# Publications

## 2022

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. cloud-controlling factors; low clouds; machine learning; satellite data; trend analysis
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.
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. Arctic region; FengYun-3D; machine learning; MERSI-2; satellite observation; surface downward longwave radiation
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. climate models; cloud feedback; pattern effect
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.
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. budget; convection; global storm-resolving model; ICON; stratosphere; water vapor
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. aerosol/cloud interactions; global change; global climate models; land/atmosphere interactions
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. Atmospheric rivers; Dust aerosols; European Alps; Sahara Desert; Snow melting; Water vapour
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; Sahara; Tropical Atlantic; WRF-Chem
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.
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. Data evaluation; Irradiance data; PV power model; Re-analysis; Satellite; Station observations
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; energy exascale earth system model; high resolution; multiscale modelling framework; precipitation; United States
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.
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. constraint; energy balance; ERA5; mid-low latitude; modeling; MODIS; net radiation; random forest; temporal expansion
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.
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. East Asian atmospheric circulation variability; Eurasian teleconnection; shortwave cloud radiative effect; Ural blocking
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.
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
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.
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. cirrus; convection; DYAMOND; global storm-resolving models; microphysics; tropical tropopause layer
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
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.
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. Arctic amplificantion; climate models; cloud feedback; ice nucleation; satellite
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
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. Atmospheric modeling; Broadband communication; Climate change; Earth; energy budget; Moderate Resolution Imaging Spectroradiometer (MODIS); MODIS; ocean bidirectional reflectance distribution function (BRDF); Oceans; radiative transfer (RT) simulations; Sea surface; top-of-atmosphere (TOA) albedo; Wind speed
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., -1(aop). 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 7 pressure layers and 6 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 multi-channel 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. Congolese rainforests; DSCOVR EPIC; Leaf area; Long-term trends; MISR; MODIS; Phenology; Remote sensing
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
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; DYAMOND; global storm-resolving models; life cycle; model comparison; tropical tropopause layer
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, 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. Aerosol emissions; Black carbon; CMIP6; Surface solar radiation
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
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). Bayesian model averaging; CMIP5; CMIP6; GCMs; Multimodel ensemble; Surface downward longwave radiation (SDLR)
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%. AVHRR; CERES; Earth's energy budget; Machine learning; TOA albedo
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, 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
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.
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, 2022: Integration of Multisource Data to Estimate Downward Longwave Radiation Based on Deep Neural Networks. IEEE Transactions on Geoscience and Remote Sensing, 60, 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)

## 2021

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; climate; convection; general circulation model experiments; seasonal prediction; tropics
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
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. active and passive sensors; CALIPSO; CERES; cloud cover 2; ISCCP; satellite remote sensing
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.; 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, 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.
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, Archana; Satheesh, Sreedharan KrishnakumariDevi, A., S. K. Satheesh, 2021: Global maps of aerosol single scattering albedo using combined CERES-MODIS retrieval. Atmospheric Chemistry and Physics Discussions, 1-18. doi: 10.5194/acp-2021-521. 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 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. The method has been validated using the data from aircraft-based measurements of various field campaigns. The retrieval uncertainty is ±0.03 and depends on both the surface albedo and aerosol absorption. 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. 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.
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.”
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
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). Antarctic; climate; GHG; radiation; temperature
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. air-sea interaction; atmospheric cold pool; Bay of Bengal; mixed layer processes; sea surface temperature
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.
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. cloud-top radiative cooling scheme; EASM rain belt; low clouds; low-level southwesterlies; Tibetan Plateau
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.
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
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. climate model; cloud; ITCZ; 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. extreme rainfall; low-level jet; moisture flux; monsoon; 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. E3SM; FIVE; low-level cloud; marine boundary layer; stratocumulus cloud; vertical resolution
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, 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.
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.
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); Diffuse radiation fraction; LUE models
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
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
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
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; 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
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; global cloud-resolving model; mixed-phase clouds; seasonal variation; supercooled water
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. all-sky infrared radiance; bias; cloud; data assimilation; Himawari-8; radiative transfer model
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.
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. buoy data; CERES; empirical model; longwave radiation; net radiation; sea surface; shortwave radiation
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
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
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
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.
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
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%. CALIPSO; cloud radiative effects; CloudSat; ERA5; MERRA2; MLS; 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. caliop; cloud; enso; ice water content; ice water path; 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. CrIS; NOAA-20; NUCAPS; OLR; outgoing longwave radiation; radiation budget; validation
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
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, 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). Bayesian model averaging; CMIP5; CMIP6; GCMs; 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. Indo–China Peninsula; quantitative analysis; reference evapotranspiration; 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, 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, 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. Land surface; Atmospheric modeling; Ocean temperature; Spatial resolution; Himawari-8; Clouds; Temperature distribution; Deep convolutional neural network (DCNN); downward longwave radiation (DLR); Estimation; 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; polar WRF; surface energy balance; West Antarctic surface melting

## 2020

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
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.
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.
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
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.
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.
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
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
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.
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.
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.
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.
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; 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%.
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
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.
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.
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, 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, 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.; 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, 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.
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&rsquo;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 &ndash; 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 &ndash; 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
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
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
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.
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