# 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. satellite data; low clouds; trend analysis; machine learning; cloud-controlling factors
Andrews, Timothy; Bodas-Salcedo, Alejandro; Gregory, Jonathan M.; Dong, Yue; Armour, Kyle C.; Paynter, David; Lin, Pu; Modak, Angshuman; Mauritsen, Thorsten; Cole, Jason N. S.; Medeiros, Brian; Benedict, James J.; Douville, Hervé; Roehrig, Romain; Koshiro, Tsuyoshi; Kawai, Hideaki; Ogura, Tomoo; Dufresne, Jean-Louis; Allan, Richard P.; Liu, ChunleiAndrews, T., A. Bodas-Salcedo, J. M. Gregory, Y. Dong, K. C. Armour, D. Paynter, P. Lin, A. Modak, T. Mauritsen, J. N. S. Cole, B. Medeiros, J. J. Benedict, H. Douville, R. Roehrig, T. Koshiro, H. Kawai, T. Ogura, J. Dufresne, R. P. Allan, C. Liu, 2022: On the Effect of Historical SST Patterns on Radiative Feedback. Journal of Geophysical Research: Atmospheres, 127(18), e2022JD036675. doi: 10.1029/2022JD036675. We investigate the dependence of radiative feedback on the pattern of sea-surface temperature (SST) change in 14 Atmospheric General Circulation Models (AGCMs) forced with observed variations in SST and sea-ice over the historical record from 1871 to near-present. We find that over 1871–1980, the Earth warmed with feedbacks largely consistent and strongly correlated with long-term climate sensitivity feedbacks (diagnosed from corresponding atmosphere-ocean GCM abrupt-4xCO2 simulations). Post 1980, however, the Earth warmed with unusual trends in tropical Pacific SSTs (enhanced warming in the west, cooling in the east) and cooling in the Southern Ocean that drove climate feedback to be uncorrelated with—and indicating much lower climate sensitivity than—that expected for long-term CO2 increase. We show that these conclusions are not strongly dependent on the Atmospheric Model Intercomparison Project (AMIP) II SST data set used to force the AGCMs, though the magnitude of feedback post 1980 is generally smaller in nine AGCMs forced with alternative HadISST1 SST boundary conditions. We quantify a “pattern effect” (defined as the difference between historical and long-term CO2 feedback) equal to 0.48 ± 0.47 [5%–95%] W m−2 K−1 for the time-period 1871–2010 when the AGCMs are forced with HadISST1 SSTs, or 0.70 ± 0.47 [5%–95%] W m−2 K−1 when forced with AMIP II SSTs. Assessed changes in the Earth's historical energy budget agree with the AGCM feedback estimates. Furthermore satellite observations of changes in top-of-atmosphere radiative fluxes since 1985 suggest that the pattern effect was particularly strong over recent decades but may be waning post 2014. observations; climate models; climate feedback; climate sensitivity; pattern effect; historical record
Aparna, A. R.; Girishkumar, M. S.Aparna, A. R., M. S. Girishkumar, 2022: Mixed layer heat budget in the eastern equatorial Indian Ocean during the two consecutive positive Indian Ocean dipole events in 2018 and 2019. Climate Dynamics. doi: 10.1007/s00382-021-06099-8. The Indian Ocean hosted a strong positive Indian Ocean Dipole (pIOD) event in 2019–2020, and a weak event in 2018–2019, such as the magnitude of the cold sea surface temperature anomaly (SSTA) during June-December in the former case is a factor of two higher (~ − 1.5 °C) than the latter (~ − 0.75 °C) at the western periphery of the eastern IOD zone at 5° S, 95° E. The plausible mechanisms responsible for this difference in the SSTA between these two events are examined using the mixed layer heat budget estimate using the moored buoy measurements. It is found that the enhanced cooling during June-December in 2019–2020 is determined primarily by the anomalous cooling due to the vertical processes associated with the combined effect of the anomalous thin barrier layer (BL), shallow thermocline, weak near-surface stratification, and strong wind speed induced vertical mixing, and secondarily by the enhancement in the latent heat flux (LHF) loss from the ocean. Conversely, the magnitude of cooling due to the vertical processes is much smaller in 2018–2019 due to the near-climatological states such as a thick BL, deep thermocline, and weak wind speed. During these events, the warming tendency by the horizontal advection dampens the cooling tendency associated with the vertical processes and LHF. These characteristics are distinct from the past study that suggested that the horizontal advection was responsible for the cool SSTA at the exact location during an extreme pIOD event in 2006–2007.
Atlas, R.l.; Bretherton, C.s.; Khairoutdinov, M.f.; Blossey, P.n.Atlas, R., C. Bretherton, M. Khairoutdinov, P. Blossey, 2022: Hallett-Mossop rime splintering dims cumulus clouds over the Southern Ocean: New insight from nudged global storm-resolving simulations. AGU Advances, n/a(n/a), e2021AV000454. doi: 10.1029/2021AV000454. In clouds containing both liquid and ice with temperatures between − 3°C and − 8°C, liquid droplets collide with large ice crystals, freeze, and shatter, producing a plethora of small ice splinters. This process, known as Hallett-Mossop rime splintering, and other forms of secondary ice production, can cause clouds to reflect less sunlight and to have shorter lifetimes. We show its impact on Southern Ocean shallow cumuli using a novel suite of five global storm-resolving simulations, which partition the Earth’s atmosphere into 2-4 km wide columns. We evaluate simulated clouds and radiation over the Southern Ocean with aircraft observations from the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES), and satellite observations from Clouds and the Earth’s Radiant Energy System (CERES) and Himawari. Simulations with large concentrations of ice crystals in boundary layer clouds, which agree better with SOCRATES observations, have reduced mixed-phase cumulus cloud cover and weaker shortwave cloud radiative effects that are less biased compared with CERES. Using a pair of simulations differing only in their treatment of Hallett-Mossop rime splintering, we show that including this process increases ice crystal concentrations in cumulus clouds and weakens shortwave cloud radiative effects over the Southern Ocean by 10 W m−2. We also demonstrate the key role that global storm-resolving models can play in detangling the effects of clouds on Earth’s climate across scales, making it possible to trace the impact of changes in individual cumulus cloud anvils (10 km2) on the radiative budget of the massive Southern Ocean basin (108 km2). Southern Ocean; Boundary layer; Global cloud-resolving simulations; Hallett-Mossop rime splintering; Open cell cumuli; Secondary ice production
Atmoko, Dwi; Lin, Tang-HuangAtmoko, D., T. Lin, 2022: Sea Salt Aerosol Identification Based on Multispectral Optical Properties and Its Impact on Radiative Forcing over the Ocean. Remote Sensing, 14(13), 3188. doi: 10.3390/rs14133188. The ground-based measurement of sea salt (SS) aerosol over the ocean requires the massive utilization of satellite-derived aerosol products. In this study, n-order spectral derivatives of aerosol optical depth (AOD) based on wavelength were examined to characterize SS and other aerosol types in terms of their spectral dependence related to their optical properties such as particle size distributions and complex refractive indices. Based on theoretical simulations from the second simulation of a satellite signal in the solar spectrum (6S) model, AOD spectral derivatives of SS were characterized along with other major types including mineral dust (DS), biomass burning (BB), and anthropogenic pollutants (APs). The approach (normalized derivative aerosol index, NDAI) of partitioning aerosol types with intrinsic values of particle size distribution and complex refractive index from normalized first- and second-order derivatives was applied to the datasets from a moderate resolution imaging spectroradiometer (MODIS) as well as by the ground-based aerosol robotic network (AERONET). The results after implementation from multiple sources of data indicated that the proposed approach could be highly effective for identifying and segregating abundant SS from DS, BB, and AP, across an ocean. Consequently, each aerosol’s shortwave radiative forcing and its efficiency could be further estimated in order to predict its impact on the climate. particle size; sea salt aerosol; aerosol optical depth (AOD); complex refractive index; normalized derivative aerosol index (NDAI); spectral derivatives
Bai, Jianhui; Zong, Xuemei; Lanconelli, Christian; Lupi, Angelo; Driemel, Amelie; Vitale, Vito; Li, Kaili; Song, TaoBai, J., X. Zong, C. Lanconelli, A. Lupi, A. Driemel, V. Vitale, K. Li, T. Song, 2022: Long-Term Variations of Global Solar Radiation and Its Potential Effects at Dome C (Antarctica). International Journal of Environmental Research and Public Health, 19(5), 3084. doi: 10.3390/ijerph19053084. An empirical model to predict hourly global solar irradiance under all-sky conditions as a function of absorbing and scattering factors has been applied at the Dome C station in the Antarctic, using measured solar radiation and meteorological variables. The calculated hourly global solar irradiance agrees well with measurements at the ground in 2008–2011 (the model development period) and at the top of the atmosphere (TOA). This model is applied to compute global solar irradiance at the ground and its extinction in the atmosphere caused by absorbing and scattering substances during the 2006–2016 period. A sensitivity study shows that the responses of global solar irradiance to changes in water vapor and scattering factors (expressed by water vapor pressure and S/G, respectively; S and G are diffuse and global solar irradiance, respectively) are nonlinear and negative, and that global solar irradiance is more sensitive to changes in scattering than to changes in water vapor. Applying this empirical model, the albedos at the TOA and the surface in 2006–2016 are estimated and found to agree with the satellite-based retrievals. During 2006–2016, the annual mean observed and estimated global solar exposures decreased by 0.05% and 0.09%, respectively, and the diffuse exposure increased by 0.68% per year, associated with the yearly increase of the S/G ratio by 0.57% and the water vapor pressure by 1.46%. The annual mean air temperature increased by about 1.80 °C over the ten years, and agrees with the warming trends for all of Antarctica. The annual averages were 316.49 Wm−2 for the calculated global solar radiation, 0.332 for S/G, −46.23 °C for the air temperature and 0.10 hPa for the water vapor pressure. The annual mean losses of solar exposure due to absorbing and scattering substances and the total loss were 4.02, 0.19 and 4.21 MJ m−2, respectively. The annual mean absorbing loss was much larger than the scattering loss; their contributions to the total loss were 95.49% and 4.51%, respectively, indicating that absorbing substances are dominant and play essential roles. The annual absorbing, scattering and total losses increased by 0.01%, 0.39% and 0.28% per year, respectively. The estimated and satellite-retrieved annual albedos increased at the surface. The mechanisms of air-temperature change at two pole sites, as well as a mid-latitude site, are discussed. albedo; energy balance; air temperature; absorbing and scattering substances; climate and climate change
Baxter, Ian; Ding, QinghuaBaxter, I., Q. Ding, 2022: An Optimal Atmospheric Circulation Mode in the Arctic Favoring Strong Summertime Sea Ice Melting and Ice–Albedo Feedback. J. Climate, 35(20), 3027-3045. doi: 10.1175/JCLI-D-21-0679.1. Abstract The rapid decline of summer Arctic sea ice over the past few decades has been driven by a combination of increasing greenhouse gases and internal variability of the climate system. However, uncertainties remain regarding spatial and temporal characteristics of the optimal internal atmospheric mode that most favors summer sea ice melting on low-frequency time scales. To pinpoint this mode, we conduct a suite of simulations in which atmospheric circulation is constrained by nudging tropospheric Arctic (60°–90°N) winds within the Community Earth System Model, version 1 (CESM1), to those from reanalysis. Each reanalysis year is repeated for over 10 model years using fixed greenhouse gas concentrations and the same initial conditions. Composites show the strongest September sea ice losses are closely preceded by a common June–August (JJA) barotropic anticyclonic circulation in the Arctic favoring shortwave absorption at the surface. Successive years of strong wind-driven melting also enhance declines in Arctic sea ice through enhancement of the ice–albedo feedback, reaching a quasi-equilibrium response after repeated wind forcing for over 5–6 years, as the effectiveness of the wind-driven ice–albedo feedback becomes saturated. Strong melting favored by a similar wind pattern as observations is detected in a long preindustrial simulation and 400-yr paleoclimate reanalysis, suggesting that a summer barotropic anticyclonic wind pattern represents the optimal internal atmospheric mode maximizing sea ice melting in both the model and natural world over a range of time scales. Considering strong contributions of this mode to changes in Arctic climate, a better understanding of its origin and maintenance is vital to improving future projections of Arctic sea ice.
Boudala, Faisal S.; Milbrandt, Jason A.; Isaac, George A.Boudala, F. S., J. A. Milbrandt, G. A. Isaac, 2022: Evaluation of CanESM Cloudiness, Cloud Type and Cloud Radiative Forcing Climatologies Using the CALIPSO-GOCCP and CERES Datasets. Remote Sensing, 14(15), 3668. doi: 10.3390/rs14153668. In this study, the annual and seasonal climatology of cloud fraction (CF) and cloud type simulated by the Canadian Environmental System Models (CanESMs) version 5 (CanESM5) and version 2 (CanESM2) at their fully coupled and AMIP configurations were validated against the CALIPSO-GOCCP-based CF. The CFs produced using the CALIPSO-COSP simulator based on the CanESMs data at their atmospheric (AMIP) configuration are also evaluated. The simulated shortwave, longwave, and net cloud radiative forcing using the AMIP version of the CanESM5 were also validated against satellite observations based on the recent CERES radiation satellite products. On average, all models have a negative bias in the total CF with global mean biases (MBs) of 2%, 2.4%, 3.9%, 6.4%, 5.6%, and 7.1% for the coupled-CanESM5, AMIP-CanESM5, COSP-AMIP-CanESM5, coupled-CanESM2, AMIP-CanESM2, and COSP-AMIP-CanESM2, respectively, indicating that the CanESM5 has a smaller MB. There were no significant differences between AMIP and coupled versions of the model, but the COSP-based model-simulated data showed larger biases. Although the models captured well the climatological features of CF, they also exhibited a significant bias in CF reaching up to 40% over some geographical locations. This is particularly prevalent over the low level (LL) marine stratocumulus/cumulus, convectively active tropical latitudes that are normally dominated by high level (HL) clouds and at the polar regions where all models showed negative, positive, and positive bias corresponding to these locations, respectively. The AMIP-CanESM5 model performed reasonably well simulating the global mean cloud radiative forcing (CRF) with slight negative biases in the NetCRF at the TOA and surface that would be expected if the model has a positive bias in CF. This inconsistent result may be attributed to the parameterization of the optical properties in the model. The geographical distributions of the model bias in the NetCRF, however, can be significant reaching up to ±40 Wm−2 depending on the location and atmospheric level. The Pearson correlation showed that there is a strong correlation between the global distribution of model bias in NetCRF and CF and it is significantly influenced by the LL and HL clouds. cloud fraction; satellite data; cloud radiative forcing; GCM model evaluation
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. satellite observation; surface downward longwave radiation; Arctic region; machine learning; FengYun-3D; MERSI-2
Chakraborty, T.; Lee, X.; Lawrence, D. M.Chakraborty, T., X. Lee, D. M. Lawrence, 2022: Diffuse Radiation Forcing Constraints on Gross Primary Productivity and Global Terrestrial Evapotranspiration. Earth's Future, 10(8), e2022EF002805. doi: 10.1029/2022EF002805. The diffuse radiation fertilization effect—the increase in plant productivity in the presence of higher diffuse radiation (K↓,d)—is an important yet understudied aspect of atmosphere-biosphere interactions and can modify the terrestrial carbon, energy, and water budgets. The K↓,d fertilization effect links the carbon cycle with clouds and aerosols, all of which are large sources of uncertainties for our current understanding of the Earth system and for future climate projections. Here we establish to what extent observational and modeling uncertainty in sunlight's diffuse fraction (kd) affects simulated gross primary productivity (GPP) and terrestrial evapotranspiration (λE). We find only 48 eddy covariance sites with simultaneous sufficient measurements of K↓,d with none in the tropical climate zone, making it difficult to constrain this mechanism globally using observations. Using a land modeling framework based on the latest version of the Community Land Model, we find that global GPP ranges from 114 Pg C year−1 when using kd forcing from the Modern-Era Retrospective analysis for Research and Applications, version 2 reanalysis to a ∼7% higher value of 122 Pg C year−1 when using the Clouds and the Earth's Radiant Energy System satellite product, with especially strong differences apparent over the tropical region (mean increase ∼9%). The differences in λE, although smaller (−0.4%) due to competing changes in shaded and sunlit leaf transpiration, can be greater than regional impacts of individual forcing agents like aerosols. Our results demonstrate the importance of comprehensively and systematically validating the simulated kd by atmosphere modules as well as the response to differences in kd within land modules across Earth System Models. evapotranspiration; gross primary productivity; atmosphere-biosphere interactions; diffuse radiation fertilization effect; land-surface models
Chan, Man-Yau; Chen, Xingchao; Leung, L. RubyChan, M., X. Chen, L. R. Leung, 2022: A High-Resolution Tropical Mesoscale Convective System Reanalysis (TMeCSR). Journal of Advances in Modeling Earth Systems, 14(9), e2021MS002948. doi: 10.1029/2021MS002948. Modern global reanalysis products have greatly accelerated meteorological research in synoptic-to-planetary-scale phenomena. However, their use in studying tropical mesoscale convective systems (MCSs) and their regional-to-global impact has mostly been limited to supplying initial and boundary conditions for MCS-resolving simulations and providing information about the large-scale environments of MCSs. These limitations are due to difficulties in resolving tropical MCS dynamics in the relatively low-resolution global models and that tropical MCSs often occur over poorly observed regions. In this work, a Tropical MCS-resolving Reanalysis product (TMeCSR) was created over a region with frequent tropical MCSs. This region spans the tropical Indian Ocean, tropical continental Asia, Maritime Continent, and Western Pacific. TMeCSR is produced by assimilating all-sky infrared radiances from geostationary satellites and other conventional observations into an MCS-resolving regional model using the Ensemble Kalman Filter. The resulting observation-constrained high-resolution (9-km grid spacing) data set is available hourly during the boreal summer (June-August) of 2017, during which widespread severe flooding occurred. Comparisons of TMeCSR and European Center for Medium Range Weather Forecast Reanalysis version 5 (ERA5) against independent satellite retrievals indicate that TMeCSR's cloud and multiscale rain fields are better than those of ERA5. Furthermore, TMeCSR better captured the diurnal variability of rainfall and the statistical characteristics of MCSs. Forecasts initialized from TMeCSR also have more accurate rain and clouds than those initialized from ERA5. The TMeCSR and ERA5 forecasts have similar performances with respect to sounding and surface observations. These results indicate that TMeCSR is a promising MCS-resolving data set for tropical MCS studies. reanalysis; data assimilation; mesoscale convective system
Chao, Li-Wei; Muller, Jacob C.; Dessler, Andrew E.Chao, L., J. C. Muller, A. E. Dessler, 2022: Impacts of the Unforced Pattern Effect on the Cloud Feedback in CERES Observations and Climate Models. Geophysical Research Letters, 49(2), e2021GL096299. doi: 10.1029/2021GL096299. The equilibrium climate sensitivity estimated from different sources is inconsistent due to its dependence on the surface warming pattern. Cloud feedbacks have been identified as the major contributor to this so-called pattern effect. We find a large unforced pattern effect in CERES data, with cloud feedback estimated from two consecutive 125-month periods (March 2000–July 2010 and August 2010–December 2020) changing from −0.45 ± 0.85 to +1.2 ± 0.78 W/m2/K. When comparing to models, 27% of consecutive 10-year segments in CMIP6 control runs have differences similar to the observations. We also compare the spatial patterns in the CERES data to those in climate models and find they are similar, with the East Pacific playing a key role. This suggests that the impact of the unforced pattern effect can be significant and that models are capable of reproducing its global-average magnitude. climate models; cloud feedback; pattern effect
Chen, Guangcan; Zhang, Xiangdong; Fu, YunfeiChen, G., X. Zhang, Y. Fu, 2022: Diurnal Variation in Clouds and Radiative Budgets Over the Tibetan Plateau During Summer Using CERES Data. Journal of Geophysical Research: Atmospheres, 127(16), e2021JD036329. doi: 10.1029/2021JD036329. Diurnal variations in clouds and radiation budgets over four subareas of the Tibetan Plateau (TP) during summer (June–August) are analyzed using the Clouds and the Earth's Radiant Energy System (CERES) synoptic 1° (SYN1deg) data from 2000 to 2020. The results show that the total cloud amount decreases from southeast to northwest and is larger during daytime (71.1%) than nighttime (67.2%) over the entire TP. High-clouds develop in the afternoon, persist during nighttime, and dissipate after sunrise. Low clouds develop after sunrise and dissipate in the afternoon over the entire TP, but show opposite temporal variation over the Kunlun Mountains. The net radiation budget at the top-of-atmosphere reaches its maximum at noon. The surface net radiation budget is positive in the daytime and negative at nighttime. These features are mainly adjusted by the cloud distribution. The diurnal variations in heating rate over the four subareas are similar in the upper atmosphere but different in the lower layer. The low-atmosphere heating rate shows a maximum value over the center-south (CS) subarea, while it is lowest over the west (W) subarea. Internal cloud forcing has distinct regional differences over the four subareas: it shows a heating effect in the low atmosphere and a cooling effect in the middle atmosphere over the CS subarea, whereas over the W subarea it shows a radiative cooling effect in the low atmosphere and no significant radiative effect in the middle layer. The findings of this study help toward improving our understanding of the TP's energy cycle. diurnal variation; heating rate; cloud cover; internal cloud forcing; Tibet Plateau
Chen, Xingan; Huang, Yuefei; Nie, Chong; Zhang, Shuo; Wang, Guangqian; Chen, Shiliu; Chen, ZhichaoChen, X., Y. Huang, C. Nie, S. Zhang, G. Wang, S. Chen, Z. Chen, 2022: A long-term reconstructed TROPOMI solar-induced fluorescence dataset using machine learning algorithms. Scientific Data, 9(1), 427. doi: 10.1038/s41597-022-01520-1. Photosynthesis is a key process linking carbon and water cycles, and satellite-retrieved solar-induced chlorophyll fluorescence (SIF) can be a valuable proxy for photosynthesis. The TROPOspheric Monitoring Instrument (TROPOMI) on the Copernicus Sentinel-5P mission enables significant improvements in providing high spatial and temporal resolution SIF observations, but the short temporal coverage of the data records has limited its applications in long-term studies. This study uses machine learning to reconstruct TROPOMI SIF (RTSIF) over the 2001–2020 period in clear-sky conditions with high spatio-temporal resolutions (0.05° 8-day). Our machine learning model achieves high accuracies on the training and testing datasets (R2 = 0.907, regression slope = 1.001). The RTSIF dataset is validated against TROPOMI SIF and tower-based SIF, and compared with other satellite-derived SIF (GOME-2 SIF and OCO-2 SIF). Comparing RTSIF with Gross Primary Production (GPP) illustrates the potential of RTSIF for estimating gross carbon fluxes. We anticipate that this new dataset will be valuable in assessing long-term terrestrial photosynthesis and constraining the global carbon budget and associated water fluxes. Phenology; Ecosystem ecology
Chen, Zhe; Wang, Minghuai; Zhang, Haipeng; Lin, Shuheng; Guo, Zhun; Jiang, Yiquan; Zhou, ChenChen, Z., M. Wang, H. Zhang, S. Lin, Z. Guo, Y. Jiang, C. Zhou, 2022: Long-term change in low-cloud cover in Southeast China during cold seasons. Atmospheric and Oceanic Science Letters, 15(6), 100222. doi: 10.1016/j.aosl.2022.100222. Southeast China has comparable stratus cloud to that over the oceans, especially in the cold seasons (winter and spring), and this cloud has a substantial impact on energy and hydrological cycles. However, uncertainties remain across datasets and simulation results about the long-term trend in low-cloud cover in Southeast China, making it difficult to understand climate change and related physical processes. In this study, multiple datasets and numerical simulations were applied to show that low-cloud cover in Southeast China has gone through two stages since 1980—specifically, a decline and then a rise, with the turning point around 2008. The regional moisture transport plays a crucial role in low-cloud cover changes in the cold seasons and is mainly affected by the Hadley Cell in winter and the Walker Circulation in spring, respectively. The moisture transport was not well simulated in CMIP6 climate models, leading to poor simulation of the low-cloud cover trend in these models. This study provides insights into further understanding the regional climate changes in Southeast China. 摘要 中国东南地区在冬春冷季节盛行低云, 对局地能量平衡和水文循环有重要的作用. 本研究使用多套数据和数值模拟结果, 分析这一地区冷季节内低云云量在1980年至2017年的长期变化. 结果表明, 低云云量经历了先下降后上升的趋势变化, 转折点出现在2008年左右. 局地水汽通量输送在影响低云云量的变化中起着至关重要的作用, 其在冬季和春季分别受到哈德莱环流和沃克环流的影响. CMIP6中的气候模式对水汽通量输送的模拟能力欠佳, 影响了对低云云量的模拟结果. Hadley cell; Large-scale circulation; Low-cloud cover; Pacific walker circulation; 低云云量; 关键词:; 哈德莱环流; 大尺度环流场; 沃克环流
Chtirkova, Boriana; Folini, Doris; Correa, Lucas Ferreira; Wild, MartinChtirkova, B., D. Folini, L. F. Correa, M. Wild, 2022: Internal Variability of All-Sky and Clear-Sky Surface Solar Radiation on Decadal Timescales. Journal of Geophysical Research: Atmospheres, 127(12), e2021JD036332. doi: 10.1029/2021JD036332. Internal variability comprises all processes that occur within the climate system without any natural or anthropogenic forcing. Climate-driving variables like the surface solar radiation (SSR) are shown to exhibit unforced trends (i.e., trends due to internal variability) of magnitudes comparable to the magnitude of the forced signal even on decadal timescales. We use annual mean data from 50 models participating in the preindustrial control experiment (piControl) of the Coupled Model Intercomparison Project-Phase 6 (CMIP6) to give quantitative grid-box specific estimates of the magnitudes of unforced trends. To characterize a trend distribution, symmetrical around 0, we use the 75th percentile of all possible values, which corresponds to a positive trend with 25% chance of occurrence. For 30-year periods and depending on geographical location, this trend has a magnitude between 0.15 and 2.1 W m−2/decade for all-sky and between 0.04 and 0.38 W m−2/decade for clear-sky SSR. The corresponding area-weighted medians are 0.69 W m−2/decade for all-sky trends and 0.17 W m−2/decade for clear-sky trends. The influence of internal variability is on average six times smaller in clear-sky, compared to all-sky SSR. The relative uncertainties in the physical representation, derived from the CMIP6 inter-model spread, are ±32% for all-sky and ±43% for clear-sky SSR trends. Reasons for differences between models like horizontal resolution, aerosol handling, and the representation of atmospheric and oceanic phenomena are investigated. The results can be used in the analysis of observational time series by attributing a probability for a trend to be caused by internal variability, given its magnitude, length, and location. internal variability; surface solar radiation; dimming and brightening; CMIP6; unforced trends
Chu, Wenchao; Lin, Yanluan; Zhao, MingChu, W., Y. Lin, M. Zhao, 2022: Implementation and Evaluation of a Double-Plume Convective Parameterization in NCAR CAM5. J. Climate, 35(2), 617-637. doi: 10.1175/JCLI-D-21-0267.1. Abstract Performance of global climate models (GCMs) is strongly affected by the cumulus parameterization (CP) used. Similar to the approach in GFDL AM4, a double-plume CP, which unifies the deep and shallow convection in one framework, is implemented and tested in the NCAR Community Atmospheric Model version 5 (CAM5). Based on the University of Washington (UW) shallow convection scheme, an additional plume was added to represent the deep convection. The shallow and deep plumes share the same cloud model, but use different triggers, fractional mixing rates, and closures. The scheme was tested in single-column, short-term hindcast, and AMIP simulations. Compared with the default combination of the Zhang–McFarlane scheme and UW scheme in CAM5, the new scheme tends to produce a top-heavy mass flux profile during the active monsoon period in the single-column simulations. The scheme increases the intensity of tropical precipitation, closer to TRMM observations. The new scheme increased subtropical marine boundary layer clouds and high clouds over the deep tropics, both in better agreement with observations. Sensitivity tests indicate that regime-dependent fractional entrainment rates of the deep plume are desired to improve tropical precipitation distribution and upper troposphere temperature. This study suggests that a double-plume approach is a promising way to combine shallow and deep convections in a unified framework.
Cutler, Lauren; Brunke, Michael A.; Zeng, XubinCutler, L., M. A. Brunke, X. Zeng, 2022: Re-Evaluation of Low Cloud Amount Relationships With Lower-Tropospheric Stability and Estimated Inversion Strength. Geophysical Research Letters, 49(12), e2022GL098137. doi: 10.1029/2022GL098137. Lower-tropospheric stability (LTS) and estimated inversion strength (EIS) have a widely accepted relationship with low cloud amount and are key observational foundations for understanding and modeling low-level stratiform clouds. Using the updated surface-based and satellite cloud data, we find that low cloud amount is not as strongly correlated with LTS, and not as sensitive to LTS, as established in the past. EIS does not provide a stronger correlation with low cloud amount than LTS over all eight regions (including the midlatitudes). Further analyzing the relationships between LTS and EIS with different types of low clouds, we find that there is a strong correlation of LTS and EIS with stratocumulus only. This explains the weaker correlation of low cloud fraction (including cumulus, stratocumulus, and stratus) to both LTS and EIS. These results also suggest the need to re-evaluate these relationships in Earth system models.
Dauhut, Thibaut; Hohenegger, CathyDauhut, T., C. Hohenegger, 2022: The Contribution of Convection to the Stratospheric Water Vapor: The First Budget Using a Global Storm-Resolving Model. Journal of Geophysical Research: Atmospheres, 127(5), e2021JD036295. doi: 10.1029/2021JD036295. The deepest convection on Earth injects water in the tropical stratosphere, but its contribution to the global stratospheric water budget remains uncertain. The Global Storm-Resolving Model ICOsahedral Non-hydrostatic is used to simulate the moistening of the lower stratosphere for 40 days during boreal summer. The decomposition of the water vapor budget in the tropical lower stratosphere (TLS, 10°S–30°N, and 17–20 km altitude) indicates that the average moistening (+21 Tg) over the simulated 40-day period is the result of the combined effect of the vertical water vapor transport from the troposphere (+27 Tg), microphysical phase changes and subgrid-scale transport (+2 Tg), partly compensated by horizontal water vapor export (−8 Tg). The very deep convective systems, explicitly represented thanks to the employed 2.5 km grid spacing of the model, are identified using the very low Outgoing Longwave Radiation of their cold cloud tops. The water vapor budget reveals that the vertical transport, the sublimation and the subgrid-scale transport at their top contribute together to 11% of the water vapor mass input into the TLS. convection; water vapor; budget; global storm-resolving model; ICON; stratosphere
Devi, Archana; Satheesh, Sreedharan K.Devi, A., S. K. Satheesh, 2022: Global maps of aerosol single scattering albedo using combined CERES-MODIS retrieval. Atmospheric Chemistry and Physics, 22(8), 5365-5376. doi: 10.5194/acp-22-5365-2022. Abstract. Single scattering albedo (SSA) is a leading contributor to the uncertainty in aerosol radiative impact assessments. Therefore accurate information on aerosol absorption is required on a global scale. In this study, we have applied a multi-satellite algorithm to retrieve SSA (550 nm) using the concept of critical optical depth. Global maps of SSA were generated following this approach using spatially and temporally collocated data from Clouds and the Earth's Radiant Energy System (CERES) and Moderate Resolution Imaging Spectroradiometer (MODIS) sensors on board Terra and Aqua satellites. Limited comparisons against airborne observations over India and surrounding oceans were generally in agreement within ±0.03. Global mean SSA estimated over land and ocean is 0.93 and 0.97, respectively. Seasonal and spatial distribution of SSA over various regions are also presented. Sensitivity analysis to various parameters indicate a mean uncertainty around ±0.044 and shows maximum sensitivity to changes in surface albedo. The global maps of SSA, thus derived with improved accuracy, provide important input to climate models for assessing the climatic impact of aerosols on regional and global scales.
Diamond, Michael S.; Gristey, Jake J.; Kay, Jennifer E.; Feingold, GrahamDiamond, M. S., J. J. Gristey, J. E. Kay, G. Feingold, 2022: Anthropogenic aerosol and cryosphere changes drive Earth’s strong but transient clear-sky hemispheric albedo asymmetry. Communications Earth & Environment, 3(1), 1-10. doi: 10.1038/s43247-022-00546-y. A striking feature of the Earth system is that the Northern and Southern Hemispheres reflect identical amounts of sunlight. This hemispheric albedo symmetry comprises two asymmetries: The Northern Hemisphere is more reflective in clear skies, whereas the Southern Hemisphere is cloudier. Here we show that the hemispheric reflection contrast from differences in continental coverage is offset by greater reflection from the Antarctic than the Arctic, allowing the net clear-sky asymmetry to be dominated by aerosol. Climate model simulations suggest that historical anthropogenic aerosol emissions drove a large increase in the clear-sky asymmetry that would reverse in future low-emission scenarios. High-emission scenarios also show decreasing asymmetry, instead driven by declines in Northern Hemisphere ice and snow cover. Strong clear-sky hemispheric albedo asymmetry is therefore a transient feature of Earth’s climate. If all-sky symmetry is maintained, compensating cloud changes would have uncertain but important implications for Earth’s energy balance and hydrological cycle. Atmospheric chemistry; Climate and Earth system modelling; Cryospheric science
Dodson, J. Brant; Robles, Marilé Colón; Rogerson, Tina M.; Taylor, Jessica E.Dodson, J. B., M. Robles, . Colón, T. M. Rogerson, J. E. Taylor, 2022: Do citizen science Intense Observation Periods increase data usability? A deep dive of the NASA GLOBE Clouds data set with satellite comparisons. Earth and Space Science, n/a(n/a), e2021EA002058. doi: 10.1029/2021EA002058. The Global Learning and Observations to Benefit the Environment (GLOBE) citizen science program has recently conducted a series of month-long intensive observation periods (IOPs), asking the public to submit daily reports on cloud and sky conditions from all regions of Earth. This provides a wealth of crowdsourced observations from the ground, which complements other conventional scientific cloud data. In addition, the GLOBE reports are matched in space and time with geostationary and low Earth orbit satellites, which allows for a straightforward comparison of cloud properties, and minimizes the biases associated with mismatched sampling between participants and satellites. The matched GLOBE dataset is used to calculate the mean observed cloud cover by atmospheric level both worldwide and by region. The overall magnitudes of cloud cover between the GLOBE participants and the matched satellites agree within 10%, which is notable given the distinctly different natures of the data sources. The mean vertical cloud profiles show GLOBE reporting more low-level clouds and fewer high-level clouds than satellites. The low cloud disagreement is likely related to satellites missing low clouds when high clouds block their view. Conversely, the high cloud disagreement is related primarily to cloud opacity, as satellites may miss some optically thin clouds. Monte Carlo testing shows the results to be robust, and the tripled amount of IOP data reduces uncertainty by half. These findings also highlight ways in which citizen science IOP data may be used to support scientific research while accounting for their unique properties. Monte Carlo; cloud cover; citizen science; global data set; satellite validation; vertical cloud structure
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. land/atmosphere interactions; aerosol/cloud interactions; global climate models; global change
Feng, Chunjie; Zhang, Xiaotong; Xu, Jiawen; Yang, Shuyue; Guan, Shikang; Jia, Kun; Yao, YunjunFeng, C., X. Zhang, J. Xu, S. Yang, S. Guan, K. Jia, Y. Yao, 2022: Comprehensive assessment of global atmospheric downward longwave radiation in the state-of-the-art reanalysis using satellite and flux tower observations. Climate Dynamics. doi: 10.1007/s00382-022-06366-2. The atmospheric downward longwave radiation at the Earth’s surface (Ld) is an important parameter for investigating greenhouse effects and global climate changes. Reanalysis data have been widely applied to obtain surface radiation components. Since new generation reanalysis data have been released, a comprehensive evaluation of the Ld predictions from the latest reanalysis data using ground measurements is still necessary. In this study, the Ld estimates of four representative reanalysis data (CFSR, JRA-55, ERA5, and MERRA2) were evaluated using ground observations at 383 stations from the AmeriFlux, AsiaFlux, BSRN, Buoy, FLUXNET, and SURFEAD networks. The evaluation results manifested that the overall root mean square errors (mean bias errors) of daily mean Ld values over the global surface were 21.1 (− 1.8) W m−2, 22.4 (− 3.9) W m−2, 19.3 (− 3.6) W m−2, 25.2 (− 12.6) W m−2, and 20.5 (3.1) W m−2 for CFSR, JRA-55, ERA5, MERAA2, and CERES-SYN, respectively. Compared with the CERES-SYN satellite retrievals, the ERA5 (CFSR) daily mean Ld estimates had relatively smaller overall root mean square errors (mean bias errors) over the global land surface. Over the global ocean surface, the JRA-55 daily mean Ld estimates had comparable mean bias errors (MBEs) with CERES-SYN. After removing the MBEs, the best annual mean Ld estimate was 344.0 (± 3) W m−2 over the global surface of 2001 to 2020. The spatial distributions and long-term trends of Ld for the selected four reanalysis data and CERES-SYN were also investigated in this study. The comprehensive assessment of the Ld products from reanalysis data and satellite retrievals in this study would be helpful for climate change studies. Reanalysis; Surface downward longwave radiation; CERES-SYN; Ground observation
Ferris, Laur; Gong, Donglai; Clayson, Carol Anne; Merrifield, Sophia; Shroyer, Emily L.; Smith, Madison; Laurent, Louis StFerris, L., D. Gong, C. A. Clayson, S. Merrifield, E. L. Shroyer, M. Smith, L. S. Laurent, 2022: Shear Turbulence in the High-Wind Southern Ocean Using Direct Measurements. J. Phys. Oceanogr., 52(10), 2325-2341. doi: 10.1175/JPO-D-21-0015.1. Abstract The ocean surface boundary layer is a gateway of energy transfer into the ocean. Wind-driven shear and meteorologically forced convection inject turbulent kinetic energy into the surface boundary layer, mixing the upper ocean and transforming its density structure. In the absence of direct observations or the capability to resolve subgrid-scale 3D turbulence in operational ocean models, the oceanography community relies on surface boundary layer similarity scalings (BLS) of shear and convective turbulence to represent this mixing. Despite their importance, near-surface mixing processes (and ubiquitous BLS representations of these processes) have been undersampled in high-energy forcing regimes such as the Southern Ocean. With the maturing of autonomous sampling platforms, there is now an opportunity to collect high-resolution spatial and temporal measurements in the full range of forcing conditions. Here, we characterize near-surface turbulence under strong wind forcing using the first long-duration glider microstructure survey of the Southern Ocean. We leverage these data to show that the measured turbulence is significantly higher than standard shear-convective BLS in the shallower parts of the surface boundary layer and lower than standard shear-convective BLS in the deeper parts of the surface boundary layer; the latter of which is not easily explained by present wave-effect literature. Consistent with the CBLAST (Coupled Boundary Layers and Air Sea Transfer) low winds experiment, this bias has the largest magnitude and spread in the shallowest 10% of the actively mixing layer under low-wind and breaking wave conditions, when relatively low levels of turbulent kinetic energy (TKE) in surface regime are easily biased by wave events. Significance Statement Wind blows across the ocean, turbulently mixing the water close to the surface and altering its properties. Without the ability to measure turbulence in remote locations, oceanographers use approximations called boundary layer scalings (BLS) to estimate the amount of turbulence caused by the wind. We compared turbulence measured by an underwater robot to turbulence estimated from wind speed to determine how well BLS performs in stormy places. We found that in both calm and stormy conditions, estimates are 10 times too large closest to the surface and 10 times too small deeper within the turbulently mixed surface ocean.
Francis, Diana; Fonseca, Ricardo; Nelli, Narendra; Bozkurt, Deniz; Picard, Ghislain; Guan, BinFrancis, D., R. Fonseca, N. Nelli, D. Bozkurt, G. Picard, B. Guan, 2022: Atmospheric rivers drive exceptional Saharan dust transport towards Europe. Atmospheric Research, 266, 105959. doi: 10.1016/j.atmosres.2021.105959. This study highlights the occurrence of atmospheric rivers (ARs) over northwest Africa towards Europe, which were accompanied by intense episodes of Saharan dust transport all the way to Scandinavia, in the winter season. Using a combination of observational and reanalysis data, we investigate two extreme dusty AR events in February 2021 and assess their impact on snow melt in the Alps. The warm, moist, and dusty air mass (spatially-averaged 2-meter temperature and water vapour mixing ratio anomalies of up to 8 K and 3 g kg−1, and aerosol optical depths and dust loadings of up to 0.85 and 11 g m−2, respectively) led to a 50% and 40% decrease in snow depth and surface albedo, respectively, in less than one month during the winter season. ARs over northwest Africa show increasing trends over the past 4 decades, with 78% of AR events associated with severe dust episodes over Europe. Dust aerosols; Atmospheric rivers; European Alps; Sahara Desert; Snow melting; Water vapour
Francis, Diana; Fonseca, Ricardo; Nelli, Narendra; Teixido, Oriol; Mohamed, Ruqaya; Perry, RichardFrancis, D., R. Fonseca, N. Nelli, O. Teixido, R. Mohamed, R. Perry, 2022: Increased Shamal winds and dust activity over the Arabian Peninsula during the COVID-19 lockdown period in 2020. Aeolian Research, 55, 100786. doi: 10.1016/j.aeolia.2022.100786. While anthropogenic pollutants have decreased during the lockdown imposed as an effort to contain the spread of the Coronavirus disease 2019 (COVID-19), changes in particulate matter (PM) do not necessarily exhibit the same tendency. This is the case for the eastern Arabian Peninsula, where in March–June 2020, and with respect to the same period in 2016–2019, a 30 % increase in PM concentration is observed. A stronger than normal nocturnal low-level jet and subtropical jet over parts of Saudi Arabia, in response to anomalous convection over the tropical Indian Ocean, promoted enhanced and more frequent episodes of Shamal winds over the Arabian Peninsula. Increased surface winds associated with the downward mixing of momentum to the surface fostered, in turn, dust lifting and increased PM concentrations. The stronger low-level winds also favoured long-range transport of aerosols, changing the PM values downstream. The competing effects of reduced anthropogenic and increased dust concentrations leave a small positive signal (20 W m−2 with respect to the baseline period, owing to a clearer environment and weaker winds. It is concluded that a reduction in anthropogenic emissions due to the lockdown does not necessarily go hand in hand with lower particulate matter concentrations. Therefore, emissions reduction strategies need to account for feedback effects in order to reach the planned long-term outcomes. Arabian Peninsula; Low-level jet; Particulate Matter; Rossby Wavetrain; Shamal Winds; Surface Radiation Budget
Francis, Diana; Nelli, Narendra; Fonseca, Ricardo; Weston, Michael; Flamant, Cyrille; Cherif, CharfeddineFrancis, D., N. Nelli, R. Fonseca, M. Weston, C. Flamant, C. Cherif, 2022: The dust load and radiative impact associated with the June 2020 historical Saharan dust storm. Atmospheric Environment, 268, 118808. doi: 10.1016/j.atmosenv.2021.118808. In June 2020, a major dust outbreak occurred in the Sahara that impacted the tropical Atlantic Ocean. In this study, the dust load and radiative forcing of the dust plumes on both the atmosphere and ocean surface is investigated by means of observations and modelling. We estimated dust loadings in excess of 8 Tg over the eastern tropical Atlantic, comparable to those observed over the desert during major Saharan dust storms. The dust induced an up to 1.1 K net warming of the ocean surface and a 1.8K warming of the air temperature (i.e., two to three times the respective climatological standard deviations), with a +14 W m−2 (∼28% of the mean value) increase in the surface net radiation flux at night. As the dust plumes extended all the way to the Caribbean, it is possible that this historical dust event helped fuel the record-breaking 2020 Atlantic hurricane season. Dust aerosols; Radiative forcing; WRF-Chem; Sahara; Tropical Atlantic
Giraldo, Jorge A.; del Valle, Jorge I.; González-Caro, Sebastián; Sierra, Carlos A.Giraldo, J. A., J. I. del Valle, S. González-Caro, C. A. Sierra, 2022: Intra-annual isotope variations in tree rings reveal growth rhythms within the least rainy season of an ever-wet tropical forest. Trees, 36(3), 1039-1052. doi: 10.1007/s00468-022-02271-7. Isotope variation (δ18O) in wood suggests new insights on growth rhythms in trees growing in tropical forest with extremely high precipitation, without seasonal droughts or flooding. Biogeographical Chocó region; C isotopes; Dendrochronology; O isotopes; Tropical trees
González-Bárcena, David; Bermejo-Ballesteros, Juan; Pérez-Grande, Isabel; Sanz-Andrés, ÁngelGonzález-Bárcena, D., J. Bermejo-Ballesteros, I. Pérez-Grande, Á. Sanz-Andrés, 2022: Selection of time-dependent worst-case thermal environmental conditions for Low Earth Orbit spacecrafts. Advances in Space Research, 70(7), 1847-1868. doi: 10.1016/j.asr.2022.06.060. When facing the thermal analysis of a Low Earth Orbit satellite, selecting the worst-case orbit where the minimum and maximum temperatures are reached is essential for ensuring the success of the mission. Typical orbits have a non-constant Solar Beta Angle throughout the year providing a wide range of orbits with different heat loads and eclipses. It is possible to focus the analysis on a single orbit configuration by a rough analysis using a simple model. In order to achieve this, every potential orbit with their corresponding thermal environmental parameters must be analysed based on real data. The direct solar radiation, the albedo and the Earth Outgoing Longwave Radiation (OLR) characterize the thermal environment to be taken into account. However, their values have a wide variability which depend on many parameters. Based on the characteristics of the orbit and the system thermo-optical properties and characteristic time, it is possible to obtain particularized profiles of albedo and OLR that would lead the system to its maximum and minimum temperatures. The conventional criteria, which is studied here in depth, provides two constant values of albedo and OLR as the hot and cold worst-cases. This is suitable for massive system or cases in which the characteristics times of the system are high. For lighter elements or low characteristic times, temperatures throughout the orbit deviate considerably from the real behaviour. In contrast, the methodology here proposed provides a time-dependant profile that allows for the determination of a system temperature response closer to the real one, together with the potential minimum and maximum temperatures of the orbit, in order to optimize the design and avoid the oversizing. Albedo; Thermal environment; OLR; LEO; Thermal analysis; Worst-case
Haghighatnasab, Mahnoosh; Kretzschmar, Jan; Block, Karoline; Quaas, JohannesHaghighatnasab, M., J. Kretzschmar, K. Block, J. Quaas, 2022: Impact of Holuhraun volcano aerosols on clouds in cloud-system-resolving simulations. Atmospheric Chemistry and Physics, 22(13), 8457-8472. doi: 10.5194/acp-22-8457-2022. Abstract. Increased anthropogenic aerosols result in an enhancement in cloud droplet number concentration (Nd), which consequently modifies the cloud and precipitation process. It is unclear how exactly the cloud liquid water path (LWP) and cloud fraction respond to aerosol perturbations. A volcanic eruption may help to better understand and quantify the cloud response to external perturbations, with a focus on the short-term cloud adjustments. The goal of the present study is to understand and quantify the response of clouds to a selected volcanic eruption and to thereby advance the fundamental understanding of the cloud response to external forcing. In this study we used the ICON (ICOsahedral Non-hydrostatic) model in its numerical weather prediction setup at a cloud-system-resolving resolution of 2.5 km horizontally, to simulate the region around the Holuhraun volcano for 1 week (1–7 September 2014). A pair of simulations, with and without the volcanic aerosol plume, allowed us to assess the simulated effective radiative forcing and its mechanisms, as well as its impact on adjustments of LWP and cloud fraction to the perturbations of Nd. In comparison to MODIS (Moderate Resolution Imaging Spectroradiometer) satellite retrievals, a clear enhancement of Nd due to the volcanic aerosol is detected and attributed. In contrast, no changes in either LWP or cloud fraction could be attributed. The on average almost unchanged LWP is a result of some LWP enhancement for thick clouds and a decrease for thin clouds.
Ham, Seung-Hee; Kato, Seiji; Rose, Fred G.; Sun-Mack, Sunny; Chen, Yan; Miller, Walter F.; Scott, Ryan C.Ham, S., S. Kato, F. G. Rose, S. Sun-Mack, Y. Chen, W. F. Miller, R. C. Scott, 2022: Combining Cloud Properties from CALIPSO, CloudSat, and MODIS for Top-of-Atmosphere (TOA) Shortwave Broadband Irradiance Computations: Impact of Cloud Vertical Profiles. J. Appl. Meteor. Climatol., 61(10), 1449-1471. doi: 10.1175/JAMC-D-21-0260.1. Abstract Cloud vertical profile measurements from the CALIPSO and CloudSat active sensors are used to improve top-of-atmosphere (TOA) shortwave (SW) broadband (BB) irradiance computations. The active sensor measurements, which occasionally miss parts of the cloud columns because of the full attenuation of sensor signals, surface clutter, or insensitivity to a certain range of cloud particle sizes, are adjusted using column-integrated cloud optical depth derived from the passive MODIS sensor. Specifically, we consider two steps in generating cloud profiles from multiple sensors for irradiance computations. First, cloud extinction coefficient and cloud effective radius (CER) profiles are merged using available active and passive measurements. Second, the merged cloud extinction profiles are constrained by the MODIS visible scaled cloud optical depth, defined as a visible cloud optical depth multiplied by (1 − asymmetry parameter), to compensate for missing cloud parts by active sensors. It is shown that the multisensor-combined cloud profiles significantly reduce positive TOA SW BB biases, relative to those with MODIS-derived cloud properties only. The improvement is more pronounced for optically thick clouds, where MODIS ice CER is largely underestimated. Within the SW BB (0.18–4 μm), the 1.04–1.90-μm spectral region is mainly affected by the CER, where both the cloud absorption and solar incoming irradiance are considerable. Significance Statement The purpose of this study is to improve shortwave irradiance computations at the top of the atmosphere by using combined cloud properties from active and passive sensor measurements. Relative to the simulation results with passive sensor cloud measurements only, the combined cloud profiles provide more accurate shortwave simulation results. This is achieved by more realistic profiles of cloud extinction coefficient and cloud particle effective radius. The benefit is pronounced for optically thick clouds composed of large ice particles.
Hartmann, Dennis L.; Dygert, Brittany D.Hartmann, D. L., B. D. Dygert, 2022: Global Radiative Convective Equilibrium With a Slab Ocean: SST Contrast, Sensitivity and Circulation. Journal of Geophysical Research: Atmospheres, 127(12), e2021JD036400. doi: 10.1029/2021JD036400. Warming experiments with a uniformly insolated, non-rotating climate model with a slab ocean are conducted by increasing the solar irradiance. As the global mean surface temperature is varied across the range from 289 to 319K, the sea surface temperature (SST) contrast at first declines, then increases then declines again. Increasing SST contrast with global warming is associated with reduced climate sensitivity, while decreasing SST contrast is associated with enhanced climate sensitivity. The changing SST contrast and climate sensitivity are both related fundamentally to the effect of water vapor on clear-sky radiative cooling. The clouds in the convective region are always more reflective than those in the subsiding region and so always act to reduce the SST contrast. At lower temperatures between 289 and 297 K the shortwave suppression of SST contrast increases faster than the longwave enhancement of SST contrast. At warmer temperatures between 297 and 309 K the longwave enhancement of SST contrast with warming is stronger than the shortwave suppression of SST contrast, so that the SST contrast increases. Above 309 K the greenhouse effect in the subsiding region begins to grow, the SST contrast declines and the climate sensitivity increases. The transitions at 297 and 309 K can be related to the increasing vapor pressure path with warming. The mass circulation rate between warm and cool regions consists of shallow and deep cells. Both cells increase in strength with SST contrast. The lower cell remains connected to the surface, while the upper cell rises to maintain a roughly constant temperature. climate change; climate model; climate feedbacks
Heidinger, Andrew K.; Foster, Michael J.; Knapp, Kenneth R.; Schmit, Timothy J.Heidinger, A. K., M. J. Foster, K. R. Knapp, T. J. Schmit, 2022: Using GOES-R ABI Full-Disk Reflectance as a Calibration Source for the GOES Imager Visible Channels. Remote Sensing, 14(15), 3630. doi: 10.3390/rs14153630. The availability of onboard calibration for solar reflectance channels on recently launched advanced geostationary imagers provides an opportunity to revisit the calibration of the visible channels on past geostationary imagers, which lacked onboard calibration systems. This study used the data from the Advanced Baseline Imager (ABI) on GOES-16 and GOES-17 to calibrate the visible channels on the GOES-IP (GOES-8, -9, -10, -11, -12, -13, and -15) sensors (1994–2021). The visible channels are dominant sources of information for many of the essential climate variables from these sensors. The technique developed uses the stability of the integrated full-disk reflectance to define a calibration target that is applied to past sensors to generate new calibration equations. These equations are found to be stable and agree well with other established techniques. Given the lack of assumptions and ease of application, this technique offers a new calibration method that can be used to complement existing techniques used by the operational space agencies with the GSICS Project. In addition, its simplicity allows for its application to data that existed prior to many of the reference data employed in current calibration methods. calibration; climate; GOES
Herrington, Adam R.; Lauritzen, Peter H.; Lofverstrom, Marcus; Lipscomb, William H.; Gettelman, Andrew; Taylor, Mark A.Herrington, A. R., P. H. Lauritzen, M. Lofverstrom, W. H. Lipscomb, A. Gettelman, M. A. Taylor, 2022: Impact of grids and dynamical cores in CESM2.2 on the surface mass balance of the Greenland Ice Sheet. Journal of Advances in Modeling Earth Systems, n/a(n/a), e2022MS003192. doi: 10.1029/2022MS003192. Six different configurations, a mixture of grids and atmospheric dynamical cores available in the Community Earth System Model, version 2.2 (CESM2.2), are evaluated for their skill in representing the climate of the Arctic and the surface mass balance of the Greenland Ice Sheet (GrIS). The finite-volume dynamical core uses structured, latitude-longitude grids, whereas the spectral-element dynamical core is built on unstructured meshes, permitting grid flexibility such as quasi-uniform grid spacing globally. The 1° − 2° latitude-longitude and quasi-uniform unstructured grids systematically overestimate both accumulation and ablation over the GrIS. Of these 1° − 2° grids, the latitude-longitude grids outperform the quasi-uniform unstructured grids because they have more degrees of freedom to represent the GrIS. Two Arctic-refined meshes, with 1/4° and 1/8° refinement over Greenland, were developed for the spectral-element dynamical core and are documented here as newly supported configurations in CESM2.2. The Arctic meshes substantially improve the simulated clouds and precipitation rates in the Arctic. Over Greenland, these meshes skillfully represent accumulation and ablation processes, leading to a more realistic GrIS surface mass balance. As CESM is in the process of transitioning away from conventional latitude-longitude grids, these new Arctic-refined meshes improve the representation of polar processes in CESM by recovering resolution lost in the transition to quasi-uniform grids, albeit at increased computational cost.
Hu, Zhiyuan; Jin, Qinjian; Ma, Yuanyuan; Ji, Zhenming; Zhu, Xian; Dong, WenjieHu, Z., Q. Jin, Y. Ma, Z. Ji, X. Zhu, W. Dong, 2022: How Does COVID-19 Lockdown Impact Air Quality in India?. Remote Sensing, 14(8), 1869. doi: 10.3390/rs14081869. Air pollution is a severe environmental problem in the Indian subcontinent. Largely caused by the rapid growth of the population, industrialization, and urbanization, air pollution can adversely affect human health and environment. To mitigate such adverse impacts, the Indian government launched the National Clean Air Programme (NCAP) in January 2019. Meanwhile, the unexpected city-lockdown due to the COVID-19 pandemic in March 2020 in India greatly reduced human activities and thus anthropogenic emissions of gaseous and aerosol pollutants. The NCAP and the lockdown could provide an ideal field experiment for quantifying the extent to which various levels of human activity reduction impact air quality in the Indian subcontinent. Here, we study the improvement in air quality due to COVID-19 and the NCAP in the India subcontinent by employing multiple satellite products and surface observations. Satellite data shows significant reductions in nitrogen dioxide (NO2) by 17% and aerosol optical depth (AOD) by 20% during the 2020 lockdown with reference to the mean levels between 2005–2019. No persistent reduction in NO2 nor AOD is detectable during the NCAP period (2019). Surface observations show consistent reductions in PM2.5 and NO2 during the 2020 lockdown in seven cities across the Indian subcontinent, except Mumbai in Central India. The increase in relative humidity and the decrease in the planetary boundary layer also play an important role in influencing air quality during the 2020 lockdown. With the decrease in aerosols during the lockdown, net radiation fluxes show positive anomalies at the surface and negative anomalies at the top of the atmosphere over most parts of the Indian subcontinent. The results of this study could provide valuable information for policymakers in South Asia to adjust the scientific measures proposed in the NCAP for efficient air pollution mitigation. AOD; air quality; COVID-19; India subcontinent; NO2; PM2.5
Ito, Masato; Masunaga, HirohikoIto, M., H. Masunaga, 2022: Process-level Assessment of the Iris Effect over Tropical Oceans. Geophysical Research Letters, n/a(n/a), e2022GL097997. doi: 10.1029/2022GL097997. The iris hypothesis suggests a cloud feedback mechanism that a reduction in the tropical anvil cloud fraction (CF) in a warmer climate may act to mitigate the warming by enhanced outgoing longwave radiation. Two different physical processes, one involving precipitation efficiency and the other focusing on upper-tropospheric stability, have been argued in the literature to be responsible for the iris effect. In this study, A-Train observations and reanalysis data are analyzed to assess these two processes. Major findings are as follows: (1) the anvil CF changes evidently with upper-tropospheric stability as expected from the stability iris theory, (2) precipitation efficiency is unlikely to have control on the anvil CF but is related to mid- and low-level CFs, and (3) the day and nighttime cloud radiative effects are expected to largely cancel out when integrated over a diurnal cycle, suggesting a neutral cloud feedback.
Jia, Aolin; Wang, Dongdong; Liang, Shunlin; Peng, Jingjing; Yu, YunyueJia, A., D. Wang, S. Liang, J. Peng, Y. Yu, 2022: Global daily actual and snow-free blue-sky land surface albedo climatology from 20-year MODIS products. Journal of Geophysical Research: Atmospheres, n/a(n/a), e2021JD035987. doi: 10.1029/2021JD035987. Land surface albedo plays a critical role in climate, hydrological and biogeochemical modeling, and weather forecasting. It is often assigned in models and satellite retrievals by albedo climatology look-up tables using land cover type and other variables; however, there are considerable differences in albedo simulations among models, which partially result from uncertainty in obsolete albedo climatology. Therefore, this study introduces a new global 500 m daily blue-sky land surface albedo climatology dataset under both actual and snow-free surface conditions utilizing 20-year Moderate Resolution Imaging Spectroradiometer (MODIS) products from Google Earth Engine. In situ measurements from 38 long-term-maintained sites were utilized to validate the accuracies of different albedo climatology datasets. The root-mean-square error, bias, and correlation coefficient of the new climatology are 0.031, -0.003, and 0.96, respectively, which are more accurate than the GLASS, GlobAlbedo, and 16 model datasets. Data intercomparison suggests that ERA5 exhibits better performance than MERRA2 and 14 CMIP6 models. However, it contains positive biases in the snow-free season, while MERRA2 underestimates the snow albedo. Global albedo variation associated with basic surface plant functional types was also characterized, and snow impact was considered separately. Temporal variability analysis indicates that traditional climatology datasets with coarser temporal resolutions (≥8 days) cannot capture albedo variation over areas with distinct snow seasons, especially in central Eurasia and boreal regions. These results confirm the high reliability and robustness of the new albedo climatology in model assessment, data assimilation, and satellite product retrievals. MODIS; satellite retrieval; climatology; land surface albedo; model assessment
Jiang, Shuyi; Zhao, Chuanfeng; Xia, YanJiang, S., C. Zhao, Y. Xia, 2022: Distinct response of near surface air temperature to clouds in North China. Atmospheric Science Letters, n/a(n/a), e1128. doi: 10.1002/asl.1128. Using the daily 2 m maximum temperature (Tmax), 2 m minimum temperature (Tmin) and cloud cover data measured at ground sites of the China Meteorological Administration in North China from 2000 to 2017, this study investigates the influence of clouds on the daily temperature range (DTR) defined as the difference between Tmax and Tmin. As expected, the cloud cover shows the similar averaged spatial distribution and monthly variation with Tmin. Surprisingly, it also shows the similar average spatial distribution and monthly variation with Tmax, suggesting the more important roles of regions (latitude) and seasons associated with the variations of land surface temperature, which is further related to solar radiation absorbed and surface heat capacity. By comparing monthly variations of temperature between cloudy and clear skies, we find that clouds can weaken Tmax and increase Tmin, and thus decrease DTR. As a result, the spatial distribution of DTR is opposite to the cloud cover. The clouds have relatively stronger impact on Tmin and DTR over mountain region, which is most likely caused by the stronger longwave cloud radiative forcing associated with higher cloud tops over the mountain region. cloud cover; cloud top; daily temperature range; spatial distribution; temporal variation
Jiao, Zhong-Hu; Mu, XihanJiao, Z., X. Mu, 2022: Single-footprint retrieval of clear-sky surface longwave radiation from hyperspectral AIRS data. International Journal of Applied Earth Observation and Geoinformation, 110, 102802. doi: 10.1016/j.jag.2022.102802. Surface longwave radiation (SLR) derived from remotely sensed data facilitates understanding of the SLR in global climate change. Hyperspectral infrared sounders aboard space platforms provide information on the surface and vertical structure of Earth’s atmosphere. However, currently, SLR products estimated from these observations are unavailable, which hampers their application potential for Earth’s radiation budget in the context of global warming. To address this issue, we developed simple and effective SLR model under clear-sky conditions using at-sensor spectral radiances from Atmospheric Infrared Sounder (AIRS). The model was found to be insensitive to AIRS instrument noise, and showed good performances based on a simulation dataset. The AIRS footprint geometrical model was proposed to match the AIRS and Moderate Resolution Imaging Spectroradiometer (MODIS) data to estimate the cloud fraction. Validation against ground-based measurements found that the surface upward longwave radiation model has a bias of 3.18 W/m2, root-mean-square error (RMSE) of 30.51 W/m2, and R2 of 0.84; the surface downward longwave radiation model has a bias of 0.77 W/m2, RMSE of 29.09 W/m2, and R2 of 0.78. The large validation biases at two ground sites reflect the limited spatial representativeness for AIRS footprints. Terrain-induced altitude differences and spatial inhomogeneity can redistribute the spatial distributions of SLR. Moreover, the model performances were weakly dependent on seasonal variation. The results indicate that the proposed model provides a foundation for the further development of operational SLR products. Surface radiation budget; Atmospheric Infrared Sounder (AIRS); Hybrid method; Hyperspectral infrared remote sensing; Spatial representativeness; Surface longwave radiation
Jin, Daeho; Oreopoulos, Lazaros; Lee, Dongmin; Tan, Jackson; Kim, Kyu-myongJin, D., L. Oreopoulos, D. Lee, J. Tan, K. Kim, 2022: A New Organization Metric for Synoptic Scale Tropical Convective Aggregation. Journal of Geophysical Research: Atmospheres, 127(13), e2022JD036665. doi: 10.1029/2022JD036665. Organization metrics were originally developed to measure how densely convective clouds are arranged at mesoscales. In this work, we apply organization metrics to describe tropical synoptic scale convective activity. Such activity is identified by cloud-precipitation (hybrid) regimes defined at 1-degree and 1-hourly resolution. Existing metrics were found to perform inadequately for such convective regime aggregates because the large domain size and co-existence of sparse aggregate occurrences with noisy isolated convection often violate assumptions inherent in these metrics. In order to capture these characteristics, in this study the existing “convective organization potential” (COP) metric was modified so as to focus on local organization and provide increased weight to aggregate size. The resulting “area-based COP” (ABCOP) follows the principle that the more numerous the objects, the higher the chance of organization. It is thus optimized to capture large-scale convective events occurring during phenomena such as ENSO and MJO, while also performs as well as existing metrics for small domain sizes. tropical convection; cloud-precipitation regime; organization metric
Jönsson, Aiden; Bender, Frida A.-M.Jönsson, A., F. A. Bender, 2022: Corrigendum. J. Climate, 35(15), 5233-5234. doi: 10.1175/JCLI-D-22-0128.1. "Corrigendum" published on 01 Aug 2022 by American Meteorological Society.
Jönsson, Aiden; Bender, Frida A.-M.Jönsson, A., F. A. Bender, 2022: Persistence and Variability of Earth’s Interhemispheric Albedo Symmetry in 19 Years of CERES EBAF Observations. J. Climate, 35(1), 249-268. doi: 10.1175/JCLI-D-20-0970.1. Abstract Despite the unequal partitioning of land and aerosol sources between the hemispheres, Earth’s albedo is observed to be persistently symmetric about the equator. This symmetry is determined by the compensation of clouds to the clear-sky albedo. Here, the variability of this interhemispheric albedo symmetry is explored by decomposing observed radiative fluxes in the CERES EBAF satellite data record into components reflected by the atmosphere, clouds, and the surface. We find that the degree of interhemispheric albedo symmetry has not changed significantly throughout the observational record. The variability of the interhemispheric difference in reflected solar radiation (asymmetry) is strongly determined by tropical and subtropical cloud cover, particularly those related to nonneutral phases of El Niño–Southern Oscillation (ENSO). As ENSO is the most significant source of interannual variability in reflected radiation on a global scale, this underscores the interhemispheric albedo symmetry as a robust feature of Earth’s current annual mean climate. Comparing this feature in observations with simulations from coupled models reveals that the degree of modeled albedo symmetry is mostly dependent on biases in reflected radiation in the midlatitudes, and that models that overestimate its variability the most have larger biases in reflected radiation in the tropics. The degree of model albedo symmetry is improved when driven with historical sea surface temperatures, indicating that the degree of symmetry in Earth’s albedo is dependent on the representation of cloud responses to coupled ocean–atmosphere processes.
Jungclaus, J.h.; Lorenz, S.j.; Schmidt, H.; Brovkin, V.; Brüggemann, N.; Chegini, F.; Crüger, T.; De-Vrese, P.; Gayler, V.; Giorgetta, M.a; Gutjahr, O.; Haak, H.; Hagemann, S.; Hanke, M.; Ilyina, T.; Korn, P.; Kröger, J.; Linardakis, L.; Mehlmann, C.; Mikolajewicz, U.; Müller, W.a.; Nabel, J.e.m.s; Notz, D.; Pohlmann, H.; Putrasahan, D.a.; Raddatz, T.; Ramme, L.; Redler, R.; Reick, C.h.; Riddick, T.; Sam, T.; Schneck, R.; Schnur, R.; Schupfner, M.; Storch, J.-S. von; Wachsmann, F.; Wieners, K.-H.; Ziemen, F.; Stevens, B.; Marotzke, J.; Claussen, M.Jungclaus, J., S. Lorenz, H. Schmidt, V. Brovkin, N. Brüggemann, F. Chegini, T. Crüger, P. De-Vrese, V. Gayler, M. Giorgetta, O. Gutjahr, H. Haak, S. Hagemann, M. Hanke, T. Ilyina, P. Korn, J. Kröger, L. Linardakis, C. Mehlmann, U. Mikolajewicz, W. Müller, J. Nabel, D. Notz, H. Pohlmann, D. Putrasahan, T. Raddatz, L. Ramme, R. Redler, C. Reick, T. Riddick, T. Sam, R. Schneck, R. Schnur, M. Schupfner, J. v. Storch, F. Wachsmann, K. Wieners, F. Ziemen, B. Stevens, J. Marotzke, M. Claussen, 2022: The ICON Earth System Model Version 1.0. Journal of Advances in Modeling Earth Systems, n/a(n/a), e2021MS002813. doi: 10.1029/2021MS002813. This work documents the ICON-Earth System Model (ICON-ESM V1.0), the first coupled model based on the ICON (ICOsahedral Non-hydrostatic) framework with its unstructured, icosahedral grid concept. The ICON-A atmosphere uses a nonhydrostatic dynamical core and the ocean model ICON-O builds on the same ICON infrastructure, but applies the Boussinesq and hydrostatic approximation and includes a sea-ice model. The ICON-Land module provides a new framework for the modelling of land processes and the terrestrial carbon cycle. The oceanic carbon cycle and biogeochemistry are represented by the Hamburg Ocean Carbon Cycle module. We describe the tuning and spin-up of a base-line version at a resolution typical for models participating in the Coupled Model Intercomparison Project (CMIP). The performance of ICON-ESM is assessed by means of a set of standard CMIP6 simulations. Achievements are well-balanced top-of-atmosphere radiation, stable key climate quantities in the control simulation, and a good representation of the historical surface temperature evolution. The model has overall biases, which are comparable to those of other CMIP models, but ICON-ESM performs less well than its predecessor, the Max Planck Institute Earth System Model. Problematic biases are diagnosed in ICON-ESM in the vertical cloud distribution and the mean zonal wind field. In the ocean, sub-surface temperature and salinity biases are of concern as is a too strong seasonal cycle of the sea-ice cover in both hemispheres. ICON-ESM V1.0 serves as a basis for further developments that will take advantage of ICON-specific properties such as spatially varying resolution, and configurations at very high resolution. Earth; Model; System
Kenny, Darragh; Fiedler, StephanieKenny, D., S. Fiedler, 2022: Which gridded irradiance data is best for modelling photovoltaic power production in Germany?. Solar Energy, 232, 444-458. doi: 10.1016/j.solener.2021.12.044. Model estimates of expected photovoltaic (PV) power production rely on accurate irradiance data. Reanalysis and satellite products freely provide irradiance data with a high temporal and spatial resolution including locations for which no ground-based measurements are available. We assess differences in such gridded irradiance data and quantify the subsequent bias propagation from individual radiation components to capacity factors in a contemporary PV model. PV power production is simulated based on four reanalysis (ERA5, COSMO-REA6, COSMO-REA6pp, COSMO-REA2) and three satellite products (CAMS, SARAH-2, CERES Syn1Deg). The results are compared against simulations using measurements from 30 weather stations of the German Weather Service. We compute metrics characterizing biases in seasonal and annual means, day-to-day variability and extremes in PV power. Our results highlight a bias of −1.4% (COSMO-REA6) to ＋8.2% (ERA5) in annual and spatial means of PV power production for Germany. No single data set is best in all metrics, although SARAH-2 and the postprocessed COSMO-REA6 data (COSMO-REA6pp) outperform the other products for many metrics. SARAH-2 yields good results in summer, but overestimates PV output in winter by 16% averaged across all stations. COSMO-REA6pp represents day-to-day variability in the PV power production of a simulated PV fleet best and has a particularly small bias of 0.5% in annual means. This is at least in parts due to compensating biases in local and seasonal means. Our results imply that gridded irradiance data should be used with caution for site assessments and ideally be complemented by local measurements. Satellite; Data evaluation; Irradiance data; PV power model; Re-analysis; Station observations
Khairoutdinov, Marat F.; Blossey, Peter N.; Bretherton, Christopher S.Khairoutdinov, M. F., P. N. Blossey, C. S. Bretherton, 2022: Global System for Atmospheric Modeling: Model Description and Preliminary Results. Journal of Advances in Modeling Earth Systems, 14(6), e2021MS002968. doi: 10.1029/2021MS002968. The extension of a cloud-resolving model, the System for Atmospheric Modeling (SAM), to global domains is described. The resulting global model, gSAM, is formulated on a latitude-longitude grid. It uses an anelastic dynamical core with a single reference profile (as in SAM), but its governing equations differ somewhat from other anelastic models. For quasihydrostatic flows, they are isomorphic to the primitive equations (PE) in pressure coordinates but with the globally uniform reference pressure playing the role of actual pressure. As a result, gSAM can exactly maintain steady zonally symmetric baroclinic flows that have been specified in pressure coordinates, produces accurate simulations when initialized or nudged with global reanalyses, and has a natural energy conservation equation despite the drawbacks of using the anelastic system to model global scales. gSAM employs a novel treatment of topography using a type of immersed boundary method, the Quasi-Solid Body Method, where the instantaneous flow velocity is forced to stagnate in grid cells inside a prescribed terrain. The results of several standard tests designed to evaluate the accuracy of global models with and without topography as well as results from real Earth simulations are presented. global cloud-resolving model; model description; global storm-resolving model; anelastic dynamical core; system for atmospheric modeling
Knippertz, Peter; Gehne, Maria; Kiladis, George N.; Kikuchi, Kazuyoshi; Rasheeda Satheesh, Athul; Roundy, Paul E.; Yang, Gui-Ying; Žagar, Nedjeljka; Dias, Juliana; Fink, Andreas H.; Methven, John; Schlueter, Andreas; Sielmann, Frank; Wheeler, Matthew C.Knippertz, P., M. Gehne, G. N. Kiladis, K. Kikuchi, A. Rasheeda Satheesh, P. E. Roundy, G. Yang, N. Žagar, J. Dias, A. H. Fink, J. Methven, A. Schlueter, F. Sielmann, M. C. Wheeler, 2022: The intricacies of identifying equatorial waves. Quarterly Journal of the Royal Meteorological Society, 148(747), 2814-2852. doi: 10.1002/qj.4338. Equatorial waves (EWs) are synoptic- to planetary-scale propagating disturbances at low latitudes with periods from a few days to several weeks. Here, this term includes Kelvin waves, equatorial Rossby waves, mixed Rossby–gravity waves, and inertio-gravity waves, which are well described by linear wave theory, but it also other tropical disturbances such as easterly waves and the intraseasonal Madden–Julian Oscillation with more complex dynamics. EWs can couple with deep convection, leading to a substantial modulation of clouds and rainfall. EWs are amongst the dynamic features of the troposphere with the longest intrinsic predictability, and models are beginning to forecast them with an exploitable level of skill. Most of the methods developed to identify and objectively isolate EWs in observations and model fields rely on (or at least refer to) the adiabatic, frictionless linearized primitive equations on the sphere or the shallow-water system on the equatorial β$$\beta$$-plane. Common ingredients to these methods are zonal wave-number–frequency filtering (Fourier or wavelet) and/or projections onto predefined empirical or theoretical dynamical patterns. This paper gives an overview of six different methods to isolate EWs and their structures, discusses the underlying assumptions, evaluates the applicability to different problems, and provides a systematic comparison based on a case study (February 20–May 20, 2009) and a climatological analysis (2001–2018). In addition, the influence of different input fields (e.g., winds, geopotential, outgoing long-wave radiation, rainfall) is investigated. Based on the results, we generally recommend employing a combination of wave-number–frequency filtering and spatial-projection methods (and of different input fields) to check for robustness of the identified signal. In cases of disagreement, one needs to carefully investigate which assumptions made for the individual methods are most probably not fulfilled. This will help in choosing an approach optimally suited to a given problem at hand and avoid misinterpretation of the results. convection; equatorial Rossby waves; Kelvin waves; mixed Rossby–gravity waves; spatial projection; time–space filtering; tropical rainfall
Kooperman, G. J.; Akinsanola, A. A.; Hannah, W. M.; Pendergrass, A. G.; Reed, K. A.Kooperman, G. J., A. A. Akinsanola, W. M. Hannah, A. G. Pendergrass, K. A. Reed, 2022: Assessing Two Approaches for Enhancing the Range of Simulated Scales in the E3SMv1 and the Impact on the Character of Hourly US Precipitation. Geophysical Research Letters, 49(4), e2021GL096717. doi: 10.1029/2021GL096717. Improving the representation of precipitation in Earth system models is essential for understanding and projecting water cycle changes across scales. Progress has been hampered by persistent deficiencies in representing precipitation frequency, intensity, and timing in current models. Here, we analyze simulated US precipitation in the low-resolution (LR) configuration of the Energy Exascale Earth System Model (E3SMv1) and assess the effect of two approaches to enhance the range of explicitly resolved scales: high-resolution (HR) and multiscale modeling framework (MMF), which incur similar computational expense. Both E3SMv1-MMF and E3SMv1-HR capture more intense and less frequent precipitation on hourly and daily timescales relative to E3SMv1-LR. E3SMv1-HR improves the intensity over the Eastern and Northwestern US during winter, while E3SMv1-MMF improves the intensity over the Eastern US and summer diurnal timing over the Central US. These results indicate that both methods may be needed to improve simulations of different storm types, seasons, and regions. United States; precipitation; earth system model; energy exascale earth system model; high resolution; multiscale modelling framework
Koppa, Akash; Rains, Dominik; Hulsman, Petra; Poyatos, Rafael; Miralles, Diego G.Koppa, A., D. Rains, P. Hulsman, R. Poyatos, D. G. Miralles, 2022: A deep learning-based hybrid model of global terrestrial evaporation. Nature Communications, 13(1), 1912. doi: 10.1038/s41467-022-29543-7. Terrestrial evaporation (E) is a key climatic variable that is controlled by a plethora of environmental factors. The constraints that modulate the evaporation from plant leaves (or transpiration, Et) are particularly complex, yet are often assumed to interact linearly in global models due to our limited knowledge based on local studies. Here, we train deep learning algorithms using eddy covariance and sap flow data together with satellite observations, aiming to model transpiration stress (St), i.e., the reduction of Et from its theoretical maximum. Then, we embed the new St formulation within a process-based model of E to yield a global hybrid E model. In this hybrid model, the St formulation is bidirectionally coupled to the host model at daily timescales. Comparisons against in situ data and satellite-based proxies demonstrate an enhanced ability to estimate St and E globally. The proposed framework may be extended to improve the estimation of E in Earth System Models and enhance our understanding of this crucial climatic variable. Hydrology; Ecological modelling
Kuma, Peter; Bender, Frida A.-M.; Schuddeboom, Alex; McDonald, Adrian J.; Seland, ØyvindKuma, P., F. A. Bender, A. Schuddeboom, A. J. McDonald, Ø. Seland, 2022: Machine learning of cloud types shows higher climate sensitivity is associated with lower cloud biases. Atmospheric Chemistry and Physics Discussions, 1-32. doi: 10.5194/acp-2022-184. Abstract. Uncertainty in cloud feedback in climate models is a major limitation in projections of future climate. Therefore, to ensure the accuracy of climate models, evaluation and improvement of cloud simulation is essential. We analyse cloud biases and cloud change with respect to global mean near-surface temperature (GMST) in climate models relative to satellite observations, and relate them to equilibrium climate sensitivity, transient climate response and cloud feedback. For this purpose, we develop a supervised deep convolutional artificial neural network for determination of cloud types from low-resolution (approx. 1°×1°) daily mean top of atmosphere shortwave and longwave radiation fields, corresponding to the World Meteorological Organization (WMO) cloud genera recorded by human observers in the Global Telecommunication System. We train this network on a satellite top of atmosphere radiation observed by the Clouds and the Earth’s Radiant Energy System (CERES), and apply it on the Climate Model Intercomparison Project phase 5 and 6 (CMIP5 and CMIP6) historical and abrupt-4xCO2 experiment model output and the ECMWF Reanalysis version 5 (ERA5) and the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) reanalyses. We compare these with satellite observations, link biases in cloud type occurrence derived from the neural network to change with respect to GMST to climate sensitivity, and compare our cloud types with an existing cloud regime classification based on the Moderate Resolution Imaging Spectroradiometer (MODIS) and International Satellite Cloud Climatology Project (ISCCP) satellite data. We show that there is a significant negative linear relationship between the root mean square error of cloud type occurrence derived from the neural network and model equilibrium climate sensitivity and transient climate response (Bayes factor 22 and 17, respectively). This indicates that models with a better representation of the cloud types globally have higher climate sensitivity. Factoring in results from other studies, there are two possible explanations: either high climate sensitivity models are plausible, contrary to combined assessments of climate sensitivity by previous review studies, or the accuracy of representation of present-day clouds in models is negatively correlated with the accuracy of representation of future projected clouds.
Kuwano, A.; Evan, A.Kuwano, A., A. Evan, 2022: A Method to Account for the Impact of Water Vapor on Observation-Based Estimates of the Clear-Sky Shortwave Direct Radiative Effect of Mineral Dust. Journal of Geophysical Research: Atmospheres, 127(17), e2022JD036620. doi: 10.1029/2022JD036620. The shortwave direct radiative effect of dust, the difference between net shortwave radiative flux in a cloud free and cloud and aerosol free atmosphere, is typically estimated using forward calculations made with a radiative transfer model. However, estimates of the direct radiative effect made via this initial method can be highly uncertain due to difficultly in accurately describing the relevant optical and physical properties of dust used in these calculations. An alternative approach to estimate this effect is to determine the forcing efficiency, or the direct radiative effect normalized by aerosol optical depth. While this approach avoids the uncertainties associated with the initial method for calculating the direct effect, random errors and biases associated with this approach have not been thoroughly examined in literature. Here we explore biases in this observation-based approach that are related to atmospheric water vapor. We use observations to show that over the Sahara Desert dust optical depth and column-integrated atmospheric water vapor are positively correlated. We use three idealized radiative models of varying complexity to demonstrate that a positive correlation between dust and water vapor produces a positive bias in the dust forcing efficiency estimated via the observation-based method. We describe a simple modification to the observation-based method that correctly accounts for the correlation between dust and water vapor when estimating the forcing efficiency and use this method to estimate the instantaneous forcing efficiency of dust over the Sahara Desert using satellite data, obtaining −12.3 ± 6.68 to 20.9 ± 11.9 W m−2 per unit optical depth. shortwave; radiative transfer; satellite data; observations; dust; forcing efficiency
Lee, Jae N.; Wu, Dong L.Lee, J. N., D. L. Wu, 2022: Non-Gaussian Distributions of TOA SW Flux as Observed by MISR and CERES. Journal of Geophysical Research: Atmospheres, 127(14), e2022JD036636. doi: 10.1029/2022JD036636. The Top of Atmosphere (TOA) shortwave (SW) flux, converted from Terra Multi-angle Imaging SpectroRadiometer (MISR) narrow band albedos, is compared with that measured from Clouds and the Earth's Radiant Energy System (CERES). We describe the probability density function (PDF) of the monthly TOA SW flux and how the statistical third moment, skewness, can impact the quantification of the flux. The PDF of the SW flux is not normally distributed but positively skewed. In both sets of observations, the near-global (80 S–80 N) median value of the SW flux is ∼3 W/m2 less than the mean value, due to the positive skewness of the distribution. The near-global mean TOA SW flux converted from MISR is about 7 W/m2 (∼7%) less than CERES measured flux during the last two decades. Surprisingly, a hemispheric asymmetry exists with TOA SW observations from the Terra platform. SH reflects 3.92 and 1.15 W/m2 more mean SW flux than NH, from MISR and CERES Single Scanner Footprint products, respectively. We can infer that the offsetting by morning clouds in the SH is greater than the effect of hemispheric imbalance of SW flux caused by different land masses in two hemispheres. While the characteristics of the two SW fluxes broadly agree with each other, differences in the regional PDF from two different SW fluxes are substantial over high cloud regions and high altitude regions. Our analysis shows that some parts of the different skewness from the two measurements may be attributed to the different calibration of the radiance anisotropy over high cloud scenes. CERES; MISR; hemispheric asymmetry; non-Gaussian; TOA SW flux
Lee, Jiheun; Kang, Sarah M.; Kim, Hanjun; Xiang, BaoqiangLee, J., S. M. Kang, H. Kim, B. Xiang, 2022: Disentangling the effect of regional SST bias on the double-ITCZ problem. Climate Dynamics. doi: 10.1007/s00382-021-06107-x. This study investigates the causes of the double intertropical convergence zone (ITCZ) bias, characterized by too northward northern Pacific ITCZ, too dry equatorial Pacific, and too zonally elongated southern Pacific rainband. While the biases within one fully coupled model GFDL CM2.1 are examined, the large-scale bias patterns are broadly common to CMIP5/6 models. We disentangle the individual contribution of regional sea surface temperature (SST) biases to the double-ITCZ bias pattern using a series of slab ocean model experiments. A previously suggested Southern Ocean warm bias effect in displacing the zonal-mean ITCZ southward is manifested in the northern Pacific ITCZ while having little contribution to the zonally elongated wet bias south of the equatorial Pacific. The excessive southern Pacific precipitation is instead induced by the warm bias along the west coast of South America. The Southern Ocean bias effect on the zonal-mean ITCZ position is diminished by the neighboring midlatitude bias of opposite sign in GFDL CM2.1. As a result, the northern extratropical cold bias turns out to be most responsible for a southward-displaced zonal-mean ITCZ. However, this southward ITCZ displacement results from the northern Pacific branch, so ironically fixing the extratropical biases only deteriorates the northern Pacific precipitation bias. Thus, we emphasize that the zonal-mean diagnostics poorly represent the spatial pattern of the tropical Pacific response. Examination of longitude-latitude structure indicates that the overall tropical precipitation bias is mostly locally driven from the tropical SST bias. While our model experiments are idealized with no ocean dynamics, the results shed light on where preferential foci should be applied in model development to improve particular features of tropical precipitation bias.
Leng, Song; Huete, Alfredo; Cleverly, Jamie; Gao, Sicong; Yu, Qiang; Meng, Xianyong; Qi, Junyu; Zhang, Rongrong; Wang, QianfengLeng, S., A. Huete, J. Cleverly, S. Gao, Q. Yu, X. Meng, J. Qi, R. Zhang, Q. Wang, 2022: Assessing the Impact of Extreme Droughts on Dryland Vegetation by Multi-Satellite Solar-Induced Chlorophyll Fluorescence. Remote Sensing, 14(7), 1581. doi: 10.3390/rs14071581. Satellite-estimated solar-induced chlorophyll fluorescence (SIF) is proven to be an effective indicator for dynamic drought monitoring, while the capability of SIF to assess the variability of dryland vegetation under water and heat stress remains challenging. This study presents an analysis of the responses of dryland vegetation to the worst extreme drought over the past two decades in Australia, using multi-source spaceborne SIF derived from the Global Ozone Monitoring Experiment-2 (GOME-2) and TROPOspheric Monitoring Instrument (TROPOMI). Vegetation functioning was substantially constrained by this extreme event, especially in the interior of Australia, in which there was hardly seasonal growth detected by neither satellite-based observations nor tower-based flux measurements. At a 16-day interval, both SIF and enhanced vegetation index (EVI) can timely capture the reduction at the onset of drought over dryland ecosystems. The results demonstrate that satellite-observed SIF has the potential for characterizing and monitoring the spatiotemporal dynamics of drought over water-limited ecosystems, despite coarse spatial resolution coupled with high-retrieval noise as compared with EVI. Furthermore, our study highlights that SIF retrieved from TROPOMI featuring substantially enhanced spatiotemporal resolution has the promising capability for accurately tracking the drought-induced variation of heterogeneous dryland vegetation. SIF; dryland; EVI; extreme drought; TROPOMI
Leng, Song; Huete, Alfredo; Cleverly, Jamie; Yu, Qiang; Zhang, Rongrong; Wang, QianfengLeng, S., A. Huete, J. Cleverly, Q. Yu, R. Zhang, Q. Wang, 2022: Spatiotemporal Variations of Dryland Vegetation Phenology Revealed by Satellite-Observed Fluorescence and Greenness across the North Australian Tropical Transect. Remote Sensing, 14(13), 2985. doi: 10.3390/rs14132985. Accurate characterization of spatial patterns and temporal variations in dryland vegetation is of great importance for improving our understanding of terrestrial ecosystem functioning under changing climates. Here, we explored the spatiotemporal variability of dryland vegetation phenology using satellite-observed Solar-Induced chlorophyll Fluorescence (SIF) and the Enhanced Vegetation Index (EVI) along the North Australian Tropical Transect (NATT). Substantial impacts of extreme drought and intense wetness on the phenology and productivity of dryland vegetation are observed by both SIF and EVI, especially in the arid/semiarid interior of Australia without detectable seasonality in the dry year of 2018–2019. The greenness-based vegetation index (EVI) can more accurately capture the seasonal and interannual variation in vegetation production than SIF (EVI r2: 0.47~0.86, SIF r2: 0.47~0.78). However, during the brown-down periods, the rate of decline in EVI is evidently slower than that in SIF and in situ measurement of gross primary productivity (GPP), due partially to the advanced seasonality of absorbed photosynthetically active radiation. Over 70% of the variability of EVI (except for Hummock grasslands) and 40% of the variability of SIF (except for shrublands) can be explained by the water-related drivers (rainfall and soil moisture). By contrast, air temperature contributed to 25~40% of the variability of the effective fluorescence yield (SIFyield) across all biomes. In spite of high retrieval noises and variable accuracy in phenological metrics (MAE: 8~60 days), spaceborne SIF observations, offsetting the drawbacks of greenness-based phenology products with a potentially lagged end of the season, have the promising capability of mapping and characterizing the spatiotemporal dynamics of dryland vegetation phenology. SIF; EVI; NATT; phenology
Li, Lingfeng; Qiu, Bo; Guo, Weidong; Zhang, Yiping; Song, Qinghai; Chen, JiuyiLi, L., B. Qiu, W. Guo, Y. Zhang, Q. Song, J. Chen, 2022: Phenological and physiological responses of the terrestrial ecosystem to the 2019 drought event in Southwest China: Insights from satellite measurements and the SSiB2 model. International Journal of Applied Earth Observation and Geoinformation, 111, 102832. doi: 10.1016/j.jag.2022.102832. Understanding plant phenological and physiological changes in response to drought will provide key insight into the response of terrestrial ecosystems to climate change, but is still limited due to the increased drought severity and frequency in recent decades. Here, we combine solar-induced chlorophyll fluorescence (SIF) along with SSiB2 (Simplified Simple Biosphere Model) simulations to investigate the plant phenological and physiological responses to the 2019 drought in southwestern China. Our results show that this 2019 drought had substantial impacts on vegetation phenology and photosynthesis due to the soil moisture deficit in spring, while the rewatering process in July alleviated the water deficit and reduced drought damage to plants. Moreover, SIF observations provide a physiology-related vegetation response, as the recovery of plant photosynthesis indicated by fluorescence yield (SIFyield) is much stronger than the recovery of greenness described by vegetation indices during the rewatering in July. The SSiB2 simulations captured the physiological response of plants to moisture deficit during drought period, while the lack of realistic energy dissipation mechanisms under stressed conditions may lead to discrepancies in the timing of peak response to drought. Our findings highlight the prospective application of remote sensing SIF measurements in monitoring the timely response of plant physiology to changes in water conditions and to provide important information for model evaluation and improvement. Solar-induced chlorophyll fluorescence; Drought; Plant physiological response; Water stress
Li, Meng; Chu, Ronghao; Sha, Xiuzhu; Xie, Pengfei; Ni, Feng; Wang, Chao; Jiang, Yuelin; Shen, Shuanghe; Islam, Abu Reza Md TowfiqulLi, M., R. Chu, X. Sha, P. Xie, F. Ni, C. Wang, Y. Jiang, S. Shen, A. R. M. T. Islam, 2022: Monitoring 2019 Drought and Assessing Its Effects on Vegetation Using Solar-Induced Chlorophyll Fluorescence and Vegetation Indexes in the Middle and Lower Reaches of Yangtze River, China. Remote Sensing, 14(11), 2569. doi: 10.3390/rs14112569. Monitoring drought precisely and evaluating drought effects quantitatively can establish a scientific foundation for understanding drought. Although solar-induced chlorophyll fluorescence (SIF) can detect the drought stress in advance, the performance of SIF in monitoring drought and assessing drought-induced gross primary productivity (GPP) losses from lush to senescence remains to be further studied. Taking the 2019 drought in the middle and lower reaches of the Yangtze River (MLRYR) as an example, this study aims to monitor and assess this drought by employing a new global, OCO-2-based SIF (GOSIF) and vegetation indexes (VIs). Results showed that the GPP, GOSIF, and VIs all exhibited significant increasing trends during 2000–2020. GOSIF was most consistent with GPP in spatial distribution and was most correlated with GPP in both annual (linear correlation, R2 = 0.87) and monthly (polynomial correlation, R2 = 0.976) time scales by comparing with VIs. During July–December 2019, the precipitation (PPT), soil moisture, and standardized precipitation evapotranspiration index (SPEI) were generally below the averages during 2011–2020 and reached their lowest point in November, while those of air temperature (Tem), land surface temperature (LST), and photosynthetically active radiation (PAR) were the contrary. For drought monitoring, the spatial distributions of standardized anomalies of GOSIF and VIs were consistent during August–October 2019. In November and December, however, considering vegetation has entered the senescence stage, SIF had an obvious early response in vegetation physiological state monitoring compared with VIs, while VIs can better indicate meteorological drought conditions than SIF. For drought assessment, the spatial distribution characteristics of GOSIF and its standardized anomaly were both most consistent with that of GPP, especially the standardized anomaly in November and December. All the above phenomena verified the good spatial consistency between SIF and GPP and the superior ability of SIF in capturing and quantifying drought-induced GPP losses. Results of this study will improve the understanding of the prevention and reduction in agrometeorological disasters and can provide an accurate and timely method for drought monitoring. drought; solar-induced chlorophyll fluorescence; gross primary productivity; the middle and lower reaches of Yangtze River; vegetation indexes
Li, Ming; Letu, Husi; Peng, Yiran; Ishimoto, Hiroshi; Lin, Yanluan; Nakajima, Takashi Y.; Baran, Anthony J.; Guo, Zengyuan; Lei, Yonghui; Shi, JianchengLi, M., H. Letu, Y. Peng, H. Ishimoto, Y. Lin, T. Y. Nakajima, A. J. Baran, Z. Guo, Y. Lei, J. Shi, 2022: Investigation of ice cloud modeling capabilities for the irregularly shaped Voronoi ice scattering models in climate simulations. Atmospheric Chemistry and Physics, 22(7), 4809-4825. doi: 10.5194/acp-22-4809-2022. Abstract. Both weather–climate models and ice cloud remote sensing applications need to obtain effective ice crystal scattering (ICS) properties and the parameterization scheme. An irregularly shaped Voronoi ICS model has been suggested to be effective in remote sensing applications for several satellite programs, e.g., Himawari-8, GCOM-C (Global Change Observation Mission–Climate) and EarthCARE (Earth Cloud Aerosol and Radiation Explorer). As continuation work of Letu et al. (2016), an ice cloud optical property parameterization scheme (Voronoi scheme) of the Voronoi ICS model is employed in the Community Integrated Earth System Model (CIESM) to simulate the optical and radiative properties of ice clouds. We utilized the single-scattering properties (extinction efficiency, single-scattering albedo and asymmetry factor) of the Voronoi model from the ultraviolet to the infrared, combined with 14 408 particle size distributions obtained from aircraft measurements to complete the Voronoi scheme. The Voronoi scheme and existing schemes (Fu, Mitchell, Yi and Baum-yang05) are applied to the CIESM to simulate 10-year global cloud radiative effects during 2001–2010. Simulated globally averaged cloud radiative forcings at the top of the atmosphere (TOA) for Voronoi and the other four existing schemes are compared to the Clouds and the Earth's Radiant Energy System Energy Balanced and Filled (EBAF) product. The results show that the differences in shortwave and longwave globally averaged cloud radiative forcing at the TOA between the Voronoi scheme simulations and EBAF products are 1.1 % and 1.4 %, which are lower than those of the other four schemes. Particularly for regions (from 30∘ S to 30∘ N) where ice clouds occur frequently, the Voronoi scheme provides the closest match with EBAF products compared with the other four existing schemes. The results in this study fully demonstrated the effectiveness of the Voronoi ICS model in the simulation of the radiative properties of ice clouds in the climate model.
Li, Shaopeng; Jiang, Bo; Peng, Jianghai; Liang, Hui; Han, Jiakun; Yao, Yunjun; Zhang, Xiaotong; Cheng, Jie; Zhao, Xiang; Liu, Qiang; Jia, KunLi, S., B. Jiang, J. Peng, H. Liang, J. Han, Y. Yao, X. Zhang, J. Cheng, X. Zhao, Q. Liu, K. Jia, 2022: Estimation of the All-Wave All-Sky Land Surface Daily Net Radiation at Mid-Low Latitudes from MODIS Data Based on ERA5 Constraints. Remote Sensing, 14(1), 33. doi: 10.3390/rs14010033. The surface all-wave net radiation (Rn) plays an important role in the energy and water cycles, and most studies of Rn estimations have been conducted using satellite data. As one of the most commonly used satellite data sets, Moderate Resolution Imaging Spectroradiometer (MODIS) data have not been widely used for radiation calculations at mid-low latitudes because of its very low revisit frequency. To improve the daily Rn estimation at mid-low latitudes with MODIS data, four models, including three models built with random forest (RF) and different temporal expansion models and one model built with the look-up-table (LUT) method, are used based on comprehensive in situ radiation measurements collected from 340 globally distributed sites, MODIS top-of-atmosphere (TOA) data, and the fifth generation of European Centre for Medium-Range Weather Forecasts Reanalysis 5 (ERA5) data from 2000 to 2017. After validation against the in situ measurements, it was found that the RF model based on the constraint of the daily Rn from ERA5 (an RF-based model with ERA5) performed the best among the four proposed models, with an overall validated root-mean-square error (RMSE) of 21.83 Wm−2, R2 of 0.89, and a bias of 0.2 Wm−2. It also had the best accuracy compared to four existing products (Global LAnd Surface Satellite Data (GLASS), Clouds and the Earth’s Radiant Energy System Edition 4A (CERES4A), ERA5, and FLUXCOM_RS) across various land cover types and different elevation zones. Further analyses illustrated the effectiveness of the model by introducing the daily Rn from ERA5 into a “black box” RF-based model for Rn estimation at the daily scale, which is used as a physical constraint when the available satellite observations are too limited to provide sufficient information (i.e., when the overpass time is less than twice per day) or the sky is overcast. Overall, the newly-proposed RF-based model with ERA5 in this study shows satisfactory performance and has strong potential to be used for long-term accurate daily Rn global mapping at finer spatial resolutions (e.g., 1 km) at mid-low latitudes. modeling; MODIS; net radiation; energy balance; ERA5; constraint; mid-low latitude; random forest; temporal expansion
Li, Xiaohan; Zhang, Yi; Peng, Xindong; Chu, Wenchao; Lin, Yanluan; Li, JianLi, X., Y. Zhang, X. Peng, W. Chu, Y. Lin, J. Li, 2022: Improved Climate Simulation by Using a Double-Plume Convection Scheme in a Global Model. Journal of Geophysical Research: Atmospheres, 127(11), e2021JD036069. doi: 10.1029/2021JD036069. Convective parameterization can drastically regulate the mean climate and tropical transient activity of a General circulation model (GCM). In this study, the physics suite of the NCAR Community Atmosphere Model, version 5 (CAM5) was first ported to the Global-to-Regional Integrated Forecast System model. Then, the original convective parameterization of CAM5—with a separate representation of deep convection Zhang–Mcfarlane (ZM) and shallow convection University of Washington (UW)—was replaced by a double-plume (DP) scheme. This DP scheme adopts a quasi-unified representation of shallow and deep convection within a single framework. Results demonstrate that the new scheme brings about several improvements in the modeled climate. The differences in the trigger and closure assumptions, lateral mixing rate, and cloud model for the deep convection result in systematic regional differences in the simulated precipitation pattern, cloud vertical structure, and the associated radiative forcing. Compared with ZM-UW, DP reduces the biases in precipitation over the Indian Ocean, ameliorates the “high-frequency and low-intensity” problem of tropical precipitation, and leads to an improved representation of tropical variability, including the Madden–Julian Oscillation. Double-plume reduces low clouds and increases high clouds in the tropics, due to its internal parallel-split convective processes and smaller cumulus cloud fraction. Discussions related to parametric tuning of convective parameterization are also presented.
Liang, Hui; Jiang, Bo; Liang, Shunlin; Peng, Jianghai; Li, Shaopeng; Han, Jiakun; Yin, Xiuwan; Cheng, Jie; Jia, Kun; Liu, Qiang; Yao, Yunjun; Zhao, Xiang; Zhang, XiaotongLiang, H., B. Jiang, S. Liang, J. Peng, S. Li, J. Han, X. Yin, J. Cheng, K. Jia, Q. Liu, Y. Yao, X. Zhao, X. Zhang, 2022: A global long-term ocean surface daily/0.05° net radiation product from 1983–2020. Scientific Data, 9(1), 337. doi: 10.1038/s41597-022-01419-x. The all-wave net radiation (Rn) on the ocean surface characterizes the available radiative energy balance and is important to understand the Earth’s climate system. Considering the shortcomings of available ocean surface Rn datasets (e.g., coarse spatial resolutions, discrepancy in accuracy, inconsistency, and short duration), a new long-term global daily Rn product at a spatial resolution of 0.05° from 1983 to 2020, as part of the Global High Resolution Ocean Surface Energy (GHOSE) products suite, was generated in this study by fusing several existing datasets including satellite and reanalysis products based on the comprehensive in situ measurements from 68 globally distributed moored buoy sites. Evaluation against in-situ measurements shows the root mean square difference, mean bias error and correlation coefficient squared of 23.56 Wm−2, 0.88 Wm−2 and 0.878. The global average ocean surface Rn over 1983–2020 is estimated to be 119.71 ± 2.78 Wm−2 with a significant increasing rate of 0.16 Wm−2 per year. GHOSE Rn product can be valuable for oceanic and climatic studies. Physical oceanography
Lin, Qiao-Jun; Yu, Jia-YuhLin, Q., J. Yu, 2022: The potential impact of model horizontal resolution on the simulation of atmospheric cloud radiative effect in CMIP6 models. Terrestrial, Atmospheric and Oceanic Sciences, 33(1), 21. doi: 10.1007/s44195-022-00021-3. The simulations of atmospheric cloud-radiative effect (ACRE) from 54 Coupled Model Intercomparison Project phase 6 (CMIP6) models during the historical period of 2000/03–2014/12 are compared and evaluated against the satellite-based Clouds and the Earth’s Radiant Energy System (CERES) products. For ease of comparison, all CMIP6 models are divided into high-, medium-, and low-resolution groups to examine the potential impact of model horizontal resolution change on the simulations of ACRE distribution over the tropical oceans. The results show that ACRE is positive inside the ITCZs but negative in the subtropics and cold tongue areas, owing to the very different radiative forcing between deep and shallow clouds. Simulations of ACRE are sensitive to the model horizontal resolution used and the finer resolution models generally produce a better performance of ACRE simulations against the CERES observations. The reduced ACRE biases in finer resolution models are mainly contributed by the improved longwave ACRE (i.e., LWACRE) simulations, especially over the Pacific and Atlantic cold tongue areas where shallow stratocumulus clouds prevail. CMIP6; Atmospheric cloud-radiative effect; Model horizontal resolution
Lindzen, Richard S.; Choi, Yong-SangLindzen, R. S., Y. Choi, 2022: The Iris Effect: A Review. Asia-Pacific Journal of Atmospheric Sciences, 58(1), 159-168. doi: 10.1007/s13143-021-00238-1. This study reviews the research of the past 20-years on the role of anvil cirrus in the Earth’s climate – research initiated by Lindzen et al. (Bull. Am. Meteor. Soc. 82:417-432, 2001). The original study suggested that the anvil cirrus would shrink with warming, which was estimated to induce longwave cooling for the Earth. This is referred to as the iris effect since the areal change hypothetically resembles the light control by the human eye’s iris. If the effect is strong enough, it exerts a significant negative climate feedback which stabilizes tropical temperatures and limits climate sensitivity. Initial responses to Lindzen et al. (Bull. Am. Meteor. Soc. 82:417-432, 2001) denied the existence and effectiveness of the iris effect. Assessment of the debatable issues in these responses will be presented later in this review paper. At this point, the strong areal reduction of cirrus with warming appears very clearly in both climate models and satellite observations. Current studies found that the iris effect may not only come from the decreased cirrus outflow due to increased precipitation efficiency, but also from concentration of cumulus cores over warmer areas (the so-called aggregation effect). Yet, different opinions remain as to the radiative effect of cirrus clouds participating in the iris effect. For the iris effect to be most important, it must involve cirrus clouds that are not as opaque for visible radiation as they are for infrared radiation. However, current climate models often simulate cirrus clouds that are opaque in both visible and infrared radiation. This issue requires thorough examination as it seems to be opposed to conventional wisdom based on explicit observations. This paper was written in the hope of stimulating more effort to carefully evaluate these important issues.
Liu, Chunlei; Yang, Yazhu; Liao, Xiaoqing; Cao, Ning; Liu, Jimmy; Ou, Niansen; Allan, Richard P.; Jin, Liang; Chen, Ni; Zheng, RongLiu, C., Y. Yang, X. Liao, N. Cao, J. Liu, N. Ou, R. P. Allan, L. Jin, N. Chen, R. Zheng, 2022: Discrepancies in Simulated Ocean Net Surface Heat Fluxes over the North Atlantic. Advances in Atmospheric Sciences. doi: 10.1007/s00376-022-1360-7. The change in ocean net surface heat flux plays an important role in the climate system. It is closely related to the ocean heat content change and ocean heat transport, particularly over the North Atlantic, where the ocean loses heat to the atmosphere, affecting the AMOC (Atlantic Meridional Overturning Circulation) variability and hence the global climate. However, the difference between simulated surface heat fluxes is still large due to poorly represented dynamical processes involving multiscale interactions in model simulations. In order to explain the discrepancy of the surface heat flux over the North Atlantic, datasets from nineteen AMIP6 and eight highresSST-present climate model simulations are analyzed and compared with the DEEPC (Diagnosing Earth’s Energy Pathways in the Climate system) product. As an indirect check of the ocean surface heat flux, the oceanic heat transport inferred from the combination of the ocean surface heat flux, sea ice, and ocean heat content tendency is compared with the RAPID (Rapid Climate Change-Meridional Overturning Circulation and Heat flux array) observations at 26°N in the Atlantic. The AMIP6 simulations show lower inferred heat transport due to less heat loss to the atmosphere. The heat loss from the AMIP6 ensemble mean north of 26°N in the Atlantic is about 10 W m−2 less than DEEPC, and the heat transport is about 0.30 PW (1 PW = 1015 W) lower than RAPID and DEEPC. The model horizontal resolution effect on the discrepancy is also investigated. Results show that by increasing the resolution, both surface heat flux north of 26°N and heat transport at 26°N in the Atlantic can be improved. observations; ocean heat transport; discrepancy; ocean net surface heat flux; simulations
Liu, Le; Wu, Bingyi; Ding, ShuoyiLiu, L., B. Wu, S. Ding, 2022: On the Association of the Summertime Shortwave Cloud Radiative Effect in Northern Russia With Atmospheric Circulation and Climate Over East Asia. Geophysical Research Letters, 49(2), e2021GL096606. doi: 10.1029/2021GL096606. This study employs ERA5 reanalysis and CERES/EBAF Ed4.1 data to evaluate the dominant features of summer shortwave cloud radiative effect (SWCRE) variability and associated atmospheric circulation anomalies. Our findings suggest that the greatest variability in summer SWCRE occurs over the Barents, Kara, and Laptev seas and northern Eurasia. We also observe a close relationship between summertime SWCRE, particularly in northern Russia, and atmospheric circulation variability over East Asia. Significant positive SWCRE anomalies over northern Russia favor the generation of the Ural blocking, and dynamically trigger the emergence of positive Eurasian (EU) pattern, resulting in positive (negative) precipitation anomalies in northern (southeastern) China and persistent East Asian heatwaves between 20°N and 40°N. In contrast to previous work, which has focused mainly on local atmospheric responses to SWCRE, this study provides a broader perspective, thereby helping bridge summertime circulation between high latitudes and East Asia. shortwave cloud radiative effect; East Asian atmospheric circulation variability; Eurasian teleconnection; Ural blocking
Liu, Yawen; Wang, Minghuai; Qian, Yun; Ding, AijunLiu, Y., M. Wang, Y. Qian, A. Ding, 2022: A Strong Anthropogenic Black Carbon Forcing Constrained by Pollution Trends Over China. Geophysical Research Letters, 49(10), e2022GL098965. doi: 10.1029/2022GL098965. Estimates of the effective radiative forcing from aerosol-radiation interaction (ERFari) of anthropogenic Black Carbon (BC) have been disputable and require better constraints. Here we find a substantial decline in atmospheric absorption of −5.79Wm−2decade−1 over eastern central China (ECC) responding to recent anthropogenic BC emission reductions. By combining the observational finding with advances from Coupled Model Intercomparison Project phase6 (CMIP6), we identify an emergent constraint on the ERFari of anthropogenic BC. We show that across CMIP6 models the simulated trends correlate well with simulated annual mean shortwave atmospheric absorption by anthropogenic BC over China. Making use of this emergent relationship allows us to constrain the aerosol absorption optical depth of anthropogenic BC and further provide a constrained range of 2.4–3.0 Wm−2 for its top-of-atmosphere ERFari over China, higher than existing estimates. Our work supports a strong warming effect of BC over China, and highlights the need to improve BC simulations over source regions. CMIP6 models; anthropogenic black carbon; effective radiative forcing from aerosol-radiation interaction; long-term trend; observational constraint
Loeb, Norman G.; Mayer, Michael; Kato, Seiji; Fasullo, John T.; Zuo, Hao; Senan, Retish; Lyman, John M.; Johnson, Gregory C.; Balmaseda, MagdalenaLoeb, N. G., M. Mayer, S. Kato, J. T. Fasullo, H. Zuo, R. Senan, J. M. Lyman, G. C. Johnson, M. Balmaseda, 2022: Evaluating Twenty-Year Trends in Earth's Energy Flows From Observations and Reanalyses. Journal of Geophysical Research: Atmospheres, 127(12), e2022JD036686. doi: 10.1029/2022JD036686. Satellite, reanalysis, and ocean in situ data are analyzed to evaluate regional, hemispheric and global mean trends in Earth's energy fluxes during the first 20 years of the twenty-first century. Regional trends in net top-of-atmosphere (TOA) radiation from the Clouds and the Earth's Radiant Energy System (CERES), ECMWF Reanalysis 5 (ERA5), and a model similar to ERA5 with prescribed sea surface temperature (SST) and sea ice differ markedly, particularly over the Eastern Pacific Ocean, where CERES observes large positive trends. Hemispheric and global mean net TOA flux trends for the two reanalyses are smaller than CERES, and their climatological means are half those of CERES in the southern hemisphere (SH) and more than nine times larger in the northern hemisphere (NH). The regional trend pattern of the divergence of total atmospheric energy transport (TEDIV) over ocean determined using ERA5 analyzed fields is similar to that inferred from the difference between TOA and surface fluxes from ERA5 short-term forecasts. There is also agreement in the trend pattern over ocean for surface fluxes inferred as a residual between CERES net TOA flux and ERA5 analysis TEDIV and surface fluxes obtained directly from ERA5 forecasts. Robust trends are observed over the Gulf Stream associated with enhanced surface-to-atmosphere transfer of heat. Within the ocean, larger trends in ocean heating rate are found in the NH than the SH after 2005, but the magnitude of the trend varies greatly among datasets.
Lv, Mingzhu; Song, Yan; Li, Xijia; Wang, Mengsi; Qu, YingLv, M., Y. Song, X. Li, M. Wang, Y. Qu, 2022: Spatiotemporal characteristics and driving factors of global planetary albedo: an analysis using the Geodetector method. Theoretical and Applied Climatology, 147(1), 737-752. doi: 10.1007/s00704-021-03858-9. As an important parameter of the Earth’s energy budget, the planetary albedo of Earth varies with the dynamics of atmospheric and surface variables. In this study, we investigated the spatiotemporal characteristics and driving factors of the global planetary albedo using the Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) dataset and the Geodetector method. The results revealed that the planetary albedo can be decomposed into atmospheric and surface contributions, and the planetary albedo in the middle and low latitudes was predominantly affected by the atmospheric contribution. The global planetary albedo and the atmospheric and surface contributions exhibited decreasing trends of − 0.0020, − 0.0015, and − 0.0004/decade from 2001 to 2018, respectively, which were closely related to the variations of atmospheric and surface variables. The cloud fraction was the driving factor of the atmospheric contribution in the middle and low latitudes, and its influence was further enhanced by the aerosol optical thickness (AOT), ice water path (IWP), and liquid water path (LWP). The snow/ice coverage and normalized difference vegetation index (NDVI) were the driving factors of the surface contribution in the snow/ice-covered and vegetated areas, respectively. The interaction relationships between the surface variables were mainly bi-enhanced and nonlinearly enhanced. These results provide useful information about the driving factors of the planetary albedo and are benefit for improving the parametrization of the planetary albedo.
Ma, Mengnan; Ou, Tinghai; Liu, Dongqing; Wang, Shuyu; Fang, Juan; Tang, JianpingMa, M., T. Ou, D. Liu, S. Wang, J. Fang, J. Tang, 2022: Summer regional climate simulations over Tibetan Plateau: from gray zone to convection permitting scale. Climate Dynamics. doi: 10.1007/s00382-022-06314-0. The Tibetan Plateau (TP) is often referred to as ‘the Third Pole’ and plays an essential role in the global climate. However, it remains challenging for most global and regional models to realistically simulate the characteristics of climate over the TP. In this study, two Weather Research and Forecasting model (WRF) experiments using spectral nudging with gray-zone (GZ9) and convection-permitting (CP3) resolution are conducted for summers from 2009 to 2018. The surface air temperature (T2m) and precipitation from the two simulations and the global reanalysis ERA5 are evaluated against in-situ observations. The results show that ERA5 has a general cold bias over southern TP, especially in maximum T2m (Tmax), and wet bias over whole TP. Both experiments can successfully capture the spatial pattern and daily variation of T2m and precipitation, though cold bias for temperature and dry bias for precipitation exist especially over the regions south of 35° N. Compared with ERA5, the added value of the two WRF experiments is mainly reflected in the reduced cold bias especially for Tmax with more improvement found in CP3 and the reduced wet bias. However, the ability of the convection-permitting WRF experiment in improving the simulation of precipitation seems limited when compared to the gray-zone WRF experiment, which may be related to the biases in physical parameterization and lack of representativeness of station observation. Further investigation into surface radiation budget reveals that the underestimation of net shortwave radiation contributes a lot to the cold bias of T2m over the southeastern TP in GZ9 which is improved in CP3. Compared with GZ9, CP3 shows that larger specific humidity at low-level (mid-high level) coexists with more precipitation (clouds) over the southern TP. This improvement is achieved by better depiction of topographic details, underlying surface and atmospheric processes, land–atmosphere interactions and so on, leading to stronger northward water vapor transport (WVT) in CP3, providing more water vapor for precipitation at surface and much wetter condition in the mid-high level. Tibetan Plateau; Convection permitting; Gray zone; Spectral nudging; Summer precipitation; Surface air temperature
Ma, Wen; Ding, Jianli; Wang, Jinlong; Zhang, JunyongMa, W., J. Ding, J. Wang, J. Zhang, 2022: Effects of aerosol on terrestrial gross primary productivity in Central Asia. Atmospheric Environment, 288, 119294. doi: 10.1016/j.atmosenv.2022.119294. Aerosols significantly contribute to global and regional climate change by altering the surface solar radiation, thereby affecting plant productivity. Central Asia is a primary source of global dust aerosols. However, the mechanisms of how aerosols affect terrestrial gross primary productivity (GPP), especially in Central Asia, are not clearly understood. In this study, we investigated the spatial variation in aerosol optical depth (AOD) and GPP and the relationship between them during the growing season (April–October) from 2001 to 2018 using remote sensing data from several sources. We created a GWR-SEM model consisting of a geographically weighted model (GWR) coupled with a structural equation model (SEM) to quantify and analyze the effects of AOD on GPP. The results show that AOD decreased slightly at a rate of −0.0002 y−1 during the study period and that there was a tendency towards spatial aggregation. The extent of AOD pollution in the northwest region (around the Aral Sea) was slightly greater than that in the southeast. GPP increased significantly at a rate of 7.2965 g C m−2 y−2, especially in the northern region. There were some differences in the effects of AOD on GPP between different vegetation types; the highest AOD–GPP correlation was found in shrublands and croplands. Analysis of the GWR-SEM model suggested that AOD and two forms of radiation (surface net radiation, SNR, and photosynthetically active radiation, PAR) explained 72.4% (63.4% for 2001, 66.8% for 2018) of the spatial variation in GPP. SNR had the greatest effect on GPP, followed by AOD. Diffuse PAR had the greatest indirect effect on GPP. The findings of this study highlight the importance of aerosol pollution on spatial variation in gross primary productivity, and they provide a methodological framework for investigating the relationship between AOD and GPP in arid areas. GPP; Aerosol optional depth; Central Asia; SEM
Maity, Suman; Nayak, Sridhara; Nayak, Hara Prasad; Bhatla, R.Maity, S., S. Nayak, H. P. Nayak, R. Bhatla, 2022: Comprehensive assessment of RegCM4 towards interannual variability of Indian Summer Monsoon using multi-year simulations. Theoretical and Applied Climatology. doi: 10.1007/s00704-022-03961-5. In this study, the interannual variability (IAV) of Indian Summer Monsoon (ISM) is investigated using multi-year (1982‒2016) seasonal scale simulations (May‒September) of the regional climate model RegCM4. Model-simulated fields such as surface temperature, wind and rainfall are validated initially to testify the climatological behaviour of ISM. Subsequently, different aspects of IAV associated with ISM are discussed primarily focusing on model simulated rainfall and are verified against high-resolution rainfall analysis from India Meteorological Department (IMD). Analysis indicated that RegCM4 shows reasonable accuracy in simulating major large-scale features, however, has cold bias over entire India and wet (dry) bias over northwest and peninsular (central) India. Easterly (westerly) bias is noticed in the model simulated low (upper) level wind that affects regional Hadley circulation. The cold bias is found to be associated with the feedback cycle of land–atmosphere interaction. Surface evaporative cooling likely affects the static instability in the atmospheric column, thereby limiting the convection and thus reducing rainfall. While categorizing, it is noticed that the efficacy of the model is found to be better in simulating normal monsoon as compared to contrasting monsoon (deficit and excess) year, thereby reducing the simulation skill for the entire period. EOF analysis revealed that first two leading modes of IMD rainfall are linked with large-scale variabilities, viz. El-Nino Southern Oscillation and Indian Ocean Dipole, respectively, but RegCM4 could not well reproduce these relationships. The spectral analysis showed 2–7 year periodicity in the model. However, the associated spectral peaks are close to the red noise spectrum due to their weak power suggesting limited model skill to capture large-scale variability. Overall, this study advocates that the RegCM4 could capture the climatological features of ISM fairly well, but needs further improvement in representing the IAV more accurately.
Maloney, Christopher; Toon, Brian; Bardeen, Charles; Yu, Pengfei; Froyd, Karl; Kay, Jennifer; Woods, SarahMaloney, C., B. Toon, C. Bardeen, P. Yu, K. Froyd, J. Kay, S. Woods, 2022: The balance between heterogeneous and homogeneous nucleation of ice clouds using CAM5/CARMA. Journal of Geophysical Research: Atmospheres, e2021JD035540. doi: 10.1029/2021JD035540. We present a modification to the Community Aerosol and Radiation model for Atmospheres (CARMA) sectional ice microphysical model where we have added interactive nucleation of sulfates and heterogeneous nucleation onto dust in order to create a more comprehensive representation of ice nucleation within the CARMA sectional ice model. The convective wet removal fix has also been added in order to correctly transport aerosol within the Community Atmosphere Model version 5 (CAM5) and the 3-mode Modal Aerosols Model (MAM3). In CARMA, the balance of homogeneous and heterogeneous nucleation is controlled by the presence of temperatures below 240 °K, supersaturation, and the availability of heterogeneous nuclei. Due to a paucity of dust at altitudes above about 7 km, where temperatures over most of the Earth fall below 240 °K, cirrus clouds above 7 km nucleate primarily via homogeneous nucleation on aqueous sulfate aerosols in our simulations. Over mid-latitudes of the Northern Hemisphere, dust is more common above 7 km during spring through fall, and both heterogeneous nucleation and homogenous freezing occur in our model. Below 7 km heterogeneous nucleation dominates in situ formation of ice. Furthermore, we find an improvement of the representation of in-cloud ice within mixed phase clouds in CAM5/CARMA when compared to simulations with only homogeneous ice nucleation. Other modes of nucleation such as contact nucleation of liquid cloud droplets or liquid cloud droplet freezing on immersion nuclei, were not directly compared with classical depositional heterogeneous nucleation in this study. Cloud modeling; Dust Aerosol; Heterogeneous nucleation; Homogeneous nucleation; Ice nucleation
Matthews, G.Matthews, G., 2022: Direct Solar Viewing Calibration Concept for Future CERES-, GERB-, or Libera-Type Earth Orbital Climate Missions. J. Atmos. Oceanic Technol., 39(7), 1085-1091. doi: 10.1175/JTECH-D-21-0002.1. Abstract Better predictions of global warming can be enabled by tuning legacy and current computer simulations to Earth radiation budget (ERB) measurements. Since the 1970s, such orbital results exist, and the next-generation instruments such as one called “Libera” are in production. Climate communities have requested that new ERB observing system missions like these have calibration accuracy obtaining significantly improved calibration SI traceability and stability. This is to prevent untracked instrument calibration drifts that could lead to false conclusions on climate change. Based on experience from previous ERB missions, the alternative concept presented here utilizes directly viewing solar calibration, for cloud-size Earth measurement resolution at
Matthews, GrantMatthews, G., 2022: Assessment of Terra/Aqua MODIS and Deep Convective Cloud Albedo Solar Calibration Accuracies and Stabilities Using Lunar Calibrated MERBE Results. Remote Sensing, 14(11), 2517. doi: 10.3390/rs14112517. Moon calibrated radiometrically stable and relatively accurate Earth reflected solar measurements from the Moon and Earth Radiation Budget Experiment (MERBE) are compared here to primary channels of coaligned Terra/Aqua MODIS instruments. A space-based climate observing system immune to untracked drifts due to varying instrument calibration is a key priority for climate science. Measuring these changes in radiometers such as MODIS and compensating for them is critical to such a system. The independent MERBE project using monthly lunar scans has made a proven factor of ten improvement in calibration stability and relative accuracy of measurements by all devices originally built for another project called ‘CERES’, also on the Terra and Aqua satellites. The MERBE comparison shown here uses spectrally invariant Deep Convective Cloud or DCC targets as a transfer, with the objective of detecting possible unknown MODIS calibration trends or errors. Most MODIS channel 1–3 collection 5 calibrations are shown to be correct and stable within stated accuracies of 3% relative to the Moon, much in line with changes made for MODIS collection 6. Stable lunar radiance standards are then separately compared to the sometimes used calibration metric of the coldest DCCs as standalone calibration targets, when also located by MODIS. The analysis overall for the first time finds such clouds can serve as an absolute solar target on the order of 1% accuracy and are stable to ±0.3% decade−1 with two sigma confidences, based on the Moon from 2000–2015. Finally, time series analysis is applied to potential DCC albedo corrected Terra data. This shows it is capable of beginning the narrowing of cloud climate forcing uncertainty before 2015; some twenty five years sooner than previously calculated elsewhere, for missions yet to launch. earth radiation budget; MODIS; earth observation; lunar calibration; MERBE; climate observing system; deep convective cloud (DCC) albedo; solar forcing
Mayer, Johannes; Mayer, Michael; Haimberger, Leopold; Liu, ChunleiMayer, J., M. Mayer, L. Haimberger, C. Liu, 2022: Comparison of Surface Energy Fluxes from Global to Local Scale. J. Climate, 35(14), 4551-4569. doi: 10.1175/JCLI-D-21-0598.1. Abstract This study uses the ECMWF ERA5 reanalysis and observationally constrained top-of-the-atmosphere radiative fluxes to infer net surface energy fluxes covering 1985–2018, which can be further adjusted to match the observed mean land heat uptake. Various diagnostics are applied to provide error estimates of inferred fluxes on different spatial scales. For this purpose, adjusted as well as unadjusted inferred surface fluxes are compared with other commonly used flux products. On a regional scale, the oceanic energy budget of the North Atlantic between the RAPID array at 26.5°N and moorings located farther north (e.g., at the Greenland–Scotland Ridge) is evaluated. On the station scale, a comprehensive comparison of inferred and buoy-based fluxes is presented. Results indicate that global land and ocean averages of unadjusted inferred surface fluxes agree with the observed heat uptake to within 1 W m−2, while satellite-derived and model-based fluxes show large global mean biases. Furthermore, the oceanic energy budget of the North Atlantic is closed to within 2.7 (−0.2) W m−2 for the period 2005–09 when unadjusted (adjusted) inferred surface fluxes are employed. Indirect estimates of the 2004–16 mean oceanic heat transport at 26.5°N are 1.09 PW (1.17 PW with adjusted fluxes), which agrees well with observed RAPID transports. On the station scale, inferred fluxes exhibit a mean bias of −20.1 W m−2 when using buoy-based fluxes as reference, which confirms expectations that biases increase from global to local scales. However, buoy-based fluxes as reference are debatable, and are likely positively biased, suggesting that the station-scale bias of inferred fluxes is more likely on the order of −10 W m−2.
Mazhar, Usman; Jin, Shuanggen; Hu, Ting; Bilal, Muhammad; Ali, MD Arfan; Atique, LuqmanMazhar, U., S. Jin, T. Hu, M. Bilal, M. A. Ali, L. Atique, 2022: Long-time Variation and Mechanism of Surface Energy Budget over Diverse Geographical Regions in Pakistan. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 1-13. doi: 10.1109/JSTARS.2022.3185177. Earth's Energy budget is a major force that drives global climate. The long-term pattern of land surface energy budget with pronounced biophysical effects on climate was normally ignored at a regional scale, particularly in Pakistan. In this paper, the land surface energy budget from 2001 to 2018 was estimated and analyzed from Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud and the Earth's Radiant Energy System (CERES) observations over three geographical regions (Northern highlands, Indus plains and Baluchistan plateau) in Pakistan. Biophysical and energy budget parameters such as Land Surface Temperature (LST), albedo, emissivity, and Normalized Difference Vegetation Index (NDVI) were obtained from MODIS, while the downward shortwave solar and longwave thermal radiation were obtained from CERES satellite data. Spatiotemporal trends of three energy budget parameters: net radiation, latent heat flux and sensible heat flux, and three biophysical parameters, albedo, NDVI and LST, were investigated from 2001 to 2018. The latent heat flux showed a significant increase with a trend of 0.24, while a decrease in sensible heat flux with a trend of−0.21 was observed over Pakistan. Net radiation showed an ignorable increase with a trend of 0.054 over whole Pakistan. A significant negative relation was found between net radiation and sensible heat flux with albedo while a significant positive relation was found between latent heat flux and NDVI. Biophysical parameters such as NDVI, albedo and LST successively explain the trends of radiative and non-radiative fluxes. This study comprehensively explains the mechanism and patterns of the regional energy budget. Land surface; CERES; Meteorology; MODIS; Land surface temperature; Net radiation; Heating systems; and Pakistan; IP networks; Land surface Energy budget; Spatiotemporal phenomena
McCoy, Daniel T.; Field, Paul; Frazer, Michelle E.; Zelinka, Mark D.; Elsaesser, Gregory S; Mülmenstädt, Johannes; Tan, Ivy; Myers, Timothy A.; Lebo, Zachary J.McCoy, D. T., P. Field, M. E. Frazer, M. D. Zelinka, G. S. Elsaesser, J. Mülmenstädt, I. Tan, T. A. Myers, Z. J. Lebo, 2022: Extratropical shortwave cloud feedbacks in the context of the global circulation and hydrological cycle. Geophysical Research Letters, n/a(n/a), e2021GL097154. doi: 10.1029/2021GL097154. Shortwave (SW) cloud feedback (SWFB) is the primary driver of uncertainty in the effective climate sensitivity (ECS) predicted by global climate models (GCMs). ECS for several GCMs participating in the sixth assessment report exceed 5K, above the fifth assessment report ‘likely’ maximum (4.5K) due to extratropical SWFB’s that are more positive than those simulated in the previous generation of GCMs. Here we show that across 57 GCMs Southern Ocean SWFB can be predicted from the sensitivity of column-integrated liquid water mass (LWP) to moisture convergence and to surface temperature. The response of LWP to moisture convergence and the response of albedo to LWP anti-correlate across GCMs. This is because GCMs that simulate a larger response of LWP to moisture convergence tend to have higher mean-state LWPs, which reduces the impact of additional LWP on albedo. Observational constraints suggest a modestly negative Southern Ocean SWFB— inconsistent with extreme ECS. Feedback; Moisture; Clouds; Climate; Simulations
Miyamoto, Ayumu; Nakamura, Hisashi; Miyasaka, Takafumi; Kosaka, YuMiyamoto, A., H. Nakamura, T. Miyasaka, Y. Kosaka, 2022: Wintertime Weakening of Low-Cloud Impacts on the Subtropical High in the South Indian Ocean. J. Climate, 35(1), 323-334. doi: 10.1175/JCLI-D-21-0178.1. Abstract To elucidate the unique seasonality in the coupled system of the subtropical Mascarene high and low-level clouds, the present study compares wintertime cloud radiative impacts on the high with their summertime counterpart through coupled and atmospheric general circulation model simulations. A comparison of a fully coupled control simulation with another simulation in which the radiative effects of low-level clouds are artificially switched off demonstrates that the low-cloud effect on the formation of the Mascarene high is much weaker in winter. Background climatology plays an important role in this seasonality of the Mascarene high reinforcement. Relative to summer, the suppression of deep convection due to low-level clouds that acts to reinforce the high is much weaker in winter. This arises from 1) seasonally lower sea surface temperature in concert with the smaller sea surface temperature reduction due to the deeper ocean mixed layer and the weaker cloud radiative effect under weaker insolation and 2) seasonally stronger subtropical subsidence associated with the Hadley circulation in winter. As verified through atmospheric dynamical model experiments, enhanced cloud-top radiative cooling by low-level clouds acts to reinforce the wintertime Mascarene high in comparable magnitude as in summer. The present study reveals that the self-sustaining feedback with low-level clouds alone is insufficient for replenishing the full strength of the wintertime Mascarene high. This implies that another internal feedback pathway and/or external driver must be operative in maintaining the wintertime high.
Nugent, J. M.; Turbeville, S. M.; Bretherton, C. S.; Blossey, P. N.; Ackerman, T. P.Nugent, J. M., S. M. Turbeville, C. S. Bretherton, P. N. Blossey, T. P. Ackerman, 2022: Tropical Cirrus in Global Storm-Resolving Models: 1. Role of Deep Convection. Earth and Space Science, 9(2), e2021EA001965. doi: 10.1029/2021EA001965. Pervasive cirrus clouds in the upper troposphere and tropical tropopause layer (TTL) influence the climate by altering the top-of-atmosphere radiation balance and stratospheric water vapor budget. These cirrus are often associated with deep convection, which global climate models must parameterize and struggle to accurately simulate. By comparing high-resolution global storm-resolving models from the Dynamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) intercomparison that explicitly simulate deep convection to satellite observations, we assess how well these models simulate deep convection, convectively generated cirrus, and deep convective injection of water into the TTL over representative tropical land and ocean regions. The DYAMOND models simulate deep convective precipitation, organization, and cloud structure fairly well over land and ocean regions, but with clear intermodel differences. All models produce frequent overshooting convection whose strongest updrafts humidify the TTL and are its main source of frozen water. Intermodel differences in cloud properties and convective injection exceed differences between land and ocean regions in each model. We argue that, with further improvements, global storm-resolving models can better represent tropical cirrus and deep convection in present and future climates than coarser-resolution climate models. To realize this potential, they must use available observations to perfect their ice microphysics and dynamical flow solvers. convection; microphysics; cirrus; tropical tropopause layer; DYAMOND; global storm-resolving models
Nuncio, M.; Satheesan, K.; Acharya, Asutosh; Chatterjee, Sourav; Subeesh, M. P.; Athulya, R.Nuncio, M., K. Satheesan, A. Acharya, S. Chatterjee, M. P. Subeesh, R. Athulya, 2022: A southerly wind event and precipitation in Ny Ålesund, Arctic. Journal of Atmospheric and Solar-Terrestrial Physics, 231, 105869. doi: 10.1016/j.jastp.2022.105869. Precipitation in the Arctic is expected to increase with implications to ecosystems and changes to atmospheric circulation. In the Arctic strong southerly wind, often known as atmospheric rivers, supply enormous moisture and heat into the Arctic and is expected to increase in future warming scenarios. The impact of these events on Arctic climate change is not yet understood fully. In this study precipitation associated with such an event is studied for Ny Ålesund, Svalbard for 2016 March. During the event, the high precipitation was noticed between 22 and 23 UTC and 6–9 UTC on 12th March and 13th March respectively. It has been shown that during these two time periods, downwelling longwave radiation increased due to clouds. The enhanced downwelling longwave radiation increased the surface temperature locally. Above the shallow planetary boundary, advection dominated the temperature changes and initiated a shallow convection in the atmosphere leading to intensified precipitation in the lower layers during the event. Enhanced vertical velocity in MRR could be a result of this convection. Thus, the largescale southerly winds, that developed into an atmospheric river has not only contributed to the supply of heat and moisture but also enhanced cloud radiative effects and resulted in local warming. The moisture sources for this event appears to be Norwegian Sea and the east coast of Greenland. The scenario we have investigated was characterised by a warm Arctic with southerly warm winds. Studies suggest that convective scale precipitation is increasing in Eurasia under warm conditions. Our study points to the change in precipitation regime that Arctic may characterise as the warming continues. Cloud radiative effects; Arctic precipitation; Atmospheric river
Oreopoulos, Lazaros; Cho, Nayeong; Lee, Dongmin; Lebsock, Matthew; Zhang, ZhiboOreopoulos, L., N. Cho, D. Lee, M. Lebsock, Z. Zhang, 2022: Assessment of Two Stochastic Cloud Subcolumn Generators Using Observed Fields of Vertically Resolved Cloud Extinction. J. Atmos. Oceanic Technol., 39(8), 1229-1244. doi: 10.1175/JTECH-D-21-0166.1. Abstract We evaluate two stochastic subcolumn generators used in GCMs to emulate subgrid cloud variability enabling comparisons with satellite observations and simulations of certain physical processes. Our evaluation necessitated the creation of a reference observational dataset that resolves horizontal and vertical cloud variability. The dataset combines two CloudSat cloud products that resolve two-dimensional cloud optical depth variability of liquid, ice, and mixed-phase clouds when blended at ∼200 m vertical and ∼2 km horizontal scales. Upon segmenting the dataset to individual “scenes,” mean profiles of the cloud fields are passed as input to generators that produce scene-level cloud subgrid variability. The assessment of generator performance at the scale of individual scenes and in a mean sense is largely based on inferred joint histograms that partition cloud fraction within predetermined combinations of cloud-top pressure–cloud optical thickness ranges. Our main finding is that both generators tend to underestimate optically thin clouds, while one of them also tends to overestimate some cloud types of moderate and high optical thickness. Associated radiative flux errors are also calculated by applying a simple transformation to the cloud fraction histogram errors, and are found to approach values almost as high as 3 W m−2 for the cloud radiative effect in the shortwave part of the spectrum. Significance Statement The purpose of the paper is to assess the realism of relatively simple ways of producing fine-scale cloud variability in global models from coarsely resolved cloud properties. The assessment is achieved via comparisons to observed cloud fields where the fine-scale variability is known in both the horizontal and vertical directions. Our results show that while the generators have considerable skill, they still suffer from consistent deficiencies that need to be addressed with further development guided by appropriate observations.
Paca, Victor Hugo da Motta; Espinoza-Dávalos, Gonzalo E.; da Silva, Rodrigo; Tapajós, Raphael; dos Santos Gaspar, Avner BrasileiroPaca, V. H. d. M., G. E. Espinoza-Dávalos, R. da Silva, R. Tapajós, A. B. dos Santos Gaspar, 2022: Remote Sensing Products Validated by Flux Tower Data in Amazon Rain Forest. Remote Sensing, 14(5), 1259. doi: 10.3390/rs14051259. This work compares methods of climate measurements, such as those used to measure evapotranspiration, precipitation, net radiation, and temperature. The satellite products used were compared and evaluated against flux tower data. Evapotranspiration was validated against the SSEBop monthly and GLEAM daily and monthly products, respectively, and the results were RMSE = 24.144 mm/month, NRMSE = 0.223, r2 = 0.163, slope = 0.411; RMSE = 1.781 mm/day, NRMSE = 0.599, r2 = 0.000, slope = 0.006; RMSE = 36.17 mm/month, NRMSE = 0.401, r2 = 0.002, and slope = 0.026. Precipitation was compared with the CHIRPS data, K67 was not part of the CHIRPS station correction. The results for both the daily and monthly comparisons were RMSE = 18.777 mm/day, NRMSE = 1.027, r2 = 0.086, slope = 0.238 and RMSE = 130.713 mm/month, NRMSE = 0.706, r2 = 0.402, and slope = 0.818. The net radiation validated monthly with CERES was RMSE = 75.357 W/m2, NRMSE = 0.383, r2 = 0.422, and slope = 0.867. The temperature results, as compared to MOD11C3, were RMSE = 2.829 °C, NRMSE = 0.116, r2 = 0.153, and slope = 0.580. Comparisons between the remote sensing products and validation against the ground data were performed on a monthly basis. GLEAM and CHIRPS daily were the data sets with considerable discrepancy. comparison and validation; hydro-meteorological variables; remote sensing products
Peng, Liran; Pritchard, Michael; Hannah, Walter M.; Blossey, Peter N.; Worley, Patrick H; Bretherton, Christopher S.Peng, L., M. Pritchard, W. M. Hannah, P. N. Blossey, P. H. Worley, C. S. Bretherton, 2022: Load-balancing intense physics calculations to embed regionalized high-resolution cloud resolving models in the E3SM and CESM climate models. Journal of Advances in Modeling Earth Systems, n/a(n/a), e2021MS002841. doi: 10.1029/2021MS002841. We design a new strategy to load-balance high-intensity sub-grid atmospheric physics calculations restricted to a small fraction of a global climate simulation’s domain. We show why the current parallel load balancing infrastructure of CESM and E3SM cannot efficiently handle this scenario at large core counts. As an example, we study an unusual configuration of the E3SM Multiscale Modeling Framework (MMF) that embeds a binary mixture of two separate cloud-resolving model grid structures that is attractive for low cloud feedback studies. Less than a third of the planet uses high-resolution (MMF-HR; sub-km horizontal grid spacing) relative to standard low-resolution (MMF-LR) cloud superparameterization elsewhere. To enable MMF runs with Multi-Domain CRMs, our load balancing theory predicts the most efficient computational scale as a function of the high-intensity work’s relative overhead and its fractional coverage. The scheme successfully maximizes model throughput and minimizes model cost relative to precursor infrastructure, effectively by devoting the vast majority of the processor pool to operate on the few high-intensity (and rate-limiting) HR grid columns. Two examples prove the concept, showing that minor artifacts can be introduced near the HR/LR CRM grid transition boundary on idealized aquaplanets, but are minimal in operationally relevant real-geography settings. As intended, within the high (low) resolution area, our Multi-Domain CRM simulations exhibit cloud fraction and shortwave reflection convergent to standard baseline tests that use globally homogenous MMF-LR and MMF-HR. We suggest this approach can open up a range of creative multi-resolution climate experiments without requiring unduly large allocations of computational resources.
Quaas, Johannes; Jia, Hailing; Smith, Chris; Albright, Anna Lea; Aas, Wenche; Bellouin, Nicolas; Boucher, Olivier; Doutriaux-Boucher, Marie; Forster, Piers M.; Grosvenor, Daniel; Jenkins, Stuart; Klimont, Zig; Loeb, Norman G.; Ma, Xiaoyan; Naik, Vaishali; Paulot, Fabien; Stier, Philip; Wild, Martin; Myhre, Gunnar; Schulz, MichaelQuaas, J., H. Jia, C. Smith, A. L. Albright, W. Aas, N. Bellouin, O. Boucher, M. Doutriaux-Boucher, P. M. Forster, D. Grosvenor, S. Jenkins, Z. Klimont, N. G. Loeb, X. Ma, V. Naik, F. Paulot, P. Stier, M. Wild, G. Myhre, M. Schulz, 2022: Robust evidence for reversal in the aerosol effective climate forcing trend. Atmospheric Chemistry and Physics Discussions, 1-25. doi: 10.5194/acp-2022-295. Abstract. Anthropogenic aerosols exert a cooling inﬂuence that offsets part of the greenhouse gas warming. Due to their short tropospheric lifetime of only up to several days, the aerosol forcing responds quickly to emissions. Here we present and discuss the evolution of the aerosol forcing since 2000. There are multiple lines of evidence that allow to robustly conclude that the anthropogenic aerosol effective radiative forcing – both aerosol-radiation and aerosol-cloud interactions – has become globally less negative, i.e. that the trend in aerosol effective radiative forcing changed sign from negative to positive. Bottom-up inventories show that anthropogenic primary aerosol and aerosol precursor emissions declined in most regions of the world; observations related to aerosol burden show declining trends, in particular of the ﬁne-mode particles that make up most of the anthropogenic aerosols; satellite retrievals of cloud droplet numbers show trends consistent in sign, as do observations of top-of-atmosphere radiation. Climate model results, including a revised set that is constrained by observations of the ocean heat content evolution show a consistent sign and magnitude for a positive forcing relative to 2000 due to reduced aerosol effects. This reduction leads to an acceleration of the forcing of climate change, i.e. an increase in forcing by 0.1 to 0.3 W m-2, up to 12 % of the total climate forcing in 2019 compared to 1750 according to IPCC.
Ramesh, Nandini; Boos, William R.Ramesh, N., W. R. Boos, 2022: The Unexpected Oceanic Peak in Energy Input to the Atmosphere and Its Consequences for Monsoon Rainfall. Geophysical Research Letters, 49(12), e2022GL099283. doi: 10.1029/2022GL099283. Monsoons have historically been understood to be caused by the low thermal inertia of land, allowing more energy from summer insolation to be transferred to the overlying atmosphere than over adjacent ocean. Here, we show that during boreal summer, the global maximum net energy input (NEI) to the atmosphere unexpectedly lies over the Indian Ocean, not over land. Observed radiative fluxes suggest that cloud-radiative effects (CRE) almost double the NEI over ocean, shifting the NEI peak from land to ocean. Global climate model experiments with both land and interactive sea surface temperatures confirm that CRE create the oceanic NEI maximum. Interactions between CRE, NEI, circulation, and land-sea contrast in surface heat capacity shift precipitation from Southeast to South Asia. CRE thus alter the global partitioning of precipitation between land and ocean and the spatial structure of Earth's strongest monsoon, in ways that can be understood through the NEI. cloud radiative effects; monsoons; atmospheric dynamics; land-sea contrast; tropical climate
Ramos, R. D.; LeGrande, A. N.; Griffiths, M. L.; Elsaesser, G. S.; Litchmore, D. T.; Tierney, J. E.; Pausata, F. S. R.; Nusbaumer, J.Ramos, R. D., A. N. LeGrande, M. L. Griffiths, G. S. Elsaesser, D. T. Litchmore, J. E. Tierney, F. S. R. Pausata, J. Nusbaumer, 2022: Constraining Clouds and Convective Parameterizations in a Climate Model Using Paleoclimate Data. Journal of Advances in Modeling Earth Systems, 14(8), e2021MS002893. doi: 10.1029/2021MS002893. Cloud and convective parameterizations strongly influence uncertainties in equilibrium climate sensitivity. We provide a proof-of-concept study to constrain these parameterizations in a perturbed parameter ensemble of the atmosphere-only version of the Goddard Institute for Space Studies Model E2.1 simulations by evaluating model biases in the present-day runs using multiple satellite climatologies and by comparing simulated δ18O of precipitation (δ18Op), known to be sensitive to parameterization schemes, with a global database of speleothem δ18O records covering the Last Glacial Maximum (LGM), mid-Holocene (MH) and pre-industrial (PI) periods. Relative to modern interannual variability, paleoclimate simulations show greater sensitivity to parameter changes, allowing for an evaluation of model uncertainties over a broader range of climate forcing and the identification of parts of the world that are parameter sensitive. Certain simulations reproduced absolute δ18Op values across all time periods, along with LGM and MH δ18Op anomalies relative to the PI, better than the default parameterization. No single set of parameterizations worked well in all climate states, likely due to the non-stationarity of cloud feedbacks under varying boundary conditions. Future work that involves varying multiple parameter sets simultaneously with coupled ocean feedbacks will likely provide improved constraints on cloud and convective parameterizations. PPE; cloud and convective parameterization; paleoclimate model; proxy-model comparison; speleothem; water isotopes
Ren, Tong; Yang, Ping; Wei, Jian; Huang, Xianglei; Sang, HuiyanRen, T., P. Yang, J. Wei, X. Huang, H. Sang, 2022: Performance of Cloud 3D Solvers in Ice Cloud Shortwave Radiation Closure Over the Equatorial Western Pacific Ocean. Journal of Advances in Modeling Earth Systems, 14(2), e2021MS002754. doi: 10.1029/2021MS002754. For retrieving cloud optical properties from satellite images or computing these properties from climate model output, computationally efficient treatments of cloud horizontal inhomogeneity include the Monte Carlo Independent Column Approximation (McICA) and the Tripleclouds method. Computationally efficient treatment of cloud horizontal radiation exchanges includes the SPeedy Algorithm for Radiative TrAnsfer through CloUd Sides (SPARTACUS). As a test to derive properties from satellite images, we collocate Moderate Resolution Imaging Spectroradiometer (MODIS) cloud retrievals with near-nadir Cloud and the Earth's Radiant Energy System (CERES) footprints in July 2008 over an equatorial western Pacific Ocean region to compare the performance of the McICA, Tripleclouds, and SPARTACUS solvers to the conventional plane-parallel homogeneous (PPH) treatment. PPH overestimates cloud albedo, and the three solvers effectively reduce overestimation with root mean square error of shortwave upwelling irradiance decreasing between 15.72 and 18.53 W m−2, or about 22%–25%. Although cloud top variability does not get fed into the simulations, all three solvers also reduce the effect of cloud top variability on cloud albedo. Entrapment (energy reflected downward from clouds) and horizontal radiation transfer have opposite effects on the SPARTACUS cloud albedo simulation. The net effect depends on the cloud vertical extent, the unawareness of which limits the performance of the SPARTACUS solver. cloud 3D effect; cloud top variability; cloud vertical extent
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.
Salzmann, M.; Ferrachat, S.; Tully, C.; Münch, S.; Watson-Parris, D.; Neubauer, D.; Siegenthaler-Le Drian, C.; Rast, S.; Heinold, B.; Crueger, T.; Brokopf, R.; Mülmenstädt, J.; Quaas, J.; Wan, H.; Zhang, K.; Lohmann, U.; Stier, P.; Tegen, I.Salzmann, M., S. Ferrachat, C. Tully, S. Münch, D. Watson-Parris, D. Neubauer, C. Siegenthaler-Le Drian, S. Rast, B. Heinold, T. Crueger, R. Brokopf, J. Mülmenstädt, J. Quaas, H. Wan, K. Zhang, U. Lohmann, P. Stier, I. Tegen, 2022: The Global Atmosphere-aerosol Model ICON-A-HAM2.3–Initial Model Evaluation and Effects of Radiation Balance Tuning on Aerosol Optical Thickness. Journal of Advances in Modeling Earth Systems, 14(4), e2021MS002699. doi: 10.1029/2021MS002699. The Hamburg Aerosol Module version 2.3 (HAM2.3) from the ECHAM6.3-HAM2.3 global atmosphere-aerosol model is coupled to the recently developed icosahedral nonhydrostatic ICON-A (icon-aes-1.3.00) global atmosphere model to yield the new ICON-A-HAM2.3 atmosphere-aerosol model. The ICON-A and ECHAM6.3 host models use different dynamical cores, parameterizations of vertical mixing due to sub-grid scale turbulence, and parameter settings for radiation balance tuning. Here, we study the role of the different host models for simulated aerosol optical thickness (AOT) and evaluate impacts of using HAM2.3 and the ECHAM6-HAM2.3 two-moment cloud microphysics scheme on several meteorological variables. Sensitivity runs show that a positive AOT bias over the subtropical oceans is remedied in ICON-A-HAM2.3 because of a different default setting of a parameter in the moist convection parameterization of the host models. The global mean AOT is biased low compared to MODIS satellite instrument retrievals in ICON-A-HAM2.3 and ECHAM6.3-HAM2.3, but the bias is larger in ICON-A-HAM2.3 because negative AOT biases over the Amazon, the African rain forest, and the northern Indian Ocean are no longer compensated by high biases over the sub-tropical oceans. ICON-A-HAM2.3 shows a moderate improvement with respect to AOT observations at AERONET sites. A multivariable bias score combining biases of several meteorological variables into a single number is larger in ICON-A-HAM2.3 compared to standard ICON-A and standard ECHAM6.3. In the tropics, this multivariable bias is of similar magnitude in ICON-A-HAM2.3 and in ECHAM6.3-HAM2.3. In the extra-tropics, a smaller multivariable bias is found for ICON-A-HAM2.3 than for ECHAM6.3-HAM2.3. modeling; aerosol
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. climate models; cloud feedback; satellite; ice nucleation; Arctic amplificantion
Shi, Yang; Liu, Xiaohong; Wu, Mingxuan; Zhao, Xi; Ke, Ziming; Brown, HunterShi, Y., X. Liu, M. Wu, X. Zhao, Z. Ke, H. Brown, 2022: Relative importance of high-latitude local and long-range-transported dust for Arctic ice-nucleating particles and impacts on Arctic mixed-phase clouds. Atmospheric Chemistry and Physics, 22(4), 2909-2935. doi: 10.5194/acp-22-2909-2022. Abstract. Dust particles, serving as ice-nucleating particles (INPs), may impact the Arctic surface energy budget and regional climate by modulating the mixed-phase cloud properties and lifetime. In addition to long-range transport from low-latitude deserts, dust particles in the Arctic can originate from local sources. However, the importance of high-latitude dust (HLD) as a source of Arctic INPs (compared to low-latitude dust, LLD) and its effects on Arctic mixed-phase clouds are overlooked. In this study, we evaluate the contribution to Arctic dust loading and INP population from HLD and six LLD source regions by implementing a source-tagging technique for dust aerosols in version 1 of the US Department of Energy's Energy Exascale Earth System Model (E3SMv1). Our results show that HLD is responsible for 30.7 % of the total dust burden in the Arctic, whereas LLD from Asia and North Africa contributes 44.2 % and 24.2 %, respectively. Due to its limited vertical transport as a result of stable boundary layers, HLD contributes more in the lower troposphere, especially in boreal summer and autumn when the HLD emissions are stronger. LLD from North Africa and East Asia dominates the dust loading in the upper troposphere with peak contributions in boreal spring and winter. The modeled INP concentrations show better agreement with both ground and aircraft INP measurements in the Arctic when including HLD INPs. The HLD INPs are found to induce a net cooling effect (−0.24 W m−2 above 60∘ N) on the Arctic surface downwelling radiative flux by changing the cloud phase of the Arctic mixed-phase clouds. The magnitude of this cooling is larger than that induced by North African and East Asian dust (0.08 and −0.06 W m−2, respectively), mainly due to different seasonalities of HLD and LLD. Uncertainties of this study are discussed, which highlights the importance of further constraining the HLD emissions.
Shukla, Abhivyakti; Pattnaik, Sandeep; Trivedi, DhananjayShukla, A., S. Pattnaik, D. Trivedi, 2022: Study of Mesoscale Convective System and its Associated Cloud Structure over Indian Region Using Satellite Observations and Model Simulations. Journal of the Indian Society of Remote Sensing. doi: 10.1007/s12524-022-01573-0. The present study has discussed the identification of mesoscale convective systems (MCS) events using Cloud top temperatures from Cloud and the Earth’s Radiant Energy System and INSAT 3D imageries over the Indian region. The parameters such as height, areal extent, and vertical depth are considered as the criteria for identifying these intense rain-bearing MCS. High equivalent potential temperature, pronounced warm advection, low-level convergence, and local maximum in relative vorticity is associated with large-scale environments are the key indicators in identifying MCS. A total of five heavy rainfall events associated with MCS are simulated using the Weather Research and forecasting at a horizontal resolution of 3 km with a lead time of up to 96 h. In addition, the performance of two cumulus and four cloud microphysical parameterizations and their optimized combination are investigated for these MCS systems causing heavy rainfall over the region. The Betts–Miller–Janjic–Thompson combination simulated the best results in terms of rainfall, convective available potential energy, vertical updrafts, and reflectivity and its pre-formation environment of MCS. Further, this optimized combination is able to accurately represent the dominant hydrometeors (i.e., rain, graupel and snow), which have played a key role in simulating the MCS. Large-scale forcing such as moisture advection, convergence, relative vorticity, and equivalent potential temperature play a dominant role in the evolution and sustenance of MCS. Finally, a more robust (weaker) intensity MCS is better (poorly) predicted by the model. The findings of this study will further augment our understanding for better prediction of MCS associated with heavy rainfall events over the Indian region. Hydrometeors; Mesoscale convective system (MCS); WRF-ARW
Simonetti, Paolo; Vladilo, Giovanni; Silva, Laura; Maris, Michele; Ivanovski, Stavro L.; Biasiotti, Lorenzo; Malik, Matej; Hardenberg, Jost vonSimonetti, P., G. Vladilo, L. Silva, M. Maris, S. L. Ivanovski, L. Biasiotti, M. Malik, J. v. Hardenberg, 2022: EOS: Atmospheric Radiative Transfer in Habitable Worlds with HELIOS. The Astrophysical Journal, 925(2), 105. doi: 10.3847/1538-4357/ac32ca. We present EOS, a procedure for determining the outgoing longwave radiation (OLR) and top-of-atmosphere (TOA) albedo for a wide range of conditions expected to be present in the atmospheres of rocky planets with temperate conditions. EOS is based on HELIOS and HELIOS-K, which are novel and publicly available atmospheric radiative transfer (RT) codes optimized for fast calculations with GPU processors. These codes were originally developed for the study of giant planets. In this paper we present an adaptation for applications to terrestrial-type, habitable planets, adding specific physical recipes for the gas opacity and vertical structure of the atmosphere. To test the reliability of the procedure, we assessed the impact of changing line opacity profile, continuum opacity model, atmospheric lapse rate, and tropopause position prescriptions on the OLR and the TOA albedo. The results obtained with EOS are in line with those of other RT codes running on traditional CPU processors, while being at least one order of magnitude faster. The adoption of OLR and TOA albedo data generated with EOS in a zonal and seasonal climate model correctly reproduces the fluxes of the present-day Earth measured by the CERES spacecraft. The results of this study disclose the possibility to incorporate fast RT calculations in climate models aimed at characterizing the atmospheres of habitable exoplanets.
Singh, Sachchidanand; Mishra, Amit Kumar; Jose, Sandhya; Lodhi, Neelesh K.Singh, S., A. K. Mishra, S. Jose, N. K. Lodhi, 2022: Chapter 7 - Atmospheric pollution and solar ultraviolet radiation in Asia. Asian Atmospheric Pollution, 129-146. This chapter deals with atmospheric pollution, particularly the aerosol optical depth (AOD) and its impact on ultraviolet radiation flux reaching the Earth's surface, and its subsequent effect on vitamin D levels observed in the Asian region. It begins with the mean distribution during the last 16 years (2001–2016) of AOD, UVA, and UVB fluxes over Asia along with their trends on a 1°×1° grid scale. The Clouds and Earth Radiant Energy System (CERES) is the main source of data supported by data from MISR. High AOD values over Asia are well anticorrelated with the UVA and UVB fluxes reaching the surface. The reducing trend in UVB due to an increasing trend in AOD is a matter of concern, as UVB has a direct relation with the level of vitamin D prevalent in the Asian population, particularly in the South, Southeast Asian region. The accelerated economic development during the last two decades in Asia has led to an enhancement in AOD leading to a decrease in UVB reaching the surface and possibly reducing the production of vitamin D on a huge population in the region. Further targeted studies are however required to quantify the amount of reduction in vitamin D due to enhanced air pollution and AOD. CERES; Aerosol optical depth; MISR; Air pollution; UVA flux; UVB flux; Vitamin D
Sismanidis, Panagiotis; Bechtel, Benjamin; Perry, Mike; Ghent, DarrenSismanidis, P., B. Bechtel, M. Perry, D. Ghent, 2022: The Seasonality of Surface Urban Heat Islands across Climates. Remote Sensing, 14(10), 2318. doi: 10.3390/rs14102318. In this work, we investigate how the seasonal hysteresis of the Surface Urban Heat Island Intensity (SUHII) differs across climates and provide a detailed typology of the daytime and nighttime SUHII hysteresis loops. Instead of the typical tropical/dry/temperate/continental grouping, we describe Earth’s climate using the Köppen–Geiger system that empirically maps Earth’s biome distribution into 30 climate classes. Our thesis is that aggregating multi-city data without considering the biome of each city results in temporal means that fail to reflect the actual SUHII characteristics. This is because the SUHII is a function of both urban and rural features and the phenology of the rural surroundings can differ considerably between cities, even in the same climate zone. Our investigation covers all the densely populated areas of Earth and uses 18 years (2000–2018) of land surface temperature and land cover data from the European Space Agency’s Climate Change Initiative. Our findings show that, in addition to concave-up and -down shapes, the seasonal hysteresis of the SUHII also exhibits twisted, flat, and triangle-like patterns. They also suggest that, in wet climates, the daytime SUHII hysteresis is almost universally concave-up, but they paint a more complex picture for cities in dry climates. MODIS; LST; land surface temperature; ESA-CCI; Köppen–Geiger climate zones; seasonal hysteresis; SUHI; surface urban heat island
Södergren, A. H.; McDonald, A. J.Södergren, A. H., A. J. McDonald, 2022: Quantifying the Role of Atmospheric and Surface Albedo on Polar Amplification Using Satellite Observations and CMIP6 Model Output. Journal of Geophysical Research: Atmospheres, 127(12), e2021JD035058. doi: 10.1029/2021JD035058. Understanding polar amplification (PA) and its underlying processes is key to accurately predicting the climate system's response to increasing anthropogenic forcings. We examine the amplified warming in the Arctic and Antarctic in 17 global climate models from the Coupled Model Intercomparison Project 6 (CMIP6) against satellite data. Large hemispheric differences in PA strength was found in the CMIP6 models. Changes in surface temperature and strength of PA is closely coupled to changes in albedo. The planetary albedo of Earth (αp) is partitioned into a component associated with surface albedo (defined as surface contribution to planetary albedo, ), and a component associated with atmospheric albedo (atmospheric contribution to planetary albedo, ). To assess the hemispheric differences in PA strengths, the relative importance of and were investigated. The surface reflection looks different as seen at the surface (defined as surface albedo, αsurf) compared to (as seen at the top of the atmosphere). We find a stronger correlation between surface temperature and αsurf in the Arctic than in the Antarctic, with correlation coefficients of −0.94 and −0.88, respectively. Interestingly, the correlation for surface temperature and is stronger in the Antarctic than in the Arctic with correlation coefficients of −0.93 and −0.90, respectively. In the southern high latitudes, albedo changes at the surface are more important than changes in the atmosphere, while the opposite applies in the northern high latitudes. Surface temperature changes in the low- and mid-latitudes are strongly associated with changes in , dominated by changes in cloud properties. climate change; albedo; climate models; cmip6; polar amplification
Song, Yajuan; Qiao, Fangli; Liu, Jiping; Shu, Qi; Bao, Ying; Wei, Meng; Song, ZhenyaSong, Y., F. Qiao, J. Liu, Q. Shu, Y. Bao, M. Wei, Z. Song, 2022: Effects of Sea Spray on Large-Scale Climatic Features over the Southern Ocean. J. Climate, 35(14), 4645-4663. doi: 10.1175/JCLI-D-21-0608.1. Abstract The Southern Ocean, characterized by strong westerly winds and a rough sea state, exhibits the most pronounced sea spray effects. Sea spray ejected by ocean surface waves enhances heat and water exchange at the air–sea interface. However, this process has not been considered in current climate models, and the influence of sea spray on the coupled air–sea system remains largely unknown. This study incorporated a parameterization of the sea spray influence on latent and sensible heat fluxes into the First Institute of Oceanography Earth System Model version 2.0 (FIO-ESM v2.0), a climate model coupled with an ocean surface waves component. The results indicate that the spray-mediated enthalpy flux accounted for over 20%–50% of the total value. Sea spray promoted ocean evaporation and heat transport, resulting in air and ocean surface cooling and strengthened westerly winds. Furthermore, a moist and stable atmosphere favored an increase in cloud fraction over the Southern Ocean, particularly low-level clouds. Increased clouds reflected downward shortwave radiation and reduced solar radiation absorption at the surface. At present, the climate models participating in phase 6 of the Coupled Model Intercomparison Project (CMIP6) still suffer notable deficiencies in reasonably reproducing the climatological features of the Southern Ocean, including warm SST and underestimated clouds biases with more absorbed shortwave radiation. Our results suggest that consideration of sea spray effects is a feasible solution to mitigate these common biases and enhance the confidence in simulations and predictions with climate models.
Song, Zhen; Liang, Shunlin; Zhou, HongminSong, Z., S. Liang, H. Zhou, 2022: Top-of-Atmosphere Clear-Sky Albedo Estimation Over Ocean: Preliminary Framework for MODIS. IEEE Transactions on Geoscience and Remote Sensing, 60, 1-9. doi: 10.1109/TGRS.2021.3116620. Top-of-atmosphere (TOA) albedo is a significant factor of earth energy budget, climate change, and environmental change. As tremendous regional and global changes are happening over ocean, more details are needed to monitor the ocean environment. However, there were still no high-spatial resolution TOA albedo products over ocean. In this study, a new algorithm for clear-sky TOA albedo estimation over ocean was proposed, based on Moderate Resolution Imaging Spectroradiometer (MODIS) data. Instead of building angular distribution models, direct retrieval models between TOA reflectance and TOA albedo were developed based on extensive radiative transfer (RT) simulations, covering thousands of ocean and atmosphere types. Three-component ocean water albedo model was involved to take account for the ocean surface anisotropy at different wind speed, wind direction, and chlorophyll concentration, while Modtran 5 was utilized to simulate different atmospheric conditions. Our results showed good agreement with the Clouds and the Earth’s Radiant Energy System (CERES) based on a global comparison on August 4, 2011, with RMSE = 0.015 and bias = 0.002. And our MODIS-based products provide more spatial details due to higher spatial resolution (1 km), which will be a good data source for regional environmental and climatic research and will also enhance the understanding of Earth’s radiation budget. Earth; Oceans; Wind speed; MODIS; Atmospheric modeling; energy budget; Moderate Resolution Imaging Spectroradiometer (MODIS); Sea surface; Climate change; Broadband communication; ocean bidirectional reflectance distribution function (BRDF); radiative transfer (RT) simulations; top-of-atmosphere (TOA) albedo
Sreenath, A. V.; Abhilash, S.; Vijaykumar, P.; Mapes, B. E.Sreenath, A. V., S. Abhilash, P. Vijaykumar, B. E. Mapes, 2022: West coast India’s rainfall is becoming more convective. npj Climate and Atmospheric Science, 5(1), 1-7. doi: 10.1038/s41612-022-00258-2. A disastrous cloudburst and associated floods in Kerala during the 2019 monsoon season raise the hypothesis that rainfall over the west coast of India, much of which is stratiform, may be trending towards being more convective. As a first exploration, we sought statistically significant differences in monthly ERA-5 reanalysis data for the monsoon season between two epochs, 1980–1999 and 2000–2019. Results suggest a more convective (deeper, ice-rich) cloud population in recent decades, with patterns illustrated in ERA-5 spatial maps. Deepening of convection, above and beyond its trend in amount, is also indicated by the steeper regression slope of outgoing longwave radiation trends against precipitation than that exhibited in interannual variability. Our reanalysis results are strengthened by related trends manifested in more direct observations from satellite and gauge-based rainfall and a CAPE index from balloon soundings data. Attribution; Climate-change impacts
Srinivasan, Ashwanth; Chin, T. M.; Chassignet, E. P.; Iskandarani, M.; Groves, N.Srinivasan, A., T. M. Chin, E. P. Chassignet, M. Iskandarani, N. Groves, 2022: A Statistical Interpolation Code for Ocean Analysis and Forecasting. J. Atmos. Oceanic Technol., 39(3), 367-386. doi: 10.1175/JTECH-D-21-0033.1. Abstract We present a data assimilation package for use with ocean circulation models in analysis, forecasting, and system evaluation applications. The basic functionality of the package is centered on a multivariate linear statistical estimation for a given predicted/background ocean state, observations, and error statistics. Novel features of the package include support for multiple covariance models, and the solution of the least squares normal equations either using the covariance matrix or its inverse—the information matrix. The main focus of this paper, however, is on the solution of the analysis equations using the information matrix, which offers several advantages for solving large problems efficiently. Details of the parameterization of the inverse covariance using Markov random fields are provided and its relationship to finite-difference discretizations of diffusion equations are pointed out. The package can assimilate a variety of observation types from both remote sensing and in situ platforms. The performance of the data assimilation methodology implemented in the package is demonstrated with a yearlong global ocean hindcast with a 1/4° ocean model. The code is implemented in modern Fortran, supports distributed memory, shared memory, multicore architectures, and uses climate and forecasts compliant Network Common Data Form for input/output. The package is freely available with an open source license from www.tendral.com/tsis/.
Storto, Andrea; Cheng, Lijing; Yang, ChunxueStorto, A., L. Cheng, C. Yang, 2022: Revisiting the 2003–18 Deep Ocean Warming through Multiplatform Analysis of the Global Energy Budget. J. Climate, 35(14), 4701-4717. doi: 10.1175/JCLI-D-21-0726.1. Abstract Recent estimates of the global warming rates suggest that approximately 9% of Earth’s excess heat has been cumulated in the deep and abyssal oceans (below 2000-m depth) during the last two decades. Such estimates assume stationary trends deducted as long-term rates. To reassess the deep ocean warming and potentially shed light on its interannual variability, we formulate the balance between Earth’s energy imbalance (EEI), the steric sea level, and the ocean heat content (OHC), at yearly time scales during the 2003–18 period, as a variational problem. The solution is achieved through variational minimization, merging observational data from top-of-atmosphere EEI, inferred from Clouds and the Earth’s Radiant Energy System (CERES), steric sea level estimates from altimetry minus gravimetry, and upper-ocean heat content estimates from in situ platforms (mostly Argo floats). Global ocean reanalyses provide background-error covariances for the OHC analysis. The analysis indicates a 2000-m–bottom warming of 0.08 ± 0.04 W m−2 for the period 2003–18, equal to 13% of the total ocean warming (0.62 ± 0.08 W m−2), slightly larger than previous estimates but consistent within the error bars. The analysis provides a fully consistent optimized solution also for the steric sea level and EEI. Moreover, the simultaneous use of the different heat budget observing networks is able to decrease the analysis uncertainty with respect to the observational one, for all observation types and especially for the 0–700-m OHC and steric sea level (more than 12% reduction). The sensitivity of the analysis to the choice of the background time series proved insignificant. Significance Statement Several observing networks provide complementary information about the temporal evolution of the global energy budget. Here, satellite observations of Earth’s energy imbalance (EEI) and steric sea level and in situ–derived estimates of ocean heat content anomalies are combined in a variational analysis framework, with the goal of assessing the deep ocean warming. The optimized solution accounts for the uncertainty of the different observing networks. Furthermore, it provides fully consistent analyses of global ocean heat content, steric sea level, and EEI, which show smaller uncertainty than the original observed time series. The deep ocean (below 2000-m depth) exhibits a significant warming of 0.08 ± 0.04 W m−2 for the period 2003–18, equal to the 13% of the total ocean warming.
Subba, Tamanna; Gogoi, Mukunda M.; Moorthy, K. Krishna; Bhuyan, Pradip K.; Pathak, Binita; Guha, Anirban; Srivastava, Manoj Kumar; Vyas, B. M.; Singh, Karamjit; Krishnan, Jayabala; Lakshmi Kumar, T. V.; Babu, S. SureshSubba, T., M. M. Gogoi, K. K. Moorthy, P. K. Bhuyan, B. Pathak, A. Guha, M. K. Srivastava, B. M. Vyas, K. Singh, J. Krishnan, T. V. Lakshmi Kumar, S. S. Babu, 2022: New estimates of aerosol radiative effects over India from surface and satellite observations. Atmospheric Research, 276, 106254. doi: 10.1016/j.atmosres.2022.106254. Multi-year measurements of surface-reaching solar (shortwave) radiation fluxes across a network of aerosol observatories (ARFINET) are combined with concurrent satellite (CERES)-based top of the atmosphere (TOA) fluxes to estimate regional aerosol direct radiative forcing (ARF) over the Indian region. The synergistic approach improves the accuracy of ARF estimates, which otherwise results in an overestimation or underestimation of the atmospheric forcing. During summer, an overestimation of ~5 W m−2 (corresponding heating rate ~ 0.15 K day−1) is noticed. The regional average ARF from the synergistic approach reveals the surface forcing reaching −49 W m−2 over the Indo Gangetic Plains, −45 W m−2 over northeast India, −34 W m−2 over the southern Peninsula, and − 16 W m−2 in the oceanic regions of the Bay of Bengal. The ARF over the northern half of the Indian subcontinent is influenced mainly by anthropogenic sulfate and carbonaceous aerosols. Dust is dominant in the western region of India during MAM and JJAS. Overall, the clear sky surface reaching solar radiation fluxes is reduced by 3–22% due to the abundance of aerosols in the atmosphere, with the highest reduction over the IGP during autumn and winter. CERES; Heating rate; MERRA-2; ARFINET; SW-radiation; Aerosol composition; Aerosol radiative forcing
Sun, Moguo; Doelling, David R.; Loeb, Norman G.; Scott, Ryan C.; Wilkins, Joshua; Nguyen, Le Trang; Mlynczak, PamelaSun, M., D. R. Doelling, N. G. Loeb, R. C. Scott, J. Wilkins, L. T. Nguyen, P. Mlynczak, 2022: Clouds and the Earth’s Radiant Energy System (CERES) FluxByCldTyp Edition 4 Data Product. J. Atmos. Oceanic Technol., 39(3), 303-318. doi: 10.1175/JTECH-D-21-0029.1. Abstract The Clouds and the Earth’s Radiant Energy System (CERES) project has provided the climate community 20 years of globally observed top of the atmosphere (TOA) fluxes critical for climate and cloud feedback studies. The CERES Flux By Cloud Type (FBCT) product contains radiative fluxes by cloud type, which can provide more stringent constraints when validating models and also reveal more insight into the interactions between clouds and climate. The FBCT product provides 1° regional daily and monthly shortwave (SW) and longwave (LW) cloud-type fluxes and cloud properties sorted by seven pressure layers and six optical depth bins. Historically, cloud-type fluxes have been computed using radiative transfer models based on observed cloud properties. Instead of relying on radiative transfer models, the FBCT product utilizes Moderate Resolution Imaging Spectroradiometer (MODIS) radiances partitioned by cloud type within a CERES footprint to estimate the cloud-type broadband fluxes. The MODIS multichannel derived broadband fluxes were compared with the CERES observed footprint fluxes and were found to be within 1% and 2.5% for LW and SW, respectively, as well as being mostly free of cloud property dependencies. These biases are mitigated by constraining the cloud-type fluxes within each footprint with the CERES Single Scanner Footprint (SSF) observed flux. The FBCT all-sky and clear-sky monthly averaged fluxes were found to be consistent with the CERES SSF1deg product. Several examples of FBCT data are presented to highlight its utility for scientific applications.
Sun, Yuanheng; Knyazikhin, Yuri; She, Xiaojun; Ni, Xiangnan; Chen, Chi; Ren, Huazhong; Myneni, Ranga B.Sun, Y., Y. Knyazikhin, X. She, X. Ni, C. Chen, H. Ren, R. B. Myneni, 2022: Seasonal and long-term variations in leaf area of Congolese rainforest. Remote Sensing of Environment, 268, 112762. doi: 10.1016/j.rse.2021.112762. It is important to understand temporal and spatial variations in the structure and photosynthetic capacity of tropical rainforests in a world of changing climate, increased disturbances and human appropriation. The equatorial rainforests of Central Africa are the second largest and least disturbed of the biodiversly-rich and highly productive rainforests on Earth. Currently, there is a dearth of knowledge about the phenological behavior and long-term changes that these forests are experiencing. Thus, this study reports on leaf area seasonality and its time trend over the past two decades as assessed from multiple remotely sensed datasets. Seasonal variations of leaf area in Congolese forests derived from MODIS data co-vary with the bimodal precipitation pattern in this region, with higher values during the wet season. Independent observational evidence derived from MISR and EPIC sensors in the form of angular reflectance signatures further corroborate this seasonal behavior of leaf area. The bimodal patterns vary latitudinally within this large region. Two sub-seasonal cycles, each consisting of a dry and wet season, could be discerned clearly. These exhibit different sensitivities to changes in precipitation. Contrary to a previous published report, no widespread decline in leaf area was detected across the entire extent of the Congolese rainforests over the past two decades with the latest MODIS Collection 6 dataset. Long-term precipitation decline did occur in some localized areas, but these had minimal impacts on leaf area, as inferred from MODIS and MISR multi-angle observations. Remote sensing; MODIS; Phenology; MISR; Congolese rainforests; DSCOVR EPIC; Leaf area; Long-term trends
Tan, Ivy; Barahona, DonifanTan, I., D. Barahona, 2022: The Impacts of Immersion Ice Nucleation Parameterizations on Arctic Mixed-Phase Stratiform Cloud Properties and the Arctic Radiation Budget in GEOS-5. J. Climate, 35(13), 4049-4070. doi: 10.1175/JCLI-D-21-0368.1. Abstract The influence of four different immersion freezing parameterizations on Arctic clouds and the top-of-the atmosphere (TOA) and surface radiation fluxes is investigated in the fifth version of the National Aeronautics and Space Administration (NASA) Goddard Earth Observing System (GEOS-5) with sea surface temperature, sea ice fraction, and aerosol emissions held fixed. The different parameterizations were derived from a variety of sources, including classical nucleation theory and field and laboratory measurements. Despite the large spread in the ice-nucleating particle (INP) concentrations in the parameterizations, the cloud properties and radiative fluxes had a tendency to form two groups, with the lower INP concentration category producing larger water path and low-level cloud fraction during winter and early spring, whereas the opposite occurred during the summer season. The stability of the lower troposphere was found to strongly correlate with low-cloud fraction and, along with the effect of ice nucleation, ice sedimentation, and melting rates, appears to explain the spring-to-summer reversal pattern in the relative magnitude of the cloud properties between the two categories of simulations. The strong modulation effect of the liquid phase on immersion freezing led to the successful simulation of the characteristic Arctic cloud structure, with a layer rich in supercooled water near cloud top and ice and snow at lower levels. Comparison with satellite retrievals and in situ data suggest that simulations with low INP concentrations more realistically represent Arctic clouds and radiation.
Taylor, Patrick Charles; Itterly, Kyle Frederick; Corbett, Joe; Bucholtz, Anthony; Sejas, Sergio; Su, Wenying; Doelling, David R.; Kato, SeijiTaylor, P. C., K. F. Itterly, J. Corbett, A. Bucholtz, S. Sejas, W. Su, D. R. Doelling, S. Kato, 2022: A Comparison of Top-of-Atmosphere Radiative Fluxes from CERES and ARISE. doi: 10.1002/essoar.10512242.1. Uncertainty in Arctic top-of-atmosphere (TOA) radiative flux observations stems from the low sun angles and the heterogeneous scenes. Advancing our understanding of the Arctic climate system requires
Tezaur, Irina; Peterson, Kara; Powell, Amy; Jakeman, John; Roesler, ErikaTezaur, I., K. Peterson, A. Powell, J. Jakeman, E. Roesler, 2022: Global Sensitivity Analysis Using the Ultra-Low Resolution Energy Exascale Earth System Model. Journal of Advances in Modeling Earth Systems, 14(8), e2021MS002831. doi: 10.1029/2021MS002831. For decades, Arctic temperatures have increased twice as fast as average global temperatures. As a first step toward quantifying parametric uncertainty in Arctic climate, we performed a variance-based global sensitivity analysis (GSA) using a fully coupled, ultra-low resolution (ULR) configuration of version 1 of the U.S. Department of Energy's Energy Exascale Earth System Model (E3SMv1). Specifically, we quantified the sensitivity of six quantities of interests (QOIs), which characterize changes in Arctic climate over a 75 year period, to uncertainties in nine model parameters spanning the sea ice, atmosphere, and ocean components of E3SMv1. Sensitivity indices for each QOI were computed with a Gaussian process emulator using 139 random realizations of the random parameters and fixed preindustrial forcing. Uncertainties in the atmospheric parameters in the Cloud Layers Unified by Binormals (CLUBB) scheme were found to have the most impact on sea ice status and the larger Arctic climate. Our results demonstrate the importance of conducting sensitivity analyses with fully coupled climate models. The ULR configuration makes such studies computationally feasible today due to its low computational cost. When advances in computational power and modeling algorithms enable the tractable use of higher-resolution models, our results will provide a baseline that can quantify the impact of model resolution on the accuracy of sensitivity indices. Moreover, the confidence intervals provided by our study, which we used to quantify the impact of the number of model evaluations on the accuracy of sensitivity estimates, have the potential to inform the computational resources needed for future sensitivity studies. Arctic climate state; Energy Exascale Earth System Model (E3SM); fully coupled; global sensitivity analysis (GSA); ultra-low resolution (ULR); uncertainty quantification (UQ)
Thompson, Chelsea R.; Wofsy, Steven C.; Prather, Michael J.; Newman, Paul A.; Hanisco, Thomas F.; Ryerson, Thomas B.; Fahey, David W.; Apel, Eric C.; Brock, Charles A.; Brune, William H.; Froyd, Karl; Katich, Joseph M.; Nicely, Julie M.; Peischl, Jeff; Ray, Eric; Veres, Patrick R.; Wang, Siyuan; Allen, Hannah M.; Asher, Elizabeth; Bian, Huisheng; Blake, Donald; Bourgeois, Ilann; Budney, John; Bui, T. Paul; Butler, Amy; Campuzano-Jost, Pedro; Chang, Cecilia; Chin, Mian; Commane, Róisín; Correa, Gus; Crounse, John D.; Daube, Bruce; Dibb, Jack E.; DiGangi, Joshua P.; Diskin, Glenn S.; Dollner, Maximilian; Elkins, James W.; Fiore, Arlene M.; Flynn, Clare M.; Guo, Hao; Hall, Samuel R.; Hannun, Reem A.; Hills, Alan; Hintsa, Eric J.; Hodzic, Alma; Hornbrook, Rebecca S.; Huey, L. Greg; Jimenez, Jose L.; Keeling, Ralph F.; Kim, Michelle J.; Kupc, Agnieszka; Lacey, Forrest; Lait, Leslie R.; Lamarque, Jean-Francois; Liu, Junhua; McKain, Kathryn; Meinardi, Simone; Miller, David O.; Montzka, Stephen A.; Moore, Fred L.; Morgan, Eric J.; Murphy, Daniel M.; Murray, Lee T.; Nault, Benjamin A.; Neuman, J. Andrew; Nguyen, Louis; Gonzalez, Yenny; Rollins, Andrew; Rosenlof, Karen; Sargent, Maryann; Schill, Gregory; Schwarz, Joshua P.; Clair, Jason M. St; Steenrod, Stephen D.; Stephens, Britton B.; Strahan, Susan E.; Strode, Sarah A.; Sweeney, Colm; Thames, Alexander B.; Ullmann, Kirk; Wagner, Nicholas; Weber, Rodney; Weinzierl, Bernadett; Wennberg, Paul O.; Williamson, Christina J.; Wolfe, GlenThompson, C. R., S. C. Wofsy, M. J. Prather, P. A. Newman, T. F. Hanisco, T. B. Ryerson, D. W. Fahey, E. C. Apel, C. A. Brock, W. H. Brune, K. Froyd, J. M. Katich, J. M. Nicely, J. Peischl, E. Ray, P. R. Veres, S. Wang, H. M. Allen, E. Asher, H. Bian, D. Blake, I. Bourgeois, J. Budney, T. P. Bui, A. Butler, P. Campuzano-Jost, C. Chang, M. Chin, R. Commane, G. Correa, J. D. Crounse, B. Daube, J. E. Dibb, J. P. DiGangi, G. S. Diskin, M. Dollner, J. W. Elkins, A. M. Fiore, C. M. Flynn, H. Guo, S. R. Hall, R. A. Hannun, A. Hills, E. J. Hintsa, A. Hodzic, R. S. Hornbrook, L. G. Huey, J. L. Jimenez, R. F. Keeling, M. J. Kim, A. Kupc, F. Lacey, L. R. Lait, J. Lamarque, J. Liu, K. McKain, S. Meinardi, D. O. Miller, S. A. Montzka, F. L. Moore, E. J. Morgan, D. M. Murphy, L. T. Murray, B. A. Nault, J. A. Neuman, L. Nguyen, Y. Gonzalez, A. Rollins, K. Rosenlof, M. Sargent, G. Schill, J. P. Schwarz, J. M. S. Clair, S. D. Steenrod, B. B. Stephens, S. E. Strahan, S. A. Strode, C. Sweeney, A. B. Thames, K. Ullmann, N. Wagner, R. Weber, B. Weinzierl, P. O. Wennberg, C. J. Williamson, G. Wolfe, 2022: The NASA Atmospheric Tomography (ATom) Mission: Imaging the Chemistry of the Global Atmosphere. Bull. Amer. Meteor. Soc., 103(3), E761-E790. doi: 10.1175/BAMS-D-20-0315.1. Abstract This article provides an overview of the NASA Atmospheric Tomography (ATom) mission and a summary of selected scientific findings to date. ATom was an airborne measurements and modeling campaign aimed at characterizing the composition and chemistry of the troposphere over the most remote regions of the Pacific, Southern, Atlantic, and Arctic Oceans, and examining the impact of anthropogenic and natural emissions on a global scale. These remote regions dominate global chemical reactivity and are exceptionally important for global air quality and climate. ATom data provide the in situ measurements needed to understand the range of chemical species and their reactions, and to test satellite remote sensing observations and global models over large regions of the remote atmosphere. Lack of data in these regions, particularly over the oceans, has limited our understanding of how atmospheric composition is changing in response to shifting anthropogenic emissions and physical climate change. ATom was designed as a global-scale tomographic sampling mission with extensive geographic and seasonal coverage, tropospheric vertical profiling, and detailed speciation of reactive compounds and pollution tracers. ATom flew the NASA DC-8 research aircraft over four seasons to collect a comprehensive suite of measurements of gases, aerosols, and radical species from the remote troposphere and lower stratosphere on four global circuits from 2016 to 2018. Flights maintained near-continuous vertical profiling of 0.15–13-km altitudes on long meridional transects of the Pacific and Atlantic Ocean basins. Analysis and modeling of ATom data have led to the significant early findings highlighted here.
Tian, Lei; Zhang, Baoqing; Wang, Xuejin; Chen, Shuoyu; Pan, BaotianTian, L., B. Zhang, X. Wang, S. Chen, B. Pan, 2022: Large-Scale Afforestation Over the Loess Plateau in China Contributes to the Local Warming Trend. Journal of Geophysical Research: Atmospheres, 127(1), e2021JD035730. doi: 10.1029/2021JD035730. Afforestation is a major anthropogenic forcing to the global and regional climate. However, the biophysical impacts of large-scale afforestation on local temperature in temperate regions remain unclear, due to the closely matched but compensating radiative and non-radiative effects. The Grain for Green Program (GFGP) is a large-scale afforestation program implemented over the Loess Plateau (LP) in China. The GFGP thus provides an ideal platform to explore the temperature effect of afforestation. This study investigated such a temperature effect through long-term, high-resolution simulations incorporating satellite observations in a coupled land-atmosphere model. With an optimal combination of physical schemes proposed by this study, we greatly improved the accuracy of regional climate modeling. The results reveal that the afforestation caused a significant decline (−0.50% yr−1) in albedo. An increment in net shortwave radiation mainly led to an increment in net radiation (7.95 W m−2). The afforestation also led to an increment in sensible heat flux (3.78 W m−2). Consequently, the afforestation caused a warming effect (0.36°C) in 2-meter air temperature at the inter-annual scale. At the intra-annual scale, there was a cooling effect in July and August, while other months demonstrated a warming effect. The radiative effect dominated local temperature change induced by the afforestation over the LP. Therefore, the large-scale afforestation contributed to the local warming trend. Our findings highlight the temperature effect of afforestation, and imply that more attention should be paid to future revegetation to carefully assess its potential influence on regional climate. temperature; regional climate; evapotranspiration; afforestation; energy and water cycle; land-atmosphere model
Truong, Son C. H.; Huang, Yi; Siems, Steven T.; Manton, Michael J.; Lang, FranciscoTruong, S. C. H., Y. Huang, S. T. Siems, M. J. Manton, F. Lang, 2022: Biases in the thermodynamic structure over the Southern Ocean in ERA5 and their radiative implications. International Journal of Climatology, n/a(n/a). doi: 10.1002/joc.7672. The thermodynamic structure of the lower troposphere in the 37 standard levels ERA5 reanalysis has been evaluated against 2,186 high-resolution upper air soundings collected over the Southern Ocean (SO). The reanalysis, which incorporated these soundings, was found to be skilled in depicting the general synoptic meteorology and thermodynamic structure as defined by the cluster analysis of Truong et al. (2020) Journal of Geophysical Research: Atmospheres, 125, e2020JD033214. Using dew-point depression as a proxy for cloud, however, we found a significant reduction in the number of inferred cloud layers, which is inherited from a bias in the specific humidity in the ERA5 reanalysis, most notably over the high latitudes of the SO, where a multilayer cloud structure is frequently observed. The reanalysis was also found to have thinner inferred cloud geometric layer and shallower cloud top heights. Further analysis showed that the reanalysis displays a greater percentage of soundings having no inversion with this bias being more pronounced at high latitudes that tends to be associated with the colder sea surface temperature. While the statistics of the main inversion height are largely consistent, the average inversion strength in the ERA5 reanalysis is found to be weaker than the observations. We anticipate the 137-level ERA5 reanalysis simulation yields a smoothed vertical structure, from which the 37 standard levels ERA5 reanalysis is linearly interpolated. An examination of the sensitivity of the radiative transfer to cloud macrophysics suggests that the correct representation of thin multiple cloud layers can help reduce the amount of downward shortwave surface radiation over the SO. Southern Ocean; marine atmospheric boundary layer; inversion; multilayer clouds; radiation bias
Turbeville, S. M.; Nugent, J. M.; Ackerman, T. P.; Bretherton, C. S.; Blossey, P. N.Turbeville, S. M., J. M. Nugent, T. P. Ackerman, C. S. Bretherton, P. N. Blossey, 2022: Tropical Cirrus in Global Storm-Resolving Models: 2. Cirrus Life Cycle and Top-of-Atmosphere Radiative Fluxes. Earth and Space Science, 9(2), e2021EA001978. doi: 10.1029/2021EA001978. Cirrus clouds of various thicknesses and radiative characteristics extend over much of the tropics, especially around deep convection. They are difficult to observe due to their high altitude and sometimes small optical depths. They are also difficult to simulate in conventional global climate models, which have coarse grid spacings and simplified parameterizations of deep convection and cirrus formation. We investigate the representation of tropical cirrus in global storm-resolving models (GSRMs), which have higher spatial resolution and explicit convection and could more accurately represent cirrus cloud processes. This study uses GSRMs from the DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) project. The aggregate life cycle of tropical cirrus is analyzed using joint albedo and outgoing longwave radiation (OLR) histograms to assess the fidelity of models in capturing the observed cirrus cloud populations over representative tropical ocean and land regions. The proportions of optically thick deep convection, anvils, and cirrus vary across models and are portrayed in the vertical distribution of cloud cover and top-of-atmosphere radiative fluxes. Model differences in cirrus populations, likely driven by subgrid processes such as ice microphysics, dominate over regional differences between convectively active tropical land and ocean locations. cirrus; life cycle; tropical tropopause layer; model comparison; DYAMOND; global storm-resolving models
Volvach, Alexandr; Kurbasova, Galina; Volvach, LarisaVolvach, A., G. Kurbasova, L. Volvach, 2022: Time series analysis of temperatures and insolation of the Earth's surface at Kara-Dag using satellite observation. Advances in Space Research, 69(12), 4228-4239. doi: 10.1016/j.asr.2022.04.016. This article discusses the results of a numerical analysis of the time series of the surface temperature, air temperature at a height of 2 m, as well as the total insolation falling to the earth at the Kara-Dag point over the past 38 years. Statistical analysis of observations and continuous time-frequency wavelet analysis are performed. Models of seasonal fluctuations in three time series of observations are compared. Coherent fluctuations were established between variations in total insolation data and data variations: of length of the day (LOD) (the period of variations is 11.8 years, the square of the coherence modulus is 0.85); of solar activity (the period of variations is 10.5 years, the squared modulus of coherence is 0.8; and the period of variations is 3.6 years, the squared modulus of coherence is 0.85); of global temperature indices (the period of variations is 2.3 years, the squared modulus of coherence is 0.7; and the period of variations is 3.5 years, the squared modulus of coherence is 0.9), respectively. The time evolution of observations in order to detect signs of chaotic oscillations is discussed. Earth; Insolation; Chaotic oscillations; Global temperature; POWER
Wall, Casey J.; Lutsko, Nicholas J.; Vishny, David N.Wall, C. J., N. J. Lutsko, D. N. Vishny, 2022: Revisiting Cloud Radiative Heating and the Southern Annular Mode. Geophysical Research Letters, n/a(n/a), e2022GL100463. doi: 10.1029/2022GL100463. Cloud-circulation interactions have a potentially large but uncertain influence on regional climate. Here we use satellite observations to investigate relationships between atmospheric cloud radiative heating and hemispheric-scale shifts in the Southern Hemisphere extratropical jet stream, as represented by the Southern Annular Mode. In contrast to a previous study, we find that poleward jet shifts cause bottom-heavy heating anomalies. The heating anomalies arise from two distinct mechanisms: First, poleward jet shifts promote anomalous large-scale subsidence equatorward of the mean jet latitude. This increases the fraction of low clouds that are exposed to space, thereby enhancing lower-tropospheric radiative cooling. Second, deep and multi-layer clouds in extratropical cyclones shift poleward with the jet, causing radiative heating anomalies throughout the troposphere. The bottom-heavy structure of the heating anomalies occurs because low clouds strongly emit radiation. These results establish new observational benchmarks for understanding extratropical cloud-circulation interactions. Annular Modes; Cloud Radiative Effects; Cloud-Circulation Interactions
Wall, Casey J.; Storelvmo, Trude; Norris, Joel R.; Tan, IvyWall, C. J., T. Storelvmo, J. R. Norris, I. Tan, 2022: Observational Constraints on Southern Ocean Cloud-Phase Feedback. J. Climate, 35(15), 5087-5102. doi: 10.1175/JCLI-D-21-0812.1. Abstract Shortwave radiative feedbacks from Southern Ocean clouds are a major source of uncertainty in climate projections. Much of this uncertainty arises from changes in cloud scattering properties and lifetimes that are caused by changes in cloud thermodynamic phase. Here we use satellite observations to infer the scattering component of the cloud-phase feedback mechanism and determine its relative importance by comparing it with an estimate of the overall temperature-driven cloud feedback. The overall feedback is dominated by an optical thinning of low-level clouds. In contrast, the scattering component of cloud-phase feedback is an order of magnitude smaller and is primarily confined to free-tropospheric clouds. The small magnitude of this feedback component is a consequence of counteracting changes in albedo from cloud optical thickening and enhanced forward scattering by cloud particles. These results indicate that shortwave cloud feedback is likely positive over the Southern Ocean and that changes in cloud scattering properties arising from phase changes make a small contribution to the overall feedback. The feedback constraints shift the projected 66% confidence range for the global equilibrium temperature response to doubling atmospheric CO2 by about +0.1 K relative to a recent consensus estimate of cloud feedback. Significance Statement Understanding how clouds respond to global warming is a key challenge of climate science. One particularly uncertain aspect of the cloud response involves a conversion of ice particles to liquid droplets in extratropical clouds. Here we use satellite data to infer how cloud-phase conversions affect climate by changing cloud albedo. We find that ice-to-liquid conversions increase cloud optical thickness and shift the scattering angles of cloud particles toward the forward direction. These changes in optical properties have offsetting effects on cloud albedo. This finding provides new insight about how changes in cloud phase affect climate change.
Wang, Fei; Zhang, Hua; Wang, Qiuyan; Xie, Bing; Zhou, Xixun; Liu, QingquanWang, F., H. Zhang, Q. Wang, B. Xie, X. Zhou, Q. Liu, 2022: An Assessment of Short-term Global and East Asian Local Climate Feedbacks using New Radiative Kernels. Climate Dynamics. doi: 10.1007/s00382-022-06369-z. This study estimates short-term climate feedbacks by using a new set of radiative kernels applied to observations and the Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations. The new kernels are generated based on multiyear satellite observations, and they can well reproduce the top-of-atmosphere (TOA) radiation budget. The choice of radiative kernels influences the feedback estimation, especially the surface albedo feedback and cloud feedback in the Arctic and the Southern Ocean. Observational estimates show that tropospheric water vapor feedback makes the largest contribution to global warming, while lapse rate feedback is the largest contributor to local warming over East Asia. Compared to the observations, biases occur but differ when simulating global and East Asian local climate feedbacks. CMIP6 models overestimate global mean Planck, lapse rate, stratospheric temperature and water vapor, and cloud feedbacks, but underestimate global mean tropospheric water vapor and surface albedo feedbacks. Over East Asia, local Planck and lapse rate feedbacks are underestimated, while tropospheric water vapor, stratospheric temperature, and cloud feedbacks are overestimated. The simulation biases in local longwave (LW) and shortwave (SW) cloud feedbacks over East Asia are considerable, probably due to the failure in simulating cloud fraction response of marine cirrostratus, deep convective cloud, and stratus. The intermodel spread of cloud feedback is the largest for both global and East Asian local feedback processes. Our results suggest that contemporary climate models are still difficult to accurately simulate global and local climate feedback processes. East Asia; CMIP6 models; Observations; Radiative kernels; Short-term climate feedback
Wang, Hao; Wang, Minghuai; Zhang, Zhibo; Larson, Vincent E.; Griffin, Brian M.; Guo, Zhun; Zhu, Yannian; Rosenfeld, Daniel; Cao, Yang; Bai, HemingWang, H., M. Wang, Z. Zhang, V. E. Larson, B. M. Griffin, Z. Guo, Y. Zhu, D. Rosenfeld, Y. Cao, H. Bai, 2022: Improving the treatment of subgrid cloud variability in warm rain simulation in CESM2. Journal of Advances in Modeling Earth Systems, n/a(n/a), e2022MS003103. doi: 10.1029/2022MS003103. Representing subgrid variability of cloud properties has always been a challenge in global climate models (GCMs). In many cloud microphysics schemes, the warm rain non-linear process rates calculated based on grid-mean cloud properties are usually scaled by an enhancement factor (EF) to account for the effects of subgrid cloud variability. In our study, we find that the EF derived from Cloud Layers Unified by Binormals (CLUBB) in Community Atmosphere Model version 6 (CAM6) is severely overestimated in most of the cloudy oceanic areas, which leads to strong overestimation of the autoconversion rate. We improve the EF in warm rain simulation by developing a new formula for in-cloud subgrid cloud water variance. With the updated subgrid cloud water variance and EF treatment, the liquid cloud fraction (LCF) and cloud optical thickness (COT) increases noticeably for marine stratocumulus, and the shortwave cloud forcing (SWCF) matches better with observations. The updated formula improves the relationship between autoconversion rate and cloud droplet number concentration (CDNC), and it decreases the sensitivity of autoconversion rate to aerosols. The sensitivity of liquid water path (LWP) to aerosols decreases noticeably and is in better agreement with that in MODIS. Although the sensitivity of COT is similar to that in MODIS, CAM6 underestimates the sensitivity of grid-mean SWCF to aerosols because of the underestimation in the sensitivities of LCF and in-cloud SWCF. Our results indicate the importance of representing reasonable subgrid cloud variability in the simulation of cloud properties and aerosol-cloud interaction in GCMs. aerosol-cloud interaction; CLUBB; marine boundary layer clouds; CAM6; subgrid variability
Wang, Shiyao; Wang, Tianxing; Leng, Wanchun; Wang, Gaofeng; Letu, HusiWang, S., T. Wang, W. Leng, G. Wang, H. Letu, 2022: Toward an Improved Global Longwave Downward Radiation Product by Fusing Satellite and Reanalysis Data. IEEE Transactions on Geoscience and Remote Sensing, 60, 1-16. doi: 10.1109/TGRS.2022.3179017. Surface longwave downward radiation (LWDR) plays an important role in modulating greenhouse effect and climate change. Constructing a global longtime series LWDR dataset is greatly necessary to systematically and in-depth study the LWDR effect on the climate. However, the current multisource LWDR products (satellite and reanalysis) show large differences in terms of both spatiotemporal resolutions and accuracy in various regions. Therefore, it is necessary to fuse multisource datasets to generate more accurate LWDR with high spatiotemporal resolution on a global scale. To this end, a downscaling strategy is first proposed to generate LWDR dataset with 0.25° resolution from CERES-SYN data with 1° scale, by incorporating the land surface temperature (LST), total column water vapor (TCWV), and elevation. Then, a machine learning-based fusion method is provided to generate a global hourly LWDR dataset with a spatial resolution of 0.25° by combining three products (CERES-SYN, ERA5, and GLDAS). Compared with ground measurements, the performance of generated LWDR product reveals that the correlation coefficient ( $R$ ), mean bias error (BIAS), and root-mean-square error (RMSE) were 0.97, −0.95 W/m2, and 22.38 W/m2 over the land and 0.99, −0.88 W/m2, and 10.96 W/m2 over the ocean, respectively. In particular, it shows improved accuracy in the low and middle latitude regions compared with other LWDR products. Considering its better accuracy and higher spatiotemporal resolution, the new LWDR product can provide essential data for deeply understanding the global energy balance and even the global warming. Moreover, the proposed fusion strategy can be enlightening for readers in the fields of multisource data combination and big data analysis. Remote sensing; data fusion; Ocean temperature; Spatial resolution; Land surface temperature; GLDAS; Data models; machine learning; ERA5; CERES-SYN; Machine learning; Fuses; surface longwave downward radiation (LWDR)
Wang, Yipu; Li, Rui; Hu, Jiheng; Fu, Yuyun; Duan, Jiawei; Cheng, Yuanxi; Song, BinbinWang, Y., R. Li, J. Hu, Y. Fu, J. Duan, Y. Cheng, B. Song, 2022: Evaluation of evapotranspiration estimation under cloud impacts over China using ground observations and multiple satellite optical and microwave measurements. Agricultural and Forest Meteorology, 314, 108806. doi: 10.1016/j.agrformet.2021.108806. Evapotranspiration (ET) is an important component of the hydrological cycle and energy balance in a land-atmosphere system. Satellite remote sensing has been widely used to estimate regional and global ET, but most previous methods depend on optical measurements that are limited to cloud-free conditions. This makes ET estimation challenging under cloudy sky. Currently, evaluations of satellite ET estimation under various cloud conditions remain lacking at the regional scale. Owing to the ability to penetrate clouds, satellite passive microwave measurements are powerful tools for retrieving ET under clouds. This study evaluated a satellite microwave-based daily ET method under all sky conditions over the part of China between 18°N and 50°N from 2003 to 2010, using microwave emissivity difference vegetation index (EDVI) as the proxy of vegetation water content (VWC). Validations using the surface water balance method found that the estimated ET (EDVI-ET) had an overall small bias (6.18%) in eight river basins. EDVI-ET displayed consistent spatiotemporal patterns with global MOD16 ET, with high spatial correlation (R>0.71) and monthly temporal correlation (R>0.82) throughout four seasons. Their differences were also small ( cloudy sky; Evapotranspiration (ET); microwave Emissivity Difference Vegetation Index (EDVI); MOD16
Wang, Zhenquan; Ge, Jinming; Yan, Jialin; Li, Wenxue; Yang, Xuan; Wang, Meihua; Hu, XiaoyuWang, Z., J. Ge, J. Yan, W. Li, X. Yang, M. Wang, X. Hu, 2022: Interannual shift of tropical high cloud diurnal cycle under global warming. Climate Dynamics. doi: 10.1007/s00382-022-06273-6. This research focuses on the observed tropical oceanic high clouds above the 300 hPa level, to investigate their diurnal cycles and radiative effects at the top of atmosphere. The diurnal centroid is used to quantify the diurnal cycle based on circular statistics to indicate the daily peaking time of cloud cover. It is found that the diurnal cycle of the tropical oceanic high clouds can significantly impact their cloud radiative effects, with a correlation coefficient of − 0.63 at the 95% significant level and a slope of − 14.5 Wm−2 h−1 between the net cloud radiative effects and the diurnal centroid shifting from midnight towards noon. This implies that the changes of the diurnal cycle can strongly influence the Earth radiative budget, and thus possibly impose radiative feedbacks to affect atmospheric circulations under global climate warming. It is also found that the strength of convection and the cold point temperature are two major environmental factors in influencing the diurnal-cycle centroid of the tropical oceanic high clouds. Furthermore, according to observations, the correlation coefficient between the diurnal-cycle centroid of the tropical oceanic high clouds and the global mean temperature is 0.75 at the 95% significant level, indicating a 2-h shift of the tropical oceanic high clouds towards noon with 1℃ increases of the global mean temperature.
Wang, Zhili; Wang, Chense; Yang, Su; Lei, Yadong; Che, Huizheng; Zhang, Xiaoye; Wang, QiuyanWang, Z., C. Wang, S. Yang, Y. Lei, H. Che, X. Zhang, Q. Wang, 2022: Evaluation of surface solar radiation trends over China since the 1960s in the CMIP6 models and potential impact of aerosol emissions. Atmospheric Research, 268, 105991. doi: 10.1016/j.atmosres.2021.105991. Accurate representation of surface solar radiation (SSR) trends is an important indicator for global climate models (GCMs) to correctly reproducing the historical climate evolution. This study examines the annual mean SSR trends in China under all-sky and clear-sky conditions for the period 1961–2014 in 34 Coupled Model Intercomparison Project Phase 6 (CMIP6) models using the latest homogenized in-situ SSR dataset. The site-observed annual mean SSR over China shows a significant decadal decline during 1961–2005 but an uptrend during 2006–2014, with the trends being −6.4 (−8.6) W m−2 and + 2.5 (+5.9) W m−2 per decade under all-sky (clear-sky) condition, respectively. All CMIP6 models simulate the sustained decline in SSR over China for the period 1961–2005 but significantly underestimate the dimming. The model results show trends of −1.9 ± 0.5 W m−2 and -2.5 ± 0.7 W m−2 per decade during 1961–2005 under all-sky and clear-sky conditions, respectively, which are around one third of the observed results. Furthermore, the models fail to capture the reversal of SSR trends in China during 2006–2014, with the trends being −1.1 ± 1.7 W m−2 and -2.2 ± 0.9 W m−2 per decade under all-sky and clear-sky conditions, respectively. We infer that the underestimation of anthropogenic aerosol emissions, especially absorbing black carbon emissions cause the underestimated simulation of SSR in dimming period over China. After 2005, the unseasonal increase in carbonaceous aerosol emissions and the weaker decline of sulfur dioxide emissions in China in the models result in an opposite SSR trends relative to the trends based on the site-observations. Our results suggest that improving the anthropogenic aerosol emissions inventory will be useful for generating a more accurate reproduction of the regional SSR evolution over China in GCMs. Surface solar radiation; CMIP6; Aerosol emissions; Black carbon
Wei, Linyi; Lu, Zheng; Wang, Yong; Liu, Xiaohong; Wang, Weiyi; Wu, Chenglai; Zhao, Xi; Rahimi, Stefan; Xia, Wenwen; Jiang, YiquanWei, L., Z. Lu, Y. Wang, X. Liu, W. Wang, C. Wu, X. Zhao, S. Rahimi, W. Xia, Y. Jiang, 2022: Black carbon-climate interactions regulate dust burdens over India revealed during COVID-19. Nature Communications, 13(1), 1839. doi: 10.1038/s41467-022-29468-1. India as a hotspot for air pollution has heavy black carbon (BC) and dust (DU) loadings. BC has been identified to significantly impact the Indian climate. However, whether BC-climate interactions regulate Indian DU during the premonsoon season is unclear. Here, using long-term Reanalysis data, we show that Indian DU is positively correlated to northern Indian BC while negatively correlated to southern Indian BC. We further identify the mechanism of BC-dust-climate interactions revealed during COVID-19. BC reduction in northern India due to lockdown decreases solar heating in the atmosphere and increases surface albedo of the Tibetan Plateau (TP), inducing a descending atmospheric motion. Colder air from the TP together with warmer southern Indian air heated by biomass burning BC results in easterly wind anomalies, which reduces dust transport from the Middle East and Sahara and local dust emissions. The premonsoon aerosol-climate interactions delay the outbreak of the subsequent Indian summer monsoon. Climate change; Atmospheric science
Wu, Wen-Ying; Yang, Zong-LiangWu, W., Z. Yang, 2022: Aridity-Dependent Land Surface Skin Temperature Biases in CMIP5/6. Geophysical Research Letters, 49(15), e2022GL098952. doi: 10.1029/2022GL098952. Land surface skin temperature, a critical indicator of climate change, connects the water and energy cycles between the land and the atmosphere. Here, we evaluate the simulations of land surface skin temperature from the Coupled Model Intercomparison Project Phase 5 (CMIP5) and CMIP6 models with satellite-based datasets and reanalysis. We find systematic cold skin temperature biases over arid regions in CMIP5/CMIP6 simulations. Over arid and semi-arid regions, latent heat biases drive skin temperature biases by evaporative cooling. Over humid regions, surface downward shortwave and albedo biases are relatively more critical. Spatial patterns of biases remain similar in the latest CMIP6 simulations, suggesting systematic biases in land-atmosphere interactions. These biases need to be corrected or considered while using models for future projections. CMIP; land surface temperature; land-atmosphere interaction
Xie, Xiaoming; He, Bin; Guo, Lanlan; Huang, Ling; Hao, Xingming; Zhang, Yafeng; Liu, Xuebang; Tang, Rui; Wang, SifanXie, X., B. He, L. Guo, L. Huang, X. Hao, Y. Zhang, X. Liu, R. Tang, S. Wang, 2022: Revisiting dry season vegetation dynamics in the Amazon rainforest using different satellite vegetation datasets. Agricultural and Forest Meteorology, 312, 108704. doi: 10.1016/j.agrformet.2021.108704. There has been a debate regarding whether the Amazon rainforest is greening during the dry season. This is partially because of the great uncertainty associated with the ability of different vegetation indices to accurately assess tropical vegetation status. This paper, revisit this issue by comprehensively examining the seasonal variations in vegetation recorded in various satellite-based vegetation datasets, namely, the leaf area index (LAI), contiguous solar-induced fluorescence (CSIF), enhanced vegetation index (EVI), and vegetation optical depth (VOD). All four of these vegetation datasets show an increase in vegetation during the dry season in most parts of the Amazon; however, the vegetation changes are not only spatially variable, but also differ among the datasets. This may be attributable in part to the different physical characteristics captured by each of the datasets. For example, the seasonal maximum value occurs first in the LAI, followed by the CSIF, EVI, and VOD, in that order. The seasonal cycle of the LAI agrees reasonably well with in-situ observations of leaf flush and leaf fall. As new leaf production offsets senescence and abscission, the dry-season vegetation increases in most parts of the Amazon rainforest. Partial correlation analysis was used to further investigate the potential climatic cues (i.e., precipitation, temperature and radiation) associated with the seasonal changes recorded in the vegetation data. We found that precipitation and radiation were the dominant potential cues for seasonal VOD (48%) and LAI (59%) changes, respectively. However, CSIF appears to be associated more closely with temperature and precipitation, with significant correlations observed across ∼x223C 37% of the Amazon rainforest area for both with CSIF. Finally, variations in the EVI showed similar sensitivity to all three climatic variables considered. The findings presented here will greatly improve our understanding of vegetation dynamics and the carbon cycle in the Amazon rainforest ecosystem. Amazon; Dry season; Greening; Rainforest; Vegetation data
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). CMIP5; GCMs; CMIP6; Bayesian model averaging; Multimodel ensemble; Surface downward longwave radiation (SDLR)
Yadav, Ramashray; Giri, R. K.; Bhan, S. C.Yadav, R., R. K. Giri, S. C. Bhan, 2022: High-resolution outgoing long wave radiation data (2014–2020) of INSAT-3D Imager and its comparison with Clouds and Earth’s Radiant Energy System (CERES) data. Advances in Space Research, 70(4), 976-991. doi: 10.1016/j.asr.2022.05.053. As a proxy of convection INSAT-3D satellite-derived product Outgoing Long Wave Radiation (OLR) data is available in both high temporal and spatial ranges over 40°N–40°S & 35°E–135°E. Daily gridded data set of 7 years of data (2014–2020) has been generated at 10 km × 10 km resolution and the same is compared with Clouds and Earth’s Radiant Energy System (CERES) instrument data taken from CERES as reference. Almost all the INSAT-3D data set generated is Global Space-based Inter-Calibration System (GSICS) corrected. The spatiotemporal consistency of the data set was statistically analyzed and found to be reasonably good agreement having a bias of ∼±5–6 W/m2 over above said domain. This inter-comparison is essential to get confidence in the data sets and release it further in the public domain for any scientific study. Again, this data set will be very useful in diagnosing the variations of convection at different scales (daily, weekly, monthly, annual, seasonal, intra-seasonal, etc.) & an important repository of Daily Climate Data Records (DCDR) for future studies. The specified domain of the present study is affected throughout the year with variable (weak, moderate, intense, or severe) spatiotemporal Inter-Tropical Convergence Zone (ITCZ) convection streams due to different types of weather activities (winter, pre-monsoon, monsoon, and post-monsoon) throughout the year. To visualize the importance of this high-resolution OLR data set a case study of Cyclone Amphan and Vayu is presented. The extremely severe intense convection (OLR departure −112 W/m2 with INSAT-3D new data set whereas −104 W/m2 in CERES data) was observed in both the data sets on 18th May-2020 at 13.7–16°N & 86.2–86.8°E during the super cyclonic stage of Amphan. A similar type of variation in the OLR has been noticed for Vayu Cyclone (OLR departure −94 W/m2 with INSAT-3D new data set whereas −86 W/m2 in CERES data). This information is very useful in impact-based forecasting and further future actions for disaster managers/decision-makers. The localized convective features during cyclone activity over the Indian Ocean region both in the Arabian Sea and the Bay of Bengal are well captured with this new data set and the difference in OLR of INSAT -3D and CERES -9 W/m2 and -12 W/m2 respectively. CERES; ITCZ; OLR; GSICS & DCDR; INSAT-3D; Spatiotemporal
Yang, Jie; Zhao, Chuanfeng; Sun, Yue; Chi, Yulei; Yang, YikunYang, J., C. Zhao, Y. Sun, Y. Chi, Y. Yang, 2022: Aerosol first indirect effect over narrow longitude regions of North Pacific and same-latitude lands. Atmospheric Environment, 277, 119081. doi: 10.1016/j.atmosenv.2022.119081. Aerosol first indirect effect (FIE), which causes variations of cloud droplet effective radius (re) and then cloud radiative effect (CRE), is one of the critical factors leading to uncertainties in climate model simulations. Different from most previous studies over continental regions, using 10-year observation data from CERES, this study investigates the statistical relationships between aerosol optical depth (AOD) and non-precipitating single-layer liquid phase cloud re and surface shortwave CRE (CRESW) over narrow longitude regions of North Pacific and its eastern and western lands at equal latitudes, along with the estimation of aerosol FIE. Both surface CRESW and cloud re are highly affected by aerosols. When AOD is less than 0.3–0.4 and liquid water path (LWP) is greater than 30 g/m2, positive AOD-CRESW and negative AOD-cloud re relationships are found over both ocean and land. With the increase of AOD, the sensitivity of CRESW and cloud re to aerosol is weakened, but both have greater fluctuations. The latitude dependence of the CRESW and cloud re variations with AOD are weak. The increases in liquid water path (LWP) when LWP is in a certain range (30–120 g/m2 over ocean and 30–90 g/m2 over land) can highly increase CRESW and promote the growth of cloud droplets. We also find that FIE values are positive under clean condition, while negative under polluted condition. Associated with the much less aerosol amount and more sufficient water supply, the FIE values over the ocean are distinctly larger than that over the land. Ocean; Liquid water path; Aerosol first indirect effect; Cloud droplet effective radius; Land; Shortwave cloud radiative effect
Yi, BingqiYi, B., 2022: Diverse cloud radiative effects and global surface temperature simulations induced by different ice cloud optical property parameterizations. Scientific Reports, 12(1), 10539. doi: 10.1038/s41598-022-14608-w. The representation of ice cloud optical properties in climate models has long been a difficult problem. Very different ice cloud optical property parameterization schemes developed based on very different assumptions of ice particle shape habits, particle size distributions, and surface roughness conditions, are used in various models. It is not clear as to how simulated climate variables are affected by the ice cloud optical property parameterizations. A total of five ice cloud optical property parameterization schemes, including three based on the ice habit mixtures suitable for general ice clouds, mid-latitude synoptic ice clouds, and tropical deep convective ice clouds, and the other two based on single ice habits (smooth hexagonal column and severely roughened column aggregate), are developed under a same framework and are implemented in the National Center for Atmospheric Research Community Atmospheric Model version 5. A series of atmosphere-only climate simulations are carried out for each of the five cases with different ice parameterizations. The differences in the simulated top of the atmosphere shortwave and longwave cloud radiative effects (CREs) are evaluated, and the global averaged net CRE differences among different cases range from − 1.93 to 1.03 Wm−2. The corresponding changes in simulated surface temperature are found to be most prominent on continental regions which amount to several degrees in Kelvin. Our results indicate the importance of choosing a reasonable ice cloud optical property parameterization in climate simulations. Environmental sciences; Climate sciences
Zeppetello, Lucas R. Vargas; Battisti, David S.; Baker, Marcia B.Zeppetello, L. R. V., D. S. Battisti, M. B. Baker, 2022: The Physics of Heat Waves: What Causes Extremely High Summertime Temperatures?. J. Climate, 35(7), 2231-2251. doi: 10.1175/JCLI-D-21-0236.1. Abstract We analyze observations and develop a hierarchy of models to understand heat waves—long-lived, high temperature anomalies—and extremely high daily temperatures during summertime in the continental extratropics. Throughout the extratropics, the number of extremely hot days found in the three hottest months is much greater than expected from a random, single-process model. Furthermore, in many locations the temperature skewness switches from negative on daily time scales to positive on monthly time scales (or shifts from positive on daily time scales to higher positive values on monthly time scales) in ways that cannot be explained by averaging alone. These observations motivate a hierarchy of models of the surface energy and moisture budgets that we use to illuminate the physics responsible for daily and monthly averaged temperature variability. Shortwave radiation fluctuations drive much of the variance and the negative skewness found in daily temperature observations. On longer time scales, precipitation-induced soil moisture anomalies are important for temperature variability and account for the shift toward positive skewness in monthly averaged temperature. Our results demonstrate that long-lived heat waves are due to (i) the residence time of soil moisture anomalies and (ii) a nonlinear feedback between temperature and evapotranspiration via the impact of temperature on vapor pressure deficit. For most climates, these two processes give rise to infrequent, long-lived heat waves in response to randomly distributed precipitation forcing. Combined with our results concerning high-frequency variability, extremely hot days are seen to be state-independent filigree driven by shortwave variability acting on top of longer-lived, moisture-driven heat waves.
Zhan, Chuan; Liang, ShunlinZhan, C., S. Liang, 2022: Improved estimation of the global top-of-atmosphere albedo from AVHRR data. Remote Sensing of Environment, 269, 112836. doi: 10.1016/j.rse.2021.112836. The top-of-atmosphere (TOA) albedo, a key component of the earth's energy balance, can be monitored regularly by satellite observations. Compared to the previous study Song et al. (2018), this paper estimates TOA albedo by directly linking Advanced Very High Resolution Radiometer (AVHRR) narrowband reflectance with TOA broadband albedo determined by NASA's Clouds and the Earth's Radiant Energy System (CERES) instead of Moderate Resolution Imaging Spectroradiometer (MODIS). The TOA albedo product developed in this study has an increased spatial resolution, from 1° to 0.05°, and its starting year has been extended from 2000 to 1981, compared to the CERES TOA albedo product. Models of lands and oceans are established separately under different atmospheric and surface conditions using gradient boosting regression tree (GBRT) method instead of the linear regression models in the previous study. The root mean square errors (RMSEs) of the cloudy-sky, clear-sky and snow-cover models over land are 11.2%, 9.2% and 2.3%, respectively; over oceans they are 14.6%, 10.6% and 5.6%, respectively. Compared to Song et al. (2018), the improvements of the three models over land are 28.8%, 29.2% and 68.6%, respectively. Compared to the CERES product, the new product is much more accurate than that from our previous study. The global monthly mean differences of the TOA albedo obtained with the GBRT product and CERES from 2001 to 2014 are mostly less than 5%. CERES; AVHRR; TOA albedo; Earth's energy budget; Machine learning
Zhang, Honghai; Seager, Richard; Xie, Shang-PingZhang, H., R. Seager, S. Xie, 2022: How Does Sea Surface Temperature Drive the Intertropical Convergence Zone in the Southern Indian Ocean?. J. Climate, 35(16), 5415-5432. doi: 10.1175/JCLI-D-21-0870.1. Abstract The Indian Ocean has an intriguing intertropical convergence zone (ITCZ) south of the equator year-round, which remains largely unexplored. Here we investigate this Indian Ocean ITCZ and the mechanisms for its origin. With a weak semiannual cycle, this ITCZ peaks in January–February with the strongest rainfall and southernmost location and a northeast–southwest orientation from the Maritime Continent to Madagascar, reaches a minimum around May with a zonal orientation, grows until its secondary maximum around September with a northwest–southeast orientation, weakens slightly until December, and then regains its mature phase in January. During austral summer, the Indian Ocean ITCZ exists over maximum surface moist static energy (MSE), consistent with convective quasi-equilibrium theory. This relationship breaks up during boreal summer when the surface MSE maximizes in the northern monsoon region. The position and orientation of the Indian Ocean ITCZ can be simulated well in both a linear dynamical model and the state-of-the-art Community Atmosphere Model version 6 (CAM6) when driven by observed sea surface temperature (SST). To quantify the contributions of the planetary boundary layer (PBL) and free-atmosphere processes to this ITCZ, we homogenize the free-atmosphere diabatic heating over the Indian Ocean in CAM6. In response, the ITCZ weakens significantly, owing to a weakened circulation and deep convection. Therefore, in CAM6, the SST drives the Indian Ocean ITCZ directly through PBL processes and indirectly via free-atmosphere diabatic heating. Their contributions are comparable during most seasons, except during the austral summer when the free-atmosphere diabatic heating dominates the mature-phase ITCZ. Significance Statement The intertropical convergence zone (ITCZ) is the globe-encircling band where trade winds converge and strong rainfall occurs in the tropics. Its rains provide life-supporting water to billions of people. Its associated latent heating invigorates the tropical atmospheric circulation and influences climate and weather across the planet. The ITCZ is located north of the equator in most tropical oceans, except in the Indian Ocean where it sits south of the equator year-around. In contrast to the well-known northern ITCZs, the origin of the southern ITCZ in the Indian Ocean remains unknown. This work provides the first explanation for how ocean surface temperature works together with processes in the lower and upper atmosphere to shape the unique ITCZ in the Indian Ocean.
Zhang, Jianhao; Zhou, Xiaoli; Goren, Tom; Feingold, GrahamZhang, J., X. Zhou, T. Goren, G. Feingold, 2022: Albedo susceptibility of northeastern Pacific stratocumulus: the role of covarying meteorological conditions. Atmospheric Chemistry and Physics, 22(2), 861-880. doi: 10.5194/acp-22-861-2022. Abstract. Quantification of the radiative adjustment of marine low clouds to aerosol perturbations, regionally and globally, remains the largest source of uncertainty in assessing current and future climate. One of the important steps towards quantifying the role of aerosol in modifying cloud radiative properties is to quantify the susceptibility of cloud albedo and liquid water path (LWP) to perturbations in cloud droplet number concentration (Nd). We use 10 years of spaceborne observations from the polar-orbiting Aqua satellite to quantify the albedo susceptibility of marine low clouds to Nd perturbations over the northeast (NE) Pacific stratocumulus (Sc) region. Mutual information analysis reveals a dominating control of cloud state (e.g., LWP and Nd) on low-cloud albedo susceptibility, relative to the meteorological states that drive these cloud states. Through a LWP–Nd space decomposition of albedo susceptibilities, we show clear separation among susceptibility regimes (brightening or darkening), consistent with previously established mechanisms through which aerosol modulates cloud properties. These regimes include (i) thin non-precipitating clouds (LWP < 55 g m−2) that exhibit brightening (occurring 37 % of the time), corresponding to the Twomey effect; (ii) thicker non-precipitating clouds, corresponding to entrainment-driven negative LWP adjustments that manifest as a darkening regime (36 % of the time); and (iii) another brightening regime (22 % of the time) consisting of mostly precipitating clouds, corresponding to precipitation-suppression LWP positive adjustments. Overall, we find an annual-mean regional low-cloud brightening potential of 20.8±2.68 W m−2 ln(Nd)−1, despite an overall negative LWP adjustment for non-precipitating marine stratocumulus, owing to the high occurrence of the Twomey–brightening regime. Over the NE Pacific, clear seasonal covariabilities among meteorological factors related to the large-scale circulation are found to play an important role in grouping conditions favorable for each susceptibility regime. When considering the covarying meteorological conditions, our results indicate that for the northeastern Pacific stratocumulus, clouds that exhibit the strongest brightening potential occur most frequently within shallow marine boundary layers over a cool ocean surface with a stable atmosphere and a dry free troposphere above. Clouds that exhibit a darkening potential associated with negative LWP adjustments occur most frequently within deep marine boundary layers in which the atmospheric instability and the ocean surface are not strong and warm enough to produce frequent precipitation. Cloud brightening associated with warm-rain suppression is found to preferably occur either under unstable atmospheric conditions or humid free-tropospheric conditions that co-occur with a warm ocean surface.
Zhang, Ke; Zhao, Long; Tang, Wenjun; Yang, Kun; Wang, JingZhang, K., L. Zhao, W. Tang, K. Yang, J. Wang, 2022: Global and Regional Evaluation of the CERES Edition-4A Surface Solar Radiation and Its Uncertainty Quantification. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 15, 2971-2985. doi: 10.1109/JSTARS.2022.3164471. This article presents a comprehensive evaluation of the 2000–2018 Clouds and Earth's Radiant Energy System Synoptic 1° Ed4A (CERES SYN1deg Edition 4A) surface solar radiation (SSR) product. In particular, the global assessment is conducted over different temporal scales (i.e., hourly, daily, and monthly-average) with special attention given to the impact of clouds, and a regional evaluation is further implemented over the Mainland of China (MC) using SSR measurements from a denser observational network provided by the China Meteorological Administration. Evaluation across all valid station-grid pairs yields mixed performance with |MBE|≤2.8 (6.2) W m−2, RMSE≤89.5 (31.6) W m−2, and R≥0.95 (0.93) over the globe (MC) for different temporal scales, and the monthly CERES SSR, with RMSE≤20 W m−2, is found to hold promise for global numerical weather prediction and climate monitoring. In addition, CERES is found to generally underestimate and overestimate SSR over land and ocean, respectively. Comparison between year-round and cloudy-season suggests that the presence of clouds may potentially impact the SSR retrievals, especially at the hourly temporal scales, with an increase in RMSE values larger than 10 W m−2 for most stations. Further investigation of subgrid heterogeneity suggests that most in situ SSR measurements can reasonably represent the 1° grid average except for some stations with specific geographic deployments, which may raise significant spatial representativeness issues and, therefore, need to be used with great caution. Earth; Satellites; cloud; Solar radiation; Sea measurements; Sea surface; surface solar radiation; Clouds; uncertainty quantification; Cloud computing; Clouds and Earth's radiant energy system synoptic (CERES); spatial representativeness
Zhang, Kun; Zhu, Gaofeng; Ma, Ning; Chen, Huiling; Shang, ShashaZhang, K., G. Zhu, N. Ma, H. Chen, S. Shang, 2022: Improvement of evapotranspiration simulation in a physically based ecohydrological model for the groundwater–soil–plant–atmosphere continuum. Journal of Hydrology, 613, 128440. doi: 10.1016/j.jhydrol.2022.128440. Accurate quantification of terrestrial evapotranspiration (ET) is essential to understanding the interaction between land and atmosphere, as well as the feedback response of vegetation dynamics. In our previous work, a physically based ecohydrological model called the simple terrestrial hydrosphere (SiTH) model was developed to estimate ET and the other ET-related variables based on the groundwater–soil–plant–atmosphere continuum (GSPAC). However, the SiTH model (SiTHv1) still has some deficiencies in the model structure and parameters, which can result in potential uncertainty in the estimation of terrestrial ET. In this study, we aimed to address these limitations by developing a new version of the SiTH model (SiTHv2). The main modifications of the SiTHv2 model include: (1) the vegetation moisture constraint module is updated with vegetation optical depth observations; (2) the critical model parameters associated with root distribution are constrained using flux observations; (3) the soil module is extended to a three-layer module with 5 m of total depth; (4) an irrigation input water strategy is applied in the cropland areas; and (5) the latest ERA5-Land reanalysis data with a finer spatial resolution are used as the meteorological forcing data. The estimated ET of the SiTHv2 model was validated/compared at multiple scales (i.e., site/plot, basin, and global) with flux data, basin water balance data, and other mainstream global ET products, respectively. The results demonstrate that the SiTHv2 model performs better than the SiTHv1 model, with an improvement in the overall model root-mean-square error of 0.66 mm day−1 (plot scale) and 98.58 mm year−1 (basin scale), representing 27% and 22% improvements over the SiTHv1 model in the same circumstances, respectively. In addition, the performance of the SiTHv2 model ranks well when compared to the existing terrestrial ET models and products. The improvements to the SiTH model should allow improved estimation of terrestrial ET and provide support to potential studies in water transfer within the GSPAC. Evapotranspiration; Water stress; Multi-scale verification; SiTH model
Zhang, Wanchun; Liu, Jian; Zhang, Peng; Sun, Ling; Xu, Hanlie; Wang, Yanjiao; Chen, LinZhang, W., J. Liu, P. Zhang, L. Sun, H. Xu, Y. Wang, L. Chen, 2022: Evaluation of Reprocessed Fengyun-3B Global Outgoing Longwave Radiation Data: Comparison with CERES OLR. Journal of Meteorological Research, 36(3), 417-428. doi: 10.1007/s13351-022-1132-4. Outgoing longwave radiation (OLR) at the top of the atmosphere (TOA) is a key parameter for understanding and interpreting the relationship between clouds, radiation, and climate interactions. It has been one of the operational products of the Fengyun (FY) meteorological satellites. OLR accuracy has gradually improved with advancements in satellite payload performance and the OLR retrieval algorithm. Supported by the National Key R&D Program Retrospective Calibration of Historical Chinese Earth Observation Satellite data (Richceos) project, a long-term OLR climate data record (CDR) was reprocessed based on the recalibrated Level 1 data of FY series satellites using the latest OLR retrieval algorithm. In this study, Fengyun-3B (FY-3B)’s reprocessed global OLR data from 2010 to 2018 were evaluated by using the Clouds and the Earth’s Radiant Energy System (CERES) global daily OLR data. The results showed that there was a high consistency between the FY-3B instantaneous OLR and CERES Single Scanner Footprint (SSF) OLR. Globally, between the two CDR datasets, the correlation coefficient reached 0.98, and the root-mean-square error (RMSE) was approximately 8–9 W m−2. The bias mainly came from the edge regions of the satellite orbit, which may be related to the satellite zenith angle and cloud cover distribution. It was shown that the long-term FY-3B OLR had temporal stability compared to CERES OLR long-term data. In terms of spatial distribution, the mean deviations showed zonal and seasonal characteristics, although seasonal fluctuations were observed in the differences between the two datasets. Effects of FY-3B OLR application to the South China Sea monsoon region and ENSO were demonstrated and analyzed, and the results showed that the seasonal deviation of FY-3B’s OLR comes mainly from the retrieval algorithm. However, it has little effect on the analysis of climate events. Clouds and the Earth’s Radiant Energy System (CERES); El Niño—Southern Oscillation (ENSO); Fengyun-3B (FY-3B); outgoing longwave radiation (OLR); South China Sea monsoon
Zhang, Xiyue; Schneider, Tapio; Shen, Zhaoyi; Pressel, Kyle G.; Eisenman, IanZhang, X., T. Schneider, Z. Shen, K. G. Pressel, I. Eisenman, 2022: Seasonal Cycle of Idealized Polar Clouds: Large Eddy Simulations Driven by a GCM. Journal of Advances in Modeling Earth Systems, 14(1), e2021MS002671. doi: 10.1029/2021MS002671. The uncertainty in polar cloud feedbacks calls for process understanding of the cloud response to climate warming. As an initial step toward improved process understanding, we investigate the seasonal cycle of polar clouds in the current climate by adopting a novel modeling framework using large eddy simulations (LES), which explicitly resolve cloud dynamics. Resolved horizontal and vertical advection of heat and moisture from an idealized general circulation model (GCM) are prescribed as forcing in the LES. The LES are also forced with prescribed sea ice thickness, but surface temperature, atmospheric temperature, and moisture evolve freely without nudging. A semigray radiative transfer scheme without water vapor and cloud feedbacks allows the GCM and LES to achieve closed energy budgets more easily than would be possible with more complex schemes. This enables the mean states in the two models to be consistently compared, without the added complications from interaction with more comprehensive radiation. We show that the LES closely follow the GCM seasonal cycle, and the seasonal cycle of low-level clouds in the LES resembles observations: maximum cloud liquid occurs in late summer and early autumn, and winter clouds are dominated by ice in the upper troposphere. Large-scale advection of moisture provides the main source of water vapor for the liquid-containing clouds in summer, while a temperature advection peak in winter makes the atmosphere relatively dry and reduces cloud condensate. The framework we develop and employ can be used broadly for studying cloud processes and the response of polar clouds to climate warming. cloud; GCM; Arctic; mixed-phase cloud; LES; seasonal cycle
Zhao, Guangyu; Yang, Muqun; Gao, Yizhao; Zhan, Yizhe; Lee, H. Joe; Di Girolamo, LarryZhao, G., M. Yang, Y. Gao, Y. Zhan, H. J. Lee, L. Di Girolamo, 2022: PYTAF: A Python Tool for Spatially Resampling Earth Observation Data. Earth Science Informatics, 15(3), 1443-1448. doi: 10.1007/s12145-020-00461-w. Earth observation data have revolutionized Earth science and significantly enhanced the ability to forecast weather, climate and natural hazards. The storage format of the majority of Earth observation data can be classified into swath, grid or point structures. Earth science studies frequently involve resampling between swath, grid and point data when combining measurements from multiple instruments, which can provide more insights into geophysical processes than using any single instrument alone. As the amount of Earth observation data increases each day, the demand for a high computational efficient tool to resample and fuse Earth observation data has never been greater. We present a software tool, called pytaf, that resamples Earth observation data stored in swath, grid or point structures using a novel block indexing algorithm. This tool is specially designed to process large scale datasets. The core functions of pytaf were implemented in C with OpenMP to enable parallel computations in a shared memory environment. A user-friendly python interface was also built. The tool has been extensively tested on supercomputers and successfully used to resample the data from five instruments on the EOS-Terra platform at a mission-wide scale. Grid; Nearest Neighbor; Pytaf; Python; Resample; Swath
Zhao, Lijun; Wang, Yuan; Zhao, Chuanfeng; Dong, Xiquan; Yung, Yuk L.Zhao, L., Y. Wang, C. Zhao, X. Dong, Y. L. Yung, 2022: Compensating Errors in Cloud Radiative and Physical Properties over the Southern Ocean in the CMIP6 Climate Models. Advances in Atmospheric Sciences. doi: 10.1007/s00376-022-2036-z. The Southern Ocean is covered by a large amount of clouds with high cloud albedo. However, as reported by previous climate model intercomparison projects, underestimated cloudiness and overestimated absorption of solar radiation (ASR) over the Southern Ocean lead to substantial biases in climate sensitivity. The present study revisits this long-standing issue and explores the uncertainty sources in the latest CMIP6 models. We employ 10-year satellite observations to evaluate cloud radiative effect (CRE) and cloud physical properties in five CMIP6 models that provide comprehensive output of cloud, radiation, and aerosol. The simulated longwave, shortwave, and net CRE at the top of atmosphere in CMIP6 are comparable with the CERES satellite observations. Total cloud fraction (CF) is also reasonably simulated in CMIP6, but the comparison of liquid cloud fraction (LCF) reveals marked biases in spatial pattern and seasonal variations. The discrepancies between the CMIP6 models and the MODIS satellite observations become even larger in other cloud macro- and micro-physical properties, including liquid water path (LWP), cloud optical depth (COD), and cloud effective radius, as well as aerosol optical depth (AOD). However, the large underestimation of both LWP and cloud effective radius (regional means ∼20% and 11%, respectively) results in relatively smaller bias in COD, and the impacts of the biases in COD and LCF also cancel out with each other, leaving CRE and ASR reasonably predicted in CMIP6. An error estimation framework is employed, and the different signs of the sensitivity errors and biases from CF and LWP corroborate the notions that there are compensating errors in the modeled shortwave CRE. Further correlation analyses of the geospatial patterns reveal that CF is the most relevant factor in determining CRE in observations, while the modeled CRE is too sensitive to LWP and COD. The relationships between cloud effective radius, LWP, and COD are also analyzed to explore the possible uncertainty sources in different models. Our study calls for more rigorous calibration of detailed cloud physical properties for future climate model development and climate projection. cloud physics; cloud radiative effect; global climate models; the Southern Ocean
Zheng, Cheng; Ting, Mingfang; Wu, Yutian; Kurtz, Nathan; Orbe, Clara; Alexander, Patrick; Seager, Richard; Tedesco, MarcoZheng, C., M. Ting, Y. Wu, N. Kurtz, C. Orbe, P. Alexander, R. Seager, M. Tedesco, 2022: Turbulent Heat Flux, Downward Longwave Radiation, and Large-Scale Atmospheric Circulation Associated with Wintertime Barents–Kara Sea Extreme Sea Ice Loss Events. J. Climate, 35(12), 3747-3765. doi: 10.1175/JCLI-D-21-0387.1. Abstract We investigate wintertime extreme sea ice loss events on synoptic to subseasonal time scales over the Barents–Kara Sea, where the largest sea ice variability is located. Consistent with previous studies, extreme sea ice loss events are associated with moisture intrusions over the Barents–Kara Sea, which are driven by the large-scale atmospheric circulation. In addition to the role of downward longwave radiation associated with moisture intrusions, which is emphasized by previous studies, our analysis shows that strong turbulent heat fluxes are associated with extreme sea ice melting events, with both turbulent sensible and latent heat fluxes contributing, although turbulent sensible heat fluxes dominate. Our analysis also shows that these events are connected to tropical convective anomalies. A dipole pattern of convective anomalies with enhanced convection over the Maritime Continent and suppressed convection over the central to eastern Pacific is consistently detected about 6–10 days prior to extreme sea ice loss events. This pattern is associated with either the Madden–Julian oscillation (MJO) or El Niño–Southern Oscillation (ENSO). Composites show that extreme sea ice loss events are connected to tropical convection via Rossby wave propagation in the midlatitudes. However, tropical convective anomalies alone are not sufficient to trigger extreme sea ice loss events, suggesting that extratropical variability likely modulates the connection between tropical convection and extreme sea ice loss events.
Zhou, Hao; Yue, Xu; Lei, Yadong; Tian, Chenguang; Zhu, Jun; Ma, Yimian; Cao, Yang; Yin, Xixi; Zhang, ZhidingZhou, H., X. Yue, Y. Lei, C. Tian, J. Zhu, Y. Ma, Y. Cao, X. Yin, Z. Zhang, 2022: Distinguishing the impacts of natural and anthropogenic aerosols on global gross primary productivity through diffuse fertilization effect. Atmospheric Chemistry and Physics, 22(1), 693-709. doi: 10.5194/acp-22-693-2022. Abstract. Aerosols can enhance ecosystem productivity by increasing diffuse radiation. Such diffuse fertilization effects (DFEs) vary among different aerosol compositions and sky conditions. Here, we apply a suite of chemical, radiation, and vegetation models in combination with ground- and satellite-based measurements to assess the impacts of natural and anthropogenic aerosol species on gross primary productivity (GPP) through DFE from 2001–2014. Globally, aerosols enhance GPP by 8.9 Pg C yr−1 under clear-sky conditions but only 0.95 Pg C yr−1 under all-sky conditions. Anthropogenic aerosols account for 41 % of the total GPP enhancement, though they contribute only 25 % to the increment of diffuse radiation. Sulfate/nitrate aerosols from anthropogenic sources make dominant contributions of 33 % (36 %) to aerosol DFE under all-sky (clear-sky) conditions, followed by the fraction of 18 % (22 %) by organic carbon aerosols from natural sources. In contrast to other species, black carbon aerosols reduce global GPP by 0.28 (0.12) Pg C yr−1 under all-sky (clear-sky) conditions. Long-term simulations show that aerosol DFE increases 2.9 % yr−1 under all-sky conditions mainly because of a downward trend in cloud amount. This study suggests that the impacts of aerosols and cloud should be considered in projecting future changes of ecosystem productivity under varied emission scenarios.
Zhou, Xingyu; Chen, Hua; Jiang, Weiping; Chen, Yan; Jin, Taoyong; Liu, Tianjun; Gao, YangZhou, X., H. Chen, W. Jiang, Y. Chen, T. Jin, T. Liu, Y. Gao, 2022: A new ambiguity resolution method for LEO precise orbit determination. Journal of Geodesy, 96(7), 49. doi: 10.1007/s00190-022-01629-6. Ambiguity resolution (AR) is an effective approach to improve the orbit accuracy of the low Earth orbit satellites using the Global Navigation Satellite System (GNSS). The most commonly used single-difference (SD) AR requires prior knowledge of the GNSS hardware biases, while the potential unavailability of the bias products may hinder the AR process for users. The track-to-track (T2T) AR can work as an alternative without the GNSS bias products, but the performance may be degraded by the receiver hardware biases. To provide a better alternative in this condition, a new AR method called SD T2T (SDT2T) is proposed in this study, where the GNSS and receiver biases can be greatly eliminated without external knowledge. The performance of the SD AR, SDT2T AR, and T2T AR methods are assessed based on the gravity recovery and climate experiment follow on and SWARM data. The results show that the improvements contributed by the SDT2T AR are comparable to the SD AR. The multiple iterations required by the T2T AR can be avoided by the SDT2T AR, and the accuracy of the T2T AR can be further improved with the preprocessed ambiguities of the SDT2T AR. Considering the efficiency and stable performance, the SDT2T AR is recommended as the preferred alternative single-receiver AR method in the absence of the GNSS hardware bias products. Ambiguity resolution; K-band range validation; LEO; Precise orbit determination; SLR orbit validation
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. 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, Jiang; Otto-Bliesner, Bette L.; Brady, Esther C.; Gettelman, Andrew; Bacmeister, Julio T.; Neale, Richard B.; Poulsen, Christopher J.; Shaw, Jonah K.; McGraw, Zachary S.; Kay, Jennifer E.Zhu, J., B. L. Otto-Bliesner, E. C. Brady, A. Gettelman, J. T. Bacmeister, R. B. Neale, C. J. Poulsen, J. K. Shaw, Z. S. McGraw, J. E. Kay, 2022: LGM paleoclimate constraints inform cloud parameterizations and equilibrium climate sensitivity in CESM2. Journal of Advances in Modeling Earth Systems, n/a(n/a), e2021MS002776. doi: 10.1029/2021MS002776. The Community Earth System Model version 2 (CESM2) simulates a high equilibrium climate sensitivity (ECS > 5°C) and a Last Glacial Maximum (LGM) that is substantially colder than proxy temperatures. In this study, we examine the role of cloud parameterizations in simulating the LGM cooling in CESM2. Through substituting different versions of cloud schemes in the atmosphere model, we attribute the excessive LGM cooling to the new CESM2 schemes of cloud microphysics and ice nucleation. Further exploration suggests that removing an inappropriate limiter on cloud ice number (NoNimax) and decreasing the time-step size (substepping) in cloud microphysics largely eliminate the excessive LGM cooling. NoNimax produces a more physically consistent treatment of mixed-phase clouds, which leads to an increase in cloud ice content and a weaker shortwave cloud feedback over mid-to-high latitudes and the Southern Hemisphere subtropics. Microphysical substepping further weakens the shortwave cloud feedback. Based on NoNimax and microphysical substepping, we have developed a paleoclimate-calibrated CESM2 (PaleoCalibr), which simulates well the observed 20th century warming and spatial characteristics of key cloud and climate variables. PaleoCalibr has a lower ECS (∼4°C) and a 20% weaker aerosol-cloud interaction than CESM2. PaleoCalibr represents a physically more consistent treatment of cloud microphysics than CESM2 and is a valuable tool in climate change studies, especially when a large climate forcing is involved. Our study highlights the unique value of paleoclimate constraints in informing the cloud parameterizations and ultimately the future climate projection. Cloud parameterizations; Cloud feedback; Community Earth System Model version 2; Equilibrium Climate Sensitivity; Last Glacial Maximum

## 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; convection; tropics; climate; general circulation model experiments; seasonal prediction
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. CERES; satellite remote sensing; ISCCP; CALIPSO; active and passive sensors; cloud cover 2
Bouniol, D.; Guichard, F.; Barbier, J.; Couvreux, F.; Roehrig, R.Bouniol, D., F. Guichard, J. Barbier, F. Couvreux, R. Roehrig, 2021: Sahelian Heat Wave Characterization From Observational Data Sets. Journal of Geophysical Research: Atmospheres, 126(11), e2020JD034465. doi: 10.1029/2020JD034465. This paper makes use of spaceborne observational data sets in order to characterize radiative processes involved in spring time heat waves in the Sahel. Spring corresponds to the hottest period of the year, with a high aerosol load, a gradual moistening, and the presence of clouds contributing to greenhouse effect. Heat waves are defined as synoptic events that have a large spatial extent and a duration longer than 3 days. Two types of heat waves are studied: daytime heat waves, detected with the daily maximum temperature and nighttime heat waves, detected with the daily minimum temperature. Daytime heat waves correspond to situations where cloud optical thickness is lower than the climatology and a large number of these situations are also associated with a lower aerosol load and a drier atmosphere. Nighttime heat waves correspond to a moister atmosphere compared to the climatology. In a large fraction of them, an increase in aerosol loading is also observed. This study, only based on observational data sets, highlights the subtle but different radiative balance at play in both types of events. radiation budget; observations; West Africa; heat wave
Caldwell, P. M.; Terai, C. R.; Hillman, B.; Keen, N. D.; Bogenschutz, P.; Lin, W.; Beydoun, H.; Taylor, M.; Bertagna, L.; Bradley, A. M.; Clevenger, T. C.; Donahue, A. S.; Eldred, C.; Foucar, J.; Golaz, J.-C.; Guba, O.; Jacob, R.; Johnson, J.; Krishna, J.; Liu, W.; Pressel, K.; Salinger, A. G.; Singh, B.; Steyer, A.; Ullrich, P.; Wu, D.; Yuan, X.; Shpund, J.; Ma, H.-Y.; Zender, C. S.Caldwell, P. M., C. R. Terai, B. Hillman, N. D. Keen, P. Bogenschutz, W. Lin, H. Beydoun, M. Taylor, L. Bertagna, A. M. Bradley, T. C. Clevenger, A. S. Donahue, C. Eldred, J. Foucar, J. Golaz, O. Guba, R. Jacob, J. Johnson, J. Krishna, W. Liu, K. Pressel, A. G. Salinger, B. Singh, A. Steyer, P. Ullrich, D. Wu, X. Yuan, J. Shpund, H. Ma, C. S. Zender, 2021: Convection-Permitting Simulations With the E3SM Global Atmosphere Model. Journal of Advances in Modeling Earth Systems, 13(11), e2021MS002544. doi: 10.1029/2021MS002544. This paper describes the first implementation of the Δx = 3.25 km version of the Energy Exascale Earth System Model (E3SM) global atmosphere model and its behavior in a 40-day prescribed-sea-surface-temperature simulation (January 20 through February 28, 2020). This simulation was performed as part of the DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) Phase 2 model intercomparison. Effective resolution is found to be the horizontal dynamics grid resolution despite using a coarser grid for physical parameterizations. Despite this new model being in an immature and untuned state, moving to 3.25 km grid spacing solves several long-standing problems with the E3SM model. In particular, Amazon precipitation is much more realistic, the frequency of light and heavy precipitation is improved, agreement between the simulated and observed diurnal cycle of tropical precipitation is excellent, and the vertical structure of tropical convection and coastal stratocumulus look good. In addition, the new model is able to capture the frequency and structure of important weather events (e.g., tropical cyclones, extratropical cyclones including atmospheric rivers, and cold air outbreaks). Interestingly, this model does not get rid of the erroneous southern branch of the intertropical convergence zone nor the tendency for strongest convection to occur over the Maritime Continent rather than the West Pacific, both of which are classic climate model biases. Several other problems with the simulation are identified, underscoring the fact that this model is a work in progress. general circulation model; E3SM; cloud resolving model; convection permitting model; storm resolving model
Campbell, James R.; Dolinar, Erica K.; Lolli, Simone; Fochesatto, Gilberto J.; Gu, Yu; Lewis, Jasper R.; Marquis, Jared W.; McHardy, Theodore M.; Ryglicki, David R.; Welton, Ellsworth J.Campbell, J. R., E. K. Dolinar, S. Lolli, G. J. Fochesatto, Y. Gu, J. R. Lewis, J. W. Marquis, T. M. McHardy, D. R. Ryglicki, E. J. Welton, 2021: Cirrus Cloud Top-of-the-Atmosphere Net Daytime Forcing in the Alaskan Subarctic from Ground-Based MPLNET Monitoring. J. Appl. Meteor. Climatol., (In Press). doi: 10.1175/JAMC-D-20-0077.1. AbstractCirrus cloud daytime top-of-the-atmosphere radiative forcing (TOA CRF) is estimated for a two-year NASA Micro-Pulse Lidar Network (532 nm; MPLNET) dataset collected at Fairbanks, Alaska. Two-year averaged daytime TOA CRF is estimated at between -1.08 and 0.78 W·m-2 (-0.49 to 1.10 W·m-2 in 2017, and -1.67 to 0.47 W·m-2 in 2018). This subarctic study completes a now trilogy of MPLNET ground-based cloud forcing investigations, following midlatitude and tropical studies by Campbell et al. (2016; C16) at Greenbelt, Maryland and Lolli et al. (2017) at Singapore. C16 hypothesize a global meridional daytime TOA CRF gradient that begins positive at the equator (2.20 – 2.59 W·m-2 over land and -0.46 – 0.42 W·m-2 over ocean at Singapore), becomes neutral in the midlatitudes (0.03 – 0.27 W·m-2 over land in Maryland) and turns negative moving poleward. This study does not completely confirm C16, as values are not found as exclusively negative. Evidence in historical reanalysis data suggests that daytime cirrus forcing in and around the subarctic likely once was exclusively negative. Increasing tropopause heights, inducing higher and colder cirrus, have likely increased regional forcing over the last forty years. We hypothesize that subarctic inter-annual cloud variability is likely a considerable influence on global cirrus cloud forcing sensitivity, given the irregularity of polar versus midlatitude synoptic weather intrusions. This study and hypothesis lays basis for an extrapolation of these MPLNET experiments to satellite-based lidar cirrus cloud datasets.
Ceppi, Paulo; Fueglistaler, StephanCeppi, P., S. Fueglistaler, 2021: The El Niño–Southern Oscillation Pattern Effect. Geophysical Research Letters, 48(21), e2021GL095261. doi: 10.1029/2021GL095261. El Niño–Southern Oscillation (ENSO) variability is accompanied by out-of-phase anomalies in the top-of-atmosphere tropical radiation budget, with anomalous downward flux (i.e., net radiative heating) before El Niño and anomalous upward flux thereafter (and vice versa for La Niña). Here, we show that these radiative anomalies result mainly from a sea surface temperature (SST) “pattern effect,” mediated by changes in tropical-mean tropospheric stability. These stability changes are caused by SST anomalies migrating from climatologically cool to warm regions over the ENSO cycle. Our results are suggestive of a two-way coupling between SST variability and radiation, where ENSO-induced radiative changes may in turn feed back onto SST during ENSO. clouds; climate change; radiation budget; ENSO; climate feedbacks; climate variability
Ceppi, Paulo; Nowack, PeerCeppi, P., P. Nowack, 2021: Observational evidence that cloud feedback amplifies global warming. Proceedings of the National Academy of Sciences, 118(30). doi: 10.1073/pnas.2026290118. Global warming drives changes in Earth’s cloud cover, which, in turn, may amplify or dampen climate change. This “cloud feedback” is the single most important cause of uncertainty in Equilibrium Climate Sensitivity (ECS)—the equilibrium global warming following a doubling of atmospheric carbon dioxide. Using data from Earth observations and climate model simulations, we here develop a statistical learning analysis of how clouds respond to changes in the environment. We show that global cloud feedback is dominated by the sensitivity of clouds to surface temperature and tropospheric stability. Considering changes in just these two factors, we are able to constrain global cloud feedback to 0.43 ± 0.35 W⋅m−2⋅K−1 (90% confidence), implying a robustly amplifying effect of clouds on global warming and only a 0.5% chance of ECS below 2 K. We thus anticipate that our approach will enable tighter constraints on climate change projections, including its manifold socioeconomic and ecological impacts. clouds; climate change; climate feedbacks; climate modeling; climate sensitivity
Cerasoli, Sara; Yin, Jun; Porporato, AmilcareCerasoli, S., J. Yin, A. Porporato, 2021: Cloud cooling effects of afforestation and reforestation at midlatitudes. Proceedings of the National Academy of Sciences, 118(33). doi: 10.1073/pnas.2026241118. Because of the large carbon sequestration potential, reforestation and afforestation (R&A) are among the most prominent natural climate solutions. However, while their effectiveness is well established for wet tropics, it is often argued that R&A are less advantageous or even detrimental at higher latitudes, where the reduction of forest albedo (the amount of reflected solar radiation by a surface) tends to nullify or even overcome the carbon benefits. Here, we carefully analyze the situation for R&A at midlatitudes, where the warming effects due to vegetation albedo are regarded to be almost balanced by the cooling effects from an increased carbon storage. Using both satellite data and atmospheric boundary-layer models, we show that by including cloud–albedo effects due to land–atmosphere interactions, the R&A cooling at midlatitudes becomes prevalent. This points to a much greater potential of R&A for wet temperate regions than previously considered. cloud feedback; afforestation; carbon mitigation
Cesana, Grégory V.; Del Genio, Anthony D.Cesana, G. V., A. D. Del Genio, 2021: Observational constraint on cloud feedbacks suggests moderate climate sensitivity. Nature Climate Change, 11(3), 213-218. doi: 10.1038/s41558-020-00970-y. Global climate models predict warming in response to increasing GHG concentrations, partly due to decreased tropical low-level cloud cover and reflectance. We use satellite observations that discriminate stratocumulus from shallow cumulus clouds to separately evaluate their sensitivity to warming and constrain the tropical contribution to low-cloud feedback. We find an observationally inferred low-level cloud feedback two times smaller than a previous estimate. Shallow cumulus clouds are insensitive to warming, whereas global climate models exhibit a large positive cloud feedback in shallow cumulus regions. In contrast, stratocumulus clouds show sensitivity to warming and the tropical inversion layer strength, controlled by the tropical Pacific sea surface temperature gradient. Models fail to reproduce the historical sea surface temperature gradient trends and therefore changes in inversion strength, generating an overestimate of the positive stratocumulus cloud feedback. Continued weak east Pacific warming would therefore produce a weaker low-cloud feedback and imply a more moderate climate sensitivity (3.47 ± 0.33 K) than many models predict.
Chakraborty, T.; 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, 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). climate; temperature; radiation; Antarctic; GHG
Gasparini, Blaž; Rasch, Philip J.; Hartmann, Dennis L.; Wall, Casey J.; Dütsch, MarinaGasparini, B., P. J. Rasch, D. L. Hartmann, C. J. Wall, M. Dütsch, 2021: A Lagrangian Perspective on Tropical Anvil Cloud Lifecycle in Present and Future Climate. Journal of Geophysical Research: Atmospheres, 126(4), e2020JD033487. doi: https://doi.org/10.1029/2020JD033487. The evolution of tropical anvil clouds from their origin in deep convective cores to their slow decay determines the climatic effects of clouds in tropical convective regions. Despite the relevance of anvil clouds for climate and responses of clouds to global warming, processes dominating their evolution are not well understood. Currently available observational data reveal instantaneous snapshots of anvil cloud properties, but cannot provide a process-based perspective on anvil evolution. We therefore conduct simulations with the high resolution version of the exascale earth system model in which we track mesoscale convective systems over the tropical Western Pacific and compute trajectories that follow air parcels detrained from peaks of convective activity. With this approach we gain new insight into the anvil cloud evolution both in present day and future climate. Comparison with geostationary satellite data shows that the model is able to simulate maritime mesoscale convective systems reasonably well. Trajectory results indicate that anvil cloud lifetime is about 15 h with no significant change in a warmer climate. The anvil ice mixing ratio is larger in a warmer climate due to a larger source of ice by detrainment and larger depositional growth leading to a more negative net cloud radiative effect along detrained trajectories. However, the increases in sources are counteracted by increases in sinks of ice, particularly snow formation and sedimentation. Furthermore, we find that the mean anvil cloud feedback along trajectories is positive and consistent with results from more traditional cloud feedback calculation methods. cirrus clouds; cloud feedbacks; radiative effects; tropical convection; anvil clouds; convective life cycle
Ge, Jinming; Wang, Zhenquan; Wang, Chen; Yang, Xuan; Dong, Zixiang; Wang, MeihuaGe, J., Z. Wang, C. Wang, X. Yang, Z. Dong, M. Wang, 2021: Diurnal variations of global clouds observed from the CATS spaceborne lidar and their links to large-scale meteorological factors. Climate Dynamics. doi: 10.1007/s00382-021-05829-2. Diurnal cycle of cloud (DCC), referring to the diurnal variation of cloud macro- and micro-physical properties, thus largely determining the strength of net cloud radiative forcing (CRF), is a critical feature of clouds’ variation and is important for weather and climate evolutions. Nevertheless, neither the DCC vertical structures and their links to meteorology are well understood, nor the DCCs for different cloud type are accurately represented in current climate models. With unique orbit of the international space station, Cloud-Aerosol Transport System (CATS) lidar onboard the international space station (ISS) can sample cloud profiles at different local times and provide DCC vertical structures. In this study, we analyzed 2-year CATS data and found that the amplitude of diurnal cycle is significantly correlated with the mean frequency of occurrence. High clouds and oceanic low clouds have strong vertical development during nighttime, and continental low clouds tend to develop in daytime. These DCC features can impact the strength and the direction of CRF. Overall, large cloud cover and amplitude can amplify net cloud cooling effects, and high cloud nighttime (18:00 PM–06:00 AM) occurrence frequency can strengthen the cloud warming effects. To explain the DCC phenomenon, the instantaneous links between cloud vertical structure and lower-tropospheric stability (LTS), vertical velocity and cold point temperature (CPT) are discussed individually to show the evidence of their controls on cloud properties from tropics to midlatitude. Our results confirm that tropical water clouds and cirrus are more affected by LTS and CPT, respectively. Towards midlatitude from tropics, vertical velocity gradually plays a more important role in cloud development and dissipation. According to the diurnal cycles of these factors, temperature and static stability have the largest daily amplitude in the boundary layer of tropics and subtropics, which can explain the diurnal cycle of relative humidity and low clouds evolution, whereas vertical velocity has the largest daily amplitude in midlatitude, which is more related to the diurnal cycle of relative humidity and clouds in upper level of troposphere.
Gettelman, A.; Gagne, D. J.; Chen, C.-C.; Christensen, M. W.; Lebo, Z. J.; Morrison, H.; Gantos, G.Gettelman, A., D. J. Gagne, C. Chen, M. W. Christensen, Z. J. Lebo, H. Morrison, G. Gantos, 2021: Machine Learning the Warm Rain Process. Journal of Advances in Modeling Earth Systems, 13(2), e2020MS002268. doi: https://doi.org/10.1029/2020MS002268. Clouds are critical for weather and climate prediction. The multiple scales of cloud processes make simulation difficult. Often models and measurements are used to develop empirical relationships for large-scale models to be computationally efficient. Machine learning provides another potential tool to improve our empirical parameterizations of clouds. To explore these opportunities, we replace the warm rain formation process in a General Circulation Model (GCM) with a detailed treatment from a bin microphysical model that causes a 400% slowdown in the GCM. We analyze the changes in climate that result from the use of the bin microphysical calculation and find improvements in the rain onset and frequency of light rain compared to high resolution process models and observations. We also find a resulting change in the cloud feedback response of the model to warming, which will significantly impact the climate sensitivity. We then replace the bin microphysical model with several neural networks designed to emulate the autoconversion and accretion rates produced by the bin microphysical model. The neural networks are organized into two stages: the first stage identifies where tendencies will be nonzero (and the sign of the tendency), and the second stage predicts the magnitude of the autoconversion and accretion rates. We describe the risks of overfitting, extrapolation, and linearization by using perfect model experiments with and without the emulator. We can recover the solutions with the emulators in almost all respects, and get simulations that perform as the detailed model, but with the computational cost of the control simulation. clouds; microphysics; machine learning
Ghiz, Madison L.; Scott, Ryan C.; Vogelmann, Andrew M.; Lenaerts, Jan T. M.; Lazzara, Matthew; Lubin, DanGhiz, M. L., R. C. Scott, A. M. Vogelmann, J. T. M. Lenaerts, M. Lazzara, D. Lubin, 2021: Energetics of surface melt in West Antarctica. The Cryosphere, 15(7), 3459-3494. doi: 10.5194/tc-15-3459-2021. Abstract. We use reanalysis data and satellite remote sensing of cloud properties to examine how meteorological conditions alter the surface energy balance to cause surface melt that is detectable in satellite passive microwave imagery over West Antarctica. This analysis can detect each of the three primary mechanisms for inducing surface melt at a specific location: thermal blanketing involving sensible heat flux and/or longwave heating by optically thick cloud cover, all-wave radiative enhancement by optically thin cloud cover, and föhn winds. We examine case studies over Pine Island and Thwaites glaciers, which are of interest for ice shelf and ice sheet stability, and over Siple Dome, which is more readily accessible for field work. During January 2015 over Siple Dome we identified a melt event whose origin is an all-wave radiative enhancement by optically thin clouds. During December 2011 over Pine Island and Thwaites glaciers, we identified a melt event caused mainly by thermal blanketing from optically thick clouds. Over Siple Dome, those same 2011 synoptic conditions yielded a thermal-blanketing-driven melt event that was initiated by an impulse of sensible heat flux and then prolonged by cloud longwave heating. The December 2011 synoptic conditions also generated föhn winds at a location on the Ross Ice Shelf adjacent to the Transantarctic Mountains, and we analyze this case with additional support from automatic weather station data. In contrast, a late-summer thermal blanketing period over Pine Island and Thwaites glaciers during February 2013 showed surface melt initiated by cloud longwave heating and then prolonged by enhanced sensible heat flux. One limitation thus far with this type of analysis involves uncertainties in the cloud optical properties. Nevertheless, with improvements this type of analysis can enable quantitative prediction of atmospheric stress on the vulnerable Antarctic ice shelves in a steadily warming climate.
Ghosh, Sudipta; Riemer, Nicole; Giuliani, Graziano; Giorgi, Filippo; Ganguly, Dilip; Dey, SagnikGhosh, S., N. Riemer, G. Giuliani, F. Giorgi, D. Ganguly, S. Dey, 2021: Sensitivity of Carbonaceous Aerosol Properties to the Implementation of a Dynamic Aging Parameterization in the Regional Climate Model RegCM. Journal of Geophysical Research: Atmospheres, 126(17), e2020JD033613. doi: 10.1029/2020JD033613. Freshly emitted soot is hydrophobic, but condensation of secondary aerosols and coagulation with other particles modify its hygroscopic optical properties. This conversion is referred to as “aerosol aging.” Many climate models represent this aging process with a fixed aging time scale, whereas in reality, it is a dynamic process that depends on environmental conditions. Here, we implement a dynamic aging parameterization scheme in the regional climate model RegCM4 in place of the fixed aging timescale of 1.15 days (∼27.6 h) and examine its impact on the aerosol life cycle over the Indian subcontinent. The conversion from hydrophobic to hydrophilic aerosol is usually lower than 27.6 h over the entire landmass and lower than 10 h over the polluted Indo-Gangetic Basin (IGB), with seasonal variability. Due to the implementation of the dynamic aging scheme, the column burden and surface mass concentration of carbonaceous aerosols increase during the drier season (December–February) when washout is negligible. The burden is reduced during the wet season (June–September) due to a more efficient washout except over the IGB, where a reduction in precipitation as a result of radiative feedbacks increases the aerosol concentrations. Over the polluted IGB, surface dimming increases due to the dynamic aging scheme, with the top of the atmosphere forcing remaining mostly unchanged. As a result, atmospheric heating increases by at least 1.2 W/m2. Our results suggest that climate models should incorporate dynamic aging for a more realistic representation of aerosol simulations, especially in highly polluted regions. climate; black carbon; regional climate model; dynamic aging; feedback; India
Gibbins, Goodwin; Haigh, Joanna D.Gibbins, G., J. D. Haigh, 2021: Comments on “Global and Regional Entropy Production by Radiation Estimated from Satellite Observations”. J. Climate, 34(9), 3721-3728. doi: 10.1175/JCLI-D-20-0685.1. AbstractA recent paper by Kato and Rose reports a negative correlation between the annual mean entropy production rate of the climate and the absorption of solar radiation in the CERES SYN1deg dataset, using the simplifying assumption that the system is steady in time. It is shown here, however, that when the nonsteady interannual storage of entropy is accounted for, the dataset instead implies a positive correlation; that is, global entropy production rates increase with solar absorption. Furthermore, this increase is consistent with the response demonstrated by an energy balance model and a radiative–convective model. To motivate this updated analysis, a detailed discussion of the conceptual relationship between entropy production, entropy storage, and entropy flows is provided. The storage-corrected estimate for the mean global rate of entropy production in the CERES dataset from all irreversible transfer processes is 81.9 mW m−2 K−1 and from only nonradiative processes is 55.2 mW m−2 K−1 (observations from March 2000 to February 2018).
Girishkumar, M. S.; Joseph, Jofia; McPhaden, M. J.; Pattabhi Ram Rao, E.Girishkumar, M. S., J. Joseph, M. J. McPhaden, E. Pattabhi Ram Rao, 2021: Atmospheric Cold Pools and Their Influence on Sea Surface Temperature in the Bay of Bengal. Journal of Geophysical Research: Oceans, 126(9), e2021JC017297. doi: 10.1029/2021JC017297. Recent observations show that atmospheric cold pool (ACP) events are plentiful in the Bay of Bengal (BoB) during summer (May–September) and fall (October–November) and that these events can significantly modify local air-sea interaction processes on sub-daily time scales. In this study, we examine whether the magnitude of sea surface temperature (SST) drop associated with ACP events shows any diurnal variability during summer and fall. For this purpose, we use moored buoy data with a 10-min temporal resolution at 8°, 12°, and 15°N along 90°E and a one-dimensional mixed layer (ML) model. The analysis shows a reduction in SST (ΔSST) due to ACPs in the BoB during summer and fall, with a maximum magnitude of ΔSST during the afternoon (1200–1600 LST). However, the maximum magnitude of ΔSST during the afternoon is a factor of two higher during fall (∼−0.14°C) than summer (∼−0.07°C). Analysis based on observations and ACP sensitivity experiments indicates that the shallow daytime thermocline and associated thin surface ML is the primary factor regulating the day to night difference in ΔSST associated with ACPs. The presence of this shallow daytime thermocline and thin ML amplifies the effects on SST of net surface heat loss and entrainment of cold sub-surface water associated with enhanced ACP wind speeds. sea surface temperature; Bay of Bengal; air-sea interaction; mixed layer processes; atmospheric cold pool
Goode, P. R.; Pallé, E.; Shoumko, A.; Shoumko, S.; Montañes-Rodriguez, P.; Koonin, S. E.Goode, P. R., E. Pallé, A. Shoumko, S. Shoumko, P. Montañes-Rodriguez, S. E. Koonin, 2021: Earth's Albedo 1998–2017 as Measured From Earthshine. Geophysical Research Letters, 48(17), e2021GL094888. doi: 10.1029/2021GL094888. The reflectance of the Earth is a fundamental climate parameter that we measured from Big Bear Solar Observatory between 1998 and 2017 by observing the earthshine using modern photometric techniques to precisely determine daily, monthly, seasonal, yearly and decadal changes in terrestrial albedo from earthshine. We find the inter-annual fluctuations in albedo to be global, while the large variations in albedo within individual nights and seasonal wanderings tend to average out over each year. We measure a gradual, but climatologically significant 0.5 decline in the global albedo over the two decades of data. We found no correlation between the changes in the terrestrial albedo and measures of solar activity. The inter-annual pattern of earthshine fluctuations are in good agreement with those measured by CERES (data began in 2001) even though the satellite observations are sensitive to retroflected light while earthshine is sensitive to wide-angle reflectivity. The CERES decline is about twice that of earthshine. atmospheres; methods; observational; planetary systems; planets and satellites; spectroscopic techniques; stars: low mass
Grise, Kevin M.; Kelleher, Mitchell K.Grise, K. M., M. K. Kelleher, 2021: Midlatitude Cloud Radiative Effect Sensitivity to Cloud Controlling Factors in Observations and Models: Relationship with Southern Hemisphere Jet Shifts and Climate Sensitivity. J. Climate, 34(14), 5869-5886. doi: 10.1175/JCLI-D-20-0986.1. AbstractAn effective method to understand cloud processes and to assess the fidelity with which they are represented in climate models is the cloud controlling factor framework, in which cloud properties are linked with variations in large-scale dynamical and thermodynamical variables. This study examines how midlatitude cloud radiative effects (CRE) over oceans covary with four cloud controlling factors—midtropospheric vertical velocity, estimated inversion strength (EIS), near-surface temperature advection, and sea surface temperature (SST)—and assesses their representation in CMIP6 models with respect to observations and CMIP5 models. CMIP5 and CMIP6 models overestimate the sensitivity of midlatitude CRE to perturbations in vertical velocity and underestimate the sensitivity of midlatitude shortwave CRE to perturbations in EIS and temperature advection. The largest improvement in CMIP6 models is a reduced sensitivity of CRE to vertical velocity perturbations. As in CMIP5 models, many CMIP6 models simulate a shortwave cloud radiative warming effect associated with a poleward shift in the Southern Hemisphere (SH) midlatitude jet stream, an effect not present in observations. This bias arises because most models’ shortwave CRE are too sensitive to vertical velocity perturbations and not sensitive enough to EIS perturbations, and because most models overestimate the SST anomalies associated with SH jet shifts. The presence of this bias directly impacts the transient surface temperature response to increasing greenhouse gases over the Southern Ocean, but not the global-mean surface temperature. Instead, the models’ climate sensitivity is correlated with their shortwave CRE sensitivity to surface temperature advection perturbations near 40°S, with models with more realistic values of temperature advection sensitivity generally having higher climate sensitivity.
Gryspeerdt, Edward; McCoy, Daniel T.; Crosbie, Ewan; Moore, Richard H.; Nott, Graeme J.; Painemal, David; Small-Griswold, Jennifer; Sorooshian, Armin; Ziemba, LukeGryspeerdt, E., D. T. McCoy, E. Crosbie, R. H. Moore, G. J. Nott, D. Painemal, J. Small-Griswold, A. Sorooshian, L. Ziemba, 2021: The impact of sampling strategy on the cloud droplet number concentration estimated from satellite data. Atmospheric Measurement Techniques Discussions, 1-25. doi: 10.5194/amt-2021-371. Abstract. Cloud droplet number concentration (Nd) is of central importance to observation-based estimates of aerosol indirect effects, being used to quantify both the cloud sensitivity to aerosol and the base state of the cloud. However, the derivation of Nd from satellite data depends on a number of assumptions about the cloud and the accuracy of the retrievals of the cloud properties from which it is derived, making it prone to systematic biases. A number of sampling strategies have been proposed to address these biases by selecting the most accurate Nd retrievals in the satellite data. This work compares the impact of these strategies on the accuracy of the satellite retrieved Nd, using a selection of insitu measurements. In stratocumulus regions, the MODIS Nd retrieval is able to achieve a high precision (r2 of 0.5–0.8). This is lower in other cloud regimes, but can be increased by appropriate sampling choices. Although the Nd sampling can have significant effects on the Nd climatology, it produces only a 20 % variation in the implied radiative forcing from aerosol-cloud interactions, with the choice of aerosol proxy driving the overall uncertainty. The results are summarised into recommendations for using MODIS Nd products and appropriate sampling.
Guigma, Kiswendsida H.; Guichard, Françoise; Todd, Martin; Peyrille, Philippe; Wang, YiGuigma, K. H., F. Guichard, M. Todd, P. Peyrille, Y. Wang, 2021: Atmospheric tropical modes are important drivers of Sahelian springtime heatwaves. Climate Dynamics, 56(5), 1967-1987. doi: 10.1007/s00382-020-05569-9. Heatwaves pose a serious threat to human health worldwide but remain poorly documented over Africa. This study uses mainly the ERA5 dataset to investigate their large-scale drivers over the Sahel region during boreal spring, with a focus on the role of tropical modes of variability including the Madden–Julian Oscillation (MJO) and the equatorial Rossby and Kelvin waves. Heatwaves were defined from daily minimum and maximum temperatures using a methodology that retains only intraseasonal scale events of large spatial extent. The results show that tropical modes have a large influence on the occurrence of Sahelian heatwaves, and, to a lesser extent, on their intensity. Depending on their convective phase, they can either increase or inhibit heatwave occurrence, with the MJO being the most important of the investigated drivers. A certain sensitivity to the geographic location and the diurnal cycle is observed, with nighttime heatwaves more impacted by the modes over the eastern Sahel and daytime heatwaves more affected over the western Sahel. The examination of the physical mechanisms shows that the modulation is made possible through the perturbation of regional circulation. Tropical modes thus exert a control on moisture and the subsequent longwave radiation, as well as on the advection of hot air. A detailed case study of a major event, which took place in April 2003, further supports these findings. Given the potential predictability offered by tropical modes at the intraseasonal scale, this study has key implications for heatwave risk management in the Sahel.
Guo, Huan; Ming, Yi; Fan, Songmiao; Zhou, Linjiong; Harris, Lucas; Zhao, MingGuo, H., Y. Ming, S. Fan, L. Zhou, L. Harris, M. Zhao, 2021: Two-Moment Bulk Cloud Microphysics With Prognostic Precipitation in GFDL's Atmosphere Model AM4.0: Configuration and Performance. Journal of Advances in Modeling Earth Systems, 13(6), e2020MS002453. doi: 10.1029/2020MS002453. A two-moment Morrison-Gettelman bulk cloud microphysics with prognostic precipitation (MG2), together with a mineral dust and temperature-dependent ice nucleation scheme, have been implemented into the Geophysical Fluid Dynamics Laboratory's Atmosphere Model version 4.0 (AM4.0). We refer to this configuration as AM4-MG2. This paper describes the configuration of AM4-MG2, evaluates its performance, and compares it with AM4.0. It is shown that the global simulations with AM4-MG2 compare favorably with observations and reanalyses. The model skill scores are close to AM4.0. Compared to AM4.0, improvements in AM4-MG2 include (a) better coastal marine stratocumulus and seasonal cycles, (b) more realistic ice fraction, and (c) dominant accretion over autoconversion. Sensitivity tests indicate that nucleation and sedimentation schemes have significant impacts on cloud liquid and ice water fields, but higher horizontal resolution (about 50 km instead of 100 km) does not.
Guo, Zhun; Zhou, Tianjun; Wang, Minghuai; Yang, Ben; Wu, BoGuo, Z., T. Zhou, M. Wang, B. Yang, B. Wu, 2021: The role of Tibetan summer low clouds in the simulation of the East Asian summer monsoon rain belt. International Journal of Climatology, 1-13. doi: 10.1002/joc.7405. It has been challenging to simulate the East Asian summer monsoon (EASM) using general circulation models. By evaluating the cloud layers unified by binormals (CLUBB) model and its revised version in the version-5 Community Atmosphere Model, we find that EASM simulations benefit from improving the reproduction of low clouds over the Tibetan Plateau. When a cloud-top radiative cooling scheme (RAD) is coupled with CLUBB, it significantly improves the resulting EASM rain belt and western Pacific subtropical high (WPSH) simulations compared to the default simulations without RAD; in these default simulations, the low-level southwesterlies, WPSH ridge, and EASM rain belt are displaced northward. The moisture budget analyses indicate that the improvements in EASM simulations are mainly contributed to by the improved presentation of low-level stationary eddy meridional flow convergence over East Asia; this convergence shifts northward during the default model runs. Because the RAD scheme enables the model to better represent the subgrid radiation–turbulence interaction, the model produces stronger turbulent fluxes and lower clouds but reduces incoming solar radiation over the Tibetan Plateau. It thus shifts the Tibetan High southward, ultimately resulting in an improved simulation of the low-level southwesterlies. These improvements in CLUBB_RAD highlight the importance of improving the representation of low clouds when simulating EASM rainfall. Tibetan Plateau; low clouds; cloud-top radiative cooling scheme; EASM rain belt; low-level southwesterlies
Hakuba, M. Z.; Frederikse, T.; Landerer, F. W.Hakuba, M. Z., T. Frederikse, F. W. Landerer, 2021: Earth's Energy Imbalance From the Ocean Perspective (2005–2019). Geophysical Research Letters, 48(16), e2021GL093624. doi: 10.1029/2021GL093624. Earth's energy imbalance (EEI) represents the rate of global energy accumulation in response to radiative forcings and feedbacks. Ocean heat uptake (OHU) poses a vital constraint on EEI and its uncertainty. Considering recent geodetic observations, geophysical corrections, and new estimates of the ocean's expansion efficiency of heat, we translate steric sea-level change, the difference of total sea-level and ocean-mass change, into an OHU of 0.86 [0.62, 1.10, 5%–95%] Wm−2 for the period 2005–2019. Adding components of non-oceanic heat uptake, we obtain an EEI of 0.94 [0.70, 1.19] Wm−2, which is at the upper end of previous assessments, but agrees within uncertainty. Interannual geodetic OHU variability exhibits a higher correlation with top-of-the-atmosphere net radiative flux than hydrographic-only data, but has a three times larger standard deviation. The radiation fluxes and the geodetic approach suggest an increase in heat uptake since 2005, most markedly in recent years. ocean heat uptake; Earth's energy imbalance; Geodesy; sea level budget; thermal expansion
Ham, Seung-Hee; Kato, Seiji; Rose, Fred G.; Loeb, Norman G.; Xu, Kuan-Man; Thorsen, Tyler; Bosilovich, Michael G.; Sun-Mack, Sunny; Chen, Yan; Miller, Walter F.Ham, S., S. Kato, F. G. Rose, N. G. Loeb, K. Xu, T. Thorsen, M. G. Bosilovich, S. Sun-Mack, Y. Chen, W. F. Miller, 2021: Examining Cloud Macrophysical Changes over the Pacific for 2007–17 Using CALIPSO, CloudSat, and MODIS Observations. J. Appl. Meteor. Climatol., 60(8), 1105-1126. doi: 10.1175/JAMC-D-20-0226.1. AbstractCloud macrophysical changes over the Pacific Ocean from 2007 to 2017 are examined by combining CALIPSO and CloudSat (CALCS) active-sensor measurements, and these are compared with MODIS passive-sensor observations. Both CALCS and MODIS capture well-known features of cloud changes over the Pacific associated with meteorological conditions during El Niño–Southern Oscillation (ENSO) events. For example, midcloud (cloud tops at 3–10 km) and high cloud (cloud tops at 10–18 km) amounts increase with relative humidity (RH) anomalies. However, a better correlation is obtained between CALCS cloud volume and RH anomalies, confirming more accurate CALCS cloud boundaries than MODIS. Both CALCS and MODIS show that low cloud (cloud tops at 0–3 km) amounts increase with EIS and decrease with SST over the eastern Pacific, consistent with earlier studies. It is also further shown that the low cloud amounts do not increase with positive EIS anomalies if SST anomalies are positive. While similar features are found between CALCS and MODIS low cloud anomalies, differences also exist. First, relative to CALCS, MODIS shows stronger anticorrelation between low and mid/high cloud anomalies over the central and western Pacific, which is largely due to the limitation in detecting overlapping clouds from passive MODIS measurements. Second, relative to CALCS, MODIS shows smaller impacts of mid- and high clouds on the low troposphere (<3 km). The differences are due to the underestimation of MODIS cloud layer thicknesses of mid- and high clouds.
He, Haozhe; Kramer, Ryan J.; Soden, Brian J.He, H., R. J. Kramer, B. J. Soden, 2021: Evaluating Observational Constraints on Intermodel Spread in Cloud, Temperature, and Humidity Feedbacks. Geophysical Research Letters, 48(17), e2020GL092309. doi: 10.1029/2020GL092309. Uncertainty in climate feedbacks is the primary source of the spread in projected surface temperature responses to anthropogenic forcing. Cloud feedback persistently appears as the main source of disagreement in future projections while the combined lapse-rate plus water vapor (LR + WV) feedback is a smaller (30%), but non-trivial source of uncertainty in climate sensitivity. Here we attempt to observationally constrain the feedbacks in an effort to reduce their intermodel uncertainties. The observed interannual variation provides a useful constraint on the long-term cloud feedback, as evidenced by the consistency of global-mean values and regional contributions to the intermodel spread on both interannual and long-term timescales. However, interannual variability does not serve to constrain the long-term LR + WV feedback spread, which we find is dominated by the varying tropical relative humidity (RH) response to interhemispheric warming differences under clear-sky conditions and the RH-fixed LR feedback under all-sky conditions. cloud feedback; emergent constraint; intermodel spread; lapse-rate plus water vapor feedback
Henry, Matthew; Merlis, Timothy M.; Lutsko, Nicholas J.; Rose, Brian E. J.Henry, M., T. M. Merlis, N. J. Lutsko, B. E. J. Rose, 2021: Decomposing the Drivers of Polar Amplification with a Single-Column Model. J. Climate, 34(6), 2355-2365. doi: 10.1175/JCLI-D-20-0178.1. AbstractThe precise mechanisms driving Arctic amplification are still under debate. Previous attribution methods compute the vertically uniform temperature change required to balance the top-of-atmosphere energy imbalance caused by each forcing and feedback, with any departures from vertically uniform warming collected into the lapse-rate feedback. We propose an alternative attribution method using a single-column model that accounts for the forcing dependence of high-latitude lapse-rate changes. We examine this method in an idealized general circulation model (GCM), finding that, even though the column-integrated carbon dioxide (CO2) forcing and water vapor feedback are stronger in the tropics, they contribute to polar-amplified surface warming as they produce bottom-heavy warming in high latitudes. A separation of atmospheric temperature changes into local and remote contributors shows that, in the absence of polar surface forcing (e.g., sea ice retreat), changes in energy transport are primarily responsible for the polar-amplified pattern of warming. The addition of surface forcing substantially increases polar surface warming and reduces the contribution of atmospheric dry static energy transport to the warming. This physically based attribution method can be applied to comprehensive GCMs to provide a clearer view of the mechanisms behind Arctic amplification.
Hourdin, Frédéric; Williamson, Daniel; Rio, Catherine; Couvreux, Fleur; Roehrig, Romain; Villefranque, Najda; Musat, Ionela; Fairhead, Laurent; Diallo, F. Binta; Volodina, VictoriaHourdin, F., D. Williamson, C. Rio, F. Couvreux, R. Roehrig, N. Villefranque, I. Musat, L. Fairhead, F. B. Diallo, V. Volodina, 2021: Process-based climate model development harnessing machine learning: II. model calibration from single column to global. Journal of Advances in Modeling Earth Systems, (In Press). doi: https://doi.org/10.1029/2020MS002225. AbstractWe demonstrate a new approach for climate model tuning in a realistic situation. Our approach, the mathematical foundations and technical details of which are given in Part I, systematically uses a single-column configuration of a global atmospheric model on test cases for which reference large-eddy-simulations are available. The space of free parameters is sampled running the single-column model from which metrics are estimated in the full parameter space using emulators. The parameter space is then reduced by retaining only the values for which the emulated metrics match large eddy simulations within a given tolerance to error. The approach is applied to the 6A version of the LMDZ model which results from a long investment in the development of physics parameterizations and by-hand tuning. The boundary layer is revisited by increasing the vertical resolution and varying parameters that were kept fixed so far, which improves the representation of clouds at process scale. The approach allows us to automatically reach a tuning of this modified configuration as good as that of the 6A version. We show how this approach helps accelerate the introduction of new parameterizations. It allows us to maintain the physical foundations of the model and to ensure that the improvement of global metrics is obtained for a reasonable behavior at process level, reducing the risk of error compensations that may arise from over-fitting some climate metrics. That is, we get things right for the right reasons.
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. cloud; ITCZ; climate model; Southern Ocean
Kim, Rachel; Tremblay, L. Bruno; Brunette, Charles; Newton, RobertKim, R., L. B. Tremblay, C. Brunette, R. Newton, 2021: A Regional Seasonal Forecast Model of Arctic Minimum Sea Ice Extent: Reflected Solar Radiation versus Late Winter Coastal Divergence. J. Climate, 34(15), 6097-6113. doi: 10.1175/JCLI-D-20-0846.1. AbstractThinning sea ice cover in the Arctic is associated with larger interannual variability in the minimum sea ice extent (SIE). The current generation of forced or fully coupled models, however, has difficulty predicting SIE anomalies from the long-term trend, highlighting the need to better identify the mechanisms involved in the seasonal evolution of sea ice cover. One such mechanism is coastal divergence (CD), a proxy for ice thickness anomalies based on late winter ice motion, quantified using Lagrangian ice tracking. CD gains predictive skill through the positive feedback of surface albedo anomalies, mirrored in reflected solar radiation (RSR), during melt season. Exploring the dynamic and thermodynamic contributions to minimum SIE predictability, RSR, initial SIE (iSIE), and CD are compared as predictors using a regional seasonal sea ice forecast model for 1 July, 1 June, and 1 May forecast dates for all Arctic peripheral seas. The predictive skill of June RSR anomalies mainly originates from open water fraction at the surface; that is, June iSIE and June RSR have equal predictive skill for most seas. The finding is supported by the surprising positive correlation found between June melt pond fraction (MPF) and June RSR in all peripheral seas: MPF anomalies indicate the presence of ice or open water, which is key to creating minimum SIE anomalies. This contradicts models that show correlation between melt onset, MPF, and the minimum SIE. A hindcast model shows that for a 1 May forecast, CD anomalies have better predictive skill than RSR anomalies for most peripheral seas.
Koppa, Akash; Alam, Sarfaraz; Miralles, Diego G.; Gebremichael, MekonnenKoppa, A., S. Alam, D. G. Miralles, M. Gebremichael, 2021: Budyko-Based Long-Term Water and Energy Balance Closure in Global Watersheds From Earth Observations. Water Resources Research, 57(5), e2020WR028658. doi: https://doi.org/10.1029/2020WR028658. Earth observations offer potential pathways for accurately closing the water and energy balance of watersheds, a fundamental challenge in hydrology. However, previous attempts based on purely satellite-based estimates have focused on closing the water and energy balances separately. They are hindered by the lack of estimates of key components, such as runoff. Here, we posit a novel approach based on Budyko’s water and energy balance constraints. The approach is applied to quantify the degree of long-term closure at the watershed scale, as well as its associated uncertainties, using an ensemble of global satellite data sets. We find large spatial variability across aridity, elevation, and other environmental gradients. Specifically, we find a positive correlation between elevation and closure uncertainty, as derived from the Budyko approach. In mountainous watersheds the uncertainty in closure is 3.9 ± 0.7 (dimensionless). Our results show that uncertainties in terrestrial evaporation contribute twice as much as precipitation uncertainties to errors in the closure of water and energy balance. Moreover, our results highlight the need for improving satellite-based precipitation and evaporation data in humid temperate forests, where the closure error in the Budyko space is as high as 1.1 ± 0.3, compared to only 0.2 ± 0.03 in tropical forests. Comparing the results with land surface model-based data sets driven by in situ precipitation, we find that Earth observation-based data sets perform better in regions where precipitation gauges are sparse. These findings have implications for improving the understanding of global hydrology and regional water management and can guide the development of satellite remote sensing-based data sets and Earth system models. precipitation; remote sensing; water balance; evapotranspiration; Budyko hypothesis; energy Balance
Kottayil, Ajil; Xavier, Anu; Xavier, Prince; Koovekkallu, Prajwal; Mohanakumar, KesavapillaiKottayil, A., A. Xavier, P. Xavier, P. Koovekkallu, K. Mohanakumar, 2021: Evolution of large-scale factors influencing extreme rainfall over south western coast of India. International Journal of Climatology, 1-15. doi: 10.1002/joc.7455. The life cycle and the large-scale factors driving extreme heavy rainfall events over the south west coast of India are studied. The extreme rainfall events are linked to the development of monsoon depressions and the associated large-scale dynamics. Strengthening of these parameters intensifies the monsoon low-level circulation over the Arabian Sea and the west coast via steepened meridional pressure gradient. The intensification of the low-level jet stream speed and its extension in the vertical causes an increase in the humidity flux in the lower and midtroposphere. The consequent ascending motion is from the midtroposphere to the upper troposphere, resulting in the formation of deep convective cloud clusters over the west coast and eastern parts of the Arabian Sea. This results in the incidence of extreme heavy rainfall over the south west coast of India. It is observed that during days of extreme rainfall, the direction of wind in the lower troposphere tends to be almost perpendicular to the Western Ghats favouring a strong orographic lift. The extreme rainfall events over the south west coast do not necessarily occur during the active cycle of monsoon intraseasonal oscillation, but are linked to the north westwards propagating monsoon depressions. We show that the signatures of extreme rainfall can be observed in several meteorological variables developing over different parts of the monsoon region. A synergistic analysis of these variables may help in the accurate and timely prediction of these events. monsoon; extreme rainfall; low-level jet; moisture flux; Western Ghats
Kramer, Ryan J.; He, Haozhe; Soden, Brian J.; Oreopoulos, Lazaros; Myhre, Gunnar; Forster, Piers M.; Smith, Christopher J.Kramer, R. J., H. He, B. J. Soden, L. Oreopoulos, G. Myhre, P. M. Forster, C. J. Smith, 2021: Observational evidence of increasing global radiative forcing. Geophysical Research Letters, n/a(n/a), e2020GL091585. doi: https://doi.org/10.1029/2020GL091585. Changes in atmospheric composition, such as increasing greenhouse gases, cause an initial radiative imbalance to the climate system, quantified as the instantaneous radiative forcing. This fundamental metric has not been directly observed globally and previous estimates have come from models. In part, this is because current space-based instruments cannot distinguish the instantaneous radiative forcing from the climate’s radiative response. We apply radiative kernels to satellite observations to disentangle these components and find all-sky instantaneous radiative forcing has increased 0.53±0.11 W/m2 from 2003 through 2018, accounting for positive trends in the total planetary radiative imbalance. This increase has been due to a combination of rising concentrations of well-mixed greenhouse gases and recent reductions in aerosol emissions. These results highlight distinct fingerprints of anthropogenic activity in Earth’s changing energy budget, which we find observations can detect within 4 years. aerosols; radiative forcing; greenhouse gases; radiative kernels
Lang, Simon T. K.; Dawson, Andrew; Diamantakis, Michail; Dueben, Peter; Hatfield, Samuel; Leutbecher, Martin; Palmer, Tim; Prates, Fernando; Roberts, Christopher D.; Sandu, Irina; Wedi, NilsLang, S. T. K., A. Dawson, M. Diamantakis, P. Dueben, S. Hatfield, M. Leutbecher, T. Palmer, F. Prates, C. D. Roberts, I. Sandu, N. Wedi, 2021: More accuracy with less precision. Quarterly Journal of the Royal Meteorological Society, 147(741), 4358-4370. doi: 10.1002/qj.4181. Reducing the numerical precision of the forecast model of the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF) from double to single precision results in significant computational savings without negatively affecting forecast accuracy. The computational savings allow to increase the vertical resolution of the operational ensemble forecasts from 91 to 137 levels earlier than anticipated and before the next upgrade of ECMWF's high-performance computing facility. This upgrade to 137 levels harmonises the vertical resolution of the medium-range deterministic forecasts and the medium-range and extended-range ensemble forecasts. Increasing the vertical resolution of the ensemble forecasts substantially improves forecast skill for all lead times as well as the mean of the model climate. ECMWF's ensemble and deterministic forecasts will run operationally at single precision from IFS model cycle 47R2 onwards. ensemble forecasting; reduced precision
Lang, Simon T. K.; Lock, Sarah-Jane; Leutbecher, Martin; Bechtold, Peter; Forbes, Richard M.Lang, S. T. K., S. Lock, M. Leutbecher, P. Bechtold, R. M. Forbes, 2021: Revision of the Stochastically Perturbed Parametrisations model uncertainty scheme in the Integrated Forecasting System. Quarterly Journal of the Royal Meteorological Society, 147(735), 1364-1381. doi: https://doi.org/10.1002/qj.3978. The Stochastically Perturbed Parametrisations scheme (SPP) represents model uncertainty in numerical weather prediction by introducing stochastic perturbations into the physical parametrisation schemes. The perturbations are constructed in such a way that the internal consistency of the physical parametrisation schemes is preserved. We developed a revised version of SPP for the Integrated Forecasting System of the European Centre for Medium-Range Weather Forecasts (ECMWF). The revised version introduces perturbations to additional quantities and modifies the probability distributions sampled by the scheme. Medium-range ensemble forecasts with the revised SPP are considerably more skilful than ensemble forecasts with the original implementation of SPP. The revised version of SPP is similar, in terms of forecast skill, to the Stochastically Perturbed Parametrisation Tendency scheme (SPPT), which is currently used to represent model uncertainty in the operational ECMWF ensemble forecasts. stochastic physics; ensemble forecasting; ensemble perturbation methods; SPP; SPPT
Lee, Hsiang-He; Bogenschutz, Peter; Yamaguchi, TakanobuLee, H., P. Bogenschutz, T. Yamaguchi, 2021: The Implementation of Framework for Improvement by Vertical Enhancement Into Energy Exascale Earth System Model. Journal of Advances in Modeling Earth Systems, 13(6), e2020MS002240. doi: 10.1029/2020MS002240. The low cloud bias in global climate models (GCMs) remains an unsolved problem. Coarse vertical resolution in GCMs has been suggested to be a significant cause of low cloud bias because planetary boundary layer parameterizations cannot resolve sharp temperature and moisture gradients often found at the top of subtropical stratocumulus layers. This work aims to ameliorate the low cloud problem by implementing a new computational method, the Framework for Improvement by Vertical Enhancement (FIVE), into the Energy Exascale Earth System Model (E3SM). Three physics schemes representing microphysics, radiation, and turbulence as well as vertical advection are interfaced to vertically enhanced physics (VEP), which allows for these processes to be computed on a higher vertical resolution grid compared to the rest of the E3SM model. We demonstrate the better representation of subtropical boundary layer clouds with FIVE while limiting additional computational cost from the increased number of levels. When the vertical resolution approaches the large eddy simulation-like vertical resolution in VEP, the climatological low cloud amount shows a significant increase of more than 30% in the southeastern Pacific Ocean. Using FIVE to improve the representation of low-level clouds does not come with any negative side effects associated with the simulation of mid- and high-level cloud and precipitation, that can occur when running the full model at higher vertical resolution. marine boundary layer; E3SM; vertical resolution; stratocumulus cloud; FIVE; low-level cloud
Lee, Jiwoo; Planton, Yann Y.; Gleckler, Peter J.; Sperber, Kenneth R.; Guilyardi, Eric; Wittenberg, Andrew T.; McPhaden, Michael J.; Pallotta, GiulianaLee, J., Y. Y. Planton, P. J. Gleckler, K. R. Sperber, E. Guilyardi, A. T. Wittenberg, M. J. McPhaden, G. Pallotta, 2021: Robust Evaluation of ENSO in Climate Models: How Many Ensemble Members Are Needed?. Geophysical Research Letters, 48(20), e2021GL095041. doi: 10.1029/2021GL095041. Large ensembles of model simulations require considerable resources, and thus defining an appropriate ensemble size for a particular application is an important experimental design criterion. We estimate the ensemble size (N) needed to assess a model’s ability to capture observed El Niño-Southern Oscillation (ENSO) behavior by utilizing the recently developed International CLIVAR ENSO Metrics Package. Using the larger ensembles available from CMIP6 and the US CLIVAR Large Ensemble Working Group, we find that larger ensembles are needed to robustly capture baseline ENSO characteristics (N > 50) and physical processes (N > 50) than the background climatology (N ≥ 12) and remote ENSO teleconnections (N ≥ 6). While these results vary somewhat across metrics and models, our study quantifies how larger ensembles are required to robustly evaluate simulated ENSO behavior, thereby providing some guidance for the design of model ensembles. ENSO; CMIP6; large ensemble; CLIVAR ENSO metrics; Monte-Carlo sampling; PCMDI metrics package (PMP)
Li, 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); LUE models; Diffuse radiation fraction
Liu, Ziwei; Yang, HanboLiu, Z., H. Yang, 2021: Estimation of Water Surface Energy Partitioning With a Conceptual Atmospheric Boundary Layer Model. Geophysical Research Letters, 48(9), e2021GL092643. doi: 10.1029/2021GL092643. Open water surface evaporation (E) or the latent heat flux (λE) is of great importance to surface water and energy budget. However, partitioning of the available energy into sensible heat flux (H) and λE, quantified as the Bowen ratio (), is implicitly discrepant between models and observations. In this study, an explicit equation for the estimation of Bo (thus for the λE) is derived based on an atmospheric boundary layer model combined with the potential vapor pressure deficit budget. Derived equation only requires the air temperature (Ta) and specific humidity (Q) as inputs, and performs well in λE estimation with a relative error of
Loeb, Norman G.; Johnson, Gregory C.; Thorsen, Tyler J.; Lyman, John M.; Rose, Fred G.; Kato, SeijiLoeb, N. G., G. C. Johnson, T. J. Thorsen, J. M. Lyman, F. G. Rose, S. Kato, 2021: Satellite and Ocean Data Reveal Marked Increase in Earth’s Heating Rate. Geophysical Research Letters, 48(13), e2021GL093047. doi: 10.1029/2021GL093047. Earth's Energy Imbalance (EEI) is a relatively small (presently ∼0.3%) difference between global mean solar radiation absorbed and thermal infrared radiation emitted to space. EEI is set by natural and anthropogenic climate forcings and the climate system's response to those forcings. It is also influenced by internal variations within the climate system. Most of EEI warms the ocean; the remainder heats the land, melts ice, and warms the atmosphere. We show that independent satellite and in situ observations each yield statistically indistinguishable decadal increases in EEI from mid-2005 to mid-2019 of 0.50 ± 0.47 W m−2 decade−1 (5%–95% confidence interval). This trend is primarily due to an increase in absorbed solar radiation associated with decreased reflection by clouds and sea-ice and a decrease in outgoing longwave radiation (OLR) due to increases in trace gases and water vapor. These changes combined exceed a positive trend in OLR due to increasing global mean temperatures. CERES; Earth energy imbalance; planetary heat uptake
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; mixed-phase clouds; global cloud-resolving model; supercooled water; seasonal variation
Obregón, María Ángeles; Serrano, Antonio; Costa, Maria João; Silva, Ana MariaObregón, M. Á., A. Serrano, M. J. Costa, A. M. Silva, 2021: Global Spatial and Temporal Variation of the Combined Effect of Aerosol and Water Vapour on Solar Radiation. Remote Sensing, 13(4), 708. doi: 10.3390/rs13040708. This study aims to calculate the combined and individual effects of the optical thickness of aerosols (AOT) and precipitable water vapour (PWV) on the solar radiation reaching the Earth’s surface at a global scale and to analyse its spatial and temporal variation. For that purpose, a novel but validated methodology is applied to CERES SYN1deg products for the period 2000–2019. Spatial distributions of AOT and PWV effects, both individually and combined, show a close link with the spatial distributions of AOT and PWV. The spatially averaged combined effect results in a −13.9% reduction in irradiance, while the average AOT effect is −2.3%, and the PWV effect is −12.1%. The temporal analysis focuses on detecting trends in the anomalies. The results show overall positive trends for AOT and PWV. Consequently, significant negative overall trends are found for the effects. However, significant positive trends for the individual AOT and the combined AOT-PWV effects are found in specific regions, such as the eastern United States, Europe or Asia, indicating successful emission control policies in these areas. This study contributes to a better understanding of the individual and combined effects of aerosols and water vapour on solar radiation at a global scale. CERES; aerosol optical depth; precipitable water vapour; combined effects; global radiative effects
Okamoto, Kozo; Hayashi, Masahiro; Hashino, Tempei; Nakagawa, Masayuki; Okuyama, ArataOkamoto, K., M. Hayashi, T. Hashino, M. Nakagawa, A. Okuyama, 2021: Examination of all-sky infrared radiance simulation of Himawari-8 for global data assimilation and model verification. Quarterly Journal of the Royal Meteorological Society, 147(740), 3611-3627. doi: 10.1002/qj.4144. The systematic difference between observations and simulation from weather forecast model hampers effective data assimilation and model improvement. The purpose of this study is to identify the characteristics and cause of the systematic difference or observation-minus-background (O − B) bias for all-sky infrared radiances of the Himawari-8 satellite, and propose data assimilation preprocessings and model verification. The O − B bias in cloudy scenes showed substantial negative values because of the shortage of high-altitude clouds generated in the forecast model. Additionally, a positive bias appeared for thin ice clouds because of the excessive absorption of radiative transfer models (RTMs). These biases were traced based on a bottom-up approach investigating individual uncertainty of RTMs, observation calibration, and the forecast model using two RTMs, reference hyperspectral sounders and synergetic measurements of CloudSat and CALIPSO. Based on these findings, data assimilation preprocessing such as quality-control procedures excluding samples that models poorly reproduced was developed. Although the quality controls reduced the number of biased samples, non-negligible O − B biases remained. Possible problems and treatments for the biases were discussed, including bias correction, observation error inflation, and correction of the cloud effect parameter. The O–B statistics also suggested insufficient representation of the diurnal variation in the cloud fraction in the tropics. Modified physical processes in the forecast model to increase ice clouds were tested to help improve the model bias and develop data assimilation. This trial indicated the difficulty in improving both O − B bias and variance and the necessity of adjusting the cloud effect parameters in data assimilation. cloud; data assimilation; bias; Himawari-8; radiative transfer model; all-sky infrared radiance
Painemal, David; Corral, Andrea F.; Sorooshian, Armin; Brunke, Michael A.; Chellappan, Seethala; Gorooh, Vesta Afzali; Ham, Seung-Hee; O'Neill, Larry; Smith, William L.; Tselioudis, George; Wang, Hailong; Zeng, Xubin; Zuidema, PaquitaPainemal, D., A. F. Corral, A. Sorooshian, M. A. Brunke, S. Chellappan, V. A. Gorooh, S. Ham, L. O'Neill, W. L. Smith, G. Tselioudis, H. Wang, X. Zeng, P. Zuidema, 2021: An Overview of Atmospheric Features Over the Western North Atlantic Ocean and North American East Coast—Part 2: Circulation, Boundary Layer, and Clouds. Journal of Geophysical Research: Atmospheres, 126(6), e2020JD033423. doi: https://doi.org/10.1029/2020JD033423. The Western North Atlantic Ocean (WNAO) is a complex land-ocean-atmosphere system that experiences a broad range of atmospheric phenomena, which in turn drive unique aerosol transport pathways, cloud morphologies, and boundary layer variability. This work, Part 2 of a 2-part paper series, provides an overview of the atmospheric circulation, boundary layer variability, three-dimensional cloud structure, and precipitation over the WNAO; the companion paper (Part 1) focused on chemical characterization of aerosols, gases, and wet deposition. Seasonal changes in atmospheric circulation and sea surface temperature explain a clear transition in cloud morphologies from small shallow cumulus clouds, convective clouds, and tropical storms in summer, to stratus/stratocumulus and multilayer cloud systems associated with winter storms. Synoptic variability in cloud fields is estimated using satellite-based weather states, and the role of postfrontal conditions (cold-air outbreaks) in the development of stratiform clouds is further analyzed. Precipitation is persistent over the ocean, with a regional peak over the Gulf Stream path, where offshore sea surface temperature gradients are large and surface fluxes reach a regional peak. Satellite data show a clear annual cycle in cloud droplet number concentration with maxima (minima) along the coast in winter (summer), suggesting a marked annual cycle in aerosol-cloud interactions. Compared with satellite cloud retrievals, four climate models qualitatively reproduce the annual cycle in cloud cover and liquid water path, but with large discrepancies across models, especially in the extratropics. The paper concludes with a summary of outstanding issues and recommendations for future work. air-sea interactions; atmospheric boundary layer; climate model evaluation; stratiform clouds; Western North Atlantic
Painemal, David; Spangenberg, Douglas; Smith Jr., William L.; Minnis, Patrick; Cairns, Brian; Moore, Richard H.; Crosbie, Ewan; Robinson, Claire; Thornhill, Kenneth L.; Winstead, Edward L.; Ziemba, LukePainemal, D., D. Spangenberg, W. L. Smith Jr., P. Minnis, B. Cairns, R. H. Moore, E. Crosbie, C. Robinson, K. L. Thornhill, E. L. Winstead, L. Ziemba, 2021: Evaluation of satellite retrievals of liquid clouds from the GOES-13 Imager and MODIS over the midlatitude North Atlantic during NAAMES campaign. Atmospheric Measurement Techniques Discussions, 1-23. doi: 10.5194/amt-2021-7. Abstract. Satellite retrievals of cloud droplet effective radius (re) and optical depth (t) from the Thirteenth Geostationary Operational Environmental Satellite (GOES-13), and the MOderate resolution Imaging Spectroradiometer (MODIS) onboard Aqua and Terra are evaluated with airborne data collected over the midlatitude boundary layer during the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES). The airborne dataset comprises in-situ re from the Cloud Droplet Probe (CDP) and remotely sensed re and t from the airborne Research Scanning Polarimeter (RSP). GOES-13 and MODIS (Aqua and Terra) re values are systematically greater than those from the CDP and RSP by at least 4.8 um (GOES-13) and 1.7 um (MODIS) despite relatively high linear correlations coefficients (r = 0.52–0.68). In contrast, the satellite t underestimates its RSP counterpart by −3.0, with r = 0.76–077. Overall, MODIS yields better agreement with airborne data than GOES-13, with biases consistent with those reported for subtropical stratocumulus clouds. While the negative bias in satellite t is mostly due to the retrievals having been collected in highly heterogeneous cloud scenes, the causes for the positive bias in satellite re, especially for GOES-13, are more complex. Although the high viewing zenith angle (~65°) and coarser pixel resolution for GOES-13 could explain a re bias of at least 0.7 um, the higher GOES-13 re bias relative to that from MODIS is likely rooted in other factors. In this regard, a near monotonic increase was also observed in GOES-13 re up to 1.0 um with satellite scattering angle (ϴ) over the angular range 116°–165°, that is, re increases toward the backscattering direction. Understanding the variations of re with ϴ will require the combined use of theoretical computations along with inter-comparisons of satellite retrievals derived from sensors with dissimilar viewing geometry.
Pathak, Raju; Sahany, Sandeep; Mishra, Saroj KantaPathak, R., S. Sahany, S. K. Mishra, 2021: Impact of Stochastic Entrainment in the NCAR CAM Deep Convection Parameterization on the Simulation of South Asian Summer Monsoon. Climate Dynamics. doi: 10.1007/s00382-021-05870-1. Model simulations are highly sensitive to the formulation of the atmospheric mixing process or entrainment in the deep convective parameterizations used in their atmospheric component. In this paper, we have implemented stochastic entrainment in the deep convection scheme of NCAR CAM5 and analyzed the improvements in model simulation, focusing on the South Asian Summer Monsoon (SASM), as compared to the deterministic entrainment formulation in the default version of the model. Simulations using stochastic entrainment (StochCAM5) outperformed default model simulations (DefCAM5), as inferred from multiple metrics associated with the SASM. StochCAM5 significantly alleviated some of the longstanding SASM biases seen in DefCAM5, such as precipitation pattern and magnitude over the Arabian Sea and western Equatorial Indian ocean, early monsoon withdrawal, and the overestimation in the frequency of light precipitation and the underestimation in the frequency of large-to-extreme precipitation. Related SASM dynamical and thermodynamical features, such as Somali Jet, low-level westerly winds, and meridional tropospheric temperature gradient (MTTG), are improved in StochCAM5. Further, the simulation of monsoon intra-seasonal oscillation (MISO), Madden Julian Oscillation (MJO), and equatorial Kelvin waves are improved in StochCAM5. Many essential climate variables, such as shortwave and longwave cloud forcing, cloud cover, relative and specific humidity, and precipitable water, show significant improvement in StochCAM5.
Payez, Alexandre; Dewitte, Steven; Clerbaux, NicolasPayez, A., S. Dewitte, N. Clerbaux, 2021: Dual View on Clear-Sky Top-of-Atmosphere Albedos from Meteosat Second Generation Satellites. Remote Sensing, 13(9), 1655. doi: 10.3390/rs13091655. Geostationary observations offer the unique opportunity to resolve the diurnal cycle of the Earth’s Radiation Budget at the top of the atmosphere (TOA), crucial for climate-change studies. However, a drawback of the continuous temporal coverage of the geostationary orbit is the fixed viewing geometry. As a consequence, imperfections in the angular distribution models (ADMs) used in the radiance-to-flux conversion process or residual angular-dependent narrowband-to-broadband conversion errors can result in systematic errors of the estimated radiative fluxes. In this work, focusing on clear-sky reflected TOA observations, we compare the overlapping views from Meteosat Second Generation satellites at 0° and 41.5°E longitude which enable a quantification of viewing-angle-dependent differences. Using data derived from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI), we identify some of the main sources of discrepancies, and show that they can be significantly reduced at the level of one month. This is achieved, separately for each satellite, via a masking procedure followed by an empirical fit at the pixel-level that takes into account all the clear-sky data from that satellite, calculated separately per timeslot of the day, over the month of November 2016. The method is then applied to each month of 2017, and gives a quadratic mean of the albedo root-mean squared difference over the dual-view region which is comparable from month to month, with a 2017 average value of 0.01. Sources of discrepancies include the difficulty to estimate the flux over the sunglint ocean region close to the limbs, the fact that the data processing does not include dedicated angular distribution models for the aerosol-over-ocean case, and the existence of an observer-dependent diurnal-asymmetry artefact affecting the clear-sky-albedo dependence on the solar zenith angle particularly over land areas. angular distribution models; SEVIRI; geostationary satellites; top-of-atmosphere albedo; reflected solar radiation; diurnal-asymmetry artefact
Pei, Suyang; Shinoda, Toshiaki; Steffen, John; Seo, HyodaePei, S., T. Shinoda, J. Steffen, H. Seo, 2021: Substantial Sea Surface Temperature Cooling in the Banda Sea Associated With the Madden-Julian Oscillation in the Boreal Winter of 2015. Journal of Geophysical Research: Oceans, 126(6), e2021JC017226. doi: 10.1029/2021JC017226. Substantial (∼2°C) basin averaged sea surface temperature (SST) cooling in the Banda Sea occurred in less than a 14-day period during the 2015 boreal winter Madden-Julian Oscillation (MJO). Such rapid and large cooling associated with the MJO has not been reported at least in the last two decades. Processes that control the substantial cooling during the 2015 MJO event are examined using high-resolution ocean reanalysis and one-dimensional (1-D) ocean model simulations. Previous studies suggest that MJO-induced SST variability in the Banda Sea is primarily controlled by surface heat flux. However, heat budget analysis of the model indicates that entrainment cooling produced by vertical mixing contributes more than surface heat flux for driving the basin-wide SST cooling during the 2015 event. Analysis of the ocean reanalysis further demonstrates that the prominent coastal upwelling around islands in the southern basin occurs near the end of the cooling period. The upwelled cold waters are advected by MJO-induced surface currents to a large area within the Banda Sea, which further maintains the basin-wide cold SST. These results are compared with another MJO-driven substantial cooling event during the boreal winter of 2007 in which the cooling is mostly driven by surface heat flux. Sensitivity experiments, in which initial temperature conditions for the two events are replaced by each other, demonstrate that the elevated thermocline associated with the 2015 strong El Niño is largely responsible for the intensified cooling generated by the vertical mixing with colder subsurface waters. sea surface temperature; Banda Sea; El Niño-Southern Oscillation (ENSO); Madden-Julian Oscillation (MJO); Maritime Continent; mixed layer processes
Peng, Jianghai; Jiang, Bo; Chen, Hongkai; Liang, Shunlin; Liang, Hui; Li, Shaopeng; Han, Jiakun; Liu, Qiang; Cheng, Jie; Yao, Yunjun; Jia, Kun; Zhang, XiaotongPeng, J., B. Jiang, H. Chen, S. Liang, H. Liang, S. Li, J. Han, Q. Liu, J. Cheng, Y. Yao, K. Jia, X. Zhang, 2021: A New Empirical Estimation Scheme for Daily Net Radiation at the Ocean Surface. Remote Sensing, 13(20), 4170. doi: 10.3390/rs13204170. Ocean surface net radiation (Rn) is significant in research on the Earth’s heat balance systems, air–sea interactions, and other applications. However, there have been few studies on Rn until now. Based on radiative and meteorological measurements collected from 66 globally distributed moored buoys, it was found that Rn was dominated by downward shortwave radiation (Rg↓) when the length ratio of daytime (LRD) was greater than 0.4 but dominated by downward longwave radiation (Rl↓) for the other cases (LRD ≤ 0.4). Therefore, an empirical scheme that includes two conditional models named Case 1 (LRD > 0.4) utilizing Rg↓ as a major input and Case 2 (LRD ≤ 0.4) utilizing Rl↓ as a major input for Rn estimation was successfully developed. After validation against in situ Rn, the performance of the empirical scheme was satisfactory with an overall R2 value of 0.972, an RMSE of 9.768 Wm−2, and a bias of −0.092 Wm−2. Specifically, the accuracies of the two conditional models were also very good, with RMSEs of 9.805 and 2.824 Wm−2 and biases of −0.095 and 0.346 Wm−2 for the Case 1 and Case 2 models, respectively. However, due to the limited number of available samples, the performances of these new models were poor in coastal and high-latitude areas, and the models did not work when the LRD was too small (i.e., LRD < 0.3). Overall, the newly developed empirical scheme for Rn estimation has strong potential to be widely used in practical use because of its simple format and high accuracy. CERES; longwave radiation; net radiation; shortwave radiation; buoy data; empirical model; sea surface
Perpina, Miguel; Noel, Vincent; Chepfer, Helene; Guzman, Rodrigo; Feofilov, Artem G.Perpina, M., V. Noel, H. Chepfer, R. Guzman, A. G. Feofilov, 2021: Link Between Opaque Cloud Properties and Atmospheric Dynamics in Observations and Simulations of Current Climate in the Tropics, and Impact on Future Predictions. Journal of Geophysical Research: Atmospheres, 126(17), e2020JD033899. doi: 10.1029/2020JD033899. Using spaceborne lidar observations and reanalyzes (2008–2014), we relate the vertical wind speed at 500 hPa (ω500), indicator of atmospheric circulation, to properties of opaque clouds (altitude and cover) and to the Cloud Radiative Effect (CRE) in the Tropics. We confront those observations with simulations by IPSL-CM6 and CESM1 climate models using early 21st century emissions. Both models overestimate the average opaque cloud cover. IPSL-CM6 puts high opaque clouds too high (+2 km), especially in ascendance. CESM1 overestimates the intermediate opaque cloud cover and underestimates small and large opaque cloud covers. Both models agree that cloud properties behave differently at wind speed above (strong subsidence) or below (weak subsidence and ascendance) 20 hPa/day. In future climate (2089–2095), variables affected by biases in current climate are affected by notable changes: IPSL-CM6 puts high opaque clouds even higher (+2 km) while opaque cloud cover above 30% decreases and below 30% increases in CESM1. Both models predict very little change in the average net CRE in the future. We find that predicted changes of cloud properties can be regionally driven by dynamic or thermodynamic changes, depending on the relationship between opaque cloud altitude and ω500 in the model. Overall, most changes are due to thermodynamic changes in the relationship between cloud property and atmospheric dynamics.
Peters, Ian Marius; Buonassisi, TonioPeters, I. M., T. Buonassisi, 2021: How changes in worldwide operating conditions affect solar cell performance. Solar Energy, 220, 671-679. doi: 10.1016/j.solener.2021.01.017. In field operation, solar cells are exposed to constantly changing operating conditions. These changing conditions have an impact on energy yield. Present-day yield predictions mostly use linear correction coefficients derived from lab experiments. These corrections neglect interactions between meteorological parameters like temperature and humidity. In this study, we reverse this approach by analyzing simulated solar cell performance under varying conditions worldwide. We use meteorological data measured between 2006 and 2015 to establish trends in the development of meteorological conditions and solar cell performance. From these two trends, we obtain linear correlation coefficients. The obtained implied temperature coefficient, on average, has a value of −0.52 ± 0.03%/K. This value is 15% higher than the tabulated temperature coefficient (−0.45%/K) used in the simulation, demonstrating the impact of coinciding meteorological factors. Light absorption due to elevated humidity levels is likely the strongest contributor to the deviation. One application of these findings is a projection of how today's crystalline silicon solar panels would perform due to rising temperature at the end of the 21st century. Using the established implied temperature coefficient, we project performance reductions of between 0.7% and 2.5%, depending on the warming scenario. The effect is reduced in higher efficient, upcoming photovoltaic technologies, providing further motivation to develop and improve these solar cells. Modelling; Performance ratio; Silicon solar cell; Temperature dependence
Pi, Chia-Jung; Chen, Jen-PingPi, C., J. Chen, 2021: Integrated cloud macro- and micro-physics schemes with kinetic treatment of condensation processes for global models. Atmospheric Research, 261, 105745. doi: 10.1016/j.atmosres.2021.105745. A new parameterization scheme was developed to remove the saturation adjustment assumption and resolve the condensation process in the grid-scale cloud macrophysics scheme to build an integrated cloud microphysics scheme for global climate models. By applying a saturation prediction equation with calculations based on cloud hydrometeor properties, supersaturation or subsaturation can be determined within the macrophysics scheme. This treatment provides the basis for condensation calculation and allows the Wegener–Bergeron–Findeisen process to be resolved explicitly to render a realistic liquid–ice partition in mixed-phase clouds. The cloud fraction scheme was modified based on physics principles to complement the condensation scheme. The new scheme's performance was examined by incorporating it into the Community Atmosphere Model version 5 (CAM5) single-column model to simulate a Tropical Warm Pool–International Cloud Experiment (TWP–ICE) case. The results revealed that grid-scale cloud properties are sensitive to the condensation process's treatment, and the new scheme can produce a more reasonable cloud fraction and liquid–ice partition than the original CAM5. The theory-based scheme developed in this study may provide insight for addressing consistency between the macrophysical and microphysical schemes in global climate models. Cloud microphysics; Cloud macrophysics; Liquid-ice partition; Mixed-phase supersaturation; Wegener–Bergeron–Findeisen process
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%. CloudSat; CALIPSO; MERRA2; cloud radiative effects; MLS; ERA5; ozone; stratosphere-troposphere exchange
Wang, Qiuyan; Zhang, Hua; Yang, Su; Chen, Qi; Zhou, Xixun; Shi, Guangyu; Cheng, Yueming; Wild, MartinWang, Q., H. Zhang, S. Yang, Q. Chen, X. Zhou, G. Shi, Y. Cheng, M. Wild, 2021: Potential Driving Factors on Surface Solar Radiation Trends over China in Recent Years. Remote Sensing, 13(4), 704. doi: 10.3390/rs13040704. The annual mean surface solar radiation (SSR) trends under all-sky, clear-sky, all-sky-no-aerosol, and clear-sky-no-aerosol conditions as well as their possible causes are analyzed during 2005–2018 across China based on different satellite-retrieved datasets to determine the major drivers of the trends. The results confirm clouds and aerosols as the major contributors to such all-sky SSR trends over China but play differing roles over sub-regions. Aerosol variations during this period result in a widespread brightening, while cloud effects show opposite trends from south to north. Moreover, aerosols contribute more to the increasing all-sky SSR trends over northern China, while clouds dominate the SSR decline over southern China. A radiative transfer model is used to explore the relative contributions of cloud cover from different cloud types to the all-types-of-cloud-cover-induced (ACC-induced) SSR trends during this period in four typical sub-regions over China. The simulations point out that the decreases in low-cloud-cover (LCC) over the North China Plain are the largest positive contributor of all cloud types to the marked annual and seasonal ACC-induced SSR increases, and the positive contributions from both high-cloud-cover (HCC) and LCC declines in summer and winter greatly contribute to the ACC-induced SSR increases over East China. The contributions from medium-low-cloud-cover (mid-LCC) and LCC variations dominate the ACC-caused SSR trends over southwestern and South China all year round, except for the larger HCC contribution in summer. radiative transfer model; cloud and aerosols; different types of cloud cover; relative contributions; SSR trends under different conditions
Wang, Tao; Wu, Dong L.; Gong, Jie; Wang, ChenxiWang, T., D. L. Wu, J. Gong, C. Wang, 2021: Long-Term Observations of Upper-Tropospheric Cloud Ice From the MLS. Journal of Geophysical Research: Atmospheres, 126(9), e2020JD034058. doi: 10.1029/2020JD034058. Upper tropospheric cloud ice varies across different timescales and plays an important role in regulating Earth's climate, but knowledge of the abundances and the variability of cloud ice has been limited for decades. The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) provides an unprecedented record of cloud ice measurements since its launch in April 2006. However, CALIPSO has left the A-Train in September 2018 and entered the C-Train orbit which follows a slightly different ground track with a different local crossing time. This orbit change challenges the continuation of a long-term record of cloud ice since ice is subject to stronger diurnal cycle. Fortunately, the Aura Microwave Limb Sounder (MLS), still as a member of the A-Train, has a consistent local crossing time and has measured high quality radiance since launch in 2004, and will probably continue beyond 2024. We present the use of MLS 640-GHz cloud-induced radiance (Tcir) to build a robust upper tropospheric partial ice water path (pIWP) product due to its high dynamical range to different sizes of ice particles. The MLS rebuilt pIWP, which extends nearly two decades, captures the spatial and temporal variabilities of upper tropospheric cloud ice that CALIOP is capable of measuring. This provides valuable alternative for studying the upper tropospheric cloud ice and possibly provides a more consistent input to climate studies. cloud; ice water path; ice water content; caliop; enso; mls
Wang, Tianyuan; Zhou, Lihang; Tan, Changyi; Divakarla, Murty; Pryor, Ken; Warner, Juying; Wei, Zigang; Goldberg, Mitch; Nalli, Nicholas R.Wang, T., L. Zhou, C. Tan, M. Divakarla, K. Pryor, J. Warner, Z. Wei, M. Goldberg, N. R. Nalli, 2021: Validation of Near-Real-Time NOAA-20 CrIS Outgoing Longwave Radiation with Multi-Satellite Datasets on Broad Timescales. Remote Sensing, 13(19), 3912. doi: 10.3390/rs13193912. The Outgoing Longwave Radiation (OLR) package was first developed as a stand-alone application, and then integrated into the National Oceanic and Atmospheric Administration (NOAA) Unique Combined Atmospheric Processing System (NUCAPS) hyperspectral sounding retrieval system. An objective of this package is to provide near-real-time OLR products derived from the Cross Track Infrared Sounder (CrIS) onboard the Joint Polar Satellite System (JPSS) satellites. It was initially developed and validated with CrIS onboard the Suomi National Polar-orbiting Partnership (SNPP) satellite, and has been expanded to JPSS-1 (renamed NOAA-20 after launch) datasets that are currently available to the public. In this paper, we provide the results of detailed validation tests with NOAA-20 CrIS for large and wide representative conditions at a global scale. In our validation tests, the observations from Clouds and Earth’s Radiant Energy System (CERES) on Aqua were treated as the absolute reference or “truth”, and those from SNPP CrIS OLR were used as the transfer standard. The tests were performed on a 1°×1° global spatial grid over daily, monthly, and yearly timescales. We find that the CrIS OLR products from NOAA-20 agree exceptionally well with those from Aqua CERES and SNPP CrIS OLR products in all conditions: the daily bias is within ±0.6 Wm−2, and the standard deviation (STD) ranges from 4.88 to 9.1 Wm−2. The bias and the STD of OLR monthly mean are better, within 0.3 and 2.0 Wm−2, respectively. These findings demonstrate the consistency between NOAA-20 and SNPP CrIS OLR up to annual scales, and the robustness of NUCAPS CrIS OLR products. radiation budget; validation; outgoing longwave radiation; OLR; NOAA-20; CrIS; NUCAPS
Wang, Tongxin; Zhang, Hongyan; Zhao, Jianjun; Guo, Xiaoyi; Xiong, Tao; Wu, RihanWang, T., H. Zhang, J. Zhao, X. Guo, T. Xiong, R. Wu, 2021: Shifting Contribution of Climatic Constraints on Evapotranspiration in the Boreal Forest. Earth's Future, 9(8), e2021EF002104. doi: 10.1029/2021EF002104. The global evapotranspiration (ET) shows an increasing trend with global warming in recent decades, while ET variation in different regions is still uncertain. Boreal forest ecosystem, as one of the most sensitive regions to climate change, are still poorly understood due to the sparse observation and the changing of ET in the boreal forest has been covered up for lower values compared to lower-latitude regions. Based on the PT-JPL model, we estimated the ET in the boreal forest during 1982–2015. The annual ET showed an increasing trend (0.5073 mm year−1). Seventy percentage of the boreal forest area is increasing which mainly occurred in Central Canada, Alaska, Central Siberia and Northern Europe, while 24% is decreasing, which occurred in the southern Siberia, Northern Mongolia and Northern Canada. The quantification of basic climatic factors shows that atmospheric demand is the main factor with an increasing trend which is accordance with the (a) increasing temperature; (b) annual precipitation is increasing providing increasing water supply for boreal forest. Factorial experiments were also conducted and showed that the climatic constraints that contribute mainly to ET have gradually shifted from net radiation to moisture restriction in the boreal forest. The moisture control tendency indicated that ET in the boreal forest was gradually controlled by humidity rather than energy, suggesting a limited water supply and an intensifying water cycle in the boreal forest. climate change; PT-JPL model; evapotranspiration; boreal forest
Wang, Wei; Chakraborty, T. C.; Xiao, Wei; Lee, XuhuiWang, W., T. C. Chakraborty, W. Xiao, X. Lee, 2021: Ocean surface energy balance allows a constraint on the sensitivity of precipitation to global warming. Nature Communications, 12(1), 2115. doi: 10.1038/s41467-021-22406-7. Climate models generally predict higher precipitation in a future warmer climate. Whether the precipitation intensification occurred in response to historical warming continues to be a subject of debate. Here, using observations of the ocean surface energy balance as a hydrological constraint, we find that historical warming intensified precipitation at a rate of 0.68 ± 0.51% K−1, which is slightly higher than the multi-model mean calculation for the historical climate (0.38 ± 1.18% K−1). The reduction in ocean surface albedo associated with melting of sea ice is a positive contributor to the precipitation temperature sensitivity. On the other hand, the observed increase in ocean heat storage weakens the historical precipitation. In this surface energy balance framework, the incident shortwave radiation at the ocean surface and the ocean heat storage exert a dominant control on the precipitation temperature sensitivity, explaining 91% of the inter-model spread and the spread across climate scenarios in the Intergovernmental Panel on Climate Change Fifth Assessment Report.
Wang, Xuejia; Chen, Deliang; Pang, Guojin; Anwar, Samy A.; Ou, Tinghai; Yang, MeixueWang, X., D. Chen, G. Pang, S. A. Anwar, T. Ou, M. Yang, 2021: Effects of cumulus parameterization and land-surface hydrology schemes on Tibetan Plateau climate simulation during the wet season: insights from the RegCM4 model. Climate Dynamics. doi: 10.1007/s00382-021-05781-1. Dynamical downscaling generally performs poorly on the Tibetan Plateau (TP), due to the region’s complex topography and several aspects of model physics, especially convection and land surface processes. This study investigated the effects of the cumulus parameterization scheme (CPS) and land-surface hydrology scheme (LSHS) on TP climate simulation during the wet season using the RegCM4 regional climate model. To address these issues and seek an optimal simulation, we conducted four experiments at a 20 km resolution using various combinations of two CPSs (Grell and MIT-Emanuel), two LSHSs (the default TOPMODEL [TOP], and Variable Infiltration Capacity [VIC]). The simulations in terms of 2-m air temperature, precipitation (including large-scale precipitation [LSP] and convective precipitation [CP]), surface energy-water balance, as well as atmospheric moisture flux transport and vertical motion were compared with surface and satellite-based observations as well as the ERA5 reanalysis dataset for the period 2006–2016. The results revealed that the model using the Grell and TOP schemes better reproduced air temperature but with a warm bias, part of which could be significantly decreased by the MIT scheme. All schemes simulated a reasonable spatial distribution of precipitation, with the best performance in the experiment using the MIT and VIC schemes. Excessive precipitation was produced by the Grell scheme, mainly due to overestimated LSP, while the MIT scheme largely reduced the overestimation, and the simulated contribution of CP to total precipitation was in close agreement with the ERA5 data. The RegCM4 model satisfactorily captured diurnal cycles of precipitation amount and frequency, although there remained some differences in phase and magnitude, which were mainly caused by the CPSs. Relative to the Grell scheme, the MIT scheme yielded a weaker surface heating by reducing net radiation fluxes and the Bowen ratio. Consequently, anomalous moisture flux transport was substantially reduced over the southeastern TP, leading to a decrease in precipitation. The VIC scheme could also help decrease the wet bias by reducing surface heating. Further analysis indicated that the high CP in the MIT simulations could be attributed to destabilization in the low and mid-troposphere, while the VIC scheme tended to inhibit shallow convection, thereby decreasing CP. This study’s results also suggest that CPS interacts with LSHS to affect the simulated climate over the TP.
Wang, Yi-Chi; Hsu, Huang-Hsiung; Chen, Chao-An; Tseng, Wan-Ling; Hsu, Pei-Chun; Lin, Cheng-Wei; Chen, Yu-Luen; Jiang, Li-Chiang; Lee, Yu-Chi; Liang, Hsin-Chien; Chang, Wen-Ming; Lee, Wei-Liang; Shiu, Chein-JungWang, Y., H. Hsu, C. Chen, W. Tseng, P. Hsu, C. Lin, Y. Chen, L. Jiang, Y. Lee, H. Liang, W. Chang, W. Lee, C. Shiu, 2021: Performance of the Taiwan Earth System Model in Simulating Climate Variability Compared With Observations and CMIP6 Model Simulations. Journal of Advances in Modeling Earth Systems, 13(7), e2020MS002353. doi: 10.1029/2020MS002353. This study evaluates the performance of the Taiwan Earth System Model version 1 (TaiESM1) in simulating the observed climate variability in the historical simulation of the Coupled Model Intercomparison Phase 6 (CMIP6). TaiESM1 is developed on the basis of the Community Earth System Model version 1.2.2, with the inclusion of several new physical schemes and improvements in the atmosphere model. The new additions include an improved triggering function in the cumulus convection scheme, a revised distribution-based formula in the cloud fraction scheme, a new aerosol scheme, and a unique scheme for three-dimensional surface absorption of shortwave radiation that accounts for the influence of complex terrains. In contrast to the majority of model evaluation processes, which focus mainly on the climatological mean, this evaluation focuses on climate variability parameters, including the diurnal rainfall cycle, precipitation extremes, synoptic eddy activity, intraseasonal fluctuation, monsoon evolution, and interannual and multidecadal atmospheric and oceanic teleconnection patterns. A series of intercomparisons between the simulations of TaiESM1 and CMIP6 models and observations indicate that TaiESM1, a participating model in CMIP6, can realistically simulate the observed climate variability at various time scales and are among the leading CMIP6 models in terms of many key climate features. model evaluation; CMIP6; climate variability; TaiESM
Wang, Yipu; Li, Rui; Hu, Jiheng; Wang, Xuewen; Kabeja, Crispin; Min, Qilong; Wang, YuWang, Y., R. Li, J. Hu, X. Wang, C. Kabeja, Q. Min, Y. Wang, 2021: Evaluations of MODIS and microwave based satellite evapotranspiration products under varied cloud conditions over East Asia forests. Remote Sensing of Environment, 264, 112606. doi: 10.1016/j.rse.2021.112606. Satellite remote sensing is an important tool to retrieve terrestrial evapotranspiration (ET). Widely-used MOD16 ET product (MOD-ET) is a representative of Penman-Monteith method coupled with MODerate Resolution Imaging Spectroradiometer (MODIS) optic observations. Although MOD-ET has been extensively evaluated over the world, its accuracy under various cloud conditions remains unevaluated. Combining MODIS-observed cloud cover (Frc) and in-situ measurements at sixteen forests sites in East Asia, we evaluated 8-day MOD-ET and its primary MODIS inputs (i.e. LAI, FPAR and albedo) from clear to cloudy sky. A new satellite microwave ET method based on microwave Emissivity Difference Vegetation Index (EDVI-ET) was also compared with MOD-ET. Results showed that the accuracy of MOD-ET was highly variable under the changing Frc over the forests. The largest bias (>30%) in MOD-ET was found under Frc 30%) deteriorated the bias in MOD-ET (20%–30%). In contrast, EDVI-ET performed stably with lower bias (0.81) under other sky conditions. Further investigation found that MOD-ET over four tropical coastal forests contributed most to the bias, especially under least cloudy sky. A case study at a tropical forest showed that MODIS LAI/FPAR and surface albedo products were overestimated, which could directly cause the overestimation of canopy-scale conductance and the underestimation of net solar radiation in MOD-ET method, respectively. Analysis showed that the bias in MOD-ET was significantly related to the bias in MODIS LAI under various Frc, but it was weakly related to that in MODIS albedo, suggesting that LAI-based conductance might dominate the overestimation of MOD-ET. During a consecutive cloud cover period when fewer reliable MODIS pixels are available, slight increase of clouds partly reduced MODIS-observed signals of LAI/FPAR and increased those of albedo over the tropical forest, resulting in the lower bias in MOD-ET. More clouds reduced surface MODIS albedo and might increase the uncertainty in all-sky shortwave radiation from reanalysis data, which deteriorated MOD-ET accuracy under overcast sky. Our study highlighted the importance of cloud impacts on the satellite ET estimation. Emissivity difference vegetation index (EDVI); Cloudy effects; Evapotranspiration (ET); Forest; MODIS ET
Wang, Yonglin; Zhou, Lei; Zhuang, Jie; Sun, Leigang; Chi, YonggangWang, Y., L. Zhou, J. Zhuang, L. Sun, Y. Chi, 2021: The spatial heterogeneity of the relationship between gross primary production and sun-induced chlorophyll fluorescence regulated by climate conditions during 2007–2018. Global Ecology and Conservation, 29, e01721. doi: 10.1016/j.gecco.2021.e01721. The strong relationship between gross primary productivity (GPP) and sun-induced chlorophyll fluorescence (SIF) provided a novel perspective to estimate the terrestrial GPP based on satellite SIF. However, the influence of environmental conditions on the relationship between GPP and SIF is still unclear. In this study, we synthesized GOME-2 SIF and FLUXCOM GPP coupled with climate data to explore the spatial pattern of the GPP-SIF relationship and its sensitivity to climate conditions at global scale during 2007–2018. The slope (GPP/SIF) of the intercept-free linear regression, which contained information about the allocation of light energy for fluorescence and photosynthesis, was used to represent the GPP-SIF relationship. Our study found that the slope and R2 of the GPP-SIF relationship were spatially heterogeneous, with high slope mainly distributed in the tropical regions and boreal regions and the high R2 mainly concentrated in temperate ecosystems of the Northern Hemisphere. In climate regimes, we found that the GPP-SIF relationship was jointly constrained by environmental variables and the slope had a significant decreasing trend in climate regions from high mean annual temperature (MAT) and low mean annual photosynthetically active radiation (MAR) to low MAT and high MAR. Furthermore, the slope and mean annual precipitation (MAP) have a positive correlation, which indicated the GPP-SIF relationship was climate-dependent. Environmental stress may destroy the relationship between fluorescence and photosynthesis by increasing non-photochemical quenching (NPQ). Our research showed that environmental conditions regulated the light energy distribution for fluorescence and photosynthesis, so accurate estimation of terrestrial ecosystem productivity based on SIF should consider the constraints of climate variables. Climate-dependent; GPP/SIF; Seasonality; Spatial pattern; The GPP-SIF relationship
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). CMIP5; GCMs; CMIP6; Bayesian model averaging; multimodel ensemble; surface upward longwave radiation (SULR)
Xu, Lingxuan; Sun, Shanlei; Chen, Haishan; Chai, Rongfan; Wang, Jiazhi; Zhou, Yang; Ma, Qianrong; Chotamonsak, Chakrit; Wangpakapattanawong, PrasitXu, L., S. Sun, H. Chen, R. Chai, J. Wang, Y. Zhou, Q. Ma, C. Chotamonsak, P. Wangpakapattanawong, 2021: Changes in the reference evapotranspiration and contributions of climate factors over the Indo–China Peninsula during 1961–2017. International Journal of Climatology, 41(15), 6511-6529. doi: 10.1002/joc.7209. Given the key roles of the Indo–China Peninsula (ICP) in weather and climate systems, hydrometeorology, and ecology, the annual and monthly changes in the Food and Agriculture Organization-56 Penman–Monteith reference evapotranspiration (ET0), which was calculated based on the Climatic Research Unit datasets, were investigated in ICP during 1961–2017. The annual ICP ET0 significantly (p < .05) increased, with different increasing tendencies in most months. In particular, larger and more significant (p < .05) ET0 values were found during October–December. The annual and monthly ET0 changes showed evident spatial differences, characterized by increases in more than 50% of the ICP area except for decreases in around 70% of that area during March–May. A sensitivity experiment-based separation method was utilized to evaluate the contribution of each influential factor, and the corresponding determinants were identified by comparing the contributions. Results showed that the annual ICP ET0 increase was attributed to the increased vapour pressure deficit (Vpd). However, the annual determinants varied spatially, with net solar radiation (Rn) in the southern region of ICP, wind speed (Wnd) in the northeast, and Vpd in the remaining regions. The monthly ICP determinant was Wnd in January, March–May and December, and Vpd for the remaining months. Despite different spatial patterns of monthly dominants, Vpd and Wnd were the determinants with the most extensive distributions over ICP (>75% of ICP in total). The results of this study can significantly fulfil the research gap regarding the ICP ET0 changes and the underlying mechanisms. Meanwhile, this study provides fundamental and necessary information for protecting biodiversity and understanding hydrometeorological extreme events, thus promoting specific measures to sustain the ICP development. reference evapotranspiration; Indo–China Peninsula; quantitative analysis; separation method; trends
Yamazaki, Kuniko; Sexton, David M. H.; Rostron, John W.; McSweeney, Carol F.; Murphy, James M.; Harris, Glen R.Yamazaki, K., D. M. H. Sexton, J. W. Rostron, C. F. McSweeney, J. M. Murphy, G. R. Harris, 2021: A perturbed parameter ensemble of HadGEM3-GC3.05 coupled model projections: part 2: global performance and future changes. Climate Dynamics, 56(11), 3437-3471. doi: 10.1007/s00382-020-05608-5. This paper provides a quantitative assessment of large-scale features in a perturbed parameter ensemble (PPE) of Met Office Unified Model HadGEM-GC3.05 in coupled global historical and future simulations. The main motivation for the simulations is to provide a major component of the UK Climate Projections 2018 (UKCP18), but they will also be used to make worldwide projections and inform future model development. Initially, a 25-member PPE, with 25 different parameter combinations, was simulated. Five members were subsequently dropped because either their simulated climate was unrealistically cool by 1970 or they suffered from numerical instabilities. The remaining 20 members were evaluated after completing the historical phase (1900–2005) against 13 separately selected Climate Model Intercomparison Project Phase 5 (CMIP5) models, and five more members were dropped. The final product is a combined projection system of 15 PPE members and 13 CMIP5 models, which has a number of benefits. In particular, the range of outcomes available from the combined set of 28 is often larger than from either of the two constituent ensembles, thus providing users with a more complete picture of plausible impacts. Here we mainly describe the evaluation process of the 20 PPE members. We evaluate biases in a number of important properties of the global coupled system, including assessment of climatological averages, coupled modes of internal variability and historical and future changes. The parameter combinations yielded plausible yet diverse atmosphere and ocean model behaviours. The range of global temperature changes is narrow, largely driven by use of different CO2 pathways. The range of global warming is seemingly not linked to range of feedbacks estimated from atmosphere-only runs, though we caution that the range of the latter is narrow relative to CMIP5, and therefore this result is not unexpected. This is the second of two papers describing the generation of the PPE for UKCP18 projections. Part 1 (Sexton et al. 2021) describes the selection of 25 parameter combinations of 47 atmosphere and land surface parameters, using a set of cheap atmosphere-only runs at a coarser resolution from nearly 3000 samples of parameter space.
Yang, Feng; Cheng, Jie; Zeng, QiYang, F., J. Cheng, Q. Zeng, 2021: Validation of a Cloud-Base Temperature-Based Single-Layer Cloud Model for Estimating Surface Longwave Downward Radiation. IEEE Geoscience and Remote Sensing Letters, 1-5. doi: 10.1109/LGRS.2021.3083502. As one of the four components of surface radiation balance, surface longwave downward radiation (SLDR) greatly affects the accurate characterization of hydrological, ecological, and biochemical processes. Since cloud-base temperature (CBT)-based single-layer cloud models (SLCMs) have advantages in both their strong physical mechanisms and abilities to produce high spatial resolution SLDR products, this study validated a CBT-based SLCM developed at the global scale using in situ observations collected by the baseline surface radiation network (BSRN) in conjunction with Aqua and Terra Moderate Resolution Imaging Spectroradiometer (MODIS) cloud products and Modern-Era Retrospective Analysis For Research And Applications, Version 2 (MERRA-2) reanalysis data. Overall, the CBT-based SLCM achieved a relatively high SLDR estimation accuracy for the Terra and Aqua satellites, with biases better than -1.2 W/m² and root-mean-squared error (RMSE) values better than 29.9 W/m². However, its random RMSE was slightly worse than those of two Clouds and the Earth's Radiant Energy System (CERES) Single Scanner Footprint (SSF) SLDR products due to the larger spatial variability that exists at the Earth's surface when it is quantified at a high spatial resolution (1 km). Additionally, the CBT-based SLCM outperformed two existing cloud-top temperature (CTT)-based SLCMs. In the future, we will continue to improve the performance of the CBT-based SLCM and will update the Global LAnd Surface Satellite (GLASS) SLDR product under cloudy sky conditions. Land surface; Satellites; Spatial resolution; Land surface temperature; remote sensing; Clouds; Cloud computing; validation.; Cloud-base temperature (CBT); single-layer cloud model (SLCM); surface longwave downward radiation (SLDR); Temperature distribution
Yarahmadi, Mehran; Mahan, J. Robert; Kowsary, FarshadYarahmadi, M., J. R. Mahan, F. Kowsary, 2021: A New Approach to Inverse Boundary Design in Radiation Heat Transfer. Advances in Heat Transfer and Thermal Engineering, 377-383. doi: 10.1007/978-981-33-4765-6_65. Inverse boundary design problems in surface-to-surface radiation heat transfer occur when both the temperature and net heat flux are prescribed on some of the surfaces while neither is known on the remaining surfaces. The problem is to find the unknown surface temperatures required to produce the prescribed temperatures and net heat fluxes. This chapter presents a novel approach in which a transcendental function of position—in this case a Fourier cosine series—is used to represent the spatial distribution of the unknown fourth power of surface temperature. The problem then becomes one of the findings the Fourier coefficients and fundamental angular frequency that minimize the difference between the prescribed and calculated surface temperature distributions. The approach is shown to produce more accurate results than the classical optimization approach in a fraction of the execution time for the example of an industrial processing oven.
Ye, Shuchao; Feng, Huihui; Zou, Bin; Ding, Ying; Zhu, Sijia; Li, Feng; Dong, GuotaoYe, S., H. Feng, B. Zou, Y. Ding, S. Zhu, F. Li, G. Dong, 2021: Satellite-Based Estimation of the Influence of Land Use and Cover Change on the Surface Shortwave Radiation Budget in a Humid Basin. Remote Sensing, 13(8), 1447. doi: 10.3390/rs13081447. The surface shortwave radiation budget (Rsn) is one of the main drivers of Earth’s ecosystems and varies with atmospheric and surface conditions. Land use and cover change (LUCC) alters radiation through biogeophysical effects. However, due to the complex interactions between atmospheric and surface factors, it is very challenging to quantify the sole impacts of LUCC. Based on satellite data from the Global Land Surface Satellite (GLASS) Product and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments, this study introduces an observation-based approach for detecting LUCC influences on the Rsn by examining a humid basin over the Dongting Lake Basin, China from 2001 to 2015. Our results showed that the Rsn of the study area presented a decreasing trend due to the combined effects of LUCC and climate change. Generally, LUCC contributed −0.45 W/m2 to Rsn at the basin scale, which accounted for 2.53% of the total Rsn change. Furthermore, the LUCC contributions reached −0.69 W/m2, 0.21 W/m2, and −0.41 W/m2 in regions with land transitions of forest→grass, grass→forest, and grass→farmland, which accounted for 5.38%, −4.68%, and 2.40% of the total Rsn change, respectively. Physically, LUCC affected surface radiation by altering the surface properties. Specifically, LUCC induced albedo changes of +0.0039 at the basin scale and +0.0061, −0.0020, and +0.0036 in regions with land transitions of forest→grass, grass→forest, and grass→farmland, respectively. Our findings revealed the impact and process of LUCC on the surface radiation budget, which could support the understanding of the physical mechanisms of LUCC’s impact on ecosystems. albedo; satellite; Dongting Lake Basin; land-use and cover change; surface shortwave radiation budget
You, Cheng; Tjernström, Michael; Devasthale, AbhayYou, C., M. Tjernström, A. Devasthale, 2021: Eulerian and Lagrangian views of warm and moist air intrusions into summer Arctic. Atmospheric Research, 256, 105586. doi: 10.1016/j.atmosres.2021.105586. In this study, warm and moist air intrusions (WaMAI) over the sea sectors of Kara, Laptev, East Siberian and Beaufort from 1979 to 2018 are identified in ERA5 reanalysis and their air-mass transformation is analysed using interpolation in ERA5 and satellite products along trajectories. The analysis shows that WaMAIs, driven by blocking high-pressure systems over the respective ocean sectors, induce surface warming (11–18 W m−2) and sea ice melt from positive anomalies of net longwave radiation (5–8 W m−2) and turbulent flux (8–13 W m−2) to the surface, although the anomaly of net shortwave radiation (−9 ~ +1 W m−2) is negative. From a Lagrangian perspective, the surface energy-budget anomaly decreases linearly, while total column cloud liquid water (TCLW) increases linearly with the downstream distance from the sea-ice edge. However, the cloud radiative effects of both longwave and shortwave radiation reach an equilibrium as TCLW increases in a much lower rate beyond 7 degrees north of the sea ice edge. The boundary-layer energy-budget pattern can be categorized into two classes: radiation-dominated and turbulence-dominated, comprised of 26% and 62% WaMAIs respectively. Statistically, turbulence-dominated cases occur with 3 times stronger large-scale subsidence, and also feature a larger anomaly in net shortwave radiation. In radiation-dominated WaMAIs, stratocumulus develops more strongly and hence exerts larger longwave and shortwave forcing to the surface. In both categories, a well-mixed boundary layer deepens by 500 m along the trajectories, from the continuous turbulent mixing. Arctic climate; Boundary-layer; Trajectories; Warm and moist air intrusion
Zeitler, Lea; Corbin, Armin; Vielberg, Kristin; Rudenko, Sergei; Löcher, Anno; Bloßfeld, Mathis; Schmidt, Michael; Kusche, JürgenZeitler, L., A. Corbin, K. Vielberg, S. Rudenko, A. Löcher, M. Bloßfeld, M. Schmidt, J. Kusche, 2021: Scale Factors of the Thermospheric Density: A Comparison of Satellite Laser Ranging and Accelerometer Solutions. Journal of Geophysical Research: Space Physics, 126(12), e2021JA029708. doi: 10.1029/2021JA029708. A major problem in the precise orbit determination (POD) of satellites at altitudes below 1,000 km is the modeling of the aerodynamic drag which mainly depends on the thermospheric density and causes the largest non-gravitational acceleration. Typically, empirical thermosphere models are used to calculate density values at satellite positions but current thermosphere models cannot provide the required accuracy. Thus, unaccounted variations in the thermospheric density may lead to significantly incorrect satellite positions. For the first time, we bring together thermospheric density corrections for the NRLMSISE-00 model in terms of scale factors with a temporal resolution of 12 hr derived from satellite laser ranging (SLR) and accelerometer measurements. Whereas, the latter are in situ information given along the satellite orbit, SLR results have to be interpreted as mean values along the orbit within the underlying time interval. From their comparison, we notice a rather similar behavior with correlations of up to 80% and more depending on altitude. During high solar activity, scale factors vary around 30% at low solar activity and up to 70% at high solar activity from the value one. In addition, we found the scaled thermospheric density decreasing stronger as the modeled density of NRLMSISE-00. To check the reliability of the SLR-derived scale factors, we compare the POD result of two different software packages, namely DOGS-OC from DGFI-TUM and GROOPS from IGG Bonn. Furthermore, a validation of our estimated scale factors with respect to an external data set proofs the high quality of the obtained results.
Zhang, Caijin; Long, Di; Zhang, Yucui; Anderson, Martha C.; Kustas, William P.; Yang, YangZhang, C., D. Long, Y. Zhang, M. C. Anderson, W. P. Kustas, Y. Yang, 2021: A decadal (2008–2017) daily evapotranspiration data set of 1 km spatial resolution and spatial completeness across the North China Plain using TSEB and data fusion. Remote Sensing of Environment, 262, 112519. doi: 10.1016/j.rse.2021.112519. Daily continuous evapotranspiration (ET) estimates of 1 km spatial resolution can benefit agricultural water resources management at regional scales. Thermal infrared remote sensing-derived land surface temperature (LST) is a critical variable for ET estimation using energy balance-based models. However, missing LST information under cloudy conditions remains a long-standing barrier for spatiotemporally continuous monitoring of daily ET at regional scales. In this study, LST data of 1 km spatial resolution at 11:00 local solar time under all-weather conditions across the North China Plain (NCP) were first generated using a data fusion approach developed previously. Second, combined with the generated LST data, MODIS products, and meteorological forcing from the China Land Data Assimilation System, the Two-Source Energy Balance model (TSEB) and a temporal upscaling method were jointly used to estimate daily ET at 1 km spatial resolution across the NCP for a decade from 2008 to 2017. In particular, to better incorporate the impact of crop phenology on ET and improve the ET estimation, the fraction of greenness in TSEB was determined in terms of a leaf area index threshold during the crop growth period. Compared with observed instantaneous latent heat flux (LE) corrected for energy balance closure, the estimated LE reasonably captures inter- and intra-annual variations in LE measured at the Huailai, Daxing, Weishan, and Guantao flux towers, with R2 of 0.63–0.79. Estimated daily ET against in situ ET measurements with energy balance closure at the Huailai, Daxing, and Guantao sites showed good performance in terms of R2 greater than 0.70 and RMSE below 0.91 mm/d. These accuracies are comparable with published results, with our ET data set validated by many more observations than previous studies and featuring spatiotemporal continuity and high spatial resolution across the entire NCP for a decade. Furthermore, seasonal ET variations reflected by our product outperform two widely used global products in capturing water consumption characteristics in the winter wheat-summer maize rotation system. In terms of temporal trends, annual ET estimates across the NCP show a decreasing and then increasing trend over the past decade, which is attributed to the increased cropping intensity over the recent years reflected by an increase in leaf area index. Evapotranspiration; Land surface temperature; Data fusion; Two-source energy balance
Zhang, Chunyan; Wang, Donghai; Pang, Zihao; Zhang, Yu; Jiang, Xiaoling; Zeng, Zhilin; Wu, ZhenzhenZhang, C., D. Wang, Z. Pang, Y. Zhang, X. Jiang, Z. Zeng, Z. Wu, 2021: Large-scale dynamic, heat and moisture structures of monsoon-influenced precipitation in the East Asian monsoon rainy area. Quarterly Journal of the Royal Meteorological Society, 147(735), 1007-1030. doi: https://doi.org/10.1002/qj.3956. This study investigated large-scale dynamic structures along with heat and moisture budgets associated with monsoon-influenced precipitation over a typical rainy domain in the East Asian monsoon region. Large-scale dynamically and thermodynamically consistent forcing data based on multiple measurements were produced by a one-dimensional constrained variational analysis method. Using the forcing data, distinct characteristics of large-scale states were documented for cases of notable pre-monsoon rainfall before the South China Sea monsoon onset (SCSMO), extreme rainfall during SCSMO, and persistent strong rainfall after SCSMO. The pre-monsoon period mainly resulted from weak and discrete cloud regimes. The extreme-rain period was associated with a severe deep convective system moving from the west, and the persistent-rain period was related to moderate convective cells separated from the strong convective system over the northern South China Sea. Large-scale features including vertical velocity, wind convergence, and diabatic heating and drying were the strongest (weakest) during the extreme-rain (pre-monsoon) period. For the pre-monsoon and persistent-rain periods, the period-averaged profiles of vertical velocity and diabatic heating and drying showed a one-peak structure. However, during the extreme-rain period, a leap-forward mutation was seen in the vertical structure and magnitude of these large-scale states. The multiple peaks shown in the vertical profiles of vertical velocity and diabatic heating during the extreme-rain period may indicate various convective cloud systems co-existed. The diabatic heating profiles of extreme rainfall indicated that the first rainfall peak was related to the successive occurrence of stratiform anvils and convective clouds, while the second rainfall peak, which was most intense, was associated with shallow convective clouds, severe deep convective clouds, and detraining stratiform anvils. constrained variational analysis; heating profile; large-scale structures; monsoon-influenced precipitation; upward motion
Zhang, 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; surface energy balance; polar WRF; 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