The intercalibrations described here are being continued on a routine basis.
Minnis, Patrick; Nguyen, Louis; Doelling, David R.; Young, David F.; Miller, Walter F.; Kratz, David P.Minnis, P., L. Nguyen, D. R. Doelling, D. F. Young, W. F. Miller, D. P. Kratz, 2002: Rapid Calibration of Operational and Research Meteorological Satellite Imagers. Part I: Evaluation of Research Satellite Visible Channels as References. J. Atmos. Oceanic Technol., 19(9), 1233-1249. doi: 10.1175/1520-0426(2002)019<1233:RCOOAR>2.0.CO;2. Abstract Operational meteorological satellites generally lack reliable onboard calibration systems for solar-imaging channels. Current methods for calibrating these channels and for normalizing similar channels on contemporaneous satellite imagers typically rely on a poorly calibrated reference source. To establish a more reliable reference instrument for calibration normalization, this paper examines the use of research satellite imagers that maintain their solar-channel calibrations by using onboard diffuser systems that rely on the sun as an absolute reference. The Visible Infrared Scanner (VIRS) on the Tropical Rainfall Measuring Mission (TRMM) satellite and the second Along-Track Scanning Radiometer (ATSR-2) on the second European Remote Sensing Satellite (ERS-2) are correlated with matched data from the eighth Geostationary Operational Environmental Satellite (GOES-8), the fifth Geostationary Meteorological satellite (GMS-5), and with each other to examine trends in the solar channels. VIRS data are also correlated with the Terra satellite's Moderate Resolution Imaging Spectroradiometer (MODIS) provisional data as a preliminary assessment of their relative calibrations. As an additional check on their long-term stability, the VIRS data are compared to the relevant corresponding broadband shortwave radiances of the Clouds and the Earth's Radiant Energy System (CERES) scanners on TRMM. No statistically significant trend in the calibration of the VIRS 0.65- and 1.64-μm channels could be detected from the comparisons with CERES data taken during 1998 and 2000. The VIRS-to-GOES-8 correlations revealed an annual degradation rate for the GOES-8 visible (0.67 μm) channel of ∼7.5% and an initial drop of 16% in the gain from the prelaunch value. The slopes in the GOES-8 visible-channel gain trend lines derived from VIRS data taken after January 1998 and ATSR-2 data taken between October 1995 and December 1999 differed by only 1%–2% indicating that both reference instruments are highly stable. The mean difference of 3%–4.8% between the VIRS–GOES-8 and ATSR-2–GOES-8 gains is attributed to spectral differences between ATSR-2 and VIRS and to possible biases in the ATSR-2 channel-2 calibration. A degradation rate of 1.3% per year found for the GMS-5 visible channel was confirmed by comparisons with earlier calibrations. The MODIS and VIRS calibrations agreed to within −1% to 3%. Some of the differences between VIRS and the provisional MODIS radiances can be explained by spectral differences between the two instruments. The MODIS measures greater reflectance than VIRS for bright scenes. Although both VIRS and ATSR-2 provide temporally stable calibrations, it is recommended that, at least until MODIS calibrations are finalized, VIRS should be used as a reference source for normalizing operational meteorological satellite imagers because of its broader visible filter.
Mlynczak, MartyMlynczak, M., 2002: A comparison of space-based observations of the energy budgets of the mesosphere and the troposphere. Journal of Atmospheric and Solar-Terrestrial Physics, 64(8–11), 877-887. doi: 10.1016/S1364-6826(02)00043-3. The flow of energy from the Sun, through the atmosphere, to the Earth's surface and oceans, and ultimately back to space, controls the weather and climate of the planet. Since the dawn of the Space Age, the energy balance of the planet has been measured by orbiting satellites. Over the past 40 years the technology and the scientific understanding have developed to the point where we can measure not only the energy balance of the entire Earth and its atmosphere but also of the various regions of the atmosphere including the troposphere, the stratosphere, and the mesosphere. With the planned space-based observations of the sources and sinks of energy in the mesosphere, the energy balance of this region of the atmosphere may soon be better understood from observations than the energy balance of the troposphere on seasonal to annual timescales. Fundamental to this assertion is the fact that the primary sources and sinks of radiative and chemical potential energy, the thermal structure, and the winds in the mesosphere are to be directly observed by space-based instrumentation at high vertical resolution, in contrast to the troposphere. In this paper we review some of the planned measurements of the energy budgets of the atmosphere from existing and future space-based platforms. We particularly show how the airglow can be used to determine many of the key sources of energy in the mesosphere. These ideas provide the basis for interpretation of new space-based measurements of the mesosphere planned in the near future. Satellites; energy budget; Mesosphere; Troposhere
Nasiri, Shaima L.; Baum, Bryan A.; Heymsfield, Andrew J.; Yang, Ping; Poellot, Michael R.; Kratz, David P.; Hu, YongxiangNasiri, S. L., B. A. Baum, A. J. Heymsfield, P. Yang, M. R. Poellot, D. P. Kratz, Y. Hu, 2002: The Development of Midlatitude Cirrus Models for MODIS Using FIRE-I, FIRE-II, and ARM In Situ Data. Journal of Applied Meteorology, 41(3), 197-217. doi: 10.1175/1520-0450(2002)041<0197:TDOMCM>2.0.CO;2. Abstract Detailed in situ data from cirrus clouds have been collected during dedicated field campaigns, but the use of the size and habit distribution data has been lagging in the development of more realistic cirrus scattering models. In this study, the authors examine the use of in situ cirrus data collected during three field campaigns to develop more realistic midlatitude cirrus microphysical models. Data are used from the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE)-I (1986) and FIRE-II (1991) campaigns and from a recent Atmospheric Radiation Measurement (ARM) Program campaign held in March–April of 2000. The microphysical models are based on measured vertical distributions of both particle size and particle habit and are used to develop new scattering models for a suite of moderate-resolution imaging spectoradiometer (MODIS) bands spanning visible, near-infrared, and infrared wavelengths. The sensitivity of the resulting scattering properties to the underlying assumptions of the assumed particle size and habit distributions are examined. It is found that the near-infrared bands are sensitive not only to the discretization of the size distribution but also to the assumed habit distribution. In addition, the results indicate that the effective diameter calculated from a given size distribution tends to be sensitive to the number of size bins that are used to discretize the data and also to the ice-crystal habit distribution.
Pope, Shelly K.; Valero, Francisco P. J.; Collins, William D.; Minnis, PatrickPope, S. K., F. P. J. Valero, W. D. Collins, P. Minnis, 2002: Comparison of ScaRaB, GOES 8, aircraft, and surface observations of the absorption of solar radiation by clouds. Journal of Geophysical Research: Atmospheres, 107(D11), ACL 1-1. doi: 10.1029/2001JD001139. Data obtained by the Scanner for Radiation Budget (ScaRaB) instrument on the Meteor 3 satellite have been analyzed and compared to satellite (GOES 8), aircraft (Radiation Measurement System, RAMS), and surface (Baseline Solar Radiation Network (BRSN), Solar and Infrared Observations System (SIROS), and RAMS) measurements of irradiance obtained during the Atmospheric Radiation Measurements Enhanced Shortwave Experiment (ARESE). It is found that the ScaRaB data covering the period from March 1994 to February 1995 (the instrument's operational lifetime) indicate excess absorption of solar radiation by the cloudy atmosphere in agreement with previous aircraft, surface, and GOES 8 results. The full ScaRaB data set combined with BSRN and SIROS surface observations gives an average all-sky absorptance of 0.28. The GOES 8 data set combined with RAMS surface observations gives an average all-sky absorptance of 0.26. The aircraft data set (RAMS) gives a mean all-sky absorptance of 0.24 (for the column between 0.5 and 13 km). clouds; 0360 Radiation: transmission and scattering; 1610 Atmosphere; 0320 Cloud physics and chemistry; 0394 Instruments and techniques; Absorption; radiation; observations
Priestley, K. J; Wielicki, B. A; Green, R. N; Haeffelin, M. P. A; Lee, R. B; Loeb, N. GPriestley, K. J., B. A. Wielicki, R. N. Green, M. P. A. Haeffelin, R. B. Lee, N. G. Loeb, 2002: Early radiometric validation results of the CERES Flight Model 1 and 2 instruments onboard NASA's Terra Spacecraft. Advances in Space Research, 30(11), 2371-2376. doi: 10.1016/S0273-1177(02)80278-2. The CERES Flight Model 1 and 2 instruments were launched aboard NASA's Earth Observing System (EOS) Terra Spacecraft on December 18, 1999 into a 705 Km sun-synchronous orbit with a 10:30 a.m. equatorial crossing time. These instruments supplement measurements made by the CERES Proto Flight Model (PFM) instrument launched aboard NASA's Tropical Rainfall Measuring Mission (TRMM) spacecraft on November 27, 1997 into a 350 Km, 38-degree mid-inclined orbit. An important aspect of the EOS program is the rapid archival and dissemination of datasets measured by EOS instruments to the scientific community. On September 22, 2000 the CERES Science Team voted to archive the Edition 1 CERES/Terra Level 1b and Level 2 and 3 ERBE-Like data products. These products consist of instantaneous filtered and unfiltered radiances through temporally and spatially averaged TOA fluxes. CERES filtered radiance measurements cover three spectral bands including shortwave (0.3 to 5 μm), total (0.3 to <100 μm) and an atmospheric window channel (8 to 12 μm). The current work summarizes both the philosophy and results of validation efforts undertaken to quantify the quality of the Terra data products as well as the level of agreement between the Terra and TRMM datasets.
Rajeev, K.; Ramanathan, V.Rajeev, K., V. Ramanathan, 2002: The Indian ocean experiment: aerosol forcing obtained from satellite data. Advances in Space Research, 29(11), 1731-1740. doi: 10.1016/S0273-1177(02)00086-8. The tropical Indian Ocean provides an ideal and unique natural laboratory to observe and understand the role of anthropogenic aerosols in climate forcing. Since 1996, an international team of American, European and Indian scientists have been collecting aerosol, chemical and radiation data from ships and surface stations, which culminated in a multi-platform field experiment conducted during January to March of 1999. A persistent haze layer that spread over most of the northern Indian Ocean during wintertime was discovered. The layer, a complex mix of organics, black carbon, sulfates, nitrates and other species, subjects the lower atmosphere to a strong radiative heating and a larger reduction in the solar heating of the ocean. We present here the regional distribution of aerosols and the resulting clear sky aerosol radiative forcing at top-of-atmosphere (TOA) observed over the Indian Ocean during the winter months of 1997, 1998 and 1999 based on the aerosol optical depth (AOD) estimated using NOAA14-AVHRR and the TOA radiation budget data from CERES on board TRMM. Using the ratio of surface to TOA clear sky aerosol radiative forcing observed during the same period over the Indian Ocean island of Kaashidhoo (Satheesh and Ramanathan, 2000), the clear sky aerosol radiative forcing at the surface and the atmosphere are discussed. The regional maps of AVHRR derived AOD show abnormally large aerosol concentration during the winter of 1999 which is about 1.5 to 2 times larger than the AOD during the corresponding period of 1997 and 1998. A large latitudinal gradient in AOD is observed during all the three years of observation, with maximum AOD in the northern hemisphere. The diurnal mean clear sky aerosol forcing at TOA in the northern hemisphere Indian Ocean is in the range of −4 to −16 Wm−2 and had large spatio-temporal variations while in the southern hemisphere Indian Ocean it is in the range of 0 to −6Wm−2. The importance of integrating in-situ data with satellite data to get reliable picture of the regional scale aerosol forcing is demonstrated.
Randall, David; Curry, Judith; Duynkerke, Peter; Krueger, Steven; Moncrieff, Mitchell; Ryan, Brian; Starr, David OC; Miller, Martin; Rossow, William; Tselioudis, George; al, etRandall, D., J. Curry, P. Duynkerke, S. Krueger, M. Moncrieff, B. Ryan, D. O. Starr, M. Miller, W. Rossow, G. Tselioudis, e. al, 2002: Confronting Models with Data: The GEWEX Cloud Systems Study. The GEWEX Cloud System Study was organized to promote development of improved parameterizations of cloud systems for use in climate and numerical weather prediction models, with an emphasis on the climate applications. The strategy of GCSS is to use two distinct kinds of models to analyze and understand observations of the behavior of several different types of clouds systems. Cloud-system-resolving models have high enough spatial and temporal resolutions to represent individual cloud elements, but cover a wide enough range of space and time scales to permit statistical analysis of simulated cloud systems. Results from CSRMs are compared with detailed observations, representing specific cases based on field experiments, and also with statistical composites obtained from satellite and meteorological analyses. Single-column models are the surgically extracted column physics of atmospheric general circulation models. SCMs are used to test cloud parameterizations in an un-coupled mode, by comparison with field data and statistical composites. In the original GCSS strategy, data is collected in various field programs and provided to the CSRM Community, which uses the data to "certify" the CSRMs as reliable tools for the simulation of particular cloud regimes, and then uses the CSRMs to develop parameterizations, which are provided to the GCM Community. We report here the results of a re-thinking of the scientific strategy of GCSS, which takes into account the practical issues that arise in confronting models with data. The main elements of the proposed new strategy are a more active role for the large-scale modeling community, and an explicit recognition of the importance of data integration. clouds; data processing; climate; hydrological cycle; Water; atmospheric general circulation models; atmospheric models; computerized simulation; numerical weather forecasting; statistical analysis; temporal resolution
Roca, Rémy; Viollier, Michel; Picon, Laurence; Desbois, MichelRoca, R., M. Viollier, L. Picon, M. Desbois, 2002: A multisatellite analysis of deep convection and its moist environment over the Indian Ocean during the winter monsoon. Journal of Geophysical Research: Atmospheres, 107(D19), INX2 11-1. doi: 10.1029/2000JD000040. The aim of this paper is to characterize the deep convective systems over the Indian Ocean during Indian Ocean Experiment (INDOEX) and their relationship to cloudiness and to the Upper Tropospheric Humidity (UTH) of their environment together with the relevant longwave radiation fields. Multisatellite analyses are performed (Meteosat, Scanner for Radiation Budget (ScaRaB), and Special Sensor Microwave Imager (SSM/I)) to measure these environmental parameters. The use of Meteosat water vapor (WV) channel appears very efficient not only for estimating UTH but also for separating high level cloudiness, including thin cirrus, from clear sky and low clouds. The Meteosat infrared (IR) and WV channels are also used for correlating Meteosat and ScaRaB measurements, allowing to retrieve continuously the longwave radiative flux. The longwave flux is used to compute the cloud radiative forcing as well as the clear-sky greenhouse effect. Spatial relationships between upper level cloudiness and UTH are established. A strong positive linear relationship is found suggesting a local moistening of the upper troposphere by convection. The temporal analysis reveals that during the active phase of the intraseasonal oscillation, the longwave cloud radiative forcing reaches a mean value up to 40 W m−2 over a large region in the open ocean, while the average clear-sky greenhouse effect is in excess of 180 W m−2. These radiative parameters are strongly correlated with the upper level cloudiness and upper level moisture, respectively. The temporal variability of UTH explains up to 80% of the greenhouse effect variability. The structure of the convective cloud systems is then studied. The observed population of systems spans a wide spectrum of area from 100 to 1,000,000 km2. The contribution to the high level cloudiness of the systems with a strong vertical development is dominant. These systems, with at least one convective cell reaching the highest levels (below 210 K), present indices of overshooting tops and are the most horizontally extended. The largest system exhibits an average longwave radiative forcing of around 100 W m−2. Their contribution to the cloud forcing over the Indian Ocean is overwhelming. The spatial and temporal variability of the systems is finally related to the UTH and to the clear-sky greenhouse effect. Strong correlations are found indicating that these organized convective systems at mesoscale play a leading role in the Indian Ocean climate. The analysis suggests that deeper convection is associated with larger cloud desks with larger cloud radiative forcing. It is also associated with a moister upper troposphere and a larger clear-sky greenhouse effect. These two effects would provide a positive feedback on the surface conditions. 1610 Atmosphere; 1640 Remote sensing; 1620 Climate dynamics; 1655 Water cycles; convection; longwave radiation; 3314 Meteorology and Atmospheric Dynamics: Convective processes; humidity; Indian Ocean; Intraseasonal variability
Satheesh, S. K.; Ramanathan, V.; Holben, B. N.; Moorthy, K. Krishna; Loeb, N. G.; Maring, H.; Prospero, J. M.; Savoie, D.Satheesh, S. K., V. Ramanathan, B. N. Holben, K. K. Moorthy, N. G. Loeb, H. Maring, J. M. Prospero, D. Savoie, 2002: Chemical, microphysical, and radiative effects of Indian Ocean aerosols. Journal of Geophysical Research: Atmospheres, 107(D23), 4725. doi: 10.1029/2002JD002463. Extensive and long-term multistation measurements of aerosol properties and radiative fluxes were carried out in the haze plume off the South Asian continent. These experiments are carried out at Kaashidhoo Climate Observatory (KCO) (4.95°N, 73.5°E), Minicoy (8.5°N, 73.0°E), and Trivandrum (8.5°N, 77.0°E). In addition, the top of the atmosphere fluxes were measured simultaneously by the CERES radiation budget instrument. Long-term observations (more than 15 years) over Trivandrum show that there is a gradual increase in aerosol visible optical depth from ∼0.2 in 1986 to ∼0.4 in 1999. Pre- and post-monsoon aerosol characteristics are examined to study the seasonal variations. The impact of aerosols on short-wave radiation budget is estimated using direct observations of solar radiation using several independent ground-based radiometers and satellite data as well as from modeled aerosol properties. It was observed that “excess absorption” is not needed to model diffuse fluxes. The lower atmospheric heating due to absorbing aerosols was as high as ∼20 W m−2 which translates to a heating rate perturbation of ∼0.5°K/day. The effect of aerosol mixing state (internally and externally) on aerosol forcing appears to be negligible. A sensitivity study of the effect of aerosols over land in contrast to that over the ocean shows an enhancement in lower atmosphere heating by about 40% simultaneous with a reduction of ∼33% in surface cooling. Increasing sea-surface winds increase aerosol cooling due to increased sea salt aerosol concentrations, which can partly offset the heating effect due to absorbing aerosols. 1610 Atmosphere; 0305 Aerosols and particles; aerosols; chemical composition; radiative forcing; climate; 4801 Aerosols; 1704 Atmospheric sciences
Smith, G. L.; Bess, T. D.; Manalo-Smith, N.; Ramanathan, V.; Lee III, R. B.; Barkstrom, B. R.Smith, G. L., T. D. Bess, N. Manalo-Smith, V. Ramanathan, R. B. Lee III, B. R. Barkstrom, 2002: The CERES 8–12 micron window channel. Advances in Space Research, 30(11), 2377-2382. doi: 10.1016/S0273-1177(02)80280-0. The CERES (Clouds and Earth Radiant Energy System) scanning radiometer has 3 channels: a short-wave channel for measuring solar radiation reflected from the Earth, a total channel, which combined with 8 to 12 μ window of the atmosphere. The CERES instrument aboard the Tropical Rainfall Measurement Mission (TRMM) spacecraft provided 8 months of data. This paper discusses the 8–12 μ channel of the CERES. In order to compute fluxes from radiance measurements, limb-darkening functions are required. These limb-darkening functions are also computed from CERES measurements and are then used to compute fluxes from the measured radiances. Finally, maps are examined to show features of radiation in the window channel.
Smith, G. Louis; Pandey, D. K.; Lee, Robert B.; Barkstrom, Bruce R.; Priestley, Kory J.Smith, G. L., D. K. Pandey, R. B. Lee, B. R. Barkstrom, K. J. Priestley, 2002: Numerical Filtering of Spurious Transients in a Satellite Scanning Radiometer: Application to CERES. J. Atmos. Oceanic Technol., 19(2), 172-182. doi: 10.1175/1520-0426(2002)019<0172:NFOSTI>2.0.CO;2. Abstract The Clouds and Earth Radiant Energy System (CERES) scanning radiometer was designed to provide high accuracy measurements of the radiances from the earth. Calibration testing of the instruments showed the presence of an undesired slow transient in the measurements of all channels at 1% to 2% of the signal. Analysis of the data showed that the transient consists of a single linear mode. The characteristic time of this mode is 0.3 to 0.4 s and is much greater than that the 8–10-ms response time of the detector, so that it is well separated from the detector response. A numerical filter was designed for the removal of this transient from the measurements. Results show no trace remaining of the transient after application of the numerical filter. The characterization of the slow mode on the basis of ground calibration data is discussed and flight results are shown for the CERES instruments aboard the Tropical Rainfall Measurement Mission and Terra spacecraft. The primary influence of the slow mode is in the calibration of the instrument and the in-flight validation of the calibration. This method may be applicable to other radiometers that are striving for high accuracy and encounter a slow spurious mode, regardless of the underlying physics.
Smith, G. Louis; Wilber, Anne C.; Gupta, Shashi K.; Stackhouse, Paul W.Smith, G. L., A. C. Wilber, S. K. Gupta, P. W. Stackhouse, 2002: Surface Radiation Budget and Climate Classification. J. Climate, 15(10), 1175-1188. doi: 10.1175/1520-0442(2002)015<1175:SRBACC>2.0.CO;2. Abstract The surface radiation budget of a region is strongly tied to its climate. An 8-yr climatology of surface radiation budget components for 2.5° regions over the earth is examined in order to learn how the regional climate and surface radiation are related. The yearly cycles of a few individual regions were studied by plotting monthly mean net longwave flux as a function of net shortwave flux at the surface. These plots show trajectories that are characteristic of the climate class. The behavior of the trajectories of surface radiation and their relation to the regional climate can be understood with simple conceptual models for many cases. From an examination of these trajectories, a set of parameters is developed, such as mean net longwave flux and range of net shortwave flux, which distinguish various climate classes on the basis of the surface radiation. These criteria are applied to produce a map of regional climate classes based on surface radiation, similar to those of Koeppen or Trewartha and Horn, which were based on vegetation, temperature, and precipitation. The current maps can be used to explore the relationships between surface radiation and regional climate.
Stackhouse Jr, Paul W; Whitlock, Charles H; DiPasquale, Roberta C; Brown, DE; Chandler, William SStackhouse Jr, P. W., C. H. Whitlock, R. C. DiPasquale, D. Brown, W. S. Chandler, 2002: Meeting Energy-Sector Needs with NASA Climate Datasets. Earth Observation Magazine, 11(8), 6–10.
Stephens, Graeme L.; Vane, Deborah G.; Boain, Ronald J.; Mace, Gerald G.; Sassen, Kenneth; Wang, Zhien; Illingworth, Anthony J.; O'Connor, Ewan J.; Rossow, William B.; Durden, Stephen L.; Miller, Steven D.; Austin, Richard T.; Benedetti, Angela; Mitrescu, Cristian; CloudSat Science Team, TheStephens, G. L., D. G. Vane, R. J. Boain, G. G. Mace, K. Sassen, Z. Wang, A. J. Illingworth, E. J. O'Connor, W. B. Rossow, S. L. Durden, S. D. Miller, R. T. Austin, A. Benedetti, C. Mitrescu, T. CloudSat Science Team, 2002: The cloudsat mission and the a-train. Bull. Amer. Meteor. Soc., 83(12), 1771-1790. doi: 10.1175/BAMS-83-12-1771. Abstract CloudSat is a satellite experiment designed to measure the vertical structure of clouds from space. The expected launch of CloudSat is planned for 2004, and once launched, CloudSat will orbit in formation as part of a constellation of satellites (the A-Train) that includes NASA's Aqua and Aura satellites, a NASA–CNES lidar satellite (CALIPSO), and a CNES satellite carrying a polarimeter (PARASOL). A unique feature that CloudSat brings to this constellation is the ability to fly a precise orbit enabling the fields of view of the CloudSat radar to be overlapped with the CALIPSO lidar footprint and the other measurements of the constellation. The precision and near simultaneity of this overlap creates a unique multisatellite observing system for studying the atmospheric processes essential to the hydrological cycle. The vertical profiles of cloud properties provided by CloudSat on the global scale fill a critical gap in the investigation of feedback mechanisms linking clouds to climate. Measuring these profiles requires a combination of active and passive instruments, and this will be achieved by combining the radar data of CloudSat with data from other active and passive sensors of the constellation. This paper describes the underpinning science and general overview of the mission, provides some idea of the expected products and anticipated application of these products, and the potential capability of the A-Train for cloud observations. Notably, the CloudSat mission is expected to stimulate new areas of research on clouds. The mission also provides an important opportunity to demonstrate active sensor technology for future scientific and tactical applications. The CloudSat mission is a partnership between NASA's JPL, the Canadian Space Agency, Colorado State University, the U.S. Air Force, and the U.S. Department of Energy.
Su, Wenying; Charlock, Thomas P.; Rutledge, KenSu, W., T. P. Charlock, K. Rutledge, 2002: Observations of reflectance distribution around sunglint from a coastal ocean platform. Applied Optics, 41(35), 7369-7383. doi: 10.1364/AO.41.007369. A scanning spectral photometer is deployed on a rigid coastal ocean platform to measure upwelling solar radiances from the sea surface at nine elevation angles spanning 150° of azimuth. Measured radiance distributions at 500 nm wavelength have been compared with traditional model simulations employing the Cox and Munk distribution of wave slopes. The model captures the general features of the observed angular reflectance distributions, but: (a) the observed peak value of sunglint near the specular direction is larger than simulated, except for a very calm sea; the model-measurement differences increase with wind speed and are largest for low solar elevation; (b) the observed sunglint is wider than simulated. In contrast to some previous studies, our results do not show a clear dependence of the mean square sea-surface slope on stability (air-sea temperature difference). radiative transfer; Oceanic optics; Spectrometers and spectroscopic instrumentation
Sun, Wenbo; Loeb, Norman G.; Fu, QiangSun, W., N. G. Loeb, Q. Fu, 2002: Finite-difference time-domain solution of light scattering and absorption by particles in an absorbing medium. Applied Optics, 41(27), 5728-5743. doi: 10.1364/AO.41.005728. The three-dimensional (3-D) finite-difference time-domain (FDTD) technique has been extended to simulate light scattering and absorption by nonspherical particles embedded in an absorbing dielectric medium. A uniaxial perfectly matched layer (UPML) absorbing boundary condition is used to truncate the computational domain. When computing the single-scattering properties of a particle in an absorbing dielectric medium, we derive the single-scattering properties including scattering phase functions, extinction, and absorption efficiencies using a volume integration of the internal field. A Mie solution for light scattering and absorption by spherical particles in an absorbing medium is used to examine the accuracy of the 3-D UPML FDTD code. It is found that the errors in the extinction and absorption efficiencies from the 3-D UPML FDTD are less than ∼2%. The errors in the scattering phase functions are typically less than ∼5%. The errors in the asymmetry factors are less than ∼0.1%. For light scattering by particles in free space, the accuracy of the 3-D UPML FDTD scheme is similar to a previous model [Appl. Opt.38, 3141 (1999)]. Atmospheric scattering; Scattering, particles; Oceanic optics; Numerical approximation and analysis; Particles; Water
Tahnk, William R.; Coakley, James A.Tahnk, W. R., J. A. Coakley, 2002: Aerosol optical depth and direct radiative forcing for INDOEX derived from AVHRR: Observations, January–March 1996–2000. Journal of Geophysical Research: Atmospheres, 107(D19), INX2 9-1. doi: 10.1029/2000JD000183. Visible and near infrared reflectances from NOAA-14 Advanced Very High Resolution Radiometer (AVHRR) daytime passes are used to derive optical depths at 0.55 μm, an index of aerosol type, continental or marine, and the direct effect of the aerosol on the top of the atmosphere and surface solar radiative fluxes for the oceans in the Indian Ocean Experiment (INDOEX) region (30°S to 30°N and 50°–110°E) during the January–March 1996–2000 winter monsoons. Comparison of aerosol optical depth and radiative forcing in the Northern Hemisphere with those in the Southern Hemisphere suggests that the additional pollution sources augment the 0.55-μm optical depth by, on average, 0.1 in the Northern Hemisphere. As a result of the aerosol, the region of the Indian Ocean in the Northern Hemisphere loses about 1.6 Wm−2 in reflected sunlight and the ocean surface loses about 5 Wm−2 during the months of the winter monsoon. Aerosol burdens and the aerosol direct radiative forcing are a relatively constant feature of the Northern Hemisphere, although the southeastern Arabian Sea experienced considerably larger aerosol burdens during the February–March 1999 INDOEX Intensive Field Phase (IFP) than in other years. Frequency distributions of the optical depth for 1° × 1° latitude-longitude regions are well represented by gamma distribution functions. The day-to-day and year-to-year variability of the optical depth for such regions is correlated with the long-term average optical depth. Interannual variability of the monthly mean optical depths for such regions is found to be as large as the day-to-day variability. Such large variability suggests that long-term records of in situ observations will be required in order to assess the performance of models that generate climatologies of aerosol concentrations. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1640 Remote sensing; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0305 Aerosols and particles; aerosols; Aerosol optical depth; aerosol climatology; INDOEX; radiative forcing of climate; remote sensing of aerosols
Tian, Baijun; Ramanathan, V.Tian, B., V. Ramanathan, 2002: Role of Tropical Clouds in Surface and Atmospheric Energy Budget. J. Climate, 15(3), 296-305. doi: 10.1175/1520-0442(2002)015<0296:ROTCIS>2.0.CO;2. Abstract In this paper diagnostic estimates of cloud radiative forcing (CRF) and clear-sky radiation budget at the surface and in the atmosphere, based on satellite-observed radiation budget at the top of the atmosphere (TOA) and empirical parameterizations derived from radiation models and field observations, are presented. This analysis is restricted to the tropical Pacific. High clouds over the intertropical convergence zone (ITCZ), the South Pacific convergence zone (SPCZ), and the warm pool (WP) exert a positive CRF of about 70 W m−2 within the atmosphere and a negative CRF of about −70 W m−2 at the surface, although with a negligible net CRF at the TOA. On the other hand, low clouds over the eastern subtropical Pacific and the equatorial cold tongue exert a negative CRF of about −20 W m−2 at the surface as well as in the atmosphere. The spatial gradients of the clear-sky radiation budget at the surface and in the atmosphere are small. In particular, it is shown that the clear-sky radiative cooling in the atmosphere is larger over the ITCZ, the SPCZ, and the WP, when compared with that over the subtropics and the cold tongue. Next, based on these diagnostic estimates and available surface turbulent heat flux data, the role of atmospheric CRF in the large-scale atmospheric moist static energy (MSE) transport is quantified. It is found that the atmospheric CRF provides the major energy source for balancing the divergence of MSE transport (from the ITCZ, the SPCZ, and the WP to the subtropics and the cold tongue) by the large-scale atmospheric circulation. On the other hand, the clear-sky radiative flux convergence and the surface turbulent heat fluxes have just the reverse spatial pattern and hence cannot satisfy the large-scale atmospheric MSE transport requirements.
Trenberth, Kevin E.Trenberth, K. E., 2002: Changes in Tropical Clouds and Radiation. Science, 296(5576), 2095-2095. doi: 10.1126/science.296.5576.2095a.
Viollier, Michel; Standfuss, Carsten; Parol, FrédéricViollier, M., C. Standfuss, F. Parol, 2002: Monthly means of reflected solar flux from POLDER (ADEOS-1) and comparison with ERBE, ScaRaB and CERES. Geophysical Research Letters, 29(10), 141-1. doi: 10.1029/2001GL014255. A diurnal cycle model is applied to POLDER instantaneous albedo determinations (Nov. 1996–June 1997) in order to compute daily and monthly means of the reflected flux at the top of the atmosphere. These results are compared to the ERBE, ScaRaB and CERES records. The quantitative comparison of the tropical means shows that the POLDER reflected flux density is on average lower by about 7 Wm−2 compared to ERBE (1985–1989) and ScaRaB-1 (1994–1995) and by 2.7 Wm−2 compared to ScaRaB-2 (Nov. 1998–March 1999) and CERES/Terra (2000–). The maps of POLDER albedo reveal strong deviations in the tropical Pacific. They correspond to the beginning of the 1997–1998 ENSO event. 1610 Atmosphere; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3394 Meteorology and Atmospheric Dynamics: Instruments and techniques; 3309 Meteorology and Atmospheric Dynamics: Climatology; 1694 Instruments and techniques
Wang, Pi-Huan; Minnis, Patrick; Wielicki, Bruce A.; Wong, Takmeng; Vann, Lelia B.Wang, P., P. Minnis, B. A. Wielicki, T. Wong, L. B. Vann, 2002: Satellite observations of long-term changes in tropical cloud and outgoing longwave radiation from 1985 to 1998. Geophysical Research Letters, 29(10), 37-1. doi: 10.1029/2001GL014264. Cloud vertical distributions and radiation data from satellites taken between 1985 and 1998 were analyzed to determine the impact of clouds on outgoing longwave radiation (OLR) in the Tropics. Clouds with a 1-μm optical depth greater than 0.025 above 12 km decreased, while those below 12 km increased. The OLR mean and decadal trend were 254 Wm−2 and 3.9 Wm−2/decade, respectively. The mean cloud and OLR results were used to derive a value of 0.36 for the tropical mean cloud longwave effective emissivity. Changes in cloud vertical distributions account for 40% of the OLR trend. A change in cloud effective emissivity of −0.026/decade could account for the remainder of the OLR changes. These changes suggest reduced mean cloud opacity, a drier troposphere, and a strengthened large-scale circulation in the Tropics during the period. 1640 Remote sensing; 0320 Cloud physics and chemistry; 3319 Meteorology and Atmospheric Dynamics: General circulation; 3374 Meteorology and Atmospheric Dynamics: Tropical meteorology
Wielicki, BA; Del Genio, AD; Wong, TM; Chen, JY; Carlson, BE; Allan, RP; Robertson, F; Jacobowitz, H; Slingo, A; Randall, DA; Kiehl, JT; Soden, BJ; Gordon, CT; Miller, AJ; Yang, SK; Susskind, JWielicki, B., A. Del Genio, T. Wong, J. Chen, B. Carlson, R. Allan, F. Robertson, H. Jacobowitz, A. Slingo, D. Randall, J. Kiehl, B. Soden, C. Gordon, A. Miller, S. Yang, J. Susskind, 2002: Changes in tropical clouds and radiation - Response. SCIENCE, 296(5576). doi: 10.1126/science.296.5576.2095a.
Wielicki, Bruce A.; Wong, Takmeng; Allan, Richard P.; Slingo, Anthony; Kiehl, Jeffrey T.; Soden, Brian J.; Gordon, C. T.; Miller, Alvin J.; Yang, Shi-Keng; Randall, David A.; Robertson, Franklin; Susskind, Joel; Jacobowitz, HerbertWielicki, B. A., T. Wong, R. P. Allan, A. Slingo, J. T. Kiehl, B. J. Soden, C. T. Gordon, A. J. Miller, S. Yang, D. A. Randall, F. Robertson, J. Susskind, H. Jacobowitz, 2002: Evidence for Large Decadal Variability in the Tropical Mean Radiative Energy Budget. Science, 295(5556), 841-844. doi: 10.1126/science.1065837. It is widely assumed that variations in Earth's radiative energy budget at large time and space scales are small. We present new evidence from a compilation of over two decades of accurate satellite data that the top-of-atmosphere (TOA) tropical radiative energy budget is much more dynamic and variable than previously thought. Results indicate that the radiation budget changes are caused by changes in tropical mean cloudiness. The results of several current climate model simulations fail to predict this large observed variation in tropical energy budget. The missing variability in the models highlights the critical need to improve cloud modeling in the tropics so that prediction of tropical climate on interannual and decadal time scales can be improved.
Woick, H.; Dewitte, S.; Feijt, A.; Gratzki, A.; Hechler, P.; Hollmann, R.; Karlsson, K. -G.; Laine, V.; Löwe, P.; Nitsche, H.; Werscheck, M.; Wollenweber, G.Woick, H., S. Dewitte, A. Feijt, A. Gratzki, P. Hechler, R. Hollmann, K. -. Karlsson, V. Laine, P. Löwe, H. Nitsche, M. Werscheck, G. Wollenweber, 2002: The satellite application facility on climate monitoring. Advances in Space Research, 30(11), 2405-2410. doi: 10.1016/S0273-1177(02)80290-3. The Satellite Application Facility on Climate Monitoring is a joint project of the National Meteorological Services and other institutes from Belgium, Finland, Germany, Sweden and The Netherlands. The objective of the project is to set up a system to provide atmospheric and oceanographic data sets from (primarily) operational geostationary and polar orbiting meteorological satellites for climate monitoring, research and applications at regional European scale, for some products on a global scale. Initial operational SAF products are related to clouds, radiation budget, ocean status and water vapour content in the atmosphere. SAF operations are foreseen to start in 2004.
Xu, Kuan-Man; Cederwall, Richard T.; Donner, Leo J.; Grabowski, Wojciech W.; Guichard, Françoise; Johnson, Daniel E.; Khairoutdinov, Marat; Krueger, Steven K.; Petch, Jon C.; Randall, David A.; Seman, Charles J.; Tao, Wei-Kuo; Wang, Donghai; Cheng Xie, Shao; Yio, J. John; Zhang, Ming-HuaXu, K., R. T. Cederwall, L. J. Donner, W. W. Grabowski, F. Guichard, D. E. Johnson, M. Khairoutdinov, S. K. Krueger, J. C. Petch, D. A. Randall, C. J. Seman, W. Tao, D. Wang, S. Cheng Xie, J. J. Yio, M. Zhang, 2002: An intercomparison of cloud-resolving models with the atmospheric radiation measurement summer 1997 intensive observation period data. Quarterly Journal of the Royal Meteorological Society, 128(580), 593-624. doi: 10.1256/003590002321042117. This paper reports an intercomparison study of midlatitude continental cumulus convection simulated by eight two-dimensional and two three-dimensional cloud-resolving models (CRMs), driven by observed large-scale advective temperature and moisture tendencies, surface turbulent fluxes, and radiative-heating profiles during three sub-periods of the summer 1997 Intensive Observation Period of the US Department of Energy's Atmospheric Radiation Measurement (ARM) program. Each sub-period includes two or three precipitation events of various intensities over a span of 4 or 5 days. The results can be summarized as follows. CRMs can reasonably simulate midlatitude continental summer convection observed at the ARM Cloud and Radiation Testbed site in terms of the intensity of convective activity, and the temperature and specific-humidity evolution. Delayed occurrences of the initial precipitation events are a common feature for all three sub-cases among the models. Cloud mass fluxes, condensate mixing ratios and hydrometeor fractions produced by all CRMs are similar. Some of the simulated cloud properties such as cloud liquid-water path and hydrometeor fraction are rather similar to available observations. All CRMs produce large downdraught mass fluxes with magnitudes similar to those of updraughts, in contrast to CRM results for tropical convection. Some inter-model differences in cloud properties are likely to be related to those in the parametrizations of microphysical processes. There is generally a good agreement between the CRMs and observations with CRMs being significantly better than single-column models (SCMs), suggesting that current results are suitable for use in improving parametrizations in SCMs. However, improvements can still be made in the CRM simulations; these include the proper initialization of the CRMs and a more proper method of diagnosing cloud boundaries in model outputs for comparison with satellite and radar cloud observations. Copyright © 2002 Royal Meteorological Society Continental cumulus convection; Model intercomparison study
Yang, Ping; Gao, Bo-Cai; Wiscombe, Warren J.; Mishchenko, Michael I.; Platnick, Steven E.; Huang, Hung-Lung; Baum, Bryan A.; Hu, Yong X.; Winker, Dave M.; Tsay, Si-Chee; Park, Seon K.Yang, P., B. Gao, W. J. Wiscombe, M. I. Mishchenko, S. E. Platnick, H. Huang, B. A. Baum, Y. X. Hu, D. M. Winker, S. Tsay, S. K. Park, 2002: Inherent and apparent scattering properties of coated or uncoated spheres embedded in an absorbing host medium. Applied Optics, 41(15), 2740-2759. doi: 10.1364/AO.41.002740. The conventional Lorenz-Mie formalism is extended to the case for a coated sphere embedded in an absorbing medium. The apparent and inherent scattering cross sections of a particle, derived from the far field and near field, respectively, are different if the host medium is absorptive. The effect of absorption within the host medium on the phase-matrix elements associated with polarization depends on the dielectric properties of the scattering particle. For the specific cases of a soot particle coated with a water layer and an ice sphere containing an air bubble, the phase-matrix elements -P12/P11 and P33/P11 are unique if the shell is thin. The radiative transfer equation for a multidisperse particle system embedded within an absorbing medium is discussed. Conventional multiple-scattering computational algorithms can be applied if scaled apparent single-scattering properties are applied. Meteorology; atmospheric optics; Aerosol and cloud effects; Atmospheric scattering; Scattering, particles
Zhang, Junhua; Lohmann, Ulrike; Lin, BingZhang, J., U. Lohmann, B. Lin, 2002: A new statistically based autoconversion rate parameterization for use in large-scale models. Journal of Geophysical Research: Atmospheres, 107(D24), 4750. doi: 10.1029/2001JD001484. The autoconversion rate is a key process for the formation of precipitation in warm clouds. In climate models, physical processes such as autoconversion rate, which are calculated from grid mean values, are biased, because they do not take subgrid variability into account. Recently, statistical cloud schemes have been introduced in large-scale models to account for partially cloud-covered grid boxes. However, these schemes do not include the in-cloud variability in their parameterizations. In this paper, a new statistically based autoconversion rate considering the in-cloud variability is introduced and tested in three cases using the Canadian Single Column Model (SCM) of the global climate model. The results show that the new autoconversion rate improves the model simulation, especially in terms of liquid water path in all three case studies. 3337 Meteorology and Atmospheric Dynamics: Numerical modeling and data assimilation; 0320 Cloud physics and chemistry; 3354 Meteorology and Atmospheric Dynamics: Precipitation; ARM; autoconversion rate; cloud modeling; SHEBA; statistical cloud scheme; subgrid-scale variability
Zhang, Ying; Li, Zhanqing; Macke, AndreasZhang, Y., Z. Li, A. Macke, 2002: Retrieval of Surface Solar Radiation Budget under Ice Cloud Sky: Uncertainty Analysis and Parameterization. J. Atmos. Sci., 59(20), 2951-2965. doi: 10.1175/1520-0469(2002)059<2951:ROSSRB>2.0.CO;2. Abstract This study investigates and accounts for the influence of various ice cloud parameters on the retrieval of the surface solar radiation budget (SSRB) from reflected flux at the top of the atmosphere (TOA). The optical properties of ice clouds depend on ice crystal shape, size distribution, water content, and the vertical profiles of geometric and microphysical structure. As a result, the relationship between the SSRB and TOA-reflected flux for an ice cloud atmosphere is more complex and differs from that for water cloud and cloudless atmospheres. The sensitivities of the relationship between the SSRB and TOA-reflected flux are examined with respect to various ice cloud parameters. Uncertainties in the retrieval of the SSRB due to inadequate knowledge of various ice cloud parameters are evaluated thoroughly. The uncertainty study is concerned with both pure ice clouds and multiphase clouds (ice cloud above water cloud). According to the magnitudes of errors in the SSRB retrieval caused by different input variables, parameterized correction terms were introduced. If the input variables are known accurately, errors in the retrieval of the SSRB under a wide range of ice cloud conditions are expected to diminish substantially, to less than 10 W m−2 for 91% of the simulated ice cloud cases. In comparison, the same accuracy may be attained for only 19% of the retrievals for the same ice cloud cases using the retrieval algorithm designed for non-ice-cloud conditions.
Zhao, Tom X-P.; Stowe, Larry L.; Smirnov, Alexander; Crosby, David; Sapper, John; McClain, Charles R.Zhao, T. X., L. L. Stowe, A. Smirnov, D. Crosby, J. Sapper, C. R. McClain, 2002: Development of a Global Validation Package for Satellite Oceanic Aerosol Optical Thickness Retrieval Based on AERONET Observations and Its Application to NOAA/NESDIS Operational Aerosol Retrievals. J. Atmos. Sci., 59(3), 294-312. doi: 10.1175/1520-0469(2002)059<0294:DOAGVP>2.0.CO;2. Abstract In this paper, a global validation package for satellite aerosol optical thickness retrieval using the Aerosol Robotic Network (AERONET) observations as ground truth is described. To standardize the validation procedure, the optimum time–space match-up window, the ensemble statistical analysis method, the best selection of AERONET channels, and the numerical scheme used to interpolate/extrapolate these observations to satellite channels have been identified through sensitivity studies. The package is shown to be a unique tool for more objective validation and intercomparison of satellite aerosol retrievals, helping to satisfy an increasingly important requirement of the satellite aerosol remote sensing community. Results of applying the package to the second-generation operational aerosol observational data (AEROBS) from the NOAA-14 Advanced Very High Resolution Radiometer (AVHRR) in 1998 and to the same year aerosol observation data [Clouds and the Earth's Radiant Energy System-Single Scanner Foodprint version 4 (CERES-SSF4)] from the Tropical Rainfall Measuring Mission (TRMM) Visible Infrared Scanner (VIRS) are presented as examples of global validation. The usefulness of the package for identifying improvements to the aerosol optical thickness τ retrieval algorithm is also demonstrated. The principal causes of systematic errors in the current National Oceanic and Atmospheric Administration (NOAA)/National Environmental Satellite, Data, and Information Service (NESDIS) operational aerosol optical thickness retrieval algorithm have been identified and can be reduced significantly, if the correction and adjustment suggested from the global validation are adopted. Random error in the τ retrieval is identified to be a major source of error on deriving the effective Ångström wavelength exponent α and may be associated with regional differences in aerosol particles, which are not accounted for in the current second-generation operational algorithm. Adjustments to the nonaerosol and aerosol radiative transfer model parameters that reduce systematic errors in τ retrievals are suggested for consideration in the next-generation algorithm. Basic features that should be included in the next-generation algorithm to reduce random error in τ retrievals and the resulting error in the effective Ångström wavelength exponent have also been discussed. Compared to the AERONET observation, the NOAA-14 AVHRR (AEROBS) τ values for mean conditions are biased high by 0.05 and 0.08, with random errors of 0.08 and 0.05, at 0.63 and 0.83 μm, respectively. Correspondingly, the TRMM VIRS (CERES-SSF4) values for mean conditions are biased high by 0.06 and 0.02, with random errors of 0.06 and 0.04 at 0.63 and 1.61 μm, respectively. After corrections and adjustments to the retrieval algorithm, the biases in both channels of AVHRR and VIRS are reduced significantly to values close to zero, although random error is almost unchanged. The α exponent derived directly from the aerosol optical thicknesses (τs) has been shown to be poorly correlated both before and after adjustments, indicating that random error in the τ measurement (possibly related to aerosol model parameter variations or cloud–surface reflectance contamination) needs to be reduced.
Buriez, Jean-Claude; Doutriaux-Boucher, Marie; Parol, Frédéric; Loeb, Norman G.Buriez, J., M. Doutriaux-Boucher, F. Parol, N. G. Loeb, 2001: Angular Variability of the Liquid Water Cloud Optical Thickness Retrieved from ADEOS–POLDER. J. Atmos. Sci., 58(20), 3007-3018. doi: 10.1175/1520-0469(2001)058<3007:AVOTLW>2.0.CO;2. Abstract The usual procedure for retrieving the optical thickness of liquid water clouds from satellite-measured radiances is based on the assumption of plane-parallel layers composed of liquid water droplets. This study investigates the validity of this assumption from Advanced Earth Orbiting Satellite–Polarization and Directionality of the Earth's Reflectances (ADEOS–POLDER) observations. To do that, the authors take advantage of the multidirectional viewing capability of the POLDER instrument, which functioned nominally aboard ADEOS from November 1996 to June 1997. The usual plane-parallel cloud model composed of water droplets with an effective radius of 10 μm provides a reasonable approximation of the angular dependence in scattering at visible wavelengths from overcast liquid water clouds for moderate solar zenith angles. However, significant differences between model and observations appear in the rainbow direction and for the smallest observable values of scattering angle (Θ < 90°). A better overall agreement would be obtained for droplets with an effective radius of about 7–8 μm for continental liquid water clouds. On the other hand, changing the water droplet size distribution would not lead to a significant improvement for maritime situations. When horizontal variations in cloud optical thickness are considered by using the independent pixel approximation (IPA), a small improvement is obtained over the whole range of scattering angles but significant discrepancies remain for Θ < 80°, that is for large solar zenith angles in the forward-scattering direction. The remaining differences between various models based on the plane-parallel radiative transfer and POLDER observations are thought to be due to variations in cloud shape.
Cess, Robert D.; Zhang, Minghua; Wang, Pi-Huan; Wielicki, Bruce A.Cess, R. D., M. Zhang, P. Wang, B. A. Wielicki, 2001: Cloud structure anomalies over the tropical Pacific during the 1997/98 El Niño. Geophysical Research Letters, 28(24), 4547-4550. doi: 10.1029/2001GL013750. Satellite measurements of both cloud vertical structure and cloud-radiative forcing have been used to show that during the strong 1997/98 El Niño there was a substantial change in cloud vertical structure over the tropical Pacific Ocean. Relative to normal years, cloud altitudes were lower in the western portion of the Pacific and higher in the eastern portion. The reason for these redistributions was a collapse of the Walker circulation and enhanced large-scale upward motion over the eastern Pacific, both caused by the lack of a zonal sea surface temperature gradient during the El Niño. It is proposed that these cloud structure changes, which significantly impact satellite measurements of the tropical Pacific's radiation budget, would serve as one useful means of testing cloud-climate interactions in climate models. 3337 Meteorology and Atmospheric Dynamics: Numerical modeling and data assimilation; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1600 Global Change
Cess, Robert D.; Zhang, Minghua; Wielicki, Bruce A.; Young, David F.; Zhou, Xue-Long; Nikitenko, YuriCess, R. D., M. Zhang, B. A. Wielicki, D. F. Young, X. Zhou, Y. Nikitenko, 2001: The Influence of the 1998 El Niño upon Cloud-Radiative Forcing over the Pacific Warm Pool. J. Climate, 14(9), 2129-2137. doi: 10.1175/1520-0442(2001)014<2129:TIOTEN>2.0.CO;2. Abstract Clouds cool the climate system by reflecting shortwave radiation and warm it by increasing the atmospheric greenhouse. Previous studies have shown that in tropical regions of deep convection there is a near cancellation between cloud-induced shortwave cooling and longwave warming. The present study investigates the possible influence of the 1998 El Niño upon this near cancellation for the tropical western Pacific’s warm pool; this was accomplished by employing satellite radiometric measurements (Earth Radiation Budget Experiment, and Clouds and the Earth’s Radiant Energy System). With the exclusion of the 1998 El Niño, this study also finds near cancellation between the shortwave and longwave cloud forcings and demonstrates that it refers to the average of different cloud types rather than being indicative of a single cloud type. The shortwave cooling slightly dominates the longwave warming, and there is considerable interannual variability in this modest dominance that appears attributable to interannual variability of tropopause temperature. For the strong 1998 El Niño, however, there is a substantially greater tendency toward net radiative cooling, and the physical mechanism for this appears to be a change in cloud vertical structure. For normal years, as well as for the weaker 1987 El Niño, high clouds dominate the radiation budget over the warm pool. In 1998, however, the measurements indicate the radiation budget is partially governed by middle-level clouds, thus explaining the net cooling over the warm pool during the 1998 El Niño as well as emphasizing differences between this event and the weaker 1987 El Niño.
Chambers, L. H.; Wielicki, B. A.; Loeb, N. G.Chambers, L. H., B. A. Wielicki, N. G. Loeb, 2001: Shortwave Flux from Satellite-Measured Radiance: A Theoretical Study over Marine Boundary Layer Clouds. Journal of Applied Meteorology, 40(12), 2144-2161. doi: 10.1175/1520-0450(2001)040<2144:SFFSMR>2.0.CO;2. Abstract Earth radiation budget measurements, important to climate monitoring and to validating climate models, require that radiances measured by satellite instruments be converted to hemispherical flux. This paper examines that problem theoretically, using inhomogeneous cloud models constructed from Landsat scenes of marine boundary layer clouds. The spherical harmonics discrete ordinates method (SHDOM) code is applied to the model scenes to compute full two-dimensional radiation fields, which then simulate measured radiances. Inversion to flux is performed by several different methods, including plane-parallel table lookup and empirical angular distribution models with three different ways of determining scene identification, to examine error sources and relative magnitudes. Using a simple plane-parallel table lookup results in unacceptably large flux bias errors of 11%–60%, depending on the orbital viewing geometry. This bias can be substantially reduced, to no more than 6%, by using empirical angular distribution models. Further improvement, to no more than 2% flux bias error, is obtained if known biases in optical-depth retrievals are taken into account when building the angular models. Last, the bias can be further reduced to a fraction of a percent using scene identification based on multiple views of the same area. There are limits, however, to the reduction in the instantaneous error with this approach. Trends in the flux error are also identified, in particular an equator-to-pole trend in the flux bias. Given the importance of satellite measurements for determining heat transport from equator to pole, this consistent bias should be kept in mind, and efforts should be made to reduce it in the future.
Chou, Ming-Dah; Chan, Pui-King; Yan, Michael M.-H.Chou, M., P. Chan, M. M. Yan, 2001: A sea surface radiation data set for climate applications in the tropical western Pacific and South China Sea. Journal of Geophysical Research: Atmospheres, 106(D7), 7219-7228. doi: 10.1029/2000JD900661. The sea surface shortwave and longwave radiative fluxes have been retrieved from the radiances measured by Japan's Geostationary Meteorological Satellite 5. The surface radiation data set covers the domain 40°S-40°N and 90°E–170°W and a period starting from January 1998. The temporal resolution is 1 day, and the spatial resolution is 0.5°×0.5° latitude-longitude. The retrieved surface radiation has been validated with the radiometric measurements at the Atmospheric Radiation Measurement (ARM) site on Manus Island in the equatorial western Pacific. It has also been validated with the measurements at the radiation site on Dungsha Island during the South China Sea Monsoon Experiment (SCSMEX) (May and June 1998). The data set is used to study the effect of El Niño and East Asian summer monsoon on the heating of the ocean. Interannual variations of clouds associated with El Niño and the East Asian summer monsoon have a large impact on the radiative heating of the ocean, exceeding 40 W m−2 in seasonal mean over large areas. Together with the Clouds and the Earth's Radiant Energy System (CERES) shortwave fluxes at the top of the atmosphere and the radiative transfer calculations of clear-sky fluxes, this surface radiation data set is also used to study the impact of clouds on the solar heating of the atmosphere. It is found that clouds enhance the atmospheric solar heating by ∼21 W m−2 in the tropical western Pacific and the South China Sea. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3339 Meteorology and Atmospheric Dynamics: Ocean/atmosphere interactions; 3374 Meteorology and Atmospheric Dynamics: Tropical meteorology
Clarke, A. D.; Collins, W. G.; Rasch, P. J.; Kapustin, V. N.; Moore, K.; Howell, S.; Fuelberg, H. E.Clarke, A. D., W. G. Collins, P. J. Rasch, V. N. Kapustin, K. Moore, S. Howell, H. E. Fuelberg, 2001: Dust and pollution transport on global scales: Aerosol measurements and model predictions. Journal of Geophysical Research: Atmospheres, 106(D23), 32555-32569. doi: 10.1029/2000JD900842. Vertical profiles of aerosol and gas phase species were measured on flights near Hawaii on April 9 and 10, 1999, during NASA's Pacific Exploratory Mission (PEM) Tropics B program. These measurements characterized aerosol microphysics, inferred chemistry, optical properties, and gases in several extensive dust and pollution plumes, also detected by satellites, which had 10,000-km trajectories back to sources in Asia. Size-resolved measurements indicative of aerosol sulfate, black carbon, dust, light scattering, and absorption allowed determination of their concentrations and contributions to column aerosol optical depth. A new Chemical Transport Model (CTM) that includes aerosol, meteorological fields, dynamics, gas and particle source emissions, a chemistry component (MATCH), and assimilated satellite data was used to predict aerosol and gas concentrations and the aerosol optical effects along our flight path. Flight measurements confirmed the “river-like” plume structures predicted by the CTM and showed close agreement with the predicted contributions of dust and sulfate to aerosol concentrations and optical properties for this global-scale transport path. Consistency between satellite, model and in situ assessment of aerosol optical depth was found, with noted exceptions, within ∼25%. Both observations and model results confirmed that this aerosol was being entrained into the marine boundary layer between Hawaii and California where it can be expected to modify the type and concentration of cloud condensation nuclei in ways that may alter properties of low-level clouds. These observations document the significance and complexity of long-range aerosol transport and highlight the potential of emerging CTM models to extend observational data and address related issues on global scales. 0305 Aerosols and particles; 0368 Troposphere: constituent transport and chemistry
Collins, William D.; Rasch, Phillip J.; Eaton, Brian E.; Khattatov, Boris V.; Lamarque, Jean-Francois; Zender, Charles S.Collins, W. D., P. J. Rasch, B. E. Eaton, B. V. Khattatov, J. Lamarque, C. S. Zender, 2001: Simulating aerosols using a chemical transport model with assimilation of satellite aerosol retrievals: Methodology for INDOEX. Journal of Geophysical Research: Atmospheres, 106(D7), 7313-7336. doi: 10.1029/2000JD900507. A system for simulating aerosols has been developed using a chemical transport model together with an assimilation of satellite aerosol retrievals. The methodology and model components are described in this paper, and the modeled distribution of aerosols for the Indian Ocean Experiment (INDOEX) is presented by Rasch et al. [this issue]. The system generated aerosol forecasts to guide deployment of ships and aircraft during INDOEX. The system consists of the Model of Atmospheric Transport and Chemistry (MATCH) combined with an assimilation package developed for applications in atmospheric chemistry. MATCH predicts the evolution of sulfate, carbonaceous, and mineral dust aerosols, and it diagnoses the distribution of sea salt aerosols. The model includes a detailed treatment of the sources, chemical transformation, transport, and deposition of the aerosol species. The aerosol forecasts involve a two-stage process. During the assimilation phase the total column aerosol optical depth (AOD) is estimated from the model aerosol fields. The model state is then adjusted to improve the agreement between the simulated AOD and satellite retrievals of AOD. During the subsequent integration phase the aerosol fields are evolved using meteorological fields from an external model. Comparison of the modeled AOD against estimates of the AOD from INDOEX Sun photometer data show that the differences in daily means are −0.03±0.06. Although the initial application is limited to the Indian Ocean, the methodology could be extended to derive global aerosol analyses combining in situ and remotely sensed aerosol observations. 3337 Meteorology and Atmospheric Dynamics: Numerical modeling and data assimilation; 0305 Aerosols and particles; 0345 Pollution: urban and regional; 0368 Troposphere: constituent transport and chemistry
Davis, Anthony B.; Marshak, AlexanderDavis, A. B., A. Marshak, 2001: Multiple Scattering in Clouds: Insights from Three-Dimensional Diffusion/P1 Theory. Nuclear Science and Engineering, 137(3), 251-280.
Dewitte, S.; Joukoff, A.; Crommelynck, D.; Lee, R. B.; Helizon, R.; Wilson, R. S.Dewitte, S., A. Joukoff, D. Crommelynck, R. B. Lee, R. Helizon, R. S. Wilson, 2001: Contribution of the Solar Constant (SOLCON) program to the long-term total solar irradiance observations. Journal of Geophysical Research: Space Physics, 106(A8), 15759-15765. doi: 10.1029/2000JA900160. On long timescales the variation of the total solar irradiance (TSI) received by the Earth is believed to be one of the climate change drivers. Therefore accurate and time-stable measurements of the total solar irradiance are necessary. The Solar Constant (SOLCON) instrument made TSI measurements in April 1992 and during the International Extreme Ultraviolet Hitchhiker (IEH) 3 STS 95 shuttle flight in autumn 1998. We assume that the SOLCON instrument remained stable within 0.01 % in between those measurements, and we verify this assumption as well as possible. From the SOLCON measurements we conclude the following: (1) The 1998 Space Absolute Radiometric Reference (SARR) adjustment coefficient applicable to the Active Cavity Radiometer Irradiance Monitor II (ACRIM II) during the IEH 3 period is 1.000438 with a one sigma uncertainty of 18 ppm, compared to the 1993 SARR adjustment coefficient of 1.000258. (2) The solar monitor on the Earth Radiation Budget Satellite (ERBS), with a 1993 SARR adjustment coefficient of 1.000453, has not aged within a one sigma uncertainty level of 130 ppm; and (3) the 1998 SARR adjustment coefficients for the Variability of Solar Irradiance and Gravity Oscillations (VIRGO) radiometers have been determined with a one sigma uncertainty of 10 ppm: They are 1.000025 for the Differential Absolute Radiometer left channel (DIARAD-L) and 1.000279 for the version 1.2 data from the PMO6-VA radiometer. 7538 Solar irradiance; 7594 Instruments and techniques
Doelling, David R.; Minnis, Patrick; Spangenberg, Douglas A.; Chakrapani, Venkatesan; Mahesh, Ashwin; Pope, Shelly K.; Valero, Francisco P. J.Doelling, D. R., P. Minnis, D. A. Spangenberg, V. Chakrapani, A. Mahesh, S. K. Pope, F. P. J. Valero, 2001: Cloud radiative forcing at the top of the atmosphere during FIRE ACE derived from AVHRR data. Journal of Geophysical Research: Atmospheres, 106(D14), 15279-15296. doi: 10.1029/2000JD900455. Cloud radiative forcing at the top of the atmosphere is derived from narrowband visible and infrared radiances from NOAA-12 and NOAA-14 advanced very high resolution radiometer (AVHRR) data taken over the Arctic Ocean during the First ISCCP Regional Experiment Arctic Cloud Experiment (FIRE ACE) during spring and summer 1998. Shortwave and longwave fluxes at the top of the atmosphere (TOA) were computed using narrowband-to-broadband conversion formulae based on coincident Earth Radiation Budget Experiment (ERBE) broadband and AVHRR narrowband radiances. The NOAA-12/NOAA-14 broadband data were validated using model calculations and coincident broadband flux radiometer data from the Surface Heat Budget of the Arctic Ocean experiment and from aircraft data. The AVHRR TOA albedos agreed with the surface- and aircraft-based albedos to within one standard deviation of ±0.029 on an instantaneous basis. Mean differences ranged from −0.012 to 0.023 depending on the radiometer and platform. AVHRR-derived longwave fluxes differed from the model calculations using aircraft- and surface-based fluxes by −0.2 to −0.3 W m−2, on average, when the atmospheric profiles were adjusted to force agreement between the observed and the calculated downwelling fluxes. The standard deviations of the differences were less than 2%. Mean total TOA albedo for the domain between 72°N and 80°N and between 150°W and 180°W changed from 0.695 in May to 0.510 during July, while the longwave flux increased from 217 to 228 W m−2. Net radiation increased from −89 to −2 W m−2 for the same period. Net cloud forcing varied from −15 W m−2 in May to −31 W m−2 during July, while longwave cloud forcing was nearly constant at ∼8 W m−2. Shortwave cloud forcing dominated the cloud effect, ranging from −22 W m−2 during May to −40 W m−2 in July. The mean albedos and fluxes are consistent with previous measurements from the ERBE, except during May when the albedo and longwave flux were greater than the maximum ERBE values. The cloud-forcing results, while similar to some earlier estimates, are the most accurate values hitherto obtained for regions in the Arctic. When no significant melting was present, the clear-sky longwave flux showed a diurnal variation similar to that over land under clear skies. These data should be valuable for understanding the Arctic energy budget and for constraining models of atmosphere and ocean processes in the Arctic. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3309 Meteorology and Atmospheric Dynamics: Climatology; 3349 Meteorology and Atmospheric Dynamics: Polar meteorology; 9315 Information Related to Geographic Region: Arctic region
Dong, Xiquan; Mace, Gerald G.; Minnis, Patrick; Young, David F.Dong, X., G. G. Mace, P. Minnis, D. F. Young, 2001: Arctic stratus cloud properties and their effect on the surface radiation budget: Selected cases from FIRE ACE. Journal of Geophysical Research: Atmospheres, 106(D14), 15297-15312. doi: 10.1029/2000JD900404. To study Arctic stratus cloud properties and their effect on the surface radiation balance during the spring transition season, analyses are performed using data taken during three cloud and two clear days in May 1998 as part of the First ISCCP Regional Experiment (FIRE) Arctic Cloud Experiment (ACE). Radiative transfer models are used in conjunction with surface- and satellite-based measurements to retrieve the layer-averaged microphysical and shortwave radiative properties. The surface-retrieved cloud properties in Cases 1 and 2 agree well with the in situ and satellite retrievals. Discrepancies in Case 3 are due to spatial mismatches between the aircraft and the surface measurements in a highly variable cloud field. Also, the vertical structure in the cloud layer is not fully characterized by the aircraft measurements. Satellite data are critical for understanding some of the observed discrepancies. The satellite-derived particle sizes agree well with the coincident surface retrievals and with the aircraft data when they were collocated. Optical depths derived from visible-channel data over snow backgrounds were overestimated in all three cases, suggesting that methods currently used in satellite cloud climatologies derive optical depths that are too large. Use of a near-infrared channel with a solar infrared channel to simultaneously derive optical depth and particle size appears to alleviate this overestimation problem. Further study of the optical depth retrieval is needed. The surface-based radiometer data reveal that the Arctic stratus clouds produce a net warming of 20 W m−2 in the surface layer during the transition season suggesting that these clouds may accelerate the spring time melting of the ice pack. This surface warming contrasts with the net cooling at the top of the atmosphere (TOA) during the same period. An analysis of the complete FIRE ACE data sets will be valuable for understanding the role of clouds during the entire melting and refreezing process that occurs annually in the Arctic. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3307 Meteorology and Atmospheric Dynamics: Boundary layer processes; 3349 Meteorology and Atmospheric Dynamics: Polar meteorology
Donner, Leo J.; Seman, Charles J.; Hemler, Richard S.; Fan, SongmiaoDonner, L. J., C. J. Seman, R. S. Hemler, S. Fan, 2001: A Cumulus Parameterization Including Mass Fluxes, Convective Vertical Velocities, and Mesoscale Effects: Thermodynamic and Hydrological Aspects in a General Circulation Model. J. Climate, 14(16), 3444-3463. doi: 10.1175/1520-0442(2001)014<3444:ACPIMF>2.0.CO;2. Abstract A cumulus parameterization based on mass fluxes, convective-scale vertical velocities, and mesoscale effects has been incorporated in an atmospheric general circulation model (GCM). Most contemporary cumulus parameterizations are based on convective mass fluxes. This parameterization augments mass fluxes with convective-scale vertical velocities as a means of providing a method for incorporating cumulus microphysics using vertical velocities at physically appropriate (subgrid) scales. Convective-scale microphysics provides a key source of material for mesoscale circulations associated with deep convection, along with mesoscale in situ microphysical processes. The latter depend on simple, parameterized mesoscale dynamics. Consistent treatment of convection, microphysics, and radiation is crucial for modeling global-scale interactions involving clouds and radiation. Thermodynamic and hydrological aspects of this parameterization in integrations of the Geophysical Fluid Dynamics Laboratory SKYHI GCM are analyzed. Mass fluxes, phase changes, and heat and moisture transport by the mesoscale components of convective systems are found to be large relative to those of convective (deep tower) components, in agreement with field studies. Partitioning between the convective and mesoscale components varies regionally with large-scale flow characteristics and agrees well with observations from the Tropical Rainfall Measuring Mission (TRMM) satellite. The effects of the mesoscale components of convective systems include stronger Hadley and Walker circulations, warmer upper-tropospheric Tropics, and moister Tropics. The mass fluxes for convective systems including mesoscale components differ appreciably in both magnitude and structure from those for convective systems consisting of cells only. When mesoscale components exist, detrainment is concentrated in the midtroposphere instead of the upper troposphere, and the magnitudes of mass fluxes are smaller. The parameterization including mesoscale components is consistent with satellite observations of the size distribution of convective systems, while the parameterization with convective cells only is not. The parameterization of convective vertical velocities is an important control on the intensity of the mesoscale stratiform circulations associated with deep convection. The mesoscale components are less intense than in TRMM observations if spatially and temporally invariant convective vertical velocities are used instead of parameterized, variable velocities.
Duda, David P.; Minnis, Patrick; Nguyen, LouisDuda, D. P., P. Minnis, L. Nguyen, 2001: Estimates of cloud radiative forcing in contrail clusters using GOES imagery. Journal of Geophysical Research: Atmospheres, 106(D5), 4927-4937. doi: 10.1029/2000JD900393. Using data from the Geostationary Operational Environmental Satellite (GOES), the evolution of solar and longwave radiative forcing in contrail clusters is presented in several case studies. The first study examines contrails developing over the midwestern United States in a region of upper tropospheric moisture enhanced by the remnants of Hurricane Nora on September 26, 1997. Two other cases involve contrail clusters that formed over the Chesapeake Bay and the Atlantic Ocean on February 11 and March 5, 1999, respectively. The last study includes contrails forming over the tropical Pacific near Hawaii. Observations of tropical contrails near Hawaii show that the contrail optical properties are similar to those measured from satellite in the midlatitudes, with visible optical depths between 0.3 and 0.5 and particle sizes between 30 and 60 μm as the contrails mature into diffuse cloudiness. Radiative transfer model simulations of the tropical contrail case suggest that ice crystal shape may have an important effect on radiative forcing in contrails. The magnitudes of the observed solar and longwave radiative forcings were 5.6 and 3.2 W m−2 less than those from the corresponding model simulations, and these differences are attributed to the subpixel scale low clouds and uncertainties in the anisotropic reflectance and limb-darkening models used to estimate the observed forcing. Since the broadband radiative forcing in contrails often changes rapidly, contrail forcing estimates based only on the polar orbiting advanced very high resolution radiometer (AVHRR) data could be inaccurate due to the lack of sufficient temporal sampling. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1640 Remote sensing; 3360 Meteorology and Atmospheric Dynamics: Remote sensing
Duvel, J-Ph; Viollier, M.; Raberanto, P.; Kandel, R.; Haeffelin, M.; Pakhomov, L. A.; Golovko, V. A.; Mueller, J.; Stuhlmann, R.; Scientific Working Group, International Sca Ra B.Duvel, J., M. Viollier, P. Raberanto, R. Kandel, M. Haeffelin, L. A. Pakhomov, V. A. Golovko, J. Mueller, R. Stuhlmann, I. S. R. B. Scientific Working Group, 2001: The ScaRaB–Resurs Earth Radiation Budget Dataset and First Results. Bull. Amer. Meteor. Soc., 82(7), 1397-1408. doi: 10.1175/1520-0477(2001)082<1397:TSRERB>2.3.CO;2. Abstract Measurements made by the second flight model of the Scanner for Radiation Budget (ScaRaB) instrument have been processed and are now available for the scientific community. Although this set of data is relatively short and sparse, it is of excellent quality and is the only global broadband scanner radiance information for the period between October 1998 and April 1999. This second flight model marks the conclusion of the ScaRaB cooperative program of France, Russia, and Germany. The two flight models of the ScaRaB instrument gave broadband radiance measurements comparable in quality to those made by the Earth Radiation Budget Experiment and the Clouds and Earth Radiant Energy System scanning instruments. In addition, the ScaRaB instrument gave unique results for the comparison between narrowband (visible and infrared atmospheric window) and broadband radiance measurements. These measurements were mostly used to improve the broadband data processing and to study the error budget resulting when narrowband channel data are used to estimate the earth radiation budget. These concomitant narrow– and broadband measurements made by the two flight models of ScaRaB contain original information of considerable interest for further scientific use.
Garreaud, RenéD.; Rutllant, José; Quintana, Juan; Carrasco, Jorge; Minnis, PatrickGarreaud, R., J. Rutllant, J. Quintana, J. Carrasco, P. Minnis, 2001: CIMAR–5: A Snapshot of the Lower Troposphere over the Subtropical Southeast Pacific. Bull. Amer. Meteor. Soc., 82(10), 2193-2207. doi: 10.1175/1520-0477(2001)082<2193:CASOTL>2.3.CO;2. Abstract The extensive and persistent deck of stratocumulus (SCu) off the west coast of subtropical South America plays an important role in the regional and global climate, as well as in coastal weather. As in other subtropical regions, the SCu form at the top of a marine boundary layer (MBL) bounded by a relatively cold ocean and a large–scale subsidence inversion. Nevertheless, details of the structure and variability of the lower troposphere over this region are largely unknown. Ship–based meteorological observations taken along a transect at 27°S from the Chilean coast (71°W) to Easter Island (110°W) during the second half of October 1999 provide a preliminary description of the low–level circulation, thermodynamic structure, and cloudiness over the subtropical southeast Pacific. Three types of observations were made: (a) 15–min average of air temperature, relative humidity, solar radiation, pressure, and wind by an automatic weather station on the ship deck; (b) 15–min average of vertical reflectivity and cloud base by a laser ceilometer on the ship deck; and (c) twice–daily rawinsondes. Several cloud and radiation properties were derived from GOES–8 imagery and validated against the ship–based observations. A preliminary assessment of the ability of NCEP–NCAR reanalysis and scatterometer winds in representing the atmosphere over a largely in situ data–void area is also presented. Sea surface temperature and near–surface air temperature increase gradually westward, while near–surface relative humidity remains nearly constant at ~80%. A significant increase in the free–tropospheric moisture indicates an offshore decrease in the large–scale subsidence. Consistently, the MBL evolves from a shallow, well–mixed MBL topped by compact SCu near the coast; to a deeper, decoupled MBL with a cumuli rising into a patchy SCu deck near Easter Island, in a similar fashion to the transition from subtropical–stratus regime to trade–cumulus regime described elsewhere. In addition to these "climatological" features, the ship data also reveal the large sensitivity of the MBL–trade inversion structure to synoptic–scale disturbances over the subtropical Pacific. Cloud droplet effective sizes increase from the coast to open ocean. Furthermore, cloud fraction, cloud–top height, liquid water path, and optical depth all peaked during the morning and reached a minimum by midafternoon.
Gupta, Shashi K.; Kratz, David P.; Stackhouse, Paul W.; Wilber, Anne C.Gupta, S. K., D. P. Kratz, P. W. Stackhouse, A. C. Wilber, 2001: The Langley Parameterized Shortwave Algorithm (LPSA) for Surface Radiation Budget Studies. 1.0. An efficient algorithm was developed during the late 1980's and early 1990's by W. F. Staylor at NASA/LaRC for the purpose of deriving shortwave surface radiation budget parameters on a global scale. While the algorithm produced results in good agreement with observations, the lack of proper documentation resulted in a weak acceptance by the science community. The primary purpose of this report is to develop detailed documentation of the algorithm. In the process, the algorithm was modified whenever discrepancies were found between the algorithm and its referenced literature sources. In some instances, assumptions made in the algorithm could not be justified and were replaced with those that were justifiable. The algorithm uses satellite and operational meteorological data for inputs. Most of the original data sources have been replaced by more recent, higher quality data sources, and fluxes are now computed on a higher spatial resolution. Many more changes to the basic radiation scheme and meteorological inputs have been proposed to improve the algorithm and make the product more useful for new research projects. Because of the many changes already in place and more planned for the future, the algorithm has been renamed the Langley Parameterized Shortwave Algorithm . energy budgets; atmospheric radiation; Algorithms; spatial resolution; meteorological parameters
Haeffelin, Martial; Kato, Seiji; Smith, Amie M.; Rutledge, C. Ken; Charlock, Thomas P.; Mahan, J. RobertHaeffelin, M., S. Kato, A. M. Smith, C. K. Rutledge, T. P. Charlock, J. R. Mahan, 2001: Determination of the thermal offset of the Eppley precision spectral pyranometer. Applied Optics, 40(4), 472-484. doi: 10.1364/AO.40.000472. Eppley’s precision spectral pyranometer (PSP) is used in networks around the world to measure downwelling diffuse and global solar irradiance at the surface of the Earth. In recent years several studies have shown significant discrepancy between irradiances measured by pyranometers and those computed by atmospheric radiative transfer models. Pyranometer measurements have been questioned because observed diffuse irradiances sometimes are below theoretical minimum values for a pure molecular atmosphere, and at night the instruments often produce nonzero signals ranging between +5 and -10 W m-2. We install thermistor sondes in the body of a PSP as well as on its inner dome to monitor the temperature gradients within the instrument, and we operate a pyrgeometer (PIR) instrument side by side with the PSP. We derive a relationship between the PSP output and thermal radiative exchange by the dome and the detector and a relationship between the PSP output and the PIR thermopile output (net–IR). We determine the true PSP offset by quickly capping the instrument at set time intervals. For a ventilated and shaded PSP, the thermal offset can reach -15 W m-2 under clear skies, whereas it remains close to zero for low overcast clouds. We estimate the PSP thermal offset by two methods: (1) using the PSP temperatures and (2) using the PIR net–IR signal. The offset computed from the PSP temperatures yields a reliable estimate of the true offset (±1 W m-2). The offset computed from net–IR is consistent with the true offset at night and under overcast skies but predicts only part of the true range under clear skies. Instrumentation, measurement, and metrology; Thermal effects
Haeffelin, Martial; Wielicki, Bruce; Duvel, Jean Philippe; Priestley, Kory; Viollier, MichelHaeffelin, M., B. Wielicki, J. P. Duvel, K. Priestley, M. Viollier, 2001: Inter-calibration of CERES and ScaRaB Earth Radiation Budget datasets using temporally and spatially collocated radiance measurements. Geophysical Research Letters, 28(1), 167-170. doi: 10.1029/2000GL012233. Comparisons of radiance measurements from overlapping independent Earth and cloud radiation budget (ERB) missions are an important contribution to the validation process of these missions and are essential to the construction of a consistent long-term record of ERB observations. Measurements from two scanning radiometers of different design and calibration, the Clouds and the Earth's Radiant Energy System (CERES) and the Scanner for Radiation Budget (ScaRaB), are compared during simultaneous operation in January and March 1999. The instruments are found to be consistent to within 0.5% and 1.5% in the longwave and shortwave spectral domains, respectively. 1694 Global Change: Instruments and techniques
Herring, DavidHerring, D., 2001: NASA Earth Observatory :. Thanks to a team at NASA's Langley Research Center (LaRC), engineers and amateur inventors worldwide now have free access to global-scale data on natural renewable energy resources. Private companies are using these data to design, build, and market new technologies for harnessing this energy. The best part is many of these new systems will be marketed at affordable prices in underdeveloped countries for those who need them most.
Hobbs, Peter V.; Rangno, Arthur L.; Shupe, Matthew; Uttal, TaneilHobbs, P. V., A. L. Rangno, M. Shupe, T. Uttal, 2001: Airborne studies of cloud structures over the Arctic Ocean and comparisons with retrievals from ship-based remote sensing measurements. Journal of Geophysical Research: Atmospheres, 106(D14), 15029-15044. doi: 10.1029/2000JD900323. Information on the heights and microphysical structures of two cloud systems derived from a 35 GHz radar, microwave and infrared radiometers, and a lidar aboard a ship in the Arctic Ocean are compared with simultaneous airborne in situ measurements. The cloud systems considered are a single layer of thin altocumulus with virga (June 3, 1998), and a more complex cloud system consisting of several altocumulus-altostratus layers that precipitated into a boundary layer, stratus-stratocumulus system (May 29, 1998). For the first cloud system the cloud top deduced from the 35 GHz radar was close to that measured from the aircraft. The radar detected virga below cloud base even when the virga was composed of very low concentrations of ice crystals; this prevented measurement of the cloud base height with the radar. Because of the sensitivity of the 35 GHz radar to ice crystals, cloud liquid water contents derived from it are confounded by just a few ice crystals. In the case of the second more complex cloud system, embedded cloud liquid water layers into which ice particles fell were not resolved by the radar. Consequently, although five altocumulus layers were intercepted by the aircraft, the radar display depicts a single deep precipitating system. These cases illustrate that liquid water content in mixed-phase clouds cannot be retrieved reliably using the radar-microwave radiometer technique. 1640 Remote sensing; 0320 Cloud physics and chemistry; 0394 Instruments and techniques; 3349 Meteorology and Atmospheric Dynamics: Polar meteorology
Hou, Arthur Y.; Zhang, Sara Q.; da Silva, Arlindo M.; Olson, William S.; Kummerow, Christian D.; Simpson, JoanneHou, A. Y., S. Q. Zhang, A. M. da Silva, W. S. Olson, C. D. Kummerow, J. Simpson, 2001: Improving Global Analysis and Short–Range Forecast Using Rainfall and Moisture Observations Derived from TRMM and SSM/I Passive Microwave Sensors. Bull. Amer. Meteor. Soc., 82(4), 659-679. doi: 10.1175/1520-0477(2001)082<0659:IGAASF>2.3.CO;2. Abstract As a follow–on to the Tropical Rainfall Measuring Mission (TRMM), the National Aeronautics and Space Administration in the United States, the National Space Development Agency of Japan, and the European Space Agency are considering a satellite mission to measure the global rainfall. The plan envisions an improved TRMM–like satellite and a constellation of eight satellites carrying passive microwave radiometers to provide global rainfall measurements at 3–h intervals. The success of this concept relies on the merits of rainfall estimates derived from passive microwave radiometers. This article offers a proof–of–concept demonstration of the benefits of using rainfall and total precipitable water (TPW) information derived from such instruments in global data assimilation with observations from the TRMM Microwave Imager (TMI) and two Special Sensor Microwave/Imager (SSM/I) instruments. Global analyses that optimally combine observations from diverse sources with physical models of atmospheric and land processes can provide a comprehensive description of the climate systems. Currently, such data analyses contain significant errors in primary hydrological fields such as precipitation and evaporation, especially in the Tropics. It is shown that assimilating the 6–h–averaged TMI and SSM/I surface rain rate and TPW retrievals improves not only the hydrological cycle but also key climate parameters such as clouds, radiation, and the upper–tropospheric moisture in the analysis produced by the Goddard Earth Observing System Data Assimilation System, as verified against radiation measurements by the Clouds and the Earth's Radiant Energy System instrument and brightness temperature observations by the Television Infrared Observational Satellite Operational Vertical Sounder instruments. Typically, rainfall assimilation improves clouds and radiation in areas of active convection, as well as the latent heating and large–scale motions in the Tropics, while TPW assimilation leads to reduced moisture biases and improved radiative fluxes in clear–sky regions. Ensemble forecasts initialized with analyses that incorporate TMI and SSM/I rainfall and TPW data also yield better short–range predictions of geopotential heights, winds, and precipitation in the Tropics. These results were obtained using a variational procedure based on a 6–h time integration of a column model of moist physics with prescribed dynamical and other physical tendencies. The procedure estimates moisture tendency corrections at observation locations by minimizing the least square differences between the observed TPW and rain rates and those generated by the column model over a 6–h analysis window. These tendency corrections are then applied during the assimilation cycle to compensate for errors arising from both initial conditions and deficiencies in model physics. Our results point to the importance of addressing deficiencies in model physics in assimilating data types such as precipitation, for which the forward model based on convective parameterizations may have significant systematic errors. This study offers a compelling illustration of the potential of using rainfall and TPW information derived from passive microwave instruments to significantly improve the quality of four–dimensional global datasets for climate analysis and weather forecasting applications.
Hu, Yong-X.; Winker, David; Yang, Ping; Baum, Bryan; Poole, Lamont; Vann, LeliaHu, Y., D. Winker, P. Yang, B. Baum, L. Poole, L. Vann, 2001: Identification of cloud phase from PICASSO-CENA lidar depolarization: a multiple scattering sensitivity study. Journal of Quantitative Spectroscopy and Radiative Transfer, 70(4–6), 569-579. doi: 10.1016/S0022-4073(01)00030-9. A fast Monte Carlo simulation scheme is developed to assess the impact of multiple scattering on space-based lidar backscattering depolarization measurements. The specific application of our methodology is to determine cloud thermodynamic phase from satellite-based lidar depolarization measurements. Model results indicate that multiple scattering significantly depolarizes backscatter return from water clouds. Multiple scattering depolarization is less significant for non-spherical particles. There are sharp contrasts in the depolarization profile between a layer of spherical particles and a layer of non-spherical particles. Although it is not as obvious as ground-based lidar observations, it is likely that we can identify cloud phase not only for a uniform cloud layer, but also for overlapping cloud layers where one layer contains ice and the other water droplets.
Kato, Seiji; Mace, Gerald G.; Clothiaux, Eugene E.; Liljegren, James C.; Austin, Richard T.Kato, S., G. G. Mace, E. E. Clothiaux, J. C. Liljegren, R. T. Austin, 2001: Doppler Cloud Radar Derived Drop Size Distributions in Liquid Water Stratus Clouds. J. Atmos. Sci., 58(19), 2895-2911. doi: 10.1175/1520-0469(2001)058<2895:DCRDDS>2.0.CO;2. Abstract A cloud particle size retrieval algorithm that uses radar reflectivity factor and Doppler velocity obtained by a 35-GHz Doppler radar and liquid water path estimated from microwave radiometer radiance measurements is developed to infer the size distribution of stratus cloud particles. Assuming a constant, but unknown, number concentration with height, the algorithm retrieves the number concentration and vertical profiles of liquid water content and particle effective radius. A novel aspect of the retrieval is that it depends upon an estimated particle median radius vertical profile that is derived from a statistical model that relates size to variations in particle vertical velocity; the model posits that the median particle radius is proportional to the fourth root of the particle velocity variance if the radii of particles in a parcel of zero vertical velocity is neglected. The performance of the retrieval is evaluated using data from two stratus case study days 1.5 and 8.0 h in temporal extent. Aircraft in situ microphysical measurements were available on one of the two days and the retrieved number concentrations and effective radii are consistent with them. The retrieved liquid water content and effective radius increase with height for both stratus cases, which agree with earlier studies. Error analyses suggest that the error in the liquid water content vanishes and the magnitudes of the fractional error in the effective radius and shortwave extinction coefficient computed from retrieved cloud particle size distributions are half of the magnitudes of the fractional error in the estimated cloud particle median radius if the fractional error in the median radius is constant with height.
Kato, Seiji; Smith, G. Louis; Barker, Howard W.Kato, S., G. L. Smith, H. W. Barker, 2001: Gamma-Weighted Discrete Ordinate Two-Stream Approximation for Computation of Domain-Averaged Solar Irradiance. J. Atmos. Sci., 58(24), 3797-3803. doi: 10.1175/1520-0469(2001)058<3797:GWDOTS>2.0.CO;2. Abstract An algorithm is developed for the gamma-weighted discrete ordinate two-stream approximation that computes profiles of domain-averaged shortwave irradiances for horizontally inhomogeneous cloudy atmospheres. The algorithm assumes that frequency distributions of cloud optical depth at unresolved scales can be represented by a gamma distribution though it neglects net horizontal transport of radiation. This algorithm is an alternative to the one used in earlier studies that adopted the adding method. At present, only overcast cloudy layers are permitted.
Kelly, Michael A.; Randall, David A.Kelly, M. A., D. A. Randall, 2001: A Two-Box Model of a Zonal Atmospheric Circulation in the Tropics. J. Climate, 14(19), 3944-3964. doi: 10.1175/1520-0442(2001)014<3944:ATBMOA>2.0.CO;2. Abstract A simple fixed-SST model of a zonal circulation in the tropical atmosphere has been developed that has separate boxes for the ascending and descending branches of the atmospheric circulation. This circulation resembles the Walker circulation. This is the first box model to determine the fractional widths of the warm and cold pools. The atmospheric model contains an explicit hydrologic cycle, a simplified but physically based radiative transfer parameterization, and interactive clouds. Results indicate that the intensity of the tropical circulation is crucially dependent on the amount and vertical distribution of water vapor above the cold-pool boundary layer (CPBL). In response to increasing precipitable water over the CPBL, the radiative cooling rate of the free troposphere increases. To a good approximation, subsidence warming balances radiative cooling in the subsiding branches of the circulation. If the fractional width of the cold pool (CP) does not change too much, the circulation must intensify as the subsidence rate increases. To compensate for a stronger circulation and to restore energy balance in the Walker cell, the precipitable water over the warm pool (WP) must decrease. A “moist-outflow” experiment shows that the Walker circulation intensifies if air is advected to the subsiding regions from lower altitudes in the WP. As the advection level decreases, air supplied to the CP becomes warmer and moister, and so the column water vapor in the CP free troposphere increases. The mechanism described above then leads to a strengthening of the circulation. This moist-outflow experiment also shows that when the authors try to moisten the atmosphere by specifying a lower advection level for water vapor, the atmosphere adjusts so as to dry out. This effect is very strong.
Khairoutdinov, Marat F.; Randall, David A.Khairoutdinov, M. F., D. A. Randall, 2001: A cloud resolving model as a cloud parameterization in the NCAR Community Climate System Model: Preliminary results. Geophysical Research Letters, 28(18), 3617-3620. doi: 10.1029/2001GL013552. Preliminary results of a short climate simulation with a 2-D cloud resolving model (CRM) installed into each grid column of an NCAR Community Climate System Model (CCSM) are presented. The CRM replaces the conventional convective and stratiform cloud parameterizations, and allows for explicit computation of the global cloud fraction distribution for radiation computations. The extreme computational cost of the combined CCSM/CRM model has thus far limited us to a two-month long climate simulation (December-January) using 2.8° × 2.8° resolution. The simulated geographical distributions of the total rainfall, precipitable water, cloud cover, and Earth radiation budget, for the month of January, look very reasonable. 3337 Meteorology and Atmospheric Dynamics: Numerical modeling and data assimilation; 3319 Meteorology and Atmospheric Dynamics: General circulation; 3314 Meteorology and Atmospheric Dynamics: Convective processes
Li, Zhanqing; Trishchenko, Alexander P.Li, Z., A. P. Trishchenko, 2001: Quantifying Uncertainties in Determining SW Cloud Radiative Forcing and Cloud Absorption due to Variability in Atmospheric Conditions. J. Atmos. Sci., 58(4), 376-389. doi: 10.1175/1520-0469(2001)058<0376:QUIDSC>2.0.CO;2. Abstract The concept of cloud radiative forcing (CRF) has been widely employed in studying the effects of clouds on the earth’s radiation budget and climate. CRF denotes, in principle, the net influence of cloud alone on the radiation budget of a system. In practice, however, observational determination of CRF is fraught with uncertainties due to factors other than cloud that induce changes in atmospheric background conditions. The most notable variables include aerosol, water vapor, and the data sampling scheme. The impact of these factors on the derivation of CRF and cloud absorption is investigated here by means of modeling and analysis of multiple datasets. Improved estimation of CRF is attempted at the top of the atmosphere (TOA) and at the surface from spatially and temporally collocated ground and satellite measurements for broadband shortwave fluxes. Satellite data employed include pixel measurements from ERBE (1988–90), ScaRaB (1994–95), and CERES (1998), as well as surface data acquired across the Canadian radiation network, the ARM Central Facility site in Oklahoma, the US/NOAA SURFRAD networks, and the world BSRN (WMO) networks. It is found that surface CRF is much more susceptible to the variability in background conditions than TOA CRF. Selection of overly clear sky conditions often leads to significant overestimation of surface CRF, but TOA CRF remains intact or only slightly affected. As a result, the ratio of CRF at the surface and TOA is prone to overestimation. With careful treatments of these effects, the CRF ratio turns out to vary mostly between 0.9 and 1.1, implying approximately the same magnitude of atmospheric absorption under clear-sky and cloudy-sky conditions.
Liljegren, James C.; Clothiaux, Eugene E.; Mace, Gerald G.; Kato, Seiji; Dong, XiquanLiljegren, J. C., E. E. Clothiaux, G. G. Mace, S. Kato, X. Dong, 2001: A new retrieval for cloud liquid water path using a ground-based microwave radiometer and measurements of cloud temperature. Journal of Geophysical Research: Atmospheres, 106(D13), 14485-14500. doi: 10.1029/2000JD900817. A new method to retrieve cloud liquid water path using 23.8 and 31.4 GHz microwave radiometer brightness temperature measurements is developed. This method does not depend on climatological estimates of either the mean radiating temperature of the atmosphere Tmr or the mean cloud liquid water temperature Tcloud. Rather, Tmr is estimated from surface temperature and relative humidity measurements, while Tcloud is estimated using millimeter-wave cloud radar data, together with atmospheric temperature profiles obtained from either radiosonde or rapid update cycle (RUC) model output. Simulations demonstrate that the new retrieval method significantly reduces the biases in the liquid water path estimates that are apparent in a site-specific retrieval based on monthly stratified, local climatology. An analysis of the liquid water path estimates produced by the two retrievals over four case study days illustrates trends and retrieval performances consistent with the model simulations. 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0320 Cloud physics and chemistry; 3394 Meteorology and Atmospheric Dynamics: Instruments and techniques; 0394 Instruments and techniques
Lin, Bing; Minnis, Patrick; Fan, Alice; Curry, Judith A.; Gerber, H.Lin, B., P. Minnis, A. Fan, J. A. Curry, H. Gerber, 2001: Comparison of cloud liquid water paths derived from in situ and microwave radiometer data taken during the SHEBA/FIREACE. Geophysical Research Letters, 28(6), 975-978. doi: 10.1029/2000GL012386. Mean cloud liquid water path LWP derived from microwave measurements using the standard ARM retrieval technique is nearly twice as large as coincident in situ aircraft data taken over the SHEBA ice camp in the Arctic during FIRE ACE. Using an algorithm adopted from satellite remote sensing that more completely accounts for the temperature dependence of water absorption and atmospheric gas absorption results in a 25 to 45 % reduction in LWP values relative to the standard ARM estimates. If possible precipitation cases are excluded, the mean results from the new technique differ by only 3% from the in situ data. Greater differences for heavier clouds may result from in situ probe uncertainties. This algorithm should provide accurate LWP retrievals for a variety of cloud conditions from the tropics to the highly supercooled Arctic clouds. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0320 Atmospheric Composition and Structure: Cloud physics and chemistry; 3349 Meteorology and Atmospheric Dynamics: Polar meteorology
Loeb, Norman G.; Priestley, Kory J.; Kratz, David P.; Geier, Erika B.; Green, Richard N.; Wielicki, Bruce A.; Hinton, Patricia O’Rawe; Nolan, Sandra K.Loeb, N. G., K. J. Priestley, D. P. Kratz, E. B. Geier, R. N. Green, B. A. Wielicki, P. O. Hinton, S. K. Nolan, 2001: Determination of Unfiltered Radiances from the Clouds and the Earth’s Radiant Energy System Instrument. Journal of Applied Meteorology, 40(4), 822-835. doi: 10.1175/1520-0450(2001)040<0822:DOURFT>2.0.CO;2. Abstract A new method for determining unfiltered shortwave (SW), longwave (LW), and window radiances from filtered radiances measured by the Clouds and the Earth’s Radiant Energy System (CERES) satellite instrument is presented. The method uses theoretically derived regression coefficients between filtered and unfiltered radiances that are a function of viewing geometry, geotype, and whether cloud is present. Relative errors in instantaneous unfiltered radiances from this method are generally well below 1% for SW radiances (std dev ≈0.4% or ≈1 W m−2 equivalent flux), less than 0.2% for LW radiances (std dev ≈0.1% or ≈0.3 W m−2 equivalent flux), and less than 0.2% (std dev ≈0.1%) for window channel radiances. When three months (June, July, and August of 1998) of CERES Earth Radiation Budget Experiment (ERBE)-like unfiltered radiances from the Tropical Rainfall Measuring Mission satellite between 20°S and 20°N are compared with archived Earth Radiation Budget Satellite (ERBS) scanner measurements for the same months over a 5-yr period (1985–89), significant scene-type dependent differences are observed in the SW channel. Full-resolution CERES SW unfiltered radiances are ≈7.5% (≈3 W m−2 equivalent diurnal average flux) lower than ERBS over clear ocean, as compared with ≈1.7% (≈4 W m−2 equivalent diurnal average flux) for deep convective clouds and ≈6% (≈4–6 W m−2 equivalent diurnal average flux) for clear land and desert. This dependence on scene type is shown to be partly caused by differences in spatial resolution between CERES and ERBS and by errors in the unfiltering method used in ERBS. When the CERES measurements are spatially averaged to match the ERBS spatial resolution and the unfiltering scheme proposed in this study is applied to both CERES and ERBS, the ERBS all-sky SW radiances increase by ≈1.7%, and the CERES radiances are now consistently ≈3.5%–5% lower than the modified ERBS values for all scene types. Further study is needed to determine the cause for this remaining difference, and even calibration errors cannot be ruled out. CERES LW radiances are closer to ERBS values for individual scene types—CERES radiances are within ≈0.1% (≈0.3 W m−2) of ERBS over clear ocean and ≈0.5% (≈1.5 W m−2) over clear land and desert.
Lucas, L. E.; Waliser, D. E.; Xie, P.; Janowiak, J. E.; Liebmann, B.Lucas, L. E., D. E. Waliser, P. Xie, J. E. Janowiak, B. Liebmann, 2001: Estimating the Satellite Equatorial Crossing Time Biases in the Daily, Global Outgoing Longwave Radiation Dataset. J. Climate, 14(12), 2583-2605. doi: 10.1175/1520-0442(2001)014<2583:ETSECT>2.0.CO;2. Abstract Due to its long record length (approximately 25 years), the outgoing longwave radiation (OLR) dataset has been used in a multitude of climatological studies including studies on tropical circulation and convection, the El Niño–Southern Oscillation (ENSO) phenomenon, and the earth's radiation budget. Although many of the climatological studies using OLR have proven invaluable, proper interpretation of the low-frequency components of the data could be limited by the presence of biases introduced by changes in the satellite equatorial crossing time (ECT). Since long-term global changes could be masked or contaminated by this instrumental bias, it is necessary to take steps to ensure that the daily, global OLR dataset is free from such biases and is as accurate as possible. The goal of this study is to derive a method for estimating the ECT biases in the daily, global OLR dataset. Our analysis utilizes a Procrustes targeted empirical orthogonal function rotation (REOF) on an interpolated OLR dataset to try to isolate and remove the two major ECT biases—afternoon satellite orbital drift and the abrupt transitions from a morning satellite to an afternoon satellite—from the dataset. Two targeted REOF analyses are performed to separate and distinguish between these two artificial satellite bias modes. A “common ECT” of approximately 0245 LST is established for the dataset by removing an estimate of these two ECT biases. Results from the analysis indicate that changes in ECTs can cause large regional biases over both ocean and tropical landmasses. The afternoon satellite ECT drift-bias accounts for 0.4% of the pentad anomaly variance. During a single satellite series (e.g., NOAA-11), the afternoon drift-bias can introduce a difference as large as 10.5 W m−2 in the OLR values collected over most tropical landmasses. The morning to afternoon satellite transition bias accounts for 0.9% of the pentad anomaly variance, and is shown to cause a bias of 12 W m−2 in the OLR values over most tropical landmasses during the NOAA-SR satellite series. The data are corrected by removing a statistically derived synthetic eigenvector that is associated with each of the ECT bias modes. This synthetic eigenvector is used instead of the exact values of the satellite bias eigenvector to ensure that only the artificial variability is removed from the dataset. The two REOF modes produced in this study are nearly orthogonal to each other having a correlation of only 0.17. This near orthogonality suggests that the use of the two-mode method presented in this study can more adequately describe the individual nature of each of the two ECT biases than a single REOF mode examined in previous studies. However, due to the presence of other forms of variability, it is likely that this study's estimate of the ECT bias includes ECT-related bias as well as some aspects of variability that may be associated with sensor changes, intersatellite calibration and/or natural climate variability. The strengths and limitations of the above technique are discussed, as are suggestions for future efforts.
Miller, S. D.; Stephens, G. L.Miller, S. D., G. L. Stephens, 2001: CloudSat instrument requirements as determined from ECMWF forecasts of global cloudiness. Journal of Geophysical Research: Atmospheres, 106(D16), 17713-17733. doi: 10.1029/2000JD900645. In the years preceding the launch of CloudSat in 2003, important questions regarding instrument requirements sufficient to fulfilling the mission's science objectives must be addressed. Qualified and useful answers to these questions require in turn a careful simulation strategy whereupon the observing system and modeled environment are represented as realistically as possible. In this paper, we consider the W band (94 GHz) cloud radar minimum detectable signal (MDS) requirement in the context of specified boundary fluxes and in-cloud heating rates. Realistic cloud distribution and water contents from short-range forecasts produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) are converted to attenuated equivalent radar reflectivity to yield full-orbit virtual CloudSat observations. The radiative implications of variable radar MDS are examined using a two-stream radiative transfer model. Simulations show that a MDS of ∼−28 dBZ will detect a fraction of the true cloud field sufficient to reconstruct the instantaneous top-of-atmosphere and surface fluxes to within Clouds and the Earth's Radiant Energy System (CERES) requirements. The results of this analysis form collectively a statement on instrument engineering requirements that is predicated on and hence mappable directly to the physical parameters that define CloudSat science objectives. 0360 Radiation: transmission and scattering; 0320 Cloud physics and chemistry; 0394 Instruments and techniques; 6309 Decision making under uncertainty
Minnis, Patrick; Chakrapani, Venkatesan; Doelling, David R.; Nguyen, Louis; Palikonda, Rabindra; Spangenberg, Douglas A.; Uttal, Taneil; Arduini, Robert F.; Shupe, MatthewMinnis, P., V. Chakrapani, D. R. Doelling, L. Nguyen, R. Palikonda, D. A. Spangenberg, T. Uttal, R. F. Arduini, M. Shupe, 2001: Cloud coverage and height during FIRE ACE derived from AVHRR data. Journal of Geophysical Research: Atmospheres, 106(D14), 15215-15232. doi: 10.1029/2000JD900437. Cloud cover and height are derived from NOAA-12 and NOAA-14 advanced very high resolution radiometer (AVHRR) data taken over the Arctic Ocean for an 8° latitude by 30° longitude domain centered on the Surface Heat Budget of the Arctic Ocean (SHEBA) ship Des Groseilliers. Multispectral thresholds were determined subjectively and applied to each image, providing excellent temporal coverage during the May-July 1998 First ISCCP Regional Experiment Arctic Clouds Experiment (FIRE ACE). Mean cloud amounts were near 70% for the entire period but varied regionally from 55 to 85%. On the basis of a limited climatology of ship observations, these values appear to be typical for this part of the Arctic, suggesting that most of FIRE ACE was conducted in representative cloud conditions. A diurnal cycle of mean cloud amount was found for the domain during June and July having a range of 10% with a middle-to-late morning maximum. The AVHRR-derived cloud amounts are in good agreement with visual and radar measurements taken from the Des Groseilliers, except for a few subvisual and low cloud cases. Average AVHRR-derived cloudiness differ from the mean values obtained at the surface by −1 to +3%; this represents a significant improvement over previous satellite retrievals. The satellite-derived cloud heights are very accurate for most of the low cloud cases. Higher cloud altitudes are less certain because cloud optical depths were not available to adjust the temperature observed for the optically thin high clouds, and the radiating temperature of many of the high clouds is representative of some altitude deep in the cloud rather than the highest altitude level of condensate. The development of a more accurate automated algorithm for detecting polar clouds at AVHRR wavelengths will require inclusion of variable thresholds to account for the angular dependence of the surface reflectance as well as the seasonally changing albedos of the ice pack. The use of a 1.6-μm channel on the AVHRR, or other complement of instruments, will greatly enhance the capabilities for detecting clouds over poles during summer. 1640 Remote sensing; 0320 Cloud physics and chemistry; 3309 Meteorology and Atmospheric Dynamics: Climatology; 3349 Meteorology and Atmospheric Dynamics: Polar meteorology
Nordeen, M. L.; Minnis, P.; Doelling, D. R.; Pethick, D.; Nguyen, L.Nordeen, M. L., P. Minnis, D. R. Doelling, D. Pethick, L. Nguyen, 2001: Satellite observations of cloud plumes generated by Nauru. Geophysical Research Letters, 28(4), 631-634. doi: 10.1029/2000GL012409. A cloud plume is generated by the interaction of low-level easterly flow and diurnal surface heating on the island of Nauru in the tropical Pacific. Diurnal and seasonal cycles of cloud plume length, frequency, and heading were obtained by inspection of a year of hourly daytime GMS images. The cloud plume extends downwind and typically grows during the day to a mean length of 125 km by late afternoon with a maximum observed length of 425 km. The longest average plumes occur during March and April. The afternoon plume frequency was 63% compared to 50% for all observations. Further evaluation of the plume effects is needed to fully assess their impact on the development of long-term statistics of cloud and radiation parameters derived from surface instruments on the island's leeward side. 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3307 Meteorology and Atmospheric Dynamics: Boundary layer processes; 3322 Meteorology and Atmospheric Dynamics: Land/atmosphere interactions
Rajeev, K.; Ramanathan, V.Rajeev, K., V. Ramanathan, 2001: Direct observations of clear-sky aerosol radiative forcing from space during the Indian Ocean Experiment. Journal of Geophysical Research: Atmospheres, 106(D15), 17221-17235. doi: 10.1029/2000JD900723. This study presents the regional estimates of the seasonal and diurnal mean broadband (0.3–5.0 μm) clear-sky aerosol radiative forcing at the top of atmosphere (TOA) due to both the natural and the anthropogenic aerosols over the tropical Indian Ocean from 25°N to 25°S. We propose two new methods, the slope method and the differencing method, to obtain clear sky aerosol forcing from solely satellite measurements. The focus of the study is January to March 1997, 1998, and 1999. The TOA clear-sky aerosol forcing was obtained by integrating satellite data for aerosol optical depth (AOD) and the broadband radiation budget. Over 30,000 pixels were collocated to estimate that the diurnal and seasonal mean reflected broadband solar radiation at TOA increases by about 24 W m−2 per unit increase in AOD at the wavelength of 500 nm. The observed TOA clear-sky aerosol forcing varied between −4 and −14 W m−2 in the Northern Hemisphere (NH) and between 0 and −6 Wm−2 in the Southern Hemisphere. Assuming a ratio of surface to TOA clear-sky aerosol forcing of 3 which was observed over Kaashidhoo Climate Observatory (4.96°N, 73.46°E) during the same period [Satheesh and Ramanathan, 2000], this leads to a clear-sky aerosol forcing of −12 to −42 Wm−2 at the surface in the NH. The difference between the TOA forcing and the surface forcing is the atmospheric forcing. As a result, the atmosphere is subject to a large net forcing of about 8–28 Wm−2 in the NH, largely due to the presence of black carbon. Of equal importance is the fact that the Indian Ocean aerosols introduce a large interhemispheric gradient in the solar heating during the wintertime. The implications for climate and monsoonal circulation may be major and need to be explored with coupled model studies. 1610 Atmosphere; 0305 Aerosols and particles; 3309 Meteorology and Atmospheric Dynamics: Climatology; 1620 Climate dynamics
Ramanathan, V.; Crutzen, P. J.; Lelieveld, J.; Mitra, A. P.; Althausen, D.; Anderson, J.; Andreae, M. O.; Cantrell, W.; Cass, G. R.; Chung, C. E.; Clarke, A. D.; Coakley, J. A.; Collins, W. D.; Conant, W. C.; Dulac, F.; Heintzenberg, J.; Heymsfield, A. J.; Holben, B.; Howell, S.; Hudson, J.; Jayaraman, A.; Kiehl, J. T.; Krishnamurti, T. N.; Lubin, D.; McFarquhar, G.; Novakov, T.; Ogren, J. A.; Podgorny, I. A.; Prather, K.; Priestley, K.; Prospero, J. M.; Quinn, P. K.; Rajeev, K.; Rasch, P.; Rupert, S.; Sadourny, R.; Satheesh, S. K.; Shaw, G. E.; Sheridan, P.; Valero, F. P. J.Ramanathan, V., P. J. Crutzen, J. Lelieveld, A. P. Mitra, D. Althausen, J. Anderson, M. O. Andreae, W. Cantrell, G. R. Cass, C. E. Chung, A. D. Clarke, J. A. Coakley, W. D. Collins, W. C. Conant, F. Dulac, J. Heintzenberg, A. J. Heymsfield, B. Holben, S. Howell, J. Hudson, A. Jayaraman, J. T. Kiehl, T. N. Krishnamurti, D. Lubin, G. McFarquhar, T. Novakov, J. A. Ogren, I. A. Podgorny, K. Prather, K. Priestley, J. M. Prospero, P. K. Quinn, K. Rajeev, P. Rasch, S. Rupert, R. Sadourny, S. K. Satheesh, G. E. Shaw, P. Sheridan, F. P. J. Valero, 2001: Indian Ocean Experiment: An integrated analysis of the climate forcing and effects of the great Indo-Asian haze. Journal of Geophysical Research: Atmospheres, 106(D22), 28371-28398. doi: 10.1029/2001JD900133. Every year, from December to April, anthropogenic haze spreads over most of the North Indian Ocean, and South and Southeast Asia. The Indian Ocean Experiment (INDOEX) documented this Indo-Asian haze at scales ranging from individual particles to its contribution to the regional climate forcing. This study integrates the multiplatform observations (satellites, aircraft, ships, surface stations, and balloons) with one- and four-dimensional models to derive the regional aerosol forcing resulting from the direct, the semidirect and the two indirect effects. The haze particles consisted of several inorganic and carbonaceous species, including absorbing black carbon clusters, fly ash, and mineral dust. The most striking result was the large loading of aerosols over most of the South Asian region and the North Indian Ocean. The January to March 1999 visible optical depths were about 0.5 over most of the continent and reached values as large as 0.2 over the equatorial Indian ocean due to long-range transport. The aerosol layer extended as high as 3 km. Black carbon contributed about 14% to the fine particle mass and 11% to the visible optical depth. The single-scattering albedo estimated by several independent methods was consistently around 0.9 both inland and over the open ocean. Anthropogenic sources contributed as much as 80% (±10%) to the aerosol loading and the optical depth. The in situ data, which clearly support the existence of the first indirect effect (increased aerosol concentration producing more cloud drops with smaller effective radii), are used to develop a composite indirect effect scheme. The Indo-Asian aerosols impact the radiative forcing through a complex set of heating (positive forcing) and cooling (negative forcing) processes. Clouds and black carbon emerge as the major players. The dominant factor, however, is the large negative forcing (-20±4 W m−2) at the surface and the comparably large atmospheric heating. Regionally, the absorbing haze decreased the surface solar radiation by an amount comparable to 50% of the total ocean heat flux and nearly doubled the lower tropospheric solar heating. We demonstrate with a general circulation model how this additional heating significantly perturbs the tropical rainfall patterns and the hydrological cycle with implications to global climate. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1610 Atmosphere; 0305 Aerosols and particles; 1620 Climate dynamics
Rasch, Philip J.; Collins, William D.; Eaton, Brian E.Rasch, P. J., W. D. Collins, B. E. Eaton, 2001: Understanding the Indian Ocean Experiment (INDOEX) aerosol distributions with an aerosol assimilation. Journal of Geophysical Research: Atmospheres, 106(D7), 7337-7355. doi: 10.1029/2000JD900508. We use the aerosol assimilation procedure described by Collins et al. [2000] to help explain INDOEX aerosol distributions. The procedure combines modeled aerosol with AVHRR satellite estimates. The result is consistent with satellite measurements, regular in space and time, and provides information where retrievals are difficult (over land, coincident with clouds, and at night). Extra information on aerosol composition, vertical distribution, and region of origin is also produced. Carbonaceous, sulfate, and sea salt aerosols agree with the in situ measurements to 10–20%. Carbonaceous aerosols were estimated to be the dominant contributor (36%) to the aerosol optical depth (AOD); dust (31%) and sulfate (26%) were also important. The residence time for sulfate and carbon is ∼7 and ∼8 days respectively, longer than globally averaged residence times of many modeling studies. Thus aerosols produced here during the winter monsoon may have a larger climate impact than the same emissions occurring where the residence time is shorter. Three points of entry are found for anthropogenic aerosol to the INDOEX region: a strong near surface southward flow near Bombay; a deeper plume flowing south and east off Calcutta and a westward flow originating from southeast Asia and entering the Bay of Bengal. All three plumes are strongly modulated by a low-frequency change of meteorological regime associated with the Madden Julian Oscillation. The analysis suggests that India is the dominant source of aerosol in the Arabian Sea and Bay of Bengal near the surface but that Asia, Africa and the rest of world also contribute at higher altitudes. India and Asia contribute ∼40% each to the total column mass of air reaching the Maldives, the balance of air comes from other source regions. The assimilation procedure produces an analysis that is a synergy in information about aerosols, that is not easily accessible by independent estimates from remote sensing, in situ measurements, or global transport models by themselves. 3337 Meteorology and Atmospheric Dynamics: Numerical modeling and data assimilation; 0305 Aerosols and particles; 0345 Pollution: urban and regional; 0368 Troposphere: constituent transport and chemistry
Shupe, Matthew D.; Uttal, Taneil; Matrosov, Sergey Y.; Frisch, A. ShelbyShupe, M. D., T. Uttal, S. Y. Matrosov, A. S. Frisch, 2001: Cloud water contents and hydrometeor sizes during the FIRE Arctic Clouds Experiment. Journal of Geophysical Research: Atmospheres, 106(D14), 15015-15028. doi: 10.1029/2000JD900476. During the year-long Surface Heat Budget of the Arctic Experiment (1997–1998) the NOAA Environmental Technology Laboratory operated a 35-GHz cloud radar and the DOE Atmospheric Radiation Measurement Program operated a suite of radiometers at an ice station frozen into the drifting ice pack of the Arctic Ocean. The NASA/FIRE Arctic Clouds Experiment took place during April-July 1998, with the primary goal of investigating cloud microphysical, geometrical, and radiative properties with aircraft and surface-based measurements. In this paper, retrieval techniques are utilized which combine the radar and radiometer measurements to compute height-dependent water contents and hydrometeor sizes for all-ice and all-liquid clouds. For the spring and early summer period, all-ice cloud retrievals showed a mean particle diameter of about 60 μm and ice water contents up to 0.1 g/m3, with the maximum sizes and water contents at approximately one fifth of the cloud depth from the cloud base. The all-liquid cloud retrievals had a mean effective particle radius of 7.4 μm, liquid water contents up to 0.7 g/m3, and a mean droplet concentration of 54 cm−3. Maximum retrieved liquid drop sizes, water contents, and concentrations occurred at three fifths of the cloud depth from the cloud base. As a measure of how representative the FIRE-ACE aircraft flight days were of the April-July months in general, retrieval statistics for flight-day clouds are compared to the mean retrieval statistics. From the retrieval perspective the ice particle sizes and water contents on flight days were ∼30% larger than the mean retrieved values for the April-July months. Retrieved liquid cloud parameters during flight days were all about 20% smaller. All-ice and/or all-liquid clouds acceptable for these retrieval techniques were observed about 34% of the time clouds were present; at all other times, mixed-phase clouds precluded the use of these single-phase retrieval techniques. 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0320 Cloud physics and chemistry; 3394 Meteorology and Atmospheric Dynamics: Instruments and techniques; 3349 Meteorology and Atmospheric Dynamics: Polar meteorology
Standfuss, Carsten; Viollier, Michel; Kandel, Robert S.; Duvel, Jean PhilippeStandfuss, C., M. Viollier, R. S. Kandel, J. P. Duvel, 2001: Regional Diurnal Albedo Climatology and Diurnal Time Extrapolation of Reflected Solar Flux Observations: Application to the ScaRaB Record. J. Climate, 14(6), 1129-1146. doi: 10.1175/1520-0442(2001)014<1129:RDACAD>2.0.CO;2. Abstract A regional (2.5° × 2.5° resolved) diurnal (hourly) albedo climatology for low and midlatitudes is derived for each month from the 5⅓-yr narrow-field-of-view data record obtained from the Earth Radiation Budget Satellite (ERBS). It is used in a quasi-operational diurnal interpolation/extrapolation procedure (DIEP) to calculate regional monthly means of the reflected shortwave radiation flux (RSR) from instantaneous albedo observations. This climatological approach (CDIEP) replaces the questionable assumption of diurnally constant cloud conditions made in the conventional DIEP by assuming a diurnal variation of cloudiness corresponding to the mean long-term diurnal variation of the planetary albedo. Validation of CDIEP, using the three-satellite Earth Radiation Budget Experiment (ERBE) data for December of 1986, indicates that on regional scales monthly time sampling errors for single satellite products are generally reduced but not completely removed in comparison with the currently applied diurnal model (EDIEP). On a global scale, rms errors are reduced by 16% and 28% for ERBE NOAA-10 and NOAA-9 monthly mean RSR, respectively. The efficiency of CDIEP is satisfactory by accounting for coherent diurnal variations of cloudiness, if present, and by reproducing the results obtained by EDIEP elsewhere. Applying CDIEP to the full-year record of ScaRaB-Meteor ERB measurements enables the analysis of its impact with regard to the varying local observation time of each month. The standard deviation between regional monthly means of the RSR calculated by CDIEP and EDIEP varies between less than 2 W m−2 and about 4 W m−2 for high-noon and near-terminator time sampling conditions, respectively. On regional scales, time sampling errors with a 3½-month period, induced by the orbit’s precession, can be reduced, in particular for marine areas characterized by persistent stratocumulus, where the amplitude often exceeds 10 W m−2.
Trishchenko, Alexander P.; Li, Zhanqing; Chang, Fu-Lung; Barker, HowardTrishchenko, A. P., Z. Li, F. Chang, H. Barker, 2001: Cloud optical depths and TOA fluxes: Comparison between satellite and surface retrievals from multiple platforms. Geophysical Research Letters, 28(6), 979-982. doi: 10.1029/2000GL012067. Performances of two cloud property retrieval schemes are assessed by comparison with each other. The study is limited to liquid phase clouds. Two parameters are assessed: cloud optical depth in the visible band and broadband shortwave (SW) flux at the top-of-atmosphere (TOA). Retrievals are based on look-up tables for a variety of conditions using an adding-doubling code coupled with LOWTRAN-7 transmittance models. Comparisons of cloud optical depths retrieved from ground measurements with those from ISCCP DX data agree better than previously reported comparisons with the original ISCCP CX data. Likewise, good agreement is obtained between retrieved and inferred TOA SW fluxes. Differences fall within uncertainties of input parameters, as well as shortcomings in the use of a plane-parallel radiative transfer model and in the inversion schemes themselves. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0320 Atmospheric Composition and Structure: Cloud physics and chemistry
Udelhofen, Petra M.; Cess, Robert D.Udelhofen, P. M., R. D. Cess, 2001: Cloud cover variations over the United States: An influence of cosmic rays or solar variability?. Geophysical Research Letters, 28(13), 2617-2620. doi: 10.1029/2000GL012659. To investigate whether galactic cosmic rays (GCR) may influence cloud cover variations, we analyze cloud cover anomalies from 1900–1987 over the United States. Results of spectral analyses reveal a statistically significant cloud cover signal at the period of 11 years; the coherence between cloud cover and solar variability proxy is 0.7 and statistically significant with 95% confidence. In addition, cloud data derived from the NCAR Climate System Model (CSM) forced with solar irradiance variations show a strong signal at 11 years that is not apparent in cloud data from runs with constant solar input. The cloud cover variations are in phase with the solar cycle and not the GCR. Our results suggest that cloud variabilities may be affected by a modulation of the atmospheric circulation resulting from variations of the solar-UV-ozone-induced heating of the atmosphere. 1600 Global Change; 1620 Global Change: Climate dynamics; 1650 Global Change: Solar variability
Wang, Pi-Huan; Veiga, Robert E.; Vann, Lelia B.; Minnis, Patrick; Kent, Geoffrey S.Wang, P., R. E. Veiga, L. B. Vann, P. Minnis, G. S. Kent, 2001: A further study of the method for estimation of SAGE II opaque cloud occurrence. Journal of Geophysical Research: Atmospheres, 106(D12), 12603-12613. doi: 10.1029/2001JD900138. Information on vertical cloud distribution is important to atmospheric radiative calculation, general circulation modeling, and climate study. The method used for estimating the vertical structure of opaque cloud occurrence from the solar occultation observations obtained by the Stratospheric Aerosol and Gas Experiment (SAGE) II has been reviewed for further understanding of the nature of the derived cloud statistics. Most importantly, based on the SAGE II tropical observations (1985–1998), the present study illustrates that the derived opaque cloud occurrence at a given altitude is generally independent of the cloud occurrence at other altitudes, except for some anticorrelation between high-level (12.5 km) and low-level (1–3 km) clouds. This feature of the layer cloud frequency independence is also evident when regional data over the Pacific warm pool and the eastern Pacific are examined. The independent information of the layer cloud frequency is significant and makes it possible to use the derived vertical distribution of cloud occurrence to estimate the probability of multilayer clouds. The limitation is that it is difficult to determine how frequently the multilayer clouds are actually overlapping or how frequently thick cloud (>1 km) really occurs based on the SAGE II observations alone. A discussion of the SAGE II tropical opaque cloud occurrence in relation to the cloud climatology based on visual observations from surface stations and ships, the International Satellite Cloud Climatology Project data, and the cloud statistics using rawinsonde records is also provided. 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0320 Cloud physics and chemistry; 0365 Troposphere: composition and chemistry; 0933 Remote sensing
Whitlock, C. H.; Brown, D. E.; Chandler, W. S.; DiPasquale, R. C.; Ritchey, Nancy A.; Gupta, Shashi K.; Wilber, Anne C.; Kratz, David P.; Stackhouse, Paul W.Whitlock, C. H., D. E. Brown, W. S. Chandler, R. C. DiPasquale, N. A. Ritchey, S. K. Gupta, A. C. Wilber, D. P. Kratz, P. W. Stackhouse, 2001: Global Surface Solar Energy Anomalies Including El Niño and La Niña Years*. Journal of Solar Energy Engineering, 123(3), 211-215. doi: 10.1115/1.1384570. Weather anomalies that increase clouds influence the reliability of both renewable energy and building environmental-control systems. Non-grid solar power systems may run out of capacity for such items as communications electronics, flood-warning stream gages, refrigerators, and small village power systems. This paper provides 1×1-degree resolution global maps that identify those regions which experienced large abnormal solar energy during a 10-year period. A source is identified where specific values for maximum year-to-year variability can be obtained in regions where ground-site measurements do not exist. The information may aid in the selection of safety factors for solar power systems.
Wilcox, Eric M.; Ramanathan, V.Wilcox, E. M., V. Ramanathan, 2001: Scale Dependence of the Thermodynamic Forcing of Tropical Monsoon Clouds: Results from TRMM Observations. J. Climate, 14(7), 1511-1524. doi: 10.1175/1520-0442(2001)014<1511:SDOTTF>2.0.CO;2. Abstract Clouds exert a thermodynamic forcing on the ocean–atmosphere column through latent heating, owing to the production of rain, and through cloud radiative forcing, owing to the absorption of terrestrial infrared energy and the reflection of solar energy. The Tropical Rainfall Measuring Mission (TRMM) satellite provides, for the first time, simultaneous measurements of each of these processes on the spatial scales of individual clouds. Data from TRMM are used to examine the scale dependence of the cloud thermodynamic forcing and to understand the dominant spatial scales of forcing in monsoonal cloud systems. The tropical Indian Ocean is chosen, because the major monsoonal cloud systems are located over this region. Using threshold criteria, the satellite data are segmented into rain cells (consisting of only precipitating pixels) and clouds (consisting of precipitating as well as nonprecipitating pixels), ranging in scales from 103 km2 to 106 km2. For each rain cell and cloud, latent heating is estimated from the microwave imager and radiative forcing is estimated from the Cloud and the Earth’s Radiant Energy System radiation budget instrument. The sizes of clouds and rain cells over the tropical Indian Ocean are distributed lognormally. Thermodynamic forcing of clouds increases with rain cell and cloud area. For example, latent heating increases from about 100 W m−2 for a rain cell of 103 km2 to as high as 1500 W m−2 for a rain cell of 106 km2. Correspondingly, the liquid water path increases tenfold from 0.3 to nearly 3 kg m−2, the longwave cloud forcing from 30 to 100 W m−2, and the diurnal mean shortwave cloud forcing from −50 to −150 W m−2. Previous studies have shown that in regions of deep convection, large clouds and rain cells express greater organization into structures composed of convective core regions attached to stratiform anvil cloud and precipitation. Entrainment of moist, cloudy air from the stratiform anvil into the convective core helps to sustain convection against the entrainment of unsaturated air. Thus large clouds produce more rain, trap more terrestrial radiation, and reflect more solar energy than do smaller clouds. The combined effect of increased forcing and increased spatial coverage means that larger clouds contribute most of the total forcing. Rain cells larger than 105 km2 make up less than 2% of the rain cell population, yet contribute greater than 70% of the latent heating. Similarly, the clouds larger than 105 km2, in which the largest rain cells are embedded, make up less than 3% of clouds, yet are the source of greater than 90% of the total thermodynamic forcing. Significant differences are apparent between the scales of latent heating and radiative forcing, as only about 25% of cloud area is observed to precipitate. The fraction of clouds that contain some rain increases dramatically from about 5% for the smaller scale (103 km2) to as high as 90% for the largest scale considered here (106 km2). The fractional area of the precipitating cloud ranges from 0.2 to 0.4 with a hybrid-scale dependence. Greater than one-half of radiative forcing is provided by nonprecipitating anvil portions of deep convective cloud systems. The results presented here have significant implications for the parameterization of clouds and rain in GCMs and washout of solute trace gases and aerosols in chemistry and transport models.
Wu, Man Li C.; Schubert, Siegfried; Lin, Ching I.; Štajner, IvankaWu, M. L. C., S. Schubert, C. I. Lin, I. Štajner, 2001: A method for assessing the quality of model-based estimates of ground temperature and atmospheric moisture using satellite data. Journal of Geophysical Research: Atmospheres, 106(D10), 10129-10144. doi: 10.1029/2000JD900478. A method is developed for validating model-based estimates of atmospheric moisture and ground temperature using satellite data. The approach relates errors in estimates of clear-sky longwave fluxes at the top of the Earth-atmosphere system to errors in geophysical parameters. The fluxes include clear-sky outgoing longwave radiation (CLR) and radiative flux in the window region between 8 and 12 μm (RadWn). The approach capitalizes on the availability of satellite estimates of CLR and RadWn and other auxiliary satellite data, and multiple global four-dimensional data assimilation (4-DDA) products. The basic methodology employs off-line forward radiative transfer calculations to generate synthetic clear-sky longwave fluxes from two different 4-DDA data sets. Simple linear regression is used to relate the clear-sky longwave flux discrepancies to discrepancies in ground temperature (δTg) and broad-layer integrated atmospheric precipitable water (δpw). The slopes of the regression lines define sensitivity parameters which can be exploited to help interpret mismatches between satellite observations and model-based estimates of clear-sky longwave fluxes. For illustration we analyze the discrepancies in the clear-sky longwave fluxes between an early implementation of the Goddard Earth Observing System Data Assimilation System (GEOS2) and a recent operational version of the European Centre for Medium-Range Weather Forecasts data assimilation system. The analysis of the synthetic clear-sky flux data shows that simple linear regression employing δTg and broad layer δpw provides a good approximation to the full radiative transfer calculations, typically explaining more than 90% of the 6 hourly variance in the flux differences. These simple regression relations can be inverted to “retrieve” the errors in the geophysical parameters. Uncertainties (normalized by standard deviation) in the monthly mean retrieved parameters range from 7% for δTg to ∼20% for the lower tropospheric moisture between 500 hPa and surface. The regression relationships developed from the synthetic flux data, together with CLR and RadWn observed with the Clouds and Earth Radiant Energy System instrument, are used to assess the quality of the GEOS2 Tg and pw. Results showed that the GEOS2 Tg is too cold over land, and pw in upper layers is too high over the tropical oceans and too low in the lower atmosphere. 3337 Meteorology and Atmospheric Dynamics: Numerical modeling and data assimilation; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 9820 Techniques applicable in three or more fields
Yang, Ping; Gao, Bo-Cai; Baum, Bryan A.; Hu, Yong X.; Wiscombe, Warren J.; Mishchenko, Michael I.; Winker, Dave M.; Nasiri, Shaima L.Yang, P., B. Gao, B. A. Baum, Y. X. Hu, W. J. Wiscombe, M. I. Mishchenko, D. M. Winker, S. L. Nasiri, 2001: Asymptotic solutions for optical properties of large particles with strong absorption. Applied Optics, 40(9), 1532-1547. doi: 10.1364/AO.40.001532. The transverse wave condition is not applicable to the refracted electromagnetic wave within the context of geometrical optics when absorption is involved. Either the TM or the TE wave condition can be assumed for the wave to locally satisfy the electromagnetic boundary condition in a ray-tracing calculation. The assumed wave mode affects both the reflection and the refraction coefficients. As a result, nonunique solutions for these coefficients are inevitable. In this study the appropriate solutions for the Fresnel reflection–refraction coefficients are identified in light-scattering calculations based on the ray-tracing technique. In particular, a 3 × 2 refraction or transmission matrix is derived to account for the inhomogeneity of the refracted wave in an absorbing medium. An asymptotic solution that completely includes the effect of medium absorption on Fresnel coefficients is obtained for the scattering properties of a general polyhedral particle. Numerical results are presented for hexagonal plates and columns with both preferred and random orientations. Meteorology; atmospheric optics; Aerosol and cloud effects; Atmospheric scattering; Scattering, particles
Yang, Ping; Gao, Bo-Cai; Baum, Bryan A.; Hu, Yong X.; Wiscombe, Warren J.; Tsay, Si-Chee; Winker, Dave M.; Nasiri, Shaima L.Yang, P., B. Gao, B. A. Baum, Y. X. Hu, W. J. Wiscombe, S. Tsay, D. M. Winker, S. L. Nasiri, 2001: Radiative properties of cirrus clouds in the infrared (8–13 μm) spectral region. Journal of Quantitative Spectroscopy and Radiative Transfer, 70(4–6), 473-504. doi: 10.1016/S0022-4073(01)00024-3. Atmospheric radiation in the infrared (IR) 8–13 μm spectral region contains a wealth of information that is very useful for the retrieval of ice cloud properties from aircraft or space-borne measurements. To provide the scattering and absorption properties of nonspherical ice crystals that are fundamental to the IR retrieval implementation, we use the finite-difference time-domain (FDTD) method to solve for the extinction efficiency, single-scattering albedo, and the asymmetry parameter of the phase function for ice crystals smaller than 40 μm. For particles larger than this size, the improved geometric optics method (IGOM) can be employed to calculate the asymmetry parameter with an acceptable accuracy, provided that we properly account for the inhomogeneity of the refracted wave due to strong absorption inside the ice particle. A combination of the results computed from the two methods provides the asymmetry parameter for the entire practical range of particle sizes between 1 and 10,000 μm over the wavelengths ranging from 8 to 13 μm. For the extinction and absorption efficiency calculations, several methods including the IGOM, Mie solution for equivalent spheres (MSFES), and the anomalous diffraction theory (ADT) can lead to a substantial discontinuity in comparison with the FDTD solutions for particle sizes on the order of 40 μm. To overcome this difficulty, we have developed a novel approach called the stretched scattering potential method (SSPM). For the IR 8–13 μm spectral region, we show that SSPM is a more accurate approximation than ADT, MSFES, and IGOM. The SSPM solution can be further refined numerically. Through a combination of the FDTD and SSPM, the extinction and absorption efficiencies are computed for hexagonal ice crystals with sizes ranging from 1 to 10,000 μm at 12 wavelengths between 8 and 13 μm. Calculations of the cirrus bulk scattering and absorption properties are performed for 30 size distributions obtained from various field campaigns for midlatitude and tropical cirrus cloud systems. Ice crystals are assumed to be hexagonal columns randomly oriented in space. The bulk scattering properties are parameterized through the use of second-order polynomial functions for the extinction efficiency and the single-scattering albedo and a power-law expression for the asymmetry parameter. We note that the volume-normalized extinction coefficient can be separated into two parts: one is inversely proportional to effective size and is independent of wavelength, and the other is the wavelength-dependent effective extinction efficiency. Unlike conventional parameterization efforts, the present parameterization scheme is more accurate because only the latter part of the volume-normalized extinction coefficient is approximated in terms of an analytical expression. After averaging over size distribution, the single-scattering albedo is shown to decrease with an increase in effective size for wavelengths shorter than 10.0 μm whereas the opposite behavior is observed for longer wavelengths. The variation of the asymmetry parameter as a function of effective size is substantial when the effective size is smaller than 50 μm. For effective sizes larger than 100 μm, the asymmetry parameter approaches its asymptotic value. The results derived in this study can be useful to remote sensing studies of ice clouds involving IR window bands. Infrared; cirrus; Crystal
Yang, Ping; Gao, Bo-Cai; Baum, Bryan A.; Wiscombe, Warren J.; Hu, Yong X.; Nasiri, Shaima L.; Soulen, Peter F.; Heymsfield, Andrew J.; McFarquhar, Greg M.; Miloshevich, Larry M.Yang, P., B. Gao, B. A. Baum, W. J. Wiscombe, Y. X. Hu, S. L. Nasiri, P. F. Soulen, A. J. Heymsfield, G. M. McFarquhar, L. M. Miloshevich, 2001: Sensitivity of cirrus bidirectional reflectance to vertical inhomogeneity of ice crystal habits and size distributions for two Moderate-Resolution Imaging Spectroradiometer (MODIS) bands. Journal of Geophysical Research: Atmospheres, 106(D15), 17267-17291. doi: 10.1029/2000JD900618. A common assumption in satellite imager-based cirrus retrieval algorithms is that the radiative properties of a cirrus cloud may be represented by those associated with a specific ice crystal shape (or habit) and a single particle size distribution. However, observations of cirrus clouds have shown that the shapes and sizes of ice crystals may vary substantially with height within the clouds. In this study we investigate the sensitivity of the top-of-atmosphere bidirectional reflectances for two Moderate-Resolution Imaging Spectroradiometer (MODIS) bands centered at 0.65 μm and 2.11 μm to cirrus models composed of either a single homogeneous layer or three distinct, but contiguous, layers. First, we define the single- and three-layer cirrus cloud models with respect to ice crystal habit and size distributions on the basis of in situ replicator data acquired during the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE-II), held in Kansas during the fall of 1991. Subsequently, fundamental light-scattering and radiative transfer theory is employed to determine the single-scattering and the bulk radiative properties of the cirrus cloud. For radiative transfer computations we present a discrete form of the adding/doubling principle that is computationally straightforward and efficient. For the 0.65 μm band, at which absorption by ice is negligible, there is little difference between the bidirectional reflectances calculated for the one- and three-layer cirrus models. This result suggests that the vertical inhomogeneity effect is relatively unimportant at 0.65 μm. At 2.11 μm the bidirectional reflectances computed for both optically thin (τ = 1) and thick (τ = 10) cirrus clouds show significant differences between the results for the one- and three-layer models. The reflectances computed for the three-layer cirrus model are substantially larger than those computed for the single-layer cirrus. Furthermore, our analysis shows that the cirrus reflectances at both the 0.65 and 2.11 μm bands are very sensitive to the optical properties of the small crystals that predominate in the top layer of the three-layer cirrus model. It is critical to define the most realistic geometric shape for the small “quasi-spherical” ice crystals in the top layer for obtaining reliable single-scattering parameters and bulk radiative properties of cirrus. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 0360 Radiation: transmission and scattering; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0305 Aerosols and particles
Zhou, Y. P.; Rutledge, K. C.; Charlock, T. P.; Loeb, N. G.; Kato, S.Zhou, Y. P., K. C. Rutledge, T. P. Charlock, N. G. Loeb, S. Kato, 2001: Atmospheric corrections using MODTRAN for TOA and surface BRDF characteristics from high resolution spectroradiometric/angular measurements from a helicopter platform. High-resolution spectral radiance measurements were taken by a spectral radiometer on board a helicopter over the US Oklahoma Southern Great Plain near the Atmospheric Radiation Measurements (ARM) site during August 1998. The radiometer has a spectral range from 350 nm to 2500 nm at 1 nm resolution. The measurements covered several grass and cropland scene types at multiple solar zenith angles. Detailed atmospheric corrections using the Moderate Resolution Transmittance (MODTRAN) radiation model and in-situ sounding and aerosol measurements have been applied to the helicopter measurements in order to retrieve the surface and top of atmosphere (TOA) Bidirectional Reflectance Distribution Function (BRDF) characteristics. The atmospheric corrections are most significant in the visible wavelengths and in the strong water vapor absorption wavelengths in the near infrared region. Adjusting the BRDF to TOA requires a larger correction in the visible channels since Rayleigh scattering contributes significantly to the TOA reflectance. The opposite corrections to the visible and near infrarred wavelengths can alter the radiance difference and ratio that many remote sensing techniques are based on, such as the normalized difference vegetation index (NDVI). The data show that surface BRDFs and spectral albedos are highly sensitive to the vegetation type and solar zenith angle while BRDF at TOA depends more on atmospheric conditions and the vi ewing geometry. Comparison with the Clouds and the Earth's Radiant Energy System (CERES) derived clear sky Angular Distribution Model (ADM) for crop and grass scene type shows a standard deviation of 0.08 in broadband anisotropic function at 25 degrees solar zenith angle and 0.15 at 50 degrees solar zenith angle, respectively.
Zhou, Yaping; Cess, Robert D.Zhou, Y., R. D. Cess, 2001: Algorithm development strategies for retrieving the downwelling longwave flux at the Earth's surface. Journal of Geophysical Research: Atmospheres, 106(D12), 12477-12488. doi: 10.1029/2001JD900144. Algorithm development strategies for retrieving the surface downwelling longwave flux (SDLW) have been formulated on the basis of detailed studies with radiative transfer models and observational data. The model sensitivity studies were conducted with the column radiation model from the National Center for Atmospheric Research Community Climate Model Version 3 and the Moderate-Resolution Transmittance radiation model. The studies show the clear-sky SDLW can be largely determined from only two parameters: the surface upwelling longwave flux and the column precipitable water vapor. Cloudy-sky sensitivity tests show that, as would be expected, cloud base height is an important factor in determining the SDLW, especially for low clouds. However, when considering broken clouds as occur in reality, there is no way of logically defining an average cloud base height. Instead, cloud liquid water path is shown to be a preferable parameter for use in an all-sky algorithm, not because it serves as a direct cloud input parameter, but rather that it serves as a useful surrogate for cloud base height. Observational data from the Atmospheric Radiation Measurements Program at the U.S. Southern Great Plains (SGP) Oklahoma Central Facility and the Tropical Western Pacific (TWP) Manus Island were used in deriving and validating an illustrative algorithm. The observations show similar relations as found in the model sensitivity tests and suggest that a single algorithm could be applicable for both clear and cloudy conditions as well as for diverse geographical locations. For example, when applied to the TWP data, an algorithm based on a regression of SGP all-sky data produces a relative bias error in SDLW of only 1.4% under all-sky conditions and −0.2% for clear skies. 3337 Meteorology and Atmospheric Dynamics: Numerical modeling and data assimilation; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3367 Meteorology and Atmospheric Dynamics: Theoretical modeling
Cess, Robert D.; Qian, Taotao; Sun, MoguoCess, R. D., T. Qian, M. Sun, 2000: Consistency tests applied to the measurement of total, direct, and diffuse shortwave radiation at the surface. Journal of Geophysical Research: Atmospheres, 105(D20), 24881-24887. doi: 10.1029/2000JD900402. Motivated by recent studies suggesting that the clear-sky atmosphere absorbs more shortwave (solar) radiation than the theoretical models, we have performed two consistency tests on the data used in several of these studies. These data consist of broadband measurements of shortwave irradiance to the surface (total, direct, and diffuse) taken in Oklahoma. In the absence of aerosols, Rayleigh scattering is the sole source of diffuse radiation and thus without any unknown source of atmospheric SW absorption, the measured diffuse irradiance should not be less than that produced by a model incorporating both Rayleigh scattering and conventional atmospheric absorption. The measurements of broadband diffuse irradiance, however, exhibit considerable sub-Rayleigh behavior. On the other hand, measurements of the diffuse irradiance in narrow spectral bands, centered at 415, 500, and 608 nm, indicate no sub-Rayleigh behavior, suggesting that exhibited by the broadband measurements is probably unrealistic. Related to this is the finding that the total surface SW irradiance, when evaluated as the sum of the direct-beam irradiance (pyrheliometer) and the diffuse irradiance (shaded pyranometer), differs considerably and diurnally from the single measurement of the total irradiance by the unshaded pyranometer under conditions in which possible cosine response errors of the unshaded pyranometer have been minimized. This indicates that the pyranometer daytime offsets differ from each other, suggesting their daytime offsets likewise differ from their nighttime offsets, which are nearly identical. We emphasize that these conclusions apply solely to the data for Oklahoma, and they are focused upon obtaining a better understanding of the clear-sky absorption problem that analyses of these data have raised. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3367 Meteorology and Atmospheric Dynamics: Theoretical modeling; 3394 Meteorology and Atmospheric Dynamics: Instruments and techniques
Chambers, Lin H.; Costulis, P. Kay; Young, David F.; Green, Carolyn J.; Stoddard, Douglas B.; Haberer, Susan J.Chambers, L. H., P. K. Costulis, D. F. Young, C. J. Green, D. B. Stoddard, S. J. Haberer, 2000: What is Success? Evaluating S'COOL, an Educational Outreach Project Focused on NASA's CERES Program. The Students' Cloud Observations On-Line Project involved students in K-16 as ground truth observers for a NASA Earth-Observing satellite instrument. The Clouds and Earth's Radiant Energy System instrument allows scientists to study the Earth's energy budget and how clouds affect it. Student reports of cloud conditions help scientists verify their algorithms and allow students to be involved in obtaining and analyzing real scientific data. The presentation contains 23 slides. clouds; education; energy budgets; ground truth; satellite instruments; students; visual observation
Chang, Fu-Lung; Li, Zhanqing; Ackerman, Steven A.Chang, F., Z. Li, S. A. Ackerman, 2000: Examining the Relationship between Cloud and Radiation Quantities Derived from Satellite Observations and Model Calculations. J. Climate, 13(21), 3842-3859. doi: 10.1175/1520-0442(2000)013<3842:ETRBCA>2.0.CO;2. Abstract This study examines the consistency and inconsistency in shortwave (SW) top-of-atmosphere (TOA) reflectances and albedos obtained from satellite measurements of the Earth Radiation Budget Experiment (ERBE) and radiation modeling based on cloud properties retrieved from the Advanced Very High Resolution Radiometer (AVHRR). The examination focuses on completely overcast scenes covered by low-level, single-layered, maritime stratus with uniform cloud-top heights as determined from AVHRR measurements at near nadir. A radiation model was then applied to the retrieved cloud optical depths, droplet effective radii, and top temperatures to compute the SW TOA reflectances and albedos that are compared with coincident ERBE observations. ERBE-observed and AVHRR-based modeled reflectances show excellent agreement in terms of both trend and magnitude, but the two albedos exhibit significant differences that have a strong dependence on cloud optical properties and solar zenith angle (SZA). To unravel the differences, two major factors, that is, scene identification and angular dependence model (ADM), involved in converting reflectance to albedo are examined. It is found that the dependence is mainly caused by the use of a single ERBE–ADM for all overcast scenes, regardless of cloud optical properties. The mean difference in SW TOA flux is about 4–12 W m−2, depending on SZA, but individual differences may reach up to 40–50 W m−2 for persistent large or small cloud optical depths. Nearly all of the uniform low-level overcast scenes as determined by AVHRR are identified as mostly cloudy by ERBE, but the misidentification does not have any adverse effect on the albedo differences. In fact, replacing the ERBE mostly cloudy ADM with the overcast ADM exacerbates the albedo comparisons. The mean fluxes obtained with the two ADMs differ by ∼8 W m−2 at SZA ≈ 33° and by 30 W m−2 at SZA ≈ 60°.
Chang, Fu-Lung; Li, Zhanqing; Trishchenko, Alexander P.Chang, F., Z. Li, A. P. Trishchenko, 2000: The Dependence of TOA Reflectance Anisotropy on Cloud Properties Inferred from ScaRaB Satellite Data. Journal of Applied Meteorology, 39(12), 2480-2493. doi: 10.1175/1520-0450(2000)039<2480:TDOTRA>2.0.CO;2. Abstract An angular dependence model (ADM) describes the anisotropy in the reflectance field. ADMs are a key element in determining the top-of-the-atmosphere (TOA) albedos and radiative fluxes. This study utilizes 1-yr satellite data from the Scanner for Radiation Budget (ScaRaB) for overcast scenes to examine the variation of ADMs with cloud properties. Using ScaRaB shortwave (SW) overcast radiance measurements, an SW mean overcast ADM, similar to the Earth Radiation Budget Experiment (ERBE) ADM, was generated. Differences between the ScaRaB and ERBE overcast ADMs lead to biases of ∼0.01–0.04 in mean albedos inferred from specific angular bins. The largest biases are in the backward scattering direction. Overcast ADMs for the visible (VIS) wavelength were also generated using ScaRaB VIS measurements. They are very similar to, but a little smaller at large viewing angles and a little larger at nadir, than the SW overcast ADMs. To evaluate the effect of cloud properties on ADMs, ScaRaB overcast observations were further classified into thin, thick, warm, and cold cloud categories to generate four subsets of ADMs. The resulting ADMs for thin and thick clouds show opposite trends and deviate significantly from the overall mean ADM by more than 10%. Deviations from the mean ADM were also noted for the ADMs developed for warm water clouds and cold ice clouds. These deviations were attributed to the different scattering phase functions of water and ice particles and were compared with results from model simulations. Use of a single mean overcast ADM results in albedo biases of 0.01–0.04, relative to the use of specific ADMs for particular cloud types. The biases reduced to ∼0.005 when averaged over all cloud types and viewing geometry.
Chevallier, F.; Morcrette, J.-J.Chevallier, F., J. Morcrette, 2000: Comparison of Model Fluxes with Surface and Top-of-the-Atmosphere Observations. Mon. Wea. Rev., 128(11), 3839-3852. doi: 10.1175/1520-0493(2001)129<3839:COMFWS>2.0.CO;2. Abstract The global observation network of the atmospheric broadband radiation reached an unprecedent extent in 1998 with the simultaneous availability of longwave and shortwave measurements of the Clouds and the Earth’s Radiant Energy System instrument on board the Tropical Rainfall Measuring Mission spacecraft, and of a number of surface stations as part of the Atmospheric Radiation Measurement, Baseline Surface Radiation Network, and Surface Radiation network programs. In this paper, these observations are used to assess the quality of the longwave and shortwave components of both the top-of-the-atmosphere and the surface radiation budget computed by the ECMWF operational forecast system. The main features of the boundary radiation are well captured by the system. Clouds appear to be the main modulator of the uncertainty of the top-of-the-atmosphere radiation and of the shortwave surface radiation. This is explained by both model cloud deficiencies and inadequate cloud representation in the radiative transfer schemes. The longwave surface radiation uncertainty is marked by a clear sky bias, common to most of the parameterized longwave radiative transfer models.
Christopher, Sundar A.; Chou, Joyce; Zhang, Jianglong; Li, Xiang; Berendes, Todd. A.; Welch, Ronald M.Christopher, S. A., J. Chou, J. Zhang, X. Li, T. A. Berendes, R. M. Welch, 2000: Shortwave direct radiative forcing of biomass burning aerosols estimated using VIRS and CERES data. Geophysical Research Letters, 27(15), 2197-2200. doi: 10.1029/1999GL010923. Using collocated data from the Visible Infrared Scanner (VIRS) and the Clouds and the Earth's Radiant Energy Budget Scanner (CERES) from the Tropical Rainfall Measuring (TRMM) satellite, observational estimates of the instantaneous Shortwave Aerosol Radiative Forcing (SWARF) of smoke aerosols at the top-of-atmosphere (TOA) are obtained for four days in May 1998 during a biomass-burning episode in Central America. The detection of smoke aerosols is demonstrated using VIRS imagery. Assuming a single scattering albedo (ωo) of 0.86 (at 0.63 µm) that is representative of absorbing aerosols, smoke optical thickness (τ0.63) is retrieved over ocean areas. The average τ0.63 for these four days was 1.2 corresponding to a SWARF value of −68 Wm−2. The SWARF changes from −24 to −99 Wm−2 as τ0.63 changes from 0.2 to 2.2. Global observational estimates of biomass burning aerosol radiative forcing can be obtained by combining data sets from TRMM and Terra satellites.
Christopher, Sundar A.; Li, Xiang; Welch, Ronald M.; Reid, Jeffrey S.; Hobbs, Peter V.; Eck, Thomas F.; Holben, BrentChristopher, S. A., X. Li, R. M. Welch, J. S. Reid, P. V. Hobbs, T. F. Eck, B. Holben, 2000: Estimation of Surface and Top-of-Atmosphere Shortwave Irradiance in Biomass-Burning Regions during SCAR-B. Journal of Applied Meteorology, 39(10), 1742-1753. doi: 10.1175/1520-0450-39.10.1742. Abstract Using in situ measurements of aerosol optical properties and ground-based measurements of aerosol optical thickness (τs) during the Smoke, Clouds and Radiation—Brazil (SCAR-B) experiment, a four-stream broadband radiative transfer model is used to estimate the downward shortwave irradiance (DSWI) and top-of-atmosphere (TOA) shortwave aerosol radiative forcing (SWARF) in cloud-free regions dominated by smoke from biomass burning in Brazil. The calculated DSWI values are compared with broadband pyranometer measurements made at the surface. The results show that, for two days when near-coincident measurements of single-scattering albedo ω0 and τs are available, the root-mean-square errors between the measured and calculated DSWI for daytime data are within 30 W m−2. For five days during SCAR-B, however, when assumptions about ω0 have to be made and also when τs was significantly higher, the differences can be as large as 100 W m−2. At TOA, the SWARF per unit optical thickness ranges from −20 to −60 W m−2 over four major ecosystems in South America. The results show that τs and ω0 are the two most important parameters that affect DSWI calculations. For SWARF values, surface albedos also play an important role. It is shown that ω0 must be known within 0.05 and τs at 0.55 μm must be known to within 0.1 to estimate DSWI to within 20 W m−2. The methodology described in this paper could serve as a potential strategy for determining DSWI values in the presence of aerosols. The wavelength dependence of τs and ω0 over the entire shortwave spectrum is needed to improve radiative transfer calculations. If global retrievals of DSWI and SWARF from satellite measurements are to be performed in the presence of biomass-burning aerosols on a routine basis, a concerted effort should be made to develop methodologies for estimating ω0 and τs from satellite and ground-based measurements.
Dong, Xiquan; Minnis, Patrick; Ackerman, Thomas P.; Clothiaux, Eugene E.; Mace, Gerald G.; Long, Charles N.; Liljegren, James C.Dong, X., P. Minnis, T. P. Ackerman, E. E. Clothiaux, G. G. Mace, C. N. Long, J. C. Liljegren, 2000: A 25-month database of stratus cloud properties generated from ground-based measurements at the Atmospheric Radiation Measurement Southern Great Plains Site. Journal of Geophysical Research: Atmospheres, 105(D4), 4529-4537. doi: 10.1029/1999JD901159. A 25-month database of the macrophysical, microphysical, and radiative properties of isolated and overcast low-level stratus clouds has been generated using a newly developed parameterization and surface measurements from the Atmospheric Radiation Measurement central facility in Oklahoma. The database (5-min resolution) includes two parts: measurements and retrievals. The former consist of cloud base and top heights, layer-mean temperature, cloud liquid water path, and solar transmission ratio measured by a ground-based lidar/ceilometer and radar pair, radiosondes, a microwave radiometer, and a standard Eppley precision spectral pyranometer, respectively. The retrievals include the cloud-droplet effective radius and number concentration and broadband shortwave optical depth and cloud and top-of-atmosphere albedos. Stratus without any overlying mid or high-level clouds occurred most frequently during winter and least often during summer. Mean cloud-layer altitudes and geometric thicknesses were higher and greater, respectively, in summer than in winter. Both quantities are positively correlated with the cloud-layer mean temperature. Mean cloud-droplet effective radii range from 8.1 μm in winter to 9.7 μm during summer, while cloud-droplet number concentrations during winter are nearly twice those in summer. Since cloud liquid water paths are almost the same in both seasons, cloud optical depth is higher during the winter, leading to greater cloud albedos and lower cloud transmittances. 0300 Atmospheric Composition and Structure; 3307 Meteorology and Atmospheric Dynamics: Boundary layer processes; 3309 Meteorology and Atmospheric Dynamics: Climatology
Duvel, Jean Philippe; Bouffiès-Cloché, Sophie; Viollier, MichelDuvel, J. P., S. Bouffiès-Cloché, M. Viollier, 2000: Determination of Shortwave Earth Reflectances from Visible Radiance Measurements: Error Estimate Using ScaRaB Data. J. Appl. Meteor. Climatol., 39(7), 957-970. doi: 10.1175/1520-0450(2000)039<0957:DOSERF>2.0.CO;2. Abstract The error resulting from the use of a visible channel to estimate shortwave (SW) (0.2–4 μm) fluxes reflected by the earth is analyzed. First, the authors compute regression coefficients between visible (0.55–0.65 μm) and SW radiance measurements made by the ScaRaB (Scanner for Radiation Budget) instrument aboard the Meteor-3/7 satellite between March 1994 and February 1995. These regression coefficients are computed from the 10 months of available ScaRaB measurements in different classes of geotypes and different classes of solar and viewing angles. The regression is applied to the visible radiance measurements to simulate the SW measurements in the operational processing of ScaRaB. For instantaneous fluxes, the visible-to-SW conversion gives a standard deviation of the error smaller than 8%. By comparison, the standard deviation of the instantaneous flux error coming from the angular sampling and the bidirectional reflectance uncertainty is estimated to be about 10%. For monthly mean values the standard deviation of the error is smaller than 4% and is comparable to the expected temporal sampling error made by two polar orbiting satellites. In addition, using ScaRaB visible data with these regression coefficients and with the ScaRaB processing gives a bias smaller than 2% for either instantaneous or monthly mean fluxes. However, calibration and processing problems certainly remain important practical issues for the determination of the earth planetary albedo using only narrowband radiometers.
Duvel, Jean Philippe; Raberanto, PatrickDuvel, J. P., P. Raberanto, 2000: A Geophysical Cross-Calibration Approach for Broadband Channels: Application to the ScaRaB Experiment. J. Atmos. Oceanic Technol., 17(12), 1609-1617. doi: 10.1175/1520-0426(2000)017<1609:AGCCAF>2.0.CO;2. Abstract For the determination of the earth radiation budget (ERB) from space, the reflected solar flux and the emitted longwave (LW: 4–100 μm) fluxes are estimated using radiance measurements made in shortwave (SW: 0.2–4.5 μm) and “total” (TW: 0.2–100 μm) channels. An accurate (1%) calibration and cross-calibration of these two channels is required for the determination of the ERB and for daylight determination of the LW radiance based on differences between the TW and the SW radiances. This paper presents an approach to calibrate the SW channel by using a cross-calibration between the SW channel and the SW part of the TW channel. This approach is applied and validated using data from the Scanner for Radiation Budget (ScaRaB) experiment. The principle of this cross-calibration is to estimate the LW radiance from the infrared window (IR: 10.5–12.5 μm) radiance measurements over deep convective cloudiness in the Tropics. This estimate makes it possible to subtract the LW signal from the TW radiance measurement during daylight and thus to compare directly the SW radiances measured by the SW and the TW channels. An IR channel is already implemented on ScaRaB and on the Cloud and the Earth’s Radiant Energy System (CERES) instruments. Using ScaRaB data, it is shown that it is possible to estimate the LW radiance over deep convective cloudiness in the Tropics from IR radiance measurement with accuracy better than 1 W m−2 sr−1. The method applied to ScaRaB measurements gives calibration and cross-calibration parameters with accuracy better than 1%.
Fowler, Laura D.; Wielicki, Bruce A.; Randall, David A.; Branson, Mark D.; Gibson, Gary G.; Denn, Fredrick M.Fowler, L. D., B. A. Wielicki, D. A. Randall, M. D. Branson, G. G. Gibson, F. M. Denn, 2000: Use of a GCM to explore sampling issues in connection with satellite remote sensing of the Earth radiation budget. Journal of Geophysical Research: Atmospheres, 105(D16), 20757-20772. doi: 10.1029/2000JD900239. Collocated in time and space, top-of-the-atmosphere measurements of the Earth radiation budget (ERB) and cloudiness from passive scanning radiometers, and lidar- and radar-in-space measurements of multilayered cloud systems, are the required combination to improve our understanding of the role of clouds and radiation in climate. Experiments to fly multiple satellites “in formation” to measure simultaneously the radiative and optical properties of overlapping cloud systems are being designed. Because satellites carrying ERB experiments and satellites carrying lidars- or radars-in space have different orbital characteristics, the number of simultaneous measurements of radiation and clouds is reduced relative to the number of measurements made by each satellite independently. Monthly averaged coincident observations of radiation and cloudiness are biased when compared against more frequently sampled observations due, in particular, to the undersampling of their diurnal cycle. Using the Colorado State University General Circulation Model (CSU GCM), the goal of this study is to measure the impact of using simultaneous observations from the Earth Observing System (EOS) platform and companion satellites flying lidars or radars on monthly averaged diagnostics of longwave radiation, cloudiness, and its cloud optical properties. To do so, the hourly varying geographical distributions of coincident locations between the afternoon EOS (EOS-PM) orbit and the orbit of the ICESAT satellite set to fly at the altitude of 600 km, and between the EOS PM orbit and the orbits of the PICASSO satellite proposed to fly at the altitudes of 485 km (PICA485) or 705 km (PICA705), are simulated in the CSU GCM for a 60-month time period starting at the idealistic July 1, 2001, launch date. Monthly averaged diagnostics of the top-of-the-atmosphere, atmospheric, and surface longwave radiation budgets and clouds accumulated over grid boxes corresponding to satellite overpasses are compared against monthly averaged diagnostics obtained from hourly samplings over the entire globe. Results show that differences between irregularly (satellite) and regularly (true) sampled diagnostics of the longwave net radiative budgets are the greatest at the surface and the smallest in the atmosphere and at the top-of-the-atmosphere, under both cloud-free and cloudy conditions. In contrast, differences between the satellite and the true diagnostics of the longwave cloud radiative forcings are the largest in the atmosphere and at the top-of-the atmosphere, and the smallest at the surface. A poorer diurnal sampling of the surface temperature in the satellite simulations relative to the true simulation contributes a major part to sampling biases in the longwave net radiative budgets, while a poorer diurnal sampling of cloudiness and its optical properties directly affects diagnostics of the longwave cloud radiative forcings. A factor of 8 difference in the number of satellite overpasses between PICA705 and PICA485 and ICESAT leads to a systematic factor of 3 difference in the spatial standard deviations of all radiative and cloudiness diagnostics. 3337 Meteorology and Atmospheric Dynamics: Numerical modeling and data assimilation; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3319 Meteorology and Atmospheric Dynamics: General circulation
Frisch, A. Shelby; Martner, Brooks E.; Djalalova, Irina; Poellot, Michael R.Frisch, A. S., B. E. Martner, I. Djalalova, M. R. Poellot, 2000: Comparison of radar/radiometer retrievals of stratus cloud liquid-water content profiles with in situ measurements by aircraft. Journal of Geophysical Research: Atmospheres, 105(D12), 15361-15364. doi: 10.1029/2000JD900128. In situ sampling of cloud droplets by aircraft in Oklahoma in 1997 is used to evaluate a ground-based remote sensing technique for retrieving profiles of cloud liquid-water content. The technique uses vertically pointing measurements from a high-sensitivity millimeter-wavelength radar and a collocated dual-frequency microwave radiometer to obtain height-resolved estimates of the liquid content of stratiform clouds. Comparisons with the aircraft measurements are made for 16 overpasses through thin cloud layers within a 1.5-km radius of the remote sensor site. Over a range of liquid-water contents from 0.04 to 0.57 g m−3 the mean difference between the aircraft and the radar/radiometer values was 0.02 g m−3, and the maximum difference was 0.09 g m−3. Although the number of comparisons is limited, these results suggest that the ground-based estimates may be sufficiently accurate for many scientific purposes.
Grant, I. F.; Prata, A. J.; Cechet, R. P.Grant, I. F., A. J. Prata, R. P. Cechet, 2000: The Impact of the Diurnal Variation of Albedo on the Remote Sensing of the Daily Mean Albedo of Grassland. J. Appl. Meteor. Climatol., 39(2), 231-244. doi: 10.1175/1520-0450(2000)039<0231:TIOTDV>2.0.CO;2. Abstract The correction of a land surface albedo estimate made at one solar zenith angle (SZA) from a polar-orbiting satellite to a standard SZA or to a daily mean albedo requires knowledge of the dependence of the albedo on SZA. This paper uses ground-based measurements of the clear-sky albedo at a uniform grassland site at Uardry (34.39°S, 145.30°E) in southeastern Australia to investigate the accuracy to which the daily mean albedo can be inferred from the albedo at 1030 LST, given knowledge of the SZA dependence of albedo to various levels of detail. During nine months in which the daily mean albedo varied from 0.20 to 0.27, the albedo always had the expected minimum near noon but the strength of the albedo’s SZA dependence varied greatly. For a few months, albedos were up to 0.04 higher in the afternoon than in the morning, and variations on finer timescales of up to 0.02 also appeared in the diurnal albedo cycle for days or weeks. These features of the diurnal variation were all seen at two or three surface points separated by up to 750 m and so are expected to appear at the ∼1-km resolution of many satellite sensors. For the Uardry grassland site, the error in estimating the daily mean albedo from the 1030 LST, albedo can be up to 0.03, which is 15% of an albedo of 0.20, if the albedo is assumed to be constant through the day. The maximum error is reduced to about 0.02 if a simple model of the SZA dependence is used with even an approximate value for the parameter that controls the strength of the dependence, and to 0.01 or less if the strength of the dependence is appropriate to the state of the vegetation on the day. Afternoon–morning asymmetry in the albedo can contribute almost 0.01 to the error in inferring a daily albedo from a morning measurement.
Han, Qingyuan; Rossow, William B.; Chou, Joyce; Welch, Ronald M.Han, Q., W. B. Rossow, J. Chou, R. M. Welch, 2000: Near-global survey of cloud column susceptibilities using ISCCP data. Geophysical Research Letters, 27(19), 3221-3224. doi: 10.1029/2000GL011543. A new parameter, cloud column susceptibility, is introduced to study the aerosol indirect effect, which describes the aerosol indirect effect more directly without assuming how cloud droplet size will respond to changes of droplet number concentration. Between the two approaches that used to retrieve cloud column susceptibilities, the one that makes no assumption of constant liquid water content leads to smaller, even negative cloud column susceptibilities. This finding is consistent with results of model studies and observations from the 1998–1999 Indian Ocean Experiment (INDOEX) that suggest that cloud liquid water content may be reduced during aerosol-cloud interactions. The results of this survey suggest that using constant liquid water content in models may lead to significant overestimation of the aerosol indirect effect. 0320 Atmospheric Composition and Structure: Cloud physics and chemistry; 0345 Atmospheric Composition and Structure: Pollution—urban and regional; 0394 Atmospheric Composition and Structure: Instruments and techniques; 1640 Global Change: Remote sensing
Hou, Arthur Y.; Zhang, Sara Q.; da Silva, Arlindo M.; Olson, William S.Hou, A. Y., S. Q. Zhang, A. M. da Silva, W. S. Olson, 2000: Improving Assimilated Global Datasets Using TMI Rainfall and Columnar Moisture Observations. J. Climate, 13(23), 4180-4195. doi: 10.1175/1520-0442(2000)013<4180:IAGDUT>2.0.CO;2. Abstract A global analysis that optimally combines observations from diverse sources with physical models of atmospheric and land processes can provide a comprehensive description of the climate systems. Currently, such data products contain significant errors in primary hydrological fields such as precipitation and evaporation, especially in the Tropics. In this study it is demonstrated that assimilating precipitation and total precipitable water (TPW) derived from the Tropical Rainfall Measuring Mission Microwave Imager (TMI) can significantly improve the quality of global analysis. It is shown that assimilating the 6-h averaged TMI rainfall and TPW retrievals improves not only the hydrological cycle, but also key climate parameters such as clouds, radiation, and the large-scale circulation produced by the Goddard Earth Observing System (GEOS) data assimilation system (DAS). Notably, assimilating TMI rain rates improves clouds and radiation in areas of active convection, as well as the latent heating distribution and the large-scale motion field in the Tropics, while assimilating TMI TPW retrievals leads to reduced moisture biases and improved radiative fluxes in clear-sky regions. Assimilating these data also improves the instantaneous wind and temperature fields in the analysis, leading to better short-range forecasts in the Tropics. Ensemble forecasts initialized with analyses incorporating TMI rain rates and TPW yield smaller biases in tropical precipitation forecasts beyond 1 day, better 500-hPa geopotential height forecasts up to 5 days, and better 200-hPa divergent winds up to 2 days. These results demonstrate the potential of using high quality spaceborne rainfall and moisture observations to improve the quality of assimilated global data for climate analysis and weather forecasting applications.
Ignatov, Alexander; Stowe, LarryIgnatov, A., L. Stowe, 2000: Physical Basis, Premises, and Self-Consistency Checks of Aerosol Retrievals from TRMM VIRS. Journal of Applied Meteorology, 39(12), 2259-2277. doi: 10.1175/1520-0450(2001)040<2259:PBPASC>2.0.CO;2. Abstract This paper outlines the processing stream for aerosol retrievals over oceans from the visible and infrared scanner [VIRS; a five-channel radiometer similar to the National Oceanic and Atmospheric Administration’s Advanced Very High Resolution Radiometer (AVHRR)] aboard the Tropical Rainfall Measuring Mission (TRMM) satellite, launched in November 1997. Emphasis is on 1) the applying the previously developed AVHRR second-generation aerosol retrieval algorithm to VIRS data to derive an aerosol parameter, indicative of particle size; 2) removing the unwanted “thermal leak” signal in the 1.61-μm channel; 3) giving examples of the first aerosol retrievals from space at this wavelength; and 4) assessing the accuracy of the retrievals with theoretical error analyses and empirical self- and interconsistency checks. Aerosol optical depths τA1 and τA2 are retrieved from reflected solar radiances in VIRS channels 1 and 2 centered at wavelengths λ1 = 0.63 and λ2 = 1.61 μm, using two independent lookup tables. When τA1 and τA2 exceed a certain threshold τAmin an effective Ångström exponent α related to particle size is derived as α = −ln(τA1/τA2)/ln(λ1/λ2). Channel 2 is contaminated by a thermal leak, originating from a secondary spectral response peak centered at ∼5.2 μm. If uncorrected, it leads to errors in τA2 of 100% or more. To minimize this error, nighttime VIRS “dark” radiances in channel 2 have been related empirically to radiances in channels 4 and 5 (10.8 and 12 μm, respectively), and view angle through regression analyses. The reflected component in channel-2 daytime measurements is estimated by subtracting the empirically derived thermal component from the total signal and is used in the retrieval of τA2. Theoretical error analysis is used to identify the limitations of the VIRS retrieval algorithm, whereas actual retrievals are preliminarily evaluated using a set of specially developed empirical checks. The checks show, on average, a high degree of self- and interconsistency but also identify problems with the retrievals, the most noteworthy being trends in retrieved optical depths with viewing and illumination angles. These problems will be tackled in the next-generation aerosol retrieval algorithm.
Karlsson, Karl-GöranKarlsson, K., 2000: Satellite sensing techniques and applications for the purpose of BALTEX. Meteorologische Zeitschrift, 9, 111-116.
Kato, Seiji; Bergin, Michael H.; Ackerman, Thomas P.; Charlock, Thomas P.; Clothiaux, Eugene E.; Ferrare, Richard A.; Halthore, Rangasayi N.; Laulainen, Nels; Mace, Gerald G.; Michalsky, Joseph; Turner, David D.Kato, S., M. H. Bergin, T. P. Ackerman, T. P. Charlock, E. E. Clothiaux, R. A. Ferrare, R. N. Halthore, N. Laulainen, G. G. Mace, J. Michalsky, D. D. Turner, 2000: A comparison of the aerosol thickness derived from ground-based and airborne measurements. Journal of Geophysical Research: Atmospheres, 105(D11), 14701-14717. doi: 10.1029/2000JD900013. The extinction optical thickness of particles obtained from scattering and absorption coefficients measured by an airborne integrating nephelometer and particle soot absorption photometer, respectively, is compared with the aerosol optical thickness derived from a ground-based multifilter rotating shadowband radiometer, a Sun photometer, and a Raman lidar for 9 days. These 9 days are selected from intensive operation periods of the Atmospheric Radiation Measurement in April 1997, September 1997, and August 1998 at the southern Great Plains. For April 1997 and September 1997 cases the difference between the extinction optical thickness of particles estimated from vertical profiles and the extinction optical thickness of aerosol derived from the multifilter rotating shadowband radiometer is not significant. For August 1998 cases when the boundary layer relative humidity is higher than April 1997 and September 1997 cases, the extinction optical thickness of particles is 0.03 to 0.07 less than the extinction optical thickness of aerosol. The difference corresponds to 25% to 31% of the extinction optical thickness of aerosol. Based on these comparisons, the upper and lower limits of the single-scattering albedo of particles present in the lower part of troposphere are 0.97 and 0.84, respectively. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0305 Aerosols and particles
Legrand, Michel; Pietras, Christophe; Brogniez, Gérard; Haeffelin, Martial; Abuhassan, Nader Khalil; Sicard, MichaëlLegrand, M., C. Pietras, G. Brogniez, M. Haeffelin, N. K. Abuhassan, M. Sicard, 2000: A High-Accuracy Multiwavelength Radiometer for In Situ Measurements in the Thermal Infrared. Part I: Characterization of the Instrument. J. Atmos. Oceanic Technol., 17(9), 1203-1214. doi: 10.1175/1520-0426(2000)017<1203:AHAMRF>2.0.CO;2. Abstract The new infrared radiometer (conveyable low-noise infrared radiometer for measurements of atmosphere and ground surface targets, or CLIMAT) is a highly sensitive field instrument designed to measure brightness temperatures or radiances in the infrared, from the ground level, or from an aircraft. It can be equipped with up to six channels in the 8–14-μm range. This instrument is characterized by its portability (total mass less than 5 kg), its self-sufficiency, and its automated operation. It can be operated either manually or automatically. The optical head of the instrument contains an objective lens and a condenser mounted according to the Köhler design, providing a uniform irradiation on the detector and a well-delimited field of view. The radiation is measured by a low-noise fast thermopile whose responsivity is slightly temperature dependent. The radiometric noise expressed as an equivalent brightness temperature is on the order of 50 mK for a 1-μm bandwidth at room temperature. The application of a thermal shock reveals no noticeable degradation of the measurements, even though the cavity of the thermopile is not stabilized in temperature.
Li, Xiang; Christopher, Sundar A.; Chou, Joyce; Welch, Ronald M.Li, X., S. A. Christopher, J. Chou, R. M. Welch, 2000: Estimation of Shortwave Direct Radiative Forcing of Biomass-Burning Aerosols Using New Angular Models. Journal of Applied Meteorology, 39(12), 2278-2291. doi: 10.1175/1520-0450(2001)040<2278:EOSDRF>2.0.CO;2. Abstract Using a new angular distribution model (ADM) for smoke aerosols, the instantaneous top-of-atmosphere (TOA) shortwave aerosol radiative forcing (SWARF) is calculated for selected days over biomass-burning regions in South America. The visible and infrared scanner data are used to detect smoke aerosols and the Clouds and the Earth’s Radiant Energy System (CERES) scanner data from the Tropical Rainfall Measuring Mission are used to obtain the broadband radiances. First, the ADM for smoke aerosols is calculated over land surfaces using a discrete-ordinate radiative transfer model. The instantaneous TOA shortwave (SW) fluxes are estimated using the new smoke ADM and are compared with the SW fluxes from the CERES product. The rms error between the CERES SW fluxes and fluxes using the smoke ADM is 13 W m−2. The TOA SWARFs per unit optical thickness for the six surface types range from −29 to −57 W m−2, showing that smoke aerosols have a distinct cooling effect. The new smoke ADM developed as part of this study could be used to estimate radiative impact of biomass-burning aerosols.
Lin, Xin; Randall, David A.; Fowler, Laura D.Lin, X., D. A. Randall, L. D. Fowler, 2000: Diurnal Variability of the Hydrologic Cycle and Radiative Fluxes: Comparisons between Observations and a GCM. J. Climate, 13(23), 4159-4179. doi: 10.1175/1520-0442(2000)013<4159:DVOTHC>2.0.CO;2. Abstract The simulated diurnal cycle is in many ways an ideal test bed for new physical parameterizations. The purpose of this paper is to compare observations from the Tropical Rainfall Measurement Mission, the Earth Radiation Budget Experiment, the International Satellite Cloud Climatology Project, the Clouds and the Earth’s Radiant Energy System Experiment, and the Anglo-Brazilian Amazonian Climate Observation Study with the diurnal variability of the Amazonian hydrologic cycle and radiative energy budget as simulated by the Colorado State University general circulation model, and to evaluate improvements and deficiencies of the model physics. The model uses a prognostic cumulus kinetic energy (CKE) to relax the quasi-equilibrium closure of the Arakawa–Schubert cumulus parameterization. A parameter, α, is used to relate the CKE to the cumulus mass flux. This parameter is expected to vary with cloud depth, mean shear, and the level of convective activity, but up to now a single constant value for all cloud types has been used. The results of the present study show clearly that this approach cannot yield realistic simulations of both the diurnal cycle and the monthly mean climate state. Improved results are obtained using a version of the model in which α is permitted to vary with cloud depth.
Loeb, Norman G.; Parol, Frédéric; Buriez, Jean-Claude; Vanbauce, ClaudineLoeb, N. G., F. Parol, J. Buriez, C. Vanbauce, 2000: Top-of-Atmosphere Albedo Estimation from Angular Distribution Models Using Scene Identification from Satellite Cloud Property Retrievals. J. Climate, 13(7), 1269-1285. doi: 10.1175/1520-0442(2000)013<1269:TOAAEF>2.0.CO;2. Abstract The next generation of earth radiation budget satellite instruments will routinely merge estimates of global top-of-atmosphere radiative fluxes with cloud properties. This information will offer many new opportunities for validating radiative transfer models and cloud parameterizations in climate models. In this study, five months of Polarization and Directionality of the Earth’s Reflectances 670-nm radiance measurements are considered in order to examine how satellite cloud property retrievals can be used to define empirical angular distribution models (ADMs) for estimating top-of-atmosphere albedo. ADMs are defined for 19 scene types defined by satellite retrievals of cloud fraction and cloud optical depth. Two approaches are used to define the ADM scene types. The first assumes there are no biases in the retrieved cloud properties and defines ADMs for fixed discrete intervals of cloud fraction and cloud optical depth (fixed-τ approach). The second approach involves the same cloud fraction intervals, but uses percentile intervals of cloud optical depth instead (percentile-τ approach). Albedos generated using these methods are compared with albedos inferred directly from the mean observed reflectance field. Albedos based on ADMs that assume cloud properties are unbiased (fixed-τ approach) show a strong systematic dependence on viewing geometry. This dependence becomes more pronounced with increasing solar zenith angle, reaching ≈12% (relative) between near-nadir and oblique viewing zenith angles for solar zenith angles between 60° and 70°. The cause for this bias is shown to be due to biases in the cloud optical depth retrievals. In contrast, albedos based on ADMs built using percentile intervals of cloud optical depth (percentile-τ approach) show very little viewing zenith angle dependence and are in good agreement with albedos obtained by direct integration of the mean observed reflectance field (
Matrosov, Sergey Y.; Heymsfield, Andrew J.Matrosov, S. Y., A. J. Heymsfield, 2000: Use of Doppler radar to assess ice cloud particle fall velocity-size relations for remote sensing and climate studies. Journal of Geophysical Research: Atmospheres, 105(D17), 22427-22436. doi: 10.1029/2000JD900353. Knowledge of ice crystal terminal velocities, both for individual crystals and for size distributions, is important for an adequate representation of ice particle sedimentation in climate models. While the terminal velocities (υt) of individual crystals of simple shapes have been measured, theoretical relations of the form υt = ADB (where D is the maximum particle dimension), obtained using expressions for the aerodynamic drag force, are often more useful because they can be applied to a wide range of particle sizes and heights and temperatures in the atmosphere. For high tropospheric ice clouds the coefficient A has been found to vary over 1 order of magnitude; the exponent B is generally within the range 0.7–1.4. Aerodynamic drag force calculations show that A and B are related. A and B can also be used to characterize terminal-velocity-particle characteristic size relations for size distributions. In this study we use collocated, vertically pointing measurements of ice cloud radar reflectivity, Doppler velocity, and IR brightness temperatures to estimate the vertical profiles of cloud particle characteristic size, cloud ice water content, and vertically averaged value of the coefficient A, emphasizing cirrus clouds. We analyze variations in terminal-velocity-size relations for individual particles and corresponding variations for ensembles of particles: for example, in relations between the reflectivity-weighted terminal velocity and the median volume size and between the mass-weighted terminal velocity and the median volume size. The retrievals indicate that A ranges from ∼250 to almost 4000 (cgs units), similar to the range found from the theoretical calculations. The coefficient A tends to decrease as a characteristic particle size (e.g., median size) increases. As a simplification for climate modeling efforts, we present an empirical relation between median size and A, although there is a fair amount of variability about this relation. Using the Doppler measurements and retrieval data, we also derive relations between the mass-weighted terminal velocity and cloud ice water content. Such relations are useful for representing fallout of ice particles in climate and cloud-resolving models. 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0320 Cloud physics and chemistry; 6952 Radar atmospheric physics
Minomura, Mituo; Ru, Jianfei; Kuze, Hiroaki; Takeuchi, NobuoMinomura, M., J. Ru, H. Kuze, N. Takeuchi, 2000: Atmospheric correction of satellite data using multi-wavelength lidar data with MODTRAN3 code. Advances in Space Research, 25(5), 1033-1036. doi: 10.1016/S0273-1177(99)00468-8. Standard atmospheric models are employed in radiative transfer codes such as MODTRAN3. The actual atmospheric conditions, especially those due to aerosol particles, change both spatially and temporally. For the atmospheric correction of satellite data it is highly desirable to use the data measured simultaneously with the satellite overflight. Lidars are quite useful to obtain the aerosol information. The Atmospheric Data Correction Lidar, a multi-wavelength lidar system at CEReS, Chiba University, has been applied for that purpose. Lidar signals are collected on June 27, 1997 and December 15, 1997, and analyzed to obtain the aerosol extinction profile. The extinction at 550 nm is interpolated from lidarderived data and substituted into MODTRAN3 as user-defined 26 layers. To compare this with the result using standard atmospheric model (urban spring/summer and urban fall/winter), the meteorological ground visibility for the latter is adjusted to give the optical thickness the same as the lidar data. The atmospheric correction to NOAA AVHRR data (channel 1 and 2) is performed with two step correction, the first step removing the atmospheric scattering contributions. The second correction, on the other hand, deals with the adjacency effect. This algorithm gives rise to appropriate albedo values in the range of 0.1 to 0.3 for land surfaces and 0.01 to 0.03 for sea surfaces. Although the effect of atmospheric correction is significant, the difference between the results based on lidar data and the standard model is found to be relatively small.
O'Neill, N. T.; Ignatov, A.; Holben, B. N.; Eck, T. F.O'Neill, N. T., A. Ignatov, B. N. Holben, T. F. Eck, 2000: The lognormal distribution as a reference for reporting aerosol optical depth statistics; Empirical tests using multi-year, multi-site AERONET Sunphotometer data. Geophysical Research Letters, 27(20), 3333-3336. doi: 10.1029/2000GL011581. Aerosol optical depth data representative of various types of aerosols was employed to empirically demonstrate that the lognormal probability distribution is a better reference for reporting optical depth statistics than a normal probability distribution. 0305 Atmospheric Composition and Structure: Aerosols and particles; 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 4801 Oceanography: Biological and Chemical: Aerosols
Podgorny, I. A.; Conant, W.; Ramanathan, V.; Satheesh, S. K.Podgorny, I. A., W. Conant, V. Ramanathan, S. K. Satheesh, 2000: Aerosol modulation of atmospheric and surface solar heating over the tropical Indian Ocean. Tellus B, 52(3), 947-958. doi: 10.1034/j.1600-0889.2000.d01-4.x. The major finding of this study is that aerosols over the tropical Indian Ocean enhance clear sky atmospheric solar heating significantly and decrease the surface solar heating by even a larger amount. The results presented here are based on aerosol chemical, microphysical, and optical and radiometric data collected at the island of Kaashidhoo (4.97°N, 73.47°E) during February and March of 1998, as part of the first field phase of the Indian Ocean experiment (INDOEX). The aerosol optical properties were integrated with a multiple scattering Monte Carlo radiative transfer model which was validated at the surface with broadband flux measurements and at the top of the atmosphere (TOA) with the clouds and earth's radiant energy system (CERES) radiation budget measurements. We consider both externally and internally mixed aerosol models with very little difference between the two models in the estimated forcing. For the February–March period, the aerosols increase the monthly mean clear sky atmospheric solar heating by about 12 W/m2(about 15% of the total atmospheric solar heating) and decrease the sea surface clear sky solar heating by about 16 W/m2 with a daily range from 5 to 23 W/m2. The net aerosol forcing at the top of the atmosphere is about −4 W/m2 with a daily range from −2 to −6 W/m2. Although the soot contributes only about 10% to the aerosol optical thickness, it contributes more than 50% to the aerosol induced atmospheric solar heating. The fundamental conclusion of this study is that anthropogenic aerosols over the tropical Indian Ocean are altering the clear sky radiation budget of the atmosphere and surface in a major manner.
Priestley, Kory J.; Barkstrom, Bruce R.; Lee, Robert B.; Green, Richard N.; Thomas, Susan; Wilson, Robert S.; Spence, Peter L.; Paden, Jack; Pandey, D. K.; Al-Hajjah, AimanPriestley, K. J., B. R. Barkstrom, R. B. Lee, R. N. Green, S. Thomas, R. S. Wilson, P. L. Spence, J. Paden, D. K. Pandey, A. Al-Hajjah, 2000: Postlaunch Radiometric Validation of the Clouds and the Earth’s Radiant Energy System (CERES) Proto-Flight Model on the Tropical Rainfall Measuring Mission (TRMM) Spacecraft through 1999. Journal of Applied Meteorology, 39(12), 2249-2258. doi: 10.1175/1520-0450(2001)040<2249:PRVOTC>2.0.CO;2. Abstract Each Clouds and the Earth’s Radiant Energy System (CERES) instrument contains three scanning thermistor bolometer radiometric channels. These channels measure broadband radiances in the shortwave (0.3–5.0 μm), total (0.3–>100 μm), and water vapor window regions (8–12 μm). Ground-based radiometric calibrations of the CERES flight models were conducted by TRW Inc.’s Space and Electronics Group of Redondo Beach, California. On-orbit calibration and vicarious validation studies have demonstrated radiometric stability, defined as long-term repeatability when measuring a constant source, at better than 0.2% for the first 18 months of science data collection. This level exceeds by 2.5 to 5 times the prelaunch radiometric performance goals that were set at the 0.5% level for terrestrial energy flows and 1.0% for solar energy flows by the CERES Science Team. The current effort describes the radiometric performance of the CERES Proto-Flight Model on the Tropical Rainfall Measuring Mission spacecraft over the first 19 months of scientific data collection.
Randall, David; Curry, Judith; Duynkerke, Peter; Krueger, Steven; Miller, Martin; Moncrieff, Mitchell; Ryan, Brian; Starr, David; Rossow, William; Tselioudis, George; othersRandall, D., J. Curry, P. Duynkerke, S. Krueger, M. Miller, M. Moncrieff, B. Ryan, D. Starr, W. Rossow, G. Tselioudis, . others, 2000: The second GEWEX cloud system study science and implementation plan. IGPO Publication Series, 34, 45.
Redelsperger, J.-L.; Brown, P. R. A.; Guichard, F.; How, C.; Kawasima, M.; Lang, S.; Montmerle, T.; Nakamura, K.; Saito, K.; Seman, C.; Tao, W. K.; Donner, L. J.Redelsperger, J., P. R. A. Brown, F. Guichard, C. How, M. Kawasima, S. Lang, T. Montmerle, K. Nakamura, K. Saito, C. Seman, W. K. Tao, L. J. Donner, 2000: A gcss model intercomparison for a tropical squall line observed during toga-coare. I: Cloud-resolving models. Quarterly Journal of the Royal Meteorological Society, 126(564), 823-863. doi: 10.1002/qj.49712656404. Results from eight cloud-resolving models are compared for the first time for the case of an oceanic tropical squall line observed during the Tropical Ocean/Global Atmosphere Coupled Ocean-Atmosphere Response Experiment. There is broad agreement between all the models in describing the overall structure and propagation of the squall line and some quantitative agreement in the evolution of rainfall. There is also a more qualitative agreement between the models in describing the vertical structure of the apparent heat and moisture sources. The three-dimensional (3D) experiments with an active ice phase and open lateral boundary conditions along the direction of the system propagation show good agreement for all parameters. The comparison of 3D simulated fields with those obtained from two different analyses of airborne Doppler radar data indicates that the 3D models are able to simulate the dynamical structure of the squall line, including the observed double-peaked updraughts. However, the second updraught peak at around 10 km in height is obtained only when the ice phase is represented. The 2D simulations with an ice-phase parametrization also exhibit this structure, although with a larger temporal variability. In the 3D simulations, the evolution of the mean wind profile is in the sense of decreasing the shear, but the 2D simulations are unable to reproduce this behaviour. clouds; cloud-resolving models; Doppler radar; GCSS
Satheesh, S. K.; Ramanathan, V.Satheesh, S. K., V. Ramanathan, 2000: Large differences in tropical aerosol forcing at the top of the atmosphere and Earth's surface. Nature, 405(6782), 60-63. doi: 10.1038/35011039. The effect of radiative forcing by anthropogenic aerosols is one of the largest sources of uncertainty in climate predictions. Direct observations of the forcing are therefore needed, particularly for the poorly understood tropical aerosols. Here we present an observational method for quantifying aerosol forcing to within 5 per cent. We use calibrated satellite radiation measurements and five independent surface radiometers to quantify the aerosol forcing simultaneously at the Earth's surface and the top of the atmosphere over the tropical northern Indian Ocean. In winter, this region is covered by anthropogenic aerosols of sulphate, nitrate, organics, soot and fly ash from the south Asian continent. Accordingly, mean clear-sky solar radiative heating for the winters of 1998 and 1999 decreased at the ocean surface by 12 to 30 W m-2, but only by 4 to 10 W m-2 at the top of the atmosphere. This threefold difference (due largely to solar absorption by soot) and the large magnitude of the observed surface forcing both imply that tropical aerosols might slow down the hydrological cycle.
Stephens, G. L.; Miller, S. D.; Benedetti, A.; McCoy, R. B.; McCoy, R. F.; Ellingson, R. G.; Vitko, J.; Bolton, W.; Tooman, T. P.; Valero, F. P. J.; Minnis, P.; Pilewskie, P.; Phipps, G. S.; Sekelsky, S.; Carswell, J. R.; Lederbuhr, A.; Bambha, R.Stephens, G. L., S. D. Miller, A. Benedetti, R. B. McCoy, R. F. McCoy, R. G. Ellingson, J. Vitko, W. Bolton, T. P. Tooman, F. P. J. Valero, P. Minnis, P. Pilewskie, G. S. Phipps, S. Sekelsky, J. R. Carswell, A. Lederbuhr, R. Bambha, 2000: The Department of Energy's Atmospheric Radiation Measurement (ARM) Unmanned Aerospace Vehicle (UAV) Program. Bull. Amer. Meteor. Soc., 81(12), 2915-2938. doi: 10.1175/1520-0477(2000)081<2915:TDOESA>2.3.CO;2. Abstract The U.S. Department of Energy has established an unmanned aerospace vehicle (UAV) measurement program. The purpose of this paper is to describe the evolution of the program since its inception, review the progress of the program, summarize the measurement capabilities developed under the program, illustrate key results from the various UAV campaigns carried out to date, and provide a sense of the future direction of the program. The Atmospheric Radiation Measurement (ARM)–UAV program has demonstrated how measurements from unmanned aircraft platforms operating under the various constraints imposed by different science experiments can contribute to our understanding of cloud and radiative processes. The program was first introduced in 1991 and has evolved in the form of four phases of activity each culminating in one or more flight campaigns. A total of 8 flight campaigns produced over 140 h of science flights using three different UAV platforms. The UAV platforms and their capabilities are described as are the various phases of the program development. Examples of data collected from various campaigns highlight the powerful nature of the observing system developed under the auspices of the ARM–UAV program and confirm the viability of the UAV platform for the kinds of research of interest to ARM and the clouds and radiation community as a whole. The specific examples include applications of the data in the study of radiative transfer through clouds, the evaluation of cloud parameterizations, and the development and evaluation of cloud remote sensing methods. A number of notable and novel achievements of the program are also highlighted.
Su, Wenying; Mao, Jietai; Ji, Fei; Qin, YuSu, W., J. Mao, F. Ji, Y. Qin, 2000: Outgoing longwave radiation and cloud radiative forcing of the Tibetan Plateau. Journal of Geophysical Research: Atmospheres, 105(D11), 14863-14872. doi: 10.1029/2000JD900201. In order to study the energy balance and the cloud radiative forcing (CRF) of the Tibetan Plateau in detail, 2 years of GMS5 satellite data are employed to analyze the monthly mean outgoing longwave radiation (OLR) and CRF. It should be noted that the temporal resolution of GMS5 data is 1 hour, so the data can be used to study the diurnal variations of OLR. First, a method is presented to retrieve the OLR from split-window channels (10.5–11.5 and 11.5–12.5 μm) and the water vapor channel (6.5–7.0 μm) of GMS5. The method applies the discrete ordinates radiative transfer (DISORT) model together with the radiosonde profiles of the Tibetan Plateau to simulate radiances and fluxes of the three channels. A regression relationship is then developed to calculate the OLR from the observations of the three channels. Since the Tibetan Plateau is located nearly out of the effective observational range of the GMS5 satellite, the regression results of GMS5's split-window channels and water vapor channel are corrected by using simultaneously retrieved results from TIROS Operational Vertical Sounder (TOVS). The correlation coefficient of GMS5 and TOVS results is 0.8510, which is large enough for 1% significant level. The OLR distributions are calculated for the Tibetan Plateau using 2 years of GMS5 data and the regression and correction methods. The average of the OLR images for the same month and same time gives the monthly mean OLR distribution for each hour. The 24-hour OLR distributions of the same month are then averaged to yield the monthly mean OLR distribution for that month. Then our monthly mean OLR distributions are compared with the Clouds and the Earth's Radiant Energy System (CERES) results, and they are generally in good agreement with differences of 0312 Air/sea constituent fluxes; 0360 Radiation: transmission and scattering; 1610 Atmosphere; 1640 Remote sensing
Wong, Takmeng; Young, David F.; Haeffelin, Martial; Weckmann, StephanieWong, T., D. F. Young, M. Haeffelin, S. Weckmann, 2000: Validation of the CERES/TRMM ERBE-Like Monthly Mean Clear-Sky Longwave Dataset and the Effects of the 1998 ENSO Event. J. Climate, 13(24), 4256-4267. doi: 10.1175/1520-0442(2000)013<4256:VOTCTE>2.0.CO;2. Abstract The Clouds and the Earth’s Radiant Energy System (CERES) is a new National Aeronautics and Space Administration space-borne measurement project for monitoring the radiation environment of the earth–atmosphere system. The first CERES instrument was launched into space on board the Tropical Rainfall Measuring Mission (TRMM) satellite on 27 November 1997. The purpose of this paper is 1) to describe the initial validation of the new CERES/TRMM Earth Radiation Budget Experiment (ERBE)–like monthly mean clear-sky longwave (CLW) dataset and 2) to demonstrate the scientific benefit of this new dataset through a data application study on the 1998 El Niño–Southern Oscillation (ENSO) episode. The initial validation of the CERES CLW data is carried out based on comparisons with both historical ERBE observations and radiative transfer simulations. While the observed CERES CLWs are initially larger than the historical ERBE record during the first part of the 1998 ENSO event, these differences are diminished by the end of the ENSO event in July 1998. These unique ENSO-related CLW radiation signatures are captured well by the radiative transfer model simulations. These results demonstrate that the new CERES CLW fluxes are theoretically consistent with the underlying physics of the atmosphere. A CERES data application study is performed to examine the relationship between the CERES CLW anomaly and changes in sea surface temperature (SST) and atmospheric column precipitable water content (PWC) during the January 1998 ENSO event. While the changes in the SST pattern are basically uncorrelated with changes in the CLW field, a negative correlation is found between the PWC anomaly and the changes in the CLW radiation field. These observed features point to 1) the significant role of the water vapor field in modulating the tropical outgoing CLW radiation field during the 1998 ENSO event and 2) the important effects of water vapor absorption in decoupling the top of the atmosphere tropical outgoing CLW radiation from the surface upward CLW field.
Zhou, Y. P.; Cess, Robert D.Zhou, Y. P., R. D. Cess, 2000: Validation of longwave atmospheric radiation models using Atmospheric Radiation Measurement data. Journal of Geophysical Research: Atmospheres, 105(D24), 29703-29716. doi: 10.1029/2000JD900557. Data taken at the Atmospheric Radiation Measurement Program's central facility in Oklahoma and processed as part of the Clouds and the Earth's Radiant Energy System-Atmospheric Radiation Measurement-Global Energy and Water Cycle Experiment (CAGEX) project have been used to validate the top-of-the-atmosphere and surface longwave radiative fluxes for two widely used radiation models: the Column Radiation Model from the National Center for Atmospheric Research Community Climate Model (CCM), and the Moderate Resolution Transmittance (MODTRAN3) radiation code. The results show that for clear skies the models slightly overestimate outgoing longwave radiation at the top of the atmosphere (OLR) and underestimate the surface downwelling longwave flux (SDLW). The accuracy of the radiation models is quite consistent with their respective levels of complexity. For MODTRAN3, for example, the OLR overestimate is 7.1 Wm−2 while the SDLW underestimate is 4.2 Wm−2. For cloudy skies it is emphasized that the cloud input parameters, as determined from measurements by various instruments, require careful examination and preprocessing. Spatial and temporal averaging could result in the parameters representing different volumes of the atmosphere. The discrepancy between model calculations and observations is shown to be significantly reduced through the proper choice of input parameters. 3337 Meteorology and Atmospheric Dynamics: Numerical modeling and data assimilation; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3367 Meteorology and Atmospheric Dynamics: Theoretical modeling
Andronache, C.; Donner, L. J.; Seman, C. J.; Ramaswamy, V.; Hemler, R. S.Andronache, C., L. J. Donner, C. J. Seman, V. Ramaswamy, R. S. Hemler, 1999: Atmospheric sulfur and deep convective clouds in tropical Pacific: A model study. Journal of Geophysical Research: Atmospheres, 104(D4), 4005-4024. doi: 10.1029/1998JD200085. A high-resolution limited area nonhydrostatic model was used to simulate sulfate-cloud interactions during the convective activity in a case study from the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment, December 20–25, 1992. The model includes a new detailed sulfate-cloud microphysics scheme designed to estimate the effects of sulfate on cloud microphysics and radiative properties and the effects of deep convection on the transport and redistribution of aerosol. The data for SO2 and SO4(2−) species were taken from the Pacific Exploratory Mission West B observations during February-March 1994. Results show that a change in sulfate loading from the minimum to the maximum observed value scenarios (i.e., from about 0.01 to 1 μg m−3) causes a significant decrease of the effective radius of cloud droplets (changes up to 2 μm on average) and an increase of the diagnostic number concentration of cloud droplets (typical changes about 5–20 cm−3). The change in the average net shortwave (SW) radiation flux above the clouds was estimated to be on average −1.5 W m−2, with significant spatial and temporal variations. The horizontal average of the changes in the net SW radiation fluxes above clouds has a diurnal cycle, reaching typical values approximately −3 W m−2. The changes in the average net longwave radiation flux above the clouds were negligible, but they showed significant variations, typically between −10 W m−2 and 10 W m−2 near the surface. These variations were associated mainly with the changes in the distribution of cloud water, which showed typical relative changes of cloud water path of about 10–20%. Other notable changes induced by the increase of aerosol were the variations in air temperature of the order of 1°C. The case study presented here suggests that characteristics of convective clouds in tropical areas are sensitive to atmospheric sulfate loading, particularly during enhanced sulfate episodes. 0320 Cloud physics and chemistry; 0305 Aerosols and particles; 0394 Instruments and techniques; 9310 Information Related to Geographic Region: Antarctica; 1863 Snow and ice; 3045 Seafloor morphology, geology, and geophysics
Barkstrom, B. R.Barkstrom, B. R., 1999: CERES: The start of the next generation of radiation measurements. Advances in Space Research, 24(7), 907-914. doi: 10.1016/S0273-1177(99)00354-3. This paper describes current state of the investigation of Clouds and the Earth's Radiant Energy System (CERES), which had its first instrument launched on the Tropical Rainfall Measuring Mission (TRMM) from Japan in late November 1998. This instrument performed extremely well during its first six months in orbit. The ERBE-like data products from the CERES instrument on TRMM are being archived, so that geolocated radiances are already available for scientific research, about six months after launch. This paper also describes some of the validation work the CERES Team has undertaken and identifies differences between ERBE data and CERES. Because of the complexity of the measurement process, several factors must be considered in dealing with the question of whether these differences are the result of changes between the ERBE and CERES measurements or are real changes in the radiation budget. Based on this work, the CERES investigation appears poised to provide a major improvement in our understanding of the interaction between clouds, radiation, and climate.
Dewitte, S.; Clerbaux, N.Dewitte, S., N. Clerbaux, 1999: First experience with GERB ground segment processing software: Validation with CERES PFM data. Advances in Space Research, 24(7), 925-929. doi: 10.1016/S0273-1177(99)00357-9. The Geostationary Earth Radiation Budget (GERB) instrument is designed for an accurate measurement of the radiation budget terms at the top of the earth's atmosphere. Flux products with a spatial resolution of 50 km at nadir and with a temporal resolution of 15 minutes will be generated from raw measurements, within 4 hours after their acquisition. With this goal, near real time software is developed with the use of METEOSAT 6 narrowband data as preliminary input data. The corresponding output data are compared with Clouds and the Earth's Radiant Energy System ProtoFlight Model (CERES PFM) data during March 1998. The correctness of the calibration and the spectral modelling of the METEOSAT 6 narrowband channels is checked by comparison with colocated coangular data. In addition, the correctness of the Angular Dependency Models used is checked by comparison with colocated non coangular data.
Diner, David J.; Asner, Gregory P.; Davies, Roger; Knyazikhin, Yuri; Muller, Jan-Peter; Nolin, Anne W.; Pinty, Bernard; Schaaf, Crystal B.; Stroeve, JulienneDiner, D. J., G. P. Asner, R. Davies, Y. Knyazikhin, J. Muller, A. W. Nolin, B. Pinty, C. B. Schaaf, J. Stroeve, 1999: New Directions in Earth Observing: Scientific Applications ofMultiangle Remote Sensing. doi: 10.1175/1520-0477(1999)080<2209:NDIEOS>2.0.CO;2. The physical interpretation of simultaneous multiangle observations represents a relatively new approach to remote sensing of terrestrial geophysical and biophysical parameters. Multiangle measurements enable retrieval of physical scene characteristics, such as aerosol type, cloud morphology and height, and land cover (e.g., vegetation canopy type), providing improved albedo accuracies as well as compositional, morphological, and structural information that facilitates addressing many key climate, environmental, and ecological issues. While multiangle data from wide field-of-view scanners have traditionally been used to build up directional “signatures” of terrestrial scenes through multitemporal compositing, these approaches either treat the multiangle variation as a problem requiring correction or normalization or invoke statistical assumptions that may not apply to specific scenes. With the advent of a new generation of global imaging spectroradiometers capable of acquiring simultaneous visible/near-IR multiangle observations, namely, the Along- Track Scanning Radiometer-2, the Polarization and Directionality of the Earth’s Reflectances instrument, and the Multiangle Imaging SpectroRadiometer, both qualitatively new approaches as well as quantitative improvements in accuracy are achievable that exploit the multiangle signals as unique and rich sources of diagnostic information. This paper discusses several applications of this technique to scientific problems in terrestrial atmospheric and surface geophysics and biophysics.
Donner, Leo J.; Seman, Charles J.; Hemler, Richard S.Donner, L. J., C. J. Seman, R. S. Hemler, 1999: Three-Dimensional Cloud-System Modeling of GATE Convection. J. Atmos. Sci., 56(12), 1885-1912. doi: 10.1175/1520-0469(1999)056<1885:TDCSMO>2.0.CO;2. Abstract Deep convection and its associated mesoscale circulations are modeled using a three-dimensional elastic model with bulk microphysics and interactive radiation for a composite easterly wave from the Global Atmospheric Research Program Atlantic Tropical Experiment. The energy and moisture budgets, large-scale heat sources and moisture sinks, microphysics, and radiation are examined. The modeled cloud system undergoes a life cycle dominated by deep convection in its early stages, followed by an upper-tropospheric mesoscale circulation. The large-scale heat sources and moisture sinks associated with the convective system agree broadly with diagnoses from field observations. The modeled upper-tropospheric moisture exceeds observed values. Strong radiative cooling at the top of the mesoscale circulation can produce overturning there. Qualitative features of observed changes in large-scale convective available potential energy and convective inhibition are found in the model integrations, although quantitative magnitudes can differ, especially for convective inhibition. Radiation exerts a strong influence on the microphysical properties of the cloud system. The three-dimensional integrations exhibit considerably less sporadic temporal behavior than corresponding two-dimensional integrations. While the third dimension is less important over timescales longer than the duration of a phase of an easterly wave in the lower and middle troposphere, it enables stronger interactions between radiation and dynamics in the upper-tropospheric mesoscale circulation over a substantial fraction of the life cycle of the convective system.
Fowler, Laura D.; Randall, David A.Fowler, L. D., D. A. Randall, 1999: Simulation of upper tropospheric clouds with the Colorado State University general circulation model. Journal of Geophysical Research: Atmospheres, 104(D6), 6101-6121. doi: 10.1029/1998JD200074. We have compared the climatology of upper tropospheric clouds simulated with the Colorado State University (CSU) general circulation model against cloud products retrieved by the International Satellite Cloud Climatology Project (ISCCP). Following the ISCCP cloud classification, upper tropospheric clouds are defined as clouds with cloud tops above 440 hPa. We refined our comparison by considering separately clouds with cloud tops above 180, 310, and 440 hPa in order to exhibit the optical characteristics of the highest clouds in the model and satellite cloud products. Four ranges of visible optical depths (τ) were used to distinguish cirrus (τ ≤ 3.6) from optically thicker cirrostratus (3.6 < τ ≤ 23) and deep convective clouds (τ > 23) and to further differentiate between thin (0.02 < τ ≤ 1.6) and thick (1.6 < τ ≤ 3.6) cirrus. Results show that the CSU GCM simulates satisfactorily the zonally averaged distribution of upper tropospheric clouds when all values of τ are included but systematically underpredicts the frequency of occurrence of clouds with values of τ less than 3.6 when compared against ISCCP-D1 data. This result reveals that simulated total-column optical depths for columns that include upper tropospheric clouds are too large relative to satellite-derived values. The CSU GCM simulates upper tropospheric clouds in the tropics more successfully than those in the middle latitudes. In the middle latitudes the model fails to simulate upper tropospheric clouds over the continents, especially over high plateaus and mountain ranges. Discrepancies between the CSU GCM and the ISCCP cloud products can be addressed in terms of our simple formulation of the optical thickness as a function of the prognostic liquid/ice water content, the prescribed value of the effective radius, and the geometrical thickness of the upper tropospheric model layers. We investigate the impact of the vertical resolution used in the GCM on the calculation of the optical depths of single-layer clouds using estimates of the geometrical thickness of cloudy layers from the Lidar In-Space Technology Experiment. 3319 Meteorology and Atmospheric Dynamics: General circulation; 3309 Meteorology and Atmospheric Dynamics: Climatology; 0340 Middle atmosphere: composition and chemistry; 1899 General or miscellaneous
Gupta, Shashi K.; Ritchey, Nancy A.; Wilber, Anne C.; Whitlock, Charles H.; Gibson, Gary G.; Stackhouse, Paul W.Gupta, S. K., N. A. Ritchey, A. C. Wilber, C. H. Whitlock, G. G. Gibson, P. W. Stackhouse, 1999: A Climatology of Surface Radiation Budget Derived from Satellite Data. J. Climate, 12(8), 2691-2710. doi: 10.1175/1520-0442(1999)012<2691:ACOSRB>2.0.CO;2. Abstract Climatological averages of surface radiation budget parameters, namely, the shortwave and longwave surface radiative fluxes, have been derived for each month of the year on a global scale. These climatological averages were derived from an 8-yr (96 month) time series of monthly average fluxes. The monthly averages were computed using fast radiation parameterizations and satellite data from the International Satellite Cloud Climatology Project and the Earth Radiation Budget Experiment. Results are presented as time series of hemispheric and global averages and as geographical distributions and time–latitude cross sections of climatological averages. The spatial/temporal variabilities of the results were found to be clearly related to the corresponding variabilities of meteorological and other inputs to the parameterizations. Numerous comparisons of the present results were made with available surface measurements for the purpose of validation. In most cases, the differences were found to be within the uncertainties of the measurements. In some cases, where they were large, the differences were attributable to identifiable deficiencies in the meteorological inputs and/or the surface measurements. However, large differences remained unexplained in a few cases. Anomalies of shortwave and longwave surface fluxes during the 1986/87 El Niño–Southern Oscillation episode show a strong relationship with corresponding top-of-atmosphere anomalies derived from an independent data source. Comparisons with results from several general circulation models showed large differences, but, in most cases, these were attributable to well-recognized deficiencies in model simulations. Global annual average downward and net shortwave fluxes were found to be about 185 and 161 W m−2, respectively. These values are 10–20 W m−2 lower than those obtained from the general circulation models, but they are in good agreement with other satellite-derived estimates. Global annual average downward and net longwave fluxes were found to be about 348 and −48 W m−2, respectively, which are about 10–15 W m−2 higher than corresponding values from general circulation models. Atmospheric shortwave absorption derived from the present results is 10–15 W m−2 larger than from the general circulation models, but it is in good agreement with another estimate based on satellite data.
Haeffelin, Martial; Kandel, Robert; Stubenrauch, ClaudiaHaeffelin, M., R. Kandel, C. Stubenrauch, 1999: Improved Diurnal Interpolation of Reflected Broadband Shortwave Observations Using ISCCP Data. J. Atmos. Oceanic Technol., 16(1), 38-54. doi: 10.1175/1520-0426(1999)016<0038:IDIORB>2.0.CO;2. Abstract The multisatellite Earth Radiation Budget Experiment (ERBE) was designed to provide complete temporal coverage of the solar-reflected and earth-emitted radiation. Following operation of ERBE scanners on as few as one and as many as three satellites between November 1984 and February 1990, narrow-field-of-view earth radiation budget measurements were resumed in March 1994 by the Scanner for Radiation Budget (ScaRaB) mission and in December 1997 by the first Clouds and the Earth’s Radiant Energy System (CERES) instrument, each time on a single satellite. Due to sparse temporal sampling, diurnal variations must be accounted for in order to establish accurate unbiased daily and monthly mean radiant exitance. When the ERBE diurnal interpolation algorithm is used alone, large discrepancies appear between monthly mean radiative fluxes obtained from single- and multisatellite data. The authors extend the algorithm by accounting for diurnally varying cloud cover using International Satellite Cloud Climatology Project (ISCCP) data products. Significant improvements are found in regions where clouds have a pronounced diurnal cycle. Further improvements are obtained by also taking into account diurnal variations of cloud properties such as optical thickness using either ISCCP cloud radiance data or a cloud classification. These approaches require the development of directional models to represent the angular dependence of the cloud albedo corresponding to the ISCCP cloud classification.
Han, Qingyuan; Rossow, William B.; Chou, Joyce; Kuo, Kwo-Sen; Welch, Ronald M.Han, Q., W. B. Rossow, J. Chou, K. Kuo, R. M. Welch, 1999: The effects of aspect ratio and surface roughness on satellite retrievals of ice-cloud properties. Journal of Quantitative Spectroscopy and Radiative Transfer, 63(2–6), 559-583. doi: 10.1016/S0022-4073(99)00039-4. This study investigates the effects of non-sphericity on satellite retrievals of ice-cloud properties including optical thickness and particle sizes. Ray-tracing technique is used to calculate single scattering phase function and single scattering albedo for both smooth and rough surfaces of hexagonal columns and plates at visible and near-infrared wavelengths. Two parameters, aspect ratio and distortion parameter, are used to simulate different, randomly oriented, ice crystal shapes and surface roughnesses in the ray-tracing process. A wide range of aspect ratio and distortion parameter is explored in the calculations. The resultant phase functions and single scattering albedos are used to compute bidirectional reflection functions by a radiative transfer model with adding–doubling technique. The results show that in a direct backscattering regima (Θ>150°), if no information of particle shape is available, the uncertainties in the retrieved optical thickness (a factor of more than ten) would make the retrieval meaningless. For images with viewing geometry outside of this region, the typical range of uncertainty of retrieved optical thickness is less than a factor of about two. Using averaged phase function will cut this uncertainty in half. That is, the uncertainty in the retrieved optical thickness is about 40%. Sensitivity tests show that aspect ratios are critical in reducing the uncertainties of the retrieved optical thickness using satellite data. The uncertainties in the retrieved ice particle sizes are also estimated in a similar way. It is found that using an averaged aspect ratio and roughness, the uncertainty of retrieved particle size is about 30% for small particles and 10% for large particles at λ=3.7 μm. The corresponding uncertainties are about 70% for small particles and 35% for large particles if data at λ=1.6 or 2.2 μm are used in the retrieval. However, at λ=1.6 and 2.2 μm, retrieval of particle size may encounter even larger uncertainties for thin ice-clouds (τ<3).
Hollmann, R.; Müller, J.; Rockel, B.; Stuhlmann, R.Hollmann, R., J. Müller, B. Rockel, R. Stuhlmann, 1999: Satellite retrieved clouds and the radiation budget in support of BALTEX regional studies. Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere, 24(1–2), 111-115. doi: 10.1016/S1464-1909(98)00020-3. We present in our paper two methods to use satellite data for a comparison with a regional scale model for the Baltic sea area. Two examples are given, first to derive the radiation budget from measurements with a scanning radiometer and second to make use of the cloud information from ISCCP. First results show good agreement and demonstrate their capability to improve regional scale models. The disadvantages are mainly the poor sampling (first method) and in the second case the coarse resolution. After an introduction and a brief discussion of the regional scale model and the instrument design of the Scanner for Radiation Budget, we present the comparison of ScaRaB and the model calculated radiation. After that we discuss a comparison of the ISCCP cloud data with the model.
Kato, S.; Ackerman, Thomas P; Mather, James H; Clothiaux, Eugene EKato, S., T. P. Ackerman, J. H. Mather, E. E. Clothiaux, 1999: The k-distribution method and correlated-k approximation for a shortwave radiative transfer model. Journal of Quantitative Spectroscopy and Radiative Transfer, 62(1), 109-121. doi: 10.1016/S0022-4073(98)00075-2. Absorption cross sections are tabulated for water vapor, including continuum absorption, ozone, oxygen and carbon dioxide in the solar spectral region by adopting the k-distribution method. These tables are generated based on line-by-line code results for ranges of total pressure, temperature and water vapor concentration typical of values throughout the troposphere. These tables are incorporated into a shortwave radiative transfer code, which has 32 wavelength intervals across the solar spectrum, by using the correlated-k approximation in order to evaluate the accuracy in the broad band direct normal irradiance computation. A comparison of the direct normal irradiance with MODTRAN3 demonstrates that these tables can be used for shortwave broad band irradiance computations; the difference in the transmissivity is within 0.01 throughout most of the solar spectral region.
KATO, SEIJI; ACKERMAN, THOMAS P.; DUTTON, ELLSWORTH G.; LAULAINEN, NELS; LARSON, NELSKATO, S., T. P. ACKERMAN, E. G. DUTTON, N. LAULAINEN, N. LARSON, 1999: A COMPARISON OF MODELED AND MEASURED SURFACE SHORTWAVE IRRADIANCE FOR A MOLECULAR ATMOSPHERE. Journal of Quantitative Spectroscopy and Radiative Transfer, 61(4), 493-502. doi: 10.1016/S0022-4073(98)00032-6. We compare the downward diffuse and direct normal irradiance computed by a two-stream model with measurements taken at the Mauna Loa Observatory when the atmosphere was close to a molecular atmosphere. The modeled downward diffuse irradiance agrees with measurements taken by a shaded pyranometer within the uncertainty of the measurement. Therefore, the two-stream approximation is adequate for computing the downward diffuse irradiance in a molecular atmosphere. This result also indicates that neglecting the state of polarization introduces a negligible error in the irradiance computation.
KRATZ, DAVID P.; ROSE, FRED G.KRATZ, D. P., F. G. ROSE, 1999: ACCOUNTING FOR MOLECULAR ABSORPTION WITHIN THE SPECTRAL RANGE OF THE CERES WINDOW CHANNEL. Journal of Quantitative Spectroscopy and Radiative Transfer, 61(1), 83-95. doi: 10.1016/S0022-4073(97)00203-3. Infrared active molecular species residing within the atmosphere cause the emerging thermal infrared spectrum of the Earth to be characterized by both line and continuum absorption (emission). Accounting for the molecular absorption within the atmosphere is critical for the proper interpretation of the satellite measured radiances. Thus, correlated k-distribution procedures have been created to account for the molecular line absorption located within the spectral range of the Clouds and the Earth’s Radiant Energy System (CERES) infrared window channel (8–12 μm). The derivation of the correlated k-distributions is based upon an exponential sum fitting of transmissions (ESFT) procedure that has been applied to monochromatic calculations at predetermined reference pressure and temperature conditions. In addition, an empirically derived, yet highly accurate parameterization of the CKD-2.1 code has been developed to calculate the atmospheric absorption attributed to the water vapor continuum located within the spectral range of the CERES infrared window channel. The multiplication transmissivity approximation has been employed to account for the overlap of the spectral features of different molecular species. The accuracy of the radiative transfer procedures incorporating the correlated k-distribution routines and the parameterized CKD2.1 continuum routines has been established through comparisons with the reference monochromatic procedures. The correlated k-distribution yields an upwelling top of atmosphere (TOA) flux for the midlatitude summer (MLS) atmosphere that is within 0.1% of the monochromatic procedures for the CERES window channel. Neglecting the contributions from all the molecular species in the correlated k-distribution except H2O and O3 yields an upwelling TOA flux for the MLS atmosphere with a 1.5% overestimation. Under circumstances where rapid processing is extremely critical, an error of this magnitude may be deemed acceptable. Neglecting the contributions from all of the molecular species yields an upwelling TOA flux for the MLS atmosphere with a 17.7% overestimation. An error of this magnitude is certainly not acceptable but does emphasize the need to account for the molecular absorption within the spectral range of the CERES window channel instrument.
Li, Zhanqing; Trishchenko, AlexanderLi, Z., A. Trishchenko, 1999: A Study toward an Improved Understanding of the Relationship between Visible and Shortwave Measurements. J. Atmos. Oceanic Technol., 16(3), 347-360. doi: 10.1175/1520-0426(1999)016<0347:ASTAIU>2.0.CO;2. Abstract Narrowband (NB) to broadband (BB) conversion is a common practice to acquire radiation budget data from operational imagery data. This study attempts to gain further insights into the relationship between NB visible (VIS) albedo and BB shortwave (SW) albedo by means of observational analysis and radiative transfer modeling. Multiple observation datasets were employed including Scanner for Radiation Budget (ScaRaB) satellite measurements, National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis of precipitable water and temperature profiles, Total Ozone Mapping Spectrometer ozone amount, etc. Radiative transfer modeling was done with an adding–doubling model of high spectral resolution for a range of surface, atmospheric, and cloud conditions. ScaRaB provided calibrated synergistic measurements of VIS and SW albedos. The two types of albedos were found to be linearly correlated with much higher correlation coefficients than previously obtained from other instruments. In combination with other datasets, the impact of various parameters on the VIS–SW relation was investigated and compared with the results of modeling. The most significant parameter influencing the relation is the solar zenith angle, followed by cloud-top height, precipitable water amount, ozone amount, aerosol, and cloud microphysics. Narrow- to broadband conversion models with a varying number of input parameters were developed and validated.
Loeb, Norman G.; Hinton, Patricia O'Rawe; Green, Richard N.Loeb, N. G., P. O. Hinton, R. N. Green, 1999: Top-of-atmosphere albedo estimation from angular distribution models: A comparison between two approaches. Journal of Geophysical Research: Atmospheres, 104(D24), 31255-31260. doi: 10.1029/1999JD900935. Empirical angular distribution models (ADMs) are commonly used to convert satellite-measured radiances to top-of-atmosphere (TOA) radiative fluxes. This study compares two methods of developing ADMs: (1) the radiance pairs method (RPM), which composits ratios of near-simultaneous radiance measurements over the same scene to construct the ADMs; (2) the sorting-into-angular-bins (SAB) method, which estimates ADM anisotropic factors from the ratio of the mean radiance in each angular bin to the mean flux determined by direct integration of the mean radiances. Theoretical simulations and analyses of measurements from the CERES (Clouds and Earth's Radiant Energy System) satellite instrument show that the RPM method provides a better estimate of the true mean ADM for a population of scenes, while the SAB method is better suited for top-of-atmosphere flux estimation. The CERES results also show that a variable field of view size with viewing zenith angle can cause an ≈10% (relative) change in estimated all-sky mean albedo with viewing zenith angle. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1640 Remote sensing; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 1620 Climate dynamics; 1694 Instruments and techniques; 4504 Air/sea interactions
Masutani, M.; Campana, K.; Lord, S.; Yang, S. K.Masutani, M., K. Campana, S. Lord, S. K. Yang, 1999: Note on cloud cover of the ECMWF Nature Run used for OSSE/NPOESS project.
Mavromatis, T.; Jones, P. D.Mavromatis, T., P. D. Jones, 1999: Evaluation of HadCM2 and Direct Use of Daily GCM Data in Impact Assessment Studies. Climatic Change, 41(3-4), 583-614. doi: 10.1023/A:1005336608651. This paper investigates two important aspects of methods used to explore possible effects of climatic changes on agricultural productivity on regional spatial scales. First, an evaluation of precipitation and near surface air temperature in two successive versions of the Hadley Centre General Circulation Model (GCM) has been performed to consider to what extent GCMs are capable of simulating the mean and variability of local climates. This is explored by comparing the output of an individual GCM grid box with three station observations. Several ancillary issues associated with the comparisons of observations of daily precipitation and model output that affect the statistical results are also discussed. Finally, daily data from the control and sulphate runs of the latest Hadley Centre GCM (HadCM2) have been used directly as input to the CERES-Wheat model, and the modelled yield distribution is compared to that produced with the historical data series. Our results imply that for this particular grid box covering the study region in central France, the daily raw data from HadCM2 experiment can be used directly to assess the potential impact of the greenhouse gas and sulphate aerosol radiative induced forcings and the associated climatic change on average regional winter wheat production. On the other hand, less confidence should be placed on their use regarding the estimation of future agricultural risk and variability assessment. Furthermore, a possibly more severe methodological problem that has arisen from our study is the inability of CERES-Wheat to simulate the waterlogging effects of excessive soil water on crop growth and development. Finally, we assess the potential impact of changing climate on regional winter wheat production by using the daily data from the sulphate integration up to the end of the 21st century. Meteorology/Climatology
Satheesh, S. K.; Ramanathan, V.; Li-Jones, Xu; Lobert, J. M.; Podgorny, I. A.; Prospero, J. M.; Holben, B. N.; Loeb, N. G.Satheesh, S. K., V. Ramanathan, X. Li-Jones, J. M. Lobert, I. A. Podgorny, J. M. Prospero, B. N. Holben, N. G. Loeb, 1999: A model for the natural and anthropogenic aerosols over the tropical Indian Ocean derived from Indian Ocean Experiment data. Journal of Geophysical Research: Atmospheres, 104(D22), 27421-27440. doi: 10.1029/1999JD900478. The physical, chemical and radiative properties of aerosols are investigated over the tropical Indian Ocean during the first field phase (FFP) of the international Indian Ocean Experiment. The FFP was conducted during February 20 to March 31, 1998. The results shown here are from the Kaashidhoo Climate Observatory (KCO), a new surface observatory established on the tiny island of Kaashidhoo (4.965°N, 73.466°E) in the Republic of Maldives. From simultaneous measurements of aerosol physical, chemical, and radiative properties and the vertical structure from lidar, we have developed an aerosol model which, in conjunction with a Monte Carlo radiative transfer model, successfully explains (within a few percent) the observed solar radiative fluxes at the surface and at the top of the atmosphere. This agreement demonstrates the fundamental importance of measuring aerosol physical and chemical properties for modeling radiative fluxes. KCO, during the northeast monsoon period considered here, is downwind of the Indian subcontinent and undergoes variations in the aerosol visible optical depth τν from ∼0.1 to 0.4, with a monthly mean of ∼0.2. Lidar data suggest that the aerosol is confined largely to the first 3 kms. Sulfate and ammonium contribute ∼29% to τν; sea-salt and nitrate contributes ∼17%; mineral dust contributes ∼15%; and the inferred soot, organics, and fly ash contribute 11%, 20%, and 8% respectively. We estimate that anthropogenic sources may contribute as much as 65% to the observed τν. We consider both an externally and an internally mixed aerosol model with very little difference between the two in the computed radiative forcing. The observed scattering coefficients are in the upper range of those reported for other oceanic regions, the single-scattering albedos are as low as 0.9, and the Angstrom wavelength exponents of ∼1.2 indicate the abundance of submicron aerosols. In summary, the data and the model confirm the large impact of anthropogenic sources. The surface global fluxes (for overhead Sun) decrease by as much as 50 to 80 W m−2 owing to the presence of the aerosols, and the top of the atmosphere fluxes increase by as much as 15 W m−2, thus indicating that anthropogenic aerosols are having a large impact on the tropical Indian Ocean. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1610 Atmosphere; 0345 Pollution: urban and regional; 1836 Hydrological cycles and budgets; 1866 Soil moisture
Smith, G. LouisSmith, G. L., 1999: Critical overview of radiation budget estimates from satellites. Advances in Space Research, 24(7), 887-895. doi: 10.1016/S0273-1177(99)00359-2. The progress of Earth radiation budget research has been due to the improvement of instrument accuracy and reliability, and also due to the vast progress in computer capability. The increase of instrument reliability and the resulting longer measurement records has brought the organizational support which is necessary for the improvement of analysis methods for generation of data products and to bring together the science teams which are needed to make good use of the data products. Computers today can process enough data so that we can bring in data streams from more than a single instrument and perform extensive computations. As a consequence, the field has progressed from producing monthly global maps at the top of the atmosphere to producing daily maps and producing radiation profiles through the atmosphere. Radiation data are now used together with other data types to study the weather and climate as a system. Scientific questions addressed by radiation data have evolved from monthly-mean zonal descriptions toward smaller time and space scales.
Volkov, Y. A.; Plakhina, I. N.; Repina, I. A.Volkov, Y. A., I. N. Plakhina, I. A. Repina, 1999: Parametrization of the surface radiative budget on the basis of the CAGEX-1 experiment within the program of atmospheric radiation measurements. Izvestiya Akademii Nauk Fizika Atmosfery I Okeana, 35(1), 66-72. An analysis of the daily variations of all components of radiative budget measured under clear sky and cloudy conditions is performed on the basis of the data of the program of atmospheric radiation measurements (the CERES/ARM/GEWEX Exercise, CAGEX). These data contain ground-based meteorological information, experimental values of surface radiation fluxes, and fundamental atmospheric parameters, such as profiles of temperature and humidity and also satellite and lidar estimates of the amount, type, height, and optical thickness of clouds, The effect of daytime heating of the underlying surface manifesting itself in the asymmetry of the daily variations of radiative budget is estimated quantitatively. By regression analysis, the daily variations of radiative budget under clear sky conditions and continuous middle-layer cloudiness is parametrized. As-a result, the surface local cloud-radiative forcing under continuous middle-layer cloudiness is estimated for the CAGEX-1 experiment.
Waliser, Duane E.; Weller, Robert A.; Cess, Robert D.Waliser, D. E., R. A. Weller, R. D. Cess, 1999: Comparisons between buoy-observed, satellite-derived, and modeled surface shortwave flux over the subtropical North Atlantic during the Subduction Experiment. Journal of Geophysical Research: Atmospheres, 104(D24), 31301-31320. doi: 10.1029/1999JD900946. Two years of surface shortwave flux data, from five buoys in the subtropical North Atlantic Ocean during the Subduction Experiment, were used to examine shortwave absorption in the atmosphere, and its partitioning between the clear and cloudy sky. Robust methods were used to isolate the clear-sky shortwave observations so that they could be directly compared to values derived using a single-column version of the National Center for Atmospheric Research Community Climate Model radiation code. The model-derived values agreed with the observations to within 0.5% mean relative error. Additional analysis showed that the model-data clear-sky surface shortwave differences showed no systematic relationship with respect to column water vapor amount. These results indicate that clear-sky absorption of shortwave radiation appears to be well modeled by current theory. Model-derived clear-sky surface shortwave values were combined with the observed (all-sky) values to determine the surface shortwave cloud forcing. The mean of these series were combined with 5-year mean Earth Radiation Budget Experiment derived top of the atmosphere (TOA) cloud forcing values to estimate the surface to TOA cloud forcing ratio. The resulting values range between 1.25 and 1.59. These values, along with the agreement between modeled and observed clear-sky surface shortwave, support the suggestion that our current theoretical radiative transfer models do not properly account for the amount of shortwave energy absorbed by the cloudy atmosphere. Mean values from the 2-year shortwave flux time series were compared to mean values from two climatologies derived from bulk parameterizations that utilize ship-based cloud reports. These comparisons show that the Oberhuber climatology underestimates the surface shortwave flux by ∼20% (∼40 W m−2), while the Esbensen and Kushnir climatology underestimates the flux by ∼4% (∼8 W m−2). The observed mean values were also compared to five satellite-derived climatologies. These comparisons showed much better and more consistent agreement, with relative bias errors ranging from about −1 to 6%. Comparisons to contemporaneous, daily-average satellite derived values show relatively good agreement as well, with relative biases of the order of 2% (∼3–9 W m−2) and root-mean-square differences of ∼10% (25–30 W m−2). Aspects of the role aerosols play in the above results are discussed along with the implications of the above results on the integrity of open-ocean buoy measurements of surface shortwave flux and the possibility of using the techniques developed in this study to remotely monitor the operating condition of buoy-based shortwave radiometers. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3394 Meteorology and Atmospheric Dynamics: Instruments and techniques; 0394 Instruments and techniques; 3339 Meteorology and Atmospheric Dynamics: Ocean/atmosphere interactions; 4572 Upper ocean and mixed layer processes; 9310 Information Related to Geographic Region: Antarctica
Wilber, Anne C.; Kratz, David P.; Gupta, Shashi K.Wilber, A. C., D. P. Kratz, S. K. Gupta, 1999: Surface Emissivity Maps for Use in Satellite Retrievals of Longwave Radiation. Accurate accounting of surface emissivity is essential for the retrievals of surface temperature from remote sensing measurements, and for the computations of longwave radiation budget of the Earth?s surface. Past studies of the above topics assumed that emissivity for all surface types, and across the entire LW spectrum is equal to unity. There is strong evidence, however, that emissivity of many surface materials is significantly lower than unity, and varies considerably across the LW spectrum. We have developed global maps of surface emissivity for the broadband LW region, the thermal infrared window region , and 12 narrow LW spectral bands. The 17 surface types defined by the International Geosphere Biosphere Programme were adopted as such, and an additional surface type was introduced to represent tundra-like surfaces. Laboratory measurements of spectral reflectances of 10 different surface materials were converted to corresponding emissivities. The 10 surface materials were then associated with 18 surface types. Emissivities for the 18 surface types were first computed for each of the 12 narrow spectral bands. Emissivities for the broadband and the window region were then constituted from the spectral band values by weighting them with Planck function energy distribution. energy budgets; atmospheric radiation; Biosphere; broadband; computation; emissivity; infrared windows; lithosphere; long wave radiation; spectral bands; spectral reflectance; surface properties; surface temperature; temperature sensors; tundra
Yang, Shi-Keng; Hou, Yu-Tai; Miller, Alvin J.; Campana, Kenneth A.Yang, S., Y. Hou, A. J. Miller, K. A. Campana, 1999: Evaluation of the Earth Radiation Budget in NCEP–NCAR Reanalysis with ERBE. J. Climate, 12(2), 477-493. doi: 10.1175/1520-0442(1999)012<0477:EOTERB>2.0.CO;2. Abstract This study presents an evaluation of the NCEP–NCAR Reanalysis (the reanalysis) by comparing its components of the earth radiation budget to satellite data. Monthly mean clear sky (CS) and total sky of outgoing longwave radiation (OLR), as well as reflected solar radiation (RSW) for 1985 and 1986, are compared to the top-of-the-atmosphere (TOA) measurements from the Earth Radiation Budget Experiment (ERBE). The ERBE-derived data of Staylor and Wilbur are also utilized to validate surface albedo. There are two objectives to this study: (i) to document the general quality of the reanalysis radiation budget, and (ii) to identify some of the general problem areas in the reanalysis global data assimilation system (GDAS). The OLR comparisons show that the global annual mean from the reanalysis is approximately 1.5% higher than that of ERBE. The zonal-average differences are strongly seasonal, which is particularly evident at high latitudes for the CS OLR, and at most latitudes for total-sky OLR. For the geographical distribution, the synoptic patterns from the reanalysis are in good agreement with the observations. Yet many regions in the Tropics and subtropics pose significant systematic biases. Possible causes are from shortcomings in the the cloud/moisture parameterizations of the reanalysis GDAS. The complex topography unresolvable by the T62 model could also be the cause for the biases in tall mountain regions. The global RSW comparisons show that the CS data from the reanalysis is in very good agreement with ERBE, while the total-sky RSW data overestimate ERBE by 12.6 W m−2 (∼10%) globally. Persistent overestimates of RSW throughout the period indicate that the global energy budget for the reanalysis is not balanced. This result also is consistent with the finding in OLR suggesting that the reanalysis GDAS contains shortcomings in the cloud/moisture parameterizations. Another possibility for the difference in RSW is deficiencies in the GDAS shortwave parameterizations. Over the Sahara Desert, the reanalysis underestimates RSW, and overestimates OLR, both in the clear-sky and total-sky conditions. Comparison with the Staylor and Wilber ERBE-derived surface albedo suggests that GDAS surface albedo in this region should be increased by up to 0.1 (in albedo units). A comparison with the interannual variations of the satellite data for the boreal summer illustrates that the radiation budget data of the reanalysis contains a realistic climate signal.
Boucher, O.; Schwartz, S. E.; Ackerman, T. P.; Anderson, T. L.; Bergstrom, B.; Bonnel, B.; Chýlek, P.; Dahlback, A.; Fouquart, Y.; Fu, Q.; Halthore, R. N.; Haywood, J. M.; Iversen, T.; Kato, S.; Kinne, S.; Kirkevåg, A.; Knapp, K. R.; Lacis, A.; Laszlo, I.; Mishchenko, M. I.; Nemesure, S.; Ramaswamy, V.; Roberts, D. L.; Russell, P.; Schlesinger, M. E.; Stephens, G. L.; Wagener, R.; Wang, M.; Wong, J.; Yang, F.Boucher, O., S. E. Schwartz, T. P. Ackerman, T. L. Anderson, B. Bergstrom, B. Bonnel, P. Chýlek, A. Dahlback, Y. Fouquart, Q. Fu, R. N. Halthore, J. M. Haywood, T. Iversen, S. Kato, S. Kinne, A. Kirkevåg, K. R. Knapp, A. Lacis, I. Laszlo, M. I. Mishchenko, S. Nemesure, V. Ramaswamy, D. L. Roberts, P. Russell, M. E. Schlesinger, G. L. Stephens, R. Wagener, M. Wang, J. Wong, F. Yang, 1998: Intercomparison of models representing direct shortwave radiative forcing by sulfate aerosols. Journal of Geophysical Research: Atmospheres, 103(D14), 16979-16998. doi: 10.1029/98JD00997. The importance of aerosols as agents of climate change has recently been highlighted. However, the magnitude of aerosol forcing by scattering of shortwave radiation (direct forcing) is still very uncertain even for the relatively well characterized sulfate aerosol. A potential source of uncertainty is in the model representation of aerosol optical properties and aerosol influences on radiative transfer in the atmosphere. Although radiative transfer methods and codes have been compared in the past, these comparisons have not focused on aerosol forcing (change in net radiative flux at the top of the atmosphere). Here we report results of a project involving 12 groups using 15 models to examine radiative forcing by sulfate aerosol for a wide range of values of particle radius, aerosol optical depth, surface albedo, and solar zenith angle. Among the models that were employed were high and low spectral resolution models incorporating a variety of radiative transfer approximations as well as a line-by-line model. The normalized forcings (forcing per sulfate column burden) obtained with the several radiative transfer models were examined, and the discrepancies were characterized. All models simulate forcings of comparable amplitude and exhibit a similar dependence on input parameters. As expected for a non-light-absorbing aerosol, forcings were negative (cooling influence) except at high surface albedo combined with small solar zenith angle. The relative standard deviation of the zenith-angle-averaged normalized broadband forcing for 15 models was 8% for particle radius near the maximum in this forcing (∼0.2 μm) and at low surface albedo. Somewhat greater model-to-model discrepancies were exhibited at specific solar zenith angles. Still greater discrepancies were exhibited at small particle radii, and much greater discrepancies were exhibited at high surface albedos, at which the forcing changes sign; in these situations, however, the normalized forcing is quite small. Discrepancies among the models arise from inaccuracies in Mie calculations, differing treatment of the angular scattering phase function, differing wavelength and angular resolution, and differing treatment of multiple scattering. These results imply the need for standardized radiative transfer methods tailored to the direct aerosol forcing problem. However, the relatively small spread in these results suggests that the uncertainty in forcing arising from the treatment of radiative forcing of a well-characterized aerosol at well-specified surface albedo is smaller than some of the other sources of uncertainty in estimates of direct forcing by anthropogenic sulfate aerosols and anthropogenic aerosols generally. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 0360 Radiation: transmission and scattering; 1610 Atmosphere; 0305 Aerosols and particles
Capderou, MichelCapderou, M., 1998: Confirmation of Helmholtz Reciprocity Using ScaRaB Satellite Data. Remote Sensing of Environment, 64(3), 266-285. doi: 10.1016/S0034-4257(98)00004-2. The Helmholtz reciprocity principle is often invoked to derive the bidirectional reflectance distribution functions, then the anisotropic function, used for converting satellite radiance measurements into fluxes in Earth radiation budget studies. However, it has seldom been checked by satellite observation. This is only possible using satellites in low but non-Sun-synchronous Earth orbit, and even in this case situations allowing reciprocity verification are rare. The ScaRaB (Scanner for Radiation Budget) radiometer on board Meteor-3-07 provided non-Sun-synchronous observations of the Earth from March 1994 to February 1995. Considering only clear-sky desert scenes which may be presumed to be unchanging, enough viewing/illumination geometry pairs to check the reciprocity principle, using reflectances averaged over a small (1.25°×1.25°) study areas can be obtained. We define a normalized reciprocity departure, which is zero when reciprocity is perfectly respected. The distribution of this parameter shows that the reciprocity principle is verified to better than 5% in 75% of the cases (and 1% in a third of the cases). We also define a parameter analogous to the normalized reciprocity departure, measuring anisotrophy of reflectance for arbitrary viewing/illumination geometry pairs, which would be zero for Lambertian reflection. Comparing the distributions of these parameters with the normalized reciprocity departure, we show that the reciprocal viewing/illumination geometry pairs are very distinct from the arbitrary pairs. This confirmation of the Helmholtz reciprocity principle reinforces our confidence in using it to construct anisotropic reflectance function from measurements for which not all viewing or illumination geometries are sampled.
Christopher, Sundar A.; Wang, Min; Berendes, Todd A.; Welch, Ronald M.; Yang, Shi-KengChristopher, S. A., M. Wang, T. A. Berendes, R. M. Welch, S. Yang, 1998: The 1985 Biomass Burning Season in South America: Satellite Remote Sensing of Fires, Smoke, and Regional Radiative Energy Budgets. Journal of Applied Meteorology, 37(7), 661-678. doi: 10.1175/1520-0450(1998)037<0661:TBBSIS>2.0.CO;2. Abstract Using satellite imagery, more than five million square kilometers of the forest and cerrado regions over South America are extensively studied to monitor fires and smoke during the 1985 biomass burning season. The results are characterized for four major ecosystems, namely, 1) tropical rain forest, 2) tropical broadleaf seasonal, 3) savanna/grass and seasonal woods (SGW), and 4) mild/warm/hot grass/shrub (MGS). The spatial and temporal distribution of fires are examined from two different methods using the multispectral Advanced Very High Resolution Radiometer Local Area Coverage data. Using collocated measurements from the instantaneous scanner Earth Radiation Budget Experiment data, the direct regional radiative forcing of biomass burning aerosols is computed. The results show that more than 70% of the fires occur in the MGS and SGW ecosystems due to agricultural practices. The smoke generated from biomass burning has negative instantaneous net radiative forcing values for all four major ecosystems within South America. The smoke found directly over the fires has mean net radiative forcing values ranging from −25.6 to −33.9 W m−2. These results confirm that the regional net radiative impact of biomass burning is one of cooling. The spectral and broadband properties for clear-sky and smoke regions are also presented that could be used as input and/or validation for other studies attempting to model the impact of aerosols on the earth–atmosphere system. These results have important applications for future instruments from the Earth Observing System (EOS) program. Specifically, the combination of the Visible Infrared Scanner and Clouds and the Earth’s Radiant Energy System (CERES) instruments from the Tropical Rainfall Measuring Mission and the combination of Moderate Resolution Imaging Spectrometer and CERES instruments from the EOS morning crossing mission could provide reliable estimates of the direct radiative forcing of aerosols on a global scale, thereby reducing the uncertainties in current global aerosol radiative forcing values.
Di Girolamo, Larry; Várnai, Tamás; Davies, RogerDi Girolamo, L., T. Várnai, R. Davies, 1998: Apparent breakdown of reciprocity in reflected solar radiances. Journal of Geophysical Research: Atmospheres, 103(D8), 8795-8803. doi: 10.1029/98JD00345. Observations of reflected solar radiation measurements from natural surfaces (e.g., clouds and forested biomes) are often noted as disobeying the principle of reciprocity. In these contexts the application of reciprocity has been in its directional form. We note that the general principle of reciprocity also encompasses spatial attributes and reduces to a directional form only when the areas of illumination and measurement are the same. In either form a proper reciprocal set of reflected solar radiation measurements can never be obtained due to our inability to control the area illuminated by the Sun. This may appear as a breakdown in the directional reciprocity of the observations, which has serious implications for remote sensing. Using Monte Carlo radiative transfer simulations, we demonstrate that the magnitude of the apparent reciprocity breakdown depends on three factors: (1) measurement resolution, with larger deviations occurring for higher resolutions; (2) Sun-view geometry, with larger deviations occurring for larger Sun/view zenith angles and differences between Sun and view angles; and (3) the distribution of scatterers within and surrounding the measurement area, making the deviations depend on scene type. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1640 Remote sensing; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 9820 Techniques applicable in three or more fields
Inamdar, Anand K.; Ramanathan, V.Inamdar, A. K., V. Ramanathan, 1998: Tropical and global scale interactions among water vapor, atmospheric greenhouse effect, and surface temperature. Journal of Geophysical Research: Atmospheres, 103(D24), 32177-32194. doi: 10.1029/1998JD900007. We employ a multitude of global data sets to extend recent analyses of atmospheric greenhouse effect and its dependence on surface temperature (Ts) and vertical water vapor distribution. The new data encompasses a global domain including both the continents and the oceans as well as both the ascending and descending branches of the Walker and Hadley cells and the extratropical storm track regions. We adopt the radiometric definition of the atmospheric greenhouse effect, Ga, which is the difference between the surface longwave emission and the outgoing longwave radiation. We derive the global average greenhouse effect over both oceans and land areas. The east to west variations of the normalized atmospheric greenhouse effect (ga) and precipitable water (w) are just as strong as the north to south variations, thus illustrating the strong role of the dynamics in w and ga. Between 60°N and 60°S the lowest values of ga (0.11–0.15) are found over the Saharan and other deserts; while the largest values (0.35–0.40) are found over the warm oceans with a deep convective atmosphere. The coupling between Ga, and the vertical distribution of atmospheric water vapor and temperature, is examined from monthly mean annual cycle. When averaged from the southern to the northern latitudes, these quantities exhibit a statistically significant annual cycle. The annual cycle of Ts, about 1 K for the tropics (30°N to 30°S) and about 4 K for the globe, is large enough to obtain a statistically significant estimate for the sensitivity parameter dGa/dTs. It is as large as 5.5–6 W m−2 K−1 for tropical mean conditions (30°N to 30°S) and reduces to a global mean value of 3.5 W m−2 K−1 (with a 2σ range of 2.9–4.1 W m−2 K−1). Consistent with earlier studies, the tropics exhibit a strong positive coupling between Ts, Ga, and water vapor distribution with large increases in the midtroposphere humidity. However, poleward of 30°N, water vapor increases are about half as much as that in the tropics, and the sensitivity parameter dGa/dTs decreases. This is because poleward of 30°, the annual cycle is dominated by land surface temperature changes which are not so effective as sea surface temperature changes in enhancing the water vapor greenhouse effect. Irrespective of the region (ocean or land) or the latitude domain (tropics or extratropics), the data presented here do not offer any support for the suggestion that increases in tropical or global mean surface temperature would lead to a decrease in water vapor greenhouse effect by drying the middle to upper troposphere. If any, the global scale sensitivity derived from the annual cycle is consistent with the magnitude of the positive feedback obtained by general circulation models. 1610 Atmosphere; 1640 Remote sensing; 1620 Climate dynamics; 1655 Water cycles
Kandel, R.; Viollier, M.; Raberanto, P.; Duvel, J. Ph; Pakhomov, L. A.; Golovko, V. A.; Trishchenko, A. P.; Mueller, J.; Raschke, E.; Stuhlmann, R. R.; Scientific Working Group (ISSWG), International Sca Ra B.Kandel, R., M. Viollier, P. Raberanto, J. P. Duvel, L. A. Pakhomov, V. A. Golovko, A. P. Trishchenko, J. Mueller, E. Raschke, R. R. Stuhlmann, I. S. R. B. Scientific Working Group (ISSWG), 1998: The ScaRaB Earth Radiation Budget Dataset. Bull. Amer. Meteor. Soc., 79(5), 765-783. doi: 10.1175/1520-0477(1998)079<0765:TSERBD>2.0.CO;2. Abstract Following an overview of the scientific objectives and organization of the French–Russian–German Scanner for Radiation Budget (ScaRaB) project, brief descriptions of the instrument, its ground calibration, and in-flight operating and calibration procedures are given. During the year (24 February 1994–6 March 1995) of ScaRaB Flight Model 1 operation on board Meteor-3/7, radiometer performance was generally good and well understood. Accuracy of the radiances is estimated to be better than 1% in the longwave and 2% in the shortwave domains. Data processing procedures are described and shown to be compatible with those used for the National Aeronautics and Space Administration's (NASA) Earth Radiation Budget Experiment (ERBE) scanner data, even though time sampling properties of the Meteor-3 orbit differ considerably from the ERBE system orbits. The resulting monthly mean earth radiation budget distributions exhibit no global bias when compared to ERBE results, but they do reveal interesting strong regional differences. The “ERBE-like” scientific data products are now available to the general scientific research community. Prospects for combining data from ScaRaB Flight Model 2 (to fly on board Ressurs-1 beginning in spring 1998) with data from the NASA Clouds and the Earth's Radiant Energy System (CERES) instrument on board the Tropical Rainfall Measurement Mission (TRMM) are briefly discussed.
Kaufman, Y.J.; Herring, D.D.; Ranson, K.J.; Collatz, G.J.Kaufman, Y., D. Herring, K. Ranson, G. Collatz, 1998: Earth Observing System AM1 mission to Earth. IEEE Transactions on Geoscience and Remote Sensing, 36(4), 1045-1055. doi: 10.1109/36.700989. In 1998, NASA launches EOS-AMI, the first of a series of the Earth Observing System (EOS) satellites. EOS will monitor the evolution of the state of the earth for 18 years, starting with the morning observations of EOS-AM1 (10:30 a.m. equatorial crossing time). An integrated view of the earth, as planned by EOS, is needed to study the interchange of energy, moisture, and carbon between the lands, oceans, and atmosphere. The launch of EOS-AM1 and other international satellites marks a new phase of climate and global change research. Both natural and anthropogenic climate change have been studied for more than a century. It is now recognized that processes that vary rapidly in time and space-e.g. aerosol, clouds, land use, and exchanges of energy and moisture-must be considered to adequately explain the temperature record and predict future climate change. Frequent measurements with adequate resolution, as only possible from spacecraft, are key tools in such an effort. The versatile and highly accurate EOS-AM1 data, together with previous satellite records, as well as data from ADEOS, TRMM, SeaWiFS, ATSR, MERIS, ENVISAT, EOS-PM1, Landsat and ground-based networks is expected to revolutionize the way scientists look at climate change. This article introduces the EOS-AM1 mission and the special issue devoted to it. Following a brief historical perspective for an insight into the purpose and objectives of the mission, the authors summarize the characteristics of the five instruments onboard EOS-AM1. Specifically, they concentrate on the innovative elements of these five instruments and provide examples of the science issues that require this type of data atmosphere; clouds; Land surface; Remote sensing; Satellites; surface temperature; aerosols; atmospheric techniques; cloud; Earth Observing System; Instruments; measurement technique; Meteorology; satellite remote sensing; chemical composition; climate change; Moisture; Monitoring; NASA; Oceans; optical method; visible spectra
Kummerow, Christian; Barnes, William; Kozu, Toshiaki; Shiue, James; Simpson, JoanneKummerow, C., W. Barnes, T. Kozu, J. Shiue, J. Simpson, 1998: The Tropical Rainfall Measuring Mission (TRMM) Sensor Package. J. Atmos. Oceanic Technol., 15(3), 809-817. doi: 10.1175/1520-0426(1998)015<0809:TTRMMT>2.0.CO;2. Abstract This note is intended to serve primarily as a reference guide to users wishing to make use of the Tropical Rainfall Measuring Mission data. It covers each of the three primary rainfall instruments: the passive microwave radiometer, the precipitation radar, and the Visible and Infrared Radiometer System on board the spacecraft. Radiometric characteristics, scanning geometry, calibration procedures, and data products are described for each of these three sensors.
Lee, R.B.; Barkstrom, B.R.; Bitting, H.C.; Crommelynck, D.A.H.; Paden, J.; Pandey, D.K.; Priestley, K.J.; Smith, G.L.; Thomas, S.; Thornhill, K.L.; Wilson, R.S.Lee, R., B. Barkstrom, H. Bitting, D. Crommelynck, J. Paden, D. Pandey, K. Priestley, G. Smith, S. Thomas, K. Thornhill, R. Wilson, 1998: Prelaunch calibrations of the Clouds and the Earth's Radiant Energy System (CERES) Tropical Rainfall Measuring Mission and Earth Observing System morning (EOS-AM1) spacecraft thermistor bolometer sensors. IEEE Transactions on Geoscience and Remote Sensing, 36(4), 1173-1185. doi: 10.1109/36.701024. The Clouds and the Earth's Radiant Energy System (CERES) spacecraft scanning thermistor bolometer sensors measure Earth radiances in the broadband shortwave solar (0.3-5.0 μm) and total (0.3->100 μm) spectral bands as well as in the 8-12-μm water vapor window spectral band. On November 27, 1997, the launch of the Tropical Rainfall Measuring Mission (TRMM) spacecraft placed the first set of CERES sensors into orbit, and 30 days later, the sensors initiated operational measurements of the Earth radiance fields. In 1998, the Earth Observing System morning (EOS-AM1) spacecraft will place the second and third sensor sets into orbit. The prelaunch CERES sensors' count conversion coefficients (gains and zero-radiance offsets) were determined in vacuum ground facilities. The gains were tied radiometrically to the International Temperature Scale of 1990 (ITS-90). The gain determinations included the spectral properties (reflectance, transmittance, emittance, etc.) of both the sources and sensors as well as the in-field-of-view (FOV) and out-of-FOV sensor responses. The resulting prelaunch coefficients for the TRMM and EOS-AM1 sensors are presented. Inflight calibration systems and on-orbit calibration approaches are described, which are being used to determine the temporal stabilities of the sensors' gains and offsets from prelaunch calibrations through on-orbit measurements. Analyses of the TRMM prelaunch and on-orbit calibration results indicate that the sensors have retained their ties to ITS-90 at accuracy levels better than ±0.3% between the 1995 prelaunch and 1997 on-orbit calibrations atmosphere; calibration; clouds; Earth; Extraterrestrial measurements; infrared imaging; Remote sensing; atmospheric techniques; CERES; Clouds and the Earth's Radiant Energy System; measurement technique; Meteorology; radiometers; satellite remote sensing; Space vehicles; 0.3 to 100 mum; atmospheric measuring apparatus; Bolometers; Earth Observing System morning spacecraft; Energy measurement; EOS-AM1; IR radiometry; meteorological instruments; prelaunch calibration; radiometry; rain; rainfall; Sensor systems; Thermal sensors; thermistor bolometer sensor; Thermistors; TRMM; Tropical Rainfall Measuring Mission; visible region
Mace, Gerald G.; Ackerman, Thomas P.; Minnis, Patrick; Young, David F.Mace, G. G., T. P. Ackerman, P. Minnis, D. F. Young, 1998: Cirrus layer microphysical properties derived from surface-based millimeter radar and infrared interferometer data. Journal of Geophysical Research: Atmospheres, 103(D18), 23207-23216. doi: 10.1029/98JD02117. Observational data regarding the properties of cirrus clouds are needed to aid in the development of accurate, physically based parameterizations in climate models. The Atmospheric Radiation Measurement (ARM) program, sponsored by the U.S. Department of Energy, is providing continuous observations of cirrus clouds with a suite of instrumentation at several locales. In this paper, we describe an algorithm to derive the microphysical properties of optically thin cirrus clouds. This algorithm uses radar reflectivity and infrared emission spectra from an interferometer and is tailored for the specific instruments at the ARM sites. We present in situ validation of the technique and examine a cirrus case study to illustrate the sensitivity of the algorithm. In the case study, solar fluxes calculated from the retrieved microphysical parameters are compared to observed fluxes to build confidence in the algorithm results. Comparison of the retrieved quantities to microphysical parameters retrieved from satellite data is also presented. 1640 Remote sensing; 0320 Cloud physics and chemistry; 1694 Instruments and techniques
Manalo-Smith, N.; Smith, G. L.; Tiwari, S. N.; Staylor, W. F.Manalo-Smith, N., G. L. Smith, S. N. Tiwari, W. F. Staylor, 1998: Analytic forms of bidirectional reflectance functions for application to Earth radiation budget studies. Journal of Geophysical Research: Atmospheres, 103(D16), 19733-19751. doi: 10.1029/98JD00279. Analytic expressions for the bidirectional reflectance functions are formulated and fit to the Earth Radiation Budget Experiment (ERBE) operational models, which were developed using Nimbus 7 ERB data. The analytic bidirectional reflectance distribution functions (BRDFs) are based on theoretical considerations and are functions of viewing geometry and scene type. The models consist of a Rayleigh scattering term and a term for scattering due to clouds and surface. The darkness of the ocean permits the empirical determination of the Rayleigh component of scattering from the atmosphere. The models have the advantage that they are smooth in terms of view and solar zenith angles and relative solar azimuth angle and satisfy reciprocity. Results are presented for the ERBE scene types. The analytic functions closely model the reflectances in the forward scatter direction, but in the backscatter direction, the analytic models are slightly more limb brightened than the ERBE operational models. The model was also fit to the Dlhopolsky/Cess BRDF for clear ocean, which provides a finer angular resolution than the ERBE BRDFs. The results of this study provide a set of BRDFs for ERBE scene types in terms of a set of simple equations and few coefficients for each scene type. These models can be used for mission planning and interpretation of data from future Earth radiation budget missions such as the Clouds and Earth's Radiant Energy System (CERES). 0399 General or miscellaneous; 3399 Meteorology and Atmospheric Dynamics: General or miscellaneous
Mather, J. H.; Ackerman, T. P.; Clements, W. E.; Barnes, F. J.; Ivey, M. D.; Hatfield, L. D.; Reynolds, R. M.Mather, J. H., T. P. Ackerman, W. E. Clements, F. J. Barnes, M. D. Ivey, L. D. Hatfield, R. M. Reynolds, 1998: An Atmospheric Radiation and Cloud Station in the Tropical Western Pacific. Bull. Amer. Meteor. Soc., 79(4), 627-642. doi: 10.1175/1520-0477(1998)079<0627:AARACS>2.0.CO;2. Abstract The interaction of clouds and radiation is a particularly difficult issue in the study of climate change. Clouds have a large impact on the earth's radiation budget but the range of spatial and temporal scales and the complexity of the physical processes associated with clouds made these interactions difficult to simulate. The Department of Energy's Atmospheric Radiation Measurement (ARM) program was established to improve the understanding of the interaction of radiation with the atmosphere with a particular emphasis on the effects of clouds. To continue its role of providing data for the study of these interactions, the ARM program deployed an Atmospheric Radiation and Cloud Station (ARCS) in the tropical western Pacific. This site began operation in October 1996. The tropical western Pacific is a very important climatic region. It is characterized by strong solar heating, high water vapor concentrations, and active convection. The ARCS is equipped with a comprehensive suite of instruments for measuring surface radiation fluxes and properties of the atmospheric state and is intended to operate for the next 10 years. The ARCS is an integrated unit that includes a data management system, a site monitor and control system, an external communications system, redundant electrical power systems, and containers that provide shelter for the equipment as well as work space for site operators, technicians, and visiting scientists. The dataset the ARCS produces will be invaluable in studying issues related to clouds and radiation in the Tropics. The site is located in Manus Province, Papua New Guinea, at 2.060°S, 147.425°E, 300 km north of the island of New Guinea. Two more ARCS are planned for deployment across the tropical Pacific.
Minnis, Patrick; Garber, Donald P.; Young, David F.; Arduini, Robert F.; Takano, YoshihideMinnis, P., D. P. Garber, D. F. Young, R. F. Arduini, Y. Takano, 1998: Parameterizations of Reflectance and Effective Emittance for Satellite Remote Sensing of Cloud Properties. J. Atmos. Sci., 55(22), 3313-3339. doi: 10.1175/1520-0469(1998)055<3313:PORAEE>2.0.CO;2. Abstract The interpretation of satellite-observed radiances to derive cloud optical depth and effective particle size requires radiative transfer calculations relating these parameters to the reflectance, transmittance, and emittance of the cloud. Such computations can be extremely time consuming when used in an operational mode to analyze routine satellite data. Adding–doubling (AD) radiative transfer models are used here to compute reflectance and effective emittance at wavelengths commonly used by operational meteorological satellite imagers for droplet effective radii ranging from 2 to 32 μm and for distributions of randomly oriented hexagonal ice crystals with effective diameters varying from 6 to 135 μm. Cloud reflectance lookup tables were generated at the typical visible-channel wavelength of 0.65 μm and the solar–infrared (SI) at wavelengths of 3.75 and 3.90 μm. A combination of four-point Lagrangian and linear interpolation between the model nodal points is the most accurate and economical method for estimating reflectance as a function of particle size for any set of solar zenith, viewing zenith, and relative azimuth angles. Compared to exact AD calculations, the four-point method retrieves the reflectance to within ±3%–9% for water droplets and ice crystals, respectively. Most of the error is confined to scattering angles near distinct features in the phase functions. The errors are reduced to ∼±2% for ice when the assessment is constrained to only those angles that are actually useful in satellite retrievals. Effective emittance, which includes absorption and scattering effects, was computed at SI, infrared (IR; 10.7 and 10.8 μm), and split-window (WS; 11.9 and 12.0 μm) wavelengths for a wide range of surface and cloud temperatures using the same ice crystal and water droplet distributions. The results were parameterized with a 32-term polynomial model that depends on the clear-cloud radiating temperature difference, the clear-sky temperature, and viewing zenith angle. A four-point Lagrangian method is used to interpolate between optical depth nodes. The model reproduces the adding–doubling results with an overall accuracy better than ±2%, 0.4%, and 0.3%, respectively, for the SI, IR, and WS emittances, a substantial reduction in the error compared to earlier parameterizations. Temperatures simulated with the emittance models are within 0.6 and 1 K for water droplets and ice crystals, respectively, in the SI channels. The IR temperatures are accurate to better than ±0.05 K. During the daytime, the simulations of combined reflectance and emittance for the SI channels are as accurate as the emittance models alone except at particular scattering angles. The magnitudes of the errors depend on the angle, particle size, and solar zenith angle. Examples are given showing the parameterizations applied to satellite data. Computational time exceeds that of previous models but the accuracy gain should yield emittances that are more reliable for retrieval of global cloud microphysical properties.
Moran, Kenneth P.; Martner, Brooks E.; Post, M. J.; Kropfli, Robert A.; Welsh, David C.; Widener, Kevin B.Moran, K. P., B. E. Martner, M. J. Post, R. A. Kropfli, D. C. Welsh, K. B. Widener, 1998: An Unattended Cloud-Profiling Radar for Use in Climate Research. Bull. Amer. Meteor. Soc., 79(3), 443-455. doi: 10.1175/1520-0477(1998)079<0443:AUCPRF>2.0.CO;2. Abstract A new millimeter-wave cloud radar (MMCR) has been designed to provide detailed, long-term observations of nonprecipitating and weakly precipitating clouds at Cloud and Radiation Testbed (CART) sites of the Department of Energy's Atmospheric Radiation Measurement (ARM) program. Scientific requirements included excellent sensitivity and vertical resolution to detect weak and thin multiple layers of ice and liquid water clouds over the sites and long-term, unattended operations in remote locales. In response to these requirements, the innovative radar design features a vertically pointing, single-polarization, Doppler system operating at 35 GHz (Ka band). It uses a low-peak-power transmitter for long-term reliability and high-gain antenna and pulse-compressed waveforms to maximize sensitivity and resolution. The radar uses the same kind of signal processor as that used in commercial wind profilers. The first MMCR began operations at the CART in northern Oklahoma in late 1996 and has operated continuously there for thousands of hours. It routinely provides remarkably detailed images of the ever-changing cloud structure and kinematics over this densely instrumented site. Examples of the data are presented. The radar measurements will greatly improve quantitative documentation of cloud conditions over the CART sites and will bolster ARM research to understand how clouds impact climate through their effects on radiative transfer. Millimeter-wave radars such as the MMCR also have potential applications in the fields of aviation weather, weather modification, and basic cloud physics research.
Ohmura, Atsumu; Gilgen, Hans; Hegner, Herman; Müller, Guido; Wild, Martin; Dutton, Ellsworth G.; Forgan, Bruce; Fröhlich, Claus; Philipona, Rolf; Heimo, Alain; König-Langlo, Gert; McArthur, Bruce; Pinker, Rachel; Whitlock, Charlie H.; Dehne, KlausOhmura, A., H. Gilgen, H. Hegner, G. Müller, M. Wild, E. G. Dutton, B. Forgan, C. Fröhlich, R. Philipona, A. Heimo, G. König-Langlo, B. McArthur, R. Pinker, C. H. Whitlock, K. Dehne, 1998: Baseline Surface Radiation Network (BSRN/WCRP): New Precision Radiometry for Climate Research. Bull. Amer. Meteor. Soc., 79(10), 2115-2136. doi: 10.1175/1520-0477(1998)079<2115:BSRNBW>2.0.CO;2. Abstract To support climate research, the World Climate Research Programme (WCRP) initiated a new radiometric network, the Baseline Surface Radiation Network (BSRN). The network aims at providing validation material for satellite radiometry and climate models. It further aims at detecting long-term variations in irradiances at the earth's surface, which are believed to play an important role in climate change. The network and its instrumentation are designed 1) to cover major climate zones, 2) to provide the accuracy required to meet the objectives, and 3) to ensure homogenized standards for a long period in the future. The limits of the accuracy are defined to reach these goals. The suitable instruments and instrumentations have been determined and the methods for observations and data management have been agreed on at all stations. Measurements of irradiances are at 1 Hz, and the 1-min statistics (mean, standard deviation, and extreme values) with quality flags are stored at a centralized data archive at the WCRP's World Radiation Monitoring Center (WRMC) in Zurich, Switzerland. The data are quality controlled both at stations and at the WRMC. The original 1-min irradiance statistics will be stored at the WRMC for 10 years, while hourly mean values will be transferred to the World Radiation Data Center in St. Petersburg, Russia. The BSRN, consisting of 15 stations, covers the earth's surface from 80°N to 90°S, and will soon be joined by seven more stations. The data are available to scientific communities in various ways depending on the communication environment of the users. The present article discusses the scientific base, organizational and technical aspects of the network, and data retrieval methods; shows various application possibilities; and presents the future tasks to be accomplished.
Rice, J. P.; Johnson, B. C.Rice, J. P., B. C. Johnson, 1998: The NIST EOS thermal-infrared transfer radiometer. Metrologia, 35(4), 505. doi: 10.1088/0026-1394/35/4/51. A portable thermal-infrared transfer radiometer (TXR) has been developed for use in comparisons and scale verifications of sources used to calibrate thermal-infrared (TIR) channels of the National Aeronautics and Space Administration's (NASA's) Earth Observing System (EOS) flight instruments. The TXR is designed to measure the radiance temperature of large-area black-body sources in cryogenic vacuum environments, either at the National Institute of Standards and Technology (NIST) or at the EOS instrument-calibration facilities. It can be operated in ambient conditions of room temperature and pressure, or in EOS instrument thermal/vacuum chambers at temperatures as low as 77 K. The TXR is a liquid-nitrogen-cooled filter radiometer with two channels: one centred at 5 µm based on a photovoltaic InSb detector, and the other centred at 10 µm based on a photovoltaic HgCdTe (MCT) detector. The spectral, spatial and temporal characterization of the TXR using state-of-the-art NIST ambient-infrared instrumentation is reported.
Trishchenko, Alexander; Li, ZhanqingTrishchenko, A., Z. Li, 1998: Use of ScaRaB Measurements for Validating a GOES-Based TOA Radiation Product. Journal of Applied Meteorology, 37(6), 591-605. doi: 10.1175/1520-0450(1998)037<0591:UOSMFV>2.0.CO;2. Abstract Lack of calibrated radiation measurements at the top of the atmosphere (TOA) between major spaceborne radiation missions entails inference of the TOA radiation budget from operational weather sensors. The inferred data are subject to uncertainties due to calibration, narrow- to broadband conversion, etc. In this study, a surrogate TOA earth radiation budget product generated from GOES-7 (Geostationary Operational Environmental Satellite) imagery data for use in the U.S. Atmospheric Radiation Measurement (ARM) program was validated using measurements from the ScaRaB radiometer flown on board the METEOR-3/7 satellite. Comparisons were made between coincident and collocated shortwave and longwave radiative quantities derived from GOES and ScaRaB sensors over an ARM experimental locale in the South Great Plains of Oklahoma, during April and July 1994. The comparisons are proven to be instrumental in validating the calibration and narrow- to broadband conversion used to obtain broadband radiative quantities from GOES digital counts. Calibrations for both visible and infrared window channels have small uncertainties, whereas narrow- to broadband conversion of shortwave measurements contains large systematic errors. The caveat stems from use of a quadratic conversion equation instead of a linear one, as was found from ScaRaB narrow- and broadband measurements. The ensuing errors in the estimates of broadband albedo depend on scene brightness, underestimation for bright scenes, and overestimation for dark scenes. As a result, the magnitude of the TOA cloud radiative forcing is underestimated by about 14 W m−2 or 7.5% on a daytime mean basis. After correcting this error, the ratio of cloud radiative forcing (a measure of the impact of clouds on atmospheric absorption) derived from ARM measurements turns out to be 1.07, which is in even closer agreement with radiative transfer models than found from previous studies using original GOES products.
Wielicki, B.A.; Barkstrom, B.R.; Baum, B.A.; Charlock, T.P.; Green, R.N.; Kratz, D.P.; Lee, R.B.; Minnis, P.; Smith, G.L.; Wong, Takmeng; Young, D.F.; Cess, R.D.; Coakley, J.A.; Crommelynck, D.A.H.; Donner, L.; Kandel, R.; King, M.D.; Miller, A.J.; Ramanathan, V.; Randall, D.A.; Stowe, L.L.; Welch, R.M.Wielicki, B., B. Barkstrom, B. Baum, T. Charlock, R. Green, D. Kratz, R. Lee, P. Minnis, G. Smith, T. Wong, D. Young, R. Cess, J. Coakley, D. Crommelynck, L. Donner, R. Kandel, M. King, A. Miller, V. Ramanathan, D. Randall, L. Stowe, R. Welch, 1998: Clouds and the Earth's Radiant Energy System (CERES): algorithm overview. IEEE Transactions on Geoscience and Remote Sensing, 36(4), 1127-1141. doi: 10.1109/36.701020. The Clouds and the Earth's Radiant Energy System (CERES) is part of NASA's Earth Observing System (EOS), CERES objectives include the following. (1) For climate change analysis, provide a continuation of the Earth Radiation Budget Experiment (ERBE) record of radiative fluxes at the top-of-the-atmosphere (TOA), analyzed using the same techniques as the existing ERBE data. (2) Double the accuracy of estimates of radiative fluxes at TOA and the Earth's surface. (3) Provide the first long-term global estimates of the radiative fluxes within the Earth's atmosphere. (4) Provide cloud property estimates collocated in space and time that are consistent with the radiative fluxes from surface to TOA. In order to accomplish these goals, CERES uses data from a combination of spaceborne instruments: CERES scanners, which are an improved version of the ERBE broadband radiometers, and collocated cloud spectral imager data on the same spacecraft. The CERES cloud and radiative flux data products should prove extremely useful in advancing the understanding of cloud-radiation interactions, particularly cloud feedback effects on the Earth's radiation balance. For this reason, the CERES data should be fundamental to the ability to understand, detect, and predict global climate change. CERES results should also be very useful for studying regional climate changes associated with deforestation, desertification, anthropogenic aerosols, and ENSO events. This overview summarizes the Release 3 version of the planned CERES data products and data analysis algorithms. These algorithms are a prototype for the system that will produce the scientific data required for studying the role of clouds and radiation in the Earth's climate system atmosphere; clouds; geophysical signal processing; Remote sensing; atmospheric radiation; aerosols; algorithm; atmospheric techniques; CERES; Change detection algorithms; cloud; Clouds and the Earth's Radiant Energy System; Data analysis; data processing; Earth Observing System; EOS; Feedback; infrared radiation; Instruments; measurement technique; Meteorology; radiative flux; radiometers; satellite remote sensing; Space vehicles; Terrestrial atmosphere; thermal radiation
Young, D. F.; Minnis, P.; Doelling, D. R.; Gibson, G. G.; Wong, T.Young, D. F., P. Minnis, D. R. Doelling, G. G. Gibson, T. Wong, 1998: Temporal Interpolation Methods for the Clouds and the Earth’s Radiant Energy System (CERES) Experiment. Journal of Applied Meteorology, 37(6), 572-590. doi: 10.1175/1520-0450(1998)037<0572:TIMFTC>2.0.CO;2. Abstract The Clouds and the Earth’s Radiant Energy System (CERES) is a NASA multisatellite measurement program for monitoring the radiation environment of the earth–atmosphere system. The CERES instrument was flown on the Tropical Rainfall Measuring Mission satellite in late 1997, and will be flown on the Earth Observing System morning satellite in 1998 and afternoon satellite in 2000. To minimize temporal sampling errors associated with satellite measurements, two methods have been developed for temporally interpolating the CERES earth radiation budget measurements to compute averages of top-of-the-atmosphere shortwave and longwave flux. The first method is based on techniques developed from the Earth Radiation Budget Experiment (ERBE) and provides radiation data that are consistent with the ERBE processing. The second method is a newly developed technique for use in the CERES data processing. This technique incorporates high temporal resolution data from geostationary satellites to improve modeling of diurnal variations of radiation due to changing cloud conditions during the day. The performance of these two temporal interpolation methods is evaluated using a simulated dataset. Simulation studies show that the introduction of geostationary data into the temporal interpolation process significantly improves the accuracy of hourly and daily radiative products. Interpolation errors for instantaneous flux estimates are reduced by up to 68% for longwave flux and 80% for shortwave flux.
Young, David F.; Minnis, Patrick; Baumgardner, Darrel; Gerber, H.Young, D. F., P. Minnis, D. Baumgardner, H. Gerber, 1998: Comparison of in situ and satellite-derived cloud properties during SUCCESS. Geophysical Research Letters, 25(8), 1125-1128. doi: 10.1029/98GL00116. The validation of cloud microphysical properties derived from satellite data with in situ observations is generally difficult due to the spatial and temporal variability of observed clouds. Two missions during SUCCESS concentrated on orographic wave clouds that exhibited relative spatial and temporal homogeneity. A comparison has been made of effective ice particle diameters derived from multispectral satellite data with in situ measurements from the MASP and PVM instruments aboard the DC-8 aircraft. For both days, the satellite-derived effective diameters fall well within the bounds of the in situ data. 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 0320 Atmospheric Composition and Structure: Cloud physics and chemistry
Chambers, L. H.; Wielicki, B. A.; Evans, K. F.Chambers, L. H., B. A. Wielicki, K. F. Evans, 1997: Accuracy of the independent pixel approximation for satellite estimates of oceanic boundary layer cloud optical depth. Journal of Geophysical Research: Atmospheres, 102(D2), 1779-1794. doi: 10.1029/96JD02995. A theoretical study has been conducted on the effects of cloud horizontal inhomogeneity on the retrieval of optical depth by remote sensing of visible reflectance. Forty-five Landsat scenes of oceanic boundary layer clouds provide a sampling of real cloud fields, including trade cumulus, open and closed cell broken stratocumulus, and solid stratocumulus. The spherical harmonic discrete ordinate method (SHDOM) radiative transfer model is used to calculate two-dimensional reflectances from subsampled cloud strips representing the Landsat scenes. The independent pixel approximation (IPA) is used to retrieve optical depth for comparison to the original input. Results for τIPA versus τref are presented on scales from the Landsat pixel scale (28.5 m) to an imager pixel scale (6 km) to near mesoscale (60 km). The random error decreases as the averaging scale increases, but error due to inhomogeneity remains. At the 60 km scale the average error is about 6% for high Sun, 2% for low Sun. Individual scenes, however, have retrieved optical depth errors as high as 45% due to horizontal radiative transport. The ability to retrieve higher statistical moments of the frequency distribution of optical depth is also assessed. Sigma, (σ), the standard deviation of τ, is retrieved quite well up to a point, then is underestimated due to the smoothing effect of horizontal radiative transport. The gamma function parameter ν, another measure of the width of the τ frequency distribution, is retrieved quite well over a wide range but with a systematic bias which varies with solar zenith angle, again due to horizontal radiative transport. A method is sought to reduce the optical depth retrieval error using a simple correction based on remotely sensed cloud properties. Of those considered, cloud physical aspect ratio (computed here from one possible relation which depends on properties obtainable from remote sensing) is found to be the most effective correction parameter. The aspect ratio correction reduces the retrieved optical depth bias error by 50 to 100% and the RMS error by 20 to 50%. Correction coefficients are presented at three solar zenith angles. This work is limited by its consideration of only single-level marine boundary layer clouds, assumptions of conservative scattering, constant cloud droplet size, no gas absorption or surface reflectance, and restriction to two-dimensional radiative transport. Future work will attempt to remove some of these limitations. The Landsat data used are also limited due to radiative smoothing. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 0360 Radiation: transmission and scattering; 0320 Cloud physics and chemistry
Chambers, L. H.; Wielicki, Bruce A.; Evans, K. F.Chambers, L. H., B. A. Wielicki, K. F. Evans, 1997: Independent Pixel and Two-Dimensional Estimates of Landsat-Derived Cloud Field Albedo. J. Atmos. Sci., 54(11), 1525-1532. doi: 10.1175/1520-0469(1997)054<1525:IPATDE>2.0.CO;2. Abstract A theoretical study has been conducted on the effects of cloud horizontal inhomogeneity on cloud albedo bias. A two-dimensional (2D) version of the Spherical Harmonic Discrete Ordinate Method (SHDOM) is used to estimate the albedo bias of the plane-parallel (PP–IPA) and independent pixel (IPA–2D) approximations for a wide range of 2D cloud fields obtained from Landsat. They include single-layer trade cumulus, open and closed cell broken stratocumulus, and solid stratocumulus boundary layer cloud fields over ocean. Findings are presented on a variety of averaging scales and are summarized as a function of cloud fraction, mean cloud optical depth, cloud aspect ratio, standard deviation of optical depth, and the gamma function parameter ν (a measure of the width of the optical depth distribution). Biases are found to be small for small cloud fraction or mean optical depth, where the cloud fields under study behave linearly. They are large (up to 0.20 for PP–IPA bias, −0.12 for IPA–2D bias) for large ν. On a scene-average basis, PP–IPA bias can reach 0.30, while IPA–2D bias reaches its largest magnitude at −0.07. Biases due to horizontal transport (IPA–2D) are much smaller than PP–IPA biases but account for 20% rms of the bias overall. Limitations of this work include the particular cloud field set used, assumptions of conservative scattering, constant cloud droplet size, no gas absorption or surface reflectance, and restriction to 2D radiative transport. The Landsat data used may also be affected by radiative smoothing.
Haeffelin, Martial P. A.; Mahan, J. Robert; Priestley, Kory J.Haeffelin, M. P. A., J. R. Mahan, K. J. Priestley, 1997: Predicted dynamic electrothermal performance of thermistor bolometer radiometers for Earth radiation budget applications. Applied Optics, 36(28), 7129-7142. doi: 10.1364/AO.36.007129. The Earth Radiation Budget Experiment (ERBE) and the Clouds and the Earth’s Radiant Energy System (CERES) rely on scanning thermistor bolometer radiometers of a similar design for accomplishing their mission. High-level dynamic electrothermal models of these instruments have been developed on the basis of the Monte Carlo ray-trace, finite-difference, and finite-element methods. The models are capable of simulating the end-to-end response of the ERBE and the CERES instruments to simulated sequences of Earth scenes. Such models will prove useful in the design of future generations of similar instruments, in defining ground-based and in-flight calibration and data-reduction strategies, in the interpretation of flight data, and in understanding data anomalies that might arise after the instruments have been placed in orbit. Two modules that make up the end-to-end model are presented: the optical–thermal radiative module and the thermistor bolometer dynamic electrothermal module. The optics module is used to determine the point-spread function of the optics, which establishes that the instrument has sharply defined footprints on the Earth. Results obtained with the thermistor bolometer dynamic electrothermal module provide valuable insights into the details of channel operation and establish its high level of equivalence. The combination of the two modules allows the point-spread function of the instrument to be determined and reveals the potential of this tool for scanning realistic Earth scenes.
Inamdar, A. K.; Ramanathan, V.Inamdar, A. K., V. Ramanathan, 1997: On monitoring the atmospheric greenhouse effect from space. Tellus B, 49(2), 216-230. doi: 10.1034/j.1600-0889.49.issue2.8.x. We propose an analysis technique for monitoring the planetary greenhouse effect from space. 2 quantities are used as a measure of the atmospheric greenhouse effect: (1) Ga, which is the reduction in the clear sky outgoing longwave radiation (OLR) due to the atmosphere; it is the radiative heating of the surface-atmosphere column; (2) Ga*, which is the back radiation from the atmosphere to the surface; it is the radiative heating of the surface by the atmosphere. Ga is obtained from satellite observations of OLR and surface temperature. Here, we develop a technique to obtain Ga* from a combination of OLR (broadband and window channel), surface temperature, column water vapor amount and near-surface air temperature. The difference, Ga–Ga*, yields the net radiative cooling of the atmospheric column. While the technique is applicable for any radiometric observations, it is demonstrated here for the proposed cloud and the earth's radiant energy systems (CERES). CERES will have in addition to the broadband channel (4 to 200 µm), a channel in the atmospheric window (8-12 µm) to provide continuous radiation flux data. The potential benefits of the window channel in estimating the surface downward longwave flux, as also in addressing the water vapor feedback and continuum-related studies are explored in this paper. The success of the method in unravelling the water vapor — radiative interactions is illustrated by 2 case studies using ship and satellite data for the 1985-1990 period: (a) the seasonal and latitudinal variation in the northern tropical oceans; (b) seasonal to interannual variations averaged over the entire tropical (30°N to 30°S) pacific ocean. In both instances, the column greenhouse effect (Ga) varies significantly on seasonal and inter annual time scales and is larger in the warmer months. Furthermore, variations in Ga* exceed those in Ga, such that the atmospheric cooling increases in the warmer, moist atmosphere. The water vapor continuum plays a significant role in the tropical variations of Ga* and tropospheric radiative cooling.
Kato, Seiji; Ackerman, Thomas P.; Clothiaux, Eugene E.; Mather, James H.; Mace, Gerald G.; Wesely, Marvin L.; Murcray, Frank; Michalsky, JosephKato, S., T. P. Ackerman, E. E. Clothiaux, J. H. Mather, G. G. Mace, M. L. Wesely, F. Murcray, J. Michalsky, 1997: Uncertainties in modeled and measured clear-sky surface shortwave irradiances. Journal of Geophysical Research: Atmospheres, 102(D22), 25881-25898. doi: 10.1029/97JD01841. A comparison of five independent measurements of the clear-sky downward shortwave irradiance at the surface shows that they scatter within a 5% range depending on their calibration constants. When the measurements are corrected using data from two cavity radiometers, three of the five independent measurements agree within 3 W m−2 over three clear-sky days, which is well within the estimated error limit of ±1.5%. A comparison of these three sets of irradiance measurements with the computed irradiance by a δ2-stream model reveals that the model overestimates the irradiance by 5%. Detailed investigation of the approximations and uncertainties associated with the computations (including the measurement error in the water vapor and ozone amounts, neglecting the state of polarization and trace gas absorption, the 2-stream approximation, the neglect of the spectral dependence of the surface albedo, and the uncertainties associated with aerosols) demonstrates that the discrepancy is not due to these approximations. Further analysis of the modeled and measured irradiance shows that the discrepancy is almost entirely due to the difference between modeled and measured diffuse field irradiances. An analysis of narrow-band diffuse to total irradiance ratios shows that this discrepancy is the largest near 400 nm and decreases with wavelength. These results rely on the absolute calibrations of two cavity radiometers, two shaded pyranometers, and one unshaded pyranometer, as well as ratios of irradiances measured by a multifilter rotating shadow-band radiometer. Therefore, in order for instrumental error to account for the diffuse field discrepancy, three independent measurements of the diffuse field irradiance must be biased low by at least 40%. For an aerosol to account for this discrepancy, it must be highly absorbing with a single-scattering albedo as low as 0.3. The unlikelihood of instrumental errors of 40% and aerosol single-scattering albedos of 0.3 suggests a third possibility: the neglect of some gaseous absorption process at visible wavelengths. 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 0360 Radiation: transmission and scattering
Minnis, P.; Mayor, S.; Smith, W.L.; Young, D.F.Minnis, P., S. Mayor, W. Smith, D. Young, 1997: Asymmetry in the diurnal variation of surface albedo. IEEE Transactions on Geoscience and Remote Sensing, 35(4), 879-890. doi: 10.1109/36.602530. Remote sensing of surface properties and estimation of clear-sky and surface albedo generally assume that the albedo depends only on the solar zenith angle. The effects of dew, frost, and precipitation as well as evaporation and wind can lead to some systematic diurnal variability resulting in an asymmetric diurnal cycle of albedo. This paper examines the symmetry of both surface-observed and top-of-the-atmosphere (TOA) albedos derived from satellite data. Broadband surface albedos were measured at the Department of Energy Atmospheric Radiation Measurement (ARM) Program Southern Great Plains Central Facility near Lamont, Oklahoma and several extended facilities. GOES satellite radiance data are converted to broadband albedo using bidirectional reflectance functions and an empirical narrowband-to-broadband relationship. The surface and top-of-atmosphere albedos vary in a consistent fashion during both the morning and afternoon. The initial results indicate that surface moisture, probably in the form of dew, has a significant effect and can change the albedo by 10% at a given solar zenith angle between the morning and afternoon. Wind speed is well correlated with the diurnal albedo asymmetry. Light winds and small dew point depressions are associated with the greatest morning/afternoon albedo differences. Aerosols tend to moderate those differences. Changes in the surface properties from dew may alter the bidirectional reflectance characteristics of the scene, affecting the interpretation of remote sensing data. Errors in the diurnally averaged albedos derived from Sun-synchronous satellite measurements that arise from albedo asymmetry are generally less than 3%. Further examination of surface albedo asymmetry is needed to assess its influence on satellite measurements and the surface energy budget over a range of land surface types atmosphere; geophysical techniques; Land surface; Remote sensing; Satellites; terrain; aerosols; Energy measurement; Moisture; 350 to 850 nm; afternoon; albedo; asymmetric diurnal cycle; asymmetry; Atmospheric measurements; atmospheric optics; Bidirectional control; bidirectional reflectance functions; diurnal variation; Lamont; land surface properties; land surface types; Layout; Light scattering; morning; Oklahoma; optics; Southern Great Plains; surface albedo; surface moisture; United States; USA; Wind speed
Otterman, J.; Starr, D.; Brakke, T.; Davies, R.; Jacobowitz, H.; Mehta, A.; Cheruy, F.; Prabhakara, C.Otterman, J., D. Starr, T. Brakke, R. Davies, H. Jacobowitz, A. Mehta, F. Cheruy, C. Prabhakara, 1997: Modeling zenith-angle dependence of outgoing longwave radiation: Implication for flux measurements. Remote Sensing of Environment, 62(1), 90-100. doi: 10.1016/S0034-4257(97)00084-9. As shown in previous studies, outgoing-longwave radiation (OLR) can be in error by ∼7% when evaluated from directional measurements by applying time-averaged angular distribution models (ADMs) to account for the emission anisotropy. In order to develop an insight into the problem of assessing hemispheric emission from directional measurements, we formulate the directional (monochromatic) greenhouse factor gd specified as the ratio of a longwave radiance measured above the atmosphere to that emitted from the surface at the same zenith angle θv. The explicit expressions for gd involve two atmospheric parameters, the optical thickness and the temperature-profile parameter. Our analysis indicates that under clear conditions a narrow-band radiance, if measured at θv≈57° in atmospheric windows (low values of optical thickness) and at θv≈47° in absorption bands, determines the hemispheric-average radiance to within about 1%. For broad spectral bands, whether under clear or cloudy (solid cover, or “randomly scattered” clouds) conditions, the same finding applies at θv≈50°. Thus, the, zenith angle of equivalence θeq varies by about ±5° for different values of the optical thickness; it varies only slightly for different temperature profiles (even though different temperature profiles produce quite different patterns of radiance vs. θv, that is, different ADMs apply). Measurements at or near θeq therefore constitute direct assessment of OLR, without resorting to ADMs to adjust for the variations of emission with view angle (anisotropy). The existing OLR data should be reexamined, accepting measurements only within the range 45–60% of view zenith angles.
Wong, Takmeng; Harrison, Edwin F.; Gibson, Gary G.; Denn, Frederick M.Wong, T., E. F. Harrison, G. G. Gibson, F. M. Denn, 1997: On the Determination of the Optimal Scan Mode Sequence for the TRMM CERES Instrument. J. Atmos. Oceanic Technol., 14(5), 1230-1236. doi: 10.1175/1520-0426(1997)014<1230:OTDOTO>2.0.CO;2. Abstract Clouds and the Earth’s Radiant Energy System (CERES) is a NASA spaceborne measurement program for monitoring the radiation environment of the earth–atmosphere system. The first CERES instrument is scheduled to be launched on board the Tropical Rainfall Measuring Mission (TRMM) satellite in late 1997. In addition to gathering traditional cross-track fixed azimuth measurements for calculating monthly mean radiation fields, this single CERES scanner instrument will also be required to collect angular radiance data using a rotating azimuth configuration for developing new angular dependence models (ADMs). Since the TRMM single CERES instrument can only be run in either one of these two configurations at any one time, it will need to be operated in a cyclical pattern between these two scan modes to achieve the intended measurement goals. To minimize the errors in the derived monthly mean radiation field due to missing cross-track scanner measurements during this satellite mission, determination of the optimal scan mode sequence for the TRMM single CERES instrument is carried out. The Earth Radiation Budget Experiment S-4 daily mean cross-track scanner data product for April and July 1985 and January 1986 is used with a simple temporal sampling scheme to produce simulated daily mean cross-track scanner measurements under different TRMM CERES operational scan mode sequences. Error analysis is performed on the monthly mean radiation fields derived from these simulated datasets. It is found that the best monthly mean result occurred when the cross-track scanner is operated on a “2 days on and 1 day off” mode. This scan mode sequence will effectively allow for 2 consecutive days of cross-track scanner data and 1 day of angular radiance measurement for each 3-day period. The root-mean-square errors for the monthly mean all-sky (clear sky) longwave and shortwave radiation field, due to missing cross-track scanner measurements for this particular case, are expected to be less than 2.5 (0.5) and 5.0 (1.5) W m−2, respectively.
Zhang, Y-C.; Rossow, W. B.Zhang, Y., W. B. Rossow, 1997: Estimating Meridional Energy Transports by the Atmospheric and Oceanic General Circulations Using Boundary Fluxes. J. Climate, 10(9), 2358-2373. doi: 10.1175/1520-0442(1997)010<2358:EMETBT>2.0.CO;2. Abstract The annual-mean meridional energy transport in the atmosphere–ocean system (total transport) is estimated using 4-yr mean net radiative fluxes at the top of the atmosphere (TOA) calculated from the International Satellite Cloud Climatology Project cloud datasets. In addition, the net atmospheric and surface radiative fluxes are calculated. When supplemented by a climatology of the surface latent and sensible heat fluxes, these radiative fluxes are used to derive the separate atmospheric and oceanic energy transports using a surface and planetary energy-balance method. Most previous results are based on direct calculations of the atmospheric energy transport from in situ measurements of horizontal wind velocity, temperature, and humidity in the atmosphere and on inference of oceanic heat transports as the difference between the atmospheric transports and the total energy transport (the planetary energy-balance method). Total, atmospheric, and oceanic energy transports from this study are in good agreement with more recent results (within mutual uncertainties). A detailed assessment is made of the uncertainties in the atmospheric and ocean energy transports that arise from uncertainties in the TOA and surface energy fluxes: the largest uncertainties are associated with the surface radiative and latent heat fluxes. Since the errors in the present method are from different sources and have different geographic distributions, the results of this study complement previous estimates of the atmospheric and oceanic energy transports. Assessment of error sources also suggests that improvement of this type of result is more likely in the near future than for the other methods. Because the radiative fluxes are calculated from physical quantities, the authors can characterize the mean effects of clouds on the atmospheric and oceanic energy transports: 1) cloud effects on the TOA radiation budget reduce hemispheric differences introduced by hemispheric differences of surface properties, 2) the cloud effects on the atmospheric and surface radiation budgets induce hemispheric differences in the heating/cooling of the atmosphere and ocean that require cross-equatorial transports in opposite directions by the atmosphere and ocean, and 3) all other factors held constant, clouds tend to reduce oceanic energy transports and increase atmospheric energy transports.
Charlock, Thomas P.; Alberta, Timothy L.Charlock, T. P., T. L. Alberta, 1996: The CERES/ARM/GEWEX Experiment (CAGEX) for the Retrieval of Radiative Fluxes with Satellite Data. Bull. Amer. Meteor. Soc., 77(11), 2673-2683. doi: 10.1175/1520-0477(1996)077<2673:TCEFTR>2.0.CO;2. Abstract Results from a temporally intensive, limited area, radiative transfer model experiment are on-line for investigating the vertical profile of shortwave and longwave radiative fluxes from the surface to the top of the atmosphere (TOA). The CERES/ARM/GEWEX Experiment (CAGEX) Version 1 provides a record of fluxes that have been computed with a radiative transfer code; the atmospheric sounding, aerosol, and satellite-retrieved cloud data on which the computations have been based; and surface-based measurements of radiative fluxes and cloud properties from ARM for comparison. The computed broadband fluxes at TOA show considerable scatter when compared with fluxes that are inferred empirically from narrowband operational satellite data. At the surface, LW fluxes computed with an alternate sounding dataset compare well with pyrgeometer measurements. In agreement with earlier work, the authors find that the calculated SW surface insulation is larger than the measurements for clear-sky and total-sky conditions. This experiment has been developed to test retrievals of radiative fluxes and the associated forcings by clouds, aerosols, surface properties, and water vapor. Collaboration is sought; the goal is to extend the domain of meteorological conditions for which such retrievals can be done accurately. CAGEX Version 1 covers April 1994. Subsequent versions will (a) at first span the same limited geographical area with data from October 1995, (b) then expand to cover a significant fraction of the GEWEX Continental-Scale International Project region for April 1996 through September 1996, and (c) eventually be used in a more advanced form to validate CERES.
Hucek, Richard; Stowe, Larry; Joyce, RobertHucek, R., L. Stowe, R. Joyce, 1996: Evaluating the Design of an Earth Radiation Budget Instrument with System Simulations. Part III: CERES-I Diurnal Sampling Error. J. Atmos. Oceanic Technol., 13(2), 383-399. doi: 10.1175/1520-0426(1996)013<0383:ETDOAE>2.0.CO;2. Abstract Accuracy estimates for the broadband CERES-I (Clouds and Earth's Radiant Energy System Instrument) measurements of daily average radiant exitance are presented. This is a continuation of the authors’ earlier CERES sampling studies published as Part I and II. Daily averaging errors result from not sampling the entire 24-h period with a system of polar satellites. Instantaneous errors, the subject of the previous studies, are also included. Separate estimates for daily average emitted longwave (LW) and reflected shortwave (SW) radiant fluxes are given. The earth SW and LW reference radiation fields are derived from 3-h Geosynchronous Operational Environmental Satellite data, time interpolated between image times, and partitioned into upwelling radiances using scene-dependent angular dependence models (ADMs). Perturbations in these ADMs are introduced to cause instantaneous angular sampling errors (also referred to as ADM errors). These ADM errors, along with spatial sampling errors, are propagated through the time integration process for a more realistic estimate of the daily average error. Three satellite observing configurations are considered. They represent individually, and in combination, a proposed European Polar Orbiting Platform and National Aeronautics and Space Administration Earth Observing System-A sun-synchronous polar-orbiting satellite system. The Earth Radiation Budget Experiment single and multiple satellite time and space averaging algorithms are used for the satellite retrieval. One-satellite spatial root-mean-square (rms) daily averaged SW flux errors of 11–17 W m−2 are obtained for 2.5° latitude-longitude regions over the area studied (15°S–45°N, 50°–120°W). The two-satellite system has errors that are some 40%–60% less, having values between 5 and 9 W m−2. Only the two-satellite system can meet the 10 W m−2 user accuracy requirement for regional daily averaged SW fluxes. Longwave flux errors of 5–6 W m−2 and 3–4 W m−2, respectively, are found for the one- and two-satellite configurations. The largest component of CERES 2.5° daily averaged target area error is due to sparse temporal sampling. The ADM error propagated into the daily average becomes more important as the temporal sampling error is reduced with the two-satellite system. For this system, the ADM error component (of the daily averaged error) for SW radiation reaches a magnitude that can be as large as 8 W m−2 at high solar zenith angles (SZA), where scene anisotropy is usually greatest. Over the study domain, up to 15% of the total rms error is due to ADM errors. Moreover, CERES 2.5° zonal mean daily averaged errors exhibit a latitudinal dependence of some 7 W m−2 for a 60° change in latitude in the presence of 30% systematic errors in the ADMs. This is largely attributable to the SZA dependence of instantaneous ADM error. Without ADM errors, zonal mean daily averaged target area biases range up to 3–4 W m−2 with an irregular latitudinal variation.
Lee, Robert B.; Barkstrom, Bruce R.; Smith, G. Louis; Cooper, John E.; Kopia, Leonard P.; Lawrence, R. Wes; Thomas, Susan; Pandey, Dhirendra K.; Crommelynck, Dominique A. H.Lee, R. B., B. R. Barkstrom, G. L. Smith, J. E. Cooper, L. P. Kopia, R. W. Lawrence, S. Thomas, D. K. Pandey, D. A. H. Crommelynck, 1996: The Clouds and the Earth's Radiant Energy System (CERES) Sensors and Preflight Calibration Plans. J. Atmos. Oceanic Technol., 13(2), 300-313. doi: 10.1175/1520-0426(1996)013<0300:TCATER>2.0.CO;2. Abstract The Clouds and the Earth's Radiant Energy System (CERES) spacecraft sensors are designed to measure broadband earth-reflected solar shortwave (0.3–5 µm) and earth-emitted longwave (5– > 100 µm) radiances at the top of the atmosphere as part of the Mission to Planet Earth program. The scanning thermistor bolometer sensors respond to radiances in the broadband shortwave (0.3–5 µm) and total-wave (0.3– > 100 µm) spectral regions, as well as to radiances in the narrowband water vapor window (8–12 µm) region. The sensors are designed to operate for a minimum of 5 years aboard the NASA Tropical Rainfall Measuring Mission and Earth Observing System AM-I spacecraft platforms that are scheduled for launches in 1997 and 1998, respectively. The flight sensors and the in-flight calibration systems will he calibrated in a vacuum ground facility using reference radiance sources, tied to the international temperature scale of 1990. The calibrations will be used to derive sensor gains, offsets, spectral responses, and point spread functions within and outside of the field of view. The shortwave, total-wave, and window ground calibration accuracy requirements (1 sigma) are ±0.8, ±0.6, and ±0.3 W m−2 sr−1, respectively, while the corresponding measurement precisions are ±0.5% and ±1.0% for the broadband longwave and shortwave radiances, respectively. The CERES sensors, in-flight calibration systems, and ground calibration instrumentation are described along with outlines of the preflight and in-flight calibration approaches.
Wielicki, Bruce A.; Barkstrom, Bruce R.; Harrison, Edwin F.; Lee, Robert B.; Louis Smith, G.; Cooper, John E.Wielicki, B. A., B. R. Barkstrom, E. F. Harrison, R. B. Lee, G. Louis Smith, J. E. Cooper, 1996: Clouds and the Earth's Radiant Energy System (CERES): An Earth Observing System Experiment. Bull. Amer. Meteor. Soc., 77(5), 853-868. doi: 10.1175/1520-0477(1996)077<0853:CATERE>2.0.CO;2. Abstract Clouds and the Earth's Radiant Energy System (CERES) is an investigation to examine the role of cloud/radiation feedback in the Earth's climate system. The CERES broadband scanning radiometers are an improved version of the Earth Radiation Budget Experiment (ERBE) radiometers. The CERES instruments will fly on several National Aeronautics and Space Administration Earth Observing System (EOS) satellites starting in 1998 and extending over at least 15 years. The CERES science investigations will provide data to extend the ERBE climate record of top-of-atmosphere shortwave (SW) and longwave (LW) radiative fluxes. CERES will also combine simultaneous cloud property data derived using EOS narrowband imagers to provide a consistent set of cloud/radiation data, including SW and LW radiative fluxes at the surface and at several selected levels within the atmosphere. CERES data are expected to provide top-of-atmosphere radiative fluxes with a factor of 2 to 3 less error than the ERBE data. Estimates of radiative fluxes at the surface and especially within the atmosphere will be a much greater challenge but should also show significant improvements over current capabilities.
Thomas, D.; Duvel, J.P.; Kandel, R.Thomas, D., J. Duvel, R. Kandel, 1995: Diurnal bias in calibration of broad-band radiance measurements from space. IEEE Transactions on Geoscience and Remote Sensing, 33(3), 670-683. doi: 10.1109/36.387582. Examines the problem of determining the separate shortwave (SW) and longwave (LW) components of the Earth radiation budget from space. Because true broad-band longwave filters do not exist, daytime LW radiance determinations can depend entirely or in part on subtraction of the measured SW radiance from the “Total” (TW) radiance involving integration over the entire electromagnetic pectrum. Examining radiances measured in the three channels (SW, imperfectly filtered broad-band LW, TW) of the Earth Radiation Budget Experiment (ERBE) scanners on board the NOAA-9, ERBS and NOAA-10 satellites, the authors find small discrepancies in the daytime estimates of broad-band (“unfiltered”) LW radiances using the ERBE “spectral correction” procedure. The authors show that these result from errors (of order 2.5%) in the calibration of the SW channel and possibly in the spectral characterization of the SW and/or TW channel of the ERBE scanners on NOAA-9 and NOAA-10. Nighttime estimates show no such bias, and there appears to be no such error in the data from ERBS. Considering the LW radiant exitances determined from ERBE scanner data from the three satellites, the authors find systematic differences in individual satellite estimates of simultaneous instantaneous regional means and of regional monthly means, consistent with the radiance discrepancies, instantaneous daytime LW estimates can be in error by 20% in the extreme case of very bright cold cloud, and LW cloud radiative forcing may be significantly biased. They consider the implications of these small SW-dependent errors on the determination of diurnal variation and of cloud radiative forcing in the longwave domain. They show how the ERBE estimates can be corrected, and consider how procedures can be used to validate results of future experiments (ScaRaB and CERES) atmosphere; broad-band radiance; calibration; clouds; diurnal bias; Earth; earth radiation budget; Electromagnetic measurements; ERBE; Extraterrestrial measurements; Filters; geophysical measurement technique; geophysical signal processing; geophysical techniques; infrared imaging; Land surface; longwave; optical imaging mapping; Radiation detectors; Remote sensing; Sampling methods; Satellites; shortwave; terrain; visible infrared IR method
Wielicki, Bruce A.; Harrison, Edwin F.; Cess, Robert D.; King, Michael D.; Randall, David A.Wielicki, B. A., E. F. Harrison, R. D. Cess, M. D. King, D. A. Randall, 1995: Mission to Planet Earth: Role of Clouds and Radiation in Climate. Bull. Amer. Meteor. Soc., 76(11), 2125-2153. doi: 10.1175/1520-0477(1995)076<2125:MTPERO>2.0.CO;2. Abstract The role of clouds in modifying the earth's radiation balance is well recognized as a key uncertainty in predicting any potential future climate change. This statement is true whether the climate change of interest is caused by changing emissions of greenhouse gases and sulfates, deforestation, ozone depletion, volcanic eruptions, or changes in the solar constant. This paper presents an overview of the role of the National Aeronautics and Space Administration's Earth Observing System (EOS) satellite data in understanding the role of clouds in the global climate system. The paper gives a brief summary of the cloud/radiation problem, and discusses the critical observations needed to support further investigations. The planned EOS data products are summarized, including the critical advances over current satellite cloud and radiation budget data. Key advances include simultaneous observation of radiation budget and cloud properties, additional information an cloud particle size and phase, improved detection of thin clouds and multilayer cloud systems, greatly reduced ambiguity in partially cloud-filled satellite fields of view, improved calibration and stability of satellite-observed radiances, and improved estimates of radiative fluxes at the top of the atmosphere, at the surface, and at levels within the atmosphere. Outstanding sampling and remote sensing issues that affect data quality are also discussed. Finally, the EOS data are placed in the context of other satellite observations as well as the critical surface, field experiment, and laboratory data needed to address the role of clouds in the climate system. It is concluded that the EOS data are a necessary but insufficient condition for solution of the scientific cloud/radiation issues. A balanced approach of satellite, field, and laboratory data will be required. These combined data can span the necessary spatial scales of global, regional, cloud cell, and cloud particle physics (i.e., from 108 to 10−7 m).
Smith, G. L.; Barkstrom, B. R.; Harrison, E. F.; Lee III, R. B.; Wielicki, B. A.Smith, G. L., B. R. Barkstrom, E. F. Harrison, R. B. Lee III, B. A. Wielicki, 1994: Radiation budget measurements for the eighties and nineties. Advances in Space Research, 14(1), 81-84. doi: 10.1016/0273-1177(94)90351-4. The Earth Radiation Budget Experiment (ERBE) consisted of a scanning radiometer and non-scanning radiometers on each of three spacecraft. These instruments began flying in October 1984. The nonscanning radiometers continue to operate, providing broadband radiation measurements of the Earth's outgoing longwave radiation and reflected solar radiation, in addition to measurements of the solar output. The Clouds and Earth Radiant Energy System (CERES) features a scanning radiometer, which is an improved version of the ERBE scanning radiometer, and will fly on the Tropical Rainfall Measurement Mission and Earth Observation System platforms in the late nineties. The CERES project will provide not only radiant fluxes at the “top of the atmosphere” (TOA), but also at the surface and will compute radiant flux divergence through the atmosphere.
Smith, G. LouisSmith, G. L., 1994: Effects of time response on the point spread function of a scanning radiometer. Applied Optics, 33(30), 7031. doi: 10.1364/AO.33.007031.
Stowe, Larry; Hucek, Richard; Ardanuy, Philip; Joyce, RobertStowe, L., R. Hucek, P. Ardanuy, R. Joyce, 1994: Evaluating the Design of an Earth Radiation Budget Instrument with System Simulations. Part II: Minimization of Instantaneous Sampling Errors for CERES-I. J. Atmos. Oceanic Technol., 11(5), 1169-1183. doi: 10.1175/1520-0426(1994)011<1169:ETDOAE>2.0.CO;2. Abstract Much of the new record of broadband earth radiation budget satellite measurements to be obtained during the late 1990s and early twenty-first century will come from the dual-radiometer Clouds and Earth's Radiant Energy System Instrument (CERES-1) flown aboard sun-synchronous polar orbiters. Simulation studies conducted in this work for an early afternoon satellite orbit indicate that spatial rms sampling errors of instantaneous CERES-I shortwave flux estimates will range from about 8.5 to 14.0 W m−2 on a 2.5° latitude and longitude grid resolution. Root-mean-square errors in longwave flux estimates are only about 20% as large and range from 1.5 to 3.5 W m−2. These results are based on an optimal cross-track scanner design that includes 50% footprint overlap to eliminate gaps in the top-of-the-atmosphere coverage, and a “smallest” footprint size to increase the ratio in the number of observations lying within to the number of observations lying on grid area boundaries. Total instantaneous measurement error depends additionally on the variability of anisotropic reflectance and emission patterns and on the retrieval methods used to generate target area fluxes. Three retrieval procedures are investigated, all relying on a maximum-likelihood estimation technique for scene identification. Observations from both CERES-1 scanners (cross-track and rotating azimuth plane) are used. One method is the baseline Earth Radiation Budget Experiment (ERBE) procedure, which assumes that errors due to the use of mean angular dependence models (ADMs) in the radiance-to-flux inversion process nearly cancel when averaged over grid areas. In a second (estimation of N) method, instantaneous ADMs are estimated from the multiangular, collocated observations of the two scanners. These observed models replace the mean models in the computation of the satellite flux estimates. In the third (scene flux) approach, separate target-area retrievals are conducted for each ERBE scene category and their results are combined using area weighting by scene type. The ERBE retrieval performs best when the simulated radiance field departs from the ERBE mean models by less than 10%. For larger perturbations, both the scene flux and collocation methods produce less error than the ERBE retrieval. The scene flux technique is preferable, however, because it involves fewer restrictive assumptions.
Foukal, P. V.; Jauniskis, L.Foukal, P. V., L. Jauniskis, 1993: Application of Cryogenic Electrical Substitution Radiometers in the Calibration of Solar-Terrestrial Remote Sensing Instruments. Metrologia, 30(4), 279. doi: 10.1088/0026-1394/30/4/012. We describe two recent applications of cryogenic Electrical Substitution Radiometers (ESRs), which can provide significantly improved accuracy and sensitivity in the calibration of solar-terrestrial remote sensing instruments. In the first, a portable UV filter radiometer was calibrated at 257 nm using a cryogenic ESR and an intensity-stabilized laser. This filter radiometer was then used to measure the UV irradiance at 257 nm of deuterium lamps and of the SURF II synchrotron. Our results indicate that the accuracy of these measurements is three to eight times better than presently achieved with calibrations of these source standards, at this wavelength. Improvement of UV calibrations is critical to the success of NASA remote sensing of ozone, and of related solar UV irradiance variations. In the second application, a fast cryogenic ESR was developed for use at TRW as a spectrally flat transfer standard, to provide radiometric calibrations of the CERES spectroradiometer with accuracies of better than 1% in the short-wave band and 0,5% in the long-wave and total bands. The CERES instrument is designed to provide improved measurements of the Earth's radiation budget for climate studies.
Jarecke, P. J.; Folkman, M. A.; Hedman, T. R.; Frink, M. E.Jarecke, P. J., M. A. Folkman, T. R. Hedman, M. E. Frink, 1993: Clouds and the Earth's Radiant Energy System (CERES): Long-wave Calibration Plan and Radiometric Test Model (RTM) Calibration Results. Metrologia, 30(4), 223. doi: 10.1088/0026-1394/30/4/003. The CERES instrument has three radiometers which operate in the short-wave (0,3 μm to 5 μm), the long-wave (8 μm to 12 μm) and total broadband (0,3 μm to >200 μm) spectral regions. The long-wave calibration plan for CERES provides for absolute radiometric calibration of the two CERES sensors operating in the long-wave portion of the spectrum. Ground calibration is carried out in the TRW Radiometric Calibration Facility (RCF), a cryogenic vacuum chamber with the capability to simulate radiometrically both cold space and Earth viewing conditions. Absolute calibration is made using a temperature-based radiometric scale created by a black-body radiance standard controlled at temperatures from 200 K to 320 K. In May 1992, the CERES radiometric test model (RTM), a developmental but functionally flight-like instrument, was calibrated at TRW in the RCF. This was the first end-to-end long-wave calibration of a CERES sensor and provided a test and initial validation of the long-wave calibration plan and procedures. The gain, offset, out-of-field response and spectral response were determined for each sensor. The end-to-end long-wave calibration plan is described and the RTM calibration and validation results are presented.
Morel, M.; Jegou, R.; Readings, C.; Tabarie, N.Morel, M., R. Jegou, C. Readings, N. Tabarie, 1993: ENVISATS EARTH RADIATION-BUDGET INSTRUMENT - SCARAB. Esa Bulletin-European Space Agency(76), 53-57. The SCARAB instrument was proposed by CNES as an Announcement of Opportunity instrument for Envisat-1 following the withdrawal by NASA of the CERES instrument originally selected as part of the POEM payload complement. SCARAB (Scanner Radiatsionnogo Balansa) will make an essential contribution to the monitoring of the Earth's radiation budget, which is a key element in our climatic system. Its data can also be used to refine existing climate models.
Stowe, Larry; Ardanuy, Philip; Hucek, Richard; Abel, Peter; Jacobowitz, HerbertStowe, L., P. Ardanuy, R. Hucek, P. Abel, H. Jacobowitz, 1993: Evaluating the Design of an Earth Radiation Budget Instrument with System Simulations. Part I: Instantaneous Estimates. J. Atmos. Oceanic Technol., 10(6), 809-826. doi: 10.1175/1520-0426(1993)010<0809:ETDOAE>2.0.CO;2. Abstract A set of system simulations has been performed to evaluate candidate scanner designs for an Earth Radiation Budget Instrument (ERBI) for the Earth Observing System (EOS) of the late 1990s. Five different instruments are considered: 1) the Active Cavity Array (ACA), 2) the Clouds and Earth's Radiant Energy System-Instrument (CERES-1), 3) the Conically Scanning Radiometer (CSR), (4) the Earth Radiation Budget Experiment Cross-Track Scanner (ERBE), and 5) the Nimbus-7 Biaxial Scanner (N7). Errors in instantaneous, top-of-the-atmosphere (TOA) satellite flux estimates are assumed to arise from two measurement problems: the sampling of space over a given geographic domain, and sampling in angle about a given spatial location. In the limit where angular sampling errors vanish [due to the application of correct angular dependence models (ADMs) during inversion], the accuracy of each scanner design is determined by the instrument's ability to map the TOA radiance field in a uniform manner. In this regard, the instruments containing a cross-track scanning component (CERES-1 and ERBE) do best. As errors in ADMs are encountered, cross-track instruments incur angular sampling errors more rapidly than biaxial instruments (N7, ACA, and CSR) and eventually overtake the biaxial designs in their total error amounts. A latitude bias (north-south error gradient) in the ADM error of cross-track instruments also exists. This would be objectionable when ADM errors are systematic over large areas of the globe. For instantaneous errors, however, cross-track scanners outperform biaxial or conical scanners for 2.5° latitude × 2.5° longitude target areas. providing that the ADM error is less than or equal to 30%. A key issue is the amount of systematic ADM error (departures from the mean models) that is present at the 2.5° resolution of the ERBE target areas. If this error is less than 30%, then the CERES-I, ERBE, and CSR, in order of increasing error, provide the most accurate instantaneous flux estimates, within 2–3 W m−2 of each other in reflected shortwave flux. The magnitude of this error is near the 10 W m−2 accuracy requirement of the user community. Longwave flux errors have been found to have the same space and time characteristics as errors in shortwave radiation, but only about 25% as large.
Stubenrauch, C. J.; Duvel, J-P. H.; Kandel, R. S.Stubenrauch, C. J., J. H. Duvel, R. S. Kandel, 1993: Determination of Longwave Anisotropic Emission Factors from Combined Broad-and Narrowband Radiance Measurements. Journal of Applied Meteorology, 32(5), 848-856. doi: 10.1175/1520-0450(1993)032<0848:DOLAEF>2.0.CO;2. Abstract The conversion of measured radiances into radiative fluxes requires application of angular corrections; in the Earth Radiation Budget Experiment (ERBE), the longwave anisotropic emission factors (AEFS) were tabulated for different viewing zenith angles, seasons, latitude bands, and scene types, including four differment cloud-cover classes. An alternative approach is investigated using simultaneous infrared atmospheric window (10.5-12.5 µm) and broadband longwave (LW) measurements. Such measurements will be available from the ScaRaB (Scanner for Radiation Balance) instrument whose launch is planned to occur in 1993. Using a radiative transfer model to simulate the combined measurements, the AEF is parameterized as a function of viewing zenith angle and a single other variable—atmospheric pseudoabsorptance—defined as the normalized difference between the broadband LW radiance and the integrated Planck emission at the 11.5-µm brightness temperature. For validation of the parameterization with existing satellite data, simultaneous collocated NOAA-9 ERBE Advanced Very High Resolution Radiometer data were used for broad- and narrowband radiances. The comparison between fluxes corrected with the parameterized AEF and those corrected with the ERRE AEF shows that the parameterization provides more realistic AEFs as a function of scene brightness temperature, which is related to cloud-top height. Analysis of classified cloud data indicates that there are only a few extreme cases in which additional anisotropy due to broken clouds will affect the usefulness of this parameterization. Enhanced anisotropy of semitransparant cirrus was also considered. Model and data show that although not explicitly treated in this procedure, the parameterization gives good results. This parameterization may also be adapted for somewhat different wavelength bands as in the NASA CERES (Clouds and the Earth's Radiant Energy System) project.
